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 central region of the carrier sheet coated on both sides with electrode material and edge regions of the carrier sheet free from the electrode material, the edge regions completely surrounding the central region of the carrier sheet; b) applying a first sealing bead of extrudable sealing material onto the edge region of the carrier sheet, preferably in the form of a closed ring surrounding the central region of the carrier sheet; c) placing an electrically insulating, ion-permeable separator sheet on the first sealing bead, the separator sheet laterally extending all around the periphery beyond the central region of the carrier sheet; d) applying a second sealing bead of extrudable sealing material onto the separator's edge region that protrudes beyond the carrier sheet central region, preferably in the form of a closed ring that surrounds the carrier sheet central region; e) placing another similarly constructed and oriented bipolar electrode on the second sealing bead with its carrier sheet edge region; 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:

[0002] The present invention further provides a bipolar battery stack, comprising: a plurality of bipolar electrodes stacked in a stacking direction, each having an electrically conductive carrier sheet, the carrier sheet having a central region coated on both sides with an electrode material and edge regions of the carrier sheet free from the electrode material that completely surround the central region, with an intermediate chamber filled with an electrolyte located between each two adjacent bipolar electrodes; a plurality of electrically insulating, ion-permeable planar separators disposed in the intermediate chambers, the number of which corresponds to the number of the intermediate chambers, the separators projecting laterally beyond the central region of the carrier sheet on their entire periphery; a sealing wall that seals the intermediate chamber in the lateral direction 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 and the method for manufacturing the bipolar battery stack described in the preamble are known from US Pat. No. 5,649,999.

[0004] As the electrification of automobiles progresses, traction batteries with high power density are becoming increasingly important. Compact, high-power batteries are also desired in other technical fields. The concept of so-called stacked batteries (also known as bipolar battery stacks) has been demonstrated here. This concept allows for significantly increased power density compared to conventional batteries still in mainstream use today. Stacked batteries comprise a stack of multiple bipolar electrodes. A bipolar electrode is an electrically conductive, often sheet-like, carrier layer covered on both sides with active material. The active material forms the electrodes of adjacent cells in the battery, i.e., the anode and cathode. The active materials used for the anode, on the one hand, and the cathode, on the other, vary depending on the particular battery type selected and are generally referred to here as electrode materials. Such bipolar electrodes are stacked so that one anode and one cathode face each other across the free space. An electrically insulating, ion-permeable separator, often in the form of a ceramic nonwoven or ion-permeable sheet, is disposed in the free space between the electrodes and reliably prevents direct contact of the electrodes. In the final product, the free space is filled with an electrolyte, which, together with the anode and cathode bounding it, forms one functional cell of the stacked battery, which as a whole consists of many 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 references, which form the basis of the present invention, describe in detail how to construct such bipolar battery stacks. Starting from the bottom of the housing, a monopolar electrode, i.e., a carrier sheet coated on only one side with electrode material, is first placed. A sealing edge in the form of a bead of extrudable, e.g., paste-like, gel-like, or viscous sealing material is then applied around the central region of the carrier sheet, i.e., around the surface covered with electrode material. The term "sealing bead" is used for this purpose within the scope of this document. The sealing bead is applied, in particular, directly adjacent to the outer edge of the carrier sheet. Its height is slightly greater than the height of the electrode material coating. A separator is then placed in a known manner. The separator is dimensioned so that it extends laterally over the entire periphery of the central region of the carrier sheet, i.e., the area coated with electrode material, but does not extend beyond the sealing bead. Instead, the separator edge rests on the sealing bead and can be lightly pressed into the more or less flexible sealing material. In the case of a nonwoven separator, the sealant passes through the perforations of the separator nonwoven. A known method uses a UV-curable sealing material, which is irradiated with UV light after the separator is placed and thus hardened. The separator is thus fixed. The next step involves applying a second sealing bead exactly on top of the first sealing bead in the stacking direction and hardening it using UV radiation. The second sealing bead thus forms a hardened sealing edge in a recess having an area equal to the central region of the carrier sheet and a depth slightly greater than the height of the electrode material coating of the bipolar electrode. The bipolar electrode is then placed on the sealing edge, specifically so that the coating on the underside of the bipolar electrode fits into 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 process continues as described, with the placement of additional separators and subsequent second sealing beads on these separators, until a bipolar electrode stack of the desired height is constructed. The cited document also describes the placement of an electrolyte in the free space between each of two opposing electrode material coatings of adjacent bipolar electrodes, but this aspect is not critical to the present invention. In any case, the constructed stack is subjected at a given time to targeted application of pressure in the stacking direction or opposite to the stacking direction in order to press all components together. This leads to compression of the entire structure and, in particular, to improved contact between the electrolyte and the electrode materials, which in turn leads to 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 required for each battery cell. Attempts to perform curing only after the target stack height has been reached, or at least to simultaneously cure both seal beads of one battery cell, have failed. The inventors attributed this failure to short circuits between the carrier sheets of adjacent bipolar electrodes. Apparently, uncured sealing material is not suitable for reliably holding the edge regions of the carrier sheets apart, even temporarily. Only after the first sealing bead has cured can a sufficiently stable base be provided on which the second sealing bead can be placed, and this second sealing bead must also be cured before the next bipolar electrode can be placed. Otherwise, warping of the carrier sheet edge regions would occur in the uncured sealing material, which would subsequently lead to short circuits between adjacent battery cells. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] German Patent Application Publication No. 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 bipolar battery stack can be constructed more quickly and therefore more economically while avoiding short circuits between individual battery cells, or to provide a more economical bipolar battery stack manufactured in this way. [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 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 region of any bipolar electrode does not protrude laterally beyond the separator immediately adjacent to the carrier sheet edge region.

