S.E.M. studies of the Li-film growth and the voltage-delay phenomenon associated with the lithium-thionyl chloride inorganic electrolyte system

The “voltage-delay” exhibited by the Li/SOCl₂ inorganic electrolyte cells has been determined to be due to the Li anode which presumably reacts with the soluble depolarizer SOCl₂ and forms a protective film. The morphology and the growth of the Li film have been studied at temperatures of 25°, 45°, 55°, 70° and 85°C employing S.E.M. The results show that Li is coated with LiCi crystals formed due to the chemical reaction between Li and inorganic electrolyte (LiAlCl₄-SOCl₂). The LiCl film (many microns thick) grows with time and temperature of storage resulting in the voltage delay. The voltage recovery appears to occur due to the mechanical disruption of the film during the anodic dissolution of Li from under the film at isolated spots. The Li film growth is significantly reduced in the absence of LiAlCl₄ in SOCl₂.     

Passivation of porous carbon cathodes in lithium-thionyl chloride cells

The passivation of porous carbon cathodes in 1.8 M LiAlCl₄–SOCl₂ solution has been studied. The electrodes were galvanostatically discharged for a range of current densities and electrode thicknesses. The results show that the passivation of the cathode is controlled by the rate of diffusion of the LiCl product away from the electrode. This was shown by the ability of passivated glassy carbon to recover capacity for SOCl₂ reduction when allowed to stand in the electrolyte solution.The results show that there is a limiting cathode thickness beyond which additional carbon loading fails to increase the passivation time.     

Impedance analysis of the lithium discharge in Li-SOCl2 cells: Synergetic effect of SO2 and LiAl(SO3Cl)4

A study of the anodic discharge of the Li electrode in LiAlCl₄/SOCl₂ electrolyte shows the occurrence of a diffusion process mainly when the surface layer was formed in the presence of the inorganic additives SO₂ and LiAl(SO₃Cl)₄. A model of the electrode kinetics is proposed on the assumption that the ionic diffusion is hindered by the precipitation of the solute LiAlCl₄ at the bottom of holes formed in the compact polycrystalline LiCl surface layer by a dissolution-dilation mechanism.     

The i.r. analysis of water traces in electrolytes for Li/SOCl2 cells

It is established that the absorbance of the SOCl₂/LiAlCl₄ electrolyte solutions at 2800 cm^–1 is due the HCl, generated in the solution as a result of the hydrolysis reaction of SOCl₂. A slow self-desiccation reaction of the hydrated AlOHCl₂ is also postulated to occur in these solutions.     

Properties of surface layers formed on lithium in Li-SOCl2 cells: synergetic effect of SO2 and LiAl(SO3Cl)4

Kinetic and morphological properties of surface layers formed on the Li anode during storage in SOCl₂/LiAlCl₄ solution have been investigated. The synergetic effect of SO₂ and LiAl(SO₃Cl)₄, used for voltage delay alleviation, changes the shape and size of the microcrystals of LiCl constituting the surface layer. It also leads to separate and modify the conduction and charge transfer processes involved in the kinetic properties of the surface layer at the equilibrium potential. These properties appear to be similar to those of a polycrystalline solid electrolyte where the grain boundaries induce an intergranular conduction process.     

STABILITY OF NONAQUEOUS ELECTROLYTES FOR AMBIENT TEMPERATURE RECHARGEABLE LITHIUM CELLS

Three tests have been used lo determine the stability of solutions of two nonaqueous solvents, propylene carbonate and 2-methyl-tetrahydrofuran and their solutions of LiAlCl₄. LiAsF₆ and LiClO₄ in contact with lithium. The procedures identify the effect of surface layers, open-circuit stand, anodic and cathodic polarization. They employ (1) contact with liquid Li amalgam and solid sheet Li; (2) open circuit potential measurements of cathodic deposits and (3) anodic dissolution of deposits with ramped potential. The stability of solvents is found to depend on the dissolved electrolyte. Polymeric materials containing other products of the reaction between metal and electrolytes have been identified by X-ray diffraction.     

