CN114497489A - Composite material, negative plate and battery comprising same - Google Patents

Composite material, negative plate and battery comprising same Download PDF

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Publication number
CN114497489A
CN114497489A CN202210038580.8A CN202210038580A CN114497489A CN 114497489 A CN114497489 A CN 114497489A CN 202210038580 A CN202210038580 A CN 202210038580A CN 114497489 A CN114497489 A CN 114497489A
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composite material
silicon oxide
negative electrode
silicon
oxide particles
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Inventor
范洪生
汪辉
刘春洋
李素丽
李俊义
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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Priority to CN202210038580.8A priority Critical patent/CN114497489A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes

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

Abstract

The invention provides a composite material, and a negative plate and a battery comprising the composite material. The composite material contains silicon oxide particles and a carbon coating; the size d of the silicon oxide particles is less than or equal to 4 mu m; the composite material has a secondary particle structure; the composite material has a Raman shift of 1300-1400cm in a Raman spectrum test‑1、1550‑1650cm‑1The region having an intensity of I1、I2And 0.1. ltoreq.I1/I2<0.5; the composite material has a common Electron Paramagnetic Resonance (EPR) testAnd (5) vibrating the signal. The battery assembled by the composite material has high-rate lithium intercalation capacity, has a high constant-current charging ratio under the condition of high-rate charging, and can prevent the lithium precipitation phenomenon of a negative electrode in a cycle based on high-rate charging.

Description

Composite material, negative plate and battery comprising same
Technical Field
The application relates to the field of lithium ion batteries, in particular to a composite material, and a negative plate and a battery comprising the composite material.
Background
The silicon oxide is formed by the general formula of SiOx(x is more than or equal to 0 and less than or equal to 2). In fast-charge lithium ion battery applications, silicon oxide has two advantages over graphite: firstly, under the condition of the same capacity area density, the thickness of the negative plate containing silicon oxide is smaller, so that a shorter liquid-phase lithium ion diffusion path is provided; secondly, the silicon oxide structure is amorphous and in an alloy type lithium storage mode, so that more lithium insertion channels are provided.
However, silicon oxide has a significant disadvantage of poor electron conductivity. When lithium is embedded under higher multiplying power, the negative plate assembled by silicon oxide has larger polarization effect and lithium precipitation risk. Therefore, how to obtain the silicon-based composite material with high electronic conductivity is a research direction with great application prospect.
Disclosure of Invention
Silicon oxide is not a good conductor of electrons, and the electron conductivity of silicon oxide can be improved by covering the surface with amorphous carbon having high conductivity. However, since the amount of amorphous carbon is generally less than 5 wt%, the amount of amorphous carbon has a limited contribution to improvement of electron conductivity of silicon oxide, since amorphous carbon has a large number of defects and a large specific surface area and, if the amount is too high, side reactions significantly increase to degrade cycle stability of silicon oxide. The inventor of the present application has found that increasing the structural order of the carbon coating can reduce the defect density, which provides a possibility to increase the carbon coating content. Further research shows that: on one hand, thinning the particle size of the silicon oxide can shorten the transmission path of electrons inside; on the other hand, the chemical bonding action between the silicon oxide and the carbon coating can be constructed to improve the stability of the circulating structure of the material. Based on the research and analysis, the invention is provided for solving the problems of large polarization effect of a negative plate assembled by silicon oxide, high lithium precipitation risk and short cycle life when lithium is embedded under high multiplying power.
In the present invention, the high magnification is 3C or more.
According to a first aspect of the present application, there is provided a composite material comprising silicon oxide particles and a carbon coating;
the size d of the silicon oxide particles is less than or equal to 4 mu m;
the composite material has a secondary particle structure;
the composite material has a Raman shift of 1300-1400cm in a Raman spectrum test-1、1550-1650cm-1The region having an intensity of I1、I2And 0.1. ltoreq.I1/I2<0.5；
The composite material has a resonance signal in an Electron Paramagnetic Resonance (EPR) test.
According to the invention, the composite material is a silicon-based composite material.
According to the invention, the composite material has a secondary particle structure comprising a number of silicon oxide particles and a carbon coating. Also for example, the composite material has a secondary particle structure consisting of a number of silicon oxide particles and a carbon coating.
According to the invention, the secondary particle structure has an irregular shape.
In the present invention, the "plurality" may be one or more.
According to the present invention, the silicon oxide particles have a primary particle structure.
According to the invention, the silicon oxide particles have the chemical formula SiOx(0 ≦ x ≦ 2), illustratively, x ≦ 0, 0.5, 1.0, 1.5, or 2.0; if the silicon oxide particles are a mixture, x may be any value within the range of the composition of the points described above.
According to the invention, the median particle diameter Dv50 of the composite material is such that 5 μm ≦ Dv50 ≦ 10 μm, the median particle diameter Dv50 of the composite material being, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.
According to the invention, the maximum particle size Dmax of the composite material satisfies 15 μm Dmax <25 μm, for example 15 μm Dmax <20 μm. When the maximum particle diameter Dmax of the composite material meets the condition that the Dmax is not less than 15 mu m and not more than 25 mu m (preferably, the Dmax is not less than 15 mu m and not more than 20 mu m), the rate performance of the composite material is better, and if the maximum particle diameter Dmax is less than 15 mu m, the specific surface area of the composite material is larger, the surface side reactions are increased, and the cycle performance of the composite material is deteriorated.
