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

Abstract

The present invention relates to the technical field of battery materials, and discloses a modified hard carbon material, a preparation method thereof, a negative electrode and a sodium ion battery. The modified hard carbon material includes hard carbon particles and nanoscale sodium ion-modified thiophene loaded on the surface of the hard carbon particles; the mass ratio of the hard carbon powder to the sodium ion-modified thiophene is 100:1 to 10; the sodium ion-modified thiophene is easily soluble in water, which is convenient for the processing of the aqueous negative electrode. The modified hard carbon has excellent conductivity, and has a high initial efficiency and better kinetic performance when applied in a battery.

Description

Technical Field

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

[0002] With the gradual depletion of fossil energy and the continuous development of energy technologies, rechargeable batteries mainly based on lithium ion batteries have become the most suitable technical means for portable energy storage at present due to their excellent electrochemical performance. However, the resource amount of lithium element is small and unevenly distributed, which greatly limits the development of its large-scale application. Based on this, the research and development of rechargeable batteries have gradually turned to other metal ion batteries. Due to similar electrochemical principles, and the abundant reserves and low cost of sodium element, sodium ion batteries have received extensive attention in recent years. Graphite has a narrow interlayer spacing and cannot form a stable sodium intercalation compound with sodium, resulting in poor sodium storage performance, while hard carbon has better comprehensive performance, wide sources of precursors, and low production cost, and is a better negative electrode material for sodium ion batteries. Hard carbon has a wider interlayer spacing and additional sodium storage sites, has a higher specific capacity and good cycle stability, but has a complex structure, resulting in poor rate performance.

[0003] At present, common precursors of hard carbon include high molecular polymers such as resins, celluloses, starches, and sucrose, as well as various biomass raw materials such as nut shells and plants, and petrochemical by-products and coal-based materials. They have the following deficiencies respectively: 1. High molecular precursors are mainly chemical products extracted from biomass, including glucose, sucrose, starch, cellulose, and lignin, etc., but have disadvantages such as poor electrical conductivity, which is not conducive to electron transmission and is not suitable for preparing hard carbon materials; 2. Petrochemical by-products and coal-based materials are mainly coal, pitch, petroleum coke, etc., which have advantages such as low cost and high carbon yield, but are prone to graphitization during the high-temperature carbonization process, thus forming a highly ordered carbon layer structure, which is not conducive to sodium ion storage. These disadvantages lead to high raw material prices and low carbon yield in the preparation of existing hard carbon materials. In contrast, biomass precursors are mainly agricultural and forestry plant wastes, such as lotus, peanut shells, pomelo peels, etc. Using them as raw materials to prepare hard carbon materials can greatly reduce the cost.

[0004] However, during the pyrolysis process of preparing biomass carbon materials, carbon atoms are prone to agglomeration, the active sites of the material are reduced, resulting in a large irreversible capacity, low first efficiency, and generally low compaction of biomass hard carbon materials; in addition, current sodium ion battery applications focus on low temperature, which puts forward high requirements for kinetic performance, and requires 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 temperature.

[0005] In view of this, the present invention is particularly proposed. SUMMARY OF THE INVENTION

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

[0007] The present invention is implemented as follows:

[0008] In a first aspect, the present invention provides a modified hard carbon material, which is characterized by comprising hard carbon particles and nano-scale sodium ion-modified thiophene loaded on the surface of the hard carbon particles;

[0009] The mass ratio of the hard carbon particles to the sodium ion-modified thiophene is 100:1 to 10; the structural formula of the sodium ion-modified thiophene is: .

[0010] In a second aspect, the present invention provides a preparation method of the above-mentioned modified hard carbon material, comprising:

[0011] Performing spray drying on the mixed slurry;

[0012] The mixed slurry comprises uniformly dispersed hard carbon powder and nano-scale sodium ion-modified thiophene.

[0013] In an optional embodiment, the D50 and D90 of the hard carbon powder are respectively about 4 - 9 μm and 10 - 20 μm.

[0014] In an optional embodiment, the mixed slurry further comprises a surfactant, and the mass ratio of the surfactant to the mass of the hard carbon powder is 1 - 3:100;

[0015] In an optional embodiment, the solid content of the mixed slurry is 10 - 40%;

[0016] Optionally, the spray drying temperature is 100 - 180 °C.

