Surface modified hard carbon negative electrode material, preparation method therefor and use thereof

Abstract

A surface modified hard carbon negative electrode material, a preparation method therefor and a use thereof, relating to the field of sodium ion batteries. The preparation method comprises mixing hard carbon powder, water, and a surface modifier to form a solid-liquid mixture, drying the solid-liquid mixture, and performing vacuum dehydration to obtain the surface modified hard carbon negative electrode material. The surface modifier is an organic compound containing both a carboxyl group and a carbonyl group. The carboxyl group in the surface modifier reacts with the hydroxyl group on the surface of a hard carbon negative electrode, so that the carbonyl group is accurately and uniformly insert into the surface of hard carbon. The introduced carbonyl groups can be used as active "anchoring points" in the electrolysis process to preferentially control and catalyze the decomposition of an inorganic salt and inhibit the excessive decomposition of an organic solvent, so that a uniformly distributed inorganic salt-rich SEI film is formed. The inorganic salt-rich SEI film is beneficial to the transmission of Na+ at an interface and maintenance of the structural stability of the SEI film, and finally the surface modified hard carbon negative electrode material having high first coulombic efficiency and excellent cycling stability is obtained.

Description

A surface-modified hard carbon negative electrode material and its preparation method and application Technical Field

[0001] The present disclosure relates to the field of sodium ion batteries, and in particular to a surface-modified hard carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries are expected to be applied to large-scale energy storage and smart grids due to their abundant sodium resources and high cost-effectiveness. The development of sodium-ion batteries depends largely on electrode materials, and the construction of low-cost, high-performance negative electrode materials is particularly critical. Hard carbon negative electrode materials are considered to be the most promising negative electrode materials for sodium-ion batteries due to their low cost and high theoretical specific capacity. However, the low first coulombic efficiency and poor cycle stability of hard carbon negative electrode materials hinder their large-scale commercial application. Regulating the hard carbon / electrolyte interface and establishing a suitable solid electrolyte membrane (SEI membrane) are the key to improving the performance of hard carbon negative electrode materials.

[0003] Commercialized ester electrolytes offer advantages such as low cost, good stability, and compatibility with high-voltage cathode materials. However, the organic-rich SEI film derived from ester electrolytes is uneven in thickness and cannot fully protect the hard carbon anode material, resulting in low first coulombic efficiency and poor cycling stability.

[0004] In view of this, the present disclosure is proposed.

[0005] Summary of the Invention

[0006] The purpose of the present disclosure is to provide a surface-modified hard carbon negative electrode material and a preparation method and application thereof.

[0007] The present disclosure is achieved as follows:

[0008] In a first aspect, the present disclosure provides a surface-modified hard carbon negative electrode material, which includes a hard carbon core layer and a surface modification layer, wherein the surface modification layer is coated on the hard carbon core layer, and the surface modification layer is formed by reacting a surface modifier containing both carboxyl and carbonyl groups with hydroxyl groups in the hard carbon core layer.

[0009] In an optional embodiment, the mass ratio of the hard carbon core layer to the surface modification layer is 1:(0.05-0.15).

[0010] In a second aspect, the present disclosure provides a method for preparing a surface-modified hard carbon negative electrode material, which includes mixing hard carbon powder, water and a surface modifier to form a solid-liquid mixture, wherein the surface modifier is an organic matter containing both a carboxyl group and a carbonyl group; drying the solid-liquid mixture to form a composite powder, and vacuum dehydrating the composite powder to obtain a surface-modified hard carbon negative electrode material.

[0011] In an alternative embodiment, the surface modifier includes at least one of p-carboxybenzaldehyde, o-carboxybenzaldehyde, and 3-carboxybenzaldehyde.

[0012] In an optional embodiment, the mass ratio of the hard carbon powder to the water is 1:(3-5), and the mass of the surface modifier is 5%-15% of the mass of the hard carbon powder.

[0013] In an optional embodiment, drying the solid-liquid mixture includes stirring and heating the solid-liquid mixture at 60°C-80°C.

[0014] In an optional embodiment, the vacuum degree of the vacuum dehydration is ≤10 -3 Pa, the temperature of the vacuum dehydration is 100°C-120°C.

