WO2012105187A1

WO2012105187A1 - Capacitance-varying type power-generation element

Info

Publication number: WO2012105187A1
Application number: PCT/JP2012/000455
Authority: WO
Inventors: 坂下　幸雄
Original assignee: 富士フイルム株式会社
Priority date: 2011-02-04
Filing date: 2012-01-25
Publication date: 2012-08-09
Also published as: JP2012164727A

Abstract

[Objective] To attain a capacitance-varying type power generation element having high power-generation efficiency. [Solution] A power generation element (1) is provided with a laminate (12) that is constituted by laminating a dielectric-polarization body (10) and a dielectric elastomer layer (11), and a pair of electrodes (21, 22) that are arranged at the upper and lower sides in the laminating direction of the laminate (12). The dielectric-polarization body (10) comprises a ferroelectric that has crystal orientation.

Description

Capacitance change type power generation element

The present invention relates to a power generation element that generates power by a change in capacitance between electrodes.

There has been proposed an electrostatic induction conversion element that converts kinetic energy and electric energy by electrostatic induction using an electret capable of generating an electrostatic field semi-permanently by charging a dielectric.

At present, fluorine-based resins such as polytetrafluoroethylene, Teflon (registered trademark), and CYTOP® (registered trademark) are mainly used as dielectrics used in electrets (Patent Documents 1 to 4).

As the electret material, the higher the surface charge density after charging, the better. However, these resin materials cannot have a very high surface charge density. According to reports up to now, the surface charge density of the fluorine-based resin material is generally about 0.005 μC / cm ² , and even a high one is about 0.15 μC / cm ² .

On the other hand, Patent Document 5 proposes an electromechanical conversion element using a dielectric polarization plate made of a ferroelectric material as an electret material having a high surface charge density.

In Patent Documents 1 to 4, there is a gap between the electret material and one electrode, and electrostatic induction is induced in the electrode with relative movement (movement in the horizontal direction) between the electret material and the electrode. An element that performs mechanical-electrical conversion by utilizing the change in the amount of charge is disclosed.

Further, in Patent Document 5, as an electret is inserted between capacitors, one of the capacitor electrodes is used as a vibration plate, and the electrodes are displaced by being vibrated by sound. It is disclosed that a ferroelectric material having a high surface charge density is used as an electret in an electret condenser microphone (EMC) that converts it into a signal.

JP 2006-180450 A JP 2007-31551 A JP 2008-266563 A JP 2010-136598 A JP 2007-298297 A

For the surface charge density of a ferroelectric material, its remanent polarization value is one measure. In general, a ferroelectric has a large remanent polarization value and is considered to be 10 μC / cm ² or more. Therefore, by using an electret made of a ferroelectric ceramic described in Patent Document 5, it is larger than a polymer material. The electromechanical conversion efficiency can be achieved, and it is considered that there is a certain effect in the use as a microphone. However, when utilization as a power generation element is studied, sufficient power generation efficiency has not been obtained yet.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a capacitance change type power generation element with high power generation efficiency.

A capacitance change type power generating element of the present invention includes a laminate in which a dielectric polarization body and a dielectric elastomer layer are laminated, and a pair of electrodes arranged above and below in the lamination direction of the laminate,
The dielectric polarization body is made of a ferroelectric material having crystal orientation.

Another dielectric layer may be provided between the laminate and the electrode.
The ferroelectric material may contain inevitable impurities.

Here, having crystal orientation is defined as the orientation rate F measured by the Lottgering method being 50% or more.
The orientation rate F is represented by the following formula.
F (%) = (P−P0) / (1−P0) × 100 (i)
In formula (i), P is the ratio of the total reflection intensity from the orientation plane to the total reflection intensity. In the case of (001) orientation, P is the sum ΣI (00l) of the reflection intensity I (00l) from the (00l) plane and the sum ΣI (hkl) of the reflection intensity I (hkl) from each crystal plane (hkl). ({ΣI (00l) / ΣI (hkl)}). For example, in the case of (001) orientation in the perovskite crystal, P = I (001) / [I (001) + I (100) + I (101) + I (110) + I (111)].
P0 is P of a sample having a completely random orientation.
When the orientation is completely random (P = P0), F = 0%, and when the orientation is complete (P = 1), F = 100%.

