Determination of the chemical diffusion coefficient of lithium in Li3V2(PO4)3

The chemical diffusion of lithium ion in Li₃V₂(PO₄)₃ were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. The CV results show that there exists a linear relationship between the peak current (i_p) and the square root of the scan rate (ν^1/2). The impedance spectrum exhibits a single semicircle and a straight line in a very low frequency region. A linear behavior was observed for every curve of the real resistance as a function of the inverse square root of the angular frequency in a very low frequency region. The obtained chemical diffusion coefficient from EIS measurements varies within 10^− 9 to 10^− 8 cm²·s^− 1, in good agreement with those from CV results.     

Synthesis and electrochemical properties of Nb-doped Li3V2(PO4)3/C cathode materials for lithium-ion batteries

Li₃V_2−xNb_x(PO₄)₃/C cathode materials were synthesized by a sol-gel method. X-ray diffraction patterns demonstrated that the appropriate addition of Nb did not destroy the lattice structure of Li₃V₂(PO₄)₃, and enlarged the unit cell volume, which could provide more space for lithium intercalation/de-intercalation. Transmission electron microscopy and energy dispersive X-ray spectroscopy analysis illustrated that Nb could not only be doped into the crystal lattice, but also form an amorphous (Nb, C, V, P and O) layer around the particles. As the cathode materials of Li-ion batteries, Li₃V_2−xNb_x(PO₄)₃/C (x ≤ 0.15) exhibited higher discharge capacity and better cycle stability than the pure one. At a discharge rate of 0.5C, the initial discharge capacity of Li₃V_1.85Nb_0.15(PO₄)₃/C was 162.4 mAh/g. The low charge-transfer resistances and large lithium ion diffusion coefficients confirmed that Li₃V_2−xNb_x(PO₄)₃/C samples possessed better electronic conductivity and lithium ion mobility. These improved electrochemical performances can be attributed to the appropriate amount of Nb doping in Li₃V₂(PO₄)₃ system by enhancing structural stability and electrical conductivity.     

Synthesis and electrochemical properties of Ti doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li_3 − xFe_2 − xTi_x(PO₄)₃/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li₃Fe₂(PO₄)₃/C (x = 0) and Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C (x = 0.2) possess two plateau potentials of Fe³⁺/Fe²⁺ couple (around 2.8 V and 2.7 V vs. Li⁺/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C has higher reversibility and better capacity retention than that of the undoped Li₃Fe₂(PO₄)₃/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.     

Photoluminescence and radioluminescence of pure and Ce activated Na3Gd(PO4)2

The spectroscopic properties of Na₃Gd(PO₄)₂ and Na₃Gd(PO₄)₂:Ce³⁺ phosphors in the VUV-UV spectral range were investigated. Five excitation bands of Ce³⁺ ions at Gd³⁺ sites are observed at wavelengths of 205, 246, 260, 292, and 321 nm. Doublet Ce³⁺ 5d → 4f emission bands are observed at 341 and 365 nm with a decay constant τ_1/e around 26 ns. The X-ray excited luminescence of Na₃Gd_0.99Ce_0.01(PO₄)₂ at room temperature shows a photon yield of ∼17,000 photons/MeV of absorbed X-ray energy.     

Thermoluminescence properties of Ce-doped LiSr4(BO3)3 phosphor

Borates LiSr₄(BO₃)₃ were synthesized by high-temperature solid-state reaction. The thermoluminescence (TL) and some of the dosimetric characteristics of Ce³⁺-activated LiSr₄(BO₃)₃ were reported. The TL glow curve is composed of only one peak located at about 209 °C between room temperature and 500 °C. The optimum Ce³⁺ concentration is 1 mol% to obtain the highest TL intensity. The TL kinetic parameters of LiSr₄(BO₃)₃:0.01Ce³⁺ were studied by the peak shape method. The TL dose response is linear in the protection dose ranging from 1 mGy to 1 Gy. The three-dimensional thermoluminescence emission spectra were also studied, peaking at 441 and 474 nm due to the characteristic transition of Ce³⁺.     

