Nitrogen-doped porous carbon spheres prepared based on arginine as well as preparation method and application of nitrogen-doped porous carbon spheres

Abstract

The invention discloses nitrogen-doped porous carbon spheres prepared on the basis of arginine as well as a preparation method and application of the nitrogen-doped porous carbon spheres, and belongs to the technical field of sodium-ion battery negative electrode materials. The preparation method comprises the following steps: adding arginine and phthalaldehyde into a reaction solvent, uniformly mixing, transferring into a reaction kettle, and carrying out solvothermal reaction to obtain a nitrogen-doped porous carbon sphere precursor; and carbonizing the nitrogen-doped porous carbon sphere precursor at 650-850 DEG C in a protective gas atmosphere to obtain the nitrogen-doped porous carbon sphere. The nitrogen-containing polymer spheres obtained through reaction of phthalaldehyde and arginine are used as carbon precursors, the nitrogen-doped porous carbon spheres are obtained through one-step carbonization, and the nitrogen-doped porous carbon spheres can be used as sodium-ion battery negative electrode materials and have excellent electrochemical sodium storage performance.

Description

Technical Field

[0001] The technical field of the negative electrode material for sodium ion batteries, specifically relates to a method for preparing nitrogen-doped porous carbon spheres based on arginine and its preparation method and application. Background Art

[0002] Carbon materials are a kind of electrochemical energy storage materials with great development potential. They have excellent electrical conductivity, high specific surface area, good electrochemical stability and low price, and are the most widely used negative electrode materials for sodium ion batteries at present. However, pure carbon materials generally have a low specific capacity value, so the electrochemical energy storage performance needs to be further improved. Chemical modification of carbon materials can make them have more active sites, thus having a higher specific capacity.

[0003] At present, introducing heteroatoms into porous carbon materials can significantly improve the specific capacity of carbon materials. Nitrogen atoms are considered to be the best doping atoms for carbon materials due to their excellent chemical properties. Nitrogen-doped porous carbon materials are mainly obtained by carbonizing nitrogen-containing carbon precursors. There are mainly two types of nitrogen-containing carbon precursors, one is artificially synthesized nitrogen-containing polymers, such as polyaniline, polypyrrole, polyacrylonitrile, etc., and the other is natural nitrogen-containing polymers, such as chitosan, amino acids, etc. Among them, natural nitrogen-containing carbon precursors are the simplest, efficient and low-cost nitrogen-containing carbon precursors. However, most of the existing natural nitrogen-containing carbon precursors have problems such as low carbonization yield and poor structure retention. Therefore, how to prepare nitrogen-doped porous carbon materials with a clear structure using natural nitrogen-containing carbon precursors is still a hot research field. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for preparing nitrogen-doped porous carbon spheres based on arginine and its preparation method and application. The present invention uses the nitrogen-containing polymer spheres obtained by the reaction of terephthalaldehyde and arginine as carbon precursors, and obtains nitrogen-doped porous carbon spheres through one-step carbonization, which can be used as the negative electrode material for sodium ion batteries and has excellent electrochemical sodium storage performance.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The first object of the present invention is to provide a preparation method for preparing nitrogen-doped porous carbon spheres based on arginine, including the following steps:

[0007] Add arginine and terephthalaldehyde to a reaction solvent, mix evenly and transfer to a reaction kettle for solvothermal reaction to obtain a nitrogen-doped porous carbon sphere precursor;

[0008] Carbonize the nitrogen-doped porous carbon sphere precursor under a protective gas atmosphere at 650-850 °C to obtain nitrogen-doped porous carbon spheres.

[0009] Preferably, the molar ratio of arginine to phthalaldehyde is 1:1 - 1.1, and the phthalaldehyde is o-phthalaldehyde, m-phthalaldehyde or p-phthalaldehyde.

[0010] Preferably, the molar concentration of arginine in the reaction solvent is 0.06 - 0.075 mmol / L; the molar concentration of phthalaldehyde in the reaction solvent is 0.06 - 0.075 mol / L.

[0011] Preferably, the reaction solvent includes one or a combination of two of ethylene glycol and water.

[0012] Preferably, the temperature of the solvothermal reaction is 160 - 180 °C, and the time is 8 - 10 h.

[0013] Preferably, the carbonization time is 2 - 3 h, and the heating rate is 2 - 5 °C / min.

[0014] Preferably, the protective gas is helium, neon, argon or nitrogen, and the gas flow rate of the protective gas is 30 - 50 mL / min.

[0015] The second object of the present invention is to provide the nitrogen-doped porous carbon spheres prepared by the above preparation method.

[0016] The third object of the present invention is to provide the application of the above nitrogen-doped porous carbon spheres in sodium-ion batteries, and the nitrogen-doped porous carbon spheres are used to prepare the negative electrode of sodium-ion batteries.

[0017] Preferably, the preparation method of the negative electrode of the sodium-ion battery includes the following steps:

[0018] Mix the nitrogen-doped porous carbon spheres, binder and conductive agent according to a mass ratio of 7:2:1, coat the mixture on the surface of copper foil, dry it at 80 °C until the surface is dry, and then vacuum dry it at 60 °C for 12 h to obtain the nitrogen-doped porous carbon sphere copper foil composite negative electrode material.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention uses phthalaldehyde and arginine as reaction monomers, and obtains arginine polymer microspheres through Schiff base polycondensation reaction. The arginine polymer contains a large number of nitrogen-containing groups and a stable skeleton structure. When used as a carbon precursor, it can maintain a stable structure and a high carbonization yield (37 - 40%); the nitrogen-doped porous carbon spheres are obtained by one-step carbonization of the arginine polymer, which can be used as the negative electrode material of sodium-ion batteries and has excellent electrochemical sodium storage performance.

[0021] (2) The nitrogen-doped porous carbon spheres prepared by the present invention are used for preparing the negative electrode of a sodium-ion battery. The capacity reaches 132 mAh / g at a current density of 0.2 A / g. When the current density increases to 2 A / g, the capacity can still be maintained at 84 mAh / g, and the capacity retention rate reaches 64%; when the current density is 0.5 A / g, the capacity of the first cycle can reach 366.7 mAh / g, the Coulomb efficiency reaches 36.8%, and the capacity is still 107.2 mAh / g after 400 cycles. Description of the Drawings

[0022] Figure 1 It is the scanning electron microscope image of the nitrogen-doped flower-like porous carbon prepared in Example 1 of the present invention;

[0023] Figure 2 It is the scanning electron microscope image of the nitrogen-doped flower-like porous carbon prepared in Example 2 of the present invention;

[0024] Figure 3 It is the scanning electron microscope image of the nitrogen-doped flower-like porous carbon prepared in Example 3 of the present invention;

[0025] Figure 4 It is the scanning electron microscope image of the nitrogen-doped flower-like porous carbon prepared in Example 4 of the present invention;

[0026] Figure 5 It is the scanning electron microscope image of the nitrogen-doped flower-like porous carbon prepared in Comparative Example 1 of the present invention;

[0027] Figure 6 It is the nitrogen adsorption / desorption isotherm diagram and pore size distribution diagram of Example 1 of the present invention; Figure 6 In it, a is the nitrogen adsorption / desorption isotherm diagram, and b is the pore size distribution diagram;

[0028] Figure 7 It is the cyclic voltammogram of the nitrogen-doped porous carbon spheres prepared in Example 1 of the present invention as the negative electrode material of a sodium-ion battery;

[0029] Figure 8 It is the specific capacitance change diagram of the nitrogen-doped porous carbon spheres prepared in Example 1 of the present invention as the negative electrode material of a sodium-ion battery at different current densities;

[0030] Figure 9 It is the cycle stability diagram of the nitrogen-doped porous carbon spheres prepared in Example 1 of the present invention as the negative electrode material of a sodium-ion battery at a current density of 0.5 A / g. Detailed Embodiments

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0032] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the following embodiments of the present invention can be obtained through the market or prepared by existing methods.

