KR20200068422A - Preparing method of composite thermoelectric material and the composite thermoelectric material obtained thereby - Google Patents

Abstract

The present disclosure relates to a method of manufacturing a composite thermoelectric material having a composition of Cu_xBi_y Sb_(2-y)Te_3 (0 <x <= 0.1, 0 <y <2) using a melt spinning process. Therefore, the composite thermoelectric material according to the present invention can provide an excellent performance index and can be used in applications requiring high thermoelectric performance.

Description

Manufacturing method of composite thermoelectric material and composite thermoelectric material obtained thereby {PREPARING METHOD OF COMPOSITE THERMOELECTRIC MATERIAL AND THE COMPOSITE THERMOELECTRIC MATERIAL OBTAINED THEREBY}

The present invention relates to a method for manufacturing a composite thermoelectric material having a high performance index, in particular, a Bi-Te based composite thermoelectric material comprising a dopant metal and a composite thermoelectric material obtained thereby.

Thermoelectric (TE) technology is an energy collection technology, and has been developed as a renewable and sustainable energy source in response to global demand for reducing greenhouse gases causing global warming. The thermoelectric phenomenon was first discovered by the German physicist TJSeebeck, and refers to a phenomenon in which current or voltage occurs when different temperatures are applied to the contact points between conductors in one circuit composed of two different conductors. , Heat flow from hot to cold generates current. This phenomenon is called the Seebeck Effect. France's Jean-Charles Athanas Peltier discovered another important thermoelectric phenomenon, which causes a direct current to flow through a circuit made up of different conductors, while heating one side of the junction between the different conductors depending on the direction of the current, The other side is a phenomenon of cooling. This is called the Peltier Effect. Thermoelectric elements, which are called by various names such as thermoelectric modules, Peltier elements, thermoelectric coolers (TEC), and thermoelectric modules (TEM), are small heat pumps (absorb heat from low temperature heat sources) Device to give heat to a high temperature heat source. When a DC voltage is applied to both ends of the thermoelectric element, heat moves from the heat absorbing portion to the heat generating portion, and thus, as time passes, the temperature of the heat absorbing portion decreases and the temperature of the heat generating portion increases. At this time, if the polarity of the applied voltage is changed, the heat absorbing part and the heat generating part are interchanged, and the heat flow is reversed.

This thermoelectric technology is expected to play an important role in generating power by utilizing waste heat. Since the efficiency of a thermoelectric device is greatly influenced by the performance of a thermoelectric material, a high performance thermoelectric material is very important in cooling by converting waste heat into electricity to generate electric power or using electricity to generate a temperature difference.

The performance of thermoelectric materials is determined by the ZT value, which is a dimensionless figure of merit. However, there are many difficulties in manufacturing a thermoelectric material having a high ZT value.

The performance index is defined as the power factor (PF) multiplied by the square of the electrical conductivity (σ) and the Seebeck coefficient (S) multiplied by the temperature (T) and divided by the thermal conductivity (κ). In addition, the thermal conductivity (κ) is mainly determined by the sum of the lattice thermal conductivity (κ _lat ) and electrical thermal conductivity (κ _el ).

ZT = σS ² T / κ

Here, since the electrical conductivity and Seebeck coefficient have an inverse relationship with carrier concentration, it is difficult to increase the performance coefficient.

For this reason, the coefficient of performance was considered to have a limit on the value of the performance index for a long period of time. Recently, thermoelectric materials having improved performance coefficients have been developed by lowering thermal conductivity, but various materials having a high performance index are still needed.

Korean Registered Patent Publication No. 10-1719928 (2017.03.20)

The embodiments described below provide a technique for manufacturing a composite thermoelectric material having a high coefficient of performance.

As one aspect for achieving the above object, the present invention is a method of manufacturing a composite thermoelectric material having a composition of M _x Bi _y Sb _2-y Te ₃ (0 <x ≤ 0.1, 0 <y <2),

M is any one selected from the group consisting of copper, lead, silver, and combinations thereof,

The manufacturing method

Preparing a composite raw material by mixing Bi, Sb, Te, and M raw material;

Manufacturing a composite thermoelectric material in the form of an ingot or pellet using the composite raw material;

Forming a ribbon by melt-spinning the ingot or pellet-shaped composite thermoelectric material;

Pulverizing the ribbon; And

Sintering the crushed ribbon

It provides a method for producing a composite thermoelectric material, including.

In order to provide thermoelectric materials with high performance index values, many Bi-Te-based thermoelectric materials have been studied, among which thermoelectric materials having a composition of Bi _y Sb _2-y Te ₃ (0 <y <2) (hereinafter “BST”) Also referred to as), preferably Bi _0.5 Sb _1.5 Te _{3 has} a composition of thermoelectric material has been studied a lot. These BST thermoelectric materials have relatively high thermoelectric performance up to room temperature, but there are many limitations in their use when a temperature higher than room temperature is required, for example, at a temperature higher than this, for example, at a temperature of about 100° C., the thermoelectric performance is significantly lower.

In particular, thermoelectric performance is directly affected not only by increasing the performance index value, but also by shifting the temperature representing the maximum performance index value to a high temperature range or maintaining the performance index value for a wider temperature range. . The maximum energy conversion efficiency (η _max ) of a TE generator is estimated by the following equation:

In the above equation, T _h , T _c , T _avg , and ΔT are the hot temperature, cold temperature, average temperature ((T _h +T _c )/2), and hot temperature and cold temperature, respectively. It is the temperature difference (T _h -T _c ). That is, the maximum TE efficiency depends on the average ZT value of the thermoelectric material. Therefore, there is a need to solve the problem of a significant decrease in ZT value at high temperatures in Bi-Te-based thermoelectric materials. In particular, in order to use such a Bi-Te-based thermoelectric material in a technique for producing energy from waste heat, it is very important to move a temperature exhibiting a high performance index from room temperature to a higher temperature range.

On the other hand, many attempts have been made to add various dopant materials to the thermoelectric material in order to increase the performance of the thermoelectric material, especially to move the temperature region having high thermoelectric performance, and many attempts have been made to add various dopant materials to the BST matrix. ought. However, there are still difficulties in providing a BST composite thermoelectric material exhibiting excellent thermoelectric performance even at a temperature higher than room temperature, that is, in the temperature range of about 298K to about 550K, which is the medium temperature region. Accordingly, the present inventors confirmed that when a specific metal, specifically, Cu, Pb, or Ag is added to the BST matrix as a dopant, and a composite thermoelectric material is manufactured through a melt spinning process, it exhibits high thermoelectric performance in a room temperature to medium temperature region. This disclosure is based on this.

The step of preparing the composite raw material may be prepared by calculating the molar ratio of each BST and dopant metal M finally produced. Each of the metals, Bi, Sb, Te, and M previously calculated according to the molar ratio may be mixed to prepare a composite raw material. The composite thermoelectric material finally produced may have a composition of M _x Bi _y Sb _2-y Te ₃ (0 <x ≤ 0.1, 0 <y <2). Specifically, the composition of the resulting composite thermoelectric material may be 0.005 ≤ x ≤ 0.05, 0.01 ≤ x ≤ 0.04, or 0.015 ≤ x ≤ 0.025. In addition, the composition of the resulting composite thermoelectric material may be 0 <y <1, 0.4 ≤ y ≤ 0.6, or y = 0.5. In one embodiment, the composition of the BST of the composite thermoelectric material may be Bi _0.5 Sb _1.5 Te ₃ . It is calculated to include each metal according to the composition of the resulting composite thermoelectric material, so that each calculated amount of metals can be mixed.

The step of manufacturing a composite thermoelectric material in the form of an ingot or pellet using the composite raw material includes heating and rapidly cooling the composite raw material produced in the previous step. Specifically, the composite raw material can be sealed in a vacuum quartz ampoule, heated at 1200K to 1300K for 4-8 hours, and quenched using cold water.

The melting spinning of the step of forming the ribbon may include melting a composite thermoelectric material in the form of an ingot or pellet and ejecting the molten thermoelectric material through a nozzle to a metal wheel, for example, a Cu wheel. In the step of ejecting the molten thermoelectric material through the nozzle in the melt spinning method, the chamber pressure is performed in a range of 0.01 MPa to 0.1 MPa, specifically 0.02 MPa to 0.05 MPa, more specifically about 0.03 MPa, and the chamber interior is inactive It may be carried out under a gas, specifically an argon gas atmosphere.

The rotational speed of the wheel may be performed at 100 to 4000 rpm, specifically 200 to 1000 rpm, and more specifically 400 to 600 rpm. In one embodiment, it was confirmed that a composite thermoelectric material exhibiting excellent thermoelectric performance can be manufactured using 500 rpm. By adjusting the rotational speed, it is possible to manufacture a composite thermoelectric material exhibiting different thermoelectric performance, and in one embodiment, when the rotational speed is 500 rpm, the rotational speed has better thermoelectric performance than 1000 rpm, 2000 rpm, and 4000 rpm. It was confirmed that the thermoelectric material was produced.

The step of pulverizing the ribbon includes ball milling, attrition milling, high energy milling, jet milling, a method of crushing in a mortar, etc. It can be used, but is not necessarily limited to these, and any method that can be used in the art as a method of manufacturing a powder by crushing a raw material by dry is possible.

The step of sintering the crushed ribbon may include packing the crushed ribbon in a graphite mold before sintering. The sintering process may use a spark plasma sintering method, hot press sintering, and the like, but is not limited thereto, and other methods known to be used as a sintering method in the art are also possible. . In addition, the sintering may be performed for 1 minute to 10 minutes at a pressure of 500K to 1000K, specifically 700K to 800K, 1Pa to 100Pa, specifically 10 to 90Pa, more specifically 50 to 70Pa and vacuum, but necessarily under these conditions It is not limited to and may be appropriately changed within a range capable of improving the performance coefficient of the composite thermoelectric material. The sintered composite thermoelectric material may be formed into pellets, specifically, cylindrical pellets. The pellets prepared in one embodiment have a diameter of 10 to 15 mm and a height of 5 to 15 mm.

The M-BST composite thermoelectric material manufactured by the manufacturing method according to the present disclosure may have an average grain size of 1-5 μm, 2-3 μm, or 2.5-2.99 μm.

The M-BST composite thermoelectric material manufactured by the manufacturing method according to the present disclosure may be one in which the dopant metal M is incorporated into the BST crystal structure without forming a separate secondary phase due to the addition of the dopant metal. Specifically, pristine (pristine) BST has the following crystal structure.

When the dopant metal M is doped into the BST structure, the metal M is substituted into the Bi position or the Sb position. The atomic radii of Bi and Sb are 160 pm and 145 pm, respectively, and the atomic radii of the dopant metals Pb, Cu, Ag are 180 pm, 135 pm, and 160 pm, respectively, and have similar sizes. Thus, when doped with Cu, Ag, or Pb, these elements can be substituted with positions of Bi and Sb having similar sizes. However, since the secondary phase may be formed when the content of the dopant metal exceeds 0.1 mol per 1 mol of BST, in the present disclosure, dopant metal of 0.1 mol or less is doped. In one embodiment, a thermoelectric material was prepared using Cu as a dopant metal, and as a result of observing the SEM image of the prepared composite thermoelectric material, it was confirmed that a secondary phase was not formed in the thermoelectric material having all Cu content. That is, it was confirmed that all of the doped Cu is incorporated into the BST crystal structure.

The M-BST composite thermoelectric material manufactured by the manufacturing method according to the present disclosure may be a p-type thermoelectric material. In a typical thermoelectric element, a pair of n-type and p-type thermoelectric materials is a basic unit. When a direct current (DC) voltage is applied to both ends, heat is moved according to the flow of electrons in the n-type and in the flow of holes in the p-type, so that the temperature of the heat absorbing portion is lowered. This is because electrons in the metal have a potential energy difference, and in order for electrons to move from a metal having a low potential energy to a metal having a high potential, energy must be obtained from the outside, thereby dissipating thermal energy from the contact point and vice versa. That is the principle. This endotherm (cooling) is proportional to the flow of current and the number of thermoelectric couples (1 pair of n-type and p-type). The present inventors confirmed that the composite thermoelectric material according to the present disclosure shows excellent thermoelectric performance as a p-type thermoelectric material. Particularly, it was confirmed that a specific dopant metal Cu, Ag, or Pb was added to the p-type thermoelectric material BST to improve the electrical conductivity of the thermoelectric material. In one embodiment, it was confirmed that the thermoelectric material containing Cu has better electrical conductivity than the thermoelectric material not containing Cu. This improvement in electrical conductivity is due to the increase in carrier concentration with the addition of Cu. The carrier mobility is slightly decreased due to the addition of Cu, and the opposite results are obtained, but when all of these effects are combined, the Cu-BST electrical conductivity is very high compared to the BST due to the addition of Cu.

The M-BST composite thermoelectric materials produced by the manufacturing method according to the present disclosure have similar results as long as they use specific dopant metals Cu, Ag, and Pb. As described above, the dopant metal is substituted at the Bi or Sb position and increases the electrical conductivity due to the difference in its oxidation number. Specifically, Cu, Ag, and Pb are all elements stabilized with divalent cations, and Bi and Sb are elements stabilized with trivalent cations. Therefore, when the Bi or Sb position is replaced with Cu, Ag, or Pb, holes are generated, and the carrier concentration is increased in the BST material, which is a p-type material. Accordingly, the electrical conductivity of the BST thermoelectric material doped with Cu, Ag, or Pb has a higher value than Pristine BST, which leads to an improvement in the power factor and an increase in the high temperature performance index.

The M-BST composite thermoelectric material produced by the manufacturing method according to the present disclosure has superior thermoelectric performance than BST in the medium temperature region, specifically 298K to 550K, more specifically 300K to 500K, and up to about 1.2 to 1.4, specifically It has a performance index value of about 1.34. In addition, the M-BST composite thermoelectric material manufactured by the manufacturing method according to the present disclosure may have a performance index (ZT) value of 0.8 or higher at 298K to 523K, specifically, a performance index value of 1.0 or higher at 298K to 473K. Can be.

BST has a significant decrease in thermoelectric performance at temperatures above room temperature, but has excellent thermoelectric performance even at temperatures above room temperature due to the addition of dopant metal M. In one embodiment, when Cu is added as a dopant metal, and when 0.02 mol of Cu is added per 1 mol of BST, it is confirmed that it has a performance index value of about 1.34 at about 400K. In addition, it was confirmed that the performance index value steadily increased from room temperature to about 400K and decreased from the above temperature, but continued to have a performance index value of 1 or more during the temperature range from about 300K to 473K. That is, it was confirmed that the thermoelectric material according to the present disclosure can maintain a very high performance index value at a temperature suitable for using waste heat or the like. In addition, in one embodiment, the average of the performance index values according to the temperature range from room temperature to 523K was analyzed, and all of the BST composite thermoelectric materials containing Cu showed superior average performance index values compared to the BST thermoelectric materials not containing Cu. Showed.

In particular, the effect of adding this particular dopant metal identified in the present disclosure is not an effect confirmed by simple doping, but an effect in combination with a melt-spinning method. In one embodiment, Cu is used as a dopant metal, and the Cu-BST produced by using the melt spinning process and the Cu-BST manufactured without the melt spinning process, that is, the thermoelectric of Cu-BST manufactured according to the conventional method of manufacturing a thermoelectric material The performance was compared, and it was confirmed that the thermoelectric performance of the thermoelectric material subjected to the melt spinning process was much superior. That is, the present disclosure relates to the synergistic effect of the thermoelectric performance that can be obtained when a specific manufacturing process is used together with the addition of a specific dopant, namely Cu, Pb, or Ag, in the production of a composite thermoelectric material.

In one embodiment, the composite thermoelectric material produced by the manufacturing method according to the present disclosure has a composition of Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ , and is manufactured through a melt spinning process, wherein the rotational speed of the wheel is 500 rpm. This composite thermoelectric material has a performance index value of about 1.34 at about 400K, an average performance index value of about 1.17 at 298K to 523K at a medium temperature region, and maintains a performance index value of 1.0 or higher at a temperature of 473K at 298K. Was confirmed.

In another aspect, the present invention is a composite thermoelectric produced by the method of manufacturing a composite thermoelectric material having the composition of M _x Bi _y Sb _2-y Te ₃ (0 <x ≤ 0.1, 0 <y <2) described above Provide material. The composite thermoelectric material produced is the same as described above.

The composite thermoelectric material according to the present disclosure can provide an excellent performance index. Therefore, it can be used in applications requiring high thermoelectric performance. The composite thermoelectric material of the present disclosure is a thermoelectric power generation that uses a voltage generated by a Seebeck effect when a temperature difference between both ends of a material is applied, and one side generates heat when a DC current is applied between both ends of the material. And it can be applied to the thermoelectric cooling (Thermoelectric Cooling) using the Peltier (Peltier) effect of the other side endothermic. In particular, the composite thermoelectric material according to the present disclosure has such excellent thermoelectric performance in a medium temperature region, and thus can be applied to a field requiring such a thermoelectric effect in a medium temperature region higher than room temperature.

1 shows XRD results of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500 rpm) prepared according to Preparation Example 3. For comparison, the XRD pattern of pristine Bi _0.5 Sb _1.5 Te ₃ is shown together.
2 shows XRD results of MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm) and CM-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ prepared according to Preparation Example 3.
FIG. 3 is an SEM image observed at a scale of 1 μm of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500 rpm) without grinding and sintering in the form of a ribbon manufactured through a melt spinning (MS) process according to Preparation Example 2. to be. a is an image of Pristine Bi _0.5 Sb _1.5 Te ₃ , b is an image of Cu _0.01 Bi _0.5 Sb _1.5 Te ₃ , c is an image of Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ , d is an image of Cu _0.04 Bi _0.5 Sb _1.5 Te ₃ to be.
Figure 4 is a cross-sectional SEM image of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) without a grinding and sintering process in the form of a ribbon manufactured through a melt spinning (MS) process according to Preparation Example 2, each scale 10㎛ , 300nm, images observed at 300nm. ac is an image of Pristine Bi _0.5 Sb _1.5 Te ₃ , df is an image of Cu _0.01 Bi _0.5 Sb _1.5 Te ₃ , gi is an image of Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ , jl is an image of Cu _0.04 Bi _0.5 Sb _1.5 Te ₃ to be. Also, the left image shows the overall cross-section, the middle image shows the contact surface to the copper wheel, and the right image shows the free surface.
5 is a SEM image observed at a scale of 10 μm of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500 rpm) prepared according to Preparation Example 3. f is an image of Pristine Bi _0.5 Sb _1.5 Te ₃ , g is an image of Cu _0.01 Bi _0.5 Sb _1.5 Te ₃ , h is an image of Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ , i is an image of Cu _0.04 Bi _0.5 Sb _1.5 Te ₃ to be.
6 is an SEM image observed at a scale of 50 μm of CM-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ prepared according to Preparation Example 3.
Figure 7 shows the electrical conductivity according to the temperature of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3.
Figure 8 shows the carrier concentration according to the temperature of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3.
Figure 9 shows the carrier mobility according to the temperature of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3.
Figure 10 shows the mobility (left) and carrier concentration (right) according to the Cu content of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3.
Figure 11 shows the Seebeck coefficient according to the temperature of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3.
Figure 12 shows the power factor (PF) according to the temperature of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3.
Figure 13 shows the thermal conductivity according to the temperature of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3.
Figure 14 shows the performance index according to the temperature of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3.
Figure 15 shows the average value of the performance index according to the composition of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3. Specifically, it shows the average value in the temperature range from 298K to 523K.
Figure 16 is obtained through the process of Preparation Example 2 MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3, CM-Cu obtained according to Preparation Example 3 without going through the process of Preparation Example 2 _0.02 Bi _0.5 Sb _1.5 Te _{3 It} shows the electrical conductivity according to the temperature of the thermoelectric material.
FIG. 17 shows the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm) thermoelectric material obtained according to Preparation Example 3 through the process of Preparation Example 2, and the CM-Cu obtained according to Preparation Example 3 without going through the Preparation Example 2 procedure. _0.02 Bi _0.5 Sb _1.5 Te _{3 The} Seebeck coefficient according to the temperature of the thermoelectric material.
FIG. 18 shows the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm) thermoelectric material obtained according to Preparation Example 3 through the process of Preparation Example 2, and the CM-Cu obtained according to Preparation Example 3 without going through the Preparation Example 2 procedure. _0.02 Bi _0.5 Sb _1.5 Te _{3 It} shows the power factor according to the temperature of the thermoelectric material.
FIG. 19 shows the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm) thermoelectric material obtained according to Preparation Example 3 through the process of Preparation Example 2, and the CM-Cu obtained according to Preparation Example 3 without going through the Preparation Example 2 procedure. _0.02 Bi _0.5 Sb _1.5 Te _{3 It} shows the thermal conductivity according to the temperature of the thermoelectric material.
20 is obtained through the process of Preparation Example 2 MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500rpm) thermoelectric material obtained according to Preparation Example 3, and the CM-Cu obtained according to Preparation Example 3 without going through the process of Preparation Example 2 _0.02 Bi _0.5 Sb _1.5 Te _{3 It} shows the performance index value according to the temperature of thermoelectric material.
Figure 21 shows the electrical conductivity according to the temperature of the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ thermoelectric materials obtained according to Preparation Example 3, the rotational speed during the process of Preparation Example 2 400 rpm, 1000 rpm, 2000 rpm, respectively And thermoelectric materials obtained by setting to 4000 rpm.
Figure 22 shows the Seebeck coefficient according to the temperature of the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ thermoelectric material obtained according to Preparation Example 3, the rotational speed during the process of Preparation Example 2 400 rpm, 1000 rpm, 2000 rpm, respectively And thermoelectric materials obtained by setting to 4000 rpm.
Figure 23 shows the power factor according to the temperature of the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ thermoelectric materials obtained according to Preparation Example 3, the rotational speed during the process of Preparation Example 2 400 rpm, 1000 rpm, 2000 rpm, respectively And thermoelectric materials obtained by setting to 4000 rpm.
Figure 24 shows the thermal conductivity according to the temperature of the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ thermoelectric materials obtained according to Preparation Example 3, the rotational speed during the process of Preparation Example 2 400 rpm, 1000 rpm, 2000 rpm, respectively And thermoelectric materials obtained by setting to 4000 rpm.
Figure 25 shows the performance index value according to the temperature of the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ thermoelectric material obtained according to Preparation Example 3, the rotational speed during the process of Preparation Example 2 400 rpm, 1000 rpm, 2000 rpm, respectively , And the results of thermoelectric materials obtained by setting to 4000 rpm.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, various changes may be made to the embodiments, and the scope of the patent application right is not limited or limited by these embodiments. It should be understood that all modifications, equivalents, or substitutes for the embodiments are included in the scope of rights.

The terms used in the examples are used for illustrative purposes only and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the embodiment belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

In addition, in the description with reference to the accompanying drawings, the same reference numerals are assigned to the same components regardless of reference numerals, and redundant descriptions thereof will be omitted. In describing the embodiments, when it is determined that detailed descriptions of related known technologies may unnecessarily obscure the subject matter of the embodiments, detailed descriptions thereof will be omitted.

Throughout this specification, "%" used to indicate the concentration of a specific substance, unless otherwise specified, solids/solids (weight/weight)%, solids/liquids (weight/volume)%, and The liquid/liquid is (volume/volume) %.

Manufacturing example: BST thermoelectric material (Cu with dopant metal Cu added) _x Preparation of BST)

Preparation Example 1: Ingot synthesis

A thermoelectric material was prepared using Cu as a dopant metal. High purity raw metals Bi (99.999%, 5N Plus), Sb (99.999%, 5N Plus), so that a thermoelectric semiconductor having a composition formula of Cu _x Bi _0.5 Sb _1.5 Te ₃ (x= 0, 0.01, 0.02 and 0.04) is obtained, A mixture was prepared by mixing Te (99.999%, 5N Plus) granules and Cu wire (99.9%, Sigma Aldrich) according to the composition ratio. At this time, excessive Te was added due to evaporation of Te. Each metal was mixed using the amounts listed in Table 1 below. As a control, Cu-free Bi _0.5 Sb _1.5 Te ₃ material was prepared together.

Chemical composition Weight of material used (g) Bi Sb Te Cu Bi _0.5 Sb _1.5 Te ₃ 3.12 5.45 11.42 0 Cu _0.01 Bi _0.5 Sb _1.5 Te ₃ 3.12 5.45 11.41 0.02 Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ 3.11 5.44 11.40 0.04 Cu _0.04 Bi _0.5 Sb _1.5 Te ₃ 3.11 5.43 11.38 0.08

The mixture was sealed in a vacuum quartz ampule and then heated at 1273K for 6 hours. Thereafter, quenching was performed with cold water to prepare an ingot type thermoelectric material.

Preparation Example 2: Melt-Spinning (MS) process

20 g of the ingot type thermoelectric semiconductor obtained in Preparation Example 1 was melt-spinned (using a melt-spinning device of Yeintech). Specifically, the ingot type thermoelectric material was melted through the induction coil in the chamber of the melt spinning and then ejected through a nozzle to a Cu wheel having a diameter of about 50 cm. The inside of the chamber was an argon atmosphere, the chamber pressure was 0.03 MPa, and the rotation speed of the Cu wheel was 500 rpm (~6.6 m/s). It is possible to eject the thermoelectric material melted through the high pressure argon gas to the Cu wheel, and since the Cu wheel rotates at a high speed, the ejected thermoelectric material is obtained in the form of a ribbon. During the melt spinning process, a thin ribbon is formed with an amorphous structure on the contact surface and a dendrite nanostructure (300-500 nm) on the free surface. By this process, a ribbon-shaped thermoelectric material intermediate was obtained.

On the other hand, in order to evaluate the performance of the thermoelectric material according to the rotational speed, the above processes were repeated with rotational speeds of 1000 rpm, 2000 rpm, and 4000 rpm, respectively.

Production Example 3: Grinding and sintering process

Powder was prepared by hand grinding using agate mortar and pestle, and the powder was packed into a graphite mold at 753 K, 60 MPa using spark plasma sintering (SPS). Sintering was performed for 3 minutes. The cylindrical pellet obtained after sintering had a diameter of 12.5 mm and a height of 10 mm.

On the other hand, in order to evaluate the performance of the thermoelectric material according to the melt spinning process, as a control (conventional method, hereinafter referred to as "CM"), the ingot obtained in Preparation Example 1 without going through the melting spinning step of Preparation Example 2 The thermoelectric material was directly prepared using the thermoelectric material of Example 3 through the process of Preparation Example 3.

Experimental Example 1: Crystal analysis of thermoelectric material

In order to confirm the components of the composite thermoelectric material obtained according to Preparation Example 3, an X-ray diffraction (XRD) pattern was examined. An X-ray diffractometer (New D8 Advance, Bruker) was used.

The results are shown in FIGS. 1 and 2. Figure 1 shows the results of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) after Preparation Example 2, for comparison, without Cu, that is, the XRD pattern of Pristine (pristine) Bi _0.5 Sb _1.5 Te ₃ together It is shown in 1. Referring to FIG. 1, it can be seen that Bi _0.5 Sb _1.5 Te ₃ structure was formed, and since Cu is small, a secondary phase does not appear. On the other hand, Fig. 2 shows the results of MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm), which has passed through Preparation Example 2, and the results of CM-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ without Preparation Example 2. It can be seen that regardless of which method was prepared, a Bi _0.5 Sb _1.5 Te ₃ structure was produced.

Experimental Example 2: Surface image analysis of thermoelectric material

The surface of the composite material obtained according to Preparation Example 3 was observed through a scanning electron microscope (SEM, JSM-7600F, JEOL).

First, an image observed at a scale 1 μm of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500 rpm) without grinding and sintering in the form of a ribbon manufactured through a melt spinning (MS) process according to Preparation Example 2 is shown. It is shown in 3. (a) image of Pristine Bi _0.5 Sb _1.5 Te ₃ , (b) image of Cu _0.01 Bi _0.5 Sb _1.5 Te ₃ , (c) image of Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ , (d) Cu _0.04 Bi _0.5 Sb _1.5 Te ₃ image. All ribbon structures showed uniform nanostructures with a thickness of 300-500 nm. There was no significant difference according to the addition of Cu and its content.

Figure 4 is a cross-sectional SEM image of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm) without a grinding and sintering process in the form of a ribbon manufactured through a melt spinning (MS) process according to Preparation Example 2, each scale 10㎛ , 300nm, images observed at 300nm. ac is an image of Pristine Bi _0.5 Sb _1.5 Te ₃ , df is an image of Cu _0.01 Bi _0.5 Sb _1.5 Te ₃ , gi is an image of Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ , jl is an image of Cu _0.04 Bi _0.5 Sb _1.5 Te ₃ to be. Also, the left image represents the overall cross-section, the middle image represents the contact surface, and the right image represents the free surface. An amorphous phase appeared on the contact surface in contact with the Cu wheel, and a nanocrystalline structure appeared on the free surface. No separate secondary phase was observed because Cu entered into the Bi _0.5 Sb _1.5 Te ₃ crystal structure.

5 is a SEM image observed at a scale of 10 μm of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500 rpm) prepared according to Preparation Example 3. f is an image of Pristine Bi _0.5 Sb _1.5 Te ₃ , g is an image of Cu _0.01 Bi _0.5 Sb _1.5 Te ₃ , h is an image of Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ , i is an image of Cu _0.04 Bi _0.5 Sb _1.5 Te ₃ to be. Their average grain size was 3.01 μm in Pristine BST, 2.90 μm in Cu _0.01 BST, 2.95 μm in Cu _0.02 BST, and 2.67 μm in Cu _0.04 BST, respectively. The average size was calculated with 20 or more grains. Morphology according to Cu content appeared similar.

6 is an SEM image observed at a scale of 50 μm of CM-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ prepared according to Preparation Example 3. In the thermoelectric material that has not been subjected to the MS-process, a separate secondary phase was not observed.

Experimental Example 3: Analysis of thermoelectric performance of composite materials

The performance of the thermoelectric material obtained according to Preparation Example 3 was confirmed.

Electrical conductivity, Seebeck coefficient, and power factor were measured using ZEM-3 equipment (ULVAC-RIKO). In addition, the thermal conductivity of the thermoelectric material obtained according to Preparation Example 3 was measured using a laser-flash method (LFA, TA, DLF 1300).

Experimental Example 3-1. Analysis of thermoelectric performance by adding Cu: MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500rpm)

Electrical conductivity of the MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500 rpm) thermoelectric material obtained according to Preparation Example 3 (FIG. 7), carrier concentration (FIG. 8), carrier mobility (FIG. 9), carrier concentration according to Cu content And carrier mobility (FIG. 10), Seebeck coefficient (FIG. 11), power factor (FIG. 12), thermal conductivity (FIG. 13), performance index (ZR) value (FIG. 14), and average performance index value (FIG. 15). ) Were measured and are shown in FIGS. 7 to 15, respectively.

For electrical conductivity (σ), Cu _x Bi _0.5 Sb _1.5 Te ₃ showed better results than Pristine Bi _0.5 Sb _1.5 Te ₃ . In particular, Cu _0.04 BST containing 0.04 mol of Cu showed the best electrical conductivity. This shows that Cu acts as an effective p-type dopant and shows a significant increase even with the addition of very small amount of Cu. Specifically, electrical conductivity at room temperature (RT) was 740.7, 1343.0, 1680.6, and 2357.7 S/cm at Pristine BST, Cu _0.01 BST, Cu _0.02 BST, and Cu _0.04 BST, respectively. It was confirmed that the increase in electrical conductivity with the addition of Cu was due to the increase in the carrier concentration (see FIG. 8). Carrier concentration and mobility can be determined by measuring Hall coefficient from the following equation.

