A nitrogen-doped amorphous carbon material, a preparation method and application thereof

Abstract

The application discloses a nitrogen-doped amorphous carbon material and a preparation method and application thereof. The preparation method comprises the following steps: adding a catalyst into a pyrrole solution to make the pyrrole undergo a polymerization reaction, separating the obtained product and drying to obtain polypyrrole; placing the polypyrrole in a protective atmosphere to perform pre-carbonization treatment, and obtaining a pre-carbonization material; and placing the pre-carbonization material in an ammonia atmosphere to perform high-temperature carbonization, and obtaining the nitrogen-doped amorphous carbon material. The regulation strategy can effectively regulate the atomic configuration of the polypyrrole in the carbonization process, and form a structure more favorable to sodium ion adsorption and storage. Compared with the prior art, the nitrogen-doped amorphous carbon material prepared by the application has super-high initial coulomb efficiency, super-long cycle life and excellent rate performance when used as a negative electrode of a sodium ion battery, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon materials, in particular to a nitrogen-doped amorphous carbon material and a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries are considered as an ideal electrochemical energy storage system due to high energy density, abundant raw materials and low cost, and are expected to be widely used in low-speed electric vehicles and large-scale energy storage. The negative electrode material, as one of the core components of sodium-ion batteries, directly affects the electrochemical performance of the battery. Compared with the low-cost graphite negative electrode used in the mature lithium-ion battery, the selection of the negative electrode material for sodium-ion batteries is still in its infancy, mainly because sodium ions and graphite cannot form stable intercalation compounds, so graphite cannot be directly used as the negative electrode material for sodium-ion batteries. Therefore, it is urgent to find a negative electrode material with excellent comprehensive performance to further improve the energy density of sodium-ion batteries.

[0003] As the main category of carbon-based materials, amorphous carbon materials have low sodium storage potential, moderate sodium storage capacity, small volume change after sodium intercalation, good cycle performance, and the best comprehensive performance among many candidates. In addition, from the perspective of raw materials, amorphous carbon precursors are widely available and easy to prepare, making them the most likely material to be first industrialized in the field of sodium-ion battery negative electrode materials. However, amorphous carbon materials prepared from biomass carbon materials and coal, pitch and other fossil raw materials usually face the problems of low initial coulombic efficiency and low capacity, which affect their practical application. Further research is needed to find amorphous carbon materials with higher electrochemical performance for industrialization. SUMMARY

[0004] To overcome the deficiencies in the prior art, the present application provides a nitrogen-doped amorphous carbon material and a preparation method and application thereof. The present application uses polypyrrole as a carbon source precursor, and by adjusting the atomic configuration of the carbon source precursor during carbonization, a crystal structure more conducive to sodium ion adsorption and storage is formed. Compared with the prior art, the nitrogen-doped amorphous carbon material prepared by the present application exhibits ultra-high initial coulombic efficiency, ultra-long cycle life and excellent rate performance when used as a negative electrode for sodium-ion batteries, and has good application prospects.

[0005] To achieve the above-mentioned purposes, the technical solution adopted by the present application is as follows:

[0006] The first object of the present application is to provide a preparation method of a nitrogen-doped amorphous carbon material, comprising the following steps:

[0007] A catalyst is added to the pyrrole solution to cause polymerization of the pyrrole, and the resulting product is separated and dried to obtain polypyrrole; preferably, the catalyst is ammonium persulfate solution.

[0008] The polypyrrole is pre-carbonized in a protective atmosphere to obtain a pre-carbonized material; preferably, the pre-carbonization temperature is 300-400℃, and the pre-carbonization time is 1-3h; the pre-carbonization temperature rising rate is 1-5℃ / min.

[0009] The pre-carbonized material is high-temperature carbonized in an ammonia atmosphere to obtain a nitrogen-doped amorphous carbon material. Preferably, the high-temperature carbonization temperature is 400-800℃, and the high-temperature carbonization time is 1-3h; the high-temperature carbonization temperature rising rate is 2-5℃ / min; the ammonia flow rate is 10-200mL / min.

