A novel synthesis of spherical LiFePO4 nanoparticles

An effective, simple and green synthesis method based on hydrothermal stripping technique, in which ferrous ion was stripped and precipitated directly from iron (II)-loaded organic phase, has been successfully developed. X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) showed that the samples synthesized at 140-250 °C with raw materials LiOH, H₃PO₄ and FeSO₄·7H₂O are well-defined spherical LiFePO₄ nanoparticles, and the particle size can be easily controlled by changing the temperature and time. Electrochemical tests showed that the sample has a higher cell performance as a cathode material. Our results suggest that hydrothermal stripping synthesis is a promising method for obtaining spherical LiFePO₄ nanoparticles without agglomeration.     

A modified mechanical activation synthesis for carbon-coated LiFePO4 cathode in lithium batteries

An efficient synthesis based on mechanical activation (MA) was developed for carbon-coated lithium iron phosphate (LiFePO₄/C). The conventional MA process was modified by introducing two initial steps of slurry phase blending of the ingredients and solvent removal by rotary evaporation, so as to get an intimate mixing and homogenous dispersion of conductive carbon in the sample. Phase-pure, nanometer-sized particles of the active material covered with a porous, nanometer-sized web of carbon were obtained. LiFePO₄/C exhibited remarkably good electrochemical properties when evaluated as cathodes in room temperature lithium cells. An initial discharge capacity of 166 mAh/g (corresponding to 97.6% of theoretical capacity) was achieved at 0.1 C-rate. A very stable cycle performance was also realized; good capacity retention up to 100 cycles was achieved at different current densities.     

Preparation and electrochemical performance of LiFePO4/C composite with network connections of nano-carbon wires

LiFePO₄/C composite with network connections of nano-carbon wires was successfully prepared by using polyvinyl alcohol as carbon source. The composite was characterized by X-ray diffraction and transmission electron microscopic, and its electrochemical performance was investigated by galvanostatic charge and discharge tests. The experimental results show that LiFePO₄ grains are tightly connected by the network of nano-carbon wires. Moreover LiFePO₄/C composite exhibits high capacity of 168 mAh g⁻¹ applied 15 mA g⁻¹ current density (C/10), excellent cyclic ability and rate capability. When 1500 mA g⁻¹ current density (10C) was applied, the high discharge capacity of 129 mAh g⁻¹ has been obtained at room temperature.     

Enhanced electrochemical performance of LiFePO4 coated with Li0.34La0.51TiO2.94 by rheological phase reaction method

Li_0.34La_0.51TiO_2.94 (LLTO), as a high ionically conductive material, has been coated on the surface of olivine-type LiFePO₄ by rheological phase reaction method. The structure and electrochemical properties of the prepared cathode were investigated. The XRD results indicate that the LLTO coating does not affect the structure of LiFePO₄ and the LLTO-coated LiFePO₄ cathode material still has olivine structure. The electrochemical measurements of LLTO-coated LiFePO₄ show that the rate performance of LiFePO₄ is greatly improved by the surface treatment. At the room temperature, LLTO-coated LiFePO₄ exhibits high discharge capacity of 109.9 mAh g⁻¹ at 10 C, whereas the uncoated LiFePO₄ has the discharge capacity less than 80 mAh g⁻¹ at the same rate. Besides, LLTO-coated LiFePO₄ also shows better cycle stability and low-temperature performance than that of uncoated LiFePO₄.     

Needle-like LiFePO4 thin films prepared by an off-axis pulsed laser deposition technique

Lithium iron phosphate (LiFePO₄) thin films were prepared by pulsed laser deposition with an off-axis geometry. Amorphous, needle-like and crystallized granular thin films were prepared on Si and titanium substrates. The preferred orientation of these crystallized LiFePO₄ thin films is (120). Microstructures of the deposited films are dependant on the substrate temperature (room temperature, 500 °C and 700 °C) and Ar pressure (5 Pa and 30 Pa) in the chamber. The needle-like film grows following a self-shadowing mechanism. LiFePO₄ thin film with high crystallinity shows a voltage plateau which is a typical feature of the phase transition reaction for bulk material, while the sloped profiles are observed clearly in the charging and discharging curves of LiFePO₄ thin films with low cystallinity.     

