Pouch-type electrochemical cell for storing electrical energy

Abstract

Electrochemical cell (1), comprising an envelope (2) in which is arranged at least one elementary unit comprising a positive electrode (5) composed of a positive current collector and at least one layer of active materials and a negative electrode (9) composed of a negative current collector and at least one layer of active materials, and a separator (7) between said stacked positive (5) and negative (9) electrodes, said current collectors of said at least one elementary unit each having a terrace free of active materials, said electrochemical cell (1) being characterized in that it comprises at least one first orifice (15) passing through the envelope (2) so that the terrace (11) of the cathode current collector of the cell is accessible through this first orifice (15),and at least one second orifice (17) passing through the casing (2) so that the terrace (13) of the anode collector of the cell is accessible through this second orifice (17). Abstract figure: Figure 1,

Description

Title of the invention: Pouch-type electrochemical cell for storing electrical energy

[0001] The present invention relates to a pouch-type electrochemical cell for storing electrical energy, in particular for motor vehicle accumulator batteries.

[0002] Electric or hybrid motor vehicles comprise electric accumulator batteries or, more generally, electrical energy storage devices, comprising electrochemical electrical energy storage cells.

[0003] Conventionally, a pouch-type electrochemical cell is composed of one or more positive electrodes stacked alternately with one or more negative electrodes, as well as one or more separators so as to separate the positive and negative electrodes, the separator being soaked in electrolyte to allow ionic conduction between the electrodes. Each stack of a positive electrode and a negative electrode separated by a separator forms an elementary unit.

[0004] In the remainder of the description, unless otherwise specified, the term “unitary” refers to a component of this elementary unit. Each unit electrode, positive or negative, is composed of an electrically conductive material and a layer of active, porous materials. Said layer of active materials is composed of an electrochemical material to store energy and additive materials to allow electrical conductivity, cohesion of the material and the appropriate morphology. The conductive material is called a positive or negative current collector depending on the electrode considered. The unit current collectors each have a part without a coating of porous materials, called a terrace, allowing it to be connected to an electrically conductive connector, generally metallic, also called a terminal. The metallic connector must be accessible from the outside of the cell in order to connect it to an electrical circuit.

[0005] In general, the cell comprises several elementary units separated from each other by an electrically insulating separator which nevertheless allows ionic transfer.

[0006] The set of unit positive current collectors forms the cathode current collector of the cell. The set of respective unit terraces of the unit positive current collectors forms the cathode current collector terrace of the cell. The set of unit positive electrodes are connected to the positive terminal of the cell by the set of respective terraces of the unit positive current collectors, in other words by the cathode current collector terrace of the cell. For example, the positive terminal of the cell is soldered to the cathode terrace of the cell. The set of unit negative current collectors forms the anode current collector of the cell. The set of respective terraces of the unit negative current collectors forms the anode current collector terrace of the cell. All the unit negative electrodes are connected to the negative terminal of the cell by all the terraces of the unit negative current collectors, in other words by the anode terrace of the cell. For example, the negative terminal of the cell is welded to the terrace of the anode current collector of the cell. Each unit current collector is for example a metal foil or film.

[0007] All of these components are contained in a sealed manner in an envelope made of a flexible material acting as a protective film. The film is positioned so as to envelop the electrodes. At each terminal, the film is closed by thermal welding to fuse the polymer layers that comprise said protective film. Each metal terminal extends from the inside to the outside of the envelope so as to be accessible from the outside.

[0008] Document US20010046623 A1 published in 2001 describes the architecture of a non-aqueous pouch-type electrolytic cell, encapsulated by thermal fusion in a protective film and in which the terminals of the positive and negative electrodes are exposed outside the protective film through the joint of the protective film. The terminals of the positive and negative electrodes are welded on an area without active material coating of the current collector.

