CN114212775B - Silicon-carbon composite electrode material and preparation method thereof - Google Patents

Silicon-carbon composite electrode material and preparation method thereof Download PDF

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CN114212775B
CN114212775B CN202111320525.XA CN202111320525A CN114212775B CN 114212775 B CN114212775 B CN 114212775B CN 202111320525 A CN202111320525 A CN 202111320525A CN 114212775 B CN114212775 B CN 114212775B
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silicon
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conductive polymer
carbon composite
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CN114212775A (en
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张辉
董珂琪
柏晓
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China Academy of Space Technology CAST
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    • C01B32/15—Nano-sized carbon materials
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    • C01B32/205—Preparation
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
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    • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
    • H—ELECTRICITY
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    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a silicon-carbon composite electrode material and a preparation method thereof, comprising the following steps: pretreating a substrate by adopting a pretreatment solution to obtain a conductive substrate with charges on the surface; electrostatic adsorption of conductive polymer on the surface of silicon material to prepare silicon/conductive polymer powder; mixing a silicon material and a carbon material to prepare silicon/carbon composite powder; dispersing the silicon/conductive polymer powder and the silicon/carbon composite powder into polyelectrolyte and/or inorganic salt solution with opposite electric properties respectively to obtain silicon/conductive polymer slurry and silicon/carbon slurry; alternately depositing the silicon/conductive polymer slurry and the silicon/carbon slurry on the conductive substrate opposite to the surface of the conductive substrate, and drying to obtain a silicon-based composite film; and sintering the silicon-based composite film at a high temperature under the protection of inert atmosphere to obtain the silicon-carbon composite electrode material. By the preparation method, the cycling stability and the multiplying power performance of the lithium ion battery anode material can be improved.

Description

Silicon-carbon composite electrode material and preparation method thereof
Technical Field
The invention relates to the technical field of energy storage battery material preparation, in particular to a silicon-carbon composite electrode material and a preparation method thereof.
Background
In the context of increasingly severe global energy situations, electrochemical energy storage cells are considered as ideal candidates for various types of electronic devices and electric vehicles. Lithium ion batteries are one of the most important energy storage devices at present due to high power, high capacity, long service life and high safety. In order to promote the better development of high-energy power lithium ion batteries, development of low-cost and high-energy density electrode materials is urgently needed. The silicon-carbon composite material has theoretical capacity up to 4200 mAh.g -1 Is the best candidate for the cathode material of the battery. However, the silicon-carbon composite material with high silicon content can generate huge volume and structure change in the charge and discharge process, thereby inducing the crack and breaking of the negative electrode of the lithium ion battery, and finally causing the abrupt attenuation of the battery capacity, the reduction of coulomb efficiency and the limitation of the service life, so that the lithium ion battery has the advantages of high energy consumption, low cost and low costThe progress of commercialization has become very slow.
In general, the volume effect of improving silicon delithiation mainly includes the following three strategies: (1) And directly coating a carbon layer on the surface of the nano silicon particles by adopting a template method, a vapor deposition method, a pyrolysis method or the like so as to adapt to the volume change of the silicon material. However, the strategy has the advantages of harsh preparation means conditions and complex preparation flow, and the risk of cracking the surface carbon layer due to too large volume expansion in the lithiation process of the silicon material, so that the composite material structure collapses and the internal silicon particles lose protection. (2) And embedding the silicon particles into the carbon material by mechanical mixing and electrostatic spinning to obtain a highly dispersed silicon-carbon mixed system. However, this strategy is not easily used to alleviate the volume effect for a long time, considering that the difficulty of uniform dispersion is high and that silicon-carbon is difficult to be in close contact with each other at a high silicon content. (3) The silicon material coated by the conductive polymer is obtained by utilizing polymerization reaction, and the high molecular polymer with a chain structure has higher flexibility and can well regulate the stress change of the silicon material in the circulation process. However, silicon materials in this manner are relatively deficient in electron transport capacity compared to conventional carbon material conductive polymers. The key to solve the problems is to break through the defect of single structural composition of the current silicon-carbon composite material.
In order to improve the circulation performance of active substances, chinese patent CN105390687B discloses a high-performance three-dimensional carbon nanotube composite anode material, a preparation method and application thereof, wherein carboxylated carbon nanotubes are used as a three-dimensional network skeleton, a layer-by-layer self-assembled modified high-capacity material is used as an active substance, the carbon nanotubes and the active substance are uniformly mixed under the action of electrostatic attraction, and then a carbon source doped with a hetero element N or S is coated in situ to serve as a three-dimensional coating layer to prepare the high-performance three-dimensional carbon nanotube composite anode material through high-temperature treatment. In order to obtain an electrode material with excellent electron transmission performance and mechanical properties, chinese patent CN107204438B discloses a silicon-carbon composite material, a preparation method and application thereof, wherein a silicon nanomaterial, a carbon nanomaterial and a binder are dispersed in a solvent to form slurry, so as to prepare a carbon-silicon composite macroscopic body; and carrying out heat treatment on the obtained carbon-silicon composite macroscopic body in a non-oxidizing atmosphere to obtain the carbon-silicon composite material.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention aims to provide a silicon-carbon composite electrode material and a preparation method thereof, which solve the problems of silicon expansion, poor contact of silicon and carbon components and the like, thereby improving the cycle stability and the rate capability of the lithium ion battery cathode material.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
the invention provides a preparation method of a silicon-carbon composite electrode material, which comprises the following steps: first, a substrate is pretreated by a pretreatment solution to obtain a conductive substrate with charges on the surface, so that the surface of the conductive substrate has specific electrical property. And then the conductive polymer is electrostatically adsorbed on the surface of the silicon material to prepare the silicon/conductive polymer powder. Meanwhile, mixing a silicon material and a carbon material to prepare the silicon/carbon composite powder. And then, dispersing the silicon/conductive polymer powder and the silicon/carbon composite powder into polyelectrolyte and/or inorganic salt solution with opposite electric properties respectively to obtain silicon/conductive polymer slurry and silicon/carbon slurry. And alternately depositing the silicon/conductive polymer slurry and the silicon/carbon slurry on the conductive substrate opposite to the surface of the conductive substrate, and drying to obtain the silicon-based composite film. The first slurry film deposited on the surface of the conductive substrate has opposite electrical property to the surface of the conductive substrate. And finally, sintering the silicon-based composite film at a high temperature under the protection of inert atmosphere to obtain the silicon-carbon composite electrode material.
Preferably, the pretreatment process comprises: and placing the substrate in a pretreatment solution with the solute mass fraction of 0.01-10% for soaking for 5-60 min, drying, and cleaning by using ultrapure water.
Optionally, the substrate is a copper foil, aluminum foil, zinc film, carbon coated copper foil, nickel-chromium film, titanium-gold film or indium tin oxide film.
Preferably, the substrate is one of copper foil, aluminum foil and carbon-coated copper foil.
Preferably, the pretreatment solution is a sodium hydroxide solution, a hydrochloric acid solution, a polyacrylic acid solution, a polyethyleneimine solution, a polyacrylamide hydrochloride solution, a sodium carboxymethyl cellulose solution or a polyurethane solution.
Preferably, during the preparation of the silicon/carbon composite powder, the silicon material and the carbon material are mixed by means of ultrasonic waves, ball milling, sand milling or grinding.
Preferably, the ball milling mode is wet milling, the speed of the wet milling is 500-1500 rpm, and the time is 0.5-72 h.
Optionally, when the silicon/conductive polymer powder is prepared, the mass ratio of silicon of the silicon material to the conductive polymer is 100-0: 0 to 100.
Preferably, the mass ratio of silicon of the silicon material to the conductive polymer is 80-20: 20 to 80 percent.
Optionally, when the silicon/carbon composite powder is prepared, the mass ratio of silicon of the silicon material to carbon of the carbon material is 0-100: 100 to 0.
Preferably, in the preparation of the silicon/carbon composite powder, the mass ratio of silicon of the silicon material to carbon of the carbon material is 20-80: 80-20.
Preferably, the silicon material is at least one of simple substance silicon or a modified substance thereof, silicon oxide SiOx or a modified substance thereof, and the at least one of simple substance silicon or a modified substance thereof, silicon oxide SiOx or a modified substance thereof is at least one of particles, porous particles, nanowires or nanotubes with the particle size of 10 nm-10 mu m, wherein x is more than 0 and less than or equal to 2.
Optionally, the conductive polymer is at least one of polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylacetylene.
Preferably, the conductive polymer is at least one of polyaniline, polypyrrole and polythiophene.
Preferably, the carbon material is at least one of graphite or a modified product thereof, carbon fiber or a modified product thereof, carbon nanotube or a modified product thereof, graphene or a modified product thereof, soft carbon or a modified product thereof, hard carbon or a modified product thereof, amorphous carbon or a modified product thereof.
Preferably, the preparation process of the silicon/conductive polymer slurry and the silicon/carbon slurry comprises the following steps: and respectively carrying out magnetic stirring on the silicon/conductive polymer powder and the silicon/carbon composite powder, and then carrying out ultrasonic treatment until a uniform and stable mixed solution is formed, wherein the stirring time is 60-360 min, and the ultrasonic treatment time is 30-180 min.
