CN114883546A - Silicon-carbon composite active material, preparation method thereof, negative plate and secondary battery - Google Patents
Silicon-carbon composite active material, preparation method thereof, negative plate and secondary battery Download PDFInfo
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- 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
- H01M4/364—Composites as mixtures
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- 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
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/134—Electrodes based on metals, Si or alloys
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- H—ELECTRICITY
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- 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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
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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
- H01M4/58—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
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- 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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention belongs to the technical field of secondary batteries, and particularly relates to a silicon-carbon composite active material and a preparation method thereof, a negative plate and a secondary battery, wherein the method comprises the following steps: step S1, embedding a silica material into a graphite material to obtain a silicon-carbon mixture, and screening, wherein oversize products are the silicon-embedded mixture; step S2, mixing the silicon-embedded mixture with a sealing agent, sealing, crushing and screening to obtain a silicon-carbon composite active material; wherein the particle diameter D50 of the silica material is 1-60 μm, and the particle diameter D50 of the graphite material is 0.1-10 μm. According to the preparation method of the silicon-carbon composite active material, the silica material and the graphite material with certain particle sizes are arranged, so that the silica material and the graphite material have more contact sites, the silica material is easier to embed into the graphite material to form a silicon-embedded mixture, and the silicon-carbon composite active material is obtained through sealing treatment.
Description
Technical Field
The invention belongs to the technical field of secondary batteries, and particularly relates to a silicon-carbon composite active material, a preparation method thereof, a negative plate and a secondary battery.
Background
In the past two decades, people have been devoted to research and development of high-performance lithium ion battery technology to meet the requirements of consumers on the electric energy storage and use capacity of lithium ion batteries of communication equipment, electric vehicles and the like. Silicon-based materials (such as Si and SiOx) are considered to be one of the most promising candidate materials for replacing carbon cathode materials due to the characteristics of ultrahigh specific capacity, abundant reserves in nature, relatively low lithium absorption voltage and the like. However, when a pure silicon negative electrode is completely lithiated, a huge volume expansion rate can be generated, the expansion rate can reach 200% -300%, the electrode is easy to pulverize and even break, and an active material is easily layered, so that an SEI film on the surface of the negative electrode is repeatedly broken and generated, a new SEI film continuously grows and continuously consumes electrolyte, the capacity of a battery is rapidly attenuated, and the problem how to solve the problem is a research hotspot of a silicon-based negative electrode material.
At present, more solution strategies are to introduce a matrix material with small volume effect and good electrical property into a silicon-based material to prepare a silicon-based composite material, so that on one hand, the mechanical flexibility of the matrix material is utilized as a spatially expanded base material of the silicon-based negative electrode material, and further the purpose of optimizing the cycle performance of the silicon-based composite material is achieved, and on the other hand, the low conductivity of the silicon-based negative electrode material is overcome through the good conductivity of the matrix material. Graphite has good mechanical properties, but it is still a difficult problem how to overcome the side effects of the volume expansion of SiOx particles in graphite materials.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the preparation method of the silicon-carbon composite active material is provided, the particle diameters of the graphite material and the silica material are limited, so that the silica material is more easily embedded into the graphite material to form a silicon-embedded mixture, and the silica composite active material is obtained after sealing treatment and has good electrochemical performance and less volume expansion.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a silicon-carbon composite active material comprises the following steps:
step S1, embedding a silica material into a graphite material to obtain a silicon-carbon mixture, and screening, wherein oversize products are the silicon-embedded mixture;
step S2, mixing the silicon-embedded mixture with a sealing agent, sealing, crushing and screening to obtain a silicon-carbon composite active material;
wherein the particle diameter D50 of the silica material is 1-60 μm, and the particle diameter D50 of the graphite material is 0.1-10 μm.
Preferably, the weight part ratio of the silicon oxide material to the graphite material in the step S1 is 0.1-40: 100 to 120.
Preferably, the embedding manner in step S1 includes at least one of mechanical stirring, ball milling, ultrasonic vibration, mechanical vibration, spraying, sedimentation, deposition, spraying, wetting, gasification, polymerization, soaking, and liquefaction.
Preferably, the graphite material is at least one of artificial porous graphite, natural porous graphite, modified porous graphite, porous soft carbon and porous hard carbon; the silicon oxide material is SiOx, wherein x is more than or equal to 0 and less than or equal to 2, and the SiOx comprises at least one of silicon oxide, silicon dioxide and metal-containing composite SiOx.
Preferably, the weight part ratio of the silicon-embedded mixture to the sealing agent in the step S2 is 100-120: 20 to 40.
Preferably, the sealing process in step S2 specifically includes: and mixing the sealing agent and the silicon-embedded mixture at the temperature of 15-400 ℃.
Preferably, the sealing agent in step S2 is at least one of lithium borate, polyvinylidene fluoride, polyvinyl fluoride, urea, lithium silicofluoride, and lithium oxalyldifluoroborate.
The second purpose of the invention is: aiming at the defects of the prior art, the silicon-carbon composite active material is provided, and has good electrochemical performance and lower volume expansion rate.
In order to achieve the purpose, the invention adopts the following technical scheme:
a silicon-carbon composite active material is prepared by the preparation method of the silicon-carbon composite active material.
The third purpose of the invention is that: aiming at the defects of the prior art, the negative plate is provided, and has good electrochemical performance and a lower volume expansion rate.
In order to achieve the purpose, the invention adopts the following technical scheme:
the negative plate comprises a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector, wherein the negative active material layer comprises the silicon-carbon composite active material.
The fourth purpose of the invention is that: in order to overcome the defects in the prior art, the secondary battery is provided, and has good electrochemical performance and low volume expansion rate.
In order to achieve the purpose, the invention adopts the following technical scheme:
a secondary battery comprises the negative plate.
Compared with the prior art, the invention has the beneficial effects that: according to the preparation method of the silicon-carbon composite active material, the silica material and the graphite material with certain particle sizes are arranged, so that the silica material and the graphite material have more contact sites, the silica material is easier to embed into the graphite material to form a silicon-embedded mixture, and the silicon-carbon composite active material is obtained through sealing treatment.
Detailed Description
1. A preparation method of a silicon-carbon composite active material comprises the following steps:
step S1, embedding the silica material into the graphite material to obtain a silicon-carbon mixture, and screening, wherein the oversize product is the silicon-embedded mixture;
step S2, mixing the silicon-embedded mixture with a sealing agent, sealing, crushing and screening to obtain a silicon-carbon composite active material;
wherein the particle diameter D50 of the silicon-oxygen material is 1-60 μm, preferably 4-30 μm, and the particle diameter D50 of the graphite material is 0.1-10 μm, preferably 3-6 μm.
According to the preparation method of the silicon-carbon composite active material, the silica material and the graphite material with certain particle sizes are arranged, so that the silica material and the graphite material have more contact sites, the silica material is easier to embed into the graphite material to form a silicon-embedded mixture, and the silicon-carbon composite active material is obtained through sealing treatment. The sealing treatment can seal the embedded silicon, ensure that the silicon is firmly combined with the porous graphite, avoid the silica material with expanded volume from expanding and overflowing from pores or a sheet layer, leave a certain buffer space in the pores or the sheet layer of the graphite material, avoid the volume of the pores or the sheet layer from being low, reduce the pulverization of Si particles, ensure the physical integrity of the pole piece and avoid the embedment; after sealing treatment, drying at the temperature of 60-150 ℃, and screening oversize products with the grain size of more than or equal to L mu m to obtain the silicon-carbon composite active material; furthermore, the range of L is 1-5.
