Thermoelectric material powder, thermoelectric material sintered body, and manufacturing method therefor

Abstract

Disclosed in the present invention are a thermoelectric material powder, a thermoelectric material sintered body, and a manufacturing method therefor. The present invention comprises the steps of: preparing a precursor solution by dissolving a metal inorganic precursor in a solvent; forming a metal chalcogen compound coating layer on the surface of thermoelectric material alloy powder by stirring the thermoelectric material alloy powder into the precursor solution through a chemical solution deposition method; and preparing thermoelectric material powder by filtering and drying the thermoelectric material alloy powder in which the metal chalcogen compound coating layer is formed.

Description

Thermoelectric material powder, thermoelectric material sintered body, and method for manufacturing the same

[0001] The present invention relates to a thermoelectric material powder, a thermoelectric material sintered body, and a method for manufacturing the same. More specifically, the invention relates to a thermoelectric material powder with an improved thermoelectric performance index by forming a coating layer on the thermoelectric material powder, a thermoelectric material sintered body, and a method for manufacturing the same.

[0002]

[0003] Thermoelectric materials are special materials capable of converting temperature differences into electrical energy or controlling temperature using electricity, and they particularly utilize the Seebeck effect and the Peltier effect.

[0004] Recently, research on thermoelectric materials has been actively conducted with the goal of higher efficiency and diverse application possibilities, including the development of high-performance thermoelectric materials and new thermoelectric materials. They are widely applied in thermoelectric-based electronic devices such as automotive motors, home appliances, and wearable devices, and are attracting attention for their promising applicability.

[0005] Accordingly, coating technology is used as a method to increase the efficiency of thermoelectric materials or expand their applicability, and the coated thermoelectric material powder can provide effects such as improved performance, enhanced mechanical durability, corrosion prevention, and microstructure formation for thermoelectric devices to which it is applied.

[0006] Conventionally, Atomic Layer Deposition (ALD), Water Atomization, and Electroless Plating are used as coating technologies to improve the performance of thermoelectric materials, but they have disadvantages such as high costs due to expensive equipment and long coating times.

[0007] Accordingly, the present invention aims to develop interface engineering technology to improve the performance of thermoelectric materials using a Chemical Bath Deposition (CBD) method, and to improve thermoelectric performance by coating the surface of thermoelectric powder in an economical and efficient manner.

[0008]

[0009] One objective of the present invention is to provide a thermoelectric material powder, a thermoelectric material sintered body, and a method for manufacturing the same, which can improve thermoelectric performance by forming a coating layer on a thermoelectric material alloy powder using a chemical solution deposition method and fabricating a thermoelectric material sintered body using the same.

[0010] One objective of the present invention is to provide a thermoelectric material powder, a thermoelectric material sintered body, and a method for manufacturing the same, which can improve the thermoelectric performance index by improving the Seebeck coefficient and reducing the lattice thermal conductivity.

[0011]

[0012] A method for manufacturing a thermoelectric material powder according to one embodiment of the present invention comprises: a step of preparing a precursor solution by dissolving a metal inorganic precursor in a solvent; a step of forming a metal chalcogenide coating layer on the surface of the thermoelectric material alloy powder by stirring the thermoelectric material alloy powder in the precursor solution through a chemical solution deposition method; and a step of manufacturing a thermoelectric material powder by filtering and drying the thermoelectric material alloy powder having the metal chalcogenide coating layer formed thereon.

[0013] According to one embodiment, the metal chalcogenide coating layer may be formed on part or all of the surface of the thermoelectric material alloy powder.

[0014] According to one embodiment, the metal chalcogenide coating layer may be represented by the following chemical formula 1.

[0015] [Chemical Formula 1]

[0016] M a X b

[0017] (M is Zn 2+ , Cd 2+ , Sn 4+ , Al 3+ , Ti 4+ , Fe 3+ , Zr 4+ , Cu 2+ , In 3+ and Ce 4+ It is any one metal ion selected from among, X is any one chalcogen element selected from O, S, and Se, 1 ≤ a ≤ 4 is an integer, and 1 ≤ b ≤ 5 is an integer)

[0018] According to one embodiment, the metal chalcogenide coating layer may be formed on the surface of the thermoelectric material alloy powder by using the chemical solution deposition method to mix and react the metal ions and chalcogen elements contained in the precursor solution.

[0019] According to one embodiment, the thermoelectric material alloy powder may include at least two elements selected from transition metals, rare earth elements, group 13 elements, group 14 elements, group 15 elements, and group 16 elements.

[0020] According to one embodiment, in the step of forming the metal chalcogenide coating layer, if the metal chalcogenide coating layer is zinc sulfide (ZnS), the time for forming the coating layer may be 150 seconds to 450 seconds.

[0021] According to one embodiment, in the step of forming the metal chalcogenide coating layer, if the metal chalcogenide coating layer is cadmium sulfide (CdS), the time for forming the coating layer may be 30 seconds to 120 seconds.

[0022] According to one embodiment, in the step of forming the metal chalcogenide coating layer, if the metal chalcogenide coating layer is tin dioxide (SnO2), the time for forming the coating layer may be 90 seconds to 270 seconds.

[0023] According to one embodiment, the step of manufacturing the thermoelectric material powder may further include a step of reducing the thermoelectric material powder.

[0024] A thermoelectric material powder according to one embodiment of the present invention is manufactured according to a method for manufacturing a thermoelectric material powder according to one embodiment of the present invention.

[0025] A method for manufacturing a sintered body according to one embodiment of the present invention comprises: a step of preparing a precursor solution by dissolving a metal inorganic precursor in a solvent; a step of forming a metal chalcogenide coating layer on the surface of the thermoelectric material alloy powder by stirring the thermoelectric material alloy powder in the precursor solution through a chemical solution deposition method; a step of manufacturing a thermoelectric material powder by filtering and drying the thermoelectric material alloy powder having the metal chalcogenide coating layer formed thereon; and a step of manufacturing a thermoelectric material sintered body by sintering the thermoelectric material powder.

[0026] According to one embodiment, in the step of manufacturing the thermoelectric material sintered body, the metal chalcogenide coating layer is formed at the grain boundaries of the thermoelectric material alloy by proceeding with the sintering, and can suppress the grain growth of the thermoelectric material alloy.

[0027] A thermoelectric material sintered body according to one embodiment of the present invention is manufactured according to a method for manufacturing a thermoelectric material sintered body according to one embodiment of the present invention.

[0028]

[0029] According to one embodiment of the present invention, a thermoelectric material powder, a sintered thermoelectric material body, and a method for manufacturing the same can be provided, which can improve the thermoelectric performance of a thermoelectric material through a simple process of forming a coating layer on a thermoelectric material alloy powder using a simple chemical bath deposition (CBD) method and then sintering.

[0030] According to one embodiment of the present invention, a thermoelectric material powder, a thermoelectric material sintered body, and a method for manufacturing the same can be provided, which can optimize the thermoelectric performance of the thermoelectric material powder by controlling the coating layer formation time in a chemical bath deposition (CBD).

[0031] According to one embodiment of the present invention, a thermoelectric material powder, a thermoelectric material sintered body, and a method for manufacturing the same can be provided, which can improve the thermoelectric performance index of a thermoelectric material by improving the Seebeck coefficient and reducing the lattice thermal conductivity by manufacturing a thermoelectric material sintered body including a metal chalcogenide coating layer.

[0032]

[0033] FIG. 1 is a flowchart illustrating a method for manufacturing thermoelectric material powder according to an embodiment of the present invention.

[0034] Figure 2 is a transmission electron microscope (TEM) image of Comparative Example 1 and Example 1-1.

[0035] Figure 3 is a transmission electron microscope (TEM) image of Example 1-1.

[0036] Figure 4 is a scanning electron microscope (SEM) image of Comparative Example 1 and Examples 1-2.

[0037] Figure 5 is a graph showing carrier concentration and mobility using the Hall measurement method of Example 1-2.

[0038] Figure 6 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis of Example 1-2.

[0039] Figure 7 is a graph showing the band diagrams of Comparative Example 1 and Example 1-2.

