CN117747764A

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

Info

Publication number: CN117747764A
Application number: CN202211150663.2A
Authority: CN
Inventors: 宋怀河; 张家鹏; 李昂; 张鹏; 李叶晶; 屈国莹
Original assignee: Beijing University of Chemical Technology; Beijing CHJ Automobile Technology Co Ltd
Current assignee: Beijing University of Chemical Technology; Beijing CHJ Automobile Technology Co Ltd
Priority date: 2022-09-21
Filing date: 2022-09-21
Publication date: 2024-03-22

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 material, preparation method thereof, negative electrode active material, negative electrode plate, electrochemical device and vehicle

Technical Field

The disclosure relates to the technical field of electrochemistry, in particular to a silicon-carbon composite material and a preparation method thereof, a negative electrode active material, a negative electrode plate, an electrochemistry device and a vehicle.

Background

With the high-speed development of electronic devices and electric automobiles, various electronic devices are increasingly required to rapidly charge secondary batteries. For example, fast charge and endurance of lithium ion batteries have become important metrics for measuring batteries. Currently, most of the negative electrodes of commercial lithium ion batteries are made of graphite materials. However, with the rapid development of technology, graphite materials have failed to meet the development needs of people (theoretical capacity 372 mAh/g). In addition, in the charging and discharging process of the graphite material, lithium ions can only be inserted and extracted through the end face of graphite, the diffusion path is long, the diffusion speed of the lithium ions is seriously influenced, and the requirement of a quick-charging battery cannot be met.

In order to improve the fast charge performance, the structure and/or composition of the negative electrode active material is improved in the related art, for example, a silicon-containing material is used, but silicon undergoes volume expansion during lithiation, thereby affecting the cycle performance of the lithium ion battery.

Disclosure of Invention

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

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

Optionally, the silicon-carbon material is of a core-shell structure, the inner 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 master batch, and the particle size of the silicon-carbon master batch is 1-5 mu m.

Alternatively, both the graphite material and the silicon-carbon material form silicon-carbon composite particles, the silicon-carbon composite particles having a particle size of 10 μm to 80 μm.

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

Optionally, the silicon-carbon composite material further comprises a conductive agent, wherein the conductive agent is inserted between the silicon-carbon material and the graphite material and is used for forming a conductive network inside the silicon-carbon composite material, and preferably, the mass percentage content of the conductive agent in the silicon-carbon composite material is 1% -2%; the silicon-carbon composite material also comprises a binder, the silicon-carbon material and the graphite material are connected through an adhesive, the silicon-carbon composite particles are connected through the adhesive, and the adhesive accounts for 2% -20% of the total weight of the silicon-carbon composite material.

Optionally, the conductive agent is selected from carbon nanomaterial, preferably, the carbon nanomaterial is selected from at least one of zero-dimensional, one-dimensional, two-dimensional, and three-dimensional carbon nanomaterial; the graphite material comprises at least one of graphite and graphite-like material, and the graphite is 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; 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 0.4-0.6 g/cm ³ The lithium storage capacity of the silicon-carbon composite material is 400-2000 mAh/g.

The disclosure also provides a preparation method of the silicon-carbon composite material, which at least comprises the following steps:

s1, preparing a silicon-carbon material;

s2, taking a silicon-carbon material, a graphite material and a conductive agent, uniformly mixing, adding a binder precursor solution, and continuing mixing;

and S3, carbonizing the mixed raw materials under the inert atmosphere condition to obtain the silicon-carbon composite material.

Optionally, in S1, dispersing nano silicon in a liquid carbon source to obtain a dispersion, pyrolyzing and preserving heat of the dispersion in an inert atmosphere to obtain a silicon carbon material, wherein the liquid carbon source is preferably selected from chain hydrocarbon, cyclic hydrocarbon or mixed hydrocarbon; and/or the number of the groups of groups,

in S2, mixing a silicon carbon material, a graphite material and a conductive agent in a wet granulator for 5-10 minutes, wherein the cutting speed is 1500-2500 rpm, and the mixing speed is 120-180 rpm; then adding the binder precursor solution, stirring for 10-30 minutes, wherein the cutting speed is 1500-2500 rpm, and the mixing speed is 120-180 rpm; and/or the number of the groups of groups,

in S3, the carbonization temperature is 600-1200 ℃, and the carbonization time is 1-3 hours.