[0033] A preparation method of nitrogen-doped porous carbon spheres based on arginine includes the following steps:

[0034] Add arginine and phthalaldehyde to a reaction solvent, mix evenly and transfer to a reaction kettle for solvothermal reaction to obtain a nitrogen-doped porous carbon sphere precursor;

[0035] Carbonize the nitrogen-doped porous carbon sphere precursor under a protective gas atmosphere at 650 - 850 °C to obtain nitrogen-doped porous carbon spheres.

[0036] The present invention uses phthalaldehyde and arginine as reaction monomers to obtain arginine polymer microspheres through Schiff base polycondensation reaction. The arginine polymer contains a large number of nitrogen-containing groups and a stable skeleton structure, and can maintain a stable structure and a high carbonization yield (37% - 40%) when used as a carbon precursor.

[0037] In some preferred embodiments, the molar ratio of arginine to phthalaldehyde is 1:1 - 1.1, and the phthalaldehyde is o-phthalaldehyde, m-phthalaldehyde, or p-phthalaldehyde. In a specific embodiment, the phthalaldehyde is p-phthalaldehyde or m-phthalaldehyde.

[0038] In some preferred embodiments, the molar concentration of arginine in the reaction solvent is 0.06 - 0.075 mmol / L; the molar concentration of phthalaldehyde in the reaction solvent is 0.06 - 0.075 mol / L.

[0039] In some preferred embodiments, the reaction solvent includes one or a combination of two of ethylene glycol and water. The present invention uses ethylene glycol and / or water, which can completely dissolve arginine and phthalaldehyde. During the reaction process, the polymer grows uniformly in the solution to form a spherical morphology, and has a larger specific surface area to expose more active sites.

[0040] In some preferred embodiments, the temperature of the solvothermal reaction is 160 - 180 °C and the time is 8 - 10 h. In a specific embodiment, the temperature of the solvothermal reaction is 180 °C and the time is 10 h.

[0041] In some preferred embodiments, the carbonization time is 2 - 3 h and the heating rate is 2 - 5 °C / min. In a specific embodiment, the carbonization time is 2 h and the heating rate is 2 °C / min.

[0042] In some preferred embodiments, the protective gas is helium, neon, argon or nitrogen, and the gas flow rate of the protective gas is 30 - 50 mL / min.

[0043] Application of the prepared nitrogen-doped porous carbon spheres in a sodium-ion battery, the nitrogen-doped porous carbon spheres are used to prepare the negative electrode of the sodium-ion battery. The method includes the following steps: mixing the nitrogen-doped porous carbon spheres, binder and conductive agent according to a mass ratio of 7:2:1, coating the mixture on the surface of copper foil, drying at 80 °C until the surface is dry, and then drying in vacuum at 60 °C for 12 h to obtain the nitrogen-doped porous carbon sphere-aluminum foil composite negative electrode material.

[0044] The present invention obtains nitrogen-doped porous carbon spheres by one-step carbonization of arginine polymers, which can be used as the negative electrode material of sodium-ion batteries and have excellent electrochemical sodium storage performance. The prepared nitrogen-doped porous carbon spheres are used to prepare the negative electrode of sodium-ion batteries. The capacity reaches 132 mAh / g at a current density of 0.2 A / g. When the current density increases to 2 A / g, the capacity can still be maintained at 84 mAh / g, and the capacity retention rate reaches 64%; when the current density is 0.5 A / g, the capacity of the first cycle can reach 366.7 mAh / g, the Coulomb efficiency reaches 36.8%, and the capacity is still 107.2 mAh / g after 400 cycles.

[0045] The following is further illustrated by specific examples.

[0046] Example 1

[0047] A preparation method of nitrogen-doped porous carbon spheres based on arginine includes the following steps:

[0048] S1. Dissolve 0.52 g (0.075 mmol) of arginine and 0.4 g (0.075 mmol) of terephthalaldehyde in 40 mL of ethylene glycol, mix evenly, transfer to a high-pressure reaction kettle, place it in an oven, carry out a solvothermal reaction at 180 °C for 10 h, filter by suction after the reaction, wash with ethanol, and finally obtain the nitrogen-doped porous carbon sphere precursor in a vacuum drying at 60 °C.

