Preparation method of hard carbon composite material for negative electrode of capacity type sodium-ion battery

Abstract

The invention discloses a preparation method of a hard carbon composite material for a negative electrode of a capacity type sodium-ion battery, which comprises the following steps: S1, premixing a first precursor: mixing a first carbon source and a second carbon source, and then carrying out pre-carbonization treatment to obtain the first precursor; s2, modification treatment of a second precursor: carrying out a mixed liquid phase reaction on the first precursor and an oxidation reactant for modification to obtain a modified second precursor; s3, deliming treatment: carrying out a deliming reaction on the second precursor in a mixed acid solution to obtain a delimed second precursor; s4, performing heat treatment on a third precursor: mixing the delimed second precursor with a third carbon source, and performing heat treatment to obtain the third precursor; and S5, coating treatment: mixing the third precursor with a coating agent, and performing multi-stage heat treatment to obtain the composite hard carbon material for the negative electrode of the sodium-ion battery. The lithium ion battery has the characteristics of high rate performance, high capacity and high first cycle efficiency.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a method for preparing a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and no memory effect, have been widely used in energy storage systems, consumer electronics, and new energy vehicles. Sodium-ion batteries, due to their abundant resources, wide distribution, and similar working principle to lithium-ion batteries, are considered a promising next-generation energy storage technology.

[0003] Unlike lithium-ion batteries, which commonly use graphite as the negative electrode, graphite cannot be used in sodium-ion batteries because it lacks sodium storage activity.

[0004] Currently, sodium-ion batteries mostly use hard carbon as the negative electrode active material, which has the advantages of high sodium storage capacity, suitable sodium storage potential, and low cost. However, the capacity of industrially prepared hard carbon negative electrode materials is typically only around 300 mAh / g, significantly lower than the theoretical capacity of graphite lithium storage (375 mAh / g). This gap limits the energy density of sodium-ion batteries, making them less competitive compared to lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a hard carbon composite material for the negative electrode of a capacity sodium-ion battery, which features high rate performance, high capacity and high first-cycle efficiency.

[0006] This invention can be achieved through the following technical solutions:

[0007] The present invention discloses a method for preparing a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery, comprising the following steps:

[0008] S1. Premixing of the first precursor: The first carbon source and the second carbon source are mixed and then pre-carbonized to obtain the first precursor.

[0009] S2. Modification of the second precursor: The first precursor is modified by reacting a mixture of the first precursor and the oxidizing agent in the liquid phase to obtain the modified second precursor.

[0010] S3. Deashing treatment: The second precursor is deashed in a mixed acid solution, followed by deacidification, water washing and drying to obtain the deashed second precursor.

[0011] S4. Heat treatment of the third precursor: The deashed second precursor and the third carbon source are mixed and then heat-treated to obtain the third precursor.

[0012] S5. Coating treatment: The third precursor is mixed with the coating agent and then subjected to multi-stage heat treatment to obtain a sodium-ion battery anode composite hard carbon material.

[0013] Further, in step S1, the first carbon source is a biomass-based carbon source, and the second carbon source is a coal-based carbon source; the mass ratio of the first carbon source to the second carbon source is 1:0.1-0.5. The low residual carbon content of the biomass raw material leads to a low yield, and the resulting hard carbon material has high disorder and low electronic conductivity. The high residual carbon content of the coal-based raw material results in a high degree of graphitization and good electronic conductivity in the resulting hard carbon material, but the narrow carbon interlayer spacing is unfavorable for sodium ion insertion / extraction. Combining biomass and coal raw materials can improve the carbonization yield, and the resulting hard carbon possesses both high electronic conductivity and a wide carbon interlayer spacing. The mass ratio of the first carbon source to the second carbon source is the result of balancing the electronic conductivity and average carbon interlayer spacing of the resulting hard carbon.

