CN111146433B - Negative electrode, electrochemical device and electronic device including the same - Google Patents

Negative electrode, electrochemical device and electronic device including the same Download PDF

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CN111146433B
CN111146433B CN201911373724.XA CN201911373724A CN111146433B CN 111146433 B CN111146433 B CN 111146433B CN 201911373724 A CN201911373724 A CN 201911373724A CN 111146433 B CN111146433 B CN 111146433B
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silicon
negative electrode
based particles
polymer
polymer layer
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CN111146433A (en
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陈志焕
姜道义
崔航
谢远森
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Ningde Amperex Technology 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
    • H01M4/36—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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • 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
    • H01M4/48—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
    • 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
    • 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
    • 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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Abstract

The present application relates to a negative electrode, and an electrochemical device and an electronic device including the same. The negative electrode comprises a current collector and a coating layer positioned on the current collector, wherein the coating layer comprises silicon-based particles and graphite particles, the silicon-based particles comprise a silicon-containing matrix and a polymer layer, the polymer layer comprises a polymer and carbon nano tubes, the polymer layer is positioned on the surface of at least one part of the silicon-containing matrix, and the minimum value of the sheet resistance at different positions on the surface of the coating layer is R 1 Maximum value is R 2 ，R 1 /R 2 And the weight of the silicon-based particles is N, wherein M is more than or equal to 0.5, and N is 2-80 wt%. The lithium ion battery prepared from the negative electrode has improved cycle performance, rate performance and deformation resistance, and reduced direct current resistance.

Description

Negative electrode, electrochemical device and electronic device including the same
Technical Field
The present disclosure relates to the field of energy storage, and in particular, to a negative electrode, an electrochemical device and an electronic device including the same, and a lithium ion battery.
Background
With the popularization of consumer electronics products such as notebook computers, mobile phones, tablet computers, mobile power supplies, unmanned aerial vehicles and the like, the requirements on electrochemical devices therein are becoming more and more stringent. For example, not only is the battery required to be lightweight, but the battery is also required to have a high capacity and a long service life. Lithium ion batteries have been in the mainstream position in the market by virtue of their outstanding advantages of high energy density, high safety, no memory effect, long working life, and the like.
Disclosure of Invention
Embodiments of the present application provide a negative electrode in an attempt to solve at least one problem existing in the related art to at least some extent. The embodiment of the application also provides an electrochemical device using the anode and an electronic device.
In one embodiment, the present application provides a negative electrode comprising a current collector and a coating on the current collector, the coating comprising silicon-based particles and graphite particles, the silicon-based particles comprising a silicon-containing matrix and a polymer layer comprising a polymer and carbon nanotubes, the polymer layer being on a surface of at least a portion of the silicon-containing matrix, wherein the minimum value of sheet resistance at different locations on the surface of the coating is R 1 Maximum value is R 2 ，R 1 /R 2 And the weight of the silicon-based particles is N, wherein M is greater than or equal to about 0.5 and N is from about 2wt% to about 80wt%.
In another embodiment, the present application provides an electrochemical device comprising a negative electrode according to an embodiment of the present application.
In another embodiment, the present application provides an electronic device comprising an electrochemical device according to an embodiment of the present application.
The lithium ion battery prepared from the negative electrode has improved cycle performance, rate performance and deformation resistance, and reduced direct current resistance.
Additional aspects and advantages of embodiments of the application 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 embodiments of the application.
Drawings
The drawings that are necessary to describe embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application. It is apparent that the figures in the following description are only some of the embodiments in this application. It will be apparent to those skilled in the art that other embodiments of the drawings may be made in accordance with the structures illustrated in these drawings without the need for inventive faculty.
Fig. 1 shows a schematic structural diagram of a silicon-based anode active material in one embodiment of the present application.
Fig. 2 shows a Scanning Electron Microscope (SEM) picture of the surface of SiO particles.
Fig. 3 shows SEM pictures of the surface of the silicon-based anode active material in example 2 of the present application.
Fig. 4 shows SEM pictures of a screenshot of the negative electrode in example 2 of the present application.
Fig. 5 shows SEM pictures of a screenshot of the negative electrode in example 8 of the present application.
Fig. 6 shows an SEM picture of a screenshot of the negative electrode in example 9 of the present application.
Fig. 7 shows SEM pictures of a screenshot of the negative electrode in comparative example 1 of the present application.
Detailed Description
Embodiments of the present application will be described in detail below. The examples of the present application should not be construed as limiting the present application.
As used in this application, the term "about" is used to describe and illustrate small variations. When used in connection with an event or circumstance, the terms can refer to instances where the event or circumstance occurs precisely and instances where it occurs to the close approximation. For example, when used in connection with a numerical value, the term can refer to a range of variation of less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.
In the present application, dv50 is the particle size in μm corresponding to the cumulative volume percentage of the silicon-based anode active material reaching 50%.
In the present application, dn10 is the particle size corresponding to the cumulative percentage of the silicon-based anode active material reaching 10%, in μm.
Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.
In the detailed description and claims, a list of items connected by the terms "one of," "one of," or other similar terms may mean any of the listed items. For example, if items a and B are listed, the phrase "one of a and B" means either only a or only B. In another example, if items A, B and C are listed, one of the phrases "A, B and C" means only a; only B; or only C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.
In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.
1. Negative electrode
In some embodiments, the present application provides a negative electrode comprising a current collector and a coating on the current collector, the coating comprising silicon-based particles and graphite particles, the silicon-based particles comprising a silicon-containing matrix and a polymer layer comprising a polymer and carbon nanotubes, the polymer layer being on a surface of at least a portion of the silicon-containing matrix, wherein the minimum value of sheet resistance at different locations on the surface of the coating is R 1 Maximum value is R 2 ，R 1 /R 2 Has a value of M, andthe weight of the silicon-based particles is N, wherein M is greater than or equal to about 0.5. In other embodiments, the polymer layer is located on the entire surface of the silicon-containing substrate.
In some embodiments, the minimum value of R, R 1 About 5-500mΩ. In some embodiments, the minimum value of R, R 1 Is about 5mΩ, about 10mΩ, about 20mΩ, about 30mΩ, about 40mΩ, about 50mΩ, about 100mΩ, about 150mΩ, about 200mΩ, about 250mΩ, about 300mΩ, about 400mΩ, about 450mΩ, about 500mΩ, or a range of any two of these values.
In some embodiments, the maximum value of R, R 2 About 5-800mΩ. In some embodiments, the maximum value of R, R 2 Is about 5mΩ, about 10mΩ, about 20mΩ, about 30mΩ, about 40mΩ, about 50mΩ, about 100mΩ, about 150mΩ, about 200mΩ, about 250mΩ, about 300mΩ, about 400mΩ, about 500mΩ, about 600mΩ, about 700mΩ, about 800mΩ, or a range of any two of these values.
In some embodiments, the ratio M of the minimum value to the maximum value of R is greater than or equal to about 0.6. In some embodiments, the ratio M of the minimum value to the maximum value of R is greater than or equal to about 0.7. In some embodiments, the ratio M of the minimum value to the maximum value of R is about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1.0, or a range of any two of these values.
In some embodiments, M/N is greater than or equal to about 4. In some embodiments, M/N is greater than or equal to about 5. In some embodiments, M/N is greater than or equal to about 6. In some embodiments, M/N is about 4, about 5, about 6, about 7, about 8, about 9, about 10, or a range of any two of these values.
In some embodiments, the weight of the silicon-based particles is about 2wt% to about 80wt% of the total weight of the silicon-based particles and the graphite particles. In some embodiments, the proportion N of the weight of the silicon-based particles to the total weight of the silicon-based particles and the graphite particles is from about 10wt% to 70wt%. In some embodiments, the proportion N of the weight of the silicon-based particles to the total weight of the silicon-based particles and the graphite particles is about 2wt%, about 3wt%, about 4wt%, about 5wt%, about 10wt%, about 15wt%, about 20wt%, about 25wt%, about 30wt%, about 40wt%, about 50wt%, about 60wt%, about 70wt%, about 80wt%, or a range of any two of these values.
In some embodiments, the silicon-based particles have a maximum intensity value I in the range of about 28.0 DEG to about 29.0 DEG for 2 theta in the X-ray diffraction pattern 2 The highest intensity value is I within the range of about 20.5 DEG to 21.5 DEG 1 Wherein about 0 < I 2 /I 1 And less than or equal to about 1. In some embodiments, I 2 /I 1 Is about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1, or a range of any two of these values.
In some embodiments, the silicon-based particles have an average particle size of about 500nm to 30 μm. In some embodiments, the silicon-based particles have an average particle size of about 1 μm to 25 μm. In some embodiments, the silicon-based particles have an average particle size of about 0.5 μm, about 1 μm, about 5 μm, about 10 μm, about 15 μm, about 20 μm, about 25 μm, about 30 μm, or a range of any two of these values.
In some embodiments, the silicon-based particles have a particle size distribution that satisfies: dn10/Dv50 is about 0.3.ltoreq.Dn 10.ltoreq.0.6. In some embodiments, the silicon-based particles have a particle size distribution that satisfies: dn10/Dv50 is about 0.4.ltoreq.Dn 10.ltoreq.0.5. In some embodiments, the silicon-based particles have a particle size distribution of about 0.3, about 0.35, about 0.4, about 0.45, about 0.5, about 0.55, about 0.6, or a range of any two of these values.
In some embodiments, the polymer comprises carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, polybutene-styrene rubber, epoxy resin, polyester resin, polyurethane resin, polyfluorene, or any combination thereof.
In some embodiments, the silicon-containing substrate comprises SiO x And x is more than or equal to 0.6 and less than or equal to 1.5.
In some embodiments, the silicon-containing substrate comprises Si, siO, siO 2 SiC, or any combination thereof.
In some embodiments, the Si has a particle size of less than about 100nm. In some embodiments, the Si has a particle size of less than about 50nm. In some embodiments, the Si has a particle size of less than about 20nm. In some embodiments, the Si has a particle size of less than about 5nm. In some embodiments, the Si has a particle size of less than about 2nm. In some embodiments, the Si has a particle size of less than about 0.5nm. In some embodiments, the Si has a particle size of about 10nm, about 20nm, about 30nm, about 40nm, about 50nm, about 60nm, about 70nm, about 80nm, about 90nm, or a range of any two of these values.
