Modified hard carbon material and preparation method thereof, negative electrode and sodium ion battery

Abstract

The invention relates to the technical field of battery materials, and discloses a modified hard carbon material and a preparation method thereof, a negative electrode and a sodium ion battery. The modified hard carbon material comprises hard carbon particles and nano-scale sodium ion modified thiophene loaded on the surfaces of the hard carbon particles, the mass ratio of the hard carbon powder to the sodium ion modified thiophene is 100: (1-10); sodium ion modified thiophene is easy to dissolve in water, and water system negative electrode processing is facilitated. The modified hard carbon has excellent electric conductivity, and has relatively high first efficiency and relatively good dynamic performance when being applied to batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a modified hard carbon material and a preparation method thereof, a negative electrode and a sodium ion battery. Background Art

[0002] With the depletion of fossil energy and the continuous development of energy technology, rechargeable batteries, mainly lithium-ion batteries, have become the most suitable technical means for portable energy storage with their excellent electrochemical performance. However, the resources of lithium are scarce and unevenly distributed, which greatly limits the development of its large-scale application. Based on this, the research and development of rechargeable batteries has gradually turned to other metal ion batteries. Due to similar electrochemical principles, abundant sodium reserves and low cost, sodium-ion batteries have received widespread attention in recent years. Graphite has a narrow interlayer spacing and cannot form stable sodium-intercalated compounds with sodium, resulting in poor sodium storage performance. Hard carbon has better comprehensive performance, a wide source of precursors, and low production cost, making it a better negative electrode material for sodium-ion batteries. Hard carbon has a wider interlayer spacing and additional sodium storage sites, with higher specific capacity and good cycle stability, but its complex structure leads to poor rate performance.

[0003] At present, common precursors of hard carbon include high molecular polymers such as resin, cellulose, starch, sucrose, various nut shells, plants and other biomass raw materials, as well as petrochemical by-products and coal-based materials. There are the following shortcomings: 1. High molecular precursors are mainly chemical products extracted from biomass, including glucose, sucrose, starch, cellulose and lignin, but they have disadvantages such as poor conductivity, which is not conducive to the transmission of electrons and are not suitable for the preparation of hard carbon materials; 2. Petrochemical by-products and coal-based materials are mainly coal, asphalt, petroleum coke, etc., which have the advantages of low cost and high carbon yield, but graphitization is easy to occur during high-temperature carbonization, thus forming a highly ordered carbon layer structure, which is not conducive to sodium ion storage. The above shortcomings lead to the preparation of existing hard carbon materials, with high raw material prices and low carbon yields. In contrast, biomass precursors are mainly agricultural and forestry plant wastes, such as lotus, peanut shells, grapefruit peels, etc., and using them as raw materials to prepare hard carbon materials can greatly reduce costs.

[0004] However, in the process of preparing biomass carbon materials by pyrolysis, carbon atoms tend to agglomerate, and the active sites of the materials are reduced, resulting in large irreversible capacity, low first efficiency, and generally low compaction of biomass hard carbon materials; in addition, the current application of sodium ion batteries focuses on low temperature, which places high demands on kinetic performance, requiring hard carbon materials to have high electronic and ionic conductivity. Therefore, there is an urgent need for a material with excellent first efficiency and excellent kinetics at low temperatures.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The object of the present invention is to provide a modified hard carbon material and a preparation method thereof, a negative electrode and a sodium ion battery, aiming to improve at least one of the problems mentioned in the background technology.

[0007] The present invention is achieved in that: In a first aspect, the present invention provides a modified hard carbon material, characterized in that it comprises hard carbon particles and nanoscale sodium ion-modified thiophene supported on the surface of the hard carbon particles; The mass ratio of hard carbon particles to sodium ion modified thiophene is 100:1~10; the structural formula of sodium ion modified thiophene is: .

