Flexible pressure sensor and its fabrication method

Abstract

This application belongs to the field of sensor technology, and particularly relates to a flexible pressure sensor and its fabrication method. The fabrication method of the flexible pressure sensor includes the following steps: preparing a first self-healing hydrogel layer and a second self-healing hydrogel layer containing water; attaching the first and second self-healing hydrogel layers to the two sides of an electrolyte layer respectively to obtain a pressure sensing layer; fabricating a first flexible electrode on the surface of the first self-healing hydrogel layer and a second flexible electrode on the surface of the second self-healing hydrogel layer in the pressure sensing layer to obtain the flexible pressure sensor. The flexible pressure sensor of this application, when subjected to external pressure, can sense pressure both through the change in the intrinsic impedance of the electrolyte layer and the self-healing hydrogel layer under pressure, and through the change in the interfacial contact resistance caused by the change in the contact area between the self-healing hydrogel layer and the electrode layer. It exhibits high pressure sensing sensitivity and a wide pressure sensing range.

Description

Technical Field

[0001] This application belongs to the field of sensor technology, and in particular relates to a flexible pressure sensor and its fabrication method. Background Technology

[0002] Flexible pressure sensors, as crucial components in wearable smart products, have potential applications in health monitoring, electronic skin, prosthetics, and human-computer interaction. With the rapid development of wearable devices, higher demands are being placed on the durability and portability of flexible pressure sensors to meet the requirements of real-time, long-term signal monitoring. In practical use, these devices are prone to mechanical damage such as creases, scratches, and even cracks due to bending, friction, and impacts. This damage not only reduces the sensor's operational stability but can also cause electrical performance failure, thus shortening the lifespan of the flexible device. Therefore, using self-healing materials is crucial for enhancing the durability of flexible pressure sensors, extending their lifespan, and reducing electronic waste. Currently, among traditional types of flexible pressure sensors such as piezoresistive, capacitive, piezoelectric, and triboelectric sensors, self-healing materials are more commonly used in piezoresistive and capacitive flexible pressure sensors. However, due to limitations in their sensing mechanisms, most of these require an external power source; while piezoelectric and triboelectric sensors can achieve passive sensing by converting mechanical energy into electrical energy. However, they face difficulties in measuring static forces, and stable static force detection is crucial for the development of flexible pressure sensors in fields such as electronic skin and health monitoring.

[0003] Currently, researchers have proposed a potential conversion mechanism based on a galvanic cell using hydrated graphene oxide (GO) as the electrolyte and sensing layer. This mechanism achieves self-powered pressure sensing of dynamic and static forces by converting pressure stimulation into a potential difference between two electrodes. However, hydrated GO is susceptible to water loss due to external environmental influences, which affects the sensing performance of the device. Therefore, the device needs to be encapsulated to isolate it from the external environment. This not only complicates the fabrication process and increases costs, but also leads to deterioration or even failure of the sensing performance if mechanical damage occurs during use. Furthermore, the electrodes and electrolyte materials cannot be replaced or repaired, resulting in reduced long-term durability and reliability, and a shortened lifespan. There is still an urgent need to research flexible pressure sensors that are easy to wear, have a simple fabrication process, a long lifespan, can detect static pressure, and possess self-generating power capabilities. Summary of the Invention

[0004] The purpose of this application is to provide a flexible pressure sensor and its fabrication method, which aims to address, to some extent, the shortcomings of existing flexible sensors in terms of service life, static pressure detection, and self-generating performance.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] In a first aspect, this application provides a method for fabricating a flexible pressure sensor, comprising the following steps:

[0007] A first self-healing hydrogel layer and a second self-healing hydrogel layer are prepared, wherein the first self-healing hydrogel layer and the second self-healing hydrogel layer each contain water.

[0008] An electrolyte layer is prepared by attaching the first self-healing hydrogel layer and the second self-healing hydrogel layer to the two sides of the electrolyte layer to obtain a pressure sensing layer.

[0009] A first flexible electrode is fabricated on the surface of the first self-healing hydrogel layer in the pressure sensing layer, and a second flexible electrode is fabricated on the surface of the second self-healing hydrogel layer to obtain a flexible pressure sensor.

[0010] Secondly, this application provides a flexible pressure sensor, which includes a first flexible electrode, a composite pressure sensing layer, and a second flexible electrode sequentially bonded together; wherein, the composite pressure sensing layer includes at least one pressure sensing layer consisting of a first self-healing hydrogel layer, an electrolyte layer, and a second self-healing hydrogel layer sequentially bonded together; wherein, the first self-healing hydrogel layer and the second self-healing hydrogel layer each contain water.

[0011] The first aspect of this application provides a method for fabricating a flexible pressure sensor. Two self-healing hydrogel layers containing water are prepared and respectively bonded to the two sides of an electrolyte layer to form a sandwich-structured pressure sensing layer, which is also a solid electrolyte. Flexible electrodes are then fabricated on the surface of the self-healing hydrogel layers of the pressure sensing layer, resulting in a flexible pressure sensor. This flexible pressure sensor is designed based on a potential conversion mechanism and possesses both self-healing and self-powering characteristics. Specifically, the self-healing hydrogel layers on both sides, through the self-healing function of the hydrogel, enable the electrolyte layer and electrode layer to self-heal, thereby giving the flexible pressure sensor self-healing properties. It can achieve a self-repairing effect when subjected to external damage, resulting in a long service life. On the other hand, the pressure sensing layer consists of a sandwich structure formed by an electrolyte layer and water-containing self-healing hydrogel layers on both sides. The self-healing hydrogel layers on both sides have a certain water content, which not only provides an appropriate amount of water molecules to the middle electrolyte layer, enhancing its ion transport capability, but also encapsulates the middle electrolyte layer and retains water, maintaining the water molecule content within the electrolyte layer. This ensures the ion transport capability of the electrolyte layer without requiring additional hydration or re-encapsulation, simplifying the process. The sandwich structure of the pressure sensing layer, consisting of a first self-healing hydrogel layer, an electrolyte layer, and a second self-healing hydrogel layer, allows the sensor to sense pressure not only through changes in the intrinsic impedance of the electrolyte layer and the self-healing hydrogel layer under pressure, but also through changes in the interfacial contact resistance caused by changes in the contact area between the self-healing hydrogel layer and the electrode layer. The combination of these two structures improves the pressure sensing sensitivity of the flexible pressure sensor and expands its pressure sensing range.

[0012] The flexible pressure sensor provided in the second aspect of this application is designed based on a potential conversion mechanism. The self-healing hydrogel layers disposed on both sides of the electrolyte layer in the pressure sensing layer enable self-healing of both the electrolyte and electrode layers, giving the flexible pressure sensor self-healing properties. It can self-repair when subjected to external damage, resulting in a long service life. Simultaneously, the self-healing hydrogel layers on both sides have a certain water content, providing water molecules necessary for ion transport in the intermediate electrolyte layer and retaining water in the electrolyte layer, ensuring its ion transport capability. The flexible pressure sensor possesses both self-healing and self-powered characteristics through the synergistic effect of its functional layers. Under external pressure, sensing is achieved both through the change in the intrinsic impedance of the electrolyte and self-healing hydrogel layers under pressure and through the change in the interfacial contact resistance caused by the change in the contact area between the self-healing hydrogel layer and the electrode layer. It exhibits high pressure sensing sensitivity and a wide pressure sensing range. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic flowchart of the fabrication method of the flexible pressure sensor provided in the embodiments of this application;

[0015] Figure 2 This is a schematic diagram of a flexible pressure sensor provided in an embodiment of this application;

[0016] Figure 3 This is a schematic diagram of another structure of the flexible pressure sensor provided in the embodiments of this application;

[0017] Figure 4 This is a diagram showing the output voltage signal of the flexible pressure sensor provided in Embodiment 1 of this application under constant cyclic pressures of 2 kPa, 5 kPa, and 10 kPa.

[0018] Figure 5 This is a diagram of the output voltage signal of the flexible pressure sensor provided in Embodiment 1 of this application after self-repair following a break, under a constant cyclic pressure of 10 kPa. Detailed Implementation

[0019] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0021] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0022] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0023] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0024] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0025] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0026] As attached Figure 1 As shown, the first aspect of this application provides a method for fabricating a flexible pressure sensor, comprising the following steps:

[0027] S10. Prepare a first self-healing hydrogel layer and a second self-healing hydrogel layer, wherein the first self-healing hydrogel layer and the second self-healing hydrogel layer each contain water.

[0028] S20. Prepare an electrolyte layer by attaching the first self-healing hydrogel layer and the second self-healing hydrogel layer to the two sides of the electrolyte layer to obtain a pressure sensing layer.

[0029] S30. A first flexible electrode is prepared on the surface of the first self-healing hydrogel layer in the pressure sensing layer, and a second flexible electrode is prepared on the surface of the second self-healing hydrogel layer to obtain a flexible pressure sensor.

[0030] The first aspect of this application provides a method for fabricating a flexible pressure sensor. Two self-healing hydrogel layers containing water are prepared and respectively bonded to the two sides of an electrolyte layer to form a sandwich-structured pressure sensing layer, which is also a solid electrolyte. Flexible electrodes are then fabricated on the surface of the self-healing hydrogel layers of the pressure sensing layer to obtain the flexible pressure sensor. This flexible pressure sensor is designed based on a potential conversion mechanism and possesses both self-healing and self-powering characteristics. Specifically, the self-healing hydrogel layers on both sides, through the self-healing function of the hydrogel, enable the electrolyte layer and electrode layer to self-heal, thereby giving the flexible pressure sensor self-healing properties. It can achieve a self-repairing effect when subjected to external damage, resulting in a long service life. On the other hand, the pressure sensing layer consists of a sandwich structure formed by an electrolyte layer and water-containing self-healing hydrogel layers on both sides. The self-healing hydrogel layers on both sides have a certain water content, which not only provides an appropriate amount of water molecules to the middle electrolyte layer, enhancing its ion transport capability, but also encapsulates the middle electrolyte layer and retains water, maintaining the water molecule content within the electrolyte layer. This ensures the ion transport capability of the electrolyte layer without requiring additional hydration or re-encapsulation, simplifying the process. The sandwich structure of the pressure sensing layer, consisting of a first self-healing hydrogel layer, an electrolyte layer, and a second self-healing hydrogel layer, allows the sensor to sense pressure not only through changes in the intrinsic impedance of the electrolyte layer and the self-healing hydrogel layer under pressure, but also through changes in the interfacial contact resistance caused by changes in the contact area between the self-healing hydrogel layer and the electrode layer. The combination of these two structures improves the pressure sensing sensitivity of the flexible pressure sensor and expands its pressure sensing range.

[0031] In some embodiments, step S10 above, the steps of preparing the first self-healing hydrogel layer and the second self-healing hydrogel layer, respectively, independently include:

[0032] S11. Dissolve the self-healing gel material and the water-absorbing material in a solvent to form a precursor slurry.

