Nitrogen and iodine co-doped silicon-carbon negative electrode material, preparation method thereof and application in lithium ion battery

Abstract

The application provides a nitrogen and iodine co-doped silicon-carbon negative electrode material and a preparation method and application in lithium ion batteries, and belongs to the technical field of lithium ion battery negative electrode materials.The application uses povidone iodine as a single carbon source, nitrogen source and iodine source precursor, forms a uniform coating layer on the surface of silicon particles, and obtains a nitrogen and iodine co-doped carbon-coated silicon composite material after high-temperature carbonization.The iodine atoms in the material are chemically bonded to the nitrogen-doped carbon skeleton through I-C-N covalent bonds, effectively overcoming the technical problem that iodine is prone to volatilization and loss during high-temperature carbonization, and realizing efficient and stable doping of iodine.The synergistic effect of nitrogen and iodine significantly improves the interface stability and cycle performance of the material.The initial coulombic efficiency of the material can be more than 87.5%, and the capacity retention rate after 0.5C cycle for 200 times is more than 72%.The method is simple in process, controllable in cost, suitable for large-scale production, and has a wide application prospect in the next generation of high-energy-density lithium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, and particularly relates to a nitrogen and iodine co-doped silicon-carbon anode material, its preparation method, and its application in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronics, electric vehicles, and energy storage devices due to their high energy density, long cycle life, and lack of memory effect. However, with the increasing market demand for high-energy-density batteries, the theoretical specific capacity of existing commercial graphite anode materials (approximately 372 mAh / g) is insufficient to meet the requirements of next-generation high-performance lithium batteries. Silicon, with its theoretical specific capacity of up to 4200 mAh / g, is considered one of the most promising next-generation lithium-ion battery anode materials. However, two key issues severely restrict the commercial application of silicon anode materials during charge and discharge: first, silicon undergoes a dramatic volume expansion of over 300% during lithium insertion / extraction, leading to pulverization of the active material, detachment from the current collector, and rapid capacity decay; second, silicon has low intrinsic conductivity, affecting the kinetics of electrochemical reactions.

[0003] To address the aforementioned issues, various solutions have been proposed in existing technologies. Carbon coating is recognized as one of the most effective methods, as it improves the conductivity of silicon particles by coating them with a carbon layer, and also acts as a buffer layer to suppress volume expansion. To further optimize performance, research has attempted to dope the carbon layer with heteroatoms. For example, nitrogen-doped carbon materials, due to their high electron affinity and electronegativity, can improve the conductivity of carbon materials and stabilize the SEI film, and have been widely used in the modification of silicon-carbon anodes. Patent application CN202211679790.1 discloses a method for preparing nitrogen-phosphorus co-doped carbon-coated modified silicon suboxide anode materials. This method obtains silicon-carbon composite materials with good electrochemical performance through steps such as ball milling, spray drying, and secondary doping. Patent application CN202410939174.8 discloses a method for preparing silicon-carbon anode materials using multi-element (N, S, F, Li) doped porous carbon substrates, with a specific capacity of over 1800 mAh / g and a first-pass coulombic efficiency of up to 93%.

