Rechargeable Silicon Redox Batteries

Abstract Despite its high abundance and ease of production, the possibility of using silicon as an active multivalent rechargeable anode has never been explored, until now. As a proof of concept, a novel rechargeable silicon cell, its design and architecture are reported, enabling Si to be reversibly discharged at 1.1 V and charged at 1.5 V. It is proven that during the discharge process silicon is dissolved and upon charging, elemental silicon is deposited. Several discharge–charge cycles are achieved, utilizing heavy doped n‐type Si wafer anodes and hybrid‐based ionic liquid electrolytes, along with dissolved halides, functioning as conversion cathodes. Cell characterizations correlate the discharge and charge processes with the presence of dissolved fluoride and Si species in the electrolyte. The presence of appreciable fluoride species is crucial in both establishing surface activation and battery operation, and their depletion is directly linked to cell performance degradation. Quantum‐chemical calculations based on density functional theory in the framework of a continuum model for solvation in ionic liquids are performed to shed light on Si ion deposition mechanism.