The effects of Methylene MethaneDiSulfonate (MMDS) as an electrolyte additive for Li-ion cells have been studied using Li(Ni1/3Mn1/3Co1/3)O-2/Li (NMC/Li), Li(Ni0.8Co0.15Al0.05)O-2)/Li, Coke/Li coin cells and NMC/graphite pouch cells. Storage experiments on all cell types showed that adding MMDS to the electrolyte reduced the rate of parasitic reactions, e.g. electrolyte oxidation, at the LixMO2 electrode while it did not affect the rate of reaction of intercalated lithium in coke with electrolyte. NMC/graphite pouch cells with electrolytes containing MMDS produced less gas during formation than cells without MMDS. Impedance tests show MMDS greatly decreases the impedance of the NMC/graphite pouch cells after storage and cycling. Charge discharge cycling experiments confirm that MMDS is a useful electrolyte additive for Li-ion cells. (C) 2013 The Electrochemical Society. All rights reserved.