Hard carbon materials, their preparation methods and batteries

Abstract

The present invention relates to the field of new energy batteries, and particularly relates to a hard carbon material, a preparation method thereof, and a battery. The hard carbon material includes first hard carbon particles and a second hard carbon coating layer coated on the surface of the first hard carbon particles. Among them, the first hard carbon particles have micropores inside, and the average pore diameter of the micropores is 1 to 2.5 nm. The present invention has good sodium storage performance and significantly improved material capacity.

Description

Technical Field

[0001] The present invention relates to the field of new energy batteries, and specifically, to a hard carbon material, a preparation method thereof, and a battery. Background Art

[0002] As an important supplement to lithium-ion batteries, sodium-ion batteries have a working mechanism and composition similar to those of lithium-ion batteries, and at the same time have advantages such as rich resources, low price, and excellent performance. Hard carbon negative electrode materials have the advantages of rich sources, simple preparation, high sodium storage capacity, low average working potential, and excellent cycle performance, and are the most promising sodium battery negative electrode materials. The surface adsorption of hard carbon, the interlayer and internal micropores of the material can all provide rich sodium storage space. Although the surface defects of the material can provide part of the capacity, too many surface defects will also lead to excessive side reactions and irreversible loss of Na; for the internal micropores of the material, efficient sodium storage can only be achieved within a suitable pore size range, otherwise the specific capacity will be greatly reduced. Therefore, reasonably regulating the surface defects and internal micropores of hard carbon can effectively improve the first efficiency of sodium batteries and increase the sodium storage space to improve the capacity. Summary of the Invention

[0003] In view of this, the present invention is committed to providing a hard carbon material, a preparation method thereof, and a battery to solve the problem in the prior art that the surface of the hard carbon material has defects and cannot efficiently store sodium, thereby reducing the specific capacity of the material.

[0004] To solve the above technical problems, the present invention is implemented as follows:

[0005] In a first aspect of the present invention, there is provided a hard carbon material, which includes first hard carbon particles and a second hard carbon coating layer coated on the surface of the first hard carbon particles;

[0006] Wherein, the first hard carbon particles have micropores inside, and the average pore diameter of the micropores is 1-2.5 nm.

[0007] Optionally, the specific surface area of the first hard carbon particles is 2-10 m 2 / g; the pore volume of the first hard carbon particles is 0.01-0.6 cm 3 / g; the D50 of the first hard carbon particles is 2.5-7.8 μm.

[0008] Optionally, the second hard carbon coating layer has pores, the pore diameter of the pores is 0.5-10 nm, and the porosity of the second hard carbon coating layer is 5-15%; the thickness of the second hard carbon coating layer is 200-500 nm.

[0009] Optionally, the D50 of the hard carbon material is 3-8 μm.

[0010] The second aspect of the present invention provides a method for preparing a hard carbon material, and the preparation method includes the following steps:

[0011] S1. Place the porous carbon source powder in a first inert atmosphere for a first carbonization treatment to obtain a carbonized material;

[0012] S2. Wash the carbonized material, then mix it with water, perform a negative pressure treatment and filtration to obtain a first material; place the first material in a second inert atmosphere for a pressurized heating treatment to obtain first hard carbon particles;

[0013] S3. Mix the liquid resin with an organic solvent to obtain a mixed solution; mix and cure the first hard carbon particles with the mixed solution to obtain a second material;

[0014] S4. Crush and granulate the second material to obtain second particles; place the second particles in a third inert atmosphere for a second carbonization treatment.

[0015] Optionally, the porous carbon source powder includes a natural porous carbon source powder; the natural porous carbon source powder is selected from at least one of cotton powder, rice bran powder, coconut shell powder, reed rod powder, poplar wood powder, and bamboo powder; and / or, the liquid resin is selected from at least one of liquid phenolic resin, liquid epoxy resin, and liquid acrylic resin; and / or, the organic solvent is selected from at least one of methanol, ethanol, and ethylene glycol; and / or, the first inert atmosphere, the second inert atmosphere, and the third inert atmosphere are each independently selected from at least one of argon, helium, and nitrogen.

[0016] Optionally, the mass ratio of the washed carbonized material to water after mixing is 10 to 20:1; and / or, the mass concentration of the liquid resin in the mixed solution is 30 to 50%; and / or, the mass ratio of the first hard carbon particles to the mixed solution during mixing is 1 to 1.5:1; and / or, the D50 of the second particles is 3 to 8 μm.

[0017] Optionally, in step S1, the conditions for the first carbonization treatment include: the carbonization temperature is 750-850°C, and the carbonization time is 2-4 h; in step S2, the washing treatment includes washing the carbonized material with an acid solution; the acid solution is selected from hydrochloric acid aqueous solution and / or nitric acid aqueous solution; the mass concentration of the acid in the acid solution is 20-30%; the conditions for the negative pressure treatment include: pumping to 100-150 Pa, and the pumping time is 10-30 s; or, the conditions for the negative pressure treatment include: introducing an inert gas into the system to 0.4-0.6 standard atmospheric pressures, and maintaining for 1-2 h; the conditions for the pressurized heating treatment include: the pressure for pressurization is 0.4-0.6 MPa, the temperature for heating is 750-850°C, and the treatment time is 10-30 min; in step S3, the conditions for the mixing treatment include: the temperature is 150-180°C, and the time is 2-4 h; the conditions for the curing treatment include: the temperature is 750-850°C, and the time is 1-2 h; in step S4, the conditions for the second carbonization treatment include: the temperature is 1200-1400°C, and the time is 2-4 h.

[0018] The third aspect of the present invention provides a negative electrode plate, which includes a current collector and a negative electrode material layer provided on at least one surface of the current collector, wherein the negative electrode material layer includes the above-mentioned hard carbon material and / or the hard carbon material prepared according to the above-mentioned preparation method.

[0019] The fourth aspect of the present invention provides a battery, which includes a negative electrode plate, and the negative electrode plate is the above-mentioned negative electrode plate.

[0020] Through the above technical solutions, the beneficial technical effects of the present invention are as follows:

[0021] (1) The hard carbon material of the present invention includes first hard carbon particles and a second hard carbon coating layer coated on the surface of the first hard carbon particles; wherein the first hard carbon particles have micropores inside, have good sodium storage performance, and greatly improve the material capacity.

[0022] (2) In the present invention, a biomass material is used as the carbon source substrate, which has abundant pores inside. First, water is filled into the pores through air pressure in the present invention, and then it is placed in a high-temperature and high-pressure environment. The water inside the pores will quickly produce water vapor and react with the carbon around the pores to generate CO and H2 gases, thereby effectively controlling the shape and pore size of the pores. Under appropriate conditions, the generated pores have good sodium storage performance, greatly improving the material capacity. The present invention uses a mixed solution containing liquid resin and organic solvent to form a hard carbon coating layer with fewer defects and abundant pores on the surface of the material, which can make up for the deficiency of side reactions caused by more defects on the surface of biomass carbon, reduce the loss of active sodium and improve the initial efficiency. During the process of forming the coating layer, the volatilization of the organic solvent will generate abundant pores on the surface of the coating layer. These pores can not only store sodium but also improve the migration rate of sodium ions on the surface of the material to ensure the rate performance.

[0023] Other features and advantages of the present invention will be described in detail in the following specific implementation part. Brief Description of the Drawings

[0024] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific implementation, they are used to explain the present invention, but do not constitute a limitation to the present invention.

[0025] Figure 1 The figure shows a schematic diagram of the hard carbon material provided by the present invention.

[0026] Description of the Reference Numerals in the Drawings

[0027] 1, inner hard carbon; 2, internal micropores; 3, outer hard carbon. Specific Embodiments

[0028] The present invention discloses a hard carbon material, a preparation method thereof, and a battery. Those skilled in the art can draw on the content of this article and appropriately improve the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments. Relevant personnel can obviously make changes or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0029] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0030] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0031] If there is no special instruction, all embodiments and alternative embodiments of the present invention can be combined with each other to form new technical solutions.

[0032] If there is no special instruction, all technical features and alternative technical features of the present invention can be combined with each other to form new technical solutions.

[0033] If there is no special instruction, the "including" and "comprising" mentioned in the present invention mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or it can only include or comprise the listed components.

[0034] In order to solve the problem that there are defects on the surface of hard carbon materials in the prior art, which cannot store sodium efficiently, and thus lead to a reduction in the specific capacity of the materials, the present invention adopts the following technical solutions:

[0035] The first aspect of the present invention provides a hard carbon material, as Figure 1 shown, the hard carbon material includes first hard carbon particles and a second hard carbon coating layer coated on the surface of the first hard carbon particles;

[0036] Wherein, the first hard carbon particles have micropores inside, and the average pore diameter of the micropores is 1 - 2.5 nm.

[0037] The hard carbon material of the present invention includes first hard carbon particles and a second hard carbon coating layer coated on the surface of the first hard carbon particles; wherein the first hard carbon particles have micropores inside, have good sodium storage performance, and greatly improve the material capacity.

[0038] According to the present invention, the specific surface area of the suitable first hard carbon particles can have the technical effect of ensuring the lithium ion insertion / extraction rate and reducing side reactions. The specific surface area of the first hard carbon particles can be 2 to 10 m 2 / g. Exemplarily, the specific surface area of the first hard carbon particles can be 2 m 2 / g, 4 m 2 / g, 6 m 2 / g, 8 m 2 / g, and 10 m 2 / g, or any value within the range formed by any two of the above values. In the present invention, if the specific surface area of the first hard carbon particles is too large, it may lead to excessive side reactions between the hard carbon and the electrolyte during charge and discharge, resulting in capacity loss; if the specific surface area of the first hard carbon particles is too small, it may lead to a decrease in the lithium ion insertion / extraction area, affecting the charge and discharge rate. As a preferred embodiment, the specific surface area of the first hard carbon particles is 3 to 6 m 2 / g.

[0039] According to the present invention, the pore volume of the suitable first hard carbon particles can have the technical effect of balancing capacity utilization and lithium ion diffusion efficiency. The pore volume of the first hard carbon particles can be 0.01 to 0.6 cm 3 / g. Exemplarily, the pore volume of the first hard carbon particles can be 0.01 cm 3 / g, 0.1 cm 3 / g, 0.2 cm 3 / g, 0.3 cm 3 / g, 0.4 cm 3 / g, 0.5 cm 3 / g, and 0.6 cm 3 / g, or any value within the range formed by any two of the above values. In the present invention, if the pore volume of the first hard carbon particles is too large, it may lead to an increase in side reactions and a decrease in capacity utilization; if the pore volume of the first hard carbon particles is too small, it may lead to hindered ion diffusion and poor electrolyte wettability, affecting the lithium ion diffusion efficiency. Preferably, the pore volume of the first hard carbon particles is 0.1 to 0.2 cm 3 / g.

[0040] According to the present invention, the D50 of the suitable first hard carbon particles can have the technical effect of ensuring the lithium ion insertion / extraction rate and reducing side reactions. The D50 of the first hard carbon particles can be 2.5 to 7.8 μm. Exemplarily, the D50 of the first hard carbon particles can be any value among 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, and 7.8 μm or any value within the range formed by any two of the above values. In the present invention, if the D50 of the first hard carbon particles is too large, it may lead to an increase in the migration distance of lithium ions inside the material and a decrease in the lithium ion migration rate; if the D50 of the first hard carbon particles is too small, it may lead to excessive side reactions between the hard carbon and the electrolyte during charge and discharge, resulting in capacity loss. Preferably, the D50 of the first hard carbon particles is 3.65 to 5.75 μm.

[0041] According to the present invention, the second hard carbon coating layer has pores. On the one hand, the pores of the second hard carbon coating layer can store sodium, and on the other hand, they can improve the sodium ion migration rate on the material surface to ensure the rate performance. In the present invention, the pore diameter of the pores can be 0.5 to 10 nm. Exemplarily, the pore diameter of the pores can be any value among 0.5 nm, 1 nm, 2 nm, 4 nm, 6 nm, 8 nm, and 10 nm or any value within the range formed by any two of the above values.

[0042] According to the present invention, the suitable porosity of the second hard carbon coating layer can have the technical effect of improving the migration rate of lithium ions on the surface layer of the hard carbon. The porosity of the second hard carbon coating layer can be 5 to 15%. Exemplarily, the porosity of the second hard carbon coating layer can be any value among 5%, 7%, 9%, 11%, 13%, and 15% or any value within the range formed by any two of the above values.

[0043] According to the present invention, the suitable thickness of the second hard carbon coating layer can have the technical effects of ensuring capacity utilization, reducing side reactions, and ensuring the lithium ion migration rate. The thickness of the second hard carbon coating layer can be 200 to 500 nm. Exemplarily, the thickness of the second hard carbon coating layer can be any value among 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, and 500 nm or any value within the range formed by any two of the above values. In the present invention, if the thickness of the second hard carbon coating layer is too large, it may lead to a decrease in the material capacity and the lithium ion migration rate; if the thickness of the second hard carbon coating layer is too small, it may lead to a weakened protection effect of the coating layer on the inner layer, ineffective suppression of side reactions, and rapid capacity decay during the cycling process. Preferably, the thickness of the second hard carbon coating layer is 250 to 350 nm.

[0044] In the present invention, if the D50 of the hard carbon material is too large, it may lead to an increase in the migration distance of lithium ions inside the material and a decrease in the lithium ion migration rate; if the D50 of the hard carbon material is too small, it may lead to excessive side reactions between the hard carbon and the electrolyte during charge and discharge, resulting in capacity loss. The D50 of the hard carbon material can be 3-8 μm. Exemplarily, the D50 of the hard carbon material can be any value among 3 μm, 4 μm, 5 μm, 6 μm, 7 μm and 8 μm or any value within the range composed of any two of the above values. As a preferred embodiment, the D50 of the hard carbon material is 4-6 μm.

[0045] The second aspect of the present invention provides a method for preparing a hard carbon material, and the preparation method includes the following steps:

[0046] S1. Place the porous carbon source powder in a first inert atmosphere for a first carbonization treatment to obtain a carbonized material;

[0047] S2. Wash the carbonized material, then mix it with water, perform negative pressure treatment and filtration to obtain a first material; place the first material in a second inert atmosphere for a pressure heating treatment to obtain first hard carbon particles;

[0048] S3. Mix the liquid resin with an organic solvent to obtain a mixed solution; mix and cure the first hard carbon particles with the mixed solution to obtain a second material;

[0049] S4. Crush and granulate the second material to obtain second particles; place the second particles in a third inert atmosphere for a second carbonization treatment.

[0050] The present invention uses a biomass material as the carbon source substrate, which has rich pores inside. First, the present invention fills water into the pores through air pressure, and then places it in a high-temperature and high-pressure environment. The water inside the pores will quickly produce water vapor and react with the carbon around the pores to generate CO and H2 gases, thereby effectively controlling the shape and pore size of the pores. The pores generated under suitable conditions have good sodium storage performance and greatly improve the material capacity. The present invention uses a mixed solution containing a liquid resin and an organic solvent to generate a hard carbon coating layer with fewer defects and rich pores on the surface of the material, which can make up for the deficiency of side reactions caused by more defects on the surface of the biomass carbon, reduce the loss of active sodium and improve the initial efficiency. During the process of generating the coating layer, the volatilization of the organic solvent will generate rich pores on the surface of the coating layer. These pores can not only store sodium, but also improve the sodium ion migration rate on the surface of the material to ensure the rate performance.

[0051] According to the present invention, the porous carbon source powder may include natural porous carbon source powder; illustratively, the natural porous carbon source powder may be selected from at least one of cotton powder, rice bran powder, coconut shell powder, reed stem powder, poplar powder and bamboo powder.

