ELECTRICAL ENERGY STORAGE MODULE FOR A VEHICLE

Description

[0001] The present invention relates to the field of electric batteries for storing electrical energy. More specifically, the invention relates to an electrical energy storage module for a vehicle and in particular for a motor vehicle.

[0002] Electric batteries based on lithium-ion electrochemical accumulators, commonly referred to as "lithium-ion cells", are increasingly used as a stand-alone energy source, particularly in applications related to electric mobility. This trend is explained in particular by significantly higher mass and volume energy densities than conventional nickel cadmium (Ni-Cd) and nickel-metal hydride (Ni-MH) accumulators, an absence of memory effect, low self-discharge compared to other accumulators and also a low cost per kilowatt-hour.

[0003] An electric battery generally comprises a plurality of energy storage modules arranged side by side and electrically connected. Each energy storage module comprises a plurality of electrical energy accumulators. These accumulators are arranged side by side in a housing participating in delimiting the energy storage module and these accumulators are electrically connected to each other. Such a configuration allows the battery to have significant energy storage and to increase the voltage available for powering the vehicle while remaining operational in the event of a short circuit of one of the accumulators, in particular by making it possible to deactivate the module corresponding to this defective accumulator and to continue to provide power with the other energy storage modules, by means of additional switching and control devices.

[0004] During use, the electric battery may experience an electrical problem such as a short circuit in an accumulator and / or a mechanical problem such as a shock impacting an accumulator. These problems can lead to thermal runaway of the electric battery, particularly when it includes lithium-ion accumulators. Thermal runaway can result in an increase in pressure in the accumulator and / or in the module, gas release, smoke release, fire and / or material projections.

[0005] In this context, international regulations require car manufacturers to detect thermal runaway of the electric battery early enough in order to, on the one hand, guarantee the safety of the occupants of the motor vehicle by allowing them to evacuate the vehicle before the passenger compartment is filled with smoke, and on the other hand to allow appropriate operating safety means to electrically isolate the battery to facilitate possible safety interventions.

[0006] Thermal runaway detection is based, in the majority of cases, on measuring the pressure prevailing within the sealed modules. This pressure measurement consists in particular of sending thermal runaway information when the measured pressure is higher than a predetermined critical threshold. Such a technique is based on the evolution of existing conditions within the storage module and it has the disadvantage of being dependent on environmental conditions. As non-limiting examples, the circulation of the motor vehicle at different altitudes can impact the pressure in the battery and / or within the energy storage modules, and the passage of this vehicle in a tunnel can modify the composition of the air likely to penetrate into the battery and therefore modify the distribution of the gaseous components and the pressure measurements carried out.It is therefore necessary to provide a sufficiently high detection threshold to avoid false alarms regarding thermal runaway. Consequently, the time required to reach this detection threshold is extended and consequently the time available for occupants to evacuate the vehicle may be considerably reduced and their safety may be compromised.

[0007] Alternatively to the method previously described, document US9046580 discloses a method for detecting a failure of an accumulator in a battery module based on measuring variations in the resistance of the electrical insulation of the module. This method may also include monitoring secondary effects of the failure of the accumulator and / or the module such as loss of continuity of the voltage chain, the temperature of the module exceeding a threshold temperature, the humidity exceeding a threshold humidity and / or the temperature of the coolant associated with a cooling system of the module exceeding a threshold cooling temperature.

[0008] These methods therefore have the disadvantage of having to evaluate a rise in temperature and / or a rise in pressure and / or a change in the humidity level to detect the failure of the accumulator and / or the module, taking into account the environmental conditions. In accordance with what has been mentioned previously, the safety of the occupants may then be delayed, which has the consequence of putting them in a dangerous situation. Other relevant elements of the prior art are disclosed in US2019 / 081370 A1.

[0009] The present invention aims to overcome at least one of the aforementioned drawbacks and to further lead to other advantages by proposing a new type of energy storage module for an electric vehicle battery, in particular an automobile. The present invention is defined in the appended claims.

