Synthesis Process and Properties of V5+-Doped LiFePO4/C

Olivine structure LiFe_1?xV_xPO₄/C (x = 0.02, 0.04, 0.06) composite materials as the cathode for lithium ion batteries were synthesized by carbon-thermal reduction method, using Fe(NO₃)₃ · 9H₂O, LiH₂PO₄, NH₄VO₃, and C₆H₁₂O₆ (glucose) as raw materials. The X-ray diffraction (XRD), scanning electronic microscope (SEM) laser particle size analysis, specific surface area tester, and electrochemical performance testing were used to study its structure, morphology, and electrochemical properties. The results showed that the diffraction peaks of the prepared materials correspond to the single phase of LiFePO₄/C and can be indexed as the olivine structure. Particle diameter of LiFe_1?xV_xPO₄/C (x = 0.04) was uniform. Specific surface areas of materials are all increased. An electrochemical test showed that LiFe_1?xV_xPO₄/C (x = 0.04) demonstrated a better electrochemical capacity of 141.065 mAh · g^?1 at 0.1C rate, and which had an increase of 10.77% than the un-doped sample. After 20 cycles, charge and discharge specific capacity almost had no attenuation.     

Preparation and Properties of Al2O3-doping LiNi1/3Co1/3Mn1/3O2 Cathode Materials

LiNi_1/3Co_1/3-xMn_1/3O₂ doped with Al₂O₃ (x = 0%, 2.5%, 5%, 10%) was synthesized by co-precipitation of Ni, Co, and Mn acetates. The influence of Al₂O₃ doping on structure and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ was studied using X-ray diffraction (XRD) analysis, scanning electron microscopy, charge/discharge tester, and electrochemical workstation. It was found that the materials achieved the best electrochemical properties when x was 5%. The first discharge capacity was 156.3 mAh · g^?1(0.1 C, 2.0–4.8 V), which was close to the un-doped sample (156.8 mAh · g^?1). After 20 cycles, the capacity retention ratios at the C-ratios of 0.1C, 0.2C, and 0.5 C were 96.1%, 94.9%, and 89.4%, respectively, while the capacity retention ratios of the un-doped samples were only 92.6% (0.1 C), 91.8% (0.2 C), and 88.7% (0.5C). The alternating current impedance shows that the charge transfer in the electrode interface was the easiest when x was 5%.     

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%.     

Synthesis of LiFePO4/C doped with Mg2+ by reactive extrusion method

Reactive extrusion method is used to synthesizing LiMg_xFe_1−xPO₄/C, using LiOH⋅H₂O, FeC₂O₄⋅2H₂O, P₂O₅ and nano-MgO as raw materials and glucose as carbon source. Samples are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), TG–DTA analysis and electrochemical performance test. Results show that amorphous product can be achieved after the reactive extrusion process. The particle size increases with the increase of magnesium content. Appropriately Mg²⁺ doping can reduce the electrode polarization effectively without seriously effect on material structure and morphology. LiMg_0.04Fe_0.96PO₄/C, showing the best electrochemical performances, has an initial discharge capacity of 155, 148, 140 and 137 mA h g⁻¹ at 0.2 C, 0.5 C, 1 C and 2 C rate, respectively. The discharge capacities remain above 99% after 20 cycles.     

Ruthenium doped LiMn1.5Ni0.5O4 microspheres with enhanced electrochemical performance as lithium-ion battery cathode

Ruthenium doped LiNi_0.5Mn_1.5O₄ (LNMO) microspheres has been prepared by a simple solid-state reaction process. The as-prepared sample was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and electrochemistry performance test. The sample shows a spinel crystal structure without RuO₂ impurity phase, and Ru doped sample crystal plane spacing increases. Combined with EDS spectrum, it indicates that the Ru ion was doped in the LNMO and distributed homogeneously. The XPS also further confirm the existence of Ru ions, and Ru has no obvious influence on Ni and Mn elements. The SEM images show that all the samples are sphere-like, with many polyhedral particles attached to the surface. When doped with 4% Ru ion, many cavities appear on the surface to form a porous structure. Electrochemical analysis confirms that the Ru-doped sample exhibits better electrochemical properties regarding discharge capacity, cycle stability, and rate performance. The 4% Ru-doped sample owns an initial discharge capacity of 125 mAh g^?1 at 0.25C rate, with a capacity retention of 92% after 50 charge–discharge cycles. Moreover, at high current density (1C), Ru doped sample’s discharge capacity is 103 mAh g^?1 while the original is only 86 mAh g^?1. The excellent electrochemical properties are attributed to the Ru doping that increases the interlayer spacing and reduces the charge-transfer impedance (R_ct), which is beneficial to lithium ion-exchange.