[0052] Illustratively, the liquid resin may be selected from at least one of liquid phenolic resin, liquid epoxy resin, and liquid acrylic resin.

[0053] Illustratively, the organic solvent may be selected from at least one of methanol, ethanol, and ethylene glycol.

[0054] Illustratively, the first inert atmosphere, the second inert atmosphere, and the third inert atmosphere may each be independently selected from at least one of argon, helium, and nitrogen.

[0055] According to the present invention, the mass ratio of the carbonized material after washing and water can be 10~20:1; and / or, the mass concentration of the liquid resin in the mixed solution can be 30~50%; and / or, the mass ratio of the first hard carbon particles and the mixed solution can be 1~1.5:1; and / or, the D50 of the second particles can be 3~8μm.

[0056] According to the present invention, in step S1, the conditions of the first carbonization treatment may include: a carbonization temperature of 750~850°C and a carbonization time of 2~4h; in step S2, the washing treatment may include washing the carbonized material with an acid solution; the acid solution may be selected from a hydrochloric acid aqueous solution and / or a nitric acid aqueous solution; the mass concentration of the acid in the acid solution may be 20~30%.

[0057] In one embodiment of the present invention, the negative pressure treatment conditions may include: pumping the pressure to 100-150 Pa for 10-30 seconds. In another embodiment of the present invention, the negative pressure treatment conditions may include: introducing an inert gas into the system to 0.4-0.6 standard atmospheric pressure and maintaining it for 1-2 hours.

[0058] According to the present invention, the conditions for the pressurized heating treatment may include: a pressurized pressure of 0.4~0.6MPa, a heating temperature of 750~850℃, and a treatment time of 10~30min; in step S3, the conditions for the mixing treatment may include: a temperature of 150~180℃, and a time of 2~4h; the conditions for the curing treatment may include: a temperature of 750~850℃, and a time of 1~2h; in step S4, the conditions for the second carbonization treatment may include: a temperature of 1200~1400℃, and a time of 2~4h.

[0059] The third aspect of the present invention provides a negative electrode plate, which includes a current collector and a negative electrode material layer disposed on at least one surface of the current collector. Among them, the negative electrode material layer includes the above-mentioned hard carbon material and / or the hard carbon material prepared according to the above-mentioned preparation method.

[0060] The fourth aspect of the present invention provides a battery, which includes a negative electrode plate, and the negative electrode plate is the above-mentioned negative electrode plate.

[0061] The present invention is further described in detail below through examples. All raw materials used in the examples can be obtained through commercial channels.

[0062] Example 1

[0063] (1) Preparation of hard carbon material

[0064] Put coconut shell powder in the first inert atmosphere for the first carbonization treatment to obtain the carbonized material. Among them, the first inert atmosphere is argon, the temperature of the first carbonization treatment is 750 °C, and the time is 2 h. After cooling the carbonized material, it is washed thoroughly with a 20% hydrochloric acid aqueous solution, and then mixed with deionized water at a ratio of 1:15 for negative pressure treatment. The conditions for negative pressure treatment are: put the mixture in a vacuum box and evacuate to 100 Pa, and keep it for 2 h; filter the material after negative pressure treatment to obtain the first material, put the first material in a high-pressure reaction kettle, fill it with argon to adjust the pressure in the kettle to 0.4 Mpa, then heat the reaction kettle to 750 °C, and keep it warm for 10 min to complete the reaction of H2O and the carbon on the inner wall of the pores, and obtain the first hard carbon particles.

[0065] Mix the solute liquid phenolic resin and the solvent ethanol to prepare a mixed solution with a mass concentration of 40%. Add the first hard carbon particles to the mixed solution to obtain a mixed material. The mass ratio of the first hard carbon particles to the mixed solution is 1.5. After stirring the mixed material at 150 °C for 2 h, keep it at 750 °C for 1 h to obtain the second material; granulate the second material into second particles with a D50 of 3 μm; put the second particles in the third inert atmosphere for the second carbonization treatment; the third inert atmosphere is argon, the temperature of the second carbonization treatment is 1200 °C, and the time is 2 h to obtain the hard carbon material of this example.

[0066] (2) Preparation of negative electrode sheet

[0067] Mix the hard carbon material, conductive carbon and binder (carboxymethyl cellulose CMC) of this example according to a mass ratio of 95:2.5:2.5, then dissolve them in N-methylpyrrolidone (NMP), stir evenly, coat them on a 10-μm aluminum foil, and dry and roll to obtain the negative electrode sheet.

[0068] (3) Preparation of sodium-ion battery

[0069] Then, the negative electrode sheet, the counter electrode sheet (sodium metal), the electrolyte (1 mol / L NaPF6 with the solvent being EC:DEC = 1:1), and a 12-μm PE separator are assembled into a battery.

[0070] Example 2

[0071] (1) Preparation of hard carbon material

[0072] The coconut shell powder is placed in a first inert atmosphere for the first carbonization treatment to obtain the carbonized material. Here, the first inert atmosphere is argon, the temperature of the first carbonization treatment is 850 °C, and the time is 4 h. After the carbonized material is cooled, it is thoroughly washed with a 30% hydrochloric acid aqueous solution and then mixed with deionized water at a ratio of 1:15 for negative pressure treatment. The conditions for the negative pressure treatment are as follows: the mixture is placed in a vacuum chamber and evacuated to 150 Pa and maintained for 1 h; after the material after the negative pressure treatment is filtered, the first material is obtained. The first material is placed in a high-pressure reaction kettle, and argon is introduced to adjust the pressure in the kettle to 0.6 Mpa. Subsequently, the reaction kettle is heated to 850 °C and kept warm for 30 min to complete the reaction between H2O and the carbon on the inner wall of the pores, obtaining the first hard carbon particles.