In some embodiments, the polymer layer is present in an amount of about 0.05 to 15wt% based on the total weight of the silicon-based particles. In some embodiments, the polymer layer is present in an amount of about 1 to 10wt% based on the total weight of the silicon-based particles. In some embodiments, the polymer layer is present in an amount of about 2wt%, about 3wt%, about 4wt%, about 5wt%, about 6wt%, about 7wt%, about 8wt%, about 9wt%, about 10wt%, about 11wt%, about 12wt%, about 13wt%, about 14wt%, or a range of any two of these values, based on the total weight of the silicon-based particles.
In some embodiments, the polymer layer has a thickness of about 5nm to 200nm. In some embodiments, the polymer layer has a thickness of about 10nm to 150nm. In some embodiments, the polymer layer has a thickness of about 50nm to 100nm. In some embodiments, the thickness of the polymer layer is about 5nm, about 10nm, about 20nm, about 30nm, about 40nm, about 50nm, about 60nm, about 70nm, about 80nm, about 90nm, about 100nm, about 110nm, about 120nm, about 130nm, about 140nm, about 150nm, about 160nm, about 170nm, about 180nm, about 190nm, about 200nm, or a range of any two of these values.
In some embodiments, the carbon nanotubes comprise single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination thereof.
In some embodiments, the carbon nanotubes are present in an amount of about 0.01 to 10wt%, based on the total weight of the silicon-based particles. In some embodiments, the carbon nanotubes are present in an amount of about 1 to 8wt%, based on the total weight of the silicon-based particles. In some embodiments, the carbon nanotubes are present in an amount of about 0.01wt%, about 0.02wt%, about 0.05wt%, about 0.1wt%, about 0.5wt%, about 1wt%, about 1.5wt%, about 2wt%, about 3wt%, about 4wt%, about 5wt%, about 6wt%, about 7wt%, about 8wt%, about 9wt%, about 10wt%, or a range of any two of these values, based on the total weight of the silicon-based particles.
In some embodiments, the weight ratio of polymer in the polymer layer to the carbon nanotubes is about 0.5:1 to about 10:1. In some embodiments, the weight ratio of polymer to carbon material in the polymer layer is about 1:1, about 2:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, or a range of any two of these values.
In some embodiments, the carbon nanotubes have a diameter of about 1-30nm. In some embodiments, the carbon nanotubes have a diameter of about 5-20nm. In some embodiments, the carbon nanotubes have a diameter of about 10nm, about 15nm, about 20nm, about 25nm, about 30nm, or a range of any two of these values.
In some embodiments, the carbon nanotubes have an aspect ratio of about 50-30000. In some embodiments, the carbon nanotubes have an aspect ratio of about 100-20000. In some embodiments, the carbon nanotubes have an aspect ratio of about 500, about 2000, about 5000, about 10000, about 15000, about 2000, about 25000, about 30000, or a range of any two of these values.
In some embodiments, the silicon-based particles have a specific surface area of about 1-50m 2 /g, e.g. about 2.5-15m 2 And/g. In some embodiments, the silicon-based particles have a specific surface area of about 5-10m 2 And/g. In some embodiments, the silicon-based particles have a specific surface area of about 3m 2 /g, about 4m 2 /g, about 6m 2 /g, about 8m 2 /g, about 10m 2 /g, about 12m 2 /g, about 14m 2 /g or any two of these values.
In some embodiments, embodiments of the present application provide a method of preparing any one of the above silicon-based particles, the method comprising:
(1) Adding the carbon nano tube into a solution containing a polymer, and dispersing for about 1-24 hours to obtain slurry;
(2) Adding the silicon-containing substrate into the slurry, and dispersing for about 2-10 hours to obtain mixed slurry;
(3) Removing the solvent in the mixed slurry; and
(4) Crushing and sieving.
In some embodiments, the silicon-containing matrix, the carbon nanotubes, and the polymer are each defined as described above.
In some embodiments, the weight ratio of the polymer to the carbon nanotubes is about 1:1 to about 10:1. In some embodiments, the weight ratio of polymer to carbon material in the polymer layer is about 1:1, about 2:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, or a range of any two of these values.
In some embodiments, the weight ratio of the silicon-containing matrix to the polymer is about 200:1 to about 10:1. In some embodiments, the weight ratio of silicon-containing matrix to polymer is about 150:1 to 20:1. In some embodiments, the weight ratio of silicon-containing substrate to polymer is about 200:1, about 150:1, about 100:1, about 50:1, about 10:1, or a range of any two of these values.
In some embodiments, the solvent comprises water, ethanol, methanol, N-hexane, N-dimethylformamide, pyrrolidone, acetone, toluene, isopropanol, or any combination thereof.
In some embodiments, the dispersion time in step (1) is about 1h, about 5h, about 10h, about 15h, about 20h, about 24h, or a range of any two of these values.
In some embodiments, the dispersion time in step (2) is about 2 hours, about 2.5 hours, about 3 hours, about 3.5 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, or a range of any two of these values.
In some embodiments, the method of removing the solvent in step (3) comprises rotary evaporation, spray drying, filtration, freeze drying, or any combination thereof.
In some embodiments, the screening in step (4) is a 400 mesh screening.
