Double-layer carbon-coated sodium ion battery hard carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion negative electrode material preparation, and particularly relates to a double-layer carbon-coated sodium ion battery hard carbon negative electrode material as well as a preparation method and application thereof. The method comprises the following steps: firstly, dispersing activated carbon powder into a tris (hydroxymethyl) aminomethane hydrochloride buffer solution, and then adding dopamine hydrochloride to carry out self-polymerization reaction, so as to obtain activated carbon powder coated with a first layer of polydopamine; then putting the activated carbon powder into a second layer of carbon source precursor solution, and heating in a water bath to obtain double-layer carbon-coated activated carbon powder; and finally, carrying out heat treatment. The preparation method comprises the following steps: firstly, coating the surface of activated carbon with a first layer of polydopamine by an in-situ polymerization method, then promoting uniform coating of a second layer of carbon source precursor by utilizing strong adhesion of the polydopamine, and carrying out heat treatment to obtain the double-layer carbon-coated hard carbon negative electrode material. The hard carbon negative electrode material can improve the energy density of the current sodium ion battery and accelerate the industrial application of the sodium ion battery.

Description

Technical Field

[0001] The present application belongs to the technical field of sodium ion negative electrode material preparation technology, and specifically relates to a double-layer carbon-coated sodium ion battery hard carbon negative electrode material and its preparation method and application. Background Art

[0002] Sodium-ion batteries, with their abundant sodium resources and low cost, are considered one of the most promising technologies for large-scale energy storage. The core of their industrialization lies in the development of high-performance and low-cost positive and negative electrode materials. Within the negative electrode material system, alloying and conversion materials exhibit high theoretical specific capacities, but in practice face bottlenecks such as insufficient conductivity and drastic volume expansion during the reaction, making it difficult to break through commercial barriers in the short term. In contrast, hard carbon materials stand out due to their low sodium storage potential and high reversible capacity, becoming the most promising negative electrode candidate material. Their unique short-range ordered / long-range disordered graphite-like microcrystalline structure not only forms abundant defect sites and microporous structures, providing multi-dimensional storage sites for sodium ions, but also has a large interlayer spacing (typically greater than 0.37 nm) that significantly reduces the diffusion barrier for sodium ions and improves the material's rate performance. However, hard carbon negative electrodes still have key defects such as low coulombic efficiency in the first cycle and obvious capacity decay over long cycles. This is mainly due to irreversible electrolyte decomposition on the material surface, structural stress accumulation during sodium ion insertion / extraction, and irreversible capture of sodium ions in micropores. These technical pain points have seriously restricted its large-scale application in sodium-ion batteries. Summary of the Invention

[0003] The purpose of the present invention is to address the deficiencies of the prior art and provide a double-layer carbon-coated hard carbon negative electrode material for sodium ion batteries, a preparation method thereof, and applications thereof, specifically adopting the following technical solutions: In a first aspect, the present invention provides a method for preparing a double-layer carbon-coated hard carbon negative electrode material for a sodium ion battery, comprising the following steps: The activated carbon powder is dispersed in tris(hydroxymethylaminomethane) hydrochloride buffer, and then dopamine hydrochloride is added to carry out a self-polymerization reaction. After the reaction is completed, the activated carbon powder is filtered and dried to obtain a first layer of polydopamine-coated activated carbon powder; placing the first layer of polydopamine-coated activated carbon powder in a second layer of carbon source precursor solution and heating the mixture in a water bath to obtain a double-layer carbon-coated activated carbon powder; The double-layer carbon-coated activated carbon powder is placed in a tubular furnace protected by an inert atmosphere for heat treatment to obtain the double-layer carbon-coated sodium ion battery hard carbon negative electrode material.