[0017] In an optional embodiment, the preparation method of the hard carbon powder comprises:

[0018] Pre-carbonizing the biomass raw material pellets at 300 - 700 °C for 1 - 4 h to obtain a first intermediate material;

[0019] Grinding and classifying the first intermediate material to obtain a second intermediate material with D50 and D90 of 4 - 9 μm and 10 - 20 μm respectively;

[0020] Placing the second intermediate material in an acid solution for purification, the purification temperature is 50 - 100 °C, the time is 5 - 15 h, and after purification, washing is performed to obtain a third intermediate material;

[0021] Placing the third intermediate material in an inert atmosphere at 1100 - 1500 °C and carbonizing for 2 - 4 h to obtain the hard carbon powder.

[0022] In an optional embodiment, the acid solution is a mixed solution of one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid and nitric acid.

[0023] In an optional embodiment, the preparation method of sodium ion-modified thiophene includes:

[0024] Mix sodium hydroxide solution, 1,4-butanesultone, reaction precursor and tetrabutylammonium bromide in a solution system, and carry out an anaerobic reaction for 2-4 h to obtain a solid-liquid mixture;

[0025] Extract the solid product from the solid-liquid mixture to obtain sodium ion-modified thiophene;

[0026] The structural formula of the reaction precursor is: ;

[0027] According to the molar dosage ratio, the dosage of sodium hydroxide is 86%-87%, 1,4-butanesultone is 10-11%, the reaction precursor is 2-3%, and tetrabutylammonium bromide is 0.1-0.2%;

[0028] Optionally, the mass concentration of the sodium hydroxide solution is 80-90%.

[0029] In an optional embodiment, the biomass raw material pellets are pellets of at least one of walnut shell, bamboo and coconut shell.

[0030] 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. The components of the active layer include the modified hard carbon material as described in the foregoing embodiments, or the modified hard carbon prepared by the preparation method of any one of the foregoing embodiments.

[0031] In a fourth aspect, the present invention provides a sodium ion battery, including the negative electrode as described in the foregoing embodiments.

[0032] The present invention has the following beneficial effects:

[0033] For the modified hard carbon provided by the present invention, since the organic material modified by sodium ions not only has good electronic conductivity, but also has excellent ionic conductivity. Loading it on the surface of hard carbon particles can improve the ionic and electronic conductivity of hard carbon. Moreover, the nano-scale modified sodium ion-modified thiophene is loaded on the surface of hard carbon particles, reducing the irreversible adsorption of hard carbon particles to sodium ions, improving the initial efficiency of the material, and improving the conductivity of the negative electrode SEI film, promoting the transport of sodium ions inside the negative electrode, thereby improving the kinetic performance of the material. Description of the Drawings

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0035] Figure 1 It is a schematic diagram of the simulated structure of the modified hard carbon prepared in the embodiment of the present invention. Specific embodiments

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0037] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.

[0038] The modified hard carbon material, its preparation method, negative electrode, and battery provided by the embodiments of the present invention will be specifically described below.

[0039] The present invention provides a modified hard carbon material, which includes hard carbon particles and nano-scale sodium-ion modified thiophene loaded on the surface of the hard carbon particles;

[0040] The mass ratio of the hard carbon particles to the sodium-ion modified thiophene is 100:1 to 10. The structural formula of the sodium-ion modified thiophene is: .

[0041] For the modified hard carbon material provided by the embodiments of the present invention, since the sodium-ion modified thiophene not only has good electronic conductivity but also excellent ionic conductivity, loading it on the surface of the hard carbon particles can improve the ionic and electronic conductivity of the hard carbon. Moreover, the nano-scale sodium-ion modified thiophene loaded on the surface of the hard carbon particles reduces the irreversible adsorption of sodium ions by the hard carbon particles, improves the first efficiency of the material, and improves the conductivity of the negative electrode SEI film, promoting the transport 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, facilitating the processing of the aqueous negative electrode.

[0042] It should be noted that the loading amount of the 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 performance of the hard carbon is not obvious. If it is too much, it will affect the stability of the surface SEI film, resulting in a reduction in the cycle performance.

