Silicon-carbon negative electrode material with cavity buffer structure and preparation method thereof
By using molecular self-assembly and polydopamine sacrificial layer preparation methods, a tightly connected carbon nanotube-silicon core and carbon shell structure is formed, which solves the problems of environmental protection and poor conductive network connection in the preparation process of existing silicon-carbon materials, and improves the cycling stability and transport efficiency of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHENGZHOU ZHONGKE EMERGING IND TECH RES INST
- Filing Date
- 2026-05-25
- Publication Date
- 2026-07-24
AI Technical Summary
Existing cavity buffer structure silicon-carbon materials have problems such as poor environmental performance, insufficient buffer space, and only partial connection of the core and shell conductive network during the preparation process, which leads to limited ion and electron transport and poor cycle stability.
A silicon-carbon anode material with a cavity buffer structure was prepared by combining nano-silicon with quaternary ammonium salt and carboxylated carbon nanotubes using molecular self-assembly technology and a polydopamine sacrificial layer. The sacrificial layer was decomposed by alkaline treatment to form tightly connected carbon nanotubes with silicon core and carbon shell, thereby improving the electron and ion transport rate.
An environmentally friendly and efficient cavity buffer structure was achieved, which enhanced the material's cycle stability and electronic and ion conduction capabilities, thereby improving the material's overall performance.
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Figure CN122455643A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery anode material technology, and particularly relates to a method for preparing silicon-carbon anode material. Background Technology
[0002] With the development of the times, the application of new energy vehicles, drones, and intelligent robots is becoming increasingly widespread, and the demand for high-energy-density batteries from these intelligent devices is becoming more and more urgent. Silicon-based materials have attracted widespread attention due to their high theoretical specific capacity. Among silicon-based anode materials, silicon has a specific capacity of 4200 mAh / g, making it the lithium-ion battery anode material with the highest capacity currently available. However, its huge volume effect leads to a sharp decline in battery cycle life.
[0003] However, the practical application of silicon-carbon has long been limited by three core bottlenecks: extremely low intrinsic electronic conductivity, volume expansion of up to 300% during charge and discharge, and the resulting repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, leading to severe initial irreversible capacity loss and poor cycle stability. To address these issues, carbon coating modification has become one of the main technical methods for silicon-carbon coating modification in recent years. Patent CN 116525791 A provides a method for preparing multi-layer coated silicon-carbon materials, achieving good results. Core-shell structure materials have certain problems in practical applications, namely, the carbon shell experiences significant expansion stress during material cycling, making it prone to peeling off and affecting the material's cycle stability. Patent CN119324206 A proposes a hollow yolk-shell structure with a silicon core and a carbon outer layer, where the hollow structure is formed by sublimation of elemental sulfur. Although this has achieved good results, the sublimation of elemental sulfur presents pollution and recycling issues. Patent CN120569348 A reports a method for preparing a yolk-shell structured silicon-carbon material. It employs atomic deposition (ADP) technology to deposit a uniformly thick inorganic layer as a sacrificial layer on the surface of silicon particles. The cavity in the sacrificial layer accommodates the volume expansion of silicon, suppressing the peeling of the outermost carbon film caused by this expansion. While ADP eliminates the need for HF etching, its high cost limits its large-scale industrial application. Although the cavity provides a buffer for volume expansion, the conductive network between the core and the outer shell is only partially connected, restricting ion and electron transport. Summary of the Invention
[0004] To address the technical problems of limited ion and electron transport and poor cycle stability caused by the environmentally unfriendly formation of cavities, insufficient buffer space, and only partial connection of the core and shell conductive networks in the preparation process of existing cavity-buffered silicon-carbon materials, this invention proposes a silicon-carbon anode material with a cavity-buffered structure, its preparation method, and its application.
