Study On In-situ Construction Of High Stability Lithium Metal Anode Interface By Film-forming Electrolyte Additives

Lithium(Li)metal is a promising anode material for next-generation energy storage devices due to its high theoretical specific capacity(3860 mA h g-1)and low negative potential(-3.04 V vs the standard hydrogen electrode).However,the dendrite formation and growth on the surface of Li anode during Li plating/stripping process lead to safety problems and short life of Li metal batteries(LMBs),thus impeding the commercial application of LMBs.To overcome above problems,this paper presents employment of electrolyte additives to suppress the formation and growth of Li dendrites,stabilize the interface between Li anode and electrolyte and improve the stability and safety of LMBs.The main research contents are as follows:(1)The interface stability of Li anode can be improved by addition of HMDS into ether-based electrolyte.HMDS can induce the formation of a compact and dendrite-free SEI film,which contains abundant Li3N and LixSiOy so that the structure of Li anode still remains stable after 200 cycles.The XPS results show that HMDS can inhibit decomposition of electrolyte and participate in the formation of effective components in SEI film to improve the stability of Li anode.After adding 1 wt.%HMDS,the Li |Li symmetrical batteries can remain extraordinarily stable at the current density of 1 mA cm-2,3 mA cm-2 and 5 mA cm-2,and the rate performance and cycling stability of Li |LiFePO4 batteries are observably improved.(2)The interface stability of Li anode can be improved by addition of HFiP,the highly fluorinated phosphate ester,into ether-based electrolyte.HFIP can induce the formation of steady and compact solid electrolyte interphase(SEI),which contains a mass of abundant inorganic components(LiF and Li3PO4)and organic component(ROCO2Li).The multi-component SEI with flexibility and mechanical strength can restrain the growth of dendrites.The XPS analysis proves that HFiP can also effectively inhibit the decomposition of LiTFSI.The surface of Li anode still exhibits a smoother,denser,more uniform and dendrite-free deposition morphology after 200 cycles.In addition,when 1 wt.%of HFiP is added to electrolyte,the coulombic efficiency of the Li | Cu battery is maintained at about 98%within 100 cycles,and the average coulombic efficiency is 97.5%.A smaller and more stable polarization voltage can be obtained in Li | Li symletrical batteries.(3)The interface stability of Li anode can be improved by addition of PFPN into ether-based electrolyte.Addition of PFPN can form a stable SEI film on Li anode,which can promote the uniform deposition of Li+ to inhibit dendrites formation and growth,and no dendrites and dead Li are found on the surface of anode after 200 cycles.The Li | Li symmetrical batteries can remain excellent cycle stability at the current density of 1 mA cm-2,3 mA cm-2 and 5 mA cm-2 after adding 1 wt.%PFPN.The capacity retention rate of Li | LiFePO4 batteries is nearly 100%after a long cycle of 400 cycles.