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

Abstract

The application belongs to the technical field of sodium ion negative electrode material preparation technology, and particularly relates to a double-layer carbon-coated sodium ion battery hard carbon negative electrode material and a preparation method and application thereof. The method comprises the following steps: dispersing active carbon powder in a trimethylol aminomethane hydrochloride buffer solution, then adding hydrochloric acid dopamine for self-polymerization reaction to obtain first-layer polydopamine-coated active carbon powder; then placing the active carbon powder in a second-layer carbon source precursor solution, water-bath heating to obtain double-layer carbon-coated active carbon powder; and finally performing heat treatment to obtain the double-layer carbon-coated hard carbon negative electrode material. The method of the application firstly coats the first-layer polydopamine on the surface of the active carbon through in-situ polymerization, then promotes uniform coating of the second-layer carbon source precursor by using the strong adhesion of the polydopamine, and obtains the double-layer carbon-coated hard carbon negative electrode material after heat treatment; the hard carbon negative electrode material can improve the energy density of the current sodium ion battery and accelerate the industrialization application of the sodium ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion negative electrode material preparation technology, and particularly relates to a double-layer carbon-coated sodium ion battery hard carbon negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Sodium ion batteries are considered as one of the most promising technical routes in the field of large-scale energy storage due to the advantages of abundant sodium resources and low cost. The core of the industrialization process is to develop positive and negative electrode materials with high performance and low cost. In the negative electrode material system, although alloying and conversion materials exhibit high theoretical specific capacity, they still face some bottleneck problems such as insufficient conductivity and severe volume expansion during the reaction process, which are difficult to break through the commercialization barrier in the short term. In contrast, hard carbon materials stand out due to their low sodium storage potential and high reversible capacity, and become the most practical negative electrode candidate material. Its unique short-range ordered / long-range disordered graphite-like microcrystalline structure not only forms a large number of defect sites and microporous structures to provide multi-dimensional storage sites for sodium ions, but also significantly reduces the diffusion barrier of sodium ions and improves the rate performance due to the large interlayer spacing (usually greater than 0.37 nm). However, the hard carbon negative electrode still has some key defects such as low first-cycle coulombic efficiency and obvious capacity decay during long-term cycling, which are mainly caused by the problems such as irreversible decomposition of electrolyte on the surface of the material, accumulation of structural stress during sodium ion intercalation / deintercalation, and irreversible capture of sodium ions in micropores, which seriously restrict the large-scale application process of sodium ion batteries. SUMMARY

[0003] The purpose of the present application is to solve the problems of the prior art, and to provide a double-layer carbon-coated sodium ion battery hard carbon negative electrode material and a preparation method and application thereof. The technical scheme adopted is as follows:

[0004] In a first aspect, the present application provides a preparation method of a double-layer carbon-coated sodium ion battery hard carbon negative electrode material, comprising the following steps:

[0005] The active carbon powder is dispersed in a tris-hydroxymethyl aminomethane hydrochloride buffer solution, and then dopamine hydrochloride is added for self-polymerization reaction. After the reaction is completed, the product is filtered and dried to obtain a first layer of polydopamine-coated active carbon powder;

[0006] The first layer of polydopamine-coated active carbon powder is placed in a second layer of carbon source precursor solution and subjected to water bath heating to obtain double-layer carbon-coated active carbon powder;

[0007] The double-layer carbon-coated active carbon powder is placed in a tube furnace under inert atmosphere protection for heat treatment to obtain the double-layer carbon-coated sodium ion battery hard carbon negative electrode material.

[0008] The present application firstly 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 present 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.

[0009] 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.

[0010] As a further preferred embodiment, the mass ratio of the activated carbon powder to the dopamine hydrochloride is 100:1-10.

[0011] As a further preferred embodiment, the second layer of carbon source precursor solution includes at least one of a water solution containing phenolic resin, an ethanol solution containing phenolic resin, a tetrahydrofuran solution containing pitch, a toluene solution containing pitch, and an acetone solution containing pitch.

[0012] 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.

