CN111710832A - Silicon-containing negative plate, preparation method thereof and lithium ion secondary battery manufactured by silicon-containing negative plate - Google Patents
Silicon-containing negative plate, preparation method thereof and lithium ion secondary battery manufactured by silicon-containing negative plate Download PDFInfo
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- CN111710832A CN111710832A CN202010668673.XA CN202010668673A CN111710832A CN 111710832 A CN111710832 A CN 111710832A CN 202010668673 A CN202010668673 A CN 202010668673A CN 111710832 A CN111710832 A CN 111710832A
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- Prior art keywords
- silicon
- negative electrode
- containing negative
- porous composite
- composite layer
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Images
Classifications
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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
- 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
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
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- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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- H—ELECTRICITY
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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
- H01M4/139—Processes of manufacture
- H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
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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
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- H01M4/66—Selection of materials
- H01M4/665—Composites
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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
- 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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Composite Materials (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention relates to a silicon-containing negative plate, a preparation method thereof and a lithium ion secondary battery manufactured by the silicon-containing negative plate. The silicon-containing negative electrode sheet comprises: 1) a current collector; 2) a porous composite layer on the current collector; and 3) a silicon-containing negative electrode material layer on the porous composite layer, wherein the porous composite layer can be arranged on one side or two sides of the current collector, and the silicon-containing negative electrode material layer is arranged on the porous composite layer. The bonding force between the silicon-containing negative electrode material and the current collector in the silicon-containing negative electrode piece is improved, so that the lithium ion secondary battery prepared from the silicon-containing negative electrode piece has higher energy density and better cycle performance, and can well meet the industrial application.
Description
Technical Field
The invention belongs to the field of lithium ion secondary batteries, and particularly relates to a silicon-containing negative plate, a preparation method thereof and a lithium ion secondary battery comprising the same.
Background
The negative electrode material (also called as negative electrode active material or negative electrode active material) is one of the important components of the lithium ion battery, and directly influences the key indexes of the energy density, cycle life, safety performance and the like of the battery. Compared with a graphite cathode, the silicon-containing cathode material has obvious energy density advantage. The theoretical specific capacity of the graphite is 372mAh/g, and the theoretical specific capacity of the silicon negative electrode material is more than 10 times of that of the graphite and is up to 4200mAh/g, so that the capacity of a monomer cell can be greatly improved, and the endurance mileage of the electric automobile is increased.
However, the silicon particles are accompanied by volume expansion and contraction during lithium intercalation and deintercalation, which leads to particle pulverization and exfoliation, particularly exfoliation of the silicon anode material layer from the current collector, and significant degradation of cycle performance occurs. If in the size mixing of pole piece preparation process, directly increase the quantity of gluing, the quantity of negative pole material will reduce, and the glue volume of distributing on silicon particle surface can be many simultaneously, influences the electron conductivity of silicon to influence the embedding reaction rate of lithium ion, thereby influence the capacity and the multiplying power performance of battery. Currently, in industrial application, silicon and other anode materials are used in a compounding manner to reduce expansion and improve cycle performance, but the expansion performance is still larger than that of an industrialized graphite material, so that the application of the silicon anode material is limited. In order to solve the cycle performance of the high-capacity battery, CN110148708A discloses a silicon-containing negative electrode sheet, which is prepared by a two-layer coating method, wherein the first layer is a graphite coating layer close to the current collector, the second layer is a silicon-containing coating layer far away from the current collector, and the silicon material in the negative electrode sheet can only account for 5% -20% of the total weight of the negative electrode material of the negative electrode sheet. The technology aims to solve the problem that the silicon-containing coating falls off from the current collector, graphite is coated on the current collector, and then the silicon-containing coating is coated, so that the problem of cycle degradation caused by the fact that the silicon-containing coating falls off from the current collector can be solved. However, the capacity of graphite is far lower than that of silicon, and the graphite electrode plate also has the problem of about 10% volume expansion in the charging and discharging processes, so that the volume energy density of the battery manufactured by using the negative electrode plate is limited by the graphite material.
Disclosure of Invention
It is a technical object of the present invention to provide a silicon-containing negative electrode sheet for preparing a lithium ion secondary battery having a high capacity while having an advantage of a long cycle life.
The invention also aims to provide a preparation method of the silicon-containing negative plate.
It is still another technical object of the present invention to provide a lithium ion secondary battery comprising the silicon-containing negative electrode sheet.
In one aspect, the present invention provides a silicon-containing negative electrode sheet, including:
1) a current collector;
2) a porous composite layer on the current collector; and
3) a silicon-containing anode material layer on the porous composite layer.
The porous composite layer is arranged on one side or two sides of the current collector, and the silicon-containing negative electrode material layer is arranged on the porous composite layer.
In embodiments, the current collector may be a metal foil with electronic conductivity, a foil with modified metal with electronic conductivity, or a modified composite foil with electronic conductivity, including a copper foil and an electronic conductive foil coated and/or deposited with copper and carbon, wherein the copper foil or carbon-coated copper foil is preferred. The thickness of the current collector may be the conventional thickness of a current collector conventionally used for a negative electrode tab of a lithium ion secondary battery without particular limitation, and for example, may be 2 to 25 μm, preferably 3 to 20 μm, such as 2 μm, 3 μm, 4 μm, 5.5 μm, 6 μm, 7.5 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, and the like.
In an embodiment, the porous composite layer is composed of a polymer material having adhesive properties and an inorganic conductive material. Wherein the polymer material is a polymer or a mixture of polymers, and the inorganic conductive material is an inorganic conductive material or a mixture of inorganic conductive materials. The polymer material or the mixture material of the polymers in the porous composite layer is distributed in a dot shape or/and a net shape, and the inorganic conductive material is connected in the porous composite layer through the polymers and has gaps.
In embodiments, the thickness of the porous composite layer on one side may be 0.02 to 12 μm, such as 0.025 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2.8 μm, 3 μm, 4.2 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, and the like. The thickness of the porous composite layer can be adjusted according to the particle size of the inorganic conductive material and the particle size of the silicon-containing negative electrode material. The larger the particles of the inorganic conductive material, the larger the thickness of the porous composite layer. The larger the particle size of the silicon-containing negative electrode material is, the larger the volume expansion during charge and discharge is, and the stronger the adhesion of the porous composite layer is required, and the more the buffer function of the porous composite layer needs to be exerted.
In the present invention, the porosity of the porous composite layer may be 10% to 90%, preferably 20% to 90%, such as 10%, 20%, 30%, 40%, 57%, 70%, 80%, 90%. If the porosity is less than 10%, the content of the polymer in the polymer layer is high, the content of the inorganic conductive material is low, the electronic conductivity is reduced, the internal resistance of the pole piece is high, and if the porosity is more than 90%, the content of the inorganic conductive material is high, the content of the polymer is low, the adhesion is poor, and the cycle performance is poor due to volume expansion of silicon-containing negative electrode material particles in the charging and discharging processes. Within the porosity range, the battery can realize better electronic conductivity and better adhesion, thereby achieving the effects of improving the battery capacity and prolonging the cycle life. The porosity can be controlled by adjusting the mass ratio of the inorganic conductive particles and the polymer, and the particle size and coating thickness of the inorganic conductive particles and the polymer.
