CN117747764A - Silicon-carbon composite material, preparation method thereof, negative electrode active material, negative electrode plate, electrochemical device and vehicle - Google Patents

Abstract

The present disclosure relates to the field of electrochemical technology, and more particularly, to a silicon-carbon composite material, a method of preparing the same, a negative electrode active material, a negative electrode tab, an electrochemical device, and a vehicle, the silicon-carbon composite material including a graphite material and a silicon-carbon material fixed in a gap between the graphite materials. In the silicon-carbon composite material, the silicon-carbon material is wrapped by the graphite material, so that the volume expansion of silicon in the lithiation process can be effectively inhibited, and the battery has stable cycle performance when the silicon-carbon composite material is used as a negative electrode material of a lithium ion battery.

Description

Silicon-carbon composite materials and preparation methods thereof, negative active materials, negative electrode sheets, electrochemical equipment and vehicles

Technical field

The present disclosure relates to the field of electrochemistry technology, and in particular to a silicon-carbon composite material and a preparation method thereof, anode active material, anode plate, electrochemical device and vehicle.

Background technique

With the rapid development of electronic equipment and electric vehicles, various types of electronic equipment have put forward increasingly higher requirements for the fast charging performance of secondary batteries. For example, the fast charging and battery life of lithium-ion batteries have become important indicators for measuring batteries. At present, most of the negative electrodes of commercial lithium-ion batteries are graphite materials. However, with the rapid development of science and technology, graphite materials can no longer meet people's development needs (theoretical capacity 372mAh/g). Moreover, during the charging and discharging process of graphite materials, lithium ions can only be embedded and extracted through the end faces of graphite. The diffusion path is long, which seriously affects the lithium ion diffusion speed and cannot meet the needs of fast-charging batteries.

In order to improve fast charging performance, in related technologies, the structure and/or composition of the negative active material has been improved, such as using silicon-containing materials. However, silicon will expand in volume during the lithiation process, thus affecting the cycle performance of lithium-ion batteries. .

Contents of the invention

In order to solve the above technical problems, the present disclosure provides a silicon-carbon composite material and a preparation method thereof, a negative active material, a negative electrode sheet, an electrochemical device and a vehicle. The silicon-carbon composite material of the present disclosure has better cycle performance.

The present disclosure provides a silicon-carbon composite material, including graphite material and silicon-carbon material fixed in the gaps between the graphite materials.

Optionally, the silicon carbon material has a core-shell structure, the core of the silicon carbon material is nano-silicon, and the outer shell of the silicon carbon material is a carbon layer; and/or the silicon carbon material is a silicon carbon masterbatch, and the particle size of the silicon carbon masterbatch is It is 1μm～5μm.

Optionally, the graphite material and the silicon-carbon material form silicon-carbon composite particles, and the particle size of the silicon-carbon composite particles is 10 μm to 80 μm.

Optionally, the mass percentage content of the silicon element in the silicon carbon material is 20% to 60%; and/or the mass percentage content of the silicon carbon material in the silicon carbon composite material is 20% to 50%; the graphite in the silicon carbon composite material The mass percentage content of the material is 48% to 79%.

Optionally, the silicon carbon composite material also includes a conductive agent. The conductive agent is interspersed between the silicon carbon material and the graphite material to form a conductive network inside the silicon carbon composite material. Preferably, the conductive agent in the silicon carbon composite material is The mass percentage content is 1% to 2%; the silicon-carbon composite material also includes a binder. The silicon-carbon material and the graphite material and the graphite materials are connected through an adhesive, and the silicon-carbon composite particles are connected through an adhesive. For connection, preferably, the adhesive accounts for 2% to 20% of the total weight of the silicon-carbon composite material.

Optionally, the conductive agent is selected from carbon nanomaterials. Preferably, the carbon nanomaterials are selected from at least one of zero-dimensional, one-dimensional, two-dimensional and three-dimensional carbon nanomaterials; graphite materials include at least one of graphite and graphite-like materials. One, the graphite is selected from at least one of artificial graphite and natural graphite; the graphite-like material is selected from at least one of onion-shaped carbon microspheres and MCMB; preferably, the particle size of the graphite material is 1 μm to 25 μm.

Optionally, the tap density of the silicon-carbon composite material is 0.4~0.6g/cm ³ , and the lithium storage capacity of the silicon-carbon composite material is 400~2000mAh/g.

The present disclosure also provides a method for preparing the above-mentioned silicon-carbon composite material, which at least includes the following steps:

S1. Preparation of silicon carbon materials;

S2. Take the silicon carbon material, graphite material and conductive agent, mix them evenly, add the binder precursor solution and continue mixing;

S3. Carbonize the mixed raw materials under inert atmosphere conditions to obtain silicon-carbon composite materials.

