Methods for testing the reliability of the connection in a high-voltage battery and methods for manufacturing a high-voltage battery

Abstract

A method for testing the reliability of a connection made by thermal paste during the creation of a high-voltage battery between at least one battery cell (30) and a cooling surface structure (on a battery cell tray (10)) involves reversibly deforming the cooling surface structure and determining whether the deformed cooling surface structure exhibits irregularities. In particular, gaps (70) in the thermal paste application can be detected in this way, and preferably such irregularities can be detected with millimeter precision by generating interference patterns using a coherent light source (60).

Description

[0001] The invention relates to a method for testing the reliability of a connection between at least one battery cell and a cooling base structure, which connection is made using thermally conductive paste for, or in the context of, creating a high-voltage battery. The cooling base structure is typically provided, in particular, as part of a battery tray. The invention also relates to a method for manufacturing a high-voltage battery, during which the reliability of the connection is determined according to the aforementioned testing method.

[0002] A method for testing such a connection between the heat sink and a battery cell arrangement by means of a heat conducting agent is known, for example, from DE 10 2020 108 537 A1, wherein an external radar or ultrasonic sensor is used in the method.

[0003] DE 10 2019 117 530 A1 discloses a method for testing an arrangement for cooling or heating a battery cell, wherein a measuring device measures a current-voltage relationship between two measuring points. The corresponding measuring points are located on the receiving structure and on the heat transfer structure.

[0004] Finally, DE 10 2009 018 079 A1 discloses a method for operating a battery with at least one galvanic cell, which is subjected to a non-destructive testing process. Electromagnetic radiation is used in particular in this testing process.

[0005] The general background of the invention also includes the disclosure in DE 10 2011 121 206 A1, DE 10 2021 113 418 A1 and DE 10 2018 222 459 A1.

[0006] The difficulty in using thermal paste (in the form of thermally conductive adhesive and / or gap filler) to create a connection between a battery cell or a plurality of battery cells in a series arrangement and the cooling base structure, in particular a battery tray, has the disadvantage that the thermal paste reacts unpredictably. Thus, when the thermal paste is applied by assembly personnel and even with a certain degree of automation, it is not always guaranteed that the battery cells are actually fully attached to the cooling base structure. If the thermal paste is not present with a sufficient degree of wetting, too much heat can be generated during rapid charging and when the high-voltage battery is called upon to power, which heat is then not effectively dissipated. To achieve a high degree of wetting, the thermal paste is applied in a bead-like manner to the cooling base in the still empty compartment.The subsequently inserted battery cells (also known as battery modules) successively press the thermal paste into the surface. The battery cells are then mechanically secured.

[0007] Naturally, it's not easy to determine whether the degree of wetting is sufficient. The use of X-rays or the aforementioned radar or ultrasonic sensors has proven unsatisfactory.

[0008] The object of the invention is to demonstrate an improved method for testing the degree of wetting by thermal paste between a battery cell and a cooling base structure. In particular, it is also intended to enable a high-voltage battery to be manufactured more reliably.

[0009] The problem is solved by a method according to claim 1 for testing the reliability of a connection between at least one battery cell and a cooling base structure, which connection is made using thermal paste during the creation of a high-voltage battery. The method for producing a high-voltage battery according to claim 7 also solves the problem and improves the state of the art.

[0010] The method according to the invention for testing the reliability of a connection of at least one battery cell to a cooling base structure by means of thermal paste when creating a high-voltage battery comprises: - Causing reversible deformation of the high-voltage battery (if already built), in particular (only) the cooling floor structure; - Determine whether the deformed high-voltage battery (the deformed cooling floor structure) has irregularities of a certain minimum level; and if not, determine that the connection is reliable (and if irregularities of a certain minimum level are detected in the deformed high-voltage battery / cooling floor structure, the connection is considered unreliable).

[0011] The invention is based on the discovery that (as is known from shearography, for example) deformation behavior can be examined to detect imperfections in the wetting of the thermal paste, because the degree of wetting affects this deformation behavior. An irregular degree of wetting of the thermal paste leads to irregularities in the deformed high-voltage battery / cooling base structure.

