CN114447294B - Silicon-carbon composite negative electrode material with high compact structure and preparation method thereof - Google Patents
Silicon-carbon composite negative electrode material with high compact structure and preparation method thereof Download PDFInfo
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- CN114447294B CN114447294B CN202111626115.8A CN202111626115A CN114447294B CN 114447294 B CN114447294 B CN 114447294B CN 202111626115 A CN202111626115 A CN 202111626115A CN 114447294 B CN114447294 B CN 114447294B
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Classifications
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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
- H01M4/362—Composites
- H01M4/366—Composites as layered products
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
-
- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
Abstract
The invention provides a silicon-carbon composite anode material with a high compact structure and a preparation method thereof, wherein the silicon-carbon composite anode material comprises a silicon/graphite composite core, wherein the silicon/graphite composite core comprises a plurality of layers of flaky graphite and nano silicon, the flaky graphite is arranged in an oriented manner, the nano silicon is positioned between the flaky graphite to form a sandwich structure, and gaps of particles in the silicon/graphite composite core are filled with carbon materials; the silicon/graphite composite inner core is coated with a carbon layer. The preparation method comprises the following steps: dispersing the combination of nano silicon and flake graphite or flake graphite and other carbon materials in a solvent, carrying out ultrasonic treatment, adding a binder, and uniformly mixing; coating the obtained silicon/graphite slurry on a high polymer substrate, and drying to obtain a sheet material; stacking and hot pressing; roasting; crushing and shaping; carbon coating treatment; depolymerizing and sieving; the material disclosed by the invention is high in density and strength, and solves the problems of poor circulation and limited volume energy density improvement when the silicon-carbon negative electrode is applied to a battery.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery anode materials, and particularly relates to a silicon-carbon composite anode material with a high compact structure and a preparation method thereof.
Background
In order to meet the requirements of the market on the battery of the portable digital product and the requirement that the energy density of a battery unit of the pure electric vehicle proposed by the industrial information department reaches 300Wh/kg, the development of a new generation of high-capacity negative electrode material becomes a development direction. As a traditional negative electrode material, the graphite capacity is difficult to meet the requirement, while the silicon-based negative electrode has a future mass production trend due to the high capacity, but the silicon-based negative electrode has poor conductivity and large volume expansion, so that the problems of low initial efficiency and poor cycle performance in the application process of the battery are directly caused, and the silicon-based negative electrode is difficult to be used in large-scale commerce. In the current industrialized application, the silicon is doped into the graphite to be regarded as a more reasonable strategy, so that on one hand, the capacity of the negative electrode is improved, and on the other hand, the silicon and the carbon material are compounded, so that a series of problems in the application of the silicon-based negative electrode material can be solved. The excellent conductivity of graphite compensates for the low conductivity of silicon and also serves as a buffer medium to relieve the volume expansion of silicon during charging and discharging.
The shape and structure of the silicon-carbon negative electrode material in the current industry are different, and the silicon-carbon negative electrode material is generally prepared by mixing nano silicon, graphite and other carbon materials, granulating into secondary particles and then coating. Although the energy density of the battery is improved compared with that of a pure graphite cathode, the cycle performance and the compaction density of the product are still not higher than those of a graphite cathode, and the key is that the problems of dispersion of silicon and graphite and interface impedance between silicon and graphite are difficult to solve. The specific surface area of the nano silicon is large, agglomeration is easy, the nano silicon is difficult to uniformly disperse with graphite, and the formed silicon is enriched to cause local excessive expansion; the graphite is of a lamellar structure, the grain diameter and the nano silicon have order-of-magnitude difference, and the grain diameter and the nano silicon are compounded to form larger pores, so that the compactness and the structural stability of the material are poor. Meanwhile, more coating agents are needed for repairing pores on the surface of the material, so that the capacity and the compaction density of the material are reduced, the energy density of a battery is further influenced, and the capacity advantage of the silicon-based material is difficult to embody.
Patent CN107785560a discloses a method for preparing a silicon-carbon negative electrode material by mixing, kneading and pressing, which can better improve the strength of a particle core, but nano silicon and graphite cannot be prevented from filling pores formed by filling flake graphite in a direct granulation mode by spray drying, so that the charge-discharge stability of the material is not high.
In the patent CN112310363a, amorphous carbon is dispersed between gaps of a graphite skeleton to control the size of internal pores of the material to be not more than 50nm, so that the structural stability of the composite material is improved to a certain extent, but from the structural design, the pores formed by disordered graphite sheets in granulation are not solved, and the non-compact morphology of the particle surface influences the processing performance of the material.
Disclosure of Invention
The invention aims to solve the technical problems and overcome the defects and shortcomings in the background art, and provides a silicon-carbon composite anode material with a high compact structure and a preparation method thereof.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
the silicon-carbon composite anode material with the high compact structure comprises a silicon/graphite composite core, wherein the silicon/graphite composite core comprises a plurality of layers of flaky graphite and nano silicon, the flaky graphite is arranged in an orientation manner (along the outer surface of particles of the flaky graphite), the nano silicon is positioned between the flaky graphite and forms a sandwich structure, gaps of each particle in the silicon/graphite composite core are filled with carbon materials, and the particles comprise the flaky graphite and the nano silicon; the silicon/graphite composite inner core is coated with a carbon layer.
The silicon-carbon composite anode material with the high compact structure has a core-shell structure, and the material structure of the silicon/graphite composite inner core is a compact sandwich structure, and takes a graphite layer which is arranged in an oriented way as a support. The carbon material filled in the gaps among the particles in the silicon/graphite composite core plays a role in bonding.
Preferably, the compacted density of the silicon-carbon composite anode material is 1.7g/cm 3 The particle strength is above 140MPa, and the specific surface area is 3m 2 And/g or less. The material of the invention has the advantages of high density and high strength, and can effectively solve the problems of poor circulation and volume energy of the silicon-carbon negative electrode applied to the batteryThe problem of limited bulk density improvement.
Preferably, the median particle diameter of the flake graphite is 1-15 mu m, and the median particle diameter of the nano silicon is 10-150 nm; the median particle diameter of the silicon/graphite composite core is 7-15 mu m. The flaky graphite and the nano silicon with the proper particle sizes have good matching effect, and are beneficial to improving the compactness of the silicon/graphite composite inner core.
Preferably, the silicon/graphite composite inner core is in a cobble shape; the carbon layer is amorphous carbon; the difference value of the median particle diameter of the silicon-carbon composite anode material minus the median particle diameter of the silicon/graphite composite core is 1-4 mu m;
preferably, in the silicon-carbon composite anode material, the mass percentage of silicon is 15% -45%.
As a general inventive concept, the invention provides a preparation method of a high-density silicon-carbon composite anode material, which comprises the following steps:
(1) Dispersing nano silicon and flake graphite in a solvent, or dispersing a composition of nano silicon, flake graphite and other carbon materials in the solvent, adding a binder after ultrasonic treatment, and uniformly mixing to obtain silicon/graphite slurry;
(2) Coating the silicon/graphite slurry on a high polymer substrate by a tape casting method, and drying to obtain a sheet material with the high polymer substrate and a silicon/graphite coating;
(3) Stacking a plurality of sheet materials to obtain a silicon/graphite blank;
(4) Placing the silicon/graphite blank obtained in the steps into a sintering furnace for roasting to obtain a silicon/graphite sintered blank;
(5) Crushing and shaping the silicon/graphite sintered compact to obtain silicon/graphite composite particles;
(6) Carrying out surface carbon coating treatment on the silicon/graphite composite particles;
(7) And (3) depolymerizing and sieving the material obtained in the step (6) to obtain the silicon-carbon composite anode material.
The silicon-carbon composite anode material is prepared by the method, wherein the silicon/graphite composite particles are in a sandwich structure, and the defect that gaps are formed by disordered arrangement of flaky graphite in the granulating process is overcome, so that the particle strength and compaction density are influenced.
Preferably, after step (2) and before step (3), the sheet material is rolled to obtain a rolled sheet material, and then stacked. Under roll action, the powder orientation in the coating tends to be more stably aligned.
Preferably, the rolling treatment is carried out by adopting a pair roller machine, and the thickness of the obtained rolling sheet laminated material is 0.5-1 mm. The roller is adopted to carry out rolling treatment, so that the orientation arrangement of the powder in the coating is more stable, and the consistency is further improved. Further preferably, the rolling treatment is carried out by adopting a hot roller press, and the temperature of the rolling treatment is 100-150 ℃; the hot rolling can further remove moisture and pores in the coating, and further improve compactness.
Preferably, in the step (3), the multi-layer sheet material is stacked and then subjected to hot pressing treatment, so as to obtain a silicon/graphite blank. In the heating and pressurizing process of the hot pressing treatment, the adhesive and the high polymer material in the sheet are in a molten state to form a uniform adhesive skeleton, so that the adhesive force among particles is improved, and gaps among the particles are filled to form a compact silicon/graphite blank.
Preferably, stacking 50-100 layers of sheet materials with proper size, and performing hot pressing treatment in a hot pressing forming machine, wherein the hot pressing temperature is 150-200 ℃; when the sheet materials are stacked, one surface of the polymer substrate is downward or upward (i.e. the sheet materials are stacked by the same direction when being rolled). Through the hot pressing process, the compactness of the silicon/graphite blank is high.
Preferably, in the step (1), after ultrasonic treatment, a surfactant is added in addition to the binder; the surfactant is an organosiloxane flatting agent or an acrylic flatting agent, and the addition amount of the surfactant is 0.2-1% of the total mass of the nano silicon and the flake graphite. According to the invention, the surfactant is added and adsorbed on the surface of the powder through hydrogen bonds, a bonding network formed by branched chains enables the system to be in a stable state, the powder is uniformly dispersed, and meanwhile, the surface tension, the fluidity and the substrate wettability of the slurry are improved, so that film formation is smooth in the slurry drying process, and the graphite orientation and the sheet diameter direction are consistent. In the invention, the surfactant and the binder cooperate to better realize the directional arrangement of the powder under a specific process.
Preferably, in the step (2), the polymer substrate is one of a polyethylene film, a polyester film and a polyvinyl chloride film; the thickness of the polymer substrate is 0.02-0.1 mm. The melting and decomposition temperature of the polymer substrate is low, the melting is about 200 ℃, the decomposition is more than 300 ℃, and the bonding and carbonization effects are easy to achieve.
Preferably, in the step (2), the casting method adopts casting coating equipment, the drying temperature is 80-120 ℃, and the thickness of the silicon/graphite coating is 1-10 mm.
Preferably, in the step (1), the median particle diameter of the nano silicon is 10-300 nm; further preferably, the median particle diameter of the nano silicon is 10-150 nm; the median particle diameter of the flaky graphite is 1-20 mu m, and the median particle diameter of the other carbon materials is 1-20 mu m; the median particle diameter of the flaky graphite and the like is not excessively large, otherwise, the uniformity of silicon and carbon components and the subsequent crushing particle diameter are difficult to control. Further preferably, the flake graphite has a median particle diameter of 3 to 10 μm;
the mass ratio of the nano silicon to the flake graphite is 1:0.1-1:20; in the composition of the flaky graphite and other carbon materials, the mass content of the flaky graphite is more than 70 percent; further preferably, the mass ratio of the nano silicon to the flake graphite is 1:1-1:10;
the flake graphite comprises at least one of natural graphite and artificial graphite, and the natural graphite comprises flake graphite; the other carbon materials comprise one or more of hard carbon, mesophase carbon microspheres, graphene and graphite oxide;
the binder is one or a combination of at least two of asphalt, phenolic resin, epoxy resin, acrylic resin, stearic acid, citric acid and styrene-butadiene rubber; the addition amount of the binder is 2-10% of the total mass of the nano silicon and the flake graphite.
In the step (1), the solvent has good compatibility with the binder and the surfactant and has a low boiling point, and the solvent is one or more of water, alcohols, hydrocarbons, ketones, esters and ethers; further preferably, the solvent is one or more of ethanol, isopropanol and methyl acetate;
preferably, in the step (4), during the roasting, a protective gas is introduced into the sintering furnace, wherein the protective gas is nitrogen or argon; the roasting temperature is 600-1100 ℃, and the heat preservation time is 0.5-10 h. Further preferably, the roasting temperature is 700-1000 ℃ and the heat preservation time is 2-5 h. In the roasting process, a binder and the like in the material are carbonized, a carbon coating layer can be formed on the surfaces of the nano silicon and the flake graphite, and the carbon coating layer can inhibit the volume expansion of the nano silicon and provide a conductive shell.
Preferably, in the step (5), the crushing is specifically that the silicon/graphite sintered compact is sequentially processed by a jaw crusher and a crusher, the median particle size of the materials obtained after jaw crushing is 1-3 mm, and the median particle size of the materials obtained after crushing is 7.5-20 μm; further preferably, the median particle diameter of the material obtained after pulverization is 8 to 16 μm; and the shaping is to put the crushed material into crushing equipment with shaping function for particle trimming, remove redundant edges and corners, improve the surface roughness of particles, improve the regularity and the surface smoothness of the particles, and the median particle diameter of the shaped material is 7-15 mu m.
The step (6) specifically comprises the following steps: mixing the silicon/graphite composite particles with organic carbon, and then carrying out coating treatment, wherein the coating treatment temperature is 800-1100 ℃ and the coating treatment time is 2-4 h; the organic carbon material is asphalt or resin powder, and the median particle diameter of the powder is 3-5 mu m; the weight ratio of the silicon/graphite composite particles to the organic carbon is 2:1-10:1. Further preferably, the weight ratio of the silicon/graphite composite particles to the organic carbon material is 3:1-6:1. Because the silicon/graphite composite particles are of a layered structure, the surface layer graphite enables the coating section process to be easier to realize, the organic carbon is compatible with the graphite, uniform amorphous carbon is formed on the surface, and the coating effect is obvious.
In the step (8), the material obtained in the step (7) is treated by a depolymerizer and a vibrating screen to obtain a silicon-carbon precursor material. The depolymerization adopts a depolymerization machine, the depolymerization machine is a pulverizer device, the material is impacted by a rotor rotating at a high speed, and multiparticulate bonded macroparticles caused by carbonization are pulverized and reduced.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, uniformly dispersed silicon and graphite are effectively bonded and directionally arranged, the prepared silicon-carbon composite anode material is of a compact lamellar structure, the problem of interface impedance between silicon and graphite is effectively solved by the structure, wherein lamellar graphite is uniformly arranged, macropores are avoided due to lamellar dislocation, meanwhile, nano silicon is filled in interlayer gaps to form a sandwich structure, lamellar distributed graphite provides a lithium ion rapid channel in the charging and discharging process of the material, and provides a buffer space for volume expansion of lithium intercalation of silicon, so that the silicon-carbon composite anode material not only has high compaction density, but also has good electrochemical cycle performance. The invention forms a homogeneous layer structure by utilizing a powder directional arrangement technology, fully utilizes hot pressing treatment to eliminate structural gaps, and finally obtains the high-performance and high-compaction silicon-carbon composite anode material by matching shaping and cladding.
2. In the process of preparing the silicon-carbon composite anode material, the silicon-carbon composite anode material with a sandwich structure is prepared by the technologies of casting method homogenizing film formation, hot press forming, shaping and the like, and the material has high density and high strength, so that the problems of poor circulation and limited volume energy density improvement when the silicon-carbon anode is applied to a battery are solved. The invention has controllable operation and high efficiency, and is easy to realize large-scale continuous production.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is an SEM test chart of a silicon-carbon composite anode material prepared in example 1 of the present invention;
FIG. 2 is a cross-sectional SEM test chart of a silicon-carbon composite anode material prepared in example 1 of the present invention;
fig. 3 is a first charge-discharge curve of a button cell corresponding to the silicon-carbon composite anode material prepared in example 1 of the present invention;
fig. 4 is a charge-discharge cycle comparison chart of 0.5C/1C of a 2.5Ah soft pack battery corresponding to the silicon-carbon composite anode material of the embodiment 1 and the comparative embodiment 1.
Detailed Description
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown, for the purpose of illustrating the invention, but the scope of the invention is not limited to the specific embodiments shown.
Unless defined otherwise, all technical and scientific terms used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the scope of the present invention.
Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or may be prepared by existing methods.
