Test stand for evaluating materials for use in batteries and test method using the test stand

Abstract

The present invention relates to a test stand (1) for evaluating materials used in batteries under conditions that may occur during thermal runaway, the test stand (1) comprising a honeycomb housing (10) having a hexagonal housing base (11), wherein at least one activatable start cell (31) and a plurality of cylindrical battery cells (32, 33, 34, 35, 36) are arranged in the internal space (15) of the housing (10), the material to be evaluated is arranged in the internal space (15) or on the housing (10), the start cell (31) and the battery cells (32, 33, 34, 35, 36) are arranged in a honeycomb pattern, and in the honeycomb pattern, each cell (30) not located at the boundary of the honeycomb pattern has six adjacent cells located at the corners of a regular hexagon having a side length corresponding to the distance A between the cell (30) and the adjacent cell. The present invention also relates to a test method using the test stand (1).

Description

Technical Field

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[0003]

[0001] The present invention relates to a test stand for evaluating materials that can be used in batteries under conditions that can occur during thermal runaway.

Background Art

[0002] Today, high-voltage batteries are used in a number of applications, particularly those related to electromobility. For this purpose, individual battery cells are assembled into larger battery arrays. Individual battery cells are often designed as cylindrical battery cells and are arranged adjacent to and in proximity to each other within a battery housing and connected in series and / or in parallel. Depending on the number and type of battery cells used, the battery can thus store an amount of energy that enables electric driving for several hundred kilometers without intermediate charging.

Summary of the Invention

Problems to be Solved by the Invention

[0003] A local short circuit between the internal electrodes of a battery cell causes a high short-circuit current that heats the battery cell extremely rapidly. Thermal heating, due to external mechanical damage or thermal overheating, such as a failure of the battery cooling system, can also cause extreme heating or thermal runaway of the battery cell. This thermal runaway of the battery cell can easily or rapidly spread to adjacent battery cells. This causes a chain reaction, whereby the energy stored in the battery is explosively released. This explosive release of energy is also called thermal propagation and can be accompanied by toxic gases as well as the formation of flames and sparks.

[0004] To reduce the risk of heat transfer, it is known from the prior art to provide materials with low thermal conductivity, high dielectric strength, and high heat resistance (fire resistance) between individual battery cells. For example, from EP3753056B1, it is known to embed individual battery cells in a potting compound consisting of polyurethane foam with a high proportion of flame retardant. Preferably, the polyurethane foam has a flame retardancy of level V0 as measured according to the UL94 test for flammability of plastics.

[0005] UL94 testing is performed with an open flame. The classification determined during the test (e.g., level V0) has limited value regarding the suitability of materials for use in batteries, with the aim of avoiding heat transfer as much as possible, because the test conditions differ significantly from those of batteries. Therefore, materials such as potting compounds made from polyurethane are also tested in batteries where heat transfer in the battery cells is initiated. However, this is done in non-standard arrangements or methods, as each battery manufacturer uses its own battery design for the test stand. Therefore, the test results of initiated thermal runaway obtained in this way cannot be directly compared to one another.

[0006] Therefore, the present invention is based on the objective of providing a test stand for materials usable in batteries that ensures a good balance between the effort (cost, working time, test environment) and benefits related to material evaluation in the event of thermal runaway. [Means for solving the problem]

[0007] The fundamental objective of the present invention is achieved by the combination of features described in claim 1. Examples of embodiments of the present invention can be taken from the dependent claims to claim 1.

[0008] According to the present invention, a test stand for evaluating materials used in batteries under conditions that may occur during thermal runaway comprises a honeycomb-shaped housing having a hexagonal housing base, wherein at least one activateable start cell and a plurality of battery cells are arranged in the internal space of the housing, the material to be evaluated is arranged in the internal space or on the housing, the start cell and the battery cells are arranged in a honeycomb pattern, and the honeycomb pattern has six adjacent cells, each located at a corner of a regular hexagon with a side length corresponding to the distance A between the cell and the adjacent cell.

