Abstract: Although the fast development of potassium-ion hybrid capacitors (PIHC) recently, the issues such as the slow kinetics and poor durability of potassium ion hosts greatly restric their applications. Herein, a freestanding fiber (NHF fiber) with necklace-like configuration and CoPSe@N-doped carbon (CoPSe@NCNT) heterostructured units is introduced as the anode in PIHC. The highly porous network of NHF fiber facilitates the fast ion transports and promises the good high-rate property. Additionally, the nanoscle crystallites inside in-situ grown NCNT favor the high adaption to volume expansion/shrinkage and endow good structure stability during ion insertion/deinsertion. Density function theoretical (DFT) calculations disclose the CoPSe@NCNT heterostructure has improved intrinsic conductivity, fast potassium migration, and decreased energy barrier. Meanwhile, the finite element simulation analysis (FEA) reveals the decreased stress inside the NHF architecture during charge/discharge processes. Moreover, the electrochemical tests confirm the fast and durable properties of the CoPSe@NCNT NHF fibers for potassium storage. Furthermore, the PIHC full cell with the anode of CoPSe@NCNT NHF fiber is assembled, which obtains the superior energy/power densities and high capacity retention (89%) after 2000 cycles at 2 A g^-1. When the polymer electrolyte is incooperated, the flexible PIHC device achieves the good pliability and good adaptation during wide temperature changes from -20 to 25 °C. Therefore, this work introduces a novel anode for fast potassium ion storage, and opens a new approach to assemble the power sources for flexible electronics in diverse conditions.

Key words: CoPSe@NCNT heterostructure, Freestanding fiber, Fast kinetics, Hybrid capacitor