Hierarchically Porous SnO2/Cu Composites via Freeze Casting and Selective Cu Reduction

Abstract

Lamellar SnO₂/Cu foams are created by directional freeze casting of SnO₂/CuO slurries followed by liquid phase sintering and subsequent hydrogen reduction to achieve a two-phase, interpenetrating SnO₂-30 vol% Cu lamellar structure. The resulting SnO₂/Cu foams exhibit both lamellar channels (millimeters in length) from the freeze-casting step and submicron porosity within the Cu phase from the reduction step. This hierarchical microstructure provides increased electronic conductivity relative to unmodified SnO₂. When applied as a negative electrode material for lithium-ion batteries, the interaction between the mesoporous Cu phase and embedded SnO₂ enables the conversion reaction of the SnO₂ and Li to become reversible, improving the capacity of the electrode. However, the lamellar structure is ultimately unable to accommodate the expansion of the Sn during lithiation, resulting in a breakdown of the architecture during cycling.