CN114212775A - 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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CN114212775A
CN114212775A CN202111320525.XA CN202111320525A CN114212775A CN 114212775 A CN114212775 A CN 114212775A CN 202111320525 A CN202111320525 A CN 202111320525A CN 114212775 A CN114212775 A CN 114212775A
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silicon
carbon
carbon composite
conductive polymer
electrode material
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CN114212775B (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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    • 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
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a silicon-carbon composite electrode material and a preparation method thereof, wherein the preparation method comprises the following steps: pretreating the substrate by adopting a pretreatment solution to obtain a conductive substrate with charges on the surface; electrostatically adsorbing a conductive polymer on the surface of a 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 surface of the conductive substrate opposite to the electrical property of the surface of the conductive substrate, and drying to obtain a silicon-based composite film; and (3) sintering the silicon-based composite film at high temperature under the protection of inert atmosphere to obtain the silicon-carbon composite electrode material. By the preparation method, the cycle stability and the rate capability of the lithium ion battery cathode 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
Under the increasingly severe global energy situation, electrochemical energy storage batteries are considered as an ideal choice for various electronic devices and electric transportation vehicles as a power source. Lithium ion batteries are one of the most important energy storage devices at present due to their high power, high capacity, long life and high safety. In order to promote the development of high-energy power lithium ion batteries, the development of low-cost and high-energy-density electrode materials is urgently needed. The silicon-carbon composite material has the theoretical capacity up to 4200mAh g-1Silicon and highly conductive carbon materials of (2) are the best candidates for battery negative electrode materials. However, the silicon-carbon composite material with high silicon content can generate huge volume and structure changes in the charging and discharging processes, so as to induce the cracking and the crushing of the negative electrode of the lithium ion battery, and finally, the battery capacity is sharply attenuated and storedThe efficiency is reduced, the service life is limited, and the process of commercial development becomes very slow.
In general, the improvement of the volume effect of silicon in lithium deintercalation mainly includes the following three strategies: (1) the carbon layer is directly coated on the surface of the nano silicon particles by adopting a template method, a vapor deposition method or a high-temperature pyrolysis method and the like so as to adapt to the volume change of the silicon material. However, this strategy not only has harsh conditions of preparation means and complex preparation flow, but also has the risk of cracking the surface carbon layer due to too large volume expansion in the process of lithiation of the silicon material, so that the composite material structure collapses and the internal silicon particles lose protection. (2) The silicon particles are embedded into the carbon material by mechanical mixing and electrostatic spinning to obtain a highly dispersed silicon-carbon mixed system. However, this strategy is not readily used to alleviate the volume effect for a long period of time, considering the difficulty of uniform dispersion and the difficulty of intimate contact of silicon and carbon with 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 adjust the stress change of the silicon material in the circulating process. However, the silicon material has a relatively poor electron transport ability compared to conventional carbon conductive polymers. The key point for solving the problems lies in breaking through the defect that the structure of the existing silicon-carbon composite material is single in composition.
In order to improve the cycle performance of active substances, Chinese patent CN105390687B discloses a high-performance three-dimensional carbon nanotube composite negative electrode material and a preparation method and application thereof, wherein a carboxylated carbon nanotube is used as a three-dimensional network framework, a high-capacity material which is subjected to layer-by-layer self-assembly modification is used as an active substance, the carbon nanotube and the active substance are uniformly mixed under the action of electrostatic attraction, and then a carbon source which contains N or S doped impurity elements is coated in situ and is used as a three-dimensional coating layer to prepare the high-performance three-dimensional carbon nanotube composite negative electrode material through high-temperature treatment. In order to obtain an electrode material with excellent electron transfer performance and mechanical performance, Chinese patent CN107204438B discloses a silicon-carbon composite material and a preparation method and application thereof, wherein a silicon nano material, a carbon nano material and a binder are dispersed in a solvent to form slurry, and a carbon-silicon composite macroscopic body is prepared; 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 poor contact between silicon expansion and silicon-carbon components and the like, and thus improve the cycle stability and rate capability of the lithium ion battery cathode material.
In order to achieve the 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: firstly, a pretreatment solution is adopted to pretreat a substrate 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, silicon material and carbon material are mixed to prepare silicon/carbon composite powder. And then, respectively dispersing the silicon/conductive polymer powder and the silicon/carbon composite powder into polyelectrolyte and/or inorganic salt solution with opposite electric properties 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 surface of the conductive substrate in a manner opposite to the electrical property of the surface of the conductive substrate, and drying to obtain the silicon-based composite film. The first layer of slurry film deposited on the surface of the conductive substrate has an electrical property opposite to that of the surface of the conductive substrate. And finally, sintering the silicon-based composite film at high temperature under the protection of inert atmosphere to obtain the silicon-carbon composite electrode material.
Preferably, the pre-treatment process comprises: and placing the substrate in a pretreatment solution with solute mass fraction of 0.01-10% to soak for 5-60 min, then drying, and then cleaning with ultrapure water.
Optionally, the substrate is a copper foil, an aluminum foil, a zinc film, a carbon-coated copper foil, a nickel-chromium film, a titanium-gold film, or an 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 carboxymethylcellulose solution or a polyurethane solution.
Preferably, in the process of preparing the silicon/carbon composite powder, the silicon material and the carbon material are mixed by adopting an ultrasonic, ball milling, sand milling or grinding mode.
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 to the conductive polymer of the silicon material is 100-0: 0 to 100.
Preferably, the mass ratio of silicon to the conductive polymer in the silicon material is 80-20: 20 to 80 parts.
Optionally, when the silicon/carbon composite powder is prepared, the mass ratio of silicon in the silicon material to carbon in the carbon material is 0-100: 100 to 0.
Preferably, when the silicon/carbon composite powder is prepared, the mass ratio of silicon in the silicon material to carbon in 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 the simple substance silicon or the modified substance thereof, the silicon oxide SiOx or the modified substance thereof is at least one of granular, porous granular, nanowire or nanotube with the grain diameter of 10 nm-10 μm, 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 nanotubes 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, and amorphous carbon or a modified product thereof.
Preferably, the preparation process of the silicon/conductive polymer paste and the silicon/carbon paste comprises the following steps: respectively carrying out magnetic stirring and ultrasonic treatment on the silicon/conductive polymer powder and the silicon/carbon composite powder 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 polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, polyurethane, polyvinyl sulfonic acid, polyvinyl pyrrolidone, polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyethylene (ene) 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 mass of the conductive polymer. The silicon/conductive polymer slurry comprises silicon/conductive polymer powder, polyelectrolyte and solvent. The mass fraction means the total specific gravity of the polyelectrolyte in the silicon/conductive polymer slurry, and the mass ratio means 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 masses of the silicon material and 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 in 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 speed of spin-coating a layer of the silicon/conductive polymer paste film or the silicon/carbon paste film is 500-5000 rpm, and/or the spin-coating time is 10-300 s.
Preferably, the speed of spin-coating a layer of the silicon/conductive polymer paste film or the silicon/carbon paste film is 1000-3000 rpm, and/or the spin-coating time is 20-150 s.
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 selected drying modes, different drying time can be adaptively selected in order to achieve good drying effect.
Preferably, the treatment process of high-temperature sintering comprises the following steps: the sintering temperature is gradually increased from room temperature to 200-1000 ℃, the heating rate is 2-5 ℃/min, and the sintering temperature is kept at the highest calcining temperature for 0-360 min and then is naturally cooled.
Preferably, the silicon-carbon composite electrode material is prepared according to the preparation method.
Preferably, the silicon-carbon composite electrode material is of a layer-by-layer self-assembly 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 number of layers of the silicon-carbon composite electrode material is 1-200.