[0073] The solute liquid phenolic resin and the solvent ethanol are mixed to prepare a mixed solution with a mass concentration of 30% - 50%. The first hard carbon particles are added to the mixed solution to obtain a mixed material. The mass ratio of the first hard carbon particles to the mixed solution is 1.5. After the mixed material is stirred at 150 °C for 2 h, it is placed at 750 °C and kept warm for 1 h to obtain the second material; the second material is granulated into second particles with a D50 of 3 μm; the second particles are placed in a third inert atmosphere for the second carbonization treatment; the third inert atmosphere is argon, the temperature of the second carbonization treatment is 1200 °C, and the time is 2 h, obtaining the hard carbon material of this example.

[0074] (2) Preparation of negative electrode sheet

[0075] In this example, the preparation method of the negative electrode sheet is the same as that in Example 1.

[0076] (3) Preparation of sodium-ion battery

[0077] In this example, the preparation method of the sodium-ion battery is the same as that in Example 1.

[0078] Example 3

[0079] (1) Preparation of hard carbon material

[0080] The coconut shell powder is placed in a first inert atmosphere for a first carbonization treatment to obtain a carbonized material. Herein, the first inert atmosphere is argon, the temperature of the first carbonization treatment is 750 °C, and the time is 2 h. After the carbonized material is cooled, it is thoroughly washed with a 20% hydrochloric acid aqueous solution, and then mixed with deionized water at a ratio of 1:15 for negative pressure treatment. The conditions of the negative pressure treatment are as follows: The mixture is placed in a vacuum chamber and evacuated to 100 Pa and maintained for 2 h; after the material treated under negative pressure is filtered, a first material is obtained. The first material is placed in a high-pressure reactor, and argon is introduced to adjust the pressure in the reactor to 0.4 Mpa. Subsequently, the reactor is heated to 750 °C and kept warm for 10 min to complete the reaction of H2O with the carbon on the inner wall of the pores, obtaining first hard carbon particles.

[0081] The solute liquid phenolic resin and the solvent ethanol are mixed and configured to obtain a mixed solution with a mass concentration of 50%. The first hard carbon particles are added to the mixed solution to obtain a mixed material. The mass ratio of the first hard carbon particles to the mixed solution is 1. After the mixed material is stirred at 150 °C for 2 h, it is then kept at 850 °C for 2 h to obtain a second material; the second material is granulated into second particles with a D50 of 3 μm; the second particles are placed in a third inert atmosphere for a second carbonization treatment; the third inert atmosphere is argon, the temperature of the second carbonization treatment is 1200 °C, and the time is 2 h, obtaining the hard carbon material of this example.

[0082] (2)Preparation of the negative electrode sheet

[0083] In this example, the preparation method of the negative electrode sheet is the same as that in Example 1.

[0084] (3)Preparation of the sodium-ion battery

[0085] In this example, the preparation method of the sodium-ion battery is the same as that in Example 1.

[0086] Example 4

[0087] (1)Preparation of the hard carbon material

[0088] In this example, the preparation method of the hard carbon material is the same as that in Example 1, except that: the second material is granulated into second particles with a D50 of 8 μm.

[0089] (2)Preparation of the negative electrode sheet

[0090] In this example, the preparation method of the negative electrode sheet is the same as that in Example 1.

[0091] (3)Preparation of the sodium-ion battery

[0092] In this example, the preparation method of the sodium-ion battery is the same as that in Example 1.

[0093] Example 5

[0094] (1)Preparation of the hard carbon material

[0095] In this embodiment, the preparation method of the hard carbon material is the same as that of Example 1, except that the coconut shell powder is replaced with bamboo powder.

[0096] (2)Preparation of the negative electrode sheet

[0097] In this embodiment, the preparation method of the negative electrode sheet is the same as that of Example 1.

[0098] (3)Preparation of the sodium-ion battery

[0099] In this embodiment, the preparation method of the sodium-ion battery is the same as that of Example 1.

[0100] Example 6

[0101] (1)Preparation of the hard carbon material

[0102] The coconut shell powder is placed in a first inert atmosphere for the first carbonization treatment to obtain the carbonized material. Among them, the first inert atmosphere is argon, the temperature of the first carbonization treatment is 750 °C, and the time is 2 h. After the carbonized material is cooled, it is thoroughly washed with a 20% hydrochloric acid aqueous solution, and then mixed with deionized water at a ratio of 1:15 for negative pressure treatment. The conditions for the negative pressure treatment are: the mixture is placed in a vacuum box and evacuated to 500 Pa and kept for 0.5 h; the material after the negative pressure treatment is filtered to obtain the first material. The first material is placed in a high-pressure reaction kettle, and argon is introduced to adjust the pressure in the kettle to 0.2 Mpa. Subsequently, the reaction kettle is heated to 650 °C and kept warm for 30 min to complete the reaction between H2O and the carbon on the inner wall of the pores, obtaining the first hard carbon particles.