It is preferable that the polarization axis that minimizes the relative dielectric constant of the ferroelectric material is oriented substantially parallel to the layer thickness direction.

The dielectric polarization body preferably has a remanent polarization value of 5 μC / cm ² or more and a relative dielectric constant of 400 or less. The relative dielectric constant is more preferably less than 200.

Further, it is preferable that the ferroelectric is a single crystal.

The Young's modulus of the dielectric elastomer layer is preferably 100 MPa or less, and more preferably 10 MPa or less.

The crystal structure of the ferroelectric material is preferably a perovskite structure, a bismuth layer structure, or a tungsten bronze structure, and the ferroelectric material mainly contains a perovskite oxide that does not contain lead. preferable. As such a perovskite oxide, a bismuth-containing perovskite oxide is preferable.

The electrostatic capacity change type power generating element of the present invention uses a ferroelectric material having crystal orientation as a dielectric polarization body. According to such a configuration, a ferroelectric material having a large remanent polarization value is further oriented to form a dielectric polarization material, thereby having a very large surface charge density. In addition, a dielectric elastomer is disposed between the dielectric polarization body and one of the electrodes, and the distance between the electrode and the dielectric polarization body can be greatly changed by the elasticity of the dielectric elastomer, thereby improving the amount of power generation. be able to.

Furthermore, when the polarization axis that minimizes the dielectric constant of the ferroelectric material is oriented parallel to the thickness direction of the dielectric polarization layer, the dielectric constant of the dielectric polarization layer may be lowered. And greater power generation characteristics can be achieved.

In addition, a configuration using an inorganic material such as a perovskite oxide as a ferroelectric provides a capacitance change type power generation element having higher heat resistance and higher power generation characteristics than a resin material. be able to.

1 is a schematic cross-sectional view in the thickness direction showing the configuration of a capacitance change power generating element according to an embodiment of the present invention.

Referring to FIG. 1, the capacitance change type power generation element of the present invention will be described. FIG. 1 is a schematic cross-sectional view of a power generating element 1 according to an embodiment of the present invention, where (A) shows a state before element compression (state A), and (B) shows an element compression state (state B). In order to facilitate visual recognition, the scales of the constituent elements of each part are appropriately changed and shown.

As shown in FIG. 1, the power generating element 1 includes a laminated body 12 including a dielectric polarization body layer 10 made of a ferroelectric material having crystal orientation and a dielectric elastomer layer 11 laminated on the dielectric polarization body layer 10. In addition, a lower electrode 21 and an upper electrode 22 which are a pair of electrodes provided on the upper and lower surfaces of the laminate 12 are provided.

The dielectric polarization layer 10 is made of a polarized ferroelectric layer and has a surface charge due to remanent polarization in the ferroelectric.

The lower electrode 21 and the upper electrode 22 are electrically connected to a load (not shown), and the power generating element 1 generates electric energy by changing the capacitance by changing the distance between the

electrodes

21 and 22. This is a capacitance change type power generating element. The distance between the

electrodes

21 and 22 is changed in a state where charges are electrostatically induced in the

electrodes

21 and 22 by the electrostatic field formed by the dielectric polarization layer 10. As the distance between the electrodes changes, an asymmetry occurs in the charge distribution, and a potential difference occurs between the electrodes. Charge transfer occurs so that this potential difference becomes 0, and this becomes a current flowing in the external circuit (load).

As described above, the state B before the compressive force is applied to the power generating element 1 shown in FIG. 1A in the stacking direction from the state A before the compressive force shown in FIG. By changing from the state B to the state A, a potential difference is generated between the

electrodes

21 and 22, and a function as a power generation element is obtained by taking out the change in the potential difference as electric power. The thickness of the elastomer layer 11 is changed by the external pressure (compression force), and the ferroelectric layer 10 is hardly changed.

The principle of power generation will be described.
The power generation amount P in the element of the present invention is defined by the following formula (1), where f is the frequency at which the compressive force is applied between the electrodes.

Here, ΔQ is the surface charge density on the surface of the electrode that moves when the state A changes to the state B, and this is represented by the amount of change in the surface charge amount of the elastomer layer. That is, ΔQ = _Δq _e = q _eB −q _eA . Here, q _eA is the surface charge density of the elastomer in state A, and q _eB is the surface charge density of the elastomer after charge transfer that occurs after becoming compressed state B.
ΔV is the amount of change in potential difference when changing from state A to state B. Here, assuming that the thickness of the ferroelectric layer does not change, the amount of change in potential difference is the potential difference of the elastomer layer. The amount of change can be regarded as _ΔV≈ΔV _e = V _eA −V _eB . Here, V _eA is the potential of the elastomer side electrode in the state A, and ΔV _eB is the potential of the elastomer side electrode before the charge transfer in the compressed state B.

In the state A, the charge density q _eA electrostatically induced on the surface of the elastomer layer by dielectric polarization by the ferroelectric layer and the charge density q _{f on the} surface of the ferroelectric layer can be expressed by the following formula (2). .

From the above relational expression, the power generation amount P is expressed by the following expression (3).

(D _eA thickness of the elastomer layer in the state A, d _eB thickness of the elastomer layer in the state B, d _f is the thickness of the dielectric polarization layer (which is assumed to not change the state A, B.) A is opposed (The electrode area, ε _e is the dielectric constant of the elastomer layer, ε _f is the dielectric constant of the dielectric polarization layer, and ε ₀ is the vacuum dielectric constant.)

From the above formula (3), it can be seen that it is preferable that the dielectric polarization layer 10 has a higher surface charge density q _f and a smaller relative dielectric constant ε _f because a higher power generation amount can be obtained.
Further, the thickness d _eA in the state A of the elastomeric layer, as the difference between the thickness d _eB in state B (the amount of change in thickness) is large, it is also clear that the power generation amount increases.

The lower electrode 21 is not particularly limited as long as it is a base material made of a conductor that does not impair the crystal orientation of the dielectric polarization layer 10 formed on the surface thereof. However, it is preferable that the upper electrode 22 is made of a hard material such as metal or conductive ceramic. Specifically, a metal or metal oxide such as Au, Pt, Ir, Al, Ta, Cr, Fe, Ni, Ti, Cu, IrO ₂ , RuO ₂ , LaNiO ₃ , and SrRuO ₃ , and combinations thereof are used. Can be mentioned. When the dielectric polarization body 10 is a ferroelectric film formed on the lower electrode 21, it is preferable that the dielectric polarization body 10 has good lattice matching with the formed ferroelectric film.

The upper electrode 22 is not particularly limited as long as it is a conductor, but is preferably made of a stretchable conductive material. For example, a stretchable conductive material obtained by containing a conductive filler in an elastomer material can be used. If the electrode has elasticity, it is easy to follow the change in expansion and contraction of the dielectric elastomer, and the effect of suppressing peeling between the upper electrode 22 and the elastomer layer 11 can be obtained.

The thicknesses of the lower electrode 21 and the upper electrode 22 are not particularly limited, and may be a minimum thickness for having sufficient conductivity for taking out a current generated by a change in potential difference between both electrodes. The thickness can be determined by the conductivity of the electrode material and the overall size of the power generating element 1, and is preferably, for example, 50 nm to 100 μm. Each electrode may have a multilayer structure.

As described above, since the electrostatic capacity is changed by greatly expanding and contracting the dielectric elastomer layer 11 in the thickness direction by an external force, the dielectric elastomer layer 11 has a small Young's modulus, and the thickness can be greatly changed with respect to the force. In particular, the Young's modulus is preferably 100 MPa or less, more preferably 10 MPa or less. The external force is used to expand and contract the dielectric elastomer layer 11, and almost no external force is applied to the dielectric polarization layer made of a ferroelectric material, and the thickness hardly changes. Therefore, it is considered that the piezoelectricity hardly functions in the dielectric polarization layer.

Examples of dielectric elastomer materials include thermosetting elastomers such as acrylic rubber, acrylonitrile butadiene rubber, isoprene rubber, silicone rubber and fluoro rubber, which are synthetic rubbers, and thermoplastic elastomers such as polystyrene, polyolefin and polyurethane. Can be used.

The ferroelectric constituting the dielectric polarization layer 10 may be an organic ferroelectric, an inorganic ferroelectric, or a composite material thereof as long as it has crystal orientation. Since higher power generation efficiency can be obtained, it is preferable to use a ferroelectric having a higher remanent polarization value as the ferroelectric. Further, from the viewpoint of heat resistance, an inorganic ferroelectric is preferable, and a ferroelectric having a higher Curie temperature is preferable.

Further, in order to give a larger remanent polarization value, it is preferable that the dielectric polarization layer 10 has a uniform polarization axis of the ferroelectric and is substantially parallel to the thickness direction.

In such a configuration, it is more preferably a single crystal, an oriented ceramic, or an epitaxial film.

In the ferroelectric, the surface charge density q _f can be estimated by the magnitude of the remanent polarization value. Therefore, it is preferable that the dielectric polarization layer 10 is mainly composed of an inorganic ferroelectric material capable of giving a large remanent polarization value.

Examples of the crystal structure of an inorganic ferroelectric that can give a large remanent polarization value (excellent ferroelectricity) include a perovskite structure, a bismuth layered structure, and a tungsten bronze structure, with a perovskite structure being preferred.

As perovskite type oxides having excellent ferroelectricity, lead-based perovskite type oxides are known, but from the viewpoint of environmental impact, those containing a perovskite type oxide containing no lead as a main component are preferable. The containing perovskite oxide is more preferable.

Specific examples of perovskite-type oxides include lead titanate, lead zirconate titanate (PZT), lead zirconate, lead lanthanum titanate, lead lanthanum zirconate titanate, lead zirconium titanate titanate niobate. Lead-containing compounds such as lead zirconium titanate nickel niobate and lead zirconium niobate titanate, and mixed crystals thereof;
In the lead-free system, barium titanate, strontium barium titanate, bismuth sodium titanate, bismuth potassium titanate, sodium niobate, potassium niobate, lithium niobate, etc., and mixed crystals thereof, the following general formula (PX) Perovskite-type oxides (which may contain inevitable impurities) having the composition represented by
_{_{_{_{(Bi x, A 1-x}}}} ) (B y, C 1-y) O 3 ··· (PX)
(In the formula (PX), A is an A-site element having an average ionic valence other than Pb and bivalent, B is a B-site element having an average ionic valence of 3 and C is B having an average ionic valence greater than 3 A, B and C are each one or more kinds of metal elements, O is oxygen, B and C have different compositions, 0.6 ≦ x ≦ 1.0, x-0 .2 ≦ y ≦ x The ratio of the total number of moles of the A-site element and the total number of moles of the B-site element to the number of moles of oxygen atoms is typically 1: 3, but within the range where a perovskite structure can be taken May deviate from 1: 3.)

On the other hand, even if the remanent polarization value is high, the amount of power generation decreases as the relative dielectric constant increases. Therefore, the polarization axis parallel to the thickness direction is preferably the polarization axis that minimizes the relative dielectric constant when the polarization treatment is performed.

