Preparation and electrochemical properties of Li-rich spinel-type lithium manganate coated LiMn2O4

Li-rich spinel-type lithium manganate (SC) coated LiMn₂O₄ composites were prepared and characterized by XRD, SEM, FT-IR, ICP, etc. Their charge/discharge behaviors were studied between 3.0 and 4.3 V at 40 mA g⁻¹ under room temperature, and the results showed that SC coated on surface of LiMn₂O₄ could improve cycling stability of composite electrodes. The composite (S1) containing 4.8 wt% of SC exhibited noticeably improved cycling stability, whereas the initial specific capacity was very close to that of LiMn₂O₄.     

Alanine-assisted low-temperature combustion synthesis of nanocrystalline LiMn2O4 for lithium-ion batteries

Nanocrystalline LiMn₂O₄ powders have been synthesized by combustion process in a single step using a novel fuel, l-alanine. Thermogravimetric analysis and differential thermal analysis of the gel indicate a sharp combustion at a temperature as low as 149 °C. Quantitative phase analysis of X-ray diffraction data shows about 97% of phase purity in the as-synthesized powder, which on further calcination at 700 °C becomes single phase LiMn₂O₄. High Brunauer, Emmett, and Teller surface area values obtained for ash (53 m²/g) and calcined powder (23 m²/g) indicate the ultrafine nature of the powder. Average crystallite size is found to be ∼60-70 nm from X-ray diffraction analysis and transmission electron microscopy. Fourier transformed infra-red spectrum shows two strong bands at 615 and 511 cm⁻¹ originating from asymmetrical stretching of MnO₆ octahedra. A nominal composition of Li_0.88 Mn₂O₄ is calculated from the inductive coupled plasma analysis. From UV-vis spectroscopy, an optical band gap of 1.43 eV is estimated which is assigned to a transition between t_2g and e_g bands of Mn 3d. Electrochemical charge-discharge profiles show typical LiMn₂O₄ behavior with a specific capacity of 76 mAh/g.     

Cr modified LiMn2O4 spinel intercalation cathodes through oxalic acid assisted sol-gel method for lithium rechargeable batteries

To improve the cycle performance of eco-friendly and cost-effective spinel LiMn₂O₄ as the cathode of 4 V class Li secondary batteries, the spinel phase LiCr_xMn_2 − xO₄ (x = 0.01-0.20) was synthesized by soft chemistry method using oxalic acid as chelating agent. The present technique results in better homogeneity, good surface morphology, shorter heat treatment time, sub-micron sized particles, good agglomeration and better crystallinity. Electrochemical studies were monitored in the potential range of 3-4.5 V. The present paper reveals that chromium substituted manganese spinel improves the structural stability of the parent material.     

Synthesis and performance of LiMn0.7Fe0.3PO4 cathode material for lithium ion batteries

Pure and carbon-containing olivine LiMn_0.7Fe_0.3O₄ were synthesized at 600 °C by the method of solid-state reaction. Structure, surface morphology and charge/discharge performance of LiMn_0.7Fe_0.3O₄ were characterized by X-ray diffraction, scanning electron microscopy, and electrochemical measurement, respectively. The prepared materials with and without carbon both show the single olivine structure. The morphologies of primary particles are greatly affected by the addition of carbon. Large particles (500-1000 nm) and densely sintered blocks were observed in pure LiMn_0.7Fe_0.3PO₄, which made the insertion and extraction of lithium ions difficult. Battery made from this sample can not charge and discharge effectively. The carbon-containing LiMn_0.7Fe_0.3PO₄ has a small particle size (100-200 nm) and a regular appearance. This material demonstrates high reversible capacity of about 120 mAh g⁻¹, perfect cycling performance, and excellent rate capability. It is obvious that the addition of carbon plays an important role in restricting the particle size of the material, which helps to prepare LiMn_0.7Fe_0.3PO₄ with excellent electrochemical performance. The electrochemical reaction resistance is much lower in the partly discharged state than in the fully charged or fully discharged state by the measurement of ac impedance for carbon-containing LiMn_0.7Fe_0.3PO₄. It is indicated that the mixed-valence of Fe³⁺/Fe²⁺ or Mn³⁺/Mn²⁺ is beneficial to the transfer of electron which happens between the interface.     

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.     

