One Sulfonate and Three Sulfate Electrolyte Additives Studied in Graphite/LiCoO2 Pouch Cells

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 sulfonate additive, methylene methane disulfonate (1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide (MMDS)) were studied in graphite/LiCoO2 (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[Ni1/3Mn1/3Co1/3]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. (C) The Author(s) 2015. Published by ECS.