[0010] The second object of the present application is to provide a nitrogen-doped amorphous carbon material prepared by the preparation method as described in the first object.

[0011] The third object of the present application is to provide the application of the nitrogen-doped amorphous carbon material as described in the second object as a negative electrode material in a sodium ion battery.

[0012] The present application has the following beneficial effects:

[0013] Compared with the prior art, the synthesis method provided by the present application is simple, does not require complex equipment and expensive raw materials, and uses nitrogen-rich pyrrole as a raw material, which is beneficial to the formation of more nitrogen-doped carbon in the subsequent carbonization process. During the low-temperature pre-carbonization process, the polypyrrole as a carbon source precursor mainly undergoes pyrolysis reaction, in which process CO2, CH4 and other gases are generated and overflowed, forming a large number of pores. The product after pre-carbonization needs to be further high-temperature carbonized, by adjusting the gas flow rate and temperature rising rate in the high-temperature carbonization process, the carbon layer spacing is reduced, the open pores left by the gas overflow are gradually closed, and sufficient time is provided for carbon atom recombination, thereby improving the first coulombic efficiency of the material.

[0014] The present application adjusts the carbonization temperature to control the amount of nitrogen atom doping to change the structural defects of the polymer-based carbon material, and provides more active sites. Specifically, a large number of pyridine nitrogens are formed in the sample after the ammonia treatment process, thereby inducing additional defects and sodium storage sites, at the same time, high-temperature conditions will be more conducive to the change of the electronic structure of the carbon skeleton, bringing more edge defect sites, which is helpful to the enrichment of pyridine nitrogen. In addition, in this process, ammonia is used as the final heat treatment atmosphere, which is beneficial to the formation of NH 4+ into the amorphous carbon material, forming NH 4+ -N, which is beneficial to achieving high slope capacity. The amorphous carbon material obtained on this basis not only has high first charge-discharge coulombic efficiency, charge-discharge capacity and cycle life, but also exhibits more excellent rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to make the objectives, technical solutions and beneficial effects of the present application clearer, the present application is described below with the help of the following drawings:

[0016] Figure 1 is an XRD pattern of the product obtained in Example 1 of the present application;

[0017] Figure 2 is an SEM pattern of the product obtained in Example 1 of the present application;

[0018] Figure 3 is a TEM pattern of the product obtained in Example 1 of the present application;

[0019] Figure 4 is an N1s high-resolution XPS fitting spectrum of the product obtained in Example 1 of the present application;

[0020] Figure 5 is a first three circle constant current charge-discharge curve of the battery assembled with the product obtained in Example 1 of the present application;

[0021] Figure 6 is a cycle curve of the battery assembled with the product obtained in Example 1 of the present application;

[0022] Figure 7 is a rate performance curve of the battery assembled with the product obtained in Example 1 of the present application;

[0023] Figure 8 is a TEM pattern of the product obtained in the comparative example of the present application;

[0024] Figure 9 is a first three circle constant current charge-discharge curve of the battery assembled with the product obtained in the comparative example of the present application;

[0025] Figure 10 is a cycle curve of the battery assembled with the product obtained in the comparative example of the present application;

[0026] Figure 11 is a rate performance curve of the battery assembled with the product obtained in the comparative example of the present application. DETAILED DESCRIPTION

[0027] The preferred embodiments of the present application will be described in detail below with the help of examples. The described examples are only a part of the embodiments of the present application, but not all the embodiments. The scope of the present application should not be interpreted as being limited to the examples described below. All the other embodiments obtained by those skilled in the art without creative efforts based on the examples in the present application are within the scope of protection of the present application.

