Electrode arrangement for electrochemical storage cell and electrochemical storage cell

Abstract

An electrode arrangement for an electrochemical storage cell comprises a sequence of layers with at least one cathode (10) and one anode (20), as well as a separator (30) arranged between the anode and cathode (10, 20). The cathode (10) comprises a first current collector film (11) coated with a first cathode active material (12). The first current collector film (11) is structured with a second cathode active material (15) such that areas (13) of the first current collector film (11) are free of the second cathode active material (13) and contact areas (14) contain the second cathode active material (13).

Description

[0001] The following description concerns an electrode arrangement for an electrochemical storage cell and an electrochemical storage cell. State of the art

[0002] Battery cells form the basis not only for electromobility but for virtually all areas of modern life. With the rapid proliferation of batteries, the question of their safety also arises. Internal short circuits are a factor that should be considered during the design of lithium-ion batteries (LiB). For example, deformation of the anode due to external forces can lead to misalignment of the electrodes, loss of contact, and structural damage within the battery, which can impair its performance. Deformation can result in an internal short circuit.

[0003] One of the most common measures is the use of a thicker separator or a ceramic coating on the surfaces of the anode or separator. Using a thicker separator or ceramic coating increases the internal resistance, thus preventing a short circuit between the cathode and anode. Overall, these measures are approaches to increasing the safety and reliability of lithium-ion batteries and avoiding internal short circuits. However, these measures can lead to a reduction in capacity because they take up space that could otherwise contribute to cell capacity. Furthermore, the weight of the cell can increase, which is an important factor in vehicle design.

[0004] The task is to design an electrode arrangement for an electrochemical storage cell and an electrochemical storage cell that is less prone to internal short circuits.

[0005] These problems are solved by the electrochemical storage cell and the electrochemical storage cell, with the features of the independent and dependent claims. Advantageous embodiments and further developments of the invention are described in the dependent claims. Summary

[0006] It is hereby assumed that each feature described for any embodiment can be used alone or in combination with other features described herein, and can be used in combination with one or more features of any other embodiment, or in any combination of any other embodiment, unless expressly described as an alternative. Furthermore, equivalents and modifications not described below may be used without departing from the scope of the claimed subject matter.

[0007] In the following, an electrochemical storage cell refers to an electrochemically based energy storage device, in particular a rechargeable energy storage device, that is suitable for storing electrical energy and supplying it to a consumer, for example, a consumer in a vehicle. The term "lithium-ion battery" is used synonymously with all terms commonly used in the prior art for lithium-containing galvanic cells and electrochemical storage cells (or simply "cell"), such as lithium battery, lithium cell, lithium-ion cell, lithium polymer cell, lithium-ion battery cell, and lithium-ion accumulator. Rechargeable batteries, so-called secondary batteries, are specifically included. The terms "battery" and "electrochemical storage cell" are also used synonymously with "lithium-ion battery" and "lithium-ion cell."

[0008] The term "electrode array" refers to a sequence of layers or films. In an electrochemical storage cell, the layers follow one another. However, this does not mean that the layers listed here must follow each other directly. Intermediate layers can also be included, such as a separator, insulator, electrode binder, coatings, and electrically conductive additives, which can be applied to an electrically conductive substrate for the respective electrodes.

[0009] An electrochemical storage cell typically has several electrodes: a positive electrode (cathode) and a negative electrode (anode), which can be electrically contacted via current collectors. Each of these electrodes contains at least one active material, optionally together with additives such as electrode binders and electrically conductive additives, which are applied to an electrically conductive substrate (for example, a metal foil) or to a current collector of the respective electrode. Typically, non-porous and solid conductive substrates made of aluminum (for the positive electrode) or copper (for the negative electrode) are used. Such conductive substrates are typically impermeable to liquid electrolyte and gases.

[0010] An electrochemical storage cell comprises one or more electrochemical electrode arrays, for example, with multiple anodes and cathodes in the layer sequence. In addition, the electrochemical storage cell includes further components such as a housing and electrical contacts.

[0011] The following describes an electrode arrangement for an electrochemical storage cell. According to one embodiment, the electrode arrangement comprises a sequence of layers with at least one cathode and one anode, as well as a separator arranged between the anode and cathode. The cathode comprises a first current collector film coated with a first cathode active material, in particular layered with the first cathode active material over an entire area. The first current collector film is also structured with a second cathode active material and coated with the second cathode active material in such a way that areas of the first current collector film are free of the second cathode active material and other areas contain the second cathode active material.