[0013] 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.

[0014] As a further preferred embodiment, the heat treatment is a two-step heat treatment, and the specific process is as follows:

[0015] The double-layer carbon-coated activated carbon powder is placed in a tube furnace protected by an inert atmosphere, heated to 400-600 ℃ at a heating rate of 1-5 ℃ / 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 ℃ at a heating rate of 1-5 ℃ / min, and kept for 2-4 h.

[0016] In a second aspect, the present application provides a double-layer carbon-coated sodium ion battery hard carbon negative material prepared by the above preparation method.

[0017] In a third aspect, the present application provides the use of the above-mentioned double-layer carbon-coated sodium ion battery hard carbon negative material in the preparation of a sodium ion battery or a sodium ion battery negative electrode sheet.

[0018] In a fourth aspect, the present application provides a battery negative plate, comprising the above-mentioned double-layer carbon-coated sodium-ion battery hard carbon negative material; the specific preparation process is as follows:

[0019] The double-layer carbon-coated sodium-ion battery hard carbon negative material, a conductive agent, a binder and a solvent are uniformly mixed, coated on a metal substrate, and then vacuum dried to obtain the battery negative plate.

[0020] In a fifth aspect, the present application provides a sodium-ion battery, comprising the above-mentioned battery negative plate.

[0021] The present application has the following beneficial effects:

[0022] (1) The present application first coats a first layer of polydopamine on the surface of activated carbon by 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, so as to obtain a double-layer carbon-coated hard carbon negative material after heat treatment.

[0023] (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.

[0024] (3) The double-layer carbon-coated hard carbon negative material obtained by the method of 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

[0025] 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.

[0026] Figure 1 The figure shows the charge-discharge curve of the sodium-ion battery hard carbon negative material prepared in Example 1;

[0027] Figure 2 The figure shows the charge-discharge curve of the sodium-ion battery hard carbon negative material prepared in Example 2;

[0028] Figure 3 The figure shows the charge-discharge curve of the sodium-ion battery hard carbon negative material prepared in Example 3;

[0029] Figure 4 The figure shows the charge-discharge curve of the sodium-ion battery hard carbon negative material prepared in Comparative Example 1;

[0030] Figure 5 Figure 4 shows the charge-discharge curve of the sodium-ion battery hard carbon negative material prepared in Comparative Example 2;

[0031] Figure 6 Figure 5 shows the charge-discharge curve of the sodium-ion battery hard carbon negative material prepared in Comparative Example 3. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0033] Example 1

[0034] A preparation method of a double-layer carbon-coated sodium-ion battery hard carbon negative material, which specifically comprises the following steps:

[0035] Step 1: 5 g of coconut shell-based activated carbon is uniformly dispersed in a Tris-HCl buffer solution, then 0.25 g of dopamine hydrochloride (DA) is added, and stirring is performed for 12 hours to initiate a self-polymerization reaction. After the reaction is completed, suction filtration and drying are performed to obtain a first layer of polydopamine (PDA)-coated activated carbon powder (denoted as P1);

[0036] Step 2: 1.5 g of phenol formaldehyde resin is added to a beaker containing 40 mL of alcohol to form a phenol formaldehyde resin alcohol solution (denoted as L1), and 5 g of P1 powder obtained in step 1 is added to L1 and dispersed uniformly. Then the beaker is placed in a water bath kettle and heated and stirred at 70°C until the alcohol is completely evaporated, to obtain a double-layer carbon precursor-coated activated carbon powder (denoted as P2);

[0037] Step 3: The P2 powder obtained in step 2 is heated from room temperature to 600°C in a low-temperature tube furnace at a heating rate of 3°C / min, and is kept at 600°C for 2 hours. After being crushed, ball milled and sieved, it is heated from room temperature to 1500°C in a high-temperature tube furnace at a heating rate of 3°C / min, and is kept at 1500°C for 2 hours, to obtain a double-layer carbon-coated hard carbon powder (denoted as P3). Thus, a sodium-ion battery hard carbon negative material A is obtained.