In some embodiments, the silicon-containing substrate may be commercially available silicon oxide SiO x Can also be prepared by the method of the application to satisfy about 0 < I 2 /I 1 Silicon oxide SiO of less than or equal to about 1 x Wherein the preparation method comprises the following steps:
(1) Mixing silicon dioxide and metal silicon powder in a molar ratio of about 1:5-5:1 to obtain a mixed material;
(2) At about 10 -4 -10 -1 Heating the mixed material at a temperature in the range of about 1100-1500 ℃ for about 0.5-24 hours under a pressure in the range of kPa to obtain a gas;
(3) Condensing the obtained gas to obtain a solid;
(4) Crushing and sieving the solid to obtain the silicon-based particles; and
(5) Heat treating the solid at a temperature in the range of about 400-1200 ℃ for about 1-24 hours, and cooling the heat treated solid to obtain the silicon-based particles.
In some embodiments, the molar ratio of silica to metallic silicon powder is about 1:4 to 4:1. In some embodiments, the molar ratio of silica to metallic silicon powder is about 1:3 to 3:1. In some embodiments, the molar ratio of silica to metallic silicon powder is about 1:2 to 2:1. In some embodiments, the molar ratio of silica to metallic silicon powder is about 1:1.
In some embodiments, the pressure range is about 10 -4 -10 -1 And kPa. In some embodiments, the pressure is in a range consisting of about 1Pa, about 10Pa, about 20Pa, about 30Pa, about 40Pa, about 50Pa, about 60Pa, about 70Pa, about 80Pa, about 90Pa, about 100Pa, or any two of these values.
In some embodiments, the heating temperature is about 1100-1450 ℃. In some embodiments, the heating temperature is about 1200 ℃, about 1300 ℃, about 1400 ℃, about 1500 ℃, about 1200 ℃, or a range of any two of these values.
In some embodiments, the heating time is about 1-20 hours. In some embodiments, the heating time is about 5-15 hours. In some embodiments, the heating time is about 2 hours, about 4 hours, about 6 hours, about 8 hours, about 10 hours, about 12 hours, about 14 hours, about 16 hours, about 18 hours, or a range of any two of these values.
In some embodiments, the mixing is performed by a ball mill, a V-blender, a three-dimensional blender, an air-flow blender, or a horizontal mixer.
In some embodiments, the heating is under an inert gas blanket. In some embodiments, the inert gas comprises nitrogen, argon, helium, or a combination thereof.
In some embodiments, the temperature of the heat treatment is about 400-1200 ℃. In some embodiments, the temperature of the heat treatment is about 400, about 600 ℃, about 800 ℃, about 1000 ℃, about 1200 ℃, or a range of any two of these values.
In some embodiments, the heat treatment is for a time period of about 1 to 24 hours. In some embodiments, the heat treatment is for a period of about 2-12 hours. In some embodiments, the heat treatment is for a time of about 2 hours, about 5 hours, about 10 hours, about 15 hours, about 20 hours, about 24 hours, or a range of any two of these values.
In some embodiments, the present application provides a method of preparing a negative electrode, the method comprising:
(1) Mixing the silicon-based particles in any of the above embodiments with graphite, and dispersing for 0.1-2 hours at a rotation speed of 10-100r/min to obtain a mixed anode active material;
(2) Adding a binder, a solvent and a conductive agent into the mixed anode active material obtained in the step (1), stirring for 0.5-3h at the rotating speed of 10-100r/min, and dispersing for 0.5-3h at the rotating speed of 300-2500r/min to obtain anode slurry; and
(3) And coating the negative electrode slurry on a current collector, drying, and cold pressing to obtain the negative electrode.
In some embodiments, the solvent comprises: deionized water, N-methylpyrrolidone, or any combination thereof.
In some embodiments, the binder comprises: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethyleneoxy-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, or any combination thereof.
In some embodiments, the conductive agent comprises: natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver, polyphenylene derivatives, or any combination thereof.
In some embodiments, the current collector comprises: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.
In some embodiments, the weight ratio of silicon-based particles to graphite particles is about 10:1 to about 1:20. In some embodiments, the weight ratio of the silicon-based particles to graphite particles is about 10:1, about 8:1, about 5:1, about 3:1, about 1:1, about 1:3, about 1:5, about 1:8, about 1:10, about 1:12, about 1:15, about 1:18, about 1:20, or a range of any two of these values.
In some embodiments, the weight ratio of the binder to the silicon-based particles is about 1:10 to 2:1. In some embodiments, the weight ratio of the binder to the silicon-based particles is about 1:10, about 1:9, about 1:8, about 1:7, about 1:6, about 1:5, about 1:4, about 1:3, about 1:2, about 1:1, about 2:1, or a range of any two of these values.
In some embodiments, the weight ratio of the conductive agent to the silicon-based particles is about 1:100 to about 1:10. In some embodiments, the weight ratio of the binder to the silicon-based particles is in the range of about 1:100, about 1:90, about 1:80, about 1:70, about 1:60, about 1:50, about 1:40, about 1:30, about 1:20, about 1:10, or any two of these values.
The silicon-based anode material has gram capacity of up to 1500-4200mAh/g and is considered as the anode material of the next generation lithium ion battery with the most application prospect. But the low conductivity of silicon and its volume expansion of about 300% during charge and discharge and unstable Solid Electrolyte Interface (SEI) film have somewhat hindered its further application. At present, the cycle stability and the rate capability of the silicon-based material can be improved through the introduction of Carbon Nanotubes (CNTs).
