Flexible pressure sensor, preparation method thereof and data acquisition system

Abstract

The invention belongs to the technical field of cell monitoring, and discloses a flexible pressure sensor and a data acquisition circuit and application thereof. The flexible pressure sensor comprises a flexible substrate, an elastomer array, a constantan sensing grid and a packaging layer which are sequentially arranged from bottom to top, the elastomer array comprises a plurality of elastomers which are linearly arranged, and a gap is formed between every two adjacent elastomers; a cavity is defined by the packaging layer and the two adjacent elastomers. The constantan of which the resistivity is slightly influenced by temperature is used as a sensing material, so that the problems of large time drift and large temperature drift of a traditional pressure sensor are effectively solved; the elastic body array is arranged on the flexible substrate, and the change of pressure is converted into the length change of the constantan sensing grid through the deformation of the elastic bodies, so that a resistance signal is amplified, the sensitivity of the flexible pressure sensor is remarkably improved, and the problem that the signal of a traditional film strain type pressure sensor is weak is successfully solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery cell monitoring, and in particular relates to a flexible pressure sensor, a preparation method thereof, and a data acquisition system. Background Art

[0002] At present, the research on lithium batteries is mainly focused on electrochemical performance, such as how to improve the capacity and cycle performance of batteries. The health monitoring technology used to monitor and locate battery damage in real time during the operation of lithium-ion batteries is still immature. The aging of battery materials during use seriously affects the safety of the battery, causing local overheating or sudden increase in pressure. External influences such as overcharging, over-discharging, impact, falling, puncture, extrusion, etc. may also cause problems such as internal short circuits and swelling of the battery, causing a sudden increase in internal pressure of the battery and causing safety problems. Therefore, it is crucial to closely monitor and effectively control the state of pressure in lithium-ion batteries.

[0003] At present, many achievements have been made in battery monitoring and evaluation systems. Existing power and energy storage battery systems generally use external sensors to monitor battery status, but this method cannot monitor each battery cell, let alone obtain parameter changes in the pressure characteristics of the battery cell. This leads to deviations in the collected information and the corresponding models / algorithms, and it is impossible to accurately evaluate the health status, safety status and evolution trend of the battery cell throughout its life cycle. Some studies have attempted to implant sensors into the battery to monitor the internal pressure status of the battery, but the unique electrochemical corrosion environment inside the battery makes existing sensors extremely prone to device structure failure and packaging material corrosion, which cannot meet the long life requirements of the sensor.

[0004] Optical sensors are one of the solutions to the problem of electrochemical corrosion of sensors in electrolyte environments. Optical fibers have good corrosion resistance, and optical fiber sensors consist of periodic modulation of the refractive index of the fiber core. This periodic modulation in the optical fiber acts as a selective filter, reflecting a narrow band of light that satisfies the Bragg law, which determines the center of the band known as the Bragg wavelength. When the optical fiber is stretched or compressed along its axis, the modulated portion is physically changed, and the Bragg wavelength moves accordingly. Therefore, monitoring the center wavelength of the reflection band can provide feedback on the pressure information in the optical fiber, but both temperature and pressure signals will affect the results, making accurate decoupling difficult. Moreover, after the optical fiber sensor is implanted, using SEM to observe the disassembled cycled battery will reveal that the implanted optical fiber will destroy the integrity of the electrode and cause damage to the battery structure, so its application is limited.

[0005] The internal space of a single cell is small, and the positive and negative electrode materials, current collectors, and diaphragms are closely arranged, making it very difficult to implant rigid and large sensors inside the battery. Therefore, compared with rigid sensors, the implantation of flexible thin-film sensors can greatly reduce the damage to the electrodes, and combined with the battery manufacturing process, it can reduce the battery sealing problems caused by the implantation of sensors. However, some current thin-film pressure sensors have poor stability, serious time drift and temperature drift, and cannot reliably monitor the internal pressure conditions of the battery with high accuracy for a long time. Summary of the invention

[0006] The present invention aims to improve at least one technical problem in the background technology.

