Preparation method and application of lithium ion battery negative electrode material based on metal organic framework structure silicon material

Abstract

The invention discloses a preparation method and application of a lithium ion battery negative electrode material based on a metal organic framework structure silicon material. The preparation method comprises the following steps: (1) preparing an MOF material: dissolving zinc ions and an organic ligand in a solvent to obtain a precursor solution, carrying out a solvothermal method reaction to obtain an MOF precursor, and drying to obtain the MOF material; (2) depositing a silicon material: uniformly distributing the silicon material in pores of the MOF material by using a plasma-assisted pulse gradient chemical vapor deposition method to obtain an MOF-Si material; and (3) preparing a carbon coating layer: forming the carbon coating layer on the surface of the MOF-Si material through a chemical vapor deposition method or a high-temperature pyrolysis method, and performing high-temperature annealing to obtain an MOF-Si-C composite material, namely the lithium ion battery negative electrode material. The lithium ion battery negative electrode material has high specific capacity and excellent cycle stability, conductivity and interface stability, and when the lithium ion battery negative electrode material is applied to a lithium ion battery negative electrode sheet, the energy density and the service life of the battery can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a preparation method and application of a lithium ion battery negative electrode material based on a metal organic framework structure silicon material. Background Art

[0002] Lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and environmentally friendly features. However, the theoretical specific capacity of traditional graphite negative electrode materials is relatively low (approximately 372mAh / g), making it difficult to meet the growing demand for high energy density. In contrast, silicon materials are considered to be an ideal choice for the next generation of negative electrode materials due to their theoretical specific capacity of up to 4200mAh / g. However, during the charge and discharge process, silicon materials will undergo severe volume expansion (approximately 300%), resulting in electrode pulverization, capacity attenuation, and shortened cycle life.

[0003] While existing technologies such as silicon-carbon composites and nanostructured silicon have been used to mitigate the volume expansion problem, these approaches still have numerous drawbacks. For example, silicon-carbon composites offer limited capacity enhancement and poor rate performance; nanostructured silicon is expensive to prepare, making it difficult to implement on a large scale; and conventional materials' inadequate optimization of lithium-ion transport also limits battery performance.

[0004] Metal-organic framework (MOF) materials show great potential in energy storage due to their high specific surface area, tunable pore structure, and excellent chemical stability. However, when used directly as anode materials, MOFs suffer from low capacity and poor conductivity. Therefore, the development of lithium-ion battery anode materials with improved performance is crucial for advancing battery technology. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a method for preparing a lithium-ion battery anode material based on a metal-organic framework silicon material and its application. The lithium-ion battery anode material prepared by the present invention addresses the volume expansion problem of silicon materials in lithium-ion battery applications while also improving the material's specific capacity, cycle stability, and rate performance.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for preparing a lithium-ion battery negative electrode material based on a metal-organic framework silicon material, the preparation method comprising the following steps:

[0008] (1) Preparation of MOF material: zinc ions and organic ligands are dissolved in a solvent to obtain a precursor solution, and then a MOF precursor is obtained by a solvothermal reaction, and the MOF material is obtained by drying;

[0009] (2) Deposition of silicon material: using plasma-assisted pulsed gradient chemical vapor deposition to uniformly distribute silicon material in the pores of the MOF material to obtain MOF-Si material;

[0010] The plasma-assisted pulsed gradient chemical vapor deposition method is implemented in three steps, including a silicon material pre-decomposition stage, a diffusion stage, and a crystallization process;

[0011] (3) Preparation of carbon coating: A carbon coating is formed on the surface of the MOF-Si material by chemical vapor deposition or high-temperature pyrolysis, and after high-temperature annealing, a MOF-Si-C composite material is obtained, i.e., the negative electrode material for lithium-ion batteries.

[0012] Furthermore, in step (1), the organic ligand is selected from any one of terephthalic acid and 2-methylimidazole; the solvent is selected from any one of DMF and methanol; the concentration of the zinc ion in the solvent is 0.1-0.5 mol / L; and the molar ratio of the zinc ion to the organic ligand is 1:1-3.

[0013] Furthermore, in step (1), the reaction temperature is 80-150°C; the pressure is 0.5-3Mpa; the time is 12-48h; and the drying method is supercritical CO2 drying technology, the temperature is 40-60°C, and the time is 6-12h.

[0014] Furthermore, in step (2), the silicon material includes any one of silicon nanoparticles or silane precursors.