In an embodiment, the inorganic conductive material may be one or more selected from a metal material having electron conductivity and a carbon material, and the inorganic conductive material has a resistivity of 9 × 10-5Omega m or less. The carbon material comprises nano carbon, carbon black, graphite, graphene, carbon nano tube and the like with conductivityAn electrically conductive carbon material. The metal material comprises metals such as gold, silver, copper, nickel, tungsten and the like. In addition, the average particle size of the inorganic conductive material is not particularly limited, and may be a conventional average particle size of the inorganic conductive material of the negative electrode sheet of the lithium ion secondary battery, for example, 0.01 to 10 μm, such as 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, and the like.
In embodiments, the polymeric material may be selected from cellulose acetate propionate, cellulose acetate, polyvinyl alcohol, polyvinylidene fluoride, polycarbonate, polypropylene, polymethyl methacrylate, carboxymethyl cellulose, polyamide, polyimide-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyacrylonitrile, polyvinyl, pyrrolidone, sodium alginate, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate butyrate, polyvinyl chloride, butadiene-co-acrylonitrile, tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene fluoride, ethylene-co-acrylic acid, styrene-butadiene rubber, polyethylene-co-hexafluoropropylene, polyvinyl chloride, polyvinyl acetate, polyvinyl chloride, butadiene-co-acrylonitrile, tetrafluoroethylene-co-hexafluoropropylene-vinylidene fluoride, polyethylene-co-acrylic acid, styrene-butadiene rubber, One or more of polyacrylonitrile.
In an embodiment, in the porous composite layer, the mass ratio of the polymer material/the inorganic conductive material may be 5:95 to 90:10, preferably 10:90 to 85:15, for example, 5:95, 10:90, 18:82, 20:80, 25:75, 30:70, 40:60, 50:50, 60:40, 70:30, 75:25, 85: 15. If the mass ratio of the polymer material to the inorganic conductive material is less than 5:95, the bonding performance is reduced, the silicon-containing negative electrode material which repeatedly expands in the charge-discharge process cannot be bonded, and the cycle performance is deteriorated, whereas if the mass ratio is more than 90:10, too much binder is distributed on the surface of the current collector, the conductive material is less distributed, and the electronic conductivity is reduced, the internal resistance of the battery is increased, and the capacity and the cycle performance of the battery are reduced. Within the proportion range, the conductive material can play a role in effectively transmitting electrons, and can play a role in strengthening adhesion, so that the silicon-containing negative electrode material which repeatedly expands in the charge and discharge process is firmly adhered to the surface of the current collector, and plays a role in buffering, thereby realizing better cycle performance.
Further, in the case where two porous composite layers are present, the thicknesses of the two porous composite layers may be the same or different, and the polymer material and the inorganic conductive material used, as well as the composition, porosity, and the like, may also be the same or different.
The addition of the porous composite layer can improve the adhesion between the silicon-containing negative electrode material layer and the current collector by 0.5 to 100N/m, preferably 1 to 80N/m, as compared with the case where the porous composite layer is not included.
The silicon-containing negative electrode material layer is not particularly limited, and may be any silicon-containing negative electrode material layer applied to a negative electrode sheet in the art, which may be formed using any suitable method.
The thickness of the silicon-containing negative electrode material layer is not particularly limited, and a conventional thickness applied to a negative electrode sheet in the art may be employed. For example, the thickness of one surface may be 0.02 to 150. mu.m, such as 0.05. mu.m, 0.5. mu.m, 1. mu.m, 10. mu.m, 20. mu.m, 30. mu.m, 40. mu.m, 50. mu.m, 60. mu.m, 70. mu.m, 80. mu.m, 90. mu.m, 100. mu.m, 110. mu.m, 120. mu.m, 130. mu.m, 140. mu.m, 150. mu.m, etc.
In particular, the porous composite layer and the silicon-containing negative electrode material layer may have the following relationship in thickness: 3 ≦ a/b ≦ 500, where a represents the thickness of the silicon-containing anode material layer, b represents the thickness of the porous composite layer, preferably 5 ≦ a/b ≦ 300, e.g., a/b may be 3, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500. If a/b is less than 3, the occupation ratio of the porous composite layer is too high, and the occupation ratio of the silicon-containing negative electrode material layer is too low, so that the energy density of the manufactured lithium ion secondary battery is lower; if a/b is more than 500, the occupation ratio of the porous composite layer is too low, the occupation ratio of the silicon-containing negative electrode material layer is too high, the strengthened bonding effect of the porous composite layer is weakened, and the expansion of the silicon-containing negative electrode material can not be well inhibited, so that the cycle performance is influenced.
In an embodiment, the silicon-containing anode material layer may include: silicon-containing negative electrode material, conductive agent, thickening agent and adhesive. Further, a lithium simple substance, a lithium-containing compound, or the like may be contained as necessary.
In particular, the silicon-containing anode material may be any silicon-containing composite material used in the art as an anode material, such as a silicon-carbon composite material (including nano silicon-carbon material), a silicon-oxygen composite material (including a silica composite material).
In an embodiment, the silicon-containing composite material may be a commercially available product, for example, a nano silicon carbon material manufactured by tianmu lead battery materials science and technology ltd, a silicon oxygen composite material manufactured by shin-yue chemical industries co, a silicon carbon composite material or a silicon oxygen composite material manufactured by jiang xi violet chen science and technology ltd, a silicon oxygen composite material or a silicon-based composite material manufactured by beidou new materials group ltd, but is not limited thereto. The silicon-containing composite material may also be a silicon-containing composite material prepared according to the methods disclosed in the literature and variations thereof.
In another embodiment, the silicon-containing negative electrode material may be formed by further mixing one or more of the above commercially available silicon-containing composite materials with one or more carbon materials. The carbon material may be one or more selected from natural graphite, artificial graphite, mesocarbon microbeads, hard carbon and soft carbon. The carbon material may be a commercially available product. For example, it may be artificial graphite produced by Jiangxi purple chen technology, Inc., artificial graphite or natural graphite produced by Shanghai fir technology, and artificial graphite or natural graphite produced by Bistri New Material group, Inc., but is not limited thereto. The carbon material may also be a carbon material prepared according to the methods disclosed in the literature and variants thereof. By mixing a commercially available silicon-containing composite material with a carbon material to prepare a silicon-containing anode material, the proportion of silicon in the silicon-containing anode material can be controlled and changed.
The capacity of the silicon-containing anode material is not limited, for example, the capacity can be 300-4000mAh/g, such as 380mAh/g, 450mAh/g, 600mAh/g, 800mAh/g, 1400mAh/g, 2000mAh/g, 3000mAh/g, 3500mAh/g, and the like.
