Housing for an individual battery cell

Abstract

The invention relates to a housing (2) for an individual battery cell (1) comprising at least one electrode / separator arrangement (4) which is impregnated with a liquid electrolyte (E), wherein housing walls (3) surround the at least one electrode / separator arrangement (4). The housing according to the invention is characterised in that the surfaces of the housing walls (3) facing the at least one electrode separator arrangement (4) have an at least partially roughened surface (10).

Description

[0001] Housing for a single battery cell

[0002] The invention relates to a housing for a single battery cell having at least one electrode-separator arrangement impregnated with a liquid electrolyte, according to the type defined in more detail in the preamble of claim 1. The invention also relates to a single battery cell having such a housing.

[0003] Such individual battery cells are generally known from the prior art. They consist, for example, of a coil or stack as an electrode-separator arrangement, with at least one such electrode-separator arrangement arranged in the housing. In addition, and this applies in particular to prismatic individual battery cell arrangements with two stacks, i.e., two independent electrode-separator arrangements, are also known from the prior art.

[0004] In practice, the electrode-separator assemblies are then inserted into the housing and subsequently filled with electrolyte. In general, DE 199 11 800 C1 describes a suitable method and device for filling the electrolyte. DE 102008 010 827 A1 describes a method for closing an electrolyte filling opening of a single battery cell.

[0005] In current practice, the housings for the individual battery cells are evacuated and heated before being filled with electrolyte, and then the electrolyte is added. Inside the cell there is one or more electrode-separator assemblies, for example in the form of an electrode stack, which is wetted with electrolyte. Capillary forces draw the electrolyte from the outside to the inside into this stack. The electrolyte is essentially “sucked in”. Such a process is described in the article “Visualization of electrolyte filling process and influence of vacuum during filling for hard case prismatic lithium ion cells by neutron imaging to optimize the production process” by Weydanz et al. in the Journal of Power Sources 380 (2018) 126-134. Corresponding images of an individual battery cell during filling with electrolyte are shown.These images show that, for a certain time after filling the housing, the electrolyte surrounds the entire electrode stack and is evenly drawn into the electrode stack from all sides. In practice, this leads to any moisture and gases remaining in the electrode stack, despite the evacuation, concentrating in the center of the electrode stack at the end of the filling process. Such areas, which are not or not completely saturated with the electrolyte, then impair the performance of the individual battery cell and reduce its service life.

[0006] Regarding the state of the art, reference can also be made to DE 102004 038 072 A1 and DE 698 06 722 T2, which describe roughened surfaces in individual battery cells. The introduced roughness serves to improve contact and / or static friction for mechanical stabilization. DE 10 2019 208 063 A1 describes the introduction of structures into individual battery cells using a laser or electron beam.

[0007] The object of the present invention is to provide an improved housing for a single battery cell, which is optimized in such a way that the filling process with liquid electrolyte is improved.

[0008] According to the invention, this object is achieved by a housing having the features of claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and further developments emerge from the dependent subclaims. Furthermore, the object is achieved by a single battery cell having such a housing. Advantageous embodiments and further developments emerge from the dependent subclaims.

[0009] The considerations are based on the process most commonly used in practice for filling a single battery cell with electrolyte. For this purpose, the housing with the at least one inserted electrode-separator assembly is evacuated and filled with electrolyte, for example, through a filling opening that is later to be closed in accordance with the aforementioned prior art. The electrolyte then begins to move from the side from which it was filled into the housing, on the one hand, directly into the electrode-separator assembly, as it is sucked in by the latter via capillary forces. Furthermore, and this process typically occurs more quickly, the electrolyte spreads along the inner surface of the housing walls and flows around the electrode-separator assembly, so that the assembly ultimately begins to suck in the electrolyte from all sides.