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.     

High performance LiFePO4/C cathode for lithium ion battery prepared under vacuum conditions

LiFePO₄/C with smaller particle size (0.3-0.6 μm) was synthesized via a two-step vacuum sintering method. X-ray diffraction and scanning electron microscopy were used to detect the phases presented in the composites and observe sample morphology. In addition, AC electrochemical impedance spectroscopy, cyclic voltammetry, along with constant current discharge/charge tests, were used to characterize the electrochemical properties of the composites. It was shown that LiFePO₄/C with a single olive crystal structure could deliver discharge capacity of 145.5 and 108.7 mAh g⁻¹ at 0.5 and 6C for the fist cycle, and kept reversible capacity of 147.5 and 117.1 mAh g⁻¹ after 100 cycles.     

Chemical vapor deposition of NiSi using Ni(PF3)4 and Si3H8

NiSi_x films were deposited using chemical vapor deposition (CVD) with a Ni(PF₃)₄ and Si₃H₈/H₂ gas system. The step coverage quality of deposited NiSi_x was investigated using a horizontal type of hot-wall low pressure CVD reactor, which maintained a constant temperature throughout the deposition area. The step coverage quality improved as a function of the position of the gas flow direction, where PF₃ gas from decomposition of Ni(PF₃)₄ increased. By injecting PF₃ gas into the Ni(PF₃)₄ and Si₃H₈/H₂ gas system, the step coverage quality markedly improved. This improvement in step coverage quality naturally occurred when PF₃ gas was present, indicating a strong relationship. The Si/Ni deposit ratio at 250 °C is larger than at 180 °C. It caused a decreasing relative deposition rate of Ni to Si. PF₃ molecules appear to be adsorbed on the surface of the deposited film and interfere with faster deposition of active Ni deposition species.     

Suppressing Li3PO4 impurity formation in LiFePO4/Fe2P by a nonstoichiometry synthesis and its effect on electrochemical properties

Lithium iron phosphate (LiFePO₄) was synthesized by a solid-state reaction from a nonstoichiometric mixture of starting materials with an iron: phosphorus excess ratio of 2:1 at a high temperature. The nonstoichiometry synthesis did not affect conductive Fe₂P formation, lattice constants of LiFePO₄ and materials morphology, but could effectively suppress insulating Li₃PO₄ impurity formation which was clearly observed in the stoichiometric sample. Our results demonstrate that the positive effect of the conductive Fe₂P could be masked by the insulating Li₃PO₄ impurity presence, and the creation of Fe₂P without Li₃PO₄ formation from carbothermal reduction could be successfully achieved by our nonstoichiometry synthesis.     

Spray-drying technology for the synthesis of nanosized LiMn2O4 cathode material

Spinel LiMn₂O₄ cathode material has been synthesized by a spray-drying method for lithium ion batteries. During the entire process, the as-prepared powders were characterized using TGA/DTA, XRD, FTIR, SEM and TEM. The results showed that this method not only reduces the sintering time to 5 h at 750 °C, but also decreases the average particle size of LiMn₂O₄ powders to the order of nanometers. The electrochemical performance of nanosized LiMn₂O₄ was investigated by the galvanostatic charge-discharge tests. The data indicate that the nanosized LiMn₂O₄ has a specific capacity of about 130 mA h g^− 1 (1/5 C), and at higher rate (1 C), still has good cycling stability.     

