Triazinyl covalent organic framework coated nano-silicon negative electrode, preparation method and application of triazinyl covalent organic framework coated nano-silicon negative electrode

Abstract

The invention relates to a triazinyl covalent organic framework coated nano silicon negative electrode, a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. Melamine and nano silicon are combined through Van der Waals' force, electrostatic adsorption and more than one of acting forces of peptide bonds, then pyromellitic dianhydride and melamine are cross-linked through secondary amine bonds, and finally a triazinyl covalent organic framework coating layer is formed on the surface of nano silicon. In the lithiation process, a C = N bond on a triazine ring serves as a reaction site to be preferentially combined with lithium ions to be converted into an inorganic Li3N component, and Li3N has high modulus, so that the mechanical strength of an SEI film is effectively improved, SEI film breakage caused by volume expansion of a silicon negative electrode is avoided, and the cycle life of the electrode is prolonged. The synthesized negative electrode material has excellent long cycle stability when being applied to a negative electrode of a lithium ion battery.

Description

Technical Field

[0001] The invention relates to a triazine-based covalent organic framework-coated nano-silicon negative electrode, a preparation method and application thereof, and belongs to the technical field of lithium-ion batteries. Background Art

[0002] Currently, renewable energy technologies have been developed as supplementary or alternative technologies to fossil fuels commonly used in modern society. However, renewable energy is generated intermittently, resulting in the inability of the power grid to provide large-scale, long-term, and periodic supply of electricity. Therefore, the research and development of large-scale energy storage systems is particularly important for the storage and conversion of renewable energy. Among the many energy storage systems, lithium-ion batteries, which have the advantages of long cycle life, high power density and the fastest charge and discharge rate, have been widely used in various electronic devices such as computers, mobile phones, power tools, industrial equipment, energy-saving hybrid ships, aircraft, drones, plug-in hybrid and pure electric vehicles in the field of large-scale energy storage and conversion. However, traditional graphite anodes are difficult to meet the growing demand for high-energy batteries. Nanosilicon (Si NPs) have high theoretical capacity (4200 mAh g -1 ) and shorter ion / electron transport paths, as a promising negative electrode material for the next generation of lithium-ion batteries, it has also attracted great interest from researchers. However, its large specific surface area leads to the easy formation of a thick solid-electrolyte interface (SEI) film in the first cycle. This SEI usually has poor mechanical strength and cannot adapt to the huge volume expansion (~300%) of the silicon-based negative electrode. It will break and continue to grow during repeated lithiation / delithiation, eventually leading to the formation of "dead silicon". An effective way to solve the above problems is to construct an artificial SEI with excellent mechanical properties and density on the surface of silicon, such as organic / inorganic coatings rich in fluoride / nitride, which can be in situ converted into components rich in LiF or Li3N during the cycle, thereby increasing the modulus of the SEI and avoiding the rupture of the SEI during continuous lithiation / delithiation. Summary of the invention

[0003] In view of this, the object of the present invention is to provide a triazine-based covalent organic framework-coated nano-silicon negative electrode, a preparation method and application thereof.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows.

[0005] A triazine-based covalent organic framework-coated nano-silicon negative electrode, wherein melamine and nano-silicon are firstly combined through one or more forces including van der Waals force, electrostatic adsorption and peptide bond, and then pyromellitic anhydride and melamine are cross-linked through secondary amine bonds, and finally a triazine-based covalent organic framework coating layer is formed on the surface of the nano-silicon.

[0006] A method for preparing a triazine-based covalent organic framework-coated nano-silicon negative electrode, the method steps comprising: Nano-silicon powder and melamine are added to dimethyl sulfoxide (DMSO), stirred and dispersed evenly while ultrasonicating, and then a DMSO solution of pyromellitic anhydride is added, and the mixture is stirred at a stirring rate of 100-400 rpm for 12-24 hours. After the stirring, the mixture is centrifuged and dried to obtain a triazine-based covalent organic framework-coated nano-silicon negative electrode (Si@COF).

[0007] Preferably, the mass ratio of nano silicon powder, melamine and pyromellitic anhydride is 1:1-2:1-2.

[0008] Preferably, the ultrasonic power is 200-300 W, the stirring rate is 100-300 rpm, and the dispersion time is 2-4 hours.

[0009] Preferably, the particle size of the nano silicon powder is 50-100 nm.

[0010] Preferably, a DMSO solution of pyromellitic anhydride is added, and the mixture is mixed and stirred at a stirring rate of 200 to 300 rpm for 14 to 16 hours.

[0011] An application of the triazine-based covalent organic skeleton-coated nano-silicon negative electrode of the present invention, wherein the nano-silicon negative electrode is used as a negative electrode of a lithium-ion battery.

