High-performance n-type PbS-based medium-entropy thermoelectric material and preparation method thereof

Abstract

The invention belongs to the technical field of energy materials, relates to a thermoelectric material, and particularly provides a high-performance n-type PbS-based medium-entropy thermoelectric material and a preparation method thereof, which are used for solving the problem of poor thermoelectric performance of a PbS-based material in the practical application process of the thermoelectric field. The medium-entropy thermoelectric material PbS (1-x) Sex-yTey is obtained by performing solid solution on a designed amount of Se element and Te element in a PbS-based material, x is more than or equal to 0.48 and less than or equal to 0.5, y is more than or equal to 0.15 and less than or equal to 0.25, and the thermal conductivity of the PbS-based material is effectively reduced; the preparation method comprises the following steps: preparing a medium-entropy thermoelectric material PbS (1-x) Sex-yTey, performing gap doping on the medium-entropy thermoelectric material PbS (1-x) Sex-yTey with a designed amount of Cu element to optimize the carrier concentration, and finally obtaining the high-performance n-type PbS-based medium-entropy thermoelectric material, the room-temperature ZT value and the average ZT value of the material are up to 0.53 and 1.08 respectively, and the material has excellent thermoelectric performance; meanwhile, the high-performance n-type PbS-based medium-entropy thermoelectric material has the obvious advantage of low cost, and wide application of the thermoelectric technology is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy materials, relates to thermoelectric materials, and specifically provides a high-performance n-type PbS-based medium-entropy thermoelectric material and a preparation method thereof. Background Art

[0002] With the increasingly serious energy crisis and environmental pollution problems, the development of clean energy and the improvement of energy utilization efficiency have become the focus of global attention; thermoelectric conversion technology includes thermoelectric power generation technology and thermoelectric refrigeration technology, which have significant characteristics such as being green and pollution-free. Thermoelectric devices made of thermoelectric materials can directly realize the mutual conversion of thermal energy and electrical energy, and have important applications in the fields of aerospace, new energy, electronic communication, etc.; thus, the development of high-performance thermoelectric materials is conducive to promoting the wide application of thermoelectric technology.

[0003] Traditional high-performance thermoelectric materials are represented by Bi2Te3-based alloys and PbTe-based materials. However, due to the scarcity of Te element, the prices of Bi2Te3-based alloys and PbTe-based materials are high, which greatly limits the large-scale application of thermoelectric technology. As a homologous compound of PbTe, PbS has the same NaCl-type crystal structure and intrinsically has a high carrier mobility and electrical conductivity; moreover, due to the rich reserves and low price of S element, the production cost of PbS is lower; at the same time, the higher melting point of PbS makes its chemical stability stronger and also has higher mechanical properties; however, the intrinsically high thermal conductivity and low carrier concentration characteristics of PbS materials result in poor thermoelectric performance, which seriously restricts the practical application of PbS-based materials in the thermoelectric field. Therefore, the research on high-performance PbS-based thermoelectric materials has become the focus of the present invention. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-performance n-type PbS-based medium-entropy thermoelectric material and a preparation method thereof, so as to solve the problem of poor thermoelectric performance existing in the practical application process of PbS-based materials in the thermoelectric field; the present invention first solid-solves a designed amount of Se element and Te element in the PbS-based material to obtain a medium-entropy thermoelectric material PbS 1-x Se x-y Te y , 0.48 ≤ x ≤ 0.5, 0.15 ≤ y ≤ 0.25, effectively reducing the thermal conductivity of the PbS-based material; then, on the basis of the medium-entropy thermoelectric material PbS 1-x Se x-y Te y , interstitial doping of a designed amount of Cu element is carried out to optimize the carrier concentration of the medium-entropy thermoelectric material PbS 1-x Se x-y Te y , and finally a high-performance n-type PbS-based medium-entropy thermoelectric material is obtained. The room-temperature ZT value and average ZT value (ZTave The values are as high as 0.53 and 1.08 respectively in the range of 300K - 773K), showing excellent thermoelectric performance. At the same time, due to the low cost of PbS-based materials, Se element, and Cu element, and the low solid solubility of Te element (especially compared with Bi2Te3-based alloys and PbTe-based materials), the high-performance n-type PbS-based medium-entropy thermoelectric material in the present invention has an obvious low-cost advantage, which is conducive to promoting the wide application of thermoelectric technology.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A high-performance n-type PbS-based medium-entropy thermoelectric material, characterized in that the chemical formula of the high-performance n-type PbS-based medium-entropy thermoelectric material is: PbS 1-x Se x-y Te y -z%Cu, 0.48 ≤ x ≤ 0.5, 0.15 ≤ y ≤ 0.25, 0 < z ≤ 1.4; wherein, Se and Te are dissolved in the PbS-based material to form the medium-entropy thermoelectric material PbS 1-x Se x-y Te y ; The medium-entropy thermoelectric material PbS 1- x Se x-y Te y is doped with Cu in the interstitial position to form the high-performance n-type PbS-based medium-entropy thermoelectric material.

