CN115966658A - Silicon composite nanofiber, silicon composite nanofiber membrane and preparation method and application thereof - Google Patents

Abstract

The application discloses a silicon composite nanofiber, a silicon composite nanofiber membrane, a preparation method thereof, and a secondary battery. The silicon composite nanofiber includes a carbon-silicon composite core fiber and a graphene cladding layer covering the carbon-silicon composite core fiber; wherein the carbon-silicon composite core fiber includes carbon fiber and at least silicon-based material particles embedded in the carbon fiber. The silicon composite nanofiber membrane is a membrane layer formed by the silicon composite nanofiber of the present application. The negative plate of the secondary battery is formed by cutting silicon composite nanofiber membrane. The silicon composite nanofiber and the silicon composite nanofiber membrane of the present application have high capacity and electrical conductivity, excellent structure and cycle performance, and excellent mechanical properties. The preparation method can ensure that the structure and electrochemical performance of the silicon-containing composite nanofiber membrane are stable, and the efficiency is high. The secondary battery has high capacity, excellent cycle performance and good rate capability.

Description

Silicon composite nanofiber, silicon composite nanofiber membrane, preparation method and application thereof

technical field

The application belongs to the field of secondary batteries, and in particular relates to a silicon composite nanofiber, a silicon composite nanofiber membrane and a preparation method and application thereof.

Background technique

To meet the increasing storage demands of electronics, electric vehicles, and smart grids, rechargeable batteries based on advanced electrodes have been rapidly developed as high-energy-density storage systems. With the advantages of high energy density, high operating voltage, abundant resources, and long cycle life, lithium-ion batteries have always been the backbone of energy storage and conversion.

As we all know, the electrochemical performance of lithium-ion batteries is still mainly restricted by electrode materials, especially anode materials. Among various anode materials, silicon (Si) has a high theoretical ratio of 4200mAh g ^-1 (equivalent to Li _4.4 Si) Capacity, low electrochemical potential of Li ⁺ intercalation/extraction (<0.5V vs. Li/Li ⁺ ), natural abundance, environmental friendliness, etc., are most likely to replace graphite as the anode material for the next generation of high energy density lithium-ion batteries. However, silicon anodes face several major challenges that severely limit their practical applications. During the electrochemical reaction, the volume change of silicon is 300%, which leads to severe silicon particle pulverization, unstable solid electrolyte interface (SEI) formation and loss of electrical contact of the electrode layer, resulting in fast capacity fading and poor rate performance. and limited cycle life, etc. In addition, the low conductivity of the silicon anode itself leads to slow reaction kinetics, especially at higher current densities, and the rapid Li ⁺ intercalation/extraction further leads to the volume expansion of the silicon anode during charge and discharge, resulting in the loss of the entire electrode. Low electronic conductivity and high ion transport resistance lead to failure of their electrochemical performance.

So far, great efforts have been made in the rational design and preparation of new silicon-based anode materials to improve the cycle life and fast charging performance of batteries as much as possible without sacrificing energy density. The specific strategies include: (i ) design and synthesis of various nanostructured materials, including 0D (nanoparticles, nanospheres), 1D (nanowires and nanotubes), 2D (thin films and nanosheets) and 3D (porous silicon, silicon-carbon composite structures), nanostructures It can alleviate the volume change of silicon and shorten the Li ⁺ diffusion distance; (ii) add carbonaceous materials as a supporting matrix to improve conductivity and buffer volume expansion, such as graphite, amorphous carbon, carbon nanotubes, graphene; (iii) Construction of core-shell nanostructures with short ion diffusion lengths, efficient electron transport pathways, and strong volume suppression. Among these approaches, core-shell nanostructures with dense carbon shells as outer layers have proven to be an attractive option to accommodate volume expansion and enhance reaction kinetics in silicon. In recent years, a variety of core-shell nanostructures have been reported, including nanospheres, nanorods, pomegranates, and many other novel nanostructures. For example, Wei et al. studied SiC as a protective layer to stabilize silicon-based anodes by inhibiting chemical reactions. Taking advantage of the high strength and high toughness of silicon carbide, a silicon carbide layer is introduced between the inner silicon layer and the outer carbon layer to suppress the formation of Li ₂ SiF ₆ . The Si@SiC@C composite exhibits remarkable initial Coulombic efficiency (CE) and maintains a stable cycle life of over 88.5% after 800 cycles. Cho et al. reported a silicon nanolayer embedded graphite/carbon hybrid anode using a chemical vapor deposition (CVD) process. This design has been shown to increase the reversible capacity (517mAh g ^-1 ), resulting in a A high CE (92%) was obtained in . Even at high electrode density (>1.6 g cm ^-2 ), the composite anode effectively overcomes the electrode swelling problem and exhibits high areal capacity (>3.3 mAh cm ^-2 ). Although the electrochemical performance of the silicon-carbon composite anode obtained by the above improvement strategy has been improved, the basic research and industrialization process of the silicon-carbon anode still face many challenges, such as: a) the poor solubility of primary silicon nanoparticles in any solvent It leads to uneven dispersion; b) the commonly used processing methods for non-uniform carbon coating treatment are ball milling, solution mixing and template method, which have amorphous state and low degree of graphitization; c) the silicon content of the whole electrode is low, resulting in low energy density , which weakens the capacity advantage of silicon; 4) The uncontrollable thickness, uniformity and compactness of the carbon layer make it difficult to maintain a good lithium ion and electron transport balance. Therefore, it is particularly important to develop a silicon-carbon composite anode with high silicon content, excellent electrical conductivity, and remarkable mechanical strength.

Furthermore, electrospinning is a simple, versatile and continuous method for preparing nanofibers by utilizing surface electrostatic repulsion and using viscous fluids as raw materials. Adding silicon particles into the spinning solution to prepare silicon-coated carbon composite fibers takes full advantage of the advantages of high conductivity, large specific surface area, uniform and compact structure, and flexibility of nanofibers. The materials prepared in this way can be directly used as self-supporting negative electrodes. The electrode resistance is low, and the mass specific capacity, cycle performance and rate performance of the battery are all improved. However, the silicon content (<20%) in most of the published research reports is too low to meet the actual needs. In the published individual research, the silicon content is increased to 40% of the total mass of the electrode, but the cycle performance is poor. It is due to the fact that carbon nanofibers are difficult to completely wrap excess silicon particles, resulting in part of the silicon powder attached or embedded on the surface of carbon nanofibers. During the electrochemical reaction, carbon nanofibers cannot provide a buffer layer for the silicon powder exposed on its surface. It is thus difficult to suppress its volume expansion.

Contents of the invention

The purpose of this application is to overcome the above-mentioned deficiencies of the prior art, to provide a silicon composite nanofiber, a silicon composite nanofiber film formed by silicon composite nanofibers and a method for preparing a silicon composite nanofiber film to solve the problem of existing silicon-based materials. Unsatisfactory cycle performance or technical problems that are difficult to balance cycle performance, capacity and conductivity at the same time.

Another object of the present application is to provide a negative electrode sheet and a secondary battery containing a negative electrode, so as to solve the problem that existing secondary batteries containing a silicon-based negative electrode sheet have unsatisfactory cycle performance or difficulty in balancing cycle performance, capacity and rate performance at the same time technical problems.

In order to achieve the purpose of the above application, the first aspect of the present application provides a silicon composite nanofiber. The silicon composite nanofiber of the present application includes a carbon-silicon composite core fiber and a graphene cladding layer covering the carbon-silicon composite core fiber; wherein, the carbon-silicon composite core fiber includes carbon fiber and at least silicon-based material particles embedded in the carbon fiber .

