CN113644231A - Composite negative plate, preparation method thereof and secondary battery - Google Patents
Composite negative plate, preparation method thereof and secondary battery Download PDFInfo
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- CN113644231A CN113644231A CN202110800223.6A CN202110800223A CN113644231A CN 113644231 A CN113644231 A CN 113644231A CN 202110800223 A CN202110800223 A CN 202110800223A CN 113644231 A CN113644231 A CN 113644231A
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Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
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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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- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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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
Abstract
The invention belongs to the technical field of batteries, and particularly relates to a composite negative plate, a preparation method thereof and a secondary battery. The composite negative plate comprises a current collector and a carbon active layer combined on the surface of the current collector, wherein a plurality of micropores are formed in the surface of the carbon active layer, which is far away from the surface of the current collector, second active materials are filled in the micropores, and the specific capacity of the second active materials is higher than that of carbon materials in the carbon active layer; the opening depth of the micropores is lower than the thickness of the carbon active layer. According to the composite negative plate, the carbon active layer and the second active material with higher specific capacity filled in the micropores of the carbon active layer are synergistic, so that the capacity of the composite negative plate can be improved, the capacity density of the battery is improved, the volume expansion effect of the active material can be relieved or even inhibited through the carbon active layer, the micropore structure is favorable for improving the ion migration transmission efficiency, the liquid retention capacity of the electrode plate on electrolyte is improved, and the electrochemical performance of the composite electrode plate is improved.
Description
Technical Field
The invention belongs to the technical field of batteries, and particularly relates to a composite negative plate, a preparation method thereof and a secondary battery.
Background
The lithium ion battery is a rechargeable battery widely applied in the fields of power, energy storage and consumption at present, and the positive electrode of the lithium ion battery mostly adopts transition metal oxide lithium salts such as Lithium Cobaltate (LCO) and lithium Nickel Cobalt Manganese (NCM), or transition metal phosphate lithium salts such as lithium iron phosphate (LFP) and Lithium Manganese Phosphate (LMP); a carbon material mainly containing graphite is often used for the negative electrode. In order to further improve the specific energy of the battery, attention is increasingly paid to novel negative electrode materials such as silicon materials, tin materials, silica materials and the like, wherein the theoretical specific capacity of the negative electrode materials is 5-10 times higher than that of graphite carbon materials. However, the silicon-oxygen material, the silicon material and the tin material have huge volume changes in the charging and discharging processes, so that the materials are rapidly broken and pulverized, and are separated from an electronic communication channel with a current collector, the cycle life of the battery is seriously shortened, and even the cycle life is only tens of weeks or less. To this end, improved approaches have been proposed from several aspects. For example, the silicon material is processed by nano treatment to reduce the surface damage caused by volume expansion; the one-dimensional conductive agents such as carbon nano tubes are adopted to improve the conductivity and limit the expansion of the active substances; a binder such as polyacrylate or the like is used. However, these methods still cannot solve the problem of short cycle life caused by the expansion of the silicon material in the negative electrode having a silicon content of more than 10 wt%.
In addition, in order to increase the energy density of the battery, it is necessary to increase the thickness of the active material coating layer in the electrode, increase the compaction density of the active material coating layer, and decrease the thickness of the inactive material (e.g., current collector), but this causes difficulty in wetting the electrode active layer with the electrolyte, and also slows down the transport of lithium ions in the thick electrode. Therefore, the prior art proposes that the electrode is three-dimensionally formed by punching, but the ratio of positive and negative active materials (namely, NP ratio) around the electrode hole is changed by the punching position, which may cause potential safety risks such as lithium precipitation.
Disclosure of Invention
The invention aims to provide a composite negative plate, a preparation method thereof and a secondary battery, and aims to solve the problem that the conventional negative plate is difficult to improve the capacity and the cycling stability at the same time to a certain extent.
In order to achieve the purpose of the application, the technical scheme adopted by the invention is as follows:
in a first aspect, the invention provides a composite negative plate, which comprises a current collector and a carbon active layer combined on the surface of the current collector, wherein the surface of the carbon active layer, which is far away from the current collector, is provided with a plurality of micropores, second active materials are filled in the micropores, and the specific capacity of the second active materials is higher than that of the carbon materials in the carbon active layer; the opening depth of the micropores is lower than the thickness of the carbon active layer.
According to the composite negative plate provided by the first aspect of the invention, on one hand, the second active material with high specific capacity is filled in the micropores of the carbon active layer, so that the capacity of the composite negative plate can be improved, the energy density of the battery can be improved, and the influence of the opening of the negative plate on the ratio (NP ratio) of positive and negative active materials around the electrode hole can be reduced. On the other hand, the opening depth of the micropores is lower than the thickness of the carbon active layer, so that the second active material is limited in the micropores of the carbon active layer, and compared with the second active material with high specific capacity, the carbon active layer has a lower volume expansion effect, so that the volume expansion of the second active material with high specific capacity in the cyclic charge-discharge process can be effectively inhibited, the active layer can be prevented from being separated from the current collector due to the volume expansion effect, the combination stability of the active layer and the current collector in the negative plate is improved, the cycle stability of the composite negative plate can be improved, and the cycle stability of the battery is improved. On the other hand, the micropores formed in the carbon active layer of the composite negative plate not only can provide a rapid channel for ion transmission and improve the transmission efficiency of ions in the electrode, but also is beneficial to improving the wetting effect of the electrolyte on the plate and increasing the liquid retention capacity of the negative plate on the electrolyte, thereby improving the electrochemical performance of the battery.
Furthermore, the volume of the micropores accounts for 1-50% of the total volume of the carbon active layer; the volume ratio of the micropores in the carbon active layer not only ensures the structural stability of the carbon active layer, but also ensures the improvement of the electrochemical properties such as the capacity of the negative plate.
Furthermore, the opening depth of the micropores is 50% -90% of the thickness of the carbon active layer; the micropores with the opening depth not only have better inhibiting effect on the volume expansion effect of the second active material, but also form a better ion rapid transmission channel, increase the liquid retention capacity of the composite negative plate to the electrolyte and enable the negative plate to have better electrochemical performance.
Furthermore, the pore size of the micropores is 10-100 μm; the pore size pores facilitate filling of the second active material.
Further, the carbon active layer includes a carbon material, a first conductive agent, and a first binder; the first conductive agent is used for improving the conductivity of the carbon active layer, and the first adhesive is used for enabling the carbon active layer to be stably combined on the surface of the current collector, so that the stability of the pole piece is improved.
Further, the mass ratio of the carbon material to the first conductive agent to the first binder is (80-95): (5-30): (5-15); the mass ratio ensures that the raw material components have the best matching effect, and simultaneously ensures the capacity, the conductivity, the compact stability of the film layer and the binding performance with the current collector of the carbon active layer.
Furthermore, the thickness of the carbon active layer is 100-200 μm, the opening depth of the micropores is 10-150 μm, and the opening depth of the micropores is lower than the thickness of the carbon active layer.
Further, the particle size D50 of the carbon material is 1-20 μm; the carbon material with the particle size is beneficial to improving the compactness of a film layer of the carbon active layer.
Further, the compacted density of the carbon active layer is 1.5-1.7 g/cm3(ii) a If the compaction density of the carbon active layer is too high, the electrolyte is not favorably infiltrated into the pole piece; if the compacted density of the carbon active layer is too low, the carbon active layer has poor stability and low gram volume.
Further, the carbon material comprises at least one of artificial graphite, natural graphite, hard carbon, soft carbon and carbon microspheres; the conductive agents are beneficial to electron transfer and migration, and can effectively improve the conductivity of the negative plate.
Further, the micropores also comprise a second conductive agent and a second binder, the conductivity of the negative plate is further improved through the second conductive agent, the bonding stability between the negative plate and the carbon active layer is improved through the second binder, and the second active material is prevented from falling off and falling off in the charging and discharging processes.
Further, in the micropores, the mass ratio of the second active material, the second conductive agent and the second binder is (80-95): (5-30): (5-15); the mass ratio ensures that the raw material components have the best matching effect, thereby being beneficial to improving the electrochemical properties of the negative plate such as capacity, conductivity and the like and also being beneficial to improving the filling effect of the second active material in the micropores.
Further, the filling volume percentage of a mixture formed by the second active material, the second conductive agent and the second binder in the micropores is 1% -90%; the capacity of the composite negative pole piece is improved, and an accommodating space is provided for the volume expansion effect of the active material in the charging and discharging processes, so that the stability of the pole piece is improved. Furthermore, the filling volume percentage of the mixture in the micropores is 30% -60%, and the filling volume has better effects on improving the capacity of the pole piece and inhibiting the volume expansion effect of the active material.
Furthermore, the volume of the micropores accounts for 25-40% of the total volume of the carbon active layer; the volume ratio of the micropores in the carbon active layer can better ensure the stability of the structure of the carbon active layer and the promotion effect on the polar plate.
Further, the particle size D50 of the second active material is 0.1-30 μm; the second active material with the particle size is more favorable for the micropores of the carbon active layer filled with the active material.
Further, the second active material includes at least one of a carbon material, a silicon carbon material, a silicon oxygen material, tin, and lithium; these second active materials all have a relatively high specific capacity.
Further, the first conductive agent and the second conductive agent are respectively and independently selected from at least one of carbon black, Ketjen black, single-walled carbon tubes, multi-walled carbon tubes, graphene and organic polymer ablation in-situ generation of conductive carbon materials; the conductive agents are beneficial to electron transfer and migration, and can effectively improve the conductivity of the negative plate.
Furthermore, the first binder and the second binder are respectively and independently selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid and polyacrylonitrile, and the binders have good adhesion, so that the bonding tightness between the active material, the conductive agent and other components can be improved.
In a second aspect, the present invention provides a method for preparing a composite negative electrode sheet, comprising the following steps:
preparing a carbon active layer on the surface of a current collector, and then carrying out pore-forming treatment on the carbon active layer, wherein a plurality of micropores are formed on the surface of the carbon active layer; the opening depth of the micropores is lower than the thickness of the carbon active layer;
filling the mixed slurry of the second active material in the micropores, and drying to obtain a composite negative plate; wherein the specific capacity of the second active material is higher than the specific capacity of the carbon material in the carbon active layer.
The preparation method of the composite negative plate is simple in process operation and suitable for industrial large-scale production and application, the prepared composite negative plate can improve the capacity of the composite negative plate through the synergistic effect of the carbon active layer and the second active material with higher specific capacity filled in the micropores of the carbon active layer, so that the capacity density of the battery is improved, the volume expansion effect of the second active material can be relieved or even inhibited through the carbon active layer, the micropore structure is favorable for improving the ion migration transmission efficiency, the liquid retention capacity of the plate on electrolyte is improved, and the electrochemical performance of the composite plate is improved.
Further, the step of preparing the carbon active layer on the surface of the current collector comprises the following steps: preparing a carbon material, a first conductive agent, a first binder and a first solvent into first mixed slurry, depositing the first mixed slurry on the surface of a current collector, and drying the first mixed slurry to form a carbon active layer on the surface of the current collector; the preparation method of the carbon active layer comprises the steps of preparing a carbon material, a first conductive agent, a first binder and a first solvent into mixed slurry, depositing the mixed slurry on the surface of a current collector, and drying to remove the solvent in the slurry, so that the carbon active layer can be formed on the surface of the current collector.
