Studies of Zn|ZnX2|polyaniline batteries. II. X=I

The characteristics of a Zn|ZnI₂|polyaniline battery have been examined. It is demonstrated that the polymer has a charge storage capacity of 143 A h kg^–1 and an energy efficiency above 70%. The battery has an open circuit voltage of 1.2 V and polarization during charges and discharges at 30–120 mA were low. Self discharge is low compared to the chloride and bromide electrolyte batteries and charge recovery was 60% after 12 days stored on open circuit. It is shown that these promising characteristics may be interpreted in terms of a system where the polyaniline largely acts as a current collector and the I ₃ ^– /I^– couple is rapid within the film. The kinetics of the system are determined by a.c. impedance.     

Polyaniline: characterization as a cathode active material in rechargeable batteries in aqueous electrolytes

An analytically pure form of chemically synthesized polyaniline having the emeraldine oxidation state has been used as a cathode active material together with a Zn anode in the fabrication of rechargeable cells in 1.0 M aqueous ZnCl₂ electrolyte (pH4). The experimental capacity and energy density based only on the weight of polymer employed in constructing the cell are 151.5 Ah kg^–1 and 159.1 Wh kg^–1 respectively at a constant discharge current of 0.75 mA cm^–2 (average discharge voltage 1.05V). The cell reactions in the charge and discharge processes have been determined. The modified capacity and energy density, when taking into account the calculated weights of Zn and HCl involved in the discharge reactions, are 109.3 Ah kg^–1 and 114.8 Wh kg^–1 respectively. The cell shows excellent recyclability and coulombic efficiency.     

Preparation and electrochemical characteristics of a new Li-Mn-V-O system formed from heat-treatment of a MnO2, NH4VO3 and LiNO3 mixture

New quarternary oxides (Li₂O) _x · MnO₂ · yV₂O₅ (x = 0.125 0.25, y = 0.125 0.25), formed by heating mixtures of MnO₂, NH₄VO₃ and LiNO₃ at various Li/Mn and V/Mn atomic ratios and at different temperatures (300 400 °C in air, have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy (ESCA) and infrared spectroscopy. The quarternary oxide with x = 0.25 and y = 0.25 showed a discharge capacity of 220 A h (kg oxide)^–1 and an energy density of ca. 600 W h (kg oxide)^–1 at a current density of 0.20 mA cm^–1 in 1 m LiClO₄-propylene carbonate at 25 °C. When charge-discharge cycling with the (Li₂O) · MnO₂ · 0.25V₂O₅ electrode was performed at a constant capacity of 30 A h (kg oxide)^–1 and at a constant current density of 0.10 0.20 mA cm^–2, the electrode sustained over 100 cycles at a high mean discharge potential of ca. 3 V vs Li/Li⁺.This paper was originally presented at the 183rd meeting of the Electrochemical Society (Honolulu, Hawaii, 1993).     

Effects of electrochemically incorporated bismuth on the discharge and recharge of electrodeposited manganese dioxide films in 9m aqueous KOH

Previous reported work has demonstrated that MnO₂ can be made multiple rechargeable over the two-electron capacity by chemical modification through incorporation of a small concentration of Bi(iii) species. In the present work, conditions required for inclusion of bismuth species in electrolytically produced MnO₂ deposits on porous graphite are reported together with resulting electrochemical effects of the bismuth species on rechargeability of the electrodeposited MnO₂. The optimum conditions for deposition were found to be: temperature 85–90°C; bath composition 0.5 to 2m H₂SO₄, 0.5m MnSO₄, 0.005 to 0.01m Bi³⁺ and current density 5 to 20 mA cm^–2 (apparent). The mechanism proposed for the inclusion of bismuth species is by continuous precipitation caused by high local acidity generated at the electrode by the reaction of anodic deposition of MnO₂. With respect to the mechanism of reduction and reoxidation of MnO₂ in 9m KOH with bismuth species present, a previously suggested role of soluble intermediates is confirmed. It is proposed that bismuth may aid in the nucleation and growth process associated with formation of Mn(OH)₂ or MnO₂ from a soluble Mn(iii) intermediate. Such a process must take place in order for completion of either discharge or recharge to take place at the electrode. It seems that the role of the included Bi species is to promote a discharge and recharge mechanism of the so-called heterogeneous kind involving a soluble Mn(iii) intermediate over an alternative, solid-state, homogeneous pathway.     

Zinc-air cell with neutral electrolyte

The zinc-air electrochemical system in 5m NH₄Cl was studied. The optimum electrolyte-zinc ratio was found to be 50 ml g^–1 Zn and the optimum electrolyte-cathode ratio, 15 ml cm^–2 of carbon cathode. The air cathode polarization is not increased by intermittent usage of the cell. Electrodes made from zinc sponge with addition of lead show the smallest corrosion in the given electrolyte. The cell voltage is about 0.9–0.95 V at a load of 10 mA cm^–2 of carbon cathode at ambient temperature.     

Development of anodes for aluminium/air batteries — solution phase inhibition of corrosion

The discharge characteristics of aluminium in inhibited and uninhibited 4 M KOH at 50°C have been explored. The performance of pure aluminium as a fuel is compared with that for two leading alloy fuels that had been evaluated in our previous work, Alloy BDW (Al–1Mg–0.1In–0.2Mn) and Alloy 21 (Al–0.2Ga–0.1In–0.1Tl). The inhibitors employed in this study, SnO ₃ ^2– , In(OH)₃, BiO ₃ ^3– , Ga(OH) ₄ ^– , MnO ₄ ^2– , and binary combinations thereof, are either present in Alloys BDW and 21 or have been investigated previously (SnO ₃ ^2– ). We found that potassium manganate (K₂MnO₄) and Na₂SnO₃+In(OH)₃ are effective inhibitor systems, particularly at high discharge rates (400 mA cm^–2), but at low discharge rates only manganate offers a significant advantage in coulombic efficiency over the uninhibited solution. Alloy BDW exhibits a very low open circuit (standby) corrosion rate, but its coulombic efficiency under discharge, as determined by delineating the partial anodic and cathodic reactions, was found to be no better than that of aluminium in the same uninhibited solution. Alloy 21 was found to exhibit a comparable performance to Alloy BDW under open circuit conditions and a much higher coulombic efficiency at low discharge rates (100 mA cm^–2), but the performance of this alloy under high discharge rate conditions was not determined. Alloy 21 has the significant disadvantage that it contains thallium.     

Investigation of the 1-methyl-3-ethylimidazolium chloride-AlCl3/LiAlCl4 system for lithium battery application Part I: Physical properties and preliminary chronopotentiometric study

The applicability of the 1-methyl-3-ethylimidazolium chloride — AlCl₃ system for lithium battery application was investigated. Lithium chloride was found to dissolve up to 1.59 mole ratio of LiAlCl₄/MeEtImAlCl₄ upon reaction between LiCl and AlCl₃ in the melt. Density, conductivity and viscosity of the melt upon addition of LiAlCl₄ were determined. The density was found to increase monotonically from 1280 to 1480 kg m^–3, while the conductivity decreased rapidly from the initial value of 5.6 mS to a steady plateau at 3.4 mS. The viscosity was varied from 1.46 Ns m^–2 to a small but distinct initial fall prior to rising to 2.75 Ns m^–2 when the mole ratio of LiAlCl₄ increased from zero to 1.59. The chronopotentiometric studies indicate a satisfactory electrochemical behaviour with no apparent attack of the melt by the formation of the reactive lithium alloys. 350 cycles were achieved with cycling efficiency over 90% using an optimal c.d. of 6 mA cm^–2 for lithium deposition on aluminium substrate in the melt. Prolonged cycling improved the nucleation rate but led to an increase in the internal resistance and a gradual reduction in the charge and discharge capacity.     

