A core-shell structure porous silicon-carbon negative electrode material and a preparation method and application thereof

Abstract

The application discloses a kind of porous silicon-carbon negative materials of core-shell structure and its preparation method and application, the preparation method includes: (1) Si nanoparticles, pore-forming agent, polyvinylpyrrolidone, carbon precursor and solvent are mixed uniformly, and suspension solution is obtained;Spray drying is carried out to suspension solution, and Si / PVP / carbon precursor / pore-forming agent microspheres are obtained;(2) in the presence of inert gas, Si / PVP / carbon precursor / pore-forming agent microspheres are carbonized, and Si / C / pore-forming agent microspheres are obtained;(3) Si / C / pore-forming agent microspheres and C2H2 gas are reacted, and Si / C@C / pore-forming agent microspheres are obtained;(4) Si / C@C / pore-forming agent microspheres and water are stirred, centrifugal washing, drying, and the porous silicon-carbon negative material of core-shell structure is obtained.The porous silicon-carbon negative material of core-shell structure prepared by the application exhibits high specific capacity and excellent cycle stability, and is an ideal lithium ion battery negative material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and more specifically, relates to a core-shell structured porous silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of new technologies and industries such as new energy vehicles, smartphones, and 5G networks, people have placed higher demands on the capacity, cycle life, and manufacturing cost of lithium-ion batteries. Graphite, as a traditional anode material for lithium-ion batteries, has a theoretical specific capacity of only 372 mAh g / g. -1 This is no longer sufficient to meet the current demands of lithium-ion batteries. Silicon anode materials have a theoretical capacity as high as 4200 mAh / g. -1 Silicon exhibits a conductivity more than 10 times that of commercial graphite anodes. Furthermore, it boasts advantages such as environmental friendliness, abundant crustal content, low price, and low discharge potential, making it a highly promising next-generation lithium-ion battery anode material. However, silicon, as an intrinsic semiconductor, has poor conductivity and undergoes a massive volume change (approximately 400%) during energy storage. This volume change generates significant mechanical stress on the silicon surface, causing silicon particle pulverization, damaging the entire electrode structure, and increasing internal resistance. It also disrupts the stability of the solid electrolyte interphase (SEI) film, continuously consuming lithium ions and leading to a sustained decline in the cycle life of the silicon anode. Silicon-carbon composites are widely used to address these issues. Carbon materials can alleviate the volume change of silicon during charging and discharging, improve the overall conductivity of the material, and prevent silicon particle agglomeration. Therefore, silicon-carbon anode materials are currently a research hotspot. Summary of the Invention

[0003] The purpose of this invention is to provide a core-shell structured porous silicon-carbon anode material, its preparation method, and its application. The core-shell structured porous silicon-carbon anode material prepared by this invention exhibits high specific capacity and excellent cycle stability, making it an ideal anode material for lithium-ion batteries.

[0004] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a core-shell structured porous silicon-carbon anode material, the method comprising: (1) Si nanoparticles, pore-forming agent, polyvinylpyrrolidone (PVP), carbon precursor and solvent are mixed evenly to obtain a suspension solution; the suspension solution is spray-dried to obtain Si / PVP / carbon precursor / pore-forming agent microspheres; (2) In the presence of an inert gas, the Si / PVP / carbon precursor / pore-forming agent microspheres are carbonized to obtain Si / C / pore-forming agent microspheres; (3) The Si / C / pore-forming agent microspheres are reacted with C2H2 gas to obtain Si / C@C / pore-forming agent microspheres; (4) Stir, centrifuge, wash and dry the Si / C@C / pore-forming agent microspheres and water to obtain the core-shell structured porous silicon-carbon anode material (porous Si / C@C microspheres).

[0005] In this invention, silicon nanoparticles are tightly fixed on a micron-scale cross-linked carbon matrix to prevent Si agglomeration. The matrix is ​​then covered by a thin carbon layer. A low-cost spray drying method and chemical vapor deposition process are used, along with the addition of a pore-forming agent. The resulting composite material exhibits high porosity, providing sufficient internal voids to mitigate the significant volume expansion of Si. The outer carbon shell not only prevents contact between silicon and the electrolyte, reducing electrolyte consumption, but also inhibits silicon volume expansion.

[0006] According to the present invention, preferably, the pore-forming agent is sodium chloride, potassium chloride or calcium chloride.

[0007] According to the present invention, preferably, in step (1), the carbon precursor is at least one of glucose, sucrose and starch.

