Electrode mass ratio impact on electrochemical capacitor performance

Sub-millisecond lithiothermal synthesis of graphitic meso-microporous carbon

Porous carbons with concurrently high specific surface area and electronic conductivity are desirable by virtue of their desirable electron and ion transport ability, but conventional preparing methods suffer from either low yield or inferior quality carbons. Here we developed a lithiothermal approach to bottom-up synthesize highly meso-microporous graphitized carbon (MGC). The preparation can be finished in a few milliseconds by the self-propagating reaction between polytetrafluoroethylene powder and molten lithium (Li) metal, during which instant ultra-high temperature (>3000 K) was produced. This instantaneous carbon vaporization and condensation at ultra-high temperatures and in ultra-short duration enable the MGC to show a highly graphitized and continuously cross-coupled open pore structure. MGC displays superior electrochemical capacitor performance of exceptional power capability and ultralong-term cyclability. The processes used to make this carbon are readily scalable to industrial levels.

The effect of the pyrolysis temperature and biomass type on the biocarbons characteristics

The conversion of biomass and natural wastes into carbon-based materials for various applications such as catalysts and energy-related materials is a fascinating and sustainable approach emerged during recent years. Precursor nature and characteristics are complex, hence, their effect on the properties of resulting materials is still unclear. In this work, we have investigated the effect of different precursors and pyrolysis temperature on the properties of produced carbon materials and their potential application as negative electrode materials in Li-ion batteries. Three biomasses, lignocellulosic brewery spent grain from a local brewery, catechol-rich lignin and tannins, were selected for investigations. We show that such end-product carbon characteristic as functional and elemental composition, porosity, specific surface area, defectiveness level, and morphology strictly depend on the precursor composition, chemical structure, and pyrolysis temperature. The electrochemical characteristics of produced carbon materials correlate with the characteristics of the produced materials. A higher pyrolysis temperature is shown to be favourable for production of carbon material for the Li-ion battery application in terms of both specific capacity and long-term cycling stability.

Novel Insight into the Concept of Favorable Combination of Electrodes in High Voltage Supercapacitors: Toward Ultrahigh Volumetric Energy Density and Outstanding Rate Capability

Most of the biomass-derived carbon-based supercapacitors using organic electrolytes exhibit very low energy density due to their low operating potential range between 2.7 and 3.0 V. A novel insight into the concept of the different porous architecture of electrode materials that is employed to extend a device's operating potential up to 3.4 V using TEABF4 in acetonitrile, is reported. The combination of two high surface area activated carbons derived from abundant natural resources such as industrial waste cotton and wheat flour as sustainable and green carbon precursors is explored as an economical and efficient supercapacitor carbon electrode. Benefitting from the simultaneous achievement of the higher potential window (3.4 V) with higher volumetric capacitance (101 F cm-3), the supercapacitor electrodes exhibit higher volumetric energy density (42.85 Wh L-1). Bimodal pore size distribution of carbon with a tuned pore size and high specific surface area of the electrode can promote the fast transport of cations and anions. Hence, it exhibits a high rate capability even at 30 A g-1. In addition, the electrodes remain stable during operation cell voltage at 3.4 V upon 15 000 charging-discharging cycles with 90% capacitance retention.

Recent Advances on Boosting the Cell Voltage of Aqueous Supercapacitors

Due to its ultra-fast charge/discharge rate, long cyclic life span, and environmental benignity, aqueous supercapacitor (SC) is considered as a proper next-generation energy storage device. Unfortunately, limited by undesirable water electrolysis and unreasonable electrode potential range, aqueous SC normally generates a narrow cell voltage, resulting in a low energy density. To address such challenge, enormous efforts have been made to construct high-voltage aqueous SCs. Despite these achievements, the systematic reviews about this field are still rare. To fill this knowledge gap, this review summarizes the recent advances about boosting the cell voltage of aqueous SCs. From the viewpoint of electrode, doping alkali cations, modulating the electrode mass ratio, and optimizing the surface charge density are regarded as three effective pathways to achieve this goal. However, adjusting the appropriate pH level, introducing redox mediators, and constructing "water-in-salt" electrolyte are other three universal routes from the electrolyte aspect. Furthermore, it is also effective to obtain the high-voltage aqueous SCs through asymmetric design, such as designing asymmetric SCs. The confronting challenges and future development tendency towards the high-voltage aqueous SCs are further discussed.

Integrated System of Solar Cells with Hierarchical NiCo2O4 Battery-Supercapacitor Hybrid Devices for Self-Driving Light-Emitting Diodes

An integrated system has been provided with a-Si/H solar cells as energy conversion device, NiCo₂O₄ battery-supercapacitor hybrid (BSH) as energy storage device, and light emitting diodes (LEDs) as energy utilization device. By designing three-dimensional hierarchical NiCo₂O₄ arrays as faradic electrode, with capacitive electrode of active carbon (AC), BSHs were assembled with energy density of 16.6 Wh kg^-1, power density of 7285 W kg^-1, long-term stability with 100% retention after 15,000 cycles, and rather low self-discharge. The NiCo₂O₄//AC BSH was charged to 1.6 V in 1 s by solar cells and acted as reliable sources for powering LEDs. The integrated system is rational for operation, having an overall efficiency of 8.1% with storage efficiency of 74.24%. The integrated system demonstrates a stable solar power conversion, outstanding energy storage behavior, and reliable light emitting. Our study offers a precious strategy to design a self-driven integrated system for highly efficient energy utilization.