A spherical silicon-carbon negative electrode material and its preparation method and application

Abstract

The present invention relates to the technical field of lithium battery materials, and specifically discloses a spherical silicon-carbon negative electrode material, a preparation method thereof, and an application thereof. The spherical silicon-carbon negative electrode material comprises an inner core and a coating layer coated on the outer core; the inner core comprises porous hard carbon doped with nitrogen and a carbon layer coated on the outer core, wherein silicon nanoparticles are deposited in the porous hard carbon; and the coating layer is a trimethylaluminum-functionalized polyethylene oxide cross-linked network coating layer. The spherical silicon-carbon negative electrode material provided by the present invention is coated with a methylaluminum-functionalized polyethylene oxide cross-linked network. The coating layer can provide a transmission channel for ions, promote ion transmission, and is conducive to enhancing the lithium storage performance of the negative electrode material. The high-strength three-dimensional network structure can effectively inhibit the volume expansion of the silicon-carbon negative electrode material and prevent particle cracking or pulverization.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery materials, and in particular to a spherical silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, as high-energy-density energy storage devices, have been widely used in portable electronic devices, electric vehicles, and other fields. However, traditional graphite anode materials have a low theoretical specific capacity, making it difficult to meet the demand for high-energy-density lithium-ion batteries in the future. Silicon, with its high theoretical specific capacity of 4200mAh / g, has attracted much attention and is considered the most promising anode material for next-generation lithium-ion batteries. However, silicon undergoes dramatic volume expansion during lithium-ion insertion and extraction, resulting in the fragmentation and pulverization of silicon particles and the collapse of the electrode structure, which can lead to rapid battery capacity decay and reduced cycle performance.

[0003] Currently, the industry uses methods such as carbon coating to improve the structural stability and electrical conductivity of silicon-based anode materials. However, the electrical performance of these silicon-carbon anode materials cannot be further improved. The stress distribution is uneven during lithium insertion and expansion, making them prone to cracking. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a spherical silicon-carbon negative electrode material, a preparation method and application thereof. The spherical silicon-carbon negative electrode material is coated with a methylaluminum-functionalized polyethylene oxide cross-linked network. The coating layer can provide a transmission channel for ions, promote the transmission of ions, and is beneficial to enhancing the lithium storage performance of the negative electrode material. The high-strength three-dimensional network structure can effectively inhibit the volume expansion of the silicon-carbon negative electrode material and prevent particle cracking or pulverization.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention first provides a spherical silicon-carbon negative electrode material, which includes an inner core and a coating layer coated outside the inner core; the inner core includes porous hard carbon doped with nitrogen elements and a carbon layer coated outside the porous hard carbon, and silicon nanoparticles are deposited in the porous hard carbon; the coating layer is a trimethylaluminum-functionalized polyethylene oxide cross-linked network coating layer.

[0007] As a further improvement of the above solution of the present invention, in the spherical silicon-carbon negative electrode material, the particle size of the core is 5-10 μm, the thickness of the carbon layer is 5-30 nm, and the thickness of the coating layer is 10-20 nm.

[0008] The present invention also provides a method for preparing the spherical silicon-carbon negative electrode material as described above, which comprises the following steps:

[0009] S1. Aniline and its derivatives are added to deionized water, an organic acid is added under stirring, mixed evenly, an oxidant is added to react, and post-treated to obtain polyaniline nanospheres; the polyaniline nanospheres are pre-carbonized to obtain porous hard carbon;

[0010] S2. The porous hard carbon is sequentially subjected to silicon deposition and carbon coating to obtain a core material;

[0011] S3. Under a protective atmosphere, the core material is dispersed in an organic solvent, polyethylene oxide PEO is added, stirred, and trimethylaluminum TMA is added to react to obtain a spherical silicon-carbon negative electrode material.

[0012] As a further improvement of the above solution of the present invention, in step S1, the aniline and its derivatives are at least one of aniline, m-toluidine, o-toluidine, 4-ethylaniline, and N-ethylaniline.

[0013] As a further improvement of the above solution of the present invention, in step S1, the organic acid is at least one of formic acid, acetic acid, benzoic acid, and 2-hydroxypropionic acid.

[0014] As a further improvement of the above solution of the present invention, in step S1, the oxidant is at least one of hydrogen peroxide, potassium permanganate, and potassium dichromate.

[0015] As a further improvement of the above solution of the present invention, in step S1, the reaction is carried out by stirring at room temperature for 8 to 12 hours, and the pre-carbonization is carried out under a protective atmosphere at 700 to 900° C. for 2 to 4 hours.