[0015] In an optional embodiment, the method for preparing the hard carbon powder includes calcining a hard carbon precursor to form a burnt carbon, and crushing, washing, and drying the burnt carbon to obtain the hard carbon powder.

[0016] In an optional embodiment, the hard carbon precursor includes at least one of phenolic resin, epoxy resin, corn starch and coconut shell.

[0017] In an optional embodiment, the calcination includes a low-temperature sintering treatment at 200-600° C. for 3-6 hours, followed by a high-temperature carbonization treatment at 1200-1600° C. for 10-20 hours.

[0018] In an optional embodiment, the heating rate of the low-temperature sintering is 3-5°C / min.

[0019] In an optional embodiment, the heating rate of the high-temperature carbonization is 5-10°C / min.

[0020] In an optional embodiment, the low-temperature sintering and the high-temperature carbonization are both performed under inert gas protection.

[0021] In an optional embodiment, the inert gas is one of nitrogen, argon and helium.

[0022] In an optional embodiment, the oxygen concentration during the low-temperature sintering and the high-temperature carbonization heat preservation process is lower than 200 ppm.

[0023] In an optional embodiment, the pulverization includes crushing with a roller mill and using air flow milling.

[0024] In an optional embodiment, the particle size of the burnt char after crushing using a double-roll mill is less than 0.5-2 mm.

[0025] In an optional embodiment, the particle size of the burnt char after air flow milling is 3-6 μm in Dv50, 1-4 μm in Dv10, and 10-15 μm in Dv99.

[0026] In an optional embodiment, the washing includes first acid washing and then filtering and washing with water until neutrality.

[0027] In an optional embodiment, the H in the pickling acid + The concentration is 0.5-1mol / L.

[0028] In an optional embodiment, the drying temperature is 80-100° C. and the drying time is 12-24 hours.

[0029] In a third aspect, the present disclosure provides a surface-modified hard carbon negative electrode material prepared by the preparation method of the surface-modified hard carbon negative electrode material described in any one of the above embodiments.

[0030] In a fourth aspect, the present disclosure provides the use of the surface-modified hard carbon negative electrode material as described in the above embodiment in the preparation of a negative electrode material for a sodium ion battery.

[0031] The present disclosure has the following beneficial effects:

[0032] The preparation method of the surface modified hard carbon negative electrode material provided by the present invention is to select an organic matter containing carboxyl and carbonyl groups as a surface modifier, mix it with hard carbon powder to form a solid-liquid mixture, and the surface modifier adheres to the surface of the hard carbon powder during the drying process. During the vacuum dehydration process, the carboxyl groups in the surface modifier react with the hydroxyl groups on the surface of the hard carbon negative electrode to accurately and evenly insert the carbonyl groups into the hard carbon surface. It should be understood that the surface modification layer does not achieve complete coating, but introduces carboxyl and carbonyl groups to the sites containing hydroxyl groups on the hard carbon surface and achieves coating of the sites. Therefore, there are partial coating and partial non-coating on the surface of the hard carbon. The surface modified hard carbon negative electrode material provided by the present invention serves as a supporting material for the growth of SEI film, which plays a vital guiding role in the formation process of SEI film. The introduced carbonyl group can serve as an active "anchor point" in the electrolysis process to preferentially control the decomposition of catalytic inorganic salts and inhibit excessive decomposition of organic solvents, thereby forming a uniformly distributed inorganic salt-rich SEI film. The inorganic salt-rich SEI film is conducive to Na + The surface-modified hard carbon anode material can be widely used in the preparation of sodium-ion battery anode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0034] FIG1 is a schematic structural diagram of a surface-modified hard carbon negative electrode material prepared by the method for preparing a surface-modified hard carbon negative electrode material provided in Example 1 of the present disclosure;

[0035] FIG2 is a TEM image of a surface-modified hard carbon negative electrode material prepared by the preparation method of the surface-modified hard carbon negative electrode material provided in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0036] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0037] The present disclosure provides a surface-modified hard carbon anode material comprising a hard carbon core layer and a surface modification layer. The surface modification layer is coated on the hard carbon core layer. The surface modification layer is formed by reacting a surface modifier containing both carboxyl and carbonyl groups with hydroxyl groups in the hard carbon core layer. It should be understood that the surface modification layer does not completely coat the hard carbon surface, but rather introduces carboxyl and carbonyl groups to target and coat hydroxyl groups on the hard carbon surface. Consequently, the hard carbon surface may be partially coated and partially uncoated. The mass ratio of the hard carbon core layer to the surface modification layer is 1:(0.05-0.15).

