Improving the Electrochemical Performance of Garnet-Type Electrolytes through Ion Doping and Surface Treatment

Garnet-based solid-state batteries are promising as the next generation of energy storage systems due to their high energy density and safety. However, the cubic phase of solid-state electrolyte Li7La3Zr2O12 (LLZO) is unstable at room temperature, leading to reduced Li+ conductivity. Additionally, the poor wettability of the Li/LLZO interface causes Li dendrite growth, hindering their commercial application. Therefore, it is crucial to stabilize the LLZO structure and improve the Li/LLZO interface to enhance the overall electrochemical performance of LLZO. This study stabilized the cubic phase structure of the LLZO electrolyte by introducing Ta5+ into Zr sites, achieving an optimal ion conductivity of 4.83 × 10–4 S cm–1. Furthermore, the impact of surface conditions on LLZO before coating was carried out. It was found that the Li/Ag@LLZTO interface resistance was 83 Ω cm2, and the Li/Ag@LLZTO/Li cell critical current density (CCD) was 0.42 mA cm–2. In contrast, after polishing to remove Li2CO3, the Li/Ag@Polished-LLZTO interface resistance decreased to 27 Ω cm2, and the Li/Ag@Polished-LLZTO/Li cell CCD increased to 1.02 mA cm–2, and continuous cycling for 1000 h at a current density of 0.1 mA cm–2. In addition, the Li/Ag@Polished-LLZTO/LFP full cell exhibited a superior electrochemical performance, which demonstrated that surface treatment of LLZTO before introducing the coating layer could improve its electrochemical performance. This study provides comprehensive insights into enhancing the electrochemical performance of solid-state electrolytes, making a significant contribution to the development of solid-state Li batteries.