FR3073323A1 - ELECTROCHEMICAL ACCUMULATOR WITH SPECIFIC BIPOLAR ARCHITECTURE - Google Patents

Abstract

The invention relates to an electrochemical accumulator with bipolar architecture comprising a first (27) and second plate (73), called end plates, respectively associated with a first current collector substrate (35) and a second current collector substrate (71). ), said terminal current collecting substrates, between which is arranged a stack of at least a first electrochemical cell (50) and a second electrochemical cell (66) in which: each of the first and second electrochemical cells comprises a positive electrode, a negative electrode and a separator (49, 67) comprising an ion-conducting electrolyte; the first and second electrochemical cells are separated from each other by a current collector substrate, called a bipolar substrate (53), which supports on a first face an electrode (51) of the first electrochemical cell and on a second opposite side to the first face an electrode (65) of opposite sign of the second electrochemical cell, characterized in that each of the first and second electrochemical cells are housed in a space delimited internally by a frame traversed by a feed channel allowing the supplying the cell with electrolyte, the bipolar current-collecting substrate being clamped via a free edge between the frame of the first cell and the frame of the second cell and cooperating with each of them via at least one seal and the accumulator further comprises means for clamping the frame of the first cell against the frame of the second e cell.

Description

The invention relates to an electrochemical cell with bipolar architecture comprising a first (27) and second plate (73), called end plates, associated respectively with a first current collector substrate (35) and a second current collector substrate (71 ), said terminal current collecting substrates between which is disposed a stack of at least a first electrochemical cell (50) and a second electrochemical cell (66) in which:

each of the first and second electrochemical cells comprises a positive electrode, a negative electrode and a separator (49, 67) comprising an ion-conducting electrolyte;

the first and second electrochemical cells are separated from each other by a current collector substrate, called a bipolar substrate (53), which supports on an first face an electrode (51) of the first electrochemical cell and on a second opposite to the first face an electrode (65) of opposite sign of the second electrochemical cell, characterized in that each of the first and second electrochemical cells are housed in a space delimited internally by a frame crossed by a supply channel allowing the supply of the cell with electrolyte, the bipolar current collector substrate being clamped via a free edge between the frame of the first cell and the frame of the second cell and cooperating with each of them by means of at least one gasket and the accumulator further comprises means for clamping the frame of the first cell against the frame of the second th cell.

ELECTROCHEMICAL ACCUMULATOR WITH SPECIFIC BIPOLAR ARCHITECTURE DESCRIPTION

TECHNICAL AREA

The present invention relates to an electrochemical accumulator with specific bipolar architecture which does not require the installation of a sealed structure (that is to say requiring the addition of a sealing agent), which is modular, for example, allowing the easy incorporation of a desired number of electrochemical cells and which is easily removable and reassemblable at will, in particular to ensure, if necessary, the repair or replacement of defective electrochemical cells and which can allow the supply independent of each cell making up the accumulator. Finally, this accumulator must also not sacrifice the sealing requirement to avoid leakage of reagents and / or electrolytes detrimental to the proper functioning thereof.

The general field of the invention can thus be defined as that of energy storage devices, in particular that of electrochemical accumulators.

PRIOR STATE OF THE ART

Electrochemical accumulators operate on the principle of electrochemical cells capable of delivering an electric current thanks to the presence in each of them of a pair of electrodes (respectively, a positive electrode and a negative electrode) separated by an electrolyte, the electrodes comprising specific materials capable of reacting according to a redox reaction, whereby there is production of electrons at the origin of the electric current and production of ions which will circulate from one electrode to the other by through an electrolyte.

Among the accumulators subscribing to this principle, it can be mentioned:

-lead-acid accumulators using lead and lead oxide PbO ₂ as active electrode materials;

Ni-MH accumulators using metal hydride and nickel oxyhydroxide as active electrode materials;

-accumulators using nickel or a nickel-based compound to constitute the active material of at least one of the electrodes, such as Ni-MH accumulators using, in particular a metal hydride and nickel oxyhydroxide as active materials electrode; Ni-Cd accumulators using cadmium and nickel oxyhydroxide as active electrode materials or nickel-zinc accumulators using nickel hydroxide and zinc oxide as active electrode materials; and

-lithium-ion accumulators using, in whole or in part, lithiated materials to constitute the active electrode materials and operating according to the lithium insertion-disinsertion principle.