Optionally, in S2, the concentration of the solute in the binder precursor solution is 2% -30% by mass, and the additive amount of the binder precursor solution is 20% -120% by mass of the total mass of the silicon carbon material, the graphite material and the conductive agent;

preferably, the binder precursor solution is selected from an aqueous binder or an oily binder; preferably, the aqueous binder is at least one selected from the group consisting of sodium carboxymethyl cellulose aqueous solution, sodium alginate aqueous solution, and polyacrylic acid aqueous solution; preferably, the oily binder is selected from at least one of polyvinylidene fluoride/N, N-dimethylformamide solution, asphalt-pyridine mixture, asphalt-tetrahydrofuran mixture.

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

The present disclosure also provides a negative electrode tab, wherein a negative electrode active material in the negative electrode tab is selected from the above-described negative electrode active materials.

The present disclosure also provides an electrochemical device, including an anode plate, a cathode plate, and an isolation film, the cathode plate is the anode plate.

The present disclosure also provides a vehicle including the above electrochemical device.

Compared with the prior art, the technical scheme provided by the embodiment of the disclosure has the following advantages:

in the silicon-carbon composite material disclosed by the invention, the silicon-carbon material is fixed in the gaps among the graphite materials, namely, the silicon-carbon material is wrapped by the graphite materials, so that the volume expansion of silicon in the silicon-carbon material in the lithiation process can be effectively inhibited, and when the silicon-carbon material is used as a negative electrode material of a lithium ion battery, the battery can be ensured to have stable cycle performance.

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 invention or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, and it will be obvious to a person skilled in the art that other drawings can be obtained from these drawings without inventive effort.

FIG. 1 is a schematic structural view of a silicon-carbon composite particle according to an embodiment of the present disclosure;

FIGS. 2 and 3 are electron scanning photomicrographs of a silicon carbon composite material of an embodiment of the present disclosure;

fig. 4 is a charge-discharge performance test result of a half cell according to an embodiment of the present disclosure;

fig. 5 is a magnification performance test result of a full cell of an embodiment of the present disclosure.

Wherein:

1-graphite material;

2-a binder;

3-silicon carbon material.

Detailed Description

In order that the above objects, features and advantages of the present disclosure may be more clearly understood, a further description of the aspects of the present invention will be provided below. It should be noted that, without conflict, the embodiments of the present disclosure and features in the embodiments may be combined with each other.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure, but the present disclosure may be practiced otherwise than as described herein; it will be apparent that the embodiments in the specification are only some, but not all, embodiments of the disclosure.

In order to further improve the cycle performance of the existing negative electrode active material, a first aspect of an embodiment of the present disclosure proposes a silicon-carbon composite material including a graphite material and a silicon-carbon material fixed in a gap between the graphite materials; a schematic structural diagram of the silicon carbon composite particles is shown in fig. 1. As can be seen from fig. 1, after the particles of the graphite material 1 are stacked, gaps are formed between the particles, and the silicon-carbon material 3 is fixed and confined in the gaps formed by the close stacking of the particles of the graphite material 1, so that the volume expansion of silicon in the lithiation process is effectively inhibited, and when the silicon-carbon material is used as a negative electrode material of a lithium ion battery, the battery has stable cycle performance.

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

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

As an improvement of the embodiment of the disclosure, the silicon-carbon material is a silicon-carbon master batch, the particle size of the silicon-carbon master batch is 1-5 mu m, and the smaller and uniform particles of the silicon-carbon master batch can further improve the tap density of the cathode material and improve the energy density of the battery.

