EP0555461A1

EP0555461A1 - Electrochemical battery with movable electrodes

Info

Publication number: EP0555461A1
Application number: EP92919063A
Authority: EP
Inventors: Jacques Rebondy; Jean-Pierre Galves
Original assignee: Thomson Tubes Electroniques
Current assignee: Thales Electron Devices SA
Priority date: 1991-09-03
Filing date: 1992-08-28
Publication date: 1993-08-18
Also published as: US5389461A; FR2680915A1; KR930702792A; WO1993005542A1

Abstract

L'invention concerne les piles électrochimiques du type dit ''à réserve''. Suivant une caractéristique de l'invention, la pile comporte des moyens (38, 40) pour, durant une période de stockage de la pile, maintenir les électrodes (E+, E-) à l'extérieur des cellules (C1 à C14), et d'autre part pour placer ces électrodes dans les cellules pour amorcer la pile.The invention relates to electrochemical cells of the so-called “reserve” type. According to one characteristic of the invention, the cell comprises means (38, 40) for, during a period of storage of the cell, maintaining the electrodes (E +, E-) outside the cells (C1 to C14), and on the other hand to place these electrodes in the cells to prime the battery.

Description

ELECTROCHEMICAL CELL Λ MOBILE ELECTRODES

The invention relates to electrochemical plaice, in particular electrochemical cells of the so-called "reserve" type. It particularly relates to means for initiating such batteries.

Electrochemical cells of the reserve type are cells intended to be put into operation after a storage period of which the duration is variable, and can range for example up to 15 years and more.

This type of battery is widely used to supply electrical energy in ballistic missiles, for example shells, missiles, etc. . . But these batteries are also of great interest in other fields, for example that of security devices.

Reserve type batteries provide electrical energy from the moment they are primed. Priming the battery consists in bringing together the different elements which, in a conventional manner, transform the chemical reaction into electrical energy.

Such an electrochemical cell can comprise one or more electrochemical cells, the number of these cells being a function of the voltage to be obtained. In operation, that is to say after ignition, each cell comprises two electrodes of opposite polarities in contact with a quantity of liquid electrolyte. Most often, the liquid electrolyte is kept outside the cell in a storage tank, until the moment of priming. Priming the battery consists in releasing the electrolyte.

In the case for example of rockets or artillery shells, during the storage period, most often all the quantities of electrolyte necessary for all the cells are contained in a single storage tank. Priming the battery consists in releasing the liquid electrolyte from the reservoir and driving it into the different cell or cells. This priming can be obtained by combining the effects of the strong acceleration and the speed of rotation which appear at the start of the blow: the electrolyte is released for example by rupture of a seal under the effect of the longitudinal acceleration, the instant of the shot; and the electrolyte is distributed in the cells helped in this by the centrifugal force due to the rotation of the machine on itself.

In structures having a single storage tank for several cells, an important problem lies in balancing, that is to say the most equal possible distribution of the electrolyte between the different cells, while minimizing the communications between cells. Indeed, in the most common case where the electrodes are of the "bipolar electrodes" type, any quantity of electrolyte contained in communication conduits between cells generates a phenomenon of self-consumption of the battery, which reduces the capacity of the latter to supply energy to the load of use. In addition, the electrolyte contained in these conduits can cause an annoying fluctuation in the voltages delivered by the battery.

This leads in practice to adopt different compromises in the production of these batteries, which make the structure more complex without completely eliminating the problem of self-consumption. There are examples of embodiment of such electrochemical cells, reserve and "blow-startable", in particular in US Pat. No. 2,996,564, and in French Patent Applications Nos. 88 15331 and 89 09637.

It should be noted that the problem posed by priming the reserve batteries, in the case of rotating ammunition, is made even more difficult in the case where the battery is mounted in a missile or projectile which can undergo slight accelerations, by example a mortar shell. The case of the mortar shell is particularly difficult indeed, because of its possible weak acceleration at the start, and the absence of rotation.

Also, the principles explained above for achieving the release and distribution of the electrolyte in the cells are inapplicable. Other solutions are envisaged, which are much more technologically complex.

In fact, these more complex solutions do not seem to have yet succeeded industrially. To date, the electrical supply of mortar rockets is done using turbine and alternator systems, the implementation of which is complex and expensive, but which have the merit of existing.

