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2021, Vol. 55, No. 4　Online: 15 April 2021

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A robust interface enabled by electrospun membrane with optimal resistance in lithium metal batteries Chen Dong, Zhenkang Lin, Yuxin Yin, Yaoxuan Qiao, Wei Wang, Qibing Wu, Chengxiang Yang, David Rooney, Cheng Fan, Kening Sun 2021, 55(4): 1-9.  DOI: 10.1016/j.jechem.2020.06.060 Abstract ( 9 )   PDF (10055KB) ( 4 )   A uniform diffusion layer is essential for non-dendritic deposition of lithium in high-density lithium batteries. However, natural pristine solid electrolyte interface (SEI) is always porous and inhomogeneous because of repeated breakdown and repair cycles, whereas ideal materials with excellent mechanical property for artificial SEIs remain a challenge. Herein, a robust and stable interface is achieved by spinning soft polymer associated with few MoO3 into fibers, and thus mechanical property of fibers other than materials determines mechanical performance of the interface which can be optimized by adjusting parameters. Furthermore, lithium deposited underneath the layer is enabled by constructing an optimal resistance to make the membrane serve as an artificial SEI rather than lithium host. As a result, dendrite-free lithium was observed underneath the membrane, and stable interface for long-term cycling was also indicated by EIS measurements. The lithium iron phosphate (LiFePO4) full-cell with coated electrode demonstrated an initial capacity of 155.2 mAh g-1, and 80% of its original capacity was retained after 500 cycles at 2.0 °C without any additive in carbonate-based electrolyte.

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In-situ surface self-reconstruction in ternary transition metal dichalcogenide nanorod arrays enables efficient electrocatalytic oxygen evolution Qiang Chen, Yulu Fu, Jialun Jin, Wenjie Zang, Xiong Liu, Xiangyong Zhang, Wenzhong Huang, Zongkui Kou, John Wang, Liang Zhou, Liqiang Mai 2021, 55(4): 10-16.  DOI: 10.1016/j.jechem.2020.07.005 Abstract ( 20 )   PDF (4473KB) ( 3 )   Water splitting has received more and more attention because of its huge potential to generate clean and renewable energy. The highly active and durable oxygen evolution reaction (OER) catalysts play a decisive factor in achieving efficient water splitting. The identification of authentic active origin under the service conditions can prompt a more reasonable design of catalysts together with well-confined micro-/nano-structures to boost the efficiency of water splitting. Herein, Fe, Co, and Ni ternary transition metal dichalcogenide (FCND) nanorod arrays on Ni foam are purposely designed as an active and stable low-cost OER pre-catalyst for the electrolysis of water in alkaline media. The optimized FCND catalyst demonstrated a lower overpotential than the binary and unary counterparts, and a 27-fold rise in kinetic current density at the overpotential of 300 mV compared to the nickel dichalcogenide counterpart. Raman spectra and other structural characterizations at different potentials reveal that the in-situ surface self-reconstruction from FCND to ternary transition metal oxyhydroxides (FCNOH) on catalyst surfaces initiated at about 1.5 V, which is identified as the origin of OER activity. The surface self-reconstruction towards FCNOH also enables excellent stability, without fading upon the test for 50 h.

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Tuning electronic configuration of WP2 nanosheet arrays via nickel doping for high-efficiency hydrogen evolution reaction Wei Liu, Peng Geng, Shiqing Li, Wenhui Liu, Dayong Fan, Huidan Lu, Zhenhuan Lu, Yongping Liu 2021, 55(4): 17-24.  DOI: 10.1016/j.jechem.2020.06.068 Abstract ( 12 )   PDF (4881KB) ( 2 )   Modulate the electronic structure and surface energy by nanostructure and heteroatom doping is an efficient strategy to improve electrocatalytic activity of hydrogen evolution reaction (HER). Herein, nickel incorporated WP2 self-supporting nanosheet arrays cathode was synthesized on carbon cloth (Ni-WP2 NS/CC) by in-situ phosphating reduction of the Ni-doped WO3. It shows that heteroatom doping and the three-dimensional (3D) nanosheet arrays morphology both facilitate to reduce the interfacial transfer resistance and increase electrochemical-active surface areas, which effectively improve electrocatalytic hydrogen evolution reaction (HER) activity. The optimized catalyst, 1% Ni-WP2 NS/CC, exhibits an outstanding electrocatalytic performance with an overpotential of 110 mV at 10 mA cm-2 and a Tafel slope of 65 mV dec-1 in the acid solution. DFT calculations further demonstrate the nickel doping can adjust the intrinsic structure of electronics, lower the Gibbs free energy of adsorption of hydrogen (ΔGH*), and effectively improve the HER performance.

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Highly stable aqueous rechargeable Zn-ion battery: The synergistic effect between NaV6O15 and V2O5 in skin-core heterostructured nanowires cathode Lanlan Fan, Zhenhuan Li, Weimin Kang, Bowen Cheng 2021, 55(4): 25-33.  DOI: 10.1016/j.jechem.2020.06.075 Abstract ( 9 )   PDF (5513KB) ( 2 )   The aqueous rechargeable Zn-ion batteries based on the safe, low cost and environmental benignity aqueous electrolytes are one of the most compelling candidates for large scale energy storage applications. However, pursuing suitable insertion materials may be a great challenge due to the strong electrostatic interaction between Zn2+ and cathode materials. Hence, a novel NaV6O15/V2O5 skin-core heterostructure nanowire is reported via a one-step hydrothermal method and subsequent calcination for high-stable aqueous Zn-ion batteries (ZIBs). The NaV6O15/V2O5 cathode delivers high specific capacity of 390 mAh/g at 0.3 A/g and outstanding cycling stability of 267 mAh/g at 5 A/g with high capacity retention over 92.3% after 3000 cycles. The superior electrochemical performances are attributed to the synergistic effect of skin-core heterostructured NaV6O15/V2O5, in which the sheath of NaV6O15 possesses high stability and conductivity, and the V2O5 endows high specific capacity. Besides, the heterojunction structure not only accelerates intercalation kinetics of Zn2+ transport but also further consolidates the stability of the layers of V2O5 during the cyclic process. This work provides a new perspective in developing feasible insertion materials for rechargeable aqueous ZIBs.

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The recent progress of pitch-based carbon anodes in sodium-ion batteries Mingchi Jiang, Ning Sun, Razium Ali Soomro, Bin, Xu 2021, 55(4): 34-47.  DOI: 10.1016/j.jechem.2020.07.002 Abstract ( 19 )   PDF (13096KB) ( 14 )   Sodium-ion batteries (SIBs) have attracted significant attentions as promising alternatives to lithium-ion batteries for large-scale energy storage applications. Here carbon materials are considered as the most competitive anodes for SIBs based on their low-cost, abundant availability and excellent structural stability. Pitch, with high carbon content and low cost, is an ideal raw precursor to prepare carbon materials for large-scale applications. Nevertheless, the microstructures of pitch-based carbon are highly ordered with smaller interlayer distances, which are unfavorable for Na ion storage. Many efforts have been made to improve the sodium storage performance of pitch-based carbon materials. This review summarizes the recent progress about the application of pitch-based carbons for SIBs anodes in the context of carbon's morphology and structure regulation strategies, including morphology adjustment, heteroatoms doping, fabricating heterostructures, and the increase of the degree of disorder. Besides, the advantages, present challenges, and possible solutions to current issues in pitch-based carbon anode are discussed, with the highlight of future research directions. This review will provide a deep insight into the development of low-cost and high-performance pitch-based carbon anode for SIBs.

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Graphene-nickel nitride hybrids supporting palladium nanoparticles for enhanced ethanol electrooxidation Tong Wu, Xiao Wang, Ahmet Emrehan Emre, Jinchen Fan, Yulin Min, Qunjie Xu, Shigang, Sun 2021, 55(4): 48-54.  DOI: 10.1016/j.jechem.2020.06.056 Abstract ( 7 )   PDF (4007KB) ( 2 )   Electrocatalysts for ethanol oxidation reaction (EOR) are generally limited by their poor durability because of the catalyst poisoning induced by the reaction intermediate carbon monoxide (CO). Therefore, the rapid oxidation removal of CO intermediates is crucial to the durability of EOR-based catalysts. Herein, in order to effectively avoiding the catalyst CO poisoning and improve the durability, the graphene-nickel nitride hybrids (AG-Ni3N) were designed for supporting palladium nanoparticles (Pd/AG-Ni3N) and then used for ethanol electrooxidation. The density functional theory (DFT) calculations demonstrated the introduction of AG-Ni3N depresses the CO absorption and simultaneously promotes the adsorption of OH species for CO oxidation removal. The fabricated Pd/AG-Ni3N catalyst distinctively exhibits excellent electroactivity with the mass catalytic activity of 3499.5 mA mg-1 on EOR in alkaline media, which is around 5.24 times higher than Pd/C (commercial catalyst). Notably, the Pd/AG-Ni3N hybrids display excellent stability and durability after chronoamperometric measurements with a total operation time of 150,000 s.

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Confining Li2O2 in tortuous pores of mesoporous cathodes to facilitate low charge overpotentials for Li-O2 batteries Yin Zhou, Yong Zhao, Zhenjie Liu, Zhangquan Peng, Li Wang, Wei Chen 2021, 55(4): 55-61.  DOI: 10.1016/j.jechem.2020.06.063 Abstract ( 5 )   PDF (6253KB) ( 2 )   Achieving low charge overpotentials represents one of the most critical challenges for pursuing high-performance lithium-oxygen (Li-O2) batteries. Herein, we propose a strategy to realize low charge overpotentials by confining the growth of lithium peroxide (Li2O2) inside mesoporous channels of cathodes (CMK-8). The CMK-8 cathode with tortuous pore structures can extend the diffusion distance of lithium superoxide (LiO2) in the mesoporous channels, facilitating the further reduction of LiO2 to lithium peroxide (Li2O2) inside the pores and preventing them to be diffused out of the pores. Therefore, Li2O2 is trapped in the mesoporous channels of CMK-8 cathodes, ensuring a good Li2O2/CMK-8 contact interface. The CMK-8 electrode exhibits a low charge overpotential of 0.43 V and a good cycle life for 72 cycles with a fixed capacity of 500 mAh g-1 at 0.1 A g-1. This study proposes a strategy to achieve a low charge overpotential by confining Li2O2 growth in the mesoporous channels of cathodes.

