Boosting the Sodium-Ion Transport and Surface Pseudocapacitance of a SnO₂ Nanoflower at a High Mass Loading Level for High Areal Capacity and Fast Sodium-Ion Storage

The exploitation of electrode materials with high areal capacity and rate performance under high mass loading is critical for the practical application of sodium-ion batteries (SIBs), and 3D nanocomposite electrode materials based on nanoelectrode materials and 3D carbon-based material frameworks have shown extraordinary promise. However, the areal capacity and rate performance are unsatisfactory because of the low utilization efficiency and sluggish Na⁺ kinetics of active Na⁺ storage materials. To address this problem, we developed a 3D SnO₂ nanoflower-holey graphene (SnO₂ NF-HG) composite electrode. The 3D HG framework can provide a fully interconnected hierarchical porous channel for Na⁺ transport to the SnO₂ surface, and the flower-like SnO₂ nanomaterials with larger surface area can provide more active sites for Na⁺ storage. The electrochemical test results indicate the low Na⁺ resistance and high pseudocapacitance contribution of the as-prepared 3D SnO₂ NF-HG electrodes. As a result, the low utilization efficiency and sluggish Na⁺ kinetics of the active Na⁺ storage materials were substantially boosted, and the 3D composite electrodes show impressive properties of high areal capacity and fast Na⁺ storage. Under a high current density of 5 mA cm^-2, the 3D SnO₂ NF-HG composite electrodes with high mass loading of 10 mg cm^-2 achieve a strikingly high and stable areal capacity of 3 mAh cm^-2. This high areal capacity is the same as those of commercial lithium-ion battery electrode materials and greatly exceeds those of most reported SIB electrode materials. Our work shows that rationally designed active Na⁺ storage electrode materials with large surface area represent an effective strategy for promoting high-mass-loading 3D composites and high-specific-capacity electrode materials toward practical SIB applications.