Preparation method of closed-pore-adjusted biomass hard carbon and application of closed-pore-adjusted biomass hard carbon in negative electrode of sodium-ion battery

Abstract

The invention belongs to the technical field of electrode materials, and particularly relates to a preparation method of biomass hard carbon with closed pore adjustment and application of the biomass hard carbon in a sodium-ion battery negative electrode. A biomass precursor is subjected to a high-temperature stirring reaction in a deep eutectic solvent, a large amount of amorphous lignin and hemicellulose are removed, and an intermediate rich in crystalline cellulose is obtained; pre-oxidizing the obtained crystalline cellulose intermediate in an air atmosphere to obtain a pre-oxidized intermediate; the pre-oxidized intermediate is subjected to high-temperature carbonization in an inert atmosphere to obtain closed-pore-adjusted biomass hard carbon, and the biomass hard carbon is used as an active component in the negative electrode of the sodium ion battery, so that the first charge-discharge efficiency is remarkably improved, and the capacity retention capacity under a large-current charge-discharge condition is also remarkably improved; and the technical bottlenecks of insufficient initial coulombic efficiency and poor rate capability of the traditional hard carbon negative electrode material are effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and more specifically relates to a method for preparing closed-pore regulated biomass hard carbon and its application in the negative electrode of a sodium ion battery. Background Art

[0002] With the rapid development of renewable energy and energy storage technologies, sodium-ion batteries (SIBs) have become an important supplement to lithium-ion batteries due to their abundant resources and low cost. Hard carbon materials, as core candidate materials for sodium-ion battery anodes, have attracted much attention due to their high specific capacity, excellent cycling stability, and low sodium storage potential. However, the practical application of hard carbon still faces bottlenecks: low initial coulombic efficiency, insufficient reversible capacity, poor rate performance, and cycling stability. The root cause is closely related to the closed-pore structure within hard carbon materials.

[0003] At present, the precursor materials for preparing hard carbon include biomass, polymers and fossil fuels. Biomass precursors have attracted widespread attention due to their advantages of low cost and high environmental compatibility, and the closed-pore structure of hard carbon derived from them can be controlled by adjusting the content of crystalline cellulose and amorphous components (hemicellulose and lignin). Among them, highly crystalline cellulose is conducive to the production of rich closed-pore structures during the carbonization process, while amorphous components will hinder the development of closed pores. The main method for regulating biomass components is to use strong acids, strong bases or oxidants to etch amorphous components, but such methods are highly corrosive, easily destroy the integrity of crystalline cellulose, and cause environmental pollution.

[0004] How to significantly improve the first coulombic efficiency, reversible capacity, rate performance and cycle stability of hard carbon materials to meet the commercialization needs of sodium-ion batteries has become a difficult problem that technicians in this field urgently need to overcome. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing closed-pore regulated biomass hard carbon and its application in the negative electrode of sodium ion battery, by selecting a suitable biomass precursor to synthesize hard carbon material, and pre-treating it with an alcohol-based DES system to optimize the closed-pore structure and increase the Na + The reversible intercalation and deintercalation ability is used to solve the problems existing in the above-mentioned existing technologies, and to achieve a significant improvement in the coulombic efficiency, reversible capacity, rate performance and cycle stability of hard carbon materials for sodium ion batteries for the first time to meet commercial needs.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing closed-pore regulated biomass hard carbon, comprising the following steps:

[0008] The biomass precursor is mixed with a deep eutectic solvent and reacted with stirring at high temperature to obtain an intermediate rich in crystalline cellulose;

[0009] The crystalline cellulose-rich intermediate is pre-oxidized and carbonized to obtain the biomass hard carbon.

[0010] In the preparation method of the present invention, a biomass precursor is subjected to a high-temperature stirring reaction in a deep eutectic solvent to remove a large amount of amorphous lignin and hemicellulose to obtain an intermediate rich in crystalline cellulose; the obtained crystalline cellulose intermediate is pre-oxidized in an air atmosphere to obtain a pre-oxidized intermediate; and the pre-oxidized intermediate is carbonized at a high temperature under an inert atmosphere to obtain closed-pore regulated biomass hard carbon.

[0011] Furthermore, the biomass precursor is a biomass containing crystalline cellulose, hemicellulose and lignin.

[0012] Optionally, the biomass precursor includes at least one of bamboo, corn stalks and coconut shells.

[0013] Furthermore, the deep eutectic solvent consists of choline chloride, ethylene glycol and sulfuric acid.

[0014] Optionally, the molar ratio of choline chloride to ethylene glycol is 1:1-3.

[0015] Preferably, the molar ratio of choline chloride to ethylene glycol is 1:2.

[0016] Optionally, the mass of the sulfuric acid is 0.5-2% of the sum of the masses of the choline chloride and the ethylene glycol.