[0015] Furthermore, in step (2), the flow rate of the silicon material in the pre-decomposition stage is 8-10 sccm, the temperature is 300-400°C, the deposition rate is 0.8-1.0 nm / min, and the deposition time is 30-50 min;

[0016] The diffusion stage adopts a three-zone temperature gradient control, with a heating rate of 4-6°C / min, firstly from 300°C to 440-460°C, holding for 30-50 minutes, and then continuing to heat to 540-560°C. The silicon material is pushed to penetrate along the mesoporous channels of the MOF material by H2 carrier gas, and the treatment time is 60-80 minutes; the flow rate of H2 is 15-25 sccm;

[0017] The crystallization stage uses pulsed Si2H6 auxiliary gas combined with laser irradiation to induce directional rearrangement of silicon atoms; the temperature of the crystallization stage is 540-560°C, and the time is 30-50 minutes; the pulse cycle is 10 seconds on / 5 seconds off; the wavelength of the laser irradiation is 520-540nm, and the power density is 25-35mW / cm 2 .

[0018] Furthermore, in step (3), the carbon coating layer has a three-layer structure, which is composed of a PDA transition layer, a graphene layer, and a carbon nanotube network layer from the inside to the outside; the thickness ratio of the PDA transition layer, the carbon nanotube network layer, and the graphene layer is 2:3:8; and the thickness of the carbon coating layer is 13-15 nm.

[0019] Furthermore, in step (3), the MOF-Si-C composite material has a multi-level pore structure, including micropores, mesopores and macropores; and the porosity of the MOF-Si-C composite material is greater than 85%.

[0020] Furthermore, the micropores account for 60-65%; the mesopores account for 30-35%; and the macropores account for 5-10%.

[0021] An application of a lithium ion battery negative electrode material prepared by the preparation method, wherein the lithium ion battery negative electrode material is used to prepare a lithium ion battery negative electrode sheet.

[0022] Furthermore, the application method is: mixing the lithium ion battery negative electrode material, conductive agent and adhesive to form a slurry, coating the slurry on copper foil, and drying and pressing the slurry to obtain a lithium ion battery negative electrode sheet.

[0023] The beneficial technical effects of the present invention are:

[0024] The metal-organic framework-based silicon-based lithium-ion battery anode material prepared by this invention uses multi-level pores to buffer silicon volume expansion, improving the battery's cycling stability and achieving a capacity retention rate of >95% after 500 cycles. By constructing a gradient carbon layer to enhance conductivity, the specific capacity reaches 2060.1 mAh / g. This metal-organic framework-based silicon-based lithium-ion battery anode material is suitable for high-energy-density lithium-ion battery anode sheets, significantly extending battery life.

[0025] Compared to traditional silicon-carbon anodes, which have a single pore structure (dominated by mesopores) and cannot achieve both high specific capacity and expansion suppression, the present invention, through the synergistic effect of multi-level pores, achieves for the first time a silicon-based anode with a capacity retention rate of >95% after 500 cycles.

[0026] The present invention achieves a synergistic improvement in specific capacity (2060.1 mAh / g), cycle stability (>95% after 500 cycles) and conductivity (impedance <20Ω) through multi-level pores, CVD silicon deposition and gradient carbon coating technology, significantly improving the electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an SEM image of the lithium-ion battery negative electrode material prepared in Example 1 of the present invention.

[0028] Figure 2This is an AC impedance test diagram of a button battery prepared using the lithium-ion battery negative electrode sheets of Example 1 and Comparative Examples 3-4 of the present invention.

[0029] Figure 3 The charge and discharge curves of button batteries prepared using the lithium-ion battery negative electrode sheets of Example 1 and Comparative Examples 3-4 of the present invention are shown. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0031] The porosity of the material in the present invention is measured by combining nitrogen adsorption-desorption isotherms (BET method) and mercury intrusion porosimetry; the micropore distribution is analyzed using the Horvath-Kawazoe (HK) model; the mesopore distribution is calculated using the Barrett-Joyner-Halenda (BJH) model; the macropore structure is characterized by a mercury intrusion porosimeter under a high pressure of 414 MPa; and the overall pore volume distribution is verified by small-angle X-ray scattering (SAXS).

[0032] Example 1

[0033] A method for preparing a lithium-ion battery negative electrode material based on a metal-organic framework silicon material is as follows:

[0034] (1) Preparation of MOF material: 0.08 mol of zinc nitrate and 0.08 mol of terephthalic acid were dissolved in 200 mL of DMF and stirred until dissolved to obtain a precursor solution. The MOF precursor was then obtained by a solvothermal method at 120°C and 1.5 MPa for 30 h. The MOF material was then obtained by drying with supercritical CO2 at 50°C for 9 h.

[0035] (2) Deposition of silicon material: Using plasma-assisted pulsed gradient chemical vapor deposition process to load silicon:

[0036] ① In the pre-decomposition stage, a SiH4 / Ar mixture (5% SiH4) was introduced at a flow rate of 10 sccm and decomposed by radio frequency plasma (power 50 W, frequency 13.56 MHz) at 300°C to form 2-3 nm silicon quantum dot clusters (deposition rate 0.8 nm / min) for 30 minutes;

[0037] ②Diffusion stage: Using three-zone gradient control, the temperature was first raised from 300°C to 450°C at a heating rate of 5°C / min, kept at this temperature for 40 minutes, and then continued to rise to 550°C. H2 carrier gas (flow rate 20 sccm) was used to push silicon atoms to penetrate along the mesoporous channels of the MOF material (penetration depth > 200 μm). The treatment time was 60 minutes.