[0043] Its preparation method is:

[0044] Using a thiophene with the structural formula as a reaction precursor, the following reaction is carried out:

[0045] Mix sodium hydroxide solution, 1,4-butanesultone, the reaction precursor and tetrabutylammonium bromide in a solution system, and carry out an anaerobic reaction for 2 - 4 h to obtain a solid-liquid mixture;

[0046] Extract the solid product from the solid-liquid mixture to obtain the modified organic material;

[0047] According to the molar dosage ratio, the dosage of sodium hydroxide is 86% - 87%, 1,4-butanesultone is 10 - 11%, the reaction precursor is 2 - 3%, and tetrabutylammonium bromide is 0.1 - 0.2%.

[0048] Optionally, the mass concentration of the sodium hydroxide solution is 80 - 90%.

[0049] Specifically:

[0050] Put 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) into a reaction flask. Bubble nitrogen through dimethyl sulfoxide (DMSO) (10 ml) for 10 min to remove oxygen, then inject it into the reaction flask. Then add an 85% NaOH aqueous solution (3.53 g) through a syringe, and then add 1,4-butanesultone (0.69 m, 6.72 mmol). After reacting under anaerobic conditions at 25 °C for 3 hours, slowly pour the reaction mixture into acetone (200 mL) while stirring, collect the precipitate by filtration, and wash it three times with a 1:1 mixture of acetone and ethanol to obtain the product.

[0051] The reaction formula for the above reaction is:

[0052] .

[0053] A preparation method of a modified hard carbon material provided by an embodiment of the present invention includes:

[0054] Perform spray drying on the mixed slurry;

[0055] The mixed slurry includes uniformly dispersed hard carbon powder and sodium ion-modified thiophene at the nanoscale;

[0056] The mass ratio of the hard carbon powder to the sodium ion-modified thiophene is 100:1 - 10.

[0057] The preparation method provided by the present invention can prepare the modified hard carbon provided by the embodiment of the present invention.

[0058] Optionally, to enable the modified hard carbon to 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.

[0059] Specifically, the preparation method is as follows:

[0060] S1. Prepare hard carbon

[0061] Crush the biomass raw material to obtain biomass raw material pellets.

[0062] Pre-carbonize the biomass raw material pellets at 300-700 °C (such as 300 °C, 400 °C, 500 °C, 600 °C or 700 °C) for 1-4 h (such as 1 h, 2 h, 3 h or 4 h) to obtain a first intermediate material.

[0063] Pre-carbonization at an appropriate temperature can remove volatile components and moisture in the biomass raw material.

[0064] Grind and classify the first intermediate material to obtain a second intermediate material with D50 and D90 of 4-9 μm (such as 4 μm, 6 μm, 8 μm or 9 μm) and 10-20 μm (such as 10 μm, 15 μm or 20 μm), respectively.

[0065] Place the second intermediate material in an acid solution for purification. The purification temperature is 50-100 °C (such as 50 °C, 80 °C or 100 °C), and the time is 5-15 h (such as 5 h, 10 h or 15 h). After purification, wash to obtain a third intermediate material.

[0066] Purify with an acid solution to remove impurities such as metal elements and silicon elements in the first intermediate material.

[0067] Place the third intermediate material in an inert atmosphere at 1100-1500 °C (such as 1100 °C, 1300 °C or 1500 °C) and carbonize for 2-4 h (such as 2 h, 3 h or 4 h) to obtain hard carbon powder.

[0068] The second carbonization reduces the interlayer spacing and increases the order degree of the third intermediate material to obtain a hard carbon material.

[0069] Optionally, the biomass raw material pellets are pellets of at least one of walnut shells, moso bamboo, and coconut shells.

[0070] Optionally, the acid solution is a mixed solution of one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid.

[0071] Optionally, the pH of the acid solution is less than 3.

[0072] Optionally, the amount of the acid solution is sufficient to submerge the second intermediate material.

[0073] S2. Spray drying

[0074] (1) Mix the hard carbon powder obtained in step S1, the sodium ion-modified thiophene, and the surfactant uniformly 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 to 10 (such as 100:1, 100:5, and 100:10); the mass ratio of the hard carbon powder to the surfactant is 100:1 to 3 (such as 1:100, 100:2, and 100:3).

[0075] Optionally, adding an appropriate amount of surfactant to the mixed slurry can make the dispersion uniformity of each component in the slurry better.

