• 한국전기전자재료학회논문지
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• 제19권7호
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• pp.636-643
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• 2006

Si-C materials were synthesized by the heating the mixture of silicon and polyvinylidene fluoride (PVDF). The electrochemical properties of the Si-C materials as the high capacitive anode materials of lithium secondary batteries were evaluated by the galvanostatic charge-discharge test through 2032 type $Si-C{\mid}Li$ coin cells. Charge-discharge tests were performed at C/10 hour rate(C = 372 mAh/g). Initial discharge and charge capacities of $Si-C{\mid}Li$ cell using a Si-C material derived from PVDF(20wt.%) were found to be 1,830 and 526 mAh/g respectively. The initial discharge-charge characteristics of the developed Si-C electrode were analyzed by the electrochemical galvanostatic test adopting the capacity limited charge cut-off condition(GISOC). The range of reversible specific capacity IIE(intercalation efficiency at initial discharge-charge) and IICs(surface irreversible specific capacity) were 216 mAh/g, 68 % and 31 mAh/g, respectively.

• Advances in materials Research
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• 제8권1호
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• pp.37-46
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• 2019

Electrochemical double layer capacitors (EDLCs) which are fabricated using carbon based electrodes have been emerging at an alarming rate to fulfill the energy demand in the present day world. Activated charcoal has been accepted as a very suitable candidate for electrodes but its cost is higher than natural graphite. Present study is about fabrication of EDLCs using composite electrodes with activated charcoal and Sri Lankan natural graphite as well as a gel polymer electrolyte which is identified as a suitable substitute for liquid electrolytes. Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Galvanostatic Charge Discharge test were done to evaluate the performance of the fabricated EDLCs. Amount of activated charcoal and natural graphite plays a noticeable role on the capacity. 50 graphite : 40 AC : 10 PVdF showed the optimum single electrode specific capacity value of 15 F/g. Capacity is determined by the cycling rate as well as the potential window within which cycling is being done. Continuous cycling resulted an average single electrode specific capacity variation of 48 F/g - 16 F/g. Capacity fading was higher at the beginning. Later, it dropped noticeably. Initial discharge capacity drop under Galvanostatic Charge Discharge test was slightly fast but reached near stable upon continuous charge discharge process. It can be concluded that initially some agitation is required to reach the maturity. However, the results can be considered as encouraging to initiate studies on EDLCs using Sri Lankan natural graphite.

• Bulletin of the Korean Chemical Society
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• 제27권8호
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• pp.1175-1180
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• 2006

Si-C composites were prepared by the carbonization of polyaniline (PAn) coated on silicone powder. The physical and electrochemical properties of the Si-C composites were characterized by particle-size analysis, X-ray diffraction, scanning electron microscopy, and battery electrochemical tests. The average particle size of Si was increased by the coating of Pan but somewhat reduced by the carbonization to give silicone-carbon composites. The co-existence of crystalline silicone and amorphous-like carbon was confirmed by XRD analyses. SEM photos showed that the silicone particles were well covered with carbonaceous materials, depending on the PAn content. Si-C$\mid$Li cells were fabricated using the Si-C composites and tested using galvanostatic charge-discharge. Si-C$\mid$Li cells gave better electrochemical properties than Si|Li cells. Si-C$\mid$Li cells using Si-C from HCl-undoped precursor PAn showed better electrochemical properties than precursor PAn doped in HCl. The addition of an electrolyte containing 4-fluoroethylene carbonate (FEC) increased the initial discharge capacity. Also, another electrochemical test, the galvanostatic charge-discharge test with GISOC (gradual increasing of the state of charge) was carried out. Si-C(Si:PAn = 50:50 wt. ratio)|Li cell showed 414 mAh/g of reversible specific capacity, 75.7% of IIE (initial intercalation efficiency), 35.4 mAh/g of IICs (surface irreversible specific capacity).