The effect of B4C addition to MnO2 in a cathode material for battery applications

Boron carbide (B₄C) added manganese dioxide (MnO₂) used as a cathode material for a Zn-MnO₂ battery using aqueous lithium hydroxide (LiOH) as the electrolyte is known to have higher discharge capacity but with a lower average discharge voltage than pure MnO₂ (additive free). The performance is reversed when using potassium hydroxide (KOH) as the electrolyte. Herein, the MnO₂ was mixed with 0, 5, 7 and 10 wt.% of boron carbide during the electrode preparation. The discharge performance of the Zn|LiOH|MnO₂ battery was improved by the addition of 5-7 wt.% boron carbide in MnO₂ cathode as compared with the pure MnO₂. However, increasing the additive to 10 wt.% causes a decrease in the discharge capacity. The performance of the Zn|KOH|MnO₂ battery was retarded by the boron carbide additive. Transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy analysis (EDS) results show evidence of crystalline MnO₂ particles during discharging in LiOH electrolyte, whereas, manganese oxide particles with different oxygen and manganese counts leading to mixture of phases is observed for KOH electrolyte which is in agreement with X-ray diffraction (XRD) data. The enhanced discharge capacity indicates that boron atoms promote lithium intercalation during the electrochemical process and improved the performance of the Zn|LiOH|MnO₂ battery. This observed improvement may be a consequence of B₄C suppressing the formation of undesirable Mn(III) phases, which in turn leads to enhanced lithium intercalation. Too much boron carbide hinders the charge carrier which inhibits the discharge capacity.     

Lithium secondary cells using LiX (X=ClO4, BF4) as electrolyte and poly(2,5-pyrrolylene) and poly(2,5-thienylene) as materials for positive electrodes

Repeated charge-discharge cycles of lithium secondary cells using poly(2,5-pyrrolylene) and poly(2,5-thienylene) on carbon fibre plates as the materials for positive electrodes have been tested. When the Li|LiBF₄|poly(2,5-pyrrolylene) secondary cell is charged and discharged at 0.1 mA cm^–2, it gives 91% current efficiency and 70% energy efficiency with an average discharging voltage of 2.75 V at the 9th charge-discharge cycle. This secondary cell has a theoretical energy density of 135 kW kg^–1 based on the energy stored and the weights of poly(2,5-pyrrolylene) and the active materials. The Li|LiClO₄|poly(2,5-thienylene) secondary cells show somewhat lower current efficiency and energy efficiency at the 9th charge-discharge cycle. The lithium cells using the polymers are rechargeable more than 50 times, but after about 50 cycles considerable lowering of the current efficiency and energy efficiency of the cells is observed, presumably due to degradation of the polymer.     

The Effect of Aluminum Ions on the DC Etching of Aluminum Foil

A study has been made of the electrochemical etching of 99.99% aluminum foils at a current density of 50 mA cm^–2in AlCl₃–HCl solutions (1 m Cl^–) at 80 °C. The solutions were made by dissolving metallic aluminum into 1m HCl solution, to give a Cl^– concentration of 1 m. The number density of etch tunnels and the homogeneity of tunnel length decreased, and the mean pit size and its standard deviation increased with increasing Al³⁺ concentration. The results were discussed based on potential transients at a current density of 50 mA cm^–2, current–potential curves at a scan rate of 10 m Vs^–1 and electrochemical impedance spectra.     

Electrodeposition of Zn−Ni−Fe alloy in acidic chloride bath with separated anodes

The electrodeposition of ternary Zn–Ni–Fe alloy films was investigated in acidic chloride electrolyte. Electrodeposition was performed onto mild steel plates at pH 3 and 43°C. The influence of the chloride concentration (ZnCl₂, NiCl₂ and FeCl₂) on the surface appearance and deposit composition, as well as cathodic current efficiency, were investigated. Bright Zn–Ni–Fe alloy deposits were obtained in the electrolyte containing 0.4m of each of ZnCl₂ and NiCl₂ with 0.02 to 0.08m FeCl₂. The influence of current density, pH and temperature were also examined.     