[0033] S12. The precursor slurry is deposited onto the substrate surface, dried to form a thin film, and then placed in an environment with a humidity of 40-70% for 24-48 hours to obtain a first self-healing hydrogel layer or a second self-healing hydrogel layer.

[0034] The self-healing hydrogel layer in this embodiment is prepared by dissolving a self-healing gel material and a water-absorbing material in a solvent to form a precursor slurry. The self-healing gel material provides self-healing functionality, while the water-absorbing material provides water absorption and retention. This slurry is then deposited onto a substrate surface via casting or other methods, forming a wet film. After drying, a dried film is formed. The film is then placed in an environment with a humidity of 40-70% for 24-48 hours to allow it to absorb a certain amount of moisture, resulting in a self-healing hydrogel layer with a specific water content. When the prepared self-healing hydrogel layer breaks, the mobility of the polymer chains allows it to form non-covalent forces such as hydrogen bonds between the damaged materials, thereby repairing the crack. The repair speed can be accelerated by the presence of water. However, if the ambient humidity is too high, the resulting self-healing hydrogel layer will have an excessively high water content, leading to high conductivity and ion mobility between the electrolyte layer and the self-healing hydrogel layer. This causes the potential difference between the two electrodes to quickly reach saturation after the electrolyte comes into contact with the electrode, making pressure sensing impossible. In addition, when the water content of hydrogels is too high, the difference between their humidity and that of the air is large, making it difficult for them to remain stable in the air.

[0035] In some embodiments, in step S11 above, the self-healing gel material is added to deionized water and stirred at a temperature of 60-100°C until it is completely dissolved. Then, an absorbent material is added and stirred to fully dissolve the self-healing gel material and the absorbent material in the deionized water. The mixed solution is then allowed to stand for a period of time to eliminate bubbles. Once the bubbles are completely eliminated, a precursor slurry is formed.

[0036] In some embodiments, the self-healing gel material includes at least one of polyvinyl alcohol, chitosan, agar, sodium alginate, polyacrylamide, and gelatin; these materials all have good self-healing properties. In some embodiments, the self-healing gel material includes two or more of polyvinyl alcohol, chitosan, agar, sodium alginate, polyacrylamide, and gelatin, forming a double-network or triple-network hydrogel through the composite of several materials, thereby enabling the flexible pressure sensor to have a better self-healing effect.

[0037] In some embodiments, the water-absorbing material includes at least one of glycerol, ethylene glycol, lithium chloride, magnesium chloride, and calcium chloride; these materials all have good water absorption properties, which makes the self-healing hydrogel layer have water absorption and water retention properties, which is beneficial for providing water molecules to the electrolyte layer in the flexible pressure sensor, improving its electron transport performance, and also helps to maintain a stable content of water molecules in the electrolyte layer, avoid water loss, and ensure the electron transport performance of the electrolyte layer.

[0038] In some embodiments, the mass ratio of the self-healing gel material to the absorbent material is (1-3):(1-2); this ratio ensures both the self-healing performance and the water absorption and retention properties of the self-healing hydrogel layer. Increasing the content of the self-healing gel material improves its self-healing performance, but it also leads to excessive viscosity in the self-healing hydrogel layer, making demolding difficult. In some specific embodiments, the mass ratio of the self-healing gel material to the absorbent material includes, but is not limited to, 1:2, 1:1, 2:1, 3:1, etc.

[0039] In some embodiments, the mass fraction of the self-healing gel material in the precursor slurry is 5-25%. When the concentration of the self-healing gel material in the precursor slurry is too low, it is prone to dehydration and shrinkage, making it impossible to form a stable physically cross-linked hydrogel. When the concentration of the self-healing gel material is high, it is difficult for the self-healing gel material to dissolve in water, and the resulting gel has an excessively large modulus, making it difficult to deform. In some specific embodiments, the mass fraction of the self-healing gel material in the precursor slurry includes, but is not limited to, 5-10%, 10-15%, 15-20%, and 20-25%.

[0040] In some embodiments, in step S12 above, the precursor slurry is deposited onto the surface of a substrate such as sandpaper by casting or other methods. Spacers are placed on both sides of the sandpaper to control the wet film thickness. The slurry is then uniformly and smoothly coated onto the sandpaper surface using a casting method. Afterward, the solution, along with the mold, is placed in a fume hood for 20-48 hours to dry, and then demolded to obtain a thin film. Then, the film is placed in an environment with a humidity of 40-70% for 24-48 hours to allow it to absorb a certain amount of moisture, resulting in a self-healing hydrogel layer with a small water content. In this application embodiment, sandpaper with irregular concave and convex microstructures is used as an example of the substrate. Substrates with regular concave and convex structures, such as micropyramids, microspheres, and micropillars, can also be used to construct the microstructure on the surface of the self-healing hydrogel layer. The microstructure can regulate the contact resistance; when the microstructure is deformed under stress, the contact resistance can be regulated by changing the contact area.

[0041] In some embodiments, the substrate is selected from sandpaper with a surface mesh size of 1000 to 10000, so that the surfaces of the first and second self-healing hydrogel layers in contact with the sandpaper have microstructures. In this application embodiment, by constructing microstructures on the surface of the self-healing hydrogel layer, the contact area between the electrolyte layer and the electrode layer increases when the device is subjected to pressure, thereby changing the interfacial contact resistance and realizing pressure sensing. Using sandpaper with this surface mesh size as a substrate allows for the preparation of self-healing hydrogel layers with rich microstructures, which is beneficial for improving the pressure sensing sensitivity of flexible pressure sensors and expanding the pressure sensing range.