According to the invention, the specific surface area BET of the composite material satisfies 2m2/g≤BET≤8m2In g, the specific surface area BET of the silicon-based composite material is, for example, 2m2/g、3m2/g、4m2/g、5m2/g、6m2/g、7m2G or 8m2/g。
When the median particle diameter Dv50 of the composite material satisfies that the median particle diameter Dv50 is less than or equal to 5 mu m and less than or equal to 10 mu m, the maximum particle diameter Dmax satisfies Dmax<25 μm, a specific surface area BET of 2m2/g≤BET≤8m2At the time of/g, the composite material has better high-rate lithium intercalation capacity and cycling stability. When the median particle diameter Dv50 of the composite material<5 μm or BET>8m2In the case of/g, the surface of the composite material has more side reactions and cannot maintain the lasting high-rate lithium intercalation capability; when the median particle diameter Dv50 of the composite material>10 μm or Dmax>25 μm or BET<2m2At/g, the solid-phase lithium ion diffusion path is increased, or the surface lithium insertion sites are fewer, so that the high-rate lithium insertion performance of the composite material is reduced.
For the median particle diameter Dv50 and the maximum particle diameter Dmax, the laser particle size test method was used. For example, the measurement is carried out using a Malvern particle size tester, the test procedure is as follows: dispersing a sample to be tested in deionized water containing a dispersing agent (such as nonylphenol polyoxyethylene ether with the content of 0.03 wt%) to form a mixture, carrying out ultrasonic treatment on the mixture for 2 minutes, and then placing the mixture into a particle size tester for testing.
For the BET specific surface area, the Brunauer-Emmett-Teller test method was used. For example, the measurement was performed using Tri Star II specific surface Analyzer.
According to the invention, the composite material contains an O element and an Si element (or the silicon oxide contains an O element and an Si element), and the molar ratio y of the O element to the Si element satisfies 0.8. ltoreq. y.ltoreq.1.3, and the molar ratio y of the O element to the Si element is, for example, 0.8, 0.9, 1.0, 1.1, 1.2 or 1.3. When the molar ratio y of the O element to the Si element is more than or equal to 0.8 and less than or equal to 1.3, the composite material has higher gram capacity and more stable structure. When y is less than 0.8, the oxygen content is too low, and the composite material cannot maintain a stable structure in a continuous high-rate lithium intercalation cycle; when y >1.3, the oxygen content is too high, the composite material has a reduced gram capacity and an increased electron transport resistance.
For the molar ratio of the O element to the Si element, an energy spectrum (EDS) analysis method was employed. For example, the test is performed using an Oxford spectrometer.
According to the invention, the content n of the carbon coating in the composite material satisfies 5% or more and n or less than 20%, and the content n of the carbon coating in the composite material is, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%. Wherein, the content of the carbon coating is the percentage of the carbon coating in the total mass of the composite material. When the content n of the carbon coating in the composite material is more than or equal to 5% and less than or equal to 20%, the composite material has higher electronic conductivity and gram volume. When n is less than 5%, the electronic conductivity of the composite material is lower; when n > 20%, the carbon defect density increases and irreversible reactions increase, resulting in deterioration of cycle performance.
The content n of the carbon coating is measured by a thermogravimetric analysis method. For example, the measurement is carried out by using a TGA550 thermogravimetric analyzer, during the measurement, an air atmosphere is introduced, the temperature is increased from room temperature to 800 ℃, the temperature rising rate is 10 ℃/min, and the maximum value of the mass loss ratio during the temperature rising process is taken as n.
According to the present invention, the size d of the silicon oxide particles refers to the maximum value of the length of the silicon oxide particles in either direction, i.e., the diameter of the smallest circle capable of completely containing the silicon oxide particles. The composite material may be cut by an ion milling method and observed under a scanning electron microscope, and the diameter of the smallest circle capable of completely containing silicon oxide is taken as the size d of the silicon oxide particles.
According to the invention, the silicon oxide particles comprise silicon oxide A and silicon oxide B, wherein the dimension d of silicon oxide AAD is more than or equal to 2 mu mALess than or equal to 4 mu m, size d of silicon oxide BBSatisfy dB<2μm。
According to the invention, the mass percentage of the silicon oxide A to the total mass of the silicon oxide particles is greater than or equal to 0% and less than 100%, and the mass percentage of the silicon oxide B to the total mass of the silicon oxide particles is greater than 0% and less than or equal to 100%.
According to the invention, a plurality of silicon oxides B and/or carbon coatings are filled between adjacent silicon oxides A.
According to the invention, the distance h between adjacent silicon oxides AASatisfy hA≥0.2μm。
When the size d of the silicon oxide particles is less than or equal to 4 mu m and hANot less than 0.2 μm, or the size d of silicon oxide<At 2 μm, the composite material has high rate lithium intercalation capability. When the size d of the silicon oxide particles>4 μm and/or hA<At 0.2 μm, the electron transport path or resistance of the composite material increases, and the high-rate lithium intercalation ability decreases.
For the size d of the silicon oxide particles and the distance h between adjacent silicon oxides AAThe composite material is cut by an ion grinding method, observed under a scanning electron microscope, and 20 particles are randomly selected for measurement.
According to the invention, the composite material has a resonance signal in an Electron Paramagnetic Resonance (EPR) test, which indicates the presence of chemical bonding between the silicon oxide particles and the carbon coating. Specifically, when the composite material contains an EPR resonance signal, it is indicated that the silicon oxide particles and the carbon coating have a strong chemical bonding effect, and at this time, the structure of the composite material is stable. When the composite material does not contain an EPR resonance signal, the silicon oxide particles and the carbon coating do not have a chemical bonding effect, and the structural stability of the composite material is reduced.
For the EPR resonance signal, an electron paramagnetic resonance method is adopted for testing. For example, testing was performed using Bruker a200 electron paramagnetic resonance spectrometer.
