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.     

New strategy to prepare nitrogen self-doped graphene nanosheets by magnesiothermic reduction and its application in lithium ion batteries

Nitrogen self-doped graphene (N/G) nanosheets were prepared through magnesiothermic reduction of melamine. The obtained N/G features porous structure consisting of multi-layer nanosheets. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra and X-ray diffraction (XRD). As anode of lithium ion batteries (LIBs), it exhibits excellent reversible specific capacity of 1753 mAh g⁻¹ at 0.1 A g^-1 after 200 cycles. The reversible capacity can maintain at 1322 mAh g⁻¹ after 500 cycles at 2 A g⁻¹. At the same time, all results indicate remarkable cycle stability and rate performance as anode materials. Furthermore, this study demonstrates an economical, clean and facile strategy to synthesize N/G nanosheets from cheap chemicals with excellent electrochemical performance in LIBs.     

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.     

Fabrication and performance evaluation of graphene-supported PtRu electrocatalyst for high-temperature electrochemical hydrogen purification

The main aim of this study is to investigate the high-temperature electrochemical hydrogen purification (HT-ECHP) performances of graphene nanoplatelet (GNP) support material decorated with platinum (Pt) and platinum-ruthenium (PtRu) nanoparticles prepared by microwave irradiation technique. Prepared catalysts coupled to the phosphoric acid doped polybenzimidazole (PBI) membrane for HT-ECHP application. The structural and electrochemical properties of the catalysts were examined by thermogravimetric analysis (TGA), X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transition electron microscopy (TEM) and cyclic voltammetry (CV) analyses. The characterization results indicate that the catalysts provided the necessary properties for HT-ECHP application. The HT-ECHP performances are investigated with reformate gas mixture containing hydrogen (H₂), carbon dioxide (CO₂) and carbon monoxide (CO) in the range of 140–180 °C. The results show that the electrochemical purification performances of the catalysts increase with increasing operating temperature. The highest H₂ purification performance is obtained with PtRu/GNP catalyst. The high electrochemical H₂ purification performance of the PtRu/GNP catalyst can be attributed to the strong synergistic interactions between Pt and Ru particles decorated on the GNP. These results advocate that the PtRu/GNP catalyst is a hopeful catalyst for HT-ECHP application.     

Effect of Sn and Zn alloying with Al on its electrochemical performance in an alkaline media containing CO2 for Al-air batteries application

Aluminum alloyed with other metals, such as Sn and Zn, was synthesized via fusion to trace the impact of alloying elements on the electrochemical characteristics of Al anodes. The corrosion inhibition and electrochemical tests were performed in a 5 M KOH medium in the absence and presence of CO₂ for the Al–Sn, and Al–Zn anodes and compared to the commercial aluminum. Tafel polarization exhibited that the anodic and cathodic branches display lower current densities than Al metal in pure KOH. The steady state of the open circuit voltage (E_corr.) for the studied alloys was shifted to a more negative magnitude than for Al. The corrosion current is sharply decreased, and potential is significantly shifted to less negative values in the presence of CO₂. This is due to forming of a protective layer from the carbonate of Al, Sn, and Zn on the surface. Amazing results were obtained and discussed in the case of CO₂. Electrochemical impedance spectroscopy (EIS) results exhibited that charge transfer resistance (R_ct) values rise with alloying elements. The data of Tafel plots are consistent with those of EIS. The alloying of Al with Sn and Zn elements significantly affects capacitance, hydrogen evolution process suppression, and charge-discharge efficiency. This reveals that the highest potential value in the presence of CO₂ in the charging process is obtained for Al–Zn alloy, while the most negative potential is obtained for Al in the discharging process with CO₂. Moreover, the discharge time is higher in the alloys than in commercial Al in the absence and more in the presence of CO₂. The produced alloys are thought to provide good anodes for long-life rechargeable batteries.     

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.     

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⁺.     

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.     

Effect of nitrogen and sulfur co-doping on the performance of electrochemical hydrogen storage of graphene

In recent decades, finding a solution to replace metal catalysts with inexpensive and available elements has been investigated extensively. Carbon nanomaterials doped with heteroatom such as (N, B and S) which do not have any metal content can provide sustainable materials with a remarkable electrocatalytic activity that can compete with their metal counterparts. Doped graphene has been considered as an electrode material for oxygen reduction reaction, supercapacitor and Li-ion batteries. In this present account, co-doped graphene with nitrogen and sulfur was studied in order to investigate their electrochemical hydrogen storage performance. The dual doped sample was prepared via a simple hydrothermal method, using thiourea as a nitrogen and sulfur source. The nitrogen and sulfur co-doped graphene (NSG) showed excellent electrical conductivity and electrochemical performance compared with the nitrogen doped graphene (NG) and graphene oxide (GO). Doping graphene with foreign atoms is a method to create a semiconducting gap in it and can act as an n-type semiconductor, therefore the electrochemical performance is remarkable when used as an electrode. According to the results by increasing the electrical conductivity of graphene, the storage capacity of hydrogen was increased. The discharge capacity of GO after 20 cycles was increased from 653 mAh/g to 1663 mAh/g (5.88 wt% hydrogen) and 2418 mAh/g (8.55 wt% hydrogen) in single doped graphene (NG) and co-doped graphene (NSG), respectively. The prepared samples were characterized via X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Brunauer-Emmet-Teller analysis (BET), vibration sample magnetometer (VSM) and infrared spectrum (FT-IR).     

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.     

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.     

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.     

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.     

Synergistic effect of titanium-oxide integrated with graphitic nitride hybrid for enhanced electrochemical performance in lithium-sulfur batteries

Lithium-sulfur (Li-S) secondary batteries have been limited by the poor cyclic stability, mainly caused by the dissolution polysulfide species into the electrolyte and subsequent irreversible shuttling effect. Recently, addition of the polysulfide adsorbents within sulfur cathode is effectively improving the electrochemical performance. Herein, TiO₂ integrated with g-C₃N₄ (TiO₂@g-C₃N₄: TOCN) hybrid was prepared by a facile heating treatment from the precursor of urea and TiO₂composites, which used as host material for elemental sulfur (TOCN@S) in Li-S batteries. The multifunctional TOCN not only reduced the electrochemical resistance but also provided strong adsorption sites to immobilize sulfur and polysulfide. As a result, the TOCN@S cathode with a sulfur content of 74.5 wt% and a sulfur loading of 3.1 mg cm⁻²exhibits a high initial capability of 804 mAh g⁻¹ at 0.5°C with capacity retention of 67.2% after 500 cycles. Additionally, the composite cathode also possesses excellent high-rate performance, retaining a remarkable specific capacity of 630 mAh g⁻¹ even at a rate of 2°C.