As an improvement of the embodiments of the present disclosure, the graphite material includes at least one of graphite and a graphite-like material, the graphite being selected from at least one of artificial graphite and natural graphite; the graphite-like material is at least one selected from onion-like carbon microspheres and mesophase carbon microspheres (Mesocarbon microbeads, MCMB for short). The onion-shaped carbon microsphere refers to graphitized onion carbon, the inner core is fullerene, the graphite layer is spherical, the whole onion-shaped carbon microsphere has a particle size of 1-25 μm, and the minimum value of the particle size range can be 2 μm, 3 μm, 4 μm, 5 μm, 7 μm and 9 μm according to different types; the minimum particle size ranges are 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 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. Further, onion-like carbon microspheres are preferred, and since they have a spherical shape, a higher density can be achieved when they are stacked, and since the graphite layers are arranged in onion-like fashion, they do not dissociate when they are subjected to a large stress.

As an improvement of the embodiment of the disclosure, the mass percentage of the silicon-carbon master batch in the silicon-carbon composite material is 20% -50%, for example, 25%, 30%, 40%, 45%, preferably 25% -40%; the mass percentage of the graphite material in the silicon-carbon composite material is 48% -79%, for example, 50%, 55%, 60%, 65%, 70%, 75%, preferably 48% -74%. Under the combined action of a specific mass ratio and material particle size distribution, the silicon-carbon material can be further completely fixed in gaps formed between graphite materials, and meanwhile, the silicon-carbon composite material is ensured to contain enough silicon-carbon material to ensure the battery capacity.

As an improvement of the embodiment of the disclosure, the silicon-carbon composite material further comprises a conductive agent, wherein the conductive agent is inserted between the silicon-carbon material and the graphite material and is used for forming a conductive network inside the silicon-carbon composite particles, and the formation of the conductive network can effectively realize high-speed transfer of electrons and quick transfer of lithium ions.

As an improvement of the embodiments of the present disclosure, the conductive agent is selected from carbon nanomaterial selected from at least one of zero-dimensional, one-dimensional, two-dimensional, and three-dimensional carbon nanomaterial. Carbon nanomaterial refers to a material having a size in at least one dimension (e.g., length, width, height) between 1nm and 100 nm. Zero-dimensional carbon nanomaterial refers to carbon nanomaterial such as fullerenes C60 and C70 having a size of each dimension ranging from 1nm to 100 nm. The one-dimensional nano material is a material with two dimensions of which the size is not between 1nm and 100nm, such as a carbon nano tube; the two-dimensional nanomaterial refers to a material with one dimension of which the size is not between 1nm and 100nm, such as graphene; three-dimensional nanomaterials refer to composite materials, such as carbon black, that are composed of one or more basic structural units in the zero, one, and two dimensions.

As an improvement of the embodiments of the present disclosure, the carbon nanomaterial is selected from graphene. The graphene is of a two-dimensional structure, has good conductivity, can be connected with a silicon carbon material and a graphite material, and is used for coating 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% -2%, for example, may be 1%, 1.2%, 1.5%, 1.8%, 2%. The conductive agent in the 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 further includes a binder, and the silicon-carbon material 3 and the graphite material 1 are connected by an adhesive 2 as shown in fig. 1. And, the silicon carbon composite particles may be further connected by an adhesive. The binder is pyrolytic carbon formed by high-temperature carbonization, so that all raw material particles are stably fixed together.

As an improvement of the embodiment of the disclosure, the binder accounts for 2% -20% of the total weight of the silicon-carbon composite material, for example, 3%, 5%, 8%, 10%, 15%, 18%; and is preferably 3 to 18%, more preferably 5 to 15%. The binder is used for connecting and fixing the particles, so that the mass of the binder in the silicon-carbon composite material is relatively small. And if the binder ratio is too large, the tap density of the silicon-carbon composite material and thus the energy density thereof are affected.

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

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

The second aspect of the embodiments of the present disclosure further provides a method for preparing the silicon-carbon composite material, at least comprising the following steps:

s1, preparing a silicon-carbon material;

s2, taking a silicon-carbon material, a graphite material and a carbon nanomaterial, uniformly mixing, adding a binder precursor solution, and continuing mixing;

The preparation method of the embodiment of the disclosure has the advantages of simplicity and controllability, so that the wide use of the anode active material can be promoted.

