CN113782717B - Modified graphite nano-silicon composite material and preparation method and application thereof - Google Patents
Modified graphite nano-silicon composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a preparation method of a modified graphite nano-silicon composite material, which comprises the following steps: carrying out first ball milling on graphite nano-silicon composite particles, boron modified phenolic resin and an organic solvent, and then carrying out desolventizing treatment to obtain a composite material precursor; the mass ratio of the boron modified phenolic resin to the graphite nano silicon composite particles is (0.05-0.5) to 1; pressing the composite material precursor, and then carrying out carbonization treatment to form a first carbon coating layer to obtain a first carbon-coated composite material; the carbonization treatment is carried out in the protective gas atmosphere, and the temperature of the carbonization treatment is 800-1100 ℃; and carrying out vapor deposition on the composite material coated by the first carbon to form a second carbon coating layer, so that the obtained modified graphite nano-silicon composite material has good combination properties of tap density, volume specific capacity, first coulombic efficiency and cycling stability.
Description
Technical Field
The invention relates to the field of batteries, in particular to a modified graphite nano-silicon composite material and a preparation method and application thereof.
Background
The lithium ion battery has the advantages of high energy density, small self-discharge, no memory effect, long service life and the like, is widely applied to electronic products, and is gradually developed into a power supply of an electric automobile. Wherein, the silicon has extremely high theoretical specific capacity of 4200 mA.h/g, and is a better choice for the cathode material of the high-capacity lithium ion battery. However, silicon is a semiconductor material with low electronic conductivity, and when lithium is deintercalated, silicon can generate a volume change of more than 300%, which destroys the structural integrity of the electrode material, thereby affecting the service life of the lithium ion battery. Graphite is used as a carbon material with excellent conductivity, the source is wide, the electrochemical performance is stable, silicon and graphite are compounded and an organic carbon precursor is used for structural regulation, the conductivity of the silicon-carbon composite material can be improved, and the huge volume expansion of the silicon material can be buffered.
In the traditional preparation method of the silica-graphite composite negative electrode material, silicon and graphite are mixed, and a coating layer is arranged on the surfaces of the silicon and the graphite. However, since the specific surface area of silicon is large and the surface energy is high, problems of silicon particle agglomeration, low interface bonding strength and the like occur in the conventional preparation method. Along with the charging and discharging, the silicon enrichment area can be quickly pulverized, the volume specific capacity is attenuated, and the tap density of the material is reduced. In addition, the traditional preparation method is easy to have the condition of uneven coating or incomplete coating, so that the silicon material is exposed, the volume of the silicon material is repeatedly changed due to frequent contact with electrolyte, the coating layer is collapsed, and the problem of poor stability of the silica ink composite negative electrode material is caused.
Disclosure of Invention
Based on the modified graphite nano-silicon composite material, the preparation method and the application thereof, the prepared modified graphite nano-silicon composite material has good stability, so that the modified graphite nano-silicon composite material is applied to a negative electrode material, and the first coulombic efficiency and the cycling stability of the modified graphite nano-silicon composite material can be improved.
The technical scheme of the invention for solving the technical problems is as follows.
A preparation method of a modified graphite nano-silicon composite material comprises the following steps:
carrying out first ball milling on graphite nano-silicon composite particles, boron modified phenolic resin and an organic solvent, and then carrying out desolventizing treatment to obtain a composite material precursor; the mass ratio of the boron modified phenolic resin to the graphite nano silicon composite particles is (0.05-0.5) to 1;
pressing the composite material precursor, and then carrying out carbonization treatment to form a first carbon coating layer to obtain a carbon-coated composite material; the carbonization treatment is carried out in the protective gas atmosphere, and the temperature of the carbonization treatment is 800-1100 ℃;
and carrying out vapor deposition on the carbon-coated composite material by adopting an organic carbon source to form a second carbon coating layer, thus obtaining the modified graphite nano-silicon composite material.
In some embodiments, in the preparation method of the modified graphite nano silicon composite material, the mass ratio of the boron modified phenolic resin to the graphite nano silicon composite particles is (0.05-0.3): 1.
In some embodiments, in the preparation method of the modified graphite nano-silicon composite material, the boron-modified phenolic resin is added in the form of a boron-modified phenolic resin ethanol solution, and the mass fraction of the boron-modified phenolic resin ethanol solution is 10-40%.
In some embodiments, the modified graphite nano-silicon composite material is prepared by at least one of pressing and isostatic pressing, wherein the pressing pressure is 100MPa to 200MPa.
In some of the embodiments, the vapor deposition conditions in the preparation method of the modified graphitic nano-silicon composite material are:
introducing mixed gas of an organic carbon source and hydrogen in the protective gas atmosphere, and depositing for 10-60 min at the temperature of 600-1100 ℃; the organic carbon source is organic gas.
In some of the embodiments, in the method for preparing the modified graphite nano-silicon composite material, the organic carbon source is selected from at least one of acetylene, ethylene, ethanol, thiophene and toluene.
In some of the embodiments, the method for preparing the modified graphitic nano-silicon composite material, wherein preparing the graphitic nano-silicon composite particles comprises the steps of:
and (3) pretreating the nano silicon particles by using a cationic surfactant, mixing the pretreated nano silicon particles with graphite, and performing second ball milling to obtain the graphite nano silicon composite particles.
In some embodiments, in the preparation method of the modified graphite nano-silicon composite material, the particle size of the nano-silicon is 50nm to 80nm.
In some embodiments, in the preparation method of the modified graphite nano-silicon composite material, the cationic surfactant is a quaternary ammonium salt type cationic surfactant, and the concentration of the cationic surfactant is 0.01 mol/L-0.05 mol/L.
In some of the embodiments, in the method of preparing the modified graphite nano-silicon composite, the cationic surfactant is selected from at least one of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride.
The invention provides a modified graphite nano-silicon composite material, which is prepared by the preparation method of the modified graphite nano-silicon composite material.
The invention provides application of the modified graphite nano-silicon composite material in preparation of a negative electrode material.
The invention provides a negative electrode, which comprises a current collector and a negative electrode material layer formed on the current collector, wherein the negative electrode material layer contains the modified graphite nano-silicon composite material.
The invention provides a battery, which comprises an electrolyte, a diaphragm, a positive electrode and the negative electrode.
Compared with the prior art, the preparation method of the modified graphite nano-silicon composite material has the following beneficial effects:
according to the invention, the graphite nano-silicon composite particles and the specific boron modified phenolic resin are subjected to ball milling, so that the interface bonding between nano-silicon and graphite is effectively improved; the composite material precursor obtained by ball milling is pressed, so that the interface bonding between the nano silicon and the graphite can be further improved, the charge transfer resistance of the graphite nano silicon composite material is reduced, the porosity is reduced, and the tap density is improved; on the basis, the pressed composite material precursor is carbonized at a specific temperature, so that the boron modified phenolic resin has higher carbon residue rate, and a first carbon coating layer which is compact, low in porosity, uniformly dispersed with boron, less in surface functional group and higher in conductivity is formed; and further carrying out vapor deposition by adopting an organic carbon source, and forming a uniform second carbon coating layer on the carbonization layer formed by the carbonization treatment. Through carbonization treatment and vapor deposition in sequence, first and second carbon coating layers which are compact and tightly combined are formed on the surfaces of the graphite nano-silicon composite particles, so that the tight combination of nano-silicon and graphite is realized, and the stability of the prepared modified graphite nano-silicon composite material is improved.
Furthermore, when the modified graphite nano-silicon composite material prepared by the method is applied to an electrode material, the volume specific capacity is effectively improved, the volume effect of nano-silicon is inhibited, the electric contact between the nano-silicon and graphite is ensured, the impact of the volume change of the nano-silicon in the process of lithium intercalation and deintercalation on an electrode structure is effectively avoided, the integrity of the electrode is ensured, and the first coulomb efficiency of the electrode and the cycle life of a battery are improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a cycle test chart of a lithium ion battery corresponding to the modified graphite nano-silicon composite material prepared in example 1 at a current density (100 mA/g).
Detailed Description
The modified graphite nano-silicon composite material of the present invention, the preparation method and the application thereof will be described in further detail with reference to specific examples. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In the description of the present invention, it is to be understood that the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any order to or between indicated technical features or order of process steps. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
The weight of the related components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present invention as long as it is in accordance with the description of the embodiments of the present invention. Specifically, the weight described in the description of the embodiment of the present invention may be a unit of mass known in the chemical industry field, such as μ g, mg, g, and kg.
An embodiment of the invention provides a preparation method of a modified graphite nano-silicon composite material, which comprises the steps of S20-S60.
Step S20: carrying out first ball milling on graphite nano-silicon composite particles, boron modified phenolic resin and an organic solvent, and then carrying out desolventizing treatment to obtain a composite material precursor; the mass ratio of the boron modified phenolic resin to the graphite nano silicon composite particles is (0.05-0.5) to 1;
step S40: pressing the composite material precursor, and then carrying out carbonization treatment to form a first carbon coating layer to obtain a carbon-coated composite material; the carbonization treatment is carried out in the protective gas atmosphere, and the temperature of the carbonization treatment is 800-1100 ℃;
step S60: and carrying out vapor deposition on the carbon-coated composite material by adopting an organic carbon source to form a second carbon coating layer so as to obtain the modified graphite nano-silicon composite material.