Further, the method for carrying out pore-forming treatment on the carbon active layer comprises at least one of laser etching, mechanical punching and chemical etching. The invention does not specifically limit the pore-forming mode of the carbon active layer, and can flexibly adopt methods such as laser etching, mechanical punching, chemical etching and the like to carry out pore-forming treatment according to different pore-forming requirements.
Further, the step of filling the mixed slurry of the second active material in the micro-holes includes: and preparing a second mixed slurry from a second active material, a second conductive agent, a second binder and a second solvent, and filling the mixed slurry into the micropores in a coating and depositing manner.
Furthermore, the volume of the micropores accounts for 1-50% of the total volume of the carbon active layer;
furthermore, the opening depth of the micropores is 50% -90% of the thickness of the carbon active layer;
furthermore, the pore size of the micropores is 10-100 μm;
further, the filling volume percentage content of the second mixed slurry in the micropores is 1% -90%;
furthermore, the thickness of the carbon active layer is 100-200 μm, the opening depth of the micropores is 10-150 μm, and the opening depth of the micropores is lower than the thickness of the carbon active layer;
further, the particle size D50 of the carbon material is 1-20 μm;
further, the particle size D50 of the second active material is 0.1-30 μm;
further, the compacted density of the carbon active layer is 1.5-1.7 g/cm3。
In a third aspect, the invention provides a secondary battery, which comprises the composite negative electrode sheet or the composite negative electrode sheet prepared by the method.
The secondary battery provided by the third aspect of the invention has the composite negative electrode sheet with the characteristics of high capacity, good cycle stability, stable structure, high ion transfer and transmission efficiency and the like, so that the electrochemical properties of the secondary battery, such as energy density, cycle life and the like, are improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed for the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a composite negative electrode sheet provided in an embodiment of the present invention;
fig. 2 is a schematic flow chart of a preparation method of the composite negative electrode sheet provided by the embodiment of the invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the present invention, the term "and/or" describes the association relationship of the associated objects, and means that there may be three relationships, for example, a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.
In the present invention, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (one) of a, b, or c," or "at least one (one) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.
It should be understood that, in various embodiments of the present invention, the sequence numbers of the above-mentioned processes do not mean the execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the examples of the invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The weight of the related components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present invention as long as it is in accordance with the description of the embodiments of the present invention. Specifically, the mass in the description of the embodiments of the present invention may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.
The terms "first" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances from one another, and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the invention. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.
As shown in fig. 1, a first aspect of an embodiment of the present invention provides a composite negative electrode sheet, where the composite negative electrode sheet includes a current collector and a carbon active layer bonded to a surface of the current collector, a surface of the carbon active layer away from the current collector is provided with a plurality of micropores, the micropores are filled with a second active material, and a specific capacity of the second active material is higher than a specific capacity of a carbon material in the carbon active layer; the opening depth of the micropores is lower than the thickness of the carbon active layer.
The composite negative electrode sheet provided by the first aspect of the embodiment of the invention comprises a current collector, a carbon active layer combined on the surface of the current collector and provided with a plurality of micropores, and a second active material filled in the micropores, wherein the specific capacity of the second active material is higher than that of the carbon material in the carbon active layer. On one hand, the second active material with high specific capacity is filled in the micropores of the carbon active layer, so that the capacity of the composite negative plate can be improved, the energy density of the battery can be improved, and the influence of the opening of the negative plate on the ratio (NP ratio) of positive and negative active materials around the electrode hole can be reduced. On the other hand, the opening depth of the micropores is lower than the thickness of the carbon active layer, so that the second active material is limited in the micropores of the carbon active layer, and compared with the second active material with high specific capacity, the carbon active layer has a lower volume expansion effect, so that the volume expansion of the second active material with high specific capacity in the cyclic charge-discharge process can be effectively inhibited, the active layer can be prevented from being separated from the current collector due to the volume expansion effect, the combination stability of the active layer and the current collector in the negative plate is improved, the cycle stability of the composite negative plate can be improved, and the cycle stability of the battery is improved. On the other hand, the micropores formed in the carbon active layer of the composite negative plate not only can provide a rapid channel for ion transmission and improve the transmission efficiency of ions in the electrode, but also is beneficial to improving the wetting effect of the electrolyte on the plate and increasing the liquid retention capacity of the negative plate on the electrolyte, thereby improving the electrochemical performance of the battery.
According to the embodiment of the invention, the opening depth of the micropores on the surface of the carbon active layer is lower than the thickness of the carbon active layer, so that the second active material filled in the micropores is not in direct contact with the current collector, the second active material is limited in the micropores to form a semi-wrapping form, the carbon active layer has a better inhibition buffer effect on the volume expansion of the second active material, and the circulation stability of the composite negative plate is improved. In some embodiments, the opening depth of the micropores is 50% to 90% of the thickness of the carbon active layer, and the micropores with the opening depth not only have a better inhibition effect on the volume expansion effect of the second active material, but also form a better ion rapid transmission channel, increase the liquid retention amount of the composite negative electrode sheet on the electrolyte, and enable the negative electrode sheet to have better electrochemical performance. In some embodiments, the opening depth of the micropores is 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, etc. of the thickness of the carbon active layer.
In some embodiments, the thickness of the carbon active layer is 100 to 200 μm, the opening depth of the micro-holes is 10 to 150 μm, and the opening depth of the micro-holes is lower than the thickness of the carbon active layer. According to the embodiment of the invention, the thickness of the carbon active layer and the depth range of the opening effectively ensure the comprehensive performances of the negative plate such as capacity, circulation stability, ion migration and transmission efficiency and the like.
In some embodiments, the volume of the micropores accounts for 1% to 50% of the total volume of the carbon active layer; the volume ratio of the micropores in the carbon active layer not only ensures the structural stability of the carbon active layer, but also ensures the improvement of the electrochemical properties such as the capacity of the negative plate. If the volume ratio of the micropores is too high, the structural stability of the carbon active layer is affected, and the risk of collapse of a carbon active layer substrate is caused; if the volume ratio of the micropores is too low, the filling of the second active material is not facilitated, and the effect of improving the performances such as the capacity of the negative plate is not obvious. In some preferred embodiments, the volume of the micropores accounts for 25% to 40% of the total volume of the carbon active layer; the volume ratio of the micropores in the carbon active layer can better ensure the stability of the structure of the carbon active layer and the promotion effect on the polar plate.
In some embodiments, the pores have a pore size of 10 to 100 μm; the micropores with the pore size are beneficial to filling the second active material, and if the pore size of the micropores is too small, the micropores are not beneficial to filling the second active material therein, so that the process difficulty is high; if the pore diameter of the micropores is too large, the uniformity and the quick charging performance of the active layer of the negative plate are affected. In some embodiments, the pore size of the micropores may be 10-20 μm, 20-30 μm, 30-40 μm, 40-50 μm, 50-60 μm, 60-70 μm, 70-80 μm, 80-90 μm, 90-100 μm, etc.
In some embodiments, the carbon active layer comprises a carbon material, a first conductive agent and a first binder, the first conductive agent improves the conductivity of the carbon active layer, and the first binder can improve the dispersion uniformity of the carbon material, the conductive agent and the like and ensure the bonding tightness between each component and the current collector, so that the carbon active layer is stably bonded on the surface of the current collector, and the stability of the pole piece is improved.
In some embodiments, the mass ratio of the carbon material, the first conductive agent and the first binder is (80-95): (5-30): (5-15), the mass ratio enables the raw material components to have the best matching effect, and meanwhile, the capacity, the conductivity, the film layer compactness and stability and the binding performance with a current collector of the carbon active layer are ensured, if the content of the first conductive agent is too high, the content of a carbon material of the carbon active layer is reduced, and therefore the capacity of the active layer is reduced; if the content of the first conductive agent is too low, it is not favorable for improving the conductivity of the carbon active layer. If the content of the binder is too high, the content of the carbon material of the carbon active layer is reduced, so that the capacity of the active layer is reduced; if the content of the binder is too low, the improvement of the combination performance of each component in the active layer and the current collector is not facilitated, and the stability of the film layer is poor.
In some embodiments, the carbon material comprises at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and carbon microspheres, and the carbon material facilitates ion intercalation and deintercalation and has good stability during charge and discharge.
In some embodiments, the carbon material has a particle size D50 of 1-20 μm, which is beneficial for increasing the compactness of the membrane layer of the carbon active layer, and if the particle size of the carbon material is too large or too small, the compactness of the carbon active layer will be reduced, thereby affecting the compacted density of the carbon active layer. In some embodiments, the particle size D50 of the carbon material may be 1-5 μm, 5-10 μm, 10-15 μm, 15-20 μm, etc.
In some embodiments, the first binder is selected from at least one of carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, polyacrylonitrile; the binding agents have good binding property, can improve the binding tightness between components such as carbon materials, conductive agents and the like, and can improve the binding tightness between the carbon active layer and the current collector.
In some embodiments, the first conductive agent is selected from at least one of carbon black, ketjen black, single-walled carbon tubes, multi-walled carbon tubes, graphene, organic polymer ablation in situ generated conductive carbon materials; the conductive agents are beneficial to electron transfer and migration, and can effectively improve the conductivity of the negative plate.
In some embodiments, the carbon active layer has a compacted density of 1.5 to 1.7g/cm3(ii) a If the compaction density of the carbon active layer is too high, the opening treatment on the surface of the carbon active layer is not facilitated, the process difficulty is increased, and the electrolyte is not facilitated to be infiltrated into the pole piece; if the compaction density of the carbon active layer is too low, the carbon active layer is too loose, the stability of the carbon active layer is poor, the gram volume is low, the energy density of the battery is too low, the active layer is easy to crack and peel off during the hole opening treatment, and the stability of the pole piece is poor.
In some embodiments, the micropores further include a second conductive agent and a second binder in addition to the second active material, the second conductive agent further improves the conductivity of the negative plate, and the second binder can improve the dispersion uniformity of the second active material, the conductive agent and the like, ensure the combination stability among the components and between the components and the carbon active layer, and prevent the second active material from falling off and falling off during charging and discharging.
In some embodiments, the mass ratio of the second active material, the second conductive agent and the second binder in the micropores is (80-95): (5-30): (5-15); the mass ratio ensures that the raw material components have the best matching effect, which is beneficial to improving the capacity, the conductivity and other electrochemical properties of the negative plate and the filling effect of the second active material in the micropores; if the content of the second conductive agent is too low, the conductivity of the negative plate is not favorably improved. If the content of the binder is too high, the content of the second active material is reduced, and the effect of improving the capacity of the negative plate is not good; if the content of the binder is too low, it is not preferable to improve the bonding stability of the second active material, the conductive agent, and the like to the carbon active layer.
In some embodiments, the mixture of the second active material, the second conductive agent, and the second binder has a filling volume percentage of 1% to 90% in the micro holes. According to the embodiment of the invention, the filling percentage of the mixture formed by the second active material, the second conductive agent and the second binder in the micropores improves the capacity of the composite negative electrode plate by filling the second active material, and provides an accommodation space for the volume expansion effect of the active material in the charging and discharging processes, so that the stability of the electrode plate is improved. If the filling amount of the mixture in the micropores is too high, the quick charging performance of the battery is influenced, the effect of the carbon active layer on relieving the volume expansion effect of the active material in the micropores is not facilitated, and the process difficulty is increased greatly; if the filling amount of the mixture in the micropores is too low, the composite pole piece cannot achieve the obvious capacity improving effect. In some embodiments, the mixture has a percentage of 30% to 60% of the fill volume in the micropores, which has a greater effect on both the improvement of the capacity of the plate and the suppression of the effect of the volume expansion of the active material. In some embodiments, the mixture may be 30-35%, 35-40%, 40-45%, 45-50%, 50-60%, etc. by volume percent filled in the micropores.
