• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.242-246
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• 2017

The application of composite cathode materials including $LiFePO_4$ (lithium iron phosphate) of olivine crystal structure, which has high thermal stability, were investigated as alternatives for hybrid battery-capacitors with a $LiMn_2O_4$ (spinel crystal structure) cathode, which exhibits decreased performance at high temperatures due to Mn-dissolution. However, these composite cathode materials have been shown to have a reduction in capacity by conducting life cycle experiments in which a $LiFePO_4$/activated carbon cell was charged and discharged between 1.0 V and 2.3 V at two temperatures, $25^{\circ}C$ and $60^{\circ}C$, which caused a degradation of the anode due to the lowered voltage in the anode. To avoid the degradation of the anode, composite cathodes of $LiFePO_4/LiMn_2O_4$ (50:50 wt%), $LiFePO_4$/activated carbon (50:50 wt%) and $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ (50:50 wt%) were prepared and the life cycle experiments were conducted on these cells. The composite cathode including $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ of layered crystal structure showed stable voltage behavior. The discharge capacity retention ratio of $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ was about twice as high as that of a $LiFePO_4/LiMn_2O_4$ cell at thermal stability experiment for a duration of 1,000 hours charged at 2.3 V and a temperature of $80^{\circ}C$.

• Journal of the Korean Electrochemical Society
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• v.16 no.4
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• pp.191-197
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• 2013

The one of the cathode material, $Li(Ni_{0.5}Co_{0.2}Mn_{0.3})O_2$, was synthesized by the precursor, $Ni_{0.5}Co_{0.2}Mn_{0.3}(OH)_2$, from the co-precipitation method and the morphologies of the primary particle of precursors were flake and needle-shape by controlling the precipitation parameters. Identical powder properties, such as particle size, tap density, chemical composition, were obtained by same process of lithiation and heat-treatment. The relation between electrochemical performances of $Li(Ni_{0.5}Co_{0.2}Mn_{0.3})O_2$ and the primary particle morphology of precursors was analyzed by SEM, XRD and EELS. In the $Li(Ni_{0.5}Co_{0.2}Mn_{0.3})O_2$ cathode from the needle-shape precursor, the primary particle size was smaller than that from flake-shape precursor and high Li concentration at grain edge comparing grain center. The cycle and rate performances of the cathode from needle-shape precursor shows superior to those from flake-shape precursor, which might be attributed to low charge-transfer resistance by impedance measurement.

• Bulletin of the Korean Chemical Society
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• v.30 no.11
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• pp.2603-2607
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• 2009

$LiNi_{0.5-x}Co_{2x}Mn_{0.5-x}O_{2}$ (x = 0, 0.1, 1/6, 1.2, 0.3) were synthesized by the solid-state reaction method. The crystal structure was analyzed by X-ray powder diffraction and Rietveld refinement. $LiNi_{0.5-x}Co_{2x}Mn_{0.5-x}O_{2}$ samples give single phases of hexagonal layered structures with a space group of R-3m for x = 0.1, 1/6, 0.2, and 0.3. The lattice constants of a and c-axis were decreased with the increase in Co contents in samples. The thickness of MO2 slab was decreased and inter-slab distance was increased with the increase in Co contents in $LiNi_{0.5-x}Co_{2x}Mn_{0.5-x}O_{2}$. According to XPS analysis, the valence states of Mn, Co, and Ni in the sample are mainly +4, +3, and +3, respectively. The discharge capacity of 202 mAh/g at 0.1C-rate in the potential range of 4.7 - 3.0 V was obtained in $LiNi_{0.3}Co_{0.4}Mn_{0.3}O_2$ sample, and $LiNi_{0.4}Co_{0.2}Mn_{0.4}O_2$ gives excellent cycle performance in the same potential range.

• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2571-2576
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• 2011

Surface film formation on $Li(Ni_{1/3}Co_{1/3}Mn_{1/3})O_2$ cathodes upon oxidation of electrolyte during electrochemical cycling was investigated. Information on the important factors for film formation on the cathode can facilitate the design of additives that improve the properties of the cathode. Pyrazole is added to the electrolyte because it is readily oxidized to form a surface film on the cathode. The results of differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR) showed that the active material played a dominant role in the interfacial film formation with the electrolyte. Carbon black played a negligible role in the surface film formation.

• 한국전기화학회:학술대회논문집
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• 2003.10a
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• pp.23-23
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• 2003

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.10
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• pp.850-854
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• 2011

Nano-fibers of the $Li[Ni_{1/3}Co_{1/3}Mn_{1/3}]O_2$ electrode were synthesized from a metal oxide precursor using the electrospun method. The XRD patterns of all prepared powders showed a hexagonal ${\alpha}$ - $NaFeO_2$ structure (space group: R-3 m, 166). Scanning electron microscopy showed that all the synthesized samples were comprised of nanofibers with a size of 100~800 nm. Among the samples tested, the calcined $Li[Ni_{1/3}Co_{1/3}Mn_{1/3}]O_2$ nanowires in oxygen heating atmosphere showed a high charge and discharge capacity of 239.22 and 172.81 $mAhg^{-1}$ at the $1^{st}$ cycle, respectively. In addition, the charge transfer resistance was also improved significantly compared to the other samples.

