EP4740715A1

EP4740715A1 - An electroactive polymer-based device and method for manufacturing

Info

Publication number: EP4740715A1
Application number: EP24736828.5A
Authority: EP
Inventors: Zihang XU; Kai Wu; Zepeng LV; Aurore Claverie; Emmanuel TAINE; Peter MORSHUIS
Original assignee: Single Buoy Moorings Inc
Current assignee: Single Buoy Moorings Inc
Priority date: 2023-07-03
Filing date: 2024-07-02
Publication date: 2026-05-13
Also published as: WO2025008336A1; CN121753523A

Abstract

The present application shows an electroactive polymer, EAR, based device (10, 20) including: a dielectric layer (13, 23) arranged between two electrode layers (12, 14), the dielectric layer (13, 24) consisting of a stretchable material, the two electrode layers (12, 14) including a carbon based conductive material and a solid state oxidant material forming stretchable layers, the EAP-based device further including an additional dielectric layer (11, 15) of the stretchable material arranged on each of the two electrode layers (11, 13), and configured together with the dielectric layer (13, 23) to seal each of the two electrode layers (12, 14) therein.

Description

An electroactive polymer-based device and method for manufacturing

Field of the invention

The invention relates to an electroactive polymer-based device. The invention further relates to a method of manufacturing an EAP-based device, use of such a device and a method of self-clearing such a device.

Background

Electro-mechanical energy conversion systems using an electroactive polymer (EAP) based device are for example disclosed in WO2010/146457.

Such an EAP-based device comprises a dielectric elastomer layer. On the surfaces of the dielectric elastomer layer, electrode layers are arranged. The EAP-based device can be considered as a variable capacitor of which the capacitance changes as a function of an amount of deformation exerted on a layer of EAP material. Due to an external force the electroactive polymer material can be stretched which causes that a distance between the electrode layers decreases. The distance increases again when the external force diminishes and the electro-active polymer layer relaxes.

By applying electrical charges on the electrode layers at substantially the maximal deformation and removing the electrical charges at minimal deformation, energy can be harvested from the EAP-based device.

Electrode layers made of metal show plastic deformation and cracking at relatively low stretch rates of the elastomer carrier layer and deteriorate strongly during a relatively low number of stretching cycles. For this reason, carbon-based electrodes which show enhanced stretching properties have emerged as candidates to manufacture EAP-based device layers.

However, despite the enhanced stretching properties of the carbon-based electrodes, local defects, such as air bubbles or contamination, may be present in the dielectric layer forming small openings or thinned regions. When exposed to an electrical field, a dielectric breakdown will occur at low field strengths, causing a pinhole defect across the thickness of the dielectric layer and above all a shortcut, so that the EAP-based device is no more operational to harvest energy. Therefore the device fails at a time that is much shorter than the design lifetime

It is therefore an object of the present invention to provide an EAP-based device with carbon based electrode layers having an improved lifetime and electrical performance during exposure to mechanical cycling with relatively high deformation. Summary of the invention

According to a first aspect of the invention, an EAP-based device is disclosed, the EAP-based device comprising: a dielectric layer arranged between two electrode layers, the dielectric layer consisting of a stretchable material, the two electrode layers comprising a carbon based conductive material and a solid state oxidant material forming stretchable layers, the EAP-based device further comprising an additional dielectric layer of the stretchable material arranged on each of the two electrode layers, and configured together with the dielectric layer to seal each of the two electrode layers therein. The EAP-based device of the invention comprises composite electrode layers made of a strong oxidant and a carbon material which offer both stretchability and an excellent conductivity. Each dielectric layer of the EAP-based device is also stretchable and is surrounded by one electrode layer at each side, forming a stack alternating dielectric layer and electrode layer, so as to form a capacitor. Thanks to their high conductivity and stretchability, the electrodes will efficiently conduct current, and be capable of repetitive stretching together with the dielectric layers. The EAP-based device may therefore be used in a variety of flexible electronic components, such as actuators or sensors, as well as electrical equipment. When connected to power electronics the EAP- based device can be used as a variable capacitor to harvest energy.

Furthermore, the electrode layers of the EAP-based device comprise solid state oxidant, which makes them capable of self-clearing. When an electrical breakdown occurs, the electrode layers comprising the oxidant will decompose and thereby will isolate the area from the current and generate the clearing of the electrode in the breakdown area: the oxygen integrated in solid status in the electrode will be vapourised by the energy delivered by the breakdown and will react with carbon material of the electrode layer to form carbon oxidated molecules. The volume of electrode layer nearing a damaged section of the dielectric layer is thereby cleared up, insulating the short-circuited section from the rest of the EAP-based device. The EAP-based device of the invention will hence quickly return to a working state. The oxygen present in the oxidant can only interact with the electrode layers at breakdown, when it is released by the energy created by the breakdown from the electrode layers themselves as otherwise the electrode layers are sealed from the ambient air by the dielectric layers. The device which can complete self-clearing is therefore provided with an increased lifetime and is operable at high electric fields.

In an embodiment the EAP-based device further comprises an encapsulant sealing the electrode layers and the dielectric layer from ambient air. By provision of an encapsulant, any contact with ambient air is minimized before breakdown, where the electrode layers are provided a substantially free, preferably oxygen-free environment. Therefore it is ensured that the electrode layers have no contact with air before breakdown which improves the self-clearing.

In an embodiment, the encapsulant is made of a polymer material, such as silicone (polysiloxane), epoxy or polyurethane. Polymer material, and in particular silicone, as an outer layer, provides superior protection to the EAP-based device against shock and stress. Furthermore, silicone may withstand extreme temperatures way above 200 degrees C and as low as -60 degrees C without deforming. The EAP-based device is adaptable to a variety of environments.

In an embodiment, the electrode layers and the dielectric layer are encapsulated under vacuum or under nitrogen ambient. The layers may as well be encapsulated under an overpressure of nitrogen. By providing the electrode stack an oxygen-depleted atmosphere within the encapsulant, control of the self-clearing process is enhanced, where there is no partial pressure of oxygen in the EAP-based device before dielectric breakdown occurs.

In an embodiment, the carbon based conductive material is mixed with the solid state oxidant material. Rather than comprising a surface layer of a oxidant, composite electrode layers comprising a mixture of the oxidant and the carbon based conductive material promote release of oxygenated components and vaporisation of the electrode layers resulting in an isolated area where the breakdown occurred.

In an embodiment, the solid state oxidant material comprises one or more compounds selected from: a group comprising: permanganate, nitrate, dichromate, perborate, and chlorate. Selection of one or more of the solid state oxidant materials for manufacturing the electrode layer will allow sufficient decomposition of the electrode layer at dielectric breakdown with no need for an additional energy input.

In an embodiment, the solid state oxidant material comprises sodium or potassium as cation of the one or more compounds. For instance, potassium nitride (KNO3) with a concentration equal to or lower than about 10 wt% in the electrode layer provides for self-clearing of the EAP-based device in a substantially oxygen- depleted environment. In an embodiment the concentration does not exceed about 10wt% and the electrode layer has a thickness under about 5 microns.

In an embodiment, the EAP-based device further comprises at least one stack alternating an electrode layer comprising the carbon based conductive material and the solid state oxidant material and a dielectric layer of the stretchable material on at least one of the additional dielectric layers, the dielectric layer of the stack configured together with the additional dielectric layers to seal the electrode layer of the stack therein. Such a device in a multi-layer configuration provides for a plurality of capacitors connected in parallel and therefore allows for an increased harvest of energy while maintaining self-clearing properties.

