High-cycle battery negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of battery electrode materials, in particular to a high-cyclicity battery negative electrode material and a preparation method thereof, and the high-cyclicity battery negative electrode material comprises a core body and a shell layer; the core body is a metal organic framework derived porous carbon matrix, silicon quantum dots are loaded in three-dimensional channels of the matrix, and the silicon quantum dots are combined with the porous carbon matrix through Si-O-C covalent bonds; the shell layer is a dynamic cross-linked polymer coating coated on the surface of the core body, and the coating is formed by dynamically cross-linking oxidized polyvinyl alcohol and dopamine through a Schiff base bond. A core-shell structure is constructed, silicon quantum dots are loaded by porous carbon three-dimensional channels, Si-O-C bonds are formed, and the surface is coated with a dynamic cross-linked polymer coating. According to the structure, through dynamic reversible characteristics of covalent bonding and Schiff base bonds, multi-stage buffering of uniform dispersion and volume expansion of the silicon quantum dots is realized, so that the capacity retention rate of the battery is greater than or equal to 90% and the pole piece expansion rate is less than or equal to 12% after 1000 times of circulation at 1C multiplying power, and the problem of structural collapse of the silicon-based negative electrode is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of battery electrode materials technology, specifically to a high-cycle battery anode material and its preparation method. Background Technology

[0002] With the widespread application of lithium-ion batteries in the new energy field, higher requirements have been placed on the energy density and cycle stability of electrode materials. Traditional graphite anodes, due to their low theoretical specific capacity, are no longer sufficient to meet the development needs of high-capacity batteries. Silicon-based materials, with their ultra-high theoretical specific capacity of 4200 mAh / g, have gradually become the focus of anode material research. In recent years, researchers have continuously explored ways to improve the volume expansion and poor cycle performance of silicon-based materials through the design of nanostructures, composite carbon materials, and surface coatings, accumulating a substantial research foundation for their practical application.

[0003] Despite some progress in the research of silicon-based anode materials, many challenges remain in practical applications. While nano-silicon particles can alleviate volume expansion, their high surface energy makes them prone to aggregation, leading to a decrease in active area. In carbon composite systems, silicon and the carbon matrix are often physically combined, resulting in insufficient interfacial compatibility. During charge-discharge cycles, volume changes can easily cause interfacial separation, leading to structural collapse. Surface coatings often use rigid polymers or inorganic materials, lacking dynamic adjustment capabilities and unable to adapt to the repeated expansion and contraction of silicon-based materials. After long-term cycling, the coating is prone to cracking and cannot effectively prevent electrolyte penetration. These problems collectively restrict the improvement of cycle life and structural stability of silicon-based anode materials. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned problems and provide a high-cycle battery anode material and its preparation method. To achieve the above objective, this invention adopts the following technical solution:

[0005] A high-cycle battery anode material has a core-shell structure, comprising a core and a shell. The core is a metal-organic framework-derived porous carbon matrix, with silicon quantum dots loaded in the three-dimensional channels of the matrix. The silicon quantum dots are bonded to the porous carbon matrix via Si-OC covalent bonds. The shell is a dynamically cross-linked polymer coating covering the surface of the core. The coating is formed by the dynamic cross-linking of oxidized polyvinyl alcohol and dopamine via Schiff base bonds.

[0006] Furthermore, the precursor for the metal-organic framework-derived porous carbon matrix is ​​a ZIF-8 zeolite imidazole framework, with a pore size of 5-20 nm and a specific surface area of ​​800-1200 m². 2 / g, with a porosity of 40-50%.

[0007] Furthermore, the silicon quantum dots have a particle size of 3-5 nm and a loading of 15-25 wt% in the porous carbon matrix. The silicon quantum dots are uniformly dispersed in the three-dimensional channels of the porous carbon matrix without obvious agglomeration.

[0008] Furthermore, in the dynamic cross-linked polymer coating, the mass ratio of oxidized polyvinyl alcohol to dopamine is 3:1, the degree of cross-linking is 30-50%, and the coating thickness is 5-10 nm.

