WO2023056706A1

WO2023056706A1 - Silicon composite negative electrode material and preparation method therefor, and secondary battery

Info

Publication number: WO2023056706A1
Application number: PCT/CN2021/137617
Authority: WO
Inventors: 薛冬峰; 彭超; 王晓明; 王鑫
Original assignee: 中国科学院深圳先进技术研究院
Priority date: 2021-10-09
Filing date: 2021-12-13
Publication date: 2023-04-13
Also published as: CN113964303A

Abstract

The present application belongs to the technical field of batteries, and more particularly, relates to a silicon composite negative electrode material and a preparation method therefor, and a secondary battery. The silicon composite negative electrode material has a core-shell structure and comprises a silicon-based material inner core, and an intermediate layer and a shell layer which are sequentially coated on the outer surface of the inner core, the intermediate layer comprising a carbon nanomaterial loaded with a metal element, and the shell layer comprising an amorphous carbon material. In the silicon composite negative electrode material provided by the present application, a synergistic effect of the core silicon-based material, intermediate layer carbon nanomaterial loaded with the metal element and the shell layer amorphous carbon material, causes the silicon composite negative electrode material to not only have excellent specific capacity, but also to have good structural stability and high ion and electron mobility and transport efficiency, and can effectively improve the energy density, cycle life, safety and other electrochemical properties of a battery.

Description

Silicon composite negative electrode material, preparation method thereof, and secondary battery

technical field

The application belongs to the technical field of batteries, and in particular relates to a silicon composite negative electrode material and a preparation method thereof, and a secondary battery.

Background technique

At present, the theoretical specific capacity of graphite-based anode materials widely used in lithium-ion batteries is only 372mAh·g ^-1 , while the theoretical specific capacity of silicon is as high as 4200mAh·g ^-1 , and the lithium intercalation potential is lower than 0.5V. Silicon is abundant in earth reserves, cheap and environmentally friendly. Under the urgent need to improve the performance of lithium-ion batteries, silicon is expected to become a new generation of high-capacity anode materials. However, silicon anode materials for lithium-ion batteries have these bottleneck problems in the charging and discharging process: (1) silicon will produce more than 300% volume expansion in the process of lithiation/delithiation, which will lead to problems such as particle breakage, pulverization and shedding , eventually leading to battery performance attenuation; (2) Due to the continuous change of electrode volume during charge and discharge, the solid electrolyte film (SEI) on the surface of the silicon negative electrode will be repeatedly destroyed and regenerated, resulting in a decrease in the conductivity of the material and a decrease in charge and discharge efficiency, etc. Problems; (3) Silicon has poor electrical conductivity, and the diffusion coefficient of lithium ions in silicon materials is small, resulting in poor power density of silicon negative electrode materials, and it is difficult to meet the requirements of high specific capacity.

In this regard, in terms of structural design of composite materials, more egg yolk-shell structures are used. Generally, egg yolk-shell structure silicon carbon materials with carbon as the shell and silicon as the core have a certain gap between the inner core and the outer shell. This structure can provide a buffer layer for the volume expansion of the electrode, and avoid the direct contact between the silicon anode and the electrolyte to improve the instability of the SEI film. Although the existing technology has alleviated the problem caused by the volume change of silicon to a certain extent, there is still room for improvement in improving the ionic conductivity and electronic conductivity of the silicon anode.

Contents of the invention

The purpose of this application is to provide a silicon composite negative electrode material and its preparation method, as well as a secondary battery, which aims to solve the problems of large volume expansion and poor ion and electronic conductivity of existing silicon-based materials to a certain extent.

In order to realize the above-mentioned application purpose, the technical scheme adopted in this application is as follows:

In the first aspect, the present application provides a silicon composite negative electrode material, the silicon composite negative electrode material is a core-shell structure, including a silicon-based material core and an intermediate layer and an outer shell layer that are sequentially coated on the outer surface of the core; wherein, the The middle layer includes carbon nanomaterials loaded with metal elements, and the outer shell layer includes amorphous carbon materials.

Further, in the carbon nanomaterial loaded with metal elements, the metal elements include: at least one of copper and silver.

Further, in the carbon nanomaterials loaded with metal elements, the carbon nanomaterials include: at least one of graphene and carbon nanotubes.

Further, in the carbon nanomaterial loaded with metal elements, the loading amount of metal elements is 18-23wt%.

Further, the carbon nanomaterial loaded with metal elements is selected from: copper-graphene composite material.

Further, in the silicon composite negative electrode material, the mass ratio of the silicon-based material inner core, the intermediate layer and the outer shell layer is 1:(0.5-0.8):(0.5-0.8).

Further, in the silicon composite negative electrode material, the particle diameter D50 of the inner core of the silicon-based material is 200 nm-1 μm, the thickness of the middle layer is 100 nm-1 μm, and the thickness of the outer shell layer is 100 nm-1 μm.

Further, the silicon-based material is selected from at least one of simple silicon, silicon oxide, and silicon carbide.

In a second aspect, the present application provides a method for preparing a silicon composite negative electrode material, comprising the following steps:

Preparation of carbon nanomaterials loaded with metal elements;

Obtaining a silicon-based material, forming a coating intermediate layer on the surface of the silicon-based material with the carbon nanomaterial loaded with metal elements to obtain an intermediate product;

A shell layer of amorphous carbon material is prepared on the outer surface of the intermediate product to obtain a silicon composite negative electrode material.

