Kyeongse Song

α-MnO2 nanowire catalysts with ultra-high capacity and extremely low overpotential in lithium-air batteries through tailored surface arrangement

We here report on very high capacity (11,000 mA h g(-1)), superb rate capability (4500 mA h g(-1) at 5000 mA g(-1)) and high reversibility of Li-air batteries using α-MnO2 NW catalysts mainly associated with their relatively large amount of Mn(3+) exposed on the NW surface and a unique mechanism for deposition of discharge products. Our findings of the unprecedentedly fast Li ion transport and reversible formation-decomposition of discharge products attributed to the modified surface arrangement of α-MnO2 NWs suggest a strategy for achieving high-power Li-air batteries in combination with nano-architecture tailoring.

Tailored Oxygen Framework of Li4Ti5O12 Nanorods for High-Power Li Ion Battery

Here we designed the kinetically favored Li4Ti5O12 by modifying its crystal structure to improve intrinsic Li diffusivity for high power density. Our first-principles calculations revealed that the substituted Na expanded the oxygen framework of Li4Ti5O12 and facilitated Li ion diffusion in Li4Ti5O12 through 3-D high-rate diffusion pathway secured by Na ions. Accordingly, we synthesized sodium-substituted Li4Ti5O12 nanorods having not only a morphological merit from 1-D nanostructure engineering but also sodium substitution-induced open framework to attain ultrafast Li diffusion. The new material exhibited an outstanding cycling stability and capacity retention even at 200 times higher current density (20 C) compared with the initial condition (0.1 C).

Na3V2(PO4)3 particles partly embedded in carbon nanofibers with superb kinetics for ultra-high power sodium ion batteries

We here describe the extraordinary performance of NASICON Na3V2(PO4)3-carbon nanofiber (NVP–CNF) composites with ultra-high power and excellent cycling performance. NVP–CNFs are composed of CNFs at the center part and partly embedded NVP nanoparticles in the shell. We first report this unique morphology of NVP–CNFs for the electrode material of secondary batteries as well as for general energy conversion materials. Our NVP–CNFs show not only a high discharge capacity of ∼88.9 mA h g−1 even at a high current density of 50 C but also ∼93% cyclic retention property after 300 cycles at 1 C. The superb kinetics and excellent cycling performance of the NVP–CNFs are attributed to the facile migration of Na ions through the partly exposed regions of NVP nanoparticles that are directly in contact with an electrolyte as well as the fast electron transfer along the conducting CNF pathways.

Phosphidation of Li4Ti5O12 nanoparticles and their electrochemical and biocompatible superiority for lithium rechargeable batteries

Phosphidated-Li(4)Ti(5)O(12) shows high capacity with a significantly enhanced kinetics opening new possibilities for ultra-fast charge/discharge of lithium rechargeable batteries. The in vitro cytotoxicity test proves its fabulous cell viability, indicating that the toxicity problem of nanoparticles can be also solved by phosphidation.

Tailored materials for high-performance MgB2 wire

High electrical current without dissipation is valuable, not only for power transmission, but also in other fi elds, such as energy storage or high-fi eld magnets for medical applications. The superconductor magnesium diboride (MgB 2 ) has a transition temperature of about 40 K [ 1 ] and thus can be operated without the need for liquid helium, which is expensive. MgB 2 wire made from inexpensive, clean, starting materials will further accelerate the spread of practical superconductor applications. Here we report on an economical way of producing high-performance MgB 2 wire using carbon-encapsulated boron nanopowder and coarse magnesium powder. It was found that carbon encapsulation suppresses surface oxidation, while nanometer-sized boron can be fully reacted with magnesium at low sintering temperature. Ductile magnesium coarse powders are elongated during the cold-working, leading to alignment of voids and enhanced

Comprehensive design of carbon-encapsulated Fe3O4 nanocrystals and their lithium storage properties.

Controlling the bulk and surface structure of metal oxide nanostructures is crucial to obtain superior electronic and electrochemical properties. However, the synthetic or post-treatment techniques for preparing such structures, especially those with complex configurations, still remains a challenge. Herein, we report a completely novel approach-an amorphous carbon coating on the surface coupled with a controlled metal oxidation state in the bulk-via a simple glucose treatment. The bulk and surface structures of iron oxides are controlled by the carbothermal reaction associated with the decomposition of glucose. These novel configurations of iron oxides possess an amorphous carbon layer and ferrous state with high electronic conductivity, which definitely enhances their electrochemical properties compared to pristine iron oxides. Our findings provide an effective solution for the synthesis of complex metal oxide nanostructures, which can pave the way to further expand the electronic or electrochemical applications of metal oxides.

Hollow Sn–SnO2 Nanocrystal/Graphite Composites and Their Lithium Storage Properties

Hollow spheres have been constructed by applying the Kirkendall effect to Sn nanocrystals. This not only accommodates the detrimental volume expansion but also reduces the Li(+) transport distance enabling homogeneous Li-Sn alloying. Hollow Sn-SnO2 nanocrystals show a significantly enhanced cyclic performance compared to Sn nanocrystal alone due to its typical structure with hollow core. Sn-SnO2/graphite nanocomposites obtained by the chemical reduction and oxidation of Sn nanocrystals onto graphite displayed very stable cyclic performance thanks to the role of graphite as an aggregation preventer as well as an electronic conductor.

SnS 3D Flowers with Superb Kinetic Properties for Anodic Use in Next-Generation Sodium Rechargeable Batteries

Tin sulfide (SnS) 3D flowers containing hierarchical nanosheet subunits are synthesized using a simple polyol process. The Li ion cells incorporating SnS 3D flowers exhibit an excellent rate capability, as well as good cycling stability, compared to SnS bulks and Sn nanoparticles. These desirable properties can be attributed to their unique morphology having not only large surface reaction area but also enough space between individual 2D nanosheets, which alleviates the pulverization of SnS.

Polymorphism-induced catalysis difference of TiO2 nanofibers for rechargeable Li–O2 batteries

The polymorphic change of TiO2 nanofiber catalysts from anatase to rutile enabled Li–O2 cells to have higher round-trip efficiency and lower overpotential followed by a better cyclic retention. This is due to enhanced catalytic activity probably associated with the smaller Li+ chemisorption energy and band gap of the rutile phase compared with the anatase phase.

An improved catalytic effect of nitrogen-doped TiO2 nanofibers for rechargeable Li–O2 batteries; the role of oxidation states and vacancies on the surface

This work deals with nitrogen-doped TiO2 nanofibers with increased ionic conductivity and good catalytic activity, as a potential cathode catalyst for lithium–air battery. The electrochemical enhancement with nitrogen-doped TiO2 in comparison with pristine TiO2 could be realized by the changed electronic properties correlated with the evolution of oxygen vacancies altering the surface oxidation state of TiO2. A discharge capacity greater than 11 000 mA h g−1(carbon) and a cyclic retention more than 25 cycles were achieved with the corresponding nitrogen-doped TiO2 catalyst.