CN116364859A - Negative plate, secondary battery and electric equipment - Google Patents

Negative plate, secondary battery and electric equipment Download PDF

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Publication number
CN116364859A
CN116364859A CN202310255512.1A CN202310255512A CN116364859A CN 116364859 A CN116364859 A CN 116364859A CN 202310255512 A CN202310255512 A CN 202310255512A CN 116364859 A CN116364859 A CN 116364859A
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negative electrode
active layer
particles
silicon
carbon
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张�浩
蒋亚琴
韩定宏
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Jiangsu Zenio New Energy Battery Technologies Co Ltd
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Jiangsu Zenio New Energy Battery Technologies Co Ltd
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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
    • H01M4/134—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
    • 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
    • H01M4/36—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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Composite Materials (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention discloses a negative plate, which comprises: the surface of the negative electrode current collector is distributed with raised carbon particles; a first negative active layer attached to at least one side surface of the negative current collector; the first negative electrode active layer contains first graphite particles and first silicon particles; a second anode active layer attached to a surface of the first anode active layer; the second negative electrode active layer contains second graphite particles and second silicon particles; wherein the D50 particle size of the first graphite particles is 4.5-16 mu m, and the D50 particle size of the first silicon particles is 4.5-15.5 mu m; the second graphite particles have a D50 particle diameter of 11.2 to 18.9 μm, the second silicon particles have a D50 particle diameter of 3.2 to 16 μm, and the second graphite particles have a D50 particle diameter larger than the second silicon particles. The invention also discloses a secondary battery and electric equipment. The negative electrode plate provided by the invention can improve the cycle stability of the battery under high-rate charging.

Description

Negative plate, secondary battery and electric equipment
Technical Field
The invention relates to the technical field of secondary batteries, in particular to a negative electrode plate, a secondary battery and electric equipment.
Background
In lithium ion batteries, high capacity silicon negative electrode materials are the most potential negative electrode materials, and are expected to gradually replace existing graphite negative electrodes. However, the lithium ion battery using the silicon anode material inevitably has the following problems at the time of rapid charge: (1) Under the condition of large current, li is quickly embedded in the negative plate + Unstable interface reactions (such as lithium intercalation and ohmic heat release) of the silicon material in the pole piece can be caused; (2) Under the condition of high current, the structure of the silicon-containing negative electrode plate can be irreversibly transformed, so that the problems of volume expansion of silicon materials, crushing, falling of an active material layer of a pole piece and the like are caused, and the cycle life of the lithium ion battery is seriously shortened.
Disclosure of Invention
The invention aims to provide a negative plate which can improve the cycle stability of a battery under high-rate charging.
In order to solve the technical problems, the invention provides the following technical scheme:
the first aspect of the present invention provides a negative electrode sheet comprising:
the surface of the negative electrode current collector is distributed with raised carbon particles;
a first negative electrode active layer attached to at least one side surface of the negative electrode current collector; the first negative electrode active layer contains first graphite particles and first silicon particles;
a second anode active layer attached to a surface of the first anode active layer; the second negative electrode active layer contains second graphite particles and second silicon particles;
wherein the D50 particle size of the first graphite particles is 4.5-16 mu m, and the D50 particle size of the first silicon particles is 4.5-15.5 mu m;
the second graphite particles have a D50 particle size of 11.2 to 18.9 μm, the second silicon particles have a D50 particle size of 3.2 to 16 μm, and the second graphite particles have a D50 particle size greater than the second silicon particles.
Further, the ratio of the D50 particle size of the second graphite particles to the D50 particle size of the second silicon particles is 1:1.08-4.2.
Further, the negative electrode current collector is selected from one of copper foil, carbon-plated copper foil, nickel-plated copper foil, zinc-plated copper foil, iron-plated copper foil and titanium-plated copper foil;
and/or the carbon particles have a particle diameter of 0.02 to 15 μm;
and/or spraying carbon powder on the negative electrode current collector, and curing for 1-2 hours at 180-500 ℃.
Further, the first negative electrode active layer and the second negative electrode active layer each further comprise a conductive agent and a binder;
in the first negative electrode active layer, the mass ratio of the first graphite particles to the first silicon particles to the conductive agent to the binder is 0.5-35:25-95:0.8-7.0:1.0-12.0;
in the second negative electrode active layer, the mass ratio of the second graphite particles to the second silicon particles to the conductive agent to the binder is 0.5-35:25-95:0.8-7.0:1.0-12.0.
Further, the content of the binder in the second anode active layer is higher than the content of the binder in the first anode active layer.
Further, the total thickness of the first negative electrode active layer and the second negative electrode active layer is 0.032-0.180 mm;
and/or, the thickness of the second anode active layer is less than or equal to 0.015mm and less than or equal to the thickness of the first anode active layer;
and/or the compacted density of the first negative electrode active layer and the second negative electrode active layer is 1.30-1.88 g/cm 3 。
Further, the second silicon particles are silicon-carbon composite particles coated with a carbon layer on the surface; the silicon content of the silicon-carbon composite particles is 22.5-74 wt%.
Further, the carbon layer is a modified amorphous carbon layer;
the modified amorphous carbon layer is obtained by heat treatment of the silicon carbon composite particles and 0.03-0.9 wt% of hexafluorophosphate at 40-60 ℃.
A second aspect of the present invention provides a secondary battery comprising the aforementioned negative electrode sheet.
A third aspect of the present invention provides an electric device, including the aforementioned secondary battery.
Compared with the prior art, the invention has the beneficial effects that:
1. in the negative electrode plate, the raised carbon particles are arranged on the surface of the negative electrode current collector, so that the conductivity of the negative electrode plate is improved, the combination between the negative electrode current collector and the negative electrode active layer is enhanced, the separation of the whole negative electrode active layer is avoided, the strength of the plate structure is improved, and the stability of the plate under the condition of heavy current charging is improved.
2. In the negative plate, the small-particle-size silicon material is matched with the large-particle-size graphite to serve as the second negative active layer, and the large-particle-size graphite pores are reserved for the small-particle-size silicon material to serve as expansion spaces, so that the expansion influence of the silicon material in the charge and discharge process is reduced, and the high-rate charging performance of the battery is improved; in addition, the second negative electrode active layer can also play a role in protecting the first negative electrode active layer, effectively slows down the expansion of the first negative electrode active layer in the circulation process, improves the overall structural stability of the negative electrode sheet, and is beneficial to improving the cycle life of the battery.
Drawings
Fig. 1 is a schematic structural view of a negative plate according to an embodiment of the present application;
fig. 2 is a schematic structural view of a negative electrode sheet according to another embodiment of the present application;
wherein: 1. a negative electrode current collector; 2. carbon particles; 3. a first anode active layer; 31. a first graphite particle; 32. a first silicon particle; 4. a second anode active layer; 41. second graphite particles; 42. and second silicon particles.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
Referring to fig. 1, the present invention provides a silicon-containing negative electrode sheet capable of improving the cycle stability of a battery under high-rate charge, which includes a negative electrode current collector 1, a first negative electrode active layer 3, and a second negative electrode active layer 4.
In the present application, the negative electrode current collector may be made of a material with high conductivity commonly used in the art, for example, the negative electrode current collector may be one of copper foil, carbon-plated copper foil, nickel-plated copper foil, zinc-plated copper foil, iron-plated copper foil, titanium-plated copper foil, and the like. In some preferred embodiments, the negative electrode current collector employs a copper foil or a carbon-plated copper foil.
In the negative electrode current collector 1 of the present application, the surface thereof is distributed with the protruding carbon particles 2. The carbon particles have excellent conductivity, and the existence of the carbon particles can promote ion transmission, so that the overall conductivity of the anode sheet can be improved, and the sheet can meet the charge and discharge requirements under high current. In addition, the carbon particles can play an anchoring role, and can strengthen the combination between the negative electrode current collector and the negative electrode active layer on the surface of the negative electrode current collector, so that the whole negative electrode active layer is prevented from being separated from the negative electrode current collector, and the structural strength of the pole piece is improved.
In the present application, the shape of the carbon particles is not limited, and may be, for example, spherical, hemispherical, block-shaped, plate-shaped, surface microporous, or the like. In some embodiments of the present application, the carbon particles have a particle size of 0.02 to 15 μm, such as 0.02 μm, 0.1 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, or a range between any two of the foregoing.
In some embodiments of the present application, the raised carbon particles are obtained by spraying carbon powder on the surface of the negative electrode current collector and then curing the carbon particles at a high temperature, and the carbon particles can be firmly attached to the surface of the negative electrode current collector by the high temperature treatment. In some embodiments, the temperature of the high temperature curing process may be 180-500 ℃, such as 180 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, or a range between any two of the foregoing values; the time of the high temperature curing treatment may be 1 to 2 hours, for example 1 hour, 1.5 hours, 2 hours, or a range between any two of the above values.