Further, the step of preparing the carbon nanomaterials loaded with metal elements comprises: after modifying the surface of the carbon nanomaterials with a complexing agent, complexing with a metal salt, reducing the metal salts, and obtaining the carbon nanomaterials loaded with metal elements.

Further, the step of forming the coating intermediate layer includes: mixing the carbon nanomaterial loaded with metal elements and the silicon-based material and then vacuum drying to obtain an intermediate product of the intermediate layer coating the silicon-based material.

Further, the step of preparing the outer shell layer of the amorphous carbon material includes: after mixing the intermediate product with the amorphous carbon source, performing vapor deposition to form the outer shell layer of the amorphous carbon material to obtain a silicon composite negative electrode material.

Further, the complexing agent is selected from at least one of octadecylamine, ethylenediamine, sec-butylamine, dodecylamine, and hexadecylamine.

Further, the metal salt is selected from at least one of copper salt and silver salt.

Further, the carbon nanomaterial is selected from at least one of graphene and carbon nanotubes.

Further, the amorphous carbon source is selected from at least one of glucose, citric acid, pitch, phenolic resin, and epoxy resin.

Further, the carbon nanomaterial loaded with metal elements is selected from a copper-graphene composite material, and the step of preparing the copper-graphene composite material includes:

Mixing and grinding the complexing agent and graphene to obtain complexing agent-modified graphene;

After dissolving the copper salt and the graphene modified by the complexing agent in an organic solvent, adding a reducing agent to reduce the copper salt to obtain the copper-graphene composite material.

Further, the copper salt is selected from at least one of: Cu(CH ₃ COO) ₂ ·H ₂ O, copper sulfate, copper acetate, and copper chloride.

Further, the mass ratio of the copper salt to the graphene modified by the complexing agent is (0.01˜2):1.

Further, the reducing agent is selected from at least one of acetaldehyde, hydrazine hydrate, sodium borohydride, formaldehyde and propionaldehyde.

Further, the organic solvent is selected from at least one of sec-butanol, tert-butanol and ethanol.

In a third aspect, the present application provides a secondary battery, wherein the negative electrode sheet of the secondary battery contains the above-mentioned silicon composite negative electrode material, or contains the silicon composite negative electrode material prepared by the above method.

The silicon composite negative electrode material provided by the first aspect of the present application is a core-shell structure, including a silicon-based material core with a high theoretical specific capacity and an intermediate layer and an outer shell layer that are sequentially coated on the outer surface of the inner core; wherein the intermediate layer contains Carbon nanomaterials loaded with metal elements, on the one hand, the toughness of the metal and the flexibility of the carbon nanomaterials enable the middle layer to well absorb the stress generated by the drastic volume change of the silicon-based material in the core, thereby avoiding the extreme stress caused by the volume change of the silicon-based material. On the other hand, metal and carbon nanomaterials have high ion or electronic conductivity, which can effectively improve the migration and transmission rate of lithium ions and electrons between the outer shell of amorphous carbon materials and the inner core of silicon-based materials, thereby Improve the overall power density of the silicon composite negative electrode material. In addition, the outer shell layer contains amorphous carbon materials, which have high reversible specific capacity, high conductivity, good compatibility with electrolyte, and have a certain buffering effect on the volume change of the inner core silicon nanomaterials.

The preparation method of the silicon composite negative electrode material provided by the second aspect of the present application has simple process flow and high efficiency, and is suitable for large-scale industrial production and application. And the prepared structure is a silicon composite anode material with a core silicon-based material-a carbon nanomaterial loaded with metal elements in the middle layer-amorphous carbon material in the outer shell layer, which not only has excellent specific capacity, but also has good structural stability, and ion electron migration and transmission High efficiency can effectively improve the electrochemical performance of the battery such as energy density, cycle life, and safety.

In the secondary battery provided by the third aspect of the present application, because the negative electrode sheet contains the above-mentioned silicon composite negative electrode material, the silicon composite negative electrode material has excellent specific capacity, good structural stability, and high ion electron migration and transmission efficiency, so it can be used Effectively improve the electrochemical performance of the secondary battery such as energy density, cycle life, and safety.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the accompanying drawings that need to be used in the descriptions of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings in the following description are only for the present application For some embodiments, those of ordinary skill in the art can also obtain other drawings based on these drawings without any creative effort.

Fig. 1 is the structural representation of the silicon composite negative electrode material that the embodiment of the present application provides;

Fig. 2 is a schematic flowchart of a method for preparing a silicon composite negative electrode material provided in an embodiment of the present application.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application clearer, the present application will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not intended to limit the present application.

In this application, the term "and/or" describes the association relationship of associated objects, indicating that there may be three relationships, for example, A and/or B may mean: A exists alone, A and B exist simultaneously, and B exists alone Condition. Among them, A and B can be singular or plural. The character "/" generally indicates that the contextual objects are an "or" relationship.

In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one (one) of a, b or c", or "at least one (one) of a, b and c" can mean: a, b, c, a-b (that is, a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

It should be understood that in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the order of execution, and some or all steps may be executed in parallel or sequentially, and the execution order of each process shall be based on its functions and The internal logic is determined and should not constitute any limitation to the implementation process of the embodiment of the present application.

Terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of this application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

The weight of the relevant components mentioned in the description of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the various components. The scaling up or down of the content of the fraction is within the scope disclosed in the description of the embodiments of the present application. Specifically, the mass in the description of the embodiments of the present application may be μg, mg, g, kg and other well-known mass units in the chemical industry.

The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be called the second XX, and similarly, the second XX can also be called the first XX. Thus, a feature defined as "first" and "second" may explicitly or implicitly include one or more of these features.

As shown in Figure 1, the first aspect of the embodiment of the present application provides a silicon composite negative electrode material. The silicon composite negative electrode material has a core-shell structure, including a silicon-based material core, an intermediate layer and a shell that are sequentially coated on the outer surface of the core. layer; wherein, the middle layer contains carbon nanomaterials loaded with metal elements, and the outer shell layer contains amorphous carbon materials.

The silicon composite anode material provided in the first aspect of the embodiment of the present application is a core-shell structure, including a silicon-based material core with a high theoretical specific capacity and an intermediate layer and an outer shell layer that are sequentially coated on the outer surface of the inner core; wherein the intermediate layer contains Carbon nanomaterials of metal elements, on the one hand, the toughness of metals and the flexibility of carbon nanomaterials enable the middle layer to well absorb the stress generated by the drastic volume change of the silicon-based material in the core, thereby avoiding the pole piece damage caused by the volume change of the silicon-based material and other adverse consequences; on the other hand, metal and carbon nanomaterials have high ion or electronic conductivity, which can effectively increase the migration and transmission rate of lithium ions and electrons between the outer layer of amorphous carbon material and the inner core of silicon-based materials, thereby improving the silicon The overall power density of the composite negative electrode material. In addition, the outer shell layer contains amorphous carbon materials, which have high reversible specific capacity, high conductivity, good compatibility with electrolyte, and have a certain buffering effect on the volume change of the inner core silicon nanomaterials. Therefore, the silicon composite negative electrode material provided by the embodiment of the present application, through the synergistic effect of the inner silicon-based material, the carbon nanomaterial loaded with metal elements in the middle layer, and the amorphous carbon material in the outer layer, makes the silicon composite negative electrode material not only have excellent The specific capacity, good structural stability, and high ion and electron migration and transmission efficiency can effectively improve the electrochemical performance of the battery such as energy density, cycle life, and safety.

In some embodiments, in the carbon nanomaterials loaded with metal elements, the metal elements include: at least one of copper and silver; these metal elements not only have excellent electron migration and transport properties, but also improve electron transfer between the inner core and the outer shell. Diffusion rate; and has excellent ductility and toughness, which can well absorb the stress generated by the dramatic volume change of the core silicon-based material during charge and discharge, reduce the volume change of the pole piece, improve the stability of the pole piece, and prevent the pole piece Cracking, powder falling, etc., improve battery cycle stability.

In some embodiments, among the carbon nanomaterials loaded with metal elements, the carbon nanomaterials include: at least one of graphene and carbon nanotubes; these carbon nanomaterials all have excellent ion conductivity, which can improve the charging performance of the battery. The ion intercalation and deintercalation effect during the discharge process improves the rate performance of the battery. Moreover, these carbon nanomaterials are easy to form a loose intermediate cladding layer through mutual van der Waals force and other forces, which provide a buffer space for the volume change of the core silicon-based material during charge and discharge, and further improve the performance of the silicon nano-core material. stability.

In the middle layer of the silicon negative electrode material in the embodiment of the present application, the metal is loaded in the carbon nanomaterial, which can improve the loading uniformity of the metal element, and through the synergistic effect of the metal element and the carbon nanomaterial, the volume deformation of the core silicon-based material can be alleviated, and the improvement can be achieved. The transfer efficiency of ionic electrons in the inner core and outer shell. In some embodiments, in the carbon nanomaterials loaded with metal elements, the loading amount of metal elements is 18-23wt%, which fully ensures that the intermediate layer can relieve the volume deformation of the core silicon-based material, and at the same time ensures that the silicon Gram capacity of matrix composites. If the loading of metal elements is too high, neither the metal elements nor carbon nanomaterials can participate in the intercalation and deintercalation cycle of ions during the charging and discharging process of the battery, which will significantly reduce the gram capacity of the silicon composite negative electrode material, thereby reducing the energy density of the battery. However, when the metal element directly forms an independent coating layer, not only will the gram capacity of the silicon composite negative electrode material be significantly reduced, but the metal element coating layer will affect the insertion and extraction efficiency of lithium ions in the core silicon-based material, thereby reducing The rate performance of the battery.

In some embodiments, the carbon nanomaterials loaded with metal elements are selected from: copper-graphene composite materials. The intermediate layer formed by the copper-graphene composite material in the embodiment of the present application, on the one hand, the toughness of copper and the flexibility of graphene enable it to well absorb the stress generated by the drastic volume change of the core silicon-based material, thereby avoiding the volume change On the other hand, the high ionic conductivity of copper and graphene can effectively increase the diffusion rate of lithium ions between the amorphous carbon shell and the silicon-based material core, thereby increasing the overall power density of the negative electrode material.

