Battery pack comprising a heat-transfer fluid capable of containing the thermal runaway of the electrochemical accumulators of the battery pack

Abstract

The invention relates to a battery comprising: - at least one electrochemical accumulator (3) including an active portion and a shell enclosing the active portion; - a casing (2) housing the at least one accumulator (3); and - a heat-transfer fluid (5) contained in the casing (2), the shell (300) including a weakened zone configured to open under the effect of an overpressure in the accumulator (3) and to discharge gases produced by the active portion of the accumulator (3) that caused the overpressure. During the overpressure in the at least one accumulator (3), the heat-transfer fluid (5) comes into contact with the gases produced by the accumulator (3) so as to contain the gases and cool the accumulator.

Description

DESCRIPTION Title of the invention: Battery pack comprising a heat transfer fluid capable of containing the thermal runaway of the electrochemical accumulators of the battery pack

[0001] The invention relates to the field of batteries comprising electrochemical accumulators, in particular accumulators with liquid and / or gel electrolyte. They are composed of two electrodes (cathode and anode) separated by an insulating membrane (or separator) and the whole immersed in a liquid or gel electrolyte.

[0002] There are many different chemical compounds used to produce high-capacity batteries. The most commonly used compound is currently associated with the Lithium-Ion technology family, and subfamilies exist using other combinations of chemical materials such as Lithium Iron Phosphate (LFP), Lithium Cobalt Oxide (LCO), Lithium Nickel Cobalt Aluminum (NCA) and Lithium Nickel Manganese Cobalt (NMC). In addition to these subfamilies, other combinations are being studied with solid Lithium and Lithium-Air compounds. Another family is emerging to overcome the lithium supply problem: Sodium-Ion technology.

[0003] These accumulators have high energy capacities to meet application needs. High energy capacity is particularly useful in the field of transportation. These accumulators are assembled in battery packs to integrate into propulsion systems, which are called all-electric when the battery (or battery pack) is the sole energy source or called hybrid when the battery pack shares the energy supply with another energy source. These accumulators are also used to create high-capacity battery packs to meet a need for so-called stationary energy storage such as the storage of renewable energy on electrical grids. The areas of application are vast and are not limited to the fields of land and aeronautical transport, and electrical grids.Also, the application of the present invention concerns all fields which can use high capacity electrochemical accumulators subject to thermal runaway in the event of abusive use.

[0004] The origin of thermal runaway can be linked to internal alterations of the accumulator (degradation of the accumulator materials generating a short- internal circuit, such as a perforation of a separator by the appearance of dendrites). Figure 1 schematically illustrates a perforation P of a separator S of an accumulator between an anode A and a cathode C. Thermal runaway can also be linked to abusive external environmental conditions (temperature, vibrations, shocks) and / or functional to the charging or discharging of the accumulators.

[0005] These internal alterations or abusive conditions of use generate thermal heating within the elementary accumulators which lead to thermal runaway of the latter and can be the cause of the outbreak of smoke / gas or even fire.

[0006] For example, when hot, an electrochemical accumulator must operate within a defined temperature range, generally less than 70°C at its external surface. Beyond the defined temperature range, damage to the materials constituting the accumulator occurs and is the cause of thermal runaway in the accumulator. Thermal runaway persists in the accumulator when the energy released by the exothermic reactions occurring inside it exceeds the capacity to dissipate it to the outside, as well as when the defective accumulator cannot be isolated to cool it.

[0007] Furthermore, in this type of battery, thermal runaway can start in one accumulator and spread to one or more neighboring accumulators, or even to the entire battery.

[0008] It is therefore necessary to contain the thermal runaway of battery accumulators.

[0009] Solutions for cooling batteries exist. For example, document DE 122013017396A1 discloses a battery comprising a housing in which cells / accumulators are arranged. The cells are bathed in a fluid contained in the housing in order to control their temperature.

[0010] The invention aims to improve this solution not only by cooling the accumulators but above all by limiting, in the event of thermal runaway starting in an accumulator, the thermal runaway to the accumulator concerned only.

[0011] The invention proposes for this purpose a battery comprising: at least one electrochemical accumulator comprising an active part and an envelope enclosing said active part; a casing housing said at least one accumulator; and a heat transfer fluid contained in the casing, the casing comprising a weakened zone configured to open under the effect of overpressure in the accumulator and to evacuate gases produced by the active part of the accumulator causing the overpressure. When the pressure in said at least one accumulator increases, said heat transfer fluid comes into contact with the gases produced by the accumulator so as to contain said gases and cool the accumulator. When there is an overpressure in said at least one accumulator, the heat transfer fluid in contact with the gases produced by the accumulator changes from a liquid state to a gaseous state.

[0012] The solution provided by the invention thus makes it possible to contain the start of a thermal runaway causing overpressure in the defective accumulator by directly containing the gases produced by the accumulator. Opening the weakened zone of the casing of the defective accumulator allows the fluid to quickly access the gases produced by the accumulator, and thus to confine the thermal runaway as close as possible to its origin and prevent its progression to the heart of the accumulator.

[0013] The invention reduces the risk of thermal runaway spreading to adjacent cells by directly and rapidly cooling the faulty accumulator.

[0014] Particular preferred convenient features of the battery according to the invention are presented below.

[0015] When there is overpressure in said at least one accumulator, the heat transfer fluid enters through the open weakened zone so as to contain at least part of the gases produced by the accumulator.

[0016] When there is an overpressure in said at least one accumulator, the heat transfer fluid comes into contact, outside the accumulator, with at least part of the evacuated gases.

[0017] The heat transfer fluid has a liquid / gaseous state change temperature higher than a skin temperature during thermal runaway causing the opening of the weakened zone of said at least one electrochemical accumulator.

[0018] The casing includes a structural weakness forming the weakened zone, the weakened zone being configured to rupture open under the effect of overpressure in the accumulator.

[0019] The heat transfer fluid is a non-flammable oil.

[0020] The heat transfer fluid has a viscosity between 0.3 mm 2 .s and 5 mm 2 .s, preferably between 1 mm 2 .s and 5 mm 2 .s.

[0021] The battery further includes a bladder assembled to the housing and configured to absorb pressure variations within the housing.

[0022] The battery further includes a pressure sensor configured to detect overpressure in the housing.

[0023] The housing comprises a valve configured to open during overpressure in the housing and / or in said at least one accumulator.

[0024] The battery comprises several accumulators and several envelopes, the accumulators being arranged in series or in parallel in the housing, each envelope enclosing one of the accumulators.

[0025] Other features and advantages of the invention will become apparent in the description below with reference to the appended drawings, given by way of non-limiting example: Figure 1 schematically represents an accumulator comprising a perforated separator; Figure 2 schematically represents a battery pack according to one embodiment of the invention; Figure 3 represents an accumulator of the battery pack; Figure 4 is a detail view of Figure 3; Figure 5 represents the battery pack according to another embodiment; and Figure 6 is a sectional view of the battery pack of Figure 5.

[0026] Figure 2 represents a battery or battery pack 1 according to an exemplary embodiment of the invention.

[0027] The battery pack 1 comprises a housing 2 and several electrochemical accumulators or cells 3.

[0028] An upper wall of the housing 2 is not shown in Figure 2 but is visible in Figures 5 and 6 representing another embodiment.

[0029] The housing 2 is preferably rigid. The housing 2 may be made of metallic material or composite material.

[0030] The case 2 here has a parallelepiped shape but can of course have a different shape.

[0031] The accumulators 3 are arranged in series or in parallel in the housing 2. The accumulators 3 of the same housing 2 form a module. Fourteen accumulators 3 are shown in Figure 2.

[0032] Modules provide a first barrier to the propagation of a battery fault 3. The presence of modules is optional. In the absence of modules, all the batteries are combined in a single housing. Module integration is dictated by reasons of manufacturability and maintenance of the battery pack.

[0033] The battery pack may include a housing (not shown) housing all of the modules. In other words, said housing houses several housings 2.

[0034] The accumulators 3 are connected to each other, generally by connection bars 4, usually called busbars. The busbars 4 are for example screwed or welded to the accumulators 3. The busbars 4 allow the electrical connection between the accumulators 3.

[0035] The modules are also connected to each other, notably by 4 busbars.

[0036] The 4 busbars are for example made of copper.

[0037] Battery packs for high energy capacity applications consist of several electrochemical accumulators connected in series - parallel to meet the voltage, energy and power requirements of the intended application. The voltage level is obtained by connecting the accumulators in series and the energy and power level is obtained by connecting the accumulators in parallel. accumulators. For safety reasons, achieving the voltage, energy, and power levels requires grouping the accumulators together to form a module. The modules are then positioned in series-parallel to meet the specifications of the intended application.

[0038] For example, each module consists of up to sixteen 3 accumulators connected in series, each module having a voltage of 60V. Nine modules can be connected together to obtain the desired voltage, for example 540V in the case of a series connection of all the modules.

[0039] Each electrochemical accumulator 3 comprises an active part and an envelope 300.

[0040] The active part of the accumulator 3 comprises two electrodes, namely a cathode and an anode. The active part also comprises at least one separator for insulating the electrodes from each other. The assembly may be impregnated with a liquid or gel electrolyte. The active part of the accumulator thus comprises the electrodes, at least one separator, and an electrolyte. For the sake of simplification, these components or active part of the accumulator 3 are not shown in Figures 2 to 5 but are shown in Figure 1 showing in a simplified manner the architecture of the accumulator 3.

[0041] Each envelope 300 contains the active part of one of the accumulators 3. The envelope 300 is sealed or hermetic.

[0042] The casing 300 is generally rigid (hard). The rigid casing 300 is made, for example, from a metallic material such as aluminum, nickel, or steel. According to another exemplary embodiment, the casing 300 may be flexible. The flexible casing 300 is made from nylon-type materials.

[0043] In the example illustrated in Figures 2 to 4, the envelope 300 has a cylindrical shape. The envelope 300 comprises a side wall 301 and transverse walls 302.

[0044] A transverse plane is understood to be a plane orthogonal to a median plane of the envelope passing through a height of the envelope.

[0045] The envelope 300 may have a different shape, for example, prismatic (as is the case in figure 6), button (in English “button cell” whose shape is cylindrical and flat) or a so-called “pocket” format.

[0046] The envelope 300 may be formed in one piece or comprise several parts.

[0047] In the example shown in Figures 3 and 4, the casing 300 comprises several parts. In particular, the casing 300 comprises a main body 303 and a closing disc 304.

[0048] The main body 303 is here substantially cylindrical. The main body 303 is in particular cylindrical, the accumulator 3 having a generally cylindrical shape. As variants, the main body 303 may have other shapes, for example oblong, oval, or having straight edges and rounded ends.

[0049] The main body 303 has a transverse opening 305 on one end.

[0050] The closure disc 304 is assembled to the main body 303. The closure disc 304 closes the transverse opening 305 of the main body 303. The closure disc 304 thus forms one of the transverse walls 302 of the casing 300.

[0051] The casing 300 also includes a seal 306. The seal 306 is disposed between the main body 303 and the sealing disc 304.

[0052] The casing 303 comprises a weakened zone 307 configured to open under the effect of an overpressure in the accumulator 3. The weakened zone 307 is an area in which the casing 300 is weakened so that said area is the first to open in the event of an overpressure in the accumulator 3. In other words, the casing 300 may comprise a structural weakness forming the weakened zone 307.

[0053] The weakened zone 307 is calibrated and set to open at a certain pressure level or threshold. Overpressure can occur in an accumulator 3 during thermal runaway of the accumulator. This phenomenon is detailed later.

[0054] The structural weakness forms a mechanical fuse. The structural weakness may typically be a reduction in the thickness of the envelope 300 over an area of ​​the envelope 300. The structural weakness may also be a local weakening, for example by marking or punching, on one of the walls of the envelope 300.

[0055] The weakened zone 307 is here formed in the transverse wall, here the closure disc 304. The weakened zone 307 is formed by a boss made on the closure disc 304. The boss is for example made by punching in order to locally weaken the closure disc 304. The boss has a smaller thickness than the rest of the closure disc.

[0056] The weakened zone 307 may be provided elsewhere in the envelope 300, for example in the side wall 301.

[0057] The weakened zone 307 may be shaped and / or have a shape other than a boss.

[0058] The weakened zone 307 is configured to open by rupture under the effect of the overpressure in the accumulator 3. When there is overpressure, the weakened zone 307 deforms to the point of opening the casing 300 at the level of said weakened zone 307. The size of the opening becomes increasingly larger depending on the pressure of the gases released by the accumulator 3.

[0059] The battery pack 1 further comprises a heat transfer fluid 5. The heat transfer fluid is contained in the housing. The casing of each accumulator 3 is thus in contact with the heat transfer fluid.