In some embodiments, the second active material comprises at least one of a carbon material, a silicon carbon material, a silicon oxygen material, tin, lithium. In some embodiments, the carbon material may be artificial graphite, natural graphite, hard carbon, or the like. The second active materials filled in the carbon active layer in the embodiment of the invention have higher specific capacity, and particularly, the active materials such as silicon materials, silicon carbon materials, silicon oxygen materials, tin, lithium and the like can effectively improve the capacity of the negative electrode plate by filling the active materials. However, these materials also have higher volume expansion in the charging and discharging processes, and in the embodiment of the present invention, by filling these second active materials in the form of micropores in the carbon active layer, the micropore accommodating space provided by the carbon active layer can effectively alleviate or even inhibit the volume expansion of these active materials, thereby improving the capacity and stability of the composite pole piece at the same time.
In some embodiments, the second binder and at least one selected from the group consisting of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile; the bonding agents have good bonding property, and can improve the bonding tightness between the second active material, the conductive agent and other components, so that the bonding tightness between the second active material and the carbon active layer is improved.
In some embodiments, the second conductive agent is selected from at least one of carbon black, ketjen black, single-walled carbon tubes, multi-walled carbon tubes, graphene, and organic polymer ablation in-situ generated conductive carbon materials, and these conductive agents are favorable for electron transport and migration and can effectively improve the conductivity of the negative plate.
In some embodiments, the particle size D50 of the second active material is 0.1-30 μm, which is more favorable for the active material to fill in the micropores of the carbon active layer, and if the particle size is too large, the difficulty of filling the micropores with the active material is increased. In some embodiments, the particle diameter D50 of the second active material may be 0.1-1 μm, 1-5 μm, 5-10 μm, 10-15 μm, 15-20 μm, 20-30 μm, etc.
In some embodiments, the current collector in the composite negative electrode sheet may be a copper foil or a copper mesh, etc.
The composite negative plate of the embodiment of the invention can be prepared by the following method of the embodiment.
As shown in fig. 2, a second aspect of the embodiment of the present invention provides a method for preparing a composite negative electrode sheet, including the following steps:
s10, preparing a carbon active layer on the surface of a current collector, and then carrying out pore-forming treatment on the carbon active layer, wherein a plurality of micropores are formed in the surface of the carbon active layer; the opening depth of the micropores is lower than the thickness of the carbon active layer;
s20, filling the mixed slurry of the second active material in the micropores, and drying to obtain a composite negative plate; wherein the specific capacity of the second active material is higher than the specific capacity of the carbon material in the carbon active layer.
In the preparation method of the composite negative electrode sheet provided in the second aspect of the embodiment of the present invention, after the carbon active layer is prepared on the surface of the current collector, pore-forming treatment is performed on the carbon active layer, and micropores with a depth lower than the thickness of the carbon active layer are formed on the surface of the carbon active layer; and filling the mixed slurry containing the second active material with higher specific capacity into the micropores, and drying to obtain the composite negative plate. The preparation method of the composite negative plate provided by the embodiment of the invention is simple in process operation and suitable for industrial large-scale production and application, the prepared composite negative plate can improve the capacity of the composite negative plate through the synergistic effect of the carbon active layer and the second active material with higher specific capacity filled in the micropores of the carbon active layer, so that the capacity density of a battery is improved, the volume expansion effect of the second active material can be relieved or even inhibited through the carbon active layer, and the micropore structure is also beneficial to improving the ion migration transmission efficiency and improving the liquid retention capacity of the plate to electrolyte, so that the electrochemical performance of the composite plate is improved.
In some embodiments, in the above embodiment S10, the step of preparing the carbon active layer on the surface of the current collector includes: the carbon material, the first conductive agent, the first binder and the first solvent are prepared into first mixed slurry, then the first mixed slurry is deposited on the surface of the current collector, and the carbon material, the first conductive agent, the first binder and the first solvent are dried to form a carbon active layer on the surface of the current collector. According to the preparation method of the carbon active layer, the carbon material, the first conductive agent, the first binder and the first solvent are prepared into mixed slurry, then the mixed slurry is deposited on the surface of the current collector, and the solvent in the slurry is removed through drying, so that the carbon active layer can be formed on the surface of the current collector.
In some embodiments, the first solvent comprises: at least one of N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran, wherein the solvents have good dissolving or dispersing effects on components such as carbon materials, conductive agents, binders and the like, so that the raw material components can form uniformly and stably dispersed mixed slurry, the slurry can be deposited in a coating mode and other modes to form a carbon active layer with uniform thickness, smooth surface and compactness, and the film forming performance of the slurry is improved.
In some embodiments, in the above embodiment S10, the method for performing the pore-forming process on the carbon active layer includes at least one of laser etching, mechanical drilling, and chemical etching. The embodiment of the invention does not specifically limit the pore-forming mode of the carbon active layer, and can flexibly adopt methods such as laser etching, mechanical punching, chemical etching and the like to carry out pore-forming treatment according to different pore-forming requirements.
In some embodiments, the step of filling the mixed slurry of the second active material in the micro holes in step S20 includes: and preparing a second mixed slurry from a second active material, a second conductive agent, a second binder and a second solvent, and filling the second mixed slurry into the micropores. In the embodiment of the invention, the second active material, the second conductive agent, the second binder and the second solvent are prepared into the mixed slurry, and then the mixed slurry is filled into the micropores through coating and deposition. In some embodiments, in order to improve the filling effect of the mixed slurry, the carbon active layer after pore formation may be subjected to a vacuum process to remove air in the micropores, and then the filling efficiency of the mixed slurry into the micropores may be improved by pressurizing or vacuumizing during the filling process of the mixed slurry. And filling the mixed slurry containing the second active material into the micropores of the carbon active layer, and drying to remove the solvent in the mixed slurry to obtain the composite negative plate.