[0010] In the housing according to the invention, it is now provided that the housing walls surrounding the at least one electrode-separator arrangement are at least partially, and according to a particularly advantageous embodiment, completely, provided with a roughened surface on their surface facing the at least one electrode-separator arrangement. Such a roughened surface ensures that the electrolyte no longer moves as quickly in the edge channel created between the housing walls and the at least one electrode-separator arrangement as in the structures according to the prior art. The roughened surface increases the pressure loss and thus delays the spread of the electrolyte in the edge channel. The electrolyte can no longer distribute around the entire electrode-separator arrangement as quickly as in the prior art.The electrolyte is then sucked into the electrode-separator assembly via capillary forces in such a way that it primarily starts from the electrolyte filling side and then increasingly from the side edges of their ends facing the electrolyte filling opening. The end of the electrode-separator assembly opposite the electrolyte filling opening remains without electrolyte in the edge channel there for a relatively long time due to the higher pressure loss caused by the roughened inner surface of the housing walls. With appropriate design of the edge channel and a suitable selection of the roughness of the roughened surface, this results in the side edge of the electrode-separator assembly facing away from the electrolyte filling opening remaining free of electrolyte until the electrode-separator assembly is completely saturated with electrolyte.Any gases and residual moisture in the electrode-separator assembly can therefore escape the drawn-in electrolyte on this side and escape from the electrode-separator assembly into the edge channel, which is still at least partially free there. This altered process during electrolyte filling, made possible by the roughened inner surface of the housing walls, now results in the electrolyte being able to completely saturate the electrode-separator assembly. Undesired gases and moisture are not trapped inside the electrode-separator assembly but can escape into the area of ​​the edge channel not yet filled with electrolyte, typically on the side of the electrode-separator assembly opposite the opening for electrolyte filling. Moisture and residual gases can thus completely leave the electrode-separator assembly.In the edge channel, the gases and moisture are harmless, unlike those inside the electrode separator arrangement, so that they can remain there without having a detrimental effect on the performance and service life of the individual battery cell.

[0011] The housing according to the invention provides that, instead of a complete or completely uniform distribution of roughness across the inner surfaces of the housing walls, as used in the prior art to improve electrical conductivity, a varying roughness is provided on the housing walls, so that the electrolyte is subjected to different pressure losses in different contact areas with the housing. This allows the electrolyte to be directed very precisely to areas where it is desired and kept away from areas where it is not.

[0012] According to a further very advantageous embodiment of the housing according to the invention, it can be provided that the roughened surface is achieved by surface processing. Such surface processing, which according to a further very advantageous embodiment can be implemented in particular as laser processing, allows the inner surfaces of the housing walls to be provided with the desired roughness in a very targeted manner. It is also conceivable, for example, to provide varying roughnesses so that the pressure losses in the first part of the edge channel, viewed from the electrolyte filling opening, are lower than in the further course of the edge channel, in particular in the area opposite the electrolyte filling opening.

[0013] Alternatively, or in combination with this, the roughened surface of the housing walls can also be achieved by a coating according to another very advantageous embodiment. Such a coating, which according to a very advantageous development is designed as a ceramic coating, can also be used to change the roughness of the housing walls. A ceramic coating in particular has the decisive advantage of being very chemically and thermally resistant, so that a reaction between the coating and the electrolyte can be ruled out. Accordingly, the coating not only influences the roughness of the surface but also protects the material of the housing wall.

[0014] A further very advantageous embodiment of the housing according to the invention provides that, in addition to the roughened surface of the housing walls, elevations are provided as flow resistances. These elevations are also arranged on the side of the housing walls facing the electrode-separator arrangement. They are arranged at least in the regions facing the side edges of the electrode-separator arrangement. In the case of an electrode-separator arrangement designed as a stack, they ideally extend across the entire width of the housing in the stacking direction. In addition to the roughened surface, which increases the flow resistance for the electrolyte, these elevations also increase the flow resistance and form barriers for the electrolyte by leaving only small gaps between the side edges of the electrode-separator arrangement and the elevations.Ideally positioned elevations can thus influence the penetration of the electrolyte in addition to the roughened surfaces by slowing down the flow in the edge channel and can thus ensure an even better and more uniform saturation of the electrode-separator arrangement with electrolyte.

