Thermoelectric power generation element, thermoelectric battery, and method for stabilizing power generation

Abstract

The purpose of the present invention is to provide a thermoelectric power generating battery having excellent battery characteristics.　The problem can be addressed using the thermoelectric power generating element not requiring a temperature gradient of the present invention. In this thermoelectric power generating element, a first portion including a semiconductor that generates thermally excited electrons and holes, a second portion that includes an electrolyte through which a charge transport ion pair can move, and a third portion including a material that serves as an electrode are in contact in this order. The valence band potential of the semiconductor of the first portion is more positive than the oxidation-reduction potential of the charge transport ion pair, an oxidation reaction of the ion that is more easily oxidized of the two ions occurs at the interface between the first portion and the second portion, and a reduction reaction of the ion that is more easily reduced of the two ions occurs at the interface between the third portion and the second portion. This thermoelectric power generating element also satisfies formula (I): L / IDT = 1 to 20 (I) (in the formula, L is "the shortest distance between the first portion and the second portion," and IDT is "ion diffusion thickness").

Description

[Technical Field]

[0001] The present invention relates to a thermoelectric power generation element and a method for stabilizing power generation. [Background technology]

[0002] Conventionally, thermoelectric power generation utilizing the Seebeck effect has been known as a method of generating electricity using geothermal energy or waste heat from factories (Patent Documents 1 and 2, and Non-Patent Document 1), and its practical application is expected in order to efficiently utilize thermal energy. Thermoelectric power generation using the Seebeck effect is a power generation principle that utilizes the fact that a voltage is generated when a temperature gradient is applied to a metal or semiconductor. Specifically, it is a thermoelectric power generation system that converts thermal energy into electrical energy by applying a temperature gradient to a thermoelectric conversion element that combines a p-type semiconductor and an n-type semiconductor.

[0003] However, conventional thermoelectric conversion elements that utilize temperature gradients have several problems, including the high cost of the semiconductors that make up the element, a wide operating temperature range, and low conversion efficiency. Furthermore, the physical durability of the coupling is weak, making it unsuitable for installation in locations subject to vibration. In addition, because a temperature gradient is required for power generation, there are limitations on the installation location, and in some cases, a cooling device for the temperature gradient is necessary. In particular, since one dimension of the thermoelectric conversion module is used for the temperature gradient, the utilization of the heat source is two-dimensional, and it is not possible to use all the surrounding heat three-dimensionally, resulting in the disadvantage of low heat utilization efficiency. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-147236 [Patent Document 2] Japanese Patent Publication No. 2003-219669 [Patent Document 3] International Publication No. 2017 / 038988 [Patent Document 4] International Publication No. 2020 / 031992 [Non-patent literature]

[0005] [Non-Patent Document 1] "Renewable and Sustainable Energy Reviews" (Netherlands), 2014, Vol. 33, p. 371. [Overview of the project] [Problems that the invention aims to solve]

[0006] The inventors have developed a thermoelectric power generation element that can convert thermal energy into electrical energy by combining a semiconductor that generates thermally excited electrons and holes with a specific electrolyte (Patent Document 3). However, they believe that further improvements in battery characteristics are necessary, such as improving the short-circuit current, improving the discharge capacity, increasing the number of discharge cycles or extending the discharge time, and lowering the power generation temperature. Therefore, the object of the present invention is to provide a thermoelectric battery having excellent battery characteristics. [Means for solving the problem]

[0007] The inventors of this invention, through diligent research into thermoelectric power generation batteries with excellent battery characteristics, have surprisingly discovered that optimizing the thickness of the electrolyte between the semiconductor and the electrode, depending on the electrolyte, improves the battery characteristics. This invention is based on these findings. Therefore, the present invention is [1] A thermoelectric power generation element that does not require a temperature gradient, wherein a first part containing a semiconductor that generates thermally excited electrons and holes, a second part containing an electrolyte to which charge transport ion pairs can move, and a third part containing a material that serves as an electrode are in contact in this order, the valence electron charge of the semiconductor of the first part is positive than the redox potential of the charge transport ion pairs, an oxidation reaction occurs at the interface between the first part and the second part for the ion that is more easily oxidized of the two ions, and a reduction reaction occurs at the interface between the third part and the second part for the ion that is more easily reduced of the two ions, satisfying the following equation (I): L / IDT = 1~20(I) (wherein L is the "shortest distance between the first part and the third part", and IDT is the "ion diffusion thickness"), [2] The thermoelectric power generation element according to [1], wherein the first part, the second part, and the third part are layered. [3] The thermoelectric power generation element described in [1], wherein the first part, the second part, and the third part are arranged concentrically. A thermoelectric power generation device including a thermoelectric power generation element as described in any of [4][1] to [3], A thermoelectric power generation cell including a thermoelectric power generation element as described in any of [5][1]~[3], A thermoelectric power generation module including a thermoelectric power generation element as described in any of [6][1] to [3], and [7] A thermoelectric power generation element that does not require a temperature gradient, wherein a first part containing a semiconductor that generates thermally excited electrons and holes, a second part containing an electrolyte to which charge transport ion pairs can move, and a third part containing a material that serves as an electrode are in contact in this order, the valence electron charge of the semiconductor of the first part is positive than the redox potential of the charge transport ion pairs, an oxidation reaction occurs at the interface between the first part and the second part for the ion that is more easily oxidized of the two ions, and a reduction reaction occurs at the interface between the third part and the second part for the ion that is more easily reduced of the two ions, characterized in that the value of L / IDT (where L is the shortest distance between the first part and the third part, and IDT is the ion diffusion thickness) is set to 1 to 20, Regarding. [Effects of the Invention]

