FR3117682A1 - BATTERY VENTILATION SAFETY DEVICE - Google Patents

Abstract

Security device comprising a membrane (1) having a first (2) and a second (3) face, this membrane (1) comprising: - a first peripheral zone (Z1) comprising only on the first face (2) an adhesive coating , - a second zone (Z2), central to the first zone (Z1), arranged so as to open according to a surrounding physical parameter, - a succession of several of this membrane (1), joined to each other others by the first peripheral zone (Z1) forming a strip (4). Figure 2

Description

BATTERY VENTILATION SAFETY DEVICE

The invention relates to a safety device for a battery, in particular a battery of an electrically powered vehicle.

The term battery will be understood throughout the text of this document to mean an assembly comprising at least one battery module containing at least one electrochemical cell. This battery optionally comprises electrical or electronic means for managing the electrical energy of this at least one module. When there are several modules, they are grouped together in a tray or casing and then form a battery pack, this battery pack being often designated by the English expression "battery pack", this casing generally containing a mounting interface, and connection terminals.

Furthermore, the term electrochemical cell will be understood throughout the text of this document to mean cells generating current by chemical reaction, for example of the lithium-ion (or Li-ion) type, of the Ni-Mh or Ni-Cd or lead or fuel cells.

In this field, the chemical reactions internal to the electrochemical cells cause variations in the temperature of the cells. These cells, these modules, or this tank are sealed and these temperature variations cause an internal overpressure in the event of heating, or an internal depression in the event of cooling, so that these cells, these modules, or this tank are generally equipped means of breathing.

Throughout the text of this document, breathing will be understood to mean a flow of gas sufficient to compensate for a small pressure difference between an enclosure and an environment outside this enclosure, in both directions. Low pressure means, for example, a pressure due to the expansion or contraction of this gas or parts inside this enclosure, in particular due to a change in operating temperature. The term ventilation will be understood for a higher gas flow, following an incident of the battery thermal runaway type.

In addition, the use of a sealed battery outside nominal conditions, for example following an incident such as during an accidental overload, a short circuit, or during exposure to a temperature higher than the maximum operating temperature of the battery, creates a risk of explosion. Indeed, such situations lead to electrochemical reactions that generate gases. The accumulation of these gases causes an increase in the internal pressure of the battery, which can lead to a violent bursting of the container and the projection of harmful and corrosive chemical compounds for the environment and the people located nearby. The flow rate of these gases is then too high for the breathing means.

Thus safety devices, called ventilation, are added, devices which prevent the accumulation of gases inside the tank or the hermetic casing of a battery, and allow their evacuation when the internal pressure exceeds a predetermined value.

We know from patent document EP-A1-2244318 a safety device comprising a fusible membrane beyond a temperature threshold and adhered around an opening made through the tank, and masking this opening.

A first problem with this safety device is the difficulty of positioning this device relative to this opening, and this difficulty is repeated as many times as there are openings. Improper positioning of these membranes can reduce or even cancel the effect of the safety device, i.e. allow a significant flow of gas in suppression in the event of thermal runaway of the battery.

A second problem is that the tank is under overpressure before the membrane exceeds this temperature threshold: thus this safety device may release the gases too late, causing the tank to explode.

The object of the invention is to remedy this first problem by proposing an optimized security device.

To this end, the subject of the invention is a safety device comprising a membrane having a first and a second face, this membrane comprising:
- a first peripheral zone comprising only on the first face an adhesive coating,
- a second zone, central to the first zone, arranged so as to open according to a surrounding physical parameter,
this device comprising a succession of several of this membrane, united to each other by the first peripheral zone to form a band.

Thus the center distance between the second zones is predefined and is fixed during the manufacture of the strip. When an operator has to apply this adhesive strip to cover a multitude of openings of a tray as previously presented, he no longer needs to position the second zones relative to each other so that they correspond to the openings, and only has one strip to position instead of a multitude of adhesive membranes. The operator thus gains in precision and assembly time. The strip is also easier to grasp by the operator than the multitude of membranes.

According to one embodiment of the invention, the strip is packaged rolled up on itself.

According to one embodiment of the invention, the strip comprises a pre-cut separation between assemblies comprising at least a succession of two membranes.

According to one embodiment of the invention, the strip comprises separation markings between the sets comprising at least the succession of two membranes.

According to one embodiment of the invention, the surrounding physical parameter is a limit of a pressure difference of a surrounding gas between the first and the second face.

Thus the gas will be released before the rise in temperature of the second zone.

According to one embodiment of the invention, the surrounding physical parameter is a limit of the temperature of the second zone.

According to one embodiment of the invention, the second zone comprises a reduction in local thickness.

The invention also relates to an electrical energy storage battery comprising a hermetic container receiving an electrochemical cell, this container comprising several openings obstructed by a safety device as previously described, the second zones being in correspondence of the openings.