[0004] The application first adopts polydopamine as a first layer of coating material to coat the activated carbon powder, wherein the polydopamine is a kind of biomimetic polymer inspired by the adhesion mechanism of mussels; the application utilizes the strong adhesion of polydopamine to promote the uniform coating of the second layer of carbon, so that the open pore structure of the activated carbon is completely closed by the carbon coating layer, thereby obtaining a hard carbon negative material with more closed pore structure, and improving the sodium storage capacity and the first coulombic efficiency of the hard carbon negative electrode.

[0005] As a further preferred embodiment, the activated carbon powder is at least one of biomass-based activated carbon, phenolic resin-based activated carbon and pitch-based activated carbon.

[0006] As a further preferred embodiment, the mass ratio of the activated carbon powder to the dopamine hydrochloride is 100:1-10.

[0007] As a further preferred embodiment, the second layer of carbon source precursor solution includes at least one of a phenolic resin-containing aqueous solution, a phenolic resin-containing ethanol solution, a pitch-containing tetrahydrofuran solution, a pitch-containing toluene solution and a pitch-containing acetone solution. As a further preferred embodiment, the mass ratio of the first layer of polydopamine-coated activated carbon powder to the second layer of carbon source precursor in the second layer of carbon source precursor solution is 100:30-80.

[0008] If the amount of the second layer of carbon source precursor is too small in the above preparation process, the carbon coating layer formed cannot completely cover the open pore structure of the activated carbon, resulting in low first efficiency; if the amount is too large, the carbon coating layer formed is too thick, hindering the storage of sodium ions in the closed pores of the activated carbon, resulting in a decrease in reversible capacity.

[0009] As a further preferred embodiment, the heat treatment is a two-step heat treatment, and the specific process is as follows: The double-layer carbon-coated activated carbon powder is placed in a tube furnace protected by an inert atmosphere, heated to 400-600 DEG C at a heating rate of 1-5 DEG C / min, and kept for 2-4 h; then it is crushed, ball milled and sieved, and then placed in a tube furnace protected by an inert atmosphere, heated to 1300-1500 DEG C at a heating rate of 1-5 DEG C / min, and kept for 2-4 h.

[0010] In a second aspect, the application provides a double-layer carbon-coated hard carbon negative material for sodium ion batteries, which is prepared by the above preparation method.

[0011] In a third aspect, the application provides the use of the above double-layer carbon-coated hard carbon negative material for sodium ion batteries in the preparation of sodium ion batteries or negative sheets for sodium ion batteries.

[0012] In a fourth aspect, the present application provides a battery negative plate comprising the double-layer carbon-coated sodium-ion battery hard carbon negative material described above; the specific preparation process is as follows: The double-layer carbon-coated sodium-ion battery hard carbon negative material, a conductive agent, a binder and a solvent are mixed uniformly, coated on a metal substrate, and then vacuum dried to obtain the battery negative plate.

[0013] In a fifth aspect, the present application provides a sodium-ion battery comprising the battery negative plate described above.

[0014] The present application has the following beneficial effects: (1) The present application first coats a first layer of polydopamine on the surface of activated carbon through an in-situ polymerization method, and then uses the strong adhesion of polydopamine to promote the uniform coating of a second layer of carbon source precursor, and obtains a double-layer carbon-coated hard carbon negative material after heat treatment.

[0015] (2) The method of the present application can completely close the open pore structure of activated carbon with the carbon coating layer, so as to obtain a hard carbon negative material with more closed pore structure, and improve the sodium storage capacity and the first coulombic efficiency of the hard carbon negative electrode.

[0016] (3) The double-layer carbon-coated hard carbon negative material obtained by the method provided by the present application can improve the energy density of the current sodium-ion battery and accelerate the industrialization application of the sodium-ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0018] Figure 1 The sodium-ion battery hard carbon negative material prepared in Example 1 is shown in the charge-discharge curve graph; Figure 2 The sodium-ion battery hard carbon negative material prepared in Example 2 is shown in the charge-discharge curve graph; Figure 3 The sodium-ion battery hard carbon negative material prepared in Example 3 is shown in the charge-discharge curve graph; Figure 4 The sodium-ion battery hard carbon negative material prepared in Comparative Example 1 is shown in the charge-discharge curve graph; Figure 5 The sodium-ion battery hard carbon negative material prepared in Comparative Example 2 is shown in the charge-discharge curve graph; Figure 6 The sodium-ion battery hard carbon negative material prepared in Comparative Example 3 is shown in the charge-discharge curve graph. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0020] Example 1 A method for preparing a double-layer carbon-coated hard carbon negative electrode material for sodium ion batteries, which specifically comprises the following steps: Step 1: 5 g of coconut shell-based activated carbon was evenly dispersed in a tris-hydroxymethylaminomethane hydrochloride (Tris-HCl) buffer solution, followed by the addition of 0.25 g of dopamine hydrochloride (DA) and stirring for 12 hours to initiate a self-polymerization reaction. After the reaction, the mixture was filtered and dried to obtain the first layer of polydopamine (PDA)-coated activated carbon powder (denoted as P1). Step 2: Add 1.5 g of phenolic resin to a beaker containing 40 mL of alcohol and stir to form a phenolic resin alcohol solution (denoted as L1). Take 5 g of the P1 powder obtained in step 1 and add it to L1 and disperse it evenly. Then place the beaker in a water bath and heat and stir at 70°C until the alcohol is completely evaporated to obtain a double-layer carbon precursor-coated activated carbon powder (denoted as P2). Step 3: The P2 powder obtained in Step 2 was heated in a low-temperature tube furnace from room temperature to 600°C at a heating rate of 3°C / min and held for 2 hours. After crushing, ball milling, and sieving, it was then heated in a high-temperature tube furnace from room temperature to 1500°C at a heating rate of 3°C / min and held for 2 hours to produce a double-layer carbon-coated hard carbon powder (denoted as P3). This is the hard carbon anode material A for sodium-ion batteries.

[0021] The electrical performance test of the sodium ion battery hard carbon negative electrode material A was carried out in the form of a button cell, and its preparation method includes the following steps: The prepared hard carbon negative electrode material A, super-p conductive agent, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder were mixed in a mass ratio of 90:5:5, with a mass ratio of CMC to SBR of 1:1. Deionized water was added to form a uniform slurry, which was evenly coated on copper foil by coating. After drying, it was punched into circular electrode sheets and vacuum-dried at 120°C for 12 h. 2032-type button cells were assembled in a glove box using the prepared hard carbon as the working electrode, the metal sodium sheet as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio of 1:1) as the electrolyte, and a glass fiber separator. The button cells were tested for electrical performance on a Xinwei battery tester (room temperature 25°C, voltage range 0-2V vs. Na / Na +The result is as follows. Figure 1 As shown in the test results, the hard carbon material A has a current density of 15 mA·g -1 The first discharge capacity is 316.25 mAh·g -1 , the charge capacity is 267.78mAh·g -1 , the first Coulombic efficiency is 84.67%.

[0022] Example 2 A method for preparing a double-layer carbon-coated hard carbon negative electrode material for sodium ion batteries, which specifically comprises the following steps: Step 1: 5 g of coconut shell-based activated carbon was evenly dispersed in a tris-hydroxymethylaminomethane hydrochloride (Tris-HCl) buffer solution, followed by the addition of 0.25 g of dopamine hydrochloride (DA) and stirring for 12 hours to initiate a self-polymerization reaction. After the reaction, the mixture was filtered and dried to obtain the first layer of polydopamine (PDA)-coated activated carbon powder (denoted as P1). Step 2: Add 2.5 g of phenolic resin to a beaker containing 40 mL of alcohol and stir to form a phenolic resin alcohol solution (denoted as L1). Take 5 g of the P1 powder prepared in step 1 and add it to L1 and disperse it evenly. Then place the beaker in a water bath and heat and stir at 70°C until the alcohol is completely evaporated to obtain a double-layer carbon precursor-coated activated carbon powder (denoted as P2). Step 3: The P2 powder prepared in Step 2 was heated in a low-temperature tube furnace from room temperature to 600°C at a heating rate of 3°C / min and held for 2 hours. After crushing, ball milling, and sieving, it was then heated in a high-temperature tube furnace from room temperature to 1500°C at a heating rate of 3°C / min and held for 2 hours to produce a double-layer carbon-coated hard carbon powder (denoted as P3). This is the hard carbon anode material B for sodium-ion batteries.