It can be understood that the modified graphite nano-silicon composite material obtained by the preparation method comprises graphite nano-silicon composite particles and a first carbon coating layer and a second carbon coating layer which are sequentially coated on the surfaces of the graphite nano-silicon composite particles, wherein the first coating layer contains boron, and the boron may be B 4 C, B-O, or a graphite-like B form.
The graphite nano-silicon composite particles are tightly combined by a compaction block process under the coating of boron modified phenolic derived carbon, and then are coated by carbonization treatment and vapor deposition acetylene cracking carbon to form a mosaic structure, so that the tap density of the graphite nano-silicon composite particles can be effectively improved, and the formed modified graphite nano-silicon composite material has good stability. The ball milling and pressing process can enable silicon with low conductivity to be tightly combined with graphite with good conductivity, and the change of the microstructure influences the specific surface area, pore structure parameters and charge transfer resistance of the material, so that the electrochemical performance of the material is improved; the secondary carbon coating can avoid the direct contact of the nano-silicon and the electrolyte, inhibit the decomposition of the electrolyte, remarkably promote the uniformity and compactness of the surface carbon film, effectively block the co-insertion of solvated ions, improve the first coulombic efficiency, buffer the volume expansion of the silicon nano-material during the lithium removal and insertion, and maintain the stability of the material structure.
In some examples, in step S20, the mass ratio of the boron-modified phenolic resin to the graphite nano-silicon composite particles is (0.05-0.3): 1; optionally, the mass ratio of the boron modified phenolic resin to the graphite nano-silicon composite particles is (0.1-0.15): 1; preferably, the mass ratio of the boron-modified phenolic resin to the graphite nano-silicon composite particles is 0.15. The thickness of the carbon coating layer on the surface of the composite material can be controlled by controlling the mass ratio of the boron modified phenolic resin to the graphite nano-silicon composite particles, so that the first coulombic efficiency and the cycle life of the electrode material are improved.
In some examples, in step S20, the organic solvent is selected from at least one of ethanol, methanol, and acetone.
It will be appreciated that in some of these examples, the boron-modified phenolic resin is added as a solution of the boron-modified phenolic resin after mixing with the organic solvent. For example, when the organic solvent is ethanol, the boron-modified phenolic resin is added in the form of an ethanol solution of the boron-modified phenolic resin; when the organic solvent is methanol, the boron-modified phenolic resin is added in the form of a methanol solution of the boron-modified phenolic resin. Preferably, the boron-modified phenolic resin is added in the form of an ethanol solution of the boron-modified phenolic resin.
In some examples, in step S20, the mass fraction of the boron-modified phenolic resin solution is 10% to 40%; optionally, the mass fraction of the boron modified phenolic resin solution is 10-30%; preferably, the mass fraction of the boron modified phenolic resin solution is 15-30%. The concentration of the boron modified phenolic resin ethanol solution is controlled, so that the mixing uniformity degree of the composite material and the density of the carbon coating layer can be regulated, and the tap density, the first coulombic efficiency and the circulation stability of the electrode material are influenced.
In some specific examples, in step S20, the mass fraction of the boron-modified phenolic resin ethanol solution is 10% to 40%; optionally, the mass fraction of the boron modified phenolic resin ethanol solution is 10-30%; preferably, the mass fraction of the boron modified phenolic resin ethanol solution is 20-30%.
It can be understood that the ball milling of the graphite nano-silicon composite particles, the boron modified phenolic resin and the organic solvent is wet ball milling.
In some examples, in the step S20, the ratio of the total mass of the graphite nano-silicon composite particles and the boron-modified phenolic resin to the mass of the grinding balls in the ball milling process is 1 (1 to 10). Optionally, the mass ratio of the total mass of the graphite nano-silicon composite particles and the boron modified phenolic resin to the grinding ball is 1 (1-8); preferably, the mass ratio of the total mass of the graphite nano silicon composite particles and the boron modified phenolic resin to the grinding balls is 1 (5-8).
In some examples, in step S20, the rotation speed of the ball mill is 100rpm to 1000rpm, and the time is 20min to 1440min; optionally, the rotation speed of the ball mill is 200-500 rpm, and the time is 200-800 min; preferably, the rotation speed of the ball mill is 300rpm, and the time is 300min.
By controlling the addition amount of the grinding balls and the rotating speed and time of ball milling, the mixing uniformity of the composite material and the crushing degree of the material can be controlled, so that the wettability of the electrolyte can be improved, and the specific capacity of the electrode material can be improved.
In some examples, the desolvation process is water bath evaporation or vacuum drying in step S20.
In some specific examples, the desolvation process is a water bath evaporation method in step S20.
In some examples, the preparation of the graphite nano-silicon composite particles in step S20 includes step S10.
Step S10: and pretreating the nano silicon particles by using a cationic surfactant, mixing the pretreated nano silicon particles with graphite, and performing second ball milling to obtain the graphite nano silicon composite particles.