[0028] Example 1

[0029] A preparation method of a nitrogen-doped amorphous carbon material, comprising the following steps:

[0030] Step 1: ammonium persulfate powder was dissolved in deionized water to prepare a 0.1 mmol / L ammonium persulfate solution; 1.2 mL of pyrrole solution was dissolved in 30 mL of water, and then 60 mL of ammonium persulfate solution was added dropwise, stirred at room temperature for 4 h, and the product was separated and dried to obtain polypyrrole, i.e. the preparation of the carbon source precursor was completed;

[0031] Step 2: the polypyrrole in step 1 was placed in an argon atmosphere, heated to 300℃ at a heating rate of 1℃ / min and kept for 2 hours for pre-carbonization treatment;

[0032] Step 3: the material after pre-carbonization treatment was placed in an ammonia atmosphere, heated to 700℃ at a heating rate of 2℃ / min and kept for 3 hours, the ammonia flow rate was 150 mL / min, high-temperature carbonization was completed, and a nitrogen-doped amorphous carbon material was obtained, denoted as N@AC-700.

[0033] Referring to Figure 1 , Figure 1 is the XRD pattern of the product obtained in Example 1 of the present application, and two severely broadened diffraction peaks appear near 24° and 43°, corresponding to the (002) and (101) diffraction planes of amorphous carbon, respectively.

[0034] Referring to Figure 2 , Figure 2 is the SEM image of the product obtained in Example 1 of the present application, and it can be seen that the sample obtained in this example has a particle structure with a rough surface and a diameter of about 0.2-0.5 μm.

[0035] Referring to Figure 3 , Figure 3 is the TEM image of the product obtained in Example 1 of the present application, and it can be seen that the sample particles obtained in this example have a porous structure.

[0036] Referring to Figure 4 , Figure 4 is the N1s high-resolution XPS fitting spectrum of the product obtained in Example 1 of the present application, and it can be seen that the sample after ammonia treatment forms an Amine-N bond, and there is a large amount of pyridine nitrogen in the final sample, which has a higher sodium adsorption capacity, is more conducive to the adsorption of Na + , and further improves the sodium storage performance of the material.

[0037] The amorphous carbon material prepared in Example 1 was mixed with super carbon black and CMC at a mass ratio of 8:1:1 in water, and coated on a copper foil, vacuum dried, and cut to obtain an electrode sheet; a 2032 button cell was assembled with metal sodium as the counter electrode, an electrolyte obtained by dissolving 1M NaPF6 in diethylene glycol dimethyl ether, and glass microfiber (GF / D) as a separator. A blue cell test system was used, and the voltage range was 0.01-3V vs Na / Na+ .

[0038] Referring to Figure 5 , Figure 5 is the first three cycles of constant current charge-discharge curve of the battery assembled by the product of Example 1 of the present application.

[0039] Referring to Figure 6 , Figure 6 is the cycle curve of the battery assembled by the product of Example 1 of the present application.

[0040] Referring to Figure 7 , Figure 7 is the rate performance graph of the battery assembled by the product of Example 1 of the present application.

[0041] The first three cycles of charge-discharge curve are shown in Figure 5 , the first discharge specific capacity is 464mAh g -1 , the first charge specific capacity is 421mAh g -1 , and the first charge-discharge efficiency is 90%; the cycle performance is shown in Figure 6 , after 3000 cycles at a current density of 5Ag -1 , the discharge specific capacity remains 263mAh g -1 ; the rate performance is shown in Figure 7 , there is still a specific capacity of 273mAh g -1 at a large current density of 20Ag -1 .

[0042] Comparative Example

[0043] The difference between the present comparative example and Example 1 is that step 2 is omitted, i.e. the polypyrrole obtained in step 1 is directly carbonized in step 3, and other processes are the same as Example 1.

[0044] Referring to Figure 8 , Figure 8 is the TEM graph of the product obtained in the present comparative example, from which it can be seen that the surface of the material particles obtained without pre-carbonization treatment is relatively smooth, and there is no porous structure.

[0045] Referring to Figure 9 , Figure 9 is the first three cycles of constant current charge-discharge curve of the battery assembled by the product of the present comparative example.

[0046] Referring to Figure 10 , Figure 10 is the cycle curve of the battery assembled by the product of the present comparative example.

[0047] Referring to Figure 11 , Figure 11 is the rate performance graph of the battery assembled by the product of the present comparative example.

