Mixed salts for lithium iron phosphate-based batteries operated at wide temperature range

To achieve good performance for LiFePO4-based batteries operated at a wide temperature range, mixed salts of LiBF4–LiBOB (lithium bis(oxalato)borate) and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide)–LiBOB were investigated as alternative lithium salts to LiPF6 in non-aqueous electrolytes. LiFePO4/Li half cells using LiPF6, LiBF4–LiBOB and LiTFSI–LiBOB slats as lithium salts were investigated by galvanostatic cycling, cyclic voltammetry, thermogravimetric analysis. The results show that LiBF4–LiBOB and LiTFSI–LiBOB mixed salts are much more thermally stable than LiPF6. Corrosion of Al foil in the LiTFSI-based electrolytes can be suppressed successfully by the addition of LiBOB as a co-salt. The electrochemical performance of LiBF4–LiBOB and LiTFSI–LiBOB mixed salts based cells are both better than that of LiPF6-based cell. LiTFSI–LiBOB mixed salt based electrolyte is considered to be a very promising electrolyte candidate for Li-ion batteries that will be used in wide-temperature applications.