Preparation method of nitrogen-oxygen co-doped walnut type structure silicon-carbon negative electrode

Abstract

The invention provides a preparation method of a nitrogen-oxygen co-doped walnut-type structure silicon-carbon negative electrode, which comprises the following steps: putting nano silicon and an amination reagent into an organic solvent for blending, and synthesizing an amination nano silicon solution; the preparation method comprises the following steps: dispersing dicyandiamide and glucose in an organic solvent, then adding an aminated nano-silicon solution, stirring to obtain a mixed solution, and then carrying out spray drying on the mixed solution to obtain a precursor; and calcining the precursor in an inert atmosphere to obtain the catalyst. According to the preparation method, through improvement of a preparation process, selection of raw materials and optimization of the ratio of different raw materials, side reaction at a negative electrode / electrolyte interface is inhibited on the premise of not influencing lithium ion transmission, and volume expansion is inhibited; meanwhile, the volume expansion of the silicon can be relieved and the occurrence probability of electrode structure collapse and electrode material stripping can be reduced by a wrinkle structure formed by high-temperature carbonization after the silicon is compounded with the organic saccharides, so that the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular to a method for preparing a silicon-carbon negative electrode with a walnut-shaped structure co-doped with nitrogen and oxygen. Background Art

[0002] With the rapid development of the economy, the energy crisis and environmental problems are becoming increasingly serious. Lithium-ion batteries have been widely used in portable consumer electronics, power tools, medical electronics and other fields due to their advantages such as high energy density, high power density, long cycle life, no memory effect, low self-discharge rate, wide operating temperature range, safety and reliability, and environmental friendliness. At the same time, they also show good application prospects in pure electric vehicles, hybrid vehicles and energy storage.

[0003] However, the demand for battery energy density has increased rapidly in various fields in recent years, and there is an urgent need to develop lithium-ion batteries with higher energy density. Currently, commercial lithium-ion batteries mainly use graphite as the negative electrode material. The theoretical specific capacity of graphite is 372 mAh / g, while high-end graphite materials on the market can reach 360-365 mAh / g. Therefore, the room for improving the energy density of lithium-ion batteries is quite limited.

[0004] Silicon-based anode materials, due to their high theoretical specific capacity (4200 mAh / g at high temperature, 3580 mAh / g at room temperature) and low delithiation potential (<0.5 V), have higher gravimetric and volumetric energy densities than graphite anodes. Lithium-ion batteries using silicon anode materials can increase their gravimetric energy density by over 8% and their volumetric energy density by over 10%, while reducing the cost per kilowatt-hour by at least 3%. Therefore, silicon anode materials are considered to be highly promising anode materials for next-generation, high-energy-density lithium-ion batteries. However, silicon anode materials are prone to repeated expansion and contraction during use, leading to battery failure. The continuous growth of the SEI film on the silicon material surface causes battery capacity degradation, significantly limiting the development of silicon anode materials.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a method for preparing a silicon-carbon negative electrode with a walnut-shaped structure co-doped with nitrogen and oxygen. The preparation method achieves the suppression of side reactions at the negative electrode / electrolyte interface and volume expansion without affecting lithium ion transmission through improvements in the preparation process, selection of raw materials, and optimization of the ratio between different raw materials. At the same time, the wrinkled structure formed by high-temperature carbonization after compounding with organic sugars can also alleviate the volume expansion of silicon, reduce the probability of electrode structure collapse and electrode material peeling, and thus improve the battery cycle performance.

[0007] The second object of the present invention is to provide a silicon-carbon negative electrode prepared by the preparation method of the above-mentioned nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0009] The present invention provides a method for preparing a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode, comprising the following steps:

[0010] The nano-silicon and the amination reagent are placed in an organic solvent and mixed to synthesize an amination nano-silicon solution;

[0011] Dispersing dicyandiamide and glucose in an organic solvent, then adding the synthesized amino-silicon solution, stirring, adding graphite, and continuing to stir to obtain a mixture;

[0012] The mixture is then spray-dried to obtain a precursor;

[0013] The precursor is calcined under an inert atmosphere to obtain the product.

[0014] In the present invention, the nano-silicon is aminated, which can effectively improve the wettability and dispersibility of the nanospheres, and at the same time can provide more active sites, which is more conducive to the adsorption and diffusion of lithium ions. Dicyandiamide and glucose can be synthesized into a g-C3N4 structure through high-temperature pyrolysis, so that the nitrogen atoms produced by the decomposition of dicyandiamide are doped into the carbon skeleton formed by the carbonization of glucose, thereby forming graphene with a specific nitrogen doping concentration. In theory, citric acid or melamine can produce similar effects with dicyandiamide. Aminated nano-silicon is combined with dicyandiamide and glucose to form a structure in which silicon nanoparticles are wrapped in a wrinkled walnut-shaped nitrogen oxide layer, which can effectively alleviate the specific volume change of the silicon negative electrode material, build a conductive network, and thus improve the conductive performance.

[0015] Preferably, as a further specific embodiment, the calcination step is:

[0016] The precursor is heated at a rate of 5°C / min under an inert atmosphere to 400°C-600°C for pre-calcination, and kept at this temperature for 0.5h-2h;

[0017] Continue to heat up to 800-1000℃ and calcine, keeping warm for 0.5h-2h;

[0018] Preferably, as a further specific embodiment, the calcining step is:

[0019] The precursor was heated at a rate of 5°C / min under an inert atmosphere to 500°C for pre-calcination, and kept at this temperature for 1 hour;

[0020] Continue to heat up to 900℃ and calcine, keeping warm for 1 hour.

[0021] In the present invention, a staged heating method is employed, initially maintaining the temperature at a moderate temperature of 400-600°C for 0.5-2 hours, and then raising the temperature to a high temperature of 800-1000°C. This moderate temperature stage allows dicyandiamide to decompose, vaporize, and generate a precursor, providing the foundation for the subsequent formation of a nitrogen-doped carbon layer. Simultaneously, glucose is partially carbonized during this stage, forming a porous carbon framework, but not completely graphitized, retaining abundant hydroxyl and carboxyl functional groups, providing active sites for subsequent nitrogen and oxygen doping. During the pre-calcination process, the temperature should not be raised directly to 800-1000°C. Doing so could cause the organic matter to rapidly decompose, generating large amounts of gases (such as CO₂ and NH₃), leading to a loose material structure or the formation of pores, which could disrupt the uniform coating of the silicon particles. Furthermore, the pre-calcination temperature should not be too high or too low, as this can significantly degrade the material's performance. In addition, the pre-calcination time and temperature need to be controlled. The pre-calcination time cannot be too long or too short. When the pre-calcination time is too long, the hydroxyl and carboxyl groups of glucose will be gradually oxidized or decomposed in the medium temperature stage, so that the oxygen doping source is exhausted, the oxygen content in the carbon layer is reduced, and the promotion effect on lithium ion diffusion is weakened. At the same time, too long pre-carbonization time of glucose will cause the carbon skeleton to shrink and densify prematurely, lose its porous properties, hinder the rapid diffusion path of lithium ions in the cycle, and reduce the rate performance; and when the calcination time is too short, undecomposed dicyandiamide remains, and a uniform nitrogen-doped carbon layer cannot be formed during subsequent high-temperature calcination, or the carbon layer structure formed by amino-modified nano-silicon, dicyandiamide and glucose is loose, and the silicon particles cannot be effectively wrapped, reducing the mechanical support effect.

[0022] High-temperature calcination (800-1000°C) promotes the carbonization of glucose to form a graphitized carbon layer, enhancing the material's conductivity and thus improving electron transfer efficiency. Simultaneously, the g-C3N4 produced by the decomposition of dicyandiamide couples with silicon nanoparticles at high temperatures through nitrogen lone-pair electrons, forming a stable chemical bond that inhibits silicon's volume expansion.

[0023] Therefore, the calcination temperature and sintering time will greatly affect the stability of the prepared silicon-carbon negative electrode. When the sintering temperature is too high or the time is too long, it may lead to excessive sintering of silicon nanoparticles, affecting their bonding with the carbon layer, resulting in poor electrochemical stability of the silicon-carbon material and rapid capacity decay; when the temperature is too low or the sintering time is too short, the required nitrogen and oxygen co-doped carbon shell cannot be effectively formed, resulting in a loose structure and inability to effectively suppress the volume expansion of silicon. Therefore, the pre-calcination temperature is ultimately controlled at 400℃-600℃, and kept warm for 0.5h-2h; preferably, the pre-calcination temperature is 500℃, and kept warm for 1h; the calcination temperature is controlled at 800℃-1000℃, and kept warm for 0.5h-2h; preferably, the calcination temperature is 900℃, and kept warm for 1h, which can maximize the balance between reaction completeness and structural optimization, and ultimately achieve high electrochemical stability.

[0024] Preferably, as a further specific embodiment, the mass ratio of the nano-silicon to the amination reagent is (5:1)-(20:1);

[0025] Preferably, the mass ratio of the nano-silicon to the amination reagent is (8:1)-(15:1);

[0026] Preferably, the mass ratio of the nano-silicon to the amination reagent is 10:1.

[0027] In the present invention, the mass ratio of nano-silicon to the amination reagent can also be 6:1, 7:1, 9:1, 11:1, 12:1, 13:1, 14:1, 16:1, 17:1, 18:1, or 19:1.

[0028] The purpose of limiting the mass ratio of nano-silicon to amination reagent is to enable the two to react fully, so that the amination nano-silicon is positively charged and its zeta potential is controlled at +48.8mV to +36.6mV.

[0029] In the present invention, the mass ratio of nano-silicon to amination reagent is limited. When the amination reagent is excessive, the surface of the nano-silicon will be over-coated, forming an excessively thick organic layer, which will hinder the subsequent direct contact between the precursor and the nano-silicon; at the same time, excessive amination reagent will cause residue, and non-conductive organic matter will remain after high-temperature calcination, which will hinder electron transmission and reduce the overall conductivity of the material.

[0030] However, when the amount of amination reagent is insufficient, that is, when there is an excess of nanosilicon, the amination coverage of the silicon surface is low, resulting in poor dispersion of the nanosilicon, a loose structure, and easy agglomeration. If it comes into direct contact with the electrolyte, it may also accelerate the growth and volume expansion of the SEI film. At the same time, the number of amino groups is too small to effectively anchor the precursor or provide a sufficient nitrogen source, resulting in weak silicon-carbon interface bonding and low nitrogen doping concentration, which leads to poor cycling performance. Therefore, the mass ratio of nanosilicon to amination reagent needs to be controlled between (5:1) and (20:1), preferably in the range of (8:1) to (15:1), and more preferably 10:1.

[0031] Preferably, as a further specific embodiment, the mass ratio of dicyandiamide to glucose is (1:1)-(5:1);

[0032] Preferably, the mass ratio of dicyandiamide to glucose is (2:1)-(4:1);

[0033] Preferably, the mass ratio of dicyandiamide to glucose is 2:1.

[0034] In the present invention, the mass ratio of dicyandiamide to glucose can also be 3:1.

[0035] In this invention, dicyandiamide serves as a nitrogen source, providing nitrogen doping sites. It decomposes at high temperatures to form a g-C3N4 precursor, which enhances the stability of the silicon-carbon interface through chemical bonding. Glucose, on the other hand, serves as a carbon source, carbonizing at high temperatures to form a wrinkled carbon shell. Its hydroxyl groups also provide oxygen doping sites, effectively optimizing the lithium-ion transport pathway. During high-temperature calcination, nitrogen atoms generated by the decomposition of dicyandiamide are doped into the carbon skeleton formed by the carbonization of glucose, forming graphene with a specific nitrogen doping concentration.

