Powder Electrodes Research Articles

Simultaneous recycling of nickel metal hydride, lithium ion and primary lithium batteries: Accomplishment of European Guidelines by optimizing mechanical pre-treatment and solvent extraction operations

In this paper the recycling of nickel metal hydride (NiMH), lithium ion (Li-ion) and primary lithium batteries was examined. Three mechanical routes of treatment were developed for each type recovering mainly three fractions: ferrous metals, non-ferrous metals and electrodic powders. The above mentioned types of spent batteries were also treated together by a unique mechanical route, obtaining in this way a powder enriched in cobalt, nickel and manganese which can be further extractable by chemical leaching. Experimental tests of solvent extraction were performed on synthetic leach liquors simulating a feed mixture of spent devices with weight composition 40% NiMH, 40% primary lithium, and 20% Li-ion (as determined by manual sorting of 3 tons of end of life batteries collected in Northern Italy). Under these conditions nickel and cobalt can be easily separated by using Cyanex 272 (stoichiometric ratio Cyanex/Co = 4, pH 5–6), but in presence of manganese Cyanex 272 loses its selectivity towards cobalt. Thus manganese must be preliminarily removed by using D2EHPA (stoichiometric ratio D2EHPA/Mn = 2, pH 4). Mechanical treatments and hydrometallurgical section to recover metals from electrodic powder are unavoidable operations in order to recover at least 50% of batteries as weight according to European Guideline 2006/66/EC.

Peroxodisulfate assisted leaching of chalcopyrite

This research investigated the effectiveness of peroxodisulfate (S2O82−) for enhancing copper leaching rates from chalcopyrite. Batch and column experiments were performed using sulfuric acid leach solutions at pH=2, with and without Na2S2O8. The presence of peroxodisulfate greatly increased copper leaching rates. Tafel analysis and electrochemical impedance spectroscopy experiments performed using chalcopyrite powder electrodes indicated that peroxodisulfate increased the corrosion rate by decreasing the charge transfer resistance for chalcopyrite oxidation. In contrast to the preferential leaching of iron that has been observed for other oxidants added to chalcopyrite leach solutions, peroxodisulfate assisted leaching resulted in the release 1mol of Cu per mole of Fe, which is identical to their stoichiometric ratio in chalcopyrite. Rates of Cu leaching from chalcopyrite followed a surface reaction rate limited, shrinking-core model with an apparent activation energy of 41kJ/mol.

In-situ investigation of the water absorption/desorption behavior of LiFePO4

We utilize high-sensitive in-situ thermogravimetric measurements under controlled relative humidity levels to elucidate in detail the water absorption/desorption characteristics of the positive electrode material LiFePO4. Both plain (with carbon-coating only) and composite–electrode powder samples are investigated. It is revealed that not only the amount of absorbed water but also the speed of absorption depend on the humidity level of the surrounding atmosphere. The additives used for manufacturing the LiFePO4 composite electrode protect the material to some extent against the water absorption. Partial substitution of iron by manganese increases the amount of absorbed water but at the same time improves the reversibility of the water absorption/desorption process.

Reversible Deposition and Dissolution of Magnesium from Imidazolium-Based Ionic Liquids

The electrochemical performance of six imidazolium cation-based ionic liquids (ILs) containing 0.3 mol L-1Mg(CF3SO3)2as the electrolytes for magnesium deposition-dissolution was examined by cyclic voltammogramms and constant current discharge-charge techniques. Scanning electron microscopy and energy dispersive X-ray spectroscopy measurements were conducted to characterize the morphologies and components of the deposits. The cathodic satiability of imidazolium cations can be improved by increasing the length of alkyls at the 1-position and introducing methyl group at the 2-position of the imidazolium cations. A reversible magnesium deposition-dissolution can be achieved at room temperature. After adding appreciate amount of tetrahydrofuran (THF) organic solvent, the conductivity and the peak currents for Mg deposition and dissolution can be significantly improved. The potential polarization of deposition-dissolution process is decreased using Mg powder electrode.

Cone-shaped cylindrical Ce0.9Gd0.1O1.95 electrolyte prepared by slip casting and its application to solid oxide fuel cells

A cone-shaped gadolinium doped ceria (Ce0.9Gd0.1O1.95, GDC) electrolyte cylinder with a thin wall was fabricated using slip casting technique. The diameter of the larger open end of the cone-shaped cylinder was 0.85 cm, the length was 1.0 cm, and the thickness of the wall was 0.026 cm after sintering. Both the electrolyte and electrode powders were fabricated by using a glycine-nitrate process. A single solid oxide fuel cell (SOFC) was prepared with the cone-shaped electrolyte, NiO-GDC (70:30 wt.%) anode and Sm0.5Sr0.5CoO3 (SSC) cathode. Its electrochemical performance (I-V curve) and electrochemical impedance spectroscopy (EIS) were studied with humidified hydrogen as the fuel and air as the oxidant. The maximum output power density was about 300 mW/cm2 at 700 °C. The EIS results showed that the dominant loss of the SOFC was from the ohmic resistance of the electrolyte.

Thermal stability of silicon negative electrode for Li-ion batteries

A silicon/disordered-carbon powder was applied as the negative electrode material in Li ion batteries. The thermal characteristics of the Si/C electrode mixed with or without the electrolyte were investigated by DSC. Both lithiated (with capacity of 1120 mAh g −1) and delithiated Si/C electrode powder showed exothermic peaks in DSC curves due to the reactions between the Li in the electrode and the SEI. The lithiated electrode caused much larger exothermic heat than the delithiated one, especially when they were mixed with the electrolyte. By changing the ratio between the lithiated Si/C electrode and the coexisting electrolyte, the thermal behavior of the mixture could be studied in detail. At about 290 °C, a mixture containing 0.5 mg lithiated Si/C electrode and 0.5 μl electrolyte showed the most drastic exothermic heat of 2.2 J among all mixtures due to a direct reaction between the residual lithiated electrode and the solvent of the electrolyte after the thermal breakdown of the SEI. Under this condition, the heat value based on the electrode weight was 4.4 J mg −1, and that based on capacity was 5.1 J mA h −1. These values of graphite were estimated to be 1.9 J mg −1 and 5.8 J mA h −1, respectively. The generated heat was found to be very sensitive to the electrode/electrolyte ratio.

Optimal parameter settings for rough and finish machining of die steels in powder-mixed EDM

The present study was undertaken to identify the appropriate parameter settings for rough and finish machined surface for EN31, H11, and high carbon high chromium (HCHCr) die steel materials in a powder-mixed electric discharge machining process. The effect of seven different process variables along with some of their interactions was evaluated using a dummy-treated experimental design and analysis of variance. Material removal rate (MRR), tool wear rate, and surface finish were measured after each trial and analyzed. The parameter settings for rough and finished machining operations were obtained. EN31 exhibited maximum MRR as compared to the other two materials at similar process settings. Copper (Cu) electrode with aluminum suspended in the dielectric maximized the MRR. Suspending powder in the dielectric resulted in surface modification. Graphite powder showed a lower MRR but improved the surface finish. HCHCr require higher current and pulse on settings for initiating a machining cut and works best in combination with tungsten–Cu electrode and graphite powder for improved finish. The MRR for H11 is lower than EN31 but significantly higher than HCHCr under same process conditions.

High power supercapacitor electrodes based on flexible TiC-CDC nano-felts

Flexible electrospun titanium carbide (TiC) nano-felts were converted into carbide-derived carbon (CDC) by dry chlorination at temperatures between 200 and 1000 °C and used as binder-free supercapacitor electrodes. In the carbide nano-felt, TiC nano-crystals (20–30 nm) were embedded in a matrix of disordered carbon. After chlorination, the porous CDC nano-fibers/felts maintain their size, shape, and flexibility. With the increase of synthesis/chlorination temperature, the degree of carbon ordering increased. Electrochemical characterizations in 1 M H 2SO 4 and 1.5 M tetraethylammonium tetrafluoroborate in acetonitrile were carried out on binder-free electrodes with galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. The highest gravimetric capacitance was identified for the CDC nano-felt synthesized at the highest temperature of 1000 °C, reaching 135 F g −1 in aqueous and 120 F g −1 in organic electrolytes. In contrast to powder or monolithic supercapacitor electrodes made of conventional activated, templated, or carbide-derived carbons, this material demonstrated excellent high-power handling ability; and ∼50% of the low-rate capacitance was maintained at a very high scan rate of 5 V s −1.

(Invited) ALD of Thin Films for Lithium-Ion Batteries

Atomic layer deposition (ALD) technique is a thin film deposition method that provides highly conformal films on 3D structured supports, including powder materials. The technique relies on sequential self-limiting gas-to-surface reactions which enable control of thin film depositions even down to the atomic level on complex surface geometries. Even if ALD technique has been used in the semiconductor industry in production scale for several years now, there are rather few reports on ALD of battery materials. However, the recent development in processes for lithium containing films clearly opens up new possibilities. Promising applications of ALD include 3D structured all-solid-state batteries and surface modification of electrode powders. The present paper presents an overview of the present status in application of ALD in the field of lithium ion batteries.

Surface Modification of High Carbon High Chromium, EN31 and Hot Die Steel Using Powder Mixed EDM Process

This paper investigates the effect of electric discharge machining (EDM) process parameters and powder mixed in dielectric on surface properties of three die steel work materials; namely High Carbon High Chromium (HCHCr), EN 31 and Hot Die Steel (HDS). The mechanism of material deposition from the suspended powder and/or tool electrode is reported. Current emerged as the most significant factor affecting the microhardness along with powder mixed in the dielectric and electrode material. Amongst the two electrode materials, copper-tungsten along with tungsten powder had the best microhardness. Selected samples were analyzed for X-ray Diffraction (XRD) followed by microstructure analysis using a Scanning Electron Microscope (SEM). The results showed significant material transfer from the electrode as well as powder either in free form or in compound form. It was concluded that surface modification of die steels can be done by incorporating simple modifications in the EDM set-up resulting in higher microhardness and superior wear resistance of the machined surface.

Electrochemical behavior of a silicon particle anode cell synthesized by an induction furnace

Nano-size Si powder was fabricated via an induction furnace and pulverization from Si-Al alloy. Though the primary Si particles were collected and etched by sulfuric acid, a small amount of Al remained in the powders. The existence of this Al was identified by XRD and EDX. A battery cell, which was synthesized with a Si powder electrode and Li foil as a counter electrode, exhibited improved cyclability and less impedance in comparison to those of a typical pure Si powder electrode cell. This resulted from the role of the Al remaining in the Si powder, which served as a conductive agent. The new method allows for a large amount of micro- or nano-size Si powder with the metal component to be synthesized very easily and inexpensively for Li rechargeable cells.

Effect of Gold Nanoparticles on the Photocatalytic and Photoelectrochemical Performance of Au Modified BiVO4

Abstract An efficient visible light driven photocatalyst, gold nanoparticles (NPs) modified BiVO4 (Au/BiVO4), has been synthesized by deposition-precipitation with urea method. Au/BiVO4 exhibits enhanced photocatalytic activity for phenol degradation under λ>400 nm irradiation but negligible activity under λ>535 nm, indicating that the surface plasmon resonance (SPR) effect is too weak for organic photodegradation. According to the photoelectrochemical results of the porous powder electrodes of BiVO4 and Au/BiVO4, the SPR effect of Au NPs has been assessed. The role of Au NPs as electron sinks or sources, which is controllable by incident photon energy and applied potentials, has been discussed.

