A hard-carbon negative electrode material for fast-charging sodium-ion batteries and a preparation method thereof

Abstract

The application discloses a kind of fast charging sodium ion battery hard carbon negative electrode material and preparation method thereof, its preparation method includes the following steps: S1, pretreatment: hard carbon raw materials are broken and sieved, and the hard carbon raw materials with particle size less than 3cm are obtained;S2, low-temperature carbonization: the hard carbon raw materials obtained in step S1 are low-temperature carbonized, and the hard carbon precursor is obtained;S3, crushing and shaping: the hard carbon precursor obtained in step S2 is crushed and treated, and the hard carbon precursor powder is obtained by crushing D50 to 3-200 μm;S4, wet grinding: the hard carbon precursor powder obtained in step S3 is wet sand ground to D50 0.1-3 μm, and the sand grinding slurry is obtained;S5, spray drying: the sand grinding slurry obtained in step S4 is spray dried, and the carbon intermediate is obtained;S6, high-temperature carbonization: the carbon intermediate obtained in step S5 is high-temperature sintered, and the fast charging hard carbon negative electrode material is obtained.The application has the characteristics of good rate performance, excellent fast charging performance and high cycle stability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a hard carbon anode material for fast-charging sodium-ion batteries and its preparation method. Background Technology

[0002] Hard carbon is the mainstream anode material in commercial sodium-ion batteries, boasting advantages such as abundant resources, low cost, and high capacity. However, hard carbon materials have a low sodium intercalation potential, close to the deposition potential of sodium metal. Therefore, during charging, the anode is prone to polarization, causing the potential to drop below the deposition potential of sodium metal, leading to sodium metal deposition. This phenomenon is particularly severe under high-current charging conditions.

[0003] During the sodium deposition process on the negative electrode surface during charging, an irreversible reaction occurs at the contact area between the sodium metal surface and the electrolyte, forming an electrolyte interphase (SEI). This leads to problems such as SEI growth, irreversible capacity loss, gas generation, and electrolyte consumption, affecting battery performance. When sodium deposition is severe, sodium metal grows perpendicular to the electrode surface, forming sodium dendrites, which may pierce the separator and reach the positive electrode, causing a short circuit and rapid heat generation inside the battery, resulting in serious safety issues. For example, sodium-ion batteries are prone to sodium deposition at the negative electrode during charging. The irreversible reaction between the sodium metal surface and the electrolyte forms an SEI, leading to SEI growth, irreversible capacity loss, gas generation, and electrolyte consumption, affecting the improvement of fast-charging performance. If sodium dendrites form on the negative electrode surface, they may pierce the separator and reach the positive electrode, causing a short circuit and rapid heat generation inside the battery, resulting in serious safety issues. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a hard carbon anode material for fast-charging sodium-ion batteries, which has the characteristics of good rate performance, excellent fast-charging performance and high cycle stability.

[0005] This invention can be achieved through the following technical solutions: This invention discloses a method for preparing a hard carbon anode material for fast-charging sodium-ion batteries, comprising the following steps: S1. Pretreatment: The hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3cm. S2, Low-temperature carbonization: The hard carbon raw material obtained in step S1 is carbonized at a low temperature to obtain a hard carbon precursor; S3. Crushing and shaping: The hard carbon precursor obtained in step S2 is crushed and pulverized to 3-200μm with D50 to obtain hard carbon precursor powder. S4. Wet grinding: The hard carbon precursor powder obtained in step S3 is wet-milled to a D50 of 0.1-3μm to obtain a sand milling slurry; S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried to obtain a carbon intermediate; S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is sintered at high temperature to obtain a fast-charging hard carbon anode material.

[0006] In this invention, during the wet grinding process in step S4, the hard carbon precursor is ground into primary particles with a smaller particle size (D50 = 0.1-3 μm). During the spray drying process in step S5, the primary particles agglomerate and accumulate under the action of the coating agent to form secondary particles with a relatively small specific surface area (D50 = 0.5-3 μm). During the high-temperature carbonization process in step S6, on the one hand, the graphitization degree of the carbon material gradually increases during the heating process, that is, the carbon layer gradually grows and the size of the graphite crystallite gradually increases. On the other hand, the oxygen-containing functional groups in the crosslinking agent gradually undergo crosslinking reactions with the coating agent and the low-temperature carbon to form chemical bonds such as -O- and -C=O, which inhibits the narrowing of the interlayer spacing of the graphite crystallite and thus enhances the transport kinetics of sodium ions between carbon layers.

