DEVICE FOR TESTING AT LEAST ONE BATTERY CELL

Description

[0001] The invention relates to a device for testing at least one battery cell, in particular a secondary battery, having a first plate and a second plate, wherein the battery cell is clamped between the two substantially rectangular plates and at least one plate is pressed against the battery cell with a defined mechanical contact force, with at least one force measuring element arranged between a plate and a contact device for measuring a reaction force between the battery cell and the contact device, wherein the change in the thickness of the battery cell can be measured by means of at least one displacement measuring element - preferably simultaneously with the reaction force. Furthermore, the invention relates to a method for testing at least one battery cell, in particular a secondary battery, using this device.

[0002] "Substantially rectangular" here means that the panels each have the shape of a rectangle in plan with two pairs of parallel edges, whereby the corners of the rectangle may also be rounded.

[0003] The characterization of battery cells with regard to their chemical and physical properties is a necessary development step for the design of a battery pack.

[0004] The energy storage capacity of a battery cell depends heavily on the cell chemistry used. In addition to the cell chemistry, external influences, such as the installation situation within the battery assembly, also affect the performance of a battery cell. Battery cells can be connected to the battery pack in a "floating" configuration (elastic plastic components are positioned between the battery cells) or a "rigid" configuration (cell to cell).

[0005] Battery cells have the property that their external dimensions, especially their thickness, change during electrical charging or discharging. This effect is also known as the breathing and / or swelling effect. "Breathing" refers to a cyclical, reversible increase and decrease in volume during the battery's charging and discharging processes. "Swelling" refers to an irreversible increase in volume, for example, due to aging. Furthermore, there is a relationship between the cell surface pressure and the cell's storage capacity.

[0006] Testing of battery cells of different types (pouch cells, prismatic cells) is usually carried out between two fixed metal plates.

[0007] For example, a pouch cell is clamped between two metal plates near the cell body and then tensioned to a desired surface pressure using a screw connection and a calculated torque. The cell conductors remain freely accessible for contacting the power supply.

[0008] Only the stiffness of the clamping plates and the torque can be adjusted in this test setup.

[0009] DE 2018 123 626 A1 discloses a battery temperature control device comprising a first plate for supporting a battery cell and a second plate for pressing the battery cell onto the first plate. A heating / cooling device is provided for temperature control of the battery cell. A clamping device allows the second plate to be pressed against the first plate with a defined contact force, with a load cell arranged between the clamping device and the first plate.

[0010] US 2020 / 132577 A1 discloses a device for measuring a battery cell with a force measuring element arranged at each corner of a plate and a pressing device for measuring a reaction force between the battery cell and the pressing device, wherein the device further comprises a strain measuring element with which the reaction force and the thickness of the battery cell can be measured simultaneously in real time during a charge-discharge cycle.

[0011] Publication EP 3 621 128 A1 discloses a battery pack comprising a battery module and a pressure sensor device for measuring an expansion force. A displacement measuring element is not provided.

[0012] Furthermore, devices for measuring the cell expansion of a battery cell are known, for example from the documents EP 3 377 363 A1, US 2015 / 188198 A1, US 2014 / 311223 A1, US 2014 / 107949 A1 or US 2013 / 323554 A1.

[0013] The devices known from the state of the art all have the property that surface pressure and expansion of the battery cell cannot be measured simultaneously.

[0014] The object of the invention is to increase the accuracy and significance of battery cell tests.

[0015] According to the invention, the stated object is achieved in a device of the type mentioned at the outset in that at least one plate, preferably the first plate, has at least one thermal measuring element for measuring the cell body temperature of the battery cell, and in that at least one plate, preferably the second plate, has at least one contact element which establishes an electrical connection between at least one cell pole and a preferably flexible power cable, wherein a temperature sensor is integrated into at least one contact element.

[0016] Thus, the reaction force and the change in the thickness of the battery cell can be measured simultaneously.

[0017] By having at least one plate with at least one thermal measuring element, which advantageously contacts the cell body, accurate measurement of the cell body temperature of the battery cell is possible. This allows for simple and precise monitoring of the cell body's surface temperature.

[0018] By integrating the contact elements that form electrical conductors into the second plate, an electrical connection between the power cable and the cell terminals is established when the second plate is placed on the battery cell, simultaneously with the compression of the battery cell. This enables quick replacement and reconnection of the battery cells.

[0019] Because a temperature sensor is integrated into at least one contact element, the temperature of the cell poles can be continuously measured during charging and discharging processes.

[0020] The reaction force is not entirely imposed by the clamping device as a preload, but is composed of the initially imposed clamping force and the operating force of the battery cell resulting from the test, which is formed by chemical processes inside the cell body.

[0021] The force measuring element and the displacement measuring element are preferably formed by separate and / or spatially separated components, allowing force and displacement measurements to be performed completely independently of each other. For example, the force measuring element and the displacement measuring element can be arranged at different locations on the device. This largely prevents mutual influence of the measurement results.

[0022] Simple and precise displacement measurement is possible if at least one displacement measuring element is arranged in the region of a longitudinal center plane and / or a longitudinal transverse plane of the cell and / or at least one plate. The longitudinal center plane and the longitudinal transverse plane, which extend parallel to the direction of the contact force or reaction force, preferably run through the center of gravity of the cell and / or through the center of gravity of the first and / or second plate.

[0023] Accurate distance measurement with a single distance measuring element is possible if the distance measuring element is arranged in the area of ​​an intersection line between the longitudinal center plane and the transverse center plane.

[0024] In one embodiment of the invention, it is provided that the first plate and the second plate are connected to one another by at least one pressing device, wherein the pressing device is preferably arranged in the region of a corner of the first and second plate.

[0025] Preferably, in the region of at least two corners of at least one plate, in particular at each corner of at least one plate, a force measuring element is arranged between the plate and a pressing device.

[0026] An embodiment variant according to the invention provides that at least one force measuring element is designed as a force measuring ring, wherein the force measuring ring is preferably penetrated by a bolt- or sleeve-shaped section of the pressing device.

[0027] Simple and accurate force measurement can be achieved if at least one force measuring element is designed as a strain gauge sensor. Strain gauge sensors (DMS = strain gauge) are force-measuring devices that rely on the change in electrical resistance caused by stretching or compressing deformation.

[0028] The displacement measuring element is preferably designed as an inductive displacement sensor.

[0029] It is particularly advantageous if an electrical voltage sensor is integrated into at least one contact element. This allows the electrical voltage of the cell poles to be continuously measured during charging and discharging processes.

[0030] Within the scope of the invention, it can further be provided that a cell compression cushion is arranged between at least one plate and the battery cell.

[0031] With the device according to the invention, it is possible to test battery cells with regard to their electrochemical and physical properties (such as stiffness).

[0032] The device clamps the battery cell between a first plate and a second plate, and at least one plate is pressed against the battery cell with a defined mechanical contact force, measuring a reaction force between the battery cell and at least one plate. This problem is solved by measuring at least one change in the thickness of the battery cell—preferably simultaneously with the reaction force.

[0033] In an embodiment according to the invention, it is provided that at least two reaction forces are measured at different locations on the battery cell.

[0034] In a further embodiment of the invention, it is provided that the change in thickness is measured at a different location on the battery cell than the reaction force.

[0035] This makes it possible to create an exact cell expansion profile of the battery cell.

[0036] A further increase in the accuracy of the significance of the investigation can be achieved if, based on the measurement results, a model calculation is carried out with a virtual calculation model of the device - preferably by means of inverse parameter identification - whereby disturbances and influencing variables of the device are filtered out.

[0037] The invention is explained in more detail below with reference to the non-limiting embodiment shown in the figures. Fig. 1 shows a device according to the invention in an axonometric view; Fig. 2 shows the device in a further axonometric view; Fig. 3 shows the device in an exploded view; Fig. 4 shows a pressing device of the device in a sectional axonometric view; Fig. 5 shows the device in section along the line VV in Fig. 1 ; Fig. 6 the device in a section through the second plate according to the line VI-VI in Fig. 3 ; Fig. 7 a detailed section of the device Fig. 6 ; Fig. 8 a contact element of the device in an axonometric view; Fig. 9 a force measuring element of the device in an axonometric view; Fig. 10 the force measuring element in a side view; Fig. 11 the detail XI from Fig. 5 ; and Fig. 12 a test bench for the application of the device.

