Preparation method of surface-modified hard carbon sodium ion battery negative electrode material

Abstract

The application discloses a preparation method of surface-modified hard carbon sodium ion battery negative electrode material, and comprises the following steps: S1, preparation of a precursor: crushing hard carbon raw materials, sieving, and obtaining a precursor powder; S2, low-temperature carbonization: performing low-temperature carbonization on the precursor powder in a protective atmosphere, and obtaining low-temperature carbonization materials; S3, crushing and refining: crushing the low-temperature carbonization materials, and obtaining refined low-temperature carbonization materials; S4, sand modification: wet sanding the refined low-temperature carbonization materials with a modifier to obtain surface-modified low-temperature carbonization slurry; S5, drying treatment: centrifuging, washing and drying the surface-modified low-temperature carbonization slurry, and obtaining surface-modified low-temperature carbonization materials; and S6, high-temperature carbonization: performing high-temperature carbonization on the surface-modified low-temperature carbonization materials in a protective atmosphere, and obtaining surface-modified hard carbon materials. The application has the characteristics of high safety, excellent rate performance, high cycle stability and strong process realization.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a preparation method of surface-modified hard carbon sodium ion battery negative electrode material. BACKGROUND

[0002] With the rapid development of renewable energy technology, the world energy structure is changing from traditional fossil energy to renewable energy. The efficient use of renewable energy requires supporting energy storage facilities to ensure the continuity and stability of power supply.

[0003] Among many energy storage technologies, sodium ion batteries are considered an ideal choice for future large-scale energy storage due to their abundant resources, low cost, high safety and other advantages. Hard carbon negative electrode material, as an important part of sodium ion batteries, plays a decisive role in its electrochemical performance.

[0004] However, the rate performance and cycle performance of hard carbon material are poor, and sodium dendrites are easily formed on the surface during the charging process due to polarization, which can pierce the separator and cause serious safety hazards. Therefore, it is necessary to explore hard carbon negative electrode materials with excellent cycle performance, rate performance and safety performance, which is the key to the industrialization of sodium ion batteries. SUMMARY

[0005] The application aims to provide a preparation method of surface-modified hard carbon sodium ion battery negative electrode material, which has the characteristics of high safety, excellent rate performance, high cycle stability and strong process realization.

[0006] The application can be implemented by the following technical scheme:

[0007] The application discloses a preparation method of surface-modified hard carbon sodium ion battery negative electrode material, which comprises the following steps:

[0008] S1, preparation of a precursor: crushing hard carbon raw materials, sieving, and obtaining a precursor powder;

[0009] S2, low-temperature carbonization: performing low-temperature carbonization on the precursor powder obtained in step S1 in a protective atmosphere to obtain a low-temperature carbonized material;

[0010] S3, crushing and refining: crushing the low-temperature carbonized material obtained in step S2 to obtain a refined low-temperature carbonized material;

[0011] S4, sand modification: wet sand grinding the refined low-temperature carbonized material obtained in step S3 with a modifier to obtain a surface-modified low-temperature carbonized slurry;

[0012] S5, drying treatment: centrifuging, washing and drying the surface-modified low-temperature carbonized slurry obtained in step S4 to obtain a surface-modified low-temperature carbonized material;

[0013] S6, high-temperature carbonization: the surface-modified low-temperature carbonized material obtained in step S5 is subjected to high-temperature carbonization under a protective atmosphere to obtain a surface-modified hard carbon material.

[0014] Further, in step S2, the low-temperature calcination is performed at a temperature increasing rate of 2-15 ℃ / min, a pretreatment temperature of 300-800 ℃, and a pretreatment time of 1-5 h, and the protective atmosphere is nitrogen and / or argon. The conditions for the low-temperature carbonization in step S2 affect the effect of the present application. A slow temperature increasing rate, a high treatment temperature, and a long treatment time result in a high carbonization degree of the low-temperature carbonized material; otherwise, the carbonization degree of the low-temperature carbonized material is low. A too low carbonization degree results in incomplete carbonization of the hard carbon raw material and a too high volatile content, which is not conducive to subsequent sand milling and fine grinding of the particle size; a too high carbonization degree results in a too low volatile content of the carbonized material and a low reactivity, which is not conducive to surface oxidation modification in the sand milling process.

