A silicon-carbon negative electrode material with a double carbon layer structure, a preparation method therefor, and an application thereof

Abstract

The application discloses a silicon-carbon negative electrode material with a double-carbon-layer structure and a preparation method and application thereof, and the preparation method comprises the following steps: (1) dissolving a buffering agent in a first solvent, adjusting pH, then adding a carbon source, and stirring uniformly to obtain a carbon source buffer solution; (2) uniformly stirring nano silicon and the carbon source buffer solution, then filtering, washing and drying to obtain a Si / C precursor; (3) performing carbonization treatment on the Si / C precursor to obtain a Si / C material; (4) uniformly mixing the Si / C material and a second solvent, then adding a zinc source and a cobalt source, and stirring to obtain a uniform solution; (5) adding an organic ligand to the uniform solution, stirring, then filtering, washing and drying to obtain a Si / C / ZnCo-N-C precursor material; and finally, performing carbonization treatment on the Si / C / ZnCo-N-C precursor material to obtain the silicon-carbon negative electrode material with the double-carbon-layer structure. The single-layer carbon shell is easy to break, and the second coating layer has high mechanical strength, which is beneficial to maintaining the structural integrity of the material.

Description

Technical Field

[0001] This invention belongs to the field of silicon-carbon anode material technology, and more specifically, relates to a silicon-carbon anode material with a double carbon layer structure, its preparation method and application. Background Technology

[0002] Silicon-based materials have attracted research attention due to their high theoretical capacity (4200 mAh g⁻¹), abundant reserves, and environmental friendliness. However, the significant volume expansion (300%-400%) and low conductivity during lithium insertion / extraction / deintercalation in silicon-based materials hinder their commercial development. The volume expansion / contraction of silicon during repeated charge / discharge cycles causes pulverization and structural collapse, leading to rapid capacity decay and poor cycle performance. Furthermore, it is difficult to form a stable solid electrolyte interphase (SEI) film on the silicon electrode surface because the large volume changes of silicon particles during cycling expose them to the electrolyte, and new SEI films continue to grow on the newly exposed silicon electrode surface. In addition, the poor conductivity of silicon electrodes significantly hinders electron transfer and reduces their rate performance.

[0003] Introducing carbon materials into silicon composites can alleviate the aforementioned problems of silicon anode materials to some extent. Silicon-carbon composite anode materials can prevent silicon aggregation and increase its conductivity. Furthermore, carbon can act as a buffer barrier, releasing the mechanical stress of silicon and preventing direct contact between the electrolyte and silicon, thus stabilizing the electrode / electrolyte interface and reducing the re-decomposition of the organic electrolyte. However, current silicon-carbon composite anode materials still exhibit significant capacity decay during long-term cycling. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon-carbon anode material with a double carbon layer structure, its preparation method, and its application. This invention involves coating nano-silicon particles with a double carbon layer. The first carbon layer can effectively alleviate the stress caused by the volume expansion of silicon, thereby preventing the silicon anode from cracking. The second coating layer forms a cage containing two transition metals and nitrogen doping. The zinc-cobalt synergy and nitrogen co-doping can improve the lithium-ion mobility and reduce the electrode impedance. On the other hand, its high mechanical strength is beneficial to maintaining the integrity of the material structure and the stability of the SEI, effectively resisting structural damage during cycling.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a silicon-carbon anode material with a double carbon layer structure, the method comprising: (1) Dissolve the buffer in the first solvent, adjust the pH, then add the carbon source and stir until homogeneous to obtain a carbon source buffer solution; (2) The nano-silicon and the carbon source buffer solution are stirred evenly, and then filtered, washed and dried to obtain the Si / C precursor; (3) In the presence of a first inert gas, the Si / C precursor is carbonized to obtain Si / C material; (4) Mix the Si / C material and the second solvent evenly, then add the zinc source and the cobalt source, and stir to obtain a uniform solution; (5) Add organic ligands to the homogeneous solution, stir, and then filter, wash and dry to obtain Si / C / ZnCo-NC precursor material; finally, in the presence of a second inert gas, carbonize the Si / C / ZnCo-NC precursor material to obtain the silicon-carbon anode material with the double carbon layer structure.

[0006] In this invention, nano-silicon is first modified by liquid-phase stirring and carbonized to obtain Si / C material. Then, a metal framework ZnCo-ZIF composite structure is introduced and carbonized again to obtain Si / C / ZnCo-NC derived nano-carbon cages encapsulating silicon double carbon shells.

[0007] According to the present invention, preferably, in step (1), the carbon source is at least one of tannic acid, glucose, starch and sucrose; The first solvent includes two of methanol, N,N-dimethylformamide, and ethanol; The buffer is tris(hydroxymethyl)aminomethane; Adjust the pH to 8-10.

[0008] According to the present invention, preferably, in step (2), the average particle size of the nano-silicon is 3 to 50 nm; The stirring time is 4-8 hours; The drying temperature is 40-100℃, and the time is 6-12 hours.

[0009] According to the present invention, preferably, in step (3), the first inert gas is selected from at least one of argon, helium and nitrogen; The carbonization treatment conditions include: heating to 700-900℃ at a heating rate of 10-20℃ / min, and maintaining at 700-900℃ for 1-5 hours; The flow rate of the first inert gas is 1-3 L / min.

[0010] According to the present invention, preferably, in step (4), the zinc source is selected from at least one of zinc acetate, zinc sulfate, zinc nitrate and zinc chloride; The cobalt source is selected from at least one of cobalt acetate, cobalt sulfate, cobalt nitrate, and cobalt chloride; The second solvent includes two of methanol, N,N-dimethylformamide, and ethanol; The stirring time is 4-8 hours.

[0011] According to the present invention, preferably, in step (5), the organic ligand is at least one of benzimidazole, 2-methylbenzimidazole and 2-methylimidazole.

[0012] According to the present invention, preferably, in step (5), the molar ratio of zinc source, cobalt source and organic ligand is 1:1:(2-8), more preferably 1:1:(2-4).

[0013] According to the present invention, preferably, in step (5), the second inert gas is selected from at least one of argon, helium and nitrogen; The carbonization treatment conditions include: heating to 700-900℃ at a heating rate of 10-20℃ / min, and maintaining at 700-900℃ for 2-5 hours; The flow rate of the second inert gas is 1-3 L / min.

[0014] A second aspect of the present invention provides a silicon-carbon anode material with a double carbon layer structure prepared by the above-described preparation method.

[0015] A third aspect of the present invention provides the application of the silicon-carbon anode material with the above-described double carbon layer structure in lithium batteries.

[0016] The technical solution of the present invention has the following beneficial effects: (1) The present invention coats the nano-silicon particles with a double layer of carbon. The first layer of carbon coating can effectively alleviate the stress caused by the volume expansion of silicon, thereby avoiding the cracking of the silicon anode. The second coating layer forms a cage containing two transition metals and N doping. The co-doping of zinc and cobalt and nitrogen can improve the mobility of lithium ions and reduce the impedance of the electrode.

[0017] (2) The single-layer carbon shell is easy to break, while the second coating layer has high mechanical strength, which is beneficial to the material to maintain the integrity of the structure.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0020] Figure 1 A schematic structural diagram of a silicon-carbon anode material with a double carbon layer structure according to an embodiment of the present invention is shown. Detailed Implementation

[0021] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0022] The present invention is further illustrated by the following examples: In the following examples and comparative examples, the average particle size of the nano-silicon used is 5 nm.

[0023] Example 1

[0024] (1) Dissolve the buffer tris(hydroxymethyl)aminomethane in a mixed solvent consisting of 50 ml methanol and 50 ml N,N-dimethylformamide, adjust the pH to 9.6, then add 0.5 g tannic acid, stir until dissolved, and obtain a carbon source buffer solution.