The invention also relates to a vehicle comprising a battery as previously described.

Other features and advantages will appear on reading the description below of a particular, non-limiting embodiment of the invention, made with reference to the figures in which:

: shows a schematic perspective of a battery box according to the invention, from a section of the box.

: represents a view of an example of a security device according to the invention.

It should be borne in mind that the figures are given by way of examples and do not limit the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily at the scale of practical applications. Further, in what follows, reference is made to all figures taken in combination. When reference is made to a specific figure or figures, these figures are to be taken in combination with the other figures for the recognition of the designated reference numerals. The references of the unchanged elements or having the same function are common to all the figures, and the variant embodiments.

Figures 1 and 2 disclose an example of a security device according to the invention. This safety device comprising a membrane 1 having a first 2 and a second 3 face.

This membrane 1 comprises:
- a first peripheral zone Z1 comprising only on the first face 2 an adhesive coating,
- a second zone Z2, central to the first zone Z1, arranged so as to open according to a surrounding physical parameter.

This second zone Z2 is for example circular and takes the form of a disk, but other shapes such as elliptical, rectangular or square or triangular or polygonal shapes can be envisaged. For example, the first zone Z1 completely encircles the second zone Z2 continuously, this first zone Z1 having a rectangular outer perimeter for example.

This device is such that it comprises a succession of several of this membrane 1, joined to each other by the first peripheral zone Z1 to form a strip 4.

In the example of the first rectangular zones Z1, a first membrane 1 will be joined to a second membrane 1, successive, by a common edge of the first two zones Z1 belonging to the first membrane 1 and the second membrane 1, so that these two membranes 1 are part of a single strip 4. Of course, this demonstration is repeated if necessary with a third membrane 1 and so on until a strip 4 of a multitude of membranes 1 is formed. These successive membranes 1 are preferentially identical , but the size and shape of the first and second zones Z1, Z2 may vary from one membrane 1 to another.

This strip 4 is for example packaged rolled up on itself, which facilitates the storage of these membranes on the edge of an assembly line for example, and which also facilitates the manufacture of these membranes 1. But this is not not mandatory, and this packaging can be in the form of strips cut to their final length, and for example stacked flat on top of each other.

Of course, so that this rolled-up strip can unroll, the second face 3 will show a material whose adhesion strength with the adhesive coating is less than a breaking force of the membrane 1 or of the strip 4.

The strip 4 comprises for example a pre-cut 5 for separation between assemblies comprising at least a succession of two membranes 1, but this is not compulsory since this strip 4 can be cut by any cutting tool, for example a shear. There illustrates this pre-cut 5 by a dotted line, separating two sets of two membranes 1. According to the invention, this set can be a set of three membranes 1 or more. Similarly, each set can have a different number of membranes 1. This pre-cut 5 is here rectilinear and orthogonal to the strip but this is not compulsory: this pre-cut 5 can have other shapes, and advantageously a shape adapted to center the strip 4 with respect to a support for which it is intended, for example a tray 8 of battery 7 as will be seen later.

As a variant or in addition, the band 1 comprises separation markings between the sets comprising at least the succession of two membranes 1. For example, this marking will be an aid for manual cutting with a pair of scissors.

The surrounding physical parameter is for example a limit of a pressure difference of a surrounding gas between the first 2 and the second 3 face. This limit is for example between 0.344 and 1.03 MPa (50 to 150 psi) for an application on a traction battery of an electric vehicle. But to guarantee the opening of the second zone Z2, for example before a seal of the tray 8 of the battery 7 yields to a temperature or to the pressure difference, this limit can advantageously be of the order of 0.2 MPa (29 psi), more precisely at a value between 0.1 and 0.2 MPa. Thus if this limit is reached or exceeded, the second zone Z2 opens by tearing or cutting, under the effect of the pressure or depression prevailing on one side or the other of the second zone Z2. This limit may therefore take a value between 0.1 MPa (14.5 PSI) and 1.03 MPa (150 psi) limits included. It should be noted that tank 8 is hermetic, more precisely it must remain sealed to an external pressure of immersion in water at a depth of 1m, i.e. the equivalent of 0.1 MPa. A limit strictly greater than 0.1 MPa will therefore be preferable, around 0.2 MPa (29 psi).

As a variant or in addition, the surrounding physical parameter is a limit of the temperature of the second zone Z2, for example between 100 and 300°C, in particular between 150 and 300°C, in particular 200°C. The second zone Z2 of the membrane 1 is for example a heat-fusible zone which will melt when the temperature limit of the second zone Z2 is reached or exceeded. For example, if this second zone Z2 has previously been torn under the effect of the pressure, there may still remain parts of the membrane 1 of the second zone Z2 which obstruct the passage of gas. In this case, if after this tearing the temperature reaches this temperature limit, these parts of the membrane 1 will be melted, thus releasing the whole of the second zone Z2 for the passage of the gas.