[0038] ③ During the crystallization stage, pulsed Si2H6 auxiliary gas (pulse cycle 10s on / 5s off) was introduced into an argon atmosphere at 550℃, and at the same time, a wavelength of 532nm and 30mW / cm 2 Laser irradiation was performed at a power density of 30 minutes to induce directional rearrangement of silicon atoms, and finally a β-Si phase with a crystallinity of >95% (XRD half-peak width 0.12°) was obtained to obtain MOF-Si material.

[0039] (3) Preparation of carbon coating: A carbon coating was constructed on the surface of MOF-Si material by plasma-enhanced pulsed chemical vapor deposition: First, 0.25g of polydopamine was mixed with 5g of MOF-Si material, and a single-layer polydopamine transition layer (2nm) was formed on the surface of MOF-Si material through self-assembly as an interface enhancement layer. Subsequently, argon / hydrogen plasma activation was performed at 400℃ and 50Pa, and acetylene (5ms pulse) and methane (20ms pulse) were introduced in an alternating pulse mode, thereby directionally growing wrinkled graphene (8nm) with nitrogen-doped sites on the amorphous carbon matrix. Then, argon / hydrogen plasma activation was performed at 800℃ and 50Pa, and 8g of FeCo@Mo bimetallic catalyst was added. Acetylene (5ms pulse) and methane (20ms pulse) were introduced in an alternating pulse mode, forming a composite network of single-layer helical carbon nanotubes (3nm). In-situ laser annealing technology was used to achieve nanometer-level precise control of the carbon layer thickness. Finally, MOF-Si-C composite material was obtained by high temperature pyrolysis at 800℃ for 2h, which is the negative electrode material of lithium ion battery (SEM picture as shown in Figure 2). Figure 1 shown).

[0040] After testing, it was found that the number of graphene layers is 3-5, and the interlayer spacing is 0.38nm; the single-layer spiral carbon nanotube network layer is a unique double-wall-triple-wall alternating structure (inner wall spacing 0.34nm, outer wall spacing 0.39nm), the tube diameter is 6-8nm and the axial direction has a periodic bamboo-node morphology (node spacing 10-15nm).

[0041] The pore structure of the MOF-Si-C composite material exhibits a multi-level distribution: micropores (<2nm) account for 65%, mesopores (2-50nm) account for 30%, and macropores (>50nm) account for approximately 5%. The silicon crystallization process transforms 5-15% of the micropores into mesopores (pore diameter 2-5nm), but the graphene / carbon nanotube composite structure coating suppresses the collapse of the pore structure. Atomic force microscopy (AFM) phase imaging confirms that the composite carbon layer exhibits a gradient thickness distribution of 13±2nm (the surface layer is a carbon nanotube network of 3nm, the middle layer is dense graphene of 8nm, and the bottom layer is a PDA transition layer of 2nm), ultimately maintaining a porosity of 90%.

[0042] Example 2

[0043] (1) Preparation of MOF material: 0.02 mol zinc nitrate and 0.02 mol terephthalic acid were dissolved in 200 mL DMF and stirred until dissolved to obtain a precursor solution. The precursor solution was then reacted by a solvothermal method at 80°C and 0.5 MPa for 12 h, and dried by supercritical CO2 at 40°C for 6 h to obtain the MOF material.

[0044] (2) Deposition of silicon material: Using plasma-assisted pulsed gradient chemical vapor deposition process to load silicon:

[0045] ① In the pre-decomposition stage, SiH4 / Ar (SiH4 accounts for 5%) is introduced at a flow rate of 8 sccm, and radio frequency plasma (50W, 13.56MHz) is treated at 300℃ for 30min to form 2-3nm silicon quantum dot clusters (deposition rate 0.8nm / min).

[0046] ②Diffusion stage, three-zone gradient control is adopted, with a heating rate of 5℃ / min, first from 300℃ to 450℃, keeping warm for 40min, and then continuing to heat up to 550℃. H2 carrier gas (flow rate 20sccm) is used to promote silicon atom penetration, and the processing time is 60min.

[0047] ③ During the crystallization stage, pulsed Si2H6 auxiliary gas (pulse cycle 10s on / 5s off) was introduced into an argon atmosphere at 550℃, at a wavelength of 532nm and a power of 30mW / cm 2 Laser irradiation was performed at a power density of 30 minutes to induce directional rearrangement of silicon atoms, and finally a β-Si phase with a crystallinity of >95% (XRD half-peak width 0.12°) was obtained to obtain MOF-Si material.