[0038] Its preparation method includes mixing hard carbon powder, water and a surface modifier to form a solid-liquid mixture, wherein the surface modifier is an organic matter containing both carboxyl and carbonyl groups; drying the solid-liquid mixture to form a composite powder, and vacuum dehydrating the composite powder to obtain a surface-modified hard carbon negative electrode material. The present invention uses an organic matter rich in carboxyl (-COOH) and carbonyl (-C=O) as a surface modifier, and accurately and uniformly inserts the carbonyl group into the hard carbon surface through the reaction of the carboxyl group of the surface modifier with the hydroxyl (-OH) on the surface of the hard carbon powder. These carbonyl groups can act as active "anchor points" to preferentially control the decomposition of catalytic inorganic salts and inhibit excessive decomposition of organic solvents, thereby forming a uniformly distributed inorganic salt-rich SEI film. The inorganic salt-rich SEI film is beneficial to the Na at the interface + The transport of SEI and the maintenance of its structural stability ultimately lead to the acquisition of a surface-modified hard carbon anode material with high first coulombic efficiency and excellent cycle stability.

[0039] Specifically, the present disclosure provides a method for preparing a surface-modified hard carbon negative electrode material, comprising the following steps:

[0040] S1. Preparation of hard carbon powder.

[0041] The hard carbon precursor is calcined to form burnt carbon, which is then crushed, washed and dried to obtain hard carbon powder.

[0042] The hard carbon precursor includes but is not limited to at least one of phenolic resin, epoxy resin, corn starch and coconut shell.

[0043] The calcination process involves heating the material to 200-600°C at a rate of 3-5°C / min for a low-temperature sintering treatment for 3-6 hours, followed by a high-temperature carbonization treatment at a rate of 5-10°C / min for a period of 10-20 hours. Both the low-temperature sintering and high-temperature carbonization processes are performed under an inert gas atmosphere, such as nitrogen, argon, or helium. The oxygen concentration during the heat preservation process is maintained below 200 ppm. In some embodiments, the heating rate of low-temperature sintering can be, for example, any one of 3°C / min, 4°C / min, 5°C / min, or a range value between any two of them; the temperature of low-temperature sintering can be, for example, any one of 200°C, 300°C, 400°C, 500°C, 550°C, 600°C, or a range value between any two of them; the holding time of low-temperature sintering can be, for example, any one of 3h, 4h, 5h, 6h, or a range value between any two of them. In some embodiments, the heating rate of high-temperature carbonization can be, for example, any one of 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or a range value between any two of them; the temperature of high-temperature carbonization can be, for example, any one of 1200°C, 1300°C, 1400°C, 1500°C, 1550°C, 1600°C, or a range value between any two of them; the holding time of high-temperature carbonization can be, for example, any one of 10h, 12h, 15h, 20h, or a range value between any two of them.

[0044] The pulverization process involves crushing with a roller mill and fine grinding using a jet mill. The particle size of the char after crushing with the roller mill is less than 0.5 mm to 2 mm. The particle size of the char after fine grinding using the jet mill is 3 μm to 6 μm in Dv50, 1 μm to 4 μm in Dv10, and 10 μm to 15 μm in Dv99.

[0045] Washing includes pickling first, then filtering and washing with water until it is neutral. + The concentration is 0.5 mol / L-1 mol / L. In some embodiments, H+ The concentration is any one of 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, and 1 mol / L, or a range between any two of them. The pickling acid may be, for example, hydrochloric acid, sulfuric acid, or hydrofluoric acid.

[0046] The drying temperature is 80°C-100°C, and the drying time is 12 hours-24 hours. In some embodiments, the drying temperature can be, for example, any one of 80°C, 85°C, 90°C, 95°C, and 100°C, or a range between any two thereof. The drying time can be, for example, any one of 12 hours, 15 hours, 18 hours, 21 hours, and 24 hours, or a range between any two thereof.

[0047] S2. Preparation of solid-liquid mixture.

