• 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/$Li^+$).

• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1598-1602
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• 2009

The particle size of Li[$Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ cathode powder was controlled effectively by dispersion using lauric acid as a surfactant. The samples treated by lauric acid showed smaller particles of approximately half the original size compared to the particles of a pristine sample. A structural change due to the dispersion of Li[$Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ powder was not detected. The rate performance of the Li[$Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ cathode was improved by dispersion using lauric acid, which was likely due to the decrease of the particle size. In particular, a sample dispersed pristine powder using lauric acid (L2) presented a greatly enhanced discharge capacity and capacity retention at a high C rate. The discharge capacity of a pristine sample was only 133 m$Ahg^{-1}$ (3C rate) and 96 m$Ahg^{-1}$ (12C rate) at the tenth cycle. In contrast, the L2 electrode delivered higher discharge capacities of 160 m$Ahg^{-1}$ (3C rate) and 129 m$Ahg^{-1}$ (12C rate) at the tenth cycle. The capacity retention at a rate of 12C/2C was also enhanced from ~ 45% (pristine sample) to 57% (L2) by treatment with lauric acid.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.371-374
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• 2004

저온동시 소성용(low temperature co-fired ceramics, LTCC) 마이크로파 유전체을 만들기 위해 $Ca(Li_{1/4}Nb_{3/4})O_3$ 마이크로파 유전체 세라믹스에 zinc-borosililcate glass를 첨가하여 소결 특성과 마이크로파 유전 특성을 조사하였다. $Ca(Li_{1/4}Nb_{3/4})O_3$과 $0.7Ca(Li_{1/4}Nb_{3/4})O_3-0.3CaTiO_3$에 zinc-borosilicate를 $5{\sim}30wt%$ 첨가하여 소결한 결과 $875{\sim}925^{\circ}C$에서 동시 소성이 가능한 것으로 확인되었으며 zinc-borosilicate glass의 함량이 증가할수록 저온에서 소성이 가능하였지만 과량의 액상과 2차상이 형성되면서 유전율과 품질계수가 저하되는 경향을 나타내었다. $Ca(Li_{1/4}Nb_{3/4})O_3$에 5wt%의 zinc-borosilicate를 첨가하여 $900^{\circ}C$에서 소성한 결과 가장 우수한 유전 특성$(\epsilon_r=17.45,\;Q{\times}f_0=5487)$을 나타내었고, 유전율을 높이기 위해 $CaTiO_3$를 0.3mol% 첨가한 $0.7Ca(Li_{1/4}Nb_{3/4})O_3-0.3CaTiO_3$에 10wt%의 zinc-borosilicate를 첨가하여 $925^{\circ}C$에서 소성한 결과 가장 우수한 유전특성$(\epsilon_r=44.92,\;Q{\times}f_0=5567)$을 나타내었다.

• Journal of the Korean Chemical Society
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• v.57 no.1
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• pp.12-19
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• 2013

The single-crystal structure of fully dehydrated partially $Li^+$-exchanged zeolite Y, ${\mid}Li_{50}Na_{25}{\mid}[Si_{117}Al_{75}O_{384}]$-FAU, was determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group $Fd\bar{3}m$ at 100(1) K. Ion exchange was accomplished by flowing stream of 0.1 M aqueous $LiNO_3$ for 2 days at 293 K, followed by vacuum dehydration at 623 K and $1{\times}10^{-6}$ Torr for 2 days. The structure was refined using all intensities to the final error indices (using only the 801 reflections with ($F_o$ > $4{\sigma}(F_o)$) $R_1/R_2=0.043/0.140$. The 50 $Li^+$ ions per unit cell are found at three different crystallographic sites. The 19 $Li^+$ ions occupy at site I' in the sodalite cavity: the $Li^+$ ions are recessed 0.30 ${\AA}$ into the sodalite cavity from their 3-oxygens plane (Li-O = 1.926(5) ${\AA}$ and $O-Li-O=117.7(3)^{\circ}$). The 20 $Li^+$ ions are found at site II in the supercage, being recessed 0.23 ${\AA}$ into the supercage (Li-O = 2.038(5) ${\AA}$ and $O-Li-O=118.7(3)^{\circ}$). Site III' positions are occupied by 11 $Li^+$ ions: these $Li^+$ ions bind strongly to one oxygen atom (Li-O = 2.00(8) ${\AA}$). About 25 $Na^+$ ions per unit cell are found at four different crystallographic sites: 4 $Na^+$ ions are at site I, 5 at site I', 12 at site II, and the remaining 4 at site III'.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.433-436
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• 2013