In this application, the anode active layer is composed of a first anode active layer and a second anode active layer, and the first anode active layer is attached to at least one side surface of the anode current collector. Fig. 1 and 2 show the case where the first anode active layer is attached to the one-side surface and the two-side surface of the anode current collector, respectively.
In the present application, the first negative electrode active layer 3 includes first graphite particles 31 and first silicon particles 32. Wherein, the first graphite particles and the first silicon particles adopt graphite materials and silicon materials with conventional particle sizes. The first graphite particles have a D50 particle size of from 4.5 to 16. Mu.m, for example, 4.5. Mu.m, 5. Mu.m, 8. Mu.m, 10. Mu.m, 12. Mu.m, 15. Mu.m, 16. Mu.m, or a range between any two of the foregoing values. The first silicon particles have a D50 particle size of 4.5 to 15.5 μm, for example 4.5 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15.5 μm, or a range between any two of the above.
In this application, the second anode active layer 4 is attached to the surface of the first anode active layer 3, and the second anode active layer 4 also contains second graphite particles 41 and second silicon particles 42 therein. Unlike the first negative electrode active layer, the second negative electrode active layer adopts silicon particles of small particles in combination with graphite particles of large particles, i.e., the D50 particle size of the second graphite particles is larger than the D50 particle size of the second silicon particles. The purpose of this arrangement is: the pores exist among the large-particle graphite particles, and the pores are reserved for the small-particle silicon material to serve as an expansion space, so that the influence of the expansion of the silicon particles on the pole piece can be reduced in the high-current charge-discharge process, the stability of the pole piece structure is improved, the integrity of the negative electrode active layer is ensured, and the high-rate charging performance of the battery is improved.
In the present application, the second graphite particles have a D50 particle diameter of 11.2 to 18.9. Mu.m, for example, 11.2. Mu.m, 12. Mu.m, 14. Mu.m, 15. Mu.m, 16. Mu.m, 18. Mu.m, 18.9. Mu.m, or a range between any two of the above values. The second silicon particles have a D50 particle size of 3.2 to 16 μm, for example, 3.2 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, or a range between any two of the above values.
In some embodiments of the present application, the ratio of the D50 particle size of the second graphite particles to the D50 particle size of the second silicon particles is 1:1.08 to 4.2, for example 1:1.08, 1: 2. 1: 3. 1:4. 1:4.2, or a range between any two of the foregoing values.
In the negative plate of this application, the second negative electrode active layer sets up in the outside of first active layer, and it can play the effect of protection first negative electrode active layer, has slowed down the expansion of first negative electrode active layer in cyclic process effectively, improves the holistic structural stability of negative plate, is favorable to improving the cycle life of battery.
In the application, the first graphite particles and the second graphite particles can be made of graphite materials such as artificial graphite and modified natural graphite.
In some embodiments of the present application, the first silicon particles are silicon-carbon composite materials, such as carbon-coated silicon, or carbon-coated silicon oxide SiO x (0 < x < 0). The silicon-carbon composite material can be a micron-sized material or a nano-sized material; either as granular material or as wire-like or other shaped material.
In some embodiments of the present application, the second silicon particles are silicon-carbon composite materials, such as carbon-coated silicon, or carbon-coated silicon oxide SiO x (0 < x < 0). Wherein in some embodiments, the silicon content in the second silicon particles is 22.5-74 wt%, such as 22.5wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 74wt%, or a range between any two of the foregoing.
In the present application, the carbon-coated layer of the second silicon particles may be obtained by either vapor deposition or liquid phase coating. Wherein the carbon source of the vapor deposition process includes, but is not limited to, at least one of methane, ethane, acetylene, butyne, propane, butane, and the like. The carbon source of the liquid phase cladding process includes, but is not limited to, at least one of pitch, petroleum coke, needle coke, polybutadiene resin, epoxy resin, carboxymethyl cellulose, amino resin, phenolic resin, acrylate, polyurethane resin, silicone resin, acrylic acid, acrylamide, polyvinyl alcohol, polyimide, polyaniline, and the like. The liquid phase cladding method comprises the following specific steps: heating and other means to make the carbon source liquid and stirring at uniform speed to obtain coating liquid; and adding the silicon material into the coating liquid, stirring, cooling the obtained mixture, and then placing the mixture into a heating furnace for heat treatment, namely obtaining the carbon-coated layer on the surface of the silicon material. The heat treatment temperature is 420-900deg.C, such as 420 deg.C, 450 deg.C, 500 deg.C, 550 deg.C, 600 deg.C, 650 deg.C, 700 deg.C, 750 deg.C, 800 deg.C, 850 deg.C, 900 deg.C, or a range between any two of the above values; the heat treatment time is 2 to 15 hours, for example 2 hours, 4 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, or a range between any two of the above values.