Preparation and characterization of nanostructured NiO/MnO2 composite electrode for electrochemical supercapacitors

Nanostructured nickel-manganese oxides composite was prepared by the sol-gel and the chemistry deposition combination new route. The surface morphology and structure of the composite were characterized by scanning electron microscope and X-ray diffraction. The as-synthesized NiO/MnO₂ samples exhibit higher surface area of 130-190 m² g⁻¹. Cyclic voltammetry and galvanostatic charge/discharge measurements were applied to investigate the electrochemical performance of the composite electrodes with different ratios of NiO/MnO₂. When the mass ratio of MnO₂ and NiO in composite material is 80:20, the specific capacitance value of NiO/MnO₂ calculated from the cyclic voltammetry curves is 453 F g⁻¹, for pure NiO and MnO₂ are 209, 330 F g⁻¹ in 6 mol L⁻¹ KOH electrolyte and at scan rate of 10 mV s⁻¹, respectively. The specific capacitance of NiO/MnO₂ electrode is much larger than that of each pristine component. Moreover, the composite electrodes showed high power density and stable electrochemical properties.     

Synthesis and electrochemical properties of LiV3O8 phase

Lithium vanadium oxide was synthesized by a new method in which LiOH, V₂O₅ and NH₄OH were used as the starting materials to synthesize a precursor containing Li and V, and then obtain the resulting product by calcining the precursor. The LiV₃O₈ compound prepared by this synthesis method gave a good charge-discharge and cycle performance. A specific capacity of 258 mAh/g is obtained in the range of 1.8−4.0 V in the first cycle and 247 mAh/g in the eighth cycle.     

Enhanced cycling stability of microsized LiCoO2 cathode by Li4Ti5O12 coating for lithium ion battery

The effect of Li₄Ti₅O₁₂ (LTO) coating amount on the electrochemical cycling behavior of the LiCoO₂ cathode was investigated at the high upper voltage limit of 4.5 V. Li₄Ti₅O₁₂ (≤5 wt.%) is not incorporated into the host structure and leads to formation of uniform coating. The cycling performance of LiCoO₂ cathode is related with the amount of Li₄Ti₅O₁₂ coating. The initial capacity of the LTO-coated LiCoO₂ decreased with increasing Li₄Ti₅O₁₂ coating amount but showed enhanced cycling properties, compared to those of pristine material. The 3 wt.% LTO-coated LiCoO₂ has the best electrochemical performance, showing capacity retention of 97.3% between 2.5 V and 4.3 V and 85.1% between 2.5 V and 4.5 V after 40 cycles. The coulomb efficiency shows that the surface coating of Li₄Ti₅O₁₂ is beneficial to the reversible intercalation/de-intercalation of Li⁺. LTO-coated LiCoO₂ provides good prospects for practical application of lithium secondary batteries free from safety issues.     

Studies on LiNi0.7Al0.3−xCoxO2 solid solutions as alternative cathode materials for lithium batteries

A series of phase-pure Co- and Al-substituted lithium nickel oxide solid solutions of the composition LiNi_0.7Al_0.3−xCo_xO₂ with x=0.0, 0.1, 0.15, 0.2, and 0.3, has been synthesized by adopting urea-assisted combustion (UAC) route. The structure and the physico-electrochemical features of the doped materials have been evaluated through PXRD, FTIR, SEM, CV, and charge/discharge studies. The stabilization of Ni in the +3 state and the existence of enhanced 2D-layered structure without any cation mixing have been substantiated from XRD. The results of the XRD and FTIR studies have established the complete mixing of Al and Co with Ni, especially at the various levels and the combinations of the dopants attempted in the present study. The enhanced electrochemical performance of LiNi_0.7Al_0.3−xCo_xO₂ may be attributed to the “synergetic effect” resulting from the presence of both Al³⁺ and Co³⁺ dopants in the LiNiO₂ matrix. From CV studies, it was understood that the addition of 10% Co is effective in suppressing the phase transformation during Li⁺ intercalation process that leads to better electrochemical properties. The effect and the extent of substitution of Ni with Al and Co on the structural and electrochemical performance of LiNi_0.7Al_0.3−xCo_xO₂ are discussed elaborately in this communication.     

Fluorine-doped LiNi0.5Mn1.5O4 for 5 V cathode materials of lithium-ion battery

Fluorine-doped 5 V cathode materials LiNi_0.5Mn_1.5O_4−xF_x (0.05 ≤ x ≤ 0.2) have been prepared by sol-gel and post-annealing treatment method. The results from X-ray diffraction and scanning electron microscopy (SEM) indicate that the spinel structure changes little after fluorine doping, but the particle size varies with fluorine doping and the preparation conditions. The electrochemical measurements show that stable cycling performance can be obtained when the fluorine amount x is higher than 0.1, but the specific capacity is decreased and 4 V plateau capacity resulting from a conversion of Mn⁴⁺/Mn³⁺ remains. Moreover, influence of the particle size on the reversible capacity of the electrode, especially on the kinetic property, has been examined.     