[0042] In some embodiments, the water content of the first self-healing hydrogel layer and the second self-healing hydrogel layer are independently 5–35 wt%. Since the potential conversion mechanism of the electrolyte layer depends on the ion transport capability of the electrolyte, and a completely dehydrated graphene oxide electrolyte layer is equivalent to a dielectric layer and does not possess electrolyte properties, the insertion of water molecules is beneficial to improving the ion transport capability of the electrolyte layer. Therefore, the electrolyte layer needs to have a certain water content and not be dehydrated by environmental influences. The self-healing hydrogel layers on both sides of the electrolyte layer in this embodiment contain a certain amount of water, which can provide water molecules to the electrolyte layer, ensuring that the electrolyte layer has good ion transport capability with the participation of water molecules. At the same time, the self-healing hydrogel layer also has water retention properties, ensuring that water molecules in the electrolyte layer are not lost, thereby ensuring the electron transport stability of the electrolyte layer. If the water content in the self-healing hydrogel layer is too low, the electrolyte layer will capture fewer water molecules, resulting in poor ion transport. Furthermore, the low water content increases the density of the hydrogel polymer network within the self-healing hydrogel layer, hindering ion transport and hindering ion transport between the self-healing hydrogel layer and the electrolyte layer, thus preventing the potential conversion mechanism from being realized. Conversely, if the water content in the self-healing hydrogel layer is too high, the conductivity and ion mobility of both the electrolyte layer and the self-healing hydrogel layer are high. After the electrolyte contacts the electrode, the potential difference between the two electrodes will quickly reach saturation, making pressure sensing impossible. Additionally, excessive water content in the self-healing hydrogel layer leads to a significant difference in humidity compared to the air, making it difficult to maintain the stability of the flexible pressure sensor in air. In some specific embodiments, the water content of the first and second self-healing hydrogel layers is independently 5–10 wt%, 10–15 wt%, 15–20 wt%, 20–25 wt%, 25–30 wt%, and 30–35 wt%, respectively.

[0043] In some embodiments, the thicknesses of the first self-healing hydrogel layer and the second self-healing hydrogel layer are independently 0.2–3 mm, which is beneficial for ensuring the detection sensitivity of the flexible pressure sensor. If the thickness of the self-healing hydrogel layer is too small, the deformation space is too low and the water retention is limited; if the thickness of the self-healing hydrogel layer is too large, the self-healing hydrogel layer is not easily deformed, and the sensitivity will decrease. In some specific embodiments, the thicknesses of the first self-healing hydrogel layer and the second self-healing hydrogel layer are independently 0.2–0.5 mm, 0.5–0.8 mm, 0.8–1 mm, 1–1.5 mm, 1.5–2 mm, 2–2.5 mm, 2.5–3 mm, etc.

[0044] In some embodiments, step S20 above, the step of preparing the electrolyte layer includes: dispersing the electrolyte material in water to form a dispersion, and then preparing the electrolyte layer from the dispersion by vacuum filtration. In some specific embodiments, a certain mass of electrolyte material is added to deionized water and subjected to ultrasonic treatment for a certain period of time to ensure sufficient dispersion. Then, the electrolyte material dispersion is prepared into a film by vacuum filtration and cut into a certain size for later use. Alternatively, the electrolyte layer can also be prepared using methods such as spraying or printing.

[0045] In some embodiments, the electrolyte material includes at least one selected from graphene oxide, metal-organic frameworks, covalent organic frameworks, hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide. These electrolyte materials all possess a two-dimensional sheet structure and can self-assemble during film formation, readily forming an electrolyte layer with a microstructure. This microstructure can modulate the contact resistance; when the microstructure is deformed under stress, the contact area can be changed, thereby controlling the contact resistance. In some preferred embodiments, the electrolyte material is selected from graphene oxide.

[0046] In some embodiments, the concentration of the dispersion is 2–7 mg / ml. This concentration of dispersion is beneficial for improving the efficiency of preparing the electrolyte layer by vacuum filtration. If the concentration is too low, the vacuum filtration time will be long and the preparation efficiency will be low; if the concentration is too high, it will easily lead to unevenness and inconsistent thickness of the prepared electrolyte layer film. In some embodiments, the concentration of the dispersion includes, but is not limited to, 2 mg / ml, 3 mg / ml, 4 mg / ml, 5 mg / ml, 6 mg / ml, 7 mg / ml, etc.

[0047] In some embodiments, the thickness of the electrolyte layer is 0.01–1 mm. A thinner electrolyte layer indicates fewer stacked layers, making the layered microstructure more prone to saturation under lower pressure and reducing device sensitivity. Conversely, fabricating an excessively thick electrolyte layer increases cost and adds ion transport paths, which can also reduce device detection sensitivity to some extent. In some specific embodiments, the thickness of the electrolyte layer includes, but is not limited to, 0.01–0.1 mm, 0.1–0.2 mm, 0.2–0.5 mm, 0.5–0.8 mm, and 0.8–1 mm.

[0048] In some embodiments, the step of attaching the first self-healing hydrogel layer and the second self-healing hydrogel layer to the two side surfaces of the electrolyte layer includes: disposing the side surface of the first and second self-healing hydrogel layers having microstructures away from the electrolyte layer. In this case, the side surface of the self-healing hydrogel layer having microstructures is in contact with the flexible electrode layer. The microstructures on the surface of the self-healing hydrogel layer can regulate the contact resistance. When the microstructures are deformed under stress, the contact resistance can be regulated by changing the contact area. In addition, the surface where the self-healing hydrogel layer is attached to the electrolyte layer is a flat surface, which is more conducive to providing water molecules required for ion transport to the electrolyte layer, while forming a better encapsulation effect for the electrolyte layer and preventing water molecules in the electrolyte layer from easily escaping.