The second zone Z2 comprises for example a decrease in local thickness 6, marked on the by dotted lines. There illustrates in particular a reduction in the shape of a cross or a star, and which in fact forms a pre-cut in the shape of a cross or a star, allowing the tearing of the second zone Z2 when the limit of the pressure difference is reached or exceeded . The term "local" is understood as local to the second zone Z2, that is to say that this reduction in thickness is for example a reduction between 50% and 80% of the thickness of the second zone Z2, excluding decreased zone, this decrease being able to take any value between 50% and 80%.

But as a variant, it is for example the entire second zone Z2 which has a thinner thickness than the first zone Z1. In this case, this reduction in thickness is for example a reduction between 50% and 80% of the thickness of the first zone Z1, this reduction possibly taking any value between 50% and 80%.

This decrease makes it possible to precisely control the limit of the pressure difference of the surrounding gas between the first 2 and the second 3 face.

This invention applies in particular to the electrical energy storage battery 7 comprising the hermetic container 8 receiving an electrochemical cell, this container 8 comprising several openings 9 obstructed by a safety device 1 as previously described, the second zones Z2 being in correspondence of the openings 9. Of course, these openings 9 cause a hermetic internal space of the hermetic container 8 to correspond with the external environment of the battery 7, in particular with the ambient air, the obstruction of the openings 9 by the device of security 1 guaranteeing the tightness of tray 8 except when the second zone Z2 tears or melts. It will be noted that the illustrated container comprises a bottom and a lid connected on their sides by one or more hollow sections closing the internal space. The openings 9 are advantageously arranged through a wall of the hollow profile, so that the gas escaping through the openings 9 is channeled towards one of the ends of this hollow profile through the hollow itself, this hollow emerging "in the open air" or in the ambient air for example.

This internal space receives at least one electrochemical cell and/or one battery module.

The openings 9 are advantageously aligned, and preferably in the same plane, but this is not compulsory and can be misaligned. This misalignment will then be reproduced on the strip 4, by shifting the second zones Z2 in the same way so that, once the strip 4 is adhered to the hollow profile, these second zones Z2 remain in correspondence of the openings 9.

As seen above, the shape of the strip 4 can be adapted to help the operator position the strip 4 on the openings 9, in particular by giving a predetermined shape to the pre-cut 5 of the strip 4, this predetermined shape corresponding to a mark or a counter-form on the support for which it is intended, in particular in this example the hollow section of the tray 8 of the battery 7.

Advantageously, this strip 4, and in particular the second zone Z2, will be transparent so that the operator can visually center the second zones Z2 with respect to the openings 9, and/or check the correct positioning of the second zones Z2 with respect to the openings 9. The membranes 1 will advantageously be made of plastic material.

Thus this safety device allows the ventilation of a battery, or any other device requiring such protection.

Advantageously, the second zone Z2 of the membrane 1 will be made of material based on EPDM, for ethylene-propylene-diene monomer, or even in addition the first zone Z1, and therefore the entire strip, so that the reduction in thickness and the pre-cuts are easily achievable, with precision.

This invention applies most particularly to a vehicle comprising the battery 7. In particular the battery 7 supplying electrical energy to an electrical motor machine of the vehicle, for example of the automobile type.

Note in particular an application for batteries 7 comprising electrochemical cells of the lithium-ion (or Li-ion) type.

Claims (9)

Security device comprising a membrane (1) having a first (2) and a second (3) face, this membrane (1) comprising:
- a first peripheral zone (Z1) comprising only on the first face (2) an adhesive coating,
- a second zone (Z2), central to the first zone (Z1), arranged so as to open according to a surrounding physical parameter,
characterized in that this device comprises a succession of several of this membrane (1), joined to each other by the first peripheral zone (Z1) to form a strip (4). Device according to claim 1, the strip (4) being packaged wound on itself. Device according to one of the preceding claims, the strip (4) comprising a pre-cut (5) for separation between assemblies comprising at least a succession of two membranes (1). Device according to one of the preceding claims, the strip (1) comprising separation markings between assemblies comprising at least a succession of two membranes (1). Device according to one of the preceding claims, the surrounding physical parameter being a limit of a pressure difference of a surrounding gas between the first (2) and the second (3) face. Device according to one of the preceding claims, the surrounding physical parameter being a limit of the temperature of the second zone (Z2). Device according to one of the preceding claims, the second zone (Z2) comprising a local decrease in thickness (6). Electrical energy storage battery (7) comprising a hermetic container (8) receiving an electrochemical cell, this container (8) comprising several openings (9) obstructed by a safety device (1) according to one of the preceding claims, the second zones (Z2) being in correspondence of the openings (9). Vehicle comprising a battery according to claim 8.