Flexible electrode based on liquid metal and preparation method thereof

Abstract

The invention discloses a flexible electrode based on liquid metal and a preparation method thereof. The method comprises the following steps: preparing a suspension containing the liquid metal and a solid conductive material; adding a polymer solution; spraying on a substrate through ultrasonic waves; wherein the melting point of the liquid metal is less than or equal to 50 DEG C. The flexible electrode provided by the invention has stretchability, and can realize relatively high conductivity under the condition of relatively low content of liquid metal. In addition, the electrode has the advantages of environment-friendly recovery, low liquid leakage risk, multiple kinetic energy, self-healing and the like. The preparation method provided by the invention can be used for preparing a planar electrode and a curved electrode, and is applied to a flexible capacitive sensor for monitoring stress, strain and non-contact fluid flow.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible electrodes and flexible capacitive sensors, and in particular to a liquid metal-based electrode and a preparation method thereof. Background Art

[0002] Electrodes made of traditional conductive materials (metal particles, carbon nanotubes, graphene) are limited in their application in smart wearable devices due to their high hardness, poor flexibility, large resistance change after stretching, and poor stability. In contrast, flexible electrodes have great potential in biomedicine, human-machine interface, intelligent robots, and human motion monitoring.

[0003] Liquid metal is a room temperature liquid conductor that has both the fluidity of liquid and the high conductivity of metal. It is widely used as a conductive filling material for flexible devices. However, liquid metal has poor compatibility with polymers and is prone to leakage. In addition, the density difference between polymers and liquid metals is large, resulting in severe sedimentation. Therefore, it is of great significance to improve the stability of flexible electrodes with liquid metal as the conductive material through process adjustment. Summary of the invention

[0004] In response to the above technical problems, the present invention provides a flexible electrode based on liquid metal and a preparation method thereof, which not only has good conductivity and can be recycled for a long time, but also has a simple preparation process and can be applied to flexible capacitive sensors for stress, strain and non-contact fluid flow.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In one aspect, the present invention provides a method for preparing a flexible electrode based on liquid metal, comprising the following steps:

[0007] (1) preparing a suspension containing liquid metal and solid conductive material;

[0008] (2) adding the polymer solution to the suspension of step (1);

[0009] (3) spraying the mixed system obtained in step (2) onto a substrate by ultrasonic spraying;

[0010] Wherein, the melting point of the liquid metal is ≤50°C.

[0011] As a preferred embodiment, in step (1), the liquid metal is a gallium indium tin (GaInSn) alloy; in some specific embodiments, the gallium indium tin (GaInSn) alloy has a Ga content of 68.5wt%, an In content of 21.5wt%, and a Sn content of 10wt%.

[0012] As a preferred embodiment, in step (1), the solid conductive material is selected from at least one of carbon nanotubes, graphene and carbon black;

[0013] Preferably, the carbon nanotubes are selected from at least one of hydroxylated multi-walled carbon nanotubes and carboxylated multi-walled carbon nanotubes;

[0014] And / or, the solvent of the suspension is selected from at least one of ethanol, water and N,N-dimethylformamide.

[0015] As a preferred embodiment, in step (1), in the suspension, the mass ratio of liquid metal to solid conductive material is 100 to 500:1.

[0016] In certain specific embodiments, the suspension is prepared by intermittent ultrasound; the total duration of the intermittent ultrasound is 30 to 100 minutes; wherein the ultrasound start time is greater than the ultrasound pause time; the ultrasound power is 150 to 1000 W; and the ultrasound temperature is 0 to 50°C.

[0017] As a preferred embodiment, in step (2), the polymer is selected from at least one of polyvinyl pyrrolidone, polyurethane and polyvinyl alcohol;

[0018] In some specific embodiments, the polymer solution is an ethanol solution of aqueous polyurethane, and the solid content of the aqueous polyurethane is 20% to 50%.

[0019] As a preferred embodiment, in the mixed system obtained in step (2), the mass ratio of the polymer to the liquid metal is 0.15 to 0.75:1;

[0020] In certain specific embodiments, in step (2), the polymer solution is added to the suspension of step (1) and stirred for 6 to 24 hours to mix evenly.

[0021] As a preferred embodiment, in step (3), the liquid supply rate of the ultrasonic spraying is 0.05 to 0.5 mL / min;

[0022] And / or, the ultrasonic spraying is performed 10 to 200 times;

[0023] And / or, the spraying interval of the ultrasonic spraying is 0.01 to 2 mm;

[0024] And / or, the ultrasonic spraying is cross spraying;

[0025] And / or, the spraying height of the ultrasonic spraying is 10 to 100 mm;

[0026] And / or, the spraying power of the ultrasonic spraying is 1-25W.

[0027] In some specific embodiments, the substrate is prepared from an elastomer; the elastomer is selected from any one of polyurethane, polydimethylsiloxane (PDMS) and nitrile rubber.

