Performance of lithium tetrafluorooxalatophosphate in methyl butyrate electrolytes

Methyl butyrate (MB) has been investigated as a co-solvent for lithium-ion battery electrolytes to improve the performance at low temperature (?10 to ?30 °C). The cycling performance of graphite/LiNi_1/3Co_1/3Mn_1/3O₂ cells with 1.2 M lithium tetrafluorooxalatophosphate (LiFOP) in 2:2:6 EC/EMC/MB was compared to 1.2 M LiPF₆ in both 3:7 EC/EMC and 2:2:6 EC/EMC/MB. The LiFOP/MB electrolyte has a good operational temperature window and comparable cycling performance to the LiPF₆ electrolyte at both room temperature and low temperature (?10 °C). However, after accelerated aging the LiFOP/MB electrolyte has worse performance at very low temperature (?30 °C) compared to LiPF₆ electrolytes. Ex-situ surface analysis was conducted by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transfer infrared spectroscopy to provide insight into the performance differences.