In some embodiments, the second solvent comprises: at least one of N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran, and the solvents have good dissolving or dispersing effects on components such as a second active material, a conductive agent, a binder and the like, so that the raw material components can form uniformly and stably dispersed mixed slurry, the mixed slurry can be filled into micropores of a carbon active layer, and the film forming performance of the slurry can be improved.
In some embodiments, the volume of the micropores is 1% to 50% of the total volume of the carbon active layer.
In some embodiments, the open pore depth of the micropores is 50% to 90% of the thickness of the carbon active layer.
In some embodiments, the pores have a pore size of 10 to 100 μm.
In some embodiments, the second mixed slurry has a fill volume percentage in the micropores of between 1% and 90%.
In some embodiments, the thickness of the carbon active layer is 100 to 200 μm, the opening depth of the micro-holes is 10 to 150 μm, and the opening depth of the micro-holes is lower than the thickness of the carbon active layer.
In some embodiments, the carbon material has a particle size D50 of 1 to 20 μm.
In some embodiments, the second active material has a particle size D50 of 0.1 to 30 μm.
In some embodiments, the carbon active layer has a compacted density of 1.5 to 1.7g/cm3。
In some embodiments, the first conductive agent and the second conductive agent are each independently at least one selected from carbon black, ketjen black, single-walled carbon tubes, multi-walled carbon tubes, graphene, and organic polymer ablation in-situ generated conductive carbon materials.
In some embodiments, the first binder and the second binder are each independently at least one selected from the group consisting of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, and polyacrylonitrile.
The technical effects of the above embodiments of the present invention are discussed in detail in the foregoing, and are not described herein again.
In a third aspect of the embodiments of the present invention, there is provided a secondary battery, including the composite negative electrode sheet described above, or the composite negative electrode sheet prepared by the above method.
The secondary battery provided by the third aspect of the embodiment of the present invention includes the composite negative electrode sheet having the characteristics of high capacity, good cycle stability, stable structure, high ion transfer and transmission efficiency, and the like, so that the electrochemical properties of the secondary battery, such as energy density, cycle life, and the like, are improved.
The embodiment of the invention does not specifically limit the positive plate, the diaphragm, the electrode liquid and the like in the secondary battery, can select proper materials according to the actual application condition, has flexible application and wide adaptability.
In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art, and to make the progress of the composite negative electrode sheet, the preparation method thereof, and the secondary battery of the embodiments of the present invention obviously manifest, the above technical solutions are exemplified by a plurality of examples below.
Example 1
Composite negative plateThe preparation method comprises the following steps:
1. graphite powder with the particle size D50 of 12 microns is mixed with carbon black powder, CMC and SBR, and the mixture is stirred to prepare graphite cathode slurry, wherein the content of the graphite powder is 85 percent, the content of the carbon black is 5 percent, and the content of the binder CMC and SBR is 10 percent.
2. And (2) coating the graphite negative electrode slurry prepared in the step (1) on copper foil, and drying to obtain a negative electrode. The density of the graphite negative electrode is increased to 1.6g/cm by roll pressing or the like3。
3. And (3) punching a square hole array with the aperture of 60 micrometers and the hole depth of 100 micrometers on the graphite cathode with the thickness of 110 micrometers obtained in the step (2) in a pulse laser ablation mode.
4. Mixing silica powder with the particle size D50 of 5 microns with carbon black powder and a binding agent PAA, and stirring to prepare silica negative electrode slurry, wherein the content of the silica powder is 90%, the content of the carbon black is 5%, and the content of the binding agent is 5%.
5. And (3) coating the silica negative electrode slurry obtained in the step (4) on the open-pore graphite negative electrode in a rotary coating mode, controlling the rotating speed and the slurry amount to enable the slurry to be partially filled in the pores, and drying to obtain the silica negative electrode material partially filled in the pores, wherein the filling ratio is 80%.
Secondary batteryThe composite negative electrode sheet prepared in example 1, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 2
Composite negative plateIt differs from example 1 in that: in step 4, silicon powder is used to replace silica powder.
Secondary batteryThe composite negative electrode sheet prepared in example 2, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 3
Composite negative plateIt differs from example 1 in that: in step 4, tin powder is used instead of silica powder.
Secondary batteryThe composite negative electrode sheet prepared in example 3 was mixed with the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte,and assembling the soft package battery, designing the battery capacity of 9Ah, and enabling the battery size to be 80 × 60 × 8.55 mm.
Example 4
Composite negative plateIt differs from example 2 in that:
in step 3, a square hole array with the aperture of 100 microns and the hole depth of 150 microns is punched on the graphite cathode with the thickness of 160 microns in a pulsed laser ablation mode.
In the step 5, the filling volume ratio of the silicon cathode slurry in the holes is 60%.
Secondary batteryThe composite negative electrode sheet prepared in example 4, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 5
Composite negative plateIt differs from example 2 in that:
in step 3, a square hole array with the aperture of 100 microns and the hole depth of 150 microns is punched on the graphite cathode with the thickness of 160 microns in a pulsed laser ablation mode.
In the step 5, the filling volume ratio of the silicon cathode slurry in the holes is 80%.
Secondary batteryThe composite negative electrode sheet prepared in example 5, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 6
Composite negative plateIt differs from example 1 in that: in the step 4, a nano silicon carbon negative electrode (nano silicon particles are attached to the surface of graphite and then carbon coating is carried out) is adopted to replace silica powder, wherein the mass percentage of nano silicon is 5%.
Secondary batteryThe composite negative electrode sheet prepared in example 6, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 7
Composite negative plateIt differs from example 1 in that: in the step 5, the filling volume ratio of the silicon cathode slurry in the holes is 95%.