[0009] Furthermore, the tap density of the negative electrode material is 1.2-1.5 g / cm³. 3 Under 25℃ and 1C charge-discharge conditions, the capacity retention rate after 1000 cycles is ≥90%, and the electrode volume expansion rate is ≤12%.

[0010] Furthermore, a method for preparing a high-cycle-performance battery anode material includes the following steps:

[0011] (1) Preparation of metal-organic framework-derived porous carbon matrix: The ZIF-8 precursor was heated to 750-850℃ in a nitrogen atmosphere at a heating rate of 5℃ / min, carbonized for 2-3 hours, and then cooled to obtain a three-dimensional porous carbon matrix.

[0012] (2) In-situ loaded silicon quantum dots: The porous carbon matrix obtained in step (1) is dispersed in ethanol, silicon source and catalyst are added, and SiO2 precursor is generated in the pores of the porous carbon matrix through sol-gel reaction. Then, a reducing agent is added to reduce SiO2 to silicon quantum dots to obtain silicon quantum dot loaded porous carbon composite material.

[0013] (3) Coating with dynamic cross-linked polymer coating: Disperse the composite material obtained in step (2) in an aqueous solution, add oxidized polyvinyl alcohol and dopamine, and adjust the pH of the system to 8.0-9.0; stir at 50-60℃ for 3-5 hours to allow oxidized polyvinyl alcohol and dopamine to form a polymer coating through dynamic cross-linking of Schiff base bonds; after drying, the target negative electrode material is obtained.

[0014] Further, in step (1), the ZIF-8 precursor is prepared by reacting zinc nitrate and 2-methylimidazole in methanol solvent at room temperature for 24-36 hours, with the molar ratio of zinc nitrate to 2-methylimidazole being 1:3-1:5.

[0015] Further, in step (2), the silicon source is tetraethyl orthosilicate, the catalyst is ammonia water with a concentration of 25-28%, and the reducing agent is NaBH4; the particle size of silicon quantum dots is adjusted to 3-5 nm by controlling the amount of tetraethyl orthosilicate added.

[0016] Further, in step (3), the molecular weight of oxidized polyvinyl alcohol is 70,000-90,000, the mass ratio of oxidized polyvinyl alcohol to dopamine is 3:1, the concentration of oxidized polyvinyl alcohol in the aqueous solution is 4-6 wt%, the drying is vacuum drying, the drying temperature is 70-90℃, and the drying time is 10-14 hours.

[0017] The advantages of this invention compared to the prior art are:

[0018] 1. This invention constructs a core-shell structure, using a metal-organic framework to derive a porous carbon matrix with three-dimensional channels to load silicon quantum dots. A polymer coating of oxidized polyvinyl alcohol and dopamine dynamically crosslinked via Schiff base bonds is then applied to the surface. This achieves uniform dispersion of silicon quantum dots and multi-level buffering of volume expansion. After 1000 cycles at 25°C and 1C charge-discharge rates, the capacity retention is ≥90%, and the electrode volume expansion rate is [not specified].

[0019] With a yield of ≤12%, it solves the key problem of structural collapse during the cycling process of silicon-based anodes.

[0020] 2. This invention strengthens the interfacial interaction between the inactive matrix and the active silicon quantum dots by forming Si-OC covalent bonds between silicon quantum dots and a porous carbon matrix. This avoids the detachment and aggregation of silicon quantum dots under traditional physical loading methods. Combined with the 40-50% porosity of the porous carbon matrix, which provides a buffer space for the volume expansion of silicon, a particle size of 1.2-1.5 g / cm³ is achieved. 3 The compatibility of the tap density with high loading of silicon quantum dots balances the energy density and structural stability of the battery.

[0021] 3. The present invention utilizes the dynamic cross-linked polymer coating formed by oxidizing polyvinyl alcohol and dopamine in a 3:1 mass ratio. By taking advantage of the dynamic reversible properties of Schiff base bonds, stress is adaptively released through bond breaking and recombination when the volume of silicon quantum dots changes. At the same time, the coating acts as a physical barrier to inhibit the erosion of silicon quantum dots by the electrolyte, thereby further improving the cycle durability and structural integrity of the negative electrode material. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application.

[0023] In the attached diagram:

[0024] Figure 1 This is a schematic diagram of the core-shell structure of a high-cycle battery anode material in one embodiment.

[0025] Figure 2This is a comparison chart of the volume expansion rate of a high-cycle battery anode material in the embodiments.

[0026] The figures are labeled as follows: 1. Porous carbon matrix; 2. Silicon quantum dots; 3. Polymer shell. Detailed Implementation

[0027] The following detailed description of the embodiments is used to exemplarily illustrate the principles of this application, but should not be used to limit the scope of this application. That is, the high-cycle battery anode material and its preparation method described in this application are not limited to the embodiments described.

[0028] Example 1

[0029] like Figure 1-2 As shown, a high-cycle battery anode material has a core-shell structure, including a core and a shell. The core is a metal-organic framework-derived porous carbon matrix, and silicon quantum dots are loaded in the three-dimensional channels of the matrix. The silicon quantum dots are bonded to the porous carbon matrix through Si-OC covalent bonds. The shell is a dynamically cross-linked polymer coating covering the surface of the core. The coating is formed by dynamic cross-linking of oxidized polyvinyl alcohol and dopamine through Schiff base bonds.

[0030] In a specific embodiment, the high-cycle-performance battery anode material adopts a core-shell structure design. The core is a porous carbon matrix derived from a metal-organic framework, whose three-dimensional pore structure provides loading space for silicon quantum dots. The silicon quantum dots are bonded to the carbon matrix via Si-OC covalent bonds. This chemical bonding originates from the dehydration condensation of hydroxyl groups on the silicon quantum dot surface with oxygen-containing functional groups on the carbon matrix, which enhances interfacial interactions and reduces the shedding of active materials during charging and discharging. The shell layer is a polymer coating formed by the dynamic crosslinking of oxidized polyvinyl alcohol and dopamine through Schiff base bonds. The aldehyde groups of oxidized polyvinyl alcohol and the amino groups of dopamine react under alkaline conditions to form a dynamically reversible crosslinked network, which can adaptively adjust with changes in the volume of silicon quantum dots, alleviating the problem of cracking in traditional rigid coatings.

[0031] Furthermore, the precursor for the metal-organic framework-derived porous carbon matrix is ​​a ZIF-8 zeolite imidazole framework, with a pore size of 5-20 nm and a specific surface area of ​​800-1200 m². 2 / g, with a porosity of 40-50%.

[0032] In a specific embodiment, the metal-organic framework-derived porous carbon matrix uses a ZIF-8 zeolite imidazole framework as a precursor. ZIF-8 has a regular cubic crystal structure and high thermal stability. During carbonization, the organic ligands decompose to form a nitrogen-doped porous carbon network, retaining the original three-dimensional channel structure. The matrix pore size is controlled within 5-20 nm. This is because the pores of the ZIF-8 precursor expand after carbonization at 750-850℃. By adjusting the carbonization temperature and holding time, this pore size range can be stabilized, accommodating silicon quantum dots of 3-5 nm while allowing volume expansion to be buffered by the elasticity of the pore walls. (800-1200 nm) 2 The specific surface area of ​​ / g and porosity of 40-50% are due to the high porosity of ZIF-8. The hierarchical pore structure retained after carbonization is conducive to electrolyte penetration and rapid lithium-ion transport.

[0033] Furthermore, the silicon quantum dots have a particle size of 3-5 nm and a loading of 15-25 wt% in the porous carbon matrix. The silicon quantum dots are uniformly dispersed in the three-dimensional channels of the porous carbon matrix without obvious agglomeration.