[0049] In some embodiments, multiple pressure sensing layers can be laminated to form a composite pressure sensing layer. For example, two or more pressure sensing layers can be laminated together to form a composite self-healing hydrogel layer through an outer self-healing hydrogel layer. Alternatively, an electrolyte layer and a self-healing hydrogel layer can be sequentially laminated onto the surface of the self-healing hydrogel layer on the outer side of the pressure sensing layer to form a composite pressure sensing layer.

[0050] In some embodiments, in step S30 above, the preparation of the first flexible electrode and the second flexible electrode each independently includes the steps of: dissolving or dispersing the electrode material in water, and forming a flexible electrode layer by vacuum filtration. Alternatively, flexible electrodes can be formed by depositing a dispersion of the electrode material onto the surface of a self-healing hydrogel layer using methods such as spraying, inkjet printing, or magnetron sputtering.

[0051] In some embodiments, the steps of fabricating a first flexible electrode on the surface of a first self-healing hydrogel layer and a second flexible electrode on the surface of a second self-healing hydrogel layer in the pressure sensing layer include attaching the prepared first flexible electrode to the surface of the first self-healing hydrogel and attaching the prepared second flexible electrode to the surface of the second self-healing hydrogel to obtain a flexible pressure sensor. In this embodiment, the first flexible electrode is attached to the surface of the first self-healing hydrogel layer, and the second flexible electrode is attached to the surface of the second self-healing hydrogel layer. The pressure sensing layer and the flexible electrode layer are attached together, allowing the self-healing function of the hydrogel to be utilized to self-repair the electrolyte layer and the flexible electrode layer when the flexible pressure sensor is accidentally damaged.

[0052] In some embodiments, the first flexible electrode and the second flexible electrode are made of electrode materials with different chemical potentials. By selecting two conductive materials with different chemical potentials to fabricate the first flexible electrode and the second flexible electrode, respectively, potential-switching pressure sensing can be realized.

[0053] In some embodiments, the electrode material includes at least one of carbon nanotubes, graphene, MXene, metal nanowires, and metal nanoparticles; these materials all have good electrical conductivity and are beneficial for conducting charges as electrode materials, thereby enabling the device to sensitively detect pressure.

[0054] In some embodiments, the thicknesses of the first and second flexible electrodes are independently 0.005–1 mm. At this thickness, the electrode thickness is moderate, its own resistance is low, and it can remain stable within a certain deformation range, resulting in high repair efficiency after breakage. When the flexible electrode is too thin, its own resistance is high, leading to low device sensitivity and low self-repair efficiency. When the flexible electrode is too thick, the portion far from the self-repairing hydrogel layer cannot self-repair, wasting material, and the overall modulus of the device becomes high, making it less prone to deformation and resulting in low sensitivity.

[0055] As attached Figure 2 As shown, a second aspect of this application provides a flexible pressure sensor, including a first flexible electrode, a composite pressure sensing layer, and a second flexible electrode sequentially bonded together; wherein, the composite pressure sensing layer includes at least one pressure sensing layer consisting of a first self-healing hydrogel layer, an electrolyte layer, and a second self-healing hydrogel layer sequentially bonded together; wherein, the first self-healing hydrogel layer and the second self-healing hydrogel layer each contain moisture.

[0056] The flexible pressure sensor provided in the second aspect of this application is designed based on a potential conversion mechanism. The self-healing hydrogel layers disposed on both sides of the electrolyte layer in the pressure sensing layer enable self-healing of both the electrolyte and electrode layers, giving the flexible pressure sensor self-healing properties. It can self-repair when subjected to external damage, resulting in a long service life. Simultaneously, the self-healing hydrogel layers on both sides have a certain water content, providing water molecules necessary for ion transport in the intermediate electrolyte layer and retaining water in the electrolyte layer, ensuring its ion transport capability. The flexible pressure sensor possesses both self-healing and self-powered characteristics through the synergistic effect of its functional layers. Under external pressure, sensing is achieved both through the change in the intrinsic impedance of the electrolyte layer and the self-healing hydrogel layer under pressure and through the change in the interfacial contact resistance caused by the change in the contact area between the self-healing hydrogel layer and the electrode layer. It exhibits high pressure sensing sensitivity and a wide pressure sensing range.

[0057] The flexible pressure sensor of this application embodiment can be prepared by the method described in the above embodiments.

[0058] In some embodiments, the composite pressure sensing layer includes two or more pressure sensing layers sequentially bonded together by a first self-healing hydrogel layer, an electrolyte layer, and a second self-healing hydrogel layer. The composite pressure sensing layer is obtained by bonding two pressure sensing layers of the same structure. Due to the excellent adhesion between the self-healing hydrogel layers, adjacent self-healing hydrogel layers can quickly form a whole after bonding. In other embodiments, two or more pressure sensing layers to be composited may be used, where one pressure sensing layer may only have a self-healing hydrogel layer on one side of the electrolyte layer. However, when two pressure sensing layers are composited, they can be bonded together through the composite pressure sensing layer of one of them to form the overall composite pressure sensing layer. In some specific embodiments, the results of the flexible pressure sensor are shown in the appendix. Figure 3 As shown, it includes a first flexible electrode, a composite pressure sensing layer and a second flexible electrode that are sequentially bonded together. The composite pressure sensing layer includes a sub-pressure sensing layer consisting of a first self-healing hydrogel layer, a first electrolyte layer and a second self-healing hydrogel layer that are sequentially bonded together, and another sub-pressure sensing layer consisting of a second electrolyte layer and a third self-healing hydrogel layer that are sequentially bonded together.