Preferably, the polyelectrolyte is at least one of polydiallyl dimethyl ammonium chloride, sodium polystyrene sulfonate, polyurethane, polyvinylsulfonic acid, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyethylene (imine) amine, and polyetherimide.
Preferably, the solvent for dispersing the silicon/conductive polymer powder and the silicon/carbon composite powder is at least one of water, ethanol, acetone, tetrahydrofuran and dimethylformamide.
Optionally, the mass fraction of the polyelectrolyte in the silicon/conductive polymer slurry is 1-80%, and the mass ratio of the total mass of the silicon/conductive polymer powder to the polyelectrolyte is 1:1-70. Wherein the total mass of the silicon/conductive polymer powder is the sum of the mass of the silicon material and the conductive polymer. The silicon/conductive polymer paste includes silicon/conductive polymer powder, polyelectrolyte, and solvent. The mass fraction refers to the total specific gravity of the polyelectrolyte to the silicon/conductive polymer paste, while the mass ratio refers to the specific gravity between the silicon/conductive polymer powder and the polyelectrolyte.
Preferably, the mass fraction of the polyelectrolyte in the silicon/conductive polymer slurry is 1-60%, and the mass ratio of the total mass of the silicon/conductive polymer powder to the polyelectrolyte is 1:3-35.
Optionally, the mass fraction of the polyelectrolyte in the silicon/carbon slurry is 1-80%, and the mass ratio of the total mass of the silicon/carbon composite powder to the polyelectrolyte is 1:1-70. Wherein the total mass of the silicon/carbon composite powder is the sum of the mass of the silicon material and the mass of the carbon material. The silicon/carbon slurry comprises silicon/carbon composite powder, polyelectrolyte and solvent. The mass fraction refers to the total specific gravity of the polyelectrolyte to the silicon/carbon slurry, and the mass ratio refers to the specific gravity between the silicon/carbon composite powder and the polyelectrolyte.
Preferably, the mass fraction of the polyelectrolyte in the silicon/carbon slurry is 1-60%, and the mass ratio of the total mass of the silicon/carbon composite powder to the polyelectrolyte is 1:3-35.
Optionally, the manner of alternately depositing the silicon/conductive polymer paste and the silicon/carbon paste is spin coating, dipping or spraying.
Preferably, the spin coating of the silicon/conductive polymer paste film or the silicon/carbon paste film has a speed of 500 to 5000rpm and/or a spin coating time of 10 to 300 seconds.
Preferably, the spin coating of the silicon/conductive polymer paste film or the silicon/carbon paste film has a speed of 1000 to 3000rpm and/or a spin coating time of 20 to 150s.
Optionally, the drying is at least one of air drying, vacuum drying and high-temperature drying, and the drying time is 1-720 min. According to the different drying modes, different drying times can be selected adaptively in order to achieve good drying effect.
Preferably, the high temperature sintering process includes: the sintering temperature is gradually increased to 200-1000 ℃ from room temperature, the heating rate is 2-5 ℃/min, and the sintering temperature is naturally cooled after being kept at the highest calcining temperature for 0-360 min.
Preferably, the silicon-carbon composite electrode material prepared by the preparation method is prepared.
Preferably, the silicon-carbon composite electrode material is of a layer-by-layer self-assembled shell-like pearl layer structure, the layer number of the film is more than or equal to 1, the thickness range of the film is 0.05-500 mu m, and the relative standard deviation is 1-5%.
Optionally, the total layer number of the silicon-carbon composite electrode material is 1-200.
Preferably, the total layer number of the silicon-carbon composite electrode material is 1-100.
The invention has the beneficial effects that:
according to the invention, a layer-by-layer self-assembly technology is adopted, silicon/conductive polymer powder and silicon/carbon composite powder with opposite electric properties, which are respectively and uniformly dispersed in cationic polyelectrolyte and anionic polyelectrolyte, are introduced on the surface of a substrate, and the silicon-carbon composite electrode material with a multilayer film structure is obtained through opposite electric charge electrostatic phase absorption. The silicon-based composite film with the shell-like pearl layer structure is formed by alternately depositing the silicon/conductive polymer film and the silicon/carbon film, so that lithium ions can be guided to be rapidly deintercalated in the growth direction of the film, and the expansion direction of the silicon-based composite film is vertical to the length direction of the film body, thereby relieving the severe volume and structure change of the lithium battery cathode in the charge and discharge process.