Optionally, in S1, nano-silicon is dispersed in a liquid carbon source to obtain a dispersion. The dispersion is pyrolyzed and kept warm under an inert atmosphere to obtain a silicon carbon material. Preferably, the liquid carbon source is selected from chain materials. Hydrocarbons, cyclic hydrocarbons or mixed hydrocarbons; and/or,

In S2, take the silicon carbon material, graphite material and conductive agent and mix them in a wet granulator for 5 to 10 minutes, with a cutting speed of 1500 to 2500 rpm and a mixing speed of 120 to 180 rpm; then add the binder precursor solution Stir for another 10 to 30 minutes, with a cutting speed of 1500 to 2500 rpm and a mixing speed of 120 to 180 rpm; and/or,

In S3, the carbonization temperature is 600°C to 1200°C, and the carbonization time is 1 to 3 hours.

Optionally, in S2, the mass percentage concentration of the solute in the binder precursor solution is 2% to 30%, and the added amount of the binder precursor solution is 20% of the total mass of the silicon carbon material, graphite material and conductive agent. %~120%;

Preferably, the binder precursor solution is selected from aqueous binders or oily binders; preferably, the aqueous binder is selected from at least one of sodium carboxymethylcellulose aqueous solution, sodium alginate aqueous solution, and polyacrylic acid aqueous solution. kind; Preferably, the oily binder is selected from at least one of polyvinylidene fluoride/N,N-dimethylformamide solution, asphalt-pyridine mixture, and asphalt-tetrahydrofuran mixture.

The present disclosure also provides a negative active material, including the above-mentioned silicon-carbon composite material or the silicon-carbon composite material prepared by the above-mentioned preparation method.

The present disclosure also provides a negative electrode piece, and the negative active material in the negative electrode piece is selected from the above-mentioned negative active materials.

The present disclosure also provides an electrochemical device, including a positive electrode piece, a negative electrode piece and an isolation film. The negative electrode piece is the above-mentioned negative electrode piece.

The present disclosure also provides a vehicle, which includes the above-mentioned electrochemical device.

Compared with the existing technology, the technical solution provided by the embodiments of the present disclosure has the following advantages:

In the silicon-carbon composite material of the present disclosure, the silicon-carbon material is fixed in the gaps between the graphite materials, that is, the silicon-carbon material is wrapped by the graphite material, which can effectively suppress the volume expansion of silicon in the silicon-carbon material during the lithiation process. , when used as anode material for lithium-ion batteries, it can ensure stable cycle performance of the battery.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the disclosure and together with the description serve to explain the principles of the invention.

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those of ordinary skill in the art, It is said that other drawings can be obtained based on these drawings without exerting creative labor.

Figure 1 is a schematic structural diagram of silicon-carbon composite particles according to an embodiment of the present disclosure;

Figures 2 and 3 are scanning electron microscope photographs of silicon-carbon composite materials according to embodiments of the present disclosure;

Figure 4 shows the charge and discharge performance test results of the half-cell according to the embodiment of the present disclosure;

Figure 5 shows the rate performance test results of the full battery according to the embodiment of the present disclosure.

in:

1- Graphite material;

2-Binder;

3-Silicon carbon material.

Detailed ways

In order to understand the above objects, features and advantages of the present disclosure more clearly, the solution of the present invention will be further described below. It should be noted that, as long as there is no conflict, the embodiments of the present disclosure and the features in the embodiments can be combined with each other.

Many specific details are set forth in the following description to fully understand the present disclosure, but the present disclosure can also be implemented in other ways different from those described here; obviously, the embodiments in the description are only part of the embodiments of the present disclosure, and Not all examples.

In order to further improve the cycle performance of existing negative active materials, the first aspect of the embodiment of the present disclosure proposes a silicon-carbon composite material, including a graphite material and a silicon-carbon material fixed in the gaps between the graphite materials; the silicon-carbon composite particles The structural diagram is shown in Figure 1. As can be seen from Figure 1, after the particles of graphite material 1 are accumulated, gaps are formed between the particles. The silicon carbon material 3 is fixed and confined in the gaps formed by the close accumulation of particles of graphite material 1, effectively inhibiting the formation of silicon during the lithiation process. The volume expansion enables the battery to have stable cycle performance when used as anode material for lithium-ion batteries.

As an improvement of the embodiment of the present disclosure, the silicon carbon material in the silicon carbon composite material has a core-shell structure, the core is nano silicon, that is, nano silicon powder, and the outer shell is a carbon layer.

