Triboelectric generator

Abstract

To provide a frictional electrification electric generator capable of efficiently outputting electric energy.SOLUTION: The frictional electrification electric generator comprises first and second power generating elements, a first electrode, and a second electrode. The first and second power generating elements are arranged such that relative motion therebetween generates a potential difference by frictional electrification and electrostatic induction. The first power generating element includes a first frictional electrification material having a first electron affinity, and the second power generating element includes a second frictional electrification material having a second electron affinity. The first frictional electrification material includes first non-conductive nanofiber, and the second frictional electrification material includes second non-conductive nanofiber. The first electrode includes first conductive nanofiber, and the second electrode includes second conductive nanofiber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a triboelectric generator.

Background Art

[0002] A triboelectric generator is a device that converts mechanical energy into electrical energy based on the principles of triboelectrification and electrostatic induction, and is also referred to as a TENG (triboelectric nanogenerator). The TENG effectively captures various types of mechanical energy, such as human motion, wind power, and sound waves, and converts it into electrical energy.

[0003] Patent Document 1 proposes a film composed of continuous fine fibers of a piezoelectric polymer with a fiber diameter of 300 nm or less, which is a single film formed by integrating a film portion in which the fine fibers are aligned in their fiber axis direction and a film portion in which the fine fibers arranged around them have no directionality in their fiber axis. The film portion in which the fine fibers are aligned in their fiber axis direction has an elongated shape. Electrodes can be provided at both ends of the piezoelectric polymer film to form a pressure sensor or an actuator, and furthermore, an interface device can be manufactured.

[0004] Patent Document 2 proposes a power generation element comprising a polymer fiber body in which fibers made of a chargeable non-piezoelectric polymer are deposited in three dimensions, wherein, when the polymer fiber body is divided by a single virtual plane, positive charges are unevenly distributed on one side compared to negative charges, and negative charges are unevenly distributed on the other side compared to positive charges. The power generation element further comprises "a first conductive member, a second conductive member disposed opposite to the first conductive member, and a holding member that holds the first conductive member and the second conductive member in a state in which the distance between the first conductive member and the second conductive member can be changed, wherein the polymer fiber is interposed between the first conductive member and the second conductive member, the first conductive member is disposed in a region facing one face of the virtual plane, the second conductive member is disposed in a region facing the other face of the virtual plane, and the holding member can take a first state in which at least one of the first conductive member and the second conductive member is separated from the polymer fiber, and a second state in which the first conductive member and the second conductive member are in contact with the polymer fiber." [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-133368 [Patent Document 2] Japanese Patent Publication No. 2020-170813 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] TENG is lightweight, offers a wide range of material choices, and allows for diverse structural designs. However, there is significant room for improvement in terms of efficiently outputting the acquired electrical energy. [Means for solving the problem]

[0007] One aspect of the present invention relates to a triboelectric generator comprising a first power generation element, a second power generation element, a first electrode connected to the first power generation element, and a second electrode connected to the second power generation element, wherein the first and second power generation elements are arranged such that the relative motion between the first and second power generation elements generates a potential difference between them by triboelectric charging and electrostatic induction, the first power generation element includes a first triboelectric material having a first electron affinity, the second power generation element includes a second triboelectric material having a second electron affinity, the first triboelectric material includes a first nonconductive nanofiber, the second triboelectric material includes a second nonconductive nanofiber, the first electrode includes a first conductive nanofiber, and the second electrode includes a second conductive nanofiber. [Effects of the Invention]

[0008] A triboelectric generator capable of outputting electrical energy acquired through triboelectric charging and electrostatic induction with high efficiency will be realized. [Brief explanation of the drawing]

[0009] [Figure 1] This is an explanatory diagram of the power generation mechanism of the triboelectric generator according to this embodiment. [Figure 2] This is a schematic cross-sectional view of an example of a triboelectric generator according to this embodiment. [Figure 3] Figure 2 is an enlarged schematic diagram of the main components of a triboelectric generator. [Figure 4] This is a schematic cross-sectional view of an example of a triboelectric generator according to another embodiment. [Figure 5] Figure 4 is an enlarged schematic diagram of a triboelectric generator. [Figure 6] These are SEM images of nylon nonwoven fabric (a), PVDF nonwoven fabric (b), silver nanofibers (c), and silver nanofibers laminated on PVDF nonwoven fabric (d). [Figure 7] This is a conceptual diagram showing the configuration of an example of a field spinning apparatus. [Figure 8]This is an illustrative diagram of a linear motor (a), oscilloscope (b), and platform (c) for power measurement. [Figure 9] This figure shows the output characteristics of a TENG in one embodiment. [Figure 10] This figure shows the output characteristics of TENG in another embodiment. [Figure 11] This figure shows a comparison of the output characteristics of the TENG in the example and comparative example. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. In addition, components other than those characteristic of this disclosure may be those of known triboelectric generators or TENG. In this specification, when "range of numerical values ​​A to numerical values ​​B", the range includes numerical values ​​A and B.

[0011] The triboelectric generator (TENG) described herein is a broad concept encompassing devices that convert mechanical energy into electrical energy based on the principles of triboelectric charging and electrostatic induction. The triboelectric generator comprises a first generating element, a second generating element, a first electrode, and a second electrode. The first generating element and the first electrode are physically connected and integrated with each other, either directly or indirectly. The second generating element and the second electrode are physically connected and integrated with each other, either directly or indirectly. On the other hand, the relative positional relationship between the first and second generating elements changes. The first and second generating elements are arranged such that their relative motion generates a potential difference between them due to triboelectric charging and electrostatic induction.

[0012] Due to triboelectric charging between the first and second power generation elements, one of the elements acquires a positive surface charge, while the other acquires a negative surface charge. This surface charge induces electrostatic induction at the first and second electrodes.

