Compacted mesoporous titania nanosheets anode for pseudocapacitance‐dominated, high‐rate, and high‐volumetric sodium‐ion storage

Surface‐redox pseudocapacitive nanomaterials show promise for fast‐charging energy storage. However, their high surface area usually leads to low density, which is not conducive to achieving both high volumetric capacity and high‐rate capability. Herein, we demonstrate that TiO2 nanosheets (meso‐TiO2‐NSs) with densely packed mesoporous are capable of fast pseudocapacitance‐dominated sodium‐ion storage, as well as high volumetric and gravimetric capacities. Through compressing treatment, the compaction density of meso‐TiO2‐NSs is up to ~1.6 g/cm3, combined with high surface area and high porosity with mesopore channels for rapid Na+ diffusion. The compacted meso‐TiO2‐NSs electrodes achieve high pseudocapacitance (93.6% of total charge at 1 mV/s), high‐rate capability (up to 10 A/g), and long‐term cycling stability (10,000 cycles). More importantly, the space‐efficiently packed structure enables high volumetric capacity. The thick‐film meso‐TiO2‐NSs anode with the mass loading of 10 mg/cm2 delivers a gravimetric capacity of 165 mAh/g and a volumetric capacity of 223 mAh/cm3 at 5 mA/cm2, much higher than those of commercial hard carbon anode (80 mAh/g and 86 mAh/cm3). This work highlights a pathway for designing a dense nanostructure that enables fast charge kinetics for high‐density sodium‐ion storage.