Electrochemical behavior of nanostructured LiV3O8 in aqueous LiNO3 solution

Despite the large number of studies on the electrochemical behavior of LiV₃O₈ as a cathode material in nonaqueous lithium ion batteries, little information is available about the electrochemical behavior of LiV₃O₈ as an anode material in aqueous rechargeable lithium batteries. In this work, nanostructured LiV₃O₈ is successfully prepared using a low-temperature solid-state method. The electrochemical properties of the LiV₃O₈ electrode in 1 M, 5 M, and saturated LiNO₃ aqueous electrolytes have been characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge experiments. The results show that LiV₃O₈ electrode in saturated LiNO₃ electrolyte exhibits good electrochemical performance in terms of specific capacity and electrochemical cycling performance. LiV₃O₈ electrode can be reversibly cycled in saturated LiNO₃ aqueous electrolyte for 300 cycles at a rate of 0.5 C (300 mA g⁻¹ is assumed to be 1 C rate) with impressive specific capacities.     

Particle size distribution and electrochemical properties of LiFePO4 prepared by a freeze-drying method

The electrochemical performance of carbon-coated nanocrystalline LiFePO₄ prepared by a freeze-drying method is examined. This method is based on the thermal decomposition of homogeneous phosphate-formate precursors. Structural and morphological characterization of LiFePO₄ is carried out by powder XRD, BET measurements, SEM and XPS analyses. The electrochemical behaviour is tested in model lithium cells using galvanostatic mode. By changing the solution concentration, the freeze-drying method allows preparing LiFePO₄ with mean particle sizes between 60 and 100 nm and different particle size distributions. The content of carbon appearing mainly on the particle surface depends on both the solution concentration and the annealing temperature. The effect of particle size distribution on the voltage profile of LiFePO₄ is also demonstrated. The specific capacity is mainly determined by the amount of carbon deposited on the particle surfaces.     

Size-controlled hydrothermal synthesis and electrochemical behavior of orthorhombic LiMnO2 nanorods

Large amount of uniform orthorhombic LiMnO₂ (o-LiMnO₂) nanorods was fabricated by a hydrothermal route in 180 °C using γ-MnOOH nanorods as precursors through an isomorphous ion exchange process. The size of as-obtained o-LiMnO₂ nanorods was determined by that of γ-MnOOH precursors, which could be deliberately controlled. The electrochemical performance of o-LiMnO₂ nanorods was characterized via galvanostatic tests, which suggested that the size of as-obtained products played an important role in their electrochemical performances.     

Synthesis and characterization of lithium manganese oxides with core-shell Li4Mn5O12@Li2MnO3 structure as lithium battery electrode materials

By a facile LiNO₃ flux method, lithium manganese oxide composites (xLi₄Mn₅O₁₂? yLi₂MnO₃) were synthesized using a hierarchical organization precursor of manganese dioxide. Li₄Mn₅O₁₂ and Li₂MnO₃ have spinel and rocksalt structures, respectively. The lithiation and structural transformation from the precursor to the composites occurred topotactically from exterior toward interior in the precursor particle with the increase of reaction time, and the composites had core-shell spinel@rocksalt structures in addition to the original hierarchical core-shell organization. The electrochemical measurements at 50 °C after 50 cycles confirmed that a typical spinel@rocksalt cathode had higher capacity retention (87.1%) than that with the composition close to the stoichiometric spinel (64.6%), indicating the Li₂MnO₃ shell can improve cycling stability for the composite electrode at elevated temperature.     

Charge-discharge characteristics of nanocrystalline Co3O4 powders via aerosol flame synthesis

Nanocrystalline Co₃O₄ powders were synthesized by aerosol flame synthesis (AFS) method for the anode of lithium ion batteries and the basic electrochemical properties were investigated. The effects of synthesis conditions and heat-treatment temperature on the morphology, crystallite size and electrochemical properties were investigated. As-prepared soot contained Co₃O₄, CoO and Co(OH)₂, which were eventually converted into cubic spinel Co₃O₄ by post heat treatment. The as-prepared particle size was in the range of 10-30 nm and grew to 50-85 nm by the heat treatment. With growing particle size and improved crystallinity, charge-discharge capacity and cycle performance were improved and the discharge capacity of the powder heat-treated at 700 °C was 571 mAh/g after 30 cycles, which was better than Co₃O₄ powder reported in the previous literature.     

Photoluminescence properties of SHI induced F2 and F3 color centers in nano-granular LiF thin films

Photoluminescence (PL) properties of swift heavy ions-induced F₂ and F₃⁺ color centers in nano-granular lithium fluoride (LiF) thin film were studied. LiF films were deposited on glass and silica substrates and irradiated with various ion species (Ag, Ni and Au) at different irradiation temperatures. The role of ion species, their fluence and the irradiation temperature on the PL intensity of color centers induced in LiF thin films is discussed.     

Improved cycling performances with high sulfur loading enabled by pre-treating lithium anode

Lithium nitrate (LiNO₃) is reported as an effective additive to protect lithium anode in rechargeable lithium-sulfur battery. However, for its strong oxidation, cells containing LiNO₃ still suffer from safety problems and poor cycle performance since LiNO₃ can be reduced on cathode to form some irreversible products. In this study, a facile and effective method to pre-passivate lithium anode is proposed by simply immersing lithium plates in LiNO₃ solution. The electrochemical properties show that the pretreatment is favorable for the construction of a protection layer on the surface of lithium anode. Cells with pretreated lithium show the coulombic efficiency of 80.6 % in the first cycle and 87.2 % after 100 cycles, far higher than the one with pure lithium. The discharge capacity is retained at 702 mA h g^?1 after 100 cycles, and the result is better than those directly adding LiNO₃ in electrolyte. It is believed that these improvements result from the high stability of surface film during the charge and discharge process, which can stabilize the structure of anode and suppress the shuttle effect.     

Surface modification by silver coating for improving electrochemical properties of LiFePO4

LiFePO₄ is a potential candidate for the cathode material of the lithium secondary battery. Fine particle LiFePO₄ was synthesized by the simple co-precipitation method, and aqueous coating on the LiFePO₄ was tried using silver nitrate solution in order to increase electronic conductivity. Highly dispersed silver on the particles enhances the electronic conductivity and increases the capacity. The electrochemical properties of the silver coated LiFePO₄ with the various current densities are analogous to those of highly conductive LiFePO₄. The silver coating can be a promising tool to preserve the capacity even at the high current densities.     

Electrochemical properties of carbon-coated LiFePO4 synthesized by a modified mechanical activation process

Carbon-coated lithium iron phosphate (LiFePO₄/C) composites were synthesized by conventional mechanical activation (MA) process and also by a modified MA process. Phase-pure particles were obtained of ∼100 nm size with a nano-meter thick web of carbon surrounding the particles. The composite prepared by the modified MA process shows good performance as cathode material in lithium cells at room temperature. A high performance was achieved at 0.1 C-rate with >96% utilization of the active material. A stable cycle performance even at higher C-rates was achieved with a cathode that has a total carbon content of only 12 wt%. The use of the modified MA process to synthesize LiFePO₄/C has promise to be an efficient process to decrease the total carbon content of the cathode, resulting in the enhanced energy density.     

Ni80Fe20 permalloy nanoparticles: Wet chemical preparation, size control and their dynamic permeability characteristics when composited with Fe micron particles

Ni₈₀Fe₂₀ permalloy nanoparticles (NPs) have been prepared by the polyol processing at 180 °C for 2 h and their particle sizes can be precisely controlled in the size range of 20-440 nm by proper addition of K₂PtCl₄ agent. X-ray diffraction results show that the Ni-Fe NPs are of FCC structure, and a homogeneous composition and a narrow size distribution of these NPs have been confirmed by scanning electron microscopy assisted with energy dispersion spectroscopy of X-ray (SEM-EDX). The saturation magnetization of ~440nm NPs is 80.8 emu/g that is comparable to that of bulk Ni₈₀Fe₂₀ alloys, but it decreases to 28.7 emu/g for ~20 nm NPs. The coercive force decreases from 90 to 3 Oe with decreasing NP size. The wide range of particle size is exploited to seek for high permeability composite particles. The planar type samples composed of the NiFe NPs exhibit low initial permeability due to the deteriorated magnetic softness and low packing density. However, when they are mixed with Fe micron particles, the initial permeability significantly increases depending on the mixing ratio and the NiFe NP size. A maximum initial permeability is achieved to be ~9.1 at 1 GHz for the Fe-10 vol%NiFe (~20 nmΦ), which is about three times that of pure Fe micron particles. The effects of Ni-Fe particle size, volume percentage and solvent on the static and dynamic permeability are discussed.     

The structural and magnetic properties of one-step mechanochemical route synthesized La0.8Pb0.2MnO3 manganites

Mechanochemical route has been used to produce La_0.8Pb_0.2MnO₃ (LPMO) nanocrystalline samples from oxide precursors. The samples were characterized using X-ray diffraction, scanning electron microscope and AC susceptibility measurements. The results showed that it is possible to produce LPMO perovskite powders after 10 h of ball milling. The crystallite size and microstrain were estimated using Williamson-Hall equation. The results showed that the crystallite size and microstrain increase initially and then decrease by the increase of milling time. By decreasing particle size the dislocation density (strain) increases and reaches to a saturation point at a particular particle size, further particle size reduction takes place through gliding motion along grain boundaries, which leads to a reduction of the strain. The dynamic properties of 15 h ball-milled sample were investigated by AC susceptibility using the Neel-Brown and Vogel-Fulcher law for superparamagnetism. The frequency dependence of blocking temperature is well described by the Vogel-Fulcher law, and fitting the experimental data with Neel-Brown law gives unphysical value for relaxation time.     

Recent development and application of Li4Ti5O12 as anode material of lithium ion battery

Lithium-ion batteries with both high power and high energy density are one of the promising power sources for electric devices, especially for electric vehicles (EV) and other portable electric devices. One of the challenges is to improve the safety and electrochemical performance of lithium ion batteries anode materials. Li₄Ti₅O₁₂ has been accepted as a novel anode material of power lithium ion battery instead of carbon because it can release lithium ions repeatedly for recharging and quickly for high current. However, Li₄Ti₅O₁₂ has an insulating character due to the electronic structure characterized by empty Ti 3d-states, and this might result in the insufficient applications of LTO at high current discharge rate before any materials modifications. This review focuses first on the present status of Li₄Ti₅O₁₂ including the synthesized method, doping, surface modification, application and theoretical calculation, then on its near future development.     

Variations in the structural, optical and electrochemical properties of CeO2-TiO2 films as a function of TiO2 content

Alcohol based sols of cerium chloride (CeCl₃·7H₂O) and titanium propoxide (Ti(OPr)₄) in ethanol mixed in different mole ratios have yielded mixed oxide films on densification at 500 °C. The reversibility of the intercalation/deintercalation reactions has shown electrochemical stability of the films. Addition of TiO₂ in an equivalent mole ratio manifests in producing highly transparent films with appreciable ion storage capacity. The electrochemical studies have revealed the significant role of TiO₂ in controlling the ion storage capacity of the films, as it tends to induce the disorder. In addition, the films prepared from an aged sol are observed to exhibit a much higher ion storage capacity than the films deposited using the as-prepared sol. The X-ray photoelectron spectroscopic studies have provided information on the variation of Ce⁴⁺/Ce³⁺ ratio as a function of increased TiO₂ content in the films. This study has led to a better understanding of the increased ion storage capacity with the increased TiO₂ proportion. The transmission electron microscopic study has demonstrated the presence of CeO₂ nanograins even in films, which are amorphous to X-rays. Elucidation of the structural, optical and electrochemical features of the films has yielded information on aspects relevant to their usage in transmissive electrochromic devices. The films have been found to exhibit properties that can find application as counter electrode in electrochromic smart windows in which they are able to retain their transparency under charge insertion, high enough for practical uses. Also, the fastest coloration-bleaching kinetics for the primary electrochromic electrode (WO₃) working in combination with Ce/Ti (1:1) electrode stimulates the use of latter in electrochromic windows (ECWs).     

Superspin glass state in MnFe2O4 nanoparticles

Nanosized MnFe₂O₄ ferrites were synthesized by a simple method, which is based on the solid state ball-milling and calcinations of nitrate precursors and citric acid. The samples were characterized by using different methods. The results indicate that the products mainly consist of MnFe₂O₄ nanoparticles. The effect of different annealing temperatures on particle sizes and crystallinity of the samples was also studied. By increasing the particle size, the coercivity and magnetization of the samples increase. The increase of magnetization by increasing the crystallite size could be attributed to the lower surface spin canting and surface spin disorder of the larger magnetic nanoparticles. Our analysis of ac susceptibility measurements shows that the interparticle magnetic interaction leads to the superspin glass-like behavior in these nanoparticle samples.     

SnO2/TiO2 mixed oxide particles synthesized in doped premixed H2/O2/Ar flames

SnO₂/TiO₂ mixed oxides with primary particle size ranging between 5 nm d_p 12 nm were synthesized by doping a H₂/O₂/Ar flame with Sn(CH₃)₄ and Ti(OC₃H₇)₄ co-currently. The effects of “flow coordinate,” concentration and flame configurations were investigated with respect to particle size and morphology of the generated mixed oxides. In situ characterization of the mixed oxides was performed using the particle mass spectrometer (PMS), while XRD, TEM, BET and UV–Vis were performed ex situ. Results obtained showed that primary particle size of mixed oxides can be controlled by varying experimental parameters. The mixed oxides have interesting properties compared to those of the pure oxides of TiO₂ and SnO₂, which were also synthesized in flames earlier. Band gap tuning opportunities are possible using mixed oxides.     

