Effects of solvent composition on the electrochemical performance of Li2FeSiO4/C cathode materials synthesized via tartaric-acid-assisted sol–gel method

Li₂FeSiO₄/C composites were synthesized via a tartaric-acid-assisted sol–gel method with ethanol and ethylene glycol (EG) as mixed solvents. Effects of solvent composition on the physical properties and electrochemical performances of Li₂FeSiO₄/C were studied. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical performances of Li₂FeSiO₄/C were evaluated by galvanostatic charge–discharge and electrochemical impedance spectra (EIS) measurements. The results show that the addition of EG to ethanol solvent during preparation has a positive effect on the electrochemical performance of Li₂FeSiO₄/C. The sample synthesized using EG–ethanol with the volume ratio of 2:7 has the best electrochemical performance. It delivers an initial discharge capacity of 105 mAh g^?1 at C/16. AC impendence investigation shows that Li₂FeSiO₄/C synthesized using the optimal EG/ethanol volume ratio has lower resistance of electrode/electrolyte interface and higher lithium-ion diffusion coefficient than that synthesized using ethanol as solvent.     

Enhanced photoluminescence properties of Zn2SiO4:Mn co-activated with Y/Li under VUV excitation

A series of green phosphors Zn_1.92−2xY_xLi_xSiO₄:0.08Mn²⁺ (0≤x≤0.03) were prepared by solid-state synthesis method. Phase and lattice parameters of the synthesized phosphors were characterized by powder X-ray diffractometer (XRD) and the co-doped effects of Y³⁺/Li⁺ upon emission intensity and decay time were investigated under 147 nm excitation. The results indicate that the co-doping of Y³⁺/Li⁺ has favorable influence on the photoluminescence properties of Zn₂SiO₄:Mn²⁺, and the optimal photoluminescence intensity of Zn_1.90Y_0.01Li_0.01SiO₄:0.08Mn²⁺ is 103% of that of commercial phosphor when the doping concentration of Y³⁺/Li⁺ is 0.01 mol. Additionally, the decay time of phosphor is much shortened and the decay time of Zn_1.90Y_0.01Li_0.01SiO₄:0.08Mn²⁺ is 3.39 ms, shorter by 1.83 ms than that of commercial product after Y³⁺/Li⁺ co-doping.     

Study on electrochemical performance of Mg-doped Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript> cathode material for Li-ion batteries

In this paper, Li₂Fe_1?yMg_ySiO₄/C (y?=?0, 0.01, 0.02, 0.03, 0.05), a cathode material for lithium-ion battery was synthesized by solid-state method and modified by doping Mg²⁺ on the iron site. The effects of Mg²⁺ doping on the crystal structure and electrochemical performance Li₂FeSiO₄ was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical tests. Electrochemical methods of measurement were applied including constant current charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), to determine the electrochemical performance of the material and the optimal doping ion and ratio. The results showed that Li₂Fe_0.98Mg_0.02SiO₄/C has the higher specific capacity and better cycle stability as well as lower impedance and better reversibility. The enhanced electrochemical performance can be attributed to the increased electronic conductivity, the decreased charge transfer impedance, and the improved Li-ion diffusion coefficient. Then, further study on the synthesis conditions was performed to find the optimal combustion temperature and time. According to the study, the material which has the best electrochemical performance, shows initial discharge specific capacity of 142.3 mAh g^?1 at 0.1 C (1 C?=?166 mA g^?1) and coulomb efficiency of 95.6%, under the condition that the temperature is 700 °C and the calcining time is 10 h.     

