A high-performance porous magnetic copper sulfide thermoelectric material and its preparation method

Abstract

The present invention relates to the technical field of porous magnetic thermoelectric materials, and discloses a high-performance porous magnetic copper sulfide thermoelectric material and a preparation method thereof. The thermoelectric material comprises a matrix phase Cu 1.8 S and the second phase Fe3O4, whose general chemical formula is Cu 1.8 S-x%Fe3O4, wherein 0.5≤x≤20. The preparation method of the thermoelectric material comprises the following steps: step (1) Cu 1.8 Preparation of S-x% Fe3O4 precursor powder: Cu elemental powder, S elemental powder and Fe3O4 magnetic powder are placed in a ball mill for mechanical alloying to obtain Cu 1.8 S-x%Fe3O4 precursor powder; step (2) Cu 1.8 Sintering of S-x%Fe3O4 bulk: Sinter the Cu prepared in step (1) 1.8 The porous magnetic copper sulfide thermoelectric material is obtained by sintering the S-x% Fe3O4 precursor powder using spark plasma sintering. This invention solves the problem of poor performance of existing copper sulfide thermoelectric materials.

Description

Technical Field

[0001] The present invention relates to the technical field of porous magnetic thermoelectric materials, and in particular to a high-performance porous magnetic copper sulfide thermoelectric material and a preparation method thereof. Background Art

[0002] As energy issues become increasingly serious, how to balance the relationship between "energy," "environment," and "development" has become a common goal of interdisciplinary and cross-disciplinary collaborative development in many fields. As a new type of green energy conversion material, thermoelectric materials can not only directly convert any form of thermal energy into electrical energy, but also use the temperature difference generated after power is applied to manufacture precise temperature control or refrigeration devices. Among them, electrical energy can be directly converted into thermal energy for use in the field of electrothermal temperature difference, that is, cooling or heating, such as chip cooling, 5G component cooling, laser component cooling, thermoelectric refrigerators, drug cooling and other civil, biological, and medical fields; it can also be converted into electrical energy through waste heat recovery to complete the energy conversion of thermoelectricity, such as industrial waste / waste heat recovery, automobile exhaust waste heat power generation, and even human body temperature conversion, artificial satellites, deep space probes and other civil, aerospace, and military fields.

[0003] Thermoelectric conversion efficiency is measured by the dimensionless thermoelectric figure of merit ZT, which can be obtained by the following formula: ZT = S 2 σT / κ, where S, σ, T, and κ represent the material's Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively. The three important performance parameters, S, σ, and κ, exhibit a mutually constrained and coupled relationship with changes in carrier concentration. Optimizing these parameters through carrier concentration adjustment is crucial for maintaining high thermoelectric performance. Currently, high-performance thermoelectric materials include Bi2Te3, PbTe, PbS, and GeTe alloys, but these materials are expensive, have limited raw material reserves, and are highly toxic. Therefore, identifying and researching compounds composed of non-toxic, inexpensive, abundant, and industrially applicable elements as suitable thermoelectric materials is a crucial research task.

[0004] Cu1.8S material is a kind of intrinsic p-type semiconductor material with the advantages of high element abundance, low raw material cost, and green and pollution-free. 1.8 S has a rhombohedral phase structure (R-3m) at room temperature and transforms into a cubic phase structure (Fm-3m) when the temperature rises above 361K. This material is a superionic conductor, that is, Cu ions migrate with extremely high mobility in the lattice framework of S. Therefore, Cu 1.8 S materials have high electrical conductivity. But it has always been an obstacle for Cu 1.8 The commercial application of S material is due to its low Seebeck coefficient and high thermal conductivity. In addition, Cu ions will 1.8Directed migration occurs within the S material, resulting in the precipitation of Cu at the cathode. This can severely affect the material's thermoelectric performance and increase contact resistance, hindering device performance. Consequently, researchers have conducted extensive research addressing the issues of poor thermoelectric performance and insufficient stability. Zhang Boping et al. used elemental Cu powder, S powder, and doped element A powder as raw materials, employing a mechanical alloying reaction combined with room-temperature high-pressure sintering to obtain a nanocrystalline Cu-S-based bulk thermoelectric material with fine grains and a dense structure (CN110117191A). However, the copper sulfide material prepared by this method exhibited poor electrical properties due to its small grain size, and the thermoelectric performance was not significantly improved. Qiu Pengfei et al. distributed at least one ion barrier layer between any two adjacent segments of fast ion conductor thermoelectric material in a thermoelectric arm formed by connecting n segments of fast ion conductor thermoelectric material along the direction of the external field to improve the service stability of the fast ion conductor thermoelectric material (CN 110544741A). However, this method is difficult to apply to mass production, and multiple ion barrier layers may reduce the mechanical strength of the entire thermoelectric device. Therefore, it is of great significance to develop a porous magnetic copper sulfide thermoelectric material with excellent thermoelectric properties and its preparation process. Summary of the Invention

