Synthesis and electrochemical characterizations of nano-scaled Zn doped LiMn2O4 cathode materials for rechargeable lithium batteries

The LiZn_xMn_2−xO₄ (x = 0.00-0.15) cathode materials for rechargeable lithium-ion batteries were synthesized by simple sol-gel technique using aqueous solutions of metal nitrates and succinic acid as the chelating agent. The gel precursors of metal succinates were dried in vacuum oven for 10 h at 120 °C. After drying, the gel precursors were ground and heated at 900 °C. The structural characterization was carried out by X-ray powder diffraction and X-ray photoelectron spectroscopy to identify the valance state of Mn in the synthesized materials. The sample exhibited a well-defined spinel structure and the lattice parameter was linearly increased with increasing the Zn contents in LiZn_xMn_2−xO₄. Surface morphology and particle size of the synthesized materials were determined by scanning electron microscopy and transmission electron microscopy, respectively. Electrochemical properties were characterized for the assembled Li/LiZn_xMn_2−xO₄ coin type cells using galvanostatic charge/discharge studies at 0.5 C rate and cyclic voltammetry technique in the potential range between 2.75 and 4.5 V at a scan rate of 0.1 mV s⁻¹. Among them Zn doped spinel LiZn_0.10Mn_1.90O₄ has improved the structural stability, high reversible capacity and excellent electrochemical performance of rechargeable lithium batteries.     

Hydrothermal synthesis of carbon-coated lithium vanadium phosphate

A novel hydrothermal synthesis was developed to prepare carbon-coated lithium vanadium phosphate (Li₃V₂(PO₄)₃) powders to be used as cathode material for Li-ion batteries. The structural, morphological and electrochemical properties were investigated by means of X-ray powder diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and constant current charge-discharge cycling. This material exhibits high initial discharge capacity of 178, 173 and 172 mAh g⁻¹ at 0.1, 0.2 and 0.5 C between 3.0 and 4.8 V, respectively. Moreover, it displays good fast rate performance, which discharge capacities of 136, 132 and 127 mAh g⁻¹ can be delivered after 100 cycles between 3.0 and 4.8 V versus Li at a different rate of 1, 2 and 5 C, respectively. For comparison, the electrochemical properties of carbon-coated lithium vanadium phosphate prepared by traditional solid-state reaction (SSR) method are also studied.     

Tin dioxide/carbon nanotube composites with high uniform SnO2 loading as anode materials for lithium ion batteries

SnO₂/multi-walled carbon nanotube (MWCNT) composites were prepared by the solvothermal method and subsequent heat treatment at 360 °C. The samples were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Results on the higher SnO₂ content composite sample indicate that a uniform layer of SnO₂ nanocrystals with crystal size around 5 nm was deposited on the surface of the carbon nanotubes. The composite demonstrates a reversible lithium storage capacity of 709.9 mAh g⁻¹ at the first cycle and excellent cyclic retention up to 100 cycles as anode for lithium ion batteries.     

Large-scale synthesis of WO3 nanoplates by a microwave-hydrothermal method

Tungsten oxide (WO₃) nanoplates were synthesized by a 270 W microwave-hydrothermal reaction of Na₂WO₄·2H₂O and citric acid (C₆H₈O₇·H₂O) in deionized water. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) were used to reveal the synthesis of WO₃ complete rectangular nanoplates in the solution of 0.2 g citric acid for 180 min, with O-W-O FTIR stretching modes at 819 and 741 cm⁻¹, and two prominent O-W-O Raman stretching modes at 804 and 713 cm⁻¹. The 2.71 eV indirect energy gap, and 430-460 nm blue emission wavelength range of WO₃ complete rectangular nanoplates were determined using UV-visible and photoluminescence (PL) spectrometers. The formation mechanism was also proposed according to the experimental results.     

Rheological phase reaction synthesis and electrochemical performance of Li3V2(PO4)3/carbon cathode for lithium ion batteries

Monoclinic lithium vanadium phosphate/carbon (Li₃V₂(PO₄)₃/C) cathode has been synthesized for applications in lithium ion batteries, via a rheological phase reaction (RPR) method. The sample is characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). This material exhibits high initial discharge capacity of 189 and 177 mAh g⁻¹ at 0.1 and 0.2 C between 3.0 and 4.8 V, respectively. Moreover, it displays good fast rate performance, which discharge capacities of 140, 133, 129 and 124 mAh g⁻¹ can be delivered after 100 cycles between 3.0 and 4.8 V vs. Li at a different rate of 0.5, 1, 2 and 5 C, respectively. The electrochemical impedance spectroscopy (EIS) is also investigated.     

Structural and electrochemical characterization of SnOx thin films for Li-ion microbattery

SnO_x thin films were prepared by reactive radio frequency magnetron sputtering with different sputtering powers. X-ray photoelectron spectroscopy suggested that all the films have similar chemical stoichiometry as SnO_1.5. X-ray diffraction and transmission electro microscopy results showed that crystal size of the SnO_x thin films gradually increases with increase of sputtering power from 50 to 150 W. Cyclic voltammetry and galvanostatic charge/discharge cycling measurements indicated that the electrochemical properties of SnO_x films strongly rely on their crystal sizes as well as surface morphologies. The SnO_x film deposited at sputtering power of 120 W exhibits the best electrochemical performances. It could deliver a reversible capacity of 670 μAh cm⁻² μm⁻¹ at 50 μA cm⁻² in the voltage range of 0.1-1.2 V up to 50 cycles.     

Preparation and electrochemical studies of electrospun TiO2 nanofibers and molten salt method nanoparticles

The TiO₂ nanofibers and nanoparticles are prepared by electrospinning and molten salt method, respectively. The materials are characterized by X-ray diffraction scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and a thermal analysis. The SEM and TEM studies showed that fibers were of average diameter ∼100 nm and composed of nanocrystallites of size 10-20 nm. Electrochemical properties of the materials are evaluated using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. Cyclic voltammetric studies show a hysteresis (ΔV) between the cathodic and the anodic peak potentials for TiO₂ nanofibers and nanoparticles (sizes ∼15-30 nm) are in the range, 0.23-0.30 V and a redox couple Ti^4+/3+ around ∼1.74/2.0 V. Electrochemical cycling results revealed that the TiO₂ nanofibers have lower capacity fading compared to that of the nanoparticles. The capacity fading for 2-50 cycles was ∼23% for nanofibers, which was nearly one-third of that of corresponding nanoparticles (∼63%). We discussed the effect of particle size on hysteresis and cycling performance of TiO₂ nanoparticles. Impedance analysis of TiO₂ nanofibers and nanoparticles during first discharge cycle is analyzed and interpreted.     

The Li3V2(PO4)3/C composites with high-rate capability prepared by a maltose-based sol-gel route

The carbon coated monoclinic Li₃V₂(PO₄)₃ (LVP/C) cathode materials are synthesized via a sol-gel method using oxalic acid as a chelating reagent and maltose as a carbon source. The effect of carbon content on the synthesis of LVP/C composites is investigated using X-ray diffraction, scanning electron microscopy, galvanostatic charge/discharge and DC resistance measurements. The results show that, among the LVP/C powders with different carbon content (5.7, 9.6, 11.6 and 15.3 wt.%), the sample with 11.6 wt.% carbon content gives rise to the corresponding (LVP/C) ∥Li half cell with a low DC resistance and superior electrochemical performance, especially with excellent rate capability. Its discharge capacity decreases by only 7.2% from 125 mAh g⁻¹ at 0.5 C to 116 mAh g⁻¹ at 5 C between 3.0 and 4.3 V. The maltose-based sol-gel method is feasible for the preparation of LVP/C composites for high power lithium ion batteries.     

Lithium-deficient LiYMn2O4 spinels (0.9 ≤ Y < 1): Lithium content, synthesis temperature, thermal behaviour and electrochemical properties

Lithium-deficient Li_YMn₂O₄ spinels (LD-Li_YMn₂O₄) with nominal composition (0.9 ≤ Y < 1) have been synthesized by melt impregnation from Mn₂O₃ and LiNO₃ at temperatures ranging from 700 °C to 850 °C. X-ray diffraction data show that LD-Li_YMn₂O₄ spinels are obtained as single phases in the range Y = 0.975-1 at 700 °C and 750 °C. Morphological characterization by transmission electron microscopy shows that the particle size of LD-Li_YMn₂O₄ spinels increases on decreasing the Li-content. The influence of the Li-content and the synthesis temperature on the thermal and electrochemical behaviours has been systematically studied. Thermal analysis studies indicate that the temperature of the first thermal effect in the differential thermal analysis (DTA)/thermogravimetric (TG) curves, T_C1, linearly increases on decreasing the Li-content. The electrochemical properties of LD-Li_YMn₂O₄ spinels, determined by galvanostatic cycling, notably change with the synthesis conditions. So, the first discharge capacity, Q_disch., at C rate increases on rising the Li-content and the synthesis temperature. The sample Li_0.975Mn₂O₄ synthesized at 700 °C has a Q_disch. = 123 mAh g⁻¹ and a capacity retention of 99.77% per cycle. This LD-Li_YMn₂O₄ sample had the best electrochemical characteristics of the series.     