[0004] However, the existing technologies still have at least the following shortcomings: (1) Existing doping systems are mostly concentrated on elements such as nitrogen, boron, sulfur, and phosphorus, with less research on the application of iodine. The application potential of iodine atoms in carbon-coated materials has not been fully explored; (2) Since elemental iodine is easily sublimated and volatilized under high temperature conditions, when simply introducing an iodine source (such as elemental iodine, hydrogen iodide, etc.) and physically mixing it with a carbon source, iodine is easily lost during high-temperature carbonization, resulting in extremely low iodine doping in the carbon layer, which cannot play a doping modification effect. This greatly limits the industrial application of iodine-doped carbon materials; (3) Although nitrogen doping can solve the conductivity problem, its effect on suppressing volume expansion is limited, and its optimization of the stability of the SEI film and the interfacial chemical environment is still insufficient. Therefore, how to introduce iodine in a stable form into the carbon coating layer and play a synergistic role with nitrogen is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a nitrogen- and iodine co-doped silicon-carbon anode material, its preparation method, and its application in lithium-ion batteries. This invention utilizes polyvinylpyrrolidone-iodine (a polyvinylpyrrolidone-iodine complex) as a single carbon, nitrogen, and iodine source precursor to form a uniform coating layer on the surface of silicon particles. After high-temperature carbonization, a nitrogen- and iodine co-doped carbon-coated silicon composite material is obtained. Utilizing the strong coordination between iodine in polyvinylpyrrolidone-iodine and the pyrrolidone groups of polyvinylpyrrolidone, iodine atoms are stably "anchored" in the nitrogen-doped carbon framework through ICN covalent bonds during carbonization, thus overcoming the technical challenge of iodine easily volatilizing and being lost during high-temperature carbonization. Simultaneously, the synergistic effect of nitrogen and iodine significantly improves the material's conductivity, interfacial stability, and cycle performance. To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a nitrogen and iodine co-doped silicon-carbon anode material, comprising the following steps: Povidone-iodine was dissolved in a solvent to obtain a povidone-iodine solution with a concentration of 1.25 wt.% to 5 wt.%. Nano-silicon powder was added to the povidone-iodine solution and ultrasonically dispersed to obtain a silicon powder dispersion. The solvent was removed by evaporation at 50-60℃ to obtain a precursor of polyvinyl iodine-coated silicon. The polyvinyl iodine-coated silicon precursor was subjected to high-temperature carbonization in an inert atmosphere to obtain the nitrogen and iodine co-doped silicon-carbon anode material. The polyvinyl iodine is a coordination complex formed by iodine and polyvinylpyrrolidone groups, and during the high-temperature carbonization process, the iodine atoms are covalently bonded to the carbon skeleton through ICN bonds.

[0006] Furthermore, the solvent is anhydrous ethanol and / or deionized water.

[0007] Furthermore, the mass ratio of the povidone-iodine to the nano-silica powder is (0.5~2):5.

[0008] Furthermore, the iodine content of the povidone-iodine is 5.0 wt.% to 20.0 wt.%.

[0009] Furthermore, the carbonization temperature of the high-temperature carbonization treatment is 450℃~550℃.

[0010] Furthermore, the carbonization holding time for the high-temperature carbonization treatment is 2 to 6 hours.

[0011] Furthermore, the inert atmosphere for the high-temperature carbonization treatment is nitrogen or argon.

[0012] Furthermore, the concentration of nano-silicon powder in the silicon powder dispersion is 11 wt%.

[0013] For example, the present invention provides a method for preparing a nitrogen and iodine co-doped silicon-carbon anode material, which specifically includes the following steps: (1) Weigh 50~200mg of povidone-iodine (PVP-I2, effective iodine content is 5.0wt.%~20.0wt.%) and dissolve it in a solvent. Stir it magnetically at room temperature until it is completely dissolved (about 20min). By adjusting the amount of solvent and povidone-iodine, a povidone-iodine solution with a total mass of 4g and a concentration of 1.25wt.%~5wt.% is obtained. (2) Add 0.5g of silicon nanoparticles to the solution obtained in step (1), and continue to stir magnetically and disperse ultrasonically to obtain a silicon powder dispersion. (3) Remove the solvent by thermal evaporation at 50~60℃ to obtain the precursor powder of polyvinyl iodine coated silicon; (4) The precursor powder of polyvinyl iodine coated silicon obtained in step (3) is placed in an inert atmosphere and carbonized at a temperature of 450℃~550℃ for 2~6 hours. Then it is naturally cooled to room temperature to obtain nitrogen and iodine co-doped silicon-carbon anode material.

[0014] The present invention also provides a nitrogen and iodine co-doped silicon-carbon anode material, which is prepared according to the above preparation method.

[0015] Furthermore, the negative electrode material includes silicon material and a carbon coating layer covering the surface of the silicon material. The carbon coating layer is an amorphous carbon layer co-doped with nitrogen and iodine elements, and the carbon coating layer is obtained by high-temperature carbonization of povidone-iodine. At least some iodine atoms in the carbon coating layer are chemically bonded to the nitrogen-doped carbon framework through ICN covalent bonds.

[0016] The present invention also provides an application of the above-mentioned nitrogen and iodine co-doped silicon-carbon anode material in lithium-ion batteries.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: 1. This invention, by selecting povidone-iodine as a specific precursor and utilizing the strong coordination between iodine and pyrrolidone groups within its molecule, achieves for the first time the stable incorporation of iodine into a carbon coating layer via ICN covalent bonds. This overcomes the long-standing technical prejudice that iodine cannot be stably incorporated during high-temperature carbonization. Furthermore, this invention discovers that only when iodine exists in this bonded form can it produce a significant synergistic effect with nitrogen doping, simultaneously improving SEI film stability, reducing interfacial impedance, and suppressing volume expansion, resulting in a comprehensive performance improvement far exceeding that of single nitrogen doping or physically mixed iodine sources.

[0018] 2. This invention is the first to propose using "povidone-iodine" as an integrated carbon / nitrogen / iodine precursor to construct a nitrogen-iodine co-doped carbon coating layer, representing a pioneering achievement in the research of carbon coating materials for silicon-carbon anodes. In the povidone-iodine molecule, iodine forms strong coordination bonds with the pyrrolidone groups of polyvinylpyrrolidone, allowing for uniform coating onto the surface of silicon particles in the liquid phase. After carbonization, a nitrogen-iodine co-doped carbon coating layer is formed in situ. This integrated precursor design avoids the complex steps of adding carbon, nitrogen, and iodine sources separately in traditional methods, and ensures uniform mixing of elements at the molecular level, resulting in more uniform and controllable doping.

[0019] 3. This invention utilizes the coordination between iodine and nitrogen atoms in povidone-iodine to form covalent ICN bonds after carbonization, which firmly fixes iodine in the carbon skeleton, solving the problem of large-scale sublimation loss of iodine when traditionally using elemental iodine or iodides to physically mix with carbon sources.

[0020] 4. The chemical environment on the surface of the nitrogen-iodine co-doped carbon layer in the anode material of this invention helps to form a thinner, denser, and more stable SEI film, reducing side reactions and irreversible capacity loss, thereby improving cycle life and rate performance. Experiments have shown that the initial coulombic efficiency of the nitrogen-iodine co-doped carbon-coated silicon material of this invention reaches over 87.5%, and the capacity retention rate after 200 cycles at 0.5C exceeds 72.7%, which is significantly better than that of the single nitrogen-doped sample.

[0021] 5. This invention requires only one precursor, povidone-iodine. Liquid phase coating and high-temperature carbonization are both mature industrial technologies, requiring no expensive equipment. The process is simple, the cost is controllable, and it is suitable for large-scale production. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1The XPS test results of N,IC@Si-1 in Example 1 are shown, where (a) is the full spectrum, (b) is the C 1s spectrum, and (c) is the I 3d spectrum. Figure 2 The results of the first coulombic efficiency test of the N,IC@Si-1 material in Example 3 after it was assembled into a coin cell; Figure 3 The graph shows a comparison of the cycling performance (200 cycles) of the N,IC@Si-2 material from Example 2 and the NC@Si-1 material from Comparative Example 1 after they were assembled into coin cells at a current density of 0.5C. Figure 4 The electrochemical impedance spectroscopy (EIS) spectra of N,IC@Si-3 from Example 3 and NC@Si-2 from Comparative Example 2 after being assembled into coin cells are compared. Figure 5 The first-week charge-discharge curves and corresponding coulombic efficiencies of the N,IC@Si-3 material assembled into a coin cell in Example 3 are shown. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] This invention provides a method for preparing a nitrogen and iodine co-doped silicon-carbon anode material, comprising the following steps: Povidone-iodine was dissolved in a solvent to obtain a povidone-iodine solution with a concentration of 1.25 wt.% to 5 wt.%. Nano-silicon powder was added to a povidone-iodine solution and ultrasonically dispersed to obtain a silicon powder dispersion. The solvent was removed by evaporation at 50-60℃ to obtain a precursor of polyvinyl iodine-coated silicon. The precursor of polyvinyl iodine coated silicon was subjected to high-temperature carbonization in an inert atmosphere to obtain the nitrogen and iodine co-doped silicon-carbon anode material. Among them, povidone-iodine is a coordination complex formed by iodine and polyvinylpyrrolidone groups, and during high-temperature carbonization, iodine atoms are covalently bonded to the carbon skeleton through ICN bonds.

[0029] In a preferred embodiment of the present invention, the solvent is water or anhydrous ethanol, or a mixture of both.

[0030] In a preferred embodiment of the present invention, the mass ratio of povidone-iodine to nano-silica powder is (0.5~2):5.

[0031] In a preferred embodiment of the present invention, the iodine content of povidone-iodine is 5.0 wt.% to 20.0 wt.%. Povidone-iodine (PVP-I2) is a polyvinylpyrrolidone-iodine complex. Here, the iodine content refers to the mass percentage of elemental iodine in the polyvinylpyrrolidone-iodine complex. All povidone-iodine with different iodine contents used in the embodiments were commercially available.

[0032] In a preferred embodiment of the present invention, the carbonization temperature of the high-temperature carbonization treatment is 450°C to 550°C.

[0033] In a preferred embodiment of the present invention, the carbonization holding time for high-temperature carbonization treatment is 2 to 6 hours.

[0034] In a preferred embodiment of the present invention, the inert atmosphere for the high-temperature carbonization treatment is nitrogen or argon.

[0035] In a preferred embodiment of the present invention, the concentration of nano-silicon powder in the silicon powder dispersion is 11 wt%.

[0036] This invention also provides a nitrogen and iodine co-doped silicon-carbon anode material, prepared according to the above preparation method.

[0037] Furthermore, the anode material includes silicon material and a carbon coating layer covering the surface of the silicon material. The carbon coating layer is an amorphous carbon layer co-doped with nitrogen and iodine elements, and the carbon coating layer is obtained by high-temperature carbonization of polyvinyl iodine. At least some of the iodine atoms in the carbon coating layer are chemically bonded to the nitrogen-doped carbon framework through ICN covalent bonds.

[0038] The present invention also provides an application of the above-mentioned nitrogen and iodine co-doped silicon-carbon anode material in lithium-ion batteries.

[0039] In this embodiment of the invention, room temperature refers to 25±2℃.

[0040] All raw materials used in the embodiments of this invention were purchased commercially.

[0041] The technical solution of the present invention will be further illustrated by the following embodiments.

[0042] Example 1 A method for preparing a nitrogen and iodine co-doped silicon-carbon anode material specifically includes the following steps: (1) Weigh 200 mg of povidone-iodine (PVP-I2, with an effective iodine content of 10%) and dissolve it in 3.8 g of anhydrous ethanol (EtOH). Dissolve it completely at room temperature by magnetic stirring (about 20 min) to obtain a PVP-I2 / EtOH solution. (2) Add 0.5g of silicon nanoparticles to the solution obtained in step (1) and continue to stir magnetically (5h). During the stirring process, after stirring for 1 hour, place the reagent bottle into an ultrasonic instrument for 30s (to further disperse the aggregated silicon particles) to obtain Si / PVP-I2 / EtOH dispersion. (3) Take out the obtained Si / PVP-I2 / EtOH dispersion, and then heat it on a heating platform at 50°C for 30 min to remove the ethanol and obtain Si precursor (Si / PVP-I2) powder coated with PVP-I2. (4) Place the PVP-I2 coated Si precursor powder obtained in step (3) in a tube furnace, heat it to 500°C while maintaining an inert atmosphere of nitrogen, keep it at that temperature for 3 hours, and then cool it naturally to room temperature to obtain the nitrogen and iodine co-doped silicon-carbon anode material, denoted as N,IC@Si-1.

