A spherical hard carbon negative electrode material, a preparation method thereof, a negative electrode sheet and a sodium ion battery

Abstract

The application discloses a spherical hard carbon negative electrode material and a preparation method thereof, a negative electrode sheet and a sodium ion battery, and belongs to the technical field of sodium ion battery negative electrode materials, and overcomes the defects of low reversible specific capacity and cycle stability performance in the prior art. The preparation method of the spherical hard carbon negative electrode material comprises the following steps: step 1, mixing a phenolic compound, an aldehyde compound and a catalyst, and reacting to obtain spherical phenolic aldehyde resin; the catalyst is an organic ammonium salt; the anion of the organic ammonium salt is OH ‑ , and the cation is a quaternary amine cation R1-R4 are alkyl groups; and step 2, carbonizing the spherical phenolic aldehyde resin. The hard carbon negative electrode material has high initial coulombic efficiency, reversible capacity and cycle stability performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion battery negative electrode materials, and particularly relates to a spherical hard carbon negative electrode material, a preparation method thereof, a negative electrode sheet and a sodium ion battery. BACKGROUND

[0002] Rechargeable lithium ion batteries (LIBs) are widely used in portable electronic products and show great potential in electric vehicles and stationary energy storage. In order to meet the growing market demand, the application of high specific capacity negative electrode materials has attracted more and more attention. However, due to the limited reserves of lithium and uneven distribution of resources, the cost of lithium ion batteries has risen sharply, so it is urgent to find a cheap alternative energy source.

[0003] Metallic sodium has similar physical and chemical properties to lithium, and sodium resources are widely distributed and low in price, which makes sodium ion batteries very suitable for large-scale energy storage. However, due to the thermodynamic instability of intercalation compounds generated by sodium and graphite, and the fact that the ionic radius of sodium ions is larger than that of lithium ions, graphite is not suitable for storing sodium ions as a commercial negative electrode material for lithium ion batteries. Hard carbon has a larger interlayer spacing of carbon layers and is considered to be an ideal negative electrode material for sodium batteries.

[0004] In recent years, hard carbon materials have been widely studied. Among them, there have been some research results on the preparation of hard carbon negative electrode materials using some types of resins, but the existing resin-based hard carbon materials still cannot meet the requirements in terms of reversible specific capacity, cycle stability and other electrochemical properties when applied to the preparation of sodium ion batteries. SUMMARY

[0005] Therefore, in order to overcome the deficiencies of the prior art, the application provides a spherical hard carbon negative electrode material with high reversible specific capacity, stable cycle performance and high first coulomb efficiency, a preparation method thereof, a negative electrode sheet and a sodium ion battery.

[0006] To this end, the application provides the following technical solutions.

[0007] In a first aspect, the application provides a preparation method of a spherical hard carbon negative electrode material, comprising the following steps:

[0008] Step 1, mixing and reacting a phenolic compound, an aldehyde compound and a catalyst to obtain a spherical phenolic aldehyde resin;

[0009] The catalyst is an organic ammonium salt; the anion of the organic ammonium salt is OH - , and the cation is a quaternary amine cation

[0010] R1-R4 are alkyl groups;

[0011] Step 2, carbonizing the spherical phenolic aldehyde resin.

[0012] Further, the R1-R4 are selected from one or more of methyl, ethyl, propyl or butyl;

[0013] Optionally, the thermal decomposition temperature of the organic ammonium salt is 100-300℃.

[0014] Optionally, the organic ammonium salt comprises at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide and dimethyldiethylammonium hydroxide.

[0015] Further, the amount of the catalyst added is 0.05-8% of the mass of the phenolic compound, including but not limited to 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or a range between any two of the values, for example, 0.05-2%, 3-5%, etc. Preferably, the amount is 0.05-5%.

[0016] Further, the step 1 comprises mixing the phenolic compound, the aldehyde compound and the catalyst in a solvent to obtain a mixed solution, and reacting to obtain the spherical phenolic resin.

[0017] Optionally, the solvent is water or a mixture of alcohol and water.

[0018] Preferably, the alcohol is ethanol, methanol, isopropanol or butanol.

[0019] Preferably, in the mixture of alcohol and water, the volume ratio of alcohol to water is 0-0.5, including but not limited to 0.1, 0.2, 0.3, 0.4, or a range between any two of the values, for example, 0.1-0.2, 0.3-0.4, etc.

