Scalable Engineering of Bulk Porous Si Anodes for High Initial Efficiency and High-Areal-Capacity Lithium-Ion Batteries.

Nano-Si has been long-hampered in its use for practical lithium battery anodes due to its intrinsic high surface area. To improve the Coulombic efficiency and areal mass loading, we extend the starting materials from nano-Si to photovoltaic waste Si powders (∼1.5 μm). Unique morphology design and interfacial engineering are designed to overcome the particle fracture of micrometer Si. First, we develop a Cu-assisted chemical wet-etching method to prepare micrometer-size bulk-porous Si (MBPS), which provides interconnected porous space to accommodate volume expansion. In addition, a monolithic, multicore, interacting MBPS/carbonized polyacrylonitrile (c-PAN) electrode with strong interfacial Si-N-C is designed to improve the interparticle electrical conductivity during volume expansion and shrinkage. Furthermore, intermediate Si nanocrystals are well-maintained during the lithiation of MBPS, which facilitates the reversibility of lithiation-delithiation process. As a result, the MBPS/c-PAN electrodes exhibit a reversible specific capacity of 2126 mAh g with a high initial Coulombic efficiency of 92%. Moreover, even after increasing the capacity loading to 3.4 mAh cm, the well-designed electrode shows a capacity retention of 94% in the first 50 cycles at a current density of 0.2 A g with deep lithiation and delithiation processes between 0.005 and 2.5 V.