[0060] The heat transfer fluid 5 exceeds the height of the accumulators 3. In other words, the heat transfer fluid 5 covers the accumulators 3.

[0061] A vacuum filling of the housing 2 with the heat transfer fluid 5 can be carried out. This makes it possible to guarantee a good distribution of the heat transfer fluid 5 over all of the accumulators 3 and to avoid trapping air bubbles in the housing 2 which could prevent contact of the heat transfer fluid 5 with the accumulators 3.

[0062] Battery pack 1 has an oil presence sensor to detect a possible leak in the pack housing.

[0063] The heat transfer fluid 5 has a viscosity such that, during an overpressure in one of the accumulators 3, the heat transfer fluid 5 penetrates through the open weakened zone 307 so as to cool the accumulator 3.

[0064] Typically, the heat transfer fluid 5 has a viscosity of between 0.3 mm 2 .s and 5 mm 2 .s, preferably between 1 mm 2 .s and 5 mm 2 .s.

[0065] The heat transfer fluid 5 is preferably non-flammable to avoid causing a fire within the battery pack 1.

[0066] The heat transfer fluid 5 is advantageously an oil.

[0067] Preferably, the heat transfer fluid 5 is a synthetic oil.

[0068] Preferably, the oil has no flash point and no auto-ignition temperature. In other words, the oil has the characteristic of being non-flammable, for example a non-flammable fluorinated type oil.

[0069] According to another exemplary embodiment, the heat transfer fluid 5 may be water, in particular demineralized water.

[0070] During thermal runaway of an accumulator 3, the temperature at the core of the accumulator 3 rises until it is no longer controllable. In particular, the temperature at the core of the accumulator 3 rises until it reaches a thermal runaway temperature Te. Due to the sealing of the accumulator 3 permitted by the casing 300, the pressure rises in the accumulator 3. When the accumulator 3 is under overpressure, the weakened zone 307 opens. The weakened zone 307 releases the electrolyte of the accumulator 3 in the form of flammable gases.

[0071] The accumulator 3 is overpressurized when it exceeds a threshold pressure Ps. This is the consequence of the temperature rise in the accumulator 3. The threshold pressure Ps is for example between 13 and 15 bars. The threshold pressure Ps is notably between 13 and 15 bars for cylindrical 18650 accumulator formats.

[0072] Thermal runaway temperature Te is a temperature threshold beyond which the temperature inside the accumulator rises uncontrollably. This threshold is reached when the exothermic reaction that occurs following a defect or misuse of the accumulator cannot be cooled. In this case, the temperature continues to rise, fueling itself by this rise in temperature, and the defective accumulator enters into a positive feedback process.

[0073] The thermal runaway temperature Te depends in particular on the components of the accumulator 3 and also on its state of charge (SoC for “State of Charge”) of the accumulator 3. The thermal runaway temperature Te is revealed by measuring the temperature of the skin of the accumulator 3. The accumulator 3 is considered to have gone into thermal runaway when the skin temperature Tp of the accumulator 3, that is to say the temperature taken on an external surface of the walls 301, 302 of the casing, reaches a temperature range of between 70°C and 120°C. The temperatures of the gases generated by thermal runaway at the heart of the accumulator can exceed 800°C or even 1000°C.

[0074] During overpressure in the accumulator 3 caused by thermal runaway, the casing 300 of the accumulator 3 deforms. The pressure rises within the accumulator 3, deforming the casing 300 and going as far as opening the weakened zone 307.

[0075] The gases generated within the accumulator 3 by the exothermic reaction are released by the opening of the weakened zone 307, the pressure threshold Ps being reached. Depending on the extent of the reaction, the opening of the casing can also be carried out at other locations on the casing 300; producing an opening in the casing through which the gases escape.