[0048] (3) Preparation of carbon coating: A carbon coating was constructed on the surface of MOF-Si material by plasma-enhanced pulsed chemical vapor deposition: First, 0.2g of polydopamine was mixed with 5g of MOF-Si material, and a single-layer polydopamine transition layer (2nm) was formed on the surface of MOF-Si material through self-assembly as an interface enhancement layer. Subsequently, argon / hydrogen plasma activation was performed at 400℃ and 50Pa, and acetylene (5ms pulse) and methane (20ms pulse) were introduced in an alternating pulse mode, thereby directionally growing wrinkled graphene (8nm) with nitrogen-doped sites on the amorphous carbon matrix. Then, argon / hydrogen plasma activation was performed at 800℃ and 50Pa, and 8g of FeCo@Mo bimetallic catalyst was added. Acetylene (5ms pulse) and methane (20ms pulse) were introduced in an alternating pulse mode, forming a composite network of single-layer helical carbon nanotubes (3nm). In-situ laser annealing technology was used to achieve nanometer-level precise control of the carbon layer thickness. Finally, the MOF-Si-C composite material, i.e., the negative electrode material for lithium-ion batteries, was obtained by high-temperature pyrolysis at 800°C for 2h.

[0049] The MOF-Si-C composite material exhibits a hierarchical pore structure: micropores (<2nm) account for 60%, mesopores (2-50nm) account for 35%, and macropores (>50nm) account for approximately 5%. Phase imaging using an atomic force microscope (AFM) confirmed that the composite carbon layer exhibits a gradient thickness distribution of 13±2nm (a 3nm surface layer of carbon nanotube network, an 8nm middle layer of dense graphene, and a 2nm bottom layer of PDA transition layer), resulting in a porosity of 86%.

[0050] Example 3

[0051] (1) Preparation of MOF material: 0.1 mol zinc nitrate and 0.3 mol 2-methylimidazole were dissolved in 200 mL methanol and stirred until dissolved to obtain a precursor solution. The precursor solution was then reacted at 150°C and 3 MPa for 48 h by a solvothermal method and dried with supercritical CO2 at 60°C for 12 h to obtain the MOF material.

[0052] (2) Deposition of silicon material: Using plasma-assisted pulsed gradient chemical vapor deposition process to load silicon:

[0053] ① In the pre-decomposition stage, SiH4 / Ar (SiH4 accounts for 5%) is introduced at a flow rate of 10 sccm, and radio frequency plasma (50W, 13.56MHz) is treated at 400℃ for 50min to form 2-3nm silicon quantum dot clusters (deposition rate 1.0nm / min).

[0054] ②Diffusion stage, three-zone gradient control is adopted, with a heating rate of 5℃ / min, first from 300℃ to 450℃, kept warm for 40min, and then continued to heat up to 550℃. H2 carrier gas (flow rate 20sccm) is used to promote silicon atom penetration, and the processing time is 80min.

[0055] ③ During the crystallization stage, pulsed Si2H6 auxiliary gas (pulse cycle 10s on / 5s off) was introduced into an argon atmosphere at 550℃, at a wavelength of 532nm and a power of 30mW / cm 2 Laser irradiation was performed at a power density of 50 min to induce directional rearrangement of silicon atoms, and finally a β-Si phase with a crystallinity of >95% (XRD half-peak width 0.12°) was obtained to obtain MOF-Si material.

[0056] (3) Preparation of carbon coating: A carbon coating was constructed on the surface of MOF-Si material by plasma-enhanced pulsed chemical vapor deposition: First, 0.3g of polydopamine was mixed with 5g of MOF-Si material, and a single-layer polydopamine transition layer (2nm) was formed on the surface of MOF-Si material through self-assembly as an interface enhancement layer. Subsequently, argon / hydrogen plasma activation was performed at 400℃ and 50Pa, and acetylene (5ms pulse) and methane (20ms pulse) were introduced in an alternating pulse mode, thereby directionally growing wrinkled graphene (8nm) with nitrogen-doped sites on the amorphous carbon matrix. Then, argon / hydrogen plasma activation was performed at 800℃ and 50Pa, and 8g of FeCo@Mo bimetallic catalyst was added. Acetylene (5ms pulse) and methane (20ms pulse) were introduced in an alternating pulse mode, forming a composite network of single-layer helical carbon nanotubes (3nm). In-situ laser annealing technology was used to achieve nanometer-level precise control of the carbon layer thickness. Finally, the MOF-Si-C composite material, i.e., the negative electrode material for lithium-ion batteries, was obtained by high-temperature pyrolysis at 800°C for 2h.

