Unraveling the performance decay of micro-sized silicon anodes in sulfide-based solid-state batteries

Solid-state batteries (SSBs) containing Si anodes have recently emerged as a promising solution to overcome challenges associated with Li anodes. However, the development of Si anodes is hindered by the requirement of high external pressure and the unclear understanding of failure mechanisms. Herein, with experiments and simulations under varying Si loads and external pressures, we report that the long diffusion path generates a large Li+ concentration gradient and a pronounced hydrostatic stress gradient, thereby restricting the Li storage capacity of Si via the stress-induced chemical potential. Additionally, the resultant uneven distribution of high Von Mises stress leads to easy cracking of Si anodes during delithiation, thus disturbing the electron/ion transport path, altering reaction sites, and deteriorating the cycle performance of SSBs. External pressure was also shown to have minimal benefits on Li+ diffusion, mainly by reducing the Von Mises stress to reduce the cracking degree for ensuring electron/ion transport, so as to realize the balance of Li+ concentration gradient and electrochemical potential, and avoid Li plating and interfacial side reactions. Our findings propose the failure mechanism of Si anodes in SSBs, emphasizes the importance of minimizing the Li+ concentration gradient under low external pressure, and provide valuable insights for the development of Si-containing SSBs.