Nuclear battery

Abstract

The problem addressed by this invention is to provide a nuclear battery which is lighter in weight and thinner.　Said problem is solved by a nuclear battery that includes a thermoelectric conversion element including: a thermoelectric conversion part demonstrating non-reciprocal conduction based on breakage of space inversion symmetry; and a pair of electrodes provided apart from each other in the thermoelectric conversion part and serving to extract a non-reciprocal thermoelectric signal, wherein at least one of the constituents of the nuclear battery includes a radioactive isotope.

Description

nuclear battery

[0001] The present invention relates to a nuclear battery that contains radioisotopes and can extract electrical energy from decay heat.

[0002] Nuclear power generation fuel contains radioactive isotopes even after use, and constantly emits nuclear decay heat, making its long-term management an extremely important issue. If there was a way to effectively convert this thermal energy and use it as electricity, it could be considered an extremely stable power source that could operate for a long period of time. In fact, deep space probes that cannot use solar power are equipped with isotope batteries that combine radioisotopes and thermoelectric elements, and these batteries have supported long-term missions spanning several decades, and continue to transmit images of deep space to Earth.

[0003] Conventional technology uses radioisotope thermoelectric generators (RTGs), which can extract electricity from radioactive decay. They use a thermocouple to convert the decay heat of radioactive materials into electricity through the Seebeck effect. For example, Patent Document 1 discloses a nuclear battery that is small in degradation due to radiation and can be made smaller.

[0004] Japanese Patent Application Laid-Open No. 2021-85774

[0005] The nuclear battery disclosed in Patent Document 1 requires cooling because it utilizes a temperature gradient, resulting in a large-scale device. Therefore, there has been a demand for a lighter and thinner nuclear battery. The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a nuclear battery that can be made lighter and thinner.

[0006] As a result of intensive research, the inventors have found that a thermoelectric conversion element capable of thermoelectric conversion from temperature fluctuations on a microscale can be provided by using a thermoelectric conversion element including a thermoelectric conversion part that exhibits nonreciprocal conduction based on the breaking of spatial inversion symmetry and a pair of electrodes that are spaced apart from each other and that extract a nonreciprocal thermoelectric signal.The inventors have then conceived of a nuclear battery that is lightweight and can be made thin by including at least one component of the nuclear battery in the thermoelectric conversion element.

[0007] That is, one aspect of the present disclosure relates to a nuclear battery containing a thermoelectric conversion element including: a thermoelectric conversion unit that exhibits nonreciprocal conduction based on the breaking of spatial inversion symmetry; and a pair of electrodes that are spaced apart from each other and that extract a nonreciprocal thermoelectric signal, wherein at least one component of the nuclear battery contains a radioisotope element.

[0008] In the present disclosure, it is preferable that the thermoelectric conversion unit is a thermoelectric conversion layer including a ferromagnetic metal layer and a paramagnetic metal layer stacked on each other, and the pair of electrodes are provided on the thermoelectric conversion layer spaced apart from each other in the in-plane direction of the thermoelectric conversion layer. This increases the thermoelectric conversion voltage based on the breaking of the spatial inversion symmetry of the thermoelectric conversion layer, thereby particularly increasing the power generation efficiency of the nuclear battery.

[0009] In the present disclosure, the distance between the pair of electrodes is preferably 0.1 μm or more and 1000 μm or less. By setting the distance in this range, the voltage of thermoelectric conversion increases, thereby increasing the power generation efficiency of the nuclear battery.

[0010] In the present disclosure, the paramagnetic metal layer preferably comprises a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the paramagnetic metal layer is preferably composed of Pt, Pd, W, an AuW alloy, Ta, a CuIr alloy, a CuBi alloy, a BiSb alloy, or a BiSe alloy. This particularly increases the nonreciprocity of conduction due to the breaking of the spatial inversion symmetry of the thermoelectric conversion layer, thereby particularly increasing the power generation efficiency of the nuclear battery.

[0011] In the present disclosure, the ferromagnetic metal layer preferably comprises a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the ferromagnetic metal layer is preferably composed of a Ni—Fe alloy, Fe, Co, Ni, Gd, a CoFeB alloy, or a (Ga,Fe)Sb alloy. These materials exhibit ferromagnetism at room temperature, and nonreciprocity of conduction is realized at room temperature, thereby increasing the power generation efficiency of the nuclear battery.

[0012] In the present disclosure, the radioisotopes are selected from the group consisting of beryllium-10, carbon-14, aluminum-26, silicon-32, chlorine-36, argon-39, potassium-40, nickel-63, selenium-79, rubidium-87, zirconium-93, indium-115, cesium-137, lanthanum-138, niobium-94, technetium-98, lutetium-71, neodymium-144, samarium-146, samarium-147, gadolinium-152, platinum-190, bismuth-210, and polonium-2 Preferably, the nuclear battery contains at least one element selected from the group consisting of 09, thorium-232, uranium-232, uranium-233, uranium-234, uranium-235, uranium-236, uranium-238, plutonium-236, plutonium-238, plutonium-239, plutonium-244, americium-241, americium-243, curium-244, curium-246, curium-247, curium-248, californium-249, and californium-251. Use of these radioactive isotopes particularly increases the power generation efficiency of the nuclear battery.

[0013] Another aspect of the present disclosure is a nuclear battery module including a plurality of any one of the nuclear batteries described above, the plurality of nuclear batteries being electrically connected to each other so that non-reciprocal thermoelectric signals from each nuclear battery can be superimposed with the same polarity, thereby enabling a large non-reciprocal thermoelectric signal to be extracted and increasing the power generation efficiency of the nuclear battery.

[0014] According to the present disclosure, it is possible to provide a nuclear battery that can be made lightweight and thin. In the thermoelectric conversion element provided in the nuclear battery according to the present disclosure, a thermoelectric signal generated in the thermoelectric conversion unit by an inflowing heat flow is non-reciprocal with respect to the direction of the heat flow due to non-reciprocal conduction in the thermoelectric conversion unit, and such a non-reciprocal thermoelectric signal can be electrically extracted by a pair of electrodes.

[0015] More specifically, when a magnetic field of 1 T or less is applied and a heat flow flows into a stack of magnetized ferromagnetic and paramagnetic metal layers, a spin current is driven in the paramagnetic metal layer, resulting in spin accumulation at the interface between the paramagnetic and ferromagnetic metal layers. The polarity of this spin accumulation is parallel or antiparallel to the magnetization direction of the ferromagnetic metal layer, depending on the direction of the heat flow. The relative orientation of the spin accumulation polarity and the magnetization direction changes the scattering of electrons, resulting in a thermoelectric signal generated in the thermoelectric conversion layer that is dependent on the direction of the heat flow, i.e., nonreciprocity. This is a nonreciprocal thermoelectric signal, and such a nonreciprocal thermoelectric signal can be electrically extracted using a pair of electrodes. Therefore, even if the direction and magnitude of a heat flow changes randomly, a thermoelectric signal can be generated in a fixed direction within the paramagnetic metal layer, enabling thermoelectric conversion from temperature fluctuations on a microscale. Using such a thermoelectric conversion element, a lightweight and thin-film nuclear battery can be provided.

[0016] Fig. 1 is a cross-sectional schematic diagram showing one embodiment of a nuclear battery; Fig. 2 is a cross-sectional schematic diagram showing one embodiment of a nuclear battery; Fig. 3 is a perspective view showing a thermoelectric conversion element according to an embodiment; Fig. 4 is a cross-sectional view of a thermoelectric conversion element according to an embodiment; Fig. 5 is a process diagram showing steps of a thermoelectric conversion method according to an embodiment; Fig. 6 is a perspective view showing the configuration of a thermoelectric conversion module using a thermoelectric conversion element; Fig. 7 is a schematic diagram of a nuclear battery according to an example;

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each drawing, the same reference numerals are used for the same elements where possible. Furthermore, the dimensional ratios within and between elements in the drawings are arbitrary for ease of viewing.

[0018] One aspect of the present disclosure is a nuclear battery containing a thermoelectric conversion element including a thermoelectric conversion unit that exhibits nonreciprocal conduction based on the breaking of spatial inversion symmetry, and a pair of electrodes that are spaced apart from each other and are provided on the thermoelectric conversion unit for extracting a nonreciprocal thermoelectric signal.

[0019] <Thermoelectric Conversion Unit> The thermoelectric conversion unit is a thermoelectric conversion element that exhibits nonreciprocal conduction based on the broken spatial inversion symmetry. The material constituting the thermoelectric conversion unit is not particularly limited as long as it exhibits nonreciprocal conduction based on the broken spatial inversion symmetry. Typically, the thermoelectric conversion unit includes a laminate of ferromagnetic metal layers and paramagnetic metal layers stacked on top of each other. The laminate has a paramagnetic metal layer on one side of the ferromagnetic metal layer, but no similar paramagnetic metal layer on the other side of the ferromagnetic metal layer. Also, a ferromagnetic metal layer on one side of the paramagnetic metal layer, but no similar ferromagnetic metal layer on the other side of the paramagnetic metal layer. Therefore, the laminate of the ferromagnetic metal layers and paramagnetic metal layers stacked on top of each other has a structure in which the spatial inversion symmetry is broken along the stacking direction. The laminate has substantial spatial inversion symmetry in the in-plane direction. Due to the broken spatial inversion symmetry along the stacking direction, the laminate exhibits nonreciprocity in the in-plane electrical conductivity.

[0020] The ferromagnetic metal layer is composed of a metal that exhibits ferromagnetism at temperatures in the environment in which the nuclear battery is used. It is preferably composed of a metal that exhibits ferromagnetism at room temperature (approximately 300 K). From this perspective, it is preferably composed of Fe, Co, Ni, Gd, or an alloy containing at least one of these, and is particularly preferably composed of a Ni—Fe alloy, Co, or CoFeB. The thickness of the ferromagnetic metal layer is not particularly limited, but can be, for example, 1 nm or more and 100 nm or less.

[0021] The paramagnetic metal layer is composed of a metal that exhibits paramagnetism at the temperature of the usage environment of the nuclear battery, and is preferably composed of a metal that exhibits paramagnetism at room temperature (300 K). The paramagnetic metal layer is preferably composed of a paramagnetic metal with high spin-orbit interaction in order to enhance the spin Nernst effect in the paramagnetic metal layer described below. From this perspective, it is preferably composed of Pt, Pd, W, an AuW alloy, Ta, a CuIr alloy, a CuBi alloy, a BiSb alloy, or a BiSe alloy, and is particularly preferably composed of Pt. The thickness of the paramagnetic metal layer is not particularly limited, but can be, for example, 1 nm or more and 100 nm or less.

[0022] <Electrodes> The electrodes are provided on the thermoelectric conversion unit at a distance from each other, and extract non-reciprocal thermoelectric signals from the thermoelectric conversion unit. Their arrangement is not particularly limited as long as they can extract non-reciprocal thermoelectric signals from the thermoelectric conversion unit, and they are typically arranged at a distance on the surface of the thermoelectric conversion unit. When a pair of electrodes are arranged at a distance on the surface of the thermoelectric conversion unit, the distance between them in the planar direction of the thermoelectric conversion unit is preferably 0.1 μm or more and 1000 μm or less. The thickness of the electrodes is not particularly limited, but can be, for example, 10 nm or more and 1 μm or less.

[0023] The electrodes are made of a material having conductivity that allows a non-reciprocal thermoelectric signal to be extracted from the thermoelectric conversion layer. Examples of such materials include metal materials such as Cu, Ag, Au, Pt, Ni, Al, constantan, Cr, In, Pd, Fe, Cu alloys, Ti / Au laminates, and Cr / Au laminates, and conductive oxides such as indium tin oxide (ITO) and zinc oxide (ZnO). Cu, Ag, Au, Pt, Ni, Al, constantan, and Cu copper alloys are preferred, and Cu, Au, Ag, Pt, Ni, Ti / Au laminates, and Cr / Au laminates are particularly preferred.

[0024] <Substrate> The nuclear battery may have a substrate that supports the thermoelectric conversion unit. The shape of the substrate is not particularly limited, and may be a plate or a film. The material of the substrate is also not particularly limited, and examples thereof include metals such as Au, Ag, Cu, and Al, silicon, sapphire, SiC, GaN, yttria-stabilized zirconia (YSZ), and resins such as polyimide, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN).

[0025] <Method for Manufacturing Thermoelectric Conversion Unit> The thermoelectric conversion unit is formed, for example, by preparing a substrate, depositing materials for forming a ferromagnetic metal layer and materials for forming a paramagnetic metal layer in this order on the substrate surface using physical vapor deposition such as DC magnetron sputtering to form a laminate, and patterning the laminate into a rectangular shape in plan view using photolithography and lift-off to form the thermoelectric conversion unit. Then, metal materials for forming a pair of electrodes are deposited in an area including the surface of the paramagnetic metal layer using physical vapor deposition such as DC magnetron sputtering to form a metal layer, and the metal layer is patterned into a predetermined shape using photolithography and lift-off to form the pair of electrodes. The ferromagnetic metal layer and paramagnetic metal layer may be deposited in the reverse order on the substrate. Alternatively, a metal layer that will serve as the electrodes may be formed on the substrate first, and then the ferromagnetic metal layer and paramagnetic metal layer may be deposited. The thermoelectric conversion unit may also include a layer made of an insulating magnetic material that is provided in contact with the ferromagnetic metal layer.

[0026] <Radioactive Isotope> In the nuclear battery of the present disclosure, at least one component of the nuclear battery contains a radioactive isotope. The radioactive isotope may be any that is capable of emitting radiation, and examples thereof include beryllium-10, carbon-14, aluminum-26, silicon-32, chlorine-36, argon-39, potassium-40, nickel-63, selenium-79, rubidium-87, zirconium-93, indium-115, cesium-137, lanthanum-138, niobium-94, technetium-98, lutetium-71, neodymium-144, samarium-146, samarium-147, gadolinium-152, and platinum. -190, bismuth-210, polonium-209, thorium-232, uranium-232, uranium-233, uranium-234, uranium-235, uranium-236, uranium-238, plutonium-236, plutonium-238, plutonium-239, plutonium-244, americium-241, americium-243, curium-244, curium-246, curium-247, curium-248, californium-249, californium-251, etc. Of these, plutonium-238 and curium-244 are preferred.

[0027] The radioisotope is contained in at least one component of the nuclear battery. Specific examples are described with reference to FIGS. 1 and 2. FIG. 1 shows a cross-sectional schematic diagram of a nuclear battery, in which the components are a thermoelectric conversion unit made up of a paramagnetic metal layer and a ferromagnetic metal layer, and a pair of electrodes. In FIG. 1, all of the components of the nuclear battery 10, i.e., the paramagnetic metal layer 11, the ferromagnetic metal layer 12, and the pair of electrodes 14, contain a radioisotope 16. There are no particular limitations on the method for incorporating the radioisotope into the components, and any known method can be used as appropriate. For example, the radioisotope can be implanted into the components using an accelerator or the like.

[0028] Other examples of arrangement of radioisotopes in nuclear batteries having the components shown in Figure 1 include: - Radioisotopes arranged only on the electrodes - Radioisotopes arranged only on the paramagnetic metal layer - Radioisotopes arranged only on the ferromagnetic metal layer - Radioisotopes arranged on both the electrodes and the paramagnetic metal layer - Radioisotopes arranged on the electrodes and the ferromagnetic metal layer - Radioisotopes arranged on the paramagnetic metal layer and the ferromagnetic metal layer.

