Interphase Regulation by Multifunctional Additive Empowering High Energy Lithium‐Ion Batteries with Enhanced Cycle Life and Thermal Safety

High energy density lithium‐ion batteries (LIBs) adopting high‐nickel layered oxide cathodes and silicon‐based composite anodes always suffer from unsatisfied cycle life and poor safety performance, especially at elevated temperatures. Electrode/electrolyte interphase regulation by functional additives is one of the most economic and efficacious strategies to overcome this shortcoming. Herein, cyano‐groups (‐CN) are introduced into lithium fluorinated phosphate to synthesize a novel multifunctional additive of lithium tetrafluoro (1,2‐dihydroxyethane‐1,1,2,2‐tetracarbonitrile) phosphate (LiTFTCP), which endows high nickel LiNi0.8Co0.1Mn0.1O2 /SiOx‐graphite composite full cell with an ultrahigh cycle life and superior safety characteristics, by adding only 0.5 wt.% LiTFTCP into a LiPF6‐carbonate baseline electrolyte. It is revealed that LiTFTCP additive effectively suppresses the HF generation and facilitates the formation of a robust and heat‐resistant cyano‐enriched CEI layer as well as a stable LiF‐enriched SEI layer. The favorable SEI/CEI layers greatly lessen the electrode degradation, electrolyte consumption, thermal‐induced gassing and total heat‐releasing. This work illuminates the importance of additive molecular engineering and interphase regulation in simultaneously promoting the cycling and thermal safety of LIBs with high‐nickel NCMxyz cathode and silicon‐based composite anode.