Preparation method of N atom self-doped hollow multi-cavity hard carbon capable of being used as sodium ion battery negative electrode material

Abstract

The invention discloses a preparation method of N-atom self-doped hollow multi-cavity hard carbon capable of being used as a sodium-ion battery negative electrode material, and belongs to the technical field of sodium-ion battery electrode materials. According to the method, ammonium persulfate is used as an initiator, aniline and pyrrole are used as polymer precursors, F127 is used as a soft template, and hollow multi-cavity carbon spheres are prepared through a one-step polymerization method; and then carbonizing at 1200 DEG C, 1300 DEG C, 1400 DEG C and 1500 DEG C in sequence in an argon atmosphere to prepare the hollow multi-cavity hard carbon. The operation method is low in raw material cost, the operation method is simple and convenient, and the prepared material has a relatively high specific surface area and a unique hollow multi-cavity structure, and has relatively high specific capacity, relatively good rate capability and relatively excellent electrochemical performance when being used as a sodium-ion battery negative electrode material.

Description

Technical Field

[0001] The invention relates to a method for preparing N atom self-doped hollow multi-cavity hard carbon that can be used as a negative electrode material for sodium ion batteries, and belongs to the field of porous carbon and electrochemical energy storage. Background Art

[0002] Low-cost sodium-ion batteries have become the most advantageous alternative to lithium-ion batteries due to the abundance of sodium resources and similar physical and chemical properties to lithium. From a commercial perspective, on the one hand, sodium resources are abundant and widely distributed, and on the other hand, cheap aluminum (Al) foil can be used for negative electrode current collectors, thereby reducing the actual cost of the battery. From a production perspective, the production of sodium-ion batteries can refer to existing lithium-ion battery production and manufacturing technology, which can save costs on a large scale. From the perspective of properties and structure, sodium is in the same family as lithium in the periodic table and has similar properties to lithium. Its redox potential is close to that of lithium (E Na+ / Na =-2.71V vs. standard hydrogen electrode (SHE), E Li+ / Li =-3.02V vs. SHE) and is more abundant in the Earth's crust (Na: 2.8wt%, Li: 0.0017wt%). However, the larger ionic radius of sodium ions inevitably leads to higher requirements for the electrode materials used in sodium-ion batteries. Graphite is the most common anode material for commercial lithium-ion batteries, but sodium ions cannot be intercalated into graphite due to the lack of a stable Na-C binary compound, which means that graphite cannot be used as an active material in sodium-ion batteries.

[0003] Hard carbon is widely considered to be a potential negative electrode candidate for sodium-ion batteries due to its high specific surface area, high conductivity, abundant resources and low cost. Hard carbon shows a structure composed of a mixture of disordered and pseudo-graphitic domains, which are randomly oriented and have some micropores between them. They are produced by pyrolysis of widely available precursors such as biomass waste, biopolymers, and synthetic polymers. However, due to the randomly oriented amorphous structure and a large number of defects in hard carbon, it also leads to problems such as low initial Coulombic efficiency, insufficient long-cycle stability and poor rate performance in practical applications, which need to be solved urgently. The main methods for improving hard carbon negative electrode materials currently include regulating structure and morphology, heteroatom doping, surface coating, etc. Heteroatom-doped materials with stable structures can usually be used as negative electrode materials for sodium-ion batteries, which give sodium-ion batteries excellent electrochemical properties. Summary of the Invention

[0004] In response to the problems of unstable structure and poor rate performance of existing sodium ion batteries, the purpose of the present invention is to provide a method for preparing N atom self-doped hollow multi-cavity hard carbon that can be used as a negative electrode material for sodium ion batteries. The preparation method is simple, green and low-cost. When used in sodium ion batteries, the material exhibits high specific capacity and excellent rate performance.

[0005] The present invention provides a method for preparing N-atom self-doped hollow multi-cavity hard carbon that can be used as a negative electrode material for sodium ion batteries. First, aniline pyrrole undergoes a copolymerization reaction under the action of ammonium persulfate initiator. Simultaneously, due to the presence of F127 as a soft template, a hollow multi-cavity structure can be formed under the action of a concentration gradient. Hollow multi-cavity carbon balls are then obtained through filtration and drying. Subsequently, carbonization is carried out under an argon atmosphere to obtain N-atom self-doped hollow multi-cavity hard carbon. The main preparation steps are as follows:

[0006] Step (1) weighing a certain amount of ammonium persulfate into a beaker, weighing an appropriate amount of deionized water, pouring it into the beaker and stirring, to prepare an ammonium persulfate aqueous solution; then weighing a certain amount of F127 into a beaker, weighing an appropriate amount of deionized water, pouring it into the beaker and stirring, then adding a certain amount of aniline and pyrrole solution to prepare an aniline-pyrrole-F127 aqueous solution, and then mixing the two at 0°C to initiate a polymerization reaction to form a uniform solution;

[0007] Step (2) filtering the solution obtained in step (1) with ethanol and water, and drying to obtain hollow multi-cavity carbon ball powder;

[0008] Step (3) transferring the hollow multi-cavity carbon ball powder obtained in step (2) into a clean graphite crucible and placing it into a tubular carbonization furnace, and performing high-temperature carbonization under an argon atmosphere to obtain hollow multi-cavity hard carbon;

[0009] Preferably, the volume ratio of aniline to pyrrole in step (1) is between 3:1 and 3:2; the stirring time is between 1 and 2 hours, and the polymerization time is between 12 and 24 hours;

[0010] Preferably, the filtration time in step (2) should be between 1-2 hours, the number of ethanol replacements should be 4-6 times, and the drying time should be between 12-24 hours;

[0011] Preferably, the specific process of high-temperature carbonization in step (3) is as follows: starting from room temperature, heating at a heating rate of 2°C / min to 500°C; then heating at a heating rate of 5°C / min to 1000°C; then heating at a heating rate of 2°C / min to 1200°C-1500°C, and holding the temperature for 2 hours. The carbonization yield of the sample is between 40% and 60%.