[0015] Further, in step S3, the particle size of the low-temperature carbonized material is controlled to be 10 μm≤ D50≤ 200 μm. If D50 is too large, the equipment will be blocked in the subsequent sand milling process, affecting the normal operation of the equipment; if D50 is too small, the energy consumption of the process will be too high, and the yield will be low, which is not conducive to the control of the production cost.

[0016] Further, in step S4, the modifier is an oxidizing agent, and the oxidizing agent is one or two or more of nitric acid and its salts, perchloric acid and its salts, heavy complex acid and its salts, permanganic acid and its salts, persulfuric acid and its salts, and sulfuric acid and its salts. The surface of the carbonized material is oxidized and modified under the action of the oxidizing agent, and active groups such as -OH and -COOH are grafted on the surface. On the one hand, the temperature is controlled, and on the other hand, the collision, friction, and shearing between the sand milling medium and the solid particles increase the surface defects of the solid particles, improve the reactivity of the material surface, and promote the occurrence of the oxidation reaction, achieving the purpose of surface modification.

[0017] Further, in step S4, the addition amount of the modifier is 0.1-5% of the mass of the low-temperature carbonized material, and the solid content is 10-50%. The addition amount of the modifier affects the effect of the present application. If the addition amount of the modifier is too low, the surface oxidation effect cannot be achieved; if the addition amount of the modifier is too high, the surface of the carbon material is excessively oxidized, the carbon layer is etched, the specific surface area is increased, and the battery performance is adversely affected. If the solid content is too high, the viscosity of the slurry is too high, the flowability is poor, and the grinding efficiency is affected; if the solid content is too low, the processing capacity of the carbon material per batch is too low, and the production cost is increased.

[0018] Further, in step S4, the particle size control of the sanding process is sanding to a material D50 of 3-8 μm. The sanding medium produces shearing and crushing forces on the low-temperature carbonized material in the sanding process, so that the material particles are further crushed to form small particles, achieving the purpose of further crushing the material particle size. Compared with other crushing methods (mechanical grinding and air flow powder) commonly used in hard carbon preparation processes, the sanding process uses sanding beads as the crushing medium, fully utilizes the collision, friction and shearing between the sanding medium and the solid particle material, achieves the purpose of rapidly reducing the particle size of the solid particles, has the advantages of low energy consumption and high efficiency, and is conducive to reducing production costs. Therefore, the present application uses step S3 as coarse grinding and step S4 as fine grinding, which fully reduces the production energy consumption on the basis of ensuring the product particle size.

[0019] Further, in step S4, the temperature control of the sanding process is 30-80℃. In the sanding process, the slurry will gradually heat up due to grinding heat, and cooling water needs to be passed to control the temperature of the sanding machine at a suitable value. On the one hand, if the sanding temperature is too low, it is not conducive to the occurrence of the oxidation reaction; if the temperature is too high and exceeds the maintenance temperature, it will affect the service life of the equipment.

[0020] Further, in step S6, the conditions for high-temperature carbonization are: a heating rate of 0.5-10 ℃ / min, a carbonization temperature of 900-1600 ℃, and a carbonization time of 2-10 h.

[0021] Further, in step S1, the hard carbon raw material is one or more than two of walnut shell, nut shell, apricot shell, straw, reed, coffee shell, coconut shell, bamboo, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, cedar, oak, anthracite, lignite, sub-bituminous coal; the screen mesh size is ≤2 cm.

[0022] Further, in step S3, the crushing method is one or more than two of roll, mechanical grinding, air flow powder, dry ball milling, and Raymond mill.

[0023] In step S5, centrifugation and water washing remove unreacted oxidizing agents and residual materials after the reaction, avoiding the introduction of impurities into the hard carbon material and affecting the battery performance.

[0024] In the present application, the hard carbon material is modified with oxygen-containing functional groups such as -OH and -COOH, thereby improving the electrochemical performance of the hard carbon negative electrode. On the one hand, the surface polarity of the modified hard carbon is enhanced, increasing the wettability with the electrolyte, so that the electrolyte fully penetrates into the pores of the material, thereby improving the diffusion coefficient of sodium ions at the interface and improving the rate performance of charging and discharging; on the other hand, the oxygen-containing functional groups on the surface of the hard carbon material interact with the electrolyte, promoting the decomposition of the electrolyte to build a more thin and stable SEI, and improving the cycle stability of the hard carbon material.

[0025] The application discloses a preparation method of a surface-modified hard carbon sodium ion battery negative electrode material.

[0026] First, the safety is good, the hard carbon material is modified with oxygen-containing functional groups such as -OH and -COOH, the surface polarity of the modified hard carbon is enhanced, the wettability with electrolyte is increased, the electrolyte is fully infiltrated into the pores of the material, the diffusion coefficient of sodium ions at the interface is further improved, the formation of sodium dendrites in the charging process is avoided, and the safety performance of the battery is further improved.

[0027] Second, the rate performance is excellent, the surface modification layer of the hard carbon increases the wettability with the electrolyte, the diffusion coefficient of sodium ions at the interface is improved, and the rate performance of the material is further improved.

[0028] Third, the cycle stability is high, the application avoids the capacity loss caused by the difficulty of sodium precipitation of the hard carbon material in the charging process, and the oxygen-containing functional groups on the surface of the hard carbon material promote the decomposition of the electrolyte to build a more thin and stable SEI, and the cycle stability of the hard carbon material is improved.

[0029] Fourth, the process implementation is strong, the core process of the application is the sanding process, compared with the common pulverizing methods such as airflow powder in the current industrial production, the energy consumption is lower, and the sanding is more suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The application examples 1 and the comparative example 1 are cycled test curves. DETAILED DESCRIPTION

[0031] In order to enable the personnel in the technical field to better understand the technical scheme of the application, the product of the application is further described in detail below in combination with examples.

[0032] The application discloses a preparation method of a surface-modified hard carbon sodium ion battery negative electrode material, comprising the following steps:

[0033] S1, preparation of a precursor: crushing a hard carbon raw material, sieving, and obtaining a precursor powder;

[0034] S2, low-temperature carbonization: performing low-temperature carbonization on the precursor powder obtained in step S1 under a protective atmosphere to obtain a low-temperature carbonized material;

[0035] S3, pulverization and refinement: pulverizing the low-temperature carbonized material obtained in step S2 to obtain a refined low-temperature carbonized material;

[0036] S4, sanding modification: wet sanding the refined low-temperature carbonized material obtained in step S3 with a modifier to obtain a surface-modified low-temperature carbonized slurry;

[0037] S5, drying treatment: centrifuging, washing and drying the surface-modified low-temperature carbonized slurry obtained in step S4 to obtain a surface-modified low-temperature carbonized material;

[0038] S6, high-temperature carbonization: performing high-temperature carbonization on the surface-modified low-temperature carbonized material obtained in step S5 under a protective atmosphere to obtain a surface-modified hard carbon material.

[0039] Further, in step S3, the particle size of the low-temperature carbonized material is controlled to be 10 μm≤ D50≤ 200 μm.

[0040] Further, in step S4, the modifier is an oxidizing agent, and the oxidizing agent is one or two or more of nitric acid and its salts, perchloric acid and its salts, heavy complex acid and its salts, permanganic acid and its salts, persulfuric acid and its salts, and sulfuric acid and its salts.

[0041] Further, in step S4, the addition amount of the modifier is 0.1-5% of the mass of the low-temperature carbonized material, and the solid content is 10-50%.

[0042] Further, in step S4, the particle size control of the sanding process is sanding to a material D50 of 3-8 μm.

[0043] Further, in step S4, the temperature control of the sanding process is 30-80℃.

[0044] Further, in step S2, the conditions for low-temperature calcination are that the heating rate is 2-15 ℃ / min, the pretreatment temperature is 300-800 ℃, and the pretreatment time is 1-5 h; and the protective atmosphere is nitrogen and / or argon.

[0045] Further, in step S6, the conditions for high-temperature carbonization are that the heating rate is 0.5-10 ℃ / min, the carbonization temperature is 900-1600 ℃, and the carbonization time is 2-10 h.

[0046] Further, in step S1, the hard carbon raw material is one or two or more of walnut shells, nut shells, apricot shells, straw, reed, coffee shells, coconut shells, bamboo, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, cedar, oak, anthracite, lignite, and sub-bituminous coal; and the screen mesh aperture is ≤ 2 cm.

[0047] Further, in step S3, the crushing method is one or two or more of roll crushing, mechanical grinding, air flow crushing, dry ball milling, and Raymond grinding.

[0048] Example 1

[0049] This embodiment relates to a surface-modified sodium-ion battery hard carbon negative electrode material, and a preparation method thereof, which comprises the following steps:

[0050] S1, Preparation of precursor: The hard carbon raw material is crushed and sieved to obtain a precursor powder. Specifically, the hard carbon raw material is walnut shell and nut shell, and the sieve mesh size is ≤2 cm.

[0051] S2, Low-temperature carbonization: The precursor powder obtained in step S1 is subjected to low-temperature carbonization under a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the conditions for low-temperature calcination are: a heating rate of 15 ℃ / min, a pretreatment temperature of 600 ℃, and a pretreatment time of 1 h; and the protective atmosphere is nitrogen.

[0052] S3, Crushing and refining: The low-temperature carbonized material obtained in step S2 is crushed to obtain a refined low-temperature carbonized material. Specifically, the particle size of the refined low-temperature carbonized material is controlled to be: 10 μm≤ D50≤ 200 μm. Optionally, the crushing method is roller or mechanical grinding.

[0053] S4, Sand modification: The refined low-temperature carbonized material obtained in step S3 is subjected to wet sanding with a modifier to obtain a surface-modified low-temperature carbonized slurry. Specifically, the particle size control during sanding is sanding to a material D50 of 3-8 μm. Optionally, the modifier is an oxidizing agent, and the oxidizing agent is nitric acid and its salts; the addition amount of the modifier is 5% of the mass of the refined low-temperature carbonized material, and the solid content is controlled to be 10-50%; and the temperature control during sanding is 60 ℃.

[0054] S5, Drying treatment: The surface-modified low-temperature carbonized slurry obtained in step S4 is subjected to centrifugation, water washing and drying to obtain a surface-modified low-temperature carbonized material.

[0055] S6, High-temperature carbonization: The surface-modified low-temperature carbonized material obtained in step S5 is subjected to high-temperature carbonization under a protective atmosphere to obtain a surface-modified hard carbon material. Specifically, the conditions for high-temperature carbonization are: a heating rate of 10 ℃ / min, a carbonization temperature of 1300 ℃, and a carbonization time of 2 h.

[0056] Example 2

[0057] This example relates to a surface-modified sodium-ion battery hard carbon anode material, and a preparation method thereof includes the following steps:

[0058] S1, Preparation of precursor: The hard carbon raw material is crushed and sieved to obtain a precursor powder. Specifically, the hard carbon raw material is walnut shell and nut shell, and the sieve mesh size is ≤2 cm.

[0059] S2, Low-temperature carbonization: The precursor powder obtained in step S1 is subjected to low-temperature carbonization under a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the conditions for low-temperature calcination are: a heating rate of 8 ℃ / min, a pretreatment temperature of 300 ℃, and a pretreatment time of 5 h; and the protective atmosphere is argon.

[0060] S3, crushing and refining: crushing the low-temperature carbonized material obtained in step S2 to obtain a refined low-temperature carbonized material. Specifically, the particle size of the refined low-temperature carbonized material is controlled to be 10 μm≤ D50≤ 200 μm. Optionally, the crushing method is dry ball milling or Raymond mill.

[0061] S4, sanding modification: sanding the refined low-temperature carbonized material obtained in step S3 with a modifier to obtain a surface-modified low-temperature carbonized slurry. Specifically, the particle size control of the sanding process is sanding to a material D50 of 3-8 μm. Optionally, the modifier is an oxidizing agent, the oxidizing agent is perchloric acid and its salt; the addition amount of the modifier is 3% of the mass of the refined low-temperature carbonized material, and the solid content is controlled to be 10-50%; the temperature control of the sanding process is 40℃.

[0062] S5, drying treatment: centrifuging, washing and drying the surface-modified low-temperature carbonized slurry obtained in step S4 to obtain a surface-modified low-temperature carbonized material.

[0063] S6, high-temperature carbonization: high-temperature carbonization of the surface-modified low-temperature carbonized material obtained in step S5 under a protective atmosphere to obtain a surface-modified hard carbon material. Specifically, the high-temperature carbonization conditions are: a heating rate of 5℃ / min, a carbonization temperature of 900℃, and a carbonization time of 10 h.

[0064] Example 3

[0065] This example relates to a surface-modified sodium-ion battery hard carbon anode material, and a preparation method thereof, which comprises the following steps:

[0066] S1, preparation of a precursor: crushing a hard carbon raw material and sieving to obtain a precursor powder. Specifically, the hard carbon raw material is walnut shell, nut shell, coffee shell, coconut shell, bamboo, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, cedar, oak, and the sieve mesh size is ≤ 2 cm.

[0067] S2, low-temperature carbonization: low-temperature carbonization of the precursor powder obtained in step S1 under a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the low-temperature carbonization conditions are: a heating rate of 2℃ / min, a pretreatment temperature of 800℃, and a pretreatment time of 3 h; the protective atmosphere is nitrogen and argon.

