Electrical energy storage module for a vehicle

Abstract

The present invention relates to an electric energy storage module (3) for a vehicle, the electric energy storage module (3) including at least one electric energy storage battery (5) including at least one negative electrode composed at least in part of lithium metal nitride, the electric energy storage module (3) further including at least one ammonia sensor (11) for detecting the release of ammonia due to decomposition of the lithium metal nitride of the negative electrode in the presence of air or moisture.

Description

[Technical Field]

[0001] The present invention relates to the field of electric batteries for storing electric energy, more precisely to a module for storing electric energy for vehicles, and in particular for motor vehicles.

[0002] Electric batteries based on lithium-ion electrochemical accumulators, often referred to as "lithium-ion cells," are increasingly being used as stand-alone power sources, especially in applications related to electric mobility. This trend is justified, in particular, by their significantly higher energy density per unit mass and per unit volume than that of conventional nickel-cadmium (Ni-Cd) and nickel-metal hydride (Ni-MH) accumulators, the absence of memory effect, their low self-discharge relative to other accumulators, and also their 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 electric energy accumulators. These accumulators are arranged side by side in a casing that contributes to delimiting the energy storage module and are electrically connected to one another. Such a configuration allows the battery to store a large amount of energy and to increase the voltage available for powering the vehicle, while allowing the battery to remain operational in the event of a short circuit of one of the accumulators, in particular because it allows the module corresponding to this defective accumulator to be deactivated and power to continue to be delivered by the other energy storage modules, provided that additional switching and control devices are provided.

[0004] During use, the electric battery may experience electrical problems, such as a short circuit within the battery, and / or mechanical problems, such as a shock that impacts the battery. These problems may lead to thermal runaway within the electric battery, particularly when the electric battery includes lithium-ion batteries. This thermal runaway may result in an increase in pressure within the battery and / or within the module, release of gas, release of smoke, burst of flames, and / or splashing of material.

[0005] In this context, international regulations require motor vehicle manufacturers to detect electric battery thermal runaway at a fairly early stage, on the one hand to ensure the safety of motor vehicle occupants by enabling them to exit the vehicle before the passenger compartment begins to fill with smoke emissions, and on the other hand to enable well-designed safety measures to electrically isolate the battery with the aim of facilitating any emergency response.

[0006] In most cases, thermal runaway detection is based on measuring the pressure inside a sealed module. This pressure measurement leads to the release of thermal runaway information, particularly when the measured pressure rises above a predetermined critical threshold. Such techniques are based on fluctuations in the conditions inside the storage module and have the disadvantage of being dependent on environmental conditions. As a non-limiting example, driving a motor vehicle at different altitudes can affect the pressure inside the battery and / or inside the energy storage module, and the vehicle's passage through a tunnel can change the composition of the air likely to get into the battery, thus altering the gas component distribution and the pressure measurements taken. Therefore, it is necessary to set the detection threshold high enough to avoid false alarms in the event of thermal runaway. Therefore, the time required to reach this detection threshold is longer, and therefore the time available for occupants to exit the vehicle can be significantly reduced, compromising their safety.

[0007] As an alternative to the method described above, document US 9046580 discloses a method for detecting the failure of a battery in a battery module based on measuring the variation in the resistance of the electrical isolation of the module, which may further comprise monitoring for secondary effects of the failure of the battery and / or of the module, such as, for example, a loss of continuity in the voltage chain, a temperature of the module above a threshold temperature, a humidity above a threshold humidity, and / or a temperature of a coolant associated with a system for cooling the module above a threshold cooling temperature.

[0008] These methods therefore have the drawback of being required to evaluate increases in temperature and / or pressure and / or changes in humidity levels, taking into account environmental conditions, in order to detect battery and / or module failures. As mentioned above, the time taken for occupants to reach safety may therefore be increased, which has the consequence of placing those occupants in a dangerous situation.

