Lithium bis(oxalato) borate (LiBOB) is investigated as an additive for the stabilization of a high-voltage cathode–electrolyte interface. It is found that the electrochemical performance of Li/LiNi0.5Mn1.5O4 cells with a LiBOB additive is improved at 60°C. To confirm the effects of LiBOB on electrolyte oxidative decomposition, the surface chemistry of separators and high-voltage LiNi0.5Mn1.5O4 cathodes cycled in electrolytes with and without a LiBOB additive are examined using ex situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS).