Battery for an electric vehicle

Abstract

Battery for an electric vehicle, comprising a battery housing (12) which defines a housing interior (14) and a battery cell pack (18) comprising several battery cells (20) which are arranged in the housing interior (20), wherein a compression pad (221, 222, 223, 224) is arranged between two adjacent battery cells (20) and / or between an edge-side battery cell (20) and a housing wall (13) of the battery housing (12), wherein the compression pad (221, 222, 223, 224) has a flexible bag element (24) which defines a bag interior (25), wherein a liquid (26) or a gel is arranged in the bag interior (25).

Description

The invention relates to a battery for an electric vehicle, comprising a battery housing which defines an interior space, and a battery cell pack comprising several battery cells which are arranged in the interior space, wherein a compression pad is arranged between two adjacent battery cells and / or between an edge-side battery cell and a housing wall of the battery housing. Such batteries are generally known from the prior art and typically have a battery casing in which a number of battery cells are stacked. A compression pad is usually arranged between each pair of battery cells, i.e., between two adjacent battery cells, and / or between a casing wall and an outermost or edge-mounted battery cell. The compression pads serve, among other things, to compensate for increasing cell thickness, also known as swelling. Swelling is a change in the volume of a battery cell, particularly a lithium-ion cell, which can be observed during charging and discharging and is also caused on a slower timescale by the aging of the battery cell. The aforementioned arrangement of compression pads between the battery cells...Between the edge of the battery cell and the housing wall in the stacking direction of the battery cells, compression can compensate for the volume change of the battery cells within the battery. Additionally, compression pads can be used to generate forces within the battery cell pack, thereby clamping it in the battery housing. To achieve sufficient preload, the outer dimensions of the battery cell pack typically differ only slightly from the inner dimensions of the battery housing. The compression pads are usually made of elastic foams, elastomers, or potting compounds, with these materials deforming homogeneously according to predefined, material-dependent spring or force-displacement characteristics. This predetermined deformation property of the compression pads does not provide the optimal counterforce or pressure distribution required for a long battery cell lifespan, thus creating a risk of damage or accelerated aging of the battery cells. From DE 10 2020 110 635 A1, a battery is known which has a battery housing and a battery cell pack arranged in the battery housing. The battery cell pack comprises several battery cells arranged side by side, wherein a bag element is arranged between two battery cells and / or between the battery housing and a battery cell, which is filled with a first fluid and / or with a second fluid. The first fluid is a gas, in particular air. The second fluid is a liquid, such as a viscous liquid, for example a gel. The second fluid is in particular a viscous polymer foam, for example polyurethane foam. From DE 10 2019 128 433 B3, a battery is known which has several battery cells arranged side by side and several elastically designed compression cushions arranged between each pair of battery cells. The battery cells are directly cooled by a coolant flow. The compression cushions are designed and arranged such that they, together with the battery cells, define several cooling channels, allowing the coolant to flow directly along the battery cells despite the compression cushions. The object of the invention is to provide a battery in which expansions of battery cells can be reliably compensated and damage as well as accelerated aging of the battery cells can be reliably avoided. The problem is solved by the features of claim 1. According to the invention, the compression pad has a flexible bag element which defines a bag interior, wherein a liquid or a gel is arranged in the bag interior, such that a battery cell-specific counterforce can be set by the compression pad. The load exerted on the battery cells by the compression pad depends on the fill level of the pouch interior. When the pouch interior is relatively full of liquid or gel, the load exerted by the compression pad is relatively high, while as the fill level decreases, the load exerted on the battery cells by the compression pad decreases. By precisely adjusting the fill level of the compression pad, the required pre-tension can be set. Furthermore, the pressure distribution or load distribution exerted by the compression pad on the battery cell changes when the battery cells, or one of the battery cells, expand unevenly. However, the inventive design of the compression pad allows for a relatively uniform pressure distribution. This is achieved by partially displacing or redistributing the liquid or gel within the bag in the area of ​​the expanded section of the battery cell, resulting in a relatively uniform pressure distribution across the entire surface. In this way, expansions of battery cells can be reliably compensated for, and damage as well as accelerated aging of the battery cells due to stress on the battery cell from the compression pad can be reliably avoided. Several compression pads are present, with the bag elements of several compression pads being manufactured as a single piece and the inner compartments of the compression pads being fluidically connected. Specifically, a compression pad is arranged in each of the spaces bounded by two battery cells, a peripheral battery cell, and the housing wall. This interconnected design of multiple compression pads simplifies the filling process and, if necessary, pressure monitoring or control. Furthermore, it reduces manufacturing effort, as all bag elements can be produced in a single process step. In this system, all bag interiors can be filled through a single filling port. Furthermore, all bag interiors are connected to the cooling circuit through a single coolant inlet and outlet. The flexible pouch element is made, for example, of an elastomer such as EPDM, VMQ, or FVMQ, or of a composite material based on one of the aforementioned elastomers. The flexible pouch element is designed as a hollow body in the shape of a cushion or a balloon. It can be manufactured, for example, by tube extrusion or blow molding. Alternatively, the pouch element can be made from a film with the ends sealed by a joining process such as gluing or welding. The liquid or gel is preferably a thermally conductive liquid or gel, such that the liquid or gel has a relatively high thermal conductivity, which allows the battery cells to be cooled via the compression pad or allows heat to be absorbed from the battery cell via the compression pad and, if necessary, dissipated. The compression pad can be filled before, during, or after its assembly. Filling the bag's interior after the battery cells and bag element have been installed, while the bag is still empty, allows for optimal adjustment and compensation of the forces required to compress the battery cells, as well as the corresponding assembly strokes, clearances, and tolerances. Preferably, the compression pad forms a closed system and has a filling port. The filling port has a filling opening which is closed by a sealing element and can be opened when the pouch interior is to be filled with liquid or gel, or when the amount of liquid or gel in the pouch interior is to be adjusted, i.e., some of the liquid or gel is to be drained from the pouch element or more liquid or gel is to be added to the pouch element. Preferably, the filling port extends from the battery housing, allowing the battery cells and the compression pads to be inserted into the battery housing first, and then the compression pads to expand externally, i.e., outside the battery housing, as the pouch interior is filled.This allows the battery to be fully assembled first, followed by the compression pads being brought into their final state. Because the filling port is accessible from outside the housing interior, the filling of the bag elements can be adjusted even at a later time, for example, after the battery has already been installed and is in use in an electric vehicle. In a preferred embodiment, a pump is arranged at the filling port. This allows the liquid or gel to be filled precisely and in a controlled manner into the interior of the bag. If the filling port is fluidically connected to a liquid tank, the filling quantity of the bag elements can be adjusted as needed by selectively controlling the pump. In particular, if one or more of the battery cells expand, the filling quantity can be adjusted to compensate for the stress exerted on the battery cells by the compression pads. Alternatively, the compression pad is designed as an open system, such that the fluid is a coolant with relatively high thermal conductivity from a cooling circuit. The compression pad has a coolant inlet and a coolant outlet, allowing the coolant to flow through the interior of the bag during operation of the cooling circuit. With such an open-system compression pad, the expansion of the bag element is achieved by the coolant circulating through the cooling circuit and the pressure present in the cooling circuit. The coolant flows into the interior of the bag through the coolant inlet and out through the coolant outlet. The flow of coolant through the compression pad allows for particularly effective cooling of the battery cells, as heat is actively dissipated from them.In this way, the compression pad is designed in such a way that it fulfills its original function on the one hand and serves to cool the battery cells on the other. Preferably, a pressure sensor is provided, which is designed to detect the pressure inside the pouch. This pressure sensor allows monitoring of the pressure inside the pouch and thus the stress on the battery cells caused by the compression pad, reliably preventing impermissible stress on the battery cells. For example, the filling of the pouch can be adjusted based on the pressure sensor signal. Furthermore, the sensor signals from the pressure sensor can be used to estimate the properties of the battery cells. For instance, in the case of swelling, a pressure change inside the pouch can be detected using the pressure sensor, and the swelling can be identified accordingly. In a preferred embodiment, a pressure accumulator is provided which is fluidically connected to the interior of the bag. The pressure accumulator compensates for pressure fluctuations within the bag, thereby reliably providing a predefined load to the battery cells via the compression pad. Several embodiments of the invention are explained in more detail with reference to the drawings. Fig. 1 shows a schematic view of a first, non-inventive embodiment of a battery, Fig. 2 shows a schematic view of a second embodiment of a battery, Fig. 3 shows a schematic view of a third embodiment of a battery, and Fig. 4 shows a schematic view of a fourth embodiment of a battery. Fig. 1 shows a first embodiment of a battery 10 of an electric vehicle, which is designed as a traction battery and thus serves to supply an electric traction unit of the electric vehicle with electrical energy. The battery 10 comprises a battery housing 12, which, together with a housing wall 13, defines an interior housing space 14. A battery cell pack 18, consisting of several battery cells 20 arranged side by side in a stacked configuration, is located within the interior housing space 14. The battery 10 further comprises several compression pads 221, 222, 223, 224, wherein two compression pads 222, 223 are arranged between each pair of adjacent battery cells 20, and two compression