[0007] Preferably, in the high-performance n-type PbS-based medium-entropy thermoelectric material, the solid solubility of Se is: x = 0.5.

[0008] Preferably, in the high-performance n-type PbS-based medium-entropy thermoelectric material, the solid solubility of Te is: y = 0.15.

[0009] Preferably, in the high-performance n-type PbS-based medium-entropy thermoelectric material, the doping amount of Cu is: 0.3 ≤ z ≤ 1.2.

[0010] More preferably, the chemical formula of the high-performance n-type PbS-based medium-entropy thermoelectric material is: PbS 0.5 Se 0.35 Te 0.15 -1%Cu.

[0011] Furthermore, the present invention provides a preparation method of the high-performance n-type PbS-based medium-entropy thermoelectric material, including the following steps:

[0012] Step 1, Mix the Pb, S, Se, Te raw materials and the Cu raw material according to PbS 1-x Se x-y Te yWeigh the raw materials with an atomic stoichiometric ratio of -z% Cu to obtain a mixed material;

[0013] Step 2: Place the mixed material in a vacuum quartz tube, seal it by flame, and keep it at a temperature of 1100 ± 50 °C for at least 6 h for a melting reaction, and then cool it to room temperature with the furnace to obtain a precursor;

[0014] Step 3: Grind the precursor into powder, load it into a mold, and perform vacuum hot pressing sintering treatment to obtain an ingot;

[0015] Step 4: Place the ingot in a vacuum quartz tube, seal it by flame, keep it at a temperature of 500 ± 50 °C for at least 6 h, and then cool it with the furnace for annealing treatment to obtain a high-performance n-type PbS-based medium-entropy thermoelectric material.

[0016] Preferably, in step 1, the elemental mass purity of the Pb, S, Se, and Te raw materials is greater than 99.999%, and the purity of the Cu raw material is greater than 99.99%.

[0017] Preferably, in step 2, the temperature control program for the melting reaction is: raise the temperature to 1100 ± 50 °C within 15 h - 30 h.

[0018] Preferably, in step 3, the specific process of the vacuum hot pressing sintering treatment is: maintain it at a pressure of 40 MPa - 50 Mpa and a temperature of 500 ± 50 °C for at least 5 minutes.

[0019] Preferably, in step 4, the temperature control program for the annealing treatment is: raise the temperature to 500 ± 50 °C within 5 h - 10 h.

[0020] Preferably, in steps 2 and 4, the vacuum degree in the vacuum quartz tube is less than 10 -3 Pa.

[0021] Based on the above technical solutions, the beneficial effects of the present invention are as follows:

[0022] The present invention provides a high-performance n-type PbS-based medium-entropy thermoelectric material and a preparation method thereof, having the following advantages:

[0023] 1) It has excellent thermoelectric performance. The ZT value at room temperature can reach 0.53, the maximum ZT value can reach 1.44, and the average ZT value (ZT ave value) in the temperature range of 300 K - 773 K is as high as 1.08, which is the material with the highest ZT ave value reported for n-type PbS-based thermoelectric materials at present; moreover, the medium-entropy strategy and the interstitial doping strategy significantly improve the thermoelectric performance of PbS in the medium and low temperature regions;

[0024] 2) It has the advantage of low raw material cost. Compared with Bi2Te3-based alloys and PbTe-based materials, the content of Te element in the n-type PbS-based medium-entropy thermoelectric material of the present invention is reduced by at least 75%, which can significantly reduce the manufacturing cost of the material;

[0025] 3) It has the advantage of low manufacturing cost. The n-type PbS-based medium-entropy thermoelectric material in the present invention is a polycrystalline PbS-based thermoelectric material, which has a short preparation cycle, a simple preparation process, and good repeatability, and is conducive to large-scale production;

[0026] 4) It has the advantage of high mechanical strength. Compared with Bi2Te3-based alloys and PbTe-based materials, the n-type PbS-based medium-entropy thermoelectric material in the present invention has higher mechanical strength (hardness and Young's modulus), which is convenient for processing;

[0027] In summary, the present invention provides a high-performance n-type PbS-based medium-entropy thermoelectric material and a preparation method thereof, which is conducive to promoting the wide application of thermoelectric technology. Brief Description of the Drawings

[0028] Figure 1 It is a comparison chart of the crustal abundances and prices of Te, Se, and S elements.