[0008] The thermoelectric power generation element of the present invention exhibits excellent discharge capacity, short-circuit current, number of discharges, and discharge time. Furthermore, it expands the range of temperatures in which power generation is possible, enabling power generation in low-temperature or high-temperature ranges. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing the thermoelectric power generation element of the present invention. [Figure 2] This figure schematically shows a specific embodiment of the thermoelectric power generation element of the present invention. [Figure 3] This graph plots the measured values ​​of the AC impedance for the thermoelectric power generation element of the present invention. [Figure 4] This graph shows the schematic (A) of the sheet-type battery of Example 1, the open-circuit voltage at 80°C (B), and the change in acquired voltage (C). [Figure 5] The diagram shows the schematic of the comb-shaped electrode in Example 2 (A), its power generation characteristics (B, C), and the temperature dependence of the ion diffusion thickness (D). [Figure 6] This graph shows the relationship between the short-circuit current and L / IDT of the batteries in Examples 1 and 2. [Figure 7] This graph shows the relationship between the discharge capacity and L / IDT of the batteries in Examples 3 and 4. [Figure 8] This graph shows the discharge time (A), open-circuit voltage (B), and the relationship between L / IDT and discharge time (C) for the battery of Example 5. [Figure 9] This graph shows the relationship between the short-circuit current at 80°C and L / IDT for the battery in Example 6. [Figure 10] This graph shows the relationship between the short-circuit current at 90°C and L / IDT for the battery in Example 7. [Figure 11] This graph shows the relationship between the electrical capacity of the battery in Example 8 at 80°C and L / IDT. [Figure 12] This graph shows the battery characteristics of the battery in Example 9 at 30°C and 80°C. [Modes for carrying out the invention]

[0010] [1] Thermoelectric power generation element and thermoelectric battery The thermoelectric power generation element of the present invention comprises a first part containing a semiconductor that generates thermally excited electrons and holes, a second part containing an electrolyte to which charge transport ion pairs can move, and a third part containing a material that serves as an electrode, all in contact in this order, wherein the valence electron charge of the semiconductor in the first part is positive compared to the redox potential of the charge transport ion pairs, an oxidation reaction occurs at the interface between the first and second parts for the ion that is more easily oxidized, and a reduction reaction occurs at the interface between the third and second parts for the ion that is more easily reduced, wherein a thermoelectric power generation element that does not require a temperature gradient is provided by the following formula (I): L / IDT = 1~20 (I) (In the formula, L is the shortest distance between the first and third parts, and IDT is the ion diffusion thickness.) It satisfies the condition.

[0011] 《Part 1》 The first part is not particularly limited insofar as it includes a semiconductor that generates thermally excited electrons and holes (hereinafter sometimes referred to as the first semiconductor). The semiconductor that generates thermally excited electrons and holes is a thermoelectric conversion material. The valence potential of the semiconductor is positive compared to the redox potential of the charge transport ion pair. Therefore, at the interface between the first part and the second part of the present invention, the ion that is more easily oxidized among the charge transport ion pair is oxidized to become the other ion. The potential difference between the redox potential of the charge transport ion pair in the second part and the valence potential of the semiconductor is not limited insofar as the effects of the present invention are obtained, but is preferably 0 to 1.0 V, more preferably 0.05 to 0.5 V, and even more preferably 0.05 to 0.3 V. For example, the potential difference between the redox potential of CuZr2(PO4)3 (Cusicon, copper ion conductor) and the valence potential of β-FeSi2 is approximately 0.05 V. For materials where the redox potential of charge-transporting ion pairs and the valence potential of the semiconductor have been measured, a person skilled in the art can appropriately select suitable ions for the semiconductor and an electrolyte to which those ions can move, according to the values ​​of those redox potentials and valence potentials. Furthermore, for materials where the valence potential of the semiconductor and the redox potential of the charge-transporting ion pairs are unknown, it is possible to measure the valence potential of the semiconductor and the redox potential of the ions. Therefore, a person skilled in the art can select appropriate charge-transporting ion pairs according to the selected semiconductor. for Electrolytes can be selected as appropriate.