Further, the carbon-silicon composite core fiber has a diameter of 200nm-3000nm.

Further, the mass ratio of silicon-based material particles to carbon fibers is not greater than 9:1.

Further, the carbon fiber material includes at least one of sintered carbon, amorphous carbon, carbon nanotubes, and carbon nanowalls.

Further, the silicon-based material of the silicon-based material particles includes at least one of silicon, silicon oxide, silicon dioxide, silicon carbide, and silicon-carbon composite materials.

Further, the particle diameter of the silicon-based material particles is 30nm-500nm.

Further, the mass of the graphene coating layer accounts for 5%-80% of the total mass of the silicon composite nanofiber.

Further, the thickness of the graphene coating layer is 20nm-1000nm.

Further, the graphene cladding layer includes graphene vertically grown on the surface of the carbon-silicon composite core fiber.

The second aspect of the present application provides a silicon composite nanofiber membrane. The silicon composite nanofiber membrane of the present application is a film layer formed by the silicon composite nanofibers of the present application.

The third aspect of the present application provides a method for preparing a silicon composite nanofiber membrane. The preparation method of the silicon composite nanofiber membrane of the present application comprises the following steps:

Formulate spinning solution with organic carbon source and silicon-based material particles;

Spinning the spinning solution to obtain organic carbon source fibers coated with silicon-based material particles by organic carbon sources, and the organic carbon source fibers form an organic carbon source fiber film;

Carrying out carbonization treatment on the organic carbon source fiber membrane to obtain the carbon-silicon composite fiber membrane formed by the carbon-silicon composite fiber;

The graphene growth treatment is performed on the carbon-silicon composite fiber membrane to form a graphene coating layer covering the carbon-silicon composite fiber to obtain a silicon composite nanofiber membrane.

Further, the method for growing graphene on the carbon-silicon composite fiber membrane comprises the following steps:

After spreading and fixing the carbon-silicon composite fiber membrane, the chemical vapor deposition method is used to deposit and grow graphene on the carbon-silicon composite fiber membrane to form a graphene coating layer.

Furthermore, in forming the graphene cladding layer, there is graphene growing vertically relative to the carbon-silicon composite fiber, and the conditions for depositing graphene by chemical vapor deposition are as follows:

The substrate temperature is 600-1000°C, the carbon source includes at least one of ethanol, acetone, benzene, methanol, isopropanol, and n-hexane, and the participating gas includes at least one of argon, hydrogen, and hydrogen-argon mixed gas. The time is 10-60 minutes.

Further, the spinning treatment is electrostatic treatment, and the conditions of electrostatic treatment are as follows:

The inner diameter of the needle is 0.6~2.2mm; the voltage is 20~30kV; the temperature is 43~47℃, the relative humidity is 43~47%RH, the advancing speed is 3~6mLh ^-1 , the receiving distance is 10~20cm, and the receiver speed is 100～500rpm min ^-1 .

Further, in the spinning solution, the mass concentration of the organic carbon source is 5%-20%, the mass concentration of silicon-based material particles is 5%-50%, and the nano silicon powder is selected to be 30-500nm.

Further, the carbon source includes at least one of N-N dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and polyacrylonitrile (PAN).

Further, the carbonization treatment includes the following steps:

After the organic carbon source fiber membrane is spread and fixed, it is kept in a protective atmosphere at a temperature of 800-1000° C. for 120-480 minutes.

Furthermore, during the carbonization process, the temperature is raised to 800-1000°C at a heating rate of 2-10°C min ^-1 .

Further, before carbonizing the organic carbon source fiber membrane, it also includes pre-oxidizing the organic carbon source fiber membrane, and the pre-oxidation treatment includes the following steps:

After the organic carbon source fiber membrane is spread and fixed, it is kept at a temperature of 255-300° C. for 120-480 minutes in an oxygen-containing atmosphere.

Furthermore, during the pre-oxidation treatment, the temperature is raised to 255-300°C at a heating rate of 1-5°C min ^-1 .

In a fourth aspect of the present application, a negative electrode sheet is provided. The negative electrode sheet of the present application is formed by cutting the silicon composite nanofiber membrane of the present application or the silicon composite nanofiber membrane prepared by the preparation method of the silicon composite nanofiber membrane of the present application.

In a fifth aspect of the present application, a secondary battery is provided. The secondary battery of the present application includes a negative electrode sheet, and the negative electrode sheet is the negative electrode sheet of the present application.

Compared with the prior art, the present application has the following technical effects:

The silicon-based composite nanofiber provided by the first aspect of the present application embeds the silicon-based material particles at least inside the carbon fiber, so that the carbon fiber forms a coated carbon layer and covers the silicon-based material particles. On the one hand, it can resist the volume expansion of the silicon-based material particles. The role of the protective functional layer, endowing the silicon composite nanofiber with high structural stability and cycle performance, and can increase the content of silicon-based material particles; on the other hand, the carbon fiber and graphene coating layer play the role of conductive modification layer , significantly improve the conductivity of silicon-based material particles, and endow silicon composite nanofibers with excellent conductivity. In addition, the carbon-silicon composite core fiber has a fiber structure, which endows the silicon composite nanofiber of the present application with excellent flexibility and good bending resistance.

The silicon composite nanofiber membrane provided by the second aspect of the application is composed of the silicon composite nanofiber of the application, therefore, the silicon composite nanofiber membrane of the application has a high content of silicon-based material particles, and has excellent resistance to volume expansion of the silicon-based material particles Features, with excellent structural stability and cycle performance; and high conductivity, good flexibility, strong bending resistance.

The preparation method of the silicon composite nanofiber membrane provided by the third aspect of the application can effectively coat the silicon-based material particles inside the carbon fiber to form a carbon-silicon composite fiber, which is the carbon-silicon composite core fiber contained in the silicon composite nanofiber of the application At the same time, the carbon-silicon composite core fiber is formed into a carbon-silicon composite fiber film, and based on the characteristics of the carbon-silicon composite fiber film itself, when the graphene is deposited and grown, it can effectively ensure that the graphene is coated with carbon in the formation of a graphene coating layer. Silicon composite fibers. Therefore, the silicon composite nanofiber membrane prepared by the silicon composite nanofiber membrane preparation method of the present application has a high content of silicon-based material particles, excellent structural stability and cycle performance, high conductivity, good flexibility, and strong bending resistance. In addition, the process conditions are easy to control, and the structure and electrochemical performance of the silicon-containing composite nanofiber membrane can be guaranteed to be stable, and the efficiency is high.

The negative electrode sheet provided by the fourth aspect of the application is formed by cutting the silicon composite nanofiber membrane of the application, so the negative electrode sheet has the physical properties and electrochemical properties of the silicon composite nanofiber membrane of the application, specifically such as a high content of silicon-based material particles , high capacity; it has excellent anti-silicon-based material particle volume expansion characteristics, structural stability and high electrical conductivity, so it has excellent cycle performance, good rate performance, good flexibility, and strong bending resistance.

The secondary battery provided by the fifth aspect of the present application contains the negative electrode sheet of the present application. Therefore, the secondary battery has high capacity, excellent cycle performance, good rate performance, and can be a flexible battery with excellent mechanical properties, which improves the battery capacity of the secondary battery. The stability of chemical properties prolongs the life of secondary batteries.