[0043] Example 2 A method for preparing a nitrogen and iodine co-doped silicon-carbon anode material specifically includes the following steps: (1) Weigh 100 mg of povidone-iodine (PVP-I2, with an effective iodine content of 12%) and dissolve it in 3.9 g of anhydrous ethanol (EtOH). Dissolve it completely at room temperature by magnetic stirring (about 10 min) to obtain a PVP-I2 / EtOH solution. (2) Add 0.5g of silicon nanoparticles to the solution obtained in step (1) and continue to stir magnetically (2h); during the stirring process, after every 0.5 hours of stirring, place the reagent bottle into an ultrasonic instrument for 30s of sonication (to further disperse the aggregated silicon particles) to obtain Si / PVP-I2 / EtOH dispersion; (3) Take out the obtained Si / PVP-I2 / EtOH dispersion, dry it in a vacuum drying oven at 55℃ for 2 hours, remove the ethanol, and obtain Si precursor powder coated with PVP-I2 (Si / PVP-I2). (4) Place the PVP-I2 coated Si precursor powder obtained in step (3) in a tube furnace, heat it to 450°C while maintaining an inert atmosphere of argon, keep it at that temperature for 2 hours, and then cool it naturally to room temperature to obtain the nitrogen and iodine co-doped silicon-carbon anode material, denoted as N,IC@Si-2.

[0044] Example 3 A method for preparing a nitrogen and iodine co-doped silicon-carbon anode material specifically includes the following steps: (1) Weigh 50 mg of povidone-iodine (PVP-I2, with an effective iodine content of 20%) and dissolve it in 3.95 g of a mixed solvent of deionized water / anhydrous ethanol (volume ratio of 1:1) (EtOH / H2O). Dissolve it completely at room temperature by magnetic stirring (about 15 min) to obtain a PVP-I2 / EtOH / H2O solution. (2) Add 0.5g of silicon nanoparticles to the solution obtained in step (1) and continue to stir magnetically (3 hours); during the stirring process, after every 0.5 hours of stirring, place the reagent bottle into an ultrasonic instrument for 30s of sonication (to further disperse the aggregated silicon particles) to obtain Si / PVP-I2 / EtOH / H2O dispersion. (3) Same as Example 2; (4) Place the dried polyvinyl iodine-coated silicon precursor powder from step (3) into a tube furnace, heat it to 550°C while maintaining an inert atmosphere of argon, keep it at that temperature for 3 hours, and then cool it naturally to room temperature to obtain the nitrogen and iodine co-doped silicon-carbon anode material, denoted as N,IC@Si-3.

[0045] Comparative Example 1 Same as Example 2, except that povidone-iodine is replaced with an equal mass of polyvinylpyrrolidone (PVP), specifically: (1) Weigh 100 mg of polyvinylpyrrolidone (PVP) and dissolve it in 3.9 g of anhydrous ethanol (EtOH). Stir the solution magnetically at room temperature until completely dissolved (about 10 min) to obtain a PVP / EtOH solution. (2) Add 0.5g of silicon nanoparticles to the solution obtained in step (1) and continue to stir magnetically (2h); during the stirring process, after stirring for about 0.5 hours, place the reagent bottle into an ultrasonic instrument for ultrasonication for 30s (to further disperse the aggregated silicon particles) to obtain Si / PVP / EtOH dispersion. (3) Take out the obtained Si / PVP / EtOH dispersion, dry it in a vacuum drying oven at 55℃ for 2 hours, remove the ethanol, and obtain PVP-coated Si precursor (Si / PVP) powder. (4) Place the PVP-coated Si precursor powder dried in step (3) into a tube furnace, heat it to 450°C while maintaining an inert atmosphere of argon, keep it at that temperature for 2 hours, and then cool it naturally to room temperature to obtain the negative electrode material, denoted as NC@Si-1.