In some examples, in step S10, the nano-silicon particles have a particle size of 50nm to 100nm; optionally, the particle size of the nano silicon particles is 50 nm-80 nm; preferably, the particle size of the nano silicon particles is 60nm to 80nm.
In some examples, in step S10, the graphite is microcrystalline graphite having a particle size of 2 μm to 25 μm; optionally, the particle size of the graphite is 2 μm to 10 μm; preferably, the particle size of the graphite is 4 to 6 μm.
In some examples, in step S10, the cationic surfactant is a quaternary ammonium salt type cationic surfactant, and the concentration of the cationic surfactant is 0.01mol/L to 0.05mol/L; optionally, the concentration of the cationic surfactant is 0.01 mol/L-0.02 mol/L; preferably, the concentration of the cationic surfactant is 0.02mol/L.
In some examples, in step S10, the cationic surfactant is selected from at least one of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride; optionally, the cationic surfactant is selected from at least one of dodecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide and hexadecyl trimethyl ammonium bromide; preferably, the cationic surfactant is cetyltrimethylammonium chloride.
In some examples, in step S10, the mass ratio of graphite to cationic surfactant treated nano-silicon particles is (1-9): 1; optionally, the mass ratio of the graphite to the nano silicon particles treated by the cationic surfactant is (2-7) to 1; preferably, the mass ratio of graphite to the cationic surfactant-treated nano-silicon particles is 3.
By adopting the specific cationic surfactant to treat the nano silicon particles, the electrostatic repulsion reduces the agglomeration among the nano silicon particles, and meanwhile, the nano silicon particles are attracted with negatively charged graphite, so that the nano silicon particles are uniformly dispersed on the surface of the graphite.
It is understood that, in step S10, the ball milling performed after mixing the nano silicon particles treated with the cationic surfactant and the graphite is dry ball milling.
In some examples, in step S10, the rotation speed of the ball mill is 100rpm to 1000rpm, and the time is 20min to 1440min; optionally, the rotation speed of the ball milling is 200-500 rpm, and the time is 100-500 min; preferably, the rotation speed of the ball mill is 300rpm, and the time is 300min.
In some examples, in step S40, the pressing is at least one of a die pressing and an isostatic pressing, and a pressure of the pressing is 100MPa to 200MPa; optionally, the pressing pressure is 150MPa to 180MPa; preferably, the pressure of the pressing is 160MPa.
By pressing the composite material precursor obtained by ball milling, the interface bonding between the nano silicon particles and graphite can be improved, the charge transfer impedance of the graphite nano silicon composite material is reduced, and the porosity is reduced, so that the tap density and the volume specific capacity are improved; the pressure intensity of pressing is controlled, and the interface bonding strength and porosity can be regulated, so that the wettability and tap density of the electrolyte on the electrode material are regulated.
In some examples, the protective gas is nitrogen or argon in step S40.
In some specific examples, the protective gas is nitrogen in step S40.
In some examples, in step S40, the temperature of the carbonization treatment is 900 ℃ to 1100 ℃ for 0.1h to 1h; preferably, the temperature of the carbonization treatment is 900 ℃ and the time is 0.5h.
And the carbon is carbonized at a specific temperature for a specific time, so that the optimal pore structure and surface state of the coated carbon can be obtained, and the first coulombic efficiency and the cycling stability of the electrode material are improved.
In some examples, the method for preparing the modified graphitic nano-silicon composite further includes step S50 before step S60.
Step S50: and (4) grinding the first carbon-coated composite material prepared in the step (S40). It can be understood that the vapor deposition is performed on the block-shaped body after the pressing in step S40, and the vapor deposition is performed after the grinding of the first coated composite material, so that the effect of the second carbon coating of the composite material can be improved.
In some examples, in step S50, the grinding parameters are: the rotation speed of the ball mill is 100 rpm-1000 rpm, and the time is 20 min-1440 min; optionally, the rotation speed of the ball mill is 200-500 rpm, and the time is 100-450 min; preferably, the rotation speed of the ball mill is 400-500 rpm, and the time is 100-120 min.
In some examples, the vapor deposition conditions in step S60 are:
introducing mixed gas of an organic carbon source and hydrogen under the protective gas atmosphere, and depositing for 10-60 min at the temperature of 600-1100 ℃; the organic carbon source is an organic gas.
It is understood that the organic gas provides a carbon source for the carbon coating layer, the hydrogen gas enables the first carbon-coated composite material to be in the reducing atmosphere, and the inert gas can adjust the concentrations of the organic gas and the hydrogen gas and play a role in supplying gas.
In some examples, the flow ratio of the protective gas, the organic gas and the hydrogen gas is (1-30): 1-10): 1-5 in step S60; optionally, the flow ratio of the protective gas, the organic gas and the hydrogen gas is (10-25) to (1-5) to (1-3). Preferably, the flow ratio of the protective gas, the organic gas and the hydrogen gas is 20.