Example 1:
a preparation method of a high-compactness silicon-carbon composite anode material comprises the following steps:
(1) Dispersing 100g of silicon powder with a median particle size of 80nm and 120g of crystalline flake graphite with a median particle size of 3 mu m in 1kg of ethanol, performing ultrasonic dispersion for 30min, adding 22g of epoxy resin and 2g of organic modified polysiloxane, and mixing for 2h to obtain silicon/graphite slurry;
(2) The silicon/graphite slurry is cast and coated on a polyethylene film with the thickness of 0.05mm by adopting casting coating equipment, and is dried at the temperature of 100 ℃ to obtain a sheet material with the thickness of 3mm and provided with a polyethylene film and a silicon/graphite coating;
(3) Rolling the sheet material by a pair roller (hot roller press) at 120 ℃ to obtain a rolled sheet material, wherein the thickness of the rolled sheet material is 1mm;
(4) Slicing the rolled sheet material into 30cm 15cm, stacking 50 layers of sheets in the same direction to a height of about 5cm, and carrying out hot pressing treatment at 120 ℃ in a hot pressing forming machine to obtain a silicon/graphite blank;
(5) Placing the silicon/graphite blank in a sintering furnace, preserving heat for 3 hours at 800 ℃ in an argon atmosphere, naturally cooling to room temperature, and taking out to obtain a silicon/graphite sintered blank;
(6) The silicon/graphite sintered compact is sequentially processed by a jaw crusher, a pulverizer and a shaper to obtain silicon/graphite composite powder with a median particle size of 15 mu m; wherein the median particle diameter of the material obtained after jaw breaking by the jaw breaker is 3mm, the median particle diameter of the material obtained after crushing by the crusher is 16 mu m, and the material obtained after crushing is shaped into particle surface finishing by putting the material obtained after crushing into crushing equipment with shaping function;
(7) Mixing the silicon/graphite composite powder and asphalt according to a mass ratio of 4:1, and then putting the mixture into a carbonization furnace for carbonization for 2 hours at the temperature of 1000 ℃;
(8) Processing the material obtained in the step (7) by a depolymerizing machine and a vibrating screen to obtain a silicon-carbon composite anode material, wherein the particle size D of the silicon-carbon composite anode material 50 17 μm, a specific surface area of 1.86m 2 Per gram, tap density 0.91g/cm 3 The silicon content was about 28%.
Fig. 1 and 2 are SEM images and cross-sectional SEM test images of the silicon carbon composite anode material prepared in example 1 above, respectively. The silicon-carbon composite anode material prepared in example 1 includes a silicon/graphite composite core, the silicon/graphite composite core is in a flat cobble shape as a whole, the silicon/graphite composite core includes a plurality of layers of flaky graphite and nano silicon, as can be seen from the figure, the flaky graphite is arranged along the outer surface of the particles, the nano silicon is positioned between the flaky graphite and forms a sandwich structure, and gaps of each particle (including the flaky graphite and the nano silicon) in the silicon/graphite composite core are filled with carbon materials due to infiltration and carbonization of a polyethylene film, a binder and the like; the silicon/graphite composite particles are coated with an amorphous carbon layer obtained by carbonizing asphalt serving as a carbon source through asphalt coating and carbonization.
Example 2:
a preparation method of a high-compactness silicon-carbon composite anode material comprises the following steps:
(1) 200g of silicon powder with the median particle size of 100nm and 400g of crystalline flake graphite with the median particle size of 8 mu m are taken to be dispersed in 4kg of isopropanol, ultrasonic dispersion is carried out for 30min, 30g of stearic acid and 2.5g of polyacrylate solution are added, and the mixture is mixed for 2h to obtain silicon/graphite slurry;
(2) The silicon/graphite slurry is cast and coated on a polyvinyl chloride film by adopting casting coating equipment, and is dried at 110 ℃ to obtain a sheet material with the thickness of 5mm and provided with the polyvinyl chloride film and the silicon/graphite coating; wherein, the thickness of the polyvinyl chloride film is 0.08mm;
(3) Carrying out rolling treatment on the sheet material by adopting a common pair of rollers to obtain a rolled sheet material, wherein the thickness of the rolled sheet material is 0.9mm;
(4) Slicing the rolled sheet material, stacking 80 layers of sheets with proper size in the same direction to form a height of about 7cm, and carrying out hot pressing treatment at 150 ℃ in a hot pressing forming machine to obtain a silicon/graphite blank;
(5) Placing the silicon/graphite blank in a sintering furnace, preserving heat for 2 hours at 700 ℃ in an argon atmosphere, naturally cooling to room temperature, and taking out to obtain a silicon/graphite sintered blank;
(6) The silicon/graphite sintered compact is sequentially processed by a jaw crusher, a pulverizer and a shaper to obtain silicon/graphite composite powder with a median particle size of 12 mu m; wherein the median particle diameter of the material obtained after jaw breaking by the jaw breaker is 2mm, the median particle diameter of the material obtained after crushing by the crusher is 13 mu m, and the material obtained after crushing is shaped into particle surface finishing by putting the material obtained after crushing into crushing equipment with shaping function;
(7) Mixing the silicon/graphite composite powder and asphalt according to a mass ratio of 5:1, and then putting the mixture into a carbonization furnace for carbonization for 4 hours at 900 ℃;
(8) Processing the material obtained in the step (7) by a depolymerizing machine and a vibrating screen to obtain a silicon-carbon composite anode material, wherein the anode material has a particle size D 50 14 μm, a specific surface area of 2.71m 2 Per g, tap Density0.84g/cm 3 The silicon content was about 25%.
