Chemistry: electrical current producing apparatus – product – and – Plural concentric or single coiled electrode
Patent
1996-12-11
1998-04-21
Skapars, Anthony
Chemistry: electrical current producing apparatus, product, and
Plural concentric or single coiled electrode
429194, 429218, H01M 458, H01M 1040
Patent
active
057416079
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a rechargeable electrochemical cell. The rechargeable electrochemical cell may be used as a storage battery or as a capacitor.
Non-rechargeable lithium electrochemical cells are well known. In one application a two cell battery is used in the consumer field and it has a manganese dioxide positive electrode. In another application a battery used in the military field employs a lithium sulphur dioxide liquid electrolyte de-polarizer system. Both of these battery systems are renowned for their high energy densities of more than 300 Watt hours/Kg, high power densities and modest raw material costs. Attempts to recharge such primary cells have met with little or no success. In the case of the manganese dioxide cell, the product formed on electrochemical reduction with lithium at the positive electrode has a radically altered chemical structure and the lithium intercalated on discharge is recoverable to a small extent only on current reversal. With the lithium sulphur dioxide liquid electrolyte/depolarizer system, the presence of sulphur dioxide in direct contact with lithium metal at the negative electrode gives an immediate reaction product on the surface of the lithium metal. This makes the plating of bulk lithium metal, as required on recharge, grossly inefficient since the regenerated electrode is being consumed as it is formed. Cells containing the highly volatile sulphur dioxide as a major electrolyte constituent have the attendant disadvantages of requiring expensive reinforced cell containers and corrosion resistant hermetic seals to obviate the expulsion of noxious sulphur dioxide fumes into the atmosphere, such as would occur under abuse conditions.
It is an aim of the present invention to provide a rechargeable electrochemical cell which combines the flat voltage characteristic of a sulphur dioxide electrode on discharge, with an immobilizing host in the form of a transition metal oxide.
Accordingly, the present invention provides a rechargeable electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, the positive electrode being such that it is a composition of an alkali or alkaline earth salt of a sulphur oxy-acid and a transition metal oxide, and the electrolyte being such that it is a non-aqueous electrolyte containing a soluble salt of the alkali or alkaline earth metal dissolved the non-aqueous electrolyte.
Preferably, the salt of a sulphur oxy-acid is a lithium salt. The lithium salt is preferably lithium sulphite (Li.sub.2 SO.sub.3), lithium dithionate (Li.sub.2 S.sub.2 O.sub.6) or lithium dithionite (Li.sub.2 S.sub.2 O.sub.4).
The transition metal is preferably one or more of ferrous oxide (FeO), titanium monoxide (TiO), manganous oxide (MnO), manganic oxide (Mn.sub.2 O.sub.3), vanadium trioxide (V.sub.2 O.sub.3), vanadium dioxide (VO.sub.2), cuprous oxide (Cu.sub.2 O) or nickelous oxide (NiO). Many other transition metal oxides may be used as will be familiar to those versed in this technology. The oxides may be used singly or in combination.
The alkali or alkaline salt in solution is preferably present in approximately 1 molar concentration. Other concentrations may however be employed with a preferred molar concentration range being 0.5-2 molar concentration.
The alkali or alkaline salt in solution in the electrolyte is preferably a lithium salt. Other alkali or alkaline earth salts may however be employed, with the corresponding sulphur oxy-acid salt in the cathode.
A soluble salt of the alkali or alkaline earth metal must always be present in the non-aqueous electrolyte solution. For lithium this can be lithium fluoroborate or lithium hexafluorophosphate or a number of other complex lithium fluorides, for example, lithium trifluoromethane sulphonimide LiN(CF.sub.3 SO.sub.2).sub.2. The said salt provides a source of alkali-metal ions or alkaline earth metal ions in solution for electroplating alkali metal or alkaline earth metal from the cathode compound or complex, for example lithium sulphite which is totally insoluble in
REFERENCES:
patent: 5278000 (1994-01-01), Huang et al.
patent: 5352548 (1994-10-01), Fujimoto et al.
patent: 5525443 (1996-06-01), Okumo et al.
patent: 5538814 (1996-07-01), Kamauchi et al.
patent: 5554458 (1996-09-01), Noda et al.
Lexcel Technology Limited
Skapars Anthony
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