The present invention relates to electrochemical cells, in particular of the reserve type. It particularly relates to means for initiating such batteries, and applies equally well in the case of strong or weak accelerations, with centrifugal force or not. It allows very rapid priming while avoiding self-consumption faults and poor distribution of the electrolyte. In addition, the invention lends itself well to economic industrial achievements to the point that it can be applied in many fields other than those already mentioned, for example the electrical supply of safety devices, such as fire extinguishers, beacons, etc. . . .

According to the invention, an electrochemical cell comprising at least one cell, the rellule comprising two opposite polarized electrodes and an electrolyte space containing an electrolyte, is characterized in that it furthermore comprises means for, on the one hand maintaining the electrodes outside the cell during a storage period of the battery, and on the other hand place these electrodes in the cell to prime the battery.

This solution is particularly advantageous in that it makes it possible to store the electrolyte in the cell itself, at the position of use, so that the placement of the electrode causes the battery to operate immediately. In addition, in the case of several cells, the distribution of the electrolyte in the cells is always correct since it is carried out during the manufacture of the cell.

The invention will be better understood and other advantages and characteristics which it presents will appear better on reading the description which follows, made with reference to the appended figures among which:

- Figure 1 shows a battery according to the invention

10 by a sectional view parallel to a cell;

- Figure 2 is a top view of the cell of the invention showing a distribution of several cells with their electrodes.

Figure 1 shows schematically, by way of example l "- ** without limitation, an electrochemical cell 1 according to the invention.

Battery 1 is of the reserve type. It comprises an enclosure 2 which, in the nonlimiting example described, has a circular section (represented by its diameter dl), the plane of this section being perpendicular to that of FIG. 1. 0 Several electrochemical cells are arranged around a longitudinal axis 5 of the enclosure, of which only two cells C2, CIO are shown in FIG. 1.

Figure 2 is a top view of the stack 1, view which is symbolized in Figure 1 by an arrow 4, and which 5 shows the stack 1 according to its section.

In the nonlimiting example described, 14 consecutive electrochemical cells C1 to C14 are distributed around the longitudinal axis 5 at a pitch p; the longitudinal axis 5 being perpendicular to the plane of Figure 2, it appears on 0 the latter as a point. Of course, in the spirit of the invention these cells can be arranged differently and be in a different number, larger or more sfaible can go up to a single cell.

Each cell C1 to C14 includes two electrodes E -, E + of opposite polarities, arranged on either side of a space called "electrolytic space" 7 containing an electrolyte 8.

The electrochemical cells C1 to CM are connected in series and add the voltages they produce, so that the total electromotive force is available between two outputs "+", "-", one of which is the positive polarity delivered by an electrode E +, from the first cell Cl, and the other "-" is the negative polarity delivered by the electrode E- of the last

10 cell C14.

In a conventional manner, the electrodes E-, E + are constituted by bipolar plates, that is to say that they are carried by separating plates PI to P15, on the two large opposite faces of the latter: the plaques

15 separators PI to P15 are made of a conductive material one side of which is covered, for example, with lead to form a negative electrode E-, and the other side of which is covered, for example, with lead dioxide (Pb0_) to form a positive electrode E + .

20 For example, the third separator plate P3 which separates the second and third electrochemical cells C2 and C3, carries on one face the negative electrode E- of the second cell C2 and carries its opposite face the electrode E + of the third cell C3.

²⁵ The separating plates PI and PI 5 do not in principle need their deposition E- (for PI) and E + (for P15), but for economic reasons, it is simpler in practice to make them in the same plate than the others, although the side forming E- in the case of PI and the side forming E + in the

- * - * - cases of P15 play no electrical role.

The electrolytic space 7 is determined in each cell C1 to C4 between the two electrodes E +, E- and between 3 insulating walls: the first called peripheral wall 10 is on the side of the enclosure 2; the second located opposite the first is called central wall 11, it is constituted by example by a crown of insulating material 13 centered on the longitudinal axis 5; the third insulating wall being formed by the insulating bottom 21 of the cell.

In each cell C1 to C14, the peripheral and central walls 10, 11 are separated by a distance D1 called separation which extends parallel to the rays (not shown) of the enclosure 2.

According to a characteristic of the invention, when the stack 1 is in operation, the separating plates PI to P15 have a length L1 parallel to the distance Dl of separation and greater than the latter, so that each of the lateral edges 16, 17 separator plates PI to P15 protrude and are inserted into the peripheral and central insulating walls 10, 11. These lateral edges 16, 17 are thus enclosed in the walls 10, 11 and protected from any contact with the electrolyte 8, in order to '' avoid the phenomenon of self-consumption.

Referring again to FIG. 1, the latter particularly represents, on the one hand, the second cell C2 in a left part of the figure located in a box marked 25; and it particularly represents the tenth cell C10 in a second box marked 26.

The purpose of box 25 is to illustrate the storage position of the battery, that is to say its state is not primed and therefore when it is not working. The purpose of Box 26 is to illustrate the primed position when the battery is put into operation.

According to another characteristic of the invention, in the battery storage position, the electrodes E +, E- are held outside the cells C1 to C14. This is illustrated by box 25, in which the separating plate P3 is kept away from the electrolytic block 30 which constitute the different cells C1 to C14 each containing an electrolyte 8. The third separating plate P3 carries on its visible face a negative electrode E- intended for the second cell C2, and carries on the other face a positive electrode E + intended for the third cell C3.

According to the invention, the priming of the cell 1 is obtained by the installation of the different electrodes E +, E- in the different cells C1 to C14. For this purpose, all the separating plates PI to P15 are moved from a high position (shown in box 25), to a low position

10 (shown in box 26) where they are engaged between the different cells C1 to C14 until they press on the insulating bottom 21 of the cell, that is to say the bottom with which the electrolyte is in contact 8.

This last position of the PI separator plates at

P15 is illustrated in Box 26 in which it is seen that a positive electrode E +, forming the visible face of the tenth separator plate P10, is placed inside the tenth CIO cell.

We can observe as indicated above, that the

20 separating plate P10 has a length L1 greater than the separation distance Dl, so that its lateral edges 16 and 17 are engaged in the insulating walls 10, 11. Furthermore the separating plates have a height Hl greater than the depth H2 of the electrolytic space 7, of

^* "such that when they are in place, on the one hand they have a lower edge 18 which penetrates into the insulating bottom 21, and on the other hand, they have an upper edge If) (opposite the lower edge 18) which remains outside of the electrolytic space 7.

-O During storage period, each cell C1 to C14 contains the quantity of electrolyte necessary for its operation, and the electrodes E +, E- are kept apart from the electrolytic block.

Priming consists in placing the electrodes E +, E- in the electrolytic block, in contact with the electrolyte. This is obtained by a relative movement between the electrolytic block and the PI P15 separator plates, and as described above, the dimensions of the latter are such that, as they are inserted into a cell, they penetrate the peripheral walls and central 10, 11 in which their lateral edges 16, 17 are embedded and isolated from the electrolyte, just as their lower edge 18 is pressed into the bottom 21; this arrangement makes it possible to avoid the phenomenon of self-consumption which occurs when the edge of a bipolar blade is immersed in the electrolyte.

Of course, the electrically insulating material in which the walls 10, 11 and the bottom 21 are made must have a structure suitable for being allowed to penetrate the edges of the plates without falling apart, and for maintaining a seal around these edges. Materials having the required qualities are for example elastometers, or gels of the silicone type.

The electrolyte can be in liquid form or preferably in solid form, that is to say in the form of a gel. Such a solid electrolyte called in the following description "electrolytic gel" can be obtained in itself simple, by adding gelling agents to the electrolyte, for example based on colloidal silica or the like.

In the nonlimiting example described where the electrodes E +, E- are made of lead and lead oxide, the electrolytic gel can for example be based on colloidal silica, plus fluoboric acid and diethylene glycol.

Whatever the nature of the electrβl te 7, it is contained in cells Cl to C14 during da storage period, at the position and in the form of its use, that is to say that it is immediately usable with perfect distribution in the cells. There is therefore no problem of balancing the quantities of electrolyte between cells, as in the prior art, because the depression of the ^• separator plates PI to P15 only has the effect of separating from each other the respective parts of electrolyte of two cells C1 to C14 consecutive. In fact the insulating walls 10, 11 and the bottom 21 as well as the electrolyte 8 can extend continuously: the cells C1 to C14 are effectively materialized by the insertion of the separating plates PI to

P15 or bipolar plates, depression which results in delimiting the part of electrolyte assigned to each cell, and placing the electrodes E-, E + on either side of this part of electrolyte. Of course, it is appropriate for this that during their insertion into cells C1 to C14, the separating plates PI to P15 are maintained at positions defined around the longitudinal axis 5, with predetermined spacings between them which correspond to the pitch p of the cells C1 to C14. For a better conservation of the electrolytic gel, vis-à-vis a drying for example, the zone containing the electrolyte that is to say the succession of electrolytic spaces 7, can be covered with a film or seal 32 waterproof, for example in thermo-welded plastic. The cover 32 also provides mechanical maintenance of the electrolytic gel.

