CN111146433A

CN111146433A - Negative electrode, and electrochemical device and electronic device comprising same

Info

Publication number: CN111146433A
Application number: CN201911373724.XA
Authority: CN
Inventors: 陈志焕; 姜道义; 崔航; 谢远森
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2019-12-26
Filing date: 2019-12-26
Publication date: 2020-05-12
Anticipated expiration: 2039-12-26
Also published as: CN111146433B

Abstract

The present application relates to a negative electrode, and an electrochemical device and an electronic device including the same. The negative electrode of the present application comprises a current collector and a coating on the current collector, the coating 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 nanotubes, the polymer layer is located on the surface of at least one part of the silicon-containing matrix, wherein the minimum value of the sheet resistance at different positions on the surface of the coating is R₁Maximum value of R₂，R₁/R₂Is M, and the weight of the silicon-based particles accounts for the proportion of N to the total weight of the silicon-based particles and the graphite particles, wherein M is more than or equal to 0.5, and N is 2 wt% -80 wt%. The lithium ion battery prepared by the negative electrode has improved cycle performance, rate capability and deformation resistance, and reduced direct current resistance.

Description

Negative electrode, and electrochemical device and electronic device comprising same

Technical Field

The application relates to the field of energy storage, in particular to a negative electrode, an electrochemical device comprising the same and an electronic device, in particular to a lithium ion battery.

Background

With the popularization of consumer electronics products such as notebook computers, mobile phones, tablet computers, mobile power sources, unmanned aerial vehicles and the like, the requirements on electrochemical devices therein are becoming stricter. For example, batteries are required not only to be lightweight but also to have high capacity and long operating life. Lithium ion batteries have already occupied a mainstream status in the market by virtue of their outstanding advantages of high energy density, high safety, no memory effect, long operating life, and the like.

Disclosure of Invention

Embodiments of the present application provide a negative electrode in an attempt to solve at least some of the problems presented in the related art. The embodiment of the application also provides an electrochemical device and an electronic device using the cathode.

In one embodiment, the present application provides a negative electrode comprising a current collector and a coating on said current collector, said coating comprising silicon-based particles and graphite particles, said silicon-based particles comprising a silicon-containing matrix and a polymer layer, said polymer layer comprising a polymer and carbon nanotubes, said polymer layer being located on the surface of at least a portion of said silicon-containing matrix, wherein the minimum value of the sheet resistance at different locations on the surface of said coating is R₁Maximum value of R₂，R₁/R₂Is M and the weight of the silicon-based particles is N in a proportion of the total weight of the silicon-based particles and the graphite particles, wherein M is greater than or equal to about 0.5 and N is about 2 wt% to 80 wt%.

In another embodiment, the present application provides an electrochemical device comprising an anode according to embodiments 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 by the negative electrode has improved cycle performance, rate capability and deformation resistance, and reduced direct current resistance.

Additional aspects and advantages of embodiments of the present 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 present application.

Drawings

Drawings necessary for describing 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 to be understood that the drawings in the following description are only some of the embodiments of the present application. It will be apparent to those skilled in the art that other embodiments of the drawings can be obtained from the structures illustrated in these drawings without the need for inventive work.

Fig. 1 shows a schematic structural view of a silicon-based negative active material in one embodiment of the present application.

Fig. 2 shows a Scanning Electron Microscope (SEM) picture of the surface of the SiO particles.

Fig. 3 shows an SEM picture of the surface of the silicon-based negative active material in example 2 of the present application.

Fig. 4 shows an SEM image of a screenshot of the negative electrode in example 2 of the present application.

Fig. 5 shows an SEM image of a screenshot of the negative electrode in example 8 of the present application.

Fig. 6 shows an SEM image of a screenshot of the negative electrode in example 9 of the present application.

Fig. 7 shows an SEM picture 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 embodiments 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 minor variations. When used in conjunction with an event or circumstance, the terms can refer to instances where the event or circumstance occurs precisely as well as instances where the event or circumstance occurs in close proximity. For example, when used in conjunction with numerical values, the term can refer to a range of variation that is less than or equal to ± 10% of the stated 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 negative active material reaching 50%.

In the present application, Dn10 is the particle size in μm corresponding to the cumulative number percentage of silicon-based negative active material reaching 10%.

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 one of the listed items. For example, if items a and B are listed, the phrase "one of a and B" means a alone or B alone. In another example, if items A, B and C are listed, the phrase "one of 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 linked by the term "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 a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means a only; 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.