[0076] Optionally, to make the distribution uniformity of the sodium ion-modified thiophene on the surface of the prepared 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% to 40% (such as 10%, 20%, 30%, or 40%).

[0077] Optionally, the surfactant can specifically be sodium carboxymethyl cellulose, etc., which are surfactants that can be conventionally used in the negative electrode slurry.

[0078] (2) Spray-dry the mixed slurry.

[0079] Optionally, the spray-drying temperature is 100 to 180 °C (such as 100 °C, 110 °C, 130 °C, 150 °C, 160 °C, or 180 °C).

[0080] The 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.

[0081] The embodiment of the present invention provides a battery, including the negative electrode provided by the embodiment of the present invention.

[0082] Example 1

[0083] Crush the coconut shell to obtain biomass raw material pellets;

[0084] Pre-carbonize the biomass raw material pellets at 500 °C for 2 h to obtain a first intermediate material;

[0085] [[ID=3*]] Grind and classify the first intermediate material to obtain a second intermediate material with D50 and D90 being 6 μm and 15 μm respectively;

[0086] Place the second intermediate material in a hydrochloric acid solution with a pH of 2 for purification, the purification temperature is 80 °C, the time is 10 h, and after purification, wash it to obtain a third intermediate material;

[0087] Place the third intermediate material in an argon atmosphere at 1300 °C and carbonize it for 3 h to obtain hard carbon powder.

[0088] Add 1000 g of hard carbon powder, 50 g of sodium ion-modified thiophene, and 20 g of a surfactant (sodium carboxymethyl cellulose) to water, and mix evenly to obtain a mixed slurry with a solid content of 30%.

[0089] Perform spray drying on the mixed slurry at 150 °C to obtain modified hard carbon.

[0090] Example 2

[0091] Crush coconut shells to obtain biomass raw material pellets.

[0092] Pre-carbonize the biomass raw material pellets at 300 °C for 4 h to obtain a first intermediate material.

[0093] Grind and classify the first intermediate material to obtain a second intermediate material with D50 and D90 of 4 μm and 10 μm respectively.

[0094] Place the second intermediate material in a hydrochloric acid solution with a pH of 2 for purification. The purification temperature is 50 °C and the time is 15 h. After purification, wash it to obtain a third intermediate material.

[0095] Place the third intermediate material in an argon atmosphere at 1400 °C and carbonize for 4 h to obtain hard carbon powder.

[0096] Add 1000 g of hard carbon powder, 100 g of sodium ion-modified thiophene, and 20 g of a surfactant (sodium carboxymethyl cellulose) to water, and mix evenly to obtain a mixed slurry with a solid content of 30%.

[0097] Perform spray drying on the mixed slurry at 100 °C to obtain modified hard carbon.

[0098] Example 3

[0099] Crush coconut shells to obtain biomass raw material pellets.

[0100] Pre-carbonize the biomass raw material pellets at 700 °C for 1 h to obtain a first intermediate material.

[0101] Grind and classify the first intermediate material to obtain a second intermediate material with D50 and D90 of 9 μm and 20 μm respectively.

[0102] Place the second intermediate material in a hydrochloric acid solution with a pH of 2 for purification. The purification temperature is 100 °C and the time is 5 h. After purification, wash it to obtain a third intermediate material.

[0103] Place the third intermediate material in an argon atmosphere at 1100 °C and carbonize for 2 h to obtain hard carbon powder.

[0104] 1000 g of hard carbon powder, 10 g of sodium ion-modified thiophene, and 20 g of surfactant (sodium carboxymethyl cellulose) were added to water and mixed evenly to obtain a mixed slurry with a solid content of 30%.

[0105] The mixed slurry was spray-dried at 180 °C to obtain modified hard carbon.

[0106] Example 4

[0107] This example is basically the same as Example 1, except that: the directly purchased hard carbon (model Type-2), sodium ion-modified thiophene, and surfactant were mixed to form a slurry and then spray-dried.

[0108] Comparative Example 1

[0109] This comparative example is basically the same as Example 1, except that: after obtaining the hard carbon powder, it was not mixed with other substances for spray-drying.

[0110] Comparative Example 2

[0111] This comparative example is basically the same as Example 1, except that: the amount of sodium ion-modified thiophene used was 500 g.