In recent years, Li-ion batteries have largely overtaken the other batteries mentioned above due to the continuous improvement of the performance of Li-ion batteries in terms of energy density. Indeed, lithium-ion accumulators make it possible to obtain densities of mass and volume energy (which can be greater than 180 Wh.kg ' ¹ ) clearly greater than those of Ni-MH and Ni-Cd accumulators (which can range from 50 and 100 Wh.kg ¹ ) and Lead acid (which can range from 30 to 35 Wh.kg ¹ ).

At present, the market for lithium-ion accumulators is dominated by a so-called “monopolar” architecture, that is to say an architecture in which an accumulator comprises only one electrochemical cell which uses, for example, a positive electrode based on lithiated cobalt oxide (LiCoO ₂ ) and a negative electrode based on graphite, separated from each other by an electrolyte conducting lithium ions, the nominal voltage of these accumulators being l of 3.6 V.

In return for this monopolar architecture, a new generation of accumulators with so-called bipolar architecture has been the subject of studies for several years.

Accumulators of this type include, as illustrated in FIG. 1, conventionally, two terminal current collecting substrates 1, 3 and a stack of electrochemical cells Ci, C ₂ , C _n ... which each include a positive electrode 5 , a negative electrode 7 and a lithium ion conductive electrolyte 9, when the accumulator is a lithium ion accumulator, which is interposed between the positive electrode and the negative electrode, a stack in which the electrochemical cells are separated from each other by a current collector substrate 11, called a bipolar current collector substrate, which is in the form of a plate one side of which is in contact with the negative electrode of an electrochemical cell while the other side is in contact with the positive electrode of the adjacent electrochemical cell. A seal 13 is produced by depositing a resin (for example, an epoxy resin) or an adhesive (for example, an acrylic adhesive) on the periphery of the electrochemical cells. As a variant, sealing can be ensured by thermoformed bags in order to join the different elements of the accumulator.

The bipolar architecture thus corresponds to a series connection of several accumulators by means of so-called bipolar current collecting substrates, which makes it possible to dispense with external connectors, which are necessary for assembling monopolar accumulators in series. It therefore leads to lighter systems than those resulting from a series assembly of monopolar accumulators. In addition, depending on the number of cells making up the stack, the final voltage of the accumulator can be easily adjustable.

However, this type of architecture has the following disadvantages in particular:

-filling with the electrolyte must be done cell by cell during assembly of the accumulator and cannot be modified thereafter due to the sealing of the different cells at the periphery of the accumulator; and

disassembly is not easy, in particular with a view to replacing defective cells, due to the need to remove the sealing material in order to carry it out.

The authors of the present invention have therefore proposed to set up a new type of accumulator with bipolar architecture which makes it possible to overcome the drawbacks mentioned above.

STATEMENT OF THE INVENTION

Thus, the invention relates to an electrochemical accumulator with bipolar architecture comprising a first and second plate, called end plates, associated respectively with a first current collector substrate and a second current collector substrate, said terminal current collecting substrates between which a stack of at least a first electrochemical cell and a second electrochemical cell is arranged in which:

each of the first and second electrochemical cells comprises a positive electrode, a negative electrode and a separator comprising an ion-conducting electrolyte;

the first and second electrochemical cells are separated from each other by a current collector substrate, called a bipolar substrate, which supports on an first face an electrode of the first electrochemical cell and on a second face opposite the first face an electrode of opposite sign of the second electrochemical cell, characterized in that each of the first and second electrochemical cells are housed in a space delimited internally by a frame crossed by a supply channel allowing the supply of the cell with electrolyte, the bipolar current collector substrate being clamped via a free edge between the frame of the first cell and the frame of the second cell and cooperating with each of them by means of at least one seal and the accumulator comprises further means for clamping the frame of the first cell against the frame of the second cell.

By positive electrode is meant, conventionally, in what precedes and what follows, the electrode which acts as a cathode, when the generator delivers current (that is to say when it is in the process of discharging) and which acts as an anode when the generator is in the process of charging.

