Nitrogen-doped silicon-oxygen-carbon negative electrode material of lithium ion battery and preparation method and application of nitrogen-doped silicon-oxygen-carbon negative electrode material

Abstract

The invention discloses a nitrogen-doped silicon-oxygen-carbon negative electrode material of a lithium ion battery as well as a preparation method and application of the nitrogen-doped silicon-oxygen-carbon negative electrode material, and belongs to the technical field of negative electrode materials of lithium ion batteries. The preparation method of the nitrogen-doped silicon-oxygen-carbon material comprises the following steps: carrying out acidic hydrolytic condensation reaction on gamma-methacryloxypropyltrimethoxysilane, and carrying out rotary evaporation, washing and drying to obtain a polysiloxane precursor; and performing high-temperature pyrolysis on the polysiloxane precursor in a nitrogen-containing atmosphere to obtain the nitrogen-doped silicon-oxygen-carbon negative electrode material. According to the nitrogen-doped silicon-oxygen-carbon negative electrode material for the lithium ion battery, the content of nitrogen in silicon-oxygen-carbon is controlled by adjusting conditions such as pyrolysis atmosphere, pyrolysis temperature and pyrolysis time, so that lithium ion storage sites are innovatively enriched from the atomic scale, and the ion and electron transmission capability of the silicon-oxygen-carbon material is improved; therefore, the electrochemical properties such as the first-circle coulombic efficiency, the reversible capacity, the rate capability and the long cycle stability of the silicon-oxygen-carbon material are remarkably improved.

Description

A nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries, its preparation method and application Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery anode materials, specifically relating to a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries, its preparation method, and its application. Background Technology

[0002] As a highly efficient electrochemical energy storage device, lithium-ion batteries have become a key energy storage solution for scientific research and industry since their commercial application, thanks to their advantages such as high energy density, compact structural design and good economic efficiency.

[0003] Silicon-based materials are not only characterized by 4200 mAh·g -1 Silicon anodes possess ultra-high theoretical capacity, abundant reserves, environmental friendliness, and moderate redox potential, making them a promising new type of lithium-ion battery anode material. However, silicon anodes have relatively low intrinsic conductivity (10⁻⁶ Ω·cm). -5 -10 -3 S·cm -1 ), lithium-ion diffusion coefficient is small (10) -14 -10 -13 cm 2 ·s -1 Furthermore, silicon anodes experience volume changes of up to 300% during charging and discharging. These issues lead to sluggish kinetics, separation of the active material from the current collector, and instability of the solid electrolyte interphase (SEI) film, ultimately resulting in rapid capacity decay and shortened cycle life, severely hindering their industrialization.

[0004] Silicon-oxygen-carbon (SiO2-C) materials have attracted widespread attention from researchers as alternatives to silicon-based anode materials due to their polymer precursor origin, considerable specific capacity, relatively stable structure during cycling, and small volume change. However, SiO2-C materials exhibit poor electronic and ionic conductivity, severely impacting their electrochemical lithium storage performance. This typically requires the addition of extra conductive agents or conductive binders during electrode fabrication. This reduces battery energy density to some extent, further hindering the commercial application of SiO2-C materials.

[0005] Nitrogen has a higher electronegativity than carbon atoms, and its atomic radius is smaller. Therefore, doping nitrogen into silicon-oxygen-carbon networks can create defects, thereby improving conductivity and enhancing Li. + The transport of Li, while enhancing the Li of silicon-oxygen-carbon materials + Storage capacity. Current research methods mainly involve introducing nitrogen atom doping through organic coating, vapor deposition, and electrospinning. However, these methods suffer from drawbacks such as complex experimental procedures, cumbersome processes, and high preparation costs, making it difficult to meet the needs of large-scale commercial production.

[0006] Chinese patent CN116344771A discloses a high-lithium-storage-performance silicon-oxygen-carbon anode material and its preparation method. The method involves preparing an unmodified silicon-oxygen-carbon (SiOC) material through a hydrolysis-condensation reaction of phenyltriethoxysiloxane followed by high-temperature pyrolysis. The surface of this SiOC is then carbon-coated using polyvinylidene fluoride (PVDF) as the carbon source, forming a SiOC@C composite material. While the carbon coating improves the cycle stability of this silicon-oxygen-carbon anode material, it does not consider the first-cycle coulombic efficiency and only mentions the high lithium-storage-performance SiOC-0.3T0.7P@C anode material at 100 mA·g. -1 After 100 cycles at current density, the capacity retention is approximately 93.1%, indicating poor long-term cycling stability. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, the present invention aims to provide a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries, its preparation method and application, so as to solve the technical problem that the silicon-oxygen-carbon anode material prepared by the existing preparation method does not take into account the first-cycle coulombic efficiency and has poor long-term cycle stability.

[0008] To achieve the above objectives, the present invention employs the following technical solution: Addressing the shortcomings of the aforementioned technical solutions, the present invention aims to provide a simple, efficient, and low-cost nitrogen-doped silicon-oxygen-carbon anode material with high lithium storage performance and its preparation method, thereby solving the problem of low electronic and ionic conductivity in silicon-oxygen-carbon materials. The technical solution of the present invention involves preparing polysiloxane by hydrolyzing and condensing a siloxane precursor under acidic conditions, followed by high-temperature pyrolysis in a nitrogen-containing atmosphere to obtain the nitrogen-doped silicon-oxygen-carbon anode material.