[0040] Figure 8 is a graph showing the electrical conductivity according to temperature of Comparative Example 1 and Example 1-2.

[0041] Figure 9 is a graph showing the Seebeck coefficient according to temperature for Comparative Example 1 and Example 1-2.

[0042] Figure 10 is a graph showing the power factor according to temperature of Comparative Example 1 and Example 1-2.

[0043] Figure 11 is a graph showing the Pisarenko curves of Comparative Example 1 and Example 1-2.

[0044] Figure 12 is a graph showing the thermal conductivity according to temperature of Comparative Example 1 and Example 1-2.

[0045] Figure 13 is a graph showing the thermal conductivity of electrons according to temperature in Comparative Example 1 and Example 1-2.

[0046] Figure 14 is a graph showing the lattice thermal conductivity according to temperature of Comparative Example 1 and Example 1-2.

[0047] Figure 15 is a graph showing the thermoelectric performance index (zT) according to temperature for Comparative Example 1 and Example 1-2.

[0048] FIG. 16 is a schematic diagram of the synthesis method of Example 2-1 and Example 2-2.

[0049] Figure 17 is a transmission electron microscope (TEM) image of Comparative Example 1 and Example 2-1.

[0050] Figure 18 is a scanning electron microscope (SEM) image of Comparative Example 1 and Example 2-1.

[0051] Figure 19 is a transmission electron microscope (TEM) image of Example 2-1 according to coating time.

[0052] Figure 20 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis of Example 2-2.

[0053] Figure 21 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis of Example 2-2.

[0054] Figure 22 is a graph showing carrier concentration and mobility using the Hall measurement method of Example 2-2.

[0055] FIG. 23 is a graph showing the band diagrams of Comparative Example 1 and Example 2-2.

[0056] Figure 24 is a graph showing the electrical conductivity according to temperature of Comparative Example 1 and Example 2-2.

[0057] Figure 25 is a graph showing the Seebeck coefficient according to temperature for Comparative Example 1 and Example 2-2.

[0058] Figure 26 is a graph showing the power factor according to temperature of Comparative Example 1 and Example 2-2.

[0059] Figure 27 is a graph showing the thermal conductivity according to temperature of Comparative Example 1 and Example 2-2.

[0060] Figure 28 is a graph showing the thermal conductivity of electrons according to temperature in Comparative Example 1 and Example 2-2.

[0061] FIG. 29 is a graph showing the lattice thermal conductivity according to temperature of Comparative Example 1 and Example 2-2.

[0062] FIG. 30 is a graph showing the thermoelectric performance index (zT) according to temperature for Comparative Example 1 and Example 2-2.

[0063] Figure 31 is a graph showing the average thermoelectric performance index (zT) of Example 2-2.

[0064] FIG. 32 is a schematic diagram of the synthesis method of Example 3-1 and Example 3-2.

[0065] Figure 33 is a scanning electron microscope (SEM) image of Comparative Example 1 and Example 3-1.

[0066] Figure 34 is a transmission electron microscope (TEM) image of Example 3-1.

[0067] Figure 35 is a graph showing carrier concentration and mobility using the Hall measurement method of Example 3-2.

[0068] Figure 36 is a graph showing the electrical conductivity of Comparative Example 1 and Example 3-2 according to temperature.

[0069] Figure 37 is a graph showing the Seebeck coefficient according to temperature for Comparative Example 1 and Example 3-2.

[0070] Figure 38 is a graph showing the power factor according to temperature of Comparative Example 1 and Example 3-2.

[0071] FIG. 39 is a graph showing the thermal conductivity of Comparative Example 1 and Example 3-2 as a function of temperature.

[0072] Figure 40 is a graph showing the lattice conductivity according to temperature of Comparative Example 1 and Example 3-2.

[0073] Figure 41 is a graph showing the thermoelectric performance index (zT) according to temperature for Comparative Example 1 and Example 3-2.

[0074] FIG. 42 is a graph showing the average thermoelectric performance index (zT) of Comparative Example 1 and Example 3-2.

[0075]

[0076] Embodiments of the present invention will be described in detail below with reference to the attached drawings and the contents described therein, but the present invention is not limited or restricted by the embodiments.

[0077] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components or steps mentioned in the description.

[0078] As used herein, terms such as “examples,” “examples,” “aspects,” “examples,” etc., are not to be interpreted as implying that any described aspect or design is superior or more advantageous than other aspects or designs.

[0079] Furthermore, the term 'or' refers to an inclusive or rather an exclusive or. That is, unless otherwise noted or is clear from the context, the expression 'x uses a or b' refers to any one of the natural inclusive permutations.

[0080] Additionally, singular expressions (“a” or “an”) used in this specification and claims should generally be interpreted to mean “one or more” unless otherwise stated or it is clear from the context that they relate to the singular form.

[0081] The terms used in the following description have been selected as common and universal in the relevant technical field, but other terms may exist depending on technological development and / or changes, conventions, preferences of the skilled technician, etc. Therefore, the terms used in the following description should not be understood as limiting the technical concept, but as illustrative terms to explain the embodiments.

[0082] In addition, in specific cases, there are terms arbitrarily selected by the applicant, and in such cases, their detailed meanings will be described in the relevant explanatory section. Therefore, the terms used in the description below must be understood not merely as their names, but based on their meanings and the content throughout the specification.

[0083] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0084] Meanwhile, in describing the present invention, if it is determined that a detailed description of related known functions or configurations could unnecessarily obscure the essence of the invention, such detailed description will be omitted. Furthermore, the terminology used in this specification is used to appropriately express embodiments of the present invention, and such terminology may vary depending on the intent of the user or operator, or the conventions of the field to which the invention belongs. Accordingly, the definitions of these terms should be based on the content throughout this specification.

[0085]

[0086] Thermoelectric materials are widely applied in electronic devices based on thermoelectric materials, such as automotive motors, home appliances, and wearable devices, and are required to have improved thermoelectric performance. To maximize thermoelectric performance, coating technology is used on thermoelectric materials, but existing coating methods used for coating thermoelectric materials, such as Atomic Layer Deposition (ALD), Water Atomization, and Electroless Plating, have limitations in that they are expensive and time-consuming.

[0087] Accordingly, the present invention solves the problems of conventional coating methods that are costly and time-consuming by utilizing Chemical Bath Deposition (CBD), and can significantly improve the thermoelectric performance of the thermoelectric material powder and the sintered thermoelectric material body to which it is applied by coating the thermoelectric material powder.

[0088]

[0089] Generally, Chemical Bath Deposition (CBD) is a thin film deposition technique that forms thin films through chemical reactions in a solution. It is utilized in various fields because it allows for the formation of thin films of various materials through a simple and economical process; conventionally, it has been primarily used for depositing thin films such as CdS and ZnS, which are used as buffer layers in solar cells.

[0090] On the other hand, the method for manufacturing thermoelectric material powder according to the embodiment of the present invention applies Chemical Bath Deposition (CBD), a simple and economical method, to coat a uniform thin film on the surface of the thermoelectric material powder, which is not a conventional application field, and the thermoelectric material powder coated by Chemical Bath Deposition (CBD) can improve electrical and thermal properties as a thermoelectric material.

[0091]

[0092] FIG. 1 is a flowchart illustrating a method for manufacturing thermoelectric material powder according to an embodiment of the present invention.

[0093] Referring to FIG. 1, the method includes the step of preparing a precursor solution by dissolving a metal inorganic precursor in a solvent (S110), the step of forming a metal chalcogenide coating layer on the surface of the thermoelectric material alloy powder by stirring the thermoelectric material alloy powder in the precursor solution through a chemical solution deposition method (S120), and the step of preparing a thermoelectric material powder by filtering and drying the thermoelectric material alloy powder with the metal chalcogenide coating layer formed thereon (S130).

[0094] First, the method for manufacturing a thermoelectric material powder according to an embodiment of the present invention proceeds with the step (S110) of preparing a precursor solution by dissolving a metal inorganic precursor in a solvent.

