Electrochemical Properties of Garnet-Type Ta and Ga Co-Doped Li7La3Zr2O12 for Solid-State Li Batteries

Li-stuffed garnet-type oxide Li 7 La 3 Zr 2 O 12 (LLZ) has attracted much attention because of the high ionic conductivity at room temperature, excellent thermal performance, and good chemical stability against Li metal. 1,2 However, poor interfacial connection causes non-uniform Li plating and intergranular penetration of Li dendrite in polycrystalline LLZ when the cell is cycled particularly at high current densities, resulting in internal short-circuit failure. 3,4 The tolerance for Li dendrite growth into LLZ is influenced by many factors such as the interfacial resistance between LLZ and Li anode, cell stacking pressure and microstructure (density and grain size) of LLZ. In this study, we fabricated Ga and Ta co-doped LLZ (Li 6.55-3x Ga x La 3 Zr 1.55 Ta 0.45 O 12 , LGLZT) ceramic electrolyte and investigated the effects on the Ga amounts on the microstructure, ionic conductivity, and the tolerance for Li dendrite growth. LGLZT with Ga amounts x = 0.025, 0.05 and 0.10 were synthesized via a conventional solid-state reaction process. Sintering condition was set to 1150 °C for 2 hours in air. Relative densities for all sintered samples were ranged from 93-95 %. From XRD analysis, each sintered sample has a cubic garnet phase and diffraction peaks from other phases were not detected. Calculated lattice parameter was decreased with increasing Ga amounts x, due to the Ga 3+ incorporation in the crystal lattice. In SEM observation, microstructure of sintered LGLZT was strongly influenced by x, because the amounts of liquid Li-Ga-O phase formed during high temperature sintering is also changed by x. 5,6 When x increases, grain growth in sintered LGLZT is promoted and the segregation for Ga and O elements becomes more remarkable. Ionic conductivity of LGLZT at room temperature also enhanced with x, and maximum value of 0.84 mS/cm, which is much superior to the value for the sample without Ga (= 0.64 mS/cm). The effect of Ga amounts in LGLZT on the tolerance for Li dendrite growth will be discussed in the presentation. This work was supported by Grant-in-Aid for Scientific Research (JSPS KAKENHI) Grant Number 22H01468 from the Japan Society for the promotion of Science (JSPS). References R. Murugan et al., Angew. Chem., Int. Ed. 46, 7778−7781 (2007). A.J. Samson et al., Energy Environ. Sci. 12, 2957−2975 (2019). R. Inada et al., Batteries 4, 26 (2018). Y. Matsuki et al., J. Electrochem. Soc. 166, A5470−A5473 (2019) Y. Matsuda et al., Solid State Ionics 311, 69−74 (2017). Y. Yamazaki et al., Batteries 8, 158 (2022).