Wherein the ratio of GR-D50/SiOx-D50 is 1-8, preferably 1.2-5; the ratio is set so that the silica material is more easily embedded in the graphite material to form a silicon-embedded mixture. Silicon-embedded mixture the particle size of the silicon-embedded mixture is slightly larger than that of the graphite material due to the embedding of the silicon-oxygen material, and the silicon-carbon mixture with the particle size larger than that of SiOx-D50 in the silicon-embedded mixture is selected through sieving.
Preferably, the weight part ratio of the silicon oxide material to the graphite material in the step S1 is 0.1-40: 100 to 120. The particle size of the graphite material is set to be larger than that of the silica material, so that the silica material is easier to embed into the graphite material, and the silica material is fully embedded into the graphite material by a certain weight part, so that a silicon-embedded mixture with better electrochemical performance is obtained, and the volume expansion rate is lower.
Further preferably, in the step S1, the weight part ratio of the silicon oxide material to the graphite material is 0.1-2: 100-105, 2-5: 100-105, 5-8: 100-105, 8-10: 100-105, 10-15: 100-105, 15-20: 100-105, 20-25: 100-105, 25-30: 100-105, 30-35: 100-105, 35-40: 100 to 105, 0.1 to 2: 105-110, 2-5: 105-110, 5-8: 105-110, 8-10: 105-110, 10-15: 105-110, 15-20: 105-110, 20-25: 105-110, 25-30: 105-110, 30-35: 105-110, 35-40: 105 to 110, 0.1 to 2: 110-115, 2-5: 110-115, 5-8: 110-115, 8-10: 110-115, 10-15: 110-115, 15-20: 110-115, 20-25: 110-115, 25-30: 110-115, 30-35: 110-115, 35-40: 110-115, 0.1-2: 115-120, 2-5: 115-120, 5-8: 115-120, 8-10: 115-120, 10-15: 115-120, 15-20: 115-120, 20-25: 115-120, 25-30: 115-120, 30-35: 115-120, 35-40: 115 to 120 in any ratio.
Preferably, the embedding manner in step S1 includes at least one of mechanical stirring, ball milling, ultrasonic vibration, mechanical vibration, spraying, sedimentation, deposition, spraying, wetting, gasification, polymerization, soaking, and liquefaction. The silicon-oxygen material and the graphite material are mixed and embedded in a physical mode, and the obtained silicon-embedded mixture has good electrochemical performance.
Preferably, the graphite material is at least one of artificial porous graphite, natural porous graphite, modified porous graphite, porous soft carbon and porous hard carbon; the silicon oxygen material is SiOx, wherein x is more than or equal to 0 and less than or equal to 2, and the SiOx comprises at least one of silicon monoxide, silicon dioxide and metal-containing composite SiOx. Silicon oxygen materials include, but are not limited to, nano silicon simple substance (Si), micro silicon simple substance (Si), nano silicon oxide (SiO), micro silicon oxide (SiO), nano silicon dioxide (SiO) 2 ) Micron silicon dioxide (SiO2), metal-containing composite nano SiOx, and metal-containing composite micron SiOx. When x is 1, SiOx is a siliconoxide SiO. Preferably, SiOx may be doped with at least one element of carbon, sulfur, hydrogen, nitrogen, phosphorus, boron, tin, selenium, lithium, magnesium, sodium, potassium, calcium, beryllium, strontium, zirconium, vanadium, titanium, boron, zinc, aluminum, silver, fluorine.
Preferably, the weight part ratio of the silicon-embedded mixture to the sealing agent in the step S2 is 100-120: 20 to 40. The sealing agent mainly seals holes in the graphite material, so that the embedded silica material is prevented from being separated, and the combination degree is improved.
Further preferably, in the step S2, the weight part ratio of the silicon-embedded mixture to the sealing agent is 100: 20. 100, and (2) a step of: 25. 100, and (2) a step of: 28. 100, and (2) a step of: 30. 100, and (2) a step of: 32. 100, and (2) a step of: 35. 100, and (2) a step of: 40. 110: 20. 110: 25. 110: 28. 110: 30. 110: 32. 110: 35. 110: 40. 120: 20. 120: 25. 120: 28. 120: 30. 120: 32. 120: 35. 120: 40.
