Highly Salt-concentrated Electrolyte Comprising Lithium Bis(Fluorosulfonyl) Imide And 1,3-Dioxolane-Based Ether Solvents For 4-V-Class Rechargeable Lithium Metal Cell

The graphite-based lithium-ion batteries（LIBs）have been widely used in portable electronic devices,electrical vehicles（EVs）and large-scale energy storage power stations.However,with a theoretical capacity of 372 m Ah g^-1（for Li C₆）,the graphite anode cannot meet the energy density requirement for the next-generation batteries(>400 Wh kg^-1).Lithium metal（Li）anode has been considered to be an ideal and promising anode material for rechargeable batteries because of its lowest redox potential（-3.04 V vs.the standard hydrogen electrode）and high theoretical specific capacity(3860 m Ah g^-1).Coupling Li metal anode with a 4-V-class intercalation cathode[e.g.,Li Ni_xMn_yCo_1-x-yO₂（NMC）]is deemed as an effective approach to improve the energy density of rechargeable lithium metal batteries（RLMBs）.However,the formation of Li dendrite on Li anode and progressive electrolyte oxidation on cathode cause rapid capacity fading and safety concerns,thereby handicapping the practical implementation of 4-V-class RLMBs to a great extent.Therefore,it is necessary to develop advanced electrolytes which can form robust solid-electrolyte-interphases（SEI）on Li anode,and simultaneously possess good anodic stabilities against 4-V-class cathodes.Herein,we propose a new type of extremely high salt-concentrated electrolyte（SCE）comprising lithium bis（fluorosulfonyl）imide（Li[（FSO₂）₂N],Li FSI）as electrolyte salt and a mixture of 1,3-dioxolane（DOL）/1,2-dimethoxyethane（DME）（3:2,by mole）as solvent with a molar ratio of[O]/[Li]=2[hereafter abbreviated as Li FSI-DOL/DME（[O]/[Li]=2;i.e.,12 moles of Li FSI per liter of DOL/DME）]for4-V-class RLMBs.Specifically,in the SCE of Li FSI-DOL/DME（[O]/[Li]=2）,1,8-diazabicyclo（5.4.0）undec-7-ene（DBU）is utilized as the protonic acid scavenger for chemically preventing the steadily ring-opening polymerization of DOL in the presence of Li FSI,as Li FSI inevitably contains ppm level of protonic acid.The resulting Li FSI-DOL-based SCE shows excellent chemical stability（150 days）,good anodic stability（ca.5.0 V vs.Li/Li⁺）,and decent ionic conductivity(1.3 m S cm^-1)at room temperature.Using the Li FSI-DOL-based SCE,the Li||Cu cells exhibit dendrite-free Li deposition/dissolution processes with high Coulombic efficiencies（>99%）,the Li||Li Fe PO₄ and Li||Li Ni_1/3Mn_1/3Co_1/3O₂ cells show good capacity retentions（94%and 81%after 400 cycles,respectively）.These results strongly suggest the feasibility of the Li FSI-DOL-based SCE as electrolyte for 4-V-class RLMBs.