Iodine-doped starch-based carbon material, method for preparing the same, and use thereof

Abstract

The application provides an iodine-doped starch-based carbon material and a preparation method and application thereof, and relates to the technical field of starch-based carbon materials. The method comprises the following steps: mixing starch, an iodine source and a water-soluble dispersant in a solvent, aging, drying and crushing to obtain a purple red to blue purple inclusion precursor; and then performing gradient carbonization treatment in an inert atmosphere to obtain the iodine-doped starch-based carbon material. The application realizes the inclusion and molecular-level anchoring through the van der Waals force between the spiral cavity of the linear starch and the iodine element, and relies on the water-soluble dispersant to form a physical encapsulation layer on the surface of the starch in situ in the low-temperature carbonization stage, cooperates with the high-temperature carbonization process, and inhibits the volatilization of the iodine element to realize the doping of high iodine content. The obtained material is characterized in that the iodine is embedded in the carbon skeleton in a P-pi conjugate state, the conductivity is significantly enhanced, the carrier concentration is improved, and the sodium ion storage capacity is improved, so that the reversible specific capacity is improved and the first circle coulombic efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of starch-based carbon materials technology, and in particular to an iodine-doped starch-based carbon material, its preparation method, and its application. Background Technology

[0002] Starch, as a widely available, inexpensive, and renewable natural polymer, is widely used as a precursor for the preparation of carbon-based materials. However, the direct carbonization of starch to prepare carbon-based materials suffers from problems such as poor thermal stability, easy gelatinization, and high pyrolysis losses, resulting in low material yields and easily destroying the inherent spherical structure of starch raw materials.

[0003] Furthermore, unmodified starch-derived carbon-based materials are prone to particle agglomeration during high-temperature carbonization, resulting in uneven particle size, increased specific surface area, and pore structure collapse, which in turn leads to insufficient electrochemical performance. In particular, when used as a negative electrode material for sodium-ion batteries, the reversible specific capacity is low and the first-cycle coulombic efficiency is not high, which seriously restricts the practical application of starch-based carbon materials in the field of energy storage.

[0004] To address the aforementioned issues, while existing technologies include physical or chemical modifications to starch, these methods typically only alleviate processing difficulties such as starch's tendency to gelatinize or its poor thermal stability, failing to simultaneously and effectively solve the problem of insufficient electrochemical performance in materials. In particular, there are shortcomings in achieving efficient doping of highly volatile elements such as iodine. Specifically, elemental iodine (I₂) has a low boiling point (184℃) and is easily sublimated and lost at conventional carbonization temperatures (>1000℃), resulting in low doping levels, uneven distribution, and weak bonding, thus failing to leverage the role of iodine atoms in enhancing the conductivity and sodium storage activity of carbon materials.

[0005] Therefore, it is both necessary and urgent to research and develop an iodine-doped starch-based carbon material that can maintain the structural integrity of starch-based carbon materials, effectively suppress the escape of iodine during carbonization, and ultimately obtain high iodine loading, high conductivity, high reversible capacity and high first-cycle coulombic efficiency, as well as its preparation method.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The first objective of this invention is to provide a method for preparing iodine-doped starch-based carbon materials. The method utilizes the synergistic effect of iodine inclusion in the helical cavity of starch and physical encapsulation on the surface of a water-soluble dispersant, combined with gradient carbonization treatment, to achieve effective retention and stable doping of iodine during high-temperature carbonization, thereby obtaining iodine-doped starch-based carbon materials with enhanced conductivity, increased carrier concentration, and improved sodium ion storage capacity.

[0008] The second objective of this invention is to provide an iodine-doped starch-based carbon material.

[0009] A third objective of this invention is to provide an application of an iodine-doped starch-based carbon material.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a method for preparing an iodine-doped starch-based carbon material, the method comprising the following steps: S1: Starch, iodine source and water-soluble dispersant are mixed in a solvent, aged and dried and then pulverized to obtain an inclusion precursor that is purple-red, purple-black, wine-red, blue, purple or blue-purple. The mass ratio of starch, iodine source, and water-soluble dispersant is 15:(0.015~0.3):(0.0075~0.3). S2: The precursor is subjected to gradient carbonization in an inert atmosphere to obtain iodine-doped starch-based carbon material.

[0011] Furthermore, the solvent is water; The amount of solvent added is (0.3~3):1 based on the amount of starch added.

