CN115832272B - Carbon-coated silicon anode material and preparation method and application thereof - Google Patents
Carbon-coated silicon anode material and preparation method and application thereof Download PDFInfo
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- CN115832272B CN115832272B CN202310163191.2A CN202310163191A CN115832272B CN 115832272 B CN115832272 B CN 115832272B CN 202310163191 A CN202310163191 A CN 202310163191A CN 115832272 B CN115832272 B CN 115832272B
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Abstract
The invention provides a carbon-coated silicon anode material, and a preparation method and application thereof. The preparation method of the anode material comprises the following steps: preparing a porous silicon source by using a silicon alloy and acid, and performing surface coating treatment by using a molten polymer; heating the obtained porous silicon source and sulfonate subjected to surface coating treatment to activate sulfonate to obtain negatively charged porous silicon solution; mixing graphite, a dispersing agent and quaternary ammonium salt to obtain a positively charged graphite solution, adding the negatively charged porous silicon solution, stirring, heating and drying to obtain graphite powder attached with porous silicon; and heating and carbonizing the graphite powder attached with the porous silicon in the mixed gas atmosphere, and removing the temperature to obtain the carbon-coated silicon anode material. According to the invention, the silicon negative electrode material with reasonable particle size and the graphite negative electrode material are used for compounding porous silicon, so that the compressive strength is improved, the cracking condition of the extrusion material when the silicon negative electrode material is made into a pole piece is reduced, the consumption of electrolyte is reduced, and the stability of the silicon negative electrode plate electrode is improved.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a carbon-coated silicon anode material and a preparation method and application thereof.
Background
Currently, lithium Ion Batteries (LIBs) are widely used in portable devices and electronic products, however, there are still some problems in the application of electric vehicles and renewable energy storage grids, including energy density, material cost, and use safety. Therefore, improving the energy density and cycle life of lithium ion batteries is a very important aspect.
Silicon (Si) has excellent theoretical capacity (4200 mAh/g), is developed as one of attractive candidate negative electrode materials, is about 10 times the available commercial graphite negative electrode capacity (about 370 mAh/g), and has great application potential. However, in Li + During the alloying/dealloying reaction, a large volume change of silicon (300%) can lead to structural failure of the anode material and to unstable Solid Electrolyte Interface (SEI), resulting in a rapid drop in capacity. Currently, various strategies are employed to enhance the junction of siliconThe structure is stable: for example, on the basis of carbon coating, the silicon particle size is reduced from bulk to nano-scale in order to produce Li + Significant volume expansion and structural damage are controlled during the reaction, or a macroporous structure is used as an auxiliary material, so that sufficient space is provided for the volume expansion of the silicon anode material, and the damage to the structure due to stress concentration is avoided.
However, the specific surface area of the nano silicon and a large amount of porous structures of the nano silicon-based material is too large, so that the contact area between the nano silicon-based material and electrolyte is increased, in addition, the carbon-coated silicon anode material is inevitably crushed and broken due to large roller pressure when a pole piece is manufactured, the material is directly contacted with the electrolyte, side reaction is increased, the consumption of the electrolyte is increased, and the stability of the pole piece is reduced. Therefore, how to design the grain size of the silicon anode material and the porous structure of the silicon anode material, improve the compressive strength and reduce the extrusion cracking problem when the silicon anode material is made into a pole piece is needed to be solved.
Disclosure of Invention
In order to solve the technical problems, the invention provides a carbon-coated silicon anode material and a preparation method and application thereof. According to the invention, the silicon negative electrode material with reasonable particle size is compounded with porous silicon based on the graphite negative electrode material, so that the compressive strength is improved, the cracking of the extrusion material when the silicon negative electrode material is made into a pole piece is reduced, the direct contact of the material with electrolyte is reduced, the consumption of the electrolyte is reduced, and the stability of the electrode of the silicon negative electrode is improved.
The invention is realized by the following scheme:
the first object of the present invention is to provide a method for preparing a carbon-coated silicon anode material, comprising the steps of:
(1) Preparing a porous silicon source by using a silicon alloy and acid, and performing surface coating treatment by using a molten polymer;
(2) Mixing the porous silicon source and sulfonate which are subjected to surface coating treatment and obtained in the step (1), activating the sulfonate, and endowing the surface of the material with negative charge to obtain a negatively charged porous silicon solution; the activation method is a method conventional in the art, preferably heat activation;
(3) Mixing graphite, a dispersing agent and quaternary ammonium salt to obtain a positively charged graphite solution, adding the negatively charged porous silicon solution obtained in the step (2), stirring, heating and drying to obtain graphite powder with porous silicon;
(4) And (3) heating and carbonizing the graphite powder with the porous silicon in the step (3) in a mixed gas atmosphere containing organic gas, removing the temperature, and sieving to obtain the carbon-coated silicon anode material.
In one embodiment of the invention, in step (1), one or more of the following conditions are satisfied:
1) The silicon alloy is selected from one or more of magnesium silicide, aluminum silicide, calcium silicide and iron silicide; the grain diameter of the silicon alloy is 0.15-3 mu m; further, the silicon content in the silicon alloy is more than or equal to 80wt%;
2) The acid is selected from one or more of hydrochloric acid, nitric acid, phosphoric acid, acetic acid and formic acid;
3) The acid content is 0.1-8wt%. Can be 0.1wt percent to 1wt percent, 1wt percent to 2wt percent, 2wt percent to 3wt percent, 3wt percent to 4wt percent, 4wt percent to 5wt percent, 6wt percent to 7wt percent and 7wt percent to 8wt percent; specifically, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%. Or any concentration value between any two values.
In one embodiment of the invention, in step (1), the steps of preparing the porous silicon source from the silicon alloy and the acid are: mixing silicon alloy and acid, and carrying out hot acid oscillation, pressure filtration, acid cleaning by water, pressure filtration, drying and dehydration at 45-80 ℃ to obtain the porous silicon source.
In one embodiment of the present invention, in the step (1), the mass-to-volume ratio of the silicon alloy to the acid is 1 to 10:20 to 50 (kg/L).
In one embodiment of the present invention, in step (1), the molten polymer is selected from one or more of polystyrene, polyethylene, polystyrene, polypropylene, and polyaniline.
In one embodiment of the present invention, in the step (1), the surface coating treatment method is as follows: and stirring and mixing the molten polymer and the porous silicon source, and heating and carbonizing to obtain the porous silicon source subjected to surface coating treatment.
Further, the mass ratio of the molten polymer to the porous silicon source is 0.2-18: 100; the heating carbonization temperature is 500-900 ℃; can be 500-600 ℃, 600-900 ℃, 700-900 ℃, 800-900 ℃, specifically 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃ and 900 ℃; or any temperature value between any two values. Heating and carbonizing for 1-12 h; can be 2 to 12 hours, 3 to 12 hours, 4 to 12 hours, 5 to 12 hours, 6 to 12 hours, 7 to 12 hours, 8 to 12 hours, 9 to 12 hours, 10 to 12 hours, 11 to 12 hours, and can be specifically 1, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours and 12 hours; or any time value between any two values.
In one embodiment of the present invention, in step (2), the sulfonate is selected from one or more of sodium styrene sulfonate, sodium polystyrene sulfonate, lithium styrene sulfonate, potassium styrene sulfonate, and potassium polystyrene sulfonate. Further, one or more of sodium styrenesulfonate, sodium polystyrene sulfonate, lithium polystyrene sulfonate, and lithium styrenesulfonate are preferable; the sulfonate salt may provide the material with a surface negative charge group.
In one embodiment of the present invention, in the step (2), the mass ratio of the porous silicon source and the sulfonate subjected to the surface film coating treatment is 50-250: 1-25; the heating temperature is 60-110 ℃. The dispersibility of the sulfonate salt is used here to disperse the porous silicon source by ultrasound.
In one embodiment of the present invention, in step (3), the quaternary ammonium salt is one or more of polydimethyl ammonium chloride, polydimethyl ammonium bromide, dodecylmethyl ammonium chloride, tetradecyl methyl ammonium chloride, hexadecyl methyl ammonium chloride, octadecyl methyl ammonium chloride, dodecylmethyl ammonium bromide, tetradecyl methyl ammonium bromide, hexadecyl methyl ammonium bromide, and octadecyl methyl ammonium bromide.
In one embodiment of the invention, in step (3), one or more of the following conditions are satisfied:
1) The graphite is obtained by graphitizing one or more of petroleum coke, asphalt cement and needle-shaped materials at high temperature;
2) The density of the glycerol solution is 5-10wt%;
3) The tap density of the graphite is 0.85g/cm 3 ~1.2g/cm 3 The Dv50 particle size is 3-26 mu m;
4) The temperature of the heating and drying is 70-120 ℃.
In one embodiment of the present invention, in the step (3), the mass ratio of graphite to quaternary ammonium salt is 20 to 100: 0.1-10; the mass volume ratio of the graphite to the glycerol solution is 100-500: 1 (g/L).
In one embodiment of the present invention, in the step (3), the mass ratio of the porous silicon source to the graphite in the negative porous silicon solution is 1 to 15: 25-60.
In one embodiment of the present invention, in step (3), adsorption of positive and negative amphiprotic surfaces is performed: and through zwitterionic polymerization, the positively charged graphite is used for electrostatically adsorbing the negatively charged porous silicon.
In one embodiment of the present invention, in step (3), the dispersant is selected from one or more of an alcohol solution, an ester solution, and polyethylene. The alcohol in the alcohol solution is one or more selected from glycerol, ethylene glycol, isopropanol, ethanol and propanol; glycerol is preferred. The esters are selected from glycerides.
In one embodiment of the present invention, in the step (4), the mixed gas atmosphere containing an organic gas includes an organic gas and an inert gas.
Further, the organic gas is hydrocarbon with 1-4C; the inactive gas is selected from one or more of nitrogen, helium, neon and argon.
Further, the hydrocarbon with 1-4C is selected from one or more of methane, ethane, ethylene, acetylene, propane, propyne, propylene, butyne, butylene and butane.
Further, the volume ratio of the organic gas to the inactive gas is 1-3: 1-5.
In one embodiment of the present invention, in the step (4), the temperature of the heating carbonization is 700 ℃ to 960 ℃, the air pressure is kept at 0kpa to 10kpa, and the heating carbonization time is 1h to 36h.
In one embodiment of the present invention, in the step (4), the temperature is reduced to 400 ℃ to 700 ℃ and kept constant for 1h to 5h.
The second object of the present invention is to provide a carbon-coated silicon anode material, wherein graphite is used as an inner core of the carbon-coated silicon anode material, a carbon-coated layer and a porous silicon layer are externally attached, and the graphite and the porous silicon layer are subjected to adsorption recombination through positive and negative charges; the porous silicon layer is coated by a film carbon layer.
In one embodiment of the invention, the carbon-coated silicon anode material meets one or more of the following conditions:
(1) Tap density of 0.7g/cm 3 ~1.35g/cm 3 Between them;
(2) The Dv50 particle size is 3.5-18 μm;
(3) Specific surface area SSA of 0.75m 2 /g~5m 2 Between/g;
(4) The pH value is 7-11.5, the pH value is obtained by mixing powder and pure water in a ratio of 9:1, and taking supernatant fluid for pH measurement;
(5) The carbon content is 35-97 wt%.
In one embodiment of the present invention, the carbon coating layer of the carbon-coated silicon anode material is a dense carbon layer, and the dense carbon layer is void-free or has few voids; preferably, the thickness of the carbon coating layer is 2-80 nm, which can be 2-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, 40-50 nm, 50-60 nm, 60-70 nm and 70-80 nm; such as 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, 40nm, 50nm, 60nm, 65nm, 75nm, 80nm, or any thickness value between any two values.
The third object of the invention is to provide a silicon negative electrode sheet, which comprises the carbon-coated silicon negative electrode material or the carbon-coated silicon negative electrode material prepared by the preparation method.
The fourth object of the present invention is to provide a method for preparing a silicon negative electrode sheet, comprising the following steps:
s1, dry-mixing and stirring a carbon-coated silicon anode material and a conductive material, and adding a binder and water to obtain a mixture;
s2, adding a conductive material, a binder and water into the mixture obtained in the step S1, stirring and mixing to obtain anode homogenate, coating the anode homogenate on at least one surface of the anode current collector to obtain an anode homogenate coating, drying and tabletting to obtain the silicon anode plate.
In one embodiment of the invention, the carbon-coated silicon anode material, the conductive material and the binder have a mass ratio of 80-99.6: 0.2-8: 0.2 to 15.0.
In one embodiment of the present invention, in S1, the stirring speed is 20r/min to 1000r/min, and the stirring time is 5min to 30min.
Further, the mixture is adjusted to have a solid content of 60% -80% by using water; preferably 65% -75%.
In one embodiment of the present invention, in S2, the solid content of the anode slurry is 40% -60%, preferably 45% -55%; the viscosity is 2.0 Pa.s-8 Pa.s, preferably 2.7 Pa.s-4 Pa.s; fineness is less than or equal to 0.25mm; the stirring speed is 1200 r/min-3000 r/min, and the stirring time is 30 min-200 min.
In one embodiment of the present invention, in S2, the thickness of the anode homogenized coating is 18 μm to 430 μm. Preferably, the thickness is 48 μm to 260 μm, for example, a thickness value that varies from 48 μm, 49 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 180 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, or any thickness value between any two values.
Further, the surface density of the anode homogenate on the obtained silicon cathode plate is 0.003g/cm 2 ~0.032g/cm 2 。
In one embodiment of the present invention, in S1 and S2, the conductive material is at least one selected from conductive carbon black, acetylene black, graphite, graphene, carbon micro-nano linear conductive material and carbon micro-nano tubular conductive material.
In one embodiment of the present invention, in S1 and S2, the binder is selected from one or more of acrylonitrile, vinylidene fluoride, vinyl alcohol, carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, methacryloyl, acrylic acid, lithium acrylate, acrylamide, amide, imide, acrylic acid ester, styrene-butadiene rubber, sodium alginate, chitosan, ethylene glycol, guar gum monomers, polymers and copolymers.
In one embodiment of the present invention, in S2, the negative electrode current collector is one or more of a copper foil, a porous copper foil, a nickel/copper foam foil, a zinc-plated copper foil, a nickel-plated copper foil, a carbon-coated copper foil, a nickel foil, a titanium foil, and a carbon-containing porous copper foil. Copper foil, zinc-plated, nickel-plated, and the like, carbon-coated copper foil, and the like are preferable.
The fifth object of the invention is to provide a lithium ion battery, which comprises the silicon negative electrode plate or the silicon negative electrode plate prepared by the preparation method.
A sixth object of the present invention is to provide a method for preparing a lithium ion battery, comprising the steps of: and winding the silicon negative plate, the isolating film and the positive plate to obtain a battery core, packaging the battery core into a battery shell, drying, injecting electrolyte, packaging, forming and separating the battery core to obtain the lithium ion battery.
In one embodiment of the present invention, the positive electrode active material in the positive electrode sheet is one or more of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickelate manganate, lithium nickelate aluminate, lithium manganese phosphate, lithium iron manganese phosphate and lithium iron phosphate.
Compared with the prior art, the technical scheme of the invention has the following advantages:
the invention utilizes sulfonate to have higher ionization degree, so that the modified porous silicon source has higher surface negative charge density, and after the modified porous silicon source and the graphite modified by quaternary ammonium salt are subjected to zwitterionic polymerization, the affinity of the graphite with positive surface charge and the porous silicon source can be obviously improved, the zwitterionic polymerization is stable and is not easy to damage, and the stability of the graphite powder attached with the porous silicon source in subsequent heating and carbonization can also be improved.
According to the invention, through surface coating treatment, the conductivity of the surface of the porous silicon source is improved, meanwhile, direct contact between silicon and electrolyte is avoided, stable SEI film formation in the circulation process is ensured, in addition, the graphite powder of the porous silicon is coated by the mixed gas containing organic gas and carbonized to form a carbon coating layer, so that the direct contact between the porous silicon source and large-particle graphite and the electrolyte is further reduced, side reaction is reduced, and the stability of the silicon negative electrode plate electrode is improved.
In order to improve the composite capability, sulfonate such as sodium styrene sulfonate and sodium polystyrene sulfonate is used for dispersing a porous silicon source to obtain a negatively charged porous silicon source, quaternary ammonium salts such as polydimethyl ammonium chloride and polydimethyl ammonium bromide are attached to the surface of graphite to obtain positively charged graphite, zwitterionic polymerization is carried out, the positively charged graphite is used for adsorbing the negatively charged porous silicon, mixed gas is used for wrapping carbonization, a small-particle porous silicon source is attached to the surface of large-particle graphite, more pore capacity of the large-particle graphite is utilized, the rolling and cracking of materials caused by high extrusion wheel pressure are reduced, and further the compressive strength is improved.
Drawings
In order that the invention may be more readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings, in which:
Fig. 1 is a schematic structural diagram of a carbon-coated silicon anode material of the present invention.
Description of the specification reference numerals: 1. coating a carbon layer; 2. a carbon coating layer; 3. a hole; 4. porous silicon; 5. graphite.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
The schematic structural diagram of the carbon-coated silicon anode material synthesized in the embodiment of the invention is shown in fig. 1, in which the structure is as follows: 1. coating a carbon layer; 2. a carbon coating layer; 3. a hole; 4. porous silicon; 5. graphite.
Example 1
The embodiment provides a carbon-coated silicon negative electrode material, a preparation method thereof, a corresponding silicon negative electrode sheet and application
1. The carbon-coated silicon anode material and the preparation method thereof are as follows:
(1) Magnesium silicide of silicon alloy with the grain diameter of 0.3-2.6 mu m and hydrochloric acid with the concentration of 0.36wt% are mixed according to the following ratio of 5: mixing the materials in a mass/volume ratio (kg/L) of 20, sequentially carrying out hot acid oscillation, pressure filtration, deionized water washing hydrochloric acid, pressure filtration, drying and dehydration on the obtained mixture at 55 ℃ to obtain a porous silicon source, and then carrying out surface film coating treatment on the obtained porous silicon source. Wherein, the specific steps of the surface coating treatment are as follows: the molten polymer polypropylene was combined with a porous silicon source according to 5:100, and placing the mixture in a reaction kettle, stirring the mixture to enable the mixture to be much Kong Guiyuan to thermally adsorb the molten polymer, and sending the obtained porous silicon source for adsorbing the molten polymer to a tubular furnace for carbonization for 12 hours at the temperature of 550 ℃ to obtain the porous silicon source with a surface coating.
(2) Adding 200g of the porous silicon source coated on the surface of the step (1) and 2g of sodium polystyrene sulfonate into 1L of deionized water in a reaction kettle provided with an ultrasonic disperser, dispersing the porous silicon source by utilizing the dispersion property of the sodium polystyrene sulfonate and heating to 95 ℃ to thermally activate the sulfonate sodium polystyrene sulfonate to obtain negatively charged porous silicon solution;
(3) Dissolving graphite graphitized by needle coke at high temperature in glycerol solution containing 6wt%, placing the graphite in a reaction kettle, adding ammonium dimethyl chloride, mixing to obtain positively charged graphite solution (mixing according to the amount of 500g graphite and 10g ammonium dimethyl chloride added into 1L glycerol solution), adding negatively charged porous silicon solution (controlling the mass ratio of porous silicon source to graphite in the negatively charged porous silicon solution to be 5:100), stirring, adsorbing the porous silicon source by the positively charged graphite (carrying out surface positive and negative amphoteric adsorption), and heating and drying at 110 ℃ to obtain graphite powder attached with porous silicon;
(4) The graphite powder with porous silicon is sent into a tube furnace, mixed gas of acetylene gas and Ar gas (the volume ratio of the acetylene gas to the Ar gas is 2:1) is introduced, the graphite powder with porous silicon wrapped by the mixed gas is obtained, the graphite powder with porous silicon is heated and carbonized (the temperature in the tube furnace is 750 ℃, the air pressure is kept at 1.2kPa, the time is 9 hours), the temperature is reduced to 550 ℃, the temperature is kept constant for 2 hours, the temperature is reduced, the carbon-coated silicon cathode material is obtained through sieving, and the particle diameter Dv50 of particles obtained through sieving is 3.5-18 mu m, and the following examples are the same.
