Bipolar battery stack and method for manufacturing such a bipolar battery stack

Abstract

The present invention relates to a method for manufacturing a bipolar battery stack (10), comprising the steps of: a) providing a first bipolar electrode (12) having an electrically conductive carrier sheet (121) with a carrier sheet central region (124) coated on both sides with electrode material and a carrier sheet edge region (125) free of electrode material, completely surrounding the carrier sheet central region (124); b) depositing a first sealing bead (201) on the carrier sheet edge region (125) in the form of a ring surrounding the carrier sheet central region (124); and c) depositing an electrically insulating, ionically permeable first sealing bead (201) on the carrier sheet edge region (125) in the form of a ring surrounding the carrier sheet central region (124). a) placing a separator (18) of a planar shape, which laterally projects over its entire circumference beyond the carrier sheet central region (124) on said first sealing bead (201), b) applying a second sealing bead (202) on the edge region of the separator (18) which projects over the carrier sheet central region (124) in the form of a ring surrounding said carrier sheet central region (124), c) placing another on said second sealing bead (202), and f) repeating steps b to e until a predetermined number of such stacked bipolar electrodes (12) is reached. The invention is characterized in that each separator (18) during each placement of the separator (18) laterally projects over its entire circumference beyond the carrier sheet edge region (125) of the bipolar electrode (12) directly adjacent to it.

Description

[Technical field]

[0001] The present invention provides a method for manufacturing a bipolar battery stack, comprising the steps of: a) providing a first bipolar electrode comprising an electrically conductive carrier sheet having a carrier sheet central region coated on both sides with electrode material and a carrier sheet edge region free of electrode material completely surrounding the carrier sheet central region; b) applying a first sealing bead of extrudable sealing material onto the carrier sheet edge region, preferably in the form of a closed ring surrounding the carrier sheet central region; c) placing an electrically insulating, ionically permeable separator sheet over the first sealing bead, the separator laterally protruding all around the periphery beyond the central region of the carrier sheet; d) applying a second sealing bead of extrudable sealing material onto the edge region of the separator that protrudes beyond the carrier sheet central region, preferably in the form of a closed ring surrounding the carrier sheet central region; e) placing another similarly constructed and oriented bipolar electrode with its carrier sheet edge region on the second seal bead; f) repeating steps b through e until a predetermined number of such stacked bipolar electrodes is reached; The present invention relates to a method comprising the steps of:

[0002] The present invention further provides a bipolar battery stack, comprising: a plurality of bipolar electrodes stacked in a stacking direction, each of which has an electrically conductive carrier sheet, the carrier sheet having a carrier sheet central region coated on both sides with electrode material and a carrier sheet edge region free from the electrode material, completely surrounding the carrier sheet central region, and between each two adjacent bipolar electrodes there is located an intermediate chamber filled with an electrolyte; a plurality of electrically insulating, ion-permeable separators arranged in the intermediate chambers, the number of which corresponds to the number of the intermediate chambers, the separators projecting laterally over the entire circumference beyond the central region of the carrier sheet; a sealing wall sealing the intermediate chamber laterally around the entire periphery, the sealing wall being made of a sealing material, in which the edge region of the carrier sheet and the edge of the separator are embedded around the entire periphery; The present invention relates to a bipolar battery stack comprising: [Background technology]

[0003] The bipolar battery stack described in the preamble and a method for producing the same are known from US Pat. No. 5,399,633.

[0004] With the increasing electrification of motor vehicles, traction batteries with high power density are becoming increasingly important. In other technical fields, compact, high-power batteries are also desired. Here, in particular, the concept of so-called stacked batteries (also called bipolar battery stacks) has been demonstrated. This concept allows a clearly increased power density compared to conventional batteries still in mainstream use today. Stacked batteries have a stack of several bipolar electrodes. A bipolar electrode is an electrically conductive, often sheet-like carrier layer covered on both sides with active material, which in the battery constitutes the electrodes of adjacent cells, i.e. the anodes or cathodes. The active materials used for the anodes on the one hand and the cathodes on the other hand vary depending on the specifically selected battery type and are here, however, commonly considered as electrode materials. Bipolar electrodes of this kind are stacked in such a way that an anode and a cathode in each case face each other across a free space. In the free space between the electrodes, an electrically insulating, ion-permeable separator, often in the form of a ceramic nonwoven or ion-permeable sheet, is arranged, which reliably prevents the electrodes from coming into direct contact. The free space is filled with an electrolyte in the final product, which together with the anode and cathode bounding it form one functional cell of a stacked battery, which as a whole consists of a large number of such cells connected in series with one another. The specific material selection for the electrolyte material, as well as the electrode material, depends on the respective battery type.

[0005] The above-mentioned documents, which form the preamble, describe in detail how to build such bipolar battery stacks. Starting from the housing bottom, a monopolar electrode is first laid, i.e. a carrier sheet coated with electrode material only on one side. A sealing edge in the form of a bead of extrudable, for example pasty, gel-like or viscous sealing material is then applied around the carrier sheet central area, i.e. around the face covered with electrode material. Within the scope of this document, the concept of a sealing bead is used for this. The sealing bead is applied in particular directly near the outer edge of the carrier sheet. The height of the sealing bead is slightly greater than the height of the electrode material coating. Then, in a known manner, a separator is laid. The separator is dimensioned in such a way that it indeed projects laterally over the entire periphery from the carrier sheet central area, i.e. the area coated with electrode material, but does not project beyond the sealing bead. Instead, the edge of the separator rests on the sealing bead and can be pressed lightly into the more or less soft sealing material. In particular in the case of a nonwoven separator, the sealant then passes through the holes in the separator nonwoven. In particular, there is a known method using a UV-curable sealing material, which is irradiated with UV light after the separator is placed and thus cured. The separator is thus also fixed. In a next step, the application of a second sealing bead follows, which is exactly superimposed on the first sealing bead in the stacking direction and the curing of the second sealing bead using UV irradiation. The second sealing bead thus forms a hardened sealing edge of a recess having an area of ​​the carrier sheet central region and a depth slightly greater than the height of the electrode material coating of the bipolar electrode. In a next step, such a bipolar electrode is placed on the sealing edge, in particular so that the coating of the lower surface of the bipolar electrode is placed in the recess. Subsequently, a further first sealing bead is applied in the region of the carrier sheet edge region of the bipolar electrode exactly overlapping the already cured sealing bead pair.The method is continued as described, by placing a further separator and placing a further second sealing bead on this separator, until a bipolar electrode stack of the desired height is built up. The cited document also describes the placement of the electrolyte in the free space between each of the two mutually facing electrode material coatings of adjacent bipolar electrodes, but this aspect is not important for the present invention. In any case, the built stack is subjected at a given time to a targeted application of pressure in the stacking direction or in the direction opposite to the stacking direction in order to press all the components together. This leads to a compression of the entire structure and in particular to an improved contact of the electrolyte and the electrode materials, which leads to an increased efficiency of the resulting battery.

[0006] One major drawback of this known method is its long duration, especially due to the two curing steps per battery cell. Attempts to perform the curing only after reaching the target stack height, or at least to cure both sealing beads of one battery cell together, have failed. The inventors found the reason for this failure in short circuits between the carrier sheets of adjacent bipolar electrodes. Apparently, uncured sealing material is not suitable to reliably hold the carrier sheet edge areas apart, even temporarily. Only after the first sealing bead has been cured does a sufficiently stable basis on which the second sealing bead can be placed, which also must first be cured before the next bipolar electrode can be placed. Otherwise, warping of the carrier sheet edge areas would occur in the still uncured sealing material, which would then lead to short circuits between adjacent battery cells. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] DE 102018201693 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to develop the manufacturing method described in the preamble in such a way that a faster and therefore more economical construction of a bipolar battery stack is possible while avoiding short circuits between the individual battery cells, or to provide a more economical bipolar battery stack thus produced. [Means for solving the problem]

[0009] In the context of the manufacturing method, this problem is solved in conjunction with the features of the preamble of claim 1 in that each separator, when placed respectively on the first sealing bead assigned to it, protrudes laterally over its entire periphery beyond the carrier sheet edge region of the bipolar electrode directly adjacent to it.

