Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@MnO<Subscript>2</Subscript> core shell arrays on nickel foam with excellent electrochemical performance for aqueous asymmetric supercapacitor

At present, a lot of attention has been paid to the reasonable design and synthesis of materials with core shell structure for high-performance supercapacitors. Herein, the Co₃O₄@MnO₂ core shell arrays on nickel foam are successfully synthesized via a facile and effective hydrothermal method followed with annealing process. The sample was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Electrochemical performance of the Co₃O₄@MnO₂ material was studied using cyclic voltammetry, charge/discharge cycling, and electrochemical impedance measurements in 6 mol L^?1 KOH aqueous electrolyte. The results indicated that the Co₃O₄@MnO₂ material presented excellent electrochemical performance in terms of specific capacitance, cyclic stability, and charge/discharge stability.     

Structural and electrical studies of LiMnVO4 cathode material for rechargeable lithium batteries

The lithium manganese vanadate (LiMnVO₄) cathode material was synthesized by using sol?Cgel method. The thermal behavior of the material has been examined by thermogravimetric and differential thermal analysis. The structure of LiMnVO₄ compound was studied by the Rietveld refined X-ray diffraction technique. Raman spectra showed that the local environment including VO₄ tetrahedra and LiO₆ octahedra as vibrational local units. X-ray photoelectron spectroscopy studies of synthesized LiMnVO₄ powder indicate that the oxidation states of manganese and vanadate are +2 and +5, respectively. The ionic conductivity of the sample is found to be 2.7?×?10^?5 Scm^?1 at 300?°C. The temperature dependent conductivity was conformed from the Arrhenius relation and the activation energy is found to be 0.3?eV. Dielectric spectra showed the decrease in dielectric constant with increase in frequency. Dielectric loss spectra reveal that dc conduction contribution predominates in the compound.     

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.     

Hexagonal-like NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanostructure based high-performance supercapacitor electrodes

A novel approach of double hydroxide-mediated synthesis of nickel cobaltite (NiCo₂O₄) electro-active material by the hydrothermal method is reported. The obtained NiCo₂O₄ electro-active material displays the spinel cubic phase and hexagonal-like morphology. Thermogravimetry analysis confirms the thermal stability of the electrode material. The functional groups and phase formation of NiCo₂O₄ have been confirmed by FT-IR and Raman spectral analysis. The modified NiCo₂O₄ electrode exhibits the highest specific capacitance of 767.5 F g^?1 at a current density of 0.5 A g^?1 in 3 M KOH electrolyte and excellent cyclic stability (94 % capacitance retention after 1000 cycles at a high current density of 5 A g^?1). The excellent electrochemical performance of the electrode is attributed to the hexagonal-like morphology, which contributes to the rich surface electro-active sites and easy transport pathway for the ions during the electrochemical reaction. The attractive Faradic behavior of NiCo₂O₄ electrode has been ascribed to the redox contribution of Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ metal species in the alkaline medium. The symmetrical two-electrode cell has been fabricated using the NiCo₂O₄ electro-active material with excellent electrochemical properties for supercapacitor applications.     

A novel synthesis of size-controllable mesoporous NiMoO<Subscript>4</Subscript> nanospheres for supercapacitor applications

A novel hydrothermal emulsion method is proposed to synthesize mesoporous NiMoO₄ nanosphere electrode material. The size of sphere-shaped NiMoO₄ nanostructure is controlled by the mass ratio of water and oil phases. Nickel acetate tetrahydrate and ammonium heptamolybdate were used as nickel and molybdate precursors, respectively. The resultant mesoporous NiMoO₄ nanospheres were characterized by X-ray diffraction, N₂ adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances were evaluated by cyclic voltammetry (CV), cyclic chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in 6 M KOH solution. The typical mesoporous NiMoO₄ nanospheres exhibit the large specific surface area of 113 m² g^?1 and high specific capacitance of 1443 F g^?1 at 1 A g^?1, an outstanding cyclic stability with a capacitance retention of 90 % after 3000 cycles of charge-discharge at a current density of 10 A g^?1, and a low resistance.     

