Electrochemical performance and thermal stability of GaF3-coated LiNi0.5Mn1.5O4 as 5 V cathode materials for lithium ion batteries

LiNi_0.5Mn_1.5O₄ coated with various amounts of GaF₃ were prepared and investigated as cathode materials for lithium ion batteries. The sample was characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDX). The results indicated that the electrochemical performance of LiNi_0.5Mn_1.5O₄ was effectively improved by the GaF₃ coating. The 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ delivered a discharge capacity of 97 mAh g^?1 at 20 C (3000 mA g^?1), while the pristine sample only yielded 80 mAh g^?1 at 10 C. Meanwhile, the 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ exhibited an obviously better cycle life than the bare sample at 60 °C, delivering a discharge capacity of 120.4 mAh g^?1 after 300 cycles, 82.9 % of its initial discharge capacity, while the pristine only gave 75 mAh g^?1. At 0.1 C, the self-discharge of 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ is about 3.4 %, while the pristine is about 10.2 % after a 5-day rest at room temperature. Furthermore, GaF₃ coating greatly reduced the self-heating rate and improved the thermal stability of LiNi_0.5Mn_1.5O₄. These improvements were attributed to the GaF₃ layer not only increasing the electronic conductivity of the LiNi_0.5Mn_1.5O₄ but also effectively suppressing the reaction between the LiNi_0.5Mn_1.5O₄ and the electrolytes, which reduced the charge-transfer impedance and the dissolution of Ni and Mn during cycling.     

MgAl2O4–LaCr0.5Mn0.5O3 composite ceramics for high temperature NTC thermistors

New negative temperature coefficient (NTC) ceramics based on xMgAl₂O₄–(1 ? x)LaCr_0.5Mn_0.5O₃ (x = 0, 0.4, 0.6, 0.8) composition were investigated. The composite ceramics (x = 0.4, 0.6, 0.8) consisted of two phases: a cubic spinel MgAl₂O₄ phase and an orthorhombic perovskite LaCr_0.5Mn_0.5O₃ phase isomorphic to LaCrO₃. The brighter regions were the LaCr_0.5Mn_0.5O₃ and the darker was the MgAl₂O_4. There was ion diffusion between these two phases. X-ray photoelectron spectroscopy analysis corroborated the presence of Cr³⁺, Cr⁴⁺, Mn³⁺ and Mn⁴⁺ ions on lattice sites, which may result in the hopping conduction. The ρ ₃₀₀ and B _400/800 constant increased with increasing MgAl₂O₄ content. The values of ρ ₃₀₀, B _400/800 and activation energy of NTC thermistors were in the range 1.76–1.22 × 10⁸ Ωcm, 2,646–8,711 K, 0.228–0.746 eV, respectively. This means the electrical properties can be adjusted to desired values, depending on the MgAl₂O₄ content.     

Post-doping via spray-drying: a novel sol–gel process for the batch synthesis of doped LiNi0.5Mn1.5O4 spinel material

Powder granulation, Ti-doping and thermal post-treatment have beneficial effects on the electrochemical performance of 5 V LiNi_0.5Mn_1.5O₄ (LNMO) spinel materials. It is shown that spray-drying combined with a post-doping process step is suitable to prepare Ti-doped 5 V materials with a defined and highly reproducible microstructure and chemical composition. Powder granulation via spray-drying and thermal post-treatment provides spherical LNMO granules with nano-crystalline primary particles and a 10 % higher specific discharge capacity compared to pristine LNMO materials due to the presence of the partially ordered P4 ₃ 32 spinel phase and the reduced Mn³⁺ content. Powder granulation combined with a post-doping process step which utilizes titanium containing sol leads to spherical LiNi_0.5Mn_1.47Ti_0.03O₄ granules with uniform nano-crystalline primary particles and a homogenous Ti distribution. The second calcination process after spray-drying as well as the Ti-doping cause a reduced content of the Li _x Ni_1?x O impurity phase. This facile sol–gel processing leads to doped LiNi_0.5Mn_1.47Ti_0.03O₄ with an increased discharge capacity of 18 % compared to the original material. All the granulated materials show a good rate performance up to 10 C due to their particular microstructure.     