[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:
[0006] A method for preparing a silicon-carbon anode material with a cavity buffer structure, comprising the following steps:
[0007] (1) Molecular self-assembly: Nano-silicon and quaternary ammonium salt were added to water and dispersed evenly, and then carboxylated carbon nanotubes were added to the solution and dispersed evenly to obtain solution A;
[0008] (2) Preparation of polydopamine sacrificial layer: Add a weak alkaline buffer (Tris-HCl buffer with pH 8) to solution A, and then add a certain amount of dopamine hydrochloride to it. Stir at high speed to disperse evenly, and obtain solution B after reaction;
[0009] (3) Preparation of carbon shell: Pyrrole, surfactant and oxidant were added to solution B and stirred. After polymerization for a period of time, the mixture was centrifuged (centrifugation speed 8000-10000 r / min, time 5-10 min) and washed to obtain precursor I with double coating layer;
[0010] (4) Decomposition of the sacrificial layer: Disperse precursor I in water, then add alkali solution for alkali treatment, stir and let stand, then centrifuge (centrifuge speed 8000-10000 r / min, time 5-10 min), wash and dry to obtain the precursor;
[0011] (5) High-temperature carbonization: Precursor II is carbonized at high temperature in an inert atmosphere (such as argon) to obtain silicon-carbon anode material with a cavity buffer structure.
[0012] In step (1) above, the mass ratio of nano-silicon, quaternary ammonium salt, and carboxylated carbon nanotubes is 10:(3-5):(0.01-0.1). The quaternary ammonium salt is at least one of polydiene dimethyl ammonium chloride, hexadecyltrimethylammonium bromide, didecyldimethylammonium chloride, and didecyldimethylammonium bromide. The carboxylated carbon nanotubes are carboxylated single-walled carbon nanotubes or carboxylated multi-walled carbon nanotubes.
[0013] In the above process, quaternary ammonium salts are used as additives to give the silicon core a positive charge, which is then self-assembled with negatively charged modified carbon nanotubes. This improves the bonding force between the carbon nanotubes and the silicon core, resulting in better carbon nanotube coating. One end of the carbon nanotube tightly coats the silicon core, while the other end is connected to the carbon shell, tightly linking the inner and outer layers and enhancing the electron and ion transport rates.
[0014] In step (2) above, the mass ratio of nano-silicon to dopamine hydrochloride is 10:4-8, and the volume ratio of weak alkaline buffer to solution A is 1:(2-4). During the reaction, the rotation speed is 600-1000 r / min, the temperature is 25-60℃, and the time is 3-6 h.
[0015] In step (3) above, the mass ratio of nano-silicon, pyrrole, surfactant, and oxidant is 10:(4-10):(0.1-0.5):(1-5). The stirring speed is 600-1000 r / min, the polymerization temperature is 0-20℃, and the time is 5-10h. The surfactant is one of sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, and sodium dodecyl sulfate, and the oxidant is ammonium persulfate. The surfactant acts as a soft template, which can adjust the morphology of polypyrrole molecules and promote the uniform deposition of the surface coating layer.
[0016] In step (4) above, the concentration of the alkali solution is 1-2 mol / L, and the solute in the alkali solution is at least one of sodium hydroxide, potassium hydroxide, trisodium phosphate and sodium sulfite; the alkali treatment is carried out under stirring, with a stirring speed of 600-1000 r / min, a temperature of 60-80℃, and a time of 5-8 h.
[0017] In step (5) above, the high-temperature carbonization temperature is 700-900℃, the heating rate is 5-10℃ / min, and the carbonization time is 2-5 h.
[0018] A silicon-carbon anode material with a cavity buffer structure was prepared using the above-described preparation method.
[0019] The above-mentioned silicon-carbon anode material with a cavity buffer structure is used in lithium-ion batteries.
[0020] The beneficial effects of this invention are:
[0021] (1) In this invention, a quaternary ammonium salt is used as an additive to positively charge the silicon core, which is then self-assembled with a negatively charged modified carbon nanotube. This improves the bonding force between the carbon nanotube and the silicon core, resulting in a better carbon nanotube coating effect. The carboxylated carbon nanotube and the silicon core are coated with an organic carbon layer within a carbon shell with high mechanical strength. The internal pores can provide a certain space for silicon expansion. At the same time, the carboxylated carbon nanotube can provide a certain constraint force on the silicon, reducing the expansion stress of the carbon shell, and can also form cross-links with the inner and outer surfaces of the carbon shell, improving the conduction speed of electrons and lithium ions and enhancing the cycling stability of the material.
