Papers by Keyword: Cathode

Abstract: An attempt has been made to synthesize hexagonal LiMnBO₃ (h-LMB) through sol-gel technique. The synthesized h-LiMnBO₃ have been examined for their physical and electrochemical characteristics by X-ray diffraction analysis (XRD) and Thermal analysis (TG), Scanning electron microscopy (SEM), Raman spectroscopy as well as through charge –discharge cycling. XRD results revealed the existence of hexagonal polymorphs with P6 space group. Stability of h-LiMnBO₃ material is analyzed by thermal analysis. SEM image shows spherical shape nanoparticle with the average diameter 50 nm. Raman spectroscopy result indicates the presence of Mn-O vibration. An electrochemical study indicates the sol-gel derived hexagonal LiMnBO₃ delivers a first charging capacity of 97.5 mAh g^-1 and discharging capacity of 55. 85 mAh g^-1 within the potential window of 2V-4.5 V at C/10 rate and retaining a reversible discharge capacity of 42.71 mAh g^-1 at the 10^th cycle.

Abstract: Perovskite La_1-xSr_xFe_0.7Ni_0.3O_3-δ with x = 0.0, 0.1 &0.2 denoted LSFN_x has been investigated as potential symmetrical electrode in solid fuel cells (SOFCs). The crystal structure is in pure orthorhombic phase for x = 0.0, orthorhombic-cubic phase coexist for x = 0.1 and pure cubic phase for x = 0.2. Structural properties are studied by X-ray powder diffraction (XRPD), refined by Rietveld analysis. SEM images show the morphology of as prepared and calcined samples either the compatibility between those electrodes and LSGM electrolyte in presence of 50% wt of Ce_0.8Gd_0.2O_2-δ, so that, lower chemical reactivity was found. Total conductivity, impedance in high, medium and low frequencies HF, MF and LF respectively, and resistance polarization (Rp) are determined in air. LaFe_0.7Ni_0.3O_3-δ has a good response in all ranges of frequencies but La_0.9Sr_0.1Fe_0.7Ni_0.3O_3-δ and La_0.8Sr_0.2Fe_0.7Ni_0.3O_3-δ have response only in HF and MF and exhibit Rp values as low as LaFe_0.7Ni_0.3O_3-δ .

Abstract: Spherical Li₃V₂(PO₄)₃/C cathode materials have been successfully synthesized by a spray drying method. The structure and morphology of the cathode materials are characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric (TG) analysis. The results show that synthesized monoclinic Li₃V₂(PO₄)₃ with high purities exhibits spherical morphology, in favor of enhancing the capacities and cycling stability of Li₃V₂(PO₄)₃/C cathode materials for lithium-ion battery. The Li₃V₂(PO₄)₃/C cathode materials sintered at 750 °C present best electrochemical performance among all the samples. It exhibits high initial discharge capacities of 99.2 mAhg^-1 and capacity retention of 93.6% after 200 cycles at a rate of 1C within a voltage range of 3.0–4.3 V.

Abstract: Rechargeable Mg batteries have received intensive attention as affordable rechargeable batteries with high electromotive force, high energy density, and high safety. Mg possesses two valence electrons and has the lowest standard electrode potential (ca. -2.36 V vs. SHE) among the air-stable metals. There is another advantage that Mg metal can be used as an active material because Mg metal hardly forms dendrites. However, the slow diffusion of Mg ions in solid crystals prevents the realization of active materials for Mg rechargeable batteries at room temperature. Although some complex oxides have been reported to work as active materials at higher temperatures, Chevrel compounds are still the gold standards, which work at room temperature. However, the working voltage of the Mg battery using a Chevrel compound for the cathode is only ca. 1.2 V, which is far below that of Li-ion batteries (3-5 V). Nevertheless, Chevrel compounds have the significant advantage that a relatively large space exists in the crystal structure, which allows for fast Mg ion diffusion. In the present study, we investigated some materials with framework structures as cathodes for Mg batteries, which can alleviate the electrostatic constraint between Mg ions and cathode constituents. Specifically, we investigated the redox behavior of the thin films of Prussian blue and Prussian blue analogues in electrolytes containing an Mg salt using electrochemical quartz crystal microbalance and X-ray absorption spectroscopy. In addition, we discuss the electrochemical insertion/extraction behavior of Mg ions and their solvation structures.

Abstract: The migration of lithium (Li) ions in electrode materials affects the rate performance of rechargeable Li ion batteries. Therefore, the application of LiMn₂O_4, which is an appealing cathode material in high power systems, requires fast electron transfer kinetics which is possible through the use of nanostructured morphologies and conductive material. Nanowires offer the advantage of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. In this study, LiMn₂O₄ nanowires with cubic spinel structure were synthesized by using a α-MnO₂ nanowire-template-based method. LiMn₂O₄ nanowires have diameters less than 10 nm and lengths of several micrometers. Fe-Au nanoparticles were synthesized and used as coating material to improve both the catalytic activities and stability of the LiMn₂O₄ nanowires. The Li[Fe_0.02Au_0.01]Mn_1.97O₄ nanowires with modified architecture effectively accommodates the structural transformation during Li⁺ ion charge and discharge. Hence, the Li[Fe_0.02Au_0.01]Mn_1.97O₄ nanowire cathode system shows outstanding stability and enhanced electrocatalytical properties. Microstructural analysis of Li[Fe_0.02Au_0.01]Mn_1.97O₄ linked its composition and processing to its properties and performance. High resolution transmission electron microscope (HR-TEM) of the nanomaterial showed good crystallinity which contributed towards good reversibility. XRD analysis revealed a pure cubic spinel structure without any impurities. Structural information provided by Raman and solid state spectroscopy further corroborated these findings. The improved rate and cycling performance is related to the conductive particles infused within the nanowires which make up the electrode.