[0038] The electrical performance test of the sodium-ion battery hard carbon negative material A is performed in the form of a button cell, and the preparation method thereof comprises the following steps:

[0039] The hard carbon negative material A prepared above, super-p conductive agent and carboxymethyl cellulose sodium (CMC), butyl benzene glue (SBR) binder are mixed into a uniform slurry in a mass ratio of 90:5:5, the mass ratio of CMC and SBR is 1:1, deionized water is added, and the mixture is uniformly coated on a copper foil. After drying, the electrode sheet is punched into a circular shape, and vacuum dried at 120 ℃ for 12 h. The prepared hard carbon is used as the working electrode, a metal sodium sheet is used as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio 1:1) are used as the electrolyte, and a glass fiber separator is used to assemble a 2032 type button cell in a glove box. The button cell is tested for electrical performance on a new battery tester (room temperature 25℃, voltage range 0-2V vs. Na / Na + ). The results are shown in Figure 1 , and the test results show that the hard carbon material A has a first discharge specific capacity of 316.25 mAh·g -1 , a charge specific capacity of 267.78 mAh·g -1 , and a first coulombic efficiency of 84.67% when the current density is 15 mA·g -1 .

[0040] Example 2

[0041] A preparation method of a double-layer carbon-coated sodium ion battery hard carbon negative material, which specifically comprises the following steps:

[0042] Step 1: 5 g of coconut shell-based activated carbon is uniformly dispersed in a Tris-HCl buffer solution, then 0.25 g of dopamine hydrochloride (DA) is added, and stirring is performed for 12 hours to initiate a self-polymerization reaction. After the reaction is completed, the mixture is filtered and dried to obtain a first layer of polydopamine (PDA)-coated activated carbon powder (denoted as P1);

[0043] Step 2: 2.5 g of phenol formaldehyde resin is added to a beaker containing 40 mL of alcohol to form a phenol formaldehyde resin alcohol solution (denoted as L1), and 5 g of the P1 powder prepared in step 1 is added to L1 and uniformly dispersed. The beaker is then placed in a water bath at 70℃ and heated and stirred until the alcohol is completely evaporated to obtain a double-layer carbon precursor-coated activated carbon powder (denoted as P2);

[0044] Step 3: The P2 powder prepared in step 2 is heated from room temperature to 600℃ in a low-temperature tube furnace at a heating rate of 3℃ / min, and held for 2 hours. After being crushed, ball milled and sieved, the powder is heated from room temperature to 1500℃ in a high-temperature tube furnace at a heating rate of 3℃ / min, and held for 2 hours to obtain a double-layer carbon-coated hard carbon powder (denoted as P3). A sodium ion battery hard carbon negative material B is obtained.

[0045] The electrical performance of sodium-ion battery hard carbon anode material B was tested using a coin cell. Its preparation method includes the following steps:

[0046] The prepared hard carbon anode material B, super-p conductive agent, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder were mixed with deionized water at a mass ratio of 90:5:5 and a CMC to SBR mass ratio of 1:1 to form a homogeneous slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the working electrode, a sodium metal sheet as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio 1:1) as the electrolyte, and a glass fiber separator, a 2032 type button cell was assembled in a glove box. The electrical performance of the button cell was tested on a Newway battery tester (room temperature, voltage range 0-2V vs. Na / Na). + The result is as follows: Figure 2 As shown, the test results indicate that hard carbon material B, at a current density of 15 mA·g... -1 At that time, the initial discharge specific capacity was 344.03 mAh·g. -1 The discharge specific capacity is 312.34 mAh·g. -1 The initial Coulomb efficiency was 90.79%.

[0047] Example 3

[0048] A method for preparing a double-layer carbon-coated hard carbon anode material for sodium-ion batteries, specifically including the following steps:

[0049] Step 1: Disperse 5 g of coconut shell-based activated carbon uniformly in a Tris-HCl buffer solution, then add 0.25 g of dopamine hydrochloride (DA) and stir for 12 hours to initiate a self-polymerization reaction. After the reaction is completed, filter and dry to obtain activated carbon powder with the first layer of polydopamine (PDA) coating (denoted as P1).