In some embodiments of the present application, the carbon-coated layer of the second silicon particles is an amorphous carbon layer, and more preferably a modified amorphous carbon layer. The modification method comprises the following steps: and co-heating the second silicon particles coated with the amorphous carbon layer and hexafluorophosphate in a solution to enable the phosphate to be attached to the amorphous carbon layer, so as to obtain the modified amorphous carbon layer. The hexafluorophosphate includes, but is not limited to, at least one of ammonium hexafluorophosphate, lithium hexafluorophosphate, sodium hexafluorophosphate, aluminum hexafluorophosphate, magnesium hexafluorophosphate, and the like, at a concentration ranging from 0.03 to 0.9wt%, for example, 0.03wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or a range between any two of the foregoing. The co-heating temperature is 40 to 60 ℃, for example 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, or a range between any two of the above values. The co-heating time is 0.25 to 6 hours, for example 0.25 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or a range between any two of the above.
In the application, the amorphous carbon layer is modified by adopting hexafluorophosphate, so that phosphorus-oxygen-fluorine bonds are introduced to the surface of the silicon-carbon material. The phosphorus-oxygen-fluorine bond can obviously reduce interface impedance of the silicon-carbon material in the SEI film, promote lithium ion migration and charge transfer, and ensure that the silicon-carbon material has excellent rate capability under high current. Therefore, through modification treatment, the electrochemical performance of the silicon-carbon material is remarkably improved while the SEI film is stabilized.
It is understood that the first and second anode active layers in this application contain a conductive agent and a binder in addition to graphite and silicon. Wherein, in the first negative electrode active layer, the mass ratio of the first graphite particles to the first silicon particles to the conductive agent to the binder is 0.5-35:25-95:0.8-7.0:1.0-12.0. In the second negative electrode active layer, the mass ratio of the second graphite particles to the second silicon particles to the conductive agent to the binder is 0.5-35:25-95:0.8-7.0:1.0-12.0.
In the present application, the binder includes, but is not limited to, at least one of acrylonitrile, vinylidene fluoride, sodium carboxymethyl cellulose, methacrylamide, acrylic acid, acrylamide, amide, imide, acrylate, styrene butadiene rubber, vinyl alcohol, sodium alginate, chitosan, ethylene glycol, and the like, and polymers or copolymers thereof. In some preferred embodiments, the binder is a blend of sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) in varying proportions (1:2, 1:3, 2:3, 1:1, etc.).
In the present application, the conductive agent includes, but is not limited to, at least one of conductive carbon black, acetylene black, graphite, graphene, micro-nano fibrous conductive substance (carbon nanofiber), micro-nano tubular conductive substance (such as single-arm carbon nanotube, multi-arm carbon nanotube), and the like.
In some embodiments of the present application, the content of the binder in the second anode active layer is higher than the content of the binder in the first anode active layer. The purpose of this arrangement is: under high temperature conditions, the binder tends to diffuse in the direction of low concentration. Therefore, in the process of subsequent high-temperature treatment of the pole piece (such as a pole piece drying process), high-temperature heating promotes the high-content binder in the second negative electrode active layer to deviate to the first negative electrode active layer on the lower layer, thereby reducing the influence of interlayer interface separation of the first negative electrode active layer and the second negative electrode active layer and promoting better interlayer fusion; and the bonding force of the interface between the two layers is higher, the toughness is stronger, and meanwhile, the structural stress caused by the volume expansion of the first silicon particles and the second silicon particles in the two layers can be relieved.
In some embodiments herein, the thickness of the anode active layer is 0.032 to 0.180mm, e.g., 0.032mm, 0.05mm, 0.08mm, 0.10mm, 0.12mm, 0.15mm, 0.18mm, etc. In some preferred embodiments, the thickness of the anode active layer is 0.055 to 0.130mm.
