A2250 Journal of The Electrochemical Society, 161 (14) A2250-A2254 (2014) Improving the High Voltage Cycling of Li[Ni0.42Mn0.42Co0.16]O2(NMC442)/Graphite Pouch Cells Using Electrolyte Additives

Li[Ni0.42Mn0.42Co0.16]O2 (NMC442)/graphite pouch cells with 1 M LiPF6 in ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7 by weight) electrolyte containing 2 wt % vinylene carbonate (VC), 2 wt % prop-1-ene-1,3 sultone (PES), or 2 wt % PES + 1 wt % tris(trimethylsilyl) phosphite (TTSPi) + 1 wt % methylene methanedisulfonate (MMDS) (“PES-211”) were subjected to cycling tests at various upper cut-off voltages from 4.2 to 4.7 V. After every 10 cycles, the pouch cells were charged or discharged to 3.8 V and evaluated using electrochemical impedance spectroscopy (EIS). This approach allows the impact of electrolyte additives on the impedance of cells cycled to different cut-off voltages to be studied systematically. The addition of 2 % PES or “PES-211” proved to be beneficial in suppressing impedance growth when cells are cycled up to and above 4.4 V. Long-term cycling tests between 3.0 V and 4.4 V at 45◦C showed that “PES-211 ” had the best capacity retention (∼85%) and the least impedance growth after 500 cycles. The results suggest the use of “PES-211 ” could lead to longer lived and higher power NMC/graphite Li-ion cells with better tolerance to high voltage (4.4 V) which will improve energy density. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY