IMPROVED METHOD FOR PRODUCING CELL STACKS BY UNIFORM THERMAL ACTIVATION OF AN ADHESIVE

Description

[0001] The invention relates to a method for producing a cell stack, in particular for an electrochemical memory, wherein at least anode layers, separator layers, and cathode layers are repeatedly stacked, folded, or wound on top of each other. The invention further relates to a device for producing cell stacks and an electrochemical memory with at least one cell stack.

[0002] In the manufacture of electrochemical storage devices, such as lithium-ion batteries, multiple alternating layers of anodes, cathodes, and separators are typically arranged in the form of cell stacks. These layers are coated with a thermally activated adhesive and then bonded together under heat and force. For this purpose, the layers are positioned between two heating plates that act on the numerous layers. Such a process is known, for example, from US 2022 / 0029246 A1. In this document, the heating plates can simultaneously function as press dies and can be controlled independently of each other in the cell stack area and in the area of ​​the cell stack's terminals.

[0003] However, heating the cell stack layers via the heating plates results in an inhomogeneous temperature distribution along the height or thickness of the cell stack. This inhomogeneous temperature distribution prevents uniform bonding between the cell stack layers and also hinders the bonding of all cell stack layers using the thermally activated adhesive. Furthermore, the electrically and thermally insulating properties of the separator layers delay the complete heating of all cell stack layers, thus limiting the output of the system during cell stack production.

[0004] Methods are already known that press the layers of the cell stack together with greater force during heating or subject the layers to a higher temperature in order to accelerate the bonding process. However, such measures can have a detrimental effect on the material properties of the cell components or the respective layers of the cell stack.

[0005] WO 2011 / 051097 A2 describes a method for bonding heat-activated and adhesive surface elements. In this method, electrically non-conductive surface elements are coated with an electrically conductive coating that is in contact with an adhesive layer. The surface elements are heated via the coating and simultaneously pressed together.

[0006] The present invention therefore aims to provide a method for producing cell stacks, particularly for electrochemical storage devices, which enables rapid and uniform bonding of the cell stack layers. This objective is achieved by the features specified in claim 1. Further advantageous embodiments of the invention are part of the dependent claims.

[0007] According to one aspect of the invention, a method for manufacturing a cell stack is provided. The cell stack is intended in particular for an electrochemical storage device, such as a lithium-ion cell. Such a cell stack consists of a plurality of anode electrodes or anode layers, separator layers, and cathode electrodes or cathode layers, which are repeatedly stacked, folded, or wound one on top of the other. Furthermore, additional layers containing, for example, graphite or other materials may be provided.

[0008] An anode electrode or anode layer can, for example, consist of a copper foil or a copper support foil coated on one or both sides with an anode substrate. Similarly, a cathode electrode or cathode layer can, for example, consist of an aluminum foil or an aluminum support foil coated on one or both sides with a cathode substrate.

[0009] For the sake of simplicity, the additional layers commonly used in lithium-ion batteries will not be described further. To form an integral or single-piece cell stack, adhesive layers are used, or certain layers are pre-coated with an adhesive. For example, the separator layers are coated or provided with a thermally activated adhesive on one or both sides.

[0010] After the arranged anode, separator, and cathode layers have been provided, electrically conductive layers, in particular the copper and aluminum foils of the anode and / or cathode electrodes and / or additional layers or grids, are electromagnetically heated. In contrast to the prior art, where a heat source is pressed against the cell stack from the outside and the heat spreads slowly from the outside in, heat is now generated directly in all electrically conductive layers of the cell stack. This eliminates time-consuming and uneven heat conduction. The heating of the anode and / or cathode electrodes directly and immediately thermally activates the adhesive of the respective separator layers.The thermal activation of the adhesive bonds the anode electrodes, separator layers, and cathode electrodes together to form a single cell stack. This completes an exemplary cell stack.

[0011] Depending on the design of the process and the requirements, additional processing steps, such as electrical connection of contact flags, setting the final dimensions, applying coatings or packaging, arranging positioning aids and the like, may follow or be implemented within the process.

