Lithium difluoro(oxalate)borate as electrolyte additive to form uniform, stable and LiF-rich solid electrolyte interphase for high performance lithium ion batteries

The electrochemical performance of lithium-ion batteries (LIBs) is closely associated with the solid electrolyte interface (SEI) film formed on the surface of the anode. The pursuit of a stable and dense SEI film to enhance the electrochemical performance of LIBs has been a focal point in this field. In this paper, the additive of lithium difluoro(oxalate)borate (LiODFB) is used into the electrolyte to optimize the SEI film for Li || graphite half-cell and LiFePO4 (LFP) || graphite full-cell. A systematic investigation is conducted to explore the influence patterns and action mechanisms of different LiODFB contents on the electrochemical performance of LIBs. For the first time, it is confirmed through cryo-TEM that LiODFB contributes to the formation of a dense, continuous, and uniform SEI layer, especially rich of LiF. This unique SEI film contributes to the high electrochemical performance of LIBs. The half-cell containing 4 wt.% LiODFB maintains a capacity retention rate of up to 94% after 300 cycles, and the full-cell still exhibits a specific capacity of 102 mAh g−1 after 600 cycles. In contrast, the sample without LiODFB only retains 76% of its capacity after 300 cycles, and 39% after 600 cycles, respectively. Furthermore, the cells with 4 wt.% LiODFB exhibit the lowest charge transfer resistance and oxidation-reduction potential polarization, and highest Li+ transport rates during charge and discharge processes.