By negative electrode is meant, conventionally, in what precedes and what follows, the electrode which acts as anode, when the generator delivers current (i.e. when it is in the process of discharge ) and which acts as a cathode, when the generator is in the process of charging.

Thus, each frame delimiting the interior space in which an electrochemical cell is housed makes it possible to ensure, in cooperation with the bipolar current collector substrate and the adjacent frame (that is to say the frame associated with an adjacent cell) the tightness of the stack, which makes it possible to dispense with the use of a sealing material surrounding the stack, as is practiced in accumulators of the prior art. More specifically, the sealing takes place via at least one seal which may be in the form of an O-ring, for example made of a nitrile compound, inserted in a groove arranged on the faces of each frame intended to be in contact with the associated current collector substrate and, more precisely, at the faces of each frame located opposite a current collector substrate, the clamping means exerting pressure on each of the seals on the substrate thus ensuring the isolation of the stack from the outside atmosphere.

In addition, each frame is traversed by at least one supply channel, which makes it possible to supply the cell concerned with electrolyte, after constitution of the stack and before it is put into operation and to supply it, if necessary, if the amount of electrolyte is insufficient after a certain number of operating cycles of the battery. More specifically, the supply channel passing through each of the frames has an opening on the outside of the accumulator (thus allowing the injection of the electrolyte by means, for example, of a syringe) communicating with an opening s' opening onto the space delimited by the frame and in which an electrochemical cell is housed (this opening thus allowing the discharge into the space of the electrolyte injected via the opening on the outside of the accumulator). It is understood that, once the electrolyte has been injected, the supply channel is closed, for example, by a removable leaktight plug, so as to guarantee the sealing of the accumulator. Depending on the thickness of the frame, the associated supply channel can be a straight channel, that is to say passing through the frame without change of direction or can comprise a bevelled portion, in particular, if necessary, to bypass the or the grooves arranged on at least one face of the frame to accommodate the seal or seals.

In addition, each of the frames may have a valve orifice, the set of orifices present on each of the frames forming a valve conduit communicating with the space defined by its associated frame and, advantageously with the outside of the accumulator via an opening or orifice made in the first and / or the second end plate mentioned above, this opening being closed by a valve, which is advantageously screwed into the opening made in the first and / or the second end plate. In this case, the opening is a tapped opening for screwing the valve. Furthermore, seals can be provided between two adjacent frames at the junction between two valve orifices.

Thus, thanks to this valve line inducing a connection between the constituent cells of the accumulator, it is possible to access a harmonization of the pressure within the stack and also in the event of excessive gas emission during of the operation of the accumulator thus avoiding a deterioration of the latter by overpressure while not losing sealing.

As specified above, the valve pipe communicates with the space defined by its associated frame (or, in other words, with the space in which the associated electrochemical cell is housed), the communication being able to be carried out conventionally by a valve channel provided within each frame and connecting said valve orifice to said space defined by the frame. This channel can be closed by a porous material allowing the gases to pass but preventing the passage of liquids, such as a hydrophobic material, so as in particular to avoid the backflow of electrolyte via the valve pipe. For example, this porous material can be porous polytetrafluoroethylene.

In addition, the valve channel, if necessary, can be a channel passing through the frame concerned, in which case it connects the space defined by the frame to the outside of the accumulator via an opening passing through the orifice of valve, the opening being, in normal operation of the accumulator, closed by a plug. According to such a configuration, the valve channel can be used in cooperation with the supply channel when the cell is supplied with electrolyte. More specifically, during this supply, it may be possible to apply vacuum via the valve channel and inject electrolyte via the supply channel, which will allow better impregnation by the electrolyte of the electrochemical cell. .

Each of the frames may be of a polymeric material, such as a methacrylate polymer (for example, polymethyl methacrylate).

The accumulator further comprises means for clamping the frame of the first cell against the frame of the second cell, which will make it possible to ensure the mechanical strength of the accumulator and also to contribute to the sealing of the latter. allowing the seals to compress against the associated current collector substrate. These clamping means can also cooperate with the first and second plate, called end plates. By way of example, these tightening means may consist of screws connecting the first plate to the second plate and passing through the frames concomitantly, which supposes that the first plate and the second plate as well as the frames have holes (such as threaded holes) for screwing the screws, which ensures the mechanical strength of the assembly.

