Silicon-carbon negative electrode material, preparation method thereof, negative electrode sheet, lithium ion battery and expansion degree test method

Abstract

This invention relates to the field of battery technology, and in particular to a silicon-carbon anode material and its preparation method, an anode sheet and a lithium-ion battery, as well as a method for testing expansion. The silicon-carbon anode material comprises a porous carbon composite, an elastic buffer layer covering the outer surface of the porous carbon composite, and a rigid constraint layer covering the outer surface of the elastic buffer layer; the porous carbon composite comprises a porous carbon framework and silicon particles disposed within the porous carbon framework. The silicon-carbon anode material of this invention constructs a three-level composite structure, achieving graded absorption and conversion of expansion stress. The porous carbon framework provides initial expansion accommodation space, the elastic buffer layer absorbs and disperses expansion stress through its deformable properties, and the rigid constraint layer acts as a final barrier to prevent overall particle breakage and convert local stress into in-plane dispersed stress.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a silicon-carbon anode material and its preparation method, an anode sheet and a lithium-ion battery, as well as a method for testing expansion. Background Technology

[0002] Silicon-based materials are considered the most promising anode materials for next-generation high-energy-density lithium batteries due to their theoretical specific capacity of up to 4200 mAh / g (more than 10 times that of graphite). Furthermore, silicon offers advantages such as low operating potential, abundant natural reserves, and environmental friendliness. However, the core challenge for the commercialization of silicon-based anodes is the approximately 300% volume expansion during charge and discharge. This drastic volume change occurs repeatedly during cycling, leading to silicon particle pulverization, electrode structure damage, and repeated rupture and regeneration of the solid electrolyte interface film, ultimately resulting in rapid capacity decay and a significantly shortened cycle life. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a silicon-carbon anode material, its preparation method, anode sheet, lithium-ion battery, and expansion test method.

[0004] To achieve the above objectives, this application adopts the following solution: A silicon-carbon anode material includes a porous carbon composite, an elastic buffer layer covering the outer surface of the porous carbon composite, and a rigid constraint layer covering the outer surface of the elastic buffer layer; the porous carbon composite includes a porous carbon framework and silicon particles disposed within the porous carbon framework.

[0005] The porous carbon framework comprises one or more of resin-based porous carbon, biomass-based porous carbon, or pitch-based porous carbon, with a specific surface area of ​​800~2000 m². 2 / g, pore volume 0.5~2.0 cm³ 3 / g, with an average particle size of 5~15 μm. Preferably, its specific surface area is 1200 m² / g. 2 / g, pore volume 1.2 cm³ 3 / g, with an average particle size of 10 μm.

[0006] Silicon particles account for 20-50% of the mass of the porous carbon framework; preferably 35%.

[0007] The material of the elastic buffer layer is asphalt; preferably, the mass ratio of porous carbon composite to asphalt is (100~200):(5~20); preferably, the thickness of the elastic buffer layer is 20~100 nm.

[0008] The rigid constraint layer comprises multi-walled carbon nanotubes and graphene; preferably, the mass ratio of multi-walled carbon nanotubes to graphene is (1~5):(5~1), more preferably 3:2; preferably, the aspect ratio of multi-walled carbon nanotubes is ≥100; preferably, the thickness of the rigid constraint layer is 5~20 nm; more preferably 12 nm.

[0009] The present invention also includes a method for preparing the silicon-carbon anode material, comprising the following steps: Step 1: Carbonize the porous carbon precursor under an inert atmosphere to obtain a porous carbon framework; preferably, carbonize at 600~1000℃ for 2~6 h. Step 2: The porous carbon framework is placed in a fluidized bed reactor, and a mixture of silane and hydrogen gas is introduced for chemical vapor deposition to obtain a porous carbon composite. Step 3: Mix the porous carbon composite with asphalt and coat it at 300~500℃ for 2~5 h in an inert atmosphere to form an elastic buffer layer on the surface of the porous carbon composite. Step 4: Disperse multi-walled carbon nanotubes and graphene in a solvent and ultrasonically disperse for 1-3 hours to obtain a coating slurry. Coat the surface of the product from Step 3 with the coating slurry, dry it, and then heat-treat it at 500-700℃ for 1-3 hours under an inert atmosphere to form a rigid constraint layer and obtain the final sample.

[0010] In step two, the deposition temperature is 450~600℃, the silane gas concentration is 5~20 vol%, the deposition time is 1~4 h, the silane gas flow rate is 0.1~0.5 L / min, and the hydrogen gas flow rate is 0.2~1.0 L / min; preferably, the deposition temperature in step two is 550℃, the silane gas concentration is 10 vol%, the deposition time is 2 h, the silane gas flow rate is 0.3 L / min, and the hydrogen gas flow rate is 0.5 L / min. Preferably, the solvent in step four is one or more of N-methylpyrrolidone, ethanol, or isopropanol.

[0011] The present invention also includes a negative electrode sheet comprising the aforementioned silicon-carbon negative electrode material.

[0012] The present invention also includes a lithium-ion battery comprising the aforementioned negative electrode.

[0013] The present invention also includes a method for testing the expansion degree of the silicon-carbon anode material, comprising the following steps: (1) taking a sample of the silicon-carbon anode material to be tested, mixing it with a conductive agent and a binder, preferably mixing them in a mass ratio of 80:10:10, coating it on the surface of a copper foil, drying it under vacuum, cutting it into a circular electrode sheet, and measuring the initial thickness T0 of the electrode sheet. (2) Assemble a coin cell using a lithium sheet as the counter electrode; (3) Let the assembled button cell battery stand for 6-24 hours, preferably 12 hours; (4) Discharge at a constant current of 0.05-0.2C, preferably 0.1C, to 0.01V; (5) Disassemble the button cell under an inert atmosphere, remove the electrode, soak and clean it with organic solvent, and then vacuum dry it. (6) Measure the thickness T1 of the electrode after drying; (7) Calculate the expansion rate using the following formula: Expansion rate (%) = (T1 - T0) / T0 × 100%; Preferably, T1 and T0 measurements are performed using a micrometer or a laser thickness gauge, with no fewer than 5 points measured for each sample, and the arithmetic mean is taken. Preferably, an expansion rate of ≤40% is considered good, 40%~60% is considered acceptable, and >60% is considered unacceptable.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The silicon-carbon anode material of the present invention constructs a three-level composite structure to achieve graded absorption and conversion of expansion stress. The porous carbon skeleton provides initial expansion accommodation space, the elastic buffer layer absorbs and disperses expansion stress through its own deformable properties, and the rigid constraint layer acts as the final barrier to prevent the overall breakage of particles and convert local stress into in-plane dispersed stress. The synergistic effect of the three-level structure significantly improves the effect of suppressing expansion throughout the entire cycle compared with the existing single buffer mechanism.

[0015] (2) Soft carbon formed by asphalt carbonization is selected as an elastic buffer layer. Its unique amorphous structure and deformable properties enable it to effectively absorb the stress generated by silicon expansion. The rigid constraint layer formed by multi-walled carbon nanotubes and graphene has both the linear strength and toughness of carbon nanotubes and the high in-plane modulus of graphene in two dimensions. It can provide physical constraint force and optimize the stress transmission path.

[0016] (3) Simple and efficient expansion rate assessment method: The button cell electrode thickness method proposed in this invention only requires conventional button cell assembly equipment and a micrometer to complete the expansion rate measurement. It is simple to operate and low in cost, and does not require expensive equipment such as in-situ expansion analyzers and XRD. It is suitable for rapid screening and process optimization in the laboratory. This method can be used as a rapid assessment tool in the material research and development stage. Attached Figure Description

[0017] Figure 1 This is an overall schematic diagram of the silicon-carbon anode material of the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] Example 1: Preparation of silicon-carbon anode material, including the following steps: (1) Preparation of porous carbon framework: Petroleum pitch-based porous carbon precursor was activated with steam under a nitrogen atmosphere and carbonized at 800℃ for 4 h at a rate of 5℃ / min to obtain a porous carbon framework. The specific surface area of ​​the obtained porous carbon framework was 1200 m². 2 / g, pore volume 1.2 cm³ 3 / g, with an average particle size of 10 μm.

[0020] (2) Silicon deposition: The porous carbon framework was placed in a fluidized bed reactor, nitrogen was introduced and the temperature was raised to 550°C, and a mixture of silane gas (high-purity silane SiH4) and hydrogen gas (silane gas concentration 10 vol%, flow rate 0.3 L / min, hydrogen gas flow rate 0.5 L / min) was introduced. After deposition for 2 h, the silane gas was stopped and the mixture was cooled to room temperature in a nitrogen atmosphere to obtain a porous carbon composite with a silicon content of 35 wt%.

[0021] (3) Elastic buffer layer coating: 100 g of porous carbon composite and 10 g of asphalt are mixed evenly and coated at 400°C for 3 h under nitrogen atmosphere to form an elastic buffer layer with a thickness of about 50 nm.