[0009] The nitrogen-doped silicon-oxygen-carbon anode material prepared by this invention not only improves conductivity by introducing nitrogen atom doping to regulate the surface charge distribution of silicon-oxygen-carbon, but also enhances its resistance to Li. + The chemical adsorption capacity further improves the electrochemical properties of silicon-oxygen-carbon materials, such as reversible capacity, rate performance, and cycle stability.

[0010] This invention provides a method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries, comprising the following steps: γ-methacryloyloxypropyltrimethoxysilane is subjected to an acidic hydrolysis-condensation reaction, followed by rotary evaporation, washing, and drying to obtain a polysiloxane precursor; the polysiloxane precursor is then subjected to high-temperature pyrolysis in a nitrogen-containing atmosphere to obtain the nitrogen-doped silicon-oxygen-carbon anode material.

[0011] Preferably, the high-temperature pyrolysis conditions include: a temperature of 800-1000℃ and a heating rate of 5℃·min. -1 The time is 2-6 hours.

[0012] Preferably, the high-temperature pyrolysis conditions include: a temperature of 900°C and a time of 2 hours.

[0013] A further preferred method involves washing the sample three times each with saturated saline solution and ether, adjusting it to neutral, and then drying it with anhydrous magnesium sulfate.

[0014] Preferably, the reaction temperature of the acidic hydrolysis-condensation reaction is 30-40℃.

[0015] Preferably, the acidic hydrolysis-condensation reaction includes: adding hydrochloric acid solution to an aqueous organic alcohol solution at 30°C, adjusting the pH value to 4-5, raising the temperature to 40°C, adding γ-methacryloyloxypropyltrimethoxysilane, and stirring.

[0016] Preferably, the organic alcohol aqueous solution is prepared by mixing anhydrous methanol, anhydrous ethanol and deionized water; the volume ratio of anhydrous methanol to anhydrous ethanol is (0.5-2):1, and the molar ratio of deionized water to γ-methacryloyloxypropyltrimethoxysilane is 10:1.

[0017] Preferably, the concentration of the hydrochloric acid solution is (0.9-1.1) mol·L⁻¹. -1 The mass percentage concentration of the γ-methacryloyloxypropyltrimethoxysilane is 18%-22%.

[0018] More preferably, the stirring time in the acidic hydrolysis-condensation reaction is 10 hours.

[0019] Preferably, the nitrogen-containing atmosphere is composed of ammonia, and the ammonia serves as a nitrogen dopant source to introduce nitrogen during the pyrolysis process.

[0020] This invention also provides a nitrogen-doped silicon-oxygen-carbon anode material prepared by the above-mentioned method for preparing nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries, wherein the nitrogen-doped silicon-oxygen-carbon anode material comprises amorphous SiO₂. x C 4-x Tetrahedral units and disordered free carbon nanoclusters, wherein the number of oxygen atoms x is 3 or 4; the nitrogen-doped silicon-oxygen-carbon anode material is a micron-sized, irregular blocky solid.

[0021] This invention also provides the application of the above-mentioned nitrogen-doped silicon-oxygen-carbon anode material in lithium-ion batteries.

[0022] The material was tested for electrochemical performance after half-cell treatment at 0.1 A·g -1 At a current density of [value missing], the first-cycle coulombic efficiency is 65.90%, and the reversible capacity is 850 mAh·g. -1 At 0.5A·g -1 Its reversible capacity is 385 mAh·g after 200 cycles at a current density. -1The capacity retention rate was 96.25%.

[0023] Compared with existing technologies, the present invention has the following beneficial effects: The present invention provides a method for preparing nitrogen-doped silicon-oxygen-carbon anode materials for lithium-ion batteries. It employs a hydrolysis-condensation combined with high-temperature pyrolysis method to introduce nitrogen atom doping in a one-step process, thereby preparing the nitrogen-doped silicon-oxygen-carbon anode material. The nitrogen-doped silicon-oxygen-carbon anode material prepared by this method can control the nitrogen atom doping and active component content by changing the pyrolysis temperature and time of the polysiloxane precursor in a nitrogen-containing atmosphere. This generates more defect structures and carbon-coated structures, introduces more lithium-ion storage sites, and enhances lithium-ion storage capacity, which is beneficial for improving the material's reversible lithium storage capacity and long-cycle stability. Simultaneously, nitrogen atom doping helps improve the surface charge distribution and enhance the material's ion-electron conductivity, thus improving the material's rate performance. More importantly, nitrogen atom doping also optimizes the material's interface stability, reducing irreversible lithium loss during the first charge-discharge process, thereby significantly improving the first-cycle coulombic efficiency. Data from Example 2 shows that the material's first-cycle coulombic efficiency reaches 65.90%. The stable structures formed by nitrogen doping (such as pyridine nitrogen and graphitic nitrogen configurations) mitigate volume changes during cycling, enhance material durability, and significantly improve long-term cycling stability. Data from Example 2 shows that the capacity retention is 96.25% after 200 cycles and 75% after 800 cycles. Furthermore, this method introduces nitrogen atom doping in one step, is simple and inexpensive, and can be used for large-scale fabrication. This one-step nitrogen doping method is simple, inexpensive, and suitable for large-scale fabrication.

[0024] Furthermore, the pyrolysis temperature was controlled between 800-1000℃. Below 800℃, the carbonization degree of the precursor was insufficient, the free carbon phase failed to form an effective conductive network, and the nitrogen doping level was low, failing to significantly improve the material's conductivity. Above 1000℃, although the carbonization degree increased, it might lead to SiO₂... x C 4-x Phase decomposition or phase separation may occur, and excessively high temperatures may cause nitrogen to escape in gaseous form, which may reduce the doping effect and may also induce crystallization in the silicon region, resulting in a large volume effect.

[0025] Furthermore, under pyrolysis conditions of 900℃ for 2 hours, the organic components in the polysiloxane precursor can be fully carbonized to form highly disordered but highly conductive free carbon nanoclusters. Simultaneously, nitrogen atoms can be effectively doped into the carbon network in the forms of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen. These different forms of nitrogen doping sites not only provide additional lithium storage sites but also significantly improve the surface wettability and lithium-ion diffusion kinetics of the material; the heating rate is controlled at 5℃·min. -1The slow heating helps the precursor achieve uniform thermal decomposition and structural reorganization during pyrolysis, avoiding structural damage and particle cracking caused by rapid temperature changes; a pyrolysis time of 2 hours ensures a balance between the adequacy and economy of heat treatment. Too short a time will result in incomplete pyrolysis, leaving unstable organic components inside the material; too long a time may lead to excessive destruction of the carbon structure and energy waste.

[0026] This precisely controlled pyrolysis condition ultimately led to the formation of SiO. x C 4-x An ideal composite structure in which tetrahedral units are uniformly dispersed in a nitrogen-doped carbon matrix. This structure not only utilizes the high specific capacity of silicon-oxygen-carbon materials, but also combines the excellent conductivity and structural stability of nitrogen-doped carbon, providing an efficient insertion / deintercalation channel for lithium ions.

[0027] Furthermore, by controlling the reaction temperature at 30-40℃, the hydrolysis rate and condensation rate of γ-methacryloxypropyltrimethoxysilane can reach equilibrium. If the temperature is too low, the reaction rate will be too slow, resulting in low production efficiency; if the temperature is too high, it may cause an increase in side reactions, such as increased volatilization of methanol or ethanol, leading to an uneven reaction system, or even premature polymerization of methacryloxy, affecting the regularity of the precursor structure.

[0028] Furthermore, in acidic hydrolysis-condensation reactions, a weakly acidic environment with a pH of 4-5 is beneficial for the hydrolysis of silane methoxy groups. However, excessively strong acidity can lead to an overly rapid condensation reaction, resulting in highly cross-linked gel-like products with difficult-to-control molecular structure. Under weakly acidic conditions, the hydrolysis and condensation rates are optimally matched, which is conducive to the formation of polysiloxane precursors with moderate molecular chain length and controllable cross-linking degree.

[0029] Furthermore, the specific ratio of the organic alcohol aqueous solution ensures the complete dissolution of reactant molecules and their reactivity. The mixed use of methanol and ethanol optimizes the solubility of the silane precursor in the water-alcohol mixed solvent, promoting the uniformity of the hydrolysis reaction. The requirement that the amount of deionized water be equal to the amount of silane ensures that the amount of water required for the hydrolysis reaction is sufficient but not excessive, avoiding the residual unstable silanol groups caused by over-hydrolysis.

[0030] Furthermore, the controlled concentrations of hydrochloric acid solution and the mass percentage concentration of γ-methacryloyloxypropyltrimethoxysilane jointly ensured that the reaction system had a suitable reaction rate and a controllable molecular assembly process. An overly diluted system would reduce reaction efficiency and increase subsequent processing costs; while an overly concentrated system might lead to excessive local cross-linking, resulting in an uneven product structure.

[0031] Furthermore, the active nitrogen atoms or amino radicals generated by the decomposition of ammonia at high temperatures possess high reactivity and can react with free radical sites formed during pyrolysis, thereby incorporating them into the carbon network. Compared to other nitrogen sources (such as urea and melamine), ammonia, as a gaseous nitrogen source, can achieve molecular-level contact with polysiloxane precursors, ensuring uniform nitrogen doping in both the bulk and surface phases of the material. This uniform doping level is beneficial for improving the overall electrical conductivity of the material and creating uniform lithium-ion storage sites.