Depending on the geometry of the desired accumulator, the frames may have a square shape, a rectangular shape or a cylindrical shape, the size of the space delimited by the frame and making it possible to accommodate an electrochemical cell being chosen according to the size of the constituent elements of the cell and in particular of the electrodes.

A square frame capable of being incorporated into an accumulator according to the invention is shown, before incorporation into the accumulator and seen from above in FIG. 2 appended hereto, this frame referenced 15 comprising, around its periphery, holes 17 allowing the passage of clamping means, such as screws and comprising a valve orifice 18 connected to a valve channel, of which only the opening (reference 19) opening onto the space delimited by the frame (reference 21) is visible from this view. This frame also includes a supply channel, of which only the opening (reference 23) also on the space delimited by the frame is visible. Finally, this frame comprises, on each of its faces, a groove (reference 25) intended to receive an O-ring seal, which will rest on the free edge of a bipolar current collector substrate as defined above or on the free edge of a terminal current collector substrate (if the electrochemical cell housed in the space delimited by the frame is a cell located at one end of the stack).

The accumulators of the invention comprise, as mentioned above, a first and second plate, called end plates constituting the ends of these, these plates each being associated with a terminal current collector substrate (for example, a metal strip ) in contact with an electrode of an electrochemical cell constituting the end of the stack. Each of these terminal current collecting substrates can be described as monopolar since they are in contact, via one of their faces with a single electrode and are advantageously clamped, via a free edge, between a terminal plate as defined above. above and the frame associated with the adjacent electrochemical cell (this frame meeting the same specifications as that defined above), the contact between the frame and the free edge of the terminal current collector substrate taking place, advantageously, via a gasket sealing, for example, an O-ring placed in a groove formed on the face of the frame which is in contact with the terminal current collector substrate (the other face of the frame being, in turn, in contact via at least one seal d sealing with the bipolar current collector substrate ensuring the separation between the two adjacent electrochemical cells).

At least one of the end plates may have an opening for the current recovery, for example, in which is fixed by welding, a cable allowing the current recovery or from which emanates a tab from a current collector substrate terminal.

Each of these end plates can be made of a polymeric material, for example, polyetheretherketone.

The accumulator can comprise, as cells, only two electrochemical cells (either a first electrochemical cell and a second electrochemical cell), such an accumulator being represented, in exploded view in FIG. 3 (that is to say with the different elements represented individually and without contact with each other but in the order in which they are linked in the stack) and comprising, from top to bottom, the following elements:

the first end plate 27 comprising, in its center, an opening 29 for the current recovery and, on its periphery, holes 31 for the introduction of the clamping means and also comprising an orifice 33 for the introduction of the valve;

a terminal current collector substrate (said first terminal current collector substrate) 35, consisting of a metal strip;

a first frame 37 comprising holes 39 for the introduction of the clamping means, these holes being intended to be opposite those 31 of the first end plate, a valve orifice 41 associated with a valve channel 43, this orifice being intended to be placed opposite that 33 of the first end plate, a supply channel 45 and comprising, on the face (called first face) placed opposite the terminal current collector substrate and the first end plate, a groove 46 receiving an O-ring, this O-ring, after assembly of the various elements, resting on the free edge of the terminal current-collector substrate, said first frame also comprising, on the face opposite to the first face (said second non-face shown) a groove receiving an O-ring intended to bear on the free edge of the bipolar current collector substrate;

a first electrode 47 comprising an active material, which will be housed in the space provided by the first frame and rest on the first terminal current collector substrate 35 leaving a free edge for the support of the O-ring of the first frame ;

a separator 49 intended to receive the electrolyte, which will also be housed in the space provided by the first frame and rest on the first electrode;

a second electrode 51 comprising an active material intended to be housed in the space provided in the first frame and to be supported via one face on the separator and via the other face on a common bipolar substrate, all of the first electrode 47, separator 49 and second electrode 51 forming the first electrochemical cell 50;