[0020] Optionally, the concentration of the phenolic compound in the mixed solution is 0.20wt%-5wt%, including but not limited to 0.20wt%, 0.25wt%, 0.3wt%, 0.4wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%.

[0021] The higher the concentration of the phenolic compound, the larger the particle size. Controlling the concentration to be 0.20wt%-5wt% can avoid the agglomeration of the materials due to the too fast reaction speed.

[0022] Further, the meta position of the phenolic hydroxyl group of the phenolic compound in the step 1 contains at least one ortho-para directing group.

[0023] In the present application, the ortho-para directing group refers to a functional group that allows the newly added substituent to mainly enter its ortho and para positions (the sum of ortho and para isomers is greater than 60%), and activates the benzene ring, including but not limited to one or more of hydroxyl, amino, ester or alkyl.

[0024] Preferably, the phenolic compound includes one or more of resorcinol or m-aminophenol;

[0025] Further, the step 1 satisfies at least one of the following conditions:

[0026] (1) The aldehyde compound includes one or more of formaldehyde, glyoxal, furfural, or terephthaldehyde;

[0027] (2) The molar ratio of the phenolic compound to the aldehyde compound is 1:1.5-1:50, including but not limited to 1:1.5, 1:2, 1:3, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50; controlling the molar ratio 1:1.5-1:50 can form a thermosetting spherical phenolic resin, avoiding the morphology being destroyed in the curing process.

[0028] (3) The reaction temperature is room temperature-100°C, including but not limited to 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, and the time is 2-24h, 2h, 3h, 4h, 5h, 6h, 7h, 9h, 10h, 15h, 20h, 22h, 24h.

[0029] Further, the step 2 includes first carbonization and second carbonization, and the second carbonization temperature is greater than the first carbonization temperature;

[0030] Further, the step 2 satisfies at least one of the following conditions:

[0031] (1) The first carbonization temperature is 300°C-1000°C, including but not limited to 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C;

[0032] (2) The second carbonization temperature is 1100°C-1800°C, including but not limited to 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C;

[0033] (3) The first carbonization and / or second carbonization time is 1h-24h, including but not limited to 1h, 2h, 3h, 4h, 5h, 10h, 15h, 20h, 22h, 24h;

[0034] (4) The first carbonization and / or second carbonization heating rate is 1°C / min-10°C / min, including but not limited to 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min;

[0035] (5) The first carbonization and / or the second carbonization are carried out in a protective atmosphere;

[0036] (6) The first carbonization and / or the second carbonization are carried out in a nitrogen, argon or helium atmosphere;

[0037] (7) The carbonization equipment used for the first carbonization and / or the second carbonization is a box furnace, tube furnace, vertical furnace or kiln.

[0038] In this invention, carbonization of spherical resin at temperatures between 300 and 1000°C helps eliminate some impurities and increases the microstructural order of the material, resulting in a rougher surface morphology and higher reversible specific capacity. During the first carbonization process, the relatively low thermal energy enhances the mobility of polymer chain segments without destroying the network macromolecular structure, leading to tighter cross-linking of the polymer chains. During the second carbonization, the cross-linked structure resulting from the first carbonization is maintained or further enhanced, improving the structural stability of the resin-based hard carbon material and exhibiting superior cycle stability in electrochemical characterization. The second carbonization temperature is between 1100 and 1800°C, preventing excessively high temperatures from causing the disappearance of some micropores in the hard carbon and affecting capacity performance.

[0039] Secondly, the present invention provides a spherical hard carbon anode material prepared by the above method.

[0040] Furthermore, the D of the spherical hard carbon anode material v 50 ranges from 1.2μm to 17μm;

[0041] Furthermore, the D of the spherical hard carbon anode material v 50 is 3μm to 15μm;

[0042] Preferably, the tap density of the spherical hard carbon anode material is ≥0.70 g / cm³. 3 Specific surface area ≤ 6m² 2 / g.

[0043] If the D of spherical phenolic resin v 50 is too small. The spherical hard carbon anode material, after carbonization, has a large specific surface area. This leads to more side reactions between the electrolyte and the hard carbon material surface during charge and discharge, which is detrimental to improving the initial coulombic efficiency of the hard carbon anode material. If the D of the spherical phenolic resin is too small... v A value of 50 is too high, resulting in significant polarization and a tendency for sodium precipitation, leading to deterioration in cycle performance. This invention utilizes an organic ammonium salt as a catalyst to improve the D-phase efficiency of spherical phenolic resin. v The 50 is controlled between 1.5μm and 20μm, which makes the final spherical hard carbon anode material have high initial coulombic efficiency, reversible capacity and cycle stability.

