Preparation method of porous hard carbon material and application of porous hard carbon material in sodium-ion battery

Abstract

The invention relates to the field of battery materials, and discloses a preparation method of a porous hard carbon material and application of the porous hard carbon material in a sodium-ion battery, the preparation method of the material comprises the following steps: S1, preparing a sucrose solution by taking sucrose as a carbon source, carrying out hydrothermal reaction treatment on the sucrose solution, and then filtering and separating to obtain a hard carbon precursor; s2, dissolving zinc salt with distilled water to prepare a solution, adding the hard carbon precursor obtained in S1 into the solution, then adding absolute ethyl alcohol into the solution, mixing and stirring at normal temperature, finally heating to evaporate the solvent to dryness, and fully grinding to obtain a uniformly mixed material containing the zinc salt; and S3, putting the material obtained in the S2 into a furnace body, heating to 600 DEG C under a protective atmosphere, carrying out primary carbonization, then heating to 1300 DEG C, carrying out high-temperature carbonization, cooling, taking out, and uniformly grinding, so as to obtain the porous hard carbon material. The material provided by the invention has the characteristics of convenient preparation method, high first-week coulombic efficiency and high specific capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a method for preparing a porous hard carbon material and application thereof in sodium ion batteries. Background Art

[0002] Secondary batteries are considered the primary rechargeable energy storage device, with lithium-ion batteries (LIBs) representing the majority. Their superior performance, including high energy density and long cycle life, has dominated the energy storage market. However, limited lithium resources and uneven resource distribution hinder the sustainable development of LIBs, necessitating the urgent need to identify alternative energy storage devices to meet energy demands. Sodium-ion batteries (SIBs), which operate on similar principles to LIBs and feature abundant sodium reserves and low cost, are considered a formidable competitor in green energy devices.

[0003] Currently, researchers have conducted extensive research on SIBs, and the search for optimal anode materials remains one of the main challenges for their commercialization. Hard carbon materials have attracted considerable attention due to their ease of synthesis, abundant resources, and low cost. However, the relatively low specific capacity of current hard carbon materials limits further improvements in the energy density of sodium-ion batteries, restricting their application in high-energy demand scenarios. Currently, strategies such as reagent activation and template methods are often used to manipulate the structure within hard carbon materials, introducing a large number of pore structures that can serve as additional sodium storage sites to increase the specific capacity. However, the use of activation reagents often produces other environmentally unfavorable byproducts, and additional acid or base reagents are required to remove the template. Furthermore, the hard carbon materials obtained by such methods generally have a large specific surface area and severe polarization, resulting in a continuous loss of active sodium and the precipitation of sodium metal in the full cell. This reduces the coulombic efficiency, specific capacity, and battery safety of sodium-ion batteries, limiting the commercialization of SIBs. Summary of the Invention

[0004] The present invention provides a method for preparing a porous hard carbon material and its application in sodium ion batteries. The material has a porous structure (<1 nm) and a small specific surface area. It constructs a thin and strong SEI membrane, inhibits the irreversible decomposition of the electrolyte, obtains a relatively ideal first-cycle coulombic efficiency, and greatly improves the specific capacity of the hard carbon material.

[0005] The technical solution of the present invention is to provide a method for preparing a porous hard carbon material, comprising the following steps: S1. Using sucrose as a carbon source, preparing a sucrose solution, subjecting it to a hydrothermal reaction treatment, and then filtering and separating to obtain a hard carbon precursor; S2. Dissolve the zinc salt in distilled water to prepare a solution, add the hard carbon precursor obtained in S1 to the zinc salt solution, then add anhydrous ethanol, mix and stir at room temperature for 4-6 hours, and finally heat to evaporate the solvent and grind thoroughly to obtain a uniform mixture containing the zinc salt; S3. Place the material obtained in S2 in a furnace, and under a protective atmosphere, first heat it to 600-800°C for preliminary carbonization, then heat it to 1100-1500°C for high-temperature carbonization, then cool it down, take it out, grind it evenly, and you have it.

[0006] Optionally, the concentration of the sucrose solution in S1 is 1-2 mol / L, the hydrothermal reaction temperature is 180-200° C., and the time is 18-20 h.

[0007] Optionally, the zinc salt in S2 is zinc chloride, zinc acetate and / or zinc gluconate.

[0008] Optionally, the mass ratio of the zinc salt in S2 to the hard carbon precursor in S1 is 0.05~2:1.

[0009] Optionally, during the initial carbonization in S3, the heating rate is 5°C / min, and the temperature is raised to 600-800°C and then kept at this temperature for 1-2 hours.

[0010] Optionally, during the high temperature carbonization in S3, the heating rate is 1°C / min, and the temperature is raised to 1100-1500°C and then kept at this temperature for 1-3 hours.

[0011] Optionally, the cooling rate in S3 is 5°C / min, down to room temperature.

[0012] The present invention relates to a porous hard carbon material obtained by the preparation method.

[0013] The present invention relates to the application of the porous hard carbon material in the negative electrode material of sodium ion batteries.

[0014] The present invention relates to the application of the porous hard carbon material in sodium ion batteries.

[0015] The present invention has the following beneficial effects: The present invention uses sucrose as the raw material of the hard carbon material, first performs a hydrothermal treatment on the sucrose to prepare a hard carbon precursor, then adds the hard carbon precursor to a prepared zinc salt aqueous solution and mixes them to ensure that the zinc salt fully enters the hard carbon precursor structure in the form of a liquid phase, and then adds a certain amount of anhydrous ethanol to the mixture to promote the rapid precipitation of the zinc salt in the form of solid phase crystals, so that the zinc salt is uniformly attached to the hard carbon precursor structure. The zinc salt self-decomposes during the high-temperature carbonization process and undergoes a complex reaction with the hard carbon precursor to produce a large number of pore structures, which provide additional sites for the storage of sodium ions and improve the specific capacity of the hard carbon material.

[0016] The preparation method provided by this invention is simple and convenient. It uses a zinc salt as a self-sacrificial template. During heat treatment, it self-decomposes, producing CO and CO₂ gases that facilitate the formation of open pores. The decomposed zinc oxide reacts with the carbon-based hard carbon precursor (ZnO + C = Zn↑ + CO↑), releasing the zinc element in gaseous form and producing a large number of closed pores, thereby achieving the goal of constructing a high-pore structure. Compared with traditional template methods, the process is simplified; there is no need to subsequently remove the template by adding acid or base. The resulting hard carbon material has a large number of open and closed pores, providing additional sites for sodium ion storage, thereby increasing the specific capacity of the hard carbon material.

[0017] The material provided by the present invention is used as a negative electrode material for sodium ion batteries. Since the hard carbon material is porous (<1 nm) and has a small specific surface area, it can construct a thin and strong SEI membrane, inhibit the irreversible decomposition of the electrolyte, and is beneficial to the improvement of the first-cycle coulombic efficiency of the hard carbon material. At the same time, the dense pores provide abundant sodium storage sites, greatly improving the specific capacity of the hard carbon material. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 These are SEM images of the porous hard carbon materials obtained in Comparative Example 4, Comparative Example 5, and Examples 4 to 7.

[0019] Figure 2 TEM images of the porous hard carbon materials in Example 6 and Example 7.

[0020] Figure 3 Pore ​​size distribution diagrams for the porous hard carbon materials in Example 7, Example 6, and Comparative Example 2, and the hard carbon precursor prepared by the method of Example 1. The addition of zinc salt facilitates the generation of a large number of pores, and the amount selected directly affects the number of pores and the pore size distribution.

[0021] Figure 4 First-cycle charge-discharge curves for the porous hard carbon materials of Example 7, Example 6, and Comparative Example 2, and the hard carbon precursor prepared using the method of Example 1. The amount of zinc salt directly affects the formation of the internal pore structure of the hard carbon material, which in turn affects the electrochemical performance and leads to differences in charge-discharge capacity. DETAILED DESCRIPTION

[0022] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials used in the following examples are commercially available products unless otherwise specified.

[0023] Example 1 This embodiment relates to a porous hard carbon material, the preparation method of which includes the following steps: S1: Preparation of hard carbon precursor: Prepare 1 mol / L sucrose solution, place the sucrose solution in a 100 ml hydrothermal reactor, then place the reactor in an oven for hydrothermal treatment at 180°C for 20 h, and then filter and dry to obtain a hard carbon precursor; S2. Dissolve 0.005 mol of zinc chloride in 10 ml of distilled water, weigh 2.5 g of a hard carbon precursor, mix the weighed hard carbon precursor into the zinc chloride solution, and ultrasonically mix; add 20 ml of anhydrous ethanol to the mixture, and ultrasonically mix; then magnetically stir the mixture at room temperature for 4 hours, and then dry it in an oven at a constant temperature of 80°C until the water and ethanol are evaporated and the zinc salt is completely and evenly precipitated in the hard carbon precursor structure to obtain a mixture, and grind the solid phase mixture uniformly in a mortar; S3: Place the dried mixed material in a low-temperature tubular furnace and heat it up in an argon atmosphere at a heating rate of 5°C / min. Heat it to 600°C and treat it for 1 hour. Heat it from room temperature to 800°C at a rate of 5°C / min in an argon atmosphere, then heat it from 800°C to 1300°C at a rate of 1°C / min, keep it at 1300°C for 1 hour, then cool it to room temperature at a rate of 5°C / min and take it out to obtain a porous hard carbon material.

[0024] Example 2 Compared with Example 1, the difference is that the added amount of zinc chloride is 0.008 mol.

[0025] Example 3 Compared with Example 1, the difference is that the added amount of zinc chloride is 0.01 mol.

[0026] Example 4 Compared with Example 1, the difference is that zinc chloride is replaced by 0.005 mol of zinc gluconate.

[0027] Example 5 Compared with Example 4, the difference is that the added amount of zinc gluconate is 0.008 mol.

[0028] Example 6 Compared with Example 4, the difference is that the added amount of zinc gluconate is 0.01 mol.

[0029] Example 7 Compared with Example 4, the difference is that the added amount of zinc gluconate is 0.012 mol.

[0030] Example 8 Compared with Example 1, the difference is that zinc chloride is replaced by 0.008 mol of zinc acetate.

[0031] Example 9 Compared with Example 8, the difference is that the added amount of zinc acetate is 0.01 mol.

[0032] Comparative Example 1 Compared with Example 1, the difference is that the added amount of zinc chloride is 0.001 mol.

[0033] Comparative Example 2 Compared with Example 1, the difference is that the added amount of zinc chloride is 0.002 mol.

[0034] Comparative Example 3 Compared with Example 1, the difference is that the added amount of zinc chloride is 0.012 mol.

[0035] Comparative Example 4 Compared with Example 4, the difference is that the zinc gluconate is 0.001 mol.

[0036] Comparative Example 5 Compared with Example 4, the difference is that the zinc gluconate is 0.002 mol.

[0037] Comparative Example 6 Compared with Example 8, the difference is that the zinc acetate is 0.001 mol.

[0038] Comparative Example 7 Compared with Example 8, the difference is that the zinc acetate is 0.002 mol.

[0039] Comparative Example 8 Compared with Example 8, the difference is that the zinc acetate is 0.005 mol.

[0040] Comparative Example 9 Compared with Example 8, the difference is that the zinc acetate is 0.012 mol.

[0041] Comparative Example 10 Same as Example 1, except that zinc chloride solution was not added to S2, but 10 ml of distilled water was directly used instead.

[0042] Comparative Example 11 Same as Example 6, except that the amount of distilled water added is 20 mL, and the amount of ethanol added is 10 mL.

[0043] Comparative Example 12 Same as Example 6, except that the zinc gluconate in S2 was dispersed with 20 ml of anhydrous ethanol, and then 10 mL of distilled water was added and ultrasonically mixed.

[0044] Comparative Example 13 Same as Example 6, except that the zinc gluconate in S2 is dissolved in 30 ml of distilled water, and no anhydrous ethanol is subsequently added.

[0045] Comparative Example 14 Same as Example 6, except that in S2, zinc gluconate is dispersed with 30 ml of anhydrous ethanol, and no distilled water is added.

[0046] Comparative Example 15 As in Example 6, 0.01 mol of zinc gluconate was added to the sucrose solution in S1 for hydrothermal reaction, S2 was omitted, and S3 was directly performed.

[0047] The hard carbon materials obtained in the above examples and comparative examples were used as active materials and ground with sodium alginate (a binder) and acetylene black (a conductive agent) in a mass ratio of 8:1:1. Water was added as a solvent to produce a uniform battery slurry. Electrode sheets with a diameter of 12 mm were obtained through coating, drying, and cutting. CR2023 button cells were assembled in a glove box using sodium metal as the counter electrode, 1 mol / L NaClO4 + G2 as the electrolyte, and a PP / PE / PP three-layer separator. These button cells were subjected to constant current charge and discharge tests at a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 2-0.001 V. Specific test results are shown in Table 1. Table 1 also lists the specific surface areas of the hard carbon materials obtained in the examples and comparative examples.

[0048] Table 1

[0049] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the appended claims.

Claims

1. A method for preparing a porous hard carbon material, characterized in that: The following steps are involved: S1. Using sucrose as a carbon source, preparing a sucrose solution, subjecting it to a hydrothermal reaction treatment, and then filtering and separating to obtain a hard carbon precursor; S2. Dissolve the zinc salt in distilled water to prepare a solution, add the hard carbon precursor obtained in S1 to the zinc salt solution, then add anhydrous ethanol, mix and stir at room temperature for 4-6 hours, and finally heat to evaporate the solvent and grind thoroughly to obtain a uniform mixture containing the zinc salt; S3. Place the material obtained in S2 in a furnace, and under a protective atmosphere, first heat it to 600-800°C for preliminary carbonization, then heat it to 1100-1500°C for high-temperature carbonization, then cool it down, take it out, grind it evenly, and you have it.

2. The preparation method according to claim 1, wherein: The concentration of the sucrose solution in S1 is 1-2 mol / L, the hydrothermal reaction temperature is 180-200° C., and the reaction time is 18-20 h.

3. The preparation method according to claim 1, wherein: The zinc salt in S2 is zinc chloride, zinc acetate and / or zinc gluconate.

4. The preparation method according to claim 1, wherein: The mass ratio of the zinc salt in S2 to the hard carbon precursor in S1 is 0.05~2:

1.

5. The preparation method according to claim 1, wherein: During the initial carbonization in S3, the heating rate is 5°C / min, and the temperature is raised to 600-800°C and then kept at this temperature for 1-2 hours.

6. The preparation method according to claim 1, wherein: During the high temperature carbonization in S3, the heating rate is 1°C / min, and the temperature is raised to 1100-1500°C and then kept at this temperature for 1-3 hours.

7. The preparation method according to claim 1, wherein: In S3, the cooling rate is 5°C / min, down to room temperature.

8. The porous hard carbon material obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the porous hard carbon material according to claim 8 in a negative electrode material for sodium ion batteries.

10. Use of the porous hard carbon material according to claim 8 in sodium ion batteries.

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