DE102022208233A1 - Cell assembly for a battery system - Google Patents

Abstract

The invention relates to a cell assembly for a battery system, with a number of battery cells (7) which are stacked one behind the other in the stacking direction, with the battery cell stack (1) being assigned a clamping unit (3) which has pressure plates (19) arranged at the opposite stack ends , via which the battery cell stack (1) is subjected to a bias voltage (F _V ). According to the invention, the two pressure plates (19) of the clamping unit (3) are connected to one another via at least one scissor linkage, which is spring-loaded by means of tension and/or compression springs (23, 25).

Description

The invention relates to a cell assembly for a battery system according to the preamble of claim 1.

A generic cell assembly can be a battery module with a module housing in which a battery cell stack with a number of battery cells is arranged, which are stacked one behind the other in a stacking direction. A clamping unit is assigned to the battery cell stack. This has a pressure plate at each of the opposite stack ends, via which the battery cell stack can be subjected to a pre-voltage. Alternatively, the cell assembly can be a cell-to-pack system that does not have a module housing and therefore has less component weight than the battery module.

It is known that the cell expands when charging and contracts when discharging. This mainly happens on the anode side. Since lithium is incorporated into the graphite structure, the graphite structure expands. As soon as the lithium is completely embedded in the graphite, an expansion of around 20% can be expected for LiC ₆ . When the graphite-based anode is discharged, the cell compresses by the same amount.

For high-speed charging, the silicon content in the active anode material is increased. Silicon can absorb lithium by forming the Li ₂₂ Si ₆ alloy. This means that 6 silicon atoms can accommodate 22 lithium atoms. This automatically leads to greater expansion of the cell. With 100% silicon, an expansion of the cell of around 300% can therefore be expected. Silicon in the anode can cause rapid charging. This means that the silicon content in the active anode material will increase in the future.

The older the cell gets, the more gas is produced due to the decomposition of the electrolyte in the cell. This gas causes internal pressure and swelling in the cell. Expansion and contraction also occur in the cathode when lithium intercalates within the active material and when lithium deintercalates outside the active material. However, the expansion and contraction is much less because the cathode material is much stiffer and can withstand higher internal pressure. Here the expansion is 2 to 5%.

A first problem is the uncontrolled expansion of the cell and thus the module: The expansion increases the distance between the particles in the active material, which leads to a loss of electrical contact. In addition, a non-conductive SEI layer increasingly builds up, which further reduces electrical conductivity. Because of this problem, a silicon anode only has a lifespan of about 750 cycles.

A second problem is that the dimensions of the module change during expansion: due to the expansion of the cell inside the module, internal pressure is created on the walls of the module. As a result, a weld between the top plate of the module and the module housing is subjected to high tensile stress. This can lead to cracks. The module can be attached to the battery system housing with screws. The expansion of the battery module can shift the mounting holes so that the modules cannot be secured in the battery pack in the correct position. The fastening screw is also under shear stress.

A third problem is the high compressive force or preload acting on the cell: if the cell is compressed by an excessively high pressure or preload, this can lead to less expansion, but there is a risk that the separator or the foil housing of the pouch cell can be damaged. When the cell is compressed with low pressure, the swelling occurs unevenly. It is important that the pressure on the cell is uniform in all areas and remains constant during the expansion and compression phases. It has been shown that compression by a spring is problematic because the spring exerts more pressure when it is compressed over a spring travel. This means that the springs arranged on the end faces of the pouch cell do not exert any pressure or preload during the compression phase and exert more than the required pressure during full expansion. However, the pressure or preload should be uniform during both cell compression and cell expansion. This means that the cell should be subjected to the same uniform compression throughout the SOC (state of charge). This is not possible with spring pressure.

A fourth problem is that the contact point at which the respective cell arrester is welded to a busbar is exposed to high mechanical stresses due to the cell expansion and cell compression of the pouch cells: If the cell swells more than the space in the module allows, the welded connection between the cell arrester and the busbar experiences shear stress and tears. The welded connection between the busbar and the cell arrester is below Shear stress and can lead to a stress crack.

