Influence of the binder types on the electrochemical characteristics of natural graphite electrode in room-temperature ionic liquid

To improve the electrochemical characteristics of the natural graphite (NG-3) negative electrode in the LiCl saturated AlCl₃-1-ethyl-3-methylimizadolium chloride + thionyl chloride (SOCl₂) melt as the electrolyte for non-flammable lithium-ion batteries, we examined the influence of the binder types on its electrochemical characteristics. The cyclic voltammograms showed that the reduction current at 1.2-3.2 V vs. Li/Li(I) was repressed using polyacrylic acid (PAA) as the binder. The charge-discharge tests showed that the discharge capacity and the charge-discharge efficiency of the NG-3 electrode coated with the PAA binder at the 1st cycle were 322.8 mAh g⁻¹ and 65.6%, respectively. Compared with the NG-3 electrode using the conventional poly(vinylidene fluoride) binder, it showed considerably a better cyclability with the discharge capacity of 302.1 mAh g⁻¹ at the 50th cycle. Li(I) ion intercalation into the graphite layers could be improved because the NG-3 electrode coated with the PAA binder changed to a golden-yellow color after the 1st charging, and the formation of first stage LiC₆ was demonstrated by X-ray diffraction (XRD) measurement. In addition, the XRD and X-ray photoelectron spectroscopy indicated that one of the side reactions during charging was the formation of LiCl on the graphite surface regardless of the binder types.     

Effect of carbon coating on thermal stability of natural graphite spheres used as anode materials in lithium-ion batteries

To investigate the effect of non-graphitic carbon coatings on the thermal stability of spherical natural graphite at elevated temperature, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements are performed. Data from DSC studies show that the thermal stability of the surface modified natural graphite electrode is improved. The surface modification results in a decrease in the BET surface specific area. An improvement in coulombic efficiency and a reduction in irreversible capacity are also observed for the carbon-coated natural graphite. X-ray diffraction analysis confirms that carbon coating alleviates the release of intercalated lithium from natural graphite at an elevated temperature and acts as a protective layer against electrolyte attack.     

KPF6 dissolved in propylene carbonate as an electrolyte for activated carbon/graphite capacitors

KPF₆ dissolved in propylene carbonate (PC) has been proposed as an electrolyte for activated carbon (AC)/graphite capacitors. The electrochemical performance of AC/graphite capacitor has been tested in XPF₆-PC or XBF₄-PC electrolytes (X stands for alkali or quaternary alkyl ammonium cations). The AC/graphite capacitor using KPF₆-PC electrolyte shows an excellent cycle-ability compared with other electrolytes containing alkali ions. The big decomposition of the PC solvent at the AC negative electrode is considerably suppressed in the case of KPF₆-PC, which fact has been correlated with the mild solvation of K⁺ by PC solvent. The relationship between the ionic radius of cation and the corresponding specific capacitance of AC negative electrode also proves that PC-solvated K⁺ ions are adsorbed on AC electrode instead of naked K⁺ ions.     

Electrochemical characterization of thermally oxidized natural graphite anodes in lithium-ion batteries

Natural graphite, which is used as an anode material in lithium-ion batteries, is thermally treated to improve its cycleability and reduce irreversible reactions with the electrolyte. Natural graphite is treated in air at 550 °C. The weight loss increases when the thermal oxidation time is increased. The BET surface area of the graphite decreases with increasing weight loss. The cycleability and efficiency of the thermally oxidized natural graphite improves significantly. Thermal oxidation decreases the irreversible capacity for side-reactions with the electrolyte on the first cycle. By contrast, it does not change the reversible capacity and rate capability. The improvement in the cycleability after thermal oxidation may be due to the removal of imperfect sites on the graphite.     

Interfacial reactions between graphite electrodes and propylene carbonate-based solutions: Electrolyte-concentration dependence of electrochemical lithium intercalation reaction

This study examines the electrochemical reactions occurring at graphite negative electrodes of lithium-ion batteries in a propylene carbonate (PC) electrolyte that contains different concentrations of lithium salts such as, LiClO₄, LiPF₆ or LiN(SO₂C₂F₅)₂. The electrode reactions are significantly affected by the electrolyte concentration. In concentrated solutions, lithium ions are reversibly intercalated within the graphite to form stage 1 lithium–graphite intercalation compounds (Li–GICs), regardless of the lithium salt used. On the other hand, electrolyte decomposition and exfoliation of the graphene layers occur continuously in the low-concentration range. In situ analysis with atomic force microscopy reveals that a thin film (thickness of ∼8 nm) forms on the graphite surface in a concentrated solution, e.g., 3.27 mol kg⁻¹ LiN(SO₂C₂F₅)₂/PC, after the first potential cycle between 2.9 and 0 V versus Li⁺/Li. There is no evidence of the co-intercalation of solvent molecules in the concentrated solution.     

Effect of succinic anhydride as an electrolyte additive on electrochemical characteristics of silicon thin-film electrode

The effect of an electrolyte additive, succinic anhydride (SA), on the electrochemical performances of a silicon thin-film electrode, which is prepared by radio-frequency magnetron sputtering, is investigated. The introduction of SA into a liquid electrolyte consisting of ethylene carbonate/diethyl carbonate/1 M LiPF₆ significantly enhances the capacity retention and coulombic efficiency of the electrode. This improvement in the electrochemical performance of the electrode is attributed to modification of the solid/electrolyte interphase (SEI) layer by the introduction of SA. The differences in the characteristic properties of SEI layers, with or without SA, are explained by analysis with scanning electron microscopy, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy.     

High‐performance porous lead/graphite composite electrode for bipolar lead‐acid batteries

In general, thicker active material bipolar electrode's specific capacity and cycle life are very poor owing to its low bonding strength between the active material and the substrate and the diffusion rate of the sulfuric acid electrolyte inside the active material. In this paper, we synthesize a novel attached and porous lead/graphite composite electrode for bipolar lead‐acid battery and can effectively solve these problems. The graphite/polytetrafluoroethylene emulsion is employed to improve the bonding strength and conductivity and the porous can provide electrolyte diffusion channels. The specific capacities of 2‐mm thick positive active material at 0.25, 0.5, 1 and 2 C can attain 75.99, 58.98, 47.97, and 33.36 mAh·g^?1. The discharge voltage platform is also relatively high and no rapid decline with increasing discharge rate. Furthermore, after 80 cycles, the specific capacity does not drop evidently. Copyright © 2017 John Wiley & Sons, Ltd.     

The dependence of natural graphite anode performance on electrode density

The effect of electrode density for lithium intercalation and irreversible capacity loss on the natural graphite anode in lithium ion batteries was studied by electrochemical methods. Both the first-cycle reversible and irreversible capacities of the natural graphite anode decreased with an increase in the anode density though compression. The reduction in reversible capacity was attributed to a reduction in the chemical diffusion coefficient for lithium through partially agglomerated particles with a larger stress. For the natural graphite in this study the potentials for Li (de)insertion shifted between the first and second formation cycles and the extent of this shift was dependent on electrode density. The relation between this peak shift and the irreversible capacity loss is probably due to the decrease in graphite surface area with compression.     

High reversible capacities of graphite and SiO/graphite with solvent-free solid polymer electrolyte for lithium-ion batteries

The combination of graphite or silicon monoxide (SiO)/graphite = 1/1 mixture with a solvent-free solid polymer electrolyte (SPE) was fabricated using a new preparation process, involving precoating the electrode with vapor-grown carbon fiber (VGCF) and binders (polyvinyl difluoride: PVdF or polyimide: PI), followed by the overcoating of the SPE. The reversible capacity of [graphite | SPE | Li] and [SiO/graphite | SPE | Li] cells were >360 and >1000 mAh g⁻¹ with 78% and 77% for the 1st Coulombic efficiency, respectively. The reversible capacities were 75% at the 250th cycle for [graphite | SPE | Li] and 72% at the 100th cycle for [SiO/graphite | SPE | Li]. The electrode used was compatible with that of the conventional liquid electrolyte system, and the SPE film could be formed on the electrode by the continuous overcoating process, which will lead to a low-cost electrodes and low-cost battery production. The solid-state lithium-ion polymer battery (SSLiPB) developed in this study, which consisted of [LiFePO₄ | SPE | graphite], showed the reversible capacity of 128 mAh g⁻¹ (based on the LiFePO₄ capacity) with favorable cycle performance.     

Development of non-flammable lithium secondary battery with room-temperature ionic liquid electrolyte: Performance of electroplated Al film negative electrode

The negative electrode performance of the electroplated Al film electrode in the LiCl saturated AlCl₃–1-ethyl-3-methylimizadolium chloride (EMIC) + SOCl₂ melt as the electrolyte for use in non-flammable lithium secondary batteries was evaluated. In the cyclic voltammogram of the electroplated Al film electrode in the melt, the oxidation and reduction waves corresponding to the electrochemical insertion/extraction reactions of the Li⁺ ion were observed at 0–0.80 V vs. Li⁺/Li, which suggested that the electroplated Al film electrode operated well in the electrolyte. The almost flat potential profiles at about 0.40 V vs. Li⁺/Li on discharging were shown. The discharge capacity and charge–discharge efficiency was 236 mAh g⁻¹ and 79.2% for the 1st cycle and it maintained 232 mAh g⁻¹ and 77.9% after the 10th cycle. In addition, the initial charge–discharge efficiencies of the electroplated Al film electrode were higher than that of carbon electrodes. The main cathodic polarization reaction was the insertion of Li⁺ ions, and side reactions hardly occurred due to the decomposition reaction of the melt because the Li content corresponding to the electricity was almost totally inserted into the film after charging.     

Comparison of multiwalled carbon nanotubes and carbon black as percolative paths in aqueous-based natural graphite negative electrodes with high-rate capability for lithium-ion batteries

The effects of multiwalled carbon nanotubes (MWNTs) and carbon black (CB) as conducting additives on the rate capability of natural graphite negative electrodes in lithium-ion (Li-ion) batteries is investigated within concentration ranges where no degradation of anode capacity is observed. MWNT or CB solutions prepared with Nafion in an 80:20 volume mixture of water:1-propanol are incorporated into graphite precursor suspensions consisting of graphite particulates, carboxymethyl cellulose, and styrene butadiene rubber prepared in an aqueous medium. While negative electrodes with MWNTs demonstrate much better rate behaviour than those without MWNTs at a high C-rate, the rate capability of negative electrodes with MWNTs is not much different from that with CB. The reason for this similar behaviour is investigated with respect to the structural changes and aspect ratio of MWNTs, as well as the density difference between MWNTs and carbon black. Scanning electron microscopy images and Raman spectra for the dispersed MWNTs indicate that MWNTs are significantly damaged and shortened during dispersion, which reduces their electrical conductivity and increases their percolation threshold. This damage negatively affects the rate capability of graphite-nanotube composite electrodes.     

Electrochemical characteristics of Sn film prepared by pulse electrodeposition method as negative electrode for lithium secondary batteries

In order to improve the cyclability of Sn negative electrode, we tried preparing the Sn film negative electrode by a pulse electrodeposition. Based on the SEM observations, the crystal grains of the Sn film after the pulse electrodeposition were comparatively homogeneous and their grain size was ca. 1 μm. The discharge capacity and the charge–discharge efficiency at the 1st cycle were 679.3 mAh g⁻¹ and 93.0%, respectively. The charge–discharge tests indicated that the initial electrochemical characteristic of Sn film electrode prepared by a pulse electrodeposition was much better than that of the Sn film electrode prepared by a constant current electrodeposition. The GD-OES profile suggested that Li⁺ ions were easily extracted during the discharge reaction. In addition, it was found that no exfoliation of the film was observed after the 1st discharge though the cracking in the film was observed after the 1st discharge. Consequently, the Sn film electrode prepared by a pulse electrodeposition exhibited a better cyclability for the initial 10 cycles compared to the Sn film electrode prepared by a constant current electrodeposition. By reducing the particle size and repressing the morphological change, the initial electrochemical characteristics were considerably improved.     