The two adjacent layers of the silicon-based composite film are tightly combined due to the attraction of opposite charges, and the formed high-compatibility interface layer is not only beneficial to load transfer, but also can slow down stress concentration. In the high-temperature calcination treatment process, the silicon/conductive polymer layer converts the conductive polymer coated on the silicon surface into a carbon coating layer through pyrolyzing the conductive polymer, the formed amorphous carbon is used as a buffer matrix to be tightly coated on the surface of a silicon material, and the mutually-interwoven carbon materials in the silicon/carbon layer inlay silicon nano particles into a conductive carbon frame, so that the silicon and carbon components are effectively contacted, the conductivity of the electrode material is improved while the expansion of silicon is solved, the structural integrity of the electrode material in the charge and discharge process is maintained, and the cycle stability and the multiplying power performance of the lithium ion battery are improved.
In addition, the silicon-carbon composite electrode material has high silicon content, nano-scale controllable thickness and a multi-layer structure, provides a channel for high-speed movement of ions and electrons, and simultaneously enables the internal mutually communicated pore structure to release mechanical stress caused by silicon expansion, so that the capacity attenuation rate in the battery circulation process can be effectively reduced. The preparation method of the invention is a low-cost, high-efficiency and expandable process technology.
Drawings
FIG. 1 schematically illustrates a flow chart of a method of preparing a silicon-carbon composite electrode material in accordance with various embodiments of the present invention;
FIG. 2 is a schematic diagram showing a scanning electron microscope of a silicon-carbon composite electrode material prepared in example 1 of the present invention;
FIG. 3 is a schematic diagram showing a scanning electron microscope of a silicon-carbon composite electrode material prepared in example 2 of the present invention;
FIG. 4 schematically shows a scanning electron microscope image of the silicon-carbon composite electrode material prepared in example 3 of the present invention.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments will be briefly described below. It is apparent that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
The present invention will be described in detail below with reference to the drawings and the specific embodiments, which are not described in detail herein, but the embodiments of the present invention are not limited to the following embodiments.
Fig. 1 schematically shows a flowchart of a method for preparing a silicon-carbon composite electrode material according to various embodiments of the present invention. The silicon materials in the following examples of the present invention are nano silicon particles (SiNPs, particle size 20 nm-60 nm), and the carbon materials are carboxylated carbon nanotubes (CNT-COOH). And is carried out according to the preparation method flow shown in figure 1.
Example 1:
the preparation method of the silicon-carbon composite electrode material provided by the embodiment comprises the following steps:
first, a substrate is pretreated: the carbon-coated copper foil is placed in a sodium polystyrene sulfonate solution with the mass percent of 0.05% to be soaked for 30min, dried and then washed with water.
Secondly, preparing silicon/polyaniline powder:
(1) Pretreatment of nano silicon particles: 0.5g SiNPs was added to the piranha solution (containing 15mL H) 2 SO 4 Solution and 5mL of H 2 O 2 Solution), magnetically stirring for 1h at 80 ℃ in a water bath, filtering and washing with ultrapure water after uniform dispersion, and drying for 12h in a 60 ℃ vacuum oven to obtain hydroxylated nano Si particles which are marked as Si-OH.
(2) Preparation of Si-PANI particles: the phytic acid was dissolved in 30mL of ultrapure water, 300mg of aniline was added dropwise, stirring was carried out for 1 hour to form a phytic acid ammonium salt, then 300mg of si-OH was added and 30mg of Sodium Dodecylbenzenesulfonate (SDBS) was added, stirring was carried out for 1 hour, and the mixture was sufficiently mixed with the above phytic acid ammonium salt to obtain a mixed solution a. Ammonium Persulfate (APS) is weighed, dissolved in ultrapure water, subjected to ultrasonic treatment for 0.5h and then placed in a low-temperature box for storage, so that a mixed solution B is obtained, wherein the atomic ratio of aniline to APS to phytic acid is 5:5:1. The solution A and the solution B are mixed for 12 hours under vigorous stirring at the temperature of minus 18 ℃ to form Si-PANI particles.
Preparing silicon/carbon composite powder: the Si-OH and carboxylated carbon nanotubes were prepared at a mass of silicon and a mass of carbon of 30:70 in absolute ethanol, wet-milling at a ball milling speed of 500rpm for 6 hours, and drying in a vacuum drying oven at 60 ℃ for 12 hours to obtain silicon/carbon composite powder, which is named as (Si 30-C70) powder.
Next, a slurry was prepared as follows:
dispersing cationic polyurethane and Si-PANI particles into deionized water, magnetically stirring for 180min, and performing ultrasonic treatment for 120min to uniformly mix to obtain silicon/polyaniline slurry. In the silicon/polyaniline slurry, the mass fraction of the polyelectrolyte is 15%, and the mass ratio of the polyelectrolyte to the total mass of the silicon/polyaniline powder is 6:1.
Dispersing anionic polyurethane, (Si 30-C70) powder into deionized water, magnetically stirring for 180min, and performing ultrasonic treatment for 120min to uniformly mix to obtain silicon/carbon slurry. In the silicon/carbon slurry, the mass fraction of the polyelectrolyte is 15%, and the mass ratio of the polyelectrolyte to the total mass of the silicon/carbon composite powder is 6:1.
Then, spin coating: 1.5ml of silicon/polyaniline slurry is dripped on the surface of the pretreated substrate after drying, spin-coated for 50s at a spin-coating speed of 2600rpm, and then vacuum-dried for 3min at 50 ℃; then taking the silicon/carbon slurry with the same quality, dripping the silicon/carbon slurry on the surface of the substrate again, spin-coating for 50s at the spin-coating speed of 2600rpm, and then drying in vacuum for 3min at 50 ℃ to obtain the silicon-based composite double-layer film. Repeating the spin coating process for 2 times to obtain a self-assembled silicon-based composite film with the total layer number of 6, which is marked as (Si/PANI-Si/C) 6 -1。
Finally, high-temperature sintering treatment: will (Si/PANI-Si/C) 6 -1 sintering at high temperature in nitrogen atmosphere to obtain layer-by-layer self-assembled siliconCarbon composite electrode material. The sintering condition is that the temperature is gradually increased to 750 ℃ from room temperature, the heating rate is 2 ℃/min, and the sintering condition is naturally cooled down after the sintering condition is kept for 120min at the highest calcination temperature, and the sintering condition is marked as (Si/C) 6 -1。
Example 2:
the preparation method of the silicon-carbon composite electrode material provided by the embodiment comprises the following steps:
first, a substrate is pretreated: the carbon-coated copper foil is placed in a sodium polystyrene sulfonate solution with the mass percent of 0.05% to be soaked for 30min, dried and then washed with water.
Secondly, preparing silicon/polyaniline powder:
(1) Pretreatment of nano silicon particles: 0.5g SiNPs was added to the piranha solution (15 mL H 2 SO 4 Solution, 5mL of H 2 O 2 Solution), magnetically stirring for 1h at 80 ℃ in a water bath, filtering and washing with ultrapure water after uniform dispersion, and drying for 12h in a 60 ℃ vacuum oven to obtain hydroxylated nano Si particles which are marked as Si-OH.
(2) Preparation of Si-PANI particles: the phytic acid was dissolved in 30mL of ultrapure water, 300mg of aniline was added dropwise, stirring was carried out for 1 hour to form a phytic acid ammonium salt, then 300mg of si-OH was added and 30mg of Sodium Dodecylbenzenesulfonate (SDBS) was added, stirring was carried out for 1 hour, and the mixture was sufficiently mixed with the above phytic acid ammonium salt to obtain a mixed solution a. Ammonium Persulfate (APS) was weighed, dissolved in ultrapure water, sonicated for 0.5 hours and stored in a low-temperature box to give a mixed solution B in which the atomic ratio of aniline, APS and phytic acid was 5:5:1. The solution A and the solution B are mixed for 12 hours under vigorous stirring at the temperature of minus 18 ℃ to form Si-PANI particles.
Preparing silicon/carbon composite powder: the Si-OH and carboxylated carbon nanotubes are prepared according to the mass of silicon and the mass of carbon of 50:50 in absolute ethyl alcohol, wet-milling for 6 hours at a ball milling speed of 500rpm, and drying for 12 hours in a vacuum drying oven at 60 ℃ to obtain silicon/carbon composite powder, which is marked as (Si 50-C50) powder.
Next, a slurry was prepared as follows:
dispersing cationic polyurethane and Si-PANI particles into deionized water, magnetically stirring for 180min, and performing ultrasonic treatment for 120min to uniformly mix to obtain silicon/polyaniline slurry. In the silicon/polyaniline slurry, the mass fraction of the polyelectrolyte is 15%, and the mass ratio of the polyelectrolyte to the total mass of the silicon/polyaniline powder is 6:1.
Dispersing anionic polyurethane, (Si 50-C50) powder into deionized water, magnetically stirring for 180min, and performing ultrasonic treatment for 120min to uniformly mix to obtain silicon/carbon slurry. In the silicon/carbon slurry, the mass fraction of the polyelectrolyte is 15%, and the mass ratio of the polyelectrolyte to the total mass of the silicon/carbon composite powder is 6:1.
Then, spin coating: 1.5ml of silicon/polyaniline slurry is dripped on the surface of the pretreated substrate after drying, spin-coated for 50s at a spin-coating speed of 2600rpm, and then vacuum-dried for 3min at 50 ℃; then taking the silicon/carbon slurry with the same quality, dripping the silicon/carbon slurry on the surface of the substrate again, spin-coating for 50s at the spin-coating speed of 2600rpm, and then drying in vacuum for 3min at 50 ℃ to obtain the silicon-based composite double-layer film. Repeating the spin coating process for 2 times to obtain a self-assembled silicon-based composite film with the total layer number of 6, which is marked as (Si/PANI-Si/C) 6 -2。
Finally, high-temperature sintering treatment: will (Si/PANI-Si/C) 6 And 2, placing the electrode material in a nitrogen atmosphere and sintering at high temperature to obtain the layer-by-layer self-assembled silicon-carbon composite electrode material. The sintering condition is that the temperature is gradually increased to 750 ℃ from room temperature, the heating rate is 2 ℃/min, and the sintering condition is naturally cooled down after the sintering condition is kept for 120min at the highest calcination temperature, and the sintering condition is marked as (Si/C) 6 -2。
Example 3:
the preparation method of the silicon-carbon composite electrode material provided by the embodiment comprises the following steps:
first, a substrate is pretreated: the carbon-coated copper foil is placed in a sodium polystyrene sulfonate solution with the mass percent of 0.05% to be soaked for 30min, dried and then washed with water.
Secondly, preparing silicon/polyaniline powder:
(1) Pretreatment of nano silicon particles: 0.5g SiNPs was added to the piranha solution (15 mL H 2 SO 4 Solution, 5mL of H 2 O 2 Solution), magnetically stirring for 1h at 80 ℃ in a water bath, filtering and washing with ultrapure water after uniform dispersion, and drying for 12h in a 60 ℃ vacuum oven to obtain hydroxylated nano Si particles which are marked as Si-OH.
(2) Preparation of Si-PANI particles: the phytic acid was dissolved in 30mL of ultrapure water, 300mg of aniline was added dropwise, stirring was carried out for 1 hour to form a phytic acid ammonium salt, then 300mg of si-OH was added and 30mg of Sodium Dodecylbenzenesulfonate (SDBS) was added, stirring was carried out for 1 hour, and the mixture was sufficiently mixed with the above phytic acid ammonium salt to obtain a mixed solution a. Ammonium Persulfate (APS) was weighed, dissolved in ultrapure water, sonicated for 0.5 hours and stored in a low-temperature box to give a mixed solution B in which the atomic ratio of aniline, APS and phytic acid was 5:5:1. The solution A and the solution B are mixed for 12 hours under vigorous stirring at the temperature of minus 18 ℃ to form Si-PANI particles.
Preparing silicon/carbon composite powder: the Si-OH and carboxylated carbon nanotubes are prepared according to the mass of silicon and the mass of carbon of 50:50 in absolute ethyl alcohol, wet-milling for 6 hours at a ball milling speed of 500rpm, and drying for 12 hours in a vacuum drying oven at 60 ℃ to obtain silicon/carbon composite powder, which is marked as (Si 50-C50) powder.
Next, a slurry was prepared as follows:
dispersing cationic polyurethane and Si-PANI particles into deionized water, magnetically stirring for 180min, and performing ultrasonic treatment for 120min to uniformly mix to obtain silicon/polyaniline slurry. In the silicon/polyaniline slurry, the mass fraction of the polyelectrolyte is 15%, and the mass ratio of the polyelectrolyte to the total mass of the silicon/polyaniline powder is 6:1.
Dispersing anionic polyurethane, (Si 50-C50) powder into deionized water, magnetically stirring for 180min, and performing ultrasonic treatment for 120min to uniformly mix to obtain silicon/carbon slurry. In the silicon/carbon slurry, the mass fraction of the polyelectrolyte is 15%, and the mass ratio of the polyelectrolyte to the total mass of the silicon/carbon composite powder is 6:1.
