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Spherical Li[NiMnCo]O was prepared by both the continuous hydroxide co-precipitation method and continuous carbonate co-precipitation method under different calcined temperatures. The physical properties and electrochemical behaviors of Li[NiMnCo]O prepared by two methods were characterized by X-ray diffraction, scanning electron microscope, and electrochemical measurements. It has been found that different preparation methods will result in the differences in the morphology (shape, particle size, and tap density), structure stability, and the electrochemical characteristics (shape of initial charge/discharge curve, cycle stability, and rate capability) of the final product Li[NiMnCo]O. The physical and electrochemical properties of the spherical Li[NiMnCo]O prepared by continuous hydroxide co-precipitation is apparently superior to the one prepared by continuous carbonate co-precipitation method. The optimal sample prepared by continuous hydroxide co-precipitation at 820 °C exhibits a hexagonally ordered layer structure, high special discharge capacity, good capacity retention, and excellent rate capability. It delivers high initial discharge capacity of 175.2 mAh g at 0.2 C rate between 3.0 and 4.3 V, and the capacity retention of 98.8 % can be maintained after 50 cycles. While the voltage range is broadened up to 2.5 and 4.6 V vs. Li/Li, the special discharge capacities at 0.2 C, 0.5 C, 1 C, 2 C, 5 C, and 10 C rates are as high as 214.3, 205.0, 198.3, 183.3, 160.1 and 135.2 mAh g, respectively. [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]

Highlights: [•] The Y2O3 coated LiMn2O4 microsphere wrapped with graphene is firstly synthesized. [•] The graphene/Y2O3/LiMn2O4 hybrid shows the notable rate and cycling performance. [•] Y2O3 and graphene modification can effectively improve the performance of material. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve the performance of the Li[Ni0.5Co0.2Mn0.3]O2, a novel spherical Li[Ni0.5Co0.2Mn0.3]O2–Li2MnO3 core–shell composite has been successfully synthesized by a simple sol–gel deposition method. It is found that the core–shell composite consists of Li[Ni0.5Co0.2Mn0.3]O2 as the core and Li2MnO3 as the outer shell according to examination by scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD). The core–shell composite delivers a high capacity of 180.4 mAh g−1 at a rate of 0.1 C in the voltage range of 2.0–4.4 V. Most importantly, the core–shell composite exhibits excellent capacity retention of 98.8% after 200 cycles at a rate of 0.5 C, and 93.8% capacity retention after 100 cycles at a rate of 5 C at room temperature. When cycled at an elevated 55 °C, the prepared sample exhibits only 2.3% capacity loss after 100 cycles. Meanwhile, the core–shell composite shows significantly improved thermal stability relative to that of the pristine Li[Ni0.5Co0.2Mn0.3]O2. The improved stability of the core–shell composite is ascribed to the stable Li2MnO3 outer shell, which can prevent the Li[Ni0.5Co0.2Mn0.3]O2 core from direct contact with the electrolyte, and the core material could operate with no risk of structural disruption at high voltages and high temperatures. [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]

Abstract: The chemical diffusion coefficients of lithium ions (D Li) in spherical Li[Ni0.5Mn0.3Co0.2]O2 are systematically determined by galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS). The D Li obtained from GITT are greatly dependent on the lithium content and cell potential. In the charge process, the D Li values are in the range of 9.0×10−11 to 3.3×10−9 cm2 s−1. In the discharge process, the D Li values are in the range of 1.9×10−11 to 3.9×10−9 cm2 s−1. In addition, the minimum values in the D Li are observed at the stoichiometry x ≈0.25 for Li1−x [Ni0.5Mn0.3Co0.2]O2, which coincide with the voltage-plateau region at about 3.75V. The D Li obtained from EIS are in the range of 1.7×10−11 to 6.5×10−9 cm2 s−1 and the variation tendency with cell potential is consistent with the results obtained from GITT during the charge process. [Copyright &y& Elsevier]