Lithium-rich layered oxide is a promising cathode material for high-energy density lithium ion batteries. Generally, it is essential to develop high-voltage electrolyte because electrolyte is one of the key factors that determines the capacity of cathode materials. In this work, lithium difluoro(oxalato) borate (LiODFB) is introduced as a novel lithium-salt for lithium-rich cathodes. The investigation reveals that the LiODFB modifies the surface film and forms a uniform and electrochemical stable cathode electrolyte interface (CEI) on the lithium-rich cathode. The LiODFB-derived CEI layer effectively suppresses severe electrolyte decomposition at high voltages and hinders undesirable phase transformation from layered to spinel-like phases during cycling. Furthermore, the Li1.2Mn0.54Ni0.13Co0.13O2/Li cell with the LiODFB-based electrolyte exhibits high capacity retention of 91.73% after 50 cycles and better rate capability of 195 mAh g−1 at 2 C. The unique function of the LiODFB on the surface chemistry of lithium-rich cathodes is confirmed through X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses.