A phthalocyanine-based covalent organic framework coated nanosilicon type composite material and a preparation method thereof

Abstract

The application discloses a phthalocyanine-based covalent organic framework coated nano-silicon type composite material and a preparation method thereof, and belongs to the technical field of lithium ion battery electrode materials. The method adopts a "solvent thermal" method to in-situ composite phthalocyanine-based covalent organic framework material and nano-silicon, realizes construction of a layer of structure-stable artificial protective layer on the surface of the nano-silicon, and then is subjected to special pre-lithiation treatment, so that the initial coulomb efficiency of the composite material as a negative electrode material is improved. The application adopts an organic small-molecule compound to prepare phthalocyanine with a large pi conjugated system, further synthesizes a structure-stable covalent organic framework to be coated on the surface of the nano-silicon, and the obtained composite material has high structure stability, high electrical conductivity and rich raw materials. When the composite material is applied to a negative electrode material of a lithium ion battery, the composite material has excellent initial coulomb efficiency and capacity, and the long cycle performance is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology. Specifically, this invention relates to a phthalocyanine-based covalent organic framework-coated nano-silicon composite material, a method for preparing the composite material, and a method for pre-lithiation treatment of the composite material. In addition, this invention also relates to the application of the phthalocyanine-based covalent organic framework-coated nano-silicon composite material as a negative electrode material for lithium-ion batteries. Background Technology

[0002] Silicon (Si) is considered one of the most promising anode materials for commercial lithium-ion batteries because it has a high theoretical specific capacity (4200 mAh / g) and a suitable voltage plateau (0.4V vs. Li / Li). + Silicon is abundant in reserves. However, the internal stress generated by the large volume expansion (~320%) during lithiation and delithiation processes leads to the pulverization of silicon particles, resulting in detachment from the current collector and rapid capacity decay of the electrode. It has been reported that since the fracture behavior of silicon particles during lithiation is strongly dependent on particle size, reducing the silicon particle size to the nanoscale (less than 150 nm) can alleviate the fracture problem. Despite the design of various nanostructures, including nanoporous silicon and silicon nanoparticles (Si NPs), to address the pulverization problem, the continuous growth of the solid electrolyte interface (SEI) layer on the silicon surface remains a critical issue in silicon anode applications. The instability of the natural SEI layer will consume the liquid electrolyte and lead to lithium-ion battery failure. Typically, due to the instability of the electrolyte at low potentials, the SEI passivation layer forms as a reduction product of the electrolyte. This SEI layer allows lithium-ion transport while blocking electrons, thereby inhibiting further reduction of the electrolyte and the continuous growth of the SEI film. The electrochemical and mechanical properties of the SEI layer play a key role in improving the cycle performance and rate performance of silicon anodes. Researchers have been working on artificial SEI layers to obtain better mechanical properties and higher lithium-ion conductivity.

[0003] Covalent organic frameworks (COFs) are two- or three-dimensional polymers with atomic structures. They have recently attracted increasing interest due to their high porosity, tunable pore geometry, chemical modifiability, and good electrochemical stability, making them potential applications in electrochemistry. The ordered pore structure and modification chemistry in COFs provide directional pathways for ion migration. The lithium conductivity of COFs is comparable to that of commercially available polymers (ethylene oxide) used in solid-state lithium-ion batteries. In addition to good ionic conductivity, COFs also exhibit excellent mechanical properties and low electronic conductivity. Therefore, using COFs as artificial SEI layers shows promise as a strategy for optimizing the electrochemical performance of SiNPs.

[0004] This invention utilizes the large π-conjugated system of phthalocyanine as a basis to prepare a COF-coated silicon nanocomposite material by solvothermal reaction with silicon. The strong confinement and buffering effect of the stable two-dimensional mesh layered structure of the covalent organic framework in the composite material structure can effectively suppress and buffer the volume change of silicon during charging and discharging, enhance structural stability, and improve its electrochemical performance. Summary of the Invention

[0005] To address the aforementioned problems, such as the volume expansion of silicon during lithiation and delithiation processes and the performance degradation caused by the continuous growth of the solid electrolyte interface layer, this invention provides a negative electrode material of a nano-silicon composite material coated with a phthalocyanine-based covalent organic framework. This invention also provides a method for preparing the composite material.

[0006] Specifically, the technical solution of the present invention is as follows:

[0007] One objective of this invention is to provide a phthalocyanine-based covalent organic framework-coated nanocrystalline silicon composite material, wherein the structural formula of the phthalocyanine-based covalent organic framework is:

[0008]

[0009] Where M represents metal;

[0010] U is selected from -NHCO-Ar-CONH-, -OCO-Ar-COO-, -CONH-Ar-NHCO-, -COO-Ar-OCO-, -NH-Ar-NH-, -O-Ar-O-, -N=N-Ar-N=N-, -C(R1)=N-Ar-N=C(R1)-, -N=C(R1)-Ar-C(R1)=N-, -Ar-, -C(R1)=N-, -N=N-, -O-, -NH-; Ar represents an organic linking group; R1 is selected from H, C1-C4 alkyl groups.

[0011] In one embodiment, M is selected from nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), yttrium (Y), europium (Eu), lanthanum (La), scandium (Sc), neodymium (Nd), erbium (Er) or lutetium (Lu), preferably nickel (Ni), cobalt (Co) or manganese (Cu).

[0012] In one embodiment, the Ar is selected from substituted or unsubstituted C1-C12 alkylene, substituted or unsubstituted C1-C12 heteroalkylene, substituted or unsubstituted C3-C15 cycloalkylene, substituted or unsubstituted C6-C30 arylene, substituted or unsubstituted 5-20 heteroarylene, and substituted or unsubstituted 5-20 heterocyclic group.

[0013] Preferably, Ar is selected from substituted or unsubstituted:

[0014]

[0015] Ra, Rb, and Rc are independently selected from H, C1-6 alkyl, and C6-C12 aryl.

[0016] In this invention, "substituted or unsubstituted" means unsubstituted or substituted by one or more substituents selected from the following: C1-C4 alkyl, halogen, -CN, -NO2, -NH2, -CHO, -OH, -COOH, substituted or unsubstituted phenyl, C1-4 alkoxy, -B(OH)2.

[0017] Preferably, Ar is selected from:

[0018]

[0019] In one implementation, U is selected from:

[0020]

[0021] In one embodiment, the structural formula of the phthalocyanine covalent organic framework is as follows:

[0022]

[0023] The halogens described in this invention include fluorine, chlorine, bromine, and iodine.

[0024] In this invention, when the position of the substituent on the aromatic ring is not fixed, it means that it can be attached to any of the corresponding optional sites on the aromatic ring. For example, Can represent And so on.

[0025] The alkyl group described in this invention refers to a hydrocarbon group formed by removing one hydrogen atom from an alkane molecule. The alkyl group can be a straight-chain alkyl group or a branched alkyl group. When the chain alkyl group described in this invention has three or more carbon atoms, it includes its isomers; for example, propyl includes n-propyl and isopropyl; butyl includes n-butyl, isobutyl, sec-butyl, and tert-butyl. The alkyl group has C1 to C12 carbon atoms, preferably C1 to C6, more preferably C1 to C4, and so on. Examples of alkyl groups include, but are not limited to, the following groups: methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, etc. The alkylene group is a group formed by further removing one hydrogen atom from an alkyl group.

[0026] The cycloalkyl group described in this invention refers to a hydrocarbon group formed by removing one hydrogen atom from a cycloalkane molecule. The cycloalkyl group includes monocyclic cycloalkyl, polycyclic cycloalkyl, and bridged cycloalkyl groups. The cycloalkyl group has 3 to 15 carbon atoms, preferably 3 to 12, and more preferably 3 to 7. Examples of cycloalkyl groups include, but are not limited to, the following groups: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, norbornelyl, etc., but are not limited thereto. The cycloalkylene group is a cycloalkyl group further formed by removing one hydrogen atom.

[0027] The aryl group described in this invention refers to the general term for a monovalent group remaining after removing one hydrogen atom from the aromatic carbon atom of an aromatic compound molecule. The aryl group includes monocyclic aryl, polycyclic aryl, fused-ring aryl, or combinations thereof. The aryl group has 6 to 30 carbon atoms, preferably 6 to 25, and more preferably 6 to 10. Examples of aryl groups include, but are not limited to, the following groups: phenyl, biphenyl, naphthyl, phenanthryl, anthraceneyl, triphenylene, pyrene, etc. The aryl derivative is a group formed by further removing one hydrogen atom from an aryl group.

[0028] The heterocyclic group described in this invention comprises at least one cyclic heteroatom, i.e., an atom other than carbon. The heteroatom can be selected from Group 15 or 16 of the periodic table, and is preferably selected from oxygen, sulfur, selenium, nitrogen, and phosphorus. The heteroaryl group can have 5 to 20 ring atoms, preferably 5 to 15, and even more preferably 5 to 7. Examples of substituted or unsubstituted heterocyclic groups include, but are not limited to, the following groups: pyrrole, furanyl, thiophene, imidazolyl, carbazole, pyridinyl, pyrazinyl, pyridazinyl, triazinyl, quinolinyl, isoquinolinyl, thienobenzothiophene, pyromellitic acid diimide, 1,4,5,8-naphthalenetetracarboxylic acid diimide, 2,3,6,7-naphthalenetetracarboxylic acid diimide, 3,4,9,10-perylenetetracarboxylic acid diimide, etc., but are not limited thereto. The sub-heterocyclic group is a heterocyclic group further reduced by one hydrogen atom.

[0029] The inert gases described in this invention include nitrogen and argon.

[0030] In one embodiment, the phthalocyanine covalent organic framework is a two-dimensional network layered structure with a pore size of approximately 1.0–5.0 nm, preferably 2.0–4.0 nm, and more preferably 3.0–3.5 nm.

[0031] In one embodiment, the nano-silicon is coated within a phthalocyanine covalent organic framework. The average particle size of the nano-silicon is 1–1000 nm, preferably 10–100 nm, more preferably 30–80 nm, and most preferably 40–60 nm. The content of nano-silicon in the composite material is 5–70%, preferably 10–60%, and more preferably 30–50%.

[0032] Another object of the present invention is to provide a method for preparing phthalocyanine-based covalent organic framework-coated nano-silicon composite materials, the method comprising the following steps:

[0033] Step 1: React the small molecule 4-R phthalonitrile with a metal salt to obtain the macromolecular product 4-R metal phthalocyanine;

[0034] Step 2: Combine 4-R metal phthalocyanine, nano-silicon, and the multifunctional monomer U A Heating in an organic solvent enables in-situ coating of nano-silicon with a phthalocyanine-based covalent organic framework, and the resulting product is a phthalocyanine-based covalent organic framework-coated nano-silicon composite material.

[0035] Wherein, R is selected from one of halogen, -OH, -NO2, -NH2, -COOH, -CN, -C(R1)=O, preferably selected from one of -NO2 and -NH2; R1 is selected from H and C1-4 alkyl;

[0036] Multifunctional monomer U A This indicates a small monomer that can react with R groups to polymerize 4-R metal phthalocyanines into phthalocyanine covalent organic frameworks.

[0037] In one embodiment, the metal salt comprises a salt of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), yttrium (Y), europium (Eu), lanthanum (La), scandium (Sc), neodymium (Nd), erbium (Er), or lutetium (Lu), preferably a salt of nickel (Ni), cobalt (Co), or manganese (Cu). The anion of the metal salt is at least one selected from chloride, nitrate, acetate, bisulfate, and sulfate ions, preferably chloride. Therefore, the metal salt is preferably nickel chloride (NiCl2), cobalt chloride (CoCl2), or manganese chloride (MnCl2).

[0038] In one embodiment, the multifunctional monomer U A It has two or more functional groups that can react with the R group, said functional groups being selected from: -X (-F, -Cl, -Br, -I), -B(OH)2, -NH2, -NO2, -COOH, -OH, C(R1)=O, -C=OOC=O- (acid anhydride), -C=ONHC=O- (imide), -COCl.

[0039] In one embodiment, the multifunctional monomer U A Selected from:

[0040] x-Ar-x(HO)2B-Ar-B(OH2)H2N-Ar-NH2 ORC-Ar-CRO O2N-Ar-NO2

[0041] HOOc-Ar-cOOH HO-Ar-OH CIOC-Ar-COCI

[0042] Wherein, X is selected from halogens, and Ar is selected from substituted or unsubstituted ones:

[0043]

[0044] Ar' is selected from substituted or unsubstituted:

[0045]

[0046] The term "substituted or unsubstituted" means unsubstituted or substituted with one or more substituents selected from the following: C1-C4 alkyl, halogen, -CN, -NO2, -NH2, -CHO, -OH, -COOH, substituted or unsubstituted phenyl, C1-4 alkoxy, -B(OH)2.

[0047] In a preferred embodiment, the multifunctional monomer U ASelected from: terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, 1,3,6,8-tetra(4-carboxylphenyl)pyrene, tetra(4-aldehydephenyl)ethylene, tetra-(4-aldehyde-(1,1-biphenyl))ethylene, tetra(4-formylphenyl)methane, tetra(4-formylphenyl)silane, 2,5-dihydroxyterephthalaldehyde, 2,5-dibromoterephthalaldehyde, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde, 2,5-dichloroterephthalaldehyde, 2,3-dihydroxyterephthalaldehyde, 3,3',5,5'-tetraaldehydebiphenyl, 2,6-hydroxy-1,5-dialdehydenaphthalene, 2,5-dialdehydepyrazine, benzo[ 1,2-b:4,5-b']dithiophene-2,6-dicarboxaldehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde, 3,3'-bipyridine-6,6'-dicarboxaldehyde, 2,2'-bipyridine-4,4'-dicarboxaldehyde, 4,4”-bis(4-aldehyde-phenyl)biphenyl, 1,2-bis(4'-formylphenyl)acetylene, N,N,N',N'-tetra(4-aldehyde-phenyl)-1,4-phenylenediamine, 5,10,15,20-tetra(4-formylphenyl)porphyrin, 5,5'-diamino-2,2'-bispyridine, 5,10,15,20-tetra(4-aminophenyl)porphyrin, tetra(4- (Aminophenyl)methane, 1,3,6,8-tetra(4-aminophenyl)pyrene, 1,3,5,7-tetra(4-aminophenyl)adamantane, 4,4'-diaminobiphenyl, 2,7-aminocarbazole, N,N,N',N'-tetra(p-aminophenyl)p-phenylenediamine, 4,4'-azodiphenylamine, tetra(4-boronicophenyl)methane, bis(4-aminophenyl)acetylene, 2,6-diaminoanthracene, p-phenylenediamine, 4,4'-biphenyldiamine, tetra-(4-aminophenyl)ethylene, 4,4'-biphenyl diboronic acid, 1,2-bis(4-boronicophenyl)acetylene, (but-1,3-diyne-1,4-dimethylbis(4, One of 1-phenylene diboronic acid, pyrene-2,7-dimethyldiboronic acid, tetra(4-boronylphenyl)methane, pyromellitic anhydride, pyromellitic diimide, 3,4,9,10-perylenetetracarboxylic anhydride, 3,4,9,10-perylenetetracarboxylic diimide, 1,4,5,8-naphthalenetetracarboxylic anhydride, 1,4,5,8-naphthalenetetracarboxylic diimide, 2,3,6,7-naphthalenetetracarboxylic anhydride, 2,3,6,7-naphthalenetetracarboxylic diimide, octahydroxy metal phthalocyanine, tetranitro metal phthalocyanine, or tetraamino metal phthalocyanine, preferably selected from p-phenylenediamine, 4,4'-biphenylenediamine, pyromellitic anhydride, or tetraamino metal phthalocyanine.

[0048] In one embodiment, the mass ratio of nano-silicon to 4-R metal phthalocyanine in step two is 1:0.5-2.0, preferably 1:0.8-1.2, and more preferably 1:1; the multifunctional monomer U A The molar ratio between the metal and 4-R phthalocyanine is 1-3:1, preferably 1.2-2.5:1, and more preferably 1.5-2.0:1.

[0049] In one embodiment, the average particle size of the nano-silicon is 1–1000 nm, preferably 10–100 nm, more preferably 30–80 nm, and most preferably 40–60 nm.

[0050] In one embodiment, the method of the present invention further includes the step of converting 4-R metal phthalocyanine (i.e., 4-nitro metal phthalocyanine) with R being nitro to 4-R metal phthalocyanine (i.e., 4-amino metal phthalocyanine) with R being amino, which includes: reacting 4-nitro metal phthalocyanine with sodium sulfide in an organic solvent by heating to obtain 4-amino metal phthalocyanine.

[0051] In one embodiment, the preparation method includes the following steps:

[0052] (1): Add organic solvent and 4-R phthalonitrile to a container, and keep it warm and stir under inert gas protection;

[0053] (2): Heat to 70-90℃, add 1,8-diazabicycloundec-7-ene (DBU) first, and when the solution turns blue, add metal salt, and continue to heat to 125-145℃ and react for 48-96 hours.

[0054] (3): After the reaction is complete, the reaction solution is cooled and transferred to ethanol, left to stand overnight, the supernatant is poured off and filtered, and the solution is washed repeatedly with ethanol until the filtrate becomes a light green transparent solution. The solid product is dried to obtain 4-R metal phthalocyanine.

[0055] (4): The 4-R metal phthalocyanine and nano-silicon obtained in step (3) are added to an organic solvent, ultrasonically treated, and then the multifunctional monomer U is added to it. A The mixture is heated to 175–190 °C under inert gas protection and reacted for 48–96 h.

[0056] (5): Cool the reaction mixture in step (4) to room temperature, wash and dry the precipitate obtained after filtration to obtain the phthalocyanine-based covalent organic framework-coated nano-silicon composite material.

[0057] In a preferred embodiment, step (1) involves adding the organic solvent and 4-R phthalonitrile to a container and stirring under inert gas protection for 1–2 hours; heating to 50–70°C and holding at that temperature for 30–60 minutes; preferably, heating to 60°C and holding at that temperature for 30 minutes. The organic solvent is selected from at least one of n-butanol, n-propanol, isopropanol, n-pentanol, toluene, 1,2-dichloroethane, and 1,4-dioxane.

[0058] In a preferred embodiment, in step (2), 1,8-diazabicycloundec-7-ene (DBU) is added after heating to 80°C at a rate of 1°C / min; the temperature is then further increased to 135°C and the reaction is carried out for 65 hours. The molar ratio of 4-R phthalonitrile to the metal salt is 3–5:1, preferably 4:1; the amount of 1,8-diazabicycloundec-7-ene is 0.2–3% of the mass of 4-R phthalonitrile, preferably 1–2%.

[0059] In a preferred embodiment, the solid product in step (3) is dried in a vacuum at 120–140 °C.

[0060] In a preferred embodiment, step (3) further includes the step of converting 4-R1 metal phthalocyanine (i.e., 4-nitro metal phthalocyanine) with R being nitro to 4-R1 metal phthalocyanine (i.e., 4-amino metal phthalocyanine) with R being amino, which includes:

[0061] (a): Add 4-R metal phthalocyanine with R as nitro, sodium sulfide nonahydrate, and organic solvent to a container and stir until dissolved. Heat to 50-85°C and react at a constant temperature for 0.5-6 hours.

[0062] (b): After cooling the mixture in step (a), transfer it to distilled water, let it stand for 24 to 72 hours, filter, wash and dry to obtain 4-R metal phthalocyanine with R being amino.

[0063] Preferably, the organic solvent in step (a) is selected from at least one of dimethylacetamide, 1,4-dioxane, N,N-dimethylformamide, N-methylpyrrolidone, and dichloromethane.

[0064] Preferably, in step (a), the molar ratio of 4-R metal phthalocyanine (R is nitro) to sodium sulfide nonahydrate is 1:(1.0-1.75), more preferably 1:(1.2-1.55), and even more preferably 1:1.2. The temperature is raised to 65°C, and the reaction is carried out for 1 hour.

[0065] Preferably, step (b) includes filtration, washing, and drying: filtering all solutions and repeatedly washing the filter cake with distilled water until the filtrate is no longer turbid and the surface of the solution does not peel; then washing with ethanol until the filtrate is light green and transparent, and drying the solid product in a vacuum at 120-140°C.

[0066] Preferably, in step (b), the product is left to stand for 48 hours; the solid product is then dried in a vacuum at 120°C.

[0067] In a preferred embodiment, the organic solvent in step (4) is selected from at least one of formamide, dimethyl sulfoxide, ethylene glycol dimethyl ether, toluene, 1,4-dioxane, and mesitylene, preferably dimethyl sulfoxide. It is preferred to reflux at 180°C for 72 hours. The mass ratio between nano-silicon and 4-R metal phthalocyanine is 1:0.5-2.0, preferably 1:0.8-1.2, more preferably 1:1; the multifunctional monomer U... A The molar ratio between the metal and 4-R phthalocyanine is 1-3:1, preferably 1.2-2.5:1, and more preferably 1.5-2.0:1.

[0068] In a preferred embodiment, step (5) of washing and drying includes washing the precipitate several times with deionized water and an organic solvent, and drying the solid product in a vacuum at 110–130°C for 10–24 hours. Preferably, the organic solvent is selected from at least one of dichloromethane, anhydrous ethanol, tetrahydrofuran, or acetone; and the solid product is dried in a vacuum at 12°C for 12 hours.

[0069] Another aspect of the present invention provides a phthalocyanine-based covalent organic framework-coated nano-silicon composite material prepared according to the preparation method described in the present invention.

[0070] Another object of the present invention is to provide a pre-lithiated phthalocyanine-based covalent organic framework-coated nanocrystalline silicon composite material, which is prepared by the following method:

[0071] Phthalocyanine-based covalent organic framework-coated nano-silicon composite material was immersed in a lithium salt aqueous solution, filtered, washed, and dried to obtain a pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material.

[0072] This invention provides a pre-lithiation treatment method for the phthalocyanine-based covalent organic framework-coated nano-silicon composite material, the method comprising the following steps:

[0073] Phthalocyanine-based covalent organic framework-coated nano-silicon composite material was immersed in a lithium salt aqueous solution, filtered, washed, and dried to obtain a pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material.

