CN113964307A - Silicon-carbon negative electrode material of lithium ion battery and preparation method thereof - Google Patents

Silicon-carbon negative electrode material of lithium ion battery and preparation method thereof Download PDF

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CN113964307A
CN113964307A CN202111236998.1A CN202111236998A CN113964307A CN 113964307 A CN113964307 A CN 113964307A CN 202111236998 A CN202111236998 A CN 202111236998A CN 113964307 A CN113964307 A CN 113964307A
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carbon
silicon
lithium ion
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ion battery
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赵明才
张娟
龚喜
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Jiangsu Zaichi Technology Co ltd
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    • 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
    • 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
    • H01M4/00—Electrodes
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • 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 cathode material of a lithium ion battery. The silicon-carbon negative electrode material is a compact and non-porous core-shell structure, the core of the core-shell structure comprises nano silicon, a carbon nano tube, amorphous carbon and a nano graphite sheet, and the shell layer of the core-shell structure is a carbon coating layer. The invention mainly forms a compact nonporous structure with a conductive network in the material by combining self-crosslinking assembly, pressurization treatment and carbonization coating, wherein nano silicon, carbon nano tubes and amorphous carbon are tightly embedded between the uniformly dispersed nano graphite sheets, thereby realizing the compact structure, promoting electron transmission, simultaneously buffering the expansion of the internal material, and reducing the formation of silicon and SEI film exposed on the surface of the carbon coating layer which is smooth and uniform outside the material. The material has excellent cycle performance and rate capability, and can meet the requirements of high-specific energy lithium ion batteries.

Description

Silicon-carbon negative electrode material of lithium ion battery and preparation method thereof
Technical Field
The invention relates to the field of lithium ion battery cathode materials, in particular to a lithium ion battery silicon-carbon cathode material and a preparation method thereof.
Background
The lithium ion battery has the advantages of high output voltage, large specific energy, long cycle life, good safety performance and the like, has been widely applied in the fields of mobile communication, notebook computers, future electric vehicles and the like, and gradually replaces the traditional chemical power sources such as lead-acid batteries and the like. Particularly, with the increasingly prominent worldwide energy and environmental problems and the call for carbon peak reaching, carbon neutralization and various works proposed by the government of China, the lithium ion battery has become the key point of the development in the field of new energy materials.
For lithium ion batteries, the performance of the positive and negative electrode materials directly determines the performance of the battery. In the aspect of the negative electrode material, the natural graphite material has the advantages of rich reserve capacity, low price, higher specific capacity, lower voltage platform and the like, and becomes the negative electrode material adopted by the traditional lithium ion battery. However, the theoretical capacity of the graphite carbon material is low (only 372mAh/g), which drives the lithium ion battery engineering industry to search for a new generation of electrode material with high energy density.
Elemental silicon, which is considered to be one of the most likely materials to replace graphite anodes because of its very high theoretical specific capacity, receives increasing attention as an anode material, however, silicon will produce about 300% volume expansion/contraction during lithium intercalation/deintercalation, and easily cause material agglomeration or powdering during cycling, resulting in rapid capacity attenuation, and thus cannot meet practical requirements.
In order to avoid the respective disadvantages of the two materials, researchers take various measures to utilize the two materials in a composite way, so that the purpose of complementary advantages can be achieved. Patent CN 103474667B discloses a core-double shell composite lithium ion battery cathode material composed of a core made of nano silicon/graphite particles, a first carbon coating layer made of carbon nanotubes and/or amorphous carbon, and an organic cracking carbon layer, and a preparation method thereof. The material has excellent rate charge and discharge performance and good cycle life, but the combination strength of the carbon source part with a loose internal structure and the silicon material is not enough, so that the carbon source part and the silicon material are not uniformly compounded, and the energy density and the cycle conductivity of the material still need to be further improved.
In a word, the carbon-silicon material prepared by compounding in the prior art is difficult to have fast electron and ion transmission rate and good cycle stability on the basis of keeping high specific energy, and simultaneously, the carbon-silicon material also meets the requirements of lower production cost and simple and environment-friendly process flow.
Disclosure of Invention
The invention aims to provide a silicon-carbon composite cathode material of a lithium ion battery, which is used for improving the specific energy of the silicon-carbon composite cathode material and has higher cycle performance and rate capability.
A silicon-carbon negative electrode material of a lithium ion battery is of a core-shell structure, wherein a core comprises silicon nanoparticles, graphite nanosheets, a one-dimensional conductive material and amorphous carbon; the shell is a carbon coating layer.
The mass ratio of the silicon nanoparticles to the graphite nanosheets to the one-dimensional conductive material to the amorphous carbon is (1-50): (1-50): (1-20): (1-10).
The one-dimensional conductive material is a carbon nanotube; the carbon nanotube has a diameter of 2-20nm and a length of 1-30 μm.
The D50 particle size of the lithium ion battery silicon-carbon composite negative electrode material is 8-24 mu m, and the specific surface area is 1.3m2/g～6.8m2(ii)/g, compacted density of 1.0g/cm3～1.8g/cm3。
The preparation method of the silicon-carbon cathode material of the lithium ion battery comprises the following steps:
step 1, dispersing the nano graphite sheet and a cross-linking agent in an organic solvent to perform a cross-linking reaction;
step 2, adding nano silicon particles, a one-dimensional conductive material and a first carbon source into the dispersion liquid obtained in the step 1, uniformly mixing, evaporating the solvent to dryness, and performing pressurization treatment to obtain a silicon carbon polymer;
step 3, calcining and crushing the silicon carbon polymer;
and 4, coating by using a second carbon source to obtain the cathode material.
The one-dimensional conductive material is selected from carbon nanotubes; the carbon nanotube has a diameter of 2-20nm and a length of 1-30 μm.
The first carbon source includes, but is not limited to, any 1 or at least 2 combinations of alkanes, cycloalkanes, alkenes, alkynes, aromatics, polymers, saccharides, organic acids, and resinous polymer materials, and other organic carbon sources commonly used in the art for coating can also be used in the present invention, preferably any 1 or at least 2 combinations of methane, ethane, ethylene, phenol, asphalt, epoxy resin, phenol-formaldehyde resin, furfural resin, urea-formaldehyde resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, acrylic resin, and polyacrylonitrile.
The mass ratio of the silicon nanoparticles to the graphite nanoplatelets to the one-dimensional conductive material to the first carbon source is (1-50): (1-50): (1-20): (1-10).
The diameter of the nano graphite sheet is 10-20 μm, and the thickness is 50-100 nm.
In the step 1, a pH buffer solution is also required to be added into the organic solvent, wherein the pH buffer solution is one or a combination of more of acetic acid, ammonium acetate, potassium acetate, ammonia water, ammonium chloride, hypophosphorous acid, sodium hypophosphite, potassium hypophosphite, sodium carbonate or sodium bicarbonate; the pH value is 5-10.
In the step 1, the cross-linking agent is a silane cross-linking agent; the silane cross-linking agent is any 1 or combination of at least 2 of dealcoholized silane, deacidified silane or ketoxime silane.
The crosslinking agent is preferably one or a combination of methyltrimethoxysilane, vinyltriethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, triacetoxyethylsilane, propyltriacetoxysilane, n-heptyltrichlorosilane, octyltrichlorosilane, decyltrichlorosilane, dodecyltrichlorosilane, tetradecyltrichlorosilane, 1, 8-bis (trichlorosilane) octane, 1, 10-bis (trichlorosilane) decane, methyltributanoxime silane, or vinyltributoxime silane.
In step 1, the organic solvent is 1 or a combination of at least 2 of tetrahydrofuran, dimethylacetamide, C1-C6 alcohol and C3-C8 ketone, the C1-C6 alcohol is 1 or a combination of at least 2 of methanol, ethanol, ethylene glycol, propanol, isopropanol, 1, 2-propanediol, 1, 3-propanediol, glycerol, N-butanol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, N-pentanol and 2-hexanol, and the C3-C8 ketone is 1 or a combination of at least 2 of acetone, methyl ethyl ketone, methyl propyl ketone, N-methyl pyrrolidone, ethyl propyl ketone, methyl butyl ketone, ethyl N-butyl ketone, methyl amyl ketone and methyl hexyl ketone.
In the step 1, a constant-temperature stirring device is adopted for heating and stirring, the heating temperature is 90-120 ℃, the stirring speed is 3000-6000 r/min, and the heating and stirring time is 2-5 h; the reaction process is carried out in an air environment with the humidity of 20-60%.
In the step 2, the D50 particle size of the nano silicon particles is 20-80 nm.
In the step 2, the heating temperature in the mixing process is 40-60 ℃, the stirring speed is 2000-5000 r/min, and the mixing time is 2-4 h.
In the step 2, the solvent is dried by adopting one or more of fluidized drying, vacuum drying, spray drying, suction filtration drying, freeze drying, rotary drying, infrared drying and microwave drying.
The spray drying is any 1 of two-fluid, gas-electricity combined two-fluid and four-fluid spray; preferably, when the spray drying is performed, the mixed solution is filled into a closed spray drying device in a spray form, and protective gas is filled into the closed spray drying device, wherein the protective gas is 1 or at least 2 of nitrogen, helium, argon and neon; and simultaneously controlling the pressure of spray drying to be 0.2-0.4 Mpa, the inlet temperature to be 100-250 ℃, the outlet temperature to be 60-140 ℃, and the frequency of a feeding pump of the spray drying equipment to be 10-30 Hz.
The vacuum drying adopts a vacuum drying machine with a condensing system, the temperature condition is 50-150 ℃, and the vacuum negative pressure is not more than 0.1 Mpa.
