Electrochemical cell

Abstract

An electrochemical cell (1) is provided as a pouch battery cell having a housing in the form of a pouch film (2) and comprises an anode (3), a cathode (4), and a reference electrode (5) arranged asymmetrically to the anode (3) and the cathode (4), such that the reference electrode (5) is integrated into the pouch film (2).

Description

[0001] P240809

[0002] - 1 -

[0003] Electrochemical cell

[0004] The invention relates to an electrochemical cell constructed as a pouch battery cell, in particular a secondary battery cell. Furthermore, the invention relates to a method for operating such an electrochemical cell.

[0005] German patent application DE 10 2018 007 151 A1 relates to a method for adjusting the capacity of an electrochemical energy storage device for a motor vehicle. The electrochemical energy storage device comprises storage cells, which can be in the form of pouch bags. Several storage cells connected in series each have a reference electrode made of a material containing lithium. According to the teaching of DE 10 2018 007 151 A1, determining and monitoring the cell voltage, in particular in the form of an anode potential relative to the reference electrode, is intended to contribute to preventing so-called "lithium plating," thereby aiming to increase the service life of the electrochemical energy storage device.

[0006] Another arrangement of pouch cells is known, for example, from US 2023 / 0122077 A1. In this arrangement, several cells are arranged in a housing, with a cooling circuit operated by a dielectric fluid that is in direct contact with the terminal elements of the pouch cells.

[0007] German patent DE 10 2020 120 746 A1 relates to a module for a high-voltage storage system with immersion cooling. The module comprises several battery cells arranged in a common housing, which can be, for example, prismatically shaped or designed as pouch cells. Reversibly deformable spacers are arranged between the side surfaces of the battery cells. A coolant with a thermal conductivity of 0.1 W / m K to 15 W / m K comes into direct contact with these side surfaces. P240809

[0008] - 2 -

[0009] Another battery module comprising multiple pouch cells is disclosed in US patent 2021 / 0305546 A1. This battery module has a metallic housing and two plastic insulating plates located at the two ends of a stacked arrangement of pouch cells. Within the stacked cell arrangement, plate-shaped insulating elements are arranged for thermal insulation between adjacent electrochemical cells, i.e., pouch cells. A metal plate is provided for heat dissipation, lying in a plane perpendicular to both the insulating elements and the cells.

[0010] US patent 2024 / 0128494 A1 discloses a solid-state battery in pouch form, comprising a reference electrode. Potential changes at each electrode are intended to be precisely measurable, with a short ion path between the reference electrode and the electrodes improving measurement accuracy.

[0011] US patent 2023 / 0091154 A1 concerns a stacked structure of electrochemical cells containing sensor arrays. Within the cell stack formed by the electrochemical cells, a reference electrode is located on one side of a separator, and a sensor array is arranged on the opposite side of the separator.

[0012] Further arrangements of electrochemical cells comprising reference electrodes are described, for example, in documents US 2023 / 0223603 A1 and US 2014 / 0375325 A1.

[0013] The invention is based on the objective of providing more advanced possibilities for monitoring electrochemical cells, in particular rechargeable battery cells, compared to the prior art.

[0014] This problem is solved according to the invention by an electrochemical cell having the features of claim 1. Likewise, the problem is solved by a device according to P240809.

[0015] - 3 -

[0016] Claim 8 describes a method designed for operating an electrochemical cell constructed as a pouch battery cell.

[0017] The electrochemical cell according to the application, designed as a pouch battery cell, has a housing in the form of a pouch film, an anode, a cathode, and a reference electrode arranged asymmetrically to the anode and the cathode, such that the reference electrode is integrated into the pouch film. Including the reference electrode, this constitutes a 3-electrode setup.

[0018] The pouch battery cell is a battery cell, particularly cuboid in shape, with at least one stacked pair consisting of a layered or foil-shaped planar anode and a layered or foil-shaped planar cathode. The pouch foil forms a pouch to contain them.

[0019] The asymmetry of the arrangement of the reference electrode in the electrochemical cell, including its housing in the form of a pouch film, represents a particularly space-saving way of accommodating the reference electrode in the electrochemical cell, while at the same time enabling a sufficiently accurate measurement of the electrical voltage between the reference electrode and the aforementioned electrodes, i.e., the anode and the cathode.