A first and a 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, the polymer layer comprising a polymer and carbon nanotubes, the polymer layer being located 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 R₁Maximum value of R₂，R₁/R₂Is M and the ratio of the weight of the silicon-based particles to the total weight of the silicon-based particles and the graphite 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, R₁Is about 5-500m omega. In some embodiments, the minimum value of R, R₁About 5m Ω, about 10m Ω, about 20m Ω, about 30m Ω, about 40m Ω, about 50m Ω, about 100m Ω, about 150m Ω, about 200m Ω, about 250m Ω, about 300m Ω, about 400m Ω, about 450m Ω, about 500m Ω, or a range consisting of any two of these values.

In some embodiments, the maximum value of R, R₂Is about 5-800m omega. In some embodiments, the maximum value of R, R₂About 5m Ω, about 10m Ω, about 20m Ω, about 30m Ω, about 40m Ω, about 50m Ω, about 100m Ω, about 150m Ω, about 200m Ω, about 250m Ω, about 300m Ω, about 400m Ω, about 500m Ω, about 600m Ω, about 700m Ω, about 800m Ω, or a range consisting of any two of these values.

In some embodiments, the ratio M of the minimum to maximum values of R is greater than or equal to about 0.6. In some embodiments, the ratio M of the minimum to maximum values of R is greater than or equal to about 0.7. In some embodiments, the ratio M of the minimum to maximum values of R is about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1.0, or a range consisting of any two of these values.

In some embodiments, M/N ≧ about 4. In some embodiments, M/N ≧ about 5. In some embodiments, M/N ≧ 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 consisting of any two of these values.

In some embodiments, the weight of the silicon-based particles is in a proportion N of about 2 wt% to 80 wt% of the total weight of the silicon-based particles and the graphite particles. In some embodiments, the weight of the silicon-based particles is in a proportion N of about 10 wt% to 70 wt% of the total weight of the silicon-based particles and the graphite particles. In some embodiments, the weight of the silicon-based particles, N, as a proportion of the total weight of the silicon-based particles and the graphite particles is about 2 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 10 wt%, about 15 wt%, about 20 wt%, about 25 wt%, about 30 wt%, about 40 wt%, about 50 wt%, about 60 wt%, about 70 wt%, about 80 wt%, or a range consisting 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 ° -29.0 ° for 2 θ in the X-ray diffraction pattern₂The highest intensity value is assigned to I in the range of about 20.5 DEG to 21.5 DEG₁Wherein about 0 < I₂/I₁Less than or equal to about 1. In some embodiments, I₂/I₁Is 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 consisting 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 consisting of any two of these values.

In some embodiments, the silicon-based particles have a particle size distribution that satisfies: about 0.3. ltoreq. Dn10/Dv 50. ltoreq.about 0.6. In some embodiments, the silicon-based particles have a particle size distribution that satisfies: about 0.4. ltoreq. Dn10/Dv 50. ltoreq.about 0.5. In some embodiments, the silicon-based particles have a particle size distribution ranging from about 0.3, about 0.35, about 0.4, about 0.45, about 0.5, about 0.55, about 0.6, or any two of these values.

In some embodiments, the polymer comprises carboxymethylcellulose, polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, polybutylenebutadiene rubber, epoxy, polyester resin, polyurethane resin, polyfluorene, or any combination thereof.

In some embodiments, the silicon-containing matrix comprises SiO_xAnd x is more than or equal to 0.6 and less than or equal to 1.5.

In some embodiments, the silicon-containing matrix comprises Si, SiO₂SiC, or any combination thereof.

In some embodiments, the Si has a particle size of less than about 100 nm. In some embodiments, the Si has a particle size of less than about 50 nm. In some embodiments, the Si has a particle size of less than about 20 nm. In some embodiments, the Si has a particle size of less than about 5 nm. In some embodiments, the Si has a particle size of less than about 2 nm. In some embodiments, the Si has a particle size of less than about 0.5 nm. 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 consisting of any two of these values.

In some embodiments, the polymer layer is present in an amount of about 0.05 to 15 wt%, 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 10 wt%, based on the total weight of the silicon-based particles. In some embodiments, the polymer layer is present in an amount of about 2 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 6 wt%, about 7 wt%, about 8 wt%, about 9 wt%, about 10 wt%, about 11 wt%, about 12 wt%, about 13 wt%, about 14 wt%, or a range consisting 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 200 nm. In some embodiments, the polymer layer has a thickness of about 10nm to 150 nm. In some embodiments, the polymer layer has a thickness of about 50nm to 100 nm. In some embodiments, the polymer layer has a thickness of 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 consisting 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 10 wt%, 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 8 wt%, based on the total weight of the silicon-based particles. In some embodiments, the carbon nanotubes are present in an amount of about 0.01 wt%, about 0.02 wt%, about 0.05 wt%, about 0.1 wt%, about 0.5 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 6 wt%, about 7 wt%, about 8 wt%, about 9 wt%, about 10 wt%, or a range consisting 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 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 consisting of any two of these values.

In some embodiments, the carbon nanotubes have a diameter of about 1-30 nm. In some embodiments, the carbon nanotubes have a diameter of about 5-20 nm. In some embodiments, the carbon nanotubes have a diameter of about 10nm, about 15nm, about 20nm, about 25nm, about 30nm, or a range consisting of any two of these values.

In some embodiments, the carbon nanotubes have an aspect ratio of about 50 to 30000. In some embodiments, the carbon nanotubes have an aspect ratio of about 100-. 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 consisting of any two of these values.

In some embodiments, the silicon-based particles have a specific surface area of about 1-50m²In g, e.g. about 2.5 to 15m²(ii) in terms of/g. In some embodiments, the silicon-based particles have a specific surface area of about 5-10m²(ii) in terms of/g. In some embodiments, the silicon-based particles have a specific surface area of about 3m²G, about 4m²G, about 6m²G, about 8m²G, about 10m²G, about 12m²G, about 14m²Or a range of any two of these values.

In some embodiments, the present application provides a method of making 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 1-24h to obtain slurry;

(2) adding a silicon-containing matrix into the slurry, and dispersing for about 2-10 hours to obtain mixed slurry;

(3) removing the solvent from the mixed slurry; and

(4) crushing and screening.

In some embodiments, the silicon-containing matrix, the carbon nanotubes, and the polymer are each as defined above.

In some embodiments, the weight ratio of the polymer to the carbon nanotubes is from 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 consisting 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 10: 1. In some embodiments, the weight ratio of silicon-containing matrix to polymer is from about 150: 1 to 20: 1. In some embodiments, the weight ratio of silicon-containing matrix to polymer is about 200: 1, about 150: 1, about 100: 1, about 50: 1, about 10:1, or a range consisting 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 dispersing time in step (1) is about 1h, about 5h, about 10h, about 15h, about 20h, about 24h, or a range consisting 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 consisting 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 screen.

In some embodiments, the silicon-containing substrate can be commercially available silicon oxide SiO_xIt is also possible for the compounds prepared by the process of the present application to satisfy a value of about 0 < I₂/I₁Silicon oxide SiO ≦ about 1_xWherein the preparation method comprises the following steps:

(1) mixing silicon dioxide and metal silicon powder in a molar ratio of about 1: 5 to 5:1 to obtain a mixed material;

(2) at about 10^-4-10^-1Heating the mixed material at a temperature in the range of about 1100-;

(3) condensing the gas obtained to obtain a solid;

(4) pulverizing and sieving the solid to obtain the silicon-based particles; and

(5) heat treating the solid in the range of about 400 ℃ and 1200 ℃ for about 1-24h, and cooling the heat treated solid to obtain the silicon-based particles.

In some embodiments, the silica to metal silicon powder molar ratio is about 1: 4 to 4: 1. In some embodiments, the silica to metal silicon powder molar ratio is about 1: 3 to 3: 1. In some embodiments, the silica to metal silicon powder molar ratio is about 1: 2 to 2: 1. In some embodiments, the silica to metal silicon powder molar ratio is about 1: 1.

In some embodiments, the pressure range is about 10^-4-10^-1kPa. In some embodiments, the pressure is about 1Pa, about 10Pa, about 20Pa, about 30Pa, about 40Pa, about 50Pa, about 60Pa, about 70Pa, about 80Pa, about 90Pa, about 100Pa, or a range consisting of any two of these values.

In some embodiments, the heating temperature is about 1100-. In some embodiments, the heating temperature is about 1200 ℃, about 1300 ℃, about 1400 ℃, about 1500 ℃, about 1200 ℃, or a range consisting 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 consisting 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 blender, or a horizontal blender.

In some embodiments, the heating is performed 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 consisting of any two of these values.

In some embodiments, the heat treatment time is about 1-24 hours. In some embodiments, the heat treatment time is about 2-12 hours. In some embodiments, the time of the heat treatment is about 2 hours, about 5 hours, about 10 hours, about 15 hours, about 20 hours, about 24 hours, or a range consisting of any two of these values.

In some embodiments, the present application provides a method of making a negative electrode, the method comprising:

(1) mixing the silicon-based particles in any embodiment with graphite, and dispersing for 0.1-2h at the rotating speed of 10-100r/min to obtain a mixed cathode active material;

(2) adding a binder, a solvent and a conductive agent into the mixed cathode 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 cathode slurry; and

(3) and coating the negative electrode slurry on a current collector, drying and cold pressing to obtain a 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, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, 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, polymer substrate coated with a conductive metal, or any combination thereof.

In some embodiments, the weight ratio of the silicon-based particles to the graphite particles is from about 10:1 to about 1: 20. In some embodiments, the weight ratio of the silicon-based particles to the graphite particles is about 10:1, about 8: 1, about 5:1, about 3: 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 consisting 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 consisting of any two of these values.

In some embodiments, the weight ratio of the conductive agent to the silicon-based particles is from about 1: 100 to about 1: 10. In some embodiments, the weight ratio of the binder to the silicon-based particles is 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 a range consisting of any two of these values.

The silicon-based negative electrode material has the gram capacity as high as 1500-4200mAh/g, and is considered to be the negative electrode material of the next generation lithium ion battery with the greatest application prospect. But the low conductivity of silicon, and its Solid Electrolyte Interface (SEI) film having a volume expansion of about 300% and instability during charge and discharge, somewhat hinder its further application. The cycle stability and rate capability of the silicon-based material can be improved by introducing the Carbon Nano Tube (CNT).

However, the present inventors found that the CNT is difficult to disperse, and easily entangled with a plurality of silicon particles during the mixing and dispersing process with silicon, causing agglomeration of the silicon particles, and finally resulting in non-uniform dispersion of the silicon particles in the graphite. Electrolyte in a silicon particle agglomeration area is seriously consumed, polarization is increased, and the cycle performance of the battery is poor. And the silicon particle agglomeration area has large volume expansion in the charging and discharging process, and is easy to pierce a diaphragm to cause short circuit risk.

In order to overcome the above problems, the present inventors 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 negative 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 cathode active material is favorably improved, and the cycle stability of the cathode active material 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 wound 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 charging and discharging 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 current collector is R₁Maximum value of R₂，R₁/R₂The value of (D) is M. The larger the value of M, the more uniform the sheet resistance distribution, indicating that the silicon is dispersed more uniformly in the graphite. The weight of the silicon-based particles in the negative electrode accounts for the total weight of the silicon-based particles and the graphite particles, and the ratio of the weight of the silicon-based particles to the total weight of the graphite particles is N.

The inventors of the present application have found that when the negative electrode satisfies that M is greater than or equal to about 0.5 and N is about 2 wt% to 80 wt%, the lithium ion battery prepared therefrom has improved cycle performance, rate capability, and deformation resistance, and reduced direct current resistance.

The inventor of the application also finds that I in the silicon-based anode active material₂/I₁The magnitude of the value reflects the degree of influence of material disproportionation. I is₂/I₁The 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 volume-based distribution and the cumulative 50% diameter D in the volume-based distribution measured by a laser scattering particle sizer_vA ratio of 50, a larger value indicating a smaller number of small particles in the material. When M is more than or equal to about 0.5 and N is about 2 wt% -80 wt%, the ratio is compared with I₂/I₁In the case that the value is larger than 1 and Dn10/Dv50 is not in the range of 0.3-0.6, when I₂/I₁The numerical value satisfies 0 < I₂/I₁When Dn10/Dv50 is not less than 1 and not more than 0.3 is not less than 0.6, is prepared fromThe lithium ion battery prepared by the silicon-based negative active material has the advantages of further improved cycle performance, rate capability and deformation resistance.

II, positive electrode

Materials, compositions, and methods of making positive electrodes useful in 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 No. US9812739B, which is incorporated by reference herein in its entirety.

In some embodiments, the positive electrode includes a current collector and a positive active material layer on the current collector.

In some embodiments, the positive active material includes, but is not limited to: lithium cobaltate (LiCoO)₂) Lithium Nickel Cobalt Manganese (NCM) ternary material, lithium iron phosphate (LiFePO)₄) Or lithium manganate (LiMn)₂O₄)。

In some embodiments, the positive active material layer further includes a binder, and optionally a conductive material. The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding 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, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, 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, artificial 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-methyl pyrrolidone.

III, electrolyte

The electrolyte that may be used in the 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 that can be used 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 additive of electrolytes.

In some embodiments, the organic solvent includes, but is not limited to: ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.

In some embodiments, the lithium salt comprises 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)₂F₂) Lithium bis (trifluoromethanesulfonylimide) LiN (CF)₃SO₂)₂(LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO)₂F)₂) (LiFSI), lithium bis (oxalato) borate LiB (C)₂O₄)₂(LiBOB) or lithium difluorooxalato borate LiBF₂(C₂O₄)(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 1.5 mol/L.

Fourth, the isolating film

In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separation film that can be used for the embodiment 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 includes a polymer or inorganic substance or the like formed of a material 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 film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or 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 more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium dioxide, 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 a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

The polymer layer comprises a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

Fifth, 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 includes 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, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

Sixth, 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 devices include, but are not limited to: a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting apparatus, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large-sized household battery or a lithium ion capacitor, and the like.

Taking a lithium ion battery as an example and describing the preparation of the lithium ion battery with reference to specific examples, those skilled in the art will understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

Examples

The following describes performance evaluation according to examples and comparative examples of lithium ion batteries of the present application.

Test method

1. And (3) testing high-temperature cycle performance: the test temperature was 45 ℃, and the voltage was charged to 4.4V at a constant current of 0.7C and 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 the initial capacity, performing 0.7C charging/0.5C discharging cycle test, and taking the ratio of the capacity of each step to the initial capacity to obtain a capacity fading curve. The number of cycles until the capacity retention rate was 80% was recorded at 45 ℃ in order to compare the high-temperature cycle performance of the batteries.

2. And (3) testing the expansion rate of the battery: and (3) testing the thickness of the fresh battery in the half-charging (50% charging State (SOC)) by using a spiral micrometer, circulating to 400cls, and testing the thickness of the battery at the moment by using the spiral micrometer, wherein the thickness of the battery is compared with the thickness of the fresh battery in the initial half-charging (50% SOC), and the expansion rate of the battery in the full-charging (100% SOC) at the moment can be obtained.

3. And (3) testing discharge rate: discharging to 3.0V at 0.2C at 25 ℃, standing for 5min, charging to 4.4V at 0.5C, charging to 0.05C at constant voltage, standing for 5min, adjusting discharge multiplying power, performing discharge tests at 0.2C, 0.5C, 1C, 1.5C and 2.0C respectively to obtain discharge capacity, comparing the capacity obtained at each multiplying power with the capacity obtained at 0.2C to obtain a ratio, and comparing multiplying power performance by comparing the ratio.

4. Direct Current Resistance (DCR) test: the actual capacity of the battery was measured at 25 ℃ (0.7C constant current charged to 4.4V, constant voltage charged to 0.025C, left to stand for 10 minutes, discharged to 3.0V at 0.1C, left to stand for 5 minutes) by 0.1C discharge to a certain SOC, test 1s discharge was sampled at 5ms, and the DCR value at 10% SOC was calculated.

5. Testing the resistance of the negative membrane:

the resistance of the negative diaphragm is tested by adopting a four-probe method, and the instrument used for testing by adopting the four-probe method is a precise direct-current voltage current source (SB118 type), and four negative diaphragm resistors are 1.5cm longCopper plates with width of 1cm and thickness of 2mm are fixed on a line at equal intervals, the distance between the two copper plates in the middle is L (1-2cm), and the base material for fixing the copper plates is an insulating material. During testing, the lower end faces of four copper plates are pressed on a tested negative electrode, the copper plates at two ends are connected with a direct current I, a 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 I and V is respectively taken_aAnd V_a，V_a/I_aThe value of (d) is the membrane resistance at the test site.

The sheet resistance values were randomly measured at 100 different locations on the coating surface, which measured locations spread over the entire coating surface of the negative current collector. Wherein the minimum resistance value is R₁Maximum resistance value of R₂Calculating R₁/R₂The value of (D) is denoted as M.

