Nitrogen / phosphorus co-doped hard carbon and preparation method and application thereof

Abstract

The application discloses nitrogen / phosphorus co-doped hard carbon and a preparation method and application thereof, and belongs to the technical field of battery materials.The nitrogen / phosphorus co-doped biomass-based hard carbon is prepared by taking yeast as raw material, through the processes of culture proliferation and high-temperature calcination, and the material is applied to a sodium ion battery as a negative electrode.Compared with the traditional biomass-based preparation method of hard carbon, the application can not only use biomass as a carbon source, but also form nitrogen / phosphorus co-doped hard carbon in the preparation process of the hard carbon by using the nitrogen and phosphorus characteristics of microorganisms.The electron-rich heteroatoms make the prepared hard carbon have more sodium ion active sites, and can improve the electronic conductivity, which is beneficial to improving the electrochemical capacity of the hard carbon, and the application of the hard carbon to the negative electrode of the sodium ion battery exhibits excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a nitrogen / phosphorus co-doped hard carbon and a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries (SIBs) have an important position in the future energy storage field due to the advantages of abundant reserves and low price of sodium element. The development of SIBs involves multiple national priority development fields such as "electrochemical energy beyond the traditional system, low-carbon energy power system, and theory and technology of efficient and high-quality utilization of electric energy", and is one of the major development needs in China.

[0003] Hard carbon has become the most potential negative electrode material in the commercialization of SIBs due to the advantages of wide raw material sources, many active sites, high sodium storage specific capacity, and high safety. However, the practical application process of hard carbon is hindered due to the problems of low first-week coulombic efficiency, poor cycle stability, and large polarization under high current density. Therefore, the introduction of heteroatoms (nitrogen, phosphorus, etc.) for doping to expand the interlayer spacing of graphite microcrystals in hard carbon and increase the sodium affinity has attracted widespread attention from researchers. However, the addition of nitrogen source and phosphorus source during the synthesis of hard carbon can easily cause uneven distribution of nitrogen / phosphorus or difficulty in introduction, and complicate the preparation steps of hard carbon. In addition, when biomass is used as a carbon source, it is difficult to uniformly and effectively add nitrogen source and phosphorus source during the preparation of hard carbon. Therefore, exploring a natural nitrogen / phosphorus-rich biomass as a carbon source to prepare hard carbon is conducive to realizing uniform co-doping of nitrogen / phosphorus, enhancing the electrochemical performance of sodium-ion batteries, and promoting the development and commercial application of new hard carbon sources. SUMMARY

[0004] In view of the above prior art, the application provides a nitrogen / phosphorus co-doped hard carbon and a preparation method and application thereof to solve the technical problems of complex hard carbon preparation process and poor electrochemical performance as an electrode material.

[0005] To achieve the above purpose, the technical scheme adopted by the application is to provide a preparation method of a nitrogen / phosphorus co-doped hard carbon, comprising the following steps:

[0006] S1: culturing yeast bacteria with a glucose solution to obtain a yeast bacteria culture solution;

[0007] S2: heat treating the yeast bacteria culture solution, and then cleaning and drying to obtain a precursor;

[0008] S3: in an inert atmosphere, heating the precursor to 900-1500℃, maintaining the temperature for 2h, then cooling to 500℃ at a cooling rate of 4℃ / min, and then cooling to room temperature with the furnace, to obtain the nitrogen / phosphorus co-doped hard carbon.

[0009] On the basis of the above technical scheme, the application can be further improved as follows.

[0010] Further, the yeast culture method in S1 is as follows: 3.5 g of yeast is inoculated into 80 mL of glucose solution with a concentration of 0.2 M, and cultured at room temperature for 24 h.

[0011] Further, the heat treatment method in S2 is as follows: the yeast culture solution is loaded into a hydrothermal kettle, and incubated at 105 DEG C for 1 h.

[0012] Further, the washing method in S2 is as follows: the yeast culture solution is washed twice with deionized water and anhydrous ethanol, respectively.

[0013] Further, the drying temperature in S2 is 60 DEG C, and the drying time is 24 h.

[0014] Further, the inert atmosphere is an argon atmosphere.

[0015] Further, the heating rate in S3 is 3 DEG C / min.

[0016] The application further discloses a nitrogen / phosphorus-rich hard carbon prepared by the preparation method.