Electrochemical oxidation of manganese(II) at a platinum electrode

Electrochemical oxidation of Mn²⁺ in sulphuric acid to form MnO₂ was studied using stationary and rotating platinum/platinum ring-disc electrodes. It appears that nucleation of MnO₂ is governed by an equilibrium involving a Mn(III) intermediate. Growth of MnO₂ involves the reduction of MnO₂ surfaces by Mn²⁺ ions in the solution to form MnOOH intermediates. The subsequent electrochemical oxidation of MnOOH releases a hydrogen ion and results in the formation of MnO₂. The rate constant of MnOOH oxidation to MnO₂ was estimated to be 40 s^–1. With a sufficient supply of Mn²⁺ ions, a layer of MnOOH is built up and the in-solid diffusion of hydrogen ions becomes the ratedetermining-step. With a low Mn²⁺ concentration, diffusion of Mn²⁺ ions from bulk electrolyte to the MnO₂/electrolyte interface is a factor controlling the growth of MnO₂. The activation energy and the pre-exponential term of the diffusion coefficient of Mn²⁺ in 0.5m sulphuric acid were determined to be 44.8 kJ mol^–1 and 100 cm² s^–1, respectively.     

The conductivity of aqueous zinc chloride solutions

The conductivity of aqueous zinc chloride reaches a maximum of 10.7 ^–1 m^–1 at 3.7 M ZnCl₂. Measurements on chlorinated ZnCl₂ showed that at low chlorine concentrations, the conductivity increased linearly with the square root of the chlorine concentration. The increase was due to the three species: dissolved chlorine, Cl ₃ ^– and HClO. Ammonium chloride additions increased the conductivity of aqueous zinc chloride substantially.     

Thermal battery cells utilizing molten nitrates as the electrolyte and oxidizer

The Ca/LiNO₃-LiCl-KCl (50-25-25 mol%) thermal battery cell can be activated at 160° C and operated over a temperature range of 250–450° C to produce 2.5–2.8 V at open-circuit and initial operating voltages above 2 V at 10 mA cm^–2. At operating temperatures between 250 and 350° C, this system shows promise for applications requiring a sixty-minute thermal battery. Cell lifetimes decrease at higher temperatures due to the accelerating reaction of calcium with the molten nitrate salt to form gaseous products. An experimental energy density value of 142 Whkg^–1 was obtained at 300° C during constant current discharge at 10 mAcm^–2. Effects of applied face pressure on cell discharge characteristics were small. At current densities above 20–30 mA cm^–2, the cell performance deteriorates due to polarization at the anode. This is probably caused by the precipitation of CaO which blocks the active sites at the anode.     

Control of oxygen deficiency in Ca1−x La x MnO3−δ and its cathodic properties in alkaline solution

Ceramic samples of composition Ca_0.9La_0.1MnO_3– having various oxygen contents were prepared by a quenching method under nitrogen atmosphere. As the 3 – value decreased from 2.97 to 2.79, the sample conductivity decreased from 10² to 10^–1 S cm^–1. The porous ceramic samples showed good properties as cathode materials in alkaline solution without using conductive material such as graphite, but the discharge capacity decreased with decreasing sample conductivity. The discharge termination is explained by a simple model considering dissipation of the conductive path (high conductivity core) present in the porous sintered ceramic.     

The cathodic behavior of microwave-treated manganese dioxide in lithium nonaqueous cells

The cathodic behavior of microwave-treated manganese dioxide (MnO₂) was studied in lithium nonaqueous cells. Two types of discharge tests, low rate continuous discharge at current densities of 0.1–5 mA cm^?2 and high rate pulse-discharge at current densities of 10–25 mA cm^?2 were carried out in 1 M LiClO₄—propylene carbonate—50% tetrahydrofuran—50% electrolyte, and it was found that the Li—microwave-treated MnO₂ cell exhibited good characteristics in both types of discharge tests. A stability test of microwave-treated MnO₂ in a cell was also carried out, and it was shown to have no problems with gassing and to provide long shelf life.     

