CN117317126A - Negative electrode sheet and application thereof - Google Patents

Negative electrode sheet and application thereof Download PDF

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Publication number
CN117317126A
CN117317126A CN202210706153.2A CN202210706153A CN117317126A CN 117317126 A CN117317126 A CN 117317126A CN 202210706153 A CN202210706153 A CN 202210706153A CN 117317126 A CN117317126 A CN 117317126A
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Prior art keywords
negative electrode
coating layer
silicon
electrode sheet
active material
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Inventor
韩晓燕
马永军
郭姿珠
高天骥
孙华军
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BYD Co Ltd
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BYD Co Ltd
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Priority to CN202210706153.2A priority Critical patent/CN117317126A/en
Priority to PCT/CN2023/101453 priority patent/WO2023246795A1/en
Publication of CN117317126A publication Critical patent/CN117317126A/en
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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • 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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • 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
    • 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
    • H—ELECTRICITY
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    • 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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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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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  • Manufacturing & Machinery (AREA)
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  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention discloses a negative plate and application thereof, wherein the negative plate comprises: a negative electrode current collector, a first coating layer, and a second coating layer, the first coating layer being provided on a surface of the negative electrode current collector, and the first coating layer including a silicon-based active material and an elastic additive; the second coating layer is provided on a surface of the first coating layer remote from the negative electrode current collector, and the second coating layer includes graphite. The negative plate not only has lower cost, but also can reduce the volume change rate generated by single cycle in the charge and discharge process of the battery, thereby improving the energy density of the battery and the cycle stability of the battery.

Description

Negative electrode sheet and application thereof
Technical Field
The invention belongs to the field of batteries, and particularly relates to a negative plate and application thereof.
Background
Along with the development of electric vehicles and the continuous improvement of the requirements of markets on the endurance mileage of the electric vehicles, the improvement of the energy density of lithium ion batteries has become the continuous pursuit direction of various battery manufacturers and research institutions. At present, most of commercial lithium ion battery cathode materials adopt graphite, but the specific capacity of the graphite is only 350mAh/g, and the energy density of the lithium ion battery can be greatly improved by adopting a silicon material as the cathode material. However, the silicon negative electrode has large volume expansion in the lithium intercalation process, and the cycle performance is still to be improved, so that the silicon negative electrode battery is not commercialized on a large scale.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, an object of the present invention is to provide a negative electrode sheet and application thereof, which can not only have low cost, but also reduce the volume change rate of a battery generated by a single cycle during charge and discharge, thereby improving the battery energy density thereof, and simultaneously improving the cycle stability thereof.
In one aspect of the invention, the invention provides a negative electrode sheet. According to an embodiment of the present invention, the negative electrode sheet includes:
a negative electrode current collector;
the first coating layer is arranged on the surface of the negative electrode current collector and comprises a silicon-based active material and a piezoelastic additive; and
the second coating layer is arranged on the surface, far away from the negative electrode current collector, of the first coating layer, and comprises graphite;
after the pressure X is applied along the thickness direction of the negative plate, the rebound rate of the negative plate is 2-40%, and the compression rate of the negative plate is 2-40%; the pressure X is more than 0 and less than or equal to 5Mpa.
According to the negative electrode sheet of the embodiment of the invention, the first coating layer comprising the silicon-based active material and the bomb additive is formed on the negative electrode current collector, and then the second coating layer comprising graphite is formed on the first coating layer, wherein the bomb additive in the first coating layer has rebound resilience and compressibility, so that the first coating layer shows bomb characteristics, when the battery is charged, as the negative electrode is intercalated with lithium, the volume of the negative electrode gradually expands, the volume expansion of the graphite negative electrode can reach 10% when intercalated with lithium, and the volume expansion of the silicon-based active material is larger when intercalated with lithium, for example, the volume expansion of silicon can reach 300% after intercalated with lithium, and SiO x The volume expansion after lithium intercalation can reach 120 percent. Under the working condition that the volume of the battery pack or the battery shell is fixed, the battery core can bear pressure from the outside (such as the pack body and the shell) due to expansion, at the moment, under the action of the pressure, the pressure bomb additive in the first coating layer is subjected to volume shrinkage under the action of the pressure, and a part of space is released for the silicon-based active material, so that larger volume expansion of the silicon-based active material in the lithium intercalation process is buffered, and larger volume expansion rate of the first coating layer in the lithium intercalation process is slowed down. In the discharging process, along with the release of lithium ions, the active material of the negative electrode plate gradually contracts in volume, the external pressure born by the battery core is gradually reduced or even eliminated, the compression spring additive in the first coating layer rebounds, the volume is gradually recovered, the space released by the volume contraction of the active material is occupied, and further the volume contraction of the first coating layer caused by the lithium release of the active material is delayed, so that the first coating layer with the compression spring characteristic can buffer the larger volume change of the negative electrode plate in the charging and discharging process. Meanwhile, the piezoelectric additive in the first coating layer has conductivity, so that the volume of the piezoelectric additive rebounds in the discharging process, on one hand, the piezoelectric additive can help good physical contact among silicon-based active material particles in the first coating layer, and ensure good electricity In the sub-conductive network, on the other hand, the volume change rate of the first coating layer in the charging and discharging process can be reduced by the pressure bomb additive, so that the difference of the volume expansion rate of the first coating layer and the volume expansion rate of the second coating layer in the charging and discharging process can be reduced, and the problem that the double layers of the first coating layer and the second coating layer gradually generate crack separation due to the large difference of the volume expansion rates in the long-term circulation process is avoided. Meanwhile, the second coating layer containing graphite is formed on the surface layer of the negative electrode plate, and the quick charge performance of the graphite is better than that of a silicon-containing negative electrode, so that the instant charge and high-rate instant discharge performance of the battery are improved. Therefore, the negative plate has lower cost, and the volume change rate of the battery generated in a single cycle in the charge and discharge process can be reduced, so that the battery energy density and the cycle stability are improved.