The pressurizing treatment in the step 2 is 1 or at least 2 of extrusion forming treatment, cold die pressing treatment, hot die pressing treatment and hot isostatic pressing treatment.
Preferably, the hot isostatic pressing treatment is to place the dried product in a hot isostatic pressing machine, increase the temperature under pressure, increase the temperature to 250-400 ℃ under 60-150 MPa, keep the temperature and pressure for 1-3 h, and then cut off the power and cool the product to room temperature along with the furnace to obtain the silicon carbon polymer.
Preferably, the cold die pressing treatment and the hot die pressing treatment control the compaction degree by controlling the die filling ratio, namely the ratio of the mass of the composite material to the volume of the die; preferably, the hot pressing treatment is to fill the dried product into a mold, wherein the filling ratio of the mold is 0.4-2.7 g/cm3And (3) carrying out hot pressing at the temperature of 150-300 ℃, under the pressure of 5-30 MPa for 30-100 min, and standing and cooling to room temperature to obtain the silicon carbon polymer.
Preferably, the extrusion molding treatment comprises putting the dried product into a double screw machine or an internal mixer for primary compaction of raw materials, and then carrying out secondary compaction through a roller press to obtain the silicon-carbon polymer.
In the step 3, in the calcining process, the temperature is firstly increased from room temperature to 300-400 ℃, the temperature is kept for 1-2 hours, then the temperature is continuously increased to 800-1000 ℃, and the temperature is kept for 3-4 hours; the sintering is carried out in a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a pushed slab kiln or a tubular furnace; the sintering process is carried out in a protective atmosphere, wherein the protective atmosphere is 1 or at least 2 of nitrogen, helium, argon and neon.
In the step 3, in the crushing process, crushing and grading the silicon-carbon polymer to obtain a silicon-carbon core material with the median particle size of 8-40 microns; preferably, the crushing is carried out in a crusher selected from at least one of a turbine crusher, a jaw crusher and a raymond mill.
In step 4, the coating method is selected from any one of a gas phase coating method, a liquid phase coating method and a solid phase coating method.
Preferably, the gas phase coating method comprises the following steps: and (2) putting the silicon-carbon core material into a vapor deposition furnace, introducing protective gas, heating to 600-800 ℃, roasting for 4-8 hours, and introducing organic carbon source gas for chemical vapor deposition for 1.5-2 hours during the roasting, so that a smooth and uniform carbon coating layer can be coated outside the material.
Preferably, the liquid phase coating method comprises the following steps: adding a silicon-carbon core material into a dispersion solvent with a liquid-phase coated carbon source, stirring, fusing and drying to obtain a coating, putting into a furnace with protective gas for sintering, wherein the sintering temperature is 800-1000 ℃, and the high-temperature sintering time is 5-8 h, so that a smooth and uniform carbon coating layer can be coated outside the material.
Preferably, the solid phase coating method comprises the following steps: mixing a silicon-carbon core material and a coated organic carbon source, placing the mixture in a coating machine for high-temperature solid-phase coating to obtain a silicon-carbon solid-phase coating material, putting the silicon-carbon solid-phase coating material into a carbonization furnace, introducing protective gas, carbonizing at the temperature of 600-1200 ℃ for 1.5-4 h, and naturally cooling to form a smooth and uniform carbon coating layer on the outer surface of the material.
Preferably, the protective gas is 1 or a combination of at least 2 of nitrogen, helium, argon, and neon.
In the step 4, the coated material is further required to be subjected to refining screening, wherein the refining method is a combination of 1 or at least 2 of mechanical crushing, airflow crushing or ball milling crushing, and the material is subjected to spheroidization treatment, and the screening mode is vibration screening and 200-mesh screening to obtain the silicon-carbon negative electrode material with the D50 particle size of 8-24 microns.
A lithium ion battery comprises the silicon-carbon negative electrode material.
Advantageous effects
The silicon-carbon negative electrode material is assembled through self-crosslinking, a three-dimensional conductive support is formed among the nano graphite sheets, nano silicon, carbon nano tubes and amorphous carbon are embedded among the graphite sheet layers and are further tightly combined through pressurization treatment, and a smooth and uniform carbon coating layer is coated outside the material, so that the silicon-carbon negative electrode material with a compact and non-porous core-shell structure inside is obtained.
A compact nonporous structure with a conductive network is formed in the material by combining self-crosslinking assembly, pressurization treatment and carbonization coating, wherein nano silicon, carbon nano tubes and amorphous carbon are tightly embedded among the uniformly dispersed nano graphite sheets, so that a compact flexible structure is realized, electron transmission is promoted, and the specific energy of the material is improved; meanwhile, the expansion of the internal material is buffered, and the formation of silicon and SEI (solid electrolyte interphase) films exposed on the surface can be reduced by the smooth and uniform carbon coating layer on the external part of the material, so that the material has higher first efficiency and cycle stability.