[0032] This invention also provides a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries prepared by the above method, including amorphous SiO₂. x C 4-x Tetrahedral units form the rigid framework of the material, providing the primary lithium-ion storage sites. Disordered, free carbon nanoclusters then form a continuous conductive network around this inorganic framework. This composite structure combines the high capacity of silicon-oxygen-carbon with the high conductivity of carbon materials. The value of x, with 3 or 4 oxygen atoms, indicates that silicon atoms primarily form [SiO4] or [SiO3C] tetrahedral structures with oxygen atoms. These structures exhibit minimal volume change during lithium-ion insertion / extraction, contributing to the material's good structural stability and enabling reversible insertion and extraction of Li. + This improves the reversible capacity of the material.

[0033] The incorporation of nitrogen further optimizes the material's performance. The doped nitrogen atoms are primarily located in the free carbon phase, forming various chemical bonding states, such as pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen. These nitrogen-doped sites not only improve the electronic conductivity of the carbon phase but also create more lithium-ion adsorption sites by inducing charge redistribution. These active sites in nitrogen-doped carbon materials can lower the lithium-ion diffusion barrier, thereby improving the material's rate performance.

[0034] This invention also provides the application of the aforementioned nitrogen-doped silicon-oxygen-carbon anode material in lithium-ion batteries, and its electrochemical performance advantages are fully demonstrated in battery testing. As a lithium-ion battery anode material, its unique microstructure brings about multifaceted performance improvements: SiO x C 4-x The tetrahedral unit cell ensures a high specific capacity; the nitrogen-doped carbon phase provides a good electronic conductivity pathway; and the synergistic effect between the two ensures the structural integrity of the material during long-term cycling.

[0035] When applied to lithium-ion batteries, this material exhibits key advantages including: high reversible capacity, stemming from the abundant lithium storage sites provided by the silicon-oxygen-carbon units and nitrogen-doped carbon phase; excellent rate performance, benefiting from the increased conductivity and optimized ion transport pathways brought about by nitrogen doping; and long cycle life, attributed to the material's stable microstructure and effective ability to suppress volume expansion. These performance characteristics enable this nitrogen-doped silicon-oxygen-carbon material to meet the requirements of modern lithium-ion batteries for high energy density, high power density, and long cycle life, demonstrating broad application prospects. Attached Figure Description

[0036] Figure 1 is a scanning electron microscope image of the nitrogen-doped silicon-oxygen-carbon material provided in Example 2 of the present invention; Figure 2 is an X-ray diffraction pattern of the nitrogen-doped silicon-oxygen-carbon material provided in all embodiments of the present invention; Figure 3 is a Raman spectrum of the nitrogen-doped silicon-oxygen-carbon material provided in all embodiments of the present invention; Figure 4 is a 0.1 A·g spectrum of the nitrogen-doped silicon-oxygen-carbon material provided in Examples 1, 2, and 3 of the present invention. -1 The first charge-discharge curves are shown in Figure 5; Figure 5 shows the nitrogen-doped silicon-oxygen-carbon materials provided in Examples 1, 2, and 3 of this invention at 0.1 A·g. -1 Figure 6 shows the rate performance of the nitrogen-doped silicon-oxygen-carbon materials provided in Examples 1, 2, and 3 of this invention; Figure 7 shows the rate performance of the nitrogen-doped silicon-oxygen-carbon materials provided in Examples 1, 2, and 3 of this invention at 0.5 A·g. -1 The following diagram shows the nitrogen-doped silicon-oxygen-carbon materials provided in Examples 2, 4, and 5 of this invention at 0.1 A·g. -1 The following diagram shows the nitrogen-doped silicon-oxygen-carbon materials provided in Examples 2, 4, and 5 of this invention at 0.5 A·g. -1 The following is a loop diagram. Detailed Implementation

[0037] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in the event of any conflict, the definitions in this specification shall prevail.

[0038] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0039] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0040] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0041] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0042] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0043] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0044] In Example 1, at 30°C, 40.5 mL of anhydrous methanol, 40.5 mL of anhydrous ethanol, and 18 mL of deionized water were added to a three-necked flask and mixed thoroughly. The mixture was then saturated with 1 mol·L⁻¹ water. -1 The pH of the system was adjusted to 4-5 with hydrochloric acid. The system was heated to 40°C, and 24.8 g of γ-methacryloyloxypropyltrimethoxysilane was slowly added dropwise. The mixture was stirred for 10 h to obtain a colorless, transparent, viscous liquid.

[0045] The above colorless, transparent, viscous liquid was transferred to a separatory funnel and allowed to stand. The lower oil phase was removed and dissolved in chloroform. The solvent was then removed by vacuum distillation using a rotary evaporator. The resulting transparent liquid was washed three times each with saturated saline and ether, adjusted to neutral, and then dried with anhydrous magnesium sulfate to obtain the polysiloxane precursor.

[0046] The above-mentioned polysiloxane was transferred to a tube furnace and heated in an ammonia atmosphere at 5°C / min. -1 The temperature was increased to 800℃ at a heating rate, and then pyrolyzed at this temperature for 2 hours to obtain nitrogen-doped silicon-oxygen-carbon material.

[0047] In Example 2, at 30°C, 40.5 mL of anhydrous methanol, 40.5 mL of anhydrous ethanol, and 18 mL of deionized water were added to a three-necked flask and mixed thoroughly. The mixture was then saturated with 1 mol·L⁻¹ water. -1 The pH of the system was adjusted to 4-5 with hydrochloric acid. The system was heated to 40°C, and 24.8 g of γ-methacryloyloxypropyltrimethoxysilane was slowly added dropwise. The mixture was stirred for 10 h to obtain a colorless, transparent, viscous liquid.

