Using Raman spectroscopy and X-ray photoelection spectroscopy (XPS), synthesized lithium iron(II) phosphate (LiFePO4) and carbon coated nanocomposites LiFePO4/С, synthesized by annealing LiFePO4 with glucose for 1 and 12 hours at 700 °C, have been investigated. According to XPS data, the synthesis conditions of LiFePO4/С nanocomposite (700 °C, 1 hour) facilitate the reduction of iron, Fe 3+ → Fe 2+ , on the sample surface. Also according to C1s spectra, sp 2 C-sp 2 C is the main bond type in the samples under investigation. Contributions relating to C-O, C=O, C-O-C, O-C=O functional groups are also present. According to X-ray diffraction analysis, a 12-hour synthesis of LiFePO4/C nanocomposite leads to the formation of impurities. According to Raman spectra, the annealing time does not affect the quality of carbon coating: the peak intensity ratio of bands D and G has a value of 1.06 for the material annealed for 1 hour and 1.04 for LiFePO4/С nanocomposite after annealing for 12 hours.
The method of lithium iron phosphate (LiFePO4) synthesis in a melt mixture of choline chloride and diethylene glycol (DEG) at 230 ?C is proposed. Powders with lamellar morphology consisting of LiFePO4 crystals (size ~30 nm) with olivine structure were synthesized. The size of crystals increased to ~60 nm during the annealing process carried out to obtain a carbon coating on the grain surface of LiFePO4. The charge-discharge curves of the electrode prepared from these powders have a horizontal portion at the potential of 3.4 and 3.5 V, corresponding to the intercalation/deintercalation of lithium in the structure of olivine. The specific discharge capacity of the LiFePO4/C is 133 mA h g-1 for a discharge current of 0.1C. The dependence of the anodic (cathodic) voltammetric current peaks, Ip, on the potential scan rate indicates the diffusion nature of the lithiating step. For the anodic and cathodic processes the averaged diffusion coefficient values are 1.3?10-10 and 1.5?10-10 cm2 s-1, respectively.
In order to find new functional materials and materials with improved performance for next-generation electrochemical devices, several new materials for various purposes have been synthesized. In particular, BiVO4 films were obtained by electrochemical synthesis using interferometric control of film thickness during their deposition. Previously, it was found that the use of thin BiVO4 films with a thickness of 150 to 400 nm is most effective, where was observed an increase in the quantum yield of photocurrent up to 0.25 at ? = 400 to 450 nm. LiFePO4 was synthesized in DES medium (low-temperature eutectic solvents): choline chloride-triethylene glycol (ChCl-TEG) and choline chlorideethylene glycol (ChCl-EG) using NH4FePO4 and CH3COOLi as precursors. It was found that the mode of synthesis of LiFePO4/C at 973 ? for 1 h does not lead to oxidation of LiFePO4, as evidenced by the values of the ratio Fe2+/Fe3+ for LiFePO4 and LiFePO4/C, which are 2.4 and 2.7, respectively. It was found that the substitution of part of lead cations (up to 20 mol.%) in the composition of the fluorideconducting phase Pb0.86Sn1.14F4 contributes to the increase of its conductivity in the whole temperature range, and to a greater extent, the higher the concentration of the substituent. Charge transfer is provided by highly mobile interstitial fluorine anions, the concentration of which increases with increasing temperature and substituent content.
High charging potential of Fe3O4 (1.75 V) 5CrO4). Cyclic voltammograms (CV) and galvanostatic charging/discharging curves were obtained within the potential region from 0.05 to 2.0 V (Li
The liquid-phase method of synthesis of lithium iron(II) phosphate (LiFePO4) in the medium of choline chloride and diethylene glycol under the action of microwave heating is proposed. With a power of microwave radiation of 920 and 1150 W, a nanocrystalline LiFePO4 without impurities was obtained. Obtained samples of microwave processes contain amorphous phase and require long annealing resulting in nanocrystalline LiFePO4/C composites with small impurities Li3PO4, Li3Fe2(PO4)3, Fe2O3. For samples obtained in the choline chloride with diethylene glycol microwave heating characteristic is lamellar morphology – the same as for LiFePO4 obtained by thermal heating, but in the case of using microwave irradiation plates are smaller. This indicates that the reaction mechanism of LiFePO4 synthesis does not change in the microwave synthesis, but the reaction rate is significantly increased (up to 6 times faster than thermal synthesis). Using the Raman spectroscopy, the nature of the carbon coating on the crystal of LiFePO4 was studied. The Raman spectra of the LiFePO4/C composites obtained from an annealed powder with glucose and malic acid have pronounced D (~ 1340 cm-1) and G (~ 1600 cm-1) peaks, as well as two additional bands at ~ 1200 and ~ 1520 cm-1 obtained after the expansion of main peaks. The ratio of peak intensities of lines D and G (ID/IG) has a value of 1.06 for the material obtained after glucose carbonation and 1.01 for LiFePO4/C composites annealed with malic acid, which correlates with the results of other investigations of the carbon coating LiFePO4 (ID/IG ~ 1-3) That means the choice of an organic precursor does not affect the nature of the carbon coating (ID/IG ~ 1). Capacity of cathode material based on LiFePO4/C composites is ~ 130 mAh/g for a current of 0.1C.
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