LiCoO 2 thin film cathodes grown by sol–gel method (original) (raw)
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Ceramics International, 2010
Nanometric-sized LiCoO 2 powders were obtained from a novel sol-gel method, in which the gels were synthesized by the polymerization of citric acid and hydroxypropyl cellulose. Molar ratios of citric acid to metal ions were varied, and the resulting effects on the properties of powders were studied using Fourier transfer infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that with a molar ratio of citric acid/metal ions = 1, the resin contains a number of bidentate ligand fractions and higher portion of C-C-O structure, which makes it possible to synthesize the low temperature phase of LiCoO 2 at a temperature as low as 300 8C. The powder calcined at 600 8C exhibits a pure high temperature phase of LiCoO 2 (HT-LiCoO 2 ) with a particle size of about 40-60 nm and a specific surface area of 25.24 m 2 /g. The electrode prepared at 600 8C exhibits a better HT-LiCoO 2 structure and demonstrates a higher first run charge/discharge capacities at 186 and 168 mAh/g, respectively.
Synthesis of LiCoO2 thin films by sol/gel process
Journal of Power Sources, 2010
LiCoO 2 thin films were synthesized by sol/gel process using acrylic acid (AA) as chelating agent. The gel formulation was optimized by varying solvent (ethylene glycol or water) and precursors molar ratios (Li, Co, AA) in order to obtain a dense film for positive electrode of lithium batteries. The gel was deposited by spin-coating technique on an Au/TiO 2 /SiN/SiO 2 /Si substrate. Thin films were deposited by either single or multistep process to enhance the density of the thin film and then calcined during 5 h at 800 • C to obtain the R-3m phase (HT-LiCoO 2 ).
Nanomaterials
The microbatteries field is an important direction of energy storage systems, requiring the careful miniaturization of existing materials while maintaining their properties. Over recent decades, LiCoO2 has attracted considerable attention as cathode materials for lithium-ion batteries due to its promising electrochemical properties for high-performance batteries. In this work, the thin films of LiCoO2 were obtained by radio-frequency magnetron sputtering of the corresponding target. In order to obtain the desired crystal structure, the parameters such as annealing time, temperature, and heating rate were varied and found to influence the rhombohedral phase formation. The electrochemical performances of the prepared thin films were examined as a function of annealing time, temperature, and heating rate. The LiCoO2 thin film cathode annealed at 550 °C for 1 h 20 min demonstrated the best cycling performance with a discharge specific capacity of around 135 mAh g−1 and volumetric capaci...
Fabrication of LiCoO2 thin films on flexible stainless steel substrate for lithium ion batteries
Solid State Ionics, 2008
The LiCoO 2 cathode coating on a flexible stainless steel has been successfully formed by using sol-gel process and spin-coating technique. The microstructures and electrochemical performance of this LiCoO 2 cathode were characterized by using an X-ray diffractometer (XRD), a scanning electron microscope (SEM) and electrochemical methods. After annealing at ca. 500°C, the results of XRD showed that the LiCoO 2 gel was crystallized and the crystallized thin films show hexagonal phase with a space group R 3 m. When the annealing temperatures kept at 700°C, the stainless steel substrate was oxidized and subsequently reacted with LiCoO 2. Such a reaction also destabilized the structure of LiCoO 2. The SEM observation indicated that the average grain size of films increased with increasing temperature and the thickness of spin-coated films is ca. 1-3 μm. The LiCoO 2 thin films prepared from sol-gel process and spin-coating exhibit reversible electrochemical behavior of Li + intercalation and de-intercalation reactions.
Studies on Bare and Mg-doped LiCoO2 as a cathode material for Lithium ion Batteries
Electrochimica Acta, 2014
In this paper, we report on the preparation of bare and Mg-doped Li(Mg x Co 1-x )O 2 (x = 0, 0.03, 0.05) phases by a molten salt method and their electrochemical properties. They were prepared at 800 • C for 6 h in air. Rietveld refined X-Ray Diffraction data of bare (x = 0) and Mg-doped (x = 0.03, 0.05) compounds show a well-ordered hexagonal layer-type structure (a ∼ 2.81Å, c ∼ 14.05Å). Scanning Electron Microscopy (SEM) show hexagonal type morphology at 800 • C. Powder density was close to 5.02 gcm −3 , which compares well with the theoretical value. Electrochemical properties were studied in the voltage range of 2.5-4.3 V vs. Li using Cyclic Voltammetry (CV) and galvanostatic cycling. CV studies on bare and Mg-doped LiCoO 2 show main cathodic and anodic redox peaks at ∼ 3.9 V and ∼ 4.0 V, respectively. Galvanostatic cycling of Li(Mg x Co 1-x )O 2 (x = 0, 0.03, 0.05) showed reversible capacity values at the 60 th cycle to be: 147 (±3) mAh g −1 (x = 0), 127 (±3) mAh g −1 (x = 0.03), and 131 (±3) mAh g −1 (x = 0.05) cycled at a current density of 30 mA g −1 . Capacity retention is also favourable at 98.5%.
