High-stability copper sulfide thermoelectric material based on grain boundary alloying and preparation method thereof

Abstract

The invention relates to the technical field of thermoelectric materials, and discloses a high-stability copper sulfide thermoelectric material based on grain boundary alloying and a preparation method thereof, the chemical general formula of the thermoelectric material is Cu2-xS-A, A is an alloy of metal M, the metal M is embedded in a Cu2S material, and the metal M is at least one of Y, Sc, Pd, Zn and Ti. According to the technical scheme, the performance of the copper sulfide-based thermoelectric material is optimized through a grain boundary alloying strategy, M metal (M is Y, Sc, Pd, Zn, Ti and other metal simple substances) is innovatively introduced into a Cu2S system, Cu2S obtains high conductivity, meanwhile, a macroscopic ion barrier layer (with the thickness of 5-10 microns) constructed through grain boundary alloying is achieved on the surfaces of grains, the material conductivity network integrity is kept, and meanwhile the performance of the copper sulfide-based thermoelectric material is improved. And the Cu < + > migration path length is increased by 3 orders of magnitude.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of thermoelectric materials, in particular to a high-stability copper sulfide thermoelectric material based on grain boundary alloying and a preparation method thereof. BACKGROUND

[0002] As a new type of green energy material capable of realizing direct conversion between heat and electricity, thermoelectric materials have broad application prospects in the fields of industrial waste heat recovery, solid-state refrigeration and wearable device power supply. The core of thermoelectric energy conversion technology is thermoelectric materials, and the research field involves the transport of carriers and phonons in solid materials and their interaction. High-performance thermoelectric devices are composed of high-performance p-type and n-type thermoelectric materials in series and have a wide range of applications. In the field of thermoelectric power generation, it can be applied in deep space exploration power supply and automobile exhaust waste heat recovery; and in the aspect of electric temperature difference, it is mainly applied in the refrigeration of electronic components and small-size components.

[0003] The performance of a thermoelectric material is mainly determined by the dimensionless thermoelectric figure of merit (ZT value, ZT = S 2 σT / κ), wherein S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. S, σ, T, κ L and κ e represent the Seebeck coefficient, electrical conductivity, absolute temperature, lattice thermal conductivity and carrier thermal conductivity, respectively. The performance optimization of a thermoelectric material essentially involves the coordinated control of three interrelated physical parameters (the Seebeck coefficient S, the electrical conductivity σ, and the electronic thermal conductivity κ e ). These parameters respond to the carrier concentration (n) in a significant mutually restrictive relationship. Current research systems such as bismuth telluride-based alloys (Bi2Te3), lead telluride (PbTe), lead sulfide (PbS) and germanium telluride (GeTe) based materials exhibit excellent performance in low-temperature thermoelectric conversion devices, but the scarce metals or toxic elements contained in their components are fundamentally incompatible with the concept of green and sustainable development. Therefore, the development of an element system based on high earth abundance and good environmental compatibility, and the establishment of a matching large-scale preparation process, have become an important research direction for the construction of new environmentally friendly thermoelectric material systems.

[0004] Cuprous sulfide (Cu2S) as a typical intrinsic p-type semiconductor material has been continuously concerned in the field of thermoelectric materials due to its excellent crust abundance, low preparation cost and ecological friendly characteristics. The compound exhibits temperature-dependent polymorphic phase transition characteristics: it is stable in monoclinic phase (P21 / c) at room temperature, and undergoes structural transitions to hexagonal phase (P63 / mmc) and cubic phase (Fm-3m) in the temperature range of 370-700K. Its unique superionic conductor behavior is that the cation sublattice exhibits liquid characteristics: Cu + ions in the rigid S2- The quasi-free migration of carriers in the framework, the synergistic effect of phonon scattering makes the material have high electrical conductivity and ultra-low lattice thermal conductivity (<1 Wm -1 K -1 However, the structural degradation problem caused by the intrinsic cation migration characteristics seriously restricts its engineering application: under the action of thermoelectric coupling field, Cu + continuously enriches to the cathode / low temperature end, and when the local concentration exceeds the thermodynamic equilibrium threshold, elemental copper phase separation occurs. This phenomenon not only leads to the degradation of thermoelectric performance caused by composition segregation (i), but also causes the device efficiency to deteriorate due to the increase of interface contact resistance (about 300% increase) (ii), which constitutes the main technical bottleneck of Cu2S commercial application.

