Bi-metal heterostructure MOF-derived Si-coated CuZn-MOF silicon carbon material and preparation and application thereof

Abstract

The invention discloses a bimetallic heterostructure MOF (Metal Organic Framework) derived Si (at) CuZn-MOF silicon carbon material, which is characterized in that a bimetallic Cu-MOF (at) Zn-MOF composite material is carbonized to obtain a CuZn-MOF carbon material, and silicon is deposited in pores and the surface of the CuZn-MOF carbon material by a chemical vapor deposition method to prepare the bimetallic heterostructure MOF derived Si (at) CuZn-MOF silicon carbon material. The bimetallic Cu-MOF (at) Zn-MOF composite material is prepared by carrying out a reaction on Cu-MOF, soluble zinc salt and 2-methylimidazole in a methanol solvent, and the Cu-MOF is prepared by carrying out a reaction on soluble copper salt, triethylamine and trimesic acid. According to the bimetal heterostructure MOF-derived Si-coated CuZn-MOF silicon carbon material, the conductivity of the silicon carbon material is improved, the ionic electricity of a silicon carbon electrode is optimized, the dynamic performance of a battery is improved, volume expansion of silicon in the charging and discharging process of the battery can be effectively relieved, the problem of electrode cracking caused by expansion is avoided, and the service life of the battery is prolonged. The mechanical strength and the electrochemical performance of the silicon-carbon negative electrode are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon-carbon negative electrode materials, in particular to a bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material, and the preparation of the silicon-carbon material, and its application in lithium ion batteries and silicon-carbon negative electrodes. BACKGROUND

[0002] Lithium ion batteries are widely used in consumer batteries, power batteries and energy storage batteries due to their high energy density, long cycle life, no memory effect and other advantages. With the rapid development of electronic devices and new energy vehicles, higher requirements are put forward for the energy density, cycle life and charging speed of lithium ion batteries. The theoretical specific capacity of traditional graphite negative electrode material is only 372 mAh / g, which has gradually approached the performance limit and is difficult to meet the demand of future high energy density batteries. Therefore, it is necessary to develop new negative electrode materials. Silicon-carbon material is a new type of electrode material formed by the combination of silicon (Si) and carbon (C), mainly used as the negative electrode of lithium ion batteries, aiming to solve the problem of low energy density of traditional graphite negative electrode.

[0003] The technical core of silicon-carbon material is to consider the advantages of silicon and carbon through structural design. The theoretical specific capacity of silicon is extremely high (4200 mAh / g), which is more than 10 times that of traditional graphite negative electrode, and is the key to improve the capacity of lithium battery. However, the volume of silicon will expand to more than 3 times during the process of lithium extraction, which will cause the active material to be rapidly pulverized and detached during the charge and discharge cycle, and the SEI film cannot be stably present, resulting in rapid capacity decay and poor battery cycle performance. Carbon has good electrical conductivity and stability, and the volume expansion is small (about 10%), and the carbon material is uniformly coated on the surface of silicon particles or dispersed between silicon particles, which can inhibit the volume expansion of silicon and form a continuous conductive network to enhance the conductivity. Therefore, the pore forming technology and pore structure of carbon directly determine the performance of silicon-carbon negative electrode.

[0004] The silicon-carbon composite material taking metal organic framework (MOF) material as a carbon source is currently in a key stage of transition from laboratory research to industrialization. The MOF material as a new type of carbon source brings revolutionary development opportunities for the silicon-carbon negative electrode material. The unique structure designability and the synergistic effect of the metal node provide a new path for breaking through the performance limit of traditional silicon-carbon materials. However, in the process of promoting from the laboratory to industrialization, the technical system still faces several key technical bottlenecks: (1) the carbon skeleton derived from single-metal MOF is difficult to effectively buffer the volume effect of the silicon material (expansion rate > 280%) in the long-term cycle process, which leads to a significant risk of collapse of the carbon framework structure, a continuous decline in the conductive network, and the actual cycle life is generally difficult to exceed 800 times (capacity retention rate < 80%), and there is a balance problem between structural stability and cycle life and the limitation of single function of the metal node; (2) the single-metal MOF silicon-carbon system cannot simultaneously improve the conductivity and inhibit the side reaction, the metal-silicon interface stability is insufficient, the regulation ability of the SEI film growth is limited, and there are technical bottlenecks in the silicon loading and dispersion efficiency; (3) the silicon-carbon negative electrode faces the problem that the dispersion uniformity sharply decreases when the silicon loading is high (> 40wt%), the pore structure and the silicon particle size are not matched, and the effective silicon utilization rate is generally less than 85%.

[0005] Therefore, through the path of designing structure and regulating performance, the cycle stability and silicon utilization rate of the silicon-carbon negative electrode are improved, and the silicon loading limit and cycle bottleneck of the traditional silicon-carbon material are broken through, which is one of the technical development directions of constructing a silicon-carbon negative electrode material with excellent performance. SUMMARY

[0006] The present application is aimed at the deficiencies of the existing silicon-carbon composite material taking MOF material as a carbon source. The Si@CuZn-MOF silicon-carbon material derived from a double-metal heterogeneous structure MOF not only improves the conductivity of the silicon-carbon material, optimizes the ionic property of the silicon-carbon negative electrode, and increases the kinetic performance of the battery, but also effectively alleviates the volume expansion of silicon in the battery charging and discharging process, avoids the problem of electrode cracking caused by expansion, and improves the mechanical strength and electrochemical performance of the silicon-carbon negative electrode.

[0007] To achieve the above-mentioned purpose, the Si@CuZn-MOF silicon-carbon material derived from a double-metal heterogeneous structure MOF provided by the present application is obtained by carbonizing a double-metal Cu-MOF@Zn-MOF composite material to obtain a CuZn-MOF carbon material, and depositing silicon in the pores and on the surface of the CuZn-MOF carbon material by a chemical vapor deposition method; the double-metal Cu-MOF@Zn-MOF composite material is prepared by reacting Cu-MOF, soluble zinc salt and 2-methyl imidazole in a methanol solvent; and the Cu-MOF is prepared by reacting soluble copper salt, triethylamine and trimesic acid.

[0008] The present application utilizes a bimetallic heterostructure MOF (Cu-MOF@Zn-MOF) as a carbon precursor. Small molecule substances (such as water or carbon dioxide) in the Cu-MOF material help form a uniform hard carbon structure during carbonization, improving the structural stability and electrical conductivity of the composite material. The hierarchical porous structure formed by the Zn-MOF material has continuous pores, which can provide more reaction interfaces, and the high specific surface area helps more lithium ions to be stored and released in the electrode material, enhancing the conductivity and ion migration ability of the electrode. The bimetallic MOF can produce a synergistic carbonization mechanism, thereby significantly improving the energy density and cycle stability of the battery, which is crucial for the charge and discharge performance of lithium batteries.

[0009] The heterostructure composed of Cu-MOF and Zn-MOF exhibits a significant synergistic effect during carbonization, which is essentially due to the differential thermal decomposition behavior of the two metal nodes and the complementarity of the carbon source conversion path. Among them, Cu-MOF has a catalytic graphitization effect, that is, Cu 2+ Cu nanoparticles are formed in situ during carbonization, and their catalytic activity promotes the ordered transformation of amorphous carbon to graphite microcrystalline, forming local sp² hybrid carbon domains. This graphitized region can serve as a "highway for electronic transmission", and the uniform embedding of Cu nanoparticles inhibits the excessive shrinkage of the carbon matrix, maintaining the mechanical integrity of the hard carbon skeleton. Zn-MOF plays a template pore-forming effect, that is, Zn 2+ During carbonization, a hierarchical porous structure (micropores <2 nm + mesopores 2~50 nm) is generated by the volatilization of ZnO intermediate phase. Micropores are derived from the molecular-level escape of ligand pyrolysis (H2O / CO2), and mesopores are formed by the volatilization and etching of ZnO nanoparticles. This dual-continuous pore structure not only provides a three-dimensional diffusion channel for lithium ions, but also relieves the volume expansion stress of silicon through capillary condensation effect. The carbon layer of Cu-MOF and the pores of Zn-MOF form a gradient pore structure at the heterojunction interface, with a continuous distribution of pore size from micropores to mesopores. The Cu-C chemical bond in the interface region enhances the cross-linking density of the carbon skeleton, making the Young's modulus of the composite material increase to 8 GPa (traditional hard carbon <5 GPa), exhibiting an interface coupling effect.

[0010] The CuZn-MOF carbon material after carbonization has a multi-scale structure that cooperates with silicon nanoparticles for lithium storage, specifically: (1) Cu nanoparticles on the Cu-C surface can naturally form a SiO xBy chemical bonding anchoring, electronic conductivity and mechanical flexibility are combined, and the pulverization of silicon particles is effectively inhibited. (Two), the hierarchical pore of Zn-C encapsulates the silicon nanoparticles in the mesoporous cavity through the "pore confinement effect", and a stress buffer microzone is generated, and the elastic modulus of the pore wall and the volume expansion of silicon form a dynamic balance, that is, when the silicon expands, the mesopore reversibly deforms elastically, avoiding direct contact between particles; when shrinking, the pore recovers the original structure, maintaining the ion / electron transport path. + Uniform deposition on the surface of silicon, inhibiting lithium dendrite growth, maintaining SEI film, improving Li + transport dynamics, and enhancing cycle stability.

[0011] As a limitation of the above technical solution, the Cu-MOF is dispersed in methanol to obtain solution one; polyvinylpyrrolidone is dissolved in methanol to obtain solution two; a soluble zinc salt is dissolved in methanol to obtain solution three; 2-methyl imidazole is dissolved in methanol to obtain solution four; solution one and solution two are mixed to obtain a mixed solution, which is added to solution three after sufficient stirring, and finally solution four is added, and the reaction is carried out after standing. A bimetallic Cu-MOF@Zn-MOF composite material is obtained; as a preferred embodiment, the soluble zinc salt is selected from any one of zinc nitrate, zinc acetate, zinc sulfate and zinc chloride.

[0012] As a limitation of the above technical solution, 0.5-1.5 g Cu-MOF is dispersed in 200 mL methanol to obtain solution one; 1.0-5.0 g polyvinylpyrrolidone is dissolved in 20 mL methanol to obtain solution two; 0.01-0.03 mol of a soluble zinc salt is dissolved in 200 mL methanol to obtain solution three; 0.5-2.0 g of 2-methyl imidazole is dissolved in 100 mL methanol to obtain solution four.

[0013] Cu-MOF provides a hard carbon structure for CuZn-MOF carbon material, and Zn-MOF plays a templating pore-forming effect to form a special structure.

[0014] As a limitation of the above technical solution, 0.005-0.015 mol of a soluble copper salt, 0.5-2.0 g of acetic acid, and 2.0-5.0 ml of triethylamine are all dissolved in 30-50 mL of ethanol, 0.2-1.0 g of trimesic acid is added after sufficient mixing, and the reaction is carried out at 90-120°C for 6-8 hours to obtain Cu-MOF; as a preferred embodiment, the soluble copper salt is selected from any one of copper acetate, copper nitrate, copper chloride and copper sulfate.

[0015] The Cu salt is used as a metal center, and the trimesic acid is used as an organic ligand, and is dissolved in a reaction solvent acetic acid to perform a coordination reaction, and triethylamine is added as a pH adjuster of a reaction system to ensure that the coordination reaction is completed in an alkaline environment, and a metal organic framework material Cu-MOF is obtained.

[0016] As a limitation of the above technical solution, the carbonization is to heat the Cu-MOF@Zn-MOF composite material to 850-950 DEG C at a rate of 2-5 DEG C / min under a N2 atmosphere, and the temperature is kept for 1-3 hours, and a porous CuZn-MOF carbon material is obtained.

[0017] As a limitation of the above technical solution, the chemical vapor deposition method is to heat the CuZn-MOF carbon material to 350-600 DEG C at a rate of 2-5 DEG C / min under a N2 atmosphere, and then keep the temperature at 350-600 DEG C for 12-24 hours under a mixed gas atmosphere of 20% SiH4-N2 by volume percentage, and then keep the temperature at 350-600 DEG C for 2-4 hours under a mixed gas atmosphere of 10% C2H2-N2 by volume percentage, and finally cool naturally under a N2 atmosphere, complete the deposition of silicon on the porous carbon material, and obtain a bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material.

[0018] Further improve the reaction conditions for obtaining the bimetallic Cu-MOF@Zn-MOF composite material, the metal organic framework material Cu-MOF, and the operation conditions of carbonization and chemical vapor deposition method, and optimize the structure and performance of the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material.

[0019] Meanwhile, the application also provides a preparation method of the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material as described above, which comprises the following operation steps: a, preparing a CuZn-MOF carbon material: a1, obtaining a metal organic framework material Cu-MOF: 0.005-0.015 mol of a soluble copper salt, 0.5-2.0 g of acetic acid and 2.0-5.0 ml of triethylamine are all dissolved in 30-50 mL of ethanol, and 0.2-1.0 g of trimesic acid is added after being mixed thoroughly, and the mixture is reacted at 90-120 DEG C for 6-8 hours, and the precipitate is collected, washed and dried at 50-80 DEG C, and the Cu-MOF is obtained. a2, obtaining a bimetallic Cu-MOF@Zn-MOF composite material: 0.5-1.5 g of Cu-MOF is dispersed in 200 mL of methanol to obtain solution one; 1.0-5.0 g of polyvinylpyrrolidone is dissolved in 20 mL of methanol to obtain solution two; 0.01-0.03 mol of a soluble zinc salt is dissolved in 200 mL of methanol to obtain solution three; 0.5-2.0 g of 2-methylimidazole is dissolved in 100 mL of methanol to obtain solution four; solution one and solution two are mixed first to obtain a mixed solution, which is added to solution three after being stirred thoroughly, and then solution four is added, and the reaction is allowed to stand, centrifuged and washed to obtain a bimetallic Cu-MOF@Zn-MOF composite material; a3, carbonization: the Cu-MOF@Zn-MOF composite material is heated at 2-5 ℃ / min to 850-950 ℃ under a N2 atmosphere, and is kept at the temperature for 1-3 h to obtain a CuZn-MOF carbon material with a porous structure; b, chemical vapor deposition: the CuZn-MOF carbon material is heated at 2-5 ℃ / min to 350-600 ℃ from room temperature under a N2 atmosphere in a tube furnace; then kept at 350-600 ℃ for 12-24 h under a 20% SiH4-N2 mixed gas atmosphere by volume percentage; then kept at 350-600 ℃ for 2-4 h under a 10% C2H2-N2 mixed gas atmosphere by volume percentage; and finally cooled naturally under a N2 atmosphere to complete the deposition of silicon on the porous carbon material, thereby obtaining a bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material.

[0020] As a limitation of the above technical solution, the preparation method of the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material comprises the following operation steps: a, preparing a CuZn-MOF carbon material: a1, obtaining a metal organic framework material Cu-MOF: 0.005 mol of Cu(CH3COO)2·H2O, 1.5 g of acetic acid and 2.5 mL of triethylamine are all dissolved in 50 mL of ethanol, 0.50 g of trimesic acid is added after being mixed thoroughly, the reaction is allowed to stand at 100 ℃ for 6 h, and then centrifuged, washed and dried at 50-80 ℃ to obtain Cu-MOF; a2, obtaining the bimetallic Cu-MOF@Zn-MOF composite material: 1.5 g of Cu-MOF was dispersed in 200 mL of methanol to obtain solution one; 1.0 g of polyvinylpyrrolidone was dissolved in 20 mL of methanol to obtain solution two; 0.01 mol of zinc nitrate hexahydrate was dissolved in 200 mL of methanol to obtain solution three; 2.0 g of 2-methylimidazole was dissolved in 100 mL of methanol to obtain solution four; first, mix solution one and solution two to obtain a mixed solution, then add it to solution three after sufficient stirring, and finally add solution four, stand for reaction, centrifuge and wash to obtain the bimetallic Cu-MOF@Zn-MOF composite material; a3, carbonization: the Cu-MOF@Zn-MOF composite material was heated to 900 ℃ at a rate of 5 ℃ / min under N2 atmosphere, and kept for 2 h to obtain the porous CuZn-MOF carbon material; b, chemical vapor deposition: the CuZn-MOF carbon material was heated to 500 ℃ at a rate of 5 ℃ / min from room temperature under N2 atmosphere in a tube furnace; then kept at 500 ℃ for 15 h under a mixed gas atmosphere of 20% SiH4-N2 by volume percentage; then kept at 550 ℃ for 2 h under a mixed gas atmosphere of 10% C2H2-N2 by volume percentage; finally, after cooling naturally under N2 atmosphere, the deposition of silicon on the porous carbon material was completed, and the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material was obtained.

