KR102021109B1 - Thermoelectric powder and materials with improved thermostability and manufacturing methods thereof - Google Patents

Abstract

The present invention provides a thermoelectric material having improved thermal stability and a method of manufacturing the same. In particular, the present invention proposes a thermoelectric powder capable of producing a thermoelectric material having improved thermostability. Such thermoelectric powders include thermoelectric material cores; And a reduced graphene oxide shell portion coated on the surface of the core portion.

Description

Thermoelectric powder and materials with improved thermostability and manufacturing methods

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric conversion technique, and more particularly, to a technique capable of improving thermal stability of a thermoelectric material constituting a thermoelectric device. In particular, the present invention relates to a thermoelectric powder suitable for producing a thermoelectric material having improved thermostability, a method for manufacturing the same, and a thermoelectric material manufactured using the thermoelectric powder.

Due to the temperature difference between the materials in the solid state, electrons (or holes) having thermal dependences generate concentration differences at both ends, which are represented by an electrical phenomenon called thermoelectric power, that is, a thermoelectric phenomenon. These thermoelectric phenomena can be classified into thermoelectric power generation, which produces electrical energy, and thermoelectric cooling / heating, which causes a temperature difference between both ends by supplying electricity.

Thermoelectric materials exhibit such thermoelectric phenomena, and many studies have been conducted due to environmentally friendly and sustainable advantages in power generation and cooling. In particular, it is of great interest as a technology that can improve fuel efficiency and reduce CO ₂ by producing electric power from industrial waste heat and automotive waste heat.

In general, a thermoelectric device has a p-type thermoelectric element made of a p-type thermoelectric material in which holes move and transfers thermal energy, and a pn thermoelectric made of n-type thermoelectric element made of an n-type thermoelectric material in which electrons move and transfer thermal energy. One pair of elements may be a basic unit, and may include a plurality of pairs of such pn thermoelectric elements, and may be configured as a module type including electrodes on and under the pn thermoelectric element, and an insulating substrate.

The energy conversion efficiency of a thermoelectric device depends on ZT (= S ² σ Tk ^-1 ), which is a dimensionless figure of merit value of the thermoelectric material. Where S is the Seebeck coefficient, sigma is the electrical conductivity, T is the absolute temperature, and k is the total thermal conductivity. Many thermoelectric materials have been proposed and developed so far. Thermoelectric materials are largely divided into metal and oxide, and the metal is based on chalcogenide, silicide, clathrate, half heusler, and skutterudite. And so on.

Although the temperature range indicating high electromotive force / efficiency is different for each material of the thermoelectric material, in general, the greater the temperature difference across the material, the higher the efficiency and electromotive force. However, the high temperature for the formation of a large temperature difference leads to a change in the thermoelectric material composition through physicochemical phenomena such as melting, diffusion, sublimation, etc., leading to degradation of the thermoelectric material. , Thermoelectric elements, modules that are a collection of these, and a reduction in the lifetime of thermoelectric devices including the same.

This problem is called a deterioration problem due to thermal stability. To increase the thermal stability of thermoelectric devices, metal thin film coating techniques utilizing various vapor depositions are known. However, the development of new technologies is required due to various problems that are formed for high cost, such as secondary diffusion of metal thin films, interfacial adhesion, and reduction of electromotive force due to contact resistance.

It is an object of the present invention to provide a thermoelectric material having improved thermal stability and a method of manufacturing the same.

In order to achieve the above object, the present invention proposes a thermoelectric powder capable of manufacturing a thermoelectric material having improved thermostability.

The thermoelectric powder according to the present invention is a composite of a thermoelectric material and reduced graphene oxide. In particular, the thermoelectric powder according to the present invention includes a thermoelectric material core portion; And a reduced graphene oxide shell portion coated on the surface of the core portion.

In an embodiment of the thermoelectric powder according to the present invention, the core part may include skutterudite particles. For example, the core part may include In-Co-Sb-based field skutterudite particles. The core portion may be one having an average particle size of 50 nm to 500 ㎛. The shell portion may further include graphene oxide. The thermoelectric powder may have a D / G peak ratio of 1.3 or more when measuring Raman.

The thermoelectric material according to the present invention includes a sintered body of such thermoelectric powder. The thermoelectric material manufacturing method according to the invention therefore comprises the step of sintering such thermoelectric powder.

The thermoelectric material including the sintered body includes thermoelectric material grains; And reduced graphene oxide located at the grain boundaries between the thermoelectric material grains.

By sintering the powder of the structure wrapped in the thermoelectric material core portion with the reduced graphene oxide shell portion in advance, such as the thermoelectric powder according to the present invention, it is possible to easily and reproducibly obtain the microstructure in which the reduced graphene oxide surrounds the thermoelectric material grain.

The thermoelectric material according to the present invention may further include amorphous carbon and / or graphene oxide at the grain boundaries. The amorphous carbon may be due to thermal decomposition of the reduced graphene oxide or the graphene oxide.

In addition, the grains may comprise scattererite. In an embodiment of the thermoelectric material of the present invention, the grains may further include a compound including In—Co—Sb-based field scattererite and including at least one of In, Sb, and Co at the grain boundaries. The grain is In-Co-Sb-based field scatterer, and may further include at least one of InSb, In ₂ O ₃ , CoSb-based material, graphene oxide, and amorphous carbon at the grain boundary.

Thermoelectric powder manufacturing method according to the present invention comprises the steps of preparing a thermoelectric material core; And forming a reduced graphene oxide shell portion on the surface of the core portion.

At this time, the step of forming the reduced graphene oxide shell portion, preparing a graphene oxide dispersion; And mixing the thermoelectric material core part and the reducing agent with the graphene oxide dispersion. In addition, after the mixing, at least one of ultrasonication, heating, stirring, and shaking may be further performed. In particular, by adjusting the concentration of the graphene oxide dispersion and the amount of the reducing agent it is possible to adjust the thickness of the reduced graphene oxide shell portion. In the graphene oxide dispersion, the thermoelectric material core part may be put first, and then a reducing agent may be added later.

In one embodiment, the preparing of the thermoelectric material core part may include preparing a powder form by synthesizing the field scatterer, and forming the reduced graphene oxide shell part may include graphene oxide. Preparing a dispersion; Mixing the thermoelectric material core portion and the reducing agent with the graphene oxide dispersion; Sonicating and / or stirring; And drying after washing.

The graphene oxide dispersion is composed of graphene oxide and deionized water.

The present invention also proposes a thermoelectric device such as a bulk thermoelectric material including such a thermoelectric material, a thermoelectric element dicing the same, and a thermoelectric module incorporating the thermoelectric material.

According to the present invention, a thermoelectric material having thermostability may be manufactured by coating reduced graphene oxide on a surface of the thermoelectric material. Reduced graphene oxide wrapped around the surface of the thermoelectric material prevents or inhibits diffusion of material from the thermoelectric material, thereby improving the heat resistance and thermal stability of the thermoelectric material. Thermoelectric devices such as thermoelectric elements and thermoelectric modules including such thermoelectric materials are excellent in thermal stability and relatively low in deterioration even in long-term use at high temperatures.

In the present invention, it is possible to coat graphene oxide on the surface of the thermoelectric material by using graphene oxide having excellent adhesion without using other organic materials, and reducing the graphene oxide to reduce the graphene oxide.

The reduced graphene oxide has higher electrical conductivity and improved output factor compared to graphene oxide, and also reduces lattice thermal conductivity, thereby improving performance index ZT and securing thermal stability.

In addition, it is possible to optimize the thermostability and thermoelectric properties by controlling the thickness of the reduced graphene oxide shell portion, it is easy to control the thermoelectric properties by controlling the electrical conductivity and carrier concentration by controlling the degree of reduction of graphene oxide.

As described above, the thermoelectric material according to the present invention has a remarkable effect of securing thermal stability while improving the output factor and ZT.

In addition, the manufacturing method of the thermoelectric powder and the thermoelectric material according to the present invention is economical because it is performed by a simple solution-based method without expensive deposition processes and the like.

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to.
1 is a view schematically showing the configuration of a thermoelectric powder according to an embodiment of the present invention.
2 is a flow chart schematically showing a method of manufacturing a thermoelectric powder according to an embodiment of the present invention.
3 is a diagram schematically illustrating a configuration of a thermoelectric material manufactured using a thermoelectric powder according to an embodiment of the present invention.
4 is a schematic diagram of an example powder preparation process.
5 is an SEM photograph of Comparative Example 1P, FIG. 6 is an SEM photograph of Comparative Example 2P, and FIG. 7 is an SEM photograph of Example 2P.
8 is a Raman analysis result measured after the sublimation test of the sintered body of Comparative Example 1S, Comparative Example 2S, and Example 1S.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you. Configurations shown in the embodiments and drawings described herein are only one of the most preferred embodiments of the present invention and do not represent all of the technical spirit of the present invention, various equivalents that may be substituted for them at the time of the present application It should be understood that there may be variations and examples.

1 is a view schematically showing the configuration of a thermoelectric powder according to an embodiment of the present invention.

Referring to FIG. 1, the thermoelectric powder 40 according to the present invention includes a core part 50 and a shell part 60.

The core part 50 may include scattererite particles. As the material constituting the core part 50, various sputterrodite materials may be employed. Scatterudite-based materials are inexpensive and have a low price of Bi ₂ Te ₃ It is a material that works well at high temperatures (mainly 400 ℃ or higher).

As mentioned above, the efficiency of the thermoelectric material is determined by the value of ZT (= S ² σ Tk ^-1 ). Therefore, good thermoelectric materials should have higher power factor (PF = S ² σ) values and lower thermal conductivity values. In other words, a good thermoelectric material must have a special transport performance, for which the phonon mean free path should be as short as possible, and the electron mean free path should be as long as possible. In this respect, the sputter ludite based on CoSb ₃ has received great attention in engineering. In addition, since CoSb ₃ has an excellent output factor value, scutterite is being evaluated as an effective method for reducing thermal conductivity.

For example, field scutterudite can be prepared by filling heterogeneous ions such as rare earth elements, alkali metals, and alkaline earth metals in the Sb-icosahedron cavities of CoSb ₃ scutterrudite, which is a lattice thermal conductivity ( It is very effective in reducing k _L ) and increasing ZT value. As described above, heterogeneous ions (hereinafter referred to as filler atoms) filled in the cavity have an independent vibration mode and thus have low mutual bonding force, and thus, have been reported to strongly inhibit lattice thermal conductivity by interacting with the general vibration mode in the lattice structure.

It has been reported that each filler atom becomes a phonon resonance scattering center close to a certain frequency, and the normal phonon mode with a frequency close to the local resonance frequency strongly interacts with the vibration mode of the filler atom. . Typically, phonon scattering should occur at a wide range of frequencies to further reduce lattice thermal conductivity. Hence, field squatterrudites, filled with a plurality of atoms with locally different vibration frequencies, have been reported to be very effective in lowering the lattice thermal conductivity even further. Therefore, many research reports have been drawn on field scutterudites which are filled by many kinds of filler atoms, and these filler atoms are filled with a single or a plurality of filler atoms. In the present invention, such field scattered particles can be used as the core portion 50.

Representatively, the core portion 50 may include CoSb _3- based scattererite particles. At this time, the CoSb _3- based scattererite may further contain other elements in addition to Co and Sb.

For example, it may further include other elements based on Co-Sb. For example, the core part 50 may further include In together with Co and Sb. In this case, In may be included in a form filled in the cavity in the unit grid. In this case, the core part 50 may be represented by a composition formula such as In _x Co ₄ Sb ₁₂ . Here, x may be, for example, 0 to 1. In this way, an In—Co—Sb-based material may be used for the core part 50.

In addition, the core part 50 may further include other metals in addition to the In. For example, materials constituting the core portion 50 include Ca, Sr, Ba, Ti, V, Cr, Mn, Cu, Zn, Pd, Ag, Cd, Sc, Y, La, Ce, Pr, Nd, Sm One or more elements selected from Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu may be further included. In this case, the material forming the core part 50 may be represented by a composition formula such as In _x M _y Co ₄ Sb ₁₂ . Here, M may mean the various metals added, such as Ca and Sr, and y may be 0 to 1.

As another example, the core part 50 may be configured in a form in which at least a part of the Co site or at least a part of the Sb site is replaced with another element. In one example, part of Co may be substituted with at least one element of Fe, Ni, Ru, Rh, Pd, Ir and Pt. As another example, a part of Sb may be substituted with at least one element of O, S, Se, Te, Sn, and In. In this case, the material forming the core part 50 may be represented by a composition formula such as In _x Co _{4 - a} A _a Sb _{12 - b} Q _b . Here, A means Co substitution elements such as Fe and Ni, and Q means Sb substitution elements such as O, S, Se, Te, Sn and In. Also, for example, a may be 0 to 1 and b may be 0 to 4.

In addition, other scattering materials, such as Fe-Sb-based, Co-Fe-Sb-based, Co-Ni-Sb-based, and Co-As-based materials, may be used as the scattererite material which can form the core part 50 Materials may be used and the present invention is not limited to sputterrudite materials of particular composition.

The core portion 50 may be made of particles of a thermoelectric material such as scattererite. The particles may be composed of powder obtained by pulverizing the thermoelectric material, aggregates thereof, or the like. For example, the core part 50 may be composed of a powder obtained by synthesizing the In-Co-Sb-based material.

In addition, the shape of the core part 50 is not necessarily limited to what is shown in FIG. For example, the core part 50 may be formed in a spherical shape, an egg shape, a needle shape, a small plate shape, or a shape (amorphous) that is not a predetermined shape. In addition, the core part 50 may be formed in various other shapes such as a cylindrical shape and a rod shape. In addition, in the case of the thermoelectric powder 40 according to the present invention, the various core parts 50 may be configured to be mixed.

In one example, the core portion 50 may be composed of one field scattererite particle. For example, the core part 50 may be composed of one In—Co—Sb-based particle. However, the present invention is not necessarily limited to these examples. The core portion 50 may be composed of a plurality of field scattererite particles. On the other hand, the plurality of field scattererite particles may be composed of only the same kind of material particles, or may comprise other types of material particles. In addition, the plurality of field scattererite particles may be present in the form of aggregated with each other. In other words, the core part 50 may be configured in such a manner that a plurality of field scattererite particles are agglomerated with at least a portion thereof in contact with each other. However, the present invention is not necessarily limited to these examples, and at least some of the plurality of field scattererite particles may be present in a form separated from other particles.

As such, the thermoelectric powder 40 according to the exemplary embodiment of the present invention may be configured in a form having a core part 50 of various forms or types. For example, in the case of the thermoelectric powder 40 according to the present invention, the number, types, and / or shapes of the particles constituting the core part 50 may be varied.

Meanwhile, the shell part 60 may exist in a form coated on the surface of the core part 50. That is, in the case of the thermoelectric powder 40 according to the present invention, the shell portion 60 may be positioned on the surface of the core portion 50 in a form surrounding the outside of the core portion 50.

This shell portion 60 includes reduced graphene oxide. 1, the reduced graphene oxide may be coated with a uniform thickness on the entire surface of the core 50 as shown in FIG. 1. In addition, the shell portion 60 may be present in a form in which only a portion of the core portion 50 is coated. In addition, the shell portion 60 may include some graphene oxide. That is, the degree of reduction of the graphene oxide of the shell portion 60 is controlled, most of which are present in the form of reduced graphene oxide, but some may remain as graphene oxide. Reduced graphene oxide and / or graphene oxide contained in the shell 60 induces phonon scattering, it is possible to increase the scattering effect through the thickness control.

As such, the thermoelectric powder 40 according to the exemplary embodiment of the present invention may be configured to have a shell part 60 having various forms.

In the thermoelectric powder 40 according to an embodiment of the present invention, the core portion 50 may be configured to have an average particle size of several tens of nanometers (nm) to several hundred micrometers (μm). For example, the average particle size of the core portion 50 may be 50 nm to 500 μm.

According to the embodiment as described above, since the shell portion 60 surrounding the core portion 50 prevents or inhibits volatilization of the core portion 50 material, a change in composition during manufacture of the thermoelectric material using the thermoelectric powder according to the present invention is improved. It is possible to improve the thermal stability of the manufactured thermoelectric material. In particular, when sintering the thermoelectric powder according to the present invention, the sintering is well performed due to the large surface area, and the reduced graphene oxide constituting the shell portion may be located at the grain boundaries between the thermoelectric material grains in the sintered body.

Graphite is a structure in which carbons are stacked in layers with planes arranged like honeycomb hexagonal nets. One layer of graphite is called graphene. Graphene has a very high physical and chemical stability with a thickness of 0.35 nm. As graphene emerges as a new material with excellent properties, a composite applied with graphene in thermoelectric materials has been studied to improve thermoelectric properties. However, the results of the studies to date have not been realized / realized the thermoelectric properties improvement effect, and various surfactants are used to improve the interfacial adhesion, which is also the cause of increasing the process cost. Graphene is used as an electrode of thermoelectric elements, as a thin film layer for preventing thermal conduction, or a method for making a carbon material composite for enhanced flexibility, but there is a known method of thermoelectric material heat, which is an essential item for practical use. It is not known how to apply graphene directly to thermoelectric materials to ensure stability.

Currently, graphene is manufactured by physical exfoliation, chemical vapor deposition (CVD), epitaxial synthesis, chemical exfoliation, graphite intercalation, and the like. It is used.

Chemical exfoliation method utilizes the oxidation-reduction properties of graphite. First, graphite is oxidized with a strong acid and an oxidizing agent to produce graphite oxide. Since graphite oxide is hydrophilic and water molecules are easily inserted between the surfaces, the contact with water causes the water molecules to penetrate between the surfaces due to the strong hydrophilicity of the graphite oxide. As a result, the interval between planes increases, so that it can be easily peeled off using a long time stirring or an ultrasonic grinder. Exfoliated graphite oxide is graphene oxide. In the present invention, such graphene oxide is used and reduced to form reduced graphene oxide.

According to the present invention, by reducing the graphene oxide coated on the surface of the thermoelectric material core portion, it is possible to prevent or suppress the volatilization of the main elements constituting the thermoelectric material, through which the thermoelectric powder, the heat of the sintered thermoelectric material Stability can be secured. Reduced graphene oxide, also called pseudo graphene, is known to have properties between graphene and graphene oxide. The reduced graphene oxide used in the present invention has a higher electrical conductivity than graphene oxide. Therefore, by reducing the graphene oxide coating it is possible to improve the thermoelectric performance while increasing the thermal stability and the electrical conductivity of the thermoelectric material.

In particular, the present invention uses a graphene oxide rather than graphene, graphene, when combined with the dispersion properties are lowered, leading to a decrease in mechanical strength. In addition, graphene has been a significant obstacle to practical applications and academic research because of its low surface charge, which tends to self-aggregate under van der Waals forces and exhibits very low solubility in any solvent. As is problematic for complexation with other materials, the application of graphene to thermoelectric materials will require modification of the graphene surface with surfactants or block copolymers.

In contrast, graphene oxide is well dispersed in water and does not aggregate. In the present invention, use of such a graphene oxide does not require the use of a surfactant or the like. In addition, by controlling the degree of reduction of the graphene oxide it is possible to control the electrical conductivity and carrier concentration it is easy to control the thermoelectric properties.

2 is a flowchart schematically showing a method of manufacturing a thermoelectric powder according to an embodiment of the present invention.

As shown in FIG. 2, the thermoelectric powder manufacturing method according to the present invention includes a material synthesis step (S110), a powder forming step (S120), and a reduced graphene oxide coating step (S130).

The material synthesizing step (S110) is, for example, a step of synthesizing a field scutterrudite material, and a conventional method of synthesizing scutterrudite material may be employed. For example, the material synthesizing step (S110) may include mixing a raw material for forming a scatterudite material and synthesizing a scatterrudite compound by heat treating the mixed raw materials. . Depending on the material type, n-type and p-type may be determined, but if necessary, a dopant may be further added to the raw material in order to obtain n-type and p-type semiconductor properties.

In this material synthesis step (S110), the mixing of raw materials may be performed by a method such as hand milling using ball mortar, ball milling, planetary ball mill, etc. The invention is not limited by this specific mixing mode.

In addition, the heat treatment step in the material synthesis step (S110) is a method using an ampoule, arc melting method, solid state reaction (SSR), metal flux method (metal flux) method, Bridgeman (Bridgeman) ) Method, optical floating zone method, vapor transport method (vapor transport) method, or mechanical alloying method.

The method using an ampoule is to heat-process the raw material by sealing it in a vacuum tube or a metal ampoule in a predetermined ratio. The arc melting method includes a step of preparing a sample by dissolving a raw material element by discharging an arc in an inert gas atmosphere by inserting a raw material element into a chamber at a predetermined ratio. SSR is a method comprising a step of mixing the raw material powder in a predetermined ratio and processing it hardly and then heat treatment, or heat-treating the mixed powder and then processing and sintering. The metal flux method is a method comprising a step of growing a crystal by placing a predetermined ratio of the raw material element and an element providing an atmosphere so that the raw material element can grow well into crystals at a high temperature in a crucible and heat treatment at a high temperature. The Bridgeman method puts a certain proportion of raw material into the crucible and heats it at a high temperature until the raw material dissolves at the end of the crucible, and then slowly moves the high temperature zone to locally dissolve the sample so that the entire sample passes through the high temperature zone. It is a way to grow crystals. The optical flow domain method creates a rod-shaped seed rod and feed rod in a proportion of the raw elements, and then dissolves the feed rod by melting the sample locally at a high temperature by focusing the light of the lamp. This is how you grow the crystal by slowly pulling the part upwards. The vapor transfer method is a method of growing a crystal at a low temperature as a raw material element is vaporized by putting a predetermined ratio of a raw material element under the quartz tube, heating the raw material part and keeping the upper portion of the quartz tube at a low temperature. The mechanical alloying method is a method in which an alloy-type thermoelectric material is formed by applying a raw powder and a steel ball to a container made of a cemented carbide and rotating the steel ball to mechanically impact the raw powder.

In particular, the heat treatment step in the present invention is preferably carried out by the SSR method of heating the mixture at a predetermined temperature by putting the mixture in a furnace (furnace). Even thermoelectric materials of the same composition, there may be a difference in the thermoelectric performance according to the reaction method between the raw materials, in the case of the sputter rudite, when each raw material is reacted by other methods, such as SSR method than the melting method, The thermoelectric performance of the manufactured material can be further improved.

For example, in the material synthesis step (S110), the heat treatment step, by pressing the raw material mixture powder to produce a green body (green body), it is charged into a chamber to maintain a vacuum to 10 ^-2 torr with a rotary pump and then heated Can be performed. At this time, it can heat in Ar atmosphere.

The powder forming step (S120) is a step of forming a powder of the sputter ludite-based composite formed in S110. As such, when the scauterite compound is formed in a powder form, it has a high surface area, and thus, coating of the reduced graphene oxide on the scaterite material in step S130 may be better. In addition, the sintered density may be further increased by forming the scatterudite composite in powder form. Preferably, in the step S120, the particle size may be 50 nm to 500 ㎛. More specifically, in the step S120, the particle size may be 26 ㎛ or less to prepare a 10 ㎛ grade material.

Such steps S110 and S120 correspond to preparing the thermoelectric material core part of the thermoelectric powder. If necessary, a commercial thermoelectric material powder may be purchased and used as the thermoelectric material core part.

The coating step (S130) is a step of coating the sputter Ludite material formed in powder form with reduced graphene oxide. For example, the coating step (S130), at least one of the ultrasonic treatment, heating, stirring and shaking by mixing the scattered powder and the reducing agent in a solution containing the graphene oxide dispersed It can be done in a manner that does the processing.

In the present invention, graphene oxide, which is cheaper than graphene and is easy to use / apply, is used. As mentioned above, graphene oxide may be used after concentration adjustment by purchasing a product dispersed in deionized water obtained through chemical exfoliation of graphite oxide.

Conventionally, the Hummers method is well known as a method of obtaining graphite oxide from graphite. In this method, in order to form graphite oxide, NaNO ₃ , H ₂ SO ₄ , and KMnO ₄ are used to break the graphite interlayer bond and attach a functional group such as -OH or -COOH. This process is described in more detail as follows.

To form graphite oxide from graphite, the graphite may be pretreated with a strong acid such as H ₂ SO ₄ and then oxidized with an oxidizing agent such as KMnO ₄ . When H ₂ SO ₄ with further addition of the NaNO ₃ HNO ₃ is generated and HNO ₃ as well as serve to act as an oxidizer to help a graphite oxide, and also helps the oxidation of the impurities contained in graphite. Deionized water is added to the mixture of NaNO ₃ , H ₂ SO ₄ , and KMnO ₄ in graphite to form an aqueous solution, and H ₂ O ₂ is added to form graphite oxide.

When the graphite oxide aqueous solution is sonicated and separated between the graphite oxide layers, a solution in which graphene oxide is dispersed is obtained. This solution is commercially available, and after diluting it to a desired concentration, the reduced graphene of the present invention is prepared by mixing and sonicating a thermoelectric material powder such as a sputter ludite powder prepared in steps S110 and S120 and a sonicating agent. The oxide coating step (S130) may be performed. After sonication, the subsequent treatment of obtaining the powder may be further performed in order to wash and dry the precipitate.

Graphene oxide is easily adsorbed on the surface of metal-based thermoelectric material such as thermoelectric material powder due to the oxide-based surface of the graphene. Therefore, there is no need to use a surfactant as compared to conventional methods of directly using graphene, and a solution containing graphene oxide dispersed in the thermoelectric powder of the present invention may be coated with graphene oxide and deionized water. It's easy, economical and reduces the number of other variables to control, making the process simple and highly reproducible.

The order in which the scattering powder and the reducing agent are added to the graphene oxide-dispersed solution is adjustable. For example, a method of simultaneously reducing the graphene oxide and coating by adding a scatterite powder and a reducing agent at the same time, and reducing the graphene oxide with a reducing agent first and then coating the surface with a scatterite powder. It may be possible.

Particularly, it is preferable to add the scattering powder first and the reducing agent later in terms of thickness uniformity control and / or uniformity, for the following reasons.

When graphene oxide is physically dispersed in deionized water, adsorption between graphene oxide and graphene oxide is not well induced. Therefore, when the thermoelectric material powder is put in a solution in which graphene oxide is dispersed, the graphene oxide may be preferentially coated with a single layer on the surface of the thermoelectric material powder. After that, if the reducing agent is added, the graphene oxide dispersed in the solution is reduced, and the graphene oxide coated with a single layer on the surface of the thermoelectric material powder is also reduced. Reduced graphene oxides are excellent in adhesion. Therefore, after graphene oxide coated with a single layer on the surface of the thermoelectric material powder is reduced, the reduced graphene oxide in the solution comes to the surface of the thermoelectric material powder and adheres well.

Since the graphene oxide is completely wrapped around the surface of the thermoelectric material powder, the thickness of the reduced graphene oxide layer adhered thereafter is also maintained. In addition, when the amount of the reduced graphene oxide in the solution is large, the amount of adhesion increases, thereby increasing the thickness of the reduced graphene oxide layer to be coated. Thus, increasing the concentration of graphene oxide dispersion and the amount of reducing agent increases the thickness of the reduced graphene oxide layer to be coated.

As such, the thermoelectric powder manufacturing method according to the present invention is economical because it is performed by a simple solution-based method without expensive deposition processes and the like. In addition, it is possible to optimize the thermal stability and thermoelectric properties by controlling the thickness of the reduced graphene oxide shell portion. By controlling the degree of reduction of graphene oxide, it is possible to control the electrical conductivity and the concentration of the carrier, so it is easy to control the thermoelectric properties.

The thermoelectric material according to the present invention may be manufactured using the thermoelectric powder according to the present invention as described above. In particular, the thermoelectric material according to the present invention can be obtained by sintering the thermoelectric powder according to the present invention. For example, the method of manufacturing a thermoelectric material according to the present invention may further include sintering the coated powder after the steps S110 to S130 and the step S130 in FIG. 2.

Therefore, the thermoelectric powder 40 including the core part 50 and the shell part 60 as shown in FIG. 1 may be referred to as a rough form, that is, before sintering, up to step S130. Then, when the thermoelectric powder according to the present invention is sintered, the thermoelectric material according to the present invention may be manufactured.

This sintering step is a step of sintering the scattered powder coated with graphene oxide reduced in step S130. Here, the sintering step may be performed by a hot press (HP) method or a spark plasma sintering (SPS) method.

The SPS or hot press is a pressure sintering method, and when sintered by this pressure sintering method, the thermoelectric material may easily obtain a high sintered density and a thermoelectric performance improvement effect. The SPS method is a step of applying pulsed electrical energy directly to a particle gap of a powder compact to effectively apply high energy of a discharge plasma generated by a spark discharge by thermal diffusion, an action of an electric field, or the like. As a pressurized pressure type using a DC pulse, firing starts and discharge occurs in the green compact, and Joule heating occurs between the particles, and the firing proceeds due to thermal diffusion and electric field diffusion. Since rapid temperature rising is possible, the growth of particles can be controlled, a compact sintered body can be obtained in a short time, and an sintered material can be easily sintered. Such a short time sintering method can be used to limit the growth of the particles, so that the thermal diffusivity can be controlled by allowing more grain boundaries to exist in the sintered body matrix.

The hot press uses a high pressure and a high temperature of 100 to 200 Mpa, and is a method of filling a capsule with a predetermined amount of powder or a molded product, degassing sealing, pressurizing and simultaneously heating and sintering.

In the case of the thermoelectric material according to the present invention, when sintered by the pressure sintering method, it is easy to obtain a high sintered density and an effect of improving thermoelectric performance. However, the present invention is not necessarily limited to this sintering method, and the sintering step may be performed by various other methods such as HPHT (High Pressure High Temperature) and HPT (High Pressure Torsion).

In addition, the sintering step may be performed in a vacuum state, while flowing a gas such as Ar, He, N ₂ or the like containing some hydrogen or no hydrogen, or in an inert gas atmosphere.

In addition, in order to further control the degree of reduction of graphene oxide, which may be included in the scatterer powder powder part, the vacuum heat treatment may be further performed after the sintering step. That is, in order to control the degree of reduction of graphene oxide, the use of a reducing agent in the thermoelectric powder manufacturing process and a vacuum heat treatment after sintering may be performed in parallel.

The p-type and n-type thermoelectric elements can be obtained if the bulk thermoelectric material obtained by pressure sintering is molded by a cutting process or the like and manufactured from the beginning into a sintered body of a desired size. Integrating such thermoelectric elements together with electrodes onto a substrate allows fabrication of modules. As the substrate, sapphire, silicon, pyrex, quartz substrate and the like can be used. The material of the electrode may be variously selected, such as aluminum, nickel, gold, titanium, etc., and the size thereof may also be variously selected. As the method for patterning the electrode, a conventionally known patterning method can be used without limitation, and for example, a lift-off semiconductor process, a deposition method, a photolithography method, or the like can be used.

The module-type thermoelectric device manufactured as described above may be, for example, a thermoelectric cooling system or a thermoelectric power generation system. The thermoelectric cooling system may be a general-purpose cooling device such as a refrigerantless refrigerator, an air conditioner, a CPU cooler, a laser diode cooling device, a CCD. Micro cooling system, such as a cooling device, a high output transistor cooling device, an IR sensor cooling device, an air conditioner, a waste heat generation system and the like, but is not limited thereto. The construction and manufacturing method of the thermoelectric cooling system is well known in the art, and thus, a detailed description thereof will be omitted.

In the production of thermoelectric materials through such thermoelectric powder sintering, the reduced graphene oxide prevents mass transfer, thereby ensuring thermal stability during manufacture. When using a thermoelectric element, a thermoelectric module, or a thermoelectric device using a sintered thermoelectric material, the reduced graphene oxide prevents oxidation, volatilization, and compositional change, thereby ensuring thermal stability in use.

3 is a diagram schematically illustrating the configuration of a thermoelectric material manufactured by sintering a thermoelectric powder according to an embodiment of the present invention, and illustrates a microstructure in a sintered body cross section.

Referring to FIG. 3, the thermoelectric material 140 manufactured by using the thermoelectric powder according to the present invention may include a plurality of scattererite grains (C) and reduced graphene oxide (D).

Here, the scattererite grains (C) are grains containing the scattererite material, and may form a matrix in the form of a plurality of adjacently gathered. And, the reduced graphene oxide (D) may be located at the grain boundary of the scattererite grains (C).

The scattererite grains C may be formed in various sizes or shapes. For example, the size of the scattererite grains (C) may be several tens of nm to several hundred μm. Moreover, the size of the scattererite grains (C) may be, for example, 1 μm to 500 μm. In addition, the scattererite grains (C) may be formed in various forms, such as spherical, needle-like, plate-like, depending on the synthetic conditions.

In particular, in the thermoelectric material 140 according to the present invention, reduced graphene oxide (D) may be interposed between such scattererite grains (C). That is, in the thermoelectric material 140 according to the present invention, a plurality of scattererite grains (C) constitute a matrix, and reduced graphene oxide (D) may exist at grain boundaries within such a matrix. In addition, the portion indicated by D may further include amorphous carbon due to thermal decomposition during sintering or graphene oxide remaining unreduced in addition to the reduced graphene oxide.

The graphene oxide (D) reduced in the thermoelectric material 140 according to an aspect of the present invention may be interposed in the form of a continuous or discontinuous film at the grain boundaries of the scattererite grains (C). That is, the reduced graphene oxide (D) may be formed along the crystal interface of the thermoelectric material matrix, as shown in FIG. 3. The grain boundary including the reduced graphene oxide (D) may be formed to have a uniform thickness as a whole, or may be formed to have a different thickness in part. In addition, the reduced graphene oxide (D) may be entirely filled at the grain boundary, or may be partially filled.

In addition, the thermoelectric material 140 according to the exemplary embodiment of the present invention may further include other elements or compounds in addition to the reduced graphene oxide (D) at the grain boundaries of the scattererite grains (C). For example, the grain boundary of the thermoelectric material according to the exemplary embodiment of the present invention may further include another compound formed during the sintering process derived from some components of the thermoelectric material constituting the core portion of the thermoelectric material powder.

For example, when grain (C) includes In—Co—Sb-based field scattererite, the grain boundary may further include a compound including at least one of In, Sb, and Co. For example, the grain boundary may further include at least one of InSb, In ₂ O ₃ , CoSb-based material including CoSb ₂ , graphene oxide, and amorphous carbon. These materials may be formed during the sintering process by being derived from some components of the thermoelectric material constituting the core portion of the thermoelectric material powder, or may be due to pyrolysis upon sintering. These may appear when the synthetic conditions are unstable and have a wide range. Or small volatilization of Sb or Sb oxide.

On the other hand, the reduced graphene oxide included in the grain boundary in the thermoelectric material according to an embodiment of the present invention, may exist in the form of a film or in the form of agglomerated particles.

As such, the thermoelectric material according to the present invention is one in which thermoelectric material grains and reduced graphene oxide located at grain boundaries between the thermoelectric material grains are consolidated.

The thermoelectric material having such a structure may be prepared by sintering the thermoelectric powder according to the present invention as described above, or may be prepared by mixing and sintering the thermoelectric material powder and graphene oxide or reduced graphene oxide. In the case of using the thermoelectric powder according to the present invention, since the reduced graphene oxide can be evenly coated over a large surface area of the thermoelectric material core part, the thermoelectric material powder and the graphene oxide or the reduced graphene oxide are mixed and sintered. Compared with the above, the effect of preventing material diffusion in the thermoelectric core part in the sintering process is excellent, and it is easy to distribute the reduced graphene oxide evenly on the grain boundary of the thermoelectric material after sintering.

The thermoelectric material according to the present invention may constitute a thermoelectric device. Such a thermoelectric device is ensured thermal stability can maintain the efficiency without deterioration even for long time use at high temperature.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the embodiment according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Preparation Example 1 ICS Synthesis and 10㎛ Class Grinding Classification

In, Co, Sb powder raw materials in powder form to In _{0 .} 21 g of a mixed powder is prepared through voltexing after weighing according to the composition of ₆ Co ₄ Sb ₁₂ . Thereafter, the mixed powder is pelleted by pressing at room temperature, and then put into a quartz tube and vacuum sealed. After the airtight tube was heated in a box furnace at 650 ° C. for 36 hours, the gray product obtained was hand milled, and a 500-mesh sieve was used for In-Co-Sb material of 26 μm or less. Hereinafter, ICS06 material) is obtained. The average particle size of the powder was 10 μm, and the surface area measured by BET analysis was about 0.5 m ² / g.

Preparation Example 2 concentration control of graphene oxide (GO) dispersion

Adjust the concentration of commercially available GO dispersions. In the preparation example, ultra high concentrated graphene oxide (UHCO) (dispersed in water, single layer 80% <, Conc. 6.2 g / L, flake size 0.5-5 mm) solution of Graphene supermarket was used. The concentration of the solution can be variously controlled by diluting with water and sonicating before use (using a sonicator for general cleaning) to increase the dispersion of graphene oxide.

Comparative example  : ICS Sintered Body Fabrication

The powder itself obtained in Preparation Example 1 is Comparative Example 1P.

Comparative Example 1P 5-10 g of powder was placed in a graphite mold to form a cylindrical sintered body of diameter 12.7-12.8 Φ through SPS (50 MPa, 650 ° C. for 10 minutes). Such a sintered compact is Comparative Example 1S.

Comparative Example: Synthesis and Sintering of Surface Coating Rate 100% GO @ ICS06 10㎛

6 g of the obtained product of Preparation Example 1 was added to 30 ml of the diluted solution of Preparation Example 2 (0.1 g L ⁻¹ ) and sonicated for 5 to 10 minutes. Centrifugation is then obtained via (5000 rpm, 10 min) and dried in an oven at 70 ° C. to obtain the final product in powder form. This powder is Comparative Example 2P, and a powder coated with graphene oxide (GO) on a thermoelectric material core.

Comparative Example 1P A sintered body was produced in the same manner as in Comparative Example 1P except that Comparative Example 2P powder was used instead of P powder. Such a sintered compact is Comparative Example 2S.

Example 1 Surface Coating Rate 100% RGO @ ICS06 Synthesis (Addition of Reduction Process) and Sintering

4 is a schematic diagram of Example 1 and Example 2 powder preparation process.

As shown in FIG. 4, (a) 30 ml of GO solution (0.1 g L ⁻¹ ) of Preparation Example 2 was added to a 70 ml vial, and (b) 6 g of the obtained Preparation Example 1 was added thereto. (c) When sonicated for 5-10 minutes, GO is coated on the surface of the powder as in Comparative Example 2P. The color of the solution is transparent if there is no GO left on the supernatant and the solution is brown if the remaining GO is dispersed. (d) Then, 0.1 g of a reducing agent (L-ascorbic acid) is added and stirred for about 18 hours to react. (e) As GO is reduced, the surface of the powder is coated with reduced graphene oxide (RGO), and it can be confirmed that all of the GO / RGO present in the solution is coated through the process of making the brown solution transparent.

After the reaction is completed, the remaining reducing agent is removed by washing the precipitate obtained by centrifugation (5000 rpm, 10 min) with deionized water. After the second centrifugation, it is dried in an oven at 70 ° C. to obtain the final product in powder form. This powder is Example 1P, and is a powder coated with reduced graphene oxide on a thermoelectric material core as proposed in the present invention.

Comparative Example 1 A sintered body was produced in the same manner as in Comparative Example 1S except that Example 1P powder was used instead of P powder. This sintered compact is Example 1S.

Example  2: surface coating rate 300% RGO @ ICS06 synthesis ( Graphene Oxide  Reduced graphene oxide coating thickness with increasing solution concentration) and sintering

A surface coating rate of 300% RGO @ ICS product was prepared by the same process as Example 1P, except that the concentration of the graphene oxide solution and the amount of the reducing agent were increased three times. This powder is Example 2P.

Comparative Example 1 A sintered body was produced in the same manner as in Comparative Example 1S except that Example 2P powder was used instead of P powder. This sintered compact is Example 2S.

Evaluation Example 1 SEM Measurement of Examples and Comparative Examples

5 is an SEM photograph of Comparative Example 1P, FIG. 6 is an SEM photograph of Comparative Example 2P, and FIG. 7 is an SEM photograph of Example 2P.

5 and 6, in the case of FIG. 6, graphene oxide is coated to observe a transparent thin film (GO coating film) on the SEM.

5 and 7, it is observed that the reduced graphene oxide is coated in FIG. 7 (RGO coating film). That is, in the case of the thermoelectric powder according to the present invention, that is, Example 2P sample, it can be seen that the coating layer is formed on the surface of the particles, unlike the Comparative Example 1P sample.

6 and 7, the thickness of the coating film is greater in FIG. 7 than in FIG. 6. In the case of the RGO coating film it can be confirmed that the thickness can be increased compared to the GO coating film.

Evaluation example 2 sublimation test of a sintered compact (650 degreeC)

The material sublimation rate can be obtained through mass changes before and after heat treatment of the comparative example 1S, the comparative example 2S, and the example 1S sintered body. The initial dimensions and initial mass of each sintered body were measured, then placed in a quartz tube and vacuum sealed. It is then placed in a box furnace and heated at 650 ° C. for 96 hours. After completion of the heat treatment, the dimensions and mass of the sintered body were measured and compared with the initial values, thereby calculating the dimensional and mass changes. Through this, the sublimation rate (gcm ^-2 h ^-1 ) of the sintered body was compared.

Table 1 summarizes the results.

Sublimation ratio in Table 1 is based on the sublimation rate when the reduced graphene oxide or graphene oxide-free ICS sintered body, that is, when the Comparative Example 1S sublimated at 650 ℃ conditions. As shown in the sublimation ratio, it can be seen that the sublimation ratio was reduced to 1/5 in Comparative Example 2S having graphene oxide or Example 1S of the present invention having reduced graphene oxide. That is, it can be seen that thermal stability can be obtained when the thermoelectric material is coated with graphene oxide or reduced graphene oxide.

Evaluation Example 3: Raman spectroscopy

8 is a Raman analysis result measured after the sublimation test of the sintered body of Comparative Example 1S, Comparative Example 2S, and Example 1S. Raman analysis was performed using a Renishaw spectrometer (wavelength 514.5 nm).

Referring to FIG. 8, D and G peaks do not appear in Comparative Example 1S, and Comparative Example 2S shows that D and G peaks are formed due to graphene oxide. G peak of 1590cm ^-1, near would resulting from E _2g mode vibration of sp ² bonded carbon, D peak in the vicinity of 1350cm ^-1 is shown when there is a defect in the sp ² carbon bond.

In the case of Example 1S, the intensity of the D peak is greater than the G peak compared to Comparative Example 2S. This is because the defects increase in the process of removing oxygen (O) of the graphene oxide through a reduction treatment. That is, in the case of the present invention, reduced graphene oxide was produced and maintained without degradation even after the sublimation test.

Table 2 is a comparative value of the Raman measurement result of the sintered compact of the comparative example 2S and Example 1S. Referring to Table 2, in Comparative Example 2S it can be seen that the level of 1.2 similar to the D / G peak ratio of the graphene oxide synthesized by the conventional graphite oxidation method. In Example 1S of the present invention, the D / G peak ratio was increased compared to Comparative Example 2S. In general, GO and RGO can be distinguished through the D / G peak ratio size, and Comparative Example 2S having a D / G peak ratio size of less than 1.3 is GO, and Example 1S having 1.3 or more can be determined to be RGO. As the degree of reduction of graphene oxide is controlled, the D / G peak ratio may change to 1.3 or more.