[0005] In view of the stability problem caused by ion migration in copper sulfide system, researchers have proposed various solutions. Qiu Pengfei team (CN 110544741 A) developed a transition metal (Cr / Mn / Fe / Co) lattice doping strategy, which is to add transition metal during the preparation of cuprous sulfide material, so that metal atoms directly enter the cuprous sulfide lattice and will not be enriched in the form of second phase at the grain boundary. Through the strong interaction of metal-Cu bond, the Cu+ migration potential barrier is improved (ΔE>0.15eV), which effectively enhances the thermoelectric stability of the material. The team also designed a multi-phase composite structure based on carbon / metal interface layer, and formed an ion migration potential barrier by constructing Cu 2-x S gradient material. However, such heterogeneous interfaces have intrinsic bonding strength defects (<30MPa), and the multi-step processing process significantly increases the manufacturing cost (process steps increase by 50%), which limits its large-scale application. Zhang Boping et al. (CN 103979549 B) synthesized Cu 1.8 S@SiO2core-shell nanoparticles (shell thickness 5-500nm) by sol-gel method, which reduces the lattice thermal conductivity to 0.7Wm -1 K -1 <500Sm -1 , and the intrinsic ion migration problem is not solved. SUMMARY

[0006] The present application aims to provide a high-stability copper sulfide thermoelectric material based on grain boundary alloying and a preparation method thereof, to solve the problems of insufficient electrical conductivity and poor service stability of existing copper sulfide thermoelectric materials.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a high-stability copper sulfide thermoelectric material based on grain boundary alloying, the chemical general formula is Cu 2-xS-A, A is an alloy of M metal, M metal is embedded in Cu2S material, M metal is at least one of Y, Sc, Pd, Zn, Ti.

[0008] Preferably, as an improvement, the amount of M metal added is 0.5-20 wt%. Preferably, as an improvement, the purity of M metal is ≥99.99%.

[0009] Preferably, as an improvement, a preparation method of a high-stability copper sulfide thermoelectric material based on grain boundary alloying, comprising the following steps: Step (1) Preparation of Cu2S precursor powder: Cu elemental powder and S elemental powder are mixed and ground, and the obtained mixed powder is alloyed to obtain Cu2S precursor powder; Step (2) Cu 2-x Preparation of S-A composite material: Cu2S precursor powder is mixed and ground with M metal to obtain Cu2S-M composite powder; Step (3) Sintering: Cu2S-M composite powder is sintered to obtain Cu 2-x S-A-based thermoelectric composite material.

[0010] Preferably, as an improvement, in step (1), the purity of Cu elemental powder and S elemental powder is ≥99.99%.

[0011] Preferably, as an improvement, in step (1), the mixing and grinding is carried out in a protective atmosphere, and the protective atmosphere is argon.

[0012] Preferably, as an improvement, in step (1), the alloying is carried out in a ball mill, the ball milling speed is 350-450 rpm, and the alloying time is 1-3 h.

[0013] Preferably, as an improvement, in step (2), the mixing and grinding time is 5-20 min.

[0014] Preferably, as an improvement, in step (3), the sintering temperature is 300-500°C, the sintering time is 5-30 min, and the sintering pressure is 10-50 Mpa.

[0015] The principle and advantages of the present scheme are: in practical application, in view of the problems of insufficient electrical conductivity and poor service stability of copper sulfide thermoelectric materials in the prior art, the performance of copper sulfide-based thermoelectric materials is optimized through grain boundary alloying strategy, and in the technical research and development stage, how to avoid alloy formation in the grain is one of the research and development difficulties of the present application. Based on this, the present scheme innovatively introduces M metal (M is Y, Sc, Pd, Zn, Ti, etc.) into the Cu2S system, and obtains a Cu 2-xThe innovative introduction of elements S and alloy phase A alloy, especially Y, Sc, Pd, enables alloying at the grain boundary. In the material preparation process, first, Cu2S precursor powder is prepared by mechanical alloying; then, the Cu2S precursor powder is mixed with metal elements M to realize grain boundary alloying by spark plasma sintering; during the sintering process, Cu in Cu2S + occurs directional migration and reacts with M to generate A alloy, and finally, A alloy (CuY, CuSc, CuPd, CuZn or CuTi) is enriched at the grain boundary of Cu 2-x S matrix, so that Cu2S obtains high electrical conductivity, and at the same time, the macroscopic ion barrier layer (thickness 5-10 μm) constructed by realizing grain boundary alloying on the grain surface maintains the integrity of the material conductive network and reduces the migration path length of Cu + by 3 orders of magnitude. Experiments prove that this design enables the Cu2S thermoelectric material of the intrinsic low-conductivity system to obtain high conductivity and ultra-high power factor.

