• Applied Chemistry for Engineering
• /
• v.9 no.7
• /
• pp.1059-1064
• /
• 1998

We have investigated various kind of graphite and MCMB6-28 to develop carbon negative electrode for lithium ion secondary battery. The interlayer length of them was $3.358{\sim}3.363{\AA}$ and the BET specific surface area was $2.95{\sim}26.15m^2/g$. From this study, When the interlayer of them was large and the BET specific surface area was high, the electrochemical characteristics of them was very excellent. Adding 0, 3, 5, wt% of KJ-Black as conducting agent to various graphitic carbon active materials, interface resistance of electrode and electrolyte was less, but rechargeability was better at 3 wt%. At constant current charge and discharge test, discharge capacity was small according to large current.

• Proceedings of the KIEE Conference
• /
• 2006.07b
• /
• pp.1203-1204
• /
• 2006

Recently, utility network is getting more and more complicated and huge. In addition to, demands of power conversion devices which have non-linear switching devices are getting more and more increased. Consequently, according to the non-linear power semiconductor devices, current harmonics are unavoidable. Those current harmonics flow back to utility network and become one of the reasons which make the voltage distortion. On the other hands, voltage sag from sudden increasing loads is also one of the terrible problems inside of utility network. In order to compensate the current harmonics and voltage sag problem, AF(Active Filter) systems could be a good solution method and SMES(Superconducting Magnetic Energy Storage) system is a very good promising source due to the high response time of charge and discharge. Therefore, the combined system of AF and SMES is a wonderful device to compensate both harmonics current and voltage sag. However, unfortunately SMES needs a superconducting magnetic coil. Because of the introduction of superconducting magnetic coil, quench problem caused by unexpected reasons is always existed. In case of discharge operation, quench is a significantly harmful factor according as it decreases the energy capacity of SMES. Therefore, this paper presents a decision method of the specification of the AF-SMES system considering internal fault condition. Especially, authors analyzed the change of the original energy capacity of SMES regarding to the size of resistance caused by quench of superconducting magnetic coil. Finally, based on this simulation, authors manufactured actual Active Filter System using DSP.

• Proceedings of the Korea Crystallographic Association Conference
• /
• 2002.11a
• /
• pp.16-16
• /
• 2002

The presently commercialized lithium-ion batteries use layer structured LiCoO₂ cathodes. Because of the high cost and toxicity of cobalt, an intensive search for new cathode materials has been underway in recent years. Recently, a concept of a one-to-one solid state mixture of LiNO₂ and LiMnO₂, i.e., Li[Ni/sub 0.5/Mn/sub 0.5/]O₂, was adopted by Ohzuku and Makimura to overcome the disadvantage of LiNiO₂ and LiMnO₂. Li[Ni/sub 0.5/Mn/sub 0.5/]O₂ has the -NaFeO₂ structure, which is characteristic of the layered LiCoO₂ and LiNiO₂ structures and shows excellent cycleability with no indication of spinel formation during electrochemical cycling. Layered Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials with high homogeneity and crystallinity were synthesized using a mechanical alloying method. The Li[Ni/sub 0.475/Co/sub 0.05/Mn/sub 0.475/]O₂ electrode delivers a high discharge capacity of 187 mAh/g between 2.8 and 4.6 V at a high current density of 0.3 mA/㎠(30 mA/g) with excellent cycleability. The charge/discharge and differential capacity vs. voltage studies of the Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials showed only one redox peak up to 50 cycles, which indicates that structural phase transitions are not occurred during electrochemical cycling. The magnitude of the diffusion coefficients of lithium ions for Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂(x = 0.5 and 0.475) are around 10/sup -9/ ㎠/s measured by the galvanostatic intermittent titration technique (GITT).

• Bulletin of the Korean Chemical Society
• /
• v.32 no.1
• /
• pp.191-195
• /
• 2011

This study reports the root cause of the improved rate performance of $LiFePO_4$ after Cr doping. By measuring the chemical diffusion coefficient of lithium ($D_{Li}$) using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the correlation between the electrochemical performance of $LiFePO_4$ and Li diffusion is acquired. The diffusion constants for $LiFePO_4$/C and $LiFe_{0.97}Cr_{0.03}PO_4$/C measured from CV are $2.48{\times}10^{-15}$ and $4.02{\times}10^{-15}cm^2s^{-1}$, respectively, indicating significant increases in diffusivity after the modification. The difference in diffusivity is also confirmed by EIS and the $D_{Li}$ values obtained as a function of the lithium content in the cathode. These results suggest that Cr doping facilitates Li ion diffusion during the charge-discharge cycles. The low diffusivity of the $LiFePO_4$/C leads to the considerable capacity decline at high discharge rates, while high diffusivity of the $LiFe_{0.97}Cr_{0.03}PO_4$/C maintains the initial capacity, even at high C-rates.

• Korean Chemical Engineering Research
• /
• v.57 no.1
• /
• pp.5-10
• /
• 2019

In this study, electrochemical characteristics of artificial graphite coated with petroleum pitch using solvent method as anode material of lithium ion battery were investigated. As the solvent, n-hexane, toluene, tetrahydrofuran and quinoline were used. The surface of the prepared anode material was analyzed by SEM and TEM. Also the electrochemical performances of the prepared anode materials were performed by constant current first charge/discharge, cycle, cyclic voltammetry and impedance tests in the electrolyte of $LiPF_6$ dissolved inorganic solvents (EC:DEC=1:1 vol%). The coating thickness of the prepared graphite was about 100-500 nm and the graphite coated with THF solvent had a smoother surface than that using other solvents. It was found that pitch-coated graphite (THF) show the low initial irreversible capacity (51 mAh/g), the high discharge capacity (360 mAh/g) and coulombic efficiency (99%).