[0013] The relative movement between both the first power generation element and the second power generation element may be a movement that causes triboelectric charging between the two and causes a potential difference due to electrostatic induction in the first electrode and the second electrode. The direction of the relative movement between the two is not limited. Typically, the operation in which the first power generation element and the second power generation element approach from a separated state, contact each other, and then separate is repeated. Triboelectric charging occurs due to the contact between the first power generation element and the second power generation element.

[0014] Here, consider the case where the first electrode integrated with the first power generation element and the second electrode integrated with the second power generation element are connected by an external circuit. When the first power generation element and the second power generation element are separated from the state where they have opposite charges and are in contact with each other, current flows through the external circuit, and a potential difference occurs between the first electrode and the second electrode. When the relative movement stops and an equilibrium state is reached, the current stops. At this time, the first electrode has a charge opposite to that of the first power generation element, and the second electrode has a charge opposite to that of the second power generation element.

[0015] Next, when the first power generation element and the second power generation element approach due to relative movement, the triboelectric charges of the first power generation element and the second power generation element are gradually shielded by the opposite charges of each other. Therefore, the potential difference between the electrodes gradually decreases, and a current flows in the opposite direction to the previous one through the external circuit. When the first power generation element and the second power generation element come into contact, the triboelectric charges are generally completely shielded, and an equilibrium state is reached. Based on the above principle, electrical energy is obtained from the reciprocating movement of the first power generation element and the second power generation element by an external force.

[0016] When the first power generation element includes a first triboelectric charging material having a first electron affinity, the second power generation element may include a second triboelectric charging material having a second electron affinity different from the first electron affinity. Due to such a difference in electron affinity, opposite triboelectric charges are likely to occur in the first power generation element and the second power generation element, respectively.

[0017] One of the main features of this embodiment is that the first triboelectric material, the second triboelectric material, the first electrode, and the second electrode each have at least a partially nanofiber form. That is, the first triboelectric material includes first non-conductive nanofibers. The second triboelectric material includes second non-conductive nanofibers. The first electrode includes first conductive nanofibers. The second electrode includes second conductive nanofibers.

[0018] Nanofibers are a general term for fibers having a nanofiber diameter. The nanofiber diameter is, for example, 900 nm or less, and may be 500 nm or less. The lower limit of the fiber diameter is not particularly limited, but considering manufacturing constraints, it is, for example, 1 nm or more, and may be 3 nm or more or 10 nm or more. Note that the fiber diameter of the nanofiber means the average fiber diameter. Here, the nanofiber is photographed with a scanning electron microscope (SEM), the fiber diameters of any 50 nanofibers are measured, and the average value of the 50 measured values is taken as the fiber diameter.

[0019] The first and second conductive nanofibers are nanofibers having conductivity (electronic conductivity), and can be obtained, for example, by spinning a conductive material. Specifically, nanofibers having conductivity can be obtained by discharging a liquid containing a raw material of the conductive material from a nozzle. Examples of the conductive material include metals, carbon, and conductive polymers. Among them, metals and carbon are desirable in terms of easy occurrence of electrostatic induction, and metals are particularly desirable. That is, the conductive nanofibers may be metal nanofibers or carbon nanofibers. Examples of the metal include Pt, Au, Ag, Ni, Cu, Al, Fe, etc. Among them, when using metal nanofibers composed of noble metals such as Ag, high antibacterial properties suitable for application to wearable devices can be imparted to the TENG.

[0020] The first and second non-conductive nanofibers are non-conductive nanofibers and can be obtained by spinning the first triboelectric material and the second triboelectric material, respectively.

[0021] At least one of the first triboelectric material and the second triboelectric material may be a polymer material. Examples of polymer materials include, but are not limited to, fluoropolymers, cellulose, polyolefins, acrylic polymers, polyamides, polyimides, polyamide-imides, and polyacrylonitriles. The polymer material may also be a polymer material having an aromatic ring, as exemplified later as a charge storage material. The first triboelectric material and the second triboelectric material may be the same polymer material or different polymer materials. For example, when generating electricity using fibers in clothing, the use of the same polymer material is envisioned.

[0022] Typically, when the first triboelectric material is a triboelectric positive material, the second triboelectric material may be a triboelectric negative material. In this case, the second electron affinity of the second triboelectric material is greater than the first electron affinity of the first triboelectric material. A triboelectric positive material has, for example, electron-donating atoms or functional groups. A triboelectric negative material has, for example, electron-withdrawing atoms or functional groups.

[0023] Examples of electron-donating atoms include nitrogen atoms and oxygen atoms. Examples of electron-donating functional groups include hydroxyl groups, alkyl groups, amide groups, and urethane groups. Examples of electron-withdrawing atoms include halogen atoms such as fluorine atoms. Examples of electron-withdrawing functional groups include sulfone groups and nitrile groups.

[0024] Friction-positive materials include, for example, polyamides containing nitrogen atoms. Friction-negative materials include, for example, fluoropolymers containing fluorine atoms.

[0025] Examples of polyamides include polycondensation products of lactams called n-nylon (where n is an integer), copolymerization reactions of alkylenediamines and dicarboxylic acids called n,m-nylon (where n and m are integers), and fully aromatic polyamides (aramids). The aramid may be para- or meta-aramid. Examples of lactams include ε-caprolactam, undecane lactam, and lauryl lactam, but are not particularly limited. Examples of alkylenediamines include hexamethylenediamine, nonanediamine, and methylpentadiamine. Examples of dicarboxylic acids include adipic acid, sebacic acid, terephthalic acid, and isophthalic acid.

[0026] Examples of fluoropolymers include, but are not limited to, polyvinylidene fluoride, polytetrafluoroethylene, perfluoroalkyl vinyl ether, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-vinylidene fluoride copolymer.

[0027] By including non-conductive nanofibers in both the first and second power generation elements, the area of ​​triboelectric charging between them is increased. Furthermore, by including conductive nanofibers in both the first and second electrodes, electrostatic induction between the first and second electrodes proceeds smoothly. As a result, the opportunities for triboelectric charging increase while electrostatic induction is promoted. Therefore, a TENG capable of outputting electrical energy with high efficiency can be obtained.

[0028] Furthermore, by incorporating nanofibers into each of the first power generation element, the second power generation element, the first electrode, and the second electrode, a lighter TENG can be realized. As a result, the power generation efficiency per unit mass of the TENG can be increased.

[0029] Furthermore, one particularly noteworthy application of TENG is in wearable devices. In this case, TENG requires high breathability and flexibility. By incorporating nanofibers not only in the first and second power generation elements, but also in the first and second electrodes, high breathability and flexibility suitable for wearable device applications are ensured. Moreover, if the nanofibers are composed of antibacterial metals such as Ag, high antibacterial properties can be imparted to TENG.

[0030] The first power generation element, the second power generation element, the first electrode, and the second electrode may be made of, for example, a nonwoven fabric in which the nanofibers constituting each are intertwined. However, each component may be a woven fabric, a knitted fabric, or in any other form.

[0031] The average thickness of the first and second electrodes (or nonwoven fabrics, woven fabrics, knitted fabrics, etc., composed of conductive nanofibers) may be, for example, 1 μm to 1000 μm, but is not particularly limited. Similarly, the average thickness of the first and second power generation elements (or nonwoven fabrics, woven fabrics, knitted fabrics, etc., composed of non-conductive nanofibers) may be, for example, 1 μm to 1000 μm, but is not particularly limited.

[0032] A first composite layer connecting a first conductive nanofiber and a first nonconductive nanofiber may be formed in the first interface region between the first power generation element and the first electrode. Similarly, a second composite layer connecting a second conductive nanofiber and a second nonconductive nanofiber may be formed in the second interface region between the second power generation element and the second electrode.

[0033] The average thickness of the first and second electrodes, and the first and second power generation elements, can be measured, for example, by the following method. First, the laminate of the first or second power generation element and the first or second electrode is cut along the lamination direction, and a cross-sectional image is taken with a scanning electron microscope (SEM). However, in the cross-sectional image, the length of the interface between the first or second power generation element and the first or second electrode should be 1000 μm or more. It is desirable to take cross-sectional images from 5 or more fields of view. Next, nine line segments are drawn perpendicular to the interface direction (i.e., in the thickness direction of the composite layer) so as to divide the cross-sectional image into 10 equal parts along the interface direction.

[0034] Next, in 10 regions of the cross-sectional image, point T1 is detected where the first or second nonconductive nanofiber is located on the innermost side of the first or second power generation element (on the side of the power generation element with opposite polarity), and point U1 is detected where the first or second nonconductive nanofiber penetrates furthest towards the first or second electrode. Then, the distance dt1 between point T1 and point U1 in a direction parallel to the line segment is determined. If there is no first or second composite layer, the average value dt1a of the 10 distances dt1 is considered to be the average thickness of the first or second power generation element. If there is a first or second composite layer, the difference between the average value dt1a and the average thickness of the first or second composite layer is considered to be the average thickness of the first or second power generation element. When measuring cross-sectional images in multiple fields of view, the average value of the average thickness of the first or second power generation element obtained in each field of view is considered to be the average thickness of the first or second power generation element.

[0035] Similarly, in 10 regions of the cross-sectional image, the point T2 where the first or second conductive nanofiber is located on the outermost edge of the first or second electrode, and the point U2 where the first or second conductive nanofiber penetrates furthest into the first or second power generation element are detected. Next, the distance dt2 between point T2 and point U2 in a direction parallel to the line segment is determined. If there is no first or second composite layer, the average value dt2a of the 10 distances dt2 is considered to be the average thickness of the first or second electrode. If there is a first or second composite layer, the difference between the average value dt2a and the average thickness of the first or second composite layer is considered to be the average thickness of the first or second electrode. When measuring cross-sectional images in multiple fields of view, the average of the average thicknesses of the first or second electrode obtained in each field of view is considered to be the average thickness of the first or second electrode.

[0036] Next, embodiments will be described separately according to the form of the composite layer. In the following definition, the average fiber diameter of nanofibers is calculated by imaging nanofibers with a scanning electron microscope (SEM), measuring the fiber diameter of any 50 nanofibers, and averaging the result.

[0037] (First Embodiment) The first composite layer may be formed, for example, by the entanglement of a first nonconductive nanofiber and a first conductive nanofiber. Similarly, the second composite layer may be formed by the entanglement of a second nonconductive nanofiber and a second conductive nanofiber. In each composite layer, conductive nanofibers and nonconductive nanofibers having nanoscale fiber diameters are adjacent to each other and entangled, significantly increasing the contact points between conductive and nonconductive nanofibers, thereby smoothly inducing electrostatic induction.

[0038] It is desirable that the degree of entanglement between the first conductive nanofibers and the first non-conductive nanofibers, and the degree of entanglement between the second conductive nanofibers and the second non-conductive nanofibers be as large as possible. For example, it is desirable to deeply penetrate the first or second conductive nanofibers into the gaps of the network of the first or second non-conductive nanofibers. Alternatively, it is desirable to deeply penetrate the first or second non-conductive nanofibers into the gaps of the network of the first or second conductive nanofibers.

[0039] Note that the first or second non-conductive nanofibers are usually relatively stiffer than the first or second conductive nanofibers. Therefore, it is effective to penetrate the first or second conductive nanofibers into the gaps of the network of the first or second non-conductive nanofibers.

[0040] In order to deeply penetrate the first or second conductive nanofibers into the gaps of the network of the first or second non-conductive nanofibers, it is desirable to make the average fiber diameter of the first or second conductive nanofibers smaller than the average fiber diameter of the first or second non-conductive nanofibers. Conversely, in order to deeply penetrate the first or second non-conductive nanofibers into the gaps of the network of the first or second conductive nanofibers, it is desirable to make the average fiber diameter of the first or second non-conductive nanofibers smaller than the average fiber diameter of the first or second conductive nanofibers.

[0041] Here, let the average fiber diameter of the first and second non-conductive nanofibers be Dnc, and the average fiber diameter of the first and second conductive nanofibers be Dc.

[0042] In each composite layer, Dnc = Dc may be used. However, when an entanglement between thick fibers and thin fibers is formed, it is considered that the contacts between the nanofibers are more likely to increase and the electrostatic induction is attracted more smoothly. Therefore, when Dnc > Dc, the Dnc / Dc ratio is desirably, for example, 3 or more, and may be within the range of 3 to 20. Similarly, when Dnc < Dc, the Dc / Dnc ratio is desirably, for example, 3 or more, and may be within the range of 3 to 20.

[0043] The average thickness of the first or second composite layer may be smaller than the average thickness of the first electrode, second electrode, first power generation element, and second power generation element, and may be less than half of their respective average thicknesses. The first or second composite layer only needs to be thick enough to form the vicinity of the interface between the first or second electrode and the first or second power generation element. The thickness of the first or second composite layer may be, for example, 1 μm to 500 μm.

[0044] The average thickness of the first or second composite layer can also be expressed as the depth to which the first or second conductive nanofibers penetrate from one surface of the first or second power generation element, or the depth to which the first or second nonconductive nanofibers penetrate from one surface of the first or second electrode.

[0045] The average thickness of the first or second composite layer can be measured, for example, by the following method. First, the laminate of the first or second power generation element and the first or second electrode is cut along the lamination direction, and a cross-sectional image is taken with a scanning electron microscope (SEM). However, in the cross-sectional image, the length of the interface between the first or second power generation element and the first or second electrode should be 1000 μm or more. It is desirable to take cross-sectional images from 5 or more fields of view. Next, nine line segments are drawn perpendicular to the interface direction (i.e., in the thickness direction of the composite layer) so as to divide the cross-sectional image into 10 equal parts along the interface direction. Next, in the 10 regions of the cross-sectional image, point P where the first or second conductive nanofiber penetrates furthest into the first or second power generation element side and point Q where the first or second nonconductive nanofiber penetrates furthest into the first or second electrode side are detected. Next, the distance d1 between point P and point Q in the direction parallel to the line segment is determined. The average value d1a of the 10 distances d1 is considered to be the average thickness of the first or second composite layer. When measuring cross-sectional images in multiple fields of view, the average value of d1a obtained in each field of view is considered as the average thickness of the first or second composite layer.

[0046] (Second Embodiment) The first or second composite layer may include a charge storage material. The charge storage material has a predetermined chemical structure that attracts and stabilizes charges, for example. The predetermined chemical structure is typically, but not limited to, a structure having π-conjugated electron orbitals. The charge storage material may have a chemical structure that can trap charges for a longer period than the first or second power generation element or the first or second nonconductive nanofiber.

[0047] Generally, much of the charge generated by triboelectric charging tends to be neutralized by opposing charges in the air or escape to the first or second electrode, making it difficult for surface charge to accumulate on the first or second power generation element. The magnitude of the current generated by electrostatic induction depends on the amount of surface charge accumulated. By including a charge storage material in the first or second composite layer, the charge generated by triboelectric charging firmly binds to the composite layer, functioning like a water pump. As a result, the potential difference induced between the first and second electrodes increases, stimulating strong electrostatic induction and enabling the generation of higher output.

[0048] The charge storage material may be a polymer material having an aromatic ring. The aromatic ring has a stable π-conjugated electron orbital. Therefore, it can highly stabilize the charge generated by triboelectric charging and trap the charge for a longer period of time. The aromatic ring may be a monoring or a fused ring. The aromatic ring may be a benzene ring or a heteroring.

[0049] Examples of polymer materials having aromatic rings include polystyrene and aramid. The polymer material may also be a π-conjugated polymer. Examples of π-conjugated polymers include polyaniline, polypyrrole, and polythiophene, but are not particularly limited.

[0050] The charge storage material may have at least partially the form of nanofibers. That is, the charge storage material may include a third nonconductive nanofiber different from the first or second nonconductive nanofibers. In this case, it is desirable that in each composite layer, the first or second conductive nanofibers and the third nonconductive nanofibers are intertwined, and the third nonconductive nanofibers are intertwined with the first or second nonconductive nanofibers. In particular, the composite of the first or second electrode and the charge storage material is important, and it is desirable that the first or second conductive nanofibers and the third nonconductive nanofibers are sufficiently intertwined.

[0051] Each composite layer has a first composite region in which at least a first or second conductive nanofiber and a third nonconductive nanofiber are intertwined, a second composite region in which the third nonconductive nanofiber and the first or second nonconductive nanofiber are intertwined, and an intermediate region composed solely of the third nonconductive nanofiber. The first composite region is particularly important, as it significantly increases the contact points between the conductive nanofiber and the nonconductive nanofiber, allowing electrostatic induction to be smoothly induced.

[0052] The degree of entanglement between the first or second conductive nanofibers and the third nonconductive nanofibers is desirable to be as large as possible. For example, it is desirable to allow the third nonconductive nanofibers to penetrate deeply into the gaps in the network of the first or second conductive nanofibers. Similarly, the first or second conductive nanofibers may penetrate deeply into the gaps in the network of the third nonconductive nanofibers.

[0053] To allow third nonconductive nanofibers to penetrate deeply into the gaps of the first or second conductive nanofiber network, it is desirable to make the average fiber diameter of the third nonconductive nanofibers smaller than the average fiber diameter of the first or second conductive nanofibers. Conversely, to allow first or second conductive nanofibers to penetrate deeply into the gaps of the third nonconductive nanofiber network, it is desirable to make the average fiber diameter of the first or second conductive nanofibers smaller than the average fiber diameter of the third nonconductive nanofibers.

[0054] Here, let the average fiber diameter of the third non-conductive nanofiber be Dnc3.

[0055] In each composite layer, Dc = Dnc3 may be used. However, when entanglement between thick fibers and thin fibers is formed, it is considered that the contact points between the nanofibers are more likely to increase, and electrostatic induction is more smoothly induced. Therefore, when Dc > Dnc3, the Dc / Dnc3 ratio is preferably, for example, 3 or more, and may be within the range of 3 to 20. Similarly, when Dc < Dnc3, the Dnc3 / Dc ratio is preferably, for example, 3 or more, and may be within the range of 3 to 20.

[0056] In order to deeply penetrate the third non-conductive nanofiber into the gaps of the network of the first or second non-conductive nanofibers, it is desirable to make the average fiber diameter of the third non-conductive nanofiber smaller than the average fiber diameter of the first or second non-conductive nanofibers. Conversely, in order to deeply penetrate the first or second non-conductive nanofiber into the gaps of the network of the third non-conductive nanofibers, it is desirable to make the average fiber diameter of the first or second non-conductive nanofibers smaller than the average fiber diameter of the third non-conductive nanofibers.

[0057] When Dnc > Dnc3, the Dnc / Dnc3 ratio is preferably, for example, 3 or more, and may be within the range of 3 to 20. Similarly, when Dnc < Dnc3, the Dnc3 / Dnc ratio is preferably, for example, 3 or more, and may be within the range of 3 to 20.

[0058] Among the first or second composite layers, the average thickness of the first composite region where the first or second conductive nanofibers and the third non-conductive nanofibers are intertwined is smaller than the thicknesses of the first electrode, the second electrode, the first power generation element, and the second power generation element, respectively, and may be less than half of each average thickness. The thickness of the first or second composite layer may be, for example, 1 μm to 500 μm.

[0059] The average thickness of the first composite region of the first or second composite layer can be measured, for example, by the following method. First, the laminate of the first or second power generation element and the first or second electrode is cut along the lamination direction, and a cross-sectional image is taken with a scanning electron microscope (SEM). The laminate contains the first or second composite layer. In the cross-sectional image, the length of the first or second composite layer (interface region between the power generation element and the electrode) interposed between the first or second power generation element and the first or second electrode is set to 1000 μm or more. It is desirable to take the cross-sectional image with 5 or more fields of view. Next, nine line segments are drawn perpendicular to the interface direction (i.e., in the thickness direction of the composite layer) so as to divide the cross-sectional image into 10 equal parts along the interface. Next, in the 10 regions of the cross-sectional image, the point R where the third non-conductive nanofiber penetrates furthest on the first or second electrode side and the point S where the first or second conductive nanofiber penetrates furthest on the charge storage material side (i.e., the first or second power generation element side) are detected. Next, the distance d2 between point R and point S in the direction parallel to the line segment is determined. The average value d2a of the 10 distances d2 is considered to be the average thickness of the first composite region. When measuring cross-sectional images in multiple fields of view, the average value of d2a obtained in each field of view is considered to be the average thickness of the first composite region.

[0060] The TENG according to this embodiment will be further described below with reference to the drawings. However, the following embodiments are not limiting to the present invention, and various modifications are possible within the scope of the invention. In the following drawings, the same reference numerals indicate the same part or a corresponding part.

[0061] Figure 1 is an explanatory diagram showing the power generation mechanism of the TENG according to this embodiment. The TENG 100 comprises a first power generation element 110 and a second power generation element 120, each being sheet-shaped, a first electrode 111, and a second electrode 121. The first electrode 111 and the second electrode 121 are electrically connected via an external circuit 101 having a resistance R. Here, the first power generation element 110 includes a friction-positive material, and the second power generation element 120 includes a friction-negative material.

[0062] The first power generation element 110 and the first electrode 111 are integrated while in contact with each other, and the second power generation element 120 and the second electrode 121 are integrated while in contact with each other. The first power generation element 110 and the second power generation element 120 are separated from each other at their respective first positions (Figure 1(c)), gradually approach each other, come into contact at their respective second positions (Figure 1(a)), and then move apart and back to their first positions, repeating this process.

[0063] Figure 1(a) shows the state in which the first power generation element 110 and the second power generation element 120 are in contact at their respective second positions. When both are subjected to compressive pressure, triboelectric charging occurs at the contact interface. That is, the first power generation element 110 has a positive surface charge, and the second power generation element 120 has a negative surface charge. In this state, the positive and negative surface charges almost completely shield each other, resulting in a static equilibrium state. At this time, no current flows through the external circuit 101.

[0064] Figure 1(b) shows the state in which the first power generation element 110 and the second power generation element 120 are separated and in the process of moving to the first position. As the distance between the first power generation element 110 and the second power generation element 120 increases, the shielding effect of the surface charge weakens, a negative charge is induced on the first electrode and a positive charge on the second electrode (i.e., a current I flows in the external circuit 101), and the potential difference between the electrodes gradually increases.

[0065] Figure 1(c) shows the state in which the first power generation element 110 and the second power generation element 120 are stopped in their respective first positions. This state is a static equilibrium state, and no current flows through the external circuit 101.

[0066] Figure 1(d) shows the state in which the first power generation element 110 and the second power generation element 120 are approaching each other and moving to the second position. As the distance between the first power generation element 110 and the second power generation element 120 decreases, the shielding effect of the surface charge becomes stronger, the negative charge of the first electrode and the positive charge of the second electrode decrease (that is, a current I flows in the external circuit 101 in the opposite direction to before), and the potential difference between the electrodes gradually decreases.

[0067] Figure 2 is a schematic cross-sectional view of an example of TENG100 according to this embodiment. The first triboelectric material included in the first power generation element 110 is a friction-positive material. Here, the friction-positive material has the form of nanofibers (first nonconductive nanofibers 110ncF). The first power generation element 110 is, for example, a nonwoven fabric composed of the first nonconductive nanofibers 110ncF. On the other hand, the second triboelectric material included in the second power generation element 120 is a friction-negative material. The friction-negative material has the form of nanofibers (second nonconductive nanofibers 120ncF). The second power generation element 120 is, for example, a nonwoven fabric composed of the second nonconductive nanofibers 120ncF.