[0017] Preferably, the mass of the sulfuric acid is 1% of the sum of the masses of the choline chloride and ethylene glycol.

[0018] The molar ratio of choline chloride to ethylene glycol typically ranges from 1:1 to 1:3. A 1:1 ratio results in a relatively high solvent viscosity, which may slow penetration into bamboo, but enhances its ability to dissolve components like lignin. A 1:3 ratio, on the other hand, results in improved fluidity and quicker access to the bamboo material, but a slightly weaker ability to dissolve lignin and other substances. Therefore, a 1:2 ratio is preferred. Sulfuric acid acts as a catalyst, increasing the removal rate of hemicellulose and lignin. However, low levels of sulfuric acid weaken the catalytic ability, while high levels corrode crystalline cellulose, limiting the range to 0.5-2%.

[0019] Deep eutectic solvents (DES) are formed by hydrogen bond donors and hydrogen bond acceptors through intermolecular interactions and have the advantages of low toxicity, biodegradability, low cost, and strong designability. The present invention defines deep eutectic solvents based on alcohol systems. During biomass pretreatment, their mild reaction conditions and high solubility can selectively decompose hemicellulose or lignin while retaining the crystalline cellulose skeleton. In addition, the coordination effect of metal ions in DES induces the generation of edge defect sites during carbonization, which increases the Na + reversible embedding and de-embedding ability.

[0020] Furthermore, the mass ratio of the biomass precursor to the deep eutectic solvent is 1:5-20.

[0021] In the present invention, the mass ratio of the biomass precursor to the deep eutectic solvent is 1:5-20. The solvent is sufficient and the mass transfer resistance is small. It can quickly penetrate the cell wall of bamboo, accelerate the hydrolysis of hemicellulose and the removal of lignin. When the solvent is relatively insufficient, it will lead to limited mass transfer, and the processing time needs to be extended or the temperature needs to be increased to compensate.

[0022] Furthermore, the temperature of the high-temperature stirring reaction is 50-200° C., the stirring rate is 200-600 rpm, and the time is 2-10 h.

[0023] Furthermore, the pre-oxidation temperature is 200-500° C., the heating rate is 1-5° C. / min, and the time is 2-10 h.

[0024] Furthermore, the carbonization temperature is 1100-1500° C., the heating rate is 5-10° C. / min, the time is 2-4 hours, and the atmosphere is an inert atmosphere.

[0025] Optionally, the inert atmosphere is a nitrogen atmosphere.

[0026] The present invention optimizes the closed-pore structure by using an alcohol-based deep eutectic system to increase the Na + The optimized material effectively solves the problems of low first coulombic efficiency and rate performance of hard carbon negative electrodes in existing technologies.

[0027] The second technical solution of the present invention is to provide a closed-pore regulated biomass hard carbon, which is prepared by the above-mentioned preparation method.

[0028] The third technical solution of the present invention is to provide an application of the above-mentioned closed-pore regulated biomass hard carbon in the preparation of sodium ion batteries.

[0029] The fourth technical solution of the present invention is to provide a sodium ion battery electrode, wherein the sodium ion battery electrode uses the above-mentioned closed-pore regulated biomass hard carbon as an active ingredient.

[0030] The fifth technical solution of the present invention: provides a sodium ion battery, using the above-mentioned sodium ion battery electrode as the negative electrode.

[0031] The present invention discloses the following technical effects:

[0032] The biomass-based hard carbon material prepared by the present invention is used in sodium ion batteries, and exhibits high reversible specific capacity, high initial coulombic efficiency, high rate performance, and good cycle stability. Compared with traditional hard carbon negative electrode materials, it not only achieves a significant improvement in the initial charge and discharge efficiency, but also significantly improves the capacity retention ability under high current charge and discharge conditions, effectively solving the technical bottlenecks of insufficient initial coulombic efficiency and poor rate performance of traditional hard carbon negative electrode materials.

[0033] The raw materials for preparing biomass-based hard carbon materials in the present invention have the advantages of both easy accessibility of renewable resources and the economic efficiency of large-scale production, providing a feasible path for the development of low-cost, high-performance energy storage devices.

[0034] The present invention cuts and dissolves the hemicellulose branch and lignin cross-linked network through the hydrogen bonding effect of choline chloride / ethylene glycol / sulfuric acid ternary deep eutectic solvent (CEH-DES), retains the crystalline cellulose, and thus increases the concentration of closed pores during carbonization. The coordination effect of metal ions in CEH-DES induces the generation of edge defect sites during carbonization, thereby increasing the Na + The reversible intercalation and deintercalation ability of the ion can significantly improve the ion diffusion efficiency and structural stability in the negative electrode of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 This is the SEM image of CEH-HC.