[0038] The Fig. 1 bis Fig. 11 The device 1 shown for testing a battery cell 2 of a secondary battery has a first plate 3 and a second plate 4. The battery cell 2 can be, for example, a pouch cell or a prismatic cell.

[0039] The first plate 3 forms a lower base platform into which the battery cell 2 is inserted. Depending on the cell size, the base platform can be of different sizes.

[0040] The second plate 4 forms a pressure body, which is connected to the lower base platform via clamping devices 9. The battery cell 2 is clamped between the pressure body and the base platform.

[0041] The battery cell 2 to be tested, which has a cell body 20 and cell poles 2a, 2b, is thus held and clamped between the two essentially rectangular plates 3, 4. In the exemplary embodiment, the plates 3, 4 are designed essentially symmetrically with respect to a longitudinal center plane 5 and a transverse center plane 6 arranged perpendicularly thereto, wherein the longitudinal center plane 5 and the transverse center plane 6 run through the centroid 7 of the sides of the plates 3, 4 with the largest surfaces. Reference numeral 8 denotes the intersection line of the longitudinal center plane 5 and the transverse center plane 6 running through the centroid 7.

[0042] At least one plate 3, 4 is pressed against the battery cell 2 with at least one defined mechanical contact force F, wherein the two plates 3, 4 are held under prestress by the pressing devices 9. The contact forces F run parallel to the Fig. 1 drawn vertical axis z, i.e. parallel to the longitudinal center plane 5 and to the transverse center plane 6, as well as parallel to the intersection lines 8 of the longitudinal center plane 5 and transverse center plane 6.

[0043] The pressing devices 9 are formed by screw connections 10 arranged symmetrically with respect to the longitudinal plane 5 and the transverse plane 6, wherein bolt- or sleeve-shaped sections 11 of the screw connections 10 are guided through and penetrate openings 12 of the plates 3, 4. At each corner 3a, 3b, 3c, 3d; 4a, 4b, 4c, 4d of the plates 3, 4, an opening 12 is arranged for receiving a respective screw connection 10. The corners 3a, 3b, 3c, 3d; 4a, 4b, 4c, 4d of the plates 3, 4 can be rounded, as can be seen, for example, from the Fig. 1 bis Fig. 3 clearly shows.

[0044] The contact force F is applied to the cell body 20 by means of the screw connection 10 between the base platform - the first plate 3 - and the pressure body - the second plate 4 - via bolt- or sleeve-shaped sections 11, for example, designed as stud bolts. A force measuring element 13 is provided for each screw connection 10 to measure the reaction force R. The reaction force R is composed of the contact force F initially applied as preload by the contact pressure device 9 and the operating force of the battery cell resulting from the test conditions due to temperature and state of charge as well as charging / discharging processes. The operating force is essentially attributable to chemical processes inside the cell body.

[0045] This force measuring element 13 measures the current screw force and thus the surface pressure on the battery cell 2. A force measuring element 13 is thus arranged between at least one plate - for example, the second plate 4 - and each pressing device 9. The force measuring element 13 - such as a strain gauge sensor - is designed, for example, as a force measuring ring 14, through which a bolt- or sleeve-shaped section of the pressing device 9 passes. Precise force measurement can be achieved if a force measuring element 13 is arranged at each corner 3a, 3b, 3c, 3d; 4a, 4b, 4c, 4d of at least one plate 3, 4, between the plate 3, 4 and a pressing device 9. Fig. 9 und Fig. 10 show an example of a force measuring element 13.

[0046] As an extension, at least one spring (not shown) can be integrated into each screw connection 10 between the first plate 3 and the second plate 4. This serves to simulate a "floating" mounting of the battery cell 2 in the battery assembly and allows a relative movement of the pressure hull to the base platform, i.e., the second plate 4 relative to the first plate 3.

[0047] Alternatively - or in addition - to the springs, at least one cell compression pad formed, for example, by an elastomer mat can be placed between the battery cell 2 and the second plate 4 (not shown in the figures).

