CAPACITIVE PRESSURE SENSOR

Description

[0001] The present invention relates to a capacitive pressure sensor based on printed electrodes, in particular for pressure sensing in battery modules.

[0002] Battery modules, such as those used in new energy vehicles, typically consist of several closely spaced and / or stacked battery cells in which electrodes are immersed in a solid or gel-like electrolyte. During charging and discharging, battery cells undergo minor volume changes, for example, due to the incorporation of ions into the electrodes. These volume changes, in turn, lead to changes in the internal battery cell pressure. Furthermore, degradation processes occurring in lithium-ion battery cells, which are accompanied by gas evolution, can lead to an increase in the internal battery cell pressure. An excessive increase in battery cell pressure, particularly in pouch cells (i.e., battery cells encapsulated by a flexible outer film), can lead to serious defects and, in the worst case, to a fire.

[0003] To ensure reliable and safe operation throughout the battery's entire life cycle, it is desirable to implement battery cell pressure monitoring. Since significant pressure changes can potentially occur in any single battery cell, it would be advantageous to implement the relevant sensors in such a way as to allow monitoring of a large number of battery cells, preferably each individual cell within the battery module.

[0004] Due to the considerably limited space between the densely packed battery cells, a particularly compact and lightweight design for the pressure sensors is required. At the same time, sufficient sensitivity of the pressure sensor must be ensured. This is where conventional sensors currently available on the market reach their limits.

[0005] For example, SMD-based pressure sensors are considered unsuitable in this context, as sufficient sensitivity could only be achieved with a comparatively bulky sensor design. Furthermore, resistive pressure sensors are known, which can be designed, for example, in strip form and thus be relatively compact. However, such sensors are not sufficiently reliable due to their susceptibility to drift. Document CN 112 649 128 A (UNIV EAST CHINA SCIENCE & TECH) dated April 13, 2021 (2021-04-13) discloses an example of a measuring device and a method for detecting three-dimensional contact loads using interdigital capacitor units.

[0006] Document CN 113 551 811 A (UNIV JILIN) October 26, 2021 (2021-10-26) describes a design method for a 4D-printed multifunctional tactile sensor.

[0007] One object of the present invention is to provide a particularly compact and simultaneously sensitive pressure sensor. In particular, a pressure sensor is to be provided that enables easy-to-implement and reliable monitoring of the battery cell pressure in battery modules with densely packed battery cells. At the very least, an alternative to known pressure sensors is to be provided.

[0008] The problem is solved by a pressure sensor with the features of claim 1, a battery module with the features of claim 6, and a method with the features of claim 7. Preferred features are the subject of the dependent claims. Further advantages and features can be found in the general description and the exemplary embodiments.

[0009] The pressure sensor according to the invention is a capacitive pressure sensor with a flexible substrate and a sensor layer arranged on the substrate. Within the sensor layer, an interdigital electrode is arranged with two electrodes printed onto the substrate and interlocking in a comb-like manner. Within the sensor layer, between the electrodes, a pressure-sensitive material is arranged, which is formed from a compressible dielectric material and contains particles with a different permittivity than the dielectric material and / or clusters of such particles, arranged in isolation from one another. A protective layer is arranged on the sensor layer to shield the electrodes. In particular, the particles have a significantly higher or a significantly lower permittivity than the dielectric material.

[0010] The interlocking, comb-like electrodes are arranged within the same layer, with their respective "comb teeth" extending along the layer plane. The opposing conductive surfaces of the electrodes are spaced apart along the layer plane, thus providing a space within the layer for the pressure-sensitive material. When the sensor layer is subjected to pressure, this leads to elastic deformation of the pressure-sensitive material. This changes the distances between the insulated particles. Because the particles have a significantly different permittivity than the dielectric material—that is, a considerably higher or lower permittivity—a change in the distances between the particles causes...Clusters relative to each other cause a change in the permittivity of the pressure-sensitive material, which can be measured as a change in capacitance.

[0011] One advantage of the sensor according to the invention is that the components necessary for capacitance measurement can be arranged within the same layer, which enables a particularly flat and compact design of the sensor.

[0012] Another advantage of the sensor according to the invention is that high sensor sensitivity is achieved even with compact sensor geometries, since the change in permittivity of the pressure-sensitive material is significantly influenced by the pronounced pressure-dependent change in distance between the particles contained therein.

[0013] A further advantage of the sensor according to the invention is that, due to its simple design, it can be easily and automatically produced in large quantities. Furthermore, sensor arrays can be easily manufactured based on the sensor according to the invention, for example, by printing several sensors according to the invention onto a common substrate. In particular, the sensor according to the invention is ideally suited for monitoring battery cell pressure, since the sensor can be easily positioned even between densely packed battery cells to reliably detect changes in pressure. The sensor according to the invention is especially well-suited for retrofit solutions.

[0014] Various materials are generally suitable for the substrate layer, provided they are non-conductive and flexible. Preferably, the substrate layer material is selected from the group consisting of polyamide (PA), e.g., PA6, PA6.6, PA11, PA12, PA6.10, PA6.12, and / or copolyamides and / or polyester (PES) and / or rayon and / or polyethylene terephthalate (PET) and / or polyethylene naphthalate (PEN) and / or polybutylene terephthalate (PBT) and / or polycarbonate (PC) and / or unsaturated polyester resin (UP) and / or poly(1,4-cyclohexanedimethylene terephthalate) (PCDT) and / or polyvinyl alcohol (PVAL) and / or polyoxybenzonaphtoate and / or polyvinyl acetal (PVA) and / or polyetheretherketone (PEEK) and / or polyethylene-2.6-naphthalate (PEN) and / or polyphenylene and / or polyphenylene oxide (PPO) and / or polyphenylene sulfide (PPS) and / or polyphenylene ether and / or polybenzoxazole (PBO) and / or polyoxadiazole (POD) and / or polyetherimide (PEI) and / or m-aramid and / or p-aramid and / or glass and / or cellulose and / or paper and / or basalt and / or metal and / or carbon and / or ceramic and / or carbon and / or wool and / or cotton and / or polypropylene and / or melamine and / or modified viscose and / or rock and / or highly crystalline polymer fibers and / or fluoropolymers, such as fluorosilicone, polytetrafluoroethylene (PTFE) and perfluoroethylene propylene (FEP), and / or fluoro copolymers. If the substrate material is a thermoplastic polymer,Polyethylene terephthalate (PET) is therefore the preferred material. Compared to other substrates, PET is particularly cost-effective and exhibits very good properties (such as temperature stability, surface finish, surface energy, etc.).

[0015] In a preferred embodiment of the invention, the material of the support layer comprises at least one inorganic non-metallic material, such as ceramic or glass, provided that it is implemented in a thin layer that does not impair flexibility. In a further preferred embodiment of the invention, the material of the support layer comprises at least one fibrous material, such as paper.

[0016] In particular, the support layer has a thickness of 1 µm to 150 µm, preferably 1 µm to 125 µm, and most preferably 1 µm to 50 µm. This allows for a particularly compact sensor design. At the same time, the weight of the sensor according to the invention can be kept low.

[0017] Preferably, the material of the support layer has a density of less than 1.5 g / cm³, preferably less than or equal to 1 g / cm³. This allows the weight of the sensor according to the invention to be kept low.

[0018] In a further preferred embodiment of the invention, a flexible outer shell of a battery cell forms the carrier layer. To complete the pressure sensor, the sensor layer and the cover layer can, in this case, be produced directly on the battery cell. In this way, a separate carrier layer can be eliminated.

[0019] Various inorganic materials (such as metals) and organic materials (such as conductive polymers, carbon, graphite, graphene, etc.) are suitable for the electrodes, provided they are conductive and can be processed (e.g., as ink) using printing methods. Preferably, the electrode thickness is between 1 nm and 10 µm. This allows for a particularly compact sensor design. A thickness of 1 nm to 500 nm is especially preferred, enabling reliable production of the electrodes using established printing methods. The electrode thickness is measured perpendicular to the layer plane. Preferably, the thickness of the sensor layer is identical to the thickness of the electrodes.

