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 A degrees C). The cycling performance of graphite/LiNi1/3Co1/3Mn1/3O2 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 A degrees C). However, after accelerated aging the LiFOP/MB electrolyte has worse performance at very low temperature (-30 A degrees 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.