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

[0012] The central idea of the present invention is to design the separator to be larger in area than the bipolar electrode. In particular, the separator should extend laterally across 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. Any warping of the edge areas of the carrier sheet 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, thus reliably preventing 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, the separator still overhangs the carrier sheet edges, or at least maintains a flush termination between the separator edges and the carrier sheet edges.

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

[0014] Those skilled in the art will understand that the order of steps c) and d) in particular can be interchanged. The section of claim 1 does not limit the method in this respect in terms of time, i.e., the order of the individual method steps. It is therefore possible within the scope of the present invention to apply a second sealing bead to the separator to be applied already outside the stack, and then 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 practice, the first-mentioned variant has proven to be particularly advantageous.

[0015] Those skilled in the art will also appreciate that the sealing bead does not necessarily have to form a closed ring, but rather that multiple separate portions of sealant can be applied in a ring shape, which portions of sealant will subsequently intermingle and merge upon application of pressure, particularly in the direction of stacking or opposite to the stacking direction.

[0016] A method variant in which each second sealing bead is applied laterally outwardly relative to the corresponding first sealing bead has proven particularly advantageous. That is, the two sealing beads of a battery cell do not overlap perpendicularly in the stacking direction. This offset arrangement allows the separator material, if made of a flexible material, to fold in accordance with the contours of the sealing beads, at least between the sealing beads bordering each separator, under the action of pressure applied in the stacking direction. In other words, the laterally offset sealing beads exert shear forces on the separator's edge regions, causing it to fold and thus stabilize itself, as is known from reinforcing beads in sheet metal or corrugated sheet or cardboard. The separator thus becomes an active spacer between adjacent bipolar electrodes, at least in its edge regions, and can even abut directly against the carrier sheet at the extreme points of its waves. Indeed, if a porous separator material, such as a ceramic nonwoven fabric, is selected that allows the sealing material to pass through, this results in a very stable structure, which can be further stabilized by appropriate curing if a curable sealing material is selected. However, it is obvious that other separator materials, such as single- or multi-layer plastic sheets, can also be selected.

[0017] Furthermore, although it was mentioned above that the separator folds according to the contour of the sealing bead, this does not mean that the rigidity of the sealing bead is higher than that of the separator material. When pressure is applied, especially in the stacking direction, the (still) flexible sealing bead also deforms and changes its contour. The sealing bead and the separator thus adhere to each other. The exact shape of the separator and / or carrier sheet edge regions in the finished product is therefore not predictable in the last detail. However, predictability is not necessary according to the invention, since the separator's flaring according to the invention precludes contact between adjacent carrier sheets and thus short circuits.

[0018] Deformation of the sealing 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 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. That is, the stack should present a uniform wall from the outside, so that the components essential for the generation of electrical energy are not in contact with the surroundings. As mentioned above, the exact positions 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 will be sufficient to ensure such complete embedding. Therefore, in one development of the invention, between steps b) and e), a further sealing bead, preferably in the form of a closed ring surrounding the second sealing bead, is applied to the edge region of each separator that protrudes beyond the central region of the carrier sheet. In other words, the outermost edges of the separators are coated with further sealing beads, which extend between adjacent separators and are positioned and dimensioned so that all outer edges of the separators and carrier sheets are embedded in the sealing material in the transverse direction. Optionally, these outer sealing beads may be smoothed to form a smooth outer wall in a final method step.

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

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

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

[0023] Figure 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 mainly comprises a plurality of bipolar electrodes 12 stacked one on top of the other, which are shown in isolation in Figure 2 in a side view (Figure 2a) and in a plan view (Figure 2b). Each bipolar electrode comprises, as is basically known in the prior art, an electrically conductive carrier sheet 121, both sides of which are coated with electrode material forming the electrodes, i.e., the anode 122 and the cathode 123. However, the coating with electrode material extends only over the carrier sheet central region 124, whereas the carrier sheet edge region 125, which surrounds 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 Figure 1 includes a plurality of such bipolar electrodes 12, stacked one on top of the other in a stacking direction 14. The bipolar electrodes 12 are oriented in the same direction in this case, so that the anode 122 of each bipolar electrode 12 faces the cathode 123 of the immediately adjacent bipolar electrode 12 across an intermediate chamber 16. The intermediate chamber 16 is filled with an electrolyte (not shown separately). Thus, the anode 122 and cathode 123 of adjacent bipolar electrodes 12, together with the electrolyte therebetween, form individual battery cells, and the bipolar battery stack 12 includes a number of battery cells connected in series with each other via their respective electrically conductive carrier sheets 121.

