Theoretical Calculation And Preparation Performance Research Of Oxide Solid Electrolyte For Lithium Battery

As the core component of all-solid-state battery,the performance of solid-state electrolyte directly determines the electrochemical performance of all-solid-state battery.Among many oxide solid electrolytes,Li₇La₃Zr₂O₁₂（LLZO）materials have a lot of room for development in the improvement of ionic conductivity and stability and the control of synthesis process,which is of great research significance.This topic is based on the four-square phase LLZO as the research object,and the density function（DFT）is used to electronically structural,lithium ion migration calculations for different doping models,theoretically screening,and then explorating the different preparations of LLZO materials by experiments.Process,analyze the effects of different temperature and time on material properties,determine the best preparation method and process parameters,study lithium ion migration mechanism,and assemble full solid batteries,assemble the full solid state battery,and study electrochemical properties with lithium ion migration（NCM）.The calculation shows that element doping can improve the structural stability of LLZO,and the lowest total energy of Zn doping at Li site.The results of electronic structure analysis show that the electrical conductivity of LLZO ion is low,and the element doping leads to the decrease of band gap and the increase of electrical conductivity,in which the lowest band gap is 2.74e V and the highest conductivity is found in Ta doping.This conclusion is also proved by bond population and bond length analysis.The migration mechanism of lithium vacancies in different model phases is studied by calculation.The results show that the lowest migration barrier of Ta doped system is 0.3864e V.The formation of lithium vacancy is beneficial to improve the ionic conductivity and improve the properties of the materials.Based on the calculation,the effects of temperature and time on the properties of materials were investigated by ball milling solid state method and wet solid state method respectively.The results show that the best technological condition is sintering at 800℃for 8h.The highest ionic conductivity of the sample prepared by ball milling is 1.23×10^-6S/cm,and the lithium ion transfer number is 0.16.In order to better compare the two preparation methods,Wet-NCM/LLZO/Li and Ball-NCM/LLZO/Li batteries were assembled to test the electrochemical performance.The results show that Ball-NCM/LLZO/Li battery first charge and discharge specific capacity at 0.1C rate is 134.10m Ah/g and 116.68m Ah/g,the coulombic efficiency is87.00%,and the electrochemical performance is relatively good.The cycle test shows that the discharge specific capacity is 91.88m Ah/g,and the capacity retention is 78.74%after 50 cycles at 0.1C rate.Under these conditions,different doping samples were prepared.The results show that element doping can improve the ionic conductivity of the materials in different degrees.The ionic conductivity of Ta-LLZO samples is up to4.10×10^-5S/cm,and the maximum lithium ion transfer number is 0.36.The calculated results are verified by experiments.According to the electrochemical performance test results of the NCM/LLZTO/Li battery,the first charge-discharge specific capacity of the battery reaches 179.87m Ah/g and 163.84m Ah/g at a rate of 0.1C,and the coulombic efficiency is 91.13%,reaching the theoretical ratio of the traditional NCM battery.Capacity,after 50 cycles at 0.2C rate,the specific discharge capacity can still be maintained at 114.39m Ah/g,and the capacity retention rate is 81.62%.Compared with the Ball-NCM/LLZO/Li battery,the electrochemical performance is obviously improved,but the specific capacity attenuation is larger at high rate due to the problem of solid-solid interface.