From the DE 10 2018 114 226 A1 a load-bearing battery module is known. From the US 2022/0029190 A1 A battery cell stack is known with a clamping unit which exerts a preload on the battery cell stack in the stacking direction.

The object of the invention is to provide a cell assembly, in particular a battery module or a cell-to-pack system, for a battery system, which can be operated with increased operational reliability compared to the prior art.

The task is solved by the features of claim 1. Preferred developments of the invention are disclosed in the subclaims.

The function and the advantageous effects of the invention are explained below using a battery module as an example. However, it is understood that the invention is not limited to a battery module with a module housing, but also includes, for example, a cell-to-pack system without a module housing.

In the module housing of a battery module, a battery cell stack is arranged in the module housing, which consists of a number of battery cells stacked one behind the other in the stacking direction. A clamping unit is assigned to the battery cell stack. This has pressure plates at opposite stack ends, via which the battery cell stack is subjected to a preload. The clamping unit can preferably be arranged within the module housing and functionally independent of the module housing. In this way, the module housing can remain essentially free of bias during the expansion and contraction of the battery cell stack in battery operation. The battery cell stack according to the invention, in particular consisting of battery pouch cells, is under tension during the entire expansion and contraction phase.

The battery cell stack is composed of the battery cells with intermediate compression pads. These just help create even compression. However, they do not contribute to exerting a bias on the cells. The cell stack is located in a clamping unit. There is free space between the clamping unit and the module housing. The clamping unit can be attached to the module housing using positioning strips or metal strips that can bend and align depending on the distance between the clamping unit and the module housing. It should be emphasized that the metal strips do not act as springs. You simply connect the cell stack to the module housing. The free space between the clamping unit and the module housing can be used for air cooling of the cell stack.

A core of the invention is that the two front pressure plates of the clamping unit are connected by a linkage and a spring combination. In cell stack expansion or cell stack contraction, one spring expands, one spring expands while the other spring contracts. In this way, the effective total spring pressure is kept constant during the movement of the rod (caused by cell stack expansion or cell stack contraction). The linkage with the springs is always under spring tension. The linkage can be located on both the top and bottom sides of the cell stack. The clamping unit pressure plates move outward as the cell stack expands. The module housing, on the other hand, remains free of the cell stack bias. As the cell stack contracts, the pressure plates of the clamping unit move inward. The module housing is not subject to voltage. This means that the expansion and contraction of the cell stack has no impact on the module housing. The module housing can be attached to the battery system without the risk of the dimensions of the module and the system changing due to voltage.

Another aspect concerns the at least one busbar installed in the battery module. The busbar is designed so that it can follow the expansion or contraction paths of the cell stack. The busbar can preferably be connected to the movable pressure plates of the clamping unit. In this way, no shear stresses arise at the welded connection between the respective cell arrester and the busbar. The busbar consists of a plastic part and a metal part. The metal part may have folds or loops that can flatten as the busbar expands. The plastic part can consist of at least two components, one of which is movable and the other is fixedly attached to the module housing. In this way, the plastic part can also expand. This means that the busbar can follow the expansion and contraction of the cell stack without any tension.

By combining pressure plates, rods and springs, it is possible to apply uniform compression pressure to the cell stacks throughout the entire SOC range. The entire mechanism is stretchable, meaning it can accommodate a very high cell stack expansion, as occurs when using silicon anodes. The dimensions of the module housing remain unchanged. It does not experience expansion and contraction forces. At least one positioning bar connects the pressure plates of the clamping unit to the fixed module housing. The positioning bar is essentially not loaded during cell stack expansion or cell stack contraction.

The linkage of the clamping unit can be a scissor linkage made up of two coupling rods, which are arranged diagonally to one another and are pivotally connected to one another via a central pivot point. For example, the scissor linkage can have four springs. These can be positioned in any quadrant of the scissor linkage. Alternatively, two springs can be arranged in a quadrant. A linkage arranged on the bottom can be separated from a thermal paste via a cover. In this way, the thermal paste cannot come into contact with the rod.

The clamping unit is made of aluminum and can therefore also transfer heat from the cell stack to the module plate. If a target preload acting on the cell stack is set during assembly of the clamping unit, this target preload remains unchanged during the operational expansion and contraction of the cell stack.

