Study On The Protective Interface Structure Design And Related Protective Mechanism For Lithium Metal Anodes

Lithium(Li)metal has been considered as the“Holy Grail”of electrochemical energy storage because of its ultrahigh specific capacity and lowest electrochemical potential,which can dramatically boost the energy density.Moreover,it can provide the active Li~+ion for battery,emancipating the limitation of Li~+ion source only comes from cathode materials.However,the mismatch energy level gives birth to the severe side reactions between Li and electrolyte whether in the liquid or solid state battery,consuming active Li and electrolyte.As such,Li metal battery commonly possesses low coulombic efficiency and short lifespan,even some malignant issues such as fire and explosion.Focusing on this essential problem,the protective interface structures between Li and electrolyte have been designed and prepared in this thesis.Meanwhile,the related protective mechanisms have been studied.The details are listed as follows.1.Native solid electrolyte interphase(SEI)with rich lithium fluoride(LiF)and high modulus.The influence of some kinds of Li salts on the native protective interfaces on Li metal has been studied.The results demonstrated that lithium bis(fluorosulfonyl)imide(LiFSI)could be decomposed into LiF on the Li surface.An SEI with high Young’s modulus of>10 GPa and rich content of LiF was detected under the electrolyte of 2 M LiFSI with 1,2-dimethoxyethane(DME)as solvent.According to the results of electrochemical performances,it can be concluded that the Li cyclic stability can be effectively improved by the SEI with high Young’s modulus.However,the native SEI is greatly depended on Li metal because of its direct growth on the surface of Li metal.2.SEI-functionalized artificial protective interface.To avoid the risk of side reactions induced from native SEI cracks and to further increase the interfacial stability of panel Li metal,a composite membrane of home-made stack graphene with LiF decorated was prepared as a protective interface.It was shown that C-F_x components were formed during the initial Li deposition,which reduced the electronic conductivity to～1/300 and slightly increased the Li~+ionic conductivity,presenting the characteristic of SEI.When used in practical condition,Li~+ions transfer through this SEI functionalized artificial interface and are deposited beneath it,realizing the effective separation panel Li metal from electrolyte.The cyclic stability of panel Li metal is remarkly increased due to the peaceable interface.3.Graphene oxide(GO)-3D current collector protective structure.An interfacial Li-GO dipolar structure can be formed after the initial Li deposition surrounding the defects of GO since the charge should transfer from the Li surface towards the GO layer,elevating LUMO energy of the interface.The interfacial stability between Li and electrolyte,therefore,can be increased.However,since the huge volumetric change during Li deposition,the cyclic stability of panel Li electrode cannot be ameliorated with alone GO as protective interface.A 3D current collector was used to offer enough room for Li deposition to mitigate the volumetric change.Combined with the GO decoration,the novel protective structure enhanced the cyclic stability whether in the liquid or solid state battery.Especially in solid state battery,the function of Li-GO dipole is similar to that of indium metal,reducing the cost of Li metal solid state battery.The abovementioned works focused on the constructions of buffer layer between Li and electrolyte to enhance the stability of Li/electrolyte interface,notably extending the working life of Li metal.These work provided new ways to realize efficient and stable cycling of lithium metal battery.