[0012] A device for producing cell stacks is configured to carry out the method according to the invention. For this purpose, the device may have a receiving chamber for receiving at least one bundle of layers that are assembled to form a cell stack. Furthermore, at least one heat source is provided which can electromagnetically induce heat in the electrically conductive layers of the bundle. Depending on the design of the device, a pressing device with a lower tool and an upper tool can be used to exert a pressing force on the layers. A control unit can be used to control and regulate the generation of heat and the provision of a pressing force by the pressing device, for example, based on measurement data from sensors.

[0013] An electrochemical storage device produced using this method comprises at least one cell housing and can, for example, be designed as a battery cell based on lithium-ion technology. At least one cell stack, produced according to the inventive method, is arranged within the cell housing. The cell stack produced by this method is not limited to lithium-ion technology and can accordingly be used in a variety of different electrochemical cells that require a multi-layered, single-piece cell stack.

[0014] Internal heat release for thermal activation of the adhesive reduces the heating time required for the adhesive to develop its bonding properties. Furthermore, inducing heat into the electrically conductive layers allows for a more homogeneous temperature distribution, both laterally and within the layers, as well as across the thickness of the cell stack. This homogeneous temperature distribution within the cell stack means that the outer layers are not subjected to thermal stress, or are only minimally stressed, compared to the inner layers. This prevents adverse changes in the material properties of the cell stack layers.

[0015] The thermally activated adhesive can be a hot melt adhesive, for example, polyurethane-based, which cures below a certain temperature threshold and remains tacky or adhesive above that threshold. Alternatively, a two-component adhesive with a thermally activated hardener can be used. The hardener liquefies with increasing temperature and can then react with the resin. For example, the thermally activated adhesive can be PVDF (polyvinylidene fluoride).

[0016] The electrically conductive layers of the cell stack can be heated particularly efficiently if at least one magnetic coil is positioned adjacent to the anode and / or cathode electrodes. The magnetic coil is driven to generate a time-varying magnetic field, which inductively heats the anode and / or cathode electrodes. This process particularly heats components of the anode and / or cathode electrodes that exhibit high electrical conductivity. For example, such components can be the copper and aluminum foils.

[0017] Depending on the dimensions of the cell stack, the use of multiple magnetic coils can be advantageous for generating a uniform induction of eddy currents in the electrically conductive layers. The anode electrodes and / or the cathode electrodes typically feature aluminum and copper support foils embedded or integrated into corresponding anode and cathode substrates. Due to their high electrical conductivity, the aluminum and copper support foils are heated inductively particularly quickly and efficiently.

[0018] Advantageously, the magnetic field direction of the magnetic field generated by the coil can be perpendicular to a plane of the layers or aligned parallel to a surface normal. Thus, according to Maxwell's third equation, a resulting eddy current can be induced in the electrically conductive layers as a consequence of the time-varying magnetic field. However, the induced eddy currents exhibit power loss, which manifests as heating of each individual foil of the anode and cathode electrodes. The eddy currents are preferably induced in all electrically conductive layers of the cell stack according to the magnitude of the time-varying magnetic field.

[0019] According to one example, the anode electrodes and / or the cathode electrodes, in particular the copper foils and aluminum foils, are electrically contacted at at least two contact positions by at least one current source and subjected to a constant or varying current in order to heat the anode electrodes and / or cathode electrodes by Joule heating. This alternative or additional measure allows the electrically conductive layers to be heated by direct application of current and the resulting generation of power loss, thus thermally activating the adhesive.

[0020] In a further embodiment, the anode electrodes, cathode electrodes, and separator layers are positioned in a pressing device. Advantageously, the anode electrodes, cathode electrodes, and separator layers are pressed together by the pressing device with a constant or a time-varying force during or after the adhesive of the separator layers has been thermally activated. Applying the pressing force of the device ensures a final bonding result. Furthermore, varying the pressing force over time allows for particularly precise control of the adhesive properties.

[0021] The cell stack can be heated particularly evenly if the anode electrodes and / or the cathode electrodes are inductively heated by at least two magnetic coils integrated into an upper and / or lower die of the press. This heating is achieved, for example, by inducing eddy currents in the copper and aluminum foils of the respective electrodes.

