• Journal of the Korean Electrochemical Society
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• v.7 no.4
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• pp.173-178
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• 2004

Silicon thin film were synthesized from silane and argon gas mixture directly on copper foil by rf PECVD and then lithium ion batteries were prepared from them employed as the negative electrodes without any further treatment. In the present study, two different kinds of silicon thin films, amorphous silicon and copper silicide were prepared by changing deposition temperature. Amorphous silicon film was prepared below $200^{\circ}C$, but copper silicide film with granular shape was formed by the reaction between silicon radical and diffused copper ions under elevating temperature above $400^{\circ}C$. The amorphous silicon film gives higher capacity than copper silicide, but the capacity decreases sharply with charge-discharge cycling. This is possibly due to severe volume changes. The cyclability is improved, however, by employing the copper silicide as a negative electrode. The copper silicide plays an important role as an active material of the electrode, which mitigates volume change cause by the existence of silicon and copper chemical bonding and provides low electrical resistance as well.

• Journal of the Korean Electrochemical Society
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• v.3 no.4
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• pp.224-231
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• 2000

The exfoliation of graphite (layer) was progressed due to the irreversible insertion of PC molecules between graphene layers, when propylene carbonate (PC) solvent was used as the organic solvents. The problem could be mitigated by the replacement of PC by ethylene carbonate (EC). But, the freezing point of EC-based electrolyte increased due to the high freezing point of $EC(36.2^{\circ}C)$. Therefore, EC+PC mixed electrolyte is expected as a good organic electrolyte for lithium ion battery. The EC-based organic electrolyte containing PC within pertinent quantity can be expected to have high molar conductivity and reduced exfoliation of graphite layer. The dielectric constant and molar conductivity of $LiPF_6/PC+EC+DEC$ electrolyte was investigated with a variation in the PC content. The electrochemical properties of carbon electrode in the electrolyte were also investigated. Molar conductivity and dielectric constant increased linearly by increasing the PC volume fraction in the electrolyte. The results of charge-discharge test for carbon/electrolyte/Li cell indicated that the initial irreversible specific capacity(IIC) of MCMB-6-28s and MPCF3000 decreased by the addition of $0.83 vol\%$ of PC, but increased with PC content over than $0.83 vol\%$. In the case of MPCF3000 and PCG100 having less than $10 vol\%$ PC, IIC was lower than 50 mAh/g. The discharge specific capacities varied with carbon material, but did not vary with PC content in the electrolyte.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.462-462
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• 2009

$CeO_2$는 고체 산화물 연료전지 (SOFC, soild oxide fuel cell)의 전해질 재료와 CMP(Chemical Mechanical Polishing) 슬러리 재료, 자동차의 3원 촉매, gas sensor, UV absorbent등 여러 분야에서 사용되고 있다. 본 연구에서는 위의 활용범위 외에 $CeO_2$의 구조적 안정성과 빠른 $Ce^{3+}/Ce^{4+}$의 전환 특성을 이용하여 lithium ion battery의 anode 재료로서 전기화학적 특성을 알아보고자 실험을 실시하였다. $CeO_2$ 합성에 사용되는 전구체인 cerium carbonate의 형상 및 크기, 비표면적과 같은 물리화학적 특성이 $CeO_2$ 분말의 특성에 직접적인 영향을 주기 때문에 전구체의 합성 단계에서 입자의 특성을 조절하였다. 전구체 합성의 출발원료로 cerium nitrate hexahydrate 와 ammonium carbonate를 사용하였고 반응온도 및 농도 등을 변화시켜 입자의 형상 및 결정상을 fiber형태의 orthorombic $Ce_2O(CO_3)_2{\cdot}H_2O$와 구형의 hexagonal $CeCO_3OH$의 세리아 전구체를 합성하였다. 이를 $300^{\circ}C$에서 30분 동안 하소하여 전구체의 입자형상을 유지하는 cubic $CeO_2$를 합성하고 X-ray diffraction, FE-SEM, micropore physisorption analyzer 분석을 통하여 입자의 결정상과 형상, 비표면적 등을 비교 분석하고 $Li/CeO_2$ couple의 충,방전 용량과 수명특성을 비교 분석하여 $CeO_2$의 전기화학적 특성을 알아보았다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.660-666
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• 1998

We discussed structure, energy state, characteristics of thermal stability, and electrochemical properties of Li-GFICs, Li-PCICs, and Li-AGICs during the intercalation process. According to X-ray diffraction patterns, we observed phase of stage 2 mainly from Li-GFICs, while stage 1 phase as well as stage 2 from Li-PCICs. For the structure of Li-AGICs, stage 1 phase was dominant, but it was not possible to obtain pure stage 1 compound probably due to structural characteristics of artificial graphite. We measured energy state of the compounds to stage stability, and revealed that Li-AGICs and Li-GFICs were in more stable state than Li-PCICs. Therefore, those two compounds could be excellent candidate for energy reserve material. From the study of thermal degradation, Li-GFICs showed strong exothermic reaction at around 300 and $400^{\circ}C$. In the study of thermal stability of Li-AGIC at various temperatures, we observed that lithium was not completely deintercalated and high stage was maintained even at high temperature. In the case of charge, discharge, and electrochemical studies, Li-GFICs showed the best results.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.2
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• pp.165-170
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• 2005