[0049] S2. Place the nitrogen-doped porous carbon sphere precursor in a nitrogen atmosphere with a flow rate of 30 mL / min, heat it to 750 °C at a heating rate of 2 °C, carbonize for 2 h, and then cool it naturally to room temperature to obtain nitrogen-doped porous carbon spheres. The yield of the nitrogen-doped porous carbon spheres is 37%.

[0050] Example 2

[0051] A preparation method of nitrogen-doped porous carbon spheres based on arginine, comprising the following steps:

[0052] S1. Dissolve 0.416 g (0.06 mmol) of arginine and 0.4 g (0.075 mmol) of terephthalaldehyde in 40 mL of ethylene glycol, transfer the mixture to a high-pressure reaction kettle and then place it in an oven, carry out a solvothermal reaction at 180 °C for 10 h, filter the reaction mixture by suction after the reaction and wash it with ethanol, and finally obtain the nitrogen-doped porous carbon sphere precursor by vacuum drying at 60 °C;

[0053] S2. Place the nitrogen-doped porous carbon sphere precursor in a nitrogen atmosphere with a flow rate of 30 mL / min, heat it to 750 °C at a heating rate of 2 °C, carbonize for 2 h, and then cool it naturally to room temperature to obtain nitrogen-doped porous carbon spheres. The yield of the nitrogen-doped porous carbon spheres is 40%.

[0054] Example 3

[0055] A preparation method of nitrogen-doped porous carbon spheres based on arginine, comprising the following steps:

[0056] S1. Dissolve 0.52 g (0.075 mmol) of arginine and 0.32 g (0.06 mmol) of terephthalaldehyde in a mixed solution of 50 mL of water and ethylene glycol with a volume ratio of water to ethylene glycol of 2:3, transfer the mixture to a high-pressure reaction kettle and then place it in an oven, carry out a solvothermal reaction at 180 °C for 10 h, filter the reaction mixture by suction after the reaction and wash it with ethanol, and finally obtain the nitrogen-doped porous carbon sphere precursor by vacuum drying at 60 °C;

[0057] S2. Place the nitrogen-doped porous carbon sphere precursor in a nitrogen atmosphere with a flow rate of 50 mL / min, heat it to 750 °C at a heating rate of 2 °C, carbonize for 2 h, and then cool it naturally to room temperature to obtain nitrogen-doped porous carbon spheres. The yield of the nitrogen-doped porous carbon spheres is 38%.

[0058] Example 4

[0059] A preparation method of nitrogen-doped porous carbon spheres based on arginine, comprising the following steps:

[0060] S1. Dissolve 0.52 g (0.075 mmol) of arginine and 0.4 g (0.075 mmol) of isophthalaldehyde in a mixed solution of 40 mL of ethylene glycol. After mixing evenly, transfer it to a high-pressure reaction kettle and place it in an oven. Carry out a solvothermal reaction at 180 °C for 10 h. After the reaction is completed, filter by suction and wash with ethanol. Finally, obtain a nitrogen-doped porous carbon sphere precursor by vacuum drying at 60 °C;

[0061] S2. Place the nitrogen-doped porous carbon sphere precursor under a nitrogen atmosphere with a flow rate of 50 mL / min and heat it to 750 °C at a heating rate of 2 °C for carbonization for 2 h. Naturally cool to room temperature to obtain nitrogen-doped porous carbon spheres. The yield of the nitrogen-doped porous carbon spheres is 37%.

[0062] Comparative Example 1

[0063] A preparation method of porous carbon spheres based on arginine includes the following steps:

[0064] S1. Dissolve 0.52 g (0.075 mmol) of arginine and 0.32 g (0.06 mmol) of terephthalaldehyde in a mixed solution of 50 mL of 1,4-dioxane and ethylene glycol, and the volume ratio of ethylene glycol to 1,4-dioxane is 2:3. After mixing evenly, transfer it to a high-pressure reaction kettle and place it in an oven. Carry out a solvothermal reaction at 180 °C for 10 h. After the reaction is completed, filter by suction and wash with ethanol. Finally, obtain a nitrogen-doped porous carbon precursor by vacuum drying at 60 °C;

[0065] S2. Place the nitrogen-doped porous carbon sphere precursor under a nitrogen atmosphere with a flow rate of 50 mL / min and heat it to 750 °C at a heating rate of 2 °C for carbonization for 2 h. Naturally cool to room temperature to obtain nitrogen-doped porous carbon. The yield of the nitrogen-doped porous carbon spheres is 40%.