[0074] In one embodiment, the lithium salt is selected from at least one of lithium acetate, lithium nitrate, lithium chloride, lithium hydrogen sulfate, and lithium sulfate. The concentration of the aqueous lithium salt solution is 1–5 M, preferably 2–3 M.

[0075] In one embodiment, the soaking time is 1 to 10 days, preferably 2 to 8 days, and more preferably 3 to 5 days.

[0076] In one embodiment, the washing is performed using deionization.

[0077] In one embodiment, the drying includes vacuum drying the resulting solid at 100–120°C for 12–24 hours, preferably vacuum drying the resulting solid at 120°C for 12 hours.

[0078] Therefore, the phthalocyanine-based covalent organic framework-coated nano-silicon composite material of the present invention includes an un-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material and a pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material.

[0079] Another object of the present invention is to provide the application of the phthalocyanine-based covalent organic framework-coated nano-silicon composite material as a negative electrode material for lithium-ion batteries.

[0080] Another objective of this invention is to provide a lithium-ion battery anode comprising the phthalocyanine-based covalent organic framework-coated nano-silicon composite material as the anode material.

[0081] Another object of the present invention is to provide a lithium-ion battery comprising the phthalocyanine-based covalent organic framework-coated nano-silicon composite material as the negative electrode material, the lithium-ion battery comprising:

[0082] Negative electrode, positive electrode, diaphragm, electrolyte;

[0083] The negative electrode comprises the phthalocyanine-based covalent organic framework-coated nano-silicon composite material as the negative electrode material.

[0084] Compared with the prior art, the beneficial effects of the present invention are:

[0085] (1) This invention improves the structural stability of silicon materials during the charge and discharge process by using a stable layered network structure of phthalocyanine covalent organic framework, thereby enhancing the cycle stability of silicon anode materials.

[0086] (2) The phthalocyanine covalent organic framework coating layer of the present invention, as an artificial SEI layer, can reduce the formation of SEI film on nano-silicon electrodes, thereby reducing lithium ion consumption and improving the electrochemical performance of silicon anode materials.

[0087] (3) The phthalocyanine-based covalent organic framework-coated nano-silicon composite material after pre-lithiation treatment of the present invention improves the first coulombic efficiency of the electrode material by more than 30% on the basis of pure phthalocyanine-based covalent organic framework as a negative electrode material.

[0088] (4) The phthalocyanine-based covalent organic framework-coated nano-silicon composite material of the present invention exhibits excellent electrochemical performance. Its actual capacity is significantly higher than the theoretical capacity (372 mAh / g) of traditional graphite anode material. The lithiation capacity can reach 1570 mAh / g at a current density of 0.1 A / g, and it still has a reversible capacity of 495 mAh / g at an extremely high current density of 5 A / g. When it is used as a lithium-ion battery anode material to assemble a half cell, it can still maintain a reversible capacity of 654 mAh / g after 2000 cycles at a current density of 2 A / g.

[0089] (5) The method for preparing phthalocyanine-based covalent organic framework-coated nano-silicon composite material of the present invention is simple and low in cost. When the prepared phthalocyanine-based covalent organic framework-coated nano-silicon anode material is assembled into a lithium-ion battery, the long cycle performance and rate performance are significantly improved. [Attached Image Description]

[0090] Figure 1 The IR spectra of the synthesis examples 1 and 1 comparative example 1 are shown.

[0091] Figure 2 The XRD patterns of the synthesis examples 1, 1 comparative example, and nano-Si anode materials are shown.

[0092] Figure 3 TEM image of the target product described in Example 1.

[0093] Figure 4 The first charge-discharge curves of the lithium-ion batteries described in Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0094] Figure 5 The above are rate curves of the lithium-ion batteries described in Example 1, Comparative Example 1, and Comparative Example 2.

[0095] Figure 6 The image shows the cycle curve of the lithium-ion battery described in Example 1, with a current density of 0.1 A / g.

[0096] Figure 7 The image shows the cycle curve of the lithium-ion battery described in Example 1, with a current density of 1 A / g.

[0097] Figure 8 The image shows the cycle curve of the lithium-ion battery described in Example 1, with a current density of 2 A / g.

[0098] Figure 9 For the cycling curve of the lithium-ion battery described in Comparative Example 1, the current density is 0.1 A / g.

[0099] Figure 10 For the comparison of the lithium-ion battery cycle curves described in Example 1, the current density is 1 A / g.

[0100] Figure 11 For the comparison of the lithium-ion battery cycle curve described in Example 1, the current density is 2 A / g.

[0101] Figure 12 For the comparison of the lithium-ion battery cycle curve described in Example 2, the current density is 0.1 A / g.

[0102] Figure 13 For the comparison of the lithium-ion battery cycle curves described in Example 2, the current density is 1 A / g.

[0103] Figure 14 For the comparison of the lithium-ion battery cycle curve described in Example 2, the current density is 2 A / g.

Detailed Implementation Methods

[0104] The present invention will be described in detail below with reference to specific embodiments.

[0105] Those skilled in the art will recognize that the chemical reactions described in this invention can be suitably used to prepare many other composite material compounds of this invention, and that other methods for preparing the composite material compounds of this invention are considered to be within the scope of this invention. For example, the synthesis of those non-illustrative composite material compounds according to this invention can be successfully accomplished by those skilled in the art through modification methods, such as appropriately protecting interfering groups, utilizing other known reagents besides those described in this invention, or making some conventional modifications to the reaction conditions. Furthermore, the reactions disclosed in this invention or the known reaction conditions are also generally accepted to be applicable to the preparation of other composite material compounds of this invention.

