• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.05a
• /
• pp.5-5
• /
• 2011

The research and development of hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV) and electric vehicle (EV) are intensified due to the energy crisis and environmental concerns. In order to meet the challenging requirements of powering HEV, PHEV and EV, the current lithium battery technology needs to be significantly improved in terms of the cost, safety, power and energy density, as well as the calendar and cycle life. One new technology being developed is the utilization of composite cathode by mixing two different types of insertion compounds [e.g., spinel $LiMn_2O_4$ and layered $LiMO_2$ (M=Ni, Co, and Mn)]. Recently, some studies on mixing two different types of cathode materials to make a composite cathode have been reported, which were aimed at reducing cost and improving self-discharge. Numata et al. reported that when stored in a sealed can together with electrolyte at $80^{\circ}C$ for 10 days, the concentrations of both HF and $Mn^{2+}$ were lower in the can containing $LiMn_2O_4$ blended with $LiNi_{0.8}Co_{0.2}O_2$ than that containing $LiMn_2O_4$ only. That reports clearly showed that this blending technique can prevent the decline in capacity caused by cycling or storage at elevated temperatures. However, not much work has been reported on the charge-discharge characteristics and related structural phase transitions for these composite cathodes. In this presentation, we will report our in situ x-ray diffraction studies on this mixed composite cathode material during charge-discharge cycling. The mixed cathodes were incorporated into in situ XRD cells with a Li foil anode, a Celgard separator, and a 1M $LiPF_6$ electrolyte in a 1 : 1 EC : DMC solvent (LP 30 from EM Industries, Inc.). For in situ XRD cell, Mylar windows were used as has been described in detail elsewhere. All of these in situ XRD spectra were collected on beam line X18A at National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory using two different detectors. One is a conventional scintillation detector with data collection at 0.02 degree in two theta angle for each step. The other is a wide angle position sensitive detector (PSD). The wavelengths used were 1.1950 ${\AA}$ for the scintillation detector and 0.9999 A for the PSD. The newly installed PSD at beam line X18A of NSLS can collect XRD patterns as short as a few minutes covering $90^{\circ}$ of two theta angles simultaneously with good signal to noise ratio. It significantly reduced the data collection time for each scan, giving us a great advantage in studying the phase transition in real time. The two theta angles of all the XRD spectra presented in this paper have been recalculated and converted to corresponding angles for ${\lambda}=1.54\;{\AA}$, which is the wavelength of conventional x-ray tube source with Cu-$k{\alpha}$ radiation, for easy comparison with data in other literatures. The structural changes of the composite cathode made by mixing spinel $LiMn_2O_4$ and layered $Li-Ni_{1/3}Co_{1/3}Mn_{1/3}O_2$ in 1 : 1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ~5.2 V vs. $Li/Li^+$, the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component only. When the cell voltage reaches at ~4.0 V vs. $Li/Li^+$, lithium extraction from the spinel $LiMn_2O_4$ component starts and becomes the major contributor for the cell capacity due to the higher rate capability of $LiMn_2O_4$. When the voltage passed 4.3 V, the major structural changes are from the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, while the $LiMn_2O_4$ component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel $LiMn_2O_4$ component, with much less changes in the layered $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research. More detailed discussion will be presented at the meeting.

• Journal of the Korean Electrochemical Society
• /
• v.9 no.4
• /
• pp.158-169
• /
• 2006

The present article is concerned with the overview of the chemically/surface modified cubic spinel $LiMn_2O_4$ as a cathode electrode far lithium ion secondary batteries. Firstly, this article presented a comprehensive survey of the cubic spinel structure and its correlated electrochemical behaviour of $LiMn_2O_4$. Subsequently, the various kinds of the chemically/surface modified $LiMn_2O_4$ and their electrochemical characteristics were discussed in detail. Finally, this article reviewed our recent research works published on the mechanism of lithium transport through the chemically/surface modified $Li_{1-\delta}Mn_2O_4$ electrode from the kinetic view point by the analyses of the experimental potentiostatic current transients and ac-impedance spectra.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.387-390
• /
• 1999

To improve the cycle performance LiM $n_2$ $O_4$as the cathode of 4V class lithium secondary batteries, the cathode properties of the cubic spinel phases LiM $g_{x}$ /M $n_{2-x}$/ $O_4$ synthesized at 80$0^{\circ}C$ were examined. All cathode material showed spinel phase based on cubic phase in X-ray diffraction however. other peaks gradually exhibited and became intense with the increase of x value in LiM $g_{x}$ /M $n_{2-x}$/ $O_4$. The cycle performance of the LiM $g_{x}$ /M $n_{2-x}$/ $O_4$was improved by the substitution of $Mg^{2+}$ for M $n^{3+}$ in the octahedral sites. Specially LiM $g_{0.1}$/M $n_{1.9}$ / $O_4$cathode materials showed the charge and discharge capacity of about 130~125mAh/g at first cycle and about 105mAh/g after 50th cycle. It is excellent than that of pure LiM $n_{2}$/ $O_4$ which 125mAh/g at first cycle 70mAh/g at 50th. In addition cathode material prepared at 80$0^{\circ}C$ for 24hr and 42hr in the charge and discharge capapcity as well as the cycle stability.ility.y.y.