As an improvement of the embodiment of the present disclosure, the graphite material and the silicon carbon material form silicon carbon composite particles. The particle size of the silicon carbon composite particles is 10 μm ~ 80 μm. The minimum value of the particle size range of the silicon carbon composite particles can be 10 μm. , 13 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, the maximum value of the particle size range of the silicon carbon composite particles can be 80 μm, 75 μm, 70 μm, 65 μm, 60 μm, 55 μm, 50 μm, 45 μm, 40 μm, 35 μm, and is preferably 10 μm. ~40μm. As an improvement of the embodiment of the present disclosure, the mass percentage content of silicon element in the silicon carbon material is 20% to 60%, for example, it can be 20%, 30%, 40%, 50%, 60%, preferably 50% to 60% %, the increased proportion of silicon element can more effectively increase the battery capacity.

As an improvement of the embodiment of the present disclosure, the silicon carbon material is silicon carbon masterbatch, and the particle size of the silicon carbon masterbatch is 1 μm to 5 μm. The smaller and uniform particles of the silicon carbon masterbatch can further increase the tap density of the negative electrode material. , improve the energy density of the battery.

As an improvement of the embodiment of the present disclosure, the graphite material includes at least one of graphite and graphite-like materials, the graphite is selected from at least one of artificial graphite and natural graphite; the graphite-like material is selected from onion-like carbon microspheres and intermediate At least one of Mesocarbon microbeads (MCMB for short). Onion-like carbon microspheres refer to graphitized onion carbon. The core is fullerene. The graphite layer is spherical. The overall shape is onion. Its particle size is 1μm~25μm. Depending on its model, the minimum particle size range can be 2μm, 3 μm, 4 μm, 5 μm, 7 μm, 9 μm; the minimum value of the particle size range is 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, preferably 5 μm to 25 μm or 3 μm to 15 μm. In order to facilitate the formation of voids for fixing the silicon-carbon material in the silicon-carbon composite particles, the graphite material is preferably a spherical or nearly spherical raw material. Onion-shaped carbon microspheres are further preferred because they are spherical in shape and can achieve higher density when stacked. The graphite layers are arranged in an onion shape, so they will not dissociate when subjected to large stress.

As an improvement of the embodiment of the present disclosure, the mass percentage content of silicon carbon masterbatch in the silicon carbon composite material is 20% to 50%, for example, it can be 25%, 30%, 40%, 45%, preferably 25% to 45%. 40%; the mass percentage content of graphite material in the silicon-carbon composite material is 48% to 79%, for example, it can be 50%, 55%, 60%, 65%, 70%, 75%, preferably 48% to 74%. Under the combined action of a specific mass ratio and material particle size distribution, all silicon-carbon materials can be further fixed in the gaps formed between graphite materials, while ensuring that the silicon-carbon composite material contains a sufficient amount of silicon-carbon material to ensure the battery capacity.

As an improvement to the embodiment of the present disclosure, the silicon-carbon composite material also includes a conductive agent. The conductive agent is interspersed between the silicon-carbon material and the graphite material to form a conductive network inside the silicon-carbon composite particles. The conductive network can be effectively formed. Achieve high-speed transfer of electrons and rapid transfer of lithium ions. When using this material as an anode material for lithium-ion batteries, the battery has better fast charging performance.

As an improvement of the embodiment of the present disclosure, the conductive agent is selected from carbon nanomaterials, and the carbon nanomaterials are selected from at least one of zero-dimensional, one-dimensional, two-dimensional and three-dimensional carbon nanomaterials. Carbon nanomaterials refer to materials with dimensions ranging from 1 nm to 100 nm in at least one dimension (such as length, width, and height). Zero-dimensional carbon nanomaterials refer to carbon nanomaterials with the size of each dimension between 1nm and 100nm, such as fullerene C60 and C70. One-dimensional nanomaterials are materials in which two of the three dimensions are not between 1nm and 100nm, such as carbon nanotubes; two-dimensional nanomaterials are materials in which one of the three dimensions is not between 1nm and 100nm. materials, such as graphene; three-dimensional nanomaterials refer to composite materials composed of one or more basic structural units in zero, one, and two dimensions, such as carbon black.

As an improvement of the embodiment of the present disclosure, the carbon nanomaterial is selected from graphene. Graphene has a two-dimensional structure, which not only has good electrical conductivity, but can also connect silicon-carbon materials and graphite materials and coat silicon-carbon particles.

As an improvement of the embodiment of the present disclosure, the mass ratio of the conductive agent in the silicon-carbon composite material is 1% to 2%, for example, it can be 1%, 1.2%, 1.5%, 1.8%, or 2%. The conductive agent within this proportion can effectively form a conductive network inside the silicon-carbon composite particles.

As an improvement of the embodiment of the present disclosure, the silicon-carbon composite material also includes a binder. The schematic diagram is shown in Figure 1. The silicon-carbon material 3 and the graphite material 1 and the graphite materials 1 are connected through the binder 2. . Furthermore, the silicon-carbon composite particles may be further connected through an adhesive. The binder is pyrolytic carbon that is carbonized at high temperatures, thereby stably fixing the raw material particles together.

