One Sulfonate and Three Sulfate Electrolyte Additives Studied in Graphite/LiCoO 2 Pouch Cells

Abstract

The effectiveness of three cyclic sulfate additives, ethylene sulfate (or 1,3,2-dioxathiolane-2,2-dioxide (DTD)), trimethylene sulfate (or 1,3,2-dioxathiane 2,2-dioxide (TMS)) and propylene sulfate (or 4-methyl-1,3,2-dioxathiolane-2,2-dioxide (PLS)) and one sul-fonate additive, methylene methane disulfonate (1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide (MMDS)) were studied in graphite/LiCoO 2 (LCO) pouch cells. The additives were studied singly and in combination with 2% vinylene carbonate (VC) using high precision coulometry, AC impedance spectroscopy, volume change to infer gas evolution and open circuit storage experiments. During formation , TMS can significantly reduce the irreversible capacity and gas evolution while PLS and DTD cannot. When added alone, cells with DTD, TMS or PLS perform much worse than cells with 2% VC in all of coulombic efficiency, charge endpoint capacity slippage and voltage drop during storage. When combined with 2% VC, cells with TMS and VC provide similar performance to cells with 2% VC alone, cells with VC + MMDS are better and cells with VC + DTD and VC + PLS are worse. The trends found here are different from the results obtained using the same additives in graphite/Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC) pouch cells where cells with VC + DTD and VC + MMDS were found to provide benefit compared to VC alone. It is hard to distinguish any difference between 2% VC and 2%VC + 1% TMS in both graphite/LCO cells and graphite/NMC cells, suggesting that TMS is nearly "inert" in the presence of VC in these cells.