[0046] Comparative Example 2 Same as Example 3, except that povidone-iodine is replaced with an equal mass of polyvinylpyrrolidone (PVP), specifically: (1) Weigh 50 mg of polyvinylpyrrolidone (PVP) and dissolve it in 3.95 g of deionized water / anhydrous ethanol (volume ratio 1:1) mixed solvent (EtOH / H2O). Dissolve it completely at room temperature by magnetic stirring (about 15 min) to obtain PVP / EtOH / H2O solution. (2) Add 0.5g of silicon nanoparticles to the solution obtained in step (1) and continue to stir magnetically (3h); during the stirring process, after stirring for about 0.5 hours, place the reagent bottle into an ultrasonic instrument for ultrasonication for 30s (to further disperse the aggregated silicon particles) to obtain Si / PVP / EtOH / H2O dispersion. (3) Take out the obtained Si / PVP / EtOH dispersion, dry it in a vacuum drying oven at 55℃ for 2 hours, remove the ethanol, and obtain PVP-coated Si precursor (Si / PVP) powder. (4) Place the PVP-coated Si precursor powder dried in step (3) into a tube furnace, heat it to 550°C while maintaining an inert atmosphere of argon, keep it at that temperature for 3 hours, and then cool it naturally to room temperature to obtain the negative electrode material, denoted as NC@Si-2.

[0047] Performance testing Example 1 yielded a precursor Si / PVP-I2 powder with a mass of 0.6906 g, and the N,IC@Si-1 powder obtained after high-temperature carbonization treatment had a mass of 0.5222 g. Calculations showed that the carbon coating content of the N,IC@Si-1 anode material was approximately 5.6%. XPS measurements (e.g.) Figure 1In Figure a), the nitrogen doping content of the carbon coating layer is 5.2 wt.% and the iodine doping content is 0.8 wt.%, indicating that the generated carbon coating layer contains both nitrogen and iodine co-doping elements. Figure 1 The C 1s spectrum of b shows that the peak at 285.8 eV corresponds to the CN / CI bond; Figure 1 The 3d spectrum of I in the carbon coating shows that the IN bonds are located at 631.5 eV and 620 eV, while the IC bonds are located at 630.5 eV, 619 eV, and 618 eV. The XPS test results indicate that nitrogen-iodine co-doping and IC bonds were simultaneously formed in the carbon coating. The initial coulombic efficiency of the N,IC@Si-1 half-cell prepared in Example 1 was further tested, and the results are as follows... Figure 2 As shown, the first-cycle coulombic efficiency of the nitrogen-iodine co-doped carbon-coated silicon anode (N,IC@Si-1) is approximately 84.3%.

[0048] The N,IC@Si-2 obtained in Example 2 and the NC@Si-1 obtained in Comparative Example 1 were assembled into coin cells, and the cycle stability of the cells was tested. The initial reversible capacity released by N,IC@Si-2 at a current density of 0.1C was 1541 mAh / g, with a corresponding first-cycle coulombic efficiency of 84.9%, while the initial reversible capacity released by NC@Si-1 was 1625 mAh / g. Subsequently, the cycle stability was tested at a current density of 0.5C after capacity normalization. A comparison of the cycle performance (200 cycles) of N,IC@Si-2 and NC@Si-1 materials assembled into coin cells at a current density of 0.5C is shown in the figure. Figure 3 As can be seen, the nitrogen-iodine co-doped carbon-coated silicon anode (N,IC@Si-2) exhibits better cycle stability, with a capacity retention of 72.7% after 200 cycles, which is higher than the 52.3% of the nitrogen-doped carbon-coated silicon anode (NC@Si). This is directly related to the enhanced interface stability brought about by the synergistic effect of nitrogen-iodine co-doping.

[0049] The N,IC@Si-3 obtained in Example 3 and the NC@Si-2 of Comparative Example 2 were assembled into a coin cell, and the EIS performance of the cell was tested. The results are as follows: Figure 4 As shown, the nitrogen-iodine co-doped carbon-coated silicon anode (N,IC@Si-3) exhibits low charge transfer impedance, which is directly related to the enhanced interface stability brought about by the synergistic effect of nitrogen-iodine co-doping. The initial coulombic efficiency of the N,IC@Si-3 half-cell was further tested, and the results are as follows... Figure 5 As shown, the first-week coulombic efficiency of the nitrogen-iodine co-doped carbon-coated silicon anode (N,IC@Si-3) is approximately 87.8%.