[0048] Both the springs and the cell compression cushion can be defined in terms of stiffness to suit the application and thus represent a realistic comparison of the installation situation in the battery pack.

[0049] The stiffness of the device 1 can be variably adjusted by means of springs of different stiffness, so that constant forces can be realized over the entire extension range from 300N up to 10kN.

[0050] Furthermore, it is possible to screw stiffening elements, for example formed by profiles, onto the side edges of the first plate 3 and / or second plate 4, which allow for further variable stiffening. For example, the stiffness of the pressure hull formed by the second plate 4 can be increased in discrete steps by attaching lateral profiles of different heights (not shown). In the stiffest variant, a reaction force of up to 40 kN is thus possible.

[0051] Furthermore, the device 1 has at least one distance measuring element 15 with which the change in the thickness D ( Fig. 5 ) of battery cell 2 can be measured ( Fig. 1 ). The change in thickness is in the direction of Fig. 1 measured along the vertical axis z shown, i.e. in the exemplary embodiment in the direction of the smallest extent of the cell body 20. The displacement measuring element 15 can, for example, be designed as an inductive displacement sensor which is arranged in the region of the intersection line 8 between the longitudinal center plane 5 and the transverse center plane 6.

[0052] The displacement measuring element 15 is formed as a separate component and is spatially separated from the force measuring elements 13. The displacement measuring element 15 can be attached directly to the device 1. The displacement measuring element 15 serves to measure the volume change (breathing) of the cell body 20 during charging or discharging at different charge states and at different temperatures. The displacement measuring element 15 serves to measure the breathing of the battery cell 2 at different temperatures during charging or discharging. The expansion (swelling) of the cell body 20 due to aging of the battery cell 2 can also be measured with the displacement measuring element 15.

[0053] Due to the different positions of the force measuring elements 13 and the displacement measuring element 15, force and displacement measurements can be carried out simultaneously and thus an exact cell expansion profile of the battery cell 2 under investigation can be created.

[0054] In the area of ​​the cell poles 2a, 2b of the battery cell 2, contact elements 16 are arranged in the second plate 4, each with electrical contact pins 17 preloaded by a compression spring 17a, which establish electrical contact between the cell poles 2a, 2b and a flexible power cable 18. A temperature sensor 19 is integrated into at least one of the contact elements 16. For precise temperature monitoring, it is particularly advantageous if a temperature sensor 19 is provided for each electrical contact element 16. The electrical voltage can also be measured via the contact element 16, for example, to enable compensation for line losses.

[0055] The firm integration of the contact elements 16 in the second plate 4 enables quick changing and rapid re-contacting.

[0056] For heat dissipation and cell pole cooling, a heat dissipation plate 23 may be provided ( Fig. 6 ).

[0057] Furthermore, a spring-loaded thermal measuring element 21 is arranged in the first plate 3, which is pressed against the battery cell 2 from below in a central area, as shown in Fig. 11 is shown. The cell body temperature of the battery cell 2 can be measured via the thermal measuring element 21.

[0058] All measurements (current, voltage, compressive forces, relative movement) can be recorded during operation and directly compared. The stiffness of the springs or cell compression pads can be selected as required.

[0059] The device 1 is suitable for test environments in temperature chambers with temperatures, for example, between approximately -30°C - +70°C.

[0060] The compact size of device 1 allows or facilitates the testing of multiple test specimens in temperature chambers. Experience has shown that at least twelve different test configurations, each with at least three repetitions, are necessary to obtain reliable results. This can provide both monetary and economic benefits.

[0061] If limited testing resources (temperature chambers / climate chambers) are available and, for example, each battery cell 2 has to be tested one after the other, the compact design offers a significant time advantage in obtaining the desired test results.

[0062] By simultaneously measuring force and extension, it is possible to determine the stiffness of the test environment as well as the stiffness of the battery cell 2 at any time during cycling / aging. Since cell stiffness changes during electrical cycling, this is a key parameter in the mechanical design of the assembly of multiple battery cells 2 into a module. This aspect has not been considered in conventional devices to date, resulting in insufficient data.