[0012] The selective structuring of the cathode or current collector foil with a second cathode active material can help increase the flexibility and voltage absorption of an electrochemical storage cell, thus further mitigating the effects of potential mechanical deformation of the anode. This can prevent or at least reduce the occurrence of internal short circuits and improve the cell's lifespan and safety. Furthermore, two cathode active materials are present on the current collector foil. The first cathode active material contributes to the capacity of the electrochemical storage cell. The second cathode active material also contributes to the capacity of the electrochemical storage cell and additionally serves a safety function. Even if the anode deforms as a result of mechanical stress on the electrodes, a thermal event can be prevented or at least reduced.

[0013] The second cathode active material acts as an additional protective layer to prevent a short circuit between the anode and cathode. This reduces the risk of overheating and thermal runaway in the battery, thus increasing safety. Even if local contact occurs between the anode and cathode, the second cathode active material can remain electrochemically active. This ensures that the battery can at least partially maintain its performance despite deformation. Furthermore, the structure of the second cathode active material allows the first cathode active material to remain electrochemically active, as it is protected by the second cathode active material acting as an additional protective layer.

[0014] The improved concept presented here is based in particular on the considerations outlined below. Internal short circuits between the cathode and anode can arise from various causes. In many cases, the short circuit is caused by foreign materials such as metal particles during production or by deformation of the anode due to external forces acting on the cell. The concept described here primarily addresses the latter case. Even if a short circuit occurs due to mechanical deformation of the anode, a highly resilient subcathode active material (second cathode active material) coated in the potential short-circuit areas can prevent a thermal event.

[0015] Therefore, there are two active materials on the cathode: a first active material that primarily contributes to capacity, and a second active material that contributes to safety and capacity, as well as forming a safety layer. These two active materials are selectively coated on the current collector foil, for example, in the edge areas of the current collector foil. The use of this safety layer reduces the occurrence of battery short circuits without affecting the overall capacity.

[0016] Lithium iron phosphate (LFP) is one example of a suitable second cathode active material. LFP is characterized by high safety, stability, and cycle stability. A suitable variant is lithium manganese iron phosphate (LMFP), in which some of the iron in LFP is replaced by manganese. The second cathode active material can also be mixed with a small amount of ceramic material (for example, aluminum oxide, boehmite, etc.).

[0017] Similarly, the improved concept presented here can be applied to the anode either alternatively or additionally. In one embodiment, the electrode arrangement for an electrochemical storage cell comprises a sequence of layers with at least one cathode and one anode, as well as a separator arranged between the anode and cathode.

[0018] The anode comprises a second current collector foil coated with a first anode active material. The second current collector foil is structured with a second anode active material such that areas of the second current collector foil are free of the second anode active material, while contact areas contain the second anode active material.

[0019] According to one embodiment, the first current collector foil is structured such that the contact areas comprise the second cathode active material with the first cathode active material underneath. Alternatively, or additionally, the second cathode active material is coated directly onto the first current collector foil in the contact areas.

[0020] According to one embodiment, the contact areas are provided at such points on the first current collector foil where an internal short circuit can occur.

[0021] According to one embodiment, the contact areas are provided at one or more edges of the first current collector foil.

[0022] According to one embodiment, the contact areas completely or partially surround the first current collector foil.

[0023] According to one embodiment, the contact areas are arranged along a longitudinal direction of the first current collector foil such that the contact areas are at least partially opposite each other when the layer sequence is wound spirally to form an electrode coil.

[0024] Furthermore, an electrochemical storage cell is proposed. According to one embodiment, the electrochemical storage cell comprises an electrode arrangement according to one or more of the preceding aspects and is arranged in a battery housing.

[0025] According to one embodiment, the electrode arrangement is wound into an electrode coil and arranged in the housing, forming a cylindrical storage cell.

[0026] Furthermore, a method for manufacturing an electrode arrangement for an electrochemical storage cell is proposed. The method comprises the following steps: - Manufacturing a cathode by coating a first current collector foil with a first cathode active material, - The first current collector foil is structured with a second cathode active material, such that areas of the first current collector foil are free of the second cathode active material and contact areas contain the second cathode active material, and - Producing a layer sequence with at least a cathode and an anode, as well as a separator arranged between the anode and cathode, for example by calendering.

[0027] According to one embodiment, the layer sequence is wound spirally into an electrode coil and arranged in a cylindrical housing. In this way, a so-called cylindrical cell can be formed.

[0028] The following describes exemplary embodiments with reference to the accompanying drawings. Further details, preferred embodiments, and refinements will be derived from these. Identical or functionally equivalent components are identified by the same reference numerals in the figures. The components shown, as well as their relative sizes, are not to be considered to scale. Where components and parts function identically across different figures, their descriptions will not necessarily be repeated for each subsequent figure. Brief description of the drawings

[0029] In detail: Fig. 1A to 1C Examples of an electrode arrangement in side view, Fig. 2A to 2C Examples of a cathode for an electrochemical storage cell in side view, and Fig. 3A to 3C Examples of an electrode arrangement in top view. Detailed description

[0030] The Fig. Figures 1A to 1C show exemplary embodiments of an electrode arrangement for an electrochemical storage cell in side view. The electrode arrangement comprises several electrodes 10, 20, which are shown here as anodes 20 and cathode 10. The anode 20 is separated from the cathode 10 and electrically insulated by a separator 30. Together, the cathode 10, anode 20, and separator 30 form a layer sequence. The figure shows, for example, a section of an electrode winding to which the layer sequence can be wound in a spiral. As an electrode winding, the electrochemical electrode arrangement can, for example, be inserted into a cylindrical storage cell (also called a round cell). Alternatively, the layer sequence can be designed as a stack, which can, for example, be inserted into a battery housing.

[0031] The cathode 10 comprises a first current collector 11 and a first cathode active material 12. The first cathode active material 12 can, for example, comprise a variety of particles embedded in an electrode binder. The first cathode active material can be a layered oxide such as lithium nickel manganese cobalt oxide (NMC, for example, NMC 622 or NMC 811), lithium nickel cobalt aluminum oxide (NCA), lithium cobalt oxide (LCO), or lithium nickel cobalt oxide (LNCO). The layered oxide can, in particular, be an overlithiated layered oxide (OLO). Other suitable cathode active materials 12 are compounds with a spinel structure, such as lithium manganese oxide (LMO) or lithium manganese nickel oxide (LMNO). In addition to a binder, the cathode 10 may contain a conductivity additive or solid electrolyte.

[0032] The anode 20 comprises a second current collector foil 21 and an anode active material 22. The anode active material 22 is, for example, a material from the group consisting of carbon-containing materials, silicon, silicon suboxide, silicon alloys, aluminum alloys, indium, indium alloys, tin, tin alloys, cobalt alloys, and mixtures thereof. Preferably, the anode active material 22 is selected from the group consisting of synthetic graphite, natural graphite, graphene, mesocarbon, doped carbon, hard carbon, soft carbon, fullerene, silicon-carbon composite, silicon, surface-coated silicon, silicon suboxide, silicon alloys, lithium, aluminum alloys, indium, tin alloys, cobalt alloys, and mixtures thereof.

[0033] The current collector foils 11, 21 are made of conductive materials. Examples of lithium-ion storage cells are copper (Cu) current collectors for an anode current collector foil 21 and aluminum (Al) for a cathode current collector foil 11. Typically, the current collector foils 11, 21 are designed as metal foils.

[0034] In addition to the first cathode active material 12, the cathode 10 has a further active material, or a second cathode active material 15. For example, the first cathode active material 12 is coated directly onto the cathode current collector foil 11, and the second cathode active material 15 is structured on the first cathode active material 12. The second cathode active material 15 is structured such that areas 14 of the first current collector foil 11, or of the cathode current collector, are free of the second cathode active material 15. Further areas 15 contain the second cathode active material 15 with the first cathode active material 12 underneath. The structuring is described with reference to the Fig. 3A to 3C are explained in more detail in a top view.

[0035] Exemplary compounds suitable as a second cathode active material 15 are lithium iron phosphate (LFP, LiFePO4) or lithium manganese iron phosphate (LMFP), which form an olivine structure. LFP is characterized by high safety, stability, and cycle stability. In this exemplary embodiment, LFP is used as the second active material 15, with NMC being used as the first highly specific energy active material 12. LFP can be coated as a layer on NMC or mixed with NMC or another material with high specific capacity.

[0036] Fig. Figure 1A shows an embodiment of an electrode arrangement for an electrochemical storage cell. The figure is schematic and not to scale in order to better illustrate the proposed concept. The electrode arrangement shown is, for example, wound into an electrode winding of a cylindrical cell. In this sense, the figure shows a section of the electrode winding with a cathode 10 and an anode 20, which are electrically insulated by a separator 30. The edges of the cathode 10 and the anode 20 are shown enlarged in the figure. As a result of coating the current collector foils 11, 21 with the corresponding active material 12, 22, the active materials are conically shaped at the edges (for example, by subsequent calendering). This allows the current collector foils 11, 21 to exhibit a certain degree of flexibility in these areas and to bend under pressure.Under sufficiently high pressure (for example, due to external influence on the storage cell or the electrode arrangement), the current collector foils 11, 21 can contact each other, potentially causing an internal short circuit. This effect is described in . Fig. 1C shown.