[0007] In this invention, the primary particles of the hard carbon material have a smaller particle size, resulting in a shorter diffusion path for sodium ions to diffuse into the hard carbon material during charging. This reduces the polarization caused by sodium ion diffusion, thereby improving the kinetic performance of the hard carbon material. Simultaneously, the primary particles, under the action of the coating agent, form larger secondary particles, which can reduce the specific surface area of ​​the hard carbon material, decrease the contact area between the hard carbon material and the electrolyte, reduce irreversible capacity loss of the electrolyte, and thus improve the stability of the hard carbon material.

[0008] Furthermore, in the wet milling process of step S4, the amounts of dispersant, coating agent, and crosslinking agent added are 0.05-0.3%, 0.5-5%, and 0.5-2% of the mass of the hard carbon precursor, respectively. In this invention, the crosslinking agent inhibits the narrowing of the carbon interlayer spacing during graphitization. A wider carbon interlayer spacing is beneficial for sodium ion transport, further improving the sodium ion transport kinetics within the bulk phase of the hard carbon material. Under the synergistic effect of multiple actions, the hard carbon material of this invention exhibits good cycle performance, rate performance, and fast-charging performance.

[0009] Preferably, the solid content of the dispersion system is 20-45%, and the dispersant is one or more of the following: sodium isoascorbate, polyvinylpyrrolidone, ethanol, ethylene glycol, polyvinyl alcohol, polyethylene glycol, glycerol, dodecyl sulfonate, triethylhexyl phosphate, methylpentanol, cellulose derivatives, polyacrylamide, fatty acid polyethylene glycol esters, and polyacrylic acid. In this invention, the dispersant can reduce the aggregation between carbon material particles and reduce the viscosity of the system, thereby improving the grinding efficiency and grinding uniformity.

[0010] Preferably, the coating agent is a carbon-containing organic compound, which is one or more of glucose, citric acid, PEG, sucrose, water-soluble resin, polyacrylic acid, ascorbic acid, maltose, and lignin.

[0011] Preferably, the crosslinking agent is one or more of glyoxal, propylenediamine, urea-formaldehyde, formaldehyde, benzaldehyde, furfural, and terephthalaldehyde.

[0012] Furthermore, in the wet grinding process of step S4, the diameter of the grinding beads is 0.3-1.5 mm, the grinding time is 0.5-5 h, and the grinding temperature is 25-80℃.

[0013] Furthermore, in step S5, the spray drying conditions are: inlet air temperature of 230-300℃ and outlet air temperature of 90-150℃.

[0014] Further, in step S6, the conditions for high-temperature carbonization are: a heating rate of 0.5-5 °C / min, a carbonization temperature of 900-1600 °C, and a carbonization time of 2-10 h. Specifically, the carbonization temperature affects the electrochemical performance of the hard carbon material. During the heating process, the degree of graphitization of the carbon material gradually increases, that is, the size of the graphite crystallites gradually increases, while the carbon interlayer spacing of the graphite crystallites gradually narrows. A larger graphite crystallite size is beneficial to improving the sodium storage capacity of the hard carbon material, but a narrower carbon interlayer spacing is not conducive to the diffusion of sodium ions between the carbon layers. Therefore, it is necessary to control the high-temperature carbonization temperature of the hard carbon material.

[0015] Further, in step S2, the low-temperature carbonization conditions are: heating rate 2-20 ℃ / min, pretreatment temperature 300-800 ℃, and pretreatment time 0.5-5 h; the protective gas is nitrogen and / or argon. In this invention, the low-temperature carbonization temperature affects the effectiveness of the invention: if the carbonization temperature is too high, the carbon content of the hard carbon precursor is high and the content of oxygen-containing functional groups is low, which is not conducive to subsequent crosslinking and coating reactions; if the carbonization temperature is too low, the yield of subsequent high-temperature carbonization is low, the tar discharge is high, resulting in excessively high carbonization costs and heavy equipment burden, which is not conducive to industrial production.

[0016] Furthermore, in step S2, low-temperature carbonization is carried out in a low-temperature furnace, which is one or more of the following: pusher kiln, rotary kiln, roller kiln, box furnace, tube furnace, and vacuum furnace.

[0017] Furthermore, in step S3, the crushing and shaping method is one or more of the following: roller mill, mechanical mill, ball mill, and air-jet mill.

[0018] Furthermore, in step S1, the hard carbon raw material is one or more of the following: biomass raw material, phenolic resin, glucose, lignin, anthracite, lignite, etc.

