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 similar to 1.6 g/cm(3), 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/cm(2) delivers a gravimetric capacity of 165 mAh/g and a volumetric capacity of 223 mAh/cm(3) at 5 mA/cm(2), much higher than those of commercial hard carbon anode (80 mAh/g and 86 mAh/cm(3)). This work highlights a pathway for designing a dense nanostructure that enables fast charge kinetics for high-density sodium-ion storage.