In an embodiment, the carbon based conductive material of the electrode layers comprises nanoparticles of at least one of carbon black material, such as single-wall carbon nanotube material, multi-wall carbon nanotube material or graphene material. Such carbon-based conductive materials could provide electrode patterns including at least one of a film electrode, linear electrode, or mesh electrode providing high flexibility to the electrode layer, and enhanced deformability. In an embodiment, the stretchable material of the dielectric layer is selected from a group comprising silicone, rubber, thermoplastic polyurethane (TPU). Such dielectric layers provide high stretchability, stability, reliability and tolerance to high temperatures.

In an embodiment, the electrode layers further comprise an additive, such as a silane-based coupling agent. An example of suitable silane-based coupling agent is 3-Aminopropyltriethoxysilane.The additive provides enhanced adhesion of an electrode layer to the dielectric layers, and improves the mechanical homogeneity of the composite electrode layer.

According to a second aspect of the invention, a method for manufacturing an electroactive polymer, EAP, based device is disclosed, the method comprising: providing in a processing volume two or more dielectric layers consisting of a stretchable material; arranging an electrode layer made of a carbon based conductive material on at least one of the two or more dielectric layers wherein the electrode layer comprises a carbon based conductive material, covering an exposed surface of at least one of the electrode layers with another dielectric layer made of the stretchable material, adding a solid state oxidant material to the carbon based conductive material of the electrode layers; while the electrode layers are being arranged on at least one of the two or more dielectric layers, the method characterized in that it further comprises: maintaining a substantially oxygen free atmosphere or vacuum in the processing volume and configuring the dielectric layers to seal one of the electrode layers therebetween. By having the oxidant introduced into the carbon material, a self-clearing electrode layer with high conductivity and compliance is provided.

In an embodiment the step of arranging the electrode layer on at least one of the two or more dielectric layers comprises spraying a carbon-based dispersion solution comprising the solid state oxidant and an additive on the at least one dielectric layer, the additive promoting adhesion of the electrode layer to the at least one dielectric layer. By utilizing spraying, (composite) electrode layers of a thickness of less than one micron can be manufactured. Thin electrode layers allow to achieve optimal electrode resistivity, in the range of a few hundred ohms. The dispersion solution can be easily prepared from powder or flakes of carbon-based material diluted in a solvent, to which the oxidant is further added and dissolved. The mixture is evenly stirred to obtain a mixed electrode dispersion solution containing the oxidant. The electrode dispersion is evenly covered on one side of a dielectric substrate until the solution evaporates. In the process of solvent evaporation carbon/oxidant composite electrodes with uniformly distributed oxidants are formed. Such fabrication of the composite electrode is simple and easy to control. In so doing, carbon/oxidant composite electrodes with uniformly distributed oxidants may be formed. Finally adhesion of the electrode layers to the dielectric layers is improved.

According to a third aspect of the invention, use of a EAP-based device as described in the first aspect, or as manufactured according to the second aspect is disclosed. In particular, the stacked electroactive polymer comprises deformable dielectric and oxygenated electrode may be used in a power converter system, to convert the mechanical energy of parts that repeatedly move back and forth to useful electricity wherein the EAP-based device is coupled to a power extraction unit. Thanks to its deformability the electrode may be used in the form of a sheet, or wound into a spiral. For example, such a power converter system relates to a wave energy converter.

According to a fourth aspect of the invention, a method of self-clearing a EAP-based device according to the first aspect, or manufactured according to the third aspect is disclosed, the method comprising releasing gaseous oxygen from the electrode layers into the sealed space of the EAP-based device formed by the encapsulant, generating for example oxygen based components as carbon dioxide and/or carbon monoxide by reaction of the released gaseous oxygen with the carbon-based material of the electrodes. Oxygen participates in the self-clearing process. The successful completion of self-clearing in carbon based electrodes requires oxygen and generates the combustion. This allows a successful isolation of the dielectric area damaged during the breakdown and allows to continue to operate the system. The repeatability of the self-clearing process is also guaranteed.

Brief description of the drawings

An embodiment of a EAP-based device, and methods of making and using such electrode will by way of non-limiting example be described in detail with reference to the accompanying drawings. In the drawings:

Figure 1 shows a cross-sectional view of a conventional electro-active polymer structure in both a strained (continuous line) and unstrained state (dashed contour line) during application of a voltage.