Then, spin coating: 1.5ml of silicon/polyaniline slurry is dripped on the surface of the pretreated substrate after drying, spin-coated for 50s at a spin-coating speed of 2600rpm, and then vacuum-dried for 3min at 50 ℃; then taking the silicon/carbon slurry with the same quality, dripping the silicon/carbon slurry on the surface of the substrate again, spin-coating for 50s at the spin-coating speed of 2600rpm, and then drying in vacuum for 3min at 50 ℃ to obtain the silicon-based composite double-layer film. Repeating the spin coating process for 4 times to obtain a self-assembled silicon-based composite film with the total layer number of 10, which is marked as (Si/PANI-Si/C) 10 -1。
Finally, the high temperature sintering partAnd (3) treatment: will (Si/PANI-Si/C) 10 And (1) placing the electrode material in a nitrogen atmosphere for high-temperature sintering to obtain the silicon-carbon composite electrode material self-assembled layer by layer. The sintering condition is that the temperature is gradually increased to 750 ℃ from room temperature, the heating rate is 2 ℃/min, and the sintering condition is naturally cooled down after the sintering condition is kept for 120min at the highest calcination temperature, and the sintering condition is marked as (Si/C) 10 -1。
Material and electrochemical characterization:
FIGS. 2 to 4 schematically show scanning electron microscope images of the silicon-carbon composite electrode materials prepared in examples 1, 2 and 3 of the present invention, respectively. As can be seen from fig. 2, 3 and 4, the carbon nanotube CNTs are uniformly interwoven and intertwined with each other to construct a conductive frame, and the silicon particles are uniformly embedded in the channels overlapped by the carbon nanotube CNTs and adhered to the surfaces of the carbon nanotube CNTs. And channels which are communicated with each other are reserved between the silicon-carbon composite electrode material layers, so that space is provided for the volume expansion of silicon.
Table 1 shows the specific discharge capacity of the silicon-carbon composite electrode material according to the number of cycles at a current density of 500mAh/g when the silicon-carbon composite electrode material prepared in each of the above examples of the present invention is applied to a lithium battery. The silicon-carbon composite electrode materials prepared in example 1, example 2 and example 3 are directly used as battery active materials, and a half-battery test method is adopted to carry out charge-discharge cycle test on the silicon-carbon composite electrode materials, so as to examine the performances of cycle reversibility, discharge capacity and the like. The half cell mainly comprises a metal lithium sheet serving as a negative electrode, a PP/PE/PP film serving as a diaphragm, a silicon-carbon composite electrode material serving as a positive electrode and prepared by the above embodiments respectively, wherein the electrolyte is 1M LiPF 6 +ec: DMC: emc=1: 1:1 (volume ratio) and 10% by mass of fluoroethylene carbonate (FEC) with respect to all the substances in the electrolyte. The half-cells were assembled in a glove box under an inert atmosphere. The voltage range of the charge and discharge test is set to be 0.01-1.5V, the constant charge and discharge current density is 500mAh/g, the test temperature is room temperature, and the cycle performance test results of the silicon-carbon composite electrode materials prepared in each embodiment are shown in table 1.
TABLE 1
According to table 1, test results show that the half batteries assembled by the silicon-carbon composite anode materials prepared in the examples 1, 2 and 3 have better initial capacity. Moreover, the initial discharge specific capacities can reach 1191.1mAh/g, 2182.2mAh/g and 1739.3mAh/g respectively, and the discharge specific capacities at the 2 nd turn are 996mAh/g, 1324.3mAh/g and 1093.8mAh/g respectively. Compared with the discharge specific capacity of the 2 nd turn, the silicon-carbon composite anode materials of the example 1 and the example 2 maintain higher discharge capacity retention rates after 100 cycles, which can reach 86.4% and 80.2% respectively. Further, after 100 cycles, the coulombic efficiencies of the silicon-carbon composite anode materials of example 1, example 2 and example 3 were 100.7%, 103.88%, 101.53%, respectively, all showed very good cycle reversibility. Therefore, the silicon-carbon composite electrode material prepared by the embodiments of the invention has good cycle stability, and can provide reliable guarantee for the development of long-life lithium ion batteries.