As an improvement to the embodiment of the present disclosure, the binder accounts for 2% to 20% of the total weight of the silicon-carbon composite material, for example, it can be 3%, 5%, 8%, 10%, 15%, 18%; and preferably It is 3% to 18%, and more preferably 5% to 15%. The function of the adhesive is to connect and fix the particles, so it accounts for a relatively small mass in the silicon-carbon composite material. If the proportion of binder is too large, it will affect the tap density of silicon-carbon composite materials, thereby affecting its energy density.

As an improvement of the embodiment of the present disclosure, the tap density of the silicon-carbon composite material is 0.4-1g/cm3, for example, it can be 0.5g/ ^cm3 , 0.6g/ ^cm3 , 0.7g/ ^cm3 , 0.75g/cm ³ , 0.9g/cm ³ , 0.95g/cm ³ . The tap density of the silicon-carbon composite material in the embodiment of the present disclosure is high, indicating that the silicon-carbon composite material has a higher energy density.

As an improvement of the embodiment of the present disclosure, the lithium storage capacity of the silicon-carbon composite material is 400-2000mAh/g, for example, it can be 450mAh/g, 500mAh/g, 530mAh/g, 600mAh/g, 700mAh/g, 800mAh/ g, 900mAh/g, 1000mAh/g, 1200mAh/g. The silicon-carbon composite material of the embodiment of the present disclosure has a lithium storage capacity significantly higher than that of graphite material.

The second aspect of the embodiment of the present disclosure further proposes a preparation method of the silicon-carbon composite material, which at least includes the following steps:

S1. Preparation of silicon carbon materials;

S2. Take the silicon carbon material, graphite material and carbon nanomaterial, mix them evenly, add the binder precursor solution and continue mixing;

S3. Carbonize the mixed raw materials under inert atmosphere conditions to obtain silicon-carbon composite materials.

The preparation method of the embodiment of the present disclosure has the advantages of simplicity and controllability, thereby promoting the widespread use of negative active materials.

In S1, core-shell structured silicon carbon materials can be prepared by conventional methods, and the following methods can be selected for preparation: disperse nano-silica powder in a liquid carbon source to obtain a dispersion, and add the dispersion to the preheated chemical vapor phase In the pyrolysis reaction furnace, the silicon carbon material is obtained by pyrolysis and heat preservation under an inert atmosphere.

Specifically, the liquid carbon source is selected from chain hydrocarbons, cyclic hydrocarbons or mixed hydrocarbons, such as n-heptane and toluene, and a mixture of hydrocarbons such as industrial washing oil can also be selected. The mass ratio of nano-silica powder to liquid carbon source can be 1:5-10. The temperature of preheating and pyrolysis can be 600℃～1200℃, for example, it can be 700℃, 800℃, 850℃, 900℃, 950℃. The heat preservation time can be 0.5～2 hours, for example, it can be 0.5 hour, 1 hours, 1.5 hours. In order to speed up the dispersion efficiency, ultrasonic dispersion can be used, and the wavelength and power of ultrasonic can be used under conventional conditions.

As an improvement of the embodiment of the present disclosure, in S2, the mass percentage concentration of the solute in the binder precursor solution is 2% to 30%, and can further be 3%, 5%, 10%, 15%, 20% ,25%.

As an improvement of the embodiment of the present disclosure, in S2, the amount of the binder precursor solution added is 20% to 120% of the total mass of the silicon carbon material, graphite material and conductive agent. The amount of the binder precursor solution added is 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100% of the total mass of the silicon carbon material, graphite material and conductive agent.

As an improvement of the embodiment of the present disclosure, in S2, the binder precursor solution is selected from a water-based binder or an oil-based binder; a water-based binder refers to a polymer chain that is fully extended and dispersed in water, specifically It can be selected from at least one of water-based PVDF, polyacrylic acid, polyurethane, polyvinyl alcohol, polyacrylate, polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer, or polysaccharides. Substances such as sodium carboxymethyl cellulose, sodium alginate, etc. The mass percentage concentration of the solute in the water-based binder can be 10% to 20%; for example, it can be 10%, 12%, 15%, or 18%. Oily binder means that the polymer molecular chain is completely extended and dispersed in the oily solvent. For example, the oily solvent solution of polyvinylidene fluoride, the mixture of asphalt and oily solvent, etc. For oily solvents, organic solvents with smaller viscosity such as N,N-dimethylformamide, pyridine, and tetrahydrofuran can be selected. Specifically, polyvinylidene fluoride/N,N-dimethylformamide solution, asphalt-pyridine mixture, and asphalt-tetrahydrofuran mixture can be used. Wherein, the mass percentage concentration of polyvinylidene fluoride in N,N-dimethylformamide can be 10% to 20%, for example, it can be 10%, 12%, 15%, 18%; the asphalt in the asphalt-pyridine mixture The mass percentage concentration of asphalt can be 10% to 20%, for example, it can be 10%, 12%, 15%, 18%; the mass percentage concentration of asphalt in the asphalt-tetrahydrofuran mixture can be 10% to 20%, for example, it can be 10 %, 12%, 15%, 18%.