[0009] This structure, although widely used, has a high internal electrical resistance value due to the resistance of the connection and the resistance of the solder. In addition, the contact area between the terminal and the protective film is a fragile area which could present a risk of leakage or moisture absorption of the cell during movement of the vehicle containing the cell.

[0010] Finally, the energy volume capacity of the cell is reduced due to the use of the terminal and in particular the welding zone between the terminal and the current collector which will reduce the ratio between the surface taken by the surface of the electrodes and the total surface of the cell.

[0011] There is therefore a need for an electrochemical cell having a better energy volume capacity while reducing its internal electrical resistance value.

[0012] For this purpose, an electrochemical cell for storing electrical energy is proposed, comprising an envelope in which at least one unit is arranged elementary unit comprising a positive electrode composed of a positive current collector and at least one layer of active materials and a negative electrode composed of a negative current collector and at least one layer of active materials, and a separator between said stacked positive and negative electrodes. Said positive current collector and said negative current collector of the at least one elementary unit each have a terrace, part of the collector free of active materials. The terrace of the positive current collector of said at least one elementary unit forms the terrace of the cathode current collector of the cell, and the terrace of the negative current collector of said at least one elementary unit forms the terrace of the anode current collector of the cell.The electrochemical cell comprises at least one first orifice passing through the casing such that the terrace of the cathode current collector of the cell is accessible through this first orifice, and at least one second orifice passing through the casing such that the terrace of the anode current collector of the cell is accessible through this second orifice.

[0013] More particularly, said at least one first orifice is opposite the terrace of the cathode current collector of the cell, and said at least one second orifice is opposite the terrace of the anode current collector of the cell. The surfaces of the terraces delimited by the orifices thus form direct connection zones for an external element with the cell.

[0014] This electrochemical cell architecture according to the invention makes it possible to avoid the use of a metal terminal coming out of the cell, thus making it possible to use less materials, in particular metals, and to reduce the costs of the cell. This architecture also makes it possible to reduce the weight and volume of the cell since less material is used but also the lifespan of the battery.

[0015] It also makes it possible to electrically connect the cell directly at the electrodes, which makes it possible, compared to the prior art, to reduce the internal electrical resistance of the cell and to increase the volume and mass energy densities of the cell. It also advantageously increases the lifespan of the cell because it reduces internal heating.

[0016] More particularly, the cell thus formed has a generally parallelepiped shape.

[0017] Advantageously, the at least one first and at least one second orifices are surrounded by a polymer film secured in a sealed manner to the envelope and to respectively the terrace of the cathode current collector of the cell and the terrace of the anode current collector of the cell, in order to guarantee the sealing of the cell.

[0018] Thus, the envelope can be perforated at any time during the manufacture of the cell or just before its use, for example at the time of its connection with a circuit external electrical, to avoid misuse which could cause a short circuit.

[0019] Advantageously, the polymer film is hot-melt and has adhesive properties.

[0020] Preferably, the polymer film is made of thermoplastic polymer, preferably polyolefin, in particular polypropylene or polyethylene.

[0021] Advantageously, the envelope is perforated so as to form at least one first and at least one second orifice.

[0022] According to a particular embodiment of the invention, the electrochemical cell comprises two first orifices distributed on either side of the cathode current collector of the cell and / or two second orifices distributed on either side of the anode current collector of the cell.

[0023] Preferably, the electrochemical cell comprises several said elementary units composed of a positive electrode and a negative electrode and a separator between the electrodes, and in that the respective terraces of the positive current collectors of each unit extend and overlap to form the terrace of the cathode current collector of the cell and the respective terraces of the negative current collectors of each unit extend and overlap to form the terrace of the anode current collector of the cell.

[0024] Thus, when the cell comprises several elementary units, therefore several positive electrodes, the unit current collectors of the positive electrodes extend outside the other components of the stack formed by the positive, negative electrodes and the separators. The respective extensions of the unit current collectors of the positive electrodes are placed next to each other. These extensions have the terraces of the unit positive electrodes which are superimposed and are thus assembled together to form the terrace of the cathode (positive) current collector of the cell, or in other words to form the positive pole of the cell.

