Daejung EM Co.

Incheon, South Korea

Daejung EM Co.

Incheon, South Korea

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Jeong J.-H.,Korea Electrotechnology Research Institute | Jin B.-S.,Korea Electrotechnology Research Institute | Kim W.-S.,Daejung em Co. | Wang G.,University of Wollongong | Kim H.-S.,Korea Electrotechnology Research Institute
Journal of Power Sources | Year: 2011

Cathode materials prepared by a co-precipitation are 0.3Li 2MnO3·0.7LiMn1-xNiyCo 0.1O2 (0.2 ≤ x ≤ 0.4) cathode materials with a layered-spinel structure. In the voltage range of 2.0-4.6 V, the cathodes show more than one redox reaction peak during its cyclic voltammogram. The Li/0.3Li2MnO3·0.7LiMn1-xNi yCo0.1O2 (x = 0.3, y = 0.2) cell shows the initial discharge capacity of about 200 mAh g-1. However, when x = 0.2 and y = 0.1, the cell exhibits a rapid decrease in discharge capacity and poor cycle life. © 2011 Elsevier B.V.


Aravindan V.,Chonnam National University | Aravindan V.,Nanyang Technological University | Karthikeyan K.,Chonnam National University | Kang K.S.,Korea Advanced Institute of Science and Technology | And 3 more authors.
Journal of Materials Chemistry | Year: 2011

Superior lithium storage in Li2MnSiO4 cathodes was observed by altering carbon content during the formulation of electrodes. Initially, Li2MnSiO4 was prepared by a conventional solid-state reaction at 900°C under Ar flow with a fixed amount of adipic acid, which acts as a gelating agent during synthesis. The phase formation was confirmed through powder X-ray diffraction measurements. Scanning electron microscope pictures indicate the particulate morphology of synthesized Li 2MnSiO4 particles. Various compositions of electrodes were formulated using the conducting carbon (ketjen black) from 3 to 11 mg along with active material. All the fabricated electrodes were cycled in a Li/Li 2MnSiO4 cell configuration to evaluate its lithium storage performance at 0.05 C rate. Among the electrodes, 42% carbon in the composite electrode exhibited a very stable discharge behaviour ∼140 mA h g -1 for 40 cycles at room temperature. Such storage performance was ascribed to the improved electronic conductivity of Li2MnSiO 4 electrodes by incorporating carbon. This improvement was supported by electrochemical impedance spectroscopy measurements. Rate performance studies were also conducted and presented in the manuscript. © 2011 The Royal Society of Chemistry.


Aravindan V.,Chonnam National University | Aravindan V.,Nanyang Technological University | Ravi S.,Mepco Schlenk Engineering College, Sivakasi | Kim W.S.,Daejung EM Co. | And 2 more authors.
Journal of Colloid and Interface Science | Year: 2011

Size controlled, nanoparticulate Li2MnSiO4 cathodes were successfully prepared by sol-gel route. Effects of calcination temperature and carbon content (adipic acid) were studied during synthesis process. EPR study was conducted to ensure the formation of phase through oxidation state of manganese. Microscopic pictures indicate spherical shape morphology of the synthesized Li2MnSiO4 nanoparticles. Transmission electron microscopic pictures confirmed the presence of carbon coating on the surface of the particles. Further, the optimization has been performed based on phase purity and its battery performance. From the optimization, 700°C and 0.2mol adipic acid (against total metal ion present in the compound) were found better conditions to achieve high performance material. The Li2MnSiO4 nanoparticles prepared in the aforementioned conditions exhibited an initial discharge capacity of ∼113mAhg-1 at room temperature in Li/1M LiPF6 in EC:DMC/Li2MnSiO4 cell configuration. All the Li2MnSiO4 nanoparticles prepared at various conditions experienced the capacity fade during cycling. © 2010 Elsevier Inc.


