Improving sulfolane-based electrolyte for high voltage Li-ion cells with electrolyte additives

An electrolyte mixture containing 1 M LiPF6 in sulfolane:ethylmethyl carbonate 3:7 with vinylene carbonate and other electrolyte additives exhibited promising cycling and storage performance in high voltage Li(Ni0·4Mn0·4Co0.2)O2/graphite pouch type Li-ion cells tested to 4.5 V. Voltage drop during storage, coulombic efficiency, charge endpoint capacity slippage during ultra high precision cycling, charge-transfer resistance after storage or cycling, gas evolution during storage and cycling as well as capacity retention during long-term cycling were examined. The results for cells with sulfolane-based electrolytes were compared with those for cells with ethylene carbonate-based electrolytes containing state-of-the-art electrolyte additives. This survey showed that the combination of vinylene carbonate and triallyl phosphate as electrolyte additives in sulfolane:ethylmethyl carbonate electrolyte yielded cells capable of better performance during tests to 4.5 V than cells with ethylene carbonate-based electrolytes. These results suggest that sulfolane-based electrolytes may be promising for high voltage Li-ion cells.