Towards ultrahigh volumetric capacitance: graphene derived highly dense but porous carbons for supercapacitors

Abstract

A small volumetric capacitance resulting from a low packing density is one of the major limitations for novel nanocarbons finding real applications in commercial electrochemical energy storage devices. Here we report a carbon with a density of 1.58 g cm−3, 70% of the density of graphite, constructed of compactly interlinked graphene nanosheets, which is produced by an evaporation-induced drying of a graphene hydrogel. Such a carbon balances two seemingly incompatible characteristics: a porous microstructure and a high density, and therefore has a volumetric capacitance for electrochemical capacitors (ECs) up to 376 F cm−3, which is the highest value so far reported for carbon materials in an aqueous electrolyte. More promising, the carbon is conductive and moldable, and thus could be used directly as a well-shaped electrode sheet for the assembly of a supercapacitor device free of any additives, resulting in device-level high energy density ECs.

Holey graphene frameworks for highly efficient capacitive energy storage

“…5c,d), further suggesting that little restacking is occurring in the compressed HGF films. This can be attributed to the robust interlock of graphene sheets that allows mechanical compression to reduce the pore size without significantly modifying the stacking characteristics of graphene and its 3D interconnected porous structure 18 . Importantly, these compressed HGF films can exhibit excellent electrical conductivity of B1,000 S m À 1 , and are mechanically strong enough to be used as the EC electrodes directly.…”

“…Although gravimetric capacitance was traditionally used as the figure-of-merit to evaluate an EC electrode, the volumetric performance is becoming an increasingly important metric to consider for many practical applications with limited space such as portable electronic products [14][15][16][17][18][19][20] . However, there is usually a trade-off relationship between the gravimetric and volumetric capacitances for most electrode design.…”

Highly densified carbon electrode materials towards practical supercapacitor devices

“…By carefully controlling the capillary evaporation-induced drying process, as shown in Fig. 4, Tao et al [59] reported a tightly packed yet porous graphene assembly with a density of 1.58 g cm −3 . In the drying process, the surface tension exerted on the graphene layers led to the shrinking of the assembly, resulting in a compactly compressed yet ion penetrable carbon.…”

Engineering Graphenes from the Nano- to the Macroscale for Electrochemical Energy Storage

“…This inherited the high surface area, excellent conductivity, and flexibility of the graphene and the CNTs and gave a high capacitance of 200 F g −1 [46]. A 3D graphene network deposited with manganese dioxide 1.58 -KOH [147] (MnO 2 ) nanoparticles was constructed on graphene fibers (MnO 2 /G/GF), and an all-solid-state supercapacitor based on this hybrid not only had excellent mechanical flexibility and but also exhibited a high capacitance which was mainly contributed by the EDLC of 3D graphene and the pseudocapacitance of MnO 2 [47]. Graphene-based fibers can also be woven into a network to obtain a film electrode.…”

“…Furthermore, this porous and dense monolith is conductive and moldable, and can therefore be used directly as a well-shaped electrode sheet free of additives, yielding a high device-level energy density for supercapacitors (Fig. 13) [147]. Moreover, by embedding high-capacity non-carbon materials in the void space of the dense graphene matrix, the carbon-non-carbon hybrid delivered high volumetric capacitances even at a high mass loading of active materials and a high current density [83][84][85]116].…”