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Millimeter-sized few-layer graphene sheets with aligned channels for fast lithium-ion charging kinetics Yu-Qi Zhou, Xiao-Ling Dong, Wen-Cui Li, Guang-Ping Hao, Dong Yan, An-Hui Lu 2021, 55(4): 62-69.  DOI: 10.1016/j.jechem.2020.05.069 Abstract ( 4 )   PDF (4103KB) ( 2 )   Assembly of the top-down graphene units mostly results in 3D porous structure with randomly organized pores. The direct bottom-up synthesis of macroscopic 2D graphene sheets with organized pores are long sought in materials chemistry field, but rarely achieved. Herein, we present a self-catalysis-assisted bottom-up route using L-glutamic acid and iron chloride as starting materials for the fabrication of the millimeter-sized few-layer graphene sheets with aligned porous channels parallel to the 2D direction. The amino- and carboxyl-functional groups in L-glutamic acid can coordinate with iron cations, thus allowing an atomic dispersion of iron cations. The pyrolysis thus initiated the growth of graphene catalyzed by in-situ generated iron nanoparticles, and a dynamic flow of iron nanoparticles eventually led to the formation of millimeter-sized few-layer graphene sheets with aligned channels (60-85 nm in diameter). Used as anodes in lithium-ion batteries, these graphene sheets showed a good rate capability (142 mA h g-1 at 2 A g-1) and high capacity retention of 93% at 2 A g-1 after 1200 cycles. Kinetic analysis revealed that lithium ions storage was dominated by diffusion behavior and capacitive behavior together, in that graphene sheets with aligned channels could accelerate electron transfer and shorten lithium ions transport pathway. This work provides a novel approach to prepare unique porous graphene materials with specific structure for energy storage.

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Fullerenes for rechargeable battery applications: Recent developments and future perspectives Zhipeng Jiang, Yuming Zhao, Xing Lu, Jia Xie 2021, 55(4): 70-79.  DOI: 10.1016/j.jechem.2020.06.065 Abstract ( 7 )   PDF (9808KB) ( 3 )   The development of high-performance batteries is inseparable from the exploration of new materials. Among them, fullerene C60 as an allotrope of carbon has many unique properties that are beneficial for battery applications, including precise structure, controllable derivatization, good solubility, and rich redox chemistry. In this review, we summarize the recent progress of fullerene-based materials in the field of rechargeable batteries and the key issues that need to be solved in the future application of fullerene. We hope this review can provide guidance and stimulate research about the applications of fullerenes in the field of energy storage.

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Electrolyte solvation chemistry for lithium-sulfur batteries with electrolyte-lean conditions Long Kong, Lihong Yin, Fei Xu, Juncao Bian, Huimin Yuan, Zhouguang Lu, Yusheng Zhao 2021, 55(4): 80-91.  DOI: 10.1016/j.jechem.2020.06.054 Abstract ( 4 )   PDF (7310KB) ( 2 )   Lithium-sulfur (Li-S) batteries possess overwhelming energy density of 2654 Wh kg-1, and are considered as the next-generation battery technology for energy demanding applications. Flooded electrolytes are ubiquitously employed in cells to ensure sufficient redox kinetics and preclude the interference of the electrolyte depletion due to side reactions with the lithium metal anode. This strategy is capable of enabling long-lasting, high-capacity and excellent-rate battery performances, but it mask the requirements of practical Li-S batteries, where high-sulfur-loading/content and lean electrolyte are prerequisite to realize the energy-dense Li-S batteries. Sparingly and highly solvating electrolytes have emerged as effective yet simple approaches to decrease the electrolyte/sulfur ratio through altering sulfur species and exerting new reaction pathways. Sparingly solvating electrolytes are characterized by few free solvents to solvate lithium polysulfides, rendering a quasi-solid sulfur conversion and decoupling the reaction mechanisms from electrolyte quantity used in cells; while highly solvating electrolytes adopt high-donicity or high-permittivity solvents and take their advantages of strong solvation ability toward polysulfide intermediates, thereby favoring the polysulfide formation and stabilizing unique radicals, which subsequently accelerate redox kinetics. Both solvation chemistry approaches have their respective features to allow the operation of cells under electrolyte-starved conditions. This Review discusses their unique features and basic physicochemical properties in the working Li-S batteries, presents remaining technical and scientific issues and provides future directions for the electrolyte chemistry to attain high-energy Li-S batteries.

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High-precision regulation synthesis of Fe-doped Co2P nanorod bundles as efficient electrocatalysts for hydrogen evolution in all-pH range and seawater Yan Lin, Kaian Sun, Xiaomeng Chen, Chen Chen, Yuan Pan, Xiyou Li, Jun Zhang 2021, 55(4): 92-101.  DOI: 10.1016/j.jechem.2020.06.073 Abstract ( 7 )   PDF (12398KB) ( 2 )   The hydrogen evolution reaction (HER) via water electrolysis has gained immense research attention. Seawater electrolysis provides great opportunities for sustainable energy production, but is extremely challenging. Transition metal phosphides are promising candidate electrocatalysts. Herein, we prepared a novel Fe-Co2P bundle of nanorods (BNRs) for catalyzing the HER in seawater electrolysis and over the entire pH range. Cobalt phosphides with different crystal phases and morphologies were obtained by varying the Fe doping amount. The Co:Fe molar ratio of 1:0.5 was found to be optimum. The Fe doping improved the HER performance of Co2P over the entire pH range by providing favorable electronic properties and morphology, lattice distortion, and special coordination environment. The Fe-Co2P BNRs showed higher catalytic activity than 20% Pt/C in seawater at high potentials. The density functional theory calculations revealed that the Fe doping reduced the hydrogen binding strength of Co2P to efficiently accelerate the HER kinetics and produce a favorable charge density. This study provides valuable insights into the design and development of high-efficiency HER catalysts for large-scale seawater electrolysis.

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Controllable conversion of rice husks to Si/C and SiC/C composites in molten salts Da Pang, Wei Weng, Jing Zhou, Dong Gu, Wei Xiao 2021, 55(4): 102-107.  DOI: 10.1016/j.jechem.2020.06.072 Abstract ( 7 )   PDF (6049KB) ( 2 )   Direct conversion of biomass to functional materials is an ideal solution to relieve challenges in environmental and energy sustainability. We herein demonstrate a molten salt thermoelectrolysis of rice husks (RHs) mainly consisting of organic mass and biosilica to achieve high-efficiency and upgraded utilization of both Si and C in RHs. By coupling pyrolysis of organic mass with electrochemical reduction of silica in molten salts, the thermoelectrolysis of RHs in molten CaCl2-NaCl at 800 °C refines the RHs and acid-leached RHs to SiC nanowire/C (SiC-NW/C) and Si nanoparticle/C (Si-NP/C), respectively. The present study highlights the molten salt thermoelectrolysis for reclamation of biomass wastes in an affordable and controllable manner.

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Electrochemical and structural evolution of structured V2O5 microspheres during Li-ion intercalation Sul Ki Park, Puritut Nakhanivej, Jeong Seok Yeon, Kang Ho Shin, Wesley M. Dose, Michael De Volder, Jin Bae Lee, Hae Jin Kim, Ho Seok Park 2021, 55(4): 108-113.  DOI: 10.1016/j.jechem.2020.06.028 Abstract ( 4 )   PDF (2563KB) ( 2 )   With the development of stable alkali metal anodes, V2O5 is gaining traction as a cathode material due to its high theoretical capacity and the ability to intercalate Li, Na and K ions. Herein, we report a method for synthesizing structured orthorhombic V2O5 microspheres and investigate Li intercalation/de-intercalation into this material. For industry adoption, the electrochemical behavior of V2O5 as well as structural and phase transformation attributing to Li intercalation reaction must be further investigated. Our synthesized V2O5 microspheres consisted of small primary particles that were strongly joined together and exhibited good cycle stability and rate capability, triggered by reversible volume change and rapid Li ion diffusion. In addition, the reversibility of phase transformation (α, ε, δ, γ and ω-LixV2O5) and valence state evolution (5+, 4+, and 3.5+ ) during intercalation/de-intercalation were studied via in-situ X-ray powder diffraction and X-ray absorption near edge structure analyses.

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Boosting cell performance of LiNi0.8Co0.1Mn0.1O2 cathode material via structure design Lin-bo Tang, Yang Liu, Han-xin Wei, Cheng Yan, Zhen-jiang He, Yun-jiao Li, Jun-chao Zheng 2021, 55(4): 114-123.  DOI: 10.1016/j.jechem.2020.06.055 Abstract ( 7 )   PDF (8195KB) ( 2 )   Ni-rich cathodes exhibit appealing properties, such as high capacity density, low cost, and prominent energy density. However, the inferior ionic conductivity and bulk structural degradation become bottlenecks for Ni-rich cathodes and severely limit their commercial utilization. Traditional coating and doping methods suffer fatal drawbacks in functioning as a unit and cannot radically promote material performance to meet the needs of Li-ion batteries (LIBs). Herein, we successfully devised an ingenious and facile synthetic method to establish Ni-rich oxides with a La2Zr2O7 coating and Zr doping. The coating layer improves the ion diffusion kinetics and enhances Li-ion transportation while Zr doping effectively suppresses the phase transition of LiNi0.8Co0.1Mn0.1O2 cathode. Owing to the synergetic effect of Zr doping and La2Zr2O7 coating, the modified material shows prominent initial discharge capacity of 184.7 mAh g-1 at 5 °C and maintains 177.5 mAh g-1 after 100 cycles at 1 °C. Overall, the proposed feasible electrode design method can have a far-reaching impact on further fabrication of advanced cathodes for high-performance LIBs.

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Electrochemical reactivity of In-Pb solid solution as a negative electrode for rechargeable Mg-ion batteries Lucie Blondeau, Suzy Surblé, Eddy Foy, Hicham Khodja, Magali Gauthier 2021, 55(4): 124-128.  DOI: 10.1016/j.jechem.2020.07.004 Abstract ( 3 )   PDF (1654KB) ( 2 )   A composite In-Pb:carbon was successfully synthetized by a two-step mechanochemical synthesis in order to obtain an adequate particles size and structure to investigate the electrochemical reactivity of the In-Pb solid solution towards Mg. A potential synergetic coupling of electroactive elements In and Pb was examined using electrochemical and ex situ X-ray diffraction analyses. The potential profile of the solid solution indicates the formation of Mg2Pb and MgIn. However, the diffraction study suggests a peculiar electrochemically-driven amorphization of MgIn during the magnesiation, in strong contrast to MgIn crystallization in In-based and InBi-based electrodes reported in the literature. Combining In and Pb favors the amorphization of MgIn and a high first magnesiation capacity of about 550 mAh g-1, but is thereafter detrimental to the material's reversibility. These results emphasize the possible influence of electrochemically-driven amorphization and crystallization processes on electrochemical performance of battery materials.

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Constructing a uniform lithium iodide layer for stabilizing lithium metal anode Yingxin Lin, Zhipeng Wen, Jiaxiang Liu, Dongzheng Wu, Peng Zhang, Jinbao Zhao 2021, 55(4): 129-135.  DOI: 10.1016/j.jechem.2020.07.003 Abstract ( 3 )   PDF (4521KB) ( 2 )   The metallic lithium (Li) is the ultimate option in the development of anodes for high-energy secondary batteries. Unfortunately, inferior cycling reversibility and Li dendrites growth of Li metal as anode enormously impede its commercialization. Here, a uniform LiI protective layer is constructed on Li metal anode via a facile and direct solid-gas reaction of Li metal with iodine vapor. The pre-constructed LiI layer possesses more steadily and faster Li ion transport than the conventional SEI layer and contributes to a steady interface for the Li metal anode, which affords a smooth Li deposition morphology without Li dendrites formation. The symmetrical cell with the Li metal anode protected by LiI layer exhibits a longer cycling lifetime of over 700 h at a current density of 1 mA cm-2 with Li plating capacity of 1 mAh cm-2. Moreover, the LiI layer protected Li metal anode can still remain high capacity retention of 74.6% after 500 cycles in the full cell paired with NCM523 cathode. The work proposes an easy and effective method to fabricate a uniform and stable protective layer on the Li metal anode and offers a practicable thinking for the commercial implementation of Li metal batteries.