In addition, the negative electrode sheet according to the above embodiment of the present invention may have the following additional technical features:
in some embodiments of the invention, the first coating layer has a single-sided thickness of 5 to 50 μm. Thereby, the cycle stability thereof can be improved while improving the battery energy density thereof.
In some embodiments of the invention, the mass ratio of the silicon-based active material to the piezoelastic additive is 100:3 to 30. Thereby, the cycle stability thereof can be improved while improving the battery energy density thereof.
In some embodiments of the invention, the silicon-based active material comprises 3% to 100% of the total active material mass in the first coating layer. Thereby, the cycle stability thereof can be improved while improving the battery energy density thereof.
In some embodiments of the invention, the first coating layer further comprises graphite, the mass ratio of the total mass of the silicon-based active material and the graphite to the piezoelastic additive being 100:3 to 30.
In some embodiments of the invention, the silicon-based active material comprises SiO x At least one of Si, si/C of Si-C material and Si-based alloy, wherein x has a value of 0<x<2, the silicon-based alloy contains Si in addition to SiIncluding at least one of Al, mg, B, ni, fe, cu and Co.
In some embodiments of the invention, the first coating layer further comprises a first conductive agent comprising at least one of single-walled carbon nanotubes and carbon black.
In some embodiments of the invention, the first coating layer further comprises a first binder comprising at least one of polyacrylic acid, sodium alginate, and polyimide.
In some embodiments of the invention, the piezoelastic additive is three-dimensional graphene. Thereby improving the cycle stability of the battery.
In some embodiments of the present invention, the three-dimensional graphene satisfies at least one of the following conditions (1) - (5):
(1) The particle size of the three-dimensional graphene is 500 nm-20 mu m;
(2) The pore volume of the three-dimensional graphene is 1-10 cm 3 /g；
(3) The three-dimensional graphene comprises mutually overlapped graphene sheets, and the breaking strength between the graphene sheets is 20-50N/m;
(4) The three-dimensional graphene comprises mutually overlapped graphene sheets, and the transverse dimension of the graphene sheets is 10nm-100nm, preferably 10nm-20nm;
(5) The average pore diameter of the three-dimensional graphene is not more than 250nm.
In some embodiments of the invention, the second coating layer has a single-sided thickness of 5 to 80 μm.
In some embodiments of the present invention, the silicon-based negative electrode material in the negative electrode sheet accounts for 3% -90% of the total active material mass of the negative electrode. Thereby, the battery energy density is increased while the cost thereof is reduced.
In a second aspect of the present invention, the present invention proposes a secondary battery. According to an embodiment of the present invention, the secondary battery includes the above-described negative electrode sheet. Thus, the secondary battery has higher cycle stability while having higher energy density.
In a third aspect of the present invention, the present invention provides an electrical device. According to the embodiment of the invention, the electric equipment is provided with the secondary battery.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
fig. 1 is a schematic structural view of a negative electrode sheet according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method of preparing a negative electrode sheet according to one embodiment of the invention;
fig. 3 is a cycle spectrum of the battery corresponding to example 1 and comparative example 1.
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present invention and should not be construed as limiting the invention.
The technical scheme of the application is completed based on the following findings: in the prior art, a mode of mixing silicon and graphite is adopted to prepare the negative electrode plate, namely, si/C silicon-carbon material or SiO is doped into the graphite negative electrode active material x As a negative electrode material for improving battery energy density. However, after silicon is doped in the graphite cathode, the cycle performance of the battery is obviously reduced compared with that of graphite; meanwhile, the silicon-based material has large volume expansion in the lithium intercalation process, for example, the volume expansion of silicon after lithium intercalation can reach 300 percent, and SiO x The volume expansion after lithium intercalation can reach 120 percent. Conventional adhesives have insufficient adhesion to silicon-based materials, and more strongly adhering adhesives such as polyacrylic acid and the like are required. Moreover, conventional conductive agents such as carbon black have failed to satisfy SiO x Is required to be added with carbon nano-tubes or even withHigh-cost single-wall carbon nanotubes are added to ensure the normal exertion of the capacity of the single-wall carbon nanotubes. However, the graphite does not need the high-cost polyacrylic acid binder and the single-wall carbon nano tube conductive agent, but the silicon-based material and the graphite are mixed, so that the two high-cost binders and the conductive agent are adopted in the whole anode active layer, and the battery cost is greatly increased. The other mode is to coat the cathode plate in a double-layer way, wherein the bottom layer adopts a silicon-rich layer, and the surface layer adopts a graphite layer. The mode of double-layer coating of the silicon-rich layer and the graphite layer is adopted, so that the silicon-rich layer can adopt a high-cost binder and a high-cost conductive agent, and the graphite layer still adopts a conventional binder and conductive agent combination, so that the cost can be effectively reduced. However, in experiments, the problem that the double layers are gradually peeled off in the cycle process is caused because of the volume expansion rate of the silicon-rich layer and the graphite layer which are different in the charge-discharge process, so that the cycle performance of the battery is reduced in a cliff type.
In view of this, in one aspect of the present invention, the present invention proposes a negative electrode sheet. According to an embodiment of the present invention, referring to fig. 1, the negative electrode sheet includes a negative electrode current collector 100, a first coating layer 200, and a second coating layer 300.
It should be noted that, a person skilled in the art may select the material of the negative electrode current collector 100 according to actual needs, for example, copper foil is used.
According to an embodiment of the present invention, referring to fig. 1, a first coating layer 200 is provided on a surface of a negative electrode current collector 100, and the first coating layer 200 includes a silicon-based active material and a piezoelastic additive. The second coating layer 300 is disposed on a surface of the first coating layer 200 remote from the negative electrode current collector 100, and the second coating layer 300 includes graphite. After the pressure X is applied along the thickness direction of the negative plate, the rebound rate of the negative plate is 2-40%, and the compression rate is 2-40%; the pressure X is more than 0 and less than or equal to 5Mpa. The inventors have found that the elastic additive has resiliency and compressibility such that the first coating layer 200 exhibits a piezoelastic character, and that as the negative electrode is intercalated with lithium, the volume of the negative electrode gradually expands, e.g., silicon expands by 300% in volume after intercalation with lithium, and SiO x The volume expansion after lithium intercalation can reach 120 percent. In which the battery pack or battery casing is fixed Under the long-term working condition, the battery core can bear pressure from the outside (such as a bag body and a shell) due to expansion, at the moment, under the action of the pressure, the pressure bomb additive in the first coating layer 200 is subjected to volume shrinkage under the action of the pressure, and a part of space is released for the silicon-based active material, so that larger volume expansion of the silicon-based active material in the lithium intercalation process is buffered, and larger volume expansion rate of the first coating layer 200 in the lithium intercalation process is slowed down. In the discharging process, along with the release of lithium ions, the active material in the negative electrode plate gradually contracts in volume, the external pressure born by the battery core is gradually reduced or even eliminated, the compression spring additive in the first coating layer 200 rebounds, the volume is gradually recovered, the space released by the volume contraction of the active material is occupied, and further the volume contraction of the first coating layer 200 caused by the lithium release of the active material is delayed, so that the first coating layer 200 with the compression spring characteristic can buffer larger volume change of the negative electrode plate in the charging and discharging process. That is, the first coating layer 200 having the piezoelastic property can buffer a large volume change of the negative electrode sheet during charge and discharge. Meanwhile, the volume rebound of the bomb additive in the first coating layer 200 in the discharging process can help good physical contact among silicon-based active material particles in the first coating layer 200 on one hand, and ensure a good electronic conductive network, and on the other hand, because the bomb additive can reduce the volume change rate of the first coating layer 200 in the charging and discharging process, the difference of the volume expansion rate of the first coating layer 200 and the second coating layer 300 in the charging and discharging process can be reduced, and the problem that the double layers of the first coating layer 200 and the second coating layer 300 gradually crack and separate due to the large difference of the volume expansion rate in the long-term circulating process is avoided.
In the invention, the method for testing the rebound performance and the compression performance of the negative plate comprises the following steps: applying a value X to the negative plate along the thickness direction of the negative plate 1 Pressure of Mpa, measuring negative electrode plate at X 1 Thickness H under pressure of Mpa 1 The method comprises the steps of carrying out a first treatment on the surface of the Then the pressure is removed, and after the thickness of the negative plate is stable, the thickness of the negative plate is measured and is recorded as H 2 Thickness rebound rate r of the negative electrode sheet 1 ＝(H 2 -H 1 )/H 1 . Initial thickness along the thickness direction of the negative plateIs H 3 Is applied with a value X to the negative electrode sheet 2 Pressure of Mpa, measuring negative electrode plate at X 2 The thickness under pressure of Mpa is denoted as H 4 The thickness compression rate p= (H) of the negative electrode sheet 3 -H 4 )/H 3 . Therefore, the above-mentioned "after the first pressure X is applied in the thickness direction of the negative electrode sheet, the rebound rate of the negative electrode sheet is 2% to 40%, the compression rate is 2% to 40%; the first pressure X satisfying 0 < X.ltoreq.5 MPa "can be understood as: applying 0 < X to the negative plate along the thickness direction of the negative plate 1 Pressure X less than or equal to 5Mpa 1 Measuring the pressure X of the negative plate 1 The thickness under is H 1 The method comprises the steps of carrying out a first treatment on the surface of the Then the pressure is removed, and after the thickness of the negative plate is stable, the thickness of the negative plate is measured and is recorded as H 2 Thickness rebound rate r of negative electrode sheet 100 1 ＝(H 2 -H 1 )/H 1 ，r 1 In the range of 2% -40%; the initial thickness of the negative plate is H 3 Is applied to the negative electrode sheet of 0 < X 2 Pressure X less than or equal to 5Mpa 2 Measuring the pressure X of the negative plate 2 The thickness below is denoted as H 4 The thickness compression rate p= (H) of the negative electrode sheet 3 -H 4 )/H 3 P is in the range of 2% -40%. r is (r) 1 And p may be the same or different, X 1 And X 2 May be the same or different.
In some embodiments of the present invention, the thickness of one side of the first coating layer 200 is 5 to 50 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm.
Since the coating layer in the negative electrode sheet may be coated on one side of the current collector or both sides of the current collector, when the coating layer is coated on one side of the current collector, "one-side thickness" in the present invention means the thickness of the first coating layer 200 or the second coating layer 300 of the coating layer; when the coating layers are coated on both sides in the current collector, the "one-side thickness" in the present invention refers to the thickness of the first coating layer 200 or the second coating layer 300 in the coating layer on either side.
In some embodiments of the invention, the mass ratio of the silicon-based active material to the piezoelastic additive is 100:3 to 30. If the addition amount of the spring-pressing additive is too low, the compression resilience performance of the pole piece cannot be realized. Thus, the addition of the above-described proportion of the bomb additive to the first coating layer 200 can improve battery energy density and cycle stability while reducing costs.
In some embodiments of the present invention, the silicon-based active material accounts for 3-100% of the total active material mass fraction in the first coating layer 200, preferably 10-60%. The inventors found that the active material in the first coating layer 200 may be a pure silicon-based active material, and if the silicon-based active material is too small, although the effect of improving the energy density of the battery can be achieved, the benefit is not significant from the viewpoint of process cost and benefit.