[0012] (First Semiconductor) The first semiconductor is not particularly limited as long as it can generate thermally excited electrons and holes when an appropriate temperature is applied, but examples include metal semiconductors, tellurium compound semiconductors, silicon germanium (Si-Ge) compound semiconductors, silicide compound semiconductors, skutterudite compound semiconductors, clathrate compound semiconductors, Heusler compound semiconductors, half-Heusler compound semiconductors, metal oxide semiconductors, organic semiconductors, sulfide semiconductors, and other semiconductors. The semiconductor used in the present invention functions as a thermoelectric conversion material. Examples of metallic semiconductors include Si semiconductors and Ge semiconductors. Examples of tellurium compound semiconductors include Bi-Te compounds (e.g., Bi2Te3, Sb2Te3, CsBi4Te6, Bi2Se3, Bi 0.4 S 1.6 Te3, Bi2(Se,Te)3, (Bi,Sb)2(Te,Se)3, (Bi,Sb)2Te3, or Bi2Te 2.95 Se 0.05 ), Pb-Te compounds (e.g., PbTe, or Pb 1-x Sn x Te), SnTe, Ge-Te, AgSbTe2, Ag-Sb-Ge-Te compounds (e.g., GeTe-AgSbTe2(TAGS)), Ga2Te3, (Ga 1-x In x)2Te3, Tl2Te-Ag2Te, Tl2Te-Cu2Te, Tl2Te-Sb2Te3, Tl2Te-Bi2Te3, Ti2Te-GeTe, Ag8Tl2Te5, Ag9TlTe5, Tl9BiTe6, Tl9SbTe6, Tl9CuTe5, Tl4SnTe3, Tl4PbTe3, or Tl 0.02 Pb 0.98 Te can be mentioned. As silicon germanium (Si-Ge) compound semiconductors, Si x Ge 1-x , or SiGe-GaP can be mentioned. As silicide compound semiconductors, β-FeSi2 compounds (e.g., β-FeSi2, Fe 1-x Mn x Si2, Fe 0.95 Mn 0.05 Si (2-y) Al y , FeSi (2-y) Al y Fe 1-y Co y Si2), Mg2Si, MnSi 1.75-x , Ba8Si 46 , Ba8Ga 16 Si 30 , or CrSi2 can be mentioned. As skutterudite compound semiconductors, compounds represented by the formula TX3 (where T is a transition metal selected from the group consisting of Co, Fe, Ru, Os, Rh, and Ir, and X is a pnictogen selected from the group consisting of P, As, and Sb), derivatives of the said compounds of the formula RM4X 12 (where R is a rare earth selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, M is selected from the group consisting of Fe, Ru, Os, and Co, and X is selected from the group consisting of P, As, and Sb) compounds represented by, Yb y Fe 4-x Co x Sb 12 , (CeFe3CoSb 12 ) 1-x (MoO2) x or (CeFe3CoSb12 ) 1-x (WO2) x We can list some examples. As a clathrate compound semiconductor, formula M8X 46 A compound represented by (M is selected from the group consisting of Ca, Sr, Ba, and Eu, and X is selected from the group consisting of Si, Ge, and Sn), and a derivative of the said compound, formula (II)8(III) 16 (IV) 30 (In the formula, II is a group II element, III is a group III element, and IV is a group IV element) tribe Examples of compounds represented by the element (II)8(III) can be given. 16 (IV) 30 Examples of compounds include Ba8Ga x Ge 46-x Ba 8-x (Sr,Eu) x Au6Ge 40 , or Ba 8-x EU x Cu6Si 40 ) can be cited. Examples of Heusler compound semiconductors include Fe2VAl, (Fe 1-x Re x )2VAl, or Fe2(V 1-x-y Ti x Ta y Al can be mentioned. Examples of half-Heusler compound semiconductors include compounds represented by the formula MSiSn (wherein M is selected from the group consisting of Ti, Zr, and Hf), compounds represented by the formula MNiSn (wherein M is Ti or Zr), compounds represented by the formula MCoSb (wherein M is selected from the group consisting of Ti, Zr, and Hf), or compounds represented by the formula LnPdX (wherein Ln is selected from the group consisting of La, Gd, and Er, and X is Bi or Sb). Examples of metal oxide semiconductors include In2O3-SnO2, (CaBi)MnO3, Ca(Mn,In)O3, and Na x V2O5, V2O5, ZnMnGaO4 and its derivatives, LaRhO3, LaNiO3, SrTiO3, SrTiO3:Nb, Bi2Sr2Co2Oy kaNa x CoO2, NaCo2O4, CaPd3O4, formula Ca a M 1 b Co c M 2 d Ag e O f (In the formula, M 1 M is one or more elements selected from the group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y and rare earth elements. 2 (where is one or two elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, Ta, and Bi, and the values ​​are 2.2≦a≦3.6, 0≦b≦0.8, 2≦c≦4.5, 0≦d≦2, 0≦e≦0.8, 8≦f≦10), compounds represented by ZnO, Na(Co,Cu)2O4, ZnAlO, Zn 1-x Al x O, or La 1.98 Sr 0.02 CuO4 can be mentioned. Examples of organic semiconductors include organic perovskites, polyaniline, polyacetylene, polythiophene, polyalkylthiophene, or polypyrrole. Examples of sulfide semiconductors include Ag2S, ZnS, CdS, or ZnS. Other thermoelectric compounds include alloys containing Co and Sb (e.g., CoSb3, CeFe3CoSb) 12 CeFe4CoSb 12 , or YbCo4Sb 12 ), alloys containing Zn and Sb (e.g., ZnSb, Zn3Sb2, or Zn4Sb3), alloys containing Bi and Sb (e.g., Bi 88 S 12 ), CeInCu2, (Cu,Ag)2Se, Gd2Se3, CeRhAs, or CeFe4Sb 12 Li 7.9 B 105 BaB6, SrB6, CaB6, AlPdRe compounds (e.g., Al 71 Pd 20 (Re1-x Fe x )9), AlCuFe quasicrystal, Al 82.6-x Re 17.4 Si x 1 / 1 - stand direction Approximate crystal, YbAl3, YbMn x Al3, β - CuAgSe, B4C / Ba3C, (Ce 1-x La x )Ni2, or (Ce 1-x La x )In3 can be mentioned.

[0013] In addition to the first semiconductor, the first part may further have an electron transport material. The electron transport material is located on the opposite side of the contact surface with the second part of the semiconductor. Examples of the electron transport material include a semiconductor or a metal. The electron conduction band potential of the electron transport material is the same as or positive with respect to the conduction band potential of the semiconductor (the first semiconductor) that generates thermally excited electrons and holes.

[0014] The electron conduction band potential of the electron transport material is not particularly limited as long as it is the same as or positive with respect to the conduction band potential of the first semiconductor. Examples of the electron transport material include a semiconductor or a metal. Specific examples of the electron transport material include, for example, at least one selected from the group consisting of niobium, titanium, zinc, tin, vanadium, indium, tungsten, tantalum, zirconium, molybdenum, and manganese, an N - type metal oxide, an N - type metal sulfide, an alkali metal halide, an alkali metal, or an electron - transporting organic substance. More specifically, for example, titanium oxide, tungsten oxide, zinc oxide, niobium oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, zinc sulfide, or SrTiO3 can be mentioned. Also, examples of the electron - transporting organic substance include an N - type conductive polymer, an N - type low - molecular - weight organic semiconductor, a π - electron conjugated compound, a surfactant. Specifically, for example, an oxadiazole derivative, a triazole derivative, a perylene derivative, or a quinolinol metal complex, a cyano - group - containing polyphenylene vinylene, a boron - containing polymer, bathocuproine, bathophenanth ReExamples include hydroxyquinolinatoaluminum, oxadiazole compounds, benzimidazole compounds, naphthalenetetracarboxylic acid compounds, perylene derivatives, phosphine oxide compounds, phosphine sulfide compounds, fluorogroup-containing phthalocyanines, fullerenes and their derivatives, phenylenevinylene polymers, and perylenetetracarboxylic acid imide derivatives.

[0015] The potential difference between the electron conduction potential of the electron transport material and the conduction potential of the first semiconductor is not limited insofar as the effects of the present invention are obtained, but is preferably 0.01 to 1 V, more preferably 0.01 to 0.5 V, even more preferably 0.01 to 0.3 V, and most preferably 0.05 to 0.2 V. For example, the potential difference between the conduction potential of n-type silicon, i.e., the electron conduction potential, and the conduction potential of β-FeSi2 is approximately 0.01 V. For materials where the conduction potential of the first semiconductor and the electron conduction potential of the electron transport material have been measured, a person skilled in the art can appropriately select an appropriate electron transport material for the first semiconductor in the first part according to the values ​​of those potentials. Furthermore, for materials where the conduction potential of the semiconductor and the electron conduction potential of the electron transport material are unknown, their potentials can be measured, for example, by electrochemical measurement or inverse photoelectron spectroscopy (XPS). Therefore, a person skilled in the art can appropriately select an appropriate electron transport material according to the first semiconductor in the first part used in a thermoelectric power generation element.

[0016] The first semiconductor in the first portion can be fabricated by, for example, squeegeeing, screen printing, electrostatic plasma sintering, compression molding, sputtering, vacuum deposition, or spin coating. When using the spin coating method, the first semiconductor can be fabricated by dispersing β-FeSi2 in a polar solvent such as acetone and spin coating the solution onto the electron transport material or the second portion. Alternatively, β-FeSi2 may be fabricated by electrostatic plasma sintering, and the resulting β-FeSi2 powder and a conductive binder (e.g., a high-temperature conductive coating) may be squeegeeed onto the electron transport material or the second portion. Furthermore, the electron transport material can also be fabricated by methods such as squeegeeing, screen printing, sputtering, vacuum deposition, single crystal growth, or spin coating. When using the spin coating method, the electron transport material can be fabricated by dissolving an oxadiazole derivative in a polar solvent such as acetone and spin coating the solution onto a substrate or the first semiconductor. For example, the n-type silicon described later can be obtained by single crystal growth, and the first semiconductor can be stacked on this n-type silicon as a substrate.

[0017] The first portion constituting the thermoelectric power generation element of the present invention may include other components, insofar as the first semiconductor generates a sufficient number of thermally excited electrons and holes for power generation when an appropriate temperature is applied. Examples of such components, though not limited to, include binders (such as polyvinyl alcohol, methylcellulose, acrylic resin, and agar) and sintering aids that assist in the molding of the first semiconductor (such as magnesium oxide, yttrium oxide, and calcium oxide). Furthermore, residual solvents used in the manufacturing process may also be present. The first portion used in the present invention functions substantially as a thermoelectric conversion layer.

[0018] 《Second part》 The second part is not particularly limited in that it includes an electrolyte to which charge-transporting ion pairs can move. Examples of electrolytes include solid electrolytes or electrolyte solutions. The electrolyte is not limited in that it can transport the two ions of the charge-transporting ion pair. In other words, the electrolyte included in the second part is not particularly limited, as long as its oxidation-reduction potential is at an appropriate position with respect to the valence electron charge position of the first semiconductor used in the thermoelectric power generation element, and charge transport ion pairs can move freely within the electrolyte. Preferably, the electrolyte is physically and chemically stable at the temperature at which the first semiconductor generates a sufficient number of thermally excited electrons and holes for power generation.

[0019] The electrolyte may be a solid electrolyte or an electrolyte solution (liquid electrolyte), depending on its form. Here, the electrolyte may be in the form of an electrolyte solution (liquid electrolyte) or a solid electrolyte depending on the temperature. In other words, the compounds contained in the electrolyte solution (liquid electrolyte) and the compounds contained in the solid electrolyte overlap. The electrolyte also includes molten salts, ionic liquids, or deep eutectic solvents. A molten salt is a salt composed of cations and anions that is in a molten state. Among molten salts, those with relatively low melting points (for example, those below 100°C or below 150°C) are called ionic liquids. In this specification, molten salts in a solid state are referred to as solid electrolytes, and those in solution form are referred to as electrolyte solutions (liquid electrolytes). The following are specific examples of electrolyte solutions (liquid electrolytes), solid electrolytes, and molten salts, but these may overlap. The electrolyte solution used is in a liquid state at a temperature at which the first semiconductor generates a sufficient number of thermally excited electrons and holes for power generation. Specifically, the electrolyte solution can include, but is not limited to, methoxide ions, hydrogen ions, ammonium ions, pyridinium ions, lithium ions, sodium ions, potassium ions, calcium ions, magnesium ions, aluminum ions, iron ions, copper ions, zinc ions, cobalt ions, fluoride ions, cyanide ions, thiocyanate ions, chloride ions, acetate ions, sulfate ions, carbonate ions, phosphate ions, bicarbonate ions, and bromide ions.

[0020] The solid electrolyte uses a solid-state one in which charge-transporting ion pairs can move inside at a temperature where the semiconductor in the first part generates a sufficient number of thermally excited electrons and holes for power generation. By using a high-temperature solid electrolyte, it can be used in a thermoelectric power generation element using a thermoelectric power generation element body that generates thermally excited electrons and holes at high temperatures. Specifically, examples of the solid electrolyte include, but are not limited to, sodium ion conductors, copper ion conductors, lithium ion conductors, silver ion conductors, hydrogen ion conductors, strontium ion conductors, aluminum ion conductors, fluorine ion conductors, chlorine ion conductors, or oxide ion conductors. Specific solid electrolytes include, for example, RbAg4I5, Li3N, Na2O·11Al2O3, Sr-β alumina, Al(WO4)3, PbF2, PbCl2, (ZrO2) 0.9 (Y2O3) 0.1 , (Bi2O3) 0.75 (Y2O3) 0.25 , CuZr2(PO4)3, CuTi2(PO4)3, Cu x Nb 1-x Ti 1+x (PO4)3, H 0.5 Cu 0.5 Zr2(PO4)3, Cu 1+x Cr x Ti 2-x (PO4)3, Cu 0.5 TiZr(PO4)3, CuCr2Zr(PO4)3, Cu2ScZr(PO4)3, CuSn2(PO4)3, CuHf2(PO4)3, Li7La3Zr2O 12 , Li7La3Zr 2-x Nb x O 12 , Li7La3Zr 2-x TaxO 12 , Li5La3Ta2O 12 , Li 0.33 La 0.55 , Li 1.5 Al 0.5 Ge 1.5 P3O 12 , Li 1.3 Al[[ID=B55]] 0.3 Ti 1.7 P3O 12Examples include Li3PO4 (LiPON), Li4SiO4-Li3PO4, Li4SiO4, or Li3BO3. Furthermore, molten salts can be used as solid electrolytes or electrolyte solutions. In the case of thermoelectric power generation elements used at relatively low temperatures, ionic liquids can also be used. Deep eutectic solvents (DES) can be used as ionic liquids. Examples of molten salts include those containing at least one cation selected from the group consisting of imidazolium cation, pyridinium cation, piperidinium cation, pyrrolidinium cation, phosphonium cation, morpholinium cation, sulfonium cation, and ammonium cation, and at least one anion selected from the group consisting of carboxylic acid anions, sulfonate anions, halogen anions, tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, and bis(fluorosulfonyl)imide. The electrolyte in the present invention functions as a hole-transfer material.

