Method for connecting battery cells while maintaining air and creepage distances

Abstract

In various embodiments, a method for interconnecting battery cells (1) is provided, comprising forming electrical connections (2) between battery cells (1) and providing an insulating coating (6) on the electrically connected battery cells (1); wherein the formation of the electrical connections (2) between the battery cells (1) takes place in a pressurized environment (5).

Description

[0001] The present invention relates to methods for interconnecting battery cells while maintaining clearance and creepage distances.

[0002] Electric vehicles are enjoying increasing popularity, not least due to the fact that the electric motors that power them achieve unattainably high efficiencies of up to 90% compared to combustion engines. Equally important are the HV batteries or traction batteries used to store the drive energy. Lithium-ion cells are used in the HV batteries of fully and partially electric vehicles because, among other things, they are characterized by a relatively high energy density and lack the memory effect.

[0003] In HV batteries, clearance and creepage distances must be maintained – these are the required distances between live conductors of different polarity that depend on environmental parameters. Li-ion cells cannot be switched on and off electrically. If these battery cells are connected in series during the manufacture of a battery module or battery, high voltage (U>60V DC) can be present, with corresponding requirements for clearance and creepage distances. The relevant standards that define the distances to be maintained are DIN EN 60664-1 VDE 0110-1:2008-01 and IEC 60664-1:2007. Generally speaking, the lower the air pressure, the greater the clearance and creepage distance for a given voltage level. The degree of air pollution is also an influence, which must be taken into account when determining the clearance and creepage distance.

[0004] In HV batteries, a housing (battery module or complete battery) made of metal insulated on both sides is typically installed around the interconnected battery cells to ensure EMC and high-voltage insulation requirements. The individual components used in the manufacture of HV batteries are often delivered electrically insulated, such as cells encased in insulating film and busbars partially coated with insulating material. When the components are connected by welding or screwing, the connection area is not electrically insulated. This must be protected later with a cover if necessary.

[0005] In this context, reference is made to document DE 10 2012 224 330 A1, from which a battery with several battery cells is known, wherein the battery cells are completely encapsulated in a potting compound in order to extend the creepage distance and reduce the distances between the battery cells.

[0006] A battery with several battery cells is also known from DE 102016214640 A1, wherein the battery cells are encapsulated with a potting compound in order to extend the creepage distance.

[0007] Document DE 10 2020 125 942 A1 discloses a method for coating printed circuit boards in control units, in which a coating forming a measuring capacitor is applied to an electrical or electronic component of a control unit. Upon a temperature change, in particular a temperature increase, in the area of ​​the electrical or electronic component, a dielectric layer of the coating changes its dielectric constant.

[0008] Document CN 106299504 A discloses a high-pressure lithium-ion battery module suitable for vacuum environments. The high-pressure lithium-ion battery module is characterized by an insulating plate assembly completely covering the outer surface of a lithium-ion battery pack, providing insulation to the lithium-ion battery pack. Furthermore, a battery shielding case encloses the insulating plate assembly as an electromagnetic shield for the lithium-ion battery pack. The high-pressure lithium-ion battery module has the advantages of being simple in structure and convenient to use, preventing Paschen breakdown, and ensuring the safety of the high-pressure lithium-ion battery module during periods of low atmospheric pressure.The high-pressure lithium-ion battery module is suitable for vacuum environments and has multiple insulation protection features, so that the lithium-ion battery pack of a spacecraft can operate safely and stably.

[0009] Document US 2019 / 0006776 A1 discloses an apparatus, method, and system comprising a series of physical fuses disposed within a terminal of a battery cell. The fuses are configured as legs connecting a raised platform of a battery cell cap to a conductive base portion of the battery cell cap. Each of the fuse link legs is sized and shaped to function as a fusible link. The fuse link legs comprise a controlled cross-sectional area disposed along a length of the material from which the fuse link leg is made. In an overcurrent situation, the connection between an electrical system and a battery cell having the integrated fuse link legs is interrupted by the overcurrent melting the legs.

[0010] Against this background, the object of the present invention can be seen in providing a method for producing batteries or battery modules, by means of which air and creepage distances are maintained during the production of a battery cell arrangement.

[0011] This object is achieved by the subject matter of the independent patent claim. Further preferred embodiments can be found in the dependent patent claims.