[0025] (2) Add 0.2 g of nano-silicon (mass ratio of silicon to carbon source is 1:2.5) to the above carbon source buffer solution, stir for 6 hours, filter, wash, and dry at 60℃ for 10 hours to obtain Si / C precursor. Place the Si / C precursor powder in a calcination device, heat to 800℃ at a heating rate of 15℃ / min under argon protection (argon flow rate is 1 L / min), and carbonize at 800℃ for 2 hours to form sample Si / C material.

[0026] (3) All the Si / C materials obtained in step (2) were added to a mixed solvent consisting of 50 ml methanol and 50 ml N,N-dimethylformamide, and ultrasonically dispersed. Then, 0.594 g zinc nitrate hexahydrate and 0.582 g cobalt nitrate hexahydrate were added, and the mixture was mechanically stirred for 6 h to form a homogeneous solution. Then, 0.656 g 2-methylimidazole was added, and the mixture was stirred vigorously for 30 min. The above solution was filtered and washed 6 times, and then dried in an oven at 80℃ for 10 h to obtain the Si / C / ZnCo-NC precursor material. Finally, the Si / C / ZnCo-NC precursor material was placed in a calcination apparatus and heated to 800℃ at a heating rate of 15℃ / min under the protection of a nitrogen atmosphere (nitrogen flow rate of 1 L / min). It was then carbonized at 800℃ for 2 h to form the final sample Si / C / ZnCo-NC (a silicon-carbon anode material with a double carbon layer structure, such as...). Figure 1 (As shown).

[0027] Examples 2-5

[0028] The silicon-carbon anode material with a double carbon layer structure was prepared according to the method in Example 1. The specific differences are shown in Table 1.

[0029] Table 1

[0030] Note that in Table 1, “carbonization temperature, time” and “inert gas flow rate” refer to the carbonization parameters and the flow rate and time of the inert gas in steps (2) and (3), respectively.

[0031] Comparative Example 1

[0032] The Si / C material was prepared according to steps (1) and (2) of Example 1; that is, the only difference between this comparative example and Example 1 is the removal of step (3).

[0033] Comparative Example 2

[0034] Steps (1) and (2) are the same as in Example 1; The only difference between step (3) and Example 1 is that cobalt nitrate hexahydrate is not added, and the amount of zinc nitrate hexahydrate is adjusted to 0.594g and the amount of 2-methylimidazole is adjusted to 0.656g, finally obtaining Si / C / Zn-NC (silicon-carbon anode material with a double carbon layer structure).

[0035] Comparative Example 3

[0036] Steps (1) and (2) are the same as in Example 1; The only difference between step (3) and Example 1 is that zinc nitrate hexahydrate is not added, the amount of cobalt nitrate hexahydrate is adjusted to 0.582g, and the amount of 2-methylimidazole is adjusted to 0.656g, finally obtaining Si / C / Co-NC (silicon-carbon anode material with a double carbon layer structure).

[0037] Test case

[0038] The above-described embodiments and comparative examples were assembled into button cells for half-cell testing. The electrode materials finally prepared in Examples 1-5 and Comparative Examples 1-2 were used as positive electrode materials to prepare positive electrode sheets. Cells were assembled using CR2032 type battery cases. A battery slurry was prepared using the silicon-carbon negative electrode material prepared above, with a mass ratio of acetylene black (AB) and LA133 binder of 80:10:10. After uniform grinding, the slurry was coated onto the upper surface of copper foil (coating density of 30 g / m²). 2The cathode was prepared by placing the cathode in an oven at 100°C for 4 hours. Lithium metal was used as the anode, and ethylene carbonate / dimethyl carbonate (volume ratio 1:1) was used as the electrolyte, which also contained lithium hexafluorophosphate at a concentration of 1.0 mol / L. The cathode, anode, electrolyte, and polyethylene separator were assembled into a coin cell. The battery assembly was tested in an argon-filled glove box (MBRAUN MB Labstar1500 / 780) where both water and oxygen content were less than 0.1 ppm. Electrochemical tests were performed using a Newway testing system at room temperature, with a cutoff charge / discharge voltage of 0.02–1.5 V and a charge / discharge current density of 0.2 mA / cm². 2 The discharge specific capacity was tested at 0.1C, and the constant current and constant voltage charge-discharge test was conducted at 2C. The cycle efficiency was tested 100 times at 0.1C. The test results are shown in Table 2 below.

