Starch-based hard carbon materials, their preparation methods and applications

Abstract

This invention relates to the field of sodium-ion battery technology, specifically to starch-based hard carbon materials, their preparation methods, and applications. The preparation method provided by this invention uses starch as a raw material, which is inexpensive, widely available, and easily scalable. The aminotrimethylene phosphate is fully pre-crosslinked with starch. The addition of aminotrimethylene phosphate effectively inhibits the melting and foaming of starch during carbonization, maintaining the spherical particle morphology of the material, and simultaneously serving as a source of N and P doping, forming abundant closed-pore structures and doping sites within the material. This method is simple and low-cost. The resulting hard carbon material exhibits high sodium storage capacity, rate performance, first-cycle coulombic efficiency, and compaction density, making it suitable as a negative electrode active material for sodium-ion batteries. The assembled sodium-ion batteries demonstrate excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to starch-based hard carbon materials, their preparation methods, and applications. Background Technology

[0002] The large-scale grid connection of renewable energy and various scenarios have placed demands on rechargeable batteries for "low cost, long cycle life, and high safety," while the trillion-dollar energy storage market has spurred diverse explorations of battery technologies. Although lithium-ion batteries have a high degree of commercialization and wide application, they face resource and safety bottlenecks: lithium resources are scarce and unevenly distributed, the supply chain is risky, and long-term cost reductions are limited; at the same time, their high risk of thermal runaway and the serious consequences of safety accidents make them unsuitable for large-scale energy storage. In contrast, sodium resources are not only abundant in the Earth's crust and widely distributed globally, but their mining and purification costs are also significantly lower than those of lithium resources; moreover, sodium-ion batteries have advantages in thermal stability and other safety performance. These outstanding characteristics make them a recognized highly promising alternative technology in the field of large-scale energy storage.

[0003] The anode material is a core component determining the key performance of sodium-ion batteries, and hard carbon materials have become the best practical choice due to their multiple advantages. It possesses a unique multi-step sodium storage mechanism of "adsorption-intercalation-filling," combining high specific capacity potential with excellent structural stability. Its precursors are widely available, derived from biomass, coal chemical byproducts, polymer resins, and industrial waste, further enhancing the low-cost advantage of sodium-ion batteries. Among various precursors, starch has a stable supply and low ash content, while also possessing a spherical morphology, giving it a natural advantage in improving compaction density and promoting industrialization. However, starch particles are prone to melting and foaming during high-temperature carbonization, leading to uncontrolled product morphology, which not only reduces compaction density but also results in insufficient first-cycle coulombic efficiency, increasing the overall battery process cost.

[0004] To address the issue of starch melting and foaming, a common method is pre-oxidative cross-linking treatment. However, this not only increases processing time but also significantly raises costs. Therefore, there is a need to develop a simple and low-cost starch pre-cross-linking method to promote the application of starch-based hard carbon in sodium-ion batteries. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide starch-based hard carbon materials, their preparation methods and applications. The preparation method provided by the present invention can significantly improve the sodium storage capacity, rate performance, first-cycle coulombic efficiency and compaction density of the obtained starch-based hard carbon materials.

[0006] This invention provides a method for preparing starch-based hard carbon materials, comprising the following steps:

[0007] S1) Disperse aminotrimethylene phosphoric acid and starch in water, and then dry the product obtained after dispersion;

[0008] S2) The product obtained in step S1) is carbonized under a protective gas atmosphere to obtain starch-based hard carbon material.

[0009] The inventors of this application have creatively discovered that by fully pre-crosslinking aminotrimethylene phosphate with starch, the melting and foaming of starch particles during subsequent heating can be effectively suppressed, maintaining the spherical particle morphology of the material, effectively suppressing the side reactions between starch-based hard carbon and electrolyte, and improving the first-cycle coulombic efficiency. Based on the carbonization treatment of this pre-crosslinked modified starch, a rich closed-pore structure can also be induced. Furthermore, aminotrimethylene phosphate can serve as a source of N and P, enabling in-situ co-doping of N and P elements, further increasing sodium ion storage sites, and improving the rate performance and sodium storage capacity of hard carbon materials.

