Papers by Keyword: LiFePO₄/C

Abstract: LiFePO4 has attracted broad attention as a promising cathode material for lithium ion batteries. The key issues related to LiFePO₄ performance lie on the intrinsic characteristic of poor diffusion of lithium ions through an interface between LiFePO₄ and FePO₄. To explore the effect of polyaniline on performances, LiFePO₄/C cathode materials were prepared via hydrothermal method, using glucose as a carbon source and polyaniline as a modifier. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), galvanostatic charge–discharge test and cyclicvoltammetry (CV). The results show that the olivine-type phase of LiFePO₄/C is not changed by polyanilines and LiFePO₄/C is composed of relatively large particles of about 400nm and some nano-sized polyaniline particles, which favor the electronic conductivity. The LiFePO₄/C cathode material modified by 10% polyaniline has the highest uniformity. It delivers the capacity of 167.9mAh/g at 0.1C, and has good reversibility and high capacity retention.

Abstract: LiFePO₄/C cathode material with particle size of 5~6 μm and tap density of 1.67 g•cm-3 was prepared based on spherical crystal FePO₄•2H₂O powders. The spherical crystal FePO₄•2H₂O powders were first prepared by a simple hydrothermal synthesis via the amorphous FePO₄•2H₂O solution maintained at 150°C for 12 h without any supplementary equipment. The produced LiFePO4/C powders exhibited the initial discharge capacity of 137 and 118 mAh•g-1 at 0.1 C and 0.5 C, respectively. The volumetric capacity of the spherical LiFePO₄/C powders corresponded to 230 and 197 mAh•cm-3, which are remarkably higher than irregularity powders. The high-density spherical LiFePO₄/C powders produced by this novel method can be considered as a very promising candidate in the high-power batteries.

Abstract: LiFePO₄/C composite powders were prepared by a simple reaction of as-synthesized FePO₄•2H₂O, LiOH•H₂O, oxalic acid and citric acid. The influence of oxalic acid and citric acid in different ratios was investigated on morphology and electrochemical performance of LiFePO₄/C composite powders. The characterization of the composites included X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis indicates that the material is well crystallized without impurities. The obtained LiFePO₄/C composite powders with well dispersion at CA/OA ratio of 1:1.50 and the initial charge capacity reached 159.3 mAhg^-1 at 0.1C rate, meanwhile, the particles prepared at 1:0.75 were close to spherical in shape and the specific capacity value was 149.8 mAhg^-1 at 0.1C rate, with a slight decrease on greater C-rates reaching 141.3 mAhg^-1 at 1C.

Abstract: Positive-electrode material LiFePO₄/C was prepared using FePO₄•2H₂O as raw material via a rheological phase method. Orthogonal experiment was designed to systematically investigate the effects of the ratio of raw materials, calcining temperature and holding time on the morphology and electrochemical performance of LiFePO₄/C. The results showed that the optimal parameters were as follows: synthesis temperature 650 °C, time 10 h. The sample prepared with optimal parameters showed discharge capacities of 147.5 mAh•g^-1 at 0.2 C and 133.7 mAh•g^-1 at 1 C rate, with good cycle performance.

Abstract: A new simple electrode based on a blended cathode as a practicable method for industrial application was introduced to improve the capacities of LiFePO4 cathodes. Here, the effects of physical blending with a small amount of Li₃V₂(PO₄)₃ on the electrochemical performance of LiFePO₄ were studied. The influence of blended ratios on the capacity of LiFePO₄ was examined by galvanostatic charge and discharge test. The results showed that the discharge capacity of LiFePO₄/Li₃V₂(PO₄)₃ was increased from 146 mAh/g to 156 mAh/g by adding 20 wt.% Li₃V₂(PO₄)₃ and the mixture cathode exhibited excellent capacity retention (93.4% after 12 cycles) compared with prismatic ones. Moreover, the rate performance of LiFePO₄ was also improved greatly by adding Li₃V₂(PO₄)₃. The beneficial effects of adding Li₃V₂(PO₄)₃ were found to be related to an improvement of the rate performance of LiFePO₄ cathode, which was ascribed to the better electron conductivity of Li₃V₂(PO₄)₃.