[0008] In a second aspect, the present invention provides a method for preparing the modified hard carbon material, comprising: spray drying the mixed slurry; The mixed slurry comprises hard carbon powder and nanometer-scale sodium ion-modified thiophene which are uniformly dispersed with each other.

[0009] In an optional embodiment, D50 and D90 of the hard carbon powder are approximately 4-9 μm and 10-20 μm, respectively.

[0010] In an optional embodiment, the mixed slurry further includes a surfactant, and the ratio of the mass of the surfactant to the mass of the hard carbon powder is 1 to 3:100; In an optional embodiment, the solid content of the mixed slurry is 10-40%; Optionally, the spray drying temperature is 100-180°C.

[0011] In an optional embodiment, the method for preparing the hard carbon powder comprises: Pre-carbonizing the biomass raw material pellets at 300-700° C. for 1-4 hours to obtain a first intermediate material; The first intermediate material is ground and classified to obtain a second intermediate material with D50 and D90 of 4-9 μm and 10-20 μm respectively; The second intermediate material is placed in an acid solution for purification at a temperature of 50-100°C for 5-15 hours, and after purification, it is washed to obtain a third intermediate material; The third intermediate material is placed in an inert atmosphere at 1100-1500° C. and carbonized for 2-4 hours to obtain hard carbon powder.

[0012] In an optional embodiment, the acid solution is a mixture of one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid and nitric acid.

[0013] In an optional embodiment, the method for preparing sodium ion-modified thiophene comprises: Mixing sodium hydroxide solution, 1,4-butanesulfonate, a reaction precursor and tetrabutylammonium bromide in a solution system, and reacting in the absence of oxygen for 2 to 4 hours to obtain a solid-liquid mixture; A solid product is extracted from the solid-liquid mixture to obtain sodium ion-modified thiophene; The structural formula of the reaction precursor is: ; According to the molar dosage ratio, the dosage of sodium hydroxide is 86%~87%, 1,4-butane sultone is 10~11%, the reaction precursor is 2~3%, and tetrabutylammonium bromide is 0.1~0.2%; Optionally, the mass concentration of the sodium hydroxide solution is 80-90%.

[0014] In an optional embodiment, the biomass raw material pellets are pellets of at least one of walnut shells, bamboo and coconut shells.

[0015] In a third aspect, the present invention provides a negative electrode, which includes a current collector and an active layer coated on the surface of the current collector, wherein the components of the active layer include the modified hard carbon material as described in the aforementioned embodiment, or include modified hard carbon prepared by the preparation method of any one of the aforementioned embodiments.

[0016] In a fourth aspect, the present invention provides a sodium ion battery comprising a negative electrode as described in the aforementioned embodiment.

[0017] The present invention has the following beneficial effects: The modified hard carbon provided by the present invention has not only good electronic conductivity but also excellent ionic conductivity. When the organic material modified by sodium ions is loaded on the surface of hard carbon particles, the ionic and electronic conductivity of the hard carbon can be improved. Nanoscale modified sodium ion-modified thiophene is loaded on the surface of hard carbon particles, which reduces the irreversible adsorption of sodium ions by hard carbon particles, improves the primary efficiency of the material, improves the conductivity of the negative electrode SEI film, and promotes the transmission of sodium ions inside the negative electrode, thereby improving the kinetic performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 This is a schematic diagram of the simulated structure of the modified hard carbon prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0021] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0022] The modified hard carbon material and its preparation method, negative electrode and battery provided in the embodiments of the present invention are described in detail below.

[0023] The present invention provides a modified hard carbon material including hard carbon particles and nanometer-scale sodium ion-modified thiophene loaded on the surface of the hard carbon particles; The mass ratio of hard carbon particles to sodium ion modified thiophene is 100:1~10. The structural formula of sodium ion modified thiophene is: .