[0007] A first aspect of the present invention provides a flexible pressure sensor, comprising a flexible substrate, an elastomer array, a constantan sensor grid and a packaging layer arranged in sequence from bottom to top; the elastomer array comprises a plurality of elastomers, the plurality of elastomers are arranged linearly, and a gap is formed between two adjacent elastomers; a cavity is enclosed between the packaging layer and the two adjacent elastomers.

[0008] According to the law of resistance, the resistance R of a conductor is proportional to the length L and the resistivity ρ, and inversely proportional to the cross-sectional area S. The formula is R=ρL / S, where ρ is the resistivity of the material used to make the resistor, L is the length of the wire wound into the resistor, S is the cross-sectional area of ​​the wire wound into the resistor, and R is the resistance value. The sensing principle of the flexible pressure sensor of the present invention is that the external pressure causes the L and cross-sectional area S of the flexible pressure sensor to change, thereby changing the resistance R of the constantan sensor grid, and the resistance change of the constantan sensor grid presents a monotonic function relationship with the external pressure.

[0009] The beneficial effects of the first aspect of the present invention are as follows: the present invention adopts constantan, whose resistivity is less affected by temperature, as the sensing material, which effectively solves the problems of large time drift and temperature drift existing in traditional pressure sensors; by arranging an elastomer array on a flexible substrate, the change in pressure is converted into a change in the length of the constantan sensor grid through the deformation of the elastomer, thereby amplifying the resistance signal, significantly improving the sensitivity of the flexible pressure sensor, and successfully solving the problem of weak signal of traditional thin film strain pressure sensors.

[0010] Furthermore, the shape of the elastomer is a rounded rectangular parallelepiped. Common elastomer structures are pyramid-shaped, rectangular, and cylindrical. However, these elastomer structures will cause the metal film to break at the steps, thereby making the pressure sensor unstable. The present invention is based on the improvement of the rectangular elastomer structure, replacing the right angle with a transition radius, thereby increasing the mechanical stability of the constantan sensor grid on the elastomer.

[0011] Furthermore, the flexible substrate is a first polyimide film, and the encapsulation layer is a second polyimide film. Polyimide has high heat resistance, chemical stability, mechanical strength, dimensional stability and electrical insulation, which can improve the performance and reliability of the flexible sensor; the elastomer is a thermoplastic polyurethane elastomer.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned flexible pressure sensor, comprising the following steps:

[0013] According to the preset specification parameters of the elastic body array, a rounded rectangular parallelepiped elastic body array mold is prepared;

[0014] On the flexible substrate, the elastic body array is formed by a rounded rectangular parallelepiped elastic body array mold to obtain a first flexible substrate with an elastic body array formed on the surface, which is recorded as the first material;

[0015] Using a metal mask, magnetron sputtering a constantan sensing grid on the first material, and annealing;

[0016] The packaging layer is used for packaging to obtain a flexible pressure sensor.

[0017] The beneficial effect of the second aspect of the present invention is that the method for preparing the flexible pressure sensor of the present invention has a simple process and is easy to industrially produce by combining with a specific rounded rectangular elastomer array mold and a metal mask.

[0018] Furthermore, the rounded rectangular parallelepiped elastomeric mold is obtained by 3D printing.

[0019] Furthermore, the forming of the elastic body array comprises the following steps:

[0020] Laminating the rounded rectangular elastomer array mold to the flexible substrate, and then applying a thermoplastic polyurethane solution by scraping, and drying to obtain the first material;

[0021] The scraping treatment includes the following process: scraping the thermoplastic polyurethane solution onto the rounded rectangular elastomer array mold, standing for 5-15 minutes, drying for 5-15 minutes, repeating 3-5 times, and eliminating the irregular shape of the elastomer caused by solvent evaporation through multiple scraping. Furthermore, the power of magnetron sputtering is 180W-220W, the time of magnetron sputtering is 30-60 minutes, and the thickness of the constantan sensor grid is 80nm-120nm.

[0022] Furthermore, the annealing is performed at 90° C.-110° C. for 1 h-3 h. The annealing treatment can improve the crystallinity of the film and reduce the stress and lattice defects in the film.