Abstract: Olivine LiFe1−xMnxPO4/C composites were prepared by high temperature solid phase method using MnO2, NH4H2PO4, Li2CO3, FeC2O4•2H2O, glucose as the starting materials. XRD, SEM and constant-current charging/discharging tests were used to study the structure and electrochemical properties of the material. The result showed that when x=0.2 the material exhibited the optimal electrochemical performance, with a higher specific energy of 484.94 Wh/kg.

Abstract: LiFePO4/C composite cathode material prepared by carbothermal reduction method was coated by metal oxide MnO2, Al2O3, CuO, respectively, by a chemical precipitation method. The effects of metal oxide coating on the structure and electrochemical performance of LiFePO4/C composites were systematically investigated. The structure and morphology of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the electrochemical properties were evaluated by constant-current charge/discharge cycling tests. It is found that the coating of metal oxide could greatly improve its high-rate dischargeability and cycling performance. The LiFePO4/C cathode material coated by MnO2 exhibits a specific discharge capacity of 118.5 mAh/g at 3C rate, much higher than the uncoated sample (95.1 mAh/g), with a capacity degradation rate of only 6.3 % after 250 cycles at 3C rate.

Abstract: The LiFePO₄ nanoparticles with high crystallinity were prepared using polyol process without any further heating as a post step, which will greatly economize in time and energy comparing with other conventional synthesis method. The temperature of the polyol solution was rapidly increased up to 550 K and maintained for 24 h in a round-bottomed flask attached to refluxing condenser to obtain nanoparticles. The X-ray diffraction (XRD) pattern was indexed on the basis of orthorhombic olivine-type structure without any unwanted second phase. The scanning electron microscopy (SEM) images of the samples showed the needled and flaky shapes of particles with uniform size in the range of 50-250 nm. It is noted that the nanoparticle was in favor of shortening the diffusion path to improve electrochemical performance. A reversible specific capacity around 160 mAh·g^-1 at 0.1C rate was achieved without capacity fading during the 20 cycles.

Abstract: LiFePO₄/C were successfully synthesized by carbon thermal reduction method at sintering temperature of 650 °C for 12h, using Li₂CO₃, FePO₄ and three organic carbon sources (citric acid, glucose and ascorbic acid) as starting materials. The crystal structure, morphology and electrochemical performances were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Charge/Discharge Test. The results showed that the sample using glucose as carbon source was shuttle type porous particles with bore diameter from 50 to 100 nm, charge/discharge test showed that the sample had not only high initial discharge capacity of 155.1mAh/g at 0.1C (17mA/g), and 144.8 mAh/g at 1C, but also excellent rate performance. Moreover, the capacities lose which was only 0.97% after 10 cycling number at 1C indicate its good cycling stability.

Abstract: The LiFePO₄/MWCNTs composite used as cathode was synthesized by ball milling. XRD and SEM experiments demonstrated that MWCNTs didn’t change the olivine structure of LiFePO₄ and that MWCNTs decentralized into the grains of LiFePO₄ and working as electric bridge improving the electrochemical properties of LiFePO₄. The electrochemical performance of the composite electrodes with different MWNTs in diameter were studied by button cell. The result indicated that the composite with largest diameter MWNTs exhibited best electrochemical performance. The first charge-discharge specific capacity of the composite with MWNTs of 60-100nm in diameter were 136mAh/g-1 and 129 mAh/g-1 respectively at 0.1C rate under room temperature. The difference between charge-discharge platforms of the composite electrode was the least compared to the others. This phenomenon showed that the material had the largest chemical diffusion coefficient of lithium. At the same time, the capacity of the composite only lost 4.0％ after 10 cycles and kept constant after 20 cycles.