• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1102-1106
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• 2015

A hybrid supercapacitor (HS) is an energy storage device used to enhance the low weight energy density (Wh/kg) of a supercapacitor. On the other hand, a sudden decrease in capacity has been pointed out as a reliability problem after many charge/discharge cycles. The reliability problem of a HS affects the early aging process. In this study, the capacity performance of a HS was observed after charge/discharge. For detailed analysis of the initial charge/discharge cycles, the charge and discharge curve was measured at a low current density. In addition, a solid electrolyte interphase (SEI) layer was confirmed after the charge/discharge. A HC composed of a lithium titanate (LTO) anode and active carbon cathode was used. The charge/discharge efficiency of the first cycle was lower than the late cycles and the charge/discharge rate was also lower. This behavior was induced by SEI layer formation, which consumed Li ions in the LTO lattice. The formation of a SEI layer after the charge/discharge cycles was confirmed using a range of analysis techniques.

• 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.

• 대한안전경영과학회지
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• 제2권2호
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• pp.187-200
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• 2000

The charge and discharge current in EPR(Ethylene Propylene Rubber), which were irradiated with the radiant capacity of 0~600 ［kgy/h］, have been measured in order to investigate the influence of the atmosphere (oxygen, air and vacuum) on electrical properties. It has been shown that the charge and discharge current increase as the amount of radiant capacity increases in air and vacuum atmosphere. This electrical property degradation can be speculated due to that the C＝O radicals or impurities, which comes from during shaping process, may act as dipoles. On the other hand, the charge and discharge current are shown to be higher in the amount of 1［kgy/h］ than these in 10［kgy/h］ in air atmosphere, because the charge and discharge current can be increased as the exposure time is extended with slower rate. Under the same amount of irradiation, the charge and discharge current in oxygen atmosphere are shown to be higher than those in vacuum. This is possibly due to that the main chain can be broken by oxidation when it is exposed to the $\gamma$ -rays.

• 한국세라믹학회지
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• 제37권2호
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• pp.128-133
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• 2000

In this work, soft carbons produced by pyrolysis of petroleum and coal-tar pitch were used as the negative electrode for Li-ion batteries. We studeid the charge/discharge capacity and the interfacial reaction of these electrodes by constructing a half cell. Charge/discharge property was studied by a constant-current step and the interfacial reaction between the electrolyte and the surface of a carbon electrode was studied by the cyclic voltammetry. The initial charge/discharge capacity for the coal-tar pitch carbon increased exceedingly with the heat treatment temperature. On hte other hand, the capacity of the petroleum pitch carbon increased with temperature up to 1000$^{\circ}C$, thereafter decreased continuously. While the charge capacity decreased with the cycle number, the reversibility increased above 90%. In addition, the thermal stability and crystallization of petroleum and coal-tar pitches were analyzed by TGA and XRD, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 춘계학술대회 논문집 센서 박막재료
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• pp.18-22
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• 2001

Spinel $LiMn_{2-y}Mn_{y}O_4$ powder was prepared solid-state method by calcining the mixture of $LiOH{\cdot}H_2O$, $MnO_2$ and MgO at $800^{\circ}C$ for 36h. To investigate the effect of temperature for cycle behaviour of cathode material during cycling, charge-discharge experiments and initial impedance spectroscopy performed by the condition of the charge-discharge temperature. Initial charge-discharge capacity was gradually increased by rising charge-discharge temperature. However, capacity was suddenly decreased at high temperature during cycling. Capacity at low temperature was almost constant during cycling. It confirmed because Mn dissolution is more serious at high temperature than at low temperature.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.351-354
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• 2000

AC impedance of LiM $n_2$ $O_4$ and LiM $g_{0.1}$M $n_{1.9}$ $O_4$ samples have been studied at various temperature with charge-discharge test. AC impedance of LiM $n_2$ $O_4$ measured at -2$0^{\circ}C$, room temperature and 5$0^{\circ}C$ revealed that initial impedance before charge-discharge test was gradually decreased and become small by becoming law temperature. It indicates that the Li ion diffusion and the transfer resistance of the cathode are related to the temperature of cycling. Impedance at high temperature was suddenly increased because Mn dissolution and decomposition of electrolyte had been increased during cycling, compared to impedance at low temperature. Therefore, charge-discharge capacity was suddenly decreased at high but was slowly at low. In LiM $g_{0.1}$M $n_{1.9}$ $O_4$, impedance and capacity were stability at room temperature than there at 5$0^{\circ}C$, too. Initial impedance at 5$0^{\circ}C$ before charge-discharge test was small and impedance was suddenly increased during cycling than that at room temperature.ure.ure.

