Nitrogen-doped wood-based hard carbon material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrode materials, and discloses a nitrogen-doped wood-based hard carbon material and a preparation method and application thereof. The preparation method comprises the following steps: selecting waste wood, shearing the waste wood, carrying out oxidation and alkali treatment, removing precursor impurities, carrying out step calcination in an inert atmosphere to obtain wood-based hard carbon, carrying out acid treatment, and carrying out mixed calcination with melamine to obtain the nitrogen-doped wood-based hard carbon material. The method disclosed by the invention is short in process flow, simple to operate, low in cost and easy to realize large-scale production; the obtained nitrogen-doped wood-based hard carbon material is used in a sodium ion battery and has the advantages of high theoretical specific capacity and high first coulombic efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and particularly relates to a nitrogen-doped wood-based hard carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous growth of global energy demand, energy storage technology has become an important field for promoting sustainable development and realizing the green energy transformation. Among them, sodium-ion batteries have gradually become one of the potential alternative technologies to lithium-ion batteries due to their rich resources, low cost, and high safety, and have broad application prospects especially in the fields of large-scale energy storage and electric transportation. The optimization of the anode material of sodium-ion batteries is one of the keys to its performance. Among them, hard carbon materials have become the focus of current research due to their good electrochemical performance and chemical stability. However, hard carbon has the disadvantages of low specific capacity and low initial Coulomb efficiency.

[0003] Currently, the sources of hard carbon anodes for sodium-ion batteries are mainly various biomass raw materials, such as coconut shells, moso bamboo, reeds, straws, and woods. Due to the complex composition of biomass and the unclear influence of each component on the carbonization structure and performance, how to modify biomass to control the pore structure and carbon layer spacing of the final carbon and improve the sodium storage performance of hard carbon has become a key issue. Summary of the Invention

[0004] In order to overcome the above-mentioned disadvantages and deficiencies of the prior art, the primary object of the present invention is to provide a preparation method of a nitrogen-doped wood-based hard carbon material.

[0005] Another object of the present invention is to provide a nitrogen-doped wood-based hard carbon material prepared by the above method.

[0006] Another object of the present invention is to provide an application of the above nitrogen-doped wood-based hard carbon material in sodium-ion batteries.

[0007] The object of the present invention is achieved by the following solutions:

[0008] A preparation method of a nitrogen-doped wood-based hard carbon material includes the following steps:

[0009] S1. Shearing: Cutting waste wood into wood blocks, washing, and drying;

[0010] S2. Oxidation: Reacting the wood blocks obtained in step S1 with a mixed solution of sodium chlorite and acetic acid to remove lignin and hemicellulose components, washing to neutrality, and drying;

[0011] S3. Alkali treatment: Placing the wood blocks obtained in step S2 into a sodium hydroxide solution, stirring, washing to neutrality, and drying;

[0012] S4. Calcination: The wood blocks obtained in step S3 are subjected to carbonization calcination in an inert gas atmosphere;

[0013] S5. Pickling: The product obtained in step S4 is ground into powder, added to an acidic solution, stirred, washed until neutral, dried, and sieved to obtain a wood-based hard carbon material;

[0014] S6. Nitrogen doping: The wood-based hard carbon material obtained in step S5 is mixed with melamine and calcined in an inert gas atmosphere to obtain a nitrogen-doped wood-based hard carbon material.

[0015] The washing in steps S1 - S3 and step S5 is washing with water.

[0016] The drying temperature in steps S1 - S3 and step S5 is 60°C - 80°C; the time is 24 - 36 h.

[0017] The wood in step S1 includes at least one of African padauk and rosewood.

[0018] The particle size of the wood blocks in step S1 is 1 - 3 mm.

[0019] In the mixed solution in step S2, the concentration of sodium chlorite is 0.1 M - 0.5 M, and the concentration of acetic acid is 0.5 M - 1.0 M.