In some examples, in step S60, the organic carbon source is selected from at least one of acetylene, ethylene, ethanol, thiophene, and toluene; preferably, the organic gas is acetylene.
In some examples, the vapor deposition temperature is 800-1100 ℃ and the deposition time is 10-30 min in step S60.
In some preferred examples, in step S60, the flow ratio of the protective gas, the organic gas and the hydrogen gas is 20.
By controlling the particle sizes of nano-silicon particles and graphite, treating the nano-silicon by using a specific surfactant, mixing the nano-silicon with the graphite, and performing ball milling to enable the nano-silicon to be adsorbed on the surface of the graphite to form graphite nano-silicon composite particles; further mixing with boron modified phenolic resin, performing ball milling, pressing, carbonization treatment and grinding in sequence, performing vapor deposition, and controlling condition parameters in each step; the steps have synergistic effect under specific conditions, so that the prepared modified graphite nano-silicon composite material coated with two carbide layers has high coulombic efficiency for the first time and good circulation stability.
An embodiment of the invention provides a modified graphite nano-silicon composite material, which is prepared by the preparation method of the modified graphite nano-silicon composite material.
An embodiment of the invention provides application of the modified graphite nano-silicon composite material in preparation of a negative electrode material.
Some specific embodiments of the invention provide application of the modified graphite nano-silicon composite material in preparation of a negative electrode material for a lithium ion battery.
One embodiment of the invention provides a negative electrode, which comprises a current collector and a negative electrode material layer formed on the current collector, wherein the negative electrode material layer contains the modified graphite nano-silicon composite material.
An embodiment of the present invention provides a battery including a separator, a positive electrode, and the negative electrode as described above.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
Hereinafter, the modified graphite nano-silicon composite material, the method for preparing the same and the use thereof according to the present invention will be described by way of example, and it will be understood that the modified graphite nano-silicon composite material, the method for preparing the same and the use thereof are not limited to the following examples.
The boron-modified phenolic resins used in the following examples were obtained from Tianyu high temperature resin materials, inc., unionidae.
Example 1
1) Soaking silicon particles with the particle size of 60 nm-80 nm in 0.01mol/L cationic surfactant tetradecyl trimethyl ammonium chloride, and drying for later use;
mixing 3g of nano-silicon treated by a cationic surfactant with 9g of microcrystalline graphite with the particle size of 4-6 microns, carrying out dry ball milling for 300min at the rotating speed of 300rpm, wherein the mass of a milling ball is 80g, and enabling the nano-silicon to be attached to the surface of the microcrystalline graphite through the action of mechanical-chemical force to obtain graphite nano-silicon composite particles;
2) Mixing the graphite nano-silicon composite particles prepared in the step 1) with 8g of 15% boron modified phenolic resin ethanol solution, performing wet ball milling for 300min at the rotating speed of 300rpm, and performing desolventizing treatment by a water bath evaporation method to obtain a composite material precursor;
3) Molding the composite material precursor obtained in the step 2) under the pressure of 180MPa, and then carrying out N 2 Carbonizing at 900 ℃ for 0.5h in the atmosphere to obtain a composite material coated with a first carbon coating layer;
4) Grinding the composite material coated with the first carbon coating layer obtained in the step 3), wherein the ball milling speed is 500rpm, the time is 100min, sieving the composite material by a 400-mesh sieve, then placing the powder in a tube furnace, and performing N reaction on the powder in the tube furnace 2 Heating to 900 deg.C in atmosphere, adjusting furnace atmosphere to be mixed gas of nitrogen, acetylene and hydrogen at flow rates of 100mL/min, 10mL/min and 5mL/min, performing vapor deposition, ventilating for 10min, and cooling.
Example 2
1) Dipping silicon particles with the particle size of 60 nm-80 nm by using 0.02mol/L cationic surfactant cetyl trimethyl ammonium chloride, and drying for later use;
mixing 3g of nano-silicon treated by a cationic surfactant with 9g of microcrystalline graphite with the particle size of 4-6 microns, carrying out dry ball milling for 300min at the rotating speed of 300rpm, wherein the mass of a grinding ball is 80g, and attaching the nano-silicon to the surface of the microcrystalline graphite through the action of mechanical-chemical force to obtain graphite nano-silicon composite particles;
2) Mixing the graphite nano-silicon composite particles prepared in the step 1) with 6g of 30% boron modified phenolic resin ethanol solution, performing wet ball milling for 300min at the rotation speed of 300rpm, and performing desolventizing treatment by a water bath evaporation method to obtain a composite material precursor;
3) Isostatic pressing the composite material precursor obtained in the step 2) under the pressure of 160MPa, and then carrying out N 2 Carbonizing at 900 ℃ for 0.5h in the atmosphere to obtain a composite material coated with a first carbon coating layer;
4) Grinding the composite material coated with the first carbon coating layer obtained in the step 3), wherein the ball milling speed is 400rpm, the time is 120min, sieving the composite material by a 400-mesh sieve, then placing the powder in a tube furnace, and performing N reaction on the powder in the tube furnace 2 Heating to 900 deg.C in atmosphere, adjusting furnace atmosphere to be mixed gas of nitrogen, acetylene and hydrogen at flow rates of 100mL/min, 10mL/min and 5mL/min, performing vapor deposition, ventilating for 20min, and cooling.