the bipolar current collector substrate 53 formed here of two strips joined together and intended to receive on one face (called the first face) the second electrode and on the free edge of this face the seal of the second face of the first frame and comprising a second face (opposite the first) which will serve as a support for an electrode of the adjacent cell (called the third electrode) and on the free edge of this face the seal of the first face of the second frame defined here - below;

the second frame 55 comprising holes 57 for the introduction of the clamping means, these holes being intended to be opposite those of the first end plate and the first frame, a valve orifice 59 associated with a valve channel 61 , this orifice being intended to be placed opposite that of the first end plate and of the first frame, a supply channel 63 and comprising, on the face (said first face) placed opposite the bipolar current collector substrate, a groove receiving an O-ring 64, this O-ring, after assembly of the various elements, resting on the free edge of the common bipolar substrate, said second frame also comprising, on the face opposite to the first face (said second face not shown) a groove receiving an O-ring intended to bear on the free edge of the second terminal current collector substrate;

a third electrode 65 comprising an active material, which will be housed in the space provided by the second frame and rest on the bipolar current collector substrate 53, leaving a free edge on this substrate for the support of the O-ring of the first face of the second frame;

a separator 67 intended to receive the electrolyte, which will also be housed in the space provided by the second frame and rest on the third electrode;

a fourth electrode 69 comprising an active material intended to be housed in the space provided in the second frame and to bear via one side on the separator and via the other side on a terminal current collector substrate (called second substrate) terminal current collector), the assembly of the third electrode 65, of the separator 67 and of the fourth electrode 69 forming the second electrochemical cell 66;

a terminal current collector substrate (said second terminal current collector substrate) 71, consisting of a metal strip which rests, via one face, on the second electrode while providing a free edge which will rest on the joint toric of the second face of the second frame and via another face on the second end plate;

the second end plate 73 comprising, in its center, an opening for the current recovery (not shown) and, on its periphery, holes 75 for the introduction of the clamping means and also comprising an orifice 77 for the introduction of the valve, the holes and the valve orifice being aligned with those of the second frame, the first frame and the first end plate.

Once assembled, the different elements shown in exploded view and defined above will constitute an accumulator comprising two electrochemical cells housed respectively in the space delimited by a first frame and in the space delimited by a second frame, said first and second frame being sandwiched between a first end plate and a second end plate.

Such an accumulator is represented in FIG. 4 attached in the annex in top view revealing the following elements:

the first end plate 27 comprising, in its center, the opening 29 for the current recovery and, on its periphery, the clamping holes 31 occupied by clamping means 32 and a valve orifice 33;

the first frame 37 and the second frame 55 bearing on one another after tightening the clamping means; and

the second end plate 73, this accumulator also being represented in a sectional view passing through the middle of the first end plate so as to illustrate the elements internal to the accumulator, this representation being that of FIG. 5 appended in annex and illustrating the following:

the first end plate 27 comprising, in its center, the opening 29 for the current recovery, the clamping holes 31 occupied by clamping means 32 and the valve orifice 33;

the first frame 37 framing a first electrochemical cell (consisting of the stack of a positive electrode, a separator and a negative electrode) comprising a first O-ring 46 resting on the first terminal current collector substrate 35 and, on its opposite face, a second O-ring 42 resting on the bipolar current collector substrate 53;

the second frame 55 framing a second electrochemical cell (consisting of the stack of a positive electrode, a separator and a negative electrode) comprising a first O-ring 64 resting on the bipolar current collector substrate 53 and, on its opposite face, a second O-ring 62 resting on the second terminal current collector substrate 71;

the second end plate 73 comprising, in its center, the opening 74 for the current recovery, the clamping holes occupied by clamping means and the valve orifice.

An enlarged view of the area around the valve ports is illustrated in Figure 6 attached, which more specifically presents the following:

the valve orifices (33, 41, 59, 77) of the first end plate, the first frame, the second frame and the second end plate placed opposite one another to form a valve line 60 which connects the different cells together (in this case, two cells in this case);

-O rings at the junction between two valve orifices (respectively an O-ring 79 around the valve opening made on the second end plate, an O-ring 81 around the valve opening of the second frame and a O-ring 83 around the valve opening of the first frame);

-for each of the frames, a non-linear valve channel (respectively 43 for the first frame and 61 for the second frame) which connects the outside of the accumulator to the space delimited by the frame and in which the cell is housed electrochemical concerned, this channel also passing through the valve orifice, these valve channels being closed by plugs 85, when they are not used.