[0020] The reaction temperature in step S2 is 80°C - 100°C, and the time is 12 - 24 h.

[0021] The amount of the mixed solution in step S2 satisfies: completely submerging the wood blocks.

[0022] In the sodium hydroxide solution in step S3, the mass fraction of sodium hydroxide is 6 - 12%.

[0023] The stirring time in step S3 is 12 - 24 h.

[0024] The amount of the sodium hydroxide solution in step S3 satisfies: completely submerging the wood blocks.

[0025] The inert gas in steps S4 and S6 is at least one of nitrogen, argon, helium, and neon; the flow rate of the inert gas is 20 - 100 mL min -1 .

[0026] The carbonization calcination in step S4 is to increase the temperature to 1300°C at a heating rate of 2°C min -1 and carbonize for 2 h, and then decrease the temperature to 50°C at a cooling rate of 2°C min -1 .

[0027] The acidic solution described in step S5 is one of hydrochloric acid solution, sulfuric acid solution, acetic acid solution, and nitric acid solution; the concentration of the acidic solution is 0.5 - 2 mol / L -1 .

[0028] The dosage of the acidic solution described in step S5 satisfies: completely submerging the powder.

[0029] The stirring time in step S5 is 2 - 6 h; the mesh number of the sieve for sieving is 50 - 300 meshes.

[0030] The mass ratio of the wood-based hard carbon material to melamine described in step S6 is 1:3 - 5.

[0031] The calcination in step S6 is carried out at a heating rate of 2 °C / min -1 to rise to 800 °C and carbonize for 2 h.

[0032] A nitrogen-doped wood-based hard carbon material prepared by the above method.

[0033] Application of the above nitrogen-doped wood-based hard carbon material as a negative electrode material in a sodium-ion battery.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] (1) The present invention first screens waste wood raw materials, removes lignin and hemicellulose components through alkali treatment to obtain a purified precursor, and then obtains a hard carbon material with high theoretical specific capacity and high first Coulomb efficiency through carbonization, pickling, and nitrogen doping.

[0036] (2) In the pickling and drying step of the present invention, not only can the ash carried on the material be removed, but also the excess alkali in the prior alkali treatment can be neutralized, and the inorganic salts generated by the neutralization reaction are also eluted and removed to avoid the residual various inorganic substances becoming harmful ash during the subsequent carbonization and calcination processes.

[0037] (3) The present invention can prepare a high-capacity wood-based hard carbon material through simple pretreatment and nitrogen doping treatment. The preparation method has a short process flow, simple operation, low cost, and is easy to realize large-scale production. Description of the Drawings

[0038] Figure 1 X-ray diffraction pattern comparison of the materials C-900, C-1100, C-1300, C-1500, and N-C-1300 obtained in Comparative Examples 1 - 4 and Example 1.

[0039] Figure 2 Raman spectrum comparison of the materials C-900, C-1100, C-1300, C-1500, and N-C-1300 obtained in Comparative Examples 1 - 4 and Example 1.

[0040] Figure 3 X-ray photoelectron spectroscopy (XPS) comparison of C-1300 obtained in Comparative Example 3 and N-C-1300 obtained in Example 1.

[0041] Figure 4 Scanning electron microscopy (SEM) comparison of C-1300 obtained in Comparative Example 3 and N-C-1300 obtained in Example 1, where a is C-1300 and b is N-C-1300.

[0042] Figure 5 Transmission electron microscopy (TEM) (a is C-1300, b is N-C-1300) and line scan (c is C-1300, d is N-C-1300) comparison of C-1300 obtained in Comparative Example 3 and N-C-1300 obtained in Example 1.

[0043] Figure 6 Elemental energy spectrum of N-C-1300 obtained in Example 1.

[0044] Figure 7 Charge-discharge curves of the first cycle of the materials C-900, C-1100, C-1300, C-1500 and N-C-1300 obtained in Comparative Examples 1-4 and Example 1 at 0.1C (1C = 300 mA g -1 ) for comparison.