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.     

Titanium-modified Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> with a synergistic effect of surface modifying,bulk doping,and size reducing

In this work, a one-step solid-phase sintering process via TiO₂ and Li₂CO₃ under an argon atmosphere, with ultra-fine titanium powder as the modifying agent, was used to prepare a nano-sized Li₄Ti₅O₁₂/Ti composite (denoted as LTO–Ti) at 800 °C. The introduction of ultra-fine metal titanium powder played an important role. First, X-ray photoelectron spectroscopy demonstrates that Ti⁴⁺ was partially changed into Ti³⁺, through the reduction of the ultra-fine metal titanium powder. Second, X-ray diffraction revealed that the ultra-fine metal titanium powder did not react with the bulk structure of Li₄Ti₅O₁₂, while some pure titanium peaks could be seen. Additionally, the size of LTO–Ti particles could be significantly reduced from micro-scale to nano-scale. The structure and morphology of LTO–Ti were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical tests showed a charge/discharge current of 0.5, 1, 5, and 10 C; the discharge capacity of the LTO–Ti electrode was 170, 161, 140, and 111 mAh g^?1. It is believed that the designed LTO–Ti composite makes full use of both components, thus offering a large contact area between the electrolyte and electrode, high electrical conductivity, and lithium-ion diffusion coefficient during electrochemical processes. Furthermore, ultra-fine titanium powder, as the modifying agent, is amenable to large-scale production.     

Influence of surface modification by vanadium oxide and carbon on the electrochemical performance of LiFePO4/C

Surface modification with metal oxides is an efficient method to improve the performance of LiFePO₄. Carbon and V₂O₃ co-coated LiFePO₄ is synthesized by carbothermal reduction method combined with star-balling technique, and vanadium oxide is produced in situ. The structure and pattern of LiFePO₄/C modified with different amounts of vanadium oxide (0–5 mol%) were studied by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy. The electrochemical performance of material electrodes was analyzed by constant current charge–discharge and electrochemical impedance spectra (EIS). Electrochemical test results show that sample B (1.0 mol%) exhibits the best electrochemical performance, whose discharge capacity is up to 160.1, 127.2, and 88.4 mAh?g^?1 at 1, 5, and 10 °C, respectively. It indicates that V₂O₃ modification efficiently improves specific capacity and rate capability. The EIS experiment demonstrates that catalytic activity and reversibility of the cathode electrode are obviously increased by the surface modification of vanadium oxide.     

The composite of ZnSn(OH)<Subscript>6</Subscript> and Zn–Al layered double hydroxides used as negative material for zinc–nickel alkaline batteries

A series of Zn–Al layered double hydroxides (LDHs) and ZnSn(OH)₆ composites were successfully synthesized by hydrothermal method. The characteristic diffraction peaks of composites analyzed by X-ray diffraction (XRD) display that Zn–Al LDHs have been coupled with ZnSn(OH)₆, among which the composite containing 10% ZnSn(OH)₆ shows the best crystallinity. Besides, scanning electron microscopy (SEM) was conducted to observe the crystal morphologies. The electrodes were carried out by electrochemical measurements such as cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), and cycling performance. The results suggest that the discharge specific capacity of composite containing 10% ZnSn(OH)₆ is basically kept at 354 mAh g^?1 with a capacity retention rate about 98.3% after 800 cycles. Meanwhile, the CV measurement manifests that this material has the smallest redox peak potential difference (0.31 V) than that of others. And the electrode reaction of composite containing 10% ZnSn(OH)₆ occurs easily because the EIS test implies that its charge transfer resistance has been declined by 11.57 Ω cm², accompanied by the ohmic resistance decreasing by 0.48 Ω cm². The findings mentioned above can be attributed to the high electron mobility and electrical conductivity of ZnSn(OH)₆. All the results show that the electrode of LDHs with 10% ZnSn(OH)₆ has quite outstanding electrochemical performances when used as the negative material for zinc–nickel alkaline batteries.     