[0068] The first electrode 111 has the form of a nanofiber (first conductive nanofiber 111cF). The first electrode 111 is, for example, a nonwoven fabric composed of the first conductive nanofiber 111cF. Similarly, the second electrode 121 has the form of a nanofiber (second conductive nanofiber 121cF). The second electrode 121 is, for example, a nonwoven fabric composed of the second conductive nanofiber 121cF.

[0069] Figure 3 is an enlarged schematic diagram of the first composite layer 130, which is the main part of TENG100 in Figure 2. In Figures 2 and 3, the region containing the first composite layer 130 is enclosed by a dashed line. The first composite layer 130 is the region where the entanglement of the first nonconductive nanofiber 110ncF and the first conductive nanofiber 111cF, enclosed by the dashed line, is formed. Figure 3 corresponds to one of the 10 regions of the cross-sectional image described above. In Figure 3, the distance d1 between point P, where the first conductive nanofiber 111cF penetrates furthest towards the first power generation element 110, and point Q, where the first nonconductive nanofiber 110ncF penetrates furthest towards the first electrode 111, is shown.

[0070] Figure 4 is a schematic cross-sectional view of an example of TENG100A according to another embodiment. This embodiment has a structure that is generally similar to the embodiment in Figure 2, except that the configuration of the first composite layer is different. The first composite layer 130A includes a charge storage material, which has the form of nanofibers. That is, the charge storage material includes a third nonconductive nanofiber 130ncF, which is different from the first or second nonconductive nanofibers.

[0071] Figure 5 is an enlarged schematic diagram of the first composite layer 130A, which is the main part of TENG100A in Figure 4. In Figures 4 and 5, the region containing the first composite layer 130A is enclosed by a dashed line. The first composite region 130B is enclosed by a dashed line. In the first composite layer 130A, the first conductive nanofiber 111cF and the third nonconductive nanofiber 130ncF are intertwined, and the third nonconductive nanofiber 130ncF and the first nonconductive nanofiber 110ncF are intertwined. In the first composite region 130B, the first conductive nanofiber 111cF and the third nonconductive nanofiber 130ncF are intertwined. Figure 5 corresponds to one of the 10 regions of the cross-sectional image described above. Figure 5 shows the distance d2 between point R, where the third nonconductive nanofiber 130ncF penetrates furthest into the first electrode 111 side, and point S, where the first conductive nanofiber 111cF penetrates furthest into the charge storage material side.

[0072] Next, an example of a method for manufacturing TENG according to this embodiment will be described.

[0073] (First or second power generation element) Here, as an example, a method for producing a nonwoven fabric containing a first or second nonconductive nanofiber as a first or second power generation element is described using the electrospinning method. The first and second nonconductive nanofibers can be obtained by spinning a first triboelectric material and a second triboelectric material, respectively.

[0074] A method for producing non-conductive nanofibers by electrospinning includes, for example, the steps of preparing a solution containing a triboelectric material, discharging the electrostatically charged solution into a nanofiber formation space to generate nanofibers using an electric field, and depositing the generated nanofibers to form a nonwoven fabric.

[0075] The method for preparing the solution is not particularly limited; for example, it may be prepared by dissolving the triboelectric material in a solvent. The solvent is not particularly limited as long as it can dissolve the triboelectric material and can be removed by volatilization. Examples of such solvents include aprotic polar organic solvents. Specifically, examples include amides (such as linear or cyclic amides) such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP), sulfoxides such as dimethyl sulfoxide, and acetone. These solvents may be used individually or in combination of two or more.

[0076] The concentration of the triboelectric material in the solution can be set as appropriate. The solution may also contain known additives used in electrospinning, if necessary.

[0077] Next, nanofibers are generated from a solution in a nanofiber formation space. In the electrospinning method, nanofibers are generated by the electrostatic stretching phenomenon. Specifically, when a charged solution is discharged into a space with an electric field (nanofiber formation space), the solvent in the solution gradually evaporates as the droplet flies through the space, and the volume of the solution droplet decreases. As a result, the charge density of the droplet flying through the space gradually increases, and when the repulsive force of the charge overcomes the surface tension of the droplet, the droplet is explosively stretched into a linear shape. Nanofibers can be manufactured efficiently using the electrostatic stretching phenomenon.

[0078] When nanofibers generated in a nanofiber formation space are deposited onto a predetermined substrate surface, a nonwoven fabric is obtained. The formed nonwoven fabric can be easily peeled off the substrate surface.

[0079] An apparatus for producing non-conductive nanofibers by electrospinning comprises, for example, a nozzle for dispensing a solution containing a triboelectric material, a charging means for charging the solution, and a collector section for depositing nanofibers. The charging means includes, for example, a voltage application device for applying a high voltage to the nozzle. The charging means may also have a counter electrode positioned further from the nozzle than the collector section and parallel to the collector section. The collector section or the counter electrode can be grounded. This creates a potential difference between the nozzle and the counter electrode, that is, a nanofiber formation space is formed between the nozzle and the collector section or the counter electrode.

[0080] (Charge storage material) The charge storage material is formed by electrospinning, for example, by spinning and depositing a third nonconductive nanofiber onto one surface of a nonwoven fabric containing a first or second nonconductive nanofiber formed as a power generation element. By placing a nonwoven fabric containing the first or second nonconductive nanofiber in the collector section and generating the third nonconductive nanofiber in the nanofiber formation space, the charge storage material containing the third nonconductive nanofiber can be deposited onto one surface of the first or second power generation element.