[0016] As a further improvement of the above solution of the present invention, in step S3, the stirring is carried out at room temperature for 2 to 4 hours.

[0017] As a further improvement of the above solution of the present invention, in step S3, the reaction is first stirred at room temperature for 6 to 10 hours, and then heated to 60 to 120° C. for 6 to 10 hours.

[0018] The present invention also provides a use of the spherical silicon-carbon negative electrode material as described above as a negative electrode material for a lithium battery.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The spherical silicon-carbon negative electrode material provided by the present invention uses TMA as a crosslinker on the surface of the silicon-carbon material to form an Al-OC covalent bond network with PEO, constructing a high-strength three-dimensional structure with certain pores and channels. Polyethylene oxide itself has flexible chain segments that can undergo chain segment movement to a certain extent. After crosslinking with trimethylaluminum, although the movement of these chain segments is restricted to a certain extent, dynamic spaces can still be formed locally, providing transmission channels for ions. At the same time, the charge distribution and chemical environment around the aluminum-oxygen (Al-O) clusters serving as crosslinking nodes also affect the transmission of ions, which may attract and guide the movement of ions in the network. The polyethylene oxide chain segments have a certain polarity and can interact with ions. For example, lithium ions can form coordination interactions with oxygen atoms on the polyethylene oxide chain. When the chain segments move, this coordination interaction is continuously formed and broken, thereby driving the movement of ions in the network. In addition, the aluminum atoms introduced after trimethylaluminum functionalization and the chemical bonds around them may also interact with ions, further promoting ion transmission. Therefore, the coating of the methylaluminum functionalized polyethylene oxide cross-linked network of the present invention is beneficial to enhancing the lithium storage performance of the silicon-carbon negative electrode material. And this cross-linked network wraps the silicon-carbon negative electrode particles like an elastic cage, providing rigid constraints during the charge and discharge process, and suppressing the volume expansion of the silicon-carbon negative electrode material; the network structure can also uniformize the stress distribution and suppress local stress concentration. The uniform coating of the cross-linked network can avoid the local stress concentration caused by uneven expansion of the negative electrode material during the lithiation / delithiation process, and prevent the particles from cracking or pulverizing. In addition, it can also adapt to volume changes. The elasticity of PEO allows the coating layer to undergo reversible deformation as the negative electrode expands / contracts, and the cross-linked structure ensures that the coating layer will not fail due to excessive deformation. And the Al of TMA can form Al-O-Si bonds with the surface of the silicon-carbon negative electrode, enhancing the adhesion of the coating layer to the hard carbon substrate, and preventing the coating layer from peeling off due to expansion.

[0021] The spherical silicon-carbon negative electrode material provided by the present invention reduces continuous expansion and inhibits electrolyte penetration by constructing a cross-linked network structure on the surface of the silicon-carbon material to stabilize the SEI layer. The dense TMA-PEO layer can block the electrolyte from penetrating into the interior of the negative electrode, reducing the repeated growth of the SEI layer caused by electrolyte decomposition (SEI accumulation will aggravate volume expansion).

[0022] The spherical silicon-carbon negative electrode material provided by the present invention is made by doping nitrogen elements into a porous hard carbon substrate. The nitrogen atoms can enhance the structural stability of the material through chemical bonding and other means. In the silicon-carbon-nitrogen composite material, the nitrogen atoms can form covalent bonds with silicon and carbon, and play a buffering and supporting role when the volume of the silicon material expands and contracts during the charging and discharging process, thereby enhancing the structural stability. In addition, the electronegativity of nitrogen atoms is greater than that of carbon, and they will introduce additional electronic states into the conjugated system of carbon. These new electronic states can provide more conductive channels, reduce the resistance of the material, and thus improve the conductivity of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an electron microscope image of the spherical silicon-carbon negative electrode material prepared in Example 1;

[0024] Figure 2 This is an electron microscope image of the spherical silicon-carbon negative electrode material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0025] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0027] Example 1

[0028] This embodiment provides a spherical silicon-carbon negative electrode material, the preparation method of which includes the following steps:

[0029] Preparation of porous hard carbon: 10 mL of aniline solution (5 mol / L) and 10 mL of N-ethylaniline solution (5 mol / L) were added to 50 mL of deionized water and stirred at 300 r / min. 100 mL of acetic acid (1 mol / L) was slowly added dropwise. After stirring for 10 minutes, 15 mL of hydrogen peroxide (6.53 mol / L) was added and stirred at room temperature for 10 hours. After filtration, washing, and drying, polyaniline nanospheres were obtained. The polyaniline nanospheres were pre-carbonized at 800°C under a nitrogen atmosphere for 3 hours to obtain porous hard carbon.