[0112] Comparative Example 3

[0113] This comparative example is basically the same as Example 1, except that: sodium ion-modified thiophene, sodium carboxymethyl cellulose, and the obtained hard carbon were directly dry-mixed without using spray-drying.

[0114] Experimental Example

[0115] The hard carbon materials prepared in each example and comparative example were mixed according to the ratio of hard carbon: carbon black: CMC: SBR = 94: 1.5: 1.7: 2.8 to prepare a slurry, which was coated on aluminum foil to make a negative electrode sheet.

[0116] NFPP: carbon black: CNT: PVDF were mixed according to the ratio of 96: 1.2: 1.1: 1.7 to prepare a slurry, which was coated on aluminum foil to make a positive electrode sheet.

[0117] The positive electrode sheet, the negative electrode sheets prepared in each example and comparative example, and a PP separator were assembled into a sodium ion battery, and the electrolyte was 1 mol / L NaPF6, 40% PC + 60% EMC.

[0118] The performance of the battery was tested at 25 °C. The test results were recorded in Table 1.

[0119] Table 1 Electrochemical performance of the batteries prepared from the hard carbon of each example and comparative example

[0120]

[0121] As can be seen from Table 1, each embodiment of the present invention has better initial efficiency and rate performance compared to Comparative Example 1. This shows that the electrochemical performance of hard carbon can be improved by loading sodium ions on the surface of hard carbon to modify thiophene. Comparing Example 1 with Comparative Example 2, the cycle performance of the battery cell in Comparative Example 2 is significantly worse than that in Example 1. This indicates that if too much sodium ion-modified thiophene is loaded on the surface of hard carbon, 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 achieve better results. Comparing Example 1 with Comparative Example 3, the battery cell performance in Comparative Example 3 is worse than that in Example 1. This shows that the hard carbon particles obtained by spray drying and uniformly coating on the surface are better.

[0122] Comparing the test results of Example 1 with those of Comparative Example 3, it can be seen that the test results of Example 1 are significantly better than those of the control group. This shows that on the premise of the same composition of the negative electrode active layer, the method of coating sodium ion-modified thiophene on the surface of hard carbon can produce a negative electrode sheet with better performance compared to the method of directly adding it to the slurry.

[0123] In summary, for the modified hard carbon material provided by the embodiments of the present invention, due to the excellent conductivity of sodium ion-modified thiophene, loading it on the surface of hard carbon particles can improve the ionic and electronic conductivity of hard carbon. Moreover, the nano-scale sodium ion-modified thiophene loaded on the surface of hard carbon particles reduces the irreversible adsorption of hard carbon particles to sodium ions, thereby improving the initial efficiency of the material.

[0124] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a modified hard carbon material, characterized in that: include: spray drying the mixed slurry; The mixed slurry includes hard carbon powder and nano-scale sodium ion-modified thiophene that are uniformly dispersed with each other; The mass ratio of the hard carbon powder to the sodium ion modified thiophene is 100:1-10; The preparation method of the sodium ion modified thiophene comprises: Sodium hydroxide solution, 1,4-butane sultone, a reaction precursor and tetrabutylammonium bromide are mixed in a solution system and reacted 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 ratio, the amount of sodium hydroxide is 86% to 87%, 1,4-butane sultone is 10 to 11%, the reaction precursor is 2 to 3%, and tetrabutylammonium bromide is 0.1 to 0.2%.

2. The preparation method according to claim 1, characterized in that The D50 and D90 of the hard carbon powder are 4-9 μm and 10-20 μm respectively.

3. The preparation method according to claim 1, 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.

4. The preparation method according to claim 1, characterized in that The solid content of the mixed slurry is 10-40%.

5. The preparation method according to claim 1, characterized in that The spray drying temperature is 100~180℃.

6. The preparation method according to claim 1, 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 then 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.

8. The preparation method according to claim 6, characterized in that: The biomass raw material pellets are pellets of at least one of walnut shells, bamboo and coconut shells.

9. The preparation method according to claim 6, characterized in that: During the preparation of the sodium ion-modified thiophene, the mass concentration of the sodium hydroxide solution is 80-90%.

10. A negative electrode, characterized in that: The invention 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 prepared by the preparation method according to any one of claims 1 to 9.

11. A sodium ion battery, characterized in that: The negative electrode according to claim 10 is included.

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