Effect of salt concentration in aqueous LiTFSI electrolytes on the performance of carbon-based electrochemical capacitors

Black goes green: single-step solvent exchange for sol-gel synthesis of carbon spherogels as high-performance supercapacitor electrodes

Nanoporous carbon materials with customized structural features enable sustainable and electrochemical applications through improved performance and efficiency. Carbon spherogels (highly porous carbon aerogel materials consisting of an assembly of hollow carbon nanosphere units with uniform diameters) are desirable candidates as they combine exceptional electrical conductivity, bespoke shell porosity, tunability of the shell thickness, and a high surface area. Herein, we introduce a novel and more environmentally friendly sol-gel synthesis of resorcinol-formaldehyde (RF) templated by polystyrene spheres, forming carbon spherogels in an organic solvent. By tailoring the molar ratio of resorcinol to isopropyl alcohol (R/IPA) and the concentration of polystyrene, the appropriate synthesis conditions were identified to produce carbon spherogels with adjustable wall thicknesses. A single-step solvent exchange process from deionized water to isopropyl alcohol reduces surface tension within the porous gel network, making this approach significantly time and cost-effective. The lower surface tension of IPA enables solvent extraction under ambient conditions, allowing for direct carbonization of RF gels while maintaining a specific surface area loss of less than 20% compared to supercritically dried counterparts. The specific surface areas obtained after physical activation with carbon dioxide are 2300-3600 m2 g-1. Transmission and scanning electron microscopy verify the uniform, hollow carbon sphere network morphology. Specifically, those carbon spherogels are high-performing electrodes for energy storage in a supercapacitor setup featuring a specific capacitance of up to 204 F g-1 at 200 mA g-1 using 1 M potassium hydroxide (KOH) solution as the electrolyte.

Interfacial engineered PANI/carbon nanotube electrode for 1.8 V ultrahigh voltage aqueous supercapacitors

Flexible three-dimensional interconnected carbon nanotubes on the carbon cloth (3D-CNTs/CC) were obtained through simple magnesium reduction reactions. According to the Nernst equation, the cell voltage based on these pure carbon electrodes without any additives could reach 1.5 V due to the higher di-hydrogen evolution over potential in neutral 3.5 M LiCl electrolytes. In order to improve the electrochemical performance of the electrodes, 3D-CNTs/CC electrodes covered with polyaniline barrier layer (3D-PANI/CNTs/CC) were prepared byin situelectropolymerization using interfacial engineering method. The assembled symmetric supercapacitors display a broadened voltage of 1.8 V, high areal capacitance of 380 mF cm^-2, outstanding areal energy density of 85.5μWh cm^-2and 84% of its initial capacitance after 20 000 charge-discharge cycles. This work demonstrated that the interface engineering strategy provides a promising way to improve the energy density of carbon-based aqueous supercapacitors by widening the voltage and boosting the capacitance simultaneously.

Capacitive Behavior of Aqueous Electrical Double Layer Based on Dipole Dimer Water Model

The aim of the present paper is to investigate the possibility of using the dipole dimer as water model in describing the electrical double layer capacitor capacitance behaviors. Several points are confirmed. First, the use of the dipole dimer water model enables several experimental phenomena of aqueous electrical double layer capacitance to be achievable: suppress the differential capacitance values gravely overestimated by the hard sphere water model and continuum medium water model, respectively; reproduce the negative correlation effect between the differential capacitance and temperature, insensitivity of the differential capacitance to bulk electrolyte concentration, and camel-shaped capacitance-voltage curves; and more quantitatively describe the camel peak position of the capacitance-voltage curve and its dependence on the counter-ion size. Second, we fully illustrate that the electric dipole plays an irreplaceable role in reproducing the above experimentally confirmed capacitance behaviors and the previous hard sphere water model without considering the electric dipole is simply not competent. The novelty of the paper is that it shows the potential of the dipole dimer water model in helping reproduce experimentally verified aqueous electric double layer capacitance behaviors. One can expect to realize this potential by properly selecting parameters such as the dimer site size, neutral interaction, residual dielectric constant, etc.

A MOF-derived hollow Co3O4/NiCo2O4 nanohybrid: a novel anode for aqueous lithium ion batteries with high energy density and a wide electrochemical window

Aqueous lithium-ion batteries (LIBs) have attracted increasing attention because of their higher safety and nontoxicity compared to traditional LIBs. However, crucial shortcomings impede their practical applications. A narrow electrochemical window restricts the capacity of aqueous LIBs so the ultrahigh concentration electrolyte lithium bistrifluoromethosulfonimide (LiTFSI) is introduced to widen the electrochemical window in this work. With the addition of LiTFSI, the electrochemical window of the created aqueous LIBs is improved to 2 V. Moreover, the material design promotes the high density of aqueous LIBs, in which hollow Co₃O₄ nanocrystals obtained by the metal organic framework (MOF) template are connected with NiCo₂O₄ nanorods to form three-dimensional nanohybrids. The formed Co₃O₄/NiCo₂O₄ (CN) materials can provide NiCo₂O₄ channels for electron transfer between hollow Co₃O₄ which can offer more lithium-ions insertion. These effects work together synergistically to achieve aqueous LIBs with a wide electrochemical window and high energy density (93.07 W h kg^-1 at 0.5 C). CN-6/LiMn₂O₄-based aqueous LIBs with LiTFSI as the electrolyte take into account both environmental friendliness and sustainable energy storage and exhibit great potential for producing novel clean energy storage devices from the concepts of material design and synthesis.