[0023] The electrical performance test of the sodium ion battery hard carbon negative electrode material B was carried out in the form of a button cell, and its preparation method includes the following steps: The hard carbon negative electrode material B prepared above, super-p conductive agent and sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) binder were mixed in a mass ratio of 90:5:5, and the mass ratio of CMC and SBR was 1:1. Deionized water was added to mix into a uniform slurry, and evenly coated on copper foil by coating. After drying, it was punched into a round electrode sheet and vacuum dried at 120 ° C for 12 h. The prepared hard carbon was used as the working electrode, the metal sodium sheet was used as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio of 1:1) were used as the electrolyte, and a glass fiber separator was used to assemble a 2032 type button cell in a glove box. The electrical performance of the button cell was tested on a Xinwei battery tester (room temperature, voltage range 0-2V vs. Na / Na + The result is as follows. Figure 2As shown in the test results, the hard carbon material B has a current density of 15 mA·g -1 The first discharge capacity is 344.03 mAh·g -1 , the discharge capacity is 312.34 mAh·g -1 , the first Coulombic efficiency was 90.79%.

[0024] Example 3 A method for preparing a double-layer carbon-coated hard carbon negative electrode material for sodium ion batteries, which specifically comprises the following steps: Step 1: 5 g of coconut shell-based activated carbon was evenly dispersed in a tris-hydroxymethylaminomethane hydrochloride (Tris-HCl) buffer solution, followed by the addition of 0.25 g of dopamine hydrochloride (DA) and stirring for 12 hours to initiate a self-polymerization reaction. After the reaction, the mixture was filtered and dried to obtain the first layer of polydopamine (PDA)-coated activated carbon powder (denoted as P1). Step 2: Add 3.5 g of phenolic resin to a beaker containing 40 mL of alcohol and stir to form a phenolic resin alcohol solution (denoted as L1). Take 5 g of the P1 powder prepared in step 1 and add it to L1 and disperse it evenly. Then place the beaker in a water bath and heat at 70°C with stirring until the alcohol is completely evaporated to obtain a double-layer carbon precursor-coated activated carbon powder (denoted as P2). Step 3: The P2 powder prepared in Step 2 was heated in a low-temperature tube furnace from room temperature to 600°C at a heating rate of 3°C / min and held for 2 hours. After crushing, ball milling, and sieving, it was then heated in a high-temperature tube furnace from room temperature to 1500°C at a heating rate of 3°C / min and held for 2 hours to produce a double-layer carbon-coated hard carbon powder (denoted as P3). This is the hard carbon anode material C for sodium-ion batteries.

[0025] The electrical performance test of the hard carbon negative electrode material C for sodium ion batteries was carried out in the form of button cells, and the preparation method thereof comprises the following steps: The hard carbon negative electrode material C prepared above, super-p conductive agent and sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) binder were mixed in a mass ratio of 90:5:5, and the mass ratio of CMC and SBR was 1:1. Deionized water was added to mix into a uniform slurry, and evenly coated on copper foil by coating. After drying, it was punched into a round electrode sheet and vacuum dried at 120 ° C for 12 h. The prepared hard carbon was used as the working electrode, the metal sodium sheet was used as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio of 1:1) were used as the electrolyte, and a glass fiber separator was used to assemble a 2032 type button cell in a glove box. The electrical performance of the button cell was tested on a Xinwei battery tester (room temperature, voltage range 0-2V vs. Na / Na + The result is as follows. Figure 3As shown in the test results, the hard carbon material C has a current density of 15 mA·g -1 The first discharge capacity is 335.67 mAh·g -1 , the charge capacity is 303.86 mAh g -1 , the first Coulombic efficiency is 90.53%.