[0029] Figure 2 It is a comparison chart of the mechanical properties of PbQ (Q = Te, Se, and S).

[0030] Figure 3 It is a comparison chart of the thermoelectric properties of existing n-type PbS-based thermoelectric materials.

[0031] Figure 4 It is a schematic diagram of the working principle of the high-performance n-type PbS-based medium-entropy thermoelectric material in the present invention.

[0032] Figure 5 It is a schematic diagram of the preparation process of the high-performance n-type PbS-based medium-entropy thermoelectric material in the present invention.

[0033] Figure 6 It is a test result chart of the medium-entropy matrix prepared in the embodiment of the present invention.

[0034] Figure 7 It is a test result chart of the thermoelectric properties of the high-performance n-type PbS-based medium-entropy thermoelectric material prepared in the embodiment of the present invention.

[0035] Figure 8 It is a performance comparison chart of the high-performance n-type PbS-based medium-entropy thermoelectric material prepared in the embodiment of the present invention and the existing n-type PbS-based thermoelectric materials. Detailed Embodiments

[0036] To better clarify the objectives, technical solutions, and beneficial effects of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. However, the present invention is not limited solely to the following embodiments.

[0037] The present invention provides a high-performance n-type PbS-based medium-entropy thermoelectric material. The chemical formula of the high-performance n-type PbS-based medium-entropy thermoelectric material is: PbS 1-x Se x-y Te y -z% Cu, 0.48 ≤ x ≤ 0.5, 0.15 ≤ y ≤ 0.25, 0 < z ≤ 1.4; wherein, Se and Te are dissolved in the PbS-based material to form the medium-entropy thermoelectric material PbS 1-x Se x-y Te y ; the medium-entropy thermoelectric material PbS 1-x Se x- y Te y is doped with Cu in the interstitial sites to form the high-performance n-type PbS-based medium-entropy thermoelectric material; it should be noted additionally that: the doping amount z% of Cu represents the molar percentage of Cu in the medium-entropy thermoelectric material PbS 1-x Se x-y Te y .

[0038] In terms of the working principle:

[0039] As Figure 1 shows the crustal abundances and prices of Te, Se, and S elements. It can be seen from the figure that the S element has the highest crustal abundance and the lowest price. Therefore, the PbS-based material has an obvious cost advantage; as Figure 2 shows the mechanical properties of PbQ (Q = Te, Se, and S), including the hardness and Young's modulus of the medium-temperature thermoelectric materials PbTe, PbSe, and PbS. It can be seen from the figure that PbS has the highest hardness and Young's modulus, that is, it has stronger mechanical properties; as Figure 3 shows the thermoelectric properties of the currently existing n-type PbS-based thermoelectric materials. It can be seen from the figure that, under the optimization of various strategies, the n-type PbS-based thermoelectric materials have made breakthrough progress. However, the average ZT value in the temperature range of 300K - 773K is still relatively low, which greatly limits the wide application of the n-type PbS-based thermoelectric materials.

[0040] Excellent thermoelectric materials should have high electrical transport performance to maintain high-speed electron transport and low thermal conductivity to maintain a large temperature difference. On the one hand, intrinsic PbS has a relatively high thermal conductivity. To address this issue, the present invention adopts an entropy-increasing strategy, that is, increasing the microstrain and disorder degree of the PbS matrix, effectively enhancing phonon scattering, and thereby significantly reducing the thermal conductivity of the material. Since S, Se, and Te are elements in the same main group and have a high solubility in each other, especially Se. Therefore, the present invention first solid-solves a designed amount of Se and Te in the PbS matrix to obtain PbS 1-x Se x-y Te y , which gradually increases the microstrain and entropy value of the PbS matrix, significantly reducing its thermal conductivity, and obtaining a medium-entropy thermoelectric material PbS 1-x Se x-y Te y , where 0.48 ≤ x ≤ 0.5 and 0.15 ≤ y ≤ 0.25. On the other hand, intrinsic PbS has a relatively low carrier concentration. Therefore, on the basis of PbS 1-x Se x-y Te y with low thermal conductivity, the present invention further optimizes its carrier concentration by using Cu interstitial doping to obtain PbS 1-x Se x-y Te y -z%Cu; The interstitial formation energy of Cu in Pb-rich PbS (Cu i ) is the lowest, and it is easier to enter the lattice interstitial sites of PbS to form interstitial Cu ions (Cu + ), providing additional free electrons for the substrate and optimizing the carrier concentration. At the same time, the interstitial Cu is prone to aggregation to form clusters or dislocation arrays, further hindering phonon transport, which is also beneficial to reducing the thermal conductivity, as Figure 7 shown;

