N-(triphenylphosphoranylidene) aniline as a novel electrolyte additive for high voltage LiCoO2 operations in lithium ion batteries

We report N-(triphenylphosphoranylidene) aniline (TPPA) as a new electrolyte additive for high performance lithium cobalt oxide (LiCoO2) electrodes during high voltage operations. When cycled in the voltage range of 3.0-4.4 V. graphite-LiCoO2 full cells with 0.2 wt%TPPA exhibited 10% increased discharge capacities after 200 cycles compared to those of control cells with no such additive. The enhanced cycling performance is attributed to the additive effect toward the modified surface films on LiCoO2 electrodes that suppress the decomposition of both solvent and salt in the electrolyte. This additive effect was characterized by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). (C) 2011 Elsevier Ltd. All rights reserved.