[0026] Comparative Example 1 A method for preparing a hard carbon negative electrode material for a sodium ion battery comprises the following specific steps: directly placing coconut shell-based activated carbon in a high-temperature tubular furnace for heat treatment from room temperature to 1500°C at a heating rate of 3°C / min and holding the temperature for 2 hours to obtain a hard carbon negative electrode material D for a sodium ion battery.

[0027] The electrical performance test of the hard carbon negative electrode material D for sodium ion batteries was carried out in the form of button cells. The preparation method thereof includes the following steps: The hard carbon negative electrode material D prepared above, super-p conductive agent and sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) binder were mixed in a mass ratio of 90:5:5, and the mass ratio of CMC and SBR was 1:1. Deionized water was added to mix into a uniform slurry, and evenly coated on copper foil by coating. After drying, it was punched into a round electrode sheet and vacuum dried at 120 ° C for 12 h. The prepared hard carbon was used as the working electrode, the metal sodium sheet was used as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio of 1:1) were used as the electrolyte, and a glass fiber separator was used to assemble a 2032 type button cell in a glove box. The electrical performance of the button cell was tested on a Xinwei battery tester (room temperature, voltage range 0-2V vs. Na / Na + The result is as follows. Figure 4 As shown in the test results, the hard carbon material D has a current density of 15 mA·g -1 The first discharge capacity is 118.25 mAh·g -1 , the charge capacity is 87.22 mAh g -1 , the first Coulombic efficiency is 73.76%.

[0028] Comparative Example 2 A method for preparing a single-layer carbon-coated hard carbon negative electrode material for a sodium ion battery comprises the following steps: Step 1: 5 g of coconut shell-based activated carbon was evenly dispersed in a tris-hydroxymethylaminomethane hydrochloride (Tris-HCl) buffer solution, followed by the addition of 0.25 g of dopamine hydrochloride (DA) and stirring for 12 hours to initiate a self-polymerization reaction. After the reaction, the mixture was filtered and dried to obtain the first layer of polydopamine (PDA)-coated activated carbon powder (denoted as P1). Step 2: The P1 powder prepared in Step 1 was heated in a low-temperature tube furnace from room temperature to 600°C at a heating rate of 3°C / min and held for 2 hours. After crushing, ball milling, and sieving, it was then heated in a high-temperature tube furnace from room temperature to 1500°C at a heating rate of 3°C / min and held for 2 hours to produce a single-layer carbon-coated hard carbon powder (denoted as P4). This is the hard carbon anode material E for sodium-ion batteries.

[0029] The electrical performance test of the hard carbon negative electrode material E for sodium ion batteries was carried out in the form of button cells, and the preparation method thereof includes the following steps: The hard carbon negative electrode material E, super-p conductive agent, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder prepared above were mixed in a mass ratio of 90:5:5, and the mass ratio of CMC and SBR was 1:1. Deionized water was added to mix into a uniform slurry, and evenly coated on the copper foil by coating. After drying, it was punched into a circular electrode sheet and vacuum dried at 120 ° C for 12 h. The prepared hard carbon was used as the working electrode, the metal sodium sheet was used as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio of 1:1) were used as the electrolyte, and a glass fiber separator was used to assemble a 2032 type button battery in a glove box. The electrical performance of the button battery was tested on a Xinwei battery tester (room temperature, voltage range 0-2V vs.Na / Na+). The results are as follows Figure 5 As shown in the test results, the hard carbon material E has a current density of 15 mA·g -1 The first discharge capacity is 92.17 mAh·g -1 , the charge capacity is 126.6 mAh g -1 , the first Coulombic efficiency is 72.81%.

