Quasi-Solid Polymer Electrolytes Composited With LiAlO₂/Al₂O₃ Nanosheets And Their Applications In Alkali Metal Batteries

The development of electrochemical energy storage systems with high energy density,long cycle lifetime and low cost plays an integral role to fulfil the goal of“peaking carbon dioxide emissions”and“carbon neutrality”.Alkali metal batteries are one of the most promising electrochemical energy storage systems due to their high energy density.However,current commercial organic liquid electrolytes have serious side reactions with alkali metal anodes,leading to uncontrolled dendrite growth.In addition,the electrolytes are flammable,volatile and prone to leakage,posing a serious safety hazard to the development of alkali metal batteries.Quasi-solid polymer electrolytes have higher safety,but the low room-temperature ionic conductivity,low cationic transference number and poor electrolyte/alkali metal anode interfacial compatibility,seriously hinder them from applications in alkali metal batteries.To solve the above problems,this thesis aims to improve the cationic transference number and enhance the quasi-solid electrolyte/alkali metal anode interface compatibility via composition design of quasi-solid polymer electrolytes and optimization of electrolyte/alkali metal anode interface.The main research contents are as follows:（1）From the perspective of quasi-solid polymer electrolyte design,fillers with strong anion adsorption capacity were designed and developed to endow quasi-solid polymer electrolyte with high cationic transference number.α-Li Al O₂/γ-Al₂O₃（LAO）composite nanosheets with strong anion adsorption ability were synthesized by the solvothermal method and calcination process,and LAO nanosheets were used as fillers to composite with polyvinylidene fluoride-hexafluoropropylene copolymer to prepare polymer electrolytes.The prepared electrolyte has a high lithium ion transference number（0.92）,high ionic conductivity(0.85 m S cm^-1@25℃).Using the electrolyte,the Li||Li cell can be cycled stably for more than 1000 h at a current density of 0.5 m A cm^-2,and Li Fe PO₄||Li and high voltage Li Ni_0.85Co_0.05Al_0.1O₂||Li batteries show excellent rate performance and long-term cycle stability.（2）From the perspective of electrolyte/anode interfacial design,polyacrylate-derived quasi-solid polymer electrolytes were prepared by in-situ thermo-polymerization to improve the quasi-solid electrolyte/alkali metal anode interfacial compatibility.A quasi-solid electrolyte with excellent electrochemical properties was successfully prepared by in-situ thermo-initiated polymerization of polyethylene glycol diacrylate and triethylene glycol diacrylate in the battery.The prepared electrolyte presents a high ionic conductivity of 1.4m S cm^-1@25℃and a wide electrochemical window（>4.8 V）.The polyacrylate derived crosslinking network can prevent side reactions of the solvent on the surface of the sodium metal anode,and carbonyl groups（C=O）in the network participate in the coordination of Na⁺in the electrolyte,reducing the desolvation energy,promoting the uniform Na deposition and inhibiting the dendrite growth.Using the quasi-solid polymer electrolyte,the Na||Na battery can be stably cycled for more than 2000 h at room temperature and at a current density of 0.1 m A cm^-2.Moreover,Na₃V₂（PO₄）₃@C||Na batteries with the electrolyte show good electrochemical performances.（3）Combining points（1）and（2）,a quasi-solid polymer electrolyte with both high cationic transference number and good electrolyte/electrode interface compatibility was designed to further suppress the dendrite growth and realize high-performance alkali metal batteries.By designing a porous polyvinylidene fluoride-hexafluoropropylene copolymer/polyethylene oxide/LAO network as the mechanical support for the polyacrylate derived polymer electrolyte network,a double network quasi-solid polymer electrolyte with high cationic transference number and good interfacial compatibility was acquired.The obtained electrolyte exhibits high ionic conductivity(3.4×10^-4 S cm^-1@30°C)and high sodium ion transference number（～0.62）.The LAO and polyacrylate-derived cross-linked networks in the electrolyte enhance the diffusion kinetics and promote the uniform deposition of Na⁺,therefore,the Na||Na battery with the electrolyte can be cycled stably for more than 900 h,and Na₃V₂（PO₄）₃@C||Na battery with a high cathode loading(9.7 mg cm^-2)shows excellent discharge capacity and cycling stability.