Example 3
1) Dipping silicon particles with the particle size of 60 nm-80 nm by using 0.01mol/L cationic surfactant cetyl trimethyl ammonium chloride, and drying for later use;
mixing 3g of nano-silicon treated by a cationic surfactant with 9g of microcrystalline graphite with the particle size of 4-6 microns, carrying out dry ball milling for 300min at the rotating speed of 300rpm, wherein the mass of a milling ball is 80g, and enabling the nano-silicon to be attached to the surface of the microcrystalline graphite through the action of mechanical-chemical force to obtain graphite nano-silicon composite particles;
2) Mixing the graphite nano-silicon composite particles prepared in the step 1) with 9g of 40% boron modified phenolic resin ethanol solution, performing wet ball milling for 300min at the rotating speed of 300rpm, and performing desolventizing treatment by a water bath evaporation method to obtain a composite material precursor;
3) Isostatic pressing the composite material precursor obtained in the step 2) under the pressure of 150MPa, and then carrying out N 2 Carbonizing at 1000 ℃ for 0.5h in the atmosphere to obtain a composite material coated with a first carbon coating layer;
4) Grinding the composite material coated with the first carbon coating layer obtained in the step 3), wherein the ball milling speed is 400rpm, the time is 120min, sieving the composite material by a 400-mesh sieve, then placing the powder in a tube furnace, and performing N reaction on the powder in the tube furnace 2 Heating to 900 deg.C in atmosphere, adjusting furnace atmosphere to be mixed gas of nitrogen, acetylene and hydrogen at flow rates of 100mL/min, 10mL/min and 5mL/min, performing vapor deposition, ventilating for 30min, and cooling.
Example 4
1) Silicon particles with the particle size of 80 nm-100 nm are soaked by 0.05mol/L cationic surfactant cetyl trimethyl ammonium chloride and dried for later use;
mixing 3g of nano-silicon treated by a cationic surfactant with 12g of microcrystalline graphite with the particle size of 6-10 microns, carrying out dry ball milling for 300min at the rotating speed of 300rpm, wherein the mass of a grinding ball is 150g, and attaching the nano-silicon to the surface of the microcrystalline graphite through the action of mechanical-chemical force to obtain graphite nano-silicon composite particles;
2) Mixing the graphite nano-silicon composite particles prepared in the step 1) with 3.75g of 20% boron modified phenolic resin ethanol solution, performing wet ball milling for 300min at the rotating speed of 300rpm, and performing desolventizing treatment by a water bath evaporation method to obtain a composite material precursor;
3) Isostatic pressing the composite material precursor obtained in the step 2) under the pressure of 100MPa, and then carrying out N 2 Carbonizing at 1100 ℃ for 0.5h in the atmosphere to obtain a composite material coated with a first carbon coating layer;
4) Grinding the composite material coated with the first carbon coating layer obtained in the step 3), wherein the ball milling speed is 400rpm, the time is 120min, sieving the composite material by a 400-mesh sieve, then placing the powder in a tube furnace, and performing N reaction on the powder in the tube furnace 2 Heating to 1100 deg.C in atmosphere, adjusting furnace atmosphere to be mixed gas of nitrogen, acetylene and hydrogen at flow rates of 100mL/min, 10mL/min and 5mL/min, performing vapor deposition, ventilating for 30min, and cooling.
Example 5
1) Dipping silicon particles with the particle size of 60 nm-80 nm by using 0.01mol/L cationic surfactant cetyl trimethyl ammonium chloride, and drying for later use;
mixing 3g of nano-silicon treated by a cationic surfactant with 3g of microcrystalline graphite with the particle size of 4-6 microns, carrying out dry ball milling for 150min at the rotating speed of 500rpm, wherein the mass of a milling ball is 60g, and enabling the nano-silicon to be attached to the surface of the microcrystalline graphite through the action of mechanical-chemical force to obtain graphite nano-silicon composite particles;
2) Mixing the graphite nano-silicon composite particles prepared in the step 1) with 18g of 10% boron modified phenolic resin ethanol solution, performing wet ball milling for 500min at the rotating speed of 500rpm, and performing desolventizing treatment by a water bath evaporation method to obtain a composite material precursor;
3) Isostatic pressing the composite material precursor obtained in the step 2) under the pressure of 200MPa, and then carrying out N 2 Carbonizing at 800 ℃ for 0.5h in the atmosphere to obtain a composite material coated with a first carbon coating layer;
4) Grinding the composite material coated with the first carbon coating layer obtained in the step 3), wherein the ball milling speed is 400rpm, the time is 450min, sieving the composite material by a 400-mesh sieve, then placing the powder in a tube furnace, and performing N reaction on the powder in the tube furnace 2 Heating to 800 deg.C in atmosphere, adjusting furnace atmosphere to be mixed gas of nitrogen, acetylene and hydrogen at flow rates of 100mL/min, 10mL/min and 5mL/min, performing vapor deposition, ventilating for 10min, and cooling.