[0103] The solute liquid phenolic resin and the solvent ethanol are mixed and configured to obtain a mixed solution with a mass concentration of 30%-50%. The first hard carbon particles are added to the mixed solution to obtain a mixed material. The mass ratio of the first hard carbon particles to the mixed solution is 1.5. After the mixed material is stirred at 150 °C for 2 h, it is placed at 750 °C and kept warm for 1 h to obtain the second material; the second material is granulated into second particles with a D50 of 3 μm; the second particles are placed in a third inert atmosphere for the second carbonization treatment; the third inert atmosphere is argon, the temperature of the second carbonization treatment is 1200 °C, and the time is 2 h to obtain the hard carbon material of this embodiment.

[0104] (2)Preparation of the negative electrode sheet

[0105] In this embodiment, the preparation method of the negative electrode sheet is the same as that of Example 1.

[0106] (3)Preparation of the sodium-ion battery

[0107] In this embodiment, the preparation method of the sodium-ion battery is the same as that of Example 1.

[0108] Example 7

[0109] (1)Preparation of hard carbon material

[0110] Put the coconut shell powder in the first inert atmosphere for the first carbonization treatment to obtain the carbonized material. Among them, the first inert atmosphere is argon, the temperature of the first carbonization treatment is 750 °C, and the time is 2 h. After cooling the carbonized material, wash it thoroughly with a 20% hydrochloric acid aqueous solution, and then mix it with deionized water at a ratio of 1:15 for negative pressure treatment. The conditions for negative pressure treatment are: put the mixture in a vacuum box and evacuate it to 100 Pa, and keep it for 2 h; filter the material after negative pressure treatment to obtain the first material, put the first material in a high-pressure reactor, fill it with argon to adjust the pressure in the reactor to 0.4 Mpa, then heat the reactor to 750 °C, and keep it warm for 10 min to complete the reaction of H2O with the carbon on the inner wall of the pores, and obtain the first hard carbon particles.

[0111] Mix the solute liquid phenolic resin and the solvent ethanol to prepare a mixed solution with a mass concentration of 60%. Add the first hard carbon particles to the mixed solution to obtain a mixed material. The mass ratio of the first hard carbon particles to the mixed solution is 0.5. After stirring the mixed material at 200 °C for 2 h, keep it at 900 °C for 2 h to obtain the second material; granulate the second material into the second particles with a D50 of 3 μm; put the second particles in the third inert atmosphere for the second carbonization treatment; the third inert atmosphere is argon, the temperature of the second carbonization treatment is 1200 °C, and the time is 2 h to obtain the hard carbon material of this example.

[0112] (2)Preparation of negative electrode sheet

[0113] In this example, the preparation method of the negative electrode sheet is the same as that in Example 1.

[0114] (3)Preparation of sodium-ion battery

[0115] In this example, the preparation method of the sodium-ion battery is the same as that in Example 1.

[0116] Example 8

[0117] (1)Preparation of hard carbon material

[0118] In this example, the preparation method of the hard carbon material is the same as that in Example 1, the difference is: granulate the second material into the second particles with a D50 of 2 μm.

[0119] (2)Preparation of negative electrode sheet

[0120] In this example, the preparation method of the negative electrode sheet is the same as that in Example 1.

[0121] (3)Preparation of sodium-ion battery

[0122] In this example, the preparation method of the sodium-ion battery is the same as that in Example 1.

[0123] Example 9

[0124] (1) Preparation of hard carbon material

[0125] In this example, the preparation method of the hard carbon material is the same as that in Example 1, except that: the solute liquid phenolic resin and the solvent ethanol are mixed to prepare a mixed solution with a mass concentration of 80%.

[0126] (2) Preparation of negative electrode sheet

[0127] In this example, the preparation method of the negative electrode sheet is the same as that in Example 1.

[0128] (3) Preparation of sodium-ion battery

[0129] In this example, the preparation method of the sodium-ion battery is the same as that in Example 1.

[0130] Comparative Example 1

[0131] (1) Preparation of hard carbon material

[0132] The coconut shell powder is placed in a first inert atmosphere for the first carbonization treatment to obtain the carbonized material. Among them, the first inert atmosphere is argon, the temperature of the first carbonization treatment is 750 °C, and the time is 2 h.

[0133] The solute liquid phenolic resin and the solvent ethanol are mixed to prepare a mixed solution with a mass concentration of 30%-50%. The carbonized material is added to the mixed solution to obtain a mixed material. The mass ratio of the carbonized material to the mixed solution is 1.5. After the mixed material is stirred at 150 °C for 2 h, it is placed at 750 °C for heat preservation for 1 h to obtain a second material; the second material is granulated into second particles with a D50 of 3 μm; the second particles are placed in a third inert atmosphere for the second carbonization treatment; the third inert atmosphere is argon, and the temperature of the second carbonization treatment is 1200 °C, and the time is 2 h to obtain the hard carbon material of this example.

[0134] (2) Preparation of negative electrode sheet

[0135] In this comparative example, the preparation method of the negative electrode sheet is the same as that in Example 1.

[0136] (3) Preparation of sodium-ion battery

[0137] In this comparative example, the preparation method of the sodium-ion battery is the same as that in Example 1.