[0048] Hard carbon powder, water, and a surface modifier are mixed to form a solid-liquid mixture.

[0049] The surface modifier includes at least one of p-carboxybenzaldehyde, o-carboxybenzaldehyde, and 3-carboxybenzaldehyde. The surface modifier selected in the present disclosure is rich in carboxyl groups (-COOH) and carbonyl groups (-C=O). The carboxyl groups of the surface modifier can subsequently react with hydroxyl groups (-OH) on the surface of the hard carbon powder to accurately and uniformly insert the carbonyl groups into the hard carbon surface.

[0050] The mass ratio of hard carbon powder to water is 1:(3-5), and the mass of the surface modifier is 5%-15% of the mass of the hard carbon powder. In some embodiments, the mass of the surface modifier can be, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% of the mass of the hard carbon powder, or a range therebetween. In the present disclosure, by controlling the mass ratio of the surface modifier to the hard carbon powder, the thickness of the surface modifier ultimately formed on the surface of the hard carbon powder can be controlled to ensure a good reaction and coating effect.

[0051] S3. Preparation of surface modified hard carbon negative electrode materials.

[0052] The solid-liquid mixture is stirred and heated at 60-80°C to dry to form a composite powder, and the composite powder is vacuum dehydrated with a vacuum degree of ≤10 -3 Pa, and the vacuum dehydration temperature is 100°C-120°C to obtain a surface-modified hard carbon negative electrode material. In some embodiments, the stirring and heating temperature can be, for example, any one of 60°C, 65°C, 70°C, 75°C, and 80°C, or a range between any two thereof. The vacuum dehydration temperature can be, for example, any one of 100°C, 105°C, 110°C, 115°C, and 120°C, or a range between any two thereof.

[0053] The surface modified hard carbon negative electrode material prepared by the above preparation method is a core-shell structure, wherein the interior is a hard carbon core layer, and the exterior is a surface modification layer formed by a surface modifier, and the surface modification layer is coated on the outside of the hard carbon core layer, wherein, during the vacuum dehydration process, the carboxyl group in the surface modifier reacts with the hydroxyl group on the surface of the hard carbon negative electrode to accurately and uniformly insert the carbonyl group into the hard carbon surface. It should be understood that the surface modification layer does not achieve complete coating, but introduces carboxyl and carbonyl groups to the sites containing hydroxyl groups on the hard carbon surface and achieves coating of the sites. Therefore, there are partial coating and partial non-coating on the surface of the hard carbon. These carbonyl groups can serve as active "anchor points" to preferentially control the decomposition of catalytic inorganic salts and inhibit excessive decomposition of organic solvents, thereby forming a uniformly distributed inorganic salt-rich SEI film. The inorganic salt-rich SEI film is beneficial to Na at the interface + The surface-modified hard carbon anode material can be widely used in the preparation of sodium-ion battery anode materials.

[0054] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0055] Example 1:

[0056] A method for preparing a surface-modified hard carbon negative electrode material comprises the following specific steps:

[0057] S1. Phenolic resin powder is placed in a graphite sagger, and the temperature is increased to 300°C at 3°C / min in a nitrogen-protected sintering furnace and kept warm for 6 hours, then the temperature is increased to 1300°C at 5°C / min and kept warm for 10 hours, and the sintered carbon is cooled to room temperature to obtain a sintered carbon; the phenolic resin sintered carbon is crushed to a particle size of less than 1 mm using a double-roll mill, and the sintered carbon is processed using a jet mill to a Dv50 of 5 μm, a Dv10 of 2 μm, and a Dv99 of 12 μm; the sintered carbon powder is placed in a hydrochloric acid solution for pickling, the concentration of the hydrochloric acid is 1 mol / L, the product after pickling is washed by suction filtration until the pH value of the filtered water is neutral, and then dried in an 80°C oven for 12 hours.

[0058] S2. Add the acid-washed hard carbon powder into water and add o-carboxybenzaldehyde to form a solid-liquid mixture, wherein the mass ratio of the hard carbon powder to water is 1:3, and the mass of o-carboxybenzaldehyde is 10% of the mass of the hard carbon powder.