[0050] Comparative Example 3 The iodine source is introduced using a physical mixing method, and the preparation steps are as follows: (1) Weigh 80 mg of polyvinylpyrrolidone and 12 mg of elemental iodine, grind and mix them thoroughly in an agate mortar to obtain a physical mixture of PVP / I2, dissolve it in 3.9 g of anhydrous ethanol (EtOH), and completely dissolve it at room temperature by magnetic stirring (about 15 min) to obtain a PVP-I2 / EtOH solution. (2) Same as step (2) in Example 2; (3) Take out the obtained Si / PVP-I2 / EtOH dispersion, dry it in a vacuum drying oven at 70℃ for 5 hours, remove the ethanol, and obtain PVP-I2 coated Si precursor (Si / PVP-I2) powder. (4) The carbonization conditions are the same as in Example 2, and the resulting material is denoted as I+PVP-C@Si.

[0051] The first-cycle coulombic efficiency of the I+PVP-C@Si electrode half-cell prepared in Comparative Example 3 was further tested. The results showed that the first-cycle coulombic efficiency of the nitrogen-iodine co-doped carbon-coated silicon anode (I+PVP-C@Si) was approximately 72.3%. The low first-cycle coulombic efficiency of the silicon anode prepared in this comparative example may be attributed to the significant loss of iodine during the treatment in step (3).

[0052] Comparative Example 4 Same as Example 2, except that the carbonization temperature in step (4) is changed to 550℃ and held for 3 hours. The resulting material is denoted as N,IC@Si-550℃.

[0053] The initial coulombic efficiency of the silicon half-cell prepared in Comparative Example 4 was further tested, and its initial coulombic efficiency was approximately 86.1%. The initial coulombic efficiency of the silicon anode prepared in this comparative example is higher than that of the N,IC@Si-2 anode, indicating that the carbonization temperature affects the initial efficiency.

[0054] Comparative Example 5 Same as Example 2, except that the carbonization temperature in step (4) is changed to 500℃ and held for 3 hours. The resulting material is denoted as N,IC@Si-500℃.

[0055] The initial coulombic efficiency of the silicon half-cell prepared in Comparative Example 5 was further tested, and its initial coulombic efficiency was approximately 85.8%. The initial coulombic efficiency of the silicon anode prepared in this comparative example was also higher than that of the N,IC@Si-2 anode. Combined with the data from Comparative Example 4, the test results indicate that a carbonization temperature of 550℃ is optimal. However, to prevent the formation of inert SiC and SiI4 during the carbonization process, higher carbonization temperatures were not tested.

[0056] Comparative Example 6 Same as Example 2, except that the effective iodine content of the povidone-iodine used is 5.0 wt.%.

[0057] The initial coulombic efficiency of the silicon half-cell prepared in Comparative Example 6 was further tested, and its initial coulombic efficiency was approximately 76.1%. The initial coulombic efficiency of the silicon anode prepared in this comparative example is much lower than that of the N,IC@Si-2 anode. This is attributed to the influence of the iodine content in the povidone-iodine used to prepare the precursor. With a low iodine content, there is even less residual iodine after carbonization, and the initial efficiency is close to that of PVP alone. Therefore, the iodine content in povidone-iodine affects the initial efficiency of carbon-coated silicon anodes.

[0058] Comparative Example 7 Same as Example 2, except that the effective iodine content of the povidone-iodine used is 25.0 wt.%.

[0059] The initial coulombic efficiency of the silicon half-cell prepared in Comparative Example 7 was further tested, and its initial coulombic efficiency was approximately 84.1%. The initial coulombic efficiency of the silicon anode prepared in this comparative example is still lower than that of the N,IC@Si-2 anode. Combined with the data from Comparative Example 6, the results indicate that increasing the iodine content in povidone-iodine can improve the initial coulombic efficiency to some extent; however, there is no single positive correlation between the effective iodine content and the initial coulombic efficiency of the prepared carbon-coated silicon anode.