Pulsed laser deposited FeOF as negative electrodes for rechargeable Li batteries

FeOF thin film has been successfully fabricated by reactive pulsed laser deposition for the first time, and its electrochemical behavior was examined as a negative electrode active material in lithium-ion batteries. The electrochemical properties of the as-deposited FeOF thin film during the first charging and discharging have been investigated by the galvanostatic cycling and cyclic voltammetry measurements. By using ex situ X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction measurements (SAED), it can be found that FeOF was initially decomposed into Fe⁰, LiF, and Fe₂O₃ after discharging to 1.0 V. The newly formed Fe₂O₃ is then subsequently reduced into Li₂O and Fe⁰ after further discharging to 0.01 V. In the subsequent cycle, the reduction peaks at 0.76 V and the oxidation-reduction peaks at 1.6 and 1.9 V could be attributed to the reversible decomposition and formation of Li₂O with the conversion reaction of Fe₂O₃ into Fe.     

Structure and electrochemical behavior of lithium vanadate materials for lithium batteries

New vanadate compounds having the molecular structure Li_xMg_1−xV_2−xMo_xO₆ (0 ≤ x ≤ 1) were studied. Six samples were prepared by sol-gel process from precursor using the following ratios of x = 0, 0.2, 0.4, 0.6, 0.8 and 1, respectively. These samples were labeled S1, S2, S3, S4, S5 and S6. The final process of firing occurred at 750 °C for 18 h in air. The prepared materials were characterized by XRD, SEM, IR, electron spin resonance (ESR) and magnetic measurements. The morphologies of S1, S2, S5 and S6 are prismatic as they have monoclinic crystal structures. S3 and S4 differ in the crystal morphology from the other previous samples due to their triclinic crystal lattice structure. IR spectra revealed that the bond lengths of the vanadyl groups ν_VO, ν_{sy V-O} and σ_V-O increase in the same direction from S1 to S6. The data of the ESR explain the existence of V⁴⁺ beside V⁵⁺ in S1, S4 and S6 and also presence of Mo⁵⁺ with Mo⁶⁺ in S4 and S6. S4 exhibited better magnetic susceptibility and saturated magnetization than the other samples. The first specific discharge capacities of the samples were performed. S4 showed the maximum specific capacity of 265 mAh g⁻¹ in comparison with the other samples. Cyclic voltammogram of S4 exhibited the highest current intensity in comparison with the other samples. This sample showed two peaks at 0.53 and 1.3 V versus Li/Li⁺ characterizing double de-insertions of two lithium atoms from Li_1.6Mg_0.4V_1.4Mo_0.6O_6−x and Li_0.6Mg_0.4V_1.4Mo_0.6O₆, respectively. Also, two additional peaks were characterized for the oxidation of Mo⁵⁺ to Mo⁶⁺ and V⁴⁺ to V⁵⁺ at 3.5 and 4 V, respectively.     

High capacity three-dimensional ordered macroporous CoFe2O4 as anode material for lithium ion batteries

A three-dimensional ordered macroporous (3DOM) cobalt ferrite (CoFe₂O₄) was prepared using polystyrene (PS) colloidal crystal template. The scanning electron microscopy (SEM) and the transmission electron microscopy (TEM) micrographs showed that the as-prepared CoFe₂O₄ material had a typical 3DOM structure, which was constructed with about 130 nm-sized macropores and 10-20 nm-sized walls. The obtained CoFe₂O₄ material had a specific surface area of 66.67 m² g⁻¹, and could deliver a relatively high capacity of 702 mAh g⁻¹ (about double that of graphite) at a current density of 0.2 mA cm⁻² after 30 cycles. Owing to the 3DOM nanoarchitecture, the as-prepared CoFe₂O₄ electrode exhibited a good rate performance. The results suggest a promising application of the 3DOM CoFe₂O₄ as anode material for lithium ion batteries.     