[0022] (4) Rigid constraint layer coating: Multi-walled carbon nanotubes (aspect ratio of about 150) and graphene were dispersed in N-methylpyrrolidone at a mass ratio of 3:2 and ultrasonically dispersed for 2 h to obtain a coating slurry. The slurry was uniformly coated on the surface of the product in step (3), dried, and then heat-treated at 600℃ for 2 h under a nitrogen atmosphere to form a rigid constraint layer with a thickness of about 12 nm, thus obtaining a graded stress-relieving silicon-carbon anode material.

[0023] Figure 1 The diagram illustrates a silicon-carbon anode material comprising a porous carbon composite, an elastic buffer layer 3 covering the outer surface of the porous carbon composite, and a rigid constraint layer 4 covering the outer surface of the elastic buffer layer; the porous carbon composite comprises a porous carbon framework 2 and silicon particles 1 disposed within the porous carbon framework.

[0024] Example 2: The only difference between Example 2 and Example 1 is the thickness of the elastic buffer layer: only the amount of asphalt added is adjusted, while the other raw materials, heating rate, temperature, holding time, silicon deposition parameters, and rigid coating process are completely the same; the asphalt feeding is changed from 10 g to 5 g, the holding time is 400℃ for 3 h, the thickness of the elastic buffer layer is about 25 nm, and the subsequent rigid constraint layer is still 12 nm, thus obtaining a silicon-carbon anode.

[0025] Example 3: The only difference between Example 2 and Example 1 is the thickness of the elastic buffer layer: only the amount of asphalt added is adjusted, while the other raw materials, heating rate, temperature, heat preservation time, silicon deposition parameters, and rigid coating process are completely the same; the asphalt feeding is changed to 20 g, coating at 400℃ for 3 h, the thickness of the elastic buffer layer is about 100 nm, and the rigid layer of 12 nm remains unchanged.

[0026] Comparative Example 1: The only difference between Comparative Example 1 and Example 1 is the rigid constraint layer; the elastic buffer layer is absent. The preparation steps of the elastic buffer layer, including asphalt mixing and low-temperature coating, in Example 1 are omitted. Multi-walled carbon nanotubes (aspect ratio approximately 150) and graphene were directly dispersed in N-methylpyrrolidone at a mass ratio of 3:2 and ultrasonically dispersed for 2 h to obtain a uniformly coated slurry. The slurry was uniformly coated onto the surface of the above-mentioned porous carbon composite without asphalt coating, dried, and then heat-treated at 600°C in a nitrogen atmosphere for 2 h to form a rigid constraint layer with a thickness of approximately 12 nm on the particle surface, thus obtaining a silicon-carbon anode comparative material containing only a rigid constraint layer.

[0027] The expansion rate was tested for both the examples and the comparative examples, specifically including the following steps: 1) Take a sample of silicon-carbon anode material to be tested, mix it with conductive agent and binder, preferably in a mass ratio of 80:10:10, coat it on the surface of copper foil, dry it under vacuum and cut it into circular electrode sheets, and measure the initial thickness T0 of the electrode sheets. (2) Assemble a coin cell using a lithium sheet as the counter electrode; (3) Let the assembled button cell battery stand for 6-24 hours, preferably 12 hours; (4) Discharge at a constant current of 0.05-0.2C, preferably 0.1C, to 0.01V; (5) Disassemble the button cell under an inert atmosphere, remove the electrode, soak and clean it with organic solvent, and then vacuum dry it. (6) Measure the thickness T1 of the electrode after drying; (7) Calculate the expansion rate using the following formula: Expansion rate (%) = (T1-T0) / T0 × 100%.

[0028] T1 and T0 measurements were performed using a micrometer or laser thickness gauge, with at least 5 points measured for each sample, and the arithmetic mean was taken. The results of thickness expansion rates for different comparative examples and embodiments are shown in Table 1.

[0029] Table 1

[0030] Based on the expansion rate being ≤40% for good, 40%~60% for acceptable, and >60% for unacceptable, in this application, an expansion rate ≤40% is considered good.

[0031] In summary, the silicon-carbon anode material of this invention constructs a three-level composite structure, achieving hierarchical absorption and conversion of expansion stress. The porous carbon framework provides initial expansion-accommodating space, the elastic buffer layer absorbs and disperses expansion stress through its deformable properties, and the rigid constraint layer acts as a final barrier to prevent overall particle breakage and convert local stress into in-plane dispersed stress. The synergistic effect of the three-level structure significantly improves the expansion suppression effect throughout the entire cycle compared to existing single buffer mechanisms.