Electrochemical characterization on layered lithium ruthenate for electrochemical supercapacitors

Electrochemical characteristics of lithium ruthenate (Li_xRuO_2+0.5x·nH₂O) for electrochemical capacitors' electrode material were first examined in this paper by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests. Results show that Li_xRuO_2+0.5x·nH₂O has electrochemical capacitive characteristic within the potential range of − 0.2–0.9 V (vs. SCE) in 1 M Li₂SO₄ solution. The capacitance mainly arises from pseudo-capacitance caused by lithium ions' insertion/extraction into/out of the Li_xRuO_2+0.5x·nH₂O electrode. The specific capacitance of 391 F g^− 1 can be delivered at 1 mA charge–discharge current for Li_xRuO_2+0.5x·nH₂O electrode with an energy density of 65.7 W h kg^− 1. This material also exhibits an excellent cycling performance and there is no attenuation of capacitance over 600 cycles.     

Li0.5Fe2.5−xMnxO4 ferrite sintered from microwave-induced combustion

Li_0.5Fe_2.5−xMn_xO₄ (0≦x≦1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, ferric nitrate, manganese nitrate and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Mn-substituted lithium ferrite powders. The resultant powders annealed at 650 ^°C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the Mn content were strongly influenced the magnetic properties and Curie temperature of Mn-substituted lithium ferrite powder. As for sintered Li_0.5Fe_2.5−xMn_xO₄ specimens, substituting an appropriate amount of Mn for Fe in the Li_0.5Fe_2.5−xMn_xO₄ specimens markedly improved the complex permeability and loss tangent.     

Hydrothermal synthesis of spinel Li1+x Mn2O4 as cathode material for rechargeable lithium battery

Abstract

The hydrothermal synthesis of Li-Mn spinel oxide (Li_1+xMn₂O₄) was undertaken in order to develop high quality, low cost cathode material for a rechargeable lithium battery. In our experiments, γ-MnOOH, LiOH · H₂O and H₂O₂ were used as starting materials to synthesize Li-Mn spinel oxide under hydrothermal conditions of 180-230°C and about 1.0-2.8 MPa. The chemical composition and particle size of the Li_1+xMn₂O₄ is easily controlled in the hydrothermal reaction. The Li_1+xMn₂O₄ produced was characterized by X-ray diffraction, with the spinel phase having a Li/Mn ratio of 0.50-0.60. There is convincing evidence, as a result of this work, that our synthesis process is most suitable for producing high quality cathode material that can be used in a rechargeable lithium battery.     

Determination of the sites of Fe atoms in Fe-substituted Mn12

In this paper neutron diffraction experiments were performed for Fe-substituted Mn12 in order to determine the sites of Fe atoms. The results of structure refinements for the sample with our accessed highest Fe content showed that all Fe atoms occupied Mn（3） sites in the Mn12 skeleton. The x-ray absorption fine structure experiments as well as multiple scattering simulations gave the same result. Thus we concluded that Fe atoms only occupied Mn（3） sites. This conclusion also means that Fe-substituted Mn12 series only includes the four single-molecule magnets of [Mn12-xFexO12（CH3COO）16（H2O）4]·2CH3COOH·4H2O （x = 1, 2, 3, and 4）, denoted by Mn11Fe1, Mn10Fe2, MngFe3, and Mn8Fe4, respectively.     

Structure and magnetic properties of a new single-molecule magnet [Mn11Fe1O12 (CH3COO)16(H2O)4].2CH3COOH.4H2O

A new single-molecule magnet [Mn₁₁Fe₁O₁₂ (CH₃COO)₁₆(H₂O)₄]?2CH₃COOH?4H₂O (Mn₁₁Fe₁) has been synthesized.The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn--Teller distortion between Fe³⁺ and Mn³⁺ ion reveals that Fe³⁺ ion substitutes for Mn³⁺ ion on the Mn(3) sites in the Mn₁₂ skeleton. The temperature dependence of the magnetization gives a blocking temperature T_B=1.9K for Mn₁₁Fe₁. Based on the magnetization process analysis of the crystal at T=2K, we suggest that Mn₁₁Fe₁ has the ground state with a total spin S= 11/2.     