[0021] Furthermore, in this specification, "charge-transporting ion pair" refers to two stable ions with different valencies, where one ion is oxidized or reduced to become the other ion, and which can transport electrons and holes. These ions may be of the same element but with different valencies. For example, in the case of copper ions, monovalent and divalent copper ions are preferred, and in the case of iron ions, divalent and trivalent iron ions are preferred. As monovalent copper ions, for example, CuCl, CuBr, copper(I) acetate, copper(I) iodide, or copper(I) sulfate can be used. As divalent copper ions, CuCl2, CuTSFI2, copper(II) acetate, copper(II) sulfate, or copper(II) acetylacetonate can be used. As divalent iron ions, Fe(C5H5)2 (ferrocene), K4[Fe(CN)6], iron(II) acetylacetonate, iron(II) chloride iron(II) sulfate, or iron(II) acetate can be used. As trivalent iron ions, FeCl3, K3[Fe(CN)6], iron(III) acetylacetonate, or iron(III) sulfate can be used.

[0022] At the interface between the first and second parts, an oxidation reaction occurs between the two ions that are more easily oxidized, and at the interface between the third and second parts, a reduction reaction occurs between the two ions that are more easily reduced. In the present invention, the valence potential of the first semiconductor in the first part is positive compared to the redox potential of the charge transport ion pair in the second part. Therefore, at the interface between the first part and the second part (electrolyte) of the present invention, the more easily oxidized ion in the charge transport ion pair is oxidized to become the other ion. The potential difference between the redox potential of the charge transport ion pair in the electrolyte and the valence potential of the thermoelectric conversion material is not limited as long as the effects of the present invention are obtained, but is preferably 0 to 1.0 V, more preferably 0.05 to 0.5 V, and even more preferably 0.05 to 0.3 V. For example, the potential difference between the redox potential of CuZr2(PO4)3 (Cusicon, copper ion conductor) and the valence potential of β-FeSi2 is approximately 0.05 V. For materials where the redox potential of charge-transporting ion pairs and the valence potential of the thermoelectric conversion material have been measured, a person skilled in the art can appropriately select suitable ions for the thermoelectric conversion material and select an electrolyte to which those ions can move, according to the values ​​of those redox potentials and valence potentials. Furthermore, for materials where the valence potential of the first semiconductor and the redox potential of the charge-transporting ion pairs are unknown, it is possible to measure the valence potential of the first semiconductor and the redox potential of the ions. Therefore, a person skilled in the art can select an appropriate charge-transporting ion pair according to the selected first semiconductor. for Electrolytes can be selected as appropriate.

[0023] The present invention electric The battery preferably contains alkali metal ions as an additive in the second part (Patent Document 4). Examples of alkali metal ions include lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, or francium ions, but lithium ions, sodium ions, or potassium ions are preferred. By including alkali metal ions, the battery life can be extended and the discharge characteristics can be restored by leaving it under a heat source. The alkali metal ions are not limited to, but may be added to the electrolyte in the form of halides, perchloric acid (e.g., LiClO4), sulfates, or strong salts. For example, alkali metal compounds can be used in various forms as long as they do not degrade the solvent. Examples of halogens that form halides with alkali metal ions include fluorine, chlorine, bromine, iodine, and astatine. For example, compounds of alkali metal ions and chlorine include LiCl, NaCl, KCl, RbCl, CsCl, or FrCl.

[0024] The amount of alkali metal compound added is not particularly limited as long as it extends the battery life, but for example, it is 0.001 to 100 parts by weight, preferably 0.01 to 10 parts by weight, and more preferably 0.03 to 0.1 parts by weight, per 100 parts by weight of electrolyte. By staying within this range, a particularly excellent effect of extending battery life can be obtained.

[0025] The second part may contain components other than a solid electrolyte or electrolyte solution. Examples of such components include, but are not limited to, polar solvents (water, methanol, toluene, tetrahydrofuran, etc.) used to dissolve or disperse the electrolyte when preparing the second part, binders (polyvinyl alcohol, methylcellulose, acrylic resin, agar, etc.) used to bind the electrolyte, and sintering aids (magnesium oxide, yttrium oxide, calcium oxide, etc.) used to help form hole-transfer materials.

[0026] The second part can be fabricated by methods such as squeegeeing, screen printing, sputtering, vacuum deposition, sol-gel method, or spin coating. For example, CuZr2(PO4)3 is fabricated by the sol-gel method. The resulting sol can be prepared as the second part by squeegeeing. Furthermore, if the electrolyte is an electrolyte solution (liquid electrolyte), the second part will be in the liquid phase. When the second part is in the liquid phase, it is preferable to prepare the second part of the thermoelectric power generation element during the fabrication of the thermoelectric power generation device, thermocell, or thermoelectric power generation module. That is, the second part can be fabricated by providing a tank for holding the electrolyte solution (liquid electrolyte).

[0027] 《Part 3》 The third part is not particularly limited insofar as it includes an electrode material. The electrode material is not limited insofar as it can transport electrons, but examples include fluorine-doped tin oxide (FTO), tin-doped indium oxide (ITO), antimond-doped tin oxide (ATO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), zinc oxide (ZnO), indium oxide (In2O3), tin oxide (SnO2), IZO (In-Zn-O), or IGZO (In-Ga-Zn-O). Also, metals that do not react with charge-transporting ion pairs can be used, such as titanium, gold, platinum, silver, copper, tin, tungsten, niobium, tantalum, stainless steel, aluminum, graphene, molybdenum, indium, vanadium, rhodium, niobium, chromium, nickel, carbon, alloys thereof, or combinations thereof. The third part may be provided as a layer or in the form of a wire. In the case of layers, they can be manufactured by methods such as vacuum deposition or spin coating.

[0028] When the first semiconductor is subjected to an appropriate temperature, a sufficient number of thermally excited electrons and holes are generated to produce electricity. The redox potential of the electrolyte contained in the second part is negative relative to the valence electron charge of the first semiconductor in the first part, so holes are transported from the first part to the third part (sometimes called the positive electrode). That is, ion redox occurs in the electrolyte, electrons are transported from the third part (positive electrode) to the first part, and holes are transported from the first part to the third part (positive electrode). Through this mechanism, electrons move and electricity can be generated.