[0009] By arranging battery cells in a honeycomb pattern, the impact of thermal runaway on surrounding adjacent cells can be investigated in a very compact arrangement. The honeycomb pattern preferably extends parallel to the housing base, which should be located in the XY plane. Perpendicular to the XY plane, the battery cells may extend in the Z direction. The battery cells preferably have a cylindrical shape with a longitudinal axis and a circular cross-section. The length L of the battery cell can be 3, 5, or 7 times greater than the maximum spatial dimension perpendicular to the longitudinal axis. In the case of a battery cell with a circular cross-section, the maximum spatial dimension perpendicular to the longitudinal axis corresponds to the diameter D.

[0010] In a preferred embodiment, the spatial dimensions of the battery cells correspond to the spatial dimensions of the starter cell. For example, if the battery cells are cylindrical, the starter cell can also be cylindrical with the same length and diameter D. This ensures a realistic test environment, as heat transfer in an actual battery originates from the (defective) battery cells and is simulated in the test by the activatable starter cell.

[0011] Due to the honeycomb pattern, the initiation cell has 6 neighboring cells, each neighboring cell located at the same distance A from the initiation cell. Therefore, when the initiation cell is activated, all 6 neighboring cells are equally affected by the energy released by the initiation cell. In an example of a preferred embodiment, the initiation cell is located at the center of the honeycomb pattern, and 6n n-th order battery cells, n=1, 2, 3, ... N, are arranged around the initiation cell, with the distance between the initiation cell and the n-th order battery cells corresponding to n times A. In an example of one embodiment, N is equal to 5, resulting in 6 primary battery cells, 12 secondary battery cells, 18 tertiary battery cells, 24 quaternary battery cells, and 30 quintic battery cells. The secondary battery cells are arranged in a regular hexagon with side lengths equal to 2A. The 12 battery cells are located at the 6 corners of the hexagon and in the center between each of the 6 corners. The fifth-tier battery cells are arranged in the outermost hexagon, each side having a length of 5A. Together with the centrally located start cell, the honeycomb pattern of this embodiment thus has a total of 91 cells.

[0012] The initial tests showed that higher-order or additional battery cells located at a distance greater than 5A from the starting cell were not affected by heat transfer from the centrally located starting cell. Therefore, these additional battery cells can be omitted for cost reasons, as they do not provide additional findings when evaluating the test results. The honeycomb-shaped housing allows for a compact encasing of the honeycomb pattern. Naturally, depending on the type of battery cell, the distance A between battery cells, and the material being tested on the test stand, more or fewer batteries than the fifth order can be provided.

[0013] Theoretically, since the honeycomb pattern provides the same geometric state in all directions of the XY plane, heat propagation in the XY plane continues uniformly in all directions. This facilitates the evaluation of the obtained test results and allows for comparative observation of heat propagation in different directions.

[0014] The material being tested and evaluated on the test bench may be an insulating material that can be placed between individual battery cells. The insulating material may be a curable potting compound poured into the gaps between battery cells. However, the material being evaluated may also be a material surrounding conduits in a battery cooling system that can be used to cool individual battery cells. Materials for embedding battery cooling conduits typically have a higher thermal conductivity than the insulating material between battery cells.

[0015] The housing may have six side walls extending vertically from the housing base toward the housing opening. The test stand may include a cover that can close the housing opening. The material for the seal between the cover and the housing or the coating of the cover can also be tested for suitability in the battery by the test stand according to the present invention.

[0016] The housing can be made from metal. Other materials for the housing include, for example, plastic or reinforced plastic.

[0017] Pressure limiting means can be provided to restrict the pressure spreading within the internal space of the housing. During thermal runaway or heat transfer, very high pressures can be generated in the internal space, and this pressure can be limited, for example, by a pressure relief valve. Another inexpensive version of pressure limiting means is a plug made of rock wool. Rock wool ensures continuous pressure equalization and good insulation, as well as preventing excessive heat loss through the plug, allowing for a realistic replica of the actual battery conditions. Pressure limiting means can be mounted on the housing and / or cover.

