N-type CNT thermoelectric material and preparation method thereof

Abstract

The invention relates to the technical field of thermoelectric materials, in particular to an n-type CNT thermoelectric material and a preparation method thereof. The preparation method of the n-type CNT thermoelectric material comprises the following steps: adding a non-polar dopant and an ionic liquid into an organic solvent according to a molar ratio, and stirring to obtain a doped solution; carrying out dipping treatment on CNT by using the doping solution to obtain the CNT subjected to dipping treatment; and carrying out drying treatment on the CNT subjected to the dipping treatment to obtain the n-type CNT thermoelectric material. According to the method, the n-type CNT thermoelectric material with excellent air stability, excellent bending stability, high conductivity, high Seebeck coefficient and high power factor can be prepared; the method is simple to operate and short in preparation period, and can be widely popularized and applied.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, and in particular to an n-type CNT thermoelectric material and a preparation method thereof. Background Art

[0002] Thermoelectric devices are functional devices that can realize the mutual conversion of heat energy and electrical energy. They are mainly used in the fields of thermoelectric power generation and thermoelectric cooling / heating. Thermoelectric materials used in thermoelectric devices are environmentally friendly and have broad application prospects. The thermoelectric performance of thermoelectric materials can be determined by the thermoelectric figure of merit ZT (ZT = σS 2 T / κ, where σ is conductivity, S is the Seebeck coefficient, T is temperature, and κ is conductivity) or power factor PF (PF = σS 2 , where σ is the electrical conductivity and S is the Seebeck coefficient), so high-performance thermoelectric materials need to have high electrical conductivity and high Seebeck coefficient.

[0003] In recent years, carbon nanotubes (CNTs) have garnered widespread attention in the field of thermoelectric materials due to their high flexibility and electrical conductivity. CNT thermoelectric materials are categorized into two types, n-type and p-type, depending on the type of charge carrier in the thermoelectric material. The preparation of p-type CNT thermoelectric materials is straightforward and requires almost no additional processing. This is because CNTs absorb oxygen and moisture from the air, resulting in defects in their conjugated structure, causing pure CNTs to exhibit p-type thermoelectric properties at room temperature. However, the preparation of n-type CNT thermoelectric materials is more complex and typically requires doping.

[0004] Currently, in order to achieve the transformation of CNTs from p-type to n-type, existing n-type doping methods generally utilize n-type dopants to dope CNTs to prepare n-type CNT thermoelectric materials. Reported n-type dopants include alkali metal dopants (High PerformaNce N-Type CarboN NaNotube Field-Effect Transistors with Chemically Doped CoNtacts, NaNo letters, 2005, 5, 345-348.), non-ionic organic dopants (Systematic CoNversioN of SiNgle Walled CarboN NaNotubes iNto N-type Thermoelectric Materials by Molecular DopaNts, Scientific reports, 2013, 3, 3344.), and ionic dopants (Air-stable fabric thermoelectric modules made of N-aNd P-type carboNNaNotubes, ENergy & ENviroNmental Science, 2012, 5, 9481-9486.). However, these n-type dopants will inevitably produce Coulomb bound ion pairs during the charge or hydride transfer process with the host (CNT) during the doping process, that is, the n-type dopant counterions compensate for the negative charge of the host (CNT), resulting in the prepared n-type CNT thermoelectric materials having low electrical conductivity and low Seebeck coefficient.

[0005] Therefore, developing an n-type doping method that can simultaneously improve the electrical conductivity and Seebeck coefficient of CNT thermoelectric materials is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The present invention provides a method for preparing an n-type CNT thermoelectric material. By this method, an n-type CNT thermoelectric material with excellent air stability, excellent bending stability, high electrical conductivity, high Seebeck coefficient and high power factor can be prepared; the method is simple to operate, has a short preparation cycle, and can be widely promoted and applied.

[0007] The present invention also provides an n-type CNT thermoelectric material, which is prepared by the above-mentioned preparation method. Therefore, the n-type CNT thermoelectric material has the advantages of excellent air stability, excellent bending stability, high electrical conductivity, high Seebeck coefficient and high power factor.