[0059] S3, heating and stirring at 80 ° C until the water is completely evaporated to obtain composite powder, and then vacuum ≤ 10 -3Pa, the obtained composite powder is subjected to high-temperature dehydration treatment at a dehydration temperature of 100°C to obtain a surface-modified hard carbon negative electrode material. Please refer to Figures 1 and 2. It can be seen that the surface-modified hard carbon negative electrode material provided in this embodiment is a core-shell structure, the interior of which is a hard carbon core layer, and the outside is a surface modification layer formed by a surface modifier, and the surface modification layer is coated on the outside of the hard carbon core layer.

[0060] Example 2:

[0061] A method for preparing a surface-modified hard carbon negative electrode material is substantially the same as that of Example 1, with the only difference being that the raw material in step S1 in this embodiment is epoxy resin.

[0062] Example 3:

[0063] A method for preparing a surface-modified hard carbon negative electrode material is substantially the same as that of Example 1, with the only difference being that the raw material in step S1 in this embodiment is corn starch.

[0064] Example 4:

[0065] A preparation method of a surface-modified hard carbon negative electrode material is basically the same as that of Example 1, except that the raw material in step S1 of this embodiment is coconut shell.

[0066] Example 5:

[0067] A preparation method of a surface-modified hard carbon negative electrode material is substantially the same as that of Example 1, with the only difference being that the mass of p-carboxybenzaldehyde in step S4 of this embodiment is 5% of the mass of the hard carbon.

[0068] Example 6:

[0069] A method for preparing a surface-modified hard carbon negative electrode material is substantially the same as that of Example 1, with the only difference being that the mass of p-carboxybenzaldehyde in step S4 of this embodiment is 15% of the mass of the hard carbon.

[0070] Example 7:

[0071] A preparation method of a surface-modified hard carbon negative electrode material is substantially the same as that of Example 1, with the only difference being that the surface modifier in step S4 of this embodiment is 3-carboxybenzaldehyde.

[0072] Example 8:

[0073] A preparation method of a surface-modified hard carbon negative electrode material is substantially the same as that of Example 1, with the only difference being that the surface modifier in step S4 of this embodiment is o-carboxybenzaldehyde.

[0074] Comparative Example 1

[0075] This comparative example is substantially the same as Example 1, except that steps S2 and S3 in Example 1 are omitted.

[0076] The specific steps include:

[0077] S1. Phenolic resin powder is placed in a graphite crucible, and the temperature is increased to 300°C at 3°C / min in a nitrogen-protected sintering furnace and kept warm for 6 hours, then the temperature is increased to 1300°C at 5°C / min and kept warm for 10 hours, and the carbon is cooled to room temperature to obtain a carbonized product; the phenolic resin carbonized product is crushed to a particle size of less than 1 mm using a double-roll mill and the carbonized product is processed using a jet mill to a Dv50 of 5 μm, a Dv10 of 2 μm, and a Dv99 of 12 μm; the carbonized product is placed in a hydrochloric acid solution for pickling, and the concentration of the hydrochloric acid is 1 mol / L. The product after pickling is washed by suction filtration until the pH value of the filtered water is neutral, and then dried in an 80°C oven for 12 hours to obtain a finished hard carbon negative electrode material.

[0078] Comparative Example 2:

[0079] This comparative example is substantially the same as Example 2, except that steps S2 and S3 in Example 2 are omitted.

[0080] The specific steps include:

[0081] S1. Place epoxy resin in a graphite crucible, heat it to 300°C at 3°C / min in a nitrogen-protected sintering furnace and keep it warm for 6 hours, then heat it to 1300°C at 5°C / min and keep it warm for 10 hours, and cool it to room temperature to obtain a carbonized product; use a double-roll mill to crush the epoxy resin carbonized product to a particle size of less than 1 mm and use a jet mill to process the carbonized product to a Dv50 of 5μm, a Dv10 of 2μm, and a Dv99 of 12μm; place the carbonized product in a hydrochloric acid solution for pickling, the concentration of hydrochloric acid is 1 mol / L, and the product after pickling is washed by suction filtration until the pH value of the filtered water is neutral, and then dry it in an 80°C oven for 12 hours to obtain a finished hard carbon negative electrode material.

[0082] Comparative Example 3:

[0083] This comparative example is substantially the same as Example 3, except that steps S2 and S3 in Example 3 are omitted.

