Browsing by Author "Yongguang, Zhang"

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    Effect of nanosized Mg0.6Ni0.4O prepared by self-propagating high temperature synthesis on sulfur cathode performance in Li/S batteries
    (Powder Technology, 2013-02-01) Zhang, Yongguang; Bakenov, Zhumabay; Zhao, Yan; Konarov, Aishuak; Doan, The Nam Long; Sun, Kyung Eun Kate; Yermukhambetova, Assiya; Chen, P.; Yongguang, Zhang
    Abstract Nanostructured magnesium nickel oxide Mg0.6Ni0.4O was successfully synthesized by self-propagating high temperature synthesis (SHS) followed by heat treatment. The effect of the precursor composition and calcination temperature on the Mg0.6Ni0.4O powder properties was investigated. These particles were used as an additive to prepare S/Mg0.6Ni0.4O composite via ball-milling with sulfur. The composite preparation conditions were optimized to achieve the higher specific surface area without compromising the sample crystallinity. The SEM observation revealed that the sulfur morphology was drastically changed by the Mg0.6Ni0.4O addition, from smooth to rough agglomerated particles. This change has enhanced the electrochemical performance of the composite cathode. Cyclic voltammetry and charge–discharge tests demonstrated enhanced reversibility and high sulfur utilization in a Li/S cell with S/Mg0.6Ni0.4O cathode, delivering about 850mAhg−1 of reversible capacity at the initial cycle. The effect of the Mg0.6Ni0.4O heat treatment temperature on the S/Mg0.6Ni0.4O cycling performance was also investigated. The cathode with Mg0.6Ni0.4O calcined at 700°C exhibited enhanced capacity retention which could be due to its high specific surface area and nanosized structure.
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    Electrochemical performance of carbon-encapsulated Fe3O4 nanoparticles in lithium-ion batteries: morphology and particle size effects
    (Electrochimica Acta, 2016-10-20) Zhang, Yongguang; Li, Yue; Li, Haipeng; Zhao, Yan; Yin, Fuxing; Bakenov, Zhumabay; Yongguang, Zhang
    Abstract Carbon-encapsulated Fe3O4 nanoparticles (Fe3O4@C) with varied microstructures were produced by controlling the relative concentrations of glucose and iron nitrate hydrate in a hydrothermal process, followed by heat treatment in Ar atmosphere. Three Fe3O4@C nanocomposites with different particle sizes (mean diameter 31.2, 45.1 and 55.3nm) and Fe3O4 core size (26.8, 15.4 and 10.3nm) were investigated for lithium storage performance. The Fe3O4@C nanoparticles with 15.4nm Fe3O4 core exhibit excellent initial specific capacity (1215mAhg−1) and significantly improved cycling performance (806mAhg−1 after 100 cycles) and rate capability (573mAhg−1 at current density of 1500mAg−1), in comparison to the other Fe3O4@C composites. This superior performance is attributed to microstructural effects spawned from the pomegranate-like carbon coating architecture of the composite, the appropriate carbon content, and the optimized particle size of Fe3O4@C nanoparticles, which combined suppress the agglomeration and pulverization of Fe3O4 nanoparticle upon cycling and enhance the electrical conductivity of the Fe3O4 anode.
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    One-step synthesis of branched sulfur/polypyrrole nanocomposite cathode for lithium rechargeable batteries
    (Journal of Power Sources, 2012-06-15) Zhang, Yongguang; Bakenov, Zhumabay; Zhao, Yan; Konarov, Aishuak; Doan, The Nam Long; Malik, Muhammad; Paron, Todd; Chen, P.; Yongguang, Zhang
    Abstract A nanostructured sulfur/polypyrrole binary composite was prepared by a simple one-step ballmilling without heat-treatment. High resolution transmission and scanning electronic microscopy showed the formation of a highly developed branched structure consisting of polypyrrole with uniform sulfur coating on its surface. Exclusion of heat-treatment in the composite preparation avoided the sulfur loss; the composite contained 65wt% of sulfur. AC impedance spectroscopy data exhibited remarkable reduction in charge transfer resistance of the composite compared with pristine sulfur. This may be due to the high conductivity and large surface area of polypyrrole. This charge transfer enhancement led to the electrochemical performance improvement of the composite cathode, delivering first discharge capacity of 1320mAhg−1.
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    Preparation of novel network nanostructured sulfur composite cathode with enhanced stable cycle performance
    (Journal of Power Sources, 2014-12-15) Zhang, Yongguang; Zhao, Yan; Bakenov, Zhumabay; Konarov, Aishuak; Chen, P.; Yongguang, Zhang
    Abstract In situ polymerization of acrylonitrile with nano-sulfur particles has been developed as a synthetic route to prepare sulfur/polyacrylonitrile (S/pPAN) composite as a cathode material for lithium/sulfur battery. Transmission electronic microscopy revealed the formation of a highly developed network structure consisting of PAN and sulfur homogeneous mixing at nanosized level, providing the “buffering” space to accommodate the volume change of sulfur upon cycling and retaining the structural integrity preventing the material agglomeration and degradation. Benefiting from this unique structure, the S/pPAN composite cathode demonstrated enhanced reversibility, resulting in a discharge capacity of 1177 mAh g−1 at the second cycle and retained about 100% of this value over 100 cycles at 0.5C. Furthermore, the S/pPAN composite cathode delivered a discharge capacity of 981 mAh g−1 at the 100th cycle at 1C.
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    Synthesis of Hierarchical Porous Sulfur/Polypyrrole/Multiwalled Carbon Nanotube Composite Cathode for Lithium Batteries
    (Electrochimica Acta, 2014-10-10) Zhang, Yongguang; Zhao, Yan; Bakenov, Zhumabay; Tuiyebayeva, Madina; Konarov, Aishuak; Chen, P.; Yongguang, Zhang
    Abstract A novel porous sulfur/polypyrrole/multiwalled carbon nanotube composite (S/PPy/MWNT) was synthesized via in situ polymerization of pyrrole monomer with nano-sulfur and MWNT aqueous suspension followed by a low temperature heat-treatment. Scanning electronic microscopy revealed the formation of a highly hierarchical mesoporous and macroporous structure. High resolution transmission electronic microscopy confirmed homogeneous dispersion of S, PPy and MWNT in the composite. In this composite, polypyrrole with its high adhesion ability to MWNT acts as a conductive binder to connect sulfur and MWNT matrix, as well as absorbs polysulfides into its porous structure positively affecting the composite performance as a cathode in a Li/S cell. The resulting S/PPy/MWNT composite cathode exhibited greatly enhanced cyclability and delivered a reversible discharge capacity of 751 mAh g−1 after 100 cycles at 0.2C.