     

On the thermal stability of the copper–titanium–zirconium phosphate solid-solution series: CuTi2?xZrx(PO4)3 (0?≤?x?≤?2) under air

The solid copper(I) electrolytes: CuTi₂(PO₄)₃; CuTiZr(PO₄)₃; and CuZr₂(PO₄)₃; were prepared as powders by high temperature synthesis and analysed by powder XRD. These materials were then annealed in air at 400 °C for 72 h. The results of powder XRD showed that the degree of oxidation under these conditions varies progressively and enormously across this series, with the passivity dependent upon the Ti/Zr ratio; CuTi₂(PO₄)₃ being the least reactive under these conditions. The results of the thermogravimetric analyses in artificial air ( P_\textO2 P_{{{\text{O}}_{2} }}  = 0.2 bar) corroborate with the above, and reveal in all cases that T _eqm = 500 ± 25 °C for the reversible reaction: 4Cu (Ti, Zr)₂(PO₄)₃ + O₂ ⇆ 4Cu_0.5 (Ti, Zr)₂(PO₄)₃ + 2CuO. Green Cu_0.5TiZr (PO₄)₃ has been prepared as a new compound and was shown to belong to a rhombohedral system with hexagonal cell constants: a = 8.599(1) ?; c = 22.355(3) ?; Z = 6.     

Improved electrochemical Li insertion performances of Li3V2(PO4)3/carbon composite materials prepared by a sol–gel route

A novel sol–gel route based on V₂O₅·nH₂O hydro-gel was developed to prepare Li₃V₂(PO₄)₃/carbon composite materials. In this route, V₂O₅·nH₂O hydro-gel, NH₄H₂PO₄, Li₂CO₃ and glucose were used as starting materials and Li₃V₂(PO₄)₃/carbon composite materials were obtained by sintering precursor in flowing argon. The samples were characterized by XRD, SEM, galvanostatically discharge/discharge and CV techniques. XRD results showed Li₃V₂(PO₄)₃/carbon has a monoclinic structure indexed to the P2₁/n space group. Li₃V₂(PO₄)₃/carbon cycled between 3.0 and 4.8 V showed that the first discharge capacity was 167.0 mAh/g, and after 50 cycles, the discharge capacity was 160.1 mAh/g. The testing results showed that Li₃V₂(PO₄)₃/carbon has good electrochemical Li insertion performance.     

Synthesis and electrochemical properties of Co3O4 nanofibers as anode materials for lithium-ion batteries

Co₃O₄ nanofibers as anode materials for lithium-ion batteries were prepared from sol precursors by using electrospinning. The morphology, structure and electrochemical properties of Co₃O₄ nanofibers were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and charge-discharge experiments. The results show that Co₃O₄ nanofibers possessed typical spinel structure with average diameter of 200 nm. The initial capacity of Co₃O₄ nanofibers was 1336 mAhg^− 1 and the capacity reached 604 mAhg^− 1 up to 40 cycles. It was suggested that the high reversible capacity could be ascribed to the high surface area offered by the nanofibers' structure.     

Phase transformation in Cu2SnS3 (CTS) thin films through pre-treatment in sulfur atmosphere

In this study, Cu₂SnS₃ (CTS) thin films prepared by a two-step sulfurization process were characterized. Cu and Sn metallic layers were first deposited on glass substrates by sputtering and then annealed in-situ while in the sputtering chamber to obtain CuSn (CT) alloys. This was followed by a pre-treatment step at temperatures between 200 and 350 °C in presence of S vapors. Finally, a full sulfurization step was performed at 525 °C to obtain the desired CTS phase. CTS films were characterized using EDX, XRD, Raman spectroscopy, SEM, optical transmission and Van der Pauw methods. It was found that all CTS samples had Cu-poor chemical composition. XRD data revealed only diffraction peaks belonging to CTS structure after the full sulfurization step. Raman spectra of the samples showed that except for the CTS sample pre-treated at 250 °C (CTS-250), which displayed the tetragonal crystal system, the films were dominated by the monoclinic structure. SEM surface images showed dense and polycrystalline microstructure, CTS-200 sample exhibiting a more uniform morphology. Optical band gap values were found to be ranging from 0.92 to 1.19 eV. All samples showed p-type conductivity but the sample pre-treated at 350 °C had higher resistivity and lower carrier concentration values. Overall, the CTS layer prepared using the pre-treatment step at 200 °C exhibited more promising structural and optical properties for potential photovoltaic applications. This work demonstrated that it is possible to change the crystal structure of sulfurized CTS thin films through a pre-treatment step.

