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Lithium-rich (Li-rich) cathode materials with different layered-spinel phase ratios are successfully synthesized by solvothermal and gradient calcination processes. The structure and electrochemical performances of the lithium-rich cathode materials with different layered-spinel phase ratios are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), high rate transmission electron microscopy (HRTEM), fast Fourier transformation (FFT) and electrochemical charge-discharge measurements. The results show that the calcination time and calcination temperature in gradient calcination processes jointly influence the phase ratios of the layered Li 2 MnO 3 and spinel Li 4 Mn 5 O 12 in the hybrid structure. Moreover, the spinel phase can lead to an excellent coulombic efficiency and cycle stability, while the layered phase will provide a high capacity. The materials with different layered-spinel phase ratios prepared in different gradient calcination processes show apparently different electrochemical performances, e.g., the maximum discharge capacity of the sample reaches 297 mAh/g at 0.1 C, it even exhibits high capacity retention of 90.6% after 200 cycles at 0.5 C. Furthermore, the temperatures at 750 and 800 °C are considered to be the suitable selection for the gradient calcination process. The spinel phase can profitably grow at 750 °C, and the layered phase is produced at 800 °C. [ABSTRACT FROM AUTHOR]

Abstract: The LiFePO4/(C + La0.56Li0.33TiO3) composites with spherical morphology are synthesized for the first time via ammonia assisted hydrothermal method. The structure and electrochemical performance of LiFePO4/(C + La0.56Li0.33TiO3) are investigated by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), charge/discharge tests and cyclic voltammetry (CV). It has been found that the hybrid coating layer composing of electron conductive C and fast Li ion conductive La0.56Li0.33TiO3 is synchronously deposited on the surface of LiFePO4 microspheres. The hybrid coating layer can be favourable for fast electron and Li+ transport, and avoid HF eroding LiFePO4 in electrolyte, thus improve the electrochemical performance. The initial discharge capacity of LiFePO4/(C + La0.56Li0.33TiO3) is 126.3 mAh g−1, the capacity retention is still as high as 98.3% even after 100 cycles at 5 C. Even at high rate of 30 C, it still reveals a high discharge capacity of 62.3 mAh g−1. [Copyright &y& Elsevier]

Abstract: The pristine LiFePO4/C and Ni and Mn co-doping LiFe1−x−y Ni x Mn y PO4/C (x = 0.01–0.04; y = 0.04–0.01) composites are synthesized for the first time by a simple high-temperature solid-state route. The structure, morphology and electrochemical performance of the samples are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, scanning electron microscope (SEM), charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results indicate that the Ni and Mn co-doping does not destroy the olivine structure of LiFePO4, but it can stabilize the crystal structure, lengthen the Li–O bond, decrease charge transfer resistance, enhance Li ion diffusion velocity, and thus improve its cycling and high-rate capability of the LiFePO4/C. Especially, the LiFe0.95Ni0.02Mn0.03PO4/C shows the best cycling stability and rate capability among all the doped samples. The first discharge capacity of LiFe0.95Ni0.02Mn0.03PO4/C is 145.4 mAh g−1 with the capacity retention ratio of 98.6% till 100 cycles at 1C. Even at a high rate of 10C, it still reveals a high discharge capacity of 115.2 mAh g−1. [Copyright &y& Elsevier]

Abstract: Na and Ti co-doping Li1−x Na x Fe1−x Ti x PO4/C (x =0.00, 0.01, 0.03 and 0.05) composites were synthesized by a simple high-temperature solid-state method. The structure, morphology and electrochemical performance of the samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), charge/discharge tests, electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The results showed that the Na and Ti co-doped samples kept the olivine structure of LiFePO4, but Na and Ti co-doping can optimize the crystal microstructure, modify the particle morphology, decrease charge transfer resistance, enhance exchange current density, electrical conductivity and Li ion diffusion velocity, and thus improve the electrochemical performance of the LiFePO4/C. Among all the doped samples, Li0.97Na0.03Fe0.97Ti0.03PO4/C showed the best rate capability and cycling stability. The initial discharge capacity of Li0.97Na0.03Fe0.97Ti0.03PO4/C was 151.0mAhg−1 with the capacity retention ratio of 99.3% after 100 cycles at 1C. Especially, it still showed a high discharge capacity of over 97.3mAhg−1 even at a high rate of 20C. [Copyright &y& Elsevier]