[0022] (2) The sacrificial layer of the present invention is polydopamine, an organic polymer that decomposes when exposed to alkali. The etching of the sacrificial layer can be completed using alkaline substances. Compared with the conventional method of etching SiO2 sacrificial layer using HF, it is safer and more environmentally friendly. Attached Figure Description
[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.
[0024] Figure 1 This is a schematic diagram of the structure of the silicon-carbon material prepared in this invention. Detailed Implementation
[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0026] Example 1
[0027] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this embodiment includes the following steps:
[0028] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 3 g of polydienedimethylammonium chloride quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min. Then, 0.1 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A.
[0029] S2. Preparation of polydopamine sacrificial layer: 25 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of the two is 1:4), and then 4 g of dopamine hydrochloride was added to it. The mixture was stirred at 25 °C for 3 h at 600 r / min to obtain solution B.
[0030] S3. Preparation of carbon shell: Add 4 g pyrrole, 0.1 g surfactant sodium dodecylbenzenesulfonate and 1 g oxidant ammonium persulfate to solution B, stir at 600 r / min, polymerize at 0℃ for 10 h, then centrifuge (centrifuge speed 10000 r / min, 5 min) and wash to obtain precursor I with double shell layer;
[0031] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 50 mL of NaOH solution (1 mol / L) was added to the dispersion. The mixture was stirred at 600 r / min and 60 °C for 5 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0032] S5. High-temperature carbonization: Precursor II was carbonized at 700℃ for 2 h in an argon inert atmosphere at a rate of 5℃ / min to obtain a silicon-carbon anode material with a cavity buffer structure. For example... Figure 1 As shown, the silicon-carbon anode material prepared by the present invention has a cavity buffer structure including a silicon core, carboxylated carbon nanotubes coated on the silicon surface, a cavity sacrificial layer, and an amorphous carbon shell.
[0033] Example 2
[0034] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this embodiment includes the following steps:
[0035] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 5 g of polydienedimethylammonium chloride quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min. Then, 0.02 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A.
[0036] S2. Preparation of polydopamine sacrificial layer: 25 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of 1:4), and then 8 g of dopamine hydrochloride was added to it. The mixture was stirred at 25 °C for 6 h at 600 r / min to obtain solution B.
[0037] S3. Preparation of carbon shell: 6 g pyrrole, 0.5 g surfactant sodium dodecylbenzenesulfonate and 5 g oxidant ammonium persulfate were added to solution B. The mixture was stirred at 600 r / min and polymerized at 0℃ for 12 h. After centrifugation (centrifugation speed 10000 r / min, 5 min) and washing, precursor I with a double-layer coating was obtained.
[0038] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 50 mL of KOH solution (1 mol / L) was added to the dispersion. The mixture was stirred at 600 r / min and 70 °C for 6 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0039] S5. High-temperature carbonization: Precursor II was carbonized at 800℃ for 5 h at a rate of 5℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0040] Example 3
[0041] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this embodiment includes the following steps:
[0042] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 4 g of polydimethylammonium chloride quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min. Then, 0.08 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A.
[0043] S2. Preparation of polydopamine sacrificial layer: 25 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of the two is 1:4), and then 6 g of dopamine hydrochloride was added to it. The mixture was stirred at 25 °C for 4 h at 600 r / min to obtain solution B.
[0044] S3. Preparation of carbon shell: 5 g pyrrole, 0.3 g surfactant sodium dodecylbenzenesulfonate and 3 g oxidant ammonium persulfate were added to solution B. The mixture was stirred at 600 r / min and polymerized at 0℃ for 16 h. After centrifugation (centrifugation speed 10000 r / min, 5 min) and washing, precursor I with a double-layer coating was obtained.
[0045] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 50 mL of NaOH solution (2 mol / L) was added to the dispersion. The mixture was stirred at 600 r / min and 80 °C for 8 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0046] S5. High-temperature carbonization: Precursor II was carbonized at 900℃ for 3 h at a rate of 5℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0047] Example 4
[0048] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this embodiment includes the following steps:
[0049] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 3 g of hexadecyltrimethylammonium bromide quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min. Then, 0.1 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A.
