Abstract
Lithium trimethyl alkyl and aryl borates (LTMB) has been prepared and investigated as a novel cathode film forming additive to improve the performance of LiNi0.5Mn1.5O4 cathodes cycled to high potential (4.8 V). Addition of LTMB to 1.2 M LiPF6 in EC/EMC (3/7) improves the capacity retention of graphite/LiNi0.5Mn1.5O4 cells cycled at 55 oC. The added LTMB is sacrificially oxidized on the surface of the cathode during the first charging cycle. The LTMBs can be used as a functional group delivery agent via reaction of trimethyl borate with of the appropriate lithium alkoxide. Over 40 different LTMBs have been prepared and investigated. Ex-situ surface analysis of the LiNi0.5Mn1.5O4 by Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR), Transmission Electron Microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) reveals inhibition of electrolyte oxidation on the cathode surface and the presence of a borate based passivating layer. The novel cathode electrolyte interface (CEI) leads to the performance improvements.
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