[0029] The thermoelectric power generation element of the present invention is represented by the following formula (I): L / IDT = 1~20 (I) (In the formula, L is the shortest distance between the first and third parts, and IDT is the ion diffusion thickness.) It satisfies the condition. The lower limit of L / IDT is 1 or more, preferably 1.5 or more, and more preferably 2 or more. The upper limit of L / IDT is 20 or less, preferably 15 or less, more preferably 10 or less, even more preferably 8 or less, and most preferably 5 or less. The lower limit and upper limit can be combined as appropriate.

[0030] The aforementioned "shortest distance between the first and third parts" will be explained using Figure 2. Figure 2 schematically shows several specific embodiments of the thermoelectric power generation element of the present invention. For example, the thermoelectric power generation element of the present invention can be constructed by stacking the first, second, and third parts in layers (Figure 2A). In this case, the thickness L of the second part is the "shortest distance between the first and third parts". As shown in Figure 2B, the first, second, and third parts can also be arranged on a single plane. This arrangement is also considered to be a layered arrangement of the first, second, and third parts. In this case, the thickness L (width) of the second part sandwiched between the first and third parts is the "shortest distance between the first and third parts". The thermoelectric power generation element of the present invention may have the first, second, and third parts arranged concentrically (Figures 2C and 2D). For example, as shown in Figure 2C, the first part can be placed in the center, the second part around it, and the third part around the second part. Alternatively, as shown in Figure 2D, the third part can be placed in the center, the second part around it, and the first part around the second part. In either case, the thickness L of the second part between the first and third parts (the thickness of the thinnest part) is the "shortest distance between the first and third parts". As shown in Figure 2E, the thermoelectric power generation element of the present invention can have its second portion arranged in a T-shape. That is, the lower part of the T-shape of the second portion can be sandwiched between the first and third portions. In this case, the thickness L of the lower part of the second portion sandwiched between the first and third portions is the "shortest distance between the first and third portions". These thicknesses L can be measured using a caliper, contact needle, or optical microscope.

[0031] The aforementioned "ion diffusion thickness" is a unique value that can be calculated from the oxidation-reduction ions, electrolytes, and temperature in the second part. However, since different values ​​may be calculated depending on the model, it is preferable to determine it by measurement. The "ion diffusion thickness" can be measured as follows. For a thermoelectric power generation element (battery) having three parts, AC impedance measurements are performed. When the measured AC impedance values ​​are plotted, the resulting graph will have a shape such as a combination of semicircles and curves, or a combination of curves, as shown in Figure 3. From this plotted graph, a fitting equation for the equivalent circuit is created. Using the obtained fitting equation and equation (II) below, the ion diffusion thickness IDT (corresponding to "δ" in the following equation) is calculated.

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[0032] Using the ion diffusion thickness IDT obtained by the above calculation, the value of "L / IDT" can be calculated from the shortest distance L between the first and third parts and the ion diffusion thickness IDT.

[0033] The thermoelectric power generation device, thermoelectric battery, and thermoelectric power generation module of the present invention include the thermoelectric power generation element of the present invention, preferably including a negative electrode on the outside of the first part. The electron transport material of the thermoelectric power generation element used in the thermoelectric power generation device, thermoelectric battery, and thermoelectric power generation module of the present invention can play the role of the negative electrode, and the third part plays the role of the positive electrode as described above. 。 Book In this specification, "thermoelectric battery" means a battery that includes the thermoelectric power generation element of the present invention and generates electricity when a temperature capable of generating thermally excited electrons and holes is applied to the first semiconductor of the thermoelectric power generation element.

[0034] Thermoelectric power generation can be carried out using the thermoelectric power generation device, thermoelectric battery, and thermoelectric power generation module of the present invention. For example, power can be generated by the steps of installing the thermoelectric power generation module, etc., at a heat generation location, and heating the thermoelectric power generation module with heat to generate electricity. In the installation process of the thermoelectric power generation module, the thermoelectric power generation module of the present invention is installed at a heat generation location. The heat generation location is not particularly limited as long as it is a location that generates heat above the temperature at which the thermoelectric conversion material generates a sufficient number of excited electrons and holes for power generation. Examples of heat generation locations include geothermal heat sources or waste heat sources such as factories. Geothermal heat is not limited to heat in the soil, but also includes hot water or steam heated by geothermal heat. Furthermore, geothermal heat includes hot water or steam from the sea, lakes, or rivers heated by geothermal heat. Waste heat is not particularly limited, but examples include waste heat from steel furnaces, waste incinerators, substations, subways, or automobiles. In particular, waste heat from steel furnaces and waste incinerators, which have a large amount of energy, is released without utilizing that energy, and it is preferable to reuse it using the thermoelectric power generation method of the present invention. Furthermore, the thermoelectric power generation element of the present invention can generate electricity even at low temperatures (for example, room temperature) and can be used in various devices that operate at room temperature.

[0035] In the power generation process, electricity is generated by heating the thermoelectric power generation module of the present invention. The heat generated from the heat generation location heats the thermoelectric conversion material of the thermoelectric power generation module to a temperature above which a sufficient number of excited electrons and holes are generated for power generation, thereby enabling the thermoelectric power generation module to generate electricity.

[0036] Furthermore, the temperature for power generation is preferably such that the thermally excited electron density is 10 15 / m 3 That's all. This is the temperature at which, more preferably 10 18 / m 3 The temperature is above this level, and more preferably 10 20 / m 3 The temperature is above this, and most preferably 1022 / m 3 The temperatures are as described above. The power generation temperature basically varies depending on the first semiconductor, but those skilled in the art can appropriately determine the power generation temperature from the common technical knowledge of the field to which this invention belongs and from the description in this specification. Furthermore, the power generation temperature of the present invention is preferably a temperature at which charge transport ion pairs can move back and forth within the electrolyte. The specific temperature is not limited, but for example, it is 5°C or higher, preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher. The upper limit of the temperature is also not particularly limited, as long as it is a temperature at which charge transport ion pairs can move back and forth within the electrolyte, but for example, it is 1500°C or lower, preferably 1000°C or lower. The temperature at which the thermoelectric power generation element of the present invention actually generates electricity is determined not only by the temperature at which a sufficient number of thermally excited electrons and holes are generated in the first semiconductor within the first part for power generation, but also by the ease of electron transfer inherent to the material and the ease of electron transfer at the interface with the first part when combined with the second part. These conditions are preferably in the range of L / IDT = 1 to 20.