However, the present inventors found that CNTs are difficult to disperse, and they are easily entangled with a plurality of silicon particles during the mixing and dispersion process with silicon, causing agglomeration of the silicon particles, and eventually causing non-uniform dispersion of the silicon particles in graphite. The electrolyte consumption in the silicon particle agglomeration area is serious, the polarization is increased, and the battery cycle performance is deteriorated. And the silicon particle agglomeration area has larger volume expansion in the charge and discharge process, and is easy to puncture the diaphragm to cause short circuit risk.
To overcome the above problems, the inventors of the present application first coated a composite layer of polymer and CNT on the surface of a silicon-containing substrate. As shown in the schematic structural diagram of the silicon-based anode active material in fig. 1, the inner layer 1 is a silicon-containing matrix, and the outer layer 2 is a polymer layer containing carbon nanotubes. The polymer layer containing the carbon nano tube is coated on the surface of the silicon-containing matrix, and the carbon nano tube can be bound on the surface of the silicon-based particles by using the polymer, so that the interface stability of the carbon nano tube on the surface of the anode active material is improved, and the cycle stability of the carbon nano tube is improved. Meanwhile, the CNT is bound on the surface of the silicon-based anode active material by the polymer, so that the CNT is not easy to be entangled with other silicon-based particles, and the silicon-based particles can be uniformly dispersed in the graphite. Under the condition, the graphite can effectively relieve the volume change of the silicon-based particles in the charge and discharge process, so that the expansion of the battery is reduced, and the use safety of the battery is improved.
The minimum value of the sheet resistance at different positions of the coating surface on the negative electrode current collector is R 1 Maximum value is R 2 ，R 1 /R 2 Is M. The larger the M value, the more the membrane resistance distribution is representedUniformity also indicates that the more uniformly silicon is dispersed in the graphite. The weight of the silicon-based particles in the negative electrode is N, which is the proportion of the total weight of the silicon-based particles and the graphite particles.
The inventors of the present application found that when the negative electrode satisfies M.gtoreq.about 0.5 and N is about 2wt% to 80wt%, the lithium ion battery prepared therefrom has improved cycle performance, rate performance and deformation resistance, and reduced direct current resistance.
The inventors of the present application have also found that I in a silicon-based anode active material 2 /I 1 The magnitude of the values reflects the extent of the effect of disproportionation of the material. I 2 /I 1 The larger the value, the larger the size of the nano-silicon crystal grains inside the silicon-based anode active material. The Dn10/Dv50 value is the cumulative 10% diameter Dn10 in the number reference distribution and the cumulative 50% diameter D in the volume reference distribution obtained by the laser scattering particle sizer test v 50, the larger the value of which indicates a smaller number of small particles in the material. In the case where M.gtoreq.about.0.5 is satisfied and N is about 2wt% to 80wt%, compared with I 2 /I 1 In the case where the value is greater than 1 and Dn10/Dv50 is not in the range of 0.3 to 0.6, when I 2 /I 1 The numerical value satisfies 0 < I 2 /I 1 When Dn10/Dv50 is more than or equal to 1 and less than or equal to 0.3 and less than or equal to 0.6, the lithium ion battery prepared from the silicon-based negative electrode active material has further improved cycle performance, rate capability and deformation resistance.
2. Positive electrode
Materials, compositions, and methods of making the same that may be used for the positive electrode in the embodiments of the present application include any of the techniques disclosed in the prior art. In some embodiments, the positive electrode is the positive electrode described in U.S. patent application US9812739B, which is incorporated by reference herein in its entirety.
In some embodiments, a positive electrode includes a current collector and a positive electrode active material layer on the current collector.
In some embodiments, the positive electrode active material includes, but is not limited to: lithium cobalt oxide (LiCoO) 2 ) Ternary materials of lithium Nickel Cobalt Manganese (NCM), lithium iron phosphate (LiFePO) 4 ) Or lithium manganate (LiMn) 2 O 4 )。
In some embodiments, the positive electrode active material layer further includes a binder, and optionally includes a conductive material. The binder enhances the bonding of the positive electrode active material particles to each other, and also enhances the bonding of the positive electrode active material to the current collector.
In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethyleneoxy-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or the like.
In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, synthetic graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.
In some embodiments, the current collector may include, but is not limited to: aluminum.
The positive electrode may be prepared by a preparation method well known in the art. For example, the positive electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include, but is not limited to: n-methylpyrrolidone.
3. Electrolyte solution
The electrolyte that may be used in embodiments of the present application may be an electrolyte known in the art.
In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent of the electrolyte according to the present application may be any organic solvent known in the art as a solvent of the electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and may be any electrolyte known in the art. The additive of the electrolyte according to the present application may be any additive known in the art as an electrolyte additive.
In some embodiments, the organic solvent includes, but is not limited to: ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.
In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.
In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF) 6 ) Lithium tetrafluoroborate (LiBF) 4 ) Lithium difluorophosphate (LiPO) 2 F 2 ) Lithium bis (trifluoromethanesulfonyl) imide LiN (CF) 3 SO 2 ) 2 (LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO) 2 F) 2 ) (LiLSI), lithium bisoxalato borate LiB (C) 2 O 4 ) 2 (LiBOB) or lithium difluorooxalato borate LiBF 2 (C 2 O 4 )(LiDFOB)。
In some embodiments, the concentration of lithium salt in the electrolyte is: about 0.5 to 3mol/L, about 0.5 to 2mol/L, or about 0.8 to 1.5mol/L.
