• 한국전기화학회:학술대회논문집
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• 2002.11a
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• pp.57-65
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• 2002

The presence of tetragonal phase at the surface of $LiMn_2O_4$ pinicle due to a Jahn-Teller offset was previously reported to be one of the causes for capacity fading observed during cycling of $Li//Li_xMn_2O_4$ in 4V range. Further, it is reported that a Jahn-Teller effect in 4V range may be suppressed by substitution of Mn ions with Li ions or other transition metal ions. However, the direct evidence of the suppression of a Jahn-Teller effect in 4V range by substitution of Mn ions with other metal ions has not been reported. The dissolution and formation of surface film at the surface of $LiMn_2O_4$ electrodes also reportedly affect the capacity fading or rate capability. This study reports on the evidence of the onset and suppression of a Jahn-Teller effect in 4V range and the dissolution and formation of surface film at the surface of $LiMn_2O_4$ thin film electrodes using in situ bending beam method (BBM) in situ electrochemical quartz crystal microbalance (EQCM).

• Journal of Industrial Technology
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• v.42 no.1
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• pp.1-5
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• 2022

Although the mileage of electric vehicles can be increased based on the excellent energy density of the LiNi_0.9Co_0.05Mn_0.05O₂, it is known that the reason for limiting its use is the low lifespan and poor surface stability due to the structural deformation of the LiNi_0.9Co_0.05Mn_0.05O₂. To improve the structural stability of LiNi_0.9Co_0.05Mn_0.05O₂, electrochemical performance is improved by La coating on the surface. La-modified LiNi_0.9Co_0.05Mn_0.05O₂ shows an initial capacity of 210.6 mAh/g, a capacity retention rate of 89.9 % after 50 cycles, and a retention rate of 52.5% at 6.0 C. These are superior performances than the pristine sample, because the structural stability of the LiNi_0.9Co_0.05Mn_0.05O₂ cathode is improved by the La coating.

• Journal of Electrochemical Science and Technology
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• v.3 no.2
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• pp.72-79
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• 2012

$Li_2MnSiO_4$ was synthesized using the solid-state method under an Ar atmosphere at three different calcination temperatures (900, 950, and $1000^{\circ}C$). The optimization of the carbon coating was also carried out using various molar concentrations of adipic acid as the carbon source. The XRD pattern confirmed that the resulting $Li_2MnSiO_4$ particles exhibited an orthorhombic structure with a $Pmn2_1$ space group. Cyclic voltammetry was utilized to investigate the capacitive behavior of $Li_2MnSiO_4$ along with activated carbon (AC) in a hybrid supercapacitor with a two-electrode cell configuration. The $Li_2MnSiO_4$/AC cell exhibited a high discharge capacitance and energy density of $43.2Fg^{-1}$ and $54Whkg^{-1}$, respectively, at $1.0mAcm^{-2}$. The $Li_2MnSiO_4$/AC hybrid supercapacitor exhibited an excellent cycling stability over 1000 measured cycles with coulombic efficiency over > 99 %. Electrochemical impedance spectroscopy was conducted to corroborate the results that were obtained and described.

• 한국전기화학회:학술대회논문집
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• 2001.04a
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• pp.55-55
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• 2001

• Korean Chemical Engineering Research
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• v.45 no.2
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• pp.178-182
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• 2007

Non-aqueous supercapacitors by using activated C and $LiMn_2O_4$ as an active material in a positive electrode were prepared and characterized. From the cyclic voltammetry and AC impedance analysis, the capacitive effect by electric double layer of activated carbon and the faradic effect by intercalation/deintercalation of $Li^+$ ion were observed. Increasing the ratio of $LiMn_2O_4$, specific capacitances and energy densities of supercapacitor were increased. At the ratio of 0.86:0.14 ($LiMn_2O_4:C$), the maximum specific capacitance of 17.51 Wh/L and energy density of 23.83 F/cc were obtained, which were more than twice of those for a conventional electric double layer capacitor. Even after 1,000 charge/discharge cycle, the supercapacitor by using the electrode containing 14% of activated carbon and 86% of $LiMn_2O_4$ showed 60% better specific capacitance and energy density than that by using the electrode containing 100% activated carbon.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.1
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• pp.64-70
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• 2006