[0008] In a first aspect, the present invention provides a method for preparing an n-type CNT thermoelectric material, comprising the following steps:

[0009] Adding a non-polar dopant and an ionic liquid into an organic solvent in a molar ratio, and stirring to obtain a doping solution;

[0010] impregnating the CNTs with the doping solution to obtain impregnated CNTs;

[0011] The CNTs after the impregnation treatment are dried to obtain an n-type CNT thermoelectric material.

[0012] In the above-mentioned method for preparing the n-type CNT thermoelectric material, the molar ratio includes: the molar ratio of the non-polar dopant to the ionic liquid is (1-3):1.

[0013] In the preparation method of the n-type CNT thermoelectric material as described above, the non-polar dopant is at least one of triphenyl phosphate, 1,3-bis(diphenylphosphino)propane, diethylenetriamine, polyethyleneimine, and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole.

[0014] In the above-mentioned method for preparing the n-type CNT thermoelectric material, the ionic liquid is at least one of 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium chloride.

[0015] The method for preparing the n-type CNT thermoelectric material as described above, wherein the organic solvent comprises dimethyl sulfoxide;

[0016] In the doping solution, the molar concentration of the non-polar dopant is 0.1-0.3 mol / L.

[0017] In the above-mentioned method for preparing the n-type CNT thermoelectric material, the temperature during the immersion treatment is 25-30° C. and the time is 1-24 hours.

[0018] In the above-mentioned method for preparing the n-type CNT thermoelectric material, the stirring process is performed at a temperature of 25-30° C. and for a time of 30-45 minutes.

[0019] In the above-mentioned method for preparing the n-type CNT thermoelectric material, the drying process is performed at a temperature of 60-70° C. and for a time of 1-3 hours.

[0020] As described above, the preparation method of n-type CNT thermoelectric material, the CNT includes single-walled, double-walled or multi-walled CNT films, fibers or yarns prepared by any one of chemical vapor deposition, floating gas phase catalysis, arc discharge or laser evaporation methods, or films, fibers or yarns obtained by mixing any proportion of these three different types of CNTs.

[0021] In a second aspect, the present invention provides an n-type CNT thermoelectric material, which is prepared by the above-mentioned method for preparing the n-type CNT thermoelectric material.

[0022] The solution of the present invention has at least the following effects:

[0023] The present invention provides a method for preparing an n-type CNT thermoelectric material. The present invention uses a doping solution containing a non-polar dopant and an ionic liquid to impregnate CNTs, and utilizes the dipole constructed by the ionic liquid on the CNT surface to optimize the doping level of the non-polar dopant on the CNT, thereby preparing an n-type CNT thermoelectric material with excellent air stability, excellent bending stability, high electrical conductivity, high Seebeck coefficient and high power factor. The method is simple to operate, has a short preparation cycle, and can be widely promoted and applied.

[0024] The n-type CNT thermoelectric material provided by the present invention has the advantages of excellent air stability, excellent bending stability, high electrical conductivity, high Seebeck coefficient and high power factor, and has broad application prospects in the fields of thermoelectrics, smart wearables, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 Schematic diagram of the principle of preparing n-type CNT thermoelectric material in Example 1 of the present invention;

[0027] Figure 2 Raman spectra of the CNT film (pristine carbon nanotubes) of the present invention, the n-type CNT thermoelectric material (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole + 1-ethyl-3-methylimidazolium acetate / carbon nanotubes) in Example 1, the n-type CNT thermoelectric material (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole / carbon nanotubes) in Comparative Example 2, and the n-type CNT thermoelectric material (1-ethyl-3-methylimidazolium acetate / carbon nanotubes) in Comparative Example 3;

[0028] Figure 3 The bending stability test results of the n-type CNT thermoelectric material in Example 1 of the present invention;

[0029] Figure 4 This is the air stability test result of the n-type CNT thermoelectric material in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0031] If no specific techniques or conditions are specified in the examples of the present invention, the techniques or conditions described in the literature in the field or the product instructions shall be followed. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0032] In the present invention, the term "at least one" refers to one or more, and "more than one" refers to two or more.

[0033] In the present invention, CNT refers to carbon nanotubes.