[0076] The gases evacuated at least in part from the accumulator by the weakened zone 307 are at least at the thermal runaway temperature or even at a higher temperature. The gases come into contact with the heat transfer fluid 5 which changes phase, thus absorbing the calories evacuated by these hot gases. The heat transfer fluid 5 thus locally contains the temperature. The heat transfer fluid 5 comes into contact with the gases produced by the accumulator 3 outside and / or inside the accumulator. The heat transfer fluid can come into contact with the gases evacuated by the weakened zone. The heat transfer fluid 5 can also come into contact with the gases inside the accumulator 3. The heat transfer fluid 5 enters through the weakened zone 307 of the casing 300 of the accumulator 3 and diffuses inside, mixing with the electrolyte and approaching the origin of the start of the thermal runaway. The heat transfer fluid 5 comes into contact with the core of the accumulator 3. The returning heat transfer fluid 5 migrates towards the core of the accumulator 3 and therefore near the central heating point to smother it. This prevents the thermal runaway from continuing to progress both inside the accumulator 3 and outside the accumulator 3. This also prevents the thermal runaway from spreading to neighboring accumulators 3. It is thus possible to limit the source of the fault.

[0077] In other words, the present invention takes advantage of the property of the latent heat of vaporization of the heat transfer fluid 5 to contain the thermal runaway of the defective accumulator within the accumulator when the latter opens during a thermal runaway. The heat transfer fluid 5 enters the accumulator 3 and dilutes in the liquid of the electrolyte of the accumulator 3 gradually reaching the contact of the zone where thermal heating has occurred. In other words again, the heat transfer fluid 5 penetrates the accumulator 3 contributing to accessing as close as possible to the heating which has been created in the accumulator 3. This makes it possible to act as close as possible to the fault and thus to stifle the heating.

[0078] The heat transfer fluid 5, in contact with the hot gases leaving the accumulator 3, passes from a liquid state to a gaseous state.

[0079] The heat transfer fluid 5 has a liquid / gaseous state change temperature Te. Preferably, the heat transfer fluid 5 has a liquid / gaseous state change temperature Te higher than the skin temperature Tp of the casing. Thus, during thermal runaway, the heat transfer fluid 5 around the accumulator 3 remains liquid. A heat exchange then takes place with the walls 301, 302 of the accumulator 3.

[0080] The liquid / gas state change temperature Te is higher than the skin temperature Tp of the casing when the weakened zone 307 is open. For example, thermal runaway generates a rise in the internal temperature such that the skin temperature Tp of the accumulator reaches a temperature between 70°C and 120°C and such that this rise in temperature also causes the weakened zone 307 to open, releasing hot gases. The liquid / gas state change temperature Te is chosen so as to change phase when the heat transfer fluid is in contact with the hot gases. This change of phase can operate between 80°C and 250°C depending on the choice of heat transfer fluid. The temperature or threshold of change of liquid / gaseous state Te of the heat transfer fluid 5 is thus defined in relation to the skin temperature threshold Tp when the thermal runaway generates the opening of the weakened zone 307. This makes it possible to have the phase change of the heat transfer fluid at the moment when the hot gases leave the accumulator. The temperatures of the hot gases leaving the accumulator being linked to the chemical components constituting the accumulator and also to the energy stored in the accumulator at the time of the thermal runaway, they extend from 70°C at the start of the runaway and rise very quickly towards 400°C to reach 1000°C if no measures are taken to contain the reaction. Note that the envelope 300 necessarily opens at the weakened zone 307, the latter being calibrated for such opening during overpressure.It is possible that the casing 300 also opens at other locations, depending in particular on the intensity of the reaction within the accumulator 3, allowing the heat transfer fluid 5 to come into contact with the evacuated gases at these locations as well.

[0081] The returned heat transfer fluid 5 reaches the hot spot and evaporates on contact with the hot parts and limits the temperature rise. The heat transfer fluid 5 acts as a heat extractor. The heat transfer fluid 5 prevents the remaining material of the defective accumulator 3 from contributing to the thermal runaway. The heat transfer fluid 5 stabilizes and then stops the thermal runaway within the accumulator 3. Thus, by containing the thermal runaway at the source, this solution prevents the propagation of this thermal runaway to the adjacent accumulators 3.

[0082] The properties of the heat transfer fluid 5 are adapted to the needs of the accumulators 3 to contain their thermal runaway for the liquid / gaseous state change temperature Te. Depending on the chemistries of the accumulators and the energy stored at the time of thermal runaway, the thermal runaway threshold Te is different. Consequently, the formulation of the heat transfer fluid 5 must be adapted to have a liquid / gaseous phase change threshold Te compatible with the thermal runaway threshold Te.