According to the invention, the composite materialIn the Raman spectrum test, the Raman shift is 1300-1400cm-1、1550-1650cm-1The region having an intensity of I1、I2And 0.1. ltoreq.I1/I2<0.5; this indicates that the carbon coating has a higher degree of structural order than amorphous carbon. Specifically, when 0.1. ltoreq.I1/I2<At 0.5, the structural order degree of the carbon coating is higher than that of the amorphous carbon, the carbon coating has a certain layered structure and can play a role in transmitting electrons and lithium ions, and at the moment, the composite material has high-rate lithium intercalation capacity. When I is1/I2>When the carbon coating material is 0.5 hour, the ordered degree of the carbon coating material structure is similar to that of the amorphous carbon, the defect site density is high, the electronic and ionic conduction resistance is increased, the side reaction in the electrolyte is increased, and the high-rate lithium intercalation performance of the composite material is reduced. When I is1/I2<At 0.1, the ordered degree of the carbon coating structure is similar to that of graphite, but the carbon coating has a thicker lamellar structure and is not easy to form stable chemical bonding with silicon oxide particles.
For raman spectroscopy testing, the testing can be performed using a Thermo Fisher raman spectrometer.
According to a second aspect of the present application, there is provided a negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprising the above-mentioned composite material.
According to the present invention, the composite material serves as a silicon negative electrode active material.
According to a third aspect of the present application, there is provided a battery comprising the above-described composite material, or, alternatively, the above-described negative electrode sheet.
According to the invention, the battery is a lithium ion battery.
Has the beneficial effects that:
the invention provides a composite material, and a negative plate and a battery comprising the composite material, wherein the composite material is different from micron-sized silicon oxide coated by amorphous carbon. The composite material has high gram volume, strong high-rate lithium intercalation capability and good cycling stability; when lithium is embedded under high multiplying power, the polarization effect of the negative plate assembled by the composite material is small, the risk of lithium precipitation does not exist, and meanwhile, the battery assembled by the composite material has good cycle performance under high multiplying power.
Furthermore, the battery assembled by the composite material has high-rate lithium intercalation capacity, has a high constant-current charging ratio under the condition of high-rate charging, and can prevent the lithium precipitation phenomenon of the negative electrode in the cycle based on high-rate charging.
Drawings
Fig. 1 is an SEM surface photograph of the composite material of example 1 of the present application.
Fig. 2 is an SEM cross-sectional photograph of the composite material of example 1 of the present application. The photograph was taken in a backscattered electron mode, in which there was a significant difference in brightness between the silicon oxide particles and the carbon coating. Wherein the brightness of the silicon oxide particles is high, a representative silicon oxide A with the size of 2-4 μm is marked by 11, and a representative silicon oxide B with the size of less than 2 μm is marked by 12. The brightness of the carbon coating is low and a representative carbon coating is indicated by "13" in the figure. As can be seen from fig. 2, the composite material has a secondary particle structure including a number of silicon oxide primary particles and a carbon coating, wherein the carbon coating is on the surface of the silicon oxide primary particles or between the number of silicon oxide primary particles.
FIG. 3 is an SEM cross-sectional photograph of a composite material of comparative example 7 of the present application. The photograph was taken in a backscattered electron mode, in which there was a significant difference in brightness between the silicon oxide particles and the carbon coating. Wherein the brightness of the silicon oxide particles is high, the silicon oxide A with the size of 2-4 μm is marked by 21 and 22 in the figure, and the distance between the silicon oxide A and the silicon oxide A is less than 0.2 μm; representative silicon oxides B with dimensions less than 2 μm are marked with "23". The brightness of the carbon coating is low and a representative carbon coating is indicated by "24" in the figure.
Fig. 4 is an SEM cross-sectional photograph of the composite material of comparative example 8 of the present application. The photograph was taken in a backscattered electron mode, in which there was a significant difference in brightness between the silicon oxide particles and the carbon coating. Among them, the brightness of the silicon oxide particles is high, and the silicon oxide having a size of more than 4 μm is indicated by "31" in the figure.
Detailed Description
< method for producing composite Material >
The invention provides a preparation method of the composite material, which comprises the following steps:
(a) mixing silicon and silicon dioxide, placing the mixture under the conditions of low pressure and high temperature for reaction, and then carrying out primary crushing treatment;
(b) mixing the material subjected to the primary crushing treatment with the crystalline flake graphite in an inert atmosphere, and then performing secondary crushing treatment;
(c) mixing the materials subjected to the secondary crushing treatment with the aromatic polymer, drying, and then performing tertiary crushing treatment;
(d) fusing the materials after the third crushing treatment;
(e) under an inert atmosphere, carbonizing the fused material, then crushing for the fourth time, and grading to obtain the composite material;
according to the invention, the method comprises the following steps:
(1) mixing silicon powder and silicon dioxide powder to obtain a mixture 1;
(2) placing the mixture 1 under the conditions of low pressure and high temperature, reacting for a period of time, and cooling to obtain a solid 1;
(3) crushing the solid 1 to obtain powder 1;
(4) mixing the powder 1 with the flake graphite in an inert atmosphere to obtain a mixture 2;
(5) crushing the mixture 2 by using a vibration ball mill under an inert atmosphere to obtain powder 2;
(6) adding the aromatic polymer into toluene, and uniformly stirring to obtain a mixture 3;
(7) adding the powder 2 into the mixture 3, and uniformly stirring to obtain a mixture 4;
(8) drying the mixture 4 to obtain powder 3;
(9) adding the powder 3 into a high-speed fusion machine for fusion treatment to obtain powder 4;
(10) adding the powder 4 into a heating stirring kettle, introducing inert gas for protection, and carrying out carbonization treatment at the rotation frequency of 100-300 rpm to obtain powder 5;
(11) and performing ball milling treatment on the powder 5, and removing oversize particles by using particle size grading equipment to obtain the composite material.
In the step (1), the molar ratio a of the silicon dioxide powder to the silicon powder is within the range of 0.67-1.85.
In the step (2) of the method, the reaction pressure is<10-4The temperature is 1050-1350 ℃ under the MPa, and the time is 3-8 h.
In the step (3), the crushing treatment method comprises using a horizontal ball mill, a planetary ball mill, a vibration ball mill, etc., and the maximum particle diameter Dmax of the powder 1 is less than 100 μm.