[0024] The modified hard carbon material provided by the embodiment of the present invention has not only good electronic conductivity but also excellent ionic conductivity. When the sodium ion-modified thiophene is loaded on the surface of hard carbon particles, the ionic and electronic conductivity of the hard carbon can be improved. The nanoscale sodium ion-modified thiophene is loaded on the surface of hard carbon particles, which reduces the irreversible adsorption of sodium ions by hard carbon particles, improves the first effect of the material, and improves the conductivity of the negative electrode SEI film, promotes the transmission of sodium ions inside the negative electrode, thereby improving the kinetic performance of the material. In addition, the sodium ion-modified thiophene is easily soluble in water, which is convenient for processing aqueous negative electrodes.

[0025] It should be noted that the loading amount of sodium ion-modified thiophene needs to be within the range required by the present invention. If it is too little, the improvement effect on the hard carbon performance will not be obvious. If it is too much, it will affect the stability of the surface SEI film, thereby reducing the cycle performance.

[0026] Its preparation method is: The structural formula is Thiophene is used as a reaction precursor to carry out the following reaction: Mixing sodium hydroxide solution, 1,4-butanesulfonate, a reaction precursor and tetrabutylammonium bromide in a solution system, and reacting in the absence of oxygen for 2 to 4 hours to obtain a solid-liquid mixture; The solid product is extracted from the solid-liquid mixture to obtain the modified organic material; According to the molar dosage ratio, the dosage of sodium hydroxide is 86%~87%, 1,4-butane sultone is 10~11%, the reaction precursor is 2~3%, and tetrabutylammonium bromide is 0.1~0.2%.

[0027] Optionally, the mass concentration of the sodium hydroxide solution is 80-90%.

[0028] Specifically: 4-R-4H-dithieno[3,2-B:2',3'-D]pyrrole (0.5 g, 1.4 mmol) and tetrabutylammonium bromide (45.0 mg, 0.07 mmol) were placed in a reaction flask, dimethyl sulfoxide (DMSO) (10 ml) was deoxygenated by bubbling with nitrogen for 10 min, and then injected into the reaction flask, and then 85% NaOH H2O solution (3.53 g) was added by syringe, and then 1,4-butanesulfonic acid lactone (0.69 m, 6.72 mmol) was added. After reacting for 3 hours under anaerobic conditions at 25°C, the reaction mixture was slowly poured into acetone (200 mL) while stirring, and the precipitate was collected by filtration, and then washed three times with acetone and ethanol mixed in a ratio of 1:1 to obtain the product.

[0029] The reaction formula of the above reaction is: .

[0030] An embodiment of the present invention provides a method for preparing a modified hard carbon material, comprising: spray drying the mixed slurry; The mixed slurry includes hard carbon powder and nano-scale sodium ion-modified thiophene which are uniformly dispersed in each other; The mass ratio of the hard carbon powder to the sodium ion modified thiophene is 100:1-10.

[0031] The preparation method provided by the present invention can produce the modified hard carbon provided by the embodiment of the present invention.

[0032] Optionally, in order to make the modified hard carbon have better electrochemical performance when applied to the negative electrode, the D50 and D90 of the hard carbon powder are approximately 4-9 μm and 10-20 μm, respectively.

[0033] Specifically, the preparation method is: S1. Preparation of hard carbon The biomass raw material is crushed to obtain biomass raw material pellets.

[0034] The biomass raw material pellets are pre-carbonized at 300-700° C. (eg, 300° C., 400° C., 500° C., 600° C. or 700° C.) for 1-4 h (eg, 1 h, 2 h, 3 h or 4 h) to obtain a first intermediate material.

[0035] Pre-carbonization at a suitable temperature can remove volatile matter and moisture from biomass raw materials.

[0036] The first intermediate material is ground and classified to obtain a second intermediate material with D50 and D90 of 4-9 μm (for example, 4 μm, 6 μm, 8 μm or 9 μm) and 10-20 μm (for example, 10 μm, 15 μm or 20 μm), respectively.