[0012] Furthermore, the starch includes at least one of potato starch, corn starch, wheat starch, sweet potato starch, cassava starch, rice starch, and sorghum starch; Furthermore, the iodine source includes at least one of elemental iodine, iodophor, and iodic acid (which requires a reducing agent); Furthermore, the water-soluble dispersant is polyvinylpyrrolidone.

[0013] Furthermore, the aging and drying temperature is 50~90℃, and the time is 12~36 h; Preferably, the aging and drying temperature is 75°C and the time is 24 hours.

[0014] Furthermore, the particle size of the pulverized inclusion precursor is 5~150μm.

[0015] Furthermore, the gradient carbonization process includes a low-temperature carbonization process and a high-temperature carbonization process performed sequentially.

[0016] Furthermore, the low-temperature carbonization treatment is carried out at a temperature of 200~400℃ for a time of 1~3 hours.

[0017] Furthermore, the high-temperature carbonization treatment is carried out at a temperature of 1100~1700℃ for a time of 1~6 h.

[0018] This invention provides an iodine-doped starch-based carbon material prepared by the above method.

[0019] This invention provides an application of the above-mentioned iodine-doped starch-based carbon material in the preparation of energy storage products.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This application provides a method for preparing iodine-doped starch-based carbon material. The method involves mixing starch, an iodine source, and a water-soluble dispersant in a solvent. An inclusion complex is formed by the van der Waals forces between the helical structure of amylose and elemental iodine. The water-soluble dispersant precipitates and uniformly coats the starch granules during aging and drying, constructing a physical encapsulation structure. Subsequent gradient carbonization under an inert atmosphere allows iodine to be stably anchored within the carbon framework, resulting in an iodine-doped starch-based carbon material with enhanced conductivity, increased carrier concentration, and improved sodium ion storage capacity. Ultimately, this manifests as an increase in reversible specific capacity and improved first-cycle coulombic efficiency.

[0021] The iodine-doped starch-based carbon material provided in this application achieves effective retention and uniform distribution of iodine under high-temperature carbonization conditions through the molecular-level inclusion of iodine by the starch helical structure and the synergistic effect of in-situ encapsulation of water-soluble dispersants during the carbonization process. This allows iodine to be embedded into the carbon skeleton in a non-covalent form, thereby increasing the carrier concentration and intrinsic conductivity, and improving its structural stability and electrochemical activity.

[0022] The iodine-doped starch-based carbon material provided by this invention can be widely used in the preparation of energy storage products, and is especially suitable as a negative electrode active material for electrochemical energy storage devices such as sodium-ion batteries. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 Optical images of the inclusion complex precursors prepared in Examples 1-4 of this invention, provided in Experimental Example 1 of this invention; Figure 2 Optical images of Comparative Example 1 before and after sintering, provided in Experimental Example 1 of this invention; Figure 3 Optical images before and after sintering in Example 4 of Experimental Example 1 of this invention; Figure 4 This is a SEM image of the carbon material obtained in Comparative Example 1 provided in Experimental Example 1 of the present invention; Figure 5The image shows a SEM image of the carbon material obtained in Example 1 of Experimental Example 1 of this invention. Figure 6 The image shows a SEM image of the carbon material obtained in Example 4 of Experimental Example 1 of this invention. Figure 7 The voltage distribution curves of the carbon materials obtained in Examples 1-4 and Comparative Example 1 are provided for Experimental Example 1 of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] According to one aspect of the present invention, a method for preparing an iodine-doped starch-based carbon material includes the following steps: S1: Starch, iodine source and water-soluble dispersant are mixed in a solvent, aged and dried and then pulverized to obtain an inclusion precursor that is purple-red, purple-black, wine-red, blue, purple or blue-purple. The mass ratio of starch, iodine source, and water-soluble dispersant is 15:(0.015~0.3):(0.0075~0.3). S2: The precursor is subjected to gradient carbonization in an inert atmosphere to obtain iodine-doped starch-based carbon material.