[0095] In the step of preparing the precursor solution (S110), the metal inorganic precursor may be dissolved in a solvent, and the solvent may preferably be deionized water (DI water), but is not limited thereto.

[0096] In the step (S110) of preparing a precursor solution, the precursor solution may further include a reactivity regulator to form a uniform coating layer and stabilize the precursor, and the reactivity regulator includes at least one selected from ammonium hydroxide (NH4OH) or hydrazine hydrate (N2H4·H2O), but is not limited thereto.

[0097] A reactivity modifier is additionally added to the precursor solution and, specifically, can help form a uniform coating layer by acting as an ion source or a pH regulator.

[0098] According to one embodiment, in the step (S110) of preparing the precursor solution, the precursor solution may further include thiourea (SC(NH2)2).

[0099] Thiourea (SC(NH2)2) added to the precursor solution ions (S 2- As a source of ), supplied sulfur ions (S 2- ) can form a coating layer by combining with metal ions of a precursor solution containing a metal inorganic precursor.

[0100] For example, when zinc sulfate (ZnSO4) is used as a metal inorganic precursor, the zinc ions (Zn) of zinc sulfate (ZnSO4) 2+ ) and sulfur ions (S) of thiourea (SC(NH2)2) 2- ) can combine to form a sulfide coating layer (ZnS).

[0101] According to one embodiment, in the step (S110) of preparing the precursor solution, the precursor solution may further include ammonium hydroxide (Ammonium hydroxide; NH4OH).

[0102] Ammonium hydroxide (NH4OH) added to the precursor solution maintains the pH of the solution as alkaline, providing the conditions necessary for the formation of a sulfide coating layer, and can form a uniform coating layer under optimized pH conditions.

[0103] For example, when zinc sulfate (ZnSO4) is used as a metal inorganic precursor, ammonium hydroxide (NH4OH) can optimize the conditions for forming a sulfide coating layer by maintaining the solution at an alkaline pH of 9 to 11.

[0104] For example, in the step (S110) of preparing the precursor solution, if the metal inorganic precursor introduced is zinc sulfate (ZnSO4), it may further include thiourea (SC(NH2)2) and ammonium hydroxide (NH4OH).

[0105] At this time, the concentrations of zinc sulfate (ZnSO4) and thiourea (SC(NH2)2) may be 0.0002M:1.0M to 0.001M:5.0M, and preferably, zinc sulfate (ZnSO4) and thiourea (SC(NH2)2) may be included in a volume ratio of 1:5. In addition, the concentration of ammonium hydroxide (NH4OH) may be added so that the pH is maintained at 9 to 11.

[0106]

[0107] For example, in the step (S110) of preparing the precursor solution, if the metal inorganic precursor introduced is cadmium sulfate (CdSO4), it may further include thiourea (SC(NH2)2) and ammonium hydroxide (NH4OH).

[0108] At this time, the concentrations of cadmium sulfate (CdSO4) and thiourea (SC(NH2)2) may be 0.0002M:1.0M to 0.001M:5.0M, and preferably, cadmium sulfate (CdSO4) and thiourea (SC(NH2)2) may be included in a volume ratio of 0.167:0.0005. In addition, the concentration of ammonium hydroxide (NH4OH) may be added so that the pH is maintained at 9 to 11.

[0109]

[0110] Subsequently, the method for manufacturing a thermoelectric material powder according to an embodiment of the present invention proceeds with the step (S120) of forming a metal chalcogenide coating layer on the surface of the thermoelectric material alloy powder by stirring the thermoelectric material alloy powder in a precursor solution through a chemical solution deposition method.

[0111] In the method for manufacturing a thermoelectric material powder according to an embodiment of the present invention, the thermoelectric material alloy powder can be formed by using a chemical solution deposition method to mix and react metal ions and chalcogen elements contained in a precursor solution on the surface of the thermoelectric material alloy powder.

[0112] In the method for manufacturing a thermoelectric material powder according to an embodiment of the present invention, the metal chalcogenide coating layer may be represented by the following chemical formula 1.

[0113] [Chemical Formula 1]

[0114] M a X b

[0115] At this time, in Chemical Formula 1, M may be a metal ion, and preferably, a metal cation (M n+ It can be ), and metal cation (M n+ ) is Zn 2+ , Cd 2+ , Sn 4+ , Al 3+ , Ti 4+ , Fe 3+ , Zr 4+ , Cu 2+ , In 3+ and Ce 4+ It may include any one selected from the above, and may be an integer value of 1 ≤ a ≤ 4. Additionally, X may be a chalcogen element, and the chalcogen element (X) may include any one selected from oxygen (O), sulfur (S), and selenium (Se), and b may be an integer value of 1 ≤ b ≤ 5. a and b represent values ​​determined to maintain chemical neutrality between the charge magnitude of the metal ion (M) and the negative charge magnitude of the chalcogen element (X).

[0116] For example, if the metal chalcogenide coating layer is tin dioxide (SnO), the metal cation (M n+ ) This Sn 4+ And, the chalcogen element (X) is oxygen (O), and at this time, Sn 4+ and O 2- This can mean that it is combined in a 1:2 ratio.

[0117] In the method for manufacturing a thermoelectric material powder according to an embodiment of the present invention, a metal chalcogenide coating layer may be formed on part or all of the surface of the thermoelectric material alloy powder.

[0118] In the method for manufacturing a thermoelectric material powder according to an embodiment of the present invention, the thermoelectric material alloy powder may include at least two elements selected from transition metals, rare earth elements, group 13 elements, group 14 elements, group 15 elements, and group 16 elements.

[0119] According to one embodiment, in the step (S120) of forming a metal chalcogenide coating layer, if the metal chalcogenide coating layer is zinc sulfide (ZnS), the time for forming the coating layer using a chemical solution deposition method may be 150 seconds to 450 seconds, and preferably 225 seconds.

[0120] According to one embodiment, when the metal chalcogenide coating layer is zinc sulfide (ZnS), if the time for forming the coating layer is less than 150 seconds, Zn 2+ and S 2- If the reaction between the two is not sufficiently carried out, ZnS may not be properly formed, and if it exceeds 450 seconds, ZnS aggregation occurs, increasing the particle size, which may cause the ZnS coating layer to easily detach from the surface of the thermoelectric alloy powder.

[0121] In addition, according to one embodiment, when the metal chalcogenide coating layer is zinc sulfide (ZnS), the temperature for forming the coating layer may be 60°C to 90°C. If the temperature is below 60°C, the chemical reaction may not proceed sufficiently, resulting in the formation of an incomplete coating layer or making it difficult to form a uniform coating layer. If the temperature exceeds 90°C, non-homogeneous aggregation of ZnS is formed due to excessive reaction, which reduces the uniformity of the coating layer and causes a problem of reduced thermal stability of the thermoelectric material alloy powder.

[0122] According to one embodiment, in the step (S120) of forming a metal chalcogenide coating layer, if the metal chalcogenide coating layer is cadmium sulfide (CdS), the time for forming the coating layer may be 30 seconds to 120 seconds, and preferably 90 seconds.

[0123] According to one embodiment, when the metal chalcogenide coating layer is cadmium sulfide (CdS), if the time for forming the coating layer is less than 30 seconds, Cd 2+ and S 2-If the reaction between the two is not sufficiently carried out, CdS may not be properly formed, and if it exceeds 120 seconds, aggregation of CdS occurs, increasing the particle size, which may cause the CdS coating layer to easily detach from the surface of the thermoelectric material alloy powder.

[0124] In addition, according to one embodiment, when the metal chalcogenide coating layer is cadmium sulfide (CdS), the temperature at which the coating layer is formed may be 40°C to 90°C. If the temperature is below 40°C, the chemical reaction may not proceed sufficiently, resulting in the formation of an incomplete coating layer or making it difficult to form a uniform coating layer. If the temperature exceeds 90°C, non-homogeneous aggregation of CdS is formed due to excessive reaction, which reduces the uniformity of the coating layer and causes a problem of reduced thermal stability of the thermoelectric material alloy powder.

[0125] According to one embodiment, in the step (S120) of forming a metal chalcogenide coating layer, if the metal chalcogenide coating layer is tin dioxide (SnO2), the time for forming the coating layer may be 90 seconds to 270 seconds, and preferably 210 seconds.

[0126] According to one embodiment, when the metal chalcogenide coating layer is tin dioxide (SnO2), if the time for forming the coating layer is less than 90 seconds, Sn 2+ Wow O 2- If the reaction between the particles is not sufficiently carried out, SnO2 may not be properly formed, and if the reaction exceeds 270 seconds, aggregation between SnO2 particles occurs, increasing the particle size, and there is also a problem that the oxidizing properties of SnO2 cause chemical changes at the contact interface of the thermoelectric material alloy powder.

[0127] In addition, according to one embodiment, when the metal chalcogenide coating layer is tin dioxide (SnO2), the temperature for forming the coating layer may be 25°C to 90°C. If the temperature is below 25°C, the chemical reaction may not proceed sufficiently, resulting in the formation of an incomplete coating layer or making it difficult to form a uniform coating layer. If the temperature exceeds 90°C, heterogeneous aggregation of SnO2 is formed, which reduces the uniformity of the coating layer and causes problems such as oxidation of the thermoelectric material alloy powder or reduced thermal stability.

[0128]

[0129] Finally, the method for manufacturing a thermoelectric material powder according to an embodiment of the present invention includes the step (S130) of manufacturing a thermoelectric material powder by filtering and drying a thermoelectric material alloy powder having a metal chalcogenide coating layer formed thereon.

[0130] In the step (S130) of manufacturing the thermoelectric material powder, filtration may be performed using conventional methods, preferably using a vacuum filtration device, but is not limited thereto.

[0131] In the step (S130) of manufacturing the thermoelectric material powder, drying can be performed using a commonly used method, preferably using an oven, but is not limited thereto.

[0132] When drying using an oven, the drying temperature may be 40°C or higher, and the drying time may be 4 to 8 hours.

[0133] At this time, if the drying temperature (e.g., less than 40℃) or drying time (e.g., less than 4 hours) is insufficient, the moisture in the powder is not sufficiently removed, and there is a problem that the quality of the metal chalcogenide coating layer deteriorates.

[0134] In addition, if the drying temperature (e.g., exceeding 90°C) or drying time (e.g., exceeding 8 hours) is exceeded, there is a problem that the thermoelectric material alloy powder of the metal chalcogenide coating layer oxidizes.

[0135] According to one embodiment, the step of manufacturing the thermoelectric material powder (S130) may further include a step of reducing the thermoelectric material powder.

[0136] The heat treatment temperature of the reduction heat treatment can be carried out at 300°C to 500°C, and the heat treatment time can be carried out at 2 hours to 4 hours.

[0137] At this time, if the heat treatment temperature (e.g., less than 300℃) or heat treatment time (e.g., less than 2 hours) of the reduction heat treatment is insufficient, there is a problem that the reduction reaction cannot occur sufficiently.

[0138] In addition, if the heat treatment temperature (e.g., exceeding 500°C) or heat treatment time (e.g., exceeding 4 hours) of the reduction heat treatment is exceeded, some of the thermoelectric material alloy powder (e.g., Te in Bi-Sb-Te) volatilizes, and excessive grain growth occurs, resulting in a problem of reduced thermoelectric performance.

[0139] The thermoelectric material powder according to an embodiment of the present invention is manufactured according to the method for manufacturing the thermoelectric material powder according to an embodiment of the present invention.

[0140] Since the method for manufacturing a thermoelectric material powder according to an embodiment of the present invention includes the same components as the thermoelectric material powder according to an embodiment of the present invention, the description of the same components is omitted.

[0141] A method for manufacturing a thermoelectric material sintered body according to an embodiment of the present invention further includes the step of manufacturing a thermoelectric material sintered body by sintering thermoelectric material powder.

[0142] In the method for manufacturing a thermoelectric material sintered body according to an embodiment of the present invention, a metal chalcogenide coating layer is formed at the grain boundaries of the thermoelectric material alloy by proceeding with sintering, and can suppress the grain growth of the thermoelectric material alloy.

[0143] Specifically, the metal chalcogenide coating layer can sinter thermoelectric material powder to form a thermoelectric material alloy and inhibit grain growth at the grain boundaries of the thermoelectric material alloy formed during the sintering process.

[0144] Generally, a grain boundary refers to the boundary region formed where individual grains meet in polycrystalline materials, and in thermoelectric materials, grain boundaries act as one of the main causes of conduction electron scattering and phonon scattering, thereby controlling thermoelectric performance.

[0145] Phonons play a role in transferring energy within a lattice, and since phonon scattering plays an important role in thermoelectric materials, consequently, phonon scattering can lower thermal conductivity, maintain conductivity, and increase the efficiency of thermoelectric materials.

[0146] Therefore, a thermoelectric alloy manufactured by sintering thermoelectric powder with a metal chalcogenide coating layer is enhanced with multiple phonons, and the enhanced multiple phonons lower thermal conductivity while maintaining electrical conductivity, thereby achieving high thermoelectric efficiency.

[0147] Generally, if the crystal grains grow excessively, phonon scattering decreases, leading to increased thermal conductivity. This increased thermal conductivity may cause a problem where the thermoelectric performance of the thermoelectric material deteriorates. Additionally, as the bipolar effect becomes stronger, the electrical conductivity of the thermoelectric material increases, which may lead to a problem where the thermoelectric performance index (zT) value decreases.

[0148] Accordingly, in the method for manufacturing a thermoelectric material sintered body according to an embodiment of the present invention, thermoelectric performance can be improved by suppressing the crystal grain growth and bipolar effect of the thermoelectric material produced by sintering a thermoelectric material powder having a metal chalcogenide coating layer formed thereon.

[0149] In the method for manufacturing a thermoelectric material sintered body according to an embodiment of the present invention, sintering may be performed using a conventionally used method, preferably spark plasma sintering (SPS), but is not limited thereto.

[0150] The sintering temperature of the discharge plasma sintering (SPS) can be carried out at 350°C to 500°C, and the sintering time can be carried out at 5 minutes to 30 minutes.

[0151] At this time, if the sintering temperature (e.g., less than 350℃) or sintering time (e.g., less than 5 minutes) is insufficient, the inter-particle bonding is not sufficiently formed due to the insufficient sintering time, resulting in weakened thermoelectric properties and mechanical strength, and also, recrystallization is not properly carried out, causing defects and degrading thermoelectric performance.

[0152] In addition, if the sintering time (e.g., exceeding 5000℃) or the sintering time (e.g., exceeding 30 minutes) is exceeded, the crystals grow too large, increasing the size of the crystals, and some of the thermoelectric material alloy powder (e.g., Te in Bi-Sb-Te) volatilizes, causing a problem of reduced thermoelectric performance.

[0153] A sintered body according to an embodiment of the present invention is manufactured according to a method for manufacturing a thermoelectric material sintered body according to an embodiment of the present invention.

[0154] Since the method for manufacturing a thermoelectric material sintered body according to an embodiment of the present invention includes the same components as the thermoelectric material sintered body according to an embodiment of the present invention, the description of the same components is omitted.

[0155] Accordingly, the thermoelectric material sintered body according to an embodiment of the present invention comprises a thermoelectric material alloy powder having a metal chalcogenide coating layer formed thereon, and the metal chalcogenide coating layer can improve thermoelectric performance by suppressing grain growth and bipolar effect within the thermoelectric material sintered body.

[0156] In addition, the thermoelectric material sintered body according to an embodiment of the present invention can improve thermoelectric performance (zT) by optimizing electrical conductivity, Seebeck coefficient, and thermal conductivity.

[0157]

[0158] The present invention will be explained in more detail below through examples. These examples are intended to explain the invention more specifically, and the scope of the invention is not limited by these examples.

[0159]

[0160] [Comparative Example 1] Bi-Sb-Te based material

[0161] Bi-Sb-Te alloy powder was prepared by synthesizing it using a general solid-state synthesis method.