[0019] Another aspect of the present invention is to protect a hard carbon anode material for fast-charging sodium-ion batteries, which is prepared by the above-described preparation method. The anode material is composed of secondary particles, which are formed by the stacking of primary particles. The secondary particles have a particle size D50 of 3-10 μm, the primary particles have a particle size D50 of 0.5-3 μm, and the average carbon interlayer spacing inside the primary particles is 0.38-0.40 nm.

[0020] This invention discloses a hard carbon anode material for fast-charging sodium-ion batteries and its preparation method, which has the following beneficial effects: First, it has good rate performance. In this invention, the carbon layer spacing inside the hard carbon material is relatively wide, and the kinetics of sodium ion transport are relatively fast, thus exhibiting good rate discharge capability. Secondly, it exhibits excellent fast charging performance. In this invention, the primary particle size of the hard carbon material is small, and the spacing between the carbon layers inside the primary particles is wide. During the charging process, the diffusion path of sodium ions into the interior of the hard carbon material is short and the diffusion is fast, which reduces the polarization phenomenon caused by sodium ion diffusion and avoids the precipitation of sodium metal, thus demonstrating good fast charging capability.

[0021] Third, it has high cycle stability. In this invention, the primary particles agglomerate under the action of the coating agent to form secondary particles. The secondary particles have a larger particle size and a carbon coating layer on the surface, thus exhibiting a smaller specific surface area. This reduces the contact area between the hard carbon material and the electrolyte, reduces the irreversible capacity loss of the electrolyte, and thus improves the stability of the hard carbon material.

[0022] Fourth, it has good safety performance. In this invention, the hard carbon material has good fast charging performance, avoids the precipitation of sodium metal during charging, and is not prone to the formation of sodium dendrites, thus exhibiting good safety performance. Attached Figure Description

[0023] Figure 1 The XRD curves of Application Example 1 and Comparative Example 1 are shown. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0025] This invention discloses a method for preparing a hard carbon anode material for fast-charging sodium-ion batteries, comprising the following steps: S1. Pretreatment: The hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3cm. S2, Low-temperature carbonization: The hard carbon raw material obtained in step S1 is carbonized at a low temperature to obtain a hard carbon precursor; S3. Crushing and shaping: The hard carbon precursor obtained in step S2 is crushed and pulverized to 3-200μm with D50 to obtain hard carbon precursor powder. S4. Wet grinding: The hard carbon precursor powder obtained in step S3 is wet-milled to a D50 of 0.1-3μm to obtain a sand milling slurry; S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried to obtain a carbon intermediate; S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is sintered at high temperature to obtain a fast-charging hard carbon anode material.

[0026] Furthermore, in the wet milling process of step S4, the amounts of dispersant, coating agent and crosslinking agent added are 0.05-0.3%, 0.5-5% and 0.5-2% of the mass of hard carbon precursor, respectively.

[0027] Preferably, the solid content of the dispersion system is 20-45%, and the dispersant is one or more of the following: sodium isoascorbate, polyvinylpyrrolidone, ethanol, ethylene glycol, polyvinyl alcohol, polyethylene glycol, glycerol, dodecyl sulfonate, triethylhexyl phosphate, methylpentanol, cellulose derivatives, polyacrylamide, fatty acid polyethylene glycol esters, and polyacrylic acid.

[0028] Preferably, the coating agent is a carbon-containing organic compound, which is one or more of glucose, citric acid, PEG, sucrose, water-soluble resin, polyacrylic acid, ascorbic acid, maltose, and lignin.

[0029] Preferably, the crosslinking agent is one or more of glyoxal, propylenediamine, urea-formaldehyde, formaldehyde, benzaldehyde, furfural, and terephthalaldehyde.

[0030] Furthermore, in the wet grinding process of step S4, the diameter of the grinding beads is 0.3-1.5 mm, the grinding time is 0.5-5 h, and the grinding temperature is 25-80℃.

[0031] Furthermore, in step S5, the spray drying conditions are: inlet air temperature of 230-300℃ and outlet air temperature of 90-150℃.

[0032] Furthermore, in step S6, the conditions for high-temperature carbonization are: a heating rate of 0.5-5 ℃ / min, a carbonization temperature of 900-1600℃, and a carbonization time of 2-10 h.

[0033] Further, in step S2, the low-temperature carbonization conditions are: heating rate 2-20 ℃ / min, pretreatment temperature 300-800 ℃, and pretreatment time 0.5-5 h; the protective gas is nitrogen and / or argon. Further, in step S2, the low-temperature carbonization is carried out in a low-temperature furnace, which is one or more of the following: pusher kiln, rotary kiln, roller kiln, box furnace, tube furnace, and vacuum furnace.