In the case of a liquid electrolyte, based on HBF. for example, the cover 32 is necessary to keep the electrolyte in its housing which constitutes the succession of electrolytic spaces 8. Of course the cover 32 is perforated by the lower edges 18 of the separating plates PI to P15, during the 'sinking of the latter into the; ^* * cells. In order to facilitate the penetration of the separating plates PI to P15 in the walls 10, 11, and the bottom 21 and possibly the cover 32, the inner edge 18 and possibly the edges 16, 17 of these plates can be made sharp, by example by giving them a triangular shape (not shown).

The movement which must lead to the insertion of the electrodes E +, E- in the cells C1 to C14 can be obtained by a displacement of the separating plates PI to P15 and / or by a displacement of the electrolytic block 30. For practical and mechanical reasons, it may be preferable to fix the latter in the enclosure 2, and to make the separating plates PI to P15 mobile, as in the nonlimiting example represented in the figure 1.

It is also preferable to guide the plates PI to P15, particularly in the case of the example shown where cells C1 to C14 follow one another along a circle (see FIG. 2), and where the space between the first and the last Cl cells, C14 is formed of an insulating space 33 without electrolyte.

In the nonlimiting example described, the separating plates PI to P15 are overmolded in a plastic part

38 which is common to all these plates, so that all these plates are held in the part 38 by their upper edge 19.

The plastic part 38 extends above the succession of cells C1 to C3, and it carries the separating plates PI to P15 with which it constitutes a possibly displaceable block called "electrode block" 35. The separating plates PI to P15 are thus fixed to each other, and maintained with a spacing between them which corresponds to the pitch p according to which the cells C1 to C14 are arranged.

The displacement of the electrode block 35 is symbolized by an arrow 29; it must be carried out over a distance d2 which is that necessary to transport the separating plates PI to P15 from the storage position (represented in box 25), to the primed position where they are in the cells, as shown in box 26. In this movement, the electrode block 35 can slide for example along a shaft 44 disposed along the longitudinal axis 5. The electrode block 35 can be guided in different ways, it can be guided for example using a rib 70 on the shaft 44. The displacement of the electrode block 35 from the storage position to the primed position can be accomplished using various means which are known per se, in particular depending on the application of the battery 1.

For example, if the battery 1 is used with an artillery shell which has a very strong acceleration, the block of electrodes 35 can behave like a counterweight whose inertia at the moment of the departure of the shell, causes the displacement and consequently the insertion of the electrodes in the

10 cells C1 to C14. It should be noted however that the force which causes the displacement of the electrode block 35 must be relayed, in order to keep the separating plates PI to P15 pressed between the cells C1 to C14.

It is also possible to move the

15 electrode block 35, using a conventional ignition device 40 using the pressure of a gas coming from a gas generator 41. The electrode block 35 acts like a piston and slides on the central shaft 44 so as to be movable along the longitudinal axis 5, between two positions PS and PA: the

20 first position PS is that which is closest to an upper wall 38 of the enclosure 2, and. it constitutes the storage position, the second position A being the primed position. The electrode block 35 is maintained in the storage position PS by conventional means (not shown). ^{• *} * - ^• 'The generator 41 is arranged in the example in a space 43 formed between the electrode block 35 and the upper wall of the enclosure 2. When the priming of the cell 1 is decided, a gas released by the generator 41 pushes the electrode block 35 like a piston, and causes the

30 electrodes E-, E + in cells C1 to C14. The control of the gas generator 41 can be carried out in a conventional manner generally by an electrical pulse.

In order to maintain the electrode block 35 in the priming position after it has been put into position by the gas generator 41 (or by the start acceleration of the blow), the shaft 44 is equipped a non-return device. Various means are known for this purpose. In the nonlimiting example described, this is accomplished using a leaf spring 71 which, during storage, is retracted into the shaft 44 itself; when the electrode block 35 is pressed, the spring 71 escapes and thus prevents a return movement of the electrode block 35.