[0009] The object of the present invention is to reduce at least one of the above-mentioned drawbacks and also to achieve other advantages by providing a new type of energy storage module for batteries of electric vehicles, and in particular motor vehicles.

[0010] The present invention provides a module for storing electrical energy for a vehicle, particularly a motor vehicle, comprising a plurality of electrical energy accumulator batteries, each comprising at least one negative electrode composed at least in part of lithium-metal nitride, said module for storing electrical energy further comprising at least one ammonia sensor for detecting the release of ammonia due to decomposition of the lithium-metal nitride of the negative electrode in the presence of air or moisture.

[0011] It should be understood here, and in all that follows, that the term "ammonia" refers to the compound of formula NH3 in gaseous form at room temperature.

[0012] The present invention is based on detecting the presence of ammonia instead of measuring pressure, temperature, and / or humidity levels as described in the prior art. It should thus be noted that the present invention advantageously differs from the prior art in that it is based on early detection of thermal runaway by detecting a gas that is not present in the storage module under normal operating conditions of the vehicle; this gas only appears under abnormal conditions, such as due to a crash or wear that results in the negative electrode of at least one storage battery coming into contact with air.

[0013] More specifically, the various layers of a lithium-ion electric energy storage battery are housed in an airtight pouch, and therefore each of these layers, and in particular the negative electrode, can be exposed to air and / or the moisture contained in the air only when a leak appears in the pouch. In the event of such a leak, which may result from the battery's wear or from a crash experienced by a vehicle, this exposure causes the decomposition of the lithium metal nitride and its transformation into ammonia. The ammonia sensor in the energy storage module will then detect the presence of ammonia. Given that the ammonia sensor is specific to ammonia, it is therefore independent of environmental conditions and its detection threshold can be very low. Detection of a malfunction can therefore be immediate, as soon as a single ammonia particle is detected; it is not necessary for the amount of ammonia present in the air to reach a critical threshold.

[0014] It is noteworthy in this context that decomposition of the lithium metal nitride of the negative electrode is not necessarily synonymous with thermal runaway, and that a leak in the sealed pouch of the battery is likely due to wear and tear and does not pose an imminent threat. However, it would be advantageous for the vehicle occupants to be made aware of this leak early, before thermal runaway of the energy storage module occurs. This may allow the occupants time to safely visit a dealer to have the energy storage module or even the electric battery replaced. Occupant safety is therefore improved.

[0015] Furthermore, at high temperatures, the ammonia formed by the decomposition of the lithium metal nitride of the negative electrode, which is unique to the present invention, in the presence of oxygen contained in the air, leads to the formation of dinitrogen gas, which therefore allows the amount of oxidizer inside the electrical storage module to be reduced even if / when, for example, a fire breaks out, and therefore allows thermal runaway to be delayed, especially until the arrival of firefighters.

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

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

[0018] According to one embodiment, each electrical energy storage battery includes at least a jacket in which the stack formed by the positive electrode, the separator, and the negative electrode is placed. As opposed to what has been explained above, it will be understood that the jacket forms a sealed enclosure in which the various electrodes are placed, and that it is the failure of the seal of this jacket that will cause the negative electrode to be exposed to free air and ammonia to be produced.

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

[0020] According to one embodiment, the metal of the lithium metal nitride is selected from the group comprising iron, manganese, and alloys thereof of iron and manganese.

[0021] According to one embodiment, the lithium metal nitride is delithiated. By "delithiated," it should be understood here and everywhere that follows that the lithium metal nitrite contains vacancies within its structure, which vacancies allow it to accommodate lithium ions, particularly when the electrical energy storage battery is recharged.

[0022] According to one embodiment, the lithium metal nitride has the formula Li 7-x MnN4, where x≦2.0, and / or from lithium manganese nitride, the formula of which is Li 3-x It is at least partially composed of lithium iron nitride, FeN2, where x≦1.2.

