Stretchable electrode and preparation method and application thereof

Abstract

The application discloses a stretchable electrode and a preparation method and application thereof, relates to flexible electronic technology, and aims at the problem of insufficient mechanical / electrical performance in the prior art. The stretchable electrode comprises an elastic polymer layer and a piezoelectric polymer layer which are arranged in a stack, and the piezoelectric polymer layer is embedded with a conductive network. The preparation method comprises the following steps: S1, a step of preparing a conductive network on a substrate; S2, a step of filling the conductive network with a piezoelectric polymer on the substrate to form a piezoelectric polymer layer; S3, a step of covering an elastic polymer layer on the piezoelectric polymer layer; and S4, a step of stripping the substrate. The stretchable electrode is applied to a piezoelectric pressure sensor. The stretchable electrode can improve the stretchability and surface roughness of the stretchable electrode, effectively improve the output characteristics of the piezoelectric device, and has the characteristics of easy patterning.

Description

TECHNICAL FIELD

[0001] The present application relates to flexible electronics, in particular to a stretchable electrode and its preparation method and application. BACKGROUND

[0002] In recent years, the research of new generation electronic devices such as electronic skin, wearable devices, portable energy devices has developed rapidly. Among them, the device based on piezoelectric effect can convert mechanical energy into electrical energy, which has great application potential in wearable sensors and nanogenerators. Among the many components, the electrode is one of the most important components of wearable devices, and how to achieve high stretchability, high conductivity and more effective collection and transfer of induced charge generated is crucial.

[0003] The stretchable electrode is usually composed of conductive materials and high-stretch elastic polymers. Common conductive materials include graphene, carbon nanotubes, conductive polymers, silver nanowires, copper nanowires, metal nanoparticles, metal mesh, etc. Common high-stretch elastic polymers include polydimethylsiloxane (PDMS), polyurethane (PU), thermoplastic polyurethane (TPU), etc. There are huge differences in physical and chemical properties between the two materials, for example, the Young's modulus of gold is several tens of GPa, while the Young's modulus of PDMS is only a few MPa. The difference in relevant properties seriously affects the stretchability, mechanical stability and surface roughness of the stretchable electrode, thereby adversely affecting the piezoelectric output of the piezoelectric sensor. SUMMARY

[0004] The present application aims to provide a stretchable electrode and its preparation method and application to solve the problems existing in the prior art.

[0005] The stretchable electrode described in the present application comprises an elastic polymer layer and a piezoelectric polymer layer arranged in layers, and the piezoelectric polymer layer is embedded with a conductive network.

[0006] The preparation method of the stretchable electrode described in the present application comprises the following steps:

[0007] S1. The step of preparing a conductive network on a substrate;

[0008] S2. The step of filling the conductive network with piezoelectric polymer on the substrate to form a piezoelectric polymer layer;

[0009] S3. The step of covering the piezoelectric polymer layer with an elastic polymer layer;

[0010] S4. The step of peeling off the substrate.

[0011] The stretchable electrode described in the present application is applied to a piezoelectric pressure sensor.

[0012] The stretchable electrode and its preparation method and application described in the present invention have the advantages of not only improving the stretchability and surface roughness of the stretchable electrode, but also effectively improving the output characteristics of the piezoelectric device, and at the same time having the characteristic of easy patterning. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the structure of the stretchable electrode in the present invention.

[0014] Figure 2 It is a schematic diagram of the preparation process of the stretchable electrode described in the present invention.

[0015] Figure 3 is a scanning electron microscope image of the stretchable electrode described in the present invention.

[0016] Figure 4 is an atomic force microscope image of the stretchable electrode described in the present invention.

[0017] Figure 5 3 is a resistance change curve of the stretchable electrode under tensile strain in the present invention.

[0018] Figure 6 3 is an output response curve diagram of a piezoelectric pressure sensor using the stretchable electrode of the present invention and two comparative electrodes under an external force of 1N.

[0019] Reference numerals:

[0020] 101-elastic polymer layer, 102-piezoelectric polymer layer, 103-conductive network;

[0021] 201-base. DETAILED DESCRIPTION

[0022] like Figure 1 and Figure 2 As shown, the stretchable electrode described in the present invention includes a stacked elastic polymer layer 101 and a piezoelectric polymer layer 102, wherein the piezoelectric polymer layer 102 is embedded with a conductive network 103. The elastic polymer layer 101 can achieve high stretchability of the electrode and wrinkle-free adhesion to irregular surfaces. The piezoelectric polymer layer 102 is used to enhance the structure's ability to resist deformation, improve the stretchability of the stretchable electrode; and induce the collection of piezoelectric induced charges to improve the output characteristics of the piezoelectric device. The conductive network 103 is used to electrically connect the piezoelectric sensitive layer of the piezoelectric device to an external wire. It has broad application prospects in the fields of stretchable nanogenerators and stretchable piezoelectric tactile sensors.

