石榴石固态电解质的冷烧结工艺制备及性能

以LiNO3、Al(NO3)3·9H2O、La(NO3)3·6H2O、ZrO(NO3)2·5H2O为原料，采用溶胶-凝胶法制备Li5.95Al0.35La3Zr2O12粉体，随后加入聚乙烯醇（PVA）水溶液作为液相介质，通过冷烧结工艺制备Li5.95Al0.35La3Zr2O12石榴石固态电解质。冷烧结工艺后采用后续热处理改善离子传导性能。采用质量体积法和电化学阻抗谱对Li5.95Al0.35La3Zr2O12石榴石固态电解质的体积密度和离子电导率进行了测试，采用XRD与SEM进行晶体结构与形貌表征。结果表明，冷烧结时间和压力对样品的晶体结构几乎没有影响。冷烧结时间过长会导致样品开裂，在15~30 min时，冷烧结时间对样品的致密性和电导率影响不大，在烧结时间较短的样品中发现了杂相。提高冷烧结压力可明显提高样品的致密性和电导率，在200℃、510 MPa、30 min的冷烧结条件下可以获得具有较高离子电导率（2.66×10-6 S/cm）的Li5.95Al0.35La3Zr2O12石榴石固态电解质，此时材料的晶界电阻较小。但继续增加冷烧结压力，由于热处理过程中第二相的分解和晶粒生长受到抑制，样品的致密性和电导率反而下降。

Preparation and properties of garnet solid-state electrolyte via cold sintering process

Li5.95Al0.35La3Zr2O12 powder was prepared by sol-gel method with LiNO3, Al(NO3)3·9H2O, La(NO3)3·6H2O, and ZrO(NO3)2·5H2O as raw materials, then polyvinyl alcohol (PVA) aqueous solution was added as liquid medium to prepare Li5.95Al0.35La3Zr2O12 garnet solid electrolyte via cold sintering process. Finally, subsequent heat treatment was employed to improve ionic conduction properties. The density and ionic conductivity of Li5.95Al0.35La3Zr2O12 garnet solid-state electrolyte were evaluated by mass volume method and electrochemical impedance spectroscopy (EIS), the crystal structure and morphology were characterized by XRD and SEM respectively. The results showed that cold sintering holding time and pressure had slight effect on crystal structure of Li5.95Al0.35La3Zr2O12 garnet solid-state electrolyte. The crack was observed for too long cold sintering holding time. The density and ionic conductivity changed slightly for the sample sintered within 15 to 30 min, and impurity phase was detected for short sintering time. It was effective to improve density and ionic conductivity by increasing cold sintering pressure. Li5.95Al0.35La3Zr2O12 garnet solid electrolyte with higher ionic conductivity of 2.66×10-6 S/cm could be obtained at 510 MPa, 200oC and 30 min, which exhibited lower grain boundary resistance. However, the density and ionic conductivity decreased when cold sintering pressure increased further, due to the decomposition of second phase and limitation of grain growth during heat treatment.