[0045] Figure 8 a in is the comparison of rate cycling diagrams of the materials C-900, C-1100, C-1300, C-1500 and N-C-1300 obtained in Comparative Examples 1-4 and Example 1 at rates of 0.1, 0.2, 0.4, 1, 2 and 5C (1C = 300 mA g -1 ) for comparison; b is the comparison of the first cycle charge-discharge curve and the first Coulombic efficiency diagram of C-1300 obtained in Comparative Example 3 and N-C-1300 obtained in Example 1 at 0.1C.

[0046] Figure 9 Long-term cycling test diagram of N-C-1300 obtained in Example 1 and C-1300 obtained in Comparative Example 3 at 1C. Detailed implementation mode

[0047] The present invention will be further described in detail below with reference to the examples and the accompanying drawings, but the implementation modes of the present invention are not limited thereto. For those not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0048] Unless otherwise specified, the reagents used in the examples can be conventionally purchased from the market.

[0049] Comparative Example 1

[0050] A preparation method of wood-based hard carbon material for the negative electrode, successively including the following steps:

[0051] S1. Shearing: Cut the waste African padauk wood into wood blocks to obtain coarse materials with a particle size of 1-3 mm, then wash and dry them with deionized water. The drying temperature is 60 °C and the drying time is 24 h;

[0052] S2. Oxidation: Add the wood blocks obtained in step S1 to a mixed solution of sodium chlorite and acetic acid (the concentration of sodium chlorite in the mixed solution is 0.1 M and the concentration of acetic acid is 0.5 M), react at 80 °C for 24 h to remove lignin and hemicellulose components, and wash with deionized water until neutral, then dry at 60 °C for 24 h;

[0053] S3. Alkali treatment: Put the wood blocks obtained in step S2 into a sodium hydroxide solution with a mass fraction of 6% and stir for 24 h, then wash with deionized water until neutral, and dry at 60 °C for 24 h;

[0054] S4. Calcination: Put the wood blocks obtained in step S3 into a corundum crucible and then into a tubular furnace. Under a nitrogen atmosphere with a flow rate of 60 mL / min, raise the temperature to 900 °C at a heating rate of 2 °C / min, carbonize for 2 h, and then immediately lower the temperature to 50 °C at a cooling rate of 2 °C / min; -1 -1 -1

[0055] S5. Acid washing: Grind the sample obtained in step S4 into powder and transfer it to a 1 M hydrochloric acid solution for stirring and washing. The stirring time is 24 h, then filter with deionized water until neutral, and then carry out drying treatment. The drying temperature is 60 °C and the drying time is 24 h. Pass through a 200-mesh sieve to obtain the wood-based hard carbon material (sample name: C-900).

[0056] Comparative example 2

[0057] The difference from Comparative example 1 is that: in step S4, the calcination temperature is 1100 °C to obtain the wood-based hard carbon negative electrode material (sample name C-1100).

[0058] Comparative example 3

[0059] The difference from Comparative example 1 is that: in step S4, the calcination temperature is 1300 °C to obtain the wood-based hard carbon negative electrode material (sample name C-1300).

[0060] Comparative example 4

[0061] The difference from Comparative example 1 is that: in step S4, the calcination temperature is 1500 °C to obtain the wood-based hard carbon negative electrode material (sample name C-1500). ​​​

[0062] Example 1

[0063] A method for preparing a nitrogen-doped wood-based hard carbon material for a negative electrode comprises the following steps in sequence:

[0064] S1. Shearing: Cut waste African padauk wood into wood blocks to obtain coarse materials with a particle size of 1-3 mm, then wash with deionized water and perform a drying treatment. The drying temperature is 60 °C and the drying time is 24 h;

