Preparation method of nitrogen-doped porous carbon-silicon-based composite material

Abstract

This invention discloses a method for preparing nitrogen-doped porous carbon-silicon-based composite materials, relating to the field of lithium-ion battery material preparation technology. The method includes the following steps: Step 1, mixing azobisisobutyronitrile, styrene, and a crosslinking agent uniformly and then performing a polymerization reaction to obtain precursor A; Step 2, mixing precursor A, an organic solvent, a silane coupling agent, and a silicon-oxygen material uniformly and then reacting, followed by spray drying to obtain precursor B; Step 3, mixing precursor B uniformly with concentrated sulfuric acid, manganese nitrate, and ammonium persulfate and then performing an oxidation reaction, followed by washing and drying to obtain the nitrogen-doped porous carbon-silicon-based composite material. This invention utilizes nitrogen-doped amorphous carbon to reduce defects and improve electronic conductivity in silicon-based composite materials, and its surface oxidation (oxidation reaction) increases the specific surface area of ​​the silicon-based composite material, improves the liquid retention performance of the silicon-based composite material, and reduces the expansion of the silicon-based composite material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery material preparation technology, and in particular to a method for preparing a nitrogen-doped porous carbon-silicon-based composite material. Background Technology

[0002] Silicon-based materials are widely used in high-energy-density lithium-ion batteries and other fields due to their high energy density and wide availability. However, their high full-charge expansion, poor cycle performance, and high impedance limit their applications. Many factors can reduce the expansion and impedance of silicon-based materials, such as nano-sizing, core or surface doping, and porosity. While there are methods on the market to reduce material expansion, such as Chinese patent application number 202110750168.4 which discloses a method for preparing nitrogen-doped carbon-coated porous silicon, using a silicon-magnesium alloy as a precursor, mixing it with carbon nitride, and then heat-treating and acid-treating it under an inert atmosphere or vacuum, the porous structure can reduce expansion. However, this method suffers from poor silicon dispersion uniformity, weak bonding between silicon and nitrogen / carbon, and high impedance. Furthermore, the high density of amorphous carbon coating on the nano-silicon surface is detrimental to buffering silicon expansion during charge-discharge processes, thus reducing cycle performance. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing nitrogen-doped porous carbon-silicon composite materials. By utilizing nitrogen-doped amorphous carbon to reduce the impedance of silicon-based composite materials, the electronic conductivity of silicon-based composite materials is improved, and the surface oxidation (oxidation reaction) of the material increases the specific surface area of ​​silicon-based composite materials, reduces expansion, and improves liquid retention and cycle performance.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] One of the technical solutions of this invention is a method for preparing a nitrogen-doped porous carbon-silicon-based composite material, comprising the following steps:

[0006] Step 1: Azobisisobutyronitrile, styrene, and crosslinking agent are mixed evenly and then subjected to polymerization to obtain precursor A;

[0007] Step 2: After uniformly mixing the precursor A, organic solvent, silane coupling agent, and silicon oxide material, the mixture is reacted and then spray-dried to obtain precursor B.

[0008] Step 3: The precursor B is mixed evenly with concentrated sulfuric acid, manganese nitrate and ammonium persulfate and then subjected to an oxidation reaction. After washing and drying, the nitrogen-doped porous carbon silicon-based composite material is obtained.

[0009] In step 1, styrene is polymerized using azobisisobutyronitrile (AIBN) as an initiator to obtain polystyrene, and a network-connected polystyrene (spherical precursor A) is prepared using a crosslinking agent. Polystyrene mainly serves as a matrix for adsorbing silica materials; after carbonization, it yields a porous polymer, enabling the preparation of silica composite materials and reducing expansion.

[0010] Through repeated experiments, this invention has been verified that the silicon-based composite material prepared in step 1 has good performance only when the raw materials are azobisisobutyronitrile (AIBN) and styrene. No other particularly suitable raw materials were found besides AIBN and styrene.

[0011] In step 2, the role of the silane coupling agent is to couple the silicon-oxygen materials to form a network structure and reduce expansion; at the same time, the silicon-oxygen materials are adsorbed on the spherical precursor A to form a spherical polystyrene organic / silicon-oxygen composite material (precursor B).

[0012] In step 3, precursor B is oxidized with concentrated sulfuric acid, manganese nitrate, and ammonium persulfate to leave pores, increase the specific surface area of ​​the material, and reduce expansion.

[0013] Further, in step 1, the mass ratio of azobisisobutyronitrile, styrene, and crosslinking agent is 10-50:10-50:1-5; the crosslinking agent is one of 3-phenylpropanal, phenylpropenal, 4-methylbenzaldehyde, cinnamaldehyde, and 3-aminobenzaldehyde.

[0014] Further, in step 1, the polymerization reaction is specifically a polymerization reaction at 50-120℃ for 0.5-2 hours.

[0015] Further, in step 2, the mass ratio of precursor A, organic solvent, silane coupling agent, and silicon oxide material is 100:500-1000:1-5:100-200; the reaction is specifically carried out at 100-150℃ for 1-6 hours.

[0016] Further, in step 2, the organic solvent is one of carbon tetrachloride, cyclohexane, tetrahydrofuran, and N,N-dimethylformamide; the silane coupling agent is one of γ-(methacryloyloxy)propyltrimethoxysilane, 3-(isobutenyloxy)propyltrimethoxysilane, bis[γ-(triethoxysilane)propyl]-tetrasulfide, and γ-methacryloyloxypropyltrimethoxysilane; and the silicon-oxygen material is SiO2. x , where 0 < x < 2.

[0017] Further, in step 3, the mass ratio of precursor B, concentrated sulfuric acid, manganese nitrate and ammonium persulfate is 10-100:10-50:100:150-300.

[0018] Exceeding the above range in the proportions of precursor B, concentrated sulfuric acid, manganese nitrate, and ammonium persulfate will result in poor oxidation effect, which is not conducive to pore formation and reducing silicon expansion.

[0019] Furthermore, in step 3, the oxidation reaction is specifically an oxidation reaction at 150-200℃ for 3-12 hours.

[0020] If the oxidation reaction temperature is too low, the reaction cycle is long, resulting in fewer oxygen-containing groups and fewer pores on the surface; if the oxidation reaction temperature is too high, the pores become too large, reducing the compaction density and thus the energy density. Therefore, the preferred oxidation reaction temperature in this invention is 150-200℃.

[0021] The second technical solution of the present invention is a nitrogen-doped porous carbon-silicon-based composite material prepared by the above-mentioned preparation method.

[0022] The third technical solution of this invention is the application of the above-mentioned nitrogen-doped porous carbon-silicon-based composite material in the preparation of lithium-ion battery anode materials.

[0023] The fourth technical solution of the present invention is a lithium-ion battery anode material, comprising the above-mentioned nitrogen-doped porous carbon-silicon-based composite material.

[0024] The present invention discloses the following technical effects:

[0025] This invention utilizes nitrogen-doped amorphous carbon to reduce defects and improve electronic conductivity in silicon-based composite materials. Simultaneously, it increases the specific surface area of ​​porous carbon through oxidation, thereby enhancing the liquid retention capacity and reducing the expansion of the silicon-based composite material. When applied to lithium-ion batteries, it exhibits characteristics such as low expansion, good cycle performance, and excellent power performance.

[0026] This invention uses a chemical method to nitrogen-dope amorphous carbon, resulting in good uniformity and strong bonding. Furthermore, through the action of a crosslinking agent, a porous and isotropic amorphous carbon material can be formed, reducing the impedance and expansion of silicon-based composite materials. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The image shows a SEM image of the silicon-based composite material prepared in Example 1. Detailed Implementation

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Unless otherwise specified, the term "parts" in this invention refers to parts by weight.