[0020] An "asymmetrical" arrangement of the reference electrode is understood here to mean that the reference electrode is not located between the anode and the cathode, but rather outside the electrode stack, which consists of stacked pairs of an anode and a cathode. The reference electrode therefore has different distances to the nearest anode and cathode. In principle, the reference electrode lies outside the outermost electrode of the pouch battery cell, which can be either an anode or a cathode. According to the invention, the reference electrode is integrated into the pouch film, and thus there is no symmetrical arrangement, in particular no point- or area-symmetrical arrangement, of the reference electrode with respect to its position relative to the outer anode and cathode in the pouch battery cell.

[0021] The surface area of ​​the reference electrode differs from the surface area of ​​the electrodes, i.e., the anode and the cathode. P240809

[0022] - 4 -

[0023] In addition to the reference electrode, which preferably has a planar shape, in particular is designed as an electrically conductive layer or film, the pouch film can have two insulating layers, each of which at least partially covers the reference electrode. Compared to pouch films of conventional, unclaimed electrochemical cells, the pouch film of the device according to the application does not necessarily have an increased thickness. Rather, an existing metallic layer in the structure of the pouch film can be used as a reference electrode and electrically connected accordingly.

[0024] In general, the two insulating layers of the pouch film are an inner and an outer insulating layer, both made of an electrically insulating material. The two insulating layers on the reference electrode can be made of the same material or different materials, for example, as coatings or plastic layers. Both insulating layers can be of the same or different thicknesses. If the insulating layers are of different thicknesses, the inner insulating layer, for example, will be thicker. In particular, each insulating layer can be thicker than the reference electrode, which is also a flat, sandwich-like structure sandwiched between the insulating layers. Alternatively, configurations are also possible in which the foil-like reference electrode is thicker than either of the two insulating layers.

[0025] The inner insulating layer can, in the order listed, that is, with increasing distance from this insulating layer, face a current collector, an electrode active material, and an electrolyte. The inner insulating layer can have at least one cavity, and in particular several cavities, extending from the current collector to the reference electrode. The cavities represent spaces in which charge carriers can flow. In cross-section, the cavities have, for example, a rectangular, and in particular a square, shape. This means that each of the cavities formed in the inner insulating layer has, for example, a cuboid or cubic shape. In three dimensions, the cavities have, for example, the shape of rods tangent to the reference electrode with a polygonal or P240809

[0026] - 5 - round, especially circular, cross-section. The cavities can be holes, which can be produced, for example, with a laser.

[0027] Regardless of how the holes or other cavities in the inner insulating layer are created, these cavities can initially be left empty during the manufacturing of the electrochemical cell. In the assembled cell, the cavities then fill with liquid electrolyte. This is the same liquid electrolyte used in the pouch battery cell, which is also used between the anodes and cathodes.

[0028] Alternatively, cavities can be filled with a solid ionic conductor before assembly to achieve the desired insulating and ion-conducting properties. When using a solid electrolyte, the cavities are filled in such a way that there is permanent contact between the solid ionic conductor and the active material of the electrode. Suitable solid electrolytes include, for example, polyethylene oxide (PEO), lithium phosphorus sulfide (LisPS₄, LPS), lithium phosphorus sulfur chloride (LiePSCl, LPSCI), lithium lanthanum zirconium oxide (La₃Li₂O₆₂Zr₂, LLZO), or lithium aluminum germanium phosphate (Li₂₅Al₂O₆₅Ge₅₅(PO₄)₃, LAGP).

[0029] Depending on the presence of a filling material in the holes, an outermost separator layer may or may not be present in the cell.

[0030] The holes can, in principle, be recesses of a geometrically defined shape or of a geometrically undefined shape.

[0031] One possible variant of the electrochemical cell involves the reference electrode extending laterally beyond both insulating layers. In this case, the outwardly projecting section of the reference electrode constitutes a third electrical connection point, in addition to the anode and cathode terminals. To enable an electrical connection at this section, either the corresponding section may be present without an outer insulating layer from the outset, or the outer insulating layer may have been subsequently removed. P240809

[0032] - 6 -

[0033] An alternative variant involves the reference electrode not protruding beyond the body of the electrochemical cell, but rather making electrical contact via recesses in the outer insulating layer. These recesses are covered by the inner insulating layer bordering the cell interior. Various methods exist for creating these recesses, such as laser or photochemical processes.

[0034] The reference electrode of the electrochemical cell is typically designed as an electrically conductive foil made of a light metal, that is, a foil which, regardless of the exact alloy composition, is referred to as aluminum foil. Electrically conductive layers made of other materials with sufficient electrical conductivity are also suitable materials for the reference electrode.