4. Isolation film
In some embodiments, a separator is provided between the positive and negative electrodes to prevent shorting. The materials and shape of the separator that can be used in the embodiments of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic, etc., formed from a material that is stable to the electrolyte of the present application.
For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.
The surface treatment layer is provided on at least one surface of the base material layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic substance.
The inorganic layer comprises inorganic particles and a binder, wherein the inorganic particles are selected from one or a combination of more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from one or more of polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
The polymer layer contains a polymer, and the material of the polymer is at least one selected from polyamide, polyacrylonitrile, acrylic polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).
5. Electrochemical device
Embodiments of the present application provide an electrochemical device including any device in which an electrochemical reaction occurs.
In some embodiments, the electrochemical device of the present application comprises a positive electrode having a positive electrode active material capable of occluding and releasing metal ions; a negative electrode according to an embodiment of the present application; an electrolyte; and a separator interposed between the positive electrode and the negative electrode.
In some embodiments, the electrochemical devices of the present application include, but are not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors.
In some embodiments, the electrochemical device is a lithium secondary battery.
In some embodiments, lithium secondary batteries include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.
6. Electronic device
The electronic device of the present application may be any device using the electrochemical device according to the embodiment of the present application.
In some embodiments, the electronic device includes, but is not limited to: notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, headsets, video recorders, liquid crystal televisions, hand-held cleaners, portable CD-players, mini-compact discs, transceivers, electronic notebooks, calculators, memory cards, portable audio recorders, radios, stand-by power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game machines, watches, electric tools, flash lamps, cameras, household large-sized batteries or lithium-ion capacitors, and the like.
The preparation of lithium ion batteries is described below by way of example in connection with specific examples, and those skilled in the art will appreciate that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.
Examples
The following description is made of performance evaluation of examples and comparative examples of lithium ion batteries according to the present application.
1. Test method
1. High temperature cycle performance test: the test temperature was 45℃and was charged to 4.4V at a constant current of 0.7C, charged to 0.025C at a constant voltage, and discharged to 3.0V at 0.5C after standing for 5 minutes. And taking the capacity obtained in the step as an initial capacity, performing a 0.7C charge/0.5C discharge cycle test, and obtaining a capacity attenuation curve by taking the ratio of the capacity of each step to the initial capacity. The number of turns at 45℃until the capacity retention rate was 80% was recorded, thereby comparing the high temperature cycle performance of the battery.
2. Cell expansion rate test: and testing the thickness of the fresh battery in a half-charged (50% state of charge (SOC)) by using a spiral micrometer, and when the battery is circulated to 400cls, testing the thickness of the battery at the moment by using the spiral micrometer, and comparing the thickness of the fresh battery in the initial half-charged (50% SOC) with the thickness of the fresh battery to obtain the expansion rate of the full-charged (100% SOC) battery at the moment.
3. Discharge rate test: discharging to 3.0V at 25 ℃, standing for 5min at 0.2C, charging to 4.4V at 0.5C, standing for 5min after constant voltage charging to 0.05C, adjusting discharge multiplying power, respectively performing discharge tests at 0.2C, 0.5C, 1C, 1.5C and 2.0C to obtain discharge capacity, respectively comparing the obtained capacity at each multiplying power with the obtained capacity at 0.2C to obtain a ratio, and comparing multiplying power performances by comparing the ratio.
4. Direct Current Resistance (DCR) test: the actual capacity of the battery (constant current charge to 4.4V at 0.7C, constant voltage charge to 0.025C, standing for 10 minutes, discharge to 3.0V at 0.1C, standing for 5 minutes) was measured at 25 ℃ using Maccor machine, discharge was performed at 0.1C to a certain SOC, discharge was measured for 1s at 5ms, and DCR value at 10% SOC was calculated.
5. And (3) testing the resistance of the negative electrode diaphragm:
four-probe method is adopted to test the resistance of the negative electrode diaphragm, an instrument used for testing by the four-probe method is a precise direct current piezoelectric current source (SB 118), four copper plates with the length of 1.5cm and the width of 1cm and the thickness of 2mm are equidistantly fixed on a line, the distance between two copper plates in the middle is L (1-2 cm), and a base material for fixing the copper plates is an insulating material. During testing, the lower end surfaces of the four copper plates are pressed on the tested negative electrode, the copper plates at the two ends are connected with direct current I, voltage V is measured by the two copper plates in the middle, the values of I and V are read three times, and the average value I of the I and the V is respectively obtained a And V a ，V a /I a The value of (2) is the resistance of the diaphragm at the test site.
The sheet resistance values were randomly measured at 100 different locations on the coating surface, which locations were spread over the entire coating surface of the negative current collector. Wherein the minimum resistance value is R 1 The maximum resistance value is R 2 Calculating R 1 /R 2 Is denoted as M.
6. XRD test: 1.0 g to 2.0g of the sample is weighed and poured into a groove of a glass sample holder, compacted and ground with a glass sheet, and measured by an X-ray diffractometer (brookfield,d8 Testing according to JJS K0131-1996 general rule of X-ray diffraction analysis method, setting 40kV for test voltage, 30mA for current, 10-85 degree for scanning angle, 0.0167 degree for scanning step length, 0.24s for each step length, obtaining XRD diffraction pattern, obtaining 2 theta belonging to 28.4 degree maximum intensity value I from the figure 2 And is assigned to the highest intensity I of 21.0 DEG 1 Thereby calculating I 2 /I 1 Is a ratio of (2).
