1,2,6-Oxadithiane 2,2,6,6-tetraoxide as an Advanced Electrolyte Additive for Li[Ni0.5Mn0.3Co0.2]O2/Graphite Pouch Cells

Abstract

1,2,6-oxadithiane 2,2,6,6-tetraoxide (ODTO) as a novel electrolyte additive was evaluated in both uncoated and coated single crystal Li[Ni0.5Mn0.3Co0.2]O2/graphite pouch cells with 1.2M LiPF6 in ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7 by weight) as the electrolyte. ODTO passivates the graphite negative electrode at ∼1.4V (vs. Li/Li+) and also forms a solid electrolyte interphase layer at the positive electrode side. X-ray photoelectron spectra of cells filled with 1% ODTO demonstrate that ODTO mainly converted to sulfur-containing species at both electrode surfaces after formation. The performances of cells containing up to 5% ODTO and binary additive blends including 2% vinylene carbonate (VC) + 1% ODTO, 2% fluoroethylene carbonate (FEC) + 1% ODTO and 1% LiPO2F2 + 1% ODTO were evaluated and compared to cells with 2% VC, 2% FEC and 1% LiPO2F2. Ultra-high precision coulometry (UHPC) and long-term cycling show that 3% ODTO alone increased coulombic efficiency (CE) and led to high capacity retention for both uncoated and coated cells. Cells with uncoated NMC532 and additive blends containing 1%ODTO along with 1%LiPO2F2, 2% VC or 2%FEC showed virtually identical cycling performance to cells with coated NMC532 and the same electrolytes, suggesting that coatings are not required if effective additives are used.