[0048] The first three charge-discharge curves are shown in Figure 9 , the first discharge specific capacity is 558mAh g -1 , the first charge specific capacity is 289mAh g -1 , the first charge-discharge efficiency is 52%; the cycle performance is shown in Figure 10 , after 3000 cycles at a current density of 5Ag -1 , the discharge specific capacity remains only 78mAh g -1 ; the rate performance is shown in Figure 11 , only 82mAh g -1 of specific capacity at a large current density of 20A g -1 , the performance is far lower than that of Example 1.

[0049] Example 2

[0050] A preparation method of a nitrogen-doped amorphous carbon material, comprising the following steps:

[0051] Step 1: Dissolve ammonium persulfate powder in deionized water to prepare an ammonium persulfate solution with a concentration of 0.1mmol / L, then dissolve 1.2mL of pyrrole solution in 30mL of water, add 60mL of ammonium persulfate solution dropwise, stir at room temperature for 4h, and then perform centrifugal drying treatment to obtain polypyrrole, completing the preparation of the carbon source precursor;

[0052] Step 2: Place the carbon source precursor in step 1 in an argon atmosphere, heat to 300℃ at a heating rate of 1℃ / min, and perform pre-carbonization treatment for 2h;

[0053] Step 3: Place the material after pre-carbonization treatment in an ammonia atmosphere, heat to 500℃ at a heating rate of 2℃ / min, and perform high-temperature carbonization for 3h, with an ammonia flow rate of 100mL / min, to obtain a nitrogen-doped amorphous carbon material, denoted as N@AC-500.

[0054] Mix the amorphous carbon material prepared in this example with super carbon black and CMC in a mass ratio of 8:1:1 in water, and coat on a copper foil, vacuum dry, and cut to obtain an electrode sheet, with metallic sodium as the counter electrode, an electrolyte obtained by dissolving 1M NaPF6 in diethylene glycol dimethyl ether, glass microfiber (GF / D) as a separator, and assembled into a 2032 button cell. Use a blue cell test system, and test the voltage range of 0.01-3V vs Na / Na + .

[0055] The first discharge specific capacity of the battery assembled from the product is 501mAh g -1 , the first charge specific capacity is 355mAh g -1, the first charge-discharge specific capacity is 70%; after 3000 cycles at a current density of 5 Ag -1 , the discharge specific capacity is maintained at 254 mAh g -1 ; at a large current density of 20 Ag -1 , the discharge specific capacity is maintained at 142 mAh g -1 .

[0056] Example 3

[0057] A preparation method of a nitrogen-doped amorphous carbon material, comprising the following steps:

[0058] Step 1: ammonium persulfate powder is dissolved in deionized water to prepare an ammonium persulfate solution with a concentration of 0.1 mmol / L, 1.2 mL of pyrrole solution is dissolved in 30 mL of water, and 60 mL of the ammonium persulfate solution is added dropwise, stirred at room temperature for 4 h, and then centrifuged and dried to obtain polypyrrole, completing the preparation of the carbon source precursor;

[0059] Step 2: the carbon source precursor in step 1 is placed in an argon atmosphere, heated to 300℃ at a heating rate of 1℃ / min, and kept for 2 hours for pre-carbonization treatment;

[0060] Step 3: the material after pre-carbonization treatment is placed in an ammonia atmosphere, heated to 600℃ at a heating rate of 2℃ / min, and kept for 3 hours, with an ammonia flow rate of 100 mL / min, completing carbonization, to obtain a nitrogen-doped amorphous carbon material, denoted as N@AC-600.

[0061] The amorphous carbon material prepared in this example is mixed with super carbon black and CMC at a mass ratio of 8:1:1 in water, and coated on a copper foil, vacuum dried, and cut to obtain an electrode sheet. A 2032 button cell is assembled with metal sodium as the counter electrode, an electrolyte obtained by dissolving 1M NaPF6 in diethylene glycol dimethyl ether, and glass microfiber (GF / D) as a separator. A blue cell test system is used to test the voltage range of 0.01-3V vs Na / Na + .