[0010] This invention first disperses aminotrimethylene phosphoric acid and starch in water. Specifically, after dispersing starch in water by stirring, aminotrimethylene phosphoric acid is added and stirred thoroughly to disperse the starch. The mass ratio of aminotrimethylene phosphoric acid to starch in this invention is (0.01~0.3):1; the mass ratio of starch to water is 1:(14~16). The dispersion time in this invention is 1 h~12 h; the dispersion time refers to the time during which starch and aminotrimethylene phosphoric acid are stirred and dispersed in water.

[0011] This invention disperses aminotrimethylene phosphoric acid and starch in water, and then dries the resulting product. The drying temperature is 50℃~80℃, and the drying time is 12 h~48 h. By mixing starch with aminotrimethylene phosphoric acid in deionized water and optimizing the drying temperature and time, this invention achieves full cross-linking of starch and aminotrimethylene phosphoric acid during the drying process. The process is simple, convenient, and suitable for large-scale industrial production.

[0012] This invention involves drying the dispersed product and then carbonizing it under a protective gas atmosphere to obtain a starch-based hard carbon material. Specifically, the product is ground and then carbonized under a protective gas atmosphere to obtain the starch-based hard carbon material. The protective gas used in this invention is selected from one or more of helium, neon, argon, and nitrogen. The flow rate of the protective gas is 60 mL / min to 90 mL / min. The carbonization temperature is 1100 ℃ to 1500 ℃; the carbonization time is 2 h to 4 h; and the heating rate is 5 ℃ / min to 10 ℃ / min. After carbonization, the material is allowed to cool naturally to room temperature.

[0013] In step S1), the present invention uses aminotrimethylene phosphoric acid and starch as raw materials for pre-crosslinking. Some of the aminotrimethylene phosphoric acid that does not participate in the pre-crosslinking decomposes into gaseous substances such as ammonia and phosphorus vapor during the high-temperature carbonization stage and escapes. This escape process can not only regulate the pore structure of the hard carbon material and induce the formation of a rich closed-pore structure, thereby improving the sodium storage capacity of the hard carbon material, but also remove impurities in the hard carbon material at the same time, eliminating the need for additional subsequent purification treatment of the hard carbon material and further simplifying its preparation process.

[0014] This invention also provides a starch-based hard carbon material obtained by any of the preparation methods described above. The starch-based hard carbon material obtained by this invention has a granular morphology with abundant closed-cell structures and is doped with N and P elements, effectively increasing sodium ion storage sites. The starch-based hard carbon material obtained by this invention has applications in the preparation of sodium-ion battery anodes and the assembly of sodium-ion batteries.

[0015] This invention provides a sodium-ion battery anode, comprising a carrier and an active material disposed on the carrier; the active material includes a conductive agent, a binder, and a starch-based hard carbon material obtained by any of the preparation methods described above. Specifically, the sodium-ion battery anode of this invention includes a carrier and an active material layer disposed on the carrier, the active material layer comprising a conductive agent, a binder, and a starch-based hard carbon material obtained by any of the preparation methods described above. The carrier of this invention is a current collector, preferably selected from uncoated copper foil, carbon-coated copper foil, or carbon paper.

[0016] This invention also provides a sodium-ion battery comprising a positive electrode and a negative electrode, wherein the negative electrode is any of the sodium-ion battery negative electrodes described above. Sodium-ion batteries assembled using the sodium-ion battery negative electrode made from the starch-based hard carbon material of this invention exhibit high sodium storage capacity, rate performance, first-cycle coulombic efficiency, and compaction density.

[0017] This invention provides starch-based hard carbon materials, their preparation methods, and applications. The preparation method uses starch as a raw material, which is inexpensive, widely available, and easily scalable. The method involves fully pre-crosslinking starch with aminotrimethylene phosphate. The addition of aminotrimethylene phosphate effectively inhibits the melting and foaming of starch during carbonization, maintaining the spherical particle morphology of the material. Simultaneously, it serves as a source of N and P doping, forming abundant closed-pore structures and doping sites within the material. This method is simple and inexpensive. The resulting hard carbon material exhibits high sodium storage capacity, rate performance, first-cycle coulombic efficiency, and compaction density, making it suitable as a negative electrode active material for sodium-ion batteries. The assembled sodium-ion batteries demonstrate excellent electrochemical performance. Attached Figure Description

[0018] Fig. 1 This is one of the SEM images of the starch-based hard carbon material in Example 2 of the present invention;

[0019] Fig. 2 The second SEM image is shown for the starch-based hard carbon material of Example 2 of this invention.