[0063] The size of the present device 1 is particularly compact, making it possible to accommodate multiple devices 1 within a commercially available cell test chamber. This also allows the influence of different ambient temperatures to be captured. Furthermore, this makes it possible to test many battery cells in parallel, which is necessary to adequately characterize cell swelling and / or cell breathing behavior.

[0064] Device 1 is advantageously supplemented by a virtual calculation model, which can be used to perform model calculations alongside or in addition to the hardware tests. The virtual calculation model of device 1 makes it possible to obtain the pure cell properties of battery cell 2 and filter out all interference from the measuring equipment. This prevents the data generated by device 1 from being distorted by the device 1 and the measurement setup itself. This enables greater accuracy and better significance compared to conventional methods.

[0065] The following tests can be carried out using device 1: 1. Simulation of the surface pressure on the cell body of battery cell 2, for example, up to 40 kN or more. This allows us to investigate at which preload pressure the battery cell achieves its highest performance. For this purpose, a real-time surface pressure measurement is carried out using the four force measuring elements 13. Furthermore, reproducible surface pressures are determined by the force measuring elements 13 for each test and for each battery cell 2. Finally, a temperature measurement is also carried out on the cell body 20 of battery cell 2 on the one hand and on the contact elements 16 on the other. 2. Simulation of different stiffnesses to compensate for cell expansion (breathing, swelling) of battery cell 2. This allows us to investigate how the battery assembly must be designed with regard to the expansion of the battery cells.This can be achieved, for example, by integrating cell compression pads and / or springs between plates 3, 4 and battery cell 2. 3. Determination of the battery cell expansion at different battery charge levels and temperatures. This allows investigation of how the geometry (thickness) of the battery cell 2 changes at different charge levels and different temperatures. This is achieved by additional displacement measurement using at least one displacement measuring element 15.

[0066] The present device 1 was specifically developed to fully characterize cell breathing and / or cell swelling (cell thickness growth due to electrochemical conversion processes during electrical cycling) of battery cells 2 (pouch cells and prismatic cell types). The data thus generated can then be used to perform a detailed mechanical design of a cell assembly (e.g., a battery module).

[0067] The virtual calculation model of device 1 is provided for this purpose. By combining device 1 with the virtual calculation model, the true cell properties (adjusted for the influence of the measuring equipment) can be determined using inverse parameter identification, and a simulation model for the breathing and / or swelling behavior of the battery cell 2 being tested can be created.