[0037] [2] Methods for stabilizing power generation In the power generation stabilization method of the present invention, a thermoelectric power generation element that does not require a temperature gradient comprises a first part including a semiconductor that generates thermally excited electrons and holes, a second part including an electrolyte to which charge transport ion pairs can move, and a third part including a material that serves as an electrode, all of which are in contact in this order, the valence electron charge of the semiconductor of the first part is positive compared to the redox potential of the charge transport ion pairs, an oxidation reaction occurs at the interface between the first and second parts for the ion that is more easily oxidized, and a reduction reaction occurs at the interface between the third and second parts for the ion that is more easily reduced. L / IDT (Here, L is the shortest distance between the first and third parts, and IDT is the ion diffusion thickness.) Let the value be between 1 and 20.

[0038] The shortest distance L and ion diffusion thickness IDT of the first and third parts can be measured and calculated in accordance with the description in the section "[1] Thermoelectric power generation elements and thermoelectric batteries". in particular, (1) A step of measuring the shortest distance L between the first and third parts, (2) A step of measuring the AC impedance of the thermoelectric power generation element, (3) A step of creating a fitting equation for the equivalent circuit from the obtained AC impedance values, (4) A step of calculating the ion diffusion thickness IDT (corresponding to "δ" in the following formula) from the obtained fitting formula and the following formula (II), and

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[0039] In the power generation stabilization method of the present invention, by adjusting the shortest distance L between the first part and the third part so that L / IDT is in the range of "1 to 20", improvements in battery characteristics such as improved short-circuit current and / or improved discharge capacity can be observed. The lower limit of L / IDT is 1 or more, in some embodiments it is 1.5 or more, and in other embodiments it is 2 or more. The upper limit of L / IDT is 20 or less, in some embodiments it is 15 or less, in other embodiments it is 10 or less, in other embodiments it is 8 or less, and in other embodiments it is 5 or less. The lower limit and upper limit can be combined as appropriate. The shortest distance L between the first part and the third part is adjusted so that L / IDT falls within the above range.

[0040] 《Action》 The reason why the thermoelectric power generation element of the present invention exhibits excellent battery characteristics has not been analyzed in detail, but it can be presumed as follows. However, the present invention is not limited by the following presumption. In thermoelectric power generation elements, it is generally believed that the closer the distance between the first part containing the semiconductor and the third part containing the electrode material, the better the performance of the thermoelectric power generation element (battery). However, in reality, the distance between the first part and the third part that improves the power generation performance of the thermoelectric power generation element (battery) is considered to be. 3 There exists an appropriate distance between the parts. This first part and the second part 3 It is not easy to provide a logical explanation for why the appropriate distance from the part is L / IDT = 1 to 20. However, in the examples described later, when measurements were taken under different conditions such as "oxidation-reduction ions," "electrolyte," and "temperature," excellent battery performance was obtained in all cases within the range of L / IDT = 1 to 20. Therefore, it is presumed that setting L / IDT within an appropriate range allows the thermoelectric power generation element to exhibit excellent battery characteristics. [Examples]

[0041] The present invention will be specifically described below with reference to examples, but these examples are not intended to limit the scope of the present invention.

[0042] Example 1 In this example, a sheet-type battery was fabricated using n-Si / Ge as the first part, PEG, CuCl, CuCl2, and LiCl as the second part, and FTO as the third part. As the first part, a 1.5 cm × 2.5 cm n-Si / Ge substrate was prepared. As the third part, a 1.5 × 2.5 cm FTO transparent electrode was prepared. As the electrolyte for the second part, polyethylene glycol (PEG) was mixed with CuCl, CuCl2, and LiCl at concentrations of 0.5 mmol / PEG(g), 0.5 mmol / PEG(g), and 0.6 mmol / PEG(g), respectively. The electrolyte from the second part was dropped onto the FTO transparent electrode from the third part, and then the n-Si / Ge substrate from the first part was laminated to fabricate a sheet-type battery as shown in the schematic diagram in Figure 4(A). The distance between the first and third parts was set to 85 μm, 114 μm, 228 μm, and 342 μm, and four sheet-type batteries were fabricated. The battery characteristics of the four obtained batteries were measured at 80°C. The results are shown in Figure 4(B). When the distance between the electrodes widened, the open-circuit voltage decreased, and re-discharge no longer occurred.

[0043] Example 2 In this example, a comb-shaped cell was fabricated using Ge as the first part, PEG as the second part, and CuCl, CuCl2, and LiCl as the third part, and Pt as the third part. A Ge electrode was sputtered in a comb shape onto a quartz substrate as the first part, and a Pt electrode as the third part. On these electrodes, a mixture of PEG with CuCl, CuCl2, and LiCl at concentrations of 0.5 mmol / PEG(g), 0.5 mmol / PEG(g), and 0.6 mmol / PEG(g), respectively, was dropped as the second part (Figure 5A). The comb-shaped electrode width was 2 μm. The battery characteristics were measured at installation temperatures of 80°C and room temperature. No power generation occurred at 80°C, but power generation was confirmed at room temperature (Figures 5B, C). Figure 5D shows the temperature dependence of ion diffusion thickness. Ion diffusion thickness decreases as the temperature decreases. At 30°C, it was slightly larger than at 40°C, but this was thought to be because the measurement limit for this measurement was ion diffusion thickness of 2 μm or less.

[0044] L / IDT measurement For the four sheet-type batteries (80°C) of Example 1 and the comb-type batteries (30°C, 40°C, 50°C, and 60°C) of Example 2, L / IDT was calculated from the shortest distance L between the first and third parts and the ion diffusion thickness IDT. For each battery and temperature, the AC impedance was measured at an amplitude of 10mV and a frequency of 7MHz-50mHz. The measured values ​​were plotted using Zplot (Toyo Technica), and a fitting equation for the equivalent circuit was created. Using the obtained fitting equation and equation (II) below, the ion diffusion thickness IDT (corresponding to "δ" in the equation below) was calculated.