[0066] The nitrogen-doped porous carbon spheres prepared in Examples 1-4 and Comparative Example 1 were characterized by scanning electron microscopy. The specific steps for characterizing the samples by scanning electron microscopy include: fixing the prepared nitrogen-doped porous carbon spheres on the sample stage with conductive glue, placing the sample stage in a vacuum drying oven for drying treatment for 12 h, and after sputtering with gold, observing the structural morphology of the sample with a JSM-6330F cold field emission scanning electron microscope produced by JEOL Ltd. at a voltage of 10 kV. The results are as Figures 1-5 shown; it can be seen from Figures 1-4 that micron spherical morphologies can be obtained with single solvents such as water or ethylene glycol and mixed solvents. When terephthalaldehyde is replaced with isophthalaldehyde, the micron spheres adhere. From Figure 5It can be seen that when 1,4-dioxane is added to ethylene glycol, the micron-scale spherical morphology is destroyed and becomes a bulk morphology. As described above, due to the low solubility of 1,4-dioxane in arginine, the polymer grows unevenly in the solution during the reaction, forming a bulk morphology. The spherical morphology has a larger specific surface area than the bulk morphology, which can expose more active sites.

[0067] The nitrogen adsorption / desorption test was carried out on the nitrogen-doped porous carbon spheres prepared in Example 1. The obtained adsorption / desorption isotherm diagram and pore size distribution diagram are as Figure 6 shown. The specific surface area and pore volume data are shown in Table 1 below.

[0068] Among them, the nitrogen adsorption-desorption isotherm of the sample was measured by a 3H-2000PM1 adsorption instrument produced by Beijing Bettersize Instruments Co., Ltd. The specific steps include: weighing 0.05 g of the prepared nitrogen-doped porous carbon sphere sample, and vacuum degassing the sample at 250 °C for 6 h before the test. The specific surface area S BET was calculated by the BET method, the total pore volume was calculated by the t-polt method, and the full pore size distribution was calculated using the DFT theory.

[0069] Table 1 Specific surface area and pore volume data of the nitrogen-doped porous carbon spheres in Example 1

[0070] Item <![CDATA[Specific surface area (S BET ) / m 2 / g]]> <![CDATA[Pore volume / cm 3 / g]]> Example 1 383.6 0.24

[0071] From Figure 6 it can be seen that the specific surface area of the nitrogen-doped porous carbon spheres prepared in Example 1 ranges from 270.3 m 2 / g, and the pore volume is 0.24 cm 3 / g. The nitrogen adsorption-desorption isotherm curves of Example 1 are all type IV. In the region where the initial relative pressure is 0, the adsorption amount increases sharply, indicating that Example 1 has a rich microporous structure. It can be seen from the pore size distribution curve that the pore sizes of Example 1 are mainly concentrated at 0.4 nm and 0.5 nm.

[0072] Application Example 1

[0073] To further illustrate the beneficial effects of the present invention, the nitrogen-doped porous carbon spheres prepared in Example 1 were used as the anode material for sodium-ion batteries. The electrochemical performance of the samples was measured using a CS2350M electrochemical workstation produced by Wuhan Kost Instrument Co., Ltd. The specific steps were as follows: The nitrogen-doped porous carbon spheres: binder: conductive agent were mixed in a ratio of 7:2:1 and then coated on a copper foil. After drying in a blast dryer at 80 °C until the surface was dry, it was transferred to a vacuum dryer at 60 °C for 12 h, and then stamped to obtain 12 mm electrode sheets for standby; the conductive agent was carbon black, and the binder was polyvinylidene fluoride. Using the active material as the cathode and a lithium metal sheet as the anode, a CR-2032 type coin-shaped half-cell was assembled in the order of cathode shell - active material electrode sheet - separator - lithium sheet - gasket - spring sheet - anode shell. Among them, the separator used was a PP separator, and the electrolyte used was a 1M lithium hexafluorophosphate (LiPF6) solution, and the solvent was ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1.