[0044] The preparation method of the application controls the size of the spherical hard carbon negative material in a reasonable range, and does not need additional spheroidization treatment, and the preparation process is simple.

[0045] In the application, the organic ammonium salt forms quaternary amine cations in the ionization process, the catalysis of the quaternary amine cations can form more emulsion droplets as growth cores to accelerate the nucleation speed, and the quaternary amine cations can also adhere to the surface of the liquid droplets to provide positive charges to prevent the liquid droplets from agglomerating with each other. In addition, hydroxyl ions are also generated in the ionization process, and the presence of the hydroxyl ions can effectively improve the reaction efficiency in the sol-gel process, shorten the reaction time, and be beneficial to industrial production, so that the D v 50 is a spherical phenolic resin with a size of 1.5 μm-20 μm. At the same time, the organic ammonium salt can decompose into small molecules such as ammonia, methanol and dimethyl ether during the carbonization process, and the prepared spherical hard carbon does not contain alkali residues, which can improve the stability of the negative electrode slurry. At the same time, the escape of small molecules can form many microporous structures in the spherical hard carbon, and these microporous structures can act as sodium storage sites during the charging and discharging process of the sodium battery, thereby greatly improving the reversible specific capacity of the resin-based hard carbon. If only inorganic strong alkali is added, the phenolic resin cannot be spheroidized due to too fast reaction; if only ammonia water is added, the reaction activity is too slow, the reaction time is too long, and it is not conducive to industrial production.

[0046] In a third aspect, the application provides a negative electrode sheet comprising the spherical hard carbon negative material.

[0047] In a fourth aspect, the application provides a sodium ion battery comprising the negative electrode sheet.

[0048] The positive progress effect of the application is that:

[0049] 1. The spherical resin hard carbon negative material has large reversible specific capacity, high first coulomb efficiency and good cycle performance, and the comprehensive performance of the button cell prepared therefrom is excellent, and has the following advantages: 1) good electrochemical performance, reversible specific capacity is above 326 mAh / g; 2) high first coulomb efficiency, above 92.3%; 3) good cycle performance (1000 cycles, capacity retention is ≥90.9%).

[0050] 2. The preparation method is simple and feasible, and is suitable for industrial production. DETAILED DESCRIPTION

[0051] The following examples are provided to better further understand the application, and do not limit the content and protection scope of the application. Any person who is inspired by the application or combines the application with other prior art features to obtain any product identical or similar to the application falls within the protection scope of the application.

[0052] The specific experimental procedures or conditions are not indicated in the examples, and the operation or conditions can be performed according to the conventional experimental procedures described in the literature in the art. The reagents or instruments used are not indicated by the manufacturer, and are conventional reagent products that can be obtained by purchase.

[0053] Example 1

[0054] The present embodiment provides a preparation method of a spherical hard carbon negative electrode material, comprising the following steps:

[0055] 1) Synthesis of spherical phenolic resin: 2.5 g of resorcinol, 20.5 g of formaldehyde and 0.125 g of catalyst tetramethylammonium hydroxide were dissolved in 1000 ml of water, reacted at room temperature for 24 h, and then centrifuged, washed and dried to obtain spherical phenolic resin.

[0056] 2) First carbonization: the spherical phenolic resin prepared in step 1) was transferred to a box furnace, nitrogen was introduced to remove oxygen, and the temperature was raised to 500℃ at a rate of 3℃ / min in a nitrogen atmosphere, and the temperature was maintained for 6 h.

[0057] 3) Second carbonization: the product of step 2) was subjected to high-temperature pyrolysis, nitrogen was introduced to remove oxygen, and the temperature was raised to 1500℃ at a rate of 3℃ / min in a nitrogen atmosphere, and the temperature was maintained for 6 h to obtain a spherical hard carbon negative electrode material.

[0058] Example 2

[0059] The present embodiment provides a preparation method of a spherical hard carbon negative electrode material, comprising the following steps:

[0060] 1) Synthesis of spherical phenolic resin: 50 g of resorcinol, 204.5 g of formaldehyde and 0.25 g of catalyst tetraethylammonium hydroxide were dissolved in 1000 ml of water, reacted at 100℃ for 2 h, and then centrifuged, washed and dried to obtain spherical phenolic resin.