[0034] Furthermore, in step S3, the crushing and shaping method is one or more of the following: roller mill, mechanical mill, ball mill, and air-jet mill.

[0035] Furthermore, in step S1, the hard carbon raw material is one or more of the following: biomass raw material, phenolic resin, glucose, lignin, anthracite, lignite, etc.

[0036] Another aspect of the present invention is to protect a hard carbon anode material for fast-charging sodium-ion batteries, which is prepared by the above-described preparation method. The anode material is composed of secondary particles, which are formed by the stacking of primary particles. The secondary particles have a particle size D50 of 3-10 μm, the primary particles have a particle size D50 of 0.5-3 μm, and the average carbon interlayer spacing inside the primary particles is 0.38-0.40 nm. Example

[0037] This embodiment relates to a hard carbon anode material for fast-charging sodium-ion batteries, the preparation method of which includes the following steps: S1. Pretreatment: The hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3 cm. Specifically, the hard carbon raw material is biomass raw material and phenolic resin.

[0038] S2. Low-temperature carbonization: The hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization to obtain a hard carbon precursor. Specifically, the low-temperature carbonization conditions are: heating rate 20 ℃ / min, pretreatment temperature 550 ℃, pretreatment time 0.5 h; the protective gas is nitrogen; the low-temperature carbonization is carried out in a low-temperature furnace, which is a pusher kiln.

[0039] S3. Crushing and Shaping: The hard carbon precursor obtained in step S2 is crushed and pulverized to 3-200μm with a D50 to obtain hard carbon precursor powder. Specifically, the crushing and shaping method is a roller crushing process.

[0040] S4. Wet Milling: The hard carbon precursor powder obtained in step S3 is wet-milled to a D50 of 0.1-3 μm to obtain a milled slurry. Specifically, during the wet milling process, the amounts of dispersant, coating agent, and crosslinking agent added are 0.3%, 3%, and 0.5% of the mass of the hard carbon precursor, respectively. The solid content of the dispersion system is 45%, and the dispersant is sodium isoascorbate and polyvinylpyrrolidone. The coating agent is a carbon-containing organic compound, which is glucose, citric acid, PEG, or sucrose. The crosslinking agent is glyoxal, propylenediamine, urea-formaldehyde, formaldehyde, or benzaldehyde. The diameter of the milling beads is 1.5 mm, the milling time is 3 hours, and the milling temperature is 25°C.

[0041] S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried to obtain a carbon intermediate. Specifically, the spray drying conditions are: inlet air temperature of 300℃ and outlet air temperature of 120℃.

[0042] S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is sintered at high temperature to obtain a fast-charging hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 5 °C / min, carbonization temperature of 1300 °C, and carbonization time of 2 h. Example

[0043] This embodiment relates to a hard carbon anode material for fast-charging sodium-ion batteries, the preparation method of which includes the following steps: S1. Pretreatment: The hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3 cm. Specifically, the hard carbon raw material is lignin, anthracite, or lignite.

[0044] S2. Low-temperature carbonization: The hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization to obtain a hard carbon precursor. Specifically, the low-temperature carbonization conditions are: heating rate 10 ℃ / min, pretreatment temperature 300 ℃, pretreatment time 5 h; the protective gas is argon; the low-temperature carbonization is carried out in a low-temperature furnace, which is a rotary kiln.

[0045] S3. Crushing and Shaping: The hard carbon precursor obtained in step S2 is crushed and pulverized to a D50 of 3-200 μm to obtain hard carbon precursor powder. Specifically, the crushing and shaping method is mechanical grinding.

[0046] S4. Wet Milling: The hard carbon precursor powder obtained in step S3 is wet-milled to a D50 of 0.1-3 μm to obtain a milled slurry. Specifically, during the wet milling process, the amounts of dispersant, coating agent, and crosslinking agent added are 0.2%, 0.5%, and 2% of the mass of the hard carbon precursor, respectively. The solid content of the dispersion system is 35%, and the dispersant is ethanol, ethylene glycol, polyvinyl alcohol, polyethylene glycol, glycerol, and dodecyl sulfonate. The coating agent is a carbon-containing organic compound, which is sucrose or a water-soluble resin. The crosslinking agent is terephthalaldehyde. The diameter of the milling beads is 1 mm, the milling time is 0.5 h, and the milling temperature is 80 °C.

[0047] S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried to obtain a carbon intermediate. Specifically, the spray drying conditions are: inlet air temperature of 260℃ and outlet air temperature of 90℃.

