Impacts of lithium tetrafluoroborate and lithium difluoro(oxalate)borate as additives on the storage life of Li-ion battery at elevated temperature

The impacts of boron-based Li salt additives including lithium tetrafluoroborate (LiBF4) and lithium difluoro(oxalate)borate (LDFOB) on the storage life of Li-ion battery at elevated temperature are investigated. Adding 1 wt% additives in the electrolyte significantly affects the storage life of the LiNi0.8Co0.15Al0.05O2/graphite full cell at 55 degrees C. The anode solid electrolyte interphase (SEI), preventing the loss of Li+ and e(-) in anode, is the key factor affecting the storage life. The formation and aging of SEI on the graphite anode with and without additives are investigated. It is found that the SEI formed with the addition of LiBF4 is thick and loose due to LiF crystals produced by the decomposition of LiBF4 and the SEI cannot prevent the Li+ and e(-) loss in anode and the decomposition of the electrolyte solvent, resulting in shorter storage life of the battery. On the contrary, the SEI formed with the addition of LDFOB is thick and compact due to formation of the lithium oxalate in the SEI, produced by the decomposition of LDFOB. The SEI efficiently inhibits decomposition of the electrolyte solvent on anode and makes a longer storage life of the battery.