Precisely Designed Mesoscopic Titania for High-Volumetric-Density Pseudocapacitance

Abstract

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 TiO 2 structure with precisely controlled mesoporous frameworks as a high-density pseudocapacitive model system. The dense-packed mesoscopic TiO 2 in micrometer size offers a high accessible surface area (124 m 2 g −1 ) and radially aligned mesopore channels, but high tap density (1.7 g cm −3 ) that is much higher than TiO 2 nanoparticles (0.47 g cm −3 ). As a pseudocapacitive sodium-ion storage anode, the precisely designed mesoscopic TiO 2 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.

A Simple Strategy for Constructing Hierarchical Composite Electrodes of PPy‐Posttreated 3D‐Printed Carbon Aerogel with Ultrahigh Areal Capacitance over 8000 mF cm–2

“…[11][12][13] Besides, for supercapacitor electrodes, the design of more doses of active materials means that there exists plenty of active sites available for reversible redox reactions. [14] As a result, it seems desirable to configure a supercapacitor electrode with a high mass loading (per unit area or volume) of active materials, such as a relatively dense distribution or a large thickness. However, such designs usually tend to cause the sluggish electron/ion diffusion, as well as the insufficient use of active materials, which instead limits the overall performance of supercapacitors.…”

Versatile Synthesis of Mesoporous Crystalline TiO2 Materials by Monomicelle Assembly

“…[78][79][80] Considerable interest is emerging in creating materials that combine the short charging times and long cycle life of pseudocapacitive nanomaterials with a high tap density for enhanced areal capacity. With this aim, a mesoscopic TiO 2 microsphere anode was designed, in which the cylindrical TiO 2 nanocrystals were radially aligned from the microsphere center and with conductive carbon distributed in the whole mesostructured frameworks [81] (Figure 10a). The ordered arrangement of TiO 2 nanocrystals provides a greatly improved tap density (1.1-1.7 g cm À 3 ), which in turn increases the volume and areal capacities of the electrode.…”

“…g) Separation of the capacitive and diffusion currents in meso-TiO 2 at 1 mV s À 1 . Reproduced from Ref [81]. with permission.…”

Faster Intercalation Pseudocapacitance Enabled by Adjustable Amorphous Titania Where Tunable Isomorphic Architectures Reveal Accelerated Lithium Diffusivity

“…[8,9] Materials that have exhibited intercalation pseudocapacitive responses have sufficiently fast solid-state diffusion and an absence of phase transitions upon intercalation. [7][8][9][10][11][12][13][14] The introduction of dopants or other defects have been used to increase the rates of solid-state diffusion with examples for Cu[Fe(CN) 6 ] 0.63 * & 0.37 * 3.4H 2 O, [15] T-Nb 2 O 5 , [16][17][18] MoO 3 , [19] TiO 2 , [20,21] and others. [22,23] Nanoscale materials can also differ from bulk analogs, for example, nanoscale anatase can lithiate as a solid solution whereas larger anatase crystals undergo a phase separation of discrete lithium rich and lithium poor domains.…”

“…Intercalation pseudocapacitive responses exhibit surface‐limited kinetics by definition, where the current response is proportional to the voltage sweep rate ( v ) [8,9] . Materials that have exhibited intercalation pseudocapacitive responses have sufficiently fast solid‐state diffusion and an absence of phase transitions upon intercalation [7–14] . The introduction of dopants or other defects have been used to increase the rates of solid‐state diffusion with examples for Cu[Fe(CN) 6 ] 0.63 ⋅□ 0.37 ⋅3.4H 2 O, [15] T‐Nb 2 O 5 , [16–18] MoO 3 , [19] TiO 2 , [20,21] and others [22,23] .…”