[0081] (First or second electrode) The first or second electrode can be manufactured, for example, as a nonwoven fabric containing the first or second conductive nanofibers by the polyol method. The polyol method is an example of a method for synthesizing metal nanofibers in the liquid phase, in which metal ions are reduced with a polyol (polyhydric alcohol) in water or a solvent in the presence of a protective agent such as a surfactant or polymer to grow nanofibers. According to the polyol method, metal nanofibers with various fiber diameters and lengths can be synthesized by controlling the concentration and temperature conditions of the metal salt solution. For example, polyvinylpyrrolidone (PVP) is used as a protective agent. For example, silver nitrate is used as a metal salt. For example, ethylene glycol is used as a polyol. For example, the reduction reaction of silver ions in a silver nitrate solution proceeds with its direction controlled in one direction by a protective agent such as PVP, and silver nanofibers are produced. Adding sodium chloride as a derivative to the solution promotes the growth of silver nanofibers. After conductive nanofibers (metal nanofibers) are layered or deposited on a triboelectric material or charge storage material, an entanglement between conductive and non-conductive nanofibers is formed by applying a predetermined external force. For example, the formation of entanglement between conductive and non-conductive nanofibers can be promoted by applying pressure to the conductive nanofibers against the triboelectric material or charge storage material, or by attracting the conductive nanofibers from the triboelectric material (or charge storage material) side through the triboelectric material (or charge storage material).

[0082] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0083] Example 1 (1) First and second power generation elements As the first triboelectric material, polyamide (nylon-6,6), a triboelectric positive material, was prepared. Nylon-6,6 was dissolved in hexafluoroisopropanol (HFIP) to prepare a nylon solution with a nylon-6,6 content of 7.5% by mass. The nylon solution was electrospun using a predetermined electrospinning apparatus, and first nonconductive nanofibers (nylon nanofibers) with an average fiber diameter of 400 nm were deposited in the collector portion to form a nylon nonwoven fabric (thickness 50 μm) as the first power generation element. An SEM image of the nylon nonwoven fabric is shown in Figure 6(a).

[0084] Polyvinylidene fluoride (PVDF), a friction-negative material, was prepared as the second triboelectric material. The PVDF was dissolved in a mixed solvent of DMF and acetone in a volume ratio of 7:3 to prepare a PVDF solution with a PVDF content of 20% by mass. The PVDF solution was electrospun using a predetermined electrospinning apparatus, and second nonconductive nanofibers (PVDF nanofibers) with an average fiber diameter of 300 nm were deposited in the collector portion to form a PVDF nonwoven fabric (thickness 50 μm) as the second power generation element. An SEM image of the PVDF nonwoven fabric is shown in Figure 6(b).

[0085] Electrospinning was performed using an electrospinning apparatus having the configuration shown in Figure 7. The electrospinning apparatus 200 comprises a syringe (nozzle) 210 for dispensing a solution containing a triboelectric material, a syringe pump 220 for supplying the solution to the syringe 210, a voltage application device (charging means) 230 for charging the syringe 210, and a rotating body 240 (collector) for depositing nanofibers. The rotating body 240 is grounded. Nanofibers are generated in the nanofiber formation space between the syringe 210 and the rotating body 240 and are wound onto the rotating body 240 as a sheet-like nonwoven fabric.

[0086] The parameters for electrospinning are shown in Table 1.

[0087] [Table 1]

[0088] (2) First and second electrodes Silver nanofibers (average fiber diameter 50 nm, average length 100 μm) produced by the polyol method were used as the first and second conductive nanofibers. An example of a silver nanofiber (AgNWs) SEM image is shown in Figure 6(c). The silver nanofiber dispersion was deposited onto one surface of a nylon nonwoven fabric and a PVDF nonwoven fabric by suction filtration, respectively, to form the first and second electrodes in nonwoven fabric form. Specifically, the nylon nonwoven fabric and the PVDF nonwoven fabric were placed on the surface of an absorption filter funnel, and then the silver nanofiber dispersion was injected into the absorption filter funnel and aspirated, followed by washing with ethanol. The aspiration time was 10 minutes. The resulting laminates of nylon nonwoven fabric or PVDF nonwoven fabric and silver nanofibers were dried at 60°C. The thickness of the first and second electrodes was 5 μm each. Figure 6(d) shows the silver nanofibers laminated on the PVDF nonwoven fabric (especially on the right side of the figure).

[0089] Through the suction filtration process, silver nanofibers penetrated deeply into the gaps in the network of nylon nanofibers and PVDF nanofibers (nylon nonwoven fabric and PVDF nonwoven fabric), forming a first composite layer in which nylon nanofibers and silver nanofibers were intertwined, and a second composite layer in which PVDF nanofibers and silver nanofibers were intertwined.

[0090] In the first composite layer, the ratio of the average fiber diameter of nylon nanofibers (Dnc) to the average fiber diameter of silver nanofibers (Dc) was Dnc / Dc = 8, and the thickness of the first composite layer, as determined by the method described above, was 1 μm.

[0091] In the second composite layer, the ratio of the average fiber diameter Dnc of the PVDF nanofibers to the average fiber diameter Dc of the silver nanofibers was Dnc / Dc = 6, and the thickness of the second composite layer, as determined by the method described above, was 1 μm.

[0092] (3) Assembling the TENG TENGA1 was assembled using laminates of nylon nonwoven fabric and silver nanofibers, and laminates of PVDF nonwoven fabric and silver nanofibers. TENGA1 was then driven by a linear motor as shown in Figure 8(a), and its output was measured via an oscilloscope as shown in Figure 8(b). TENGA1 was placed on a power measurement platform as shown in Figure 8(c). The linear motor's drive frequency and drive force were controlled to 1-5 Hz and 12 N, respectively. Figure 9 shows the output characteristics of TENGA1. In Figure 9, Voc is the output voltage of TENGA1. High output voltages were obtained at all frequencies from 1 to 5 Hz.