[0027] This application provides a method for preparing iodine-doped starch-based carbon material. The method involves mixing starch, an iodine source, and a water-soluble dispersant in a solvent. An inclusion complex is formed by the van der Waals forces between the helical structure of amylose and elemental iodine. The water-soluble dispersant precipitates and uniformly coats the starch granules during aging and drying, constructing a physical encapsulation structure. Subsequent gradient carbonization under an inert atmosphere allows iodine to be stably anchored within the carbon framework, resulting in an iodine-doped starch-based carbon material with enhanced conductivity, increased carrier concentration, and improved sodium ion storage capacity. Ultimately, this manifests as an increase in reversible specific capacity and improved first-cycle coulombic efficiency.

[0028] As an optional implementation, the mass ratio of starch, iodine source and water-soluble dispersant is 15 : (0.015~0.3) : (0.0075~0.3), for example, it can be 15 : 0.015 : 0.0075, 15 : 0.05 : 0.02, 15 : 0.1 : 0.05, 15 : 0.2 : 0.15, 15 : 0.3 : 0.3, or any combination within this range.

[0029] In a preferred embodiment of the present invention, the solvent is water; The amount of solvent added is (0.3~3):1 based on the amount of starch added.

[0030] In a preferred embodiment of the present invention, the starch includes at least one of potato starch, corn starch, wheat starch, sweet potato starch, cassava starch, rice starch, and sorghum starch. The iodine source includes at least one of elemental iodine, iodophor, and iodic acid (which requires a reducing agent); The water-soluble dispersant is polyvinylpyrrolidone.

[0031] As a preferred embodiment, this application selects one or more of potato starch, corn starch, wheat starch, sweet potato starch, cassava starch, rice starch, or sorghum starch with high amylose content, which facilitates the embedding of elemental iodine into its helical cavities to form a stable inclusion complex. Using elemental iodine, iodophor, or iodic acid (which requires a reducing agent) as the iodine source ensures effective release and in-situ doping of iodine during carbonization. Using polyvinylpyrrolidone as a water-soluble dispersant forms a thermally stable and film-forming encapsulation layer on the surface of starch granules during aging, drying, and low-temperature carbonization, synergistically achieving efficient retention and uniform distribution of iodine during high-temperature carbonization, thereby improving the conductivity and electrochemical performance of the resulting carbon material.

[0032] In a preferred embodiment of the present invention, the aging and drying temperature is 50-90°C, for example, it can be 50°C, 60°C, 70°C, 75°C, 80°C, or 90°C, or any temperature value between 50-90°C; the time is 12-36 hours, for example, it can be 12 hours, 18 hours, 24 hours, 30 hours, or 36 hours, or any time period between 12-36 hours.

[0033] In a preferred embodiment, this application promotes the full inclusion reaction between starch and iodine source by aging and drying at 50–90°C for 12–36 h, forming a structurally stable iodine-starch inclusion complex. This also allows the water-soluble dispersant to precipitate uniformly and coat the surface of the starch granules, providing the necessary precursor structure for inhibiting the volatilization and escape of iodine during the subsequent carbonization process.

[0034] Preferably, the aging and drying temperature is 75°C and the time is 24 hours.

[0035] In a preferred embodiment of the present invention, the particle size of the pulverized inclusion precursor is 5~150μm.

[0036] In a preferred embodiment of the present invention, the particle size of the pulverized inclusion precursor is 5 to 150 μm, for example, it can be 15 μm, 30 μm, 50 μm, 75 μm, 100 μm, 120 μm, 150 μm, or any particle size value between 5 and 150 μm.

[0037] In a preferred embodiment, this application obtains uniformly sized inclusion precursor powder by pulverizing the aged and dried material to a particle size range of 5–150 μm. This is beneficial for achieving uniform heat and mass transfer during subsequent carbonization, ensuring the uniformity of iodine doping distribution and the consistency of carbon material structure.

[0038] In a preferred embodiment of the present invention, the gradient carbonization process includes a low-temperature carbonization process and a high-temperature carbonization process performed sequentially.

[0039] As a preferred embodiment, the gradient carbonization process of this application includes two stages: low-temperature carbonization and high-temperature carbonization performed sequentially. The low-temperature carbonization stage (200~400℃) promotes the thermal cross-linking of the water-soluble dispersant, forming a continuous, dense, and thermally stable encapsulation network in situ on the surface of the starch granules, effectively suppressing the volatilization and sublimation of iodine in the early stage of heating. The subsequent high-temperature carbonization stage (1100~1700℃) completes the deep aromatization and graphitization of the starch skeleton under the protection of the encapsulation layer, so that iodine is stably embedded in the carbon matrix in the form of P-π conjugated state, which not only maintains the integrity of the spherical structure of the material, but also realizes the effective regulation of the carbon electronic structure by iodine doping.