[0010] The present invention provides an electrical energy storage module for a vehicle, in particular a motor vehicle, which comprises a plurality of electrical energy accumulators each comprising at least one negative electrode composed at least in part of lithium metal nitride, and said energy storage module further comprises at least one ammonia sensor for detecting a release of ammonia due to the decomposition of the lithium metal nitride of the negative electrode in the presence of air or humidity.

[0011] It should be understood here, as in everything that follows, that the term "ammonia" designates a compound with the chemical formula NH 3 which is present in the form of a gas at room temperature.

[0012] The invention is based on the detection of the presence of ammonia instead of a measurement of pressure, temperature and / or humidity level as described in the prior art. It should then be noted that the invention advantageously differs from the prior art in that it bases the early detection of thermal runaway on a detection of a gas not present in the storage module under normal driving conditions of the vehicle, this gas only appearing under abnormal conditions due to an impact or wear which involve bringing the negative electrode of at least one accumulator into contact with air.

[0013] More specifically, the different layers of a lithium-ion type electrical energy accumulator are enclosed in an airtight pouch so that each of these layers, and in particular the negative electrode, can only be exposed to air and / or moisture contained in the air when a leak appears at the pouch. In the event of such a leak, which may be due to wear of the accumulator or an impact suffered by the vehicle, this exposure causes the decomposition of the lithium metal nitride and its transformation into ammonia. The ammonia sensor of the energy storage module will then detect the presence of ammonia. Since the ammonia sensor is specific to ammonia, it is therefore independent of environmental conditions and the detection threshold can be very low.The detection of a malfunction can then be immediate, as soon as an ammonia particle is detected, without it being necessary for the level of ammonia present in the air to reach a critical threshold.

[0014] It is noteworthy in this context that the decomposition of the lithium-metal nitride of the negative electrode is not necessarily synonymous with thermal runaway, as the leak at the sealed pocket of the accumulator may be due to wear and be without immediate danger. However, it is advantageous for the vehicle occupant to be warned of this leak in advance, before thermal runaway of the energy storage module. This can give the occupant time to reliably go to the dealership to have the energy storage module, or even the electric battery, replaced. Occupant safety is therefore improved.

[0015] Furthermore, the ammonia formed by the decomposition of the lithium metal nitride of the negative electrode, specific to the present invention, will generate the formation of gaseous nitrogen in the presence of oxygen contained in the air and at high temperature. This will then make it possible to reduce the quantity of oxidant inside the electrical storage module during the outbreak of a fire, for example, and therefore to delay thermal runaway, in particular until the arrival of the firefighters.

[0016] According to one embodiment, each electrical energy accumulator comprises at least one positive electrode and a separator, in addition to a negative electrode.

[0017] According to one embodiment, the separator is arranged between the negative electrode and the positive electrode, thus forming a stack.

[0018] According to one embodiment, each electrical energy accumulator comprises an envelope in which the stack formed by at least the positive electrode, the separator and the negative electrode is arranged. It is understood, in relation to what has been mentioned previously, that the envelope forms a sealed enclosure in which the different electrodes are arranged and that it is the breaking of the seal of this envelope which will create the release of the negative electrode into the open air and the creation of ammonia.

[0019] According to one embodiment, the metal of the lithium metal nitride is chosen from the group of transition metals.

[0020] According to one embodiment, the metal of the lithium metal nitride is chosen from the group comprising iron, manganese and their mixture.

[0021] According to one embodiment, the lithium metal nitride is delithiated. Here, as in everything that follows, the term "delithiated" means that the lithium metal nitride includes vacancies in its structure allowing it to accommodate lithium ions, particularly when the electrical energy accumulator is recharged.

[0022] According to one embodiment, the lithium metal nitride is composed at least in part of lithium manganese nitride whose formula is Li 7-x MnN 4 with x ≤ 2.0 and / or lithium iron nitride whose formula is Li 3-x FeN 2 , with x ≤ 1.2.