In S1, the silicon-carbon material with the core-shell structure may be prepared by a conventional method, and may be prepared by selecting the following method: dispersing nano silicon powder in a liquid carbon source to obtain a dispersion liquid, adding the dispersion liquid into a preheated chemical vapor pyrolysis reaction furnace, and pyrolyzing and preserving heat in an inert atmosphere to obtain the silicon carbon material.

In particular, the liquid carbon source is selected from chain hydrocarbons, cyclic hydrocarbons or mixed hydrocarbons, such as n-heptane, toluene, and mixtures of hydrocarbons, such as industrial oil washes, etc. The mass ratio of the nano silicon powder to the liquid carbon source can be 1:5 to 10. The preheating and pyrolysis temperatures may be 600 to 1200 ℃, for example 700 ℃, 800 ℃, 850 ℃,900 ℃, 950 ℃, and the holding time may be 0.5 to 2 hours, for example 0.5 hour, 1 hour, 1.5 hours. In order to accelerate the dispersion efficiency, an ultrasonic dispersion mode can be adopted, and the wavelength and the power of the ultrasonic wave can be adopted under conventional conditions.

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

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

As an improvement of the embodiments of the present disclosure, in S2, the binder precursor solution is selected from an aqueous binder or an oily binder; the aqueous binder is prepared by dispersing polymer chain in water, and specifically can be at least one selected from aqueous PVDF, polyacrylic acid, polyurethane, polyvinyl alcohol, polyacrylate, polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer, and polysaccharide substances such as sodium carboxymethylcellulose, sodium alginate, etc. The mass percentage concentration of the solute in the aqueous binder can be 10% -20%; for example, 10%, 12%, 15%, 18%. The oily binder means that the polymer chains are completely stretched and dispersed in an oily solvent. Such as an oily solvent solution of polyvinylidene fluoride, a mixture of asphalt and an oily solvent, and the like. The oily solvent can be selected from N, N-dimethylformamide, pyridine, tetrahydrofuran, etc. Specifically, polyvinylidene fluoride/N, N-dimethylformamide solution, asphalt-pyridine mixture and asphalt-tetrahydrofuran mixture can be selected. Wherein, the mass percentage concentration of the polyvinylidene fluoride in the N, N-dimethylformamide can be 10% -20%, for example, 10%, 12%, 15% and 18%; the mass percentage concentration of the asphalt in the asphalt-pyridine mixture can be 10% -20%, for example, 10%, 12%, 15%, 18%; the concentration of the asphalt in the asphalt-tetrahydrofuran mixture may be 10% to 20% by mass, for example, 10%, 12%, 15%, 18%.

As an improvement of the embodiment of the disclosure, in S2, silicon carbon material, graphite material and conductive agent are firstly mixed in a wet granulator for 5-10 minutes, and the cutting speed is 1500-2500 rpm; the mixing rotating speed is 120-180 rpm; then adding the binder precursor solution, stirring for 10-30 minutes, cutting at 1500-2500 rpm, and mixing at 120-180 rpm. Further alternatively, the wet granulator may be operated under the following conditions: the cutting speed can be 1800rpm, 2000rpm and 2200rpm, and the mixing speed can be 125rpm, 130rpm, 140rpm, 150rpm, 160rpm and 175rpm; and further optionally: the cutting speed was 2000rpm and the mixing speed was 150rpm. Step 2 of the embodiment of the disclosure is performed in the wet granulator, that is, the raw materials are fully mixed by using the mixing paddles inside the wet granulator, so that the mixing time can be further shortened, and the production efficiency is improved. After granulation, the silicon-carbon material with small particles is limited in the gaps where graphite particles are closely piled, so that the volume expansion of silicon in the lithiation process is effectively inhibited, and the silicon-carbon composite electrode has stable cycle performance. The model of the selectable wet granulator is as follows: HLSG series wet mixer granulator, GHL series wet mixer granulator, SMG series wet mixer granulator, dionna mixed wet granulator.

As a modification of the embodiment of the present disclosure, in S3, the carbonization temperature may be 600-1200 ℃, for example 800 ℃,900 ℃, 1000 ℃, 1100 ℃, and the carbonization time may be 1-3 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.