[0065] S2. Oxidation: Add the wood blocks obtained in step S1 to a mixed solution of sodium chlorite and acetic acid (the concentration of sodium chlorite in the mixed solution is 0.1 M and the concentration of acetic acid is 0.5 M), react at 80 °C for 24 h to remove lignin and hemicellulose components, wash with deionized water until neutral, and dry at 60 °C for 24 h;

[0066] S3. Alkali treatment: Put the wood blocks obtained in step S2 into a sodium hydroxide solution with a mass fraction of 6% and stir for 24 h, then wash with deionized water until neutral, and dry at 60 °C for 24 h;

[0067] S4. Calcination: Place the wood blocks obtained in step S3 in a corundum crucible and then put it into a tube furnace. Under a nitrogen atmosphere with a flow rate of 60 mL / min, raise the temperature at a rate of 2 °C / min to 1300 °C, carbonize for 2 h, and then immediately lower the temperature at a rate of 2 °C / min to 50 °C; -1 to -1 of -1 cooling rate to 50 °C;

[0068] S5. Pickling: Grind the sample obtained in step S4 into powder and transfer it to a 1 M hydrochloric acid solution for stirring and cleaning. The stirring time is 24 h, then filter with deionized water until neutral, and then perform a drying treatment. The drying temperature is 60 °C and the drying time is 24 h. Pass through a 200-mesh sieve to obtain a wood-based hard carbon material;

[0069] S6. Nitrogen doping: Grind and mix the wood-based hard carbon material obtained in step S5 with melamine at a mass ratio of 1:3, and then perform calcination under an inert gas nitrogen atmosphere. Raise the temperature at a rate of 2 °C / min to 800 °C, carbonize for 2 h, and cool to room temperature to obtain a nitrogen-doped wood-based hard carbon material (sample name: N-C-1300). -1 heating rate to 800 °C, carbonize for 2 h, and cool to room temperature to obtain a nitrogen-doped wood-based hard carbon material (sample name: N-C-1300).

[0070] Example 2

[0071] The difference from Example 1 is that in step S6, the wood-based hard carbon material obtained in step S5 is ground and mixed with melamine at a mass ratio of 1:5 to obtain a nitrogen-doped wood-based hard carbon material (sample name: N-C2-1300).

[0072] Sodium-ion battery performance test

[0073] The active material (the hard carbon material obtained in any one of Comparative Examples 1-4 and Examples 1-2), sodium carboxymethyl cellulose (CMC), and carbon black were mixed at a mass ratio of 8:1:1 to obtain a negative electrode; sodium metal was used as the positive electrode, the electrolyte was sodium hexafluorophosphate NP-001 (1M NaPF6 in DIGLYME = 100 Vol%), and a glass fiber was used as the separator to assemble a coin cell for testing (model 2032).

[0074] The above hard carbon materials were each subjected to 5 performance tests, and the average value was taken and recorded in the following table;

[0075] Table 1 Comparison table of main electrochemical performance data of negative electrodes of sodium-ion batteries assembled with hard carbon materials obtained in Comparative Examples 1-4 and Examples 1-2

[0076] Table 1

[0077]

[0078] Material structure characterization

[0079] Figure 1 The X-ray diffraction patterns of C-900, C-1100, C-1300, C-1500, and N-C-1300 are shown. As shown in the figure, all samples have two broad diffraction peaks at about 23° and 44°, corresponding to the (002) and (101) crystal planes in the carbon structure, respectively, which are consistent with the characteristic peaks of typical amorphous hard carbon. Compared with C-900, C-1100, and C-1500, the broad diffraction peak at 23° of C-1300 shifts to the left, indicating that with the increase in the carbonization temperature, the interlayer spacing (d 002 ) of the graphite microcrystalline layer increases, which may be related to the reorganization of the graphite microcrystalline structure and defect evolution during the high-temperature carbonization process. Because heat treatment at a higher temperature may promote the relaxation of the disordered carbon structure, slightly increasing the local graphitization degree, while introducing more non-hexagonal carbon defects, thus affecting the stacking mode and resulting in an increase in the interlayer spacing. Compared with C-1300, the broad diffraction peak at 23° of N-C-1300 further shifts to the left, indicating that the interlayer spacing (d 002 ) increases, which may be related to the incorporation of nitrogen atoms and their regulation effect on the carbon structure. Nitrogen doping introduces larger heteroatoms (the atomic radius of N is larger than that of C), resulting in local lattice distortion and increased interlayer repulsion, thus increasing the carbon layer spacing.

