Double core-shell of Si@PANI@TiO2 nanocomposite as anode for lithium-ion batteries with enhanced electrochemical performance

A unique double core-shell structure of Si@PANI@TiO₂ nanocomposite is synthesized by a simple in-situ growth method. The two shells of polyaniline (PANI) and TiO₂, hand in hand, play a key role to improve the electrochemical performance: First, the flexible properties of polyaniline (PANI) effectively accommodate the volume change of Si during the cycling. Second, the good mechanical feature of TiO₂ can maintain the structural integrity and attenuate the volume expansion of Si cores. Finally, both of polyaniline and the lithiated TiO₂ enhance the conductivity of Si, which promotes the electrons transport. Resulting in the Si@PANI@TiO₂ double core-shell nanocomposite exhibits remarkable synergy in large, reversible lithium storage, delivering a reversible capacity as high as 1027 mAh g^?1 after 500 cycles and a superior rate capacity of 640 mAh g^?1, at a current of 500 and 4000 mA g^?1, respectively. This excellent cycling and high-rate capability can be ascribed to the unique and well-designed double core-shell structure with the synergistic effect between polyaniline (PANI) and TiO₂.     

One-dimensional nanostructures as electrode materials for lithium-ion batteries with improved electrochemical performance

One-dimensional (1D) nanosize electrode materials of lithium iron phosphate (LiFePO₄) nanowires and Co₃O₄–carbon nanotube composites were synthesized by the hydrothermal method. The as-prepared 1D nanostructures were structurally characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. We tested the electrochemical properties of LiFePO₄ nanowires as cathode and Co₃O₄–carbon nanotubes as anode in lithium-ion cells, via cyclic voltammetry and galvanostatic charge/discharge cycling. LiFePO₄ nanorod cathode demonstrated a stable performance over 70 cycles, with a remained specific capacity of 140 mAh g⁻¹. Nanocrystalline Co₃O₄–carbon nanotube composite anode exhibited a reversible lithium storage capacity of 510 mAh g⁻¹ over 50 cycles. 1D nanostructured electrode materials showed strong potential for lithium-ion batteries due to their good electrochemical performance.     

Enhanced electrochemical performance of porous NiO-Ni nanocomposite anode for lithium ion batteries

The nickel foam-supported porous NiO-Ni nanocomposite synthesized by electrostatic spray deposition (ESD) technique was investigated as anodes for lithium ion batteries. This anode was demonstrated to exhibit improved cycle performance as well as good rate capability. Ni particles in the composites provide a highly conductive medium for electron transfer during the conversion reaction of NiO with Li⁺ and facilitate a more complete decomposition of Li₂O during charge with increased reversibility of conversion reaction. Moreover, the obtained porous structure is benefical to buffering the volume expansion/constriction during the cycling.     

Anodic deposition of manganese oxide electrodes with rod-like structures for application as electrochemical capacitors

The electrochemical properties of nanocrystalline manganese oxide electrodes with rod-like structures were investigated to determine the effect of morphology, chemistry and crystal structure on the corresponding electrochemical behavior of manganese electrodes. Manganese oxide electrodes of high porosity composed of 1-1.5 μm diameter rods were electrochemically synthesized by anodic deposition from a dilute solution of Mn(CH₃COO)₂ (manganese acetate) onto Au coated Si substrates without any surfactants, catalysts or templates under galvanostatic control. The morphology of the electrodes depended on the deposition current density, which greatly influenced the electrochemical performance of the capacitor. Electrochemical property and microstructure analyses of the manganese oxide electrodes were conducted using cyclic voltammetry and microstructural techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The synthesized rod-like manganese oxide electrodes at low current densities exhibited a high specific capacitance due to their large surface areas. The largest value obtained was 185 F g⁻¹ for deposits produced at .5 mA cm⁻². Specific capacity retention for all deposits, after 250 charge-discharge cycles in an aqueous solution of 0.5 M Na₂SO₄, was about 75% of the initial capacity.     