In some embodiments in the present application, at h 1 Represents the thickness of the first anode active layer, expressed as h 2 Indicating the thickness of the first anode active layer, h 1 And h 2 The following relationship is satisfied: h is more than or equal to 0.015mm 2 ≤h 1 。
In some embodiments herein, the negative electrode active layer has a compacted density of 1.30 to 1.88g/cm 3 For example 1.30g/cm 3 、1.4g/cm 3 、1.50g/cm 3 、1.60g/cm 3 、1.70g/cm 3 、1.80g/cm 3 、1.88g/cm 3 Etc. In some preferred embodiments, the negative electrode active layer has a compacted density of 1.45 to 1.60g/cm 3 。
The negative electrode plate can be prepared by a conventional electrode plate preparation process. In some embodiments, the negative electrode sheet is prepared by the following method: firstly, mixing first graphite particles, first silicon particles, a conductive agent and a binder, and adding water to prepare slurry to obtain first negative electrode slurry; then, a second anode slurry was prepared in the same manner. And then, sequentially extruding and coating the first negative electrode slurry and the second negative electrode slurry on one side or two sides of a negative electrode current collector, and obtaining the negative electrode plate after rolling, slicing, slitting and drying. In some embodiments, the pressure of the roll may be 0.05-0.55 MPa, the drying temperature may be 80-180deg.C, and the drying time may be 4-20 h.
The present invention further provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the separator is provided to isolate the positive electrode sheet from the negative electrode sheet. In specific implementation, the positive plate, the negative plate, the diaphragm, the electrolyte and the like are assembled into the secondary battery. The secondary battery may be a lithium ion battery or other battery such as a sodium ion battery.
Taking a lithium ion battery as an example, the positive active material in the positive electrode sheet may be at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickelate aluminate, lithium manganese phosphate, lithium iron manganese phosphate and lithium iron phosphate.
The separator is not particularly limited in kind, and may be any separator material used in conventional batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, nonwoven fabric, multilayer composite films thereof, and modified separators obtained by subjecting the above separator to ceramic modification, PVDF modification, or the like, but is not limited thereto.
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
The experimental methods used in the following examples are conventional methods unless otherwise specified, and materials, reagents, etc. used, unless otherwise specified, are commercially available.
Example 1
1. Preparation of negative electrode sheet
(1) Spraying carbon powder with the particle size of 0.02-15 mu m on the surface of the nickel-plated copper foil, and curing for 1h at 180 ℃ to obtain the negative electrode current collector with the surface provided with the raised carbon particles.
(2) Mixing first graphite particles, first silicon particles, a conductive agent and a binder according to the mass ratio of 6.7:89.8:1.2:2.3, and adding deionized water for pulping to obtain first negative electrode slurry; and mixing the second graphite particles, the second silicon particles, the conductive agent and the binder according to the mass ratio of 6.7:89.8:1.0:2.5, and adding deionized water for pulping to obtain second negative electrode slurry. Wherein:
the first graphite particles are modified natural graphite with the D50 particle size of 10.6 mu m, and the second graphite particles are modified natural graphite with the D50 particle size of 13.4 mu m;
the first silicon particles are carbon-coated micron silicon materials with the D50 particle diameter of 5.3 mu m;
the second silicon particles are silicon-carbon materials with a D50 particle diameter of 4.9 μm and a carbon-coated layer, and contain 38.4wt% of silicon; the carbon-coated layer is a modified amorphous carbon layer, wherein the preparation method of the modified amorphous carbon layer comprises the following steps: and (3) depositing an amorphous carbon layer on the surface of the silicon particles by acetylene vapor deposition at 700 ℃, and then co-heating with 0.18wt% of ammonium hexafluorophosphate solution for 1h at 55 ℃ to obtain the modified amorphous carbon layer.
The adhesive is prepared by mixing sodium carboxymethyl cellulose and styrene-butadiene rubber according to a mass ratio of 1:1;
the conductive agent is a carbon nanotube.
(3) Sequentially extruding and coating a first negative electrode slurry and a second negative electrode slurry on one side of the negative electrode current collector to form a first negative electrode active layer and a second negative electrode active layer; and (3) rolling, slicing and slitting, and drying at 155 ℃ for 12 hours to obtain the negative plate. Wherein the thickness of the first anode active layer is 0.05mm, and the thickness of the second anode active layer is 0.022mm.