[0034] In a specific embodiment, the silicon quantum dot particle size is set to 3-5 nm. The amount of SiO2 precursor generated by hydrolysis is adjusted by controlling the amount of tetraethyl orthosilicate added, and then reduced by NaBH4 to obtain nanoscale silicon particles. The smaller particle size can shorten the lithium-ion diffusion path and reduce volume expansion stress. The loading of silicon quantum dots in the porous carbon matrix is ​​15-25 wt%, which is calculated by adjusting the ratio of silicon source to carbon matrix and combining it with the pore volume of carbon matrix to ensure that the pores are fully filled without exceeding the load-bearing limit. The physical confinement effect of the three-dimensional pores and the chemical anchoring effect of Si-OC covalent bonds jointly inhibit particle agglomeration, so that the silicon quantum dots are uniformly dispersed in the pores.

[0035] Furthermore, in the dynamic cross-linked polymer coating, the mass ratio of oxidized polyvinyl alcohol to dopamine is 3:1, the degree of cross-linking is 30-50%, and the coating thickness is 5-10 nm.

[0036] In a specific embodiment, the mass ratio of oxidized polyvinyl alcohol to dopamine in the dynamically crosslinked polymer coating is 3:1. By controlling the amount of feed, the stoichiometric ratio of aldehyde groups to amino groups is achieved, ensuring efficient Schiff base bond formation. The degree of crosslinking, 30-50%, is achieved by adjusting the system pH to 8.0-9.0 and controlling the reaction temperature to 50-60℃. Moderate crosslinking ensures the stability of the coating structure while preserving the reversibility of the dynamic bonds. The coating thickness, 5-10 nm, is controlled by adjusting the concentration of oxidized polyvinyl alcohol and the reaction time, providing a physical barrier without increasing ion transport resistance, thus balancing the protective effect with electrochemical kinetic performance.

[0037] Furthermore, the tap density of the negative electrode material is 1.2-1.5 g / cm³. 3Under 25℃ and 1C charge-discharge conditions, the capacity retention rate after 1000 cycles is ≥90%, and the electrode volume expansion rate is ≤12%.

[0038] In a specific embodiment, the tap density of the negative electrode material reaches 1.2-1.5 g / cm³. 3 Thanks to the dense carbon skeleton formed by ZIF-8 carbonization, the uniform filling of silicon quantum dots, and the dense coating, the internal voids of the material are reduced, thereby increasing the volumetric energy density. Under 25℃ and 1C charge-discharge conditions, the capacity retention rate is ≥90% after 1000 cycles, and the electrode volume expansion rate is ≤12%. This is because the porous carbon matrix buffers the volume expansion, covalent bonds inhibit the shedding of active materials, and the dynamic coating adaptively adjusts the stress, all of which work together to maintain the long-term stability of the electrode structure.

[0039] Furthermore, a method for preparing a high-cycle-performance battery anode material includes the following steps:

[0040] (1) Preparation of metal-organic framework-derived porous carbon matrix: The ZIF-8 precursor was heated to 750-850℃ in a nitrogen atmosphere at a heating rate of 5℃ / min, carbonized for 2-3 hours, and then cooled to obtain a three-dimensional porous carbon matrix.

[0041] (2) In-situ loaded silicon quantum dots: The porous carbon matrix obtained in step (1) is dispersed in ethanol, silicon source and catalyst are added, and SiO2 precursor is generated in the pores of the porous carbon matrix through sol-gel reaction. Then, a reducing agent is added to reduce SiO2 to silicon quantum dots to obtain silicon quantum dot loaded porous carbon composite material.

[0042] (3) Coating with dynamic cross-linked polymer coating: Disperse the composite material obtained in step (2) in an aqueous solution, add oxidized polyvinyl alcohol and dopamine, and adjust the pH of the system to 8.0-9.0; stir at 50-60℃ for 3-5 hours to allow oxidized polyvinyl alcohol and dopamine to form a polymer coating through dynamic cross-linking of Schiff base bonds; after drying, the target negative electrode material is obtained.