[0062] The battery assembled from the obtained product has a first discharge specific capacity of 472 mAh g -1 , a first charge specific capacity of 376 mAh g -1 , and a first charge-discharge efficiency of 79%; after 3000 cycles at a current density of 5 Ag -1 , the discharge specific capacity is maintained at 167 mAh g -1 ; at a large current density of 20 Ag -1 , the discharge specific capacity is maintained at 201 mAh g -1 .

[0063] Example 4

[0064] A preparation method of a nitrogen-doped amorphous carbon material, comprising the following steps:

[0065] Step 1: ammonium persulfate powder is dissolved in deionized water to prepare an ammonium persulfate solution with a concentration of 0.1 mmol / L, 1.2 mL of a pyrrole solution is dissolved in 30 mL of water, and 60 mL of the ammonium persulfate solution is added dropwise, and after stirring at room temperature for 4 h, centrifugal drying treatment is performed to obtain a polypyrrole, and the preparation of a carbon source precursor is completed;

[0066] Step 2: the carbon source precursor in step 1 is placed in an argon atmosphere, and heated to 300℃ at a heating rate of 1℃ / min for 2 h for pre-carbonization treatment;

[0067] Step 3: the material after pre-carbonization treatment is placed in an ammonia atmosphere, and heated to 800℃ at a heating rate of 2℃ / min for 3 h, with an ammonia flow rate of 100 mL / min, to complete carbonization, and obtain a nitrogen-doped amorphous carbon material, denoted as N@AC-800.

[0068] The amorphous carbon material prepared in this example is mixed with super carbon black and CMC at a mass ratio of 8:1:1 in water, and is coated on a copper foil, vacuum dried, and cut to obtain an electrode sheet. A 2032 button cell is assembled with a metal sodium as a counter electrode, an electrolyte obtained by dissolving 1M NaPF6 in diethylene glycol dimethyl ether, and glass microfiber (GF / D) as a separator. A blue cell test system is used to test the voltage range of 0.01-3V vs Na / Na + .

[0069] The battery assembled from the obtained product has an initial specific discharge capacity of 527mAh g -1 , an initial specific charge capacity of 448mAh g -1 , and an initial charge-discharge efficiency of 85%; after 3000 cycles at a current density of 5Ag -1 , the discharge capacity is maintained at 262mAh g -1 ; and at a large current density of 20Ag -1 , the discharge capacity is maintained at 200mAh g -1 .

[0070] Example 5

[0071] A preparation method of a nitrogen-doped amorphous carbon material, comprising the following steps:

[0072] Step 1: Ammonium persulfate powder was dissolved in deionized water to prepare an ammonium persulfate solution with a concentration of 0.1 mmol / L. Then, 1.2 mL of pyrrole solution was dissolved in 30 mL of water, and 60 mL of the ammonium persulfate solution was added dropwise. After stirring at room temperature for 4 h, centrifugal drying was performed to obtain polypyrrole, completing the preparation of the carbon source precursor;

[0073] Step 2: The carbon source precursor from Step 1 was placed in an argon atmosphere and heated to 400℃ at a heating rate of 1℃ / min for 3 h for pre-carbonization treatment.

[0074] Step 3: The material after pre-carbonization treatment was placed in an ammonia atmosphere and heated to 700℃ at a heating rate of 5℃ / min for 3 h, with an ammonia flow rate of 100 mL / min, to complete carbonization, obtaining a nitrogen-doped amorphous carbon material.

[0075] The amorphous carbon material prepared in this example was mixed with super carbon black and CMC at a mass ratio of 8:1:1 in water, and then coated on a copper foil. After vacuum drying, an electrode sheet was obtained by cutting. A 2032 button cell was assembled using metal sodium as the counter electrode, an electrolyte obtained by dissolving 1M NaPF6 in diethylene glycol dimethyl ether, and glass microfiber (GF / D) as the separator. The blue cell test system was used to test the voltage range of 0.01-3V vs Na / Na + .