[0018] For example, a plate-shaped cell holder with several centering means in the shape of round holes can be provided in the housing, through which the position of the starting element and the position of the battery cell are determined. One cell is inserted into each hole so that the cell holder defines a honeycomb pattern. Preferably, the cell holder is located close to or on the housing base. The cell holder preferably has a hexagonal basic shape so that it can be inserted into the housing with little play. The plate-shaped cell holder can be made from plastic and can be manufactured by a 3D printer.

[0019] Metal plates may be provided at the ends of battery cells facing away from the base of the housing. The metal plates in the housing of the test stand are intended to represent the wiring or interconnections of the battery cells in the battery (busbar). Like the battery cell wiring / interconnections, the metal plates have high thermal conductivity. The metal plates may have openings for receiving or securing the battery cells.

[0020] Insofar as the focus is on investigating insulating materials placed between two adjacent cells, and thus capable of reporting on heat transfer between cells, the test stand according to the present invention can also be used to investigate heat transfer between two battery modules. In a battery module, several battery cells are housed in a module carrier, which further protects the battery cells located within it.

[0021] In one embodiment, a first group of cells is housed in a first module carrier, and a second group of cells is housed in a second module carrier. The first module carrier may comprise a trapezoidal carrier base having a longer base edge, a shorter base edge parallel to the longer base edge, and two legs. The lengths of the shorter base edge and the legs approximate the length of one edge of a hexagonal housing base. The first module carrier can be positioned in the internal space of the housing and can cover about half of the hexagonal housing base when in the insertion position. The second module carrier preferably has the same structure as the first module support and can also be positioned in the internal space such that the two longer base edges of the two module supports face each other. One or more start cells can be placed in one of the module carriers. A test stand can then be used to investigate the extent to which heat propagation spreads from the module carrier with the start cells to the other module carrier.

[0022] At least two temperature sensors may be provided, positioned at different distances from the start cell within the internal space of the housing. The temperature sensors preferably record the time course of the temperature from the time of activation of the start cell. Comparing the time courses of temperature sensors at different locations allows for important conclusions about how heat propagation spreads internally. For example, several temperature sensors may be arranged in a row, so that the first temperature sensor is positioned between the start element and the primary battery cell, and the second temperature sensor is positioned between the primary and secondary battery cells, and so on.

[0023] In one embodiment, at least one of the temperature sensors protrudes vertically from below through an opening in the housing base, thereby its height in the internal space can be fixed by screw connections. The height of the temperature sensor means the height at which the temperature is measured. If the temperature sensor is, for example, a thermocouple with a measuring tip, the height of the measuring tip corresponds to the height of the temperature sensor.

[0024] The test stand can have several feet by which the housing is supported such that free space remains between the housing base and the ground on which the test stand stands. This free space can be used for the attachment and placement of temperature sensors, which can protrude downward through the housing base.

[0025] The provision of a method for testing a material that can be used in a battery, which is a further object of the present invention, is achieved by the combination of features according to claim 14.

[0026] The method for testing a material according to the present invention includes the use of the test stand described herein, at least one starting cell is activated to initiate thermal runaway, the temperatures measured by at least two temperature sensors during thermal runaway are recorded, and after the test operation, the state of the individual battery cells and the time course (time curve) of the measured temperatures are evaluated.

Brief Description of the Drawings

[0027] The present invention will be described in more detail with reference to the embodiments shown in the drawings.

[0028] [Figure 1] The test stand according to the present invention is schematically shown. [Figure 2] It is a view along the line II-II of FIG. 1. [Figure 3] The arrangement of the battery cell and the starting cell is shown. [Figure 4] An alternative arrangement of the battery cells and the starting cell of two module carriers is shown. [Figure 5] A further example of the embodiment in the longitudinal section is shown. [Figure 6] The arrangement of the battery cell, the starting cell and the temperature sensor is shown. [Figure 7] The housing base provided with holes for the temperature sensors is shown.