Example 3:
a preparation method of a high-compactness silicon-carbon composite anode material comprises the following steps:
(1) Dispersing 150g of silicon powder with a median particle size of 80nm and 750g of crystalline flake graphite with a median particle size of 5 μm in 3kg of ethanol, performing ultrasonic dispersion for 30min, adding 35g of citric acid, and mixing for 2h to obtain silicon/graphite slurry;
(2) The silicon/graphite slurry is cast and coated on a polyethylene film by adopting casting coating equipment, and is dried at 90 ℃ to obtain a sheet material with the thickness of 3mm and provided with the polyethylene film and the silicon/graphite coating; wherein, the thickness of the polyester film is 0.025mm;
(3) Rolling the sheet material by a pair roller (hot roller press) at 110 ℃ to obtain a rolled sheet material, wherein the thickness of the rolled sheet material is 0.5mm;
(4) Slicing the rolled sheet material, stacking 100 layers of sheets with proper size in the same direction to form a height of about 5cm, and carrying out hot pressing treatment at 120 ℃ in a hot pressing forming machine to obtain a silicon/graphite blank;
(5) Placing the silicon/graphite blank in a sintering furnace, preserving heat for 4 hours at 800 ℃ in an argon atmosphere, naturally cooling to room temperature, and taking out to obtain a silicon/graphite sintered blank;
(6) The silicon/graphite sintered compact is sequentially processed by a jaw crusher, a pulverizer and a shaper to obtain silicon/graphite composite powder with a median particle size of 10 mu m; wherein the median particle diameter of the material obtained after jaw breaking by the jaw breaker is 3mm, the median particle diameter of the material obtained after crushing by the crusher is 11 mu m, and the material obtained after crushing is shaped into particle surface finishing by putting the material obtained after crushing into crushing equipment with shaping function;
(7) Mixing the silicon/graphite composite powder and asphalt according to a mass ratio of 3:1, and then putting the mixture into a carbonization furnace for carbonization for 2 hours at 1100 ℃;
(8) Processing the material obtained in the step (7) by a depolymerizing machine and a vibrating screen to obtain a silicon-carbon composite anode material, wherein the anode material has a particle size D 50 13 μm, a specific surface area of 2.59m 2 Per g, tap Density0.82g/cm 3 The silicon content was about 19%.
Comparative example 1:
the preparation method of the silicon-carbon composite anode material comprises the following steps:
(1) Dispersing 120g of silicon powder with a median particle size of 80nm and 180g of crystalline flake graphite with a median particle size of 10 mu m in 1kg of ethanol, performing ultrasonic dispersion for 30min, adding 15g of phenolic resin, and mixing for 2h to obtain silicon/graphite slurry;
(2) Drying the silicon/graphite slurry at 100 ℃ in vacuum to obtain silicon/graphite powder; carrying out mould pressing treatment on the dry powder in a mould to obtain a silicon/graphite blank;
(3) Placing the silicon/graphite blank in a sintering furnace, preserving heat for 2 hours at 700 ℃ in an argon atmosphere, naturally cooling to room temperature, and taking out to obtain a silicon/graphite sintered blank;
(4) The silicon/graphite sintered compact is sequentially processed by a jaw crusher, a pulverizer and a shaper to obtain silicon/graphite composite powder with a median particle size of 15 mu m; wherein the median particle diameter of the material obtained after jaw breaking by the jaw breaker is 4mm, the median particle diameter of the material obtained after crushing by the crusher is 16 mu m, and the material obtained after crushing is shaped into particle surface finishing by putting the material obtained after crushing into crushing equipment with shaping function;
(5) Mixing the silicon/graphite composite powder and asphalt according to a mass ratio of 4:1, and then putting the mixture into a carbonization furnace for carbonization for 2 hours at the temperature of 1000 ℃;
(6) Processing the material obtained in the step (5) by a depolymerizing machine and a vibrating screen to obtain a silicon-carbon composite anode material, wherein the anode material has a particle size D 50 18 μm, a specific surface area of 10.32m 2 Per gram, tap density 0.71g/cm 3 The silicon content was about 29%.