[0014] Furthermore, the third carbon source is a hydroxyl-containing organic compound, and its addition amount is 5-20 wt.% of the second precursor's addition amount. The -OH group in the third carbon source reacts with the -COOH group in the second precursor to form an ester cross-linked structure. The open pores (exterior pores) formed by oxidation in step S2 are transformed into closed pores (interior pores) due to cross-linking. The open pores in the hard carbon material can contact the electrolyte but cannot store sodium ions, resulting in a large contact area between the hard carbon material and the electrolyte, excessive irreversible capacity loss, and low first-cycle coulombic efficiency. The closed pores do not contact the electrolyte and can effectively store sodium ions, thus improving the sodium storage capacity of the hard carbon material without affecting its first-cycle coulombic efficiency. In addition, the cross-linked structure has strong rigidity, which can effectively suppress the shrinkage of carbon interlayer spacing during the graphitization process of carbon materials, ensuring that the resulting hard carbon has a wide carbon interlayer spacing. If the amount of the third carbon source added is too small, the -OH in the precursor cannot be completely cross-linked, which will not achieve the purpose of this invention. If the amount of the third carbon source added is too large, the excess third carbon source will not participate in the reaction, resulting in unnecessary waste.

[0015] Furthermore, in step S1, the pre-carbonization temperature is 300-500℃, and the holding time is 1-5h. If the carbonization temperature is too high, the carbon source will be completely carbonized, resulting in fewer functional groups, which is not conducive to the subsequent oxidation reaction; if the carbonization temperature is too low, the carbon source will not be carbonized, and the subsequent oxidant will oxidize the biomass raw material, causing it to be over-oxidized, its structure completely destroyed, and affecting the electrochemical performance of the obtained hard carbon material.

[0016] Further, in step S2, the concentration of the oxidizing agent is 0.2-3 wt.%; the temperature of the modification reaction is 40-90℃, and the reaction time is 0.5-3 h; under the oxidizing action of the oxidizing agent, the chemical bonds such as -COC- in the first precursor break to form -OH functional groups, destroying the structural integrity of the precursor and forming a porous structure; the -OH functional groups are further oxidized to carboxyl groups; if the concentration of the oxidizing agent is high, the reaction temperature is high, and the reaction time is long, the oxidation degree of the first precursor is high, and vice versa. If the oxidation degree of the first precursor is too high, the precursor will be over-oxidized, broken down, and decomposed into small molecule organic compounds that dissolve in the aqueous solution, resulting in a low yield; if the oxidation degree is too low, the precursor structure cannot be destroyed, and the content of introduced carboxyl groups is low.

[0017] Furthermore, in step S4, the heat treatment temperature is 100-300℃; the heat treatment atmosphere is a nitrogen and / or argon atmosphere. If the heat treatment temperature is too low, the required reaction temperature will not be reached, and the crosslinking reaction cannot occur; if the heat treatment temperature is too high, the third carbon source will be carbonized and decomposed at high temperature, and it will be unable to crosslink with -COOH in the precursor.

[0018] Further, in step S5, the multi-stage heat treatment includes several stages: the first stage temperature is 180-400℃; the second stage temperature is 500-800℃; and the third stage temperature is 1200-1500℃. Specifically, the first stage treatment temperature is slightly higher than the melting point of asphalt but lower than its carbonization point. At this temperature, the asphalt melts and penetrates into the pores of the precursor material. The second stage temperature is slightly higher than the carbonization temperature of asphalt. At this temperature, the molten asphalt carbonizes at high temperature, achieving the purpose of filling pores and reducing the specific surface area of ​​the hard carbon material. At the third stage treatment temperature, the hard carbon material is graphitized at high temperature, forming an amorphous hard carbon anode material with a certain degree of graphitization.

[0019] Further, in step S5, the coating agent is an asphalt-based coating agent, and the amount of asphalt-based coating agent added is 1-5 wt.% of the third precursor. The amount of asphalt-based coating agent added affects the effect of the present invention. Adding an appropriate amount of asphalt to melt into the pores of the precursor material can effectively reduce the specific surface area of ​​the material; excessive addition results in a higher coating layer formed on the surface of the hard carbon material. Asphalt-derived hard carbon is a soft carbon with narrow carbon layer spacing, which affects the insertion / extraction of sodium ions.

[0020] Further, in step S3, the mixed acid is one or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid, and the concentration of the mixed acid is 2-25 wt.%. The purpose of the mixed acid is to remove metallic impurities, i.e., ash, from the precursor, thereby purifying the carbon material.

[0021] Furthermore, the primary carbon source is one or more of the following: walnut shells, coconut shells, apricot shells, wood, reeds, bamboo, nut shells, rice husks, straw, and corn cobs.