[0050] 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 and stir at 70°C until the alcohol is completely evaporated to obtain activated carbon powder coated with a double-layer carbon precursor (denoted as P2).

[0051] Step 3: The P2 powder obtained in Step 2 is heated from room temperature to 600℃ in a low-temperature tube furnace at a heating rate of 3℃ / min and held for 2 hours. After pulverizing, ball milling, and sieving, it is then heated from room temperature to 1500℃ in a high-temperature tube furnace at a heating rate of 3℃ / min and held for 2 hours to obtain a double-layer carbon-coated hard carbon powder (denoted as P3). This yields the hard carbon anode material C for sodium-ion batteries.

[0052] The electrical performance of the hard carbon anode material for sodium-ion batteries (C) was tested using a coin cell. Its preparation method includes the following steps:

[0053] The prepared hard carbon anode material C, super-p conductive agent, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder were mixed with deionized water at a mass ratio of 90:5:5 and a CMC to SBR mass ratio of 1:1 to form a homogeneous slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the working electrode, a sodium metal sheet as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio 1:1) as the electrolyte, and a glass fiber separator, a 2032 type button cell was assembled in a glove box. The electrical performance of the button cell was tested on a Newway battery tester (room temperature, voltage range 0-2V vs. Na / Na). + The result is as follows: Figure 3 As shown, the test results indicate that hard carbon material C can withstand current densities of 15 mA·g. -1 At that time, the initial discharge specific capacity was 335.67 mAh·g. -1 The charging specific capacity is 303.86 mAh·g. -1 The initial Coulomb efficiency was 90.53%.

[0054] Comparative Example 1

[0055] A method for preparing a hard carbon anode material for sodium-ion batteries involves directly placing coconut shell-based activated carbon in a high-temperature tube furnace for heat treatment, raising the temperature from room temperature to 1500°C at a rate of 3°C / min, and holding the temperature for 2 hours to obtain the hard carbon anode material D for sodium-ion batteries.

[0056] The electrical performance of the sodium-ion battery hard carbon anode material D was tested using a coin cell. Its preparation method includes the following steps:

[0057] The prepared hard carbon anode material D, super-p conductive agent, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder were mixed with deionized water at a mass ratio of 90:5:5 and a CMC to SBR mass ratio of 1:1 to form a homogeneous slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the working electrode, a sodium metal sheet as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio 1:1) as the electrolyte, and a glass fiber separator, a 2032 type button cell was assembled in a glove box. The electrical performance of the button cell was tested on a Newway battery tester (room temperature, voltage range 0-2V vs. Na / Na). + The result is as follows: Figure 4 As shown, the test results indicate that hard carbon material D, at a current density of 15 mA·g -1 At that time, the initial discharge specific capacity was 118.25 mAh·g. -1 The charging specific capacity is 87.22 mAh·g. -1 The initial Coulomb efficiency was 73.76%.

[0058] Comparative Example 2

[0059] A method for preparing a single-layer carbon-coated hard carbon anode material for sodium-ion batteries, specifically including the following steps:

[0060] Step 1: Disperse 5 g of coconut shell-based activated carbon uniformly in a Tris-HCl buffer solution, then add 0.25 g of dopamine hydrochloride (DA) and stir for 12 hours to initiate a self-polymerization reaction. After the reaction is completed, filter and dry to obtain activated carbon powder with the first layer of polydopamine (PDA) coating (denoted as P1).

[0061] Step 2: The P1 powder obtained in Step 1 is heated from room temperature to 600℃ in a low-temperature tube furnace at a heating rate of 3℃ / min and held for 2 hours. After pulverizing, ball milling, and sieving, it is then heated from room temperature to 1500℃ in a high-temperature tube furnace at a heating rate of 3℃ / min and held for 2 hours to obtain a single-layer carbon-coated hard carbon powder (denoted as P4). This yields the hard carbon anode material E for sodium-ion batteries.