Comparative example 2:
the preparation method of the silicon-carbon composite anode material comprises the following steps:
(1) 200g of silicon powder with the median particle size of 100nm and 400g of crystalline flake graphite with the median particle size of 15 mu m are taken to be dispersed in 4kg of isopropanol, and are subjected to ultrasonic dispersion for 30min, and are mixed for 2h to obtain silicon/graphite slurry;
(2) Spray drying the silicon/graphite slurry to obtain powder with a median particle diameter of 25 mu m;
(3) Mixing the powder with 120g of stearic acid, and adopting a pair roller machine to carry out rolling treatment to obtain a sheet material with the thickness of 1mm;
(4) Stacking 80 layers of the sheet materials into blocks with the height of about 7cm, and carrying out hot pressing treatment at 150 ℃ in a hot pressing forming machine to obtain a silicon/graphite blank;
(5) Placing the silicon/graphite blank in a sintering furnace, preserving heat for 2 hours at 700 ℃ in an argon atmosphere, naturally cooling to room temperature, and taking out to obtain a silicon/graphite sintered blank;
(6) The silicon/graphite sintered compact is sequentially processed by a jaw crusher, a pulverizer and a shaper to obtain silicon/graphite composite powder with a median particle size of 17 mu m; wherein the median particle diameter of the material obtained after jaw breaking by the jaw breaker is 3mm, the median particle diameter of the material obtained after crushing by the crusher is 18 mu m, and the material obtained after crushing is shaped into particle surface finishing by putting the material obtained after crushing into crushing equipment with shaping function;
(7) Mixing the silicon/graphite composite powder and asphalt according to a mass ratio of 5:1, and then putting the mixture into a carbonization furnace for carbonization for 4 hours at 900 ℃;
(8) Processing the material obtained in the step (7) by a depolymerizing machine and a vibrating screen to obtain a silicon-carbon composite anode material, wherein the anode material has a particle size D 50 21 μm, a specific surface area of 6.53m 2 Per gram, tap density 0.75g/cm 3 The silicon content was about 24%.
Performance test:
1. physical and chemical performance test
The relative physical and chemical properties of the anode material prepared by the invention are shown in table 1.
TABLE 1 physicochemical Properties related to silicon carbon composite negative electrode Material
| Experimental example | Density of compaction (g/cm) 3 ) | Specific surface area (m) 2 /g) | Particle strength (MPa) |
| Example 1 | 1.81 | 1.86 | 233.7 |
| Example 2 | 1.78 | 2.71 | 206.8 |
| Example 3 | 1.73 | 2.59 | 144.5 |
| Comparative example 1 | 1.65 | 10.32 | 88.1 |
| Comparative example 2 | 1.63 | 6.53 | 47.2 |
* And (3) injection: the strength was measured by a powder hardness tester.
As can be seen from Table 1, the homogeneous layer structure material prepared by the powder orientation arrangement technique in the embodiment of the invention has obvious advantages in specific surface area, compaction density and particle strength compared with the comparative example material. By the adoption of the inventionThe specific surface area of the silicon-carbon composite anode material prepared by the method is lower than 3m 2 Per gram, a compaction density of greater than 1.7g/cm 3 The particle strength is 140MPa or more.
2. Electrical property test
Electrochemical performance evaluation the electrochemical performance evaluation was made and evaluated as follows: preparing slurry by the silicon-carbon composite anode material prepared in each experimental example, conductive carbon black and LA133 binder according to the mass ratio of 7:2:1, coating the slurry on a copper foil, and taking the slurry as an anode through vacuum drying and rolling; the metal lithium is used as a counter electrode, and the CR2430 button cell is assembled by the positive electrode shell, the pole piece, the electrolyte, the diaphragm, the electrolyte, the lithium piece, the foam nickel and the negative electrode shell in sequence. The test uses 0.2C constant current charge and discharge, and the voltage is limited to 0-1.5V.
The results of the first reversible capacity and first efficiency tests of the respective button cells are shown in table 1.
Table 2 results of first reversible capacity and first efficiency tests of button cell
As can be seen from Table 2, the reversible capacity of the button cell prepared by the silicon-carbon composite anode material prepared in the embodiment of the invention is more than 1050mAh/g, the initial coulomb efficiency is more than 81%, and the capacity retention rate at 50 weeks is more than 85%.
Fig. 3 is a first-cycle charge-discharge graph of the button cell corresponding to the silicon-carbon composite negative electrode material prepared in example 1, and fig. 4 is a 0.5C/1C charge-discharge cycle comparison graph of the 2.5Ah soft pack cell corresponding to the silicon-carbon composite negative electrode material of example 1 and comparative example 1. As can be seen from fig. 4, the soft pack battery cycle life of the button cell corresponding to the silicon-carbon composite anode material of example 1 reached 500 weeks, which is significantly longer than that of comparative example 1.
