FR2503936A1 - Mfr. of thin non-planar electrodes, gas electrodes - with current conductors as used in electrochemical appts. - Google Patents

Abstract

Method for manufacturing thin electrodes, in particular gas electrodes, in any non-planar shape required. A homogeneous mixture of dry particles of the active components is prepared including at least one compound with electrocatalytic activity, one with electronic conductivity and PTFE fibres. A lubricant is added together with an adhesive substance which aids the covering of the dry particles with lubricant and then this mixture is formed into the electrode shape. This electrode can then be combined with a current collector by depositing a thin porous metallic film on at least part of the electrode surface. Thin electrodes are used for electrochemical apparatus such as piles and accumulators and particularly gas electrodes. Combined electrode-current accumulator assemblies and for positive electrodes or cathodes for electrochemical generators.

Description

Process for the preparation of current collectors for electrochemical devices, by deposition on electrodes for such devices, and unitary electrode-collector assemblies obtained by this process
The present invention relates to the preparation of current collectors for electrochemical devices (batteries and accumulators) and more specifically to electrode-collector current unit assemblies,
Numerous methods are known for producing composite (and not unitary) assemblies of a current collector electrode. They consist in making a current collector facing each other which is then fixed on the electrode to which it must be functionally associated.

So
- According to US Pat. Nos. 3,149,900 and France No. 1,282,491, the collector is produced in the form of a metal grid which is then embedded in the electrode by rolling or pressing;
t in the French patent No. 2,143,593, the collector is a grid or an expanded metal or a porous conductive layer, made of nickel sintered, for example, and it constitutes a support which is incorporated within the electrode or on which is laminated the electrode ;;
French Patent No. 2,163,944 provides a grid which is applied against the electrode using a piece, elastically deformable and conductive, which constitutes the current collector;
- in the French patent No. 2,143,594, the current collector is a metal tube pierced with holes incorporated in the cylindrical block constituting the electrode; - France patent 110 2,296,278 provides for a thin embossed steel outlet: pierced with slots, in which the electrode paste is brought back under pressure,
- dans.le US Patent No. 3,788,900, the outlet is constituted by a single wire pressing against the surface of the electrode.

In all these patents, the current collector is a separate conductive part (grid, deployed, perforated tube, socket pierced with slots, wire) prepared separately, then mechanically associated with the electrode,
This requires giving the electrode and the collector relatively simple geometric shapes.

Contrary to previous practice, the invention relates to a process for preparing current collectors for electrochemical devices consisting in depositing the collector on the electrode in the form of a thin conductive film, inseparable (unless it provokes it damage) to this electrode. The film is more particularly a porous metallic film, adhering to the surface of the electrode. It follows the shape of the electrode, which can be arbitrary,
The invention is particularly suitable for depositing a collector on an electrode of any non-planar shape that is manufactured by the process which is the subject of the patent application filed on the same day by the applicant for "Process for manufacturing thin electrodes, in particular gas electrodes, for electrochemical devices and thin electrodes obtained by this process ", as well as on a thin planar electrode prepared by one of the processes discussed in the preamble of said application (US Pat. Nos. 3,419,900, France 1,522,224 and 2,143,593).

 The subject of the invention is therefore, first of all, a process for preparing a current collector for an electrode of an electrochemical device, characterized in that a film is deposited on at least part of the surface of this electrode. thin porous metal, adherent to the electrode.

 This deposition can be carried out for example by chemical deposition, painting, cathode sputtering and, advantageously, by electroplating.

The deposit is preferably made of nickel; it can also be made of copper, silver, gold, platinum, ''Monel'l alloy, titanium, iron,
Its thickness is generally between 0.01 mm and 5 mm; it is preferably of the order of 0.05 mm.

 The pore diameter of the deposit is less than 0.5 mm, with a permeability greater than 100 cm / h.

 The electrode on which the current collector is deposited is preferably obtained by the crit process in the aforementioned French patent application of the applicant, a process which is characterized in that a homogeneous mixture of dry particles of active compounds is prepared , consisting of at least one compound with electrocatalytic activity and optionally with at least one compound having electronic conductivity, and dry polytetrafluoroethylene fibers are added a lubricant and optionally a surfactant, in order to coat the particles of the mixture with lubricant, and the lubricated particles of the mixture are shaped.

 The electrode is preferably a positive electrode or cathode for an electrochemical generator.

 The subject of the invention is also a unitary electrode-current collector assembly obtained by the method defined above, the current collector being constituted by an adherent porous thin metallic film, deposited on an electrode.

 Thanks to the invention, it is possible to deposit a current collector on an electrode of any shape, the collector very closely matching the surface of the electrode, whatever its shape, even if it is very complex. We can make a very thin film, although securely attached to the electrode, so we can make a very light collector which reduces the mass of the collector electrode assembly and therefore the electrochemical generator (battery or accumulator) who has it. Finally, the porosity of the collector is favorable for gas diffusion through to the electrode.

 The invention therefore ultimately makes it possible to produce a porous and light electrode-collector assembly. the collector strongly adhering to the electrode.