[0030] S2. Silicon Deposition and Carbon Coating: The porous hard carbon obtained in step S1 was placed in a fluidized bed vapor deposition apparatus and introduced with silane and argon (volume ratio of silane to argon: 2:1) for vapor deposition at 400°C for 3 hours. The apparatus was then flushed with argon for 30 minutes, and acetylene and argon (volume ratio of acetylene to argon: 2:1) were introduced for vapor deposition at 450°C for 3 hours to obtain the core material.

[0031] S3. Trimethylaluminum functionalized polyethylene oxide cross-linked network coating: Under nitrogen protection, add 20 mL of anhydrous ethanol to the core material obtained in step S2. After complete ultrasonic dispersion, add 50 mL of polyethylene oxide PEO solution (concentration is 2 mol / L) and stir at room temperature for 4 hours; then slowly add 25 mL of trimethylaluminum TMA solution (concentration is 4 mol / L) and stir at room temperature for 10 hours to graft TMA onto the PEO molecular chain and form TMA-functionalized PEO on the surface of the core material; then heat to 100°C and react for 8 hours to allow condensation reaction to occur between TMAs to obtain a spherical silicon-carbon negative electrode material.

[0032] Example 2

[0033] This embodiment provides a spherical silicon-carbon negative electrode material, the preparation method of which includes the following steps:

[0034] Preparation of porous hard carbon: 12 mL of aniline solution (5 mol / L) and 12 mL of 4-ethylaniline solution (5 mol / L) were added to 50 mL of deionized water and stirred at 300 r / min. 100 mL of formic acid (1 mol / L) was slowly added dropwise. After stirring for 10 min, 15 mL of hydrogen peroxide (6.53 mol / L) was added and stirred at room temperature for 12 h. Polyaniline nanospheres were obtained after filtration, washing, and drying. The polyaniline nanospheres were pre-carbonized at 700°C under a nitrogen atmosphere for 4 h to obtain porous hard carbon.

[0035] S2. Silicon Deposition and Carbon Coating: The porous hard carbon obtained in step S1 was placed in a fluidized bed vapor deposition apparatus and introduced with silane and argon (volume ratio of silane to argon: 2:1) for vapor deposition at 400°C for 3 hours. The apparatus was then flushed with argon for 30 minutes, and acetylene and argon (volume ratio of acetylene to argon: 2:1) were introduced for vapor deposition at 450°C for 3 hours to obtain the core material.

[0036] S3. Trimethylaluminum functionalized polyethylene oxide cross-linked network coating: Under nitrogen protection, add 20 mL of dichloromethane to the core material obtained in step S2. After complete ultrasonic dispersion, add 50 mL of polyethylene oxide PEO solution (concentration is 2 mol / L) and stir at room temperature for 3 hours; then slowly add 25 mL of trimethylaluminum TMA solution (concentration is 4 mol / L) and stir at room temperature for 10 hours to graft TMA onto the PEO molecular chain and form TMA-functionalized PEO on the surface of the core material; then heat to 60°C for 10 hours to allow condensation reaction to occur between TMAs to obtain a spherical silicon-carbon negative electrode material.

[0037] Example 3

[0038] This embodiment provides a spherical silicon-carbon negative electrode material, the preparation method of which includes the following steps:

[0039] Preparation of porous hard carbon: 14 mL of aniline solution (5 mol / L) and 14 mL of o-toluidine solution (5 mol / L) were added to 50 mL of deionized water and stirred at 300 r / min. 100 mL of benzoic acid (1 mol / L) was slowly added dropwise. After stirring for 10 min, 23 mL of hydrogen peroxide (6.53 mol / L) was added and stirred at room temperature for 8 h. Polyaniline nanospheres were obtained after filtration, washing, and drying. The polyaniline nanospheres were pre-carbonized at 900°C under a nitrogen atmosphere for 2 h to obtain porous hard carbon.

[0040] S2. Silicon Deposition and Carbon Coating: The porous hard carbon obtained in step S1 was placed in a fluidized bed vapor deposition apparatus and introduced with silane and argon (volume ratio of silane to argon: 2:1) for vapor deposition at 400°C for 3 hours. The apparatus was then flushed with argon for 30 minutes, and acetylene and argon (volume ratio of acetylene to argon: 2:1) were introduced for vapor deposition at 450°C for 3 hours to obtain the core material.

