Interface engineering strategy via electron-defect trimethyl borate additive toward 4.7 V ultrahigh-nickel LiNi0.9Co0.05Mn0.05O2 battery

The Li metal battery with ultrahigh-nickel cathode (LiNixM1−xO2, M = Mn, Co, and x ≥ 0.9) under high-voltage is regarded as one of the most promising approaches to fulfill the ambitious target of 400 Wh/kg. However, the practical application is impeded by the instability of electrode/electrolyte interface and Ni-rich cathode itself. Herein we proposed an electron-defect electrolyte additive trimethyl borate (TMB) which is paired with the commercial carbonate electrolyte to construct highly conductive fluorine- and boron-rich cathode electrolyte interface (CEI) on LiNi0.9Co0.05Mn0.05O2 (NCM90) surface and solid electrolyte interphase (SEI) on lithium metal surface. The modified CEI effectively mitigates the structural transformation from layered to disordered rock-salt phase, and consequently alleviate the dissolution of transition metal ions (TMs) and its “cross-talk” effect, while the enhanced SEI enables stable lithium plating/striping and thus demonstrated good compatibility between electrolyte and lithium metal anode. As a result, the common electrolyte with 1 wt% TMB enables 4.7 V NCM90/Li cell cycle stably over 100 cycles with 70% capacity retention. This work highlights the significance of the electron-defect boron compounds for designing desirable interfacial chemistries to achieve high performance NCM90/Li battery under high voltage operation.