[0012] Beneficial Effects The present invention provides a triazine-based covalent organic framework-coated nano-silicon anode (Si@COF), which has a triazine-based covalent organic framework (COF) layer on the surface of nano-silicon particles, and the triazine-based COF layers are connected together by secondary amine bonds. During the lithiation process, the C=N bond on the triazine ring preferentially combines with lithium ions as a reaction site to be converted into an inorganic Li3N component. Li3N has a high modulus, which effectively improves the mechanical strength of the SEI film, avoids the rupture of the SEI film due to the volume expansion of the silicon anode, and improves the cycle life of the electrode. The synthesized Si@COF material has excellent long-cycle stability when applied to the anode of lithium-ion batteries.

[0013] The present invention provides a method for preparing a triazine-based covalent organic framework-coated nano-silicon negative electrode. By self-assembly in a solution, melamine and nano-silicon powder are first mixed, and the two are combined by one or more forces of van der Waals force, electrostatic adsorption and peptide bond, and then pyromellitic anhydride is added. Two small molecular monomers of melamine and pyromellitic anhydride form a triazine-based COF layer on the surface of Si NPs. This triazine-based COF layer can form a high modulus component rich in lithium nitride (Li3N) in an electrochemical reaction, thereby enhancing the mechanical properties of SEI. The method has mild reaction conditions and will not damage the bulk structure of the silicon negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the SEM image of Si@COF-1 prepared in Example 1.

[0015] Figure 2 This is the SEM image of Si NPs in Comparative Example 1.

[0016] Figure 3 The performance graph of Si@COF-1, Si NPs, Si@COF-2 and Si@COF-3 in Example 1 and Comparative Examples 1-3 within the voltage range of 0.01-1.5 V and 0.3C cycle for 100 cycles.

[0017] Figure 4 Performance diagram of Si@COF-1, Si NPs, Si@COF-2 and Si@COF-3 in Example and Comparative Examples 1-3 within the voltage range of 0.01-1.5 V and 2C cycle for 1000 cycles. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below in conjunction with specific embodiments.

[0019] In the following examples and comparative examples, nano silicon powder was purchased from Kejing CW-Si-003 100 nm nano silicon powder, product model: CW-Si-003, standard packaging: 100 g / bag, product code: 02005600.

[0020] Scanning electron microscope (SEM) test: The morphology of the material was tested using a JSM-6360LV scanning electron microscope.

[0021] Assembly and testing of CR2032 button batteries: The final products obtained in the comparative example and the embodiment were used as active materials, acetylene black, and a polyacrylic acid binder were made into a slurry in a mass ratio of 8:1:1 and coated on a copper foil. The dried copper foil loaded with the slurry was cut into small discs with a diameter of about 1 cm using a cutting machine as the positive electrode. A metal lithium sheet was used as the negative electrode, Celgard2300 was used as a diaphragm, and a 1M carbonate solution was used as an electrolyte (wherein the solvent was a mixed solution of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, and the solute was LiPF6). CR2032 button batteries were assembled in an argon glove box (water pressure ≤0.01 ppm, oxygen pressure ≤0.01 ppm); the assembled CR2032 button batteries were subjected to constant current charge and discharge tests at different current densities using a CT2001A Land battery tester, and the test temperature was 25°C.

[0022] Example 1 (1) Disperse 0.5 g of nano-silicon particles and 0.5 g of melamine in 32 ml of DMSO and stir for 3 h under ultrasonic conditions at a stirring rate of 200 rpm. After complete dispersion, a mixed solution of nano-silicon / small molecule A is obtained.

[0023] (2) Dissolve 0.5 g of pyromellitic anhydride in 16 ml of DMSO and stir at room temperature for 3 h at a stirring rate of 200 rpm to obtain a pyromellitic anhydride solution after complete dissolution.

[0024] (3) The pyromellitic anhydride solution and the nano-silicon / melamine solution were mixed and stirred for 12 h at a stirring rate of 200 rpm to obtain a Si@COF-1 solution.

[0025] (4) The Si@COF-1 solution was centrifuged at a rate of 6000 rpm / min, and then washed with DMSO three times. The obtained product was dried in a vacuum oven at 60 °C for 12 h to obtain Si@COF-1 powder.

[0026] Comparative Example 1 Pure nano silicon powder Si NPs is comparative example 1.

[0027] Comparative Example 2 (1) Disperse 0.5 g of nano-silicon particles and 0.25 g of melamine in 32 ml of DMSO and stir for 3 h under ultrasonic conditions at a stirring rate of 200 rpm. After complete dispersion, a nano-silicon / melamine mixed solution is obtained.

[0028] (2) Dissolve 0.25 g of pyromellitic anhydride in 16 ml of DMSO and stir at room temperature for 3 h at a stirring rate of 200 rpm to obtain a cyanuric acid solution after complete dissolution.

[0029] (3) The cyanuric acid solution and the nano-silicon / pyromellitic anhydride solution were mixed and stirred for 12 h at a stirring rate of 200 rpm to obtain a Si@COF-2 solution.

[0030] (4) The Si@COF-1 solution was centrifuged at a rate of 6000 rpm / min, and then washed with DMSO three times. The obtained product was dried in a vacuum oven at 60 °C for 12 h to obtain Si@COF-2 powder.

