Development And Study Of Highly Ion-conductive Metal-organic Frameworks For Lithium Metal Batteries

Lithium metal batteries are deemed to be one of the most promising next generation electrochemical energy storage devices due to their high energy density.However,safety issues and poor cycling stability hindered their practical applications.Solid electrolytes can effectively improve the safety and lifetime of lithium metal batteries.However,current solid electrolytes still suffer from low ionic conductivity and poor interfacial contact between electrolyte and electrodes.Metal-organic frameworks(MOFs)have shown great potential as advanced solid electrolytes due to their porosity and pore tunability.By designing the organic linkers and metal clusters of MOFs,the chemical environment inside pores and particle surfaces was modulated to facilitate the ion transport of MOFs and investigate its influence for performance of lithium metal batteries.Firstly,three MOFs with the same structure but different densities of functional groups(-CO₂H)were prepared by selecting different organic linkers.The combination of theoretical simulations and experimental results demonstrates that the functional groups(-CO₂H)facilitate ion conduction in MOFs.The higher the density of-CO₂H,the higher the ionic conductivity of the MOF.Meanwhile,the solid electrolytes fabricated with the MOFs with the highest density of-CO₂H(Ui O-66-2-CO₂H)shows high ionic conductivity,wide electrochemical window,ability for suppressing the formation of lithium dendrites and low interface resistances.The lithium metal batteries with Ui O-66-2-CO₂H as solid electrolyte exhibit excellent cycling stability at a wide operating temperature range from-20°C to60°C.Secondly,different Lewis base molecules are chemically anchored on the open metal sites(OMSs)of MIL-101(Cr)to facilitate the Li⁺transport inside and between MOF particles.The advantages of molecular-scale chemical engineering of MOFs have been demonstrated a series of electrochemical tests.The MOF decorated with long chain Lewis base exhibits the highest ionic conductivity,ability of single ion conduction,capability of inhibiting lithium dendrite growth and reduced interfacial resistance.The Solid-state lithium metal battery assembled with the such MOFs as solid electrolytes shows improved specific capacity of 47%and outstanding stability with a low decay rate of 0.02%after 700 cycles at 5 C.