2. Preparation of lithium ion secondary battery
And (3) sequentially winding the positive plate (containing 92wt% of nickel cobalt lithium manganate), the polypropylene isolating film and the negative plate to obtain a bare cell, ultrasonically welding the tab, putting the bare cell into a battery shell, drying to remove water, injecting electrolyte, and packaging the battery shell to obtain the lithium ion secondary battery. The preparation method of the electrolyte comprises the following steps: mixing Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) according to a volume ratio of 1:1:1, and then fully drying lithium salt LiPF 6 Dissolving in the mixed organic solvent to prepare the electrolyte with the concentration of 1 mol/L.
Example 2
Example 2 differs from example 1 in that:
(1) The ratio of the first graphite particles, the first silicon particles, the conductive agent, and the binder is 6.7:89.8:1.6:2.1, and the ratio of the second graphite particles, the second silicon particles, the conductive agent, and the binder is 6.7:89.6:1.2:2.5;
(2) The modified amorphous carbon layer is obtained by co-heating silicon particles deposited with the amorphous carbon layer and 0.32wt% ammonium hexafluorophosphate solution at 55 ℃;
(3) The drying time of the pole piece is 14h.
Example 3
Example 3 differs from example 1 in that:
(1) The ratio of the first graphite particles, the first silicon particles, the conductive agent, and the binder is 6.7:92.9:1.0:2.0, and the ratio of the second graphite particles, the second silicon particles, the conductive agent, and the binder is 6.7:92.9:1.0:2.5;
(2) The modified amorphous carbon layer is obtained by co-heating silicon particles on which the amorphous carbon layer is deposited with 0.45wt% ammonium hexafluorophosphate solution at 55 ℃.
Example 4
Example 4 differs from example 1 in that:
(1) The ratio of the first graphite particles, the first silicon particles, the conductive agent and the binder is 18.9:75.8:1.2:4.0, and the ratio of the second graphite particles, the second silicon particles, the conductive agent and the binder is 18.9:75.8:1.2:4.5;
(2) The first silicon particles are carbon-coated micron silicon oxide materials with the D50 particle diameter of 8.3 mu m;
(3) The second silicon particles are silicon-carbon materials with a carbon-coated layer having a D50 particle diameter of 5.7 μm, and contain 46.8wt% silicon; the carbon-coated layer is obtained by vapor deposition of a carbon source at 650 ℃; the modified amorphous carbon layer is obtained by co-heating silicon particles deposited with the amorphous carbon layer and ammonium hexafluorophosphate solution at 50 ℃;
(4) The second graphite particles are modified natural graphite with the D50 particle size of 13.9 mu m;
(5) The thickness of the first negative electrode active layer is 0.075mm, and the thickness of the second negative electrode active layer is 0.028mm;
(6) The drying time of the pole piece is 13h;
(7) The positive plate contains 95.5wt% of nickel cobalt lithium manganate.
Example 5
Example 5 differs from example 4 in that:
(1) The ratio of the first graphite particles, the first silicon particles, the conductive agent and the binder is 18.9:75.8:1.2:3.5, and the ratio of the second graphite particles, the second silicon particles, the conductive agent and the binder is 18.9:75.8:1.2:4.0;
(2) The second silicon particles contained 42.2wt% silicon; the modified amorphous carbon layer is obtained by co-heating silicon particles deposited with the amorphous carbon layer and 0.32 weight percent of ammonium hexafluorophosphate solution;
(3) The drying time of the pole piece is 16h.
Example 6
Example 6 differs from example 4 in that:
(1) The ratio of the first graphite particles, the first silicon particles, the conductive agent and the binder is 18.9:75.8:1.2:3.2, and the ratio of the second graphite particles, the second silicon particles, the conductive agent and the binder is 18.9:75.8:1.2:3.5;
(2) The second silicon particles contained 43.6wt% silicon; the modified amorphous carbon layer is obtained by co-heating silicon particles deposited with the amorphous carbon layer and 0.45 weight percent ammonium hexafluorophosphate solution;
(3) The drying time of the pole piece is 12 hours.
Comparative example 1
Comparative example 1 differs from example 2 in that: there is no second anode active layer.
Comparative example 2
Comparative example 2 differs from example 2 in that: in the second negative electrode active layer, the first silicon material is a silicon-carbon material containing a carbon-containing layer with a D50 particle size of 10.2 μm, and the second graphite is modified natural graphite with a D50 particle size of 10.6 μm.
