Nitrogen-doped carbon negative electrode material with three-dimensional conductive network and preparation method of nitrogen-doped carbon negative electrode material

Abstract

The invention provides a nitrogen-doped carbon negative electrode material with a three-dimensional conductive network and a preparation method thereof.The preparation method comprises the steps that polyvinyl alcohol sponge adsorbs an aqueous solution containing polyvinylpyrrolidone and liquid asphalt, and after freeze drying, a precursor is obtained; and performing high-temperature carbonization on the precursor to obtain the nitrogen-doped carbon negative electrode material with the three-dimensional conductive network. According to the invention, nitrogen doping is carried out while the hard carbon negative electrode material is prepared, so that the problems of low initial coulombic efficiency caused by surface defects of existing polymer-based hard carbon and difficulty in intercalation of a lithium ion carbon layer of an asphalt-based hard carbon material are solved, and the charge-discharge performance and long-life cycle performance of the asphalt-based hard carbon material when the asphalt-based hard carbon material is used for a lithium ion battery are improved.

Description

Technical Field

[0001] This invention belongs to the field of anode material technology, and particularly relates to a nitrogen-doped carbon anode material with a three-dimensional conductive network and its preparation method. Background Technology

[0002] With the increasing demand for multifunctional portable electronic devices in the information age and the rapid development of electric vehicles, the research and development of new lithium-ion battery electrode materials with high specific energy, high rate capability, high safety, long life and low cost has become an important cutting-edge research field internationally.

[0003] Currently, relatively successful carbon anode materials include artificial graphite, mesophase carbon microspheres (MCMB), and petroleum coke. However, their specific capacity of 372 mAh / g is too low and increasingly fails to meet requirements. Furthermore, their fragile structure leads to limited stability and high sensitivity to electrolytes. Therefore, attention has shifted to other carbon materials, such as soft carbon and hard carbon. Hard carbon, in particular, has attracted significant interest due to its high capacity, low cost, and excellent cycling performance resulting from its random arrangement. Hard carbon refers to carbon that is difficult to graphitize; it is the pyrolytic carbon of polymers, and this type of carbon exhibits a high specific capacity.

[0004] Hard carbon precursors are mainly classified into four categories: biomass precursors, polymer precursors, pitch-based precursors, and coal-based precursors. Pitch-based precursors are widely available and have higher carbon yields than resin and biomass precursors. However, pitch is prone to graphitization at high temperatures, and direct carbonization of coal tar pitch results in small interlayer spacing, making it difficult for lithium ions to intercalate within the carbon layers. Moreover, most hard carbon precursors still suffer from low initial coulombic efficiency, low capacity, and short cycle life. Summary of the Invention

[0005] Based on the above-mentioned technical problems, the present invention provides a nitrogen-doped carbon anode material with a three-dimensional conductive network and its preparation method. By preparing the hard carbon anode material while performing nitrogen doping, the problems of low initial coulombic efficiency caused by surface defects of existing polymer-based hard carbon and difficulty in lithium-ion carbon layer intercalation of pitch-based hard carbon materials are solved, thereby improving its charge-discharge performance and long-life cycle performance when used in lithium-ion batteries.

[0006] The present invention proposes a method for preparing a nitrogen-doped carbon anode material with a three-dimensional conductive network, comprising the following steps: S1. Polyvinyl alcohol sponge is adsorbed with an aqueous solution containing polyvinylpyrrolidone and liquid asphalt, and then freeze-dried to obtain the precursor; S2. The precursor is carbonized at high temperature to obtain the nitrogen-doped carbon anode material with a three-dimensional conductive network.

[0007] Preferably, in step S1, the mass ratio of the polyvinyl alcohol sponge, polyvinylpyrrolidone, and liquid asphalt is 1-1.5:0.05-0.2:3-4; Preferably, the concentration of polyvinylpyrrolidone in the aqueous solution is 10-30 mg / mL.

[0008] Preferably, in step S1, the adsorption temperature is 50-60℃ and the time is 3-6h.

[0009] Preferably, in step S1, the freeze-drying temperature is -(20-30)℃ and the time is 10-12h.

[0010] Preferably, in step S2, the high-temperature carbonization temperature is 1300-1400℃, and the time is 2-4 hours; Preferably, the high-temperature carbonization is carried out under an inert atmosphere, and the heating rate of the high-temperature carbonization is 2-4℃ / min.

