Lithium difluoro(oxalate)borate improving the zero-volt storage performance of lithium-ion batteries by offering anode SEI film tolerance to high potentials

Keeping lithium-ion batteries (LIBs) in a state of zero charge is an effective way to prevent the risks of thermal runaway during their storage and transportation. It is of importance to achieve excellent zero-volt storage performance, meaning that the performance of LIBs changes little after long-term storage at zero volt. This paper proposes a reliable approach to improve the zero-volt storage performance, that is, the combination of electrochemical pre-lithiation to lower the zero-volt crossing potential (ZCP) and the use of appropriate electrolyte additives to enhance the stability of solid electrolyte interface (SEI) film on anodes to tolerate high potentials for a long time. We use an electrolyte additive, lithium difluoro(oxalate) borate (LiDFOB), as an SEI-film stabilizer. By comparing the chemical composition of SEI film on mesocarbon microbeads (MCMB) anode prior and subsequent to holding at 3.3 V for 10 days, we clarify how LiDFOB offers the SEI film tolerance to high potentials. The validity of the approach is confirmed by a LiCoO2 full cell using an MCMB anode pre-lithiated in the electrolyte containing 2 wt% LiDFOB. This full cell shows a recovery ratio of capacity as high as 93.3% after 7-week zero-volt storage.