A preparation method of esterified modified starch-derived hard carbon anode material and its application in sodium-ion batteries

Abstract

This invention discloses a method for preparing hard carbon anode materials derived from esterified modified starch and their application in sodium-ion batteries, belonging to the field of sodium-ion battery anode technology. The invention first performs a one-step hydrothermal pretreatment on inexpensive cross-linked-esterified composite modified starch, followed by a one-step high-temperature carbonization to obtain spherical hard carbon anode materials. The compact packing density formed by the spherical morphology facilitates the shortening of ion and electron diffusion paths. Because acetyl groups replace some hydroxyl groups within the starch molecule, the amylose content is reduced, enhancing the structural stability of the starch and improving sodium storage performance. Furthermore, the hard carbon anode sheet is pre-sodium-treated using liquid-phase pre-sodiumization technology, improving the battery's initial efficiency and promoting long-cycle stability. This preparation process is simple, requires basic equipment, has good repeatability, requires no extensive post-processing, and is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery anode technology, specifically relating to the preparation of biomass-derived anode materials, particularly Na... + High-capacity, highly reversible storage. Background Technology

[0002] Sodium-ion batteries, due to their abundant sodium resources and relatively low cost, hold promise for large-scale application in the future. Hard carbon, with its high theoretical capacity and good stability, has become the primary anode material in sodium-ion batteries. Biomass, as a key raw material for hard carbon production, boasts extremely wide availability and is green and renewable. Therefore, through the scientific and rational design of the microstructure of biomass, the storage and diffusion of sodium ions can be effectively promoted, thereby significantly improving the electrochemical performance of sodium-ion batteries and laying a solid foundation for their further development and widespread application. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a hard carbon anode material derived from esterified modified starch and its application in sodium-ion batteries. Compared with ordinary starch, esterified modified starch undergoes chemical structural modification, altering its molecular skeleton. The molecular chains may be cleaved, rearranged, or have substituents introduced. The disruption of intermolecular hydrogen bonds allows water molecules to enter, making the starch more swellable in aqueous solutions and significantly enhancing its solubility and dispersibility. High-temperature and high-pressure dehydration of the molecular chains initially forms a carbonized precursor rich in porous structures. Subsequently, a one-step high-temperature carbonization of the precursor yields a hard carbon anode material rich in closed pores, thus improving sodium-ion storage performance. However, due to internal defects in the hard carbon anode material, sodium ion storage inevitably deteriorates during the first discharge. + Irreversible consumption. Therefore, the use of liquid-phase pre-sodiuming technology to effectively replenish sodium in the negative electrode sheet greatly improves the reversibility of sodium storage in the hard carbon negative electrode, achieving a long cycle life for sodium-ion batteries.

[0004] The technical solution of this invention:

[0005] The preparation method of starch-based hard carbon anode material includes the following preparation steps:

[0006] (1) Preparation of carbonized precursor: Esterified modified starch was dispersed in a solvent, transferred to a high-temperature and high-pressure reactor, and then kept in a drying oven at 180-220℃ for 8-12 hours; after the reaction, the product was washed, filtered and freeze-dried to obtain the carbonized precursor.

[0007] (2) Preparation of hard carbon anode material: After grinding the carbonization precursor, it is transferred to a high-temperature tube furnace and the reaction temperature is 1000-1500℃ for 2-3 hours. After carbonization, the sample is ground finely to finally obtain esterified modified starch-derived hard carbon anode material.

[0008] (3) Preparation of hard carbon negative electrode sheet: The hard carbon negative electrode material obtained in (2), conductive carbon black and binder are mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 10-15 min to obtain a uniform electrode slurry. The slurry is then coated onto an aluminum foil current collector and transferred to a 100-120℃ forced-air drying oven to dry for 10-12 h to obtain a hard carbon negative electrode sheet.

[0009] (4) Pre-sodium treatment of negative electrode: The prepared electrode is immersed in PAHs-Na-ether pre-sodium treatment agent for pre-sodium treatment for 10-20 min; the working electrode after immersion is rinsed clean with ether solvent and placed in a vacuum oven at 70℃ until completely dry to obtain pre-sodium hard carbon negative electrode.

[0010] Further, in step (1), the esterified modified starch is one of acetylated distarch phosphate, maleic acid esterified sulfosuccinate starch, or octenyl succinate starch; the solvent is deionized water, and the mass fraction of the mixture is 4-6 wt.%; the filling amount of the hydrothermal reactor is 60-70 vol.%.

[0011] Furthermore, in step (2), the heating rate is 2–5 °C / min.

