Propagation barrier with reinforcing filler material and method for its production

Description

[0001] The present invention relates to a barrier for preventing the propagation of a thermal event within a multi-cell battery module (so-called "propagation barrier"), comprising a heat-absorbing protective layer based on a hydrogel and a reinforcing filler material. The invention further relates to a battery module comprising the barrier and to the use of the barrier for compensating for volume fluctuations within a battery module. A method for producing the propagation barrier is also described. Technical background and state of the art

[0002] Thermal events can occur in all battery types. One of the most feared thermal events is thermal runaway. This can happen when the rate at which the battery generates heat exceeds the rate at which it can dissipate it. If a critical temperature is exceeded, the heat-generating process inside the battery becomes self-reinforcing, causing the battery to heat up to several hundred degrees Celsius within a very short time. Simultaneously, there is an extreme pressure increase within the cell, which can lead to an explosive release of decomposition gases and a fire.

[0003] In multi-cell battery modules, the danger posed by such a thermal event is amplified. The spacing between individual cells does not provide sufficient protection against the propagation of thermal runaway. Due to the high temperature reached in the cell affected by thermal runaway, the adjacent cells also heat up beyond their critical temperature. Consequently, the thermal runaway of a single cell can easily lead to the destruction of the entire battery module.

[0004] Lithium-ion batteries are particularly susceptible to thermal runaway. They possess a significantly higher energy density than other battery types and can potentially release decomposition gases with a high oxygen content, which can lead to even higher temperatures in the event of a failure. In applications where the battery module's footprint is critical, many battery manufacturers have resorted to maximizing the packing density of lithium-ion cells. This leaves very little space for barriers to prevent the propagation of thermal events, often resulting in insufficient thermal insulation between the cells.

[0005] Against this background, various barrier materials for batteries are proposed in the state of the art.

[0006] WO 2010 / 017169 A1 also addresses the problem of thermal runaway in multi-cell battery packs, particularly lithium-ion battery packs, and proposes strategies to prevent the transmission of a thermal event from one battery cell to an adjacent one. For this purpose, a propagation barrier using a hydrogel as the heat-absorbing material is specified. The hydrogel is contained in a flexible pouch or a rigid container and inserted into the battery module. The flexible pouch conforms to the shape of the battery cells to ensure the transfer of heat from the battery cell to the hydrogel. The container can be custom-made to also make contact with the cell surface. However, both of these solutions have room for improvement. The element can only act as a barrier to a limited extent.In the embodiment where the hydrogel is contained in a pouch, there is no spacer between the cells that would withstand the thermal runaway of an adjacent cell. Once the water evaporates and the matrix material of the hydrogel decomposes, neighboring cells can come into direct contact with each other. In the embodiment where the hydrogel is contained in a container, the cells are not in direct contact with each other; however, the container walls, made of a solid material, form a thermal bridge across which the thermal event can propagate after the water contained in the hydrogel has evaporated.

[0007] CN 105 169 613 A also recommends the use of hydrogel comprising 0.5-40 parts by mass of hydrogel material and at least 50 parts by mass of water in lithium batteries. More precisely, the hydrogel is applied to the packaging elements of the lithium battery. Object of the invention

[0008] Based on this prior art, the object of the present invention was to provide a barrier with a dimensionally stable, heat-absorbing material that is at least as effective in preventing the propagation of a thermal event within a multi-cell battery module as conventional barriers. In particular, a barrier was to be developed that can also effectively compensate for expansion effects of battery cells. Furthermore, a corresponding battery module was to be specified. The present invention also aimed to provide a method for producing such a barrier. Summary of the invention

[0009] This problem is solved by the barrier according to claim 1, the use of a barrier according to claim 11, the battery module according to claim 12 and the method according to claim 14.

[0010] According to the invention, a barrier for preventing the propagation of a thermal event within a multi-cell battery module is provided, comprising a heat-absorbing protective layer containing 70.0 - 97.5 wt.% of a hydrogel and 2.5 - 30.0 wt.% of a reinforcing filler material, wherein the hydrogel comprises a matrix material and water, and the reinforcing filler material is dispersed in the hydrogel, and wherein the reinforcing filler material is a particulate material.

[0011] Due to its high hydrogel content, the heat-absorbing protective layer can absorb heat particularly effectively and thermally insulate adjacent cells within the battery module. The higher the hydrogel content, the greater the amount of water it contains, which evaporates, generating heat, and thus the better the heat dissipation.

[0012] A reinforcing filler material within the meaning of the present invention is understood to be a particulate material. The particulate material can be free-flowing and / or pourable, in particular as a powder or granules. Accordingly, a pre-formed structure, for example a support matrix in the form of a lattice structure and / or honeycomb structure, does not fall under the term "reinforcing filler material".

[0013] The presence of at least 2.5 wt% of a reinforcing filler material ensures the dimensional stability of the heat-absorbing protective layer. This dimensional stability is particularly evident in the fact that the heat-absorbing protective layer is self-supporting. At the same time, the maximum filler content of 30 wt% ensures that the protective layer retains a certain degree of flexibility.

[0014] Furthermore, the reinforcing filler material can prevent the formation of thermal bridges between adjacent cells in the battery module. Due to its dispersion, the filler material is statistically distributed within the heat-absorbing protective layer and can still act as an insulator between adjacent cells even after the water has evaporated and the matrix material has decomposed in the event of a thermal event.

[0015] In a preferred embodiment, the heat-absorbing protective layer in the barrier according to the invention contains 70.0 - 95.0 wt.% of a hydrogel and 5.0 - 30.0 wt.% of a reinforcing filler material.

[0016] The addition of 5 to 30 wt% reinforcing filler material minimizes water leakage from the hydrogel during thermal cycling (freezing / thawing) of the barrier. This makes the barrier suitable for use in batteries and battery modules installed outdoors and exposed to winter conditions.

[0017] In particular, the heat-absorbing protective layer in the barrier according to the invention contains 80.0 - 92.5 wt.% of a hydrogel and 7.5 - 20.0 wt.% of a reinforcing filler material.

[0018] The reinforcing filler material preferably consists of particles with an aspect ratio in the range of 0.5 to 10, the aspect ratio being measured according to ISO standard 9276-6. Particularly preferably, the reinforcing filler material consists of spherical particles.

[0019] In one embodiment, the particles are inorganic. Preferably, the particles have a mean particle size d 50 of 1 nm to 5 mm, more preferably of 100 nm to 5 mm, and in particular of 1000 nm to 2 mm, wherein the mean particle size d 50 is measured according to ISO standard 13320-1.

[0020] The heat-absorbing protective layer can be wrapped or enclosed in a water vapor-impermeable film, for example, shrink-wrapped. Unlike conventional propagation barriers, however, packaging in a film is not necessary to prevent unwanted spread of the hydrogel. The film is only intended to protect the heat-absorbing protective layer from long-term water loss, thus counteracting water diffusion loss.

[0021] The water vapor-impermeable film is preferably a polymer film, a metal film, or a laminate of the aforementioned films, particularly preferably with a film thickness of less than 0.3 mm, and especially less than 0.2 mm. The polymer film can be selected, for example, from the group consisting of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polyphenylene sulfide (PPS), ethylene tetrafluoroethylene copolymer (ETFE), polyurethanes (PU), polyamides (PA), polyesters, in particular polyethylene terephthalate (PET), and combinations thereof. The metal film is preferably an aluminum foil.

[0022] In an advantageous embodiment, the matrix material consists of at least 85% by weight of a natural polymer. The natural polymer is preferably based on biogenic raw materials. For the purposes of this invention, the term "biogenic raw materials" includes organic raw materials produced in agriculture and forestry or isolated from bacterial, yeast, fungal, aqua, or marine cultures, as well as organic raw materials of animal origin, namely those that are generated as a by-product of animal slaughter and require utilization. Furthermore, "biogenic raw materials" for the purposes of this invention are biodegradable according to DIN EN 13432. Biogenic raw materials are contrasted with fossil raw materials and petrochemical-based energy carriers, including substances obtained through chemical synthesis processes and / or those that are not biodegradable.

[0023] Preferably, the matrix material consists of at least 85 wt% of a natural polymer selected from the group consisting of alginate, agar-agar, starch, starch derivatives, κ-carrageenan, i-carrageenan, pectin, gellan, scleroglucan, and combinations thereof.

[0024] Although the origin and composition of the aforementioned polysaccharides are known to those skilled in the art, individual polysaccharides will be discussed in more detail below: Alginate is the main structural component of the cell walls of brown macroalgae. It is a linear copolymer of the uronic acid β-D-mannuronate (M) and its C-5 epimer α-L-guluronate (G), comprising homopolymeric blocks of 1,4-linked consecutive M units (polyM) or G units (polyG), or blocks of alternating M and G units (polyMG). Alginate can exist in the form of its salts, e.g., alkali or alkaline earth metal salts, or in esterified form, e.g., as an alkyl ester, such as a methyl ester.

[0025] Agar-agar is also obtained from the cell walls of algae, e.g., from blue-green or red algae. It essentially corresponds to a mixture of the polysaccharides agarose and agaropectin, with agarose preferably comprising 60-80 wt.% of the mixture. Agarose is a polysaccharide composed of D-galactose and 3,6-anhydro-L-galactose linked by glycosidic bonds. Agaropectin is a polysaccharide composed of β-1,4- and α-1,3-glycosidically linked D-galactose and 3,6-anhydro-L-galactose. Approximately one in ten galactose residues is esterified at O-6 with sulfuric acid and contains additional sulfate residues. Agar-agar is a particularly preferred naturally occurring gelling agent within the meaning of the present invention. The reason for this is that an agar-agar-based hydrogel is dimensionally stable at temperatures below approximately 85°C and only releases water above this temperature.

[0026] κ-Carrageenan consists of repeating monomers of D-galactose-4-sulfate and 3,6-anhydro-D-galactose. ε-Carrageenan differs from κ-carrageenan only in that the 3,6-anhydro-D-galactose unit carries an additional sulfate group at the C-2 position. Both carrageenans occur naturally as a basic component of the cell walls of a variety of red algae.

[0027] Gellan is a polysaccharide comprising a repeating unit consisting of one rhamnose, one glucuronic acid, and two glucose base units esterified with acetic and glyceric acids. It can be produced, for example, by the fermentation of carbohydrates by the bacterial strain glycerol. Pseudomonas elodea be manufactured.

[0028] Scleroglucan is a β-1,3-glucan that, on average, carries a glucose residue as a side chain on every third sugar. Scleroglucan is primarily obtained from fungal cultures.

[0029] The matrix material of the hydrogels can consist of at least 85 wt.%, preferably at least 95 wt.%, particularly preferably at least 99 wt.%, calcium alginate.

[0030] The matrix material can further comprise up to 15 wt.%, preferably up to 5 wt.%, and particularly up to 1 wt.%, of a thickening agent. Adding a thickening agent allows the mechanical properties of the heat-absorbing protective layer to be adjusted over an even wider range. In particular, flexibility and compressibility can be tailored as desired, taking into account the requirements of the specific application. This is advantageous, for example, to compensate for expansion effects of the battery cells that can occur during charging and discharging and due to aging.

[0031] The thickening agent is preferably selected from the group consisting of cellulose derivatives, in particular hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose and / or carboxycellulose, guar gum, xanthan gum or mixtures thereof. These materials are also "biogenic raw materials" and are part of a sustainable approach to battery production. In particular, they contribute to improving the CO₂ balance associated with the barrier production process.

[0032] The reinforcing filler material is preferably selected from the group consisting of hydroxyapatite, calcium carbonate, calcium sulfate, aluminum oxide, magnesium oxide, hydrates of the aforementioned substances, and mixtures thereof. The aforementioned materials have low thermal conductivity and are available in suitable particle sizes. If hydrates are used as fillers, the heat-absorbing property of the protective layer is further enhanced, since the water of crystallization can also absorb heat and evaporate.

[0033] The hydrogel can contain or consist of 5–30 wt% matrix material and 70–95 wt% water. Particularly preferably, the hydrogel contains or consists of 5–20 wt% matrix material and 80–95 wt% water.

[0034] The heat-absorbing protective layer has a thickness of 0.25–10.0 mm, preferably a thickness of 1.5–3.0 mm, and particularly a thickness of 1.5–2.5 mm. This ensures that the barrier occupies as little space as possible within the battery module while still fulfilling its function of thermally shielding the battery cells from each other after installation in a battery module.

[0035] To further adjust the compressibility, openings can be incorporated into the heat-absorbing protective layer. In a state without external force acting on the propagation barrier, these openings are recesses or holes in the protective layer—i.e., cavities that are not filled with material. When force is applied, the material mixture of which the protective layer consists can be displaced into the cavities of the openings. This results in a high compressibility of the protective layer compared to a solid material. Reversible and irreversible volume changes of the battery cells contained within a battery module can be compensated for.

[0036] The volume fraction of the penetration openings in the protective layer is preferably between 1% and 90%, more preferably between 8% and 80%, particularly preferably between 10% and 75%, and especially between 20% and 60%.