pads 221, 224 are arranged between the outermost, edge-side battery cells 20 and the housing wall 13. Thus, in the state shown, the two compression pads 222, 223 arranged between two battery cells 20 each have one side in contact with one battery cell 222, 223 and the other side with the other battery cell 222, 223. The two compression pads 221, 224 arranged between the edge-side battery cell 20 and the housing wall 13 are in contact with the battery cell 221, 224 on one side and with the housing wall 13 on the other. The compression pads 221, 222, 223, 224 each comprise a pouch element 24 and a low-viscosity liquid 26, the low-viscosity liquid 26 filling a pouch interior 25. The liquid 26 has a relatively high thermal conductivity, which cools the battery cells 20 through the compression pads 221, 222, 223, 224. Alternatively, the pouch interiors 25 can be filled with a gel. In the first embodiment of the battery 10 according to Fig. 1, the bag elements 24 are filled with a liquid and sealed fluid-tight. Subsequently, the compression pads 221, 222, 223, 224 are inserted into the housing interior 14 together with the battery cells 20. The advantage of the present compression pads 221, 222, 223, 224 compared to other known designs of compression pads is that the load acting on the battery cells 20 depends on the filling of the bag interior 25. This allows the load on the battery cells 20 to be individually and precisely adjusted by the compression pads 221, 222, 223, 224. Furthermore, the pressure distribution or load distribution acting on the battery cells 20 by the compression pad 221, 222, 223, 224 changes if the battery cells 20 expand unevenly. However, the described design of the compression pads 221, 222, 223, 224 ensures a uniform load distribution on the battery cells 20 by partially displacing the liquid 26 or gel in the interior of the bag 25 and redistributing the liquid 26 within the bag 25. Figure 2 shows a second embodiment of the battery 10. The crucial difference from the first embodiment is that, according to the invention, the compression pads 221, 222, 223, 224 are interconnected such that the nearest compression pads 221, 222, 223, 224 are connected to each other via sections 281, 282, 283. The bag elements 24 of the compression pads 221, 222, 223, 224 are designed such that the bag interiors 25 of the compression pads 221, 222, 223, 224 are fluidically connected to each other via sections 281, 282, 283. Figure 3 shows a third embodiment of the battery 10, which is a modification of the second embodiment shown in Figure 2. The battery 10 of the third embodiment includes a filling port 30, which is a line extending from the interior of the housing 14 to the external environment. A pressure sensor 32, a pressure accumulator 34, and a pump 36 are provided on a section of the filling port 30 located in the external environment. The pump 36 serves to fill the compression pads 221, 222, 223, 224, whereby a liquid from a liquid tank (not shown) is pumped into the compression pads 221, 222, 223, 224 in a controlled manner, causing the bag elements 24 to expand until they abut the battery cells 20 or the housing wall 13.Furthermore, the pump 36 serves to adjust the filling of the bag interiors 25 as needed during operation of the battery 10, thereby adjusting the load on the battery cells 20 by the compression pads 221, 222, 223, 224 as required. The pressure sensor 32 is designed to detect the pressure in the bag interiors 25. This allows the load on the battery cells 20 to be monitored and changes in the battery cells 20, in particular swelling, to be detected. The pump 36 can be controlled based on the sensor signal from the pressure sensor 32. The pressure accumulator 34 serves to maintain a predefined pressure in the bag interiors 25 and to compensate for pressure fluctuations in the bag interiors 25, thus reliably providing a predefined load on the battery cells 20 by the compression pads 221, 222, 223, 224. The embodiments shown in Figs. 1, 2, and 3 are designed as closed systems. The first embodiment shown in Fig. 1 and the second embodiment shown in Fig. 2 are also passive, such that the bag elements 24 are filled to a predefined level, which is maintained continuously during operation of the battery 10. The third embodiment shown in Fig. 3 is active, with the pressure sensor 32 detecting the pressure within the bag elements 24 and, based on this, controlling the pump 36. This pump draws the liquid 26 from or pumps it into the bag interiors 25, allowing the pressure in the bag interiors 25 to be adjusted to a predefined value. Figure 4 shows a fourth embodiment of the battery 10, which is also a modification of the second embodiment from Figure 2. Here, the compression pads 221, 222, 223, 224 are designed as an open system, wherein the compression pads 221, 222, 223, 224 are fluidically connected to a cooling circuit (not shown) via a coolant inlet 301 and a coolant outlet 302 such that the liquid 26 is formed by a coolant which flows through the bag interiors 25 during operation of the coolant circuit. The compression pads 221, 222, 223, 224 are connected to each other on both sides via a section 281, 282, 283 formed on a first side of the battery cells 20 and via a section 291, 292, 293 formed on a second side of the battery cells 20.The pressure sensor 32 and the pressure accumulator 34 are arranged in a section forming the coolant inlet 301, thereby monitoring the pressure in the inner compartments 25 of the bags and preventing overloading of the battery cells 25 by the compression pads 221, 222, 223, 224. This open system allows the expansion of the compression pads 221, 222, 223, 224 by the coolant circulating through the cooling circuit and the pressure present in the cooling circuit. The flow of coolant through the compression pads 221, 222, 223, 224 enables particularly effective cooling of the battery cells 20, as heat is actively and continuously dissipated from the battery cells 20.