With an appropriate sensor, a priming device 40 allows the priming of the battery 1 in a large number of situations and applications: control by electric pulse, percussion or others.

It should be noted that an electrochemical cell in accordance with the invention is of very particular interest in the case of mortar fire, because the placement of the electrolyte in the cells of the electrolyte and the balancing in the cells of this electrolyte does not require the presence of a centrifugal force.

In the nonlimiting example of FIG. 2, the outputs "+" and "-" of the electromotive force of battery 1 (that is to say coming from the placing in series of all cells C1 to C14) , are symbolized as being available at first ends 60, of two connecting wires FI, F2; these outputs "+" and "-" being fixed. The two wires FI, F2 are connected at their second end 61 respectively to the plates PI and P15, the electrical contacts being obtained for example by soldering.

If the electrodes are mobile, that is to say if the insertion of the separating plates PI to P15 between the cells C1 to C14 results from a displacement of these separating plates as explained above, it is necessary to connect the first and the last PI plate, P15 to the fixed connections of the battery, for example by a flexible wire; the wires FI, F2 then have sufficient clearance to absorb the displacement of the electrodes. Of course, it is also possible to use a connection by spring leaf (not shown) in itself conventional, as described for example in US Pat. No. 4,331,848. In the opposite case where the electrodes are fixed, the output connections are conventionally and simply carried out on the electrodes themselves.

Claims

1. Electrochemical cell, comprising at least one cell (Cl to C14), the cell comprising two electrodes (E +, E-) of opposite polarities and an electrolytic space (7) containing an electrolyte (8), characterized in that it further comprises means (38, 40) for, on the one hand holding the electrodes (E +, E-) outside the cell during a storage period of the battery, and on the other hand for placing these electrodes in the cell to prime the cell.

2. An electrochemical cell according to claim 1,

10 characterized in that it comprises at least two consecutive cells (C1 to C14) separated by a separating plate (PI to P15) carrying an electrode (E +, E-) on each of its opposite faces so as to constitute electrodes of the bipolar type, each separating plate carrying two polarity electrodes

- opposites belonging to consecutive cells, each separating plate being on the one hand kept apart from the cells (C1 to C14) during the storage period, and on the other hand being disposed between the cells when the stack is primed.

3. Electrochemical cell according to claim 2, 0 characterized in that during the storage period the electrolytic spaces (7) of two consecutive cells (CI to C14) are communicating.

4. Electrochemical cell according to any one of claims 2 or 3, characterized in that each electrolytic space (7) is formed on the one hand between two insulating walls (10,11) separated by electrodes (E +, E- ) and on the other hand on an insulating bottom (21), and in that each separating plate (PI to P15) has on the one hand a length (L1) greater than a separation distance (PI) between the two 0 insulating walls (10, 11), and on the other hand a height (Hl) greater than the depth (H2) of the electrolytic space (7), so that in the relative movement between the cells (Cl to C14) and the separating plate (s) (PI to P15), edges (16, 17, 18), of the latter penetrate the insulating walls and the bottom (10, 11), and are housed therein in order to be isolated from the electrolyte.

5. Electrochemical cell according to any one of claims 2 or 3 or 4, characterized in that during the storage period, the electrolyte (8) is arranged in an uninterrupted manner from the first cell (Cl) to the last cell (C14).

6. Electrochemical cell according to one of the preceding claims, characterized in that the electrolyte is in the form of a gel.

7. Electrochemical cell according to claim 6, characterized in that the electrolyte is based on colloidal silica and fluoboric acid.

8. Electrochemical cell according to one of the preceding claims, characterized in that each electrolyte space is closed by a seal (32).

9. An electrochemical cell according to claim 8, characterized in that the electrolyte is a liquid electrolyte.

10. Electrochemical cell according to any one of claims 2 to 9, characterized in that it comprises several separating plates (PI to P15) fixed to each other using an insulating part (38), according to a step (p) corresponding to the step of the cells (C1 to C15).

11. Electrochemical cell according to one of the preceding claims, characterized in that the cell or cells (Cl to C14) are fixed relative to the enclosure (2), and in that the electrode or electrodes (E +, E- ) are mobile.