Preparation of LiFePO4/C composite powders by ultrasonic spray pyrolysis followed by heat treatment and their electrochemical properties

LiFePO₄ powders could be successfully prepared from a precursor solution, which was composed of Li(HCOO)·H₂O, FeCl₂·4H₂O and H₃PO₄ stoichiometrically dissolved in distilled water, by ultrasonic spray pyrolysis at 500 °C followed by heat treatment at sintering temperatures ranging from 500 to 800 °C in N₂ + 3% H₂ gas atmosphere. Raman spectroscopy revealed that α-Fe₂O₃ thin layers were formed on the surface of as-prepared LiFePO₄ powders during spray pyrolysis, and they disappeared after sintering above 600 °C. The LiFePO₄ powders prepared at 500 °C and then sintered at 600 °C exhibited a first discharge capacity of 100 mAh g⁻¹ at a 0.1 C charge-discharge rate. To improve the electrochemical properties of the LiFePO₄ powders, LiFePO₄/C composite powders with various amounts of citric acid added were prepared by the present method. The LiFePO₄/C (1.87 wt.%) composite powders prepared at 500 °C and then sintered at 800 °C exhibited first-discharge capacities of 140 mAh g⁻¹ at 0.1 C and 84 mAh g⁻¹ at 5 C with excellent cycle performance. In this study, the optimum amount of carbon for the LiFePO₄/C composite powders was 1.87 wt.%. From the cyclic voltammetry (CV) and AC impedance spectroscopy measurements, the effects of carbon addition on the electrochemical properties of LiFePO₄ powders were also discussed.     

Microporous carbon derived from polyaniline base as anode material for lithium ion secondary battery

Microporous carbon with large surface area was prepared from polyaniline base using K₂CO₃ as an activating agent. The physicochemical properties of the carbon were characterized by scanning electron microscope, X-ray diffraction, Brunauer-Emmett-Teller, elemental analyses and X-ray photoelectron spectroscopy measurement. The electrochemical properties of the microporous carbon as anode material in lithium ion secondary battery were evaluated. The first discharge capacity of the microporous carbon was 1108 mAh g⁻¹, whose first charge capacity was 624 mAh g⁻¹, with a coulombic efficiency of 56.3%. After 20 cycling tests, the microporous carbon retains a reversible capacity of 603 mAh g⁻¹ at a current density of 100 mA g⁻¹. These results clearly demonstrated the potential role of microporous carbon as anode for high capacity lithium ion secondary battery.     

A PEG assisted sol-gel synthesis of LiFePO4 as cathodic material for lithium ion cells

In order to obtain fine-particle LiFePO₄ with excellent electrochemical performance, LiFePO₄/C powders were synthesized by a poly(ethylene glycol) (PEG) assisted sol-gel method. All samples were characterized by X-ray powder diffraction and scanning electron microscopy, and their electrochemical properties were investigated by cycle voltammograms and charge-discharge tests. The sample, synthesized with the n_PEG/n_LFP = 1:1 under sintering temperature of 600 °C, possesses the global morphology and particle size of about 100 nm. This sample delivers the first discharge capacity of 162 mAh g⁻¹, i.e. 95.3% of the theoretical capacity, at the 15 mA g⁻¹ discharge current between 2.5 and 4.0 V (versus Li/Li⁺). The sample also displays a robust rate capability and stable cycle-life. The improved electrochemical performance originates mainly from the fine particle of nanometric dimension, regular global morphology and uniform dispersing in the product as well as the increased electronic conductivity by carbon coating.     

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.     

Low temperature synthesis of Fe3O4 nanoparticles and its application in lithium ion batteries

Well dispersed Fe₃O₄ nanoparticles with mean size about 160 nm are synthesized by a simple chemical method at atmosphere pressure. The products are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ nanoparticles as anode electrodes of lithium ion batteries are studied by conventional charge/discharge tests, showing initial discharge and charge capacities of 1140 mAh g⁻¹ and 1038 mAh g⁻¹ at a current density of 0.1 mA cm⁻². The charge and discharge capacities of Fe₃O₄ electrode decrease along with the increase of cycle number, arriving at minimum values near the 70th cycle. After that, the discharge and charge capacities of Fe₃O₄ electrode begin to increase along with the increase of cycle number, arriving at 791 and 799 mAh g⁻¹ after 393 cycles. The morphology and size of the electrode after charge and discharge tests are characterized by SEM, which exhibits a large number of dispersive particles with mean size about 150 nm.     

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.     

Preparation of hexagonal-MoO3 and electrochemical properties of lithium intercalation into the oxide

Metastable hexagonal molybdenum trioxide has been synthesized by chemical precipitation and hydrothermal treatment at low temperature. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize the product, which has a unique hexagonal prism-like morphology. Excellent electrochemical performances were exhibited: the first reversible discharge specific capacity can reach 402 mAh g⁻¹ versus Li metal at 0.1 mA cm⁻² (voltage range 1.2-4.0 V).     

