[4,4′-bi(1,3,2-dioxathiolane)] 2,2′-dioxide: A novel cathode additive for high-voltage performance in lithium ion batteries

High-voltage operation of lithium-ion batteries (LIBs) is a facile approach to obtaining high specific energy density, especially for LiNi0.5Mn0.3CO0.2O2 (NMC532) cathodes currently used in mid- and large-sized energy storage devices. However, high-voltage charging (> 4.3 V) is accompanied by a rapid capacity fade over long cycles due to severe continuous electrolyte decomposition and instability at the cathode surface. In this study, the sulfite-based compound, [4,4'-bi(1,3,2-dioxathiolane)] 2,2'-dioxide (BDTD) is introduced as a novel electrolyte additive to enhance electrochemical performances of alumina-coated NMC532 cathodes cycled in the voltage range of 3.0-4.6 V. X-ray photoelectron spectroscopy (XPS) and AC impedance of cells reveal that BDTD preferentially oxidizes prior to the electrolyte solvents and forms stable film layers on to the cathode surface, preventing increased impedance caused by repeated electrolyte solvent decomposition in high-voltage operation. The cycling performance of the Li/NMC532 half-cell using an electrolyte of 1.0 M LiPF6 in ethylene carbonate/ethyl methyl carbonate (3/7, in volume) can be improved by adding a small amount of BDTD into the electrolyte. BDTD enables the usage of sulfite-type additives for cathodes in high-voltage operation.