[0012] Furthermore, in step (3), the conductive carbon black is one or two of SuperP, CNT, carbon nanofibers, Ketjen black or acetylene black; the binder is one of sodium carboxymethyl cellulose or sodium alginate.

[0013] Furthermore, in step (4), the polycyclic aromatic hydrocarbons (PAHs) are either biphenyl monoethyl ketone or 4-methoxybiphenyl; the ether solvent is either ethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0014] This invention also provides the application of starch-based hard carbon anode materials in sodium-ion batteries, as follows:

[0015] Battery Assembly: A two-electrode system was assembled in a CR2032 coin cell using a pre-sodium-modified hard carbon negative electrode, a glass fiber separator, and metallic sodium. Electrochemical performance was then tested. 1M sodium hexafluorophosphate (NaPF6) dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC = 1, vol.%) was used as the electrolyte. The entire battery assembly process was conducted in an anhydrous and oxygen-free argon-filled glove box (water and oxygen content <0.01ppm).

[0016] Advantages and beneficial effects of the present invention:

[0017] Starch, as a raw material for biomass hard carbon anode materials, possesses advantages such as wide availability, green renewability, and low cost. However, during pyrolysis, a melting and foaming phenomenon occurs, causing structural collapse and making it difficult to achieve high capacity and highly reversible Na+. + Storage. This invention utilizes esterified modified starch with superior swelling properties. During precursor preparation, it induces and maintains a regular morphology while enriching the precursor with a porous structure. This allows for the formation of a hard carbon anode material rich in closed pores during subsequent carbonization, benefiting from pore shrinkage. Secondly, a simple liquid-phase pre-sodiumization technique is used to wet the hard carbon anode, achieving effective sodium replenishment and significantly improving the reversibility and cycle life of sodium storage. This preparation process is simplified, requires simple equipment, has excellent repeatability, requires minimal post-processing, and is suitable for large-scale production. Attached Figure Description

[0018] Figure 1 XRD patterns of different samples, including samples of modified starch directly carbonized and samples carbonized after hydrothermal pretreatment.

[0019] Figure 2 SEM images of different samples: (A) Morphology of modified starch directly carbonized; (B) Morphology of carbonized starch after hydrothermal pretreatment.

[0020] Figure 3 TEM images of carbonized samples after hydrothermal pretreatment: (A) High-resolution lattice; (B) Elemental analysis.

[0021] Figure 4 Raman spectra of different samples, including those directly carbonized from modified starch and those carbonized after hydrothermal pretreatment.

[0022] Figure 5 Cyclic performance comparison at a current density of 0.1 A / g: (A) Direct carbonized electrode performance; (B) Hydrothermal-carbonized hard carbon electrode.

[0023] Figure 6 Comparison of charge-discharge curves of hydrothermal-carbonized hard carbon anode before and after pre-sodiumization at a current density of 0.1 A / g: (A) Before pre-sodiumization; (B) After pre-sodiumization; (C) Comparison of constant current cycling performance. Detailed Implementation

[0024] Example 1

[0025] (1) Preparation of carbonized precursor: Acetylated distarch phosphate was dispersed in deionized water with a mass fraction of 4 wt.%; after dissolution, it was transferred to a high-temperature and high-pressure reactor with a filling amount of 65%; it was kept in a 200℃ drying oven for 12 h; after the reaction, the product was washed, filtered and freeze-dried to obtain the carbonized precursor.

[0026] (2) Preparation of hard carbon anode material: After grinding the carbonization precursor, it was transferred to a high-temperature tube furnace and the reaction temperature was 1300℃ for 2h. After carbonization, the sample was ground finely to finally obtain esterified modified starch-derived hard carbon anode material.

[0027] (3) Preparation of hard carbon negative electrode sheet: The hard carbon negative electrode material obtained in (2), Ketjen black and sodium alginate binder are mixed in a mass ratio of 8:1:1 in a homogenizer and processed for 15 min to obtain a uniform electrode slurry. The slurry is then coated onto an aluminum foil current collector and dried in a 100℃ forced-air drying oven for 10 h to obtain a hard carbon negative electrode sheet. The electrode sheet is then cut into circular electrode sheets with a diameter of 10 mm.

[0028] Example 2

[0029] (1) Preparation of carbonized precursor: Maleate sulfosuccinate starch was dispersed in deionized water with a mass fraction of 5 wt.%; after dissolution, it was transferred to a high-temperature and high-pressure reactor with a filling amount of 70%; it was kept in a blast drying oven at 210℃ for 10 h; after reaction, the product was washed, filtered and freeze-dried to obtain carbonized precursor.