A third aspect of the embodiments of the present disclosure also proposes a negative electrode active material, including the silicon-carbon composite material proposed by the first aspect of the embodiments of the present disclosure. The negative electrode active material is composed of the silicon-carbon composite material, and other components can be added continuously to form a composition.

The fourth aspect of the embodiments of the present disclosure also proposes a negative electrode tab, which may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer may include the negative electrode active material, the binder, the conductive agent, and the like proposed in the third aspect of the embodiments of the present disclosure. The kind and content of the conductive agent and the binder are not particularly limited, and may be selected according to actual requirements. The type of the negative electrode current collector is not particularly limited, and may be selected according to actual requirements, and conventional metal foils, such as copper foil, may be used.

The fifth aspect of the presently disclosed embodiments also proposes an electrochemical device, which may be a battery, for example, comprising a positive electrode tab, a negative electrode tab, and a separator, the negative electrode tab being the negative electrode tab proposed in the fourth aspect of the presently disclosed embodiments. The positive electrode sheet for use with the negative electrode sheet according to the embodiments of the present disclosure may be selected from various conventional positive electrode sheets commonly used in the art, and the constitution and preparation methods thereof are well known in the art. The separator for the battery of the embodiments of the present disclosure may be selected from various separators commonly used in the art.

The battery of embodiments of the present disclosure also typically includes an electrolyte. Various electrolytes commonly used in the art, such as solutions of electrolyte salts in nonaqueous solvents, may be used. For example, for a lithium battery, a mixed solution of an electrolyte lithium salt and a nonaqueous solvent may be used. The lithium electrolyte salt may be selected from lithium hexafluorophosphate (LiPF) ₆ ) One or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium halide, lithium chloroaluminate and lithium fluorocarbon sulfonate. The organic solvent may be selected from chain carbonates, cyclic carbonates or a mixed solvent composed of them. The chain carbonate may be at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), dipropyl carbonate (DPC) and other chain organic esters containing fluorine, sulfur or unsaturated bonds. The cyclic carbonate may be Ethylene Carbonate (EC), propylene Carbonate (PC), vinylene Carbonate (VC), gamma-butyrolactone (gamma-BL), sultoneOther cyclic organic esters containing fluorine, sulfur or unsaturated bonds.

The battery of the embodiments of the present disclosure may be a primary battery or a secondary battery. The battery of the embodiments 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. The construction and preparation methods of these batteries are known per se, except for the use of a negative electrode tab as described above. And the preparation method of the anode active material according to the embodiment of the present disclosure is simple, so that the manufacturing cost of the battery using the anode tab according to the embodiment of the present disclosure can be reduced. The negative electrode active material has higher specific capacity and electronic conductivity, and the carbon nanotube conductive network inserted 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 presently disclosed embodiments also proposes an electric vehicle loaded with the electrochemical device set forth in the fifth aspect described above, and in particular, the electric vehicle may be any vehicle that requires an electrochemical device as a power source, such as an electric bus, a light rail electric vehicle, an electric vehicle, and the like. The electrochemical device according to any one of the embodiments has the advantageous effects of the electrochemical device according to any one of the embodiments.

The method of preparing the silicon carbon composite of the present disclosure is further illustrated by the following specific examples. It should be apparent to those skilled in the art that the following specific examples are included to facilitate an understanding of the present disclosure and are not to be construed as limiting the present disclosure in any way.

Preparation of the silicon-carbon composite material in the embodiment of the disclosure:

s1, preparing a silicon-carbon material:

silicon carbon master batch No.1: 5g of nano silicon powder is weighed and dispersed in 50g of toluene, the mixture is added into a chemical gas phase reaction furnace preheated to 900 ℃ in a dropwise manner after ultrasonic dispersion, and the heat preservation is carried out for 1 hour, so that silicon-carbon master batches are prepared, wherein the mass percentage content of silicon elements in the silicon-carbon master batches is 64%, and the particle size is 1-5 mu m;

silicon carbon master batch No.2: the preparation method is the same as that of the silicon carbon master batch No.1, except that the liquid carbon source adopts industrial wash oil; the mass percentage content of silicon element in the silicon-carbon master batch is 45%, and the grain diameter is 1 mu m-5 mu m;

silicon carbon master batch No.3: the preparation method is the same as that of the silicon-carbon master batch No.1, except that the industrial wash oil is 30g; the silicon element content of the silicon-carbon master batch is 45 percent by mass, and the grain diameter is 1-5 mu m.