Selenium: Another metalloid beneficial for the electrochemical performance of Co electrode in alkaline rechargeable batteries

Many inactive materials have been found to be helpful for improving the electrochemical performance of Co electrode in alkaline rechargeable batteries, including B, P, Si, S, Si₃N₄, and BN. In this paper we find for the first time that selenium has a similar effect with them. Selenium incorporation is realized through a liquid-reduction method. The obtained Co-Se sample is investigated as the negative electrode material of alkaline rechargeable battery. Experimental results demonstrate that the Co-Se sample electrode shows excellent electrochemical reversibility and considerably high charge-discharge capacity, showing a great potential to enhance the electrochemical performance of Co-based alkaline rechargeable batteries. The electrochemical reaction mechanism and function mechanism of Se are also investigated.     

Morphology effect on the electrochemical performance of NiO films as anodes for lithium ion batteries

NiO films were prepared by chemical bath deposition and electrodeposition method, respectively, using nickel foam as the substrate. The films were characterized by scanning electron microscopy (SEM) and the images showed that their morphologies were distinct. The NiO film prepared by chemical bath deposition was highly porous, while the film prepared by electrodeposition was dense, and both of their thickness was about 1 μm. As anode materials for lithium ion batteries, the porous NiO film prepared by chemical bath deposition exhibited higher coulombic efficiency and weaker polarization and its specific capacity after 50 cycles was 490 mAh g⁻¹ at the discharge–charge current density of 0.5 A g⁻¹, and 350 mAh g⁻¹ at 1.5 A g⁻¹, higher than the electrodeposited film (230 mAh g⁻¹ at 0.5 A g⁻¹, and 170 mAh g⁻¹ at 1.5 A g⁻¹). The better electrochemical performances of the film prepared by chemical bath deposition are attributed to its highly porous morphology, which shorted diffusion length of lithium ions, and relaxed the volume change caused by the reaction between NiO and Li⁺.     

Particle Image Velocimetry study on the formation of gas bubbles and electrolyte velocity due to electrochemical reactions for different distances between the electrodes of Flooded Lead_ Acid batteries

During the charging processes in Flooded Lead_ Acid batteries (FLA), the production of gas bubbles occurs and it effects on the FLA performance. In this experimental investigation, the effect of distance between electrodes at different charge-discharge rates on the electrolyte flow velocity and bubbles behavior is investigated based on the Particle Image Velocimetry method. The reduction in the distance decreases the FLA capacity linearly at the same processes. It leads to an increase in the void fraction of bubbles and a decline in the diameter and rising velocity of the bubbles. The maximum diameter of the bubbles during the charging processes is very small compared to the distances between the electrodes. The effect of electrolyte velocity compared to the effect of the average rising velocity of bubbles on the FLA performance is negligible. The results show that the increase in the void fraction of the bubbles and the formation of bubble layers in the vicinity of the electrodes is the most critical factor at the increase of the ohmic resistance.     

Synthesis of LiFe1−xNixPO4/C composites and their electrochemical performance

LiFePO₄/C and LiFe_1−xNi_xPO₄/C (x = 0, 0.02, 0.04, and 0.06) composites were prepared using solid-state reaction. The as-prepared composites were characterized by using X-ray diffraction, charge–discharge cycling, cyclic voltammograms, Raman spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and other techniques. The experimental results show that all as-prepared composites have a single phase of orthorhombic olivine-type structure with the Pnmb space group. The as-prepared LiFe_1−xNi_xPO₄/C composites exhibit high capacities and good cycling performance; e.g., the LiFe_0.98Ni_0.02PO₄/C composite delivers 142 and 138 mAh g⁻¹ at the 0.1 C rate for the first and fifth cycles, respectively. Such composites also show good rate capabilities; e.g., when discharged at the 2 C rate the LiFe_0.98Ni_0.02PO₄/C composite delivers an initial capacity of 121 mAh g⁻¹, 85% of the discharge capacity at the 0.1 C rate. The reason why the LiFe_1−xNi_xPO₄/C composites have better electrochemical performance compared to the LiFePO₄/C composites is because nickel doping enhances the PO bond, stabilizes the structure, and thus the charge-transfer resistance and cathode particle resistance of the composites are decreased.     

The effect of alkalinity and temperature on the performance of lithium-air fuel cell with hybrid electrolytes

A lithium-air fuel cell combined an air cathode in aqueous electrolyte with a metallic lithium anode in organic electrolyte can continuously reduce O₂ to provide capacity. Herein, the performance of this hybrid electrolyte based lithium-air fuel cell under the mixed control of alkalinity and temperature have been investigated by means of galvanistatic measurement and the analysis of electrochemical impedance spectra. Electromotive force and inner resistance of the cell decrease with the increase of LiOH concentration in aqueous electrolyte. The values ranged from 0.5 to 1.0 M could be the suitable parameters for the LiOH concentration of aqueous electrolyte. Environment temperature exhibited a significant influence on the performance of lithium-air fuel cell. The lithium-air fuel cell can provide a larger power at elevated temperature due to the decrease of all resistance of elements.     

Grafting effect on the wetting and electrochemical performance of carbon cloth electrode and polypropylene separator in electric double layer capacitor

Activated carbon (AC) fiber cloths and hydrophobic microporous polypropylene (PP) membrane, both modified by plasma-induced graft polymerization of acrylic acid (AAc) under UV irradiation, and filled with saturated lithium hydroxide solution were used as electrodes, a separator and electrolyte in electric double layer capacitors (EDLCs). The modification process changed the hydrophobic character of AC and PP materials to hydrophilic, made them wettable and serviceable as components of an electrochemical capacitor. The presence of poly(acrylic acid) on the AC and PP surface was confirmed by SEM and XPS methods. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge-discharge cycle tests and also by impedance spectroscopy. At the 1000th cycle of potential cycling (1 A g⁻¹) the specific capacitance of 110 F g⁻¹ was obtained with a specific energy of 11 Wh kg⁻¹ at power density of 1 kW kg⁻¹. The above results provide valuable information which may be used when developing novel compositions of EDLCs.     

Synthesis and electrochemical performance of Li2CoSiO4 as cathode material for lithium ion batteries

Li₂CoSiO₄ has been prepared successfully by a solution route or hydrothermal reaction for the first time, and its electrochemical performance has been investigated primarily. Reversible extraction and insertion of lithium from and into Li₂CoSiO₄ at 4.1 V versus lithium have shown that this material is a potential candidate for the cathode in lithium ion batteries. At this stage reversible electrochemical extraction was limited to 0.46 lithium per formula unit for the Li₂CoSiO₄/C composite materials, with a charge capacity of 234 mAh g⁻¹ and a discharge capacity of 75 mAh g⁻¹.     

Fe and Ni impurity distribution and electrochemical performance of LiCoO2 electrode materials for lithium ion batteries

The distribution of Fe³⁺ and Ni³⁺ impurities and the electrochemical performance of LiCoO₂ electrodes were examined. Commercial LiCoO₂ powders supplied by Aldrich were used. The electrochemical performance of LiCoO₂ was modified by rotor blade grinding of LiCoO₂ followed by thermal treatment. Structural information on Fe³⁺ and Ni³⁺ impurities was obtained using both conventional X-band and high-frequency electron paramagnetic resonance spectroscopy (EPR). It was found that Fe³⁺ occupies a Co-site having a higher extent of rhombic distortion, while Ni³⁺ is in a trigonally distorted site. After rotor blade grinding of LiCoO₂, isolated Fe³⁺ ions display a tendency to form clusters, while isolated Ni³⁺ ions remain intact. Re-annealing of ground LiCoO₂ at 850 °C leads to disappearance of iron clusters; isolated Fe³⁺ ions are recovered. The electrochemical performance of LiCoO₂ was discussed on the basis of isolated and clustered ions.     

Fe3O4 submicron spheroids as anode materials for lithium-ion batteries with stable and high electrochemical performance

A magnetite (Fe₃O₄) powder composed of uniform sub-micrometer spherical particles has been successfully synthesized by a hydrothermal method at low temperature. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and galvanostatic cell cycling are employed to characterize the structure and electrochemical performance of the as-prepared Fe₃O₄ spheroids. The magnetite shows a stable and reversible capacity of over 900 mAh g⁻¹ during up to 60 cycles and good rate capability. The experimental results suggest that the Fe₃O₄ synthesized by this method is a promising anode material for high energy-density lithium-ion batteries.     