[0023] According to one embodiment, the energy storage module comprises an ammonia sensor common to several electrical energy accumulators. More particularly, the electrical energy storage module comprises a housing forming a housing for the plurality of electrical energy accumulators, the ammonia sensor being arranged inside the housing. The ammonia sensor can be fixed on an internal face of one of the walls of the housing. When the sensor detects the presence of ammonia in the module, a venting of an accumulator is identified and the accumulators present in the module must be changed preventively for the safety of the occupant.

[0024] Alternatively, an ammonia sensor can be provided for each electrical energy accumulator. It is understood that in this alternative, detection is more precise and that it is possible to specifically identify which accumulator has a fault and in particular which accumulator casing is letting air through. This alternative embodiment, however, has a higher manufacturing cost and a compromise may be preferred in which an ammonia sensor is common to several accumulators, to reduce costs and still allow intervention without requiring replacement of all the accumulators but only those close to the sensor.

[0025] According to one embodiment, the ammonia sensor is chosen from a catalytic detector, a catharometric detector, an infrared radiation detector, an electrochemical detector or a photoionization detector.

[0026] The present invention further relates to an electric battery comprising a plurality of energy storage modules and in which at least one module of the plurality of modules has at least one of the characteristics previously described.

[0027] The present invention also relates to a vehicle comprising at least one electric battery according to one aspect of the invention.

[0028] The vehicle may be a motor vehicle, a two- or three-wheeled motorized electric road vehicle, an electric bicycle, or an electric scooter.

[0029] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which: [ fig 1 ] There figure 1 is a schematic representation of an electric vehicle battery comprising a plurality of energy storage modules according to the invention; [ fig 2 ] There figure 2 is a schematic representation of an energy storage module according to one aspect of the invention; [ fig 3 ] There figure 3 is a schematic representation of an electrical energy accumulator capable of equipping the energy storage module of the figure 2 ; [ fig 4 ] There figure 4 is a partial schematic representation of the electrical energy accumulator of the figure 3 , a section showing the components of the accumulator housed inside the casing visible on the figure 3 .

[0030] It should first be noted that while the figures set out the invention in detail for its implementation, they can of course be used to better define the invention where appropriate. It should also be noted that, throughout the figures, elements that are similar and / or fulfill the same function are indicated by the same numbering.

[0031] The invention relates in particular to a particular electrical energy storage module in that it comprises at least one accumulator whose constitution is specific with a negative electrode different from what can be conventionally implemented and in that it comprises in this context an ammonia sensor.

[0032] In reference to the figure 1 , a plurality of these electrical energy storage modules 3 have been illustrated, each comprising a plurality of electrical energy accumulators 5. Such electrical energy storage modules 3 may constitute an electric battery 1 but also a capacitor or a supercapacitor. The electric battery may be used in any vehicle, for example a motor vehicle, a two- or three-wheeled motorized road electric vehicle, an electric bicycle, or an electric scooter.

[0033] The electrical energy storage module 3 comprises a housing 7 whose walls 9 form a housing for a plurality of electrical energy accumulators 5 and at least one ammonia sensor 11. In the example illustrated, the housing 7 here has a parallelepiped shape with six walls, among which one can distinguish, as is notably more visible on the figure 2 , a bottom wall 90, side walls 92 and a closing cover 94.

[0034] The electrical energy accumulators 5 are arranged against the bottom wall 90, if necessary in a matrix 96 which makes it possible to ensure the positioning of the accumulators relative to each other and relative to the walls of the housing 7.

[0035] The ammonia sensor 11 is arranged inside the housing, i.e., as shown in the figure 2 , in the housing formed by the walls 9 of the casing 7 of the electrical energy storage module 3. In this way, an ammonia sensor 11 is common to a plurality of accumulators 5.

[0036] The ammonia sensor 11 comprises, or is associated with, communication means 12 configured to transmit ammonia detection information to a control module capable of emitting a warning signal to the occupant and / or emitting an instruction to cut off the power supply to the electric battery or at least to the corresponding energy storage module. In the example illustrated, the communication means consist of wireless communication means, it being understood that this is not limiting of the invention.