In the present invention, the silicon-containing anode material contains silicon in an amount of 0.1 to 60 wt%, preferably 15 to 50 wt%, and for example, may be 0.1 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, based on the total weight of the silicon-containing anode material. If the content of silicon is less than 0.1 percent, because the content of silicon is very low, the expansion caused by the charge and discharge of silicon is small, and the falling-off of the silicon-containing negative electrode material and the current collector can not be caused, a porous composite layer is not required to be added; if the silicon content is more than 60%, the expansion caused by the charge and discharge of silicon is too large, the theoretical expansion reaches about 180%, and the function of the porous composite layer is not obvious.
In an embodiment, the silicon-containing anode material is present in the form of regular or irregular particles. The particles may have an average particle diameter D50 of 0.01 to 30 μm, preferably 0.05 to 25 μm, for example 0.03 μm, 0.1 μm, 1 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm. Within the particle size range, the silicon-containing negative electrode material can realize good size mixing process and electrical property, and can meet the requirements of manufacturing high-capacity and long-service-life lithium ion batteries on the negative electrode material. If the average particle diameter is less than 0.01 μm, the silicon-containing anode material is less dispersed and agglomeration is easily occurred, and if the average particle diameter is more than 30 μm, a solid phase transport path of lithium ions is too long, resulting in a decrease in electrical properties.
In the silicon-containing anode material layer, the content of the silicon-containing anode material may be 90.0 wt% to 99.0 wt%, preferably 93.0 wt% to 98.5 wt%, for example, 90%, 91%, 92%, 93 wt%, 94.0 wt%, 94.5 wt%, 95 wt%, 95.8 wt%, 96 wt%, 97 wt%, 98.5 wt%, etc., based on the total weight of the silicon-containing anode material layer. Within the content range, the adhesion among powder particles can be maintained, the conductivity among the powder can be improved, and a pole piece with high capacity can be ensured. If the content is less than 90.0 wt%, the content of the silicon-containing negative electrode material is reduced, high capacity is limited, and the volumetric energy density and the mass energy density of the battery are reduced. If the content is more than 99.0 wt%, the content of the adhesive and the conductive agent is reduced, the powder falling phenomenon is easy to occur on the silicon-containing negative electrode material layer in the negative electrode plate, and meanwhile, the internal resistance of the battery manufactured by the negative electrode plate is larger, and the battery capacity is reduced.
In the silicon-containing negative electrode material layer, the conductive agent may be a mixture of one or more selected from conductive carbon black, acetylene black, ketjen black, nano-carbon, conductive graphite, carbon nanotubes, and graphene. In the silicon-containing anode material layer, the content of the conductive agent may be adjusted according to the desired conductive property, and may be, for example, 0.01 to 10.0 wt%, preferably 0.01 to 8 wt%, such as 0.01, 0.1, 0.2, 0.3, 0.4, 1, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, 10 wt%, etc., based on the total weight of the silicon-containing anode material layer. Within the content range, the conductive agent can improve the battery capacity, reduce the internal resistance and improve the cycle performance. If the content is less than 0.01 wt%, the addition amount of the conductive agent is too small, the conductive agent distributed among the silicon-containing negative electrode materials is not uniform, the lithium ion intercalation speed is not uniform, the particle expansion is not uniform, and the cycle performance is finally influenced, and if the content is more than 10.0 wt%, the dosage of the binder is too small, so that the adhesion among the silicon-containing negative electrode material particles is reduced, the pole piece dusting phenomenon is caused, and the cycle performance of the battery is influenced.
The thickener may be a polymer having a thickening effect selected from sodium carboxymethylcellulose or polyvinyl alcohol, etc., for adjusting the viscosity of the silicon-containing anode material slurry to make it suitable for coating. The content of the thickener may be adjusted according to the desired viscosity of the silicon-containing anode material slurry, and for example, may be 0.3 to 5.0 wt%, preferably 0.5 to 3 wt%, such as 0.3 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 4.0 wt%, 5.0 wt%, etc., based on the total weight of the silicon-containing anode material layer. Within the content range, the coating viscosity requirement of the pole piece can be met, and meanwhile, the material does not have the sedimentation problem; if the content is less than 0.3 wt%, a problem of slurry sedimentation occurs, and if the content is more than 5.0 wt%, the viscosity of the slurry is excessively high, which affects the uniformity of coating of the electrode sheet.
The binder may be a polymer having adhesive properties selected from styrene-butadiene rubber (SBR), vinylidene fluoride homopolymers and copolymers (such as PVDF, etc.), tetrafluoroethylene homopolymers and copolymers (such as PTFE), acrylic copolymers and homopolymers (such as PAA, etc.), sodium alginate-based polymers (such as SAA, etc.), and the like. The binder may be contained in the silicon-containing anode material layer in an amount of 0.3 to 10 wt%, preferably 0.5 to 5 wt%, for example, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 5.0 wt%, 6.0 wt%, 7.0 wt%, 8.0 wt%, 9.0 wt%, 10.0 wt%, etc., based on the total weight of the silicon-containing anode material layer. Within the content range, the particles are bonded together through the adhesive, so that the silicon-containing negative electrode material is ensured not to fall off powder in the charging and discharging processes. If the content is less than 0.5 wt%, the bonding property between particles is deteriorated, and if the content is more than 10.0 wt%, the binder content on the surface of the silicon-containing anode material particles is large, the capacity of the silicon-containing anode material layer is reduced, and the resistance is increased.
In addition, in the case where two silicon-containing anode material layers are present, the thicknesses of the two silicon-containing anode material layers may be the same or different, and materials, such as a silicon-containing anode material, a conductive agent, a thickener, a binder, and the like, and compositions, and the like, which are used may be the same or different.
In another aspect, the present invention provides a method for preparing the silicon-containing negative electrode sheet as described above, which includes the following steps:
1) forming a porous composite layer on a current collector, wherein the porous composite layer comprises a polymer material having adhesive properties and an inorganic conductive material,
2) and forming a silicon-containing negative electrode material layer on the formed porous composite layer, thereby obtaining the silicon-containing negative electrode sheet.
In a specific embodiment, in steps 1 and 2, the porous composite layer or the silicon-containing negative electrode material layer may be formed by mixing the components of the porous composite layer or the silicon-containing negative electrode material layer to form a slurry, and then performing one or more methods of spin coating, thermal compression bonding, electrostatic spraying, slit coating, cross-hatch coating, micro-gravure coating, blade coating, screen printing, and centrifugal spraying to form the porous composite layer or the silicon-containing negative electrode material layer.
The preparation method of the porous composite layer slurry is not particularly limited as long as the components of the porous composite layer can be uniformly mixed and have properties suitable for coating, and for example, the porous composite layer slurry can be prepared by adding an organic solvent or water in a stirring tank, adding an inorganic conductive material, stirring, and then adding a polymer material; according to the characteristics of the polymer, the conductive polymer can also be prepared by adding the organic solvent or water into a stirring tank, then adding the polymer material and stirring, and then adding the conductive material and stirring. The description of the polymer material and the inorganic conductive material is the same as that of the porous composite layer components, and the description is omitted.