[0043] In a specific embodiment, the preparation method includes three consecutive steps. Step (1) When preparing the porous carbon matrix, the ZIF-8 precursor is heated to 750-850℃ for 2-3 hours under a nitrogen atmosphere at a rate of 5℃ / min. Nitrogen prevents the carbon material from oxidizing, stabilizes the heating rate to avoid cracking of the carbon skeleton, and high-temperature carbonization promotes the complete decomposition of ligands to form a highly conductive graphitized carbon network. Step (2) When loading silicon quantum dots in situ, the carbon matrix is ​​dispersed in ethanol. After adding silicon source and catalyst, SiO2 precursor is generated in the pores through sol-gel reaction, and then reduced to silicon quantum dots. Ethanol dispersion ensures uniform distribution of the carbon matrix, and the in-situ reaction achieves precise loading of silicon quantum dots in the pores. Step (3) When coating, the composite material is dispersed in an aqueous solution. Oxidized polyvinyl alcohol and dopamine are added, and the pH is adjusted to 8.0-9.0. Then, the mixture is stirred at 50-60℃ for 3-5 hours. The aqueous environment promotes the diffusion of polymer molecules. Under specific conditions, Schiff base bonds crosslink to form a uniform coating. The structure is fixed after drying.

[0044] Further, in step (1), the ZIF-8 precursor is prepared by reacting zinc nitrate and 2-methylimidazole in methanol solvent at room temperature for 24-36 hours, with the molar ratio of zinc nitrate to 2-methylimidazole being 1:3-1:5.

[0045] In a specific embodiment, the ZIF-8 precursor was prepared by reacting zinc nitrate and 2-methylimidazole in methanol at room temperature for 24-36 hours, with a molar ratio of 1:3-1:5. Methanol, as a polar solvent, dissolves the raw materials and promotes the coordination reaction; excess 2-methylimidazole ensures the Zn... 2+ Complete coordination forms a complete ZIF-8 crystal; room temperature conditions avoid high temperature damage to the crystal structure, and a reaction time of 24-36 hours ensures sufficient crystal growth. The generated ZIF-8 has a regular porous structure, which lays the foundation for the performance of the carbon matrix after carbonization.

[0046] Further, in step (2), the silicon source is tetraethyl orthosilicate, the catalyst is ammonia water with a concentration of 25-28%, and the reducing agent is NaBH4; the particle size of silicon quantum dots is adjusted to 3-5 nm by controlling the amount of tetraethyl orthosilicate added.

[0047] In a specific embodiment, tetraethyl orthosilicate is selected as the silicon source. It undergoes hydrolysis and condensation under the catalysis of 25-28% ammonia water to generate a SiO2 precursor. The ammonia concentration provides a suitable alkaline environment to regulate the hydrolysis rate and prevent excessive particle growth. NaBH4 reduces SiO2 to silicon quantum dots. The physical confinement of the carbon matrix channels prevents silicon particle growth. By controlling the amount of tetraethyl orthosilicate added, the particle size of the silicon quantum dots is adjusted to 3-5 nm. This particle size shortens the lithium-ion diffusion path and reduces volume expansion stress.

[0048] Further, in step (3), the molecular weight of oxidized polyvinyl alcohol is 70,000-90,000, the mass ratio of oxidized polyvinyl alcohol to dopamine is 3:1, the concentration of oxidized polyvinyl alcohol in the aqueous solution is 4-6 wt%, the drying is vacuum drying, the drying temperature is 70-90℃, and the drying time is 10-14 hours.

[0049] In a specific embodiment, the molecular weight of oxidized polyvinyl alcohol is 70,000-90,000, with a mass ratio of 3:1 to dopamine, and a concentration of 4-6 wt% in aqueous solution. This molecular weight ensures a suitable molecular chain length, balancing the number of reaction sites with coating flexibility; the 3:1 ratio enables efficient cross-linking of aldehyde and amino groups; and the 4-6 wt% concentration balances solubility and deposition efficiency, avoiding excessively thick or incomplete coatings. Drying is performed under vacuum at 70-90℃ for 10-14 hours. Vacuum accelerates solvent evaporation and avoids impurity contamination. The temperature and time parameters ensure that moisture is removed without damaging Schiff base bonds, ultimately yielding a structurally stable anode material.