[0035] In each variant, the electrochemical cell according to the patent application allows separate observation of the cathode and anode potentials, thus enabling conclusions to be drawn about the condition of the individual electrodes. In particular, information on the aging behavior of the electrodes can be obtained. A reference electrode can be located only on the cathode side, only on the anode side, or on both the cathode and anode sides, without having the same shape, size, or symmetrical arrangement.

[0036] The electrochemical cell is in particular a secondary battery cell, for example a lithium-ion battery.

[0037] To operate the electrochemical cell, which is constructed as a pouch battery cell, two terminal electrodes, i.e., a cathode and an anode, as well as the reference electrode, are electrically connected to each other, with voltages between the reference electrode and the electrode being measured separately. P240809

[0038] - 7 - electrical voltages, for example, can be measured in matching or overlapping time windows or at defined separate times.

[0039] The invention is explained below by way of example with reference to drawings. These show, in some simplified forms:

[0040] Fig. 1 shows a top view of an electrochemical cell in the form of a pouch battery cell,

[0041] Fig. 2 shows a side view of the pouch battery cell shown in Figure 1,

[0042] Fig. 3 shows an enlarged partial section through the pouch battery cell according to Figure 2, and

[0043] Fig. 4 shows a further enlarged partial section through another pouch battery cell according to Figure 2, in a representation analogous to Fig. 3.

[0044] Unless otherwise stated, the following explanations refer to all embodiments according to Figures 1 to 4. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0045] In the exemplary embodiments, an electrochemical cell 1 is designed as a pouch battery cell. Characteristically for pouch battery cells, the electrochemical cell 1 has a cushion-like shape, with the electrochemically active components of the cell 1 enclosed by a pouch film 2.

[0046] Several such pouch battery cells of the same design can be arranged in an enclosure (not shown), and can be temperature-controlled, in particular by immersion cooling. The pouch battery cells can, for example, be part of a traction battery used in a motor vehicle. P240809

[0047] - 8 - In the exemplary embodiments, the electrochemical cells 1 are pouch battery cells of a lithium-ion battery. Figure 1 shows a top view of an electrochemical cell 1 in the form of a pouch battery cell comprising two current collectors 9 and a pouch film 2, which is laterally folded and therefore has two folds 14. Each pouch battery cell has two electrodes 3, 4, namely an anode 3 and a cathode 4, each of which is connected to one of the current collectors 9. The position of a reference electrode 5 within the pouch film 2 is indicated by a dashed line. According to Figure 1, the reference electrode 5 is covered by an outer insulating layer 6.

[0048] Figure 2 shows a side view of the electrochemical cell 1 in the form of the pouch battery cell according to Figure 1. The position of a reference electrode 5 within the pouch film 2 is indicated by a dashed line.

[0049] Figure 3 shows an enlarged partial section through the pouch battery cell according to Figure 2. Figure 4 shows, in a representation analogous to Figure 3, an enlarged partial section through another pouch battery cell according to Figure 2.

[0050] Figure 3 shows only the anode 3 as an example, and Figure 4 shows only the cathode 4. Collectively, the anode 3 and the cathode 4 are referred to as electrodes.

[0051] In addition to electrodes 3 and 4, there is a reference electrode 5, which is integrated into the pouch film 2 in the form of an aluminum foil. The reference electrode 5 is largely covered by the outer insulating layer 6 and an inner insulating layer 7. The total thickness of the pouch film 2, designated D2, comprises the thickness D5 of the reference electrode 5, the thickness D6 of the outer insulating layer 6, and the thickness D7 of the inner insulating layer 7. The outer insulating layer 6 borders an external space AR outside the electrochemical cell 1. The interior of the electrochemical cell 1 is designated IR. P240809

[0052] - 9 -

[0053] The thickness D6 of the outer insulating layer 6 is more than twice the thickness D5 of the reference electrode 5. The thickness D7 of the inner insulating layer 7 is greater than the thickness D6 of the outer insulating layer 6 in both cases. In alternative embodiments not shown, different relationships between the various thicknesses D5, D6, and D7 may apply.

[0054] According to Figures 3 and 4, electrodes 3 and 4 are associated with an electrode active material 8 and a planar current collector 9. The thickness of the current collector 9, designated D9, is greater than the thickness D5 of the reference electrode 5. This underscores the extremely small space requirement of the reference electrode 5, which is already a part of the pouch film 2.