[0138] Comparative Example 2

[0139] (1) Preparation of hard carbon material

[0140] The coconut shell powder is placed in a first inert atmosphere for a first carbonization treatment to obtain a carbonized material. Herein, the first inert atmosphere is argon, the temperature of the first carbonization treatment is 750 °C, and the time is 2 h. After the carbonized material is cooled, it is thoroughly washed with a 20% hydrochloric acid aqueous solution and then mixed with deionized water at a ratio of 1:15 for a negative pressure treatment. The conditions of the negative pressure treatment are as follows: the mixture is placed in a vacuum chamber and evacuated to 100 Pa and maintained for 2 h; after the material treated under negative pressure is filtered, a first material is obtained. The first material is placed in a high-pressure reactor, and argon is introduced to adjust the pressure in the reactor to 0.4 Mpa. Subsequently, the reactor is heated to 750 °C and kept warm for 10 min to complete the reaction of H2O with the carbon on the inner wall of the pores, obtaining first hard carbon particles.

[0141] The second material is granulated into first hard carbon particles with a D50 of 3 μm; the first hard carbon particles are placed in a third inert atmosphere for a second carbonization treatment; the third inert atmosphere is argon, the temperature of the second carbonization treatment is 1200 °C, and the time is 2 h, obtaining the hard carbon material of this comparative example.

[0142] (2)Preparation of the negative electrode sheet

[0143] In this comparative example, the preparation method of the negative electrode sheet is the same as that in Example 1.

[0144] (3)Preparation of the sodium-ion battery

[0145] In this comparative example, the preparation method of the sodium-ion battery is the same as that in Example 1.

[0146] Performance test

[0147] (I)Perform performance tests on the hard carbon materials prepared in Examples 1-9 and Comparative Examples 1-2, and the test results are shown in Table 1

[0148] (1)Use a transmission electron microscope to test the cross-section of the hard carbon material, measure the diameter and quantity of closed pores within an area of 1*1 μm, and the average pore diameter is the average value of the diameters of all observable closed pores.

[0149] (2)Default the closed pores as circular, estimate the area of each closed pore by measuring the diameter, and the proportion of internal micropores = the sum of the areas of all closed pores per unit area / 1 μm 2

[0150] (II)Perform charge and discharge experiments on the batteries prepared in Examples 1-9 and Comparative Examples 1-2 at 25 ± 2 °C, with a charge and discharge voltage of 5 mV to 3 V, and test the following performances.

[0151] (1)Gram capacity: First, place the coin cell in an environment of 25 ± 2 °C and let it stand for 8 h, then discharge it at a constant current of 0.05 C to 0.005 V; immediately let it stand for 5 min, then charge it at a constant current of 0.05 C to a voltage of 3.0 V; then let it stand for 5 min, and then discharge it at a constant current of 0.05 C to 0.005 V. Record the discharge capacity C0 at this time as the gram capacity.

[0152] (2)Rate performance (rate capacity retention rate): First, place the coin cell in an environment of 25 ± 2 °C and let it stand for 0.5 h, then discharge it at a constant current of 0.05 C to 0.005 V; immediately let it stand for 5 min, then charge it at a constant current of 0.05 C to a voltage of 3.0 V; immediately let it stand for 5 min, and then discharge it at a constant current of 1 C to 0.005 V. Record the discharge capacity at this time as C1. The rate capacity retention rate = C1 / C0 * 100%. The larger this value is, the better the rate performance.

[0153] (3)Initial efficiency: First, place the coin cell in an environment of 25 ± 2 °C and let it stand for 8 h, then discharge it at a constant current of 0.05 C to 0.005 V. The obtained capacity is recorded as the 0.05 C charge capacity; then let it stand for 5 min and charge it at a constant current of 0.05 C to a voltage of 3.0 V. The obtained capacity is recorded as the 0.05 C discharge capacity. The initial efficiency = 0.05 C charge capacity / 0.05 C discharge capacity * 100%.

[0154] Table 1

[0155]

[0156] As can be seen from Table 1, in Examples 1 - 5, the preparation process parameters, the pore size of the hard carbon, the proportion of micropores, and the thickness of the outer hard carbon are all within the preferred range. The reasonable micropore arrangement inside provides a rich sodium storage space, effectively improving the gram capacity. The outer hard carbon is relatively dense and has fewer defects. Although the capacity is slightly lower than that of the inner layer, its high stability can inhibit the loss of active sodium during the charge and discharge process, achieving the purpose of improving the initial efficiency.

[0157] From the results of Example 1 and Example 6, it can be seen that although Example 6 is improved compared to Comparative Example 1, the specific capacity is still low. Therefore, adjusting the process parameters of the pore optimization process will cause the pore size and micropore ratio to deviate from the design values. From the results of Example 1 and Example 7, it can be seen that adjusting the process parameters of the surface hard carbon coating makes the thickness of the surface hard carbon coating layer thicker. The capacity of this layer is lower than that of the inner hard carbon layer, and the power is also lower than that of the inner hard carbon layer. Once the thickness of the coating layer exceeds the specification, this will have an adverse effect on the specific capacity of the material, and the rate performance will also be greatly attenuated. From the results of Example 1 and Example 8, it can be seen that if the material particle size is too small, the specific surface area of the material will increase. The increase in the contact interface with the electrolyte will lead to excessive side reactions, resulting in loss of specific capacity and first effect. It can be seen from the results of Example 1 and Example 9 that during the outer hard carbon coating process, the ethanol ratio is too low, and there is not enough ethanol volatilization in the coating layer to generate rich pores. In addition to reducing the proportion of surface hard carbon micropores and affecting the outer hard carbon capacity, its sodium ion migration efficiency will also be greatly weakened, which will not only increase the charge transfer impedance and affect the internal hard carbon capacity, but also greatly deteriorate the negative electrode rate performance. It can be seen from the results of Example 1 and Comparative Example 1 that in the internal pore optimization process, the material has uneven pore size and shape, and the proportion of closed pores that can efficiently store sodium is low, resulting in a waste of internal sodium storage space, resulting in a significant decrease in gram capacity. It can be seen from the results of Example 1 and Comparative Example 2 that when the outer hard carbon is removed, the more defects on the surface of the biomass hard carbon cannot be effectively protected. During the first charge film formation process, a large amount of sodium undergoes side reactions at the defects and is deposited on the material surface. Unlike the active sodium embedded in the material, these side reaction products cannot return to the positive electrode during the discharge process, resulting in a large amount of active sodium loss, resulting in a decrease in the first efficiency, and the gram capacity will also be reduced.