[0035] Example 1

[0036] Step S1: Add 30g of styrene to 30g of azobisisobutyronitrile, disperse evenly, add 3g of 3-phenylpropanal, and carry out polymerization reaction at 80℃ for 1h to obtain precursor material A;

[0037] Step S2: 100g of precursor material A prepared in step S1 is added to 800g of carbon tetrachloride organic solvent and dispersed evenly. Then, 3g of γ-(methacryloyloxy)propyltrimethoxysilane and 150g of silicon oxide material (SiO) are added, and the reaction is carried out at 120℃ for 3h by magnetic stirring. After spray drying, precursor material B is obtained.

[0038] Step S3: Mix 50g of precursor material B prepared in step S2 with 30g of concentrated sulfuric acid (98wt%), 100g of manganese nitrate and 150g of ammonium persulfate, and oxidize at 180℃ for 6h. Wash and vacuum dry at 80℃ for 24h to obtain silicon-based composite material (nitrogen-doped porous carbon silicon-based composite material).

[0039] Example 2

[0040] Step S1: Add 10g of styrene to 10g of azobisisobutyronitrile, disperse evenly, then add 1g of benzyl acrolein and carry out a polymerization reaction at 50℃ for 2h to obtain precursor material A.

[0041] Step S2: 100g of precursor material A prepared in step S1 is added to 500g of cyclohexane organic solvent and dispersed evenly. Then, 1g of bis[γ-(triethoxysilyl)propyl]-tetrasulfide and 100g of SiO silicon oxide material are added, and the reaction is carried out at 100℃ for 6h by magnetic stirring. After spray drying, precursor material B is obtained.

[0042] Step S3: Mix 10g of precursor material B prepared in step S2 with 10g of concentrated sulfuric acid, 100g of manganese nitrate and 200g of ammonium persulfate, and oxidize at 150℃ for 12h. Wash and vacuum dry at 80℃ for 24h to obtain silicon-based composite material (nitrogen-doped porous carbon silicon-based composite material).

[0043] Example 3

[0044] Step S1: Add 10g of styrene to 50g of azobisisobutyronitrile, disperse evenly, then add 5g of cinnamaldehyde and carry out a polymerization reaction at 120℃ for 0.5h to obtain precursor material A;

[0045] Step S2: 100g of precursor material A prepared in step S1 is added to 1000g of N,N-dimethylformamide and dispersed evenly. Then, 5g of γ-methacryloyloxypropyltrimethoxysilane and 200g of SiO silicon oxide material are added, and the mixture is reacted at 150℃ for 1h by magnetic stirring. After spray drying, precursor material B is obtained.

[0046] Step S3: Mix 100g of precursor material B prepared in step S2 with 50g of concentrated sulfuric acid, 100g of manganese nitrate and 300g of ammonium persulfate, and oxidize at 200℃ for 3h. Wash and vacuum dry at 80℃ for 24h to obtain silicon-based composite material (nitrogen-doped porous carbon silicon-based composite material).

[0047] Comparative Example 1

[0048] 100g of azobisisobutyronitrile was added to 800g of carbon tetrachloride organic solvent and dispersed evenly. Then, 150g of silicon oxide material (SiO) was added, and the reaction was carried out at 120℃ for 3h by magnetic stirring. After spray drying, precursor material B was obtained. Then, precursor material B was transferred to a tube furnace and heated to 600℃ for 3h under argon atmosphere to obtain amorphous carbon-coated silicon oxide composite material.

[0049] Comparative Example 2

[0050] 100g of precursor material A prepared in step S1 of Example 1 was weighed and mixed with 150g of silicon oxide material (SiO). The mixture was then stirred magnetically and reacted at 120°C for 3 hours. After spray drying, precursor material B was obtained. Then, 50g of precursor material B was mixed with 30g of concentrated sulfuric acid, 100g of manganese nitrate, and 150g of ammonium persulfate and oxidized at 180°C for 6 hours. After washing and vacuum drying at 80°C for 24 hours, silicon-based composite material was obtained.