[0028] In some specific embodiments, a stretching sintering step is further included; preferably, the stretching sintering is uniaxial stretching sintering, and the liquid metal nanodroplets can be broken by the stretching sintering to form a conductive path and complete the connection of the conductive path.

[0029] In another aspect, the present invention provides a flexible electrode obtained by the above preparation method.

[0030] The above technical solution has the following advantages or beneficial effects:

[0031] The present invention prepares a flexible electrode with uniform thickness, low liquid metal content and high conductivity by ultrasonic spraying a non-sedimentation conductive slurry containing liquid metal and polymer solution. The polymer liquid can increase the adhesion of the electrode material to the substrate, and the liquid metal mass fraction of 82.4% can achieve lower resistance, which better meets the requirements of low cost and simple process for preparing flexible electrodes.

[0032] When hydroxylated carbon nanotubes are used as nanofillers in the present invention, since the hydroxylated carbon nanotubes have hydroxyl groups on their surfaces, some of the hydroxyl groups on the surfaces of the hydroxylated carbon nanotubes can interact with liquid metals, allowing liquid metal nanodroplets to adhere to the surfaces of the hydroxylated carbon nanotubes, thereby helping to reduce leakage and sedimentation of the liquid metal and increase the conductivity, stability and uniformity of the flexible electrode.

[0033] The preparation method provided by the present invention has the possibility of industrial production due to its low liquid metal content, simple preparation process, easy acquisition of raw materials, and easy regulation of the formula. It can prepare planar electrodes and curved electrodes and has potential application value in the fields of flexible electronics, flexible sensors, and electromagnetic shielding, especially flexible capacitive sensors, which can detect stress, strain, flow, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a graph showing the stability test results of the conductive paste prepared in step (2) of Examples 7-8 of the present invention.

[0035] Figure 2 It is a physical picture of the flexible electrode prepared by using substrates of different materials in Example 6 of the present invention and a resistance test result picture.

[0036] Figure 3 1 is a graph showing the resistivity test results of flexible electrodes prepared with different amounts of liquid metal added in Examples 1-6 of the present invention.

[0037] Figure 4 The capacitance-time diagram of the interdigital electrode prepared by the preparation method in Example 6 of the present invention during the detection of the movement of the human index finger.

[0038] Figure 5 This is a test result diagram of the flow rate and liquid level of a sodium chloride aqueous solution detected by using an interdigital electrode prepared by the preparation method in Example 6 of the present invention. DETAILED DESCRIPTION

[0039] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0040] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0041] In the following embodiments:

[0042] Waterborne polyurethane (WPU) was purchased from Meisheng Plastics Co., Ltd. with a solid content of 30±1%.

[0043] The liquid metal is a gallium indium tin (GaInSn) alloy, and its composition is: 68.5wt% gallium, 21.5wt% indium, and 10wt% tin.

[0044] Hydroxylated multi-walled carbon nanotubes were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with an inner diameter of 5-10 nm, an outer diameter of 30-50 nm, and a length of 10-20 μm.

[0045] Example 1

[0046] The method for preparing the flexible electrode based on liquid metal in this embodiment includes the following steps:

[0047] (1) adding 1.25 g of liquid metal to 15 mL of ethanol and 5 mg of hydroxylated multi-walled carbon nanotubes in an ultrasonic cell disruptor for 60 min at a power of 630 W, on for 1 second and off for 2 seconds, to obtain a mixed suspension of liquid metal and hydroxylated multi-walled carbon nanotubes;

[0048] (2) adding 15 mL of ethanol and 1.25 g of WPU to the mixed suspension, stirring at 1000 rpm on a stirring table for 24 h to obtain an aqueous conductive slurry containing liquid metal;

[0049] (3) Inject the aqueous conductive slurry into the ultrasonic spray system syringe, the spraying mode is cross spraying, the spraying times are set to 100 times, the liquid supply rate is 0.1 mL / min, the ultrasonic power is 3.5 W, the thermoplastic polyurethane elastomer substrate is placed on the spraying table, the spraying height is 50 mm, the spraying interval is 1 mm, and spraying begins on the thermoplastic polyurethane elastomer substrate;

[0050] (4) The sprayed substrate is subjected to uniaxial stretching and sintering with a stretching parameter of 200% and stretched 100 times to obtain a flexible electrode.

[0051] Example 2

[0052] The preparation process of the liquid metal-based flexible electrode in this embodiment is the same as that in Embodiment 1, except that in step (1), the amount of liquid metal added is 1.50 g.

[0053] Example 3

[0054] The preparation process of the liquid metal-based flexible electrode in this embodiment is the same as that in Embodiment 1, except that in step (1), the amount of liquid metal added is 1.75 g.

[0055] Example 4

[0056] The preparation process of the liquid metal-based flexible electrode in this embodiment is the same as that in Embodiment 1, except that in step (1), the amount of liquid metal added is 2.00 g.

[0057] Example 5

[0058] The preparation process of the liquid metal-based flexible electrode in this embodiment is the same as that in Embodiment 1, except that in step (1), the amount of liquid metal added is 2.25 g.

