Structure and electrochemical performance of nickel hydroxide synthesized by rapid quench method

Nickel hydroxide with amorphous structure has been synthesized successfully by chemical precipitation method combined with rapid quench technique. The microstructure and morphology of the prepared samples were analyzed by XRD, Raman spectra, IR spectra, and SEM. The electrochemical performance of the sample was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests. The discharge capacity of the amorphous nickel hydroxide is 330.0 mAh g⁻¹ at 0.2C, much higher than that of the theoretical capacity of β-nickel hydroxide (289.0 mAh g⁻¹). Moreover, the amorphous nickel hydroxide exhibits higher electrochemical reaction reversibility, lower electrochemical impedance, and better cyclic stability compared with β-nickel hydroxide.     

High rate performances of the cathode material LiNi1/3Co1/3Mn1/3O2 synthesized using low temperature hydroxide precipitation

A low-temperature reaction route is introduced based on hydroxide precipitation method to synthesize the cathode material LiNi_1/3Co_1/3Mn_1/3O₂. The crystal structure and morphology of the prepared powder have been characterized by X-ray diffraction and Scan electron microscope, respectively. The charge–discharge tests were performed between 2.5 and 4.5 V. The discharge capacity of the material is strongly impacted by the reaction temperature. The powders sintered at 850 °C show the best electrochemical performance and the initial discharge capacity is about 160 mAh g⁻¹ at 5 C. Powder X-ray diffraction and Scan electron microscope results reveal that the excellent electrochemical performances should be ascribed to the lower precursor reaction temperature, the lower degree of cation mixing and analogous spherical small particles, which can improve the transfer of Li ions and electrons. All these results indicate that this material has potential application in lithium-ion batteries.     

Synthesis, structure, and electrochemical characteristics of LiNi1/3Co1/3Mn1/3O2 prepared by thermal polymerization

A thermal polymerization route was adopted to synthesize layered LiNi_1/3Co_1/3Mn_1/3O₂ materials. After annealing the polymer gel containing metal salts at different temperatures from 850 to 1000 °C for different time between 6 and 25 h, powders of pure α-NaFeO₂ phase were obtained. The crystal structure, morphology and electrochemical properties of the products were investigated by XRD, SEM, electrochemical cell cycling and AC impedance spectroscopy. It is found that the powder annealed at 950 °C for 15 h shows the best electrochemical property with the first specific discharge capacity of 188 mAh/g at C/10 and 87% retention after 100 cycles. It exhibits good rate capability with the specific capacity of 169 mAh/g at 1 C and 110 mAh/g at 6 C. Adopting a slowly cooling procedure during the powder annealing can improve the electrochemical performance of the LiNi_1/3Co_1/3Mn_1/3O₂ powder.     

Planar defects in layered hydroxides: Simulation and structure refinement of β-nickel hydroxide

Although nickel hydroxide can be obtained by various methods in a highly ordered form, this work shows that most such preparations are not free of stacking faults. The stacking faults belong to more than one type, which differ from one another in their structure as described by the local stacking sequence. The incidence of such residual stacking faults varies in the range 1-3% depending on the method of preparation.     

Effect of pH value on particle morphology and electrochemical properties of LiFePO4 by hydrothermal method

Lithium iron phosphate was prepared by hydrothermal synthesis using LiOH·H₂O, FeSO₄·7H₂O and H₃PO₄ as raw materials. The effects of pH value of reaction solution on particle morphology and electrochemical property were investigated. The pH value of the reaction solution was adjusted in the range of 2.5-8.8 by dilute sulfuric acid and ammonia water. The samples were characterized by field-emission scanning electronic microscope (FE-SEM), X-ray powder diffraction (XRD), constant-current charge/discharge cycling tests and chemical analysis. The results indicated that the particles exhibited acute angle diamond flake-like morphology at pH = 2.5, and as the pH value increased, the particle became hexagon flake-like, round flake-like and irregular flake-like morphology gradually. The optimal sample synthesized at pH = 6.4 exhibited discharge capacities of 151.8 mAh g⁻¹ at 0.2 C rate and 129.3 mAh g⁻¹ at 3 C rate. It was found that pH value affected the morphologies and properties of the product by means of different crystal growth rates.     

Synthesis and electrochemical performances of spinel LiCr0.1Ni0.4Mn1.5O4 compound

The spinel compound LiCr_0.1Ni_0.4Mn_1.5O₄ was synthesized by a solid reaction method and a sol-gel method using citric acid as chelating agent. The pure phase LiCr_0.1Ni_0.4Mn_1.5O₄ was obtained by the wet method. The electrochemical performances of the pure phase sample were measured at different current rates. There were three voltage plateaus at about 4.9, 4.7 and 4.0 V in the charge-discharge curves, which were attributed to the oxidation/reduction of chromium, nickel and manganese respectively. In the range of 3.5-5.0 V, its first discharge capacity was 143, 118 and 111 mAh/g corresponding to current densities of 1.0, 4.0 and 5.0 mA/cm², respectively. After 50 cycles, the capacity retention remained well at the current densities of 1.0, 4.0 and 5.0 mA/cm². The electrochemical performances of pure phase LiCr_0.1Ni_0.4Mn_1.5O₄ at 55 °C was also measured, and the results were discussed.     