The obtained silicon-carbon negative electrode material has the reversible specific capacity of more than 1100mAh/g, the first cycle coulomb efficiency of more than 85 percent, the capacity retention rate of more than 90 percent after 50 cycles, low preparation cost, simple and controllable process and suitability for the negative electrode material of a high-capacity lithium ion battery.
Drawings
Fig. 1 is a cross-sectional SEM image of a silicon carbon composite negative electrode material of a lithium ion battery of example 1.
Fig. 2 is a cross-sectional SEM image of the silicon carbon composite negative electrode material of the lithium ion battery of comparative example 1.
Fig. 3 is a cross-sectional SEM image of the lithium ion battery silicon carbon composite anode material of comparative example 2.
Fig. 4 is a graph of a compaction cycle for a silicon carbon composite anode material of a lithium ion battery of example 1.
Detailed Description
Example 1
(1) Adding 7g of nano graphite sheet, 2 g of octyl trichlorosilane and 10 g of sodium bicarbonate into 150g of mixed solution of methanol and isopropanol in a mass ratio of 4:1, stirring by using a constant-temperature stirring device at a heating temperature of 100 ℃ for 3h at a rotation speed of 4000r/min to fully hydrolyze and condense the octyl trichlorosilane in the precursor solution to form cross-linked product polymeric silica gel, wherein the reaction process is as follows:
2nCH3(CH2)6CH2SiCl3+3nH2O→[CH3(CH2)6CH2SiO3Si(CH2)6CH3]n+6nHCl，
obtaining nano graphite sheet dispersion liquid with a three-dimensional cross-linked bracket inside;
(2) adding 8 g of nano silicon particles, 4 g of carbon nano tubes and 7g of asphalt into the prepared nano graphite sheet dispersion liquid, and stirring and mixing for 30min in a dispersion machine at the rotating speed of 2000r/min to form a mixed liquid; filling the mixed solution into a closed spray drying device in a spraying mode, introducing nitrogen into the closed spray drying device, and controlling the pressure of the closed spray drying device to be 0.2Mpa, the temperature of a feed inlet to be 180 ℃, the temperature of a discharge outlet to be 100 ℃ and the flow rate of the formed spray to be 6.4 mL/min; placing the dried product in a hot isostatic pressing machine, pressurizing and heating, obtaining three materials with different densities by adjusting different pressure values (adjusting within the range of 50-100 MPa), keeping the temperature to 350 ℃ in the pressurizing process, keeping the temperature and the pressure for 2h, and then cutting off the power and cooling to the room temperature along with the furnace to obtain a silicon carbon polymer;
(4) putting the silicon carbon polymer into a box type furnace, heating to 300 ℃ at a heating rate of 5 ℃/min, keeping the heat treatment temperature for 1h, then continuously heating to 900 ℃ at the same speed, keeping the temperature for 3.5h, naturally cooling to room temperature, and introducing protective gas nitrogen in the whole process; crushing, grading and fine screening the sintered product in a Raymond machine to obtain a silicon-carbon core material with the median particle size of 20 mu m;
(5) dispersing the obtained silicon-carbon core material in absolute ethyl alcohol, simultaneously adding sucrose accounting for 5% of the weight of the silicon-carbon core material, fully stirring for 1h, and then performing secondary drying granulation by using a spray drying method, wherein the inlet temperature during spray drying is controlled to be 150 ℃, the discharge port temperature is controlled to be 80 ℃, so as to obtain material particles after liquid phase coating modification; and (3) performing spheroidization treatment on the material particles by using a ball mill, sieving the ball-milled material by using a 200-mesh sieve, continuously performing ball milling on the powder which is not sieved, and repeatedly iterating until all the powder is sieved to obtain the silicon-carbon negative electrode material with the D50 particle size of 16 microns.
Example 2
The difference from example 1 is that step (1):
adding 7g of graphite nanoplatelets, 2 g of n-heptyl trichlorosilane and 12 g of sodium bicarbonate into 150g of mixed solution of methanol and isopropanol with the mass ratio of 4:1, stirring by using a constant-temperature stirring device at the heating temperature of 100 ℃ for 2.5h at the rotating speed of 4500r/min to fully hydrolyze and condense the n-heptyl trichlorosilane in the precursor solution to form cross-linked product polymeric silica gel, wherein the reaction process is as follows:
2nCH3(CH2)5CH2SiCl3+3nH2O→[CH3(CH2)5CH2SiO3Si(CH2)5CH3]n+6nHCl，
obtaining nano graphite sheet dispersion liquid with a three-dimensional cross-linked bracket inside;
and preparing the silicon-carbon cathode material under the same other process conditions.