Modes for Carrying Out the Invention

[0029] Figures 1 and 2 schematically show a test stand 1 comprising a metal housing 10 having a hexagonal housing base 11. The basic shape of the hexagonal housing base 11 corresponds to a regular hexagon. The housing 10 has six sidewalls 12 (12a to 12e) extending perpendicularly from the housing base 11 toward the housing opening 13. The housing opening 13 can be closed by a hexagonal cover 20. To secure the cover 20, a housing flange 14 is provided, which makes the cover 20 flat when the housing opening 13 is closed. Fastening means, for example in the form of screws and nuts, which can firmly connect the cover 20 and the housing flange 14 to each other, are not shown. The cover 20 has a pressure relief valve 21 so as to limit the pressure in the internal space 15 of the housing 10 upward. Additionally or alternatively, the pressure relief valve 21 can be mounted on the housing base 11 or one of the sidewalls 12.

[0030] In Figure 2, which shows a diagram along line II-II in Figure 1, components that can be placed in the internal space 15 of the housing 10 are not shown, although they are only shown by dashed lines in Figure 1.

[0031] Figure 3 shows the housing 10 viewed from above, with the housing flange 14 not shown here. A number of cylindrical cells 30 are arranged in a honeycomb pattern within the housing 10. Each cell has the same diameter D.

[0032] The cylindrical starting cell 31 is located at the center of the honeycomb pattern. Six adjacent cells, shaped like primary battery cells 32, are arranged around the starting cell 31, located at the corners of a regular hexagon, each having a distance A from the starting cell 31 (in the honeycomb pattern, every cell 30 has a distance A from its neighbors). In this embodiment, distance A corresponds to the diameter D of the cell 30. Distance A can be greater than the diameter D, resulting in adjacent cells 30 being spaced apart with gaps between them. For example, distance A can be between 1.0 and 1.3 times the diameter D.

[0033] Six primary battery cells 32 are surrounded by twelve secondary battery cells 33 arranged in a hexagon, connected radially outward. Following the secondary battery cells 33 are tertiary battery cells 34, quaternary battery cells 35, and quinary battery cells 36.

[0034] Energy can be supplied to the starting cell 31, causing it to heat up. This simulates thermal runaway in this cell. The temperature rise in the starting cell 31 also triggers thermal runaway in the primary battery cell 32, resulting in a chain reaction in a honeycomb pattern, affecting other battery cells through this heat transfer. The scale on the left side of Figure 3 shows that lower-order battery cells are more affected by heat transfer than higher-order battery cells.

[0035] With the test stand 1 and cells 30 arranged in a honeycomb pattern, for example, the effect of the material filling the gaps between cells on heat propagation can be investigated. If the material has very low thermal conductivity and high heat resistance (fire resistance), a simulated thermal runaway in the centrally located cell 30 (see starting cell 31) will not damage all cells 30 in the honeycomb pattern in the same way, but for example, the primary battery cells 32 and secondary battery cells 33 will be completely affected, while the higher-order battery cells will be only partially or slightly affected.

[0036] Figure 4 shows a housing 10 in which a first battery module 40 and a second battery module 41 are housed in an internal space 15. The first battery module 40 has a tray-shaped first module carrier 42 with a trapezoidal carrier base. The carrier base has a longer base edge portion 43, a shorter base edge portion 44, and two legs 45, 46 connecting the two mutually parallel base edge portions 43, 44. Four start cells 31 are arranged in a row adjacent to each other on the module carrier 42 of the first battery module 40. Twelve primary battery cells 32 surround these four start cells 31. Again, the cells 30 are arranged in a honeycomb pattern, which allows the cells 30 to be placed at equal intervals from directly adjacent cells. Secondary, tertiary, and quaternary battery cells 33, 34, 35 are also arranged on the module carrier 42.

[0037] The second module carrier 47 of the second battery module 41 has the same structure as the first module carrier 42 of the first battery module 40. Only cells 30 that were not actually affected by heat propagation after the simulated thermal runaway in the first battery module 40 are placed in the module carrier 47 of the second battery module 41. Using this test setup, the protective effect of the battery module can be checked in the test stand according to the present invention.