Influence of isovalent ion substitution on the electrochemical performance of LiCoPO4

LiCo_1−xM_xPO₄ (M = Mg²⁺, Mn²⁺ and Ni²⁺; 0 ≤ x ≤ 0.2) compounds have been synthesized by solid-state reaction method and studied as cathode materials for secondary lithium batteries. LiCoPO₄ exhibits a discharge plateau at ∼4.7 V with an initial discharge capacity of 125 mAh/g and on cycling capacity falls. Substitution of Co²⁺ with Mg²⁺/Mn²⁺/Ni²⁺ in LiCoPO₄ has an influence on the initial discharge capacity and on cycling behaviour. The capacity retention of LiCoPO₄ is improved by manganese substitution. Among the manganese substituted phases, LiCo_0.95Mn_0.05PO₄ shows good reversible capacity of ∼50 mAh/g.     

Influence of the precipitation pH on the compositions and properties of Bi-based oxyiodide photocatalysts

A series of Bi-based oxyiodide photocatalysts with different compositions were synthesized via a precipitation-filtration process followed by hydrothermal treatment. The compositions of the bismuth oxyiodides could be controlled by adjusting the precipitation pH values. The effects of the precipitation pH values on the compositions and photocatalytic activities of the bismuth oxyiodides were investigated and the relationship between structure and photocatalytic property is discussed. All the as-prepared powders exhibit photocatalytic activity on decomposing methyl orange under visible light irradiation. The activity increases with increasing content of iodine in the bismuth oxyiodides.     

Effect of Cu-doping on the electrochemical performance of FeS2

FeS₂ reportedly has a high specific capacity of 893 mAh/g; however, its poor cyclic performance limits its commercialization. To circumvent this limitation, strategies such as preparation of high-purity FeS₂ and Ni-doping were adopted to modify the electrochemical properties of FeS₂. Nevertheless, these approaches resulted only in limited improvements in the electrochemical properties. Therefore, in this study, we synthesized Cu-doped FeS₂ via a solvothermal process, aiming at improved electrochemical properties. Systematic studies indicated that Cu doping changed the morphology of FeS₂ from larger irregular particles to smaller spherical ones. The charge–discharge measurements indicated that the Cu-doped FeS₂ exhibited two discharge plateaus, at 1.6 V and 1.4 V. The initial specific discharge capacity of Cu-doped FeS₂ was about 866 mAh/g at a current density of 90 mA/g, which is approximately 11% higher than that of the undoped FeS₂. The initial discharge capacity of the Cu-doped FeS₂ at a current density of 2700 mA/g was 518 mAh/g, and its cyclic discharge capacity exceeded 105 mAh/g at the 20th cycle. Cyclic voltammetry and resistance measurements revealed that Cu-doping reduces both the internal resistance and polarization of Li/FeS₂ batteries.     

A simple method to synthesize layered double hydroxide nanoscrolls

Layered double hydroxide (LDH) is a promising drug carrier, ion exchanger, absorbent, and catalyst or even catalyst support due to its inimitable sandwich structure. If the LDH could be synthesized into the nanoscrolls, it will be promising ion channels for the biomolecule transfer, ion exchange, or catalysis. In this report, a simple technique has been developed to prepare layered double hydroxide nanoscrolls on a large scale. The composition of LDH nanoscrolls can be conveniently adjusted through experiment conditions. We proved the “rolling mechanism” to explain the formation of LDH nanoscrolls. Moreover, we unambiguously proposed the driving force for “rolling mechanism”, which is the change of the forces between the brucite-like sheets and the interanions and between the cations and cations in the brucite-like sheets.     

The synthesis of composite Sn-SnSb films for lithium-ion batteries by electrochemical deposition

Composite Sn-SnSb nano-crystalline films were fabricated on Cu substrate by an electrochemical deposition process. X-ray diffraction, scanning electron microscopy, and galvanostatic cell cycling were used to characterize the structures and electrochemical properties of the films. The as-deposited films consist of only Sn/SnSb composite nanocrystals with a rather dense morphology. The Sn-SnSb composite electrode gives rise to a very small (6%) initial capacity loss and a rather high specific capacity of about 650 mAh/g, which is significantly higher than the values reported in the literature. The coulombic efficiency during charge-discharge cycles is close to 100%.     