Preferably, the total number of layers of the silicon-carbon composite electrode material is 1-100.
The invention has the beneficial effects that:
the invention adopts a layer-by-layer self-assembly technology, 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 electrostatic attraction of opposite charges. The silicon-based composite membrane with the shell-like pearl layer structure is formed by alternately depositing the silicon/conductive polymer membrane and the silicon/carbon membrane, so that lithium ions can be guided to be rapidly de-embedded in the growth direction of the membrane, and the expansion direction of the silicon-based composite membrane is perpendicular to the length direction of the membrane body, thereby relieving the violent volume and structure changes of the negative electrode of the lithium battery in the charging and discharging process.
The adjacent two layers of the silicon-based composite film obtained by the invention are tightly combined due to the attraction of opposite charges, and the formed highly compatible interface layer is not only favorable for 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 by pyrolyzing the conductive polymer, the formed amorphous carbon is tightly coated on the surface of the silicon material as a 'buffer matrix', and silicon nanoparticles are embedded in a conductive carbon frame by the carbon material interwoven in the silicon/carbon layer, so that the two components of silicon and carbon are effectively contacted, the problem of silicon expansion is solved, the conductivity of the electrode material is favorably improved, the structural integrity of the electrode material in the charging and discharging processes is kept, and the cycle stability and the rate capability of the lithium ion battery are improved.
In addition, the silicon-carbon composite electrode material has high silicon content, nanoscale controllable thickness and a multilayer structure, provides a channel for high-speed movement of ions and electrons, and simultaneously, internal mutually communicated pore structures can release mechanical stress caused by silicon expansion, so that the capacity decay rate in the battery cycle process can be effectively reduced. The preparation method is a low-cost, high-efficiency and extensible process technology.
Drawings
FIG. 1 schematically shows a flow chart of a method of preparing a silicon carbon composite electrode material according to various embodiments of the present invention;
FIG. 2 is a scanning electron microscope image schematically illustrating a silicon carbon composite electrode material prepared in example 1 of the present invention;
FIG. 3 is a scanning electron microscope image schematically illustrating 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 used in the embodiments will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
The present invention is described in detail below with reference to the drawings and the specific embodiments, which are not repeated herein, but the embodiments of the present invention are not limited to the following embodiments.
Fig. 1 schematically shows a flow chart of a method for preparing a silicon-carbon composite electrode material according to various embodiments of the present invention. In the following embodiments of the present invention, the silicon material is selected from silicon nanoparticles (SiNPs, particle size is 20 nm-60 nm), and the carbon material is selected from carbon nanotubes (CNT-COOH). And was carried out according to the procedure of the preparation method shown in FIG. 1.
Example 1:
the preparation method of the silicon-carbon composite electrode material provided by the embodiment comprises the following steps:
firstly, substrate pretreatment: and (3) placing the carbon-coated copper foil in a sodium polystyrene sulfonate solution with the mass fraction of 0.05% for soaking for 30min, drying and then washing with water.
Secondly, preparing silicon/polyaniline powder:
(1) pretreatment of nano silicon particles: add 0.5gSiNPs to piranha solution (containing 15mL of H)2SO4Solution and 5mL of H2O2Solution), magnetically stirring for 1h in a water bath at 80 ℃, uniformly dispersing, then performing suction filtration and washing by using ultrapure water, and drying for 12h in a vacuum oven at 60 ℃ to obtain hydroxylated nano Si particles, which are marked as Si-OH.
(2) Preparation of Si-PANI particles: dissolving phytic acid in 30mL of ultrapure water, dropwise adding 300mg of aniline, fully stirring for 1h to form phytic acid ammonium salt, then adding 300mg of Si-OH, adding 30mg of Sodium Dodecyl Benzene Sulfonate (SDBS), stirring for 1h, and fully mixing with the phytic acid ammonium salt to obtain a mixed solution A. Ammonium Persulfate (APS) is weighed, dissolved in ultrapure water, and placed in a low-temperature box for preservation after ultrasonic treatment for 0.5h, so as to obtain a mixed solution B, wherein the atomic ratio of aniline to APS to phytic acid is 5:5: 1. The solution A and the solution B are mixed vigorously at-18 ℃ for 12h to form Si-PANI particles.