[0050] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0051] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A high-cycle-performance battery anode material, characterized in that, The negative electrode material has a core-shell structure, including a core and a shell. The core is a metal-organic framework-derived porous carbon matrix, and silicon quantum dots are loaded in the three-dimensional channels of the matrix. The silicon quantum dots are bonded to the porous carbon matrix through Si-OC covalent bonds. The shell is a dynamically cross-linked polymer coating that coats the surface of the core. The coating is formed by dynamic cross-linking of oxidized polyvinyl alcohol and dopamine through Schiff base bonds.

2. The high-cycle-capacity battery anode material according to claim 1, characterized in that: The precursor of the metal-organic framework-derived porous carbon matrix is ​​a ZIF-8 zeolite imidazole framework, and the matrix has a pore size of 5-20 nm and a specific surface area of ​​800-1200 m². 2 / g, with a porosity of 40-50%.

3. The high-cycle battery anode material according to claim 2, characterized in that: The silicon quantum dots have a particle size of 3-5 nm and a loading of 15-25 wt% in the porous carbon matrix. The silicon quantum dots are uniformly dispersed in the three-dimensional channels of the porous carbon matrix without obvious agglomeration.

4. The high-cycle battery anode material according to claim 3, characterized in that: In the dynamic cross-linked polymer coating, the mass ratio of oxidized polyvinyl alcohol to dopamine is 3:1, the degree of cross-linking is 30-50%, and the coating thickness is 5-10 nm.

5. The high-cycle-capacity battery anode material according to claim 4, characterized in that: The tap density of the negative electrode material is 1.2-1.5 g / cm³. 3 Under 25℃ and 1C charge-discharge conditions, the capacity retention rate after 1000 cycles is ≥90%, and the electrode volume expansion rate is ≤12%.

6. A method for preparing the high-cycle battery anode material according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Preparation of metal-organic framework-derived porous carbon matrix: The ZIF-8 precursor was heated to 750-850℃ in a nitrogen atmosphere at a heating rate of 5℃ / min, carbonized for 2-3 hours, and then cooled to obtain a three-dimensional porous carbon matrix. (2) In-situ loaded silicon quantum dots: The porous carbon matrix obtained in step (1) is dispersed in ethanol, silicon source and catalyst are added, and SiO2 precursor is generated in the pores of the porous carbon matrix through sol-gel reaction. Then, a reducing agent is added to reduce SiO2 to silicon quantum dots to obtain silicon quantum dot loaded porous carbon composite material. (3) Coating with dynamic cross-linked polymer coating: Disperse the composite material obtained in step (2) in an aqueous solution, add oxidized polyvinyl alcohol and dopamine, and adjust the pH of the system to 8.0-9.0; stir at 50-60℃ for 3-5 hours to allow oxidized polyvinyl alcohol and dopamine to form a polymer coating through dynamic cross-linking of Schiff base bonds; after drying, the target negative electrode material is obtained.

7. The method for preparing a high-cycle battery anode material according to claim 6, characterized in that: In step (1), the ZIF-8 precursor is prepared by reacting zinc nitrate and 2-methylimidazole in methanol solvent at room temperature for 24-36 hours, wherein the molar ratio of zinc nitrate to 2-methylimidazole is 1:3-1:

5.

8. The method for preparing a high-cycle battery anode material according to claim 6, characterized in that: In step (2), the silicon source is tetraethyl orthosilicate, the catalyst is ammonia water with a concentration of 25-28%, and the reducing agent is NaBH4; the particle size of the silicon quantum dots is adjusted to 3-5 nm by controlling the amount of tetraethyl orthosilicate added.

9. The method for preparing a high-cycle battery anode material according to claim 6, characterized in that: In step (3), the molecular weight of the oxidized polyvinyl alcohol is 70,000-90,000, the mass ratio of the oxidized polyvinyl alcohol to dopamine is 3:1, the concentration of the oxidized polyvinyl alcohol in the aqueous solution is 4-6 wt%, the drying is vacuum drying, the drying temperature is 70-90℃, and the drying time is 10-14 hours.

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