[0037] Each passage opening preferably has a cross-sectional area of ​​0.025 mm² - 50.0 mm², more preferably of 0.5 mm² - 8.0 mm², and in particular of 2.0 mm² - 5.0 mm².

[0038] The cross-sectional area can be identical for all openings, but it doesn't have to be. It should be noted that an identical cross-sectional area for all openings may simplify the manufacturing process.

[0039] The penetration openings can have cross-sectional shapes selected from the group consisting of circular, elliptical, superelliptical, star-shaped, slit-shaped, crescent-shaped, rhomboid, polygonal, and combinations thereof. The use of non-circular cross-sections leads to specific force-displacement or force-compression curves of the propagation barrier. For example, by using star-shaped penetration openings, a force-displacement curve can be realized in which a certain compression level is reached with very little force, but then considerably more force is required to compress the barrier further.

[0040] In a preferred embodiment, the penetration openings are unevenly distributed, in particular such that in a first region, which is closer to the center of the propagation barrier than to its edge, there is an area density ρ1 of penetration openings, and in a second region, which is closer to the edge of the propagation film than to its center, there is an area density ρ2 of penetration openings, where ρ1 ≠ ρ2. Generally, the distribution of the penetration openings in the protective layer should be adapted to the structure and geometry of the battery module. This means that the higher area density of penetration openings is present where the adjacent battery cells exhibit greater reversible and irreversible expansion during operation. Within the scope of the present invention, area density is understood to be the proportion of the cross-sectional area of ​​penetration openings relative to a surface element of the propagation barrier.

[0041] Furthermore, the cross-section of the penetration openings can be constant across the thickness of the protective layer, or alternatively, it can either taper or widen.

[0042] It is evident from the above that a further aspect of the present invention is the use of the barrier to compensate for volume fluctuations within a battery module. These volume fluctuations can be due to reversible dilation effects during charging and discharging processes or to irreversible dilation effects due to the aging of the battery cells.

[0043] The invention also provides a battery module comprising several battery cells and at least one of the barriers described above. The barrier is preferably arranged between two adjacent battery cells in the battery module.

[0044] Since lithium-ion cells are particularly susceptible to thermal runaway, it is still advantageous if the battery cells in the battery module are lithium-ion cells.

[0045] Finally, the invention also provides a method for producing the barrier according to the invention. In the method, a heat-absorbing protective layer is first produced, wherein the production of the heat-absorbing protective layer comprises the following steps i) - iii): i) Sodium alginate powder, a reinforcing filler material and water are mixed to form a viscous mass, ii) the mass is poured onto a flat surface or into a mold with a flat bottom, and iii) the poured mass is wetted with or immersed in a calcium ion-containing solution.

[0046] The hardened mass can then be dabbed dry and wrapped in a water vapor-impermeable film and / or sealed. This manufacturing process is simple and requires no expensive equipment. Furthermore, the process has a low CO2 footprint. Description of preferred embodiments

[0047] Preferred embodiments of the invention are explained in more detail with reference to the figures and the following example, without limiting the invention thereto. In particular, the following example describes only one manufacturing method for the barriers according to the invention. It can be assumed that industrial production of the barriers by extrusion is also possible. Figure 1Figure 5 shows the arrangement of a barrier 3 according to the invention in a battery (test) module comprising two battery cells 1 and 2. 5a and 5b are thermal insulation components which, after the proactive triggering of the thermal event, prevent some of the released thermal energy from being absorbed by the clamping plates 6a and 6b, which have a certain heat capacity. This avoids measurement errors. The clamping plates ensure the mechanical cohesion of the module. The measuring points, where a temperature measurement is taken, are located on the front and back of each cell. Figure 2 Figure 1 shows the temperature profile of cells 1 and 2 after nail penetration of cell 1. The temperature profile indicates that the barrier 3 according to the invention successfully thermally shields cell 2. This prevents cell 2 from reaching the critical temperature. Example: 1) Production of the barrier according to the invention

[0048] 80 wt% water, 15 wt% sodium alginate, and 5 wt% filler (calcium carbonate) are mixed for approximately 3 minutes. The resulting mixture is applied to a shallow, open mold approximately 2.3 mm thick. The 2.3 mm thick mixture, along with the mold, is immersed in an aqueous CaCl₂ solution (5 wt%) for 30 seconds. This creates a heat-absorbing protective layer comprising a flexible, homogeneous hydrogel 2.6 mm thick. Compared to the dimensions of the mold in which the mixture was applied, the heat-absorbing protective layer exhibits a shrinkage of approximately 5% in both length and width. The protective layer contains approximately 80 wt% water.