Preparing silicon/carbon composite powder: and (3) mixing Si-OH and carboxylated carbon nanotubes, wherein the mass of silicon and the mass of carbon are 30: 70 in an absolute alcohol, wet-milling at a ball milling speed of 500rpm for 6h, and drying in a vacuum drying oven at 60 ℃ for 12h to obtain a silicon/carbon composite powder, noted as (Si30-C70) powder.
Then, preparing slurry, which comprises the following specific steps:
dispersing the cationic polyurethane and Si-PANI particles into deionized water, performing magnetic stirring for 180min, performing ultrasonic treatment for 120min, and uniformly mixing to obtain silicon/polyaniline slurry. In the silicon/polyaniline slurry, the mass fraction of polyelectrolyte is 15%, and the mass ratio of polyelectrolyte to the total mass of silicon/polyaniline powder is 6: 1.
Dispersing anionic polyurethane and (Si30-C70) powder into deionized water, magnetically stirring for 180min, performing ultrasonic treatment for 120min, and uniformly mixing to obtain the 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: dropwise adding 1.5ml of silicon/polyaniline slurry on the surface of the dried pretreated substrate, spin-coating at the spin-coating speed of 2600rpm for 50s, and then vacuum-drying at 50 ℃ for 3 min; and then, dropwise adding the same mass of 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 silicon-based composite film with a total self-assembly number of layers of 6, and marking as (Si/PANI-Si/C)6-1。
And finally, high-temperature sintering treatment: will (Si/PANI-Si/C)6-1 placing under nitrogenAnd sintering at high temperature in the atmosphere to obtain the silicon-carbon composite electrode material which is self-assembled layer by layer. The sintering condition is that the temperature is gradually increased from the room temperature to 750 ℃, the temperature rising rate is 2 ℃/min, the sintering temperature is kept for 120min at the highest calcining temperature, and then the sintering temperature is naturally cooled and reduced, which 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:
firstly, substrate pretreatment: and (3) placing the carbon-coated copper foil in a sodium polystyrene sulfonate solution with the mass fraction of 0.05% for soaking for 30min, drying and then washing with water.
Secondly, preparing silicon/polyaniline powder:
(1) pretreatment of nano silicon particles: add 0.5gSiNPs to piranha solution (15mL of H)2SO4Solution, 5mL of H2O2Solution), magnetically stirring for 1h in a water bath at 80 ℃, uniformly dispersing, then performing suction filtration and washing by using ultrapure water, and drying for 12h in a vacuum oven at 60 ℃ to obtain hydroxylated nano Si particles, which are marked as Si-OH.
(2) Preparation of Si-PANI particles: dissolving phytic acid in 30mL of ultrapure water, dropwise adding 300mg of aniline, fully stirring for 1h to form phytic acid ammonium salt, then adding 300mg of Si-OH, adding 30mg of Sodium Dodecyl Benzene Sulfonate (SDBS), stirring for 1h, and fully mixing with the phytic acid ammonium salt to obtain a mixed solution A. Weighing Ammonium Persulfate (APS), dissolving in ultrapure water, performing ultrasonic treatment for 0.5h, and then placing in a low-temperature box for storage to obtain a mixed solution B, wherein the atomic ratio of aniline, APS and phytic acid is 5:5: 1. The solution A and the solution B are mixed vigorously at-18 ℃ for 12h to form Si-PANI particles.
Preparing silicon/carbon composite powder: and (3) mixing Si-OH and carboxylated carbon nanotubes, wherein the mass of silicon and the mass of carbon are as follows: 50 in absolute ethyl alcohol, wet-milled for 6h at a ball milling speed of 500rpm, and dried in a vacuum drying oven at 60 ℃ for 12h to obtain silicon/carbon composite powder, which is marked as (Si50-C50) powder.
