Well‐Aligned Hierarchical Graphene‐Based Electrodes for Pseudocapacitors with Outstanding Low‐Temperature Stability

Abstract

The relatively poor performance stability of pseudocapacitors over a wide temperature window (i. e. temperature stability), particularly at low temperatures, hinders their practical applications. Here, well‐aligned hierarchical pseudocapacitive electrodes are fabricated, featuring run‐through channels in a graphene network (GN) as ion‐buffering reservoirs, open inter‐sheet channels between vertical graphene nanosheets (VGNSs) for fast ion transport and MnO2 nanopetals on VGNSs for efficient interfacial pseudocapacitive reactions. With reduced ion diffusion length and charge‐transfer resistance as well as improved ion‐transport rate, the capacitance of pseudocapacitive electrodes decreases from 541 to 490 F g−1 at 1 A g−1 as the temperature drops from 25 to 0 °C, revealing a high capacitance retention of 90.7 %. Furthermore, the specific capacitance of a symmetric device based on the hierarchical electrodes at −30 °C maintains 80.8 % of the room‐temperature capacitance. Such outstanding temperature stability is comparable to the state‐of‐the‐art electric double‐layer capacitors. Importantly, 86.0 % of capacitance is retained after repeated heating and cooling at temperatures ranging from −30 to 60 °C for 5000 cycles. Asymmetric supercapacitors with the hierarchical architecture in the positive electrode exhibit stable performance over a wide temperature range. These results demonstrate the rationality of the electrode design for practical energy storage applications in harsh temperature environments.

Freeze Casting: From Low‐Dimensional Building Blocks to Aligned Porous Structures—A Review of Novel Materials, Methods, and Applications

“…A further proposed application for aligned porous materials is supercapacitors. [ 29f,32a,65b,126 ] 3D cellular graphene films as the active material in supercapacitors were fabricated by filtration assembly of partially reduced GO and a subsequent freeze‐casting process. [ 32a ] The structure and conductivity of freeze‐cast graphene films facilitates good performance in terms of power density and energy density, with attained performance values of 7.8–14.3 kW kg −1 and 1.11 Wh L −1 respectively (Figure 18D,E).…”

Progress and Prospects on the Fabrication of Graphene‐Based Nanostructures for Energy Storage, Energy Conversion and Biomedical Applications

“…The as prepared material exhibited high temperature tolerance as it retained 90.7% of capacitance when temperature was reduced from 25°C (541 Fg À 1 at 1 Ag À 1 ) to 0°C (490 Fg À 1 at 1 Ag À 1 ). [187] The newly developed technology is the hybrid SCs (HSC), which provides a higher energy density than conventional EDLC with the combination of batteries and SCs. HSC lead us into the next generation of energy storage devices with ultrahigh performance that could be the ultimate power source for electric vehicles.…”

“…Schematic illustration of (a) the hierarchical GN/VGNS/MnO 2 structure and its features and (b) the fabrication process of GN/VGNS/ MnO 2 . [187] GWF/Si schottky junction solar cell is elicited from the comprehensive understanding of the hybrid structure. PVA + HNO 3 -GWF/Si solar cells were assembled and the PCE reached as high as 11%, which is comparable to that of graphene film derived solar cells.…”

Zinc Metal Energy Storage Devices under Extreme Conditions of Low Temperatures

“…doped carbon materials can provide pseudocapacitive reactions, resulting in higher capacitance [100] . For capacitive materials, the performance will be significantly attenuated at low temperatures, mainly due to the sluggish ion transport and charge transfer [101] . The nanoporous structure can shorten the diffusion distance and improve the diffusion rate of ions.…”

“…[100] For capacitive materials, the performance will be significantly attenuated at low temperatures, mainly due to the sluggish ion transport and charge transfer. [101] The nanoporous structure can shorten the diffusion distance and improve the diffusion rate of ions. Besides, high conductivity and good wettability with the electrolyte can reduce the charge transfer resistance.…”