[0030] (2) Preparation of hard carbon anode material: After grinding the carbonization precursor, it was transferred to a high-temperature tube furnace, the reaction temperature was 1200℃, and the holding time was 2.5h; after carbonization, the sample was ground finely to finally obtain esterified modified starch-derived hard carbon anode material.

[0031] (3) Preparation of hard carbon negative electrode sheet: The hard carbon negative electrode material obtained in (2), CNT and sodium alginate binder are mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 15 min to obtain a uniform electrode slurry. The slurry is then coated onto an aluminum foil current collector and dried in a 120℃ forced-air drying oven for 10 h to obtain a hard carbon negative electrode sheet. The electrode sheet is then cut into circular electrode sheets with a diameter of 10 mm.

[0032] Example 3

[0033] (1) Preparation of carbonized precursor: Octenyl succinate starch was dispersed in deionized water with a mass fraction of 5.5 wt.%; after dissolution, it was transferred to a high-temperature and high-pressure reactor with a filling amount of 60%; it was kept in a blast drying oven at 220℃ for 12 h; after the reaction, the product was washed, filtered and freeze-dried to obtain the carbonized precursor.

[0034] (2) Preparation of hard carbon anode material: After grinding the carbonization precursor, it was transferred to a high-temperature tube furnace and the reaction temperature was 1100℃ for 3h. After carbonization, the sample was ground finely to finally obtain esterified modified starch-derived hard carbon anode material.

[0035] (3) Preparation of hard carbon negative electrode sheet: The hard carbon negative electrode material obtained in (2), Super P and sodium carboxymethyl cellulose binder are mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 15 min to obtain a uniform electrode slurry. The slurry is then coated onto an aluminum foil current collector and dried in a 110℃ forced-air drying oven for 12 h to obtain a hard carbon negative electrode sheet. The electrode sheet is then cut into circular electrode sheets with a diameter of 10 mm.

[0036] Example 4

[0037] (4) Pre-sodium treatment of negative electrode: The electrode prepared in Examples 1-3 was immersed in 4-methoxybiphenyl-Na-tetraethylene glycol dimethyl ether pre-sodium agent for pre-sodium treatment for 15 min; the working electrode after immersion was rinsed with ethylene glycol dimethyl ether and placed in a vacuum oven at 70°C until completely dry to obtain a pre-sodium hard carbon negative electrode.

[0038] Battery Assembly: The dried negative electrode sheet was assembled with a 14mm diameter sodium metal counter electrode, and a 16mm diameter glass fiber separator to form a CR2032 coin cell. The electrolyte was 1M NaPF6 dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC = 1, vol.%). The entire battery assembly process was carried out in an anhydrous and oxygen-free argon-filled glove box (water and oxygen content <0.01ppm each). The voltage test range was 0.01–2.5V (vs. Na / Na). + ).

[0039] Example 5

[0040] (4) Pre-sodium treatment of negative electrode: The electrode prepared in Examples 1-3 was immersed in a solution of biphenyl monoethyl ketone-sodium-ethylene glycol dimethyl ether for pre-sodium treatment. The reaction time was 10 min. The working electrode was rinsed with ethylene glycol dimethyl ether and placed in a vacuum oven at 70°C until completely dry to obtain a pre-sodium hard carbon negative electrode.

[0041] Battery Assembly: The dried negative electrode sheet was assembled with a 14mm diameter sodium metal counter electrode, and a 16mm diameter glass fiber separator to form a CR2032 coin cell. The electrolyte was 1M NaPF6 dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC = 1, vol.%). The entire battery assembly process was carried out in an anhydrous and oxygen-free argon-filled glove box (water and oxygen content <0.01ppm each). The voltage test range was 0.01–2.5V (vs. Na / Na). + ).

[0042] Figure 1The image shows the XRD pattern of the sample. It can be seen that the disorder of the hard carbon material is reduced after hydrothermal pretreatment and carbonization, which is beneficial to the improvement of ICE and capacity.

[0043] Figure 2 The images show SEM images of the samples. It can be seen that (a) the modified starch carbonized directly exhibits an irregular, large blocky morphology, while (b) the carbonized sample after hydrothermal treatment exhibits a spherical structure, which is relatively dense and facilitates electron transport, forming a stable SEI film and thus improving electrochemical stability.

[0044] Figure 3 The image shows a TEM image of the sample after hydrothermal pretreatment and carbonization. It can be seen that (A) after hydrothermal pretreatment, the microstructure has a graphite-like structure with an interlayer spacing of 0.397 nm; (B) the elemental distribution shows a uniform distribution of carbon, oxygen, and phosphorus.