[0050] S2. Preparation of polydopamine sacrificial layer: 50 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of the two is 1:2), and then 4 g of dopamine hydrochloride was added to it. The mixture was stirred at 60 °C for 3 h at 1000 r / min to obtain solution B.
[0051] S3. Preparation of carbon shell: Add 4 g pyrrole, 0.1 g surfactant sodium dodecyl sulfate and 1 g oxidant ammonium persulfate to solution B, stir at 1000 r / min, polymerize at 20℃ for 10 h, then centrifuge (centrifuge speed 10000 r / min, 5 min) and wash to obtain precursor I with double shell layer;
[0052] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 100 mL of NaOH solution (1 mol / L) was added to the dispersion. The mixture was stirred at 1000 r / min and 60 °C for 5 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0053] S5. High-temperature carbonization: Precursor II was carbonized at 700℃ for 2 h at a rate of 10℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0054] Example 5
[0055] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this embodiment includes the following steps:
[0056] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 5 g of hexadecyltrimethylammonium bromide quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min. Then, 0.02 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A.
[0057] S2. Preparation of polydopamine sacrificial layer: 50 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of 1:2), and then 8 g of dopamine hydrochloride was added to it. The mixture was stirred at 60 °C for 6 h at 1000 r / min to obtain solution B.
[0058] S3. Preparation of carbon shell: 6 g pyrrole, 0.5 g surfactant sodium dodecyl sulfate and 5 g oxidant ammonium persulfate were added to solution B. The mixture was stirred at 1000 r / min and polymerized at 20℃ for 12 h. After centrifugation (centrifugation speed 10000 r / min, 5 min) and washing, precursor I with a double-layer coating was obtained.
[0059] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 100 mL of KOH solution (1 mol / L) was added to the dispersion. The mixture was stirred at 1000 r / min and 70 °C for 6 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0060] S5. High-temperature carbonization: Precursor II was carbonized at 800℃ for 5 h at a rate of 10℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0061] Example 6
[0062] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this embodiment includes the following steps:
[0063] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 4 g of hexadecyltrimethylammonium bromide quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min. Then, 0.08 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A.
[0064] S2. Preparation of polydopamine sacrificial layer: 50 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of 1:2), and then 6 g of dopamine hydrochloride was added to it. The mixture was stirred at 60 °C for 4 h at 1000 r / min to obtain solution B.
[0065] S3. Preparation of carbon shell: 5 g pyrrole, 0.3 g surfactant sodium dodecyl sulfate and 3 g oxidant ammonium persulfate were added to solution B. The mixture was stirred at 1000 r / min and polymerized at 20℃ for 16 h. After centrifugation (centrifugation speed 10000 r / min, 5 min) and washing, precursor I with a double-layer coating was obtained.
[0066] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 100 mL of NaOH solution (2 mol / L) was added to the dispersion. The mixture was stirred at 1000 r / min and 80 °C for 8 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0067] S5. High-temperature carbonization: Precursor II was carbonized at 900℃ for 3 h at a rate of 10℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0068] Example 7
[0069] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this embodiment includes the following steps:
[0070] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 4 g of hexadecyltrimethylammonium bromide quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min. Then, 0.01 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A.
[0071] S2. Preparation of polydopamine sacrificial layer: 40 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of 1:2.5), and then 6 g of dopamine hydrochloride was added to it. The mixture was stirred at 50 °C for 4 h at 800 r / min to obtain solution B.
[0072] S3. Preparation of carbon shell: 10 g pyrrole, 0.3 g surfactant sodium dodecyl sulfate and 3 g oxidant ammonium persulfate were added to solution B. The mixture was stirred at 800 r / min and polymerized at 10℃ for 16 h. After centrifugation (centrifugation speed 10000 r / min, 5 min) and washing, precursor I with a double-layer coating was obtained.
[0073] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 80 mL of NaOH solution (1.5 mol / L) was added to the dispersion. The mixture was stirred at 800 r / min and 80 °C for 8 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0074] S5. High-temperature carbonization: Precursor II was carbonized at 800℃ for 3 h at a rate of 7℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0075] Comparative Example 1
[0076] The preparation method of the silicon-carbon anode material in this comparative example differs from that in Example 3 in that steps S2 and S4 are omitted. The specific steps are as follows:
[0077] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 4 g of polydimethylammonium chloride quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min. Then, 0.08 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A.