The state of these polymer materials when used in the preparation of the porous composite layer slurry is not particularly limited, and may be a solid or liquid state. In the case of a solid, the polymer is usually dissolved or dispersed in an organic solvent or water and then used. Depending on the characteristics of the polymeric material, an organic solvent or water may be selected to dissolve or disperse the polymeric material. The organic solvent may be aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, esters, ketones, and the like, and specifically may be benzene, toluene, xylene, pentane, octane cyclohexane, cyclohexanone, acetone, toluene cyclohexanone, methanol, ethanol, isopropanol, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethyl acetyl, N-methyl pyrrolidone, dimethylformamide, dimethylacetamide, tetrahydrofuran, and the like. If in a liquid state, such as a solution or emulsion, it may be added directly for the preparation of the porous composite layer slurry. For example, the polymeric material is a carboxymethyl cellulose (CMC) solid or aqueous solution, a styrene-butadiene rubber (SBR) solid or emulsion, a polyvinylidene fluoride (PVDF) solid or emulsion, or the like.
The method for preparing the silicon-containing anode material layer slurry is not particularly limited as long as the components of the silicon-containing anode material layer can be uniformly mixed and have properties suitable for coating, and can be prepared, for example, in the following manner: adding an organic solvent or water into a stirring tank, adding a thickening agent, stirring to form a mixed solution, adding a silicon-containing negative electrode material while stirring, and finally adding a binder.
The descriptions of the silicon-containing anode material, the conductive agent, the thickener, the binder, and the like are the same as those of the aforementioned silicon-containing anode material layer components, and are not repeated herein.
The state of the thickener and the binder when used for preparing the silicon-containing anode material layer slurry is not particularly limited, and may be a solid state or a liquid state. If solid, it is generally necessary to use the thickener and binder after dissolving or dispersing them in an organic solvent or water. Depending on the material properties of the thickener and binder, an organic solvent or water may be selected to dissolve or disperse the thickener and binder. The organic solvent may be aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, esters, ketones, and the like, and specifically may be benzene, toluene, xylene, pentane, octane cyclohexane, cyclohexanone, acetone, toluene cyclohexanone, methanol, ethanol, isopropanol, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethyl acetyl, N-methyl pyrrolidone, dimethylformamide, dimethylacetamide, tetrahydrofuran, and the like. If in a liquid state, such as a solution or emulsion, it may be added directly for the preparation of the porous composite layer slurry.
In still another aspect, the present invention provides a lithium ion secondary battery comprising the above silicon-containing negative electrode sheet.
The lithium ion secondary battery may further include a positive electrode sheet, a separator, an electrolyte, and a battery case as needed, in addition to the above-described silicon-containing negative electrode sheet. There is no particular limitation on the positive electrode sheet, separator, electrolyte, and battery case, and any positive electrode, separator, electrolyte, and battery case known in the art to be used in lithium ion secondary batteries may be used.
The positive plate may include a current collector and a positive material layer coated on the current collector. The current collector may be an aluminum foil having a thickness of 5 to 20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, and the like. The positive electrode material layer may include a positive electrode material (may also be referred to as a positive electrode active material or a positive electrode active material), a conductive agent, a binder, and the like. The positive electrode material is a mixture of one or more compounds capable of extracting or intercalating lithium ions, such as lithium cobaltate (LiCoO)2) Lithium manganate (LiMn)2O4) Lithium nickelate (LiNiO)2) Lithium iron phosphate (LiFePO)4) Manganese cobalt binary (M)n-Co), binary nickel manganese (Mn-Ni), binary nickel cobalt (Ni-Co), ternary nickel manganese cobalt (LiNi)1-x-yCoMnO2) One or more materials of (a); the conductive agent can be one or a mixture of more selected from conductive carbon black, acetylene black, conductive graphite, carbon nanotubes and graphene; the binder may be one or more selected from polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE). The positive electrode sheet can be produced by a conventional method in the art.
The diaphragm can be a ceramic film coated with alumina/magnesium hydroxide/boehmite and the like or a polymer film or a film coated with ceramic and polymer on a polypropylene (PP), Polyethylene (PE) or PP and PE composite film.
The electrolyte may include lithium salt, solvent, and additive, such as one or more of lithium hexafluorophosphate, carbonates, alkylene carbonates, and carboxylic acid esters.
Further, there is also no particular limitation on the structure and assembly method of the lithium ion secondary battery, and any structure and assembly method known in the art that can be used for the lithium ion secondary battery may be employed.
Advantageous effects
The invention discloses a silicon-containing negative plate which comprises a current collector, a porous composite layer on the current collector and a silicon-containing negative material layer on the porous composite layer. The porous composite layer is arranged in a battery manufactured by the pole piece, and after the pole piece is rolled, the silicon-containing negative electrode material layer can be firmly bonded on the current collector. The addition of the porous composite layer can improve the adhesion between the silicon-containing negative electrode material layer and the current collector by 0.5 to 100N/m, preferably 1N to 80N/m, as compared with the case where the porous composite layer is not included. Due to the existence of the inorganic particles with electron conductivity, the electron transmission between the silicon-containing negative electrode material and the current collector can be improved, and the internal resistance of the battery is reduced. According to the lithium ion secondary battery manufactured by the method, in the charge and discharge process, the silicon-containing negative electrode material is embedded and separated in the volume expansion of lithium ions, the porous composite layer can play a role in buffering the volume, and meanwhile, the silicon-containing negative electrode material layer is firmly bonded to the current collector, so that the silicon-containing negative electrode material is prevented from falling off from the current collector, and the cycle performance of the high-capacity lithium ion secondary battery is improved.
Therefore, the lithium ion secondary battery containing the silicon-containing negative electrode plate has higher energy density and better cycle performance, and meets the industrial application. The silicon-containing negative plate and the lithium ion secondary battery manufactured by the silicon-containing negative plate solve the problem of the adhesive force between the silicon-containing negative material and the current collector and the phenomenon of negative electrode powder falling, effectively reduce the volume expansion of silicon particles and greatly improve the volume energy density of the battery. The lithium ion secondary battery manufactured by the pole piece has high capacity and effectively prolonged cycle life.
Drawings
Fig. 1 is a schematic view of a negative electrode sheet (a) not containing a porous composite layer and its cycle time after 100 weeks (B).
Fig. 2 is a schematic view of a negative electrode sheet (a) having a porous composite layer between a current collector and a silicon-containing negative electrode material layer and (B) after 100 weeks of its cycle.
Description of reference numerals:
1. current collector 2, silicon-containing negative electrode material 3, adhesive 4, inorganic conductive material 5 and polymer
Detailed Description
The present invention has been described in detail hereinabove, but the above embodiments are merely illustrative in nature and are not intended to limit the present invention. Furthermore, there is no intention to be bound by any theory presented in the preceding prior art or the summary or the following examples.
