A method for preparing a low-temperature MXene-based in-situ growth CNTs composite material

Abstract

The application belongs to the technical field of new energy material (including ion battery, catalysis, capacitor and the like), and particularly relates to a preparation method of low-temperature MXenes-based in-situ growth CNTs composite material. The method is characterized in that a catalyst is loaded between layers and on the surface of MXenes material, CNTs are in-situ grown between layers of MXenes material under a carbon source atmosphere, and a MXenes / CNT composite material is obtained. By introducing the catalyst, the growth temperature of CNTs is greatly reduced and the CNTs are uniformly distributed. The in-situ growth of CNTs between layers of MXenes increases the layer spacing of MXenes, provides a larger diffusion channel for electrolyte, and improves the specific surface area of the material and provides more electrochemical active sites. The MXenes / CNT composite material prepared by the application has high specific surface area, large layer spacing, higher structural stability, low preparation temperature, adjustable layer spacing and excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy materials (including ion batteries, catalysis, capacitors, etc.), and particularly relates to a preparation method of a low-temperature MXenes-based in-situ growth CNTs (MXenes / CNTs) composite material. BACKGROUND

[0002] With the development of science and technology, people's demand for energy is gradually increasing, but traditional energy is gradually depleted, and existing new energy materials are insufficient to meet the growing energy demand, so it is urgent to develop new energy materials with high specific energy, high catalytic performance and simple manufacturing process.

[0003] Two-dimensional transition metal carbides and nitrides (also known as MXenes) have ultra-high metal conductivity, hydrophilicity, high specific surface area and excellent mechanical properties due to their unique structure and adjustable surface chemistry, which have attracted widespread interest in the fields of battery anode materials, supercapacitors, electrocatalytic materials, etc. However, when the material is not modified, the MXene sheet layer is prone to aggregation and re-stacking, the specific surface area decreases, resulting in a large loss of exposed electrochemical active sites, and affecting the diffusion of electrolyte, greatly limiting its mass specific capacity, mass specific capacitance, and catalytic performance. Al in Ti3AlC2 is etched by HF to prepare a sheet-like MXene, which is simple and easy to implement, but the mass specific capacity of the material is very low.

[0004] In recent years, nano-carbon materials have always been highly researched. Among many carbon materials, carbon nanotubes have attracted widespread research by researchers due to their unique morphology and physical and chemical properties. Carbon nanotubes are a one-dimensional nanometer-sized tubular structure of carbon material, which is curled from a single-layer or multi-layer graphene sheet, and has excellent mechanical, electrical, thermal and other properties. With the increasing demand for excellent functional materials, the unique structure and performance of carbon nanotubes have continuously improved their application value.

[0005] Zhu Jianfeng et al. made Co + adsorbed on the surface of titanium carbide by ion exchange, using titanium carbide as a carrier, cobalt as a catalyst, and urea as a carbon source to prepare a titanium carbide CNTs three-dimensional composite material by a pyrolysis method (patent number CN106783230A), which improves the electrochemical performance of Ti3C2 nanomaterials; but in this invention, CNTs grow unevenly on the surface of Ti3C2, and the effect of expanding the layer of Ti3C2 is not obvious, and Ti3C2 will be oxidized to form TiO2 during calcination. Moreover, the growth temperature of CNTs is high, and the energy consumption is large. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art, and provides a preparation method of a low-temperature MXenes-based in-situ growth CNTs (MXenes / CNTs) composite material; the method uniformly loads catalysts between layers and on the surface of MXenes material through surface complexation, and CNTs are in-situ grown between layers of MXenes material under a carbon source atmosphere, thereby obtaining the MXenes / CNTs composite material; the use of the complexing agent enables the metal catalyst to enter between layers of the MXenes material, realizes uniform distribution of the catalyst on the surface and between layers of the MXenes, and further makes the growth of CNTs more uniform and realizes uniform and controllable growth between layers; meanwhile, the complexing agent makes the metal catalyst and the MXenes substrate more closely combined, improves the catalytic ability, and reduces the growth temperature of CNTs; the reducing gas generated in the decomposition process of the carbon source effectively prevents the oxidation of the MXenes material; CNTs are in-situ grown between layers of the MXenes, thereby increasing the interlayer spacing of the MXenes. The present application provides a larger diffusion channel for the electrolyte, and meanwhile improves the specific surface area of the material and provides more electrochemical active sites. The MXenes / CNTs composite material prepared by the present application has a high specific surface area, a large interlayer spacing, and higher structural stability, and has a low preparation temperature, a controllable interlayer spacing, and excellent electrochemical performance.

