Mass-scalable synthesis of 3D porous germanium–carbon composite particles as an ultra-high rate anode for lithium ion batteries

Ngo, Duc Tung,Le, Hang T. T.,Kim, Chanhoon,Lee, Jae-Young,Fisher, John G.,Kim, Il-Doo,Park, Chan-Jin The Royal Society of Chemistry 2015 ENERGY AND ENVIRONMENTAL SCIENCE Vol.8 No.12

<P>Electrode materials with three-dimensional (3D) mesoporous structures possess superior features, such as a shortened solid-phase lithium diffusion distance, a large pore volume, full lithium ion accessibility, and a high specific area, which can facilitate fast lithium ion transport and electron transfer between solid/electrolyte interfaces. In this work, we introduce a facile synthesis route for the preparation of a 3D nanoarchitecture of Ge coated with carbon (3D-Ge/C) <I>via</I> a carbothermal reduction method in an inert atmosphere. 3D-Ge/C showed excellent cyclability: almost 86.8% capacity retention, corresponding to a charge capacity of 1216 mA h g<SUP>−1</SUP> even after 1000 cycles at a 2C-rate. Surprisingly, the high average reversible capacity of 1122 mA h g<SUP>−1</SUP> was maintained at a high charge rate of 100C (160 A g<SUP>−1</SUP>). Even at an ultrahigh charge rate of 400C (640 A g<SUP>−1</SUP>), an average capacity of 429 mA h g<SUP>−1</SUP> was attained. Further, the full cell composed of a 3D-Ge/C anode and an LiCoO<SUB>2</SUB> cathode exhibited excellent rate capability and cyclability with 94.7% capacity retention over 50 cycles. 3D-Ge/C, which offers a high energy density like batteries as well as a high power density like supercapacitors, is expected to be used in a wide range of electrochemical devices.</P> <P>Graphic Abstract</P><P>A novel, facile synthetic route has been proposed to prepare a 3D nanoarchitecture of Ge coated with carbon (3D-Ge/C) <I>via</I> carbothermal reduction. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5ee02183a'> </P>

Highly porous coral-like silicon particles synthesized by an ultra-simple thermal-reduction method

Ngo, Duc Tung,Le, Hang T. T.,Pham, Xuan-Manh,Jung, Ji-Won,Vu, Ngoc Hung,Fisher, John G.,Im, Won-Bin,Kim, Il-Doo,Park, Chan-Jin The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.6

<P>Porous Si is considered a potential anode material for next-generation Li-ion batteries (LIBs) because of its high specific capacity, low lithiation/delithiation potential, low cost, and environmental friendliness. In this work, we introduce a simplified Mg-thermal-reduction method for the production of mass-scalable coral-like bulk-Si powder with a high surface area (38 m<SUP>2</SUP> g<SUP>−1</SUP>), broad pore-size distribution (2-200 nm), and 3-dimensionally (3D) interconnected Si structure for application in LIBs. The porous, coral-like Si electrode delivered a high reversible capacity of 2451 mA h g<SUP>−1</SUP>, corresponding to ∼70% of the theoretical capacity of Si, at a rate of C/10. After 100 cycles, the porous, coral-like Si electrode maintained a capacity of 1956 mA h g<SUP>−1</SUP>, corresponding to 79.8% of the initial reversible capacity. Importantly, a reasonably high reversible capacity of 614 mA h g<SUP>−1</SUP> was achieved even at a high rate of 10C. These outstanding results demonstrate that the 3D-networked, porous, coral-like Si powder, synthesized <I>via</I> a NaCl-assisted Mg-thermal-reduction process on a stainless-steel plate over a period of one minute, can be employed as a promising anode material for the next generation of high-energy LIBs.</P>

Sintering, Microstructure and Electrical Properties of 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 Lead-free Piezoelectric Ceramics

John G. Fisher,Ha-Young Park,Yeo-Ok Song,Sun-Joong Baek,Hung Vu,Jee-Hoon Kim,Young-Hun Kim,Jong-Sook Lee 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.1

The effect of sintering temperature on the densification, microstructure and structure of 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 lead-free piezoelectric ceramics is assessed. The 0.4(Bi0.5K0.5)TiO3- 0.6BiFeO3 powders were prepared by using the mixed-oxide method and were sintered at temperatures of 1000, 1050 and 1100 C for 1 to 5 hrs. Unlike earlier work, the sintered samples showed high densities even when sintered at 1000 C. X-ray diffraction revealed that the sintered samples shared the same rhombohedral structure as BiFeO3. With increasing sintering temperature, the rhombohedral distortion of the unit cell decreased. In addition to the relaxor-like broad peak around 400 C, a low-temperature dielectric peak was found at temperatures below 190 C by employing a low-frequency sweep down to 10 mHz. The DC conductivity of the 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 sample exhibited three temperature regions with activation energy values of 0.56 eV (T > 500 C), 0.72 eV (400 C < T <200 C) and 0.81 eV (T < 190 C). The characteristic transitions in the conductivity could be related to the N´eel temperature (370 C) and the conductivity anomaly observed at ca. 190 C in BiFeO3.