Description of drawings

In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the specific embodiments or prior art. Obviously, the accompanying drawings in the following description The drawings are some implementations of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

Fig. 1 is the structural schematic diagram of silicon composite nanofiber of the embodiment of the present application; Wherein, A picture is the main view structure schematic diagram of the silicon composite nanofiber of the embodiment of the application, B picture is the carbon silicon compound contained in the silicon composite nanofiber of the embodiment of the application Schematic diagram of the cross-sectional structure of the core fiber 01 along the axial direction;

Fig. 2 is the scanning electron microscope (SEM) picture of the silicon composite nanofiber of the embodiment of the present application;

Fig. 3 is the schematic diagram of silicon composite nanofiber membrane of the embodiment of the present application; Wherein, C picture is the SEM figure of silicon composite nanofiber membrane, and D picture is the physical photograph of silicon composite nanofiber membrane;

Fig. 4 is a flow chart of the method for preparing a silicon composite nanofiber membrane according to the embodiment of the present application;

5 is a schematic flow chart of the method for preparing a silicon composite nanofiber membrane according to an embodiment of the present application;

Fig. 6 is the SEM figure of silicon composite nanofiber and silicon composite nanofiber film in embodiment A1;

Fig. 7 is the TEM figure of silicon composite nanofiber and silicon composite nanofiber film in embodiment A1;

Fig. 8 is the TG curve diagram of silicon composite nanofiber and silicon composite nanofiber film in embodiment A1;

Fig. 9 is the XRD spectrum of silicon composite nanofiber and silicon composite nanofiber film in embodiment A1;

Fig. 10 is the Raman spectrum of silicon composite nanofiber and silicon composite nanofiber film in embodiment A1;

Fig. 11 is the charging and discharging curve diagram of lithium-ion battery in embodiment B1;

FIG. 12 is a graph showing the cycle performance of the lithium-ion battery in Example B1.

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 item (unit) of a, b, or c", or "at least one item (unit) 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, where 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", "said" 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.

In the first aspect, the embodiment of the present application provides a silicon composite nanofiber. The silicon composite nanofiber structure of the embodiment of the present application is shown in Figure A in Figure 1, and its SEM photo is shown in Figure 2, which specifically includes carbon-silicon composite core fiber 01 and graphene-coated carbon-silicon composite core fiber 01. Cladding 02.

Among them, the structure of the carbon-silicon composite core fiber 01 contained in the silicon composite nanofiber in the embodiment of the present application is shown in Figure 1 B, the carbon-silicon composite core fiber 01 includes carbon fibers 11 and at least silicon embedded in the carbon fibers 11. base material particles 12 . In the carbon-silicon composite core fiber 01, the carbon fiber 11 constitutes a coated carbon layer and covers the silicon-based material particles 12, which can play the role of a protective functional layer against the volume expansion of the silicon-based material particles 12, and improve the performance of the silicon-based composite nanostructures in this application. The structural stability and cycle performance of the fiber can be improved, and the content of silicon-based material particles 12 can be increased. At the same time, the carbon fiber 2 and the graphene coating layer 02 function as a conductive modification layer, which significantly improves the electrical conductivity of the silicon-based material particles 12, endowing the silicon composite nanofibers of the present application with excellent electrical conductivity.

In an embodiment, the mass ratio of silicon-based material particles 12 to carbon fibers 11 is 1: (0.2-0.8), specifically 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7 , 1:0.8 and other typical but non-limiting ratios. The mass ratio range of the two can realize the high content loading of the silicon-based material particles 12 in the carbon fiber 11, thereby increasing the content of the silicon-based material particles 12 in the silicon composite nanofiber of the embodiment of the application, thereby endowing the silicon composite nanofiber of the embodiment of the application. Nanofibers have electrochemical properties such as high capacity. Moreover, this mass ratio range can make the silicon-based material particles 12 completely embedded in the carbon fiber 11, thereby realizing the carbon fiber 11 covering the silicon-based material particles 12, improving the structural stability of the carbon-silicon composite core fiber 01, and also improving the carbon-silicon composite core fiber 01. The flexibility and other mechanical properties of the composite core fiber 01.

In an embodiment, the material of the carbon fiber 11 may be at least one of sintered carbon, amorphous carbon, carbon nanotube, and carbon nanowall. Wherein, the nano-wall is also an array structure formed by vertical distribution of carbon sheets or carbon nano-sheets. In the embodiment of the present application, the nano-wall is a fiber-like structure formed by vertical distribution of carbon sheets or carbon nano-sheets. The carbon fiber 11 formed from this material not only has good electrical conductivity, but also endows the carbon fiber 11 with high mechanical properties against volume expansion of silicon-based material particles 12 and good mechanical properties such as flexibility.

In addition, based on the structure of the carbon-silicon composite core fiber 01, the carbon fiber 11 determines the diameter of the carbon-silicon composite core fiber 01 to a greater extent. In the embodiment, the diameter of the carbon fiber 11 is 100nm to 3000nm, specifically 100nm or 300nm. , 500nm, 800nm, 1000nm, 1300nm, 1500nm, 1700nm, 2000nm, 2200nm, 2400nm, 2700nm, 3000nm and other typical but non-limiting diameters. Therefore, in the embodiment, the carbon-silicon composite core fiber 01 has a diameter of 200-3000 nm. The carbon fiber 11 in this diameter range can cover more silicon-based material particles 12 , and can improve the good mechanical properties and flexibility of the carbon-silicon composite core fiber 01 against volume expansion of the silicon-based material particles 12 and flexibility. In addition, the length of the carbon fiber 11 , that is, the carbon-silicon composite core layer fiber 01 can be controlled as required.

In an embodiment, the particle size of the silicon-based material particles 12 is 30 nm˜500 nm, further 30 nm˜200 nm. In other embodiments, the silicon-based material of the silicon-based material particles 12 includes at least one of elemental silicon, silicon oxide, silicon dioxide, silicon carbide, and silicon-carbon composite materials. These silicon-based materials have high capacity, endowing the silicon composite nanofiber with high capacity and other electrochemical properties.

The graphene coating layer 02 contained in the silicon composite nanofiber in the embodiment of the present application covers the carbon-silicon composite core fiber 01. The graphene coating layer 02 can form a composite coating layer with the carbon fiber 11, and coat the silicon-based material particles 12, effectively improving the mechanical properties of the composite coating layer, and improving the volume expansion effect of the silicon-based material particles 12, thereby The stability of the structure and cycle performance of the silicon composite nanofiber in the embodiment of the application is improved, and the composite coating layer formed with the carbon fiber 11 also functions as a conductive modification layer, which has excellent electrical conductivity, thus endowing the application with Excellent rate capability of silicon composite nanofibers.

In an embodiment, the graphene cladding layer 02 includes graphene vertically grown on the surface of the carbon-silicon composite core layer fiber 01 . Ideally, the graphene contained in the graphene cladding layer 02 grows vertically on the surface of the carbon-silicon composite core fiber 01 to the greatest extent. In this way, the graphene coating layer 02 of this structure, together with the carbon fiber 11, endows the silicon composite nanofiber of the embodiment of the present application with excellent flexibility and good bending resistance.

In an embodiment, the mass of the graphene coating layer 02 accounts for 5% to 80% of the total mass of the silicon composite nanofiber, further 5% to 20%, specifically 5%, 10%, 15%, 20%, 25% %, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc. are typical but non-limiting ratios. In other embodiments, the thickness of the graphene coating layer 02 is 20 nm˜1000 nm. Through the content of the graphene coating layer 02 or further control and adjustment of the thickness, the adjustment of the thickness of the graphene coating layer 02 is realized, thereby improving the resistance to silicon-based material particles 12 between the graphene coating layer 02 and the carbon fiber 11. The volume expansion effect and electrical conductivity and further improve the excellent flexibility and bending resistance of the silicon composite nanofibers in the examples of the present application.

When the graphene contained in the graphene coating layer 02 is vertically grown, in an embodiment, the height of the vertically grown graphene is 5nm-800nm, specifically 5nm, 10nm, 50nm, 100nm, 200nm, 300nm, 400nm , 500nm, 600nm, 700nm, 800nm and other typical but non-limiting heights. By controlling the height of the vertically grown graphene, the excellent flexibility and bending resistance of the silicon composite nanofibers in the embodiment of the present application are further improved.

The second aspect is based on the embodiment of the silicon composite nanofiber of the present application. The embodiment of the present application also provides a silicon composite nanofiber membrane. The silicon composite nanofiber membrane of the embodiment of the present application is a film layer formed of the silicon composite nanofiber of the above application embodiment. That is to say, the material of the silicon composite nanofiber membrane of the embodiment of the present application at least contains the silicon composite nanofiber of the above application embodiment. The SEM photo of the silicon composite nanofiber membrane is shown in Figure C in Figure 3, and the actual product is shown in Figure D in Figure 3. In this way, due to the high content of silicon-based material particles in the silicon composite nanofiber membrane of the present application, and excellent resistance to volume expansion of silicon-based material particles, excellent structural stability, and excellent cycle performance; and high conductivity, Good flexibility and strong bending resistance.

In addition, the thickness of the silicon composite nanofiber membrane can be controlled according to actual needs. The silicon composite nanofiber membrane has a three-dimensional porous structure of a fiber membrane layer, specifically, the porosity of the membrane layer formed by electrospinning.

In the third aspect, the embodiment of the present application provides the preparation method of the silicon composite nanofiber membrane in the above embodiment of the application. The technical process of the preparation method of silicon composite nanofiber membrane in the embodiment of the present application is shown in Figure 4 and Figure 5, including the following steps:

S01: preparing organic carbon source and silicon-based material particles into spinning solution;

S02: Spinning the spinning solution to obtain organic carbon source fibers coated with silicon-based material particles by organic carbon sources, and the organic carbon source fibers form an organic carbon source fiber film;

S03: Carbonizing the organic carbon source fiber membrane to obtain a carbon-silicon composite fiber membrane formed of carbon-silicon composite fibers;

S04: growing graphene on the carbon-silicon composite fiber membrane to form a graphene coating layer covering the carbon-silicon composite fiber to obtain a silicon composite nanofiber membrane.

Wherein, the organic carbon source in step S01 is the carbon source precursor for forming the carbon fiber 11 contained in the silicon composite nanofiber of the above application example. Therefore, the organic carbon source can be organic matter that forms carbon fibers. In an embodiment, the organic carbon source includes N-N dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), poly At least one of acrylonitrile (PAN). These organic carbon sources can effectively coat the silicon-based material particles, improve the spinning performance of the spinning solution, and improve the quality of the organic carbon source fibers formed by coating the silicon-based material particles with the organic carbon source.

The silicon-based material particles are the silicon-based material particles 12 contained in the silicon composite nanofibers in the above application examples. Therefore, the particle size range, material, etc. of the silicon-based material particles are the same as the silicon-based material particles 12 above.

In the embodiment, in the spinning solution in step S01, the mass concentration of the organic carbon source is 5%-20%, the mass concentration of the silicon-based material particles is 5%-50%, and the silicon-based material particles are selected to be 30-500nm, further 30-200nm. By controlling the concentration of the organic carbon source and silicon-based material particles in the spinning solution, the organic carbon source effectively covers the silicon-based material particles in the formed organic carbon source fiber, and the quality and mechanical properties of the organic carbon source fiber can be improved. Moreover, the particle size of the silicon-based material particles can be effectively dispersed evenly, and the content of the silicon-based material particles can be effectively increased, and more importantly, the volume expansion of the silicon-based material particles in circulation can be effectively reduced, and the volume expansion of the silicon-based material particles can be improved, and the volume of the silicon-based material particles formed during the spinning process can be improved. Quality of organic carbon source fibers.

In the spinning process in step S02, the spinning solution is formed into organic carbon source fibers, specifically, the organic carbon source is coated with silicon-based material particles, and the fibers are formed by spinning, that is, the formation of silicon composite nanofibers in the above application examples Fiber precursor of carbon-silicon composite core fiber 01. Since it is for preparing a silicon composite nanofiber membrane, in the step S02, the organic carbon source fiber is further formed into a film layer, that is, an organic carbon source fiber membrane.

In an embodiment, the spinning process is an electrospinning process, and the conditions of the electrospinning process are as follows:

The inner diameter of the needle is 0.6~2.2mm; the voltage is 20~30kV; the temperature is 43~47℃, the relative humidity is 43~47%RH, the advancing speed is 3~6mLh ^-1 , the receiving distance is 10~20cm, and the receiver speed is 100～500rpm min ^-1 . The conditions of the electrostatic treatment can make the organic carbon source effectively coat the silicon-based material particles in the formed organic carbon source fiber, realize high-throughput (high-efficiency, fast) spinning treatment, improve the efficiency of electrospinning and improve the The quality of the organic carbon source fibers formed.

In order to improve the efficiency of electrospinning to form organic carbon source fibers and form organic carbon source fibers to further form an organic carbon source fiber film. During the electrospinning process, the spinning solution in step S01 can be injected into syringes with different types of stainless steel needles. Ideally, the electrospinning process is carried out under the conditions of the above-mentioned electrospinning process to increase the organic carbon source. Efficient Formation of Fibers and Fiber Films from Organic Carbon Sources.

In addition, through the conditions of the spinning treatment, parameters such as the diameter of the organic carbon source fiber and the thickness of the organic carbon source fiber film are controlled and adjusted, so that the carbon-silicon composite fiber and carbon-silicon composite fiber generated after the carbonization treatment in step S03 The composite fiber membrane has the diameter of the carbon-silicon composite core fiber 01 contained in the silicon composite nanofiber of the above application example and the thickness of the silicon composite nanofiber membrane of the above application example.

During the carbonization process in step S03, the organic carbon source contained in the organic carbon source fiber in step S02 is carbonized to form carbon fiber in situ, that is, the carbon fiber 11 contained in the silicon composite nanofiber of the above application example, and realizes carbon fiber Silicon-based material particles are coated in situ to form carbon-silicon composite fibers. Therefore, the carbon-silicon composite fiber formed is the carbon-silicon composite core layer fiber 01 contained in the silicon composite nanofiber of the above application example.

In an embodiment, the carbonization treatment includes the following steps:

After the organic carbon source fiber membrane is spread and fixed, it is kept in a protective atmosphere at a temperature of 800-1000° C. for 120-480 minutes. Carbon-silicon composite fibers can be effectively generated through carbonization treatment, and the fiber quality and mechanical properties such as flexibility and tensile strength of the generated carbon-silicon composite fibers can be improved. The carbonization treatment then simultaneously produces a carbon-silicon composite fiber membrane and likewise improves the quality and mechanical properties such as flexibility and tensile strength of the carbon-silicon composite fiber membrane.