[0010] In the context of the resulting bipolar battery stack, the above problem is solved in conjunction with the features of the preamble of claim 6 in that the carrier sheet edge area of ​​any bipolar electrode does not protrude laterally beyond the separator immediately adjacent to the carrier sheet edge area.

[0011] Preferred embodiments are the subject of the dependent claims.

[0012] The central idea of ​​the invention is to configure the separator to be larger in area than the bipolar electrodes. In particular, the separator should overhang laterally over the entire periphery, i.e. on all sides, beyond the first sealing bead and beyond the carrier sheet located below the first sealing bead when the separator is placed on the first sealing bead. The warping of the carrier sheet edge area in the (yet) unhardened sealing material is then limited at the latest by abutment against the separator. The same applies to the warping of the carrier sheet of the next bipolar electrode, which is to be placed on the separator. For better contact between the electrolyte and the electrode material, the overhanging separator blocks direct contact between the carrier sheets of adjacent bipolar electrodes, even when pressure is applied in the stacking direction, and thus reliably prevents the formation of short circuits. In this case, it is desirable that the relative dimensioning of the separator area to the carrier sheet area is configured so that, even assuming warping of the (often also flexible) separator in the final laminate, an overhang of the separator beyond the carrier sheet edges, or at least a flush termination between the separator edges and the carrier sheet edges, is still maintained.

[0013] The invention makes it possible, when a curable sealing material is selected, to carry out the curing only at the end of the stack construction, or at least in a one-off curing step for each individual battery cell, which means a significant acceleration of the stack construction. However, the invention also makes it possible to use, instead of a curable material, a long-term elastic sealing material, such as, for example, butyl rubber, which is known, for example, for the liquid-tight and gas-tight sealing of insulating glass panes, and whose use also has great advantages in the field of high-power batteries.

[0014] The skilled person will understand that the order of steps c) and d) in particular can be interchanged. The division of claim 1 does not limit the method in this respect in terms of time, i.e. with respect to the sequence of the individual method steps. It is thus possible without any problem within the scope of the invention to apply the second sealing bead already outside the stack to the separator to be applied and then to apply the combination of separator and second sealing bead onto the first sealing bead. Conversely, it is also possible to apply the separator alone onto the first sealing bead and then apply the second sealing bead. In fact, in practical use, the first-mentioned variant has proven to be particularly advantageous.

[0015] Those skilled in the art will also understand that the sealing bead does not necessarily have to form a closed ring: it is also possible to apply several separate portions of the sealant in the shape of a ring, which portions of the sealant will later intermingle and merge, especially when pressure is applied in or against the stacking direction.

[0016] Particularly advantageous is a method variant in which each second sealing bead is applied laterally outwardly offset with respect to the respective corresponding first sealing bead, i.e. the two sealing beads of one battery cell are not positioned vertically one above the other in the stacking direction. The offset arrangement allows the separator material, if made of a flexible material, to fold at least between the sealing beads bordering the respective separator under the action of pressure applied in the stacking direction according to the contour of the sealing beads. In other words, the two sealing beads offset from each other laterally exert shear forces on the edge regions of the separator, as a result of which the separator folds and is thus structurally stabilized, as is known for reinforcing beads in sheet metal or corrugated sheets or cardboard. The separator thus becomes an active spacer between adjacent bipolar electrodes, at least in its edge regions, which can even abut directly against the carrier sheet at the extreme points of its waves. Indeed, if a porous separator material through which the sealing material can pass, such as a ceramic nonwoven, is selected, this results in a very stable structure, which can be further stabilized by corresponding curing when a curable sealing material is selected, but it is self-evident that other separator materials, such as single- or multi-layer plastic sheets, can also be selected.

[0017] It was further mentioned above that the separator folds according to the contour of the sealing bead, but this does not mean that the stiffness of the sealing bead is high compared to the stiffness of the separator material. When pressure is applied, especially in the stacking direction, the (still) flexible sealing bead also deforms and thereby changes its contour. The sealing bead and the separator thus come into close contact with each other. The exact shape of the separator and / or the carrier sheet edge region in the finished product is therefore also unpredictable in the last detail. However, predictability is not necessary at all according to the invention, since the inventive overhang of the separator in any case precludes contact of adjacent carrier sheets and thus short circuits.

