Anode Protection And Application Of Lithium-containing Ceramic Materials For Lithium Metal Batteries

Li-ions batteries have been widely used in all aspects of human life,such as electric vehicles and so on.However,conventional Li-ions batteries（LIBs）based on graphite anode are hardly to satisfy the growing demand for high energy density.It is extremely urgent to develop novel battery,Li metal has been considered as the“Holy Grail”among all anode materials because of its high theoretical specific capacity,low density and the lowest electrochemical potential.Therefore,it is now widely accepted that Li metal batteries（LMBs）using Li metal as anode are promising to address the anxiety about energy density.Up to now,in the application of lithium metal anodes,the problems of low coulombic efficiency and poor cycle life due to the growth of lithium dendrites have greatly restricted its development.Therefore,this thesis focuses on achieving effective inhibition of dendrites and significantly increase d cycle life through the design of lithium-containing ceramic ion-conducting electrolyte materials and protection strategies such as ex-situ artificial organic-inorganic protective film,electrolyte additive modification,and mechanical barrier on three-dimensional structural framework.The purpose is to provide theoretical support and technical reference for promoting the practical application of lithium metal anodes.Firstly,a garnet-type lithium-containing ceramic oxide Li₇La₃Zr_1.7Ti_0.3O₁₂（LLZTO）was used to prepare an ex-situ organic-inorganic composite protective film.The LLZTO ion conductor material was prepared by the solid-state method,and the LLZTO/PVDF-HFP（LLZTO/PH）composite film was obtained by spin coating method as an artificial protective film for lithium anode.The amount of LLZTO was regulated to establish a continuous potential gradient from the electrolyte to the Li metal surface.Through experimental tests and simulation calculations,the symmetric Li/Li cells optimized with 5 wt.%LLZTO/PH film exhibits the lowest polarization voltage and the most stable electrochemical stability,and the optimized Li/Cu cells can maintain a stable coulombic efficiency of about 99%in 470 cycles.Moreover,comparative researches indicate that the composite ion conductive LLZTO/PH protective film which does not react with the lithium anode is more advantageous than composite non-ionic conductive Ni O/PH protective film with Ni O/Li₂O layer（Li⁺fast migration channel）,because LLZTO/PH protective film has better chemical stability and higher mechanical strength.Secondly,the LLZTO porous framework was combined with the LLZTO/PH composite membrane to construct a three-dimensional bilayer structure framework.Furthermore,a Li PF₆ optimized electrolyte was introduced into the solid-state electrolyte,and the performance of a composite electrolyte lithium metal battery composed of a double-layer solid-state and liquid electrolyte was studied.SEI film composition analysis combined with simulation calculation revealed that Li PF6additive would promote the decomposition reaction of Li TFSI and Li PF ₆ through the association effect,and clarified the mechanism of the formation of Li F-rich high-quality SEI film on the dendrite suppression and coulombic efficiency improvement of lithium anode.Li PF₆ optimized Li/Li cells exhibit long-term stable cycling over4000 h(0.5 m A cm^-2)and 2000 h(2 m A cm^-2).Moreover,the Li PF₆ optimized electrolyte shows good electrochemical performance such as rate characteristics in full cells with Li Ni_0.8Co_0.1Mn_0.1O₂ and Li Fe PO₄ as cathode materials.Furthermore,the double-layer composite electrolyte hybrid lithium-sulfur battery exhibits a discharge capacity of 787.1 m Ah g^-1,as well as good cycle stability and cycle life.Finally,NASICON-type lithium ion conductor Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）was synthesized by molten salt method as a solid electrolyte material to construct a three-dimensional multilayer LATP solid-state framework.This structure includes the dense LATP thin film layer,the porous layer and the composite LATP/PH interface buffer layer,which effectively solves the problems of lithium anode dendrite growth and interfacial contact in lithium metal batteries.In order to solve the problems that the dense solid ceramic electrolyte is difficult to be sintered,and the film is difficult to be self-supporting,a three-dimensional integrated electrode support framework with LATP porous framework supporting the highly densified density electrolyte film was realized by the design of the pressure spin coating method.The LATP/PH composite film was introduced as a buffer layer to improve the solid-solid interface problem between the lithium anode and the LATP solid electrolyte.Moreover,the multilayer LATP solid-state electrolyte structure was applied to Li-S batteries,and a specific capacity of 396.1 m Ah g^-1 was obtained with good cycling stability after 250 cycles（high stable CE～99%）and rate characteristics.This structure effectively inhibits the growth of lithium dendrites,improves the solid-solid interface contact problem,prevents the shuttle effect of sulfur cathode,and enhances the capacity and cycle life of LMBs.