[0048] The above colorless, transparent, viscous liquid was transferred to a separatory funnel and allowed to stand. The lower oil phase was removed and dissolved in chloroform. The solvent was then removed by vacuum distillation using a rotary evaporator. The resulting transparent liquid was washed three times each with saturated saline and ether, adjusted to neutral, and then dried with anhydrous magnesium sulfate to obtain the polysiloxane precursor.

[0049] The above-mentioned polysiloxane was transferred to a tube furnace and heated in an ammonia atmosphere at 5°C / min. -1 The temperature was increased to 900℃ at a heating rate, and then pyrolyzed at this temperature for 2 hours to obtain nitrogen-doped silicon-oxygen-carbon material.

[0050] Example 3: At 30°C, 40.5 mL of anhydrous methanol, 40.5 mL of anhydrous ethanol, and 18 mL of deionized water were added to a three-necked flask and mixed thoroughly. The mixture was then saturated with 1 mol·L⁻¹ water. -1 The pH of the system was adjusted to 4-5 with hydrochloric acid. The system was heated to 40°C, and 24.8 g of γ-methacryloyloxypropyltrimethoxysilane was slowly added dropwise. The mixture was stirred for 10 h to obtain a colorless, transparent, viscous liquid.

[0051] The above colorless, transparent, viscous liquid was transferred to a separatory funnel and allowed to stand. The lower oil phase was removed and dissolved in chloroform. The solvent was then removed by vacuum distillation using a rotary evaporator. The resulting transparent liquid was washed three times each with saturated saline and ether, adjusted to neutral, and then dried with anhydrous magnesium sulfate to obtain the polysiloxane precursor.

[0052] The above-mentioned polysiloxane was transferred to a tube furnace and heated in an ammonia atmosphere at 5°C / min. -1 The temperature was increased to 1000℃ at a heating rate, and then pyrolyzed at this temperature for 2 hours to obtain nitrogen-doped silicon-oxygen-carbon material.

[0053] Example 4: At 30°C, 40.5 mL of anhydrous methanol, 40.5 mL of anhydrous ethanol, and 18 mL of deionized water were added to a three-necked flask and mixed thoroughly. The mixture was then saturated with 1 mol·L⁻¹ water.-1 The pH of the system was adjusted to 4-5 with hydrochloric acid. The system was heated to 40°C, and 24.8 g of γ-methacryloyloxypropyltrimethoxysilane was slowly added dropwise. The mixture was stirred for 10 h to obtain a colorless, transparent, viscous liquid.

[0054] The above colorless, transparent, viscous liquid was transferred to a separatory funnel and allowed to stand. The lower oil phase was removed and dissolved in chloroform. The solvent was then removed by vacuum distillation using a rotary evaporator. The resulting transparent liquid was washed three times each with saturated saline and ether, adjusted to neutral, and then dried with anhydrous magnesium sulfate to obtain the polysiloxane precursor.

[0055] The above-mentioned polysiloxane was transferred to a tube furnace and heated in an ammonia atmosphere at 5°C / min. -1 The temperature was increased to 900℃ at a heating rate, and then pyrolyzed at this temperature for 4 hours to obtain nitrogen-doped silicon-oxygen-carbon material.

[0056] In Example 5, at 30°C, 40.5 mL of anhydrous methanol, 40.5 mL of anhydrous ethanol, and 18 mL of deionized water were added to a three-necked flask and mixed thoroughly. The mixture was then saturated with 1 mol·L⁻¹ water. -1 The pH of the system was adjusted to 4-5 with hydrochloric acid. The system was heated to 40°C, and 24.8 g of γ-methacryloyloxypropyltrimethoxysilane was slowly added dropwise. The mixture was stirred for 10 h to obtain a colorless, transparent, viscous liquid.

[0057] The above colorless, transparent, viscous liquid was transferred to a separatory funnel and allowed to stand. The lower oil phase was removed and dissolved in chloroform. The solvent was then removed by vacuum distillation using a rotary evaporator. The resulting transparent liquid was washed three times each with saturated saline and ether, adjusted to neutral, and then dried with anhydrous magnesium sulfate to obtain the polysiloxane precursor.

[0058] The above-mentioned polysiloxane was transferred to a tube furnace and heated in an ammonia atmosphere at 5°C / min. -1 The temperature was increased to 900℃ at a heating rate, and then pyrolyzed at this temperature for 6 hours to obtain nitrogen-doped silicon-oxygen-carbon material.

[0059] The nitrogen-doped silicon-oxygen-carbon anode materials obtained in all embodiments of this invention were observed for their microstructure using scanning electron microscopy, as shown in Figure 1. It can be seen that the nitrogen-doped silicon-oxygen-carbon materials formed by pyrolysis at different temperatures and times did not undergo significant structural changes; they were all irregular blocky solids with dimensions of tens of micrometers.