[0037] In the example illustrated on the figure 2 , the ammonia sensor 11 is arranged on an internal face 8 of one of the walls 9 of the housing 7, and more particularly here on the internal face of the closing cover 94. It should be noted that the position of the ammonia sensor on the closing cover is not limiting of the invention. However, it is advantageous that on the one hand the ammonia sensor 11 is not in mechanical contact with the electrical energy accumulators 5, and that on the other hand the ammonia sensor 11 is arranged in a central position so that the distance between this ammonia sensor and the accumulator 5 from which the sensor is furthest is as small as possible.

[0038] The ammonia sensor 11 may be a catalytic detector, a catharometric detector, an infrared radiation detector, an electrochemical detector or a photoionization detector.

[0039] The catalytic detector is based on measuring the heat of combustion of ammonia molecules on the surface of a metal catalyst.

[0040] The catharometric detector is configured to measure the variation in thermal conductivity of the atmosphere caused by the presence of ammonia.

[0041] The infrared radiation detector is based on the absorption of infrared radiation by ammonia molecules.

[0042] The electrochemical detector is based on a redox reaction at room temperature. Ammonia molecules adsorb on the surface of a catalyst and react with ions in a solution, causing an electric current.

[0043] The photoionization detector is an ion detector that uses energetic photons in the ultraviolet range to ionize ammonia gas molecules. The ammonia gas is bombarded by photons, which strips electrons from the gas molecules, transforming them into cations. The gas molecules are then ionized, allowing an electric current to be established. The detection of an electric current can then be likened to the presence of ammonia. This type of detector is non-destructive because it does not modify the ammonia gas molecules it detects.

[0044] The choice of this or that type of ammonia sensor can be made in particular according to the size of the detectors previously mentioned and the space available in the housing of the energy storage module.

[0045] According to the invention, the presence of the ammonia sensor 11 in the energy storage module is combined with the characteristic that at least one accumulator comprises a specific electrode.

[0046] In reference to the figures 3 et 4 , each electrical energy accumulator 5 comprises at least one positive electrode 13, at least one negative electrode 15 and at least one separator 17. The electrical energy accumulators 5 are each assembled by stacking the positive electrode 13, the negative electrode 15 and the separator 17 which is interposed between the two electrodes 13, 15. The separator 17 can be impregnated with a solution containing at least one electrolyte.

[0047] This stack forms an electrochemical core 19 which is then placed in an envelope 21 so that a positive terminal 23 and a negative terminal 25 of the electrical energy accumulator 5, visible on the figure 3, are accessible from outside the enclosure 21 and can be connected to an electrical supply network within the vehicle's electric battery.

[0048] The envelope 21 forms a sealed enclosure which protects the electrochemical core 19 from the air. In the example illustrated in the figures, the envelope consists of a substantially flat pocket and the stack of electrodes and the separator within this envelope consists of a superposition of substantially flat layers. It should be understood that this is not limiting of the invention, and that other embodiments of accumulator could be implemented here, for example with a cylindrical envelope inside which the stack of electrodes and the separator also has a wound shape to be housed in the envelope.

[0049] The positive electrode 13 forms the cathode when the electrical energy accumulator 5 discharges and therefore the electric battery 1 discharges. The positive electrode 13 may be composed of at least one active material, possibly at least one electronic conduction agent, and possibly at least one binder.

[0050] The active material of the positive electrode 13 is delithiated, that is to say that it is in particular capable of reversibly inserting lithium ions at a potential higher than the operating potential of the negative electrode 15.

[0051] The active material content of the positive electrode 13 may be 5 to 98% by weight, the electronic conduction agent content may be 0.1 to 30% by weight, and the binder content may be 0 to 25% by weight, relative to the total weight of the positive electrode 13.