[0025] Similarly, the unit current collectors of the negative electrodes extend outside the other components of the stack formed by the positive and negative electrodes and the separators. The respective extensions of the unit current collectors of the negative electrodes are placed next to each other. These extensions have the terraces of the unit negative electrodes which are superimposed and are thus assembled together to form the terrace of the anode (negative) current collector of the cell, or in other words to form the negative pole of the cell.

[0026] The electrochemical cell, as described above, can be manufactured according to a method in which said at least one first orifice and at least one second orifice are perforated in the envelope of the cell before or during assembly of the cell, or after assembly of the cell, in particular just before making its connection to an external element.

[0027] Another object of the invention is an electric accumulator battery comprising at least one electrochemical cell as described above.

[0028] Another object of the invention is a motor vehicle comprising at least one battery as described above.

[0029] Other features and advantages of the invention will emerge from reading the description given below of a particular embodiment of the invention, given for informational purposes but not as a limitation, with reference to the appended drawings in which:

[0030] [Fig-1] is a schematic top view and partially cut away of a cell pocket-type electrochemical device according to the invention;

[0031] [Fig.2] is a schematic side view of the cell according to the invention shown in [Fig.l], along a section AA passing through the cathode current collector of the cell.

[0032] [Fig.3] schematically illustrates, in a top view and in cutaway (without casing), an arrangement at the level of the terrace of the cathode of the cell.

[0033] Figures 1 to 3 are commented on together.

[0034] Figures 1 to 3 illustrate a pouch-type electrochemical cell 1 as a battery Emulator for an electric storage battery. The electrochemical cell allows chemical energy to be reversibly converted into electrical energy. The number of cells required depends on the desired battery capacity.

[0035] [Fig.l] illustrates a pouch-type electrochemical cell 1 comprising a flexible envelope 2. The envelope 2, also called a protective film, is made of a flexible material so as to tightly envelop the components of the cell 1. The envelope 2 is a complex assembly of aluminum layers and polymer layers including at least one thermofusible inner surface polymer layer.

[0036] The envelope 2 is positioned so as to completely envelop all the components of the cell 1.

[0037] It is closed by thermal welding to fuse the polymer layers coming opposite each other at a heat-sealing zone 3. The heat-sealing zone can be along three sides of the cell 1 in the case where the envelope is folded on one side or along the four sides of the cell 1 in the case where the envelope is composed of two sheets arranged opposite each other on either side of the contents of the cell. The cell thus formed has a generally parallelepiped shape.

[0038] Inside the envelope 2, the cell 1 also comprises the stack of at least one porous positive electrode 5, at least one porous separator 7 and at least one porous negative electrode 9, all soaked in an electrolyte allowing ionic conduction. This stack constitutes an elementary unit, and is multiplied as many times as necessary to obtain the desired cell capacity, such as as illustrated by [Fig.2].

[0039] The unitary positive electrode 5, also called unitary cathode, is composed of an electrically conductive material, called unitary positive current collector or unitary cathode current collector 50, as well as a layer of active, porous materials, consisting of electrochemically active materials for energy storage, as well as additive materials allowing electrical conductivity, material cohesion and suitable morphology. Said unitary current collector 50 of the unitary positive electrode 5 has a bare zone 500, that is to say free from coating of active materials, called (unitary) terrace of the unitary positive electrode (or unitary cathode).

[0040] For example, said positive current collector is an aluminum film and said negative current collector is a copper film. However, the film of the negative or positive current collector is not limited to this example.

[0041] In the cell 1 as illustrated, there are several stacked elementary units. It therefore comprises several unitary positive electrodes 5, and the respective unitary positive current collectors 50 of said unitary positive electrodes 5 each extend onto an interior part of the cell, beyond the part of the stack comprising the layers of active materials, superimposing themselves as shown in [Fig.2]. Each current collector extension of a unitary positive electrode considered thus comprises a unitary terrace, and all of these unitary terraces form the terrace 11 of the cathode current collector of the cell.

