Anodic nanoporous SnO₂ grown on Cu foils as superior binder-free Na-ion battery anodes

We present a convenient, low-cost strategy to fabricate one-dimensional, vertically oriented nanoporous assembly of SnO₂ upon a Cu substrate as a potentially promising anode system for Na-ion batteries application. The major novelty of the fabrication stage resides in anodizing a Sn/Cu bilayer film that is created by a facile cold-rolling procedure amenable to large-scale production. The open, nanoporous morphology of SnO₂ facilitates the diffusion of electrolytes to access the SnO₂ surface. The high porosity of the SnO₂ phase also provides large void space to effectively accommodate the volume expansion/contraction during sodiation/desodiation. As a result, the 1-D nanoporous SnO₂ thus assembled on the Cu substrate can be directly used as an effective electrode system for Na-ion storage-without the need for additives, delivering a remarkable capacity of 326 mA h g^-1 over 200 cycles at a current rate of 0.2 C.