Improving interfacial stability of high voltage LiCoO2-based cells with 4-methylmorpholine-2,6-dione additive

Abstract

An novel electrolyte additive, 4-methylmorpholine-2,6-dione (MMD) with anhydride and amine functional groups, is come up with, which can not only construct a dense and stable cathode-electrolyte-interface (CEI) film on solid and electrolyte interphase that can automatically improve the cycling stability of lithium-ion batteries (LIBs) at high temperature and high voltage, but also effectively capture hydrofluoric acid and water in the electrolyte that can adequately inhibit carbonate decomposition and protect LiCoO2 (LCO) internal structure. The capacity retention rate of Li||LCO cells increases from 65.8% to 83.5% after 200 cycles at 1C between 3.0 and 4.6 V after just adding a trace amount of 0.03% MMD to the baseline electrolyte. Even at ultra-high voltages of 4.7 V, the retained capacity of MMD-containing Li||LCO half-cell is improved from 91 to 122 mAh g−1 after 200 cycles at 1C. Both theoretical calculation and experiments reveal that MMD can be preferentially oxidized ahead of those solvent through C–C bond breaking to construct a thin and robust CEI layer on LCO surface. Such a combination of anhydride and amine functional groups opens up a direction to exploit novel electrolyte additives for prolonging the cycle life of higher energy density LCO.