Among them, the purpose of spreading and fixing the organic carbon source fiber membrane is to improve the film quality such as the flatness of the carbon-silicon composite fiber membrane generated after the carbonization treatment, and to avoid serious deformation or loss of the carbon-silicon composite fiber membrane relative to the organic carbon source fiber membrane. Dimensional shrinkage. In an embodiment, the spreading and fixing treatment can be carried out on substrates such as graphite paper, graphite plate, carbon felt, carbon fiber cloth, etc. These substrates have the advantages of smoothness, good heat transfer, fast heat dissipation, and uniform temperature distribution, thereby improving The effect of carbonization treatment.

The protective atmosphere should be an atmosphere that ensures that the organic carbon source is cracked to generate carbon. If it is a non-oxygen atmosphere, it can specifically be a protective atmosphere formed by at least one of nitrogen and argon.

In an embodiment, during the carbonization treatment, the temperature is raised to 800-1000° C. at a heating rate of 2-10° C. min ⁻¹ . By controlling the temperature rise rate of the carbonization treatment, the quality and mechanical properties such as flexibility and tensile strength of the generated carbon-silicon composite fiber and carbon-silicon composite fiber film are further improved.

In addition, the carbonization treatment can be carried out in tube furnaces, vertical furnaces, carbonization furnaces, etc., but not only.

In a further embodiment, before performing the carbonization treatment on the organic carbon source fiber membrane, pre-oxidation treatment on the organic carbon source fiber membrane is also included. This preoxidation treatment comprises the steps:

After the organic carbon source fiber membrane is spread and fixed, it is kept at 255-300° C. and further at 255-275° C. for 120-480 minutes in an oxygen-containing atmosphere.

By performing the pre-oxidation process on the organic carbon source fiber membrane, the organic carbon source in the organic carbon source fiber membrane undergoes preliminary series of reactions such as oxidation. And further control the pre-oxidation temperature and time and conditions, so that the pre-oxidation treatment is sufficient, and effectively ensure that the carbon-silicon composite fiber membrane and the structure of the carbon-silicon composite fiber contained in the carbon-silicon composite fiber membrane will not be damaged due to excessive oxidation. Improve the stability of both structure and morphology.

Among them, the purpose of spreading and fixing the organic carbon source fiber membrane in the pre-oxidation treatment is to improve the film quality such as the flatness of the organic carbon source fiber membrane generated after the pre-oxidation treatment, and to avoid serious deformation or dimensional shrinkage of the front and rear phases. . In the embodiment, the spreading and fixing treatment can refer to the spreading and fixing treatment in the above-mentioned carbonization treatment, specifically, it can be carried out on substrates such as graphite paper, graphite plate, carbon felt, carbon fiber cloth, etc. These substrates have flatness, heat transfer Good, fast heat dissipation, uniform temperature distribution and other advantages, thereby improving the effect of carbonization treatment.

Oxygen in the oxygen-containing atmosphere is an important component to ensure the pre-oxidation of organic carbon sources and the like. Therefore, in the embodiment, the oxygen atmosphere can be directly controlled or simulated air atmosphere. Wherein, the atmosphere for simulating air may be a mixed gas of nitrogen and oxygen (volume ratio 5:1).

In an embodiment, during the pre-oxidation treatment, the temperature is raised to 255-300° C. at a heating rate of 1-5° C. min ^-1 . By controlling the heating rate of the pre-oxidation treatment, the uniformity of the pre-oxidation treatment is further improved, and the carbon-silicon composite fiber membrane and the stability of the structure and shape of the carbon-silicon composite fiber contained in the carbon-silicon composite fiber membrane are improved.

In addition, the pre-oxidation treatment can be carried out, but not only, in a high-temperature blast oven, muffle furnace, and the like.

When growing graphene on the carbon-silicon composite fiber membrane in step S04, because the carbon-silicon composite fiber membrane has a rich three-dimensional porous structure in step S03, graphene will be in the carbon-silicon composite fiber membrane in the carbon-silicon composite fiber membrane. Graphene is deposited on the surface, and a graphene coating layer is formed to obtain a silicon composite nanofiber membrane.

In an embodiment, the method for growing graphene on the carbon-silicon composite fiber membrane comprises the following steps:

After spreading and fixing the carbon-silicon composite fiber membrane, the chemical vapor deposition method is used to deposit and grow graphene on the carbon-silicon composite fiber membrane to form a graphene coating layer. The chemical vapor deposition method is used to deposit and grow graphene, which ensures that graphene grows on all carbon-silicon composite fibers, and can grow and distribute uniformly, improving the integrity of the graphene coating layer. At the same time, due to the chemical vapor phase in-situ deposition growth, the bonding force between graphene and carbon-silicon composite fibers is strong, and the coating structure of the graphene coating layer is stable.

In a further embodiment, in the formed graphene cladding layer, there are graphene grown vertically relative to the carbon-silicon composite fiber, and the conditions for depositing graphene by chemical vapor deposition are as follows:

The substrate temperature is 600-1000°C, the carbon source includes at least one of ethanol, acetone, benzene, methanol, isopropanol, and n-hexane, and the participating gas includes at least one of argon, hydrogen, and hydrogen-argon mixed gas. The time is 10-60 minutes.

By controlling the temperature and carbon source of chemical vapor deposition, the use of liquid-phase precursors can achieve low-temperature, large-area, and short-term high-efficiency growth of graphene. Compared with plasma-enhanced chemical vapor deposition (PECVD), large-scale Large-scale high-yield growth. For example, the PECVD growth substrate is basically 4*4 cm. The above conditions in the embodiment of the present application can achieve growth of 30*40 cm and above, and the growth uniformity is excellent. More importantly, after SEM analysis, the graphene grown under the above conditions can be vertically grown and in-situ bonded to the carbon-silicon composite fiber relative to the carbon-silicon composite fiber, and the graphene layer formed by the vertically grown graphene is composited with carbon-silicon The carbon fiber contained in the fiber forms a composite coating layer covering the silicon-based material particles, which effectively improves the volume expansion resistance of the silicon-based material particles, and improves the structural stability and electrical conductivity of the resulting silicon composite nanofibers and silicon composite nanofiber films. sex.

Therefore, the above-mentioned silicon composite nanofiber film preparation method can effectively coat the silicon-based material particles inside the carbon fiber to form a carbon-silicon composite fiber, that is, the carbon-silicon composite core layer fiber contained in the silicon composite nanofiber of the above application example, At the same time, the carbon-silicon composite core fiber is formed into a carbon-silicon composite fiber film, and based on the characteristics of the carbon-silicon composite fiber film itself, when the graphene is deposited and grown, it can effectively ensure that the graphene is coated with carbon silicon in the formation of a graphene coating layer. Composite fibers. Moreover, the preparation method of the silicon composite nanofiber membrane can realize the high content of silicon-based material particles in the prepared silicon composite nanofiber membrane, excellent structural stability and cycle performance, high conductivity, good flexibility, and anti-corrosion through the process steps and corresponding conditions. Strong bendability. In addition, the process conditions are easy to control, and the structure and electrochemical performance of the silicon-containing composite nanofiber membrane can be guaranteed to be stable, and the efficiency is high.