Use of copper tungsten oxide as a liquid phase sintering aid for barium hexaferrite

John G. Fisher,Phan Gia Le,MENGMENG,허상현,박태진,문별이,박인산,이동규,Wu-Hui Lee 한양대학교 세라믹연구소 2018 Journal of Ceramic Processing Research Vol.19 No.5

The sintering behavior of BaFe12O19 with the addition of one and three weight % of CuWO4 as a liquid phase sintering aidis studied. Samples are sintered in the temperature range 900-1250 oC and the effect of CuWO4 addition on density,microstructure, phase composition and magnetic properties is examined. Compared to BaFe12O19 with no sintering aidaddition, addition of 1 wt % CuWO4 retards densification. Addition of 3 wt % CuWO4 promotes densification at lowersintering temperatures but retards densification at temperatures > 1050 oC. Three wt % CuWO4 addition induces theformation of BaWO4 and Ba3WFe2O9 secondary phases at temperatures ≥ 1100 oC. Addition of CuWO4 causes a decrease insaturation magnetization, remanent magnetization and coercivity.

Influence of Sintering Atmosphere on Abnormal Grain Growth Behaviour in Potassium Sodium Niobate Ceramics Sintered at Low Temperature

Fisher, John G.,Choi, Si-Young,Kang, Suk-Joong L. The Korean Ceramic Society 2011 한국세라믹학회지 Vol.48 No.6

The present study aims to identify the effect of sintering atmosphere [$O_2$, 75$N_2$-25 $H_2$ (mol%) and $H_2$] on microstructural evolution at the relatively low sintering temperature of 1040$^{\circ}C$. Samples sintered in $O_2$ showed a bimodal microstructure consisting of fine matrix grains and large abnormal grains. Sintering in 75 $N_2$ - 25 $H_2$ (mol %) and $H_2$ caused the extent of abnormal grain growth to increase. These changes in grain growth behaviour are explained by the effect of the change in step free energy with sintering atmosphere on the critical driving force necessary for rapid grain growth. The results show the possibility of fabricating $(K_{0.5}Na_{0.5})NbO_3$ at low temperature with various microstructures via proper control of sintering atmosphere.

Preparation of lead-free piezoelectric (K0.5Na0.5)NbO3 nanopowder by a simple aqueous route

John G. Fisher,Kwi-Hak Lee,Won-Jin Moon 한양대학교 세라믹연구소 2020 Journal of Ceramic Processing Research Vol.21 No.1

(K0.5Na0.5)NbO3-based ceramic powders for lead-free piezoelectric applications are usually prepared by solid state synthesis. This generally involves wet ball milling in an organic liquid such as ethanol, which is a drawback for industrial production. In the present work, a method for the preparation of NaNbO3 nanopowders is modified to produce a simple method ofpreparing (K0.5Na0.5)NbO3 nanopowders by an aqueous route. K2CO3, Na2CO3 and NH4[NbO(C2O4)2].xH2O are mixed inwater and dried to form a gel, which is then calcined at temperatures between 400 ~ 650 °C for 1 h. The uncalcined gel andcalcination products are analysed using Thermogravimetric Analysis/Differential Thermal Analysis, X-ray Diffraction, FourierTransform Infrared Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy and Raman Scattering. A single phase tetragonal (K0.5Na0.5)NbO3 nanopowder with a particle size of ~ 30 nm can be produced after calcination at650 °C for 1 h.

Growth of Oriented Thick Films of BaFe<SUB>12</SUB>O<SUB>19</SUB> by Reactive Diffusion

John G. Fisher,Hung Vu,Muhammad Umer Farooq 한국자기학회 2014 Journal of Magnetics Vol.19 No.4

Single crystal growth of BaFe12O19 by the solid state crystal growth method was attempted. Seed crystals of α-Fe₂O₃ were pressed into pellets of BaFe12O19 + 2 wt% BaCO₃ and heat-treated at temperatures between 1150°C and 1250°C for up to 100 hours. Instead of single crystal growth taking place on the seed crystal, BaO diffused into the seed crystal and reacted with it to form a polycrystalline reaction layer of BaFe12O19. The microstructure, chemical composition and structure of the reaction layer were studied using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), x-ray Diffraction (XRD) and micro-Raman scattering and confirmed to be that of BaFe12O19. XRD showed that the reaction layer shows a strong degree of orientation in the (h00)/(hk0) planes in the sample sintered at 1200°C. BaFe12O19 layers with a degree of orientation in the (hk0) planes could also be grown by heat-treating an α-Fe₂O₃ seed crystal buried in BaCO₃ powder.