A novel anode material of Fe2VO4 for high power Lithium ion battery

Spinel Fe₂VO₄ was synthesized by solid state method and its properties were characterized using XRD, SEM, TG-DSC and specific surface area measurements. The average size of the particles was 500 nm. TG-DSC test demonstrated that the Fe₂VO₄ was thermally stable in nitrogen atmosphere within 300 °C. Lithium insertion into the sample at room temperature and 55 °C has been investigated and the highest discharge capacity approached 250 mAh/g at an average voltage of 0.6 V vs Li⁺/Li. Capacity retention was unexpectedly good at 1C discharge rate at room temperature and 55 °C. At 5C discharge rate, the specific capacity was still 136 mAh/g. The results show that the Fe₂VO₄ is a promising anode material due to its high specific capacity, thermal stability and rate performances.     

Enhanced electrochemical properties of nano-Li3PO4 coated on the LiMn2O4 cathode material for lithium ion battery at 55 °C

The electrochemical performance of LiMn₂O₄ is improved by the surface coating of nano-Li₃PO₄ via ball milling and high-temperature heating. The Li₃PO₄-coated LiMn₂O₄ powders are characterized by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). At 55 °C, capacity retention of 85% after 100 cycles was obtained for Li/Li₃PO₄-coated LiMn₂O₄ electrode at 1C rate, while that of pristine sample was only 65.6%. The Li/Li₃PO₄-coated LiMn₂O₄ electrode also showed improved rate capability especially at high C rates. At 5C-rates, the delivered capacities of pristine and Li₃PO₄-coated LiMn₂O₄ electrodes were 80.7 mAh/g and 112.4 mAh/g, respectively. The electrochemical impedance spectroscopy (EIS) indicates that the charge transfer resistance for Li/Li₃PO₄-coated LiMn₂O₄ cell was reduced compared to Li/LiMn₂O₄ cell.     

Effects of MoS2 doping on the electrochemical performance of FeF3 cathode materials for lithium-ion batteries

Orthorhombic structure FeF₃ was synthesized by a liquid-phase method. The FeF₃/MoS₂ for the application of cathode material of lithium-ion battery was prepared through mechanical milling with molybdenum bisulfide. The structure and morphology of the FeF₃/MoS₂ were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical behavior of FeF₃/MoS₂ was studied by charge/discharge, cyclic voltammetry and electrochemical impedance spectra measurements. The results show that the prepared FeF₃/MoS₂ was typical orthorhombic structure, uniform surface morphology, better particle-size distribution and excellent electrochemical performances. The initial discharge capacity of FeF₃/MoS₂ was 169.6 mAh·g^− 1 in the voltage range of 2.0-4.5 V, at room temperature and 0.1 C charge-discharge rate. After 30 cycles, the capacity retention is still 83.1%.     

锂离子电池正极材料LiFePO4的合成及电化学性能

固相反应法合成了新型锂离子电池正极材料LiFePO4,组装成电池后,室温下(23℃)初始比容量为110mAh/g.以蔗糖分解在LiFePO4电池材料的颗粒间覆碳的方法制备了改性的LiFePO4,对LiFePO4进行表面覆碳改性后其电化学性能包括比容量和充放电效率两方面都得到提高.覆碳后正极材料的初始比容量在室温下达到了140mAh/g,比覆碳前增加了30mAh/g,在循环20周后比容量仍维持在125mAh/g左右;覆碳后正极材料的平均充放电效率在23℃和50℃下分别为91%和93%.     

Chemical diffusion coefficient of lithium ion in Li3V2(PO4)3 cathode material

The kinetic properties of monoclinic lithium vanadium phosphate were investigated by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS) method. The PSCA results show that there exists a linear relationship between the current and the square root of the time. The D?_Li values of lithium ion in Li_3-xV₂(PO₄)₃ under various initial potentials of 3.41, 3.67, 3.91 and 4.07 V (vs Li/Li⁺) obtained from PSCA are 1.26 × 10^− 9, 2.38 × 10^− 9, 2.27 × 10^− 9 and 2.22 × 10^− 9 cm²·s^− 1, respectively. Over the measuring temperature range 15-65 °C, the diffusion coefficient increased from 2.67 × 10^− 8 cm²·s^− 1 (at 15 °C) to 1.80 × 10^− 7 cm²·s^− 1 (at 65 °C) as the measuring temperature increased.     