[0052] The active material of the positive electrode 13 may be composed of a number of oxides. For example, the active material of the positive electrode 13 may be: manganese dioxide (MnO 2 ); iron oxide; copper oxide; nickel oxide; lithium-manganese composite oxides (eg Li x Mn 2 O 4 or Li x MnO 2 ); lithium-nickel composite oxides (eg Li x NiO 2 ); lithium-cobalt composite oxides (eg Li x CoO 2 ); lithium-nickel-cobalt composite oxides (eg LiNi 1-y Co y O2); lithium-nickel-cobalt-manganese composite oxides (eg LiNi x Mn y Co z O 2 , with x+y+z=1); lithium-enriched lithium-nickel-cobalt-manganese composite oxides (eg Li 1+x (NiMnCo) 1-x O 2 ); lithium and transition metal composite oxides; lithium-manganese-nickel composite oxides of spinel structure (eg Li x Mn 2-y Ni y O 4 ); lithium-phosphorus oxides of olivine structure (egLi x FePO 4 , Li x Fe 1-y Mn y PO 4 or Li x CoPO 4 ); iron sulfate (Fe 2 (SO 4 ) 3 ); and vanadium oxides (eg V 2 O 5 ).

[0053] The electronic conduction agent may be a carbon material, for example carbon black, acetylene black, natural or synthetic graphite, carbon nanotubes, or a mixture thereof.

[0054] The binder may be a polymer chosen, for example, from copolymers of ethylene and propylene optionally containing a unit allowing crosslinking; styrene-butadiene copolymers, such as, for example, styrene-butadiene rubbers (SBR); acrylonitrile-butadiene copolymers (ABR); poly(tetrafluoroethylene), such as, for example, polytetrafluoroethylene (PTFE) or polyvinylidene difluoride (PVDF); cellulose derivatives, such as, for example, carboxymethyl cellulose (CMC) or hydroxyethylcellulose (HEC).

[0055] The negative electrode 15 comprises at least one active material, possibly an electronic conduction agent, and possibly a binder. The active material of the negative electrode 15 is delithiated, that is to say that it is in particular capable of reversibly inserting lithium ions at a potential lower than the operating potential of the positive electrode 13.

[0056] According to the invention, the active material of the negative electrode 15 is composed of lithium metal nitride. It is this particular configuration of an electrode of an accumulator which, combined with the presence of an ammonia sensor 11 as mentioned previously, that is to say present in the energy storage module and / or the battery in which said accumulator is positioned, which allows early detection of potential malfunction of an energy storage module.

[0057] The active material of the negative electrode 15 may be such that the lithium metal nitride metal is selected from the group of transition metals.

[0058] More specifically, the inventors were able to note that the active material of the negative electrode 15 could be composed at least in part of lithium-manganese nitride whose formula is Li 7-x MnN 4 with x ≤ 2.0 and / or lithium-iron nitride whose formula is Li 3-x FeN 2 , with x ≤ 1.2. The electrochemical potential of lithium-manganese nitride with respect to lithium is 1.18 V, and the electrochemical potential of lithium-iron nitride is 1.24 V for high specific capacities, respectively 300 mAh / g and 200 mAh / g, available at a lower potential (-0.25 V) than the working potential (1.5 V) of Lithium Titanium Oxide (LTO: Li 4 Ti 5 O 12 ). Lithium Titanium Oxide, with a specific capacity limited to 150 mAh / g, is the currently best-performing negative electrode material for high-power lithium-ion batteries. Lithium manganese nitride and lithium iron nitride therefore have a higher energy density.Lithium manganese nitride and lithium iron nitride also exhibit good resistance to the application of high current densities, which is particularly advantageous for hybrid vehicle accumulators.

[0059] The electronic conduction agent and the binder may be respectively those described above for the positive electrode 13 of the electrical energy accumulator 5.

[0060] The active material content of the negative electrode 15 may be at least 60% by weight, the electronic conduction agent content may be 0 to 30% by weight, and the binder content may be 0 to 30% by weight, relative to the total weight of the negative electrode 15.

[0061] The separator 17, located between the electrodes of an electrical energy accumulator 5, acts as an electrical insulator. The separator 17 is generally composed of porous polymers, in particular polyolefin, preferably polyethylene and / or polypropylene. It may also be made of glass microfibers. The separator 17 may be a glass microfiber separator CAT No. 1823-070 ®< marketed by Whatman.

[0062] The separator is usually soaked with at least one electrolyte solution. The electrolytes used include at least one lithium salt and at least one solvent.