[0022] Furthermore, the second carbon source is one or more of anthracite, lignite, and coal.

[0023] Furthermore, the third carbon source is one or more of the following: phenolic resin, epoxy resin, glucose, sucrose, starch, cellulose, ethylene glycol, glycerol, phenol, naphthol, and hydroquinone.

[0024] Furthermore, the coating agent is one or more of coal tar pitch, petroleum asphalt, and natural asphalt;

[0025] The oxidizing agent is one or more of the following: nitric acid, sulfuric acid, hydrogen peroxide, sodium persulfate, potassium permanganate, potassium dichromate, hypochlorous acid, sodium hypochlorite, and potassium hypochlorite.

[0026] The hard carbon anode material prepared by the method of this invention is characterized by rich micropores and wide carbon interlayer spacing, with an average carbon interlayer spacing ranging from 0.37 to 0.39 nm and a true density ranging from 1.78 to 1.90 g / cm³. 3 Electrochemical performance tests show that the negative electrode material prepared by the method of this invention has the following characteristics in terms of electrochemical performance:

[0027] First, high-rate performance: Biomass-based hard carbon materials exhibit high disorder and low electronic conductivity; coal-based raw materials have high residual carbon content, resulting in hard carbon materials with high graphitization and good electronic conductivity, but narrow carbon interlayer spacing. This invention uses a composite of biomass and coal, resulting in hard carbon that simultaneously possesses both high electronic conductivity and wide carbon interlayer spacing, facilitating rapid sodium ion insertion / extraction. Furthermore, the structure formed by precursor crosslinking exhibits strong rigidity, effectively suppressing carbon interlayer spacing shrinkage during the graphitization process, ensuring the resulting hard carbon has a wide carbon interlayer spacing.

[0028] Secondly, high capacity: the structure of the first precursor is destroyed by oxidation, forming a porous structure and functional groups such as -OH and -COOH. Subsequently, the -OH in the third carbon source reacts with the oxygen-containing functional groups in the second precursor to form an ester cross-linked structure. The open pores (exterior pores) formed by oxidation in the precursor are transformed into closed pores (interior pores) through cross-linking. The closed pores do not come into contact with the electrolyte and can effectively store sodium ions, thus improving the sodium storage capacity of hard carbon materials without affecting their first-cycle coulombic efficiency.

[0029] Third, high first-cycle efficiency: the asphalt melts into the pores of the precursor material, which can effectively reduce the specific surface area of ​​the material, reduce the contact area between the electrode interface and the electrolyte, and reduce irreversible electrolyte loss. Detailed Implementation

[0030] 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.

[0031] The present invention discloses a method for preparing a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery, comprising the following steps:

[0032] S1. Premixing of the first precursor: The first carbon source and the second carbon source are mixed and then pre-carbonized to obtain the first precursor.

[0033] S2. Modification of the second precursor: The first precursor is modified by reacting a mixture of the first precursor and the oxidizing agent in the liquid phase to obtain the modified second precursor.

[0034] S3. Deashing treatment: The second precursor is deashed in a mixed acid solution, followed by deacidification, water washing and drying to obtain the deashed second precursor.

[0035] S4. Heat treatment of the third precursor: The deashed second precursor and the third carbon source are mixed and then heat-treated to obtain the third precursor.

[0036] S5. Coating treatment: The third precursor is mixed with the coating agent and then subjected to multi-stage heat treatment to obtain a sodium-ion battery anode composite hard carbon material.

[0037] Furthermore, in step S1, the first carbon source is a biomass carbon source, and the second carbon source is a coal carbon source; the mass ratio of the first carbon source to the second carbon source is 1:0.1-0.5.

[0038] Furthermore, the third carbon source is a hydroxyl-containing organic compound, and the amount of the third carbon source added is 5-20 wt.% of the amount of the second precursor added.

[0039] Furthermore, in step S1, the pre-carbonization temperature is 300-500℃, and the holding time is 1-5h.

[0040] Furthermore, in step S2, the concentration of the oxidizing agent is 0.2-3 wt.%; the temperature of the modification reaction is 40-90℃; and the reaction time is 0.5-3h.

[0041] Further, in step S4, the heat treatment temperature is 100-300℃; the heat treatment atmosphere is a nitrogen and / or argon atmosphere.