Efficient microwave hydrothermal synthesis of nanocrystalline orthorhombic LiMnO2 cathodes for lithium batteries

Rod-like orthorhombic LiMnO₂ nanocrystals were successfully synthesized using temperature-controlled microwave hydrothermal route (TCMH) in a short time (30 min) at a temperature as low as 160 °C. o-LiMnO₂ obtained by two different methods was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemistry test. SEM revealed that the product obtained in case of TCMH was rod-like with a diameter of 40 nm, while the nanoparticles with 200 nm diameter were obtained by traditional hydrothermal route (TH). The dramatic formation of o-LiMnO₂ in the microwave hydrothermal field influenced the morphology and crystal structure of the final products. The formation and preferred growth orientation mechanism of o-LiMnO₂ in the microwave irradiation process was discussed. Electrochemistry performance exhibited that the as-synthesized o-LiMnO₂ nanorods reached the maximum discharge capacity of 194.2 mAh g⁻¹ at 0.1 C rate after several cycles between 2.2 and 4.4 V vs. Li⁺/Li at room temperature, which was higher than the electrochemical performance of o-LiMnO₂ obtained by TH. The experimental results showed that the TCMH method provided an effective way for preparing o-LiMnO₂ cathode material in lithium-ion batteries.     

Electrochemical characterization of amorphous LiFe(WO4)2 thin films as positive electrodes for rechargeable lithium batteries

Amorphous LiFe(WO₄)₂ thin films have been fabricated by radio-frequency (R.F.) sputtering deposition at room temperature. The as-deposited and electrochemically cycled thin films are, respectively, characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectra techniques. An initial discharge capacity of 198 mAh/g in Li/LiFe(WO₄)₂ cells is obtained, and the electrochemical behavior is mostly preserved in the following cycling. These results identified the electrochemical reactivity of two redox couples, Fe³⁺/Fe²⁺ and W⁶⁺/W^x+ (x = 4 or 5). The kinetic parameters and chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry and alternate-current (AC) impedance measurements. All-solid-state thin film lithium batteries with Li/LiPON/LiFe(WO₄)₂ layers are fabricated and show high capacity of 104 μAh/cm² μm in the first discharge. As-deposited LiFe(WO₄)₂ thin film is expected to be a promising positive electrode material for future rechargeable thin film batteries due to its large volumetric rate capacity, low-temperature fabrication and good electrode/electrolyte interface.     

Influence of composite LiCl-KCl molten salt on microstructure and electrochemical performance of spinel Li4Ti5O12

A series of spinel Li₄Ti₅O₁₂ samples were synthesized via a composite molten-salt method (CMSM) using the mixtures of LiCl and KCl with different L values (L is defined as the molar ratio of LiCl:KCl) as the reaction media. It is found that the melting point of the composite molten salt can effectively influence the formation of particles, and leads to different electrochemical performances of the as-prepare Li₄Ti₅O₁₂. The investigations of X-ray diffraction (XRD), particle size distribution (PSD), Brunauer-Emmet-Teller (BET) surface area, and scanning electron microscopy (SEM) indicate that the as-prepared Li₄Ti₅O₁₂ with L = 1.5 is a pure phase, and has uniform homogeneous octahedral shape particles, rather narrow PSD, and high BET surface area. Electrochemical tests show that the optimized Li₄Ti₅O₁₂ with L = 1.5 has an initial discharge capacity of 169 mAh g⁻¹ and an initial charge-discharge efficiency of 94% at 0.2 C rate, and achieves good rate performances from 0.2 C to 5 C.     

PEG-directed microwave-assisted hydrothermal synthesis of spherical α-Ni(OH)2 and NiO architectures

Spherical α-Ni(OH)₂ architectures were synthesized by the microwave-assisted hydrothermal technique using PEG-6000 as the surfactant. NiO architectures with similar morphology were obtained by a simple thermal decomposition process of the precursor α-Ni(OH)₂ at 400 °C for 2 h and were confirmed by the X-ray diffraction (XRD) analysis. Scanning electron microscopy (SEM) revealed that the synthesized spherical α-Ni(OH)₂ and NiO architectures were composed of stacked lamellar sheets and transmission electron microscopy (TEM) showed that the α-Ni(OH)₂ and NiO architectures were polycrystalline. The effect of the PEG-6000 concentration on particle size was investigated and it was found that the average particle size of α-Ni(OH)₂ architectures decreased from 4.689 μm at C_PEG=2 mmol L⁻¹ to 3.907 μm at C_PEG=4 mmol L⁻¹, and the corresponding average particle size of NiO decreased from 2.818 μm to 2.492 μm. The optical absorption band gap of NiO architectures was determined to be about 2.7–3.0 eV by UV–vis spectroscopy.     