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A Li-S battery with ultrahigh cycling stability and enhanced rate capability based on novel ZnO yolk-shell sulfur host Ruihan Zhang, Maochun Wu, Xinzhuang Fan, Haoran Jiang, Tianshou Zhao 2021, 55(4): 136-144.  DOI: 10.1016/j.jechem.2020.06.039 Abstract ( 7 )   PDF (4813KB) ( 5 )   Currently, lithium-sulfur (Li-S) batteries still suffer from fast capacity decay, poor coulombic efficiency (CE) and short cycling lifespan, which result from the severe shuttle effect issue caused by high solubility and rapid diffusion of lithium polysulfides (LiPSs) in organic electrolytes. Here, yolk-shell zinc oxide (YS-ZnO) spheres are synthesized and for the first time, applied as a host for Li-S batteries to tackle this challenge. The polar ZnO exhibits high chemical anchoring ability toward LiPSs while the unique yolk-shell structure not only provides an additional physical barrier to LiPSs but also enables much more uniform sulfur distribution, thus significantly suppressing LiPSs shuttling effect meanwhile promoting sulfur conversion reactions. As a result, the YS-ZnO enables the Li-S battery to display an initial specific capacity of 1355 mAh g-1 and an outstanding capacity retention capability (~89.44% retention rate) even after 500 cycles with the average CE of ~99.46% at the current of 0.5 C. By contrast, the capacity of conventional-ZnO-nanoparticles based battery severely decays to 472 mAh g-1 after cycling for 500 times. More impressively, the S/YS-ZnO based Li-S battery can maintain a low decay rate of 0.040% every cycle and high average CE of 98.82% over 1000 cycles at 3 C.

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Redox active polymer metal chelates for use in flexible symmetrical supercapacitors: Cobalt-containing poly(acrylic acid) polymer electrolytes Emre Cevik, Ayhan Bozkurt 2021, 55(4): 145-153.  DOI: 10.1016/j.jechem.2020.07.014 Abstract ( 3 )   PDF (10688KB) ( 2 )   The novel polymer metal chelate electrolytes (polychelates) were prepared by incorporation of cobalt sulfate (Co) into poly(acrylic acid) (PAA) host matrix. Quasi-solid state supercapacitor devices were fabricated using polychelates, PAA-CoX (X: 3, 5, 7, and 10) where X represents the doping fraction (w/w) of Co in PAA. All polymer metal electrolytes were showed excellent bending-stretching properties, thermal stability and electrochemical durability with an optimum ionic conductivity of 3.15 × 10-4 S cm-1. Hierarchically porous activated carbon and nano-sized conductive carbon were used to form carbon composite symmetrical device electrodes. The electric double-layer capacitor (EDLC) and redox reactions of Co-incorporated polychelates at the interfaces of porous activated carbon provided an optimum specific capacitance of 341.33 F g-1 with a device of PAA-Co7, which is at least 15 times enhancement compared to the device of pristine PAA. The PAA-Co7 device also provided energy density of 21.25 Wh kg-1 at a power density of 117.69 W kg-1. A prolonged cyclic stability of the device exhibited superior capacitive performance after 10,000 charge-discharge cycles and the maintained 90% of its initial performance. In addition, the supercapacitor with a dimension of 1.5 cm × 3 cm containing PAA-Co7 successfully operated the red-blue-green (RGB) LED light.

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Oxygen vacancies enable the visible light photoactivity of chromium-implanted TiO2 nanowires Xianyin Song, Wenqing Li, Xiaojing Liu, Yishang Wu, Dong He, Zunjian Ke, Li Cheng, Changzhong Jiang, Gongming Wang, Xiangheng Xiao, Yat Li 2021, 55(4): 154-161.  DOI: 10.1016/j.jechem.2020.07.013 Abstract ( 27 )   PDF (7303KB) ( 19 )   Although computational studies have demonstrated that metal ion doping can effectively narrow the bandgap of TiO2, the visible-light photoactivity of metal-doped TiO2 photoanodes is still far from satisfactory. Herein, we report an effective strategy to activate the visible-light photoactivity of chromium-implanted TiO2 via the incorporation of oxygen vacancies. The chromium-doped TiO2 activated by oxygen vacancies (Cr-TiO2-vac) exhibited an incident photon-to-electron conversion efficiency (IPCE) of ~6.8% at 450 nm, which is one of the best values reported for metal-doped TiO2. Moreover, Cr-TiO2-vac showed no obvious photocurrent decay after 100 h under visible-light illumination.

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Identifying the Zn-Co binary as a robust bifunctional electrocatalyst in oxygen reduction and evolution reactions via shifting the apexes of the volcano plot Jing Wang, Rui Xu, Yuling Sun, Qian Liu, Meirong Xia, Yan Li, Faming Gao, Yufeng Zhao, John S. Tse 2021, 55(4): 162-168.  DOI: 10.1016/j.jechem.2020.07.010 Abstract ( 6 )   PDF (6253KB) ( 3 )   The performance of an electrocatalyst is closely correlated with the binding strength of key oxygen-containing intermediates, i.e., *OOH, *O and *OH, in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Facile strategies to achieve favorable binding strength of these oxygen-containing species are urgently demanded, yet it still remains great challenges. Herein, the Zn-Co bimetallic isolation, which serves as an ideal model, is studied systematically by the density functional theory (DFT). Reaction activity volcano plots are built from 48 models, among them the ZnCoN6-gra(I) configuration is confirmed to be the most stable, featured of the strongest interaction with the oxygen-containing species. Optimal ΔG*O (free energy change of an atomic oxygen containing intermediate) is facilitated, which effectively drifts the volcano peaks of ORR and OER closer to each other, enabling promising bifunctional catalyst. Moreover, the small overpotential in the simulation of protonation and oxidation by hydroxy groups rationalizes the durability of the catalyst in both acid and alkaline media.

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Integration of cobalt selenide nanocrystals with interlayer expanded 3D Se/N Co-doped carbon networks for superior sodium-ion storage Huabin Kong, Chade Lv, Yishan Wu, Chunshuang Yan, Gang Chen 2021, 55(4): 169-175.  DOI: 10.1016/j.jechem.2020.06.066 Abstract ( 4 )   PDF (8637KB) ( 2 )   Rational electrode structure design is of great significance for realizing superior Na+ storage performance. Herein, a metal salt-induced polymer blowing-bubble approach followed by selenization procedure is developed to in-situ generate abundant sub-10 nm CoSe2 nanocrystals on 3D Se/N co-doped carbon networks (CoSe2@3DSNC). The phase transition from Co to CoSe2 and the incorporation of Se into the carbon layer are realized simultaneously to establish above configuration, in which the CoSe2 nanocrystals are anchored on interlayer expanded carbon networks. Such unique configuration endows electrode with lower Na+ diffusion energy barrier, higher Na+ storage capability and better structural durability. Reflected in SIBs, the optimized CoSe2@3DSNC delivers superior rate capability (310 mAh g-1 at 10 A g-1) and excellent long-term cycling stability (409 mAh g-1 after 1200 cycles at 5 A g-1). Moreover, this configuration can also be obtained in other metal selenides-carbon composite through a similar approach.

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Selective CO2 reduction into formate using Ln-Ta oxynitrides combined with a binuclear Ru(II) complex under visible light Kanemichi Muraoka, Miharu Eguchi, Osamu Ishitani, François Cheviré, Kazuhiko Maeda 2021, 55(4): 176-182.  DOI: 10.1016/j.jechem.2020.06.064 Abstract ( 3 )   PDF (3623KB) ( 2 )   Hybrid materials constructed from a visible-light-absorbing semiconductor and a functional metal complex have attracted attention as efficient photocatalysts for CO2 reduction with high selectivity to a desired product. In this work, defect fluorite-type Ln-Ta oxynitrides LnTaOxNy (Ln = Nd, Sm, Gd, Tb, Dy and Ho) were examined as the semiconductor component in a hybrid photocatalyst system combined with known Ag nanoparticle promoter and binuclear ruthenium(II) complex (RuRu′). Among the LnTaOxNy examined, TbTaOxNy gave the highest performance for CO2 reduction under visible light (λ > 400 nm), with a RuRu′-based turnover number of 18 and high selectivity to formate (>99%). Physicochemical analyses indicated that high crystallinity and more negative conduction band potential of LnTaOxNy with the absence of Ln-4f states in the band gap structure contributed to higher activity of the hybrid photocatalyst.

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Continuous nitrogen-doped carbon nanotube matrix for boosting oxygen electrocatalysis in rechargeable Zn-air batteries Guangda Chen, Yangyang Xu, Lei Huang, Aboulkader Ibro Douka, Bao Yu Xia 2021, 55(4): 183-189.  DOI: 10.1016/j.jechem.2020.07.012 Abstract ( 4 )   PDF (7940KB) ( 5 )   Developing robust oxygen electrocatalyst with high-performance is very significant for practical rechargeable Zn-air battery. We report herein the preparation of three-dimensional continuous nanocarbon network composed of interconnected nitrogen-doped carbon nanotubes and its application as oxygen electrocatalysis in rechargeable Zn-air battery. Except the excellent electrochemical bifunctionality, this carbon nanotube matrix also delivers an impressive battery performance. Specifically, an open-circuit voltage of 1.50 V as well as a high power density of 220 mW cm-2 with remarkable cycling stability for 1600 h is achieved in the rechargeable Zn-air battery. The study not only provides an efficient bifunctional oxygen electrocatalyst but more importantly may pave significant concepts in designing robust electrode for long-life rechargeable Zn-air battery and other energy technologies.

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A versatile nano-TiO2 decorated gel separator with derived multi-scale nanofibers towards dendrite-blocking and polysulfide-inhibiting lithium-metal batteries Huijuan Zhao, Jing Yan, Nanping Deng, Weimin Kang, Bowen Cheng 2021, 55(4): 190-201.  DOI: 10.1016/j.jechem.2020.07.015 Abstract ( 5 )   PDF (8856KB) ( 2 )   In this study, a versatile fluorine-bearing gel membrane with multi-scale nanofibers was rationally designed and synthesized via facile one-step blend electrospinning of nano-titanium dioxide (TiO2) particles and fluorinated poly-m-phenyleneisophthalamide (PMIA) polymer solution. The prepared multi-scale TiO2-assisted gel separator presented relatively high porosity, small aperture, giving rise to superior affinity to electrolyte and sufficient active sites to accelerate lithium ions migration. Meanwhile, the as-fabricated multifunctional GPE also rendered outstanding heat-resistance and well-distributed lithium-ions flux, and the mutual overlaps between the coarse fibers and the fine fibers within the multi-scale nanofiber membrane provided a strong skeleton support, which in turn laid a solid footing stone for high-security and dendrite-proof batteries. Particularly, the nano-TiO2 particles within PMIA membrane acted as “gatekeepers”, which can not only resist the growth of lithium dendrites, but also intercept the dissolved polysulfide on cathode side. Based on these merits, the gel PMIA-based lithium cobalt (LCO)/lithium battery obtained the remarkably improved rate capability and cycle performances on account of superior ionic conductivity, steady anodic stability window and weakened polarization behavior. Meanwhile, the resultant lithium-sulfur cell also delivered the outstanding cycling stability with the aid of the greatly prevented “shuttle effect” of dissolved lithium polysulfides based on the physical trapping and chemical binding of the prepared GPE to polysulfides species. This work proved that the addition of functional inorganic nanoparticles similar with TiO2 in multi-scale gel PMIA membrane can enhance the lithium ions transport capability, resist the growth of lithium dendrites as well as inhibit the shuttle effect of polysulfides, which would prompt a great development for dendrite-blocking and polysulfide-inhibiting lithium-metal cells.

