Young Hwa Jung

Encapsulated monoclinic sulfur for stable cycling of li-s rechargeable batteries.

Monoclinic S8 , an uncommon allotrope of sulfur at room temperature, can be formed when common orthorhombic S8 is heat-treated under enclosed environments in nanometer dimensions. Monoclinic S8 prevents the formation of soluble polysulfides during battery operation, resulting in unprecedented cycling performance over 1000 cycles under the highest sulfur content to date.

Graphene-supported Na3V2(PO4)(3) as a high rate cathode material for sodium-ion batteries

Substantial interest in sodium resources that are inexpensive and abundant in the earth has guided intense research on Na-based electrode materials. We report a facile synthetic strategy to improve the rate performance of Na-based electrode materials in sodium-ion batteries. Na3V2(PO4)3 (NVP) is one of the most promising cathode materials with a NASICON structure, and it has been synthesized on a graphene sheet surface using a simple method that combines sol–gel and solid-state reaction. The NVP/graphene composite displays an excellent high-rate performance; it delivers approximately 67% of the initial 0.2 C capacity at a 30 C rate, whereas bare NVP produces only 46% of the 0.2 C capacity at a 5 C rate. It also demonstrates high capacity retention both at 1 C and 10 C cycles as a promising cathode for rechargeable sodium-ion batteries. This outstanding result can be ascribed to the key role of graphene in enhancing the electronic conductivity of electrode materials compared with bare NVP.

Fast switchable electrochromic properties of tungsten oxide nanowire bundles

The authors prepared uniformly shaped WO2.72 nanowire bundles using the solvothermal synthesis method. They investigated the potential of the WO2.72 nanowire bundles to be used as a cathode electrode for electrochromic devices and the effect of the Li+ insertion (or extraction) kinetics and diffusion of Li+. An electrode consisting of arrays of WO2.72 nanowire bundles was formed and used in an experiment using the Langmuir-Blodgett technique. The one-dimensional nanostructure of WO2.72 has a high Li-ion diffusion coefficient (∼5.2×10−11cm2∕s) and low charge transfer resistance (∼28.6Ω), which result in its having a fast electrochromic response time (coloring time 55cm2∕C).

Na2FeP2O7 as a positive electrode material for rechargeable aqueous sodium-ion batteries

An iron-based pyrophosphate compound, Na2FeP2O7, is investigated as a positive electrode material for aqueous sodium-ion batteries for the first time. The high rate capability and good cyclability of this material in aqueous electrolytes are advantageous for low-cost and safe battery systems.

Na3V2O2x(PO4)2F3−2x: a stable and high-voltage cathode material for aqueous sodium-ion batteries with high energy density

The reversible electrochemical activity of the Na3V2O2x(PO4)2F3−2x compound in an aqueous solution is reported for the first time. Na3V2O2x(PO4)2F3−2x with multi-walled carbon nanotubes (MWCNTs) exhibits a long-term stability for up to 1100 cycles in aqueous electrolytes. Two different types of Na-ion full-cells demonstrate the feasibility of the Na3V2O2x(PO4)2F3−2x/MWCNT composite as a cathode for aqueous sodium-ion batteries. A high full-cell voltage of 1.7 V and a high energy density of 84 W h kg−1 were achieved using Zn metal as an anode.

High performance of MoS2 microflowers with a water-based binder as an anode for Na-ion batteries

Na-ion batteries have risen as an alternative system to current Li-ion batteries due to the wide range of availability and low price of sodium resources. Here we report the binder effect on sodium storage properties of MoS2 microflowers with nano-sized petals which are prepared by a combination of a hydrothermal reaction and solid-state reaction. The electrochemical performance of MoS2 microflowers with different binders is evaluated against pure Na metal in a half-cell configuration through a conversion reaction. Especially, the electrode of MoS2 microflowers with a Na-alginate binder shows an excellent cycling stability, delivering a high discharge capacity of 595 mA h g−1 after 50 cycles. The MoS2 microflowers with the Na-alginate binder also exhibit high rate capability, retaining a capacity of 236 mA h g−1 at 10C without any carbonaceous materials. The improved electrochemical performance was mainly attributed to the synergetic effect of the morphology of the MoS2 microflowers and good adhesive capabilities of the alginate binder. Furthermore, we report a Na-ion fuel cell using the MoS2 microflower anode with Na3V2O2x(PO4)2F3−2x/C as a cathode material.

