Modified hard carbon for electrode slurry and preparation method and application thereof

Abstract

The application discloses a modified hard carbon for electrode slurry and a preparation method and application thereof, wherein hard carbon material is crushed and dispersed in water, and middle and upper layer suspensions A are obtained by separation; the middle and upper layer suspensions A are dispersed in ethanol or an ethanol-water solvent, and middle and lower layer suspensions B are obtained by separation; the middle and lower layer suspensions B are washed with water and suction filtered to obtain a precursor mixture; and the precursor mixture is freeze-dried to obtain the modified hard carbon for electrode slurry. The application sorts hard carbon powder by using a physical method, removes impurities and poor components, and has good universality since the process is green and pollution-free. The freeze-drying technology is adopted to deeply remove water, so that the influence of water in the hard carbon material on the battery performance is greatly reduced. Meanwhile, micro-nano ice crystals formed at low temperature can produce pore-forming effect on the hard carbon, and the sodium storage performance of the hard carbon is improved. The modified hard carbon for electrode slurry is made into oily slurry, and the oily slurry has excellent stability and is convenient for subsequent rapid production.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery electrode materials, specifically relating to a modified hard carbon for electrode slurry, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries possess advantages such as low cost, unrestricted resources, and high safety, making them promising candidates for large-scale energy storage. Battery performance depends heavily on electrode materials. High-performance, cost-effective hard carbon materials are the preferred choice for sodium-ion battery anodes. Hard carbon precursors come from diverse sources, including petrochemicals (coal, asphalt, etc.), polymers, and biomass. Different types of hard carbon materials exhibit significant differences in sodium storage performance. Furthermore, for practical applications, the sodium storage capacity of hard carbon in sodium-ion batteries still needs further improvement, and it remains significantly lower than the lithium storage capacity of graphite anodes in lithium-ion batteries.

[0003] Therefore, how to further improve the capacity of hard carbon is a hot research topic. However, for precursors with complex compositions such as biomass and petrochemicals, the derived hard carbon components are diverse, with complex microstructures and varying sodium storage performance, making the selection and separation of high-performance hard carbon a challenge. Furthermore, the capacity of hard carbon in the low-voltage plateau region mainly depends on microporous sodium storage. However, during electrode manufacturing, the porous structure of hard carbon easily absorbs water, making water removal from the pores difficult, leading to processing difficulties and subsequent degradation of battery performance. Summary of the Invention

[0004] To address the problems of low capacity, poor processability, and difficulty in removing impurities in existing hard carbon materials, this invention provides a modified hard carbon for electrode slurry, its preparation method, and its application. The prepared modified hard carbon exhibits excellent sodium storage performance when applied to electrode slurry or sodium-ion battery anodes.

[0005] This invention is achieved through the following technical solution: A method for preparing modified hard carbon for electrode paste includes the following steps: (1) The hard carbon material is crushed, dispersed in water, and separated to obtain the middle and upper suspended solids A; (2) Disperse the upper and middle layer suspension A in ethanol or ethanol-water solvent, and separate to obtain the lower and middle layer suspension B; (3) The middle and lower suspended solids B were washed with water and filtered to obtain a precursor mixture; (4) The precursor mixture is freeze-dried to obtain modified hard carbon for electrode slurry.

[0006] Furthermore, the modified hard carbon used in the freeze-dried electrode slurry of step (4) has a water content of less than 1%.

[0007] Furthermore, the freeze-drying conditions in step (4) are -40~-60℃ and 10~48h.

[0008] Furthermore, the particle size D50 of the hard carbon material after pulverization in step (1) is 3-15 μm.

[0009] Furthermore, in step (2), the volume ratio of ethanol to water in the ethanol-water solvent is 4:1.

[0010] In this invention, the electrode slurry prepared by the aforementioned preparation method uses modified hard carbon.

[0011] In this invention, the electrode slurry modified with hard carbon or the electrode slurry prepared using electrode slurry modified with hard carbon is used in the anode material of sodium-ion batteries.

[0012] Furthermore, the electrode paste is prepared by uniformly mixing modified hard carbon, solvent, binder and conductive agent to obtain the electrode paste.

[0013] Furthermore, the solvent is N-methylpyrrolidone; the binder is polyvinylidene fluoride; and the conductive agent is Super-P.

[0014] Furthermore, the electrode slurry uses modified hard carbon, binder, and conductive agent in a mass ratio of 92:5:3; the electrode slurry has a viscosity of 4000-6000 cps.

[0015] Beneficial effects (1) The present invention innovatively uses physical methods to sort hard carbon powder, remove impurities and inferior components, and the process is green and pollution-free, with good universality.

[0016] (2) This invention utilizes freeze-drying technology to deeply remove water from hard carbon, reducing the impact of moisture on battery performance. At the same time, the micro-nano ice crystals formed at low temperatures can create pores in the hard carbon, improving its sodium storage performance.

[0017] (3) The present invention uses modified hard carbon to make the electrode slurry into an oily slurry, which has excellent stability and is convenient for subsequent rapid production. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of commercial hard carbon dispersed in water and ethanol solvents, respectively, as shown in Example 1. Figure 2 The pore size distribution diagrams are for modified hard carbon and commercial hard carbon used in the electrode paste of Example 1. Figure 3 XRD patterns of modified hard carbon and commercial hard carbon used in the electrode paste of Example 1; Figure 4 The graph shows the cycling performance of the modified hard carbon electrode slurry used in Example 2 and the commercial hard carbon electrode. Figure 5 The pore size distribution diagram of the modified asphalt carbon used in the electrode slurry in Example 3 is shown. Figure 6 XRD pattern of pore size distribution of asphalt carbon and modified asphalt carbon for electrode slurry in Example 3; Figure 7 The diagram shows the cycling performance of the modified asphalt carbon electrode used in Example 3, which is made from asphalt carbon and electrode slurry. Detailed Implementation

[0019] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0020] Example 1 (1) Commercial hard carbon (starch carbon) was coarsely crushed, pulverized by air jet mill, and the hard carbon powder with a particle size D50=6-8μm was obtained by air separation; 100g of hard carbon powder was dispersed in 500 mL of water, stirred at 500 rpm for 1 h and then allowed to stand for 3 h to separate and obtain the middle and upper suspended solids A. (2) Disperse the upper and middle layer suspension A in a mixed solvent of 400 mL ethanol and 100 mL water, stir at 500 rpm for 1 h and let stand for 3 h to separate and obtain the lower and middle layer suspension B. (3) The middle and lower suspended solids B were washed with water and filtered to obtain a precursor mixture; (4) The precursor mixture was freeze-dried at -60℃ for 24h, and the water content of the carbon material was measured to be 0.08%, thus obtaining modified hard carbon for electrode slurry.

[0021] A photograph of commercially available hard carbon dispersed in water and ethanol solvents in Example 1 is shown below. Figure 1 As shown, commercially available hard carbon has a lower density than water, and hard carbon containing heavy metal impurities will sink to the bottom of the beaker. Therefore, in this step, the upper and middle suspended hard carbon is retained. On the other hand, high-quality hard carbon has a higher density than ethanol, and some of the lighter carbon with a large specific surface area has poor sodium storage capacity and will suspend on the surface of the ethanol solvent. In this step, inferior hard carbon is removed.

[0022] The pore size distribution diagrams of the modified hard carbon and commercial hard carbon used in the electrode paste prepared in Example 1 are shown below. Figure 2 As shown, by utilizing the pore-forming effect of micro- and nano-ice crystals during the freeze-drying process, the micropore size of commercial hard carbon was increased from almost zero to 0.0035 cm. 3 g -1 A higher micropore content is beneficial for improving the sodium storage performance of hard carbon electrodes.

[0023] The XRD patterns of the modified hard carbon and commercial hard carbon used in the electrode paste prepared in Example 1 are shown below. Figure 3As shown, the intensity of the (002) peak of the modified hard carbon used in the electrode slurry increased and the half-peak width narrowed, indicating that the uniformity of the hard carbon particles became more consistent after sorting.

[0024] Example 2 Take 46 g of the electrode slurry prepared in Example 1, 2.5 g of modified hard carbon, 1.5 g of PVDF, 1.5 g of Super-P and 75 g of NMP, and disperse them evenly in a high-speed mixer. The viscosity of the slurry was measured to be 5238 cps. The slurry was then vacuum sealed for later use. The electrode slurry prepared above was uniformly coated onto copper foil and vacuum dried at 100°C for 12 h to obtain a negative electrode sheet. The negative electrode sheet was then pressed and shaped using a pressing machine and cut to obtain the battery negative electrode sheet. The prepared materials were assembled in a vacuum glove box in the following order: positive electrode shell - active material - glass fiber membrane - electrolyte - sodium sheet - gasket - spring sheet - negative electrode shell. The assembly was then placed in a button cell packaging machine for pressing. The pressed battery was left horizontally for 24 h before testing. The LAND Blue Battery Charge-Discharge Tester was used to test the charge-discharge performance at a current density of 30 mA g⁻¹ and a voltage range of 0.01–2 V, with the test temperature kept constant at 25°C. Electrode slurries were prepared using modified hard carbon and commercial hard carbon from Example 1, respectively, and electrodes were fabricated. The electrode cycle performance is shown in the figure below. Figure 4 As shown, after 100 cycles, the capacity of commercial hard carbon is only 15 mAh g⁻¹, while the capacity of modified hard carbon used in electrode paste is still 155.6 mAh g⁻¹. -1 .

[0025] Example 3 Modified hard carbon for electrode slurry, electrode slurry, and electrode were prepared using pitch carbon as the hard carbon raw material. The preparation method was the same as in Examples 1 and 2.

[0026] The pore size distribution diagram of modified pitch carbon for electrode slurry is shown in the figure. Figure 5 As shown, the XRD pattern is as follows Figure 6 As shown, the micropore content of pitch carbon increased from 0.0035 cm⁻¹ to 0.0049 cm⁻¹. 3 g -1 The intensity of peak (002) in the XRD pattern was also significantly improved, indicating improved particle uniformity. Electrode slurry was prepared using modified pitch carbon and pitch carbon as raw materials, and electrodes were fabricated from them. The electrode cycle performance is shown in the figure below. Figure 7 As shown; by Figure 7 It can be seen that when used as the negative electrode in sodium-ion batteries, the reversible sodium storage capacity of the modified pitch carbon electrode slurry increases from 69.9 mAh g⁻¹ to 117.8 mAh g⁻¹. -1 .

Claims

1. A method for preparing modified hard carbon for electrode paste, characterized in that, Includes the following steps: (1) The hard carbon material is crushed, dispersed in water, and separated to obtain the middle and upper suspended solids A; (2) Disperse the upper and middle layer suspension A in ethanol or ethanol-water solvent, and separate to obtain the lower and middle layer suspension B; (3) The middle and lower suspended solids B were washed with water and filtered to obtain a precursor mixture; (4) The precursor mixture is freeze-dried to obtain modified hard carbon for electrode slurry; In step (2), the volume ratio of ethanol to water in the ethanol-water solvent is 4:1; In step (4), the freeze-drying conditions are -40~-60℃ for 10~48h.

2. The method for preparing modified hard carbon for electrode paste according to claim 1, characterized in that, Step (4) The modified hard carbon used in the freeze-dried electrode slurry has a water content of less than 1%.

3. The method for preparing modified hard carbon for electrode paste according to claim 1, characterized in that, Step (1) The particle size D50 of the hard carbon material after crushing is 3-15μm.

4. A modified hard carbon for electrode slurry prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the modified hard carbon for the electrode slurry according to claim 4 in the anode material of a sodium-ion battery.

6. The application according to claim 5, characterized in that, The electrode paste is prepared by uniformly mixing modified hard carbon, solvent, binder and conductive agent.

7. The application according to claim 6, characterized in that, The solvent is N-methylpyrrolidone; the binder is polyvinylidene fluoride; and the conductive agent is Super-P.

8. The application according to claim 6, characterized in that, The electrode paste uses modified hard carbon, binder and conductive agent in a mass ratio of 92:5:3; the viscosity of the electrode paste is 4000-6000 cps.

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