[0005] The present invention aims to provide a high-performance porous magnetic copper sulfide thermoelectric material and a preparation method thereof, so as to solve the problem of poor performance of existing copper sulfide thermoelectric materials.

[0006] To achieve the above object, the present invention adopts the following technical solution: a high-performance porous magnetic copper sulfide thermoelectric material, comprising a matrix phase Cu 1.8 S and the second phase Fe3O4, whose general chemical formula is Cu 1.8 Sx%Fe3O4, where 0.5≤x≤20.

[0007] The principles and advantages of this solution are: in this technical solution, in response to the problem of poor performance of existing copper sulfide thermoelectric materials in the prior art, this technical solution comprehensively optimizes copper sulfide thermoelectric materials and preparation processes: by adding oxides to copper sulfide, the effect of pore formation is achieved, and the porous structure ensures the low thermal conductivity of the material, solving the problem of high thermal conductivity of intrinsic copper sulfide; in addition, while ensuring the porous structure, the added oxides achieve Fe doping in the matrix, introduce a second phase containing iron elements, and technically achieve magnetic transformation of copper sulfide, improve the Seebeck coefficient of the material, and solve the problem of low Seebeck coefficient of intrinsic copper sulfide; not only that, by introducing the second phase containing iron elements, the thermal conductivity of the material can be further reduced, and the Fe element inhibits the migration of Cu ions, solving the problem of poor intrinsic stability of copper sulfide materials, with outstanding advantages.

[0008] In summary, the beneficial effects of this technical solution are:

[0009] 1. In this technical solution, the addition of Fe3O4 produces SO2, which generates pores in the copper sulfide matrix, forming a porous copper sulfide thermoelectric material. The copper-rich phase in the matrix increases, which can reduce the thermal conductivity of the material;

[0010] 2. In this technical solution, the introduction of magnetic iron oxide (Fe3O4) causes the antimagnetic copper sulfide material to undergo magnetic conversion, becoming a porous copper sulfide thermoelectric material with magnetic properties, effectively improving the Seebeck coefficient of the copper sulfide material;

[0011] 3. The Fe3O4 in this technical solution is 1.8 Fe doping is achieved in the S matrix to form a second phase containing iron elements. By optimizing the carrier concentration, the thermal conductivity of the material is effectively reduced. At the same time, the Fe element can inhibit the long-range migration of Cu ions in the collective, thereby improving the stability of the copper sulfide material.

[0012] 4. In this technical solution, the dispersed distribution in Cu 1.8 The Fe3O4 in the S matrix introduces additional phase interfaces, which helps to enhance the Cu 1.8 The phonon scattering effect in S thermoelectric materials significantly reduces the lattice thermal conductivity of the material, which is beneficial to improving the thermoelectric figure of merit of the material.

[0013] Preferably, as an improvement, Fe3O4 is a black oxide powder having magnetic properties, and the addition amount of Fe3O4 is 0.5-20 wt%.

[0014] In this technical solution, the oxide powder is added to the copper sulfide, which can cause the volatilization of sulfur elements. The generated SO2 plays a good role in forming pores in the matrix. Moreover, due to its magnetic properties, it can make the copper sulfide thermoelectric material complete the magnetic transition, improve the Seebeck coefficient, and inhibit the Cu 1.8 The long-range migration of Cu ions in the S material improves the material's stability. During the technical research and development phase, the inventors discovered that the Fe3O4 content has a key impact on the thermal conductivity of the thermoelectric material. Too little Fe3O4 will not be able to block the migration of Cu ions, while an excess of Fe3O4 will significantly increase the thermal conductivity of the copper sulfide thermoelectric material.