[0017] The application further discloses application of the nitrogen / phosphorus co-doped hard carbon in preparation of a sodium ion battery.

[0018] The application has the following beneficial effects:

[0019] 1. The nitrogen / phosphorus co-doped hard carbon is prepared by using natural nitrogen / phosphorus-rich microorganism fungi (yeast), and no nitrogen source and phosphorus source need to be added in the preparation process, so that the preparation process can be simplified, and the problem of uneven distribution of nitrogen / phosphorus can be avoided.

[0020] 2. In the preparation process, the water-containing component in the precursor is removed at high temperature, the prepared nitrogen / phosphorus co-doped hard carbon contains a nanopore structure, can provide a large number of sodium storage active sites, is beneficial to embedding and removing of sodium ions in the charging and discharging process, and can improve the fast charging capacity of the hard carbon anode.

[0021] 3. This invention utilizes naturally occurring nitrogen / phosphorus-rich fungi to prepare nitrogen / phosphorus co-doped hard carbon, improving the electronic conductivity of the hard carbon material and providing more sodium storage active sites, thereby increasing the discharge specific capacity of the hard carbon material. The biomass used in this invention can not only serve as a carbon source for hard carbon preparation but also provide nitrogen and phosphorus sources. Therefore, the prepared hard carbon material has nitrogen and / or phosphorus elements uniformly dispersed on the surface and inside. This electron-rich structure facilitates the migration of sodium ions during charge and discharge, contributing to improved high-rate performance of sodium-ion batteries. The hard carbon prepared by the bacteria in this invention contains a nanoporous structure, which is beneficial for sodium ion storage and improves the reversible capacity of the hard carbon. The nitrogen / phosphorus co-doped hard carbon prepared in this invention exhibits good rate performance and cycle stability at 0.1C (1C = 300 mAh g⁻¹). -1 The capacity can reach 309mAh g. -1 Furthermore, it retains 88.9% of its capacity after 1000 cycles at 1C.

[0022] 4. The preparation process in this invention is simple to operate and can encourage the development and application of low-cost biomass containing electron-rich elements such as nitrogen / phosphorus in hard carbon. Attached Figure Description

[0023] Figure 1 The X-ray diffraction patterns of nitrogen / phosphorus co-doped hard carbon obtained in Examples 1-4 are shown.

[0024] Figure 2 The Raman spectra of nitrogen / phosphorus co-doped hard carbon obtained in Examples 1-4;

[0025] Figure 3 The X-ray electron spectrum of nitrogen / phosphorus co-doped hard carbon obtained in Example 3;

[0026] Figure 4 These are high-resolution transmission electron microscopy images of nitrogen / phosphorus co-doped hard carbon obtained in Examples 1-4. Detailed Implementation

[0027] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0028] Example 1

[0029] A nitrogen / phosphorus co-doped hard carbon is prepared by the following steps:

[0030] S1: Inoculate 3.5g of yeast into 80mL of 0.2M glucose solution and incubate at room temperature for 24h to obtain yeast culture medium;

[0031] S2: The yeast culture solution is placed in an autoclave, and is treated at 105°C for 1 h; then the obtained product is cooled, washed twice by centrifugation with deionized water and ethanol respectively, and then transferred to a blast oven, and baked at 60°C for 24 h to obtain a precursor;

[0032] S3: The precursor is transferred to a graphite porcelain boat, and the graphite porcelain boat containing the precursor is transferred to a tube furnace, and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere, and kept for 2 h to form an unordered graphite crystallite structure; then cooled to 500°C at a cooling rate of 4°C / min, and then cooled to room temperature with the furnace, to obtain the nitrogen / phosphorus co-doped hard carbon.

[0033] Example 2

[0034] A nitrogen / phosphorus co-doped hard carbon is prepared by the following steps:

[0035] S1: 3.5 g of yeast is inoculated into 80 mL of a glucose solution with a concentration of 0.2 M, and cultured at room temperature for 24 h to obtain a yeast culture solution;

[0036] S2: The yeast culture solution is placed in an autoclave, and is treated at 105°C for 1 h; then the obtained product is cooled, washed twice by centrifugation with deionized water and ethanol respectively, and then transferred to a blast oven, and baked at 60°C for 24 h to obtain a precursor;

[0037] S3: The precursor is transferred to a graphite porcelain boat, and the graphite porcelain boat containing the precursor is transferred to a tube furnace, and heated to 1100°C at a heating rate of 3°C / min under an argon atmosphere, and kept for 2 h to form an unordered graphite crystallite structure; then cooled to 500°C at a cooling rate of 4°C / min, and then cooled to room temperature with the furnace, to obtain the nitrogen / phosphorus co-doped hard carbon.