Mn-doped (Ba,Y)Fe12O19 hexaferrites: Crystal structure and oxidation states of Mn and Fe

We have fabricated Ba_0.95Y_0.05Fe_12-xMn_xO₁₉ samples with large Mn-doping amounts of x = 4 and 6, using the mechanical milling and heat treatment. X-ray diffraction analysis indicated the samples crystallized in the M-type hexaferrite structure. The Mn doping caused the modification, shift and broadening of some characteristic phonon-vibration modes, which were recorded by Raman spectroscopy. This is due to an incorporation of Mn ions into the M-type structure that disorders the periodic lattice and changes symmetry. Basing on X-ray absorption spectroscopy, we have found Fe in all samples stable with an oxidation state 3+ (Fe³⁺). Though Mn²⁺ and Mn³⁺ ions coexist, the concentration of Mn²⁺ in x = 4 is larger than that in x = 6. The analysis of Fourier-transform spectra have demonstrated the replacement of Mn^2+,3+ ions for Fe³⁺ in the M-type structure. The sites of Mn^2+,3+ ions in this structure have been discussed.     

Li-ion migration in Li2FeSiO4-related cathode materials: A DFT study

The orthosilicate family of materials Li₂MSiO₄ for M = Fe, Mn and Co are coming to be seen as potentially cheap cathode materials for large-scale Li-ion batteries, not least through the possibility for significant capacity gains if more than one Li-ion can be removed per formula unit. To gain insights into possible Li-ion migration pathways and diffusion barriers for Li-ions, model systems for Li_xFeSiO₄ (x ≈ 1, 2) are here studied using the Density Functional Theory (DFT) approach. Li-ion and ion-vacancy migration barriers are calculated for a number of model systems. The results help explain why the Li/Fe site-mixing observed during electrochemical cycling of Li₂FeSiO₄ does not lead to any noticeable loss in cell performance, despite the increased tortuosity introduced into the Li-migration pathways by this ion-mixing process.     

Reentrant spin glass behavior and large initial permeability of Co0.5−xMnxZn0.5Fe2O4

A series of polycrystalline ferrites having nominal chemical composition Co_0.50−xMn_xZn_0.5Fe₂O₄ (0<x<0.4) have been synthesized by the solid-state reaction technique. The XRD analysis confirms single phase cubic spinel structure for all compositions. Lattice constant increases from 0.84195 to 0.84429 nm with the increasing Mn content and obeys Vegard's law. The average grain size increases by increasing both Mn content and sintering temperatures. Room temperature saturation magnetization increases for x=0.1 and decreases for increasing Mn content. The coercivity decreases with increasing Mn content due to the decrease of anisotropy constant. A reentrant spin glass behavior of these samples is observed from the zero field cooled magnetization measurements. The real part of the initial permeability increases by increasing both Mn content and sintering temperatures. This is due to the homogeneous grain growth and densification of the ferrites. The highest initial permeability 137 is observed for x=0.4 sintered at 1573 K on the other hand, the highest relative quality factor (2522) is obtained for the sample Co_0.2Mn_0.3Zn_0.5Fe₂O₄ sintered at 1523 K. The Mn substituted Co_0.50−xMn_xZn_0.5Fe₂O₄ ferrites showed improved magnetic properties.     

The properties research of ferrum additive on Li [Ni<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>] O<Subscript>2</Subscript> cathode material for lithium ion batteries

Li[Ni_1/3Co_(1-x)/3Mn_1/3Fe _x/3] O₂(x?=?0.0, 0.1, 0.3, 0.5, 0.7, and 0.9) cathode materials have been synthesized via hydroxide co-precipitation method followed by a solid state reaction. Thermogravimetry (TG) and differential thermal analysis (DTA) measurements were utilized to determine the calcination temperature of precursor sample. The crystal structure features were characterized by X-ray diffraction (XRD). The electrochemical properties of Li[Ni_1/3Co_(1-x)/3Mn_1/3Fe _x/3]O₂ were compared by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy(EIS), and galvanostatic charge/discharge test. Electrochemical test results indicate that Li[Ni_1/3Co_0.9/3Mn_1/3Fe_0.1/3] O₂ decrease charge transfer resistance and enhance Li⁺ ion diffusion velocity and thus improve cycling and high-rate capability compared with Li[Ni_1/3Co_1/3Mn_1/3]O₂. The initial discharge specific capacity of Li[Ni_1/3Co_0.9/3Mn_1/3Fe_0.1/3] O₂ was 178.5 mAh/g and capacity retention was 87.11 % after 30 cycles at 0.1C, with the battery showing good cycle performance.     