[0015] Preferably, as an improvement, a method for preparing a high-performance porous magnetic copper sulfide thermoelectric material comprises the following steps:

[0016] Step (1) Cu 1.8 Preparation of Sx% Fe3O4 precursor powder: Cu elemental powder, S elemental powder and Fe3O4 magnetic powder are placed in a ball mill for mechanical alloying to obtain Cu 1.8 Sx%Fe3O4 precursor powder;

[0017] Step (2) Cu 1.8 Sintering of Sx% Fe3O4 bulk: Sinter the Cu prepared in step (1) 1.8 The Sx%Fe3O4 precursor powder is sintered by spark plasma sintering to obtain porous magnetic copper sulfide thermoelectric material.

[0018] Preferably, as an improvement, in step (1), the mechanical alloying process is carried out under a protective atmosphere.

[0019] Preferably, as an improvement, the protective atmosphere is 5% H2+95% Ar.

[0020] Preferably, as an improvement, in step (1), the purity of the Cu elemental powder and the S elemental powder are both greater than 99.99%.

[0021] Preferably, as an improvement, in step (1), the weight ratio of the balls to the material during ball milling is 20-50:1, the rotation speed during ball milling is 300-600 rpm, and the ball milling time is 1-4 h.

[0022] Preferably, as an improvement, in step (2), the sintering temperature is 300-500° C., the sintering time is 5-30 min, and the sintering pressure is 10-50 MPa.

[0023] Preferably, as an improvement, in step (2), the sintering temperature is 500° C., the sintering time is 5 min, and the sintering pressure is 50 MPa.

[0024] In this technical solution, in addition to optimizing the thermoelectric materials, the performance of the raw materials and the preparation process are also improved in an integrated manner: First, in terms of material performance, high-purity Cu elemental powder and S elemental powder can reduce the amount of impurities produced, thereby avoiding the occurrence of poor thermoelectric performance of the prepared thermoelectric composite materials. In terms of optimization of the preparation process: During the mechanical alloying stage, the mechanical alloying reaction is carried out in an environment with a protective atmosphere of 5% H2 + 95% Ar, which can effectively avoid the oxidation contamination of the raw materials. The use of unidirectional operation is conducive to the full diffusion of elements, making the reaction more complete. In the sintering stage, through the integrated optimization of sintering temperature, time and pressure, the prepared Cu 1.8 S copper sulfide thermoelectric material has high density, good thermoelectric performance, and is not easy to explode during sintering.

[0025] In summary, the beneficial effects of this technical solution are:

[0026] 1. In this technical solution, during the ball milling process, Cu 1.8When the precursor powder is Sx%, the ball milling time and the ball milling speed are adjusted to make the Cu element, S element and Fe3O4 react completely, and the second phase of Fe3O4 can be distributed more evenly in the Cu 1.8 S matrix material, to ensure the stability of the thermoelectric performance of the thermoelectric material;

[0027] 2. In this technical solution, by 1.8 The Sx% Fe3O4 precursor powder is subjected to spark plasma sintering to quickly form a bulk porous magnetic copper sulfide thermoelectric material, ensuring that the thermoelectric material meets practical use.

[0028] 3. This technical solution, through magnetic measurement, proves that the Fe3O4 second phase can convert non-magnetic Cu 1.8 S thermoelectric materials are converted into magnetic thermoelectric materials; by characterizing the phase structure, micromorphology, and thermoelectric properties of the prepared porous magnetic copper sulfide thermoelectric materials, it is found that the copper sulfide thermoelectric materials contain a Cu1.8S matrix phase and a Fe3O4 second phase, which can significantly improve the stability while improving its thermoelectric performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The morphologies of Example 1 and Comparative Example 1 of the present invention are shown below:

[0030] Figure 2 1 is a comparison chart of XRD between Example 1 of the present invention and Comparative Example 1;