[0060] For the nitrogen-doped silicon oxycarbide anode materials obtained in all embodiments of the present invention, X-ray diffraction was used for phase analysis, and the results are shown in Figure 2. It can be seen that the spectral lines of the nitrogen-doped silicon oxycarbide materials formed by pyrolysis at different temperatures and times are relatively similar. It can be considered that changing the pyrolysis temperature and pyrolysis time in an ammonia atmosphere has no significant effect on the degree of structural order of the formed nitrogen-doped silicon oxycarbide materials. All nitrogen-doped silicon oxycarbide materials show a relatively broad diffraction peak near 2θ = 23°, which can be attributed to the broad peak of amorphous carbon, and no other diffraction peaks are observed, indicating that this type of material is overall amorphous. At the same time, as the pyrolysis temperature and pyrolysis time increase, the peak position angle of the broad peak of the nitrogen-doped silicon oxycarbide material gradually decreases, which can be attributed to the increase in the amount of N atoms entering the nitrogen-doped silicon oxycarbide material with the increase of pyrolysis temperature and pyrolysis time. When N atoms enter the silicon oxycarbide material, they replace C-O to form more C-N, and the atomic radius of N is larger than that of O, thus showing a trend of decreasing peak position angle of the broad peak.

[0061] For the nitrogen-doped silicon oxycarbide anode materials obtained in all embodiments of the present invention, Raman spectroscopy was used for order analysis, and the results are shown in Figure 3. It can be seen that all nitrogen-doped silicon oxycarbide materials formed by pyrolysis at different temperatures and times have a D-band peak of disordered carbon near 1350 cm -1 and a G-band peak of graphite carbon near 1580 cm -1 . From Figure 3, it can be obtained that in Examples 1, 2, and 3, the pyrolysis time is 2 h, and the pyrolysis temperature gradually increases, resulting in more defects in the carbon in the material. At the same time, pyrolysis in an ammonia atmosphere introduces N atoms to generate more defect sites, further making the overall structure of the material more disordered; in Examples 1, 4, and 5, the pyrolysis temperature is 900 °C, and the pyrolysis time gradually increases, which is more conducive to the formation of defects. Therefore, combining Figure 2 and Figure 3, it can be further considered that all the nitrogen-doped silicon oxycarbide materials obtained in all embodiments are amorphous structures, and the carbon is disordered free carbon.

[0062] The nitrogen-doped silicon oxycarbide material is mainly composed of amorphous SiO x C[[ID=1十三]] 4-x (0 < x ≦ 4) tetrahedral units and disordered free carbon nanoclusters. Among them, the oxygen-rich SiOC phases (SiO3C, SiO2C2) in the SiO x C 4-x tetrahedral units are reversible for the storage of Li + , which can increase the reversible lithium storage capacity of the nitrogen-doped silicon oxycarbide material and improve the electrochemical performance; while the SiOC3 and SiO4 phases are not completely reversible for the storage of Li + . Through XPS fine spectrum analysis of silicon elements, and the internal SiO x C 4-xThe tetrahedral units were normalized and fitted, and the results are shown in Table 1. As can be seen from Table 1, the nitrogen-doped silicon-oxygen-carbon material obtained in Example 2 has the highest proportion of the fully reversible SiO3C phase and has the expected structure with the best reversible capacity.

[0063] Table 1: Different types of SiO in nitrogen-doped silicon-oxygen-carbon materials provided in all embodiments of the present invention x C 4-x Phase content percentage

[0064] Introducing nitrogen heteroatoms into silicon-oxygen-carbon composite structures can improve the performance of Li by creating defects and increasing conductivity. + Li transport and enhances the material + Storage capacity. Nitrogen atom doping configurations include pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen. Pyridine nitrogen and pyrrole nitrogen are both located at the edge sites of the carbon framework in nitrogen-doped silicon-oxygen-carbon materials, exhibiting high activity and enabling more efficient adsorption of Li. + Furthermore, the defect sites formed can effectively reduce Li + Mass transfer resistance. Graphite nitrogen is formed by nitrogen doping into the carbon framework, which can enhance the π electron cloud density and improve conductivity, thereby increasing the mass transfer resistance of Li. + Storage capacity, in Li + The insertion and extraction processes can also improve the reversible capacity of nitrogen-doped silicon-oxygen-carbon materials. XPS nitrogen elemental fine spectroscopy analysis was performed, and the internal nitrogen atom configurations of the nitrogen-doped silicon-oxygen-carbon materials obtained in all embodiments of this invention were normalized and fitted. The results are shown in Table 2. Table 2 shows that the nitrogen-doped silicon-oxygen-carbon material obtained in Example 2 has a moderate proportion of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen, indicating a moderate degree of defect (disordering), consistent with the results in Figures 2 and 3. It exhibits the expected structure for optimal rate performance and reversible lithium storage capacity.