The invention may, in any case, be well understood with the aid of the additional description which follows, as well as of the appended drawings, which supplement and drawings are, of course, given mainly by way of description.
Figure 1 illustrates, schematically and in section, a first embodiment of a device for implementing the method according to the invention.

FIG. 2 illustrates, in section, a second embodiment of a device for implementing the method according to the invention,
Figure 3 is a section through III-III of Figure 2.

 Figures 4, 5 and 6 show three collector structures obtained by the method according to the invention, respectively honeycomb, rib and weft, these figures being partial representations in plan (Figures 4 and 6) or in perspective (FIG. 5i of a portion of collector.

 According to the invention and more particularly according to that of its modes of application, as well as according to those of the embodiments of its various parts, to which it seems that there is reason to be given preference, proposing, for example, to produce current collectors for electrochemical devices, this is done as follows or in a similar manner.

EXAMPLE 1.
We mix intimately
45 parts by weight of polytetrafluoroethylene, in particular in the form of particles obtained from dry fibers and having an average size of the order of 0.5 mm, obtained by coagulation of a polytetrafluoroethylene emulsion
and 55 parts by weight of silver catalyzed carbon
with 50 parts by weight of a lubricant such as kerosene, so as to obtain a paste.

 This paste is calendered between cylinders heated to 500C to obtain a thick strip of 0.5 inm.

 A roller A of this strip is mounted on a mandrel 1; the unrolled strip B passes over a deflection roller 3 then over a conductive cylinder 4 disposed in an electroplating tank 5, filled with an electrolysis bath 6 containing a solution of a soluble nickel salt; a soluble nickel anode, constituted for example by nickel balls 7, is arranged in the electrolysis bath 6. Pressing rollers 8 apply the strip B against the conducting cylinder 4; the electrical voltage of the electrolysis is applied between the terminals a and b respectively connected to the axis 9 of the conductive cylinder 4 by the conductor 10 and to the soluble anode, constituted by the balls 7, by a conductor II and a plate conductive 12 in contact with these balls.

 For example, the electrolysis bath contains 80 g of nickel, in the form of nickel sulfonate and 30 g of boric acid, per liter of solution. The density of the electrodeposition current is 100 amperes / dm2 of submerged electrode and the speed of travel of the strip B is such that each portion of electrode remains in the electrolysis bath for a period of between 30 seconds and several minutes, depending on the thickness of the desired nickel deposit, this deposit having to constitute the current collector. It is the face 13 of the strip B opposite the face in contact with the conductive cylinder 4 which receives the nickel deposit which will constitute the current collector.

 The strip C comprising on its face 13 the nickel deposit which constitutes the current collector, after having passed over idler rollers 14, passes through a rinsing bath 15 placed in a tank 16, passing over a pulley 17. A leaving the rinsing bath, the cleaned strip D arrives, after passing over the return rollers 18, in a drying oven 19 in which it is dried and finally the dry electrode E is wound on a drum 20 after passing over a return roller 21.

 There is thus obtained on the drum 20 a strip formed by the electrode material coated on one side with a nickel current collector.

This strip is then cut into portions of desired shape and dimension and it is even possible then to give it the configuration in the desired space, as explained in the French patent application.
Applicant's above-mentioned facts, namely for example by compression, injection or transfer,
EXAMPLE 2.
We mix intimately
60 parts by weight of polytetrafluoroethylene from
same quality as in example 1,
30 parts by weight of carbon catalyzed with dioxide
manganese
6 parts by weight of graphite
4 parts by weight of conductive carbon black, with
45 parts of kerosene and we get a paste,
This paste is injected into a mold heated to around 500C, then ejected therefrom in the desired form, as set out in the applicant's patent application mentioned above. For example, a finger-shaped electrode is removed from the mold of frustoconical glove (truncated cone of revolution whose base part is closed by a hemispherical cap). Such an electrode is illustrated at F in FIG. 2.

 This electrode F is placed, as illustrated in FIG. 2, on a mandrel 22 which plunges into an electrolysis bath 23 having the same composition as that indicated in example 1 and which is placed in a tank 24.

The assembly of the mandrel 22 of the electrode F rests on the ribs 25 of an electrode holder 26 whose periphery 27 is pierced with holes 27a to allow the passage of the electrolysis solution. The purpose of the ribs 25 is to apply the electrode F against the mandrel 22, in order to improve the electrical contact between this mandrel, which is conductive, and the electrode. This is particularly visible in FIG. 3 which is a section through III-III in FIG. 2,
The nickel balls 28 are arranged in the space between the tank 24 and the electrode holder 26, these balls being placed in the electrolysis bath 23 and being in electrical contact with a conductive part 29, for example made of titanium , connected by a conductor 30 to one of the electric power supply terminals a, the other terminal b of which is connected to the mandrel 22 by a conductor 31.

 The current density applied is 100 amperes / dm2 of submerged electrode. The power-up, and therefore the application of deposition, lasts between 30 seconds and 2 minutes. The electrode coated with the nickel layer electrodeposited is dried and then freed from the lubricant, for example by evaporation.