[0020] The pressure-sensitive material is formed from a dielectric material containing isolated particles and / or clusters that have a significantly different permittivity than the dielectric material. In particular, the particles and / or clusters are conductive. Various materials are suitable as the dielectric material, provided they are non-conductive, compressible, and elastically deformable. The dielectric material can be processed using a printing process and, at least in its cured state, is non-conductive, compressible, and elastically deformable. Preferably, the dielectric material comprises a chemically crosslinkable (e.g., UV-crosslinkable) binder or a solvent-based binder. Examples of suitable dielectric materials include polyester, epoxy resin, silicones, acrylates, or polyurethane.

[0021] If the particles or clusters of particles present in the dielectric material are themselves electrically conductive, they are arranged within the dielectric material at such a distance from each other that the dielectric material itself remains non-conductive. Preferably, the conductive particles contain a metal, more preferably silver, copper, and / or iron.

[0022] In particular, the particles are nanoparticles, i.e., the particles have sizes in the range of 1 nm to less than 1 µm (sub-µm range). Preferably, the particles have sizes in the range of 1 nm to 50 nm.

[0023] The permittivity and particle size, as well as their proportion in the dielectric material, must be adapted to the specific application. It is evident that, on the one hand, sufficient sensor sensitivity and, on the other hand, a sufficiently high breakdown voltage must be ensured. In particular, particles arranged in isolation from one another must not touch, even when the pressure-sensitive material is subjected to pressure. Furthermore, it is evident that the particle size must be in a reasonable proportion to the electrode thickness, since the space for the pressure-sensitive material is limited by the opposing conductive surfaces of the electrodes. Specifically, the particle size is at least 10 times, and preferably at least 20 times, smaller than the electrode thickness.

[0024] Various materials are suitable for the protective coating of the electrodes, provided they are non-conductive and sufficiently impermeable to, for example, oxygen and / or moisture. For instance, a crosslinkable or solvent-based lacquer or a film laminate consisting of a suitable film and an adhesive layer (chemically crosslinkable layer or PSA adhesive), e.g., PET film, can be used as the coating. A lacquer layer can be made particularly thin and applied very efficiently and reliably using printing processes. Preferably, the thickness of the coating is 1 µm to 800 µm, more preferably 1 µm to 100 µm, and most preferably 1 µm to 10 µm.

[0025] In a further preferred embodiment of the invention, the cover layer contains the pressure-sensitive material. In this way, the cover layer not only protects the electrodes but also increases the sensor's sensitivity. Firstly, when pressure is applied to the sensor, the pressure-sensitive material in the cover layer is deformed and at least partially pressed into the space between the opposing conductive surfaces of the electrodes, resulting in an increased change in permittivity there. Simultaneously, the arrangement of pressure-sensitive material in the edge regions of the opposing conductive surfaces of the electrodes further enhances the pressure-dependent change in permittivity. In particular, the cover layer consists of the pressure-sensitive material, which significantly simplifies the sensor design and manufacturing.Although the top layer containing or consisting of the pressure-sensitive material should provide sufficient protection in many cases, in some applications it may be useful to apply a separate protective layer to the top layer, e.g. a UV-curable varnish or a film laminate (e.g. PET film).

[0026] According to the invention, the carrier layer has one or more depressions on a side facing the sensor layer in an area not adjacent to the electrodes, in which the pressure-sensitive material is arranged. This further increases the sensitivity of the sensor, since the arrangement of pressure-sensitive material also amplifies pressure-dependent changes in permittivity in the edge regions of the opposing conductive surfaces of the electrodes. In particular, the pressure-sensitive material in the depression(s) borders, preferably seamlessly, on the pressure-sensitive material in the sensor layer. The depressions can be produced, for example, by ablation of areas of the carrier layer, especially by laser ablation, or by deformation, especially by embossing.

[0027] The invention also relates to a battery module comprising a battery cell, in particular a pouch cell, and a capacitive pressure sensor according to any one of claims 1 to 5, which is designed and configured to monitor the battery cell pressure. In this way, a battery module is provided whose condition is reliably and safely determined based on the measured battery cell pressure. This makes it possible, for example, to detect a defect or the risk of fire in a timely manner. The pressure sensor according to the invention offers the advantages described above and below when implementing pressure monitoring.