Preferably, the sealing process in step S2 specifically includes: and mixing the sealing agent and the silicon-embedded mixture at the temperature of 15-400 ℃. The mixing is one of the modes of mechanical stirring/ball milling/ultrasonic vibration and the like.
Preferably, the sealing agent in step S2 is at least one of lithium borate, polyvinylidene fluoride, polyvinyl fluoride, urea, lithium silicofluoride, and lithium oxalyldifluoroborate.
2. A silicon-carbon composite active material has good electrochemical performance and low volume expansion rate.
A silicon-carbon composite active material is prepared by the preparation method of the silicon-carbon composite active material.
3. A negative plate has good electrochemical performance and low volume expansion rate.
The negative plate comprises a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector, wherein the negative active material layer comprises the silicon-carbon composite active material.
4. A secondary battery has good electrochemical properties and a low volume expansion ratio.
A secondary battery comprises the negative plate.
The secondary battery can be a lithium ion battery, a magnesium ion battery, a calcium ion battery and a sodium ion battery. The following is an example of a lithium ion battery. The utility model provides a lithium ion battery, includes positive plate, barrier film, negative pole piece, electrolyte and casing, the barrier film separates positive plate and negative pole piece, the casing encapsulates parcel with positive plate, barrier film, negative pole piece and electrolyte. The negative plate is the negative plate.
A preparation method of a lithium ion battery comprises the following steps:
step A1, mixing the silicon-carbon composite active material, the conductive additive and the binder according to a mass ratio of 80-98: 0.5-12: 0.5-5 of mixing and pulping to obtain silicon-carbon composite slurry;
step A2, coating the silicon-carbon composite slurry on a negative current collector, drying into a pole piece, tabletting, slitting and carrying out vacuum drying to obtain a silicon-carbon composite negative pole piece;
and A3, sequentially stacking and winding the silicon-carbon composite negative plate, the isolating membrane and the positive plate to obtain a battery core, encasing the battery core, injecting electrolyte into the battery case, packaging, standing, forming and grading to obtain the lithium ion battery.
In the step A1, in the step of mixing and pulping, the adding amount of the silicon-carbon composite active material accounts for 50-99% of the mass of the silicon-carbon composite slurry, and preferably 90-98%.
In the step a1, the conductive additive is at least one of copper powder, nickel powder, conductive carbon black, acetylene black, graphite, graphene, fibrous carbon conductive agent, carbon nanotube, tin oxide, iron oxide, zinc oxide, copper oxide, aluminum oxide, metal-fiber composite conductive agent, and metal-carbon composite powder conductive agent.
In the step a1, the binder is at least one of single-component classification, multi-component classification and polymerization of guar gum, sodium alginate, acrylic acid, vinyl alcohol, polyaniline, benzimidazole, styrene butadiene rubber, arabic gum, xanthan gum, carrageenan, sodium/lithium carboxymethylcellulose, PVDF and the like.
The mass of the silicon element in the silicon-carbon composite negative plate in the negative plate accounts for 0.1-80%, preferably 2-35% of the mass of the membrane on the negative current collector.
The negative current collector is at least one of copper foil, porous copper foil, foamed nickel/copper foil, tin-plated zinc copper foil, carbon-coated copper foil, alloy copper foil, nickel foil, steel foil and titanium foil.
The expansion rate of the single-layer membrane on the negative plate in the negative current collector after the first filling is 21-50%, preferably 20-30%; when the membrane on the silicon-carbon composite negative plate is n layers, the calculation formula of the expansion rate (%) is (the thickness after the silicon-carbon composite negative plate is filled-the thickness before the silicon-carbon composite negative plate is filled)/(the thickness before the silicon-carbon composite negative plate is filled-the thickness of the negative current collector) × 100% × (1/n), and n is a positive integer greater than or equal to 1, 2, 3, 4, 5, 6.