[0162]

[0163] [Example 1] Zinc sulfide (ZnS) coated Bi-Sb-Te-based thermoelectric material powder and sintered body

[0164] [Example 1-1] Zinc sulfide (ZnS) coated Bi-Sb-Te-based thermoelectric material powder

[0165] Bi-Sb-Te alloy powder was prepared by synthesizing it using a general solid-state synthesis method. 0.005 M zinc sulfate (ZnSO4) and 0.02 M thiourea (SC(NH2)2) were each dissolved in deionized water (DI water), and then 2.5 M ammonium hydroxide (NH4OH) was added.

[0166] A coating solution was prepared by adding Bi-Sb-Te alloy powder to a mixed solution containing zinc sulfate (ZnSO4), thiourea, and ammonium hydroxide and magnetically stirring at 80°C for 150 seconds, 225 seconds, 300 seconds, 450 seconds, and 600 seconds.

[0167] The prepared coating solution was filtered using a vacuum filtration device, and the filtered powder was dried in an oven at a temperature of 60°C for 6 hours to obtain zinc sulfide (ZnS) coated Bi-Sb-Te-based thermoelectric material powder.

[0168]

[0169] [Example 1-2] Zinc sulfide (ZnS) coated Bi-Sb-Te-based thermoelectric material sintered body

[0170] The zinc sulfide (ZnS) coated Bi-Sb-Te-based thermoelectric material powder prepared in Example 1-1 was sintered using Spark Plasma Sintering (SPS), and the sintering was performed at 1.2 x 10⁻⁶ -2 A zinc sulfide (ZnS) coated Bi-Sb-Te-based thermoelectric material sintered body was obtained by proceeding at a pressure of 43 MPa at 450°C for 10 minutes under a vacuum of less than torr.

[0171] A zinc sulfide (ZnS) coated Bi-Sb-Te-based thermoelectric material sintered body was prepared by cutting it using a diamond cutter and adjusting its size by polishing it with sandpaper.

[0172]

[0173] [Experimental Example 1-1] Phase Analysis and Structural Characteristics Analysis

[0174] Figure 2 is a transmission electron microscope (TEM) image of Comparative Example 1 and Example 1-1.

[0175] Referring to Figure 2, this is a transmission electron microscope (TEM) image to confirm whether a coating layer is well formed on the Bi-Sb-Te-based thermoelectric material powder after the chemical bath deposition (CBD) process.

[0176] While nothing existed on the surface of Comparative Example 1, a rough structure was observed on the surface of Example 1-1, and upon analyzing the Fast Fourier Transform (FFT) pattern of the rough region of Example 1-1, it was confirmed that it matched the pattern of zinc sulfide (ZnS), confirming that a zinc sulfide (ZnS) coating layer was formed on the surface of the Bi-Sb-Te-based thermoelectric material powder.

[0177]

[0178] Figure 3 is a transmission electron microscope (TEM) image of Example 1-1.

[0179] Referring to Fig. 3, this is a transmission electron microscope (TEM) image of Example 1-1 according to coating time to confirm whether a coating layer is well formed on the Bi-Sb-Te-based thermoelectric material powder.

[0180] When the coating time of Example 1-1 was 225 seconds, it was confirmed that zinc sulfide (ZnS) existed in a layer shape of less than 50 nm along the grain boundaries of the Bi-Sb-Te-based thermoelectric material powder, and as a result of analyzing the inverse fast Fourier transform (IFFT) pattern, it was confirmed that a dislocation arrangement existed at the interface between the Bi-Sb-Te-based thermoelectric material powder and the zinc sulfide (ZnS) layer.

[0181] However, when the coating time of Example 1-1 was 300 seconds, it was confirmed that zinc sulfide (ZnS) existed as nanoparticles of non-uniform shape and size along the grain boundaries of the Bi-Sb-Te-based thermoelectric material powder, and the non-uniform shape and size of zinc sulfide (ZnS) may be caused by aggregation between zinc sulfide (ZnS) particles occurring as the coating time increased.

[0182]

[0183] Figure 4 is a scanning electron microscope (SEM) image of Comparative Example 1 and Examples 1-2.

[0184] Referring to FIG. 4, scanning electron microscope (SEM) images of the fracture surfaces of Comparative Example 1 and Example 1-2 are shown, and it can be seen that the crystal size of Example 1-2 is significantly reduced compared to Comparative Example 1, and this may be caused by zinc sulfide (ZnS) having a high melting point (1458 K) distributed along the grain boundaries of the Bi-Sb-Te thermoelectric material sintered body (887 K) during the sintering process, which hinders the growth of crystal grains within the Bi-Sb-Te thermoelectric material powder.

[0185] Therefore, Examples 1-2 can be confirmed that zinc sulfide (ZnS) coating on the Bi-Sb-Te-based thermoelectric material sintered body had a significant effect on microstructure and grain control.

[0186]

[0187] [Experimental Example 1-2] Analysis of Carrier Transport Characteristics

[0188] Figure 5 is a graph showing carrier concentration and mobility using the Hall measurement method of Example 1-2.

[0189] Referring to Figure 5, to analyze the effect of zinc sulfide (ZnS) on the Bi-Sb-Te-based thermoelectric material sintered body, carrier concentration and mobility were determined using Hall measurement, and it was observed that the carrier concentration increased until the coating time was 150 seconds and then gradually decreased.

[0190]

[0191] Figure 6 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis of Example 1-2, and Figure 7 is a graph showing the band diagrams of Comparative Example 1 and Example 1-2.

[0192]

[0193] Referring to Fig. 6, it can be seen that in Example 1-2, p-type zinc telluride (ZnTe) had a dominant effect at a coating time of 150 seconds, and n-type zinc sulfide (ZnS) had a dominant effect at 225 seconds.

[0194] In the case where the coating time of Example 1-2 is 150 seconds, the remaining zinc sulfide (ZnS) ions may react with tellurium (Te) during the discharge plasma sintering (SPS) process due to insufficient zinc sulfide (ZnS) reaction time during the Chemical Bath deposition (CBD) process.

[0195] On the other hand, when the coating time of Example 1-2 is 225 seconds, sufficient reaction time is provided, so it can be confirmed that zinc sulfide (ZnS) is formed.

[0196]

[0197] Referring to Fig. 7, regarding carrier mobility, when the coating time of Example 1-2 is 150 seconds and 225 seconds, it can be seen that the potential barrier between the Bi-Sb-Te-based thermoelectric material sintered body and the secondary phase plays a role in increasing mobility. At this time, the potential barrier plays a role in increasing the average energy of the carriers by scattering low-energy carriers, but when the coating time of Example 1-2 is 300 seconds, it can be seen that the carrier mobility decreases as the size of zinc sulfide (ZnS) increases.

[0198] Accordingly, referring to FIGS. 5 to 7, it can be seen that the carrier mobility shows the best effect when the coating time of Example 1-2 is 225 seconds.

[0199]

[0200] [Experimental Example 1-3] Analysis of Electrical and Thermoelectric Properties

[0201] Figure 8 is a graph showing the electrical conductivity according to temperature of Comparative Example 1 and Example 1-2.

[0202] Referring to Fig. 8, it can be seen that as the coating time of Example 1-2 increases to 150 seconds, 225 seconds, 300 seconds, and 450 seconds, the electrical conductivity increases and then decreases, and due to the influence of carrier mobility, it can be seen that the electrical conductivity of Example 1-2 is best at a coating time of 255 seconds.

[0203]

[0204] Figure 9 is a graph showing the Seebeck coefficient according to temperature for Comparative Example 1 and Example 1-2, and Figure 10 is a graph showing the power factor according to temperature for Comparative Example 1 and Example 1-2.

[0205] Referring to Fig. 9, it can be seen that the Seebeck coefficient of Comparative Example 1 decreases significantly at high temperatures, whereas the Seebeck coefficient of Example 1-2 decreases relatively less, which may be due to the suppression of the bipolar effect.