Spherical clusters of β-Ni(OH) 2 nanosheets supported on nickel foam for nickel metal hydride battery

Spherical clusters of Ni(OH) 2 nanosheets are directly grown on skeletons of nickel foam via a facile template-free spontaneous growth method. The obtained electrode ( β-Ni(OH) 2/Ni-foam) is characterized by X-ray diffractometry, scanning and transmission electron microscopy and thermal analysis. Results show that Ni(OH) 2 has a β-phase structure and presents on the nickel foam skeleton mostly as spherical clusters with a diameter of ∼10 μm. The spheres are composed of nanosheets with thickness of ∼60 nm, width of ∼230 nm and length up to ∼2 μm, and the nanosheets are assembled by nanoparticles with diameter of ∼20 nm. The electrochemical performance of the β-Ni(OH) 2/Ni-foam electrode is evaluated by cyclic voltammetry and galvanostatic charge–discharge tests. The difference between the oxygen evolution reaction onset potential and the anodic peak potential for this electrode (∼100 mV) is larger than that for β-Ni(OH) 2 nanosheets and nanotubes powder electrode (∼65–77 mV) and much larger than that for commercial spherical β-Ni(OH) 2 powder electrode (∼25–47 mV), indicating that the β-Ni(OH) 2/Ni-foam electrode can be fully charged. The specific discharge capacity of β-Ni(OH) 2 in the β-Ni(OH) 2/Ni-foam electrode reaches 275 mAh g −1, which is close to the theoretical value, lower than that of β-Ni(OH) 2 nanotubes (315 mAh g −1), but higher than that of nanosheets (219.5 mAh g −1), commercial micrometer grade spherical powders (265 mAh g −1) and microtubes (232.4 mAh g −1).

Properties and Mechanism of Layered Polysilane (Si6H6) Anode

Layered polysilane (Si6H6) is graphite-like structure which has higher capacity than crystalline silicon. The rate of increase of the thickness of a layered polysilane electrode after 10 charge-discharge cycles was smaller than that for a Si powder electrode, although layered polysilane electrode has higher capacity. The structural changes of electrochemically lithiated and delithiated layered polysilane at room temperature were studied using X-ray diffraction and Raman spectroscopy. Layered polysilane became amorphous by insertion of lithium to 0 V, whereas insertion of lithium into crystalline silicon produces Li15Si4. Layered polysilane maintained the amorphous state during lithium insertion and deinsertion, whereas silicon changed between Li15Si4 and amorphous LixSi, which explains the smaller volume change of a layered polysilane electrode compared with a Si powder electrode.

Performance Evaluation of Five Types of Ag/AgCl Bio-Electrodes for Cerebral Electrical Impedance Tomography

Electrical impedance tomography (EIT) is an emerging medical imaging technique, which has already been investigated in several clinical applications due to its low-cost, non-invasiveness, non-radioactivity, high temporal resolution, and great sensitivity to impedance changes. One potential use of EIT is to perform long-term continuous imaging monitoring of brain for patients who suffer from severe cerebral diseases. However, this application requires a demanding performance of electrodes because of the characteristics of cerebral EIT measurements. Although Ag/AgCl bio-electrodes are widely used for clinical practices or EIT research at the moment, influences of different types of Ag/AgCl electrodes on cerebral EIT measurements have not been investigated. In this study, five common types of Ag/AgCl bio-electrodes were put into comparison by measuring the forearm and the brain of 10 healthy adult volunteers and evaluating those data in frequency or time domain in terms of contact impedance, uniformity, signal-to-noise ratio, and stability. Results show that Ag/AgCl powder electrode has an overall best performance with as low contact impedance as commercial ECG electrodes (p > 0.05), high SNR (60.3 ± 4.5 dB), better uniformity (coefficient of correlation 0.95 ± 0.03), and greater stability (slope 0.68 ± 0.03). After further improvement in design and instrumentation, Ag/AgCl powder electrode is likely to become the optimal choice for cerebral EIT measurements and provide feasible technical support for further research or application in cerebral EIT.

Facile secondary-template synthesis of polyaniline microtube array for enhancing glucose biosensitivity

Polyaniline (PANi) microtube arrays were synthesized by a secondary-template (fir wood and ZnO microtube array) method and confirmed by scanning electron microscopy (SEM). High magnification SEM observation revealed that the PANi microtube arrays were formed by nanospheres and nanorods. X-Ray diffraction, Fourier transform infrared spectroscopy and cyclic voltammetry were used to characterize the resultant PANi microtube arrays which were subsequently used as electrodes for glucose oxidase (GO) immobilization and the detection of glucose. Compared with the traditional PANi powder electrode, the bioelectrocatalytic activation of GO immobilized PANi microtube array electrode toward the oxidation of glucose has been significantly enhanced. The excellent properties, low cost, facile preparation and good biocompatibility of the PANi microtube arrays set a bridge between proteins/enzymes and electrodes, providing analytical access to a large group of enzymes for a variety of biosensor applications.