     

Dielectric properties of Pb[(1?x)(Zr1/2Ti1/2)?x(Zn1/3Ta2/3)]O3 ceramics prepared by columbite and wolframite methods

Polycrystalline samples of Pb[(1 − x)(Zr_1/2Ti_1/2) − x(Zn_1/3Ta_2/3)]O ₃ , where x = 0.1–0.5 were prepared by the columbite and wolframite methods. The crystal structure, microstructure, and dielectric properties of the sintered ceramics were investigated as a function of composition via X-ray diffraction (XRD), scanning electron microscopy (SEM), and dielectric spectroscopy. The results indicated that the presence of Pb(Zn_1/3Ta_2/3)O₃ (PZnTa) in the solid solution decreased the structural stability of overall perovskite phase. A transition from tetragonal to pseudo-cubic symmetry was observed as the PZnTa content increased and a co-existence of tetragonal and pseudo-cubic phases was observed at a composition close to x = 0.1. Examination of the dielectric spectra indicated that PZT–PZnTa exhibited an extremely high relative permittivity at the MPB composition. The permittivity showed a ferroelectric to paraelectric phase transition at 330 °C with a maximum value of 19,600 at 100 Hz at the MPB composition.     

Novel magnetically separable g-C3N4/Fe3O4/Ag3PO4/Co3O4 nanocomposites: Visible-light-driven photocatalysts with highly enhanced activity

In this study, a series of novel quaternary g-C₃N₄/Fe₃O₄/Ag₃PO₄/Co₃O₄ nanocomposites were fabricated. The prepared nanocomposites were characterized by XRD, EDX, SEM, TEM, UV-DRS, FT-IR, PL, TG, and VSM methods to gain insight about structure, purity, morphology, optical, thermal, and magnetic properties. Photocatalytic activity of the samples was investigated under visible-light irradiation by degradations of rhodamine B, methylene blue, methyl orange, and phenol as four organic pollutants. The highest photocatalytic degradation efficiency was observed when the sample calcined at 300 °C for 2 h with 20 wt% of Co₃O₄. The photocatalytic activity of this nanocomposite is almost 16.8, 15.7, 4.6, and 5.1 times higher than those of the g-C₃N₄, g-C₃N₄/Fe₃O₄, g-C₃N₄/Fe₃O₄/Ag₃PO₄ (20%), and g-C₃N₄/Fe₃O₄/Co₃O₄ (20%) samples in photodegradation of rhodamine B, respectively. Finally, on the basis of the energy band positions, the mechanism of enhanced photocatalytic activity was discussed.     

Polycarbosilane derived Ti3SiC2

Titanium silicon carbide (Ti₃SiC₂) ceramic was synthesized by in-situ reaction of metal titanium and polycarbosilane. Reaction mechanisms which lead to the formation of Ti₃SiC₂ were suggested on the basis of XRD analysis. The content of Ti₃SiC₂ reached 93% in products obtained from heating the Ti/polycarbosilane green compact at 1400 °C in Ar. The morphology and compositions of the products were examined by SEM equipped with EDX. The typical laminate structure of Ti₃SiC₂ particles with 1-4 μm in thickness and 4-15 μm in length was observed. EDX results showed that the atomic ratio of Ti:Si:C of grains is close to 3:1:2, which agrees with Ti₃SiC₂ composition.     