[0057] The MOF-Si-C composite material exhibits a hierarchical pore structure: micropores (<2nm) account for 65%, mesopores (2-50nm) account for 30%, and macropores (>50nm) account for 5%. Atomic force microscopy (AFM) phase imaging confirmed that the composite carbon layer exhibits a gradient thickness distribution of 13±2nm (a 3nm surface layer of carbon nanotube network, an 8nm middle layer of dense graphene, and a 2nm bottom layer of PDA transition layer), with a porosity of 88%.

[0058] Application Example 1

[0059] Prepare the negative electrode sheet of lithium-ion battery as follows:

[0060] The MOF-Si-C composite material prepared in Example 1, the SuperP conductive agent, and the polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) solvent was added to prepare a slurry, which was coated on a copper foil and pressed into a sheet after drying to obtain a lithium-ion battery negative electrode sheet.

[0061] Comparative Example 1

[0062] A preparation method of a MOF-C composite material based on a lithium-ion battery negative electrode material is as follows:

[0063] (1) Preparation of MOF material: The process is basically the same as step (1) of Example 1, except that conventional vacuum drying at 60°C for 24 h is used instead of the supercritical CO2 drying method in Example 1, and the rest remains unchanged.

[0064] (2) Preparation of carbon coating layer: same as step (3) of Example 1.

[0065] The test showed that the capillary force caused the pores to collapse during the drying process, and the carbon coating was directly coated without silane precursor treatment, resulting in a final porosity of only 68% and a BET specific surface area of 950m 2 Pore structure analysis showed that the proportion of micropores dropped sharply to 38% (<2nm), the proportion of mesopores increased abnormally to 52% (2-50nm), and the proportion of macropores was 10% (>50nm).

[0066] Comparative Example 2

[0067] A method for preparing a lithium-ion battery negative electrode material based on a metal-organic framework silicon material is as follows:

[0068] (1) Preparation of MOF material: same as step (1) in Example 1.

[0069] (2) Deposition of silicon material: silicon was loaded using conventional thermal CVD method: pure SiH4 (20 sccm) was continuously introduced at a constant temperature of 550°C, with a deposition rate of 1.2 nm / min and a deposition time of 60 min.

[0070] (3) Preparation of carbon coating: A homogeneous carbon layer (25 nm thick) without carbon nanotube structure was grown using a single methane source CVD. After treatment at 800°C for 2 h, the negative electrode material for lithium-ion batteries was obtained.

[0071] The results showed that high temperature caused the silicon particles to agglomerate rapidly (particle size 50-80nm), blocking the MOF pores. The proportion of micropores was reduced to 47%, of which micropores <1nm disappeared completely; the BET surface area was 1200m 2 Mercury intrusion curves showed that the 30-50 nm mesopores were blocked by silicon particles (the cumulative pore volume decreased by 38%), and SAXS confirmed that the pore tortuosity index increased to 4.7.

[0072] Comparative Example 3

[0073] A method for preparing a negative electrode material for a lithium-ion battery is as follows:

[0074] 0.2 mol of silicon nanoparticles were immersed in 500 mL of a methanol solution containing 0.4 mol / L zinc nitrate and 0.8 mol / L 2-methylimidazole and allowed to stand at room temperature for 24 hours. The product was washed with methanol and dried to obtain a silicon material based on the ZIF-8 structure.

[0075] Comparative Example 4

[0076] A method for preparing a negative electrode material for a lithium-ion battery is as follows:

[0077] 0.1 mol of mesoporous silica (MCM-41, Sigma-Aldrich Product No. 643645) was immersed in 500 mL of toluene solution containing 0.1 mol / L 3-aminopropyltriethoxysilane and refluxed for 12 hours. The product was washed with toluene and dried to obtain amino-modified mesoporous silica. The amino-modified mesoporous silica was then immersed in 500 mL of N,N-dimethylformamide solution containing 0.3 mol / L copper nitrate and 1.0 mol / L trimesic acid at 80°C for 24 hours. The product was washed with N,N-dimethylformamide and dried to obtain a silicon material based on the HKUST-1 structure.

[0078] Comparative Application Example 1

[0079] The negative electrode sheet of a lithium-ion battery was prepared by a preparation method that was substantially the same as that in Application Example 1, except that the MOF-C composite material prepared in Comparative Example 1 was used instead of the MOF-Si-C composite material, and the rest of the contents remained unchanged.

[0080] Application Comparative Example 2

[0081] The negative electrode sheet of a lithium ion battery was prepared. The preparation method was basically the same as that in Application Example 1, except that the negative electrode material of the lithium ion battery prepared in Comparative Example 2 was used instead of the MOF-Si-C composite material, and the rest of the contents remained unchanged.

[0082] Application Comparative Example 3

[0083] The negative electrode sheet of a lithium-ion battery was prepared by a preparation method that was substantially the same as that in Application Example 1, except that the ZIF-8 structured silicon material prepared in Comparative Example 3 was used to replace the MOF-Si-C composite material, and the rest of the contents remained unchanged.