The reaction of ceria coatings on mica with H2S: An in-situ X-ray diffraction study

Thin layers of ceria were deposited on the surface of mica platelets in solution. The reaction of such particles with hydrogen sulfide yields a red colored special effect pigment. The ceria layer reacts with H₂S to produce a variety of sulfide and oxysulfide phases. The reaction path discovered in situ by time and temperature resolved X-ray diffraction is CeO₂→CeS₂→C-Ce₂S₃→Ce₁₀S₁₄O. The reaction itself is extremely variable depending on gas flow, heating rates and decomposition atmospheres. Effects on the thin film are recorded by scanning electron microscopy (SEM) and revealed a destruction of the layer once red Ce₁₀S₁₄O was formed. The product layer then reveals the typical nonwetting behaviour of a liquid on a surface.     

Preparation and electrochemical properties of nickel oxide as a supercapacitor electrode material

Hydrothermal synthesis has been introduced to fabricate NiO precursor at different temperatures, then nanostructured NiO with a distinct flake-like morphology was obtained via heating at low temperature. The NiO nanoflakes are 50-80 nm in width and 20 nm in thickness. The electrochemical capacitive characterization of the as-prepared NiO was studied in 2 M KOH electrolyte solution. The as-prepared NiO exhibits excellent cycle performance and keeps 91.6% initial capacity over 1000 charge-discharge cycles. Electrochemical impedance spectroscopy study reveals that the NiO electrode is controlled by the mass transfer limitation, and its internal resistance is 0.2 Ω. A specific capacitance approximate to 137.7 F g⁻¹ could be achieved at the current density of 0.2 A g⁻¹ in the potential window of 0-0.46 V in 2 M KOH electrolyte solution, due to higher surface area of NiO nanoflakes, which facilitates transport of electrolyte ions during rapid charge/discharge process. Due to higher surface area of NiO nanoflakes, which facilitates transport of electrolyte ions during rapid charge/discharge process.     

A facile method to synthesize carbon coated Li1.2Ni0.2Mn0.6O2 with improved performance

Carbon-coated Li_1.2Ni_0.2Mn_0.6O₂ powders have been synthesized with Bakelite and heat process in air. The effect of carbon coating on the physical and electrochemical properties have been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), discharge and rate tests. The carbon-coated cathode exhibits much improved first discharge capacity and rate capability than the pristine sample. The discharge capacity at 0.1 and 5.0 C rates are 246 and 125 mAhg⁻¹, while that of pristine are only about 222 and 49 mAhg⁻¹, respectively. The capacity retention of Li_1.2Ni_0.2Mn_0.6O₂ electrode after 50 cycles is improved from 89.8 to 97.5% after carbon coating. EIS results indicate that R_ct of Li_1.2Ni_0.2Mn_0.6O₂ electrode is decreased from 62 to 37 Ω after carbon coating.     

A new strategy to diminish the 4 V voltage plateau of LiNi0.5Mn1.5O4

As for spinel LiNi_0.5Mn_1.5O₄, there is 4 V voltage plateau in the charge–discharge profiles. This voltage plateau can be reduced by an annealing process, however it is hard to avoid it completely. In this study, a new strategy of partial substitution for Mn by Mg is applied. There is no 4 V voltage plateau in the charge–discharge profiles of Mg-doped compound LiNi_0.5Mn_1.45Mg_0.05O₄. This compound exhibits good electrochemical properties which can be used as cathode material of lithium ion batteries. At 1 C rate, it can deliver a capacity of around 129 mAh g⁻¹ and remain good cycle performance.     

The double hydroxide of Al with Li: mechanism of formation and reversible thermal behavior

All the polymorphic modifications of Al(OH)₃ and the oxide-hydroxide of Al, boehmite, on hydrothermal treatment in Li⁺ containing solutions transform into the layered double hydroxide of Al with Li having the nominal composition [LiAl₂(OH)₆](CO₃)_1/2·1.5H₂O, suggesting that these compounds form via a dissolution-reprecipitation mechanism. The oxide residue obtained by the thermal decomposition of this layered double hydroxide also partially reconstructs the layered double hydroxide on soaking in water lending further evidence to the dissolution-reprecipitation mechanism. Under hydrothermal conditions, in water, the layered double hydroxide undergoes delithiation to yield aluminum hydroxide phases other than gibbsite, suggesting again that delithiation too proceeds by a dissolution-reprecipitation mechanism.     

