Preparation method of auricularia auricula-based nitrogen-doped biomass carbon negative electrode material applied to lithium ion capacitor

Abstract

A preparation method of an auricularia auricula-based nitrogen-doped biomass carbon negative electrode material applied to a lithium ion capacitor comprises the following steps: (1) crushing and sieving dried auricularia auricula, (2) carbonizing the auricularia auricula powder obtained in the step (1) in an inert gas atmosphere at 300-500 DEG C to obtain a precursor; and (3) mixing the precursor obtained in the step (2) with urea and alkali in a certain proportion, performing high-temperature carbonization in an inert gas atmosphere, and cleaning with HCl with a certain concentration to obtain the biomass porous carbon negative electrode material. The lithium ion capacitor prepared from the biomass porous carbon negative electrode material obtained by the preparation method is excellent in electrochemical performance and long in cycle life.

Description

Technical Field

[0001] The present invention relates to the field of preparation of negative electrode carbon materials for energy storage components, and specifically discloses a method for preparing nitrogen-doped biomass carbon negative electrode materials with high specific surface area, high energy density and long cycle life by using wood ear-based biomass as raw material, undergoing carbonization pretreatment and co-activation of urea and an alkali activator in an inert gas atmosphere. Background Art

[0002] The substantial increase in fossil fuel consumption has brought about serious environmental problems. First, the large-scale exploitation of fossil fuels has caused damage and pollution to the environment. Second, the environmental pollution caused by the combustion of fossil fuels and the greenhouse effect caused by the large amount of greenhouse gas emissions that affect the global environment. Therefore, it is imperative to develop and promote sustainable clean energy and related technologies. However, due to various conditions such as region, season, and weather, most renewable clean energy is difficult to be used continuously. Therefore, it is urgent to find an efficient, low-cost, and environmentally friendly energy storage device. Lithium-ion capacitors are a new type of fast energy storage device between traditional capacitors and chemical batteries. They overcome the shortcomings of low energy density of traditional capacitors and low power density of chemical batteries, taking into account energy density and power density, and have the advantages of long cycle life, fast charging and discharging, high safety factor, good low temperature performance, and long cycle life. It has very important application prospects in the fields of communications, transportation, and national defense.

[0003] At present, the negative electrode material used commercially in lithium-ion capacitors is mainly graphite, but the capacity and rate performance of traditional graphite are difficult to meet people's needs. Compared with graphite, the interlayer spacing of amorphous carbon is about 0.37-0.38nm, which is conducive to the embedding of lithium ions, does not cause obvious expansion of the structure, and has good rate performance. In addition, the theoretical specific capacity of amorphous carbon materials is as high as 700mAh / g, which is much higher than the 370 mAh / g of graphite materials. Therefore, amorphous carbon materials have great application potential. However, amorphous carbon materials have the disadvantage of low conductivity.

[0004] Element doping, mainly nitrogen doping, is a method that can change the band structure of carbon materials, greatly increase the diffusion rate of ions and electrons in carbon materials, and improve the electrical conductivity of materials. In the wood ear base, wood ear polysaccharides account for 60%~70% of its dry weight, and proteins account for 6%-10% of its dry weight, which makes it an ideal biomass carbon material precursor. Therefore, it is of great significance to convert the low-cost wood ear base into a high-value electrode material. At present, we first propose the preparation of nitrogen-doped biomass carbon using wood ear base and apply it to lithium ion capacitors. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings and defects of the graphite carbon materials mentioned in the above background technology, provide a method for preparing nitrogen-doped biomass carbon materials with low cost and excellent electrochemical performance, and apply the biomass carbon materials prepared by this method to lithium ion capacitors. In order to solve the above technical problems, the technical solution proposed by the present invention is: A method for preparing nitrogen-doped biomass carbon comprises the following steps: (1) Using wood ear as the precursor, nitrogen-doped biomass carbon was obtained by high-temperature pyrolysis via one-step carbonization and two-step carbonization methods.

[0006] (2) One of the one-step carbonization methods is: using wood ear base as a precursor, the wood ear base is crushed and passed through a 200-mesh sieve, and the wood ear base powder is mixed with urea and alkali in a certain mass ratio, and then pyrolyzed at high temperature under the action of a flux, and then ground, acid-washed and dried to obtain nitrogen-doped biomass carbon.