[0084] The specific steps include:

[0085] S1. Place corn starch in a graphite sagger, heat it to 300°C at 3°C / min in a nitrogen-protected sintering furnace and keep it warm for 6 hours, then heat it to 1300°C at 5°C / min and keep it warm for 10 hours, and cool it to room temperature to obtain a char; use a double-roll mill to crush the corn starch char to a particle size of less than 1 mm and use a jet mill to process the char to a Dv50 of 5 μm, a Dv10 of 2 μm, and a Dv99 of 12 μm; place the char powder in a hydrochloric acid solution for pickling, the concentration of hydrochloric acid is 1 mol / L, and the product after pickling is washed by suction filtration until the pH value of the filtered water is neutral, and then dry it in an 80°C oven for 12 hours to obtain a finished hard carbon negative electrode material.

[0086] Comparative Example 4:

[0087] This comparative example is substantially the same as Example 4, except that steps S2 and S3 in Example 4 are omitted.

[0088] The specific steps include:

[0089] S1. Place coconut shell in a graphite sagger, heat it to 300°C at 3°C / min in a nitrogen-protected sintering furnace and keep it warm for 6 hours, then heat it to 1300°C at 5°C / min and keep it warm for 10 hours, and cool it to room temperature to obtain a burned carbon; crush the coconut shell burned carbon to a particle size of less than 1 mm using a double-roll mill and use a jet mill to process the burned carbon to a Dv50 of 5μm, a Dv10 of 2μm, and a Dv99 of 12μm; place the burned carbon powder in a hydrochloric acid solution for pickling, the concentration of hydrochloric acid is 1mol / L, and the product after pickling is washed by suction filtration until the pH value of the filtered water is neutral, and then dry it in an 80°C oven for 12 hours to obtain a finished hard carbon negative electrode material.

[0090] Comparative Example 5:

[0091] This comparative example is substantially the same as Example 1, except that the surface modifier in this comparative example is sodium dodecylbenzenesulfonate which does not contain carboxyl groups or carbonyl groups.

[0092] The specific steps include:

[0093] S1. Phenolic resin powder is placed in a graphite sagger, and the temperature is increased to 300°C at 3°C / min in a nitrogen-protected sintering furnace and kept warm for 6 hours, then the temperature is increased to 1300°C at 5°C / min and kept warm for 10 hours, and the sintered carbon is cooled to room temperature to obtain a sintered carbon; the phenolic resin sintered carbon is crushed to a particle size of less than 1 mm using a double-roll mill, and the sintered carbon is processed using a jet mill to a Dv50 of 5 μm, a Dv10 of 2 μm, and a Dv99 of 12 μm; the sintered carbon powder is placed in a hydrochloric acid solution for pickling, the concentration of the hydrochloric acid is 1 mol / L, the product after pickling is washed by suction filtration until the pH value of the filtered water is neutral, and then dried in an 80°C oven for 12 hours.

[0094] S2. Add the acid-washed hard carbon powder into water and add sodium dodecylbenzenesulfonate to form a solid-liquid mixture, wherein the mass ratio of the hard carbon powder to water is 1:3, and the mass of p-carboxybenzaldehyde is 10% of the mass of the hard carbon powder.

[0095] S3, heating and stirring at 80 ° C until the water is completely evaporated to obtain composite powder, and then vacuum ≤ 10 -3 Pa, the dehydration temperature is 100 ° C. The obtained composite powder is subjected to high-temperature dehydration treatment to obtain a surface-modified hard carbon negative electrode material.

[0096] Experimental example

[0097] The negative electrode materials prepared in Examples 1-8 and Comparative Examples 1-5 were subjected to electrochemical performance tests. Button cells were used for the tests. The working electrode was prepared by mixing the active material, conductive carbon, and sodium carboxymethyl cellulose in a mass ratio of 95:2:3 in deionized water and then coating the mixture on a copper foil. Sodium foil was used as the counter electrode. The electrolyte was 1 mol / L NaClO4 dissolved in a mixed solvent of EC / PC (volume ratio of 1:1) and 5 wt% FEC was added. Glass fiber was used as the diaphragm. The button cells were assembled in a glove box with oxygen and water contents below 1 ppm. The electrochemical performance test of the battery was carried out on an electrochemical workstation with a charge and discharge current density of 0.05C.