Comparative example 1
Substantially the same as in example 2, except that no ball milling was performed in step 2) and that the vapor deposition in step 4) was not performed.
Comparative example 2
Substantially the same as in example 2, except that the pressing was not performed in step 3), and the vapor deposition of step 4) was not performed.
Comparative example 3
Substantially the same as in example 2, except that the silicon particles in step 1) were not subjected to the cationic surfactant treatment, and were not subjected to the vapor deposition of step 4).
Comparative example 4
The method is basically the same as example 2, except that a phenolic resin ethanol solution is used in step 2).
Comparative example 5
The method is basically the same as example 2, except that an epoxy resin ethanol solution is used in step 2).
Comparative example 6
The method is basically the same as example 2, except that the ethanol solution of the silicon-modified phenolic resin is used in step 2).
Comparative example 7
Substantially the same as in example 2, except that the temperature of the carbonization treatment in step 3) was 700 ℃.
Comparative example 8
Basically the same as example 2, except that the amount of boron-modified phenolic resin added in step 2) is different, and step 2) is specifically as follows:
2) Mixing the graphite nano-silicon composite particles prepared in the step 1) with 30g of 40% boron modified phenolic resin ethanol solution, performing wet ball milling for 300min at the rotation speed of 300rpm, and performing desolventizing treatment by a water bath evaporation method to obtain a composite material precursor;
some of the condition parameters of examples 1 to 5 and comparative examples 1 to 8 are shown in Table 1.
TABLE 1
The modified graphite nano-silicon composite materials obtained in examples 1 to 5 and comparative examples 1 to 8 were mixed with acetylene black and sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 8. And (3) putting the copper foil into an air-blowing drying box at 80 ℃, drying, punching into an electrode plate with the diameter of 14mm, and then carrying out vacuum drying at 80 ℃ for 12 hours. Transferring the electrode plate into a glove box filled with argon, taking a lithium plate as a counter electrode, celgard as a diaphragm and 1M LiPF 6 (EC: DEC =1, 5% fec) was used as an electrolyte, and 2016 was assembled into a button cell battery. A LAND (CT 2001A, wuhan blue power) battery test system is adopted to perform constant current charge and discharge test (the cut-off voltage range is 0.001-3.00V) on the button cell in a 30 ℃ thermostat. The specific volume capacity, the first coulombic efficiency and the capacity retention rate after 100 cycles of the examples and the comparative examples can be obtained through a charge-discharge test.
Tap density was measured using a tap density tester (FT-100A). The test results are shown in table 2.
TABLE 2
As can be seen from Table 2, the modified graphite nano-silicon composite materials of examples 1 to 5 of the invention have good tap density, volume specific capacity, first coulombic efficiency and cyclicity combination property when applied to the negative electrode material; the first coulomb efficiency and capacity retention rate in examples 1-2 have relatively better comprehensive performance; compared with the comparative examples 1 to 3, partial steps are reduced, so that the tap density and the volume specific capacity are greatly reduced, and the cyclicity is reduced; comparative example 4 Using an unmodified phenolic resin, tap density was reduced to 0.75cm 3 The volumetric specific capacity of the material is only 74% of that of example 2, and analysis is possible due to the fact that the carbon residue rate of the unmodified phenolic resin is reduced relative to that of the boron modified phenolic resin, and the porosity is increased; comparative example 5 tap Density of only 0.7cm 3 The specific volume capacity of the material is further reduced to 68% of that of the material in example 2, and simultaneously, the first coulombic efficiency and the cycle stability are also reduced, probably because the thermal stability of the epoxy resin is poor, the carbon residue rate is low, and the porosity is high, so that the coating effect is limited; compared with the prior art, the silicon modified phenolic resin adopted in the comparative example 6 has lower tap density and lower specific capacity, so that the volume specific capacity is correspondingly reduced; in comparative example 7, the cycle stability is reduced because the vapor deposition temperature is reduced and the deposition of the carbon coating layer on the surface of the material is incomplete; in the comparative example 8, the coating amount of the phenolic resin is increased, and the coating layer is too thick due to too high amount of the phenolic resin, so that the first coulombic efficiency of the material is reduced, and the cycle stability is reduced.