In some embodiments, in the silicon composite negative electrode material, the mass ratio of the silicon-based material inner core, intermediate layer, and outer shell layer is 1: (0.5-0.8): (0.5-0.8); this ratio fully ensures the silicon composite negative electrode material. Specific capacity, structural stability, cycle performance and other comprehensive properties. If the proportion of the middle layer or the shell layer is too low, the volume deformation of the core silicon-based material during charging and discharging will not be alleviated, and it will be difficult to improve the stability of the negative electrode material, and it will not be conducive to improving the concentration of ions and electrons in the silicon composite negative electrode material. If the proportion of the middle layer or the shell layer is too high, the content of silicon-based materials will be reduced, thereby reducing the gram capacity of the negative electrode material and reducing the energy density of the battery. In some specific embodiments, in the silicon composite negative electrode material, the mass ratio of the silicon-based material inner core, intermediate layer and outer shell layer includes but is not limited to 1:0.5:0.5, 1:0.5:0.6, 1:0.5:0.7, 1: 0.5:0.8, 1:0.6:0.8, 1:0.7:0.8, 1:0.8:0.8, 1:0.6:0.7, 1:0.7:0.6, 1:0.8:0.7, etc.

In some embodiments, in the silicon composite negative electrode material, the particle diameter D50 of the inner core of the silicon-based material is 200 nm to 1 μm, preferably 200 to 500 nm, the thickness of the intermediate layer is 100 nm to 1 μm, preferably 100 to 500 nm, and the thickness of the outer shell layer is 100 nm to 1 μm, preferably 100 to 500 nm. In the embodiment of the present application, in the silicon composite negative electrode material, the particle size of the silicon-based material core and the thickness of the middle layer and the outer shell layer also effectively ensure the comprehensive performance of the silicon composite negative electrode material such as specific capacity, structural stability, and cycle performance, and The ghost composite negative electrode material has a larger specific surface area, which provides a larger active specific surface area for the deintercalation of lithium ions, thereby improving the cycle charge and discharge efficiency of the battery. If the middle layer or outer shell layer is too thin, it will not be effective in alleviating the volume deformation of the core silicon-based material during charging and discharging, and it will be difficult to improve the stability of the negative electrode material, and it will not be conducive to improving the migration of ions and electrons in the silicon composite negative electrode material. Transmission effect; if the middle layer or outer shell layer is too thick, the content of silicon-based materials will be reduced, thereby reducing the gram capacity of the negative electrode material and reducing the energy density of the battery.

In some embodiments, the silicon-based material is selected from at least one of: simple silicon, silicon oxide, and silicon carbide. These silicon-based materials have a high theoretical specific capacity and can effectively increase the energy density of the battery.

The silicon composite anode material in the embodiment of the present application can be prepared by the method in the following embodiment.

As shown in accompanying drawing 2, the second aspect of the embodiment of the present application provides a kind of preparation method of silicon composite negative electrode material, comprises the following steps:

S10. preparing carbon nanomaterials loaded with metal elements;

S20. Obtain a silicon-based material, form an intermediate coating layer on the surface of the silicon-based material with a carbon nanomaterial loaded with metal elements, and obtain an intermediate product;

S30. Prepare an outer shell layer of an amorphous carbon material on the outer surface of the intermediate product to obtain a silicon composite negative electrode material.

The preparation method of the silicon composite negative electrode material provided in the second aspect of the embodiment of the present application, after preparing the carbon nanomaterial loaded with metal elements, forms a coating intermediate layer on the surface of the silicon-based material, and then prepares the outer shell layer of the amorphous carbon material A silicon composite negative electrode material with a core-shell structure comprising a silicon-based material core-a carbon nanomaterial intermediate layer loaded with metal elements-an amorphous carbon material shell layer is obtained. The preparation method of the silicon composite negative electrode material in the embodiment of the present application has a simple process flow and high efficiency, and is suitable for large-scale industrial production and application. And the prepared structure is a silicon composite anode material with a core silicon-based material-a carbon nanomaterial loaded with metal elements in the middle layer-amorphous carbon material in the outer shell layer, which not only has excellent specific capacity, but also has good structural stability, and ion electron migration and transmission High efficiency can effectively improve the electrochemical performance of the battery such as energy density, cycle life, and safety.

In some embodiments, in the above step S10, the step of preparing a carbon nanomaterial loaded with a metal element includes: after modifying the complexing agent on the surface of the carbon nanomaterial, complexing with a metal salt, reducing the metal salt, and obtaining a metal-loaded Elemental carbon nanomaterials. In the embodiment of the present application, the complexing agent is firstly modified to the surface of the carbon nanomaterial, and then the metal salt is uniformly complexed on the surface of the carbon nanomaterial through the complexing agent, and then the metal salt is reduced to a simple metal substance, so that the simple metal substance is uniform and stable. Loaded in the carbon nano material, the carbon nano material loaded with the metal element is obtained. In addition, the loading amount of metal elements in carbon nanomaterials can be controlled by changing the amount and type of complexing agent modified on the surface of carbon nanomaterials.

In some embodiments, the complexing agent is selected from: at least one of octadecylamine, ethylenediamine, sec-butylamine, dodecylamine, and hexadecylamine; these complexing agents can be modified to the surface of carbon nanomaterials, A carbon nanomaterial surface-modified with a complexing agent is formed. Moreover, these complexing agents have a good complexation effect on metal salts through ammonium ions, and can form a highly uniform and stable dispersion of carbon nanomaterials-organic amine-metal ion complexes.

In some embodiments, the metal salt is selected from: at least one of copper salt and silver salt; metal elements in these metal salts not only have excellent electron migration and transport properties, but also increase the diffusion rate of electrons between the inner core and the outer shell; Moreover, it has excellent ductility and toughness, which can well absorb the stress caused by the drastic volume change of the core silicon-based material during charging and discharging, reduce the volume change of the pole piece, and improve the stability of the pole piece.

In some embodiments, the carbon nanomaterials are selected from: at least one of graphene and carbon nanotubes; first, the surface of these carbon nanomaterials often contains more active groups such as defect sites or hydroxyl groups, which is conducive to the attachment of complexing agents grooming. In addition, these carbon nanomaterials all have excellent ionic conductivity, which can improve the effect of ion intercalation and deintercalation during the charging and discharging process of the battery, thereby improving the rate performance of the battery. Moreover, these carbon nanomaterials are easy to form a loose intermediate cladding layer through mutual van der Waals force and other forces, which provide a buffer space for the volume change of the core silicon-based material during charge and discharge, and further improve the performance of the silicon nano-core material. stability.

In some embodiments, the carbon nanomaterial loaded with metal elements is selected from the composite material of copper-graphene, and the step of preparing the composite material of copper-graphene includes:

S11. Mixing and grinding the complexing agent and graphene to obtain graphene modified by the complexing agent;

S12. After dissolving the copper salt and complexing agent-modified graphene in an organic solvent, adding a reducing agent to reduce the copper salt to obtain a copper-graphene composite material.

In some embodiments, in step S11, graphite flakes and complexing agents such as octadecylamine, ethylenediamine, sec-butylamine, dodecylamine, hexadecylamine, etc. can be dissolved and dispersed in an organic solvent, and then ground and mixed Treatment, preferably ball milling at a speed of 400r/min for 24 hours, and then the ground products are separated in different centrifugal intervals to obtain centrifugal products in different centrifugal intervals, and then the centrifugal products in different intervals are sedimented, centrifuged and washed to obtain The complexing agent-modified graphene is dispersed in an organic solvent to form a dispersion for subsequent use.

In some embodiments, the organic solvent is selected from: at least one of sec-butanol, tert-butanol, and ethanol, and these organic solvents are suitable for octadecylamine, ethylenediamine, sec-butylamine, dodecylamine, hexadecylamine, etc. All complexing agents have a good dissolving effect, and also have a good dispersion effect on graphene raw materials or graphene.

In some embodiments, in the above step S12, after dissolving the graphene modified by the copper salt and complexing agent in an organic solvent such as sec-butanol to form a highly uniform and stable graphene-organic amine-copper complex dispersion, Then add a reducing agent to reduce the copper salt to form a copper-graphene composite material.

In some embodiments, the copper salt is selected from at least one of: Cu(CH ₃ COO) ₂ ·H ₂ O, copper sulfate, copper acetate, and copper chloride, and these copper salts are dissolved and dispersed in solvents such as sec-butanol The effect is good, and it has better complexing effect with complexing agent.

In some embodiments, the reducing agent is selected from: at least one of acetaldehyde, hydrazine hydrate, sodium borohydride, formaldehyde, and propionaldehyde; these reducing agents can reduce copper salts to copper simple substances, so that the copper simple substances can be uniformly and stably Loaded in graphene material.

In some embodiments, the mass ratio of the copper salt to the graphene modified by the complexing agent is (0.01-2): 1; this ratio fully ensures the loading effect of the copper salt in the graphene, thereby ensuring that the formed copper -The middle layer of the graphene composite material alleviates the volume deformation of the core silicon-based material, while ensuring the gram capacity of the silicon-based composite material. If the addition ratio of copper salt is too high, it will be difficult to fully load the graphene, which will increase the difficulty of subsequent impurity removal. If the addition ratio of copper salt is too low, it will lead to too few metal elements loaded on the surface of graphene, which is not conducive to improving the silicon composite negative electrode. Material stability and ion electron conduction efficiency. In some embodiments, the mass ratio of copper salt to complexing agent-modified graphene includes but is not limited to (0.01～0.1):1, (0.1～0.5):1, (0.5～1):1, (1～1.5 ): 1, (1.5～2): 1, etc.

In some embodiments, in the above step S20, the step of forming the coating intermediate layer includes: mixing the carbon nanomaterial loaded with metal elements and the silicon-based material, and then vacuum drying to prevent copper from being oxidized in a high temperature environment, and obtain the intermediate layer coating Intermediate products of silicon-coated materials. In some specific embodiments, a certain amount of micron silicon is impregnated in the dispersion liquid of high-concentration copper-graphene composite material, it is uniformly mixed and ultrasonically dispersed, and then dried in a vacuum freeze-drying oven for 10 hours to form copper-graphene The intermediate layer of the composite material obtains an intermediate product in which the surface of the inner core of the silicon material is covered by the intermediate layer.

In some embodiments, in the above step S30, the step of preparing the outer shell layer of the amorphous carbon material includes: after mixing the intermediate product with the amorphous carbon source, performing vapor deposition to form the outer shell layer of the amorphous carbon material to obtain a silicon composite negative electrode Material. In some embodiments, the amorphous carbon source is selected from at least one of glucose, citric acid, pitch, phenolic resin, and epoxy resin. In the embodiment of the present application, after the intermediate product is mixed with the amorphous carbon source, the amorphous carbon source is converted into an amorphous carbon material coating shell layer by vapor deposition at high temperature.

