CN112670489A - Silicon-carbon composite material, electrode, lithium ion battery and preparation method and application thereof - Google Patents
Silicon-carbon composite material, electrode, lithium ion battery and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a silicon-carbon composite material, an electrode, a lithium ion battery, and a preparation method and application thereof. The preparation method comprises the following steps: s1, homogenizing the raw materials to obtain slurry; wherein the raw materials comprise the following components in parts by weight: 100 parts of silicon, 0.005-1 part of carbon nano tube, 0.1-10 parts of lithium supplement additive, 10-200 parts of resin and solvent; the homogenizing comprises sanding or ball milling; s2, evaporating the slurry to dryness to obtain a precursor A; s3, carrying out heat treatment on the precursor A, and crushing to obtain a precursor B; s4, mixing the precursor B with a coating agent for coating to obtain a precursor C; and S5, carrying out heat treatment on the precursor C. The lithium ion battery using the silicon-carbon composite material prepared by the method as the cathode material has high capacity, high first efficiency, excellent rate capability and cycle performance, the preparation method is simple, and industrial scale production can be realized.
Description
Technical Field
The invention relates to a silicon-carbon composite material, an electrode, a lithium ion battery, and a preparation method and application thereof.
Background
The miniaturization and intelligentization of electronic equipment have made demands for miniaturization, high power and high safety of power supply parts thereof. In addition, electrician automobiles and electrician tools have higher and higher requirements on electric energy storage and endurance. Although lithium batteries, which are a new generation of chemical power source, have been developed for over two decades, the conventional graphite-based negative electrode material has a theoretical specific capacity of only 372mAh/g, and the prior art has reached the capacity limit and power limit of graphite-based negative electrodes, which limit further improvement of the specific energy of lithium ion batteries.
The silicon and carbon elements are in the fourth main group, and many similarities exist in chemical properties. However, silicon has a specific capacity of up to 3800mAh/g at room temperature, which is 10 times that of graphite. In addition, the silicon material has a suitably low electrochemical lithium storage potential plateau. These two factors determine that silicon is the best choice for replacing graphite-based anode materials. However, the silicon material has volume change of up to 300% in the lithium intercalation and lithium deintercalation processes, which easily causes pulverization and agglomeration of silicon particles and separation of the negative electrode material from a current collector, thereby causing damage to the structure of the negative electrode material and loss of electric connection; the volume change of the silicon powder can enable silicon particles to be removed from the coating material and generate new surface area, and new and unstable solid electrolyte interface films (SEI films) are continuously formed after the surfaces of the silicon particles are contacted with the electrolyte, so that the electrolyte and lithium ions are consumed, the electrical performance is seriously attenuated, and finally the electrochemical performance attenuation, even deformation and rupture of the lithium ion battery are generated.
Chinese patent CN110148743A discloses a silicon-carbon composite negative electrode material, a preparation method thereof and a lithium ion battery. The patent constructs a silicon-carbon cathode material with a core-shell structure, wherein the core is nano-silicon coated by a carbon nano tube, and the shell is a carbon coating layer. The reserved cavity in the silicon-carbon composite negative electrode material can effectively improve the conditions of capacity attenuation and pole piece thickening caused by stress concentration and particle crushing caused by volume change of the silicon material in the charging and discharging processes; the carbon nano tube coated on the surface of the nano silicon can provide good conductivity, improve the conductivity of the silicon-carbon composite negative electrode material and improve the power performance of the lithium ion battery. The method is obtained by 3 times of coating and 1 time of etching, and has the advantages of complex operation method, more control parameters and higher difficulty in commercial production.
Chinese patent CN110190331A discloses an electrolyte for stabilizing the silicon-carbon surface of a lithium ion battery, and preparation and application thereof, wherein dimethyl dimethoxy silane and allyloxytrimethylsilane are added into the electrolyte as film-forming additives, fluoroethylene carbonate is a film-forming additive, and a silicon-oxygen-silicon cross polymerization network formed by the dimethyl dimethoxy silane and the allyloxytrimethylsilane modifies an SEI film, so that the corrosion of gas and lithium salt generated by the continuous decomposition of the fluoroethylene carbonate to a current collector is reduced. The modified SEI film is more uniform and compact, the phenomenon of lithium precipitation of a silicon-carbon negative electrode is reduced, the surface of the electrode is more stable, and the cycle stability of the battery is improved. However, SEI film modification by electrolyte additives can only use limited organic substances, and cannot perform inorganic SEI film modification.
Disclosure of Invention
The invention provides a silicon-carbon composite material, an electrode, a lithium ion battery, a preparation method and application thereof, and aims to overcome the defect that the cycle performance and the rate performance of a silicon-based negative electrode material cannot be considered at the same time in the prior art. The silicon-carbon composite material has stable performance and low expansion rate, and the lithium ion battery taking the silicon-carbon composite material as the cathode material has high capacity, high first coulombic efficiency, excellent rate capability and cycle performance, simple preparation process and excellent processing performance, and can realize industrial mass production.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a silicon-carbon composite material comprises the following steps:
s1, homogenizing the raw materials to obtain slurry; wherein the raw materials comprise the following components in parts by weight: 100 parts of silicon, 0.005-1 part of carbon nano tube, 0.1-10 parts of lithium supplement additive, 10-200 parts of resin and solvent; the homogenizing comprises sanding or ball milling;
s2, evaporating the slurry to dryness to obtain a precursor A;
s3, carrying out heat treatment on the precursor A to enable resin in the precursor A to be solidified and/or pre-carbonized, and crushing to obtain a precursor B, wherein the particle size of the precursor B is 4-15 microns;
s4, mixing the precursor B with a coating agent for coating to obtain a precursor C; the amount of the coating agent is 2-20% of the precursor B calculated according to the amount of the carbon residue, and the percentage is mass percent;
and S5, carrying out heat treatment on the precursor C to carbonize the precursor C, thus obtaining the carbon nano tube.
In step S1, the silicon may be silicon conventionally used in the art. The particle size of the silicon may be 0.01 to 10 μm, preferably 0.1 to 5 μm, and more preferably 0.1 to 0.15 μm. The purity of the silicon is generally above 99.99%. The content of magnetic foreign matter in the silicon is generally not higher than 0.1%.
In step S1, the amount of the carbon nanotubes is preferably 0.01 to 0.5 parts, more preferably 0.03 parts, based on 100 parts of silicon. The carbon nanotubes may be single-walled carbon nanotubes and/or multi-walled carbon nanotubes. Generally, the diameter of the single-walled nanotube is 0.1-10 nm, and the length of the single-walled nanotube is 0.1-10 μm; the diameter of the multi-walled nanotube is 8-100 nm, and the length of the multi-walled nanotube is 0.5-30 mu m. Preferably, the diameter of the single-walled nanotube is 1-2 nm, and the length is 5 μm.
The carbon nanotubes are preferably provided in the form of a carbon nanotube slurry. The carbon nanotube slurry may be obtained by dispersing the carbon nanotubes into a liquid medium, which may be one or more of ethanol, N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), and dimethylacetamide (DMAc). When the carbon nanotubes are provided in a carbon nanotube slurry, the amount of the carbon nanotubes is calculated as the effective amount of carbon nanotubes in the carbon nanotube slurry. The carbon nanotube slurry is preferably a single-walled carbon nanotube-ethanol slurry or a single-walled carbon nanotube-NMP slurry. The solid content of the carbon nanotube slurry is preferably 0.2 wt%.
In step S1, the amount of the lithium supplement additive is preferably 3 to 5 parts by weight based on 100 parts by weight of silicon. The lithium supplement additive may be a lithium supplement additive conventionally used in the art, and preferably is one or more of lithium carbonate, lithium bicarbonate, lithium acetate, lithium oxalate, lithium hydroxide, lithium oxide, magnesium carbonate, magnesium hydroxide, magnesium powder, and aluminum. The particle size of the lithium supplement additive can be micron-sized or nanometer-sized.
In step S1, the amount of the resin is preferably 20 to 100 parts by weight based on 100 parts by weight of silicon. The resin may be a resin conventionally used in the art, and the amount of carbon residue thereof is generally not less than 5%. The resin preferably comprises one or more of phenolic resin, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG). The phenolic resin is preferably a novolac resin, and the softening point of the novolac resin is preferably 90-110 ℃. The polyvinyl alcohol is preferably PVA 1788. The polyvinylpyrrolidone is preferably PVP K30.
The resin preferably comprises a phenolic resin. The resin preferably comprises a phenolic resin and comprises one or more of polyvinyl alcohol, polyvinylpyrrolidone and polyethylene glycol. Among them, phenol resin is generally used as a main resin (accounting for more than 90% of the total mass of the resin) to provide main carbon residue; one or more of polyvinyl alcohol, polyvinylpyrrolidone and polyethylene glycol are used as auxiliary resins, and the auxiliary resins have poor intersolubility with the main resin, leave some larger voids in the carbon residue of the main resin and reduce micropores of particles, thereby reducing the specific surface area of the material.
The resin preferably includes phenolic resin, polyvinyl alcohol and polyvinyl pyrrolidone. Wherein the mass ratio of the phenolic resin, the polyvinyl alcohol and the polyvinylpyrrolidone is preferably 100:8: 5.
When the resin comprises a phenol novolac resin, the raw material may further comprise a curing agent, which is preferably an aliphatic amine curing agent, more preferably hexamethylenetetramine. The curing agent may be used in an amount of 6% to 15%, preferably 9%, of the novolac resin.
In step S1, the solvent may be a solvent conventionally used in the art as long as it can dissolve the resin and does not react with the components. The solvent may be one or more of water, ethanol, N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), and dimethylacetamide (DMAc), and preferably is N-methylpyrrolidone (NMP) or a NMP-ethanol mixed solvent. The proportion of the NMP-ethanol mixed solvent is preferably 10: 90. The solvent is used in such an amount that the solids content of the slurry is generally not higher than 20% by weight, so that the viscosity of the slurry generally does not exceed 50mPa · s.
In step S1, the raw material preferably further includes graphite and/or graphene.
The graphene may be single-layer graphene or few-layer graphene. The particle size of the graphene is generally not more than 15 μm. The graphene is preferably provided in the form of a graphene slurry. The graphene slurry may be obtained by dispersing the graphene into a liquid medium, which may be one or more of ethanol, N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), and dimethylacetamide (DMAc). When the graphene is provided as a graphene slurry, the amount of the graphene is calculated based on the effective content of the graphene in the graphene slurry. The graphene slurry is preferably a graphene-ethanol slurry or a graphene-NMP slurry. The solid content of the graphene paste is preferably 5 wt%. The amount of the graphene is preferably 0.005-1 part by weight based on 100 parts by weight of the silicon.
The graphite may be natural graphite or artificial graphite. The particle size of the graphite is 1 to 10 μm, preferably 2 to 5 μm. The amount of the graphite is preferably 0.1 to 100 parts, more preferably 10 to 50 parts, based on 100 parts of the silicon.
In step S1, the raw materials preferably include the following components in parts by weight: 100 parts of silicon, 0.03 part of carbon nano tube, 5 parts of lithium supplement additive, 50 parts of graphite, 100 parts of novolac resin, 10 parts of PVA, 5 parts of PVP, 9 parts of hexamethylenetetramine and 900 parts of solvent.
In step S1, the raw materials preferably include the following components in parts by weight: 100 parts of silicon, 0.1 part of carbon nano tube, 3 parts of lithium supplement additive, 50 parts of graphite, 100 parts of novolac resin, 8 parts of PVA, 5 parts of PVP, 9 parts of hexamethylenetetramine and 900 parts of solvent.
In step S1, the raw materials preferably include the following components in parts by weight: 100 parts of silicon, 0.03 part of carbon nano tube, 5 parts of lithium supplement additive, 50 parts of graphite, 100 parts of novolac resin, 8 parts of PVA, 5 parts of PVP, 9 parts of hexamethylenetetramine and 900 parts of solvent.
In step S1, the raw materials preferably include the following components in parts by weight: 100 parts of silicon, 0.03 part of carbon nano tube, 3 parts of lithium supplement additive, 1 part of graphene, 200 parts of novolac resin, 8 parts of PVA, 5 parts of PVP, 18 parts of hexamethylenetetramine and 900 parts of solvent.
In step S1, the sanding process may be performed in a conventional sanding machine in the art, and typically yttria-stabilized zirconia balls with a diameter of 0.05 to 1mm, preferably 0.1 to 0.2mm are selected; the sand mill is preferably a pin-type dynamic separation high-energy sand mill. The time and operating conditions of the sanding can be selected by the person skilled in the art according to the characteristics of the raw material. The rotational speed of the sand mill can be 30-100%, preferably 90% of the design rotational speed.
In step S1, the ball milling may be performed in a ball mill conventional in the art, and is generally implemented by using yttria-stabilized zirconia balls with a diameter of 1-10 mm, preferably 1-3 mm; the ball mill is preferably a high energy attritor mill. The time and operating conditions of the ball milling can be selected by one skilled in the art according to the nature of the starting materials. The rotation speed of the ball mill can be 30-70% of the design rotation speed of the ball mill, and is preferably 40%.
In step S1, the sand milling or ball milling may be performed in one step, that is, the components of the raw material are sand milled or ball milled together; it can also be carried out stepwise. The sanding or ball milling is preferably carried out in at least two steps: firstly, the components at least comprising silicon, lithium supplement additive and solvent are sanded or ball-milled, and then the rest components at least comprising resin are added for sanding or ball-milling.
In step S1, the sanding or ball milling preferably includes high speed dispersion. The high-speed dispersion may be performed using a high-speed disperser. The time and operating conditions for the high speed dispersion can be selected by those skilled in the art according to the characteristics of the raw materials, as long as the slurry is uniformly dispersed.
In step S1, the sanding or ball milling preferably includes ultrasonic dispersion. The ultrasonic dispersion can be carried out by adopting an ultrasonic machine, and the ultrasonic machine can be an ultrasonic disperser or an ultrasonic dispersion stirrer. The time and operating conditions of the ultrasonic dispersion can be selected by those skilled in the art according to the characteristics of the raw materials, as long as the slurry is uniformly dispersed.
In a preferred embodiment, the raw materials include silicon, carbon nanotube slurry, graphene slurry, lithium carbonate, novolac resin, hexamethylenetetramine and NMP, and the homogenizing includes: dispersing the raw materials in a high-speed dispersion machine at a high speed for 0.1-1 hour; then ball milling for 0.5-3 hours in a high-energy vertical ball mill; and finally, ultrasonically dispersing for 0.5-2 hours to obtain slurry.
In a preferred embodiment, the raw materials include silicon, carbon nanotube slurry, graphite, lithium carbonate, novolac resin, hexamethylenetetramine and NMP, and the homogenizing includes: firstly, dispersing silicon, lithium carbonate, graphite and NMP in a high-speed dispersion machine at a high speed for 0.1-1 hour; then sanding for 0.5-12 hours in a pin-type dynamic separation high-energy sand mill, and converting part of graphite into graphene in the process; and then adding other components and sanding for 0.5-3 hours again to obtain the slurry.
In a preferred embodiment, the raw material comprises silicon, carbon nanotube slurry, graphene slurry or graphite, lithium carbonate, novolac resin, PVA, PVP, hexamethylenetetramine and NMP, and the homogenizing comprises: firstly, dispersing silicon, lithium carbonate, carbon nanotube slurry, graphene slurry or graphite and NMP in a high-speed dispersion machine at a high speed for 0.1-1 hour; then ball-milling for 10-60 minutes in a high-energy vertical ball mill; and then adding the linear phenolic resin, PVA, PVP and hexamethylenetetramine, and performing ball milling for 10-120 minutes again to obtain slurry.
In step S2, the evaporation may be performed in an evaporation apparatus conventional in the art, such as an oven, a rotary evaporator, a thickener, a hollow blade dryer, a freeze dryer, a double cone dryer, or a kiln. The evaporation apparatus is preferably a rotary evaporator. The rotary evaporator preferably rotates at 30 rpm.
In step S2, the temperature of the evaporation may be 60 to 85 ℃, preferably 65 ℃. The temperature of the drying can be properly adjusted according to the pressure of the slurry when the slurry is dried, and the temperature can be properly increased on the premise of avoiding bumping. The evaporation to dryness is preferably carried out under negative pressure. The pressure for evaporating to dryness can be 200-400 mbar, preferably 250 mbar.
In step S2, the evaporated atmosphere may be one or more of nitrogen, argon, hydrogen, carbon dioxide and ammonia, preferably nitrogen.
In step S3, the treatment manner and operation of the heat treatment may be conventional in the art, as long as the resin in the precursor a can be cured and/or pre-carbonized.
In step S3, the temperature of the heat treatment may be 100 ℃ to 680 ℃, preferably 150 ℃ to 300 ℃, for example 180 ℃. The heat treatment time can be 0.5-2 hours.
In step S3, the heat treatment preferably includes holding at a softening temperature, a curing temperature, and a decomposition temperature of the resin, respectively. When the resin comprises a novolac resin, the first heat treatment preferably comprises heat preservation at 130 ℃ and 280 ℃ for 0.5 to 2 hours, respectively.
In step S3, the atmosphere of the heat treatment may be one or more of air, nitrogen, argon, and hydrogen. One skilled in the art can select different atmospheres depending on the characteristics of the resin. When the resin comprises a phenolic resin, the atmosphere may be air or nitrogen.
In step S3, the heat treatment device for heat treatment may be a device conventionally used in heat treatment in the art, such as a cladding machine, a heating mixer, a rotary kiln, a roller furnace, a rotary kiln, a tube furnace, an atmosphere furnace, a box furnace, a pit furnace, a roller kiln, a tunnel kiln or a pushed slab kiln, wherein the heating mixer may be an electric heating mixer or a heat-conducting oil heating mixer. The electric heating mixer is preferably a V-shaped electric heating mixer. The operating parameters of the heat treatment apparatus for heat treatment may be conventional in the art, for example, when the heat treatment apparatus is a rotary kiln, the rotation speed of the apparatus may be 85-100%, preferably 98%, for example, 15 rpm of the design rotation speed of the apparatus; for example, when the heat treatment apparatus is a coating machine, the stirring speed may be 30 to 50Hz, preferably 45 Hz.
In step S3, the pulverization may be performed by a method conventional in the art. The comminution is preferably jet milling. The jet milling may be performed using a jet mill conventional in the art.
In a preferred embodiment of the present invention, in step S3, the pulverizing is performed in two steps: the first step is to crush the materials to millimeter-sized powder, and the second step is to crush the millimeter-sized powder to micron-sized powder. The crushing equipment adopted in the first step is preferably a jaw crusher or a double-roll machine; the second step employs a pulverizing apparatus preferably a ball mill, a jet mill, a mechanical mill or a Raymond mill.
In step S3, the particle size of the precursor B is preferably 6 to 10 μm.
In step S4, the coating agent is typically an organic coating agent, such as one or more of asphalt, asphalt-tar solution, coumarone resin, oleic acid, and heavy oil, preferably coumarone resin, and more preferably liquid coumarone resin. The amount of the coating agent is preferably 3 to 8 percent, more preferably 5 percent of the precursor B, calculated according to the amount of the carbon residue, and the percentage is mass percent.
In step S4, the mixing may be performed in a mixing device conventional in the art, which may be a fusion machine, a kneader or a compounder. The mixer can be a V-shaped mixer, a spiral ribbon mixer, a gravity-free mixer, a coulter mixer or a wire rod mixer. The mixing preferably comprises kneading with a kneader and then fusing with a fusion machine. The mixing time is preferably 0.1 to 2 hours.
In step S4, the coating may be performed in a coating machine conventional in the art. The operating conditions for the coating can be determined by the person skilled in the art according to the nature of the coating agent.
In step S4, the temperature of the coating may be 450 to 800 ℃, preferably 500 to 600 ℃. The coating time can be 0.5-2 hours.
In step S4, the atmosphere of the coating may be a nitrogen atmosphere. The stirring speed during coating can be 10-70 Hz, preferably 45 Hz.
In step S5, the treatment manner and operation of the heat treatment may be conventional in the art, as long as the precursor C can be carbonized, and the carbonization of the precursor C means the carbonization of the resin cured and/or pre-carbonized in the precursor C.
In step S5, the temperature of the heat treatment may be 800 to 1200 ℃, preferably 900 to 1100 ℃. The heat treatment time can be 0.5-2 hours. The heat treatment preferably comprises incubation at the charring temperature of the resin. When the resin comprises a novolac resin, the heat treatment comprises heat preservation at 850 ℃, 950 ℃ or 1100 ℃ for 0.5-2 hours.
In step S5, the atmosphere of the heat treatment may be one or more of nitrogen, argon, and hydrogen.
In step S5, the heat treatment apparatus for heat treatment may be an apparatus conventionally used in heat treatment in the art, such as a heating mixer, a rotary kiln, a roller furnace, a rotary kiln, a tube furnace, an atmosphere furnace, a box furnace, a shaft furnace, a roller kiln, a tunnel kiln, or a pushed slab kiln, wherein the heating mixer may be an electric heating mixer or a heat-conducting oil heating mixer. The heat treatment apparatus for the heat treatment is preferably a tube furnace. The operating parameters of the heat treatment apparatus may be conventional in the art, for example when the heat treatment apparatus is a rotary kiln, the rotational speed may be 85 to 100%, preferably 98%, for example 15 rpm of the design rotational speed of the apparatus.
The invention also provides a silicon-carbon composite material, which is prepared by the preparation method of the silicon-carbon composite material.
The silicon-carbon composite material of the invention can have the following properties: the particle size D50 is 5-15 μm (for example, 8 μm, 10 μm or 12 μm), and the specific surface area (BET method) is less than or equal to 5m2(preferably ≦ 3 m)2/g)。
The silicon-carbon composite material has a watermelon model structure: the carbon coating layer is 'melon peel' and has the effects of buffering volume expansion, isolating contact of the silicon material and electrolyte, reducing specific surface area and increasing conductivity; hard carbon formed after resin curing and carbonization is the melon pulp; the carbon nano tubes, the graphene and/or the graphite are uniformly distributed in the melon pulp to form a tendon and network or valve-like structure; silicon is uniformly distributed in the melon pulp to form melon seeds; during the preparation process, the lithium supplement additive reacts with the silicon oxide surface of the silicon surface to form a layer of silicate (such as lithium silicate) on the surface to form 'melon seed peel'. When the resin comprises phenolic resin as a main resin and one or more of polyvinyl alcohol, polyvinylpyrrolidone and polyethylene glycol as auxiliary resin, the main resin forms hard carbon in the preparation process, and the auxiliary resin forms a layer of film outside the hard carbon and is positioned between the melon peel and the melon pulp.
The invention also provides an electrode comprising the silicon-carbon composite material. The electrodes may be prepared using methods conventional in the art.
The invention also provides a lithium ion battery which takes the silicon-carbon composite material as a negative electrode material. The lithium ion battery can be prepared by a method conventional in the art.
The invention also provides application of the silicon-carbon composite material as a negative electrode material in a lithium ion battery, a lithium ion capacitor, a lithium sulfur battery or an all-solid-state battery.
Unless otherwise indicated, the particle sizes referred to herein are all volume median particle sizes (D50).
The carbon residue amount of the invention is measured according to the national standard GB/T268-92.
On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.
The reagents and raw materials used in the invention are available on the market, part of the raw materials may need to be obtained by powder preparation processes such as primary crushing, ball milling and the like, and the powder preparation processes are all conventional treatment processes in the powder industry.
The positive progress effects of the invention are as follows:
1. the silicon-carbon composite material has stable performance, low expansion rate, good particle size distribution of the product and low specific surface area.
2. When the electrode prepared by the silicon-carbon composite material is used for a battery, the electrode has high capacity, high first coulombic efficiency, excellent rate performance and cycle performance, for example, the specific capacity at 0.1C can reach more than 1500mAh/g, the first effect can reach more than 85 percent, the constant current ratio at 3C discharge can reach more than 72 percent, the capacity retention rate can reach more than 80 percent after 100 cycles, and the electrode has great application value in the fields of lithium ion batteries, solid-state batteries and the like.
3. The silicon-carbon composite material disclosed by the invention is simple in preparation process, high in working efficiency and low in environmental requirement, can realize industrial large-scale production, and is beneficial to reducing the material cost and improving the product performance.
Drawings
FIG. 1 is an SEM image of a silicon-carbon composite material obtained in example 1.
Fig. 2 is an XRD pattern of the silicon-carbon composite material obtained in example 1.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.
Silicon was purchased from sigma aldrich (sigma-aldrich) with a purity of 99.99% and a particle size of 0.1 μm.
0.2 wt% of monoThe Gemconner nanotube-NMP slurry was purchased from Shenyang Ister chemical technology Ltd, TUBALLTMBATT NMP series.
The 5 wt% graphene-NMP slurry is purchased from Shandong Yuhuang New energy science and technology Limited and has a particle size of no more than 15 μm.
The flake graphite powder was purchased from Virgie graphite Ltd of Qingdao city and had a particle size of 5 μm.
The linear phenolic resin is purchased from platinum-based casting materials of Henan, Inc., and has a softening point of 90-110 ℃.
PVA1788, PVP K30, hexamethylenetetramine, NMP were purchased from Chinese medicine.
Example 1
A preparation method of a silicon-carbon composite material comprises the following steps:
s1, homogenizing: the solvent is NMP-ethanol mixed solvent with the ratio of 10: 90. Mixing 900 parts of solvent, 100 parts of silicon, 5 parts of lithium carbonate, 0.03 part of single-walled carbon nanotube-NMP slurry (calculated by carbon nanotubes) and 50 parts of crystalline flake graphite powder, and stirring in a high-speed dispersion machine for 0.5 hour;
then transferring the mixture to a high-energy vertical ball mill for ball milling, wherein the ball mill adopts yttria stabilized zirconia balls with the diameter of 1mm, the rotating speed is 40 percent of the designed rotating speed of the equipment, and the mixture is continuously sanded for 30 minutes;
then, 100 parts of novolac resin, 9 parts of hexamethylenetetramine, 10 parts of PVA1788 and 5 parts of PVP K30 were added, and sanding was performed again for 30 minutes to obtain a slurry.
S2, drying by distillation: drying by adopting a rotary evaporator, setting the pumping pressure of a vacuum pump to be 250mbar, the temperature to be 65 ℃, the rotating speed to be 30 r/min, evaporating until no solvent is distilled off, and then taking out the material to obtain a precursor A.
S3, heat treatment: and (3) putting the precursor A into a V-shaped electric heating mixer, preserving heat for 1 hour at 150 ℃ under the air atmosphere, switching to a nitrogen atmosphere, preserving heat for 2 hours at 600 ℃, naturally cooling, and crushing by using a jet mill to obtain a precursor B with the particle size of 10 microns.
S4, coating: the coating agent adopts liquid coumarone resin, and the amount of the coating agent is 5 percent of that of the precursor B calculated according to the carbon residue amount. And uniformly mixing the precursor B with the liquid coumarone resin, kneading for 1 hour by using a kneading machine, then putting into a coating machine, protecting in a nitrogen atmosphere, stirring at the speed of 45Hz, and preserving the heat at 600 ℃ for 2 hours to obtain a precursor C.
S5, heat treatment: and (3) in a tubular furnace, preserving the heat for 2 hours at 1100 ℃ under the protection of nitrogen, and naturally cooling to obtain the silicon-carbon composite material.
Example 2
The procedure and conditions were the same as in example 1, except that 3 parts of lithium carbonate was added in step S1, and the amount of the coating agent in S4 was 8% of that of the precursor B.
Example 3
The procedure and conditions were the same as in example 1 except that the resin was added in step S1 and then the mixture was sanded again for 100 minutes.
Example 4
The procedure and conditions were the same as in example 1 except that 5 parts of PVA1788 and 10 parts of PVP K30 were added in step S1.
Comparative example 1
In this comparative example, no treatment was performed with the raw material silicon.
Comparative example 2
In this comparative example, no lithium carbonate was added and the other operations and parameters were carried out as in example 1.
Comparative example 3
In this comparative example, the coating of step S4 was not performed, and the other operations and parameters were performed as in example 1.
Effect example 1
The performance of the materials prepared in examples 1-4 and comparative examples 1-3 was tested by methods conventional in the art.
FIG. 1 is an SEM image of a silicon-carbon composite material obtained in example 1. As can be seen from the figure, the particles of the silicon-carbon composite material of the present invention are amorphous particles, and the surface of the particles has few defects such as cracks, protrusions, pits, etc., and the particles have obvious flaky graphite.