[0018] The deformation of the seal bead may be assisted by heating the laminated structure after step f). Typical heating temperatures are between 50°C and 180°C.

[0019] As in the known bipolar battery stacks, the edges of the carrier sheet and the separators are preferably completely embedded in the sealing wall in the finished product, i.e. the stack should show a uniform wall from the outside, so that the components essential for the generation of electrical energy have no contact with the surroundings. As mentioned above, the exact position of the separator edges and the carrier sheet edges cannot be predicted in detail, and therefore it is not guaranteed in all circumstances that the first and second sealing beads are sufficient to ensure such a complete embedding, in one development of the invention, between steps b) and e), a further sealing bead is applied to the edge area of ​​each separator that protrudes beyond the central area of ​​the carrier sheet, preferably in the form of a closed ring surrounding the second sealing bead. In other words, the separators are provided with further sealing beads on their outermost edges, which extend between adjacent separators and are positioned and dimensioned in such a way that all the outer edges of the separators and the carrier sheet are embedded in the sealing material in the transverse direction. Optionally, these outer sealing beads may be smoothed in a final method step to provide a smooth outer wall.

[0020] Further details and advantages of the present invention can be seen from the following specific description and drawings. [Brief description of the drawings]

[0021] [Figure 1] FIG. 2 is a schematic cross-sectional view of the lower portion of a bipolar battery stack according to the present invention. [Figure 2a] FIG. 2 is a schematic side view of a bipolar electrode. [Figure 2b] FIG. 2 is a plan view of a bipolar electrode. [Figure 3a] 1A-1D illustrate three phases of a preferred embodiment of a manufacturing method according to the present invention. [Figure 3b] 1A-1D illustrate three phases of a preferred embodiment of a manufacturing method according to the present invention. [Figure 3c] 1A-1D illustrate three phases of a preferred embodiment of a manufacturing method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The same numbers in the figures refer to the same or similar elements.

[0023] FIG. 1 shows, in a highly schematic view, a cross section through the lower region of a bipolar battery stack 10 according to the invention. The bipolar battery stack 10 essentially comprises a plurality of bipolar electrodes 12 stacked one on top of the other, which are shown in isolation in FIG. 2 in a side view (FIG. 2a) and in a plan view (FIG. 2b). Each bipolar electrode comprises, as is basically known in the prior art, an electrically conductive carrier sheet 121, which is coated on both sides with an electrode material forming the electrodes, i.e. the anode 122 and the cathode 123. The coating with electrode material, however, extends only over the carrier sheet central region 124, whereas the carrier sheet edge region 125 surrounding the entire periphery of the carrier sheet central region 124 remains excluded from the coating with electrode material.

[0024] The bipolar battery stack 10 of Fig. 1 comprises a number of such bipolar electrodes 12, which are stacked one on top of the other in a stacking direction 14. The bipolar electrodes 12 are in this case oriented in the same way, so that the anode 122 of each bipolar electrode 12 faces the cathode 123 of the directly adjacent bipolar electrode 12 across an intermediate chamber 16. The intermediate chamber 16 is filled with an electrolyte, not shown separately. The anode 122 and the cathode 123 of each adjacent bipolar electrode 12 thus form, together with the electrolyte therebetween, an individual battery cell, and the bipolar battery stack 12 includes a number of battery cells which are connected in series with each other via their respective electrically conductive carrier sheets 121.

[0025] In order to reliably prevent direct contact between the anode 122 and the cathode 123 of the individual battery cells, a separator 18 is threaded through each intermediate chamber 16. The separator 18 is made electrically insulating and ionically conductive. Preferably, the separator 18 is made as a ceramic nonwoven fabric or as a single- or multi-layer ion-permeable plastic sheet. As can be clearly seen in the cross-sectional view of FIG. 1, the separator projects laterally, i.e. practically all around, beyond the carrier sheet 121 of the respective adjacent bipolar electrode 12.

