Insulating separator for electric battery

Abstract

The present invention relates to a separator (1) suitable for separating two cells (2) of a battery (3), for example, of an electric or hybrid electric vehicle, the separator (1) comprising at least one insulating layer comprising a composite material (4), the composite material (4) comprising a binder mixed with aerogel particles (5), the volume content of the aerogel particles (5) in the composite material (4) being greater than 20%, and the binder being of mineral type. The invention also relates to a battery comprising a separator according to the invention, and to a method for producing a separator according to the invention.

Description

[Technical Field]

[0001] The present invention is in the field of electric batteries, and more particularly, the present invention relates to cell separators for electric batteries.

[0002] Due to the advantage of low CO2 emissions, electric and hybrid electric vehicles have seen significant development. These vehicles are usually equipped with lithium-ion type batteries. These batteries can experience thermal runaway, a phenomenon in which the temperature inside the battery rises spontaneously. The battery can then heat up until it catches fire or explodes. Therefore, managing this risk is a major safety issue. One of the challenges is to limit and / or slow the spread of heat and / or fire between adjacent battery cells.

[0003] WO2006137935 discloses an insulating separator that can be placed between battery cells. It contains a fiber-reinforced aerogel encapsulated in a polymer. This solution is very costly and has poor thermal insulation performance.

[0004] It is an object of the present invention to provide an insulating separator with improved thermal insulation, fire resistance and durability.

[0005] One object of the present invention is to provide a highly compressible, thermally and electrically insulating separator.

[0006] It is a further object of the present invention to provide a simple, multi-function insulating separator that comprises a single component that can be easily retrofitted into existing batteries.

[0007] The object of the present invention is to at least partially address the above-mentioned objectives by proposing a separator that is primarily composed of a binder for mechanical strength and aerogel for heat and fire resistance. To this end, the present invention proposes a separator suitable for separating two cells of, for example, an electric or hybrid electric vehicle battery, the separator comprising at least one insulating layer comprising a composite material, the composite material comprising a binder mixed with aerogel particles, preferably the volume content of the aerogel particles (5) in the composite material (4) is greater than 20%, the total weight content of the aerogel particles and the binder in the composite material (4) is greater than 80%, and the binder used is a mineral-type binder.

[0008] These provisions reduce the rate of heat and / or flame propagation between the two battery cells, reducing the risk of the fire spreading outside the battery or the battery exploding. This solution also offers good durability, since stresses applied to the battery do not damage the separator. This solution is simple to manufacture. Furthermore, this type of inorganic binder allows for the creation of pastes with a higher percentage of aerogel. As a result, the weight is further reduced, but more importantly, the thermal conductivity is also reduced, as it is closer to that of aerogel.

[0009] According to other characteristics, the separator may comprise at least one additional layer that is capable of deforming to absorb at least a portion of the reduction in volume of the separator in any square area of ​​4 cm or more located on one of its outer surfaces, thereby preventing wear of the battery cells due to cell expansion; At least one of said at least one additional layer may comprise at least one layer of ceramic fiber paper, which is a simple and robust means of implementing the invention. at least one of said at least one additional layer may have, on at least one of its faces, a three-dimensional shape, for example in the form of a honeycomb, which is a simple solution to implement and makes it possible to produce a separator with improved durability; the insulating layer may comprise at least one mechanical reinforcing element, for example in the form of a honeycomb, which ensures that the layer stays in place when, for example, the binder tends to crumble; The binder may comprise a mineral material, for example calcium hydroxide, and the volume content of the aerogel particles in the composite is greater than 90% and the weight content of the mineral material in the binder is greater than 50%, which is a solution for reducing the weight of the separator and obtaining particularly interesting thermal conductivity.

[0010] The invention also relates to a battery for an electric or hybrid electric vehicle comprising at least two cells and at least one insulating separator according to the invention disposed between the cells.

[0011] These measures reduce the rate of heat and / or fire propagation between the two battery cells, and also reduce the risk of the fire spreading outside the battery or the battery exploding. In addition, this solution has good long-term retention, stresses applied to the battery do not damage the separator, and the separator is easy to manufacture.