[0038] Example 3

[0039] A nitrogen / phosphorus co-doped hard carbon is prepared by the following steps:

[0040] S1: 3.5 g of yeast is inoculated into 80 mL of a glucose solution with a concentration of 0.2 M, and cultured at room temperature for 24 h to obtain a yeast culture solution;

[0041] S2: The yeast culture solution is placed in an autoclave, and is treated at 105°C for 1 h; then the obtained product is cooled, washed twice by centrifugation with deionized water and ethanol respectively, and then transferred to a blast oven, and baked at 60°C for 24 h to obtain a precursor;

[0042] S3: The precursor is transferred to a graphite ceramic boat, and the graphite ceramic boat containing the precursor is transferred to a tube furnace. Under an argon atmosphere, the temperature is increased to 1300℃ at a heating rate of 3℃ / min and held for 2 hours to form a disordered graphite microcrystalline structure. Then, the temperature is decreased to 500℃ at a cooling rate of 4℃ / min and then cooled to room temperature with the furnace to obtain nitrogen / phosphorus co-doped hard carbon.

[0043] Example 4

[0044] A nitrogen / phosphorus co-doped hard carbon is prepared by the following steps:

[0045] S1: Inoculate 3.5g of yeast into 80mL of 0.2M glucose solution and incubate at room temperature for 24h to obtain yeast culture medium;

[0046] S2: Place the yeast culture medium into a hydrothermal reactor and keep it at 105℃ for 1 hour; then cool the product and wash it twice with deionized water and ethanol by centrifugation. Transfer the centrifuged product to a forced-air drying oven and bake it at 60℃ for 24 hours to obtain the precursor.

[0047] S3: The precursor is transferred to a graphite ceramic boat, and the graphite ceramic boat containing the precursor is transferred to a tube furnace. Under an argon atmosphere, the temperature is increased to 1500℃ at a heating rate of 3℃ / min and held for 2 hours to form a disordered graphite microcrystalline structure. Then, the temperature is decreased to 500℃ at a cooling rate of 4℃ / min and then cooled to room temperature with the furnace to obtain nitrogen / phosphorus co-doped hard carbon.

[0048] Experimental Example

[0049] I. Structural Analysis

[0050] The nitrogen / phosphorus co-doped hard carbons prepared in Examples 1-4 were tested using X-ray electron diffraction, and the results are as follows: Figure 1 As shown in the figure, the nitrogen / phosphorus co-doped hard carbon prepared in Examples 1 to 4 has two characteristic broad peaks of hard carbon, (002) and (100). In addition, as the calcination temperature increases, the (002) peak gradually shifts to a higher angle, indicating that the degree of graphitization in the hard carbon increases.

[0051] Raman spectroscopy was performed on the nitrogen / phosphorus co-doped hard carbon prepared in Examples 1-4 to characterize the degree of defects in the hard carbon. The results are as follows: Figure 2 As shown in the figure. It can be seen from the figure that the defect peak area (A) of the nitrogen / phosphorus co-doped hard carbon prepared in Examples 1-4 is... D ) and graphite peak area (A G The ratios were 1.89, 1.77, 1.65, and 1.50, respectively, indicating that higher temperatures would remove defects such as functional groups from the surface of hard carbon.

[0052] The nitrogen / phosphorus co-doped hard carbon prepared in Example 3 was subjected to X-ray photoelectron spectroscopy (XPS) test, and the results are shown in Figure 3 From the figure, it can be seen that the prepared hard carbon contains nitrogen and phosphorus elements, which proves that the hard carbon prepared by the yeast is co-doped with nitrogen and phosphorus.

[0053] The morphology of the nitrogen / phosphorus co-doped hard carbon prepared in Examples 1-4 was observed by high-resolution transmission electron microscopy (HRTEM), and the results are shown in Figure 4 From the figure, it can be seen that the hard carbon prepared by the process in the application has the typical characteristics of hard carbon, i.e. "long-range disorder, short-range order", which is beneficial to the deintercalation of sodium ions. In addition, the existence of nanopores can be observed in the HRTEM, which is beneficial to the storage of sodium ions, thereby improving the reversible specific capacity of the hard carbon.

