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

Application of nanostructured silicon (nSi) is significantly retarded by challenges in the production of affordable nSi. We herein report a high-yield (ca. 100 %) and low-energy (2 kWh Kg-nSi-1 ) 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, allowing an automatic separation from the melts. Thus water washing and accompanying oxidation of the nSi can be avoided. The final product has a nanoporous structure and comprises Si nanorods (ca. 30 nm in diameter) with an ultrathin oxide coating. It can be used for Li storage giving a combination of high initial coulombic efficiency, high specific capacity, and long cycling stability. This nanostructuring process consumes very few chemicals except for the mSi and produces almost zero waste.