[0007] To achieve the above-mentioned purpose, the present application is implemented by the following technical solutions:

[0008] The present application provides a preparation method of a MXenes / CNTs composite material, comprising the following steps:

[0009] S1, adding a MAX phase into an etchant HF, constant temperature stirring, washing, centrifugation, vacuum drying, and obtaining a MXenes substrate material;

[0010] S2, dispersing the MXenes in deionized water, adding a metal salt, heating and stirring to disperse uniformly, and obtaining a mixed solution A;

[0011] S3, adding a complexing agent into the mixed solution A, heating and stirring until the reaction is complete, centrifuging, washing, and vacuum drying to obtain a mixture B, i.e., a MXenes precursor loaded with catalysts;

[0012] S4, adding the mixture B into a tube furnace (and adding a carbon source in front of the sample), calcining, and naturally cooling, thereby obtaining a MXenes / CNTs composite material.

[0013] As an embodiment of the present application, in step S1, the MAX phase includes, but is not limited to, any one or mixture of any combination of Ti3AlC2, Ti4AlN3, Ti3GeC2, Ti2SnC, TiVAlC, Ti2AlN, Ti3AlCN, Ti3SiC2, Ti2AlC, Nb4AlC3, Nb2AlC, VCrAlC, V4AlC3, V2AlC, Mo2Ti2AlC3, Mo2TiAlC2, MoAlB, Mo2Ga2C, Mo3AlC2, ScAl3C3, Cr2AlC, V2PC, V2ZnC, V2GaC, V2GeC, Ti3SnC2, Ti3Al0.5Cu0.5C2, Ti2VAlC2, TiNbAlC, Ta2AlC, Ta4AlC3, Cr2TiAlC2, (Mo 2 / 3Sc 1 / 3 )2AlC, (Mo 2 / 3 Sc 1 / 3 )2AlC, (Mo 2 / 3 Y 1 / 3 )2AlC i , (W 2 / 3 Y 1 / 3 )2AlC i , Mo2Ti2AlC.

[0014] As an embodiment of the present application, in step S1, the mesh number of the MAX phase is 300-500. If the mesh number of the MAX phase is too low, the particle size of the material is too large, which is not conducive to the uniform growth of CNTs between the material layers; if the mesh number is too high, the particle size of the material is too small, and the structure of the composite material is easy to break.

[0015] As an embodiment of the present application, in step S1, the reaction conditions of the MAX phase with HF are: the concentration of HF is 20-50wt%, the reaction environment temperature is 25-50℃, and the reaction time is 24-72h.

[0016] As an embodiment of the present application, in step S1, the dosage ratio of the MAX phase material to HF is 1g:10-15ml.

[0017] As an embodiment of the present application, in step S1, the vacuum drying is carried out at 60-80℃ for 12h-24h. In some embodiments, it is dried at 60℃ for 12h.

[0018] As an embodiment of the present application, in step S2, the metal salt includes, but is not limited to, any one or mixture of any combination of chlorides, nitrates, acetates, sulfates and hydrates of iron, cobalt and nickel.

[0019] As an embodiment of the present application, in step S2, the heating and stirring dispersion is stirred in a water bath at 60-90 DEG C for 2-5 h. In some embodiments, the stirring is for 1-4 h.

[0020] As an embodiment of the present application, the molar ratio of the complexing agent to the metal salt is 1:1-4:1.

[0021] As an embodiment of the present application, in step S2, the complexing agent includes but is not limited to one or more of imidazole, dimethyl imidazole, triformylphloroglucinol, imidazole-4,5-dicarboxylic acid, and C3H4N2.

[0022] As an embodiment of the present application, in step S3, the heating and stirring is stirred in a water bath at 60-100 DEG C for 2-5 h. In some embodiments, the stirring is for 1-4 h. If the water bath temperature is lower than 60 DEG C, the catalyst grows slowly on the substrate surface, the size of the growth is too large, and the catalytic effect is affected.