[0038] Figure 5 shows a longitudinal cross-section of another embodiment in which the cells 30 are arranged in a honeycomb pattern with a central start cell 31 again within the internal space 15 of the housing 10. In addition to the central start cell 31, the honeycomb pattern has primary battery cells 32, secondary battery cells 33, tertiary battery cells 34, and quaternary battery cells 35. A plate-shaped cell holder 50 rests on the housing base 11 and is provided with a plurality of round openings 51. The openings 51 are arranged in the honeycomb pattern. A single battery cell 30 can be inserted into these openings 51 so that the plate-shaped cell holder 50 determines the position of the battery cell. The plate-shaped cell holder 50 can be made from plastic.

[0039] The metal plates 60 are provided at the ends of each cell 30, far from the base 11 of the housing. The metal plates have a plurality of stepped openings 61. The metal plates 60 are intended to simulate the wiring or metal interconnections between the individual cells 30. In the case of heat transfer starting from a defective battery cell, a very large amount of heat can be transferred to other cells 30, particularly through thermally conductive metal wiring. In the test stand according to the present invention, this effect is simulated by the metal plates 60.

[0040] The cover 20 has a circumferential seal 22. This circumferential seal 32 can also be used to investigate how well the material of the circumferential seal 22 can withstand the general conditions (temperature, pressure, fire resistance) during heat transfer.

[0041] Figure 5 also shows that the housing base 11 is provided with an opening 16, through which a line 37, indicated by a dashed line, can activate or control the start cell 31.

[0042] Figure 6 shows the cells 30 of Figure 5 in a honeycomb pattern viewed from above. Here again, it can be seen that the distance A between the longitudinal central axes of two adjacent cells 30 is greater than the diameter D. Each of the same-order battery cells can be assigned to a regular hexagon, and the battery cells are placed at either the corners or sides of that hexagon. The hexagon of the primary battery 32 has a side length of A. The side length of the hexagon of the n-th-order battery cell is n times A (n=1,2,3,4). It should be noted that Figures 5 and 6 are not displayed to actual scale. For example, the distance A can be in the range of 1.02 to 1.07 times D.

[0043] The temperature sensor 70 is placed in the gaps between the individual battery cells 30, here on a straight line 71, at a different distance from the start cell 31. Using the temperature sensor 70, preferably one that records a temperature curve over time starting from the activation of the start cell 31, heat propagation can be measured as a function of time. Alternatively or additionally, the temperature sensor may also be placed on another line, for example on a dotted line 72, incidentally showing the line of intersection with the longitudinal cross-section in Figure 5.

[0044] Figure 1 shows that the temperature sensors can be positioned to measure the temperature at different heights relative to the plane of the housing base 11. This makes it possible to collect data not only on heat propagation in the XY plane (the plane parallel to the housing base 11) but also on heat propagation in the Z direction, i.e., the direction perpendicular to the XY plane.

[0045] An opening 17 (see Figure 7) can be provided in the base 11 of the housing to accommodate the temperature sensor 70, through which the temperature sensor is inserted from below through the base 11 of the housing (see also Figure 1). The height of each temperature sensor 70 can be precisely adjusted, for example, by screw connections. The hole pattern for the temperature sensors shown in Figure 7 corresponds to a test setup as shown in Figure 4, through which the performance of the battery module is tested.

[0046] To leave free space for the temperature sensor 70 between the housing base 11 and the ground 2 on which the test stand 1 stands, the feet 18 are preferably located at the corners of the hexagonal housing. Since high temperatures may be generated inside the housing 10 during testing, the feet 18 also ensure the necessary distance from the substrate 2 so as not to be damaged by the heat inside the housing. [Explanation of Symbols]

