Electrolyte System for High Voltage Li-Ion Cells

Ethylene carbonate is a co-solvent used in virtually every lithium ion cell produced today because it enables operation of both the positive and negative electrodes. Most battery scientists believe ethylene carbonate is essential. Surprisingly, totally removing all ethylene carbonate from typical organic carbonate-based electrolytes and adding small amounts of electrolyte additives creates cells that are better than those containing ethylene carbonate. For example an electrolyte of only 2% vinylene carbonate and 98% ethyl methyl carbonate, with selected additives, provides excellent performance to LiNi0.4Mn0.4Co0.2O2/graphite cells cycled up to 4.4 V which increases their energy density by at least 10%. The cells have low impedance, low rates of electrolyte oxidation, good graphite passivation, low gas generation, acceptable conductivity and low cost. This discovery opens an entirely new space for electrolyte development.