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Abstract: The cycle performance of spinel LiMn2O4 at 25 and 55°C is improved by LaF3 modification via a chemical deposition method. The physical and electrochemical performances of pristine and LaF3-coated LiMn2O4 cathode materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical measurements. The coated LiMn2O4 with 2.92wt% LaF3 (LaF3-3-LMO) displays capacity retentions of 90.1% and 84.2% at 25 and 55°C, respectively, after 100 cycles, much higher than those of pristine LiMn2O4, 72.7% and 54.8%. The concentration of manganese dissolved from LaF3-3-LMO in electrolyte is much lower than that from pristine LiMn2O4. The analysis of AC impedance indicates that the charge transfer resistance (R ct) and the increase of R ct for LaF3-3-LMO during cycling are much lower than those for pristine LiMn2O4. The significantly improved electrochemical performance of the LaF3-coated LiMn2O4 can be attributed to the reduction of manganese dissolution in electrolyte and charge transfer resistance with the help of LaF3 coating. [Copyright &y& Elsevier]

Abstract: A LiFePO4/C submicrofibers composite was prepared by a facile electrospinning method using LiNO3, Fe(NO3)3·9H2O, NH4H2PO4, citric acid and poly(4-vinyl)pyridine (PVP) as raw materials, and its physical properties and electrochemical performance were investigated by X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive analysis of X-ray (EDAX), N2 adsorption/desorption measurement and electrochemical tests. The crystal size of LiFePO4 fibers is about 30nm calculated by Debye-Scherrer equation and the LiFePO4 nanofibers aggregate to LiFePO4/C submicrofibers composite with diameters of about 270–372nm. The LiFePO4 submicrofibers are covered by an amorphous carbon layer with a thickness of about 2.6nm and the LiFePO4/C submicrofibers composite with mesopores exhibits amazing high surface area of 167.729m2 g−1. The LiFePO4/C submicrofibers composite displays high initial discharge capacities of 166 and 168mAhg−1 and excellent cycle performance at 0.1C (17mAhg−1) in the voltage range of 2.5–4.5V at 25 and 55°C, respectively. Even at high rate of 5C, the LiFePO4/C submicrofibers composite delivers discharge capacities of 132 and 138mAhg−1 and excellent cycle performance at 25 and 55°C, respectively. The results indicate that the electrospinning method is promising to prepare LiFePO4/C composite with high electrochemical performance. [Copyright &y& Elsevier]

Abstract: A carbon coated Li3V2(PO4)3 cathode material for lithium ion batteries was synthesized by a sol–gel method using V2O5, H2O2, NH4H2PO4, LiOH and citric acid as starting materials, and its physicochemical properties were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscope (TEM), and electrochemical methods. The sample prepared displays a monoclinic structure with a space group of P21/n, and its surface is covered with a rough and porous carbon layer. In the voltage range of 3.0–4.3V, the Li3V2(PO4)3 electrode displays a large reversible capacity, good rate capability and excellent cyclic stability at both 25 and 55°C. The largest reversible capacity of 130mAhg−1 was obtained at 0.1C and 55°C, nearly equivalent to the reversible cycling of two lithium ions per Li3V2(PO4)3 formula unit (133mAhg−1). It was found that the increase in total carbon content can improve the discharge performance of the Li3V2(PO4)3 electrode. In the voltage range of 3.0–4.8V, the extraction and reinsertion of the third lithium ion in the carbon coated Li3V2(PO4)3 host are almost reversible, exhibiting a reversible capacity of 177mAhg−1 and good cyclic performance. The reasons for the excellent electrochemical performance of the carbon coated Li3V2(PO4)3 cathode material were also discussed. [Copyright &y& Elsevier]