[0012] According to the invention, a method for interconnecting battery cells is provided, which comprises forming electrical connections between battery cells and providing an insulating coating on the electrically connected battery cells. The electrical connections between the battery cells are formed in an overpressure environment. Providing the insulating coating on the electrically connected battery cells can involve completely coating the battery cells (in particular, including all fastening means and connections adjacent thereto).

[0013] A pressurized environment refers to an environment in which a pressure is deliberately maintained or set to be higher than atmospheric pressure (1013.2 hPa), plus normal atmospheric pressure fluctuations. Thus, the pressure in the pressurized environment can correspond to a deliberately induced pressure that is higher than the ambient atmospheric pressure. The pressure in the pressurized environment can, for example, be 1.5 bar, 2 bar, 3 bar, or more and preferably remains stable throughout the production process.

[0014] To form the electrical connections between the battery cells, i.e., to interconnect the battery cells to form a unit used in a battery module or battery, in a pressurized environment, the process can be carried out in a closed environment, such as a pressurized chamber in which the pressure is generated. For this purpose, the battery cells, the electrical connectors, and the associated tools can be placed in the pressurized chamber, and the interconnection process can be carried out there.

[0015] The present invention is based on the basic idea of ​​carrying out the connection process for the battery cells in a production atmosphere that corresponds to an overpressure environment. This allows battery cells to be interconnected without the required air and creepage distances being exceeded. In other words, the overpressure environment can be used to provide an environment that allows open, i.e. stripped, contact points of the battery cells and possibly other open live parts / lines to be positioned closer to one another than would be the case under normal pressure. The battery cells and the electrically contacting components can then be positioned or constructed significantly closer to one another. In other words, the production atmosphere can be adapted so that the air and creepage distances are reduced compared to a production atmosphere at normal ambient pressure.Without increased ambient pressure, a given circuit layout might potentially result in insufficient clearance and creepage distances. Ambient pressure, as a parameter that can be freely selected, can be adjusted so that the smallest gaps within the production process are larger than the clearance and creepage distances for the specified pressure environment. This allows for a more aggressive circuit layout to be implemented without running the risk of damage to the battery cell arrangement during the manufacturing process due to insufficient clearance and creepage distances.

[0016] According to further embodiments of the method, the overpressure environment can comprise ambient air. In other words, the overpressure environment can be created by applying additional ambient air to a space filled with ambient air in which the interconnection process takes place.

[0017] According to further embodiments of the method, the overpressure environment can comprise a spark-quenching gas. The spark-quenching gas can constitute part or all of the gas filling the production space, and the spark-quenching gas can certainly comprise a mixture of different spark-quenching gases. For example, sulfur hexafluoride (SF6) or helium can be used for this purpose. The use of special shielding gases can have the advantage of further increasing the clearance and creepage distances.

[0018] According to further embodiments of the method, the provision of an insulating coating can take place in an overpressure environment. The provision of the insulating coating can take place in the same production room as the interconnection of the battery cells or in another room coupled to it with stable air pressure. It is important that the optimized production atmosphere with applied overpressure is maintained between the interconnection of the battery cells and the application of the insulating coating to prevent unwanted discharge due to a pressure drop.

[0019] According to further embodiments of the method, the provision of an insulating coating can be achieved by placing the electrically connected battery cells in an immersion bath containing an insulating material. The immersion bath completely wets all surfaces with the insulating material, in particular including screw connections and laser-welded joints. After subsequent coating drying, the protective effect of the insulating layer is achieved, so that the interconnected battery cells can be safely exposed to normal atmospheric pressure outside the production environment.

[0020] According to further embodiments of the method, the immersion bath can be arranged in the overpressure environment. This means that the access to the immersion bath is arranged in the overpressure environment, so that the interconnected battery cell assembly can be transferred into the immersion bath without leaving the pressurized production atmosphere in between. For this purpose, the immersion bath can be arranged in the pressurized space in which the interconnection step of the battery cells also takes place.

[0021] According to further embodiments of the method, this may further comprise providing at least one further coating on the battery cells electrically connected to one another (after they have already been coated with the insulating material.

[0022] According to further embodiments of the method, the at least one further coating may be an electrically conductive coating.