In some embodiments of the present invention, the first coating layer 200 further comprises graphite, and the mass ratio of the total mass of the silicon-based active material and the graphite to the piezoelastic additive is 100:3 to 30.
The specific types of the above silicon-based active materials and the pressure bomb additives can be selected by those skilled in the art according to actual needs, for example, silicon-based active materials including SiO x At least one of Si, si/C and silicon-based alloys, wherein x has a value of 0<x<2, and the silicon-based alloy comprises at least one of Al, mg, B, ni, fe, cu and Co elements besides Si.
In some embodiments of the invention, the first coating layer further comprises a first conductive agent including, but not limited to, at least one of single-walled carbon nanotubes and carbon black; in some embodiments of the invention, the first conductive agent comprises single-walled carbon nanotubes.
In some embodiments of the present invention, the first coating layer 200 further includes a first binder including, but not limited to, at least one of polyacrylic acid, sodium alginate, and polyimide; in some embodiments of the invention, the first binder comprises polyacrylic acid.
In some embodiments of the invention, the mass ratio of the silicon-based active material or the composite of silicon-based active material and graphite, the first conductive agent, the first binder, and the piezoelastic additive is 100:0.1 to 2.5:0.1 to 30:3 to 30. If the addition amount of the first conductive agent is too high, the cost is increased on one hand, the energy density of the battery cell is reduced on the other hand, and if the addition amount of the first conductive agent is too low, the conductivity of the battery cell is reduced; if the addition amount of the first binder is too high, besides increasing the cost and reducing the energy density of the battery core, the battery polarization and the internal resistance of the battery are increased, and if the addition amount of the first binder is too low, the silicon-based active material is pulverized in the repeated expansion and contraction process of the battery in the battery cycle process, so that the cycle performance is rapidly reduced; if the amount of the bomb additive is too high, the cost is increased, and the energy density of the battery is reduced.
In some embodiments of the invention, the piezoelastic additive is three-dimensional graphene. In some embodiments of the present invention, the three-dimensional graphene satisfies at least one of the following conditions (1) - (5):
(1) The particle size of the three-dimensional graphene is 500 nm-20 mu m;
(2) The pore volume of the three-dimensional graphene is 1-10 cm 3 /g；
(3) The three-dimensional graphene comprises mutually overlapped graphene sheets, and the breaking strength between the graphene sheets is 20-50N/m;
(4) The three-dimensional graphene comprises mutually overlapped graphene sheets, and the transverse dimension of the graphene sheets is 10nm-100nm, preferably 10nm-20nm;
(5) The average pore diameter of the three-dimensional graphene is not more than 250nm.
The pore volume of the three-dimensional graphene can be measured by adopting a nitrogen adsorption method on the three-dimensional graphene. The breaking strength of the graphene sheet can be obtained by carrying out nano indentation test on the lap joint of three-dimensional graphene by adopting an atomic force microscope (Atomic Force Microscope, AFM): fixing three-dimensional graphene on a silicon wafer with small holes on the surface, applying pressure to graphene sheets on the small holes by using a probe, wherein the pressure applying position is near the lap joint position of two adjacent graphene sheets, and recording the critical pressure capable of breaking the lap joint of the two graphene sheets, so as to obtain the breaking strength of the lap joint between the graphene sheets. The lateral dimension refers to the length, width, or the like of the graphene sheet, and can be obtained from an electron micrograph of three-dimensional graphene.
In some embodiments of the present application, the three-dimensional graphene may be grown by a plasma chemical vapor deposition (PECVD) method. An exemplary preparation method comprises the following steps: by reacting a carbon source (e.g. C 2 H 2 ) And H 2 Introducing the mixed gas into a deposition chamber heated to a certain temperature in plasma deposition equipment, starting a plasma generator to deposit and grow three-dimensional graphene materials on a substrate (such as Cu) placed in the deposition chamber by a PECVD method, introducing auxiliary gas (such as Ar, he and the like) to cool the deposition chamber to room temperature under inert atmosphere after the growth of the three-dimensional graphene is finished, taking out the obtained sample from the deposition chamber, stripping the three-dimensional graphene materials from the substrate, and crushing the three-dimensional graphene materials to the required particle size. By adjusting the growth conditions, three-dimensional graphene satisfying the following conditions can be obtained: particle diameter 500 nm-20 mu m and pore volume 1-10 cm 3 And/g, the graphene sheets with the transverse dimension of 10nm-100nm are formed by mutually overlapping and growing, the average pore diameter is not more than 250nm, and the breaking strength between the graphene sheets is 20-50N/m.
An exemplary preparation method comprises the following steps: by reacting a carbon source (e.g. C 2 H 2 ) And H 2 Introducing the mixed gas into a deposition chamber heated to a certain temperature in plasma deposition equipment, starting a plasma generator to deposit and grow three-dimensional graphene materials on a substrate (such as Cu) placed in the deposition chamber by a PECVD method, introducing auxiliary gas (such as Ar, he and the like) to cool the deposition chamber to room temperature under inert atmosphere after the growth of the three-dimensional graphene is finished, taking out the obtained sample from the deposition chamber, stripping the three-dimensional graphene materials from the substrate, and crushing the three-dimensional graphene materials to the required particle size. The PECVD process can generate plasmas with high energy density and large volume, and the carbon source C can be used 2 H 2 And decomposing into more carbon-containing reaction free radicals, thereby realizing the growth of the three-dimensional graphene. Wherein C is 2 H 2 The flow rate of the mixture is 20mL/min, H 2 The flow rate of the auxiliary gas Ar is 250mL/min, the deposition growth temperature can be 950 ℃, the flow rate of the auxiliary gas Ar is 200mL/min, and the plasma is generatedThe operating power of the sub-generator is 300W.