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Nitrogen-doped carbon encapsulated in mesoporous TiO2 nanotubes for fast capacitive sodium storage Baosong Li, Shoaib Anwer, Xinhua Huang, Shaohong Luo, Jing Fu, Kin Liao 2021, 55(4): 202-210.  DOI: 10.1016/j.jechem.2020.06.074 Abstract ( 6 )   PDF (8084KB) ( 3 )   Controllable synthesis of insertion-type anode materials with beneficial micro- and nanostructures is a promising approach for the synthesis of sodium-ion storage devices with high-reactivity and excellent electrochemical performance. In this study, we developed a sacrificial-templating route to synthesize TiO2@N-doped carbon nanotubes (TiO2@NC-NTs) with excellent electrochemical performance. The as-prepared mesoporous TiO2@NC-NTs with tiny nanocrystals of anatase TiO2 wrapped in N-doped carbon layers showed a well-defined tube structure with a large specific surface area of 198 m2 g-1 and a large pore size of ~5 nm. The TiO2@NC-NTs delivered high reversible capacities of 158 mA h g-1 at 2 C (1 C = 335 mA g-1) for 2200 cycles and 146 mA h g-1 at 5 C for 4000 cycles, as well as an ultrahigh rate capability of up to 40 C with a capacity of 98 mA h g-1. Even at a high current density of 10 C, a capacity of 138 mA h g-1 could be delivered over 10,000 cycles. Thus, the synthesis of mesoporous TiO2@NC-NTs was demonstrated to be an efficient approach for developing electrode materials with high sodium storage and long cycle life.

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A crosslinked polymer as dopant-free hole-transport material for efficient n-i-p type perovskite solar cells Linqin Wang, Fuguo Zhang, Tianqi Liu, Wei Zhang, Yuanyuan Li, Bin Cai, Lanlan He, Yu Guo, Xichuan Yang, Bo Xu, James M. Gardner, Lars Kloo, Licheng Sun 2021, 55(4): 211-218.  DOI: 10.1016/j.jechem.2020.06.062 Abstract ( 4 )   PDF (3171KB) ( 2 )   A new crosslinked polymer, called P65, with appropriate photo-electrochemical, opto-electronic, and thermal properties, has been designed and synthesized as an efficient, dopant-free, hole-transport material (HTM) for n-i-p type planar perovskite solar cells (PSCs). P65 is obtained from a low-cost and easily synthesized spiro[fluorene-9,9′-xanthene]-3′,6′-diol (SFX-OH)-based monomer X65 through a free-radical polymerization reaction. The combination of a three-dimensional (3D) SFX core unit, hole-transport methoxydiphenylamine group, and crosslinked polyvinyl network provides P65 with good solubility and excellent film-forming properties. By employing P65 as a dopant-free hole-transport layer in conventional n-i-p type PSCs, a power conversion efficiency (PCE) of up to 17.7% is achieved. To the best of our knowledge, this is the first time a 3D, crosslinked, polymeric dopant-free HTM has been reported for use in conventional n-i-p type PSCs. This study provides a new strategy for the future development of a 3D crosslinked polymeric dopant-free HTM with a simple synthetic route and low-cost for commercial, large-scale applications in future PSCs.

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Cobalt porphyrin immobilized on the TiO2 nanotube electrode for CO2 electroreduction in aqueous solution Shengshen Gu, Aleksei N. Marianov, Yuxiang Zhu, Yijiao Jiang 2021, 55(4): 219-227.  DOI: 10.1016/j.jechem.2020.06.067 Abstract ( 8 )   PDF (1433KB) ( 3 )   Herein we report CO2 electrochemical reduction reaction (CO2ERR) on the cobalt tetraphenylporphyrin (CoTPP) modified TiO2 nanotube (TNT) electrode. It was found the axial coordination of drop-casting solvent to CoTPP and the porphyrin structure are the major factors that have significant effects on the catalytic performance of the electrode. As confirmed by spectrophotometric titration, pyridine has a stronger coordination bond to CoTPP than DMF and THF thus leading to the highest efficiency among the drop-casting solvents tested in the study. Based on the spectrophotometric analysis, possible coordination mechanism between drop-casting solvents and CoTPP is put forward. On the other hand, introduction of -COOMe substituents in phenyl rings of CoTPP weakens the coordination bond between pyridine and CoTPP as clearly evidenced by deuterium NMR spectra, resulting in a detrimental effect on CO2ERR. Therefore, the manipulation of the coordination environment around the metal center of immobilized catalyst is crucial in designing an efficient electrocatalytic system.

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Lithium bis(oxalate)borate crosslinked polymer electrolytes for high-performance lithium batteries Xiao Wang, Jujie Sun, Changhao Feng, Xiujuan Wang, Minghan Xu, Jingjiang Sun, Ning Zhang, Jun Ma, Qingfu Wang, Chengzhong Zong, Guanglei, Cui 2021, 55(4): 228-235.  DOI: 10.1016/j.jechem.2020.06.070 Abstract ( 6 )   PDF (7122KB) ( 4 )   Solid electrolytes play a vital role in solid-state Li secondary batteries, which are promising high-energy storage devices for new-generation electric vehicles. Nevertheless, obtaining a suitable solid electrolyte by a simple and residue-free preparation process, resulting in a stable interface between electrolyte and electrode, is still a great challenge for practical applications. Herein, we report a self-crosslinked polymer electrolyte (SCPE) for high-performance lithium batteries, prepared by a one-step method based on 3-methoxysilyl-terminated polypropylene glycol (SPPG, a liquid oligomer). It is worth noting that lithium bis(oxalate)borate (LiBOB) can react with SPPG to form a crosslinked structure via a curing reaction. This self-formed polymer electrolyte exhibits excellent properties, including high room-temperature ionic conductivity (2.6 × 10-4 S cm-1), wide electrochemical window (4.7 V), and high Li ion transference number (0.65). The excellent cycling stability (500 cycles, 83%) further highlights the improved interfacial stability after the in situ formation of SCPE on the electrode surface. Moreover, this self-formation strategy enhances the safety of the battery under mechanical deformation. Therefore, the present self-crosslinked polymer electrolyte shows great potential for applications in high-performance lithium batteries.

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Ordered cone-structured tin directly grown on carbon paper as efficient electrocatalyst for CO2 electrochemical reduction to formate Hexiang Zhong, Yanling Qiu, Xianfeng Li, Liwei Pan, Huamin Zhang 2021, 55(4): 236-243.  DOI: 10.1016/j.jechem.2020.06.058 Abstract ( 6 )   PDF (5702KB) ( 2 )   The conversion of carbon dioxide to chemicals by the electrochemical reactions (ERC) is an efficient solution to the current energy crisis and excess CO2 emissions. It is still a great challenge and of significance to synthesize a highly selective, efficient, and non-noble metal electrocatalyst that facilitates the ERC reaction. A novel triton X-100 (C14H22O(C2H4O)n) assisted electrodeposition method was developed to synthesize the ordered cone-structured tin (OCSn) electrocatalysts with controllable morphology and structure. The results suggest that Triton X-100 plays an important role in directing the structure of the Sn electrocatalysts during the electrodeposition process. The OCSn synthesized at 60 mA cm-2 achieves the best performances. It selectively catalyzes the ERC on the onset potential about 110 mV lower than Sn synthesized without Triton X-100. In 0.5 M NaHCO3, high faradaic efficiency (92%) for formate product on OCSn has been achieved. More prominently, the catalyst presents excellent stability, showing no performance deterioration during 30 h electrolysis. This work provides an efficient, green, and scalable synthesis method of the electrocatalyst for CO2 reduction to formate.

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Design of efficient electrocatalysts for hydrogen evolution reaction based on 2D MXenes Yi Wei, Razium A. Soomro, Xiuqiang Xie, Bin Xu 2021, 55(4): 244-255.  DOI: 10.1016/j.jechem.2020.06.069 Abstract ( 9 )   PDF (9669KB) ( 4 )   The growing energy concern all over the world has recognized hydrogen energy as the most promising renewable energy sources. Recently, electrocatalytic hydrogen evolution reaction (HER) by water splitting has been extensively studied with a focus on developing efficient electrocatalysts that can afford HER at overpotential with minimum power consumption. The two-dimensional transition metal carbides and nitride, also known as MXenes, are becoming the rising star in developing efficient electrocatalysts for HER, owing to their integrated chemical and electronic properties, e.g., metallic conductivity, variety of redox-active transition metals, high hydrophilicity, and tunable surface functionalities. In this review, the recent progress about the fundamental understanding and materials engineering of MXenes-based electrocatalysts is summarized in concern with two aspects: i) the regulation of the intrinsic properties of MXenes, which include the composition, surface functionality, and defects; and ii) MXenes-based composites for HER process. In the end, we summarize the present challenges concerning the efficiency of MXenes-based HER electrocatalysts and propose the directions of future research efforts.

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Core-shell structured SnSe@C microrod for Na-ion battery anode Fanjun Kong, Zhengsi Han, Shi Tao, Bin, Qian 2021, 55(4): 256-264.  DOI: 10.1016/j.jechem.2020.07.016 Abstract ( 13 )   PDF (10103KB) ( 6 )   The SnSe nanoparticles encapsulated in the carbon nanofibers (SnSe@C) with microrod morphology and core-shell structure are prepared by electrospinning and annealing process, and investigated as anode materials for sodium ion batteries. Benefiting from this unique structure, the SnSe@C can deliver a reversible capacity of 283.8 mAh g-1 after 500 cycles at a high current density of 1.0 A g-1. The sodium ion storage mechanisms of SnSe are further characterized by ex-situ X-ray diffraction, high-resolution transmission electron microscope and selected area electron diffraction measurements. Besides, the excellent electrochemical performance of the electrodes is investigated by pseudocapacitance and in situ electrochemical impedance spectroscopy measurements. This work may provide a new avenue for synthesis of metal selenides with core-shell structure and a good idea for studying the kinetics process.