When electrospinning is used to prepare, the addition amount of silicon-based material particles in the spinning solution can be greatly increased (≥50%), and high-throughput stainless steel needles (0.6-2.2mm inner diameter) are used to achieve rapid electrospinning Organic carbon source fibers, and the formation of organic carbon source fiber membranes, established a stable, efficient, and low-cost spinning process; the use of liquid phase, cheap carbon sources can greatly reduce the decomposition temperature compared with methane, thereby achieving low temperature growth, liquid The price of relative carbon sources is also relatively cheap, which can reduce raw material costs and equipment operating costs; by optimizing the parameters of the growth process such as temperature and reaction gas flow, rapid growth in large quantities can be achieved, which greatly shortens the growth time; carbon-silicon composite fibers can be used as long-range The conductive network connects the silicon-based material particles in series into fibers, and the graphene coating layer, specifically the graphene coating layer containing vertical graphene, acts as a three-dimensionally interconnected coating layer on the surface to completely wrap the silicon-based material particles. Become a high-conductivity, high-strength, multi-contact multi-functional coating layer, endow the prepared silicon composite nanofibers and silicon composite nanofiber membranes with flexible self-supporting nanofiber membrane properties, when used as secondary battery negative electrode materials, exhibit High capacity, high energy density and excellent rate capability.

In a fourth aspect, the embodiment of the present application provides a negative electrode sheet. The negative electrode sheet of the embodiment of the present application is formed by cutting the silicon composite nanofiber membrane in the above embodiment of the application. That is to say, the silicon composite nanofiber membrane in the above application example can be directly used to prepare the negative electrode sheet. In this way, the negative electrode sheet has the physical properties and electrochemical properties of the silicon composite nanofiber membrane in the above application example, specifically such as high silicon-based material particle content and high capacity; it has excellent anti-silicon-based material particle volume expansion characteristics and stable structure Therefore, it has excellent cycle performance, good rate performance, good flexibility and strong bending resistance.

In a fifth aspect, the embodiment of the present application provides a secondary battery. The secondary battery of the present application includes a negative electrode sheet. Of course, the secondary battery also includes other necessary components of the secondary battery, such as positive electrodes, electrolytes, and the like. , wherein the negative electrode sheet is the negative electrode sheet of the embodiment of the present application. Therefore, based on the negative electrode sheet of the above-mentioned embodiment of the present application. Therefore, the secondary battery has high capacity, excellent cycle performance, and good rate capability, and can be a flexible battery with excellent mechanical properties, which improves the stability of the electrochemical performance of the secondary battery and prolongs the life of the secondary battery.

The following examples illustrate the silicon composite nanofibers, silicon composite nanofiber membranes, preparation methods and applications of the present application through a number of specific examples.

1. Examples of silicon composite nanofibers and silicon composite nanofiber membranes

Example A1

This embodiment provides a silicon composite nanofiber, a silicon composite nanofiber membrane and a preparation method thereof. The structure of silicon composite nanofibers is shown in Figure 1 and Figure 2, including carbon-silicon composite core fibers and graphene cladding layers covering carbon-silicon composite core fibers. The carbon-silicon composite core fiber includes carbon fibers and silicon-based material particles embedded at least inside the carbon fibers.

The preparation method of silicon composite nanofiber and silicon composite nanofiber film comprises the following steps:

S1. Configure spinning solution: weigh a certain amount of polyacrylonitrile (PAN) and dissolve it in an organic solvent to make a polymer solution with a certain concentration, then weigh a certain amount of nano silicon powder, add PAN solution to disperse and prepare spinning solution Silk solution; wherein, in the spinning solution, the mass concentration of PAN is 15%, and the mass concentration of nano silicon powder is 30%;

S2. Electrospinning: inject the spinning solution prepared in step S1 into syringes with different types of stainless steel needles, adjust parameters such as voltage, temperature and humidity, propulsion speed, receiving distance, receiver speed, etc., and perform electrospinning to form Si @PAN Nanofiber Membrane; Among them, the specification of the stainless steel needle for electrospinning is 12G~20G, that is, the inner diameter of the needle is 0.6~2.2mm; the voltage is 25kV; the temperature is controlled at 45±2°C and the relative humidity is controlled at 45±2% RH, propulsion speed is 5mLh ^-1 , receiving distance is 15cm, receiver rotation speed is 300rpmmin ^-1 ;

S3. Pre-oxidation: Spread the Si@PAN nanofiber membrane prepared in step S2 on a graphite plate, clamp the four sides of the Si@PAN nanofiber membrane with high-temperature clamps for fixation, put it into a muffle furnace, and In the process, the temperature was raised to 265°C at a heating rate of 3°C min ^-1 and kept for 300 minutes;

S4. Carbonization: After the pre-oxidized Si@PAN nanofiber membrane is spread and fixed according to the pre-oxidation treatment, it is placed in a carbonization furnace, and the temperature is raised to 900 at a heating rate of 6°C min-1 under a nitrogen atmosphere. ℃, and heat preservation treatment for 300min to obtain a carbon-silicon composite fiber membrane formed by Si@CNFs carbon-silicon composite fiber;

S5. CVD deposition of graphene: spread and fix the carbon-silicon composite fiber film obtained above, put it into the CVD growth equipment, raise the temperature to 1300°C, introduce the ethanol reaction gas source, and keep the deposition and growth for 35min. The vertical graphene is grown on the surface of the silicon composite fiber membrane to form a graphene coating layer, and the carbon-silicon composite fiber is covered to obtain the silicon composite nanofiber and the silicon composite nanofiber membrane formed by the silicon composite nanofiber.

Example A2

This embodiment provides a silicon composite nanofiber, a silicon composite nanofiber membrane and a preparation method thereof. The structure of silicon composite nanofibers is shown in Figure 1 and Figure 2, including carbon-silicon composite core fibers and graphene cladding layers covering carbon-silicon composite core fibers. The carbon-silicon composite core fiber includes carbon fibers and silicon-based material particles embedded at least inside the carbon fibers.

The preparation method of silicon composite nanofiber and silicon composite nanofiber film comprises the following steps:

S1. Configure spinning solution: weigh a certain amount of polyacrylonitrile (PAN) and dissolve it in an organic solvent to make a polymer solution with a certain concentration, then weigh a certain amount of nano silicon powder, add PAN solution to disperse and prepare spinning solution Silk solution; wherein, in the spinning solution, the mass concentration of PAN is 8%, and the mass concentration of nano silicon powder is 50%;

S2. Electrospinning: inject the spinning solution prepared in step S1 into syringes with different types of stainless steel needles, adjust parameters such as voltage, temperature and humidity, propulsion speed, receiving distance, receiver speed, etc., and perform electrospinning to form Si @PAN nanofiber membrane; Among them, the specification of the stainless steel needle for electrospinning is 18G, that is, the inner diameter of the needle is 0.6-2.2mm; the voltage is 25kV; the temperature is controlled at 45±2℃, the relative humidity is controlled at 45±2%RH, The propulsion speed is 5mLh ^-1 , the receiving distance is 15cm, and the receiver rotation speed is 300rpmmin ^-1 ;

S3. Pre-oxidation: Spread the Si@PAN nanofiber membrane prepared in step S2 on a graphite plate, clamp the four sides of the Si@PAN nanofiber membrane with high-temperature clamps for fixation, put it into a muffle furnace, and In the process, the temperature was raised to 265°C at a heating rate of 3°C min ^-1 and kept for 300 minutes;

S4. Carbonization: After the pre-oxidized Si@PAN nanofiber membrane is spread and fixed according to the pre-oxidation treatment, it is placed in a carbonization furnace, and the temperature is raised to 900 at a heating rate of 6°C min-1 under a nitrogen atmosphere. ℃, and heat preservation treatment for 300min to obtain a carbon-silicon composite fiber membrane formed by Si@CNFs carbon-silicon composite fiber;

S5. CVD deposition of graphene: spread and fix the carbon-silicon composite fiber film obtained above, put it into the CVD growth equipment, raise the temperature to 800°C, introduce the ethanol reaction gas source, and keep the deposition and growth for 30min. The vertical graphene is grown on the surface of the silicon composite fiber membrane to form a graphene coating layer, and the carbon-silicon composite fiber is covered to obtain the silicon composite nanofiber and the silicon composite nanofiber membrane formed by the silicon composite nanofiber.