S2, weighing silicon-carbon master batches, graphitized onion carbon and graphene according to the weight ratio, wherein the specific addition ratio is shown in a table 1; pouring into a wet granulator, shearing and stirring for 5min, wherein the cutting speed is 2000rpm, and the mixing speed is 150rpm; then, adding 10% sodium carboxymethyl cellulose water solution by mass percent, wherein the adding amount of the sodium carboxymethyl cellulose water solution is 100% of the total mass of the silicon carbon master batch, the graphite material and the conductive agent, shearing and stirring for 15min, and the cutting speed is 2000rpm, and the mixing speed is 150rpm. The silicon-carbon particle mixture is prepared, and the particle size is controlled between 3 and 25 mu m.

S3, carbonizing and preserving the silicon-carbon particle mixture prepared in the S2 for 2 hours at 900-1000 ℃ under the condition of inert atmosphere to obtain the silicon-carbon composite material.

TABLE 1

Wherein, the mass percent of the binder to the total weight of the silicon-carbon composite material is determined by adopting TG thermogravimetric analysis.

The scanning electron micrographs of the silicon carbon master batch 1# are shown in fig. 2 and 3. As shown in fig. 2 and 3, it is obvious that the large particles are formed by aggregating small particles, and the graphene is dispersed among the components to form a conductive carbon network, and the silicon carbon master batch is tightly encapsulated in the stacking gaps of the graphite material.

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

the binder precursor solution is sodium carboxymethyl cellulose water solution with the 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#: the silicon carbon master batch, graphitized onion carbon and carbon nanotubes are the same as the silicon carbon composite material 1#, and the difference is that: the binder precursor solution is sodium carboxymethyl cellulose aqueous solution with the mass percentage concentration of 2%, and the binder accounts for 1% of the total weight of the silicon-carbon composite material.

Silicon carbon composite material 10#: the silicon carbon master batch, graphitized onion carbon and carbon nanotubes are the same as the silicon carbon composite material 1#, and the difference is that: weighing silicon-carbon master batches, graphitized onion carbon and carbon nanotubes according to the weight ratio, adding the mixture into a large amount of binder precursor solution, stirring and mixing to prepare slurry, wherein the addition amount of the binder precursor solution is 600% of the total mass of the silicon-carbon master batches, the graphite material and the conductive agent; the binder precursor solution is sodium carboxymethylcellulose aqueous solution with the mass percentage concentration of 2%, the binder accounts for 5% of the total weight of the silicon-carbon composite material after sintering, and the binder is dried, calcined and crushed after being uniformly stirred and mixed.

Silicon carbon composite material 11#: the silicon carbon master batch and the carbon nano tube are the same as the silicon carbon composite material 1#, and the difference is that the graphite material adopts artificial graphite, and the addition amount is the same as that of the silicon carbon composite material 1#.

The physical parameters of the prepared silicon-carbon composite material are shown in table 2:

the physical parameter detection method is obtained according to a laser particle size analyzer and a tap density tester (tap frequency: 30000, frequency: 1 time/second).