2. Silicon negative plate and application:
2.1, a silicon negative electrode sheet and a preparation method thereof:
(1) The carbon-coated silicon anode material and the conductive carbon of the conductive material are placed in a container of a stirrer, dry-mixed and stirred for 10min at the rotating speed of 500r/min, and then binder (styrene-butadiene rubber and sodium carboxymethylcellulose are mixed according to 95wt% and 5 wt%) and deionized water are added in the container so as to add water until the solid content of substances in the container is 74.8%.
(2) And adding the conductive material, the binder and the deionized water into the container again, stirring at a high rotating speed of 1800r/min, and uniformly mixing for 120min until the solid content of substances in the container is 53.3%, thereby obtaining mixed slurry.
Wherein, the mass percentages of the carbon-coated silicon anode material, the conductive carbon of the conductive material and the binder are 95%, 2% and 3%, respectively.
(3) The viscosity of the mixed slurry in the step (2) is regulated to 3.9Pa.s, the fineness is less than or equal to 0.15mm, the anode homogenate is obtained, the anode homogenate is coated on the front and the back of the anode current collector copper foil, and the thickness is 116 mu m, and the anode homogenate surface density is 0.018g/cm 2 And (3) drying and tabletting the anode homogenate coating to obtain the silicon anode plate.
2.2, silicon negative electrode sheet application:
and winding the silicon negative plate, the isolating film and the positive plate (the positive active material is nickel cobalt lithium manganate) to obtain a battery core, packaging a battery shell of the battery core, drying, injecting electrolyte, packaging, forming and separating the electrolyte to obtain the lithium ion battery. (the separator used is one conventional in the art for the electrolyte).
Example 2
The embodiment provides a carbon-coated silicon negative electrode material, a preparation method thereof, a corresponding silicon negative electrode sheet and application
1. The carbon-coated silicon anode material and the preparation method thereof are as follows:
(1) Magnesium silicide of silicon alloy with the grain diameter of 0.3-2.6 mu m and hydrochloric acid with the concentration of 0.36wt% are mixed according to the following ratio of 5: mixing the materials in a mass/volume ratio (kg/L) of 20, carrying out hot acid oscillation at 55 ℃, filter pressing, deionized water cleaning hydrochloric acid, filter pressing, drying and dehydration on the obtained mixture to obtain a porous silicon source, and then carrying out surface film coating treatment on the obtained porous silicon source. Wherein, the specific steps of the surface coating treatment are as follows: the molten polymer polypropylene was stirred with a porous silicon source according to 5:100, and placing the mixture in a reaction kettle, stirring the mixture to enable the mixture to be much Kong Guiyuan to thermally adsorb the molten polymer, and sending the obtained porous silicon source of the adsorbed molten polymer to a tubular furnace with the temperature of 550 ℃ for carbonization for 12 hours to obtain the porous silicon source with a surface coating.
(2) 200g of the porous silicon source with the surface coated film in the step (1) and 5g of sodium polystyrene sulfonate are added into 1L of deionized water in a reaction kettle provided with an ultrasonic disperser, the dispersion performance of the sodium polystyrene sulfonate is utilized, the porous silicon source with the surface coated film is dispersed by ultrasonic, and the temperature is raised to 95 ℃ to thermally activate the sulfonate sodium polystyrene sulfonate, so that the negatively charged porous silicon solution is obtained.
(3) The needle coke graphitized graphite at high temperature is dissolved in glycerol solution containing 6wt percent, and is placed in a reaction kettle, and is added with dimethyl ammonium chloride to be mixed to obtain positively charged graphite solution (500 g of graphite and 10g of dimethyl ammonium chloride are added into 1L of glycerol solution to be mixed), then negatively charged porous silicon solution (the mass ratio of porous silicon source to graphite in the negatively charged porous silicon solution is controlled to be 5:100) is added to be stirred, the positively charged graphite adsorbs the porous silicon source (adsorption with positive and negative amphiprotic surfaces is carried out), and the graphite powder with porous silicon is obtained by heating and drying under the condition of 110 ℃.
(4) The graphite powder with the porous silicon is sent into a tube furnace, mixed gas of acetylene gas and Ar gas (the volume ratio of the acetylene gas to the Ar gas is 2:1) is introduced, the graphite powder with the porous silicon wrapped by the mixed gas is obtained, the graphite powder with the porous silicon is heated and carbonized (the temperature in the tube furnace is 700 ℃, the air pressure is kept at 1.2kPa for 10 hours), the temperature is reduced to 550 ℃, the temperature is kept for 2 hours, the temperature is reduced, the carbon-coated silicon anode material is obtained through sieving, and the particle diameter Dv50 obtained through sieving is 3.5-18 mu m.
2. Silicon negative plate and application:
2.1, a silicon negative electrode sheet and a preparation method thereof:
(1) The carbon-coated silicon anode material and the conductive carbon of the conductive material are placed in a container of a stirrer, dry-mixed and stirred for 10min at the rotating speed of 500r/min, and then binder (styrene-butadiene rubber and sodium carboxymethylcellulose are mixed according to 95wt% and 5 wt%) and deionized water are added in the container so as to add water until the solid content of substances in the container is 73.1%.
(2) Adding the conductive material, the binder and the deionized water into the container again, stirring at a high rotating speed of 1800r/min, and uniformly mixing for 120min until the solid content of substances in the container is 48.7%, thereby obtaining mixed slurry.
Wherein, the mass percentage of the carbon-coated silicon anode material, the conductive carbon of the conductive material and the binder is 95wt%, 2wt% and 3wt%.
(3) The viscosity of the mixed slurry in the step (2) is regulated to 3.1Pa.s, the fineness is less than or equal to 0.15mm, and negative electrode homogenate is obtained, and the negative electrode homogenate is coated on the front and the back of a copper foil of a negative electrode current collector, so that the surface density of the negative electrode homogenate with the thickness of 126 mu m is 0.02g/cm 2 And (3) drying and tabletting the anode homogenate coating to obtain the silicon anode plate.
2.2, silicon negative electrode sheet application:
and winding the silicon negative plate, the isolating film and the positive plate (the positive active material is nickel cobalt lithium manganate) to obtain a battery core, packaging a battery shell of the battery core, drying, injecting electrolyte, packaging, forming and separating the electrolyte to obtain the lithium ion battery.