[0076] The specific discharge capacity of the battery assembled from the obtained product was 449mAh g -1 in the first cycle, the specific charge capacity was 332mAh g -1 , and the first charge-discharge efficiency was 74%; after 1000 cycles at a current density of 5Ag -1 , the discharge capacity was maintained at 296mAh g -1 ; and at a large current density of 20Ag -1 , the discharge capacity was maintained at 240mAh g -1 .

[0077] Example 6

[0078] A method for preparing a nitrogen-doped amorphous carbon material, comprising the following steps:

[0079] Step 1: Ammonium persulfate powder was dissolved in deionized water to prepare an ammonium persulfate solution with a concentration of 0.1 mmol / L. Then, 1.2 mL of pyrrole solution was dissolved in 30 mL of water, and 60 mL of the ammonium persulfate solution was added dropwise. After stirring at room temperature for 4 h, centrifugal drying was performed to obtain polypyrrole, completing the preparation of the carbon source precursor;

[0080] Step 2: The carbon source precursor in step 1 was placed in argon, and heated to 400℃ at a heating rate of 1℃ / min for 2 hours for pre-carbonization treatment;

[0081] Step 3: The material after pre-carbonization treatment was placed in an ammonia atmosphere, and heated to 700℃ at a heating rate of 2℃ / min for 3 hours, with an ammonia flow rate of 200 mL / min, to complete carbonization, to obtain a nitrogen-doped amorphous carbon material.

[0082] The amorphous carbon material prepared in this example was mixed with super carbon black and CMC at a mass ratio of 8:1:1 in water, and coated on a copper foil, vacuum dried, and cut to obtain an electrode sheet. A 2032 button cell was assembled with metal sodium as the counter electrode, an electrolyte obtained by dissolving 1M NaPF6 in diethylene glycol dimethyl ether, and glass microfiber (GF / D) as a separator. A blue cell test system was used to test the voltage range of 0.01-3V vs Na / Na + .

[0083] The battery assembled from the obtained product had a first discharge specific capacity of 501mAh g -1 , a first charge specific capacity of 355mAh g -1 , and a first charge-discharge efficiency of 71%; after 1000 cycles at a current density of 5Ag -1 , the discharge specific capacity was maintained at 343mAh g -1 ; and at a large current density of 20Ag -1 , the discharge specific capacity was maintained at 262mAh g -1 .

[0084] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A method for preparing nitrogen-doped amorphous carbon materials, characterized in that: Includes the following steps: A catalyst was added to a pyrrole solution to induce a polymerization reaction in the pyrrole. The resulting product was then separated and dried to obtain polypyrrole. Polypyrrole is placed in a protective atmosphere for pre-carbonization treatment to obtain a pre-carbonized material; The pre-carbonized material was placed in an ammonia atmosphere for high-temperature carbonization to obtain nitrogen-doped amorphous carbon material. The pre-carbonization treatment is carried out at a temperature of 300-400 ℃ for 1-3 h. The high-temperature carbonization is carried out at a temperature of 400~800 ℃ for 1~3 h.

2. The method for preparing nitrogen-doped amorphous carbon material according to claim 1, characterized in that: The catalyst is an ammonium persulfate solution.

3. The method for preparing nitrogen-doped amorphous carbon materials according to claim 1, characterized in that: The heating rate of the pre-carbonization treatment is 1~5 ℃ / min.

4. The method for preparing nitrogen-doped amorphous carbon material according to claim 1, characterized in that: The heating rate for high-temperature carbonization is 2~5 ℃ / min.

5. The method for preparing nitrogen-doped amorphous carbon material according to claim 1, characterized in that: The flow rate of the ammonia gas is 100~200 mL / min.

6. A nitrogen-doped amorphous carbon material, characterized in that: It is prepared by the preparation method as described in any one of claims 1 to 5.

7. The application of the nitrogen-doped amorphous carbon material as described in claim 6 as a negative electrode material in sodium-ion batteries.

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