The above description is only one embodiment of the present invention and is not intended to limit the present invention, and various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (8)

1. A preparation method of a silicon-carbon composite electrode material comprises the following steps:
pretreating a substrate by adopting a pretreatment solution to obtain a conductive substrate with charges on the surface;
electrostatic adsorption of conductive polymer on the surface of silicon material to prepare silicon/conductive polymer powder;
mixing a silicon material and a carbon material to prepare silicon/carbon composite powder;
dispersing the silicon/conductive polymer powder and the silicon/carbon composite powder into polyelectrolyte with opposite electrical properties respectively to obtain silicon/conductive polymer slurry and silicon/carbon slurry;
alternately depositing the silicon/conductive polymer slurry and the silicon/carbon slurry on the conductive substrate opposite to the surface of the conductive substrate, and drying to obtain a silicon-based composite film;
sintering the silicon-based composite film at a high temperature under the protection of inert atmosphere to obtain a silicon-carbon composite electrode material;
in the process of preparing the silicon/conductive polymer powder, the mass ratio of silicon of the silicon material to the conductive polymer is 80-20: 20-80 parts;
the mass fraction of the polyelectrolyte in the silicon/conductive polymer slurry is 1-80%, and the mass ratio of the total mass of the silicon/conductive polymer powder to the polyelectrolyte is 1:1-70;
the pretreatment process comprises the following steps: placing the substrate in a pretreatment solution with the solute mass fraction of 0.01-10% for soaking for 5-60 min, drying, cleaning by using ultrapure water,
wherein the substrate is copper foil, aluminum foil, zinc film, carbon-coated copper foil, nickel-chromium film, titanium-gold film or indium tin oxide film;
the pretreatment solution is sodium hydroxide solution, hydrochloric acid solution, polyacrylic acid solution, polyethyleneimine solution, polyacrylamide hydrochloride solution, sodium carboxymethyl cellulose solution or polyurethane solution;
the conductive polymer is at least one of polyaniline, polypyrrole, polythiophene, polyacetylene and polyphenylacetylene;
the preparation process of the silicon/conductive polymer slurry and the silicon/carbon slurry comprises the following steps: and respectively carrying out magnetic stirring on the silicon/conductive polymer powder and the silicon/carbon composite powder, and then carrying out ultrasonic treatment until a uniform and stable mixed solution is formed, wherein the stirring time is 60-360 min, and the ultrasonic treatment time is 30-180 min.
2. The method for preparing a silicon-carbon composite electrode material according to claim 1, wherein the silicon material and the carbon material are mixed by ultrasonic waves, ball milling, sand milling or grinding during the preparation of the silicon/carbon composite powder,
the mass ratio of silicon of the silicon material to carbon of the carbon material is 20-80: 80-20 parts;
the ball milling mode is wet milling, the speed of the wet milling is 500-1500 rpm, and the time is 0.5-72 h.
3. The method for producing a silicon-carbon composite electrode material according to claim 1 or 2, wherein the silicon material is at least one of elemental silicon or a modified product thereof, silicon oxide SiOx or a modified product thereof, and the at least one of elemental silicon or a modified product thereof, silicon oxide SiOx or a modified product thereof is at least one of a particulate, porous particulate, nanowire or nanotube having a particle diameter of 10nm to 10 μm, wherein 0< x is not more than 2;
the carbon material is at least one of graphite or a modified matter thereof, carbon fiber or a modified matter thereof, carbon nano tube or a modified matter thereof, graphene or a modified matter thereof, soft carbon or a modified matter thereof, hard carbon or a modified matter thereof, amorphous carbon or a modified matter thereof.
4. The method for preparing a silicon-carbon composite electrode material according to claim 1, wherein the polyelectrolyte is at least one of polydiallyl dimethyl ammonium chloride, sodium polystyrene sulfonate, polyurethane, polyvinylsulfonic acid, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyethylene (imine) and polyetherimide;
the solvent for dispersing the silicon/conductive polymer powder and the silicon/carbon composite powder is at least one of water, ethanol, acetone, tetrahydrofuran and dimethylformamide;
the mass fraction of the polyelectrolyte in the silicon/carbon slurry is 1-80%, and the mass ratio of the total mass of the silicon/carbon composite powder to the polyelectrolyte is 1:1-70.
5. The method for preparing a silicon-carbon composite electrode material according to claim 1, wherein the manner of alternately depositing the silicon/conductive polymer slurry and the silicon/carbon slurry is spin coating, dipping or spraying.
6. The method for producing a silicon-carbon composite electrode material as defined in claim 5, wherein the spin-coating of the silicon/conductive polymer paste film or the silicon/carbon paste film is performed at a speed of 500 to 5000rpm and/or for a spin-coating time of 10 to 300s;
the drying is at least one of air drying, vacuum drying and high-temperature drying, and the drying time is 1-720 min.
7. The method for preparing a silicon-carbon composite electrode material according to claim 1, wherein the high-temperature sintering process comprises: the sintering temperature is gradually increased to 200-1000 ℃ from room temperature, the heating rate is 2-5 ℃/min, and the sintering temperature is naturally cooled after being kept for 120-360 min at the highest calcining temperature.
8. The silicon-carbon composite electrode material prepared by the preparation method of the silicon-carbon composite electrode material according to any one of claims 1 to 7,
the silicon-carbon composite electrode material has a shell-like pearl layer structure, the number of layers of the film is more than or equal to 1, and the thickness range of the film is 0.05-500 mu m.
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