As an improvement of the embodiment of the present disclosure, in S2, the silicon carbon material, graphite material and conductive agent are first mixed in a wet granulator for 5 to 10 minutes, the cutting speed is 1500 to 2500 rpm; the mixing speed is 120 to 120 rpm. 180rpm; then add the binder precursor solution and stir for 10 to 30 minutes, the cutting speed is 1500~2500rpm, and the mixing speed is 120~180rpm. Further optionally, the working conditions used by the wet granulator are: the cutting speed can be selected from 1800rpm, 2000rpm, and 2200rpm, and the mixing speed can be selected from 125rpm, 130rpm, 140rpm, 150rpm, 160rpm, and 175rpm; and further optional: cutting speed is 2000rpm, and the mixing speed is 150rpm. Step 2 of the embodiment of the present disclosure is performed in a wet granulator, that is, the mixing paddle inside the wet granulator is used to fully mix the raw materials, which can further shorten the mixing time and improve production efficiency. After granulation, small particles of silicon-carbon material are confined in the gaps where graphite particles are closely packed, effectively suppressing the volume expansion of silicon during the lithiation process, so that silicon-carbon composite electrodes have stable cycle performance. The models of wet granulators that can be used are: HLSG series wet mixer granulator, GHL series wet mixer granulator, SMG series wet mixer granulator, and Diosna mixed wet granulator.

As an improvement of the embodiment of the present disclosure, in S3, the carbonization temperature can be 600°C to 1200°C, for example, 800°C, 900°C, 1000°C, 1100°C, and the carbonization time can be 1 to 3 hours. For example, 1.5 hours, 2 hours, 2.5 hours. The purpose of carbonization is to carbonize the binder precursor to form a binder.

The third aspect of the embodiment of the present disclosure also provides a negative active material, including the silicon-carbon composite material proposed in the first aspect of the embodiment of the present disclosure. The negative active material is composed of the silicon-carbon composite material, and other components can also be added to form the composition.

The fourth aspect of the embodiment of the present disclosure also provides a negative electrode sheet. The negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may include the third aspect of the embodiment of the present disclosure. Proposed negative active materials, binders and conductive agents, etc. The type and content of conductive agents and binders are not subject to specific restrictions and can be selected according to actual needs. The type of negative electrode current collector is not subject to specific restrictions and can be selected according to actual needs. Conventional metal foil, such as copper foil, can be used.

The fifth aspect of the embodiment of the present disclosure also provides an electrochemical device. The electrochemical device may be, for example, a battery, including a positive electrode sheet, a negative electrode sheet and a separator. The negative electrode sheet is the one proposed in the fourth aspect of the embodiment of the present disclosure. Negative pole piece. The positive electrode piece used in conjunction with the negative electrode piece according to the embodiment of the present disclosure can be selected from various conventional positive electrode pieces commonly used in the art, and their composition and preparation methods are well known in the art. The separator used in the battery of the embodiments of the present disclosure can be selected from various separators commonly used in the art.

Batteries of embodiments of the present disclosure generally further include an electrolyte. Various electrolytes commonly used in this field can be selected, such as solutions of electrolyte salts in non-aqueous solvents. For example, for lithium batteries, a mixed solution of electrolyte lithium salt and non-aqueous solvent can be used. The electrolyte lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium halide, lithium chloroaluminate, and lithium fluoroalkylsulfonate. The organic solvent can be selected from chain carbonates, cyclic carbonates or mixed solvents thereof. Among them, the chain carbonate can be dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC) and other carbonates containing At least one of fluorine, sulfur-containing or unsaturated bond-containing chain organic esters. Cyclic carbonates can be ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), sultone and other fluorine-, sulfur- or One or more cyclic organic esters containing unsaturated bonds.

The battery of the embodiment of the present disclosure may be a primary battery or a secondary battery. The battery in the embodiment of the present disclosure may be a lithium-ion battery or a sodium-ion battery, preferably a lithium-ion battery, and may be, for example, a lithium-ion primary battery or a lithium-ion secondary battery. Apart from the use of negative electrode plates as described above, the construction and preparation of these batteries are known per se. Moreover, the preparation method of the negative active material according to the embodiment of the present disclosure is simple, so the manufacturing cost of the battery using the negative electrode sheet according to the embodiment of the present disclosure can be reduced. The negative active material of the embodiment of the present disclosure has high specific capacity and electronic conductivity. The carbon nanotube conductive network interspersed inside reduces the impedance of the composite material, promotes lithium ion transfer, and improves the rate performance of the electrode.