Example 3
The embodiment provides a carbon-coated silicon negative electrode material, a preparation method thereof, a corresponding silicon negative electrode sheet and application
1. The carbon-coated silicon anode material and the preparation method thereof are as follows:
(1) Magnesium silicide of silicon alloy with the grain diameter of 0.3-2.6 mu m and hydrochloric acid with the concentration of 0.36wt% are mixed according to the following ratio of 5: mixing the mixture in an amount of 20 mass/volume ratio (kg/L), carrying out hot acid oscillation, pressure filtration, deionized water cleaning hydrochloric acid, pressure filtration and drying dehydration on the obtained mixture at 55 ℃ to obtain a porous silicon source, and then carrying out surface coating treatment on the obtained porous silicon source, wherein the specific steps of the surface coating treatment are as follows: the molten polymer polyethylene was stirred with a porous silicon source according to 5:100, and placing the mixture in a reaction kettle, stirring the mixture to enable the mixture to be much Kong Guiyuan to thermally adsorb the molten polymer, and sending the obtained porous silicon source of the adsorbed molten polymer to a tubular furnace with the temperature of 550 ℃ for carbonization for 12 hours to obtain the porous silicon source with a surface coating.
(2) 200g of the porous silicon source with the surface coated film in the step (1) and 10g of sodium polystyrene sulfonate are added into 1L of deionized water in a reaction kettle provided with an ultrasonic disperser, the dispersion performance of the sodium polystyrene sulfonate is utilized, the porous silicon source with the surface coated film is dispersed by ultrasonic, and the temperature is raised to 95 ℃ to thermally activate the sulfonate sodium polystyrene sulfonate, so that the negatively charged porous silicon solution is obtained.
(3) The needle coke graphitized graphite at high temperature is dissolved in glycerol solution containing 6wt percent, and is placed in a reaction kettle, and is added with dimethyl ammonium chloride to be mixed to obtain positively charged graphite solution (500 g of graphite and 10g of dimethyl ammonium chloride are added into 1L of glycerol solution to be mixed), then negatively charged porous silicon solution (the mass ratio of porous silicon source to graphite in the negatively charged porous silicon solution is controlled to be 5:100) is added to be stirred, the positively charged graphite adsorbs the porous silicon source (adsorption with positive and negative amphiprotic surfaces is carried out), and the graphite powder with porous silicon is obtained by heating and drying under the condition of 110 ℃.
(4) The graphite powder with the porous silicon is sent into a tube furnace, mixed gas of acetylene gas and Ar gas (the volume ratio of the acetylene gas to the Ar gas is 2:1) is introduced, the graphite powder with the porous silicon wrapped by the mixed gas is obtained, the graphite powder with the porous silicon is heated and carbonized (the temperature in the tube furnace is 650 ℃, the air pressure is kept at 1.2kPa for 15 hours), the temperature is reduced to 550 ℃, the temperature is kept for 2 hours, the temperature is reduced, the carbon-coated silicon anode material is obtained through sieving, and the particle diameter of the particles Dv50 obtained through sieving is 3.5-18 mu m.
2. Silicon negative plate and application:
2.1, a silicon negative electrode sheet and a preparation method thereof:
(1) The carbon-coated silicon anode material and the conductive carbon of the conductive material are placed in a container of a stirrer, dry-mixed and stirred for 10min at the rotating speed of 500r/min, and then binder (styrene-butadiene rubber and sodium carboxymethylcellulose are mixed according to 95wt% and 5 wt%) and deionized water are added in the container so as to add water until the solid content of substances in the container is 72.8%.
(2) Adding the conductive material, the binder and the deionized water into the container again, stirring at a high rotating speed of 1800r/min, and uniformly mixing for 120min until the solid content of substances in the container is 51.5%, thereby obtaining mixed slurry.
Wherein, the mass percent of the carbon-coated silicon anode material, the conductive carbon of the conductive material and the binder is 95wt%, 2wt% and 3 wt%.
(3) The viscosity of the mixed slurry in the step (2) is regulated to 3.4Pa.s, the fineness is less than or equal to 0.15mm, and negative electrode homogenate is obtained, and the negative electrode homogenate is coated on the front and the back of a copper foil of a negative electrode current collector, so that the surface density of the negative electrode homogenate is 0.024g/cm, and the thickness is 153 mu m 2 And (3) drying and tabletting the anode homogenate coating to obtain the silicon anode plate.
2.2, silicon negative electrode sheet application:
and winding the silicon negative plate, the isolating film and the positive plate (the positive active material is nickel cobalt lithium manganate) to obtain a battery core, packaging a battery shell of the battery core, drying, injecting electrolyte, packaging, forming and separating the electrolyte to obtain the lithium ion battery.
Example 4
The embodiment provides a carbon-coated silicon negative electrode material, a preparation method thereof, a corresponding silicon negative electrode sheet and application
1. The carbon-coated silicon anode material and the preparation method thereof are as follows:
(1) Mixing silicon alloy aluminum silicide with the particle size of 0.6-2.9 mu m and hydrochloric acid with the concentration of 0.36wt% according to the following weight ratio of 10: mixing the mixture at a mass/volume ratio (kg/L) of 30, carrying out hot acid oscillation, pressure filtration, deionized water washing hydrochloric acid, pressure filtration and drying dehydration on the obtained mixture at 55 ℃ to obtain a porous silicon source, and then carrying out surface coating treatment on the obtained porous silicon source, wherein the specific steps of the surface coating treatment are as follows: the molten polymer polypropylene was stirred with a porous silicon source according to 12:100, and placing the mixture in a reaction kettle, stirring the mixture to enable the mixture to be much Kong Guiyuan to thermally adsorb the molten polymer, and sending the obtained porous silicon source of the adsorbed molten polymer to a tube furnace with the temperature of 830 ℃ for carbonization for 4 hours to obtain the porous silicon source with the surface coated film.
(2) And (3) adding 500g of the porous silicon source with the surface coated film in the step (1) and 8g of sodium polystyrene sulfonate into 1L of deionized water, dispersing the porous silicon source with the surface coated film by utilizing the dispersion property of the sodium polystyrene sulfonate, and heating to 105 ℃ to thermally activate the sodium polystyrene sulfonate to obtain the negatively charged porous silicon solution.
(3) The needle coke graphitized graphite at high temperature is dissolved in glycerol solution containing 10wt percent, and is placed in a reaction kettle, and is added with dimethyl ammonium chloride to be mixed to obtain positively charged graphite solution (500 g of graphite and 20g of dimethyl ammonium chloride are added into 1L of glycerol solution to be mixed), then negatively charged porous silicon solution (the mass ratio of porous silicon source to graphite in the negatively charged porous silicon solution is controlled to be 10:100) is added to be stirred, the positively charged graphite adsorbs the porous silicon source (adsorption with positive and negative surface) and is heated and dried at 105 ℃ to obtain the graphite powder with porous silicon.
