New research enhances hybrid supercapacitors by creating more efficient electrodes, marking a major step forward in energy storage technology. Like batteries, supercapacitors are energy storage devices. However, batteries store energy electrochemically, while supercapacitors store energy electrostatically, that is, by accumulating charge on the electrode surface.
Hybrid supercapacitors (HSCs) combine battery-type electrodes and capacitor-type electrodes, combining the advantages of both systems. Although synthesis techniques allow the active ingredients in HSC electrodes to be grown directly on conductive substrates without the need to add binders ("self-supporting" electrodes), the proportion of active materials in these electrodes is still too low to meet commercial needs.
Now, researchers have found an ingenious way to increase the ratio of active substances to achieve significant improvements in key metrics.
"Hybrid supercapacitors combine the advantages of high energy and power density, long cycle life and safety, and have become a promising cutting-edge technology in the field of electrochemical energy storage," said Guo Wei, the study's first author and a scientist at Northwestern Polytechnical University in China. "In our paper, we propose a new mechanism to create a family of multifunctional two-dimensional superstructures that overcomes the low active-to-mass ratio of traditional self-supporting electrodes."
In this paper, the researchers studied β-Ni(OH)2, a form of nickel hydroxide that can crystallize from solution into thin plate-like structures on carbon fiber substrates. Adding NH4F to the reaction solution can replace a hydroxide ion with a fluoride ion. A Ni-F-OH plate with a thickness of 700 nm is generated, with a mass load (active mass per square centimeter) as high as 29.8 mg cm-2, accounting for 72% of the electrode mass.
To understand the formation mechanism of the new morphology, the researchers conducted a series of theoretical and experimental analyses, including X-ray absorption spectroscopy (XAS) at the Advanced Light Source (ALS) 7.3.1 and 8.0.1 beamlines, and scanning transmission X-ray microscopy (STXM) at the 5.3.2.2 beamline.
The results show that the added F- ions modulate the surface energy of the plate (a major factor in nanocrystal growth), while the NH4+ ions consume excess local OH-, inhibiting the re-formation of the undesirable β-Ni(OH)2 phase. In addition, based on the same method, researchers can also prepare other bimetallic superstructures and their derivatives, which marks the emergence of a new family of multifunctional metal-based hydroxides that can be used in new energy storage systems to meet future needs.
Compiled source: ScitechDaily