[0158] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that, The preparation method includes the following steps: S1. Place the porous carbon source powder in a first inert atmosphere for a first carbonization treatment to obtain a carbonized material. S2. Wash the carbonized material, then mix it with water, perform a negative pressure treatment and filtration to obtain a first material. Place the first material in a second inert atmosphere for a pressurized heating treatment to obtain first hard carbon particles. S3. Mix a liquid resin with an organic solvent to obtain a mixed solution. Mix and cure the first hard carbon particles with the mixed solution to obtain a second material. S4. Crush and granulate the second material to obtain second particles. Place the second particles in a third inert atmosphere for a second carbonization treatment. The conditions of the pressurized heating treatment include: the pressure for pressurization is 0.4 - 0.6 MPa, the heating temperature is 750 - 850 °C, and the treatment time is 10 - 30 min.

2. The preparation method according to claim 1, characterized in that, The porous carbon source powder includes a natural porous carbon source powder. The natural porous carbon source powder is selected from at least one of cotton powder, rice bran powder, coconut shell powder, reed rod powder, poplar wood powder, and bamboo powder. And / or, the liquid resin is selected from at least one of liquid phenolic resin, liquid epoxy resin, and liquid acrylic resin. And / or, the organic solvent is selected from at least one of methanol, ethanol, and ethylene glycol. And / or, the first inert atmosphere, the second inert atmosphere, and the third inert atmosphere are each independently selected from at least one of argon, helium, and nitrogen.

3. The preparation method according to claim 1, wherein the mass ratio of the washed carbonized material to water for mixing is 10 - 20:1; and / or, the mass concentration of the liquid resin in the mixed solution is 30 - 50%; and / or, the mass ratio of the first hard carbon particles to the mixed solution for mixing is 1 - 1.5:1; and / or, the D50 of the second particles is 3 - 8 μm.

4. The preparation method according to claim 1, characterized in that In step S1, the conditions of the first carbonization treatment include: the carbonization temperature is 750 - 850 °C, and the carbonization time is 2 - 4 h. In step S2, the washing treatment includes washing the carbonized material with an acid solution. The acid solution is selected from an aqueous hydrochloric acid solution and / or an aqueous nitric acid solution. The mass concentration of the acid in the acid solution is 20 - 30%. The conditions of the negative pressure treatment include: pumping to 100 - 150 Pa, and the pumping time is 10 - 30 s; or, the conditions of the negative pressure treatment include: introducing an inert gas into the system to 0.4 - 0.6 standard atmospheres and maintaining for 1 - 2 h. In step S3, the conditions of the mixing treatment include: the temperature is 150 - 180 °C, and the time is 2 - 4 h; the conditions of the curing treatment include: the temperature is 750 - 850 °C, and the time is 1 - 2 h. In step S4, the conditions of the second carbonization treatment include: the temperature is 1200 - 1400 °C, and the time is 2 - 4 h.

5. A hard carbon material, characterized in that, The hard carbon material is prepared by the method according to any one of claims 1 - 4.

6. The hard carbon material according to claim 5, wherein The hard carbon material includes first hard carbon particles and a second hard carbon coating layer coated on the surface of the first hard carbon particles. The first hard carbon particles have micropores inside, and the average pore size of the micropores is 1 to 2.5 nm; The second hard carbon coating layer has pores, and the porosity of the second hard carbon coating layer is 5-15%.

7. The hard carbon material according to claim 6, wherein The specific surface area of the first hard carbon particles is 2 to 10 m 2 / g; The pore volume of the first hard carbon particles is 0.01 to 0.6 cm 3 / g; The D50 of the first hard carbon particles is 2.5 to 7.8 μm.

8. The hard carbon material according to claim 6, wherein The pores have a pore diameter of 0.5 to 10 nm; The thickness of the second hard carbon coating layer is 200-500 nm.

9. The hard carbon material according to claim 6, characterized in that, The D50 of the hard carbon material is 3 to 8 μm.

10. A negative electrode plate, characterized in that, The negative electrode plate includes a current collector and a negative electrode material layer arranged on at least one surface of the current collector, wherein the negative electrode material layer includes a hard carbon material prepared by the preparation method according to any one of claims 1 to 4 and / or a hard carbon material according to any one of claims 5 to 9.

11. A battery, characterized in that, The battery includes a negative electrode plate, and the negative electrode plate is the negative electrode plate according to claim 10.

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