[0031] Figure 3 Graph showing changes in conductivity with temperature for Example 1 of the present invention and Comparative Example 1;

[0032] Figure 4 Graph showing the Seebeck coefficient of Example 1 of the present invention and Comparative Example 1 as a function of temperature;

[0033] Figure 5 Graph showing thermal conductivity versus temperature for Example 1 and Comparative Example 1 of the present invention;

[0034] Figure 6 Graph showing the thermoelectric figure of merit (ZT value) of Example 1 of the present invention and Comparative Example 1 as a function of temperature;

[0035] Figure 7 Graph showing the magnetization curves of the samples of Example 1 and Comparative Example 1 at a temperature of 323K. DETAILED DESCRIPTION

[0036] The following is further described in detail through specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials, reagents, etc. used are all commercially available.

[0037] Program Overview:

[0038] A high-performance porous magnetic copper sulfide thermoelectric material, comprising a matrix phase Cu 1.8 S and the second phase Fe3O4, whose general chemical formula is Cu 1.8 Sx% Fe3O4, where 0.5≤x≤20, Fe3O4 is a black oxide powder with magnetic properties.

[0039] A method for preparing a high-performance porous magnetic copper sulfide thermoelectric material comprises the following steps:

[0040] Step (1) Cu 1.8 Preparation of Sx% Fe3O4 precursor powder: Cu elemental powder, S elemental powder and Fe3O4 magnetic powder were placed in a planetary ball mill and mechanically alloyed under a protective atmosphere to obtain Cu 1.8 Sx% Fe3O4 precursor powder; the purity of Cu elemental powder and S elemental powder is greater than 99.99%; the amount of Fe3O4 added is 0.5-20wt%; the weight ratio of balls to materials during ball milling is 20-50:1, the speed during ball milling is 300-600rpm, and the ball milling time is 1-4h; the protective atmosphere is 5% H2+95% Ar;

[0041] Step (2) Cu 1.8 Sintering of Sx% Fe3O4 bulk: Sinter the Cu prepared in step (1) 1.8 The Sx% Fe3O4 precursor powder is sintered by spark plasma sintering at a sintering temperature of 300-500°C, a sintering time of 5-30 minutes, and a sintering pressure of 10-50 MPa to obtain a porous magnetic copper sulfide thermoelectric material.

[0042] Examples: To further illustrate the advantages of the present technical solution, the following seven examples and five comparative examples are designed. The differences between the examples lie in the selection of magnetic powder, the amount of addition, the amount of raw materials added, and the mass percentage of the second phase. The differences between the comparative examples lie in the selection of oxide types. See Table 1 for details:

[0043] Table 1

[0044]

[0045]

[0046] Taking Example 1 as an example, a method of obtaining a porous magnetic copper sulfide thermoelectric material with excellent thermoelectric properties by using iron oxide according to the present invention is described in detail:

[0047] A method for preparing a high-performance porous magnetic copper sulfide thermoelectric material comprises the following steps:

[0048] Step (1) Cu 1.8 Preparation of S-2% Fe3O4 precursor powder:

[0049] Weigh 3.91g of pure Cu powder with a purity greater than 99.99%, 1.09g of pure S powder, and 0.1g of Fe3O4 magnetic powder, put the weighed powders into a ball mill in succession, and mechanically alloy them under a protective atmosphere to obtain Cu 1.8 Sx% Fe3O4 precursor powder; the weight ratio of the spheres and the material during ball milling is 20-50:1, the ball milling speed is 300-600rpm, and the ball milling time is 1-4h. In this embodiment, the protective atmosphere is 5% H2+95% Ar, the mass ratio of the spheres and the material is 20:1, the ball milling speed is 425rpm, and the ball milling time is 2h.

[0050] Step (2) Cu 1.8 S-2%Fe3O4 bulk sintering:

[0051] The Cu prepared in step (1) is sintered by spark plasma sintering technology. 1.8 S-2% Fe3O4 precursor powder is sintered. First, the powder is poured into a graphite mold with a diameter of 15 mm and sintered at a temperature of 300-500 ° C and a pressure of 10-50 MPa for 5-30 minutes. In this embodiment, the sintering temperature is 500 ° C, the sintering pressure is 50 MPa, and the sintering time is 5 minutes to form a block of Cu. 1.8 S-2%Fe3O4 porous magnetic copper sulfide thermoelectric material. 1.8 The main phase of S-2%Fe3O4 porous magnetic copper sulfide thermoelectric material is Cu 1.8 S.