[0041] In summary, the present invention provides the above-mentioned high-performance n-type PbS-based medium-entropy thermoelectric material. The room-temperature ZT value and average ZT value (ZT ave , 300K - 773K) of this material are as high as 0.53 and 1.08 respectively, showing excellent thermoelectric performance.

[0042] Based on the above technical solutions, the present invention provides 18 examples, namely Example 1 to Example 18 in sequence. Among them, the solid-solution amount x of Se, the solid-solution amount y of Te, and the doping amount z of Cu are shown in Table 1:

[0043] Table 1

[0044]

[0045]

[0046] The preparation process of the high-performance n-type PbS-based medium-entropy thermoelectric materials in Embodiments 1 to 18 is as follows Figure 5 and specifically includes the following steps:

[0047] Step 1: Weigh Pb blocks, S powders, Se grains, Te blocks with element mass purity greater than 99.999% and Cu wires with purity greater than 99.99% according to the atomic stoichiometric ratio of PbS 1-x Se x-y Te y -z% Cu to obtain a mixed material;

[0048] Step 2: Place the mixed material obtained in Step 1 into a flat-bottomed quartz tube with an inner diameter of 17 mm, then evacuate the quartz tube, with the vacuum degree less than 10 -3 Pa, seal the quartz tube with a flame, and then place it in a high-temperature muffle furnace for a melting reaction. As shown in (a) in Figure 5 , the melting reaction is shown;

[0049] The temperature control program of the high-temperature muffle furnace is: heat up to 1100 °C in 20 h, keep it warm for 10 h, and then cool it to room temperature with the furnace to obtain a polycrystalline n-type PbS-based thermoelectric material precursor;

[0050] Step 3: Grind the n-type PbS-based thermoelectric material ingot obtained in Step 2 into powder with an agate mortar, load it into a graphite mold (with a diameter of 15 mm) lined with carbon paper, and place the graphite mold in a vacuum hot press for sintering treatment. As shown in (b) in Figure 5 , the vacuum hot press is shown;

[0051] The pressure and temperature control program of the vacuum hot press are: first increase the pressure to 883 Kg (50 MPa), start the temperature program after 2 min, heat up to 500 °C, ensure to maintain for 5 min under the conditions of a pressure of 883 Kg and a temperature of 500 °C. After the program ends, the sample is cooled to room temperature with the furnace to obtain a dense disc-shaped sample ingot with a diameter of 15 mm and a height of 10 mm - 13 mm;

[0052] Step 4: Place the dense disc-shaped sample ingot obtained in Step 3 into a flat-bottomed quartz tube with a vacuum degree less than 10 -3 Pa again, seal it with a flame, and perform annealing treatment in a high-temperature muffle furnace. As shown in (c) in Figure 5 , the annealing treatment is shown;

[0053] The temperature control program of the high-temperature muffle furnace is: heat up to 500 °C in 5 h, keep it warm for 20 h, and then the sample is cooled to room temperature with the furnace to obtain a high-performance n-type PbS-based medium-entropy thermoelectric material.

[0054] Taking Embodiment 10, Embodiment 11, and Embodiment 12 as examples, the beneficial effects of the present invention will be described in detail in combination with tests. Other embodiments have similar excellent thermoelectric properties.

[0055] To more clearly illustrate the working principle of the present invention, in the case where the doping amount z of Cu is 0, a medium-entropy thermoelectric material PbS 0.5 Se 0.5-y Te y sample is prepared under the same preparation process, which is the medium-entropy matrix, y = 0.15, 0.2, 0.25; the sample ingot is cut into the size required for thermoelectric testing using a low-speed cutting machine, and then the samples for electrical and thermal performance testing are polished with sandpaper; among them, the sample required for electrical performance testing is a cuboid with a size of 3 mm × 3 mm × 10 mm, and the sample required for thermal performance testing is a square sheet with a size of 6 mm × 6 mm × 1.5 mm.