[0036] Therefore, it is necessary to limit the ratio of the two. When dicyandiamide is excessive, it will cause dicyandiamide to decompose and produce nitrogen-containing gas during high-temperature calcination, destroying the carbon layer structure, resulting in uneven carbon shell or holes, weakening the volume expansion inhibition effect of silicon particles; at the same time, g-C3N4 itself has poor conductivity, and excessive introduction will reduce the overall conductivity of the carbon layer and hinder electron transport. When glucose is excessive, it will cause the excess glucose to form an overly thick carbon shell after carbonization, hindering the diffusion of lithium ions and reducing rate performance; in addition, insufficient dicyandiamide will lead to low g-C3N4 production, weak silicon-carbon interface bonding, and inability to effectively inhibit volume expansion. At the same time, the mechanical strength of the carbon layer is insufficient, and it is easy to crack during the cycle, causing the silicon particles to be exposed to the electrolyte and accelerating the growth of the SEI film.

[0037] Preferably, as a further specific embodiment, the amination agent is any one or more of 3-aminopropyltriethoxysilane, polydiallyldimethylammonium hydride, triethylenetetramine, and ethylenediamine;

[0038] Preferably, the amination agent is 3-aminopropyltriethoxysilane.

[0039] In this study, 3-aminopropyltriethoxysilane is the preferred amination reagent for the preparation of high-performance silicon-carbon anodes due to its controllable hydrolysis kinetics, stable siloxane bonding, uniform amino group distribution, and synergistic contribution to nitrogen and oxygen co-doping. Compared to other reagents, 3-aminopropyltriethoxysilane exhibits superior reaction controllability, interfacial stability, and industrial suitability.

[0040] Preferably, as a further specific embodiment, the steps of the spray drying method are:

[0041] The mixture was spray-dried at a pressure of 0.3 MPa and a rotation speed of 3 rpm / min at 260°C.

[0042] Preferably, as a further specific embodiment, in the step of placing the nano-silicon and the amination reagent in an organic solvent for mixing, the organic solvent is any one or more of toluene, anhydrous ethanol or isopropanol;

[0043] Preferably, the organic solvent is toluene.

[0044] Preferably, as a further specific embodiment, in the step of dispersing dicyandiamide and glucose in an organic solvent, the organic solvent is any one or more of anhydrous ethanol or isopropanol;

[0045] Preferably, the organic solvent is anhydrous ethanol.

[0046] The organic solvent is preferably an organic solvent with good dispersibility to ensure that the reagents used in the reaction process can be dispersed more effectively.

[0047] The present invention also provides a silicon-carbon negative electrode prepared by the method for preparing the above-mentioned nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] This preparation method achieves the goal of suppressing side reactions at the negative electrode / electrolyte interface and volume expansion without affecting lithium ion transmission by improving the preparation process, selecting raw materials, and optimizing the ratio between different raw materials. At the same time, after compounding with organic sugars, the wrinkled structure formed by high-temperature carbonization can also alleviate the volume expansion of silicon, reduce the probability of electrode structure collapse and electrode material peeling, and thus improve battery cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 : The first charge and discharge curve of the 20% silicon-carbon composite material in Example 1;

[0051] Figure 2 : 500-cycle life graph of the 20% silicon-carbon composite material in Example 1;

[0052] Figure 3 : SEM image of the silicon-carbon composite material prepared in Example 1. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the present invention more apparent, exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments of the present invention, and it should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described in the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention. Example 1

[0054] 20 g of nano-silicon and 2 g of 3-aminopropyltriethoxysilane were mixed in toluene to undergo hydrolysis and polymerization reaction to synthesize an amino-containing nano-silicon solution;

[0055] Dissolve dicyandiamide and glucose in 100 mL of anhydrous ethanol at a mass ratio of 2:1. Slowly add the amino-silicon solution to the top of the solution. Stir at high speed on a magnetic stirrer for 3-4 hours. Then, add graphite to create a silicon-carbon anode with a silicon content of 20%. Continue stirring for 2 hours to obtain a mixture.