Unless expressly stated otherwise, a numerical range throughout this specification includes any sub-range therein and any numerical value incremented by the smallest sub-unit within a given value. Unless expressly stated otherwise, numerical values throughout this specification represent approximate measures or limitations to the extent that such deviations from the given values, as well as embodiments having approximately the stated values and having the exact values stated, are included. Other than in the operating examples provided at the end of the detailed description, all numbers expressing quantities or conditions of parameters (e.g., quantities or conditions) used in the specification (including the appended claims) are to be understood as being modified in all instances by the term "about" whether or not "about" actually appears before the number. "about" means that the numerical value so stated is allowed to be somewhat imprecise (with some approach to exactness in that value; about or reasonably close to that value; approximately). As used herein, "about" refers to at least variations that can be produced by ordinary methods of measuring and using such parameters, provided that the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning. For example, "about" can include less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.1% variation, and in some aspects, less than or equal to 0.01% variation.
Unless otherwise expressly stated, the terms "comprising," "including," "having," "containing," or any other similar term in this specification are intended to be open-ended terms that indicate that a composition or article may include other elements not expressly listed or inherent to such composition or article. Furthermore, in this document, the terms "comprising," including, "" having, "" containing, "and" containing "are to be construed as specifically disclosed and to cover both closed and semi-closed conjunctions, such as" consisting of … "and" consisting essentially of …. By "consisting essentially of …," it is meant that the elements listed herein constitute greater than 95%, greater than 97%, or in some aspects, greater than 99% of the composition or article.
Parts throughout this specification refer to parts by weight unless specifically stated otherwise.
Examples
The following describes specific modes of the present invention with reference to specific embodiments, so that the technical contents of the present invention can be more clearly and easily understood. The present invention may be embodied in many different forms of embodiments and the scope of the invention is not limited to the embodiments set forth herein.
Reagent and apparatus
Materials, reagents, equipment and the like used in examples are commercially available unless otherwise specified. Unless otherwise indicated, like terms refer to like materials.
The thickness test was performed using Mitutoyo Sanfeng digital outside micrometer 193- "111, Japan.
Stirring was carried out using a vacuum double planetary mixer from Ross (tin-free) Equipment Ltd.) HG-XJ-30A.
The capacity and the capacity of the battery are detected, and the cycle performance is tested by adopting a battery core test branch Bk-3512 of Guangzhou Lanqi electronic industry Co.
The following thicknesses were measured using a micrometer thickness gauge.
Preparation example 1: manufacturing a positive plate:
dissolving a positive electrode material, a conductive agent and a binder in N-methyl pyrrolidone according to a ratio of 97:1.5:1.5, stirring to prepare slurry, uniformly coating the slurry on a positive electrode current collector aluminum foil, drying, rolling, slitting and performing spot welding to prepare a positive electrode sheet of the lithium ion battery. The cathode material used in the examples is nickel manganese cobalt ternary (LiNi)1-x-yCoMnO2) The ternary material 811, after application and rolling, had a thickness of 200 μm.
Example 1: preparation of silicon-containing negative plate
Preparation of porous composite layer slurry
Carbon black (average particle size of 0.3 μm) as a conductive agent and a mixture of polyvinylidene fluoride (PVDF) and polymethyl acrylate (PMMA) as a polymer material in a mass ratio of 50:50 were dispersed in water in a mass ratio of 30:70 of a conductive agent to a polymer mixture dry powder to prepare a water-soluble suspension slurry of carbon black and polymer, the solid content of which was 30 wt%.
Preparation of silicon-containing cathode material slurry
Silicon-carbon composite material (purchased from tianmu pilot battery materials science and technology ltd, capacity of 3000mAh/g, average particle size D50 of 0.1 μm) and artificial graphite (purchased from S360-L2, D50 ═ 15 μm of new fibrate material group ltd) were mixed at a ratio of 80:20 as silicon-containing negative electrode material a, in which the silicon content was 60%.
The preparation method comprises the following steps of preparing silicon-containing negative electrode material slurry by using silicon-containing negative electrode material A, Super-P as a conductive agent, sodium carboxymethyl cellulose (CMC) as a thickening agent and SBR emulsion as a binding agent according to a solid mass ratio of 95:2:1.5:1.5, wherein the preparation method comprises the following steps: adding a sodium carboxymethylcellulose thickening agent into the aqueous solution, stirring to form a glue solution, adding a conductive agent into the glue solution, stirring to form a glue solution containing the conductive agent, adding a silicon-containing negative electrode material into the glue solution containing the conductive agent, stirring, finally adding a binder, and stirring to form silicon-containing negative electrode material slurry with the solid content of 43 wt%.
Preparation of silicon-containing negative plate
Selecting a copper foil with the thickness of 10 mu m, coating the slurry of the prepared porous composite layer on a copper foil current collector by adopting reticulate pattern coating, and drying to obtain the porous composite layer, wherein the single-side coating amount is 4.0g/m2Coating silicon-containing negative electrode material slurry on a porous composite layer in a scraper coating mode, drying to obtain a silicon-containing negative electrode material layer, coating one surface of the silicon-containing negative electrode material layer, coating the second surface of the silicon-containing negative electrode material layer, drying, rolling, slitting and spot welding to obtain the silicon-containing negative electrode sheet, wherein the thickness of one surface of the porous composite layer is 3 mu m, the thickness of the two surfaces of the porous composite layer is 6 mu m, the thickness of the coated surface of the silicon-containing negative electrode material layer is 40 mu m, the thickness of the two surfaces of the porous composite layer is 80.
Example 2: preparation of silicon-containing negative plate
Preparation of porous composite layer slurry
The conductive graphite and graphene mixture (the average particle size of the conductive graphite is 10 microns, the average particle size of the graphene is 0.02 microns, the mass ratio of the conductive graphite to the graphene is 4:1) serving as a conductive agent and the polymethyl methacrylate serving as a polymer material are dispersed in water according to the dry powder mass ratio of 5:95 to prepare water-soluble suspension slurry of the conductive graphite and the polymer, wherein the solid content is 30 wt%.
Preparation of silicon-containing cathode material slurry
A silicon oxygen composite material (available from believing more chemical industry co., a capacity of 1550mAh/G, an average particle diameter D50 of 6 μm) and artificial graphite (available from G49, D50 ═ 14 μm, manufactured by jiang purple light technologies ltd) were mixed in a ratio of 70:30 to obtain a silicon-containing negative electrode material B in which the silicon content was 26%.
The silicon-containing negative electrode material B, Super-P serving as a conductive agent, CMC serving as a thickening agent and SBR emulsion serving as a binding agent are prepared into silicon-containing negative electrode material slurry according to the solid mass ratio of 95:2:1.5:1.5, and the solid content is 43 wt%.