[0012] Finally, the present invention relates to a process for manufacturing an insulating separator according to any one of claims 1 to 5, comprising the following steps: -Production of aerogel particles. - Mixing the aerogel particles with the binder in liquid form. The resulting mixture is cured in a mold to obtain the composite material.

[0013] Thanks to these arrangements, the separator according to the invention can be produced in a simple manner.

[0014] According to other characteristics, The production of said aerogel may comprise the following sub-steps: The precursor is mixed with a synthesis solvent and a hydrolysis agent such as water, and optionally a catalyst, to obtain a gel. - granulating the product obtained by cutting the jet of said gel to obtain particles;

[0015] This results in fewer angular particles, which are less brittle and less likely to crack. The production of said aerogel may comprise the following sub-steps: -Particle drying carried out entirely at pressures above the CO2 critical point.

[0016] This avoids breakage of the aerogel particles and results in a hydrophilic aerogel. The production of said aerogel may comprise the following sub-steps: The precursor is mixed with a synthesis solvent and a hydrolysis agent such as water, and optionally a catalyst, to obtain a gel. The resulting product is granulated to obtain particles. - The particles are left in contact with the synthesis solvent and the hydrolysis agent. - Washing the particles with a washing solvent to extract the hydrolysis agent and, if available, the catalyst. The particles are dried to extract the synthesis solvent and / or washed with excess supercritical CO2.

[0017] The sub-steps of granulation, holding, washing and drying are carried out at pressures above the CO critical point, and these conditions are maintained throughout these steps, allowing aerogel to be produced continuously, significantly reducing production time and costs and improving product quality due to the elimination of dangerous state changes and decompression steps. [Brief explanation of the drawings]

[0018] The present invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings.

[0019] [Figure 1] 1 is a schematic cross-sectional view of a battery incorporating a separator according to the present invention. [Figure 2] 1 is a schematic cross-sectional view of an insulator according to the present invention;

[0020] The separator 1 according to the invention, shown in the preferred embodiment in FIG. 2, is intended to be integrated between the cells 2 of a battery 3, as shown in FIG.

[0021] In the battery 3, separators 1 are disposed between every adjacent cell 2, thereby achieving maximum efficiency in preventing the spread of heat or fire within the battery. Alternatively, to achieve a smaller battery, for example, separators 1 can be disposed between groups of cells 2, for example, every two or three cells 2.

[0022] The shape and size of the separator can vary depending on the application.

[0023] The dimensions of the face of the cell 2 adjacent to the separator are, for example, 200 x 100 mm or 300 x 100 mm, in which case the separator is preferably in the shape of a rectangular parallelepiped of these dimensions.

[0024] The thickness of the separator can be, for example, 2 to 4 mm, making the separator suitable for a wide range of applications.

[0025] The present invention may be applied to any battery, particularly batteries requiring thermal management and batteries subject to cell swelling.

[0026] The invention applies in particular to batteries for electric or hybrid electric vehicles: an electric vehicle is a vehicle whose propulsion is ensured solely by one or more electric motors, a hybrid electric vehicle is a vehicle equipped with one or more electric motors capable of ensuring the propulsion of the vehicle and one or more other types of motors (generally thermal motors) capable of ensuring the propulsion of the vehicle.

[0027] The present invention can also be applied to batteries for hydrogen vehicles.

[0028] Finally, the invention may be applied to home batteries used to store electricity generated by, for example, solar panels.

[0029] The battery 3 is preferably a lithium-ion battery. This type of battery is widely used today due to its performance in terms of autonomy and low cost. However, it is also particularly prone to thermal runaway.

[0030] The vehicle can be of any type, including a car, truck, van, or motorcycle.

[0031] The separator according to the present invention includes at least one insulating layer, which includes a composite material 4 including a binder mixed with aerogel particles 5.

[0032] The binder keeps the aerogel 5 particles optimally distributed within the separator.

[0033] Separator 1 preferably complies with the UL 94 V0 standard for flame retardancy.

[0034] The separator 1 preferably has a heat resistance that allows it to withstand 800°C on one side and maintained below 150°C on the other side for 2 minutes.

[0035] The separator 1 preferably has heat and flame resistance that allows it to withstand 10 minutes in the presence of a flame at 1400°C on one side and maintained below 300°C on the other side.

