Large Scale Self-Catalyzed Sponge-Like Silicon Nanonetwork-based 3D-Anodes for High-Capacity Lithium Ion Batteries.

Here, we report on the large scale one-step preparation, characterization and application of three-dimensional sponge-like silicon alloy composite anodes, based on the catalyst-free growth of porous silicon nano-networks directly onto highly conductive and flexible open-structure stainless steel current collectors. By the use of a key hydrofluoric acid-based chemical pre-treatment process, the originally non-catalytic stainless steel matrix becomes nano-porous and highly self-catalytic, thus greatly promoting the formation of a silicon sponge-like network at unexpectedly low growth temperatures, 380-460oC. Modulation of this unique chemical pre-treatment allows control over the morphology and loading properties of the resulting silicon network. The sponge-like silicon network growth is capable of completely filling the openings of the three-dimensional stainless steel substrates, thus allowing full control over the active material loading, while conserving high mechanical and chemical stabilities. Furthermore, extremely high silicon loadings are reached due to the super-catalytic nano-porous nature of the chemically-treated stainless steel substrates (0.5-20 mg/cm^2). This approach leads to the realization of highly electrically-conductive Si-stainless steel composite anodes, due to the formation of silicon network-to-stainless steel contact sections composed of highly conductive metal silicide alloys, thus improving the electrical interface and mechanical stability between the silicon active network and the highly conductive metal current collector. More importantly, our one-step cost-effective growth approach allows the large scale preparation of highly homogeneous ultrathin binder-free anodes, up to 2 meters long, using a home-built CVD set up. Finally, we made use of these novel anodes for the assembly of Li-ion batteries exhibiting stable cycle life (cycled for over 500 cycles with <50% capacity loss at 0.1mA), high gravimetric capacity (>3500 mAh/gSi at 0.1mAcm-2), low irreversible capacity (<10%) and high coulombic efficiency (>99.5%). Notably, these Si sponge-like composite anodes of novel architecture meet the requirements of lithium batteries for future portable and electric-vehicle applications.