Example A3

This embodiment provides a silicon composite nanofiber, a silicon composite nanofiber membrane and a preparation method thereof. The structure of silicon composite nanofibers is shown in Figure 1 and Figure 2, including carbon-silicon composite core fibers and graphene cladding layers covering carbon-silicon composite core fibers. The carbon-silicon composite core fiber includes carbon fibers and silicon-based material particles embedded at least inside the carbon fibers.

In the preparation method of silicon composite nanofibers and silicon composite nanofiber films, the carbon source is changed from ethanol to methane. Correspondingly, during the CVD growth process, the growth temperature is 1100° C., and the deposition time is 4 hours. The remaining conditions are the same as in Example A1. same.

Example A4

This embodiment provides a silicon composite nanofiber, a silicon composite nanofiber membrane and a preparation method thereof. The structure of silicon composite nanofibers is shown in Figure 1 and Figure 2, including carbon-silicon composite core fibers and graphene cladding layers covering carbon-silicon composite core fibers. The carbon-silicon composite core fiber includes carbon fibers and silicon-based material particles embedded at least inside the carbon fibers.

The preparation method of silicon composite nanofiber and silicon composite nanofiber film refers to the preparation method in Example A2, the difference is that the amount of CVD deposited graphene deposition is controlled, and the quality of the graphene coating layer accounts for 70% of the total mass of the silicon composite nanofiber. %-80%.

Comparative example A1

This comparative example provides a silicon composite nanofiber, a silicon composite nanofiber membrane and a preparation method thereof. The silicon composite nanofibers include carbon fibers and at least silicon-based material particles embedded in the carbon fibers, and the difference from Example A2 is that they do not include the graphene cladding layer covering the carbon-silicon composite core fiber. Carbon silicon composite core fiber. The silicon composite nanofiber membrane is prepared by the method for preparing the silicon composite nanofiber membrane of the silicon composite nanofiber reference example A2 of this comparative example.

2. Li-ion battery example

Embodiment B1 to embodiment B4 and comparative example B1

Embodiment B1 to embodiment B4 and comparative example B1 respectively provide a kind of lithium-ion battery, and each lithium-ion battery is prepared into a negative electrode and assembled into a lithium-ion battery according to the following methods:

Preparation of the negative electrode: cutting the silicon composite nanofiber membranes provided in the above-mentioned Examples A1 to A4 and the fiber membranes provided in Comparative Example B1 into negative electrode sheets;

Electrolyte: 1M LiPF ₆ (ethyl carbonate + dimethyl carbonate + diethyl carbonate (volume ratio 1:1:1))

Lithium-ion battery assembly: Lithium-ion batteries were assembled according to the lithium-ion batteries of each embodiment, wherein the negative electrode sheet cut from the silicon composite nanofiber membrane provided in embodiment A1 to embodiment A4 and the above-mentioned positive electrode sheet were respectively assembled into an implementation Example B1 Lithium-ion battery; the negative electrode sheet cut from the fiber membrane provided in Comparative Example A1 and the above-mentioned positive electrode sheet were respectively assembled into Comparative Example B1 lithium-ion battery.

Related characteristic test

1. Structural characterization of silicon composite nanofibers and silicon composite nanofiber membranes:

Carry out SEM and transmission electron microscope (TEM) analysis to the silicon composite nanofiber and silicon composite nanofiber film in embodiment A1 to embodiment A4: Wherein, the SEM figure of silicon composite nanofiber and silicon composite nanofiber film in embodiment A2 As shown in Figure 6, the TEM figure of silicon composite nanofiber and silicon composite nanofiber membrane in embodiment A2 is shown in Figure 7, and other embodiments provide the SEM figure and TEM figure of silicon composite nanofiber and silicon composite nanofiber membrane respectively Similar to Figure 6 and Figure 7. It can be seen from the SEM and TEM images that the silicon composite nanofibers of the present application have a complete structure, and the surface has a graphene coating layer, and the graphene grows vertically on the silicon-carbon composite fiber, that is, the carbon-silicon composite core fiber. s surface. Moreover, the silicon composite nanofiber membrane formed by the silicon composite nanofiber has a rich three-dimensional porous structure.

Further measure the related dimensions of silicon composite nanofibers in each embodiment as shown in Table 1 below:

Table 1

The silicon composite nanofibers and silicon composite nanofiber membranes in Embodiment A1 to Embodiment A4 are subjected to TG analysis: wherein, the TG curves of silicon composite nanofibers and silicon composite nanofiber membranes in Embodiment A3 are shown in Figure 8, and other The embodiment provides that the TG curves of silicon composite nanofibers and silicon composite nanofiber membranes are similar to those shown in FIG. 8 . It can be seen from the TG diagram that the silicon composite nanofibers and silicon composite nanofiber membranes of the present application have ultra-high silicon content, greater than 90%, and the lost part is the outer layer of carbon nanofibers and vertical graphene.

The silicon composite nanofiber and the silicon composite nanofiber film in embodiment A1 to embodiment A4 are carried out X-ray diffraction (XRD) analysis:

The silicon composite nanofibers and silicon composite nanofiber films in Example A1 to Example A4 are subjected to XRD analysis: wherein, the XRD patterns of silicon composite nanofibers and silicon composite nanofiber films in Example A4 are shown in Figure 9, and other The examples provide that the XRD patterns of silicon composite nanofibers and silicon composite nanofiber membranes are similar to those shown in FIG. 9 . It can be seen from the XRD spectrum that the silicon composite nanofibers and silicon composite nanofiber films of the present application examples all have characteristic peaks of graphene and silicon, which proves that the two are well combined. Therefore, the silicon composite nanofibers and silicon composite nanofiber films of the present application examples Membrane purity is high.

The silicon composite nanofiber and silicon composite nanofiber film in embodiment A1 to embodiment A4 are carried out Raman spectrum (Raman) analysis:

The silicon composite nanofibers and silicon composite nanofiber membranes in Example A1 to Example A4 were subjected to Raman analysis: wherein, the Raman spectra of silicon composite nanofibers and silicon composite nanofiber membranes in Example A4 are shown in Figure 10, Other examples provide that the Raman spectra of silicon composite nanofibers and silicon composite nanofiber membranes are similar to those shown in FIG. 10 . It can be seen from the Raman spectrum that the silicon composite nanofibers and the silicon composite nanofiber membranes of the present application have obvious characteristic peaks at 1345.9 cm ^-1 , 1578.1 cm ^-1 and 2704.8 cm ^-1 , corresponding to D and G of graphene. and 2D peaks, which further proves that vertical graphene is successfully grown on the surface of silicon composite nanofibers. Therefore, graphene and carbon nanofiber layers can form a good protective effect on silicon nanoparticles.

