Stable, Scalable Micron‐Sized Porous Silicon for High Energy Density Li‐Ion Batteries

Metallurgical‐grade silicon is a low‐cost, high‐capacity alternative material for Li‐ion battery anodes. Herein, a unique, low specific surface area (SSA) porous silicon with highly regular, parallel, internal pore structure is presented. The relatively low SSA results in a first cycle Coulombic efficiency of over 90% in a half‐cell configuration. Balancing (full) cells with high‐nickel content cathode material at a limited Si specific capacity around 1000 mAh gSi −1 limits stack expansion to under 4% in a multilayer pouch cell configuration (consisting of double‐sided coated anodes and cathode foils). This limited expansion is ascribed to the persistence of a crystalline Si backbone, directing most of the expansion inwards. This mechanism is confirmed by cross‐sectional scanning electron microscopy on a lithiated anode and Raman microscopy on a cycled electrode. After 100 cycles, just under 50% of the original amount of c‐Si is still present, as detected by X‐ray diffraction. For the optimum electrode formulation and particle size distribution (PSD), full cells using NMC622 cathodes last more than 200 cycles before falling below 80% state‐of‐health, and the porous Si powder significantly outperforms a nonporous powder with a similar PSD.