TABLE 2

Silicon carbon composite numbering	Tap density (g/cm) ³ )	Particle size (mum)
			Silicon carbon composite material 1#	0.81	25～50
Silicon carbon composite material 2#	0.80	15～50
			Silicon carbon composite 3#	0.79	10～50
Silicon carbon composite material 4#	0.95	30～80
			Silicon carbon composite 5#	0.80	40～100
Silicon carbon composite 6#	0.84	30～60
			Silicon carbon composite 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 11#	0.75	20～55

As can be seen from Table 2, the silicon carbon composites 1# to 5# all achieved higher tap densities and energy densities. In the silicon carbon composite material 6# the energy density is reduced because the addition amount of the silicon carbon master batch is too small. In the silicon carbon composite material 7# the addition amount of the graphite material is too small, so that the tap density of the silicon carbon composite material is reduced. The silicon-carbon composite material 8# has larger particle size because of overlarge proportion of the binder, which is unfavorable for close-packed particles, and the tap density and the energy density are reduced. The silicon-carbon composite material 9# has smaller particle size and smaller tap density because of the too small proportion of the binder.

Performance measurement of materials of examples of the present disclosure:

(1) Half cell testing

And (3) taking the negative electrode active materials 1# to 11# as a negative electrode of the lithium ion battery to assemble a button battery, wherein the negative electrode active materials 1# to 11# correspond to the silicon carbon composite materials 1# to 11# one by one.

The preparation method comprises the following steps: the negative electrode active materials 1# to 11#, sodium carboxymethyl cellulose and acetylene black are mixed according to the mass ratio of 91:6:3, mixing, grinding uniformly, adding a proper amount of water, continuously grinding to prepare electrode slurry, uniformly coating the slurry on the carbon-coated copper foil, and vacuum drying for 12 hours at 120 ℃ to prepare electrode slices 1# to 11#. The lithium sheets were used as counter electrodes, assembled into half batteries 1# to 12# and tested for charge and discharge performance at a current density of 200mA/g in a LAND (CT 3001A) battery test system, and the test results are shown in fig. 4 and table 3:

TABLE 3 Table 3

As can be seen from table 3, the negative electrode active materials 1# to 5# have higher capacities when used as the negative electrode, are significantly too conventional graphite materials, and have higher first coulombic efficiencies. Meanwhile, after 100 weeks of circulation, half batteries 1# to 5# have a capacity retention rate of about 90%, which indicates that the silicon-carbon negative electrode material has stable circulation performance. While the battery capacities of half batteries 6# and 8# are reduced. The capacity retention rate in half cells 7# and 9# is reduced. The battery in the half-cell has larger particle size and reduced tap density and energy density due to the excessive proportion of the binder. The silicon-carbon composite material 9# has smaller particle size and larger density because of the too small proportion of the binder.

(2) Full cell testing

And taking the anode active materials 1# to 11# as anode materials, wherein the anode active materials 1# to 11# are in one-to-one correspondence with the silicon carbon composite materials 1# to 11# and taking lithium iron phosphate as an anode, so as to assemble the button type full battery 1# to 11#. Assembled full cells were tested using the LAND battery test system.

Testing the cycle performance: the charge-discharge current density is 2C, the voltage range is 2.5V-3.65V, and the cycle number is 300.

Testing rate performance: the charge-discharge current density is 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, and the voltage range is 2.5V-3.65V. The results are shown in fig. 5 and table 4:

TABLE 4 Table 4

As can be seen from table 4, the silicon-carbon composite material of the embodiment of the disclosure has excellent rate capability and cycle stability after being assembled into a full battery, and the silicon-carbon material prepared by the embodiment of the disclosure has a stable structure, and graphite limits silicon-carbon master batch in a stacked gap, so that the volume expansion of silicon can be effectively inhibited, and meanwhile, the carbon nanotube network inside the composite material promotes the transfer of electrons and the diffusion of lithium ions, so that the rate charge-discharge performance of the composite material is improved. In the full cells 5# and 7#, it is found that if the amount of the graphite material added is too small, both the rate performance and the cycle stability are degraded. The rate performance of the full cell 9# is greatly reduced.

It should be noted that in this document, relational terms such as "first" and "second" and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.

The foregoing is merely a specific embodiment of the disclosure to enable one skilled in the art to understand or practice the disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown and described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A silicon-carbon composite material comprising a graphite material and a silicon-carbon material fixed in interstices between the graphite material.

2. The silicon-carbon composite material according to claim 1, wherein the silicon-carbon material is a core-shell structure, the inner 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 master batch, and the particle size of the silicon-carbon master batch is 1-5 mu m.