[0056] The samples are tested for thermal performance and phase analysis using a laser thermal conductivity meter and an X-ray diffractometer, including: thermal diffusivity D (the total thermal conductivity can be calculated according to the formula κ tot = ρC p D), and the lattice thermal conductivity can be calculated according to κ lat = κ tot - κ ele (κ ele is the electronic thermal conductivity) and the powder XRD pattern. The test temperature range of the material is: room temperature (300 K) to 500 °C (773 K), and the obtained results are as Figure 6 shown, Figure 6 in which (a) is the entropy ΔS and lattice thermal conductivity κ 0.5 Se 0.5-y Te y of PbS lat at room temperature as a function of y, Figure 6 in which (b) is the powder XRD pattern of PbS 0.5 Se 0.5-y Te y , Figure 6 in which (c) is the curve of the lattice thermal conductivity κ 0.5 Se 0.5-y Te y of PbS lat as a function of temperature; it can be seen from the figure that after solid solution of Se and Te, the entropy gradually increases with the increase of y content. When y ≥ 0.15, the materials are all medium-entropy materials, and the room-temperature lattice thermal conductivity gradually decreases with the increase of y content.

[0057] Furthermore, the thermoelectric properties of the annealed Cu-doped samples prepared in Example 10, Example 11, and Example 12 were tested using a Seebeck and resistivity test system and a laser thermal conductivity meter, including: electrical conductivity σ, Seebeck coefficient S, and thermal diffusivity D. The results are as Figure 7 shown. The operating temperature range of the material is: room temperature to 500 °C (773 K), and its average ZT value is obtained by calculating the thermoelectric parameters over the entire temperature range; Figure 7 in (a) is the curve of electrical conductivity σ versus temperature, Figure 7 in (b) is the curve of Seebeck coefficient S versus temperature, Figure 7 in (c) is the curve of power factor PF versus temperature, Figure 7 in (d) is the total thermal conductivity κ tot versus temperature, Figure 7 in (e) is the lattice thermal conductivity κ lat versus temperature, Figure 7 in (f) is the curve of dimensionless thermoelectric figure of merit (ZT value) versus temperature; as can be seen from the figure, by introducing Cu interstitial doping, additional electrons are released in the medium-entropy material PbS 0.5 Se 0.5-y Te y to increase the electron carrier concentration, thereby significantly enhancing the electrical conductivity of the n-type PbS-based medium-entropy thermoelectric material (PbS 0.5 Se 0.35 Te 0.15 -z% Cu); moreover, due to the optimization of the electron carrier concentration, the n-type PbS-based medium-entropy thermoelectric material (PbS 0.5 Se 0.35 Te 0.15 -z% Cu) exhibits excellent power factor PF over the entire temperature range.

[0058] Combined with the medium-entropy matrix constructed in the examples, it exacerbates the microstrain and disorder (i.e., entropy increase) of the material, enhancing phonon scattering and thus achieving an extremely low lattice thermal conductivity; further, using Cu interstitial doping to further optimize the carrier concentration of the medium-entropy matrix, interstitial Cu ions (Cu + ) provide additional free electrons for the matrix, and the Cu at the interstitial sites is prone to aggregation to form clusters or dislocation arrangements, further hindering phonon transmission and also contributing to reducing the thermal conductivity; finally, the room-temperature ZT value of n-type PbS 0.5 Se 0.35 Te 0.15 -1% Cu reaches 0.53, and the maximum ZT value reaches 1.44.

[0059] Furthermore, the high-performance n-type PbS-based medium-entropy thermoelectric material prepared in Example 11 (n-type polycrystalline PbS 0.5 Se0.35 Te 0.15 (-1% Cu) was compared with existing n-type PbS-based thermoelectric materials in terms of performance, and the results are as Figure 8 shown, Figure 8 where (a) is the ratio of weighted mobility to lattice thermal conductivity (μ W / κ lat ), Figure 8 where (b) is the ZT value at variable temperature, Figure 8 where (c) is the average ZT value (ZT ave ); from ZT = S 2 σT / κ tot , it can be seen that in the process of optimizing thermoelectric performance, it is inevitable to be limited by the coupling effect between electrons and phonons. Therefore, the improvement of the thermoelectric performance of materials is a decoupling process among multiple parameters; the n-type polycrystalline PbS 0.5 Se 0.35 Te 0.15 -1% Cu medium-entropy thermoelectric material prepared in this invention has the highest μ W / κ lat ratio in the temperature range of 300K - 773K, even higher than that of the reported high-performance single-crystal PbS-based thermoelectric materials; obviously, the highest μ W / κ lat ratio means that this invention has achieved the coordinated regulation among multiple parameters and decoupled the complex electro-acoustic relationship to the greatest extent; therefore, it shows significant performance advantages in the temperature range of 300K - 773K, and the ZT ave value is as high as 1.08.