A comparative study of polyacrylic acid and poly(vinylidene difluoride) binders for spherical natural graphite/LiFePO4 electrodes and cells

Anodes containing spherical natural graphite (SNG12) and cathodes containing LiFePO₄, both from HydroQuebec, were prepared with aqueous-based polyacrylic acid (PAAH), its neutralized derivatives polyacrylic acid (PAAX) (X = Li, Na, and K), and with conventional poly(vinylidene difluoride) (PVDF) binders. A comparison of electrode performance was made between these three binder systems. The electrodes were optimized by adding elastic styrene butadiene rubber (SBR) and conductive vapor grown carbon fiber (VGCF) in the place of some of the PAAX. Initially, SNG12 and LiFePO₄ electrodes were characterized in half cells with Li as the counter electrode. The electrochemistry results show that the use of PAAX binders can significantly improve the initial coulombic efficiency, reversible capacity, and cyclability of SNG12 anodes and LiFePO₄ cathodes as compared to that of electrodes based on a PVDF binder. By using an optimized composition for the anode and cathode, SNG12/LiFePO₄ full cells with PAALi binder cycled 847 times with 70% capacity retention, which was a significant improvement over the electrodes with PVDF (223 cycles). This study demonstrates the possibility of manufacturing Li-ion batteries that cycle longer and use water in the processing, instead of hazardous organic solvents like NMP, thereby improving performance, reducing cost, and protecting the environment.     

Structure and electrochemical properties of ball-milled Co-carbon nanotube composites as negative electrode material of alkaline rechargeable batteries

A series of cobalt-carbon nanotube (CNT) composites is synthesized by direct ball-milling of Co and CNT powders with different Co/CNT weight ratios. The microstructure, morphology and chemical state of the ball-milled Co-CNT composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It is found that metallic Co nanoparticles of 50-100 nm in size are highly dispersed on the inactive CNT matrix after ball-milling. The electrochemical performance of Co-CNT composites as negative electrode material of alkaline rechargeable batteries is investigated by galvanostatic charge-discharge, linear polarization and cyclic voltammetry (CV) techniques. The results show that the Co-CNT composite (weight ratio 5/1, BM 10 h) displays the optimized electrochemical performance, including discharge capacity and cycle stability. The reversible faradaic reaction between Co and Co(OH)₂ is dominant for ball-milled Co-CNT composites.     

Improving the electrochemical properties of graphite/LiCoO2 cells in ionic liquid-containing electrolytes

The electrochemical performance of graphite/lithium cobalt oxide (LiCoO₂) cells in N-methoxymethyl-N,N-dimethylethylammonium bis(trifluoromethane-sulfonyl) imide (MMDMEA-TFSI)-containing electrolytes is significantly enhanced by the formation of a fluoroethylene carbonate (FEC)-derived protective film on an anode during the first cycle. The electrochemical intercalation of MMDMEA cations into the graphene layer is readily visualized by ex situ transmission electron microscopy (TEM). Moreover, differences in the X-ray diffraction (XRD) patterns of graphite electrodes in cells charged with and without FEC in dimethyl carbonate (DMC)/MMDMEA-TFSI are clearly discernible. Conclusively, the presence of FEC in MMDMEA-TFSI-containing electrolytes leads to a remarkable enhancement of discharge capacity retention for graphite/LiCoO₂ cells as compared with ethylene carbonate (EC) and vinylene carbonate (VC).     

Electrochemical and thermal properties of graphite electrodes with imidazolium- and piperidinium-based ionic liquids

The electrochemical and thermal properties of graphite electrodes with electrolytes containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) and N-methyl,N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (MPPpTFSI) ionic liquids are investigated. The ionic liquids undergo extensive reductive decomposition on a graphite electrode during the first charge. The effect of a fluoroethylene carbonate (FEC) additive on the reductive decomposition of the ionic liquids is examined by electrochemical, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. Thermal reactions between a lithiated graphite electrode and an ionic liquid-containing electrolyte are investigated with differential scanning calorimetry (DSC). The introduction of an ionic liquid can effectively reduce the exothermic heat evolution from the thermal reactions between a lithiated graphite electrode and an electrolyte.     