The positive plate comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, wherein the positive active material layer comprises a positive active material, and the positive active material can include but is not limited to a chemical formula such as Li a Ni x Co y M z O 2-b N b (wherein a is more than or equal to 0.95 and less than or equal to 1.2, x>0, y is more than or equal to 0, z is more than or equal to 0, and x + y + z is 1,0 is more than or equal to b and less than or equal to 1, M is selected from one or more of Mn and Al and N is selected from F, P, S), and the positive active material can also be selected from the group consisting of but not limited to LiCoO 2 、LiNiO 2 、LiVO 2 、LiCrO 2 、LiMn 2 O 4 、LiCoMnO 4 、Li 2 NiMn 3 O 8 、LiNi 0.5 Mn 1.5 O 4 、LiCoPO 4 、LiMnPO 4 、LiFePO 4 、LiNiPO 4 、LiCoFSO 4 、CuS 2 、FeS 2 、MoS 2 、NiS、TiS 2 And the like, and the positive electrode active material may be specifically at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, and lithium iron phosphate. The positive electrode active material may also be modified, and the method of modifying the positive electrode active material should be known to those skilled in the art, for example, the positive electrode active material may be modified by coating, doping, etc., and the material used in the modification process may be one or a combination of more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc., but is not limited thereto. And the positive current collector is usually a structure for collecting current orThe positive electrode current collector may be any material suitable for use as a positive electrode current collector in lithium ion batteries in the art, for example, the positive electrode current collector may include, but is not limited to, metal foils and the like, and more specifically, may include, but is not limited to, aluminum foils and the like.
And the separator may be various materials suitable for lithium ion battery separators in the art, and for example, may be one or a combination of more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fiber, and the like, including but not limited thereto.
The lithium ion battery also comprises electrolyte, and the electrolyte comprises an organic solvent, electrolyte lithium salt and an additive. Wherein the electrolyte lithium salt may be LiPF used in a high-temperature electrolyte 6 And/or LiBOB; or LiBF used in low-temperature electrolyte 4 、LiBOB、LiPF 6 At least one of; or LiBF used in anti-overcharge electrolyte 4 、LiBOB、LiPF 6 At least one of, LiTFSI; may also be LiClO 4 、LiAsF 6 、LiCF 3 SO 3 、LiN(CF 3 SO 2 ) 2 At least one of (1). And the organic solvent may be a cyclic carbonate including PC, EC; or chain carbonates including DFC, DMC, or EMC; and also carboxylic acid esters including MF, MA, EA, MP, etc. And the additives include, but are not limited to, at least one of film forming additives, conductive additives, flame retardant additives, overcharge prevention additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low temperature performance, and multifunctional additives. Lithium salts include, but are not limited to, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorooxalato borate, lithium dioxalate borate, lithium difluorophosphate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalato phosphate.
The shell is made of at least one of an aluminum plastic film soft shell, an aluminum shell, a steel shell and a plastic hard shell.
The present invention will be described in further detail with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.
Example 1
A lithium ion secondary battery comprises a positive plate, a negative plate and a diaphragm which is arranged between the positive plate and the negative plate, wherein the negative plate is the negative plate.
Preparing a negative plate:
an anode material, comprising:
0.5kg of silica SiO (containing 0.10kg of lithium carbonate) with D50 of 3.7 mu m is mechanically stirred and mixed for 2h, the rotation speed of a stirrer is 300r/min, 4.5g of porous graphite pores with D50 of 7.4m are embedded to obtain a silicon-carbon mixture, and 4.97kg of oversize products with the particle size of more than or equal to 2 mu m are sieved to obtain a silicon-embedded mixture;
4.0kg of silicon-embedded mixture and 0.25kg of fused polyvinyl fluoride sealing agent are mechanically stirred and mixed for 2 hours at the machine rotation speed of 300r/min, and 4.11kg of oversize products with the grain diameter of more than or equal to 2 mu m are obtained through sealing treatment, crushing, drying at 65 ℃ and screening, thus obtaining the silicon-carbon composite active material.
