Two-dimensional Sheets Modified PEO-based Electrolyte And Its Application In Lithium Metal Battery

Solid-state lithium metal batteries have become the most promising next-generation energy supply source due to their ultra-high energy density and outstanding safety performance.Solid electrolyte is a key component of high energy density lithium-ion batteries,especially lithium metal batteries.The growth of lithium dendrites in this lithium metal is an inevitable obstacle in liquid electrolytes.Solid polymer electrolyte（SPE）has received extensive attention due to its flexibility,light weight,and low cost.Generally,pure polymer electrolytes have relatively low room temperature Li⁺conductivity and Li⁺transfer number,which limits their practical applications.In addition,the thermal stability,mechanical modulus and electrochemical stability of SPEs need to be further improved.At present,adding inorganic ceramic particles to polymer electrolytes to prepare composite all-solid polymer electrolytes is an effective strategy to improve ion conductivity,ion mobility,electrochemical stability and mechanical strength without losing its flexibility.On the basis of these performance improvements,the design of a composite all-solid-state polymer electrolyte that can be paired with high-voltage cathode materials and has an ultra-thin structure is the development of a safer,high-energy density all-solid-state lithium metal secondary battery Technical Support.Based on the above-mentioned shortcomings of polymer electrolyte performance,this paper takes two-dimensional vermiculite sheets（VS）as an example and proposes for the first time that two-dimensional materials are used as additives to prepare PEO-based composite all-solid polymer electrolytes.The morphology and structure of the composite all-solid polymer electrolyte can comprehensively improve the comprehensive performance of the composite all-solid polymer electrolyte system.The specific research work mainly includes three aspects:（1）Two-dimensional vermiculite nanoparticle（VS）was used as an additive to prepare VS-PEO composite solid-state polymer electrolyte,which comprehensively improved the comprehensive performance of PEO based solid polymer electrolyte.The composite polymer electrolyte can effectively inhibit the growth of lithium dendrites in lithium metal batteries in practical applications and can construct all-solid lithium metal secondary batteries with high safety performance and high specific capacity.（2）On the basis of previous studies,the distribution state of two-dimensional vermiculite nanoparticle in the composite electrolyte system was further regulated to improve its inadequate ionic conductivity at room temperature.The VAVS-PEO composite solid polymer electrolyte was prepared by using the two-dimensional vermiculite nanoparticle as a new filler by using the temperature gradient oriented freezing method.In this system,continuous and vertical active polymer-filler interface is provided for the transmission of Li⁺,with room temperature conductivity up to1.89×10^-4 S cm^-1,Li⁺transfer number close to 0.47.The LiFePO₄ was chosen as a positive material to assemble all solid-state lithium secondary battery at 35 ^oC and obtain a specific capacity of 167 mAh g^-1 at 0.1 C.（3）Through electrostatic spinning method,the two-dimensional nano vermiculite sheets can be made a large areas ultra-thin three-dimensional network structure（VMF）,and the ultrathin VMF-PEO composite solid polymer electrolyte was prepared,the thickness of the ultrathin VMF-PEO composite solid polymer electrolyte was 4.2microns,which the thinnest composite electrolyte membrane in the reported literatures.This ultra-thin structure significantly reduces the transmission distance of Li⁺in the composite electrolyte,further improves the ionic conductivity to 2.1×10^-4 S cm^-1 at room temperature and reduces the internal resistance of all-solid-state batteries to the level of batteries assembled by liquid electrolyte.The ultra-thin composite electrolyte can be paired with a high voltage positive electrode（such as NCM811）for the assembly of high safety and circulation-stable all-solid lithium metal secondary batteries.