Preparation of silicon-containing negative plate
Selecting a 15-micron carbon-coated copper foil, and coating the slurry of the prepared porous composite layer on a copper foil current collector by adopting slit coating, wherein the single-side coating amount is 10g/m2And drying to obtain a porous composite layer, coating silicon-containing negative electrode material slurry on the porous composite layer in a slit coating mode, drying to obtain a silicon-containing negative electrode material layer, coating one surface of the silicon-containing negative electrode material layer, coating the second surface of the silicon-containing negative electrode material layer, drying, rolling, slitting and spot welding to obtain the silicon-containing negative electrode sheet, wherein the thickness of one surface of the porous composite layer is 12 microns, the thickness of the two surfaces of the porous composite layer is 24 microns, the thickness of the coated surface of the silicon-containing negative electrode material layer is 65 microns, the thickness of the two surfaces of the porous composite layer is.
Example 3: preparation of silicon-containing negative plate
Preparation of porous composite layer slurry
Carbon nanotubes (the average particle size is 0.3 mu m) serving as a conductive agent and polyvinylidene fluoride-hexafluoropropylene serving as a polymer material are dispersed in acetone according to the dry powder mass ratio of 50:50 to prepare suspension slurry of the carbon nanotubes, wherein the solid content is 30 wt%.
Preparation of silicon-containing cathode material slurry
A silicon-carbon composite material (available from Jiangxi purple chen technology Co., Ltd., capacity 380mAh/g, average particle diameter D50 12 μm) having a silicon content of 1% was used as a silicon-containing negative electrode material C.
The silicon-containing negative electrode material C, Super-P serving as a conductive agent, CMC serving as a thickening agent and SBR emulsion serving as a binding agent are prepared into silicon-containing negative electrode material slurry according to the solid mass ratio of 95:2:1.5:1.5, and the solid content is 43 wt%.
Preparation of silicon-containing negative plate
Selecting a carbon-coated copper foil with the thickness of 20 mu m, and coating the slurry of the prepared porous composite layer on a copper foil current collector by adopting electrostatic spraying coating, wherein the single-side coating amount is 0.3g/m2Drying to obtain a porous composite layer, and coating the porous composite layer by a micro-concave coating methodAnd drying the silicon-containing negative electrode material slurry to obtain a silicon-containing negative electrode material layer, coating one surface of the silicon-containing negative electrode material layer, coating the second surface of the silicon-containing negative electrode material layer, drying the silicon-containing negative electrode material layer, and rolling, slitting and spot welding the silicon-containing negative electrode material layer to obtain the silicon-containing negative electrode sheet, wherein the thickness of one surface of the porous composite layer is 0.25 mu m, the thickness of the two surfaces of the porous composite layer is 0.5 mu m, the thickness of the coated single surface of the silicon-containing negative electrode.
Example 4: preparation of silicon-containing negative plate
Preparation of porous composite layer slurry
Graphene (with an average particle size of 0.02 μm) as a conductive agent and sodium alginate as a polymer material are dispersed in water according to a dry powder mass ratio of 80:20 to prepare water-soluble suspension slurry of graphene and polymer, wherein the solid content is 30 wt%.
Preparation of silicon-containing cathode material slurry
Silicon oxide composite (purchased from new material group of fibrate, ltd, capacity of 600mAh/g, average particle size D50 of 15 μm) and natural graphite (purchased from MSG18 produced by new material group of fibrate) were mixed in a ratio of 10:90 to obtain silicon-containing negative electrode material D, in which the silicon content was 7%.
The silicon-containing negative electrode material D, Super-P serving as a conductive agent, CMC serving as a thickening agent and SBR emulsion serving as a binding agent are prepared into silicon-containing negative electrode material slurry according to the solid mass ratio of 95:2:1.5:1.5, and the solid content is 43 wt%.
Preparation of silicon-containing negative plate
Selecting a silver-coated copper foil with the thickness of 3 mu m, and coating the prepared slurry of the porous layer on a copper foil current collector by adopting screen printing coating, wherein the single-side coating amount is 1.0g/m2And drying to obtain a porous composite layer, coating silicon-containing cathode material slurry on the porous composite layer in a spin coating manner, drying to obtain a silicon-containing cathode material layer, coating one surface of the silicon-containing cathode material layer, coating the second surface of the silicon-containing cathode material layer, drying, rolling, slitting and spot welding to obtain the silicon-containing cathode sheet, wherein the thickness of one surface of the porous composite layer is 0.5 mu m, the thickness of the two surfaces of the porous composite layer is 1 mu m, the thickness of the coated surface of the silicon-containing cathode material layer is 80 mu m, the thickness of the two surfaces of the porous composite layer is 160.
Example 5: preparation of silicon-containing negative plate
Preparation of porous composite layer slurry
Carbon fibers (average particle size of 0.5 μm) as a conductive agent and polyimide as a polymer material were dispersed in NMP at a dry powder mass ratio of 40:60 to prepare an organic suspension slurry of carbon fibers with a solid content of 30 wt%.
Preparation of silicon-containing cathode material slurry
A silicon-carbon composite material (purchased from Tianmu Pilot Battery materials science and technology Co., Ltd., capacity of 2400mAh/g, average particle size D50 of 20 μm) and artificial graphite (purchased from CP5-H manufactured by Shanghai fir technology Co., Ltd., average particle size of 6.5 μm were mixed in a ratio of 30:70 to form a silicon-containing negative electrode material E, in which the silicon content was 18%.
The silicon-containing negative electrode material E, Super-P serving as a conductive agent, CMC serving as a thickening agent and SBR emulsion serving as a binding agent are prepared into silicon-containing negative electrode material slurry according to the solid mass ratio of 95:2:1.5:1.5, and the solid content is 43 wt%.
Preparation of silicon-containing negative plate
Selecting a silver-coated copper foil with the thickness of 25 mu m, and coating the prepared porous composite layer slurry on a copper foil current collector by adopting thermal spraying coating, wherein the single-side coating amount is 1g/m2And drying to obtain a porous composite layer, coating silicon-containing negative electrode material slurry on the porous composite layer in a hot-pressing coating mode, drying to obtain a silicon-containing negative electrode material layer, coating one surface of the silicon-containing negative electrode material layer, coating the second surface of the silicon-containing negative electrode material layer, drying, and rolling, slitting and spot welding to obtain the silicon-containing negative electrode sheet, wherein the thickness of one surface of the porous composite layer is 0.1 mu m, the thickness of the two surfaces of the porous composite layer is 0.2 mu m, the thickness of the coated single surface of the silicon-containing negative electrode material layer is 50 mu m, the thickness of the.
Example 6: preparation of silicon-containing negative plate
Preparation of porous composite layer slurry
Silver powder (average particle size of 0.05 μm) as a conductive agent and polyvinyl chloride as a polymer material were dispersed in water at a dry powder mass ratio of 35:65 to prepare a water-soluble suspension slurry of silver powder and polymer, the solid content being 30 wt%.
Preparation of silicon-containing cathode material slurry
A silicon-carbon composite material (available from Jiangxi purple chen technology Co., Ltd., capacity 1600mAh/g, average particle diameter D50 of 8 μm) in which the silicon content was 45% was used as the silicon-containing negative electrode material F.