In the step (3), the large blocks are crushed, which belongs to primary crushing, and the maximum particle size Dmax of the particles of the powder 1 is ensured to be less than 100 mu m.
In the step (4), the mass ratio b of the crystalline flake graphite to the powder 1 is within the range of 0.04-0.20.
In step (5) of the method, the maximum particle diameter of the primary particles of the powder 2 is not more than 4 μm.
In the method step (5), since the silicon oxide particles are crushed to 4 μm or less, it is necessary to use a vibration ball mill having a better crushing effect. This process also simultaneously grinds and exfoliates the flake graphite to thoroughly mix it with the silicon oxide particles. Namely, after the flake graphite is crushed, the flake graphite and the silicon oxide crushed at the same time can form a chemical bonding effect to form a coating effect, so that the structural order degree of the carbon coating is enhanced.
In step (6) of the process, the polymer is mixed with the powder 2 in a solvent in order to form a more compact structure, which is more stable.
In step (6), the aromatic polymer is selected from homopolymers or copolymers of aromatic compounds. Illustratively, the homopolymer is selected from one or more of polystyrene, polynaphthalene, polybiphenyl, polyanthracene, poly phenanthrene, poly perylene and poly pyrene. The copolymer may be a copolymer of two or more aromatic compounds, or a copolymer of at least one aromatic compound and another monomer selected from, for example, an olefin monomer, an acrylic acid (ester) monomer, and the like.
The conjugated large pi bond in the aromatic polymer and the dangling bond of silicon can form strong interaction, so that the structural stability of the composite material is further enhanced.
In the steps (6) and (7), the mass ratio c of the polystyrene to the powder 2 is in the range of 0.05-0.15.
In the step (9), the components are uniformly mixed through fusion treatment to form a compact structure, and the procedure is as follows: continuously stirring at 1000-1500 rpm for 10-30 min.
In the step (10), the temperature control program for the carbonization treatment is as follows: heating to 250-350 ℃ at a heating rate of 2-4 ℃/min, keeping for 1.5-2.5 h, heating to 600-900 ℃ at a heating rate of 1-3 ℃/min, and keeping for 2.5-5 h.
In the step (11), the ball milling treatment is to re-grind the partially agglomerated particles during the carbonization treatment, the ball milling treatment equipment comprises a vibration ball mill, a horizontal ball mill and a planetary ball mill, the particle size grading equipment comprises an air classifier, and the oversized particles refer to particles with the particle size larger than s, wherein the unit of s is mu m, and s is less than or equal to 25 mu m.
< negative electrode sheet >
As described above, the present invention provides a negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprising a silicon negative electrode active material selected from the silicon-based composite materials described above.
According to the present invention, the anode active material includes a carbon anode active material and a silicon anode active material selected from the above silicon-based composite materials.
According to the present invention, the carbon negative electrode active material and the silicon negative electrode active material are uniformly mixed and coated on the surface of the negative electrode current collector to form an active material layer.
According to the present invention, the carbon negative electrode active material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, and organic polymer compound carbon.
According to the present invention, the mass ratio of the carbon negative electrode active material to the silicon negative electrode active material (g: g): 80-99: 20-1; further (90-99): (10-1), for example, 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2, 99: 1.
According to the present invention, the carbon negative electrode active material is in the form of particles having a median particle diameter Dv50Is 11-18 μm, preferably 12-16 μm.
According to the present invention, the active material layer further contains a conductive agent and a binder.
According to the invention, the active material layer comprises the following components in percentage by mass: 75-99 wt% of negative electrode active material, 0.5-15 wt% of conductive agent and 0.5-10 wt% of binder.
According to the invention, the active material layer comprises the following components in percentage by mass: 80-98 wt% of negative electrode active material, 1-10 wt% of conductive agent and 1-10 wt% of binder.
According to the present invention, the conductive agent is at least one selected from carbon black, acetylene black, ketjen black, carbon fiber, single-walled carbon tube, and multi-walled carbon tube.
According to the invention, the binder is selected from at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polytetrafluoroethylene, polypropylene, styrene butadiene rubber and epoxy resin.
According to the invention, the negative electrode current collector is selected from at least one of copper foil, carbon-coated copper foil and punched copper foil.
According to the invention, the thickness of the active substance layer is from 30 μm to 150 μm, preferably from 30 μm to 80 μm.
According to the present invention, the length of the negative electrode sheet is not particularly limited, preferably 80cm to 170cm, and the width of the negative electrode sheet may be determined according to the width of the battery cell, and may be 10mm to 150mm, preferably 50mm to 100 mm.
< method for producing negative electrode sheet >
The invention also provides a preparation method of the negative plate, which comprises the following steps:
A1) preparing slurry for forming an active material layer;
A2) and coating the slurry for forming the active material layer on the surface of the negative current collector by using a coating machine to prepare the negative plate.
According to the present invention, in step a1), the solid content of the active material layer-forming slurry is 40 wt% to 45 wt%.
According to the present invention, in step a1), the active material layer-forming slurry includes deionized water, a carbon negative electrode active material, a silicon negative electrode active material, a conductive agent, and a binder.
According to the invention, step a2) comprises the following steps:
and coating the slurry for forming the active material layer on a negative current collector, drying at 80 ℃, slicing, transferring to a vacuum oven at 100 ℃ for drying for 12h, and finally rolling and cutting to obtain the negative plate.
< Battery >
As described above, the present invention provides a battery including the negative electrode sheet described above.
According to the present invention, the battery further comprises a positive electrode tab. The positive plate comprises a positive current collector and a positive active material layer coated on the surface of the positive current collector, wherein the positive active material layer comprises a positive material.
According to the invention, the current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil and perforated aluminum foil.
According to the invention, the positive electrode material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron silicate, lithium cobaltate, a nickel-cobalt-manganese ternary material, a nickel-manganese/cobalt-manganese/nickel-cobalt binary material, lithium manganate and a lithium-rich manganese-based material.
