High-Pressure Evaporation-Based Nanoporous Black Sn for Enhanced Performance of Lithium-Ion Battery Anodes

Increasing the surface area to improve chemical activity is an unending task from conventional catalysis to recently emerging electrochemical energy conversion and storage. Here, a simple, vacuum-deposition-based method to form nanoporous structures of metals is reported. By utilizing thermal evaporation at a high pressure, fractal-like nanoporous structures of Sn with porosity exceeding 98% are synthesized. The obtained nanostructure consists of nanoparticle aggregates, and the morphology can be controlled by adjusting the working pressure. The formation of the nanoporous structure is explained by homogeneous nucleation and diffusion-limited aggregation, where nanoparticles produced by the repeated collisions of evaporated atoms adhere to the substrate without diffusion, forming porous aggregates. Due to the easy oxidation of Sn, the constituent nanoparticles are covered with amorphous SnO_x and crystalline SnO phases. When the nanoporous Sn/SnO_x aggregates are applied to a lithium-ion battery anode through direct deposition on a Cu foil current collector without binders or conducting additives, the nanoporous Sn/SnO_x anode shows greatly enhanced cyclability and exceptional rate performance compared to those of a dense Sn thin film anode. The approach investigated in this work is expected to provide a new platform to other fields that require highly porous structures.