[0030] Comparative Example 3 A method for preparing a single-layer carbon-coated hard carbon negative electrode material for a sodium ion battery comprises the following steps: Step 1: Add 2.5 g of phenolic resin to a beaker containing 40 mL of alcohol and stir to form a phenolic resin alcohol solution (denoted as L1). Then, take 5 g of coconut shell-based activated carbon and add it to L1 and disperse it evenly. Then, place the beaker in a water bath and heat with stirring at 70°C until the alcohol is completely evaporated to obtain a single-layer carbon precursor-coated activated carbon powder (denoted as P5). Step 2: The P5 powder prepared in Step 1 was heated in a low-temperature tube furnace from room temperature to 600°C at a heating rate of 3°C / min and held for 2 hours. After crushing, ball milling, and sieving, it was then heated in a high-temperature tube furnace from room temperature to 1500°C at a heating rate of 3°C / min and held for 2 hours to produce hard carbon powder P6 coated with a single layer of phenolic resin carbon. This is the hard carbon anode material F for sodium ion batteries.

[0031] The electrical performance test of the hard carbon negative electrode material F for sodium ion batteries was carried out in the form of button cells. The preparation method thereof includes the following steps: The hard carbon negative electrode material F prepared above, super-p conductive agent and sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) binder were mixed in a mass ratio of 90:5:5, and the mass ratio of CMC and SBR was 1:1. Deionized water was added to mix into a uniform slurry, and evenly coated on copper foil by coating. After drying, it was punched into a round electrode sheet and vacuum dried at 120 ° C for 12 h. The prepared hard carbon was used as the working electrode, the metal sodium sheet was used as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio of 1:1) were used as the electrolyte, and a glass fiber separator was used to assemble a 2032 type button cell in a glove box. The electrical performance of the button cell was tested on a Xinwei battery tester (room temperature, voltage range 0-2V vs. Na / Na + The result is as follows. Figure 6 As shown in the test results, the hard carbon material F has a current density of 15 mA·g -1 The first discharge capacity is 148.74 mAh·g -1 , the charge capacity is 193.09 mAh g -1 , the first coulombic efficiency is 77.03%.

[0032] The electrochemical performance comparison of the hard carbon negative electrode materials for sodium ion batteries prepared in Examples 1-3 and Comparative Examples 1-3 is shown in Table 1. Table 1 Comparison of electrochemical properties of materials The present invention first polymerizes dopamine hydrochloride in a liquid phase environment at pH=8.5 and coats it on the surface of activated carbon. The activated carbon surface is then modified to improve its dispersibility in the liquid phase and enhance its binding properties with phenolic resin, allowing the phenolic resin to be more evenly coated on the activated carbon surface. The phenolic resin is then coated on the activated carbon surface by liquid phase evaporation, blocking a certain number of open pores to create closed pores, thereby increasing the platform capacity and thus the reversible capacity. A comparative analysis of material ratios and electrochemical performance data shows that the introduction of dopamine hydrochloride and the composite ratio of activated carbon to phenolic resin have a significant impact on the electrochemical performance. From the data of Comparative Examples 1 and 2, simply coating the activated carbon surface with polydopamine does not have a significant effect on the capacity and initial efficiency. However, from the comparison between Comparative Example 3 and Example 2, at the same ratio of phenolic resin to activated carbon, the activated carbon coated with polydopamine has better performance. The charge capacity of Comparative Example 3 without polydopamine surface modification is 148.74 mAh g -1, the first efficiency is 77.03%, which are both lower than the charge specific capacity and first efficiency of Example 2 with polydopamine surface modification. This shows that the main role of dopamine is to make the phenolic resin coating more uniform. Under the combined action of the two, the capacity and efficiency of the activated carbon can be further improved. As the ratio of activated carbon to phenolic resin increases from 100:30 (Example 1) to 100:70 (Example 3), the initial charge / discharge capacity shows a trend of first significantly increasing and then stabilizing. The charge capacity of Examples 2 and 3 both exceed 300 mAh·g -1 , which is higher than the 87.22 mAh·g of the whole activated carbon comparative example 1. -1 , indicating that the introduction of polydopamine and phenolic resin can effectively improve the capacity performance. In summary, the pre-modification of the activated carbon surface with polydopamine before phenolic resin coating is a feasible solution, and when the activated carbon and phenolic resin are mixed in a ratio of 100:50 (Example 2), the high capacity (charge 312.34 mAh·g -1 , discharge 344.03 mAh·g -1 ) and excellent coulombic efficiency (90.79%), providing an important reference for the optimization of high-performance battery materials.