[0062] The E-electrical performance of the hard carbon anode material for sodium-ion batteries was tested using a coin cell. Its preparation method includes the following steps:

[0063] The prepared hard carbon anode material E, super-p conductive agent, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder were mixed with deionized water at a mass ratio of 90:5:5 and a CMC to SBR mass ratio of 1:1 to form a homogeneous slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the working electrode, a sodium metal sheet as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio 1:1) as the electrolyte, and a glass fiber separator, a 2032 type button cell was assembled in a glove box. The electrical performance of the button cell was tested on a Newway battery tester (room temperature, voltage range 0-2V vs. Na / Na+). The results are as follows: Figure 5 As shown, the test results indicate that hard carbon material E can withstand current densities of 15 mA·g. -1 At that time, the initial discharge specific capacity was 92.17 mAh·g. -1 The charging specific capacity is 126.6 mAh·g -1 The initial Coulomb efficiency was 72.81%.

[0064] Comparative Example 3

[0065] A method for preparing a single-layer carbon-coated hard carbon anode material for sodium-ion batteries, specifically including the following steps:

[0066] 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). Add 5 g of coconut shell-based activated carbon to L1 and disperse evenly. Then place the beaker in a water bath and heat at 70°C while stirring until the alcohol is completely evaporated to obtain activated carbon powder coated with a single layer of carbon precursor (denoted as P5).

[0067] Step 2: The P5 powder obtained in Step 1 is heated from room temperature to 600℃ in a low-temperature tube furnace at a heating rate of 3℃ / min and held for 2 hours. After pulverization, ball milling, and sieving, it is then heated from room temperature to 1500℃ in a high-temperature tube furnace at a heating rate of 3℃ / min and held for 2 hours to obtain hard carbon powder P6 coated with a single layer of phenolic resin carbon. This yields the hard carbon anode material F for sodium-ion batteries.

[0068] The electrical performance of the hard carbon anode material for sodium-ion batteries was tested using a coin cell. Its preparation method includes the following steps:

[0069] The prepared hard carbon anode material F, super-p conductive agent, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder were mixed with deionized water at a mass ratio of 90:5:5 and a CMC to SBR mass ratio of 1:1 to form a homogeneous slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the working electrode, a sodium metal sheet as the counter electrode, 1M NaClO4 and EC / DMC (volume ratio 1:1) as the electrolyte, and a glass fiber separator, a 2032 type button cell was assembled in a glove box. The electrical performance of the button cell was tested on a Newway battery tester (room temperature, voltage range 0-2V vs. Na / Na). + The result is as follows: Figure 6 As shown, the test results indicate that the hard carbon material F can withstand current densities of 15 mA·g. -1 At that time, the initial discharge specific capacity was 148.74 mAh·g. -1 The charging specific capacity is 193.09 mAh·g. -1 The initial Coulomb efficiency was 77.03%.

[0070] Table 1 compares the electrochemical performance of the sodium-ion battery hard carbon anode materials prepared in Examples 1-3 and Comparative Examples 1-3.

[0071] Table 1 Comparison of Electrochemical Performance of Materials

[0072]