[0020] Fig. 3 This is a TEM image of the starch-based hard carbon material in Example 2 of the present invention. Detailed Implementation

[0021] This invention discloses starch-based hard carbon materials, their preparation methods, and applications. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0022] Unless otherwise specified, the reagents, materials and instruments used in this invention are all conventional reagents, materials and instruments, and can be obtained commercially.

[0023] The following embodiments illustrate the assembly method of the CR2032 coin cell sodium-ion battery: a starch-based hard carbon electrode sheet is used as the working electrode, a metallic sodium sheet as the counter electrode, a Whatman glass fiber membrane as the separator, and the electrolyte is composed of sodium hexafluorophosphate and diethylene glycol dimethyl ether as the solvent, wherein the concentration of sodium hexafluorophosphate is 1 mol / L; all assembly operations are completed in a glove box (the content of O2 and H2O in the glove box is less than 0.01 ppm), and the CR2032 coin cell sodium-ion battery is obtained after encapsulation.

[0024] The preparation method of the starch-based hard carbon electrode sheet is as follows: Hard carbon material, PVDF, and superconducting carbon black are mixed in a mass ratio of 95:2:3. NMP is added dropwise and the mixture is continuously ground until it reaches an oily state to obtain an electrode slurry. The slurry is then uniformly coated onto the surface of a copper foil using a scraper, and subsequently dried in a 120 ℃ drying oven for 6 h. After rolling and punching, a disc with a diameter of 12 mm is obtained, which is the starch-based hard carbon electrode sheet. The hard carbon material is one of the starch-based hard carbon materials prepared in Examples 1-8 and Comparative Example 1 below. Each hard carbon material corresponds to the preparation of a set of sodium-ion batteries.

[0025] In the following examples, the electrochemical performance tests of the CR2032 coin cell sodium-ion batteries were all conducted on a Blue Battery Tester, with a test voltage window of 0.005~2 V and a test temperature of room temperature.

[0026] The present invention will be further described below with reference to the embodiments:

[0027] Examples 1-6

[0028] A method for preparing a starch-based hard carbon material and its application in sodium-ion batteries includes the following steps:

[0029] S1. Starch was taken as raw material, and after being dispersed in deionized water by stirring, aminotrimethylene phosphoric acid was added and stirred thoroughly. The mixture was then dried in an oven at 60 °C for 12 h to obtain a hard carbon precursor. The ratio of aminotrimethylene phosphoric acid to starch (mass ratio) is shown in Table 1, and the ratio of starch to deionized water is 1:15.

[0030] S2. Under an argon atmosphere, the hard carbon precursor was placed in a tube furnace and heated to 1300℃ at a rate of 5℃ / min and held for 2 h, and then naturally cooled to room temperature to obtain starch-based hard carbon material.

[0031] S3. According to the aforementioned method, prepare starch-based hard carbon electrode sheets, assemble sodium-ion batteries, and conduct electrochemical tests.

[0032] Table 1

[0033]

[0034] Example 7

[0035] A method for preparing starch-based hard carbon and its application in sodium-ion batteries is basically the same as in Example 2, except that "heating at a rate of 5 °C / min to 1300 °C and holding for 2 h" is replaced with "heating at a rate of 5 °C / min to 1100 °C and holding for 2 h".

[0036] Example 8

[0037] A method for preparing starch-based hard carbon and its application in sodium-ion batteries is basically the same as in Example 2, except that "heating at a rate of 5 °C / min to 1300 °C and holding for 2 h" is replaced with "heating at a rate of 5 °C / min to 1500 °C and holding for 2 h".

[0038] Comparative Example 1

[0039] A method for preparing starch-based hard carbon and its application in sodium-ion batteries is basically the same as in Example 2, except that: after dispersing starch in deionized water by stirring, aminotrimethylene phosphoric acid is not added, and the carbon is directly placed in an oven to dry.