6. XRD test: weighing 1.0-2.0g of sample, pouring the sample into a groove of a glass sample rack, compacting and grinding the sample by using a glass sheet, testing by using an X-ray diffractometer (Bruk, D8) according to JJS K0131-₂And the highest intensity I attributed to 21.0 DEG₁Thereby calculating I₂/I₁The ratio of (a) to (b).

7. And (3) testing the granularity: 0.02g of powder sample is added into a 50ml clean beaker, 20ml of deionized water is added, then a few drops of 1% surfactant are added dropwise to completely disperse the powder in the water, ultrasonic treatment is carried out in a 120W ultrasonic cleaning machine for 5 minutes, and the particle size distribution is tested by using a MasterSizer 2000.

Preparation of the cathode

Subjecting LiCoO to condensation₂The conductive carbon black and the adhesive polyvinylidene fluoride (PVDF) are fully stirred and uniformly mixed in an N-methyl pyrrolidone solvent system according to the weight ratio of 96.7: 1.7: 1.6 to prepare the anode slurry. And coating the prepared anode slurry on an anode current collector aluminum foil, drying and cold pressing to obtain the anode.

Preparation of electrolyte

Under dry argon atmosphere, LiPF is added into a solvent formed by mixing Propylene Carbonate (PC), Ethylene Carbonate (EC) and diethyl carbonate (DEC) (weight ratio is 1: 1)₆Mixing uniformly, wherein LiPF₆The concentration of (2) is 1mol/L, 10 wt% of fluoroethylene carbonate (FEC) is added and mixed evenly to obtain the electrolyte.

Preparation of isolation film

The PE porous polymer film is used as a separation film.

Preparation of cathode

1. Silicon-based negative 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 molar ratio of 1: 1 to obtain a mixed material;

(2) at Ar₂Under an atmosphere of 10 deg.C^-3-10^-1Heating the mixed material for 0.5-24h at the temperature range of 1100-1550 ℃ under the pressure range of kPa to obtain gas;

(3) condensing the obtained gas to obtain a solid, crushing, screening the solid; and

(4) heat treating the solid for 1-24h in the nitrogen atmosphere within the range of 400-1200 ℃, and cooling the heat treated solid to obtain the solid with different I₂/I₁A siliceous base material having an average particle size Dv50 of 5.2 μm;

(5) dispersing Carbon Nano Tubes (CNT) and a polymer in water at a high speed for 12h to obtain uniformly mixed slurry;

(6) adding the silicon-containing matrix material into the slurry uniformly mixed in the step (5), and stirring for 4 hours to obtain a uniformly mixed dispersion liquid;

(7) spray drying (inlet temperature 200 ℃, outlet temperature 110 ℃) the dispersion to obtain powder; and

(8) and taking out a powder sample after cooling, crushing and sieving to obtain silicon-based particles serving as the silicon-based negative electrode active material.

The preparation method of the silicon-based negative active material in comparative example 1 is similar to the above preparation method except that comparative example 1 does not add the carbon nanotube in step (5).

The silicon-based negative active materials of examples 11 and 12 were prepared in a similar manner to the above-described preparation method, except that the silicon-containing matrix in examples 11 and 12 was SiC.

2. The negative electrodes in examples 1 to 15 and comparative examples 2 to 6 were prepared by the following methods:

(1) 100g of the silicon-based negative electrode active materials in examples 1 to 15 and comparative examples 2 to 6 were mixed with 25 to 1900g of graphite, and dispersed at a rotation speed of 20r/min for 1 hour to obtain a mixed negative electrode active material;

(2) adding a binder, deionized water and a conductive agent into the mixed cathode 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 cathode slurry

(3) And coating the negative electrode slurry on a copper foil, drying and cold pressing to obtain the negative electrode.

The negative electrode in comparative example 1 is similar to the above-described preparation method except that comparative example 1 further adds CNT to the silicon-based negative active material and graphite to be mixed together in step (1).

Preparation of lithium ion battery

And stacking the anode, the isolating membrane and the cathode in sequence, so that the isolating membrane is positioned between the anode and the cathode to play an isolating role, and winding to obtain the bare cell. And arranging the bare cell in an external package, injecting electrolyte and packaging. The lithium ion battery is obtained through the technological processes of formation, degassing, edge cutting and the like.

Specific process parameters in steps (1) to (4) in the methods for preparing silicon-based negative active materials in examples 1 to 10, examples 13 to 19, and comparative examples 1 to 6 are shown in table 1.