• Proceedings of the Korean Ceranic Society Conference
• /
• 2000.04a
• /
• pp.68.2-68.2
• /
• 2000

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07b
• /
• pp.707-710
• /
• 2002

Spinel $LiMn_2O_4$ and $LiMn_{1.9}Mg_{0.05}Zn_{0.05}O_4$ powders were synthesized by solid-state method at $800^{\circ}C$ for 36h. Crystal structure and electrochemical properties were analyzed by X-ray diffraction, charge-discharge test, cyclic voltammetry and ac impedance to $LiMn_2O_4$ and $LiMn_{1.9}Mg_{0.05}Zn_{0.05}O_4/Li$. All cathode material showed spinel structure in X-ray diffraction. $LiMn_{1.9}Mg_{0.05}Zn_{0.05}O_4/Li$ cell substituted $Mg^{2+}$ and $Zn^{2+}$ showed excellent discharge capacities than other cells, which it presented about 120mAh/g at the 1st cycle and about 73mAh/g at the 250th cycle, respectively. AC impedance of $LiMn_{1.9}Mg_{0.05}Zn_{0.05}O_4/Li$ cells showed the similar resistance of about $65{\sim}110{\Omega}$ before cycling.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.11a
• /
• pp.125-128
• /
• 2007

In these recent years, low cost and stable battery electrode materials have been studied for HV/HEV application. Spinel cathode material $LiMn_2O_4$ is widely studied as a promising cathode material of lithium ion secondary batteries because of it is low cost, easily to be prepared and capable to be operated in high voltage range. In this study, $LiMn_2O_4$ was undergoing surface modification with spinel lithium titanium oxide by sol-gel method in order to enhance its capacity retention. Properties of both unmodified and surface-modified $LiMn_2O_4$ were characterized by XRD, SEM, particle size analyzer while their cycling performance was tested with charge and discharge tester.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.07a
• /
• pp.548-551
• /
• 2000

Spinel phase LiF $e_{y}$M $n_{2-y}$ $O_4$samples are synthesized by calcining a LiOH.$H_2O$, Mn $O_2$and F $e_2$ $O_3$mixture at 80$0^{\circ}C$ for 36h in air. Preparing LiF $e_{y}$M $n_{2-y}$ $O_4$showed spinel phase with cubic phase. The ununiform distortion of the crystallite of the spinel LiF $e_{y}$M $n_{2-y}$ $O_4$was more stable than that of the pure. The discharge capacity of the cathode for the Li/LiF $e_{0.1}$M $n_{1.9}$ $O_4$cell at the first than that of the pure. The discharge capacity of the cathode for the Li/LiF $e_{0.1}$M $n_{1.9}$ $O_4$cell at the first cycle and at the 70th cycle was about 113 and 90mAh/g, respectively. This cell capacity was retained about 82% of the first cycle after 70th cycle. Impedance profile of this cell was more stable than that pure. The resistance, the capacitance and chemical diffusion coefficients of lithium ion showed approximately 80$\Omega$, 36133.87$\mu$F ; 1.4$\times$10$^{-8}$ c $m^2$ $s^{-1}$ , respectively. , respectively.ely.

• Journal of the Korean Ceramic Society
• /
• v.36 no.9
• /
• pp.930-936
• /
• 1999

For LiMn2O4 based spinel structures the stoichiometric reaction conditions need be considered carefully because the electrical properties depend on the structural stability. In order to obtain the homogeneous compound the Pechini process was chosen which could obtain a stoichiometry phase even low temperature and dependency of the synthetic condition on structural stability and electrochemical performance was investigated. X-ray diffraction studies showed that the compounds doped with transition metal have smaller lattice constants than those un doped. The dc conductivity was evaluated by a four probe method in the low and high temperature region respectively. The variations of basal spacings for the cathode were detected to be dependent on the extent of current flows (under dc)

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.11a
• /
• pp.169-172
• /
• 2007

HEV용 리튬이온 전지에 대한 연구는 최근에 많은 연구가 진행되고 있으며 그중 고용량 및 저렴한 가격, 환경에 대한 안정성으로 인해 Li-Mn spinel에 대한 성능향상 연구가 많이 이루어지고 있다. 본 연구에서는 Li-Mn spinel의 입자크기에 대한 기초 물성 과 전기적 특성을 측정하여 입자크기가 용량에 미치는 영향에 대한 고찰을 하였다. Li-Mn spinel의 비표면적, C-V 특성, 전기적 용량, coulomb efficiency 등을 통하여 입자의 크기와 전해액, Li의 구동등과 관련하여 용량특성에 향상을 가져오는 입자크기 조건을 정의하였고 그에 따라 온도별로 합성 한 후 입자사이즈에 대한 특성을 나타내었다.

• Journal of the Korean Ceramic Society
• /
• v.43 no.9 s.292
• /
• pp.588-593
• /
• 2006

Spinel phase $LiMn_2O_4$ is of great interest as cathode materials for lithium-ion batteries. In this study, SHS (Self propagating High-temperature Synthesis) method to synthesize spinel $LiMn_2O_4$ directly from lithium nitrate, manganese oxide, manganese and sodium chloride were investigated. The influence of Li/Mn ratio, the heat-treated condition of product have been explored. The resultant $LiMn_2O_4$ synthesized under the optimum synthesis conditions shows perfect spinel structure, uniform particle size and excellent electrochemical performances.