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The Li-rich Li[NiMn]O microspheres are firstly prepared and subsequently transferred into the AlO-coated Li-rich Li[NiMn]O microspheres by a simple deposition method. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. The results reveal that the AlO-coated Li-rich Li[NiMn]O sample has a typical α-NaFeO layered structure with the existence of LiMnO-type integrated component, and the AlO layer is uniformly coated on the surface of the spherical Li-rich Li[NiMn]O particles with a thickness of about 4 nm. Importantly, the AlO-coated Li-rich sample exhibits obviously improved electrochemical performance compared with the pristine one, especially the 2 wt.% AlO-coated sample shows the best electrochemical properties, which delivers an initial discharge capacity of 228 mAh g at a rate of 0.1 C in the voltage of 2.0-4.6 V, and the first coulombic efficiency is up to 90 %. Furthermore, the 2 wt.% AlO-coated sample represents excellent cycling stability with capacity retention of 90.9 % at 0.33 C after 100 cycles, much higher than that of the pristine one (62.2 %). Particularly, herein, the typical inferior rate capability of Li-rich layered cathode is apparently improved, and the 2 wt.% AlO-coated sample also shows a high rate capability, which can deliver a capacity of 101 mAh g even at 10 C. Besides, the thin AlO layer can reduce the charge transfer resistance and stabilize the surface structure of active material during cycling, which is responsible for the improvement of electrochemical performance of the Li-rich Li[NiMn]O. [ABSTRACT FROM AUTHOR]

The YO nano-film is coated on the surface of the spherical spinel LiMnO by precipitation method and subsequent heat treatment at 550 °C for 5 h in air. The structure and performance of the bare LiMnO and YO-coated LiMnO are characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis X-ray spectroscopy, galvanostatic charge-discharge, cyclic voltammetry, and impedance spectroscopy. It has been found that the addition of YO does not change the bulk structure of LiMnO, and the thickness of the YO coating layer is approximate to 3.0 nm. The 1 wt% YO-coated LiMnO electrode reveals excellent cycling performance with 80.3 % capacity retention after 500 cycles at 1 C at 25 °C. When cycling at elevated temperature 55 °C, the as-prepared sample still shows 76.7 % capacity retention after 500 cycles. These remarkable improvements indicate that thin YO coating on the surface of LiMnO is an effective way to improve the electrochemistry performance. Besides, the suppression of Mn dissolution into the electrolyte via the YO coating layer can be accounted for the improved performances. [ABSTRACT FROM AUTHOR]

Highlights: [•] The kinetics of Li-ion deintercalation in Li1.12[Ni0.5Co0.2Mn0.3]0.89O2 during first charging process are studied by GITT and EIS. [•] The D Li values calculated by EIS and GITT vary from 1.9×10−14 cm2 s−1 to 8.1×10−10 cm2 s−1 and 3.1×10−16 cm2 s−1 to 7.2×10−10 cm2 s−1. [•] GITT is a preferable technology for determining the D Li in Li1.12[Ni0.5Co0.2Mn0.3]0.89O2. [•] The electrode kinetics of Li1.12[Ni0.5Co0.2Mn0.3]0.89O2 is controlled by different process of electro-chemical reactions in the voltage range of 2.0–4.8V. [ABSTRACT FROM AUTHOR]

Spinel LiMnO cathode materials were coated with 1.0, 3.0 and 5.0 wt.% of MgF by precipitation, followed by heat treatment at 400 °C for 5 h in air. The effects of MgF coating on the structural and electrochemical properties of LiMnO cathodes were investigated using XRD, SEM, and electrochemical tests. XRD and SEM results show that no significant bulk structural differences are observed between the coated and pristine LiMnO. The charge-discharge tests show that the discharge capacity of LiMnO decreases slightly, but the cyclability of LiMnO is clearly improved when the amount of the MgF coated was increased to 3.0 wt.%. The 3.0 wt.% MgF-coated LiMnO exhibits capacity retention of 80.1 and 76.7 % after 100 cycles at room temperature (25 °C) and elevated temperature (55 °C) at a rate of 1 C, respectively, much higher than those of the bare LiMnO (70.1 and 61.6 %). The improvement of electrochemical performance is attributed to the suppression of Mn dissolution into the electrolyte via the MgF coating layer. [ABSTRACT FROM AUTHOR]

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]