7. Particle size testing: 0.02g of powder sample was added to a 50ml clean beaker, 20ml of deionized water was added, and then a few drops of 1% surfactant were added dropwise to completely disperse the powder in water, and the powder was sonicated in a 120W sonicator for 5 minutes, and the particle size distribution was tested using a MasterSizer 2000.
2. Preparation of the Positive electrode
LiCoO is added with 2 And fully stirring and uniformly mixing conductive carbon black and a binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solvent system according to the weight ratio of 96.7:1.7:1.6 to prepare the anode slurry. And coating the prepared positive electrode slurry on a positive electrode current collector aluminum foil, drying, and cold pressing to obtain the positive electrode.
3. Preparation of electrolyte
In the dry argon environment, adding LiPF into a solvent formed by mixing Propylene Carbonate (PC), ethylene Carbonate (EC) and diethyl carbonate (DEC) (weight ratio is 1:1:1) 6 Uniformly mix, wherein LiPF 6 The concentration of (2) is 1mol/L, and 10wt% fluoroethylene carbonate (FEC) is added and mixed uniformly to obtain the electrolyte.
4. Preparation of a separator film
PE porous polymeric film is used as a isolating film.
5. Preparation of negative electrode
1. The silicon-based anode active materials in examples 1 to 10, examples 13 to 19, and comparative examples 2 to 6 were prepared by the following methods:
(1) Respectively carrying out mechanical dry mixing and ball milling mixing on silicon dioxide and metal silicon powder according to the mol ratio of 1:1 to obtain a mixed material;
(2) In Ar 2 Under an atmosphere at 10 -3 -10 -1 Pressure of kPaHeating the mixed material for 0.5-24h at the temperature of 1100-1550 ℃ to obtain gas;
(3) Condensing the obtained gas to obtain a solid, crushing and sieving the solid; and
(4) Heat treating the solid at 400-1200deg.C in nitrogen atmosphere for 1-24 hr, cooling the heat treated solid to obtain solid with different I 2 /I 1 A silicon-containing matrix material having an average particle diameter Dv50 of 5.2 μm;
(5) Dispersing Carbon Nano Tube (CNT) and polymer in water for 12 hours at high speed to obtain evenly mixed slurry;
(6) Adding the silicon-containing base material into the slurry uniformly mixed in the step (5), and stirring for 4 hours to obtain uniformly mixed dispersion liquid;
(7) Spray drying (inlet temperature 200 ℃, outlet temperature 110 ℃) the dispersion to obtain a powder; and
(8) And cooling, taking out a powder sample, crushing, and sieving to obtain silicon-based particles serving as a silicon-based negative electrode active material.
The preparation method of the silicon-based anode active material in comparative example 1 is similar to the above preparation method, except that the carbon nanotubes are not added in step (5) in comparative example 1.
The preparation method of the silicon-based anode active material in examples 11 and 12 was similar to the preparation method described above, except that the silicon-containing substrates in examples 11 and 12 were SiC.
2. The negative electrodes in examples 1 to 15 and comparative examples 2 to 6 were prepared by the following methods:
(1) Mixing 100g of the silicon-based anode active materials in examples 1-15 and comparative examples 2-6 with 25-1900g of graphite, and dispersing for 1h at a rotating speed of 20r/min to obtain a mixed anode active material;
(2) Adding a binder, deionized water and a conductive agent into the mixed anode active material obtained in the step (1), stirring for 2 hours at the rotating speed of 15r/min, and dispersing for 1 hour at the rotating speed of 1500r/min to obtain anode slurry
(3) And coating the negative electrode slurry on a copper foil, drying, and cold pressing to obtain the negative electrode.
The negative electrode of comparative example 1 was similar to the above-described preparation method, except that the silicon-based negative electrode active material and graphite of comparative example 1 were further mixed together with CNT added thereto in step (1).
6. Preparation of lithium ion batteries
And stacking the positive electrode, the isolating film and the negative electrode in sequence, so that the isolating film is positioned between the positive electrode and the negative electrode to play a role in isolation, and winding to obtain the bare cell. And placing the bare cell in an outer package, injecting electrolyte, and packaging. The lithium ion battery is obtained through the technological processes of formation, degassing, trimming and the like.
Specific process parameters in steps (1) to (4) in the preparation methods of silicon-based anode active materials in examples 1 to 10, examples 13 to 19 and comparative examples 1 to 6 are shown in table 1.
TABLE 1
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The kinds and amounts of the respective substances used in the preparation methods of silicon-based anode active materials in examples 1 to 19 and comparative examples 1 to 6 and the specific kinds and amounts of graphite, polymer, binder and conductive agent used in the preparation methods of anodes in examples 1 to 19 and comparative examples 1 to 6 are shown in table 2.
TABLE 2
"-" indicates that this material was not added during the preparation.
The chinese full names of the english abbreviations used in table 2 are as follows:
CMC: carboxymethyl cellulose
PAA: polyacrylic acid
Table 3 shows the relevant performance parameters of the silicon-based anode active materials in examples 1 to 19 and comparative examples 1 to 6, where N is the ratio of the weight of the silicon-based anode active material in the anode to the total weight of the silicon-based anode active material and graphite.