FIG. 2 is an XRD pattern (scanning pattern. theta. -2. theta., step 2 °/s) of a silicon carbon composite material obtained in example 1. As can be seen from the figure, the main diffraction peaks in the silicon-carbon composite material are those of graphite and silicon, and the lithium silicate peak is not obvious.
The particle sizes of the materials obtained in examples 1 to 4 and comparative examples 1 to 3 are shown in Table 1, and the particle size D50 was measured by Mastersize 2000 (Malvern 2000). The results show that the particle size D50 of the materials obtained in examples 1 to 4 was about 10 μm. The excessively large or small particle size is not beneficial to the processing of working sections such as pulping and coating and the like, and is also not beneficial to the transmission and diffusion of lithium ions; the large specific surface area is easy to cause the increase of side reaction and the reduction of first efficiency, and the poor electrolyte infiltration and the weakening of electrical property are caused by the excessively low specific surface area.
Effect example 2
(1) Preparation of the electrodes
Mixing the silicon-carbon composite materials obtained in the examples 1-4 and the comparative examples 1-3, the acetylene black conductive agent and the PVDF binder according to the mass ratio of 8:1:1 at room temperature, using NMP as a solvent to prepare uniform slurry, uniformly coating the slurry on a copper foil, wherein the coating surface density is about 3mg/cm2Then the copper foil is put into a vacuum drying oven to be dried for 12 hours at the temperature of 80 ℃. Cutting the dried copper foil into 2cm in area2The wafer of (a) is made into a working electrode.
(2) Assembly of half-cells
And (2) assembling the CR-2032 type button cell in a vacuum glove box by using a metal lithium sheet as a counter electrode, the product obtained in the step (1) as a working electrode, a Celgard 2400 polypropylene porous membrane as a diaphragm and 1mol/L LiPF6/EC: DEC (volume ratio of 1:1) solution as an electrolyte at room temperature.
(3) Specific capacity, specific capacity retention rate and 3C discharge constant current ratio test
Electrochemical testing was started after the assembled cell was allowed to stand at room temperature for 24 h. On an Arbin battery test system, according to the design capacity of 1400mAh/g, the current of 0.1C is adopted in the first test cycle, and the charging and discharging voltage interval is 5 mV-1.5V. The mixture was left for 5 minutes after the completion of the charge or discharge.
The capacity retention rate is measured by using a battery subjected to first cycle of 0.1C, and then performing charge-discharge cycle test in a range of 5 mV-1.5V by using a current of 0.5C.
The 3C discharge constant current ratio adopts a battery which is cycled for 3 weeks through 0.1C in the first week, and after the battery is fully charged, the battery is discharged to 5mV according to the current of 3C, and then the battery is discharged to 5mV at 0.1C. The calculation formula is as follows:
3C constant current ratio of 3C discharge constant current capacity/(3C discharge constant current capacity +0.1C discharge constant current)
Through tests, the capacity, the first effect and the capacity retention rate after 100 cycles of the silicon-carbon composite materials prepared in the examples 1 to 4 and the comparative examples 1 to 3 for the lithium ion battery are shown in the table 1.
TABLE 1
As can be seen from table 1, the silicon material of comparative example 1 has a capacity comparable to that of the examples, but has very low first-effect and 3C discharge constant current ratios, and very poor cycle performance, and is difficult to use in the production of commercial lithium batteries.
Although the capacities of the silicon-carbon composite materials of comparative examples 2 and 3 are close to those of the examples, the first effect, the 3C discharge constant current ratio and the capacity retention rate after 100 cycles are obviously different from those of the examples.
The silicon-carbon composite materials prepared in the embodiments 1 to 4 have high capacity, high first efficiency, high discharge constant current ratio and high capacity retention rate. For the negative electrode material of the lithium battery, the higher the first effect, the more the positive electrode material can be saved, so that the energy density of the lithium battery can be improved, and the comprehensive cost of the battery can be reduced. The discharge constant current ratio reflects the rate performance of the lithium battery, and the higher the discharge constant current ratio, the better the rate performance of the lithium battery. The capacity retention rate reflects the cycle performance of the lithium battery, and the higher the capacity retention rate is, the better the cycle performance of the lithium battery is.
According to the characteristics that the silicon-carbon composite material prepared by the embodiment of the invention has high capacity, high first-effect, excellent rate performance and cycle performance, the optimal examples of the invention can be obtained by adjusting the process parameters of each stage, or the advantages of both the capacity and the first-effect can be obtained, and the advantages of the other aspect can be highlighted.
Claims (10)
1. A preparation method of a silicon-carbon composite material comprises the following steps:
s1, homogenizing the raw materials to obtain slurry; wherein the raw materials comprise the following components in parts by weight: 100 parts of silicon, 0.005-1 part of carbon nano tube, 0.1-10 parts of lithium supplement additive, 10-200 parts of resin and solvent; the homogenizing comprises sanding or ball milling;
s2, evaporating the slurry to dryness to obtain a precursor A;
s3, carrying out heat treatment on the precursor A to enable resin in the precursor A to be solidified and/or pre-carbonized, and crushing to obtain a precursor B, wherein the particle size of the precursor B is 4-15 microns;
s4, mixing the precursor B with a coating agent for coating to obtain a precursor C; the amount of the coating agent is 2-20% of the precursor B calculated according to the amount of the carbon residue, and the percentage is mass percent;
and S5, carrying out heat treatment on the precursor C to carbonize the precursor C, thus obtaining the carbon nano tube.