Comparative example 3
Comparative example 3 differs from example 2 in that: ammonium hexafluorophosphate and the silicon carbon material are not introduced to be co-heated at 55 ℃ and a modified amorphous carbon layer is not formed.
Comparative example 4
Comparative example 4 differs from example 2 in that: the surface of the negative electrode current collector is free of raised carbon particles.
1. Pole piece stripping force and expansion condition of negative pole piece under 100% SOC
(1) The peel force of the pole pieces of the examples and comparative examples was measured by a peel force tester, respectively.
(2) Firstly, measuring the thickness of the rolled silicon-containing negative electrode sheet by using a ten-thousandth screw ruler; then disassembling the batteries of the examples and the comparative examples to obtain a silicon-containing negative electrode plate at 100% SOC, and measuring the thickness of the silicon-containing negative electrode plate of the battery at 100% SOC by using a ten-thousandth screw scale;
negative plate expansion ratio= (battery plate thickness at 100% soc-silicon negative plate thickness after rolling)/negative plate thickness after rolling.
2. Electrochemical performance test
(1) 1.5C CC Rate (1.5C charging Rate) test: at normal temperature of 25 ℃, the initial voltage is 2.8V, the cut-off voltage is 4.2V, the batteries of each example and comparative example are firstly charged to 4.2V at a low Rate of 0.5C, and are charged at a constant voltage of 4.2V until the current is reduced to 0.05C, the charge amount 1,0.5C is recorded at the moment, after the charge amount is discharged to 2.8V, the battery is charged to 4.2V at a high Rate of 1.5C, the charge amount at the moment is recorded as 2, and CC rate=charge amount 2/charge amount 1 x 100% is calculated.
(2) 2.0C CC Rate (2.0C charge Rate) test: at normal temperature of 25 ℃, the initial voltage is 2.8V, the cut-off voltage is 4.2V, the batteries of each example and comparative example are firstly charged to 4.2V at a low Rate of 0.5C, and are charged at a constant voltage of 4.2V until the current is reduced to 0.05C, the charge amount 3,0.5C is recorded at the moment, after the charge amount is discharged to 2.8V, the battery is charged to 4.2V at a high Rate of 2.0C, the charge amount at the moment is recorded to 4, and the CC rate=charge amount 4/charge amount 3×100% is calculated.
(3) 1.5C/0.5C high-rate charge low-rate discharge cycle test: the batteries of each example and comparative example were charged at 1.5C to 4.2V, charged at a constant voltage of 4.2V until the current was reduced to 0.05C, discharged at 0.5C to 2.8V, charged at 1.5C to 4.2V, charged at a constant voltage of 4.2V until the current was reduced to 0.05C at normal temperature of 25℃and charged and discharged in cycles in this manner, and the capacity retention rate of 500 cycles and the capacity retention rate of 800 cycles were recorded.
TABLE 1
Peel force/N Expansion ratio
Example 1 0.23 0.363
Example 2 0.26 0.356
Example 3 0.28 0.340
Example 4 0.37 0.356
Example 5 0.25 0.342
Example 6 0.30 0.351
Comparative example 1 0.23 0.405
Comparative example 2 0.28 0.367
Comparative example 3 0.33 0.383
Comparative example 4 0.16 0.346
Referring to table 1, in comparative example 4, since the negative electrode current collector has no protruding carbon particles on the surface, the stripping force of the electrode sheet is low; in other examples and comparative examples, the convex carbon particles are arranged on the negative electrode current collector, and play a role in anchoring, so that the combination between the negative electrode current collector and the negative electrode active layer is enhanced, and the peeling strength of the pole piece is improved.
In addition, in the negative electrode sheet of comparative example 1, since the second negative electrode active layer was not provided on the first negative electrode active layer, the expansion rate of the sheet was high. In other embodiments and comparative examples, the second anode active layer is disposed on the surface of the first anode active layer, and the second anode active layer can protect the first anode active layer, so that expansion of the anode material in the circulation process is effectively relieved, and the expansion rate of the pole piece is reduced.
TABLE 2
Figure BDA0004129430250000121
Referring to fig. 2, the charge-discharge efficiency is not greatly different from that of the comparative example except comparative example 3 under the charge-discharge condition of 1.5C. Comparative example 3 has low charge and discharge efficiency because the modified amorphous carbon layer is not formed on the surface of the silicon particles. The phosphorus-oxygen-fluorine bond is introduced into the modified amorphous carbon layer, so that the interface impedance of the silicon-carbon material in the SEI film can be obviously reduced, the lithium ion migration and charge transfer are promoted, and the excellent rate capability of the silicon-carbon material under high current is ensured, so that the charge-discharge efficiency of the battery can be improved.
