A self-driven alloying/dealloying approach to nanostructuring micro-silicon for high-performance lithium-ion battery anodes

The nanostructuring of low-cost micro-sized silicon (mSi) is paramount to achieve the practical viability of deploying high-capacity Si anodes for lithium-ion batteries (LIBs). Conventional methods for converting mSi to nanoporous Si (nSi) involve low product yield, toxic chemical reagents, high energy consumption, etc. Herein, we report a self-driven alloying/dealloying approach to converting mSi to nSi in molten salts, where mSi alloys with Mg powders to generate Mg 2 Si and, subsequently, the Mg 2 Si dealloys in a Mg 2 Si||Sn primary battery with the production of nSi at the negative electrode and the liquid Mg-Sn alloy at the positive electrode. Finally, the Mg-Sn decomposes to Mg gas and liquid Sn through a vacuum-distillation process. Taking the micro-sized Si kerf waste as an example, the pyrolytic carbon-coated (PCC) nSi delivers a capacity of 1080.2 mAh g −1 at 1 A g −1 after 1000 cycles with a capacity retention rate of 83.7%. Furthermore, a fabricated PCC-nSi-2||LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) full cell demonstrates a high energy density of 466 Wh kg −1 as well as good cycling stability for 200 cycles. The improved Li-storage performance is attributed to the synergetic effects of the nanoporous Si and carbon coating. Overall, the self-driven nanostructuring approach along with the vacuum-distillation process maintains a high utilization of mSi, eliminates the use of toxic reagents, and keeps a closed-loop material circle, and thus offers an efficient and green pathway to valorize various mSi for making enhanced lithium-storage anodes.