Role of Mn doping for obtaining of hexagonal phase in Ba0.98Zn0.02TiO3 ceramics

This paper reports the observation of hexagonal phase of barium titanate by Mn doping and its effect on dielectric and magnetic properties. Ceramic samples of Ba_0.98Zn_0.02Ti_1−xMn_xO₃ (where, x= 0.04, 0.06 and 0.08) were prepared by traditional solid-state reaction route. The hexagonal phase is stabilized in the composition Ba_0.98Zn_0.02Ti_0.92Mn_0.08O₃ and a very feeble M–H loop is also observed in that composition. This induced magnetism is expected due to the exchange interactions between magnetic polarons formed by oxygen vacancies with Mn ions. The dielectric constant as well as the ferroelectric to paraelectric transition temperature is systematically decreased with increasing of Mn doping concentration. Further to that, the temperature dependent dielectric constant curve is also broadened at transition temperature with increasing of Mn concentration. However, the ferroelectric to paraelectric transition temperature is well above room temperature.     

Effects of Mn substitution of Co and Fe in spinel CoFe2O4 thin films

Effects of Mn substitution for Co and Fe on the structural and magnetic properties of inverse-spinel CoFe₂O₄ have been investigated. Mn_xCo_1−xFe₂O₄ and Mn_yCoFe_2−yO₄ thin films were prepared by a sol–gel method. The observed increase of the lattice constant of Mn_xCo_1−xFe₂O₄ indicates that Mn²⁺ ions substitute the octahedral Co²⁺ sites. Conversion electron Mössbauer spectroscopy data indicate that a fraction of octahedral Co²⁺ ions exchange sites with tetrahedral Fe³⁺ ions through Mn doping. Vibrating-sample magnetometry data exhibit a large increase of saturation magnetization for both Mn_xCo_1−xFe₂O₄ and Mn_yCoFe_2−yO₄ films compared to that of the CoFe₂O₄ film. Such enhancement of magnetization can be explained in terms of a breaking of ferrimagnetic order induced by the Co²⁺ migration.     

Synthesis and pseudocapacitive investigation of LiCr x Mn2-x O4 cathode material for aqueous hybrid supercapacitor

A series of Cr-substituted LiMn₂O₄ samples (LiCr _x Mn_2-x O₄, 0?≤?x?≤?0.3) were synthesized by a urea-assisted combustion method to enhance pseudocapacitive properties of LiMn₂O₄ material in aqueous electrolyte. Their structure and morphology were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The LiCr _x Mn_2-x O₄ and activated carbon (AC) electrode were used as the cathode and anode in hybrid supercapacitors, respectively, which capacitive properties were determined by cyclic voltammetry (CV), galvanostatic charge/discharge test, and electrochemical impedance spectroscopy (EIS) in Li₂SO₄ solution. The results revealed that the partial substitution of Mn³⁺ by Cr³⁺ decreased initial capacity, but it prevented capacity fading. In the working voltage of 0–1.4 V, the AC/LiCr_0.1Mn_1.9O₄ capacitor delivered an initial specific capacitance of 41.6 F g^?1 (based on the total active mass of two electrodes) at a current density of 100 mA g^?1 in 1 M Li₂SO₄ solution. After 1,000 cycles, its capacity loss was only 1.7 %.     