[0029] 2 is a cross-sectional schematic diagram of a nuclear battery, the components of which are a thermoelectric conversion unit made up of a paramagnetic metal layer and a ferromagnetic metal layer, a pair of electrodes, and a substrate. In FIG. 2, all of the components of the nuclear battery 20, i.e., the paramagnetic metal layer 21, the ferromagnetic metal layer 22, the pair of electrodes 24, and the substrate 25, contain radioactive isotopes 26. Other examples of arrangement of radioisotopes in nuclear batteries having the components shown in Figure 2 include: - Radioisotopes arranged only on the electrodes - Radioisotopes arranged only on the paramagnetic metal layer - Radioisotopes arranged only on the ferromagnetic metal layer - Radioisotopes arranged only on the substrate - Radioisotopes arranged on the electrodes and paramagnetic metal layer - Radioisotopes arranged on the electrodes and ferromagnetic metal layer - Radioisotopes arranged on the electrodes and substrate - Radioisotopes arranged on the paramagnetic metal layer and ferromagnetic metal layer - Radioisotopes arranged on the paramagnetic metal layer and substrate - Radioisotopes arranged on the ferromagnetic metal layer and substrate - Radioisotopes arranged on the electrodes, paramagnetic metal layer and ferromagnetic metal layer - Radioisotopes arranged on the electrodes, paramagnetic metal layer and substrate - Radioisotopes arranged on the electrodes, ferromagnetic metal layer and substrate - Radioisotopes arranged on the electrodes, ferromagnetic metal layer and substrate - Radioisotopes arranged on the paramagnetic metal layer, ferromagnetic metal layer and substrate

[0030] As described above, any of the components constituting the nuclear battery may contain a radioisotope. This is because the thermoelectric conversion unit included in the nuclear battery according to the present disclosure generates electricity not through the spin Seebeck effect as disclosed in Patent Document 1 but through the spin Nernst effect as described below, and therefore does not need to form a temperature gradient in the stacking direction of the thermoelectric conversion element. Therefore, it is not necessary for the radioisotope to be arranged only on one side of the stacking direction of the thermoelectric conversion unit. Specifically, it is not necessary for the thermoelectric conversion unit, the substrate, and the radioisotope layer to be stacked in this order, and it is not necessary for the radioisotope layer, the thermoelectric conversion unit, and the substrate to be stacked in this order. Furthermore, it is not necessary for the radioisotope to be arranged so as to generate a temperature gradient for generating the spin Seebeck effect in the thermoelectric conversion unit. Furthermore, in the nuclear battery, multiple radioisotopes may be randomly arranged within and / or across multiple components. In other words, it is not necessary for the radioisotope to be arranged as a radioisotope layer.

[0031] Next, a thermoelectric conversion method according to this embodiment will be described. Fig. 5 is a process diagram showing the steps of the thermoelectric conversion method according to this embodiment. As shown in Fig. 5, the steps of the thermoelectric conversion method according to this embodiment include step S11 of preparing a thermoelectric conversion element, step S12 of inputting a heat flow, and step S13 of performing thermoelectric conversion while applying an external magnetic field. These steps will be described with reference to Figs. 3 and 4.

[0032] In step S11 of preparing a thermoelectric conversion element, a thermoelectric conversion element 200 is prepared as shown in Figures 3 and 4. Subsequently, in step S12 of inputting a heat flow, a heat flow H from the outside, which is the target of thermoelectric conversion, is input to the thermoelectric conversion layer 202 so as to flow along the X-axis direction, which is one of the in-plane directions (in the XY plane) of the thermoelectric conversion layer 202.

[0033] Next, in step S13 of performing thermoelectric conversion while applying an external magnetic field, an external magnetic field B generated by a magnetic field generator provided outside the thermoelectric conversion element 200 is applied to the ferromagnetic metal layer 203. The direction of application of the external magnetic field B is an in-plane direction (within the XY plane) of the thermoelectric conversion element 200, and is the negative Y-axis direction, which is one of the directions perpendicular to the direction of the flow of the heat flow H. As a result, the ferromagnetic metal layer 203 is magnetized in the direction of the external magnetic field B, and has magnetization 203M oriented in the direction of the external magnetic field B. The application of such an external magnetic field B is maintained while thermoelectric conversion of the heat flow H is being performed. The magnitude of the external magnetic field B can be, for example, 1 T or less.

[0034] In step S13, when the heat flow H flows into the paramagnetic metal layer 205, the spin current J Ｓ is generated along the Z-axis direction and flows into the ferromagnetic metal layer 203. Ｓ The polarity of the spin current J changes to the positive or negative Y-axis direction depending on the direction of the heat flow H. Therefore, when the direction of the heat flow H is reversed, the spin current J Ｓ The polarity of the spin current J Ｓ and the direction of the magnetization 203M of the ferromagnetic metal layer 203 are reversed. Ｓ The relative orientation of the polarity of the magnetization 203M and the direction of the magnetization 203M can also be reversed.

[0035] Spin current J Ｓ flows into the ferromagnetic metal layer 203, electron scattering changes depending on the relative direction between the polarity of the spin current and the direction of magnetization 203M of the ferromagnetic metal layer 203. Since the polarity of the spin current near the junction interface between the ferromagnetic metal layer 203 and the paramagnetic metal layer 205 changes depending on the direction of the heat current H, this electron scattering changes depending on the direction of the heat current H. This causes the thermoelectric signal generated in the thermoelectric conversion layer 202 to depend on the direction of the heat current H, i.e., to be non-reciprocal.

