Effect of electrolyte additives on high-temperature cycling performance of spinel LiMn 2 O 4 cathode

Lithium difluoroborate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFBOP) and lithium difluorophosphate (LiPF2O2) are investigated as electrolyte additives to alleviate the severe cycle capacity fading of spinel LiMn2O4 cathode of lithium-ion batteries, especially at elevated temperatures. Compared with that of the routine electrolyte, the capacity retention is significantly improved at both room temperature and 55 °C by adding LiBOB and LiDFOB as electrolyte additives. Moreover, surface layer formation processes on the LiMn2O4 electrode in the presence of the LiBOB, LiDFOB, LiDFBOP and LiPF2O2 are investigated by photoelectron spectroscopy (XPS) and X-ray diffraction. According to the analysis results, BOB− anions from LiBOB or LiDFOB bond with the dissolved Mn2+ to form an insoluble and stable surface layer on the LiMn2O4 surface, which is beneficial to the suppression of the LiMn2O4 dissolution and electrolyte decomposition, and eventually to the improvement of the cycling performance at elevated temperatures.