The accumulators of the invention are suitable for all types of accumulators and, in particular, for nickel-zinc type accumulators which operate by means of two electrochemical couples involving nickel (Ni ^{+ Il} / Ni ^{+ I11} with redox potential 0.49 V / ENH) and zinc (Zn ° / Zn ^{+ I1} with a redox potential of -1.24 V / ENH). More specifically, the species involved in such an accumulator are nickel oxides and oxy-hydroxides as well as zinc hydroxide and metallic zinc.

More specifically, the reactions occurring during the charging process are as follows:

Ni (OH) ₂ + 2 OH '-> 2NÎOOH + 2e + 2H ₂ O

Zn (OH) ₂ + 2e '-> Ζη + ΟΗ which corresponds to the following balance:

Zn (OH) ₂ + 2Ni (OH) ₂ A Zn + 2NÎOOH

In return, the reactions occurring during the discharge process are as follows:

2NÎOOH + 2è + 2H ₂ O - »2 Ni (OH) ₂ + 2 OH

Zn + OHZn (OH) ₂ + 2e which corresponds to the following balance:

Zn + 2NÎOOH -> Zn (OH) ₂ + 2Ni (OH) ₂

This type of accumulator gives access to an improvement in potential of 0.4 V compared to other nickel-based technologies and enables attractive specific energies to be reached (of the order of 400 Wh.kg ¹ ). In addition, the toxicity of these constituent elements is much less than that of competing technologies, such as lead-acid or nickel-cadmium type batteries.

Accumulators with bipolar architecture of the invention are particularly suitable for the following reasons:

-the good sealing of the batteries allows the use of the electrolyte commonly used in these batteries (namely, highly concentrated potassium hydroxide), which because of its strong induced corrosion and its reactivity can be difficult to use in poor sealing;

the presence of a supply channel can make it possible to supply the accumulator from the outside with the desired quantity of electrolyte so as to avoid the dissolution of active material in the electrolyte and therefore a concomitant loss of this material (and consequently, a reduction in discharge performance), which is the case for zincates which dissolve easily in electrolytes;

-the possible presence of a valve line can evacuate the gases produced during charge / discharge cycles, in particular on the side of the positive electrode by oxidation of the water causing the appearance of oxygen and of the side of the negative electrode by reducing the hydrogen-forming water.

Because of their constituent elements, the accumulators of the invention are easy to assemble and, at the same time, easy to disassemble.

The invention thus relates to a method for producing an accumulator as defined above, comprising the following steps:

a) establishment of a first electrode previously deposited on a first so-called terminal current collector substrate, by bringing the current collector substrate into direct contact with the first end plate, in which clamping means have been arranged in holes provided for this purpose;

b) placing a first frame by passing the clamping means through holes made in this first frame, this first frame comprising, on each of its faces, sealing means, the sealing means of the opposite face the first end plate being supported on the first terminal current collector substrate of the first electrode and said first frame being traversed by a supply channel;

d) bringing the first electrode into contact with a separator intended to contain the electrolyte;

e) depositing on this separator a second electrode (of opposite polarity to the first electrode) thus closing the first electrochemical cell, this second electrode being integral with one face of the bipolar current collector substrate, the free edge of this face being resting on the sealing means of the first frame, while the other face of the bipolar current collector substrate is occupied by an electrode constituting the second electrochemical cell;

f) placement of a second frame by passing the clamping means through holes made in this second frame, this second frame comprising, on each of its faces, sealing means, the sealing means of the opposite face of the bipolar current collector substrate being supported on the free edge thereof and said second frame being traversed by a supply channel;

g) bringing the electrode into contact with a separator intended to contain the electrolyte;

h) deposition on this separator of another electrode thus closing the second electrochemical cell, this electrode being associated with a terminal current collector substrate having a free edge bearing on sealing means of the second frame;

i) placing the second end plate against the terminal current collecting substrate;

j) clamping the assembly by said clamping means;

k) filling each of the cells with electrolyte via the supply channels passing through each of the frames.