[0022] According to a further embodiment, the device includes a guide for at least partially guiding the magnetic field generated by the magnetic coils, wherein the magnetic field generated by the magnetic coils is guided via an upper section of the guide on the upper tool, via a lower section of the guide on the lower tool, and via two lateral sections of the guide. The guide, or the respective sections of the guide, can, for example, form an outer section of a coil core or magnetic core, which serves to guide external magnetic field lines. The magnetic field lines generated directly by the magnetic coils can flow through the layers of the cell stack and are deflected or guided outside the cell stack via the sections of the guide.

[0023] The sections of the guide device can be in electrically conductive contact or spaced apart. Furthermore, the sections of the guide device can be made of a ferromagnetic metal alloy. To reduce eddy current losses in the guide device, the sections can be manufactured as a laminated core. This allows for controlled magnetic return and particularly energy-efficient operation of the magnet coil.

[0024] Depending on the design, the sections of the guide device can be cooled by air or a liquid. Similarly, the at least one magnetic coil can be air-cooled or liquid-cooled.

[0025] The device for producing cell stacks can be designed with particular flexibility if the magnetic field generated by the at least one magnetic coil is guided via the two lateral sections of the guide device, which are arranged in the contact direction between the upper and lower sections or laterally adjacent to the upper and lower sections of the guide device. Such an arrangement of the guide device sections allows for flexible insertion of the cell stack into the receiving chamber. For example, an upper tool with the upper section or a lateral section can be removed to arrange a bundle of layers in the receiving chamber for producing a cell stack and, after the joining process, to remove the cell stack from the receiving chamber.

[0026] According to a further embodiment, a temperature is measured by a temperature measuring device during the thermal activation of the adhesive along at least one anode layer and / or cathode layer. The use of the temperature measuring device and its corresponding connection to the control unit enables precise control of the heating in the electrically conductive layers of the cell stack. Accordingly, the at least one magnetic coil can be controlled and monitored based on the measurement data obtained by the temperature measuring device.

[0027] The temperature measuring device can be implemented in a particularly versatile way if the temperature is measured directly by at least one thermocouple and / or a measuring resistor within the device. In an alternative embodiment, the temperature is measured indirectly by measuring the electrical conductivity of at least one anode layer and / or cathode layer through the device. This allows the temperature to be determined with particular precision along the entire width or length of a layer.

[0028] Several embodiments of the invention are explained in more detail below with reference to the drawings. The drawings show: Fig. 1 a schematic sectional view of a device for producing cell stacks to illustrate a method according to an embodiment of the invention, Fig. 2 a schematic sectional view of a device for producing cell stacks according to a second embodiment, Fig. 3 a schematic sectional view of a device for producing cell stacks according to a third embodiment, Fig. 4 a schematic cross-sectional view of an electrochemical memory with a cell stack, and Fig. 5 a schematic detail view of the in Fig. 4 The cross-sectional view shown illustrates the composition of the cell stack.

[0029] In the illustrations, identical reference numbers denote the same elements or structural components. The sizes and relative positions of the elements in the illustrations are not necessarily drawn to scale, and some of these elements are shown enlarged and repositioned for clarity. Furthermore, the distinctive shapes of the drawn elements are not intended to convey information about the actual shape of the individual elements but were chosen solely for easier identification in the illustrations.

[0030] The Fig. 1 Figure 1 shows a schematic sectional view of a device 10 for producing cell stacks 100 to illustrate a method according to an embodiment of the invention. The device 10 is shown according to a first embodiment.

[0031] The cell stack 100 produced by the process is intended in particular for an electrochemical storage device 200, such as a lithium-ion cell, which is located in the Fig. 4 As shown, such a cell stack 100 in the illustrated embodiment consists of a plurality of anode electrodes 101, separator layers 103 and cathode electrodes 102, which are repeatedly stacked, folded or wound on top of each other.

[0032] To form an integral or single-piece cell stack 100, adhesive layers (not shown) are used, or certain layers are pre-coated with an adhesive. For example, the separator layers 103 are coated on one or both sides with a thermally activatable adhesive or wetted with the adhesive. Depending on the configuration of the process, any layers 101, 102, 103 can be coated with the thermally activatable adhesive. The use of the adhesive in conjunction with separator layers 103 serves here to illustrate the process.