[0023] According to one embodiment, the energy storage module includes an ammonia sensor common to the plurality of electric energy storage batteries. More specifically, the module for storing electric energy includes a casing forming a housing for the plurality of electric energy storage batteries, and the ammonia sensor is disposed inside the casing. The ammonia sensor may be fastened to an inner surface of one of the walls of the casing. When the sensor detects the presence of ammonia in the module, exposure of the storage batteries to free air is identified, and the storage batteries present in the module must be preventatively replaced for the safety of the occupants.

[0024] As an alternative, one ammonia sensor may be provided for each electrical energy storage battery. It will be appreciated that in this alternative, detection is more accurate and it is possible to identify in a targeted manner which storage batteries are faulty and in particular which storage battery jackets are aired. However, this alternative embodiment incurs higher manufacturing costs, and a compromise may be preferred, whereby one ammonia sensor is made common to multiple storage batteries in order to reduce costs and nevertheless allow remedial action to be taken, which action does not require all storage batteries to be replaced, but simply the storage batteries in the vicinity of the sensor.

[0025] According to one embodiment, the ammonia sensor is selected from a catalytic detector, a thermal conductivity detector, a detector of infrared radiation, an electrochemical detector, or a photoionization detector.

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

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

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

[0029] Other characteristics and advantages of the invention will become more apparent from the description that follows, on the one hand, and from a number of non-limiting exemplary embodiments, presented by way of representation, with reference to the accompanying schematic drawings, in which: [Brief explanation of the drawings]

[0030] [Figure 1]1 is a diagram of a schematic representation of a vehicle electric battery including multiple energy storage modules according to the present invention. [Figure 2] FIG. 1 is a schematic representation of an energy storage module according to one embodiment of the present invention. [Figure 3] 3 is a diagram of a schematic representation of an electrical energy storage battery with which the energy storage module of FIG. 2 is capable of being equipped. [Figure 4] 4 is a partial schematic representation of the electrical energy storage battery of FIG. 3, the cross section making it possible to see the components of the storage battery housed inside the jacket shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0031] It will be noted at the outset that the figures illustrate the invention in a detailed manner aimed at realizing the invention, which figures may, of course, serve, where appropriate, to better define the invention. It will further be noted that in all figures, elements that are similar and / or perform the same functions are designated by the same reference numerals.

[0032] The invention relates in particular to a module for storing electrical energy, which module comprises at least one accumulator battery, the organization of which is specific, which accumulator battery has a negative electrode different from those traditionally used, and which module is unique in this context in that it comprises an ammonia sensor.

[0033] 1 illustrates a plurality of these modules 3 for storing electric energy, each including a plurality of electric energy accumulators 5. Such modules 3 for storing electric energy may form 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 electric road vehicle, an electric tram bicycle, or an electric scooter.

[0034] The module 3 for storing electrical energy comprises a casing 7, the walls 9 of which form a housing for a plurality of electrical energy accumulators 5 and for at least one ammonia sensor 11. In the illustrated example, the casing 7 here has a parallelepiped shape with six walls, among which it is possible to distinguish between a bottom wall 90, a side wall 92 and a closing lid 94, as can be seen in more detail in FIG.

[0035] The electrical energy storage batteries 5 are arranged relative to the bottom wall 90, if appropriate in a matrix 96, which allows the storage batteries to be positioned relative to each other and relative to the wall of the casing 7.

[0036] The ammonia sensor 11 is arranged inside the casing, i.e. in a housing formed by the wall 9 of the casing 7 of the module 3 for storing electrical energy, as illustrated in Figure 2. One ammonia sensor 11 is thus common to several accumulator batteries 5.

[0037] The ammonia sensor 11 includes or is associated with communication means 12 configured to transmit ammonia detection information to a control module that can transmit a warning signal to an occupant and / or transmit a command to shut down the supply of power from the electric battery or at least from a corresponding energy storage module. In the illustrated example, the communication means comprises wireless communication means, but it will be understood that the present invention is not limited to such wireless communication means.