[0068] S3, crushing and refining: crushing the low-temperature carbonized material obtained in step S2 to obtain a refined low-temperature carbonized material. Specifically, the particle size of the refined low-temperature carbonized material is controlled to be 10 μm≤ D50≤ 200 μm. Optionally, the crushing method is dry ball milling or Raymond mill.

[0069] S4, sanding modification: the refined low-temperature carbonized material obtained in step S3 is wet sanding with a modifier to obtain a surface-modified low-temperature carbonized slurry. Specifically, the particle size control of the sanding process is sanding to a material D50 of 3-8 μm. Alternatively, the modifier is an oxidizing agent, the oxidizing agent is heavy complex acid and its salt; the addition amount of the modifier is 0.5% of the mass of the refined low-temperature carbonized material, and the solid content is controlled to be 10-50%; the temperature control of the sanding process is 80℃.

[0070] S5, drying treatment: the surface-modified low-temperature carbonized slurry obtained in step S4 is centrifuged, washed with water and dried to obtain a surface-modified low-temperature carbonized material.

[0071] S6, high-temperature carbonization: the surface-modified low-temperature carbonized material obtained in step S5 is subjected to high-temperature carbonization under a protective atmosphere to obtain a surface-modified hard carbon material. Specifically, the conditions for high-temperature carbonization are: a heating rate of 0.5 ℃ / min, a carbonization temperature of 1600 ℃, and a carbonization time of 6h.

[0072] Example 4

[0073] This embodiment relates to a surface-modified sodium-ion battery hard carbon negative material, and a preparation method thereof, which comprises the following steps:

[0074] S1, preparation of a precursor: crushing a hard carbon raw material, and sieving to obtain a precursor powder. Specifically, the hard carbon raw material is walnut shell, nut shell, apricot shell, straw, reed, and sub-bituminous coal, and the sieve mesh size is ≤2 cm.

[0075] S2, low-temperature carbonization: the precursor powder obtained in step S1 is subjected to low-temperature carbonization under a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the conditions for low-temperature carbonization are: a heating rate of 5 ℃ / min, a pretreatment temperature of 400 ℃, and a pretreatment time of 3 h; and the protective atmosphere is nitrogen and argon.

[0076] S3, pulverization and refinement: the low-temperature carbonized material obtained in step S2 is pulverized to obtain a refined low-temperature carbonized material. Specifically, the particle size control of the refined low-temperature carbonized material is: 10 μm≤ D50≤ 200 μm. Alternatively, the pulverization method is mechanical grinding.

[0077] S4, sanding modification: the refined low-temperature carbonized material obtained in step S3 is wet sanding with a modifier to obtain a surface-modified low-temperature carbonized slurry. Specifically, the particle size control of the sanding process is sanding to a material D50 of 3-8 μm. Alternatively, the modifier is an oxidizing agent, the oxidizing agent is nitric acid and its salt, permanganic acid and its salt, persulfuric acid and its salt, sulfuric acid and its salt; the addition amount of the modifier is 2% of the mass of the refined low-temperature carbonized material, and the solid content is controlled to be 10-50%; the temperature control of the sanding process is 50℃.

[0078] S5, drying treatment: centrifuging, washing and drying the surface-modified low-temperature carbonized slurry obtained in step S4 to obtain a surface-modified low-temperature carbonized material.

[0079] S6, high-temperature carbonization: performing high-temperature carbonization on the surface-modified low-temperature carbonized material obtained in step S5 under a protective atmosphere to obtain a surface-modified hard carbon material. Specifically, the high-temperature carbonization conditions are: a heating rate of 3 ℃ / min, a carbonization temperature of 1200 ℃, and a carbonization time of 3 h.

[0080] Example 5

[0081] This embodiment relates to a surface-modified sodium-ion battery hard carbon negative material, and a preparation method thereof, which comprises the following steps:

[0082] S1, preparation of a precursor: crushing and sieving a hard carbon raw material to obtain a precursor powder. Specifically, the hard carbon raw material is walnut shell, nut shell, apricot shell, coconut shell, bamboo, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, fir, oak, and the mesh size is ≤2 cm.

[0083] S2, low-temperature carbonization: performing low-temperature carbonization on the precursor powder obtained in step S1 under a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the low-temperature carbonization conditions are: a heating rate of 13 ℃ / min, a pretreatment temperature of 400 ℃, and a pretreatment time of 4 h; and the protective atmosphere is nitrogen and argon.

