High Volumetric Energy Density Hybrid Supercapacitors Based on Reduced Graphene Oxide Scrolls

Abstract

The low volumetric energy density of reduced graphene oxide (rGO)-based electrodes limits its application in commercial electrochemical energy storage devices that require high-performance energy storage capacities in small volumes. The volumetric energy density of rGO-based electrode materials is very low due to their low packing density. A supercapacitor with enhanced packing density and high volumetric energy density is fabricated using doped rGO scrolls (GFNSs) as the electrode material. The restacking of rGO sheets is successfully controlled through synthesizing the doped scroll structures while increasing the packing density. The fabricated cell exhibits an ultrahigh volumetric energy density of 49.66 Wh/L with excellent cycling stability (>10 000 cycles). This unique design strategy for the electrode material has significant potential for the future supercapacitors with high volumetric energy densities.

Electrochemical Performance of Iron Oxide Nanoflakes on Carbon Cloth under an External Magnetic Field

“…The calculated specific capacitance of the Fe 2 O 3 @CC electrode measured in 1 M Li 2 SO 4 electrolyte are 52, 40, 29, 26, 23, and 19 mF cm −2 at 1, 2, 5, 8, 10, and 20 mV s −1 , respectively. As reported in the literature, the specific capacitances reduce with increase in the scan rate in any electrolytes [33][34][35][36]. The situation could be seen in other electrolytes.…”

High Volumetric Quasi‐Solid‐State Sodium‐Ion Capacitor under High Mass Loading Conditions

“…The rGO‐TiO 2 shows a volumetric capacity of ≈429 mAh cc −1 and an areal capacity of ≈1.06 mAh cm −2 at 0.25 C. A high capacity has been retained by rGO‐TiO 2 even under a high mass loading (5 mg cm −2 ), making a favorable condition to achieve a high volumetric energy. The previous reports on NICs generally utilize a low mass loading (1–1.5 mg cm −2 ) to achieve a high capacity, and the mass loading in the present study is 3–5 orders higher than the previous reports …”

“…The cyclic voltammograms of rGO‐TiO 2 show a broad rectangular profile with redox peaks at ≈0.5 and ≈0.8 V due to sodium insertion/extraction, respectively. With increasing scan rate, the shape profile is maintained and the output currents are directly proportional to sweep rates and thereby follow the power law i = av b , where i is the current (A), a and b are the adjustable parameters, and v is the scan rate (mV s −1 ) . From the CV curves, b is calculated to be ≈0.98, demonstrating that Na‐ion storage in rGO‐TiO 2 occurs through a fast surface‐controlled redox reaction.…”

“…The BET surface area was analyzed to be ≈98 m 2 g −1 , which favorably provides a large number of active surface sites for sodium‐ion storage. Furthermore, the large number of mesopore channels aids fast sodium‐ion migration by providing a shortened ionic path …”

“…≈80% of the total capacity is identified to be from pseudocapacitive reaction at 1 mV s −1 (Figure e). The fast surface‐limited Na‐ion storage characteristic of rGO‐TiO 2 is highly favorable for achieving a high capacity at high current rates even under high mass loading conditions and thereby enables a possibility of high volumetric and high‐power NICs . The previously studied insertion compounds exhibit diffusion‐controlled reactions that unfavorably restrict the working of NICs at high power rates …”