[0036] The aerogel 5 particles range in size from 0.015 to 3 mm.

[0037] The aerogel 5 can be a hydrophobic or hydrophilic aerogel.

[0038] Preferably, the aerogel is hydrophobic.

[0039] The aerogel 5 can be based on any material relevant to this application, for example silica aerogel, silica-polymer hybrid aerogel, carbon aerogel, or a mixture of several of these aerogels.

[0040] The aerogel 5 is preferably silica aerogel, which is a very good thermal insulator, e.g., with a thermal conductivity of the order of 0.012 W / mK. Silica aerogel can be made from raw materials that are, e.g., more than 75% by weight, recycled material from the demolition industry, thereby reducing production costs and energy consumption required to produce the raw material.

[0041] The binder can be mineral, i.e., it contains a mineral material whose weight content is at least 50% of the binder. One example is calcium hydroxide, which has the advantage of being lightweight. In addition, such binders allow the paste to be made with a higher proportion of aerogel. As a result, the weight is further reduced, but especially the thermal conductivity, which is close to that of aerogel, is also reduced.

[0042] In some embodiments, the insulating layer may include a reinforcing element in the form of a honeycomb, such as the "Nomex Honeycomb" product sold by DuPont, which is made from paper coated with phenolic resin. Different types of matrices can be used, with different materials, e.g., ceramic paper, of which a person skilled in the art would know how to select. Such reinforcing elements are particularly interesting when, for example, mineral-type binders tend to crumble.

[0043] The volume content of the aerogel particles 5 in the composite material 4 is greater than 20%, which gives the composite material 4 good thermal insulation properties.

[0044] The binder and aerogel particles 5 constitute the majority of the composite material 4, and in particular, the total weight content of the aerogel particles 5 and the elastomer in the composite material 4 is greater than 80%, preferably greater than 90%. In addition to the binder and aerogel particles 5, the composite material 4 may contain various additives, such as surfactants, to optimize the distribution of the aerogel particles 5 in the composite material 4.

[0045] The separator 1 may include at least one additional layer 6. The volume of the cells 2 of the battery 3, particularly their thickness, may change during charge / discharge cycles. Since the battery pack, including the cells 2 and the separator 3, has a fixed volume, the separator 3 must be able to accommodate a reduction in the volume allocated to it. When the volume of the separator 1 decreases, the additional layer 6 is configured to limit the increase in pressure inside the composite 4, particularly in the aerogel particles 5, which are at risk of breaking under the influence of high pressure. The additional layer 6 is described in more detail below.

[0046] In certain embodiments, separator 1 comprises two additional layers, one on each side of the insulating layer.

[0047] In other embodiments, separator 1 includes an additional layer disposed between two insulating layers.

[0048] The additional layer 6 can deform to accommodate the reduction in volume of the separator 1. To achieve efficiency across the entire surface of the separator 1, the additional layer 6 can deform over any square area of ​​4 cm or more located on one of its outer surfaces.

[0049] In a preferred embodiment of the present invention, the additional layer 6 comprises at least one layer of ceramic fiber paper. Examples include EST C30 or EST C310, sold by Morgan Advanced Materials. The ceramic fiber paper can be applied, for example, by gluing or laminating, to one or both sides of the insulating layer, i.e., between the insulating layer and the walls of the cells 2 on both sides of the separator 1. This ceramic fiber paper layer absorbs the volume reduction caused by the reduction in thickness of the separator 1, and the insulating layer suffers little volume reduction. The ceramic fiber paper layer can be approximately 1 mm thick.

[0050] The additional layer 6 may comprise at least one layer of elastomer, for example a silicone elastomer.

[0051] The additional layer 6 may also comprise a silicone foam, such as that sold under the brand name Norseal® by Saint-Gobain.

[0052] In another embodiment, the additional layer 6 has a three-dimensional shape. Such a layer can be made of an elastomer. This shape can then be characterized by compression zones. For example, the shape can be honeycomb-shaped, with the edges formed by the hexagons constituting the compression zones. These compression zones allow the separator 1 to absorb volume fluctuations by deforming a portion of the separator 1, while the remaining portion of the separator 1 can maintain a volume close to its initial volume. For example, the sides of the hexagons expand in a plane perpendicular to the force, so that the thickness of the separator 1 can be reduced without a significant increase in pressure. The additional layer 6 can be directly molded or cast into a shape characterized by compression zones.