Example 3
The difference from example 1 is that step (1):
adding 7g of graphite nanoplatelets, 3 g of decyl trichlorosilane and 10 g of sodium bicarbonate into 150g of mixed solution of methanol and isopropanol in a mass ratio of 4:1, stirring by using a constant-temperature stirring device at the heating temperature of 120 ℃ for 4h at the rotation speed of 3500r/min to fully hydrolyze and condense the decyl trichlorosilane in the precursor solution to form cross-linked product polymeric silica gel, wherein the reaction process is as follows:
2nCH3(CH2)8CH2SiCl3+3nH2O→[CH3(CH2)8CH2SiO3Si(CH2)8CH3]n+6nHCl，
obtaining nano graphite sheet dispersion liquid with a three-dimensional cross-linked bracket inside;
and preparing the silicon-carbon cathode material under the same other process conditions.
Example 4
The difference from example 1 is that step (1):
adding 7g of nano graphite sheet, 4 g of tetradecyl trichlorosilane and 8 g of sodium bicarbonate into 150g of mixed solution of methanol and isopropanol in a mass ratio of 4:1, stirring by using a constant-temperature stirring device at the heating temperature of 150 ℃, stirring for 4.5h at the rotation speed of 4000r/min to fully hydrolyze and condense the tetradecyl trichlorosilane in the precursor solution to form crosslinked product polymeric silica gel, wherein the reaction process is as follows:
2nCH3(CH2)11CH2SiCl3+3nH2O→[CH3(CH2)11CH2SiO3Si(CH2)11CH3]n+6nHCl，
obtaining nano graphite sheet dispersion liquid with a three-dimensional cross-linked bracket inside;
and preparing the silicon-carbon cathode material under the same other process conditions.
Example 5
The difference from the example 1 is that the hot isostatic pressing treatment in the step (2) is changed into hot embossing treatment, and the specific steps are as follows:
and filling the dried product into a mold, wherein the filling ratio of the mold is 1.5g/cm3, the hot pressing temperature is 200 ℃, the pressurizing pressure is 20MPa, the hot pressing time is 60min, and standing and cooling to room temperature to obtain the silicon carbon polymer.
And preparing the silicon-carbon cathode material under the same other process conditions.
Example 6
The difference from the embodiment 1 is that the liquid phase coating modification in the step (4) is changed into gas phase coating modification, and the specific steps are as follows:
and (3) putting the silicon-carbon core material into a vapor deposition furnace, introducing protective gas, heating to 700 ℃, roasting for 7 hours, and introducing organic carbon source gas for chemical vapor deposition for 2 hours during the heating to obtain a smooth and uniform carbon coating layer coated outside the material.
And preparing the silicon-carbon cathode material under the same other process conditions.
Example 7
The difference from the example 1 is that the liquid phase coating modification in the step (4) is changed into solid phase coating modification, and the specific steps are as follows:
mixing a silicon-carbon core material and a coating organic carbon source, placing the mixture in a coating machine for high-temperature solid-phase coating to obtain a silicon-carbon solid-phase coating material, then putting the silicon-carbon solid-phase coating material into a carbonization furnace, introducing protective gas, carbonizing at 800 ℃ for 3h, and naturally cooling to form a smooth and uniform carbon coating layer on the outer surface of the material.
And preparing the silicon-carbon cathode material under the same other process conditions.
Comparative example 1: without addition of cross-linking agents
The difference from example 1 is that step (1) (2):
adding 8 g of nano silicon particles, 4 g of carbon nano tubes, 7g of nano graphite sheets and 10 g of asphalt into 150g of mixed solution of methanol and isopropanol with the mass ratio of 4:1, and stirring and mixing for 30min in a dispersion machine at the rotating speed of 2000r/min to form mixed solution; subsequently, drying and hot isostatic pressing were carried out in a manner equivalent to that of example 1.
And preparing the silicon-carbon cathode material under the same other process conditions.
Comparative example 2: without pressure treatment
The difference from example 1 is that the liquid mixture is spray-dried in step (2), and then the sintering and carbonization in step (3) are performed without any pressurization treatment.
And preparing the silicon-carbon cathode material under the same other process conditions.
Electrochemical performance test
The electrochemical performance of the silicon-carbon composite negative electrode material is evaluated by assembling the silicon-carbon composite negative electrode material into a CR 2032-button half cell. The button cell manufacturing process comprises the following steps: the mass ratio of the active material (Si/C), the acetylene black, the CMC and the SBR is 80: 10: 4: 6, wherein the CMC is a 1% aqueous solution. The slurry was dispersed for 30min with a high shear mixer at 10000 rpm. The homogenized slurry was then uniformly coated on a copper foil 15 μm thick. Naturally drying, placing the copper foil in a vacuum drying oven at 80 ℃ for 10 hours, and compacting the dried copper foil by using a roller press; and punching the pole piece and cutting the pole piece into a circular piece with the diameter of 13 mm. Assembling a half cell in a glove box protected by high-purity argon, wherein a counter electrode sheet adopts metal lithium foil, a diaphragm adopts a polypropylene porous membrane, and an electrolyte 1MLiPF6 is prepared by mixing ethylene carbonate/dimethyl carbonate/methyl ethyl carbonate according to a volume ratio of 1: 1: 1 as an electrolyte, 1M LiPF6 and 5 wt% fluoroethylene carbonate were added to the mixed solution obtained in 1. The battery charging and discharging test is carried out in a multi-channel battery, and the test voltage range of the silicon-carbon material is 0.01V-1.5V (vs. Li +/Li).