[0036] The thermoelectric signal J generated in the thermoelectric conversion layer 202 Ｎ is non-reciprocal with respect to the direction of the heat flow H due to the non-reciprocal conduction of the thermoelectric conversion layer 202 as described above (i.e., the thermoelectric signal J Ｎchanges nonlinearly with respect to the direction of the heat flow H), and the thermoelectric signal J Ｎ The direction of the non-reciprocal thermoelectric signal J is the positive direction of the X axis. Ｎ The inventors of the present application have found that the thermoelectric conversion element 200 according to this embodiment can extract the non-reciprocal thermoelectric signal J in a fixed direction within the thermoelectric conversion layer 202, even if the direction and magnitude of the heat flow H change randomly. Ｎ Since it is possible to generate thermoelectric power, it is possible to perform thermoelectric conversion from temperature fluctuations on a microscale.

[0037] Furthermore, by reversing the direction of the external magnetic field B to the positive Y-axis direction and reversing the direction of the magnetization 203M of the ferromagnetic metal layer 203 to the positive Y-axis direction, a non-reciprocal thermoelectric signal J Ｎ The direction of can be reversed to the negative X-axis direction.

[0038] In the thermoelectric conversion layer 202, a non-reciprocal thermoelectric signal J is extracted by a pair of electrodes 207a and 207b. Ｎ is the magnitude of the voltage V, the electric field generated in thermoelectric conversion layer 202 corresponding to V is E, the nonlinear Seebeck coefficient of thermoelectric conversion layer 202 is S, the distance between pair of electrodes 207a and 207b is L (D207 in FIG. 4), the temperature gradient within the range of distance L in thermoelectric conversion layer 202 is ∇T, and the temperature difference within the range of distance L in thermoelectric conversion layer 202 is ΔT, then electric field E=nonlinear Seebeck coefficient S×(temperature gradient ∇T) ２ By multiplying both sides of this equation by the distance L, the voltage V = nonlinear Seebeck coefficient S × (temperature difference ΔT) ２ / L, the smaller the distance L between the pair of electrodes 207a and 207b, the larger the voltage V. Therefore, by setting the separation distance D207 between the pair of electrodes 207a and 207b in the X-axis direction to a small value, preferably 1000 μm or less, as described above, the non-reciprocal thermoelectric signal J extracted by the pair of electrodes 207a and 207b can be reduced. Ｎ becomes larger.

[0039] The thermoelectric conversion element 200 may also include a heat conduction portion that is provided in contact with or close to the end face on the positive side of the X-axis and / or the end face on the negative side of the X-axis, and that facilitates the flow of heat flow H into the thermoelectric conversion layer 202. Such a heat conduction portion may be made of, for example, aluminum, copper, carbon fiber, sapphire, alumina, silicon with a thermal oxide film, or a high molecular weight polymer.

[0040] 6 is a perspective view showing the configuration of a thermoelectric conversion module using the above-described thermoelectric conversion elements. As shown in FIG. 6, a thermoelectric conversion module 300 according to this embodiment includes a plurality of thermoelectric conversion elements 200, and in this embodiment, includes four thermoelectric conversion elements 200a, 200b, 200c, and 200d. The four thermoelectric conversion elements 200a, 200b, 200c, and 200d generate non-reciprocal thermoelectric signals J from the respective thermoelectric conversion elements. Ｎ are electrically connected to each other so as to overlap with each other with the same polarity.

[0041] Specifically, in the thermoelectric conversion module 300, thermoelectric conversion elements 200a and 200c are arranged with respect to the Cartesian coordinate system C in a manner similar to that of the thermoelectric conversion element 200 shown in Figures 3 and 4, and thermoelectric conversion elements 200b and 200d are arranged with respect to the Cartesian coordinate system C in a manner obtained by rotating the thermoelectric conversion element 200 shown in Figures 3 and 4 by 180 degrees around the Y axis, and are alternately provided along the Y axis direction. The electrode 207a of the thermoelectric conversion element 200a is electrically connected to the electrode 207b of the thermoelectric conversion element 200b, the electrode 207a of the thermoelectric conversion element 200b is electrically connected to the electrode 207b of the thermoelectric conversion element 200c, and the electrode 207a of the thermoelectric conversion element 200c is electrically connected to the electrode 207b of the thermoelectric conversion element 200d. 3 and 4 , in the same manner as the thermoelectric conversion elements 200a and 200c, the thermoelectric conversion elements 200b and 200d may be arranged with respect to the orthogonal coordinate system C. In this case, the electrode 207a of the thermoelectric conversion element 200a and the electrode 207a of the thermoelectric conversion element 200b are electrically connected to the electrode 207a of the thermoelectric conversion element 200b, the electrode 207b of the thermoelectric conversion element 200b and the electrode 207b of the thermoelectric conversion element 200c are electrically connected to the electrode 207a of the thermoelectric conversion element 200d.

[0042] Moreover, the ferromagnetic metal layer 203 of each of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d is magnetized in the negative Y-axis direction by the external magnetic field B, and has a magnetization 203M oriented in the negative Y-axis direction.

[0043] The thermoelectric conversion module 300 also includes heat conduction units 301 and 302 that are provided in contact with or in close proximity to the end faces on the negative side of the X-axis and the end faces on the positive side of the X-axis of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d. This makes it easier for the heat flowing in the X-axis direction to flow into the ferromagnetic metal layers 203 of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d. The thermoelectric conversion module 300 does not necessarily have to include the heat conduction units 301 and 302.