[0038] 2, the ammonia sensor 11 is arranged on the inner surface 8 of one of the walls 9 of the casing 7, and more particularly here on the inner surface of the closing lid 94. It should be noted that the invention is not limited to this location of the ammonia sensor on the closing lid. However, it is advantageous, on the one hand, that the ammonia sensor 11 does not make mechanical contact with the electrical energy storage battery 5, and, on the other hand, that the ammonia sensor 11 is arranged in a central position so that the distance between this ammonia sensor and the storage battery 5 from which the sensor is furthest is as small as possible.

[0039] The ammonia sensor 11 may be a catalytic detector, a thermal conductivity detector, a detector of infrared radiation, an electrochemical detector, or a photoionization detector.

[0040] Catalytic detectors are based on measuring the heat of combustion of ammonia molecules on the surface of a metal catalyst.

[0041] The thermal conductivity detector is configured to measure variations in the thermal conductivity of the atmosphere caused by the presence of ammonia.

[0042] Detectors of infrared radiation are based on the absorption of infrared radiation by ammonia molecules.

[0043] Electrochemical detectors are based on a redox reaction at room temperature: ammonia molecules adsorb on the surface of a catalyst and react with ions in the solution, which causes an electric current to flow.

[0044] Photoionization detectors are ionization detectors that use high-energy photons in the ultraviolet range to ionize ammonia gas molecules. Ammonia gas is bombarded with photons, which allows electrons to be stripped from the gas molecules, converting them to cations. The gas molecules are therefore ionized, which allows an electric current to flow. Detection of an electric current is then sometimes considered synonymous with the presence of ammonia. This type of detector is nondestructive because it does not alter the ammonia gas molecules it detects.

[0045] The choice of such or such type of ammonia sensor may depend, inter alia, on the bulk of the detector as previously mentioned and on the space available within the casing of the energy storage module.

[0046] According to the invention, the presence of an ammonia sensor 11 in the energy storage module is combined with the feature according to which at least one accumulator comprises specific electrodes.

[0047] 3 and 4, each electric energy storage battery 5 includes at least one positive electrode 13, at least one negative electrode 15, and at least one separator 17. Each electric energy storage battery 5 is assembled by stacking the positive electrode 13, the negative electrode 15, and the separator 17, with the separator 17 being disposed between the two electrodes 13, 15. The separator 17 may be impregnated with a solution containing at least one electrolyte.

[0048] This stack forms an electrochemical core 19 which is then placed in a jacket 21 so that the positive and negative terminals 23 and 25 of the electrical energy storage cell 5, which can be seen in FIG. 3, are accessible from outside the jacket 21 and may be connected to an electrical feed network in the vehicle's electric battery.

[0049] The jacket 21 forms a sealed enclosure that protects the electrochemical core 19 from air. In the example illustrated in the figures, the jacket consists of a substantially flat pouch, and the electrode and separator stack within this jacket consists of a superposition of substantially flat layers. It should be noted that the invention is not limited thereto, and that other battery embodiments can be realized here, for example with a cylindrical jacket, inside which the electrode and separator stack further has a rolled shape to be housed within the jacket.

[0050] The positive electrode 13 forms a cathode when the electrical energy storage cell 5, and therefore the electrical battery 1, is discharging. The positive electrode 13 may be composed of at least one active material, optionally at least one electronically conductive agent, and optionally at least one binder.

[0051] The active material of the positive electrode 13 is delithiated, ie, lithium ions can be reversibly inserted into it, especially at potentials higher than the operating potential of the negative electrode 15 .

[0052] The content of the active material in the positive electrode 13 may be 5 to 98 wt %, the content of the electronic conductive agent may be 0.1 to 30 wt %, and the content of the binder may be 0 to 25 wt %, relative to the total weight of the positive electrode 13.