[0061] 2) First carbonization: the spherical phenolic resin prepared in step 1) was transferred to a box furnace, nitrogen was introduced to remove oxygen, and the temperature was raised to 600℃ at a rate of 5℃ / min in a nitrogen atmosphere, and the temperature was maintained for 4 h.

[0062] 3) Second carbonization: the product of step 2) was subjected to high-temperature pyrolysis, nitrogen was introduced to remove oxygen, and the temperature was raised to 1600℃ at a rate of 5℃ / min in a nitrogen atmosphere, and the temperature was maintained for 4 h to obtain a spherical hard carbon negative electrode material.

[0063] Example 3

[0064] The present embodiment provides a preparation method of a spherical hard carbon negative electrode material, comprising the following steps:

[0065] 1) Synthesis of spherical phenolic resin: 20 g of resorcinol, 8.2 g of formaldehyde and 0.4 g of catalyst tetraethylammonium hydroxide were dissolved in 1000 ml of water, reacted at 50°C for 12 h, and after centrifugation, washing and drying, spherical phenolic resin was obtained.

[0066] 2) First carbonization: the spherical phenolic resin prepared in step 1) was transferred to a box furnace, nitrogen was introduced to remove oxygen, and in a nitrogen atmosphere, the temperature was raised to 700°C at a rate of 2°C / min, and kept for 2 h.

[0067] 3) Second carbonization: the product of step 2) was subjected to high-temperature pyrolysis, nitrogen was introduced to remove oxygen, and in a nitrogen atmosphere, the temperature was raised to 1400°C at a rate of 2°C / min, and kept for 2 h, to obtain spherical hard carbon negative electrode material.

[0068] Example 4

[0069] This example is basically the same as Example 1, except that the solvent in step 1) is 900 ml of water + 100 ml of ethanol.

[0070] Example 5

[0071] This example is basically the same as Example 1, except that the solvent in step 1) is 700 ml of water + 300 ml of ethanol.

[0072] Comparative Example 1

[0073] This comparative example is basically the same as Example 1, except that the catalyst in step 1) is 0.25 g of ammonia water.

[0074] Comparative Example 2

[0075] This comparative example provides a method for preparing a spherical hard carbon negative electrode material, comprising the following steps:

[0076] 1) Synthesis of phenolic resin: 2.5 g of phenol, 20.5 g of formaldehyde and 0.125 g of catalyst sodium hydroxide were dissolved in 1000 ml of water, reacted at room temperature for 24 h, and after dehydration and drying, phenolic resin was obtained.

[0077] 2) First carbonization: the phenolic resin prepared in step 1) was transferred to a box furnace, nitrogen was introduced to remove oxygen, and in a nitrogen atmosphere, the temperature was raised to 500°C at a rate of 3°C / min, and kept for 6 h.

[0078] 3) Powdering: the phenolic resin carbon obtained in step 2) was broken down into powder by air jet milling to D v 50 = 7 μm.

[0079] 4) Second carbonization: the product of step 3) is subjected to high-temperature pyrolysis, nitrogen is introduced to discharge oxygen, and the temperature is raised to 1500℃ at a rate of 3℃ / min in a nitrogen atmosphere, and the temperature is kept for 6h to obtain a spherical hard carbon negative electrode material.

[0080] Test Example

[0081] Physical property test:

[0082] Spherical phenolic resin and spherical hard carbon negative electrode material D v Test method of 50: In the present application, D v 50 represents the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%; it can be determined by using instruments and methods known in the art. For example, it can be conveniently determined by referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, using a laser particle size analyzer. The testing instrument can be a Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK.

[0083] Test method of tap density: The tap density is a well-known meaning in the art, and can be tested by using methods known in the art. For example, it can be determined by referring to standard GB / T 5162-2006, using a powder tap density tester. If a FZS4-4B tap density tester of Beijing Iron and Steel Research General Institute is used, the test parameters are as follows: vibration frequency: 250±15 times / min, vibration amplitude: 3±0.2mm, vibration times: 5000 times, cylinder: 25mL.

[0084] Test method of specific surface area: In the present application, the specific surface area is the physical adsorption specific surface area, which can be tested by using methods known in the art. For example, it can be tested by referring to GB / T 19587-2017, using nitrogen adsorption specific surface area analysis test method, and calculated by BET (Brunauer Emmett Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be performed by using a Tri-Star 3020 specific surface area and pore size analysis tester of Micromeritics Corporation, USA.

