Investigation Of Synthesis And Electrochemical Properties Of Li₇P₃S₁₁ All-solid-state Batteries

With the development of mobile and portable devices,lithium-ion batteries have received great attention in recent decades.However,there have always been safety issues arising from their combustible organic electrolytes,and these issues are becoming more serious with the increasing size of batteries for use in electric vehicle,renewable energy storage and other particular applications that require a high temperature?such as military applications?.Replacing the organic liquid electrolyte with a solid-state electrolyte would improve device safety tremendously because of the good mechanical and thermal stability.Therefore,all-solid-state lithium batteries?ASSLBs?with nonflammable inorganic solid electrolytes,an alternative to conventional inflammable organic liquid electrolytes,are next generation batteries with low risk of leakage and explosionIn this paper,Li₇P₃S₁₁ solid electrolyte was synthesized by liquid phase method,and assembled CLTO/Li₇P₃S₁₁/Li,CNCM111/Li₇P₃S₁₁/Li and CNCM111/LGPS-Li₇P₃S₁₁/Li all-solid-state lithium batteries.We came to the following conclusions by testing the eletrochemical properties of the batteries with charge-discharge,CV and EIS.?1?Li₇P₃S₁₁ solid electrolyte was successfully synthesized,its room temperature ionic conductivity was 0.61×10^-3 S/cm,and its activation energy was 0.31eV.Its electrochemical window is greater than 6V and has good stability to lithium.We used a liquid phase method to coat Li₄Ti₅O₁₂ with carbon,and used a sol-gel method to cover the surface of LiNi_1/3Co_1/3Mn_1/3O₂ with a protective layer of LiNbO₃.?2?The first-cycle charge capacity CLTO/Li₇P₃S₁₁/Li all-solid-state battery is146.7mAh/g,and the coulomb efficiency is 68.5%.In the second charge/discharge process the coulomb efficiency reached 91.9%and the coulomb efficiency reached more than 99%after 50 cycles.After 120 cycles,the battery capacity is 150.8 mAh/g,and the capacity retention rate is 70.4%which shows excellent cycling performance.The first discharge capacity and coulomb efficiency of the CNCM111/Li₇P₃S₁₁/Li all-solid-state battery are 125mAh/g and 56.81%.The coulomb efficiency is stable at around 97.5%after 10 cycles.The battery capacity is 93.1 mAh/g,and the capacity retention rate is 74.48%after 30 cycles and the cycle performance was poor.?3?In order to improve the cycle stability of CNCM111/Li₇P₃S₁₁/Li all-solid-state battery,a LGPS transition layer was added at the electrode/electrolyte interface and the CNCM111/LGPS-Li₇P₃S₁₁/Li all-solid-state battery was prepared.The first discharge capacity and coulomb efficiency of the CNCM111/LGPS-Li₇P₃S₁₁/Li all-solid-state battery are 127.4 mAh/g and 58.73%.The coulomb efficiency is stable at around 99.2%after 10 cycles.The battery capacity decayed to99.7mAh/g and the capacity retention rate was 78.3%after 100 cycles,which shows that the cycling stability of CNCM111 on Li₇P₃S₁₁ solid electrolyte can be improved by adding an LGPS transition layer.?4?The EIS test results show that the typical Nyquist diagrams of the three all-solid-state batteries are composed of 3 parts:The semicircle in high frequency area,the semicircle in middle frequency area,and the line in the low frequency area.The semicircle in high frequency area belongs to electrode/electrolyte interface impedance,the semicircle in middle frequency area belongs to the charge transfer process and the line in the low frequency area belongs to the solid state diffusion process.It is found by fitting the electrochemical impedance spectrum that the electrolyte resistance increases to varying degrees,which indicates that the electrolyte impedance is not stable and decomposition may occur during the charge and discharge process.The interface resistance between CLTO and the electrolyte is relatively stable,but the interface resistance between CNCM111 and the electrolyte has increased greatly,which indicates that the LiNbO₃ coating may rupture during the charge and discharge process.The LGPS layer effectively controls the charge transfer resistance,which is why the cycle stability of the CNCM111 all-solid-state battery is improved.There are 56 figures,6 tables,and 125 reference articles in this paper.