Preparation And Performance Of NASICON-Type Li_1.5Al_0.5Ge_1.5（PO₄）₃ Inorganic Solid-State Electrolyte

In recent years,lithium ion battery has been successfully commercialized and developed rapidly in the field of electronic equipment.Traditional lithium ion battery usually uses organic liquid electrolyte,which causes fire safety accidents especially.Compared with it,solid electrolyte has high temperature resistance and high safety performance,etc.In order to improve the safety performance of lithium ion battery,the researchers replace liquid electrolyte with solid electrolyte and assemble solid battery.Solid electrolyte can be divided into inorganic electrolyte and polymer electrolyte.NASICON（Na super ionic conductor）-type Li_1.5Al_0.5Ge_1.5（PO₄）₃（LAGP）oxide inorganic solid electrolyte has the vast operating temperature range（-70℃～500℃）,the wide electrochemical window（>4 V）and the better air stability,etc.However,the porosity arises during sintering LAGP,and it will result in low ionic conductivity.In this paper,solid-phase sintering method and gel-sol method were used to prepare LAGP powder.And the density of LAGP powder was improved by adding sintering agent and using hot-pressing-sintering,so as to improve ionic conductivity.The main works are as follows:（1）The powder of LAGP was prepared by solid-phase sintering method and sol-gel method,respectively.The powder was pressed and sintered under different sintering conditions.The morphology,crystal phase structure,density and ionic conductivity of LAGP were studied on different sintering conditions.The result showed that the ionic conductivity of LAGP was increased with the rising of density.When sintering at 950℃for 9 h by solid-phase sintering,the ionic conductivity of LAGP was 6.28×10^-6 S·cm^-1,and the relative density was 83%.When sintering at 900℃for 8 h,the ionic conductivity and relative density of LAGP by sol-gel method were 1.59×10^-5 S·cm^-1 and 89%,respectively.LAGP prepared by sol-gel method had smaller particle size,higher purity,and its ionic conductivity was 2.53 times higher than that by solid-phase sintering method.（2）Liquid phase sintering method was used to study the effects on the conductivity of LAGP including the sintering aids B₂O₃ and Li₃PO₄,the amount of additives and the sintering temperature The result showed that when B₂O₃ was added,the relative density was 91%and the ionic conductivity was 1.34×10^-4 S·cm^-1 when sintering as 700℃and the dosage was 5wt%.When the same content of Li₃PO₄ was added,the relative density and ionic conductivity of LAGP were 92%and 1.30×10^-4 S·cm^-1 at the same sintering temperature.The addition of the sintering agent was beneficial to grain growth,reduced the number of grain boundaries and promoted the migration of Li⁺.The ionic conductivity of LAGP with the sintering agent was increased by an order of magnitude compared with that without the sintering agent.（3）LAGP material was prepared by hot pressing sintering,and the influence of hot pressing sintering temperature,hot sintering time and hot sintering pressure was investigated.Experimental result showed that the best hot pressing sintering parameters were 800℃,2 h,20 MPa,and the conductivity of LAGP was 1.08×10^-4 S·cm^-1,the highest relative density was 93%.Hot pressing reduced the formation of pores in the material,and the LAGP material with uniform grains and high density could be obtained in a short time,thus improving the ionic conductivity.