Transition metal chalcogenides are promising cathode materials for next-generation battery systems, particularly sodium-ion batteries. Ni₃Co₆S₈-pitch-derived carbon composite microspheres with a yolk-shell structure (Ni₃Co₆S₈@C-YS) were synthesized through a three-step process: spray pyrolysis, pitch coating, and post-heat treatment process. Ni₃Co₆S₈@C-YS exhibited an impressive reversible capacity of 525.2 mA h g^-1 at a current density of 0.5 A g^-1 over 50 cycles when employed as an anode material for sodium-ion batteries. However, Ni₃Co₆S₈ yolk shell nanopowder (Ni₃Co₆S₈-YS) without pitch-derived carbon demonstrated a continuous decrease in capacity during charging and discharging. The superior sodium-ion storage properties of Ni₃Co₆S₈@C-YS were attributed to the pitchderived carbon, which effectively adjusted the size and distribution of nanocrystals. The carbon-coated yolk-shell microspheres proposed here hold potential for various metal chalcogenide compounds and can be applied to various fields, including the energy storage field.

Fe₃O₄/Fe/graphene nanocomposite powder is synthesized by electrical wire explosion of Fe wire and dispersed graphene in deionized water at room temperature. The structural and electrochemical characteristics of the powder are characterized by the field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, field-emission transmission electron microscopy, cyclic voltammetry, and galvanometric discharge-charge method. For comparison, Fe₃O₄/Fe nanocomposites are fabricated under the same conditions. The Fe₃O₄/Fe nanocomposite particles, around 15-30 nm in size, are highly encapsulated in a graphene matrix. The Fe₃O₄/Fe/graphene nanocomposite powder exhibits a high initial charge specific capacity of 878 mA/g and a high capacity retention of 91% (798 mA/g) after 50 cycles. The good electrochemical performance of the Fe₃O₄/Fe/graphene nanocomposite powder is clearly established by comparison of the results with those obtained for Fe₃O₄/Fe nanocomposite powder and is attributed to alleviation of volume change, good distribution of electrode active materials, and improved electrical conductivity upon the addition of graphene.

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• Preparation of magnetic metal and graphene hybrids with tunable morphological, structural and magnetic properties
  Kyunbae Lee, Joonsik Lee, Byung Mun Jung, Byeongjin Park, Taehoon Kim, Sang Bok Lee
  Applied Surface Science.2019; 478: 733.     CrossRef

Tin is one of the most promising anode materials for next-generation lithium-ion batteries with a high energy density. However, the commercialization of tin-based anodes is still hindered due to the large volume change (over 260%) upon lithiation/delithiation cycling. To solve the problem, many efforts have been focused on enhancing structural stability of tin particles in electrodes. In this work, we synthesize tin nano-powders with an amorphous carbon layer on the surface and surroundings of the powder by electrical wire explosion in alcohol-based liquid media at room temperature. The morphology and microstructures of the powders are characterized by scanning electron microscopy, Xray diffraction, Raman spectroscopy, and transmission electron microscopy. The electrochemical properties of the powder for use as an anode material for lithium-ion battery are evaluated by cyclic voltammetry and a galvanometric dischargecharge method. It is shown that the carbon-coated tin nano-powders prepared in hexanol media exhibit a high initial charge specific capacity of 902 mAh/g and a high capacity retention of 89% after 50 cycles.

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• Optimization of carbon coating thickness to prevent crack generation in Sn nanoparticles during charge/discharge process and their electrochemical properties
  Ji-Seub Choi, Yeon-Ju Lee, Hoi-Jin Lee, Gyu-Bong Cho, Jai-Won Byeon, Hyo-Jun Ahn, Ki-Won Kim, Jou-Hyeon Ahn, Kwon-Koo Cho
  Journal of Alloys and Compounds.2020; 843: 155892.     CrossRef
• Fabrication of multilayer graphene-encapsulated Sn/SnO2 nanocomposite as an anode material for lithium-ion batteries and its electrochemical properties
  Ju-Seok Song, Gyu-Bong Cho, Ki-Won Kim, Hyo-Jun Ahn, Hye-Sung Kim, Jou-Hyeon Ahn, Kwon-Koo Cho
  Applied Surface Science.2019; 481: 736.     CrossRef