[0206] Referring to Fig. 10, when the coating time of Example 1-2 is 225 seconds, the electrical conductivity and Seebeck coefficient are simultaneously improved, and the highest power factor can be confirmed.

[0207]

[0208] Figure 11 is a graph showing the Pisarenko curves of Comparative Example 1 and Example 1-2.

[0209] Referring to FIG. 11, it can be seen that Example 1-2 is located beyond the Pisarenko plot of Comparative Example 1, and that the carrier filtering effect and the increase in effective mass contributed significantly to the increase in the Seebeck coefficient.

[0210] Therefore, it can be confirmed that the Seebeck coefficient increased as the coating time of Example 1-2 increased.

[0211]

[0212] FIG. 12 is a graph showing the thermal conductivity of Comparative Example 1 and Example 1-2 according to temperature, and FIG. 13 is a graph showing the thermal conductivity of electrons of Comparative Example 1 and Example 1-2 according to temperature.

[0213] Referring to Fig. 12, it can be seen that at temperatures above 380K, the thermal conductivity of Comparative Example 1 increases significantly, whereas the thermal conductivity of Example 1-2 increases relatively less, which may be due to the suppression of the bipolar effect.

[0214] Referring to Fig. 13, the thermal conductivity of electrons refers to the thermal conductivity generated by electrons carrying heat, and since it is advantageous to increase the thermal conductivity of electrons to improve thermoelectric performance, it can be confirmed that the highest thermal conductivity of electrons is obtained when the coating time of Example 1-2 is 225 seconds.

[0215]

[0216] Figure 14 is a graph showing the lattice thermal conductivity according to temperature of Comparative Example 1 and Example 1-2.

[0217] Referring to Fig. 14, lattice thermal conductivity refers to the method of heat transfer as atoms or ions vibrate within a crystal structure, and since it is advantageous to lower lattice thermal conductivity to increase thermoelectric performance, it can be confirmed that the lowest lattice thermal conductivity is obtained when the coating time of Example 1-2 is 225 seconds.

[0218] In addition, when the coating time of Example 1-2 is 225 seconds, the lowest lattice thermal conductivity may be caused by enhanced phonon scattering due to the presence of a very small zinc sulfide (ZnS) layer and dislocation arrangement within the Bi-Sb-Te-based thermoelectric material sintered body.

[0219]

[0220] Figure 15 is a graph showing the thermoelectric performance index (zT) according to temperature for Comparative Example 1 and Example 1-2.

[0221] Referring to Fig. 15, when the coating time of Example 1-2 was 225 seconds, the thermoelectric performance index (zT) was highest, which may be due to the simultaneous improvement in power factor and reduction in thermal conductivity.

[0222]

[0223] Accordingly, referring to FIGS. 8 to 15, it can be confirmed that the zinc sulfide (ZnS) coated Bi-Sb-Te-based thermoelectric material sintered body of Example 1-2 preferably has optimized electrical characteristics and thermoelectric performance at a coating time of 225 seconds.

[0224]

[0225] [Example 2] Cadmium Sulfide (CdS) Coated Bi-Sb-Te Based Thermoelectric Material Powder and Sintered Body

[0226] [Example 2-1] Cadmium Sulfide (CdS) Coated Bi-Sb-Te Based Thermoelectric Material Powder

[0227] Referring to FIG. 16, Bi-Sb-Te (BST) alloy powder (111) was prepared by synthesizing it using a general solid-state synthesis method. 0.167 M cadmium sulfate (CdSO4) (112), 0.0005 M thiourea (SC(NH2)2) (113), and 1 M ammonium hydroxide (NH4OH) (114) were each dissolved in deionized water (DI water).

[0228] Bi-Sb-Te (BST) alloy powder (111) was added to a mixed solution containing cadmium sulfate (CdSO4) (112), thiourea (SC(NH2)2) (113) and ammonium hydroxide (NH4OH) (114) and stirred, and the stirred mixed solution was stirred in a beaker heated to 60°C for 30 seconds, 60 seconds, 90 seconds, and 120 seconds to prepare a coating solution.

[0229] The prepared coating solution was dried using an oven to produce a powder, and to remove organic matter from the prepared powder, it was placed in an alumina ceramic vessel and subjected to reduction heat treatment at 300°C to obtain a cadmium sulfide (CdS) coated Bi-Sb-Te-based thermoelectric material powder.

[0230]

[0231] [Example 2-2] Cadmium Sulfide (CdS) Coated Bi-Sb-Te Based Thermoelectric Material Sintered Body

[0232] Referring to Fig. 16, the cadmium sulfide (CdS) coated Bi-Sb-Te-based thermoelectric material powder prepared in Example 2-1 was sintered using Spark Plasma Sintering (SPS), and the sintering was performed at 1.2 x 10⁻⁶ -2 A cadmium sulfide (CdS) coated Bi-Sb-Te-based thermoelectric material sintered body was obtained by proceeding at a pressure of 43 MPa at 450°C for 10 minutes under a vacuum of less than torr.

[0233] The cadmium sulfide (CdS)-coated Bi-Sb-Te-based thermoelectric material sintered body manufactured by sintering was prepared by cutting it using a diamond cutter and polishing it with sandpaper to adjust its size.

[0234]

[0235] [Experimental Example 2-1] Phase Analysis and Structural Characteristics Analysis

[0236] Figure 17 is a transmission electron microscope (TEM) image of Comparative Example 1 and Example 2-1.

[0237] Referring to Fig. 17, this is a transmission electron microscope (TEM) image to confirm whether a coating layer is well formed on the Bi-Sb-Te-based thermoelectric material powder after the chemical bath deposition (CBD) process.

[0238] Compared to Comparative Example 1, it was observed that small nanoparticles formed a layer on the surface of Example 2-1, and upon analyzing the Fast Fourier Transform (FFT) pattern of the small nanoparticle layer of Example 2-1, it was confirmed that it matched the pattern of cadmium sulfide (CdS), confirming that a cadmium sulfide (CdS) coating layer was formed on the surface of the Bi-Sb-Te-based thermoelectric material powder.

[0239] In addition, the coating time of Example 2-1 was carried out for 90 seconds to confirm the presence of dark gray particles, and through mapping, it was confirmed that the dark gray particles were cadmium sulfide (CdS), and it was confirmed that a cadmium sulfide (CdS) coating layer existed on the grain boundaries of the Bi-Sb-Te-based thermoelectric material powder after sintering.

[0240]

[0241] Figure 18 is a scanning electron microscope (SEM) image of Comparative Example 1 and Example 2-1.

[0242] Referring to Fig. 18, cadmium sulfide (CdS) has a large difference in melting point compared to Bi-Sb-Te alloy powder and inhibits the grain growth of Bi-Sb-Te alloy powder during the sintering process. Therefore, the fracture surfaces of Comparative Example 1 and Example 2-1 were examined using a scanning electron microscope (SEM), and it was confirmed that the grain size of Example 2-1 is significantly smaller than the grain size of Comparative Example 1.

[0243]

[0244] Figure 19 is a transmission electron microscope (TEM) image of Example 2-1 according to coating time.

[0245] Referring to Fig. 19, a transmission electron microscope (TEM) was used to determine how the cadmium sulfide (CdS) layer is formed on the Bi-Sb-Te-based thermoelectric material powder depending on the coating time.

[0246] Example 2-1 confirmed that cadmium sulfide (CdS) clusters exist as the coating time increases, and confirmed that a layer is formed and its thickness increases as the coating time increases, and confirmed that the thickness of the cadmium sulfide (CdS) layer formed can be finely controlled by adjusting the coating time.

[0247]

[0248] Figure 20 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis of Example 2-2, and Figure 21 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis of Example 2-2.

[0249] Referring to Figures 20 and 21, in Example 2-2, through X-ray photoelectron spectroscopy (XPS) analysis, it can be confirmed that cadmium sulfide (CdS) is present rather than a single element of Cd and S, and that the reduction heat treatment proceeded well by the absence of cadmium sulfate (CdSO4) in the S peak at a binding energy of 164 eV to 165 eV.