3. The silicon-carbon composite material according to claim 1, wherein both the graphite material and the silicon-carbon material form silicon-carbon composite particles, the silicon-carbon composite particles having a particle size of 10 μιη to 80 μιη.

4. The silicon-carbon composite material according to claim 1, wherein the silicon element in the silicon-carbon material is 20-60% by mass; and/or the number of the groups of groups,

the mass percentage content of the silicon-carbon material in the silicon-carbon composite material is 20% -50%;

the mass percentage content of the graphite material in the silicon-carbon composite material is 48% -79%.

5. The silicon-carbon composite according to any one of claims 3 to 4, further comprising a conductive agent interposed between the silicon-carbon material and the graphite material for forming a conductive network inside the silicon-carbon composite, preferably, the silicon-carbon composite has a mass percentage of the conductive agent of 1 to 2%;

the silicon-carbon composite material also comprises a binder, wherein the silicon-carbon material is connected with the graphite material and the graphite material through an adhesive, the silicon-carbon composite particles are connected through an adhesive, and preferably, the adhesive accounts for 2% -20% of the total weight of the silicon-carbon composite material.

6. The silicon-carbon composite according to claim 5, wherein the conductive agent is selected from carbon nanomaterials, preferably the carbon nanomaterials are selected from at least one of zero-, one-, two-and three-dimensional carbon nanomaterials;

the graphite material comprises at least one of graphite and a graphite-like material, wherein 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; 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, wherein the silicon-carbon composite material has a tap density of 0.4 to 0.6g/cm ³ The lithium storage capacity of the silicon-carbon composite material is 400-2000 mAh/g.

8. The method for producing a silicon-carbon composite material as claimed in any one of claims 5 to 7, comprising at least the steps of:

s1, preparing the silicon-carbon material;

s2, taking the silicon-carbon material, the graphite material and the conductive agent, uniformly mixing, adding a binder precursor solution, and continuing mixing;

and S3, carbonizing the mixed raw materials under the condition of inert atmosphere to obtain the silicon-carbon composite material.

9. The method according to claim 8, wherein,

in S1, dispersing nano silicon in a liquid carbon source to obtain a dispersion liquid, pyrolyzing and preserving heat of the dispersion liquid under an inert atmosphere to obtain the silicon carbon material, wherein the liquid carbon source is preferably selected from chain hydrocarbon, cyclic hydrocarbon or mixed hydrocarbon; and/or the number of the groups of groups,

in S2, mixing the silicon carbon material, the graphite material and the conductive agent in a wet granulator for 5-10 minutes, wherein the cutting speed is 1500-2500 rpm, and the mixing speed is 120-180 rpm; then adding the binder precursor solution, stirring for 10-30 minutes, wherein the cutting speed is 1500-2500 rpm, and the mixing speed is 120-180 rpm; and/or the number of the groups of groups,

10. The preparation method according to claim 8, wherein in S2, the mass percentage concentration of the solute in the binder precursor solution is 2% to 30%, and the additive amount of the binder precursor solution is 20% to 120% of the total mass of the silicon carbon material, the graphite material and the conductive agent;

preferably, the binder precursor solution is selected from an aqueous binder or an oily binder; more preferably, the aqueous binder is at least one selected from the group consisting of an aqueous sodium carboxymethyl cellulose solution, an aqueous sodium alginate solution, and an aqueous polyacrylic acid solution; more preferably, the oily binder is at least one selected from polyvinylidene fluoride/N, N-dimethylformamide solution, asphalt-pyridine mixture, asphalt-tetrahydrofuran mixture.

11. A negative electrode active material comprising the silicon-carbon composite material according to any one of claims 1 to 7 or the silicon-carbon composite material produced by the production method according to any one of claims 8 to 10.

12. A negative electrode tab, wherein the negative electrode active material in the negative electrode tab is selected from the negative electrode active materials of claim 11.

13. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the negative electrode sheet is the negative electrode sheet of claim 12.

14. A vehicle, characterized in that the electrochemical device according to claim 13 is contained in the vehicle.