[0023] The third aspect of the present invention provides a data acquisition system for the above-mentioned flexible pressure sensor, including a power management module, an array index module, an analog-to-digital conversion module and an MCU module. The power management module is used to provide voltage to the array index module, the analog-to-digital conversion module and the MCU module. The flexible pressure sensor is connected to the array index module, and the array index module is connected to the MCU module through the analog-to-digital conversion module. The array index module includes a sensor unit array composed of multiple sensor units, and the MCU module is used to communicate with a computer terminal.

[0024] The beneficial effect of the third aspect of the present invention is that based on the flexible pressure sensor of the present invention which has simple process and is easy to expand, its data acquisition system can be simplified and the accuracy of data acquisition can be guaranteed.

[0025] Furthermore, the data acquisition system also includes a single-pole double-throw switch and an analog switch, and multiple sensor units are respectively connected to the single-pole double-throw switch and the analog switch, and the analog switch is connected to the analog-to-digital conversion module. It can be based on an electrical grounding (equipotential method) signal isolation acquisition architecture to achieve row rasterization and can read the sensor unit signals one by one. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0027] Figure 1 This is a schematic diagram of the structure of the flexible pressure sensor of the present invention;

[0028] Figure 2 It is a principle schematic diagram of the data acquisition system of the present invention;

[0029] Figure 3 It is a schematic diagram of the principle of the sensor unit array circuit of the present invention;

[0030] Figure 4 The performance curves of the flexible pressure sensor of the embodiment of the present invention and the comparative example 1;

[0031] Figure 5 1 and 2 are temperature-resistance change curves of the flexible pressure sensor of the embodiment of the present invention and comparative example 2.

[0032] In the attached figure: 1-flexible substrate; 2-elastomer array; 21-elastomer; 3-constantan sensor grid; 4-packaging layer; 5-cavity. DETAILED DESCRIPTION

[0033] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0034] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0035] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0036] Example

[0037] The present embodiment relates to a flexible pressure sensor and a preparation method and a data acquisition system thereof. Some current thin-film pressure sensors have poor stability, serious time drift and temperature drift, and are unable to reliably monitor the internal pressure conditions of the battery with high accuracy for a long time.

[0038] The embodiment of the present invention provides a flexible pressure sensor, referring to Figure 1 The flexible pressure sensor includes a flexible substrate 1, an elastomer array 2, a constantan sensor grid 3 and a packaging layer 4 which are arranged in sequence from bottom to top; the elastomer array 2 includes a plurality of elastomers 21 which are arranged linearly, and a gap is formed between two adjacent elastomers 21; a cavity 5 is formed between the packaging layer 4 and the two adjacent elastomers 21.

[0039] According to the law of resistance, the resistance R of a conductor is proportional to the length L and the resistivity ρ, and inversely proportional to the cross-sectional area S. The formula is R=ρL / S, where ρ is the resistivity of the material used to make the resistor, L is the length of the wire wound into the resistor, S is the cross-sectional area of ​​the wire wound into the resistor, and R is the resistance value. The sensing principle of the flexible pressure sensor in the embodiment of the present invention is that the external pressure causes the L and cross-sectional area S of the flexible pressure sensor to change, thereby changing the resistance R of the constantan sensor grid 3, and the resistance change of the constantan sensor grid 3 presents a monotonic function relationship with the external pressure.

[0040] The embodiment of the present invention adopts constantan, whose resistivity is less affected by temperature, as the sensing material, which effectively solves the problems of large time drift and temperature drift existing in traditional pressure sensors; by adhering an elastomer array on a flexible substrate, the change in pressure is converted into a change in the length of the constantan sensor grid 3 through the deformation of the elastomer, thereby amplifying the resistance signal, significantly improving the sensitivity of the flexible pressure sensor, and successfully solving the problem of weak signal of traditional thin film strain pressure sensors.

[0041] Furthermore, the shape of the elastic body 21 is a rounded rectangular parallelepiped. This embodiment is improved on the basis of the rectangular elastic body structure, and the right angle is replaced by a transition rounded corner to increase the mechanical stability of the constantan sensor grid 3 on the elastic body 21.

[0042] Furthermore, the flexible substrate 1 is a first polyimide film, and the encapsulation layer 4 is a second polyimide film. Polyimide has high heat resistance, chemical stability, mechanical strength, dimensional stability and electrical insulation, which can improve the performance and reliability of the flexible sensor; the raw materials for preparing the elastomer 21 include thermoplastic polyurethane and N,N-dimethylacetamide.