The synthesis and catalytic activity to Li/SOCl2 battery of two new porphyrins

Two new porphyrins (3a, 3b) were synthesized and characterized by IR, UV–vis, ¹H NMR, MS and elementary analysis. The catalytic activity of the synthesized porphyrins to lithium/thionyl chloride (Li/SOCl₂) battery is evaluated by the relative energy of the battery whose electrolyte contains the porphyrins. The results indicate that the energy of Li/SOCl₂ battery catalyzed by porphyrins 3a and 3b is 101, 37% higher, respectively, than that of Li/SOCl₂ battery in the absence of the porphyrins. It can be used as a basis for the synthesis of more porphyrins with improved catalytic activity to Li/SOCl₂ battery in the future.     

Purification process for an inorganic rechargeable lithium battery and new safety concepts

We have investigated an inorganic lithium battery system in which LiCoO₂ is used as the positive electrode and lithium, intercalated into graphite, serves as negative electrode. The conducting salt is lithium tetrachloroaluminate (LiAlCl₄). The electrolyte is based on SO₂. It has been shown that a layer of lithium hydroxide is present on the surface of the lithium cobalt oxide. This has a negative impact on the stability of the electrode. To improve stability, we have developed a purification process for removing the lithium hydroxide from the surface of the positive electrode. After purification the cells show no significant change in either capacity or internal resistance when cycled. Up to 70% of the theoretical capacity of electrodes which have been purified in this way can be used without any negative effects being observed. To prevent the deposition of metallic lithium leading to a hazardous situation, a new safety concept was developed whereby local short circuits are allowable. Safe functioning of the new concept has been demonstrated with tests on complete cells.     

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.     

EIS study of the influence of BrCl on the behavior of electrodes in Li/SOCl<Subscript>2</Subscript> cells

The influence of BrCl on the impedance response of both the lithium anode and the carbon cathode in Li/SOCl₂ cells was studied. The impedance of the lithium anode increases with storage time while the addition of BrCl to Li/SOCl₂ cells decreases the impedance. However, the porous carbon cathode shows a small film resistance before discharge. The addition of BrCl to Li/SOCl₂ cells also decreases the impedance, especially for that part of the interface reaction resistance R₂. As a rule, the film resistance of the lithium anode decreases sharply during the early period of discharge, while that of the porous carbon cathode rises rapidly. It follows that the porous carbon cathode is the rate controlling electrode during discharge.     

A study of the delay effect in SOCl2 batteries

Electrical and microstructural properties of the passive layers formed on lithium in SOCl₂ containing different additives (PVC, inorganic salts, cathode additives) were studied. LiCl crystals were found to be cubic, octahedral or needle-like. Typical passive layer thicknesses were 1–20 µm. The electrical properties of the passive layer were explained by referring to the space charge model of SEI conduction. It was pointed out that impedance spectroscopy may be selectively used as a non-destructive method for estimation of the galvanostatic behaviour of lithium batteries. The best results, as regards the elimination of the delay effect, were obtained with a combination of organic and inorganic electrolyte additives.     

Solid Electrolyte Interphase (SEI) Electrodes. Part 1. The Kinetics of Lithium in LiAlCl4-SOCl2

The lithium electrode is always covered by a film of lithium chloride which acts as solid electrolyte interphase (SEI). Macropolarization curves indicate that the Tafel slope is greater than 3 V for electrodes having SEI thicker than 400 Å. This confirms that the rds for the deposition-dissolution process is the migration of lithium cations through the SEI. Increasing the electrolyte concentration increases the interfacial capacitance and decreases the resistivity of the SEI. This is explained in terms of the effect of LiAlCl₄ concentration on the concentration of the lattice defects. The effect of the concentration of the electrolyte on the resistivity of the SEI decreases as the thickness of the SEI is increased. The growth rate of the SEI increases as the concentration of the electrolyte is increased.     