[0042] The unit negative electrode 9, also called the unit anode, is composed of an electrically conductive material, called the unit negative current collector, or unit anode current collector, as well as a layer of active, porous materials, consisting of electrochemically active materials for energy storage, as well as additive materials allowing electrical conductivity, material cohesion and suitable morphology (electroactive and additives). The unit negative electrode 9 has an area without a coating of active, porous materials (electroactive and additives), called the terrace of the anode current collector.

[0043] In the cell 1, as illustrated, there are several unit stacks, therefore several negative electrodes 9, the respective unit terraces of the current collectors of the unit negative electrodes extend over an interior part of the cell, beyond the part of the stacks comprising the layers of active materials, by superimposing themselves. Each current collector extension of a unit positive electrode considered thus comprises a unit terrace, and all of these unit terraces form the terrace 13 of the anode current collector of the cell shown in [Fig.l] (not visible in [Fig.2]).

[0044] The set of respective terraces of the positive and negative electrodes is su perpose in different zones to form respectively on the one hand the terrace 11 of the cathode of the cell and on the other hand the terrace 13 of the anode of the cell, the extensions of the positive current collectors being on one side of the stack and the extensions of the negative current collectors being on the opposite side. These terraces of the cell 11, 13 are therefore separated in order to avoid short circuits. They allow contact to be made to establish a connection, for example by welding, with an external electrically conductive element (not shown in the figures), for example metallic, through orifices in the envelope as explained below. In particular, they allow contact to be made directly with an electrical circuit.

[0045] The terraces of the current collectors of the unit electrodes of the same polarity can be advantageously welded together to improve the conductivity between these terraces.

[0046] The electrochemical cell 1 comprises at least one first orifice 15 passing through the casing 2. This first orifice 15 is located at the level of the terrace 11 of the cathode current collector of the cell so that a part of the terrace 11 is directly accessible from the outside of the cell 1 to establish a connection with an external electroconductive element.

[0047] The cell 1 further comprises at least one second orifice 17 passing through the casing 2. This second orifice 17 is located at the level of the terrace 13 of the anode current collector of the cell so that part of the terrace is directly accessible from the outside of the cell 1.

[0048] With reference to [Fig.l], the cell 1 has a single first orifice 15 and a single second orifice 17. However, configurations (not shown in the figures) can be provided where there are several first orifices 15 and / or several second orifices 17. For example, the cell can have two first orifices located on either side of the terrace 11 of the cathode of the cell and two first orifices located on either side of the terrace 13 of the anode of the cell. The fact that the extensions of the current collectors are flexible makes it possible to form terraces which can be oriented in different directions, and therefore to be able to offer easier access to external elements compared to prior art pocket-type cells comprising connection terminals.

[0049] The first orifice 15 and the second orifice 17 thus make it possible to electrically connect the cell 1 directly from the outside.

[0050] For this, the envelope 2 is perforated at these first and second orifices. The envelope 2 can be perforated before or during assembly of the cell but also just before its use to avoid misuse which could cause a short circuit.

[0051] The respective surfaces of the first 15 and second 17 orifices must be sufficient to limit the electrical resistance during contact resumption. Thus, these orifices each have a width of between 1 millimeter and 1 centimeter. The surface is also adapted according to the size of the cell since the larger the cell, the larger the respective surfaces of the first and second orifices can be.

[0052] In order to ensure the sealing of the cell 1, an adhesive thermofusible polymer film 19 is installed on the periphery of the first 15 and second 17 orifices respectively, between the terraces 11 and 13 of the cell and the envelope 2. The respective area of ​​the terraces 11 and 13 is then heated and pressed to shape the thermofusible polymer film 19, which hermetically seals the envelope around the orifices, and therefore makes the cell 1 waterproof in particular to contain the liquid electrolyte inside the cell. This also makes it possible to prevent the penetration of moisture and oxygen which would reduce the electrochemical performance of the cell. Preferably, the polymer film 19 is applied to the terrace (see for example [Fig.3]), however it can also be applied to the envelope 2.