[0056] The mixture was spray dried at 260°C at a pressure of 0.3 MPa and a rotation speed of 3 rpm / min to obtain a precursor. The precursor was heated at a heating rate of 5°C / min in a nitrogen atmosphere to 500°C for pre-calcination and kept warm for 1 hour; then continued to heat to 900°C and kept warm for 1 hour to obtain the prepared negative electrode material. The SEM image of the prepared negative electrode material is shown as follows: Figure 1 As shown in the figure, it can be seen that the prepared negative electrode material has achieved uniform carbon coating and formed a relatively stable walnut structure. Example 2

[0057] 20 g of nano-silicon and 1 g of 3-aminopropyltriethoxysilane were mixed in toluene to undergo hydrolysis and polymerization reaction to synthesize an amino-containing nano-silicon solution;

[0058] Dissolve dicyandiamide and glucose in 100 mL of anhydrous ethanol at a mass ratio of 5:1. Slowly add the amino-silicon solution to the top of the solution. Stir at high speed on a magnetic stirrer for 3-4 hours. Then, add graphite to create a silicon-carbon anode with a silicon content of 20%. Continue stirring for 2 hours to obtain a mixture.

[0059] The mixture was spray-dried at 260°C at a pressure of 0.3 MPa and a rotation speed of 3 rpm / min to obtain a precursor, and the precursor was heated at a heating rate of 5°C / min in a nitrogen atmosphere to 400°C for pre-calcination and kept warm for 2 hours; then continued to heat to 800°C and kept warm for 2 hours to obtain the product. Example 3

[0060] 20 g of nano-silicon was mixed with 4 g of 3-aminopropyltriethoxysilane in toluene to undergo hydrolysis and polymerization reaction to synthesize an amino-containing nano-silicon solution;

[0061] Dissolve dicyandiamide and glucose in 100 mL of anhydrous ethanol at a mass ratio of 4:1. Slowly add the amino-silicon solution to the top of the solution. Stir at high speed on a magnetic stirrer for 3-4 hours. Then, add graphite to create a silicon-carbon anode with a silicon content of 20%. Continue stirring for 2 hours to obtain a mixture.

[0062] The mixture was spray-dried at 260°C at a pressure of 0.3 MPa and a rotation speed of 3 rpm / min to obtain a precursor, and the precursor was heated at a heating rate of 5°C / min in a nitrogen atmosphere to 600°C for pre-calcination and kept warm for 0.5 hours; then continued to heat to 1000°C and kept warm for 0.5 hours to obtain the product. Example 4

[0063] The specific implementation method is consistent with Example 1, except that the amount of 3-aminopropyltriethoxysilane is changed to 1.3 g, that is, the mass ratio of nano-silicon to 3-aminopropyltriethoxysilane is adjusted to 15:1. Example 5

[0064] The specific implementation method is consistent with Example 1, except that the amount of 3-aminopropyltriethoxysilane is changed to 2.5 g, that is, the mass ratio of nano-silicon to 3-aminopropyltriethoxysilane is adjusted to 8:1. Example 6

[0065] The specific implementation method is consistent with Example 1, except that the amination reagent is replaced by polydiallyldimethylammonium hydride. Example 7

[0066] The specific implementation method is consistent with Example 1, except that toluene is replaced by anhydrous ethanol. Example 8

[0067] The specific implementation method is consistent with Example 1, except that anhydrous ethanol is replaced by isopropyl alcohol. Comparative Example 1