[0059] In some embodiments, one side surface of the first self-healing hydrogel layer and the second self-healing hydrogel layer has a microstructure, and the side surface of the first self-healing hydrogel layer and the second self-healing hydrogel layer with the microstructure is disposed away from the electrolyte layer.

[0060] In some embodiments, the water content of the first self-healing hydrogel layer and the second self-healing hydrogel layer is independently 5 to 35 wt%.

[0061] In some embodiments, the first flexible electrode and the second flexible electrode each independently include at least one electrode material selected from carbon nanotubes, graphene, MXene, metal nanowires, and metal nanoparticles, and the first flexible electrode and the second flexible electrode contain electrode materials with different chemical potentials.

[0062] In some embodiments, the first self-healing hydrogel layer and the second self-healing hydrogel layer each independently include a self-healing gel material and a water-absorbing material in a mass ratio of (1-3):(1-2).

[0063] In some embodiments, the electrolyte layer includes at least one electrolyte material selected from graphene oxide, metal-organic framework materials, covalent organic frameworks, hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide.

[0064] In some embodiments, the area of ​​the electrolyte layer is slightly smaller than the area of ​​the self-healing hydrogel layer to ensure that the self-healing hydrogel layer can adequately cope with the deformation of the electrolyte layer and repair the electrolyte layer.

[0065] In some embodiments, the thicknesses of the first flexible electrode and the second flexible electrode are independently 0.005 to 1 mm.

[0066] In some embodiments, the thicknesses of the first self-healing hydrogel layer and the second self-healing hydrogel layer are each independently 0.2 to 3 mm.

[0067] In some embodiments, the thickness of the electrolyte layer is 0.01 to 1 mm.

[0068] The beneficial effects of the above embodiments of this application have been discussed in detail above and will not be repeated here.

[0069] To enable those skilled in the art to clearly understand the above-described implementation details and operations, and to demonstrate the significant advancements in the performance of the flexible pressure sensor and its fabrication method in the embodiments of this application, the following examples illustrate the above technical solutions.

[0070] Example 1

[0071] A flexible pressure sensor, the structure of which is shown in the attached figure. Figure 2 As shown, it includes a first flexible electrode, a first self-healing hydrogel layer, an electrolyte layer, a second self-healing hydrogel layer, and a second flexible electrode that are sequentially stacked and bonded together; wherein, the first flexible electrode and the second flexible electrode are electrically connected to a voltmeter.

[0072] Its preparation includes the following steps:

[0073] 1. Preparation of polyvinyl alcohol (PVA) / glycerol (Gly) hydrogel precursor: A certain mass of PVA powder was added to deionized water and stirred at 80°C. The mass fraction of PVA was controlled to be 10%. After the PVA powder was completely dissolved, a certain mass of Gly was added to the PVA aqueous solution and stirred for 10 minutes. The mass ratio of Gly to PVA was controlled to be 1:1. The mixed solution was then allowed to stand for a period of time to eliminate bubbles. After the bubbles were completely eliminated, the PVA / Gly hydrogel precursor was obtained.

[0074] 2. Preparation of self-healing PVA / Gly hydrogel layer: The prepared PVA / Gly hydrogel precursor was poured onto the surface of sandpaper. Spacers were placed on both sides of the sandpaper (2000 grit) to control the thickness of the film to 0.3 mm. The film was evenly and smoothly coated onto the sandpaper surface by casting. The solution and the mold were then placed in a fume hood for 24 hours. After gelation, the film was peeled off to obtain a PVA / Gly hydrogel layer with a microstructure on the surface. The film was then placed in an environment with a humidity of 56% for 24 hours to obtain a self-healing hydrogel layer with a water content of 15%, namely the first self-healing hydrogel layer and the second self-healing hydrogel layer.

[0075] 3. Preparation of GO electrolyte: A certain mass of GO was added to deionized water and sonicated for 20 minutes. The GO concentration was 3 mg / ml. Then, the GO dispersion was prepared into a film by vacuum filtration and appropriately cut. The thickness of the obtained GO film was 0.1 mm, which is the electrolyte layer.

[0076] 4. Preparation of CNT and MXene electrodes: A certain mass of carbon nanotubes (CNTs) and MXene were added to hexane and deionized water, respectively, and subjected to ultrasonic treatment for 30 min. Then, the CNT and MXene dispersions were separately prepared into films using vacuum filtration and appropriately cut. The resulting CNT and MXene electrode films had a thickness of 0.005 mm, serving as the first and second electrodes, respectively.

[0077] 5. Assemble the device: Sandwich the prepared GO film between two self-healing PVA / Gly hydrogel layers (the area of ​​the GO film should be smaller than the area of ​​the PVA / Gly hydrogel film). The side of the hydrogel with the microstructure faces away from the GO. Then attach the CNT and MXene electrodes to the self-healing PVA / Gly hydrogel layers on both sides to form a self-powered, self-healing flexible pressure sensor. Lead wires from the two electrodes to connect the device to the test equipment to complete the test.

[0078] Example 2

[0079] A flexible pressure sensor includes a first flexible electrode, a first self-healing hydrogel layer, an electrolyte layer, a second self-healing hydrogel layer, and a second flexible electrode, which are sequentially stacked and bonded together. The preparation steps and materials used for the first flexible electrode, the first self-healing hydrogel layer, the electrolyte layer, the second self-healing hydrogel layer, and the second flexible electrode are the same as in Example 1. The difference lies in that the PVA mass fraction in the first and second self-healing hydrogel layers is 15%.