[0051] Effect verification example

[0052] (1) Morphology test: The silicon-based composite material obtained in Example 1 was tested by scanning electron microscopy (SEM). The test results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the silicon-based composite material has a granular structure with a uniform and reasonable particle size distribution. The material surface has a slight porous structure, and the particle size is between 2-8 μm.

[0053] (2) Physicochemical tests: The specific surface area, tap density and carbon content of the silicon-based composite materials obtained in Examples 1-3 and Comparative Examples 1-2 were tested. The tests were conducted according to the GB / T 38823-2020 standard "Silicon Carbon", and the electrical conductivity of the silicon-based composite materials was tested using a four-probe tester.

[0054] The silicon-based composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were used as negative electrode materials for lithium-ion batteries to prepare coin cells. The preparation process is as follows:

[0055] A binder, conductive agent, and solvent were added to a silicon-based composite material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain a negative electrode sheet. The binder used was polyvinylidene fluoride (PVDF), the conductive agent was conductive carbon black (SP), and the solvent was N-methylpyrrolidone (NMP). The ratio of silicon-based composite material, SP, PVDF, and NMP was 95g:1g:4g:220mL. The electrolyte was a 1mol / L solution with LiPF6 as the electrolyte, and the solvent was a 1:1 mixture of ethylene carbonate (EC) and methyl ethyl carbonate (DEC) by volume. A lithium metal sheet was used as the counter electrode, and a polypropylene (PP) membrane was used as the separator. The coin cell assembly was performed in an argon-filled glove box.

[0056] Full-charge expansion: The thickness D1 of the negative electrode sheet of the rolled coin cell is measured. Then, the full-charge thickness D2 of the negative electrode sheet is dissected at 100% SOC of the coin cell, and the expansion rate is calculated.

[0057]

[0058] Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.005V to 2.0V, and the charge / discharge rate was 0.1C. The initial discharge specific capacity (mAh / g) and initial efficiency (%) of the battery were tested. The test results are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] As can be seen from the data in Table 1, the batteries prepared using the silicon-based composite materials obtained in Examples 1-3 exhibit significantly better initial discharge specific capacity and initial efficiency than those prepared using the comparative composite materials. This is because coating the silicon-oxygen material with nitrogen-doped amorphous carbon reduces its electronic impedance, increases its electronic conductivity, and enhances its specific capacity. Simultaneously, the high azobisisobutyronitrile deposition results in a high carbon coating, reducing impedance and restricting material expansion.

[0063] (3) Pouch Battery Testing

[0064] The silicon-based composite materials of Examples 1-3 and Comparative Examples 1-2, doped with artificial graphite, were used as negative electrode materials (the mass ratio of silicon-based composite material to artificial graphite was 1:9), and were used with a ternary positive electrode material (LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3O2), electrolyte, and separator are assembled into a 5Ah soft-pack battery. The separator is Celegard 2400, and the electrolyte is a LiPF6 solution (the solvent is a mixed solution of ethylene carbonate (EC) and methyl ethyl carbonate (DEC) in a volume ratio of 1:1, and the concentration of LiPF6 is 1.3mol / L).

[0065] 3.1 Electrode Testing

[0066] a. Liquid absorption capacity test

[0067] A 1 mL burette was used to draw 1 mL of electrolyte and add one drop to the surface of the electrode. The time was recorded until the electrolyte was completely absorbed, and the absorption rate V / t of the electrode was calculated. The test results are shown in Table 2.

[0068] b. Liquid retention rate test

[0069] The theoretical liquid absorption capacity m1 of the electrode was calculated based on the electrode parameters, and the weight m2 of the electrode was measured. The electrode was then immersed in the electrolyte for 24 hours, and its weight m3 was measured. The liquid absorption capacity m3-m2 was calculated, and the liquid retention rate was calculated using the following formula: Liquid retention rate = (m3-m2)×100% / m1. The test results are shown in Table 2.