[0068] In order to fully characterize the breathing and / or swelling behavior of a battery cell 2, the following dependencies must be tested: ) Change in thickness D of battery cell 2 via number of electrical cycles (depending on ambient stiffness): The change in thickness D of battery cell 2 is measured by a displacement measuring element 15 in the middle of cell body 20. This displacement measuring element 15 basically measures the relative displacement between the two plates 3, 4. The measured displacement value (together with the measured force value) is then further processed using the virtual calculation model in order to obtain the pure change in thickness D of battery cell 2, as well as the associated cell stiffness, the expansion profile and the pressure dependence. ) Increase in force due to change in thickness D of battery cell 2 via number of electrical cycles (depending on ambient stiffness): In order to measure the increase in force due to the change in thickness of battery cell 2, four force measuring elements 15 formed by force measuring rings 14 are at the outer corners 3a, 3b, 3c, 3d; 4a, 4b, 4c, 4d of plates 3, 4 installed.By positioning the force measuring elements 15, it is possible not only to measure the average force increase, but also local differences. The measured force value (together with the measured displacement value) is then further processed using the virtual calculation model in order to obtain the pure change in thickness D of the battery cell 2 and the associated cell stiffness, the expansion profile and the pressure dependence. ) Stiffness change of the battery cell 2 via the number of electrical cycles: If the force increase and the change in thickness D are only measured during cycling, no information about the cell stiffness is obtained, but only a statement about the stiffness of the device 1. This means that there are many pairs of cell stiffness and pure change in thickness D of the battery cell 2 which, when combined, produce the same measurement result.For this reason, the electrical cycling must be interrupted at specified cycle numbers, and the cell stiffness measured. It is important that the battery cell 2 does not, for example, have to be removed and installed in another measuring device, as this could falsify the result. The present device 1 is designed precisely for this purpose and therefore offers the possibility of simultaneous force and displacement measurement. Furthermore, by positioning the force-measuring elements 15 on the screw connections 10, the cell stiffness can be measured at any time in a force-controlled manner by synchronously loosening or tightening all screw connections 10. In other words, the screw connections 10 are loosened or tightened in several stages while the electrical cycling is stopped, without the battery cell 2 having to be removed.This produces force / displacement curves, which are then refined again using the virtual calculation model to extract the pure cell stiffness. The influence of the equipment stiffness is filtered out in the process. If the cell stiffness in relation to the number of cycles is known, there is only one value for cell thickness growth with which the measured force increase can be achieved. Only through this combination is it possible to determine the actual cell properties from the test. ) Expansion profile of battery cell 2: The change in thickness D of battery cell 2 does not occur evenly across the entire surface. Instead, a larger change in thickness D is usually observed in the cell center compared to the cell edges. This influence is crucial for the integration of a battery cell 2 into a cell composite.To measure this effect, in the present device 1, the force measuring elements 13 are attached to the four corners 3a, 3b, 3c, 3d; 4a, 4b, 4c, 4d of the plates 3, 4 at the edge of the battery cell 2, and the displacement measuring element 15 for measuring cell expansion is located in the center of the battery cell 2. If there is a large increase in force but a small change in displacement, the thickness growth is pronounced at the edge of the battery cell 2. If there is a large change in displacement and only a small change in force, the thickness growth is pronounced in the center of the battery cell 2. In this way, not only the average cell thickness growth can be characterized, but also the expansion profile. In addition to the appropriate positioning of the force measuring elements 13 and the displacement measuring element 15, the simultaneous measurement of force and displacement is necessary.) Pressure dependence of the change in thickness D of battery cell 2 over the number of electrical cycles: The expansion of battery cell 2 is generally dependent on the mechanical pressure acting on the cell surface during electrical cycling. To characterize this effect, the present device 1 is designed to be very flexible with regard to adjustable preloads and stiffnesses. The preload range, for example, extends from approximately 100 N to approximately 40 kN.

[0069] To fully characterize the pressure dependence, it is not sufficient to simply control the initial stress. Furthermore, the force / pressure curve caused by the thickness growth of the battery cell 2 during cycling must also be controlled. For this purpose, the present device 1 provides the option of varying the stiffness of the cell clamping using springs of different stiffnesses. This makes it possible to achieve a constant stress situation throughout the entire electrical cycling. By using springs with different spring stiffnesses, different pressure levels can be kept constant. In this way, the cell thickness growth for the respective pressure levels is obtained.To further characterize the influence of varying pressure during cycling, the battery cell 2 can also be rigidly clamped in the fixture 1 using the screw connection 10. In this case, the force / pressure increase depends on the stiffness of the plates 3, 4. Here, too, the option of varying the stiffness of the plates 3, 4 in two steps by additionally mounting side profiles is provided. This provides sufficient variation options to simulate all possible clamping situations in a cell assembly with the fixture 1.

[0070] Fig. 12 shows a test bench with two devices 1 for testing multiple battery cells 2, which are in different application states. The device 1 on the right, shown in the foreground, is not yet assembled, while the device 1 on the left is already fully assembled.

[0071] The preparation of device 1 is carried out in the following steps: Inserting the battery cell 2 into the base platform formed by the first plate 3; optionally placing a cell compression pad on the battery cell 2; placing the second plate 4 on the battery cell 2 or on the cell compression pad; attaching the screw connection 10 with the force measuring elements 13; connecting the force measuring elements 13 to a measuring unit 22; crosswise tightening of the screw connections 10 in several steps, whereby the cell poles 2a, 2b are automatically contacted by the contact elements 16; monitoring the symmetrical force increase at each screw connection 10.