If the accumulator comprises more than two electrochemical cells, it is understood that after step g), steps e), f) and g) will be repeated according to this sequence as many times as necessary to obtain the number of electrochemical cells. desired, the last cell of the stack being finalized by the implementation of steps h), i), j) and k).

Other steps may be provided such as the placement of a valve, the placement of a felt between an electrode and the associated separator, the felt being able to serve as an electrolyte reservoir, etc.

Other characteristics and advantages of the invention will appear from the additional description which follows and which relates to particular embodiments.

Of course, this additional description is given only by way of illustration of the invention and in no way constitutes a limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, already commented on, schematically represents a view in longitudinal section of a conventional example of an accumulator with bipolar architecture.

Figure 2, already commented, shows a top view of a frame capable of entering into the constitution of an accumulator according to the invention.

Figure 3, already discussed, shows an exploded view of an accumulator according to the invention.

FIG. 4, already commented on, represents a top view of an accumulator comprising two electrochemical cells according to the invention.

FIG. 5, already commented on, represents a view in median section of the accumulator represented in FIG. 4.

FIG. 6 is an enlarged view of the zone situated around the valve orifices for the accumulator illustrated in FIG. 4.

FIG. 7 is a graph illustrating the evolution of the capacity C (in Ah) as a function of the number of cycles N in 1C / 1D regime for the accumulator exemplified below.

DETAILED DESCRIPTION OF A PARTICULAR EMBODIMENT

The example presented below illustrates the preparation of an accumulator according to the invention, this accumulator being similar to that shown in FIG. 4, except that it is composed of a stack of nine electrochemical cells instead of two electrochemical cells.

More specifically, for this accumulator:

-the end plates (namely the first end plate and the second end plate), are places in polyetheretherketone (PEEK) having the dimensions 20 * 20 * 0.5 cm and are provided, before assembly, with 16 holes around their periphery to be able to screw and tighten the plates and the frames to each other via stainless steel screws and bolts and further comprise a valve opening and a central opening for the current recovery;

the frames (9 in number to frame each of the electrochemical cells) are polymethyl methacrylate frames which moreover meet the specific features of the invention (presence of a supply channel, of a linked valve orifice a valve channel and O-rings on each of its faces);

-the bipolar current collector substrate results from the welding or bonding by an electrically conductive resin (specifically, a silver lacquer) of a nickel strip and a bronze strip (having the dimensions 18 * 18 * 0.015 cm) with on the nickel strip the deposition of an electrode consisting of nickel foam comprising incorporated nickel hydroxide and on the bronze strip the deposition of an electrode consisting of zinc foam comprising incorporated zinc hydroxide, each of the electrodes having the following dimensions 15 * 15 * 0.1 cm, this substrate being supplied by the company SCPS;

the electrodes located at the end of the stack are only deposited on a monopolar current collector substrate, which is a nickel strip (for the electrode consisting of nickel foam comprising incorporated nickel hydroxide) or a bronze strip (for the electrode consisting of a zinc foam comprising incorporated zinc hydroxide);

each of the electrodes further comprises a hydrophobic tape oriented towards the area for filling the cell with electrolyte;

between two electrodes of the same cell, the presence of a felt playing the role of electrolyte reserve and of a polypropylene separator impregnated with the electrolyte, which is an aqueous solution of potassium hydroxide 7M.

This accumulator is produced by implementing the following operations:

a) introduction of screws into the holes of the first end plate, which then makes it possible to center each frame easily, the screws introduced into the holes of the end plate also passing through the holes made on the periphery of each of the frames;

b) introduction of the first electrode previously deposited on a monopolar current collector substrate defined above, the current collector substrate being in direct contact with the end plate;

c) placement of a first frame by passing the screws of the end plate through the holes made in this first frame, this first frame comprising, on each of its faces, an O-ring, the O-ring of the face opposite the end plate bearing on the monopolar current collector substrate of the first electrode;

d) bringing the first electrode into contact with a felt layer (Viledon® from Freudenberg) and a polypropylene separator (Celgard® 2401) respectively;