Effect of Co substitution for Mn on Y1−x Sr x MnO3 properties for SOFC cathode material

Y_0.6Sr_0.4Mn_1–y Co _y O₃ (0 y 0.4) perovskite oxides were prepared by the coprecipitation method. The effect of Co substitution for Mn on the crystal structure, electrical conductivity and thermal expansion properties were investigated. By X-ray powder diffraction, the crystal structure was found to change from hexagonal symmetry of Y_0.8Sr_0.2MnO₃ to orthorhombic of Y_0.6Sr_0.4Mn_1–y Co _y O₃. The differences in the structure of the unsubstituted Y_1–x Sr _x MnO₃ (0.2 x 0.4) are attributed to the average ionic radii of the cations and the amounts of Mn⁴⁺ present. The results of electrical conductivity analysis can be described by the small polaron hopping conductivity model. With Co substitution, the activation energy increases, possibly due to an increase of Jahn–Teller distortion, at an extent higher than the increase of the concentration of charge carriers; thus, the electrical conductivity decreases. In addition, the relative densities of the materials reached 94% with sintering at 1350°C for 12 h and had higher concentration of the available lattice sites, thus showing higher conductivity, than that with sintering at 1300°C for 6 h, which achieved 70% relative density. It is also found that the thermal expansion coefficient (TEC) increases as the Sr and Co content of Y_1–x Sr _x Mn_1–y Co _y O₃ increases and those with Co content of y = 0.2 exhibit TEC compatibility with YSZ.     

Relationship between hardness and strength characteristics of Cu–Cr microlayer composite material at elevated temperatures

We investigate the structure, hardness, strength, plasticity and fracture character of Cu–Cr microlayer composite material for electric contacts with prescribed microlayered structure and chemical composition in the temperature range from 290 to 1070 K. The correlation relationships between the hardness and strength characteristics have been established.     

The Cu–Y co-doping LiNi0.5Mn1.5O4 with modified morphology and enhanced electrochemical property for a 5 V lithium-ion battery

Journal of Materials Science: Materials in Electronics - LiNi0.5?xCuxMn1.48Y0.02O4 (x?=?0.02, 0.03, 0.04) and LiNi0.5Mn1.5O4 (LNMO) samples were prepared successfully via the...     

Low cycle fatigue and creep–fatigue interaction behaviour of 2.25Cr1MoV steel at elevated temperature

This study reports the fatigue behaviour of 2.25Cr1MoV steel under low cycle fatigue (LCF) loading and creep-fatigue interaction (CFI) loading at 355, 455 and 555 °C. Various hold durations up to 600 s were introduced in the CFI tests at the peak/valley strain under strain or stress control. In LCF tests, the steel exhibited remarkable strengthening at 455 °C, which can be ascribed to the effect of dynamic strain aging. In CFI tests, tensile holds were found more damaging than compressive holds but considerably less harmful than the combined tensile-compressive holds. A modified plastic strain energy approach based on the damage mechanisms was proposed to predict fatigue life under LCF and CFI conditions. The predictions obtained compared very favourably with the experimental results.     

Preparation and characterization of LiNi0.8Co0.15Al0.05O2 cathode material from (NH4)2C2O4·2H2O precipitant

Journal of Materials Science: Materials in Electronics - LiNi0.8Co0.15Al0.05O2 (NCA) cathode material was usually prepared with Ni2+, Co2+, Al3+ co-precipitation method using NaOH/NH3·H2O...     

