Docheon Ahn

In response to the ever-increasing global demand for viable energy-storage systems, sodium and potassium batteries appear to be promising alternatives to lithium ion batteries because of the abundance, low cost and environmental benignity of sodium/potassium. Electrical energy storage via ion-intercalation reactions in crystalline electrodes is critically dependent on the sizes of the guest ions. Herein, we report on the use of a porous amorphous iron phosphate synthesized using ambient temperat

We report a 3.8 V manganese-based mixed-phosphate cathode material for applications in sodium rechargeable batteries; i.e. , Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ).

Natural gas hydrates are solid hydrogen-bonded water crystals containing small molecular gases. The amount of natural gas stored as hydrates in permafrost and ocean sediments is twice that of all other fossil fuels combined. However, hydrate blockages also hinder oil/gas pipeline transportation, and, despite their huge potential as energy sources, our insufficient understanding of hydrates has limited their extraction. Here, we report how the presence of amino acids in water induces changes in i

Abstract Candidates for high‐energy cathodes in potassium‐ion batteries (KIBs) are selected by fully screening the inorganic compound structure database. The compounds that satisfy the specific conditions for plausible KIB cathodes are further subjected to theoretical and electrochemical verification, and KVP 2 O 7 is finally pinpointed. KVP 2 O 7 can reversibly desert/insert ≈60% of K + (60 mA h g −1 ) during either chemical or electrochemical oxidation/reduction. KVP 2 O 7 shows an average dis

We demonstrate that the Mott metal-insulator transition (MIT) in single crystalline VO(2) nanowires is strongly mediated by surface stress as a consequence of the high surface area to volume ratio of individual nanowires. Further, we show that the stress-induced antiferromagnetic Mott insulating phase is critical in controlling the spatial extent and distribution of the insulating monoclinic and metallic rutile phases as well as the electrical characteristics of the Mott transition. This affords

Natural gas hydrates are icy crystalline materials that contain hydrocarbons, which are the primary energy source for this civilization. The abundance of naturally occurring gas hydrates leads to a growing interest in exploitation. Despite their potential as energy resources and in industrial applications, there is insufficient understanding of hydrate kinetics, which hinders the utilization of these invaluable resources. Perturbation of liquid water structure by solutes has been proposed to be

Abstract Multiple applications of lithium‐ion batteries in energy storage systems and electric vehicles require highly stable electrode materials for long‐term battery operation. Among the various cathode materials, high‐Ni cathode materials enable a high energy density. However, cathode degradation accompanied by complex chemical and structural changes results in capacity and voltage fading in batteries. Cathode degradation remains poorly understood; the majority of studies have only explored t

A facile and cost-effective urea-assisted autocombustion strategy has been designed for the fabrication of Co3O4/CoFe2O4 nanocomposite and pure CoFe2O4 anode materials followed by annealing at 700 and 900 °C for 6 h, respectively. To confirm the exact structure, Rietiveld analysis was performed on the Synchrotron XRD pattern of both the CoFe2O4 samples annealed at 700 and 900 °C. The results clearly depicts the formation of two phases (Co3O4:CoFe2O4) with the ratio of [76.3(5):23.6(3)%] in the s

The layered sodium transition metal oxide, NaTMO₂ (TM = transition metal), with a binary or ternary phases has displayed outstanding electrochemical performance as a new class of strategy cathode materials for sodium-ion batteries (SIBs). Herein, an in-depth phase analysis of developed Na_1-x TMO₂ cathode materials, Na_0.76 Ni_0.20 Fe_0.40 Mn_0.40 O₂ with P2- and O3-type phases (NFMO-P2/O3) is offered. Structural

Thanks to the employment of a NSGA-II-based computation, which was used to determine the optimum multi-element doping composition at the Mn site of olivine-structured LiMnPO₄, we can propose the first examples of high-performance doped-LiMnPO₄ cathodes for Li-ion batteries.

The surfaces of layer-structured Li[Li0.2Co0.1Mn0.7]O2 nanodisks were nanocoated with polyaniline and examined by SEM and TEM studies, via the chemical oxidative polymerization of aniline in an acid medium for 10 min—Mn4+ ions in the pristine lithium manganese oxides acted as oxidants. During this reaction, the crystal structure of the pristine nanodisks was retained, and the XRD patterns showed no evidence of H+ exchange with the Li+ located between the manganese oxide layers. The nanocoated po

Cobalt-intercalated layered manganese oxide (CLMO, K0.08Co0.12MnO2), in which 75% of the potassium ions of the pristine K-birnessite (K0.32MnO2) in the interlayer region were exchanged with cobalt ions by an ion-exchanging reaction, and the polyaniline-coated CLMO prepared by chemical oxidative polymerization of aniline in an acidic medium were studied using synchrotron powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, extended X-r

Several divalent europium-doped alkali-earth silicon oxide or nitride (AESON) phosphors, which are of great use in white light-emitting diodes, exhibit a two-peak emission. We examined the two-peak emission of , which is known as a representative AESON phosphor. The two-peak emission is closely associated with the energy transfer between two different sites. The two-peak emission in light-emitting diode phosphors is a very important issue from a practical point of view because it directly relate

An Ag-embedded LiMnPO4 (LMP) cathode was synthesized by solid-state reaction using a 1 wt% Ag precursor. Structure, morphology, and electrical conductivity studies of Ag-embedded LMP were performed by high resolution powder X-ray diffraction, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and four probe measurements. An Ag nanoparticle (∼26 nm) surrounded by several olivine crystallites within a single particle dramatically improved the overall electrical