Bromine chloride as a cathode component in lithium inorganic cells

Investigations were conducted on a Li inorganic battery system using BrCl and SOCl₂ as co-depolarizers. The Li/BrCl, SOCl₂ cell exhibited an open-circuit voltage of 3.90±0.02 V at room temperature. The discharge results of cells of various sizes showed that an energy density of l W h cm^–3 is possible at low discharge rates at room temperature. The storage tests showed no significant capacity loss after a storage period of 15 months at ambient temperature or three months at 72° C. The cells were subjected to abuses such as short circuiting, forced overdischarge and charge. No hazard of any kind was encountered during these tests. In view of these results, we concluded that Li/BrCl, SOCl₂ is a practical system for high energy density batteries.     

Electrochemical studies of electrospun organic/inorganic hybrid nanocomposite fibrous polymer electrolyte for lithium battery

Poly(vinylidene fluoride-co-hexafluoropropylene) P(VdF-co-HFP)/magnesium aluminate (MgAl₂O₄) hybrid fibrous nanocomposite polymer electrolyte membranes were newly prepared by electrospinning method. The as-prepared electrospun pure and nanocomposite fibrous polymer membranes with various MgAl₂O₄ filler contents were characterized by X ray diffraction, differential scanning calorimetry and scanning electron microscopy techniques. The fibrous nanocomposite polymer electrolytes were prepared by soaking the electrospun membranes in 1 M LiPF₆ in EC:DEC (1:1, v/v). The fibrous nanocomposite polymer electrolyte membrane with 5 wt.% of MgAl₂O₄ show high electrolyte uptake, enhanced ionic conductivity is found to be 2.80 × 10⁻³ S cm⁻¹ at room temperature and good electrochemical stability window higher than 4.5 V. Electrochemical performance of commercial celgard 2320, fibrous pure and nanocomposite polymer electrolyte (PE, NCPE) membranes with different MgAl₂O₄ filler content is evaluated in Li/celgard 2320, PE, NCPE/LiCoO₂ CR 2032 coin cells at current density 0.1 C-rate. The NCPE with 5 wt.% of MgAl₂O₄ delivers an initial discharge capacity of 158 mAhg⁻¹ and stable cycle performance compared with the other cells containing celgard 2320 separator and pure membrane.     

Three electrolyte high voltage acid–alkaline hybrid rechargeable battery

Performance characteristics of a three electrolyte rechargeable acid–alkaline hybrid battery using a PbO₂ positive plate and a nickel metal hydride (NiMH_x) negative electrode in separate electrolyte of H₂SO₄ and KOH were studied. This hybrid battery has three electrolytes in a single cell. A neutral K₂SO₄ salt solution was placed between the acid and alkaline compartments of the cell, in which a cation exchange membrane and an anion exchange membrane, were employed to separate these three electrolytes. The open circuit voltage of this hybrid cell was found to be 2.64 V in an electrolyte configuration of 1 M H₂SO₄|0.2 M K₂SO₄|2 M KOH electrolyte configuration, compared to 1.92 V in the conventional lead-acid cell in 1 M H₂SO₄ and 1.40 V in a NiMH_x cell in 2 M KOH. This hybrid acid–alkaline PbO₂/NiMH_x battery was shown to operate with a voltage 20% higher than the conventional lead acid battery and 110% higher than nickel–metal hydride battery at 1/3 C discharging rate. The concentrations of the three electrolytes, the dimension of the electrolyte chamber, and other cell/operation parameters with impacts on the hybrid cell performance were investigated.     

Electrochemical Synthesis and Characterization of Conducting Copolymer: Poly(o-aniline-co-o-anisidine)

Copolymerization of o-anisidine and o-anisidine was achieved electrochemically in aqueous solution containing H₂SO₄ as supporting electrolyte. The copolymer compositions can be altered by varying the monomer feed ratios during electrosynthesis. The films were electropolymerized in solution containing monomers in various ratio (0.025–0.1 M) and 1 M sulphuric acid as electrolyte by applying sequential linear potential scan rate 50 mV/s between ? 0.2 to 1.0 V. versus Ag/AgCl electrode. The copolymers were characterized by cyclic voltammetric, conductivity measurement, UV-Visible spectroscopy, FT-IR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and CHN elemental analysis.     