In some specific embodiments, the intermediate product is mixed with a certain amount of amorphous carbon source in a mass ratio of 10:3, 10:4 or 10:5, etc., in a vibrating ball mill for 8-12 hours, and then uniformly mixed and ultrasonically dispersed. Then dry in a vacuum oven at 40-60°C for 8-15 hours. Then the ball milled product is placed in a tube furnace for chemical vapor deposition, and the temperature is raised from room temperature to 400-900°C at a rate of 1-10°C/min under an Ar/H ₂ inert atmosphere, and then in C ₂ H ₂ /Ar, etc. Chemical vapor deposition in an atmosphere of carbon source for 30-60 minutes. After chemical vapor deposition, the product is cooled in a furnace, then cleaned with hydrochloric acid, hydrofluoric acid, water, ethanol and other solutions, and vacuum-dried to obtain a silicon composite negative electrode material.

In some embodiments, in the silicon composite negative electrode material, the mass ratio of the silicon-based material inner core, intermediate layer, and outer shell layer is 1: (0.5-0.8): (0.5-0.8), which fully ensures the silicon composite negative electrode material. Specific capacity, structural stability, cycle performance and other comprehensive properties. If the proportion of the middle layer or the shell layer is too low, the volume deformation of the core silicon-based material during charging and discharging will not be alleviated, and it will be difficult to improve the stability of the negative electrode material, and it will not be conducive to improving the concentration of ions and electrons in the silicon composite negative electrode material. If the proportion of the middle layer or the shell layer is too high, the content of silicon-based materials will be reduced, thereby reducing the gram capacity of the negative electrode material and reducing the energy density of the battery.

The third aspect of the embodiment of the present application provides a secondary battery, the negative electrode sheet of the secondary battery contains the above-mentioned silicon composite negative electrode material, or contains the silicon composite negative electrode material prepared by the above method.

In the secondary battery provided in the third aspect of the embodiment of the present application, because the negative electrode sheet contains the above-mentioned silicon composite negative electrode material, the silicon composite negative electrode material has excellent specific capacity, good structural stability, and high ion electron migration and transmission efficiency. Therefore, the electrochemical properties such as energy density, cycle life, and safety of the secondary battery can be effectively improved.

In some embodiments, in addition to the above-mentioned silicon composite negative electrode material, the negative electrode sheet of the secondary battery also contains components such as adhesives and conductive agents. The application needs to select the appropriate material.

In some embodiments, the content of the binder in the active layer of the negative electrode sheet is 2wt%-4wt%. In a specific embodiment, the content of the binder may be 2wt%, 3wt%, 4wt% and other typical and non-limiting contents. In a specific embodiment, the binder includes polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer One or more of substances, sodium alginate, chitosan and chitosan derivatives.

In some embodiments, the content of the conductive agent in the active layer of the negative electrode sheet of the secondary battery is 3wt%-5wt%. In a specific embodiment, the content of the conductive agent may be 3wt%, 4wt%, 5wt% and other typical and non-limiting contents. In a specific embodiment, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotube.

In some embodiments, the preparation process of the negative electrode sheet of the secondary battery can be: mixing the silicon composite negative electrode material, the conductive agent and the binder to obtain the electrode slurry, coating the electrode slurry on the current collector, drying, Negative electrode sheets are prepared by rolling, die-cutting and other steps.

The secondary battery in the embodiment of the present application may be a lithium ion battery or a lithium metal battery.

The positive electrode sheet, electrolyte, separator, etc. of the secondary battery in the embodiment of the present application are not specifically limited, and may be applicable to any battery system.

In order to make the above-mentioned implementation details and operations of the present application clearly understood by those skilled in the art, as well as the remarkable embodiment of the silicon composite negative electrode material and its preparation method, and the improved performance of the secondary battery in the embodiments of the present application, the following is described through multiple examples Give an example to illustrate the above-mentioned technical solution.

Example 1

A silicon composite negative electrode material, the preparation of which comprises the steps of:

① Weigh 2g of graphite flakes and 400mg of octadecylamine, measure quantitative sec-butanol, put graphite flakes, octadecylamine and sec-butanol into a ball mill jar, ball mill at a speed of 400r/min for 24 hours, and ball mill the product Separation is carried out in different centrifugation intervals to obtain graphene products in different centrifugation intervals, and then the centrifugation products in different intervals are subjected to sedimentation, centrifugation and washing, and the cycle is 4 times, and the final octadecylamine-modified graphene product is dispersed in the sec-butylene Form a dispersion in alcohol for later use.

② Dissolve Cu(CH ₃ COO) ₂ ·H ₂ O in sec-butanol to form an organic solution, the concentration of copper salt is 0.1mol/L. Add surface-modified octadecylamine graphene dispersion liquid, wherein the mass ratio of surface-modified octadecylamine graphene to copper is 1:3. Stir fully and uniformly to complex the octadecylamine modified on the surface of graphene with copper ions to form a highly uniform and stable graphene-organic amine-copper complex dispersion. Adding acetaldehyde, the molar ratio of acetaldehyde: copper salt is about 0.5:1, under the action of acetaldehyde, Cu is reduced to form a copper-graphene-based composite material. In this process, the reaction rate can be controlled by changing the amount and type of organic amines on the graphene surface, such as changing the length of the carbon chain of the organic amine. The longer the carbon chain, the slower the reaction, thereby regulating the reduction rate. Finally, the obtained product was centrifuged and washed three times, and the copper-graphene-based composite product was dispersed in sec-butanol to form a dispersion, and the concentration was increased for later use.