[0033] The embodiments of the present application are described above in conjunction with the accompanying drawings. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the core idea of ​​the present application, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present application, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present application and the claims, all of which are within the protection of the present application.

Claims

1. A method for preparing a double-layer carbon-coated hard carbon negative electrode material for sodium ion batteries, characterized in that: The following steps are involved: The activated carbon powder is dispersed in tris(hydroxymethylaminomethane) hydrochloride buffer, and then dopamine hydrochloride is added to carry out a self-polymerization reaction. After the reaction is completed, the activated carbon powder is filtered and dried to obtain a first layer of polydopamine-coated activated carbon powder; placing the first layer of polydopamine-coated activated carbon powder in a second layer of carbon source precursor solution and heating the mixture in a water bath to obtain a double-layer carbon-coated activated carbon powder; The double-layer carbon-coated activated carbon powder is placed in a tubular furnace protected by an inert atmosphere for heat treatment to obtain the double-layer carbon-coated sodium ion battery hard carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that The activated carbon powder contains at least one of biomass-based activated carbon, phenolic resin-based activated carbon and asphalt-based activated carbon.

3. The preparation method according to claim 2, characterized in that The mass ratio of the activated carbon powder to the dopamine hydrochloride is 100:1-10.

4. The preparation method according to claim 1, characterized in that The second layer carbon source precursor solution includes at least one of an aqueous solution containing phenolic resin, an ethanol solution containing phenolic resin, a tetrahydrofuran solution containing asphalt, a toluene solution containing asphalt, and an acetone solution containing asphalt.

5. The preparation method according to claim 4, characterized in that The mass ratio of the first layer of polydopamine-coated activated carbon powder to the second layer of carbon source precursor in the second layer of carbon source precursor solution is 100:30-80.

6. The preparation method according to claim 1, characterized in that The heat treatment is a two-step heat treatment, and the specific process is as follows: The double-layer carbon-coated activated carbon powder is placed in a tubular furnace protected by an inert atmosphere, heated to 400-600°C at a heating rate of 1-5°C / min, and kept warm for 2-4 hours; then crushed, ball-milled, sieved, and placed in a tubular furnace protected by an inert atmosphere, and then heated to 1300-1500°C at a heating rate of 1-5°C / min, and kept warm for 2-4 hours.

7. A double-layer carbon-coated hard carbon negative electrode material for sodium ion batteries, characterized in that: The invention is prepared by the preparation process according to any one of claims 1 to 6.

8. Use of the double-layer carbon-coated sodium ion battery hard carbon negative electrode material according to claim 7 in the preparation of a sodium ion battery or a sodium ion battery negative electrode sheet.

9. A battery negative electrode sheet, characterized in that: The double-layer carbon-coated sodium ion battery hard carbon negative electrode material according to claim 7 is prepared as follows: The double-layer carbon-coated sodium ion battery hard carbon negative electrode material, a conductive agent, a binder and a solvent are mixed evenly, coated on a metal substrate, and then vacuum dried to obtain a battery negative electrode sheet.

10. A sodium ion battery, characterized in that: The battery negative electrode sheet according to claim 9 is included.

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