Synthesis of LiNi1−xCoxPO4/C nanocomposite cathode for lithium ion batteries by a combination of aerosol and powder technologies

Pure LiNi_1?xCo_xPO₄ (x?=?0, 0.2, 0.5, 0.8, 1) was synthesized by spray pyrolysis followed by heat treatment. The X-ray diffraction (XRD) patterns of LiNi_1?xCo_xPO₄ were indexed to olivine structure with a Pnma space group. The peak shift and variation of lattice parameters suggested that LiNi_1?xCo_xPO₄ solid solution was formed. Moreover, LiNi_1?xCo_xPO₄/C (x?=?0, 0.2, 0.5, 0.8, 1) nanocomposites were successfully synthesized by a combination of spray pyrolysis and wet ball milling followed by heat treatment. The XRD patterns of all samples were indexed to olivine structure with a Pnma space group. From scanning electron microscopy images, the primary particle sizes of LiNi_1?xCo_xPO₄/C nanocomposites were reduced to the range of approximately 50–100?nm. LiNi_0.5Co_0.5PO₄/C cathode exhibited a higher first discharge capacity and cyclability than those of pure LiNi_0.5Co_0.5PO₄. Cyclic voltammetry data demonstrated that reduction peaks of LiNi_0.5Co_0.5PO₄/C cathode occur at 4.44?V and 4.71?V, which were ascribed to Co³⁺/Co²⁺ and Ni³⁺/Ni²⁺ reduction couples, respectively. Electrochemical impedance spectroscopy data revealed that the LiNi_0.5Co_0.5PO₄/C cathode had a smaller charge transfer resistance, resulting in a faster redox reaction kinetics for the lithium insertion and extraction, due to reduced particle size and introduced conductive carbon.     

Temperature and Frequency Dependent Dielectric Properties of Cu0.5Tl0.5Ba2Ca3(Cu4−y Cd y )O12−δ Bulk Superconductor

The temperature and frequency dependent dielectric properties of polycrystalline Cd-doped Cu_0.5Tl_0.5Ba₂Ca₃(Cu_4?y Cd _y )O_12?δ (y=0,0.25,0.5,0.75) bulk superconductor samples are investigated. The zero resistivity critical temperature {T _c(R=0)} has decreased and normal state resistivity has increased with the increase of Cd-doping in Cu_0.5Tl_0.5Ba₂Ca₃(Cu_4?y Cd _y )O_12?δ samples. The dielectric properties such as dielectric constants (ε′,ε″), dielectric loss tangent (tanδ) and ac-conductivity (σ _ac ) are investigated by measuring the capacitance (C) and conductance (G) in the frequency range of 10 KHz to 10 MHz at different temperature from 80 K to 300 K. The negative capacitance (NC) is observed in all Cu_0.5Tl_0.5Ba₂Ca₃(Cu_4?y Cd _y )O_12?δ samples. The large values of NC observed at lower frequencies and temperatures may be due to reduced thermal vibrations and enhanced polarizability of the material. The effect of Cd-doping on bulk properties, dc-resistivity (ρ) and ac-electrical conductivity (σ _ac ) of these superconductor samples are investigated. The polarization in Cu_0.5Tl_0.5Ba₂Ca₃(Cu_4?y Cd _y )O_12?δ samples is most likely arising from the displacement of charges in CuO₂/CdO₂ planes relative to the static charges at Ba²⁺, Tl³⁺, and Cu²⁺ sites in Cu_0.5Tl_0.5Ba₂O_4?δ charge reservoir layers by external applied field.     

Scandium and gallium substitution effects in the (Y1−xScx)Ba2Cu4O8 and (Y1−xGax)Ba2Cu4O8 superconducting oxides

In this study scandium and gallium substitution effects in the YBa₂Cu₄O₈ (Y-124) superconducting cuprate have been investigated. The superconducting (Y_1?xSc_x)Ba₂Cu₄O₈ and (Y_1?xGa_x)Ba₂Cu₄O₈ (x = 0.0, 0.05, 0.1 and 0.2) compounds have been synthesized using a simple sol–gel synthesis technique. The obtained oxides were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG) and resistivity measurements. The X-ray diffraction patterns of the samples with x = 0.0, 0.05, and 0.1 showed that the single phase (Y_1?xSc_x)Ba₂Cu₄O₈ and (Y_1?xGa_x)Ba₂Cu₄O₈ compounds have formed. Moreover, the XRD results are completely supported by TG measurements. The results of resistivity measurements for the (Y_1?xSc_x)Ba₂Cu₄O₈ samples showed that the onset critical temperature of superconductivity for these samples slightly increased. Contrarily, T_C for the (Y_1?xGa_x)Ba₂Cu₄O₈ samples decreased monotonically with the increasing amount of gallium.     