[0028] In a preferred embodiment of the invention, the pressure sensor is arranged on an outer shell of the battery cell. This allows the pressure to be determined optimally without compromising the integrity of the battery cell. The pressure sensor can be arranged between the outer shell of the battery cell and a wall of the battery module or between two adjacent battery cells of the battery module.

[0029] In a further preferred embodiment of the invention, the flexible outer shell of the battery cell forms the carrier layer. To complete the pressure sensor, the sensor layer and the cover layer can, in this case, be produced directly on the battery cell. In this way, a separate carrier layer can be eliminated, so that the pressure sensor requires even less installation space.

[0030] The battery module according to the invention can preferably be installed in a motor vehicle, in particular a New Energy Vehicle. Thus, a motor vehicle is provided with a battery module whose condition can be reliably and safely determined based on the measured battery cell pressure. This makes it possible, for example, to detect a defect or the risk of fire in a timely manner.

[0031] As described above and below, the problem set out at the beginning is also solved by a method with the features of claim 7.

[0032] The inventive method for manufacturing a capacitive pressure sensor, in particular a pressure sensor according to one of claims 1 to 4, comprises the following steps: Printing two comb-like interlocking electrodes onto a substrate; applying, in particular printing, a pressure-sensitive material formed from a dielectric material containing isolated particles with a permittivity different from that of the dielectric material and / or clusters of such particles onto the substrate between the electrodes; producing a cover layer.

[0033] The properties of the components of the sensor according to the invention (support layer, electrodes, pressure-sensitive material, cover layer, etc.) and their advantages described above are also applicable to the method according to the invention and are therefore not repeated again.

[0034] The method according to the invention offers a particularly simple, fast, and cost-effective way to provide a compact pressure sensor with high sensitivity. Preferably, the electrodes and the pressure-sensitive material are printed using a printing process, which enables a cost-effective implementation of the method.

[0035] In a preferred embodiment of the invention, the production of the top layer involves applying further pressure-sensitive material to the electrodes and the pressure-sensitive material arranged between the electrodes. In this way, the application of the pressure-sensitive material between the electrodes and the production of the top layer can be combined into a single step, making the process significantly more efficient. For example, it is not necessary to wait for the pressure-sensitive material to cure before producing the top layer.

[0036] In a further preferred embodiment of the invention, prior to the application of the pressure-sensitive material to the substrate layer, an area on the side of the substrate layer facing the electrodes, not adjacent to the electrodes, is partially ablated, preferably by laser ablation, or deformed, preferably by embossing, to form one or more depressions. In this way, when the pressure-sensitive material is applied to the substrate layer, not only the spaces between the opposing conductive surfaces of the electrodes, but also the depressions are filled with pressure-sensitive material, thereby enabling the production of a pressure sensor with improved sensitivity, as already discussed.Laser ablation offers a simple and straightforward method for creating the desired indentations, as even when processing large areas of the substrate layer along with the printed electrodes, the latter are either not removed by the laser or only minimally so. Embossing, especially when implemented using rollers, provides an effective way to create the desired indentations in a very short time. The embossing die can, for example, be designed with recesses for the electrodes and projections for the indentations.

[0037] Overall, the present invention provides a compact pressure sensor with high sensitivity, suitable for a wide variety of applications. In particular, it provides a versatile pressure sensor that exhibits high sensitivity despite its small dimensions (total thickness of less than 1 mm).

[0038] Furthermore, the pressure sensor can be combined with compact, flat, and especially printed temperature sensors. This allows for even more meaningful monitoring of the battery status, such as a local temperature increase caused by a defective cell.

[0039] All known types and measuring principles that can be implemented in a flat and flexible design (e.g., by printing) can be used as temperature sensors, such as resistive temperature sensors (both with positive (PTC) and negative (NTC) resistance change), thermocouples, etc.

[0040] It is expressly pointed out that the embodiments of the invention described above can each be combined individually or in any technically meaningful combination with each other with the subject matter of the independent claims.