[0068] 20 g of nano-silicon and 200 g of 3-aminopropyltriethoxysilane were mixed in toluene to undergo hydrolysis and polymerization reaction to synthesize an amino-containing nano-silicon solution;

[0069] The amino-modified nano-silicon solution was dissolved in the glucose solution, and after high-speed stirring on a magnetic stirrer for 3-4 hours, graphite was added to prepare a silicon-carbon negative electrode with a silicon content of 20%, and stirring was continued for 2 hours to obtain a mixture;

[0070] The mixture was spray dried at 260°C at a pressure of 0.3 MPa and a rotation speed of 3 rpm / min, and then heated at a heating rate of 5°C / min in a nitrogen atmosphere to 500°C for pre-calcination and kept warm for 1 hour; then continued to heat to 900°C and kept warm for 1 hour to obtain the product. Comparative Example 2

[0071] Dissolve dicyandiamide and glucose in 100 mL of anhydrous ethanol at a mass ratio of 2:1. Then, slowly add the nanosilicon solution over the solution. After stirring at high speed on a magnetic stirrer for 3-4 hours, add graphite to form a silicon-carbon anode with a silicon content of 20%. Continue stirring for 2 hours to obtain a mixture.

[0072] The mixture was spray dried at 260°C at a pressure of 0.3 MPa and a rotation speed of 3 rpm / min, and then heated at a heating rate of 5°C / min in a nitrogen atmosphere to 500°C for pre-calcination and kept warm for 1 hour; then continued to heat to 900°C and kept warm for 1 hour to obtain the product. Comparative Example 3

[0073] The specific implementation method is consistent with Example 1, except that the mass of the amination reagent is adjusted to 0.8 g, that is, the mass ratio of nano-silicon to 3-aminopropyltriethoxysilane is adjusted to 25:1. Comparative Example 4

[0074] The specific implementation method is consistent with Example 1, except that the mass of the amination reagent is adjusted to 5 g, that is, the mass ratio of nano-silicon to 3-aminopropyltriethoxysilane is adjusted to 4:1. Comparative Example 5

[0075] The specific implementation method is consistent with Example 1, and the mass ratio of dicyandiamide to glucose is adjusted to 0.5:1. Comparative Example 6

[0076] The specific implementation method is consistent with Example 1, and the mass ratio of dicyandiamide to glucose is adjusted to 8:1. Comparative Example 7

[0077] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 900° C. and kept at this temperature for 1 hour. Comparative Example 8

[0078] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 700°C for pre-calcination and kept at this temperature for 1 hour;

[0079] Then continue to heat up to 900℃ and calcine, keeping the temperature for 1 hour. Comparative Example 9

[0080] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 200°C for pre-calcination and kept at this temperature for 1 hour;

[0081] Then continue to heat up to 900℃ and calcine, keeping the temperature for 1 hour. Comparative Example 10

[0082] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 500°C for pre-calcination and kept at this temperature for 5 hours;

[0083] Then continue to heat up to 900℃ and calcine, keeping the temperature for 1 hour. Comparative Example 11

[0084] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 500°C for pre-calcination and kept at this temperature for 15 minutes;

[0085] Then continue to heat up to 900℃ and calcine, keeping the temperature for 1 hour. Comparative Example 12

[0086] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 500°C for pre-calcination and kept at this temperature for 1 hour;

[0087] Then the temperature was raised to 1200°C for calcination and kept at this temperature for 1 hour. Comparative Example 13

[0088] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 500°C for pre-calcination and kept at this temperature for 1 hour;

[0089] Then the temperature was raised to 700°C and calcined, and kept at this temperature for 1 hour. Comparative Example 14

[0090] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 500°C for pre-calcination and kept at this temperature for 1 hour;

[0091] Then the temperature was raised to 900°C and kept at this temperature for 5 hours. Comparative Example 15

[0092] The specific implementation method is consistent with Example 1, and the precursor is directly heated to 500°C for pre-calcination and kept at this temperature for 1 hour;

[0093] Then the temperature was raised to 900°C and kept at this temperature for 15 minutes. Experimental example: making a button battery

[0094] The performance of the negative electrode material prepared in Example 1 was verified.