[0040] Comparative Example 2

[0041] A method for preparing starch-based hard carbon and its application in sodium-ion batteries is basically the same as in Example 2, except that: after dispersing starch in deionized water by stirring, sodium tripolyphosphate is added and then dried in an oven.

[0042] In the above embodiments, the hard carbon material obtained in Example 2 was imaged using scanning electron microscopy and transmission electron microscopy, and the results are as follows: Figs. 1-3 As shown, Fig. 1 This is one of the SEM images of the starch-based hard carbon material in Example 2 of the present invention. Fig. 2 The second SEM image of the starch-based hard carbon material in Embodiment 2 of the present invention shows that the starch-based hard carbon retains the granular morphology of starch, and the foaming behavior of starch during the heat treatment process is effectively suppressed. This is attributed to the reaction of aminotrimethylene phosphate with starch to form a cross-linked network structure. Fig. 3 The image shown is a TEM image of the starch-based hard carbon material in Example 2 of this invention. It shows a rich closed-pore structure, which helps to improve the sodium storage capacity of hard carbon.

[0043] The sodium-ion batteries (CR2032 coin cells) prepared from the starch-based hard carbon materials of Examples 1-8 and Comparative Examples 1-2 were subjected to their first charge-discharge test at 0.1 C, with a voltage window of 0.005-2 V (vs. Na / Na). + The test results are shown in Table 2.

[0044] Table 2

[0045]

[0046] As shown in Table 2, the starch-based hard carbon materials prepared using the method of this invention (Examples 1-8) exhibit significantly higher first-cycle coulombic efficiency (all >76%) and plateau capacity than Comparative Example 1 (which did not add a crosslinking agent, but had a first-cycle efficiency of only 61.9%). This indicates that the pre-crosslinking treatment of aminotrimethylene phosphoric acid effectively suppressed irreversible side reactions and improved the usable capacity of the material. In particular, Example 2 (crosslinking agent ratio 0.025:1, carbonization temperature 1300℃) showed the best overall performance. When the crosslinking agent ratio was too low or too high, or the carbonization temperature was unsuitable, the performance decreased slightly, but it was still far superior to the comparative example. Furthermore, the plateau capacity and first-cycle charge-discharge capacity of Example 2 were higher than those of Comparative Example 2, indicating that the ammonia and phosphorus gases decomposed during the high-temperature decomposition of aminotrimethylene phosphoric acid effectively regulated the pore structure of the hard carbon, effectively improving its capacity. The above data fully demonstrate the effectiveness and superiority of the method of this invention.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing starch-based hard carbon materials, characterized in that, Includes the following steps: S1) Disperse aminotrimethylene phosphoric acid and starch in water, and then dry the product obtained after dispersion; S2) The product obtained in step S1) is carbonized under a protective gas atmosphere to obtain starch-based hard carbon material.

2. The preparation method according to claim 1, characterized in that, In step S1), the mass ratio of aminotrimethylene phosphoric acid to starch is (0.01~0.3):

1.

3. The preparation method according to claim 1, characterized in that, In step S1), the drying temperature is 50 ℃~80 ℃; the drying time is 12 h~48 h.

4. The preparation method according to claim 1, characterized in that, In step S1), the dispersion time is 1 h to 12 h.

5. The preparation method according to claim 1, characterized in that, In step S2), the carbonization temperature is 1100 ℃~1500 ℃; the carbonization time is 2 h~4 h; and the heating rate of the carbonization process is 5 ℃ / min~10 ℃ / min.

6. The preparation method according to claim 1, characterized in that, In step S2), the flow rate of the protective gas is 60 mL / min to 90 mL / min.

7. The preparation method according to claim 1, characterized in that, Step S2) specifically involves grinding the product obtained in step S1) and then carbonizing it under a protective gas atmosphere to obtain starch-based hard carbon material.

8. The starch-based hard carbon material obtained by any of the preparation methods described in claims 1 to 7.

9. A sodium-ion battery negative electrode, characterized in that, It includes a carrier and an active material disposed on the carrier; the active material includes a conductive agent, a binder, and a starch-based hard carbon material obtained by any of the preparation methods described in claims 1 to 7.

10. A sodium-ion battery, characterized in that, It includes a positive electrode and a negative electrode, wherein the negative electrode is the sodium-ion battery negative electrode according to claim 9.

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