[0011] Preferably, in step S1, before the polyvinyl alcohol sponge absorbs the aqueous solution containing polyvinylpyrrolidone and liquid asphalt, the polyvinyl alcohol sponge is further washed and vacuum dried. Preferably, the washing solvent is anhydrous ethanol, and the vacuum drying temperature is 50-60℃ for 10-12 hours.

[0012] Preferably, step S1 further includes modifying the polyvinyl alcohol sponge with an aminosilane coupling agent.

[0013] Preferably, the aminosilane coupling agent is at least one of 3-aminopropyltriethoxysilane or 3-(2-aminoethylamino)propyltrimethoxysilane; Preferably, the mass ratio of the polyvinyl alcohol sponge to the aminosilane coupling agent is 1:0.05-0.2.

[0014] In this invention, polyvinyl alcohol sponge is modified with an aminosilane coupling agent, which grafts amino groups onto the surface of the polyvinyl alcohol sponge. These amino groups can react with the carbonyl groups of PVP to form imines during subsequent adsorption of PVP. This not only helps to improve the adsorption efficiency of PVP in the polyvinyl alcohol sponge, but also helps to construct the three-dimensional conductive network of the anode material, thereby improving the electrochemical performance of the obtained anode material.

[0015] This invention also proposes a nitrogen-doped carbon anode material with a three-dimensional conductive network, which is prepared by the above-mentioned preparation method.

[0016] The present invention also proposes a lithium-ion battery comprising the above-mentioned nitrogen-doped carbon anode material having a three-dimensional conductive network.

[0017] Compared with the prior art, the present invention has the following technical effects: This invention proposes a method for preparing a nitrogen-doped carbon anode material with a three-dimensional conductive network. The method involves immersing a porous polyvinyl alcohol (PVA) sponge in an aqueous solution containing a mixture of polyvinylpyrrolidone and liquid asphalt, followed by high-temperature carbonization treatment to obtain the nitrogen-doped carbon anode material with a three-dimensional conductive network. This improves the pore structure of the material and optimizes its electrochemical performance.

[0018] In this invention, the three-dimensional porous network of PVA sponge, after carbonization, becomes the conductive framework of the hard carbon material. Liquid asphalt, as a soft carbon precursor, has high hydrogen content molecules that can reduce oxygen-containing groups in the hard carbon precursor, thereby reducing oxygen defects and surface functional groups in the hard carbon material and lowering the risk of fixation by electrostatic adsorption or chemical bonding. The resulting capacity loss; nitrogen-containing polymer polyvinylpyrrolidone (PVP) is used as a nitrogen doping modifier to simultaneously achieve nitrogen doping between hard and soft carbon. Nitrogen doping improves the conductivity of the material by introducing the delocalized conjugated system of sp² hybridized carbon, while nitrogen atoms can serve as active sites to enhance the conductivity. This enhances the adsorption capacity, thereby increasing the material's capacity and initial coulombic efficiency. Detailed Implementation

[0019] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0020] Example 1 A nitrogen-doped carbon anode material with a three-dimensional conductive network is prepared by the following method: (1) Cut 5cm 5cm A 5cm cube of PVA sponge was ultrasonically cleaned in anhydrous ethanol for 40 minutes to remove surface oxides or impurities. Then, it was placed in a vacuum drying oven and vacuum dried at 55℃ for 11 hours to obtain dried PVA sponge. (2) Dissolve PVP in 100 mL of water to obtain a PVP aqueous solution with a mass concentration of 20 mg / mL. Add the aqueous solution to liquid asphalt and stir for 1.5 h to obtain an aqueous solution containing PVP and liquid asphalt. The dried PVA sponge is fully immersed in the aqueous solution containing PVP and liquid asphalt under ultrasonic water bath conditions. The mass ratio of PVA sponge, PVP and liquid asphalt is 1.2:0.1:3.5. The water bath temperature is 55℃ and the time is 4 h. The resulting mixed solution is placed in a freeze dryer for freeze drying at a drying temperature of -25℃ for 11 h to obtain a PVA sponge impregnated with asphalt and PVP. (3) Place the PVA sponge impregnated with asphalt and PVP in a tube furnace, introduce high-purity argon gas with a flow rate of 150 mL / min, heat it from room temperature to 1350℃ at a heating rate of 3℃ / min, keep it at that temperature for 3 hours, and then let it cool naturally to room temperature. After cooling, take out the material, grind it through a 325-mesh sieve, and you will get the nitrogen-doped carbon anode material with a three-dimensional conductive network.