[0021] The application effectively regulates the porous structure and performance of the silicon-carbon material by using the preparation conditions, the raw materials are easy to obtain, and the operation conditions are suitable for industrial promotion, thereby providing technical support for promoting the application of high-performance silicon-carbon negative electrode materials.

[0022] In addition, the application also provides the application of the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material as described above, which is used for making negative electrode materials of batteries, and is preferably used for making negative electrode materials of lithium ion batteries.

[0023] and the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon negative electrode made of the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material as described above.

[0024] In summary, the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material of the application has the following advantages: 1. Enhanced structural stability and porosity Cu-MOF@Zn-MOF, through the introduction of a dual-metal framework structure, results in a more stable structure of the final carbonized material. The interaction between copper and zinc metal-organic frameworks provides better support, allowing the material's pore structure to be maintained during high-temperature pyrolysis. Compared to single metal-organic frameworks such as Cu-MOF or Zn-MOF, Cu-MOF@Zn-MOF forms a synergistic effect between different metals during pyrolysis, enhancing the porosity and specific surface area of the final carbon material, thereby improving the specific capacity and cycle stability of the negative electrode material.

[0025] 2. Synergistic effect of metal centers The composite material formed by Cu-MOF and Zn-MOF has a unique synergistic effect. The metal centers of copper and zinc can provide additional support for electron and ion conduction during electrochemical processes, and they can help form a conductive network during pyrolysis, thereby improving the electrical conductivity of the material. This metal synergistic effect can also promote the rapid migration of lithium ions during charging and discharging, improving the cycle performance and rate performance of the battery.

[0026] 3. Adjustable pore structure and functionalized surface During the synthesis of Cu-MOF@Zn-MOF, PVP is used as a stabilizer to help control the size, distribution, and pore structure of the particles. The stable pore structure effectively alleviates the problem of volume expansion during charging and discharging, which is crucial for maintaining the long-term stability of the material. At the same time, the high porosity of Cu-MOF@Zn-MOF provides more lithium storage sites, allowing the derived carbon material to improve its charge storage capacity in lithium-ion batteries.

[0027] 4. Improved electrical conductivity The combination of Cu-MOF and Zn-MOF can form a more continuous conductive network during pyrolysis. In particular, during high-temperature pyrolysis, the metal elements of copper and zinc remain in the carbonized carbon material, providing a path for electron conduction and improving the electrical conductivity of the carbon material. Compared to single Cu-MOF or Zn-MOF, the composite conductive structure formed by the metal elements in Cu-MOF@Zn-MOF after carbonization can improve the electrical conductivity of the final carbon material and enhance the high-rate performance of the battery.

[0028] 5. Enhanced mechanical strength and stability The metal centers of zinc and copper not only help to improve the electrical conductivity, but also help to enhance the mechanical strength of the material. In the high-temperature pyrolysis process, the composite structure of Cu-MOF@Zn-MOF can maintain good integrity, avoiding the pulverization or structural damage of the material during the charging and discharging process, thereby improving the cycle stability of the material. In lithium ion batteries, the mechanical stability of the material is crucial for long-term charging and discharging cycles, and the structural stability of Cu-MOF@Zn-MOF is stronger, which helps to improve the cycle life of the negative electrode material.

[0029] 6. Functionalized surface and higher specific capacity The silicon-carbon material formed after pyrolysis of the Cu-MOF@Zn-MOF composite material can provide better electrochemical performance. Due to the high specific surface area of the metal-organic framework material and its adjustable pore structure, the carbon material after pyrolysis can provide higher specific capacity while also being able to withstand higher charging and discharging rates in the battery. Compared with Cu-MOF or Zn-MOF materials alone, the electrochemical performance of the Cu-MOF@Zn-MOF composite material is significantly improved, especially in terms of high-rate discharge and cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 , Figure 2 is a scanning electron microscope image of the Cu-MOF@Zn-MOF composite material of Example 2.

[0031] Figure 2 , Figure 2 is a scanning electron microscope image of the Cu-MOF@Zn-MOF composite material of Example 2. DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be described below in conjunction with the examples, and it is obvious that the described examples are only a part of the embodiments of the present application, rather than all the embodiments. Based on the examples in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0033] The experimental methods in the following examples and comparative examples are conventional methods unless otherwise specified, and the raw materials or test materials used are typical products purchased on the market unless otherwise specified. In the quantitative tests in the following examples and comparative examples, three repeated experiments were set up, and the average value was taken as the result.

[0034] The silicon-carbon material, silicon-carbon negative electrode, and lithium ion battery of the present application are prepared by the following methods.

[0035] I. Preparation of silicon-carbon material a. Preparation of CuZn-MOF carbon material: a1, obtaining metal organic framework material Cu-MOF: 0.005-0.015 mol of soluble copper salt, 0.5-2.0 g of acetic acid and 2.0-5.0 mL of triethylamine are dissolved in 30-50 mL of ethanol, stirred for 1 hour, then 0.2-1.0 g of trimesic acid is added, reacted at 90-120℃ for 6-8 hours, the precipitate is collected, washed with deionized water and ethanol, then vacuum dried at 50-80℃ for 12-24 hours to obtain Cu-MOF powder.

[0036] a2, obtaining bimetallic Cu-MOF@Zn-MOF composite material: 0.5-1.5 g of Cu-MOF is dispersed in 200 mL of methanol to obtain solution one; 1.0-5.0 g of polyvinylpyrrolidone (PVP) is dissolved in 20 mL of methanol to obtain solution two; 0.01-0.03 mol of soluble zinc salt is dissolved in 200 mL of methanol to obtain solution three; 0.5-2.0 g of 2-methylimidazole is dissolved in 100 mL of methanol to obtain solution four; solution one and solution two are mixed and continuously stirred for 24 h to prepare PVP-stabilized Cu-MOF, then the PVP-stabilized Cu-MOF is added to solution three and uniformly dispersed, finally solution four is added, and after standing for 24 hours, centrifugation and washing with methanol, a bimetallic Cu-MOF@Zn-MOF composite material is obtained.

[0037] a3, carbonization: the Cu-MOF@Zn-MOF composite material is heated at 2-5℃ / min to 850-950℃ under N2 atmosphere, and kept for 1-3 h, and then naturally cooled to room temperature under N2 atmosphere to obtain a porous CuZn-MOF carbon material.

[0038] b, chemical vapor deposition: the CuZn-MOF carbon material is heated at 2-5℃ / min from room temperature to 350-600℃ in a tube furnace under N2 atmosphere; then 20% SiH4-N2 mixed gas is introduced, and the deposition is kept at 350-600℃ for 12-24 h under 20% SiH4-N2 mixed gas atmosphere; then 10% C2H2-N2 mixed gas is introduced, and the deposition is kept at 350-600℃ for 2-4 h under 10% C2H2-N2 mixed gas atmosphere; finally, the temperature is naturally lowered under N2 atmosphere, and the deposition of silicon on the porous carbon material is completed to obtain a bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material.

[0039] II. Preparation of silicon-carbon negative electrode The silicon-carbon material prepared in step one 94~94.5wt% and carbon nanotubes 0.05wt%, conductive carbon black 1.5wt%, binder CMC 3.95~4.45wt% are mixed, deionized water (25%~35%) is added for homogenization, and after sieving, coated on a copper foil current collector, placed in a vacuum dryer at 85°C, pressed into a sheet, and a 100μm thick silicon-carbon negative electrode sheet is obtained.

[0040] III. Preparation of lithium ion battery The silicon-carbon negative electrode sheet prepared in step two, a separator, a positive electrode sheet, and electrolyte are prepared into a lithium ion battery according to the method in the prior art.

[0041] The obtained lithium ion battery can be used in the following electrochemical devices: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, tablet computers, mobile phones, notebook computers, etc. When applied to large devices, a battery pack or a battery module can be used.

[0042] Example 1

[0043] a. Preparation of CuZn-MOF carbon material: a1. Obtain metal organic framework Cu-MOF: dissolve 0.005 mol Cu(NO3)2·3H2O, 1.5 g acetic acid, and 2.5 mL triethylamine in 50 mL ethanol, stir and mix for 1 hour, then add 0.5 g trimesic acid, react at 100°C for 6 hours, centrifuge, wash with deionized water and ethanol several times, and dry at 60°C to obtain Cu-MOF powder.

[0044] a2. Preparation of Cu-MOF@Zn-MOF: disperse 1.5 g Cu-MOF in 200 mL methanol to obtain solution one; dissolve 1.0 g polyvinylpyrrolidone (PVP) in 20 mL methanol to obtain solution two; dissolve 0.01 mol Zn(NO3)2·6H2O in 200 mL methanol to obtain solution three; dissolve 2.0 g 2-methylimidazole in methanol to obtain solution four; first mix solution one and solution two, stir for 24 hours to prepare Cu-MOF stabilized by PVP, then add the PVP-stabilized Cu-MOF to solution three, and finally add solution four, stand for 24 hours of reaction, centrifuge, and wash with methanol to obtain bimetallic Cu-MOF@Zn-MOF.

[0045] a3. Carbonization: heat the Cu-MOF@Zn-MOF composite material obtained in the above step to 900°C at 5°C / min under N2 atmosphere, and keep the temperature for 2 hours to obtain a CuZn-MOF carbon material with a porous structure.

[0046] b. Chemical vapor deposition: CuZn-MOF carbon material was heated in a tube furnace at a rate of 5 ℃ / min from room temperature to 500 ℃ under N2 atmosphere; then 20% SiH4-N2 mixed gas was introduced, and the material was kept at 500 ℃ for 15 h under 20% SiH4-N2 mixed gas atmosphere; then 10% C2H2-N2 mixed gas was introduced, and the material was kept at 550 ℃ for 2 h under 10% C2H2-N2 mixed gas atmosphere; finally, the material was naturally cooled under N2 atmosphere to complete the deposition of silicon on the porous carbon material, and a bimetallic heterostructure MOF-derived Si@CuZn-MOF was obtained.

[0047] Example 2

[0048] The difference between this example and Example 1 is that in step a1, 0.005 mol of Cu(CH3COO)2·H2O is used as the soluble copper salt, and in step a2, solution one is obtained by dispersing 1.0 g of Cu-MOF in 200 mL of methanol. The remaining parameters and steps are the same as in Example 1.

[0049] Example 3

[0050] The difference between this example and Example 1 is that in step a2, solution one is obtained by dispersing 0.5 g of Cu-MOF in 200 mL of methanol, and in solution three, 0.01 mol of zinc acetate is used as the soluble zinc salt. The remaining parameters and steps are the same as in Example 1.