Specifically, a sufficient amount of pore volume can ensure that the three-dimensional graphene has excellent compression performance, proper pore size and breaking strength among graphene sheets, so that the three-dimensional graphene is ensured to have good rebound performance after compression, and the collapse of the structure and the loss of the rebound performance caused by pressure are avoided. Thereby stably maintaining its compression-rebound performance during battery cycling. The three-dimensional graphene with the characteristics has excellent compression-rebound performance, so that the prepared first coating layer 200 shows higher compression-rebound characteristic, and further, the larger volume expansion of the negative plate in the charging process is buffered.
According to an embodiment of the present invention, referring to fig. 1, a second coating layer 300 is provided on a surface of the first coating layer 200 remote from the negative electrode current collector 100, and the second coating layer 300 includes graphite. The inventor finds that, since silicon and graphite have different lithium removal platforms (silicon lithium removal platform is 0.4-0.5V), and the lithium removal platform of graphite is about 0.1V, at the initial stage of full battery discharge, graphite needs to bear most of discharge current, thus leading to large discharge polarization of graphite material, and in order to reduce discharge polarization of graphite negative electrode, lithium ions migrating out of the graphite negative electrode migrate to positive electrode rapidly, thus the application forms the second coating layer 300 containing graphite on the first coating layer 200, i.e. forms the second coating layer 300 containing graphite on the surface layer of the negative electrode sheet, because the quick charge performance of graphite is better than that of the silicon-containing negative electrode, thus being beneficial to improving the instantaneous charge and high-rate instantaneous discharge performance of the battery.
In some embodiments of the present invention, the second coating layer 300 has a single-side thickness of 5 to 80 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm.
In some embodiments of the present invention, second coating layer 300 further includes a second conductive agent, such as a second conductive agent including, but not limited to, acetylene black, conductive carbon black, and the like.
In some embodiments of the present invention, second coating layer 300 further includes a second binder, such as a second binder including, but not limited to, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the like.
It should be noted that the mixing ratio of the graphite, the second conductive agent, and the second binder forming the second coating layer 300 in this application may be a conventional arrangement in the art for forming a graphite anode. Meanwhile, in the application, the second coating layer 300 containing graphite is formed on the first coating layer 200 containing silicon, and the conductive agent and the binder of the first coating layer 200 and the second coating layer 300 are differentiated, so that the respective capacities and the exertion of the circulating stability of graphite in the second coating layer 300 and silicon-based active materials in the first coating layer 200 can be respectively ensured, and the cost of the negative electrode plate is obviously reduced.
In the invention, after the pressure X is applied along the thickness direction of the negative plate, the rebound rate of the negative plate is 2-40%, and the compression rate of the negative plate is 2-40%; the pressure X is more than 0 and less than or equal to 5Mpa. Therefore, the negative plate has lower volume change rate in the charge and discharge process, so that the battery energy density and the cycling stability of the negative plate are improved.
In addition, in practical application, the user usually does not charge the battery after completely discharging the battery in the process of using the battery, which belongs to the use field of shallow discharge, and at this time, for the negative electrode sheet proposed in the present application, the SiO in the first coating layer 200 near the negative electrode current collector 100 x Because of its higher discharge plateau, no discharge or only a small amount of electricity, i.e. SiO x The SiOx can be always in a shallow-discharge state in the actual use process, so that repeated volume expansion of the SiOx in the circulation process is reduced, and the improvement of the circulation performance of the battery is facilitated.
In some embodiments of the present invention, the present application defines that the silicon-based negative electrode material in the negative electrode sheet accounts for 3% -90% of the total active material mass of the negative electrode, wherein the total active material refers to all active materials in the negative electrode sheet that can undergo deintercalation of lithium. Specifically, the silicon-based active material and graphite are compounded to prepare the negative plate by adopting the proportion, so that the problem of interlayer separation during double-layer coating can be solved, and the process implementation difficulty and cost are low, so that the cost is reduced, the full play of the performances of the silicon-based active material and graphite in the negative plate can be maintained, and the energy density of the battery is improved.
Therefore, the negative plate has lower cost, and the volume expansion rate of the battery generated in a single cycle in the charging process can be reduced, so that the battery energy density and the cycle stability of the battery are improved.
For convenience of understanding, a method of preparing the above-described negative electrode sheet is described below. Referring to fig. 2, according to an embodiment of the present invention, the method includes:
s100: applying a first paste comprising a silicon-based active material and a piezoelastic additive on a negative current collector
In this step, a first paste including a silicon-based active material and a piezoelastic additive is applied on the anode current collector 100 to form a first coating layer 200 on the anode current collector 100. The inventors have found that the viscoelastic additive has resiliency and compressibility such that the first coating layer 200 exhibits a viscoelastic character, and that as the negative electrode is intercalated with lithium as the volume of the negative electrode gradually expands, the graphite negative electrode expands by up to 10% in volume upon intercalation of lithium, whereas the silicon-based active material expands more in volume upon intercalation of lithium, e.g., silicon expands by up to 300% in volume upon intercalation of lithium, and SiO x The volume expansion after lithium intercalation can reach 120 percent. Under the working condition of fixing the volume of the battery pack (such as a cylindrical battery), the battery core can bear the pressure from the external pack body due to expansion, and at the moment, under the action of the pressure, the pressure bomb additive in the first coating layer 200 is subjected to volume shrinkage under the action of the pressure to release a part of space for the silicon-based active material, so that the larger volume expansion of the silicon-based active material in the lithium intercalation process is buffered, and the larger volume expansion rate of the first coating layer 200 in the lithium intercalation process is slowed down. In the discharging process, along with the release of lithium ions, the active material in the negative electrode plate gradually contracts in volume, at this time, the external pressure born by the battery core gradually decreases or even eliminates, the compression spring additive in the first coating layer 200 rebounds, the volume gradually recovers, and occupies the space released by the volume contraction of the active material, so as to delay the volume contraction of the first coating layer 200 caused by the lithium release of the active material, thereby having the first coating layer 20 with compression spring characteristics And 0 can buffer larger volume change of the negative plate in the charge and discharge process. That is, the first coating layer 200 having the piezoelastic property can buffer a large volume change of the negative electrode sheet during charge and discharge. Meanwhile, the volume rebound of the bomb additive in the first coating layer 200 in the discharging process can help good physical contact among silicon-based active material particles in the first coating layer 200 on one hand, and ensure a good electronic conductive network, and on the other hand, because the bomb additive can reduce the volume shrinkage rate of the first coating layer 200 in the discharging process, the difference of the volume change rate of the first coating layer 200 and the second coating layer 300 in the charging and discharging processes can be reduced, and the problem that the double layers of the first coating layer 200 and the second coating layer 300 gradually have crack separation due to the large difference of the volume expansion rate in the long-term circulating process is avoided.
