Ternary Electrolyte Additive Mixtures for Li-Ion Cells that Promote Long Lifetime and Less Reactivity with Charged Electrodes at Elevated Temperatures

Abstract

Li[Ni1/3Mn1/3Co1/3]O2 (NMC111)/graphite and Li[Ni0.42Mn0.42Co0.16]O2 (NMC442)/graphite pouch cells demonstrate superb performance when ternary blends of electrolyte additives are added to the cells. These ternary blends contain one of vinylene carbonate (VC) or prop-1-ene-1,3-sultone (PES) plus a sulfur containing molecule and tris(trimethylsilyl) phosphite (TTSPi). Here, the excellent charge-discharge capacity retention of cells containing these ternary blends of additives is demonstrated at both 45°C and 55°C by comparison to cells with only VC or PES additives alone. The impact of a number of sulfur- and phosphorous-containing electrolyte additives on the reactivity of charged electrode materials with electrolyte at elevated temperatures was studied using accelerating rate calorimetry (ARC). The electrolyte additives, methylene methanedisulfonate (MMDS) and TTSPi, dramatically reduce the reactivity between lithiated (charged) graphite and electrolyte. The ternary electrolyte blends of VC + MMDS + TTSPi and PES + MMDS + TTSPi show no reactivity between charged graphite and electrolyte to above 200°C. By contrast, electrolytes with no additives or with PES alone show significant reactivity with lithiated graphite below 200°C. NMC/graphite cells with VC + MMDS + TTSPi or PES + MMDS + TTPSi additives will demonstrate long life and excellent safety.