[0106] Synthesis Example 1: Preparation and Pre-lithiation Treatment of Phthalocyanine-based Covalent Organic Framework-coated Nanocrystalline Silicon Composite Material

[0107] (1) Weigh 25.9596 g of 4-nitrophthalonitrile (0.15 mol) and place it in a 500 mL three-necked flask. Add 300 mL of n-pentanol and a stir bar. Evacuate the apparatus and purge with nitrogen (repeat the above operation 3 times, with a 3-minute interval between each step). Stir at room temperature for 2 hours to remove O2 from the entire apparatus. Heat to 60 °C and hold for 30 minutes. Then, increase the temperature to 135 °C at a rate of 1 °C / min (the boiling point of n-pentanol is 137.5 °C). When the temperature reaches 80 °C, add 7-8 drops of DBU. Continue heating until the solution turns blue, then quickly add 4.86 g (0.0375 mol) of dried nickel chloride. The molar ratio of nickel chloride to 4-nitrophthalonitrile is 1:4. React for 65 hours after the temperature reaches 135 °C. After the reaction was completed and cooled naturally to room temperature, the solution was transferred to 300 mL of anhydrous ethanol and left to stand overnight. The supernatant was then discarded and filtered. The solution was repeatedly washed with anhydrous ethanol until it became a pale green transparent solution. The solid was then dried under vacuum to obtain a blue-green powder, 4-nitronickel phthalocyanine.

[0108] (2) Weigh 7.6 g (0.01 mol) of 4-nitronickel phthalocyanine and 2.88 g (0.12 mol) of sodium sulfide nonahydrate obtained in the previous step, pour them into a 500 ml round-bottom flask, add a stir bar, and then add 300 mL of DMF after dehydration (i.e., dehydration by adding molecular sieves), and stir until dissolved. Heat the mixture to 65 °C in an oil bath, increase the stirring rate, and react at 65 °C for 1 hour. After natural cooling, pour all the substances in the round-bottom flask into a 2 L beaker, fill it with distilled water, and let it stand for 48 hours. After standing, filter all the solutions, wash the product on the filter paper repeatedly with distilled water until the filtrate is no longer turbid and the surface of the solution does not peel off, following the same steps as above. Then wash with anhydrous ethanol until the filtrate is light green and transparent, and vacuum dry to obtain dark green solid powder 4-aminonickel phthalocyanine.

[0109] (3) 4-Aminonickel phthalocyanine (0.6 g, 0.95 mmol) and nano-Si (0.6 g, APS≈50 nm, 99%) were added to 10.0 mL of dimethyl sulfoxide (DMSO). After sonication for 10 min, pyromellitic dianhydride (PMDA) (0.343 g, 1.57 mmol) and 90.0 mL of DMSO were added. After sonication for 10 min, the apparatus was evacuated and nitrogen gas was introduced (the above operation was repeated 3 times, with a 3-minute interval between each step). The mixture was heated to 180 °C and refluxed for 72 h. After the reaction was completed, the mixture was cooled to room temperature. The precipitate obtained after filtration of the solution was washed several times with deionized water and acetone. It was then vacuum dried at 120 °C for 12 h to obtain phthalocyanine-based covalent organic framework-coated nano-silicon composite material (PMDA-NiPc@Si), with a nano-Si content of approximately 40%.

[0110] (4) Pre-lithiation: The phthalocyanine-based covalent organic framework-coated nano-silicon composite material was placed in 20 mL of lithium acetate aqueous solution (concentration 25 M) and soaked for 3 days. After filtration, it was washed 3 times with deionized water. The resulting solid was dried in vacuum at 120℃ for 12 h to obtain the pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material (Li-PMDA-NiPc@Si). The characterization results are as follows: Figure 1-3 As shown.

[0111] Comparative Synthesis Example 1: Preparation of Phthalocyanine-based Covalent Organic Framework Materials

[0112] (1) Weigh 25.9596 g of 4-nitrophthalonitrile (0.15 mol) and place it in a 500 mL three-necked flask. Add 300 mL of n-pentanol and a stir bar. Evacuate the apparatus and purge with nitrogen (repeat the above operation 3 times, with a 3-minute interval between each step). Stir at room temperature for 2 hours to remove O2 from the entire apparatus. Heat to 60 °C and hold for 30 minutes. Then, increase the temperature to 135 °C at a rate of 1 °C / min (boiling point of n-pentanol is 137.5 °C). When the temperature reaches 80 °C, add 7-8 drops of DBU. Continue heating until the solution turns blue, then quickly add 4.86 g of dried nickel chloride (0.0125 mol). The molar ratio of nickel chloride to 4-nitrophthalonitrile is 1:4, and the amount of nickel chloride can be slightly excess. React for 65 hours after the temperature reaches 135 °C. After the reaction was completed and cooled naturally to room temperature, the solution was transferred to 300 mL of anhydrous ethanol and left to stand overnight. The supernatant was then discarded and filtered. The solution was repeatedly washed with anhydrous ethanol until it became a pale green transparent solution. The solid was then dried under vacuum to obtain a blue-green powder, 4-nitronickel phthalocyanine.

[0113] (2) Weigh 7.6 g (0.1 mol) of 4-nitronickel phthalocyanine and 28.8 g (0.12 mol) of sodium sulfide nonahydrate obtained in the previous step, pour them into a 500 ml round-bottom flask, add a stir bar, and then add 300 mL of DMF after dehydration (i.e., dehydration by adding molecular sieves), and stir until dissolved. Heat the mixture to 65 °C in an oil bath, increase the stirring rate, and react at 65 °C for 1 hour. After natural cooling, pour all the substances in the round-bottom flask into a 2 L beaker, fill it with distilled water, and let it stand for 48 hours. After standing, filter all the solutions, wash the product on the filter paper repeatedly with distilled water until the filtrate is no longer turbid and the surface of the solution does not peel off, following the same steps as above. Then wash with anhydrous ethanol until the filtrate is light green and transparent, and vacuum dry to obtain dark green solid powder 4-aminonickel phthalocyanine.