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Defect passivation by nontoxic biomaterial yields 21% efficiency perovskite solar cells Shaobing Xiong, Tianyu Hao, Yuyun Sun, Jianming Yang, Ruru Ma, Jiulong Wang, Shijing Gong, Xianjie Liu, Liming Ding, Mats Fahlman, Qinye Bao 2021, 55(4): 265-271.  DOI: 10.1016/j.jechem.2020.06.061 Abstract ( 9 )   PDF (2064KB) ( 3 )   Defect passivation is one of the most important strategies to boost both the efficiency and stability of perovskite solar cells (PSCs). Here, nontoxic and sustainable forest-based biomaterial, betulin, is first introduced into perovskites. The experiments and calculations reveal that betulin can effectively passivate the uncoordinated lead ions in perovskites via sharing the lone pair electrons of hydroxyl group, promoting charge transport. As a result, the power conversion efficiencies of the p-i-n planar PSCs remarkably increase from 19.14% to 21.15%, with the improvement of other parameters. The hydrogen bonds of betulin lock methylamine and halogen ions along the grain boundaries and on the film surface and thus suppress ion migration, further stabilizing perovskite crystal structures. These positive effects enable the PSCs to maintain 90% of the initial efficiency after 30 days in ambient air with 60%±5% relative humidity, 75% after 300 h aging at 85 °C, and 55% after 250 h light soaking, respectively. This work opens a new pathway for using nontoxic and low-cost biomaterials from forest to make highly efficient and stable PSCs.

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In-situ construction of a Mg-modified interface to guide uniform lithium deposition for stable all-solid-state batteries Tiefeng Liu, Jiale Zheng, Hualiang Hu, Ouwei Sheng, Zhijin Ju, Gongxun Lu, Yujing Liu, Jianwei Nai, Yao Wang, Wenkui Zhang, Xinyong Tao 2021, 55(4): 272-278.  DOI: 10.1016/j.jechem.2020.07.009 Abstract ( 10 )   PDF (10745KB) ( 2 )   Uniform lithium (Li) deposition in all-solid-state Li metal batteries is greatly influenced by the anode/electrolyte interface. Herein, a Mg-modified interface was constructed via the simple in-situ electrochemical reduction of Mg2+ from Mg(TFSI)2 in polyethylene oxide (PEO) and a Li bis(trifluoromethane)sulfonimide (LiTFSI) formulae. As confirmed by cryogenic transmission electron microscopy, the anode/electrolyte interface exhibited hybrids consisting of crystalline Mg, Li2O, and Li dots embedded in an amorphous polymer electrolyte. The crystalline Mg dots guided the uniform Li nucleation and growth, inducing a smoother anode/electrolyte interface compared with the pristine electrolyte. With 1 wt% Mg(TFSI)2 in the PEO-LiTFSI electrolyte, the Mg-modified electrolyte enabled the Li/Li symmetric cells with cycling performance of over 1700 and 1400 h at current densities of 0.1 and 0.2 mA cm-2, respectively. Moreover, the full LFP/Li cells using the novel Mg-modified electrolyte delivered a cycling lifespan of over 450 cycles with negligible capacity loss.

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Carbon quantum dots for advanced electrocatalysis Lin Tian, Zhao Li, Peng Wang, Xiuhui, Zhai, Xiang Wang, Tongxiang Li 2021, 55(4): 279-294.  DOI: 10.1016/j.jechem.2020.06.057 Abstract ( 13 )   PDF (9513KB) ( 9 )   Zero-dimensional (0D) carbon quantum dots (CQDs), as a nanocarbon material in the carbon family, have garnered increasing attention in recent years due to their outstanding features of low cost, nontoxicity, large surface area, high electrical conductivity, and rich surface functional groups. By virtue of their rapid electron transfer and large surface area, CQDs also emerge as promising functional materials for the applications in energy-conversion sectors through electrocatalysis. Besides, the rich functional groups on the surface of CQDs offer abundant anchoring sites and active sites for the engineering of multi-component and high-performance composite materials. More importantly, the heteroatom in the CQDs could effectively tailor the charge distribution to promote the electron transfer via internal interactions, which is crucial to the enhancement of electrocatalytic performance. Herein, an overview about recent progress in preparing CQDs-based composites and employing them as promising electrode materials to promote the catalytic activity and stability for electrocatalysis is provided. The introduced CQDs could enhance the conductivity, modify the morphology and crystal phase, optimize the electronic structure, and provide more active centers and defect sites of composites. After establishing a deep understanding of the relationship between CQDs and electrocatalytic performances, the issues and challenges for the development of CQDs-based composites are discussed.

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Surface pseudocapacitance of mesoporous Mo3N2 nanowire anode toward reversible high-rate sodium-ion storage Yalong Jiang, Jun Dong, Shuangshuang Tan, Qiulong Wei, Fangyu Xiong, Wei Yang, Yuanhao Shen, Qingxun Zhang, Zi'ang Liu, Qinyou An, Liqiang Mai 2021, 55(4): 295-303.  DOI: 10.1016/j.jechem.2020.07.011 Abstract ( 5 )   PDF (15157KB) ( 3 )   Sodium-ion storage devices are highly desirable for large-scale energy storage applications owing to the wide availability of sodium resources and low cost. Transition metal nitrides (TMNs) are promising anode materials for sodium-ion storage, while their detailed reaction mechanism remains unexplored. Herein, we synthesize the mesoporous Mo3N2 nanowires (Meso-Mo3N2-NWs). The sodium-ion storage mechanism of Mo3N2 is systematically investigated through in-situ XRD, ex-situ experimental characterizations and detailed kinetics analysis. Briefly, the Mo3N2 undergoes a surface pseudocapacitive redox charge storage process. Benefiting from the rapid surface redox reaction, the Meso-Mo3N2-NWs anode delivers high specific capacity (282 mAh g-1 at 0.1 A g-1), excellent rate capability (87 mAh g-1 at 16 A g-1) and long cycling stability (a capacity retention of 78.6% after 800 cycles at 1 A g-1). The present work highlights that the surface pseudocapacitive sodium-ion storage mechanism enables to overcome the sluggish sodium-ion diffusion process, which opens a new direction to design and synthesize high-rate sodium-ion storage materials.

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High and ultra-stable energy storage from all-carbon sodium-ion capacitor with 3D framework carbon as cathode and carbon nanosheet as anode Fangyuan Hu, Siyang Liu, Shengming Li, Cheng Liu, Guipeng Yu, Ce Song, Wenlong Shao, Tianpeng Zhang, Xigao Jian 2021, 55(4): 304-312.  DOI: 10.1016/j.jechem.2020.06.034 Abstract ( 8 )   PDF (5639KB) ( 3 )   Sodium-ion capacitors (SICs) are extremely promising due to the combined merits of high energy-power characteristics and considerable price advantage. However, it is still difficult to achieve high energy-power outputs and cycle stability in a typical configuration of the metal-based battery-type anode and activated carbon capacitor-type cathode due to the kinetic mismatching. In this work, a carbon nanosheet (PSCS-600) with large interlayer spacing of 0.41 nm derived from the bio-waste pine cone shell was prepared. Besides, the covalent triazine framework derived carbon (OPDN-CTF-A) was obtained through ionothermal synthesis strategy, exhibiting beneficial hierarchical pores (0.5-6 nm) and high heteroatoms (5.6 at% N, 6.6 at% O). On this basis, the all-carbon SICs were fabricated by the integration of PSCS-600 anode and OPDN-CTF-A cathode. The device delivered high energy density 111 Wh kg-1, high power output of 14,200 W kg-1 and ultra-stable cycling life (~90.7% capacitance retention after 10,000 cycles). This work provides new ideas in fabricating carbon-carbon architectural SICs with high energy storage for practical application.

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A lithiated gel polymer electrolyte with superior interfacial performance for safe and long-life lithium metal battery Jia-Jia Yuan, Chuang-Chao Sun, Li-Feng Fang, You-Zhi Song, Yan Yan, Ze-Lin Qiu, Yu-Jie Shen, Han-Ying Li, Bao-Ku Zhu 2021, 55(4): 313-322.  DOI: 10.1016/j.jechem.2020.06.052 Abstract ( 6 )   PDF (6979KB) ( 1 )   Rechargeable lithium metal batteries (LMBs) have gained much attention recently. However, the short lifespan and safety issues restrict their commercial applications. Here we report a novel gel polymer electrolyte (GPE) based on lithiated poly(vinyl chloride-r-acrylic acid) (PVCAALi) to realize dendrite-suppressing and long-term stable lithium metal cycling. PVC chains ensure the quick gelation process and high electrolyte uptake, and lithiated PAA segments enable the increase of mechanical strength, acceleration of lithium-ion transmission and improvement of interfacial compatibility. PVCAALi GPE showed much higher mechanical strength compared with other free-standing GPEs in previous works. It displays a superior ionic conductivity of 1.50 mS cm−1 and a high lithium-ion transference number of 0.59 at room temperature. Besides, the lithiated GPE exhibits excellent interfacial compatibility with lithium metal anodes. Lithium symmetrical cells with PVCAALi GPE yield low hysteresis of 50 mV over 1000 h at 1.0 mA cm−2. And the possible mechanism of the lithiated GPE with improved lithium-ion transfer and interfacial property was discussed. Accordingly, both the Li4Ti5O12/Li and lithium-sulfur (Li-S) cells assembled with PVCAALi GPE show outstanding electrochemical performance, retaining high discharge capacities of 133.8 mAh g−1 and 603.8 mAh g−1 over 200 cycles, respectively. This work proves excellent application potential of the highly effective and low-cost PVCAALi GPE in safe and long-life LMBs.

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Graphene oxide: An emerging electromaterial for energy storage and conversion Yuheng Tian, Zhichun Yu, Liuyue Cao, XiaoLi Zhang, Chenghua Sun, Da-Wei Wang 2021, 55(4): 323-344.  DOI: 10.1016/j.jechem.2020.07.006 Abstract ( 9 )   PDF (19221KB) ( 8 )   This paper gives a comprehensive review of the recent progress on electrochemical energy storage devices using graphene oxide (GO). GO, a single sheet of graphite oxide, is a functionalised graphene, carrying many oxygen-containing groups. This endows GO with various unique features for versatile applications in batteries, capacitors and fuel cells. Specific applications are considered principally including use in electrodes as the active materials to enhance the performance or as substrates to diversify the structures, in solid-state electrolytes and membranes to improve the ionic conductivity and mechanical properties, and in interlayers to protect the electrodes, membranes or current collectors. Furthermore, the challenges and future prospects are discussed in the paper for encouraging further research and development of GO applications.

