Preparation And Performance Research Of Epoxy-based Solid-state Electrolyte

The use of solid-state polymer electrolyte can not only avoid the shortcomings of liquid electrolyte,such as leakage,volatility,flammability and environmental pollution,but also can be used in conjunction with lithium metal anode to obtain high specific capacity and inhibit lithium dendrites to a certain extent.Linear polymer electrolytes have been widely studied due to their high flexibility and relatively good contact against electrodes.However,the problems of linear polymers(i.e.easily crystallization at room temperature and melting at moderate temperature)have restricted their application in lithiummetal batteries.The cross-linking strategies are usually used to solve these problems.The traditional cross-linking reaction requires the addition of solvents or initiators,and the generated by-products may cause adverse reactions with the electrode.Epoxy groups can react with amine groups to form a cross-linking network.In this reaction process,no initiator is required and no by-products are produced.Therefore,the epoxy-based crosslinked polymer electrolyte(CPE)attracts more and more attention in recent years.First of our work,we used polyethylene glycol diglycidyl ether(PEGDGE)to react with polyetheramine(D2000)by the self-catalysis of bistrifluoromethanesulfonimide lithium salt(LiTFSI)to obtain a highly flexible CPE,which was carried out at a low temperature and under the solvent-free and initiator-free conditions.The CPE has a high ductility(elongation at break of 103%),excellent mechanical property(tensile strength of 1.30 MPa)and low glass transition temperature(Tg,-60℃).The interface impedance at room temperature was reduced from 3189 Ω/cm2 to 1338 Ω/cm2 due to the in-situ strategy.In addition,CPE also has a high ionic conductivity of 2.05×10-5 S/cm at room temperature and 2.55×10-4 S/cm at 75℃.Secondly,when the epoxy-based electrolyte is combined with the spun membrane of in-situ grown zeolite imidazole ester framework material(ZIF),the electrochemical window is increased from 4.03 V to 4.15 V,and the lithium ion transference number is increased from 0.113 to 0.146.When roomtemperature ionic liquid(EMI-TFSI)is added and polyetheramine(D230)is selected as the curing agent,and the mass ratio of PEGDGE and bisphenol A diglycidyl ether epoxy resin(E51)is 3:3,the elongation at break of the electrolyte film is greater than 98%and the tensile strength can reach more than 4.32 MPa.In addition,the ion conductivity can reach 2.09×10-4 S/cm,the electrochemical window is further increased to 4.50 V,and the lithium ion transference number is increased to 0.276.Furthermore,the Li/CSE3/LiFePO4 cells show excellent cycle stability(0.2 C first cycle discharge specific capacity is 151 mAh/g,after 200 cycles,the capacity retention rate is 86.2%,and the coulombic efficiency is close to 100%).