[0023] As an embodiment of the present application, in step S3, the vacuum drying is performed at 60-80 DEG C for 12-24 h. In some embodiments, the vacuum drying is performed at 60 DEG C for 24 h.

[0024] As an embodiment of the present application, in step S4, the carbon source includes but is not limited to one of monocyamine, dicyandiamide, melamine, urea, thiourea, glucose, etc.

[0025] As an embodiment of the present application, in step S4, the mass ratio of the carbon source to the MXenes precursor loaded with the catalyst is 1:1-5:1.

[0026] As an embodiment of the present application, in step S4, the calcination conditions are: the temperature is 400-580 DEG C, and the time is 1-6 h. In some embodiments, the temperature is 400-550 DEG C, and the time is 3-6 h.

[0027] As an embodiment of the present application, the mass ratio of the etched MAX phase material to the metal salt is 1:1-1:2.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] (1) The present application uses low-temperature catalytic carbon nanotube growth, which has a lower growth temperature than traditional carbon nanotube preparation methods.

[0030] (2) The present application uses a metal catalyst with catalytic activity attached to the surface and interlayer of the two-dimensional material, and the catalyst is uniformly distributed, with excellent catalytic effect.

[0031] (3) The product prepared by the application has excellent and uniform morphology, and the material layer spacing can be controlled by adjusting the preparation conditions. The prepared MXenes / CNTs composite material has good morphology and exhibits excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0032] Other features, objects, and advantages of the application will become more apparent with reference to the following non-limiting examples, when read in conjunction with the accompanying drawings:

[0033] Figure 1 a is a 50000 times SEM image of the MXenes loaded catalyst of the application; b and c are 10000 and 50000 times SEM images of the MXenes / CNTs composite material; d is a TEM image of the MXenes / CNTs composite material;

[0034] Figure 2 is the first charge-discharge curve when the MXenes / CNTs composite material of the application is applied to the negative electrode of a lithium ion battery;

[0035] Figure 3 is the first charge-discharge curve when the MXenes / CNTs composite material of the application is applied to the negative electrode of a sodium ion battery;

[0036] Figure 4 is the first charge-discharge curve when the MXenes / CNTs composite material of the application is applied to the positive electrode of a LiS battery;

[0037] Figure 5 a is a 30000 times SEM image of the Mo3C2 / CNTs composite material in Example 4; b is the first charge-discharge curve when the Mo3C2 / CNTs composite material in Example 4 is applied to the negative electrode of a lithium ion battery;

[0038] Figure 6 a is a 30000 times SEM image of the Nb2C / CNTs composite material in Example 5; b is the first charge-discharge curve when the Nb2C / CNTs composite material in Example 5 is applied to the negative electrode of a lithium ion battery. DETAILED DESCRIPTION

[0039] The application will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that for those skilled in the art, without departing from the concept of the application, a number of adjustments and improvements can be made. These all belong to the protection scope of the application.

[0040] Example 1

[0041] Step 1: 3 g of Ti3AlC2 phase was added into 30 ml of etchant HF (40 wt%), stirred in a constant temperature water bath at 35℃ for 24 h, centrifuged and washed, and vacuum dried at 60℃ for 12 h to obtain Ti3C2 base material.

[0042] Step 2: 1 g of Ti3C2 was dispersed in deionized water, 1.2 g of nickel acetate tetrahydrate was added, and the mixture was stirred at 70℃ for 4 h to obtain a homogeneous solution A.

[0043] Step 3: 1.58 g of dimethyl imidazole was added to the mixed solution A, and the mixture was stirred at 70℃ for 4 h, centrifuged, and vacuum dried at 60℃ for 24 h to obtain a mixture B.

[0044] Step 4: The mixture B was added to a tube furnace, 2 g of melamine was added to the front end, and the mixture was calcined at 550℃ for 4 h under nitrogen atmosphere, and then naturally cooled to obtain a MXenes / CNTs composite material. Figure 1 a is a 50000 times SEM image of the MXenes loaded catalyst of the application; b and c are 10000 times and 50000 times SEM images of the MXenes / CNTs composite material, respectively; d is a TEM image of the MXenes / CNTs composite material.