[0041] Variations and embodiments of the invention, as well as further advantages and details of the invention, can be found in the following description and the drawings. The schematic figures show: Fig. 1 shows an embodiment of a pressure sensor not according to the invention in a sectional view; Fig. 2 shows another embodiment of a pressure sensor not according to the invention in a sectional view; Fig. 3 shows another embodiment of a pressure sensor according to the invention in a sectional view; and Fig. 4 shows the basic structure of an interdigital electrode printed on a substrate layer.

[0042] Parts that have the same or similar effects are provided with identical reference numerals, if applicable.

[0043] Individual technical features of the embodiments described below can also be combined with previously described embodiments as well as the features of the independent claims and any further claims to create objects according to the invention.

[0044] Figures 1 to 3 Figure 1 shows various embodiments of a capacitive pressure sensor 2. The pressure sensor 2 has a flexible carrier layer 4 and a sensor layer 6 arranged thereon. An interdigital electrode 8 is arranged within the sensor layer 6. The interdigital electrode 8 has two electrodes 8a, 8b printed onto the carrier layer 4 and interlocking like a comb. The individual "chamber teeth" of the electrodes 8a, 8b extend along an imaginary layer plane E. The basic structure of the interdigital electrode is shown in Figure 2. Fig. 4 shown. The layer plane E runs in the Figures 1 to 3 vertically and in the Figure 4parallel to the respective plane of the figure. The thickness d of the electrodes 8a, 8b, measured perpendicular to the layer plane E, is identical to the layer thickness of the sensor layer 6. Within the sensor layer 6, a pressure-sensitive material 10 is arranged between the electrodes 8a, 8. This material is formed from a compressible dielectric material and contains particles with a different permittivity than the dielectric material, for example, conductive particles, and / or clusters of such particles, arranged in isolation from one another. To protect the electrodes 8a, 8b from external influences, a cover layer 12 is arranged on the sensor layer 6.

[0045] The opposing conductive surfaces of electrodes 8a, 8b are spaced apart from each other along the layer plane E, thus providing a gap 13 within the sensor layer 6, in which the pressure-sensitive material 10 is located. With regard to the Fig. 4In the basic structure of the interdigital electrode 8 shown, the space 13 extends in a meandering shape between the two electrodes 8a, 8b. When the pressure sensor 2 is subjected to pressure, the sensor layer 6, and thus the pressure-sensitive material 10, is compressed. This changes the distances between the isolated particles in the pressure-sensitive material 10, resulting in a change in the permittivity of the pressure-sensitive material 10. This change in permittivity can be measured as a change in capacitance.

[0046] Fig. 2 shows a further embodiment of a pressure sensor 2 not according to the invention, which differs from the one in Fig. 1The embodiment shown differs from the non-inventive embodiment in that the cover layer 12 consists of the pressure-sensitive material 10. In this way, the cover layer 12 not only protects the electrodes 8a, 8b, but also increases the sensitivity of the pressure sensor 2. Firstly, when pressure is exerted on the pressure sensor 2, the pressure-sensitive material 10 located in the cover layer 12 is deformed and at least partially pressed into the space 13 between the opposing conductive surfaces of the electrodes 8a, 8b, resulting in an increased change in permittivity there. Simultaneously, the arrangement of pressure-sensitive material in the edge regions 13' of the opposing conductive surfaces of the electrodes 8a, 8b on the cover layer side further amplifies the pressure-dependent change in permittivity.

[0047] Fig. 3Figure 1 shows a further embodiment of the pressure sensor 2 according to the invention, which differs from the one in Figure 2. Fig. 2The embodiment shown differs from the non-inventive embodiment in that the carrier layer 4 has a recess 14 on one side facing the sensor layer 6 in an area not adjacent to the electrodes 8a, 8b, in which the pressure-sensitive material 10 is arranged. The recess 14 follows the meandering shape of the space 13 above it. The pressure-sensitive material 10 in the recess 14 abuts the pressure-sensitive material 10 in the sensor layer 6 seamlessly. In other words, pressure-sensitive material 10 projects into the recess 14. In this way, the sensitivity of the pressure sensor 2 is further increased, since the arrangement of pressure-sensitive material 10 also amplifies a pressure-dependent change in permittivity in further edge regions 13" on the carrier layer side of the opposing conductive surfaces of the electrodes 8a, 8b.The depression 14 can be produced in a simple manner by ablation, preferably laser ablation, or deformation, preferably embossing, of areas of the carrier layer 4.

