• Proceedings of the Materials Research Society of Korea Conference
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• 1999.11a
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• pp.157-157
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• 1999

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.106-108
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• 2001

As 3V cathode material, a new doping spinel material, LiMn1.6Se0.4O4 powder with a phase-pure polycrystalline was synthesized by a sol-gel method. In spite of Jahn-teller distortion in 3V region($2.4{\sim}3.5V$), the LiMn1.6Se0.4O4 electrode shows no capacity loss. The material in the 3V region initially delivers a discharge capacity of 100mAh/g which increase with cycling to reach 105mAh/g after 90cycles. And 5V cathode material LiNi0.5-xMxMn1.5O4(M=Cr, V, Fe) compounds have been synthesized by sol-gel method. a series of electroactive spinel compounds, LiNi0.5-xMxMn1.5O4(M=Cr, V, Fe) has been studied by crystallographic and electrochemical methods. The material presents only one plateau at around 4.5 V vs. Li/Li+ with a large discharge capacity of 152mAh/g and fairly good cyclability.

• Applied Chemistry for Engineering
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• v.10 no.6
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• pp.832-837
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• 1999

Stability of a cathode material was determined by Tafel plot in 1 M LiOH solution. The stabilized $LiM_xMn_{2-x}O_4$ (x=0.05~0.1) electrode resulted in overpotential of 0.13~0.15 mV at 100 mA. This overpotential was 0.05 mV lower than that of the spinel structured $LiMn_2O_4$ electrode. Conductivity test at various potentials showed that the conductivity of $LiM_xMn_{2-x}O_4$ was higher than that of the spinel structured $LiMn_2O_4$ and the bulk resistance of $LiM_xMn_{2-x}O_4$ due to the dissolution of $Mn^{2+}$ was lowered.

• Journal of the Korean Vacuum Society
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• v.20 no.3
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• pp.205-210
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• 2011

Structural and electrochemical properties of spinel oxide $LiMn_2O_4$ thin films prepared by using a sol-gel method on Pt/Ti/$SiO_2$/Si substrates were investigated. When Li/Mn molar ratio of the film was smaller than 0.5, $Mn_2O_3$hase was found to coexist with $LiMn_2O_4$. Half-cell batteries fabricated using the $LiMn_2O_4$ films as the cathode were put into chargedischarge (C-D) cycles and the change in structural properties of the cathode after the cycles was examined by X-ray diffraction and Raman spectroscopy. As the C-D cycle number increases, the discharge capacity of pure $LiMn_2O_4$ battery gradually decreases, being reduced to 72% of the initial capacity at 300 cycles. Such capacity fading is attributable to the decrease in the number of $Li^+$ ions that return to the tetrahedral sites of the spinel structure during the discharge step and the resultant increase in $Mn^{4+}$ density in the film. Also, $Mn_2O_3$ phase gradually appeared in the film as the cycle number increases.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.5-5
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• 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 Institute of Electrical and Electronic Material Engineers
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• v.18 no.8
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• pp.702-707
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• 2005

Spinel $LiMn_2O_4$ has become appealing because manganese is inexpensive and environmentally benign. In general, cathodes for lithium ion batteries include carbon as a conductive agent that provides electron transfer between the active material and the current collector. In this work, we selected Acetylene Black and Super P Black as conductive agents, and then carried out their comparative investigation for the performances of the $Li/LiMn_2O_4$ cells using different conductive agents with different particle size. In addition, their electrochemical impedance characteristic of $Li/Mn_2O_4$ cells using different conductive agents is effectively identified through a.c. impedance technique. As a consequence, $Li/LiMn_2O_4$ cells with Super P Black show better electrochemical performances ascribed to the significant contribution of feasible ionic conduction due to larger particle size than those with Acetylene Black.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.4
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• pp.309-315
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• 2001

Crystallized $LiMn_{2-y}Mg_{y}O_4$ powder was prepared by calcing the mixture of LiOH.$H_2O$, $MnO_2$ and MgO at $800^{\circ}C$ for 36h in an air atmosphere. The structure of $LiMn_{2-y}Mg_{y}O_4$ crystallites was analyzed from powder X-ray diffraction data as a cubic spinel, space group Fd3m. Though all cathode material showed spinel phase based on cubic phase in X-ray diffraction, other peaks gradually exhibited and became intense with increasing y value in $LiMn_{2-y}Mg_{y}O_4$. However, ununiform which calculated by (111) face and (222) face was constant in spite of the increase of y value, except pure $LiMn_2O_4$. AC impedance of Li/$LiMn_{2-y}Mg_{y}O_4$ cells revealed the similar resistance of about $70\Omega$ before cycling. In addition, The impedance of Li/$LiMn_{1.9}Mg_{0.1}O_4$ cell changed during charge and discharge or after cycling.

• Bulletin of the Korean Chemical Society
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• v.31 no.2
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• pp.309-314
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• 2010

The surface modified $LiMn_2O_4$ materials with Li-Fe composites were prepared by a sol-gel method to improve the electrochemical performance of $LiMn_2O_4$ and were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and transmission electron microscopy (TEM)-EDS. XRD results indicate that all the samples (modified and pristine samples) have cubic spinel structures, and XRD, XPS, and TEM-EDS data reveal the formation of $Li(Li_xFe_xMn_{2-2x})O_4$ solid solution on the surface of particles. For the electrochemical properties, the modified material demonstrated dramatically enhanced reversibility and stability even at elevated temperature. These improvements are attributed to the formation of the solid solution, and thus-formed solid solution phase on the surface of $LiMn_2O_4$ particle reduces the dissolution of Mn ion and suppresses the Jahn-Teller effect.

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

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4660-4665
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• 2011

New precursors as a Li adsorbent, $Li_{1.6}(MnM)_{1.6}O_4$ (M=Cu, Ni, Co, Fe), were synthesized by hydrothermal method and their physicochemical properties were discussed. XRD and HRTEM results revealed that the original spinel structure was stabilized by cobalt-doping while Cu-, Ni- and Fe-doping led to structural changes. Such a structural stabilization by Cobalt-doping was maintained after lithium leaching by acid treatment. Li absorption efficiency from seawater was significantly enhanced by using the Cobalt-doped spinel manganese oxide, $Li_{1.6}[MnCo]_{1.6}O_4$, compared to the commercially available $Li_{1.33}Mn_{1.67}O_4$; the adsorbed amount of Li from 1g-adsorbent was 35 and 16 mg by $Li_{1.6}[MnCo]_{1.6}O_4$, and $Li_{1.33}Mn_{1.67}O_4$, respectively.