• Bulletin of the Korean Chemical Society
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• v.15 no.2
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• pp.161-167
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• 1994

Rate constants have been measured spectrophotometrically for the nucleophilic substitution reactions of aryl substituted benzenesulfonates (3) with alkali metal ethoxides ($EtO^-M^+$) and butane-2,3-dione monoximates ($Ox^-M^+$) in ethanol at $25^{\circ}C$. The reactivity of the alkali metal ethoxides decreases in the order $EtO^-K^+> EtO^- > EtO^-Li^+$, indicating that $K^+$ ion behaves as a catalyst and $Li^+$ ion acts as an inhibitor for all the substrates studied. For the corresponding reactions of 3 with Ox^-M^+$, $Li^+$ ion also exhibits inhibitory effect for all the substrates, while, $K^+$ ion shows catalytic or inhibitory effects depending on the nature of substituents on the acyl and phenyl moieties. A study of substituent effect on rate has revealed that both EtO^- $and Ox^-$ systems have the same reaction mechanism. The different behavior shown by $K^+$ ion for the reaction of 3 with $EtO^-$ and $Ox^-$ would be attributed to a difference in charge polarization of S=O bond in the transition state between the two systems and/or a change in conformation of Ox^-K^+$.

• Membrane Journal
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• v.14 no.4
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• pp.263-274
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• 2004

The polymeric membrane, a component of battery devices such as Li-ion battery (LIB) and Li-polymer battery (LPB), is a typical material in which the carrier mobility dominates the battery performance. In this paper, the state-of-the-art of membranes for secondary battery is described in terms of membrane properties. Several prerequisites, which are related to stability of battery devices, are discussed to design and prepare suitable polymeric membranes. In addition, physical requirements of membranes and their measurement methods are described to develop applicable polymeric membranes in membrane preparation processes.

• Journal of Electrochemical Science and Technology
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• v.3 no.3
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• pp.135-142
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• 2012

Over the past few years, $LiFePO_4$ has been actively studied as a cathode material for lithium-ion batteries because of its advantageous properties such as high theoretical capacity, good cycle life, and high thermal stability. However, it does not have a very good power capability owing to the low lithium-ion diffusivity and poor electronic conductivity. Reduction in particle size of $LiFePO_4$ to the scale of nanometers has been found to dramatically enhance the above properties, according to many earlier reports. However, because of the intrinsically low tap density of nanomaterials, it is difficult to commercialize this method. Many studies are being carried out to improve the volumetric energy density of this material and many methods have been reported so far. This paper provides a brief summary of the synthesis methods and electrochemical performances of micro-spherical $LiFePO_4$ having high volumetric energy density.

• Korean Journal of Materials Research
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• v.14 no.9
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• pp.627-633
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• 2004

Lithium titanate whiske($Li_{x}Ti_{4}O_9$) was prepared by an ion-exchange reaction. To this end, the initial material, potassium tetratitanate ($K_{2}Ti_{4}O_9{\cdot}nH_{2}O$) was prepared by calcination of a mixture of $K_{2}CO_3\;and\;TiO_2$ with a molar ratio of 2.8 at $1050^{\circ}C$ for 3 h, followed by boiling water treatment of the calcined products for 10 h. Fibrous potassium tetratitanate could be transformed into layered hydrous titanium dioxide ($H_{2}Ti_{4}O_9{\cdot}nH_{2}O$) through an exchange of $K^{+}\;with\;H^{+}$ using 0.075 M HCl. Also, lithium titanate whisker was finally prepared as $Li^{+}\;and\;H^{+}$ ions were exchanged by adding 20 mL of a mixture solution of LiOH and $LiNO_3$ to 1g whisker and stirring for $5\~15$ days. The average length and diameter of the $Li_{x}Ti_{4}O_9$ whiskers were $10\~20{\mu}m\;and\;1\~3{\mu}m$, respectively.

• Korean Journal of Materials Research
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• v.28 no.6
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• pp.337-342
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• 2018

Using a high pressure homonizer, we report on the electrochemical performance of $Li_4Ti_5O_{12}(LTO)$ particles manufactured as anode active material for lithium ion battery. High-pressure synthesis processing is performed under conditions in which the mole fraction of Li/Ti is 0.9, the synthesis pressure is 2,000 bar and the numbers of passings-through are 5, 7 and 10. The observed X-ray diffraction patterns show that pure LTO is manufactured when the number of passings-through is 10. It is found from scanning electron microscopy analysis that the average size of synthesized particles decreases as the number of passings-through increases. $LiCoO_2-based$ active cathode materials are used to fabricate several coin half/full cells and their battery characteristics such as lifetime, rate capability and charge transfer resistance are then estimated, revealing quite good electrochemical performance of the LTO particles as an effective anode active material for lithium secondary batteries.