Carbon-coated $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials are first reported in this work, prepared by the mechanochemical process with a complex metal oxide as the precursor and sucrose as the carbon source. X-ray diffraction pattern of the composite material indicates that both olivine $LiMnPO_4$ and monoclinic $Li_3V_2(PO_4)_3$ co-exist. We further investigated the electrochemical properties of our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials using galvanostatic charging/discharging tests, where our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite electrode materials exhibit the charge/discharge efficiency of 91.9%, while $Li_3V_2(PO_4)_3$ and $LiMnPO_4$ exhibit the efficiency of 87.7 and 86.7% in the first cycle. The composites display unique electrochemical performances in terms of overvoltage and cycle stability, displaying a reduced gap of 141.6 mV between charge and discharge voltage and 95.0% capacity efficiency after $15^{th}$ cycles.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.226-226
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• 2003

The Commercial LiCoO$_2$ particles, which were 7.7${\mu}{\textrm}{m}$ in average diameter, were coated with $Al_2$O$_3$ by a gas suspension spray coating method. The coating amount of $Al_2$O$_3$ on the surface of LiCoO$_2$ was varied from 0.1 to 2 wt.% and compared their electrochemical characteristics with those of bare LiCoO$_2$. $Al_2$O$_3$ coating on the surface of LiCoO$_2$ increased surface area and electrical conductivity, and showed the better cycle and thermal stability even at the higher voltage. The observed optimum A1$_2$O$_3$ coating amount that exhibited the highest capacity retention was 0.2 wt.%.

• Journal of Electrochemical Science and Technology
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• v.7 no.2
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• pp.139-145
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• 2016

The electrochemical performance of carbon-coated LiMn₂O₄ nanoparticles was reported. The polydopamine layer was introduced as a new organic carbon source. The carbon layer was homogeneously coated onto the surface of the LiMn₂O₄ nanoparticles because the polymerization process from the dopamine solution (in a buffer solution, pH 8.5) easily and uniformly formed a polydopamine layer. The phase integrity of LiMn₂O₄ deteriorated during the carbon-coating process due to oxygen loss, although the main structure was maintained. The carbon-coated sample led to improved rate capability because of the effect of the conductive carbon layer. Moreover, the carbon coating also enhanced the cyclic performance. This indicates that the carbon layer may suppress unwanted side reactions with the electrolytes and compensate for the low electronic conductivity of the pristine LiMn₂O₄.

• Proceedings of the Korean Magnetic Resonance Society Conference
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• 2002.08a
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• pp.85-85
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• 2002

Lithiated transition metal oxides such as LiMn2O4, Lil-xMnO$_2$, LiNiO$_2$, LiCoO$_2$, and their solid solution phases are used as cathode materials for lithium rechargeable batteries. We prepared the cathode materials using a novel eutectic self-mixing method without any artificial mixing procedures. This method provides an extraordinarily simple way to make the cathode materials, and it is possible to prepare at very low temperature such as 25$0^{\circ}C$. Furthermore, the cathode materials produced have discharge capacities that are much better than cathode materials prepared by previously reported synthetic methods. The spontaneous and homogeneous mixing is verified by $^{7}$ Li magic-angle-spinning (MAS) NMR spectroscopy.

• Proceedings of the Korean Nuclear Society Conference
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• 2001.10a
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• pp.320.2-320
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• 2001

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.7
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• pp.4692-4697
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• 2014

A micro-grid including photovoltaic source and Li battery has been installed and operated for several years at the campus of USF and been used as a test bed. Photovoltaic power source has been strongly influenced by the location, weather and climate of the installed area. To compensate for the uncertainty of photovoltaic source's power output, a Li battery is connected directly to the photovoltaic source and supplies electric power to the grid. The Li battery is operated to supply power output to the grid according to the charging or discharging mode of the battery based on the average power output of the photovoltaic source, which is calculated from the monitored data for several years. The grid of the photovoltaic and Li battery system is operated as a severe loading condition and the operating characteristics of PV source and Li battery cells are analyzed in detail.