After the electrode materials prepared in examples 1 to 7 and comparative examples 1 to 2 were manufactured into batteries, the main electrochemical test results were summarized as follows:
TABLE 1
Figure BDA0003318012540000081
Figure BDA0003318012540000091
According to the test results of the embodiment, the silicon-carbon cathode material provided by the invention realizes a compact structure and promotes electron transmission, so that the specific energy of the material is improved; meanwhile, the expansion of the internal material is buffered, and the formation of silicon and SEI (solid electrolyte interphase) films exposed on the surface can be reduced by the smooth and uniform carbon coating layer on the external part of the material, so that the material has higher first efficiency and cycle stability. The obtained silicon-carbon negative electrode material has the reversible specific capacity of more than 1100mAh/g, the first cycle coulomb efficiency of more than 85 percent, the capacity retention rate of more than 90 percent after 50 cycles, low preparation cost, simple and controllable process and suitability for the negative electrode material of a high-capacity lithium ion battery.
From the comparison between example 1 and comparative example 1, the silicon-based composite anode material obtained by the invention has better performance because: according to the invention, through adding the silane cross-linking agent, self-crosslinking assembly is realized in the preparation of the precursor material, the three-dimensional conductive support is formed among the nano graphite sheets, and the nano silicon, the carbon nano tubes and the amorphous carbon are embedded among the graphite sheet layers, so that the effect of uniformly dispersing the nano silicon and the carbon is achieved, the bonding strength of the nano graphite sheets and the amorphous material silicon, the amorphous carbon and the carbon nano tubes is enhanced, and the adaptability of the nano graphite sheets in the silicon-carbon negative electrode material is improved. It can be seen from the comparison between fig. 1 and fig. 2 that the structural strength of the synthesized composite material is significantly improved by the chemical bond bonding effect formed by the cross-linking reaction compared with the physical effect, such as the mechanical pressurization, so that the prepared silicon-carbon cathode material has a compact non-porous structure, the specific energy and the electron transport capability are increased, and the structure is stable.
As is clear from comparison between example 1 and comparative example 2, high-temperature carbonization was carried out without pressure treatment, and pores were formed after pyrolysis of the coated carbon, as shown in comparison between fig. 1 and fig. 3. The large amount of cavities reduce the lower compaction density of the material, and simultaneously separate various conductive agents in the material, so that the synergistic effect cannot be exerted, and the conductivity is greatly reduced, thereby leading the reversible specific capacity to be lower and the cycling stability to be poorer. From this, it is understood that the pressure treatment is important for preparing a high-capacity anode material.

Claims (10)

1. A silicon-carbon negative electrode material of a lithium ion battery is of a core-shell structure and is characterized in that a core comprises silicon nanoparticles, graphite nanosheets, a one-dimensional conductive material and amorphous carbon; the shell is a carbon coating layer.
2. The silicon-carbon negative electrode material of the lithium ion battery as claimed in claim 1, wherein the mass ratio of the silicon nanoparticles, the graphite nanosheets, the one-dimensional conductive material and the amorphous carbon is (1-50): (1-50): (1-20): (1-10).
3. The silicon-carbon anode material for the lithium ion battery according to claim 1, wherein the one-dimensional conductive material is a carbon nanotube;
the diameter of the carbon nano tube is 2-20nm, and the length of the carbon nano tube is 1-30 mu m;
the diameter of the nano graphite sheet is 10-20 mu m, and the thickness of the nano graphite sheet is 50-100 nm;
the D50 particle size of the lithium ion battery silicon-carbon composite negative electrode material is 8-24 mu m, and the specific surface area is 1.3m2/g～6.8m2(ii)/g, compacted density of 1.0g/cm3～1.8g/cm3。
4. The preparation method of the silicon-carbon negative electrode material of the lithium ion battery of claim 1 is characterized by comprising the following steps:
step 1, dispersing the nano graphite sheet and a cross-linking agent in an organic solvent to perform a cross-linking reaction;
step 2, adding nano silicon particles, a one-dimensional conductive material and a first carbon source into the dispersion liquid obtained in the step 1, uniformly mixing, evaporating the solvent to dryness, and performing pressurization treatment to obtain a silicon carbon polymer;
step 3, calcining and crushing the silicon carbon polymer;
and 4, coating by using a second carbon source to obtain the cathode material.