In addition, the results of the cycle test of the modified graphite nano-silicon composite in example 1 are shown in fig. 1.
As can be seen from FIG. 1, the cycle stability of the modified graphite nano-silicon composite material prepared by the method is greatly improved. In the embodiment 1, the reversible specific capacity of the sample in the first circulation is 683.3 mA.h/g, the first coulombic efficiency is 88.3%, the reversible specific capacity after 100 cycles of circulation is 659.2 mA.h/g, and the capacity retention rate is up to 96.5%. That is, the capacity loss rate of the modified graphite nano-silicon composite material after one cycle is only 0.04%. The pressing process and the secondary carbon coating can reduce the direct contact of the nano silicon particles and the electrolyte, and reduce the occurrence of side reactions; on the other hand, the carbon coating layer can buffer the volume expansion effect of the nano silicon during lithium intercalation, and the stability of the structure is maintained.
All possible combinations of the technical features of the above embodiments may not be described for the sake of brevity, but should be considered as within the scope of the present disclosure as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, so as to understand the technical solutions of the present invention specifically and in detail, but not to be understood as the limitation of the protection scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. It should be understood that the technical solutions provided by the present invention, which are obtained by logical analysis, reasoning or limited experiments, are within the scope of the appended claims. Therefore, the protection scope of the present patent shall be subject to the content of the appended claims, and the description and drawings can be used to explain the content of the claims.
Claims (10)
1. A preparation method of a modified graphite nano-silicon composite material is characterized by comprising the following steps:
carrying out first ball milling on graphite nano-silicon composite particles, boron modified phenolic resin and an organic solvent, and then carrying out desolventizing treatment to obtain a composite material precursor; the mass ratio of the boron modified phenolic resin to the graphite nano silicon composite particles is (0.05-0.5) to 1; the boron modified phenolic resin is added in the form of a boron modified phenolic resin ethanol solution, and the mass fraction of the boron modified phenolic resin ethanol solution is 10-40%;
pressing the composite material precursor, and then carrying out carbonization treatment to form a first carbon coating layer to obtain a carbon-coated composite material; the carbonization treatment is carried out in a protective gas atmosphere, and the temperature of the carbonization treatment is 800-1100 ℃;
carrying out vapor deposition on the carbon-coated composite material by adopting an organic carbon source to form a second carbon coating layer so as to obtain the modified graphite nano-silicon composite material;
wherein the preparation of the graphite nano-silicon composite particle comprises the following steps:
and pretreating the nano silicon particles by using a cationic surfactant, mixing the pretreated nano silicon particles with graphite, and performing second ball milling to obtain the graphite nano silicon composite particles.
2. The method for preparing the modified graphite nano-silicon composite material as claimed in claim 1, wherein the mass ratio of the boron-modified phenolic resin to the graphite nano-silicon composite particles is (0.05-0.3): 1.
3. The preparation method of the modified graphite nano-silicon composite material of claim 2, wherein the boron modified phenolic resin is added in the form of a boron modified phenolic resin ethanol solution, and the mass fraction of the boron modified phenolic resin ethanol solution is 10-30%.
4. The method of preparing the modified graphite nano-silicon composite material according to claim 1, wherein the pressing is at least one of molding and isostatic pressing, and the pressure of the pressing is 100MPa to 200MPa; and/or
The vapor deposition conditions are as follows: introducing mixed gas of an organic carbon source and hydrogen under the protective gas atmosphere, and depositing for 10min to 60min at the temperature of 600-1100 ℃; the organic carbon source is organic gas.
5. The method for preparing the modified graphite nano-silicon composite material as claimed in any one of claims 1 to 4, wherein in the step of preparing the graphite nano-silicon composite particles, the mass ratio of the graphite to the nano-silicon particles pretreated by the cationic surfactant is (1 to 9): 1.
6. The method for preparing the modified graphite nano-silicon composite material as claimed in any one of claims 1 to 4, wherein the particle size of the nano-silicon particles is 50nm to 80nm; and/or
The cationic surfactant is a quaternary ammonium salt cationic surfactant, and the concentration of the cationic surfactant is 0.01-0.05 mol/L.
7. A modified graphite nano-silicon composite material, which is characterized by being prepared by the preparation method of the modified graphite nano-silicon composite material as claimed in any one of claims 1 to 6.
8. Use of the modified graphitic nano-silicon composite according to claim 7 for preparing negative electrode materials.
9. A negative electrode comprising a current collector and a negative electrode material layer formed on the current collector, wherein the negative electrode material layer comprises the modified graphite nano-silicon composite material according to claim 7.
10. A battery comprising the negative electrode according to claim 9.
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