[0065] Table 2: Percentage of different N configurations in nitrogen-doped silicon-oxygen-carbon materials provided in all embodiments of the present invention

[0066] To test the performance of the nitrogen-doped silicon-oxygen-carbon anode materials prepared in all examples for lithium-ion batteries, a half-cell test method was used. The half-cell test method was as follows: The nitrogen-doped silicon-oxygen-carbon materials prepared in Examples 1-5 were used as the anode active material to prepare a slurry with the following ratio: active material: acetylene black: polyvinylidene fluoride = 80%: 10%: 10%. The slurry was coated onto a copper foil surface and vacuum dried at 70°C for 24 hours. The dried electrode sheet was then stamped into a circular electrode sheet with a diameter of 14 mm using a stamping machine. The electrode solution was commercially available 1M LiPF6 (EC:DEC:EMC=1), the separator was commercially available polypropylene membrane, and the counter electrode was a lithium sheet. A half-cell was assembled in an argon-filled glove box. Constant current charge-discharge experiments were performed using a Xinwei CT-4008T battery tester, with a charge-discharge cutoff voltage of 0.01-3V (vs. Li). + / Li). The electrochemical performance of the nitrogen-doped silicon-oxygen-carbon anode materials prepared in Examples 1, 2, and 3 are shown in Figures 4, 5, 6, and 7, and the electrochemical performance of the nitrogen-doped silicon-oxygen-carbon anode materials prepared in Examples 2, 4, and 5 are shown in Figures 8 and 9.

[0067] As shown in Figure 4, the first-cycle discharge curves of the nitrogen-doped silicon-oxygen-carbon anode materials prepared in Examples 1, 2, and 3 are basically identical in shape and have a high degree of overlap, indicating that they exhibit highly consistent electrochemical behavior during the first discharge. Meanwhile, the first-cycle charging curves of the materials are basically identical in shape, but show significant separation, indicating that different reversible reactions occur during charging. It can be seen that the nitrogen-doped silicon-oxygen-carbon anode material prepared in Example 2 has the highest first-cycle charge-discharge capacity, with a discharge capacity of 1290 mAh·g. -1 The charging capacity is 850mAh·g -1 The initial coulombic efficiency was 65.90%. Its high initial coulombic efficiency is related to the highest proportion of the completely reversible SiO3C phase inside, which is consistent with Table 1.

[0068] As shown in Figure 5, the nitrogen-doped silicon-oxygen-carbon anode material prepared in Example 2 has a yield of 0.1 A·g -1 It exhibits 800 mAh·g at current density -1 The reversible capacity of the nitrogen-doped silicon-oxygen-carbon anode material prepared in Example 2 is superior to that of the nitrogen-doped silicon-oxygen-carbon anode materials prepared in Examples 1 and 3. As shown in Figure 6, the nitrogen-doped silicon-oxygen-carbon anode material prepared in Example 2 exhibits the best rate performance compared to the nitrogen-doped silicon-oxygen-carbon anode materials prepared in Examples 1 and 3, at 0.1 A·g2. -1 0.2A·g -1 0.5A·g -1 1.0A·g -1 2.0A·g -1 5.0A·g-1 They exhibited 800 mAh·g at current densities. -1 600mAh·g -1 400mAh·g -1 280mAh·g -1 170mAh·g -1 70mAh·g -1 The discharge capacity. As shown in Figure 7, at 0.5 A·g -1 Below, the reversible capacity of the nitrogen-doped silicon-oxygen-carbon anode material prepared in Example 2 is 400 mAh·g. -1 Compared to the nitrogen-doped silicon-oxygen-carbon anode materials prepared in Examples 1 and 3, this material exhibited superior reversible capacity within 800 cycles, with a reversible capacity of 385 mAh·g after 200 cycles. -1 The capacity retention rate is 96.25%, and after 800 cycles, it still has 300mAh·g. -1 The above reversible capacity and 75% capacity retention rate are shown. As can be seen from Figures 4-7, the nitrogen-doped silicon-oxygen-carbon anode material prepared in Example 2 exhibits the best overall electrochemical performance compared to the nitrogen-doped silicon-oxygen-carbon anode materials prepared in Examples 1 and 3, indicating that 900℃ is the optimal pyrolysis temperature.

[0069] As shown in Figures 8 and 9, at 0.1 A·g -1 and 0.5A·g -1 At the specified current density, compared to the nitrogen-doped silicon-oxygen-carbon anode materials prepared in Examples 4 and 5, the nitrogen-doped silicon-oxygen-carbon anode material prepared in Example 2 exhibited the highest reversible capacity and the highest capacity retention. This further demonstrates that extending the pyrolysis time at 900℃ did not further improve the electrochemical performance and may even lead to a slight decrease in performance; therefore, 2 hours is the optimal pyrolysis time. In summary, the nitrogen-doped silicon-oxygen-carbon anode material prepared in Example 2 exhibits the best overall electrochemical lithium storage performance compared to the nitrogen-doped silicon-oxygen-carbon anode materials prepared in other examples. This is inseparable from its highest proportion of the fully reversible SiO3C phase and the appropriate ratio of the three nitrogen configurations. This further demonstrates that pyrolysis at 900℃ for 2 hours under an ammonia atmosphere is the optimal preparation scheme for high-performance nitrogen-doped silicon-oxygen-carbon anode materials.