Abstract: Single phase LiMn_0.3Co_0.3Ni_0.3Ti_0.1O₂ materials are prepared using a self-propagating combustion method. The structure and morphology of the materials were characterized using X-Ray powder diffraction (XRPD) and Field Emission Scanning Electron Microscopy (FESEM). The electrochemical performances of the materials were characterized by means of galvanostatic charge-discharge test on the fabricated cells. XRD results showed that the materials are impurity-free and single phase with well ordered hexaganol structure of Rm space group. The compound was annealed at 700 °C and 800 °C for 24 h. The discharge capacities obtained was 143 mAhg^-1 in the first cycle for both materials. The voltage range was between 2.5 to 4.2 V. The 30^th cycle, however, revealed that the material annealed at 700 °C shows the better performance. The capacity fading is only about 14% compared to 17% for the 800 °C sample. This implies that LiMn_0.3Co_0.3Ni_0.3Ti_0.1O₂ material is sensitive to annealing temperature. They exhibited good specific capacity values and looked promising for Li-ion battery application.

Abstract: This paper reports on the reactivity study of composite cathode materials that comprises different weight percent of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-α (LSCF) and BaCe_0.54Zr_0.36Y_0.1O_3-α (BCZY). BCZY and LSCF powders are both prepared by a sol-gel method using metal nitrate salts as precursor. In this work, three samples with different weight percent ratios of 30, 50 & 70% of LSCF to BCZY were used and denoted as sample A1, A2 and A3, respectively. The powder mixtures of all samples were calcined at temperature of 1000 °C for 10 hours in an air. The phase formation of the samples was identified by X-ray diffractometer (XRD). As a comparison, XRD measurements for the LSCF and BCZY powders were also conducted individually, and their single-phase XRD pattern was used to identify the formation of undesired secondary reaction of the powdered mixture. The analysis of room temperature XRD data revealed that A1, A2 and A3 samples exhibit a complete solid solution between the crystal structures of LSCF cathode and BCZY electrolyte. The peaks can be indexed to (110), (020), (202), (220), (132), (224), (332) that belong to the LCSF phase and (110), (200), (211), (220), (310), (222) peaks that fit to the BCZY phase. No additional reaction products or secondary phases were observed indicating that up to 1000 °C, the prepared mixture formed a decent LSCF-BCZY composite. The average values of the lattice parameters for all the samples confirmed their phases were stable with the increasing BCZY content. Thus, it found that the LSCF is compatible with BCZY to form LSCF-BCZY composite for potential cathode material.

Abstract: The composition YSr₂Fe_3-xCo_xO₈ (for x = 0.5, 3.0) has been investigated as an alternative cathode material for Solid Oxide Fuel Cells (SOFCs). X-ray diffraction (XRD) pattern shows that the composition YSr₂Fe_2.5Co_0.5O₈ crystallizes with cubic symmetry in the space group Pm-3m and YSr₂Co₃O₈ crystallizes with tetragonal symmetry in the space group P4/mmm. Rietveld refinement of XRD data shows the cell parameter of the cubic YSr₂Fe_2.5Co_0.5O₈ is a = b = c = 4.1964(2) (Å) and tetragonal YSr₂Co₃O₈ is a = b = 9.8998(9) (Å) and c = 8.9617(6) (Å). Scanning electron microscropy (SEM) images show porous structure for both the samples, which is favourable as a cathode for Solid Oxide Fuel Cells.

Abstract: The layered LiNi_1/3Mn_1/3Co_1/3O_{2 ­­} that formed with the α-NaFeO₂ structure were synthesised by conventional solid state method. Rietveld refinement results indicated that the amount of cation disorder (or known as interlayer mixing) affected by temperature. The samples that prepared at 950°C in oxygen possessed slightly lower amount of interlayer mixing and excellent cycling performance compared to samples that prepared at 900°C. The initial charge-discharge capacity delivered was ~204 mAh/g and ~140 mAh/g, respectively. Furthermore, the structural and electrochemical properties were quite comparable to reported in literatures.

Abstract: A Cu doped V₂O₅ film for lithium-ion batteries is prepared by magnetron sputtered using a vanadium target. Coppers are doped in varying proportions to investigate the effect of doping on the electrochemical properties. In comparison, the surface of doped samples is smooth and uniform. And the results of electrochemical tests indicate that the proper doped films (V: Cu=8: 1 by area) exhibit better cycle performance, wider voltage plateaus and higher capacity than other samples.