[0080] Figure 2 The Raman spectra of further analyzed the graphitization degree of C-900, C-1100, C-1300, C-1500, and N-C-1300. As Figure 2 shown, at about 1350 cm -1and 1580cm -1 The D band representing the carbon defect vibration mode and the G band related to the vibration mode of crystalline graphite were observed at the same time. The peak intensity ratio of the D band to the G band (I D / I G ) is usually used to evaluate the disorder degree of carbon materials. The I D / I G The values are 1.78, 1.52, 1.44 and 1.40 respectively, which shows that with the increase of carbonization temperature, I D / I G This is consistent with the increase in order in hard carbon carbonized at high temperature. D / I G The increase further confirms that N-doping makes the sample disordered. The high disorder is caused by the defects caused by N-doping, which will provide additional sodium ion storage sites for NC-1300.

[0081] Figure 3 The high-resolution X-ray photoelectron spectroscopy was used to further study the surface element content and chemical oxidation state of NC-1300. As shown in the figure, the high-resolution N1s spectrum of NC-1300 shows an obvious peak at 400eV, corresponding to the CN bond, indicating that N atoms are successfully doped into hard carbon with a content of 1.8at.%.

[0082] Figure 4 The following are the scanning electron microscope images of C-1300 and NC-1300. As shown in the figure, both NC-1300 and C-1300 have distributed porous structures with a pore size of about 5μm. This shows that the nitrogen doping process has no significant effect on the pore distribution and pore size of C-1300.

[0083] Figure 5 The following are transmission electron microscope images of NC-1300 and C-1300. Figure 5 As shown in ab, NC-1300 and C-1300 both have the typical characteristics of hard carbon with locally ordered and long-range disordered graphite microcrystalline regions and a large number of micropores / mesopores. Figure 5 According to CD measurement, the interlayer spacing of NC-1300 and C-1300 is 0.393nm and 0.369nm respectively, which indicates that NC-1300 has a larger interlayer spacing, which is more conducive to accommodating more sodium ions and can better alleviate the changes in the material structure and volume caused by the charge and discharge process. This is consistent with the results of the X-ray diffraction diagram.

[0084] Figure 6 The element spectrum scan shows that the N element is evenly distributed in NC-1300. This is consistent with the results of the X-ray photoelectron spectroscopy.

[0085] Electrochemical test and analysis

[0086] Figure 7 It is a comparison chart of the first-week charge-discharge curves of C-900, C-1100, C-1300, C-1500 and N-C-1300. As shown in the figure, all samples exhibit typical electrochemical behaviors of hard carbon materials, including relatively obvious slopes and plateaus.

[0087] As Figure 8 can be seen, C-1300 can provide the highest first-week reversible charge specific capacity of 303.9 mAh g -1 at 0.1C (1C = 300 mA g -1 ), and the highest first Coulombic efficiency (ICE) of 67.8%. And the specific capacity at 5C high rate is 104.9 mAh g -1 . This result indicates that 1300°C is the optimized temperature for the carbonization of hard carbon. After nitrogen doping, N-C-1300 shows more excellent electrochemical performance, with a first-week reversible specific capacity as high as 349.8 mAh g -1 at 0.1C, ICE as high as 90.1%, and the specific capacity at 5C high rate is 178.4 mAh g -1 .

