Abstract: ‘‘Dissolution, migration, and deposition” of transition metal ions (TMIs) result in capacity degradation of lithium-ion batteries (LIBs). Understanding such detrimental mechanism of TMIs is critical to the devel-opment of LIBs with long cycle life. In most previous works, TMIs were directly introduced into the elec-trolyte to investigate such a detrimental mechanism. In these cases, the TMIs are deposited directly on the fresh anode surface. However, in the practical battery system, the TMIs are deposited on the anode covered with solid electrolyte interphase (SEI) film. Whether the pre-presence of SEI film on anode sur-face influences the deposition and detriment of TMIs is unclear. In this work, the deposition of Co element on graphite anode with and without SEI film were systematically studied. The results clearly show that, in comparison with that of fresh graphite (SEI-free), the presence of SEI film aggravates the deposition of Co ions due to the Li⁺-Co²⁺ ion exchange between the SEI and Co²⁺-containing electrolyte without the driv-ing of the electric field, leading to faster capacity fading of graphite anode. Therefore, how to regulate electrolytes and film-forming additives to design the components of SEI and prevent its exchange with TMIs, is a crucial way to inhibit the deposition and detriment of TMIs on graphite anode.

Key words: Lithium-ion batteries, Transition metal ions, Ion exchange, Graphite anode, SEI film