Binder-free 3D SnO₂-based nanocomposite anode with high areal capacity for advanced sodium-ion batteries

Nanostructured SnO₂-based electrode materials and their composites have shown extraordinary promise for sodium-ion batteries (SIBs), but these are usually limited to laboratory cells with a low areal capacity because of the rather low mass loading. We report three-dimensional (3D) ultrathin SnO₂ nanosheet/holey graphene composite frameworks (SnO₂ NS/HGFs) with a high mass loading of 9 mg cm⁻² that can deliver a high areal capacity of up to 2.5 mA h cm⁻² under a current density of 0.9 mA cm⁻² and a stable areal capacity of 1.5 mA h cm⁻² under a high current density of 9 mA cm⁻². The superior performance of the 3D SnO₂-based nanocomposite anode was realized by implanting ultrathin SnO₂ NS/graphene composites into 3D HGF, and the sluggish Na⁺ transport, poor conductivity and volume expansion problems of SnO₂ were well addressed by encapsulating ultrathin SnO₂ nanosheets into densely packed graphene sheets, where the highly interconnected 3D holey graphene network facilitates rapid charge and ion transport. This work represents a critical step forward toward practical SIBs applications of SnO₂-based electrode materials with high capacity.