Electrochemical Generator Comprising an Electrode in the Form of a Suspension

For the purpose of further illustrating the invention in a non limitative manner, a particular embodiment of an electrochemical generator according to the invention will be disclosed thereafter in conjunction with the appended drawings in which:

FIG. 1 represents diagrammatically the generator to be described,

FIG. 2 is a diagrammatic section of an "electrodeball" according to the invention and

FIG. 3 is a curve representative of the variation of the electrical current output which can be obtained from a generator of that type as a function of voltage.

In the embodiment shown, the generator is formed of a cell 1 comprising an anodic compartment A and a cathodic compartment C.

The cathodic compartment C comprises a porous air-electrode plate 2, which is connected to the positive terminal of the cell and which divides compartment C into a chamber 4 which is continuously supplied, in 5, with the air supplying the oxygen necessary for the electrochemical reaction, at the level of the cathode, and into a chamber 6 supplied with the electrolyte. In the cathodic compartment so formed, the reaction of electrochemical reduction can then be achieved at the solid-liquid-gaseous interfaces, within the porous electrode plate. The latter can be formed in any manner known per se, for instance of a sintered mixture of nickel and carbon.

The anodic compartment A is associated with an exterior flow circuit 8 comprising a pump 10 capable of causing the circulation of a suspension of the active material of the anode, such as zinc, in a liquid electrolyte, through said circuit 8 and the chamber 12 of compartment A in contact with a collector of current 14 formed of a meshed grid or of a metallic plate perforated with holes 16, of an electrochemically inert metal such as nickel.

In accordance with the invention the active material is in the form of balls 18 which comprise cores made of an inert material coated with an outer layer of the active material itself, notably zinc; the compartments A and C of the generator are separated by means of the collector 14 itself; the holes 16 of this collector have sizes sufficient for enabling the free passage of the electrolyte therethrough, these sizes being however lower than the diameter of the inert cores of the balls. Finally, the space between the collector 14 and the cathode plate 2, in the instant case chamber 6, is essentially free of any separator.

The balls which carry the active material are formed advantageously according to FIG. 2 which diagrammatically shows a section of highly enlarged scale thereof (the scales ratios shown being not representative of the actual dimensional ratios of the different parts of the balls).

These balls comprise a core 20 of an inert material (glass or plastic material) coated with a thin continuous layer of nickel 22, itself coated with a thin layer 24 of cadmium, the zinc layer 26 finally coating the cadmium layer.

During operation of the electrochemical generator so formed, the zinc coating dissolves progressively as its electrochemical oxidation proceeds to form a zincate which dissolves in the electrolyte. Because of the relative sizes of the internal cores of the balls, on the one hand, and of the holes or apertures in the collector 14, on the other hand, it will be appreciated that the balls cannot get in touch with the cathode, even when in the "unloaded" state.

Advantageously the transverse dimension of the compartiment A is small in order to authorize as many impacts of the balls 18 on the collector 14, for the sake of obtaining a yield of electrochemical oxidation as high as possible.

In the case of generator elements having low thickness, it may be necessary in practice to provide spacer means 28 between the collector 14 and the cathode 2 in order to prevent any short circuit risk between these two elements. These spacer means are advantageously formed of a loosely meshed network formed with artificial fibres, for instance of the polyamid type.

In accordance with one of its preferred embodiments, the generator according to the invention further comprises an additional circuit line 30 by-passing the circulation circuit line 8, and comprising intercalated therein an electrolysis cell referred to generally by the reference Nr. 31 which may be of any type conventionally used in the field of electroplating, for instance an electrolysis cell of the "drum" type. This by-pass enables an easy re-loading or regenerating of the electrode material through electrolysis of the suspension of the "unloaded" balls within the zincate containing electrolytic solution obtained after an extended operation of the generator. Valve members 32 and 34 enable the alternate circulation of of the suspension through either one of the two circuits 8 and 30.

For the sake of further illustrating the invention an example of preparation of balls suitable for the generator under consideration will be described hereafter.

Balls of glass or plastic material, the diameters of which have a value comprised between 0.3 and 2 mm. and preferably between 0.5 and 1.5 mm, are freed of any fats and (in the case of glass balls) subjected to a short attack by hydrochloric acid, then treated with a 20% potassium hydroxide solution at 80.degree. C. for a period of ten minutes, then in a solution of stannous chloride (containing 100 g/l of SnCl.sub.2 and 100 ml/l of HCl) for a period of five minutes and finally in a bath of palladium chloride (containing 0.2 g/l of PdCl.sup.2 and 100 ml/l of HCl) during a period of two minutes at a temperature of 25.degree. C. The balls are rinsed with water between each of the successive operations mentioned hereabove. The so pre-treated balls are then subjected to a chemical nickel-plating at a temperature of 90.degree. C. within a solution containing 30 g/l of nickel chloride, 10 g/l of sodium citrate, 10 g/l of sodium hypophosphite, and then to an electrochemical cadmium plating within a cyanurated bath. Two superposed layers of nickel and cadmium are thus formed on the glass balls which are continuous though very thin, their thickness ranging from about 0.5 to 5 microns. The zinc coating is then formed by electrolytic zinc deposition within a cyanurated bath or a zincate bath. The electrolytic deposits of cadmium and of zinc may be carried out by any known process usable for particulate products, such as by the "drum electrolytic process".

The curve of FIG. 3 is representative of the variation of the density of current I (mA/cm.sup.2) as a function of voltage (in mV) which can be produced by a generator such as disclosed hereabove and which comprises:

a conventional air-cathode formed of sintered carbon-nickel

a suspension of balls prepared as disclosed hereabove using glass balls having a 1 mm diameter, within an electrolyte formed of a potassium hydroxide solution,

a collector formed of a nickel network the meshes of which are of the order of 0.3 mm.

Obviously the invention is not limited to the particular embodiments which have been disclosed hereabove. It embraces all equivalent alternatives; particularly the cathodic compartment could be contrived in any manner known per se or even operate according to a principle analogous to that applied in the anodic compartment, the separation between the cathodic and anodic compartments then being achieved by a double-collector grid, if need be separated by spacing means such as disclosed hereabove in order to avoid short circuit risks between the two collectors.