GB1588409A

GB1588409A - Reserve basttery electrodes

Info

Publication number: GB1588409A
Application number: GB5365576A
Authority: GB
Original assignee: McMurdo Instrument Co Ltd
Current assignee: McMurdo Instrument Co Ltd
Priority date: 1977-12-07
Filing date: 1977-12-07
Publication date: 1981-04-23

Description

(54) IMPROVED RESERVE BATTERY ELECTRODES (71) We, THE MCMURDO INSTRU MENT COMPANY LIMITED, a British company of Rodney Road, Portsmouth, Hants, P04 8SG, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention is concerned with an electrode for use in a lead/lead dioxide reserve battery (that is, a battery in which the electrolyte is held in reserve, and is only introduced between the respective electrodes when an electrode potential is required).

In conventional lead/lead dioxide batteries, the lead dioxide is deposited as a thin layer on a conductive substrate (which acts as a current collector) to form an electrode.

Batteries containing such electrodes are very successful when the discharge time of the battery after priming by the introduction of the electrolyte is limited to a few minutes or hours.

We have now developed an improved reserve battery electrode, which enables a reserve battery of extended discharge time to be produced.

The reserve battery electrode according to the invention comprises a container which is pervious to liquid electrolytes and which contains separate particles of lead dioxide which are in contact with current collecting means of electrically conductive material which is insoluble in fluoboric acid.

The present invention also comprises a reserve battery which comprises a - easing having therein a cell comprising an electrode according to the invention, a metallic lead electrode and means for supplying liquid electrolyte so as to produce an electric potential between the lead electrode and the electrode according to the invention.

The liquid electrolyte for use in the reserve battery according to the invention may be, for example, fluoboric acid, such as fluoboric acid of a concentration of about 40%.

The lead dioxide may be prepared by electrolytic deposition upon a polished metal or graphite surface, to which the lead dioxide adheres only poorly, so that it is easily detached, and mechanically reduced to granules of a suitable size (preferably in the range 0 5 to 2 millimetres).

The container used to contain the lead dioxide particles may be formed of a porous fabric inert to the electrolyte, such as woven polyethylene terephthalate fibres, or of a non-porous material, such as solid poly styrene, in which case the container is pro vided with suitably disposed apertures to allow the electrolyte to have access to the electrode material. Alternatively the con tainer may be formed of a conductive, chemically inert material, such as solid carbon or a carbon-filled plastics material, in which case the container may act as the current collecting means in the electrode.

When a non-conductive container is used, a current collecting means formed of a con ductive material inert to the electrolyte is employed. A bundle of known high-strength carbon fibres may be used, or a carbonised fibre cord such as is marketed by Le Carbon Company of Portslade, Sussex, England have both proved to be quite satisfactory.

In some applications, where high currents are to be drawn from the battery, it may be found desirable to enhance the natural con ductivity of the particulate or granular lead dioxide by admixture with a chemically inert conductive material, for example, graphite or carbon black.

When a porous, apertured container is used the apertures maybe covered with porous material, for example, - carbonised woven fabric or felt to retain finer particles of lead dioxide within the electrode and to improve current collection.

An exemplary embodiment of a reserve battery positive electrode according to the invention will now be described with refer ence to the drawing accompanying the pro visional specification.

In the drawing: Figure 1 shows a partly cut away underside perspective view of an electrode; Figure 2 shows a cross-section through the electrode of Figure 1.

The electrode 10 shown in the drawing comprises a container 11 having the form of a short, hollow cylinder formed of a plastics material inert to the electrolyte to be used in a battery comprising the electrode, which electrolyte is generally fluoboric acid. The sides and base of the container are provided with an array of apertures allowing the electrolyte to gain access to the interior of the container when the battery is primed, these apertures being in the form of slots 12 extending continuously between the sides and bottom of the container. Apertures of this form are readily formed during the moulding of the side and base portion 13 of the container as one integral body. The container 11 is closed upwardly by an initially separate lid portion 14 fastened to the side and base portion 13 by any convenient means. In the illustrated embodiment, the edge of lid portion 14 is a snap fit in an internal peripheral groove 15 formed adjacent the top of the side wall of side and base portion 13.