Large-scale synthesis of Li1.2V3O8 as a cathode material for lithium secondary battery via a soft chemistry route

Layered Li_1.2V₃O₈ has been efficiently prepared via a sol-gel method. XRD and particle size analysis indicate that the final product with monoclinic structure consists of homogeneously distributed particles whose sizes are in a very narrow range. There are two different water molecules in the compound according to TGA and DTA. The structural water works as a pillar in the structure and is lost at higher temperature than the combined water. The as-prepared material was also compared with the one synthesized from the conventional solid-state method in terms of their morphology, electrochemistry capacity and electrodynamic characteristics. As a result, the Li_1.2V₃O₈ obtained at 300 °C for 10 h has excellent electrochemical properties. A high-first discharge capacity of 286.4 mAh/g was observed at a current rate of C/5 between 1.7 and 3.8 V and the structure of Li_1.2V₃O₈ remains stable in the subsequent cycles. EIS calculation suggests a better diffusion path for lithium ions in as-prepared material than in the solid-state compound.     

One-pot syntheses of Li3V2(PO4)3/C cathode material for lithium ion batteries via ascorbic acid reduction approach

Monoclinic Li₃V₂(PO₄)₃/C composite synthesized by ascorbic acid reduction method is examined as a cathode material for Li-ion batteries. Transmission electron microscopy (TEM) images show that the nano-size particles are obtained. The reversible capacity of Li₃V₂(PO₄)₃/C prepared with LiOH and H₃PO₄ is 141.2 mAh g⁻¹ after 100 cycles at 1C discharge rate between 3 V and 4.8 V, and the retention rates of discharge capacity is 93.4%. Ascorbic acid plays not only as reduction reagent, but also as carbon sources. This strategy shortens the time of solid state reaction and facilitates the procedure of synthesis. Effects of different precursors materials on the performance of the Li₃V₂(PO₄)₃/C are investigated.     

Metallization of La1/3NbO3 by lithium incorporation

Lithium ion was successfully introduced into La_1/3NbO₃ with an A-site-deficient perovskite-type structure. The crystal structure and transport properties of La_1/3Li_xNbO₃ were investigated as a function of Li content (x = 0-0.59). The lattice parameters of La_1/3Li_xNbO₃ with an orthorhombic cell were enlarged with increasing Li content for x ≤ 0.3, and the structure was transformed to a pseudo-tetragonal cell for x = 0.44. The temperature dependence of electrical resistivity gradually changed from insulating to metallic with increasing x, and thermoelectric power measurement indicated that the carriers were electrons. In X-ray photoelectron spectra of the incorporated samples, Nb_3d⁴⁺ peaks appeared in addition to Nb_3d⁵⁺ peaks, which was consistent with the change of the transport properties. In spite of the success of metallization, no diamagnetic signal indicative of supercondcutivity was observed in La_1/3Li_0.59NbO₃ down to 1.8 K.     

CTAB-assisted sol-gel synthesis of Li4Ti5O12 and its performance as anode material for Li-ion batteries

A simple CTAB-assisted sol-gel technique for synthesizing nano-sized Li₄Ti₅O₁₂ with promising electrochemical performance as anode material for lithium ion battery is reported. The structural and morphological properties are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemical performance of both samples (with and without CTAB) calcined at 800 °C is evaluated using Swagelok™ cells by galvanostatic charge/discharge cycling at room temperature. The XRD pattern for sample prepared in presence of CTAB and calcined at 800 °C shows high-purity cubic-spinel Li₄Ti₅O₁₂ phase (JCPDS # 26-1198). Nanosized-Li₄Ti₅O₁₂ calcined at 800 °C in presence of CTAB exhibits promising cycling performance with initial discharge capacity of 174 mAh g⁻¹ (∼100% of theoretical capacity) and sustains a capacity value of 164 mAh g⁻¹ beyond 30 cycles. By contrast, the sample prepared in absence of CTAB under identical reaction conditions exhibits initial discharge capacity of 140 mAh g⁻¹ (80% of theoretical capacity) that fades to 110 mAh g⁻¹ after 30 cycles.     

Preparation and characterization of nanostructured MWCNT-TiO2 composite materials for photocatalytic water treatment applications

Nanoscale composite materials containing multi-walled carbon nanotubes (MWCNT) and titania were prepared by using a modified sol-gel method. The composites were comprehensively characterized by thermogravimetric analysis, nitrogen adsorption-desorption isotherm, powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis absorption spectroscopy. The analysis revealed the presence of titania crystallites of about 7.5 nm aggregated together with MWCNT in particles of 15-20 nm of diameter. The photoactivity of the prepared materials, under UV or visible irradiation, was tested using the conversion of phenol from model aqueous solutions as probe reaction. A synergy effect on the photocatalytic activities observed for the composite catalysts was discussed in terms of a strong interphase interaction between carbon and TiO₂ phases by comparing the different roles of MWCNT in the composite materials.     

