Construction And Electrochemical Performance Of Local High-concentration Electrolyte System For Lithium Metal Batteries

Lithium metal anode is considered as the most promising anode for high energy density rechargeable batteries due to its high theoretical specific capacity(3862 m Ah g-1)and low chemical potential(-3.040 V vs.standard hydrogen electrode).However,the uncontrollable growth of Li dendrites,severe volume expansion of Li-metal,low coulombic efficiency,limited cycle life,and potential safety hazards hinder the practical wide application of Lithium metal batteries(LMBs).In this paper,the local high-concentration electrolyte system was designed to prolong the cycle life of LMBs.Meanwhile,the addition of 2-fluoropyridine(2-FP)additive prevented the growth of Li-dendrite and rise the coulombic efficiency,greatly improving the electrochemical performance of LMBs.The main research contents are as follows:(1)BTFE-based local high-concentration non-flammable electrolyte was prepared with lithium salt(lithium bis(flfluorosulfonyl)imide,Li FSI),solvent(triethyl phosphate,TEP)and diluent(bis(2,2,2-triflfluoroethyl)ether,BTFE).The BTFE-based local high-concentration electrolyte has the concentrated Li-FSI-TEP solvation structure and wide electrochemical stability.And the BTFE-based local high-concentration electrolyte overcomes the problems of insufficient wettability,high viscosity and low conductivity of common high-concentration electrolytes.Furthermore,this electrolyte system was optimized by 2-FP additive,which formed a stable solid electrolyte interfacial film(SEI)between the electrolyte and lithium metal,thereby effectively inhibiting the growth of Li-dendrites and improving the coulombic efficiency.Therefore,the cycle stability of lithium metal batteries is greatly improved.The lithium metal battery with 2-FP-BTFE-based localized high-concentration electrolyte was stably cycled for 450 cycles and kept 98.52%capacity retention rate at 1C.(2)Based on the high cost of BTFE diluent,which affects the practical application of BTFE-based local high-concentration electrolyte,hydrofluoroether(HFE)was used as a new diluent to replace BTFE.The 2-FP-HFE-based local high-concentration electrolyte system was successfully constructed.HFE has low cost and a wider electrochemical window.The novel HFE-based localized high-concentration electrolyte further inhibits the growth of Li-dendrites and improves the coulombic efficiency,thereby improving the cycling stability of LMBs.The lithium metal battery using 2-FP-HFE-based localized high-concentration electrolyte was stably cycled for 1000 cycles and realized capacity retention rate 90.6%at1C.Scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS)test results show that 2-FP decomposes on the surface of lithium metal.The decomposition products of 2-FP participate the construction of SEI and controls the deposition of Li~+to obtain a flat lithium metal anode.