By adopting a configuration in which the crystal orientation is controlled so that the polarization axes having a large remanent polarization value and a small relative dielectric constant are aligned substantially parallel to the thickness direction, the surface charge density is high and the relative dielectric constant is small. It can be a dielectric polariser layer.

For example, in the perovskite structure, the polarization axis having a large remanent polarization value and a small relative dielectric constant is the <001> direction (c-axis) for tetragonal crystal, the <110> direction for orthorhombic crystal, and the <111> direction for rhombohedral It is.
For example, a c-axis oriented layer of a perovskite oxide such as PZT has a remanent polarization value of 10 μC / cm ² or more and a relative dielectric constant of 400 or less, preferably less than 200, which is preferable.

The thickness of the dielectric polarization layer 10 is preferably thicker from the viewpoint of increasing the amount of power generation. It is preferable to design the thickness in consideration of the required power generation amount and the size of the element depending on the application. Since the power generation element 1 of the present embodiment has high mechanical-electrical conversion efficiency, it can achieve the same amount of power generation with a relatively thin film thickness as compared with conventional electret materials.

From the viewpoint of miniaturization, the dielectric polarization layer 10 is preferably a ferroelectric film formed on the lower electrode 21. The method of forming the ferroelectric film is not particularly limited, but a ferroelectric film having crystal orientation can be formed, and the direction of polarization should be made substantially uniform without polarization treatment. It is preferable to use a vapor deposition method capable of An example of such a film forming method is a sputtering method using plasma.

A ferroelectric film formed by a vapor phase method has a crystalline orientation in which the polarization axis is substantially uniform and the orientation of polarization is uniform without special polarization treatment depending on the composition of the film. There is a tendency to become a dielectric film. For example, lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT) having high ferroelectricity has a c-axis oriented film <001> orientation in the as-depo state after sputter deposition, and is spontaneous A film in which the direction of polarization is substantially uniformly aligned upward in the c-axis direction is obtained. It is known that the relative dielectric constant when polarized in the c-axis direction is the smallest relative to that when polarized in another polarization axis.

By using such a film forming method, it is possible to obtain the dielectric polarization layer 10 having a high surface charge density and a relatively low dielectric constant by a simple process without requiring a polarization treatment.

On the other hand, after forming a ferroelectric layer having crystal orientation, the dielectric polarization layer may be formed by performing polarization treatment.

The polarization method of the ferroelectric layer is not particularly limited, and examples thereof include a corona discharge treatment that is a general method. From the viewpoint of preventing characteristic deterioration due to depolarization, the coercive electric field value of the ferroelectric constituting the dielectric polarization layer is preferably high. From the viewpoints of heat resistance and deterioration of characteristics due to depolarization, it is preferable that the Curie temperature of the ferroelectric constituting the dielectric polarization layer is higher.

The electrostatic capacity change type power generating element 1 is configured as described above.

The manufacturing method of the power generation element 1 is not particularly limited as long as it has the above configuration. As a method for forming the ferroelectric layer (dielectric polarization layer before polarization treatment) 10 on the lower electrode 21, a suitable method may be used as appropriate depending on the mode of the ferroelectric layer 10.

For example, when the ferroelectric 10 is a bulk body (single crystal or ceramic), the lower electrode 21 may be vapor-deposited or coated with a conductive paste on the ferroelectric 10.

Further, when the ferroelectric 10 is a film, it can be formed by a normal thin film forming technique such as the sputtering method described above. According to the thin film formation technique, the orientation can be controlled relatively easily, and the advantages relating to the polarization treatment in the film formation by sputtering or the like are as already described.

On the other hand, as described above, as the power generation element 1, the larger the thickness of the ferroelectric 10 is, the larger the power generation amount is, but there is a limit to the film thickness that can be achieved by a normal thin film formation technique. Therefore, when the ferroelectric 10 is formed to have a thick film exceeding, for example, 10 μm, it is preferable to form the film by a screen printing method, an aerosol deposition method (AD method), a hydrothermal synthesis method, or the like.