R _H = 1/pe

σ = peμ

In the above formula, R _H , p, e, and μ represent hole coefficient, hole carrier concentration, electron charge, and hole carrier mobility, respectively. That is, electrical conductivity is affected by both carrier concentration and carrier mobility.

Looking at the carrier concentration of the thermoelectric material of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500 rpm) according to Preparation Example 3, all of the Cu _x Bi _0.5 Sb _1.5 Te ₃ showed higher carrier concentration compared to Pristine Bi _0.5 Sb _1.5 Te ₃ It was shown (see Figure 8). On the other hand, in the case of carrier mobility, it was confirmed that the addition of Cu lowered the carrier mobility (see FIG. 9). That is, as shown in Fig. 10, it can be seen that the addition of Cu has an adverse effect on carrier mobility and concentration, respectively. As can be seen in FIG. 7, the electrical conductivity of MS-Cu _x Bi _0.5 Sb _1.5 Te ₃ (500 rpm) was most affected by the carrier concentration and increased due to the addition of Cu.

In the case of Seebeck coefficient (S), positive values were shown for all thermoelectric materials. The thermoelectric material of Pristine Bi _0.5 Sb _1.5 Te ₃ showed the highest value at a temperature below 450K and the highest value at 375K. In the case of Cu _x BST to which Cu was added, it showed a lower value due to the addition of Cu. However, the aspect of the Seebeck coefficient according to the temperature was different. In the case of Pristine Bi _0.5 Sb _1.5 Te ₃ , the decrease continued with increasing temperature at 375K or higher, but in the case of Cu _x Bi _0.5 Sb _1.5 Te ₃ , the Seebeck coefficient increased with increasing temperature.

As a result, the power factor (PF=σS ² ), which is the product of the square of the electrical conductivity and the Seebeck coefficient, showed a higher value due to Cu addition. Pristine Bi _0.5 Sb _1.5 Te ₃ showed the lowest value, and all of Cu-BST showed an improved value.

If the thermal conductivity is approximately 425K or less showed a _0.5 Sb _1.5 Te ₃ Thermoelectric Material Bi with both pristine Bi _0.5 Sb _1.5 Te ₃ Thermoelectric reduced compared to the material results that include Cu. The thermal conductivity at room temperature was 1.05, 1.29, 1.39 and 1.76 W/mK in Pristine BST, Cu _0.01 BST, Cu _0.02 BST, and Cu _0.04 BST, respectively, and showed an increasing trend with Cu content. However, while Pristine Bi _0.5 Sb _1.5 Te ₃ showed a sharply high increase in thermal conductivity at high temperatures, Cu _X Bi _0.5 Sb _1.5 Te ₃ showed lower thermal conductivity than Pristine Bi _0.5 Sb _1.5 Te ₃ at high temperatures. In particular, it was confirmed that at a temperature of about 425K or higher, the thermoelectric material containing 0.02 mol of Cu showed the lowest thermal conductivity.

As a result, it was confirmed that the MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500rpm) containing 0.02 mol Cu showed the highest value of the performance index for evaluating thermoelectric performance. In particular, the thermoelectric material of MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm) included showed a maximum value of 1.34 at 400K. That is, it was realized that the maximum performance index value of Bi _0.5 Sb _1.5 Te ₃ was moved to the medium temperature region. Since the melt spinning was performed (MS)-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm) showed a high thermoelectric performance value in the mid-temperature region, its special usefulness was confirmed. In particular, in the case of Pristine Bi _0.5 Sb _1.5 Te ₃ , it maintains high performance only from room temperature to about 350 K, which is near its temperature, and at a temperature higher than that, it exhibits significantly lower thermoelectric performance, whereas in the case of MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ It continued to show excellent thermoelectric performance from room temperature to about 500K, which is a result showing the utilization at a relatively high temperature compared to room temperature, which is the temperature at which conventional BST can be used. In order to evaluate the specific thermoelectric performance at a temperature outside the room temperature, the average performance index values in the temperature range from 298K to 523K are shown in FIG. 15. All of Cu containing Bi _0.5 Sb _1.5 Te ₃ showed a higher average performance index value than Pristine Bi _0.5 Sb _1.5 Te ₃ , and 0.02 mol of Cu contained the highest value. Specifically, compared to Pristine Bi _0.5 Sb _1.5 Te ₃ , MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm) showed an average performance index value increased by 46%.

Experimental Example 3-2. Analysis of thermoelectric performance according to melt spinning (MS): MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500rpm) and CM-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ Analysis of

MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500 rpm) obtained according to Production Example 3 through Production Example 2 and CM-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ obtained according to Production Example 3 without going through Production Example 2 Thermoelectric materials were compared. The electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, and performance index values are shown in FIGS. 16 to 20, respectively.