[0078] S3. Preparation of carbon shell: 5 g pyrrole, 0.3 g surfactant sodium dodecylbenzenesulfonate and 3 g oxidant ammonium persulfate were added to solution A. The mixture was stirred at 600 r / min and polymerized at 0℃ for 16 h. After centrifugation (centrifugation speed 10000 r / min, 5 min) and washing, precursor I with a double-layer coating was obtained.
[0079] S5. High-temperature carbonization: Precursor II was carbonized at 900℃ for 3 h at a rate of 5℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0080] Comparative Example 2
[0081] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this comparative example differs from that in Example 3 in that hydroxylated carbon nanotubes are not added. The specific steps are as follows:
[0082] S1. Molecular self-assembly: 10 g of nano-silicon, 100 mL of water, and 4 g of polydienedimethylammonium chloride quaternary ammonium salt additive were dispersed evenly in a beaker at 600 r / min to obtain solution A;
[0083] S2. Preparation of polydopamine sacrificial layer: 25 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of the two is 1:4), and then 6 g of dopamine hydrochloride was added to it. The mixture was stirred at 25 °C for 4 h at 600 r / min to obtain solution B.
[0084] S3. Preparation of carbon shell: 5 g pyrrole, 0.3 g surfactant sodium dodecylbenzenesulfonate and 3 g oxidant ammonium persulfate were added to solution B. The mixture was stirred at 600 r / min and polymerized at 0℃ for 16 h. After centrifugation (centrifugation speed 10000 r / min, 5 min) and washing, precursor I with a double-layer coating was obtained.
[0085] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 50 mL of NaOH solution (2 mol / L) was added to the dispersion. The mixture was stirred at 600 r / min and 80 °C for 8 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0086] S5. High-temperature carbonization: Precursor II was carbonized at 900℃ for 3 h at a rate of 5℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0087] Comparative Example 3
[0088] The preparation method of the silicon-carbon anode material with a cavity buffer structure in this comparative example differs from that in Example 3 in that quaternary ammonium salt additives and surfactants are not added in steps S1 and S3. The steps are as follows:
[0089] S1. Molecular self-assembly: 10 g of nano-silicon and 100 mL of water were dispersed evenly in a beaker at 600 r / min, and then 0.08 g of carboxylated single-walled carbon nanotubes were added to the solution and stirred at 600 r / min for 2 h to obtain solution A;
[0090] S2. Preparation of polydopamine sacrificial layer: 25 mL of Tris-HCl buffer solution with pH 8 was added to solution A (volume ratio of the two is 1:4), and then 6 g of dopamine hydrochloride was added to it. The mixture was stirred at 25 °C for 4 h at 600 r / min to obtain solution B.
[0091] S3. Preparation of carbon shell: 5 g of pyrrole and 3 g of oxidant ammonium persulfate were added to solution B, stirred at 600 r / min, and polymerized at 0℃ for 16 h. After centrifugation (centrifugation speed 10000 r / min, 5 min) and washing, precursor I with double-layer coating was obtained.
[0092] S4. Decomposition of the sacrificial layer: Precursor I was dispersed in 100 mL of aqueous solution, and then 50 mL of NaOH solution (2 mol / L) was added to the dispersion. The mixture was stirred at 600 r / min and 80 °C for 8 h. Then, it was centrifuged (centrifugation speed 10000 r / min, 5 min), washed, and dried to obtain precursor II.
[0093] S5. High-temperature carbonization: Precursor II was carbonized at 900℃ for 3 h at a rate of 5℃ / min in an inert argon atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
[0094] Application examples
[0095] The negative electrode material obtained in the above examples (comparative examples) was used as the negative electrode active material. It was mixed with conductive agent Sp, binder CMC, and SBR in a mass ratio of 8:1:0.5:0.5 to form a slurry. This slurry was coated onto the surface of a 6-micron copper foil, dried at 90°C for 12 hours, and cut into 12 mm diameter discs to obtain the positive electrode sheet. Then, using lithium metal as the negative electrode and the coated copper foil as the positive electrode, a CR2025 button cell was assembled. Relevant electrochemical tests and 0.5C cycle tests were performed on it. The relevant electrochemical performance is shown in Table 1.