2. The method of preparing a silicon-carbon composite material according to claim 1,
in step S1, the particle size of the silicon is 0.01 to 10 μm, preferably 0.1 to 5 μm, and more preferably 0.1 to 0.15 μm; the purity of the silicon is more than 99.99 percent; the content of the magnetic foreign matters in the silicon is not higher than 0.1%;
and/or, in step S1, the amount of the carbon nanotubes is 0.01 to 0.5 parts, preferably 0.03 parts; the carbon nano tube is a single-wall carbon nano tube and/or a multi-wall carbon nano tube; preferably, the diameter of the single-walled carbon nanotube is 0.1-10 nm, and the length is 0.1-10 μm; the diameter of the multi-walled carbon nanotube is 8-100 nm, and the length of the multi-walled carbon nanotube is 0.5-30 mu m; more preferably, the diameter of the single-walled carbon nanotube is 1-2 nm, and the length is 5 μm;
and/or in step S1, the dosage of the lithium supplement additive is 3-5 parts; the lithium supplement additive is one or more of lithium carbonate, lithium bicarbonate, lithium acetate, lithium oxalate, lithium hydroxide, lithium oxide, magnesium carbonate, magnesium hydroxide, magnesium powder and aluminum, and preferably lithium carbonate;
and/or in the step S1, the using amount of the resin is 20-100 parts; the carbon residue amount of the resin is preferably not less than 5%; the resin preferably comprises one or more of phenolic resin, polyvinyl alcohol, polyvinylpyrrolidone and polyethylene glycol; the phenolic resin is preferably a novolac resin, and the softening point of the novolac resin is preferably 90-110 ℃; the polyvinyl alcohol is preferably PVA 1788; the polyvinylpyrrolidone is preferably PVP K30; the resin preferably comprises a phenolic resin, and when the resin comprises a phenolic resin, the amount of the phenolic resin is preferably 100 parts; the resin preferably comprises a phenolic resin and comprises one or more of polyvinyl alcohol, polyvinylpyrrolidone and polyethylene glycol; the resin preferably comprises phenolic resin, polyvinyl alcohol and polyvinylpyrrolidone, wherein the mass ratio of the phenolic resin to the polyvinyl alcohol to the polyvinylpyrrolidone is preferably 100:8: 5;
and/or, in step S1, when the resin includes novolac resin, the raw material further includes a curing agent, which is preferably aliphatic amine curing agent, more preferably hexamethylenetetramine; the amount of the curing agent is preferably 6 to 15%, more preferably 9% of the novolac resin;
and/or, in step S1, the solvent is one or more of water, ethanol, N-methylpyrrolidone, N-dimethylformamide and dimethylacetamide, preferably N-methylpyrrolidone or a mixed solvent of N-methylpyrrolidone and ethanol; the ratio of the N-methylpyrrolidone-ethanol mixed solvent is preferably 10: 90; the solvent is preferably used in an amount such that the solids content in the slurry is not higher than 20 wt%; alternatively, the solvent is preferably used in such an amount that the viscosity of the slurry does not exceed 50mPa · s;
and/or in step S1, the raw material further includes graphite and/or graphene; taking 100 parts of silicon and 0.005-1 part of graphene; the amount of the graphite is 0.1 to 100 parts, preferably 10 to 50 parts.
3. The method of preparing a silicon-carbon composite material according to claim 1,
in step S1, the raw materials comprise the following components in parts by weight: 100 parts of silicon, 0.03 part of carbon nano tube, 5 parts of lithium supplement additive, 50 parts of graphite, 100 parts of linear phenolic resin, 10 parts of PVA, 5 parts of PVP, 9 parts of hexamethylenetetramine and 900 parts of solvent;
in step S1, the raw materials comprise the following components in parts by weight: 100 parts of silicon, 0.1 part of carbon nano tube, 3 parts of lithium supplement additive, 50 parts of graphite, 100 parts of linear phenolic resin, 8 parts of PVA, 5 parts of PVP, 9 parts of hexamethylenetetramine and 900 parts of solvent;
in step S1, the raw materials comprise the following components in parts by weight: 100 parts of silicon, 0.03 part of carbon nano tube, 5 parts of lithium supplement additive, 50 parts of graphite, 100 parts of novolac resin, 8 parts of PVA, 5 parts of PVP, 9 parts of hexamethylenetetramine and 900 parts of solvent;
in step S1, the raw materials comprise the following components in parts by weight: 100 parts of silicon, 0.03 part of carbon nano tube, 3 parts of lithium supplement additive, 1 part of graphene, 200 parts of novolac resin, 8 parts of PVA, 5 parts of PVP, 18 parts of hexamethylenetetramine and 900 parts of solvent.
4. The method of preparing a silicon-carbon composite material according to claim 1,
in step S1, the sanding is performed in a sand mill, and yttria-stabilized zirconia balls with a diameter of 0.05 to 1mm, preferably 0.1 to 0.2mm are selected; the sand mill is preferably a pin-type dynamic separation high-energy sand mill;
and/or, in step S1, the ball milling is performed in a ball mill, which generally selects yttria-stabilized zirconia balls with a diameter of 1-10 mm, preferably 1-3 mm; the ball mill is preferably a high energy vertical ball mill;
and/or, in step S1, the sand grinding or ball milling is performed in one step, that is, the components of the raw materials are sand ground or ball milled together; or, the sand grinding or ball milling is carried out step by step; the sanding or ball milling is preferably carried out in at least two steps: firstly, sanding or ball-milling components at least comprising silicon, a lithium supplement additive and a solvent, then adding the rest components at least comprising resin, and then sanding or ball-milling;
and/or, in step S1, the high speed dispersion is included before the sanding or ball milling;
and/or, in step S1, the sanding or ball milling may include ultrasonic dispersion.
