Self-Constructed Intimate Interface on a Silicon Anode Enabled by a Phase-Convertible Electrolyte for Lithium-Ion Batteries

Promising high-capacity anodes of Si-based materials suffer from large volume expansions, thereby limiting their practical applications, especially in combination with safe inorganic solid electrolytes. Here, to achieve a high level of safety by applying Si anodes, we introduced a quasi-solid-state succinonitrile-based electrolyte (QS-SCN) that enables the practical application of the anode with long-term cycling performance. By exploiting the unique phase-convertible property of QS-SCN, the Si electrode was successfully impregnated with the liquid-state electrolyte above its melting temperature, and a simple cooling process was then used to form a quasi-solid-state Li-Si cell. Additionally, through a precycling process, the formation of a stable and rigid solid-electrolyte interphase (SEI) was induced, and the intimate contacts between the QS-SCN and Si particles were preserved. The soft QS-SCN played an important role as a buffer in the large volume expansions while maintaining favorable interface contacts, and the formation of the SEI layers contributed to the reversible lithiation and delithiation in the Si particles. As a result, the quasi-solid-state Li-Si cell fabricated with QS-SCN exhibited significantly improved capacity retention compared with an all-solid-state cell.