Redistribution of phosphoric acid in membrane electrode assemblies for high-temperature polymer electrolyte fuel cells

We demonstrate that the performance of a high-temperature polymer electrolyte fuel cell with a phosphoric acid-based electrolyte is almost independent of the way of introducing the acid into the membrane electrode assembly (MEA). The same power densities were obtained with different MEAs in which the poly(2,5-benzimidazole) membrane was either pre-doped or not and in which either one or two catalyst layers were impregnated with H₃PO₄. Chemical analysis after shut down revealed that in all these MEAs the phosphoric acid distribution between the membrane and the electrodes was nearly the same. An MEA with acid impregnation via the electrodes was started up rapidly from room temperature, delivered a power density of 120 mW cm⁻² at 600 mV (H₂/air, 160 °C, ambient pressure) after only 11 min and was operated for 1000 h (degradation rate: 0.06 mV/h). Based on the analysis of the H₃PO₄ content in the MEA components, reflections on the kinetics of the redistribution of phosphoric acid within the MEA are provided.     

Effect of Ti substitution on electrochemical properties of ZrNi alloy electrode for use in nickel-metal hydride batteries

Crystal structure and electrochemical properties of the Zr_1?xTi_xNi (0.05 ≤ x ≤ 0.5) alloys were investigated. X-ray diffraction spectra showed that the primary phase of all Zr_1?xTi_xNi alloys had the B33-type orthorhombic crystal structure, which was characteristic of ZrNi, and the unit cell volume of the primary phase linearly decreased with an increase in the x value. In the charge–discharge tests with the Zr_1?xTi_xNi alloy negative electrodes, the initial discharge curves for the alloys with x ≥ 0.3 had two plateaus. Both plateau potentials negatively shifted with an increase in the x value. The initial discharge capacity for the Zr_0.6Ti_0.4Ni alloy negative electrode was 349 mAh g^?1 at 25 mA g^?1 and 333 K, which was the highest in this study. The high-rate dischargeability and cycle performance were also improved by the partial replacement of Zr by Ti.     

Preparation and performances of LiFePO4 cathode in aqueous solvent with polyacrylic acid as a binder

Here we report the preparation of LiFePO₄ cathode for lithium ion battery in the aqueous solvent with polyacrylic acid (PAA) as a binder. Its performances were studied by cyclic voltammetry (CV), charge–discharge cycle test, electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), and scanning electron microscopy (SEM), and compared with the cathode prepared in N-methyl-2-pyrrolidone (NMP) solvent by using polyvinylidene fluoride (PVDF) as a binder. It is found that the cathode prepared in the aqueous solvent shows better performances than that in NMP solvent, including the better reversibility, the smaller resistances of solid electrolyte interphase and charge exchange, the less polarization, higher capacity and cyclic stability for lithium ion intercalation in or de-intercalation from LiFePO₄. The aqueous solvent is also more environmental friendly and cheaper than NNP. In addition, PAA is less costly than PVDF. Consequently, the preparation of LiFePO₄ cathode in the aqueous solvent by using a PAA binder provides lithium ion battery with improved performances at a less cost and in a more environmental friendly way.     

Combined cyclic voltammetry and in situ electrochemical atomic force microscopy on lead electrode in sulfuric acid solution with or without lignosulfonate

The effect of lignosulfonate (LS) on electrochemical reaction of lead electrode (as a model of negative electrode) has been investigated in 1 M, 3 M, or 7.1 M H₂SO₄ aqueous solution with 0, 10, 100 or 1000 mg l⁻¹ of LS using cyclic voltammetry (CV) combined with in situ electrochemical atomic force microscopy (EC-AFM), as well as rotating ring disk electrode (RRDE). The anodic peaks of the CVs, which correspond to overall reaction of , shifted positive when LS was added or the concentration of H₂SO₄ was lower. The anodic capacities of the CVs increased with addition of LS when the concentration of H₂SO₄ was lower. When LS was added, the anodic capacities of the CVs usually increased especially in less concentrated H₂SO₄ solution at higher sweep rate, while the anodic capacity slightly decreased in 7.1 M H₂SO₄ solution with addition of LS at sweep rate of 10 mV min⁻¹; that is, in most concentrated H₂SO₄ solution at lower sweep rate in this paper. Two cathodic peaks of the CVs were observed when LS was added, and the peak at lower potential shifted more negative with increase of LS. Lead sulfate crystals dissolved at more negative potential with increase of LS. LS up-took Pb²⁺ ions in H₂SO₄ aqueous solution during discharging.