A sixth aspect of the embodiments of the present disclosure also provides an electric vehicle, which is loaded with the electrochemical device proposed in the fifth aspect. Specifically, the electric vehicle can be any vehicle that requires an electrochemical device as a power source, such as an electric vehicle. Buses, light rail electric vehicles and electric vehicles, etc. Because it includes the electrochemical device of any of the above embodiments, it has the beneficial effects of the electrochemical device of any of the above embodiments.

The preparation method of the silicon-carbon composite material of the present disclosure will be further described below through specific implementation examples. Those skilled in the art should understand that the following specific examples are only to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

Preparation of silicon-carbon composite materials in embodiments of the present disclosure:

S1. Preparation method of silicon carbon material:

Silicon carbon masterbatch No. 1: Weigh 5g of nano-silica powder and disperse it in 50g of toluene. After ultrasonic dispersion, add it dropwise into a chemical vapor phase reactor preheated to 900°C and keep it for 1 hour to prepare silicon carbon masterbatch. Silicon carbon The mass percentage content of silicon element in the masterbatch is 64%, and the particle size is 1μm~5μm;

Silicon carbon masterbatch No.2: The preparation method is the same as silicon carbon masterbatch No.1, the difference is that the liquid carbon source uses industrial washing oil; the mass percentage of silicon element in the silicon carbon masterbatch is 45%, and the particle size is 1 μm ~5μm;

Silicon carbon masterbatch No.3: The preparation method is the same as silicon carbon masterbatch No.1, the difference is that the industrial washing oil is 30g; the mass percentage of silicon element in the silicon carbon masterbatch is 45%, and the particle size is 1μm~5μm .

S2. Weigh the silicon carbon masterbatch, graphitized onion carbon and graphene according to the weight ratio. The specific addition ratio is shown in Table 1; pour into the wet granulator, cut and stir for 5 minutes, the cutting speed is 2000rpm, and mix The rotation speed is 150rpm; then add dropwise a carboxymethylcellulose sodium aqueous solution with a mass percentage concentration of 10%. The added amount of the carboxymethylcellulose sodium aqueous solution is 100% of the total mass of the silicon carbon masterbatch, graphite material and conductive agent. Shear Cut and stir for 15 minutes, the cutting speed is 2000rpm, and the mixing speed is 150rpm. A mixture of silicon-carbon particles is prepared, with the particle size controlled between 3 μm and 25 μm.

S3. Carbonize the silicon-carbon particle mixture prepared in S2 under inert atmosphere conditions at 900°C to 1000°C for 2 hours to obtain a silicon-carbon composite material.

Table 1

Among them, the mass percentage of the binder in the total weight of the silicon-carbon composite material was measured using TG thermogravimetric analysis.

Among them, the scanning electron micrographs of silicon carbon masterbatch 1# are shown in Figures 2 and 3. As shown in Figures 2 and 3, it is obvious that large particles are aggregated from small particles, and graphene is dispersed between each component to form a conductive carbon network, and the silicon carbon masterbatch is also tightly sealed in the stacking gaps of the graphite material. middle.

Silicon carbon composite material 8#: Silicon carbon masterbatch, graphitized onion carbon and carbon nanotubes are the same as silicon carbon composite material 1#, the difference is:

The binder precursor solution is a sodium carboxymethylcellulose aqueous solution with a mass percentage concentration of 30%, and the binder accounts for 20% of the total weight of the silicon-carbon composite material.

Silicon carbon composite material 9#: silicon carbon masterbatch, graphitized onion carbon and carbon nanotubes are the same as silicon carbon composite material 1#, the difference is that the binder precursor solution is carboxymethyl fiber with a mass percentage concentration of 2% Sodium aqueous solution, the binder accounts for 1% of the total weight of the silicon-carbon composite material.

Silicon carbon composite material 10#: silicon carbon masterbatch, graphitized onion carbon and carbon nanotubes are the same as silicon carbon composite material 1#, the difference is: weigh the silicon carbon masterbatch, graphitized onion carbon and carbon nanotubes according to the weight ratio Then add it to a large amount of binder precursor solution, stir and mix to prepare a slurry. The amount of binder precursor solution added is 600% of the total mass of silicon carbon masterbatch, graphite material and conductive agent; binder precursor The solution is a sodium carboxymethylcellulose aqueous solution with a mass percentage concentration of 2%. After sintering, the binder accounts for 5% of the total weight of the silicon-carbon composite material. The mixture is stirred and mixed evenly, then dried, calcined and pulverized.

Silicon-carbon composite material 11#: Silicon-carbon masterbatch and carbon nanotubes are the same as silicon-carbon composite material 1#. The difference is that the graphite material uses artificial graphite, and the addition amount is also the same as silicon-carbon composite material 1#.

