Flexible thermoelectric device for packaging liquid metal electrode and preparation method thereof

Abstract

The invention discloses a flexible thermoelectric device for packaging a liquid metal electrode and a preparation method thereof, and the preparation method comprises the steps: carrying out the blade coating of an elastic polymer material on a hard substrate, and carrying out the solidification to form a lower packaging layer; the lower packaging layer is coated with the elastic polymer material again in a blade coating mode, before solidification, the part, with the liquid metal electrode, of the flexible thermoelectric device naturally settles to the upper surface of the lower packaging layer under the action of gravity, then solidification is conducted to form an upper packaging layer, and packaging of the liquid metal electrode is achieved; and removing the hard substrate to obtain the flexible thermoelectric device for packaging the liquid metal electrode. According to the preparation method, controllable ultra-thin high-strength packaging of the liquid metal electrode can be realized, so that stability and reliability of a flexible device are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible devices, and in particular relates to a flexible thermoelectric device encapsulating liquid metal electrodes and a preparation method thereof. Background Art

[0002] Flexible electronic technology is a rapidly developing field in recent years, involving multiple applications such as wearable devices, electronic skin, soft robots, human-machine interfaces, and implantable devices. As a key component of flexible thermoelectric devices, flexible electrodes not only need to have excellent conductivity, but also need to have biocompatibility and a certain degree of stretchability to adapt to repeated stretching in applications on deformable surfaces such as skin.

[0003] Gallium-based liquid metal has unique properties such as high electrical conductivity, high thermal conductivity, low toxicity, environmental protection, and high fluidity, which makes it show broad application potential in many fields, especially in flexible, wearable, and repairable electronic devices as a stretchable electrode, which has been deeply studied.

[0004] The invention patent application with publication number CN111551291A discloses a method for manufacturing a liquid metal film electrode and a flexible pressure sensor, including: mixing two components of the elastomer dielectric layer in proportion, stirring and removing bubbles, dripping on a first carrier treated with a surfactant, and performing spin coating; heating the first carrier, pasting a conductive tape when the elastomer dielectric layer is not completely cured; spraying liquid metal on the elastomer dielectric layer to form a liquid metal electrode, and the liquid metal electrode is connected to the conductive tape; adding a shaped body to the elastomer dielectric layer with the liquid metal electrode to form a first liquid metal elastomer composite electrode, and after curing, separating the first liquid metal elastomer composite electrode from the first carrier. The present invention has high sensitivity and is not easily disturbed by the external environment.

[0005] At present, liquid metal electrodes are usually encapsulated with elastic polymers, such as the method disclosed in the above patent application, to solve the leakage problem during use. However, stretchable encapsulation elastomers often have low thermal conductivity, which will lead to large parasitic thermal resistance when used as the encapsulation layer of liquid metal. In some electronic devices (such as thermoelectric devices), the presence of this parasitic thermal resistance will greatly reduce the performance of the device.

[0006] A large number of studies have used material composite strategies to improve the thermal conductivity of the elastic packaging layer to reduce parasitic thermal resistance, but this will also greatly reduce the stretchability of the device and limit the application of flexible devices in areas with large skin deformation. Another effective way to reduce the parasitic thermal resistance of the package elastomer is to use an ultra-thin liquid metal packaging layer.

[0007] However, currently packaging is basically carried out by directly scraping or spraying high-strength elastic materials on liquid metal electrodes, which makes it difficult to achieve controllable ultra-thin and high-strength packaging; although liquid metal electrodes can be patterned on ultra-thin elastomers first and then integrated with functional components, it is difficult to achieve high-precision and high-conductive patterning of liquid metal on high-strength elastic materials, which will also bring great challenges to the subsequent packaging of the upper layer of liquid metal.

[0008] Therefore, the development of new, simple and easy controllable ultra-thin and high-strength packaging methods for liquid metal electrodes is of great significance for improving the stretchability, working performance, reliability and device consistency of flexible thermoelectric devices. Summary of the invention

[0009] The present invention provides a method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode. The method can achieve high-strength encapsulation of the liquid metal electrode, thereby achieving stability and reliability of the flexible device.

[0010] The present invention provides a method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode, comprising:

[0011] (1) applying an elastic polymer material on a hard substrate and curing the material to form a lower encapsulation layer;

[0012] (2) The elastic polymer material is scraped again on the lower packaging layer. Before curing, the part of the flexible thermoelectric device with the liquid metal electrode is naturally settled to the upper surface of the lower packaging layer under the action of gravity, and then cured to form an upper packaging layer to achieve the packaging of the liquid metal electrode. The hard substrate is removed to obtain a flexible thermoelectric device with encapsulated liquid metal electrodes.

[0013] The present invention first forms a lower packaging layer and an uncured upper packaging layer on a hard substrate so as to better control the thickness, thereby obtaining a thinner packaging material. Then, under the action of gravity, the part of the flexible thermoelectric device with the liquid metal electrode is naturally settled to the interface between the upper and lower packaging layers, thereby avoiding the influence of the liquid metal on the thickness of the packaging material and solving the technical problem in the prior art that the packaging material is scraped on the liquid metal, making the thickness of the packaging material uncontrollable.

[0014] The present invention adopts a scraping process to first solidify to form a thinner lower packaging layer, so that the liquid metal electrode part can be stably settled between the interfaces of the upper and lower packaging layers, and after solidification again, a higher strength packaging is achieved.

[0015] Preferably, the flexible thermoelectric device comprises P-type and N-type thermoelectric particles arranged alternately;

[0016] A top electrode is provided at one end of the P-type and N-type thermoelectric particles, and the P-type and N-type thermoelectric particles are connected by a set electrode at the other end;

[0017] The set electrode is cut off, and then liquid metal is coated on the set electrode in an acidic environment so that the gap formed by the cutting is reconnected, thereby forming a flexible thermoelectric device with liquid metal electrodes.

[0018] Preferably, the electrode coated with the liquid metal solution is naturally settled to the upper surface of the lower packaging layer under the action of gravity.

[0019] Preferably, the acidic solution is a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 1-10wt.%.

[0020] Preferably, the spacing between the gaps formed by cutting the electrodes is less than 0.1 mm.

[0021] Preferably, the liquid metal is gallium-based liquid metal.

[0022] Preferably, the polymer material is a thermoplastic elastomer, and the thermoplastic elastomer is polydimethylsiloxane, polyurethane, Ecoflex or styrene.

[0023] Preferably, the thickness of the lower packaging layer is less than 0.5 mm, and the thickness of the upper packaging layer is less than 2 mm. Since the packaging layer provided by the present invention has a relatively low thickness, the manufactured flexible thermoelectric device can have higher tensile properties and lower parasitic thermal resistance.

[0024] A specific embodiment of the present invention further provides a flexible thermoelectric device encapsulating a liquid metal electrode, which is prepared by the method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. First, the thickness of the upper and lower packaging layers is precisely controlled through a simple scraping process, and then the liquid metal electrode is packaged. This makes the thickness of the upper and lower packaging layers highly controllable, and the preparation of ultra-thin packaging layers can be achieved. The controllable packaging ensures device consistency, and the ultra-thin packaging ensures low parasitic thermal resistance and high stretchability.

[0027] 2. The natural sedimentation assisted by gravity allows the liquid metal electrode to fall exactly on the interface of the upper and lower packaging layers, that is, the surface of the lower packaging layer that is solidified first, so as to better control its packaging consistency. Moreover, since the upper and lower packaging layers are continuously scraped and coated, the interface between the two layers is clean and tidy, so there is no obvious interface between the upper and lower packaging layers after the two-step curing, which ensures the high-strength packaging of the liquid metal electrode and the stability and reliability of the flexible device. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart of a method for preparing a flexible thermoelectric device encapsulating liquid metal electrodes provided in a specific embodiment of the present invention;

[0029] Figure 2 The interface diagram of the upper and lower packaging layers provided in Example 1;

[0030] Figure 3 Schematic diagram of the flexible thermoelectric device prepared in Example 1 in twisted, bent and stretched states;

[0031] Figure 4 This is a graph showing changes in the internal resistance of the flexible thermoelectric device prepared in Example 1 under tensile and bending strains;

[0032] Figure 5 This is a device cycle test diagram of the flexible thermoelectric device prepared in Example 1 under tensile and bending strain;

[0033] Figure 6 The power generation output performance of the flexible thermoelectric device prepared in Example 1 under different temperature differences. DETAILED DESCRIPTION

[0034] A specific embodiment of the present invention provides a method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode, such as Figure 1 As shown, including:

[0035] (1) Scrape coating an ultra-thin lower encapsulation layer. Scrape a layer of ultra-thin highly stretchable elastic polymer material on a flat hard substrate, which serves as the lower encapsulation layer of the liquid metal electrode after curing.

[0036] The polymer material may be polydimethylsiloxane (PDMS), polyurethane, Ecoflex, styrene-based thermoplastic elastomer, etc., and the thickness of the lower packaging layer is less than 0.5 mm.

[0037] (2) Scraping the upper encapsulation layer: Scrape a layer of highly stretchable elastic polymer material on the solidified lower encapsulation layer without curing it first, as the upper encapsulation layer of the liquid metal electrode.

[0038] The polymer material is a stretchable elastic body that can form a strong connection with the lower packaging layer after curing, and the thickness of the upper packaging layer is less than 2 mm.

[0039] (3) Gravity-assisted packaging. The flexible thermoelectric device is first connected to the liquid metal electrode, and then before the upper packaging layer solidifies, the flexible device with the liquid metal electrode is placed on the upper packaging layer. Under the action of gravity, the flexible device naturally settles to the bottom, so that the liquid metal electrode just falls on the interface of the upper and lower packaging layers. The flexible thermoelectric device includes alternatingly arranged P-type and N-type thermoelectric particles; a top electrode is set at one end of the P-type and N-type thermoelectric particles, and an electrode is set at the other end, and the P-type thermoelectric particles and the N-type thermoelectric particles are connected through the set electrode; the set electrode is cut off, and then liquid metal is coated on the set electrode in an acidic environment, so that the gap formed by the cut is reconnected, thereby forming a flexible thermoelectric device with liquid metal electrodes.

[0040] (4) Finally, after the upper packaging layer is cured, the coating and packaging of the liquid metal electrode is completed. Since the upper and lower packaging layers are continuously scraped and coated, the interface between the two layers is clean and tidy, so there is no obvious interface between the upper and lower packaging layers that are cured successively, which ensures high-strength packaging and stable and reliable devices.

[0041] (5) Then, the hard substrate is removed to obtain a flexible thermoelectric device encapsulating a liquid metal electrode, wherein the liquid metal is a gallium-based liquid metal.

[0042] Example 1

[0043] One embodiment of the present invention is a gravity-assisted packaging method for liquid metal electrodes, and the steps of preparing a high-performance stretchable flexible thermoelectric device based on liquid metal electrodes are as follows:

[0044] (1) Scrape and coat the ultra-thin lower encapsulation layer. Select a flat glass sheet with a size of 10cm*10cm*0.1cm and use it as a hard substrate after ultrasonic cleaning with ethanol. Select highly stretchable Ecoflex 00-10 as the elastic polymer encapsulation material for liquid metal. After the AB components of Ecoflex 00-10 are mixed in a ratio of 1:1, it is evenly scraped on the hard glass sheet with a controllable height scraper. After heating at 80°C for 1 hour to solidify, a liquid metal lower encapsulation layer with a thickness of about 0.15mm is formed.

[0045] (2) Scrape coating the upper encapsulation layer. Use a scraper to scrape Ecoflex 00-10 with a thickness of about 1 mm on the lower encapsulation layer. Do not cure it first, as the upper encapsulation layer of the liquid metal electrode.

[0046] (3) Prepare thermoelectric devices with liquid metal electrodes. A 0.2 mm thick copper sheet is welded to one end of the alternating P-type and N-type thermoelectric particles as the upper electrode, and then a 0.1 mm thick gold-coated copper sheet is welded to the other side of the thermoelectric particles as a transition electrode. The electrode is cut in the middle to leave a small gap of 0.06 mm, and then gallium-based liquid metal is coated on the gold-coated copper sheet electrode in a hydrochloric acid solution with a concentration of 1-10%. The cut small gap is reconnected by liquid metal to form a flexible electrical path. The purpose of coating liquid metal in an acidic environment is to prevent the liquid metal from being oxidized in the atmospheric environment.