[0048] S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is sintered at high temperature to obtain a fast-charging hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 3 ℃ / min, carbonization temperature of 900℃, and carbonization time of 10 h. Example

[0049] This embodiment relates to a hard carbon anode material for fast-charging sodium-ion batteries, the preparation method of which includes the following steps: S1. Pretreatment: The hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3 cm. Specifically, the hard carbon raw material is biomass raw material, phenolic resin, and lignite.

[0050] S2. Low-temperature carbonization: The hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization to obtain a hard carbon precursor. Specifically, the low-temperature carbonization conditions are: heating rate 2 ℃ / min, pretreatment temperature 800 ℃, pretreatment time 3h; the protective gases are nitrogen and argon; the low-temperature carbonization is carried out in a low-temperature furnace, which is a roller kiln.

[0051] S3. Crushing and Shaping: The hard carbon precursor obtained in step S2 is crushed and pulverized to a D50 of 3-200 μm to obtain hard carbon precursor powder. Specifically, the crushing and shaping method is ball milling.

[0052] S4. Wet Grinding: The hard carbon precursor powder obtained in step S3 is wet-milled to a D50 of 0.1-3 μm to obtain a sand-milled slurry. Specifically, during the wet grinding process, the amounts of dispersant, coating agent, and crosslinking agent added are 0.05%, 5%, and 1% of the mass of the hard carbon precursor, respectively. The solid content of the dispersion system is 20%, and the dispersant is sodium isoascorbate, polyethylene glycol ester of fatty acids, and polyacrylic acid. The coating agent is a carbon-containing organic compound, which is ascorbic acid, maltose, and lignin. The crosslinking agent is benzaldehyde, furfural, and terephthalaldehyde. The diameter of the sand-milling beads is 0.3 mm, the sand-milling time is 5 h, and the sand-milling temperature is 55 °C.

[0053] S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried to obtain a carbon intermediate. Specifically, the spray drying conditions are: inlet air temperature of 230℃ and outlet air temperature of 150℃.

[0054] S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is sintered at high temperature to obtain a fast-charging hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 0.5 ℃ / min, carbonization temperature of 1600℃, and carbonization time of 6 h. Example

[0055] This embodiment relates to a hard carbon anode material for fast-charging sodium-ion batteries, the preparation method of which includes the following steps: S1. Pretreatment: The hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3 cm. Specifically, the hard carbon raw material is biomass raw material, phenolic resin, and glucose.

[0056] S2. Low-temperature carbonization: The hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization to obtain a hard carbon precursor. Specifically, the low-temperature carbonization conditions are: heating rate 12 ℃ / min, pretreatment temperature 700 ℃, pretreatment time 2 h; the protective gases are nitrogen and argon; the low-temperature carbonization is carried out in a low-temperature furnace, which is a box furnace.

[0057] S3. Crushing and Shaping: The hard carbon precursor obtained in step S2 is crushed and pulverized to a D50 of 3-200 μm to obtain hard carbon precursor powder. Specifically, the crushing and shaping methods are ball milling and air-jet milling.

[0058] S4. Wet Grinding: The hard carbon precursor powder obtained in step S3 is wet-milled to a D50 of 0.1-3 μm to obtain a milled slurry. Specifically, during the wet grinding process, the amounts of dispersant, coating agent, and crosslinking agent added are 0.1%, 2%, and 0.8% of the mass of the hard carbon precursor, respectively. The solid content of the dispersion system is 30%, and the dispersant is sodium isoascorbate, polyvinylpyrrolidone, cellulose derivatives, polyacrylamide, fatty acid polyethylene glycol ester, and polyacrylic acid. The coating agent is a carbon-containing organic compound, which is glucose, citric acid, ascorbic acid, maltose, and lignin. The crosslinking agent is glyoxal, benzaldehyde, furfural, and terephthalaldehyde. The diameter of the milling beads is 0.8 mm, the milling time is 2 hours, and the milling temperature is 50℃.

[0059] S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried to obtain a carbon intermediate. Specifically, the spray drying conditions are: inlet air temperature of 270℃ and outlet air temperature of 130℃.

[0060] S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is sintered at high temperature to obtain a fast-charging hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 0.5-5 ℃ / min, carbonization temperature of 900-1600℃, and carbonization time of 2-10 h. Example

[0061] This embodiment relates to a hard carbon anode material for fast-charging sodium-ion batteries, the preparation method of which includes the following steps: S1. Pretreatment: The hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3 cm. Specifically, the hard carbon raw material is glucose, lignin, anthracite, and lignite.

