Preparation And Performance Research Of Li₇La₃Zr₂O₁₂ Eiectrolyte For Lithium Thermal Battery

Lithium thermal batteries generally use molten salt as an electrolyte,which melts to conduct at the operating temperature and flows between the positive and negative electrodes,which is prone to"flooding".The solid electrolyte has high safety,good thermal stability and a wide electrochemical window,and it is expected to be used as an electrolyte for lithium thermal batteries,so the problem of molten salt electrolyte overflow can be solved at high temperatures.At present,solid electrolytes include polymer type,sulfide type,perovskite type,NASICON type and garnet type.Among them,garnet-type Li₇La₃Zr₂O₁₂（LLZO）has the advantages of relatively small grain boundary resistance,good thermal stability,high electrical conductivity,and stability to lithium metal,and has good development prospects.However,compared with the molten salt electrolyte commonly used in lithium thermal batteries,the conductivity of LLZO is expected to be further improved.Therefore,the subject of this paper uses high-temperature solid-phase method to prepare LLZO solid electrolyte,and on this basis,doping and modification of LLZO material are used to improve the ionic conductivity;The specific capacity and other electrical properties were used to study the effect of doping etc.on the LLZO in lithium thermal batteries.In this experiment,LLZO was prepared by high-temperature solid-phase method,the phase structure and micro-morphology of the obtained material were characterized,and its element distribution was investigated by EDX.The results show that when the Li OH·H₂O is 15wt.%excess,the diffraction peak intensity of the prepared LLZO is high,so the Li OH·H₂O of 15wt.%excess was selected for subsequent research;It was found that when the addition amount was 2wt.%,the crystallinity and morphology of LLZO are better after adding the sintering aid H₃BO₃,and the sintering temperature can be reduced to 750℃after adding H₃BO₃;However,the doping of Y³⁺makes the crystallinity of LLZO lower than that of undoped LLZO,and the garnet shape is not obvious;After doping with Ti⁴⁺,it was found that the garnet shape of LLZO is obvious and the particles are small;After doping Ce⁴⁺,the composition of LLZO did not change significantly,but with the increase of the doping amount,the garnet shape gradually became less obvious;After doping with Nb⁵⁺,it was found that the crystallinity of LLZO also increased with the increase of doping amount and garnet garnet shape particles are more rounded;At the same time,the presence of Y,Ti,Ce,Nb elements can be seen in EDX-mapping.The prepared LLZO-H₃BO₃composite materials and LLZO doped with Ti⁴⁺,Ce⁴⁺,Nb⁵⁺were used as electrolytes to assemble lithium thermal batteries,and the discharge performance of the lithium thermal battery was tested.The results show that when the electrolyte is Li₇La₃Zr_1.7Ti_0.3O₁₂,the battery specific capacity and utilization rate are the largest,236 m Ah/g and 89.54%,respectively at 550℃,80 m A/cm²,which are much higher than the undoped LLZO.In addition,ceramic chips instead of powder pressing was used as new assembly method in the lithium thermal battery.As a result,it was found that when the amount of LLZO powder was 0.8 g and the tableting pressure was 20 MPa,the ceramic sheet has the best completeness in appearance.The conductivity of LLZO and Li₇La₃Zr_1.7Ti_0.3O₁₂are 2.26×10^-6S/cm and3.97×10^-6S/cm,respectively.The economic cost of solid electrolyte Li₇La₃Zr_1.7Ti_0.3O₁₂with the best discharge performance was calculated.At the same time,the production and use costs of a single thermal battery were calculated.As a result,it was found that the cost of this material is comparable to that of LLZO,and it is much lower than that of all-lithium electrolyte,so the solid electrolyte Li₇La₃Zr_1.7Ti_0.3O₁₂is expected to be applied in lithium thermal batteries.