Preparation And Conductivity Of Doped Garnet–type Li₇La₃Zr₂O₁₂ Ceramic Electrolyte

Lithium secondary batteries are mainly used in electronic products for notebook computers,mobile phones,tablet computers and digital cameras.However,with the continuous development of science and technology,the application of lithium secondary batteries is also developing toward largescale,miniaturized and flexible,such as new energy electric vehicles,miniature sensors and sports bracelets.Therefore,there is a higher requirement for safety in lithium ion batteries.Li₇La₃Zr₂O₁₂?LLZO?solid electrolyte has high room temperature ionic conductivity,chemical stability and thermal stability,which greatly improves the application prospect of garnettype electrolyte materials in allsolid lithium batteries.However,its conductivity is relatively low compared to conventional liquid electrolytes.How to improve its conductivity is the key to the application of LLZO solid electrolyte materials.In this paper,Tadoped LLZO solid electrolyte?LLZTO?was selected as the research object,and a series of optimization work was carried out.All ceramic electrolyte samples were prepared by traditional solid phase method.The effects of preparation methods,sintering process and Ta content on the phase,density,morphology and electrical properties of LLZTO ceramic electrolytes were investigated.The effects of codoping methods on their phase,density,morphology and electrical properties were also investigated.The effects of milling time on the phase and microstructure of the powder were investigated.The results show that the ball milling can make the raw material powder more uniform after 12h,and the calcined LLZTO powder can obtain a single cubic phase structure.The powder size is no longer reduced by 5?m for a prolonged period of time.The best sintering process was explored,with an optimum sintering temperature of 1230^oC and an optimum holding time of 1h.The effect of Ta content on the LLZTO ceramic electrolyte was investigated.The doping of Ta element can stabilize the cubic phase,refine the grain and increase the density of the ceramic.The doping of an appropriate amount of Ta element can increase the Li vacancy,adjust the Li ion occupancy,and improve the Li ion transport ability in the grain.However,the doping of excess Ta element leads to a decrease in the Li content in the ceramic electrolyte,a decrease in the concentration of the transportable Li ion,and a decrease in the electrical conductivity.Thus the doping Ta content has an optimum content.The sample with a Ta doping content of x=0.4 has the highest conductivity?30^oC?of 6.01×10^–4S·cm^–1 and the activation energy of 0.27eV.The effects of codoping methods on the quality and electrical properties of LLZTO ceramic electrolytes were investigated.It is found that for the Li_6.6+y.6+y La₃–_y M_y Zr_1.6Ta_0.4O₁₂?M=Ba,Ca?system,the doping of Ba and Ca causes abnormal growth of grains and a large number of pores,causing density and conductivity to decline.For the Li_6.4+y.4+y La₃–_y M_y Zr_1.4Ta_0.6O₁₂?M=Ba,Ca?system,the doping of Ba and Ca causes a slight decrease in the density,but does not affect the morphology and size of the grains in the ceramic fracture.The doping of Ba and Ca can increase the concentration of Li ions in the sample,improve the Li ion occupancy,and facilitate the migration of Li ions to improve the conductivity.The doping of Ba and Ca increases the electrical conductivity of the Li_6.4La₃Zr_1.4Ta_0.6O₁₂ceramic electrolyte.When the doping Ba content is y=0.06,the sample has the highest conductivity?30^oC?of 6.04×10^–4S·cm^–1,and the activation energy is 0.27 eV.When the doping Ca content is y=0.02,the sample has the highest conductivity?30^oC?of 5.69×10^–4S·cm^-1,and the activation energy is 0.27 eV.