[0040] In a preferred embodiment of the present invention, the temperature of the low-temperature carbonization treatment is 200~400℃ and the time is 1~3 h.

[0041] In a preferred embodiment, the temperature of the low-temperature carbonization treatment is 200-400℃, for example, it can be 200℃, 250℃, 300℃, 350℃, 400℃, or any temperature value between 200-400℃; the holding time is 1-3 h, for example, it can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or any time period between 1-3 h.

[0042] In a preferred embodiment of the present invention, the high-temperature carbonization treatment is carried out at a temperature of 1100~1700℃ for a time of 1~6 h.

[0043] In a preferred embodiment, the high-temperature carbonization treatment temperature is 1100–1700°C, for example, it can be 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, or 1700°C, or any temperature value between 1100°C and 1700°C; the holding time is 1–6 h, for example, it can be 1 h, 2 h, 3 h, 4 h, 5 h, or 6 h, or any time period between 1 and 6 h.

[0044] According to one aspect of the present invention, an iodine-doped starch-based carbon material prepared by the above method is provided.

[0045] The iodine-doped starch-based carbon material provided in this application achieves effective retention and uniform distribution of iodine under high-temperature carbonization conditions through the molecular-level inclusion of iodine by the starch helical structure and the synergistic effect of in-situ encapsulation of water-soluble dispersants during the carbonization process. This allows iodine to be embedded into the carbon skeleton in a non-covalent form, thereby enhancing the P-π conjugation effect of the material, increasing the carrier concentration and intrinsic conductivity, and improving its structural stability and electrochemical activity.

[0046] According to one aspect of the present invention, the application of the above-mentioned iodine-doped starch-based carbon material in the preparation of energy storage products.

[0047] The iodine-doped starch-based carbon material provided by this invention can be widely used in the preparation of energy storage products, and is especially suitable as a negative electrode active material for electrochemical energy storage devices such as sodium-ion batteries.

[0048] The technical solution of the present invention will be further described below with reference to the embodiments.

[0049] Example 1 A method for preparing an iodine-doped starch-based carbon material, the method comprising the following steps: (1) Place 15.0 g of corn starch in a beaker; measure 10.0 mL of medical iodine tincture as the iodine source; add it to the beaker; stir thoroughly with a glass rod until the mixture is homogeneous; The effective iodine content of the medical iodine tincture is 0.45% w / v, the density is about 1.0 g / mL, which is equivalent to about 0.045 g of elemental iodine and about 0.45 g of polyvinylpyrrolidone (PVP).

[0050] Note: Polyvinylpyrrolidone (PVP) contained in medical iodine tincture also functions as a water-soluble dispersant; (2) The slurry was aged and dried in a 75℃ forced-air oven for 24 h; after drying, it was ground to obtain a purplish-red powdery inclusion precursor. (3) The above-mentioned powdered inclusion precursor was placed in a tube furnace and heated to 300°C at 1°C / min under a nitrogen atmosphere and held for 1 h for low-temperature carbonization. The temperature was then increased to 1300℃ at a rate of 5℃ / min and held for 3 hours for high-temperature carbonization; the material was then naturally cooled to room temperature to obtain a black iodine-doped starch-based carbon material.

[0051] Example 2 This embodiment provides an iodine-doped starch-based carbon material. The difference from Embodiment 1 is that the amount of medical iodine tincture used is 15 ml. The rest of the preparation method is the same as that in Embodiment 1, and will not be described again here.

[0052] Example 3 This embodiment provides an iodine-doped starch-based carbon material. The difference from Embodiment 1 is that the amount of medical iodine tincture used is 30 ml. The rest of the preparation method is the same as that in Embodiment 1, and will not be repeated here.

[0053] Example 4 This embodiment provides an iodine-doped starch-based carbon material. The difference from Embodiment 1 is that the amount of medical iodine tincture used is 40 ml. The rest of the preparation method is the same as that in Embodiment 1, and will not be described again here.

[0054] Example 5 This embodiment provides an iodine-doped starch-based carbon material. The difference from Embodiment 1 is that potato starch is used instead of corn starch. The rest of the preparation method is the same as that of Embodiment 1, and will not be described again here.