The busbar can, for example, be constructed in three parts, namely two plastic parts and one metal part. Of the two plastic parts, one plastic part is mounted in a stationary manner on the module housing, while the other plastic part is arranged on the stationary plastic part so that it can move in the stacking direction. The movable plastic part can be connected to the pressure plates of the clamping unit so that it moves when the pressure plates of the clamping unit move. The metal part is welded to the cell conductors of the battery cells. It essentially takes the form of an embossed or curved strip of metal. This is also connected to the movable plastic part and finally to the clamping unit. As the tensioner expands, the metal band stretches and the bend becomes flat. As the cell stack contracts, the metal band contracts and flexes. In this way, there is no mechanical stress at the contact points between the busbar and the cell conductors during the expansion and contraction of the cell stacks.

The clamping unit can have a linkage on the top of the cell stack and on the bottom of the cell stack. It is also possible to arrange the linkage on only one side of the cell stack.

There may also be a recess on the top side of the cell stack in which a sensor assembly with temperature sensors is attached. It is also possible to close the upper linkage and the sensor assembly with the upper module housing cover so that no dust can penetrate into the module.

The compression pads used in the cell stack do not build up any preload, but only create an even pressure between the battery cells. Therefore you can reduce the number of compression pads. For example, it can be applied after every three cell stacks.

A higher silicon content can be used in the anode without the risk of reducing cycle time due to large expansion.

The components of the tensioning unit, i.e. coupling rods, pressure plates and springs, can be made of stainless steel. In addition, there can be a clearance between the rod and the cell stack, so that movement of the rod takes place without interference contours.

The cell stack according to the invention has a uniform bias over the entire SOC range. This reduces the overpressure during the highest SOC value and minimizes the risk of penetration into the separator. The swelling is largely uniform, which means that the conductivity of the cells also remains uniform. In addition, the clamping unit and the cell stack can be easily installed in the module. The module housing and the front/back cover do not experience any dimensional changes due to the compression and expansion of the cell stack. This also reduces the load on the fastening screws. The busbar used according to the invention is flexible with respect to changes in cell stack size. This means that no shear stress occurs at the contact points between the cell conductors and the busbar due to the expansion and contraction of the cell stacks. This results in a longer lifespan for the cell stack due to the constant preload.

Since the linkage of the clamping unit, which comes into contact with the cell stack, is metallic, it can absorb heat more quickly from the cell stack. This means that cooling is more efficient with this modified module design. There is also less need for compression pads, which leads to weight savings. No springs are required in the module to create the preload. In the present case the pre tension is only realized by the springs built into the linkage as soon as the cell stack expands or contracts, whereby the cell stack is always subjected to a constant preload, namely in the entire SOC range (ie in the entire compression and expansion range).

With the clamping unit according to the invention, a high proportion of silicon can be used in the anode without affecting the service life. Silicon in the anode helps charge the cell stacks faster.

The springs built into the linkage do not require any additional space in the module as they are arranged directly on the top and bottom of the cell stack. Furthermore, the welds in the module housing (for example welds for connecting the front/rear module cover) are largely stress-free.

The essential aspects of the invention are highlighted again in detail below: The two pressure plates of the clamping unit can be connected to one another via at least one scissor linkage. The scissor linkage is spring-loaded with the help of tension and/or compression springs.

In a technical implementation, the scissor linkage can have two coupling rods. These can be arranged diagonally across each other and connected to one another at a common central hinge point. Starting from the central pivot point, two coupling rod arms can protrude diagonally or star-shaped outwards for each coupling rod. In addition, each of the pressure plates can be assigned a linear guide in which the arm ends of the coupling rod arms are guided in a linearly adjustable manner.

A compression and/or tension spring can be supported between coupling rod arms adjacent in the circumferential direction. In addition, the linear guides formed in the pressure plates can extend in the stacking direction or transversely to the stacking direction.