[0039] Table 2

[0040] As demonstrated by Examples 1-5 and Comparative Examples 1-3, the discharge capacity, coulombic efficiency, and cycle performance of the materials prepared in each embodiment of this invention are superior to those of the comparative examples. At a discharge rate of 0.1C, the material achieves a maximum initial discharge specific capacity of 1456 mAh / g, a first-cycle coulombic efficiency of 86%, and a maximum cycle retention of 85% after 100 cycles. This indicates that the Si / C / ZnCo-NC derived nano-carbon cage-coated silicon double-carbon shell structure material synthesized using a simple liquid-phase stirring method exhibits excellent cycle stability, enhancing the advantages of silicon anode materials in lithium-ion battery fabrication.

[0041] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing a silicon-carbon anode material with a double carbon layer structure, characterized in that, The preparation method includes: (1) Dissolve the buffer in the first solvent, adjust the pH, then add the carbon source and stir until homogeneous to obtain a carbon source buffer solution; (2) The nano-silicon and the carbon source buffer solution are stirred evenly, and then filtered, washed and dried to obtain the Si / C precursor; (3) In the presence of a first inert gas, the Si / C precursor is carbonized to obtain Si / C material; (4) Mix the Si / C material and the second solvent evenly, then add the zinc source and the cobalt source, and stir to obtain a uniform solution; (5) Add organic ligands to the homogeneous solution, stir, and then filter, wash and dry to obtain Si / C / ZnCo-NC precursor material; finally, in the presence of a second inert gas, carbonize the Si / C / ZnCo-NC precursor material to obtain the silicon-carbon anode material with the double carbon layer structure.

2. The preparation method according to claim 1, wherein, In step (1), the carbon source is at least one of tannic acid, glucose, starch and sucrose; The first solvent includes two of methanol, N,N-dimethylformamide, and ethanol; The buffer is tris(hydroxymethyl)aminomethane; Adjust the pH to 8-10.

3. The preparation method according to claim 1, wherein, In step (2), the average particle size of the nano-silicon is 3-50 nm; The stirring time is 4-8 hours; The drying temperature is 40-100℃, and the time is 6-12 hours.

4. The preparation method according to claim 1, wherein, In step (3), the first inert gas is selected from at least one of argon, helium and nitrogen; The carbonization treatment conditions include: heating to 700-900℃ at a heating rate of 10-20℃ / min, and maintaining at 700-900℃ for 1-5 hours; The flow rate of the first inert gas is 1-3 L / min.

5. The preparation method according to claim 1, wherein, In step (4), the zinc source is selected from at least one of zinc acetate, zinc sulfate, zinc nitrate, and zinc chloride; The cobalt source is selected from at least one of cobalt acetate, cobalt sulfate, cobalt nitrate, and cobalt chloride; The second solvent includes two of methanol, N,N-dimethylformamide, and ethanol; The stirring time is 4-8 hours.

6. The preparation method according to claim 1, wherein, In step (5), the organic ligand is at least one of benzimidazole, 2-methylbenzimidazole and 2-methylimidazole.

7. The preparation method according to claim 1, wherein, In step (5), the molar ratio of zinc source, cobalt source and organic ligand is 1:1:(2-8), preferably 1:1:(2-4).

8. The preparation method according to claim 1, wherein, In step (5), the second inert gas is selected from at least one of argon, helium, and nitrogen; The carbonization treatment conditions include: heating to 700-900℃ at a heating rate of 10-20℃ / min, and maintaining at 700-900℃ for 2-5 hours; The flow rate of the second inert gas is 1-3 L / min.

9. A silicon-carbon anode material with a double carbon layer structure prepared by the preparation method according to any one of claims 1-8.

10. The application of the silicon-carbon anode material with a double carbon layer structure according to claim 9 in lithium batteries.

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