[0084] S3, crushing and refining: crushing the low-temperature carbonized material obtained in step S2 to obtain a refined low-temperature carbonized material. Specifically, the particle size of the refined low-temperature carbonized material is controlled to be: 10 μm≤D50≤200 μm. Optionally, the crushing method is airflow crushing or dry ball milling.

[0085] S4, sanding modification: wet sanding the refined low-temperature carbonized material obtained in step S3 with a modifier to obtain a surface-modified low-temperature carbonized slurry. Specifically, the particle size control during sanding is to sand the material to a D50 of 3-8 μm. Optionally, the modifier is an oxidizing agent, and the oxidizing agent is nitric acid and its salts, perchloric acid and its salts, heavy complex acid and its salts, permanganic acid and its salts, persulfuric acid and its salts, sulfuric acid and its salts; the addition amount of the modifier is 4% of the mass of the refined low-temperature carbonized material, and the solid content is 10-50%; and the temperature control during sanding is 70 ℃.

[0086] S5, drying treatment: centrifuging, washing and drying the surface-modified low-temperature carbonized slurry obtained in step S4 to obtain a surface-modified low-temperature carbonized material.

[0087] S6, high-temperature carbonization: the surface-modified low-temperature carbonized material obtained in step S5 is subjected to high-temperature carbonization under a protective atmosphere to obtain a surface-modified hard carbon material. Specifically, the high-temperature carbonization conditions are: a heating rate of 5 ℃ / min, a carbonization temperature of 1400 ℃, and a carbonization time of 3 h.

[0088] Application Example 1

[0089] This example relates to a surface-modified sodium-ion battery hard carbon negative material, and a preparation method thereof includes the following steps:

[0090] S1, preparation of a precursor: coconut shell raw material is crushed and sieved, with a sieve mesh size of 2 cm, to obtain a precursor powder;

[0091] S2, low-temperature carbonization: the precursor powder obtained in step S1 is subjected to low-temperature carbonization under nitrogen gas protection, wherein the heating rate is 5 ℃ / min, the treatment temperature is 600 ℃, and the pretreatment time is 2 h. A low-temperature carbonized material is obtained.

[0092] S3, crushing and refining: the low-temperature carbonized material obtained in step S2 is crushed to D50≤50 μm by ball milling to obtain a refined low-temperature carbonized material;

[0093] S4, sanding modification: the refined low-temperature carbonized material obtained in step S3, H2O2, and deionized water are mixed, wherein the addition amount of H2O2 is 1% of the carbonized material, the solid content of the slurry is 25%, and the material is sand-milled to D50=7 μm at a temperature of 50 ℃ to obtain a surface-modified low-temperature carbonized slurry.

[0094] S5, drying treatment: the surface-modified low-temperature carbonized slurry obtained in step S4 is centrifuged, washed with water, and dried to obtain a surface-modified low-temperature carbonized material.

[0095] S6, high-temperature carbonization: the surface-modified low-temperature carbonized material obtained in step S5 is subjected to high-temperature carbonization under nitrogen gas protection, with a heating rate of 5 ℃ / min, a carbonization temperature of 1400 ℃, and a carbonization time of 3 h, to obtain a surface-modified hard carbon material.

[0096] The obtained material was subjected to electrochemical performance test according to the following method: the hard carbon material of application example 1, Super P, CMC, SBR were mixed into a homogenate in a mass ratio of 94:1.5:2:2.5, then a black slurry was coated on a copper foil using a 120 um four-side preparation device, and then the film was dried in a 100℃ vacuum drying box for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a sheet punching machine, a metal sodium was used as a counter electrode, a 1mol / L NaClO4 EC+DEC (1:1vol%) was used as an electrolyte, a PP / PE / PP three-layer separator was used as a separator, and a CR2032 type button cell was assembled in a glove box. The above button cell was subjected to constant current charge and discharge test, the current density was 0.1C (1C-300 mAh / g), and the voltage range was 2-0.005V.