Use of Vanadium Oxide as a Liquid Phase Sintering Aid for Barium Hexaferrite

John G. Fisher,Phan Gia Le,Hak-Sang Han,Su-Min Jeong,Naomi Karina Cabral de Leon,Alejandro Danies Lopez 한국자기학회 2018 Journal of Magnetics Vol.23 No.3

The use of V₂O5 as a liquid phase sintering aid for BaFe12O19 is studied. Three weight % of V₂O5 is added to a BaFe12O19 powder, samples are sintered at temperatures between 900-1250 °C and the effects of sintering aid addition on densification, microstructure, phase purity and magnetic properties are examined. Compared to BaFe12O19 without sintering aid addition, addition of 3 wt% V₂O5 leads to a moderate improvement in densification behavior. Samples with 3 wt% V₂O5 addition contain considerable amounts of Fe₂O₃ and Ba₃(VO₄)₂ second phases. The BaFe12O19 sample without sintering aid addition has a Magnetization-Field hysteresis loop typical of a hard ferrimagnetic material, whereas the 97 wt% BaFe12O19 - 3 wt% V₂O5 sample has a hysteresis loop with reduced saturation magnetization and coercivity.

Low-Temperature Sintering of Barium Calcium Zirconium Titanate Lead-Free Piezoelectric Ceramics

Fisher, John G.,Lee, Dae-Gi,Oh, Jeong-Hyeon,Kim, Ha-Nul,Nguyen, Dieu,Kim, Jee-Hoon,Lee, Jong-Sook,Lee, Ho-Yong The Korean Ceramic Society 2013 한국세라믹학회지 Vol.50 No.2

The need for lead-free piezoceramics has caused a renewal of interest in $BaTiO_3$-based systems. Recently, it was found that ceramics in the $(Ba,Ca)(Zr,Ti)O_3$ system have properties comparable to those of $Pb(Zr,Ti)O_3$. However, these ceramics require rather high sintering temperatures of $1450-1550^{\circ}C$. In this work, the effect of $TiO_2$ and CuO addition on the sintering behavior, microstructure, dielectric and piezoelectric properties of $(Ba_{0.85}Ca_{0.15})(Zr_{0.1}Ti_{0.9})O_3$ (BCTZ) ceramics will be discussed. BCTZ ceramics were prepared by the mixed oxide route and 1 mol % of $TiO_2$ or CuO was added. Undoped and doped ceramics were sintered at $1350^{\circ}C$ for 1-5 h. CuO was found to be a very effective sintering aid, with samples sintered for 1 h at $1350^{\circ}C$ having a bulk density of 95% theoretical density; however the piezoelectric properties were greatly reduced, probably due to the small grain size.

Prostate Cancer Cell-Specific Cytotoxicity of Sub-Micron Potassium Niobate Powder

Fisher, John G.,Thuan, Ung Trong,Farooq, Muhammad Umer,Chandrasekaran, Gopalakrishnan,Do Jung, Young,Hwang, Eu Chang,Lee, Je-Jung,Lakshmanan, Vinoth-Kumar American Scientific Publishers 2018 Journal of Nanoscience and Nanotechnology Vol.18 No.5

<P>Oxide nanoparticles have numerous potential applications in medicine such as carriers for therapeutic drugs, contrast agents for bio-imaging and targeting agents for tumors. Oxide nanoparticles may also have an inherent cytotoxicity towards cancer cells, as recently found for cerium oxide. KNbO3 nanoparticles have a combination of low toxicity and nonlinear optical properties which make them attractive for use as a bio-imaging material. However, little is known yet about the cytotoxicity of KNbO3 particles towards cancerous cells. In the present work, the cytotoxicity of KNbO3 particles to normal and prostate cancer cell lines is studied. The mixed oxide method is used to prepare KNbO3 powder. Using dynamic light scattering the mean particle diameter of the KNbO3 powder is found to be similar to 500 nm. X-ray diffraction, Fourier transform infra-red spectroscopy and Raman scattering spectroscopy are used to examine the structure of the KNbO3 powder. Powder morphology is examined using scanning electron microscopy. MTT assays of EA. hy926, PC-3 and DU-145 cell lines are carried out to study cell-specific cytotoxicity. KNbO3 sub-micron particles are found to have low toxicity to PC-3 cells, moderate toxicity to EA. hy926 cells and high toxicity to DU-145 cells. A new avenue towards the treatment of prostate cancer may be opened by the cell-specific cytotoxicity of KNbO3.</P>