Research On The Modification Of Lithium Metal Anode By Composite Protective Layer

Lithium metal with ultra-high theoretical specific capacity（3861 m Ah/g）and ultra-low redox potential（-3.040 V vs.hydrogen standard）has become the most ideal anode material.However,the dendritic problem of lithium metal anode always hinders the development of lithium metal batteries.In this thesis,the composite protective layer with excellent electrochemical stability and mechanical properties was spin-coated on the surface of lithium anode to inhibit the formation and growth of lithium dendrites and improve the interfacial stability of lithium anode/electrolyte,thereby improving the cycle stability and safety performance of lithium batteries.1.The PVDF/TiO₂composite protective layer was constructed on the surface of lithium anode.Based on the excellent stability and lithophilic property of TiO₂,the layer can improve the interfacial stability of lithium anode,and induce the uniform deposition of lithium.The Li|Li symmetric cell with this protective layer exhibited better cycling stability at current densities of 1 m A cm^-2,3 m A cm^-2,and 8 m A cm^-2.Moreover,the Li-Cu half-cell with the protective layer also maintained 95%CE for 150 cycles,and the performance of the Li|LFP full cell with the surface-treated lithium anode was significantly optimized.2.ZnO as a lithophilic material could provide nucleation sites for lithium ions and achieve stable deposition of lithium,thus PVDF/ZnO composite protective layer was designed and prepared.The mechanical properties of PVDF/ZnO composite protective layer could also effectively inhibit the growth of lithium dendrites.The synergistic effect of PVDF and ZnO achieved long and stable cycle of Li|Li symmetric cell and significantly improved the CE of Li-Cu half-cell.In the practical application of Li|LFP full cells,both of the long cycle stability and multiplicative performance were significantly optimized.3 The PVDF/LiAlO₂composite protective layer with excellent ionic conductivity,ion migration number and mechanical properties was prepared on the Li metal surface by a simple spin coating method.The protective layer has the ability to conduct Li ions rapidly,which can induce uniform deposition of Li ions and improve dendritic growth.In addition,the compact and uniform protective layer which could isolate the lithium metal from the electrolyte alleviated the continuous consumption of electrolyte and active lithium,and suppressed the undesirable reaction.As a result,the long cycle life of the Li anode(over 1600 h at a current density of 1 m A cm^-2for Li|Li symmetric cell)and high capacity retention（91.5%after 700 cycles at 1 C）of the Li|LFP battery were achieved.Moreover,the multiplicative performance and CE were also improved.