[0037] The second cathode active material 15 is structured on the cathode current collector foil 11 such that areas 14 of the cathode current collector foil 11 are free of the second cathode active material 15, while other areas contain the second cathode active material 15. These areas coated with the second cathode active material 15 form contact areas 14, which are provided in the layer sequence at locations where an internal short circuit can occur or could presumably occur according to the design of the electrode arrangement. Fig. 1A shows contact areas 14 at an edge of the cathode 10 and Fig. 1B shows contact areas 14 at both edges of the cathode.

[0038] The contact areas 14 are provided, for example, at locations in the layer sequence opposite an area where the current collector foils 11, 21 are free of active material and thus form, in a sense, “loose ends” (cf. Fig. 1C). At these points, the layer thickness of the active material is also thinner than, for example, in the middle of the cathode 10, tapering conically as described above. At these thinned areas, the second cathode active material 15 can advantageously be coated or structured onto the cathode current collector foil 11, i.e., onto the first cathode active material 12 underneath. These areas with reduced active material thickness are more susceptible to short circuits; therefore, it is advantageous to provide special protection for the active material here. Alternatively, the second cathode active material 15 can be coated or structured onto areas of the cathode current collector foil 11 that are free of the first cathode active material 12. The contact areas 14 are specifically arranged at points where an internal short circuit could occur or is suspected.This targeted structuring of the active material can prevent short circuits at critical points.

[0039] The Fig. Figures 2A to 2C show exemplary embodiments of a cathode for an electrochemical storage cell in side view. The examples show cathodes 10 with active material 11 produced by a calendering process. The cathodes 10 can be manufactured as continuous electrode rolls using a calendering process and cut to desired lengths (for example, along the dashed lines). The figures show, for example, an electrode roll on which two cathodes 10 are prepared. These are intended to serve as an example for electrode rolls with a multitude of cathodes 10, for the purpose of simplification.

[0040] The cathodes 10 shown comprise the cathode current collector foil 11 and the first and second cathode active materials 12, 15. The cathodes are manufactured, for example, as continuous electrode rolls in a calendering process. The first and second cathode active materials 12, 15 can be structured or coated differently on the continuous cathode current collector foil 11. It is possible to coat the entire surface of the cathode current collector foil 11 with the first cathode active material 12 and then structure the second cathode active material 15 in the contact areas 14 on the first cathode active material 12. It is also possible to structure the cathode current collector foil 11 with the first cathode active material 12 so that the contact areas 14 initially remain free of the first cathode active material 12. In these free areas, the second cathode active material 15 is then coated onto the cathode current collector foil 11.Furthermore, any combination of these two approaches is possible. The shape of the contact areas 14 formed by the second cathode active material 15 can form different geometric shapes and is not restricted in this respect.

[0041] In Fig. In 2A, the contact areas 14 are rectangular and of different sizes. The electrode roll can be cut in a larger contact area 14 (dashed line) so that two cathodes 10 with respective contact areas 14 at the left and right edges are obtained. Fig. Figure 2B shows a similar example, where the contact areas 14 are U-shaped, double-U-shaped in the middle, and H-shaped, respectively. These shapes increase the protective effect on the upper and lower edges without requiring an unnecessarily large amount of the second cathode active material 13. Fig. Figure 2C shows only a central contact area 14. The contact areas 14 are structured, for example, at locations on the cathode current collector foil 11 that lie in a layer sequence rolled up to form the electrode winding, where an internal short circuit can or could presumably occur.

[0042] In Fig. Figures 3A to 3C show three exemplary cathode layers. The layers of the electrode arrangement have a substantially rectangular shape and can be wound one on top of the other in the layer sequence from a first longitudinal end 201 to a second longitudinal end 202 (indicated by the arrow). The first longitudinal end 201 is then located at the winding core. The current collector foils have a multitude of tabs via which the foils can be welded and electrically contacted.

[0043] The tabs are arranged in an area 150, which forms a strip extending from the longitudinal end 201 to the second longitudinal end 202.