The physical parameters of the prepared silicon-carbon composite materials are as shown in Table 2:

Among them, the detection method of physical parameters is obtained by laser particle size analyzer and tap density tester (number of taps: 30000, frequency: 1 time/second).

Table 2

Silicon carbon composite material number Tap density (g/cm ³ ) Particle size (μm) Silicon carbon composite material 1# 0.81 25～50 Silicon carbon composite material 2# 0.80 15～50 Silicon carbon composite material 3# 0.79 10～50 Silicon carbon composite material 4# 0.95 30～80 Silicon carbon composite material 5# 0.80 40～100 Silicon carbon composite material 6# 0.84 30～60 Silicon carbon composite material 7# 0.76 10～50 Silicon carbon composite material 8# 0.80 50～150 Silicon carbon composite material 9# 0.54 3～20 Silicon carbon composite material 10# 0.65 20～60 Silicon carbon composite material 11# 0.75 20～55

It can be seen from Table 2 that silicon-carbon composite materials 1# to 5# have obtained higher tap density and energy density. In silicon-carbon composite material 6#, because the amount of silicon-carbon masterbatch added is too small, its energy density is weakened. Since the added amount of graphite material in silicon-carbon composite material 7# is too small, its tap density is reduced. Since the proportion of binder in silicon-carbon composite material 8# is too large, its larger particle size is not conducive to close-packed particle packing, and the tap density and energy density are both reduced. Silicon-carbon composite material 9# has a smaller particle size and smaller tap density because the proportion of binder is too small.

Performance measurement of materials according to the embodiments of the present disclosure:

(1) Half cell test

The negative active materials 1# to 11# are used as negative electrodes of lithium ion batteries to assemble a button battery. The negative active materials 1# to 11# correspond to the aforementioned silicon carbon composite materials 1# to 11# one by one.

The specific preparation method is: mix the negative active materials 1# to 11#, sodium carboxymethyl cellulose, and acetylene black in a mass ratio of 91:6:3, grind them evenly, add an appropriate amount of water, and continue grinding to prepare the electrode slurry. The material is evenly coated on the carbon-coated copper foil, and vacuum dried at 120°C for 12 hours to prepare electrode sheets 1#~11#. Use the lithium sheet as the counter electrode and assemble it into half cells 1#~12#. In the LAND (CT3001A) battery test system, the charge and discharge performance is tested at a current density of 200mA/g. The test results are shown in Figure 4 and Table 3:

table 3

It can be seen from Table 3 that when using negative active materials 1# to 5# as the negative electrode, it has a higher capacity, which is obviously better than traditional graphite materials, and has a higher first Coulombic efficiency. At the same time, after 100 cycles, half cells 1# to 5# have a capacity retention rate of about 90%, indicating that the silicon carbon anode material has stable cycle performance. The battery capacity of half-battery 6# and 8# has been weakened. The capacity retention rate in half cells 7# and 9# has decreased. The battery in the half-cell has a larger particle size due to an excessive proportion of binder, and the tap density and energy density are reduced. Silicon-carbon composite material 9# has a smaller particle size and a larger density because the binder ratio is too small.

(2) Full battery test

Use negative active materials 1#~11# as negative electrode materials, negative active materials 1#~11# correspond to the aforementioned silicon carbon composite materials 1#~11# one by one, use lithium iron phosphate as the positive electrode, and assemble into a button full battery 1# ~11#. The assembled full battery is tested using the LAND battery testing system.

Test cycle performance: charge and discharge current density 2C, voltage range 2.5V ~ 3.65V, number of cycles 300 times.

Test rate performance: charge and discharge current density is 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, voltage range is 2.5V~3.65V. The results are shown in Figure 5 and Table 4:

Table 4

As can be seen from Table 4, the silicon-carbon composite materials of the embodiments of the present disclosure have excellent rate performance and cycle stability after being assembled into a full battery. The silicon-carbon materials prepared by the embodiments of the present disclosure have a stable structure. The graphite limits the silicon-carbon masterbatch. The volume expansion of silicon can be effectively suppressed in the stacked gaps. At the same time, the carbon nanotube network inside the composite material promotes the transfer of electrons and the diffusion of lithium ions, thus improving its rate charge and discharge performance. According to full cells 5# and 7#, if the amount of graphite material added is too small, the rate performance and cycle stability will decrease. The rate performance of full battery 9# dropped significantly.