[0037] Figure 2 TEM image of CEH-HC.

[0038] Figure 3 XRD patterns of CEH-HC and MB-HC.

[0039] Figure 4 XPS patterns of CEH-HC and MB-HC.

[0040] Figure 5 Raman spectra of CEH-HC and MB-HC.

[0041] Figure 6 The first cycle charge and discharge curves of CEH-HC and MB-HC.

[0042] Figure 7 Figure 2 is the rate performance diagram of CEH-HC and MB-HC.

[0043] Figure 8 Figure 2 is the cycle performance diagram of CEH-HC and MB-HC. DETAILED DESCRIPTION

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0046] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0047] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0048] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0049] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0050] The raw materials and reagents used in the specific embodiments of the present invention are all commercially available products.

[0051] The biomass precursor in the present invention is biomass materials such as bamboo, straw and coconut shell containing crystalline cellulose, hemicellulose and lignin. The following specific embodiments are described using bamboo as an exemplary biomass material, which does not limit the biomass material.

[0052] In the choline chloride / ethylene glycol / sulfuric acid ternary deep eutectic solvent (CEH-DES) used in a specific embodiment of the present invention, the molar ratio of choline chloride to ethylene glycol is 1:2, and the amount of sulfuric acid added is 1% of the sum of the masses of choline chloride and ethylene glycol.

[0053] Example 1

[0054] The preparation steps of closed-pore regulated biomass hard carbon include:

[0055] S1. Moso bamboo (MB) is used as a biomass raw material, crushed, sieved, washed and dried in a grinder to obtain a biomass precursor;

[0056] S2. The biomass precursor was mixed with choline chloride / ethylene glycol / sulfuric acid ternary deep eutectic solvent (CEH-DES) at a mass ratio of 1:8.5, and the mixture was in an oil bath at 120°C for 4 hours with continuous stirring (400 rpm). After the reaction, the mixture was centrifuged and washed with ethanol and water to obtain an intermediate rich in crystalline cellulose;

[0057] S3, pre-oxidizing the crystalline cellulose-rich intermediate in an air atmosphere to obtain a pre-oxidized sample, wherein the pre-oxidation temperature is 300° C., the time is 10 h, and the heating rate is 2° C. / min;

[0058] S4. Under nitrogen atmosphere, the pre-oxidized sample was subjected to high-temperature carbonization treatment to obtain closed-pore regulated biomass hard carbon, which was recorded as CEH-HC. The high-temperature carbonization temperature was 1300°C, the holding time was 2h, and the heating rate was 5°C / min.

[0059] Figure 1 The SEM image of CEH-HC shows that the morphology of CEH-HC is irregular blocks.

[0060] Figure 2 TEM image of CEH-HC. As can be seen from the figure, CEH-HC has a large number of closed-pore structures and many edge defect sites, which can increase the Na + reversible embedding and de-embedding ability.

[0061] Example 2

[0062] Compared with Example 1, the difference is that the reaction condition of step S2 is oil bath at 80° C. for 2 h.

[0063] Example 3

[0064] Compared with Example 1, the difference is that the reaction condition of step S2 is oil bath at 160° C. for 2 h.

[0065] Example 4

[0066] Compared with Example 1, the difference is that the reaction condition of step S2 is oil bath at 120° C. for 2 h.

[0067] Example 5

[0068] Compared with Example 1, the difference is that the reaction condition of step S2 is oil bath at 120° C. for 6 h.

[0069] Comparative Example 1

[0070] Compared with Example 1, the only difference is that step S2 is omitted, and the biomass precursor is directly pre-oxidized. The final product is recorded as MB-HC. The steps include:

[0071] S1. Moso bamboo (MB) is used as a biomass raw material, crushed, sieved, washed and dried in a grinder to obtain a biomass precursor;

[0072] S2. Pre-oxidizing the biomass precursor in an air atmosphere to obtain a pre-oxidized sample, wherein the pre-oxidation temperature is 300° C., the time is 10 h, and the heating rate is 2° C. / min;

[0073] S3. Under nitrogen atmosphere, the pre-oxidized sample was subjected to high-temperature carbonization treatment to obtain biomass hard carbon, which was recorded as MB-HC. The high-temperature carbonization temperature was 1300°C, the holding time was 2h, and the heating rate was 5°C / min.

[0074] Test example

[0075] Figure 3 The XRD patterns of CEH-HC and MB-HC are shown in the figure. As can be seen from the figure, CEH-DES treatment can increase the interlayer spacing of its derived hard carbon, which is beneficial to Na + Insertion and disembedding.

[0076] Figure 4 The XPS images of CEH-HC and MB-HC show that CEH-DES treatment can increase the surface O content of its derived hard carbon, which is beneficial to enhancing its reversible capacity.