According to the present invention, the battery further comprises a separator. The diaphragm is selected from one or more of polyethylene or polypropylene.
According to the invention, the battery comprises an electrolyte. The electrolyte is a non-aqueous electrolyte, and the non-aqueous electrolyte comprises a solvent and a lithium salt. The solvent is selected from one or more of Ethylene Carbonate (EC), Propylene Carbonate (PC), Propyl Propionate (PP), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), 1, 3-Propanesultone (PS), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC). The lithium salt is selected from LiPF6、LiBF4、LiSbF6、LiClO4、LiCF3SO3、LiAlO4、LiAlCl4、Li(CF3SO2)2N, LiBOB and LiDFOB.
According to the invention, the battery further comprises an aluminum plastic film.
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
Example 1
The silicon-based composite material of example 1 was obtained using the following procedure:
(1) SiO silicon dioxide powder with the molar ratio a of 1.222And uniformly mixing with silicon powder Si to obtain a mixture 1.
(2) Placing the mixture 1 under a pressure of 5X 10-5And (4) reacting for 4 hours at the temperature of 1200 ℃ under MPa, and cooling to obtain a solid 1.
(3) Crushing the solid 1 by using a horizontal ball mill to obtain powder 1 with the maximum particle size Dmax of 60-100 mu m, wherein the crushing details are as follows: selecting a ball milling tank and ball milling beads made of stainless steel, wherein the diameter of each ball milling bead is 2 cm; the total filling volume of the solid 1 and the ball milling beads is 30 percent of that of the container, and the mass ratio of the solid 1 to the ball milling beads is 0.1; the rotation frequency of the ball milling tank is 200rpm, and the ball milling time is 8 h.
(4) Uniformly mixing the flake graphite with the powder 1 in a mass ratio b of 0.1 under an argon atmosphere to obtain a mixture 2.
(5) And (3) crushing the mixture 2 by using a vibration ball mill under an argon atmosphere to obtain powder 2 with the maximum particle size of 2-4 microns, wherein the details of the crushing treatment are as follows: selecting a stainless steel ball milling tank and ball milling beads, wherein the diameter of each ball milling bead is 0.3 cm; the total filling volume of the solid 1 and the ball milling beads is 25 percent of that of the container, and the mass ratio of the solid 1 to the ball milling beads is 0.2; the vibration frequency of the ball milling tank is 800rpm, and the ball milling time is 4 h.
(6) Adding polystyrene into toluene, and uniformly stirring to obtain a mixture 3, wherein the mass ratio c of the polystyrene to the toluene is 0.1.
(7) Powder 2 was added to mixture 3, wherein the mass ratio c of polystyrene to powder 2 was 0.1, and mechanically stirred for 4h, yielding mixture 4.
(8) The mixture 4 was dried at 80 ℃ to give powder 3.
(9) Powder 3 was added to a high speed fusion machine and stirred continuously at 1200rpm for 20min to give powder 4.
(10) Adding the powder 4 into a heating stirring kettle, introducing inert gas for protection, heating to 300 ℃ at the heating rate of 3 ℃/min at the rotation frequency of 150rpm, keeping for 2h, heating to 700 ℃ at the heating rate of 2 ℃/min, and keeping for 3h to obtain the powder 5.
(11) The powder 5 was ball milled using a vibratory ball mill, the details of which were as follows: selecting a stainless steel ball milling tank and ball milling beads, wherein the diameter of each ball milling bead is 0.3 cm; the total filling volume of the powder 5 and the ball milling beads is 25 percent of the container, and the mass ratio of the powder 5 to the ball milling beads is 0.3; the vibration frequency of the ball milling tank is 200rpm, and the ball milling time is 8 h. And then removing particles with the particle size of more than 20 mu m by using an airflow classifier to obtain the silicon-based composite material.
Examples 2 to 4 and comparative examples 1 to 10
The steps for synthesizing the silicon-based composite materials of examples 2 to 4 and comparative examples 1 to 10 are similar to example 1, except that:
in the step (4) of example 2, the mass ratio b of the flake graphite to the powder 1 was 0.05, and the purpose was to make the carbon content of example 2 lower than that of example 1.
In the step (4) of example 3, the mass ratio b of the flake graphite to the powder 1 was 0.18, and the purpose was to make the carbon content of example 2 lower than that of example 1.
In the step (5) of example 4, the vibration frequency of the ball mill pot was 1200rpm, and the purpose was to make the particle size of the silicon oxide of example 4 2 μm or less.
In step (11) of comparative example 1, particles having a particle size of more than 15 μm were removed using a gas flow classifier in order to make the median particle size Dv50 of the silicon-based composite material of comparative example 1 <5 μm.
In step (11) of comparative example 2, particles having a particle size of more than 30 μm were removed using a gas flow classifier in order to obtain a median particle size Dv50>10 μm for the silicon-based composite material of comparative example 2.
In step (1) of comparative example 3, the molar ratio a of silica powder to silicon powder is 0.43, and the purpose is to make the molar ratio y of the O element to the Si element of comparative example 3 < 0.8.
In the step (1) of comparative example 4, the molar ratio a of silica powder to silicon powder was 3.0, and the purpose was to make the molar ratio y of the O element to the Si element of comparative example 3 > 1.3.
In step (4) of comparative example 5, the mass ratio b of flake graphite to powder 1 was 0.02 for the purpose of making the carbon content n of comparative example 5 < 0.05.
In step (4) of comparative example 6, the mass ratio b of flake graphite to powder 1 was 0.25, for the purpose of making the carbon content n of comparative example 6 > 0.2.
In step (9) of comparative example 7, the rotation speed of the high-speed fusion machine was 200rpm, and the purpose was to reduce the dispersibility of silicon oxide A in comparative example 7.
In step (5) of comparative example 8, the vibration frequency of the ball mill pot was 400rpm, and the purpose was to increase the size of silicon oxide.
