• Transactions on Electrical and Electronic Materials
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• v.10 no.3
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• pp.102-105
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• 2009

$Li[Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ cathode materials have been synthesized by a microwave-assisted sol-gel method. The structure and electrochemical properties of $Li[Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ were studied by X-ray difftactometry (XRD), scanning electron microscopy (SEM) and charge-discharge cycler. The powder prepared by microwave assisted sol-gel method showed good crystallinity and well-defined facet shapes. The $Li[Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ electrode delivered a high discharge capacity of 230 $mAhg^{-1}$ at the specific current of 40 $mAg^{-1}$ (0.2 C rate) in the voltage range of 2.0${\sim}$4.8 V. About 60 % of the discharge capacity measured at 0.2 Crate (140 $mAhg^{-1}$) was maintained at a 6 C (1200 $mAg^{-1}$)rate. The cyclic property was also stable and it did not deteriorated at a high Crate.

• Bulletin of the Korean Chemical Society
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• v.30 no.11
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• pp.2584-2588
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• 2009

The effect of $LaF_3$ coating on the structural and electrochemical properties of $Li[Ni_{0.3}Co_{0.4}Mn_{0.3}]O_{2}$ cathodes was investigated using XRD, SEM, TEM, and a cycler. The coating layer consisted of nano-sized particles attached nonuniformly to the surface of pristine powder. Despite the surface coating treatment, phase difference by $LaF_3$ coating was not detected. The discharge capacities of coated electrodes were a little lower than that of pristine sample at a 1 C rate. However, as the C rate increases, the capacity retention of the coated sample becomes obviously superior to that of the pristine sample. The cyclic performances of the electrodes in the voltage range of 4.8 $\sim$ 3.0 V were also improved by the surface coating. Such enhancement is attributed to the presence of the $LaF_3$ coating layer, which effectively suppressd the reaction between electrodes and electrolytes on the surface of the $Li[Ni_{0.3}Co_{0.4}Mn_{0.3}]O_{2}$ electrode.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2226-2230
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• 2007

As a cathode material of lithium rechargeable batteries, charged Li[Co0.1Ni0.15Li0.2Mn0.55]O2 electrodes, which were aged thermally at 25 oC and 90 oC respectively, were characterized by means of charge/discharger, impedance spectroscopy, and X-ray diffraction. The discharge capacity diminution of the electrodes aged at 25 oC and 90 oC for 1 week was 4% and 23%, respectively. The cell aged at 25 oC was recovered on cycling. However, the capacity loss after ageing at 90 oC was not recovered in a subsequent cycling test, which demonstrates that the reaction occurring during ageing at 90 oC is irreversible. A significant impedance increase of aged electrode at 90 oC is associated with irreversible capacity loss. The structural changes including phase transformation were not detected by XRD analysis, because it could be due to out of detection limit. After ageing, impedance was slightly decreased during subsequent cycling test. It could be explained the cyclic performance of aged sample is stable. The thermal stability was not deteriorated by ageing even at the high temperature of 90 oC.

• Journal of the Korean Electrochemical Society
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• v.3 no.2
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• pp.115-120
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• 2000

All solid-state thin film micro-batteries consisting of lithium metal anode, an amorphous LiPON electrolyte and cathode of vanadium oxide have been fabricated and characterized, which were fabricated with cell structure of $Li/LiPON/V_2O_5Pt$. The effect of various oxygen partial pressure on the electrochemical properties of vanadium oxide thin films formed by d.c. reactive sputtering deposition were investigated. The vanadium oxide thin film with deposition condition of $20\%\;O_2/Ar$ ratio showed good cycling behavior. In in-siか process, the LiPON electrolyte was deposited on the $V_2O_5$ films without breaking vacuum by r.f. magnetron sputtering at room temperature. After deposition of the amorphous LiPON, the Li metal films were grown by a thermal evaporator in a dry room. The charge-discharge cycle measurements as a function of current density and voltage variation revealed that the $Li/LiPON/V_2O_5$ thin film had excellent rechargeable properly when current density was $7{\mu}A/cm^2$. and cut-off voltage was between 3.6 and 2.7V In practical experiment, a stopwatch ran on this $Li/LiPON/V_2O_5$ thin film micro-battery. This result means that thin film micro-battery fabricated by in-siか process is a promising for power source for electronic devices.

• Journal of the Korean Electrochemical Society
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• v.2 no.3
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• pp.123-129
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• 1999

Initial electrochemical characteristics of $LiCoO_2$ electrode for lithium ion battery with various content of super s black as conductive material were evaluated through the charge/discharge with the potential range of 4.3V to 2.0V versus $Li^+/Li^+$. The rate of C/4 and C/2 by the 3 electrode test cell composed with an electrolytic solution of 1 mol/l $LiPF_6/EC+DEC(1:3\;by\; weight)$. Lithium was used as reference electrode. High impedance charge behavior was observed at early stage of charge. In the case of $3\%w/w$ of super s black as conductive material, the specific resistance of the high impedance releasing was $3.82\;{\Omega}\;{\cdot}\;g-LiCoCo_2$ at the current density of $0.5 mA/cm^2$, which corresponds 7 times of the specific resistance of electrode $(0.728 g-LiCoO_2)$. At second charge, the specific resistance of the high impedance releasing was 63 mn · g-Lico02, which corresponds 12eio of the specific resistance of electrode and only $1.7\%$ of that of the first charge. The first charge and discharge specific capacities at C/4 rate were 160-161 and $153\~155mAh/g-LiCoO_2$, respectively, to lead $95.4\~96.4\%$ of coulombic efficiencies and ca. $6 mAh/g-LiCoO_2$ of initial irreversible specific capacity. Specific resistance at the end of charge and rest showed low value at content of super s black between 2 and $7\%w/w$, which agreed with characteristics of irreversible specific capacity. Capacity densities were reduced by the increasing the content of conductive material. They were 447 and 431mAh/ml when 2 and $2.9\%w/w$ of super s black were used, respectively, at the rate of C/4.