[0053] Different types of additional layers 6, i.e. ceramic fiber paper, elastomer, silicone foam, or three-dimensional shapes, can be used individually or in combination.

[0054] The separator 1 according to the present invention can include a protective envelope, for example of PET, to protect its insulating layer and volume reduction management layer, which is particularly useful when the binder is of a friable mineral type.

[0055] The invention also relates to a battery 3 for an electric or hybrid electric vehicle comprising at least two cells 2 and at least one insulating separator 1 disposed between said cells 2.

[0056] Finally, the present invention relates to a process for manufacturing a separator 1, the process comprising the following steps: -Production of aerogel particles. The aerogel particles are mixed with the binder, for example calcium hydroxide, which can be dissolved in a solvent. The resulting mixture is cured in a mold to obtain the composite material. Mechanical reinforcement elements, such as a honeycomb-shaped structured matrix, can be added to the mold. Curing is achieved, for example, by increasing the temperature, adding a catalyst, or evaporating the solvent.

[0057] Example

[0058] To prepare a separator according to the present invention, 14.19% by weight of calcium hydroxide was mixed with water. Next, 85.8% by weight of hydrophobic silica aerogel having a sieved particle size of 15-3000 microns and a density of 70 kg / m³, and 0.01% by weight of an opacifier were added and mixed for 10 minutes. The result was a homogeneous composition with a paste consistency. This paste was spread on a honeycomb-shaped plate. The paste was dried in the plate at a temperature of 35°C for 10 hours. The result was an insulating separator characterized as follows:

[0059] Apparent density of paste after drying: 160 kg / m3

[0060] Separator density (paste + plate): 240kg / m3

[0061] Thermal conductivity of dried paste: 18mW / mK at 20℃

[0062] Thermal conductivity of separator (paste + plate): 23mW / mK at 20°C

[0063] In Example 1 above, nearly pure calcium hydroxide was used as the binder. Alternatively, a commercially available mixture of about 30% calcium hydroxide with other minerals can be used as the binder, in which case the weight of the binder increases slightly, e.g., to 25% by weight of such binder instead of 14.19%.

[0064] Depending on the thickness of the separator, particularly a thickness of 1 mm to 4 mm, the drying temperature can vary between 20 and 50° C., and the drying time can vary between 4 and 24 hours.

[0065] Depending on the type of aerogel used, in particular its density, which can vary between 50 and 150 kg / m³, the binder used (substantially pure calcium hydroxide or a mixture of mineral materials), and the plates used, the density of the composite can vary between 120 and 300 kg / m³.

[0066] Depending on the shape and density of the plates used, whether honeycomb shaped or not, a relatively low aerogel-to-separator volume fraction, preferably greater than 20%, can be achieved to take advantage of the insulating properties of aerogel. Thin, low-mass plates can also be used to achieve aerogel-to-separator volume fractions of greater than 80%. In some cases, for particularly good results, aerogel-to-separator volume fractions of greater than 90% or even greater than 99% are achieved.

[0067] The resulting paste can also be dried in a mold, resulting in a composite material that can be used in a separator according to the invention without the need for additional honeycomb plates. The result is a separator with an aerogel content that can easily exceed 90% by volume.

[0068] Other examples were tested. 7.5 wt% calcium hydroxide was mixed with 92.5% aerogel with a density of 50 kg / m³ to produce a paste with a density of 140 kg / m³. 3.7 wt% calcium hydroxide was mixed with 96.3% aerogel with a density of 90 kg / m³ to produce a paste with a density of 166 kg / m³. 2% by weight of calcium hydroxide was mixed with 98% aerogel with a density of 150 kg / m³ to produce a paste with a density of 207 kg / m³.

[0069] The thermal conductivities obtained were similar to those obtained in the previous examples.

[0070] When producing aerogel particles, the above process may include the following sub-steps: The precursor is mixed with a synthesis solvent and a hydrolysis agent such as water, and optionally a catalyst, to obtain a gel. - granulating the product obtained by cutting the jet of said gel to obtain particles;

[0071] The gel is passed through an aperture, for example, of a size corresponding to the desired particle size. The jet formed at the exit of the aperture is then cut at a frequency that depends on the particle size.