Steps (4) and (5) of comparative example 9 were both performed under an air atmosphere, and the purpose was to react the dangling bonds of the silicon oxide surface with oxygen in the air and prevent the formation of a chemical bonding action between the silicon oxide and the carbon coating.
In step (4) of comparative example 10, the mass ratio b of flake graphite to powder 1 was 0, and in step (6), the mass ratio c of polystyrene to toluene was 0.6, in order to reduce the structural order of the carbon coating.
Test example 1
The silicon-based composite materials prepared in the above examples and comparative examples were subjected to physical property parameter tests, the test procedures and methods are as follows, and the test results are shown in table 1-1.
For the median particle diameter Dv50 and the maximum particle diameter Dmax, the laser particle size test method was used. For example, the measurement is carried out using a Malvern particle size tester, the test procedure is as follows: dispersing a sample to be tested in deionized water containing a dispersing agent (such as nonylphenol polyoxyethylene ether with the content of 0.03 wt%) to form a mixture, carrying out ultrasonic treatment on the mixture for 2 minutes, and then placing the mixture into a particle size tester for testing.
For the BET specific surface area, the Brunauer-Emmett-Teller test method was used. For example, the measurement was performed using Tri Star II specific surface Analyzer.
For the molar ratio of the O element to the Si element, an energy spectrum (EDS) analysis method was employed. For example, the test is performed using an Oxford spectrometer.
For the carbon content n, thermogravimetric analysis was used. For example, the measurement is carried out by using a TGA550 thermogravimetric analyzer, during the measurement, an air atmosphere is introduced, the temperature is increased from room temperature to 800 ℃, the temperature rising rate is 10 ℃/min, and the maximum value of the mass loss ratio during the temperature rising process is taken as n.
For the size d of the silicon oxide particles and the distance h between the silicon oxide AAThe silicon-based composite material is cut by an ion grinding method, observed under a scanning electron microscope, and 20 particles are randomly selected for measurement.
For the EPR resonance signal, an electron paramagnetic resonance method is adopted for testing. For example, testing was performed using Bruker a200 electron paramagnetic resonance spectrometer.
For raman spectroscopy testing, the testing can be performed using a Thermo Fisher raman spectrometer.
TABLE 1-1 preparation parameters and physical Properties parameters of the silicon-based composites of examples 1 to 4 and comparative examples 1 to 10
Figure BDA0003469131480000151
As can be seen from Table 1-1, the comparison of examples 1-3 shows that the content of the carbon coating in the silicon-based composite material can be adjusted by adjusting the addition amount of the crystalline flake graphite.
In comparative example 1, Dv50<5μm，BET>8m2(ii)/g, does not satisfy the characteristic requirements of the application for particle size; in comparative example 2, Dv50>10 μm, which does not meet the characteristic requirements of the application on the particle size; in comparative example 3, y<0.8, the characteristic requirements of the application on the element content are not met; in comparative example 4, y>1.3, the characteristic requirements of the application on the element content are not met; in comparative example 5, n<0.05, the characteristic requirements of the application on the element content are not met; in comparative example 6, n>0.20, the characteristic requirements of the application on the element content are not met; in comparative example 7, hA-min<0.2 μm, which does not meet the characteristic requirements of the application on the distribution of silicon oxide; in comparative example 8, dmax>4 μm, which does not meet the characteristic requirements of the application on the particle size distribution of the silicon oxide particles; in comparative example 9, there is no EPR resonance signal and the characteristic requirements of the present application for the surface state of silicon oxide are not satisfied; in comparative example 10, I1/I2>0.5, does not meet the characteristics of the application on the ordered degree of the structure of the carbon coatingAnd (5) meeting requirements.
Test example 2
The silicon-based composites prepared in the above examples and comparative examples were subjected to the conductivity test, the test procedure is as follows, and the test results are shown in table 2.
The powder conductivity of the silicon-based composite material is obtained by testing with a four-probe resistivity tester, and the testing pressure is 38.2 MPa.
Test example 3
The button cell assembled by the silicon-based composite material is manufactured and tested by the following method:
(1) mixing the silicon-based composite material, Super P and polyacrylic acid according to the mass ratio of 85:6:9, adding deionized water, and uniformly mixing under the action of a vacuum stirrer to obtain negative electrode slurry;
(2) coating the negative electrode slurry obtained in the step (1) on a copper foil, drying in an oven at 80 ℃, and then transferring to a vacuum oven at 100 ℃ for drying for 12 hours to obtain the negative electrode slurry with the surface density of about 2.0mg/cm2The negative electrode sheet of (1);
(3) under a dry environment, the negative plate in the step (2) is arranged at about 1.3g/cm3Compacting, rolling, and then preparing a negative electrode wafer with the diameter of 12mm by using a sheet punching machine;
(4) in a glove box, the negative electrode wafer in the step (3) is taken as a working electrode, a metal lithium sheet is taken as a counter electrode, a polyethylene diaphragm with the thickness of 20 mu m is taken as an isolating membrane, and electrolyte is added to assemble a button type half cell;
(5) and (3) testing the button half cell in the step (4) by using a blue electricity (LAND) testing system, embedding lithium to 0.005V at a current of 0.1mA to obtain an embedded lithium capacity 1, standing for 10min, embedding lithium to 0.005V at a current of 0.05mA to obtain an embedded lithium capacity 2, standing for 10min, then removing lithium to 1.5V at a current of 0.1mA to obtain a first lithium removal capacity, wherein the sum of the embedded lithium capacity 1 and the embedded lithium capacity 2 is the first lithium insertion capacity, the gram capacity of the negative electrode material is obtained by dividing the first lithium removal capacity by the mass of the negative electrode material in the negative electrode wafer, and the first efficiency of the negative electrode material is obtained by dividing the first lithium removal capacity by the first lithium insertion capacity.