A Novel Flow Sheet for Processing of Used Lithium-ion Batteries for Recycling

In recent years, the demand for the lithium-ion battery is increasing due to the increasing demand for laptop computer, cellular phone and automobiles. The positive electrode of the lithium-ion secondary battery is made of lithium oxide with mainly cobalt, nickel and manganese etc.. An effective recycling method not only would collect cobalt and lithium, but also separate other materials from the used batteries. In this research, the optimum processing flow sheet is investigated and their efficiency is evaluated. The battery is safely decomposed by underwater explosion and then cutter mill. After the over 1mm in size particles are separated by the magnetic separation, eddy current separation and gravity separation by air table, the plastic, Al, Fe, and Cu products are obtained. On the other hand, the particles less than 1mm in size are effectively separated by flotation and carbon and positive electrode powders are recovered. The lithium cobalt powders are leached, neutralized and heated as Co3O4 and lithium is recovered by the adsorption method.

Reduction and oxidation of a Pd/activated carbon catalyst: evaluation of effects

A commercial Pd/activated carbon catalyst (10%) was treated using several redox processes: reduction with gaseous hydrogen at 140 °C, reduction by negative electrochemical polarization in acidic and basic environments, oxidation with aqueous hydrogen peroxide, and positive electrochemical polarization in acidic and basic environments. To establish the electrochemical reduction/oxidation conditions, the potentials of hydrogen and oxygen evolution at Pd/AC powder electrodes were determined from cyclic voltammetric (CV) measurements. The samples were examined for the presence of palladium oxide phases on dispersed metal particles using XRD, TPR, and TPD. The metal oxide phase disappeared following hydrogen and electrochemical reduction. Oxidative treatment of the commercial catalyst differentiated the palladium oxide layers on the metal particle surface. Changes in the surface chemistry of the Pd/PdO/AC system were confirmed by the electrochemical behavior of electrodes prepared from the carbon samples.

Characteristics and structural change of layered polysilane (Si 6H 6) anode for lithium ion batteries

Layered polysilane (Si 6H 6) has a graphite-like structure with higher capacity than crystalline silicon. The rate of increase of the thickness of a layered polysilane electrode after 10 charge–discharge cycles was smaller than that for a Si powder electrode, although the layered polysilane electrode has higher capacity. The structural changes of electrochemically lithiated and delithiated layered polysilane at room temperature were studied using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Layered polysilane became amorphous by insertion of lithium to 0 V, whereas insertion of lithium into crystalline silicon produces Li 15Si 4. Layered polysilane maintained an amorphous state during lithium insertion and deinsertion, whereas silicon changed between Li 15Si 4 and amorphous Li x Si, which explains the smaller volume change of a layered polysilane electrode compared with a Si powder electrode.

Electrochemical Behavior of Compacted Lithium Powder Electrode in Li / V2O5 Rechargeable Battery

Lithium powder is safely prepared by the droplet emulsion technique and compacted to provide a lithium powder anode. Using the compacted Li powder anode, high specific energy density cells are assembled with a nonlithiated cathode such as . The capacity and cycle capability of a lithium powder/ cell are tested. The lithium powder cell is found to maintain its initial capacity for more than 100 cycles, whereas the lithium foil cell exhibited capacity fading after 37 cycles. The lithium powder with a double-sided cathode cell, whose cathode/anode ratio is about 1/10 in capacity, shows a capacity of at a rate of C/2 for over 40 cycles. The morphological changes of a Li foil and a Li powder anode after 50 cycles are observed by scanning electron microscopy. Impedance behavior of the powder anode cell is also observed and compared to that of the foil cell.