[0043] The preparation method of the flexible pressure sensor of this embodiment is as follows:

[0044] According to the preset specification parameters of the elastic body array, a rounded rectangular elastic body array mold is obtained by 3D printing;

[0045] Thermoplastic polyurethane and N,N-dimethylacetamide are mixed in a mass ratio of 1:3, and stirred at a speed of 600 rad / min for 48 hours until the thermoplastic polyurethane is fully dissolved and defoamed to obtain a thermoplastic polyurethane solution;

[0046] The flexible substrate was placed in anhydrous ethanol and deionized water in turn and ultrasonicated for 10 min to remove oil and impurities on the surface of the flexible substrate, and then dried with nitrogen gas;

[0047] Laminating the rounded rectangular elastomer array mold to a flexible substrate from which surface oil and impurities have been removed;

[0048] The thermoplastic polyurethane solution was scraped onto the rounded rectangular elastomer array mold, left to stand for 10 minutes, dried for 10 minutes, repeated 3 times, and dried for 2 hours. The first polyimide film was separated from the rounded rectangular elastomer array mold to obtain the first material.

[0049] A metal mask is used to magnetron sputter a constantan sensor grid on the first material, the power of the magnetron sputtering is 200 W, the time of the magnetron sputtering is 40 minutes, and the thickness of the constantan sensor grid is 100 nm;

[0050] The constantan sensing grid was annealed at 100°C for 2h;

[0051] The packaging layer is used for packaging to obtain a flexible pressure sensor.

[0052] This embodiment provides a data acquisition system for the above-mentioned flexible pressure sensor, referring to Figure 2 and Figure 3 The data acquisition system includes a power management module, an array index module, an analog-to-digital conversion module and an MCU module. The power management module is used to provide voltage to the array index module, the analog-to-digital conversion module and the MCU module. The flexible pressure sensor is connected to the array index module. The array index module is connected to the MCU module through the analog-to-digital conversion module. The array index module includes a sensor unit array composed of multiple sensor units. The MCU module is connected to a computer terminal for communication.

[0053] Based on the flexible pressure sensor of this embodiment which has simple process and is easy to expand, the data acquisition system of this embodiment can be simplified and the accuracy of data acquisition can be guaranteed.

[0054] Furthermore, the data acquisition system also includes a single-pole double-throw switch and an analog switch, and the multiple sensing units are respectively connected to the single-pole double-throw switch and the analog switch, and the analog switch is connected to the analog-to-digital conversion module.

[0055] The data acquisition method of the data acquisition system of the flexible pressure sensor in this embodiment is exemplified as follows:

[0056] The first sensor unit is grounded through a single-pole double-throw switch, and the other sensor units are kept at a reference voltage V ref Under the condition of , read the sensor unit signal;

[0057] Adjust the state of the single-pole double-throw switch to ground the second sensor unit and keep the reference voltage V in the other sensor units. ref Under the condition of , read the sensor unit signal;

[0058] Repeatedly adjust the state of the single-pole double-throw switch until all sensor unit signals are read to obtain a sensor unit signal set;

[0059] The sensor unit signal set is transmitted to the analog-to-digital conversion module through the analog switch, converted into a digital signal through the analog-to-digital converter (ADC) and finally sent serially to the computer terminal.

[0060] This embodiment is based on a signal isolation acquisition architecture of electrical grounding (equipotential method), realizes row rasterization and can read the sensor unit signals one by one.

[0061] The flexible sensor of this embodiment is small in size and can significantly reduce damage to the electrode after being implanted into the battery cell. At the same time, it can reliably monitor the internal pressure condition of the battery with high precision for a long time.

[0062] Comparative Example 1

[0063] A flexible pressure sensor is different from the embodiment in that no elastic body array is provided.

[0064] Comparative Example 2

[0065] A flexible pressure sensor is different from the embodiment in that the constantan sensing grid is replaced by copper foil.