[0042] Furthermore, in step S5, the multi-stage heat treatment includes several stages: the first stage temperature is 180-400℃; the second stage temperature is 500-800℃; and the third stage temperature is 1200-1500℃.

[0043] Furthermore, in step S5, the coating agent is an asphalt-based coating agent, and the amount of asphalt-based coating agent added is 1-5 wt.% of the third precursor.

[0044] Further, in step S3, the mixed acid is one or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid, and the concentration of the mixed acid is 2-25 wt.%.

[0045] Furthermore, the primary carbon source is one or more of the following: walnut shells, coconut shells, apricot shells, wood, reeds, bamboo, nut shells, rice husks, straw, and corn cobs.

[0046] Furthermore, the second carbon source is one or more of anthracite, lignite, and coal.

[0047] Furthermore, the third carbon source is one or more of the following: phenolic resin, epoxy resin, glucose, sucrose, starch, cellulose, ethylene glycol, glycerol, phenol, naphthol, and hydroquinone.

[0048] Furthermore, the coating agent is one or more of coal tar pitch, petroleum asphalt, and natural asphalt;

[0049] The oxidizing agent is one or more of the following: nitric acid, sulfuric acid, hydrogen peroxide, sodium persulfate, potassium permanganate, potassium dichromate, hypochlorous acid, sodium hypochlorite, and potassium hypochlorite.

[0050] Example 1

[0051] This embodiment relates to a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery, and its preparation method includes the following steps:

[0052] S1. Premixing of the first precursor: The first carbon source and the second carbon source are mixed, followed by pre-carbonization treatment to obtain the first precursor. Specifically, the first carbon source is a biomass carbon source, and the second carbon source is a coal carbon source; the mass ratio of the first carbon source to the second carbon source is 1:0.1; the first carbon source is walnut shell, coconut shell, or apricot shell; the second carbon source is anthracite; the pre-carbonization temperature is 400℃, and the holding time is 1 hour.

[0053] S2. Modification of the second precursor: The first precursor is modified by reacting a mixture of the first precursor and an oxidizing agent in the liquid phase to obtain the modified second precursor. Specifically, the oxidizing agents are nitric acid and sulfuric acid, and the concentration of the oxidizing agents is 3 wt.%; the temperature of the modification reaction is 70℃, and the reaction time is 0.5 h.

[0054] S3. Deashing treatment: The second precursor is deashed in a mixed acid solution, followed by deacidification, washing with water, and drying to obtain the deashed second precursor. Specifically, the mixed acid is hydrochloric acid and nitric acid, and the concentration of the mixed acid is 18 wt.%.

[0055] S4. Heat treatment of the third precursor: The deashed second precursor and the third carbon source are mixed and then heat-treated to obtain the third precursor. Specifically, the third carbon source is a hydroxyl-containing organic compound, and the amount of the third carbon source added is 20 wt.% of the amount of the second precursor added. The third carbon source is phenolic resin, epoxy resin, glucose, sucrose, starch, cellulose, ethylene glycol, glycerol, phenol, naphthol, or hydroquinone. The heat treatment temperature is 200℃, and the heat treatment atmosphere is nitrogen.

[0056] S5. Coating Treatment: The third precursor is mixed with a coating agent, followed by a multi-stage heat treatment to obtain a sodium-ion battery anode composite hard carbon material. Specifically, the multi-stage heat treatment includes several stages: the first stage temperature is 400℃; the second stage temperature is 600℃; and the third stage temperature is 1200℃. The coating agent is an asphalt-based coating agent, and the amount of asphalt-based coating agent added is 5 wt.% of the third precursor.

[0057] Example 2

[0058] This embodiment relates to a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery, and its preparation method includes the following steps:

[0059] S1. Premixing of the first precursor: The first carbon source and the second carbon source are mixed and then pre-carbonized to obtain the first precursor. Specifically, the first carbon source is a biomass carbon source, and the second carbon source is a coal carbon source; the mass ratio of the first carbon source to the second carbon source is 1:0.3; the first carbon source is reed, bamboo, nut shell, rice husk, straw, or corn cob; the second carbon source is anthracite; the pre-carbonization temperature is 300℃, and the holding time is 5 hours.