[0093] Example 2 Polystyrene (PS) was prepared as a charge storage material and dissolved in DMF to prepare a PS solution with a PS content of 15% by mass. The PS solution was electrospun using a predetermined electrospinning apparatus to deposit third nonconductive nanofibers (PS fibers) with an average fiber diameter of 500 nm onto a second power generation element (PVDF nonwoven fabric).

[0094] Through the electrospinning process, PS nanofibers penetrated the gaps in the PVDF nanofiber (PVDF nonwoven fabric) network, forming a second composite region where PVDF nanofibers and PS nanofibers intertwined.

[0095] TENGA2 was assembled in the same manner as in Example 1, except that silver nanofibers were deposited on the laminate of the obtained PVDF nonwoven fabric and PS nanofibers by suction filtration. The drive frequency and drive force were controlled to 2 Hz and 10 N, respectively, and the output was evaluated. The output characteristics of TENGA2 are shown in Figure 10. Figure 10(a) shows the output characteristics of TENGA1 of Example 1 without PS nanofibers, and Figure 10(b) shows the output characteristics of TENGA2 of Example 2 with PS nanofibers. The output of TENGA2 has dramatically improved (generally more than 3 times).

[0096] In TENGA2, the ratio of the average fiber diameter Dnc of PVDF nanofibers to the average fiber diameter Dnc of PS nanofibers was Dnc3 / Dnc = 1.6, and the ratio of the average fiber diameter Dnc3 of PS nanofibers to the average fiber diameter Dc of silver nanofibers was Dnc3 / Dc = 10. The thickness of the first composite region, determined by the method described above, was 1 μm. The total thickness of the second composite layer was 80 μm.

[0097] ≪Comparative Example 1≫ TENGB1 was assembled and evaluated in the same manner as in Example 1, except that silver nanofibers were not used for the first and second electrodes (i.e., no first and second composite layers were formed), and a 300 μm thick silver sheet was pressed onto one of the surfaces of the nylon nonwoven fabric and the PVDF nonwoven fabric. The output characteristics of TENGB1 are shown in comparison with the output characteristics of TENGA1 in Figure 11. Here, the output voltage per unit mass of TENG is compared. Figure 11(a) shows the output characteristics of TENGA1 of Example 1, and Figure 11(b) shows the output characteristics of TENGB1 of Comparative Example 1. In TENGA1, where the electrodes are formed with conductive nanofibers, the output voltage per unit mass is dramatically improved compared to TENGB1, which uses a silver sheet. [Industrial applicability]

[0098] The triboelectric generator (TENG) according to the present invention can be used as a generator that converts various types of mechanical energy into electrical energy, but when the entire device is made of nanofibers, it is particularly suitable for use as a wearable device with excellent breathability. [Explanation of Symbols]

[0099] 100, 100A: Triboelectric generator (TENG) 101: External circuit 110: First power generation element 110ncF: First non-conductive nanofiber 111: 1st electrode 111cF: First conductive nanofiber 120: Second power generation element 120ncF: Second non-conductive nanofiber 121:Second electrode 121cF: Second conductive nanofiber 130, 130A: 1st composite layer 130B: 1st composite area 130ncF: Third non-conductive nanofiber R: Resistance 200: Electrospinning machine 210: Syringe (nozzle) 220: Syringe pump 230: Voltage application device (charging means) 240: Rotating body (collector part)

Claims

1. The first power generation element and The second power generation element, A first electrode connected to the first power generation element, A second electrode connected to the second power generation element, It is equipped with, The first power generation element and the second power generation element are arranged such that the relative motion between the first power generation element and the second power generation element generates a potential difference between the first power generation element and the second power generation element through triboelectric charging and electrostatic induction. The first power generation element includes a first triboelectric material having a first electron affinity, The second power generation element includes a second triboelectric material having a second electron affinity, The first triboelectric material includes a first nonconductive nanofiber, The second triboelectric material contains a second nonconductive nanofiber, The first electrode includes a first conductive nanofiber, The second electrode contains a second conductive nanofiber, The material comprises at least one of a first composite layer connecting the first conductive nanofiber and the first nonconductive nanofiber, and a second composite layer connecting the second conductive nanofiber and the second nonconductive nanofiber. The first composite layer is formed in the first interface region between the first power generation element and the first electrode. The second composite layer is formed in the second interface region between the second power generation element and the second electrode. In the first composite layer, the first conductive nanofibers and the first nonconductive nanofibers are intertwined, or In the second composite layer, the second conductive nanofiber and the second nonconductive nanofiber are intertwined, At least one of the first composite layer and the second composite layer includes a charge storage material, The charge storage material includes a third non-conductive nanofiber that is different from the first non-conductive nanofiber and the second non-conductive nanofiber, The first conductive nanofiber or the second conductive nanofiber and the third nonconductive nanofiber are intertwined, A triboelectric generator in which the third nonconductive nanofiber and the first nonconductive nanofiber or the second nonconductive nanofiber are intertwined.

2. The average fiber diameter of the first conductive nanofibers is smaller than the average fiber diameter of the first nonconductive nanofibers, or The triboelectric generator according to claim 1, wherein the average fiber diameter of the second conductive nanofibers is smaller than the average fiber diameter of the second nonconductive nanofibers.

3. The triboelectric generator according to claim 1, wherein the average fiber diameter of the third nonconductive nanofiber is smaller than the average fiber diameter of the first nonconductive nanofiber or the second nonconductive nanofiber.

4. The triboelectric generator according to any one of claims 1 to 3, wherein the charge storage material is a polymer material having an aromatic ring.

5. The triboelectric generator according to any one of claims 1 to 4, wherein at least one of the first triboelectric material and the second triboelectric material is a polymer material.

6. A triboelectric generator according to any one of claims 1 to 5, wherein the first triboelectric material is a triboelectric positive material and the second triboelectric material is a triboelectric negative material.

7. The triboelectric generator according to claim 6, wherein the friction-positive material comprises a polyamide and the friction-negative material comprises a fluoropolymer.

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