[0051] Comparative Example 1 This comparative example is a Si@Zn-MOF silicon-carbon material, and the specific preparation operation is as follows: a. Preparation of Zn-MOF carbon material: a1. Obtain metal organic framework material Zn-MOF: 0.01 mol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 1.640 g of 2-methylimidazole were added to two 125 mL methanol solutions, respectively, and then the two methanol solutions were mixed at room temperature, stirred for 30 minutes, and left to react for 24 hours. After centrifugation and washing with methanol multiple times, the material was dried in a 60 ℃ oven to obtain Zn-MOF powder; a2. Carbonization: The operation was the same as in Example 1, and a Zn-MOF carbon material was obtained. b. Chemical vapor deposition: The operation was the same as in Example 1, and a Si@Zn-MOF silicon-carbon material was obtained.

[0052] Comparative Example 2 This comparative example is a Si@Cu-MOF silicon-carbon material, and the specific preparation operation is as follows: a. Preparation of Cu-MOF carbon material: a1, obtaining metal organic framework material Cu-MOF: 0.005 mol Cu(CH3COO)2·H2O, 1.5 g acetic acid and 2.5 mL triethylamine were dissolved in 50 mL ethanol, mixed for 1 hour, then 0.50 g of trimesic acid was added, and they were reacted at 100℃ for 6 hours, centrifuged, washed with ethanol for several times, dried at 60℃, to obtain Cu-MOF powder; a2, carbonization: the operation was the same as example 1, to obtain Cu-MOF carbon material; b, chemical vapor deposition: the operation was the same as example 1, to obtain Si@Cu-MOF silicon-carbon material.

[0053] Comparative Example 3 The Si@CuZn-MOF silicon-carbon material of the present comparative example was prepared in a different sequence from example 1, and the specific operation was as follows: a, preparation of CuZn-MOF carbon material: a1, obtaining metal organic framework material Zn-MOF: 0.01 mol zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 1.640 g 2-methylimidazole were added to two 125 mL methanol respectively, then the two methanol solutions were mixed at room temperature, stirred for 30 minutes, and left to react for 24 hours, centrifuged, washed with methanol for several times, and dried in a 60℃ oven to obtain Zn-MOF powder; a2, preparation of Zn-MOF@Cu-MOF: 1.5 g Zn-MOF was dispersed in 200 mL methanol to obtain solution one; 1.0 g polyvinylpyrrolidone (PVP) was dissolved in 20 mL methanol to obtain solution two; 1.0 g Cu(CH3COO)2·H2O was dissolved in 200 mL methanol to obtain solution three; 2.0 g 2-methylimidazole was dissolved in methanol to obtain solution four; first mix solution one and solution two, stir for 24 hours, then add the mixed solution to solution three, and finally add solution four, leave to react for 24 hours, centrifuge, wash with methanol, and obtain Zn-MOF@Cu-MOF composite material.

[0054] a3, carbonization: the operation was the same as example 1, to obtain CuZn-MOF carbon material with porous structure.

[0055] b, chemical vapor deposition: the operation was the same as example 1, to obtain Si@CuZn-MOF.

[0056] Test Example The specific surface area, pore volume, average pore size and resistivity of the carbon materials obtained in the above examples and comparative examples were tested, and the test results are shown in Table 1.

[0057] The silicon-carbon material obtained in each of the above examples and comparative examples was used to prepare test batteries (CR2025 lithium ion half batteries), and the first delithiation specific capacity, the first coulombic efficiency, the capacity retention rate, the rate performance of the battery cell, etc. were tested, and the test results are shown in Table 2.

[0058] The preparation method of the CR2025 lithium ion half battery in the test is as follows: The silicon-carbon material prepared above was mixed with carbon nanotubes and polyacrylic acid LA136D in a mass ratio of 90:5:5, and an appropriate amount of deionized water was added, and a paste was prepared using a homogenizer. The paste was uniformly scraped onto a copper foil with a thickness of 180 μm, and then baked in a drying oven to prepare a negative electrode sheet.

[0059] The baked negative electrode sheet was pressed and cut into a circular electrode with a diameter of 16 mm. The above circular electrode was sequentially and neatly stacked in the glove box in the order of negative electrode shell, spring sheet, gasket, lithium sheet, separator, circular electrode, and positive electrode shell, and electrolyte was injected, and a CR2025 lithium ion half battery was obtained by packaging.

[0060] Performance test method: 1. First delithiation specific capacity The above battery was discharged to 0 V using a 0.05 C current, and then discharged to 0 V using a 50 μA current, to obtain the first lithium intercalation specific capacity of the silicon-carbon material. Then the above battery was discharged using a 0.05 C current until the voltage was >1.5 V, to obtain the first delithiation specific capacity.

[0061] 2. First coulombic efficiency The first coulombic efficiency was calculated based on the above first delithiation specific capacity and first lithium intercalation specific capacity, and the first coulombic efficiency = first delithiation specific capacity / first lithium intercalation specific capacity.

[0062] 3. Capacity retention rate The above battery was cycled at 0.2 C, and the first cycle capacity C1 and the 500th cycle capacity C2 were recorded, and the capacity retention rate = C2 / C1.

[0063] 4. Rate performance of the test battery cell 1) (25±2)℃ under static state for 5 minutes; 2) 1C constant current discharge, cut-off voltage 2.5V; 3) static state for 30min; 4) 1C constant current charge, cut-off voltage 4.25V, then constant voltage charge to current≤0.05C; 5) static state for 30min; 6) XC constant current discharge to cut-off voltage 2.5V; 7) repeat 3) to 6) to obtain the discharge capacity of the battery cell at different rates. X is 2C, 3C, 5C in turn.