Karthikeyan K.,Chonnam National University | Amaresh S.,Chonnam National University | Aravindan V.,Chonnam National University | Aravindan V.,Nanyang Technological University | And 4 more authors.
Journal of Power Sources | Year: 2013

We first report the ultra-fast charge-discharge capability of organic-inorganic (Li(Mn1/3Ni1/3Fe1/3)O 2-Polyaniline (PANI)) nanocomposites prepared by mixed hydroxide route and followed by polymerization of aniline monomers with different concentrations (0.1 and 0.2 mol concentration of PANI). Li-insertion properties are evaluated in half-cell configuration, test cell (Li/Li(Mn 1/3Ni1/3Fe1/3)O2-PANI) comprising 0.2 mol. PANI delivered the reversible capacity of ∼127, ∼114 and ∼110 mAh g-1 at ultra-high current rate of 5, 30 and 40 C, respectively with exceptional cycleability between 2 and 4.5 V vs. Li. Such an exceptional performance is mainly due to the conducting pathways promoted by PANI network and it is revealed by impedance measurements. This result certainly provides the possibility of using such layered type Fe based cathode materials in high power Li-ion batteries to drive zero emission vehicles such as hybrid electric vehicles or electric vehicles applications in near future. © 2013 Elsevier B.V. All rights reserved.


Kim M.C.,Chonnam National University | Kim S.H.,Chonnam National University | Aravindan V.,Nanyang Technological University | Kim W.S.,Daejung EM Co. | And 2 more authors.
Journal of the Electrochemical Society | Year: 2013

In this study,we present the influence of polyimide (PI) coating concentration on the electrochemical properties of high voltage, spinel phase LiNi0.5Mn1.5O4 cathodes, particularly under elevated temperature conditions. First, the adipic acid-mediated sol-gel technique was employed to synthesize sub-micron sized LiNi0.5Mn1.5O4 particles, where Mn was in the 4± state. Thermal polymerization was used to produce the PI coating from polyamic acid. The presence of the PI layer was confirmed by transmission electron microscopy and Fourier-transform infrared analyzes. All test cells delivered good cycleability under ambient temperature conditions, irrespective of the PI coating concentration, with a prominent plateau at 4.7 V vs. Li, whereas all test cells experienced the poorest electrochemical behavior under elevated temperature conditions except 0.3 wt.% PI. The 0.3 wt.% PI coated LiNi0.5Mn1.5O4 phase delivered excellent cycleability with capacity retention of > 90% at 55°C. Poor compatibility and severe reactivity toward the electrolyte solution resulted in the poorest performance which was clearly evidenced by the scanning electron microscopy analysis and supported well by impedance studies after galvanostatic cycling. © 2013 The Electrochemical Society.


Cho A.R.,Chonnam National University | Son J.N.,Chonnam National University | Aravindan V.,Chonnam National University | Aravindan V.,Nanyang Technological University | And 5 more authors.
Journal of Materials Chemistry | Year: 2012

A high rate and high performance Li 3V 2(PO 4) 3 cathode was prepared by applying a carbon coating and Al substitution using the conventional solid-state approach. X-Ray diffraction was used to observe the structural properties of the synthesized powders. The presence of the carbon coating was confirmed by HR-TEM and reflected well with the Raman analysis. The Li/C-Li 3V 1.98Al 0.02(PO 4) 3 cell displayed a discharge capacity of 182 mA h g -1 between 3 and 4.8 V vs. Li at a current density of 0.1 mA cm -1, which is ∼20 mA h g -1 higher than that of the native compound. The capacity retention was found to be 84 and 74% after 40 and 100 cycles, respectively. The C-Li 3V 1.98Al 0.02(PO 4) 3 powders demonstrated excellent rate performance at 20 C with a discharge capacity of ∼120 mA h g -1 over 100 cycles. The elevated temperature performance was also evaluated and found to be similar to that under room temperature conditions. © The Royal Society of Chemistry 2012.


Karthikeyan K.,Chonnam National University | Amaresh S.,Chonnam National University | Lee G.W.,Chonnam National University | Aravindan V.,Chonnam National University | And 5 more authors.
Electrochimica Acta | Year: 2012

Cobalt free, eco-friendly layered Li 1.2(Mn 0.32Ni 0.32Fe 0.16)O 2 compounds were synthesized using the adipic acid assisted sol-gel method. The structure and morphology of the prepared materials were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results revealed that all of the materials possess a layered α-NaFeO 2 structure with R3̄m space group. The TEM images confirmed the presence of carbon on the surface of the synthesized material. Galvanostatic charge/discharge studies demonstrated that the cyclic performance and rate capability of the materials were improved by the presence of carbon and the crystalline nature of the material. Among the synthesized materials, the sample prepared with 1 M adipic acid exhibited not only a high discharge capacity of 160 mAh g -1, but also excellent cycling performance with a capacity retention of over 92% after 25 cycles. In addition, electrochemical impedance spectroscopy (EIS) was used to confirm the improvement in the electronic conductivity and the results are discussed in detail. © 2012 Elsevier Ltd. All rights reserved.