[0077] Figure 5 The Raman spectra of CEH-HC and MB-HC are shown in Figure 2. As can be seen from the figure, CEH-DES treatment can increase the defect concentration of the derived hard carbon, which is beneficial to accelerate the sodium ion diffusion rate and thus improve the rate performance.

[0078] comprehensive Figure 3-Figure 5, it can be seen that the appropriate degree of CEH-DES treatment optimizes the closed-pore structure, interlayer spacing, surface functional groups and defect concentration of hard carbon, and improves the sodium storage performance.

[0079] The electrochemical performance of the CEH-HC prepared in Example 1 and the MB-HC prepared in Comparative Example 1 were tested in half cells.

[0080] Dissolve 90 mg of CEH-HC or MB-HC and 10 mg of sodium alginate in deionized water and stir continuously to form a uniform electrode slurry. Use the 150 μm thickness side of a four-sided applicator to evenly apply the resulting electrode slurry to an aluminum foil current collector. After drying, the slurry is punched on a tablet press to obtain a sodium-ion battery hard carbon negative electrode sheet with a diameter of 11 mm.

[0081] The above-mentioned sodium ion battery hard carbon negative electrode sheet was used as the working electrode for the preparation of CR2032 button cells, the metallic sodium sheet was used as the counter electrode, a commercially available sodium ion electrolyte (1M NaPF6 in DIGLYME = 100 Vol%) was used, and the diaphragm was selected as GF / D glass fiber membrane, and assembled in an argon-protected glove box.

[0082] Figure 6 The first cycle charge-discharge curves of CEH-HC and MB-HC are shown. As can be seen from the figure, CEH-HC has an initial reversible specific capacity of 348.6 mAh / g and a high initial coulombic efficiency of 88.5% at a current density of 0.1C (1C = 300 mA / g). This combination of high initial coulombic efficiency and high reversible specific capacity surpasses most biomass hard carbon anodes reported in existing technologies.

[0083] Figure 7 Figure 2 shows the rate performance of CEH-HC and MB-HC. As shown in the figure, CEH-HC also has excellent rate performance, with a specific capacity of 201.4 mAh / g at a high current density of 10C (10C = 3000 mA / g).

[0084] Figure 8 The figure shows the cycling performance of CEH-HC and MB-HC. As can be seen from the figure, CEH-HC also has excellent cycling stability. At 1C, the capacity retention rate is still above 90% after 300 cycles.

[0085] The materials obtained in Examples 1-3 and Comparative Example 1 were used as negative electrode materials to conduct electrochemical performance tests. The results are shown in Table 1.

[0086] Table 1

[0087]

[0088] As can be seen from Table 1, the use of the closed-pore regulated biomass hard carbon material prepared by the present invention as the negative electrode of the sodium ion battery can obtain high reversible specific capacity, high first coulombic efficiency, excellent rate performance and cycle stability.

[0089] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0090] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing closed-cell regulated biomass hard carbon, characterized in that the steps include: The biomass precursor is mixed with a deep eutectic solvent and reacted with stirring at high temperature to obtain an intermediate rich in crystalline cellulose; The crystalline cellulose-rich intermediate is pre-oxidized and carbonized to obtain the biomass hard carbon; The deep eutectic solvent consists of choline chloride, ethylene glycol and sulfuric acid.

2. The preparation method according to claim 1, wherein The biomass precursor is biomass containing crystalline cellulose, hemicellulose and lignin.

3. The preparation method according to claim 1, wherein The molar ratio of choline chloride to ethylene glycol is 1:1-3; and / or the mass of the sulfuric acid is 0.5-2% of the sum of the masses of choline chloride and ethylene glycol; and / or the mass ratio of the biomass precursor to the deep eutectic solvent is 1:5-20.

4. The preparation method according to claim 1, wherein The high temperature stirring reaction temperature is 50-200° C., the stirring rate is 200-600 rpm, and the time is 2-10 h.

5. The preparation method according to claim 1, wherein The pre-oxidation temperature is 200-500° C., the heating rate is 1-5° C. / min, and the time is 2-10 hours.

6. The preparation method according to claim 1, wherein The carbonization temperature is 1100-1500° C., the heating rate is 5-10° C. / min, the time is 2-4 hours, and the atmosphere is an inert atmosphere.

7. A closed-cell regulated biomass hard carbon, characterized in that: The closed-pore regulated biomass hard carbon is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the closed-pore regulated biomass hard carbon according to claim 7 in the preparation of sodium ion batteries.

9. A sodium ion battery electrode, characterized in that The sodium ion battery electrode uses the closed-pore regulated biomass hard carbon according to claim 7 as an active ingredient.

10. A sodium ion battery, characterized in that: The sodium ion battery electrode according to claim 9 is used as the negative electrode.

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