[0021] Example 2 A nitrogen-doped carbon anode material with a three-dimensional conductive network is prepared by the following method: (1) Cut 5cm 5cm A 5cm cube of PVA sponge was ultrasonically cleaned in anhydrous ethanol for 30 minutes to remove surface oxides or impurities. Then, it was placed in a vacuum drying oven and vacuum dried at 60℃ for 10 hours to obtain dried PVA sponge. (2) Dissolve PVP in 100 mL of water to obtain a PVP aqueous solution with a mass concentration of 10 mg / mL. Add the aqueous solution to liquid asphalt and stir for 2 h to obtain an aqueous solution containing PVP and liquid asphalt. The dried PVA sponge is fully immersed in the aqueous solution containing PVP and liquid asphalt under ultrasonic water bath conditions. The mass ratio of PVA sponge, PVP and liquid asphalt is 1:0.2:3. The water bath temperature is 50℃ and the time is 6 h. The resulting mixed solution is placed in a freeze dryer for freeze drying at a drying temperature of -30℃ for 10 h to obtain a PVA sponge impregnated with asphalt and PVP. (3) Place the PVA sponge impregnated with asphalt and PVP in a tube furnace, introduce high-purity argon gas with a flow rate of 100 mL / min, heat it from room temperature to 1300℃ at a heating rate of 4℃ / min, keep it at that temperature for 4 hours, and then let it cool naturally to room temperature. After cooling, take out the material, grind it through a 325-mesh sieve, and you will get the nitrogen-doped carbon anode material with a three-dimensional conductive network.

[0022] Example 3 A nitrogen-doped carbon anode material with a three-dimensional conductive network is prepared by the following method: (1) Cut 5cm 5cm A 5cm cube of PVA sponge was ultrasonically cleaned in anhydrous ethanol for 50 minutes to remove surface oxides or impurities. Then, it was placed in a vacuum drying oven and vacuum dried at 50℃ for 12 hours to obtain dried PVA sponge. (2) Dissolve PVP in 100 mL of water to obtain a PVP aqueous solution with a mass concentration of 30 mg / mL. Add the aqueous solution to liquid asphalt and stir for 1 h to obtain an aqueous solution containing PVP and liquid asphalt. The dried PVA sponge is fully immersed in the aqueous solution containing PVP and liquid asphalt under ultrasonic water bath conditions. The mass ratio of PVA sponge, PVP and liquid asphalt is 1.5:0.05:4. The water bath temperature is 60℃ and the time is 3 h. The resulting mixed solution is placed in a freeze dryer for freeze drying at a drying temperature of -20℃ for 12 h to obtain a PVA sponge impregnated with asphalt and PVP. (3) Place the PVA sponge impregnated with asphalt and PVP in a tube furnace, introduce high-purity argon gas with a flow rate of 200 mL / min, heat it from room temperature to 1400℃ at a heating rate of 2℃ / min, keep it at that temperature for 2 hours, and then let it cool naturally to room temperature. After cooling, take out the material, grind it through a 325-mesh sieve, and you will get the nitrogen-doped carbon anode material with a three-dimensional conductive network.

[0023] Example 4 A nitrogen-doped carbon anode material with a three-dimensional conductive network is prepared by the following method: (1) Cut 5cm 5cm A 5cm cube of PVA sponge was ultrasonically cleaned in anhydrous ethanol for 40 minutes to remove surface oxides or impurities. Then, it was placed in a vacuum drying oven and vacuum dried at 55℃ for 11 hours to obtain dried PVA sponge. (2) The above-mentioned dried PVA sponge was added to 100 mL of 5 wt% aminopropyltriethoxysilane in ethanol-water (ethanol:water = 0.5:9.5), heated to 60 °C, sonicated for 30 min, extracted, washed, and dried to obtain PVA sponge treated with aminosilane coupling agent. (3) Dissolve PVP in 100 mL of water to obtain a PVP aqueous solution with a mass concentration of 20 mg / mL. Add the aqueous solution to liquid asphalt and stir for 1.5 h to obtain an aqueous solution containing PVP and liquid asphalt. The PVA sponge treated with the above aminosilane coupling agent is fully impregnated into the aqueous solution containing PVP and liquid asphalt under ultrasonic water bath conditions. The mass ratio of PVA sponge, PVP and liquid asphalt is 1.2:0.1:3.5, the water bath temperature is 70℃ and the time is 4 h. The resulting mixed solution is placed in a freeze dryer for freeze drying at a drying temperature of -25℃ for 11 h to obtain a PVA sponge impregnated with asphalt and PVP. (4) Place the PVA sponge impregnated with asphalt and PVP in a tube furnace, introduce high-purity argon gas with a flow rate of 150 mL / min, heat it from room temperature to 1350℃ at a heating rate of 3℃ / min, keep it at that temperature for 3 hours, and then let it cool naturally to room temperature. After cooling, take out the material, grind it through a 325-mesh sieve, and you will get the nitrogen-doped carbon anode material with a three-dimensional conductive network.