[0250]

[0251] [Experimental Example 2-2] Analysis of Carrier Transport Characteristics

[0252] FIG. 22 is a graph showing carrier concentration and mobility using the Hall measurement method of Example 2-2, and FIG. 23 is a graph showing the band diagrams of Comparative Example 1 and Example 2-2.

[0253] Referring to Figure 22, to analyze the effect of cadmium sulfide (CdS) on the Bi-Sb-Te-based thermoelectric material sintered body, carrier concentration and mobility were determined using Hall measurement, and the electrical conductivity can be increased only if carrier concentration and mobility are improved.

[0254] Referring to Figures 22 and 23, it can be seen that the carrier concentration of Example 2-2 increased due to hole charge transfer.

[0255] In the case of Example 2-2, there was no significant change in carrier mobility, but it was observed that it decreased slightly as the coating time increased. This may be due to the scattering of carriers as the thickness of the coated cadmium sulfide (CdS) layer increased.

[0256]

[0257] [Experimental Example 2-3] Analysis of Electrical and Thermoelectric Properties

[0258] Figure 24 is a graph showing the electrical conductivity according to temperature of Comparative Example 1 and Example 2-2.

[0259] Referring to FIG. 24, it can be seen that the electrical conductivity of Example 2-2 improves and then decreases as the coating time increases to 30 seconds, 60 seconds, 90 seconds, and 120 seconds, and it can be seen that the electrical conductivity of Example 2-2 is best at a coating time of 90 seconds.

[0260]

[0261] Figure 25 is a graph showing the Seebeck coefficient according to temperature for Comparative Example 1 and Example 2-2.

[0262] Referring to FIG. 25, it can be seen that the Seebeck coefficient of Example 2-2 increases compared to Comparative Example 1. In particular, at temperatures above 400K, Comparative Example 1 shows a tendency for the Seebeck coefficient to decrease, whereas Example 2-2 does not decrease and continues to increase due to the bipolar effect.

[0263]

[0264] Figure 26 is a graph showing the power factor according to temperature of Comparative Example 1 and Example 2-2.

[0265] Referring to Fig. 26, the power factor is calculated using the values ​​of electrical conductivity and Seebeck coefficient, and it can be seen that the power factor is highest when the coating time of Example 2-2 is 90 seconds.

[0266]

[0267] Figure 27 is a graph showing the thermal conductivity according to temperature of Comparative Example 1 and Example 2-2.

[0268] Referring to Fig. 27, the thermal conductivity of Comparative Example 1 showed a tendency to decrease up to a temperature of 360K and then increase, whereas the thermal conductivity of Example 2-2 showed a tendency to continue decreasing, which may be due to the suppression of the bipolar effect.

[0269] Therefore, it can be confirmed that the lowest thermal conductivity is observed when the coating time of Example 2-2 is 90 seconds.

[0270]

[0271] Figure 28 is a graph showing the thermal conductivity of electrons according to temperature in Comparative Example 1 and Example 2-2.

[0272] Referring to Fig. 28, the thermal conductivity of electrons refers to the thermal conductivity generated by electrons carrying heat, and since it is advantageous to increase the thermal conductivity of electrons to improve thermoelectric performance, it can be confirmed that the highest thermal conductivity of electrons is observed when the coating time of Example 2-2 is 90 seconds.

[0273]

[0274] FIG. 29 is a graph showing the lattice thermal conductivity according to temperature of Comparative Example 1 and Example 2-2.

[0275] Referring to Fig. 29, lattice thermal conductivity refers to the method of heat transfer as atoms or ions vibrate within a crystal structure, and since it is advantageous to lower lattice thermal conductivity to increase thermoelectric performance, it can be confirmed that the highest electron thermal conductivity is observed when the coating time of Example 2-2 is 90 seconds.

[0276] Accordingly, referring to FIGS. 27 to 29, when the coating time of Example 2-2 is 90 seconds, it can be confirmed that the tendency to show the lowest thermal conductivity value is due to a large reduction in lattice thermal conductivity rather than the influence of the thermal conductivity of the electrons.

[0277]

[0278] FIG. 30 is a graph showing the thermoelectric performance index (zT) according to temperature for Comparative Example 1 and Example 2-2, and FIG. 31 is a graph showing the average thermoelectric performance index (zT) of Example 2-2.

[0279] Referring to FIGS. 30 and 31, when the coating time of Example 2-2 is 90 seconds, the highest thermoelectric performance index (zT) of approximately 1.54 can be observed, which may be due to a significant improvement in power factor and a significant reduction in lattice thermal conductivity.

[0280] Referring to Figure 31, the average thermoelectric performance index (zT) over the entire temperature range has improved, which may be due to the suppression of the bipolar effect in a relatively high temperature range.

[0281]

[0282] Accordingly, with reference to FIGS. 17 to 31, it can be confirmed that the electrical characteristics and thermoelectric performance of the cadmium sulfide (CdS) coated Bi-Sb-Te-based thermoelectric material sintered body of Example 2-2 are preferably optimized at a coating time of 90 seconds.

[0283]

[0284] [Example 3] Tin dioxide (SnO2) coated Bi-Sb-Te-based thermoelectric material powder and sintered body

[0285] [Example 3-1] Tin Dioxide (SnO2) Coated Bi-Sb-Te Based Thermoelectric Material Powder

[0286] Referring to FIG. 32, Bi-Sb-Te (BST) alloy powder (111) was prepared by synthesizing it using a general solid-state synthesis method. 0.00028 M tin(II) chloride dihydrate (SnO2) (115) was dissolved in deionized water (DI water).

[0287] Bi-Sb-Te (BST) alloy powder (111) was added to a mixed solution containing tin (II) chloride dihydrate (SnCl2·2H2O) (115) and stirred, and the stirred mixed solution was stirred in a beaker heated to 60°C for 90 seconds, 150 seconds, 210 seconds, and 270 seconds to prepare a coating solution.

[0288] The prepared coating solution was dried using an oven to produce a powder, and to remove organic matter from the prepared powder, it was placed in an alumina ceramic container and subjected to reduction heat treatment at 300°C to obtain a tin dioxide (SnO2) coated Bi-Sb-Te-based thermoelectric material powder.

[0289]

[0290] [Example 3-2] Tin Dioxide (SnO2) Coated Bi-Sb-Te Based Thermoelectric Material Powder

[0291] Referring to FIG. 32, the tin dioxide (SnO2)-coated Bi-Sb-Te-based thermoelectric material powder prepared in Example 3-1 was sintered using Spark Plasma Sintering (SPS), and the sintering was performed at 1.2 x 10⁻⁶ -2 A tin dioxide (SnO2) coated Bi-Sb-Te-based thermoelectric material sintered body was obtained by proceeding at a pressure of 43 MPa at 450°C for 10 minutes under a vacuum of less than torr.

[0292] A sintered body of a tin dioxide (SnO2) coated Bi-Sb-Te-based thermoelectric material manufactured by sintering was prepared by cutting it using a diamond cutter and polishing it with sandpaper to adjust its size.

[0293]

[0294] [Experimental Example 3-1] Phase Analysis and Structural Characteristics Analysis

[0295] Figure 33 is a scanning electron microscope (SEM) image of Comparative Example 1 and Example 3-1.

[0296] Referring to Fig. 33, the fracture surfaces of Comparative Example 1 and Example 3-2 were examined using a scanning electron microscope (SEM), and as a result of mapping the surface of Example 3-1, it was confirmed that Sn and O elements were detected.

[0297] In Example 3-1, compared to Comparative Example 1, it can be confirmed that the grain size is significantly smaller, and this can be confirmed that the grain growth of the Bi-Sb-Te alloy powder was hindered because the melting point of tin dioxide (SnO2) during the sintering process is higher than that of the Bi-Sb-Te alloy powder.

[0298]

[0299] Figure 34 is a transmission electron microscope (TEM) image of Example 3-1.

[0300] Referring to Fig. 34, high-magnification images were obtained using a transmission electron microscope (TEM) to confirm that the detected Sn and O elements were tin dioxide (SnO2). As a result, it was confirmed that tin dioxide (SnO2), which is a lattice different from the Bi-Sb-Te system lattice, was present. Additionally, mapping was performed, and it was confirmed that tin dioxide (SnO2) was present on the surface of the Bi-Sb-Te alloy powder.