[0063] The lithium salt can be an inorganic salt such as lithium hexafluorophosphate (LiPF 6 ). The lithium salt can also be an organic salt such as lithium bis[(trifluoromethyl)sulfonyl]imide (LiN(CF 3 SO 2 ) 2 ), lithium trifluoromethane sulfonate (LiCFsSOs), lithium bis(oxalato)borate (LiBOB) or lithium fluoro(oxolato)borate (LiFOB).

[0064] The lithium salt is preferably dissolved in at least one solvent chosen from polar aprotic solvents, for example, ethylene carbonate (denoted "EC"), propylene carbonate (denoted "PC"), dimethyl carbonate (denoted "DMC"), diethyl carbonate (denoted "DEC") and ethyl methyl carbonate (denoted "EMC").

[0065] Following an impact causing deformation of one or more accumulators 5 or following accelerated wear of one of these accumulators, at least one casing 21 protecting an electrochemical core 19 of an electrical energy accumulator 5 may be damaged and consequently allow air to pass through. The negative electrode 15 is then exposed to air and / or to moisture contained in the air. This exposure causes the decomposition of the lithium-metal nitride of the negative electrode 15 and this results in the release of ammonia.

[0066] The ammonia sensor 11 present in the electrical energy storage module 3 is then able to detect the ammonia molecules released by the decomposition of the lithium metal nitride. Since the ammonia sensor 11 is specific to ammonia, it is therefore independent of environmental conditions and the detection threshold can be very low, so that a warning of a malfunction is issued as soon as ammonia appears in the air.

[0067] As mentioned above, the release of ammonia which takes place according to the invention during a malfunction, and more particularly a loss of sealing of an enclosure of an accumulator 5, tends in a second stage to the formation of gaseous nitrogen in the presence of air and at high temperature. This has the effect of reducing the quantity of oxidant available inside the electrical energy storage module 3 and can therefore delay the thermal runaway of the electrical energy storage module 3 and therefore of the electric battery 1.

[0068] Of course, the invention is not limited to the examples just described. The subject matter of the invention is defined by the claims.

Claims

1. Module (3) for storing electrical energy for a vehicle comprising at least one electrical-energy accumulator (5) comprising at least one negative electrode (15) composed at least partially of lithium-metal nitride, said module (3) for storing electrical energy further comprising at least one ammonia sensor (11) for detecting a release of ammonia due to the decomposition of the lithium-metal nitride of the negative electrode (15) in the presence of air or of moisture.

2. Module (3) for storing electrical energy according to the preceding claim, wherein the metal of the lithium-metal nitride is chosen from the group of the transition metals.

3. Module (3) for storing electrical energy according to one of the preceding claims, wherein the metal of the lithium-metal nitride is chosen from the group comprising iron, manganese and an alloy thereof.

4. Module (3) for storing electrical energy according to any one of the preceding claims, wherein the lithium-metal nitride is delithiated.

5. Module (3) for storing electrical energy according to any one of the preceding claims, wherein the lithium-metal nitride is at least partially composed of lithium-manganese nitride the formula of which is Li7-xMnN4 with x ≤ 2.0 and / or of lithium-iron nitride the formula of which is Li3-xFeN2, with x ≤ 1.2.

6. Module (3) for storing electrical energy according to any one of the preceding claims and comprising a casing (7) forming a housing for the electrical-energy accumulators (5), the ammonia sensor (11) being placed on a wall (9) of the casing (7).

7. Module (3) for storing electrical energy according to the preceding claim, wherein the ammonia sensor (11) is placed on an internal face of the wall (9) of the casing (7).

8. Module (3) for storing electrical energy according to any one of the preceding claims, wherein the ammonia sensor (11) is chosen from a catalytic detector, a thermal-conductivity detector, a detector of infrared radiation, an electrochemical detector, and a photoionization detector.

9. Vehicle electrical battery (1) comprising a plurality of energy-storing modules, wherein at least one module (3) for storing electrical energy of the plurality of energy-storing modules is according to any one of the preceding claims.

10. Vehicle comprising at least one electrical battery (1) according to the preceding claim.