Qing Ai, B. Zhang, Xing Liu, Bongki Shin, Wenhua Guo, Guanhui Gao, Lihong Zhao, Xintong Weng, Qiyi Fang, Tianshu Zhai, Doug Steinbach, Yifan Zhu, Yifeng Liu, Fan Wang, Xiaoyin Tian, Hua Guo, Youtian Zhang, Xuan Zhao, Yimo Han, Ming Tang, Yan Yao, Ting Zhu, Huajian Gao, Jun Lou
The growth and penetration of lithium dendrites through electrolytes and separators remain key challenges to realizing high-energy density lithium-metal batteries. Using mechanically strong electrolytes and separators has been considered a promising strategy based on the commonly believed softness of lithium. However, dendrite formation persists in stiff solid electrolytes, suggesting distinct mechanical behaviors. We measured the mechanical properties of individual lithium dendrites using an air-free protocol. We found that lithium dendrites are unexpectedly strong and brittle, with fracture stress greater than ~150 megapascals, unlike the ductile bulk metal. Cryo-transmission electron microscopy and mechanical modeling showed that this behavior arises from solid electrolyte interface constraints and nanoscale strengthening. These findings provide alternative mechanisms for dendrite penetration and dead lithium formation as well as guidance for design strategies for lithium-metal batteries.