A preparation method of a negative plate comprises the following steps: mixing a silicon-carbon composite active material, Super-P, a conductive carbon tube CNT, sodium carboxymethyl cellulose CMC and a binder SBR (styrene butadiene rubber) according to a mass ratio to prepare a silicon-carbon composite slurry, adding deionized water, stirring in vacuum to obtain a negative electrode slurry, uniformly coating the slurry on a current collector copper foil, drying to form a pole piece, tabletting, slitting, drying in vacuum, and drying to obtain the SiO/C composite negative electrode piece.
Preparing a positive pole piece:
mixing the positive active material lithium nickel cobalt manganese oxide (LiNi) 0.8 Co 0.1 Mn 0.1 O 2 NCM811), conductive carbon Super-P and polyvinylidene fluoride PVDF serving as a binder are mixed according to the mass ratio for pulping, solvent N-methylpyrrolidone NMP is added, uniform slurry is obtained after vacuum stirring, and the slurry is uniformly coated on an aluminum foil and dried to obtain the positive plate.
Preparation of lithium ion secondary battery:
and winding the prepared negative plate, the prepared isolating membrane and the prepared positive plate to obtain a battery core, encasing the battery core, injecting electrolyte into the battery case, packaging, forming and grading to obtain the lithium ion secondary battery.
Examples 2 to 4 are different from example 1 in the amounts of the silicon oxide composite active material and Super-P used, and the specific amounts of the positive electrode raw material ratios and the negative electrode raw material ratios used in examples 1 to 4 are shown in Table 1.
Example 5
A lithium ion secondary battery comprises a positive plate, a negative plate and a diaphragm which is arranged between the positive plate and the negative plate, wherein the negative plate is the negative plate.
Preparing a negative plate:
an anode material, comprising:
0.5kg of silica SiO (containing 0.15kg of lithium carbonate) with D50 of 3.7 mu m is mechanically stirred and mixed for 2h, the rotation speed of a stirrer is 300r/min, 4.5kg of porous graphite with D50 of 7.4m is embedded to obtain a silicon-carbon mixture, and 4.99kg of oversize products with the particle size of more than or equal to 2 mu m are sieved to obtain a silicon-embedded mixture;
4.0kg of silicon-embedded mixture and 0.5kg of fused urea sealing agent are mechanically stirred and mixed for 2 hours at the machine rotation speed of 300r/min, and 4.37kg of oversize products with the grain diameter of more than or equal to 2 mu m are obtained through sealing treatment, crushing, drying at 65 ℃ and screening, thus obtaining the silicon-carbon composite active material.
A preparation method of a negative plate comprises the following steps: mixing a silicon-carbon composite active material, Super-P, a conductive carbon tube CNT, sodium carboxymethyl cellulose CMC and a binder SBR according to a mass ratio, adding deionized water, stirring in vacuum to obtain a negative electrode slurry, uniformly coating the slurry on a copper foil, tabletting, and drying to obtain the composite negative electrode sheet.
Preparing a positive pole piece:
mixing the positive active material lithium nickel cobalt manganese oxide (LiNi) 0.8 Co 0.1 Mn 0.1 O 2 ) Mixing the conductive carbon Super-P and a polyvinylidene fluoride (PVDF) binder according to a mass ratio, adding a solvent N-methyl pyrrolidone (NMP), stirring in vacuum to obtain uniform slurry, uniformly coating the slurry on an aluminum foil, and drying to obtain a positive plate。
Preparation of lithium ion secondary battery:
and winding the composite negative plate, the isolating membrane and the positive plate to obtain a battery core, encasing the battery core, injecting electrolyte into the battery case, packaging, forming and grading to obtain the lithium ion secondary battery.
