Development of Pyridine-Boron Trifluoride Electrolyte Additives for Lithium-Ion Batteries

A series of novel electrolyte additives based on Lewis acid/base adducts has been designed and successfully synthesized. The synthesis is very simple: a pyridine derivative is mixed with boron trifluoride dissolved in diethyl ether to yield a solid crystalline product. The effect of Pyridine-Boron Trifluoride (PBF) and its derivatives have been thoroughly evaluated in Li[Ni1/3Mn1/3Co1/3]O-2/graphite and Li[Ni0.42Mn0.42Co0.16]O-2/graphite pouch cells. Evaluation experiments, including high voltage storage, gas production, electrochemical impedance spectroscopy measurements, ultra high precision cycling and long-term cycling were carried out on cells containing the novel additives. The results were compared to baseline experiments on cells with well-known additives such as vinylene carbonate (VC), prop-l-ene sultone (PES), methylene methane disulfonate (MMDS), tris(-trimethyl-silyl)-phosphite (TTSPi) and triallyl phosphate (TAP). The PBF additives are competitive with all known additives in NMC/graphite cells, which, combined with their low cast and facile synthesis, suggest this series of novel additives will be useful in high-voltage/high-temperature lithium ion battery applications. The PBF additives yield cells which show excellent capacity retention and maintain low impedance during high voltage cycling, in contrast to cells containing VC. (C) The Author(s) 2015. Published by ECS. All rights reserved.