[0095] (1) Preparation of silicon-carbon negative electrode slurry: A silicon-carbon composite material, acetylene black, styrene-butadiene rubber, and carboxymethyl cellulose mixture were dispersed in N-methylpyrrolidone in a mass ratio of 8:1:1 and mixed evenly to obtain a silicon-carbon negative electrode slurry. The silicon-carbon composite material was the electrode material prepared in the example and the electrode material prepared in the comparative example, respectively.

[0096] (2) The silicon-carbon negative electrode slurry is evenly coated on the copper foil current collector, dried under vacuum conditions, and rolled to a compaction density of 1.3 g / cm 3 , and obtain the negative electrode sheet.

[0097] (3) A button cell was assembled in an argon atmosphere glove box using lithium metal foil as the counter electrode, a polypropylene film as the separator, and a 1 mol / L LiPF6 solution as the electrolyte. The solvent of the LiPF6 solution was a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1. The electrochemical performance of the button cell was tested.

[0098] The performance test was carried out using the materials prepared in the examples and comparative examples, wherein the test results of Example 1 are as follows: Figure 1 and Figure 2 shown. Figure 1 It is shown in the figure that the battery prepared using the nitrogen and oxygen co-doped walnut-shaped silicon-carbon negative electrode obtained in Example 1 has an initial discharge capacity of 1026.3 mAh / g and an initial coulombic efficiency of 91.7%; the 0.5C discharge capacity retention rate reaches 88.14% (after 500 cycles), and the 0.5C capacity is stable at 600 mAh / g.

[0099] Table 1 Initial capacity (mAh / g) First coulombic efficiency (%) 500-cycle capacity retention rate (%) Example 1 1026.3 91.7 88.14 Example 2 954.8 89.6 85.23 Example 3 983.2 90.3 86.17 Example 4 991.5 90.1 87.09 Example 5 1011.7 91.2 87.56 Example 6 972.4 88.3 83.45 Example 7 1003.6 90.7 86.28 Example 8 997.2 89.9 85.63 Comparative Example 1 852.4 85.3 70.19 Comparative Example 2 803.7 80.5 60.34 Comparative Example 3 834.6 82.1 65.87 Comparative Example 4 884.9 86.2 75.42 Comparative Example 5 823.8 78.4 58.91 Comparative Example 6 903.2 87.5 72.65 Comparative Example 7 782.5 75.6 55.78 Comparative Example 8 724.3 74.2 50.34 Comparative Example 9 683.9 70.8 45.67 Comparative Example 10 762.4 76.1 60.89 Comparative Example 11 704.7 72.9 48.52 Comparative Example 12 653.8 68.7 40.21 Comparative Example 13 754.1 75.3 55.93 Comparative Example 14 785.6 77.4 65.78 Comparative Example 15 714.2 73.5 52.46

[0100] Example 1 was compared with Comparative Examples 1 and 2. Nanosilicon and 3-aminopropyltriethoxysilane underwent hydrolysis and polymerization in toluene to synthesize amination-modified nanospheres (Si-NH2). Amination not only improves the wettability and dispersibility of the nanospheres in solution but also provides them with more active sites. The precursor combines with an aromatic carbon intermediate (derived from calcined glucose) under high temperature conditions. High-temperature calcination fully vaporizes dicyandiamide to form g-C3N4. At high temperatures, Si-NH2 nanoparticles transfer to the graphene matrix g-C3N4 through chemical coupling of nitrogen lone-pair electrons. Upon high-temperature carbonization of glucose, the glucose-based carbon layer shrinks and carbonizes into a nitrogen / oxygen co-doped carbon shell, resulting in a nitrogen-oxygen co-doped walnut-shaped silicon-carbon anode. Therefore, when nanosilicon is not amination-modified or dicyandiamide is not used, the electrical performance of the anode material is degraded to varying degrees.