(4) The graphite powder with the porous silicon is sent into a tube furnace, mixed gas of acetylene gas and Ar gas (the volume ratio of the acetylene gas to the Ar gas is 3:1) is introduced, the graphite powder with the porous silicon wrapped by the mixed gas is obtained, the graphite powder with the porous silicon is heated and carbonized (the temperature in the tube furnace is 750 ℃, the air pressure is kept to be 0.6kPa, the time is 8 hours), the temperature is reduced to 600 ℃ and kept constant for 4 hours, the temperature is reduced, the carbon-coated silicon cathode material is obtained through sieving, and the particle diameter Dv50 of particles obtained through sieving is 3.5-18 mu m.
2. Silicon negative plate and application:
2.1, a silicon negative electrode sheet and a preparation method thereof:
(1) The carbon-coated silicon anode material and the conductive carbon of the conductive material are placed in a container of a stirrer, dry-mixed and stirred for 5min at the rotating speed of 1000r/min, and then binder (styrene-butadiene rubber and sodium carboxymethylcellulose are mixed according to 95wt% and 5 wt%) and deionized water are added in the container until the solid content of substances in the container is 69.7%.
(2) Adding the conductive material, the binder and the deionized water into the container again, stirring at a high rotating speed of 2500r/min, and uniformly mixing for 100min until the solid content of substances in the container is 49.7%, thereby obtaining mixed slurry.
Wherein the mass percentages of the carbon-coated silicon anode material, the conductive carbon of the conductive material and the binder are 92wt%, 4wt% and 4 wt%.
(3) The viscosity of the slurry in the step (2) is regulated to 3.3Pa.s, the fineness is less than or equal to 0.15mm, the anode homogenate is obtained, the anode homogenate is coated on the front and the back of the anode current collector copper foil, the thickness is 56 mu m, and the anode homogenate surface density is 0.009g/cm 2 And (3) drying and tabletting the anode homogenate coating to obtain the silicon anode plate.
2.2, silicon negative electrode sheet application:
and winding the silicon negative plate, the isolating film and the positive plate (the positive active material is nickel cobalt lithium manganate) to obtain a battery core, packaging a battery shell of the battery core, drying, injecting electrolyte, packaging, forming and separating the electrolyte to obtain the lithium ion battery.
Example 5
The embodiment provides a carbon-coated silicon negative electrode material, a preparation method thereof, a corresponding silicon negative electrode sheet and application
1. The carbon-coated silicon anode material and the preparation method thereof are as follows:
(1) Mixing silicon alloy aluminum silicide with the particle size of 0.6-2.9 mu m and hydrochloric acid with the concentration of 0.36wt% according to the following weight ratio of 10: mixing the mixture at a mass/volume ratio (kg/L) of 30, carrying out hot acid oscillation, pressure filtration, deionized water washing hydrochloric acid, pressure filtration and drying dehydration on the obtained mixture at 55 ℃ to obtain a porous silicon source, and then carrying out surface coating treatment on the obtained porous silicon source, wherein the specific steps of the surface coating treatment are as follows: the molten polymer polypropylene was stirred with a porous silicon source according to 12:100, and placing the mixture in a reaction kettle, stirring the mixture to enable the mixture to be much Kong Guiyuan to thermally adsorb the molten polymer, and delivering the obtained adsorbed molten polymer porous silicon source adsorbed molten polymer to a tube furnace with the temperature of 830 ℃ for carbonization for 4 hours to obtain the porous silicon source with the surface coated film.
(2) Adding 500g of porous silicon source with the surface coated film in the step (1) and 15g of sodium polystyrene sulfonate into 1L of deionized water, dispersing the porous silicon source with the surface coated film by utilizing the dispersion performance of the sodium polystyrene sulfonate and heating to 105 ℃ to thermally activate the sodium sulfonate polystyrene sulfonate to obtain negatively charged porous silicon solution;
(3) The needle coke graphitized graphite at high temperature is dissolved in glycerol solution containing 10wt percent, and is placed in a reaction kettle, and is added with dimethyl ammonium chloride to be mixed to obtain positively charged graphite solution (500 g of graphite and 20g of dimethyl ammonium chloride are added into 1L of glycerol solution to be mixed), then negatively charged porous silicon solution (the mass ratio of porous silicon source to graphite in the negatively charged porous silicon solution is controlled to be 10:100) is added to be stirred, the positively charged graphite adsorbs the porous silicon source (adsorption with positive and negative surface) and is heated and dried at 105 ℃ to obtain the graphite powder with porous silicon.
(4) The graphite powder with the porous silicon is sent into a tube furnace, mixed gas of acetylene gas and Ar gas (the volume ratio of the acetylene gas to the Ar gas is 3:1) is introduced, the graphite powder with the porous silicon wrapped by the mixed gas is obtained, the graphite powder with the porous silicon is heated and carbonized (the temperature in the tube furnace is 700 ℃, the air pressure is kept to be 0.6kPa, the time is 9 hours), the temperature is reduced to 600 ℃ and kept constant for 4 hours, the temperature is reduced, the carbon-coated silicon cathode material is obtained through sieving, and the particle diameter Dv50 of particles obtained through sieving is 3.5-18 mu m.
2. Silicon negative plate and application:
2.1, silicon negative electrode sheet and preparation thereof:
(1) The carbon-coated silicon anode material and the conductive carbon of the conductive material are placed in a container of a stirrer, dry-mixed and stirred for 5-30 min at the rotating speed of 20-1000 r/min, and then binder (styrene-butadiene rubber and sodium carboxymethylcellulose are mixed according to 95wt% and 5 wt%) and deionized water are added in the container to add water until the solid content of substances in the container is 73.6%.
(2) Adding the conductive material, the binder and the deionized water into the container again, stirring at a high rotating speed of 2500r/min, and uniformly mixing for 100min until the solid content of substances in the container is 54.4%, thereby obtaining mixed slurry.
Wherein the mass percentages of the carbon-coated silicon anode material, the conductive carbon of the conductive material and the binder are 92wt%, 4wt% and 4 wt%.
(3) The viscosity of the slurry in the step (2) is 3.8Pa.s, the fineness is less than or equal to 0.15mm, so as to obtain anode homogenate, the anode homogenate is coated on the front and the back of the anode current collector copper foil, and the thickness is 63 mu m, and the anode homogenate surface density is 0.011g/cm 2 And (3) drying and tabletting the anode homogenate coating to obtain the silicon anode plate.