The silicon-containing negative electrode material F, Super-P serving as a conductive agent, CMC serving as a thickening agent and SBR emulsion serving as a binding agent are prepared into silicon-containing negative electrode material slurry according to the solid mass ratio of 95:2:1.5:1.5, and the solid content is 43 wt%.
Preparation of silicon-containing negative plate
Selecting a 17-micron silver-coated copper foil, and coating the prepared porous composite layer slurry on a copper foil current collector by adopting centrifugal spraying, wherein the single-side coating amount is 15g/m2And drying to obtain a porous composite layer, coating silicon-containing negative electrode material slurry on the porous composite layer in a spray coating manner, drying to obtain a silicon-containing negative electrode material layer, coating one surface of the silicon-containing negative electrode material layer, coating the second surface of the silicon-containing negative electrode material layer, drying, rolling, slitting and spot welding to obtain the silicon-containing negative electrode sheet, wherein the thickness of one surface of the porous composite layer is 4 micrometers, the thickness of the two surfaces of the porous composite layer is 8 micrometers, the thickness of the coated surface of the silicon-containing negative electrode material layer is 85 micrometers, the thickness of the two surfaces of the silicon-containing negative electrode material.
Example 7: preparation of silicon-containing negative plate
Preparation of porous composite layer slurry
A mixture of carbon fibers (average particle size of 0.1 μm) and conductive carbon black (average particle size of 0.5 μm) as a conductive agent and a polymer material (polyacrylic acid and styrene-butadiene rubber in a ratio of 90:10) as a polymer material were dispersed in water at a dry powder mass ratio of 70:30 to prepare a water-soluble suspension slurry of the conductive agent and the polymer, the solid content being 30 wt%.
Preparation of silicon-containing cathode material slurry
A silicon-carbon composite material (available from jiang purple light in science and technology ltd, capacity 900mAh/G, average particle size D50 15 μm) and soft carbon (available from HC-1, D50 ═ 13 μm, new material group ltd, fibrtri) were mixed in a ratio of 80:20 to obtain a silicon-containing negative electrode material G in which the silicon content was 15%.
The silicon-containing negative electrode material G, Super-P serving as a conductive agent, CMC serving as a thickening agent and SBR emulsion serving as a binding agent are prepared into silicon-containing negative electrode material slurry according to the solid mass ratio of 95:2:1.5:1.5, and the solid content is 43 wt%.
Preparation of silicon-containing negative plate
Selecting a silver-coated copper foil with the thickness of 20 mu m, and coating the prepared porous composite layer slurry on a copper foil current collector by adopting a rotating roller, wherein the single-side coating amount is 8g/m2And drying to obtain a porous composite layer, coating silicon-containing negative electrode material slurry on the porous composite layer in a spray coating manner, drying to obtain a silicon-containing negative electrode material layer, coating one surface of the silicon-containing negative electrode material layer, coating the second surface of the silicon-containing negative electrode material layer, drying, rolling, slitting and spot welding to obtain the silicon-containing negative electrode sheet, wherein the thickness of one surface of the porous composite layer is 7 microns, the thickness of the two surfaces of the porous composite layer is 14 microns, the thickness of the coated surface of the silicon-containing negative electrode material layer is 75 microns, the thickness of the two surfaces of the silicon-containing negative electrode material.
Comparative example 1 production of negative electrode sheet
A silicon-containing negative electrode sheet was prepared as described in example 1, except that graphite (a mixture of natural graphite and artificial graphite in a mass ratio of 50:50, and an average particle diameter of 15 μm) was used as a negative electrode material and a porous composite layer was not formed.
Comparative example 2 preparation of silicon-containing negative electrode sheet
A silicon-containing negative electrode sheet was prepared as described in example 1, except that the porous composite layer was not formed.
Experimental examples
Production of lithium ion battery
The negative electrode sheets prepared in examples 1 to 7 and comparative examples 1 to 2 were wound in order with the positive electrode sheet prepared in the preparation example and the separator having a thickness of 12 μm, respectively, and placed in a 18650 case, followed by baking, filling, sealing, forming, and the like to prepare a cylindrical 18650 battery.
Electrical Performance testing
The following electrical property tests were performed on the lithium ion secondary batteries prepared as above using the negative electrode sheets prepared in the above examples 1 to 6 and comparative examples 1 to 2, respectively, and the results are shown in table 1 below.
1) Testing the battery capacity:
after formation, the lithium ion secondary batteries manufactured from the negative electrode sheets prepared in examples 1 to 7 and comparative examples 1 to 2 were charged and discharged at 25 ℃ at a voltage ranging from 2.75 to 4.2V and 0.2C and at 0.2C, and were cycled for 3 times, and the capacity of the third time was taken as the capacity C of the batteryInitial. Since the first and second times of the unstable SEI film occurred with a large difference in capacity, the 3 rd cell capacity was selected for parallel comparison in order to compare the capacities in parallel.
2) Cycle performance test
After the lithium ion secondary batteries fabricated from the negative electrode sheets prepared in examples 1 to 7 and comparative examples 1 to 2 were fabricated, the capacity was measured at 25 ℃ in a voltage range of 2.75 to 4.2V, 1C was charged and discharged at 1C, the cut-off current was 0.001C, the cycle was repeated for 100 weeks, and the capacity C of the battery at 100 weeks was counted100The capacity retention was calculated for 100 weeks. Capacity retention rate ═ CInitial/C100*100％。
3) Negative electrode powder adhesion test
After the lithium ion secondary batteries manufactured from the negative electrode sheets prepared in examples 1 to 7 and comparative examples 1 to 2 were cycled for 100 weeks, the batteries were discharged to 0% SOC, and the batteries were disassembled at 25 ℃ to test the peeling force between the electrode sheets and the current collectors. The peel strength test was carried out by using an AGS-X electronic universal tester, a Shimadzu tensile tester.
The degree of dusting of the negative electrode sheet was evaluated according to the following criteria (P represents the peeling force):
no powder falling (no obvious floating powder is observed by eye, P is more than or equal to 1N/m),
slight dusting (a small amount of floating powder is observed visually, P is more than or equal to 0.5N/m and less than 1N/m),
moderate dusting (0N/m < P <0.5N/m),
the powder is seriously fallen (the negative electrode material directly falls off from the current collector, and P is 0N/m).