In this study, the $LiCoO_2/LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2$ mixed cathode electrodes were prepared and their electrochemical performances were measured in a high cut-off voltage. As the content of $LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2$ increased in a mixed cathode, the reversible specific capacity and cycleability of the electrode enhanced, but the rate capability was deteriorated. On the contrary the rate capability of the cathode enhanced, but the reversible specific capacity and cycleability were deteriorated, increasing the content of $LiCoO_2$ in the mixed cathode. The cell of $LiCoO_2/LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2$ ($50:50 wt\%$) mixed cathode delivered a discharge capacity of ca. 168 mAh/g at a 0.2 C rate. The capacity of the cell decreased with the current rate and a useful capacity of ca. 152 mAh/g was obtained at a 2.0 C rate. However, the cell showed very stable cycleability: the discharge capacity of the cell after 20th charge/discharge cycling maintains ca. 163 mAh/g.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1220-1221
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• 2006

[ $LiMn_2O_4$ ] powders for lithium ion batteries were synthesized from two separate raw material pairs of LiOH/MnO and $LiOH/MnO_2$. The powders prepared at 780 and $850^{\circ}C$ and their difference of electrochemical properties were investigated. Both powders calcined at 780 and $850^{\circ}C$ were composed of a single-phase spinel structure but those treated at $850^{\circ}C$ showed a lower intensity ratio of $I_{311}$ to $I_{400}$, a slightly larger lattice parameter, and an increased discharge capacity by 10% under $3.0{\sim}4.3V$ voltage range. The XPS study on the oxidation states of manganese repealed that powders made from LiOH/MnO had less $Mn^{3+}$ ion and gave better battery performances than those from $LiOH/MnO_2$.

• Korean Journal of Crystallography
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• v.15 no.1
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• pp.44-50
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• 2004

Spinel structured lithium managanese oxide $(LiMn_2O_4)$ powder with well defined facetted morphology was prepared by precipitation-evaporation method. {111}, {110}, and {100} planes are mainly observed in the $LiMn_2O_4$ powder. And powder shape of tetradecahedron and octahedron was observed depending on the calcinations temperature. The observed powder morphology observed seemed to be related to the nonstoichiometry of the oxygen in the $LiMn_2O_4$ spinel structure. Oxygen nonstoichiometry might be responsible for the Jahn-teller effect and structure transition which in turn affects the surface energy of the {111}, {110}, and {100} planes. Powder shape transition from tetradecahedron to octahedron seemed to be related to the surface energy of the {111}, {110}, and {100} planes with oxygen nonstoichiometry.

• Journal of the Korean Ceramic Society
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• v.37 no.6
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• pp.564-568
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• 2000

Spinel LiMn2O4 catalyst with submicron and single phase particles was synthesized at 48$0^{\circ}C$ for 12 hr in air by a sol-gel method. The spinel LiMn2O4 was deoxidized by hydrogen at various temperatures. Effects of physiochemical properties of the catalyst reduced by hydrogen were examined with X-ray diffractometer, thermogravimetric analysis and scanning electron microscope. The decomposition rate of carbon dioxide was measrued using the catalyst deosidized at 35$0^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.653-656
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• 2009

3-Dimensionally ordered macroporous $LiMn_2O_4$ thin film was prepared by a sol-gel and dip coating method on Pt/Ti/$SiO_2$/Si substrate. An opal structure consisting of mono dispersed polystyrene beads (300 nm) was used as a template. After solution containing Mn and Li precursors was coated on the template-deposited substrate, the template and organic materials in the precursors was removed by calcination at 400 ${^{\circ}C}$. And then the 3-dimensional $LiMn_2O_4$ thin film with spinel structure was fabricated by heat treatment at 700 ${^{\circ}C}$. The structural and electrochemical property was investigated by XRD, SEM and charge-discharge cycler.