[0072] Jet cutting granulation produces aerogel particles with a relatively regular shape and few corners, which reduces the risk of the aerogel particles 5 breaking or cracking after they are integrated into the separator 1, especially under the influence of stresses resulting from the expansion of the cells 2 of the battery 3.

[0073] When producing aerogel particles, the method for producing the separator 1 may include the following sub-steps: -Particle drying carried out entirely at pressures above the CO2 critical point.

[0074] On the one hand, this type of drying avoids the degradation of the particles during drying, and on the other hand, it ensures that the aerogel particles remain hydrophilic. Indeed, other types of drying, for example, involving an evaporation process in ambient air, can result in the loss of the hydrophilic properties of the aerogel particles.

[0075] Finally, when producing aerogel particles, the process for producing the separator 1 can be a continuous process known to those skilled in the art and described in document FR 1670366. This process comprises the following steps: The precursor is mixed with a synthesis solvent and a hydrolysis agent such as water, and optionally a catalyst, to obtain a gel. The resulting product is granulated to obtain particles. - The particles are left in contact with the synthesis solvent and the hydrolysis agent. - The particles are washed with a washing solvent to extract the hydrolysis agent and any catalyst. The particles are dried to extract the synthesis solvent and / or washed with excess supercritical CO2.

[0076] The sub-steps of granulation, holding, washing and drying are operated at pressures above the CO2 critical point, and these conditions are maintained during these steps.

[0077] Thanks to these provisions, the aerogel production process can be carried out continuously, with pressure increases occurring while the product is still fluid. As soon as the product becomes solid (i.e., after granulation), continuous pressure increases are no longer possible. Thanks to the present invention, the product does not require any pressure increases after it becomes solid, nor does it need to be depressurized separately from the final depressurization. This significantly reduces production time and costs and improves product quality by reducing the number of dangerous state changes and depressurization steps. In addition, this process allows the drying step to be carried out entirely at pressures above the CO2 critical point without increasing costs.

[0078] In this continuous process, the following features can be implemented: The mixing stage can also be operated at pressures above the critical point of CO2, allowing this stage to be slightly accelerated. During the drying step, the particles containing the solvent are subjected to a jet of supercritical CO2, placing them in fluidized bed conditions under temperature and pressure conditions such that the CO2 is supercritical and the particles containing the solvent are heavier than the particles containing CO2, thus allowing the drying step to be carried out continuously and accelerating the drying step; The synthesis and / or wash solvents can be organic solvents, and the drying step can be carried out at a pressure of 100-200 bar and a temperature of 35-50°C; ethanol is a cheap product that is suitable for the process; the conditions of 100-200 bar and 35-50°C mean that, at a particular CO2 injection rate into the fluidized bed, particles containing ethanol will not fly off, but particles containing only supercritical CO2 will fly off at the top of the column and can be recovered for the remainder of the process. the aerogel production process may include, after the drying step, a step of replacing the supercritical CO2 with an inert gas, preferably nitrogen, followed by a decompression step, preferably in stages, this additional step allowing for rapid decompression without damaging the aerogel particles; During the step of replacing the supercritical CO2 with an inert gas, the particles filled with supercritical CO2 are subjected to a jet of said inert gas under temperature and pressure conditions such that the CO2 is supercritical, bringing them into fluidized bed conditions, so that the particles filled with supercritical CO2 are heavier than those filled with an inert gas, allowing the step of replacing the supercritical CO2 with an inert gas to be carried out continuously and accelerating this step.

[0079] The continuous aerogel particle production process can be implemented in a plant for producing particulate aerogel from precursors, the plant comprising: mixing reactor, a granulation device, possibly located inside the maturation reactor, capable of forming particles from the jet of gelling liquid coming from the mixing reactor; - maturation reactor, - cleaning reactor, -drying device, a pressure reducing device.

[0080] This installation is special in that the maturation, washing and drying reactors, and the means for transferring the product between these reactors, are configured to operate at pressures above the CO2 critical point, making it possible to maintain the product from one reactor to another.

[0081] Thanks to these features, the plant can produce aerogel particles continuously, while pressure can be applied while the product is still fluid.

