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도칠훈,Angathevar Veluchamy,Duck-Jun Lee,Jung-Hoon Lee,진봉수,문성인,Cheol-Wan Park,김동원 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.5
The electrochemical performances of anode composites comprising elemental silicon (Si), silicon monoxide (SiO),and graphite (C) were investigated. The composite devoid of elemental silicon (SiO:C = 1:1) and its carbon coated composite showed reduced capacity degradation with measured values of 606 and 584 mAh/g at the fiftieth cycle. The capacity retention nature when the composites were cycled followed the order of Si:SiO:C = 3:1:4 < Si:SiO:C =2:2:4 < SiO:C = 1:1 < SiO:C = 1:1 (carbon coated). A comparison of the capacity retention properties for the composites in terms of the silicon content showed that a reduced silicon content increased the stability of the composite electrodes. Even though the carbon-coated composite delivered low capacity during cycling compared to the other composites, its low capacity degradation made the anode a better choice for lithium ion batteries.
Doh, Chil-Hoon,Veluchamy, Angathevar,Lee, Duck-Jun,Lee, Jung-Hoon,Jin, Bong-Soo,Moon, Seong-In,Park, Cheol-Wan,Kim, Dong-Won Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.5
The electrochemical performances of anode composites comprising elemental silicon (Si), silicon monoxide (SiO), and graphite (C) were investigated. The composite devoid of elemental silicon (SiO:C = 1:1) and its carbon coated composite showed reduced capacity degradation with measured values of 606 and 584 mAh/g at the fiftieth cycle. The capacity retention nature when the composites were cycled followed the order of Si:SiO:C = 3:1:4 < Si:SiO:C = 2:2:4 < SiO:C = 1:1 < SiO:C = 1:1 (carbon coated). A comparison of the capacity retention properties for the composites in terms of the silicon content showed that a reduced silicon content increased the stability of the composite electrodes. Even though the carbon-coated composite delivered low capacity during cycling compared to the other composites, its low capacity degradation made the anode a better choice for lithium ion batteries.
Doh, Chil-Hoon,Veluchamy, Angathevar,Oh, Min-Wook,Han, Byung-Chan The Korean Electrochemical Society 2011 Journal of electrochemical science and technology Vol.2 No.3
The formation of Li-Si-O phases, $Li_4SiO_4$ and $Li_2SiO_3$ from the starting materials SiO and $Li_2O$ are analyzed using Vienna Ab-initio Simulation (VASP) package and the total energies of Li-Si-O compounds are evaluated using Projector Augmented Wave (PAW) method and correlated the structural characteristics of the binary system SiO-$Li_2O$ with experimental data from electrochemical method. Despite $Li_2SiO_3$ becomes stable phase by virtue of lowest formation energy calculated through VASP, the experimental method shows presence of $Li_4SiO_4$ as the only product formed when SiO and $Li_2O$ reacts during slow heating to reach $550^{\circ}C$ and found no evidence for the formation of $Li_2SiO_3$. Also, higher density of $Li_4SiO_4$(2.42 g $ml^{-1}$) compared to the compositional mixture $1SiO_2-2Li_2O$ (2.226 g $ml^{-1}$) and better cycle capacity observed through experiment proves that $Li_4SiO_4$ as the most stable anode supported by better cycleabilityfor lithium ion battery remains as paradox from the point of view of VASP calculations.
Thermal Behavior of LixCoO2 Cathode and Disruption of Solid Electrolyte Interphase Film
도칠훈,Dong-Hun Kim,Jung-Hun Lee,Duck-Jun Lee,진봉수,김현수,문성인,황영기,Angathevar Veluchamy 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.4
Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and ion chromatography(IC) were employed to analyze the thermal behavior of LixCoO2 cathode material of lithium ion battery. The mass loss peaks appearing between 60 and 125 oC in TGA and the exothermic peaks with 4.9 and 7.0 J/g in DSC around 75 and 85 oC for the LixCoO2 cathodes of 4.20 and 4.35 V cells are explained based on disruption of solid electrolyte interphase (SEI) film. Low temperature induced HF formation through weak interaction between organic electrolyte and LiF is supposed to cause carbonate film disruption reaction, Li2CO3 + 2HF → 2LiF + CO2 + H2O. The different spectral DSC/TGA pattern for the cathode of 4.5 V cell has also been explained. Presence of ionic carbonate in the cathode has been identified by ion chromatography and LiF reported by early researchers has been used for explaining the film SEI disruption process. The absence of mass loss peak for the cathode washed with dimethyl carbonate (DMC) implies ionic nature of the film. The thermal behavior above 150 oC has also been analyzed and presented.
Doh, Chil-Hoon,Kim, Dong-Hun,Lee, Jung-Hun,Lee, Duck-Jun,Jin, Bong-Soo,Kim, Hyun-Soo,Moon, Seong-In,Hwang, Young-Gi,Veluchamy, Angathevar Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.4
Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and ion chromatography(IC) were employed to analyze the thermal behavior of $Li_xCoO_2$ cathode material of lithium ion battery. The mass loss peaks appearing between 60 and 125 ${^{\circ}C}$ in TGA and the exothermic peaks with 4.9 and 7.0 J/g in DSC around 75 and 85 ${^{\circ}C}$ for the $Li_xCoO_2$ cathodes of 4.20 and 4.35 V cells are explained based on disruption of solid electrolyte interphase (SEI) film. Low temperature induced HF formation through weak interaction between organic electrolyte and LiF is supposed to cause carbonate film disruption reaction, $Li_2CO_3\;+\;2HF{\rightarrow}\;2LiF\;+\;CO_2\;+\;H_2O$. The different spectral DSC/TGA pattern for the cathode of 4.5 V cell has also been explained. Presence of ionic carbonate in the cathode has been identified by ion chromatography and LiF reported by early researchers has been used for explaining the film SEI disruption process. The absence of mass loss peak for the cathode washed with dimethyl carbonate (DMC) implies ionic nature of the film. The thermal behavior above 150 ${^{\circ}C}$ has also been analyzed and presented.
Effect of Silicon Content over Fe-Cu-Si/C Based Composite Anode for Lithium Ion Battery
Doh, Chil-Hoon,Shin, Hye-Min,Kim, Dong-Hun,Chung, Young-Dong,Moon, Seong-In,Jin, Bong-Soo,Kim, Hyun-Soo,Kim, Ki-Won,Oh, Dae-Hee,Veluchamy, Angathevar Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.2
Two different anode composite materials comprising of Fe, Cu and Si prepared using high energy ball milling (HEBM) were explored for their capacity and cycling behaviors. Prepared powder composites in the ratio Cu:Fe:Si = 1:1:2.5 and 1:1:3.5 were characterized through X-Ray diffraction (XRD) and scanning electron microscope (SEM). Nevertheless, the XRD shows absence of any new alloy/compound formation upon ball milling, the elements present in Cu(1)Fe(1)Si(2.5)/Graphite composite along with insito generated Li2O demonstrate a superior anodic behavior and delivers a reversible capacity of 340 mAh/g with a high coulombic efficiency (98%). The higher silicon content Cu(1)Fe(1)Si(3.5) along with graphite could not sustain capacity with cycling possibly due to ineffective buffer action of the anode constituents.