[0007] (3) The two-step carbonization method can be divided into two methods: first, using the wood ear base as a precursor, the wood ear base is crushed and passed through a 200-mesh sieve. The wood ear base powder is mixed with urea and alkali in a certain mass ratio, and then pre-carbonized at a certain temperature. After carbonization for a certain period of time, it is continued to be pyrolyzed at high temperature under the action of a flux, and then ground, acid-washed and dried to obtain nitrogen-doped biomass carbon.

[0008] (4) Second, the wood ear base is used as a precursor. After the wood ear base is crushed, it is passed through a 200-mesh sieve and pre-carbonized at a certain temperature. The pre-carbonized precursor is mixed with urea and alkali in a certain mass ratio, and then pyrolyzed at high temperature under the action of a flux, and then ground, acid-washed and dried to obtain nitrogen-doped biomass carbon.

[0009] In the above preparation method, preferably, the mass ratio of the wood ear base powder is 40%-95% of the total mass.

[0010] In the above preparation method, preferably, the carbonization heating rate is 1-20°C.

[0011] In the above preparation method, preferably, the high temperature pyrolysis temperature in step (1) is 700-1800°C, and the pyrolysis time is 0.5h-8h.

[0012] In the above preparation method, preferably, the flux is one or more of chlorides, sulfates and acetates of zinc, sodium and potassium.

[0013] In the above preparation method, preferably, in step (3) and step (4), the pre-carbonization temperature is 300-500° C., and the pre-carbonization time is 0.5-8 h.

[0014] In the above preparation method, preferably, the high temperature pyrolysis temperature in step (3) and step (4) is 700-1800° C., and the pyrolysis time is 0.5-8 h.

[0015] Compared with other preparation methods, the invention has the following characteristics: 1. The raw materials used in the method of the present invention are cheap and easy to obtain, have low cost, and are renewable green resources.

[0016] 2. In the preparation process of the present invention, the rich polysaccharides contained in the raw material itself provide its carbon skeleton structure during high-temperature pyrolysis; the protein contained in it and the external nitrogen source jointly provide the nitrogen element in the biomass after pyrolysis.

[0017] 3. When the present invention prepares nitrogen-doped carbon materials, nitrogen doping changes the band structure of the carbon materials and greatly improves the ion and electron diffusion rates of the carbon materials. At the same time, the nitrogen-doped sites provide better lithium ion affinity, which is more conducive to the adsorption of lithium ions and improves the specific capacity of the material. Flux pyrolysis can increase the degree of graphitization of carbon materials, thereby improving the electrical conductivity of the materials and improving the rate performance of the materials. In the present invention, nitrogen doping and flux pyrolysis work synergistically to improve the electrochemical properties of carbon materials, and the lithium ion capacitors prepared using the nitrogen-doped carbon materials obtained by the preparation method of the present invention have excellent electrochemical properties. DETAILED DESCRIPTION

[0018] The method of the present invention is described below by specific examples, but the present invention is not limited thereto. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0019] Embodiment 1: A method for preparing nitrogen-doped biomass carbon comprises the following steps: (1) Using auricularia auricula as a precursor, crushing the auricularia auricula, passing through a 200-mesh sieve, and mixing the auricularia auricula powder with urea and alkali in a mass ratio of 1:1; (2) The mixed precursor was placed in a tube furnace, 5% NaCl was added as a flux, the temperature was raised to 900 °C at a heating rate of 5 °C / min in a nitrogen atmosphere, and the mixture was pyrolyzed for 2 h and then naturally cooled to room temperature; (3) The pyrolysis product was taken out, ground for 30 min, acid-washed, rinsed with distilled water until neutral, and then dried to obtain nitrogen-doped biomass carbon.

[0020] The scanning electron microscope image of the nitrogen-doped carbon material prepared in this example shows that the nitrogen-doped biomass carbon prepared in this example has a block structure. The nitrogen-doped biomass carbon material prepared in this example has a nitrogen content of 6.0% and is evenly distributed. In the half-cell test, the specific capacity of the nitrogen-doped carbon material is 460 mAh g -1 (Current density is 0.1A·g -1). The nitrogen-doped biomass carbon material prepared in this example is used as the negative electrode material of the lithium ion capacitor, and the soft-pack lithium ion capacitor prepared with activated carbon as the positive electrode material (mass ratio of positive and negative active materials is 1.2:1) has an energy density of 30Wh·kg -1 , the maximum power density is 12kW·kg -1 (Soft pack battery mass calculation).

[0021] Embodiment 2: A method for preparing nitrogen-doped biomass carbon comprises the following steps: (1) Using auricularia auricula as a precursor, crushing the auricularia auricula, passing through a 200-mesh sieve, and mixing the auricularia auricula powder with urea and alkali in a mass ratio of 1:1; (2) The mixed precursor was placed in a tube furnace, 5% NaCl was added as a flux, the temperature was raised to 450°C at a heating rate of 5°C / min in a nitrogen atmosphere, the temperature was raised to 950°C after pyrolysis for 2 hours, the temperature was raised to 950°C after pyrolysis for 1.5 hours, and the mixture was naturally cooled to room temperature; (3) The pyrolysis product was taken out, ground for 30 min, acid-washed, rinsed with distilled water until neutral, and then dried to obtain nitrogen-doped biomass carbon.

[0022] The specific surface area of ​​the nitrogen-doped biomass carbon material prepared in this example is 1830 m 2 / g. In the half-cell test, the specific capacity of nitrogen-doped carbon material is 490mAh·g -1 (Current density is 0.1A·g -1 ). The nitrogen-doped biomass carbon material prepared in this example is used as the negative electrode material of the lithium ion capacitor, and the soft-pack lithium ion capacitor prepared with activated carbon as the positive electrode material (mass ratio of positive and negative active materials is 1.2:1) has an energy density of 35Wh·kg -1 , the maximum power density is 13kW·kg -1 (Soft pack battery mass calculation).

Claims

1. A nitrogen-doped biomass carbon material, characterized in that: The particle size of the nitrogen-doped carbon material is less than 25 μm, the mass fraction of nitrogen is 0.5-10%, and the nitrogen element is evenly distributed therein; wherein the preparation method of the nitrogen-doped carbon material comprises the following steps: (1) Using wood ear as a precursor, nitrogen-doped biomass carbon was obtained by high-temperature pyrolysis via one-step carbonization and two-step carbonization methods.

2. (2) One of the one-step carbonization methods is: using black fungus as a precursor, the black fungus is crushed and passed through a 200-mesh sieve, the black fungus powder is mixed with urea and alkali in a certain mass ratio, and then pyrolyzed at high temperature under the action of a flux, and then ground, acid-washed and dried to obtain nitrogen-doped biomass carbon.

3. (3) The two-step carbonization method can be divided into two methods: First, using wood ear as a precursor, the wood ear is crushed and passed through a 200-mesh sieve. The wood ear powder is mixed with urea and alkali in a certain mass ratio, pre-carbonized at a certain temperature, and then carbonized for a certain period of time and then pyrolyzed at high temperature under the action of a flux, ground, acid-washed and dried to obtain nitrogen-doped biomass carbon.

4. (4) Second, using wood ear as a precursor, the wood ear is crushed, passed through a 200-mesh sieve, and pre-carbonized at a certain temperature. The pre-carbonized precursor is mixed with urea and alkali in a certain mass ratio, and then pyrolyzed at high temperature under the action of a flux, and then ground, acid-washed, and dried to obtain nitrogen-doped biomass carbon.

5. The nitrogen-doped biomass carbon material according to claim 1, wherein the wood ear powder accounts for 40%-95% of the total mass.

6. The nitrogen-doped biomass carbon material according to claim 1, wherein the carbonization heating rate is 1-20°C.

7. The nitrogen-doped biomass carbon material according to claim 1, wherein the high-temperature pyrolysis temperature in step (1) is 700-1800°C and the pyrolysis time is 0.5h-8h.

8. According to the nitrogen-doped biomass carbon material of claim 1, the flux is one or more of chlorides, sulfates and acetates of zinc, sodium and potassium.

9. The nitrogen-doped biomass carbon material according to claim 1, wherein the pre-carbonization temperature in step (3) and step (4) is 300-500°C, and the pre-carbonization time is 0.5-8h.

10. The nitrogen-doped biomass carbon material according to claim 1, wherein the high-temperature pyrolysis temperature in step (3) and step (4) is 700-1800°C and the pyrolysis time is 0.5-8h.