[0070] In summary, this invention discloses a high-lithium-storage-performance nitrogen-doped silicon-oxygen-carbon anode material and its preparation method. A polysiloxane precursor is prepared by hydrolyzing and condensing γ-methacryloyloxypropyltrimethoxysilane under acidic conditions. Five nitrogen-doped silicon-oxygen-carbon materials are prepared by varying the pyrolysis temperature and time of the polysiloxane precursor in an ammonia atmosphere. The optimal nitrogen-doped silicon-oxygen-carbon material preparation scheme is selected through battery electrochemical testing. The obtained optimal nitrogen-doped silicon-oxygen-carbon material exhibits stable nitrogen atom doping, high conductivity, and a high proportion of reversible components, resulting in superior reversible lithium-storage capacity, rate performance, and long-cycle stability.

[0071] The difference between Example 6 and Example 1 is that in the preparation of the organic alcohol aqueous solution, 27 mL of anhydrous methanol and 54 mL of anhydrous ethanol were used, while maintaining the same 18 mL of deionized water as in Example 1. That is, the volume ratio of anhydrous methanol to anhydrous ethanol is 0.5:1.

[0072] The difference between Example 7 and Example 1 is that in the preparation of the organic alcohol aqueous solution, 54 mL of anhydrous methanol and 27 mL of anhydrous ethanol were used, while maintaining the same 18 mL of deionized water as in Example 1. That is, the volume ratio of anhydrous methanol to anhydrous ethanol is 2:1.

[0073] Example 8 differs from Example 1 in that the concentration of the hydrochloric acid solution used to adjust the pH is 0.9 mol·L⁻¹. - ¹; Maintain anhydrous methanol volume of 40.5 mL and anhydrous ethanol volume of 40.5 mL (same as in Example 1), adjust the volume of deionized water to 14.5 mL, and slowly add 20.0 g of γ-methacryloxypropyltrimethoxysilane. Then, add hydrochloric acid solution to adjust the pH of the system to 4-5, so that the mass percentage concentration of γ-methacryloxypropyltrimethoxysilane is 18%.

[0074] Example 9 differs from Example 1 in that the concentration of the hydrochloric acid solution used to adjust the pH is 1.1 mol·L⁻¹. - ¹; Maintain anhydrous methanol volume of 40.5 mL and anhydrous ethanol volume of 40.5 mL (same as in Example 1), adjust the volume of deionized water to 21.8 mL, and slowly add 30.0 g of γ-methacryloxypropyltrimethoxysilane. Then, add hydrochloric acid solution to adjust the pH of the system to 4-5, so that the mass percentage concentration of γ-methacryloxypropyltrimethoxysilane is 22%.

[0075] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries, characterized in that, Includes the following steps: After acidic hydrolysis and condensation of γ-methacryloxypropyltrimethoxysilane, a polysiloxane precursor was obtained by rotary evaporation, washing, and drying. The polysiloxane precursor was then subjected to high-temperature pyrolysis in a nitrogen-containing atmosphere to obtain a nitrogen-doped silicon-oxygen-carbon anode material.

2. The method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, The high-temperature pyrolysis conditions include: a temperature of 800-1000℃ and a heating rate of 5℃·min. -1 The time is 2-6 hours.

3. The method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, The high-temperature pyrolysis conditions include: a temperature of 900℃ and a time of 2 hours.

4. The method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, The reaction temperature for the acidic hydrolysis-condensation reaction is 30-40℃.

5. The method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, The acidic hydrolysis-condensation reaction includes: adding hydrochloric acid solution to an aqueous organic alcohol solution at 30°C, adjusting the pH to 4-5, raising the temperature to 40°C, adding γ-methacryloyloxypropyltrimethoxysilane, and stirring.

6. The method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries according to claim 5, characterized in that, The organic alcohol aqueous solution is prepared by mixing anhydrous methanol, anhydrous ethanol and deionized water; the volume ratio of anhydrous methanol to anhydrous ethanol is (0.5-2):1, and the molar ratio of deionized water to γ-methacryloyloxypropyltrimethoxysilane is 10:

1.

7. The method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries according to claim 5, characterized in that, The concentration of the hydrochloric acid solution is (0.9-1.1) mol·L⁻¹ -1 The mass percentage concentration of the γ-methacryloyloxypropyltrimethoxysilane is 18%-22%.

8. The method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, The nitrogen-containing atmosphere is composed of ammonia, and the ammonia serves as a nitrogen dopant source to introduce nitrogen during the pyrolysis process.

9. The nitrogen-doped silicon-oxygen-carbon anode material prepared by the method for preparing a nitrogen-doped silicon-oxygen-carbon anode material for lithium-ion batteries according to any one of claims 1 to 8, characterized in that, The nitrogen-doped silicon-oxygen-carbon anode material comprises amorphous SiO₂. x C 4-x Tetrahedral units and disordered free carbon nanoclusters, wherein the number of oxygen atoms x is 3 or 4; the nitrogen-doped silicon-oxygen-carbon anode material is a micron-sized, irregular blocky solid.

10. The application of the nitrogen-doped silicon-oxygen-carbon anode material of claim 9 in lithium-ion batteries.

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