The effectiveness of two electrolyte additives, 1,3-propane sultone (PS) and methylene methanedisulfonate (MMDS) either singly or in combination with vinylene carbonate (VC) has been studied. Li(Ni1/3Mn1/3Co1/3)O-2 (NMC)/Graphite pouch cells containing these additives were studied using ultra high precision coulometry, automated storage experiments and electrochemical impedance spectroscopy. The two additives have the same SO3 functional group but it seems PS is more widely used by battery manufacturers. When used alone, both additives decrease the charge transfer impedance during cycling while MMDS shows better coulombic efficiency and lower charge end point capacity slippage rate than PS. Compared with 2% VC, MMDS in combination with 2% VC significantly improves the coulombic efficiency and the charge slippage rate, reduces the charge transfer impedance during cycling and decreases the voltage drop during storage while the addition of PS to VC-containing electrolyte does not show this added benefit. Compared to PS, MMDS seems to be a more beneficial additive for improving cell performance. (C) 2014 The Electrochemical Society. All rights reserved.