[0024] Comparative Example 1 A carbon anode material is prepared by the following method: (1) Cut 5cm 5cm A 5cm cube of PVA sponge was ultrasonically cleaned in anhydrous ethanol for 40 minutes to remove surface oxides or impurities. Then, it was placed in a vacuum drying oven and vacuum dried at 55℃ for 11 hours to obtain dried PVA sponge. (2) Place the dried PVA sponge in a tube furnace, introduce high-purity argon gas with a flow rate of 150 mL / min, heat it from room temperature to 1350℃ at a heating rate of 3℃ / min, keep it at that temperature for 3 hours, and then let it cool naturally to room temperature. After cooling, take out the material, grind it through a 325-mesh sieve, and you will get the nitrogen-doped carbon anode material with a three-dimensional conductive network.

[0025] Comparative Example 2 A carbon anode material is prepared by the following method: (1) Cut 5cm 5cm A 5cm cube of PVA sponge was ultrasonically cleaned in anhydrous ethanol for 40 minutes to remove surface oxides or impurities. Then, it was placed in a vacuum drying oven and vacuum dried at 55℃ for 11 hours to obtain dried PVA sponge. (2) The above-mentioned dried PVA sponge was fully impregnated in liquid asphalt under ultrasonic water bath conditions. The mass ratio of PVA sponge to liquid asphalt was 1.2:3.5, the water bath temperature was 55℃, and the time was 4h. The resulting mixed solution was placed in a freeze dryer for freeze drying at -25℃ for 11h to obtain PVA sponge impregnated with asphalt and PVP. (3) Place the above-mentioned PVA sponge impregnated with asphalt in a tube furnace, introduce high-purity argon gas with a flow rate of 150 mL / min, heat it from room temperature to 1350℃ at a heating rate of 3℃ / min, keep it at that temperature for 3 hours, and then let it cool naturally to room temperature. After cooling, take out the material, grind it through a 325-mesh sieve, and obtain the nitrogen-doped carbon anode material with a three-dimensional conductive network.

[0026] Comparative Example 3 A nitrogen-doped carbon anode material with a three-dimensional conductive network is prepared by the following method: (1) Cut 5cm 5cm A 5cm cube of PVA sponge was ultrasonically cleaned in anhydrous ethanol for 40 minutes to remove surface oxides or impurities. Then, it was placed in a vacuum drying oven and vacuum dried at 55℃ for 11 hours to obtain dried PVA sponge. (2) The dried PVA sponge was added to 100 mL of 5 wt% γ-glycidoxypropyltrimethoxysilane (ethanol:water = 0.5:9.5) solution, heated to 60 °C, sonicated for 30 min, extracted, washed, and dried to obtain the PVA sponge treated with silane coupling agent. (3) Dissolve PVP in 100 mL of water to obtain a PVP aqueous solution with a mass concentration of 20 mg / mL. Add the aqueous solution to liquid asphalt and stir for 1.5 h to obtain an aqueous solution containing PVP and liquid asphalt. The PVA sponge treated with the above silane coupling agent is fully impregnated into the aqueous solution containing PVP and liquid asphalt under ultrasonic water bath conditions. The mass ratio of PVA sponge, PVP and liquid asphalt is 1.2:0.1:3.5, the water bath temperature is 70℃ and the time is 4 h. The resulting mixed solution is placed in a freeze dryer for freeze drying at a drying temperature of -25℃ for 11 h to obtain a PVA sponge impregnated with asphalt and PVP. (4) Place the PVA sponge impregnated with asphalt and PVP in a tube furnace, introduce high-purity argon gas with a flow rate of 150 mL / min, heat it from room temperature to 1350℃ at a heating rate of 3℃ / min, keep it at that temperature for 3 hours, and then let it cool naturally to room temperature. After cooling, take out the material, grind it through a 325-mesh sieve, and you will get the nitrogen-doped carbon anode material with a three-dimensional conductive network.