It can be seen that the composite thermoelectric material subjected to the melt spinning process has a higher electrical conductivity, but a lower Seebeck coefficient value. As a result, the composite thermoelectric material subjected to the melt spinning process showed a higher power factor value. In addition, the composite thermoelectric material subjected to the melt spinning process showed lower thermal conductivity, and as a result, the composite thermoelectric material subjected to the melt spinning process showed significantly higher performance index values. These results show that even if the Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ thermoelectric material of the same composition, it can exhibit different thermoelectric performance depending on how it was manufactured. Particularly, in the case of a thermoelectric material not subjected to a melt spinning process, only a slight increase in the performance index was observed from room temperature to about 400 K, and at a temperature above that, the performance index decreased. However, in the case of a thermoelectric material subjected to a melt spinning process, a performance index value of about 0.3 was increased from room temperature to about 400 K, and at a temperature higher than that, the performance index decreased, but it was still 1.0 until it reached about 475K. It can be seen that it has excellent performance of thermoelectricity in the medium temperature region by having the director's performance index.

Experimental Example 3-2. Analysis of thermoelectric performance according to the rotational speed of melt spinning (MS): MS-Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ (500rpm-4000rpm)

In order to confirm the effect on the rotational speed during the melt spinning process, the rotational speeds of Production Example 2 were set to 500 rpm, 1000 rpm, 2000 rpm, and 4000 rpm, respectively, and the MS obtained according to Production Example 3 through Production Example 2 -Cu _0.02 Bi _0.5 Sb _1.5 Te ₃ Thermoelectric materials were compared. The electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, and performance index values are shown in FIGS. 21 to 25, respectively.

In the case of electric conductivity, Seebeck coefficient, and power factor, it can be confirmed that the difference according to the rotational speed is not large. However, in the case of thermal conductivity, the lowest value was obtained when the rotational speed was 500 rpm, and the highest value was obtained when the rotational speed was 4000 rpm. As a result, it has the highest performance index value when the rotational speed is 500 rpm, and the lowest performance index value when the rotational speed is 4000 rpm.

In the present embodiment, the performance of the thermoelectric material was confirmed by using Cu as a dopant metal, but other dopant metals Ag and Pb are also substituted with Bi or Sb positions in the BST crystal structure like Cu, so the same or similar effect will be confirmed. It is predicted enough. Therefore, the preceding embodiments should not be construed as limiting the invention of the present disclosure.

As described above, although the embodiments have been described by the limited drawings, those skilled in the art can apply various technical modifications and variations based on the above. For example, the described techniques are performed in a different order than the described method, and/or the components of the described system, structure, device, circuit, etc. are combined or combined in a different form from the described method, or other components Alternatively, even if replaced or substituted by equivalents, appropriate results can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (18)

A method of manufacturing a composite thermoelectric material having a composition of M _x Bi _y Sb _2-y Te ₃ (0 <x ≤ 0.1, 0 <y <2), wherein M is a group consisting of copper, lead, silver, and combinations thereof Any one selected from,
The manufacturing method
Preparing a composite raw material by mixing Bi, Sb, Te, and M raw material;
Manufacturing a composite thermoelectric material in the form of an ingot or pellet using the composite raw material;
Forming a ribbon by melt-spinning the ingot or pellet-shaped composite thermoelectric material;
Pulverizing the ribbon; And
Sintering the crushed ribbon
The method of manufacturing a composite thermoelectric material comprising a.
The method of claim 1, wherein the composition of the composite thermoelectric material is 0.005 ≤ x ≤ 0.05.
The method of claim 1, wherein the composition of the composite thermoelectric material is 0.01 ≤ x ≤ 0.04.
The method of claim 1, wherein the composition of the composite thermoelectric material is 0.015 ≤ x ≤ 0.025.
According to claim 1, The composition of the composite thermoelectric material is 0 <y <1, the method of manufacturing a composite thermoelectric material.
The method of claim 1, wherein the composition of the composite thermoelectric material is 0.4≦y≦0.6.
The method of claim 1, wherein the composition of the composite thermoelectric material is y = 0.5.
The method of claim 1, wherein the M is copper.
The method of claim 1, wherein the composite thermoelectric material is a p-type thermoelectric material.
According to claim 1, The step of forming the ribbon (ribbon) comprises the step of melting the composite thermoelectric material in the form of an ingot or pellet and ejecting the melted thermoelectric material to the wheel through a nozzle. Method for manufacturing thermoelectric material.
The method of claim 10, wherein the rotational speed of the wheel is 100 to 4000 rpm.
The method of claim 11, wherein the rotational speed of the wheel is 200 to 1000 rpm.
The method of claim 12, wherein the rotational speed of the wheel is 400 to 600 rpm and the composite thermoelectric material produced has a composition of Cu _x Bi _y Sb _2-y Te ₃ (0.15 ≤ x ≤ 0.25, 0.4 ≤ y ≤ 0.6) Phosphorus, composite thermoelectric material manufacturing method.
The method of claim 1, wherein the step of manufacturing the composite thermoelectric material in the form of an ingot or pellet comprises heating and quenching the composite raw material.
The method of claim 1, wherein the step of pulverizing the ribbon includes ball milling, attrition milling, high energy milling, jet milling, and pestle bowl. Method of pulverizing in, and is performed through any one selected from the group consisting of a combination of these, the method of manufacturing a composite thermoelectric material.
The method of claim 1, wherein the step of sintering the pulverized ribbon is performed through any one selected from the group consisting of Spark Plasma Sintering method, hot press sintering, and combinations thereof. Phosphorus, composite thermoelectric material manufacturing method.
A composite thermoelectric material of M _x Bi _y Sb _2-y Te ₃ produced by the method for producing a composite thermoelectric material according to any one of claims 1 to 16.
The composite thermoelectric material of claim 17, wherein the composite thermoelectric material has a performance index (ZT) value of 1.0 or higher at 298K to 473.

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