In common practice, the battery cells stacked in the battery cell stack have cell conductors that project laterally. These are electrically connected at connection points, in particular by welding, to at least one electrically conductive metal part of at least one bus bar. With the help of the busbar, the battery cells can be electrically connected to one another. Preferably, the metal part of the busbar can be loop-shaped or U-shaped with a metal part fold between the connection points. With the help of the metal part fold, length compensation is possible when the battery cell stack expands or contracts. The busbar can preferably be designed in three parts, namely from a busbar plastic part fixed in place on the module housing, at least one busbar plastic part guided therein in an adjustable manner in the stacking direction, and the already mentioned electrically conductive metal part. The metal part can preferably be connected to the adjustable busbar plastic part, while the metal part fold formed in the metal part remains free of connection in order to enable length compensation through deformation during the expansion or contraction of the battery cell stack.

The pressure plates of the clamping unit can be connected to the inside of the module housing via positioning strips. The positioning strips can compensate for expansion or contraction of the battery cell stack during battery operation through deformation.

• 1 bis 8 unterschiedliche Ausführungsvarianten eines Batteriemoduls.

Exemplary embodiments of the invention are described below with reference to the attached figures. Show it:

• 1 until 8th different design variants of a battery module.

In the 1 a battery cell stack 1 with an associated clamping unit 3 is shown in a view from above. The battery cell stack 1 can be in a module housing 5 ( 5 until 8th ) of a battery module can be arranged. In the 1 purely as an example, the battery cell stack 1 has a total of four battery pouch cells 7 stacked one behind the other in the stacking direction. Compression pads 9 are arranged between adjacent battery pouch cells 7. The battery cells 7 each have cell conductors 11 that project laterally outwards. These are welded to an electrically conductive metal part 15 of a busbar 17 at connection points 13 in the battery cell stack 1 housed in the module housing 5. With the help of the busbar 17, the battery pouch cells 7 are electrically connected to one another.

It should be emphasized that the invention is not limited to a battery module, but can also be applied to a cell-to-pack system without a module housing.

With the help of the tensioning unit 3, a uniform and constant preload Fv can be exerted on the battery stack 1 during the expansion and contraction of the battery cells 7 in the stacking direction during battery operation. For this purpose, the clamping unit 3 has a pressure plate 19 at each end of the stack. The two pressure plates 19 are connected to one another above and below the battery cell stack 1 via a scissor linkage consisting of two coupling rods 27. That shit rod is spring-loaded by means of tension and/or compression springs 23, 25.

Like from the 1 As can be seen further, the two coupling rods 27 of the scissor linkage are arranged diagonally across each other and are pivotally connected to one another at a common central articulation point 29. Starting from the central articulation point 29, two coupling rod arms 31 for each coupling rod 27 protrude outwards on opposite sides and diagonally or in a star shape. Two adjacent coupling rod arms 31 are articulated to one of the pressure plates 19. For this purpose, each of the pressure plates 19 has linear guides 33, in which the guide pins 35 of the arm ends of the coupling rod arms 31 are guided in a linearly adjustable manner. In the 1 The coupling rod arms 31 each span quadrants in the circumferential direction, in which a compression and / or tension spring 23, 25 are arranged, which are supported between adjacent coupling rod arms 31. In the 1 The linear guides 33 formed in the pressure plates 19 extend transversely to the stacking direction.

During cell stack expansion or cell stack contraction, one spring expands while the other springs contract. This means that the prestress acting on the cell stack always remains constant regardless of the cell stack expansion or contraction, so that a constant prestress is always exerted on the cell stack in all SOC areas.

During a cell stack expansion, for example, the one in the 1 Coupling rod 27 aligned to the top left around the central joint or pivot point 29 in a clockwise direction, while in the 1 Coupling rod 27 aligned to the top right rotates counterclockwise around the central joint or pivot point 29. In a cell stack contraction it is exactly the opposite.

In the 2 a process state is indicated in which the battery cell stack 1 is housed in the module housing 5. In the 2 Only the module housing bottom 37 of the module housing 5 is shown. Between the battery cell stack 1 and the module housing 5 there is a thermal paste 39, which supports heat dissipation from the battery cell stack towards the module housing bottom 37. In order not to impair the functionality of the lower scissor linkage 21, a cover 41 is arranged between the lower scissor linkage 21 and the thermal conductor paste 39, by means of which contact of the thermal paste 39 with the lower scissor linkage 21 is prevented.