[0054] II. Electrochemical performance test

[0055] 1. Preparation of button cell

[0056] The nitrogen / phosphorus co-doped hard carbon prepared in Examples 1-4 was made into CR2032 type button cells for electrochemical performance test. The specific steps are as follows: the prepared hard carbon was configured into a slurry according to a mass ratio of hard carbon: acetylene black: binder (PVDF) = 8: 1: 1, N,N-dimethylpyrrolidone (NMP) was used as a solvent, and the slurry was coated on a conductive copper foil to obtain an electrode sheet. The prepared electrode sheet was dried in a forced air oven at a temperature of 60°C for 6h, and then transferred to a vacuum oven for further drying at a temperature of 100°C for 12h. The dried electrode sheet was cut into small round pieces with a diameter of 10mm by a tablet punching machine, and the active material loading was about 1.0-1.5mg cm -2 In a glove box (oxygen content less than 0.01ppm, water content less than 0.01ppm), the obtained small round pieces were used as a negative electrode, a sodium sheet was used as a positive electrode, a glass fiber separator, an electrolyte (1M NaPF6 in Diglyme) was used as a gasket, a spring was used as a spring, and a positive and negative electrode shell was used as a shell, and the button cell was assembled in the order of assembly.

[0057] 2. Test of electrochemical performance

[0058] The assembled button cell was subjected to charge-discharge test on a new wei test channel, and the voltage range of the cycle test was 0.01-2.0V, 1C was defined as 300mAg -1 . The test results are summarized in Table 1.

[0059] Table 1 Summary of electrochemical performance of hard carbon prepared in Examples 1-4

[0060]

[0061] As can be seen from Table 1, the nitrogen / phosphorus co-doped hard carbon prepared by the preparation method provided by the application has high reversible capacity and good cycle stability. In particular, Example 3 has a retention rate of 88.9% after 1000 cycles at 1C. Due to the nitrogen / phosphorus element doping and the degree of graphitization, Examples 3 and 4 have high reversible capacity at high current density (5C). The reason why Examples 1 and 2 have low reversible capacity at 5C is that the calcination temperature is low, the interlayer spacing of the graphite microcrystal in the hard carbon is large, and the degree of graphitization is low, which is not conducive to the storage of sodium ions.

[0062] Although the specific embodiments of the application are described in detail with reference to the examples and drawings, it should not be understood as limiting the scope of protection of the patent. Various modifications and variations within the scope of the description of the claims are still within the scope of protection of the patent without creative labor by those skilled in the art.

Claims

1. A method for preparing nitrogen / phosphorus co-doped hard carbon, characterized in that, The preparation method comprises the following steps: S1: culturing yeast with a glucose solution to obtain a yeast culture solution; the yeast culture method is as follows: inoculating 3.5 g of yeast into 80 mL of a glucose solution with a concentration of 0.2 M, and culturing at room temperature for 24 h; S2: performing heat treatment on the yeast culture solution, and then performing cleaning and drying to obtain a precursor; the heat treatment method is as follows: loading the yeast culture solution into a hydrothermal kettle, and performing heat preservation at 105 ℃ for 1 h; S3: in an inert atmosphere, heating the precursor to 900-1500 ℃, performing heat preservation for 2 h, then reducing the temperature to 500 ℃ at a temperature reduction rate of 4 ℃ / min, and then cooling to room temperature along with the furnace, to obtain the product.

2. The method of claim 1, wherein: The cleaning method in S2 is to wash twice with deionized water and anhydrous ethanol respectively.

3. The method of claim 1, wherein: The drying temperature in S2 is 60 ℃, and the drying time is 24 h.

4. The method of claim 1, wherein: The inert atmosphere is an argon atmosphere.

5. The method of claim 1, wherein: The temperature increase rate in S3 is 3 ℃ / min.

6. The nitrogen / phosphorus co-doped hard carbon prepared by the preparation method in any one of claims 1-5.

7. Application of the nitrogen / phosphorus co-doped hard carbon in claim 6 in the preparation of a sodium ion battery.

8. Use according to claim 7, characterized in that: The nitrogen / phosphorus co-doped hard carbon is used as a negative electrode material of a sodium ion battery.

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