Preparation And Electrochemical Properties Of Multi-element Doped Li₇La₃Zr₂O₁₂ Solid Electrolyte Materials

Lithium-ion batteries are widely used in electric vehicles,energy storage plants and portable electronic devices because of their excellent performance.However,traditional lithium-ion batteries using organic liquid electrolytes have problems such as insufficient energy density and frequent safety accidents,which makes it difficult to meet the growing demand for high-performance batteries.However,lithium-ion batteries using solid electrolytes are expected to fundamentally solve the safety problems of traditional liquid electrolyte batteries.If used with new electrodes,the theoretical energy density is expected to be greatly increased.Among them,garnet oxide Li₇La₃Zr₂O₁₂ solid electrolyte has been widely concerned for its wide electrochemical window,good chemical stability and thermal stability.However,problems such as low ionic conductivity at room temperature and high resistance at the contact interface with electrodes hinder the commercialization of this electrolyte,and further improvement is needed.In this paper,single element,double element and three element doped Li₇La₃Zr₂O₁₂ based solid electrolytes were synthesized by atmospheric solid phase reaction sintering method.The method and mechanism of electrochemical performance optimization of Li₇La₃Zr₂O₁₂ based electrolytes were explored through element doping.The specific research results are as follows:The effects of sintering process（sintering temperature and time）on the structure and properties of Li_7-3xGa_xLa₃Zr₂O₁₂（LG_xLZO）solid electrolytes doped with Ga were investigated systematically with different doping quantities of x=0,0.05,0.1,0.15,0.2,0.25 and 0.3.With the increase of x,the phase structure of LG_xLZO prefired powder changes from tetragonal to cubic phase,and the phase structure of all LG_xLZO ceramics after sintering is cubic phase.Compared with Li₇La₃Zr₂O₁₂ ceramics,the average grain size of LG_xLZO ceramics doped with Ga is reduced.The ionic conductivity of LG_xLZO ceramics firstly increases and then decreases with the increase of x.When x=0.25,the ionic conductivity of the ceramics sintered at 1230℃for 4 h reaches the maximum.The lithium symmetric battery was assembled with the sample prepared under this condition,which could be stably cycled 500 times at 0.1 m A current.Ga and Ta doped Li_6.25-yGa_xLa₃Zr_2-yTa_yO₁₂（LGLZT_yO）solid electrolytes were prepared,and the effects of x=0.25,y=0.2,0.4,0.6 doping,sintering process（sintering temperature,time）on the properties of LGLZT_yO were investigated.The densification degree of ceramics increases with the increase of y,and the relative density of LGLZT_yO ceramics reaches the maximum when y=0.6.The ionic conductivity of LGLZT_yO ceramics decreases with y increasing.When y=0.2,the ionic conductivity of ceramics sintered at 1230℃for 4 h is the highest.Li/Li_6.25-yGa_0.25La₃Zr_2-yTa_yO₁₂/Li batteries with the highest separation conductivities were selected,which showed good polarization voltage and more stable cycle than Ga single-doped lithium symmetric batteries.Ga,Ta and Sr doped Li_6.05+zGa_0.25La_3-zSr_zZr_1.8Ta_0.2O₁₂（LGLS_zZTO）solid electrolyte was prepared.The addition of Sr²⁺can promote the growth of grain,but excessive Sr²⁺cannot enter the grain and remain in the grain boundary,which has an adverse effect on the performance.When z=0.2,the relative density of LGLS_0.2ZTO ceramics is the highest.When z=0.1,the ionic conductivity of ceramics sintered at 1220℃for 3 h is the highest,which is 41%lower than that of LGLZT_yO ceramics.Select the sample with the highest ionic conductivity to assemble the lithium symmetric battery,which can stably cycle 1000 times at 0.1 m A current.