Compressing Carbon Nanocages by Capillarity for Optimizing Porous Structures toward Ultrahigh‐Volumetric‐Performance Supercapacitors

Abstract

High volumetric energy density combined with high power density is highly desired for electrical double-layer capacitors. Usually the volumetric performance is improved by compressing carbon material to increase density but at the much expense of power density due to the deviation of the compressed porous structure from the ideal one. Herein the authors report an efficient approach to increase the density and optimize the porous structure by collapsing the carbon nanocages via capillarity. Three samples with decreasing sizes of meso- and macropores provide us an ideal model system to demonstrate the correlation of volumetric performance with porous structure. The results indicate that reducing the surplus macropores and, more importantly, the surplus mesopores is an efficient strategy to enhance the volumetric energy density while keeping the high power density. The optimized sample achieves a record-high stack volumetric energy density of 73 Wh L in ionic liquid with superb power density and cycling stability.

Recent Progress in Biomass‐Derived Electrode Materials for High Volumetric Performance Supercapacitors

“…One effective strategy for achieving high volumetric performance is the design of nanostructured electrode materials containing hierarchical pores and multiple components, [22][23][24] including transition metal composites, [25,26] metal-organic frameworks, [27] conducting polymers, [28][29][30] nanostructured carbons, [31][32][33] graphene, [34] and heteroatom-doped carbons. [35][36][37] Several reviews [8,21,[38][39][40][41] have already highlighted and summarized nanostructured carbon materials such as pure carbon or heteroatom-doped (i.e., N, B, F, O, S, and P) carbon possessing zero-to 3D microstructures.…”

Controlled Air‐Etching Synthesis of Porous‐Carbon Nanotube Aerogels with Ultrafast Charging at 1000 A g−1

“…The optimized geometry of the 1D nanotube shows ordered pores, and the calculated band structure and DOS exhibit metallic features as characterized by the high DOS and the bands crossing the Fermi level in the high symmetry k point path of Γ (0, 0, 0) → Z (0, 0, 0.5) (Figure S8, Supporting Information). In comparison, previously reported porous carbon materials are mainly in the form of particles with various shapes such as spheres, nanosheets, hollow cages, and other irregular particles …”

“…This constant represents the minimum time required to set free all the energy from the supercapacitors with an efficiency higher than 50%, and corresponds to a superior rate capability in our PCNs with a unique 1D porous structure . In comparison, other typical porous‐carbon electrodes usually exhibit τ 0 in the range of 0.08–0.6 s …”

“…Based on the above C s , we have obtained the capacitance retentions of the PCN aerogels, which are as high as 91.7% (10 A g −1 ), 85.3% (50 A g −1 ), 82.8% (100 A g −1 ), 80.1% (200 A g −1 ), 76.4% (500 A g −1 ), and 62.3% (1000 A g −1 ). In comparison, most of other porous carbon–based two‐electrode systems with aqueous or organic electrolytes show lower capacitance retentions tested in a smaller current density range (up to 200 A g −1 ) (Figure c and Table S2 (Supporting Information)) . Those electrodes were generally tested to current densities of 100 or 200 A g −1 , with only a few reaching 500 A g −1 (57% retention of the low‐current value), and one work reaching 1000 A g −1 (37% retention) by adding indole‐based macromolecules into electrolyte .…”

“…Chen et al fabricated hollow particle–based N‐doped carbon nanofibers by electrospinning, and demonstrated that 1D hollow carbon nanostructures are desired for high performance supercapacitors . Bu et al used MgO particles as template to synthesize collapsed carbon nanocages, and obtained a capacitance of 179 F g −1 at 200 A g −1 (87% retention) in aqueous electrolyte although the time constant remained large (0.6 s) . In other efforts, mesoporous graphene synthesized by a self‐propagating high‐temperature method also exhibited good properties with 98 F g −1 capacitance tested at 500 A g −1 (57% retention) in organic electrolyte .…”