5. The method for preparing the silicon-carbon anode material of the lithium ion battery according to claim 4, wherein the one-dimensional conductive material is selected from carbon nanotubes; the diameter of the carbon nano tube is 2-20nm, and the length of the carbon nano tube is 1-30 mu m;
the first carbon source includes but is not limited to any 1 or at least 2 combinations of alkanes, cycloalkanes, alkenes, alkynes, aromatics, polymers, saccharides, organic acids, resin high molecular materials, other organic carbon sources commonly used in the art for coating can also be used in the present invention, preferably any 1 or at least 2 combinations of methane, ethane, ethylene, phenol, asphalt, epoxy resin, phenolic resin, furfural resin, urea resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, acrylic resin and polyacrylonitrile;
the mass ratio of the silicon nanoparticles to the graphite nanoplatelets to the one-dimensional conductive material to the first carbon source is (1-50): (1-50):
(1～20)：(1～10)；
the diameter of the nano graphite sheet is 10-20 μm, and the thickness is 50-100 nm.
6. The method for preparing the silicon-carbon anode material of the lithium ion battery according to claim 4, wherein in the step 1, a pH buffer solution is further added to the organic solvent, wherein the pH buffer solution is one or a combination of more of acetic acid, ammonium acetate, potassium acetate, ammonia water, ammonium chloride, hypophosphorous acid, sodium hypophosphite, potassium hypophosphite, sodium carbonate or sodium bicarbonate; the pH value is 5-10;
in the step 1, the cross-linking agent is a silane cross-linking agent; the silane cross-linking agent is any 1 or the combination of at least 2 of dealcoholized silane, deacidified silane or ketoxime-removed silane;
the crosslinking agent is preferably one or a combination of methyltrimethoxysilane, vinyltriethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, triacetoxyethylsilane, propyltriacetoxysilane, n-heptyltrichlorosilane, octyltrichlorosilane, decyltrichlorosilane, dodecyltrichlorosilane, tetradecyltrichlorosilane, 1, 8-bis (trichlorosilane) octane, 1, 10-bis (trichlorosilane) decane, methyltributanoxime silane, or vinyltributoxime silane. In step 1, the organic solvent is 1 or a combination of at least 2 of tetrahydrofuran, dimethylacetamide, C1-C6 alcohol and C3-C8 ketone, the C1-C6 alcohol is 1 or a combination of at least 2 of methanol, ethanol, ethylene glycol, propanol, isopropanol, 1, 2-propanediol, 1, 3-propanediol, glycerol, N-butanol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, N-pentanol and 2-hexanol, and the C3-C8 ketone is 1 or a combination of at least 2 of acetone, methyl ethyl ketone, methyl propyl ketone, N-methyl pyrrolidone, ethyl propyl ketone, methyl butyl ketone, ethyl N-butyl ketone, methyl amyl ketone and methyl hexyl ketone;
in the step 1, a constant-temperature stirring device is adopted for heating and stirring, the heating temperature is 90-120 ℃, the stirring speed is 3000-6000 r/min, and the heating and stirring time is 2-5 h; the reaction process is carried out in an air environment with the humidity of 20-60%.
7. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 4, wherein in the step 2, the D50 particle size of the nano silicon particles is 20-80 nm;
in the step 2, the heating temperature in the mixing process is 40-60 ℃, the stirring speed is 2000-5000 r/min, and the mixing time is 2-4 h;
in the step 2, the solvent is evaporated by adopting one or more of fluidized drying, vacuum drying, spray drying, suction filtration drying, freeze drying, rotary drying, infrared drying and microwave drying;
the spray drying is any 1 of two-fluid, gas-electricity combined two-fluid and four-fluid spray; preferably, when the spray drying is performed, the mixed solution is filled into a closed spray drying device in a spray form, and protective gas is filled into the closed spray drying device, wherein the protective gas is 1 or at least 2 of nitrogen, helium, argon and neon; meanwhile, the pressure of spray drying is controlled to be 0.2-0.4 Mpa, the inlet temperature is 100-250 ℃, the outlet temperature is 60-140 ℃, and the frequency of a feeding pump of spray drying equipment is 10-30 Hz;
the vacuum drying adopts a vacuum drying machine with a condensing system, the temperature condition is 50-150 ℃, and the vacuum negative pressure is not more than 0.1 Mpa;
the pressurizing treatment in the step 2 is 1 or at least 2 of extrusion forming treatment, cold die pressing treatment, hot die pressing treatment and hot isostatic pressing treatment;
preferably, the hot isostatic pressing treatment is to place the dried product in a hot isostatic pressing machine, pressurize and heat up the product to 250-400 ℃ under the pressure of 60-150 MPa, preserve heat and pressure for 1-3 h, and then cut off the power and cool the product to room temperature along with the furnace to obtain the silicon carbon polymer;
preferably, the cold die pressing treatment and the hot die pressing treatment control the compaction degree by controlling the die filling ratio, namely the ratio of the mass of the composite material to the volume of the die; preferably, the hot pressing treatment is to fill the dried product into a mold, wherein the filling ratio of the mold is 0.4-2.7 g/cm3Hot pressing at 150-300 ℃, pressurizing at 5-30 MPa, and hot pressing for 30-100 min, and standing and cooling to room temperature to obtain a silicon-carbon polymer;
preferably, the extrusion molding treatment comprises putting the dried product into a double screw machine or an internal mixer for primary compaction of raw materials, and then carrying out secondary compaction through a roller press to obtain the silicon-carbon polymer.