Alternatively, in step S1, the raw materials include silicon, carbon nanotube slurry, graphene slurry, lithium carbonate, novolac resin, hexamethylenetetramine, and NMP, and the homogenizing includes: dispersing the raw materials in a high-speed dispersion machine at a high speed for 0.1-1 hour; then ball milling for 0.5-3 hours in a high-energy vertical ball mill; finally, ultrasonically dispersing for 0.5-2 hours to obtain slurry;
alternatively, in step S1, the raw materials include silicon, carbon nanotube slurry, graphite, lithium carbonate, novolac resin, hexamethylenetetramine, and NMP, and the homogenizing includes: firstly, dispersing silicon, lithium carbonate, graphite and NMP in a high-speed dispersion machine at a high speed for 0.1-1 hour; then sanding for 0.5-12 hours in a pin-type dynamic separation high-energy sand mill, and converting part of graphite into graphene in the process; then adding other components and sanding for 0.5-3 hours again to obtain slurry;
alternatively, in step S1, the raw material includes silicon, carbon nanotube slurry, graphene slurry or graphite, lithium carbonate, novolac resin, PVA, PVP, hexamethylenetetramine, and NMP, and the homogenizing includes: firstly, dispersing silicon, lithium carbonate, carbon nanotube slurry, graphene slurry or graphite and NMP in a high-speed dispersion machine at a high speed for 0.1-1 hour; then ball-milling for 10-60 minutes in a high-energy vertical ball mill; and then adding the linear phenolic resin, PVA, PVP and hexamethylenetetramine, and performing ball milling for 10-120 minutes again to obtain slurry.
5. The method of preparing a silicon-carbon composite material according to claim 1,
in step S2, the evaporation equipment is an oven, a rotary evaporator, a thickener, a hollow blade dryer, a freeze dryer, a double cone dryer or a kiln; the evaporation equipment is preferably a rotary evaporator; the rotation speed of the rotary evaporator is preferably 30 revolutions per minute;
and/or in step S2, the temperature of the evaporation to dryness is 60 to 85 ℃, preferably 65 ℃;
and/or in step S2, the pressure of the evaporation is 200 to 400mbar, preferably 250 mbar;
and/or, in step S2, the evaporated atmosphere is one or more of nitrogen, argon, hydrogen, carbon dioxide and ammonia, preferably nitrogen;
and/or, in step S3, the heat treatment comprises holding at the softening temperature, the curing temperature and the decomposition temperature of the resin, respectively; when the resin comprises a novolac resin, the first heat treatment preferably comprises heat preservation at 130 ℃ and 280 ℃ for 0.5-2 hours, respectively;
and/or, in step S3, the atmosphere of the heat treatment is one or more of air, nitrogen, argon and hydrogen;
and/or in step S3, the heat treatment device for heat treatment is a cladding machine, a heating mixer, a rotary furnace, a roller furnace, a rotary kiln, a tube furnace, an atmosphere furnace, a box furnace, a well furnace, a roller kiln, a tunnel kiln or a pushed slab kiln, wherein the heating mixer is preferably an electric heating mixer or a heat-conducting oil heating mixer, and the electric heating mixer is preferably a V-shaped electric heating mixer;
and/or the crushing mode is air flow crushing;
and/or, the pulverization is carried out in two steps: firstly, crushing the materials into millimeter-sized powder, wherein the adopted crushing equipment is preferably a jaw crusher or a double-roll machine; secondly, the millimeter-sized powder is crushed into micron-sized powder by adopting a crushing device which is preferably a ball mill, a jet mill, a mechanical mill or a Raymond mill;
and/or the particle size of the precursor B is 6-10 μm.
6. The method of preparing a silicon-carbon composite material according to claim 1,
in step S4, the coating agent is an organic coating agent, preferably one or more of asphalt, asphalt-tar solution, coumarone resin, oleic acid, and heavy oil, more preferably coumarone resin, and most preferably liquid coumarone resin;
and/or, in step S4, the amount of the coating agent is 3% to 8%, preferably 5%, of the precursor B, calculated according to the amount of carbon residue thereof, and the percentage is mass percent;
and/or, in step S4, the mixing is performed in a mixing device, preferably a fusion machine, a kneader or a compounder; the mixer is preferably a V-shaped mixer, a ribbon mixer, a gravity-free mixer, a coulter mixer or a wire rod mixer; the mixing preferably comprises kneading with a kneader and then fusing with a fusion machine; the mixing time is preferably 0.1 to 2 hours;
and/or, in step S4, the wrapping is performed in a wrapper; the temperature of the coating is preferably 450 to 800 ℃, more preferably 500 to 600 ℃; the coating time is preferably 0.5 to 2 hours; the atmosphere of the coating is preferably a nitrogen atmosphere; the stirring speed during coating is 10-70 Hz, preferably 45 Hz;
and/or in step S5, the temperature of the heat treatment is 800-1200 ℃, preferably 900-1100 ℃;
and/or in step S5, the heat treatment time is 0.5-2 hours;
and/or, in step S5, the heat treatment includes holding at a carbonization temperature of the resin or the coating agent; when the resin comprises a novolac resin and the coating agent is a liquid coumarone resin, the heat treatment preferably comprises heat preservation at 850 ℃, 950 ℃ or 1100 ℃ for 0.5-2 hours;
and/or in step S5, the atmosphere of the heat treatment is one or more of nitrogen, argon and hydrogen;
and/or, in step S5, the heat treatment device for heat treatment is a heating mixer, a rotary furnace, a roller furnace, a rotary kiln, a tube furnace, an atmosphere furnace, a box furnace, a well furnace, a roller kiln, a tunnel kiln or a pushed slab kiln, wherein the heating mixer is preferably an electric heating mixer or a heat-conducting oil heating mixer; the heat treatment apparatus for the heat treatment is preferably a tube furnace.
7. A silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material according to any one of claims 1 to 6.
8. An electrode comprising the silicon-carbon composite material of claim 7.
9. A lithium ion battery using the silicon-carbon composite material according to claim 7 as a negative electrode material.
10. Use of the silicon-carbon composite material according to claim 7 as a negative electrode material in a lithium ion battery, a lithium ion capacitor, a lithium sulfur battery or an all-solid-state battery.
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