• 전기화학회지
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• 제7권1호
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• pp.32-37
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• 2004

리튬 이차전지의 음극재료로서 천연흑연의 충방전 속도에 따른 용량특성을 조사하였다 정전류 조건에서 $0.0-2.0V(vs. Li/Li^+)$의 범위에서 충방전 하였을 때, 충전전류가 증가할수록 충전반응의 과전압이 증가하여 $Li^+$이온이 충분히 삽입되지 못한 상태에서 컷오프 전압(0.0 V)에 도달하기 때문에 충전용량은 충전전류의 크기가 클수록 감소하였다. 한편, 방전전류가 증가함에 따라 방전반응의 과전압도 증가하여 0.0-0.3V범위에서 방전반응이 일어나나 방전 컷오프 전압(2.0 V)과는 격차가 커서 $Li^+$이온이 탈리되지 못한 상태에서 방전 컷오프에 도달하는 현상은 없기 때문에 방전용량이 방전전류의 크기에 영향을 받지 않았다. 충전전류가 증가함에 따라 부반응인 리튬 전착반응의 과전압도 증가하므로 충전 컷오프 전압을 0.0V 이하로 낮출 수 있었다. 그러나 $Li^+$이온의 삽입반응에 비해 전착반응의 저항이 적어 충전전류에 따른 전착반응의 과전압 증가에는 한계가 있었다. 1C조건에서 -0.04V까지 충전 z컷오프 전압을 낮추었을 때 리튬의 전착반응은 없었고, 이로부터 약 $11\%$의 방전용량을 증가시킬 수 있었다.

• 에너지공학
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• 제2권3호
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• pp.300-307
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• 1993

고성능 니켈-철 축전지를 개발하기 위하여 철전극에 대한 충방전 반응 특성을 전위주사법, SEM, XRD분석으로 조사하였으며, 또한 전극용량을 정전류 충방전 시험법으로 조사하였다. 전해질 온도 및 농도가 전극용량에 크게 영향을 미쳤으며, 특히 온도가 상승함에 따라 1차 방전용량이 증가하였다. 증공제는 전극용량에 거의 영향을 미치지 못하였다. 전극용량은 방전율 0.25C에서 350㎃h/g (이용율 36%) 이상으로 나타났고, 전극의 안정성도 양호하게 나타났으나 활성화가 느리게 일어났다.

• 한국수소및신에너지학회논문집
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• 제10권3호
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• pp.177-184
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• 1999

The charge-discharge characteristics of the $Mg_2Ni-x$ wt.%Nd (x = 0~3) electrodes were investigated. The electrodes were prepared by the mechanical grinding of the induction-melted $Mg_2Ni$ alloy powders with Ni and/or Nd using planetary ball mill apparatus. The discharge capacity of the $Mg_2Ni$ alloy increased with the increase in the nickel content. The electrode possessing 100 wt.% nickel powder showed the initial capacity of 760 mAh/g and the capacity decay with the cycle number was less than that of the 55 wt.% nickel powder. The Nd was added to this composition. It was found that the $Mg_2Ni-100$ wt.%Ni -0.2 wt.%Nd alloy showed an excellent charge-discharge cycle characteristics compared with the other reported Mg-Ni alloy system. The discharge capacity was 400 mAh/g after 70 cycles. Such an improved cycle life seems to be attributed to the improvement in the corrosion characteristics of the alloy. The anodic polarization curve of the $Mg_2Ni-100$ wt.%Ni-0.2 wt.%Nd alloy exhibited better passivating behavior than that of the $Mg_2Ni-100$ wt.%Ni.

• 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.