[0008] According to the present invention, preferably, in step (1), the mass ratio of Si nanoparticles, carbon precursor and pore-forming agent is (3-5):(2-3):(1-2); The spray drying is carried out in a spray dryer with an inlet temperature of 100-200℃.

[0009] According to the present invention, preferably, in step (2), the carbonization is divided into two stages: first, the temperature is raised to 120-300℃ at a heating rate of 4-6℃ / min and held at a constant temperature for 1-3 hours; then, the temperature is raised to 700-900℃ at the same heating rate and held at a constant temperature for 1-5 hours. The inert gas is argon or nitrogen.

[0010] According to the present invention, preferably, in step (3), C2H2 gas is introduced at a flow rate of 1-2 L / min under a pressure of 0.05-0.2 MPa; The reaction time is 2-6 h.

[0011] According to the present invention, preferably, in step (4), the mass ratio of the Si / C@C / pore-forming agent microspheres to water is 1:(50-200). The stirring time is 2-8 hours.

[0012] According to the present invention, preferably, in step (4), the number of centrifugal washing cycles is 3-6; The drying temperature is 60-100℃, and the time is 6-12 hours.

[0013] A second aspect of the present invention provides a core-shell structured porous silicon-carbon anode material prepared by the above-described preparation method.

[0014] A third aspect of the present invention provides the application of the above-mentioned porous silicon-carbon anode material in the preparation of anodes for lithium-ion batteries.

[0015] The technical solution of the present invention has the following beneficial effects: (1) The core-shell structured porous silicon-carbon anode material prepared by the present invention exhibits high specific capacity and excellent cycle stability, and is an ideal lithium-ion battery anode material.

[0016] (2) In this invention, the pore-forming agent is washed away as a template to form a porous structure, which can alleviate the volume expansion of silicon, ensure the structural stability of the composite material, and improve the cycle life; and shorten the ion transport path to improve the rate performance of the composite material.

[0017] (3) In this invention, the outer carbon layer can prevent silicon from contacting the electrolyte and reduce electrolyte consumption. On the other hand, it can suppress silicon volume expansion, ensure material structure stability, and improve cycle life.

[0018] (4) The porous silicon / graphite@carbon anode material prepared by the method of the present invention has the advantages of low cost, environmental friendliness, simple operation and industrialization.

[0019] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0020] 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.

[0021] Figure 1 A schematic diagram of Si / C@C microspheres according to Embodiment 1 of the present invention is shown.

[0022] Figure 2 SEM images of Si / C@C microspheres according to Embodiment 1 of the present invention are shown. Detailed Implementation

[0023] 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.

[0024] The present invention is further illustrated by the following examples: In the following examples and comparative examples, the particle size of the Si nanoparticles used is 50-100 nm.

[0025] Example 1

[0026] This embodiment provides a core-shell structured porous silicon-carbon anode material, and the specific preparation method is as follows: (1) 450g of Si nanoparticles, 150g of NaCl (inorganic salt pore-forming agent), 150g of polyvinylpyrrolidone (PVP) and 300g of glucose were dispersed in a mixed solution composed of ethanol and deionized water (the mixed solution contained 2kg of ethanol and 0.5g of deionized water). The mixture was sonicated for half an hour to form a uniform suspension at 25℃. Then, the suspension was spray-dried using a spray dryer at an inlet temperature of 140℃ to obtain Si / PVP / carbon precursor / pore-forming agent microspheres. (2) The Si / PVP / glucose / pore-forming agent microspheres prepared above were placed in a quartz boat and heated to 200°C at a heating rate of 5°C / min under argon protection. The temperature was maintained at 200°C for 2 hours, and then heated to 900°C at a heating rate of 5°C / min. The temperature was maintained at 900°C for 1 hour to obtain Si / C / pore-forming agent microspheres. Finally, C2H2 gas was introduced at a flow rate of 1 L / min and a pressure of 0.1 MPa for 4 hours to obtain Si / C@C / pore-forming agent microspheres. (3) Add Si / C@C / pore-forming agent microspheres to deionized water at a mass ratio of 1:150, stir for 6 hours, then repeatedly centrifuge and wash 3 times, and finally place in a vacuum drying oven and dry at 80℃ for 10 hours to obtain porous Si / C@C microspheres (a core-shell structured porous silicon-carbon anode material, such as...). Figure 1 and Figure 2 (As shown).

[0027] Examples 2-5

[0028] Porous silicon-carbon anode materials with core-shell structures were prepared according to the method of Example 1, with specific differences shown in Table 1; and in Examples 2-5, the amount of pore-forming agent was 150g, the amount of PVP was 150g, and the mixed solution contained 2kg of ethanol and 0.5g of deionized water; other process parameters and amounts not specifically mentioned were the same as in Example 1.