Then, preparing slurry, which comprises the following steps:
dispersing the cationic polyurethane and Si-PANI particles into deionized water, magnetically stirring for 180min, and performing ultrasonic treatment for 120min to uniformly mix to obtain the silicon/polyaniline slurry. In the silicon/polyaniline slurry, the mass fraction of polyelectrolyte is 15%, and the mass ratio of polyelectrolyte to the total mass of silicon/polyaniline powder is 6: 1.
Dispersing anionic polyurethane and (Si50-C50) powder into deionized water, magnetically stirring for 180min, performing ultrasonic treatment for 120min, and uniformly mixing to obtain the 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: dropwise adding 1.5ml of silicon/polyaniline slurry on the surface of the dried pretreated substrate, spin-coating at the spin-coating speed of 2600rpm for 50s, and then vacuum-drying at 50 ℃ for 3 min; and then, dropwise adding the same mass of 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 silicon-based composite film with a total self-assembly number of layers of 6, and marking as (Si/PANI-Si/C)6-2。
And finally, high-temperature sintering treatment: will (Si/PANI-Si/C)6And-2, placing the silicon-carbon composite electrode material in a nitrogen atmosphere, and sintering at a 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 from the room temperature to 750 ℃, the temperature rising rate is 2 ℃/min, the sintering temperature is kept for 120min at the highest calcining temperature, and then the sintering temperature is naturally cooled and reduced, which 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:
firstly, substrate pretreatment: and (3) placing the carbon-coated copper foil in a sodium polystyrene sulfonate solution with the mass fraction of 0.05% for soaking for 30min, drying and then washing with water.
Secondly, preparing silicon/polyaniline powder:
(1) pretreatment of nano silicon particles: add 0.5gSiNPs to piranha solution (15mL of H)2SO4Solution, 5mL of H2O2Solution) and magnetically stirring for 1h in 80 ℃ water bath, after uniform dispersion, pumping and washing with ultrapure water, and drying for 12h in a vacuum oven at 60 ℃ to obtain hydroxylated nano Si particlesAnd particles, noted as Si-OH.
(2) Preparation of Si-PANI particles: dissolving phytic acid in 30mL of ultrapure water, dropwise adding 300mg of aniline, fully stirring for 1h to form phytic acid ammonium salt, then adding 300mg of Si-OH, adding 30mg of Sodium Dodecyl Benzene Sulfonate (SDBS), stirring for 1h, and fully mixing with the phytic acid ammonium salt to obtain a mixed solution A. Weighing Ammonium Persulfate (APS), dissolving in ultrapure water, performing ultrasonic treatment for 0.5h, and then placing in a low-temperature box for storage to obtain a mixed solution B, wherein the atomic ratio of aniline, APS and phytic acid is 5:5: 1. The solution A and the solution B are mixed vigorously at-18 ℃ for 12h to form Si-PANI particles.
Preparing silicon/carbon composite powder: and (3) mixing Si-OH and carboxylated carbon nanotubes, wherein the mass of silicon and the mass of carbon are as follows: 50 in absolute ethyl alcohol, wet-milled for 6h at a ball milling speed of 500rpm, and dried in a vacuum drying oven at 60 ℃ for 12h to obtain silicon/carbon composite powder, which is marked as (Si50-C50) powder.
Then, preparing slurry, which comprises the following steps:
dispersing the cationic polyurethane and Si-PANI particles into deionized water, magnetically stirring for 180min, and performing ultrasonic treatment for 120min to uniformly mix to obtain the silicon/polyaniline slurry. In the silicon/polyaniline slurry, the mass fraction of polyelectrolyte is 15%, and the mass ratio of polyelectrolyte to the total mass of silicon/polyaniline powder is 6: 1.
