Hee Dong Jang

Silicon (Si) is considered a promising anode material for lithium-ion batteries (LIBs) due to its high performance. However, when Si is exposed to an electrolyte, it forms a solid electrolyte interphase (SEI) film and the following electrode decomposition results in poor performance of the LIB. Effective coverage of Si by carbon materials is an interesting potential solution to solve this problem. In this study, we prepared carbon nanotubes-reduced graphene oxide-silicon (CNTs-RGO-Si) composite materials by eco-friendly processes and showed that they can be used as a high-performance anode material for LIBs. Fabrication of the CNTs-RGO-Si composites was composed of three steps. The first step was the preparation of well dispersed CNTs-GO colloids by bead milling without any chemical treatment and then co-assembly of the CNT-GO-Si composites by spray drying the colloidal mixture. Finally, the CNT-RGO-Si was fabricated by thermal reduction of GO in the CNTs-GO-Si composite. The morphology of the as-fabricated CNTs-RGO-Si composites was generally the shape of a crumpled paper ball and the size of the composites showed a distribution of 1 to 5 µm. The highest capacitance of the CNT-RGO-Si composite after milling three times of CNTs-GO colloids was about 1634 mAh g ^− 1 during the 100-cycle charge and discharge test at 1 C high current density. The CNT-RGO-Si composites exhibited coulombic efficiency of over 96% with excellent stability.

Structurally and chemically defective activated‐crumbled graphene (A‐CG) is employed to achieve unique synergy of large reversible potassium (K) and sodium (Na) ion storage capacity with fast charging and extended cyclability. A‐CG synthesis consists of low temperature spraying of graphene oxide slurry, followed by partial reduction annealing and air activation. For K storage, the reversible capacities are 340 mAh g⁻¹ at 0.04 A g⁻¹, 261 mAh g⁻¹ at 0.5 A g⁻¹, and 210 mAh g⁻¹ at 2 A g⁻¹. For Na storage, the reversible capacities are 280 mAh g⁻¹ at 0.04 A g⁻¹, 191 mAh g⁻¹ at 0.5 A g⁻¹, and 151 mAh g⁻¹ at 2 A g⁻¹. A‐CG shows a stable intermediate rate (0.5 Ag⁻¹) cycling with both K and Na, with minimal fade after 2800 and 8000 cycles. These are among the most favorable capacity—rate capability—cyclability combinations recorded for potassium‐ion battery and sodium‐ion battery carbons. Electroanalytical studies (cyclic voltammetry, galvanostatic intermittent titration technique, b‐value) and density functional theory (DFT) reveal that enhanced electrochemical performance originates from ion adsorption at various defects, such as Stone–Wales defects. Moreover, DFT highlights enhanced thermodynamic stability of A‐CG with adsorbed K versus with adsorbed Na, explaining the unexpected higher reversible capacity with the former.

One-dimensional alkali metal titanates containing potassium, sodium, and lithium are of great concern owing to their high ion mobility and high specific surface area. When those titanates are combined with conductive materials such as graphene, carbon nanotube, and carbon nanofiber, they are able to be employed as efficient electrode materials for supercapacitors. Potassium hexa-titanate (K₂Ti₆O₁₃, KTO), in particular, has shown superior electrochemical properties compared to other alkali metal titanates because of their large lattice parameters induced by the large radius of potassium ions. Here, we present porous rGO crumples (PGC) decorated with KTO nanoparticles (NPs) for application to supercapacitors. The KTO NP/PGC composites were synthesized by aerosol spray pyrolysis and post-heat treatment. KTO NPs less than 10 nm in diameter were loaded onto PGCs ranging from 3 to 5 µm. Enhanced porous structure of the composites was obtained by the activation of rGO by adding an excessive amount of KOH to the composites. The KTO NP/PGC composite electrodes fabricated at the GO/KOH/TiO₂ ratio of 1:3:0.25 showed the highest performance (275 F g⁻¹) in capacitance with different KOH concentrations and cycling stability (83%) after 2000 cycles at a current density of 1 A g⁻¹.

Recently, many researchers have developed advanced energy storage and energy conversion systems to address the increased demand for energy resources. The performance of these electrochemical energy storage and conversion devices depends considerably on the properties of their unique electrode materials. Among electrode materials, graphene (GR) has attracted much attention due to its unique properties of high flexibility, a large specific surface area, and superior electric conductivity rates that are well‐suited to energy storage systems. Specifically, aerosol‐made 3D GR composites are known to be more resistant to compressive forces such as paper balls owing to their stronger and harder compressive tolerance levels and higher and more stable surface areas compared to 2D GR sheets. These unique properties of 3D GR composites result in enhanced electrochemical performances for energy storage systems. This review focuses on recent studies of aerosol‐made 3D GR‐based composites for energy storage systems such as supercapacitors, lithium‐ion batteries, and sodium‐ion batteries.

The international journal of Aerosol and Air Quality Research (AAQR) covers all aspects of aerosol science and technology, atmospheric science and air quality related issues.

The international journal of Aerosol and Air Quality Research (AAQR) covers all aspects of aerosol science and technology, atmospheric science and air quality related issues.

Nanostructured graphene electrodes generally have a low density, which can limit the volumetric performance for energy storage devices. The liquid‐phase mild reduction process of graphene oxide sheets is combined with the continuous aerosol densification process to produce high‐density graphene agglomerates in the form of microspheres. The produced graphene assembly shows the cabbage‐like morphology with a high density of 0.75 g cm⁻³. In spite of such high density, the cabbage‐like graphene microspheres have narrow‐ranged mesopores and a high surface area. The cabbage‐like graphene microsphere exhibits both high gravimetric and volumetric energy densities due to the optimized microstructure, which shows a high gravimetric capacitance of 177 F g⁻¹ and volumetric capacitance of 117 F cm⁻³ in supercapacitors. As a cathode for lithium‐ion capacitors, the cabbage‐like graphene delivers a reversible capacity of ≈176 mAh g⁻¹. The stacking‐control approach provides a new pathway to control the microstructure of the graphene assembly and corresponding charge storage characteristics for energy storage applications.

Crumpled graphene (CGR) is considered a promising supercapacitor material to achieve high power and energy density because it could overcome the disadvantages of 2 D GR sheets such as aggregation during the electrode fabrication process, reduction of the available surface area, and limitation of the electron and ion transport. Even though CGR shows good results, carbon materials are limited in terms of their capacitance performance. Here, we report highly enhanced supercapacitor materials by fabricating a 3 D composite containing CGR, carbon nanotubes (CNTs), and polyaniline (PANI). The CNTs increased the basal spacing and bridged the defects for electron transfer between the GR sheets in CGR. PANI can enhance the rate of conduction of electrons and offer high pseudocapacitance originating from its redox reactions. The synergistic effect of the CNTs and PANI may also result in a higher electrochemical capacitance and better stability than each individual component as electrode materials for supercapacitors in a two‐electrode system. More importantly, the performance of the supercapacitors can be further enhanced by employing 2 D GR as the binder for the composite electrodes, resulting in specific capacitance of 456 F g⁻¹, rate capability of 89 %, and cyclic stability of 97 % after 1000 cycles.