[0064] Unless otherwise specified, the initial lithium extraction specific capacity, the initial coulombic efficiency, the capacity retention rate, and the rate performance of the battery cell of the present application are obtained by charging and discharging test of the above-mentioned CR2025 lithium ion half-battery through the Blue Electric series battery test system.

[0065] Table 1, performance data of carbon materials of each example and comparative example

[0066] Table 2, performance data of test batteries prepared by using silicon-carbon materials of each example and comparative example

[0067] Result analysis (1) The initial lithium extraction specific capacity of Example 2 is the highest, followed by Example 3 and Example 1, and all of them are significantly higher than the comparative example, indicating that the Si@CuZn-MOF silicon-carbon material significantly improves the lithium storage capacity.

[0068] (2) In terms of the initial coulombic efficiency, the example group is higher than the comparative example, especially Example 2 reaches the highest, indicating that its interface stability is better.

[0069] (3) The 500-cycle capacity retention rate of Example 2 is significantly ahead, indicating that its cycle life is better, and the CuZn-MOF structure can effectively alleviate the capacity attenuation caused by silicon expansion.

[0070] (4) The rate performance (2C~5C) of all examples is better than that of the comparative example, especially Example 2 still maintains 87.85% capacity at 5C, which is much higher than the maximum value 76.92% of the comparative example.

[0071] Comparative observation of the microstructure of the Cu-MOF@Zn-MOF composite material of Example 2 and the CuZn-MOF carbon material shows that the bimetallic heterostructure MOF-derived CuZn-MOF carbon material has a unique pore structure, which is crucial for the stability and conductivity of the silicon-carbon material. Figure 1 、 Figure 2

[0072] In summary, the bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material of the present application not only improves the conductivity of the silicon-carbon material, optimizes the ionic conductivity of the silicon-carbon negative electrode, and increases the kinetic performance of the battery, but also effectively alleviates the volume expansion of silicon during the charging and discharging process of the battery, avoids the problem of electrode cracking caused by expansion, and improves the mechanical strength and electrochemical performance of the silicon-carbon negative electrode.

[0073] ​Please note that the technical features of the above embodiments can be combined in any manner, and for the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, however, as long as the combinations of the technical features do not contradict each other, they should be considered as within the scope of the present disclosure. The above embodiments only express several implementation manners of the present application, which are described in a more specific and detailed manner, but should not be understood as a limitation on the patent scope of the present application. It should be noted that for those skilled in the art, some modifications and improvements can be made without departing from the concept of the present application, and these are within the scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material, characterized by: The bimetallic Cu-MOF@Zn-MOF composite material was carbonized to obtain a CuZn-MOF carbon material. Silicon was deposited in the pores and surface of the CuZn-MOF carbon material by chemical vapor deposition to obtain a bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material. The bimetallic Cu-MOF@Zn-MOF composite material is prepared by reacting Cu-MOF with a soluble zinc salt and 2-methylimidazole in a methanol solvent, and the Cu-MOF is prepared by reacting a soluble copper salt with triethylamine and trimesic acid.

2. The Si@CuZn-MOF silicon-carbon material derived from a bimetallic heterostructure MOF according to claim 1, characterized in that: Cu-MOF is dispersed in methanol to obtain solution one; polyvinyl pyrrolidone is dissolved in methanol to obtain solution two; a soluble zinc salt is dissolved in methanol to obtain solution three; 2-methylimidazole is dissolved in methanol to obtain solution four; solution one and solution two are first mixed to obtain a mixed solution, which is fully stirred and then added to solution three, and finally solution four is added and allowed to react to obtain a bimetallic Cu-MOF@Zn-MOF composite material; preferably, the soluble zinc salt is any one of zinc nitrate, zinc acetate, zinc sulfate, and zinc chloride.

3. The Si@CuZn-MOF silicon-carbon material derived from a bimetallic heterostructure MOF according to claim 2, characterized in that: Disperse 0.5-1.5 g of Cu-MOF in 200 mL of methanol to obtain solution one; dissolve 1.0-5.0 g of polyvinyl pyrrolidone in 20 mL of methanol to obtain solution two; dissolve 0.01-0.03 mol of soluble zinc salt in 200 mL of methanol to obtain solution three; and dissolve 0.5-2.0 g of 2-methylimidazole in 100 mL of methanol to obtain solution four.

4. The Si@CuZn-MOF silicon-carbon material derived from a bimetallic heterostructure MOF according to claim 1, characterized in that: Dissolve 0.005-0.015 mol of a soluble copper salt, 0.5-2.0 g of acetic acid, and 2.0-5.0 ml of triethylamine in 30-50 mL of ethanol. After thorough mixing, add 0.2-1.0 g of trimesic acid and react at 90-120°C for 6-8 hours to obtain a Cu-MOF. Preferably, the soluble copper salt is any one of copper acetate, copper nitrate, copper chloride, and copper sulfate.

5. The Si@CuZn-MOF silicon-carbon material derived from a bimetallic heterostructure MOF according to claim 1, characterized in that: Carbonization is to heat the Cu-MOF@Zn-MOF composite material to 850~950℃ at 2~5℃ / min under N2 atmosphere and keep it warm for 1~3 hours to obtain a porous CuZn-MOF carbon material.