[0084] Comparative Application Example 4

[0085] Prepare the negative electrode sheet of lithium-ion battery as follows:

[0086] The HKUST-1 structure-based silicon material prepared in Comparative Example 4, acetylene black conductive agent, and sodium carboxymethyl cellulose (CMC) binder were mixed in a mass ratio of 7:2:1, and N-methylpyrrolidone (NMP) solvent was added to prepare a slurry. The slurry was coated on copper foil, dried, and pressed into a sheet to obtain a lithium-ion battery negative electrode sheet.

[0087] Test Case

[0088] (1) Structural characterization of lithium-ion battery anode materials

[0089] The specific surface area, porosity, and pore size distribution characteristics of the lithium ion battery negative electrode materials prepared in Example 1 of the present invention and Comparative Examples 1-2 were tested, and the results are shown in Table 1.

[0090] Table 1 Structural characterization

[0091]

[0092] As can be seen from Table 1, the lithium-ion battery negative electrode material prepared by using supercritical CO2 drying method to dry MOF precursor, plasma-assisted pulse gradient chemical vapor deposition method to deposit silicon material, and three-layer carbon coating layer can significantly increase the BET specific surface area of the material, avoid pore collapse, maintain the proportion of micropores, and thus improve material performance.

[0093] (2) Impedance test of lithium-ion battery negative electrode

[0094] The impedance performance of the lithium-ion battery negative electrode sheets corresponding to the application examples and the comparative examples of the present invention were tested using button batteries.

[0095] Coin cell preparation: In a glove box, a lithium-ion battery negative electrode sheet, Celgard 2400 polypropylene separator, and lithium metal sheet were stacked to ensure isolation between the two electrodes. A 1M LiPF6 EC / DMC / DEC (1:2:1 v / v) electrolyte (300 μL) was then injected and packaged under vacuum to form a CR2032 coin cell.

[0096] The impedance of the button batteries prepared by the lithium ion battery negative electrode sheets of Application Example 1 and Comparative Examples 3-4 of the present invention was tested by the impedance test item in the electrochemical workstation. The results are as follows: Figure 2 As shown. Figure 2 The results show that the high-frequency and low-frequency impedances of the button cell corresponding to the lithium-ion battery negative electrode sheet prepared in Example 1 of the present invention are the smallest. This is because the gradient carbon coating in the MOF-Si-C composite material reduces the interfacial impedance, provides porous support and lithium ion transmission channels; in addition, the silicon material distributed in the MOF pores can effectively provide expansion margin for the structural changes caused by volume expansion. In addition, the graphene / carbon nanotube composite structure coated on the surface of the MOF structure also improves the conductivity and structural stability of the material, thereby reducing impedance. The synergistic effect generated by this structure achieves excellent electrochemical performance.

[0097] (3) Peel force test:

[0098] The negative electrode sheets of the lithium-ion batteries prepared in the application examples and the application comparison examples were peeled off at 180°, and the peeling strength was used to measure the bonding performance between the negative electrode coating material and the current collector (copper foil).

[0099] Testing was performed using an intelligent electronic tensile testing machine. The adhesion strength of the coating on the electrode surface was evaluated by measuring the force required to peel the coating from the copper foil using adhesive tape. The test fixture was fixed in the lower fixture, which remained stationary. The free end of the copper foil was secured in the upper fixture, and the adhesive tape used to apply the coating was secured in the lower fixture. The fixture moved upward at a set speed, driving the adhesive tape to peel the coating from the foil. A force sensor in the upper fixture recorded the force generated during the peeling process in real time, and the average force was recorded as the peeling force of the electrode coating. The results are shown in Table 2.

[0100] Table 2 Peeling force

[0101] Peel force (N / 25mm) Example 1 15.3 Comparative Example 1 5.2 Comparative Example 2 8.1 Comparative Example 3 3.7 Comparative Example 4 4.5

[0102] As can be seen from the results in Table 2, the negative electrode sheet of the lithium-ion battery prepared by the method of the present invention has high glass strength and better bonding performance. The present invention enhances the performance of the negative electrode sheet of the lithium-ion battery through the synergistic effect of the gradient carbon coating layer. The PDA transition layer enhances the bonding strength between the carbon layer and the MOF-Si interface (peeling force>15N / m). This is because the catechol group of polydopamine coordinates and bonds with the MOF surface to form a strong chemical adsorption (FTIR shows a characteristic peak of CO-Zn bond). At the same time, the carbon nanotube network layer constructs a three-dimensional conductive path and reduces the charge transfer impedance (<20Ω). This is because the FeCo@Mo bimetallic catalyst induces the carbon nanotubes to form a helical structure (TEM shows a helical angle of 15-20°), increasing the conductive contact points (EIS shows a 70% reduction in interface impedance). In addition, the graphene layer can inhibit the electrode pulverization caused by silicon volume expansion and stabilize the SEI film. This is because the wrinkled graphene (0.38nm interlayer spacing) mechanically encapsulates silicon particles, limiting their displacement (AFM shows surface deformation <5nm), and its hydrophobicity reduces side reactions (XPS shows the LiF content in the SEI increases to 35%). Compared to traditional single carbon coatings, which lack a gradient design and cannot balance conductivity and mechanical strength (the carbon layer cracking rate after cycling is >30%), the gradient carbon layer of the present invention reduces the cracking rate to <5%.