A Ni/YSZ composite containing Ce0.9Ca0.1O2−δ particles as an anode for SOFCs

A composite material (hereafter referred to as NYC) containing Ni, Y₂O₃-stabilized ZrO₂ (YSZ) and Ce_0.9Ca_0.1O_2−δ (CC10) particles was prepared and used as the anode of solid oxide fuel cells (SOFCs). The performance of NYC was better than that of conventional Ni/YSZ anodes in terms of anodic overpotential and interface impedance. The additional CC10 particles improved the anode properties. XRD results suggest that a solid solution of YSZ and CC10 was produced. From impedance measurements, it is concluded that the solid solution exhibits substantial electronic conduction. Ni/YSZ/15 wt% Ce_0.9Ca_0.1O_2−δ anodes exhibited the best properties over the experimental temperature range. A SOFC with an anode of Ni/YSZ/15 wt% Ce_0.9Ca_0.1O_2−δ provided the maximum power density and current density. Addition of CC10 with an average particle size of 0.3 μm was more advantageous than that with an average size of 3 μm.     

Synthesis of Single Crystalline ZnO Nanoparticles by Salt-Assisted Spray Pyrolysis

LiNO₃ was used as a shield in the preparation of single crystalline ZnO particles by a spray pyrolysis process in order to prevent agglomeration and enhance the crystallinity of the ZnO. LiNO₃ was added to a precursor solution of zinc acetate dihydrate prior to its atomization by means of an ultrasonic transducer. Agglomerate-free particles having a mean particle size of 26 nm were successfully obtained after washing the product. X-ray diffractometry, field-emission scanning electron micrograph and transmission electron micrograph data indicate that the size and morphology of ZnO were strongly influenced by the operating temperature used and the residence time of the particle in the reactor.     

Synthesis and optical properties of tetragonal KTa0.6Nb0.4O3 nanoparticles

Tetragonal phase KTa_0.6Nb_0.4O₃ (KTN) nanoparticles have been prepared by hydrothermal method. The obtained particles were characterized by X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and UV-vis absorption spectrum techniques. A systematic change in crystal structure from cubic to tetragonal is observed with the increase of reaction temperature and KOH concentration. Room temperature UV-vis absorption spectrums of KTN particles show that the band gap changes from 3.24 to 3.34 eV with grain size diminished, which reveals the existence of blue-shift phenomenon of absorption bands.     

A study of modified Fe3O4 nanoparticles for the synthesis of ionic ferrofluids

XRD and XPS analyses revealed that a Fe(NO₃)₃·9H₂O layer formed outside γ-Fe₂O₃ particles when Fe₃O₄ nanoparticles were treated with ferric nitrate. The particle density differed for untreated and treated particles and was not uniform for the latter. The specific saturation magnetization of both treated and untreated particles was used to estimate the thickness of the Fe(NO₃)₃·9H₂O layer and the average density of the treated particles. The density of the treated particles was used to calculate the density of ferrofluids of different particle volume fractions. These values are in agreement with measured results. Therefore, the particle volume fraction can be designed to synthesize acid ionic ferrofluids based on Fe₃O₄ nanoparticles using Massart's method.     

Layered LiCo1?xMgxO2 (x = 0.0, 0.1, 0.2, 0.3 and 0.5) cathode materials for lithium-ion rechargeable batteries

Layered LiCo_1−x Mg _x O₂ (x = 0.0, 0.1, 0.2, 0.3 and 0.5) oxide materials were synthesized using LiNO₃, Co(NO₃)₂, Mg(NO₃)₂ as the precursors, and the effect of the dopants on the electrochemical properties was investigated. thermogravimetric/differential thermal analysis was carried out to observe the phase transformations of LiCo_0.9Mg_0.1O₂. The phase purity and cation environment of the synthesized oxides were characterized using X-ray diffraction and Fourier transform infrared spectroscopy. The particle size, nature, morphological properties and composition of the synthesized oxides were examined by TEM and SEM with energy dispersive X-ray spectroscopic analysis. Finally, the electrochemical behavior of the prepared layered materials was studied using cyclic voltammetry and charge–discharge cycling. LiCo_0.8Mg_0.2O₂ has good cycling results when compare to other doped and undoped materials. These results have been also supported by cyclic voltammograms.