Claims

Battery for an electric vehicle, comprising a battery housing (12) which defines an interior space (14) and a battery cell pack (18) with several battery cells (20) which are arranged in the interior space (20), wherein a compression pad (221, 222, 223, 224) is arranged between two adjacent battery cells (20) and / or between an edge-side battery cell (20) and a housing wall (13) of the battery housing (12), characterized in that the compression pad (221, 222, 223, 224) has a flexible bag element (24) which defines an interior space (25), wherein a liquid (26) or a gel is arranged in the interior space (25), wherein several compression pads (221, 222, 223, 224) are present, wherein the bag elements (24) of several compression pads (221, 222, 223, 224) are made in one piece and the bag interiors (25) of the compression pads (221, 222, 223, 224) are fluidically connected to each other. Battery according to claim 1, characterized in that the compression pad (221, 222, 223, 224) forms a closed system and has a filling port (30). Battery according to claim 2, characterized in that the filling port (30) extends from the battery housing (12). Battery according to claim 2 or 3, characterized in that a pump (36) is arranged at the filling port (30). Battery according to claim 1, characterized in that the compression pad (221, 222, 223, 224) is designed as an open system, such that the liquid (26) is a coolant of a cooling circuit, wherein the compression pad (221, 222, 223, 224) has a coolant inlet (301) and a coolant outlet (302), such that the coolant flows through the interior of the bag (25) during operation of the coolant circuit. Battery according to one of the preceding claims, characterized in that the liquid (26) or the gel is designed as a thermal conductor. Battery according to one of the preceding claims, characterized in that a pressure sensor (32) is provided which is designed to detect the pressure in the interior of the bag (25). Battery according to one of the preceding claims, characterized in that a pressure accumulator (34) is provided which is fluidically connected to the bag interior (25). Battery according to one of the preceding claims, characterized in that a compression pad (221, 222, 223, 224) is arranged in each of the spaces bounded by two battery cells (20) and by a peripheral battery cell (20) and the housing wall (13) in the stacking direction of the battery cells (20).

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