Na+/Vacancy Disordered P2-Na0.67Co1–xTixO2: High-Energy and High-Power Cathode Materials for Sodium Ion Batteries

Although sodium ion batteries (NIBs) have gained wide interest, their poor energy density poses a serious challenge for their practical applications. Therefore, high-energy-density cathode materials are required for NIBs to enable the utilization of a large amount of reversible Na ions. This study presents a P2-type Na0.67Co1-xTixO2 (x < 0.2) cathode with an extended potential range higher than 4.4 V to present a high specific capacity of 166 mAh g-1. A group of P2-type cathodes containing various amounts of Ti is prepared using a facile synthetic method. These cathodes show different behaviors of the Na+/vacancy ordering. Na0.67CoO2 suffers severe capacity loss at high voltages due to irreversible structure changes causing serious polarization, while the Ti-substituted cathodes have long credible cycleability as well as high energy. In particular, Na0.67Co0.90Ti0.10O2 exhibits excellent capacity retention (115 mAh g-1) even after 100 cycles, whereas Na0.67CoO2 exhibits negligible capacity retention (<10 mAh g-1) at 4.5 V cutoff conditions. Na0.67Co0.90Ti0.10O2 also exhibits outstanding rate capabilities of 108 mAh g-1 at a current density of 1000 mA g-1 (7.4 C). Increased sodium diffusion kinetics from mitigated Na+/vacancy ordering, which allows high Na+ utilization, are investigated to find in detail the mechanism of the improvement by combining systematic analyses comprising TEM, in situ XRD, and electrochemical methods.

A high rate and stable electrode consisting of a Na3V2O2X(PO4)2F3−2X–rGO composite with a cellulose binder for sodium-ion batteries

Sodium ion batteries are a promising alternative to conventional lithium-ion batteries, mostly for large scale energy storage applications. In this paper, we report sodium vanadium oxy-fluorophosphate as a cathode material for sodium-ion batteries with 8.0 wt% reduced graphene oxide (rGO), synthesized via solid state reaction followed by a hydrothermal method. The newly reported Na3V2O2X(PO4)2F3−2X–rGO (NVOPF–rGO) composite with a hydrophilic carboxymethyl cellulose sodium (CMC-Na) binder shows enhanced rate performance and highly stable cyclability; it delivers a stable reversible capacity of 108 mA h g−1 in a sodium half-cell, and it exhibits 98% capacity retention at a 0.1C rate over 250 cycles. Furthermore, the as-prepared NVOPF–rGO composite exhibits discharge capacities of 98 mA h g−1 and 64 mA h g−1 at 0.2C and 2C rates, respectively, in a full-cell configuration with a NaTi2(PO4)3–MWCNT (NTP–M) anode for 1000 cycles.

A multi-element doping design for a high-performance LiMnPO4 cathode via metaheuristic computation

Low-level doping of electrode materials is known to be a common and simple method that can be used to improve electrode performance. However, multi-element doping compositions have generally been confined to the empirical intuition of researchers via trial-and-error. Here we propose a more systematic approach to designing multi-element doping compositions for electrode materials via a non-dominated sorting genetic algorithm (NSGA-II)-based computation. LiMnPO4 was selected to demonstrate our strategy not only because of its promising features such as a high operating voltage, comparable capacity, and structural stability, but also because it is known for insufficient electrochemical performance with poor reversibility and rate capability. In this study, a NSGA-II was employed to determine the optimum multi-element doping composition at the Mn site of olivine-structured LiMnPO4 through six consecutive generations, each of which contained 25 dopant sets that finally led to the pinpointing of two potential candidates for a multi-element doped LiMnPO4. The applicability of this strategy could be expanded to the discovery of a number of advanced electrode materials that would be useful in the field of battery research.

Enhancing the Sequential Conversion‐Alloying Reaction of Mixed Sn–S Hybrid Anode for Efficient Sodium Storage by a Carbon Healed Graphene Oxide

To date, the possible depletion of lithium resources has become relevant, giving rise to the interest in Na-ion batteries (NIBs) as promising alternatives to Li-ion batteries. While extensive investigations have examined various transition metal oxides and chalcogenides as anode materials for NIBs, few of these have been able to utilize their high specific capacity in sodium-based systems because of their irreversibility in a charge/discharge process. Here, the mixed Sn-S nanocomposites uniformly distributed on reduced graphene oxide are prepared via a facile hydrothermal synthesis and a unique carbothermal reduction process, producing ultrafine nanoparticle with the size of 2 nm. These nanocomposites are experimentally confirmed to overcome the intrinsic drawbacks of tin sulfides such as large volume change and sluggish diffusion kinetics, demonstrating an outstanding electrochemical performance: an excellent specific capacity of 1230 mAh g-1 , and an impressive rate capability (445 mAh g-1 at 5000 mA g-1 ). The electrochemical behavior of a sequential conversion-alloying reaction for the anode materials is investigated, revealing both the structural transition and the chemical state in the discharge/charge process. Comprehension of the reaction mechanism for the mixed Sn-S/rGO hybrid nanocomposites makes it a promising electrode material and provides a new approach for the Na-ion battery anodes.