TABLE 1
As can be seen from table 1 above, in the case of comparative example 1, when the negative electrode sheet is made of a pure graphite negative electrode material containing no silicon, the cycle performance of the lithium ion secondary battery is better, and the capacity of the lithium ion secondary battery is lower under the same battery model, which results in lower energy density. The development of the existing new energy requires that a high-energy-density negative plate is required to ensure the high energy density of the lithium ion battery. Under the condition of the comparative example 2, the capacity of the battery can be effectively improved by simply using the high-content silicon-containing negative electrode material to manufacture the negative electrode plate, so that the energy density of the battery is improved, but in the charging and discharging processes, silicon particles can be expanded continuously, and the powder falling phenomenon that the silicon-containing negative electrode material falls off from the current collector occurs after 100 weeks of circulation. Fig. 1 shows a schematic diagram of the process, wherein a shows a structural schematic diagram of an initially prepared negative electrode sheet, wherein 1 indicates a current collector, 2 indicates a silicon-containing negative electrode material in a silicon-containing negative electrode material layer, and 3 indicates a binder in the silicon-containing negative electrode material layer; b shows a schematic of the structure of the negative plate where the silicon-containing negative electrode material expanded and fell off the current collector after 100 weeks of cycling.
In the case of the silicon-containing negative electrode sheets of examples 1 to 7, due to the presence of the silicon-containing negative electrode material, the capacity of the lithium ion secondary battery can be improved compared with the comparative example 1, and meanwhile, compared with the comparative example 2, the porous composite layer on the current collector plays roles of bonding and expansion buffering, so that the phenomenon that the silicon-containing negative electrode material powder falls off from the current collector due to the expansion of silicon particles is effectively relieved, and the cycle performance of the lithium ion secondary battery is improved. As shown in table 1, after the silicon-containing negative electrode sheet was cycled for 100 weeks, the phenomenon that the silicon-containing negative electrode material was peeled off from the current collector in comparative example 2 was solved due to the presence of the porous composite layer. In addition, the existence of the porous composite layer can reduce the volume expansion of the silicon-containing negative electrode material by 2-8 percent. Fig. 2 shows a schematic diagram of the process, wherein a shows a structural schematic diagram of an initially prepared silicon-containing negative electrode sheet according to the present invention, in which 1 indicates a current collector, 2 indicates a silicon-containing negative electrode material in a silicon-containing negative electrode material layer, 3 indicates a binder in the silicon-containing negative electrode material layer, 4 indicates an inorganic conductive material in a porous composite layer, and 5 indicates a polymer material having adhesiveness in the porous composite layer; b shows a schematic of the structure of the negative electrode sheet in which the silicon-containing negative electrode material expanded but did not fall off the current collector after 100 weeks of cycling.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (10)
1. A silicon-containing negative electrode sheet comprising:
1) a current collector;
2) a porous composite layer on the current collector; and
3) a silicon-containing anode material layer on the porous composite layer,
wherein the porous composite layer may be disposed on one or both sides of the current collector, and a silicon-containing negative electrode material layer is disposed on the porous composite layer.
2. The silicon-containing negative electrode sheet according to claim 1,
the porous composite layer is composed of a polymer material having adhesive property and an inorganic conductive material, and/or
The polymer material is distributed in the porous composite layer in a dot shape or/and a net shape, the inorganic conductive material is connected in the porous composite layer through the polymer, and/or gaps exist in the inorganic conductive material
The porous composite layer has a single-side thickness of 0.02-12 μm and a porosity of 10% -90%, preferably 20% -90%, and/or
The thickness of one side of the silicon-containing negative electrode material layer is 0.02-150 mu m; and/or
The porous composite layer and the silicon-containing negative electrode material layer have the following relation in thickness: 3 & lta/b & lt 500 & gt, preferably 5 & lta/b & lt 300 & gt, wherein a represents the thickness of the silicon-containing anode material layer, and b represents the thickness of the porous composite layer.
3. The silicon-containing negative electrode sheet according to claim 2,
the inorganic conductive material is selected from one or more of a metal material with electronic conductivity and a carbon material, preferably, the carbon material is selected from one or more of carbon fiber, carbon black, graphite, graphene and carbon nanotube; the metal material is one or more selected from gold, silver, copper, nickel and tungsten, and/or
The inorganic conductive material has a resistivity of 9 × 10-5Omega m or less, and/or
The inorganic conductive material has an average particle diameter of 0.01 to 10 μm, and/or
The polymer material is one or more selected from cellulose acetate propionate, cellulose acetate, polyvinyl alcohol, polyvinylidene fluoride, polycarbonate, polypropylene, polymethyl methacrylate, carboxymethyl cellulose, polyamide, polyimide-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyacrylonitrile, polyvinyl, pyrrolidone, sodium alginate, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate butyrate, polyvinyl chloride, butadiene-co-acrylonitrile, tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene fluoride, ethylene-co-acrylic acid, styrene-butadiene rubber, polyacrylonitrile,
preferably, the mass ratio of the polymer material to the inorganic conductive material in the porous composite layer is 5: 95-90: 10, and preferably 10: 90-85: 15.
4. The silicon-containing negative electrode sheet according to claim 1, wherein the addition of the porous composite layer increases the adhesion of the silicon-containing negative electrode material layer to the current collector by 0.5-100N/m, preferably 1-80N/m.
5. The silicon-containing negative electrode sheet according to claim 1,
the current collector comprises a copper foil, or an electronically conductive foil coated and/or deposited with copper, carbon, and/or
The thickness of the current collector is 2-25 μm, preferably 3-20 μm.
6. The silicon-containing negative electrode sheet according to claim 1, wherein the silicon-containing negative electrode material layer comprises: a silicon-containing negative electrode material, a conductive agent, a thickener, and a binder.
7. The silicon-containing negative electrode sheet according to claim 6,
the silicon-containing negative electrode material is present in the form of regular or irregular particles having an average particle diameter D50 of 0.01 to 30 μm, preferably 0.05 to 25 μm, and/or
The silicon-containing anode material contains 0.1-60 wt%, preferably 15-50 wt% of silicon, based on the total weight of the silicon-containing anode material, and/or
The conductive agent is one or more selected from conductive carbon black, acetylene black, Ketjen black, nano carbon, conductive graphite, carbon nano tube and graphene; and/or
The thickener is selected from sodium carboxymethylcellulose and polyvinyl alcohol, and/or
The adhesive is selected from one or more of styrene-butadiene rubber, vinylidene fluoride homopolymer and copolymer, tetrafluoroethylene homopolymer and copolymer, acrylic copolymer and homopolymer and sodium alginate.
8. The silicon-containing negative electrode sheet according to claim 6, wherein the negative electrode material layer comprises a silicon-containing material,
the content of the silicon-containing negative electrode material is 90.0-99.0 wt%, and/or
The content of the conductive agent is 0.01-10.0 wt%, and/or
The content of the thickening agent is 0.3-5.0 wt%, and/or
The content of the adhesive is 0.3-10.0 wt%.
9. A method for preparing the silicon-containing negative electrode sheet according to any one of claims 1 to 8, comprising the steps of:
1) forming a porous composite layer on a current collector, wherein the porous composite layer comprises a polymer material having adhesive properties and an inorganic conductive material,
2) and forming a silicon-containing negative electrode material layer on the formed porous composite layer, thereby obtaining the silicon-containing negative electrode sheet.
10. A lithium ion secondary battery comprising the silicon-containing negative electrode sheet according to any one of claims 1 to 8.
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Application publication date: 20200925 |