• Advances in Energy Research
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• 제5권3호
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• pp.219-226
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• 2017

Electrochemical double layer capacitors (EDLCs) have received a tremendous interest due to their suitability for diverse applications. They have been fabricated using different carbon based electrodes including activated carbons, single walled/multi walled carbon nano tubes. But, graphite which is one of the natural resources in Sri Lanka has not been given a considerable attention towards using for EDLCs though it is a famous carbon material. On the other hand, EDLCs are well reported with various liquid electrolytes which are associated with numerous drawbacks. Gel polymer electrolytes (GPE) are well known alternative for liquid electrolytes. In this paper, it is reported about an EDLC fabricated with a nano composite polyethylene oxide based GPE and two Sri Lankan graphite based electrodes. The composition of the GPE was [{(10PEO: $NaClO_4$) molar ratio}: 75wt.% PC] : 5 wt.% $TiO_2$. GPE was prepared using the solvent casting method. Two graphite electrodes were prepared by mixing 85% graphite and 15% polyvinylidenefluoride (PVdF) in acetone and casting n fluorine doped tin oxide glass plates. GPE film was sandwiched in between the two graphite electrodes. A non faradaic charge discharge mechanism was observed from the Cyclic Voltammetry study. GPE was stable in the potential windows from (-0.8 V-0.8 V) to (-1.5 V-1.5 V). By increasing the width of the potential window, single electrode specific capacity increased. Impedance plots confirmed the capacitive behavior at low frequency region. Galvanostatic charge discharge test yielded an average discharge capacity of $0.60Fg^{-1}$.

• 전기화학회지
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• 제9권3호
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• pp.107-112
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• 2006

실리콘 분말에 polyaniline(PAn)을 중합하고 탄화하여 Si-C재료를 개발하고 물리적 특성 및 전기화학적 특성을 분석하였다. 평균입도는 PAn의 중합으로 증가하였으며 탄화로 일부 감소하였다. XRD분석으로 결정질의 실리콘과 비결정성의 탄소 재료가 공존함을 확인 하였다. Si-PAn 전구체로 부터 개발한 Si-C 재료를 이용한 Si-C|Li cell은 Si|Li cell에 비하여 우수한 특성을 나타내었으며, 탄소 전구체인 PAn의 HCl 탈도핑에 의해 전기화학적 특성을 개선할 수 있었다. 전해액 중 FEC 첨가한 경우 초기 방전 용량이 증가하였다. GISOC시험으로 구한 가역 비용량 범위는 Si-C(Si:PAn=50:50wt. ratio)|Li 전지의 경우 약 414mAh/g를 나타내었으며, 가역 범위에 대한 초기 충방전의 intercalation 효율(IIE)는 75.7%였으며, 표면 비가역 비용량은 35.4mAh/g을 나타내었다.

• Advances in Energy Research
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• 제8권1호
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• pp.41-57
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• 2022

Electrochemical double-layer capacitors (EDLCs) based on solid polymer electrolytes (SPEs) have gained an immense recognition in the present world due to their unique properties. This study is about preparing and characterizing EDLCs using a natural rubber (NR) based SPE with natural graphite (NG) electrodes. NR electrolyte was consisted with 49% methyl grafted natural rubber (MG49) and zinc trifluoromethanesulfonate ((Zn(CF₃SO₃)₂-ZnTF). It was characterized using electrochemical impedance spectroscopy (EIS) test, dc polarization test and linear sweep voltammetry (LSV) test. NG electrodes were made using a slurry of NG and acetone. EIS test, cyclic voltammetry (CV) test and galvanostatic charge discharge (GCD) test have been done to characterize the EDLC. Optimized electrolyte composition with NR: 0.6 ZnTF (weight basis) exhibited a conductivity of 0.6 x 10^-4 Scm^-1 at room temperature. Conductivity was predominantly due to ions. The electrochemical stability window was found to be from 0.25 V to 2.500 V. Electrolyte was sandwiched between two identical NG electrodes to fabricate an EDLC. Single electrode specific capacitance was about 2.26 Fg^-1 whereas the single electrode discharge capacitance was about 1.17 Fg^-1. The EDLC with this novel NR-ZnTF based SPE evidences its suitability to be used for different applications with further improvement.

• Advances in Energy Research
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• 제7권1호
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• pp.21-34
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• 2020

Energy storage devices have received a keen interest throughout the world due to high power consumption. A large number of research activities are being conducted on electrochemical double layer capacitors (EDLCs) because of their high power density and higher energy density. In the present study, an EDLC was fabricated using natural graphite based electrodes and ionic liquid (IL) based gel polymer electrolyte (GPE). The IL based GPE was prepared using the IL, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF) with the polymer poly(vinyl chloride) (PVC) and the salt magnesium trifluoromethanesulfonate (Mg(CF₃SO₃)₂ - MgTF). GPE was characterized by electrochemical impedance spectroscopy (EIS), DC polarization test, linear sweep voltammetry (LSV) test and cyclic voltammetry (CV) test. The maximum room temperature conductivity of the sample was 1.64 × 10^-4 Scm^-1. The electrolyte was purely an ionic conductor and the anionic contribution was prominent. Fabricated EDLC was characterized by EIS, CV and galvanostatic charge discharge (GCD) tests. CV test of the EDLC exhibits a single electrode specific capacitance of 1.44 Fg^-1 initially and GCD test gives 0.83 Fg^-1 as initial single electrode specific discharge capacitance. Moreover, a good stability was observed for prolonged cycling and the device can be used for applications with further modifications.