S200: applying a second slurry comprising graphite over the first coating layer
In this step, a second paste including graphite is applied on the first coating layer 200 to form a second coating layer 300 on the first coating layer 200, resulting in a negative electrode sheet. The inventors found that since silicon and graphite have different lithium removal platforms (silicon lithium removal platform 0.4-0.5V), and graphite lithium removal platform is about 0.1V, at the initial stage of full battery discharge, graphite needs to bear most of discharge current, thus leading to large discharge polarization of graphite material, and in order to reduce discharge polarization of graphite negative electrode, lithium ions migrating out of graphite negative electrode migrate rapidly to positive electrode, thus the application forms graphite-containing second coating layer 300 on first coating layer 200, i.e. graphite-containing second coating layer 300 is formed on the surface layer of negative electrode sheet, because quick charge performance of graphite is superior to that of silicon-containing negative electrode, thus improving instantaneous charge and high-rate instantaneous discharge performance of battery.
In some embodiments of the present invention, the second paste may further include a second conductive agent and a second binder. According to the method, the graphite-containing second coating layer 300 is formed on the silicon-containing first coating layer 200, and the conductive agent and the binder of the first coating layer 200 and the second coating layer 300 are differentiated, so that the respective capacities and the exertion of the cycling stability of graphite and the silicon-based active material can be respectively ensured, and the cost of the negative electrode plate is obviously reduced.
In some embodiments of the present invention, the first paste may further include a first binder and/or a first conductive agent.
Therefore, the volume expansion rate generated by the single cycle with lower cost can be obtained by adopting the method, so that the cycle stability of the battery is improved while the energy density of the battery is improved. It should be noted that the features and advantages described above for the negative electrode sheet are also applicable to the method for preparing a negative electrode sheet, and meanwhile, the solid content of the first slurry and the solid content of the second slurry are all conventional parameters for preparing a negative electrode sheet in the art, which are not described herein again.
In a third aspect of the present invention, the present invention provides a secondary battery. According to an embodiment of the present invention, the secondary battery includes the above-described negative electrode sheet. Thus, the secondary battery exhibits higher energy density and higher cycle stability by employing the above-described negative electrode sheet having high energy density and high cycle stability. It should be noted that the features and advantages described above for the negative electrode sheet and the preparation method thereof are also applicable to the secondary battery, and are not repeated here.
In a fourth aspect of the invention, the invention provides a powered device. The electric equipment can be vehicles such as a car and a ship, and can also be a notebook computer, a mobile terminal and the like. According to the embodiment of the invention, the electric equipment is provided with the secondary battery. Therefore, the electric equipment has excellent endurance mileage and safety performance by loading the secondary battery with higher energy density and higher cycle stability. It should be noted that the features and advantages described above for the secondary battery are equally applicable to the electric device, and are not repeated here.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not limiting in any way.
Example 1
The method for preparing the negative plate comprises the following steps:
(1) SiO is made of x (x=1.02), graphite, single-walled carbon nanotubes, polyacrylic acid, and three-dimensional graphene in a mass ratio of 30:70:0.2:5:5 mixing to prepare a first slurry, and then coating the first slurry on the surface of the copper foil (the density of the coated surface is the same, and the density of the single surface is 43g/m 2 ) Then, after curing, roll-pressing to form first coating layers having a single-side thickness of 27 μm on both sides of the copper foil, respectively;
(2) Graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber and carbon black are mixed according to the mass ratio of 100:1.5:1.5:1 mixing to prepare a second slurry, and then coating the second slurry on the surfaces of the first coating layers on both sides of the copper foil (one-sided area density of 43g/m 2 ) And then, after solidification, rolling so as to form second coating layers with the single-side thickness of 27 mu m on the first coating layers on the two sides of the copper foil respectively, thereby obtaining the negative plate.
The three-dimensional graphene used in example 1 comprises graphene sheets which are overlapped with each other and has a porous structure, the three-dimensional graphene has an average particle diameter of 0.6 μm and a pore volume of 2.5cm 3 And/g, wherein the average pore diameter of the porous structure in the three-dimensional graphene is 100nm; and carrying out nano indentation test by AFM (atomic force microscope), wherein the breaking strength of the joint of the graphene sheets which are mutually overlapped in the three-dimensional graphene is 30N/m, and the transverse dimension of the mutually overlapped graphene sheets is 10-100 nm.