[0047] (4) Gravity-assisted packaging. Before the upper packaging layer is solidified, the thermoelectric device with the liquid metal electrode is placed on the upper packaging layer. Under the action of gravity, the thermoelectric device naturally settles to the bottom, so that the liquid metal electrode just falls on the interface of the upper and lower packaging layers. Finally, heat at 80°C for 1 hour to solidify the upper packaging layer to complete the coating and packaging of the liquid metal electrode. Since the upper and lower packaging layers are continuously coated with the same polymer material, the interface between the two layers is clean and tidy. Figure 2 As shown, there is no obvious interface between the upper and lower packaging layers that are solidified successively, which ensures high-strength packaging and stable and reliable devices. The hard substrate is removed to obtain a flexible thermoelectric device encapsulating liquid metal electrodes.

[0048] The present embodiment provides a performance test of a flexible thermoelectric device. Figure 3 Figures ab show the final constructed flexible thermoelectric device based on liquid metal electrodes, which can be twisted, bent and stretched to a large extent.

[0049] like Figure 4 As shown in a, even if the flexible thermoelectric device is stretched by 120%, the internal resistance of the device changes by less than 10%. Figure 4 As shown in b, the internal resistance does not change even if the bending radius is less than 2 mm.

[0050] like Figure 5 A and Figure 5 As shown in b, after more than 10,000 cycles of testing at 50% tensile strain and 7mm bending radius, the internal resistance of the device did not change significantly. The excellent bending and stretching resistance of this flexible thermoelectric device enables it to be stably and reliably used in large deformation scenarios such as skin and soft robots.

[0051] like Figure 6 As shown, due to the ultra-thin packaging of the liquid metal electrode reducing the parasitic thermal resistance, the constructed flexible thermoelectric device has a higher power generation output performance. When the temperature difference is greater than 30K, the device can output an open circuit voltage greater than 0.5V, and the maximum output power can reach more than 13mW. This output performance can meet the self-powering needs of many wearable electronic devices.

Claims

1. A method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode, characterized in that: include: (1) applying an elastic polymer material on a hard substrate and curing the material to form a lower encapsulation layer; (2) The elastic polymer material is scraped again on the lower packaging layer. Before curing, the part of the flexible thermoelectric device with the liquid metal electrode is naturally settled to the upper surface of the lower packaging layer under the action of gravity, and then cured to form an upper packaging layer to achieve the packaging of the liquid metal electrode. Then, the hard substrate is removed to obtain a flexible thermoelectric device encapsulating the liquid metal electrode.

2. The method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode according to claim 1, characterized in that: The flexible thermoelectric device includes P-type and N-type thermoelectric particles arranged alternately; A top electrode is provided at one end of the P-type and N-type thermoelectric particles, and an electrode is provided at the other end, and the P-type and N-type thermoelectric particles are connected through the provided electrodes; The set electrode is cut off, and then liquid metal is coated on the set electrode in an acidic environment so that the gap formed by the cutting is reconnected, thereby forming a flexible thermoelectric device with liquid metal electrodes.

3. The method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode according to claim 2, characterized in that: The electrode coated with the liquid metal solution is naturally settled to the upper surface of the lower packaging layer under the action of gravity.

4. The method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode according to claim 2, characterized in that: The acidic solution is a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 1-10wt.%.

5. The method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode according to claim 2, characterized in that: The spacing between the electrodes formed by cutting is less than 0.1 mm.

6. The gravity-assisted packaging method for liquid metal electrodes according to claim 2, characterized in that: The liquid metal is gallium-based liquid metal.

7. The method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode according to claim 1, characterized in that: The polymer material is a thermoplastic elastomer, and the thermoplastic elastomer is polydimethylsiloxane, polyurethane, Ecoflex or styrene.

8. The method for preparing a flexible thermoelectric device encapsulating a liquid metal electrode according to claim 1, characterized in that: The thickness of the lower packaging layer is less than 0.5 mm, and the thickness of the upper packaging layer is less than 2 mm.

9. A flexible thermoelectric device encapsulating a liquid metal electrode, characterized in that: The flexible thermoelectric device is prepared by the method for preparing a flexible thermoelectric device encapsulating liquid metal electrodes as described in any one of claims 1 to 8.

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