[0062] S2. Low-temperature carbonization: The hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization to obtain a hard carbon precursor. Specifically, the low-temperature carbonization conditions are: heating rate 16 ℃ / min, pretreatment temperature 400 ℃, pretreatment time 4 h; the protective gases are nitrogen and argon; the low-temperature carbonization is carried out in a low-temperature furnace, which is a tube furnace or a vacuum furnace.

[0063] S3. Crushing and Shaping: The hard carbon precursor obtained in step S2 is crushed and pulverized to a D50 of 3-200 μm to obtain hard carbon precursor powder. Specifically, the crushing and shaping method is roller milling and ball milling.

[0064] S4. Wet Milling: The hard carbon precursor powder obtained in step S3 is wet-milled to a D50 of 0.1-3 μm to obtain a milled slurry. Specifically, during the wet milling process, the amounts of dispersant, coating agent, and crosslinking agent added are 0.2%, 1%, and 1% of the mass of the hard carbon precursor, respectively. The solid content of the dispersion system is 30%. The dispersant is sodium isoascorbate, polyvinylpyrrolidone, ethanol, ethylene glycol, cellulose derivatives, polyacrylamide, fatty acid polyethylene glycol esters, and polyacrylic acid. The coating agent is a carbon-containing organic compound, which is glucose, citric acid, PEG, sucrose, or water-soluble resin. The crosslinking agent is formaldehyde, benzaldehyde, furfural, or terephthalaldehyde. The diameter of the milling beads is 1 mm, the milling time is 2 hours, and the milling temperature is 40℃.

[0065] S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried to obtain a carbon intermediate. Specifically, the spray drying conditions are: inlet air temperature of 240℃ and outlet air temperature of 100℃.

[0066] S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is sintered at high temperature to obtain a fast-charging hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 2 ℃ / min, carbonization temperature of 1100℃, and carbonization time of 4 h.

[0067] This embodiment relates to a hard carbon anode material for fast-charging sodium-ion batteries, the preparation method of which includes the following steps: S1. Pretreatment: The coconut shell hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3cm.

[0068] S2. Low-temperature carbonization: The coconut shell hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization in a box furnace to obtain a hard carbon precursor. The heating rate is 5 ℃ / min, the pretreatment temperature is 500 ℃, and the pretreatment time is 2 h; the protective gas is nitrogen.

[0069] S3. Crushing and shaping: The coconut shell hard carbon precursor obtained in step S2 is subjected to roller milling, mechanical milling and air jet milling in sequence to obtain a coconut shell hard carbon precursor with D5 of 5μm.

[0070] S4. Wet milling: The coconut shell hard carbon precursor with a D5 of 5 μm obtained in step S3 is placed in a dispersion tank, and dispersant, coating agent, crosslinking agent and deionized water are added. After uniform dispersion, it is sand-milled until the D50 is 0.5 μm to obtain a sand-milled slurry. The dispersant, coating agent and crosslinking agent are polyvinylpyrrolidone, glucose and glyoxal, respectively, with addition amounts of 0.2%, 2% and 1.5% of the hard carbon precursor addition amount, respectively; the solid content of the dispersion system is 35%; the diameter of the sand-milling beads is 0.5 mm; the sand-milling time is 2 h; and the sand-milling temperature is 40℃.

[0071] S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried at an inlet air temperature of 280°C and an outlet air temperature of 110°C to obtain a carbon intermediate with a D50 of 5μm.

[0072] S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is placed in a high-temperature carbonization furnace and sintered at high temperature in a nitrogen protective atmosphere. The heating rate is 2 °C / min, the carbonization temperature is 1400 °C, and the carbonization time is 5 h, to obtain a long-cycle, high-rate hard carbon anode material.

[0073] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 120 μm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into a 0.6 mm radius disc using a die-cutting machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, a CR2016 button cell was assembled in a glove box. The above button cell was subjected to constant current charge-discharge testing at a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 2–0.005 V.

[0074] This embodiment relates to a hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps: S1. Pretreatment: The coconut shell hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3cm.

[0075] S2. Low-temperature carbonization: The coconut shell hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization in a box furnace to obtain a hard carbon precursor. The heating rate is 5 ℃ / min, the pretreatment temperature is 500 ℃, and the pretreatment time is 2 h; the protective gas is nitrogen.

[0076] S3. Crushing and shaping: The coconut shell hard carbon precursor obtained in step S2 is subjected to roller milling, mechanical milling and air jet milling in sequence to obtain a coconut shell hard carbon precursor with D5 of 5μm.