Figure 2 shows a schematics illustrating a problem of the prior art in use of a conventional electro-active polymer structure.

Figure 3A shows a cross-sectional view of an electro-active polymer-based device according to the invention.

Figure 3B shows a cross-sectional view of an electro-active polymer-based device according to the invention.

Figure 4 shows a flowchart of a method of manufacturing an electro-active polymer-based device according to the invention.

Figure 5A schematically illustrates chemical processes at dielectric breakdown in the EAP-based device according to the invention.

Figure 5B schematically illustrates self-clearing of the EAP-based device according to the invention. The electrodes and features thereof are shown schematically and not drawn to scale. The figures are for illustrative purposes only, and do not serve as restriction of the scope as laid down by the claims. In the drawings, identical or similar elements are indicated by the same reference sign or number.

Detailed description of the invention

Figure 1 shows a cross-sectional view of a conventional electro-active polymer layer structure 1 in both a strained (continuous line) and unstrained state (dashed contour line) under the application of a voltage (not shown). The structure 1 comprises a dielectric elastomer layer 3 sandwiched in between two electrode layers 2, 4 of a stretchable material. The electro-active polymer layer structure can function as a variable capacitor. If a deformation F is applied to the electro-active polymer layer structure 1 in a direction included in the plane of the layers , the dielectric elastomer layer 3 is stretched and the electrodes 2, 4 are forced to follow the stretched dielectric elastomer, so the dielectric and electrodes are in a strained state and the thickness of the electrode decreases.

Figure 2 schematically illustrates a problem of the prior art regarding use of a conventional electro-active polymer layer structure 1 , as a variable capacitor. The illustrated electro-active polymer structure 1 comprises a bulk volume VDEFECT which contains defect as for example defect 5 in the dielectric elastomer layer 3. While the structure 1 is strained and unstrained, a voltage V is applied between the two electrodes 2, 4 to accumulate positive charges + or negative charges - in the dielectric layer near the electrodes 2, 4 connected to power electronics. An electric field E which depends on the separation distance d between the electrodes (E has a magnitude that equals a ratio of V to d) may exceed the dielectric strength of the material at a small separation distance d in the strained state or at high applied voltage V. In this case, an electric discharge A is created in the defect bulk volume VDEFECT where the layer structure subject to the discharge melts or vaporizes. A pinhole P is created through the thickness of the structure, damaging the material, which creates a path for short-circuit current affecting the capacitance of the structure.

Figure 3A shows a cross-sectional view of an EAP-based device 10 according to the invention. The EAP- based device 10 comprises three electrode layers 12, 14, 16 and four dielectric layers 11 , 13, 15, 17. Together with the dielectric layers the electrode layers form a stack where the electrode layers are positioned on opposite surfaces of the dielectric layers. Both the electrode layers and dielectric layers are made from stretchable material, so that they can be repetitively strained and unstrained without breakage and/or plastic deformation. In particular electrode layers are made from a carbon-based conductive material, further comprising a solid state oxidant. The dielectric layers 11 , 13, 15, 17 placed around the electrode layers 12, 14, 16 seal the electrode layers from ambient air. In another embodiment, the layers 16, 17 (shown as dashed lines) are optional or the device comprises further stacks of layers identical to layers 16, 17 on either side of the EAP-based device, where each electrode layer is sealed from the ambient air by two dielectric layers surrounding it.