[0083] The viscosity of the heat transfer fluid 5 can be chosen so as to allow the heat transfer fluid 5 to enter the accumulator 3 when the weakened zone 307 of the casing 300 opens. In the event of opening also at other locations of the envelope 300 other than the weakened zone 307, the viscosity of the heat transfer fluid 5 also of course facilitates the penetration of the heat transfer fluid into the accumulator 3. It should be noted that the heat transfer fluid 5 passing into the gaseous state upon contact with the gases produced by the accumulator 3, gains in viscosity when the temperature increases. This further facilitates the penetration of the heat transfer fluid 5 into the accumulator 3.

[0084] Furthermore, when the heat transfer fluid 5 is a synthetic oil, this allows for better cooling of the accumulators 3 under nominal operating conditions, because the oil spreads throughout the housing 2 and ensures uniform contact on all the walls of the accumulators 3 and therefore good heat exchange. The oil with its intrinsic dielectric strength properties also makes it possible to facilitate the integration of high-voltage batteries by reducing the insulation distances of the parts carried at high voltages and avoiding the risks of breakdown between the parts carried at high voltage and the walls of the housing 2 of the battery pack in which the elementary accumulators 3 are integrated and or of a module housing in the case of integration into the battery pack with modules.

[0085] According to an illustrative example, the thermal runaway temperature Te begins between 70°C and 120°C and increases to reach temperatures of the order of 400 to 800°C or even 1000°C. The external temperature Tp of the casing 300 is between 70°C and 120°C depending on the composition of the accumulators and the state of charge of the accumulator at the time of thermal runaway. Under these conditions, the heat transfer fluid 5 is chosen so as to have a liquid / gaseous state change temperature Te higher than the external temperature Tp of the casing 300, for example of the order of 130°C.

[0086] Preferably, the accumulators 3 are separated from each other by a distance of at least 1 mm. This allows the heat transfer fluid 5 to effectively cool the accumulators 3.

[0087] The battery pack 1 may further comprise a bladder 6 assembled to the housing 2 (visible in the exemplary embodiment illustrated in Figures 5 and 6). The bladder 6 is configured to absorb pressure variations in the housing. The bladder 6 may be elastic and inflatable.

[0088] The bladder 6 initially compensates for the excess pressure produced during the failure of an accumulator 3 and prevents the walls of the casing 2 of the battery pack 1 from being subjected to this excess pressure.

[0089] The bladder can also compensate for pressure variations linked to the expansion of the heat transfer fluid depending on environmental conditions (temperature, altitude).

[0090] The bladder can be made of aluminum.

[0091] One or more bladders can be arranged as needed. For example, bladders can be positioned at the module level or at the battery pack level.

[0092] The battery pack 1 may further comprise a pressure sensor (not shown). The pressure sensor is configured to measure a pressure in the housing 2 and / or to detect an overpressure in the housing.

[0093] The pressure sensor can be integrated into the bladder 6.

[0094] In another example, the pressure sensor may be mounted on an internal wall of the housing 2.

[0095] The pressure sensor is configured to generate, via a contactor, an electrical signal corresponding to information representative of said pressure.

[0096] The pressure sensor can be configured to send a warning signal if there is excess pressure in the housing.

[0097] The pressure sensor can also be configured to give an order to isolate the battery pack by opening a contactor at the output of battery pack 1.

[0098] The heat transfer fluid presence sensor is present in battery pack 1 (not shown). It is configured to detect a heat transfer fluid leak.

[0099] When thermal runaway occurs, it is not necessarily detected electrically. The modules can continue to operate given the large number of accumulators. The pressure sensor therefore makes it possible to detect overpressure as early as possible. When the heat transfer fluid 5 vaporizes, the pressure rises, this is detected by the pressure sensor which can open the switch at the output of battery pack 1.

[0100] The housing may further comprise a valve 7 (visible in figures 5 and 6) configured to open during overpressure in the battery pack 1 and / or in the housing 2 of one of the modules.

[0101] The valve 7 includes, for example, conduits allowing fumes to escape to the outside of the housing 2 in the event of a malfunction of the battery pack 1.

[0102] The valve 7 also allows the fumes from the heat transfer fluid to be evacuated in the event of gas release from an accumulator 3 or several accumulators 3 which could go into thermal runaway simultaneously.

[0103] Of course, the present invention is not limited to the embodiments described and illustrated.

[0104] For example, in the case where a housing houses a set of modules, the heat transfer fluid may also be contained in said housing.