③Immerse the micron silicon in the copper-graphene-based composite dispersion, mix it uniformly and ultrasonically disperse it, and then dry it in a vacuum freeze-drying oven for 10 hours to obtain the micron silicon@copper-graphene-based composite material, in which the copper element The loading is 23%.

④Mix the micro-silicon@copper-graphene-based composite material with a certain amount of amorphous carbon at a mass ratio of 10:3 and ball mill for 10 hours under a vibrating ball mill. Then it was uniformly mixed and ultrasonically dispersed, and then dried in a vacuum oven at 50° C. for 12 hours. Then the ball-milled product was placed in a tube furnace for chemical vapor deposition, and the temperature was raised from room temperature to 500 °C at a rate of 6 °C/min under an Ar/H ₂ inert atmosphere, followed by chemical vapor deposition in a C ₂ H ₂ /Ar atmosphere for 50 minute.

⑤ After chemical vapor deposition, cool the product in the furnace, then add it to 1M hydrochloric acid solution for cleaning, then clean it with 10% hydrofluoric acid, rinse it with water and ethanol for 4-5 times, then put it in a vacuum oven Dried to obtain a silicon composite negative electrode material of silicon@copper-graphene@amorphous carbon, wherein the particle diameter D50 of the inner core of the silicon material is 1um, the mass percentage is 50%, and the mass percentage of the copper-graphene interlayer The content is 25%, and the mass percentage content of the amorphous carbon material shell layer is 25%.

A kind of lithium ion battery, its preparation comprises the steps:

⑥Preparation of negative electrode sheet: silicon@copper-graphene@amorphous carbon silicon composite negative electrode material: binder SBR: conductive agent SP is mixed and dissolved in the solvent at a mass ratio of 10:2:2 to form a uniformly dispersed and stable negative electrode After the slurry is coated on the copper foil, it is put into an oven and dried at 70°C for 2 hours, and is compacted by a roller press at a pressure of 9 MPa to obtain a negative electrode sheet;

⑦ The electrolyte is 1M LiPF ₆ /(EC:DMC=1:1), the separator is PE film, and a button half-cell is prepared in a glove box with a lithium sheet as the counter electrode.

Example 2

A silicon composite negative electrode material, the difference from Example 1 is: in the micron silicon@copper-graphene-based composite material prepared in step ③, the loading amount of copper element is 18%.

A lithium ion battery, the difference from the embodiment is that the silicon composite negative electrode material of the embodiment 2 is used in the negative electrode sheet.

Example 3

A silicon composite negative electrode material, the difference from Example 1 is: in the silicon composite negative electrode material of silicon@copper-graphene@amorphous carbon prepared in step 5, the particle diameter D50 of the silicon material core is 200nm, and the mass is 100nm. The content of copper is about 40%, the mass percentage of the copper-graphene intermediate layer is about 30%, and the mass percentage of the amorphous carbon material outer layer is about 30%.

A lithium ion battery, the difference from the embodiment is that the silicon composite negative electrode material of the embodiment 3 is used in the negative electrode sheet.

Comparative example 1

①Immerse the micron silicon in the graphene material dispersion with a mass ratio of 1:0.5, mix it uniformly and ultrasonically disperse it, and then dry it in a vacuum freeze-drying oven for 10 hours to obtain the micron silicon@graphene composite material.

④Mix the micro-silicon@graphene composite material with a certain amount of amorphous carbon at a mass ratio of 10:3, and ball mill and mix them under a vibrating ball mill for 10 hours. Then it was uniformly mixed and ultrasonically dispersed, and then dried in a vacuum oven at 50° C. for 12 hours. Then the ball-milled product was placed in a tube furnace for chemical vapor deposition, and the temperature was raised from room temperature to 500 °C at a rate of 6 °C/min under an Ar/H ₂ inert atmosphere, followed by chemical vapor deposition in a C ₂ H ₂ /Ar atmosphere for 50 minute.

⑤ After chemical vapor deposition, cool the product in the furnace, then add it to 1M hydrochloric acid solution for cleaning, then clean it with 10% hydrofluoric acid, rinse it with water and ethanol for 4-5 times, then put it in a vacuum oven Dried to obtain a silicon composite negative electrode material of silicon@graphene@amorphous carbon, wherein the particle diameter D50 of the inner core of the silicon material is 200nm, the mass percentage is 42%, and the mass percentage of the graphene intermediate layer is 26% , the mass percentage of the amorphous carbon material shell layer is 32%.

A lithium ion battery, which is different from the examples in that: the silicon composite negative electrode material of Comparative Example 1 is used in the negative electrode sheet.

