Comparative Study on Prop-1-ene-1,3-sultone and Vinylene Carbonate as Electrolyte Additives for Li(Ni1/3Mn13Co1/3)O2/Graphite Pouch Cells

The effectiveness of Prop-1-ene-1,3-sultone (PES) and Vinylene carbonate (VC) as electrolyte additives in Li(Ni1/3Mn1/3Co1/3)O2 (NMC)/graphite pouch cells was studied using in situ measurements of gas evolution, ultra high precision coulometry (UHPC), automated storage experiments and electrochemical impedance spectroscopy (EIS). Gas measurements show that cells containing PES produce less gas than cells containing 2% VC during formation and much less gas during elevated temperature storage (60°C) at 4.2 V. UHPC cycling and storage results show that cells containing 2% PES have higher coulombic efficiency, lower charge end point capacity slippage and smaller voltage drop during storage than cells containing 2% VC. The combination of VC and PES shows even better cycling performance than the single additives, however, at the expense of much higher impedance. EIS studies of positive and negative electrode symmetric cells show that the introduction of PES or VC to control electrolyte affects the individual electrode impedances in a similar way: both increase the negative electrode impedance and decrease the positive electrode impedance. Based on these experiments we suggest that PES is a very useful additive for NMC/graphite Li-ion pouch cells that may encounter high temperatures during storage and cycling.