[0096] Table 1
[0097]
[0098] The experimental results above show that the capacities of Examples 1-7 are not significantly different, and the capacity retention rate after 200 cycles at 0.5 A / g is all above 80%. Compared with Example 3, Comparative Examples 1-3 all have a capacity retention rate of less than 85% after 200 cycles at a current density of 0.5 A / g. Comparative Example 1 has no cavity, so its cycle retention rate is the lowest. Comparative Example 2 is a material without carboxylated carbon nanotubes, and its cycle stability is also worse than that of Example 3. Comparative Example 3 does not contain quaternary ammonium salts and surfactants, resulting in poor coating effect between carbon nanotubes and silicon cores. The lack of surfactants also leads to poor coating effect of the polypyrrole layer, thus the cycle performance of Comparative Example 3 is worse than that of the examples.
[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a silicon-carbon anode material with a cavity buffer structure, characterized in that, The steps are as follows: (1) Add nano-silicon and quaternary ammonium salt to water and disperse evenly, then add carboxylated carbon nanotubes to obtain solution A; (2) Add weak alkaline buffer solution and dopamine hydrochloride to solution A, and obtain solution B after reaction; (3) Pyrrole, surfactant and oxidant were added to solution B, and precursor I with a double coating layer was obtained by polymerization reaction; (4) The precursor I obtained in step (3) is dispersed in water, and after treatment with alkaline solution, centrifugation, washing and drying, precursor II is obtained; (5) The precursor II obtained in step (4) is carbonized at high temperature in an inert atmosphere to obtain a silicon-carbon anode material with a cavity buffer structure.
2. The method for preparing the silicon-carbon anode material with a cavity buffer structure according to claim 1, characterized in that, In step (1), the mass ratio of nano-silicon, quaternary ammonium salt and carboxylated carbon nanotubes is 10:(3-5):(0.01-0.1).
3. The method for preparing the silicon-carbon anode material with a cavity buffer structure according to claim 2, characterized in that, The quaternary ammonium salt is at least one of polydiene dimethyl ammonium chloride, hexadecyltrimethylammonium bromide, didecyldimethylammonium chloride, and didecyldimethylammonium bromide.
4. The method for preparing the silicon-carbon anode material with a cavity buffer structure according to claim 2, characterized in that, In step (2), the volume ratio of the weak alkaline buffer solution to solution A is 1:(2-4), and the mass ratio of nano-silicon to dopamine hydrochloride is 10:4-8. During the reaction, the rotation speed is 600-1000 r / min, the temperature is 25-60℃, and the time is 3-6 h.
5. The method for preparing the silicon-carbon anode material with a cavity buffer structure according to claim 4, characterized in that, In step (3), the mass ratio of nano-silicon, pyrrole, surfactant and oxidant is 10:(4-10):(0.1-0.5):(1-5).
6. The method for preparing the silicon-carbon anode material with a cavity buffer structure according to claim 5, characterized in that, The polymerization reaction in step (3) is carried out at a temperature of 0-20°C for 5-10 h; the surfactant is one of sodium dodecylbenzenesulfonate, polyvinylpyrrolidone and sodium dodecyl sulfate; and the oxidant is ammonium persulfate.
7. The method for preparing the silicon-carbon anode material with a cavity buffer structure according to claim 6, characterized in that, In step (4), the concentration of the alkaline solution is 1-2 mol / L, and the solute in the alkaline solution is at least one of sodium hydroxide, potassium hydroxide, trisodium phosphate and sodium sulfite; the temperature of the alkaline solution treatment is 60-80℃, and the time is 5-8 h.
8. The method for preparing the silicon-carbon anode material with a cavity buffer structure according to claim 7, characterized in that, In step (5), the high-temperature carbonization temperature is 700-900℃, the heating rate is 5-10℃ / min, and the carbonization time is 2-5 h.
9. A silicon-carbon anode material with a cavity buffer 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 cavity buffer structure as described in claim 9 in lithium-ion batteries.