Preparation method of carboxylate radical crosslinked starch derived hard carbon negative electrode material and application of carboxylate radical crosslinked starch derived hard carbon negative electrode material in sodium-ion battery
By cross-linking starch and combining low-temperature pretreatment and liquid phase pre-sodiumization technology, the problem of starch structure collapse during carbonization is solved, the thermal stability and sodium storage performance of hard carbon negative electrode materials are improved, and the cycle life of the battery is extended.
Patent Information
- Application Number
- CN202510053735.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-14
- Publication Date
- 2025-05-13
AI Technical Summary
During the carbonization process, the starch collapses due to melt foaming, which leads to low sodium storage capacity and poor reversibility of the electrode material.
Cross-linked starch is used and pretreated by low temperature to remove volatiles and avoid melt foaming, while liquid phase pre-sodiumization is used to improve initial Coulomb efficiency and battery cycle life.
Through cross-linking and low-temperature pretreatment, the thermal stability and carbon yield of hard carbon anode materials are improved, the sodium storage performance and reversibility are enhanced, and the recycling life of the battery is extended.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of sodium ion battery negative electrode, and specifically relates to the preparation and optimization of negative electrode materials, and in particular to the development and performance research of new biomass-derived hard carbon materials, which are adapted to the energy storage needs of environmental friendliness and sustainable development. Background Art
[0002] Sodium-ion batteries (SIBs) show significant application potential in the field of large-scale energy storage. Hard carbon (HC) has become the mainstream negative electrode material for SIBs due to its advantages such as low cost, stable structure and performance. Common hard carbon mainly comes from high-temperature carbonization products of biomass or polymers. In view of the increasing demand for green and sustainable electrode materials in the field of energy storage, biomass carbon sources have attracted much attention. However, biomass carbon sources are easily affected by raw materials from different sources and batches, and it is difficult to ensure the consistency of hard carbon products, which affects the electrochemical performance. Therefore, the development of low-cost, high-performance hard carbon negative electrode materials to break through key bottlenecks such as raw material consistency is beneficial to promote the practical application of SIBs. Summary of the invention
[0003] The purpose of the present invention is to solve the problem that starch collapses due to melting and foaming during the carbonization process, which leads to low sodium storage capacity and poor reversibility of electrode materials, and provides a liquid phase pre-sodiumization technology for pre-sodiumization of hard carbon negative electrodes to improve the initial coulombic efficiency (ICE). The microscopic spherical morphology of starch makes it an ideal precursor for preparing spherical hard carbon negative electrode materials. However, due to the poor thermal stability of its non-aromatic polysaccharide structure, direct pyrolysis of starch will lead to problems such as structural collapse and low carbon yield. In order to achieve controllable pyrolysis and prepare starch-carbon materials, starch is cross-linked to improve the stability of the carbon skeleton. Subsequently, a low-temperature pretreatment method is used in the carbonization process to fully release volatile substances such as tar and coke produced in the carbonization process, further remove volatile impurities, effectively prevent melt foaming during the carbonization process of corn starch, and improve carbon yield. A liquid phase pre-sodiumization strategy is selected to pre-sodiumize the best hard carbon negative electrode, improve the first effect, and extend the battery cycle life.
[0004] The technical solution of the present invention:
[0005] The preparation method of the cross-linked starch-derived hard carbon negative electrode material comprises the following preparation steps:
[0006] (1) Preparation of cross-linked starch precursor: dispersing a cross-linking agent and starch in a solvent, stirring evenly, adjusting the pH of the solution to 3-4 with sodium hydroxide, standing at room temperature, drying in an oven at 100-120° C. to remove moisture, grinding, and then placing in an oven for reaction to obtain a carbonized precursor;
[0007] (2) Preparation of cross-linked starch-derived hard carbon negative electrode material: The carbonized precursor is placed in a tube furnace and subjected to low-temperature treatment at 200-300°C for 9-12 hours under an inert gas atmosphere, and then the temperature is raised to 1000-1200°C for carbonization treatment. The reaction time is 2-3 hours, and after cooling, the cross-linked starch-derived hard carbon negative electrode material is obtained;
[0008] (3) Preparation of hard carbon negative electrode sheet: Mix the hard carbon negative electrode material, conductive carbon black and binder in a mass ratio of 8:1:1 in a homogenizer and process for 10 to 15 minutes. After it is made into a uniform slurry, it is scraped on the aluminum foil current collector and placed in a 100 to 120°C forced air drying oven for 10 to 12 hours to obtain a hard carbon negative electrode sheet, and the sheet is cut into a circular electrode sheet with a diameter of 10 to 12 mm;
[0009] (4) Pre-sodium treatment of the negative electrode: soak the prepared electrode in a polycyclic aromatic hydrocarbon-sodium-ether pre-sodium agent for pre-sodium treatment for 10 to 20 minutes and then take it out; rinse the soaked working electrode with ethylene glycol dimethyl ether and place it in a vacuum oven at 70°C until it is completely dried to obtain a pre-sodium hard carbon negative electrode.
[0010] Furthermore, in step (1), the mass ratio of starch to cross-linking agent is 1:1 to 1.5; and the drying time in the oven is 6 to 8 hours.
[0011] Furthermore, in step (1), the starch is one of corn starch, tapioca starch or potato starch; the crosslinking agent is one of citric acid, phthalic acid, succinic acid or gambogic acid; the solvent is deionized water or ethanol; and the standing time is 15 to 20 hours.
[0012] Furthermore, in step (2), the heating rate of the low temperature treatment is 3 to 5°C / min; the heating rate of the constant high temperature carbonization can be 2 to 5°C / min.
[0013] Furthermore, in step (3), the added dispersant is deionized water; the conductive carbon black is one of Ketjen black, Super P or acetylene black; and the binder is one of sodium carboxymethyl cellulose or sodium alginate.
[0014] Furthermore, in step (4), the polycyclic aromatic hydrocarbons PAHs are one of 1-naphthonitrile, 4-fluorobiphenyl or 4,4-dimethylbiphenyl; and the ether solvent is one of diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or tetrahydrofuran.
[0015] The present invention also provides the use of the carboxylate cross-linked starch-derived hard carbon negative electrode material prepared by the above method in a sodium ion battery. The specific application method is as follows:
[0016] Battery assembly: The dried negative electrode and metal sodium were assembled into CR2032 button cells using a glass fiber separator. The electrolyte was 1M sodium hexafluorophosphate (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, respectively).
[0017] Advantages and beneficial effects of the present invention:
[0018] The preparation process of the present invention is simple, has low equipment requirements, has good repeatability, does not require complicated subsequent treatment, and is suitable for large-scale production. In view of the abundant resources of starch, its sustainability and renewability, and its diverse structure, it is expected to become a key raw material for building new carbon-based materials. Therefore, the construction of its microscopic carbon skeleton network is promoted by chemical crosslinking to improve thermal stability. Small organic molecules with active carboxyl groups are selected as crosslinking agents to interact with starch molecules to form stable esterification bonds or complex bonds, strengthen the interactions between molecules (such as hydrogen bonds, ionic bonds, etc.), and build a more stable three-dimensional network structure, so that it is not easy to be structurally damaged when heated. In addition, by adopting a long-term low-temperature treatment method, the structural damage of starch due to too fast crystallization is avoided. Then, the liquid phase pre-sodiumization technology is used to achieve efficient sodium supplementation of the negative electrode, improve the reversibility of ICE and sodium storage, and extend the cycle life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 Optical photographs of samples after carbonization: (A) direct carbonization; (B) carbonization photograph after starch cross-linking.
[0020] Figure 2 This is the XRD comparison diagram of the prepared cross-linked starch and corn starch.
[0021] Figure 3 SEM morphology of the samples after carbonization: (A) direct carbonization; (B) carbonization after cross-linking and low-temperature pretreatment.
[0022] Figure 4 This is the HRTEM image of the sample after cross-linked starch carbonization.
[0023] Figure 5 Thermogravimetric analysis of the samples.
[0024] Figure 6 This is a comparison test of constant current charge and discharge curves at 0.1A / g.
[0025] Figure 7 Comparative test of cycling performance at a current density of 0.1 A / g, (A) direct carbonization; (B) cycling performance of cross-linked starch after low-temperature pretreatment and carbonization.