[0053] In the case where the envelope is perforated after the assembly of the cell, the polymer film is installed on the periphery of the locations provided respectively for the orifices for each terrace of the cell, before the installation of the envelope, and it is heated and pressed after the installation of the envelope so that the polymer film and the envelope are heated and pressed together to obtain the seal around the locations reserved for the orifices, and the orifices will be made subsequently by removing material from the envelope at the locations provided.

[0054] The hot-melt polymer film 19 is made of a thermoplastic polymer, having sealing and adhesive properties, such as polypropylene or polyethylene.

[0055] Generally, when assembling the cell, the respective terraces 11 and 13 of the cathode and anode electrodes of the cell are covered with insulating adhesive tape to prevent them from moving or short-circuiting. To avoid using insulating adhesive tape, the polymer film 19 can cover the entire surface of each terrace 11, 13 which will not be exposed to the outside of the cell 1 through the holes.

Claims

Claims

1. Electrochemical cell (1) for storing electrical energy, comprising an envelope (2) in which is arranged at least one elementary unit comprising a positive electrode (5) composed of a positive current collector (50) and at least one layer of active materials and a negative electrode (9) composed of a negative current collector and at least one layer of active materials, and a separator (7) between said stacked positive (5) and negative (9) electrodes, said positive current collector (50) and said negative current collector of said at least one elementary unit each having a terrace (500), part of the collector free of active materials,the terrace (500) of the positive current collector (50) of said at least one elementary unit forming the terrace (11) of the cathode current collector of the cell and the terrace of the negative current collector of said at least one elementary unit forming the terrace (13) of the anode current collector of the cell, said electrochemical cell (1) being characterized in that it comprises at least one first orifice (15) passing through the casing (2) so that the terrace (11) of the cathode current collector of the cell (1) is accessible through this first orifice (15), and at least one second orifice (17) passing through the casing (2) so that the terrace (13) of the anode current collector of the cell (1) is accessible through this second orifice (17).,

2. Electrochemical cell (1) according to claim 1, characterized in that the at least one first and at least one second orifices (15, 17) are surrounded by a polymer film (19) secured in a sealed manner to the casing (2) and to respectively the terrace (13) of the cathode current collector of the cell and the terrace (11) of the anode current collector of the cell.

3. Electrochemical cell (1) according to claim 2, characterized in that said polymer film (19) is heat-meltable and has adhesive properties.

4. Electrochemical cell (1) according to claim 3, characterized in that said polymer film (19) is made of thermoplastic polymer, preferably polyolefin, in particular polypropylene or polyethylene.

5. Electrochemical cell (1) according to claim 1 to 4, characterized in that the envelope (2) is perforated so as to form at least one first and at least one second orifice (15, 17).

6. Electrochemical cell (1) according to any one of claims 1 to 5, characterized in that it comprises two first orifices (15) distributed on either side of the cathode current collector of the cell and / or two second orifices (17) distributed on either side of the anode current collector of the cell.

7. Electrochemical cell according to any one of claims 1 to 6, characterized in that it comprises several said elementary units composed of a positive electrode (5) and a negative electrode (9) and a separator (7) between the electrodes, and in that the respective terraces of the positive current collectors of each unit extend and overlap to form the terrace (11) of the cathode current collector of the cell and the respective terraces of the negative current collectors of each unit extend and overlap to form the terrace (13) of the anode current collector of the cell.

8. Electric storage battery characterized in that it comprises at least one electrochemical cell (1) according to one of claims 1 to 7.

9. Motor vehicle characterized in that it comprises at least one battery according to claim 8.

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