Figure 3B shows a cross-sectional view of an EAP-based device 20 according to another embodiment of the invention. The EAP-based device 20 comprises two electrode layers 12, 14 and three dielectric layers 11 , 13, 15. The EAP-based device further comprises an encapsulant 18. Together with the dielectric layers the electrode layers form a stack where the electrode layers are positioned on opposite surfaces of the dielectric layers. Both the electrode layers and dielectric layers are made from stretchable material, so that they can be repetitively strained and unstrained without breakage and/or plastic deformation. In particular electrode layers are made from a carbon-based conductive material, further comprising a solid state oxidant. The dielectric layers 11 , 13, 15 placed around the electrode layers 12, 14 seal the electrode layers from ambient air. The encapsulant 18 seals the stack of dielectric and electrode layers and ensures a substantially oxygen free environment. In another embodiment, the EAP-based device may comprise further layers as layers 16, 17 of Fig. 3A. In any case the stack always alternates dielectric layer and electrode layer where each electrode layer is sealed from the ambient air by two dielectric layers surrounding it within encapsulant 18.

Figure 4 shows a flowchart 100 of a method of manufacturing a EAP-based device according to the invention. A carbon material dispersion is prepared in a first step 101. For this, an aqueous dispersion of solid carbon material in the form of powder or flakes may be diluted in a solvent, such as deionized water. Optionally, the mixture is thereafter ultrasonically stirred. In step 102 a certain amount of solid oxidant is weighed and added to the dispersion solution. Optionally an additive, such as a silane-based coupling agent may be added to the dispersion solution. In step 103 the newly formed dispersion solution is mixed evenly. In step 104 the dispersion is evenly covered on one or both sides of a dielectric layer and the solvent evaporated thereafter in step 105. In step 104 the dispersion may be coated on the dielectric layer by means of spraying or screen-printing. Other techniques known to the person skilled in the art for coating the dielectric layer fall within the scope of the invention. In the process of solvent evaporation, the oxidant gradually precipitates and is wrapped by carbon. In step 106 the electrode layer is covered by a dielectric layer deposited onto the electrode layer which seals the electrode layer from ambient air. The stack may also be encapsulated to ensure a substantially oxygen-free atmosphere.

Figure 5A schematically illustrates chemical processes at dielectric breakdown in the EAP-based device 10 according to the invention. Although only the EAP-based device 10 shown in Fig. 3A is illustrated, the same chemical processes will occur in an EAP-based device 20 illustrated in Fig. 3B. The same will also apply to EAP-based devices of the invention with further layers, each electrode layer of the further layers being positioned between two dielectric layers and sealed from ambient air. Under exposure to an electric field E that exceeds the dielectric strength of the dielectric layer, sparks or electric arc A form a pinhole P throughout the thickness of the dielectric layer. The electrode layers made of a composite material comprising an oxidant release oxygen in gaseous form under the effect of heat. Carbon material of the electrode layers reacts with the gaseous oxygen to form carbon monoxide CO and/or carbon dioxide CO2. CH4 may also be released. Figure 5B schematically illustrates self-clearing of a EAP-based device according to the invention, where as a result of the release of oxygen part of the electrode volume VELEC (shown as a dashed line) of electrode layer 12 near the pinhole in the dielectric layer through layers 11 , 13 has vaporized. The released gases of Fig. 5A are not shown on this figure for matter of clarity. Damaged parts of the dielectric layer at the pinhole P are thereby electrically insulated from the rest of the bulk of the EAP-based device and the EAP-based device capable to return to a working state.

The invention has been described with reference to the preferred embodiment. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims.

Claims

1 . An electroactive polymer, EAP, -based device (10, 20) comprising: a dielectric layer (13, 23) arranged between two electrode layers (12, 14), the dielectric layer (13, 23) consisting of a stretchable material, the two electrode layers (12, 14) comprising a carbon based conductive material and a solid state oxidant material forming stretchable layers, the EAP-based device further comprising an additional dielectric layer (11 , 15) of the stretchable material arranged on each of the two electrode layers (11 , 13), and configured together with the dielectric layer (13, 23) to seal each of the two electrode layers (12, 14) therein.

2. The EAP-based device according to claim 1 , further comprising an encapsulant (18) sealing the electrode layers (12, 14) and the dielectric layer (13, 23) from ambient air.

3. The EAP-based device according any one of the preceding claims, wherein the carbon based conductive material is mixed with the solid state oxidant material.