[0060] In summary, the high-performance n-type PbS-based medium-entropy thermoelectric material provided by this invention has higher cost performance and application potential, and at the same time has the advantages of low cost, strong mechanical properties, easy processing, etc. Moreover, the preparation process is simple and has good repeatability, which is conducive to large-scale use; the prepared n-type PbS 0.5 Se 0.35 Te 0.15 -1% Cu medium-entropy thermoelectric material can reach a ZT value of 0.53 at room temperature, the maximum ZT value can reach 1.44, and the ZT ave value in the temperature range of 300K - 773K is as high as 1.08, which is the material with the highest ZT ave value among the reported n-type PbS-based thermoelectric materials, and can be widely applied to thermoelectric conversion devices and realize large-scale production and development.

[0061] The above is only the specific implementation manner of this invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the disclosed features, or all the steps in any method or process, except for the mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A high-performance n-type PbS-based medium-entropy thermoelectric material, characterized in that: The chemical formula of the high-performance n-type PbS-based medium-entropy thermoelectric material is: PbS 1-x Se x-y Te y -z%Cu, 0.48≤x≤0.5, 0.15≤y≤0.25, 0<z≤1.4; Se and Te are dissolved in the PbS-based material to form the medium-entropy thermoelectric material PbS 1-x Se x-y Te y ; The medium entropy thermoelectric material PbS 1-x Se x- y Te y The mid-gap is doped with Cu to form the high-performance n-type PbS-based medium-entropy thermoelectric material.

2. The high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 1, characterized in that: In the high-performance n-type PbS-based medium-entropy thermoelectric material, the solid solution amount of Se is: x=0.

5.

3. The high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 1, characterized in that: In the high-performance n-type PbS-based medium-entropy thermoelectric material, the solid solution amount of Te is: y=0.

15.

4. The high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 1, characterized in that: In the high-performance n-type PbS-based medium-entropy thermoelectric material, the doping amount of Cu is: 0.3≤z≤1.

2.

5. The high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 1, characterized in that: The chemical formula of the high-performance n-type PbS-based medium-entropy thermoelectric material is: PbS 0.5 Se 0.35 Te 0.15 -1% Cu.

6. The method for preparing a high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 1, characterized in that: The following steps are involved: Step 1: Pb, S, Se, Te and Cu raw materials are mixed according to PbS 1-x Se x-y Te y -z%Cu atomic stoichiometric ratio to obtain a mixed material; Step 2, placing the mixed material in a vacuum quartz tube, sealing it with a flame, keeping it at a temperature of 1100±50° C. for at least 6 hours for a melting reaction, and then cooling it to room temperature with the furnace to obtain a precursor; Step 3, grinding the precursor into powder, putting it into a mold and performing vacuum hot pressing sintering to obtain an ingot; Step 4: Place the ingot in a vacuum quartz tube, seal it with a flame, keep it warm at 500±50°C for at least 6 hours, and then anneal it while cooling it in the furnace to obtain a high-performance n-type PbS-based medium-entropy thermoelectric material. Preferably, in step 1, the elemental mass purity of the Pb, S, Se and Te raw materials is greater than 99.999%, and the purity of the Cu raw material is greater than 99.99%.

7. The method for preparing a high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 6, characterized in that: In step 2, the temperature control program of the melting reaction is: raising the temperature to 1100±50°C within 15h-30h.

8. The method for preparing a high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 6, characterized in that: In step 3, the specific process of the vacuum hot pressing sintering treatment is: maintaining the pressure of 40MPa-50MPa and the temperature of 500±50°C for at least 5 minutes.

9. The method for preparing a high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 6, characterized in that: In step 4, the temperature control program of the annealing treatment is: raising the temperature to 500±50°C within 5h-10h.

10. The method for preparing a high-performance n-type PbS-based medium-entropy thermoelectric material according to claim 6, characterized in that: In step 2 and step 4, the vacuum degree in the vacuum quartz tube is less than 10 -3 Pa.

Images