• 디지털콘텐츠학회 논문지
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• 제18권6호
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• pp.1199-1205
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• 2017

산업화의 급격한 진전으로 인한 에너지 소비가 세계적으로 증가되면서 새로운 에너지 저장 소자에 대한 개발의 필요성이 늘고 있으며, 이에 빠른 충 방전 시간과 반영구적으로 사용이 가능한 슈퍼커패시터에 대한 연구가 활발히 진행 중이다. 본 연구에서는 수열반응(Hydrothermal) 제조법을 이용하여 기판인 탄소섬유(carbon cloth)에 비정질의 이산화망간($MnO_2$)을 도포하여 슈퍼커패시터를 제작하였다. 탄소섬유에 Fe 이온이 도핑 된 이산화망간을 결합한 전극으로 이루어진 슈퍼커패시터의 특성 파악을 위해 전기주사현미경(SEM), X-ray 회절분석(XRD), 그리고 X-ray 분광 분석(EDX)을 실시하였다. 또한, 1 M의 $Na_2SO_4$ 전해질에서 순환전압전류법(Cyclic Voltammetry)과 정전류충전법(Galvanostatic charge-discharge)을 통해 슈퍼커패시터의 전기화학적 특성을 조사하였으며, 이를 통해 전류밀도 1 A/g에서 정전용량이 163 F/g 임을, 그리고 1000 회의 충 방전 후 수명 측정 시에 안정적으로 87.34%가 유지됨을 확인하였다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.37.1-37.1
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• 2010

The multi-component olivine cathode material, $LiMn_{1/3}Fe_{1/3}Co_{1/3}PO_4$, was prepared via a novel coprecipitation method of the mixed transition metal oxalate, $Mn_{1/3}Fe_{1/3}Co_{1/3}(C_2O_4){\cdot}2H_2O$. The stoichiometric ratio and distribution of transition metals in the oxalate, therefore, in the olivine product, was affected sensitively by the environments in the coprecipitation process, while they are the important factors in determining the electrochemical property of electrode materials with multiple transition metals. The effect of the pH, atmosphere, temperature, and aging time was investigated thoroughly with respect to the atomic ratio of transition metals, phase purity, and morphology of the mixed transition metal oxalate. The electrochemical activity of each transition metal in the olivine synthesized through this method clearly was enhanced as indicated in the cyclic voltammetry (CV) and galvanostatic charge/discharge measurement. Three distinctive contributions from Mn, Fe, and Co redox couples were detected reversibly in multiple charge and discharge processes. The first discharge capacity at the C/5 rate was $140.5\;mAh\;g^{-1}$ with good cycle retention. The rate capability test showed that the high capacity still is retained even at the 4C and 6C rates with 102 and $81\;mAh\;g^{-1}$, respectively.

• 한국분말재료학회지
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• 제19권3호
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• pp.210-214
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• 2012

Mass production-capable $Li_2MnSiO_4$ powder was synthesized for use as cathode material in state-of-the-art lithium-ion batteries. These batteries are main powder sources for high tech-end digital electronic equipments and electric vehicles in the near future and they must possess high specific capacity and durable charge-discharge characteristics. Amorphous silicone was quite superior to crystalline one as starting material to fabricate silicone oxide with high reactivity between precursors of sol-gel type reaction intermediates. The amorphous silicone starting material also has beneficial effect of efficiently controlling secondary phases, most notably $Li_xSiO_x$. Lastly, carbon was coated on $Li_2MnSiO_4$ powders by using sucrose to afford some improved electrical conductivity. The carbon-coated $Li_2MnSiO_4$ cathode material was further characterized using SEM, XRD, and galvanostatic charge/discharge test method for morphological and electrochemical examinations. Coin cell was subject to 1.5-4.8 V at C/20, where 74 mAh/g was observed during primary discharge cycle.