[0034] In a first aspect, the present invention provides a method for preparing an n-type CNT thermoelectric material, comprising the following steps:

[0035] Adding a non-polar dopant and an ionic liquid into an organic solvent in a molar ratio, and stirring to obtain a doping solution;

[0036] impregnating the CNTs with a doping solution to obtain impregnated CNTs;

[0037] The CNTs after the impregnation treatment are dried to obtain an n-type CNT thermoelectric material.

[0038] The present invention does not particularly limit the specific equipment for the above-mentioned drying process. In some embodiments, the CNTs after the immersion process can be placed in a vacuum drying oven for drying.

[0039] The object of the present invention is to prepare n-type CNT thermoelectric materials. Specifically, the present invention first adds a non-polar dopant and an ionic liquid into an organic solvent in a molar ratio to obtain a mixture solution, and then stirs the mixture solution to obtain a doping solution. The stirring treatment is to make the non-polar dopant and the ionic liquid fully mixed and dissolved in the organic solvent, thereby improving the uniformity of CNT doping during the subsequent impregnation treatment; then, the CNT is impregnated with the doping solution to obtain impregnated CNTs. The impregnation treatment is to make the CNT surface uniformly adsorbed by the non-polar dopant and the ionic liquid. The non-polar dopant and ionic liquid themselves have a relatively high Fermi level, and electrons spontaneously flow from the dopant and ionic liquid into the CNT, causing the CNT to be doped into an n-type CNT thermoelectric material; finally, the CNT after the impregnation treatment is dried to obtain an n-type CNT thermoelectric material with excellent air stability, excellent bending stability, high electrical conductivity, high Seebeck coefficient and high power factor. The organic solvent is evaporated through the drying treatment, so that the non-polar dopant and ionic liquid are tightly attached to the CNT surface, achieving sufficient and uniform n-type doping; the method is simple to operate, has a short preparation cycle, and can be widely promoted and applied.

[0040] In a specific embodiment, the above molar ratio includes: the molar ratio of the non-polar dopant to the ionic liquid is (1-3):1, for example, the molar ratio of the non-polar dopant to the ionic liquid is 1:1, 2:1 or 3:1.

[0041] When the molar ratio of the non-polar dopant to the ionic liquid is within the above range, in addition to transferring its own electrons to the CNT, the dipole constructed by the ionic liquid on the CNT surface also causes more electrons in the non-polar dopant to be transferred to the CNT. When the molar ratio of the non-polar dopant to the ionic liquid is (1-3):1, the dipole strength constructed by the ionic liquid on the CNT surface reaches a balance with the amount of the non-polar dopant, promoting electron transfer with optimal efficiency.

[0042] In a specific embodiment, the non-polar dopant is at least one of triphenyl phosphate, 1,3-bis(diphenylphosphino)propane, diethylenetriamine, polyethyleneimine, and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole, preferably at least one of 1,3-bis(diphenylphosphino)propane and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole, and further preferably 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole.

[0043] When the above substances are used as non-polar dopants, the non-polar dopants have better compatibility with CNTs, more stable doping, reduced interface defects and polarity contamination, and are conducive to the preparation of n-type CNT thermoelectric materials with excellent air stability, excellent bending stability, high electrical conductivity, high Seebeck coefficient and high power factor.

[0044] In a specific embodiment, the ionic liquid is at least one of 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium chloride, and is preferably 1-ethyl-3-methylimidazolium acetate.

[0045] When the above substances are used as ionic liquids, the ionic liquids dissolve in organic solvents to produce anions and cations. The adsorption of anions on CNTs is stronger than that of cations. Anions are locked on the CNT surface by electrostatic action, and then cations are fixed on the CNT surface covered with anions by Coulomb force, thereby establishing an interface dipole pointing outward from the CNT on the surface, which has the effect of promoting the transfer of more electrons to the CNT.

[0046] In one embodiment, the organic solvent includes dimethyl sulfoxide.

[0047] When dimethyl sulfoxide is used as the organic solvent, dimethyl sulfoxide can dissolve the non-polar dopant and the ionic liquid, and helps the non-polar dopant and the ionic liquid to be uniformly dispersed and permeate the CNT network.

[0048] In a specific embodiment, in the doping solution, the molar concentration of the non-polar dopant is 0.1-0.3 mol / L.

