Rechargeable all-solid-state Li batteries (ASSLBs) are considered as the next generation of electrochemical energy storage systems. Development of solid-state electrolytes (SSEs), which are key materials for ASSLBs, is therefore one of the most important subjects in modern energy storage chemistry. Thus, various types of electrolytes such as polymer-, oxide-, and sulfide-based SSEs have been developed to date and the development of new superionic conductors is still ongoing. Halide SSEs (Li-M-X, M is a metal element, and X is a halogen) are emerging as promising candidates with a number of attractive properties (oxidative stability and interfacial compatibility, etc.). [1] For example, halide SSEs show advantages including high ionic conductivity, wide electrochemical stability windows (0.36-6.71 V vs. Li/Li+), and improved chemical stability toward cathode materials compared to other SSEs. [2-4] Moreover, some of the halide SSEs (such as Li3InCl6 developed by our group) can be directly synthesized in a water solvent with the capability of large-scale production, thus removing the need for special apparatus or handling in an inert atmosphere.In this talk, (i) I will demonstrate the new and salable water-mediated synthesis method of the highly conductive Li3InCl6 halide SSE [5]. (ii) I will report the anion sublattice evolution effect on Li+ conductivity for halide SSEs [6]. I will also show the humidity stability and degradation chemistry of metal halide SSEs investigated by advanced in-situ and operando synchrotron techniques [6-7]. In the end, direct synthesis of halide SSEs on cathode materials by the water-mediated route that has been used to eliminate the interfacial challenges of ASSLBs or act as an interfacial modifier for high-performance all-solid-state Li-O2 batteries will be discussed [8-9].References X. Li, J. Liang, X. Yang, K. R. Adair, C. Wang, F. Zhao, X. Sun, Progress and Perspectives of Halide-based Lithium Conductors for All-Solid-State Lithium Batteries. Energy Environ. Sci., 2020, 13, 1429-1461. J. Liang, X. Li, S. Wang, K. R. Adair, W. Li, Y. Zhao, C. Wang, Y. Hu, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, Y. Mo, X. Sun. Site-Occupation-Tuned Superionic LixScCl3+x Halide Solid Electrolytes for All-Solid-State Batteries. J. Am. Chem. Soc., 2020, 142, 7012-7022. X. Li, J. Liang, J. Luo, M. Banis, C. Wang, W. Li, S. Deng, C. Yu, F. Zhao, Y. Hu, T. Sham, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, K. R. Adair, X. Sun, Air-stable Li3InCl6 electrolyte with high voltage compatibility for all-solid-state batteries, Energy Environ. Sci., 2019, 12, 2665-2671. C. Yu, Y. Li, K. R. Adair, W. Li, K. Goubitz, Y. Zhao, M. J. Willans, M. A. Thijs, C. Wang, F. Zhao, Q. Sun, S. Deng, J. Liang, X. Li, R. Li, T. Sham, H. Huang, S. Lu, S. Zhao, L. Zhang, L. Eijck, Y. Huang, X. Sun, Tuning ionic conductivity and electrode compatibility of Li3YBr6 for high-performance all solid-state Li batteries, Nano Energy, 2020, 77, 105097. X. Li, J. Liang, N. Chen, J. Luo, K. R. Adair, C. Wang, M. Banis, T. Sham, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, X. Sun, Water-Mediated Synthesis of Superionic Halide Solid Electrolyte, Angew. Chem. Int. Ed., 2019, 58, 16427-16432. X. Li, J. Liang, K. R. Adair, J. Li, W. Li, F. Zhao, Y. Hu, T. Sham, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, N. Chen, X. Sun, “Origin of Superionic Li3Y1-xInxCl6 Halide Solid-Electrolytes with High Humidity Tolerance” Nano Lett., 2020, 20, 4384-4392. W. Li, J. Liang, M. Li, K. Adair, X. Li, Y. Hu, Q. Xiao, R. Feng, R. Li, L. Zhang, S. Lu, H. Huang, S. Zhao, T. Sham, X. Sun, Unraveling the Origin of Air Stability of Halide Solid-State Electrolytes by In situ and Operando Synchrotron X-ray analytical techniques, Chem. Mater., 2020, 32, 7019–7027. C. Wang, J. Liang, M. Jiang, X. Li, S. Mukherjee, K. Adair, M. Zheng, Y. Zhao, F. Zhao, S. Zhang, R. Li, H. Huang, S. Zhao, L. Zhang, S. Lu, C. Singh, X. Sun, Interface-Assisted In-situ Growth of Halide Electrolytes Eliminating Interfacial Challenges of All-Inorganic Solid-State Batteries. Nano Energy, 2020, 76, 105015. C. Zhao, J. Liang, X. Li, N. Holmes, C. Wang, J. Wang, F. Zhao, S. Li, Q. Sun, X. Yang, J. Liang, X. Lin, W. Li, R. Li, S. Zhao, H. Huang, L. Zhang, S. Lu, X. Sun, Halide-based solid-state electrolyte as an interfacial modifier for high performance solid-state Li–O2 batteries. Nano Energy, 2020, 75, 105036.