Protection And Electrochemical Performance Of Lithium Metal Anodes

In last 30 years,lithium-ion batteries with graphite anode materials have been commercialized successfully.However,there is an increasing demand for energy storage devices with high energy density.Traditional graphite anode with limited specific capacity of 372 m Ah g^-1 cannot satisfy such demand.To achieve high energy density,batteries with lithium metal as anodes receive considerable attention.Lithium anode has a high theoretical specific capacity of 3860 m Ah g^-1and the lowest standard reduction potential of-3.04 V（vs.standard hydrogen electrode）.Therefore,lithium anode is regarded as the most ideal anode for batteries with high energy densities.However,issues,such as the uncontrolled growth of lithium dendrites and huge volume change of lithium anode upon cycling hinder the practical application of lithium metal anode.The dendrites are induced by inhomogeneous Li⁺distribution on the surface of anode during the deposition process.The volume variation is resulted for inhomogeneous Li⁺deposition.In addition,high active Li dendrites would react with electrolyte,producing insoluble“dead Li”and consuming both electrolyte and Li metal.Consequently,this would lead to the decrease of the Coulombic efficiency and deterioration of the battery performance.Moreover,the uncontrolled growth of Li dendrites would puncture the separators,causing short circuits and even explosion of batteries.Low Coulombic efficiency and safety issue greatly hinder the application of lithium metal anode.In order to address these issues,strategies including modification of the separator and Li anode were developed in this thesis.（1）A lithiophilic Zn O@Ni was prepared via an one-step hydrothermal method,and subsequently severed as a host material for Li infusion to fabricate Zn O@Ni/Li composite anode.Zn O nanorods would enhance the lithiophilicity of pristine Ni foam and react with molten Li to produce Li Zn alloy and Li₂O coating layers.Lithium can be evenly stripped/plated along the lithiophilic Zn O@Ni skeleton,minimizing the dendrite formation and volume expansion.As a result,the Li|Li symmetric batteries with a Zn O@Ni/Li composite anode can be cycled stably over800 h at a current density of 2.0 m A cm^-2.（2）CoAl layered double hydroxide modified polypropylene（PP）separator（CoAl LDH@PP）was prepared by simply coating CoAl LDH particles onto PP membranes.The Li ions would effectively enter the octahedral vacancies of CoAl LDH,endowing fast kinetics for uniform Li nucleation.Consequently,the Li|Li symmetric batteries with CoAl LDH@PP separators can be charged/discharged stably over 1600 h at a current density of 2.0 m A cm^-2.（3）LiAl layered double hydroxide modified PP separator（LiAl LDH@PP）was prepared by simply coating[LiAl₂（OH）₆]Cl nanoflakes onto PP membranes.LiAl LDH nanoflakes with plenty of octahedral vacancies and abundant lithium ion diffusion pathways improve the ionic conductivity,surface electrolyte wettability and mechanical robustness of the separators.The modified separator promotes the interfacial lithium ionic flux,suppressing the dendrite formation and consequently increasing the cycling stability of lithium metal batteries.Even at an ultrahigh current density of 20?m A?cm^-2,the Li|Li symmetric batteries with LiAl LDH@PP separators can be charged/discharged for more than 3000?h,demonstrating the remarkably high cycling stability.