[0080] Example 3

[0081] A flexible pressure sensor, the structure of which is shown in the attached figure. Figure 3 As shown, the assembly includes a first flexible electrode, a first self-healing hydrogel layer, a first electrolyte layer, a second self-healing hydrogel layer, a second electrolyte layer, a third self-healing hydrogel layer, and a second flexible electrode, all sequentially stacked and bonded together. The preparation steps and materials used for the first and second flexible electrodes are the same as in Example 1; the preparation steps and materials used for the first and second electrolyte layers are the same as for the electrolyte layer in Example 1; and the preparation steps and materials used for the first, second, and third self-healing hydrogel layers are the same as in Example 1. The difference lies in the fact that, except for the use of a silicon wafer with a micro-pyramid structure as the mold for the first self-healing hydrogel layer, the preparation steps and materials used are the same as in Example 1.

[0082] Comparative Example 1

[0083] A flexible pressure sensor includes a first flexible electrode, an electrolyte layer, and a second flexible electrode that are sequentially stacked and bonded together; wherein the preparation steps and materials used for the first flexible electrode, the electrolyte layer, and the second flexible electrode are the same as in Example 1.

[0084] Comparative Example 2

[0085] A flexible pressure sensor includes a first flexible electrode, a self-healing hydrogel layer, and a second flexible electrode that are sequentially stacked and bonded together; wherein the preparation steps and materials used for the first flexible electrode, the self-healing hydrogel layer, and the second flexible electrode are the same as in Example 1.

[0086] Comparative Example 3

[0087] A flexible pressure sensor includes a first flexible electrode, a self-healing hydrogel layer, an electrolyte layer, and a second flexible electrode that are sequentially stacked and bonded together; wherein the preparation steps and materials used for the first flexible electrode, the self-healing hydrogel layer, the electrolyte layer, and the second flexible electrode are the same as in Example 1.

[0088] Furthermore, to verify the progressiveness of the embodiments of this application, the following performance tests were conducted:

[0089] 1. The flexible pressure sensor prepared in Example 1 was tested for its output voltage signal under constant cyclic pressures of 2 kPa, 5 kPa, and 10 kPa. The output voltage signals of the flexible pressure sensor in Example 1 under constant cyclic pressures of 2 kPa, 5 kPa, and 10 kPa are shown in the attached figure. Figure 4 As shown in the figure, the flexible pressure sensor of this application can achieve stable sensing of static forces of different magnitudes.

[0090] In addition, in Example 1, the flexible pressure sensor was treated to cause a breakage. A small amount of deionized water was then applied to the breakage, and the sensor was reassembled to heal. After the excess water evaporated, the output voltage signal was obtained under a constant cyclic pressure of 10 kPa. (See attached diagram.) Figure 5 As shown in the figure, the sensor can still perform stable sensing, indicating that the sensor has good self-healing performance.

[0091] 2. The pressure sensing sensitivity of the flexible pressure sensors prepared in each embodiment and comparative example was tested: different pressures were applied to the sensors using a mechanical testing platform, and the output voltage signal was measured simultaneously. Then, the sensitivity was calculated according to the formula S=ΔV / ΔP, where ΔV is the change in output voltage and ΔP is the change in pressure.

[0092] 3. Test the self-healing performance of the flexible pressure sensors prepared in each embodiment and comparative example: The flexible pressure sensor was treated to cause a break, and then a small amount of deionized water was applied to the break. After the broken surfaces were put back together, it was observed whether the sensor healed again. After the excess water in the healed sensor evaporated, the sensing sensitivity of the flexible pressure sensor was measured and compared with the pressure sensing sensitivity before self-healing.

[0093] The test results are shown in Table 1 below.

[0094] Table 1

[0095]

[0096]

[0097] The test results above show that the self-healing hydrogel layer in this embodiment, as a pressure sensing layer with surface microstructure, can provide and retain moisture for the electrolyte layer, significantly affecting the pressure sensing sensitivity and self-healing performance of the flexible pressure sensor. A comparison of the test results of Examples 1 and 2 shows that increasing the PVA mass fraction of the hydrogel reduces the pressure sensing sensitivity. This is because the increased elastic modulus of the hydrogel hinders deformation, thus reducing sensitivity. A comparison of the test results of Examples 1 and 3 shows that increasing the layered structure increases the deformation space, thereby improving pressure sensing sensitivity. A comparison of the test results of Example 1 and Comparative Example 2 shows that the flexible pressure sensor without a GO electrolyte layer can still achieve pressure sensing using the ion transport capability of the self-healing hydrogel layer, but its pressure sensitivity is reduced due to the loss of the layered microstructure of GO. Examples 1, 2, 3, and Comparative Example 2 all achieve self-healing performance due to the presence of the self-healing hydrogel layer, and their pressure sensing sensitivity remains almost unchanged compared to before self-healing. Comparative Example 1, lacking a self-healing hydrogel layer, cannot achieve self-healing of the device and cannot provide water molecules to the GO electrolyte layer. The dehydrated GO electrolyte layer acts as a dielectric layer, lacking electrolyte properties and ion transport capabilities, thus failing to achieve pressure sensing via a potential conversion mechanism. Comparative Example 3, with only one layer of hydrogel, lacks close contact between the second flexible electrode and the self-healing hydrogel layer, failing to completely encapsulate the GO electrolyte layer. Therefore, the GO electrolyte layer cannot retain water and is prone to dehydration, acting as a dielectric layer without electrolyte properties and ion transport capabilities, thus also failing to achieve pressure sensing via a potential conversion mechanism. Furthermore, it fails to demonstrate the self-healing performance of the entire device.

