Preparation Of Sulfide Solid Electrolyte Material And Its Modification For Polyethylene Oxide-Based Solid Electrolyte

Lithium secondary batteries have been widely used in people’s production and life because of its high energy density,good cycle life and low self-discharge rate.However,the organic electrolyte used in lithium batteries is flammable and explosive,which cause safety hazards.Replacing the flammable liquid electrolyte with inorganic eletrolyte,the problem would be solved very well.At present,there are two main types of inorganic solid electrolytes:oxide solid electrolytes and sulfide solid electrolytes.Oxide solid electrolytes have many advantages such as wider electrochemical window,but their low ionic conductivity hinder performance of solid-state batteries.Sulfide solid electrolytes have higher ionic conductivity than oxide solid electrolytes.Therefore,it has great potential in the new generation of solid state lithium batteries.However,preparation conditions of sulfide is tricky,so we have focused on the preparing conditions of sulfide electrolyte in order to synthesize high ion conductivity sulfide electrolyte.In addition,the large interfacial resistance between the inorganic solid electrolyte and the electrode also affects the electrochemical performance of the all-solid battery.Therefore,we propose to construct an inorganic-organic composite solid electrolyte to improve the interfacial contact between the electrolyte and the electrode.The main research contents are as follows:（1）Different synthesis conditions have a large effect on the ionic conductivity of binary sulfides.This chapter mainly explores the effects of different milling time and heat treatment temperature on the ionic conductivity of materials.Firstly,the binary sulfide Li₇P₃S₁₁（LPS）glassy electrolyte was prepared by wet milling method.Then the material with the best ball milling time was heat treated at different temperatures,and the all-solid lithium ion battery LiFePO₄/LPS/Li was assembled after optimizing synthesis condition.X-ray powder diffraction,Raman spectroscopy,scanning electron microscopy,transmission electron microscopy,differential scanning calorimetry,alternating current impedance and cyclic voltammetry were used to characterize the structure and electrochemical properties of the material.The electrochemical performance of all solid state batteries were tested.The results show that the material exhibits the highest ionic conductivity(σ=6.8×10^-4 S/cm)at ball milling time 15 hours and the heat treatment temperature 280℃.However,the electrochemical impedance of the all-solid lithium ion battery LiFePO₄/LPS/Li is large between the sulfide electrolyte and the electrode（2）In order to solve the interfacial impedance problem between the inorganic sulfide solid electrolyte and the electrode,we use inorganic-organic composite method to prepare PEO-LPS composite solid electrolyte,and explore the effect of mass fraction of binary sulfide solid electrolyte LPS on PEO ion conductivity.The structure morphology and electrochemical behavior of the composite solid electrolyte were characterized by X-ray powder diffraction、scanning electron microscopy and AC impedance.The results show that the composite solid electrolyte with 1%LPS show the highest ionic conductivity,and the electrochemical stability window reaches 5 V.The assembled LiFePO₄/SPE/Li all-solid battery delivers a discharge capacity of 162.3 mAh/g on the first cycle at 80℃.The capacity retention rate after 50cycles is up to 96%.