[0044] The heat flow flows into the ferromagnetic metal layer 203 of each of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d, and the non-reciprocal thermoelectric signals generated in each thermoelectric conversion element 200 are superimposed with the same polarity and can then be extracted by the electrode 207b of the thermoelectric conversion element 200a and the electrode 207a of the thermoelectric conversion element 200d, making it possible to extract a large non-reciprocal thermoelectric signal.

[0045] The nuclear battery may be provided with a shield made of a radiation-shielding material. The shield is provided for the purpose of preventing radiation emitted from radioisotopes from being released into the external environment, and may be provided as a layer on the outermost surface of the nuclear battery, or as a casing that covers the nuclear battery. The nuclear battery module may also be provided with a shield. As the shield, a known radiation-shielding material can be used, and in addition to typical radiation-shielding materials such as lead and concrete, it may also be a rubber sheet or a resin sheet having radiation-shielding properties.

[0046] The thermoelectric conversion element in the nuclear battery may be a single layer, or may be multi-layered to obtain a nuclear potential that generates a large electromotive force. A protective film may be provided to protect the thermoelectric conversion element, and the nuclear battery may be connected to terminals to be used as a nuclear battery device. The size and shape of the nuclear battery can be adjusted as desired depending on the application.

[0047] Although the nuclear battery of the present disclosure has been described in detail above, the scope of the invention is not limited to the above-described examples, and various improvements and modifications may be made without departing from the gist of the invention.

[0048] For example, in the above-described embodiment, in step S13, the external magnetic field B is applied to the ferromagnetic metal layer 203 in a direction within the plane of the thermoelectric conversion element 200 (in the XY plane) and perpendicular to the direction of the flow of the heat flow H (see FIGS. 3 and 4), but the external magnetic field B may also be applied in a direction within the plane of the thermoelectric conversion element 200 (in the XY plane) and intersecting the direction of the flow of the heat flow H at an angle other than 90 degrees. However, the external magnetic field B and the heat flow H are set so as not to be parallel or anti-parallel to each other.

[0049] Furthermore, in the above-described embodiment, thermoelectric conversion is performed while applying an external magnetic field B in step S13 (see FIGS. 3 and 4 ), but if the ferromagnetic metal layer 203 has magnetization 203M even without applying the external magnetic field B, thermoelectric conversion can be performed in step S13 without applying the external magnetic field B. Methods for achieving this include, for example, forming the ferromagnetic metal layer 203 from a material with a large coercive force so that the ferromagnetic metal layer 203 has magnetization 203M as remanent magnetization, or providing the thermoelectric conversion element 200 with a layer or member that applies a static magnetic field or an exchange coupling magnetic field to the ferromagnetic metal layer 203. For example, the thermoelectric conversion element 200 may further include an antiferromagnetic layer such as NiO, IrMn, FeMn, NiMn, PtMn, PdMn, MnAu, FeRh, or MnSb laminated on the side of the ferromagnetic metal layer 203 opposite to the paramagnetic metal layer 205 so as to apply an exchange coupling magnetic field to the ferromagnetic metal layer 203. This makes it possible to perform thermoelectric conversion without applying an external magnetic field B.

[0050] Furthermore, in the above-described embodiment, the pair of electrodes 207a, 207b are provided on the surface 205S of the paramagnetic metal layer 205 so as not to contact the ferromagnetic metal layer 203 and so as to be spaced apart from each other along the X-axis direction (see Figures 3 and 4), but they may also be provided on the side surfaces of the paramagnetic metal layer 205 in the positive and negative X-axis directions so as not to contact the ferromagnetic metal layer 203 and so as to be spaced apart from each other along the X-axis direction.

[0051] Furthermore, although the ferromagnetic metal layer 203 in the above-described embodiment is a single layer (see FIGS. 3 and 4), the ferromagnetic metal layer 203 may be composed of a plurality of stacked ferromagnetic metal layers. In this case, it is preferable that each of the plurality of layers is composed of a Ni—Fe alloy, Fe, Co, Ni, Gd, a CoFeB alloy, or a (Ga,Fe)Sb alloy. Such a plurality of stacked ferromagnetic metal layers may be, for example, a laminate in which layers made of a plurality of types of ferromagnetic metals are periodically stacked on top of each other (e.g., a laminate in which three types of layers are periodically stacked, such as Layer A, Layer B, Layer C, Layer A, Layer B, Layer C, ..., where Layer A is a layer made of a first ferromagnetic metal, Layer B is a layer made of a second ferromagnetic metal, and Layer C is a layer made of a third ferromagnetic metal), or a laminate in which layers made of a plurality of types of ferromagnetic metals are randomly stacked on top of each other (e.g., a laminate in which three types of layers are randomly stacked, such as Layer A, Layer B, Layer C, Layer B, Layer A, Layer C, ...).