Example 2
The method for preparing the negative plate comprises the following steps:
(1) SiO is made of x (x=1.02), single-walled carbon nanotubes, polyacrylic acid, and three-dimensional graphene in a mass ratio of 100:0.5:10:15, and then double-side coating the first slurry on the surface of the copper foil (the double-side coating surface density is the same, and the single-side surface density is 17.5 g/m) 2 ) And then roll-pressed after curing to form first coating layers having a single-side thickness of 11 μm on both sides of the copper foil, respectively;
(2) Graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber and carbon black are mixed according to the mass ratio of 100:1.5:1.5:1 mixing to prepare a second slurry, and then coating the second slurry on the surfaces of the first coating layers on both sides of the copper foil (one-sided denseDegree of 62g/m 2 ) And then, after solidification, rolling so as to form second coating layers with the single-side thickness of 39 mu m on the first coating layers on the two sides of the copper foil respectively, thereby obtaining the negative plate.
The three-dimensional graphene used in example 2 comprises graphene sheets which are overlapped with each other and has a porous structure, the three-dimensional graphene has an average particle diameter of 0.6 μm and a pore volume of 2.5cm 3 And/g, wherein the average pore diameter of the porous structure in the three-dimensional graphene is 100nm; and carrying out nano indentation test by AFM (atomic force microscope), wherein the breaking strength of the joint of the graphene sheets which are mutually overlapped in the three-dimensional graphene is 30N/m, and the transverse dimension of the mutually overlapped graphene sheets is 10-100 nm.
Example 3
Example 3 differs from example 1 in that the SiOx of example 1 was replaced with a silicon carbon material having a gram specific capacity of 1250mAh/g, the second coating layer having a single-sided coating area density of 46g/m 2 So as to form second coating layers with the single-side thickness of 29 mu m on the first coating layers on the two sides of the copper foil respectively, thereby obtaining the negative plate.
Example 4
Example 4 differs from example 1 in that the three-dimensional graphene employed has an average particle size of 1.5 μm and a pore volume of 4cm 3 And/g, wherein the average pore diameter of the porous structure in the three-dimensional graphene is 150nm; and carrying out nano indentation test by AFM (atomic force microscope), and measuring that the breaking strength of the joint of the graphene sheets which are mutually overlapped in the three-dimensional graphene is 45N/m.
Example 5
Example 5 differs from example 2 in that step (1) is replaced by SiO x (x=1.02), single-walled carbon nanotubes, polyacrylic acid, and three-dimensional graphene in a mass ratio of 100:0.5:10:30 to prepare a first slurry. The first slurry was double coated on the copper foil surface (the double coated surface density was the same and the single surface density was 19.6g/m 2 ) And then rolled after curing to form a first coating layer having a thickness of 12 μm on one side on the copper foil, maintaining the same first coating layer capacity as in example 2).
Example 6
Implementation of the embodimentsExample 6 differs from example 2 in that the three-dimensional graphene used in example 6 has an average particle diameter of 10 μm and a pore volume of 8cm 3 And/g, wherein the average pore diameter of the porous structure in the three-dimensional graphene is 150nm; and carrying out nano indentation test by AFM (atomic force microscope), wherein the breaking strength of the joint of the graphene sheets which are mutually overlapped in the three-dimensional graphene is 20N/m, and the transverse dimension of the mutually overlapped graphene sheets is 10-100 nm.
Comparative example 1
The method for preparing the negative plate comprises the following steps:
SiO is made of x (x=1.02), graphite, single-walled carbon nanotubes to polyacrylic acid mass ratio of 15:85:0.1:3 mixing to prepare a slurry, and then coating the slurry on the surface of the copper foil (the density of the coated surface is the same, and the density of one side is 82.5g/m 2 ) And then, after curing, roll-pressing to form coating layers with a thickness of 51.5 μm on one side on both sides of the copper foil, respectively, to obtain a negative electrode sheet.
Comparative example 2
Comparative example 2 differs from example 1 in that:
(1) The proportion of the first sizing agent is SiO x (x=1.02), graphite, single-walled carbon nanotubes, polyacrylic acid, and three-dimensional graphene in a mass ratio of 30:70:0.2:5:0.5; the density of the coated single surface is 42g/m 2 The first coating layer was formed to have a single-side thickness of 26 μm.
(2) The density of one side of the second coating layer is 41g/m 2 The resulting second coating layer had a single-sided thickness of 26 μm.
Comparative example 3
Comparative example 3 differs from example 1 in that: in the step (1), the proportion of the first slurry is SiO x (x=1.02), graphite, single-walled carbon nanotubes, polyacrylic acid, and three-dimensional graphene in a mass ratio of 30:70:0.2:5:2, the first paste was coated with an areal density of 41.8g/m on each of the two sides of the copper foil 2 The first coating layer was formed to have a single-side thickness of 26 μm.
The specific volume test battery is prepared: the negative electrode sheet, PE separator and 100-micron thick lithium foil prepared in each example and comparative example are assembled into a battery by adopting 1mol/L LiPF6 as electrolyte and 1:1 of EC to EMC volume ratio, and the battery is charged and discharged between 0.005V and 1.5V.
The preparation of the test battery for recycling: NCM811 was slurried with PVDF and the conductive agent Sup-P at a mass ratio of 100:1.6:1.2, at a single surface density of 200g/m on the aluminum foil surface 2 The positive plate is prepared by double-sided coating. Then the prepared positive plate is respectively matched with the negative plates and PE diaphragms obtained in the examples 1-6 and the comparative examples 1-3, and the electrolyte adopts LiPF of 1mol/L 6 The volume ratio of EC to EMC is 1:1, and the battery is assembled. The cycle performance of the corresponding battery was tested.
And (3) testing the specific capacity of the first charge and discharge of the cathode: after the battery was discharged to 0.005V at 0.1C constant current, it was discharged to 0.005V at 0.05C constant current, and then charged to 1.5V at 0.1C. First discharge specific capacity of negative electrode = discharge capacity/total mass of negative electrode layer; first charge specific capacity of the negative electrode = charge capacity/total mass of the negative electrode layer. Wherein the total mass of the negative electrode layer=the mass of the first coating layer+the mass of the second coating layer.