[0082] The following features are available in this installation: The mixing reactors can also be configured to operate and maintain the product from one reactor to the other at a pressure above the CO2 critical point, which allows for further reduction in reaction time. The plant also comprises a first fluidized bed column configured to make it possible to replace the solvent contained in the particles with supercritical CO2, thereby making it possible to dry the particles and to accelerate the drying phase. The plant may also comprise a second fluidized bed column configured to make it possible to replace the supercritical CO2 contained in the particles with a pressurized inert gas, preferably nitrogen, making it possible to carry out a rapid decompression without damaging the aerogel particles.

[0083] The above description is based on particular embodiments, but does not in any way limit the scope of the invention, which may be modified, inter alia, by the substitution of technical equivalents or by different combinations of all or part of the features developed above.

Claims

1. A separator (1) suitable for separating two cells (2) of a battery (3), for example of an electric or hybrid electric vehicle, characterized in that the separator (1) comprises at least one insulating layer containing a composite material (4), the composite material (4) containing a binder mixed with aerogel particles (5), the binder and the aerogel particles (5) making up the majority of the composite material (4), the binder being of mineral type, in particular the binder containing a mineral material whose weight content makes up at least 50% of the binder.

2. 2. The separator (1) according to claim 1, wherein the volume fraction of the aerogel particles (5) in the composite material (4) is greater than 20%.

3. 3. The separator (1) according to claim 1 or 2, wherein the sum of the weight contents of the aerogel particles (5) and the binder in the composite material (4) is greater than 80%.

4. 4. The separator according to claim 1, comprising at least one additional layer (6), said additional layer (6) being capable of deforming to absorb at least part of the reduction in volume of the separator at the level of any square zone of area equal to or greater than 4 cm2 located on one of its outer surfaces.

5. The separator of any one of claims 1 to 4, wherein at least one of the at least one additional layer (6) comprises ceramic fiber paper.

6. 6. A separator according to any one of claims 1 to 5, wherein at least one of said at least one additional layer (6) has, on at least one of its faces, a three-dimensional shape, for example in the form of a honeycomb.

7. The separator according to any one of claims 1 to 6, wherein the insulating layer comprises at least one mechanical reinforcing element, for example in the form of a honeycomb.

8. The separator according to any one of claims 1 to 7, wherein the binder comprises at least 30% calcium hydroxide.

9. 9. The separator of claim 8, wherein the binder comprises at least 50%, preferably at least 80%, calcium hydroxide.

10. The separator according to any one of claims 1 to 9, wherein the volume content of the aerogel particles (5) in the composite material (4) is greater than 90%.

11. A battery (3) for an electric or hybrid electric vehicle, comprising at least two cells (2) and at least one separator (1) according to any one of claims 1 to 10, disposed between said cells (2).

12. A process for manufacturing a separator (1) according to any one of claims 1 to 10, comprising: - a process for the preparation of aerogel particles (5), - mixing said aerogel particles (5) with said binder in liquid form, - curing the resulting mixture in a mould to obtain said composite material (4).

13. The production of the aerogel particles (5) - a sub-step of mixing the precursor with a synthesis solvent and a hydrolysis agent such as water, and optionally a catalyst, to obtain a gel; 13. The manufacturing process according to claim 12, comprising the sub-step of granulating the product obtained by cutting the jet of gel to obtain particles.

14. The production of the aerogel particles (5) -CO 2 14. A manufacturing process according to claim 12 or 13, comprising a sub-step of particle drying carried out entirely at a pressure above the critical point.

15. The production of the aerogel particles (5) - a sub-step of mixing the precursor with a synthesis solvent and a hydrolysis agent such as water, and optionally a catalyst, to obtain a gel; - granulating the resulting product to obtain particles, - leaving the particles in contact with the synthesis solvent and the hydrolysis agent, - a substep of washing the particles with a washing solvent to extract the hydrolysis agent and any catalyst, - excess supercritical CO 2 and drying the particles to extract the synthesis and / or washing solvent, The granulation, holding, washing and drying sub-steps are carried out by the CO 2 15. The manufacturing process of claim 14, operated at pressure above the critical point, and these conditions are maintained during these steps.

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