[0053] 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 (MnO2); iron oxide; copper oxide; nickel oxide; composite lithium manganese oxide (e.g., Li x Mn2O4 or Li x MnO2); composite lithium nickel oxides (e.g., Li x NiO2); complex lithium cobalt oxides (e.g., Li x CoO2); complex lithium nickel cobalt oxides (e.g., LiNi 1-y Co y O2); complex lithium nickel cobalt manganese oxide (e.g., LiNi where x + y + z = 1) x Mn y Co z O2); complex lithium-rich lithium nickel cobalt manganese oxide (e.g., Li 1+x (NiMnCo) 1-x O2); lithium and transition metal complex oxides; spinel-structured complex lithium manganese nickel oxides (e.g., Li x Mn 2-y Ni y O4); lithium phosphate oxides with olivine structure (e.g., Li x FePO4, Li x Fe 1-y Mn y PO4, or Li x CoPO4); iron sulfate (Fe2(SO4)3); and vanadium oxide (e.g., V2O5).

[0054] The electronically conductive agent may be one of the carbon-containing materials, such as carbon black, acetylene black, natural or synthetic graphite, carbon nanotubes, or mixtures thereof.

[0055] The binder may be, for example, a polymer selected from copolymers of ethylene and propylene, optionally containing repeat units that allow crosslinking; styrene butadiene copolymers, such as styrene butadiene rubber (SBR); acrylonitrile butadiene copolymers (ABR); poly(tetrafluoroethylene), such as polytetrafluoroethylene (PTFE), or polyvinylidene difluoride (PVDF); cellulose derivatives, such as carboxymethyl cellulose (CMC) or hydroxyethyl cellulose (HEC).

[0056] Negative electrode 15 includes at least one active material, an optional electronic conductor, and an optional binder. The active material of negative electrode 15 is delithiated, i.e., lithium ions can be reversibly inserted into the active material, particularly at potentials lower than the operating potential of positive electrode 13.

[0057] According to the present invention, the active material of the negative electrode 15 is composed of lithium metal nitride. It is this unique configuration of the accumulator's electrodes, combined with the presence of the ammonia sensor 11 as described above, i.e., in the energy storage module and / or battery in which said accumulator is located, that allows early detection of a potential malfunction of the energy storage module.

[0058] The active material of negative electrode 15 may be such that the metal of the lithium metal nitride is selected from the group of transition metals.

[0059] More specifically, the inventors have determined that the active material of the negative electrode 15 is a compound having the formula Li 7-x MnN4, where x≦2.0, and / or from lithium manganese having the formula Li 3-xIt can be noticed that the lithium manganese nitride is sometimes composed at least in part of lithium iron nitride, where x is FeN2 and x ≤ 1.2. The electrochemical potential of lithium manganese nitride is 1.18 V and that of lithium iron nitride is 1.24 V, which are values ​​close to those of lithium titanium oxide (LTO: Li4Ti5O 12 The high specific capacities (300 mAh / g and 200 mAh / g, respectively) available at potentials lower (-0.25 V) than the working potential (1.5 V) of 1000 mAh / g are due to the high specific capacities. Lithium titanium oxide, with a specific capacity limited to 150 mAh / g, is the highest-performing anode material currently available for lithium-ion power batteries. Lithium manganese nitride and lithium iron nitride therefore have higher energy densities. Lithium manganese nitride and lithium iron nitride also have good resistance to high current density applications, which is particularly advantageous for hybrid vehicle batteries.

[0060] The electronically conductive agent and binder may be the electronically conductive agent and binder, respectively, described above with respect to the positive electrode 13 of the electrical energy storage battery 5 .

[0061] The content of the active material in the negative electrode 15 may be at least 60% by weight, the content of the electronic conductive agent may be 0 to 30% by weight, and the content of the binder may be 0 to 30% by weight, relative to the total weight of the negative electrode 15.

