The successful integration of Li metal anode with solid electrolytes seems to be a must for a high-energy-density solid-state battery. However, Li dendrites tend to form in solid electrolytes during Li plating. The formation of dendrites has been observed in solid electrolytes with various crystal structures from glass, glass-ceramic, poly-crystalline to single-crystalline materials, but the mechanism of such an unexpected dendrite growth remains elusive. In this presentation, I will introduce our understandings of lithium dendrite formation in solid electrolytes based on operando neutron depth profiling characterizations. The results highlight the important role of electronic conduction in solid electrolytes in the formation of isolated Li dendrites in solid electrolytes. I will then present our recent results in understanding the intrinsic value, voltage dependence, and charge carrier of electronic transport in typical lithium solid electrolytes. Lastly, I will introduce corresponding strategies to suppress dendrite formation in solid-state Li metal batteries. Reference s : [1] F. Han, A. S. Westover, J. Yue, X. Fan, F. Wang, M. Chi, D. N. Leonard, N. J. Dudney, H. Wang, C. Wang, Nature Energy, 4 (2019) 187.[2] F. Han, J. Yue, X. Zhu, C. Wang, Advanced Energy Materials, 8 (2018) 1703644.[3] F. Han, J. Yue, C. Chen, N. Zhao, X. Fan, Z. Ma, T. Gao, F. Wang, X. Guo, C. Wang, Joule, 2 (2018) 497.[4] X. Fan, X. Ji, F. Han, J. Yue, J. Chen, L. Chen, T. Deng, J. Jiang, C. Wang, Science Advances, 4 (2018) eaau9245.[5] R. Xu, F. Han, X. Fan, J. Tu, C. Wang, Nano Energy, 53 (2018) 958.[6] Y. Huang, B. Shao, F. Han, Current Opinions in Electrochemistry, 33 (2022) 100933.[7] Y. Huang, B. Shao, F. Han, Journal of Materials Chemistry A, 10 (2022) 12350.[8] F. Han, Y. Zhu, X. He, Y. Mo, C. Wang, Advanced Energy Materials, 6 (2016) 1501590.[9] F. Han, T. Gao, Y. Zhu, K. J. Gaskell, C. Wang, Advanced Materials, 27 (2015) 3473.