[0023] The elastic polymer layer 101 is made of any one of polydimethylsiloxane, polyurethane, thermoplastic polyurethane, and styrene-ethylene-butylene-styrene block copolymer.

[0024] The material of the piezoelectric polymer layer 102 is any one of chitosan, polyvinylidene fluoride, poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride-hexafluoropropylene), polyacrylonitrile polylactic acid.

[0025] The material of the conductive network 103 is one or a combination of metal nanowires, carbon nanotubes, MXene, conductive polymer, conductive hydrogel.

[0026] Regarding the analysis of the mechanical performance improvement of the stretchable electrode: on the one hand, the conductive network 103 is uniformly embedded in the piezoelectric polymer layer 102, solving the problem of large roughness of the conductive network 103. The atomic force microscope is used to test the surface morphology of the electrode as shown in Figure 3 , the surface roughness is only 2.2 nm. On the other hand, the piezoelectric polymer layer 102 forms a double-layer structure with the elastic polymer layer 101, and the introduction of the piezoelectric polymer layer 102 as an interface transition layer solves the problem of interface mismatch between the conductive network 103 and the elastic polymer layer 101 due to the large difference in Young's modulus, greatly reducing the resistance change of the conductive network 103 in the stretched state. As shown in Figure 5 , the electrode has better mechanical stability, and even under a larger deformation, such as a tensile strain of 98.8%, the electrode can still ensure the conduction of the circuit. Figure 5 The resistance change ratio in the tensile strain and resistance change ratio curve of the electrode using only the elastic polymer layer 101 to stack the conductive network 103 without using the piezoelectric polymer layer 102 as Comparative Example 1, there is a clear eye of a hysteresis curve; while the electrode using the piezoelectric polymer layer 102 as a transition in the present embodiment, its curve can maintain good resistance change in the stretching and shrinking changes. The resistance change of the electrode in Comparative Example 1 has exceeded one time of the initial resistance when the tensile strain is 40%, and the resistance is too large after further stretching to be unsuitable for use as an electrode. In contrast, the resistance change of the electrode in the present embodiment reaches one time of the initial resistance when the tensile strain is almost 100%. By comparison, the introduction of the piezoelectric polymer layer 102 can significantly improve the mechanical performance.

[0027] Regarding the analysis of the improvement of the electrical performance of the stretchable electrode: the surface of the piezoelectric polymer layer 102 has abundant polar groups and unsaturated groups, when the piezoelectric sensitive layer of the piezoelectric device is subjected to external load to generate induced charge, the abundant polar groups and unsaturated groups are easy to produce ionization channels, improving the collection and transmission capacity of the induced charge. On the other hand, the piezoelectric polymer layer 102 is also made of piezoelectric material, when subjected to external load, the piezoelectric polymer layer 102 and the piezoelectric sensitive layer form a multi-layer piezoelectric series structure, thereby improving the output of the piezoelectric device.

[0028] When the stretchable electrode described in the present invention is used in a piezoelectric pressure sensor, it is electrically connected to the upper and lower sides of the piezoelectric sensitive layer to form an upper electrode and a lower electrode. Figure 6 As shown, a 1N tensile test was conducted on a piezoelectric pressure sensor with the same structure and parameters using three electrodes. These electrodes were: the electrode from Comparative Example 1, the conventional commercial PI / Cu electrode from Comparative Example 2, and the electrode from this embodiment. As can be seen by comparison, the output characteristics of the electrode from this embodiment are significantly superior to those of the other two comparative examples.

[0029] Those skilled in the art can understand from the inventive concept disclosed in the present invention that, in addition to being used in piezoelectric pressure sensors, the stretchable electrode can also be used in piezoelectric devices such as stretchable nanogenerators or stretchable piezoelectric tactile sensors.

[0030] like Figure 2 As shown, the method for preparing a stretchable electrode described in the present invention includes the following steps.

[0031] S1. Step of preparing a conductive network 103 on a substrate 201:

[0032] The glass substrate was cleaned with deionized water, isopropyl alcohol, and acetone, followed by drying in an 80°C oven. The surface of substrate 201 was hydroxylated using an O2 plasma treatment at 50 W for 1 minute. 10 μL of either octadecyltrichlorosilane (OTS) or tetradecyltrichlorosilane (TCS) was mixed with 10 mL of n-heptane. The piezoelectric polymer layer 102 was then immersed in the solution for 1 minute to modify the piezoelectric polymer layer. The layer was then removed and dried in a 60°C oven until ready for use.

[0033] a. When the conductive network 103 is made of metal nanowires, such as silver nanowires, the silver nanowires are spin-coated on the substrate 201 at a concentration of 10 mg / mL, a rotation speed of 2000 rpm, and a spin coating time of 20 seconds. After spin coating, the substrate is annealed at 100°C for 5 minutes, cooled naturally to room temperature, and patterned using photolithography to obtain a patterned silver nanowire conductive network.