Dispersing anionic polyurethane and (Si50-C50) powder into deionized water, magnetically stirring for 180min, performing ultrasonic treatment for 120min, and uniformly mixing to obtain the 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: dropwise adding 1.5ml of silicon/polyaniline slurry on the surface of the dried pretreated substrate, spin-coating at the spin-coating speed of 2600rpm for 50s, and then vacuum-drying at 50 ℃ for 3 min; and then, dropwise adding the same mass of 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 silicon-based composite film with a total self-assembly layer number of 10, which is marked as (Si/PANI-Si/C)10-1。
And finally, high-temperature sintering treatment: will (Si/PANI-Si/C)10And-1, placing the silicon-carbon composite electrode material in a nitrogen atmosphere, and sintering at a 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 from the room temperature to 750 ℃, the temperature rising rate is 2 ℃/min, the sintering temperature is kept for 120min at the highest calcining temperature, and then the sintering temperature is naturally cooled and reduced, which is marked as (Si/C)10-1。
Material and electrochemical characterization:
fig. 2 to 4 schematically show scanning electron micrographs of the silicon carbon composite electrode materials prepared in examples 1, 2 and 3 of the present invention, respectively. Referring to fig. 2, 3 and 4, it can be seen that the carbon nanotube CNTs are uniformly interlaced and intertwined to form a conductive frame, and the silicon particles are uniformly embedded in the channels formed by overlapping the carbon nanotube CNTs and adhered to the surface of the carbon nanotube CNTs. And interconnected channels are reserved between the silicon-carbon composite electrode material layers to provide space for the volume expansion of silicon.
Table 1 shows the specific discharge capacity of the silicon-carbon composite electrode material according to the cycle number at a current density of 500mAh/g when the silicon-carbon composite electrode material prepared in each of the above embodiments 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 were directly used as battery active materials, and the charge-discharge cycle test was performed on the silicon-carbon composite electrode materials by using a half-cell test method to examine the performances such as cycle reversibility and discharge capacity. The half cell mainly comprises a metal lithium sheet as a negative electrode, a PP/PE/PP film as a diaphragm, and a silicon-carbon composite electrode material as a positive electrode and prepared by the above embodiments respectively, wherein the electrolyte is 1M LiPF6+ 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 was added. 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 respectively prepared in the above embodiments are shown in Table 1.
Figure BDA0003345427280000131
Figure BDA0003345427280000141
TABLE 1
According to table 1, the test results show that half cells assembled by the silicon-carbon composite anode materials respectively prepared in example 1, example 2 and example 3 of the present invention all have good initial capacity. Moreover, the initial discharge specific capacity can respectively reach 1191.1mAh/g, 2182.2mAh/g and 1739.3mAh/g, and the 2 nd circle discharge specific capacity is 996mAh/g, 1324.3mAh/g and 1093.8 mAh/g. Compared with the 2 nd circle of discharge specific capacity, after 100 cycles, the silicon-carbon composite anode materials of the embodiment 1 and the embodiment 2 maintain higher discharge capacity retention rates which can respectively reach 86.4 percent and 80.2 percent. After 100 cycles, the coulombic efficiencies of the silicon-carbon composite negative electrode materials of example 1, example 2 and example 3 were 100.7%, 103.88% and 101.53%, respectively, and all showed very good cycle reversibility. Therefore, the silicon-carbon composite electrode materials respectively prepared in the embodiments of the invention have 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 it is apparent to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A preparation method of a silicon-carbon composite electrode material comprises the following steps:
pretreating the substrate by adopting a pretreatment solution to obtain a conductive substrate with charges on the surface;
electrostatically adsorbing a conductive polymer on the surface of a 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 surface of the conductive substrate opposite to the electrical property of the surface of the conductive substrate, and drying to obtain a silicon-based composite film;
and (3) sintering the silicon-based composite film at high temperature under the protection of inert atmosphere to obtain the silicon-carbon composite electrode material.