Electrochemical and impedance investigation of the effect of lithium malonate on the performance of natural graphite electrodes in lithium-ion batteries

Lithium malonate (LM) was coated on the surface of a natural graphite (NG) electrode, which was then tested as the negative electrode in the electrolytes of 0.9 M LiPF₆/EC-PC-DMC (1/1/3, w/w/w) and 1.0 M LiBF₄/EC-PC-DMC (1/1/3, w/w/w) under a current density of 0.075 mA cm⁻². LM was also used as an additive to the electrolyte of 1.0 M LiPF₆/EC-DMC-DEC (1/1/1, v/v/v) and tested on a bare graphite electrode. It was found that both the surface coating and the additive approach were effective in improving first charge-discharge capacity and coulomb efficiency. Electrochemical impedance spectra showed that the decreased interfacial impedance was coupled with improved coulomb efficiency of the cells using coated graphite electrodes. Cyclic voltammograms (CVs) on fresh bare and coated natural graphite electrodes confirmed that all the improvement in the half-cell performance was due to the suppression of the solvent decomposition through the surface modification with LM. The CV data also showed that the carbonate electrolyte with LM as the additive was not stable against oxidation, which resulted in lower capacity of the full cell with commercial graphite and LiCoO₂ electrodes.     

Electrospun nickel oxide/polymer fibrous electrodes for electrochemical capacitors and effect of heat treatment process on their performance

Electrospinning is a versatile method for preparation of submicron-size fibers under ambient temperature. We demonstrate a new approach based on this method for preparing an electrode which consists of the fibers coated with nickel oxide (NiO) and acetylene black (AB) on their surfaces. The NiO/polymer fibrous electrodes show the electrochemical responses based on the electrochemical reaction of Ni(OH)₂ which is produced from NiO in alkaline aqueous solution. The capacitance of the test half cell with the as-prepared NiO/polymer fibrous electrode in 1 mol l⁻¹ KOH aqueous solution is 5.8 F g⁻¹ (per gram of NiO). Heat treatment (at 150 °C for 1 h in the air) of the NiO/polymer fibrous electrode increases the capacitance of the NiO/polymer fibrous electrode. The capacitance of the cell with the heat treated (HT) NiO/polymer fibrous electrode is 163 F g⁻¹ (per gram of NiO). SEM observation of the heat treated electrode suggests that partial melt of the fibers on the current collector forms the conducting passes and networks between the NiO particles and the collector and increases the specific capacity of the fibrous electrode.     

Enhanced electrochemical properties of LiFePO4 cathode for Li-ion batteries with amorphous NiP coating

Here we show that the intrinsic low electrical conductivity of LiFePO₄ which seriously hinders the application of LiFePO₄ for Li-ion batteries is overcome with conductive metallic NiP nano-coating. High resolution transmission electron microscopy image reveals that the NiP coating is a nanoscale amorphous layer, which was deposited on the LiFePO₄ particles to form a so-called core/shell structure via electroless plating at room temperature. The electrochemical performances of NiP coated LiFePO₄ show that both of the rate performance and cycleability of LiFePO₄ against graphite anode are improved by the NiP coating. Analysis of electrochemical impedance spectra of the LiFePO₄/graphite cells demonstrates that the NiP coating decreases both of the surface film resistance and charge transfer resistance. The dissolution of Fe from LiFePO₄ in the LiPF₆ based electrolyte is remarkably suppressed by the protective NiP coating.     

Electrostatic spray deposition of porous Fe2O3 thin films as anode material with improved electrochemical performance for lithium-ion batteries

Iron oxide materials are attractive anode materials for lithium-ion batteries for their high capacity and low cost compared with graphite and most of other transition metal oxides. Porous carbon-free α-Fe₂O₃ films with two types of pore size distribution were prepared by electrostatic spray deposition, and they were characterized by X-ray diffraction, scanning electron microscopy and X-ray absorption near-edge spectroscopy. The 200 °C-deposited thin film exhibits a high reversible capacity of up to 1080 mAh g⁻¹, while the initial capacity loss is at a remarkable low level (19.8%). Besides, the energy efficiency and energy specific average potential (E_av) of the Fe₂O₃ films during charge/discharge process were also investigated. The results indicate that the porous α-Fe₂O₃ films have significantly higher energy density than Li₄Ti₅O₁₂ while it has a similar E_av of about 1.5 V. Due to the porous structure that can buffer the volume changes during lithium intercalation/de-intercalation, the films exhibit stable cycling performance. As a potential anode material for high performance lithium-ion batteries that can be applied on electric vehicle and energy storage, rate capability and electrochemical performance under high-low temperatures were also investigated.     