[0015] The single battery cell according to the invention now provides such a housing. According to a preferred embodiment, this housing can be prismatic. Alternatively, the battery cell can also be designed in the form of a round cell, which can result in similar problems with electrolyte wetting, especially when large-format cells are involved.

[0016] A very advantageous embodiment of the individual battery cell according to the invention provides for the electrode-separator arrangement to be designed in the form of at least one stack. The electrodes and the separator are designed, for example, in the form of individual sheets and are stacked one on top of the other. Alternatively, a Z-shaped folded separator, as is fundamentally known from the prior art, would also be conceivable, in which the individual electrodes of different polarity are then inserted laterally into the pockets created by the Z-shaped folding. The electrodes would then still be individual sheets, and the separator a Z-shaped folded strip material. Furthermore, it would also be conceivable to realize both the electrodes and the separator as Z-shaped folded strip material, which would then be inserted into one another. This structure is also fundamentally known from the prior art.

[0017] Further advantageous embodiments of the housing according to the invention and the improved impregnation of the electrode-separator arrangement with electrolyte to be achieved thereby also emerge from the exemplary embodiment which is described in more detail below with reference to the figures.

[0018] Showing:

[0019] Fig. 1 shows the impregnation of an electrode-separator arrangement with electrolyte according to the aforementioned prior art from the “Journal of Power Sources”; and

[0020] Fig. 2 is a representation of the impregnation of an electrode-separator arrangement with electrolyte analogous to the representation in Fig. 1 , but with the housing according to the invention.

[0021] The illustration in Figure 1, based on the article in the Journal of Power Sources 380 (2018) 126-134 mentioned at the beginning, shows how a conventional single battery cell 1 is impregnated with electrolyte. The single battery cell 1 consists of a housing designated 2, which in the example of a prismatic single battery cell 1 shown here is formed from several cuboid-shaped housing walls 3. Within this housing 2 is an electrode-separator arrangement 4, which here is designed as a stack of electrodes and separators, for example. It is therefore also referred to below as stack 4. Electrical connection lugs 5, 6 protrude from the single battery cell 1 through the housing wall 3 of the housing 2 shown above.Between these connection lugs 5, 6 there is a filling opening designated 7 for electrolyte E, which is indicated here and in the following figures by an irregular cross-hatching.

[0022] The electrolyte E is filled into the opening 7 according to the arrow shown, the housing 2 having been previously evacuated. The electrolyte E now begins to distribute itself in an edge channel 8, which is formed between the end faces of the stack 4 and the housing walls 3, while at the same time it is sucked into the stack 4 by capillary forces from the areas where it is present in the edge channel 8. At the first time shown in Figure 1a), this occurs primarily from the side of the filling opening 7. At a somewhat later time in Figure 1b), the electrolyte E has already penetrated further into the edge channel 8 and into the stack 4. In the illustration in Figure 1c), the entire edge channel 8 is filled with electrolyte E and the electrolyte has largely distributed itself within the stack 4, so that the stack 4 is largely saturated.If, despite evacuating and typically heating the individual battery cell 1 prior to impregnation with the electrolyte E, gases and / or moisture 9 remain in the stack 4, these gases are now enclosed within the stack by the electrolyte E drawn into the stack 4 from all sides and remain, as indicated by the white oval in Figure 3, within the stack, typically slightly below the center. In these areas, complete wetting of the active materials of the electrodes is then not achieved. Because the electrolyte E is drawn in from all sides, the gases and / or moisture cannot easily escape from the stack 4 either. In practice, this leads to a reduction in the capacity and service life of the individual battery cell 1.