[0060] S2. Modification of the second precursor: The first precursor is modified by reacting a mixture of the first precursor and an oxidizing agent in the liquid phase to obtain the modified second precursor. Specifically, the oxidizing agent is hydrogen peroxide and sodium persulfate, and the concentration of the oxidizing agent is 2 wt.%; the temperature of the modification reaction is 40℃, and the reaction time is 3 h.

[0061] S3. Deashing treatment: The second precursor is deashed in a mixed acid solution, followed by deacidification, washing with water, and drying to obtain the deashed second precursor. Specifically, the mixed acid is sulfuric acid and phosphoric acid, and the concentration of the mixed acid is 12 wt.%.

[0062] S4. Heat treatment of the third precursor: The deashed second precursor and the third carbon source are mixed and then heat-treated to obtain the third precursor. Specifically, the third carbon source is a hydroxyl-containing organic compound, and the amount of the third carbon source added is 10 wt.% of the amount of the second precursor added. The third carbon source is glycerol, phenol, naphthol, or hydroquinone. The heat treatment temperature is 200℃, and the heat treatment atmosphere is argon.

[0063] S5. Coating Treatment: The third precursor is mixed with a coating agent, followed by a multi-stage heat treatment to obtain a sodium-ion battery anode composite hard carbon material. Specifically, the multi-stage heat treatment includes several stages: the first stage temperature is 300℃; the second stage temperature is 500℃; and the third stage temperature is 1500℃. The coating agent is an asphalt-based coating agent, and the amount of asphalt-based coating agent added is 3 wt.% of the third precursor.

[0064] Example 3

[0065] This embodiment relates to a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery, and its preparation method includes the following steps:

[0066] S1. Premixing of the first precursor: The first carbon source and the second carbon source are mixed, followed by pre-carbonization treatment to obtain the first precursor. Specifically, the first carbon source is a biomass carbon source, and the second carbon source is a coal carbon source; the mass ratio of the first carbon source to the second carbon source is 1:0.5; the first carbon source is walnut shell, coconut shell, rice husk, straw, or corn cob; the second carbon source is anthracite; the pre-carbonization temperature is 300℃, and the holding time is 5 hours.

[0067] S2. Modification of the second precursor: The first precursor is modified by reacting a mixture of the first precursor and an oxidizing agent in the liquid phase to obtain the modified second precursor. Specifically, the oxidizing agent is potassium dichromate, hypochlorous acid, sodium hypochlorite, and potassium hypochlorite, and the concentration of the oxidizing agent is 0.2 wt.%; the modification reaction temperature is 90℃, and the reaction time is 2 h.

[0068] S3. Deashing treatment: The second precursor is deashed in a mixed acid solution, followed by deacidification, washing with water, and drying to obtain the deashed second precursor. Specifically, the mixed acid is hydrochloric acid and sulfuric acid, and the concentration of the mixed acid is 3 wt.%.

[0069] S4. Heat treatment of the third precursor: The deashed second precursor and the third carbon source are mixed and then heat-treated to obtain the third precursor. Specifically, the third carbon source is a hydroxyl-containing organic compound, and the amount of the third carbon source added is 5 wt.% of the amount of the second precursor added. The third carbon source is phenolic resin, sucrose, starch, or hydroquinone. The heat treatment temperature is 300℃, and the heat treatment atmosphere is nitrogen and argon.

[0070] S5. Coating Treatment: The third precursor is mixed with a coating agent, followed by a multi-stage heat treatment to obtain a sodium-ion battery anode composite hard carbon material. Specifically, the multi-stage heat treatment includes several stages: the first stage temperature is 180℃; the second stage temperature is 800℃; and the third stage temperature is 1350℃. The coating agent is an asphalt-based coating agent, and the amount of asphalt-based coating agent added is 1 wt.% of the third precursor.

[0071] Example 4

[0072] This embodiment relates to a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery, and its preparation method includes the following steps:

[0073] S1. Premixing of the first precursor: The first carbon source and the second carbon source are mixed and then pre-carbonized to obtain the first precursor. Specifically, the first carbon source is a biomass carbon source, and the second carbon source is a coal carbon source; the mass ratio of the first carbon source to the second carbon source is 1:0.4; the first carbon source is walnut shell, coconut shell, apricot shell, wood, or reed; the second carbon source is anthracite, lignite, or smokeless coal; the pre-carbonization temperature is 350℃, and the holding time is 2.5h.