Electrochemical characterizations of surface modified LiMn2O4 cathode materials for high temperature lithium battery applications

LiMn₂O₄ spinel cathode materials were coated with 2.0 wt.% of La₂O₃ by polymeric process followed by calcinations at 400 °C and 800 °C for 6 h in air. The surface coated LiMn₂O₄ cathode materials were physically characterized using X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy and X-ray photoelectron spectroscopy. La₂O₃-coated LiMn₂O₄ coating did not affect the crystal structure and space group Fd3m of the cathode materials compared to the uncoated LiMn₂O₄. The surface morphology and particle agglomeration were investigated and compact coating layer on the surface of the core materials. La₂O₃ was completely coated over the surface of the LiMn₂O₄ core cathode materials. The galvanostatic charge and discharge of the La₂O₃-coated LiMn₂O₄ cathode materials were carried out at 0.1 mA/g in the range of 3.0 and 4.5 V at 30 °C and 60 °C. Based on the results, La₂O_3-coated spinel LiMn₂O₄ cathode at 800 °C has improved the structural stability, high reversible capacity and excellent electrochemical performances of the rechargeable lithium batteries.     

Structural properties of Al2O3-La2O3 binary oxides prepared by sol-gel

The structural properties of La₂O₃ and Al₂O₃-La₂O₃ binary oxides prepared by sol-gel were studied by XRD, HRTEM and UV-vis. The binary oxides with high lanthana contents show an amorphous structure after calcination at 650 °C. At calcination temperatures higher than 1000 °C there is a phase transformation from the amorphous state to the crystalline LaAlO₃ with a perovskite structure. The structure of La₂O₃ is consistent with the hexagonal system; however, some crystalline microdomains with a monoclinic structure were detected by HRTEM. Islands of La₂O₃ and LaAl₁₁O₁₈ phases were detected at high lanthana concentration in the binary oxide. The modification in the coordination shell of the Al³⁺ cations due to the interaction with La³⁺ cations confirms the formation of phases with a perovskite structure and the presence of islands of the LaAl₁₁O₁₈ phase.     

Sol-gel derived CaCu3Ti4O12 ceramics: Synthesis, characterization and electrical properties

The giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) has been synthesized by sol-gel method, for the first time, using nitrate and alkoxide precursor. The electrical properties of CCTO ceramics, showing an enormously large dielectric constant ? ∼ 60,000 (100 Hz at RT), were investigated in the temperature range from 298 to 358 K at 0, 5, 10, 20, and 40 V dc. The phases, microstructures, and impedance properties of final samples were characterized by X-ray diffraction, scanning electron microscopy, and precision impedance analyzer. The dielectric permittivity of CCTO synthesized by sol-gel method is at least three times of magnitude larger than that synthesized by other low-temperature method and solid-state reaction method. Furthermore, the results support the internal barrier layer capacitor (IBLC) model of Schottky barriers at grain boundaries between semiconducting grains.     

Synthesis of ribbon type carbon nanostructure using LiFePO4 catalyst and their electrochemical performance

Ribbon type of carbon nanostructure has been synthesized by chemical vapor deposition using a new catalyst (LiFePO₄) introduced for the first time and its electrochemical behavior has been determined from charge/discharge characteristics. The synthesized material characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and by Raman spectroscopy confirms the graphitic structure and ribbon type morphology of material. The performance of the single cell using purified carbon nanoribbon as the anode has been studied and the reversible lithium intercalation capacity has been found about 345 mAh/g, of which 335 mAh/g remain after 14th cycle. The columbic efficiency has been stabilized at approximately 98% from the 5th cycle.     

Preparation of grape-like Bi2O3/Ti photoanode and its visible light activity

Compact and grape-like bismuth oxide (Bi₂O₃) coated titania (Ti) anode was prepared by oxalic acid (H₂C₂O₄) etching, electrodeposition and calcination in order to explore its photoelectrocatalytic activities. The Bi₂O₃ coating was demonstrated to be full of pores, and a good combination between Bi₂O₃ layer and honeycomb-like Ti substrate was observed by scanning electron microscopy. The characteristic morphology of Bi₂O₃ coating indicated that the electrode is stable during degradation. The Bi₂O₃/Ti electrode was used in oxidative degradation of Acid Orange 7 by electrolysis, photocatalytic oxidation and photoelectrocatalytic oxidation processes. The pseudo-first order kinetics parameter (K_app) of photoelectrocatalytic process was 1.15 times of the sum of electrolysis and photocatalytic oxidation under visible light irradiation at 420 nm. The results indicated that the synergy of electrolysis and photocatalysis lead to an excellent photoelectrocatalytic property of the Bi₂O₃/Ti electrode.