Hiesang Sohn

Strong Lithium Polysulfide Chemisorption on Electroactive Sites of Nitrogen-Doped Carbon Composites For High-Performance Lithium-Sulfur Battery Cathodes

Despite the high theoretical capacity of lithium-sulfur batteries, their practical applications are severely hindered by a fast capacity decay, stemming from the dissolution and diffusion of lithium polysulfides in the electrolyte. A novel functional carbon composite (carbon-nanotube-interpenetrated mesoporous nitrogen-doped carbon spheres, MNCS/CNT), which can strongly adsorb lithium polysulfides, is now reported to act as a sulfur host. The nitrogen functional groups of this composite enable the effective trapping of lithium polysulfides on electroactive sites within the cathode, leading to a much improved electrochemical performance (1200 mAh g(-1) after 200 cycles). The enhancement in adsorption can be attributed to the chemical bonding of lithium ions by nitrogen functional groups in the MNCS/CNT framework. Furthermore, the micrometer-sized spherical structure of the material yields a high areal capacity (ca. 6 mAh cm(-2)) with a high sulfur loading of approximately 5 mg cm(-2), which is ideal for practical applications of the lithium-sulfur batteries.

Mesoporous carbon-carbon nanotube-sulfur composite microspheres for high-areal-capacity lithium-sulfur battery cathodes.

Lithium-sulfur (Li-S) batteries offer theoretical energy density much higher than that of lithium-ion batteries, but their development faces significant challenges. Mesoporous carbon-sulfur composite microspheres are successfully synthesized by combining emulsion polymerization and the evaporation-induced self-assembly (EISA) process. Such materials not only exhibit high sulfur-specific capacity and excellent retention as Li-S cathodes but also afford much improved tap density, sulfur content, and areal capacity necessary for practical development of high-energy-density Li-S batteries. In addition, when incorporated with carbon nanotubes (CNTs) to form mesoporous carbon-CNT-sulfur composite microspheres, the material demonstrated superb battery performance even at a high current density of 2.8 mA/cm(2), with a reversible capacity over 700 mAh/g after 200 cycles.

Silicon core–hollow carbon shell nanocomposites with tunable buffer voids for high capacity anodes of lithium-ion batteries

Silicon core-hollow carbon shell nanocomposites with controllable voids between silicon nanoparticles and hollow carbon shell were easily synthesized by a two-step coating method and exhibited different charge-discharge cyclability as anodes for lithium-ion batteries. The best capacity retention can be achieved with a void/Si volume ratio of approx. 3 due to its appropriate volume change tolerance and maintenance of good electrical contacts.

High-performance flexible lithium-ion electrodes based on robust network architecture

Highly robust, flexible, binder-free lithium-ion electrodes were fabricated based on interpenetrative nanocomposites of ultra-long CNTs and V2O5 nanowires. Such robust composite-network architecture provides the electrodes with effective charge transport and structural integrity, leading to high-performance flexible electrodes with high capacity, high rate-capability and excellent cycling stability.

Bottom-up synthesis of high surface area mesoporous crystalline silicon and evaluation of its hydrogen evolution performance

As an important material for many practical and research applications, porous silicon has attracted interest for decades. Conventional preparations suffer from high mass loss because of their etching nature. A few alternative routes have been reported, including magnesiothermic reduction; however, pre-formed porous precursors are still necessary, leading to complicated syntheses. Here we demonstrate a bottom-up synthesis of mesoporous crystalline silicon materials with high surface area and tunable primary particle/pore size via a self-templating pore formation process. The chemical synthesis utilizes salt by-products as internal self-forming templates that can be easily removed without any etchants. The advantages of these materials, such as their nanosized crystalline primary particles and high surface areas, enable increased photocatalytic hydrogen evolution rate and extended working life. These also make the mesoporous silicon a potential candidate for other applications, such as optoelectronics, drug delivery systems and even lithium-ion batteries.

Flexible freestanding sandwich-structured sulfur cathode with superior performance for lithium–sulfur batteries

Flexible freestanding sandwich-structured sulfur cathodes are developed for lithium–sulfur batteries, which exhibit excellent cycling stability and rate capability. Moreover, a high areal capacity of ∼4 mA h cm−2 is demonstrated based on this new cathode configuration with high sulfur loading (∼4 mg S cm−2).

Porous spherical carbon/sulfur nanocomposites by aerosol-assisted synthesis: the effect of pore structure and morphology on their electrochemical performance as lithium/sulfur battery cathodes.

Porous spherical carbons (PSCs) with tunable pore structure (pore volume, pore size, and surface area) were prepared by an aerosol-assisted process. PSC/sulfur composites (PSC/S, S: ca.59 wt %) were then made and characterized as cathodes in lithium/sulfur batteries. The relationships between the electrochemical performance of PSC/S composites and their pore structure and particle morphology were systematically investigated. PSC/S composite cathodes with large pore volume (>2.81 cm(3)/g) and pore size (>5.10 nm) were found to exhibit superior electrochemical performance, likely due to better mass transport in the cathode. In addition, compared with irregularly shaped carbon/sulfur composite, the spherical shaped PSC/S composite showed better performance due to better electrical contact among the particles.

All-solid-state lithium-ion batteries with TiS2 nanosheets and sulphide solid electrolytes

Bulk-type all-solid-state lithium-ion batteries (ASLBs) using sulphide solid electrolytes (SEs) are considered as one of the promising alternative batteries because of their ultimate safety and scalable fabrication. However, they suffer from poor ionic contacts between active materials and SEs. Herein, we report, for the first time, the excellent electrochemical performances of sulphide-SE-based bulk-type ASLBs employing TiS2 nanosheets (TiS2-NSs) prepared by scalable mechanochemical lithiation, followed by exfoliation in water under ultrasonication. The TiS2-NS in all-solid-state cells exhibits an enhancement of reversible capacity which is attributed to the SE region in intimate contact with TiS2-NSs. Importantly, an exceptionally superior rate capability of the TiS2-NS compared to that of bulk TiS2 and even ball-milled TiS2, which is attributed to the ultrathin 2D structure (with short Li-ion diffusion length and intimate contacts between the TiS2-NS and SE) and high electronic conductivity, is highlighted.

Robust lithium-ion anodes based on nanocomposites of iron oxide–carbon–silicate

Robust composite particles containing Fe3O4 cores and porous conductive carbon–silicate layers were synthesized using an aerosol-assisted process followed by vapor coating using organosilanol as the precursor. Such unique synthesis enables the composites with high capacity and good cycle performance, and can be extended towards other oxide composites for energy storage.

High-performance aqueous supercapacitors based on hierarchically porous graphitized carbon

Aqueous supercapacitors were fabricated using hierarchically porous graphitized carbon as the anode and metal oxide as the cathode, exhibiting high energy and high power densities for cost-effective energy storage.