8. The preparation method of the silicon-carbon anode material for the lithium ion battery according to claim 4, wherein in the step 3, in the calcining treatment process, the temperature is raised to 300-400 ℃ from room temperature, the temperature is kept for 1-2 hours, then the temperature is raised to 800-1000 ℃ and the temperature is kept for 3-4 hours; the sintering is carried out in a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a pushed slab kiln or a tubular furnace; the sintering process is carried out under the protective atmosphere, wherein the protective atmosphere is 1 or the combination of at least 2 of nitrogen, helium, argon and neon;
in the step 3, in the crushing process, crushing and grading the silicon-carbon polymer to obtain a silicon-carbon core material with the median particle size of 8-40 microns; preferably, the crushing is carried out in a crusher selected from at least one of a turbine crusher, a jaw crusher and a raymond mill.
9. The method for preparing the silicon-carbon anode material of the lithium ion battery according to claim 4, wherein in the step 4, the coating method is selected from any one of a gas phase coating method, a liquid phase coating method or a solid phase coating method;
preferably, the gas phase coating method comprises the following steps: putting the silicon-carbon core material into a vapor deposition furnace, introducing protective gas, heating to 600-800 ℃, roasting for 4-8 h, introducing organic carbon source gas for chemical vapor deposition for 1.5-2 h, and coating a smooth and uniform carbon coating layer outside the material;
preferably, the liquid phase coating method comprises the following steps: adding a silicon-carbon core material into a dispersion solvent with a liquid-phase coated carbon source, stirring, fusing and drying to obtain a coating, putting into a furnace for protecting gas for sintering, wherein the sintering temperature is 800-1000 ℃, and the high-temperature sintering time is 5-8 h, so that a smooth and uniform carbon coating layer can be coated outside the material;
preferably, the solid phase coating method comprises the following steps: mixing a silicon-carbon core material and a coated organic carbon source, placing the mixture in a coating machine for high-temperature solid-phase coating to obtain a silicon-carbon solid-phase coating material, putting the silicon-carbon solid-phase coating material into a carbonization furnace, introducing protective gas, carbonizing at the temperature of 600-1200 ℃ for 1.5-4 h, and naturally cooling to form a smooth and uniform carbon coating layer on the outer surface of the material;
preferably, the protective gas is 1 or a combination of at least 2 of nitrogen, helium, argon and neon;
in the step 4, the coated material is further required to be subjected to refining screening, wherein the refining method is a combination of 1 or at least 2 of mechanical crushing, airflow crushing or ball milling crushing, and the material is subjected to spheroidization treatment, and the screening mode is vibration screening and 200-mesh screening to obtain the silicon-carbon negative electrode material with the D50 particle size of 8-24 microns.
10. A lithium ion battery comprising the silicon carbon negative electrode material of claim 1.
CN202111236998.1A 2021-10-24 2021-10-24 Silicon-carbon negative electrode material of lithium ion battery and preparation method thereof Pending CN113964307A (en)

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CN114361426A (en) * 2022-01-25 2022-04-15 山西大学 Preparation method and application of biomass-based silicon-carbon composite material
CN114975945A (en) * 2022-06-10 2022-08-30 洛阳联创锂能科技有限公司 Silicon-carbon negative electrode material for lithium ion battery and preparation method thereof
CN115050966A (en) * 2022-08-11 2022-09-13 楚能新能源股份有限公司 Silicon-carbon negative electrode material and preparation method thereof
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CN117117159A (en) * 2023-10-24 2023-11-24 琥崧智能装备(太仓)有限公司 Silicon-carbon negative electrode material and preparation method and application thereof
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Publication number Priority date Publication date Assignee Title
CN114361426A (en) * 2022-01-25 2022-04-15 山西大学 Preparation method and application of biomass-based silicon-carbon composite material
WO2023201774A1 (en) * 2022-04-22 2023-10-26 贝特瑞新材料集团股份有限公司 Negative electrode material and preparation method therefor, and lithium ion battery
CN114975945A (en) * 2022-06-10 2022-08-30 洛阳联创锂能科技有限公司 Silicon-carbon negative electrode material for lithium ion battery and preparation method thereof
WO2023245986A1 (en) * 2022-06-23 2023-12-28 北京卫蓝新能源科技有限公司 Core-shell structure micron silicon-carbon composite material and preparation method therefor, electrode, and battery
CN115084479A (en) * 2022-07-05 2022-09-20 浙江吉利控股集团有限公司 Lithium battery cathode composite material and preparation method thereof
CN115050966A (en) * 2022-08-11 2022-09-13 楚能新能源股份有限公司 Silicon-carbon negative electrode material and preparation method thereof
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