[0105] Thanks to the invention, a reduction in the risk or even an absence of fire starting when the accumulator goes into thermal runaway is achieved. The properties of the heat transfer fluid facilitate the heat exchanges of the accumulator with the outside by boiling as close as possible to the threshold for triggering the accumulator into thermal runaway. This boiling and the infiltration of the heat transfer fluid through the weakened zone of the accumulator casing that is in runaway help to contain the runaway and reduce the projections of flame and hot smoke that can be extracted from the accumulator during such faults. In addition, the heat transfer fluid absorbs the excess pressure generated during the explosion of the accumulator, thus reducing the mechanical stresses in the casing and the housing of the battery pack.

[0106] Thanks to the cooling of components by the heat transfer fluid, the invention allows to cool the accumulators in the nominal operating mode and to indirectly improve the reliability of the accumulators.

[0107] It also reduces the risk or even stops the spread of thermal runaway to adjacent accumulators.

[0108] The solution, by putting the heat transfer fluid in direct contact with the accumulator which is going into thermal runaway, makes it possible to trigger the phase change of the heat transfer fluid absorbing the energy evacuated by the defective accumulator and helping to contain the thermal runaway.

[0109] By using a heat transfer fluid such as non-flammable synthetic oils, these fluids have dielectric properties that help reduce the risk of electric arcing for high voltage batteries.

[0110] The invention benefits any type of battery subject to thermal runaway, particularly in cases of extreme use such as the cases listed below but not limited to shocks, internal and external short circuits and abusive temperature conditions.

Claims

CLAIMS 1. Battery comprising: at least one electrochemical accumulator (3) comprising an active part and an envelope enclosing said active part; a casing (2) housing said at least one accumulator (3); and a heat transfer fluid (5) contained in the casing (2), the casing (300) comprising a weakened zone (307) configured to open under the effect of an overpressure in the accumulator (3) and to evacuate gases produced by the active part of the accumulator (3) at the origin of the overpressure, in which, during the overpressure in said at least one accumulator (3), said heat transfer fluid (5) comes into contact with the gases produced by the accumulator (3) so as to contain said gases and cool the accumulator, and in which upon contact with the gases produced by the accumulator (3), the heat transfer fluid (5) passes from a liquid state to a gaseous state.

2. Battery according to claim 1, wherein during an overpressure in said at least one accumulator (3), said heat transfer fluid (5) penetrates through the open weakened zone (307) so as to contain at least part of the gases produced by the accumulator (3).

3. Battery according to claim 1 or claim 2, wherein during an overpressure in said at least one accumulator (3), said heat transfer fluid (5) comes into contact, outside the accumulator (3), with at least part of the evacuated gases.

4. Battery according to one of claims 1 to 3, in which the heat transfer fluid (5) has a liquid / gaseous state change temperature (Te) greater than a skin temperature (Tp) during thermal runaway causing the opening of the weakened zone (307) of said at least one electrochemical accumulator (3).

5. Battery according to one of claims 1 to 4, in which the envelope (300) comprises a structural weakness forming the weakened zone (307), the weakened zone being configured to open by rupture under the effect of the overpressure in the accumulator (3).

6. Battery according to one of claims 1 to 5, in which the heat transfer fluid (5) is a non-flammable oil.

7. Battery according to one of claims 1 to 6, in which the heat transfer fluid (5) has a viscosity of between 0.3 mm 2 .s and 5 mm 2 .s, preferably between 1 mm 2 .s and 5 mm 2 .s.

8. Battery according to one of claims 1 to 7, further comprising a bladder (6) assembled to the housing (2) and configured to absorb pressure variations in the housing (2).

9. Battery according to one of claims 1 to 8, further comprising a pressure sensor configured to detect excess pressure in the housing (2).

10. Battery according to one of claims 1 to 9, in which the housing (2) comprises a valve (7) configured to open during overpressure in the housing (2) and / or in said at least one accumulator (3).

11. Battery according to one of claims 1 to 10, in which the housing (2) comprises an oil presence sensor configured to detect a leak of the heat transfer liquid in the housing (2).

12. Battery according to one of claims 1 to 11, comprising several accumulators (3) and several envelopes (300), the accumulators (3) being arranged in series or in parallel in the housing (2), each envelope (300) enclosing one of the accumulators (3).

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