Disclosed are a cathode active material for lithium seco ndary batteries, a method for preparing the same, and lithium secondary batteries comprising the same. The cathode active material for lithium secondary batteries comprises a lithium metal oxide secondary particle core formed by aggregation of a plurality of lithium metal oxide primary particles; a first shell formed by coating the surface of the secondary particl e core with a plurality of barium titanate particles and a pl urality of metal oxide particles; and a second shell formed b y coating the surface of the first shell with a plurality of olivine-type lithium iron phosphate oxide particles and a plu rality of conductive material particles. The cathode active m aterial for lithium secondary batteries allows manufacture of lithium secondary batteries having excellent thermal stabili ty, high-temperature durability and overcharge safety.


Kim H.-J.,Korea Electrotechnology Research Institute | Kim J.-M.,Korea Electrotechnology Research Institute | Kim W.-S.,Daejung em Co. | Koo H.-J.,Battery RandD Association of Korea | And 2 more authors.
Journal of Alloys and Compounds | Year: 2011

LiFePO4/C active material was synthesized using an ultrasonic-assisted rheological phase method. In addition, polyvinyl butyral (PVB) was added in various concentrations to provide carbon coating on the surface of the LiFePO4 particles for enhanced electrical conductivity. The crystal structure, morphology, and carbon coating layer of the synthesized LiFePO4/C was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The electrochemical performance of LiFePO4/C, such as initial capacity, rate capability, cycling performance and EIS, were also evaluated. The synthesized particle had a size range of 100-150 nm and a carbon layer of about 8 nm. The LiFePO4/C (5 wt% PVB) delivered an initial discharge capacity of 167.5 mAh/g at a 0.1 C rate. It also showed an excellent capacity retention ratio of 100% after the 50th charging/discharging. EIS results demonstrate that the charge transfer resistance of the sample decreases greatly by coating with 5 wt% PVB. © 2011 Elsevier B.V. All rights reserved.


Lee S.-Y.,Kangwon National University | Park J.-H.,Kangwon National University | Cho J.-H.,Kangwon National University | Kim S.-B.,Daejung em Co. | And 2 more authors.
Journal of Materials Chemistry | Year: 2012

A new and facile approach for the surface modification of high-voltage LiNi 1/3Co 1/3Mn 1/3O 2 cathode active materials is demonstrated. This strategy is based on polyimide (PI) gel polymer electrolyte (GPE)-directed nanoscale wrapping. The PI coating layer successfully wraps a large area of the LiNi 1/3Co 1/3Mn 1/3O 2 surface via thermal imidization of (pyromellitic dianhydride/oxydianiline) polyamic acid. Salient features of the PI wrapping layer are the highly continuous surface coverage with nanometre thickness (∼10 nm) and the facile ion transport through the nanoscale layer. Based on a sound understanding of the nanoarchitectured PI wrapping layer, its influence on the cell performance and thermal stability of high-voltage LiNi 1/3Co 1/3Mn 1/3O 2 is investigated as a function of charge cut-off voltage (herein, 4.6 and 4.8 V). The anomalous PI wrapping layer substantially improves the high-voltage cycling performance and alleviates the interfacial exothermic reaction between delithiated LiNi 1/3Co 1/3Mn 1/3O 2 and liquid electrolyte. These results demonstrate that the PI wrapping layer effectively prevents the direct exposure of the LiNi 1/3Co 1/3Mn 1/3O 2 surface to liquid electrolytes that are highly vulnerable to electrochemical decomposition at high charge voltage conditions, thus behaving as a novel ion-conductive protection skin that mitigates the unwanted interfacial side reactions. © 2012 The Royal Society of Chemistry.

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