Synthesis and electrochemical properties of nanorod-shaped LiMn1.5Ni0.5O4 cathode materials for lithium-ion batteries

Nanorod-shaped LiMn_1.5Ni_0.5O₄ cathode powders were synthesized by a co-precipitation method with oxalic acid. Their structures and electrochemical properties were characterized by SEM, XRD and galvanostatic charge-discharge tests. The resulting nanorod-shaped LiMn_1.5Ni_0.5O₄ cathode active materials delivered a specific discharge capacity of 126 mAh g⁻¹ at 0.1 C rate. These active materials exhibited better capacity retention and higher rate performance than those of LiMn_1.5Ni_0.5O₄ cathode powders with irregular morphology.     

Synthesis and electrochemical performance of Li1+xTi2−xFex(PO4)3/C anode for aqueous lithium ion battery

Aqueous lithium ion batteries (ALIBs) exhibit great application prospects in energy storage system, and the anode materials is the key to the extensive development of ALIBs. In this study, Li_1+xTi_2−xFe_x(PO₄)₃/C (x = 0, 0.05, 0.10, 0.30) composites as anode for ALIBs were synthesized via sol-gel method. The effect of Fe doping on LiTi₂(PO₄)₃/C properties was assessed by electrochemical measurements. In all of these composites, Li_1.1Ti_1.9Fe_0.1(PO₄)₃/C (LCF-10) presents the best electrochemical properties. LCF-10 exhibits discharge capacity with 120.0 and 80.2 mAh g⁻¹ at 0.5 and 15C, severally, increasing by 1.2 and 1.3 times compared with the original LiTi₂(PO₄)₃/C. Besides, LCF-10 demonstrates remarkable cycling performance, whose discharge capacity retention can keep 70.2% at 5 C for 1000 cycles. Our study demonstrates that Fe doping for LiTi₂(PO₄)₃ lattice can efficiently enhance electrochemical properties of LiTi₂(PO₄)₃/C composite.     

Crystallization and magnetic properties of a 10Li2O–9MnO2–16Fe2O3–25CaO–5P2O5–35SiO2 glass

The crystallization behavior and magnetic properties of 10Li₂O–9MnO₂–16Fe₂O₃–25CaO–5P₂O₅–35SiO₂ (10LFS) glass have been studied using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) to observe the crystallization behavior and a superconducting quantum interference device (SQUID) for measurements of the magnetic properties. The DTA shows that the 10LFS glass has one broad exothermic peak at approximately 674 °C and one sharp (the highest) exothermic peak at 764 °C. When the 10LFS glass crystallized at 850 °C for 4 h, the crystalline phases identified by XRD were lithium silicate (Li₂SiO₃), β-wollastonite (β-CaSiO₃), lithium orthophosphate (Li₃PO₄), magnetite (FeFe₂O₄) and triphylite (Li(Mn_0.5Fe_0.5)PO₄). The SEM surface analysis revealed that the β-wollastonite and lithium silicate have a lath morphology. The TEM microstructure examination showed that the largest FeFe₂O₃ particles have a size of approximately 0.3 μm. When the 10LFS glass was heat treated at 850 °C for 16 h and a magnetic field of 1000 Oe was applied, a very small remnant magnetic induction of 0.01 emu g⁻¹ and a coercive force of 50 Oe were obtained, which revealed an inverse spinel structure.     

Fabrication of CuO/Fe2O3 hollow hybrid microspheres

CuO/Fe₂O₃ hollow hybrid spheres with the size of 3–5 μm were successfully synthesized by a convenient hydrothermal method, using FeSO₄·7H₂O and CuSO₄·5H₂O as the starting materials and urea as the homogeneous precipitant. The samples were characterized by XRD, TEM, ED, SEM, EDX, IR and XPS measurements. XRD and XPS analyses indicated that the nanostructured materials consisted of CuO and α-Fe₂O₃. TEM and SEM measurements showed that the morphology of binary metal oxide was in the shape of hollow sphere. Careful observation from SEM measurements could find that CuO/Fe₂O₃ hollow microsphere shell was composed of uniform and dense metal oxide nanorods with about 20–40 nm in diameter and 100–200 nm in length. Moreover, the influence of calcination temperature on the thermal stability of the hollow structures was investigated. It showed that the hollow structure was stable after being calcined at 300 °C for 2 h. The formation mechanism of the CuO/Fe₂O₃ hollow spheres under hydrothermal condition was discussed.     