Table 2 results of performance tests of the silicon-based composites of examples and comparative examples and of the button half-cells assembled therewith
Figure BDA0003469131480000171
Taking the example 1 as a reference group, in the example 2, the carbon content is reduced, the conductivity is reduced, the gram volume is increased, and the first effect is reduced; in example 3, the carbon content is increased, the conductivity is improved, the gram volume is reduced, and the first effect is improved; in example 4, silicon oxide was reduced, conductivity was improved, and gram volume and first effect variation were small;
in comparative example 1, Dv50 decreased, conductivity increased, and gram volume and first effect variation were small; in comparative example 2, Dv50 increased, conductivity decreased, and gram volume and first effect variation were small; in comparative example 3, the oxygen content was reduced, and the conductivity, gram-volume and first-effect were improved; in comparative example 4, the oxygen content increased, the conductivity, the gram volume and the first effect decreased; in comparative example 5, the carbon content was reduced, the conductivity was reduced, the gram volume was increased, and the first effect was reduced; in comparative example 6, the carbon content was increased, the conductivity was increased, the gram volume was decreased, and the first effect was increased; in comparative example 7, hA-minThe reduction, the conductivity is reduced, and the gram volume and the first effect change are small; in comparative example 8, dmax>4 μm, reduced conductivity, small gram volume and small first effect change; in comparative example 9, the ball milling and coating were not protected by inert gas, and the conductivity, gram volume and first effect were reduced; in comparative example 10, all carbon coatings were from polystyrene pyrolysis, with reduced conductivity, gram volume and first efficiency.
In conclusion, the electric conductivity of the silicon-based composite material can be improved to a certain extent by means of flake graphite, reduction of the particle size of the silicon oxide, improvement of the dispersibility of the silicon oxide, construction of a chemical bonding effect between the silicon oxide and the carbon coating and the like. It is noted that, deviating from the condition limits of the present application, it is possible to obtain a higher conductivity, but not to meet the cycling stability requirements, as will be explained in more detail below.
Test example 4
The preparation steps of the negative electrode and the lithium ion battery assembled by the silicon-based composite material are as follows:
(1) mixing the silicon-based composite material, graphite, sodium carboxymethylcellulose, styrene butadiene rubber, Super P and single-walled carbon nanotubes according to the mass ratio of 9.5:86.0:1.5:2.0:0.9:0.1, adding deionized water, and obtaining the cathode slurry under the action of a vacuum stirrer. Uniformly coating the negative electrode slurry on a copper foil with the thickness of 8 mu m, wherein the surface density of the negative electrode slurry coated on the surface of a negative electrode current collector is 5.5mg/cm2. And transferring the copper foil to an oven at 80 ℃ for drying for 12h, and then rolling and slitting to obtain the negative plate.
(2) Mixing Lithium Cobaltate (LCO), polyvinylidene fluoride (PVDF), acetylene black and Carbon Nanotubes (CNTs) according to the mass ratio of 96:2:1.5:0.5, adding N-methyl pyrrolidone, and stirring under the action of a vacuum stirrer until uniform anode slurry is mixed. The positive electrode slurry was uniformly coated on an aluminum foil having a thickness of 12 μm. Baking the coated aluminum foil in an oven, then transferring the aluminum foil into an oven at 120 ℃ for drying for 8h, and then rolling and cutting the aluminum foil to obtain the required positive pole piece. The size of the positive plate is smaller than that of the negative plate, and the reversible capacity of the positive plate in unit area is 4% lower than that of the negative plate.
(3) A polyethylene separator with a thickness of 8 μm was used.
(4) The prepared positive plate, the diaphragm and the prepared negative plate are stacked in sequence, the diaphragm is positioned between the positive plate and the negative plate to play a role in isolation, and then the naked battery cell is obtained through winding. Placing the bare cell in an aluminum-plastic film shell, injecting electrolyte into the dried bare cell, and performing vacuum packaging, standing, formation, shaping, sorting and other processes to obtain the required lithium ion battery.
The lithium ion battery test steps are as follows:
(1) a blue electron (LAND) test system was used, with a test temperature of 25 ℃.
(2) The nominal capacity test was performed as follows: charging to 4.45V at constant current of 0.7C, charging to 0.05C at constant voltage, standing for 10min, and discharging to 3.0V at 0.5C, wherein the discharge capacity is taken as the nominal capacity.
(3) An initial rate charge test was performed, with the following steps: charging to 4.45V with 3C constant current to obtain charging capacity QC1Constant voltage charging to0.05C, charging capacity Q was obtainedC2Standing for 10 minutes, and discharging to 3.0V at 0.5C; with QC1/(QC1+QC2) The initial constant current rush-in ratio.
(4) The cycle test was performed as follows: charging to 4.45V at constant current of 3C, charging to 0.05C at constant voltage, standing for 10min, discharging to 3.0V at 0.5C, standing for 10min, and circulating for 300 weeks;
(5) and (3) carrying out a 300T multiplying power charging test, and comprising the following steps: charging to 4.45V with 3C constant current to obtain charging capacity QC1 ’Charging to 0.05C at constant voltage to obtain charging capacity QC2 ’Standing for 10 minutes, and discharging to 3.0V at 0.2C; with QC1 ’/(QC1 ’+QC2 ’) Constant current rush-in ratio at week 300.
(6) And (4) disassembling the battery in the 300 th week, observing whether the lithium analysis phenomenon exists in the negative pole piece, and estimating the proportion of the lithium analysis area in the whole negative pole piece area.
Table 3 results of performance test of lithium ion batteries assembled with silicon-based composite materials of examples and comparative examples
Figure BDA0003469131480000191
As can be seen from table 3 above, based on the 3C charging regime:
the initial constant current charge ratios of the lithium ion batteries of embodiments 1 to 4 are all greater than 61%, the constant current charge ratios in the 300 th week are all greater than 44%, and no obvious lithium separation phenomenon occurs after 300 weeks of circulation, which indicates that the lithium ion batteries assembled by selecting the silicon-based composite material have the advantages of small polarization effect, good rate circulation and low lithium separation risk.
