Study On Preparation, Structure And Properties Of Phosphate Materials For Solid Electrolytes

Due to its special comprehensive properties and high safety and reliability,solid electrolytes can be used as candidate materials to replace the organic electrolytes of traditional lithium batteries.Therefore,it is an important development direction to research and develop solid electrolyte with high ionic conductivity.This paper takes NASICON（Na superionic conductor）type phosphate ceramic and glass ceramic solid electrolyte as the research object,explores the method of improving the conductivity of solid electrolyte,and provides theoretical and practical basis for the research and development of high-performance solid electrolyte materials.The main research contents are as follows:Trivalent M³⁺cations(Al³⁺,Cr³⁺)doped LiTi₂（PO₄）₃（LTP）-based ceramic electrolytes were prepared by solid-phase sintering.The effects of doping ions and heat treatment process on the phase composition,microstructure and electrical properties were mainly studied.The research shows that the appropriate preparation process and the selection of doping ions have a significant impact on the properties of the material.The ionic conductivity of the material modified by Al³⁺and Cr³⁺ions is increased by two orders of magnitude,and the relative density is increased to 92.1%.The Al³⁺ion doping effect is the best,the maximum conductivity of the prepared ceramics is 4.56×10^-4S cm^-1,which is 69 times higher than that of pure LTP ceramics,and the minimum activation energy is 0.293 e V.50Li₂O-50P₂O₅（LP）/Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）glass-ceramic material was prepared by solid-phase sintering method.The effect of adding LP glass on the structure and electrical properties of Li_1.3Al0.3Ti_1.7（PO₄）₃ceramics was studied.The phase and structure changes of glass ceramics were analyzed by DSC,SEM and Raman spectroscopy,and the high and low temperature grains,grain boundary conductivity and activation energy were analyzed by impedance spectroscopy.The results show that the low melting point glass promotes the sintering of ceramic materials in the form of liquid phase,the densification temperature is reduced to850℃,the electrical conductivity is increased to 8.20×10^-4S cm^-1,and the activation energy is reduced to 0.263 e V.Li₂O-Al₂O₃-（SiO₂）-TiO₂-P₂O₅system glass-ceramics were prepared by high temperature melting-overall controlled crystallization method.The effects of adding different SiO₂on the structure and properties were systematically studied.The crystallization kinetics of the glass was studied by DSC,and the results showed that the addition of SiO₂to the base glass increasedΔT（T_p-T_g）,which improved the glass forming ability.The crystallization activation energy of the glass is 407 KJ/mol,which means that the glass is easier to crystallize,and the crystallization index indicates that the glass is one-dimensional overall crystallization.XRD measurement shows that the main crystal phase of glass ceramics is LiTi₂（PO₄）₃,and there are a small amount of impurity phases（Al PO₄,TiO₂）.The ionic conductivity of glass is very poor at the level of 10^-7S cm-1,and the ionic conductivity of the crystallized glass ceramics reaches the level of 10^-4S cm^-1.The glass-ceramic with SiO₂=2 was added,and the maximum conductivity was 6.01×10^-4S cm^-1and the lowest activation energy was 0.298 e V,which was 1.4 times that of the glass-ceramic without SiO₂.The prepared glass ceramics are expected to be used in the field of solid electrolytes.