A Systematic Study of Electrolyte Additives in Li[Ni_1/3Mn_1/3Co_1/3]O₂(NMC)/Graphite Pouch Cells

Abstract

The effects of electrolyte additives singly or in combination on Li[Ni1/3Mn1/3Co1/3]O2 (NMC)/graphite pouch cells have been systematically investigated and compared using the ultra high precision charger (UHPC) at Dalhousie University, electrochemical impedance spectroscopy (EIS), an automated storage system, gas evolution measurements and selected long-term cycling experiments. The results of testing Li[Ni1/3Mn1/3Co1/3]O2 (NMC)/graphite pouch cells with different electrolyte additives singly or in combination were measured and the results for over 110 additive sets are compared. A "Figure of Merit" approach is used to rank the effectiveness of the additives and their combinations. The combination of vinylene carbonate (VC) and/or prop-1-ene-1,3 sultone (PES), a sulfur containing additive, such as methylene methane disulfonate (MMDS), as well as either tris(-trimethly-silyl)-phosphate (TTSP) and/or tris(-trimethyl-silyl)-phosphite (TTSPi) as additives in the electrolyte can give cells with extremely high coulombic efficiency, excellent storage properties, low impedance and superior long term cycling at 55°C. Additive mixtures such as 2% PES + 1% MMDS + 1% TTSPi are especially excellent in all respects. It is hoped that this comprehensive report sets a benchmark for future studies by others and can be used as a guide and reference for the comparison of other electrolyte additives singly or in combination.