Synthesis And Application Of Solid State Electrolyte Li₇La₃Zr₂O₁₂ In Thermal Battery

Molten salt electrolytes melt to ion conductors at high temperatures.However,due to the melting and flowing of the electrolyte,“flooding”problem may occur,which may cause short circuit of the battery.Li₇La₃Zr₂O₁₂ has characteristics of small grain boundary resistance,good thermal stability and good chemical stability,making it an ideal candidate for thermal battery electrolyte.However,the preparation process of Li₇La₃Zr₂O₁₂ material has disadvantages such as high sintering temperature and complex reaction,which needs further optimization and improvement.In practice,the conductivity of Li₇La₃Zr₂O₁₂ material is lower than that of molten salt electrolytes,resulting in poor discharge performance.Herein,a suitable process for preparing Li₇La₃Zr₂O₁₂ material is obtained.Li₇La₃Zr₂O₁₂-LiCl-LiBr-LiF composites and Li₇La₃Zr₂O₁₂ electrolyte ceramics are prepared to improve the electrical conductivity and battery life of the Li ₇La₃Zr₂O₁₂materials.Firstly,Li₇La₃Zr₂O₁₂ materials were prepared by high temperature solid-state method and sol-gel method respectively.The phase structure and microstructure of the obtained materials were characterized to determine the best preparation process of Li₇La₃Zr₂O₁₂ electrolyte materials.The results of electrochemical properties show that Li₇La₃Zr₂O₁₂ can discharge in the range of 500°C to 575°C,40mA·cm^-2 to 100mA·cm^-2.At 550°C and 80mA·cm^-2,the specific capacities of the single-cells of Li₇La₃Zr₂O₁₂ prepared by high temperature solid-state reaction and sol-gel were 171.4 mAh·g^-1 and 174.3 mAh·g^-1,respectively.The rate of64.92%and 66.02%was related to LiCl-LiBr-LiF commonly used in thermal batteries,and the utilization rate of active material is increased by at least about20%.Single cell assembled by Li₇La₃Zr₂O₁₂ did not overflow,which greatly improves the safety of the battery.Next,LiCl-LiBr-LiF and polyvinylidene fluoride were used as additives to prepare composite electrolyte material and Li₇La₃Zr₂O₁₂ ceramics.The characterization results of the phase structure and electrochemical performance show that the constant current discharge test at 550°C,80 mA·cm^-2.Li₇La₃Zr₂O₁₂prepared by high temperature solid-state method and sol-gel method.The specific capacity of the composite electrolyte single cell was 224.6 mAh·g^-1 and 200.8mAh·g^-1,and the active material utilization rate was 85.08%and 76.06%;the Li₇La₃Zr₂O₁₂ ceramic sheet assembly prepared by the two synthesis methods The discharge specific capacities of Li₇La₃Zr₂O₁₂ ceramic sheet assembled single cells were 141.2 mAh·g^-1 and 151.9 mAh·g^-1,and the active material utilization rate was 53.48%and 57.23%,respectively.Finally,the economic cost of the LLZO series electrolyte material was analyzed.The cost of the LLZO series electrolyte material was lower than the cost of the LiF-LiCl-LiBr electrolyte material.The LLZO solid electrolyte material was expected to be used as a lithium thermal battery.Electrolytes are used and have found practical applications in thermal battery technology.