[0085] The physical property test results of examples 1-5 and comparative examples 1-2 in the present application are shown in Table 1.

[0086] Electrochemical property test:

[0087] The spherical hard carbon negative electrode material prepared in Examples 1-5 and Comparative Examples 1-2 was mixed with the conductive agent Super P, the binder sodium carboxymethyl cellulose and butadiene rubber in a mass ratio of 94.5:1.5:1.5:2.5, and stirred with an appropriate amount of water to form a slurry. The slurry was then uniformly coated on a copper foil current collector, dried, and cut into a circular electrode with a diameter of 18 mm. The electrode was dried at 80°C for about 3 hours under vacuum, vacuum dried at 80°C for 6 hours, and rolled to a surface density of 6-7 mg / cm 2 The assembly of the simulated battery was carried out in an Ar atmosphere glove box, with a metal sodium sheet as the counter electrode and a 1M NaPF6 solution in ethylene carbonate as the electrolyte, to form a CR2430 button cell.

[0088] Method for testing reversible specific capacity and initial coulombic efficiency: The button cell was placed in a thermostat of a blue electric test cabinet (T-3002A-5V 1mA) at 25°C for 6 hours. The button cell was subjected to constant current charge and discharge at a current of 0.05C, with a voltage range of 0-2V. The discharge specific capacity of the button cell at this time was recorded as D, and the charge specific capacity was recorded as C. The initial coulombic efficiency was calculated by the following formula:

[0089] Initial coulombic efficiency = C / D x 100%

[0090] Method for testing cycle performance: The button cell was placed in a thermostat of a blue electric test cabinet (T-3002A-5V 1mA) at 25°C for 6 hours. The button cell was subjected to constant current charge and discharge at a current of 1C, with a voltage range of 0-2V. The specific capacity of the first cycle was recorded as C1, and the specific capacity of the 1000th cycle was recorded as C2. The 1000th cycle capacity retention rate was calculated by the following formula:

[0091] Capacity retention rate = C1 / C2 x 100%

[0092] The electrochemical test results of Examples 1-5 and Comparative Examples 1-2 in this application are shown in Table 2.

[0093] Table 1 Parameters of spherical phenolic resin and spherical hard carbon negative electrode material

[0094]

[0095]

[0096] Table 2 Performance of examples and comparative examples

[0097] Reversible specific capacity (mAh / g) First coulombic efficiency (%) 1000 cycle capacity retention (%) Example 1 331 92.3 90.4 Example 2 328 92.8 91.3 Example 3 335 93.8 92.8 Example 4 329 92.6 90.6 Example 5 326 93.2 90.9 Comparative Example 1 295 89.3 87.5 Comparative Example 2 268 90.5 64

[0098] As can be seen from Tables 1 and 2, the spherical phenolic resin D vThe size of 50 is related to the catalyst. The spherical phenolic resin D v The size of 50 is related to the catalyst. The spherical phenolic resin D

[0099] In Comparative Example 1, the particle size of the spheres is reduced by using ammonia instead of the same amount of tetramethylammonium hydroxide. When the particle size is too small, the specific surface area of the material is large, and side reactions with the electrolyte are prone to occur, resulting in a significant decrease in the initial capacity and cycle performance of the material. In Comparative Example 2, the phenolic resin obtained by using sodium hydroxide as the catalyst is a liquid and cannot be formed into spheres, and the electrochemical performance is significantly deteriorated.

[0100] As can be seen from Examples 1, 4 and 5, the addition of an alcohol as a solvent can significantly increase the particle size of the spheres.

[0101] Obviously, the above examples are merely illustrative and not limiting. Other changes or variations can be made by those skilled in the art based on the above description. It is not necessary or possible to exhaust all embodiments. The obvious changes or variations derived therefrom are still within the scope of the present invention.

Claims

1. A method for preparing a spherical hard carbon negative electrode material, characterized in that, The method comprises the following steps: Step 1, mixing, reacting a phenolic compound, an aldehyde compound and a catalyst to obtain a spherical phenolic resin; the catalyst is added in an amount of 0.05-8% of the mass of the phenolic compound; The catalyst is an organic ammonium salt; the anion of the organic ammonium salt is OH - , and the cation is a quaternary ammonium cation ; R1~R4 are alkyl groups; Step 2, carbonizing the spherical phenolic resin.