[0016] In summary, the beneficial effects of the technical solution are as follows: 1. Improved thermoelectric performance: In the technical solution, A alloy at the grain boundary forms a conductive path, reduces carrier scattering, and improves electrical conductivity (σ) and power factor (S 2 σ); 2. Enhanced stability: In the technical solution, A alloy acts as an ion barrier layer, captures migrating Cu + , inhibits long-range migration, avoids Cu element precipitation at the cathode / low-temperature end, reduces composition segregation and interface resistance surge, and reduces composition segregation and interface resistance surge; 3. Environmentally friendly: In the technical solution, no Bi2Te3, PbTe or other systems containing scarce / toxic elements are used, and the system is based on environmentally compatible elements such as Cu and S, in line with the green and sustainable development concept.

[0017] 4. The technical solution realizes "two-way optimization" through grain boundary alloying: the data of the embodiments show that the material added with 1wt% Sc, Y, Pd, etc. has an electrical conductivity of 86-106 S / cm (9-12 times that of the comparative example), a ZT value of 0.88-0.91 (2.7-2.8 times that of the comparative example), and a significant decrease in resistance change during stability testing, which is significantly lower than that of pure Cu2S. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a grain boundary alloying diagram of Example 1 of the present application; Figure 2 is an XRD diagram of Example 1 and Comparative Example 1 of the present application; Figure 3 is a graph of the electrical conductivity of Example 1 and Comparative Example 1 of the present application varying with temperature; Figure 4 A plot of the Seebeck coefficient as a function of temperature for Example 1 and Comparative Example 1 of the present application; Figure 5 A plot of the power factor as a function of temperature for Example 1 and Comparative Example 1 of the present application; Figure 6 A plot of the thermal conductivity as a function of temperature for Example 1 and Comparative Example 1 of the present application; Figure 7 A plot of the thermoelectric figure of merit (ZT value) as a function of temperature for Example 1 and Comparative Example 1 of the present application; Figure 8 A scanning electron microscope EDS spectrum of the Sc grain boundary alloying region of Example 1 of the present application; Figure 9 A plot of the stability test for Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0019] The present application will be further described in details by specific embodiments, but the embodiments of the present application are not limited thereto. If not specifically indicated, the technical means used in the following embodiments are the conventional means known to those skilled in the art; the experimental methods used are conventional methods; the materials, reagents, etc. used can be obtained from commercial channels.

[0020] General description of the scheme: A high-stability copper sulfide thermoelectric material based on grain boundary alloying, having a general chemical formula of Cu 2-x S-A, A is an alloy of M metal, the addition amount of A metal is 0.5-20 wt%, the M metal is embedded in the Cu2S material, and the M metal is at least one of Y, Sc, Pd, Zn, and Ti.

[0021] A preparation method of a high-stability copper sulfide thermoelectric material based on grain boundary alloying, comprising the following steps: Step (1) Preparation of Cu2S precursor powder: Cu elemental powder and S elemental powder with a purity of 99.99% are put into a planetary ball mill jar, vacuumized, and then argon gas is introduced, repeated three times to ensure that the mixed powder is placed in a protective atmosphere (argon). Subsequently, the mixed powder is placed in a planetary ball mill at a speed of 350-450 rpm for mechanical alloying for 1-3 h, and then Cu2S precursor powder is obtained.

[0022] Step (2) Cu 2-xPreparation of S-A composite material: the Cu2S precursor powder obtained in step (1) and M metal (M is at least one of Y, Sc, Pd, Zn, Ti metal elements, and the purity is 99.99%) are placed in an agate mortar for manual grinding and mixing, the grinding time is 5-20 min, the Cu2S precursor powder is mixed with the M metal, and the addition amount of the M metal is 0.5-20 wt%.

[0023] Step (3) sintering: the Cu2S-M composite powder prepared in step (1) is sintered by a spark plasma sintering method, the sintering temperature is 300-500℃, the sintering time is 5-30 min, and the sintering pressure is 10-50 Mpa, to obtain Cu 2-x S-A-based thermoelectric composite material.