Magnetization Fluctuation Analysis and Superconducting Parameters of La1.5−x Ba1.5+x−y Ca y Cu3O z Superconductor

In this work we report analysis of experimental data of the magnetization of La_1.5?x Ba_1.5+x?y Ca _y Cu₃O _z superconducting system. The data are analyzed in terms of thermal fluctuations on the magnetization excess M(T) for different values of temperature in each of the samples. We describe a procedure for extracting the penetration depth in the ab plane (1537–1650 Å) and the coherence length in the ab plane (21–23 Å) parameters from the magnetization, as a function of the applied magnetic field. This procedure was performed for polycrystalline samples using the theory of Bulaevskii, Ledvij and Kogan, which analyzes the vortex fluctuation in superconducting materials within the Lawrence-Doniach framework. These data allowed one to determine the characteristic temperature value T ^? (53–73 K) in the magnetization curves for several magnetic fields. We calculated the data of magnetization excess from the curves of the magnetization as a function of the logarithm of the applied field. We notice that the values for these superconducting parameters are in agreement with reports for high-temperature superconductors. The value obtained of the superconducting volumetric fraction is compared with the value obtained through the measure of the Meissner effect.     

Comparison of torsion and compression constitutive analyses for elevated temperature deformation of Al–Li–Cu–Mn alloy

Abstract

Experimental alloy 2090 (Al – 2.1Li – 2.6Cu – 0.4Mn) was deformed in torsion and compression at temperatures T=300, 400, and 500°C and strain rates ε?=10^–2 to 10 s^–1. The torsion and compression results were analysed using equation A(sinh ασ)ⁿ=Z=ε? exp(Q_HW/RT), where Z is the Zener – Hollomon parameter. The variation of stress exponent n, Arrhenius slope s, and activation energy Q_HW were calculated with variation of the stress multiplier a from 0.01 to 0.08 MPa^–1. The change of α caused the stress exponent to decrease at a declining rate and Arrhenius slope s to increase linearly, thus causing the activation energy Q_HW to become stable above α=0.04 MPa^–1. The two experimental test techniques gave very similar flow stresses and constitutive constants. At α=0.052 MPa^–1 activation energy values showed reasonable consistency with other age hardenable aluminum alloys. The compression tests were also analysed using the power law expression ε? exp(Q′_HW/RT)=Z=A″σ^n′.     

Nd substitution effects in YBa2Cu4O8 prepared using a conversion reaction from Y1−xNdxBa2Cu3O7−δ and CuO

Synthesis, crystal structure and magnetic properties of samples with partial substitution of Nd for Y in YBa₂Cu₄O₈ are considered. The samples with nominal composition Y_1−xNd_xBa₂Cu₄O₈ (x=0.0–0.75) were prepared using a solid state conversion reaction from Y_1−xNd_xBa₂Cu₃O_7−δ and CuO using LiF as a flux. The annealing was performed at 790°C in a flowing oxygen atmosphere. The products with x=0.0–0.5 showed thermal stability up to 660°C in N₂(g) atmosphere revealing a single phase composition. The success of the synthesis is considered in relation to the effective ionic size of the Nd³⁺ ion. The crystal structures of the compounds are described on the basis of powder neutron diffraction measurements. The T_c values of the Nd substituted samples were noticeably lower than for the pristine YBa₂Cu₄O₈. Possible reasons for the decrease in T_c are discussed on the basis of calculated values for hole concentrations in the Cu–O₂ planes obtained via the BVS (bond valence sum) method, and on the basis of some Nd³⁺ ions being introduced at Ba²⁺ ion sites in the lattice.     