[0033] In a first step of the process, layers 101, 102, and 103 of the cell stack 100 are placed in a receiving chamber 11 of the device 10. The respective layers 101, 102, and 103 are aligned relative to each other and can be temporarily secured against unintentional slippage by clamps, scaffolds, or by the receiving chamber 11. The respective layers 101, 102, and 103 of the cell stack 100 are in the Fig. 4 An example illustrated in detail.

[0034] The receiving chamber 11 of the device is configured to receive at least one bundle of layers 101, 102, 103, which are to be assembled to form a cell stack 100. Furthermore, at least one heat source 20, 21 is provided, which can electromagnetically induce heat in the electrically conductive layers 101, 102 of the bundle. Thus, after the layers 101, 102, 103 have been provided, the electrically conductive layers 101, 102, which in the illustrated embodiment are configured as anode electrodes 101 and / or cathode electrodes 102, are electromagnetically heated in a further step of the process.

[0035] In the illustrated embodiment, the device 10 comprises a press 30 with a lower tool 31 and an upper tool 32 to exert a pressing force F on the layers 101, 102, 103. A control unit 40 is used to control and regulate the generation of heat by the heat sources 20, 21 and the provision of a pressing force by the press 30, for example, based on measurement data from sensors. A temperature measuring device 41 is shown schematically to determine the temperature of the layers 101, 102, 103 directly or indirectly. The temperature measuring device 41 can measure the temperature of the layers 101, 102, 103 using thermal and / or electrical sensors. The thermal sensors can determine the temperature based on direct contact with the layers 101, 102, 103 or based on a non-contact measurement, for example, by recording infrared radiation.

[0036] To generate uniform heating in the electrically conductive layers 101, 102, the control unit 40 can control two magnetic coils 20 to generate a time-varying magnetic field B, by which the anode electrodes 101 and / or the cathode electrodes 102 are inductively heated. The field lines of the resulting magnetic field B are indicated by the arrows in the Fig. 1, Fig. 2 and Fig. 3 illustrated.

[0037] Alternatively or additionally, the anode electrodes 101 and / or the cathode electrodes 102 can be electrically contacted at at least two contact positions by at least one current source 21 and supplied with a constant or varying current. The current source 21 can also be controlled by the control unit 40.

[0038] By heating the anode electrodes 101 and / or the cathode electrodes 102, the adhesive of the respective separator layers 103 is directly or immediately thermally activated. This thermal activation of the adhesive bonds the anode electrodes 101, separator layers 103, and cathode electrodes 102 together to form a single cell stack 100. This step completes the cell stack 100. Depending on the specific design of the process and the requirements, additional processing steps, such as electrical connection of contact tabs, adjustment of final dimensions, application of coatings or packaging, installation of positioning aids, and the like, can follow or be implemented within the process.

[0039] The Fig. 2 Figure 1 shows a schematic sectional view of a device 10 for producing cell stacks 100 according to a second embodiment. In contrast to the one in Figure 10, the device 10 is a sectional representation of a device 10 for producing cell stacks 100 according to a second embodiment. Fig. 1 The embodiment shown here is a device 10 which has a guide device 50 for at least partially guiding the magnetic field B generated by the magnetic coils 20. For this purpose, the guide device 50 has an upper section 51, a lower section 52 and two lateral sections 53.

[0040] The upper section 51 is integrated into the upper tool 31 of the press 30. The lower section 52 is incorporated into the lower tool 32 of the press 30. The lateral sections 53 of the guide device 50 are positioned laterally next to the upper section 51 and the lower section 52 and form a substantially closed loop for magnetic return. In the illustrated embodiment, the receiving chamber 11 is located centrally within this loop.

[0041] In the illustrated embodiment, the lateral sections 53 are positioned along a thickness or in the vertical direction H between the upper section 51 and the lower section 52. In this embodiment, the vertical direction H corresponds to the contact direction.

[0042] In the Fig. 3 A schematic sectional view of a device 10 for producing cell stacks 100 according to a third embodiment is shown. In contrast to the one in Fig. 2 In the device 10 shown, the lateral sections 53 of the guide device 50 are offset laterally along a lateral direction L relative to the upper section 51 and the lower section 52. This allows the upper tool 31 and the lower tool 32 to be moved freely along the vertical direction H relative to the lateral sections 32.