[0098] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fabricating a flexible pressure sensor, characterized in that, Includes the following steps: A first self-healing hydrogel layer and a second self-healing hydrogel layer are prepared, wherein the first self-healing hydrogel layer and the second self-healing hydrogel layer each contain water; the water content of the first self-healing hydrogel layer and the second self-healing hydrogel layer are each independently 5~35wt%; and the thickness of the first self-healing hydrogel layer and the second self-healing hydrogel layer are each independently 0.2~3mm. An electrolyte layer is prepared by attaching the first self-healing hydrogel layer and the second self-healing hydrogel layer to the two sides of the electrolyte layer, that is, setting the side surface of the first self-healing hydrogel layer and the second self-healing hydrogel layer with microstructures away from the electrolyte layer; thus obtaining a pressure sensing layer. A first flexible electrode is fabricated on the surface of the first self-healing hydrogel layer in the pressure sensing layer, and a second flexible electrode is fabricated on the surface of the second self-healing hydrogel layer to obtain a flexible pressure sensor.

2. The method for fabricating the flexible pressure sensor as described in claim 1, characterized in that, The steps for preparing the first self-healing hydrogel layer and the second self-healing hydrogel layer each independently include: Self-healing gel material and water-absorbing material are dissolved in a solvent to form a precursor slurry; The precursor slurry is deposited onto the substrate surface, dried to form a thin film, and then placed in an environment with a humidity of 40-70% for 24-48 hours to obtain the first self-healing hydrogel layer or the second self-healing hydrogel layer.

3. The method for fabricating the flexible pressure sensor as described in claim 2, characterized in that, The self-healing gel material includes at least one of polyvinyl alcohol, chitosan, agar, sodium alginate, polyacrylamide, and gelatin; And / or, the absorbent material includes at least one of glycerin, ethylene glycol, lithium chloride, magnesium chloride, and calcium chloride; And / or, the mass ratio of the self-healing gel material to the absorbent material is (1~3):(1~2); And / or, in the precursor slurry, the mass fraction of the self-healing gel material is 5-25%; And / or, the substrate is selected from sandpaper with a surface mesh count of 1000 to 10000, so that the surface of the first self-healing hydrogel layer and the second self-healing hydrogel layer in contact with the sandpaper has a microstructure.

4. The method for fabricating the flexible pressure sensor according to any one of claims 1 to 3, characterized in that, The steps for preparing the electrolyte layer include: dispersing the electrolyte material in water to form a dispersion, and then using a vacuum filtration method to prepare the electrolyte layer from the dispersion.

5. The method for fabricating the flexible pressure sensor as described in claim 4, characterized in that, The electrolyte material includes at least one of graphene oxide, metal-organic framework materials, covalent organic frameworks, hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide; And / or, the concentration of the dispersion is 2~7 mg / ml; And / or, the thickness of the electrolyte layer is 0.01~1mm.

6. The method for fabricating the flexible pressure sensor as described in claim 1 or 5, characterized in that, The preparation of the first flexible electrode and the second flexible electrode each independently includes the steps of: dissolving or dispersing the electrode material in water and preparing a flexible electrode layer by means of suction filtration; And / or, the first flexible electrode and the second flexible electrode use electrode materials with different chemical potentials.

7. The method for fabricating a flexible pressure sensor as described in claim 6, characterized in that, The electrode material includes at least one of carbon nanotubes, graphene, MXene, metal nanowires, and metal nanoparticles. And / or, the thickness of the first flexible electrode and the second flexible electrode are independently 0.005~1mm.

8. A flexible pressure sensor prepared by the method according to any one of claims 1 to 7, characterized in that, The flexible pressure sensor includes a first flexible electrode, a composite pressure sensing layer, and a second flexible electrode sequentially bonded together; wherein, the composite pressure sensing layer includes at least one pressure sensing layer consisting of a first self-healing hydrogel layer, an electrolyte layer, and a second self-healing hydrogel layer sequentially bonded together; wherein, the first self-healing hydrogel layer and the second self-healing hydrogel layer each contain water; the water content of the first self-healing hydrogel layer and the second self-healing hydrogel layer are each independently 5~35wt%; the thickness of the first self-healing hydrogel layer and the second self-healing hydrogel layer are each independently 0.2~3mm.

9. The flexible pressure sensor as described in claim 8, characterized in that, One side surface of the first self-healing hydrogel layer and the second self-healing hydrogel layer has a microstructure, and the side surface of the first self-healing hydrogel layer and the second self-healing hydrogel layer with the microstructure is disposed away from the electrolyte layer; And / or, the first flexible electrode and the second flexible electrode each independently include at least one electrode material selected from carbon nanotubes, graphene, MXene, metal nanowires, and metal nanoparticles, and the first flexible electrode and the second flexible electrode contain electrode materials with different chemical potentials; And / or, the first self-healing hydrogel layer and the second self-healing hydrogel layer each independently include a self-healing gel material and a water-absorbing material in a mass ratio of (1~3):(1~2); And / or, the electrolyte layer includes at least one electrolyte material selected from graphene oxide, metal-organic framework materials, covalent organic frameworks, hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide; And / or, the thickness of the first flexible electrode and the second flexible electrode are independently 0.005~1mm; And / or, the thickness of the electrolyte layer is 0.01~1mm.

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