[0055] In the illustrated embodiments, the current collector 9 rests flat on the inner insulating layer 7. In each case, either the current collector 9 or the electrode active material 8 or a layer of an electrolyte 13 rests against the inner insulating layer 7.

[0056] To enable charge transport between the current collector 9, the electrode active material 8 or the electrolyte layer 13 and the reference electrode 5, several cavities 10 are formed in the inner insulating layer 7. The width of each cavity 10, denoted by B10, is slightly larger than the thickness D7 of the inner insulating layer 7 in the cases sketched in Figures 3 and 4, so that the cavities 10 have a rectangular, approximately square, cross-section. The cavities 10 are distributed at least approximately uniformly over the surface of the inner insulating layer 7.

[0057] Regarding the distribution of the electrode active material 8, there are no differences between the embodiment according to Figure 3 and the embodiment according to Figure 4. The same applies to the distribution of the electrolyte 13 in the interior IR of the electrochemical cell 1. The electrical contacting of the reference electrode 5 is carried out in the embodiment according to Figure 3 and in P240809.

[0058] - 10 -

[0059] The embodiment shown in Figure 4 can be implemented in different ways. In the case of Figure 3, there is a section 11 of the reference electrode 5 which projects beyond the insulating layers 6, 7, i.e., extends to the outside. In the embodiment shown in Figure 4, at least one recess 12, which is formed in the outer insulating layer 6, fulfills the corresponding purpose, so that the reference electrode 5 can be contacted from the outside space AR at least at a defined point on the pouch film 2.

[0060] P240809

[0061] - 11 -

[0062] List of reference signs

[0063] 1 electrochemical cell

[0064] 2 pouch films

[0065] 3 Electrode, anode

[0066] 4 Electrode, cathode

[0067] 5 reference electrode, aluminum foil

[0068] 6 outer insulation layer

[0069] 7 inner insulation layer

[0070] 8 electrode active material

[0071] 9 current collectors

[0072] 10 Cavity

[0073] 11 Section of the reference electrode protruding above the insulating layers

[0074] 12. Recess in the outer insulation layer

[0075] 13 Electrolyte

[0076] 14 Fold of the pouch film

[0077] AR Outdoor space

[0078] B10 Width of the cavity 10

[0079] B12 Width of the recess 12

[0080] D2 Total thickness of the pouch film

[0081] D5 Reference electrode thickness

[0082] D6 Thickness of the outer insulation layer

[0083] D7 Thickness of the inner insulation layer

[0084] D9 pantograph thickness

[0085] IR interior of the electrochemical cell

Claims

P240809 - 12 - Patent claims 1. Electrochemical cell (1 ) in the form of a pouch battery cell with a housing in the form of a pouch film (2), with an anode (3), a cathode (4), and a reference electrode (5) arranged asymmetrically to the anode (3) and the cathode (4) such that the reference electrode (5) is integrated into the pouch film (2).

2. Electrochemical cell (1 ) according to claim 1 , characterized in that the pouch film (2) is formed from the reference electrode (5) and two insulating layers (6, 7) covering it at least partially, namely an outer insulating layer (6) and an inner insulating layer (7).

3. Electrochemical cell (1 ) according to claim 2, characterized in that the outer insulating layer (6) and the inner insulating layer (7) are formed by a lacquer layer or a plastic layer.

4. Electrochemical cell (1 ) according to claim 2 or 3, characterized in that the inner insulating layer (6) faces a current collector (9), an electrode active material (8) and / or an electrolyte (13) and has at least one cavity (10) which extends from the current collector (9), the electrode active material (8) and / or the electrolyte (13) to the reference electrode (5).

5. Electrochemical cell (1 ) according to one of claims 2 to 4, characterized in that the reference electrode (5) is only partially covered by the outer insulating layer (6).

6. Electrochemical cell (1 ) according to claim 5, characterized in that the reference electrode (5) extends beyond both insulation layers (6, 7). P240809 - 13 - 7. Electrochemical cell (1 ) according to claim 5, characterized in that the reference electrode (5) has recesses (12) in the outer insulating layer (6) at locations where the reference electrode (5) is covered by the inner insulating layer (7).

8. Electrochemical cell (1) according to any one of claims 1 to 5, characterized in that the reference electrode (5) comprises a light metal, in particular aluminum.

9. Electrochemical cell (1) according to any one of claims 1 to 8, characterized in that the pouch battery cell is a cuboid cell.

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