[0045] Figure 4 The image shows the Raman spectrum of the sample. It can be seen that direct carbonization of modified starch yields I0. D / I G It is 2.05; after hydrothermal treatment and recarbonization, I D / I G The value decreased to 1.72, indicating a reduction in internal defects and an increase in the degree of graphitization in the material.

[0046] Figure 5 Comparison of cycling performance at 0.1 A / g. (a) Direct carbonization of modified starch showed low sodium storage capacity and unstable coulombic efficiency; (b) Hydrothermal pretreatment significantly improved sodium storage capacity and increased the initial coulombic efficiency (ICE) from 22.5% to 71.58%, demonstrating that reducing material defects through hydrothermal treatment helps to improve sodium storage capacity and reversibility.

[0047] Figure 6 For performance comparison before and after pre-sodium treatment. At a current density of 0.1 A / g, (A) the hard carbon anode before pre-sodium treatment has a low charge-discharge plateau and an ICE of 71.58%; (B) after pre-sodium treatment, the ICE of the hard carbon anode significantly increases to 90%, and the charge-discharge plateau does not change significantly; (C) after 120 cycles, the capacity retention rate increases from 89% to 95%, indicating that the modified starch-derived hard carbon anode has better cycle stability after pre-sodium treatment and effectively reduces the irreversible capacity during the first discharge.

[0048] This invention provides examples of methods for preparing carbonized precursors, hard carbon anode materials, and hard carbon anode sheets through Examples 1-3. Examples 4 and 5 illustrate the pre-sodium treatment of the obtained anode sheets and the application of the pre-sodium-treated hard carbon anodes in sodium-ion batteries. Examples 1-5 do not cover all material, dosage ratios, and process conditions selected in the technical solution of this invention. Therefore, the above examples are merely for understanding the technical solution of this invention and are not intended to limit the scope of protection of this invention. Any obvious adjustments and modifications made to the technical solution of this invention that are part of the inventive concept, as understood by those skilled in the art, should also fall within the scope of protection of this invention.

Claims

1. A method for preparing esterified modified starch derived hard carbon negative electrode material, comprising the following steps: (1) Preparation of carbonized precursor: disperse esterified modified starch in solvent, transfer to high-temperature high-pressure hydrothermal kettle, dry in 180-220℃ blast drying oven, reaction time is 8-12 h; after reaction, the product is washed, filtered and freeze-dried to obtain carbonized precursor; (2) Preparation of hard carbon negative electrode material: grind the carbonized precursor, transfer to high-temperature tube furnace, reaction temperature is 1000-1500℃, holding time is 2-3 h; after carbonization, the sample is finely ground to obtain esterified modified starch derived hard carbon negative electrode material; (3) Preparation of hard carbon negative electrode sheet: mix the hard carbon negative electrode material, conductive carbon black and binder obtained in (2) in a mass ratio of 8:1:1 in a homogenizer, process for 10-15 min to obtain uniform electrode slurry, and coat it on an aluminum foil current collector, transfer to a 100-120℃ blast drying oven for 10-12 h to obtain a hard carbon negative electrode sheet; (4) Pre-sodiation treatment of negative electrode sheet: immerse the prepared electrode sheet in PAHs-Na-ether pre-sodiation agent for pre-sodiation, reaction time is 10-20 min; use ether solvent to rinse the soaked working electrode, and place it in a 70℃ vacuum oven until completely dry to obtain a pre-sodiated hard carbon negative electrode; In step (1), the esterified modified starch is one of acetylated distarch phosphate, maleated sulfobutane sulfonated starch or octenyl succinate starch; the solvent is deionized water, the mass fraction of the mixture is 4-6 wt.%; the filling volume of the hydrothermal reactor is 60-70 vol.%; In step (2), the heating rate is 2-5℃ / min.

2. The method for preparing the hard carbon negative electrode material derived from esterified modified starch according to claim 1, characterized in that, In step (3), the conductive carbon black is one or two of Super P, CNT, carbon nanofiber, Ketjen black or acetylene black; the binder is one of sodium carboxymethyl cellulose or sodium alginate.

3. The preparation method of the hard carbon anode material based on esterified modified starch according to claim 1, characterized in that, In step (4), the polycyclic aromatic hydrocarbon PAHs is one of biphenyl monoethyl ketone or 4-methoxy biphenyl; the ether solvent is one of ethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

4. Application of the esterified modified starch derived hard carbon negative electrode material prepared by the method of any one of claims 1-3 in a sodium ion battery.

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