As can be seen from the test results of examples 1 to 19 and comparative examples 1 to 6, the lithium ion battery prepared from the negative electrode satisfying M.gtoreq.0.5 and N2 wt% to 80wt% has improved cycle performance, rate performance and deformation resistance, and reduced DC resistance, compared with the lithium ion battery prepared from the negative electrode not satisfying M.gtoreq.0.5 and N2 wt% to 80 wt%.
As can be seen from the test results of example 2, examples 16-19 and comparative examples 4-6, I 2 /I 1 The change in (c) has little effect on the value of M. But I 2 /I 1 The reduction can improve cycle performance and rate performance and reduce the expansion rate of the battery. It can also be seen that when Dn10/Dv50 is less than 0.3, small-particle silicon is increased, not easy to disperse, M is reduced, the rate capability can be improved, but the cycle performance and the battery expansion rate are adversely affected; and when Dn10/Dv50 > 0.6, large-particle silicon increases, the rate performance and cycle performance of the battery become poor, and the expansion ratio increases.
FIG. 2 shows a Scanning Electron Microscope (SEM) picture of the surface of SiO particles; fig. 3 shows SEM pictures of the surface of the silicon-based anode active material in example 2 of the present application, and it can be seen from fig. 3 that CNTs and polymers are uniformly distributed on the surface of silicon-based particles. Fig. 4 shows an SEM picture of a screenshot of the negative electrode in example 2 of the present application, and it can be seen from fig. 4 that silicon-based particles are uniformly dispersed in graphite. Fig. 5 shows SEM pictures of a screenshot of the negative electrode in example 8 of the present application, as can be seen from fig. 5, when the silicon-based particles are less, they are more uniformly dispersed in the graphite. Fig. 6 shows SEM pictures of a screenshot of the negative electrode in example 9 of the present application, the silicon-based particles in example 2 and example 8 being more uniformly dispersed in graphite compared to example 9. Fig. 7 shows SEM pictures of a screenshot of the negative electrode in comparative example 1 of the present application. As can be seen from fig. 7, the silicon-based particles of comparative example 1 are agglomerated together in a large amount because the CNT and the SiO are directly mixed with the graphite in comparative example 1, and the CNT is easily entangled with the SiO, thereby causing the agglomeration of the SiO.
Reference throughout this specification to "some embodiments," "one embodiment," "another example," "an example," "a particular example," or "a partial example" means that at least one embodiment or example in the present application includes the particular feature, structure, material, or characteristic described in the embodiment or example. Thus, descriptions appearing throughout the specification, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "example," which do not necessarily reference the same embodiments or examples in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.
Although illustrative embodiments have been shown and described, it will be understood by those skilled in the art that the foregoing embodiments are not to be construed as limiting the application and that changes, substitutions and alterations of the embodiments may be made without departing from the spirit, principles and scope of the application.

Claims (8)

1. A negative electrode comprising a current collector and a coating on the current collector, the coating comprising silicon-based particles and graphite particles, the silicon-based particles comprising a silicon-containing matrix and a polymer layer comprising a polymer and carbon nanotubes, the polymer layer being on a surface of at least a portion of the silicon-containing matrix, wherein the minimum value of sheet resistance at different locations on the surface of the coating is R 1 Maximum value is R 2 ，R 1 /R 2 Wherein M is greater than or equal to 0.5 and N is from 2wt% to 15wt%,
the weight ratio of the polymer in the polymer layer to the carbon nano tube is 1.5:1-10:1,
wherein the silicon-based particles have a maximum intensity value I in the range of 28.0 DEG to 29.0 DEG due to 2 theta in the X-ray diffraction pattern 2 The highest intensity value is I within the range of 20.5 DEG to 21.5 DEG 1 Wherein 0 is<I 2 /I 1 Is less than or equal to 1, and
wherein the particle size distribution of the silicon-based particles satisfies: dn10/Dv50 is more than or equal to 0.3 and less than or equal to 0.6.
2. The negative electrode of claim 1, wherein the silicon-containing substrate comprises SiO x X is more than or equal to 0.6 and less than or equal to 1.5; the silicon-containing substrate comprises Si, siO, siO 2 SiC, silicon alloys, or any combination thereof; and/or the Si has a particle size of less than 100nm.
3. The negative electrode according to claim 1, wherein the content of the polymer layer is 0.05-15wt% based on the total weight of the silicon-based particles; and/or the weight ratio of the polymer in the polymer layer to the carbon nanotubes is 2:1-10:1.
4. The negative electrode of claim 1, wherein the polymer comprises carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, polybutene-styrene rubber, epoxy resin, polyester resin, polyurethane resin, polyfluorene, or any combination thereof.
5. The anode of claim 1, wherein the thickness of the polymer layer is 5-200nm; the average particle diameter of the silicon-based particles is 500nm-30 mu m; and/or the specific surface area of the silicon-based particles is 1-50m 2 /g。
6. The negative electrode according to claim 1, wherein the content of the carbon nanotubes is 0.01-10wt% based on the total weight of the silicon-based particles.
7. An electrochemical device comprising the anode of any one of claims 1-6.
8. An electronic device comprising the electrochemical device of claim 7.
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