Synergistic effects of co-additives in constructing a robust and Li+-conductive interphase for high-voltage LiCoO2

Abstract

Elevating the charging cut-off voltage is the most effective method to improve energy density of LiCoO₂ (LCO)-based lithium-ion batteries, while high-voltage operation further leads to the instability of electrolyte and electrode-electrolyte interphase. Herein, a tailored carbonate electrolyte with functional co-additives is proposed for high-voltage LCO by constructing thin and robust cathode-electrolyte interphase (CEI). The co-additives, lithium bis(oxalato)borate (LiBOB) and tris(trimethylsilyl)phosphite (TMSPi), decompose prior to the carbonate solvents to ensure the stability of the electrolyte. The later decomposition of TMSPi not only generates Li⁺-conductive P-containing species but also suppresses the excess decomposition of LiBOB. The synergistic effects of robust B-containing species and high Li⁺-conductive P-containing species in the CEI ensure excellent performance of LCO cathode under high voltage of 4.5 V (vs. Li/Li⁺), exhibiting a high capacity retention of 95.2% for 200 cycles and improved rate capability up to 5C with a high capacity of 146 mAh g⁻¹. Moreover, the LCO||graphite full cell with the tailored electrolyte can maintain a capacity retention of 93.9% after 100 cycles, more than twice that of the BE electrolyte (44.3%). This co-additives strategy offers a guideline on constructing advanced CEI for practical application in high-voltage cathode.