[0023] According to further embodiments of the method, this may further comprise providing a second insulating coating on the electrically connected battery cells, onto which the conductive layer has been arranged. By means of such an electrically conductive layer, which is arranged between two insulating layers, additional functions can be implemented, such as EMC shielding and insulation measurements. For this purpose, the conductive layer can be connected to a corresponding evaluation device.

[0024] According to further embodiments of the method, the existing or at least one further coating may be a water vapor diffusion-inhibiting coating.

[0025] A housing arranged around the battery cells connected to each other by busbars then primarily performs mechanical functions, such as the formation of a stable (supporting) structure.

[0026] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0027] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. Fig. 1 shows a common arrangement of battery cells in a housing Fig. 2 shows a flowchart in which an embodiment of the method according to the invention is illustrated. Fig. 3 shows an enlarged view of a contact area of ​​a battery cell arrangement according to the invention.

[0028] Fig. Figure 1 shows a typical arrangement of battery cells 1, for example, Li-ion battery cells, in a housing 4 (the figure shows the bottom and top of the housing). The battery cells 1 are electrically connected to one another by means of electrical connectors / current ties 2. The distance 3 between the battery cells 1 represents a clearance and creepage distance. The housing 4, which can form a cell module or an entire battery, is made of an insulating material and surrounds the arrangement of battery cells 1 to ensure compliance with EMC and high-voltage insulation requirements.

[0029] Fig. Figure 2 shows a flowchart illustrating an embodiment of the method according to the invention. The flowchart phenomenologically outlines the various successive phases of the manufacturing process and separates them from each other by the arrows P.

[0030] In a first step, which is outlined in the upper part of the flowchart, the required battery cells 1 and the power connectors 2 required to form the interconnection are first introduced into the production environment with optimized atmospheric conditions, i.e., into the production environment subjected to overpressure 5. For example, this can be an airtight room area in which these components are introduced and in which the tools required to form the arrangement of the interconnected battery cells 1 are arranged.

[0031] In a subsequent step, which is outlined in the middle part of the flowchart, the battery cells 1 are electrically connected to each other. This process step takes place in the pressurized production environment 5.

[0032] In a subsequent step, which is outlined in the lower part of the flowchart, the battery cells 1 interconnected by means of the power connectors 2 are coated with an electrically insulating material 6. For this purpose, the battery cell arrangement formed in the previous step is placed in an immersion bath 7.

[0033] As in Fig. As shown in Figure 2, the three process steps all take place in the production environment subjected to overpressure 5. For this purpose, the immersion bath 7 can be arranged in the production chamber in which the previous process step takes place.

[0034] Fig. 3 shows an enlarged view of a contact area of ​​an arrangement according to the invention of interconnected battery cells 1. After at the end of the Fig. 2 outlined manufacturing process, a battery cell arrangement is present which is coated with an insulating material 6, a conductive layer 8 can be applied to the insulating layer 6 in a further coating process. In a still further coating process, a second layer of an insulating material 9 can be applied to the conductive layer 8. The end result is a coating structure as shown in Fig. 3, in which the layer of conductive material 8 is arranged between two insulating layers 6, 9. Using the insulated electrically conductive layer 8, additional functions, such as EMC shielding and insulation measurements, can be realized.

Claims

[1] Method for interconnecting battery cells (1), comprising: Forming electrical connections (2) between battery cells (1), and Providing an insulating coating (6) on the battery cells (1) which are electrically connected to one another; wherein the formation of the electrical connections (2) between the battery cells (1) takes place in an overpressure environment (5). [2] Method according to claim 1, wherein the overpressure environment (5) comprises air from the environment. [3] Method according to claim 1 or 2, wherein the overpressure environment (5) comprises a spark extinguishing gas. [4] Method according to one of claims 1 to 3, wherein the provision of an insulating coating (6) takes place in the overpressure environment (5). [5] Method according to one of claims 1 to 4, wherein providing an insulating coating (6) comprises: Placing the electrically connected battery cells (1) into an immersion bath (7) containing an insulating material (6). [6] Method according to claim 5, wherein the immersion bath (7) is arranged in the overpressure environment (5). [7] Method according to one of claims 1 to 6, further comprising: Providing at least one further coating on the battery cells (1) which are electrically connected to one another. [8] Method according to claim 7, wherein the at least one further coating is an electrically conductive layer (8). [9] The method of claim 8, further comprising: Providing a second insulating coating (9) on the electrically connected battery cells (1).

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