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Ultra-small Co/CoOx nanoparticles dispersed on N-doped carbon nanosheets for highly efficient electrocatalytic oxygen evolution reaction Chen Chen, Zhuojun Yang, Wei Liang, Hao Yan, Yongxiao Tuo, Yanpeng Li, Yan Zhou, Jun Zhang 2021, 55(4): 345-354.  DOI: 10.1016/j.jechem.2020.07.017 Abstract ( 4 )   PDF (5759KB) ( 2 )   In this paper, we report a facile strategy to synthesize Co-BDC-NH2 material, which is used as a precursor towards an excellent OER electrocatalyst by thermal annealing in nitrogen. Ultra-small Co/CoOx nanoparticles were uniformly dispersed on the rhombus N-doped carbon (NC) nanoflakes. Transmission electron microscopic, X-ray diffraction spectrometric, and X-ray photoelectron spectroscopic analyses revealed the coexistence of metallic Co and Co oxides nanoparticles. It was found that Co/CoOx@NC obtained at 500 °C annealing temperature exhibited the highest electrocatalytic OER activity, with 307 and 375 mV overpotential to achieve 10 and 100 mA cm-2 current densities. Besides, thanks to the in-situ annealing process, Co/CoOx@NC showed excellent catalytic stability with 97.4% current density retention after 24 h electrolysis at 1.66 V vs. RHE electrode potential. Further investigations revealed that the ultra-small Co/CoOx nanoparticles distributed on N-doped carbon template contribute significantly towards OER electrocatalysis through enlarging the activity surface areas and enhancing the intrinsic electrochemical activity due to the presence of metallic Co.

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3D star-like atypical hybrid MOF derived single-atom catalyst boosts oxygen reduction catalysis Lei Zhou, Peng Zhou, Yelong Zhang, Bingyao Liu, Peng Gao, Shaojun Guo 2021, 55(4): 355-360.  DOI: 10.1016/j.jechem.2020.06.059 Abstract ( 7 )   PDF (3381KB) ( 3 )   Developing high-efficiency, stable and non-precious electrocatalysts for oxygen reduction reaction (ORR) is highly important for energy conversion and storage. Single atom catalysts (SACs) show good potential in enhancing ORR, however, the specifical control over the coordination surroundings around single metal center to intrinsically modify the electron structure is still a great challenge. Herein, we demonstrate that a 3D hybrid MOF composed of cobalt doped ZIF-L and ZIF-8, featuring star morphology with six equal branches, can be used as an advanced precursor for making the Co SACs for greatly boosted ORR. The as-synthesized CoSA-N-C exhibits excellent ORR activity with E1/2 of 0.891 V in alkaline medium, outperforming the commercial Pt/C by 39 mV. Moreover, the E1/2 of CoSA-N-C (0.790 V) is merely 15 mV, less than that of Pt/C (0.805 V) in acid medium, which is among the best in the reported state-of-the-art SACs. DFT calculations demonstrate that the enhanced ORR performance is assigned to the formation of atomically isolated cobalt atom coordinated three N atoms and one C atom, which is easier to decrease the free energy of rate determining step and accelerate the ORR process than that of traditional cobalt atom coordinated four N atoms. In addition, a primary Zn-air battery with CoSA-N-C cathode reveals a maximum power density of 92.2 mW cm-2 at 120.0 mA cm-2, far higher than that of commercial catalysts (74.2 mW cm-2 at 110.0 mA cm-2).

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Vanadium-based polyanionic compounds as cathode materials for sodium-ion batteries: Toward high-energy and high-power applications Zhiqiang Lv, Moxiang Ling, Meng Yue, Xianfeng Li, Mingming Song, Qiong Zheng, Huamin Zhang 2021, 55(4): 361-390.  DOI: 10.1016/j.jechem.2020.07.008 Abstract ( 14 )   PDF (20585KB) ( 6 )   Sodium ion batteries (SIBs) have been regarded as one of the alternatives to lithium ion batteries owing to their wide availability and significantly low cost of sodium sources. However, they face serious challenges of low energy & power density and short cycling lifespan owing to the heavy mass and large radius of Na+. Vanadium-based polyanionic compounds have advantageous characteristic of high operating voltage, high ionic conductivity and robust structural framework, which is conducive to their high energy & power density and long lifespan for SIBs. In this review, we will overview the latest V-based polyanionic compounds, along with the respective characteristic from the intrinsic crystal structure to performance presentation and improvement for SIBs. One of the most important aspect is to discover the essential problems existed in the present V-based polyanionic compounds for high-energy & power applications, and point out most suitable solutions from the crystal structure modulation, interface tailoring and electrode configuration design. Moreover, some scientific issues of V-based polyanionic compounds shall be also proposed and related future direction shall be provided. We believe that this review can serve as a motivation for further development of novel V-based polyanionic compounds and drive them toward high energy & power applications in the near future.

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Recent progress on the recycling technology of Li-ion batteries Yuqing Wang, Ning An, Lei Wen, Lei Wang, Xiaotong Jiang, Feng Hou, Yuxin Yin, Ji Liang 2021, 55(4): 391-419.  DOI: 10.1016/j.jechem.2020.05.008 Abstract ( 16 )   PDF (16888KB) ( 15 )   Lithium-ion batteries (LIBs) have been widely applied in portable electronic devices and electric vehicles. With the booming of the respective markets, a huge quantity of spent LIBs that typically use either LiFePO4 or LiNixCoyMnzO2 cathode materials will be produced in the very near future, imposing significant pressure for the development of suitable disposal/recycling technologies, in terms of both environmental protection and resource reclaiming. In this review, we firstly do a comprehensive summary of the-state-of-art technologies to recycle LiNixCoyMnzO2 and LiFePO4-based LIBs, in the aspects of pretreatment, hydrometallurgical recycling, and direct regeneration of the cathode materials. This closed-loop strategy for cycling cathode materials has been regarded as an ideal approach considering its economic benefit and environmental friendliness. Afterward, as for the exhausted anode materials, we focus on the utilization of exhausted anode materials to obtain other functional materials, such as graphene. Finally, the existing challenges in recycling the LiFePO4 and LiNixCoyMnzO2 cathodes and graphite anodes for industrial-scale application are discussed in detail; and the possible strategies for these issues are proposed. We expect this review can provide a roadmap towards better technologies for recycling LIBs, shed light on the future development of novel battery recycling technologies to promote the environmental benignity and economic viability of the battery industry and pave way for the large-scale application of LIBs in industrial fields in the near future.

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Nitrogen/sulphur dual-doped hierarchical carbonaceous fibers boosting potassium-ion storage Junzhi Li, Junming Cao, Xifei Li, Junhua Hu, Yaohui Zhang, Hirbod Maleki Kheimeh Sari, Chunxiao Lv, Igor. V. Zatovsky, Wei Han 2021, 55(4): 420-427.  DOI: 10.1016/j.jechem.2020.07.023 Abstract ( 5 )   PDF (5286KB) ( 2 )   The carbon materials as anode electrodes have been widely studied for potassium ion batteries (PIBs). However, the large size of potassium ions prevents their intercalation/deintercalation, resulting in poor storage behaviors. Herein, a novel design of N/S codoped hierarchical carbonaceous fibers (NSHCF) formed from nanosheets self-assembled by catalyzing Aspergillus niger with Sn is reported. The as-prepared NSHCF at 600 °C (NSHCF-600) exhibits a high reversible capacity of 345.4 mAh g-1 at 0.1 A g-1 after 100 cycles and an excellent rate performance of 124.5 mAh g-1 at 2 A g-1. The excellent potassium storage performance can be ascribed to the N/S dual-doping, which enlarges interlayer spacing (0.404 nm) and introduces more defects. The larger interlayer spacing and higher pyridinic N active sites can promote K ions diffusion and storage. In addition, the ex situ transmission electron microscopy reveals the high reversibility of potassiation/depotassiation process and structural stability.

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A Pt/MnV2O6 nanocomposite for the borohydride oxidation reaction Jadranka Milikić, Marta Martins, Ana S. Dobrota, Gamze Bozkurt, Gulin S.P. Soylu, Ayşe B. Yurtcan, Natalia V. Skorodumova, Igor A. Pašti, Biljana Šljukić, Diogo M.F. Santos 2021, 55(4): 428-436.  DOI: 10.1016/j.jechem.2020.07.029 Abstract ( 5 )   PDF (3632KB) ( 3 )   Problems associated with carbon support corrosion under operating fuel cell conditions require the identification of alternative supports for platinum-based nanosized electrocatalysts. Platinum supported on manganese vanadate (Pt/MnV2O6) was prepared by microwave irradiation method and characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, and transmission electron microscopy. The borohydride oxidation reaction (BOR) on Pt/MnV2O6 was studied in highly alkaline media using voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. BOR electrocatalytic activity of Pt/MnV2O6 was also compared with that of commercial Pt/C (46 wt% Pt) electrocatalyst. The apparent activation energy of BOR at Pt/MnV2O6 was estimated to be 32 kJ mol-1 and the order of reaction to be 0.51, indicating that borohydride hydrolysis proceeds in parallel with its oxidation. Long-term stability of Pt/MnV2O6 under BOR typical conditions was observed. A laboratory-scale direct borohydride fuel cell assembled with a Pt/MnV2O6 anode reached a specific power of 274 W g-1. Experimental results on Pt/MnV2O6 were complemented by DFT calculations, which indicated good adherence of Pt to MnV2O6, beneficial for electrocatalyst stability.

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TMN4 complex embedded graphene as bifunctional electrocatalysts for high efficiency OER/ORR Zhe Xue, Xinyu Zhang, Jiaqian Qin, Riping Liu 2021, 55(4): 437-443.  DOI: 10.1016/j.jechem.2020.07.018 Abstract ( 4 )   PDF (3192KB) ( 2 )   Developing highly active bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of great significance in energy conversion and storage technologies. In this study, we systematically investigated the OER/ORR electrocatalytic activity of TMN4@G system by using density functional theory (DFT) calculations. Globally, IrN4@G is a very promising bifunctional catalyst for both OER and ORR with the extremely low overpotentials of 0.30 and 0.26 V, respectively. Such outstanding electrocatalytic performance is mainly attributed to the synergistic effect of Ir and N. More importantly, by constructing 2D activity volcano plots, we obtained the limiting overpotentials of TMN4@G system with the values of 0.26 V for OER and 0.24 V for ORR. These findings open up new opportunities for further exploring graphene-based materials for highly efficient OER/ORR electrocatalysts.

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Metal-seed assistant photodeposition of platinum over Ta3N5 photocatalyst for promoted solar hydrogen production under visible light Juhong Lian, Deng Li, Yu Qi, Nengcong Yang, Rui Zhang, Tengfeng Xie, Naijia Guan, Landong Li, Fuxiang Zhang 2021, 55(4): 444-448.  DOI: 10.1016/j.jechem.2020.07.034 Abstract ( 6 )   PDF (2148KB) ( 2 )   Cocatalysts play a vital role in accelerating the reaction kinetics and improving the charge separation of photocatalysts for solar hydrogen production. The promotion of the photocatalytic activity largely relies on the loading approach of the cocatalysts. Herein, we introduce a metal-seed assistant photodeposition approach to load the hydrogen evolution cocatalyst of platinum onto the surface of Ta3N5 photocatalyst, which exhibits about 3.6 times of higher photocatalytic proton reduction activity with respect to the corresponding impregnation or photodeposition loading. Based on our characterizations, the increscent contact area of the cocatalyst/semiconductor interface with metal-seed assistant photodeposition method is proposed to be responsible for the promoted charge separation as well as enhanced photocatalytic H2 evolution activity. It is interesting to note that this innovative deposition strategy can be easily extended to loading of platinum cocatalyst with other noble or non-noble metal seeds for promoted activities, demonstrating its good generality. Our work may provide an alternative way of depositing cocatalyst for better photocatalytic performances.