[0052] The difference between Example 2-7 and Example 1 is that the parameters shown in Table 1 are different, that is, the content of the Fe3O4 second phase is different. The material formed in Example 2 is Cu 1.8 S-0.5% Fe3O4 porous magnetic copper sulfide thermoelectric material; the material formed in Example 3 is Cu 1.8 S-1% Fe3O4 porous magnetic copper sulfide thermoelectric material; the material formed in Example 4 is Cu 1.8 S-1.5% Fe3O4 porous magnetic copper sulfide thermoelectric material; the material formed in Example 5 is Cu 1.8S-2.5% Fe3O4 porous magnetic copper sulfide thermoelectric material; the material formed in Example 6 is Cu 1.8 S-3% Fe3O4 porous magnetic copper sulfide thermoelectric material; the material formed in Example 7 is Cu 1.8 S-20% Fe3O4 porous magnetic copper sulfide thermoelectric material. The difference between Comparative Example 1 and Example 1 is that the parameters shown in Table 1 are different, that is, the type of the second phase is different. The material formed in Comparative Example 1 is Cu 1.8 S-2% Fe magnetic copper sulfide thermoelectric material. The difference between comparative examples 3-5 and example 1 is that the parameters shown in Table 1 are different, that is, the type and content of the second phase are different. The material formed in comparative example 3 is Cu 1.8 S-1% SiO2 copper sulfide thermoelectric material; the material formed in Comparative Example 4 is Cu 1.8 S-1% WO3 copper sulfide thermoelectric material; the material formed in Comparative Example 5 is Cu 1.8 S-1% SnO2 copper sulfide thermoelectric material.

[0053] Experimental Example 1 Morphology Characterization

[0054] The microscopic morphology of the porous magnetic copper sulfide thermoelectric materials prepared in Examples 1-7 and Comparative Example 1 was observed using a scanning electron microscope. Taking Example 1 as an example, the obtained electron microscope images are as follows: Figure 1 The results show that a porous magnetic copper sulfide thermoelectric material was prepared by this method, wherein Figure 1 Cu 1.8 S-2wt%Fe3O4 thermoelectric material.

[0055] Experimental Example 2 XRD (X-ray Diffraction) Characterization

[0056] The porous magnetic copper sulfide thermoelectric materials prepared in Examples 1-7 and Comparative Example 1 and the thermoelectric material provided in Comparative Example 2 were tested using an X-ray diffractometer. Taking Example 1 and Comparative Example 2 as examples, the test results are as follows: Figure 2 The XRD results show that the mechanical alloying method and spark plasma sintering technology can be used to synthesize Cu 1.8 Porous magnetic copper sulfide bulk material with S as the main phase.

[0057] Experimental Example 3 Characterization of Thermoelectric Performance

[0058] The performance of thermoelectric materials is characterized by the dimensionless thermoelectric figure of merit ZT, which is expressed as ZT = S 2 σT / κ, where S 2 σ represents the power factor, T is the absolute temperature, and κ is the thermal conductivity.

[0059] 3.1 Electrical transmission performance

[0060] The thermoelectric materials prepared in Examples 1-7, Comparative Examples 1-5, and the thermoelectric material provided in Comparative Example 2 were cut into 3×3×10 mm cuboids and the resistivity and Seebeck coefficient test system was used to test the resistivity and Seebeck coefficient of the materials. Taking Example 1 and Comparative Example 2 as examples, the conductivity test results are as follows: Figure 3 As shown, the Seebeck coefficient test results are as follows Figure 4 The electrical conductivity and Seebeck coefficient of the thermoelectric materials provided in Examples 1-7 and Comparative Examples 1-5 at 773K are shown in Table 2.