[0049] When the molar concentration parameter of the non-polar dopant in the doping solution is within the above range, the non-polar dopant can be fully dissolved by the organic solvent, so that the non-polar dopant and the ionic liquid can enter the CNT more quickly.

[0050] For example, in the doping solution, the molar concentration of the non-polar dopant may be in the range of any one of 0.1 mol / L, 0.2 mol / L, and 0.3 mol / L, or any two of the above.

[0051] In a specific embodiment, during the above-mentioned immersion treatment, the temperature is 25-30° C. and the time is 1-24 h.

[0052] When the temperature and time parameters during the impregnation process are within the aforementioned ranges, the doping solution remains liquid. When the temperature is too low, the doping solution is prone to crystallization. The impregnation time affects the immersion depth. If the treatment time is too short (less than 1 hour), the doping solution does not fully penetrate the CNTs. Extending the doping time until the CNTs are fully impregnated results in n-type CNT thermoelectric materials with excellent air stability, excellent bending stability, high electrical conductivity, high Seebeck coefficient, and high power factor. However, once the CNTs are fully impregnated, further extension of the impregnation time becomes meaningless.

[0053] For example, during the immersion treatment, the temperature may be in the range of any one or any two of 25°C, 26°C, 27°C, 28°C, 29°C, and 30°C;

[0054] The time can be any one of 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, and 24 hours, or a range consisting of any two of them.

[0055] Furthermore, during the immersion treatment, the time may preferably be 1-3 hours.

[0056] In a specific embodiment, during the above stirring treatment, the temperature is 25-30° C. and the time is 30-45 minutes.

[0057] When the temperature and time parameters during the stirring process are respectively within the above ranges, the non-polar dopant and the ionic liquid are fully mixed and dissolved in the organic solvent to obtain a completely mixed and uniform doping solution.

[0058] For example, during the stirring process, the temperature may be in the range of any one or any two of 25°C, 26°C, 27°C, 28°C, 29°C, and 30°C;

[0059] The time may be a range consisting of any one of 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, 40 min, 41 min, 42 min, 43 min, 44 min, and 45 min, or any two of them.

[0060] In a specific embodiment, during the above drying process, the temperature is 60-70° C. and the time is 1-3 hours.

[0061] When the temperature and time parameters of the drying process are within the above ranges, the organic solvent in the immersed CNTs evaporates, allowing the non-polar dopant and the ionic liquid to adhere tightly to the CNT surface, achieving sufficient and uniform n-type doping.

[0062] Illustratively, during the drying process, the temperature may be in the range of any one or any two of 60° C., 61° C., 62° C., 63° C., 64° C., 65° C., 66° C., 67° C., 68° C., 69° C., and 70° C.;

[0063] The time can be any one of 1 hour, 2 hours, 3 hours, or a range consisting of any two of them.

[0064] The present invention does not impose any particular limitation on the specific type of CNTs. In one embodiment, the CNTs include single-walled, double-walled, or multi-walled CNT films, fibers, or yarns produced by any of chemical vapor deposition, floating gas-phase catalytic methods, arc discharge, or laser evaporation methods, or films, fibers, or yarns obtained by mixing any proportion of these three different types of CNTs. Furthermore, multi-walled CNT films produced by floating gas-phase catalytic methods are preferred.

[0065] In a second aspect, the present invention provides an n-type CNT thermoelectric material, prepared by the above-mentioned method for preparing an n-type CNT thermoelectric material. The present invention involves impregnating CNTs with a doping solution containing a non-polar dopant and an ionic liquid, followed by drying to obtain the n-type CNT thermoelectric material. This n-type CNT thermoelectric material exhibits excellent air stability, excellent bending stability, high electrical conductivity, a high Seebeck coefficient, and a high power factor, and has broad application prospects in thermoelectrics, smart wearables, and other fields.

[0066] The present invention is described in detail through the following examples and comparative examples.