[0074] S2. Modification of the second precursor: The first precursor is modified by reacting a mixture of the first precursor and an oxidizing agent in the liquid phase to obtain the modified second precursor. Specifically, the oxidizing agents are hydrogen peroxide, sodium persulfate, hypochlorous acid, sodium hypochlorite, and potassium hypochlorite, with a concentration of 1.2 wt.%; the modification reaction temperature is 50℃, and the reaction time is 2 hours.

[0075] S3. Deashing treatment: The second precursor is deashed in a mixed acid solution, followed by deacidification, washing with water, and drying to obtain the deashed second precursor. Specifically, the mixed acid consists of hydrochloric acid, sulfuric acid, and phosphoric acid, with a concentration of 5 wt.%.

[0076] S4. Heat treatment of the third precursor: The deashed second precursor and the third carbon source are mixed and then heat-treated to obtain the third precursor. Specifically, the third carbon source is a hydroxyl-containing organic compound, and the amount of the third carbon source added is 15 wt.% of the amount of the second precursor added. The third carbon source is phenolic resin, epoxy resin, glucose, sucrose, or starch. The heat treatment temperature is 150℃, and the heat treatment atmosphere is nitrogen.

[0077] S5. Coating Treatment: The third precursor is mixed with a coating agent, followed by a multi-stage heat treatment to obtain a sodium-ion battery anode composite hard carbon material. Specifically, the multi-stage heat treatment includes several stages: the first stage temperature is 300℃; the second stage temperature is 700℃; and the third stage temperature is 1400℃. The coating agent is an asphalt-based coating agent, and the amount of asphalt-based coating agent added is 2 wt.% of the third precursor.

[0078] Example 5

[0079] This embodiment relates to a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery, and its preparation method includes the following steps:

[0080] S1. Premixing of the first precursor: The first carbon source and the second carbon source are mixed and then pre-carbonized to obtain the first precursor. Specifically, the first carbon source is a biomass carbon source, and the second carbon source is a coal carbon source; the mass ratio of the first carbon source to the second carbon source is 1:0.2; the first carbon source is walnut shell, coconut shell, apricot shell, wood, reed, bamboo, nut shell, rice husk, straw, or corn cob; the second carbon source is anthracite, lignite, or smokeless coal; the pre-carbonization temperature is 450℃, and the holding time is 4 hours.

[0081] S2. Modification of the second precursor: The first precursor is modified by reacting a mixture of oxidizing agents in the liquid phase to obtain the modified second precursor. Specifically, the oxidizing agents are nitric acid, sodium hypochlorite, and potassium hypochlorite, with a concentration of 1 wt.%; the modification reaction temperature is 80℃, and the reaction time is 1 h.

[0082] S3. Deashing treatment: The second precursor is deashed in a mixed acid solution, followed by deacidification, washing with water, and drying to obtain the deashed second precursor. Specifically, the mixed acid is hydrochloric acid and sulfuric acid, and the concentration of the mixed acid is 10 wt.%.

[0083] S4. Heat treatment of the third precursor: The deashed second precursor and the third carbon source are mixed and then heat-treated to obtain the third precursor. Specifically, the third carbon source is a hydroxyl-containing organic compound, and the amount of the third carbon source added is 15 wt.% of the amount of the second precursor added. The third carbon source is phenolic resin, epoxy resin, glucose, sucrose, starch, or cellulose. The heat treatment temperature is 150℃, and the heat treatment atmosphere is nitrogen and / or nitrogen.

[0084] S5. Coating Treatment: The third precursor is mixed with a coating agent, followed by a multi-stage heat treatment to obtain a sodium-ion battery anode composite hard carbon material. Specifically, the multi-stage heat treatment includes several stages: the first stage temperature is 200℃; the second stage temperature is 600℃; and the third stage temperature is 1300℃. The coating agent is an asphalt-based coating agent, and the amount of asphalt-based coating agent added is 4 wt.% of the third precursor.

[0085] Application Example 1

[0086] This embodiment relates to a hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery, and its preparation method includes the following steps:

[0087] S1. Bamboo and anthracite are mixed evenly and then pre-carbonized to obtain the first precursor; wherein the mass ratio of bamboo to anthracite is 1:0.15; the pre-carbonization temperature is 350℃ and the holding time is 2 h.