Secondary batteryThe composite negative electrode sheet prepared in example 7, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 8
Composite negative plateIt differs from example 1 in that: in step 1, the particle size D50 of the graphite powder was 22 μm.
Secondary batteryThe composite negative electrode sheet prepared in example 8, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 9
Composite negative plateIt differs from example 1 in that: in the step 2, the compacted density of the graphite cathode is 1.4g/cm3。
Secondary batteryThe composite negative electrode sheet prepared in example 9, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 10
Composite negative plateIt differs from example 1 in that:
in step 3, a hole square array with the aperture of 110 microns and the hole depth of 150 microns is punched on the graphite cathode with the thickness of 160 microns in a pulsed laser ablation mode.
In the step 5, the filling volume ratio of the silicon cathode slurry in the holes is 70%.
Secondary batteryThe composite negative electrode sheet prepared in example 10, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Example 11
Composite negative plateIt differs from example 6 in that: in step 11, a nano silicon carbon cathode is adopted to replace silica powder, wherein the mass percentage of nano silicon is 12%.
Secondary batteryThe composite negative electrode sheet prepared in example 6, the NCM811 positive electrode sheet, the 12+4 ceramic separator, and the high nickel electrolyte were assembled into a pouch battery, and the battery capacity was designed to be 9Ah, and the battery size was 80 × 60 × 8.55 mm.
Comparative example 1
Composite pole pieceThe preparation method comprises the following steps: taking silicon powder and graphite powder according to the ratio of 5: mixing the active material with 95 percent as a main active material, mixing the active material with carbon black powder, CMC and SBR, and stirring to prepare graphite cathode slurry, wherein the content of the active material is 85 percent, the content of the carbon black is 5 percent, and the content of the binder CMC and SBR is 10 percent. And then coating the negative electrode slurry on copper foil to obtain the composite negative electrode sheet of the comparative example R1.
Secondary batteryThe composite negative plate prepared in comparative example 1, the NCM811 positive plate, the 12+4 ceramic diaphragm and the high-nickel electrolyte are assembled into a soft package battery, the battery capacity is designed to be 9Ah, and the size of the battery is 80 × 60 × 8.55 mm.
Further, in order to verify the improvement of the examples of the present invention, the energy density, the cycle life, the quick charge capacity, the low temperature performance, and the like of the secondary batteries prepared in examples 1 to 10 and comparative example 1 were respectively tested, and the test results are shown in table 1 below:
TABLE 1
From the above test results, it can be seen that the composite negative electrode sheet according to examples 1 to 10 of the present invention shows better rate capability and cycle stability than the secondary battery having the composite negative electrode sheet prepared by directly mixing the silicon-based material with the carbon material, in which the silicon-based material is filled in the micropores of the carbon active layer. Specifically, the method comprises the following steps:
from the test results of comparative example 1 and example 1, it can be seen that the SiO material and the graphite material in comparative example 1 are uniformly distributed, the ratio of SiO to graphite is the same, but no favorable space is provided for the expansion of Si during the charging and discharging processes in the system, and therefore, the cycle performance is poor; the holes in example 1 provide space for the expansion of the silicon-based material and convenient paths for the shuttling of lithium ions, so the rate capability is more excellent.
From the test results of example 1 and example 2, it is understood that when O in SiO is replaced by Si in example 1, the amount of active material actually exerting capacity is large in example 2 at the same ratio, and thus the cell energy prepared therefrom is higher. The rate capability is inferior to that of example 2 because the contact with lithium ions is affected by the dielectric effect of the O atom in example 1. In addition, the cell made in example 2 had poor cycling performance because no O atoms provided a buffer for the expansion of Si.
From the test results of example 1, example 6 and example 11, it is known that in the nano silicon carbon materials of example 6 and example 11, nano silicon is attached to the graphite surface, and the proportion of silicon particles is less than that of the Si negative electrode material with the same mass, which results in a great reduction in the cell energy density, and similarly, the graphite particles in the nano silicon carbon material are larger, which is not beneficial to lithium ion shuttling, which results in a reduction in the rate capability. In addition, the silicon surface of the nano silicon carbon material is coated by a carbon layer, so that the cycle performance is poor.
From the test results of example 6 and example 11, it is understood that increasing the mass percentage of nano-silicon while maintaining the same amount of SiC composite increases the amount of actual Si that exerts capacity, and increases the cell energy density. Because the whole content of the SiC material is unchanged, the rate capability is kept flat. But the increase of the Si content causes more expansion in the circulation process, and the cell circulation performance is reduced sharply.
From the test results of example 2 and example 3, it can be seen that when Si is substituted by Sn in example 2, the cell energy of example 3 is lower at the same ratio because the theoretical capacity of Sn is lower. In addition, Sn expands less during charge and discharge, so the cell fabricated in example 3 has better cycle performance.
From the test results of comparative example 2 and example 4, it is known that when the pore size in example 4 is increased and the same amount of Si paste is added, the filling ratio is decreased. The particles that exert capacity do not change, and therefore the energy density of the battery does not change. But the holes are increased, so that a larger space is provided for the expansion of Si particles, and the rate capability and the cycle performance of the battery are improved to a certain extent.
From the test results of example 4 and examples 2, 5 and 7, it is understood that when the amount of Si paste is increased in example 5, the filling volume ratio of the silicon negative electrode paste in the pores is as same as that in example 2, that is, 80%. The number of particles for developing capacity increases, and therefore the energy density of the battery is improved to some extent. The large pores provide room for the expansion of Si and therefore the rate capability is higher than example 2, but on par with example 4. Since the Si content was increased, the cycle back loss was increased, and the cycle performance was inferior to that of example 4. However, when the filling volume ratio of the silicon negative electrode slurry in the holes of example 7 is too high, and is as high as 95%, the space provided by the holes for the volume expansion of the silicon negative electrode material is too small, and the volume expansion effect of the negative electrode material in the charging and discharging processes cannot be effectively relieved, so that the cycle performance of the battery of example 7 is reduced. And lithium ion channels are reduced, resulting in deterioration of rate performance.