• Korean Chemical Engineering Research
• /
• v.57 no.5
• /
• pp.672-678
• /
• 2019

The electrochemical properties of pitch-coated natural graphite(NG) were investigated as an anode for lithium-ion batteries. The anode materials were prepared by heat-treatment of mixture of NG and petroleum pitch at $1000^{\circ}C$. The pitches with various softening points were used as carbon precursor. The physical properties of anode materials were analyzed by TGA, SEM, PSA and BET. As the softening point increased, the thickness of the coating layer increased and the specific surface area decreased. The electrochemical performances were investigated by initial charge/discharge efficiency, cycle stability, cyclic voltammetry, rate performance and electrochemical impedance spectroscopy. The carbon-coated NG using pitch with softening points of $250^{\circ}C$ showed an initial discharge capacity of 361 mAh/g and a coulombic efficiency of 92.6%. Also, the rate performance(5 C/0.2 C) was 1.6 times higher than that of NG, and it had a capacity retention (90%) after 50 cycles at 0.5 C.

• Korean Journal of Metals and Materials
• /
• v.49 no.2
• /
• pp.174-179
• /
• 2011

We investigated the surface morphology changes of a lithium/sulfur battery using multi-walled canbon nanotube added sulfur electrode during charge-discharge cycling. The Li/S cell showed the first discharge capacity of 1286 mAh/g-S, which utilized is 71% of the theoretical value. It decreased to 328 mAh/g-S at the 100th cycle, which corresponds to about 19% utilization of the total sulfur in the cathode. The spherical lumps of the reaction product were observed on the surface of the sulfur electrode. This material was verified as lithium sulfide by X-ray diffraction measurement. The pores in the separator were filled with reaction product. Thus the diffusion of the $Li^+$ ion decreased, which resulted in the decreased capacity of the Li/S cell.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.20 no.9
• /
• pp.590-598
• /
• 2008

In this study, performance of R170/R290 mixtures is measured on a heat pump bench tester in an attempt to substitute R22. The bench tester is equipped with a commercial hermetic rotary compressor providing a nominal capacity of 3.5kW. All tests are conducted under the summer cooling and winter heating conditions of $7/45^{\circ}C$ and $-7/41^{\circ}C$ in the evaporator and condenser respectively. During the tests, the composition of R170 is varied from 0 to 10% with an interval of 2%. Test results show that the coefficient of performance (COP) and capacity of R290 are up to 15.4% higher and 7.5% lower than those of R22 for both conditions respectively. For R170/R290 mixture, the COP decreases and the capacity increases with an increase in the amount of R170. The mixture of 4%R170/96%R290 shows the similar capacity and COP as those of R22. For the mixture, the compressor discharge temperature is $16{\sim}30^{\circ}C$ lower than that of R22. There is no problem with mineral oil since the mixture is mainly composed of hydrocarbons. The amount of charge is reduced up to 58% as compared to R22. Overall, R170/R290 mixture is a good long term 'drop-in' candidate to replace R22 in residential air-conditioners and heat pumps.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.3
• /
• pp.219-225
• /
• 2000

The spinel structured $LiMn_2O_4$was obtained by two consecutive heat treatment on xerogel; the first heat treatment was at $150^{\circ}C$ and the second at $350^{\circ}C$ was obtained by sol-gel process using an aqueous solution of lithium hydroxide and manganese acetate. The synthesized $LiMn_2O_4$ by the sol-gel process showed a discharge capacity of 88~56 mAh/g after 15 cycles in Li/lM $LiClO_4$(in PC)/$LiMn_2O_4$at a current density of 0.25 mA/$\textrm{cm}^2$ and the voltage ranged 3.5 V to 4.3 V. For the second heat treatment above $350^{\circ}C$, $Mn_2O_3$was formed as a by-product during the synthesis of $LiMn_2O_4$. The heat treatment at $500^{\circ}C$, for example, showed a lower discharge capacity 81~47 mAh/g, after the 15 charge/discharge cycles. The lower capacity was due to the increment of $Mn^{3+}$ ion and this phenomenon was in agreement with the Jahn-Teller distortion.

• Korean Chemical Engineering Research
• /
• v.59 no.4
• /
• pp.487-492
• /
• 2021

In this study, the electrochemical properties of pitch coated silicon sheets/graphite anode materials were investigated. Using NaCl as a template, silicon sheets were prepared through the stöber method and the magnesiothermic reduction methode. In order to synthesize the anode composite, the silicon sheets and graphite were combined with SDBS. The pitch coated silicon sheets/graphite was synthesized using THF as a solvent for the anode material composite. The physical properties of the prepared anode composites were analysed by XRD, SEM, EDS and TGA. The electrochemical performances of the prepared anode composites were performed by the current charge/discharge, rate performance, cyclic voltammetry and EIS tests in the electrolyte LiPF₆ dissolved solvents (EC:DMC:EMC=1:1:1 vol%). As the silicon composition of silicon sheets/graphite composite material increased, the discharge capacity also increased, but the cycle stability tended to decrease. The anode material of pitch coated silicon sheets/graphite composite (silicon sheets:graphite=3:7 weight ratio) showed the initial discharge capacity of 1228.8 mAh/g and the capacity retention ratio of 77% after 50 cycles. From these results, it was found that the cycle stability of pitch coated silicon sheets/graphite was improved.