It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

The above descriptions are only specific embodiments of the present disclosure, enabling those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be practiced in other embodiments without departing from the spirit or scope of the disclosure. Therefore, the present disclosure is not to be limited to the embodiments described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (14)

1. A silicon-carbon composite material, characterized in that it includes a graphite material and a silicon-carbon material fixed in the gaps between the graphite materials. 2. The silicon-carbon composite material according to claim 1, characterized in that the silicon-carbon material has a core-shell structure, the core of the silicon-carbon material is nano-silicon, and the outer shell of the silicon-carbon material is a carbon layer; And/or, the silicon carbon material is silicon carbon masterbatch, and the particle size of the silicon carbon masterbatch is 1 μm to 5 μm. 3. The silicon-carbon composite material according to claim 1, wherein the graphite material and the silicon-carbon material form silicon-carbon composite particles, and the particle size of the silicon-carbon composite particles is 10 μm to 80 μm. 4. The silicon-carbon composite material according to claim 1, characterized in that the mass percentage content of silicon element in the silicon-carbon material is 20% to 60%; and/or, The mass percentage content of the silicon carbon material in the silicon carbon composite material is 20% to 50%; The mass percentage content of the graphite material in the silicon-carbon composite material is 48% to 79%. 5. The silicon-carbon composite material according to any one of claims 3 to 4, characterized in that the silicon-carbon composite material further includes a conductive agent, and the conductive agent is interspersed between the silicon-carbon material and the graphite. between materials, used to form a conductive network inside the silicon-carbon composite material. Preferably, the mass percentage content of the conductive agent in the silicon-carbon composite material is 1% to 2%; The silicon carbon composite material also includes a binder. The silicon carbon material and the graphite material and the graphite materials are connected through an adhesive. The silicon carbon composite particles are connected through an adhesive. For connection, preferably, the adhesive accounts for 2% to 20% of the total weight of the silicon-carbon composite material. 6. The silicon-carbon composite material according to claim 5, characterized in that the conductive agent is selected from carbon nanomaterials. Preferably, the carbon nanomaterials are selected from zero-dimensional, one-dimensional, two-dimensional and three-dimensional carbon nanomaterials. at least one of the materials; The graphite material includes at least one of graphite and graphite-like materials, the graphite is selected from at least one of artificial graphite and natural graphite; the graphite-like material is selected from at least one of onion-like carbon microspheres and MCMB. species; preferably, the particle size of the graphite material is 1 μm to 25 μm. 7. The silicon-carbon composite material according to any one of claims 1 to 6, characterized in that the tap density of the silicon-carbon composite material is 0.4-0.6 g/cm 3 , and the tap density of the silicon-carbon composite material is 0.4-0.6 g/cm ³ . The lithium storage capacity is 400~2000mAh/g. 8. The preparation method of silicon-carbon composite material according to any one of claims 5 to 7, characterized in that it at least includes the following steps: S1. Prepare the silicon carbon material; S2. Take the silicon carbon material, the graphite material and the conductive agent, mix them evenly, add the binder precursor solution and continue mixing; S3. Carbonize the mixed raw materials under inert atmosphere conditions to obtain the silicon-carbon composite material. 9. The preparation method according to claim 8, characterized in that, In S1, nano-silicon is dispersed in a liquid carbon source to obtain a dispersion. The dispersion is pyrolyzed and kept warm under an inert atmosphere to obtain the silicon carbon material. Preferably, the liquid carbon source is selected from Chain hydrocarbons, cyclic hydrocarbons or mixed hydrocarbons; and/or, In S2, take the silicon carbon material, the graphite material and the conductive agent and mix them in a wet granulator for 5 to 10 minutes, with a cutting speed of 1500 to 2500 rpm and a mixing speed of 120 to 180 rpm; then add The binder precursor solution is stirred for another 10 to 30 minutes, the cutting speed is 1500-2500rpm, and the mixing speed is 120-180rpm; and/or, In S3, the carbonization temperature is 600°C to 1200°C, and the carbonization time is 1 to 3 hours. 10. The preparation method according to claim 8, characterized in that, in S2, the mass percentage concentration of the solute in the binder precursor solution is 2% to 30%, and the concentration of the solute in the binder precursor solution is 2% to 30%. The added amount is 20% to 120% of the total mass of silicon carbon materials, graphite materials and conductive agents; Preferably, the binder precursor solution is selected from an aqueous binder or an oily binder; more preferably, the aqueous binder is selected from at least one of a sodium carboxymethyl cellulose aqueous solution, a sodium alginate aqueous solution, and a polyacrylic acid aqueous solution; more preferably, the oily binder is selected from at least one of a polyvinylidene fluoride/N,N-dimethylformamide solution, an asphalt-pyridine mixture, and an asphalt-tetrahydrofuran mixture. 11. A negative active material, including the silicon-carbon composite material according to any one of claims 1 to 7 or the silicon-carbon composite material prepared by the preparation method according to any one of claims 8 to 10. 12. A negative electrode sheet, characterized in that the negative active material in the negative electrode sheet is selected from the negative active materials as claimed in claim 11. 13. An electrochemical device, comprising a positive electrode piece, a negative electrode piece and an isolation film, wherein the negative electrode piece is the negative electrode piece according to claim 12. 14. A vehicle, characterized in that the electrochemical device according to claim 13 is included in the vehicle.