[0037] The second intermediate material is placed in an acid solution for purification at a temperature of 50-100°C (e.g., 50°C, 80°C, or 100°C) for a time of 5-15h (e.g., 5h, 10h, or 15h). After purification, it is washed to obtain a third intermediate material.

[0038] Acid purification is used to remove impurities such as metal elements and silicon elements in the first intermediate material.

[0039] The third intermediate material is placed in an inert atmosphere at 1100-1500° C. (eg, 1100° C., 1300° C., or 1500° C.) and carbonized for 2-4 h (eg, 2 h, 3 h, or 4 h) to obtain a hard carbon powder.

[0040] The second carbonization reduces the spacing between the third intermediate material layers and increases the order, thereby obtaining a hard carbon material.

[0041] Optionally, the biomass raw material pellets are pellets of at least one of walnut shells, bamboo and coconut shells.

[0042] Optionally, the acid solution is a mixture of one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid and nitric acid.

[0043] Optionally, the pH of the acid solution is less than 3.

[0044] Optionally, the amount of acid solution used is sufficient to submerge the second intermediate material.

[0045] S2. Spray drying (1) The hard carbon powder, sodium ion-modified thiophene and surfactant prepared in step S1 are uniformly mixed with water to obtain a mixed slurry; wherein the mass ratio of the hard carbon powder to the sodium ion-modified thiophene is 100:1-10 (for example, 100:1, 100:5 and 100:10); the mass ratio of the hard carbon powder to the surfactant is 100:1-3 (for example, 100:1, 100:2 and 100:3).

[0046] Optionally, adding an appropriate amount of surfactant to the mixed slurry can improve the uniformity of dispersion of the components in the slurry.

[0047] Optionally, in order to make the distribution uniformity of sodium ion-modified thiophene on the surface of the modified hard carbon better and the particle size distribution of the modified hard carbon more uniform, the solid content of the mixed slurry is 10-40% (for example, 10%, 20%, 30% or 40%).

[0048] Optionally, the surfactant may specifically be sodium carboxymethyl cellulose or the like, which is a surfactant that can be conventionally used in negative electrode slurry.

[0049] (2) The mixed slurry is spray-dried.

[0050] Optionally, the spray drying temperature is 100-180°C (eg, 100°C, 110°C, 130°C, 150°C, 160°C or 180°C).

[0051] An embodiment of the present invention provides a negative electrode, which includes a current collector and an active layer coated on the surface of the current collector, and the components of the active layer include the modified hard carbon material provided by the embodiment of the present invention.

[0052] An embodiment of the present invention provides a battery, including the negative electrode provided by the embodiment of the present invention.

[0053] Example 1 The coconut shell is crushed to obtain biomass raw material pellets; Pre-carbonizing the biomass raw material pellets at 500° C. for 2 h to obtain a first intermediate material; The first intermediate material is ground and classified to obtain a second intermediate material with D50 and D90 of 6 μm and 15 μm respectively; The second intermediate material is placed in a hydrochloric acid solution with a pH of 2 for purification at a temperature of 80° C. for 10 hours, and after purification, it is washed to obtain a third intermediate material; The third intermediate material was placed in an argon atmosphere at 1300° C. and carbonized for 3 h to obtain hard carbon powder.

[0054] 1000 g of hard carbon powder, 50 g of sodium ion-modified thiophene, and 20 g of surfactant (sodium carboxymethyl cellulose) were added into water and mixed evenly to obtain a mixed slurry with a solid content of 30%; The mixed slurry was spray-dried at 150° C. to obtain modified hard carbon.

[0055] Example 2 The coconut shell is crushed to obtain biomass raw material pellets; Pre-carbonizing the biomass raw material pellets at 300° C. for 4 hours to obtain a first intermediate material; The first intermediate material is ground and classified to obtain a second intermediate material with D50 and D90 of 4 μm and 10 μm respectively; The second intermediate material is placed in a hydrochloric acid solution with a pH of 2 for purification at a temperature of 50° C. for 15 hours, and after purification, it is washed to obtain a third intermediate material; The third intermediate material was placed in an argon atmosphere at 1400° C. and carbonized for 4 hours to obtain hard carbon powder.