[0047] 1 Test stand 2 ground 10 Housing 11 Housing Base 12 Side wall sections (12a to 12f) 13 Housing opening 14 Housing flange 15 Interior space 16 Opening 17 Opening 18 Foot 20 Covers 21 Pressure limiting means / pressure relief valve 22 stickers 30 cells 31 Starting cell 32 primary battery cells 33 secondary battery cells 34 tertiary battery cells 35 quad-stage battery cells 36 5th generation battery cells 37 lines 40. First Battery Module 41. Second Battery Module 42. First Module Carrier 43 Longer base edge section 44 Shorter base edge section 45 Legs 46 Legs 47. Second Module Carrier 50 Cell Holder 51 Opening 60 metal plates 61 Stepped opening 70 Temperature Sensor 71 Straight line 72. Straight lines

Claims

1. A test stand (1) for evaluating materials used in batteries under conditions that may occur during thermal runaway, the test stand (1) comprising a honeycomb housing (10) having a hexagonal housing base (11), wherein at least one activatable start cell (31) and a plurality of cylindrical battery cells (32, 33, 34, 35, 36) are arranged in an internal space (15) of the housing (10), the material to be evaluated is arranged in the internal space (15) or on the housing (10), the start cell (31) and the battery cells (32, 33, 34, 35, 36) are arranged in a honeycomb pattern, the honeycomb pattern wherein each cell (30) not located at the boundary of the honeycomb pattern has six adjacent cells located at the corners of a regular hexagon having a side length corresponding to the distance A between the cell (30) and the adjacent cell. Test stand (1).

2. The start cell (31) is located at the center of the honeycomb pattern, and 6n nth-order battery cells (32, 33, 34, 35, 36) having n = 1, 2, 3, ... are arranged around the start cell (31), and the distance between the start cell (31) and the nth-order battery cells (32, 33, 34, 35, 36) corresponds to n times A. The test stand (1) according to feature 1.

3. The housing (10) has six side wall portions (12) that extend vertically from the housing base (11) toward the housing opening (13). The test stand (1) according to claim 1 or 2.

4. A cover (20) is provided that can close the housing opening (13). The test stand (1) according to feature 3.

5. A pressure limiting means (21) is provided to limit the pressure spreading within the internal space (15) of the housing (10). The test stand (1) according to any one of claims 1 to 4.

6. A plate-shaped cell holder (50) having multiple centering means is provided within the housing (10), and the cell holder fixes the position of the start element (31) and the positions of the battery cells (32, 33, 34, 35, 36). The test stand (1) according to any one of claims 1 to 5.

7. The cell holder (50) is positioned in close proximity to the housing base (11). The test stand (1) according to feature 6.

8. A metal plate (60) having an opening (61) is provided at the end of the cell (30) that faces away from the housing base (11). The test stand (1) according to any one of claims 1 to 7.

9. The cells of the first group are housed in the first module carrier (41), and the cells of the second group are housed in the second module carrier (47). The test stand (1) according to any one of claims 1 to 8.

10. The first module carrier (41) has a trapezoidal carrier base having a longer base edge portion (43), a shorter base edge portion (44) parallel to the longer base edge portion (43), and two legs (45, 46), wherein the length of the shorter base edge portion (43) and the length of the legs (45, 46) substantially correspond to the length of the edge portion of the hexagonal housing base (11). The test stand (1) according to feature 9.

11. At least two temperature sensors (70) are provided within the internal space (15) of the housing (10), at different distances from the start cell (31). The test stand (1) according to any one of claims 1 to 10.

12. At least one of the temperature sensors (70) protrudes vertically upward from below through an opening (17) in the housing base (11), and its height can be fixed within the internal space (15) by screw connection. The test stand (1) according to claim 3 and claim 11.

13. The housing (10) is supported on a plurality of feet (18) such that there is free space between the housing base (11) and the ground (2) on which the test stand (1) stands using its feet (18). The test stand (1) according to any one of claims 1 to 12.

14. A method for testing battery components using a test stand (1) according to any one of claims 11 to 13, wherein at least one of the start cell (31) is activated to initiate thermal runaway, the temperature measured by at least two of the temperature sensors (70) is recorded during the thermal runaway, and the state of the individual battery cells (32, 33, 34, 35, 36) and the time curve of the measured temperature are evaluated after the thermal runaway.

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