[0067] Example 1

[0068] Figure 1 Schematic diagram of the principle of preparing n-type CNT thermoelectric material in Example 1 of the present invention, as shown in FIG. Figure 1 As shown, the method for preparing the n-type CNT thermoelectric material provided in this embodiment includes the following steps:

[0069] 1) adding 0.003 mol of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole (N-DMBI) and 0.001 mol of 1-ethyl-3-methylimidazolium acetate ([EMIM]OAC) to 10 mL of dimethyl sulfoxide to obtain a mixture solution, stirring the mixture solution at 25° C. for 30 minutes to obtain a doping solution, wherein the molar concentration of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole in the doping solution is 0.3 mol / L, and the molar concentration of 1-ethyl-3-methylimidazolium acetate is 0.1 mol / L;

[0070] 2) impregnating a multi-walled carbon nanotube film (raw carbon nanotube, CNT) prepared by a floating gas phase catalytic method with a doping solution for 3 hours at a temperature of 30° C. to obtain impregnated CNTs;

[0071] 3) The impregnated CNTs were placed in a vacuum drying oven at 60° C. for 2 h to obtain an n-type CNT thermoelectric material.

[0072] Combine Figure 1 The principle of preparing the above n-type CNT thermoelectric material is explained;

[0073] When ionic liquids are dissolved in organic solvents, anions (OAC - ) and cations (EMIM + ), when the anion size of the ionic liquid (1-ethyl-3-methylimidazolium acetate) is small, due to its higher degree of freedom, the adsorption effect between the anions in the ionic liquid and the CNT is stronger than that of the cations. The anions are locked to the CNT surface by electrostatic interaction, and then the cations are fixed to the CNT surface covered with anions by Coulombic force, thereby establishing an interface dipole pointing outward from the CNT surface. This directional dipole causes the vacuum energy level to shift downward by a distance equal to the size of the dipole. Due to the downward shift of the vacuum energy level, the electron injection barrier is reduced, which facilitates the transfer of electrons from N-DMBI to CNT, realizing dipole-assisted doping transfer and achieving a breakthrough in the dipole-assisted N-DMBI doping limit. Therefore, the doping level can be controlled without changing N-DMBI, effectively avoiding the uncontrollable and unpredictable effects of the additional introduction of dopant counterions on carrier transport. In addition, the dipole pointing outward from the CNT surface reduces the electron injection barrier, which can improve the doping level while avoiding adverse effects on carrier transport.

[0074] Example 2

[0075] The preparation method of the n-type CNT thermoelectric material provided in this embodiment is basically the same as that in Example 1, except that:

[0076] The immersion treatment for 3 hours was replaced by the immersion treatment for 1 hour.

[0077] Comparative Example 1

[0078] The preparation method of the n-type CNT thermoelectric material provided in this comparative example is basically the same as that in Example 1, except that:

[0079] 1) 0.001 mol of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole and 0.003 mol of 1-ethyl-3-methylimidazolium acetate were added to 10 mL of dimethyl sulfoxide to obtain a mixture solution. The mixture solution was stirred at 25° C. for 30 minutes to obtain a doping solution. The molar concentration of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole in the doping solution was 0.1 mol / L, and the molar concentration of 1-ethyl-3-methylimidazolium acetate was 0.3 mol / L.

[0080] Comparative Example 2 (without adding 1-ethyl-3-methylimidazole acetate)

[0081] The preparation method of the n-type CNT thermoelectric material provided in this comparative example is basically the same as that in Example 1, except that:

[0082] 1) 0.003 mol of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole was added to 10 mL of dimethyl sulfoxide to obtain a solution, and the solution was stirred at 25° C. for 30 minutes to obtain a doping solution. The molar concentration of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole in the doping solution was 0.3 mol / L.

[0083] Comparative Example 3 (without addition of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole)

[0084] The preparation method of the n-type CNT thermoelectric material provided in this comparative example is basically the same as that in Example 1, except that:

[0085] 1) 0.001 mol of 1-ethyl-3-methylimidazolium acetate was added to 10 mL of dimethyl sulfoxide to obtain a solution, and the solution was stirred at 25° C. for 30 minutes to obtain a doping solution. The molar concentration of 1-ethyl-3-methylimidazolium acetate in the doping solution was 0.1 mol / L.

