Improvement of Electrode/ Electrolyte Interfaces in Graphite/LiNi0.5Mn1.5O4 Batteries at High Voltage and Elevated Temperature By Using New Family of Lithium Pyridal Trimethyl Borates

Abstract

A novel series or lithium alkyl trimethyl borates and lithium aryl trimethyl borates have been prepared and investigated as cathode film forming additives. The borates are prepared via the reaction of lithium alkoxides or lithium phenoxides with trimethyl borate. Incorporation of 0.5-2.0 % (wt) of the lithium borates to a baseline electrolyte (1.0 M LiPF6 in 3:7 (EC/EMC)) results in improved capacity retention and efficiency of high voltage graphite / LiNi0.5Mn1.5O4 cells especially upon cycling at elevated temperature (55 oC). The improved performance results from the sacrificial oxidation of the lithium borate on the cathode surface to generate a cathode passivation film. The lithium borates can be readily structurally modified to act as a functional group delivery agent to modify the cathode surface. Ex-situ surface analysis of the electrodes after cycling confirms that the lithium borates modify the cathode surface and generate a borate rich surface film which inhibits electrolyte oxidation and Mn dissolution.