Comparative examples 1 to 4 showed a large difference in charge-discharge efficiency from examples 1 to 6 under the charge-discharge condition of 2.0C. This demonstrates that the batteries of examples 1-6 exhibit better high-rate charge-discharge performance.
After 500 cycles under 1.5C/0.5C high rate charge conditions, the capacity retention rates of the other comparative examples were all lower than 85% except that comparative example 1 maintained 87.2% capacity retention; in contrast, the capacity retention rates of examples 1 to 6 were each 87% or more. After 800 cycles, the capacity retention of each comparative example was lower than that of examples 1-6. This shows that the batteries of examples 1-6 have better cycling stability under high rate charge and discharge conditions.
The above-described embodiments are merely preferred embodiments for fully explaining the present invention, and the scope of the present invention is not limited thereto. Equivalent substitutions and modifications will occur to those skilled in the art based on the present invention, and are intended to be within the scope of the present invention. The protection scope of the invention is subject to the claims.

Claims (10)

1. A negative electrode sheet, comprising:
the surface of the negative electrode current collector is distributed with raised carbon particles;
a first negative electrode active layer attached to at least one side surface of the negative electrode current collector; the first negative electrode active layer contains first graphite particles and first silicon particles;
a second anode active layer attached to a surface of the first anode active layer; the second negative electrode active layer contains second graphite particles and second silicon particles;
wherein the D50 particle size of the first graphite particles is 4.5-16 mu m, and the D50 particle size of the first silicon particles is 4.5-15.5 mu m;
the second graphite particles have a D50 particle size of 11.2 to 18.9 μm, the second silicon particles have a D50 particle size of 3.2 to 16 μm, and the second graphite particles have a D50 particle size greater than the second silicon particles.
2. The negative electrode sheet according to claim 1, wherein the ratio of the D50 particle diameter of the second graphite particles to the D50 particle diameter of the second silicon particles is 1:1.08-4.2.
3. The negative electrode sheet according to claim 1, wherein the negative electrode current collector is one selected from the group consisting of copper foil, carbon-plated copper foil, nickel-plated copper foil, zinc-plated copper foil, iron-plated copper foil, and titanium-plated copper foil;
and/or the carbon particles have a particle diameter of 0.02 to 15 μm;
and/or spraying carbon powder on the negative electrode current collector, and curing for 1-2 hours at 180-500 ℃.
4. The anode sheet according to claim 1, wherein each of the first anode active layer and the second anode active layer further comprises a conductive agent and a binder;
in the first negative electrode active layer, the mass ratio of the first graphite particles to the first silicon particles to the conductive agent to the binder is 0.5-35:25-95:0.8-7.0:1.0-12.0;
in the second negative electrode active layer, the mass ratio of the second graphite particles to the second silicon particles to the conductive agent to the binder is 0.5-35:25-95:0.8-7.0:1.0-12.0.
5. The anode sheet according to claim 4, wherein the content of the binder in the second anode active layer is higher than the content of the binder in the first anode active layer.
6. The anode sheet according to claim 1, wherein the total thickness of the first anode active layer and the second anode active layer is 0.032 to 0.180mm;
and/or, the thickness of the second anode active layer is less than or equal to 0.015mm and less than or equal to the thickness of the first anode active layer;
and/or the compacted density of the first negative electrode active layer and the second negative electrode active layer is 1.30-1.88 g/cm 3 。
7. The negative electrode sheet according to claim 1, wherein the second silicon particles are silicon-carbon composite particles coated with a carbon layer on the surface; the silicon content of the silicon-carbon composite particles is 22.5-74 wt%.
8. The negative electrode sheet according to claim 7, wherein the carbon layer is a modified amorphous carbon layer;
the modified amorphous carbon layer is obtained by heat treatment of the silicon carbon composite particles and 0.03-0.9 wt% of hexafluorophosphate at 40-60 ℃.
9. A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 8.
10. A powered device comprising the secondary battery of claim 9.
CN202310255512.1A 2023-03-16 2023-03-16 Negative plate, secondary battery and electric equipment Pending CN116364859A (en)

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