[0098] Please refer to Table 1 for the test results.

[0099] Table 1. Statistical table of electrochemical performance test results of negative electrode materials provided by different examples

[0100] As can be seen from the above table, the performance data of Examples 1-4 and Comparative Examples 1-4 show that the first coulombic efficiency and cycle stability of the hard carbon negative electrode material after surface modification are significantly better than those of the hard carbon negative electrode material without any treatment. As can be seen from the performance data of Examples 1, 5-6, the surface modifier and hard carbon disclosed in the present invention have better first coulombic efficiency and cycle stability within a certain range. As can be seen from the performance data of Examples 1, 7-8 and Comparative Example 5, the selection of the surface modifier in the present invention has a significant effect on the first coulombic efficiency and cycle stability of the negative electrode material. Among them, the surface modifiers in Examples 1 and 7-8 contain carboxyl and carbonyl groups. The carboxyl group can react with the hydroxyl group on the surface of the hard carbon negative electrode to accurately and uniformly insert the carbonyl group into the hard carbon surface, thereby modifying the hard carbon. The surface modifier in Comparative Example 5 does not contain carboxyl and carbonyl groups. At this time, it is only coated as a coating layer, and its first coulombic efficiency and cycle stability are significantly worse than those in Example 1.

[0101] In summary, the preparation method of the surface-modified hard carbon negative electrode material provided by the present disclosure is to select an organic matter containing carboxyl and carbonyl groups as a surface modifier, mix it with hard carbon powder to form a solid-liquid mixture, and the surface modifier adheres to the surface of the hard carbon powder during the drying process. During the vacuum dehydration process, the carboxyl groups in the surface modifier react with the hydroxyl groups on the surface of the hard carbon negative electrode to accurately and evenly insert the carbonyl groups into the hard carbon surface. It should be understood that the surface modification layer does not achieve complete coating, but rather introduces carboxyl and carbonyl groups to the sites containing hydroxyl groups on the hard carbon surface and achieves coating of the sites. Therefore, there are partial coating and partial non-coating on the surface of the hard carbon. The surface-modified hard carbon negative electrode material provided by the present disclosure serves as a supporting material for the growth of the SEI film, and it plays a vital guiding role in the formation process of the SEI film. The introduced carbonyl groups can serve as active "anchor points" during the electrolysis process to preferentially control the decomposition of catalytic inorganic salts and inhibit excessive decomposition of organic solvents, thereby forming a uniformly distributed inorganic salt-rich SEI film. The inorganic salt-rich SEI film is beneficial to the Na + The surface-modified hard carbon anode material can be widely used in the preparation of sodium-ion battery anode materials.

[0102] The above describes in detail the optional embodiments of the present disclosure, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure can be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present disclosure and fall within the scope of protection of the present disclosure. Industrial Applicability

[0103] The preparation method of the surface modified hard carbon negative electrode material provided by the present invention is to select an organic matter containing carboxyl and carbonyl groups as a surface modifier, mix it with hard carbon powder to form a solid-liquid mixture, and the surface modifier adheres to the surface of the hard carbon powder during the drying process. During the vacuum dehydration process, the carboxyl groups in the surface modifier react with the hydroxyl groups on the surface of the hard carbon negative electrode to accurately and evenly insert the carbonyl groups into the hard carbon surface. It should be understood that the surface modification layer does not achieve complete coating, but introduces carboxyl and carbonyl groups to the sites containing hydroxyl groups on the hard carbon surface and achieves coating of the sites. Therefore, there are partial coating and partial non-coating on the surface of the hard carbon. The surface modified hard carbon negative electrode material provided by the present invention serves as a supporting material for the growth of SEI film, which plays a vital guiding role in the formation process of SEI film. The introduced carbonyl group can serve as an active "anchor point" in the electrolysis process to preferentially control the decomposition of catalytic inorganic salts and inhibit excessive decomposition of organic solvents, thereby forming a uniformly distributed inorganic salt-rich SEI film. The inorganic salt-rich SEI film is conducive to Na +The surface-modified hard carbon anode material can be widely used in the preparation of sodium-ion battery anode materials.