• Journal of Electrochemical Science and Technology
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• v.1 no.1
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• pp.39-44
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• 2010

1.5 V and 3.0 V-class film-type primary batteries were designed for radio frequency identification (RFID) tag. Efficient fabrication processes such as screen-printings of conducting layer ($25{\mu}m$), active material layer ($40{\mu}m$ for anode and $80{\mu}m$ for cathode), and electrolyte/separator/electrolyte layer ($100{\mu}m$), were adopted to give better performances of the 1.5 V-class film-type Leclanch$\acute{e}$ primary battery for battery-assisted passive (BAP) RFID tag. Lithium (Li) metal is used as an anode material in a 3.0 V-class film-type $MnO_2||$Li primary battery to increase the operating voltage and discharge capacity for application to active sensor tags of a radio frequency identification system. The fabricated 3.0 V-class film-type Li primary battery passes several safety tests and achieves a discharge capacity of more than 9 mAh $cm^{-2}$.

• Journal of the Korean Electrochemical Society
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• v.27 no.1
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• pp.47-54
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• 2024

In this study, ZIF67/rGO was used to minimize the battery life degradation due to the insulating properties of sulfur and the elution of lithium polysulfide. ZIF67 wrapped in rGO creates more space within the carbon sponge and can hold a large amount of sulfur. The sulfur@ZIF67/rGO composite was synthesized and prepared as a sponge to enhance the sulfur retention capacity. The result showed a high initial capacity, with a value of about 1093 mAh g^-1 and a capacity retention rate of 84% after 100 cycles. The high interaction with sulfur through the complexation of cobalt and carbon confirmed that ZIF67/rGO exhibits high performance as a carrier for sulfur, the anode active material of lithium-sulfur batteries, and the high initial capacity and improved capacity retention rate were confirmed.

• Journal of Electrochemical Science and Technology
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• v.12 no.4
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• pp.377-386
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• 2021

The Li-rich oxides are promising cathode materials due to their high energy density. However, characteristics such as low rate capability, unstable cyclic performance, and rapid capacity fading during cycling prevent their commercialization. These characteristics are mainly attributed to the phase instability of the host structure and undesirable side reactions at the cathode/electrolyte interface. To suppress the phase transition during cycling and interfacial side reactions with the reactive electrolyte, K (potassium) doping and Nb oxide coating were simultaneously introduced to a Li-rich oxide (Li_1.2Ni_0.13Co_0.13Mn_0.54O₂). The capacity and rate capability of the Li-rich oxide were significantly enhanced by K doping. Considering the X-ray diffraction (XRD) analysis, the interslab thickness of LiO₂ increased and cation mixing decreased due to K doping, which facilitated Li migration during cycling and resulted in enhanced capacity and rate capability. The K-doped Li-rich oxide also exhibited considerably improved cyclic performance, probably because the large K⁺ ions disturb the migration of the transition metals causing the phase transition and act as a pillar stabilizing the host structure during cycling. The Nb oxide coating also considerably enhanced the capacity and rate capability of the samples, indicating that the undesirable interfacial layer formed from the side reaction was a major resistance factor that reduced the capacity of the cathode. This result confirms that the introduction of K doping and Nb oxide coating is an effective approach to enhance the electrochemical performance of Li-rich oxides.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.649-656
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• 2011

A model for the numerical simulation of lithium-ion batteries (LIBs) is developed for use in battery cell design, with a view to improving the performances of such batteries. The model uses Newman-type electrochemical and transfer $theories^{(1,2)}$ to describe the behavior of the lithium-ion cell, together with the Levenberg-Marquardt optimization scheme to estimate the performance or design parameters in nonlinear problems. The mathematical model can provide an insight into the mechanism of LIB behavior during the charging/discharging process, and can therefore help to predict cell performance. Furthermore, by means of least-squares fitting to experimental discharge curves measured at room temperature, we were able to obtain the values of transport and kinetic parameters that are usually difficult to measure. By comparing the calculated data with the life-test discharge curves (SB LiMotive cell), we found that the capacity fade is strongly dependent on the decrease in the reaction area of active materials in the anode and cathode, as well as on the electrolyte diffusivity.

• Journal of the Korean institute of surface engineering
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• v.42 no.1
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• pp.8-12
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• 2009

Electronic structures and chemical bonding of Li-intercalated $LiTiS_2$ and $LiTiO_2$ were investigated by using discrete variational $X{\alpha}$ method as a first-principles molecular-orbital method. ${\alpha}-NaFeO_2$ structure is the equilibrium structure for $LiCoO_2$, which is widely used as a commercial cathode material for lithium secondary battery. The study especially focused on the charge state of Li ions and the magnitude of covalency around Li ions. The average voltage of lithium intercalation was calculated using pseudopotential method and the average intercalation voltage of $LiTiO_2$ was higher than that of $LiTiS_2$. It can be explained by the differences in Mulliken charge of lithium and the bond overlap population between the intercalated Li ions and anions in $LiTiO_2$ as well as $LiTiS_2$. The Mulliken charge, which means the ionicity of Li atom, was approximately 0.12 in $LiTiS_2$ and the bond overlap population (BOP) indicating the covalency between Ti and S was about 0.339. One the other hands, the Mulliken charge of lithium was about 0.79, which means that Li is fully ionized. The BOP, the covalency between Ti and O, was 0.181 in $LiTiO_2$. Because of high ionicity of Li and the weak covalency between Ti and the nearest anion, $LiTiO_2$ has a higher intercalation voltage than that of $LiTiS_2$.