[0086] Performance Testing

[0087] 1. Raman spectroscopy was used to analyze the structures of the multi-walled carbon nanotube film of the present invention (original carbon nanotubes), the n-type CNT thermoelectric material (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole + 1-ethyl-3-methylimidazolium acetate / carbon nanotubes) in Example 1, the n-type CNT thermoelectric material (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole / carbon nanotubes) in Comparative Example 2, and the n-type CNT thermoelectric material (1-ethyl-3-methylimidazolium acetate / carbon nanotubes) in Comparative Example 3. The results are as follows: Figure 2 As shown;

[0088] Raman spectroscopy was used to analyze the structures of the multi-walled carbon nanotube film (original carbon nanotube) of the present invention, the n-type CNT thermoelectric material (1,3-bis(diphenylphosphino)propane+1-ethyl-3-methylimidazolium acetate / carbon nanotube) in Example 1, the n-type CNT thermoelectric material (1,3-bis(diphenylphosphino)propane / carbon nanotube) in Comparative Example 2, and the n-type CNT thermoelectric material (1-ethyl-3-methylimidazolium acetate / carbon nanotube) in Comparative Example 3. The results are as follows: Figure 3 shown.

[0089] Depend on Figure 2 It can be seen that after co-doping with 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole and 1-ethyl-3-methylimidazolium acetate, the shift of the G peak to high wavenumber increases most significantly. It can be seen that the degree of electron transfer to CNTs is the highest when 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole and 1-ethyl-3-methylimidazolium acetate are co-doped. This shows that the method of the present invention has achieved n-type doping of CNTs when the dopant is 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole and the ionic liquid is 1-ethyl-3-methylimidazolium acetate, greatly improving the degree of electron transfer to CNTs and improving the doping efficiency.

[0090] 2. The following tests were performed on the n-type CNT thermoelectric materials in Examples 1-2 and Comparative Examples 1-3 of the present invention, respectively. The test results are shown in Table 1.

[0091] Seebeck coefficient (μV K -1 ): Seebeck coefficient is measured using a self-built Seebeck test system based on the slope method according to the formula S = -ΔV / ΔT, where S is the Seebeck coefficient, ΔV is the potential difference, and ΔT is the temperature difference. ΔV is generated by eight ΔT measurements recorded by a Keithley 2182A.

[0092] Conductivity (S cm -1 ):The conductivity is tested using the four-probe conductivity test method;

[0093] Power factor (μW m -1 K -2 ):Power factor is based on the formula PF=σS 2 Calculated, where PF is the power factor, σ is the conductivity, and S is the Seebeck coefficient.

[0094] Table 1 Test results

[0095]

[0096]

[0097] As shown in Table 1, the n-type CNT thermoelectric material provided by the embodiment of the present invention has a high Seebeck coefficient (up to -77.45 μV K -1 ), high conductivity (up to 1150.73S cm -1 ) and high power factor (up to 691.43μWm -1 K -2 ). Comparing Example 1 with Comparative Example 1, it was found that when the molar ratio of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole and 1-ethyl-3-methylimidazolium acetate was 3:1, the prepared n-type CNT thermoelectric material had the advantages of high Seebeck coefficient, high electrical conductivity and high power factor. Comparing Example 1 with Comparative Examples 1-2, it was found that when 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole or 1-ethyl-3-methylimidazolium acetate was not added, the Seebeck coefficient, electrical conductivity and power factor of the prepared n-type CNT thermoelectric material were all reduced, indicating that the method provided by the embodiment of the present invention can effectively improve the Seebeck coefficient, electrical conductivity and power factor of the material.

[0098] 3. The bending stability test of the n-type CNT thermoelectric material in Example 1 of the present invention was carried out: the n-type CNT thermoelectric material in Example 1 of the present invention was bent 10,000 times (each bending angle was 180°) and then the Seebeck coefficient (S), conductivity (σ) and power factor (PF) were tested respectively. The results are as follows: Figure 3 As shown; Figure 3 In the figure, the vertical axis S / S0 refers to the Seebeck coefficient change rate of the n-type CNT thermoelectric material. S / S0 is calculated by the following formula: S / S0 = (S x -S0) / S0, where subscript 0 is the initial value and subscript x is the value after bending 10,000 times; the vertical axis σ / σ0 refers to the conductivity change rate of the n-type CNT thermoelectric material, and σ / σ0 is calculated by the following formula: σ / σ0=(σ x -σ0) / σ0, where subscript 0 is the initial value and subscript x is the value after bending 10,000 times; the test methods of Seebeck coefficient (S), conductivity (σ) and power factor (PF) are the same as above.