[0103] (4) Characterization of electrochemical performance of lithium-ion battery negative electrode

[0104] The electrochemical performance of the lithium-ion battery negative electrode sheets corresponding to the application examples and the comparative examples of the present invention were tested using button batteries. The results are shown in Table 3 and the accompanying drawings. The specific testing method is as follows:

[0105] Coin cell preparation: In a glove box, a lithium-ion battery negative electrode sheet, Celgard 2400 polypropylene separator, and lithium metal sheet were stacked to ensure isolation between the two electrodes. A 1M LiPF6 EC / DMC / DEC (1:2:1 v / v) electrolyte (300 μL) was then injected and packaged under vacuum to form a CR2032 coin cell.

[0106] Electrochemical testing was conducted at room temperature (25±1)°C using a LAND CT2001A battery charger and discharge instrument. Specific capacity, rate capability, and cycle performance were measured using constant current charge and discharge. The results are shown in Table 1 and the accompanying figures. Cycle performance measured the reversible capacity after 500 cycles. A current of 0.5C was used for the charge and discharge capacity tests. Test parameters were set: the charge and discharge voltage range was 0.01V to 3.0V.

[0107] Rate performance tests the charge and discharge capacity of lithium-ion batteries at different currents at room temperature. Currents are tested at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 10C, and then back to 0.1C. This test primarily tests the battery's charge and discharge performance at high currents, followed by a return to a low current of 0.1C, to investigate the stability of the material.

[0108] The electrochemical impedance spectroscopy (EIS) test was performed using a CHI760E electrochemical workstation manufactured by Shanghai Chenhua Instrument Co., Ltd. The test frequency range was 0.01 Hz to 1000 kHz, and the amplitude was 5 mV.

[0109] Table 3 Electrochemical performance

[0110]

[0111] As shown in Table 3, the negative electrode sheet of lithium-ion battery prepared by the method of the present invention exhibits higher charge and discharge specific capacity, first efficiency and more stable long cycle life performance than the comparative example. The MOF-Si-C composite material of the present invention has a multi-level pore structure. Among them, micropores (<2nm) account for 60-65%, which can provide ultra-high specific surface area (>2200m 2 / g), exposing more lithium ion adsorption sites and improving the material's specific capacity. This is because the micropores fix silicon nanoparticles (particle size 2-5nm) through physical confinement to prevent them from agglomerating. The narrow pores can shorten the lithium ion diffusion path (the diffusion coefficient is increased to 3×10-10cm 2 / s), reducing polarization. Mesopores (2-50nm) account for 30-35%, which can buffer the volume expansion of silicon during lithium insertion / delithiation (the expansion rate is reduced from 300% to 120%) and inhibit electrode pulverization. This is because the mesopores act as "elastic space" to accommodate silicon expansion, and their curved channels disperse stress concentration (finite element simulation shows that the stress peak is reduced by 65%), avoiding channel collapse. Macropores (>50nm) account for 5-10%, which can promote electrolyte penetration and improve ion transfer efficiency (ionic conductivity>8.5×10-3S / cm). This is because the macropores form a three-dimensional interconnected network, shorten the electrolyte infiltration path (penetration time is reduced from 30min to 5min), and accelerate lithium ion migration through capillary action.

[0112] Figure 3 The gram capacity of the lithium-ion battery negative electrode sheet for button batteries is as follows: Figure 3 As shown. Figure 3 The results show that the lithium-ion battery negative electrode sheet prepared by Example 1 of the present invention has the highest gram capacity (2060.1 mAh / g), and the first-cycle efficiency can reach 91.6%. This is because the high theoretical specific capacity of the silicon material is combined with the high specific surface area of the MOF structure, which significantly improves the specific capacity of the negative electrode material. At the same time, the pores of the MOF structure can effectively alleviate the volume expansion of the silicon material during the charge and discharge process (reduced to 120%), and the carbon coating layer also enhances the conductivity of the material.