[0060] Comparative Example 8 Same as Example 2, except that the mass ratio of povidone-iodine to nano-silica powder is 1:1, specifically: (1) Weigh 0.5g of povidone-iodine (PVP-I2, with an effective iodine content of 12%) and dissolve it in 3.5g of anhydrous ethanol (EtOH). Dissolve it completely at room temperature by magnetic stirring (about 30min) to obtain a PVP-I2 / EtOH solution. (2) Add 0.5g of silicon nanoparticles to the solution obtained in step (1) and continue to stir magnetically (2h); during the stirring process, after stirring for about 0.5 hours, place the reagent bottle into an ultrasonic instrument for ultrasonication for 30s (to further disperse the aggregated silicon particles) to obtain Si / PVP-I2 / EtOH dispersion; (3) Take out the obtained Si / PVP-I2 / EtOH dispersion, dry it in a vacuum drying oven at 55℃ for 2 hours, remove the ethanol, and obtain Si precursor powder coated with PVP-I2 (Si / PVP-I2). (4) Consistent with Example 2.

[0061] The initial coulombic efficiency of the silicon half-cell prepared in Comparative Example 8 was further tested, and its initial coulombic efficiency was approximately 82.9%. The initial coulombic efficiency of the silicon anode prepared in this comparative example was lower than that of the N,IC@Si-2 anode. The results indicate that the proportion of povidone-iodine used affects the initial coulombic efficiency of the silicon anode after carbonization. The higher the proportion of povidone-iodine, the thicker the coating layer after carbonization, thus negatively impacting the initial coulombic efficiency.

[0062] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen and iodine co-doped silicon-carbon anode material, characterized in that, Includes the following steps: Povidone-iodine was dissolved in a solvent to obtain a povidone-iodine solution with a concentration of 1.25 wt.% to 5 wt.%. Nano-silicon powder was added to the povidone-iodine solution and ultrasonically dispersed to obtain a silicon powder dispersion. The solvent was removed by evaporation at 50-60℃ to obtain a precursor of polyvinyl iodine-coated silicon. The polyvinyl iodine-coated silicon precursor was subjected to high-temperature carbonization in an inert atmosphere to obtain the nitrogen and iodine co-doped silicon-carbon anode material.

2. The method for preparing the nitrogen and iodine co-doped silicon-carbon anode material according to claim 1, characterized in that, The solvent is anhydrous ethanol and / or deionized water.

3. The method for preparing the nitrogen and iodine co-doped silicon-carbon anode material according to claim 1, characterized in that, The mass ratio of povidone-iodine to nano-silica powder is (0.5~2):

5.

4. The method for preparing the nitrogen and iodine co-doped silicon-carbon anode material according to claim 1, characterized in that, The iodine content of the povidone-iodine is 5.0 wt.% to 20.0 wt.%.

5. The method for preparing the nitrogen and iodine co-doped silicon-carbon anode material according to claim 1, characterized in that, The carbonization temperature of the high-temperature carbonization treatment is 450℃~550℃.

6. The method for preparing the nitrogen and iodine co-doped silicon-carbon anode material according to claim 1, characterized in that, The carbonization holding time for the high-temperature carbonization treatment is 2 to 6 hours.

7. The method for preparing the nitrogen and iodine co-doped silicon-carbon anode material according to claim 1, characterized in that, The concentration of nano-silicon powder in the silicon powder dispersion is 11 wt%.

8. A nitrogen and iodine co-doped silicon-carbon anode material, characterized in that, It is prepared according to any one of claims 1 to 7.

9. The nitrogen and iodine co-doped silicon-carbon anode material according to claim 8, characterized in that, The negative electrode material includes silicon material and a carbon coating layer covering the surface of the silicon material. The carbon coating layer is an amorphous carbon layer co-doped with nitrogen and iodine elements, and the carbon coating layer is obtained by high-temperature carbonization of povidone-iodine. At least some iodine atoms in the carbon coating layer are chemically bonded to the nitrogen-doped carbon framework through ICN covalent bonds.

10. The application of a nitrogen and iodine co-doped silicon-carbon anode material as described in any one of claims 8 to 9 in a lithium-ion battery.

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