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[0045] Example 3 In this example, a sheet-type battery was fabricated using n-Si / Ge as the first part, PEG, CuCl, CuCl2, and LiCl as the second part, and FTO as the third part. Four sheet-type batteries were fabricated by repeating the procedure in Example 1.

[0046] Example 4 In this example, a comb-shaped cell was fabricated using Ge as the first part, PEG as the second part, and CuCl, CuCl2, and LiCl as the third part, and Pt as the third part. Except for setting the electrode distance to 2 μm or 5 μm, the procedure in Example 2 was repeated to fabricate two comb-type cells.

[0047] 《Measurement of L / IDT and Discharge Capacity》 For the four sheet-type batteries of Example 3 and the two comb-type batteries of Example 4, the L / IDT ratio was calculated by repeating the "Measurement of L / IDT" procedure described above. Furthermore, the long-term discharge capacity was measured for the four sheet-type batteries in Example 3 and the two comb-type batteries in Example 4. Each battery was discharged at 100 nA while being maintained at 80°C. It was then allowed to recover by being left at room temperature for 2 hours. The discharge at 100 nA was repeated while maintaining 80°C, and the discharge capacity for the third time was obtained. Figure 7 shows the relationship between the third discharge capacity and L / IDT for each battery. When L / IDT was between 1 and 20, it showed excellent discharge capacity.

[0048] Example 5 In this example, a comb-shaped cell was fabricated using Ge as the first part, PEG as the second part, and CuCl, CuCl2, and LiCl as the third part, and Pt as the third part. The procedure in Example 4 was repeated to fabricate two comb-type cells with electrode distances of 2 μm or 5 μm. The open-circuit voltage value remained constant even as the number of discharge cycles increased at room temperature (Figure 8B). Furthermore, the discharge time was longer with an electrode width of 5 μm, even as the number of discharge cycles increased (Figure 8A). The measurement of each discharge cycle was performed by switching off the circuit after discharge, allowing the voltage to stabilize for 1 hour, and then switching it back on. The L / IDT ratio was calculated by repeating the "Measurement of L / IDT" procedure described above. Figure 8C shows the relationship between L / IDT and discharge time. When L / IDT was between 1 and 20, the discharge time was long.

[0049] Example 6 In this example, a sheet-type battery was fabricated using n-Si / Ge as the first part, EC, NaI, and I2 as the second part, and FTO as the third part. Except for using ethylene carbonate (EC) with NaI and I2 at concentrations of 0.5 mol / EC(g) and 0.05 mmol / EC(g), respectively, as the electrolyte for the second part, the procedure of Example 1 was repeated to fabricate three sheet-type batteries with different inter-electrode distances of 114 μm and polyiodide ion chain growth times of 0, 7, 14, and 19 days. Figure 9 shows the relationship between the short-circuit current at 80°C and L / IDT. When L / IDT was between 1 and 20, the short-circuit current was high.

[0050] Example 7 In this example, a sheet-type battery was fabricated using TiO2 / Ag2S as the first part, DMSO, Cp(arene)Fe, and LiClO4 as the second part, and PtTi / PEN as the third part. Except for using TiO2 / Ag2S as the first part, 5 mmol Cp(arene)Fe / DMSO(g) and 0.4 mmol LiClO4 / DMSO(g) as the second part, and PtTi / PEN as the third part, the procedure of Example 1 was repeated to fabricate two sheet-type batteries with an inter-electrode distance of 113 μm, and the IDT was measured before and during discharge. Figure 10 shows the relationship between the short-circuit current at 90°C and L / IDT. When L / IDT was between 1 and 20, the short-circuit current was high.

[0051] Example 8 In this example, a sheet-type battery was fabricated using n-Si / Ge as the first part, DMSO, NaI, and I2 as the second part, and FTO as the third part. Except for using 0.25 moleNaI / DMSO(g) and 0.025 moleI2 / DMSO(g); 0.5 moleNaI / DMSO(g) and 0.05 moleI2 / DMSO(g); or 1.0 moleNaI / DMSO(g) and 0.1 moleI2 / DMSO(g) as the second part, the procedure of Example 1 was repeated to fabricate three sheet-type batteries with an inter-electrode distance of 114 μm. Figure 11 shows the relationship between capacitance at 80°C and L / IDT. When L / IDT was between 1 and 20, the capacitance was high.

[0052] Example 9 In this embodiment, the effect of the shortest distance between the first and third parts on the dischargeable temperature of the thermoelectric power generation element of the present invention was investigated. A second component was prepared by mixing PEGDME with I2 and NaI at concentrations of 0.05 mol / L (PEGDME) and 0.5 mol / L (PEGDME), respectively. A Ge electrode was sputtered onto a quartz substrate as the first component, and a Pt electrode as the third component, with the electrodes spaced 2 μm apart in a comb-like pattern. The battery characteristics were measured while maintaining the substrate at 30°C and 80°C. (Figure 12) The two components were sandwiched between a 1.5 cm × 2.5 cm n-Si / Ge substrate as the first component and a 1.5 × 2.5 cm FTO transparent electrode as the third component. (Diffusion distance 48.6, inter-electrode distance 114 μm) [Industrial applicability]

[0053] The thermoelectric power generation element and thermoelectric power generation module containing the same of the present invention can be used in batteries, small portable power generation devices, geothermal power generation, thermoelectric power generation utilizing waste heat from automobiles, and thermoelectric power generation utilizing waste heat from substations, steel furnaces, or waste incineration plants. [Explanation of symbols]

[0054] 1...first part; 2...Second part; 3...Third part;

Claims

[Claim 1] In a thermoelectric power generation element that does not require a temperature gradient, a first part containing a semiconductor that generates thermally excited electrons and holes, a second part containing an electrolyte to which charge-transporting ion pairs can move, and a third part containing a material that serves as an electrode are in contact in this order, the valence electron charge of the semiconductor in the first part is positive compared to the redox potential of the charge-transporting ion pairs, an oxidation reaction occurs at the interface between the first and second parts for the ion that is more easily oxidized, and a reduction reaction occurs at the interface between the third and second parts for the ion that is more easily reduced, L / IDT (Here, L is the shortest distance between the first and third parts, and IDT is the ion diffusion thickness.) A method for optimizing the thickness of an electrolyte, characterized by adjusting the shortest distance between the first and third parts so that the value of is between 1 and 20, thereby optimizing the shortest distance between the first and third parts.

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