[0012] The present invention has the following advantages:

[0013] (1) The raw material cost is low, the operation process is simple, and the carbonization yield is high;

[0014] (2) Using polymer as a hard carbon precursor material has a stable structure, a relatively large specific surface area, a hollow multi-cavity structure, and has a nitrogen atom self-doping effect;

[0015] (3) The hollow multi-cavity hard carbon after carbonization has a high specific capacity and good rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the EDS diagram of the sample obtained in Example 2.

[0017] Figure 2 The constant current charge and discharge curves of the samples obtained in Examples 1, 2, 3, and 4 are shown. DETAILED DESCRIPTION

[0018] The present invention is further described below with reference to specific examples, which however do not constitute a limitation of the present invention.

[0019] Example 1:

[0020] 2.352g of ammonium persulfate was dissolved in 10ml of deionized water and stirred at room temperature for 20min to fully dissolve to form an ammonium persulfate aqueous solution (A), which was placed in an incubator at 0℃ for 1h; 80mg of F-127 was dissolved in 100ml of deionized water and stirred at room temperature for 20min to fully dissolve, then 0.63ml of aniline and 0.25ml of pyrrole were added to the F-127 aqueous solution and stirred for 30min (B). After being fully mixed, the mixture was placed in an incubator at 0℃ for 1h; solution A and solution B were quickly stirred and mixed to initiate a polymerization reaction. After polymerization in an incubator at 0℃ for 24h, the mixture was taken out, filtered, repeatedly washed with ethanol and water, and finally placed in an oven at 120℃ for 24h, dried, and ground to obtain hollow multi-cavity carbon balls.

[0021] The hollow multi-cavity carbon ball powder was placed in a tube furnace for heating operation, and argon was introduced. The temperature was raised to 500°C at 2°C / min, then to 1000°C at 5°C / min, and finally to 1200°C at 2°C / min to obtain N atom self-doped hollow multi-cavity hard carbon.

[0022] Example 2:

[0023] The carbonization temperature was raised to 1300° C., and other conditions were the same as in Example 1.

[0024] Example 3:

[0025] The carbonization temperature was raised to 1400° C., and other conditions were the same as in Example 1.

[0026] Example 4:

[0027] The carbonization temperature was raised to 1500° C., and other conditions were the same as in Example 1.

[0028] Some embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. Those skilled in the art may make equivalent modifications or substitutions without departing from the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. The present invention provides a method for preparing hollow multi-cavity hard carbon that can be used as a negative electrode material for sodium ion batteries. The method comprises dissolving ammonium persulfate in deionized water to obtain an initiator solution, dissolving aniline pyrrole in an F127 aqueous solution, and performing a polymerization reaction at low temperature to obtain hollow multi-cavity carbon balls. The hollow multi-cavity hard carbon is then carbonized under an argon atmosphere. The main preparation steps are as follows: (1) Weigh a certain amount of ammonium persulfate into a beaker, measure an appropriate amount of deionized water, pour it into the beaker and stir to prepare an ammonium persulfate aqueous solution; then weigh a certain amount of F127 into a beaker, measure an appropriate amount of deionized water, pour it into the beaker and stir, then add a certain amount of aniline and pyrrole solution to prepare an aniline-pyrrole-F127 aqueous solution, and then mix the two at 0°C to initiate a polymerization reaction to form a uniform solution; (2) filtering the solution obtained in step (1) with ethanol and water, and drying to obtain hollow multi-cavity carbon ball powder; (3) The hollow multi-cavity carbon ball powder obtained in step (2) is transferred into a clean graphite crucible and placed in a tubular carbonization furnace, and high-temperature carbonization is performed under an argon atmosphere to obtain hollow multi-cavity hard carbon.

2. The method according to claim 1, characterized in that In step (1), the volume ratio of aniline to pyrrole should be between 3:1 and 3:2; the stirring time is between 1 and 2 hours, and the polymerization time is between 12 and 24 hours.

3. The method according to claim 1, characterized in that In step (2), the filtration time should be between 1 and 2 hours, the number of ethanol replacements should be 4 to 6 times, and the drying time should be between 12 and 24 hours.

4. The method according to claim 1, characterized in that The specific process of high-temperature carbonization in step (3) is as follows: starting from room temperature, heating at a rate of 2°C / min to 500°C; then heating at a rate of 5°C / min to 1000°C; then heating at a rate of 2°C / min to 1200°C-1500°C, and holding at that temperature for 2 hours. The carbonization yield of the sample is between 40% and 60%.

5. The N atom self-doped hollow multi-cavity hard carbon material prepared by the method according to any one of claims 1 to 4, characterized in that: The prepared material has high specific capacity and excellent rate performance. The electrochemical performance of the hollow multi-cavity hard carbon at different carbonization temperatures was evaluated in a half-cell (CR2032 coin type) with a sodium metal sheet as the counter electrode. -1 At this current density, the charge capacity can reach 302.6 mAh g -1 When the rate performance was tested and the current density was restored to a low level, the recovery rate reached 85.2%, indicating excellent electrochemical performance.

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