Improving Stability of LiCoO2 Cathode by Using Lithium Bis(Trifluoroborane)‐5‐Cyano‐2‐(Trifluoromethyl) Benzimidazolide as Additive

Abstract

AbstractLiCoO2 is an important cathode material of commercial lithium‐ion batteries (LIBs) and therefore, improving the stability when LiCoO2 cathode is overcharged can have an immediate impact on commercial LIBs. A novel Li salt, lithium 5‐cyano‐bis(trifluoroborane)‐2‐(trifluoromethyl) benzimidazolide (Li[CBTBI]) is evidenced in this study as an effective additive for improving the electrode/electrolyte interface of LiCoO2 at high voltage operation condition. The presence of 2 % additive in commercial 1 M LiPF6/EC+DEC lead to the formation of stable interface of LiCoO2 through cycles to 4.5 V, as demonstrated in cyclic voltammetry (CV). Electrochemical impedance spectroscopy (EIS) indicates a low‐impedance of the formed interface in the presence of the additive. Cyclability test also shows an improved stability in overcharging potential window by the presence of 2 % additive. In situ diffuse reflectance infrared Fourier‐transformed spectroscopy (DRIFTS) confirms the suppression of LiPF6 decomposition, delay of onset potential of solid electrolyte interphase (SEI) formation, and thin SEI comparing to that without the additive. The possible reasons of the advantageous effect of using Li salt additives are discussed.