Synthesis of carbon microtubules core structure LiFePO4 via a template-assisted method

The carbon microtubules core structure LiFePO₄ is synthesized using a cotton fiber template-assisted method. The crystalline structure and morphology of the product is characterized by X-ray diffraction and field emission scanning electron microscopy. The charge–discharge kinetics of the LiFePO₄ electrode is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The result shows that the well-crystallized carbon microtubules core structure LiFePO₄ is successfully synthesized. The as-synthesized material exhibits a high initial discharge capacity of 167 mAh g^?1 at 0.2 C rate. The material also shows good high-rate discharge performance and cycling stability, about 127 mAh g^?1 and 94.7 % capacity retention after 100 cycles even at 5.0 C rate.     

Liquid precipitation synthesis of Co3O4 for high-performance electrochemical capacitors

The amorphous Co₃O₄ nanostructure, which adopted sodium hexametaphosphate as structure-directing agent, has been successfully synthesized in large scale via two steps: preparation of the precursor and the calcination process. The results of X-ray diffraction indicate that the prepared materials are mainly composed of Co₃O₄; the formless Co₃O₄ nanoplate with loose structures is observed by scanning electron microscopy. Cyclic voltammetry, chronopotentiometry, and electrochemical impedance measurements are applied in a mild aqueous electrolyte (2 mol L^?1 KOH) to investigate the performance of the Co₃O₄, which show a high specific capacitance (SC) of 482.61 F g^?1 at 5 mA cm^?2. Besides, the SC degradation is only 10.05 % after 250 continuous charge–discharge cycles at 5 mA cm^?2, indicating an excellent electrochemical stability. The improved performance is reasonably ascribed to their irregular structure for ionic transport during the electrochemical reaction, which presents as promising candidates for supercapacitors.     

A new anode material LiZnVO4: synthesis and electrochemical measurements

LiZnVO₄ particles ware synthesized via solid-state reaction route. It was characterized by X-ray diffraction and scanning electron microscopy. As anode material for rechargeable lithium-ion battery, the electrochemical performance of the LiZnVO₄ samples was measured. It was found that a large capacity of 330 mAh g^?1 can be retained after 70 cycles. The electrochemical measurements indicate that the anode material made of LiZnVO₄ exhibits excellent cycling stability even at a high current density.     

MnO2/graphite electrodeposited under supergravity field for supercapacitors and its electrochemical properties

MnO₂/graphite electrode material is successfully synthesized by electrodeposition under supergravity field from manganese acetate and graphite suspending solution. X-ray diffraction and field emission scanning electron microscopy show that the obtained composite is γ-MnO₂/graphite. The process of depositing the MnO₂/graphite was shown by the schematic illustration. Galvanostatic charge/discharge and cyclic voltammograms tests are applied to investigate electrochemical performances of the composite electrodes prepared under supergravity fields. MnO₂/graphite synthesized under supergravity field exhibits good discharge capacitance and the specific capacitance is 367.77 F g^?1 at current density of 0.5 A g^?1. It is found that supergravity field has effects on the electrochemical performances of MnO₂/graphite material.     

Synthesis of high-performance Fe–Mg-co-doped LiMnPO<Subscript>4</Subscript>/C via a mechano-chemical liquid-phase activation technique

Carbon-coated Fe–Mg-homogeneously dispersed Li(Mn_0.9Fe_0.10)_1???x Mg _x PO₄/C (x?=?0.00, 0.01, 0.03, 0.05, and 0.07) powders are synthesized via a mechano-chemical liquid-phase activation technique. Fine-sized and Fe²⁺ and Mg²⁺ evenly distributed precursors are formed using this efficient approach successfully. The synthesis temperature and the Mg²⁺ doping ratio are investigated and optimized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electrochemical measurements. Mg doping decreases the lattice parameters of LiMn_0.9Fe_0.1PO₄/C, which will ease the expansion/shrinking effect during the insertion/de-insertion processes. Li(Mn_0.9Fe_0.1)_0.95Mg_0.05PO₄/C synthesised at 700 °C with ~3 wt% of carbon additive presents the best comprehensive electrochemical properties, and it displays good rate capability with specific discharge capacity of 153 mAh g^?1 at 0.1C, 140 mAh g^?1 at 1C, and 132 mAh g^?1 at 2C rate. The results suggest that the electrochemical performance of the LiMnPO₄-based cathode is improved as (Mn_0.9Fe_0.1) is partially substituted by Mg.     