Microwave synthesis of nanocrystalline Sb2S3 and its electrochemical properties

Nanocrystalline antimony trisulfide (Sb₂S₃) was successfully synthesized via microwave irradiation by the reaction of antimony trichloride (SbCl₃) and thiourea (CS(NH₂)₂) with PVP as the surfactant. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). XRD results show that the as-prepared sample is orthorhombic-phase Sb₂S₃. TEM image of the as-prepared Sb₂S₃ shows the rod-like structure. HRTEM image indicates that rodbundles of Sb₂S₃ consists of a number nanorods with the diameter ranging from 30 nm to 50 nm. Detailed HRTEM image demonstrates the preferential direction growth of the Sb₂S₃ nanorods. The electrochemical properties of Sb₂S₃ were primarily investigated by constant current charge/discharge cycling tests in lithium hexafluorophosphate (LiPF₆) solution. The possible electrochemical reaction mechanism was explained. The results indicate that the nanocrystalline Sb₂S₃ shows potential application in the field of the electrode materials.     

Synthesis and characterization of layered double hydroxides (LDHs) with intercalated chromate ions

Chromate intercalated layered double hydroxides (LDHs) having the formula M^II₆M′^III₂(OH)₁₆CrO₄·4H₂O (M^II = Ca, Mg, Co, Ni, Zn with M′^III = Al and M^II = Mg, Co, Ni with M′^III = Fe) have been prepared by coprecipitation. The products obtained are replete with stacking disorders. DIFFaX simulations show that the stacking disorders are of three kinds: (i) turbostratic disorder of an originally single layered hexagonal (1H) crystal, (ii) random intergrowth of polytypes with hexagonal (2H) and rhombohedral (3R) symmetries and (iii) translation of randomly chosen layers by (2/3, 1/3, z) and (1/3, 2/3, z) leading to stacking faults having a local structure of rhombohedral symmetry. IR spectra show that the CrO₄²⁻ ion is incorporated either in the T_d or in the C_3v symmetry. The interlayer spacing in the latter case is 7.3 Å characteristic of a single atom thick interlayer showing that the CrO₄²⁻ ion is grafted to the metal hydroxide slab. On thermal treatment, the CrO₄²⁻ ion transforms into Cr(III) and is incorporated into the spinel oxide or phase separates as Cr₂O₃. In the LDH of Mg with Al, Cr(III) remains in the MgO lattice as a defect and promotes the reconstruction of the LDH on soaking in water. In different LDHs, 18-50% of the CrO₄²⁻ ion is replaceable with carbonate anions showing only partial mineralization of the water-soluble chromate. The extent of replaceable chromates depends upon the solubility of the corresponding LDH, which in turn is determined by the solubility of the MCrO₄. These studies have profound implications for the possible use of LDHs for chromate amelioration in green chemistry.     

Intercalation of Ru(II) tris (1,10-phenanthroline) complex in α- and γ-zirconium dihydrogen phosphate. Synthesis, thermal behaviour and X-ray characterization

Layered inorganic systems such as ion-exchangers (α- and γ-zirconium dihydrogen phosphate) already used as hosts for larger cations, were studied for the intercalation of Ru(II) tris (1,10-phenanthroline) complex into these host matrices. The uptake of the complex occurs using the batch method; the colour of the materials changes from white to brilliant orange; the highest ion uptake is obtained in the case of the γ-phase. The materials obtained are thermally stable up to ∼350 °C and the complex decomposition occurs in two (α-phase) or three (γ-phase) steps. The complex decomposition is complete at ∼700 °C and at 550 °C (respectively for α- and γ-Ru(II) materials). As can be seen from the X-ray patterns, the Ru(II) materials are still layered and show a new phase with an increase in the interlayer distance with respect to the starting materials. The hydrogen form is always present in the case of the α-materials; whereas, in the case of the γ-materials, it is present when ≤0.12 moles of the complex/mole of exchanger are inserted. Microanalysis measurements confirm the fact that the Ru(II) complex is not modified when exchanged.     

Photochemical performance and electrochemical capacitance of titania nanocomplexes

Titania nanocomplexes, comprising the disordered nanoribbons or nanowires on the top surface and highly ordered nanotube array on the underlaying layer, has been fabricated by longitudinally splitting off nanotubes in a controlled anodization process. Anatase titania nanocomplexes show higher photovoltage and photocurrent responses and photocatalysis activity than titania nanotube array due to the enhanced light harvesting caused by nanoribbons and nanowires. Furthermore, titania nanowire-nanotube demonstrates a higher photoelectrical performance than nanoribbon-nanotube due to its thicker space charge layer caused by long nanotubes and more effective surface area contributed by nanowires. Cyclic charge-discharge measurements show that titania nanotube array exhibits a much higher electric double layer capacitance than titania nanocomplexes because the surface nanoribbons or nanowires inhibit the free diffusion and transportation of electrolyte ions into the underlaying nanotubes. Therefore, titania nanocomplexes can act as a photoactive material for photocatalysis applications and titania nanotube array can act as an electrode substrate for electrochemical supercapacitor applications.