The Mn doped spherical Li 2 FeSiO 4 /C cathode materials are successfully synthesized through a citric acid-assisted sol-gel method. The effects of Mn doping on the chemical composition, structure characteristics, morphology and elemental distribution of the as-prepared polyanionic cathode materials are investigated by the inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM) and energy-dispersive X-ray spectroscope (EDX). The results indicate that the alien atom Mn can effectively and equably dope into the samples as well as maintain the original spherical morphology. Besides, the electrochemical measurements reveal that the sample doped with 5% Mn delivers the highest initial discharge capacity of 248.5 mAh g −1 at 0.1C under ambient temperature in a voltage range of 1.5–4.8 V, the retention of the capacity is as high as 91.9% after 200 cycles. Additionally, the sample doped with 5% Mn also exhibits a good rate capability with a discharge capacity of 105.6 mAh g −1 even at a high rate of 10C. The excellent electrochemical performances can be ascribed to the appropriate Mn doping, which can effectively optimize the crystal structure of Li 2 FeSiO 4 /C and facilitate the diffusion coefficient of lithium-ion during cycling process. [ABSTRACT FROM AUTHOR]

Although FeF 3 and its hydrates have been studied as the cathode materials for Li ion batteries (LIBs), herein the FeF 3 /graphene composite with sheet-like structure is innovatively prepared and used as LIB cathode material. By scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD) and electrochemical measurement, the structure and electrochemical performance of the as-synthesized FeF 3 /graphene composite are investigated. The results indicate that the sheet-like structure hybrid is formed by the FeF 3 nanosheets and the graphene sheets. Meantime, we demonstrate that the FeF 3 /graphene composite has good rate capability and cycling performance, whether it is based on conventional intercalation reaction or reversible conversion reactions. [ABSTRACT FROM AUTHOR]

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]

• Sandwich architecture of rGO-encapsulated Ni/Co co-doped FeF 3 ·0.33H 2 O was prepared. • Ni-doping facilitate mainly the capacity improvement by expanding the cell volume. • Co-doping enhance primarily the cycling stability by accelerating Li+ migration. • NC-FF are firmly encapsulated within rGO sheets by M O C bonding interaction. • NC-FF|Graphite full-cell shows a high reversible capacity and good cycle stability. Conversion-type iron fluoride promises a high energy density and redox potential, which is considered an extremely promising candidate for next-generation high-specific-energy and low-cost Li-ion battery. Unfortunately, its commercialization is plagued by the poor rate capability and fast capacity degradation resulting from its inferior electronic conductivity and large volumetric expansion. Herein, a three-dimensional sandwich architecture of rGO-encapsulated Ni/Co dual‐doped FeF 3 ·0.33H 2 O nanoparticles (NC-FF) is fabricated by co-precipitation and subsequent calcination. The results show that the flower-like Ni/Co dual‐doped FeF 3 ·0.33H 2 O nanoparticles are firmly encapsulated within highly conductive rGO sheets through M O C bonding interaction, which constructs a robust electronic/ionic network and a buffer layer against the severe volume variation. The Ni-doping can facilitate to the capacity improvement by expanding the cell volume, and the Co-doping can promote the rate capability and cycling stability enhancement by accelerating Li+ migration. Benefiting from the synergies of Ni/Co dual-doping and encapsulation of rGO, the NC-FF exhibits a high-rate capability of 200.1 mAh g−1 at 5.0 C and good cycle stability of 177.8 mAh g−1 after 400cycles. Moreover, the NC-FF|Graphite symmetric-cell still shows a high reversible capacity of 396.2 mAh g−1 at 1.0C and good cycle stability of 247.5 mAh g−1 after 100cycles. [ABSTRACT FROM AUTHOR]

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]

Highlights: [•] BiPO4 is initially reported as a cathode material for lithium-ion batteries. [•] We have explored that BiPO4 is a cathode material based on conversion reactions. [•] Its theoretical specific capacity and output voltage are 264.5mAhg−1 and 3.14V. [•] Its theoretical volumetric energy density is close to twice higher than LiCoO2. [•] Effects of the phase transformation on electrochemistry of BiPO4 are discussed. [ABSTRACT FROM AUTHOR]

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]

Hexagonal BiPO4 is precipitated from a solution of Bi(NO3)3 in 10 wt.% aq. [ABSTRACT FROM AUTHOR]