[0044] The first current collector foil 11 is coated over its entire surface with a first cathode-active material 12, for example by calendering. Furthermore, the first current collector foil 11 is structured with the second cathode-active material 15. This structuring creates areas 14 on the first current collector foil 11 that are free of the second cathode-active material, while further areas 15 contain the second cathode-active material 13 and, underneath it, the first cathode-active material 12. The areas 15 are preferably arranged at locations on the first current collector foil 11 where mechanical deformation of the anode is most likely to lead to electrical contact (or an internal short circuit) between the anode and cathode. This could be the case, for example, at the longitudinal ends 201, 202, so that further areas 15 containing the second cathode-active material 13 are provided there, as shown in Fig. 3A (first longitudinal end 201 or second longitudinal end 202) and Fig. 3B (first longitudinal end 201 and second longitudinal end 202) is shown. In principle, other structures are also conceivable. In Fig. In section 3C, the further area 15 represents a rectangle that forms an edge of the first current collector foil 11 and consists of the second cathode active material 13. The respective structure of the further areas (one or more, discrete or connected) results from the specific geometry and design of an electrochemical storage cell, as well as the safety considerations derived therefrom.

[0045] Although the improved concept has been illustrated and described in detail using exemplary embodiments, it is not limited by these embodiments. Rather, other variations of the improved concept can be derived by those skilled in the art without departing from the scope of protection defined by the claims. In particular, the previously described aspects relating to the cathode can be applied analogously to the anode. The exemplary embodiments presented here can be transferred by replacing the terms cathode, first cathode active material, and second cathode active material with the corresponding terms anode, first anode active material, and second anode active material. Materials for the current collector foils can be selected in accordance with standard industry practices, as described above. Reference symbol list 10 Cathode 11 (Cathode) current collector foil 12 first cathode active material 13 Area (free of second cathode active material) 14 Area (coated with second cathode active material), contact area 15 second cathode active material 20 anode 21 (Anode) current collector foil 22 Anode active material 30 Separator 150 area (of the pantograph foil) 201 Longitudinal end 202 Longitudinal end

Claims

[1] An electrode arrangement for an electrochemical storage cell, comprising a layer sequence with at least one cathode (10) and one anode (20), and a separator (30) arranged between the anode and cathode (10, 20), wherein: - the cathode (10) comprises a first current collector foil (11) coated with a first cathode active material (12), and - the first current collector foil (11) is structured with a second cathode active material (15) such that areas (13) of the first current collector foil (11) are free of the second cathode active material (13) and contact areas (14) have the second cathode active material (13). [2] The electrode arrangement according to claim 1, wherein the first current collector foil (11) is structured such that the contact areas (14) have the second cathode active material (15) with underlying first cathode active material (12) and / or in the contact areas (14) the second cathode active material (15) is coated directly onto the first current collector foil (11). [3] The electrode arrangement according to one of the preceding claims, wherein the contact areas (14) are provided at such locations on the first current collector foil (11) where an internal short circuit may occur. [4] The electrode arrangement according to one of the preceding claims, wherein the contact areas (14) are provided at one or more edges of the first current collector foil (11). [5] The electrode arrangement according to one of the preceding claims, wherein the contact areas (14) completely or partially surround the first current collector foil (11). [6] The electrode arrangement according to one of the preceding claims, wherein the contact areas (14) are arranged along a longitudinal direction of the first current collector foil (11) such that the contact areas (14) are at least partially opposite each other when the layer sequence is wound spirally to form an electrode coil. [7] An electrochemical storage cell comprising an electrode arrangement according to one of the preceding claims arranged in a battery housing. [8] The electrochemical storage cell according to claim 7, wherein the electrode arrangement is wound into an electrode coil and arranged in the housing to form a cylindrical storage cell. [9] A method for manufacturing an electrode arrangement for an electrochemical storage cell, comprising the steps: - Manufacturing a cathode (10) by coating a first current collector foil (11) with a first cathode active material (12), - The first current collector foil (11) is structured with a second cathode active material (15) such that areas (13) of the first current collector foil (11) are free of the second cathode active material (13) and contact areas (14) have the second cathode active material (13), and - Producing a layer sequence with at least the cathode (10) and an anode (20), as well as a separator (30) arranged between the anode and cathode (10, 20). [10] The method according to claim 9, wherein the layer sequence is wound spirally into an electrode coil and arranged in a cylindrical housing. [11] An electrode arrangement for an electrochemical storage cell, comprising a layer sequence with at least one cathode (10) and one anode (20), and a separator (30) arranged between the anode and cathode (10, 20), wherein: - the anode (20) comprises a second current collector foil coated with a first anode active material, and - the second current collector foil is structured with a second anode active material, such that areas (13) of the second current collector foil (11) are free of the second anode active material and contact areas (14) have the second anode active material.

Images