Preparation And Properties Of Composite Lithium Ion Solid Electrolyte Based On Lithium Lanthanum Zirconate/polymer

Compared with the traditional liquid battery,the solid-state battery has the advantages of high safety,high energy density,high mechanical strength and good cycle life.The development of solidstate electrolytes with high mechanical properties,high ionic conductivity,excellent electrochemical and thermal stability,and compatibility with electrode materials is the key to the development of solid-state batteries.Garnet type solid electrolyte lithium lanthanum zirconate(LLZO)stands out due to its excellent comprehensive performance,such as stability to lithium metal,wide electrochemical window,and environmental friendliness,but the preparation scheme of LLZO is usually complex and requires high temperature calcination.In all kinds of solid electrolytes,inorganic electrolyte ions are characterized by high conductivity,good chemical and electrochemical stability and high mechanical strength,but their interface contact with the electrode is poor,usually thick and brittle,poor flexibility.Polymer electrolytes have good mechanical flexibility and good contact with electrodes,and are easy to be prepared into thin films.However,they have low ionic conductivity,poor electrochemical stability and poor flame retardancy at room temperature.Organic and inorganic composite solid electrolyte is the most promising system,which combines the advantages of polymer electrolyte and inorganic electrolyte.In order to simplify the preparation method of LLZO and reduce the calcination temperature and time,LLZO nanofibers were prepared by self-built electrostatic spinning equipment in this paper,and its formulation was optimized.In addition,in order to prepare composite solid electrolyte with high ionic conductivity,good flexibility and good contact with electrode,self-made LLZO nanofibers and LLZO particles were compounded with PVDF to prepare composite solid electrolyte and study its performance.Specific research contents are as follows:(1)Based on the current preparation process of LLZO solid electrolyte,in view of its complex preparation,long calcination time and high temperature,electrospinning method was used to prepare LLZO nanofibers.In order to obtain nanofibers with better morphology,the effects of polymer concentration and heat treatment conditions on the microscopic morphology and crystal phase were further studied.In addition,the problems encountered in electrospinning and their solutions are also summarized.Experiments show that polymer parameters,solvent parameters,solution parameters,process control parameters,environmental parameters,these five factors synergistically affect the results of electrospinning.For the preparation of LLZO nanofibers from the PVP-nitrate-DMF/acetic acid system,when the PVP content is 11 wt%,the nitrate content is 15 wt%,the calcination temperature is 750 °C,and the calcination time is 2 h,the obtained LLZO nanofibers are the best.(2)Based on the shortcomings of solid polymer electrolytes and inorganic electrolytes,composite electrolytes were prepared to solve the problem.Llzo-pvdf-litfsi electrolyte sheets were prepared by stream-casting method.In order to improve the ionic conductivity of the composite electrolyte,the influence of LLZO doping form(LLZO nanofiber,LLZO particle)and doping content on the ionic conductivity of the composite solid electrolyte was studied.When the doping amount of LLZO nanofibers reaches 20wt%,the ionic conductivity of LLZO nanofirel-PVDF-Lit FSi electrolyte sheet can reach 1.37×10-4 S/cm.