Examples 6 to 8 are different from example 5 in the amounts of the silicon oxide composite active material and Super-P used, and the specific amounts of the positive electrode raw material ratios and the negative electrode raw material ratios used in examples 5 to 8 are shown in Table 1.
Comparative example 1
A lithium ion secondary battery comprises a positive plate, a negative plate and a diaphragm which is arranged between the positive plate and the negative plate.
Preparing a negative plate:
a negative electrode material comprising 0.5kg of silica SiO (containing 0.15kg of lithium carbonate) and 4.5kg of graphite were mechanically stirred and mixed for 2 hours; wherein the rotating speed of the stirrer is 300r/min, and the SiO/C cathode material is prepared.
A preparation method of a negative plate comprises the following steps: mixing the SiO/C negative electrode material, Super-P, a conductive carbon tube CNT, sodium carboxymethyl cellulose CMC and a binder SBR according to a mass ratio, adding deionized water, stirring in vacuum to obtain uniform slurry, uniformly coating the slurry on a copper foil, tabletting and drying to obtain the SiO/C negative electrode sheet.
Preparing a positive pole piece:
mixing the positive active material lithium nickel cobalt manganese oxide (LiNi) 0.8 Co 0.1 Mn 0.1 O 2 ) Mixing the conductive carbon Super-P and the polyvinylidene fluoride (PVDF) binder according to a mass ratio, adding N-methylpyrrolidone (NMP) as a solvent, stirring in vacuum to obtain uniform slurry, uniformly coating the slurry on an aluminum foil, and drying to obtain the positive plate.
Preparation of lithium ion secondary battery:
and winding the negative plate, the isolation film and the positive plate to obtain a battery core, packaging the battery core, injecting electrolyte into the battery shell, packaging, forming and grading to obtain the lithium ion secondary battery.
Comparative examples 2 to 4 are different from comparative example 1 in the amounts of the silicon oxide composite active material and Super-P used, and specific amounts of the positive electrode raw material ratios and the negative electrode raw material ratios used in comparative examples 1 to 4 are shown in table 1.
TABLE 1
The secondary batteries prepared in the above examples 1 to 8 and comparative examples 1 to 4 were subjected to a first efficiency, capacity retention rate test, film thickness, expansion rate test and film surface appearance record, and the results are recorded in table 2.
The performance of the circulating battery is detected as follows: charging 1C to 2.8V, charging 1C to 4.35V, charging 4.35V to 0.05C, and discharging 0.2C to 2.8V at 25 deg.C;
measuring the thickness of the diaphragm by a spiral micrometer; the calculation formula of the expansion rate (%) of the membrane is (the thickness of the silicon-carbon composite negative plate after being filled with the silicon-carbon composite negative plate-the thickness of the silicon-carbon composite negative plate before being filled with the silicon-carbon composite negative plate)/(the thickness of the silicon-carbon composite negative plate before being filled with the silicon-carbon composite negative plate-the thickness of a negative current collector) × 100% (1/n), and n is 2; and observing the appearance of the membrane after the battery circulates for 400 th circle by using a scanning electron microscope.
Table 2 examples 1-8 and comparative examples 1-4 test data.