4. The EAP-based device according to any one of the preceding claims, wherein the solid-state oxidant material comprises an oxygen-containing compound.

5. The EAP-based device according to any one of the preceding claims, wherein the solid state oxidant material comprises one or more compounds selected from: a group comprising: permanganate, nitrate, dichromate, perborate, and chlorate.

6. The EAP-based device according to claim 5 or claim 5, wherein the solid state oxidant material comprises sodium or potassium as cation of the one or more compounds.

7. The EAP-based device according any one of the preceding claims, wherein the solid state oxidant material has a concentration equal to or lower than 10wt% in the electrode layer, the electrode layer having a thickness below 5 microns.

8. The EAP-based device according to any one of the preceding claims, further comprising at least one stack alternating an electrode layer (16) comprising the carbon based conductive material and the solid state oxidant material and a dielectric layer (17) of the stretchable material on at least one of the additional dielectric layers (11 , 15), the dielectric layer (17) of the stack configured together with the additional dielectric layers (11 , 15) to seal the electrode layer (16) of the stack therein.

9. The EAP-based device according to any one of the preceding claims, wherein the carbon based conductive material of the electrode layer (12, 14, 16) comprises nanoparticles of at least one of carbon black material, single-wall carbon nanotube material, multi-wall carbon nanotube material and graphene material.

10. The EAP-based device according to any one of the preceding claims, wherein the stretchable material of the dielectric layers (11 , 13, 15, 17) is selected from a group comprising silicone, rubber, thermoplastic polyurethane (TPU).

11 . The EAP-based device according to any one of the preceding claims, wherein the electrode layers (12, 14, 16) further comprise an additive, such as a silane-based coupling agent, for promoting adhesion of the electrode layer to the dielectric layers.

12. The EAP-based device according to any one of claims 2, and 3 to 11 , when dependent on claim 2 wherein the encapsulant (18) is made of a polymer material, selected from a group comprising silicone, epoxy, urethane.

13. The EAP-based device according to any one of the preceding claims, wherein the electrode layers (12, 14, 16) and the dielectric layers (11 , 13, 15, 17) are encapsulated under vacuum or under nitrogen ambient.

14. Method for manufacturing an electroactive polymer, EAP, based device (10, 20) comprising:

- providing in a processing volume two or more dielectric layers (11 , 13, 15, 17) consisting of a stretchable material;

- arranging (104) an electrode layer (12, 14, 16) made of a carbon based conductive material on at least one of the two or more dielectric layers (11 , 13, 15, 17) wherein the electrode layer (12, 14, 16) comprises a carbon based conductive material,

- covering (104) an exposed surface of at least one of the electrode layers (12, 14, 16) with another dielectric layer made of the stretchable material,

-adding (102) a solid state oxidant material to the carbon based conductive material of the electrode layers (11 , 13, 15, 17); while the electrode layers (12, 14, 16) are being arranged on the at least one of the two or more dielectric layers (11 , 13, 15, 17), the method characterized in that it further comprises: maintaining a substantially oxygen free atmosphere or vacuum in the processing volume and configuring the dielectric layers to seal one of the electrode layers therebetween.

15. Method for manufacturing a EAP-based device according to claim 13, wherein the step of arranging (104) the electrode layer on at least one of the two or more dielectric layers (11 , 13, 15, 17) comprises spraying a carbon-based dispersion solution comprising the solid state oxidant and an additive on the at least one of the dielectric layers, the additive promoting adhesion of the electrode layer to the at least one dielectric layer.

16. Use of a EAP-based device according to any one of claims 1 to 13, or manufactured according to any one of claims 13 to 14.

17. Method of self-clearing a EAP-based device according to any one of claims 1 to 12, or manufactured according to any one of claims 14 to 15, subject to dielectric breakdown comprising

- releasing gaseous oxygen from the electrode layers comprising a solid state oxidant and carbon-based material,

- generating carbon dioxide and/or carbon monoxide by reaction of the released gaseous oxygen with the carbon-based material of the electrodes.