[0070] Table 2

[0071] Aspiration rate (mL / min) Liquid retention rate Example 1 6.9 90.1％ Example 2 6.1 89.2％ Example 3 7.9 91.7％ Comparative Example 1 3.5 85.1％ Comparative Example 2 2.1 82.9％

[0072] As can be seen from Table 2, the electrode materials prepared using the silicon-based composite materials obtained in Examples 1-3 have significantly higher liquid absorption and retention capabilities than those in Comparative Examples 1-2. This may be because the porous silicon-oxygen composite materials prepared in Examples 1-3 have a larger specific surface area, thus enhancing their liquid absorption and retention capabilities.

[0073] 3.2x Ratio and Cyclic Performance Testing:

[0074] Cyclic performance test: The charge / discharge voltage range was 2.5–4.2V, the temperature was 25±3.0℃, the charge / discharge rate was 1.0C / 1.0C, and the number of cycles was 500. Rate test: The constant current ratio of the material under 2C conditions was tested (constant current ratio = constant current capacity / (constant current capacity + constant voltage capacity)). The test results are shown in Table 3.

[0075] Table 3

[0076]

[0077]

[0078] As shown in Table 3, the lithium-ion batteries prepared using the silicon-based composite materials obtained in Examples 1-3 all exhibit better cycle performance than those in Comparative Examples 1-2. This is because the nitrogen-doped porous carbon-silicon-based composite materials prepared in Examples 1-3 of this invention have lower expansion and higher specific surface area, which improves the liquid retention capacity of the material and enhances cycle performance. At the same time, the silicon-based composite materials prepared in Examples 1-3 have higher powder conductivity, which improves the kinetic performance of the lithium-ion battery, thereby improving the constant current ratio during the charge and discharge process, i.e., improving the power performance of the lithium-ion battery.

[0079] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a nitrogen-doped porous carbon-silicon-based composite material, characterized in that, Includes the following steps: Step 1: Azobisisobutyronitrile, styrene, and crosslinking agent are mixed evenly and then subjected to polymerization to obtain precursor A; Step 2: After uniformly mixing the precursor A, organic solvent, silane coupling agent, and silicon oxide material, the mixture is reacted and then spray-dried to obtain precursor B. Step 3: The precursor B is mixed evenly with concentrated sulfuric acid, manganese nitrate and ammonium persulfate and then subjected to an oxidation reaction. After washing and drying, the nitrogen-doped porous carbon silicon-based composite material is obtained. In step 2, the mass ratio of precursor A, organic solvent, silane coupling agent, and silicon oxide material is 100:500-1000:1-5:100-200; the reaction is specifically carried out at 100-150℃ for 1-6 hours. In step 3, the mass ratio of precursor B, concentrated sulfuric acid, manganese nitrate and ammonium persulfate is 10-100:10-50:100:150-300; In step 3, the oxidation reaction is specifically an oxidation reaction at 180-200℃ for 3-12 hours.

2. The preparation method according to claim 1, characterized in that, In step 1, the mass ratio of azobisisobutyronitrile, styrene, and crosslinking agent is 10-50:10-50:1-5; the crosslinking agent is one of 3-phenylpropanal, phenylpropenal, 4-methylbenzaldehyde, and 3-aminobenzaldehyde.

3. The preparation method according to claim 1, characterized in that, In step 1, the polymerization reaction is specifically a polymerization reaction at 50-120℃ for 0.5-2 hours.

4. The preparation method according to claim 1, characterized in that, In step 2, the organic solvent is one of carbon tetrachloride, cyclohexane, tetrahydrofuran, and N,N-dimethylformamide; the silane coupling agent is one of γ-(methacryloyloxy)propyltrimethoxysilane and bis[γ-(triethoxysilyl)propyl]-tetrasulfide; and the silicon-oxygen material is SiO2. x , where 0 < x < 2.

5. The nitrogen-doped porous carbon-silicon based composite material prepared by the preparation method according to any one of claims 1-4.

6. The application of the nitrogen-doped porous carbon-silicon-based composite material as described in claim 5 in the preparation of lithium-ion battery anode materials.

7. A lithium-ion battery anode material, characterized in that, Including the nitrogen-doped porous carbon-silicon-based composite material as described in claim 5.

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