We report a highly promising electrolyte based on N-allyl-N-methylpiperidinium bis(trifluoromethanesulfonyl) imide (PP13*TFSI) and lithium difluoro(oxalato)borate (LiDFOB) to greatly improve the cycle performance of a Li/Li1.1Ni0.25Mn0.65O2 battery at 2.5 V–4.6 V and 55 °C, which shows an initial discharge capacity of 181.7 mAh g−1 and a capacity retention of 90.9% after 150 cycles. A multiphase bilayer membrane structure is observed, which inhibits the decomposition of carbonate components and structure destruction. Physical characterization demonstrates the chemical interaction between PP13*+ and DFOB−, which prevents the cathode particle from structure degradation at 55 °C under high voltage.