2.2, silicon negative electrode sheet application:
and winding the silicon negative plate, the isolating film and the positive plate (the positive active material is nickel cobalt lithium manganate) to obtain a battery core, packaging a battery shell of the battery core, drying, injecting electrolyte, packaging, forming and separating the electrolyte to obtain the lithium ion battery.
Example 6
The embodiment provides a carbon-coated silicon negative electrode material, a preparation method thereof, a corresponding silicon negative electrode sheet and application
1. The carbon-coated silicon anode material and the preparation method thereof are as follows:
(1) Mixing silicon alloy aluminum silicide with the particle size of 0.6-2.9 mu m and hydrochloric acid with the concentration of 0.36wt% according to the following weight ratio of 10: mixing the mixture at a mass/volume ratio (kg/L) of 30, carrying out hot acid oscillation, pressure filtration, deionized water washing hydrochloric acid, pressure filtration and drying dehydration on the obtained mixture at 55 ℃ to obtain a porous silicon source, and then carrying out surface coating treatment on the obtained porous silicon source, wherein the specific steps of the surface coating treatment are as follows: the molten polymer polystyrene was stirred with a porous silicon source according to 12:100, and placing the mixture in a reaction kettle, stirring the mixture to enable the polymer to be much Kong Guiyuan to be heated and adsorbed, and sending the obtained porous silicon source of the adsorbed and fused polymer to a tube furnace with the temperature of 830 ℃ for carbonization for 4 hours).
(2) And (3) adding 500g of the porous silicon source with the surface coated film in the step (1) and 20g of sodium polystyrene sulfonate into 1L of deionized water, dispersing the porous silicon source with the surface coated film by utilizing the dispersion performance of the sodium polystyrene sulfonate through ultrasonic, and heating to 105 ℃ to thermally activate the sodium sulfonate polystyrene sulfonate to obtain the negatively charged porous silicon solution.
(3) The needle coke graphitized graphite at high temperature is dissolved in glycerol solution containing 10wt percent, and is placed in a reaction kettle, and is added with dimethyl ammonium chloride to be mixed to obtain positively charged graphite solution (500 g of graphite and 20g of dimethyl ammonium chloride are added into 1L of glycerol solution to be mixed), then negatively charged porous silicon solution (the mass ratio of porous silicon source to graphite in the negatively charged porous silicon solution is controlled to be 10:100) is added to be stirred, the positively charged graphite adsorbs the porous silicon source (adsorption with positive and negative surface) and is heated and dried at 105 ℃ to obtain the graphite powder with porous silicon.
(4) The graphite powder with the porous silicon is sent into a tube furnace, mixed gas of acetylene gas and Ar gas (the volume ratio of the acetylene gas to the Ar gas is 3:1) is introduced, the graphite powder with the porous silicon wrapped by the mixed gas is obtained, the graphite powder with the porous silicon is heated and carbonized (the temperature in the tube furnace is 650 ℃, the air pressure is kept at 0.6kPa for 9 hours), the temperature is reduced to 600 ℃ and kept constant for 4 hours, the temperature is reduced, the carbon-coated silicon anode material is obtained through sieving, and the particle diameter of the particles Dv50 obtained through sieving is 3.5-18 mu m.
2. Silicon negative plate and application:
2.1, silicon negative electrode sheet: (1) The carbon-coated silicon anode material and the conductive carbon of the conductive material are placed in a container of a stirrer, dry-mixed and stirred for 20min at the rotating speed of 500r/min, and then binder (styrene-butadiene rubber and sodium carboxymethylcellulose are mixed according to 95wt% and 5 wt%) and deionized water are added in the container so as to add water until the solid content of substances in the container is 70.8%.
(2) Adding the conductive material, the binder and the deionized water into the container again, stirring at a high rotating speed of 2500r/min, and uniformly mixing for 100min until the solid content of substances in the container is 47.4%, thereby obtaining mixed slurry.
Wherein the mass percentages of the carbon-coated silicon anode material, the conductive carbon of the conductive material and the binder are 92wt%, 4wt% and 4 wt%.
(3) The viscosity of the mixed slurry in the step (2) is regulated to 2.8Pa.s, the fineness is less than or equal to 0.15mm, the anode homogenate is obtained, the anode homogenate is coated on the front and the back of the anode current collector copper foil, the thickness is 98 mu m, and the anode homogenate surface density is 0.014g/cm 2 And (3) drying and tabletting the anode homogenate coating to obtain the silicon anode plate.
2.2, silicon negative electrode sheet application:
and winding the silicon negative plate, the isolating film and the positive plate (the positive active material is nickel cobalt lithium manganate) to obtain a battery core, packaging a battery shell of the battery core, drying, injecting electrolyte, packaging, forming and separating the electrolyte to obtain the lithium ion battery.
Comparative example 1:
this comparative example is similar to the preparation method of example 2, except that the porous silicon source has no surface coating treatment.
Comparative example 2
This comparative example is similar to the preparation method of example 2, except that the carbon-coated silicon anode material has no carbon coating layer.
Comparative example 3
The comparative example is similar to the preparation method of example 2, except that silicon alloy magnesium silicide with a particle size of 4.2 μm to 15 μm is selected and used, which is larger than that of example 2.
Test case
The carbon-coated silicon anode materials obtained in examples 1 to 6 and comparative examples 1 to 3 and the corresponding battery performance were tested as follows:
1. compression strength, powder resistance and swelling condition of silicon anode plate of battery under full charge of carbon-coated silicon anode material Dv 10:
(1) Compression strength of Dv 10: the silicon negative electrode materials of each example and comparative example were charged into a square groove, and by extruding the silicon negative electrode material in the square groove under a pressure of 1.3MPa and 2.6MPa, the compressive strength of Dv10 before and after extrusion was recorded = Dv10 after extrusion (particle size (μm) of 10% of the silicon negative electrode material in the volume distribution)/the higher the compressive strength of Dv10 before extrusion, the smaller the variation in the particle size of the silicon negative electrode material and the better the particle retention integrity; (2) The powder resistance of the silicon anode materials of each example and comparative example was measured by a powder resistance meter; (3) swelling condition of the silicon anode plate of the battery under full charge: the thickness of the silicon negative electrode sheet after tabletting and the thickness of the battery electrode sheet under full charge are measured, and an expansion value is calculated according to a formula, wherein the formula is silicon negative electrode sheet expansion rate= (thickness of the battery electrode sheet under full charge-thickness of the silicon negative electrode sheet after tabletting)/thickness of the negative electrode sheet after tabletting. The experimental results are shown in tables 1, 2 and 3.