[0027] The negative electrode materials obtained in the examples and comparative examples were mixed with conductive agent (SP) and binder (PVDF) at a weight ratio of 80:10:10 and stirred evenly. The PVDF was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) to prepare a negative electrode slurry, which was coated on the surface of copper foil and dried in a vacuum drying oven at 110°C for 12 hours. After stamping, a negative electrode sheet was obtained. The obtained negative electrode sheet was assembled into a simulated battery in a Braun glove box under argon protection. The electrolyte was 1 mol / L LiPF6, the solvent was EC:DMC=1:1 (v / v), the lithium metal sheet was used as the counter electrode, and the American Cellgard2400 was used as the separator. A coin cell CR 2016 was assembled.

[0028] The above-mentioned simulated battery was tested for electrochemical performance using an Arbin BT2000 battery tester from the United States. The charge / discharge voltage range was 0.005-1.5V, and the charge / discharge rate was 0.1C. The test results are shown in Table 1 below.

[0029] Table 1. Performance comparison of the negative electrode materials described in the embodiments and comparative examples.

[0030] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon negative electrode material having a three-dimensional conductive network, characterized in that, The method comprises the following steps: S1, adsorbing a water solution containing polyvinylpyrrolidone and liquid asphalt on polyvinyl alcohol sponge, and freeze-drying to obtain a precursor; S2, high-temperature carbonization of the precursor to obtain the nitrogen-doped carbon negative electrode material with three-dimensional conductive network.

2. The method for preparing nitrogen-doped carbon anode material with a three-dimensional conductive network according to claim 1, characterized in that, In step S1, the mass ratio of polyvinyl alcohol sponge, polyvinylpyrrolidone and liquid asphalt is 1-1.5:0.05-0.2:3-4. Preferably, the concentration of polyvinylpyrrolidone in the water solution is 10-30 mg / mL.

3. The method of producing a nitrogen-doped carbon negative electrode material having a three-dimensional conductive network according to claim 1 or 2, characterized in that, In step S1, the adsorption temperature is 50-60℃, and the time is 3-6 h.

4. The method for preparing a nitrogen-doped carbon negative electrode material having a three-dimensional conductive network according to any one of claims 1 to 3, characterized in that, In step S1, the freeze-drying temperature is - (20-30) ℃, and the time is 10-12 h.

5. The method for preparing the nitrogen-doped carbon negative electrode material having a three-dimensional conductive network according to any one of claims 1 to 4, characterized in that, In step S2, the high-temperature carbonization temperature is 1300-1400℃, and the time is 2-4 h. Preferably, the high-temperature carbonization is carried out in an inert atmosphere, and the heating rate of the high-temperature carbonization is 2-4℃ / min.

6. The method for preparing the nitrogen-doped carbon negative electrode material having a three-dimensional conductive network according to any one of claims 1 to 5, characterized in that, In step S1, before adsorbing the water solution containing polyvinylpyrrolidone and liquid asphalt on polyvinyl alcohol sponge, the polyvinyl alcohol sponge is washed and vacuum dried. Preferably, the washing solvent is anhydrous ethanol, the vacuum drying temperature is 50-60℃, and the time is 10-12 h.

7. The method of claim 6, wherein the nitrogen-doped carbon negative electrode material having a three-dimensional conductive network is prepared by a method comprising: mixing a carbon source and a nitrogen source to form a mixture; and heating the mixture to form the nitrogen-doped carbon negative electrode material having a three-dimensional conductive network. In step S1, the polyvinyl alcohol sponge is modified by an amino silane coupling agent.

8. The method of claim 7, wherein the nitrogen-doped carbon negative electrode material having a three-dimensional conductive network is prepared by a method comprising: mixing a carbon source and a nitrogen source to form a mixture; and heating the mixture to form the nitrogen-doped carbon negative electrode material having a three-dimensional conductive network. The amino silane coupling agent is at least one of 3-aminopropyltriethoxysilane or 3-(2-aminoethylamino) propyltrimethoxysilane. Preferably, the mass ratio of polyvinyl alcohol sponge to amino silane coupling agent is 1:0.05-0.

2.

9. A nitrogen-doped carbon negative electrode material having a three-dimensional conductive network, characterized in that, The nitrogen-doped carbon negative electrode material with three-dimensional conductive network is prepared by the preparation method of any one of claims 1-8.

10. A lithium-ion battery, characterized by, The nitrogen-doped carbon negative electrode material with three-dimensional conductive network of claim 9.

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