Low temperature synthesis of Co3O4 and (Co1−xMnx)3O4 spinels nanoparticles

The (Co_1?xMn_x)₃O₄ solid solution have been synthesized in water at 60 °C by soda addition to a cationic solution. XRD patterns show that spinel oxide has been obtained except for pure cobalt composition which exhibits also the presence of hydroxide and oxy-hydroxide. Therefore, to reach this composition, a different synthesis route has been developed: the cationic solution is added to the soda and for the first time Co₃O₄ nanoparticles have been synthesized by a direct precipitation in aqueous solution at low temperature. For each composition, the particles are well crystallized and exhibit a size close to 50 nm. Each particle is composed by several crystallographic domains of about 10 nm. The cubic to tetragonal transition reported in the literature for x = 0.46 is observed in between x = 0.33 and x = 0.50. Raman spectra show that substitution of Co by Mn, in the cubic phase, introduces a random high disorder. In the tetragonal phase, occupation of the octahedral site remains a random occupation, while the tetrahedral site seems to be preferentially occupied by Co ions. All these results show that the precipitation is a simple, fast and safe process to synthesize pure phase of (Co_1?xMn_x)₃O₄ spinel solid solution in aqueous media at low temperature.     

Oxygen-deficient ammonium vanadate for flexible aqueous zinc batteries with high energy density and rate capability at −30 °C

Aqueous zinc batteries (AZBs) have received significant attention owing to environmental friendliness, high energy density and inherent safety. However, lack of high-performance cathodes has become the main bottleneck of AZBs development. Here, oxygen-deficient NH₄V₄O_10−x·nH₂O (NVOH) microspheres are synthesized and used as cathodes for AZBs. The experimental test and theoretical calculations demonstrate that the oxygen vacancies in the lattice lower the Zn²⁺ diffusion energy barrier, which enables fast Zn²⁺ diffusion and good electrochemical performance in a wide temperature range. The suppressed side reactions also can help to improve the low temperature performance. NVOH shows a high energy density of 372.4 Wh kg⁻¹ and 296 Wh kg⁻¹ at room temperature and −30 °C, respectively. Moreover, NVOH maintains a 100% capacity retention after 100 cycles at 0.1 A g⁻¹ and ∼94% capacity retention after 2600 cycles at 2 A g⁻¹ and −30 °C. Investigation into the mechanism of the process reveals that the capacity contribution of surface capacitive behaviors is dominant and capacity attenuation is mainly caused by the decay of diffusion-controlled capacity. Furthermore, flexible AZBs can steadily power portable electronics under different bending states, demonstrating its great potential in wide-temperature wearable device.     

Electrical conduction and dielectric behaviour of the oxidic spinel Li0.5+0.5xCr0.3TixFe2.2−1.5XO4

The electrical conductivity of polycrystalline lithium-chromium ferrites substituted successively with Ti⁴⁺ was studied as a function of composition and temperature. The resistivity increased with composition and all the samples exhibited a change in slope in the resistivity-temperature curve. Two different regions with a large variation in activation energies were found. The dielectric constant and loss factor for different compositions were measured in the frequency range of 10kHz to 10 MHz. The dielectric permittivity showed a dispersion with frequency for all the samples. Peaks were observed for the samples with 0.4 x 0.8. The possible mechanisms involved are discussed.     

Li-substituted P2-Na0.66LixMn0.5Ti0.5O2 as an advanced cathode material and new “bi-functional” electrode for symmetric sodium-ion batteries

In this study, we have introduced the layered materials P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ as cathode materials for sodium ion batteries (SIBs), and then P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ was employed as bi-functional electrode in SIBs. The structural stability and electrochemical properties of P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ were promoted by inserting lithium. The Na_0.66Li_0.2Mn_0.5Ti_0.5O₂ as a cathode material can exhibit a reversible discharge capacity of 128?mA?h?g^?1 at 0.1C after 100 cycles, and even deliver 72?mA?h?g^?1 at 5C. Interestingly, the P2-Na_0.66Li_0.2Mn_0.5Ti_0.5O₂ is studied as a “bi-functional” active material for symmetric sodium-ion batteries. This novel symmetric full cell exhibits 65?mA?h?g^?1 at a current density of 20?mA?g^?1.