Tuning Interphase Chemistry to Stabilize High‐Voltage LiCoO2 Cathode Material via Spinel Coating

Cathode electrolyte interphases (CEIs) are critical to the cycling stability of high‐voltage cathodes for batteries, yet their formation mechanism and properties remain elusive. Here we report that the compositions of CEIs are largely controlled by abundant species in the inner Helmholtz layer (IHL) and can be tuned from material aspects. The IHL of LiCoO2 (LCO) was found to alter after charging, with a solvent‐rich environment that results in fragile organic‐rich CEIs. By passivated spinel Li4Mn5O12 coating, we achieve an anion‐rich IHL after charging, thus enabling robust LiF‐rich CEIs. In situ microscopy reveals that LiF‐rich CEIs maintain mechanical integrity at 500 °C, in sharp contrast to organic‐rich CEIs which undergo severe expansion and subsequent voids/cracks in the cathode. As a result, the spinel‐coated LCO exhibits a high specific capacity of 194 mAh g−1 at 0.05 C and a capacity retention of 83 % after 300 cycles at 0.5 C. Our work sheds new light on modulating CEIs for advanced lithium‐ion batteries. The compositions of cathode electrolyte interphases (CEIs) are largely controlled by the abundant species in the inner Helmholtz layer (IHL) and could be tuned from material aspects. Passivating the reactive cathode surface enables anion‐rich IHLs and LiF‐rich CEIs, not only demonstrating high thermal/cycling stability but also shedding new light on the formation, properties, and modulation of CEIs for advanced battery materials.