[0055] Example 6 This embodiment provides an iodine-doped starch-based carbon material. The difference from Example 1 is that wheat starch is used instead of corn starch. The rest of the preparation method is the same as that in Example 1, and will not be described again here.

[0056] Example 7 The difference from Example 4 is that the high-temperature carbonization temperature in step (3) is 1200 degrees Celsius. The rest of the preparation methods are the same as those in Example 1, and will not be repeated here.

[0057] Example 8 The difference from Example 4 is that the high-temperature carbonization temperature in step (3) is 1600 degrees Celsius. The rest of the preparation methods are the same as those in Example 1, and will not be repeated here.

[0058] Example 9 A method for preparing an iodine-doped starch-based carbon material, the method comprising the following steps: (1) First, weigh 0.003 g of elemental iodine powder (purity ≥99.9%) as the iodine source, and weigh 0.015 g of polyvinylpyrrolidone (PVP, molecular weight ≥40,000) as the water-soluble dispersant, and add them to the above beaker in sequence; add 10.0 mL of deionized water as the solvent, and stir thoroughly with a glass rod for 10–15 min to form a uniform solution; finally, weigh 15.0 g of corn starch and place it in the beaker; stir quickly and thoroughly until uniform.

[0059] Note: In this embodiment, the elemental iodine powder is an independent iodine source, and the added PVP is an independent water-soluble dispersant, specifically used to form an encapsulation layer on the surface of starch granules during the aging, drying, and low-temperature carbonization stages. (2) Place the slurry in a 75℃ forced-air oven to age and dry for 24 h; after drying, grind it and pass it through a 100-mesh sieve to obtain a purplish-red powdery inclusion precursor; (3) The above-mentioned powdered inclusion precursor was placed in a tube furnace and heated to 300°C at 1°C / min under a nitrogen atmosphere and held for 1 h for low-temperature carbonization; then heated to 1300°C at 5°C / min and held for 3 h for high-temperature carbonization; and naturally cooled to room temperature to obtain black iodine-doped starch-based carbon material.

[0060] Example 10 A method for preparing an iodine-doped starch-based carbon material, the method comprising the following steps: (1) Take 15.0 g of potato starch and place it in a beaker; measure 10.0 mL of medical povidone-iodine (effective iodine content is 0.45%w / v, density is about 1.0 g / mL, equivalent to about 0.045 g of elemental iodine and about 0.45 g of PVP) as the iodine source; separately weigh 0.45 g of polyvinylpyrrolidone (PVP, molecular weight ≥40,000) as a water-soluble dispersant and add it to the beaker; add 35.0 mL of deionized water (water:starch = 3:1) as the solvent and stir for 20 min until a homogeneous slurry is formed; Note: In this embodiment, medical iodine tincture provides the iodine source and part of PVP, and the additional 0.45 g of PVP ensures that a complete encapsulation layer is still formed under high iodine load; (2) The slurry was aged and dried in a 90℃ forced-air oven for 12 h; after drying, it was ground and passed through a 100-mesh sieve to obtain a purplish-red powdery inclusion precursor. (3) The above precursor was placed in a tube furnace and heated to 300°C at 1°C / min under a nitrogen atmosphere and held for 1 h for low-temperature carbonization; then heated to 1600°C at 5°C / min and held for 3 h for high-temperature carbonization; and then cooled naturally to room temperature to obtain black iodine-doped starch-based carbon material.

[0061] Comparative Example 1 Weigh 15g of corn starch and, without any solvent wetting, aging, drying, or pulverizing treatment, directly load it into a graphite boat; place it in a tube furnace, and under a high-purity nitrogen atmosphere (flow rate ≥100 mL / min), heat it to 300℃ at 1℃ / min and hold it at that temperature for 1h for low-temperature carbonization; then heat it to 1300℃ at 5℃ / min and hold it at that temperature for 3h for high-temperature carbonization; and cool it naturally to room temperature to obtain a black solid powder.

[0062] Comparative Example 2 Weigh 15g of potato starch and, without any solvent wetting, aging, drying, or pulverizing treatment, directly load it into a graphite boat; place it in a tube furnace, and under a high-purity nitrogen atmosphere (flow rate ≥100 mL / min), heat it to 300℃ at 1℃ / min and hold it at that temperature for 1h for low-temperature carbonization; then heat it to 1300℃ at 5℃ / min and hold it at that temperature for 3h for high-temperature carbonization; and allow it to cool naturally to room temperature to obtain a black solid powder.