[0048] Fig. 4 shows the basic structure of an interdigital electrode 8, as used in the embodiments shown above. Figures 1 to 3 can be used. The interdigital electrode 8 obviously comprises two electrodes 8a, 8b, which can be individually controlled or read via their respective contacts 14a, 14b.

[0049] For the purposes of this application, the words "ein" and "eine" are to be interpreted not as numerals, but as indefinite articles. Even if some terms in the description or in the claims are used in the singular or in conjunction with a numeral, the scope of the invention for these terms is not to be limited to the singular or the respective numeral. If a feature is directed to a specific number, this is indicated by an appropriate formulation, such as "exactly one" or "a single one". Reference symbol list (part of the description)

[0050] Capacitive pressure sensor 2 Flexible carrier layer 4 Sensor layer 6 Interdigital electrode 8 Electrodes 8a, 8b pressure-sensitive material 10 Top layer 12 space 13 Edge areas on the surface layer side 13' edge areas on the carrier layer side 13" Contacts 14a, 14b Layer level E Electrode thickness d

Claims

1. Capacitive pressure sensor (2) with a flexible carrier layer (4), a sensor layer (6) arranged on the carrier layer (4), wherein an interdigital electrode (8) is arranged within the sensor layer (6), which has two electrodes (8a, 8b) printed on the carrier layer (4) and interlocking in a comb-like manner, wherein within the sensor layer (6) between the electrodes (8a, 8) a pressure-sensitive material (10) is arranged, which is formed from a compressible dielectric material, which contains particles arranged in isolation from each other with a permittivity different from that of the dielectric material and / or clusters of such particles, and a top layer (12) arranged on the sensor layer (6) to protect the electrodes (8a, 8b), characterized by the fact that the carrier layer (4) has one or more depressions (14) on one side facing the sensor layer (6) in an area not adjacent to the electrodes (8a, 8b) in which the pressure-sensitive material (10) is arranged.

2. A capacitive pressure sensor (2) according to claim 1, wherein the particles are conductive, preferably a metal, preferably containing silver, copper and / or iron.

3. A capacitive pressure sensor (2) according to claim 1 or 2, wherein the particles are nanoparticles.

4. Capacitive pressure sensor (2) according to any of the preceding claims, wherein the surface layer (12) contains the pressure-sensitive material (10), in particular consists of the pressure-sensitive material (10).

5. Battery module with a battery cell, especially a pouch cell, Marked by A capacitive pressure sensor (2) according to any one of claims 1 to 4, which is designed and equipped for monitoring a battery cell pressure of the battery cell.

6. The battery module according to claim 6, wherein the pressure sensor (2) is arranged on an outer shell of the battery cell, in particular wherein the outer shell of the battery cell forms the flexible carrier layer (4) of the pressure sensor.

7. A method for the manufacture of a capacitive pressure sensor (2), in particular a pressure sensor (2) according to any one of claims 1 to 5, comprising the following steps: - Printing of two comb-like interlocking electrodes (8a, 8b) on a carrier layer (4); - before the pressure-sensitive material (10) is applied to the carrier layer (4), an area not adjacent to the electrodes (8a, 8b) on one side of the carrier layer (4) facing the electrodes (8a, 8b) is partially removed to form one or more depressions (14), - Application, in particular printing, of a pressure-sensitive material (10) consisting of a dielectric material containing particles isolated from each other with permittivity other than the dielectric material and / or clusters of such particles on the support layer (4) between the electrodes (8a, 8b); - Preparation of a surface layer (12).

8. The method of claim 7, wherein the preparation of the surface layer (12) is an application of further pressure-sensitive material (10) to the electrodes (8a, 8b) and the pressure-sensitive material (10) arranged between the electrodes (8a, 8b).

9. A method according to claim 7 or 8, wherein the region not adjacent to the electrodes (8a, 8b) on the side of the carrier layer (4) facing the electrodes (8a, 8b) is laser-ablated or deformed, preferably embossed, for the formation of one or more wells (14).