From the test results of example 1 and example 8, it is known that when the particle diameter D50 of the graphite powder used in the graphite negative electrode is too large, the compactness and film forming property of the graphite negative electrode are reduced, thereby affecting the film layer stability, resulting in a reduction in the battery cycle performance. The energy density and rate performance are on par with example 1.
From the test results of example 1 and example 9, it is known that when the compacted density of the graphite negative electrode is too low, the film stability is poor, resulting in a decrease in the battery cycle performance. The low compaction density improves the lithium ion shuttle channel to a certain extent, and the multiplying power is improved to a certain extent.
From the test results of the embodiment 1 and the embodiment 10, the amount of the filled silicon negative electrode is the same, and the energy density of the battery cell is equal; when the pore diameter of the graphite negative electrode open pore is too large and the pore volume ratio is too high, the stability of the negative electrode sheet is not improved, and the cycle performance of the battery is also influenced.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. The composite negative plate is characterized by comprising a current collector and a carbon active layer combined on the surface of the current collector, wherein a plurality of micropores are formed in the surface of the carbon active layer, which is away from the current collector, and are filled with a second active material, and the specific capacity of the second active material is higher than that of the carbon material in the carbon active layer; the opening depth of the micropores is lower than the thickness of the carbon active layer.
2. The composite negative electrode sheet according to claim 1, wherein the volume of the micropores accounts for 1 to 50% of the total volume of the carbon active layer;
and/or the opening depth of the micropores is 50% -90% of the thickness of the carbon active layer;
and/or the pore size of the micropores is 10-100 mu m;
and/or, in the carbon active layer, a carbon material, a first conductive agent and a first binder are included;
and/or a second conductive agent and a second adhesive are also included in the micropores.
3. The composite negative electrode sheet according to claim 2, wherein a mixture of the second active material, the second conductive agent, and the second binder has a filling volume percentage of 1% to 90% in the micropores;
and/or the thickness of the carbon active layer is 100-200 mu m, the opening depth of the micropores is 10-150 mu m, and the opening depth of the micropores is lower than the thickness of the carbon active layer.
4. The composite negative electrode sheet according to claim 3, wherein the particle diameter D50 of the carbon material is 1 to 20 μm;
and/or the particle size D50 of the second active material is 0.1-30 μm;
and/or the compacted density of the carbon active layer is 1.5-1.7 g/cm3；
And/or the volume of the micropores accounts for 25-40% of the total volume of the carbon active layer;
and/or the filling volume percentage of the mixture in the micropores is 30-60%.
5. The composite negative electrode sheet according to any one of claims 2 to 4, wherein the mass ratio of the carbon material, the first conductive agent, and the first binder is (80 to 95): (5-30): (5-15);
and/or in the micropores, the mass ratio of the second active material, the second conductive agent and the second binder is (80-95): (5-30): (5-15);
and/or the carbon material comprises at least one of artificial graphite, natural graphite, hard carbon, soft carbon and carbon microspheres;
and/or the second active material comprises at least one of a carbon material, a silicon carbon material, a silicon oxygen material, tin and lithium;
and/or the first conductive agent and the second conductive agent are respectively and independently at least one of carbon black, Ketjen black, single-walled carbon tubes, multi-walled carbon tubes, graphene and organic polymer ablation in-situ generation conductive carbon materials;
and/or the first binder and the second binder are respectively and independently selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid and polyacrylonitrile.
6. The preparation method of the composite negative plate is characterized by comprising the following steps of:
preparing a carbon active layer on the surface of a current collector, and then carrying out pore-forming treatment on the carbon active layer, wherein a plurality of micropores are formed in the surface of the carbon active layer; the opening depth of the micropores is lower than the thickness of the carbon active layer;
filling the mixed slurry of the second active material in the micropores, and drying to obtain a composite negative plate; wherein the specific capacity of the second active material is higher than the specific capacity of the carbon material in the carbon active layer.
7. The method for preparing the composite negative electrode sheet according to claim 6, wherein the method for performing pore-forming treatment on the carbon active layer comprises at least one of laser etching, mechanical drilling and chemical etching.
8. The method for preparing a composite negative electrode sheet according to claim 6 or 7, wherein the step of preparing the carbon active layer on the surface of the current collector comprises: preparing the carbon material, a first conductive agent, a first binder and a first solvent into first mixed slurry, depositing the first mixed slurry on the surface of the current collector, and drying the first mixed slurry to form a carbon active layer on the surface of the current collector;
and/or the step of filling the mixed slurry of the second active material in the micro-holes comprises: and preparing a second mixed slurry from a second active material, a second conductive agent, a second binder and a second solvent, and filling the second mixed slurry into the micropores.
9. The method for preparing a composite negative electrode sheet according to claim 8, wherein the volume of the micropores accounts for 1 to 50 percent of the total volume of the carbon active layer;
and/or the opening depth of the micropores is 50% -90% of the thickness of the carbon active layer;
and/or the pore size of the micropores is 10-100 mu m;
and/or the filling volume percentage of the second mixed slurry in the micropores is 1-90%;
and/or the thickness of the carbon active layer is 100-200 μm, the opening depth of the micropores is 10-150 μm, and the opening depth of the micropores is lower than the thickness of the carbon active layer;
and/or the particle size D50 of the carbon material is 1-20 μm;
and/or the particle size D50 of the second active material is 0.1-30 μm;
and/or the compacted density of the carbon active layer is 1.5-1.7 g/cm3。
10. A secondary battery comprising the composite negative electrode sheet according to any one of claims 1 to 5 or the composite negative electrode sheet prepared by the method according to any one of claims 6 to 9.
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