• Journal of the Korean Ceramic Society
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• v.45 no.2
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• pp.112-118
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• 2008

To prepare the high-capacity cathode material with improved electrochemical performances, nanoparticles of $C0_3(PO_4)_2$ were coated on the powder surface of $Li[Co_{0.1}Ni_{0.15}Li_{0.2}Mn_{0.55}]O_2$, which was already synthesized by simple combustion method. The coated powders after the heat treatment at >$700^{\circ}C$ surely showed well-structured crystalline property with nanoscale surface coating layer, which was consisted of $LiCOPO_4$ phase formed from the reaction bwtween $CO_3(PO_4)_2$ and lithium impurities. In addition, cycle performance was particularly improved by the $CO_3(PO_4)_2$-coating for the cathode material for lithium rechargeable batteries.

• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.237-245
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• 2021

Atomic layer deposition (ALD) enhances the stability of cathode materials via surface modification. Previous studies have demonstrated that an Ni-rich cathode, such as LiNi_0.8Co_0.1Mn_0.1O₂, is a promising candidate owing to its high capacity, but is limited by poor cycle stability. In this study, to enhance the stability of the Ni-rich cathode, synthesized LiNi_0.8Co_0.1Mn_0.1O₂ was coated with Al₂O₃ using ALD. Thus, the surface-modified cathode exhibited enhanced stability by protecting the interface from Ni-O formation during the cycling process. The coated LiNi_0.8Co_0.1Mn_0.1O₂ exhibited a capacity of 176 mAh g^-1 at 1 C and retained up to 72% of the initial capacity after 100 cycles within a range of 2.8-4.3 V (vs Li/Li⁺. In contrast, pristine LiNi_0.8Co_0.1Mn_0.1O₂ presented only 58% of capacity retention after 100 cycles with an initial capacity of 173 mAh g^-1. Improved cyclability may be a result of the ALD coating, which physically protects the electrode by modifying the interface, and prevents degradation by resisting side reactions that result in capacity decay. The electrochemical impedance spectra and structural and morphological analysis performed using electron microscopy and X-ray techniques establish the surface enhancement resulting from the aforementioned strategy.

• Journal of Electrochemical Science and Technology
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• v.15 no.1
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• pp.168-177
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• 2024

Ni-rich cathode is one of the promising candidates for high-energy lithium-ion battery applications. Due to its specific capacity, easy industrialization, and good circulation ability, Ni-rich cathode materials have been widely used for lithium-ion batteries. However, due to the limitation of the co-precipitation method, including sewage pollution, and the instability of the long production cycles, developing a new efficient and environmentally friendly synthetic approach is critical. In this study, the Ni_0.91Co_0.06Mn_0.03CO₃ precursor powder was successfully synthesized by an efficient spray-drying method using carbonate compounds as a raw material. This Ni_0.91Co_0.06Mn_0.03CO₃ precursor was calcined by mixing with LiOH·H₂O (5 wt% excess) at 480℃ for 5 hours and then sintered at two different temperatures (780℃/800℃) for 15 hours under an oxygen atmosphere to complete the cathode active material preparation, which is a key component of lithium-ion batteries. As a result, LiNi_0.91Co_0.06Mn_0.03O₂ cathode active material powders were obtained successfully via a simple sintering process on the Ni_0.91Co_0.06Mn_0.03CO₃ precursor powder. Furthermore, the obtained LiNi_0.91Co_0.06Mn_0.03O₂ cathode active material powders were characterized. Overall, the material sintered at 780℃ shows superior electrochemical performance by delivering a discharge capacity of 190.76 mAh/g at 1^st cycle (0.1 C) and excellent capacity retention of 66.80% even after 50 cycles.

• Journal of Electrochemical Science and Technology
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• v.5 no.1
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• pp.32-36
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• 2014

The $0.3Li_2MnO_3{\cdot}0.7LiMn_{0.55}Ni_{0.30}Co_{0.15}O_2$ cathode material was prepared via a co-precipitation method. The vapor grown carbon fiber (VGCF) was used as a conductive material and its effects on electrochemical properties of the $0.3Li_2MnO_3{\cdot}0.7LiMn_{0.55}Ni_{0.30}Co_{0.15}O_2$ cathode material were investigated. From the XRD pattern, the typical complex layered structure was confirmed and a solid solution between $Li_2MnO_3$ and $LiMO_2$ (M = Ni, Co and Mn) was formed without any secondary phases. The VGCF was properly distributed between cathode materials and conductive sources by a FE-SEM. In voltage profiles, the electrode with VGCF showed higher discharge capacity than the pristine electrode. At a 5C rate, 146 mAh/g was obtained compared with 232 mAh/g at initial discharge in the electrode with VGCF. Furthermore, the impedance of the electrode with VGCF did not changed much around $9-10{\Omega}$ while the pristine electrode increased from 21.5${\Omega}$ to $46.3{\Omega}$ after the $30^{th}$ charge/discharge cycling.