The median particle diameter Dv50 of the comparative example 1 is too small, the specific surface area BET is too large, the surface side reactions are more, the electrolyte consumption speed is high, and the polarization effect is increased in the later period of circulation, so that the constant current charging ratio is less than 30% after 300 weeks of circulation, and the lithium precipitation phenomenon occurs; the median particle diameter Dv50 and the maximum particle diameter Dmax of the comparative example 2 are too large, and the diffusion path of the solid-phase lithium ions is large, so that the initial constant current charging ratio is lower than that of the example 1, the polarization is intensified after the circulation for 300 weeks, the constant current charging ratio is less than 30%, and the phenomenon of lithium precipitation occurs; in the comparative example 3, the molar ratio y of the O element to the Si element is less than 0.8, the oxygen content is too low, the silicon-based composite material is easy to crack in the continuous high-rate lithium intercalation cycle, an SEI film is additionally generated, and the polarization effect is intensified, so that the constant current charge ratio is less than 34% after the cycle is 300 weeks, and the lithium precipitation phenomenon occurs; in the comparative example 4, the molar ratio y of the O element to the Si element is more than 1.3, the content of the oxygen element is too high, the gram capacity of the silicon-based composite material is low, and the electron transmission impedance is increased, so the initial constant current charging ratio is lower, the constant current charging ratio is less than 30 percent after the circulation for 300 weeks, and the lithium precipitation phenomenon occurs; the carbon content n in the comparative example 5 is too low, so that the electronic conductivity of the silicon-based composite material is low, the initial constant current charging ratio is low, the constant current charging ratio is less than 30% after the circulation is carried out for 300 weeks, and the lithium separation phenomenon occurs; comparative example 6 has too high carbon content n, increased carbon defect density and increased irreversible reaction, so the constant current charging ratio is less than 36% after circulating for 300 weeks, and the phenomenon of lithium precipitation occurs; in the comparative example 7, the fusion treatment is insufficient in the material synthesis stage, so that partial silicon oxide particles with the particle size of 2-4 microns are aggregated together, the electron transmission path and resistance of the silicon-based composite material are increased, and the high-rate lithium intercalation capacity is reduced, so that the initial constant current charging ratio is low, the constant current charging ratio is less than 33% after the circulation is carried out for 300 weeks, and the lithium precipitation phenomenon occurs; in the comparative example 8, the ball-milling tank has low vibration frequency and poor crushing effect in the material synthesis stage, the particle size of silicon oxide particles cannot be fully refined, the electron transmission path and resistance of the silicon-based composite material are increased, and the high-rate lithium intercalation capacity is reduced, so that the initial constant current charge ratio is lower, the constant current charge ratio is less than 32% after the circulation is carried out for 300 weeks, and the lithium precipitation phenomenon occurs; in the comparative example 9, inert gas is not used for protection in the material synthesis stage, dangling bonds on the surfaces of silicon oxide particles preferentially react with oxygen and moisture in the air, so that the silicon oxide particles and the carbon coating do not have a chemical bonding effect, the interface stability of the silicon-based composite material is poor, and the damage and repair quantity of an SEI film are increased, so that the constant current charging ratio is less than 30% after the circulation is carried out for 300 weeks, and a lithium precipitation phenomenon occurs; in the comparative example 10, the carbon coating of the silicon-based composite material has low structural order degree, high defect site density, increased electron and ion conduction resistance, increased side reactions in the electrolyte and poor high-rate lithium intercalation performance, so the initial constant current charging ratio is low, the constant current charging ratio is less than 30% after the circulation for 300 weeks, and the lithium precipitation phenomenon occurs.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A composite material comprising silicon oxide particles and a carbon coating;
the size d of the silicon oxide particles is less than or equal to 4 mu m;
the composite material has a secondary particle structure;
the composite material has a Raman shift of 1300-1400cm in a Raman spectrum test-1、1550-1650cm-1The region having an intensity of I1、I2And 0.1. ltoreq.I1/I2<0.5；
The composite material has a resonance signal in an Electron Paramagnetic Resonance (EPR) test.
2. The composite material of claim 1, wherein the composite material has a secondary particle structure comprising a plurality of silicon oxide particles and a carbon coating.
3. The composite material according to claim 1 or 2, characterized in that the silicon oxide particles have a primary particle structure;
and/or the chemical formula of the silicon oxide particles is SiOx，0≤x≤2。
4. The composite material according to claim 1 or 2, characterized in that the median particle diameter Dv50 of the composite material satisfies 5 μ ι η ≦ Dv50 ≦ 10 μ ι η;
and/or the maximum particle size Dmax of the composite material satisfies Dmax <25 μm;
and/or the specific surface area BET of the composite material satisfies 2m2/g≤BET≤8m2/g；
And/or the composite material contains O element and Si element, and the molar ratio y of the O element to the Si element is more than or equal to 0.8 and less than or equal to 1.3.
5. The composite material according to claim 1 or 2, characterized in that the content n of the carbon coating in the composite material satisfies 5% ≦ n ≦ 20%.
6. The composite material according to claim 1 or 2, wherein the silicon oxide particles comprise silicon oxide A and silicon oxide B, wherein the size d of silicon oxide AAD is more than or equal to 2 mu mALess than or equal to 4 mu m, size d of silicon oxide BBSatisfy dB<2μm。
7. The composite material according to claim 6, characterized in that between adjacent silicon oxides A there are filled several silicon oxides B and/or carbon coatings.
8. Composite material according to claim 7, characterized in that the distance h between adjacent silicon oxides AASatisfy hA≥0.2μm。
9. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprising the composite material according to any one of claims 1 to 8.
10. A battery comprising the composite material of any one of claims 1-8 or comprising the negative electrode sheet of claim 9.
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