[0062] The separator 17, located between the electrodes of the electrical energy storage battery 5, acts as an electrical insulator. The separator 17 is generally made of a porous polymer, particularly a polyolefin, and preferably polyethylene and / or polypropylene. The separator 17 may also be made of glass microfiber. The separator 17 may be a glass microfiber separator sold by Whatman (catalog number 1823-070®).

[0063] The separator is generally immersed in at least one solution of an electrolyte, the electrolyte used comprising at least one lithium salt and at least one solvent.

[0064] The lithium salt may be an inorganic salt, such as, for example, lithium hexafluorophosphate (LiPF), or may further be an organic salt, such as, for example, lithium bis[(trifluoromethyl)sulfonyl]imide (LiN(CFSO)), lithium trifluoromethanesulfonate (LiCFSO), lithium bis(oxalato)borate (LiBOB), or even lithium fluoro(oxalato)borate (LiFOB).

[0065] The lithium salt is preferably dissolved in a polar aprotic solvent, such as at least one solvent selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0066] Following a crash that leads to the deformation of one or more accumulator cells 5, or for that matter, following the premature wear of one of these accumulator cells, at least one jacket 21 protecting the electrochemical core 19 of the electrical energy accumulator cell 5 may be damaged and therefore allow air to pass through. The negative electrode 15 is then exposed to air and / or the moisture contained in the air. This exposure causes the decomposition of the lithium metal nitride of the negative electrode 15, which results in the release of ammonia products.

[0067] The ammonia sensor 11 present in the module for storing electrical energy 3 can then detect the ammonia molecules released by the decomposition of the lithium metal nitride. Given that the ammonia sensor 11 is specific to ammonia, it is therefore independent of environmental conditions and its detection threshold can be very low, so that a malfunction warning can be issued as soon as ammonia appears in the air.

[0068] As mentioned above, the release of ammonia occurring according to the invention during malfunction, and more particularly the loss of the seal of the jacket of the accumulator 5, tends to subsequently cause the formation of dinitrogen gas in the presence of air and at high temperatures. This has the effect of reducing the amount of oxidant available inside the module for storing electrical energy 3 and may therefore delay thermal runaway of the module for storing electrical energy 3 and therefore of the electric battery 1.

[0069] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

Claims

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

2. 2. A module (3) for storing electrical energy according to claim 1, wherein the metal of the lithium metal nitride is selected from the group of transition metals.

3. 3. A module (3) for storing electrical energy according to claim 1 or 2, wherein the metal of the lithium metal nitride is selected from the group comprising iron, manganese and alloys of iron and manganese.

4. 4. A module (3) for storing electrical energy according to any one of claims 1 to 3, wherein the lithium metal nitride is delithiated.

5. The lithium metal nitride has the formula Li ７－ｘ MnN ４ and x≦2.0, and / or from lithium manganese nitride having the formula Li ３－ｘ FeN ２ 5. A module (3) for storing electrical energy according to any one of claims 1 to 4, at least partially composed of lithium iron nitride, where x≦1.

2.

6. 6. A module (3) for storing electrical energy according to any one of claims 1 to 5, comprising a casing (7) forming a housing for the electrical energy accumulator (5), the ammonia sensor (11) being arranged on a wall (9) of the casing (7).

7. 7. A module (3) for storing electrical energy according to claim 6, wherein the ammonia sensor (11) is arranged on the inner surface of the wall (9) of the casing (7).

8. 8. The module (3) for storing electrical energy according to claim 1, wherein the ammonia sensor (11) is selected from a catalytic detector, a thermal conductivity detector, a detector of infrared radiation, an electrochemical detector, and a photoionization detector.

9. 9. A vehicle electric battery (1) comprising a plurality of energy storage modules, at least one module (3) for storing electric energy among said plurality of energy storage modules being as claimed in any one of claims 1 to 8.

10. A vehicle comprising at least one electric battery (1) according to claim 9.

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