Formulation development and optimization of alpha ketoglutarate nanoparticles for cyanide poisoning

The purpose of this research work was to formulate and evaluate alpha ketoglutarate nanoparticles as dry powder inhaler for treatment of cyanide poisoning. Non-polymeric particles were prepared by nano-precipitation technique using various stabilizers. Selection of co-solvent and stabilizer was a key to produce stabilized particles. A combination of lutrol F68 and PVA as a crystal growth inhibitor seems to be best in achieving minimum particle size of 110.2 nm. On the basis of preliminary trials a Box-Behnken statistical design was employed to study the effect of independent variables, drug concentration (X₁), stirring speed (X₂), stirring time (X₃), PVA concentration (X₄), poloxomer concentration (X₅) and volume of co-solvent (X₆) on average particle size. Particle size varied from 110 to 875 nm depending upon the significant terms. Optimized formulation was predicted at drug concentration (50 μg/ml), stirring speed (640 rpm), stirring time (1 min), PVA concentration (1%), poloxomer concentration (1.69%) and volume of co-solvent (30 ml) with 104.6% experimental validity. The nanosized particles were further characterized by X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FT-IR) analysis. The results of particle characterization indicate that there was no physical disparity when compared with the commercial α-KG sample.     

Synthesis of hollandite-type LixMnO2 by Li ion-exchange in molten salt and lithium insertion characteristics

The Li⁺ ion-exchange reaction of K⁺-type α-K_0.14MnO_1.93·nH₂O containing different amounts of water molecules (n = 0-0.15) with a large (2 × 2) tunnel structure has been investigated in a LiNO₃-LiCl molten salt at 300 °C. The Li⁺ ion-exchanged products were examined by chemical analysis, X-ray diffraction, and transmission electron microscopy measurements. The K⁺ ions and the hydrogens of the water molecules in the (2 × 2) tunnels of α-MnO₂ were exchanged by Li⁺ ions in the molten salt, resulting in the Li⁺-type α-MnO₂ containing different amounts of Li⁺ ions and lithium oxide (Li₂O) in the (2 × 2) tunnels with maintaining the original hollandite structure.The electrochemical properties and structural variation with initial discharge and charge-discharge cycling of the Li⁺ ion-exchanged α-MnO₂ samples have been investigated as insertion compounds in the search for new cathode materials for rechargeable lithium batteries. The Li⁺ ion-exchanged α-MnO₂ samples provided higher capacities and higher Li⁺ ion diffusivity than the parent K⁺-type materials on initial discharge and charge-discharge cyclings, probably due to the structural stabilization with the existence of Li₂O in the (2 × 2) tunnels.     

Enhanced electrochemical performance of nano-sized LiFePO4/C synthesized by an ultrasonic-assisted co-precipitation method

A simple and effective method, the ultrasonic-assisted co-precipitation method, was employed to synthesize nano-sized LiFePO₄/C. A glucose solution was used as the carbon source to produce in situ carbon to improve the conductivity of LiFePO₄. Ultrasonic irradiation was adopted to control the size and homogenize the LiFePO₄/C particles. The sample was characterized by X-ray powder diffraction, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). FE-SEM and TEM show that the as-prepared sample has a reduced particle size with a uniform size distribution, which is around 50 nm. A uniform amorphous carbon layer with a thickness of about 4-6 nm on the particle surface was observed, as shown in the HRTEM image. The electrochemical performance was demonstrated by the charge-discharge test and electrochemical impedance spectra measurements. The results indicate that the nano-sized LiFePO₄/C presents enhanced discharge capacities (159, 147 and 135 mAh g⁻¹ at 0.1, 0.5 and 2 C-rate, respectively) and stable cycling performance. This study offers a simple method to design and synthesis nano-sized cathode materials for lithium-ion batteries.     

Effects of neodymium aliovalent substitution on the structure and electrochemical performance of LiFePO4

LiFe_1−xNd_xPO₄/C (x = 0-0.08) cathode material was synthesized using a solid-state reaction. The synthesis conditions were optimized by thermal analysis of the precursor and magnetic properties of LiFePO₄/C. The structure and electrochemical performances of the material were studied using XRD, FE-SEM, EDS, electrochemical impedance spectroscopy and galvanostatic charge-discharge. The results show that a small amount of aliovalent Nd³⁺ ion-dopant substitution on Fe²⁺ ions can effectively reduce the particle size of LiFePO₄/C. Cell parameters of LiFe_1−xNd_xPO₄ (x = 0.04-0.08) were calculated, and the results showed that LiFe_1−xNd_xPO₄/C had the same olivine structure as LiFePO₄. LiFe_0.4Nd_0.6PO₄/C delivers the discharge capacity of 165.2 mAh g⁻¹ at rate of 0.2 C and the capacity retention rate is 92.8% after 100 cycles. Charge-transfer resistance decreases with the addition of glucose and Nd³⁺ ions. Poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) was synthesized and PZS nanorods were used as a carbon source to coat LiFePO₄. All of the results show that aliovalent doping substitution of Fe in LiFePO₄ is well tolerated.