Study on preparation of NiOOH by a new catalytic electrolysis method

The present paper reports a new catalytic electrolysis method to prepare NiOOH. KMnO₄ is proposed as a catalyst to play the role of electron-transfer medium in the electrolysis preparation of NiOOH for the first time. Through the self-redox reaction of KMnO₄, the highly efficient electron-transfer process between the electrolyte and the electrode of the spherical Ni(OH)₂ is realized, thus resulting in a high electrolytic efficiency and short electrolysis time. The mechanism of catalytic electrolysis is preliminarily discussed. The experimental results show that the electrode prepared with the NiOOH powders by catalytic electrolysis offers a discharge capacity of 267 mAh g⁻¹ at a current density of 120 mA g⁻¹ and exhibits good cycling performance.     

High rate performance of novel cathode material Li1.33Ni1/3Co1/3Mn1/3O2 for lithium ion batteries

Li_1.33Ni_1/3Co_1/3Mn_1/3O₂ with highly ordered structure has been successfully synthesized via a simple co-precipitation process. Charge–discharge tests showed that the initial discharge capacities are 153.0 mAh g⁻¹ and 128.9 mAh g⁻¹ at 5 C (1000 mA g⁻¹) and 10 C (2000 mA g⁻¹) between 2.5 and 4.5 V, respectively. The average full-charge time of this material is less than 12 min at 5 C and 6 min at 10 C. The electrode material composed of the prepared showed a better cyclability. The excellent high rate performance is attributed to the improved ordered layered structure and the electrical conductivity. The excess Li shorten Li⁺ diffusion distance between these submicron and nano-scaled particles. The results show that Li_1.33Ni_1/3Co_1/3Mn_1/3O₂ cathode material has potential application in lithium ion batteries.     

Nano-sized Li-Fe composite oxide prepared by a self-catalytic reverse atom transfer radical polymerization approach as an anode material for lithium-ion batteries

A novel Self-catalytic Reverse Atom Transfer Radical Polymerization (RATRP) approach that can provide the radical initiator and the catalyst by the system itself is used to synthesize a nano-sized Li-Fe composite oxide powder in large scale. Its crystalline structure and morphology have been characterized by X-ray diffraction and scanning electron microscopy. The results reveal that the composite is composed of nano-sized LiFeO₂ and Fe₃O₄. Its electrochemical properties are evaluated by charge/discharge measurements. The results show that the Li-Fe composite oxide is an excellent anode material for lithium-ion batteries with good cycling performance (1249 mAh g⁻¹ at 100th cycle) and outstanding rate capability (967 mAh g⁻¹ at 5 C). Such a self-catalytic RATRP approach provides a way to synthesize nano-sized iron oxide-based anode materials industrially with preferable electrochemical performance and can also be applied in other polymer-related area.     

Surfactant-free synthesis and electrochemical properties of chrysanthemum-like InVO4 hierarchical microstructures

Novel chrysanthemum-like hierarchical microstructures of orthorhombic InVO₄ were synthesized via a hydrothermal route without assistance of any template or organic additive. The chrysanthemum-like InVO₄ microstructures are built up of numerous nanobelts radially aligned around the spherical surface. Based on the structural feature of orthorhombic InVO₄ and the key role of the pH value, a probable mechanism of the etching-splitting growth process induced by H⁺ ions was proposed to explain the formation of InVO₄ microstructures. Furthermore, the chrysanthemum-like InVO₄ sample shows a high discharge capacity of 608.6 mAh g⁻¹ and acceptable capacity retention when used as an electrode material in lithium ion batteries. The pure orthorhombic phase and unique porous morphology play basic roles in the structural requirement to serve as transport paths for lithium ion.     

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.     

Preparation and electrochemical properties of lamellar MnO2 for supercapacitors

Lamellar birnessite-type MnO₂ materials were prepared by changing the pH of the initial reaction system via hydrothermal synthesis. The interlayer spacing of MnO₂ with a layered structure increased gradually when the initial pH value varied from 12.43 to 2.81, while the MnO₂, composed of α-MnO₂ and γ-MnO₂, had a rod-like structure at pH 0.63. Electrochemical studies indicated that the specific capacitance of birnessite-type MnO₂ was much higher than that of rod-like MnO₂ at high discharge current densities due to the lamellar structure with fast intercalation/deintercalation of protons and high utilization of MnO₂. The initial specific capacitance of MnO₂ prepared at pH 2.81 was 242.1 F g⁻¹ at 2 mA cm⁻² in 2 mol L⁻¹ (NH₄)₂SO₄ aqueous electrolyte. The capacitance increased by about 8.1% of initial capacitance after 200 cycles at a current density of 100 mA cm⁻².     