[0032] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0033] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A silicon-carbon anode material, characterized in that, It includes a porous carbon composite, an elastic buffer layer covering the outer surface of the porous carbon composite, and a rigid constraint layer covering the outer surface of the elastic buffer layer; the porous carbon composite includes a porous carbon framework and silicon particles disposed within the porous carbon framework.

2. The silicon-carbon anode material according to claim 1, characterized in that, The porous carbon framework comprises one or more of resin-based porous carbon, biomass-based porous carbon, or pitch-based porous carbon, with a specific surface area of ​​800~2000 m². 2 / g, pore volume 0.5~2.0 cm³ 3 / g, with an average particle size of 5~15 μm; preferably, its specific surface area is 1200 m². 2 / g, pore volume 1.2 cm³ 3 / g, with an average particle size of 10 μm.

3. The silicon-carbon anode material according to claim 1, characterized in that, Silicon particles account for 20-50% of the mass of the porous carbon framework, preferably 35%.

4. The silicon-carbon anode material according to claim 1, characterized in that, The material of the elastic buffer layer is asphalt; preferably, the mass ratio of porous carbon composite to asphalt is (100~200):(5~20); preferably, the thickness of the elastic buffer layer is 25~100 nm.

5. The silicon-carbon anode material according to claim 1, characterized in that, The rigid constraint layer comprises multi-walled carbon nanotubes and graphene; preferably, the mass ratio of multi-walled carbon nanotubes to graphene is (1~5):(5~1), more preferably 3:2; preferably, the aspect ratio of multi-walled carbon nanotubes is ≥100; preferably, the thickness of the rigid constraint layer is 5~20 nm; more preferably 12 nm.

6. A method for preparing the silicon-carbon anode material according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Carbonize the porous carbon precursor under an inert atmosphere to obtain a porous carbon framework; preferably, carbonize at 600~1000℃ for 2~6 h. Step 2: The porous carbon framework is placed in a fluidized bed reactor, and a mixture of silane and hydrogen gas is introduced for chemical vapor deposition to obtain a porous carbon composite. Step 3: Mix the porous carbon composite with asphalt and coat it at 300~500℃ for 2~5 h in an inert atmosphere to form an elastic buffer layer on the surface of the porous carbon composite. Step 4: Disperse multi-walled carbon nanotubes and graphene in a solvent and ultrasonically disperse for 1-3 hours to obtain a coating slurry. Coat the surface of the product from Step 3 with the coating slurry, dry it, and then heat-treat it at 500-700℃ for 1-3 hours under an inert atmosphere to form a rigid constraint layer and obtain the final sample.

7. The preparation method according to claim 6, characterized in that, In step two, the deposition temperature is 450~600℃, the silane gas concentration is 5~20 vol%, and the deposition time is 1~4 h; The flow rate of silane gas is 0.1~0.5 L / min, and the flow rate of hydrogen gas is 0.2~1.0 L / min; Preferably, the deposition temperature in step two is 550°C, the silane gas concentration is 10 vol%, and the deposition time is 2 hours. The flow rate of silane gas is 0.3 L / min, and the flow rate of hydrogen gas is 0.5 L / min; Preferably, the solvent in step four is one or more of N-methylpyrrolidone, ethanol, or isopropanol.

8. A negative electrode sheet, characterized in that, Includes the silicon-carbon anode material as described in any one of claims 1-5.

9. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 8.

10. A method for testing the expansion degree of the silicon-carbon anode material according to any one of claims 1-5, characterized in that, The following steps are included: (1) Take a sample of silicon-carbon anode material to be tested, mix it with a conductive agent and a binder, preferably in a mass ratio of 80:10:10, coat it on the surface of copper foil, dry it under vacuum and cut it into a circular electrode sheet, and measure the initial thickness T0 of the electrode sheet. (2) Assemble a coin cell using a lithium sheet as the counter electrode; (3) Let the assembled button cell battery stand for 6-24 hours, preferably 12 hours; (4) Discharge at a constant current of 0.05-0.2C, preferably 0.1C, to 0.01V; (5) Disassemble the button cell under an inert atmosphere, remove the electrode, soak and clean it with organic solvent, and then vacuum dry it. (6) Measure the thickness T1 of the electrode after drying; (7) Calculate the expansion rate using the following formula: Expansion rate (%) = (T1 - T0) / T0 × 100%; Preferably, T1 and T0 measurements are performed using a micrometer or a laser thickness gauge, with no fewer than 5 points measured for each sample, and the arithmetic mean is taken. Preferably, an expansion rate of ≤40% is considered good, 40%~60% is considered acceptable, and >60% is considered unacceptable.

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