2. The method for preparing the silicon-carbon composite electrode material according to claim 1, wherein the pretreatment comprises the following steps: placing the substrate in a pretreatment solution with solute mass fraction of 0.01-10% to soak for 5-60 min, drying, cleaning with ultrapure water,
wherein the substrate is a copper foil, an aluminum foil, a zinc film, a carbon-coated copper foil, a nickel-chromium film, a titanium-gold film or an indium tin oxide film;
the pretreatment solution is sodium hydroxide solution, hydrochloric acid solution, polyacrylic acid solution, polyethyleneimine solution, polyacrylamide hydrochloride solution, sodium carboxymethylcellulose solution or polyurethane solution.
3. The preparation method of the silicon-carbon composite electrode material as claimed in claim 1, wherein in the preparation process of the silicon/carbon composite powder, the silicon material and the carbon material are mixed by adopting an ultrasonic, ball milling, sand milling or grinding mode,
the mass ratio of silicon in the silicon material to carbon in the carbon material is 0-100: 100 to 0;
in the preparation process of the silicon/conductive polymer powder, the mass ratio of silicon to the conductive polymer of the silicon material is (100-0): 0 to 100 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.
4. The method for preparing the silicon-carbon composite electrode material as claimed in claim 1 or 3, wherein 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 the simple substance silicon or the modified substance thereof, the silicon oxide SiOx or the modified substance thereof is at least one of particles, porous particles, nanowires or nanotubes with a particle size of 10 nm-10 μm, wherein 0< x < 2;
the conductive polymer is at least one of polyaniline, polypyrrole, polythiophene, polyacetylene and polyphenylacetylene;
the carbon material is at least one of graphite or a modified substance thereof, carbon fiber or a modified substance thereof, carbon nano tube or a modified substance thereof, graphene or a modified substance thereof, soft carbon or a modified substance thereof, hard carbon or a modified substance thereof, and amorphous carbon or a modified substance thereof.
5. The method for preparing the silicon-carbon composite electrode material as claimed in claim 1, wherein the preparation process of the silicon/conductive polymer slurry and the preparation process of the silicon/carbon slurry both comprise: respectively carrying out magnetic stirring and ultrasonic treatment on the silicon/conductive polymer powder and the silicon/carbon composite powder 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.
6. The method for preparing the silicon-carbon composite electrode material according to claim 1, wherein the polyelectrolyte is at least one of polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, polyurethane, polyvinyl sulfonic acid, polyvinyl pyrrolidone, polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyethylene (ene) amine, 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 fractions of the polyelectrolytes in the silicon/conductive polymer slurry and the silicon/carbon slurry are both 1-80%, and the mass ratio of the total mass of the silicon/conductive polymer powder and the total mass of the silicon/carbon composite powder to the polyelectrolytes is 1: 1-70.
7. The method for preparing a silicon-carbon composite electrode material as claimed in claim 1, wherein the manner of alternately depositing the silicon/conductive polymer paste and the silicon/carbon paste is spin coating, dipping or spraying.
8. The method for preparing the silicon-carbon composite electrode material as claimed in claim 7, wherein the speed of spin coating a layer of the silicon/conductive polymer slurry film or the silicon/carbon slurry film is 500-5000 rpm, and/or the spin coating time is 10-300 s;
the drying is at least one of air drying, vacuum drying and high-temperature drying, and the drying time is 1-720 min.
9. The method for preparing the silicon-carbon composite electrode material according to claim 1, wherein the high-temperature sintering treatment process comprises the following steps: the sintering temperature is gradually increased from room temperature to 200-1000 ℃, the heating rate is 2-5 ℃/min, and the sintering temperature is kept at the highest calcining temperature for 0-360 min and then is naturally cooled.
10. The silicon-carbon composite electrode material prepared by the method for preparing the silicon-carbon composite electrode material according to any one of claims 1 to 9,
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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