Characterization of LTO//NMC Batteries Containing Ionic Liquid or Carbonate Electrolytes after Cycling and Overcharge

Electrochemical stabilities under cycling and overcharge of Li4Ti5O12 (LTO) // LiNi(1/3)Mni(1/3)Co(1/3)O(2) (NMC) batteries with two ionic liquid-based electrolytes and a commercial electrolyte were investigated at 25 and 60 degrees C. The electrolytes were constituted of ethylene carbonate / dimethyl carbonate mixtures with LiPF6, and of imidazolium and pyrrolidinium-based ionic liquids containing the bis(trifluoromethanesulfonyl)imide anion (NTf2) associated to LiNTf2 salt. The experiments were performed in coin and pouch cells in order to follow the evolution of the stability of both solid, liquid and gas phases. The decomposition products and stability of the electrolytes was assessed by gas chromatography coupled with infrared spectroscopy. The characterization of the electrode surfaces by SEM, XRD and XPS techniques was reported, after cycling and overcharge. The XPS analysis of both electrodes indicated that their surfaces were covered by an IL film in the case of NMC, and by several NTf2 anion decomposition products in the case of LTO. This work highlights the difference between thermal and electrochemical stability, especially for imidazolium-based electrolytes. (C) The Author(s) 2015. Published by ECS. All rights reserved.