[0063] Comparative Example 3 Weigh 15g of wheat starch and, without any solvent wetting, aging, drying, or pulverizing treatment, directly load it into a graphite boat; place it in a tube furnace, and under a high-purity nitrogen atmosphere (flow rate ≥100 mL / min), heat it to 300℃ at 1℃ / min and hold it at that temperature for 1h for low-temperature carbonization; then heat it to 1300℃ at 5℃ / min and hold it at that temperature for 3h for high-temperature carbonization; and allow it to cool naturally to room temperature to obtain a black solid powder.

[0064] Comparative Example 4 This comparative example is identical to Example 9 except that it does not contain a dispersant, as detailed below: 15.0 g of corn starch was placed in a beaker; 0.003 g of elemental iodine powder (purity ≥99.9%) was weighed as the iodine source and added to the beaker; 10.0 mL of deionized water was added as the solvent, and the mixture was stirred rapidly with a glass rod for 15 min; the slurry was placed in a 75 ℃ forced-air oven for aging and drying for 24 h; after drying, it was ground and passed through a 100-mesh sieve to obtain a purplish-red powdery inclusion precursor; the precursor was placed in a tube furnace and heated to 300 ℃ at 1 ℃ / min under a nitrogen atmosphere and held for 1 h for low-temperature carbonization; then heated to 1300 ℃ at 5 ℃ / min and held for 3 h for high-temperature carbonization; and naturally cooled to room temperature to obtain black carbon material.

[0065] This comparative example did not contain any water-soluble dispersant, and was intended to verify that, in the presence of an iodine source, if the encapsulation layer formed by the lack of a dispersant is not formed, the iodine element cannot be effectively retained during the gradient carbonization process, resulting in the final product having significantly lower electrochemical performance than that of Example 9.

[0066] Comparative Example 5 This comparative example is identical to Example 9 except for the absence of the low-temperature carbonization step. Details are as follows: 15.0 g of corn starch was placed in a beaker; 0.003 g of elemental iodine powder (purity ≥99.9%) was weighed as the iodine source, and 0.015 g of polyvinylpyrrolidone (PVP, molecular weight ≥40000) was weighed as the water-soluble dispersant, and added to the beaker in sequence; 10.0 mL of deionized water was added as the solvent, and the mixture was stirred rapidly with a glass rod for 15 min; the slurry was placed in a 75 ℃ forced-air oven for aging and drying for 24 h; after drying, it was ground and passed through a 100-mesh sieve to obtain a purplish-red powdered inclusion precursor; the precursor was placed in a tube furnace and heated to 1300 ℃ at 5 ℃ / min under a nitrogen atmosphere and held for 3 h for high-temperature carbonization; it was then naturally cooled to room temperature to obtain black carbon material.

[0067] This comparative example skips the 300°C low-temperature carbonization step to verify that, without low-temperature thermal crosslinking, the water-soluble dispersant cannot form a stable encapsulation layer, resulting in a large amount of iodine source sublimating and escaping during rapid heating, and a significant reduction in the iodine retention rate of the final product, with electrochemical performance inferior to Example 9.

[0068] Experimental Example 1 This experimental example is used to verify the microstructure characteristics and electrochemical energy storage performance of the iodine-doped starch-based carbon material prepared in this application. Specifically, it includes morphological and structural characterization and sodium-ion battery performance testing. All test samples are derived from the aforementioned examples and comparative examples.

[0069] (I) Morphological and structural characterization The carbon material powders prepared in each embodiment and comparative example were characterized as follows: 1. Optical observation: The inclusion precursors and carbon materials obtained in Examples 1-4 and Comparative Example 1 were placed in glass sample bottles and macroscopic color photographs were taken under natural light.

[0070] Figure 1 Optical images of the inclusion complex precursors prepared in Examples 1-4 of this experimental case.

[0071] Figure 2 Optical images of Comparative Example 1 before and after sintering, provided for this experimental example.

[0072] Figure 3 Optical images of Example 4 before and after sintering, provided for this experimental example.