[0049] Finally, the protective layer is sealed in a water vapor impermeable film (film thickness 0.15 mm). 2) Nail penetration test

[0050] The manufactured barrier was placed in the space between two fully charged, 40 Ah prismatic NMC 111 cells. The arrangement corresponds to the illustration in Figure 1 Subsequently, thermal runaway of cell 1 was induced by penetration with a nail. The temperature development at the front and back of both cells was measured and recorded for a duration of 7000 seconds (see Figure 1). Fig. 2 The barrier prevented the thermal transfer from cell 1 to cell 2.

Claims

1. A barrier for preventing propagation of a thermal event within a multi-cell battery module, comprising a heat-absorbing protective layer containing 70.0 - 97.5% by weight hydrogel and 2.5 - 30.0% by weight reinforcing filling material, wherein the hydrogel comprises a matrix material and water and the reinforcing filling material is dispersed in the hydrogel and wherein the reinforcing filling material is a particle-shaped material.

2. The barrier according to claim 1, wherein the protective layer is enclosed in a foil impermeable to water vapor, the foil impermeable to water vapor preferably being a polymer foil, a metal foil or a laminate of the aforementioned foils, wherein the polymer foil is more preferably selected from the group consisting of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polyphenylene sulfide (PPS), ethylene-tetrafluoroethylene copolymer (ETFE), polyurethanes (PU), polyamides (PA), polyesters, in particular polyethylene terephthalate (PET), and combinations thereof and more preferably wherein the metal foil is aluminum foil.

3. The barrier according to claim 1 or 2, wherein the matrix material consists of at least 85 % by weight natural polymer, wherein said natural polymer is preferably selected from the group consisting of alginate, agar-agar, starch, starch derivatives, κ-carrageenan, i-carrageenan, pectin, gellan, scleroglucan, and combinations thereof.

4. The barrier according to one of the preceding claims, wherein the matrix material consists of at least 85% by weight, preferably at least 95 % by weight, particularly preferably at least 99% by weight, calcium alginate.

5. The barrier according to any one of the preceding claims, wherein the matrix material further comprises up to 15% by weight thickener, wherein the thickener is preferably selected from the group consisting of cellulose derivatives, in particular hydroxyethyl cellulose; hydroxypropyl cellulose; hydroxypropylmethylcellulose and / or carboxycellulose, guar gum, xanthan gum, or mixtures thereof.

6. The barrier according to any one of the preceding claims, wherein the reinforcing filling material is selected from the group consisting of hydroxyapatite, calcium carbonate, calcium sulfate; aluminum oxide, magnesium oxide, hydrates of the aforementioned substances, and mixtures thereof.

7. The barrier according to any one of the preceding claims, wherein the hydrogel contains 5 - 30 % by weight matrix material and 70 - 95% by weight water.

8. The barrier according to any one of the preceding claims, wherein the protective layer has a thickness of 0.25-10.0 mm, preferably a thickness of 1.5-3.0 mm.

9. The barrier according to any one of the preceding claims, wherein the heat-absorbing protective layer has passage openings, wherein the volume proportion of the passage openings in the protective layer is preferably between 1% and 90%, more preferably between 8% and 80%, particularly preferably between 10% and 75%, in particular between 20% and 60%.

10. The barrier according to any one of the preceding claims, wherein the heat-absorbing protective layer has passage openings, wherein each passage opening preferably has a cross-sectional area of 0.025 mm2-50.0 mm2, more preferably of 0.5 mm2-8.0 mm2, in particular of 2.0 mm2-5.0 mm2.

11. Use of a barrier according to any one of claims 9 and 10 for compensating for volume fluctuations within a battery module.

12. A battery module comprising a plurality of battery cells and at least one barrier according to any one of claims 1 to 10, wherein the barrier is arranged between two adjacent battery cells.

13. The battery module according to claim 12, wherein the battery cells are lithium-ion cells.

14. A method of manufacturing a barrier according to any one of claims 1 to 10, in which a heat-absorbing protective layer is produced by i) mixing sodium alginate powder, a reinforcing filling material and water to form a viscous mass, ii) pouring the mass onto a flat surface or into a mold with a planar bottom, and iii) wetting the cast mass with a solution containing calcium ions or immersing it in a solution containing calcium ions.