Investigations of solid oxide fuel cells with functionally graded electrodes for high performance and safe thermal stress

A comprehensive 3D theoretical model has been developed to investigate the performance and thermal stress distributions of planar anode-supported solid oxide fuel cells with functionally graded electrodes, at an intermediate temperature. The model includes the equations of charge transport, conservation of mass, momentum, and energy along with the thermal stress and strains. The comprehensive model is simulated numerically and the numerical results are validated using experimental data. The constituent fraction ratio and porosity distribution of each electrode are controlled with a material grading parameter m. Results indicate that the solid oxide fuel cell with functionally graded electrodes perform better than the conventional cell. The power density has shown 23% increase at a working voltage of 0.6 V using functionally graded electrodes with the material grading parameter m = 2.0. Furthermore, the maximum Von Misses stress corresponding to m = 2.0 is less than half the yield stress at both cathode and electrolyte, while they exceed the yield limit for conventional electrodes (constant porosity at electrodes) at the same working conditions. The current results can guide designers of solid oxide fuel cells to adopt functionally graded electrodes for higher performance outcomes and safer thermal stress.     

The doping effect on the crystal structure and electrochemical properties of LiMnxM1−xPO4 (M = Mg, V, Fe, Co, Gd)

To substitute minor Mn²⁺ by the transition metal ion M = Mg²⁺, V³⁺, Fe²⁺, Co²⁺, or Gd³⁺, LiMn_0.95M_0.05PO₄ samples are synthesized by a solid-state reaction route. The interpretation of doping effects is complicated by the interrelations between doping microstructure and morphology, because the crystal structure would be affected by the doped elements. The lattice structure and deviation of Li-O bond lengths of the doped LiMnPO₄ are refined by XRD refinement. All the samples present a couple of oxidation and reduction peaks in cyclic voltammetry, corresponding to a redox Mn³⁺/Mn²⁺ reaction coupled with the extraction/reinsertion process of Li⁺ in LiMnPO₄ structure. During charge/discharge process, the electron flowing and Li⁺ cation diffusion in the various doped LiMnPO₄ samples should be different thermodynamic and kinetic process. For further studying which step in thermodynamic and kinetic process would affect or control the electrochemical performance, the initial charge/discharge capacities and cycleability of doped LiMnPO₄ samples are obtained under different voltage range (from 2.7 to the upper cut-off voltage 4.4, 4.6 and 4.8 V, respectively) and different environment temperatures (0, 25, and 50 °C). At relative higher measuring temperature, the discharge capacity of Co-doped LiMnPO₄ shows 151.9 mAh g⁻¹.     

Synthesis, structure and electrochemical Li insertion behaviour of Li2Ti6O13 with the Na2Ti6O13 tunnel-structure

Li₂Ti₆O₁₃ has been prepared from Na₂Ti₆O₁₃ by Li ion exchange in molten LiNO₃ at 325 °C. Chemical analysis and powder X-ray diffraction study of the reaction product respectively indicate that total Na/Li exchange takes place and the Ti-O framework of the Na₂Ti₆O₁₃ parent structure is kept under those experimental conditions. Therefore, Li₂Ti₆O₁₃ has been obtained with the mentioned parent structure. An important change is that particle size is decreased significantly which is favoring lithium insertion. Electrochemical study shows that Li₂Ti₆O₁₃ inserts ca. 5 Li per formula unit in the voltage range 1.5-1.0 V vs. Li⁺/Li, yielding a specific discharge capacity of 250 mAh g⁻¹ under equilibrium conditions. Insertion occurs at an average equilibrium voltage of 1.5 V which is observed for oxides and titanates where Ti(IV)/Ti(III) is the active redox couple. However, a capacity loss of ca. 30% is observed due to a phase transformation occurring during the first discharge. After the first redox cycle a high reversible capacity is obtained (ca. 160 mAh g⁻¹ at C/12) and retained upon cycling. Taking into consideration these results, we propose Li₂Ti₆O₁₃ as an interesting material to be further investigated as the anode of lithium ion batteries.