[0073] From the above Figure 1 It can be seen that in Examples 1-4, the color changed from purplish-red to dark purple as the iodine content increased. It is speculated that this difference is caused by the varying content of the purple complex.

[0074] At the same time, through Figure 2 , Figure 3 It can be observed from a macroscopic perspective that the doping of iodine can effectively overcome problems such as poor thermal stability and easy gelatinization during starch carbonization.

[0075] 2. Scanning electron microscopy (SEM) observation: After the sample is sputter-coated with gold, its surface morphology and particle structure are observed using a field emission scanning electron microscope; Figure 4 SEM image of the carbon material obtained in Comparative Example 1 provided for this experimental example; Figure 5 SEM image of the carbon material obtained in Example 1 provided in this experimental example; Figure 6 SEM image of the carbon material obtained in Example 4 of this experimental example; See Figures 4-6 It is not difficult to see that the carbonization of unmodified starch in Comparative Example 1 yields a layered carbon material, while in Examples 1 and 4 of this application, the carbonization of iodine-modified starch does not exhibit a coalescence effect, and the carbon material can well maintain its spherical structure. Therefore, the modified carbon material has excellent packing density, thus exhibiting outstanding electrochemical performance.

[0076] 3. Constant current charge-discharge test: The obtained carbon material was used as the active material (95% by mass) and sodium alginate was used as the binder (5%) to prepare the electrode. The CR2016 button sodium-ion battery was assembled in an argon glove box (the counter electrode was metallic sodium, the electrolyte was a carbonate solution containing 1 mol / L sodium hexafluorophosphate (the solvent was composed of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1), and the separator was a Whatman GF / D glass fiber membrane). The first constant current charge-discharge test was carried out on the Blue Battery Test System at current densities of 0.1 C and 0.01 C, and the voltage-specific capacity curve was recorded.

[0077] Figure 7 The voltage distribution curves of the carbon materials obtained in Examples 1-4 and Comparative Example 1 are provided for this experimental example.

[0078] (II) Sodium-ion battery performance testing: Sodium-ion batteries were fabricated using carbon materials obtained in Examples 1-10 and Comparative Examples 1-5. The specific steps included: Iodine-doped carbon material and sodium alginate were mixed at a mass ratio of 95:5 using deionized water as a solvent to form a slurry, which was then coated onto a clean copper foil and dried to serve as the working electrode. Metallic sodium was used as the counter electrode, and a carbonate solution containing 1 mol / L sodium hexafluorophosphate (the solvent consisted of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) was used as the electrolyte. A 19 mm diameter glass fiber was used as the separator. The working electrode, counter electrode, separator, and electrolyte were assembled into a 2016-type button cell to obtain a sodium-ion battery.

[0079] The first charge-discharge test was conducted at current densities of 0.1 C and 0.01 C. The first-cycle coulombic efficiency (first-cycle charge capacity / first-cycle discharge capacity × 100%) and the first-cycle reversible specific capacity (i.e., first-cycle charge capacity, unit: mAh / g) were recorded. The test results are shown in Table 1.

[0080] Table 1. Comparison of electrochemical performance of iodine-doped starch-based carbon materials obtained in the embodiments of the present invention and the comparative examples:

[0081] As shown in Table 1, under the same carbonization process conditions, the reversible specific capacity of Examples 1-4 gradually increased from 316.1 mAh / g to 330.4 mAh / g by gradually increasing the amount of iodine source, an increase of 4.5%; while the first-cycle coulombic efficiency remained in the high range of 90.0%~91.8%, indicating that iodine doping significantly improved sodium storage activity without significantly deteriorating the material's structural stability. The reversible specific capacities of Example 1 (corn starch), Example 5 (potato starch), and Example 6 (wheat starch) were 316.1, 317.3, and 309.2 mAh / g, respectively, all of which were significantly higher than those of Comparative Examples 1–3, proving that the proposed method has good applicability to natural starches from different sources. Among them, potato starch, due to its higher amylose content, showed slightly better performance, further confirming the molecular-level confinement and anchoring effect of amylose helical cavities on iodine. The reversible specific capacities of Example 1 (using povidone-iodine as the iodine source), Example 9 (using elemental iodine + independent PVP), and Example 10 (high water system + dual PVP) were 316.1, 319.9, and 315.1 mAh / g, respectively. Their performance was similar and significantly better than that of the comparative example, which confirmed that povidone-iodine and elemental iodine are equivalent as iodine sources, and that PVP can effectively play a physical encapsulation function in the aging, drying, and low-temperature carbonization stages. To verify the necessity of the water-soluble dispersant and the low-temperature carbonization step, this application includes a control experiment based on Example 9: Compared to Example 9, Comparative Example 4, with all other conditions identical, omitted the water-soluble dispersant (PVP), resulting in a reversible specific capacity of 291.6 mAh / g, a decrease of 28.3 mAh / g compared to Example 9; its first-cycle coulombic efficiency was 89.7%, also lower than Example 9. These results indicate that without the physical encapsulation protection of PVP, a significant amount of iodine is lost during carbonization, failing to improve capacity and potentially degrading first-cycle efficiency due to side reactions caused by the lack of iodine binding.