[0034] b. When the conductive network 103 is made of carbon nanotubes, a carbon nanotube solution is spin-coated onto the substrate 201 at a concentration of 0.5 mg / mL and a rotation speed of 1000 rpm. The thickness of the carbon nanotube conductive network can be controlled by adjusting the number of spin-coating cycles. AZ5200NJ photoresist is spin-coated on the surface of the carbon nanotube conductive network and patterned using photolithography. The areas not covered by the photoresist are then etched away using oxygen plasma at an etching power of 100 W for 3-10 minutes to obtain the final carbon nanotube conductive network.

[0035] c. When the material of the conductive network 103 is one or more combinations of MXene, or conductive polymer, or conductive hydrogel, the person skilled in the art can use the known common knowledge to prepare the spin coating of the related material without paying creative labor and in the disclosed scheme of the spin coating process.

[0036] S2. The step of filling the conductive network 103 on the substrate 201 with a piezoelectric polymer to form a piezoelectric polymer layer 102:

[0037] a. When the material of the piezoelectric polymer layer 102 is chitosan, the spin coating speed is 7000 rpm, the spin coating time is 30 s, the curing temperature is 100℃, and the curing time is 1 min.

[0038] b. When the material of the piezoelectric polymer layer 102 is polyvinylidene fluoride, the spin coating speed is 2000 rpm, and the spin coating time is 30 s.

[0039] c. According to the known common knowledge in the art, the material of the piezoelectric polymer layer 102 can also be any one of poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride-hexafluoropropylene), polyacrylonitrile polylactic acid.

[0040] S3. The step of covering the elastic polymer layer 101 on the piezoelectric polymer layer 102:

[0041] a. When the material of the elastic polymer layer 101 is polydimethylsiloxane, the spin coating speed is 2000 rpm, the spin coating time is 30 s, the curing temperature is 100℃, and the curing time is 5 min.

[0042] b. When the material of the elastic polymer layer 101 is thermoplastic polyurethane, the spin coating speed is 2000 rpm, and the spin coating time is 30 s.

[0043] c. According to the known common knowledge in the art, the material of the elastic polymer layer 101 can also be any one of polyurethane, styrene-ethylene-butylene-styrene block copolymer,

[0044] S4. The substrate 201 is separated from the piezoelectric polymer layer 102 by mechanical peeling to obtain the target product.

[0045] For those skilled in the art, other various corresponding changes and modifications can be made according to the above described technical solutions and concepts, and all of these changes and modifications should belong to the protection scope of the claims of the present application.

Claims

1. A stretchable electrode, characterized in that: It comprises an elastic polymer layer (101) and a piezoelectric polymer layer (102) which are stacked, wherein the piezoelectric polymer layer (102) is embedded with a conductive network (103); The elastic polymer layer (101) is made of any one of polydimethylsiloxane, polyurethane, thermoplastic polyurethane, and styrene-ethylene-butylene-styrene block copolymer; The material of the piezoelectric polymer layer (102) is any one of chitosan, polyvinylidene fluoride, poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride-hexafluoropropylene), polyacrylonitrile and polylactic acid; The conductive network (103) is made of one or more combinations of metal nanowires, carbon nanotubes, MXene, conductive polymers, and conductive hydrogels.

2. A method for preparing a stretchable electrode according to claim 1, characterized in that: The following steps are involved: S1. a step of preparing a conductive network (103) on a substrate (201); S2. Filling the conductive network (103) with a piezoelectric polymer on the substrate (201) to form a piezoelectric polymer layer (102); S3. A step of covering the elastic polymer layer (101) on the piezoelectric polymer layer (102); S4. The step of peeling off the substrate (201).

3. The preparation method according to claim 2, characterized in that: Before preparing the conductive network (103), the surface of the substrate (201) is first subjected to a hydroxylation treatment and then subjected to a modification treatment.

4. The preparation method according to claim 2, characterized in that In the step S1, the conductive network (103) is patterned by photolithography.

5. The preparation method according to claim 2, characterized in that: The conductive network (103), the piezoelectric polymer layer (102) and the elastic polymer layer (101) are all prepared by spin coating.

6. Application of the stretchable electrode as claimed in claim 1 in a piezoelectric pressure sensor.

7. The application according to claim 6, characterized in that The piezoelectric pressure sensor is provided with the stretchable electrodes on both sides of the piezoelectric sensitive layer to form an upper electrode and a lower electrode; the piezoelectric polymer layer (102) of the upper electrode is electrically connected to the upper end surface of the piezoelectric sensitive layer, and the piezoelectric polymer layer (102) of the lower electrode is electrically connected to the lower end surface of the piezoelectric sensitive layer.

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