[0101] Example 1 is compared with Comparative Examples 3-6. Among them, Comparative Example 3-4 has an unbalanced amination ratio, which can lead to poor dispersibility or excessive coating, and a significant decrease in the initial capacity and cycle performance; while in Comparative Examples 5-6, the ratio of dicyandiamide and glucose is unbalanced, which directly affects the nitrogen content in the negative electrode material, resulting in insufficient or excessive nitrogen doping, weakening the carbon layer structure or conductivity.

[0102] It can be seen from this that the carbon negative electrode prepared by the embodiment of the present invention can form a walnut-shaped structure, and at the same time can effectively alleviate the volume expansion of silicon, reduce the probability of electrode structure collapse and material peeling, and effectively improve the cycle performance of the battery.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode, characterized in that: The steps include: The nano-silicon and the amination reagent are placed in an organic solvent and mixed to synthesize an amination nano-silicon solution; Dispersing dicyandiamide and glucose in an organic solvent, then adding the synthesized amino-silicon solution, stirring, adding graphite, and continuing to stir to obtain a mixture; The mixture is then spray-dried to obtain a precursor; The precursor is calcined under an inert atmosphere to obtain the product.

2. The method for preparing the nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to claim 1, characterized in that: The calcination step is: The precursor is heated at a rate of 5°C / min under an inert atmosphere to 400°C-600°C for pre-calcination, and kept at this temperature for 0.5h-2h; Continue to heat up to 800℃-1000℃ and calcine, keeping warm for 0.5h-2h.

3. The method for preparing the nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to claim 2, characterized in that: The calcining steps are: The precursor was heated at a rate of 5°C / min under an inert atmosphere to 500°C for pre-calcination, and kept at this temperature for 1 hour; Continue to heat up to 900℃ and calcine, keeping warm for 1 hour.

4. The method for preparing a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to claim 1, characterized in that: The mass ratio of the nano-silicon to the amination reagent is (5:1)-(20:1); Preferably, the mass ratio of the nano-silicon to the amination reagent is (8:1)-(15:1); Preferably, the mass ratio of the nano-silicon to the amination reagent is 10:

1.

5. The method for preparing a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to claim 1, characterized in that: The mass ratio of dicyandiamide to glucose is (1:1)-(5:1); Preferably, the mass ratio of dicyandiamide to glucose is (2:1)-(4:1); Preferably, the mass ratio of dicyandiamide to glucose is 2:

1.

6. The method for preparing a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to claim 1, characterized in that: The amination agent is any one or more of 3-aminopropyltriethoxysilane, polydiallyldimethylammonium hydride, triethylenetetramine, and ethylenediamine; Preferably, the amination agent is 3-aminopropyltriethoxysilane.

7. The method for preparing a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to claim 1, characterized in that: The steps of the spray drying method are: The mixture was spray-dried at a pressure of 0.3 MPa and a rotation speed of 3 rpm / min at 260°C.

8. The method for preparing a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to claim 1, characterized in that: In the step of placing the nano-silicon and the amination reagent in an organic solvent for mixing, the organic solvent is any one or more of toluene, anhydrous ethanol or isopropanol; Preferably, the organic solvent is toluene.

9. The method for preparing a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to claim 1, characterized in that: In the step of dispersing dicyandiamide and glucose in an organic solvent, the organic solvent is any one or more of anhydrous ethanol or isopropanol; Preferably, the organic solvent is anhydrous ethanol.

10. A silicon-carbon negative electrode prepared by the method for preparing a nitrogen-oxygen co-doped walnut-shaped silicon-carbon negative electrode according to any one of claims 1 to 9.

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