Preparation Of Modified PEO Based Solid Electrolyte And Its Application In Lithium Metal Battery

To meet the needs of national energy development strategy,high energy density solid metal lithium batteries have been placed high hopes,solid electrolyte due to high safety performance has attracted much attention.Among solid electrolyte materials,polymer electrolyte based on polyvinyl oxide（PEO）has been widely studied because of its ion conduction characteristics and high stability to lithium metal.However,unmodified PEO-based polymer electrolytes can only be used for battery charge and discharge tests at 60°C.At room temperature,there are many problems such as low ionic conductivity and high crystallinity of PEO,which greatly limit the application of PEO-based solid-state electrolyte materials.In this paper,the PEO-based composite polymer electrolytes were prepared by modifying them with liquid plasticisers and doping them with niobium-doped garnet solid-state electrolytes（LLZNO）to solve the problems of high crystallinity and low ionic conductivity at room temperature,thus producing composite electrolytes with excellent electrochemical performance.In addition,the interface stability of lithium symmetric batteries and the electrochemical performance of solid metal lithium batteries were systematically studied.The main research contents include:（1）Preparation and performance of composite blended gel electrolytes:PEO/PMMA/P（VDF-HFP）films were prepared by the blending method,and then SN was blended with lithium bis（trifluoromethanesulfonyl）imide（Li TFSI）to reduce the crystallinity and form a solution,and the films were immersed in it to form a new composite gel electrolyte with high ionic conductivity.The characterisation and electrochemical performance tests show that the electrolyte is thermally stable,with an ionic conductivity of 3.2×10^-4S/cm at 20°C,lithium ion mobility of 0.66 and an electrochemical window of 5.23 V.（2）Interfacial mechanism study of composite co-blended gel electrolyte solid-state batteries:A constant current charge and discharge method was used to study the electrochemical performance of solid-state lithium metal batteries.The interfacial properties of solid-state batteries were studied using EIS,XPS and SEM.From the results of the performance study of lithium symmetric batteries,we found that the gel electrolyte modified with a plasticiser added with fluorinated ethylene carbonate（FEC）could form a stable Li F-rich interfacial layer on the lithium-metal surface.This phenomenon contributes to the enhanced lithium stability of the electrolyte,which allows for uniform lithium deposition and reduces lithium dendrite generation during constant current charging and discharging of lithium batteries.In addition,the overall electrochemical stability of the battery is greatly improved by assembling and testing lithium metal batteries with lithium iron phosphate as the cathode.（3）Preparation and performance study of multilayer LLZNO/PEO/SN composite electrolytes:firstly,LLZNO/PEO/SN composite electrolytes were prepared and the crystalline regions in the PEO chain segments have been evidenced by characterisation results.The electrolytes showed the highest ionic conductivity at room temperature when the content of LLZNO was 10 wt%PEO,and the electrochemical window was also stable above 5 V.Then a mixed gel layer of SN,lithium salt and FEC was added on the lithium metal surface to assemble a lithium symmetric cell,and obtain the most stability content when 1μL was titrated on the lithium metal.The lithium symmetric and lithium metal batteries were assembled together with the composite electrolyte and tested for their electrochemical performance.The results of the study show that the battery with the added gel layer has better cycling stability performance and can be tested for charge and discharge at room temperature.