[0012] According to a preferred embodiment, it is provided that (preferably initially) the non-deformed cooling base structure is irradiated with electromagnetic radiation, particularly preferably light, and a first measurement is carried out, and that the cooling base structure is also irradiated with similar electromagnetic radiation in the deformed state and a second measurement is carried out, wherein a comparison of the results of the first measurement and the second measurement shows whether the connection is reliable.

[0013] In this preferred embodiment, a type of calibration of the measurement is carried out in the undeformed state.

[0014] This can be particularly advantageous in the following two embodiments: In the first and second measurements, irradiation using a coherent light source can be performed, and an interference pattern can be detected. Such interference patterns react sensitively to the smallest changes in the surface structure, so that on a very large component such as a typical cooling base structure (which, in one example, measures 2 m x 1.20 m), displacements in the millimeter range or smaller can be detected. As a second embodiment, irradiation with a striped pattern can simply be performed, and this can be recorded using a camera. A projected striped pattern can also illustrate deformations in the millimeter range or smaller.

[0015] According to a preferred embodiment of the invention, the reversible deformation is achieved by heat input, preferably using a hot air blower. For detecting defects where there is insufficient thermal paste between the battery cell and the cooling base structure, the final temperature ultimately achieved is not important, as long as a certain amount of deformation takes place.

[0016] Alternatively, reversible deformation can also be achieved through the application of mechanical force. A type of vise can be used here, but preferably, vibration (vibration excitation) is introduced. Vibration excitation, in particular, can cause reversible deformation, although ultimately insignificant, but can already reveal irregularities in the wetting degree of the thermal paste (particularly in the light image, i.e., interference, or when using the stripe pattern).

[0017] The method according to the invention for producing a high-voltage battery comprises: - Providing a battery tray with a flat cooling base structure; - application of thermal paste to the top of the cooling base structure; - applying at least one, preferably cuboid-shaped, battery cell, preferably a series arrangement of a plurality of (also preferably cuboid-shaped) battery cells, to the cooling base structure with the thermally conductive paste on the top side; - Carrying out the reliability testing procedure as described above to check whether the at least one battery cell is reliably connected to the cooling base structure by means of the thermal paste, and if yes (if the outcome of the reliability test is positive), continuing the normal manufacturing process, and if no (if the outcome of the reliability test is negative), interrupting the normal manufacturing process.

[0018] The process for manufacturing a high-voltage battery is therefore extended by a testing step in which the high-voltage battery that has been built so far, i.e. the intermediate product (the battery cells are fitted into the battery tray using thermal paste), is tested non-destructively by applying a reversible deformation and examining the object for irregularities.

[0019] Continuing the normal manufacturing process includes wiring the at least one battery cell, applying a seal to the edge of the battery tray, applying a lid to the battery tray, and securing the lid.

[0020] Interrupting the normal manufacturing process may include removing at least one battery cell (preferably all battery cells of the at least one battery cell) from the cooling base structure, reapplying thermal paste, reattaching the at least one battery cell, and again performing the reliability testing process as described above.

[0021] A thermal adhesive and / or a gap filler can be used as thermal paste.

[0022] The invention also encompasses combinations of the features of the described embodiments. The invention therefore also encompasses implementations that each comprise a combination of the features of several of the described embodiments, unless the embodiments are described as mutually exclusive.

[0023] Exemplary embodiments of the invention are described below. These are illustrated by: Fig. 1A-1D the first steps of a method for manufacturing a high-voltage battery; and Fig. 2A a first test step and Fig. 2B shows a second testing step of an embodiment of the method for testing the reliability of a thermal paste connection.

[0024] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that can be considered independently of one another, each of which also develops the invention independently of one another. Therefore, the disclosure is intended to encompass combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0025] In the figures, the same reference symbols designate elements with the same function.

[0026] To produce a high-voltage battery, Fig. 1A, a battery tray 10 is first provided. In the following step, according to Fig. 1B Thermal Paste 20 is applied, typically in single lines or beads. In the next step according to Fig. 1C, a battery cell module (a battery cell) 30 is inserted into the tray 10 and pressed onto the thermal paste 20. Subsequently, a test is carried out according to Fig. 1D, here symbolically illustrated by a hot air blower 40 that generates hot air 42.