2. Lithium-ion battery chemical performance test:

The lithium ion batteries in Example B1 to Example B4 were respectively subjected to charge and discharge, cycle stability and rate performance. The test conditions for the charge and discharge, cycle stability and rate performance of each lithium-ion battery are as follows: The charge and discharge test mainly uses two key currents of 50mA cm ^-2 and 1000mA cm ^-2 to conduct constant current charge and discharge tests, and the voltage range of the test is 0-3V; the rate test is to count the battery capacity retention by changing the current density, mainly 100, 500, 1000, 5000, 10000mA cm ^-2 , and the voltage range is 0-3V.

Among them, the charge-discharge curve of the lithium-ion battery in Example B2 is shown in Figure 11 , the cycle performance curve is shown in Figure 12 , and the rate performance test results of the lithium-ion battery in Example B2 are shown in Table 2 below. Other embodiments provide that the charge-discharge curve, cycle performance curve and rateability test results of the lithium-ion battery are similar to those shown in FIG. 11 , FIG. 12 and Table 2, respectively.

Table 2

According to the charge-discharge curve, cycle performance curve and rate performance test results, the anode material obtained by the optimal scheme has a high-quality specific capacity of 3568mAh g ^-1 at a current of 100mA g ^-2 and a high-quality specific capacity of 1806mAh g at a current of 2000mA g ^{-2 -1} specific capacity, and the retention rate exceeds 92% after 100 cycles; the rate test shows that the negative electrode material still maintains a mass specific capacity of 942mAh g ^-1 at a current of 10A g ^-2 , showing excellent rate performance. In contrast, the pure silicon anode shows poor cycle stability and rate performance, specifically: the retention rate of the pure silicon anode after 100 cycles at 100mA g ^-2 current is only 40%, and its rate test shows that when When the current is greater than 1000mA g ^-2 , the electrode is basically damaged. Further testing of the lithium-ion battery in the above comparative example B1 under the same conditions shows that although the lithium-ion battery cyclability provided by comparative example B1 is better than the cyclability of the pure silicon negative electrode pure lithium-ion battery, it is still significantly lower than that of Example B2 and other lithium-ion battery cycles.

The lithium ion battery provided by the embodiment of the present application has high capacity, stable cycle performance and high rate performance. It can thus be concluded that using the silicon composite nanofiber membrane of the embodiment of the present application as the negative electrode sheet, it can have a stable structure during charging and discharging, can effectively resist the volume expansion of the silicon-based material particles contained in it, and has high capacity and electrical conductivity. High, giving the battery high capacity characteristics and excellent rate characteristics.

The above 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 scope of the application. Inside.

Claims (10)

1. A silicon composite nanofiber, characterized in that: the carbon-silicon composite core-layer fiber comprises carbon-silicon composite core-layer fibers and a graphene coating layer for coating the carbon-silicon composite core-layer fibers; wherein the carbon-silicon composite core layer fiber comprises carbon fiber and silicon-based material particles at least embedded in the carbon fiber.

2. The silicon composite nanofiber according to claim 1, wherein:

the diameter of the carbon-silicon composite core layer fiber is 200 nm-3000 nm; and/or

The mass ratio of the silicon-based material particles to the carbon fibers is not more than 9:1; and/or

The carbon fiber material comprises at least one of sintered carbon, amorphous carbon, carbon nano tubes and carbon nano walls; and/or

The silicon-based material of the silicon-based material particles comprises at least one of silicon, silicon monoxide, silicon dioxide, silicon carbide and silicon-carbon composite material; and/or

The particle size of the silicon-based material particles is 30 nm-500 nm.

3. The silicon composite nanofiber according to claim 1 or 2, wherein: the mass of the graphene coating layer accounts for 5-80% of the total mass of the silicon composite nanofiber and/or

The thickness of the graphene coating layer is 20 nm-1000 nm and/or

The graphene coating layer comprises graphene vertically growing on the surface of the carbon-silicon composite core layer fiber.

4. A silicon composite nanofiber membrane, characterized in that: a film layer formed of the silicon composite nanofiber as set forth in any one of claims 1 to 3.

5. A preparation method of a silicon composite nanofiber membrane is characterized by comprising the following steps:

preparing a spinning solution from an organic carbon source and silicon-based material particles;

spinning the spinning solution to obtain organic carbon source fibers of the silicon-based material particles coated by the organic carbon source, wherein the organic carbon source fibers form an organic carbon source fiber membrane;

carbonizing the organic carbon source fiber membrane to obtain a carbon-silicon composite fiber membrane formed by carbon-silicon composite fibers;

and carrying out graphene growth treatment on the carbon-silicon composite fiber membrane to form a graphene coating layer coating the carbon-silicon composite fiber, so as to obtain the silicon composite nanofiber membrane.

6. The preparation method according to claim 5, wherein the method for performing graphene growth treatment on the carbon-silicon composite fiber membrane comprises the following steps:

after the carbon-silicon composite fiber film is spread and fixed, depositing graphene on the carbon-silicon composite fiber film by adopting a chemical vapor deposition method, and forming a graphene coating layer;

and/or

The spinning treatment is electrostatic spinning treatment, and the conditions of the electrostatic spinning treatment are as follows:

the inner diameter of the needle head is 0.6-2.2 mm; the voltage is 20-30 kV; RH and relative humidity of 43-47% at 43-47 deg.C, and a propulsion speed of 3-6 mLh ^-1 The receiving distance is 10-20 cm, and the rotating speed of the receiver is 100-500 rpmmin ^-1 ；

And/or

In the spinning solution, the mass concentration of the organic carbon source is 5-20%, the mass concentration of the silicon-based material particles is 5-50%, and the silicon-based material particles are selected from 30-500 nm;

and/or

The organic carbon source comprises at least one of N-N dimethylformamide, N-methyl pyrrolidone, dimethyl sulfoxide and polyacrylonitrile;

and/or

The carbonization treatment comprises the following steps:

spreading and fixing the organic carbon source fiber membrane, and then preserving the heat for 120-480 min at the temperature of 800-1000 ℃ in a protective atmosphere;

and/or

Before the carbonization treatment is carried out on the organic carbon source fiber membrane, the method also comprises the step of carrying out pre-oxidation treatment on the organic carbon source fiber membrane, wherein the pre-oxidation treatment comprises the following steps:

and (3) spreading and fixing the organic carbon source fiber membrane, and then preserving the heat for 120-480 min at the temperature of 255-300 ℃ in an oxygen-containing atmosphere.

7. The preparation method according to claim 6, wherein graphene vertically grown with respect to the carbon-silicon composite fiber is grown in the formed graphene clad layer, and the conditions for depositing the graphene by the chemical vapor deposition method are as follows:

the temperature of the matrix is 600-1000 ℃, the carbon source comprises at least one of ethanol, acetone, benzene, methanol, isopropanol and n-hexane, the participating gas comprises at least one of argon, hydrogen and hydrogen-argon mixed gas, and the deposition time is 10-60 min.

8. The method according to claim 6, wherein the carbonization treatment is performed at 2 to 10 ℃ for min ^-1 The temperature is increased to 800-1000 ℃ at the temperature rising rate;

in the pre-oxidation treatment process, the temperature is 1-5 ℃ min ^-1 The temperature rises to 255-300 ℃ at the temperature rising rate.

9. Negative electrode sheet, characterized in that the negative electrode sheet is formed by cutting the silicon composite nanofiber membrane of claim 4 or the silicon composite nanofiber membrane prepared by the preparation method of any one of claims 5 to 8.

10. A secondary battery comprising a negative electrode sheet, characterized in that: the negative electrode sheet according to claim 9.

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