[0024] Examples 1-9 are examples of the present application, and Comparative Example 1 is a comparative example of the present application. The difference between each example and the comparative example lies in the composition of the material, i.e. the preparation process details, which are shown in Table 1: Table 1

[0025] The preparation method of the high-stability copper sulfide thermoelectric material based on grain boundary alloying will be described below by taking Example 1 as an example.

[0026] The preparation method of the high-stability copper sulfide thermoelectric material based on grain boundary alloying comprises the following steps: Step (1) preparation of Cu2S precursor powder: Cu elemental powder and S elemental powder are put into a planetary ball mill jar, and after vacuumizing, argon gas is introduced, and the process is repeated three times to ensure that the mixed powder is placed in a protective atmosphere. Then, the mixed powder is placed in a planetary ball mill and mechanically alloyed at a speed of 400 rpm for 2 h, the weight ratio of the ball and the material during ball milling is 35:1, and the protective atmosphere is 5% H2+95% Ar, and then the Cu2S precursor powder is obtained.

[0027] Step (2) preparation of Cu2S-M composite material: the Cu2S precursor powder obtained in step (1) and M metal (M is Sc) are placed in an agate mortar for manual grinding and mixing, the addition amount of the M metal is 1 wt%, and the grinding time is 15 min, so that the Cu2S precursor powder is mixed with the M metal.

[0028] Step (3) sintering: the Cu2S-M mixed powder prepared in step (1) is sintered by a spark plasma sintering method, the sintering temperature is 500℃, the sintering time is 20 min, and the sintering pressure is 35 Mpa, to obtain a copper sulfide-based thermoelectric composite material.

[0029] Comparative Example 1 Comparative Example 1 uses existing Cu2S thermoelectric material as a comparison.

[0030] Comparative Example 2 Comparative Example 2 differs from Example 1 in that the M metal in Comparative Example 2 is Fe and the amount added is 1%.

[0031] Comparative Example 3 Comparative Example 3 differs from Example 1 in that the amount of M metal added in Comparative Example 3 is 22%.

[0032] Comparative Example 4 Comparative Example 4 differs from Example 1 in that the ball milling time for alloying in Step (1) in Comparative Example 4 is 0.5 h.

[0033] Comparative Example 5 Comparative Example 5 differs from Example 1 in that the ball milling time for alloying in Step (1) in Comparative Example 5 is 3.5 h.

[0034] Comparative Example 6 Comparative Example 6 differs from Example 1 in that the sintering temperature in Step (3) in Comparative Example 6 is 280°C.

[0035] Comparative Example 7 Comparative Example 7 differs from Example 1 in that the sintering temperature in Step (3) in Comparative Example 7 is 520°C.

[0036] Experimental Example 1 SEM (scanning electron microscope) characterization: The copper sulfide-based high-performance thermoelectric material with good stability prepared in Example 1 was observed for micro-morphology using a scanning electron microscope, and the electron micrograph of the thermoelectric material of Example 1 is shown in Figure 1 and Figure 8 . Among them, Figure 1 is the grain boundary alloying diagram of Example 1, Figure 8 is the scanning electron microscope EDS spectrum of the Sc grain boundary alloying region of Example 1.

[0037] Experimental Example 2 XRD (X-ray diffraction) characterization: The copper sulfide-based high-performance thermoelectric material prepared in Example 1 and the thermoelectric material provided in Comparative Example 1 were detected using an X-ray diffractometer, and the X-ray diffraction detection results are shown in Figure 2 . The XRD results show that a polycrystalline bulk material with Cu2S as the main phase can be synthesized by combining the mechanical alloying method and the spark plasma sintering technology, and the phase of the material does not change significantly with the increase of the content of Sc.

[0038] Experimental Example 3 thermoelectric performance characterization The properties of thermoelectric materials are characterized by the dimensionless thermoelectric figure of merit ZT, which is given by the formula ZT = σS. 2 T / κ, where σS 2 κ represents the power factor, T is the absolute temperature, and κ is the thermal conductivity.

