Enhancing Electrochemical Performance of High Voltage (4.5 V) Graphite/LiNi0.5Co0.2Mn0.3O2 Cell by Tailoring Cathode Interface

In this study, a novel nitrile-based compound, ethylene glycol bis (propionitrile) ether (EGBE) has been investigated as a cathode film forming additive. Electrochemical performance of graphite/LiNi0.5Mn0.3Co0.2O2 full cell with 1.0 M LiPF6 EC/EMC (3/7, v/v) w/o EGBE additive electrolyte has been evaluated. The initial discharge capacity of the cell with EGBE added electrolyte is slightly lower than the cell without EGBE; while the cell with 1.0 wt% EGBE added electrolyte has superior cycling stability than the cell with baseline electrolyte upon cycling at 4.5 V (vs. Li/Li+), specifically, 82% and 42% capacity retention after 80 cycles, respectively. Ex-situ characterizations on the electrodes extracted from graphite/LiNi0.5Mn0.3Co0.2O2 cell were conducted via a combination of multi-techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and inductive coupled plasma spectroscopy (ICP-MS) as well. The improved cycling performance is ascribed to the desired surface layer built-up on electrode surface via the sacrificial decomposition of the EGBE additive. This tailored surface layer is more robust and stable than the surface film generated from baseline electrolyte decomposition, thus can stabilize the electrode/electrolyte interface, mitigate electrolyte decomposition and inhibit transition metal dissolution from the bulk cathode material upon cycling at 4.5 V. (C) 2016 The Electrochemical Society. All rights reserved.