Si-Jin Kim

Cubic and octahedral Cu2O nanostructures as anodes for lithium-ion batteries

Well-defined nanostructured electrodes are known to have improved lithium ion reaction properties for lithium-ion batteries. Herein, we prepared shape-controlled Cu2O nanostructures as an anode material using ascorbic acid as a reducing agent with and without polyvinylpyrrolidone (PVP) as a surfactant. Using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction methods, we observed that the sample prepared in the absence of PVP exhibited cubes with dominant {100} facets, whereas octahedral Cu2O nanostructures with dominant {111} facets were formed in the presence of PVP. During the charge–discharge process, an octahedron-shaped Cu2O nanostructured electrode having {111} facets favourable for lithium ion transport revealed an enhanced conversion reaction mechanism with high reversible capacity and high rate cycling performance, due to its low charge transfer resistance and high lithium ion diffusion coefficient.

In Situ Synthesis and Characterization of Ge Embedded Electrospun Carbon Nanostructures as High Performance Anode Material for Lithium-Ion Batteries

While active materials based on germanium (Ge) are considered as a promising alternative anodic electrode due to their relatively high reversible capacity and excellent lithium-ion diffusivity, the quite unstable structural/electrochemical stability and severe volume expansion or pulverization problems of Ge electrodes remain a considerable challenge in lithium ion batteries (LIBs). Here, we present the development of Ge embedded in one-dimensional carbon nanostructures (Ge/CNs) synthesized by the modified in situ electrospinning technique using a mixed electrospun solution consisting of a Ge precursor as an active material source and polyacrylonitrile (PAN) as a carbon source. The as-prepared Ge/CNs exhibit superior lithium ion behavior properties, i.e., highly reversible specific capacity, rate performance, Li ion diffusion coefficient, and superior cyclic stability (capacity retention: 85% at 200 mA g(-1)) during Li alloying/dealloying processes. These properties are due to the high electrical conductivity and unique structures containing well-embedded Ge nanoparticles (NPs) and a one-dimensional carbon nanostructure as a buffer medium, which is related to the volume expansion of Ge NPs. Thus, it is expected that the Ge/CNs can be utilized as a promising alternative anodic material in LIBs.

3-Dimensional TiO2 nanostructure supports and their improved electrochemical properties in methanol electrooxidation

The TiO2 nanostructure support consists of backbones and branches of a rutile phase forming a 3-dimensional structure with high specific surface area. The Pt catalysts on the TiO2 nanostructure supports exhibit much improved electrocatalytic activity and stability toward methanol electrooxidation in comparison with conventional Pt/C.

Mesoporous composite cathode materials prepared from inverse micelle structures for high performance lithium ion batteries

Mesoporous Li4Mn5O12/Li2MnO3 composite cathodes are prepared from inverse micelle structures for high-performance LIBs. The relative ratio of layered Li2MnO3 to spinel Li4Mn5O12 in the composite electrodes could be elaborately controlled as a function of molar ratio of LiNO3 to Mn(NO3)2 (Li/Mn) in the precursor. All Li4Mn5O12/Li2MnO3 composite cathodes exhibit relatively large specific surface areas and mesoporous character, which might be favorable for lithium-ion mobility. The relative ratio of layered Li2MnO3 to spinel Li4Mn5O12 in the composite electrodes were elaborately controlled as a function of molar ratio of LiNO3 to Mn(NO3)2 (Li/Mn) in the precursor. Our results suggest the better cycle performance of Li excess materials with a solid solution of Li4Mn5O12/Li2MnO3 is due to stabilization of the Li2MnO3 structure by addition of a layered component.

In situ formation of MoS2/C nanocomposite as an anode for high-performance lithium-ion batteries

Anode materials with excellent electrochemical properties as an alternative to carbon-based structures are suggested for advanced high-performance lithium-ion batteries. Here, composites containing MoS2 and carbon (MoS2/C) were in situ synthesized via heat treatment at 700 °C under a CH4 atmosphere with varying reaction times. XRD, Raman, XPS, and TEM data show that the MoS2/C composites consist of crystalline MoS2 and an amorphous carbon phase and show a homogeneous distribution of curved and bent MoS2 particles with a carbon matrix. In particular, the MoS2/C composite with an optimal content of the amorphous carbon phase exhibits relatively an excellent performance in lithium-ion batteries, facilitating the lithiation/delithiation process in MoS2 as an electroactive material.