High-rate performance of xLiFePO4·yLi3V2(PO4)3/C composite cathode materials synthesized via polyol process

xLiFePO₄·yLi₃V₂(PO₄)₃/C composite cathode materials were synthesized via a polyol process, using LiOH·H₂O, Fe₃(PO₄)₂·8H₂O, V₂O₅ and H₃PO₄ as raw materials, citric acid and PEG as carbon sources, and TEG as both a solvent and a reductant. Structural and morphological characterizations of as-prepared materials were carried out by X-ray diffraction (XRD) as well as scanning electron microscopy (SEM), respectively. Furthermore, electrochemical properties of as-prepared materials were analyzed by charge–discharge tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). XRD results indicated that the composites consisting of an olivine phase of LiFePO₄ and a monoclinic phase of Li₃V₂(PO₄)₃ are well-crystallized. It is found that the LF_0.6P·LV_0.4P/C composite exhibited better electrochemical performance than pristine LFP/C and LVP/C at 5 C and 10 C rate and delivered 126 mAh g^?1 and 110 mAh g^?1, respectively. The favorable particles morphology with less than 100 nm size and low extent agglomeration is believed as a factor. In addition, the co-existence of V³⁺-doped LiFePO₄/C and Fe²⁺-doped Li₃V₂(PO₄)₃/C was supposed as another reason.     

Ultrafast Charge-Discharge Capable and Long-Life Na3.9Mn0.95Zr0.05V(PO4)3/C Cathode Material for Advanced Sodium-Ion Batteries

Na₄MnV(PO₄)₃/C (NMVP) has been considered an attractive cathode for sodium-ion batteries with higher working voltage and lower cost than Na₃V₂(PO₄)₃/C. However, the poor intrinsic electronic conductivity and Jahn–Teller distortion caused by Mn³⁺ inhibit its practical application. In this work, the remarkable effects of Zr-substitution on prompting electronic and Na-ion conductivity and also structural stabilization are reported. The optimized Na_3.9Mn_0.95Zr_0.05V(PO₄)₃/C sample shows ultrafast charge-discharge capability with discharge capacities of 108.8, 103.1, 99.1, and 88.0 mAh g⁻¹ at 0.2, 1, 20, and 50 C, respectively, which is the best result for cation substituted NMVP samples reported so far. This sample also shows excellent cycling stability with a capacity retention of 81.2% at 1 C after 500 cycles. XRD analyses confirm the introduction of Zr into the lattice structure which expands the lattice volume and facilitates the Na⁺ diffusion. First-principle calculation indicates that Zr modification reduces the band gap energy and leads to increased electronic conductivity. In situ XRD analyses confirm the same structure evolution mechanism of the Zr-modified sample as pristine NMVP, however the strong Zr O bond obviously stabilizes the structure framework that ensures long-term cycling stability.     

Pb(Zr0.5, Ti0.5)O3 nanofibres by electrospinning

Lead zirconate titanate Pb(Zr_0.5, Ti_0.5)O₃ nanofibres with diameters ranging from 200–300 nm have been synthesized by calcination of the electrospun lead zirconate titanate/polyvinyl acetate composite fibres. The morphology and crystalline phase features of these lead zirconate titanate (PZT) nanofibres have been studied by various physico-chemical methods such as SEM, AFM, XRD and FT–IR. The formation of perovskite PZT phase was observed at temperatures as low as 550 °C.     

Synthesis and characterization of P-doped TiO2 nanotubes

Titanium dioxide (TiO₂) doped with phosphorus (P) was synthesized by anodization of Ti in the mixed acid electrolyte of H₃PO₄ and HF and characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–vis spectrum. The morphology greatly depends on the applied voltage. The as-formed nanotubes under the optimized condition, at 20 V for 2 h, are highly ordered with ~ 200 nm in length and the average tube diameter is about 100 nm. By annealing the initial samples at different temperatures, the importance of the crystalline nature is confirmed. Significantly, the peak positions of anatase in XRD patterns shifts to lower diffraction angles with an increase in the amount of H₃PO₄ ion. A remarkable red shift of the absorption edge has been observed for the sample formed in the electrolyte of HF and H₃PO₄, which is related to the introduction of P⁵⁺ into TiO₂ crystallization and the possible impurity energy level formed in the TiO₂ band gap. The presence of P 2p state in XPS spectrum can further confirm the P⁵⁺ which can replace a part of Ti⁴⁺ has been introduced into TiO₂ crystallization. The present convenient synthesis technique can be considered to the composition of other doped oxide materials.