[0113] The present invention uses a plasma-assisted pulse gradient chemical vapor deposition process to load silicon, which can make silicon evenly distributed, avoid silicon particle agglomeration (particle size is controlled at 5-10nm), and improve material utilization (first effect >91%). This is because the CVD process uses plasma-assisted decomposition to direct the nucleation of the silane precursor in the MOF pores, combined with gradient temperature control to achieve atomic-level uniform deposition (EDS surface scanning shows that the silicon distribution uniformity is >95%). At the same time, the silicon can protect the pore structure after deposition, and the porosity of the lithium-ion battery negative electrode material after deposition is still >85%, which can maintain the lithium ion transmission channel. This is because silicon quantum dots are formed in the low-temperature pre-decomposition stage (300-400℃), avoiding high temperature (>600℃) causing the MOF skeleton to collapse (XRD shows that the MOF crystallinity remains >90%). Compared with the traditional ball milling mixing method that causes silicon particles to block the pores (porosity <70%), the present invention uses plasma-assisted pulse gradient chemical vapor deposition in situ deposition to achieve precise silicon-pore matching.

[0114] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiment. It is understood that other improvements and variations directly derived or imagined by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-ion battery negative electrode material based on a metal-organic framework silicon material, characterized in that: The preparation method comprises the following steps: (1) Preparation of MOF material: zinc ions and organic ligands are dissolved in a solvent to obtain a precursor solution, and then a MOF precursor is obtained by a solvothermal reaction, and the MOF material is obtained by drying; (2) Depositing silicon material: using plasma-assisted pulsed gradient chemical vapor deposition to uniformly distribute silicon material in the pores of the MOF material to obtain MOF-Si material; The plasma-assisted pulsed gradient chemical vapor deposition method is implemented in three steps, including a silicon material pre-decomposition stage, a diffusion stage, and a crystallization process; (3) Preparation of carbon coating: A carbon coating is formed on the surface of the MOF-Si material by chemical vapor deposition or high-temperature pyrolysis, and after high-temperature annealing, a MOF-Si-C composite material is obtained, i.e., the negative electrode material for lithium-ion batteries.

2. The preparation method according to claim 1, characterized in that In step (1), the organic ligand is selected from any one of terephthalic acid and 2-methylimidazole; the solvent is selected from any one of DMF and methanol; the concentration of the zinc ion in the solvent is 0.1-0.5 mol / L; and the molar ratio of the zinc ion to the organic ligand is 1:1-3.

3. The preparation method according to claim 1, characterized in that In step (1), the reaction temperature is 80-150°C; the pressure is 0.5-3Mpa; the time is 12-48h; the drying method is supercritical CO2 drying technology, the temperature is 40-60°C, and the time is 6-12h.

4. The preparation method according to claim 1, characterized in that In step (2), the silicon material includes any one of silicon nanoparticles or silane precursors.

5. The preparation method according to claim 1, characterized in that In step (2), the flow rate of the silicon material in the pre-decomposition stage is 8-10 sccm, the temperature is 300-400°C, the deposition rate is 0.8-1.0 nm / min, and the deposition time is 30-50 min; The diffusion stage adopts a three-zone temperature gradient control, with a heating rate of 4-6°C / min, firstly from 300°C to 440-460°C, holding for 30-50 minutes, and then continuing to heat to 540-560°C. The silicon material is pushed to penetrate along the mesoporous channels of the MOF material by H2 carrier gas, and the treatment time is 60-80 minutes; the flow rate of H2 is 15-25 sccm; The crystallization stage uses pulsed Si2H6 auxiliary gas combined with laser irradiation to induce directional rearrangement of silicon atoms; the temperature of the crystallization stage is 540-560°C, and the time is 30-50 minutes; the pulse cycle is 10 seconds on / 5 seconds off; the wavelength of the laser irradiation is 520-540nm, and the power density is 25-35mW / cm 2 .

6. The preparation method according to claim 1, characterized in that In step (3), the carbon coating layer has a three-layer structure, which is composed of a PDA transition layer, a graphene layer, and a carbon nanotube network layer from the inside to the outside; the thickness ratio of the PDA transition layer, the carbon nanotube network layer, and the graphene layer is 2:3:8; and the thickness of the carbon coating layer is 13-15 nm.

7. The preparation method according to claim 1, characterized in that In step (3), the MOF-Si-C composite material has a multi-level pore structure, including micropores, mesopores and macropores; the porosity of the MOF-Si-C composite material is greater than 85%.

8. The preparation method according to claim 7, characterized in that The micropores account for 60-65%; the mesopores account for 30-35%; and the macropores account for 5-10%.

9. An application of a lithium ion battery negative electrode material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The lithium ion battery negative electrode material is used to prepare a lithium ion battery negative electrode sheet.

10. The use according to claim 9, characterized in that The application method comprises the following steps: mixing the lithium ion battery negative electrode material, a conductive agent and an adhesive to prepare a slurry, coating the slurry on a copper foil, and drying and pressing the slurry to obtain a lithium ion battery negative electrode sheet.

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