[0074] Figure 7 is the cyclic voltammogram of Example 1. From Figure 7 it can be seen that the reduction peaks around 0.4V in the first two cycles are related to the formation of the SEI film. By the fifth cycle, the reduction peak is around 0.8V, which is related to the strong adsorption of Na atoms at the micropores and defects of the carbon material.

[0075] Figure 8 is the capacity change diagram of Example 1 at different current densities. From Figure 8 it can be seen that Example 1 exhibits good rate performance. The capacity at a current density of 0.2 A / g reaches 132 mAh / g. When the current density increases to 2 A / g, the capacity can still be maintained at 84 mAh / g, and the capacity retention rate reaches 64%.

[0076] Figure 9 is the cycle stability diagram of Example 1. From Figure 9 it can be seen that Example 1 has good cycle stability as the anode material for sodium-ion batteries. When the current density is 0.5 A / g, the capacity in the first cycle can reach 366.7 mAh / g, and the Coulomb efficiency reaches 36.8%. After 400 cycles, the capacity is still 107.2 mAh / g.

[0077] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concepts. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0078] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and its equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A preparation method of nitrogen-doped porous carbon spheres based on arginine, characterized in that, It includes the following steps: Add arginine and phthalaldehyde into a reaction solvent. After mixing evenly, transfer it to a reaction kettle for solvothermal reaction to obtain a nitrogen-doped porous carbon sphere precursor; Carbonize the nitrogen-doped porous carbon sphere precursor under the atmosphere of a protective gas at 650 - 850 °C to obtain nitrogen-doped porous carbon spheres.

2. The preparation method of nitrogen-doped porous carbon spheres based on arginine according to claim 1, wherein, The molar ratio of arginine to phthalaldehyde is 1:1 - 1.1, and the phthalaldehyde is o-phthalaldehyde, m-phthalaldehyde or p-phthalaldehyde.

3. The preparation method of nitrogen-doped porous carbon spheres based on arginine according to claim 1, characterized in that, The molar concentration of arginine in the reaction solvent is 0.06 - 0.075 mmol / L; the molar concentration of phthalaldehyde in the reaction solvent is 0.06 - 0.075 mol / L.

4. The preparation method of nitrogen-doped porous carbon spheres based on arginine according to claim 1, characterized in that, The reaction solvent includes one or a combination of two of ethylene glycol and water.

5. The preparation method of nitrogen-doped porous carbon spheres based on arginine according to claim 1, characterized in that, The temperature of the solvothermal reaction is 160 - 180 °C, and the time is 8 - 10 h.

6. The preparation method of nitrogen-doped porous carbon spheres based on arginine according to claim 1, characterized in that, The time of carbonization is 2 - 3 h, and the heating rate is 2 - 5 °C / min.

7. The preparation method of nitrogen-doped porous carbon spheres based on arginine according to claim 1, characterized in that, The protective gas is helium, neon, argon or nitrogen, and the gas flow rate of the protective gas is 30 - 50 mL / min.

8. A nitrogen-doped porous carbon sphere prepared by the preparation method according to any one of claims 1 - 7.

9. The application of the nitrogen-doped porous carbon spheres according to claim 8 in a sodium-ion battery, characterized in that, The nitrogen-doped porous carbon sphere is used for preparing the negative electrode of a sodium-ion battery.

10. The application according to claim 9, wherein The preparation method of the negative electrode of the sodium-ion battery includes the following steps: Mix the nitrogen-doped porous carbon spheres, binder and conductive agent according to a mass ratio of 7:2:1, coat it on the surface of a copper foil, dry it at 80 °C until the surface is dry, and then vacuum dry it at 60 °C for 12 h to obtain a nitrogen-doped porous carbon sphere-aluminum foil composite negative electrode material.

Images