[0026] 1 it can be clearly seen that the battery cells are laterally, i.e. in practice all around, surrounded by a sealing wall 20. The sealing wall 20, formed from a sealing material, serves for an air-tight and liquid-tight sealing of the battery cells against the surroundings. It is clearly visible that the outer edge of the carrier sheet 121, in particular the entire carrier sheet edge region 125, as well as the edge of the separator 18 are embedded in said sealing wall 20.

[0027] In the embodiment shown, the lower electrode of the lowermost battery cell is not formed as a bipolar electrode, but as a monopolar electrode 12', which in the embodiment shown consists only of a carrier sheet 121 and a coating on one side forming the anode 122. Towards the bottom, the bipolar battery stack 12 is defined by a housing bottom 22, which also includes electrical leads, not shown, for the contact connections of the battery cells.

[0028] FIG. 3 also shows, in a highly schematic way, three phases of a particularly preferred embodiment of a method for manufacturing a bipolar battery stack 10 similar to the bipolar battery stack 10 shown in FIG. 1. These figures show only relevant excerpts of the respective bipolar battery stack precursor products, but the person skilled in the art will have no problem imagining and completing the remaining elements. FIG. 3a shows an edge section of a bipolar electrode 12, which comprises a carrier sheet 121, which is coated in its carrier sheet central area 124 with electrode materials for the anode 122 and the cathode 123. On the overhanging carrier sheet edge area 125, a first sealing bead 201 is applied. The first sealing bead 201 preferably forms a closed ring, which surrounds the entire carrier sheet central area 124. The sealing material of the sealing bead may be a long-term elastic paste, for example butyl rubber, or a hardenable material, for example an epoxy-based material, and according to the special chemistry, may be a light-curable material or a material that hardens in the sense of a single- or multi-component adhesive.

[0029] In any case, before any curing, in a next step, as shown in FIG. 3b, the separator 18 is laid on the first sealing bead 201. With its edge region, the separator 18 clearly overhangs the edge of the carrier sheet 121. In the illustrated embodiment, a second sealing bead 202 is applied on this overhanging region of the separator 18. The second sealing bead 202 surrounds the entire separator 18, preferably in the form of a closed ring. As can be clearly seen in FIG. 3b, the ring formed by the second sealing bead 202 of sealing material is slightly offset outwards with respect to the ring formed by the first sealing bead 201 of sealing material. The reverse sequence of these steps is also possible: the second sealing bead 202 may thus only be carried out following the laying of the separator 18 on the first sealing bead 201. The sealing materials of the sealing beads 201, 202 may be the same or different from each other.

[0030] The laminate thus constructed is subjected in the next step, shown in FIG. 3c, to a mechanical pressure 24 in the lamination direction 14 (or against the lamination direction 14). The application of the mechanical pressure 24 presses the sealing beads 201, 202 to form a uniform closed sealing wall 20. Depending on the relative material stiffness of the sealing beads 201, 202 on the one hand and of the separator 20 or the carrier sheet edge region 125 on the other hand, folding of the sheet material may occur. In the illustrated embodiment, folding of the separator 18 is shown. However, since the separator 18 clearly overhangs the carrier sheet 121, it is ensured that, even under adverse process conditions, adjacent carrier sheets 121 never come into direct contact and thus do not form internal short circuits. Instead, even in the folded state, the separator 18 acts as a reliable spacer and reliably prevents short circuits in any case.

[0031] Naturally, the embodiments discussed in the specific description and shown in the drawings are only illustrative examples of the invention. Within the scope of the disclosure, a wide range of variations is available to the skilled person. In particular, the skilled person has the possibility to choose from among all known, possibly further developed, variations with regard to the specific battery chemistry and / or the chemistry of the possibly hardenable sealing material of the sealing beads 201, 202. The skilled person also has a wide range of freedom with regard to the selection of the electrolyte between the bipolar electrodes 12. In particular, if an electrolyte that is liquid, at least at the time of injection, is selected, the deposition of the sealing beads 201, 202 can be coupled with the insertion of a cannula through the upcoming sealing wall, through which the liquid electrolyte is injected into the intermediate chamber 16 between the bipolar electrodes 12. [Explanation of symbols]