[0082] Compared to Example 9, Comparative Example 5, under identical conditions, skipped the 300℃ / 1 h low-temperature carbonization step and directly heated to 1300℃ for high-temperature carbonization. Its reversible specific capacity was 307.2 mAh / g, a decrease of 12.7 mAh / g compared to Example 9; the first-cycle coulombic efficiency was 89.3%, a decrease of 2.0 percentage points compared to Example 9. These results indicate that the absence of the low-temperature stage prevents PVP from forming a sealed packaging layer in situ on the starch surface. Iodine undergoes uncontrolled sublimation during the rapid heating phase; although some residue remains, its electronic state conversion is insufficient, resulting in both capacity and first-cycle efficiency not reaching their optimal levels.

[0083] In summary, this application achieves efficient retention and functional intercalation of iodine under high-temperature carbonization conditions through the synergistic effect of three factors: molecular-level initial anchoring of the helical cavity of amylose, in-situ construction of a physical encapsulation layer by a water-soluble dispersant during the low-temperature carbonization stage, and directional regulation of the electronic state of iodine by gradient carbonization. The resulting material has both high reversible specific capacity and high first-cycle coulombic efficiency, which is a substantial improvement over the control sample that did not adopt this synergistic strategy.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an iodine-doped starch-based carbon material, characterized in that, The preparation method includes the following steps: S1: Starch, iodine source and water-soluble dispersant are mixed in a solvent, aged and dried and then pulverized to obtain an inclusion precursor that is purple-red, purple-black, wine-red, blue, purple or blue-purple. The mass ratio of starch, iodine source, and water-soluble dispersant is 15:(0.015~0.3):(0.0075~0.3). S2: The precursor is subjected to gradient carbonization in an inert atmosphere to obtain iodine-doped starch-based carbon material.

2. The method for preparing iodine-doped starch-based carbon material according to claim 1, characterized in that, The solvent is water; The amount of solvent added is (0.3~3) times the mass of starch, based on the amount of starch added.

3. The method for preparing iodine-doped starch-based carbon material according to claim 1, characterized in that, The starch includes at least one of potato starch, corn starch, wheat starch, sweet potato starch, cassava starch, rice starch, and sorghum starch. And / or, the iodine source includes at least one of elemental iodine, iodophor, and iodic acid; And / or, the water-soluble dispersant is polyvinylpyrrolidone.

4. The method for preparing iodine-doped starch-based carbon material according to claim 1, characterized in that, The aging and drying process is carried out at a temperature of 50-90℃ for 12-36 hours. Preferably, the aging and drying temperature is 75°C and the time is 24 hours.

5. The method for preparing iodine-doped starch-based carbon material according to claim 1, characterized in that, The particle size of the inclusion complex precursor is 5~150 μm.

6. The method for preparing iodine-doped starch-based carbon material according to claim 1, characterized in that, The gradient carbonization process includes a low-temperature carbonization process and a high-temperature carbonization process performed sequentially.

7. The method for preparing iodine-doped starch-based carbon material according to claim 6, characterized in that, The low-temperature carbonization treatment is carried out at a temperature of 200~400℃ for 1~3 hours.

8. The method for preparing iodine-doped starch-based carbon material according to claim 6, characterized in that, The high-temperature carbonization treatment is carried out at a temperature of 1100~1700℃ for a time of 1~6 h.

9. Iodine-doped starch-based carbon material prepared by the method according to any one of claims 1 to 8.

10. The application of the iodine-doped starch-based carbon material according to claim 9 in the preparation of energy storage products.

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