Preparation and electrochemical performance of LiFePO4/C composite with network connections of nano-carbon wires

LiFePO₄/C composite with network connections of nano-carbon wires was successfully prepared by using polyvinyl alcohol as carbon source. The composite was characterized by X-ray diffraction and transmission electron microscopic, and its electrochemical performance was investigated by galvanostatic charge and discharge tests. The experimental results show that LiFePO₄ grains are tightly connected by the network of nano-carbon wires. Moreover LiFePO₄/C composite exhibits high capacity of 168 mAh g⁻¹ applied 15 mA g⁻¹ current density (C/10), excellent cyclic ability and rate capability. When 1500 mA g⁻¹ current density (10C) was applied, the high discharge capacity of 129 mAh g⁻¹ has been obtained at room temperature.     

Nitrogen-containing carbons prepared from polyaniline as anode materials for lithium secondary batteries

Nitrogen-containing carbons have been prepared from polyaniline by carbonization and activation. Lithium storage performances of the carbons have been studied by galvanostatic charge/discharge. The carbon without activation shows a first discharge capacity of 729 mAh g^− 1, after activation, the capacity improved. The first discharge capacity of the carbon prepared by H₃PO₄ activation is 1083 mAh g^− 1, and that of the carbon prepared by KOH activation is as high as 2201 mAh g^− 1, whose reversible capacity is 1027 mAh g^− 1. To the carbon prepared by KOH activation, the first coulombic efficiency is just 47%, however, from the second cycle, the coulombic efficiency goes up rapidly to above 90%, the reversible capacity is still as high as 747 mAh g^− 1 after 20 cycles. It may be a promising candidate as an anode material for lithium secondary batteries.     

Electrochemical properties of facile emulsified LiV3O8 materials

LiV₃O₈ cathode materials are post-treated by a special emulsion method (termed “EM”) and then calcinated at different temperatures. The experimental results show that the structure of these oxides is different from LiV₃O₈ prepared by the solid-state reaction (acronym “STATE”) route, although their starting materials are identical. The EM product prepared at 500 °C exhibits a better electrochemical behavior than its counterpart prepared by traditional methods (STATE) or by EM at other temperatures. Its initial discharge capacity is 305 mAh g⁻¹, and it still maintains 250.2 mAh g⁻¹ after 100 cycles at 0.2 C at the voltage range of 1.8–4.0 V vs. Li/Li⁺.     

Synthesis of FePO4 cathode material for lithium ion batteries by a sonochemical method

Hydrated amorphous FePO₄ was synthesized by a sonochemical reaction method, in which a solution of (NH₄)₂HPO₄ and FeSO₄·7H₂O was irradiated by an ultrasonic wave. From this material, two kinds of cathode materials were easily prepared: (1) an amorphous sample prepared by heating at 350 °C and (2) a crystalline sample prepared by heating at 700 °C. Both samples consisted of homogeneous sub-micron particles. The amorphous sample of FePO₄ exhibited high discharge capacities with more than 100 mAh g⁻¹ in the range of 3.9-2.0 V versus Li/Li⁺ at a current rate of 0.2 C. The sonochemical synthesis proposed herein has the following advantages: no use of oxidation agents for production of trivalent iron ions, reduction in reaction time, control of particle size, and enlargement in surface area for the preparation of the cathode material.     

Phenol-formaldehyde resin-assisted synthesis of pure porous Li4Ti5O12 for rate capability improvement

Porous Li₄Ti₅O₁₂ has been synthesized via a simple template method using phenol-formaldehyde resin as template. SEM, TEM, XRD, nitrogen adsorption, galvanostatic charge-discharge, and ac impedance tests are used to characterize the appearance, structure, and electrochemical performance of the samples. The micrometer-scale crystal particles exhibit rough surface, large specific surface area, porous structure, and superior electrochemical performance. The initial discharge specific capacity is 167 mAh g⁻¹ under 0.2 C discharge rate, when the rate increases to 2.0 C, the capacity still retains to 112 mAh g⁻¹, exhibiting excellent rate capability.     

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.     

TiN/VN composites with core/shell structure for supercapacitors

TiN/VN core-shell composites are prepared by a two-step strategy involving coating of commercial TiN nanoparticles with V₂O₅·nH₂O sols followed by ammonia reduction. The highest specific capacitance of 170 F g⁻¹ is obtained when scanned at 2 mV s⁻¹ and a promising rate capacity performance is maintained at higher voltage sweep rates. These results indicate that these composites with good electronic conductivity can deliver a favorable capacity performance.