[0097] application example 2

[0098] This example relates to a surface modified sodium ion battery hard carbon negative electrode material, and a preparation method thereof comprises the following steps:

[0099] S1, preparation of a precursor: the coconut shell raw material was crushed and sieved, the mesh size was 2cm, to obtain a precursor powder;

[0100] S2, low-temperature carbonization: the precursor powder obtained in step S1 was subjected to low-temperature carbonization under the protection of nitrogen gas, the heating rate was 5 ℃ / min, the treatment temperature was 600 ℃, and the pretreatment time was 2h. A low-temperature carbonized material was obtained;

[0101] S3, crushing and refining: the low-temperature carbonized material obtained in step S2 was crushed by ball milling to D50≤50μm, to obtain a refined low-temperature carbonized material;

[0102] S4, sanding modification: the refined low-temperature carbonized material obtained in step S3, H2O2 and deionized water were mixed, the addition amount of H2O2 was 1% of the carbonized material, the solid content of the slurry was 25%, and the material was sanded to D50=7μm at a temperature of 50℃, to obtain a surface modified low-temperature carbonized slurry;

[0103] S5, drying treatment: the surface modified low-temperature carbonized slurry obtained in step S4 was centrifuged, washed with water and dried, to obtain a surface modified low-temperature carbonized material;

[0104] S6, high-temperature carbonization: the surface modified low-temperature carbonized material obtained in step S5 was subjected to high-temperature carbonization under the protection of nitrogen gas, the heating rate was 5 ℃ / min, the carbonization temperature was 1400 ℃, and the carbonization time was 3h, to obtain a surface modified hard carbon material.

[0105] The obtained material was subjected to electrochemical performance test according to the following method: the hard carbon material of application example 2, Super P, CMC, SBR were mixed into a homogenate in a mass ratio of 94:1.5:2:2.5, then a black slurry was coated on a copper foil using a 120 um four-side preparation device, and then the film was dried in a 100℃ vacuum drying box for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a sheet punching machine, a metal sodium was used as a counter electrode, a 1mol / L NaClO4 EC+DEC (1:1vol%) was used as an electrolyte, a PP / PE / PP three-layer separator was used as a separator, and a CR2032 type button cell was assembled in a glove box. The above button cell was subjected to constant current charge and discharge test, the current density was 0.1C (1C-300 mAh / g), and the voltage range was 2-0.005V.

[0106] Comparative example 1

[0107] The present embodiment relates to a hard carbon negative material for sodium ion battery, and a preparation method thereof, which comprises the following steps:

[0108] S1, preparation of precursor: the coconut shell raw material was crushed and sieved, and the screen aperture was 2cm to obtain a precursor powder;

[0109] S2, low-temperature carbonization: the precursor powder obtained in step S1 was subjected to low-temperature carbonization under the protection of nitrogen gas, wherein the heating rate was 5 ℃ / min, the treatment temperature was 600 ℃, and the pretreatment time was 2h. A low-temperature carbonized material was obtained.

[0110] S3, crushing and refining: the low-temperature carbonized material obtained in step S2 was crushed by ball milling to D50≤50μm to obtain a refined low-temperature carbonized material;

[0111] S4, sanding modification: the refined low-temperature carbonized material obtained in step S3 was mixed with deionized water, and the solid content of the slurry was 25%. The material was sanded to D50=7μm at a temperature of 50℃ to obtain a low-temperature carbonized slurry;

[0112] S5, drying treatment: the surface modified low-temperature carbonized slurry obtained in step S4 was subjected to centrifugation, water washing and drying to obtain a low-temperature carbonized material;

[0113] S6, high-temperature carbonization: the low-temperature carbonized material obtained in step S5 was subjected to high-temperature carbonization under the protection of nitrogen gas, the heating rate was 5 ℃ / min, the carbonization temperature was 1400 ℃, and the carbonization time was 3h to obtain a hard carbon material of comparative example 1.

[0114] The obtained material was subjected to electrochemical performance test according to the following method: the hard carbon material of Comparative Example 1, Super P, CMC, SBR were mixed into a homogenate in a mass ratio of 94:1.5:2:2.5, then the black slurry was coated on a copper foil using a 120 um four-side preparation device, and then the film was dried in a 100°C vacuum drying oven for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6 mm using a sheet puncher, and a metal sodium was used as a counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) was used as an electrolyte, and a PP / PE / PP three-layer separator was used as a separator to assemble a CR2032 type button cell in a glove box. The above button cell was subjected to constant current charge and discharge test, the current density was 0.1C (1C-300 mAh / g), and the voltage range was 2-0.005 V.