[0056] 1000 g of hard carbon powder, 100 g of sodium ion-modified thiophene, and 20 g of surfactant (sodium carboxymethyl cellulose) were added into water and mixed evenly to obtain a mixed slurry with a solid content of 30%; The mixed slurry was spray-dried at 100° C. to obtain modified hard carbon.

[0057] Example 3 The coconut shell is crushed to obtain biomass raw material pellets; Pre-carbonizing the biomass raw material pellets at 700° C. for 1 h to obtain a first intermediate material; The first intermediate material is ground and classified to obtain a second intermediate material with D50 and D90 of 9 μm and 20 μm respectively; The second intermediate material is placed in a hydrochloric acid solution with a pH of 2 for purification at a temperature of 100° C. for 5 hours, and after purification, it is washed to obtain a third intermediate material; The third intermediate material was placed in an argon atmosphere at 1100° C. and carbonized for 2 h to obtain hard carbon powder.

[0058] 1000 g of hard carbon powder, 10 g of sodium ion-modified thiophene, and 20 g of surfactant (sodium carboxymethyl cellulose) were added into water and mixed evenly to obtain a mixed slurry with a solid content of 30%; The mixed slurry was spray-dried at 180° C. to obtain modified hard carbon.

[0059] Example 4 This embodiment is basically the same as the embodiment 1, except that directly purchased hard carbon (Type-2) is mixed with sodium ion-modified thiophene and a surfactant to form a slurry and then spray-dried.

[0060] Comparative Example 1 This comparative example is basically the same as Example 1, except that after the hard carbon powder is obtained, it is not mixed with other substances for spray drying.

[0061] Comparative Example 2 This comparative example is basically the same as Example 1, except that the amount of sodium ion-modified thiophene used is 500 g.

[0062] Comparative Example 3 This comparative example is basically the same as Example 1, except that the sodium ion-modified thiophene, sodium carboxymethyl cellulose and the obtained hard carbon are directly dry-mixed without spray drying.

[0063] Experimental example The hard carbon materials prepared in the examples and comparative examples were mixed in a ratio of hard carbon: carbon black: CMC: SBR = 94: 1.5: 1.7: 2.8 to prepare a slurry, which was coated on an aluminum foil to prepare a negative electrode sheet; NFPP: carbon black: CNT: PVDF were mixed in a ratio of 96:1.2:1.1:1.7 to prepare a slurry, which was coated on aluminum foil to prepare a positive electrode sheet; The positive electrode sheet, the negative electrode sheet prepared in each embodiment and the comparative example and the PP separator were assembled into a sodium ion battery, and the electrolyte was 1 mol / LNaPF6, 40%PC+60%EMC.

[0064] The performance of the battery was tested at 25°C and the test results were recorded in Table 1.

[0065] Table 1 Electrochemical properties of batteries made of hard carbon in various embodiments and comparative examples

[0066] It can be seen from Table 1 that each embodiment of the present invention has better first efficiency and rate performance than that of Comparative Example 1. This shows that the electrochemical performance of hard carbon can be improved by loading sodium ion-modified thiophene on the hard carbon surface. Comparing Example 1 with Comparative Example 2, the battery cell cycle performance of Comparative Example 2 is significantly worse than that of Example 1, which shows that if too much sodium ion-modified thiophene is loaded on the hard carbon surface, the stability of the SEI film will be reduced. Therefore, the loading amount of sodium ion-modified thiophene should be within the range required by the present invention to have a better effect. Comparing Example 1 with Comparative Example 3, the battery cell performance of Comparative Example 3 is worse than that of Example 1, which shows that the hard carbon particles obtained by spray drying and uniformly coating on the surface are better.

