Studies On Modification Of Composite Solid-state Electrolytes By Fast Ionic Conductor Li_1.4Al_0.4Ti_1.6?PO₄?₃

Lithium ion battery has the advantages of high energy density,wide electrochemical window,no memory effect and little environmental pollution,etc.,and has become the preferred energy system in many fields.However,the development of the society and the improvement of environmental protection awareness have promoted the safety standards of energy system.Especially at present,the society's needs for energy power and energy storage systems have highlighted a series of safety issues for liquid lithium-ion batteries in the process of promoting the development of lithium-ion batteries toward higher energy density.Among them,liquid electrolytes with potential safety risks such as volatility,decomposition,leak and inflammability are the key factors,which limit the improvement of safety of traditional liquid lithium ion batteries.In order to avoid and solve the potential safety problems of traditional lithium ion batteries,solid-state batteries with meritorious safety and electrochemical performance have been extensively designed and studied in recent years.Compared with liquid electrolyte,solid-state electrolyte hasn't the problems of volatilization and combustibility,meanwhile,it has the advantages of high ionic conductivity,wide electrochemical window,high cyclic stability and inhibition of lithium dendrite growth.Composite solid-state electrolyte is composed of inorganic solid-state electrolyte and polymer electrolyte,which has both high ionic conductivity of the former and low interfacial impedance and good flexibility of the latter.especially its high energy density and excellent safety have become one of the most promising candidates of the next generation.This paper studies and exploits high performance composite solid-state electrolytes.By optimizing the ratio of each component content in the electrolyte and designing a complementary organic-inorganic composite solid-state electrolyte,the problems such as reducing the large interface impedance of the inorganic solid-state electrolyte and improving the ionic conductance of the polymer electrolyte at room temperature were solved,so as to explore the function and utility of the composite electrolyte.In this paper,relevant contents are explored and the specific research contents are as follows:Study on modification of double matrix polymer electrolyte by inorganic fast ion conductor Li_1.4Al_0.4Ti_1.6?PO₄?₃.Based on the stability,compatibility and high lithium dissociation capacity of two relatively mature polymers?PVDF and PEO?substrates,as well as the high ionic conductivity of fast ionic conductor material Li_1.4Al_0.4Ti_1.6?PO₄?₃,the composite electrolytes with complementary advantages were prepared by composite modification of inorganic and organic compounds.Four series of composite solidstate electrolytes including PVDF,PVDF@ PEO with different ratios of double matrix,PVDF@PEO-LATP with gradient contents of LATP,and PVDF@ PEO-LATP-Li PF6 with different quality of Li PF6 were prepared.The optimal content ratio of each component in the composite solid-state electrolyte was studied from the aspects of ionic conductivity and ion migration number.Further electrochemical characterization showed that the modified electrolytes had more stable cyclic stability,rates performance and safety properties.The internal mechanism of the effects of dual substrates?PVDF and PEO?and modified materials?LATP and Li PF6?on the physical and electrochemical properties were systematically studied.The experimental results showed that the components in the optimal content ratio of composite solid electrolyte could produce a better synergistic effect.The hydrogen bond formed between the molecules of the double-matrix polymer could effectively reduce the crystallinity and strengthen the connection of polymers.The generation of complexation effect between fast ionic conductor LATP particles and polymer network,and the formation of organic-inorganic interface phase could further reduce crystallinity of polymer matrix and improve mechanical strength of the electrolyte.The inorganic lithium salt Li PF6 could effectively provide lithium source and directly increase the concentration of free lithium ion in the composite solid-state electrolyte.The composite solid-state electrolyte prepared in this study has been improved in aspects of ion conductivity,ion migration number,electrochemical window and mechanical properties,and thus has more prominent physical and electrochemical properties.Although the inorganic fast ion conductor LATP particles have some improvements in the modification of polymer electrolyte,they fail to fully exert their ion transport capacity.Therefore,we designed a composite solid-state electrolyte based on 3D-LATP to realize the rapid migration of lithium ions in the electrolyte,and changed the phenomenon that inorganic materials only act as modified materials or skeleton materials in common composite solid-state electrolytes.A three-dimensional inorganic fast ion conductor material?3DLATP?was constructed firstly,and then fully compounded with polymer PEO,which dissolved a certain amount of lithium salt?LITFSI?.Comparing the physical and electrochemical properties of three electrolytes PEO-LITFSI?PL?,LATP@PEO-LITFSI?LPL?and 3D-LATP@PEO-LITFSI?3D-LPL?,the effects of threedimensional ion conduction skeleton and polymer PEO in the electrolyte were systematically investigated.The test results show that compared with the electrolyte LATP,the electrolyte 3D-LATP with threedimensional ion conduction structure has higher ionic conductivity and lower internal resistance.The addition of PL could effectively enhance the cyclic stability and safety of the composite solid-state electrolyte,and at the same time reduce the large interface resistance of inorganic electrolyte,as well as avoid the side reaction caused by the direct contact between 3D-LATP and lithium metal.In addition,the interface phase generated at the interface of organic-inorganic materials could effectively promote the conduction of lithium ions,so that the composite solid-state electrolyte 3D-LPL shows excellent physical and electrochemical properties.