[0088] Figure 9 It is a comparison of the long-cycle tests at 1C for C-1300 and N-C-1300. As shown in the figure, N-C-1300 shows a first-week reversible specific capacity of 254.1 mAh g -1 , and the first-week specific capacity retention rate is as high as 99.8% after stable operation for 1200 cycles, both higher than 225.4 mAh g -1 and 81.8% of C-1300.

[0089] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a nitrogen-doped wood-based hard carbon material, characterized in that, It includes the following steps: S1. Cutting: Cut the waste wood into wood blocks, wash, and dry. S2. Oxidation: React the wood blocks obtained in step S1 with a mixed solution of sodium chlorite and acetic acid to remove lignin and hemicellulose components, wash until neutral, and dry. S3. Alkali treatment: Put the wood blocks obtained in step S2 into a sodium hydroxide solution, stir, wash until neutral, and dry. S4. Calcination: Carbonize and calcine the wood blocks obtained in step S3 in an inert gas atmosphere. S5. Acid pickling: Grind the product obtained in step S4 into powder, add it to an acidic solution, stir, wash until neutral, dry, and sieve to obtain a wood-based hard carbon material. S6. Nitrogen doping: Mix the wood-based hard carbon material obtained in step S5 with melamine and calcine it in an inert gas atmosphere to obtain a nitrogen-doped wood-based hard carbon material.

2. The preparation method of the nitrogen-doped wood-based hard carbon material according to claim 1, wherein: The drying temperature in steps S1 - S3 and step S5 is 60°C - 80°C; the time is 24 - 36 h.

3. The preparation method of the nitrogen-doped wood-based hard carbon material according to claim 1, characterized in that: The wood in step S1 includes at least one of African padauk and rosewood. The particle size of the wood blocks in step S1 is 1 - 3 mm.

4. The preparation method of the nitrogen-doped wood-based hard carbon material according to claim 1, characterized in that: In the mixed solution in step S2, the concentration of sodium chlorite is 0.1 M - 0.5 M, and the concentration of acetic acid is 0.5 M - 1.0 M. The reaction temperature in step S2 is 80°C - 100°C, and the time is 12 - 24 h.

5. The preparation method of the nitrogen-doped wood-based hard carbon material according to claim 1, characterized in that: The mass fraction of sodium hydroxide in the sodium hydroxide solution in step S3 is 6 - 12%; The stirring time in step S3 is 12 - 24 h.

6. The preparation method of the nitrogen-doped wood-based hard carbon material according to claim 1, characterized in that: The inert gas described in step S4 and step S6 is at least one of nitrogen, argon, helium, and neon; the flow rate of the inert gas is 20-100 mL min -1 ; The carbonization and calcination described in step S4 is carried out at a heating rate of 2 °C / min -1 to heat up to 1300 °C, carbonize for 2 h, and then cool down to 50 °C at a cooling rate of 2 °C / min -1 .

7. The preparation method of the nitrogen-doped wood-based hard carbon material according to claim 1, characterized in that: The acidic solution described in step S5 is one of hydrochloric acid solution, sulfuric acid solution, acetic acid solution, and nitric acid solution; the concentration of the acidic solution is 0.5-2 mol / L -1 ; The stirring time in step S5 is 2 - 6 h; the mesh number of the sieve for sieving is 50 - 300 meshes.

8. The preparation method of the nitrogen-doped wood-based hard carbon material according to claim 1, characterized in that: The mass ratio of the wood-based hard carbon material to melamine in step S6 is 1:3 - 5; The calcination described in step S6 is carried out at a heating rate of 2 °C / min -1 to raise the temperature to 800 °C and carbonize for 2 h.

9. A nitrogen-doped wood-based hard carbon material prepared by the method according to any one of claims 1 - 8.

10. Application of the nitrogen-doped wood-based hard carbon material according to claim 9 as a negative electrode material in a sodium-ion battery.

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