[0026] Figure 8 This is a comparative test of the cycling performance of the hard carbon negative electrode before and after pre-sodiumization. DETAILED DESCRIPTION
[0027] Example 1
[0028] (1) Preparation of cross-linked starch precursor: 1 g of citric acid and 1 g of corn starch were dispersed in deionized water, stirred evenly, and the pH of the solution was adjusted to 3.5 with sodium hydroxide. After standing at room temperature for 12 h, the solution was transferred to a 100° C. oven for drying and grinding to obtain a carbonized precursor.
[0029] (2) Preparation of cross-linked starch-derived hard carbon negative electrode material: The carbonized precursor was placed in a tubular furnace and subjected to low-temperature treatment at 250 °C for 12 h under an inert gas atmosphere. The temperature was then raised to 1100 °C for carbonization treatment. The reaction time was 2 h and the heating rate was 2 °C / min. After cooling, the hard carbon negative electrode material was obtained.
[0030] (3) Preparation of hard carbon negative electrode sheet: The hard carbon negative electrode material, Ketjen black and sodium alginate binder were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 10 minutes. After it was made into a uniform slurry, it was scraped on the aluminum foil current collector and placed in a 100°C forced air drying oven for 12 hours to obtain a hard carbon negative electrode sheet, and the electrode sheet was cut into a circular electrode sheet with a diameter of 10 mm.
[0031] Example 2
[0032] (1) Preparation of cross-linked starch precursor: 1 g of phthalic acid was dissolved in 30 mL of anhydrous ethanol, and 1.5 g of potato starch was dispersed in deionized water. The mixture was evenly mixed and the pH of the solution was adjusted to 4 with sodium hydroxide. The mixture was allowed to stand at room temperature for 12 h and then transferred to a 110°C oven for drying and grinding to obtain a carbonized precursor.
[0033] (2) Preparation of cross-linked starch-derived hard carbon negative electrode material: The carbonized precursor was placed in a tubular furnace and subjected to low-temperature treatment at 300 °C for 10 h under an inert gas atmosphere. The temperature was then raised to 1150 °C for carbonization treatment. The reaction time was 2 h and the heating rate was 2.5 °C / min. After cooling, the hard carbon negative electrode material was obtained.
[0034] (3) Preparation of hard carbon negative electrode sheet: The hard carbon negative electrode material, Ketjen black and sodium alginate binder were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 10 minutes. After it was made into a uniform slurry, it was scraped on the aluminum foil current collector and placed in a 120°C forced air drying oven for 10 hours to obtain a hard carbon negative electrode sheet, and the electrode sheet was cut into a circular electrode sheet with a diameter of 10 mm.
[0035] Example 3
[0036] (1) Preparation of cross-linked starch precursor: Dissolve 1 g of garcinia in 30 mL of anhydrous ethanol, and disperse 1 g of cassava starch in deionized water. After mixing well, adjust the pH of the solution to 3.5 with sodium hydroxide. After standing at room temperature for 10 h, transfer to a 100°C oven for drying and grinding to obtain a carbonized precursor.
[0037] (2) Preparation of cross-linked starch-derived hard carbon negative electrode material: The carbonized precursor was placed in a tubular furnace and subjected to low-temperature treatment at 200 °C for 10 h under an inert gas atmosphere. The temperature was then raised to 1200 °C for carbonization treatment. The reaction time was 2 h and the heating rate was 2 °C / min. After cooling, the hard carbon negative electrode material was obtained.
[0038] (3) Preparation of hard carbon negative electrode sheet: The hard carbon negative electrode material, Ketjen black and sodium alginate binder were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 10 minutes. After it was made into a uniform slurry, it was scraped on the aluminum foil current collector and placed in a 110°C forced air drying oven for 12 hours to obtain a hard carbon negative electrode sheet, and the electrode sheet was cut into a circular electrode sheet with a diameter of 10 mm.
[0039] Example 4
[0040] (4) Pre-sodium treatment of the negative electrode: The prepared electrode was immersed in a 1-naphthonitrile-sodium-ethylene glycol dimethyl ether solution for pre-sodium treatment, and the reaction time was 10 min. The working electrode was rinsed clean with ethylene glycol dimethyl ether and placed in a 70°C vacuum oven until completely dried to obtain a pre-sodium hard carbon negative electrode.