[0052] Although the paramagnetic metal layer 205 in the above-described embodiment is a single layer (see FIGS. 3 and 4 ), the paramagnetic metal layer 205 may be composed of a plurality of stacked paramagnetic metal layers. In this case, each of the plurality of layers is preferably composed of Pt, Pd, W, an AuW alloy, Ta, a CuIr alloy, a CuBi alloy, a BiSb alloy, or a BiSe alloy. Examples of such stacked paramagnetic metal layers include a laminate in which layers made of a plurality of types of paramagnetic metals are periodically stacked on top of each other (e.g., a laminate in which three types of layers are periodically stacked, such as Layer D, Layer E, Layer F, Layer D, Layer E, Layer F, etc., where Layer D is a layer made of a first paramagnetic metal, Layer E is a layer made of a second paramagnetic metal, and Layer F is a layer made of a third paramagnetic metal), or a laminate in which layers made of a plurality of types of paramagnetic metals are randomly stacked on top of each other (e.g., a laminate in which three types of layers are randomly stacked, such as Layer D, Layer E, Layer F, Layer E, Layer F, etc.). The stacked paramagnetic metal layers preferably have spin Nernst angles of the same sign, because this prevents nonreciprocal thermoelectric signals resulting from the paramagnetic metal layers from canceling each other out during thermoelectric conversion in the thermoelectric conversion layer 202, thereby increasing the overall nonreciprocal thermoelectric signal.

[0053] Furthermore, although the thermoelectric conversion layer 202 in the above-described embodiment includes only one paramagnetic metal layer (paramagnetic metal layer 205) (see FIGS. 3 and 4), the thermoelectric conversion layer 202 may include a first paramagnetic metal layer and a second paramagnetic metal layer. In this case, the thermoelectric conversion layer 202 is configured by stacking the first paramagnetic metal layer, the ferromagnetic metal layer 203, and the second paramagnetic metal layer in this order along the Z-axis direction, with the ferromagnetic metal layer 203 interposed between the first paramagnetic metal layer and the second paramagnetic metal layer. The preferred materials for the first paramagnetic metal layer and the second paramagnetic metal layer are the same as those for the paramagnetic metal layer 205, but the configurations (constituent materials, film thickness, etc.) of the first paramagnetic metal layer and the second paramagnetic metal layer are selected so that the thermoelectric conversion layer 202 has a structure in which spatial inversion symmetry is broken along the Z-axis direction.

[0054] In this case, it is preferable that the first paramagnetic metal layer and the second paramagnetic metal layer have spin Nernst angles of opposite signs (for example, this can be achieved by configuring the first paramagnetic metal layer from Pt and the second paramagnetic metal layer from Ta). This is because, during thermoelectric conversion in the thermoelectric conversion layer 202, spin currents having the same polarity are injected from the first paramagnetic metal layer and the second paramagnetic metal layer into the ferromagnetic metal layer 203, thereby increasing the nonreciprocal thermoelectric signal.

[0055] Furthermore, in this case, either or both of the first and second paramagnetic metal layers may be composed of a plurality of paramagnetic metal layers stacked as described above. In this case, it is preferable that the plurality of paramagnetic metal layers constituting either or both of the first and second paramagnetic metal layers have spin Nernst angles of the same sign, for the reasons described above.

[0056] Furthermore, in the above-described embodiment, the pair of electrodes 207a, 207b are provided on the surface 205S of the paramagnetic metal layer 205 (see Figures 3 and 4), but the pair of electrodes 207a, 207b may also be provided on the back surface (the surface on the negative side of the Z axis) of the ferromagnetic metal layer 203 so as not to contact the paramagnetic metal layer 205 and so as to be spaced apart from each other along the X-axis direction.

[0057] Furthermore, in the above-described embodiment, the thermoelectric conversion layer 202 is formed by stacking the ferromagnetic metal layer 203 and the paramagnetic metal layer 205 in this order on the substrate 201 (see FIGS. 3 and 4 ), but the thermoelectric conversion layer 202 may also be formed by stacking the paramagnetic metal layer 205 and the ferromagnetic metal layer 203 in this order on the substrate 201. In this case, the pair of electrodes 207 a, 207 b can be provided on the front surface of the ferromagnetic metal layer 203 (the surface on the positive side of the Z axis) or the back surface of the paramagnetic metal layer 205 (the surface on the negative side of the Z axis) so as to be spaced apart from each other along the X-axis direction.

[0058] The present invention will be described in more detail below with reference to specific examples. However, the present invention is not limited to the following examples. [Manufacturing Example of Thermoelectric Conversion Element] An element corresponding to the thermoelectric conversion element 200 shown in FIG. 3 was fabricated as follows. First, a 0.5 mm-thick Si substrate with a thermal oxide film was prepared as the substrate 201. On this substrate, a 5 nm-thick Ni—Fe alloy layer as the ferromagnetic metal layer 203 and a 5 nm-thick Pt layer as the paramagnetic metal layer 205 were deposited in this order by DC magnetron sputtering to form the thermoelectric conversion layer 202. Then, by photolithography and lift-off, the thermoelectric conversion layer 202 was patterned into a rectangular shape in plan view, with a width of 5 μm in the Y-axis direction and a length of 50 μm in the X-axis direction. Thereafter, a Ti / Au layer was deposited on the thermoelectric conversion layer 202 by RF magnetron sputtering, and the Ti / Au layer was patterned into a predetermined shape by photolithography and lift-off to form a pair of electrodes corresponding to the pair of electrodes 207a, 207b, thereby producing an element corresponding to the thermoelectric conversion element 200.