[0088] S2. The first precursor was mixed with sodium hypochlorite in an aqueous solution and reacted at 80°C for 1.5 h to obtain the modified second precursor. The concentration of sodium hypochlorite was 1.2 wt.%.

[0089] S3. The second precursor is deashed in a solution of hydrochloric acid and nitric acid, followed by deacidification, washing with water, and drying to obtain the deashed second precursor. The concentration of the mixed acid is 15 wt.%.

[0090] S4. The deashed second precursor and phenol are uniformly mixed, and then heat-treated at 150°C under a nitrogen atmosphere to obtain the modified third precursor. The amount of phenol added is 8 wt.% of the amount of the second precursor.

[0091] S5. The third precursor is mixed with petroleum asphalt, with the amount of petroleum asphalt added being 1.5 wt.% of the third precursor. Subsequently, a multi-stage heat treatment is performed: the first stage temperature is 250℃; the second stage temperature is 680℃; and the third stage temperature is 1300℃, to obtain a high-performance hard carbon anode material for sodium-ion batteries.

[0092] 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 drying oven at 100°C for 2 hours. The electrode membrane was punched into a disc with a radius of 0.6 mm using a punching machine. Sodium metal was used as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) was used as the electrolyte, and a PP / PE / PP three-layer separator was used. The membrane was assembled into a CR2016 type button cell 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 1-0.005 V.

[0093] Comparative Example 1

[0094] This embodiment relates to a hard carbon composite material for the negative electrode of a sodium-ion battery, and its preparation method includes the following steps:

[0095] S1. Bamboo and anthracite are mixed evenly and then pre-carbonized to obtain the first precursor; wherein the mass ratio of bamboo to anthracite is 1:0.15; the pre-carbonization temperature is 350℃ and the holding time is 2 h.

[0096] S2. The first precursor was mixed with sodium hypochlorite in an aqueous solution and reacted at 80°C for 1.5 h to obtain the modified second precursor. The concentration of sodium hypochlorite was 1.2 wt.%.

[0097] S3. The second precursor is deashed in a solution of hydrochloric acid and nitric acid, followed by deacidification, washing with water, and drying to obtain the deashed second precursor. The concentration of the mixed acid is 15 wt.%.

[0098] S4. The second precursor is mixed with petroleum asphalt, with the amount of petroleum asphalt added being 1.5 wt.% of the second precursor. Subsequently, a multi-stage heat treatment is performed: the first stage temperature is 250℃; the second stage temperature is 680℃; and the third stage temperature is 1300℃, to obtain the hard carbon anode material of Comparative Example 1.

[0099] 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 NaClO4 EC+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 1-0.005 V.

[0100] Comparative Example 2

[0101] This embodiment relates to a hard carbon composite material for the negative electrode of a sodium-ion battery, and its preparation method includes the following steps:

[0102] S1. Bamboo and anthracite are mixed evenly and then pre-carbonized to obtain the first precursor; wherein the mass ratio of bamboo to anthracite is 1:0.15; the pre-carbonization temperature is 350℃ and the holding time is 2 h.

[0103] S2. The first precursor is deashed in a solution of hydrochloric acid and nitric acid, followed by deacidification, washing with water, and drying to obtain the deashed second precursor. The concentration of the mixed acid is 15 wt.%.

[0104] S3. The deashed second precursor and phenol are uniformly mixed, and then heat-treated at 150°C under a nitrogen atmosphere to obtain the modified third precursor. The amount of phenol added is 8 wt.% of the amount of the second precursor.

[0105] S4. The third precursor was mixed with petroleum asphalt, with the amount of petroleum asphalt added being 1.5 wt.% of the third precursor. Subsequently, a multi-stage heat treatment was performed, with the first stage temperature being 250℃, the second stage temperature being 680℃, and the third stage temperature being 1300℃, to obtain the hard carbon anode material of Comparative Example 2.

[0106] 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 NaClO4 EC+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 1-0.005 V.

[0107] To effectively evaluate the application examples and comparative examples, the following tests were conducted:

[0108] The BET specific surface areas of Application Example 1, Comparative Example 1, and Comparative Example 2, as determined by nitrogen adsorption-desorption test, were 4.5, 263, and 5.2 m² / g, respectively.