Claims (7)
1. The preparation method of the silicon-carbon composite anode material with the high compact structure is characterized by comprising the following steps of:
(1) Dispersing nano silicon and flake graphite in a solvent, or dispersing a composition of nano silicon, flake graphite and other carbon materials in the solvent, adding a binder after ultrasonic treatment, and uniformly mixing to obtain silicon/graphite slurry;
(2) Coating the silicon/graphite slurry on a high polymer substrate by a tape casting method, and drying to obtain a sheet material with the high polymer substrate and a silicon/graphite coating; firstly, carrying out rolling treatment on the sheet material to obtain a rolled sheet material;
(3) Stacking a plurality of rolling sheet lamination materials and then carrying out hot pressing treatment to obtain a silicon/graphite blank; when the rolled sheet materials are stacked, one surface of the polymer substrate is downward or upward;
(4) Placing the silicon/graphite blank obtained in the steps into a sintering furnace for roasting to obtain a silicon/graphite sintered blank; during roasting, introducing protective gas into the sintering furnace, wherein the protective gas is nitrogen or argon; the roasting temperature is 600-1100 ℃, and the heat preservation time is 0.5-10 h;
(5) Crushing and shaping the silicon/graphite sintered compact to obtain silicon/graphite composite particles; the crushing method comprises the steps of sequentially processing a silicon/graphite sintered compact by a jaw crusher and a crusher, wherein the median particle size of the material obtained after jaw crushing is 1-3 mm, and the median particle size of the material obtained after crushing is 7.5-20 mu m; the shaping is that the crushed material is put into crushing equipment with shaping function for particle finishing, and the median particle diameter of the shaped material is 7-15 mu m;
(6) Mixing the silicon/graphite composite particles with organic carbon, and then carrying out coating treatment, wherein the coating treatment temperature is 800-1100 ℃ and the coating treatment time is 2-4 hours; the organic carbon material is pitch or resin powder; the weight ratio of the silicon/graphite composite particles to the organic carbon is 2:1-10:1;
(7) And (3) depolymerizing and sieving the material obtained in the step (6) to obtain the silicon-carbon composite anode material.
2. The method according to claim 1, wherein the rolling treatment is carried out by a twin-roll machine, and the thickness of the obtained rolled sheet material is 0.5-1 mm.
3. The method according to claim 1, wherein 50 to 100 sheets of sheet material with a proper size are stacked, and the sheet material is subjected to hot pressing treatment in a hot press forming machine, wherein the hot pressing temperature is 150 to 200 ℃.
4. The method according to claim 1, wherein in the step (1), a surfactant is added in addition to the binder after the ultrasonic treatment; the surfactant is an organosiloxane flatting agent or an acrylic flatting agent, and the addition amount of the surfactant is 0.2-1% of the total mass of the nano silicon and the flake graphite.
5. The method according to any one of claims 1 to 4, wherein in the step (2), the polymer substrate is one of a polyethylene film, a polyester film, and a polyvinyl chloride film; the thickness of the polymer substrate is 0.02-0.1 mm.
6. The method according to any one of claims 1 to 4, wherein in the step (2), a casting coating device is used for the casting method, the drying temperature is 80 to 120 ℃, and the thickness of the silicon/graphite coating is 1 to 10mm.
7. The method according to any one of claims 1 to 4, wherein in the step (1), the nano silicon has a median particle diameter of 10 to 150nm; the median particle diameter of the flaky graphite is 1-20 mu m, and the median particle diameter of the other carbon materials is 1-20 mu m; the mass ratio of the nano silicon to the flake graphite is 1:0.1-1:20; in the composition of the flaky graphite and other carbon materials, the mass content of the flaky graphite is more than 70 percent;
the flake graphite comprises at least one of natural graphite and artificial graphite, and the natural graphite comprises flake graphite; the other carbon materials comprise one or more of hard carbon, mesophase carbon microspheres, graphene and graphite oxide;
the binder is one or a combination of at least two of asphalt, phenolic resin, epoxy resin, acrylic resin, stearic acid, citric acid and styrene-butadiene rubber; the addition amount of the binder is 2% -10% of the total mass of the nano silicon and the flake graphite;
the solvent is one or more of water, alcohols, hydrocarbons, ketones, esters and ethers.
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