Neutralization of used Li batteries: Anodic dissolution of the iron–nickel alloy positive pins of Li–SOCl2 batteries in seawater

This paper reports a study of the neutralization of Li–SOCl₂ batteries. Immersion of these batteries in acidic seawater solutions leads to their complete discharge by short circuit, followed by corrosion of the positive pin (made of an Fe/Ni alloy). This corrosion process is desirable because it allows penetration of water into the battery, and hence, neutralization of the active mass of the batteries through their reaction with water. The most efficient corrosion of Fe/Ni electrodes is obtained in seawater containing both HCl and H₂SO₄ in a situation of no separation between the electrode compartments, due to the reaction of the H₂ liberated at the cathode with the surface films on the anode (Fe/Ni pin electrodes). This reaction prevents passivation of the positive pin. Indeed, used Li–SOCl₂ batteries whose insulating covers were removed, corroded much quicker than regular batteries because of the impact of H₂ evolved at the case (the negative pole of the battery) on the dissolution of the positive pin.     

The Conductivity of Poly(o-anisidine), Poly(o-toluidine) and Their Copolymer with Various Inorganic Dopants in the Presence of Electrolyte

ABSTRACT

An attempt has been made to prepare poly(o-anisidine) (POA), poly(o-toluidine) (POT) and copolymer poly(o-anisidine)-co-poly(o-toluidine) (POA-co-POT) thin films dopped by several inorganic salts (sulphates and chlorides) with varying size of cations using aqueous solution of H₂SO₄ as electrolyte. The effect of dopant in the presence of electrolyte is rarely studied in the field of conducting polymers. Various inorganic salts as dopants, namely, K₂SO₄, Na₂SO₄, Li₂SO₄, MgSO₄, KCl, NaCl, LiCl, and MgCl₂ are used at room temperature. The films were electropolymerized in solution containing 0.1 M monomer(s), 1 M H₂SO₄ as electrolyte and 1 M inorganic salt, by applying sequential linear potential scan rate 50 mV/sbetween ? 0.2 to 1.0 V versus Ag/AgCl electrode. The electro-synthesized films were characterized by cyclic voltammetry, UV-visible spectroscopy, and conductivity measurements. It was observed that the UV-visible peaks usually appearing at about 802–826 nm with a shoulder at 410–426 nm shows a shift in presence of doping salt for emeraldine salt (ES) phase of POA, POT, POA-co-POT. In overall study, a significant increase in conductivity is observed for all mentioned dopants and among these K₂SO₄ is found to be the best in sulphate category and KCl in chloride category. The formation of copolymer has been confirmed by differential scanning calorimetry.     

Importance of water content in formation of porous anodic niobium oxide films in hot phosphate-glycerol electrolyte

Niobium has been anodized at a constant current density to 10 V with a current decay in 0.8 mol dm⁻³ K₂HPO₄-glycerol electrolyte containing 0.08-0.65 mass% water at 433 K to develop porous anodic oxide films. The film growth rate is markedly increased when the water content is reduced to 0.08 mass%; a 28 μm-thick porous film is developed in this electrolyte by anodizing for 3.6 ks, while the thickness is 4.6 and 2.6 μm in the electrolytes containing 0.16 and 0.65 mass% water respectively. For all the electrolytes, the film thickness changes approximately linearly with the charge passed during anodizing, indicating that chemical dissolution of the developing oxide is negligible. SIMS depth profiling analysis was carried for anodic films formed in electrolyte containing ∼0.4 mass% water with and without enrichment of H₂¹⁸O. Findings disclose that water in the electrolyte is a predominant source of oxygen in the anodic oxide films. The anodic films formed in the electrolyte containing 0.65 mass% water are practically free from phosphorus species. Reduction in water content increased the incorporation of phosphorus species.     

SOCl2/EtOH: Catalytic system for synthesis of chalcones

In the presence of SOCl₂/EtOH as a catalyst, various substituted chalcones are synthesized by aldol condensation. The HCl is generated in situ by the reaction of SOCl₂ with absolute ethanol.