[0045] Step 5: The composite material prepared above was subjected to electrochemical performance test, and the specific test process was as follows: a slurry prepared from MXenes / CNTs composite material: conductive carbon: PVDF, 8:1:1 was uniformly coated on a copper foil to prepare an electrode sheet, the electrode sheet was used as a research electrode, a pure lithium sheet was used as an auxiliary electrode, a Celgard 2400 type separator was selected, and an electrolyte was 1 mol / L LiPF6. The assembly was carried out in an argon atmosphere glove box. The test results are shown in Figure 2 At a current density of 100 mA / g, the initial charge specific capacity reached 368 mAh / g, and the charge-discharge efficiency was 63.7%.

[0046] Example 2

[0047] This example is a variation of Example 1, and the only difference is that the MXenes / CNTs composite electrode material prepared above is applied in a LiS battery. The specific process is as follows: a slurry prepared from MXenes / CNT composite material: conductive carbon: PVDF, 8:1:1 is uniformly coated on a copper foil to prepare an electrode sheet, the electrode sheet is used as a research electrode, a pure Na sheet is used as an auxiliary electrode, a glass fiber separator is selected, and an electrolyte is 1 mol / L NaPF6. The assembly was carried out in an argon atmosphere glove box. The test results are shown in Figure 3 At a current density of 100 mA / g, the initial charge specific capacity reached 163.3 mAh / g, and the charge-discharge efficiency was 48.1%.

[0048] Example 3

[0049] This example is a variation of Example 1, the only change being that the MXenes / CNTs composite electrode material prepared above is applied in a sodium ion battery. The specific process is as follows: a slurry prepared from MXenes / CNTs composite material:sulfur powder:conductive carbon:PVDF, 2:6:1:1, is uniformly coated on carbon cloth to make an electrode sheet, which is used as the research electrode, a pure Li sheet is used as the auxiliary electrode, a Celgard 2400 type separator is selected, and an electrolyte is 1 mol / L LiPF6. The assembly is carried out in an argon glove box. The test results are shown in Figure 4 The initial charge specific capacity reaches 1251 mAh / g at a current density of 100 mA / g, and the charge-discharge efficiency is 94.8%.

[0050] Example 4

[0051] This example is a variation of Example 1, the only change being that Ti3AlC2 in step 1 above is changed to Mo3AlC2, and the four hydrates of nickel acetate in step 2 are changed to four hydrates of cobalt acetate, and melamine is replaced with thiourea in step 4.

[0052] The specific process is as follows:

[0053] Step 1: 3g Mo3AlC2 is added to 30ml etchant HF(50wt%), stirred in a constant temperature water bath at 55°C for 48h, centrifuged and washed, and vacuum dried at 60°C for 12h to obtain Mo3C2 base material.

[0054] Step 2: 1g Mo3C2 is dispersed in deionized water, 1.2g of four hydrates of cobalt acetate is added, and the mixture is heated and stirred at 70°C for 4h to obtain a uniform dispersion to obtain a mixed solution A.

[0055] Step 3: 1.58g of dimethyl imidazole is added to the mixed solution A, heated and stirred at 70°C for 4h, centrifuged and washed, and vacuum dried at 60°C for 24h to obtain a mixture B.

[0056] Step 4: The mixture B is added to a tube furnace, 2g of thiourea is added to the front end, and calcination is carried out at 550°C for 4h under a nitrogen atmosphere, and the natural cooling is carried out to obtain a Mo3C2 / CNTs composite material. Figure 5 The test results are shown in Figure 5 The initial charge specific capacity reaches 354 mAh / g at a current density of 100 mA / g, and the charge-discharge efficiency is 75.5%.

[0057] Example 5

[0058] This example is a variation of Example 1, the only difference is that the Ti3AlC2 in step 1 is replaced by Nb2AlC, the nickel acetate tetrahydrate in step 2 is replaced by iron acetate tetrahydrate, and the melamine in step 4 is replaced by urea. The specific process is as follows:

[0059] Step 1: 3g of Nb2AlC was added to 30ml of etchant HF (50wt%), stirred in a constant temperature water bath at 55℃ for 48h, centrifuged and washed, and vacuum dried at 60℃ for 12h to obtain the Nb2C base material.