In the 3 A second exemplary embodiment of the invention is shown, the structure and functionality of which corresponds to the structure and functionality of the one in the 1 and 2 corresponds to the first exemplary embodiment shown. In contrast to the 1 and 2 are in the 3 the effective directions of the tension/compression springs 23, 25 are identical to the stacking direction. Each of the tension/compression springs 23, 25 is connected with its spring base points to coupling rod arms 31 opposite each other in the stacking direction, in alignment with the stacking direction.

In the 3 So there are two springs 23, 25 on the left side and two springs 23, 25 on the right side. The two springs 23, 25 are of different designs. The outer spring 23 is a tension spring. This means that the spring 23 builds up force when it is pulled. The inner spring 25 is a compression spring. It therefore builds up strength when pressed. In the initial state (ie when the tensioning unit 3 is mounted) both springs 23, 25 have the same force. When the cell stack 1 expands, the two outer tension springs 23 build up more force and the two inner compression springs 25 build up less force. When the cell stack 1 contracts, the two inner compression springs 25 release more force. The outer tension springs 23 emit less force.

That in the 4 The third exemplary embodiment of the invention shown is also essentially identical in structure and functionality to the previous exemplary embodiments. In contrast to 3 are in the 4 the linear guides 33 in the two pressure plates 19 are no longer aligned transversely to the stacking direction, but rather aligned with the stacking direction. The tension/compression springs 23, 25 are in the same way as in the 3 supported between the coupling rod arms 31.

Like from the 5 As can be seen, the electrically conductive metal part 15 of the busbar 17 does not extend in a straight line between adjacent connection points 13, but rather in a loop shape or U-shape with a metal part fold 43. In this way, length compensation can be achieved in the metal part 15 when the battery cell stack 1 expands or contracts take place, so that no mechanical stresses are built up at the connection points 13. To further support such length compensation, the 7 the busbar 17 is designed in three parts, consisting of a busbar plastic part 45 fixed in place on the module housing 1, a multi-part busbar plastic part 47, for example, which is guided in the stationary busbar plastic part 45 in an adjustable manner in the stacking direction, and from the already mentioned electrically conductive metal part 15. The metal part 15 is according to 5 connected to the adjustable busbar plastic parts 47, while the metal folds 43 remain unconnected in order to be able to compensate for the length. In the 6 the metal part 15 is shown alone in a view from above.

According to the 7 and 8th the pressure plates 19 of the clamping unit 3 are connected to the inside of the module housing with the help of positioning strips 49. The positioning strips 49 compensate for expansion or contraction of the battery cell stack 1 through deformation. For this purpose, the positioning strips 49 are designed in a U-shape to ensure deformation.

In the 7 and 8th the module housing 5 is not designed as a monoblock, but rather from several components, including a lower U-profile part 51 and an upper cover plate 53. When assembling the module, the thermal paste 39 is first applied to the lower U-profile part 51. The assembly, consisting of the bus bars 17, the pressure plates 19, the coupling rods 27, the springs 23, 25 and the cell stack 1, is then inserted into the lower U-profile part 51 and placed on the thermal paste 39. Finally, the upper cover plate 53 is placed on the lower U-profile part 51 and welded to it.

The clamping unit 3 can be cooled by air cooling in the module or by conventional water cooling under the module housing 5. The clamping unit 3 is preferably made of metallic material so that the cell stack 1 can be cooled more quickly. The front/back module covers 55, 57 can be made as aluminum die-cast parts. It is screwed to the solid plastic part 45 of the busbar 17 and then welded to the other components 51, 53 of the module housing 5.

In the 8th A sensor assembly 59 with temperature sensors is also attached to the top of the cell stack and has a sensor cover 61. It is also possible to close the upper linkage and the sensor assembly with the upper module housing cover 53 so that no dust can penetrate into the module.