[0061] 3.2 Thermal conductivity

[0062] The bulk thermoelectric materials prepared in Examples 1-7 and Comparative Examples 1-5 were cut into The thermal conductivity of the circular sheet was tested with a laser thermal conductivity meter. Taking Example 1 and Comparative Example 2 as examples, the test results are as follows Figure 5 The thermal conductivity of the bulk thermoelectric composite materials prepared in Examples 1-7 and Comparative Examples 1-5 at 773K is shown in Table 2.

[0063] 3.3ZT value

[0064] According to the above formula ZT=S 2 The ZT value can be obtained by calculating σT / κ. Taking Example 1 and Comparative Example 2 as examples, the ZT values ​​are as follows: Figure 6 The ZT values ​​of the bulk thermoelectric composite materials prepared in Examples 1-7 and Comparative Examples 1-5 at 773K are shown in Table 2.

[0065] Table 2

[0066]

[0067] Experimental Example 4 Magnetic Characterization

[0068] The bulk thermoelectric material prepared in Example 1 and the thermoelectric material provided in Comparative Example 2 were cut and polished into rectangular blocks with a size of less than 2×2×2 mm for magnetic testing. Taking Example 1 and Comparative Example 2 as examples, the magnetic properties of the materials were measured using the hysteresis loop test. The hysteresis loops of the samples in Example 1 and Comparative Example 2 at 323K are as follows: Figure 7 shown.

[0069] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A method for preparing a high-performance porous magnetic copper sulfide thermoelectric material, characterized in that: The thermoelectric material includes a matrix phase Cu 1.8 S and the second phase Fe3O4, whose general chemical formula is Cu 1.8 Sx%Fe3O4, wherein 0.5≤x≤20, the preparation method comprises the following steps: Step (1) Cu 1.8 Preparation of Sx%Fe3O4 precursor powder: Cu elemental powder, S elemental powder and Fe3O4 magnetic powder are placed in a ball mill for mechanical alloying to obtain Cu 1.8 Sx%Fe3O4 precursor powder; Step (2) Cu 1.8 Sintering of Sx%Fe3O4 bulk: Sinter the Cu prepared in step (1) 1.8 The Sx%Fe3O4 precursor powder was sintered by spark plasma sintering to obtain porous magnetic copper sulfide thermoelectric material.

2. The method for preparing a high-performance porous magnetic copper sulfide thermoelectric material according to claim 1, characterized in that: In step (1), the mechanical alloying process is carried out under a protective atmosphere.

3. The method for preparing a high-performance porous magnetic copper sulfide thermoelectric material according to claim 2, characterized in that: The protective atmosphere is 5% H2+95% Ar.

4. The method for preparing a high-performance porous magnetic copper sulfide thermoelectric material according to claim 3, characterized in that: In step (1), the purity of the Cu elemental powder and the S elemental powder are both greater than 99.99%.

5. The method for preparing a high-performance porous magnetic copper sulfide thermoelectric material according to claim 4, characterized in that: In step (1), the weight ratio of the balls to the material during ball milling is 20-50:1, the rotation speed during ball milling is 300-600 rpm, and the ball milling time is 1-4 h.

6. The method for preparing a high-performance porous magnetic copper sulfide thermoelectric material according to claim 5, characterized in that: In step (2), the sintering temperature is 300~500℃, the sintering time is 5~30 min, and the sintering pressure is 10~50 MPa.

7. The method for preparing a high-performance porous magnetic copper sulfide thermoelectric material according to claim 6, characterized in that: In step (2), the sintering temperature is 500°C, the sintering time is 5 min, and the sintering pressure is 50 MPa.

8. A high-performance porous magnetic copper sulfide thermoelectric material prepared according to the method for preparing a high-performance porous magnetic copper sulfide thermoelectric material according to any one of claims 1 to 7, characterized in that: Including matrix phase Cu 1.8 S and the second phase Fe3O4, whose general chemical formula is Cu 1.8 Sx%Fe3O4, where 0.5≤x≤20.

9. The high-performance porous magnetic copper sulfide thermoelectric material according to claim 8, characterized in that: Fe3O4 is a black oxide powder with magnetic properties. The addition amount of Fe3O4 is 0.5~20 wt%.

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