[0073] This invention first polymerizes dopamine hydrochloride in a liquid phase environment at pH 8.5 and coats it onto the surface of activated carbon, modifying the activated carbon surface to improve its dispersibility in the liquid phase and enhance its binding with phenolic resin, allowing the phenolic resin to more uniformly coat the activated carbon surface. Then, the phenolic resin is coated onto the activated carbon surface through liquid-phase evaporation, blocking a certain number of open pores to create closed pores, thereby increasing the plateau capacity and ultimately improving the reversible capacity. Comparative analysis of material ratios and electrochemical performance data shows that the introduction of dopamine hydrochloride and the composite ratio of activated carbon and phenolic resin have a significant impact on electrochemical performance. Based on the data from Comparative Examples 1 and 2, simply coating the activated carbon surface with polydopamine does not significantly affect the capacity and first-time efficiency. However, comparing Comparative Example 3 and Example 2, at the same ratio of phenolic resin to activated carbon, the activated carbon coated with polydopamine exhibits superior performance. Comparative Example 3, without polydopamine surface modification, has a charge specific capacity of 148.74 mAh·g. -1The initial charge / discharge capacity was 77.03%, both lower than the specific charge capacity and initial charge / discharge capacity of Example 2, which was modified with polydopamine. This indicates that the main function of dopamine is to make the phenolic resin coating more uniform, and the combined effect of the two can greatly improve the capacity and efficiency of activated carbon. As the ratio of activated carbon to phenolic resin increased from 100:30 (Example 1) to 100:70 (Example 3), the initial charge / discharge capacity showed a trend of first significantly increasing and then stabilizing. The charge capacity of Examples 2 and 3 both exceeded 300 mAh·g. -1 It is higher than the 87.22 mAh·g of the fully activated carbon comparative example 1. -1 This indicates that the introduction of polydopamine and phenolic resin can effectively improve capacity performance. In summary, pre-modifying the activated carbon surface with polydopamine before phenolic resin coating is a feasible approach. Furthermore, when the activated carbon and phenolic resin are mixed in a 100:50 ratio (Example 2), it exhibits both high capacity (312.34 mAh·g charging capacity). -1 Discharge 344.03 mAh·g -1 Its excellent coulombic efficiency (90.79%) provides an important reference for the optimization of high-performance battery materials.

[0074] The embodiments of this application have been described above with reference to the accompanying drawings. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the core ideas of this application. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a double-layer carbon-coated hard carbon anode material for sodium-ion batteries, characterized in that, Includes the following steps: Activated carbon powder was dispersed in tris(hydroxymethyl)aminomethane hydrochloride buffer solution, and then dopamine hydrochloride was added to carry out a self-polymerization reaction. After the reaction was completed, the powder was filtered and dried to obtain the first layer of polydopamine-coated activated carbon powder. The activated carbon powder coated with the first layer of polydopamine was placed in the second layer of carbon source precursor solution and heated in a water bath to obtain activated carbon powder coated with two layers of carbon. The double-layer carbon-coated activated carbon powder was placed in a tube furnace under inert atmosphere for heat treatment to obtain the double-layer carbon-coated sodium-ion battery hard carbon anode material. The second carbon source precursor solution includes at least one of the following: an aqueous solution containing phenolic resin, an ethanol solution containing phenolic resin, a tetrahydrofuran solution containing pitch, a toluene solution containing pitch, and an acetone solution containing pitch. The mass ratio of the activated carbon powder to the dopamine hydrochloride is 100:1-10; The mass ratio of the first layer of polydopamine-coated activated carbon powder to the second layer of carbon source precursor solution is 100:30-80.

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 pitch-based activated carbon.

3. The preparation method according to claim 1, characterized in that, The heat treatment is a two-step process, as follows: The double-layer carbon-coated activated carbon powder is placed in a tube furnace under an inert atmosphere and heated to 400-600 ℃ at a heating rate of 1-5 ℃ / min, and held for 2-4 h. Then, it is pulverized, ball-milled, sieved, and placed in a tube furnace under an inert atmosphere again and heated to 1300-1500 ℃ at a heating rate of 1-5 ℃ / min, and held for 2-4 h.

4. A double-layer carbon-coated hard carbon anode material for sodium-ion batteries, characterized in that, It is prepared by the preparation process described in any one of claims 1-3.

5. The application of the double-layer carbon-coated sodium-ion battery hard carbon anode material as described in claim 4 in the preparation of sodium-ion batteries or sodium-ion battery anode sheets.

6. A battery negative electrode sheet, characterized in that, Including the double-layer carbon-coated sodium-ion battery hard carbon anode material as described in claim 4; the specific preparation process is as follows: The double-layer carbon-coated sodium-ion battery hard carbon anode material, conductive agent, binder and solvent are mixed and coated on a metal substrate, and then vacuum dried to obtain the battery anode sheet.

7. A sodium-ion battery, characterized in that, Includes the battery negative electrode sheet as described in claim 6.

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