LiNi0.5Mn1.5O4 cathode material by low-temperature solid-state method with excellent cycleability in lithium ion battery

LiNi_0.5Mn_1.5O₄ cathode material was synthesized from a mixture of LiCl, NiCl₂?6H₂O and MnCl₂?4H₂O with 70 wt.% oxalic acid by a low-temperature solid-state method. The calcination temperature was adjusted to form disorder Fd3m structure at 700-800 °C for 10 h.XRD patterns and FTIR spectroscopy showed that the LiNi_0.5Mn_1.5O₄ cathode material exhibited an impurity-free spinel Fd3m structure. Electrochemical property results revealed that the LiNi_0.5Mn_1.5O₄ cathode material charged at 1C rate to 4.9 V and discharged at 2 and 3 C to 3.5 V delivered initial capacity of 120 mAh/g and maintained a capacity retention over 80% at room temperature after 1000 charge/discharge cycles.     

Hydrothermal synthesis of Fe3O4 nanoparticles and its application in lithium ion battery

Well dispersed Fe₃O₄ nanoparticles with a mean diameter of about 160 nm were synthesized by a simple hydrothermal method in the presence of sodium sulfate. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectrum, and Fourier transform infrared spectra (FTIR). Electrochemical properties of the nanostructured Fe₃O₄ as cathode electrodes of lithium ion battery were studied by conventional charge/discharge tests, showing a high initial discharge capacity of 1267 mA h g^− 1 at a current density of 0.1 mA cm^− 2.     

Synthesis and spectroscopic investigations of Mn3O4 nanoparticles

Trimanganese tetraoxide (Mn₃O₄) nanoparticles have been synthesized via hydrothermal process. Nevertheless, homogeneous nanoparticles of Mn₃O₄ with platelet lozange shape were obtained. The crystallite size ranged from 40 to 70 nm. The Mn₃O₄ product was investigated by X-ray diffraction, transmission electron microscopy (MET), and impedance spectroscopy. Electrical conductivity measurements showed that the as-synthesized Mn₃O₄ nanomaterial has a conductivity value which goes from 1.8 10⁻⁷ Ω⁻¹ cm⁻¹ at 298 K, to 23 10⁻⁵ Ω⁻¹ cm⁻¹ at 493 K. The temperature dependence of the conductivity between 298 and 493 K obeys to Arrhenius law with an activation energy of 0.48 eV.     

High energy density lithium ion batteries using Li2.6Co0.4 − xCuxN (anode) and Cu0.04V2O5 (cathode) electrode materials

Li_2.6Co_0.4 - xCu_xN (x = 0, 0.15) anode materials were prepared by conventional solid state reaction. Between both materials, Li_2.6Co_0.25Cu_0.15N exhibited better capacity retention than that of Li_2.6Co_0.4N. According to electrochemical impedance spectroscopy, the better cycling behavior of Li_2.6Co_0.25Cu_0.15N has been attributed to the improvement in interfacial compatibility between the electrode and electrolyte interface. A possible explanation to this was given. Li_2.6Co_0.4 - xCu_xN/Cu_0.04V₂O₅ full-cells were assembled to investigate the reliability of Li_2.6Co_0.4 - xCu_xN anode materials in practical applications. The Li_2.6Co_0.25Cu_0.15N/Cu_0.04V₂O₅ cell delivered a specific capacity of 260 mA h g^− 1, and a specific energy of 505.7 mW h g^− 1, which was much higher than that of C/LiCoO₂ lithium ion batteries.     

Preparation and properties of NiFe2O4 nanowires

Polycrystalline NiFe₂O₄ nanowires have been synthesized by PEG assisted co-precipitation method. The formation mechanism of the nanowires proposed is by means of the orientational aggregation of individual nanoparticles. X-ray diffraction, high resolution scanning electron microscopy, transmission electron microscopy, microRaman and vibrating sample magnetometry studies were carried out. The results show that NiFe₂O₄ nanowires were in polycrystalline form with diameter of 58 nm. The synthesized nanowires show room temperature ferromagnetic property with high coercivity. This method is expected to be useful for large scale synthesis of NiFe₂O₄ nanowires for the application of magnetic recording.     