Capacity retention test: first, constant current was charged to 4.25V at 0.5C, then constant voltage was charged to 0.1C at 4.25V, then 1C was discharged to 2.5V, and thus cycle 300 times, the first discharge capacity and the discharge capacity after 300 times of cycle were recorded, and the capacity retention rate=the discharge capacity after 300 times of cycle/the first discharge capacity. The test results are shown in table 1 and fig. 3.
TABLE 1
As can be seen from fig. 3, the battery using the negative electrode sheet of example 1 has significantly better cycle stability than comparative example 1, and as can be seen from table 1, the batteries obtained by using examples 2 to 6 also have excellent cycle stability, which indicates that the use of the negative electrode sheet of the present application can not only reduce the battery cost, but also significantly improve the battery cycle performance.
The above-mentioned full battery after the first charge-discharge specific capacity test was disassembled, and the positive electrode sheet obtained by disassembling the full battery corresponding to each example or comparative example was respectively subjected to the test of the sheet rebound performance and the compression performance, and the results are summarized in table 2 below.
The negative electrode sheets obtained in examples 1 to 6 and comparative examples 1 to 3 were evaluated for their rebound resilience and compression properties, and the corresponding results are shown in Table 2.
The method for testing the rebound performance of the negative electrode plate comprises the following steps: applying X to the negative electrode sheet 1 The pressure of the Mpa was measured at X 1 Negative plate thickness H under Mpa pressure 1 Then the pressure is removed, and after the thickness of the negative plate is stable, the thickness H of the negative plate is measured 2 The rebound rate of the pole piece is:
pole piece rebound rate r= (H) 2 -H 1 )/H 1
The method for testing the compression performance of the negative plate comprises the following steps: for an initial thickness of H 3 Applying a pressure X to the pole piece of (C) 2 Mpa, record X 2 Thickness H of pole piece under Mpa pressure 4 The compression ratio of the negative plate is:
pole piece compressibility p= (H) 3 -H 4 )/H 3
TABLE 2 negative electrode sheet rebound and compression Property data
Remarks: test condition X 1 ＝0.5Mpa，X 2 ＝0.3Mpa。
It can be seen from the combination of tables 1 and 2 that the negative electrode sheets of examples 1 to 6 have higher rebound performance and compression performance, and meanwhile, as can be seen from the data of examples 1 and comparative example 2, when three-dimensional graphene is added according to the addition amount of the conventional conductive agent, the capacity retention rate of the assembled battery is obviously lower than that of examples 1 to 6 after 300 cycles as the performance of the conventional electrode sheet due to the fact that the addition amount of the three-dimensional graphene is small and the electrode sheet does not have compression retraction elasticity. As is clear from comparative example 3, when the rebound rate and the compression rate of the pole piece are not in the range of 2% to 40% although a certain amount of three-dimensional graphene is added, the cycle performance thereof is also somewhat reduced as compared with the examples.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.

Claims (12)

1. A negative electrode sheet, comprising:
a negative electrode current collector;
the first coating layer is arranged on the surface of the negative electrode current collector and comprises a silicon-based active material and a piezoelastic additive; and
the second coating layer is arranged on the surface, far away from the negative electrode current collector, of the first coating layer, and comprises graphite;
after the pressure X is applied along the thickness direction of the negative plate, the rebound rate of the negative plate is 2-40%, and the compression rate of the negative plate is 2-40%; the pressure X is more than 0 and less than or equal to 5Mpa.
2. The negative electrode sheet according to claim 1, wherein the first coating layer has a single-side thickness of 5 to 50 μm.
3. The negative electrode sheet according to claim 1 or 2, characterized in that the mass ratio of the silicon-based active material to the piezoelastic additive is 100:3 to 30.
4. The negative electrode sheet according to claim 1 or 2, characterized in that the first coating layer further comprises graphite, the mass ratio of the total mass of the silicon-based active material and the graphite to the piezoelastic additive being 100:3 to 30.
5. The negative electrode sheet according to any one of claims 1 to 4, wherein the silicon-based active material comprises SiO x At least one of Si, a silicon-carbon material and a silicon-based alloy, wherein x has a value of 0<x<2, and the silicon-based alloy further comprises at least one of Al, mg, B, ni, fe, cu and Co in addition to Si.
6. The negative electrode sheet according to any one of claims 1 to 5, wherein the first coating layer further comprises:
a first conductive agent comprising at least one of single-walled carbon nanotubes and carbon black; and
and a first binder including at least one of polyacrylic acid, sodium alginate, and polyimide.
7. The negative electrode sheet of any one of claims 1-6, wherein the piezoelastic additive is three-dimensional graphene.
8. The negative electrode sheet according to claim 7, wherein the three-dimensional graphene satisfies at least one of the following conditions (1) to (5):
(1) The particle size of the three-dimensional graphene is 500 nm-20 mu m;
(2) Pores of the three-dimensional grapheneThe volume is 1-10 cm 3 /g；
(3) The three-dimensional graphene comprises mutually overlapped graphene sheets, and the breaking strength between the graphene sheets is 20-50N/m;
(4) The three-dimensional graphene comprises mutually overlapped graphene sheets, and the transverse dimension of the graphene sheets is 10nm-100nm, preferably 10nm-20nm;
(5) The average pore diameter of the three-dimensional graphene is not more than 250nm.
9. The negative electrode sheet according to any one of claims 1 to 8, wherein the second coating layer has a single-side thickness of 5 to 80 μm.
10. The negative electrode sheet according to any one of claims 1 to 9, wherein the silicon-based active material in the negative electrode sheet accounts for 3 to 90% of the total active material mass of the negative electrode.
11. A secondary battery, characterized in that the secondary battery comprises the negative electrode sheet according to any one of claims 1 to 10.
12. An electric device, characterized in that the electric device has the secondary battery according to claim 11.
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