[0077] S4. Wet milling: The coconut shell hard carbon precursor with a D5 of 5 μm obtained in step S3 is placed in a dispersion tank, and a dispersant, a coating agent, and deionized water are added. After uniform dispersion, it is milled until the D50 is 0.5 μm to obtain a milled slurry. The dispersant and coating agent are polyvinylpyrrolidone and glucose, respectively, added at 0.2% and 2% of the hard carbon precursor amount; the solid content of the dispersion system is 35%; the diameter of the milling beads is 0.5 mm; the milling time is 2 hours; and the milling temperature is 40℃.

[0078] S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried at an inlet air temperature of 280°C and an outlet air temperature of 110°C to obtain a carbon intermediate with a D50 of 5μm.

[0079] S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is placed in a high-temperature carbonization furnace and sintered at high temperature in a nitrogen protective gas atmosphere. The heating rate is 2 °C / min, the carbonization temperature is 1400 °C, and the carbonization time is 5 h to obtain the hard carbon anode material of Comparative Example 1.

[0080] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 120 μm four-sided coating apparatus was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into a 0.6 mm radius disc using a die-cutting machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, a CR2016 button cell was assembled in a glove box. The above button cell was subjected to constant current charge-discharge testing at a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 2–0.001 V.

[0081] This embodiment relates to a hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps: S1. Pretreatment: The coconut shell hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3cm.

[0082] S2. Low-temperature carbonization: The coconut shell hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization in a box furnace to obtain a hard carbon precursor. The heating rate is 5 ℃ / min, the pretreatment temperature is 500 ℃, and the pretreatment time is 2 h; the protective gas is nitrogen.

[0083] S3. Crushing and shaping: The coconut shell hard carbon precursor obtained in step S2 is subjected to roller milling, mechanical milling and air jet milling in sequence to obtain a coconut shell hard carbon precursor with D5 of 5μm.

[0084] S4. Wet milling: The coconut shell hard carbon precursor with a D5 of 5 μm obtained in step S3 is placed in a dispersion tank, and dispersant, coating agent, crosslinking agent, and deionized water are added. The mixture is dispersed evenly to obtain a uniformly dispersed slurry. The dispersant, coating agent, and crosslinking agent are polyvinylpyrrolidone, glucose, and glyoxal, respectively, with addition amounts of 0.2%, 2%, and 1.5% of the hard carbon precursor addition amount; the solid content of the dispersion system is 35%; the diameter of the milling beads is 0.5 mm; the milling time is 2 hours; and the milling temperature is 40℃.

[0085] S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried at an inlet air temperature of 280°C and an outlet air temperature of 110°C to obtain a carbon intermediate with a D50 of 5μm.

[0086] S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is placed in a high-temperature carbonization furnace and sintered at high temperature in a nitrogen protective gas atmosphere. The heating rate is 2 °C / min, the carbonization temperature is 1400 °C, and the carbonization time is 5 h to obtain the hard carbon anode material of Comparative Example 2.

[0087] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 120 μm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into a 0.6 mm radius disc using a die-cutting machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, a CR2016 button cell was assembled in a glove box. The above button cell was subjected to constant current charge-discharge testing at a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 2–0.005 V.

[0088] Figure 1 The XRD curves of Application Example 1 and Comparative Example 1 were compared. The (002) peak of the hard carbon material in Application Example 1 shifted to the left compared to Comparative Example 1, indicating a wider carbon interlayer spacing. Fitting the XRD curves, the carbon interlayer spacings of the hard carbon materials in Application Example 1 and Comparative Example 1 were calculated to be 0.385 nm and 0.372 nm, respectively, indicating that the crosslinking agent significantly widened the carbon interlayer spacing. Nitrogen adsorption-desorption tests showed that the specific surface area of ​​Application Example 1 was only 5.2 m². 2 / g indicates that the formation of secondary particles by primary particle coating and stacking can effectively reduce the specific surface area of ​​hard carbon materials.

[0089] Using sodium iron phosphate composite as the positive electrode, in the rate performance test of a 1Ah soft-pack battery, the capacity retention rates of Application Example 1, Comparative Example 1, and Comparative Example 2 under high current discharge at 1C / 5C charging / discharging rates were 94.45%, 92.1%, and 91.5%, respectively, indicating that Application Example 1 has better rate performance.

[0090] Using sodium iron phosphate composite as the positive electrode, in the 1C / 1C cycle performance test of a 1Ah soft-pack battery, the capacity retention rates of Application Example 1, Comparative Example 1, and Comparative Example 2 after 1000 cycles were 95.17%, 92.91%, and 92.33%, respectively, indicating that Application Example 1 has better cycle stability.