[0066] The flexible pressure sensors of the embodiment and comparative example 1 were placed on a pressure testing machine (MTS E43.104) equipped with a high-precision commercial pressure sensor (accuracy of ±0.002N) for calibration, and a 61 / 2-digit multimeter (Agilent34410A) was used to measure the resistance change of the sensor during the process. The performance curve of the flexible pressure sensor was obtained by the test as shown in FIG. Figure 4 It can be seen that the resistance of the flexible sensor in the embodiment of the present invention increases with the increase of pressure, and the resistance-pressure presents a monotonic function relationship. However, since the elastic body array is not set in the comparative example 1, its pressure change is difficult to be directly converted into the length change of the constantan sensor grid, and the sensitivity is poor.

[0067] A 61 / 2 digit multimeter (Agilent 34410A) was used to measure the resistance change of the flexible pressure sensor of Example 1 and Comparative Example 2 at different temperatures. The temperature-resistance change curve of the flexible pressure sensor was obtained as shown in the following figure: Figure 5 It can be seen that the resistance of the flexible sensor in the embodiment of the present invention is less affected by temperature, while the resistance of the comparative example 2 is more affected by temperature, which limits its application in usage scenarios with large temperature fluctuations.

[0068] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of the present invention.

Claims

1. A flexible pressure sensor, characterized in that: It includes a flexible substrate, an elastomer array, a constantan sensor grid and a packaging layer which are arranged in sequence from bottom to top; the elastomer array includes a plurality of elastomers which are arranged linearly and a gap is formed between two adjacent elastomers; a cavity is formed between the packaging layer and the two adjacent elastomers.

2. The flexible pressure sensor according to claim 1, characterized in that: The elastic body is in the shape of a rounded rectangular parallelepiped.

3. The flexible pressure sensor according to claim 2, characterized in that: The flexible substrate is a first polyimide film, the encapsulation layer is a second polyimide film, and the elastomer is a thermoplastic polyurethane elastomer.

4. A method for preparing a flexible pressure sensor according to any one of claims 1 to 3, characterized in that: The following steps are involved: According to the preset specification parameters of the elastic body array, a rounded rectangular parallelepiped elastic body array mold is prepared; On the flexible substrate, the elastomer array is formed by the rounded rectangular parallelepiped elastomer array mold to obtain the flexible substrate with the elastomer array formed on the surface, which is recorded as the first material; The constantan sensing grid is magnetron sputtered on the first material by using a metal mask, and then annealed; and the packaging layer is used for packaging to obtain the flexible pressure sensor.

5. The method for preparing the flexible pressure sensor according to claim 4, characterized in that: The rounded rectangular elastomer mold is obtained by 3D printing.

6. The method for preparing the flexible pressure sensor according to claim 4, characterized in that: The molding of the elastic body array comprises the following steps: Laminating the rounded rectangular elastomer array mold to the flexible substrate, and then applying a thermoplastic polyurethane solution by scraping, and drying to obtain the first material; The scraping treatment includes the following process: scraping the thermoplastic polyurethane solution onto the rounded rectangular elastomer array mold, standing for 5 min-15 min, drying for 5 min-15 min, and repeating 3-5 times.

7. The method for preparing the flexible pressure sensor according to claim 4, characterized in that: The power of the magnetron sputtering is 180W-220W, the time of the magnetron sputtering is 30-60min, and the thickness of the constantan sensor grid is 80nm-120nm.

8. The method for preparing the flexible pressure sensor according to claim 4, characterized in that: The annealing is performed at 90° C.-110° C. for 1 h-3 h.

9. A data acquisition system for a flexible pressure sensor as claimed in any one of claims 1 to 3, characterized in that: It includes a power management module, an array index module, an analog-to-digital conversion module and an MCU module. The power management module is used to provide voltage to the array index module, the analog-to-digital conversion module and the MCU module. The flexible pressure sensor is connected to the array index module. The array index module is connected to the MCU module through the analog-to-digital conversion module. The array index module includes a sensor unit array composed of multiple sensor units. The MCU module is used to communicate with a computer terminal.

10. The data acquisition system of the flexible pressure sensor according to claim 9, characterized in that: The data acquisition system further comprises a single-pole double-throw switch and an analog switch, the plurality of sensing units are respectively connected to the single-pole double-throw switch and the analog switch, and the analog switch is connected to the analog-to-digital conversion module.

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