Further, in order to verify the progress of the embodiments of the present application, the following battery performance tests were carried out for each embodiment and comparative example:

The lithium-ion batteries prepared in Examples 1-5 and Comparative Example 1 were respectively discharged at 0.1C and charged to 2.5V at 0.1C, and the first lithium intercalation capacity and delithiation capacity were recorded, and the first effect was calculated. In addition, the efficiency of each battery after 50 cycles of charging and discharging was measured. The test results are shown in Table 1 below:

Table 1

It can be seen from the above test results that the silicon composite negative electrode materials prepared in Examples 1 to 3 of the present application have a core-shell structure of silicon material core-copper graphene intermediate layer-amorphous carbon material shell layer, all exhibit high capacity, high initial efficiency and high cycle stability. However, the first effect and cycle stability of Comparative Example 1 in which the middle layer only contains graphene is obviously lower than that of Examples 1-3.

The above descriptions are only preferred embodiments of the application, and are not intended to limit the application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the application should be included in the protection of the application. within range.

Claims

A silicon composite negative electrode material, characterized in that the silicon composite negative electrode material is a core-shell structure, including a silicon-based material core and an intermediate layer and a shell layer that are sequentially coated on the outer surface of the core; wherein the intermediate layer It includes carbon nanomaterials loaded with metal elements, and the shell layer includes amorphous carbon materials.
The silicon composite negative electrode material according to claim 1, wherein in the carbon nanomaterial loaded with metal elements, the metal elements include: at least one of copper and silver;

And/or, in the carbon nanomaterials loaded with metal elements, the carbon nanomaterials include: at least one of graphene and carbon nanotubes;

And/or, in the carbon nanomaterial loaded with metal elements, the loading amount of metal elements is 18-23wt%.
The silicon composite negative electrode material according to claim 2, wherein the carbon nanomaterial loaded with metal elements is selected from the group consisting of copper-graphene composite materials.
The silicon composite negative electrode material according to any one of claims 1 to 3, characterized in that, in the silicon composite negative electrode material, the mass ratio of the silicon-based material inner core, the middle layer and the outer shell layer is 1: (0.5～0.8): (0.5～0.8);

And/or, in the silicon composite anode material, the particle diameter D50 of the inner core of the silicon-based material is 200nm-1μm, the thickness of the middle layer is 100nm-1μm, and the thickness of the outer shell layer is 100nm-1μm;

And/or, the silicon-based material is selected from at least one of: simple silicon, silicon oxide, and silicon carbide.
A method for preparing a silicon composite negative electrode material, comprising the following steps:

Preparation of carbon nanomaterials loaded with metal elements;

Obtaining a silicon-based material, forming a coating intermediate layer on the surface of the silicon-based material with the carbon nanomaterial loaded with metal elements to obtain an intermediate product;

A shell layer of amorphous carbon material is prepared on the outer surface of the intermediate product to obtain a silicon composite negative electrode material.
The preparation method of silicon composite negative electrode material as claimed in claim 5, is characterized in that, the step of preparing the carbon nanomaterial loaded with metal elements comprises: after modifying the complexing agent to the surface of the carbon nanomaterial, complexing with the metal salt Combine and reduce metal salts to obtain carbon nanomaterials loaded with metal elements;

And/or, the step of forming the coating intermediate layer includes: mixing the carbon nanomaterial loaded with metal elements and the silicon-based material and then vacuum-drying to obtain an intermediate product of the intermediate layer coating the silicon-based material;

And/or, the step of preparing the outer shell layer of the amorphous carbon material comprises: after mixing the intermediate product with the amorphous carbon source, performing vapor deposition to form the outer shell layer of the amorphous carbon material to obtain a silicon composite negative electrode material .
The preparation method of silicon composite negative electrode material as claimed in claim 6, is characterized in that, described complexing agent is selected from: at least one in octadecylamine, ethylenediamine, sec-butylamine, dodecylamine, hexadecylamine kind;

And/or, the metal salt is selected from: at least one of copper salt and silver salt;

And/or, the carbon nanomaterial is selected from: at least one of graphene and carbon nanotubes;

And/or, the amorphous carbon source is selected from: at least one of glucose, citric acid, pitch, phenolic resin, epoxy resin;

And/or, in the silicon composite negative electrode material, the mass ratio of the silicon-based material inner core, the middle layer and the outer shell layer is 1:(0.5-0.8):(0.5-0.8).
The preparation method of silicon composite negative electrode material as claimed in claim 7, is characterized in that, the carbon nanomaterial that described load has metal element is selected from the composite material of copper-graphene, prepares the composite material of described copper-graphene Steps include:

Mixing and grinding the complexing agent and graphene to obtain complexing agent-modified graphene;

After dissolving the copper salt and the graphene modified by the complexing agent in an organic solvent, adding a reducing agent to reduce the copper salt to obtain the copper-graphene composite material.
The preparation method of silicon composite negative electrode material as claimed in claim 8, is characterized in that, described copper salt is selected from: at least in Cu(CH 3 COO) 2 ·H 2 O, copper sulfate, copper acetate, copper chloride A sort of;

And/or, the mass ratio of the copper salt to the graphene modified by the complexing agent is (0.01～2):1;

And/or, the reducing agent is selected from: at least one of acetaldehyde, hydrazine hydrate, sodium borohydride, formaldehyde, and propionaldehyde;

And/or, the organic solvent is selected from at least one of sec-butanol, tert-butanol and ethanol.
A secondary battery, characterized in that the negative electrode sheet of the secondary battery contains the silicon composite negative electrode material according to any one of claims 1 to 4, or contains the silicon composite negative electrode material according to any one of claims 5 to 9. The silicon composite anode material prepared by the method.