Synthesis and characterization of novel nanostructured fishbone-like Cu(OH)2 and CuO from Cu4SO4(OH)6

The Cu₄SO₄(OH)₆ was synthesized by a simple hydrothermal reaction with a yield of ~ 90%. Using Cu₄SO₄(OH)₆ as the starting material, novel fishbone-like Cu(OH)₂ was produced by a direct reaction of Cu₄SO₄(OH)₆ with NaOH solution. The Cu(OH)₂ consists of many needle-like nanorods parallel to each other and perpendicular to the direction of backbone, forming fishbone-like structure. Using the fishbone-like Cu(OH)₂ as the sacrificial precursor, CuO with similar size and morphology was obtained through a simple heat treatment. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, X-ray photoelectron spectroscopy, BET nitrogen adsorption, and UV-Vis absorption spectroscopy were employed to characterize the as-prepared samples. The conversion of the Cu₄SO₄(OH)₆ to the fishbone-like Cu(OH)₂ was visualized by time-dependent SEM images. A mechanism was also proposed based on the observed results.     

One-pot syntheses of Li3V2(PO4)3/C cathode material for lithium ion batteries via ascorbic acid reduction approach

Monoclinic Li₃V₂(PO₄)₃/C composite synthesized by ascorbic acid reduction method is examined as a cathode material for Li-ion batteries. Transmission electron microscopy (TEM) images show that the nano-size particles are obtained. The reversible capacity of Li₃V₂(PO₄)₃/C prepared with LiOH and H₃PO₄ is 141.2 mAh g⁻¹ after 100 cycles at 1C discharge rate between 3 V and 4.8 V, and the retention rates of discharge capacity is 93.4%. Ascorbic acid plays not only as reduction reagent, but also as carbon sources. This strategy shortens the time of solid state reaction and facilitates the procedure of synthesis. Effects of different precursors materials on the performance of the Li₃V₂(PO₄)₃/C are investigated.     

Organic phosphoric sources for syntheses of Li3V2(PO4)3/C via improved rheological phase reaction

Li₃V₂(PO₄)₃/C is synthesized by an improved rheological phase method using Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP) as organic phosphoric sources. The phosphoric sources with carbon chains can inhibit the grain growth of Li₃V₂(PO₄)₃ particles. X-ray powder diffraction pattern shows that the obtained Li₃V₂(PO₄)₃/C sample is monoclinic phase. Transmission electron microscope results show that the thickness of carbon layer is about 10 nm. The form of residual carbon is confirmed by Raman spectroscopy. The Li₃V₂(PO₄)₃/C sample prepared by 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP) displays the initial discharge capacity of 158 mAh g^− 1 and keeps 130 mAh g^− 1 after 100 cycles at 1 C rate. The improved rheological phase reaction method can be used for synthesis of Li₃V₂(PO₄)₃ cathode material and other polyanion materials.     

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.     

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.     

Dielectric and electric studies of the [N(CH3)4][N(C2H5)4]ZnCl4 compound at low temperature

The [N(CH₃)₄][N(C₂H₅)₄]ZnCl₄ compound was prepared and characterized by electrical technique. The temperature dependence of the dielectric permittivity shows that this compound is ferroelectric below T = 268 K. The two semi-circles observed in the complex impedance identify the presence of the grain interior and grain boundary contributions to the electrical response in the material. The equivalent circuit is modeled by a combination series of two parallel R_P–CPE circuits. The frequency dependent conductivity is interpreted in term of Jonscher's law. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (K.W.W.) function: ?(t) = exp [(−t/τ)^β]. The temperature dependence of the alternative current conductivity (σ_p), direct current conductivity (σ_dc) and the relaxation frequency (f_p) confirm the presence of the ferroelectric–paraelectric phase transition.     

Mild solvothermal synthesis of complex fluorides Li2BeF4 and LiSrAlF6

The complex fluorides Li₂BeF₄ and LiSrAlF₆ were synthesized solvothermally at 180–240 °C and characterized by means of X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The different influence factors such as solvents, molar ratios of initial mixtures, reaction temperature and reaction time were investigated. The experimental results indicated that Li₂BeF₄ and LiSrAlF₆ powders could be controllably synthesized in the solvothermal process.     

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.