[0060] Step 2: 1g of Nb2C was dispersed in deionized water, 1.47g of iron acetate tetrahydrate was added, and the mixture was heated and stirred at 70℃ for 4h to obtain a homogeneous solution A.

[0061] Step 3: 1.58g of dimethylimidazole was added to the mixed solution A, heated and stirred at 70℃ for 4h, centrifuged and washed, and vacuum dried at 60℃ for 24h to obtain a mixture B.

[0062] Step 4: The mixture B was added to a tube furnace, 2gn of urea was added to the front end, and calcined at 550℃ for 4h under nitrogen atmosphere, and naturally cooled to obtain the Nb2C / CNTs composite material. Figure 6 The SEM image of the Nb2C / CNTs composite material of the present application is shown in Figure 3. The test results are shown in Table 1. Figure 6 As shown in Figure b, the first charge specific capacity reached 291mAh / g at a current density of 100mA / g, and the charge-discharge efficiency was 63%.

[0063] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or changes within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. A method for preparing MXenes / CNTs material, characterized in that, The method comprises the following steps: S1, adding MAX phase into etchant HF, constant temperature stirring, washing, centrifugation, vacuum drying, to obtain MXenes base material; S2, dispersing MXenes in deionized water, adding metal salt, heating and stirring to disperse uniformly to obtain mixed solution A; the mass ratio of etched MAX phase material and metal salt is 1:1-1:2; S3, adding complexing agent to mixed solution A, heating and stirring until reaction is complete, centrifugation, washing, vacuum drying to obtain mixture B, i.e. MXenes precursor loaded with catalyst; the complexing agent is one or several of imidazole, dimethyl imidazole, triformylphloroglucinol, imidazole-4,5-dicarboxylic acid; the heating and stirring is water bath stirring at 60-90℃ for 2-5h; S4, adding mixture B to a tube furnace, adding carbon source, calcining, natural cooling, to obtain MXenes / CNTs composite material; the calcining conditions are: temperature is 400-580℃, time is 2-6h.

2. The method of claim 1, wherein the MXenes / CNTs material is prepared by the steps of: Any one or mixture of any combination of Ti3AlC2, Ti4AlN3, Ti3GeC2, Ti2SnC, TiVAlC, Ti2AlN, Ti3AlCN, Ti3SiC2, Ti2AlC, Nb4AlC3, Nb2AlC, VCrAlC, V4AlC3, V2AlC, Mo2Ti2AlC3, Mo2TiAlC2, MoAlB, Mo2Ga2C, Mo3AlC2, ScAl3C3, Cr2AlC, V2PC, V2ZnC, V2GaC, V2GeC, Ti3SnC2, Ti3Al0.5Cu0.5C2, Ti2VAlC2, TiNbAlC, Ta2AlC, Ta4AlC3, Cr2TiAlC2, (Mo 2 / 3 Sc 1 / 3 )2AlC, (W 2 / 3 Sc 1 / 3 )2AlC, Mo2Ti2AlC in step S1; the mesh number of the MAX phase is 300-500 mesh.

3. The method of claim 1, wherein the MXenes / CNTs material is prepared by the steps of: In step S1, the reaction conditions of MAX phase and HF are: HF concentration is 20-50wt%, reaction environment temperature is 25-50℃, reaction time is 24-72h.

4. The method of claim 1, wherein the MXenes / CNTs material is prepared by the steps of: In step S2, the metal salt includes any one or any combination of mixture of chloride, nitrate, acetate, sulfate and hydrate of iron, cobalt and nickel.

5. The method of claim 1, wherein the MXenes / CNTs material is prepared by the steps of: In step S2, the heating and stirring dispersion is water bath stirring at 60-90℃ for 2-5h.

6. The method of claim 1, wherein the MXenes / CNTs material is prepared by the method comprising: In step S4, the carbon source includes one or several of monocyane, dicyane, melamine, cyanuric acid, urea, thiourea, glucose.

7. The method of claim 1, wherein the MXenes / CNTs material is prepared by the steps of: The molar ratio of complexing agent to metal salt is 1:1-4:1; the mass ratio of carbon source to MXenes precursor loaded with catalyst is 1:1-5:1.

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