LiNi0.4Mn1.6O4/Electrolyte and Carbon Black/Electrolyte High Voltage Interfaces: To Evidence the Chemical and Electronic Contributions of the Solvent on the Cathode-Electrolyte Interface Formation

Solvent and lithium salt decomposition products on LiNixMnyO4-type electrodes are known to be ROM, ROCO2M (M = Li, Ni, Mn), LiF, LixPFyOz, polycarbonates and polyethers. These compounds are chemically formed due to the high nucleophilic character of spinel oxide and LiPF6 decomposition. The high potentials (> 4.7 V vs. Li/Li+) may cause EC and PC polymerization, while DMC forms oligomers. The use of carbon black-based electrodes highlights electronic and, surprisingly, chemical contributions to the cathode-electrolyte interface. A comparison between EC/DMC (1:1 in weight) 1 M LiPF6 and PC/DMC (1:1 in weight) 1 M LiPF6 electrolytes for Li/carbon black-PVdF cells demonstrated a superior ability of the EC/DMC solution to form a well-covering passivation film via faradaic reactions thanks to a higher stability toward oxidation. Electrochemical cycling in Li/LiNi0.4Mn1.6O4 cells confirms this EC/DMC superiority when it comes to forming passivation films, in turn leading to reduced capacity losses and a higher Columbic efficiency. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.052211jes] All rights reserved.