[0041] S3. Trimethylaluminum-functionalized polyethylene oxide cross-linked network coating: Under nitrogen protection, add 20 mL of anhydrous ethanol to the core material obtained in step S2. After complete ultrasonic dispersion, add 50 mL of polyethylene oxide solution (PEO solution) (concentration is 2 mol / L) and stir at room temperature for 2 hours; then slowly add 20 mL of trimethylaluminum TMA solution (concentration is 6 mol / L) and stir at room temperature for 8 hours to graft TMA onto the PEO molecular chain and form TMA-functionalized PEO on the surface of the core material; then heat to 90°C for 7 hours to allow condensation reaction between TMAs to obtain a spherical silicon-carbon negative electrode material.

[0042] Example 4

[0043] This embodiment provides a spherical silicon-carbon negative electrode material, the preparation method of which includes the following steps:

[0044] Preparation of porous hard carbon: 10 mL of aniline solution (5 mol / L) and 10 mL of m-toluidine solution (5 mol / L) were added to 50 mL of deionized water and stirred at 300 r / min. 100 mL of 2-hydroxypropionic acid (1 mol / L) was slowly added dropwise. After stirring for 10 min, 20 mL of potassium permanganate solution (5 mol / L) was added and stirred at room temperature for 10 h. Polyaniline nanospheres were obtained after filtration, washing, and drying. The polyaniline nanospheres were then pre-carbonized at 800°C under a nitrogen atmosphere for 3 h to obtain porous hard carbon.

[0045] S2. Silicon Deposition and Carbon Coating: The porous hard carbon obtained in step S1 was placed in a fluidized bed vapor deposition apparatus and introduced with silane and argon (volume ratio of silane to argon: 2:1) for vapor deposition at 400°C for 3 hours. The apparatus was then flushed with argon for 30 minutes, and acetylene and argon (volume ratio of acetylene to argon: 2:1) were introduced for vapor deposition at 450°C for 3 hours to obtain the core material.

[0046] S3. Trimethylaluminum functionalized polyethylene oxide cross-linked network coating: Under nitrogen protection, add 20 mL of anhydrous ethanol to the core material obtained in step S2. After complete ultrasonic dispersion, add 50 mL of polyethylene oxide PEO solution (concentration is 2 mol / L) and stir at room temperature for 4 hours; then slowly add 25 mL of trimethylaluminum TMA solution (concentration is 4 mol / L) and stir at room temperature for 6 hours to graft TMA onto the PEO molecular chain and form TMA-functionalized PEO on the surface of the core material; then heat to 120°C for 6 hours to allow condensation reaction to occur between TMAs to obtain a spherical silicon-carbon negative electrode material.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that the carbon coating step is not performed in this comparative example.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 1 is that the trimethylaluminum functionalized polyethylene oxide cross-linked network coating step is not performed in this comparative example.

[0051] Test Case

[0052] The spherical silicon-carbon negative electrode materials obtained in Example 1 and Comparative Example 2 were characterized using a scanning electron microscope. Figure 1 and Figure 2 .from Figure 1 、 Figure 2 It can be seen that the particle size of the spherical silicon-carbon negative electrode materials prepared in Example 1 and Comparative Example 2 is relatively uniform and evenly dispersed, indicating that the prepared spherical negative electrode materials have good uniformity; compared with Comparative Example 2, the surface of the spherical silicon-carbon negative electrode material prepared in Example 1 is relatively smooth and exhibits a regular morphology, indicating that Example 1 uniformly forms a trimethylaluminum-functionalized polyethylene oxide cross-linked network coating layer.

[0053] Application Examples

[0054] The spherical silicon-carbon negative electrode materials prepared in Examples 1-4 and Comparative Examples 1-2 were respectively prepared into lithium batteries: the spherical silicon-carbon negative electrode material, a binder (CMC) and a conductive agent (SuperP) were mixed in a mass ratio of 8:1:1 to obtain a slurry, the slurry was coated on the surface of a copper foil, and then vacuum-dried at 100°C for 12 hours, and finally a negative electrode sheet with a diameter of 12 mm was obtained by a sheet punching machine; metallic lithium was used as the counter electrode; Celgard2400 was used as the diaphragm; LiPF6 solution (concentration of 1 mol / L, the solvent was a mixture of ethylene carbonate EC and dimethyl carbonate DMC in a volume ratio of 1:1, containing 10% FEC additive) was used as the electrolyte, and the batteries were assembled into 2032 button cells in a glove box with a high-purity argon environment.