Improvement of electrochemical stability of LiCoO< sub> 2 cathode by a nano-crystalline coating
Journal of power sources, 2004
A nano-crystalline MgO coating was formed on the surface of LiCoO 2 particle via a sol-gel method. MgO coating can improve the cycling stability of LiCoO 2 significantly. After the 40th cycle a discharge capacity of more than 120 mAh/g was remained for 1 mol% MgO-coated LiCoO 2 , while only 13 mAh/g for pristine LiCoO 2 when both charged up to 4.7 V. During heat treatment and charge/discharge process, Mg 2+ in coatings will diffuse into LiO 2 -layers of LiCoO 2 , which does not cause any detectable shift in X-ray diffractometer (XRD) peak positions, but does impact the XRD peak intensity due to the aberrance of (0 0 3) plane. Mg 2+ ions existing in LiO 2 -layers will stabilize the lattice structure of LiCoO 2 , hence improve the cycling performance of LiCoO 2 cathode. More MgO coating on LiCoO 2 is detrimental to the electrochemical properties of LiCoO 2 cathode, probably due to the electrochemical inactivity of MgO particles.
A TEM study of cycled nano-crystalline HT-LiCoO2 cathodes for rechargeable lithium batteries
Journal of Power Sources, 2004
LiCoO 2 has ␣-NaFeO 2 structure type and it has been reported that layered cation ordering is preserved during repeated insertion and removal of Li +. We have observed, at a nano-particle scale, cation disorder induced in LiCoO 2 after prolonged cycling. LiCoO 2 cathode powders with nano-grain sized of 70-300 nm were synthesized by a mechano-chemical method. Transmission electron microscopy study of LiCoO 2 showed that the initial O 3 crystal structure partially transformed to a cubic spinel phase. This spinel phase formation may be responsible for capacity degradation after prolonged cycling of LiCoO 2-based rechargeable lithium batteries. Cycle life of small size (70 nm) LiCoO 2 powder until 200 cycles is better than that of large size (300 nm) LiCoO 2 powder due to shorter diffusion distance.
Atomic Layer Deposition of LiCoO2 Thin-Film Electrodes for All-Solid-State Li-Ion Micro-Batteries
Journal of the Electrochemical Society, 2013
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Electrochemical Properties of LiCo0.4Ni0.6O2 and its Performances in Rechargeable Lithium Batteries
Sri Lankan Journal of Physics, 2008
Intercalation cathode materials belonging to the 4-volt class electrodes, lithiated cobalt oxide LiCoO 2 and lithiated nickel cobalt oxide LiCo 0.4 Ni 0.6 O 2 , were synthesized by sol-gel technique. The structural characteristics of the compounds were studied using XRD, FTIR and DSC. The compounds were used as cathode materials for assembling rechargeable lithium-batteries and their electrochemical performances were studied. The potentiostat and galvanostat techniques were used to determine the electrochemical characteristics. The irreversible capacity loss of LiCoO 2 during the first charge-discharge is about 20% and for LiCo 0.4 Ni 0.6 O 2 is about 90% for two different current rates of 5 and 10 A kg-1. The overall electrochemical capacity of LiCo 0.4 Ni 0.6 O 2 has been drastically reduced due to the s-block or p-block metal substitution. Also the un-reacted materials remained as impurities gave a very poor cycleability. However more stable charge-discharge performances have been observed for LiCoO 2 at different current rates. Differences and similarities between these two cathode materials in batteries are also discussed. The Li-ion batteries were assembled using the sol-gel synthesized cathode materials, natural untreated vein graphite of Sri Lanka as the anode material and 1 M LiPF 6 in EC/DMC as liquid electrolyte, and their performances were tested.