Preparation Of In-situ UV Curing Electrolyte Membranes And Study On Performance Of Lithium Metal Batteries

The composite solid-state electrolytes with a high energy density and high safety are crucial for their application in the field of all solid-state lithium metal batteries.Zeolite-structured materials（13X,ZIF-8）with high porosity and large specific surface area have excellent kinetics process and diverse architectures,showing a great potential in improving the battery performance.In response to the challenges of lithium dendrite growth and interface contact between solid-state electrolytes and electrodes,which are currently difficult to overcome in solid-state electrolytes,this type of porous materials is grafted with lithium-ion liquids to prepare the ion conductor by the mixing treatment with polymer solutions under the condition of UV polymerization.Furthermore,a series of high-performance composite solid-state electrolytes are prepared by optimizing the preparation process.This thesis focuses on the material design and performance optimization of composite solid-state electrolytes.Especially,the mechanisms of in-situ UV curing and the synergistic modification of composite materials,as well as the electrochemical properties of all solid-state lithium metal batteries are studied in detail.The specific research content is as follows:（1）The problem of lithium dendrite growth can be solved by constructing the ion transport pathways using lithiated 13X molecular sieves（Li-13X）loaded with lithium ion liquids（Li-IL）.A three-dimensional porous cage-like 13X molecular sieve with larger pore size and specific surface area is employed,followed by a vacuum high-temperature treatment to remove the impurities in pores and a further activation of unsaturated sites.Then,Li-13X is filled with lithium ion liquid,resulting in the formation of Li-IL@Li-13X Ionic conductor.The lithiated 13X provides more lithium ion transport pathways,and the skeleton framework serves as an ion transport channel,increasing the amount of freely migrating lithium ions and forms a solid-state transport pathway.The three-dimensional cage-like Li-13X molecular sieve with abundant Lewis acid sites can immobilize large-sized organic ions and promote the dissociation of lithium salts.After the incorporation of monomers and photoinitiators into the ionic conductor,the luminescence polymerization reaction can be induced under the condition of UV irradiation,forming the composite solid-state electrolyte with a cross-linking network.The lithium symmetric battery equipped with the composite solid-state electrolyte is assembled and can work stably for 1400 hours at 45℃with a current density of 0.1 m A cm^-2,indicating that the composite solid-state electrolyte has a high electrochemical stability and exhibits the ability to inhibit the growth of lithium dendrites.This study provides ideas to develop the Li-IL@Li-13X-based solid-state lithium metal batteries with low-cost and high stability.（2）The metal-organic frameworks with a large pore size and high specific surface area have a positive effect on constructing high-performance solid-state electrolytes.ZIF-8nanoparticles are prepared and the loaded with lithium-ion liquid to obtain the Li-IL@ZIF-8.After mixing with a polymer solution containing the photoinitiator,the solid-state electrolyte is obtained by casting and in situ coating,followed by an irradiation with ultraviolet light.ZIF-8 crystals expose abundantly unsaturated metal sites after the activation,and can absorb a large amount of lithium-ion liquid through nanopores,promoting the dissociation of lithium salts in lithium-ion liquid,and reducing the crystallinity of polymer matrix.The solid-state electrolyte afford a high ion conductivity of6.53×10^-4 S cm^-1 at room temperature,together with an expanded electrochemical window of 5.2 V and increased lithium ion migration number of 0.38.The highly stable cycling(900hours at 0.1 m A cm^-2)demonstrates the good compatibility between solid-state electrolytes and lithium metals,as well as the ability to suppress lithium dendrite growth.After in-situ photocuring treatment,the composite solid-state electrolyte exhibits a capacity retention rate of 88.16%after 320 cycles at 0.5 C.This study gives an effective pathway to construct high-performance Li-IL@ZIF-8-based solid-state lithium metal batteries.（3）The synergistic effect of in-situ photocuring and composite positive electrode is a feasible approach to improve the interface problem between the positive electrode and solid-state electrolyte.The composite Li Fe PO₄ and NCM111 positive electrodes are prepared by mixing different ratios of Li-IL@ZIF-8 into the positive electrode material,and the composite positive electrode and Li-IL@ZIF-8-based composite solid-state electrolytes are integrated by in-situ photocuring technology,so as to achieve the"ultra-tight connection（UTC）"of the positive electrode/electrolyte interface.The Li-IL@ZIF-8 Ionic conductors provide a lithium ion transport path in the positive electrode and act as plasticizers to reduce the crystallinity of solid-state electrolyte polymers,thus creating favorable conditions for solid-state batteries operating at room temperature.The results show that the integrated positive electrode/electrolyte structure constructed by UTC cells,the in-situ technique and excellent wettability of ionic liquid cooperatively optimize the ion transport paths inside the electrode and at the interface,reducing the internal impedance of solid-state lithium metal batteries.The battery with the composite NCM111 positive electrode shows a high initial discharge capacity of 119.6 m Ah g^-1 at 0.5 C,and the capacity retention rate is 96.7%after450 cycles.In addition,the discharge specific capacity is 104 m Ah g^-1 at a high current density of 2 C,exhibiting an excellent cycle performance.This study affords an idea to realize the integration of positive electrode and solid-state electrolyte in solid-state lithium metal battery.