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

[0026] 1 clearly shows that the battery cells are laterally, i.e. practically all around, surrounded by sealing walls 20. The sealing walls 20, made of a sealing material, serve to seal the battery cells airtight and liquidtight from the surroundings. It is clearly visible that the outer edges of the carrier sheet 121, in particular the entire carrier sheet edge region 125, as well as the edges of the separators 18, are embedded in the sealing walls 20.

[0027] In the illustrated embodiment, the lower electrode of the bottommost battery cell is not formed as a bipolar electrode, but as a monopolar electrode 12', which in the illustrated embodiment consists only of a carrier sheet 121 and a coating on one side that forms 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) used for battery cell contact connections.

[0028] FIG. 3, also in highly schematic form, illustrates three phases of a particularly preferred embodiment of a method for manufacturing a bipolar battery stack 10 similar to that shown in FIG. 1. These figures show only relevant excerpts of the respective bipolar battery stack precursors, but those skilled in the art will have no difficulty imagining and filling in the remaining elements. FIG. 3a shows an edge section of a bipolar electrode 12, which includes a carrier sheet 121 coated in its central region 124 with electrode materials for the anode 122 and cathode 123. A first sealing bead 201 is applied to the overhanging carrier sheet edge region 125. The first sealing bead 201 preferably forms a closed ring that completely surrounds the central region 124. The sealing material of the sealing bead may be a long-lasting elastic paste, such as butyl rubber, or a curable material, such as an epoxy-based material, which, depending on the particular 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 the next step, as shown in FIG. 3b, the separator 18 is placed on the first sealing bead 201. The separator 18 clearly extends beyond the edge of the carrier sheet 121 with its edge region. In the illustrated embodiment, a second sealing bead 202 is applied to this extending 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 outward relative to the ring formed by the first sealing bead 201 of sealing material. The reverse order of these steps is also possible; thus, the second sealing bead 202 may be applied only following the placement 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] In the next step shown in FIG. 3c, mechanical pressure 24 is applied to the resulting laminate in the stacking direction 14 (or in the direction opposite to the stacking direction 14). This application of mechanical pressure 24 presses the sealing beads 201, 202 together, resulting in the formation of a uniform, closed sealing wall 20. Depending on the relative material stiffness of the sealing beads 201, 202, on the one hand, and 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, because the separator 18 clearly extends beyond the carrier sheet 121, this ensures that adjacent carrier sheets 121 never come into direct contact with each other, even under adverse process conditions, and thus prevents the formation of internal short circuits. Even in its folded state, the separator 18 acts as a reliable spacer, reliably preventing short circuits in any case.

[0031] Of course, the embodiments discussed in the specific description and shown in the drawings are merely illustrative examples of the invention. A wide range of variations is available to those skilled in the art within the scope of this disclosure. In particular, those skilled in the art have the possibility to choose from all known, and possibly further developed, variations regarding the specific battery chemistry and / or the chemistry of the optionally curable sealing material of the sealing beads 201, 202. Those skilled in the art also have a wide range of freedom regarding 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 combined 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 housing 24 Pressure

Claims

1. A method of manufacturing a bipolar battery stack (10), comprising: a) providing a 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 carrier sheet edge regions (125) completely surrounding the carrier sheet central region (124) and free from electrode material; 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) on the first sealing bead (201), the separator (18) laterally projecting over the entire periphery beyond the central region (124) of the carrier sheet; d) applying a second sealing bead (202) of extrudable sealing material to the separator (18) on the edge area 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 formed; Including, 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 placed on the first sealing bead (201) assigned to said separator (18), 1. A method for manufacturing a bipolar battery stack (10), comprising depositing each second seal bead (202) laterally outwardly offset relative to a corresponding first seal bead (201).

2. 2. The method according to claim 1, wherein the separators (18) are made of a flexible material, which folds according to the contours of the sealing beads (201, 202) between the sealing beads (201, 202) bordering each separator (18) under the action of a pressure (24) applied in the stacking direction (14) or in a direction opposite to the stacking direction (14).

3. 3. A method according to claim 1 or 2, characterized in that after step f, the laminated structure is subjected to a pressure (24) acting in the direction of lamination (14) or in a direction opposite to said direction of lamination (14).

4. 4. A method according to any one of claims 1 to 3, characterized in that the laminated structure is heated after step f to a temperature between 50°C and 180°C.

5. 5. The method according to claim 1, further comprising applying, between step b and step e, another sealing bead in the form of a ring surrounding the second sealing bead (202) on the edge region of each separator (18) that projects beyond the carrier sheet central region (124).

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