[0067] By comparing the test results of Example 1 with the test results of Comparative Example 3, it can be seen that the test results of Example 1 are significantly better than those of the control group, which means that under the premise of the same negative electrode active layer composition, sodium ion-modified thiophene can be coated on the hard carbon surface to produce a negative electrode sheet with better performance than directly adding it to the slurry.

[0068] In summary, the modified hard carbon material provided in the embodiment of the present invention has excellent conductivity. By loading sodium ion-modified thiophene on the surface of hard carbon particles, the ionic and electronic conductivity of the hard carbon can be improved. In addition, nanoscale sodium ion-modified thiophene is loaded on the surface of hard carbon particles, which reduces the irreversible adsorption of sodium ions by hard carbon particles and improves the primary effect of the material.

[0069] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A modified hard carbon material, characterized in that: It comprises hard carbon particles and nanometer-scale sodium ion-modified thiophene supported on the surface of the hard carbon particles; The mass ratio of the hard carbon particles to the sodium ion-modified thiophene is 100:1-10; the structural formula of the sodium ion-modified thiophene is: .

2. A method for preparing a modified hard carbon material as claimed in claim 1, characterized in that: include: spray drying the mixed slurry; The mixed slurry comprises hard carbon powder and nanometer-scale sodium ion-modified thiophene which are uniformly dispersed with each other.

3. The preparation method according to claim 2, characterized in that: The D50 and D90 of the hard carbon powder are 4-9 μm and 10-20 μm respectively.

4. The preparation method according to claim 2, characterized in that: The mixed slurry further includes a surfactant, and the ratio of the mass of the surfactant to the mass of the hard carbon powder is 1-3:

100.

5. The preparation method according to claim 2, characterized in that: The solid content of the mixed slurry is 10-40%; Optionally, the spray drying temperature is 100-180°C.

6. The preparation method according to claim 2, characterized in that: The preparation method of the hard carbon powder comprises: Pre-carbonizing the biomass raw material pellets at 300-700° C. for 1-4 hours to obtain a first intermediate material; Grinding and classifying the first intermediate material to obtain a second intermediate material with a D50 and a D90 of 4-9 μm and 10-20 μm respectively; The second intermediate material is placed in an acid solution for purification at a temperature of 50-100° C. for 5-15 hours, and after purification, it is washed to obtain a third intermediate material; The third intermediate material is placed in an inert atmosphere at 1100-1500° C. and carbonized for 2-4 hours to obtain the hard carbon powder.

7. The preparation method according to claim 6, characterized in that: The acid solution is a mixture of one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid and nitric acid; Optionally, the biomass raw material pellets are pellets of at least one of walnut shells, bamboo and coconut shells.

8. The preparation method according to claim 6, characterized in that: The preparation method of the sodium ion modified thiophene comprises: Mixing sodium hydroxide solution, 1,4-butanesulfonate, a reaction precursor and tetrabutylammonium bromide in a solution system, and reacting in the absence of oxygen for 2 to 4 hours to obtain a solid-liquid mixture; Extracting a solid product from the solid-liquid mixture to obtain the sodium ion-modified thiophene; The structural formula of the reaction precursor is: ; According to the molar dosage ratio, the dosage of sodium hydroxide is 86%~87%, 1,4-butane sultone is 10~11%, the reaction precursor is 2~3%, and tetrabutylammonium bromide is 0.1~0.2%; Optionally, the mass concentration of the sodium hydroxide solution is 80-90%.

9. A negative electrode, characterized in that It comprises a current collector and an active layer coated on the surface of the current collector, wherein the components of the active layer include the modified hard carbon material as claimed in claim 1, or include the modified hard carbon prepared by the preparation method as claimed in any one of claims 2 to 8.

10. A sodium ion battery, characterized in that: Comprising the negative electrode as claimed in claim 9.

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