2. The method for preparing the spherical hard carbon anode material according to claim 1, characterized in that, The R1~R4 are independently selected from one or more of methyl, ethyl, propyl or butyl.

3. The method for preparing the spherical hard carbon anode material according to claim 1, characterized in that, The organic ammonium salt has a thermal decomposition temperature of 100℃-300℃.

4. The method for preparing the spherical hard carbon anode material according to claim 1, characterized in that, The organic ammonium salt comprises one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide and dimethyldiethylammonium hydroxide.

5. The method for preparing the spherical hard carbon anode material according to any one of claims 1-4, characterized in that, The step 1 comprises mixing the phenolic compound, the aldehyde compound and the catalyst in a solvent to obtain a mixed solution, and reacting to obtain the spherical phenolic resin. 6.The method of claim 5, wherein the carbon source is at least one selected from the group consisting of sucrose, glucose, fructose, lactose, maltose, starch, cellulose, and dextrin. The solvent is water or a mixture of alcohol and water.

7. The method for preparing the spherical hard carbon anode material according to claim 6, characterized in that, The alcohol is ethanol, methanol, isopropanol or butanol. 8.The method of claim 6, wherein the carbon precursor is selected from the group consisting of sucrose, glucose, fructose, lactose, maltose, trehalose, raffinose, stachyose, and combinations thereof. In the mixture of alcohol and water, the volume ratio of alcohol to water is 0-0.

5. 9.The method of claim 5, wherein the carbon precursor is selected from the group consisting of sucrose, glucose, fructose, lactose, maltose, trehalose, raffinose, stachyose, and combinations thereof. The concentration of the phenolic compound in the mixed solution is 0.20wt%-5wt%.

10. The method for preparing the spherical hard carbon anode material according to any one of claims 1-4, characterized in that, The para position of the phenolic hydroxyl group of the phenolic compound contains at least one ortho-para positioning group.

11. The method for preparing the spherical hard carbon anode material according to claim 10, characterized in that, The phenolic compound comprises one or more of resorcinol or m-aminophenol.

12. The method for preparing the spherical hard carbon anode material according to any one of claims 1-4, characterized in that, The step 1 satisfies at least one of the following conditions: (1) the aldehyde compound comprises one or more of formaldehyde, glyoxal, furfural or p-xylylene glycol; (2) the molar ratio of the phenolic compound to the aldehyde compound is 1:1.5-1:50; (3) the reaction temperature is room temperature-100℃, and the reaction time is 2-24h.

13. The method for preparing the spherical hard carbon anode material according to any one of claims 1-4, characterized in that, The step 2 comprises first carbonization and second carbonization, and the second carbonization temperature is higher than the first carbonization temperature.

14. The method for preparing the spherical hard carbon anode material according to claim 13, characterized in that, At least one of the following conditions is satisfied: (1) the first carbonization temperature is 300℃-1000℃; (2) the second carbonization temperature is 1100℃-1800℃; (3) the first carbonization and / or the second carbonization time is 1h-24h; (4) the first carbonization and / or the second carbonization has a heating rate of 1℃ / min-10℃ / min; (5) the first carbonization and / or the second carbonization is carried out in a protective atmosphere; (6) the first carbonization and / or the second carbonization is carried out in a nitrogen, argon or helium atmosphere; (7) the carbonization equipment used in the first carbonization and / or the second carbonization is a box furnace, a tube furnace, a vertical furnace or a kiln.

15. A spherical hard carbon negative electrode material prepared by the method of any one of claims 1-14.

16. The spherical hard carbon negative electrode material of claim 15, wherein, The D50 of the spherical hard carbon negative electrode material is 1.2 μm to 17 μm. v 50 is 1.2 μm to 17 μm.

17. The spherical hard carbon negative electrode material of claim 15, wherein, D50 of the spherical hard carbon negative electrode material is 3 μm to 15 μm. v 50 is 3 μm to 15 μm.

18. The spherical hard carbon negative electrode material of claim 15, wherein, The tap density of the spherical hard carbon negative electrode material is ≥ 0.70 g / cm 3 The specific surface area is ≤ 6 m 2 / g.

19. A negative electrode sheet characterized by comprising: The spherical hard carbon negative electrode material of any one of claims 15-18.

20. A sodium-ion battery, characterized in that, The negative electrode sheet of claim 19.

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