Reference symbol list

1

Battery cell stack

3

Clamping unit

5

Module housing

7

Battery cells

9

Compression pads

11

Cell arrester

13

Connection points

15

electrically conductive metal part

17

Bus bar

19

printing plates

23,

25 tension and/or compression springs

27

Coupling rods

29

Articulation point

31

Coupling rod arm

33

Linear guide

35

Guide pin

37

Module housing base

39

Thermal paste

41

cover

43

Metal part fold

45

stationary busbar plastic part

47

adjustable guided busbar plastic parts

49

Positioning bar

51

lower U-profile part

53

Cover plate

55, 57

Module covers

59

Sensor assembly

61

Sensor cover

Fv

preload

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102018114226 A1 [0010]
• US 2022/0029190 A1 [0010]

Claims (10)

Cell assembly for a battery system, with a number of battery cells (7) which are stacked one behind the other in the stacking direction, the battery cell stack (1) being assigned a clamping unit (3) which has pressure plates (19) arranged at the opposite stack ends, via which the Battery cell stack (1) is subjected to a preload (F _V ), characterized in that the two pressure plates (19) of the clamping unit (3) are connected to one another via at least one scissor linkage, which is connected by means of tension and/or compression springs (23, 25). is spring-loaded, and that in particular the scissor linkage is arranged on the top and / or on the bottom of the battery cell stack (1). Cell association after Claim 1 , characterized in that the scissor linkage has two coupling rods (27), which are arranged diagonally across one another and are connected to one another at a common central articulation point (29), so that, starting from the central articulation point (29), two coupling rod arms (31) each Coupling rod (27) protrude diagonally, and in particular each of the pressure plates (19) has linear guides (33) in which the arm ends of the coupling rod arms (31) are guided in a linearly adjustable manner. Cell association after Claim 2 , characterized in that a compression and/or tension spring (23, 25) is supported between adjacent coupling rod arms (31), and in particular four compression and/or tension springs (23, 25) are installed between the coupling rod arms (31). Cell association after Claim 3 , characterized in that the preload or compressive force (F _V ) is adjusted when installing the scissor linkage on the battery cell stack (1) with the help of the tension and / or compression springs (23, 25), and / or that the preload (Fv ) remains constant during the operational expansion and contraction of the battery cell stack (1), since in particular two of the springs (23, 25) always relax, while the other two springs (23, 25) exert a tensile or compressive force on the coupling rod arms (31 ) exercise. Cell association after Claim 3 or 4 , characterized in that the linear guides (33) formed in the pressure plates (19) extend in the stacking direction or transversely to the stacking direction. Cell assembly according to one of the preceding claims, characterized in that the battery cells (7) in the battery cell stack (1) have laterally projecting cell conductors (11) which are connected to at least one electrically conductive metal part (15) at connection points (13), in particular via welding a busbar (17) are electrically connected, which electrically interconnect the battery cells (7), and in particular the busbar (17) is designed to be expandable and contractible analogous to the battery cell stack (1) in order to accommodate the expansion and contraction of the battery cell stack (1). consequences. Cell association after Claim 6 , characterized in that the metal part (15) of the busbar (17) between the connection points (13) is designed to be loop-shaped or U-shaped with a metal part fold (43) to compensate for the length when the battery cell stack (1) expands or contracts. Cell assembly according to one of the preceding claims, characterized in that the cell assembly is a battery module, in the module housing (5) of which the battery cell stack (1) is arranged, and that the clamping unit (3) within the module housing (5) and / or functionally independent of Module housing (5) is arranged so that the module housing (5) remains essentially bias-free, or that the cell assembly is a cell-to-pack system in which the battery cell stack (1) is designed without a module housing. Cell association after Claim 8 , characterized in that the busbar (17) is designed in three parts, consisting of a busbar plastic part (45) fixed in place on the module housing (5), at least one busbar plastic part (47) guided therein in an adjustable manner in the stacking direction, and the electrically conductive metal part (15), and that in particular the metal part (15) is connected to the adjustable busbar plastic part (47), while the metal part fold (43) remains free of connection. Cell assembly according to one of the preceding claims, characterized in that the pressure plates (19) of the clamping unit (3) are connected to the module housing (5) by means of positioning strips (49), and that the positioning strips (49) prevent expansion or contraction of the battery cell stack (1). compensate by deformation.

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