In examples 1 to 8, on the basis of obtaining a silicon-intercalated mixture by mixing and processing a SiO and a modified porous graphite, a silicon-carbon composite active material is obtained by adding molten polyvinyl fluoride or molten urea to the silicon-intercalated mixture, while the comparative examples 1 to 4 adopt conventional silicon monoxide and graphite to obtain SiO/C cathode materials, the battery performance obtained by the final preparation of the materials in Table 2 shows that the thickness of the cathode sheet diaphragm in the examples 1 to 8 and the comparative examples 1 to 4 is 102 to 126mm, the better cycle performance of the examples 1 to 8 is good, especially the first coulombic efficiency at 0.2C is higher, the capacity retention rate at 100 th circle and the capacity retention rate at 400 th circle are all better than the first coulombic efficiency at 0.2C, the capacity retention rate at 100 th circle and the capacity retention rate at 400 th circle in the comparative examples 1 to 4, in addition, the expansion rate of 26.17-30.35% of the 2-layer film after the 400 th circle of the examples 1-8 is lower than that of 35.32-39.10% of the 2-layer film of the comparative examples 1-4; in comparative examples 1-4, the surface of the membrane has more cracks after the 400 th cycle of cyclic charge and discharge, the cracking condition is obvious, and the structural stability of the material is poor; in the embodiment 1-8, after the 400 th cycle of charge and discharge, the surface of the membrane is few or has no fine cracks or fractures, the structural stability of the material is good, and the side effects caused by volume expansion are obviously improved and promoted. From the comparison of examples 1 to 4, it is found that as the content of the silicon oxide negative electrode active material in the negative electrode material increases, the performance of the prepared secondary battery is improved and then reduced, and when the ratio of the silicon oxide negative electrode active material to the conductive carbon is set to 92.5: and 2.5, the prepared lithium ion battery has better performance. From the comparison of examples 5 to 8, it is found that as the content of the silicon-oxygen negative active material in the negative electrode material increases, the performance of the prepared lithium ion battery increases and then decreases, and when the ratio of the silicon-oxygen negative active material to the conductive carbon is set to 90.5: and 3.5, the prepared lithium ion battery has better performance. As described above, when the silicon monoxide (SiO) (containing 0.15kg of lithium carbonate) was added and mixed, and the weight part of the silicon-inserted mixture after mixing was 4.0kg and the weight part of the molten urea was 0.5kg, the performance of the lithium ion battery prepared was better.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (10)
1. The preparation method of the silicon-carbon composite active material is characterized by comprising the following steps of:
step S1, embedding the silica material into the graphite material to obtain a silicon-carbon mixture, and screening, wherein the oversize product is the silicon-embedded mixture;
step S2, mixing the silicon-embedded mixture with a sealing agent, sealing, crushing and screening to obtain a silicon-carbon composite active material;
wherein the particle diameter D50 of the silica material is 1-60 μm, and the particle diameter D50 of the graphite material is 0.1-10 μm.
2. The method for preparing a silicon-carbon composite active material according to claim 1, wherein the ratio of the silicon oxide material to the graphite material in parts by weight in step S1 is 0.1-40: 100 to 120.
3. The method of claim 1, wherein the embedding manner in the step S1 includes at least one of mechanical stirring, ball milling, ultrasonic vibration, mechanical vibration, spraying, sedimentation, deposition, spraying, wetting, gasification, polymerization, soaking, and liquefaction.
4. The method for preparing a silicon-carbon composite active material according to claim 1, wherein the graphite material is at least one of artificial porous graphite, natural porous graphite, modified porous graphite, porous soft carbon and porous hard carbon; the silicon oxygen material is SiOx, wherein x is more than or equal to 0 and less than or equal to 2, and the SiOx comprises at least one of silicon monoxide, silicon dioxide and metal-containing composite SiOx.
5. The method for preparing a silicon-carbon composite active material as claimed in claim 1, wherein the weight ratio of the silicon-embedded mixture to the sealing agent in the step S2 is 100-120: 20-40.
6. The method for preparing a silicon-carbon composite active material according to claim 1, wherein the sealing treatment in the step S2 is specifically: and mixing the sealing agent and the silicon-embedded mixture at the temperature of 15-400 ℃.
7. The method of preparing a silicon-carbon composite active material according to claim 1, wherein the sealing agent in step S2 is at least one of lithium borate, polyvinylidene fluoride, polyvinyl fluoride, urea, lithium silicofluoride, and lithium oxalyldifluoroborate.
8. A silicon-carbon composite active material produced by the method for producing a silicon-carbon composite active material according to any one of claims 1 to 7.
9. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided to at least one surface of the negative electrode current collector, the negative electrode active material layer comprising the silicon-carbon composite active material according to claim 8.
10. A secondary battery comprising the negative electrode sheet of claim 9.
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