Synthesis of Ge/C composites as anodes using glucose as a reductant and carbon source for lithium-ion batteries

Ge-based materials as anodes in lithium ion batteries (LIBs) having a large theoretical reversible capacity are needed to overcome the unstable structural and electrochemical properties and pulverization of the electrodes for high-performance LIBs. Here, we synthesized Ge/C composites as anodes for use in LIBs via heating a mixture of GeO2 powder and glucose as both a reductant and carbon source at 900 °C under a nitrogen atmosphere. The data from X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) shows that the as-prepared samples consist of crystalline Ge particles and an amorphous carbon phase. Compared to pure Ge, the Ge/C samples exhibit discharge capacities of ∼627.1 mA h g−1, improved cyclability, and excellent rate properties at a current of 3200 mA g−1.

Synthesis of Pt-Rich@Pt–Ni alloy core–shell nanoparticles using halides

We demonstrated the synthesis of Pt–Ni alloy core–shell nanoparticles (NPs) via a one-pot thermal decomposition method, optimized by variation of the concentration of cetyltrimethylammonium chloride (CTAC) and reaction time. The samples prepared without CTAC and in 30 mM CTAC at 250 °C for 180 min exhibited the formation of single Pt-rich phases between metallic phases. With increasing CTAC concentrations (60–120 mM) at a constant temperature and time (250 °C for 180 min), the products contained both Pt-rich and Pt–Ni alloy phases, consisting of a Pt-rich core with a Pt–Ni alloy shell (Pt-rich@Pt–Ni), in contrast to the single Pt-rich phases prepared at low concentrations or in the absence of CTAC. As the reaction time increased from 10 to 180 min in 60 mM CTAC at 250 °C, the Pt-rich NPs were observed to grow in the initial stage, i.e. until a critical reaction time of 60 min, with subsequent formation of the Pt–Ni alloy phase on top of the as-formed Pt-rich NPs. The morphology and structure of the as-prepared NPs were characterized using TEM, EDX and XRD.

Reduction of NO with Fe(II) and subsequent regeneration of Fe(II) in a fuel cell

We report complete reduction reaction of NO into N2 by oxidizing Fe2+ into Fe3+. To regenerate Fe2+ as a NO absorbent from Fe3+, the H2–Fe3+ fuel cell supplied by Fe3+-containing solution at the cathode is utilized producing maximum power density of 110 mW cm−2 at 70 °C.

Micro-patterned 3D Si electrodes fabricated using an imprinting process for high-performance lithium-ion batteries

To overcome the volumetric expansion of Si used as an anode in lithium-ion batteries (LIBs), we propose 3D Si electrode structures formed on patterned Cu current collectors designed from metal molds fabricated using wire electrical discharge machining (WEDM). The line- and check-patterned Cu current collectors with microscale periods for LIBs are prepared using an imprinting technique with patterned metal molds fabricated using the WEDM process. The line- and check-patterned Si thin-film and powder-type electrodes as anodes are fabricated using radio frequency magnetron sputtering deposition method and conventional slurry casting process, respectively. The morphology of the Si electrodes before and after the cycling process is characterized using optical microscopy and scanning electron microscopy. The electrochemical properties of the Si electrodes are evaluated using a multi-channel battery tester and electrochemical impedance analyzer. In particular, the check-patterned Si electrodes exhibit relatively high-capacity and enhanced cycling performance due to the stress relief of the Si anode.Graphical Abstract

TiO 2 Branched Nanostructure Anode Material Prepared by Seeding Method for High-performance Lithium Ion Batteries

We demonstrate rutile TiO2 branched nanostructure (TiO2-BN) electrodes synthesized by seeding method for enhanced lithium intercalation properties. The morphology and crystal- line nature of the TiO2-BN were clearly observed by field-emission transmission electron microscopy and fast Fourier transform pattern. The TiO2-BN electrodes showed excellent capac- ity and high rate performance. The improved lithium-ion intercalation properties of the TiO2- BN may be attributed to relatively large specific surface area and short transport distance of the branched nanostructure.