[0091] In this invention, the primary particles of the hard carbon material have a small particle size and a wide spacing between the carbon layers within the primary particles. During charging, the diffusion path for sodium ions to diffuse into the hard carbon material is short and the diffusion is rapid. Therefore, polarization is small during high-rate charge and discharge, resulting in better rate and fast-charging performance. Simultaneously, the small primary particles agglomerate under the action of the coating agent to form secondary particles. These secondary particles have a larger particle size and a carbon coating layer on their surface, exhibiting a smaller specific surface area. This reduces the contact area between the hard carbon material and the electrolyte, minimizing irreversible capacity loss from the electrolyte and thus improving the stability of the hard carbon material.

[0092] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon anode material for a fast-charging sodium-ion battery, characterized in that... Includes the following steps: S1. Pretreatment: The hard carbon raw material is crushed and screened to obtain hard carbon raw material with a particle size of less than 3cm. S2. Low-temperature carbonization: The hard carbon raw material obtained in step S1 is subjected to low-temperature carbonization to obtain a hard carbon precursor. The low-temperature carbonization conditions are: heating rate 2-20 ℃ / min, pretreatment temperature 300-800 ℃, pretreatment time 0.5-5 h; the protective gas is nitrogen and / or argon. S3. Crushing and shaping: The hard carbon precursor obtained in step S2 is crushed and pulverized to 3-200μm with D50 to obtain hard carbon precursor powder. S4. Wet grinding: The hard carbon precursor powder obtained in step S3 is wet-milled to a D50 of 0.1-3μm to obtain a sand milling slurry; S5. Spray drying: The sand-milled slurry obtained in step S4 is spray-dried to obtain a carbon intermediate; S6. High-temperature carbonization: The carbon intermediate obtained in step S5 is sintered at high temperature to obtain a fast-charging hard carbon anode material; the conditions for high-temperature carbonization are: heating rate of 0.5-5 ℃ / min, carbonization temperature of 900-1600℃, and carbonization time of 2-10 h. In the wet milling process of step S4, the amounts of dispersant, coating agent, and crosslinking agent added are 0.05-0.3%, 0.5-5%, and 0.5-2% of the mass of the hard carbon precursor, respectively. The solid content of the dispersion system is 20-45%, and the dispersant is one or more of the following: sodium isoascorbate, polyvinylpyrrolidone, ethanol, ethylene glycol, polyvinyl alcohol, polyethylene glycol, glycerol, dodecyl sulfonate, triethylhexyl phosphate, methylpentanol, cellulose derivatives, polyacrylamide, fatty acid polyethylene glycol esters, and polyacrylic acid. The coating agent is one or more of glucose, citric acid, PEG, sucrose, water-soluble resin, polyacrylic acid, ascorbic acid, maltose, and lignin. The crosslinking agent is one or more of the following: glyoxal, propylenediamine, urea-formaldehyde, formaldehyde, benzaldehyde, furfural, and terephthalaldehyde.

2. The method for preparing the hard carbon anode material for fast-charging sodium-ion batteries according to claim 1, characterized in that: In the wet grinding process of step S4, the diameter of the grinding beads is 0.3-1.5 mm, the grinding time is 0.5-5 h, and the grinding temperature is 25-80℃.

3. The method for preparing the hard carbon anode material for fast-charging sodium-ion batteries according to claim 1, characterized in that: In step S5, the spray drying conditions are: inlet air temperature of 230-300℃ and outlet air temperature of 90-150℃.

4. The method for preparing the hard carbon anode material for fast-charging sodium-ion batteries according to claim 1, characterized in that: In step S2, low-temperature carbonization is carried out in a low-temperature furnace, which is one or more of the following: pusher kiln, rotary kiln, roller kiln, box furnace, tube furnace, and vacuum furnace.

5. The method for preparing the hard carbon anode material for fast-charging sodium-ion batteries according to claim 1, characterized in that: In step S3, the crushing and shaping method is one or more of the following: roller mill, mechanical mill, ball mill, and air-jet mill.

6. The method for preparing the hard carbon anode material for fast-charging sodium-ion batteries according to claim 1, characterized in that: In step S1, the hard carbon raw material is one or more of the following: biomass raw material, phenolic resin, glucose, lignin, anthracite, and lignite.

7. A hard carbon anode material for fast-charging sodium-ion batteries, characterized in that: The negative electrode material is prepared by any one of the preparation methods described in claims 1-6. The negative electrode material is composed of secondary particles, which are formed by the stacking of primary particles. The particle size D50 of the secondary particles is 3-10 μm, the particle size D50 of the primary particles is 0.5-3 μm, and the average carbon interlayer spacing inside the primary particles is 0.38-0.40 nm.

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