[0099] Depend on Figure 3 It can be seen that after the n-type CNT thermoelectric material in Example 1 of the present invention is bent 10,000 times, its Seebeck coefficient (S), conductivity (σ) and power factor (PF) do not decrease, indicating that the n-type CNT thermoelectric material prepared by the method provided in the embodiment of the present invention has excellent bending stability.

[0100] 4. Air stability test of the n-type CNT thermoelectric material in Example 1 of the present invention: The n-type CNT thermoelectric material in Example 1 of the present invention was exposed to air for 90 days, and the Seebeck coefficient change rate and the conductivity change rate were tested to characterize its air stability. The results are as follows: Figure 4 As shown; Figure 4 In the figure, the vertical axis S / S0 refers to the Seebeck coefficient change rate of the n-type CNT thermoelectric material. S / S0 is calculated by the following formula: S / S0 = (S x -S0) / S0, where subscript 0 is the initial value and subscript x is the value after exposure to air for different time periods; the vertical axis σ / σ0 refers to the conductivity change rate of the n-type CNT thermoelectric material, and σ / σ0 is calculated using the following formula: σ / σ0=(σ x -σ0) / σ0, where subscript 0 is the initial value and subscript x is the value after exposure to air for different time periods; the test methods for Seebeck coefficient (S), conductivity (σ) and power factor (PF) are the same as those described above.

[0101] Depend on Figure 4 It can be seen that after the n-type CNT thermoelectric material prepared by the method provided in the embodiment of the present invention is exposed to air for 90 days, the Seebeck coefficient of the n-type CNT thermoelectric material can still be maintained at 95.6%, and the electrical conductivity can still be maintained at 96.5%, indicating that the n-type CNT thermoelectric material prepared by the method provided in the embodiment of the present invention has excellent air stability.

[0102] In summary, the method provided by the embodiment of the present invention can be used to prepare n-type carbon nanotube (CNT) thermoelectric materials with excellent air stability, excellent bending stability, high electrical conductivity, high Seebeck coefficient and high power factor.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an n-type CNT thermoelectric material, characterized in that: The following steps are involved: Adding a non-polar dopant and an ionic liquid into an organic solvent in a molar ratio, and stirring to obtain a doping solution; impregnating the CNTs with the doping solution to obtain impregnated CNTs; The CNTs after the impregnation treatment are dried to obtain an n-type CNT thermoelectric material.

2. The method for preparing an n-type CNT thermoelectric material according to claim 1, characterized in that: The molar ratio includes: the molar ratio of the non-polar dopant to the ionic liquid is (1-3):

1.

3. The method for preparing an n-type CNT thermoelectric material according to claim 2, wherein: The non-polar dopant is at least one of triphenyl phosphate, 1,3-bis(diphenylphosphino)propane, diethylenetriamine, polyethyleneimine, and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole.

4. The method for preparing an n-type CNT thermoelectric material according to claim 2, wherein: The ionic liquid is at least one of 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium chloride.

5. The method for preparing an n-type CNT thermoelectric material according to claim 2, wherein: The organic solvent includes dimethyl sulfoxide; In the doping solution, the molar concentration of the non-polar dopant is 0.1-0.3 mol / L.

6. The method for preparing an n-type CNT thermoelectric material according to claim 1, wherein: During the immersion treatment, the temperature is 25-30° C. and the time is 1-24 hours.

7. The method for preparing an n-type CNT thermoelectric material according to claim 1, characterized in that: During the stirring treatment, the temperature is 25-30° C. and the time is 30-45 minutes.

8. The method for preparing an n-type CNT thermoelectric material according to claim 1, wherein: During the drying process, the temperature is 60-70° C. and the time is 1-3 hours.

9. The method for preparing an n-type CNT thermoelectric material according to claim 1, wherein: The CNTs include single-walled, double-walled or multi-walled CNT films, fibers or yarns prepared by any one of chemical vapor deposition, floating gas phase catalysis, arc discharge or laser evaporation methods, or films, fibers or yarns obtained by mixing any proportion of these three different types of CNTs.

10. An n-type CNT thermoelectric material, characterized in that: The n-type CNT thermoelectric material is prepared by the preparation method of any one of claims 1 to 9.

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