[0043] For clarity, the control unit 40 and the temperature measuring device 41 are shown in the Fig. 2 and Fig. 3 not shown.

[0044] The Fig. 4 Figure 1 shows a schematic sectional view of an electrochemical storage device 200 with a one-piece assembled cell stack 100. The electrochemical storage device 200 has a cell housing 201 and can, for example, be designed as a battery cell based on lithium-ion technology. At least one one-piece cell stack 100, manufactured according to the inventive method, is arranged in the cell housing 201. The cell stack 100 is, by way of example, electrically contacted on two opposite sides by poles 202 and 203.

[0045] In the Fig. 5 is a schematic detail view of the in Fig. 4The sectional view shown illustrates the composition of a cell stack 100. The cell stack 100 comprises a plurality of anode electrodes 101, separator layers 103, and cathode electrodes 102, which are repeatedly stacked, folded, or wound on top of each other and connected by the method already described.

[0046] In the illustrated embodiment, each anode electrode 101 has a copper foil 104 or copper support foil, which is coated on both sides with an anode substrate 105.

[0047] Similarly, each cathode electrode 102 has an aluminum foil 106 or aluminum carrier foil, which is coated on both sides with a cathode substrate 107.

[0048] The cell stack 100 is terminated on both sides along the vertical direction H by anode electrodes 101, with the anode electrodes 101, separator layers 103 and cathode electrodes 102 successively alternating along the vertical direction.

Claims

1. Method for producing a cell stack (100), in particular for an electrochemical storage device (200), at least anode layers (101), separator layers (103) and cathode layers (102) being repeatedly stacked or folded or wound on top of one another, at least one layer (101, 102, 103) being coated on one side or on both sides with a thermally activatable adhesive or being provided with the adhesive, wherein electrically conductive layers (101, 102), in particular the anode layers (101) and / or the cathode layers (102), are electromagnetically heated, wherein the adhesive is thermally activated by the heating of the electrically conductive layers (101, 102) and the anode layers (101), separator layers (103) and cathode layers (102) are bonded together to form a one-piece cell stack (100).

2. The method according to claim 1, wherein at least one magnetic coil (20) is arranged adjacent to the anode layers (101) and / or cathode layers (102), wherein the magnetic coil (20) is driven to generate a time-varying magnetic field (B) by which the anode layers (101) and / or the cathode layers (102) are inductively heated.

3. The method according to claim 1 or 2, wherein the anode layers (101), the cathode layers (102) and the separator layers (103) are positioned in a pressing device (30), wherein the anode layers (101), the cathode layers (102) and the separator layers (103) are pressed together by the pressing device (30) with a constant or a time-varying pressing force (F) while the adhesive is thermally activated or after the adhesive has been thermally activated.

4. The method according to claim 2 or 3, wherein the anode layers (101) and / or the cathode layers (102) are inductively heated by at least one magnetic coil (20) integrated into an upper tool (31) and / or lower tool (32) of the pressing device (30).

5. Method according to claim 4, wherein a guiding device (50) is provided for guiding the magnetic field (B) generated by the magnetic coil (20) at least in some areas, wherein the magnetic field (B) generated by the magnetic coil (20) is guided via an upper section (51) of the guiding device (50) on the upper tool (31), via a lower section (52) of the guiding device (50) on the lower tool (32) and via two lateral sections (53) of the guiding device (50).

6. The method according to claim 5, wherein the magnetic field (B) generated by the at least one magnetic coil (20) is conducted via the two lateral sections (53) of the guiding device (50), which are arranged in the contact pressure direction between the upper section (51) and the lower section (52) or laterally next to the upper section (51) and the lower section (52) of the guiding device (50).

7. The method according to any one of claims 1 to 6, wherein during the thermal activation of the adhesive along at least one anode layer (101) and / or cathode layer (102), a temperature is measured by a temperature measuring device (41).

8. The method according to any one of claims 1 to 7, wherein the temperature is measured directly by at least one thermocouple and / or a measuring resistor of the temperature measuring device (41); or the temperature is measured indirectly by an electrical conductivity measurement of at least one anode layer (101) and / or cathode layer (102) by the temperature measuring device (41).