The Research Of Construction,interface Modification And Electrochemical Performance Of LATP-based Solid Electrolyte

Lithium-ion batteries are widely used in portable electronic equipment,energy storage and electric vehicles.However,commercial electrolytes have poor chemical stability and thermal stability,which leads to safety issues such as fire and leakage.Therefore,solid-state batteries are one of the key routes for the development of next-generation batteries.In theory,solid-state batteries can achieve higher energy density and power density,and the key is to develop solid electrolytes with excellent performance and optimize the interface with electrode materials.In this paper,the solid electrolyte Li_1.3Al_0.3Ti_1.7（PO₄）₃,which has high ionic conductivity,low raw material cost and stable environmental conditions,is selected as the research material.The experiments were carried out on improving the sintering process of solid electrolyte LATP,the interface modification of LATP and lithium metal electrode by FeF₂,and the construction of three-dimensional LATP composite solid electrolyte.The experimental results obtained are as follows:（1）The LATP precursor powder with no impurity phase and good crystallinity was prepared by sol-gel method,and LATP solid electrolyte was prepared by spark plasma sintering（SPS）.Compared with the traditional method,the relative density of LATP obtained by SPS increased from 89.73%to 98.87%,and the ionic conductivity increased from 1.81×10^-4 S cm^-1 to 5.78×10^-4 S cm^-1.The Young’s modulus has also increased from 146 GPa to 180 GPa（2）In view of the weak electrochemical stability of LATP solid electrolyte to lithium metal,FeF₂ is used as an electrolyte additive to modify the interface of LATP|Li to prevent Ti⁴⁺from being reduced by Li.Electrochemical tests showed that after Li symmetrical lithium battery was charged and discharged for 350 h at a current density of 0.05 m A cm^-2,the overpotential of the symmetrical battery with FeF₂ added was lower than that without FeF₂.In addition,the battery added with FeF₂ still showed stable cycle performance after 50 cycles at a rate of 0.2 C,and the capacity retention and coulombic efficiency were higher than those without FeF₂;the interfacial impedance after cycling also showed that FeF₂ can helps to build a stable LATP|Li interface.The battery with FeF₂ added also showed higher cycle stability at a rate of0.5 C.（3）Aiming at the fragile problem of LATP solid electrolyte,a composite solid electrolyte LATP@PEO with a three-dimensional LATP framework was constructed by electrospinning.The electrolyte has certain flexibility due to the use of PEO as a matrix material.Compared with pure PEO solid electrolyte,the Young’s modulus of LATP@PEO increased from 250 MPa to 1 GPa,and the ionic conductivity at 60℃increased from 7.35×10^-5 S cm^-1 to 2.24×10^-4 S cm^-1.The capacity retention rate of the LATP@PEO-based solid-state battery after 250 cycles at a rate of 0.5 C is 89.65%,and the pure PEO-based solid-state battery fails after 20 cycles.The capacity retention rate of the LATP@PEO solid-state battery is 80.58%after 200 cycles at a rate of 1 C while pure PEO-based solid-state battery fails after 10 cycles.