TABLE 1

The kinds and amounts of the respective substances used in the silicon-based negative electrode active material preparation methods 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 negative electrode preparation methods 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 English abbreviations used in Table 2 are all 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.

It can be seen from the test results of examples 1-19 and comparative examples 1-6 that the lithium ion battery prepared from the negative electrode satisfying M ≥ 0.5 and N2 wt% -80 wt% has improved cycle performance, rate capability, and deformation resistance, and reduced direct current resistance, as compared to the lithium ion battery prepared from the negative electrode satisfying M ≥ 0.5 and N2 wt% -80 wt%.

As can be seen from the test results of example 2, examples 16 to 19 and comparative examples 4 to 6, I₂/I₁The change in (c) has little effect on the value of M. But I₂/I₁The reduction can improve the 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, the small silicon particles are increased, are not easy to disperse, and M is reduced, so that the rate capability can be improved, but the cycle performance and the battery expansion rate are not affected well; and when Dn10/Dv50 > 0.6, large-particle silicon increases, rate performance and cycle performance of the battery become poor, andthe expansion rate increases.

Fig. 2 shows a Scanning Electron Microscope (SEM) picture of the surface of the SiO particle; fig. 3 shows an SEM picture of the surface of the silicon-based negative active material in example 2 of the present application, and it can be seen from fig. 3 that the CNTs and the polymer are uniformly distributed on the surface of the silicon-based particles. Fig. 4 shows an SEM picture of a cross-section of the negative electrode in example 2 of the present application, and it can be seen from fig. 4 that the silicon-based particles are uniformly dispersed in the graphite. Fig. 5 shows an SEM picture of a screenshot of the negative electrode in example 8 of the present application, from fig. 5 it can be seen that the silicon based particles are more uniformly dispersed in the graphite when there are fewer silicon based particles. Fig. 6 shows SEM pictures of screenshots 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 than in example 9. Fig. 7 shows an SEM picture 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 in comparative example 1 are largely agglomerated together because comparative example 1 mixes CNT and SiO directly with graphite, and CNT easily entangles SiO with each other, thereby causing agglomeration of SiO.

Reference throughout this specification to "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example 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 illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. A negative electrode comprising a current collector and a coating on said current collector, said coating comprising silicon-based particles and graphite particles, said silicon-based particles comprising a silicon-containing matrix and a polymer layer, said polymer layer comprising a polymer and carbon nanotubes, said polymer layer being located on the surface of at least a portion of said silicon-containing matrix, wherein the minimum value of the sheet resistance at different locations on the surface of said coating is R₁Maximum value of R₂，R₁/R₂Is M, and the weight of the silicon-based particles accounts for the proportion of N to the total weight of the silicon-based particles and the graphite particles, wherein M is more than or equal to 0.5, and N is 2 wt% -80 wt%.

2. The anode of claim 1, wherein the silicon-containing matrix comprises SiO_xAnd x is more than or equal to 0.6 and less than or equal to 1.5; the silicon-containing substrate comprises Si, SiO and SiO₂SiC, silicon alloys, or any combination thereof; and/or the Si has a particle size of less than 100 nm.

3. The anode of claim 1, wherein the silicon-based particles have a maximum intensity value, I, in X-ray diffraction pattern in the range of 28.0 ° -29.0 ° 2 Θ₂The highest intensity value in the range of 20.5-21.5 is I₁Wherein 0 is<I₂/I₁≤1。

4. The anode of claim 1, wherein the silicon-based particles have a particle size distribution that satisfies: dn10/Dv50 is more than or equal to 0.3 and less than or equal to 0.6.

5. The anode of claim 1, wherein the polymer layer is present in an amount of 0.05 to 15 wt%, 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 0.5:1 to 10: 1.

6. The negative electrode of claim 1, wherein the polymer comprises carboxymethylcellulose, polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, poly (styrene-butadiene rubber), epoxy resin, polyester resin, polyurethane resin, polyfluorene, or any combination thereof.

7. The anode of claim 1, wherein the polymer layer has a thickness of 5-200 nm; the average grain diameter of the silicon-based particles is 500nm-30 mu m; and/or the specific surface area of the silicon-based particles is 1 to 50m²/g。

8. The anode of claim 1, wherein the carbon nanotubes are present in an amount of 0.01 to 10 wt% based on the total weight of the silicon-based particles.

9. An electrochemical device comprising the anode of any one of claims 1-8.

10. An electronic device comprising the electrochemical device of claim 9.