Precisely Designed Mesoscopic Titania for High-Volumetric-Density Pseudocapacitance.

Surface redox pseudocapacitance, which enables short charging times and high power delivery, is very attractive in a wide range of sites. To achieve maximized specific capacity, nanostructuring of active materials with high surface area is indispensable. However, one key limitation for capacitive materials is their low volumetric capacity due to the low tap density of nanomaterials. Here, we present a promising mesoscale TiO2 structure with precisely controlled mesoporous frameworks as a high-density pseudocapacitive model system. The dense-packed mesoscopic TiO2 in micrometer size offers a high accessible surface area (124 m2 g-1) and radially aligned mesopore channels, but high tap density (1.7 g cm-3) that is much higher than TiO2 nanoparticles (0.47 g cm-3). As a pseudocapacitive sodium-ion storage anode, the precisely designed mesoscopic TiO2 model achieved maximized gravimetric capacity (240 mAh g-1) and volumetric capacity (350 mAh cm-3) at 0.025 A g-1. Such a designed pseudocapacitive mesostructure further realized a commercially comparable areal capacity (2.1 mAh cm-2) at a high mass loading of 9.47 mg cm-2. This mesostructured electrode that enables fast sodiation in dense nanostructures has implications for high-power applications, fast-charging devices, and pseudocapacitive electrode design.