The power generating element 1 uses a ferroelectric material having crystal orientation as the dielectric polarization layer 10. At this time, the polarization axis having the smallest relative dielectric constant is oriented so as to be substantially parallel to the thickness direction. According to such a configuration, not only has a very large surface charge density but also a low dielectric constant, it is possible to achieve greater power generation characteristics. In addition, in a configuration using an inorganic material such as a perovskite oxide as the ferroelectric, the power generating element 1 having higher heat resistance and higher power generation efficiency than the resin material can be obtained.

Table 1 shows the power generation amount of the capacitance change type power generation element when the dielectric polarization layer 10 is formed using various ferroelectrics, and the surface charge density and the dielectric constant values in the above formula (1). The value estimated by substituting is shown. In Table 1, the power generation amount is the relative power generation amount when the power generation amount obtained as the dielectric polarization layer 10 made of a fluorine-based polymer (Cytop (registered trademark), manufactured by Asahi Glass Co., Ltd.) is set to the reference value “1”. It is shown.

The composition of the ferroelectrics in Table 1 is as follows: PbTTi ceramics and c-PZT are Pb (Ti _0.5 , Zr _0.5 ) O ₃ , c-BFO-BTO is (Bi _0.8 , Ba _0.2). ) (Fe _0.8 , Ti _0.2 ) O ₃ , BFO-BTO ceramics are (Bi _0.7 , Ba _0.3 ) (Fe _0.7 , Ti _0.3 ) O ₃ , KNN ceramics are ( K _0.5 , Na _0.5 ) NbO ₃ and c-BFO were BiTiO ₃ . The notation c- means c-axis orientation. The PZT component was obtained by dispersing Pb (Ti _0.5 , Zr _0.5 ) O ₃ fine particles in an organic binder at a rate of 60 vol%.

As shown in Table 1, when Cytop or an inorganic substance is used, a power generation amount that is significantly larger than a general electret material amount can be obtained. In addition, even for non-oriented inorganic materials, the amount of power generation is estimated several hundred times that of Cytop, and further, the amount of power generation is estimated to be several thousand times that of membranes and 16,000 times that of single crystals. It was. Further, a PZT composite in which PZT is dispersed in a polymer material can also generate a power generation amount several tens of times that of Cytop.

"Design changes"
The present invention is not limited to the above embodiment, and various modifications can be made without changing the gist of the invention.

For example, a power generation apparatus in which a plurality of the above-described electrodes, dielectric polarization bodies, and dielectric elastomers are stacked and connected in series or in parallel may improve the power generation amount.

The power generation element of the present invention can be used for power generation by natural energy such as wave power, hydraulic power, wind power, etc., power generation by walking of people embedded in shoes and floors, power generation by running of automobiles embedded in automobile tires, etc. It is.

Claims

A capacitance change type power generation element,
A laminated body in which a dielectric polarization body and a dielectric elastomer layer are laminated, and a pair of electrodes arranged above and below in the laminating direction of the laminated body,
The power generation element, wherein the dielectric polarization body is made of a ferroelectric having crystal orientation.
2. The power generating element according to claim 1, wherein a polarization axis at which a relative dielectric constant of the ferroelectric is minimum is oriented substantially parallel to the layer thickness direction.
3. The power generating element according to claim 1, wherein a remanent polarization value of the dielectric polarization body is 5 μC / cm 2 or more and a relative dielectric constant is 400 or less.
The power generation element according to any one of claims 1 to 3, wherein the ferroelectric is a single crystal.
The power generation element according to any one of claims 1 to 4, wherein the dielectric elastomer layer has a Young's modulus of 100 MPa or less.
The power generation element according to any one of claims 1 to 5, wherein a crystal structure of the ferroelectric material is any one of a perovskite structure, a bismuth layer structure, and a tungsten bronze structure.
The power generation element according to any one of claims 1 to 6, wherein the ferroelectric material contains a perovskite oxide containing no lead as a main component.