[0059] Example 1: A nuclear battery conceptually shown in Figure 7 was fabricated. Plutonium-238 was implanted onto a sapphire substrate using an accelerator, and a Pt (5 nm) = Py (5 nm) bilayer film (thermoelectric conversion element) was formed using RF magnetron sputtering. Electron beam lithography and Ar ion etching were used to pattern the film into a rectangular device 5 μm wide and 50 μm long. The resulting nuclear battery was placed in a magnetic field at room temperature, and the nonlinear voltage was measured.

[0060] [Example 2] A nuclear battery conceptually shown in Figure 7 was fabricated. Curium-244 was implanted onto a sapphire substrate using an accelerator, and a Pt (5 nm) = Py (5 nm) bilayer film (thermoelectric conversion element) was formed using RF magnetron sputtering. Electron beam lithography and Ar ion etching were used to pattern the film into a rectangular device 5 μm wide and 50 μm long. The resulting nuclear battery was placed in a magnetic field at room temperature, and the nonlinear voltage was measured.

[0061] The thermoelectric conversion elements manufactured in the examples are capable of generating thermoelectric signals nonlinearly with respect to the direction of a temperature gradient, enabling thermoelectric conversion from temperature fluctuations on a microscale where temperature gradients are virtually nonexistent on a macroscale. Therefore, the nuclear batteries of Examples 1 and 2, which contain radioisotopes as components of the nuclear battery, are capable of generating electrical energy from the heat of radiation randomly emitted from the radioisotopes. Therefore, unlike conventional nuclear batteries, the thermoelectric conversion element does not require components for creating a temperature gradient, and the nuclear battery of the present disclosure is lightweight and thin-film. Furthermore, because thermoelectric conversion can be performed from temperature fluctuations on a microscale, power generation using extremely weak radiation is possible, and degradation of the nuclear battery due to radiation is extremely minimal. Therefore, the nuclear battery can be put to practical use in radiation therapy power sources, space exploration power sources, generators for military equipment, power generation for traffic lights, and the nuclear energy field (such as power generation from spent nuclear fuel casks).

[0062] Although the present invention will be described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

[0063] [Additional remarks] The nuclear battery and nuclear power battery disclosed herein can be made lighter and smaller than existing nuclear batteries, and have higher power generation efficiency. Therefore, it can contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations. Goal 9: "Create indispensable infrastructure for industry, innovation and sustainable development."

[0064] 10, 20, 30... Nuclear battery 11, 21, 31... Paramagnetic metal layer 12, 22... Ferromagnetic metal layer 13, 23... Thermoelectric conversion element 14, 24... Electrode 25... Substrate 16, 26, 36... Radioactive isotope 37... Heat 38... Radiation 200... Thermoelectric conversion element 202... Thermoelectric conversion layer 203... Ferromagnetic metal layer 205... Paramagnetic metal layer 207a, 207b... Pair of electrodes 300... Thermoelectric conversion module

Claims

1. A nuclear battery containing a thermoelectric conversion element comprising: a thermoelectric conversion unit that exhibits nonreciprocal conduction based on the breaking of spatial inversion symmetry; and a pair of electrodes spaced apart from each other on the thermoelectric conversion unit for extracting a nonreciprocal thermoelectric signal, wherein at least one component of the nuclear battery contains a radioisotope.

2. The nuclear battery according to claim 1, wherein the thermoelectric conversion section is a thermoelectric conversion layer including a ferromagnetic metal layer and a paramagnetic metal layer stacked on each other, and the pair of electrodes are provided on the thermoelectric conversion layer so as to be spaced apart from each other in the in-plane direction of the thermoelectric conversion layer.

3. The nuclear battery according to claim 2, wherein the distance between the pair of electrodes is 0.1 μm or more and 1000 μm or less.

4. The nuclear battery according to claim 2, wherein the paramagnetic metal layer is composed of a single layer or a plurality of stacked layers, and each of the single layer or the plurality of stacked layers of the paramagnetic metal layer is composed of Pt, Pd, W, an AuW alloy, Ta, a CuIr alloy, a CuBi alloy, a BiSb alloy, or a BiSe alloy.

5. The nuclear battery according to claim 2, wherein the ferromagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the ferromagnetic metal layer is composed of a Ni-Fe alloy, Fe, Co, Ni, Gd, a CoFeB alloy, or a (Ga,Fe)Sb alloy.

6. The radioisotope is beryllium-10, carbon-14, aluminum-26, silicon-32, chlorine-36, argon-39, potassium-40, nickel-63, selenium-79, rubidium-87, zirconium-93, indium-115, cesium-137, lanthanum-138, niobium-94, technetium-98, lutetium-71, neodymium-144, samarium-146, samarium-147, gadolinium-152, platinum-190, bismuth-210, polonium-209, tritium-10, tetrahydrofuran-11, tetrahydrofuran-12, tetrahydrofuran-13, tetrahydrofuran-14, tetrahydrofuran-15 ...

2. The nuclear battery of claim 1, comprising at least one element selected from the group consisting of: Mu-232, Uranium-232, Uranium-233, Uranium-234, Uranium-235, Uranium-236, Uranium-238, Plutonium-236, Plutonium-238, Plutonium-239, Plutonium-244, Americium-241, Americium-243, Curium-244, Curium-246, Curium-247, Curium-248, Californium-249, and Californium-251.

7. A nuclear battery module comprising a plurality of nuclear batteries according to any one of claims 1 to 6, the plurality of nuclear batteries being electrically connected to each other so that non-reciprocal thermoelectric signals from each nuclear battery can be superimposed with the same polarity.

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