• Korean Journal of Materials Research
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• v.12 no.4
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• pp.274-278
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• 2002

Discrete-variational(DV)-$X{\alpha}$ method was applied to investigate the electronic structures of spinel- type manganese oxide which is well known to the high performance adsorbent or cathode material for lithium ion. The results of DOS(density of states) and Mulliken population analysis showed that Li was nearly fully ionized and interactions between Mn and O were strong covalent bond. The effective charge of Li and Mn was +0.77 and +1.44 respectively and the overlap population between Mn and O was 0.252 in $LiMn_2O_4$. These results from DV-X$\alpha$ method were well coincided with the experimental result by XPS analysis and supported the feasibility of theoretical interpretation for the $LiMn_2O_4$ compound.

• Bulletin of the Korean Chemical Society
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• v.31 no.11
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• pp.3385-3390
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• 2010

$Li^+$ ion complex of azacrown ether with restricted motion of freedom and pseudo-bilateral symmetry was studied by infrared spectroscopy, which has shown simplified and broadened vibrational features. The C=O and N-H stretching bands, in particular, shows anomalous broadening nearly ${\sim}50\;cm^{-1}$. The density functional calculation at the level of BP86/6-31+$G^{**}$ shows that $Li^+$ ion is trapped and rather free to move around inside the cavity, as much as about $0.70\;{\AA}$. Through the relocation of $Li^+$ ion inside the cavity, the conformational changes would occur rapidly in its symmetry $C_1\;{\rightleftarrows}\;C_2\;{\rightleftarrows}\;C_1$$. The potential barrier was obtained to be merely ~2.2 kJ/mol for $C_1\;{\rightarrow}\;C_2$. During this conformational alteration, the amide backbone twists concurrently its dihedral angle side to side about up to ${\pm}3$ degree. Selected vibrational modes were interpreted in terms of the force constant variations of local symmetry coordinates between conformations in the framework of $C_1\;{\rightleftarrows}\;C_2\;{\rightleftarrows}\;C_1$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.294-294
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• 2007

Spinel cathode material $LiMn_2O_4$ is currently studied as a promising cathode material for lithium ion secondary batteries for future applications because of it is low cost, easy to be prepared and capable to be operated in high voltage range. However as a cathode material, $LiMn_2O_4$ performs a poor capacity retention which leads to short cycle life. In this study, stoichiometric $LiMn_2O_4$ was synthesized with granulation method with ion substitution to stabilize its structure and niobium doping to improve its conductivity. These well-mixed powders were calcined at $850^{\circ}C$ for 6 hours and its properties were investigated. Correlations of dopant and electrochemical properties were examined as well.

• Resources Recycling
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• v.33 no.1
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• pp.15-21
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• 2024

The demand for electric vehicles powered by lithium-ion batteries is continuously increasing. Recovery of valuable metals from waste lithium-ion batteries will be necessary in the future. This research investigated the effect of reaction temperature on the lithium recovery ratio from hydrogen reduction followed by water leaching from lithium-ion battery NCM-based cathode materials. As the reaction temperature increased, the weight loss ratio observed after initiation increased rapidly owing to hydrogen reduction of NiO and CoO; at the same time, the H₂O amount generated increased. Above 602 ℃, the anode materials Ni and Co were reduced and existed in the metallic phases. As the hydrogen reduction temperature was increased, the Li recovery ratio also increased; at 704 ℃ and above, the Li recovery ratio reached a maximum of approximately 92%. Therefore, it is expected that Li can be selectively recovered by hydrogen reduction as a waste lithium-ion battery pretreatment, and the residue can be reprocessed to efficiently separate and recover valuable metals.

• Journal of the Korean Ceramic Society
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• v.55 no.1
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• pp.21-35
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• 2018

Spinel $LiNi_{0.5}Mn_{1.5}O_4$ has received great attention as one of the most outstanding cathode materials for Li-ion batteries (LIBs) because of its high energy density resulting from the operating voltage of ~ 4.7 V (vs. $Li^+/Li$) based on the $Ni^{2+}/Ni^{4+}$ redox reaction. However, $LiNi_{0.5}Mn_{1.5}O_4$ is known to suffer from undesirable side reactions with the electrolyte at high voltage as well as Mn dissolution from the structure. These issues prevent the realization of the optimal electrochemical performance of $LiNi_{0.5}Mn_{1.5}O_4$. Extensive research has been conducted to overcome these issues. This review presents an overview of the various surface-modification methods available to improve the electrochemical properties of $LiNi_{0.5}Mn_{1.5}O_4$ and provides perspectives on further research aimed at the application of $LiNi_{0.5}Mn_{1.5}O_4$ as a cathode material in commercialized LIBs.