Efficient Nanostructuring of Silicon by Electrochemical Alloying/Dealloying in Molten Salts for Improved Lithium Storage

Abstract

Application of nanostructured silicon (nSi) is significantly retarded by challenges in production of affordable nSi with intriguing functionalities. We herein report a high‐yield (~ 100%) and low‐energy (2 kWh/Kg‐nSi) nanostructuring of industrial microsized silicon (mSi) through a closed‐loop electrochemical Mg alloying/dealloying in molten MgCl2‐NaCl‐KCl at 773 K. The resulting nSi unexpectedly shows a salt‐unwetted character, rendering an automatic separation from the melts so serious water washing and accompanying oxidation of the nSi can be avoided. The final product has a nanoporous structure and comprises Si nanorodes (~30 nm in diameter) with ultrathin oxide coating, which endow the nSi for lithium storage with a combination of high initial coulombic efficiency, high specific capacity, and long cycling stability. This nanostructuring process consumes very little chemicals except for the mSi and discharges almost zero waste. Our findings promise large‐scale preparation of highly valuable nSi with price comparable to industrial silicon.