Al-Zn alloy/$MnO_2$, seawater cell was considered as a primary aqueous cell with an average voltage range from 1.0 to 1.1V, and the electrolyte of seawater was uptaken into the cell. Eventually, the capacity of its usage will be used for long-term. However, the more use of this cell, the higher corrosion phenomenon of the electrode occurred. Due to its corrosion phenomenon, one main default has been observed with gradual decrease during a discharge process. In this research, a common-used active material for anode was $LiNiO_2$. An active material for cathode, $Zn_{X}FeS_2$ was synthesized in high temperature by uptaken a small amount of 1.3 wt% of ZnS into $FeS_2$, one of the transition-metal dichalcogenides in high temperature. Consequently, based on their usages shown above, this secondary aqueous lithium cell could be more developed. This cell was shown as remarkable charge/discharge performance during the charge/discharge processes. This cathode with active material was given a considerable efficiency of inserting $Li^+$ ions. Moreever, in accordance with the characteristic of the crystal structure for $Zn_{x}FeS_2$, a small amount of ZnS was added which made it possible to reduce prominently velocity of corrosion during the charge/discharge cycle. By applying those merits, Al-Zn alloy/$MnO_2$ seawater cell will be used as a fundamental data in order to transform into a secondary aqueous cell.

• Journal of the Korean Chemical Society
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• v.50 no.3
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• pp.243-246
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• 2006

The LiCoO2 thin films were prepared on the Pt/Ti/SiO2/Si substrate by spin coating using citrate sol. The citrate sol was spin-coated on substrate and dried at 380oC for 15 min. to evaporate the solvents and remove the organic materials. The as-deposited films were annealed at 750oC for 10 min. in air for crystallization. The X-ray diffraction patterns for the film have been indexed hexagonal system with space group R3m. The active area of LiCoO2 films for electrochemical test was about 11cm2. A Li foil and 1M LiClO4 in propylene carbonate(PC) and ethylene carbonate(EC) (1:1)were used as an anode and an electrolyte, respectively. The galvanostatic charge-discharge test was carried out at constant current density ranging from 5 A/cm2 in the voltage window between 4.2 and 3.0 V. The first discharge capacity of the film is 0.35Ah/cm2-m. The cycling behavior of the LiCoO2 film is also reported.

• Bulletin of the Korean Chemical Society
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• v.27 no.8
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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).

• Journal of Powder Materials
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• v.24 no.4
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• pp.308-314
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• 2017

$Fe_3O_4$/Fe/graphene nanocomposite powder is synthesized by electrical wire explosion of Fe wire and dispersed graphene in deionized water at room temperature. The structural and electrochemical characteristics of the powder are characterized by the field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, field-emission transmission electron microscopy, cyclic voltammetry, and galvanometric discharge-charge method. For comparison, $Fe_3O_4$/Fe nanocomposites are fabricated under the same conditions. The $Fe_3O_4$/Fe nanocomposite particles, around 15-30 nm in size, are highly encapsulated in a graphene matrix. The $Fe_3O_4$/Fe/graphene nanocomposite powder exhibits a high initial charge specific capacity of 878 mA/g and a high capacity retention of 91% (798 mA/g) after 50 cycles. The good electrochemical performance of the $Fe_3O_4$/Fe/graphene nanocomposite powder is clearly established by comparison of the results with those obtained for $Fe_3O_4$/Fe nanocomposite powder and is attributed to alleviation of volume change, good distribution of electrode active materials, and improved electrical conductivity upon the addition of graphene.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.4
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• pp.316-322
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• 2001

Cathode materials $LiMn_{2-y}$$M_{y}$ $O_4$(M=Zn and Mg) were obtained by reacting the mixture of LiOH.$H_2O$, Mn $O_2$ and MgO ar ZnO at 80$0^{\circ}C$ for 36h in an air atmosphere. These materials showed an extended cycle life in lithium-anode cells working at room temperatue in a 3.0 to 4.3V potential window. Among these materials, LiM $n_{1.9}$M $g_{0.1}$ $O_4$ showed the best cycle performance in terms of the capacity and cycle life. The discharge capacities of the cathode for the Li/LiM $n_{1.9}$ $M_{0.1}$ $O_4$ cell at the 1st cycle and at the 70th cycle were about 120 and 105mAh/g, respectively. This cell capacity is retained by 88% after 70th cycle. In cyclic voltammetry measurement, all cells revealed tow oxidation peaks and reduction peaks. However, Li/$LiMn_{2-y}$$M_{y}$ $O_4$ cell substituted with Zn and Mg showed new reaction peak during reduction reaction.eaction.ion.ion.

• Journal of Electrochemical Science and Technology
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• v.1 no.2
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• pp.85-91
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• 2010

We have studied the origin of an additional plateau of $Li_{4+x}Ti_5O_{12}$ (LTO) observed at 0.7 V (vs. Li/$Li^+$). Some LTO has to be discharged down to below 1.0 V forming two-stage plateau (1.5 V and 0.7 V) in order to obtain most of capacity while others could achieve the same level of capacity at higher potential (1.0 V vs. Li/$Li^+$) forming one plateau (1.5 V). The particle size effect has been investigated as a possible reason of this. The 0.7 V plateau was gradually elongated with increasing the particle size. The structural variations and kinetic behaviors during discharge were carefully examined by in-situ XRD technique and OCV measurement. According to structural and electrochemical verifications, the kinetic limitation of $Li^+$ insertion is responsible primarily for the two-stage plateau which is related to the particle size of LTO rather than the formation of new intermediate phase during discharge. Herein, we propose a possible reaction model to elucidate this abnormal behavior of LTO below 1.0 V (Li/$Li^+$).