Preparation and electrochemical properties of Cr doped LiV3O8 cathode for lithium ion batteries

Chromium was incorporated into lithium trivanadate by an aqueous reaction followed by heating at 100 °C. This Cr doped LiV₃O₈ as a cathode for lithium ion batteries exhibits 269.9 mAh g^− 1 at first discharge cycle and remains 254.8 mAh g^− 1 at cycle 100, with a charge-discharge current density of 150 mA g^− 1 in the voltage range of 1.8-4.0 V. The Cr-LiV₃O₈ cathode show excellent discharge capacity, with the retention of 94.4% after 100 cycles. These result values are higher than previous reports indicating that Cr-LiV₃O₈ prepared by our low temperature synthesis method is a promising cathode material for rechargeable lithium ion batteries. The enhanced discharge capacity and cycle stability of Cr-LiV₃O₈ cathode indicate that chromium atoms promote lithium transfer or intercalation/deintercalation during the electrochemical cycles and improve the electrochemical performances of LiV₃O₈ cathode.     

Electrochemical performance of LiFePO4/Si composites as cathode material for lithium ion batteries

LiFePO₄/Si composites are synthesized via a simple milling isopropanol mixtures process, and the effects of Si-modification on the electrochemical performances of LiFePO₄ are investigated systematically by charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine LiFePO₄, LiFePO₄/Si-nanoparticle shows better cyclability and higher rate capability, especially at elevated temperature. An analysis of the electrochemical measurements indicates that Si incorporation could significantly improve the electrochemical performance at high charge/discharge rate and elevated temperature. Among the investigated samples, (LiFePO₄)₉₈/(Si)₂ sample shows the best electrochemical performance with 150 mAhg⁻¹ at 0.5C at 60 °C. The enhancement could be mainly attributed to the lower charge-transfer resistance and higher lithium diffusion coefficients. In addition, the dangling bonds of Si and fluorosilica compounds are responsible for suppressing the dissolution of Fe²⁺ from olivine phase and preventing the rise of the surface resistance and charge transfer resistance.     

Preparation and characterization of NaSm9(SiO4)6O2 powders with infrared absorptive properties

NaSm₉(SiO₄)₆O₂ powders were synthesized by mild hydrothermal method at 180 °C for 24 h. The infrared optical properties and structure of the obtained powders were characterized. There existed two narrow and sharp absorptive bands near 943 cm^− 1 (10.6 μm). The band at 938 cm^− 1 was assigned to the stretching vibrations of SiOSm groups connecting to Q¹ species and the band at 989 cm^− 1 was attributed to the stretching vibrations of SiOSm groups linking with Q⁰ species. The reflectivity was lower than 1% from 900 to 1200 nm and reached the minimum of 0.46% at 1073 nm. The prepared powders exhibit potential to act as a new kind of absorptive material for the infrared light of 10.6 μm and 1.06 μm.     

Enhanced thermoelectric properties of NaCo2O4 by adding ZnO

The primary phase present in the as-sintered Na(Co_1 − xZn_x)₂O₄ (0 ≤ x ≤ 0.1) bodies was the solid solution of the constituent oxides with a bronze-type layered structure. The electrical conductivity of the Na(Co_1 − xZn_x)₂O₄ samples significantly increased with an increase in ZnO content. The sign of the Seebeck coefficient for all samples was positive over the whole temperature range (723-1073 K), i.e., p-type conduction. The power factor of Na(Co_0.95Zn_0.05)₂O₄ showed an outstanding power factor (1.7 × 10^− 3Wm^− 1 K^− 2) at 1073 K. The power factor was above four times superior to that of ZnO-free NaCo₂O₄ (0.4 × 10^− 3Wm^− 1 K^− 2). This originates from an unusually large Seebeck coefficient (415 μVK^− 1) accompanied with high conductivity (127Ω^− 1 cm^− 1) at 1073 K.