[0023] In the illustration in Figure 1, the gases and / or moisture therefore remain in the area designated by 9. To remedy this problem, in the inventive design of the individual battery cell 1 or its housing 2 in the illustration in Figure 2, a roughened surface 10 is provided on the housing walls 3, specifically on their surfaces facing the stack 4. In the illustrations in Figure 2, this roughened surface is indicated by a dash-dotted line and provided with the reference symbol 10. Otherwise, the sequence of the chronologically successive states in Figures 2a), b) and c) is to be understood analogously to that in Figure 1. The roughened surface 10 now ensures that the electrolyte E experiences a greater pressure loss after being filled into the edge channel 8. It will therefore not move as quickly in the edge channel 8 as in the design according to the prior art.The stack 4 thus draws in the electrolyte E from the area of ​​the edge channel 8 on the side of the filling opening 7 to a greater extent, and from the edge channel 8 laterally only to the extent that electrolyte is present. The distribution of the electrolyte in the stack 4 therefore changes, so that moisture and gases 9 are no longer trapped in the center of the stack 4, but can be absorbed by the edge channel 8, which is still partially free at the time of complete impregnation of the stack 4, particularly on the side of the stack 4 facing away from the filling opening 7.

[0024] As can be seen in the illustration in Figure 2c), the stack is thus completely impregnated without an area with trapped residual gases and moisture 9 being created within the stack 4. Such an area, again designated 9 here, migrates in the edge channel 8. Unlike the area 9 located within the stack 4 in the prior art, it is uncritical there. Due to the roughened surface 10 and the resulting increased pressure loss during the spread of the electrolyte E in the edge channel 8, a significantly improved impregnation of the stack 4 with the electrolyte E is achieved, which in particular leads to complete impregnation of the stack 4 and thus to a high capacity and service life of the individual battery cell 1.

[0025] Optional elevations 11 are also shown in the illustrations in Figure 2. These ideally extend across the entire width of the stack 4 in the stacking direction into the edge channel 8. In addition to the roughened surface 10, these elevations 11 provide additional flow resistance for the electrolyte E. They can be specifically arranged, for example, at the locations shown in Figure 2 in order to, on the one hand, influence and slow the flow of the electrolyte E along the right and left side edges of the stack 4 in the edge channels 8 and, on the other hand, to reliably keep the side opposite the filling opening 7 free of electrolyte until the end. The elevations can be designed in any desired shape. Semi-cylindrical elevations 11 are shown here purely as an example. They could also be designed as hooks or similar.They could also be implemented as nubs on larger areas of the inner surface of the housing walls 3, or similar. They reinforce the effect described above, which generally emanates from the roughened surfaces 10, if necessary, but are not absolutely necessary as a supplement to the roughened surface 10.

Claims

A housing (2) for a single battery cell (1) comprising at least one electrode-separator arrangement (4) impregnated with a liquid electrolyte (E), wherein housing walls (3) surround the at least one electrode-separator arrangement (4), wherein the surfaces of the housing walls (3) facing the at least one electrode-separator arrangement (4) are at least partially provided with a roughened surface (10), characterized in that the roughened surface (10) varies in terms of its roughness over the extent of the surfaces of the housing walls (3) facing the at least one electrode-separator arrangement (4). Housing (2) according to claim 1, characterized in that the surfaces of the housing walls (3) facing the at least one electrode-separator arrangement (4) are completely provided with a roughened surface (10).Housing (2) according to claim 1 or 2, characterized in that the roughened surface (10) is realized by surface processing. Housing (2) according to claim 3, characterized in that the surface processing is implemented as laser processing. Housing (2) according to one of claims 1 to 4, characterized in that the roughened surface (10) is realized by a coating. Housing (2) according to claim 5, characterized in that the coating is designed as a ceramic coating. Housing (2) according to one of claims 1 to 6, characterized in that the surfaces of the housing walls (3) facing the at least one electrode-separator arrangement (4) have elevations (11) as flow resistances. Single battery cell (1) with a housing (2) according to one of claims 1 to 7. Single battery cell (1) according to claim 8, characterized in that the at least one electrode-separator arrangement (4) is designed as at least one stack (4). Single battery cell (1) according to claim 8 or 9, characterized in that the housing (2) is prismatic.

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