6. The Si@CuZn-MOF silicon-carbon material derived from a bimetallic heterostructure MOF according to claim 1, characterized in that: The chemical vapor deposition method is to heat the CuZn-MOF carbon material from room temperature to 350-600°C at a rate of 2-5°C / min in a N2 atmosphere; then maintain it at 350-600°C for 12-24 hours in a 20% by volume SiH4-N2 mixed atmosphere; then maintain it at 350-600°C for 2-4 hours in a 10% by volume C2H2-N2 mixed atmosphere; finally, naturally cool it in a N2 atmosphere to complete the deposition of silicon on the porous carbon material, and obtain the Si@CuZn-MOF silicon-carbon material derived from the bimetallic heterostructure MOF.

7. The method for preparing the Si@CuZn-MOF silicon-carbon material derived from the bimetallic heterostructure MOF according to any one of claims 1 to 6, characterized in that: The following steps are included: a. Preparation of CuZn-MOF carbon materials: a1. Obtaining the metal-organic framework material Cu-MOF: Dissolve 0.005-0.015 mol of a soluble copper salt, 0.5-2.0 g of acetic acid, and 2.0-5.0 mL of triethylamine in 30-50 mL of ethanol. Mix thoroughly, then add 0.2-1.0 g of trimesic acid. React at 90-120°C for 6-8 hours. Collect the precipitate, wash it, and dry it at 50-80°C to obtain Cu-MOF. a2. Obtain a bimetallic Cu-MOF@Zn-MOF composite material: disperse 0.5-1.5 g of Cu-MOF in 200 mL of methanol to obtain solution 1; dissolve 1.0-5.0 g of polyvinyl pyrrolidone in 20 mL of methanol to obtain solution 2; dissolve 0.01-0.03 mol of a soluble zinc salt in 200 mL of methanol to obtain solution 3; dissolve 0.5-2.0 g of 2-methylimidazole in 100 mL of methanol to obtain solution 4; first mix solution 1 and solution 2, and add the obtained mixture to solution 3 after thorough stirring. Finally, add solution 4, let it stand for reaction, centrifuge, and wash to obtain a bimetallic Cu-MOF@Zn-MOF composite material; a3. Carbonization: The Cu-MOF@Zn-MOF composite material was heated to 850-950°C at a rate of 2-5°C / min under N2 atmosphere and kept at this temperature for 1-3 h to obtain a porous CuZn-MOF carbon material; b. Chemical vapor deposition: The CuZn-MOF carbon material is placed in a tube furnace and heated from room temperature to 350-600°C at a rate of 2-5°C / min in a N2 atmosphere; then maintained at 350-600°C for 12-24 hours in a 20% by volume SiH4-N2 mixed atmosphere; then maintained at 350-600°C for 2-4 hours in a 10% by volume C2H2-N2 mixed atmosphere; finally, the material is naturally cooled in a N2 atmosphere to complete the deposition of silicon on the porous carbon material, obtaining a bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material.

8. The method for preparing the Si@CuZn-MOF silicon-carbon material derived from the bimetallic heterostructure MOF according to claim 7, characterized in that: The following steps are included: a. Preparation of CuZn-MOF carbon materials: a1. Obtaining the metal-organic framework material Cu-MOF: Dissolve 0.005 mol Cu(CH3COO)2·H2O, 1.5 g acetic acid, and 2.5 mL triethylamine in 50 mL ethanol. Mix thoroughly, then add 0.50 g trimesic acid. React at 100°C for 6 h. Centrifuge, wash, and dry at 60°C to obtain Cu-MOF. a2. Obtain a bimetallic Cu-MOF@Zn-MOF composite material: disperse 1.5 g of Cu-MOF in 200 mL of methanol to obtain solution 1; dissolve 1.0 g of polyvinyl pyrrolidone in 20 mL of methanol to obtain solution 2; dissolve 0.01 mol of zinc nitrate hexahydrate in 200 mL of methanol to obtain solution 3; dissolve 2.0 g of 2-methylimidazole in 100 mL of methanol to obtain solution 4; first mix solution 1 and solution 2, stir the mixture thoroughly, and then add it to solution 3, and finally add solution 4, let it stand for reaction, centrifuge, and wash to obtain a bimetallic Cu-MOF@Zn-MOF composite material; a3. Carbonization: The Cu-MOF@Zn-MOF composite material was heated to 900°C at 5°C / min under N2 atmosphere and kept at this temperature for 2 h to obtain a porous CuZn-MOF carbon material; b. Chemical vapor deposition: The CuZn-MOF carbon material was placed in a tube furnace and heated from room temperature to 500°C at a rate of 5°C / min in a N2 atmosphere; then maintained at 500°C for 15 h in a 20% by volume SiH4-N2 mixed atmosphere; then maintained at 550°C for 2 h in a 10% by volume C2H2-N2 mixed atmosphere; finally, the material was naturally cooled in a N2 atmosphere to complete the deposition of silicon on the porous carbon material, obtaining a bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon material.

9. Use of the Si@CuZn-MOF silicon-carbon material derived from a bimetallic heterostructure MOF according to any one of claims 1 to 6, characterized in that: The Si@CuZn-MOF silicon-carbon material derived from the bimetallic heterostructure MOF is used to prepare the negative electrode material of the battery, and preferably used to prepare the negative electrode material of the lithium-ion battery.

10. A bimetallic heterostructure MOF-derived Si@CuZn-MOF silicon-carbon anode, characterized by: It is made from the Si@CuZn-MOF silicon-carbon material derived from the bimetallic heterostructure MOF according to any one of claims 1 to 6.

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