Ternary and Quaternary Electrolyte Additive Mixtures for Li-Ion Cells That Promote Long Lifetime, High Discharge Rate and Better Safety

Combinations of vinylene carbonate (VC), a sulfur-containing additive like methylene methane disulfonate (MMDS), and tris(-trimethyl-silyl)-phosphite (TTSPi) and/or tris(-trimethyl-silyl)- phosphate (TTSP) used as electrolyte additives in Li(Ni 1/3 Mn 1/3 Co 1/3 )O 2 (NMC111)/graphite Li-ion cells are shown to impart exceptional properties to those cells. These ternary or quaternary additive mixtures: apparently reduce parasitic reactions, such as electrolyte decomposition, at the positive electrode above 4.1 V compared to VC alone; increase the thermal stability of the charged graphite electrode at elevated temperature; improve coulombic efficiency and also reduce impedance of the cells. These factors all suggest longer lived, safer, higher power Li-ion cells with better tolerance to high voltages which will improve energy density.