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Synergistic effect from coaxially integrated CNTs@MoS2/MoO2 composite enables fast and stable lithium storage Hui Lu, Kai Tian, Liangmin Bu, Xue Huang, Xiangyi Li, Yue Zhao, Feng Wang, Jianming Bai , Lijun Gao, Jianqing Zhao 2021, 55(4): 449-458.  DOI: 10.1016/j.jechem.2020.07.033 Abstract ( 6 )   PDF (5667KB) ( 1 )   Molybdenum oxide/sulfide materials are extensively evaluated as high-capacity anode candidates for lithium ion batteries. However, they suffer from rapid capacity decay and poor kinetics. Herein, we report on synergistic effect from structurally integrated coaxial CNTs@MoS2/MoO2 composite material on lithium storage, in which MoS2/MoO2 nanosheets are conformally decorated on carbon nanotubes (CNTs). In-situ synchrotron X-ray diffraction measurement is performed to elucidate synergistic effect among three MoS2, MoO2 and CNTs components for lithium storage. Reaction mechanism exploration reveals that the MoO2 component undergoes reversible Li+ intercalation via forming a stable Li0.98MoO2 phase over a voltage range of 3.0 to 0.01 V vs. Li+/Li, without experiencing the conversion reaction into metallic Mo, which contributes to long-term stability during charge/discharge cycles. Meanwhile, lithium storage of MoS2 is through lithium and sulfur reversible reaction after the initial conversion reaction of lithiated MoS2 forming Li2S and Mo. The CNTs component enhances electronic conductivity and structural stability by minimizing volume change and reaction strains in the CNTs@MoS2/MoO2 composite anode. A desired 68.2% capacity retention upon 2000 cycles at 10 A/g has been demonstrated for the CNTs@MoS2/MoO2 anode, revealing prominent reaction kinetics and structural stability for fast and stable lithium storage, superior to various Mo-based anode materials previously reported. The findings from this study, with the unique insight into the role of structural integrity in combining MoS2/MoO2 materials with the CNTs substrate, offers a strategy for designing composite anode materials for superior lithium storage performance.

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Intercalation-pseudocapacitance hybrid anode for high rate and energy lithium-ion capacitors Chang Liu, Ali Khosrozadeh, Qing-Qing Ren, Ling-Hui Yan, Kokswee Goh, Shi-Han Li, Jian Liu, Lei Zhao, Da-Ming Gu, Zhen-Bo Wang 2021, 55(4): 459-467.  DOI: 10.1016/j.jechem.2020.07.032 Abstract ( 3 )   PDF (5012KB) ( 3 )   Existing rechargeable batteries not only fail to meet the demand for high power applications but also cause heavy metal pollution. Li-ion capacitors (LICs), which can achieve higher charging speeds and energy densities than supercapacitors, have attracted extensive attention. Nevertheless, sluggish Li-ion diffusion of the battery-type anode results in limited rate performance of LICs. Herein, high-performance LICs using both battery and capacitor type Mn2V2O7-graphene (MVO-G) anodes and hempstem-derivated activated carbon (HSAC) cathodes with a large surface area are first reported. In addition to high pseudocapacitance, the MVO-G possesses the advantage of fast Li+ storage performance making it a suitable choice for advanced LIC anodes. Graphene is employed to enhance overall conductivity and cycling stability leading to enhanced energy storage. The MVO-G//HSAC LICs exhibit a high energy density of 148.1 Wh kg-1 at a power density of 150 W kg-1 and 25 Wh kg-1 even at 15 kW kg-1. More importantly, the MVO-G//HSAC LICs also show excellent cycling stability of 90% after 15,000 cycles, which is expected for high performance energy storage systems.

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2D spinel ZnCo2O4 microsheet-coated functional separator for promoted redox kinetics and inhibited polysulfide dissolution Jeong Seok Yeon, Tae Ho Park, Young Hun Ko, Periyasamy Sivakumar, Jun Su Kim, Youngkywon Kim, Ho Seok Park 2021, 55(4): 468-475.  DOI: 10.1016/j.jechem.2020.07.007 Abstract ( 5 )   PDF (7075KB) ( 2 )   Lithium-sulfur (Li-S) batteries are receiving increasing attention as one of the potential next-generation batteries, owing to their high energy densities and low cost. However, practical Li-S batteries with high energy densities are extremely hindered by the sulfur loss, low Coulombic efficiency, and short cycling life originating from the polysulfide (LiPS) shuttle. In this study, two-dimensional (2D) ZnCo2O4 microsheets fabricated by a facile hydrothermal process are employed to modify the separator, for improving the electrochemical performances of Li-S cells. The resulting 2D ZnCo2O4-coated separator features a coating thickness of approximately 10 μm, high ionic conductivity of 1.8 mS/cm, and low mass loading of 0.2 mg/cm2. This 2D ZnCo2O4-coated separator effectively inhibits LiPS shuttle by a strong chemical interaction with LiPS as well as promotes the redox kinetics by ZnCO2O4-coated layers, as determined by X-ray photoelectron spectroscopy analysis, self-discharge, time-dependent permeation test, Li symmetric cell test, and Li2S nucleation analyses. Consequently, the Li-S batteries based on the 2D ZnCo2O4-coated separator exhibit a high initial discharge capacity of 1292.2 mAh/g at 0.1 C. Moreover, they exhibit excellent long cycle stability at 1 and 2 C with capacity retention of 84% and 86% even after 800 cycles, corresponding to a capacity fading rate of 0.020% and 0.016% per cycle, respectively. Effectively, these Li-S cells with a high sulfur loading at 5.3 mg/cm2 and low electrolyte concentration of 9 μL/mg deliver a high discharge capacity of 4.99 mAh/cm2 after 200 cycles at 0.1 C.

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Lignin derived hierarchical porous carbon with extremely suppressed polyselenide shuttling for high-capacity and long-cycle-life lithium-selenium batteries Pengfei Lu, Fangyan Liu, Feng Zhou, Jieqiong Qin, Haodong Shi, Zhong-Shuai Wu 2021, 55(4): 476-483.  DOI: 10.1016/j.jechem.2020.07.022 Abstract ( 4 )   PDF (4039KB) ( 2 )   Lithium-selenium (Li-Se) batteries have attracted considerable attentions for next-generation energy storage systems owing to high volumetric capacity of 3265 mAh cm-3 and excellent electronic conductivity (~10-5 S cm-1) of selenium. However, the shuttling effect and capacity fading prevent their wide applications. Herein we report a low-cost strategy for scalable fabrication of lignin derived hierarchical porous carbon (LHPC) as a new high-loading Se host for high-capacity and long-term cycling Li-Se batteries in carbonate electrolyte. The resulting LHPC exhibits three-dimensional (3D) hierarchically porous structure, high specific surface area of 1696 m2 g-1, and hetero-atom doping (O, S), which can effectively confine the Se particles into the micropores, and meanwhile, offer effective chemical binding sites for selenides from hetero-atoms (O, S). As a result, our Li-Se batteries based on Se@LHPC demonstrate high capacity of 450 mAh g-1 at 0.5 C after 500 cycles, with a low capacity fading rate of only 0.027%. The theoretical simulation confirmed the strong affinity of selenides on the O and S sites of LHPC effectively mitigating the Se losing. Therefore, our strategy of using lignin as the low-cost precursor of hierarchically porous carbon for high-loading Se host offers new opportunities for high-capacity and long-life Li-Se batteries.

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Overcharge-to-thermal-runaway behavior and safety assessment of commercial lithium-ion cells with different cathode materials: A comparison study Zhenpo Wang, Jing Yuan, Xiaoqing Zhu, Hsin Wang, Lvwei Huang, Yituo Wang, Shiqi Xu 2021, 55(4): 484-498.  DOI: 10.1016/j.jechem.2020.07.028 Abstract ( 43 )   PDF (7127KB) ( 35 )   In this paper, overcharge behaviors and thermal runaway (TR) features of large format lithium-ion (Li-ion) cells with different cathode materials (LiFePO4 (LFP), Li[Ni1/3Co1/3Mn1/3]O2 (NCM111), Li[Ni0.6Co0.2Mn0.2]O2 (NCM622) and Li[Ni0.8Co0.1Mn0.1]O2 (NCM811)) were investigated. The results showed that, under the same overcharge condition, the TR of LFP Li-ion cell occurred earlier compared with the NCM Li-ion cells, indicating its poor overcharge tolerance and high TR risk. However, when TR occurred, LFP Li-ion cell exhibited lower maximum temperature and mild TR response. All NCM Li-ion cells caught fire or exploded during TR, while the LFP Li-ion cell only released a large amount of smoke without fire. According to the overcharge behaviors and TR features, a safety assessment score system was proposed to evaluate the safety of the cells. In short, NCM Li-ion cells have better performance in energy density and overcharge tolerance (or low TR risk), while LFP Li-ion cell showed less severe response to overcharging (or less TR hazards). For NCM Li-ion cells, as the ratio of nickel in cathode material increases, the thermal stability of the cathode materials becomes poorer, and the TR hazards increase. Such a comparison study on large format Li-ion cells with different cathode materials can provide deeper insights into the overcharge behaviors and TR features, and provide guidance for engineers to reasonably choose battery materials in automotive applications.

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Insight to defects regulation on sugarcane waste-derived hard carbon anode for sodium-ion batteries Kaihua Yu, Xinran Wang, Haoyi Yang, Ying Bai, Chuan Wu 2021, 55(4): 499-508.  DOI: 10.1016/j.jechem.2020.07.025 Abstract ( 7 )   PDF (6519KB) ( 7 )   A great deal of attention has been paid on developing plant-derived hard carbon (HC) materials as anodes for sodium-ion batteries (SIBs). So far, the regulation of HC has been handicapped by the well-known ambiguity of Na+ storage mechanism, which fails to differentiate the Na+ adsorption and Na+ insertion, and their relationship with the size of d-interlayer spacing and structural porosity. Herein, bagasse-derived HC materials have been synthesized through a combination of pyrolysis treatment and microwave activation. The combined protocol has enabled to synergistically control the d-interlayer spacing and porosity. Specifically, the microwave activation has created slit pores into HC and these pores allow for an enhanced Na+ adsorption with an increased sloping capacity, establishing a strong correlation between the porosity and sloping capacity. Meanwhile, the pyrolysis treatment promotes the graphitization and it contributes to an intensified Na+ insertion with an increased plateau capacity, proving that the plateau capacity is largely contributed by the Na+ insertion between interlayers. Therefore, the structural regulation of bagasse-derived HC has provided a proof on positively explaining the Na+ storage with HC materials. The structural changes in the pore size distribution, specific surface area, d-interlayer spacing, and the electrochemical properties have been comprehensively characterized, all supporting our understanding of Na+ storage mechanism. As a result, the HC sample with an optimized d-interlayer spacing and porosity has delivered an improved reversible capacity of 323.6 mAh g-1 at 50 mA g-1. This work provides an understanding of Na+ storage mechanism and insights on enhancing the sloping/plateau capacity by rationally regulating the graphitization and porosity of HC materials for advanced SIBs.