[0039] 3.1 Electrical transmission performance The thermoelectric materials provided in Example 1 and Comparative Example 1 were cut into 3*3*10mm cuboids for resistivity, Seebeck coefficient, and power factor testing. The resistivity and Seebeck coefficient testing systems were used for the tests. Taking Example 1 and Comparative Example 1 as examples, the conductivity test results are as follows: Figure 3 As shown, the Seebeck coefficient test results are as follows: Figure 4 As shown, the power factor test results are as follows: Figure 5 As shown in Table 2, the conductivity, Seebeck coefficient, and power factor of the bulk thermoelectric composite materials prepared in Examples 1-9 and the thermoelectric material provided in Comparative Example 1 at 773 K are specifically shown in Table 2.

[0040] 3.2 Thermal conductivity The bulk thermoelectric material prepared in Example 1 and the thermoelectric material provided in Comparative Example 1 were cut into 6*6mm square pieces for thermal conductivity testing, which was performed using a laser thermal conductivity meter. Taking Example 1 and Comparative Example 1 as examples, the test results are as follows: Figure 6 As shown in Table 2, the thermal conductivity of the bulk thermoelectric composite materials prepared in Examples 1-9 and the thermoelectric material provided in Comparative Example 1 at 773 K is specifically shown in Table 2.

[0041] 3.3 ZT value According to the above formula ZT=σS 2 The ZT value can be obtained from the T / κ calculation. Taking Example 1 and the comparative example as examples, the ZT values ​​are as follows: Figure 7 As shown in Table 2, the ZT values ​​of the bulk thermoelectric composite materials prepared in Examples 1-9 and the thermoelectric material provided in Comparative Example 1 at 773 K are shown in Table 2. The results show that the thermoelectric materials prepared in Examples 1-9 of this invention all possess high thermoelectric performance; moreover, the type and amount of M metal have a certain influence on the thermoelectric performance. In addition, the key parameters of alloying and sintering also have a certain impact on the thermoelectric performance of the materials.

[0042] Table 2

[0043] Experiment Example 4: Stability Characterization The bulk thermoelectric material prepared in Example 1 and the thermoelectric material provided in Comparative Example 1 were cut into 3*3*10 mm cuboids for stability testing. Resistance change under varying current density conditions was tested using an electrochemical workstation and a vacuum annealing furnace at 423 K. The results are as follows...Figure 9 Results show that the thermoelectric material of the present application has better stability. Figure 9 Results show that the thermoelectric material of the present application has better stability.

[0044] In summary, the experimental results show that the copper sulfide-based thermoelectric composite material has good thermoelectric performance and good service stability, and all the performances in the actual use process are good.

[0045] The above is only an embodiment of the present application, and the specific technical solutions and / or common knowledge of the scheme are not described in detail. It should be pointed out that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the present application. The protection scope of the present application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A high-stability copper sulfide thermoelectric material based on grain boundary alloying, characterized by: Chemical formula: Cu 2-x S-A, A is an alloy of M metal, the M metal is embedded in the Cu2S material, and the M metal is at least one of Y, Sc, Pd, Zn, and Ti.

2. The high-stability copper sulfide thermoelectric material based on grain boundary alloying according to claim 1, characterized in that: The M metal is added in an amount of 0.5-20 wt%.

3. The high-stability copper sulfide thermoelectric material based on grain boundary alloying of claim 2, wherein: The purity of the M metal is ≥99.99%.

4. The method of claim 1-3, wherein the method is characterized by, The method comprises the following steps: Step (1): Preparation of Cu2S precursor powder: Cu elemental powder and S elemental powder are mixed and ground, and the obtained mixed powder is alloyed to obtain Cu2S precursor powder; Step (2) Cu 2-x Preparation of S-A composite: Cu2S precursor powder is mixed and ground with M metal to obtain Cu2S-M composite powder; Step (3) sintering: sintering the Cu2S-M composite powder to obtain Cu 2-x S-A-based thermoelectric composite material.

5. The method of claim 4, wherein the method further comprises: In step (1), the purity of the Cu elemental powder and the S elemental powder is both ≥99.99%.

6. The method of claim 5, wherein the method further comprises: In step (1), the mixing and grinding is carried out in a protective atmosphere, and the protective atmosphere is argon.

7. The method of claim 6, wherein the method further comprises: In step (1), the alloying is carried out in a ball mill, the ball milling speed is 350-450 rpm, and the alloying time is 1-3 h.

8. The method of claim 7, wherein the method further comprises: In step (2), the mixing and grinding time is 5-20 min.

9. The method of claim 8, wherein the method further comprises: In step (3), the sintering temperature is 300-500 ℃, the sintering time is 5-30 min, and the sintering pressure is 10-50 Mpa.

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