The container is often advantageously lined with a chemically inert fabric layer 16 which may be a carbonised-fibre woven or felted cloth.

The active component of the electrode is a mass 17 of particulate or granular lead dioxide to which electricalconnecti on is made by a current collector member 18 which is here shown as consisting of a length of carbon and passing through a central aperture 19 in lid portion 14 and being led in an extended path of any preferred form through the mass 17 of lead dioxide active material.

When a positive electrode as described above was used with a sheet lead negative electrode to form a battery, using a fluoboric acid electrolyte, the battery was found to be effective for a discharge time of twenty days and would operate usefully over the temperature range of at least -320C to +55"C.

WHAT WE CLAIM IS:- 1. A reserve battery electrode comprising a container which is pervious to liquid elect trolytes and which contains separate particles of lead dioxide which are in contact with current collecting means of electrically conductive material which is insoluble in fluoboric acid.

2. An electrode according to claim 1, in which the container is formed of electrically conductive material and constitutes the current collecting means.

3. An electrode according to claim 2, in which the container is formed of carbonfilled plastics material.

4. An electrode according to claim 2, in which the container is formed of carbon.

5. An electrode according to claim 1, in which the container is formed of an electrically insulating material and the current collecting means comprises carbon fibres.

6. An electrode according to claim 5, in which the carbon fibres are in the form of carbonised fibre cord.

7. An electrode according to claim 5 or 6, in which the container is an apertured body of solid polystyrene.

8. An electrode according to claim 7, in which apertures in the body are covered by porous material.

9. An electrode according to claim 8, in which the porous material is carbonised fibre woven fabric or felt.

10. An electrode according to any of claims 1 to 9, in which the container contains graphite or carbon black in admixture with the particles of lead dioxide.

11. A reserve battery electrode, substantially as described herein with reference to the drawings accompanying the provisional specification.

12: A reserve battery which comprises a casing having therein a cell comprising an electrode according to any of claims 1 to 11, a metallic lead electrode and means for supplying liquid electrolyte so as to produce an electric potential between said electrodes.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figure 2 shows a cross-section through the electrode of Figure 1. The electrode 10 shown in the drawing comprises a container 11 having the form of a short, hollow cylinder formed of a plastics material inert to the electrolyte to be used in a battery comprising the electrode, which electrolyte is generally fluoboric acid. The sides and base of the container are provided with an array of apertures allowing the electrolyte to gain access to the interior of the container when the battery is primed, these apertures being in the form of slots 12 extending continuously between the sides and bottom of the container. Apertures of this form are readily formed during the moulding of the side and base portion 13 of the container as one integral body. The container 11 is closed upwardly by an initially separate lid portion 14 fastened to the side and base portion 13 by any convenient means. In the illustrated embodiment, the edge of lid portion 14 is a snap fit in an internal peripheral groove 15 formed adjacent the top of the side wall of side and base portion 13. The container is often advantageously lined with a chemically inert fabric layer 16 which may be a carbonised-fibre woven or felted cloth. The active component of the electrode is a mass 17 of particulate or granular lead dioxide to which electricalconnecti on is made by a current collector member 18 which is here shown as consisting of a length of carbon and passing through a central aperture 19 in lid portion 14 and being led in an extended path of any preferred form through the mass 17 of lead dioxide active material. When a positive electrode as described above was used with a sheet lead negative electrode to form a battery, using a fluoboric acid electrolyte, the battery was found to be effective for a discharge time of twenty days and would operate usefully over the temperature range of at least -320C to +55"C. WHAT WE CLAIM IS:-

1. A reserve battery electrode comprising a container which is pervious to liquid elect trolytes and which contains separate particles of lead dioxide which are in contact with current collecting means of electrically conductive material which is insoluble in fluoboric acid.