[0114] (3) 0.6 g (0.4 mmol) of 4-aminonickel phthalocyanine was added to 10.0 mL of dimethyl sulfoxide (DMSO). After sonication for 10 min, 0.343 g of pyromellitic dianhydride (PMDA) and 90.0 mL of DMSO were added. After sonication for 10 min, the apparatus was evacuated and nitrogen gas was introduced (the above operation was repeated 3 times, with a 3-minute interval between each step). The mixture was heated to 180 °C and refluxed for 72 h. After the reaction was completed, the mixture was cooled to room temperature. The precipitate obtained after filtration of the solution was washed several times with deionized water and acetone, and dried under vacuum at 120 °C for 12 h to obtain phthalocyanine-based covalent organic framework material (PMDA-NiPc). The characterization results are as follows: Figure 1-2 As shown.

[0115] Figure 1-2 The IR and XRD patterns of the obtained compounds are shown, with PMDA-NiPc and PMDA-NiPc@Si at approximately 1545 cm⁻¹ in the IR pattern. -1 Stretching bands corresponding to C=C bonds appeared at all locations, while this characteristic peak was absent in nano-Si, indicating that the two monomers were successfully polymerized in powder form on the surface of nano-Si to form a covalent organic framework (PMDA-NiPc). Furthermore, the Si-Si characteristic peaks in nano-Si were completely preserved in the composite structure (PMDA-NiPc@Si); PMDA-NiPc showed a peak at 1610 cm⁻¹. -1 The C=C characteristic peak at 1230 cm⁻¹ also appears in PMDA-NiPc@Si, with a peak at 1230 cm⁻¹. -1 The characteristic peak of Si=Si at this location originates from nano-Si. Figure 2 In the XRD pattern, the diffraction peaks at 2θ = 2.81° and 25.90° belong to the (100) and (001) planes of PMDA-NiPc, respectively, while the peaks at 28.4°, 47.3°, 56.1°, 68.9°, 76.4°, and 87.9° belong to the (111), (220), (311), (400), (331), and (442) planes of Si NPs, respectively. All of the above peaks are clearly present in PMDA-NiPc@Si, indicating that the structural characteristics of PMDA-NiPc@Si are consistent with expectations, and that PMDA-NiPc and Si NPs have been successfully composited, forming PMDA-NiPc@Si that combines a covalent organic framework with the structural characteristics of nano-Si.

[0116] Example 1:

[0117] According to lithium-ion battery manufacturing standards, the negative electrode material is a phthalocyanine-based covalent organic framework-coated nano-silicon composite material (PMDA-NiPc@Si) and a pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material (Li-PMDA-NiPc@Si). The counter electrode is a lithium sheet. Half-cells were prepared for testing at 0.1-1.5V, 0.05A / g, and 25℃. Cycling tests were then conducted at 0.1A / g, 1A / g, or 2A / g, and rate tests were conducted at 0.1, 0.2, 0.5, 1, 2, 3, 5, and 0.1A / g. The experimental results are as follows: Figure 4-6 As shown.

[0118] Comparative Example 1:

[0119] According to lithium-ion battery manufacturing standards, the negative electrode material is phthalocyanine-based covalent organic framework material (PMDA-NiPc), and the counter electrode is a lithium sheet. Half-cells were prepared for testing at 0.1-1.5V, 0.05A / g, and 25℃. Cycling tests were then conducted at 0.1A / g, 1A / g, or 2A / g, and rate tests were performed at 0.1, 0.2, 0.5, 1, 2, 3, 5, and 0.1A / g. The experimental results are as follows: Figure 9-11 As shown.

[0120] Comparative Example 2:

[0121] According to lithium-ion battery manufacturing standards, the negative electrode material is nano-silicon (Si), and the counter electrode is a lithium sheet. Half-cells were prepared and tested at 0.1-1.5V, 0.05A / g, and 25℃. Cycling tests were then conducted at 0.1A / g, 1A / g, or 2A / g, and rate tests were performed at 0.1, 0.2, 0.5, 1, 2, 3, 5, and 0.1A / g. The experimental results are as follows: Figure 12-14 As shown.

[0122] Figure 4 The first charge-discharge curves of the lithium-ion batteries described in Example 1, Comparative Example 1, and Comparative Example 2 are shown. As shown in the figure, the PMDA-NiPc@Si has a first-cycle discharge specific capacity of 2678 mAh / g, a charge specific capacity of 1840 mAh / g, and an initial coulombic efficiency of 68.7%, which is 23% higher than the initial coulombic efficiency (ICE) of a pure PMDA-NiPc electrode. Although it does not reach the ICE level of nano-Si, it represents a significant breakthrough given that the ICE of organic electrode materials is typically around 50%.

[0123] Figure 5Rate curves of the lithium-ion batteries described in Example 1, Comparative Example 1, and Comparative Example 2 are shown. As shown, the PMDA-NiPc@Si electrode exhibits superior rate performance, with a lithiation capacity of 1570 mAh / g at a current density of 100 mA / g and a reversible capacity of 495 mAh / g even at a very high current density of 5 A / g. Furthermore, when the current returns to the initial 100 mA / g, the capacity recovers to 1553 mAh / g, demonstrating excellent electrochemical reversibility (~100%). Compared to the PMDA-NiPc@Si electrode, the nano-Si electrode shows a higher lithiation capacity of 2920 mAh / g at a current density of 100 mA / g; however, at a current density of 5 A / g, it only exhibits a reversible capacity of 103 mAh / g, approximately 21% of that of the PMDA-NiPc@Si electrode.