[0041] (5) Battery assembly: The dried negative electrode was assembled with a sodium metal counter electrode with a diameter of 14 mm and a glass fiber separator with a diameter of 16 mm to form a CR2032 button cell. The electrolyte was 1 M 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 contents were <0.01 ppm, respectively). The voltage test range was 0.01 to 2.5 V (vs. Na / Na + ).
[0042] Example 5
[0043] (4) Pre-sodium treatment of the negative electrode: The prepared electrode was immersed in a 4-fluorobiphenyl-sodium-diethylene glycol dimethyl ether solution for pre-sodium treatment, and the reaction time was 15 min. The working electrode was rinsed with ethylene glycol dimethyl ether and placed in a 70°C vacuum oven until completely dried to obtain a pre-sodium hard carbon negative electrode.
[0044] (5) Battery assembly: The dried negative electrode was assembled with a sodium metal counter electrode with a diameter of 14 mm and a glass fiber separator with a diameter of 16 mm to form a CR2032 button cell. The electrolyte was 1 M 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 contents were <0.01 ppm, respectively). The voltage test range was 0.01 to 2.5 V (vs. Na / Na + ).
[0045] Example 6
[0046] (4) Pre-sodium treatment of the negative electrode: The prepared electrode was immersed in a 4,4-dimethylbiphenyl-sodium-tetrahydrofuran solution for pre-sodium treatment, and the reaction time was 15 min. The working electrode was rinsed clean with ethylene glycol dimethyl ether and placed in a vacuum oven at 70°C until completely dried to obtain a pre-sodium hard carbon negative electrode.
[0047] (5) Battery assembly: The dried negative electrode was assembled with a sodium metal counter electrode with a diameter of 14 mm and a glass fiber separator with a diameter of 16 mm to form a CR2032 button cell. The electrolyte was 1 M 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 contents were <0.01 ppm, respectively). The voltage test range was 0.01 to 2.5 V (vs. Na / Na + ).
[0048] Figure 1 Optical photographs of the carbonized samples: (A) The photo of the uncross-linked corn starch after direct carbonization shows that the sample exhibits severe melt foaming, resulting in structural collapse and a foamed carbon state; (B) The photo of the carbonized sample after citric acid cross-linking shows that cross-linking and low-temperature pretreatment effectively inhibit the melt foaming during the carbonization process, making the sample more compact.
[0049] Figure 2 The XRD patterns of the prepared cross-linked starch and corn starch show that both samples exhibit similar diffraction characteristic peaks, but the diffraction peak of the carbonized sample after cross-linking and low-temperature pretreatment at 2θ=23.5° is higher than that of the directly carbonized sample, indicating that the regularity between the starch molecules is enhanced after cross-linking, forming a more stable three-dimensional structure.
[0050] Figure 3SEM morphology of the carbonized samples: (A) Due to structural collapse and melt foaming, the directly carbonized sample presents an irregular broken block structure; (B) The sample carbonized after cross-linking and low-temperature pretreatment has a regular spherical microstructure and better maintains the original spherical structure, proving that the structural collapse has been significantly improved.
[0051] Figure 4 This is the HRTEM image of the sample after carbonization of cross-linked starch. The microstructure has a graphite domain structure accompanied by micropores.
[0052] Figure 5 Thermogravimetric analysis of the samples shows that in the second stage of corn starch pyrolysis, the precursor after cross-linking and low-temperature pretreatment has a slower pyrolysis rate than pure corn starch, indicating that the modified material has better thermal stability and also means an increase in carbon yield.
[0053] Figure 6 For the charge and discharge curve test, it can be seen through comparison that the hard carbon negative electrode material carbonized after cross-linking and low-temperature pretreatment significantly improves the sodium storage performance, and has a more obvious charge and discharge platform and higher ICE.
[0054] Figure 7 The comparison of the cycling performance at a current density of 0.1 A / g shows that (A) due to the direct carbonization of starch, foam carbon is mainly generated, resulting in sodium storage mainly relying on physical adsorption, showing a lower capacity of about 50 mAh / g; (B) In contrast, the cross-linked starch after cross-linking and low-temperature pretreatment is carbonized to obtain a structurally stable hard carbon material. It can be seen that after 200 cycles, it has a reversible capacity of more than 200 mAh / g.
[0055] Figure 8 This is the cycling performance of the electrode after pre-sodium treatment. It can be seen that after pre-sodium treatment, the electrode ICE can be increased from 65% to 90%, effectively reducing the irreversible capacity during the first discharge process, and after 150 cycles, the capacity retention rate is 100%, indicating that the pre-sodium treated electrode has better cycling stability.
