Recovery of porous silicon from waste crystalline silicon solar panels for high-performance lithium-ion battery anodes

•1) Waste Si wafer is a promising anode material for LIBs.•2) Alloying/dealloying approach takes advantage of the volume expansion.•3) Molten salt avoids the formation of SEI during the alloying process.•4) The lithium salt and Sn in alloy/dealloying process can be reused.•5) The obtained Si delivers 2427.7 mAh g−1 at 1 A g−1 after 200 cycles. A low-cost and easy-available silicon (Si) feedstock is of great significance for developing high-performance lithium-ion battery (LIB) anode materials. Herein, we employ waste crystalline Si solar panels as silicon raw materials, and transform micro-sized Si (m-Si) into porous Si (p-Si) by an alloying/dealloying approach in molten salt where Li+ was first reduced and simultaneously alloyed with m-Si to generate Li-Si alloy at the cathode. Subsequently, the as-prepared Li-Si alloy served as the anode in the same molten salt to release Li+ into the molten salt, resulting in the production of p-Si by taking advantage of the volume expansion/contraction effect. In the whole process, Li+ was shuttled between the electrodes in molten LiCl-KCl, without consuming Li salt. The obtained p-Si was applied as an anode in a half-type LIBs that delivered a capacity of 2427.7 mAh g−1 at 1 A g−1 after 200 cycles with a capacity retention rate of 91.5% (1383.3 mAh g−1 after 500 cycles). Overall, this work offers a straightforward way to convent waste Si panels to high-performance Si anodes for LIBs, giving retired Si a second life and alleviating greenhouse gas emissions caused by Si production.