Magnetic properties of the compounds N(CH3)4MnIIMIII(CN)6 ·8 H2O(MIII = Mn,Fe)

In the isostructural cyanobridged chain compounds N(CH₃)₄Mn^IIM^III(CN)₆ · 8H₂O high spin Mn(II) ions couple antiferromagnetically to low spin Mn(III) of Fe(III) ions. The Mn^II–Mn^III compound orders ferrimagnetically below T_N = 28.5 ± 1 K. The tetragonal a and b axes are easy ones for the magnetic moments. In the Mn^II–Fe^III compound antiferromagnetic order occurs below T_N = 9.3 K, with spins aligned along the tetragonal c axis. The compound undergoes a meta-magnetic transition from the antiferromagnetic to a ferrimagnetic phase. This occurs at 2 K for a field H_crit ≈ 1.2 T. The temperature dependence of H_crit, which vanishes at T_N, is followed. The tricritical temperature T¹ is ～ 5 K.     

Hydrothermal synthesis and properties of manganese-doped LiFePO4

A series of carbon-coated LiFe_1???x Mn _x PO₄ compounds are prepared by a hydrothermal method at 170 °C for 12 h. The structure and morphology of the prepared composites are characterized to examine the effects of Mn²⁺ substitution. All LiFe_1???x Mn _x PO₄ compositions are found to have an ordered olivine-type structure with homogeneous Fe²⁺ and Mn²⁺ distributions. The substitution leads to grain refinement from ~500 to ~150 nm, as well as to increased initial capacity and improved electronic conductivity. The amount of carbon coating varies with increased doping amount. The discharge curves of the LiFe_1???x Mn _x PO₄/C materials reveal a high discharge plateau corresponding to Fe^2+/3+ and no obvious plateau assigned to Mn^2+/3+, although a slight contribution of manganese is detected. However, the electrochemical performance, including the discharge capacity and cyclic performance, deteriorates with increased Mn content in the composite.     

Luminescence and energy transfer in Eu, Mn co-doped Li4SrCa(SiO4)2 for white light-emitting-diodes

Li₄(Sr_0.96Eu_0.04)(Ca_1 − xMn_x)(SiO₄)₂ phosphors were synthesized by solid-state reactions and photoluminescence (PL) properties were investigated. These phosphors have intense absorption in n-UV region, which is suitable for excitation of UV LEDs. The orange-reddish emission of Mn²⁺ can be adjusted by changing the Mn²⁺/Eu²⁺ ratio. Energy transfer from Eu²⁺ to Mn²⁺ is observed. Li₄(Sr_0.96Eu_0.04)(Ca_1 − xMn_x)(SiO₄)₂ phosphors could be used in white LEDs.     

Solvothermal synthesis of LiCo<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript>/C cathode materials for lithium-ion batteries

LiCo_1−x Mn _x PO₄/C cathode materials are selectively synthesized by a solvothermal method in ethylene glycol solvent using glucose, LiCl, H₃PO₄, MnCl₂·4H₂O, and Co(NO₃)₂·6H₂O as precursors. The obtained samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) and the electrochemical performances are also evaluated using a LAND CT2001A battery test system at room temperature. XRD result demonstrates the formation of LiCo_1−x Mn _x PO₄ solid solution and the enlarged channels are benefit for Li⁺ migration. SEM graph indicates that the particle size of LiCo_0.5Mn_0.5PO₄/C is about several hundred nanometers and aggregates to large particles located in the range of 2–3 μm. TEM image illustrates that the core/shell-structured LiCo_0.5Mn_0.5PO₄/C solid solution is indeed obtained by this method. The high specific surface area (35 m²/g) of LiCo_0.5Mn_0.5PO₄/C could make this solid solution contact with the electrolyte more sufficiently and benefit for Li⁺ transportation. The capacity, flat voltage, and cyclical stability of LiCo_1−x Mn _x PO₄/C are improved compared to LiMnPO₄ and LiCoPO₄ due to the improved electronic conductivity and lithium-ion conductivity which resulted from carbon coating and foreign element incorporation.