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Nurzhan Umirov,서덕호,김태근,김향연,김성수 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.71 No.-
This paper reports an electrochemically highly reversible Si–Ni alloy based electrode through themicrostructure and composition analysis using XRD and HR-TEM combined with EDS. Nano-Si( 200 nm) embedded in the inactive NiSi2/NiSi matrix synthesized using industrial-scale rapidsolidification process (RSP). In addition, comprehensive analysis of HR-TEM images, dQ/dV and OCV plotsprovides powerful insights into the cycle life degradation of Si-alloys caused by the material state changeupon cycling.
Umirov, Nurzhan,Yamada, Yuto,Munakata, Hirokazu,Kim, Sung-Soo,Kanamura, Kiyoshi Elsevier 2019 Journal of Electroanalytical Chemistry Vol.855 No.-
<P><B>Abstract</B></P> <P>Attractive electrochemical properties of Li<SUB>4</SUB>Ti<SUB>5</SUB>O<SUB>12</SUB> (LTO) as an anode material for lithium-ion batteries originate primarily from the lithium-ion diffusion behavior in the crystal lattice. Therefore, it is extremely important to understand the inherent material properties that are favorable for superior kinetic performance. Here we report on the intrinsic electrochemical properties of LTO without the influence of inactive electrode components (e.g., binder, conductive agent) using single-particle measurement technique. Electrochemical analysis revealed an exceptionally high rate capability of a single LTO particle compared to the conventional LTO-based electrode. In particular, a single LTO particle demonstrates capacity retention of 88% even at 440 C-rate, while conventional LTO-based electrode shows a two-fold decrease in capacity at 30 C-rate, though it is temperature dependent. Particular attention is paid to determine the correlation of phase transition behavior in a single LTO particle with activation energies of exchange current (<I>i</I> <SUB> <I>o</I> </SUB>), charge transfer resistance (<I>R</I> <SUB> <I>ct</I> </SUB>) at the electrode/electrolyte interface, and diffusivity (<I>D</I>) of lithium-ion in the lattice obtained by single-particle measurement technique.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The intrinsic properties of LTO were investigated by single particle measurement. </LI> <LI> Single LTO particle shows outstanding rate capability vs. composite LTO electrode. </LI> <LI> Activation energies of <I>i</I> <SUB> <I>o</I> </SUB>, <I>R</I> <SUB> <I>ct</I> </SUB>, and <I>D</I> evaluated in the range of −10 °C–80 °C. </LI> <LI> LTO reaction is single-phase rather than two-phase at certain temperatures. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
A porous Si-based alloy as the promissing anode material for high-performance Li-ion battery
( Nurzhan Umirov ),김성수,연지수 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0
A porous structured Si-based alloy comprising Ni, Al, Ti (Si-NAT alloy) was successfully prepared using the melt-spinning technique followed by acid treatment. The morphology and surface area of the porous Si-NAT alloy was evaluated by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) method. As prepared porous Si-NAT alloy has 15 times larger surface area, compared to the rigid sample (untreated). Improved electronic conductivity of the Si-NAT alloy was enabled due to the formation of inactive matrix along with the porous structure, which buffer the stress repeatedly generated by the volume changes during the lithiation/delithiation process. The porous Si-NAT alloy shows stable cycle performance over 30 cycles without severe capacity degradation. A galvanostatic intermittent titration technique (GITT) and single-particle measurement provided the detailed insight into the internal properties of the porous Si-NAT alloy.
Ni added Si-Al Alloys with Enhanced Li<sup>+</sup> Storage Performance for Lithium-Ion Batteries
Umirov, Nurzhan,Seo, Deok-Ho,Jung, Kyu-Nam,Kim, Hyang-Yeon,Kim, Sung-Soo The Korean Electrochemical Society 2019 Journal of electrochemical science and technology Vol.10 No.1
Here, we report on nanocrystalline Si-Al-M (M = Fe, Cu, Ni, Zr) alloys for use as an anode for lithium-ion batteries, which were fabricated via a melt-spinning method. Based on the XRD and TEM analyses, it was found that the Si-Al-M alloys consist of nanocrystalline Si grains surrounded by an amorphous matrix phase. Among the Si-Al-M alloys with different metal composition, Ni-incorporated Si-Al-M alloy electrode retained the high discharge capacity of 2492 mAh/g and exhibited improved cyclability. The superior $Li^+$ storage performance of Si-Al-M alloy with Ni component is mainly responsible for the incorporated Ni, which induces the formation of ductile and conductive inactive matrix with crystalline Al phase, in addition to the grain size reduction of active Si phase.
Microalgae-derived hollow carbon-MoS2 composite as anode for lithium-ion batteries
서정철,Nurzhan Umirov,박승빈,이규복,김성수 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.79 No.-
We developed a novel composite structure of MoS2 and naturally derived carbon as anode materials forlithium-ion batteries by using microalgae as both source materials and templates for nitrogen-dopedhollow carbon with three dimensional internal structures. The microalgae-derived carbon performed theroles as conducting matrix and template for vertically stacked MoS2 nanosheets. The electrochemicalperformance of microalgae-derived carbon-MoS2 composite materials evaluated in half-cell systemagainst lithium metal electrode secured capacity of 300 mA h/g after 880 cycles at current density of 5 A/g. We ascribe the excellent cycle performance to the unique structure of hollow spherical microalgae-derived carbon with rich inner structures and naturally doped nitrogen, which consequentially facilitatefast lithium ion transport. This kind of structuring strategy is advantageous in terms of utilizing naturallycreated structures of microbes with complexed inner organelles and trace of heteroatoms, not to mentionin respect of producing value added material from biomass residues.
Vapor deposition of Polyimide for LIB binder
박교리,( Nurzhan Umirov ),정한진,이경진,김성수 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1
When forming a lithium battery, the active material particles and polymer binder materials are mixed to form a slurry, and applied to a metal current collector. For the slurry solvent, N-methyl-2-pyrolidone( NMP) has been received many attentions due to its stability and compatible quality with water. The slurry usually coated on the metal foil, and then evaporated with heat. During this process, coating surface has a void where the solvent was evaporation, and this can reduce the connection between active material and the conductive material. As a result, capacity of the LIB can be decrease. To solve the problem, we use Polyimide(PI) vapor deposition process which can cover the void. PI is thermally stable, so it can improve safety of LIB, and vapor deposition process can get high purity PI film. We coated a slurry on the metal foil and evaporate the solvent, then vapor deposited. The stability of the PI can provide safety of LIB, and also can cover voids which cause low performance.