[0115] The test results of Application Example 1, Application Example 2 and Comparative Example 1 are shown in Table 1. Figure 1

[0116] Table 1 Performance test results

[0117]

[0118] The reversible specific capacity of the hard carbon electrode in Application Example 1 was 306 mAh / g, and the first-week coulombic efficiency was 91.5% measured by constant current charge and discharge test; the reversible specific capacity of the hard carbon electrode in Application Example 2 was 304 mAh / g, and the first-week coulombic efficiency was 91.3%; the reversible specific capacity of the hard carbon electrode in Comparative Example 1 was 301 mAh / g, and the first-week coulombic efficiency was 91.3%. By comparing Application Example 1, Application Example 2 and Comparative Example 1, the reversible capacity and first-week efficiency of the surface-modified hard carbon negative material were not adversely affected.

[0119] The capacity retention rates of Application Example 1, Application Example 2 and Comparative Example 2 at a current density of 2C in the sodium ion battery test were 73.5%, 72.4% and 61.3% respectively, indicating that the surface modification of the hard carbon material can effectively improve the rate performance of the hard carbon material. The reason is that the surface modification layer of the hard carbon increases the wettability of the hard carbon material surface and the electrolyte, improves the diffusion coefficient of sodium ions at the interface, and thus improves the rate performance of the material.

[0120] From Figure 1 ​It can be seen that the capacity retention rates of application example 1, application example 2 and comparative example 2 after 200 cycles in the sodium ion battery test are 92.8%, 91.6% and 76.4% respectively, indicating that the hard carbon surface modification layer can significantly improve the cycle performance of the hard carbon material. The reason is that the oxygen-containing functional groups on the surface of the hard carbon material can promote the decomposition of the electrolyte to build a more thin and stable SEI, and improve the cycle stability of the hard carbon material. In addition, the better rate performance makes the hard carbon negative electrode not easy to cause the loss of active sodium during the charging process, thereby causing the capacity attenuation.

[0121] The above examples are only specific embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application.

Claims

1. A method for preparing a surface-modified hard carbon sodium-ion battery anode material, characterized in that... Includes the following steps: S1. Preparation of precursor: The hard carbon raw material is crushed and sieved to obtain precursor powder; S2. Low-temperature carbonization: The precursor powder obtained in step S1 is carbonized at low temperature under a protective atmosphere to obtain low-temperature carbonized material. S3. Crushing and refining: The low-temperature carbonized material obtained in step S2 is crushed to obtain refined low-temperature carbonized material; S4. Sand Milling Modification: The refined low-temperature carbonized material obtained in step S3 is wet-milled with a modifier to obtain a surface-modified low-temperature carbonized slurry; the particle size during the sand milling process is controlled to the point where the material D50 is 3-8 μm, and the temperature during the sand milling process is controlled to be 30-80℃; the modifier is an oxidant, and the oxidant is one or more of nitric acid and its salts, perchloric acid and its salts, dichloromethane and its salts, permanganic acid and its salts, persulfate and its salts, and sulfuric acid and its salts; the amount of the modifier added is 0.1-5% of the mass of the refined low-temperature carbonized material, and the solid content is 10-50%; S5. Drying treatment: The surface-modified low-temperature carbonized slurry obtained in step S4 is centrifuged, washed with water and dried to obtain the surface-modified low-temperature carbonized material. S6. High-temperature carbonization: The surface-modified low-temperature carbonized material obtained in step S5 is carbonized at high temperature under a protective atmosphere to obtain surface-modified hard carbon material.

2. The method for preparing the surface-modified hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S3, the particle size of the refined low-temperature carbonized material is controlled as follows: 10 μm ≤ D50 ≤ 200 μm.

3. The method for preparing the surface-modified hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S2, the conditions for low-temperature carbonization are: heating rate of 2-15 ℃ / min, pretreatment temperature of 300-800 ℃, and pretreatment time of 1-5 h; the protective atmosphere is nitrogen and / or argon.

4. The method for preparing the surface-modified hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S6, the conditions for high-temperature carbonization are: heating rate of 0.5-10 ℃ / min, carbonization temperature of 900-1600℃, and carbonization time of 2-10 h.

5. The method for preparing the surface-modified hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S1, the hard carbon raw material is one or more of the following: walnut shells, apricot shells, straw, reeds, coffee shells, coconut shells, bamboo, poplar, eucalyptus, pine, fir, oak, anthracite, lignite, and bituminous coal; the screen mesh size is ≤2cm.

6. The method for preparing the surface-modified hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S3, the pulverizing method is one or more of the following: roller mill, air-flow mill, dry ball mill, and Raymond mill.

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