Claims

1. A surface-modified hard carbon anode material, characterized in that, It includes a hard carbon core layer and a surface modification layer. The surface modification layer coats the hard carbon core layer, and the surface modification layer is formed by the reaction of a surface modifier containing both carboxyl groups and carbonyl groups with the hydroxyl groups in the hard carbon core layer.

2. The surface-modified hard carbon negative electrode material according to claim 1, wherein The mass ratio of the hard carbon core layer to the surface modification layer is 1:(0.05 - 0.15).

3. A preparation method of a surface-modified hard carbon negative electrode material, characterized in that, It includes mixing hard carbon powder, water and a surface modifier to form a solid-liquid mixture. Among them, the surface modifier is an organic substance containing both carboxyl groups and carbonyl groups; drying the solid-liquid mixture to form a composite powder, and obtaining the surface-modified hard carbon negative electrode material after vacuum dehydration of the composite powder.

4. The preparation method of the surface-modified hard carbon negative electrode material according to claim 3, characterized in that, The surface modifier includes at least one of p-carboxybenzaldehyde, o-carboxybenzaldehyde and 3-carboxybenzaldehyde.

5. The preparation method of the surface-modified hard carbon anode material according to any one of claims 3-4, characterized in that, The mass ratio of the hard carbon powder to the water is 1:(3 - 5), and the mass of the surface modifier is 5% - 15% of the mass of the hard carbon powder.

6. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 3-5, characterized in that, Drying the solid-liquid mixture includes stirring and heating the solid-liquid mixture under the condition of 60°C - 80°C.

7. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 3-6, characterized in that, The vacuum degree of the vacuum dehydration is ≤ 10 -3 Pa, and the temperature of the vacuum dehydration is 100°C - 120°C.

8. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 3-7, characterized in that, The preparation method of the hard carbon powder includes roasting a hard carbon precursor to form a first-baked carbon, and the first-baked carbon is crushed, washed and dried to obtain the hard carbon powder.

9. The preparation method of the surface-modified hard carbon negative electrode material according to claim 8, characterized in that, The hard carbon precursor includes at least one of phenolic resin, epoxy resin, corn starch and coconut shell.

10. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 8-9, characterized in that, The roasting includes first performing low-temperature sintering treatment at 200°C - 600°C for 3h - 6h, and then performing high-temperature carbonization treatment at 1200°C - 1600°C for 10h - 20h.

11. The preparation method of the surface-modified hard carbon negative electrode material according to claim 10, characterized in that, The heating rate of the low-temperature sintering is 3°C / min - 5°C / min.

12. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 10-11, characterized in that, The heating rate of the high-temperature carbonization is 5°C / min - 10°C / min.

13. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 10-12, characterized in that, Both the low-temperature sintering and the high-temperature carbonization are carried out under the protection of an inert gas.

14. The preparation method of the surface-modified hard carbon negative electrode material according to claim 13, characterized in that, The inert gas is one of nitrogen, argon and helium.

15. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 10-14, characterized in that, During the heat preservation process of the low-temperature sintering and the high-temperature carbonization, the oxygen concentration is lower than 200ppm.

16. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 10-15, characterized in that, The crushing includes using a pair-roller crusher to crush and using a jet mill to refine.

17. The preparation method of the surface-modified hard carbon negative electrode material according to claim 16, wherein, After being crushed by the pair-roller crusher, the particle size of the first-baked carbon is less than 0.5mm - 2mm.

18. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 16-17, characterized in that, After being refined by the jet mill, the particle size of the first-baked carbon is Dv50 of 3μm - 6μm, Dv10 of 1μm - 4μm, and Dv99 of 10μm - 15μm.

19. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 10-18, characterized in that, The washing includes first pickling, and then filtering and washing with water until neutral.

20. The preparation method of the surface-modified hard carbon negative electrode material according to claim 19, wherein, The H in the acid used for pickling + concentration is 0.5 mol / L - 1 mol / L.

21. The preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 10-20, characterized in that, The temperature of the drying is 80°C - 100°C, and the time is 12h - 24h.

22. A surface-modified hard carbon negative electrode material, characterized in that, It is prepared by using the preparation method of the surface-modified hard carbon negative electrode material according to any one of claims 3 - 21.

23. The application of the surface-modified hard carbon negative electrode material according to any one of claims 1 - 2 or according to claim 22 in the preparation of a negative electrode material for a sodium-ion battery.

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