Aluminium alloys in sulphuric acid Part I: Electrochemical behaviour of rotating and stationary disc electrodes

Anodic oxidation of various aluminium alloys was investigated by means of rotating disc electrodes in 3 M H₂SO₄ as a function of Cl^–, F^–, Zn²⁺ and In³⁺ concentration. Al-In, Al-Zn/In and Al-Zn/Sn alloys yielded current-potential curves at the lowest overpotentials and faradaic efficiencies for anodic oxidation of up to 98% at currents 50 mA cm^–2. While these alloys were electrochemically active in the presence of chloride as the only additive in sulphuric acid, binary aluminium alloys with Ce, Ga, La, Nd, Sn, Ta, Te, Ti or Tl were only active when Cl^–, Zn²⁺ and In³⁺ species were added to the electrolyte. With the exception of Al-Ga, binary alloys displayed high faradaic efficiencies of up to 95%. Fluoride additives resulted in current-potential curves at even more negative potentials than those with chlorides. In contrast to Cl^–, fluoride ions are consumed during the aluminium oxidation process due to complexation with Al(III).     

Galvanostatic cycling of graphite intercalation electrodes with anions in aqueous acids

Natural graphite flakes (80 wt%), with polypropylene (20 wt%) as a binder, constitute a practical and non-expensive graphite electrode of high crystallinity CPP. Galvanostatic cycling of these electrodes with current densities in the range 0.3–30 mA cm^–2 (charging time 5–120 min) has been investigated in aqueous acids (12, 20 and 36 mol dm^–3 HF, 6 and 12 mol dm^–3 H₂SO₄, 4 mol dm^–3 HClO₄). The anion of the acid is anodically intercalated and cathodically de-intercalated. In spite of the high water concentrations, quantitative current efficiencies have been obtained. From variation of the rest times after charging, a corrosion current density of less than 0.03 mA cm^–2 (j _ch=3 mA cm^–2) has been derived. The overvoltage during charge and discharge is typically about 0.1 V. The potential at the start of the charging process coincides with the intercalation potential defined previously. A strong electrode formation effect is observed upon cycling. The electrode is initially smooth and non-porous; it acquires a high surface roughness after a few cycles, which is then stable. The initial charging curves increase witht ^1/2, while the charging curve after electrode formation is linear. Both clearly indicate a linear relationship between surface concentration of intercalated anions and potential. This agrees with our previous finding of linear dependence with respect to acid concentration in the solution.     

The influence of catalyst-supporting methods on electrochemical activity and the resultant stability of air electrodes activated with iron phthalocyanine

To improve the performance of air electrodes, the dependence of iron phthalocyanine (FePc) catalytic effects on preparation methods was examined. The methods used were mixture (Electrode 1), impregnation (Electrode 2) and direct synthesis (Electrode 3). Electrodes 2 and 3 showed higher potentials during cathodic polarization up to 10 mA cm^–2 than Electrode 1. The rate of chemical destruction of H₂O₂ decreased in the order Electrode 3 > Electrode 2 > Electrode 1. Electrode 3 showed the smallest potential drop for a discharge at 10 mA cm^–2, 0.09 V after 50 h. However, the potential of Electrode 2 decreased with discharge, becoming 0.09 V lower than that of Electrode 3 after a 50 h discharge at 10mA cm^–2. Once the potential drop occurred, the potential was not recovered by resting or by drying the electrode. The potential drop may be caused by deactivation of FePc. One possible reason for such deactivation is the presence of H₂SO₄, which remained on the electrode after impregnation of the FePc-H₂SO₄ solution.     

Effect on discharge of the heat treatment of graphite fluoride under a hydrogen atmosphere

Thermal decomposition of two types of graphite fluorides (CF) _n and (CF) _n , has been carried out in a hydrogen atmosphere at several temperatures between 100 and 500°C, with the object of improving the initial discharge behaviour of the Li/graphite flouride cell. The main reaction was the C-F bond rupture to form graphite-like carbon around the particle surface. The drop in cell voltage at the beginning of discharge could be minimized, and the polarization during discharge reduced by heat treatment under a hydrogen atmosphere. (CF) _n , heat treated at 400°C for 1 h, yielded a discharge capacity of 730–800 mA h per g of active material, corresponding to the discharge efficiency of 8390% at 25°C, and (C₂F) _n , heat treated at 350°C, for 10h, gave 670 mA h g^–1, corresponding to 91 % at 25°C.