e) depositing on this separator a second electrode (of opposite polarity to the first electrode) thus closing the first electrochemical cell, this second electrode being integral with one face of the bipolar current collector substrate, the free edge of this face being resting on the other O-ring of the first frame, while the other face of the current collector substrate is occupied by an electrode constituting the second electrochemical cell;

f) repeating steps c), d) and e) until 9 electrochemical cells are stacked, the last cell being closed by bringing the separator into contact with an electrode previously deposited on a current collector substrate monopolar, this current collector substrate being intended to be in contact with the second end plate;

g) placement of the second end plate, which is centered on the screws passing through the entire stack;

h) screwing of the entire stack using a torque wrench;

i) placing the valve by screwing it into the valve line resulting from the combination of valve offices present at the end plates and frames;

j) filling of the different cells with the electrolyte via the supply channels provided at each frame by exerting, in parallel, a vacuum via the valve channels;

k) sealing of the various channels with a plug to guarantee the tightness of the assembly.

It is understood that the screws introduced during step a) pass through the entire stack and slightly protrude from the holes made in the second end plate, the ends of these screws being associated with nuts for tightening by means of '' a torque wrench.

At the end of the assembly, a step called electrochemical training is to be carried out before the use at full speed thereof, this training step consisting of slow speed cycling steps.

The accumulator thus obtained has an average voltage of 14.4 V as well as a capacity of approximately 6 Ah as shown in Figure 7 which is a graph illustrating the evolution of the capacity C (in Ah) in function of the number of cycles N in 1C / 1D regime.

Claims (11)

1. Electrochemical cell with bipolar architecture comprising a first (27) and second plate (73), called end plates, associated respectively with a first current collector substrate (35) and a second current collector substrate (71), said collector substrates current terminals between which is disposed a stack of at least a first electrochemical cell (50) and a second electrochemical cell (66) in which: each of the first and second electrochemical cells comprises a positive electrode, a negative electrode and a separator (49, 67) comprising an ion-conducting electrolyte; the first and second electrochemical cells are separated from each other by a current collector substrate, called a bipolar substrate (53), which supports on an first face an electrode (51) of the first electrochemical cell and on a second opposite to the first face an electrode (65) of opposite sign of the second electrochemical cell, characterized in that each of the first and second electrochemical cells are housed in a space delimited internally by a frame crossed by a supply channel allowing the supply of the cell with electrolyte, the bipolar current collector substrate being clamped via a free edge between the frame of the first cell and the frame of the second cell and cooperating with each of them by means of at least one gasket and the accumulator further comprises means for clamping the frame of the first cell against the frame of the second th cell. 2. Accumulator according to claim 1, in which the at least one seal is in the form of an O-ring inserted in a groove (25) arranged on the faces of each frame intended to be in contact with a collecting substrate. current. 3. Accumulator according to claim 1 or 2, wherein each of the frames has a valve orifice (41, 59), the set of orifices present on each of the frames forming a valve line (60) communicating with the defined space by its associated framework. 4. Accumulator according to claim 3, wherein the valve line communicates with the outside of the accumulator via an opening made in the first and / or the second end plate, the or one of these openings being closed by a valve. 5. Accumulator according to claim 3 or 4, wherein the valve line communicates with the space defined by its associated frame by a valve channel (43, 61) provided within each frame and connecting said valve orifice to said space defined by the frame. 6. Accumulator according to claim 6, in which the valve channel is a channel passing through the frame concerned, that is to say connecting the space defined by the frame outside the accumulator via an opening passing through the valve port. 7. Accumulator according to any one of claims 3 to 6, in which seals are provided between two adjacent frames at the junction between two valve orifices. 8. Accumulator according to any one of the preceding claims, in which the clamping means cooperate with the first and second plate, called end plates. 9. Accumulator according to any one of the preceding claims, in which the clamping means consist of screws connecting the first plate to the second plate and concomitantly passing through the frames. 10. Accumulator according to any one of the preceding claims, in which at least one of the end plates has an opening (29, 74) for the recovery of current. 11. Accumulator according to any one of the preceding claims, which is a nickel-zinc type accumulator.