 The electrode which has thus just been prepared can be used very advantageously to constitute the cathode of an electrochemical generator (cell or accumulator) by associating with it an anode mass and separators. For example, it can be used to produce generators of the type described in another patent application filed by the applicant on the same day and entitled Electrochemical generator comprising a thin gas electrode ".

EXAMPLES 3, 4 AND 5.
It is possible, in accordance with the invention, to produce metallic deposits of non-uniform thickness on the surface of the electrode to be coated. It is therefore possible to produce current collectors of non-constant thickness.

 It is thus possible to give the metallic deposit and therefore the current collector a honeycomb structure (collector 32 illustrated in part in FIG. 4, on which we see ribs 33 # in excess thickness intersecting at right angles by defining " boxes "34), a rib structure (as illustrated in FIG. 5, which illustrates a portion of such a curved collector 35 comprising ribs 36 in excess thickness), in a weft (as illustrated in FIG. 6, which represents an electrode 37 comprising extra thicknesses 38 in the form of diamonds), in trellis or with tabs for example.

 Such structures make it possible to produce electrode-collector assemblies capable of better resisting mechanical forces in a certain direction or certain directions, or of promoting conductivity in one or more directions, while not disturbing the general permeability of the electrode. thanks to the reduced thickness of the deposit in the main part of the deposit (for example between the ribs or between the diamonds).

 In a variant, it is possible first to carry out a uniform deposit, then to superimpose a deposit having a particular structure on the first uniform deposit.

 The non-uniform deposits, in particular those according to examples 3 (FIG. 4), 4 (FIG. 5) and 5 (FIG. 6) can be held by means of masks applied to the electrode during the electrolytic deposition, these masks being for example analogous to the ribs 25 illustrated in FIGS. 2 and 3.

EXAMPLES 6 AND 7.
The electrolysis bath indicated in these examples is replaced in Examples 1 and 2 by the following bath: 220 g / l of copper sulphate and 30 g / l of sulfuric acid, the soluble anode consisting of an electrolytic copper plate, in place of the nickel beads. The current density used is then several tens of amps / dm2.

EXAMPLES 8 AND 9.
The electrolysis bath of Examples 1 and 2 is replaced by the following electrolysis bath: 30 g / l of silver cyanide, 70 g / l of sodium cyanide and 45 g / l of sodium carbonate, soluble anode consisting of a silver foil, instead of nickel beads; the current density used is then several tens of amperes / dm2.

 It is also possible, within the framework of the invention, to deposit gold, platinum, Monel alloy, titanium or even iron (the latter metal being, of course, more economical).

 The method according to the invention is very advantageous, because it is particularly simple, - it adapts to apply a connector to an electrode of any shape, the quantity of metal deposited can be adjusted as desired and it is easily automated.

 This process produces a current collector consisting of a metallic film deposited on an electrode of any shape, the film being porous, perfectly adherent on the electrode, whatever its shape, and perfectly adapted to the conductivity. desired and the desired mechanical strength.

It will also be noted that the method according to the invention does not require the prior purchase or storage of grids or sheets, which are necessary in the case of the methods of the prior art mentioned in the preamble to the present application,
As goes without saying and as it already follows from the above, the invention is in no way limited to those of its modes of application and embodiments which have been more especially envisaged; on the contrary, it embraces all variants,

Claims (11)

 1. Process for the preparation of a current collector for an electrode of an electrochemical device, characterized in that a porous thin metallic film adhering to the electrode is deposited on at least part of the surface of this electrode,  2. Method according to claim 1, characterized in that the deposition is carried out by electroplating.  3. Method according to claim 1, characterized in that the deposition is carried out by chemical deposition,  4. Method according to claim 1, characterized in that the deposition is carried out by sputtering.  5. Method according to claim 1, characterized in that the deposition is carried out by shooping.  6. Method according to any one of claims 1 to 5, characterized in that the deposit is made of nickel.  7. Method according to any one of claims 1 to 5, characterized in that the deposit is made of copper.  8. Method according to any one of the preceding claims, characterized in that the deposition is stopped when it has a thickness of between 0.01 mm and 5 mm, preferably of the order of 0.05 mm.  9. Method according to any one of the preceding claims, characterized in that the deposition is carried out on an electrode obtained by preparing a homogeneous mixture of dry particles of active compounds, consisting of at least one compound with electrocatalytic activity and optionally by at least one compound having electronic conductivity, and dry polytetrafluoroethylene fibers, by adding a lubricant and optionally a surfactant, in order to coat the particles of the mixture with the lubricant, and by forming the lubricated particles of the mixture.  10. unitary electrode-collector assembly obtained by the method according to any one of the preceding claims, the current collector being constituted by a thin porous metallic adherent film, deposited on an electrode.  11. Unit assembly according to claim 10, ca acterized in that the pore diameter of the deposit is less than 0.5 mm, with a permeability greater than 100 cm / h.