2. And (3) detecting the electrical performance of the battery:
at normal temperature of 25 ℃, the initial and cut-off voltages are 2.8V, 4.35V,1C to 4.35V,4.35V constant voltage to current to reduce to 0.05C, 0.5C to 2.8V, the battery is circularly charged and discharged, and the capacity retention rate of the 100 th, 500 th and 800 th circles is calculated.
TABLE 1 compressive Strength of silicon negative electrode Material Dv10
TABLE 2 powder resistance, silicon negative electrode sheet swelling behavior
TABLE 3 Battery capacity retention case
As can be seen from Table 1, the obtained silicon anode materials of comparative examples 1 to 3 had reduced compressive strength of Dv10 at 1.3MPa extrusion and 2.6MPa extrusion, and were lower than those of examples 1 to 6, wherein the Dv10 of comparative examples 1 and 2 was reduced from 3.32 μm to 3.23 μm and from 3.35 μm to 3.20 μm, respectively, indicating the lack of surface coating treatment, carbon coating layer and the use of large particle size (4.2 μm to 15 μm) silicon alloy magnesium silicide, respectively, and the corresponding obtained silicon anode materials had reduced compressive strength of Dv10, and were more prone to extrusion cracking and reduced in pulverized particles; further, the situation that the extrusion material cracks when the silicon anode material is manufactured into a pole piece can be reduced, and the better the particle retention integrity is; in table 2, the powder resistances of comparative examples 1 and 2 were slightly increased, indicating that the addition of the surface coating treatment and the carbon coating layer improved the conductivity of the silicon anode material.
As is clear from Table 2, the expansion ratios of comparative examples 1 to 3 are 0.59, 0.57 and 0.52, respectively, and compared with example 1, the silicon negative electrode sheets of comparative examples 1 and 2 have the highest expansion ratio, which means that the expansion effect of the silicon negative electrode material is the largest when the surface coating treatment and the carbon coating layer are absent, and the expansion ratio of the silicon negative electrode sheet of comparative example 3 also reaches 0.52, so that the expansion of the silicon negative electrode material in the circulation process is effectively slowed down by the surface coating treatment and the carbon coating layer, the porous silicon source and the large-particle graphite are directly contacted with the electrolyte, the side reaction is reduced, the stability of the silicon negative electrode sheet is maintained, the silicon alloy magnesium silicide with small particle size (0.3 μm to 2.6 μm) is dispersed, and the expansion of the silicon inside the silicon negative electrode material is shared by the dispersed carbon pores.
Table 3 shows that the comparison of comparative examples 1 to 3 with examples 1 to 6 can improve the capacity retention rate and the battery cycle stability by comprehensively using the surface coating treatment and the carbon coating layer.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations and modifications of the present invention will be apparent to those of ordinary skill in the art in light of the foregoing description. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.
Claims (9)
1. The preparation method of the carbon-coated silicon anode material is characterized by comprising the following steps of:
(1) Preparing a porous silicon source by using a silicon alloy and acid, and performing surface coating treatment by using a molten polymer; the molten polymer is selected from one or more of polystyrene, polyethylene, polypropylene and polyaniline; the surface coating treatment method comprises the following steps: stirring and mixing the molten polymer and a porous silicon source, and heating and carbonizing to obtain the porous silicon source subjected to surface coating treatment; the grain diameter of the silicon alloy is 0.15-3 mu m;
(2) Mixing the porous silicon source subjected to surface film coating treatment obtained in the step (1) with sulfonate, and heating to activate the sulfonate, wherein the heating temperature is 60-110 ℃, so as to obtain a negatively charged porous silicon solution;
(3) Mixing graphite, a dispersing agent and quaternary ammonium salt to obtain a positively charged graphite solution, adding the negatively charged porous silicon solution obtained in the step (2), stirring, heating and drying to obtain graphite powder with porous silicon; the graphite tap density is 0.85g/cm 3 ~1.2g/cm 3 The Dv50 particle size is 3-26 mu m;
(4) And (3) heating and carbonizing the graphite powder with the porous silicon in the step (3) in a mixed gas atmosphere containing an organic gas, and performing temperature reduction to obtain the carbon-coated silicon anode material.
2. The method of claim 1, wherein in step (1), one or more of the following conditions are satisfied:
1) The silicon alloy is selected from one or more of magnesium silicide, aluminum silicide, calcium silicide and iron silicide;
2) The acid is selected from one or more of hydrochloric acid, nitric acid, phosphoric acid, acetic acid and formic acid;
3) The acid concentration is 0.1wt% to 8wt%.
3. The preparation method according to claim 1, wherein the mass ratio of the molten polymer to the porous silicon source is 0.2 to 18:100; the heating carbonization temperature is 500-900 ℃, and the heating carbonization time is 1-12 h.
4. The method of claim 1, wherein in step (2), one or more of the following conditions are satisfied:
a) The sulfonate is selected from one or more of sodium styrene sulfonate, sodium polystyrene sulfonate, lithium styrene sulfonate, potassium styrene sulfonate and potassium polystyrene sulfonate;
b) The mass ratio of the porous silicon source and the sulfonate which are subjected to surface coating treatment is 50-250: 1-25.
5. The method according to claim 1, wherein in the step (3), the quaternary ammonium salt is one or more of polydimethyl ammonium chloride, polydimethyl ammonium bromide, dodecylmethyl ammonium chloride, tetradecyl methyl ammonium chloride, hexadecyl methyl ammonium chloride, octadecyl methyl ammonium chloride, dodecylmethyl ammonium bromide, tetradecyl methyl ammonium bromide, hexadecyl methyl ammonium bromide and octadecyl methyl ammonium bromide.
6. The carbon-coated silicon negative electrode material according to any one of claims 1 to 5, wherein the carbon-coated silicon negative electrode material takes graphite as an inner core, and is externally coated with a carbon coating layer and a porous silicon layer, and the graphite and the porous silicon are subjected to adsorption recombination through positive and negative charges; the porous silicon is coated by a carbon layer of a coating film.
7. A silicon negative electrode sheet, characterized by comprising the carbon-coated silicon negative electrode material prepared by the preparation method of any one of claims 1 to 5 or the carbon-coated silicon negative electrode material of claim 6.
8. A method for preparing the silicon negative electrode sheet according to claim 7, comprising the steps of:
s1, dry-mixing and stirring a carbon-coated silicon anode material and a conductive material, and adding a binder and water to obtain a mixture;
s2, adding a conductive material, a binder and water into the mixture obtained in the step S1, stirring and mixing to obtain anode homogenate, coating the anode homogenate on at least one surface of the anode current collector, obtaining an anode homogenate coating, drying and tabletting to obtain the silicon anode plate.
9. A lithium ion battery, comprising the silicon negative electrode sheet described in claim 7 or the silicon negative electrode sheet prepared by the preparation method described in claim 8.
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