Claims

1. Device (1) for testing at least one battery cell (2), in particular a secondary battery, having a first plate (3) and a second plate (4), wherein the battery cell (2) is clamped between the two plates (3, 4), which are preferably substantially rectangular, and at least one plate (4) is pressed against the battery cell (2) with a defined mechanical pressing force (F), having at least one force-measuring element (13) arranged between one plate (3, 4) and at least one pressing device (9) for measuring a reaction force (R) between the battery cell (2) and the pressing device (9), wherein at least one change in a thickness (D) of the battery cell (2) can be measured, preferably simultaneously with the reaction force (R), by means of at least one displacement-measuring element (15), characterised in that at least one plate (3, 4), preferably the first plate (3), has at least one thermal measuring element (21) for measuring the cell body temperature of the battery cell (2) and that at least one plate (3, 4), preferably the second plate (4), has at least one contact element (16) which establishes an electrical connection between at least one cell pole (2a, 2b) and a preferably flexible power cable (18), wherein a temperature sensor (19) is integrated in at least one contact element (16)2. Device (1) according to claim 1, characterised in that at least one force-measuring element (13) and at least one displacement-measuring element (15) are formed by separate and / or locally separated components.

3. Device (1) according to claim 1 or 2, characterised in that at least one displacement-measuring element (15) is arranged in the region of a longitudinal center plane (5) and / or a transverse center plane (6) of the battery cell (2) and / or at least one plate (3, 4).

4. Device (1) according to one of claims 1 to 3, characterised in that the displacement-measuring element (15) is arranged in the region of an intersection line (8) between a longitudinal center plane (5) and a transverse center plane (6) of the battery cell (2) and / or at least one plate (3, 4).

5. Device (1) according to one of claims 1 to 4, characterised in that the first plate (3) and the second plate (4) are connected to one another by the at least one pressing device (9), wherein the pressing device (9) is preferably arranged in the region of a corner (3a, 3b, 3c, 3d; 4a, 4b, 4c, 4d) of the first plate (3) and the second plate (4).

6. Device (1) according to one of claims 1 to 5, characterised in that in the region of at least two corners (3a, 3b, 3c, 3d; 4a, 4b, 4c, 4d) of at least one plate (3; 4), preferably at each corner (3a, 3b, 3c, 3d; 4a, 4b, 4c, 4d) of at least one plate (3; 4), a force-measuring element (13) is arranged in each case between the plate (3, 4) and a pressing device (9).

7. Device (1) according to one of claims 1 to 6, characterised in that at least one force-measuring element (13) is designed as a force measuring ring (14), wherein preferably the force measuring ring (14) is penetrated by a bolt- or sleeve-shaped section (11) of the pressing device (9).

8. Device (1) according to one of claims 1 to 7, characterised in that at least one force-measuring element (13) is designed as a strain gauge sensor.

9. Device (1) according to one of claims 1 to 8, characterised in that the displacement-measuring element (15) is designed as an inductive displacement sensor.

10. Device (1) according to one of claims 1 to 9, characterised in that a voltage sensor is integrated in at least one contact element (16).

11. Device (1) according to one of claims 1 to 10, characterised in that at least one cell compression pad and / or at least one spring with defined stiffness is arranged between at least one plate (3, 4) and the battery cell (2).

12. Method for testing at least one battery cell (2), in particular a secondary battery, having a device (1) according to one of claims 1 to 11, wherein the battery cell (2) is clamped between a first plate (3) and a second plate (4) and at least one plate (4) is pressed against the battery cell (2) with a defined mechanical pressing force (F), wherein at least one reaction force (R) between battery cell (2) and at least one plate (4) is measured, characterised in that at least one change in the thickness (D) of the battery cell (2) is also measured, preferably simultaneously with the reaction force (R).

13. Method according to claim 12, characterised in that at least one reaction force (R) and at least one change in thickness (D) of the battery cell (2) are measured at different locations of the battery cell (2).

14. Method according to claim 12 or 13, characterised in that at least two reaction forces (R) are measured at different locations of the battery cell (2).

15. Method according to one of claims 12 to 15, characterised in that, based on the measurement results, a model calculation is carried out with a virtual calculation model of the device (1) and / or the battery cell (2), preferably by means of inverse parameter identification, wherein disturbance variables and influencing variables of the device (1) are filtered out.