[0029] Table 1

[0030] In Table 1, carbonization stage 1 and carbonization stage 2 refer to the two-stage carbonization in step (2); the last two columns, "stirring time, number of washings" and "drying temperature, time", refer to the corresponding process parameters in step (3).

[0031] Comparative Example 1

[0032] Silicon-carbon anode materials were prepared according to the method in Example 1, except that 300g of NaCl was not added in step (1); finally, Si / C@C microspheres were obtained.

[0033] Comparative Example 2

[0034] Silicon-carbon anode material was prepared according to the method of Example 1, except that the vapor deposition process in step (2) was removed (i.e., the step of "introducing C2H2 gas at a flow rate of 1 L / min and a pressure of 0.1 MPa for 4 hours to obtain Si / C@C / pore-forming agent microspheres" was removed), and step (3) was also removed; finally, Si / C / pore-forming agent microspheres were obtained.

[0035] Test case

[0036] 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. The cells were assembled using a CR2032 type battery case. 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 a copper foil (coating density of 30 g / m²). 2 The positive electrode was obtained by placing it in an oven at 100°C for 4 hours. Lithium metal was used as the negative electrode, 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 positive electrode, negative electrode, 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.

[0037] Table 2

[0038] As demonstrated by Examples 1-5 and Comparative Examples 1-2, the porous Si / C@C materials prepared in the embodiments of this invention exhibit superior discharge capacity, coulombic efficiency, and cycle performance compared to the comparative examples. At a discharge rate of 0.1C, the material achieves a maximum initial discharge specific capacity of 1389 mAh / g, a first-cycle coulombic efficiency of 85%, and a maximum cycle retention of 86% after 100 cycles. This indicates that the silicon-carbon composite anode material of this invention possesses excellent cycle stability, enhancing the advantages of silicon-carbon anode materials in lithium-ion battery fabrication. Considering its simple preparation process and low cost, porous Si / C@C demonstrates significant application potential as a lithium-ion battery anode material.

[0039] 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 core-shell structured porous silicon-carbon negative electrode material, characterized in that, The preparation method includes: (1) Si nanoparticles, pore-forming agent, polyvinylpyrrolidone, carbon precursor and solvent are mixed evenly to obtain a suspension solution; the suspension solution is spray-dried to obtain Si / PVP / carbon precursor / pore-forming agent microspheres; (2) In the presence of an inert gas, the Si / PVP / carbon precursor / pore-forming agent microspheres are carbonized to obtain Si / C / pore-forming agent microspheres; (3) The Si / C / pore-forming agent microspheres are reacted with C2H2 gas to obtain Si / C@C / pore-forming agent microspheres; (4) The Si / C@C / pore-forming agent microspheres and water are stirred, centrifuged, washed and dried to obtain the core-shell structured porous silicon-carbon anode material.

2. The production method according to claim 1, wherein, The pore-forming agent is sodium chloride, potassium chloride, or calcium chloride.

3. The production method according to claim 1, wherein, In step (1), the carbon precursor is at least one of glucose, sucrose and starch.

4. The preparation method according to claim 1, wherein, In step (1), the mass ratio of Si nanoparticles, carbon precursor and pore-forming agent is (3-5):(2-3):(1-2); The spray drying is carried out in a spray dryer with an inlet temperature of 100-200℃.

5. The production method according to claim 1, wherein In step (2), the carbonization is divided into two stages. First, the temperature is raised to 120-300℃ at a heating rate of 4-6℃ / min and held at a constant temperature for 1-3 hours. Then, the temperature is raised to 700-900℃ at the same heating rate and held at a constant temperature for 1-5 hours. The inert gas is argon or nitrogen.

6. The production method according to claim 1, wherein In step (3), C2H2 gas is introduced at a flow rate of 1-2 L / min under a pressure of 0.05-0.2 MPa; The reaction time is 2-6 h.

7. The production method according to claim 1, wherein In step (4), the mass ratio of the Si / C@C / pore-forming agent microspheres to water is 1:(50-200). The stirring time is 2-8 hours.

8. The production method according to claim 1, wherein In step (4), the number of centrifugal washing cycles is 3-6; The drying temperature is 60-100℃, and the time is 6-12 hours.

9. A core-shell structured porous silicon-carbon anode material prepared by the preparation method according to any one of claims 1-8.

10. The application of the porous silicon-carbon anode material according to claim 9 in the preparation of anodes for lithium-ion batteries.

Images