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Effect of the lead deposition on the performance of the negative electrode in an aqueous lead-carbon hybrid capacitor Jinpeng Bao, Nan Lin, Haibo Lin, Jiaxiang Guo, Hongyu Gao, Weiqi Gao 2021, 55(4): 509-516.  DOI: 10.1016/j.jechem.2020.06.045 Abstract ( 4 )   PDF (12192KB) ( 1 )   Lead-carbon hybrid capacitors are the electrochemical devices between supercapacitors and lead-acid batteries, with low prices, stability in high and low temperature, good security and broad application prospects. This paper introduces an electrodeposition behavior of Pb2+ on the negative electrode, which can improve the cycle life of the lead-carbon hybrid capacitor. During the charging process, lead ions in the electrolyte can diffuse from the positive electrode of the lead-carbon hybrid capacitor into the negative electrode. When charging at a low current density, the lead ions around the negative electrode can be reduced to lead, and it is then quickly converted to lead sulfate crystals. With the increase of the number of cycles, the final result is sulfation. Sulfation can reduce the specific surface area of the electric double layer, thereby reducing the capacitance performance of the carbon material. As a result, it reduces the charge-discharge efficiency of the lead-carbon hybrid capacitor. The service life of lead-carbon hybrid capacitor is significantly improved by the inhibition of lead deposition by anion exchange membrane. The capacity retention rate at 5 A/g is improved from 84% after 1000 cycles to 95% after 10,000 cycles. The discovery of lead deposition in the negative electrode is conducive to improving the performance of long-life lead-carbon hybrid capacitors.

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Dendrite-structured FeF2 consisting of closely linked nanoparticles as cathode for high-performance lithium-ion capacitors Huanyu Liang, Zhengqiang Hu, Zhongchen Zhao, Dong Chen ⇑, Hao Zhang, Huaizhi Wang, Xia Wang, Qiang Li, Xiangxin Guo, Hongsen Li 2021, 55(4): 517-523.  DOI: 10.1016/j.jechem.2020.07.031 Abstract ( 5 )   PDF (3016KB) ( 2 )   Lithium-ion capacitors (LICs) are regarded as a good choice for next-generation energy storage devices, which are expected to exhibit high energy densities, high power densities, and ultra-long cycling stability. Nevertheless, only a few battery-type cathode materials with limited kinetic properties can be employed in LICs, and their electrochemical properties need to be optimized urgently. Here, we exploit a new dendrite-structured FeF2 consisting of closely linked primary nanoparticles using a facile solvothermal method combined with the subsequent annealing treatment. This particular architecture has favorable transport pathways for both lithium ions and electrons and exhibits an ultrafast charge-discharge capability with high reversible capacities. Furthermore, a well-designed LIC employing the prepared dendrite-structured FeF2 as the battery-type cathode and commercialized activated carbon (AC) as supercapacitor-type anode was constructed in an organic electrolyte containing Li ions. The LIC operates at an optimal voltage range of 1.1-3.8 V and shows a maximum high energy density of 152 W h kg-1 and a high power density of 4900 W kg-1 based on the total mass of cathode and anode. Long-term cycling stability (85% capacity retention after 2000 cycles) was achieved at 1 A g-1. This work suggests that the dendrite-structured FeF2 is a prime candidate for high-performance LICs and accelerates the development of hybrid ion capacitor devices.

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Evolution of the morphology, structural and thermal stability of LiCoO2 during overcharge Zhitao E, Huajun Guo, Guochun Yan, Jiexi Wang, Rukun Feng, Zhixing Wang, Xinhai Li 2021, 55(4): 524-532.  DOI: 10.1016/j.jechem.2020.06.071 Abstract ( 7 )   PDF (11033KB) ( 1 )   The overcharge behaviors of 1000 mAh LiCoO2/graphite pouch cells are systematically investigated through the analysis of morphology, structural and thermal stability of LiCoO2 under different state of charge (SOC) of 120%, 150%, 174%, 190% and 220%. The LiCoO2 experiences the phase transition from O3 to H1-3 and then O1 together with the grain breakage and boundary slip as evidenced by XRD and SEM analysis respectively, which results in the pronounced Co dissolution after the SOC of 174%. The impedance analysis of the pouch cells and coin cells demonstrates that the main contribution of impedance increase originates from the LiCoO2 electrode. Under the combined effect of structural collapse, Co dissolution, and electrolyte oxidization, the thermal stability of LiCoO2 cathode materials reduces with the progressing of overcharge as revealed by differential scanning calorimetry (DSC) results. We hope that this comprehensive understanding can provide meaningful guidance for advancing the overcharge performance of LiCoO2/graphite pouch cells.

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Recent advances of metal phosphides for Li-S chemistry Songlin Yu, Wenlong Cai, Le Chen, Lixian Song, Yingze Song 2021, 55(4): 533-548.  DOI: 10.1016/j.jechem.2020.07.020 Abstract ( 4 )   PDF (16961KB) ( 1 )   Li-S batteries have been considered as one of advanced next-generation energy storage systems owing to their remarkable theoretical capacity (1672 mAh g-1) and high energy density (2600 Wh kg-1). However, critical issues, mainly pertaining to lithium polysulfide shuttle and slow sulfur reaction kinetics, have posed a fatal threat to the electrochemical performances of Li-S batteries. The situation is even worse for high sulfur-loaded and flexible cathodes, which are the essential components for practical Li-S batteries. In response, the use of metal compounds as electrocatalysts in Li-S systems have been confirmed as an effective strategy to date. Particularly, recent years have witnessed many progresses in phosphides-optimized Li-S chemistry. This has been motivated by the superior electron conductivity and high electrocatalytic activity of phosphides. In this tutorial review, we offer a systematic summary of active metal phosphides as promoters for Li-S chemistry, aiming at helping to understanding the working mechanism of phosphide electrocatalysts and guiding the construction of advanced Li-S batteries.

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Suppressing by-product via stratified adsorption effect to assist highly reversible zinc anode in aqueous electrolyte Miao Zhou, Shan Guo, Guozhao Fang, Hemeng Sun, Xinxin Cao, Jiang Zhou, Anqiang Pan, Shuquan Liang 2021, 55(4): 549-556.  DOI: 10.1016/j.jechem.2020.07.021 Abstract ( 6 )   PDF (4834KB) ( 3 )   The development of promising zinc anodes mainly suffers from their low plating/stripping coulombic efficiencies when using aqueous electrolyte, which are mainly associated with the interfacial formation of irreversible by-products. It is urgent to develop technologies that can solve this issue fundamentally. Herein, we report an artificial Sc2O3 protective film to construct a new class of interface for Zn anode. The density functional theory simulation and experimental results have proven that the interfacial side reaction was inhibited via a stratified adsorption effect between this artificial layer and Zn anode. Benefiting from this novel structure, the Sc2O3-coated Zn anode can run for more than 100 cycles without short circuit and exhibit low voltage hysteresis, and the coulombic efficiency increases by 1.2%. Importantly, it shows a good application prospect when matched with two of popular manganese-based and vanadium-based cathodes. The excellent electrochemical performance of the Sc2O3-coated Zn anode highlights the importance of rational design of anode materials and demonstrates a good way for developing high-performance Zn anodes with long lifespan and high efficiency.

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Gallium-based anodes for alkali metal ion batteries Wenjin Yang, Xianghua Zhang, Huiteng Tan, Dan Yang, Yuezhan Feng, Xianhong Rui, Yan Yu 2021, 55(4): 557-571.  DOI: 10.1016/j.jechem.2020.07.035 Abstract ( 6 )   PDF (15143KB) ( 5 )   Alkali metal ion batteries (AMIBs) are playing an irreplaceable part in the energy revolution, due to their intrinsic advantages of large capacity/power density and abundance of alkali metal ions in the earth's crust. Despite their great promise, the inborn deficiencies of commercial graphite and other anodes being researched so far call for the quest of better alternatives that exhibit all-round performance with the balance of energy/power density and cycling stability. Gallium-based materials, with impressive capacity utilization and self-healing ability, provide an anticipated solution to this conundrum. In this review, an overview on the recent progress of gallium-based anodes and their storage mechanism is presented. The current strategies used as engineering solutions to meet the scientific challenges ahead are discussed, in addition to the insightful outlook for possible future study.

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Boost oxygen reduction reaction performance by tuning the active sites in Fe-N-P-C catalysts Yahao Li, Ketao Zang, Xuezhi Duan, Jun Luo, De Chen 2021, 55(4): 572-579.  DOI: 10.1016/j.jechem.2020.07.041 Abstract ( 4 )   PDF (3793KB) ( 3 )   Cost-effective atomically dispersed Fe-N-P-C complex catalysts are promising to catalyze the oxygen reduction reaction (ORR) and replace Pt catalysts in fuel cells and metal-air batteries. However, it remains a challenge to increase the number of atomically dispersed active sites on these catalysts. Here we report a highly efficient impregnation-pyrolysis method to prepare effective ORR electrocatalysts with large amount of atomically dispersed Fe active sites from biomass. Two types of active catalyst centers were identified, namely atomically dispersed Fe sites and FexP particles. The ORR rate of the atomically dispersed Fe sites is three orders of magnitude higher than it of FexP particles. A linear correlation between the amount of the atomically dispersed Fe and the ORR activity was obtained, revealing the major contribution of the atomically dispersed Fe to the ORR activity. The number of atomically dispersed Fe increases as the Fe loading increased and reaching the maximum at 1.86 wt% Fe, resulting in the maximum ORR rate. Optimized Fe-N-P-C complex catalyst was used as the cathode catalyst in a homemade Zn-air battery and good performance of an energy density of 771 Wh kgZn-1, a power density of 92.9 mW cm-2 at 137 mA cm-2 and an excellent durability were exhibited.

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Regulating electrodeposition behavior through enhanced mass transfer for stable lithium metal anodes Yuliang Gao, Fahong Qiao, Jingyuan You, Chao Shen, Hui Zhao, Jinlei Gu, Zengying Ren, Keyu Xie, Bingqing Wei 2021, 55(4): 580-587.  DOI: 10.1016/j.jechem.2020.07.019 Abstract ( 9 )   PDF (5896KB) ( 2 )   Electrode process kinetics is a key part that determines the morphology of metal electrodeposition. However, the liquid-phase mass transfer process and its effect on lithium (Li) metal electrodeposition are still poorly understood. Herein, the effect of mass transfer on the electrodeposition behavior of Li metal is explored. Experiments and COMSOL Multiphysics simulations reveal that the enhanced mass transfer, which is induced by ultrasonic wave, can homogenize the ion flow on the surface of electrode to obtain uniform Li nucleation. Meanwhile, the rapid mass transfer of Li+ provides sufficient cations around the germinated Li to avoid preferential growth of Li in a specific direction. Based on the simultaneous regulation of nucleation and growth behavior, a smooth and compact Li deposits can be achieved, which exhibit a small polarization voltage during repeated Li plating/striping and a considerably enhanced cyclability. This work enriches the fundamental understanding of Li electrodeposition without dendrite structure and affords fresh guidance to develop dendrite-free metal anodes for metal-based batteries.