[0055] The prepared batteries were subjected to electrochemical performance tests at a current density of 0.1C and a voltage range of 0.005-1.5V to obtain the initial charge and discharge capacity, initial coulombic efficiency, capacity retention rate after 500 cycles, and initial expansion rate of the electrode (the thickness of the active material layer after the first delithiation compared to the thickness of the active material layer before lithium insertion). The results are shown in Table 1 below.

[0056] Table 1 Electrochemical performance

[0057]

[0058] From the results in Table 1 we can see that:

[0059] Compared with Comparative Examples 1-2, the batteries assembled with the materials prepared in Examples 1-4 had significantly improved initial charge capacity, initial coulombic efficiency, and capacity retention, and had a lower initial electrode expansion rate, indicating that the spherical silicon-carbon negative electrode material prepared in the present invention has excellent electrochemical performance and structural stability.

[0060] Compared with Example 1, since comparative example 1 is not carbon coated, the initial electrode expansion rate of the spherical silicon-carbon negative electrode material is as high as 62.9%, and the capacity retention rate is also significantly reduced;

[0061] Compared with Example 1, since Comparative Example 2 did not carry out trimethylaluminum-functionalized polyethylene oxide cross-linked network coating, the first electrode expansion rate increased from 40.7% to 73.7%, the first charge capacity decreased from 2020.3 mAh / g to 1790.2 mAh / g, and the capacity retention rate decreased from 83.2% to 73.1%. This shows that the trimethylaluminum-functionalized polyethylene oxide cross-linked network coating layer of the present invention can inhibit the volume expansion of the silicon-carbon negative electrode material, which is beneficial to enhancing the lithium storage performance of the silicon-carbon negative electrode.

[0062] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A spherical silicon-carbon negative electrode material, characterized in that: It includes an inner core and a coating layer coated outside the inner core; the inner core includes porous hard carbon doped with nitrogen elements and a carbon layer coated outside the porous hard carbon, and silicon nanoparticles are deposited in the porous hard carbon; the coating layer is a trimethylaluminum functionalized polyethylene oxide cross-linked network coating layer.

2. The spherical silicon-carbon negative electrode material according to claim 1, characterized in that In the spherical silicon-carbon negative electrode material, the particle size of the core is 5-10 μm, the thickness of the carbon layer is 5-30 nm, and the thickness of the coating layer is 10-20 nm.

3. A method for preparing the spherical silicon-carbon negative electrode material according to claim 1 or 2, characterized in that: It includes the following steps: S1. Add aniline or a substituted aniline derivative to deionized water, add an organic acid with stirring, mix well, add an oxidant for reaction, and post-treat to obtain polyaniline nanospheres; pre-carbonize the polyaniline nanospheres to obtain porous hard carbon; the organic acid is at least one of formic acid, acetic acid, benzoic acid, and 2-hydroxypropionic acid; and the oxidant is at least one of hydrogen peroxide, potassium permanganate, and potassium dichromate; S2. The porous hard carbon is sequentially subjected to silicon deposition and carbon coating to obtain a core material; S3. Under a protective atmosphere, the core material is dispersed in an organic solvent, polyethylene oxide is added, stirred, and trimethylaluminum is added to react to obtain a spherical silicon-carbon negative electrode material.

4. The method for preparing a spherical silicon-carbon negative electrode material according to claim 3, wherein: In step S1, the aniline and its derivatives are at least one of aniline, m-toluidine, o-toluidine, 4-ethylaniline, and N-ethylaniline.

5. The method for preparing a spherical silicon-carbon negative electrode material according to claim 3, wherein: In step S1, the reaction is carried out under stirring at room temperature for 8 to 12 hours, and the pre-carbonization is carried out under a protective atmosphere at 700 to 900° C. for 2 to 4 hours.

6. The method for preparing a spherical silicon-carbon negative electrode material according to claim 3, wherein: In step S3, the stirring is performed at room temperature for 2 to 4 hours.

7. The method for preparing a spherical silicon-carbon negative electrode material according to claim 3, wherein: In step S3, the reaction is first stirred at room temperature for 6 to 10 hours, and then heated to 60 to 120° C. for 6 to 10 hours.

8. Use of the spherical silicon-carbon negative electrode material according to claim 1 or 2 as a negative electrode material for a lithium battery.

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