[0027] This test step is carried out using the Fig. 2A and Fig. 2B explains in more detail: In a first state (see Fig. 2A), a calibration measurement is performed on the existing intermediate product consisting of the battery tray 10 and the battery cell 30 pressed onto the thermal paste 20. In this measurement, the bottom of the battery tray 10 (suitably mounted for this purpose) is illuminated from below using a light source 60 that emits coherent light 62. The resulting interference pattern is captured by a camera 50. (The light source 60 can also be arranged differently, for example, with the light radiating in a more grazing pattern.)

[0028] In a second step according to Fig. 2B, a reversible deformation of the unit comprising the battery tray 10 with the battery cell 30 pressed onto the thermal paste 20 is now carried out by a hot air blower 40, which supplies hot air 42 to the bottom of the battery tray 10. Only or mainly the latter, i.e. the cooling base structure, is deformed. In the area of ​​a defect 70, a bulge then occurs that is not present outside of the area. This bulge causes a change in the interference image caused by the light beams 62 generated by the light source 60 and captured by the camera 50. In particular, when comparing the interference images that were created in the situation according to Fig. 2A and in the situation according to Fig. 2B, the presence of defect 70 can be inferred, and preferably, it can also be localized.

[0029] If a defect 70 has been located, the battery cell 30 should be removed again and new thermal paste 20 should be applied, then the test can be carried out again.

[0030] If no defect 70 is found, the battery cell is fixed, wired, a seal is applied, and finally a cover is placed on the battery tray and fixed.

[0031] Overall, the examples show how a method for non-destructive testing of the wetting degree of gap fillers in a high-voltage battery can be provided.

Claims

[1] Method for testing the reliability of a connection of at least one battery cell (30) to a cooling base structure by means of thermal paste (20) to create a high-voltage battery, comprising: - Causing reversible deformation of the cooling floor structure; - Determine whether the deformed cooling floor structure has any minimum irregularities; and if not, determine that the connection is reliable. [2] Method according to claim 1, in which the non-deformed cooling base structure is irradiated with electromagnetic radiation, preferably light (62), and a first measurement is carried out, and in which the cooling base structure is also irradiated with similar electromagnetic radiation in the deformed state and a second measurement is carried out, wherein a comparison of the results of the first measurement and the second measurement shows whether the connection is reliable. [3] Method according to claim 2, wherein in the first and second measurements irradiation by means of a coherent light source (60) takes place and an interference pattern is detected. [4] Method according to claim 2, wherein irradiation is carried out with a stripe pattern. [5] Method according to one of the preceding claims, in which the reversible deformation is carried out by heat input, preferably by a hot air blower (40). [6] Method according to one of claims 1 to 4, in which the reversible deformation is effected by the action of mechanical force, preferably a vibration excitation. [7] Method for producing a high-voltage battery, comprising: - Providing a battery tray (10) with a flat cooling base structure; - applying thermal paste (20) to the top of the cooling base structure; - applying at least one battery cell (30), preferably a series arrangement of a plurality of cuboid battery cells, to the cooling base structure with the thermally conductive paste (20) on the top side; - Carrying out the method according to one of the preceding claims to check whether the at least one battery cell (30) is reliably connected to the cooling base structure by means of the thermally conductive paste (20), and if yes, continuing the normal manufacturing process, and if no, interrupting the normal manufacturing process. [8] The method of claim 7, wherein continuing the normal manufacturing process includes wiring the at least one battery cell, applying a seal to an edge of the battery tray, applying a lid to the battery tray, and securing the lid. [9] Method according to claim 7 or 8, wherein, when the normal manufacturing process is interrupted, at least one battery cell is removed from the cooling base structure, thermal paste is applied again and the at least one battery cell is replaced and the method according to one of claims 1 to 6 is carried out again. [10] Method according to one of claims 7 to 9, in which a thermally conductive adhesive and / or a gap filler is used as the thermal paste.

Images