Synergistic Effects of Suberonitrile-LiBOB Binary Additives on the Electrochemical Performance of High-Voltage LiCoO2 Electrodes

Suberonitrile (SUN) and lithium bis(oxalate)borate (LiBOB) were investigated as binary additives for Li-ion batteries that used LiCoO2 as a cathode, cycled at high cutoff potentials and utilized LiPF6-based electrolyte. Linear sweep voltammetry (LSV) results revealed that LiBOB oxidized prior to the decomposition of the reference electrolyte. By contrast, SUN has a higher oxidization potential, and in the electrolyte it provided better electrolyte stability at higher potentials. In the electrolyte with binary additives, the electrochemical performance of LiCoO2 was enhanced significantly, and the initial coulombic efficiency increased to 94% compared with 90% in reference electrolyte. The cell also exhibited capacity retention of 62% after 500 cycles, a strong contrast with the 25% measured in reference electrolyte. Preliminary studies using electrochemical impedance spectra (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses indicated that the combination of the two additives had a unique influence on the structure and composition of the cathode-electrolyte interface (CEI) on LiCoO2. Ex situ X-ray diffraction (XRD) confirmed that structural change of the LiCoO2 material was not the main reason causing poor cycling performance when charging to the 4.5 V cutoff potential. (C) The Author(s) 2015. Published by ECS. All rights reserved.