Enhanced lithium storage performance of a self-assembled hierarchical porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/VGCF hybrid high-capacity anode material for lithium-ion batteries

A Co₃O₄/vapor-grown carbon fiber (VGCF) hybrid material is prepared by a facile approach, namely, via liquid-phase carbonate precipitation followed by thermal decomposition of the precipitate at 380 °C for 2 h in argon gas flow. The material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller specific surface area analysis, and carbon elemental analysis. The Co₃O₄ in the hybrid material exhibits the morphology of porous submicron secondary particles which are self assembled from enormous cubic-phase crystalline Co₃O₄ nanograins. The electrochemical performance of the hybrid as a high-capacity conversion-type anode material for lithium-ion batteries is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic discharge/charge methods. The hybrid material demonstrates high specific capacity, good rate capability, and good long-term cyclability, which are far superior to those of the pristine Co₃O₄ material prepared under similar conditions. For example, the reversible charge capacities of the hybrid can reach 1100–1150 mAh g^?1 at a lower current density of 0.1 or 0.2 A g^?1 and remain 600 mAh g^?1 at the high current density of 5 A g^?1. After 300 cycles at 0.5 A g^?1, a high charge capacity of 850 mAh g^?1 is retained. The enhanced electrochemical performance is attributed to the incorporated VGCFs as well as the porous structure and the smaller nanograins of the Co₃O₄ active material.     

Electrochemical behavior of carbonic precursor with Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>nanostructured material in hybrid battery system

The nanostructured Na₃V₂(PO₄)₃ (NVP) cathode material has been synthesized using the sol-gel route for different molar fractions of citric acid as a carbon source during the synthesis. The nanostructured NVP as cores with carbonic shell structures are fabricated with two different citric acid molar ratios. The thermal treatment has been optimized to convert the amorphous carbon shell into graphitic carbon to realize the better electrical conductivity and thus effective electron transfer during the electrochemical charge transfer process. The X-ray diffraction measurements confirmed the rhombohedral crystallographic phase (space group R-3c) with average crystallite size ~28 ± 5 nm. The coin cells are assembled in a hybrid rechargeable electrochemical cell configuration with lithium as a counter electrode and LiPF₆-EC:DEC:DMC (1:1:1 ratio) as the electrolyte. The electrochemical charge/discharge measurements are carried out at C/10 and C/20 rates and the measured specific capacities are 80 and 120 mAhg^?1 for samples with lower and higher citric acid molar ratios, respectively. The studies suggest that NVP can be used as an effective cathode material in hybrid electrochemical cells, and a higher concentration of citric acid may result in the effective carbonic shell for optimal electron transfer and thus enhanced electrochemical performance.     

Synthesis and microstructure of Co/Ni: MgGa<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

This report discusses the preparation and microstructure of Co/Ni co-doped MgGa₂O₄ nanoparticles. The nanoparticles with the size of 20–55 nm were synthesized by sol-gel method. The phase and crystallinity were confirmed by X-ray powder diffraction (XRD) pattern. The particle size was estimated according to XRD data and transmission electron microscopy. The electronic structure was studied using X-ray photoelectron spectroscopy (XPS). The XPS studies showed that Ga³⁺ ions possess tetrahedral and octahedral sites of spinel structure and the inverse degree (two times of the fraction of tetrahedral Ga³⁺ ions) has increased with the increase of the doping concentration of Co²⁺ and Ni²⁺ ions. For Co/Ni co-doped MgGa₂O₄, two broad absorption bands of 350~500 and 550~700 nm were observed in the absorption spectra. The broad band at 350~500 nm was assigned to the combination of the absorption of octahedral Co²⁺ and Ni²⁺ ions, whereas the absorption band at 550~700 nm is mainly due to tetrahedrally coordinated Co²⁺ ions and octahedrally coordinated Ni²⁺ ions.     