[0056] The present invention provides examples of preparation methods of cross-linked starch precursors, cross-linked starch-derived hard carbon negative electrode materials, and hard carbon negative electrode sheets through Examples 1-3, and provides the steps of pre-sodiumization treatment of the obtained negative electrode sheets and applying the pre-sodiumized hard carbon negative electrodes in sodium ion batteries through Examples 4-6. It should be clear that Examples 1-5 do not cover all the materials, dosage ratios, and process conditions in the technical solution of the present invention. Therefore, the above examples are only used to understand the technical solution of the present invention, and are not used to limit the scope of protection of the present invention. It is understood by those skilled in the art that any obvious adjustments and modifications to the technical solution of the present invention that belong to the technical concept of the present invention should also fall within the scope of protection of the present invention.
Claims
1. A method for preparing a carboxylate cross-linked starch-derived hard carbon negative electrode material, comprising the following preparation steps: (1) Preparation of precursor solution: Disperse starch and cross-linking agent in a solvent at a mass ratio of 1:1 to 1.5, stir evenly, adjust the solution pH to 3 to 4 with sodium hydroxide, and allow to stand at room temperature to obtain a precursor solution; (2) Preparation of carbonized precursor: placing the precursor liquid in an oven and drying it at a temperature of 100 to 120° C.; after drying, grinding is performed to obtain a carbonized precursor; (3) taking the carbonized precursor in a tube furnace, performing low-temperature pretreatment at a temperature of 200 to 300° C., then heating it to 1000 to 1200° C. for constant high-temperature carbonization, and obtaining a cross-linked starch-derived hard carbon negative electrode material after cooling; (4) Preparation of hard carbon negative electrode sheet: Mix the hard carbon negative electrode material, conductive carbon black and binder in a mass ratio of 8:1:1 in a homogenizer and process for 10 to 15 minutes. After the slurry is made into a uniform slurry, it is coated on an aluminum foil current collector and placed in a 100 to 120° C. forced air drying oven for 10 to 12 hours to obtain a hard carbon negative electrode sheet; (5) Pre-sodium treatment of the negative electrode: soak the prepared electrode in a PAHs-Na-ether pre-sodium agent for pre-sodium treatment for 10 to 20 minutes and then take it out; rinse the soaked working electrode with an ether solvent and place it in a vacuum oven at 70°C until it is completely dried to obtain a pre-sodium hard carbon negative electrode.
2. The method for preparing the carboxylate cross-linked starch-derived hard carbon negative electrode material according to claim 1, characterized in that: In step (1), the starch is one of corn starch, tapioca starch or potato starch; the cross-linking agent is one of citric acid, phthalic acid, succinic acid or gambogic acid; the solvent is deionized water or ethanol; and the standing time is 15 to 20 hours.
3. The method for preparing the carboxylate cross-linked starch-derived hard carbon negative electrode material according to claim 1, characterized in that: In step (2), the drying time is 6 to 8 hours.
4. The method for preparing the carboxylate cross-linked starch-derived hard carbon negative electrode material according to claim 1, characterized in that: In step (3), the low-temperature treatment time is 9 to 12 hours, and the heating rate is 3 to 5°C / min; in the constant high-temperature carbonization process, the carbonization time is 2 to 3 hours, and the heating rate can be 2 to 5°C / min.
5. The method for preparing the carboxylate cross-linked starch-derived hard carbon negative electrode material according to claim 1, characterized in that: In step (4), the added dispersant is deionized water; the conductive carbon black is one of Ketjen black, SuperP or acetylene black; and the binder is one of sodium carboxymethyl cellulose or sodium alginate.
6. The method for preparing the carboxylate cross-linked starch-derived hard carbon negative electrode material according to claim 1, characterized in that: In step (5), the polycyclic aromatic hydrocarbons PAHs are one of 1-naphthonitrile, 4-fluorobiphenyl or 4,4-dimethylbiphenyl; and the ether solvent is one of diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or tetrahydrofuran.
7. Use of the carboxylate cross-linked starch-derived hard carbon negative electrode material prepared by the method according to any one of claims 1 to 6 in sodium ion batteries.