[0031] Comparative Example 3 (1) Disperse 0.5 g of nano-silicon particles and 0.75 g of melamine in 32 ml of DMSO and stir for 3 h under ultrasonic conditions at a stirring rate of 200 rpm. After complete dispersion, a nano-silicon / melamine mixed solution is obtained.

[0032] (2) Dissolve 0.75 g of pyromellitic anhydride in 16 ml of DMSO and stir at room temperature for 3 h at a stirring rate of 200 rpm to obtain a cyanuric acid solution after complete dissolution.

[0033] (3) The pyromellitic anhydride solution and the nano-silicon / melamine solution were mixed and stirred for 12 h at a stirring rate of 200 rpm to obtain a Si@COF-3 solution.

[0034] (4) The Si@COF-3 solution was centrifuged at a rate of 6000 rpm / min, and then washed with DMSO three times. The obtained product was dried in a vacuum oven at 60 °C for 12 h to obtain Si@COF-3 powder.

[0035] SEM images of Si@COF-1 in Example 1 and Si NPs in Comparative Example 1 ( Figure 1 and Figure 2 ) showed that the size of pure silicon nanoparticles was about 100 nm. After being coated with COF, the particle size did not change significantly, but the surface became rough, indicating the coating of the COF layer.

[0036] The cycling performance curves of Si@COF-1, Si@COF-2, Si@COF-3 and Si NPs electrodes in the voltage range of 0.01-1.5 V and 0.3C are shown in Figure 2. Figure 3 As shown in the figure, except for Si@COF-1, the other three electrodes all show a trend of capacity decay. After 100 cycles, the discharge specific capacity of the electrodes of Si@COF-2, Si@COF-3, and Si NPs all dropped to 500 mAhg -1 Even after 100 cycles, the capacity of Si@COF-1 electrode is still 2011.0 mAh g -1 This excellent capacity retention is mainly attributed to the in-situ generation of Li3N in the COF layer during the electrochemical reaction, which induces the formation of a dense, mechanically strong SEI film on the silicon surface, thereby avoiding the formation of dead silicon and irreversible lithium loss.

[0037] The long cycle performance curves of Si@COF-1, Si@COF-2, Si@COF-3 and Si NPs electrodes in the voltage range of 0.01-1.5 V and at a high rate of 2 C are shown in Figure 2. Figure 4 As shown in the figure, the capacity of the comparative electrode shows a rapid decay at a high rate, and the capacity is close to 0. It can be seen that Si@COF-2, Si@COF-3 and Si NPs cannot withstand long-term cycling at a high rate. After 1000 cycles of stable cycling, the Si@COF-1 electrode still maintains 1230.5 mAh g -1The high capacity shows excellent cycle stability. It can be seen that the appropriate amount of triazine-based COF layer has a significant effect on improving the cycle stability of the nano-silicon negative electrode, which is mainly due to the construction of a dense and mechanically strong SEI film on the silicon surface. A lower content of COF layer may not be able to completely cover the silicon particles; a higher COF content may lead to the formation of excess monomer COF, which is not conducive to the use of silicon capacity.

[0038] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A triazine-based covalent organic framework-coated nano-silicon negative electrode, characterized in that: Melamine and nano-silicon are first combined through one or more forces including van der Waals force, electrostatic adsorption and peptide bond, and then pyromellitic anhydride and melamine are cross-linked through secondary amine bonds, finally forming a triazine-based covalent organic framework coating layer on the surface of nano-silicon.

2. A method for preparing a triazine-based covalent organic framework-coated nano-silicon negative electrode as claimed in claim 1, characterized in that: The method steps include: Nano silicon powder and melamine are added to dimethyl sulfoxide, stirred and dispersed evenly while ultrasonicating, and then a DMSO solution of pyromellitic anhydride is added, and the mixture is stirred at a stirring rate of 100-400 rpm for 12-24 hours. After the stirring is completed, the mixture is centrifuged and dried to obtain a triazine-based covalent organic framework-coated nano silicon negative electrode.

3. The method for preparing a triazine-based covalent organic framework-coated nano-silicon negative electrode according to claim 2, characterized in that: The mass ratio of nano silicon powder, melamine and pyromellitic anhydride is 1:1~2:1~2.

4. The method for preparing a triazine-based covalent organic framework-coated nano-silicon negative electrode according to claim 2, characterized in that: The ultrasonic power is 200~300W, the stirring rate is 100~300rpm, and the dispersion time is 2~4 hours.

5. The method for preparing a triazine-based covalent organic framework-coated nano-silicon negative electrode according to claim 2, characterized in that: The particle size of the nano silicon powder is 50-100 nm.

6. The method for preparing a triazine-based covalent organic framework-coated nano-silicon negative electrode according to claim 2, characterized in that: Add the DMSO solution of pyromellitic anhydride, and stir at a stirring rate of 200-300 rpm for 14-16 hours.

7. An application of the triazine-based covalent organic framework-coated nano-silicon negative electrode as claimed in claim 1, characterized in that: The nano silicon negative electrode is used as a negative electrode of a lithium ion battery.

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