[0124] Figure 6-14 Rate curves of the lithium-ion batteries described in Example 1, Comparative Example 1, and Comparative Example 2 are shown. As shown in the figure, PMDA-NiPc@Si exhibits superior cycling performance compared to nano-Si, with a capacity retention of 93.8% after 100 cycles, a 2.7-fold improvement over nano-Si. Clearly, the PMDA-NiPc@Si coating can improve the cycling stability of nano-Si. Simultaneously, PMDA-NiPc@Si maintains an ultra-high specific capacity of 1359 mAh / g after 100 cycles, 2.65 times that of pure PMDA-NiPc (512 mAh / g). At a current density of 1 A / g, the PMDA-NiPc@Si electrode shows a capacity of 1012 mAh / g, with a capacity retention of over 80% after 1000 cycles; at a high current density of 2 A / g, the initial capacity reaches 785 mAh / g, and after 2000 long cycles, it still retains 80.4% of the capacity (654 mAh / g).

[0125] It should be noted that the above-described embodiments of the present invention are only illustrative of the invention and cannot limit the invention. The claims specify the scope of the invention, while the embodiments do not specify the scope of the invention. Therefore, any changes within the meaning and scope equivalent to the claims of the present invention should be considered as included within the scope of the claims.

Claims

1. A phthalocyanine-based covalent organic framework-coated nanocrystalline silicon composite material, wherein the structural formula of the phthalocyanine-based covalent organic framework is: in, M is selected from nickel, cobalt, or manganese; U is selected from ; The average particle size of the nano-silicon is 10-100 nm; the content of nano-silicon in the composite material is 10-60%.

2. The composite material according to claim 1, characterized in that, The structural formula of the phthalocyanine covalent organic framework is as follows: 。 3. The composite material according to any one of claims 1-2, characterized in that, The phthalocyanine-based covalent organic framework is a two-dimensional network layered structure with a pore size of 2.0–4.0 nm; the average particle size of the nano-silicon is 30–80 nm; and the content of nano-silicon in the composite material is 30–50%.

4. The composite material according to claim 3, characterized in that, The phthalocyanine-based covalent organic framework is a two-dimensional network layered structure with a pore size of 3.0–3.5 nm; the average particle size of the nano-silicon is 40–60 nm.

5. A method for preparing the phthalocyanine-based covalent organic framework-coated nano-silicon composite material according to any one of claims 1-4, the method comprising the following steps: (1): Add the organic solvent and 4-R phthalonitrile to a container, and keep it warm and stirred under inert gas protection; wherein, R is selected from -NO2; (2): Heat to 70-90℃, add 1,8-diazabicycloundec-7-ene first, and when the solution turns blue, add the metal salt, and continue heating to 125-145℃ and react for 48-96 hours; wherein the metal salt is selected from the salts of nickel, cobalt and manganese, and the anion of the metal salt is at least one of chloride ion, nitrate ion, acetate ion, bisulfate ion and sulfate ion; (3): After the reaction is complete, the reaction solution is cooled and transferred to ethanol, left to stand overnight, the supernatant is discarded and filtered, and washed repeatedly with ethanol until the filtrate becomes a light green transparent solution. The solid product is dried to obtain 4-R metal phthalocyanine with R as nitro. Step (3) further includes the step of converting 4-R metal phthalocyanine with R being nitro to 4-R metal phthalocyanine with R being amino, which includes: (a): Add 4-R metal phthalocyanine with R as nitro, sodium sulfide nonahydrate, and organic solvent to a container and stir until dissolved. Heat to 50-85℃ and react at a constant temperature for 0.5-6 hours. (b): After cooling the mixture in step (a), transfer it to distilled water, let it stand for 24 to 72 hours, filter, wash and dry to obtain 4-R metal phthalocyanine with R being amino; (4): The 4-R metal phthalocyanine with R being amino obtained in step (3) and nano-silicon were added to an organic solvent, sonicated, and then the multifunctional monomer U was added to it. A The reaction is carried out under inert gas protection at 175–190 °C for 48–96 h; wherein, the multifunctional monomer U A Selected from: Ar' is selected from: ; (5): Cool the reaction mixture in step (4) to room temperature, wash and dry the precipitate obtained after filtration to obtain the phthalocyanine-based covalent organic framework-coated nano-silicon composite material.

6. A pre-lithiated phthalocyanine-based covalent organic framework-coated nanocrystalline silicon composite material, prepared by the following method: The phthalocyanine-based covalent organic framework-coated nano-silicon composite material according to any one of claims 1-4, or the phthalocyanine-based covalent organic framework-coated nano-silicon composite material prepared according to claim 5, is immersed in a lithium salt aqueous solution, filtered, washed, and dried to obtain a pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material.

7. The application of the phthalocyanine-based covalent organic framework-coated nano-silicon composite material according to any one of claims 1-4, the phthalocyanine-based covalent organic framework-coated nano-silicon composite material prepared according to claim 5, or the pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material according to claim 6 as a negative electrode material for lithium-ion batteries.

8. A lithium-ion battery anode comprising the phthalocyanine-based covalent organic framework-coated nano-silicon composite material according to any one of claims 1-4, the phthalocyanine-based covalent organic framework-coated nano-silicon composite material prepared according to claim 5, or the pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material according to claim 6 as the anode material.

9. A lithium-ion battery, the lithium-ion battery comprising: Negative electrode, positive electrode, diaphragm, electrolyte; The negative electrode comprises the phthalocyanine-based covalent organic framework-coated nano-silicon composite material according to any one of claims 1-4, the phthalocyanine-based covalent organic framework-coated nano-silicon composite material prepared according to claim 5, or the pre-lithiated phthalocyanine-based covalent organic framework-coated nano-silicon composite material according to claim 6 as the negative electrode material.

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