[0301]

[0302] [Experimental Example 3-2] Analysis of Carrier Transport Characteristics

[0303] Figure 35 is a graph showing carrier concentration and mobility using the Hall measurement method of Example 3-2.

[0304] Referring to Fig. 35, carrier concentration and mobility were determined using Hall measurement to analyze the effect of tin dioxide (SnO2) on the Bi-Sb-Te-based thermoelectric material sintered body.

[0305] In the case of Example 3-2, it can be seen that the carrier concentration decreases as the coating time increases, which may be due to the fact that the majority of carriers of tin dioxide (SnO2) are electrons.

[0306] In addition, the reason for the increase in carrier mobility in Example 3-2 may be that hole carriers with relatively low energy are scattered due to band bending, a phenomenon in which the energy band of the semiconductor material between the Bi-Sb-Te-based thermoelectric material powder and tin dioxide (SnO2) is deformed by external conditions.

[0307]

[0308] [Experimental Example 3-3] Analysis of Electrical and Thermoelectric Properties

[0309] Figure 36 is a graph showing the electrical conductivity of Comparative Example 1 and Example 3-2 according to temperature.

[0310] Referring to FIG. 36, it can be seen that the electrical conductivity of Example 3-2 improves and then decreases as the coating time increases to 90 seconds, 150 seconds, 210 seconds, and 270 seconds, and it can be seen that the electrical conductivity of Example 3-2 is best at a coating time of 210 seconds.

[0311] The tendency for electrical conductivity to improve and then decrease as coating time increases is because the increase in carrier mobility is more dominant than the decrease in carrier concentration, and the reason for the subsequent decrease may be that the decrease in carrier concentration is more dominant than mobility.

[0312]

[0313] Figure 37 is a graph showing the Seebeck coefficient according to temperature for Comparative Example 1 and Example 3-2.

[0314] Referring to FIG. 37, the Seebeck coefficient of Example 3-2 had a higher value compared to Comparative Example 1, which is because the carrier concentration of Example 3-2 is significantly lower than that of Comparative Example 1. Generally, carrier concentration and the Seebeck coefficient are inversely proportional.

[0315]

[0316] Figure 38 is a graph showing the power factor according to temperature of Comparative Example 1 and Example 3-2.

[0317] Referring to Fig. 38, the power factor is calculated using the values ​​of electrical conductivity and Seebeck coefficient, and it can be seen that the power factor is highest when the coating time of Example 3-2 is 210 seconds.

[0318] FIG. 39 is a graph showing the thermal conductivity of Comparative Example 1 and Example 3-2 as a function of temperature, and FIG. 40 is a graph showing the lattice conductivity of Comparative Example 1 and Example 3-2 as a function of temperature.

[0319] Referring to FIGS. 39 and 40, it can be seen that the thermal conductivity of Example 3-2 decreases as it increases and then increases again, and the lattice thermal conductivity also shows a similar trend.

[0320] The reason for the decrease in lattice thermal conductivity of Example 3-2 may be that phonon scattering is enhanced due to the coated tin dioxide (SnO2).

[0321]

[0322] FIG. 41 is a graph showing the thermoelectric performance index according to temperature for Comparative Example 1 and Example 3-2, and FIG. 42 is a graph showing the average thermoelectric performance index for Comparative Example 1 and Example 3-2.

[0323] Referring to FIGS. 41 and 42, it can be seen that when the coating time of Example 3-2 is 210 seconds, the highest electronic thermoelectric performance index (zT) and average thermoelectric performance index (zT) are observed.

[0324] Accordingly, referring to FIGS. 33 to 42, it can be confirmed that the tin dioxide (SnO2) coated Bi-Sb-Te-based thermoelectric material sintered body of Example 2-2 preferably has optimized electrical characteristics and thermoelectric performance at a coating time of 210 seconds.

[0325]

[0326] As described above, although the present invention has been explained by limited embodiments and drawings, the present invention is not limited to the above embodiments, and various modifications and variations are possible from this description by those skilled in the art to which the present invention belongs. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims set forth below as well as equivalents thereof.

Claims

1. A step of preparing a precursor solution by dissolving a metal inorganic precursor in a solvent; A step of forming a metal chalcogenide coating layer on the surface of the thermoelectric material alloy powder by stirring the thermoelectric material alloy powder in the precursor solution through a chemical solution deposition method; and A step of manufacturing a thermoelectric material powder by filtering and drying the thermoelectric material alloy powder having the metal chalcogenide coating layer formed thereon; A method for manufacturing thermoelectric material powder including 2. In Paragraph 1, A method for manufacturing a thermoelectric material powder characterized by forming a metal chalcogenide coating layer on part or all of the surface of the thermoelectric material alloy powder.

3. In Paragraph 1, A method for manufacturing a thermoelectric material powder characterized in that the metal chalcogenide coating layer is represented by the following chemical formula 1. [Chemical Formula 1] M a X b (M is Zn 2+ , Cd 2+ , Sn 4+ , Al 3+ , Ti 4+ , Fe 3+ , Zr 4+ , Cu 2+ , In 3+ and Ce 4+ It is any one metal ion selected from among, X is any one chalcogen element selected from O, S, and Se, 1 ≤ a ≤ 4 is an integer, and 1 ≤ b ≤ 5 is an integer) 4. In Paragraph 3, A method for manufacturing a thermoelectric material powder, characterized in that the metal chalcogenide coating layer is formed on the surface of the thermoelectric material alloy powder by mixing and reacting the metal ions and chalcogen elements contained in the precursor solution using the chemical solution deposition method.

5. In Paragraph 1, A method for manufacturing a thermoelectric material powder, characterized in that the thermoelectric material alloy powder comprises at least two elements selected from transition metals, rare earth elements, group 13 elements, group 14 elements, group 15 elements, and group 16 elements.

6. In Paragraph 1, In the step of forming the metal chalcogenide coating layer, When the above metal chalcogenide coating layer is zinc sulfide (ZnS), A method for manufacturing thermoelectric material powder, characterized in that the time for forming the coating layer is 150 seconds to 450 seconds.

7. In Paragraph 1, In the step of forming the metal chalcogenide coating layer, When the above metal chalcogenide coating layer is cadmium sulfide (CdS), A method for manufacturing thermoelectric material powder, characterized in that the time for forming the coating layer is 30 to 120 seconds.

8. In Paragraph 1, In the step of forming the metal chalcogenide coating layer, When the above metal chalcogenide coating layer is tin dioxide (SnO2), A method for manufacturing thermoelectric material powder, characterized in that the time for forming the coating layer is 90 to 270 seconds.

9. In Paragraph 1, In the step of manufacturing the above thermoelectric material powder, A method for manufacturing a thermoelectric material powder, characterized by further including the step of performing a reduction heat treatment on the thermoelectric material powder.

10. Thermoelectric material powder manufactured according to any one of paragraphs 1 to 9.

11. A step of preparing a precursor solution by dissolving a metal inorganic precursor in a solvent; A step of forming a metal chalcogenide coating layer on the surface of the thermoelectric material alloy powder by stirring the thermoelectric material alloy powder in the precursor solution through a chemical solution deposition method; A step of manufacturing a thermoelectric material powder by filtering and drying the thermoelectric material alloy powder having the metal chalcogenide coating layer formed thereon; and A step of manufacturing a sintered thermoelectric material body by sintering the above thermoelectric material powder; A method for manufacturing a thermoelectric sintered body characterized by including 12. In Paragraph 11, In the step of manufacturing the above thermoelectric material sintered body, A method for manufacturing a sintered thermoelectric material body characterized by forming the metal chalcogenide coating layer at the grain boundaries of the thermoelectric material alloy by proceeding with the sintering, and inhibiting the grain growth of the thermoelectric material alloy.

13. A thermoelectric material sintered body manufactured in accordance with either Clause 11 or Clause 12.

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