[0032] 10 Bipolar battery stack 12 Bipolar Electrodes 121 Carrier sheet 122 Anode 123 Cathode 124 Carrier sheet central region 125 Carrier sheet edge region 12' Monopolar Electrode 14 Lamination direction 16 Intermediate Room 18 Separator 20 Sealing wall 201 First Seal Bead 202 Second Seal Bead 22 Bottom of the case 24 Pressure

Claims

1. A method of manufacturing a bipolar battery stack (10), comprising the steps of: a) providing a first bipolar electrode (12), the first bipolar electrode (12) comprising an electrically conductive carrier sheet (121) having a carrier sheet central region (124) coated on both sides with electrode material and a carrier sheet edge region (125) free from electrode material, completely surrounding the carrier sheet central region (124); b) applying a first sealing bead (201) of extrudable sealing material onto the carrier sheet edge region (125) in the form of a ring surrounding the carrier sheet central region (124); c) placing an electrically insulating, ion-permeable, planar separator (18) projecting laterally beyond the carrier sheet central region (124) on the first sealing bead (201); d) applying a second sealing bead (202) of extrudable sealing material on the edge area of ​​the separator (18) protruding beyond the carrier sheet central area (124) in the form of a ring surrounding the carrier sheet central area (124); e) placing another similarly constructed and oriented bipolar electrode (12) on the second sealing bead (202) with its carrier sheet edge region (125); f) repeating steps b to e until a predetermined number of such stacked bipolar electrodes (12) are reached; A method comprising: each separator (18) projects laterally over its entire periphery beyond the carrier sheet edge region (125) of the bipolar electrode (12) directly adjacent to said separator (18) when said separator (18) is respectively placed on said first sealing bead (201) assigned to said separator (18); A method for manufacturing a bipolar battery stack (10), comprising:

2. 2. The method of claim 1, further comprising applying each second sealing bead (202) laterally outwardly offset with respect to the corresponding first sealing bead (201).

3. 3. The method according to claim 2, characterized in that the separators (18) are made of a flexible material, which folds according to the contours of the sealing beads (201, 202) at least between the sealing beads (201, 202) bordering each separator (18) under the action of a pressure (24) applied in the stacking direction (14) or opposite to the stacking direction (14).

4. 4. The method according to claim 1, characterized in that after step f, the laminated structure is subjected to a pressure (24) acting in the lamination direction (14) or opposite to said lamination direction (14).

5. 5. The method according to claim 1, characterized in that the laminated structure is heated after step f to a temperature between 50° C. and 180° C.

6. 6. The method according to claim 1, characterized in that between steps b and e, another sealing bead is applied on the edge area of ​​each separator (18) projecting beyond the carrier sheet central area (124) in the form of a ring surrounding the second sealing bead (202).

7. A bipolar battery stack (10), comprising: a plurality of bipolar electrodes (12) stacked in a stacking direction (14), each having an electrically conductive carrier sheet (121) with a carrier sheet central region (124) coated on both sides with electrode material and with carrier sheet edge regions (125) free from electrode material completely surrounding the carrier sheet central region (124), with intermediate chambers (16) filled with electrolyte located between each two adjacent bipolar electrodes (12); a plurality of electrically insulating, ion-permeable, planar separators (18) arranged in the intermediate chambers (16), the number of which corresponds to the number of the intermediate chambers (16), the separators (18) projecting laterally beyond the central region (124) of the carrier sheet on their entire periphery; a sealing wall (20) sealing the intermediate chamber (16) laterally around the entire circumference, the sealing wall (20) being made of a sealing material in which the carrier sheet edge region (125) and the edge of the separator (18) are embedded around the entire circumference; A bipolar battery stack (10) comprising: the carrier sheet edge region (125) of any bipolar electrode (12) does not protrude laterally beyond the separator (18) immediately adjacent to said carrier sheet edge region (125); A bipolar battery stack (10).

8. 8. The bipolar battery stack (10) of claim 7, wherein the area of ​​each separator (18) is greater than the area of ​​the carrier sheet (121) of the bipolar electrode (12) immediately adjacent to said separator (18).

9. 9. The bipolar battery stack (10) of claim 8, wherein the edge regions of the separators (18) embedded within the sealing walls (20) extend in a folded manner in the stacking direction (14).

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