[0059] Example 6

[0060] The preparation process of the liquid metal-based flexible electrode in this embodiment is the same as that in Embodiment 1, except that in step (1), the amount of liquid metal added is 2.50 g; and in step (3), the sprayed flexible substrates are thermoplastic polyurethane elastomer substrates, nitrile rubber substrates and silicone rubber substrates, respectively.

[0061] Example 7

[0062] The preparation process of the liquid metal-based flexible electrode in this embodiment is the same as that in Example 1, except that in step (1), the amount of liquid metal added is 0.50 g, and WPU is not added in step (2); and there are no steps (3) and (4).

[0063] Example 8

[0064] The preparation process of the liquid metal-based flexible electrode in this embodiment is the same as that in Embodiment 1, except that in step (1), the amount of liquid metal added is 0.50 g, and there are no steps (3) and (4).

[0065] Performance Test:

[0066] Figure 1 The stability test results of the aqueous conductive paste prepared in step (2) of Examples 7-8 are shown in Figures (a) and (b) respectively show the conductive paste in Example 7 after being placed for 1 day and 20 days, and it can be found that the liquid metal has completely settled; Figures (c) and (d) show the conductive paste in Example 8 after being placed for 1 day and 20 days, and it can be found that the liquid metal has not shown obvious sedimentation.

[0067] Figure 2 The actual picture of the flexible electrode obtained by using different flexible materials as the spraying substrate in Example 6 and the resistance test results are shown. It can be seen from the figure that the water-based conductive paste in the present invention has good compatibility with the thermoplastic polyurethane elastomer and the nitrile rubber, and there is no de-adhesion phenomenon after sintering, and it has good conductivity and compliance. In addition, after the liquid metal suspension is sprayed on the silicone rubber substrate and stretched and sintered, the flexible electrode layer falls off, but the conductivity and flexibility of the flexible electrode layer are still good, which shows that the flexible electrode layer can be used as an electrode alone.

[0068] Figure 3 The resistivity test diagram of the flexible electrodes prepared in Examples 1-6 with different liquid metal addition amounts. Figure 3 It can be seen from the figure that the flexible electrode prepared in the embodiment of the present invention has a lower sheet resistance, and as the liquid metal content decreases, the sheet resistance decreases.

[0069] Figure 4 In order to prepare the interdigital electrode using the preparation process in Example 6 using the mask, the capacitance-time diagram during the movement of the human index finger was detected, and it was found that the capacitance increased when the finger was bent. This is because when the finger was bent, the thermoplastic polyurethane elastomer substrate layer was squeezed and the thickness was reduced, resulting in an increase in capacitance.

[0070] Figure 5 In order to use the mask to prepare the interdigitated electrodes using the preparation process in Example 6, the flow rate and liquid level of the sodium chloride aqueous solution were detected (in this test, a small amount of indigo was added for easy observation). The test results show that the capacitance value decreases linearly when the valve is opened, and when the liquid flows out, the capacitance increases again, but cannot return to the initial value. This is because the dielectric layer changes from water to air, and the capacitance value decreases.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a flexible electrode based on liquid metal, characterized in that: The following steps are involved: (1) preparing a suspension containing liquid metal and solid conductive material; (2) adding the polymer solution to the suspension of step (1); (3) spraying the mixed system obtained in step (2) onto a substrate by ultrasonic spraying; Wherein, the melting point of the liquid metal is ≤50°C.

2. The preparation method according to claim 1, characterized in that: In step (1), the liquid metal is a gallium-indium-tin alloy.

3. The preparation method according to claim 1, characterized in that: In step (1), the solid conductive material is selected from at least one of carbon nanotubes, graphene and carbon black; And / or, the solvent of the suspension is selected from at least one of ethanol, water and N,N-dimethylformamide.

4. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of the liquid metal to the solid conductive material in the suspension is 100 to 500:

1.

5. The preparation method according to claim 1, characterized in that: In step (1), the suspension is prepared by intermittent ultrasonic preparation.

6. The preparation method according to claim 1, characterized in that: In step (2), the polymer is selected from at least one of polyvinyl pyrrolidone, polyurethane and polyvinyl alcohol.

7. The preparation method according to claim 1, characterized in that: In the mixed system obtained in step (2), the mass ratio of the polymer to the liquid metal is 0.15 to 0.75:

1.

8. The preparation method according to claim 1, characterized in that: In step (3), the liquid supply rate of the ultrasonic spraying is 0.05 to 0.5 mL / min; And / or, the ultrasonic spraying is performed 10 to 200 times; And / or, the spraying interval of the ultrasonic spraying is 0.01 to 2 mm; And / or, the ultrasonic spraying is cross spraying; And / or, the spraying height of the ultrasonic spraying is 10 to 100 mm; And / or, the spraying power of the ultrasonic spraying is 1-25W.

9. The preparation method according to claim 1, characterized in that: Step (3) also includes a stretching and sintering step after spraying.

10. A flexible electrode obtained by the preparation method according to any one of claims 1 to 9.

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