[0109] XRD test results show that the average carbon interlayer spacing of Application Example 1, Comparative Example 1, and Comparative Example 2 are 0.385, 0.382, and 0.371 nm, respectively, with Application Example 1 having a wider average carbon interlayer spacing.

[0110] The true densities of He gas measured in Application Example 1, Comparative Example 1, and Comparative Example 2 were 1.82, 1.98, and 1.94 g / cm³, respectively. The lower true density of Application Example 1 indicates that it has more internal pores.

[0111] The first-week charging specific capacities of Application Example 1, Comparative Example 1, and Comparative Example 2, measured by constant current charge-discharge testing, were 364, 268, and 316 mAh / g, respectively, with first-week coulombic efficiencies of 93.2%, 81.6%, and 92.8%, respectively. The constant current charge-discharge test results indicate that the pre-oxidation followed by cross-linking of the carbonized material significantly improves the sodium storage capacity and first-week coulombic efficiency of the hard carbon material. The reversible capacity and first-week efficiency of Comparative Example 1 are too low because, under the oxidation of the precursor by the oxidizing agent, a large number of chemical bonds break, destroying the dense structure of the precursor and forming a porous structure. The subsequent asphalt coating process showed little improvement in surface area.

[0112] 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 composite material for the negative electrode of a capacity-type sodium-ion battery, characterized in that... Includes the following steps: S1. Premixing of the first precursor: The first carbon source and the second carbon source are mixed and then pre-carbonized to obtain the first precursor. S2. Modification of the second precursor: The first precursor is modified by reacting a mixture of the first precursor and the oxidizing agent in the liquid phase to obtain the modified second precursor. S3. Deashing treatment: The second precursor is deashed in a mixed acid solution, followed by deacidification, water washing and drying to obtain the deashed second precursor. S4. Heat treatment of the third precursor: The deashed second precursor and the third carbon source are mixed and then heat-treated to obtain the third precursor. S5. Coating treatment: The third precursor is mixed with the coating agent and then subjected to multi-stage heat treatment to obtain a sodium-ion battery anode composite hard carbon material.

2. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: In step S1, the first carbon source is a biomass carbon source and the second carbon source is a coal carbon source; the mass ratio of the first carbon source to the second carbon source is 1:0.1-0.

5.

3. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: The third carbon source is a hydroxyl-containing organic compound, and the amount of the third carbon source added is 5-20 wt.% of the amount of the second precursor added.

4. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: In step S1, the pre-carbonization temperature is 300-500℃, and the holding time is 1-5h.

5. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: In step S2, the concentration of the oxidizing agent is 0.2-3 wt.%; the temperature of the modification reaction is 40-90℃, and the reaction time is 0.5-3h.

6. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: In step S4, the heat treatment temperature is 100-300℃; the heat treatment atmosphere is nitrogen and / or argon atmosphere.

7. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: In step S5, the multi-stage heat treatment includes several stages: the first stage temperature is 180-400℃; the second stage temperature is 500-800℃; and the third stage temperature is 1200-1500℃.

8. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: In step S5, the coating agent is an asphalt-based coating agent, and the amount of asphalt-based coating agent added is 1-5 wt.% of the third precursor.

9. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: In step S3, the mixed acid is one or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid, and the concentration of the mixed acid is 2-25 wt.%.

10. The method for preparing the hard carbon composite material for the negative electrode of a capacity-type sodium-ion battery according to claim 1, characterized in that: The primary carbon source is one or more of the following: walnut shells, coconut shells, apricot shells, wood, reeds, bamboo, nut shells, rice husks, straw, and corn cobs. The second carbon source is one or more of anthracite, lignite, and coal. The third carbon source is one or more of the following: phenolic resin, epoxy resin, glucose, sucrose, starch, cellulose, ethylene glycol, glycerol, phenol, naphthol, and hydroquinone. The coating agent is one or more of coal tar pitch, petroleum asphalt, and natural asphalt; The oxidizing agent is one or more of the following: nitric acid, sulfuric acid, hydrogen peroxide, sodium persulfate, potassium permanganate, potassium dichromate, hypochlorous acid, sodium hypochlorite, and potassium hypochlorite.