Evaluation Example 4: Thermoelectric Characteristic Evaluation

After processing the sintered compacts of Comparative Example 1S, Comparative Example 2S, Example 1S to a suitable size, the thermal conductivity is measured by laser flash analysis, the sample of the sample at a predetermined temperature interval through the ZEM-3 (Ulvac-Riko, Inc) equipment The electrical conductivity and the Seebeck coefficient were evaluated to measure the output factor (PF) and the figure of merit (ZT), and the results are summarized in Table 3.

Contribution in Table 3 is shown based on the value of Comparative Example 1S. Referring to Table 3, in Example 1S according to the present invention over the entire temperature range it can be seen that the Seebeck coefficient, the output factor is increased, and the thermal conductivity is reduced compared to Comparative Example 1S according to the RGO coating. That is, as in Example 1S, due to the reduced graphene oxide, the D / G peak ratio may be greater than 1.3 when measuring Raman, in the case of the present invention, thermal stability and ZT may be improved. . In addition, the ZT enhancement effect is clear as compared to Comparative Example 2S coated with graphene oxide, which may have a D / G peak ratio of less than 1.3 when measuring Raman. In conclusion, RGO coating improves thermal stability and power factor and ZT.

As described above, according to the present invention, a reduced graphene oxide may be coated on the surface of the thermoelectric material to prepare a thermoelectric material having thermal stability. Reduced graphene oxide wrapped around the surface of the thermoelectric material prevents or inhibits diffusion of material from the thermoelectric material, thereby improving the heat resistance and thermal stability of the thermoelectric material. Thermoelectric devices such as thermoelectric elements and thermoelectric modules including such thermoelectric materials are excellent in thermal stability and relatively low in deterioration even in long-term use at high temperatures.

In the present invention, it is possible to coat graphene oxide on the surface of the thermoelectric material by using graphene oxide having excellent adhesion without using other organic materials, and reducing the graphene oxide to reduce the graphene oxide.

The reduced graphene oxide has higher electrical conductivity and improved output factor compared to graphene oxide, and also reduces lattice thermal conductivity, thereby improving performance index ZT and securing thermal stability.

In addition, it is possible to optimize the thermostability and thermoelectric properties by controlling the thickness of the reduced graphene oxide shell portion, it is easy to control the thermoelectric properties by controlling the electrical conductivity and carrier concentration by controlling the degree of reduction of graphene oxide.

As described above, the thermoelectric material according to the present invention has a remarkable effect of securing thermal stability while improving the output factor and ZT.

In addition, the manufacturing method of the thermoelectric powder and the thermoelectric material according to the present invention is economical because it is performed by a simple solution-based method without expensive deposition processes and the like.

As mentioned above, although the preferred embodiment of the present invention has been illustrated and described, the present invention is not limited to the specific preferred embodiment described above, and the present invention belongs to the present invention without departing from the gist of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

40: thermoelectric powder
50 core part
60 shell part

Claims (21)

A thermoelectric material core portion composed of powder or aggregates thereof pulverizing the thermoelectric material; And
And a reduced graphene oxide shell portion coated on the surface of the core portion in a form surrounding the outside of the core portion, wherein the shell portion prevents or inhibits volatilization of the core portion material. Thermoelectric powder of shell structure. The thermoelectric powder of claim 1, wherein the core part comprises scattererite particles. The thermoelectric powder of claim 1, wherein the core part includes In—Co—Sb-based field scattererite particles. The thermoelectric powder of claim 1, wherein the core part has an average particle size of 50 nm to 500 μm. The thermoelectric powder of claim 1, wherein the shell part further comprises graphene oxide. The thermoelectric powder of claim 1, wherein the thermoelectric powder has a D / G peak ratio of 1.3 or more in the Raman measurement. A thermoelectric material comprising the sintered body of the thermoelectric powder according to any one of claims 1 to 6. A thermoelectric device comprising the thermoelectric material according to claim 7. A sintered body of the thermoelectric powder according to claim 1, wherein the sintered body
Thermoelectric material grains; And
A reduced graphene oxide located at grain boundaries between the thermoelectric material grains,
The reduced graphene oxide is thermoelectric material, characterized in that it is present in the form of particles interposed or aggregated in a continuous or discontinuous film form at the grain boundaries of the thermoelectric material grain. 10. The thermoelectric material of claim 9, further comprising amorphous carbon and / or graphene oxide at the grain boundaries. 10. The thermoelectric material of claim 9, wherein said grains comprise scattererite. The thermoelectric material of claim 9, wherein the grain further comprises a compound including In—Co—Sb-based field scattererite and at least one of In, Sb, and Co at the grain boundary. 10. The method of claim 9, wherein the grain is In-Co-Sb-based field scattererite, and the grain boundary further comprises at least one of InSb, In ₂ O ₃ , CoSb-based material, graphene oxide and amorphous carbon. Thermoelectric material. A thermoelectric device comprising the thermoelectric material according to claim 9. Preparing a thermoelectric material core portion composed of powder or aggregates thereof pulverizing the thermoelectric material; And
Forming a reduced graphene oxide shell portion on the surface of the core portion in a form surrounding the core portion to produce a thermoelectric powder of the core-shell structure, characterized in that for producing a thermoelectric powder. The method of claim 15, wherein forming the reduced graphene oxide shell portion,
Preparing a graphene oxide dispersion consisting of graphene oxide and deionized water only; And
The thermoelectric powder manufacturing method comprising the step of first putting the thermoelectric material core portion in the graphene oxide dispersion and then put a reducing agent. The method of claim 16, wherein after the mixing, at least one of ultrasonication, heating, stirring, and shaking is further performed. The method of claim 16, wherein the reduced graphene oxide shell portion thickness is adjusted by adjusting the concentration of the graphene oxide dispersion and the amount of the reducing agent. delete The method of claim 15, wherein preparing the thermoelectric material core portion comprises:
Preparing a powder form by synthesizing a field scatterudite material,
Forming the reduced graphene oxide shell portion,
Preparing a graphene oxide dispersion consisting of graphene oxide and deionized water only;
Adding the thermoelectric material core to the graphene oxide dispersion first and then adding a reducing agent to the graphene oxide dispersion;
Sonicating and / or stirring; And
Thermoelectric powder manufacturing method comprising the step of drying after washing. delete

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