Electrochemical Properties Of Fluorosulfonimide Lithium And Its Composite Salts

Lithium ion batteries have been extensive applied in fields ranging from smart grids to electric vehicles during the last two decades owning to their unique properties such as high performance,safety,non-memory effect,environmental friendliness and high energy density.The electrolytes play an important role in higher density lithium batteries not only the cycling performance and power but also the safety and capacity.LiPF₆ is the most extensive used lithium salt in commercial Li-ion batteries.Nevertheless,it is very sensitive to moisture and liable to thermally decompos.These inherent problems of LiPF₆ cannot be totally solved by additives in electrolytes.Thus,alternative Lisalts that are steady both elevated temperatures and against water are necessary for Li-ion batteries.In this paper,we mainly take four measures to build new electrolyte systems.Mixed salts of lithium bis(fluorosulfonyl)imide Li[N(SO₂F)₂](LiFSI)and Lithium difluoro(oxalato)borate(LiDFOB)were used to improve excellent long-term cycling stability of Lithium cobaltate(LiCoO₂)-based batteries and substituted the Lithium hexafluorophosphate(LiPF₆)salt in non-aqueous electrolytes.SEM and CV demonstrated that adding LiDFOB into LiFSI-based electrolytes could restrain aluminum corrosion caused by LiFSI-based electrolytes.Compared to LiCoO₂-based batteries using LiPF₆-based electrolytes,the cycling stability and rate capability of LiCoO₂-based batteries using LiFSI_0.7-LiDFOB_0.3-based electrolytes were excellent.Lithium bis(trifluoromethanesulfonyl)imide(LiTFSI)is a promising electrolyte salt for Li-ion batteries.LiTFSI,however,is controlled to severe corrosion of Al currentcollector.This study investigates ionic liquids1-ethyl-3-methyl-imidazoliumbis(trifluoromethanesulfonyl)imide(EMITFSI)as Al corrosion inhibitors in LiTFSI electrolytes.Different concentration of EMITFSI was added to 1M LiTFSI based electrolytes in the performance of lithium iron phosphate(LiFePO₄)cathode was systematically investigated.The results of SEM,CV and XPS indicated that adding EMITFSI into LiTFSI-based electrolytes could effectively suppress aluminum corrosion caused by LiTFSI-based electrolytes.The LiFePO₄ cells using 1M LiTFSI+11% EMITFSI based electrolytes demonstrate superior cycling stability and rate capability when compared to the cells using the LiTFSI-based electrolyte.Due to the severe uncontrolled growth of lithium(Li)dendrites and their high reactivity with electrolyte,lithium metal batteries(LMBs)always suffer from rapid capacity deterioration and high safety risk,especially at high charge/discharge rates and over a wide temperature range.In this study,self-synthesized lithium trifluoro(perfluoro-tert-butyloxyl)borate(LiTFPFB)is firstly proposed to combine with lithium bis(trifluoromethanesulfonyl)imide(LiTFSI)to formulate a novel 1 M dual-salt electrolyte,which is assisted by lithium difluorophosphate(LiPO₂F₂)additive and contains dominate carbonates solvents with low melting point and high boiling point.This well-designed LiPO₂F₂-assissted dual-salt electrolyte is used to dramatically improve the cycleability and rate capability of a LiNi_0.5Mn_0.3Co_0.2O₂/Li(NMC/Li)LMB system,unprecedentedly ranging from-40°C to 90°C.The NMC/Libatteries adopt a Li-metal anode with low thickness of 100?m(even 50?m)and a moderately high cathode mass loading level of 10 mg·cm^-2.It is revealed that LiPO₂F₂ additive contributes to the formation of a compact and protective solid electrolyte interphase(SEI)layer at the surface of both Li-metal anode and NMC cathode.Especially,LiPO₂F₂ additive can efficiently suppress the growth of Lidendrites at Li-metal anode.For the first time,this paper provides valuable perspectives for developing practical LMBs over a wide temperature range.In the last part of the paper,we explore a carbonate-free electrolyte system based on a single sulfone solvent,in which a newly discovered synergy between solvent and salt simultaneously addresses the interfacial requirements of both SiO_x-C anode and high-voltage cathode(LiNi_0.6Mn_0.2Co_0.2O₂).Experimental measurements reveal the electrolyte system at the anode,interphase generated by early-onset reduction of the salt anion effectively suppresses solvent decomposition in a pure sulfone system.Under oxidative conditions,FEC additives in high salt concentration are beneficial for forming a compact and homogeneous cathode SEI layer,alleviating dissolution of transition metals,structure degradation and loss of active lithium.