Synthesis and luminescence properties of Na2Ba2Si2O7:Eu2+ phosphor

Green-emitting phosphor Na₂Ba₂Si₂O₇:Eu²⁺ has been synthesized by a conventional high-temperature solid-state reaction. The phase structure and luminescence properties are characterized by the X-ray powder diffraction, diffuse reflectance spectra, photoluminescence excitation and emission spectra, temperature-dependent emission spectra, respectively. It can be efficiently excited in the wavelength range of 325–400 nm and consists of a strong broad green band centered at about 501 nm, which is ascribed to 4f⁶6s⁰5d¹ → 4f⁷6s²5d⁰ transition of Eu²⁺. The critical quenching concentration of Eu²⁺ in the Na₂Ba₂Si₂O₇ host is about 0.8 mol % and corresponding quenching behavior is ascribed to be electric dipole–dipole interaction. Furthermore, the phosphor has good thermal stability property, and the activation energy for thermal quenching is calculated as 0.34 eV.     

Microwave-sintered Pr<Superscript>3+</Superscript>, Sm<Superscript>3+</Superscript>, and Gd<Superscript>3+</Superscript> triple-doped ceria electrolyte material for IT-SOFC applications

The Pr³⁺, Sm³⁺, and Gd³⁺ triple-doped ceria Ce_0.76Pr_0.08Sm_0.08Gd_0.08O_2-δ material as solid electrolyte for IT-SOFC has been successfully synthesized by sol–gel auto-combustion route. The effect of microwave sintering (1300 °C for 15, 30, and 60 min, named as PSG-MS15, PSG-MS30, and PSG-MS60, respectively) on structural, electrical, and thermal properties of prepared electrolyte material has been studied. Powder X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and Raman analysis revealed the single phase, microstructure, elemental confirmation, and structural oxygen vacancy formation of all the samples. Impedance spectroscopy analysis revealed the highest total ionic conductivity, i.e., 3.47 × 10^?2 S cm^?1 at 600 °C with minimum activation energy of 0.69 eV, in PSG-MS30 sample when compared to PSG-MS15 and PSG-MS60. The thermal expansion measurements have been carried out for PSG-MS30 specimen. The highest total ionic conductivity with minimum activation energy and moderate thermal expansion coefficient of PSG-MS30 sample makes the possibility of its use as solid electrolyte in IT-SOFC applications.     

Synthesis and electrochemical performance of mixed phase α/β nickel hydroxide by codoping with Ca<Superscript>2+</Superscript> and PO<Subscript>4</Subscript><Superscript>3−</Superscript>

Nickel hydroxide with a unique mixed phase α/β-Ni(OH)₂ was prepared by partially substituting Ca²⁺ for Ni²⁺ with supersonic co-precipitating method firstly. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The results show that the Ca-substituted Ni(OH)₂ by adding PO₄ ^3? is α/β mixed phase, while the undoped Ni(OH)₂ and the Ca-substituted Ni(OH)₂ without adding PO₄ ^3? are pure β phase. Furthermore, the Ca-substituted Ni(OH)₂ by adding PO₄ ^3? exhibits irregular shape and contains many intercalated water molecules and anions as proven by SEM and FT-IR. Meanwhile, the prepared samples were added into micro-sized beta nickel hydroxide to form biphase electrode materials for Ni-MH battery. The electrochemical performances of the biphase electrodes were characterized by cyclic voltammetry (CV) and charge/discharge tests. The results demonstrate that the biphase electrode with mixed phase α/β-Ni(OH)₂ exhibits higher electrochemical activity, better electrochemical reversibility and charge efficient, higher discharge potential, and better cyclic stability. The specific discharge capacity of Ca-substituted α/β-Ni(OH)₂ electrode can retain 271.7 and 238 mAh/g after 80 cycles at 0.2 and 0.5 C, respectively. This indicates that it may be a promising positive active material for alkaline secondary batteries. The results reported in this work may be useful for the designing and synthesizing of nickel hydroxide materials with superior performance.