WO2025190035A1 - 一种二次电池和电子装置 - Google Patents

一种二次电池和电子装置

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Publication number
WO2025190035A1
WO2025190035A1 PCT/CN2025/077358 CN2025077358W WO2025190035A1 WO 2025190035 A1 WO2025190035 A1 WO 2025190035A1 CN 2025077358 W CN2025077358 W CN 2025077358W WO 2025190035 A1 WO2025190035 A1 WO 2025190035A1
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WO
WIPO (PCT)
Prior art keywords
silicon
secondary battery
line segment
material layer
carbon
Prior art date
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Pending
Application number
PCT/CN2025/077358
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English (en)
French (fr)
Inventor
周著人
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ningde Amperex Technology Ltd
Original Assignee
Ningde Amperex Technology Ltd
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Publication date
Application filed by Ningde Amperex Technology Ltd filed Critical Ningde Amperex Technology Ltd
Publication of WO2025190035A1 publication Critical patent/WO2025190035A1/zh
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • 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
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device.
  • Secondary batteries such as lithium-ion batteries, boast high theoretical specific capacity and superior safety, and have gradually become the primary power source for the 3C (computer, communications, and consumer electronics) and power (EV) sectors.
  • the positive, negative, and electrolyte components of lithium-ion batteries significantly impact their performance, making continuous optimization and improvement of these materials crucial to further optimize secondary battery performance.
  • the purpose of this application is to provide a secondary battery and an electronic device to improve the fast charging capability and cycle performance of the secondary battery.
  • lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries.
  • the specific technical solutions are as follows:
  • a first aspect of the present application provides a secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a first material layer and a second material layer disposed on the negative electrode current collector, the second material layer being located on a surface of the first material layer, the first material layer comprising graphite, the second material layer comprising the graphite and a silicon-carbon composite material, the silicon-carbon composite material comprising a porous carbon matrix, silicon grains located in pores of the porous carbon matrix, and a carbon material located on a surface of the porous carbon matrix;
  • the length of the first line segment is a ⁇ m
  • the length of the second line segment is b ⁇ m
  • the silicon-carbon composite material has fewer edges and corners, the decomposition of the electrolyte is reduced, and the cycle performance and fast charging capability of the secondary battery are improved; at the same time, two layers of material are provided on the surface of the negative electrode current collector, thereby further improving the fast charging capability of the secondary battery.
  • the average particle size of the silicon grains is 0.5 nm to 8 nm.
  • the thickness of the carbon material is 0.5 nm to 100 nm.
  • the silicon-carbon composite material is less susceptible to breakage during the delithiation and insertion processes, reducing electrolyte consumption, thereby improving the cycle performance and fast charging capability of the secondary battery.
  • the average pore size of the porous carbon matrix is between 0.1 nm and 10 nm.
  • space can be provided for the silicon grains to accommodate and expand, improving the expansion problem of the silicon material and thereby enhancing the cycling performance of the secondary battery. This also ensures the efficient transmission of lithium ions and improves the fast-charging capability of the secondary battery.
  • the secondary battery satisfies at least one of the following:
  • the average particle size of the silicon grains is 0.8 nm to 6 nm;
  • the thickness of the carbon material is 1 nm to 50 nm;
  • the average pore size of the porous carbon matrix is 0.1 nm to 8 nm.
  • the secondary battery satisfies at least one of the above characteristics, and its cycle performance and fast charging capability are improved.
  • the silicon-carbon composite material further includes a silicon material located on the surface of the porous carbon matrix.
  • the mass percentage of silicon is 40% to 60% based on the mass of the silicon-carbon composite material.
  • the silicon-carbon composite material has a higher specific capacity, which is conducive to obtaining a secondary battery with higher energy density and first efficiency; at the same time, the problem of silicon material expansion is weakened, which is conducive to improving the cycle performance of the secondary battery.
  • the average particle size Dv50 of the silicon-carbon composite material is 4 ⁇ m to 12 ⁇ m.
  • the silicon-carbon composite material has a suitable particle size and specific surface area, a suitable lithium ion diffusion path, and the resulting secondary battery has good charge and discharge kinetics.
  • the thickness of the first material layer is H1
  • the thickness of the second material layer is H2, and 0.2 ⁇ H1/H2 ⁇ 3.
  • the graphite is artificial graphite, having a Dv50 of 4 ⁇ m to 20 ⁇ m and a specific surface area of 0.6 m 2 /g to 2.5 m 2 /g.
  • the artificial graphite has a suitable particle size and specific surface area, good fast charging capability, and low electrolyte consumption, thereby achieving a better balance between the fast charging capability, cycling performance, and expansion performance of the secondary battery.
  • a second aspect of the present application provides an electronic device comprising the secondary battery according to any one of the aforementioned embodiments.
  • the present application provides a secondary battery and an electronic device.
  • the secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector, and a first material layer and a second material layer disposed on the negative electrode current collector, the second material layer being located on the surface of the first material layer, the first material layer including graphite, the second material layer including graphite and a silicon-carbon composite material, the silicon-carbon composite material including a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon material located on the surface of the porous carbon matrix.
  • the longest line segment between any two points of the outer contour of the silicon-carbon composite material particle is the first line segment
  • the line segment intersecting the midpoint of the first line segment is the second line segment
  • the second line segment is the shortest line segment between the two points intersecting the outer contour of the silicon-carbon composite material particle.
  • the length of the first line segment is a ⁇ m
  • the length of the second line segment is b ⁇ m
  • the silicon-carbon composite material has fewer edges and corners, the decomposition of the electrolyte is reduced, and the cycle performance and fast charging capability of the secondary battery are improved; at the same time, two layers of material are provided on the surface of the negative electrode current collector, thereby further improving the fast charging capability of the secondary battery.
  • FIG1 is an electron microscope photograph of a cross section along the thickness direction of the negative electrode sheet prepared in Example 1.
  • lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.
  • silicon-carbon materials are used in lithium-ion secondary batteries. Silicon-carbon materials are often mixed with graphite as the negative electrode active material. Due to the poor electronic and ionic conductivity of silicon materials, the electrode impedance increases, which reduces the fast-charging capability of the secondary battery. Silicon-carbon materials are often synthesized by vapor deposition, and crushed porous carbon materials are often used as the deposition base during the synthesis process. However, the crushed porous carbon material particles have more angular structures. Due to the existence of the tip discharge effect, more electrolyte decomposition occurs at the angular positions, and more solid electrolyte interface film (SEI film) is generated at the negative electrode, resulting in poor cycle performance and fast-charging capability of the secondary battery.
  • SEI film solid electrolyte interface film
  • the present application provides a secondary battery and an electronic device to improve the fast charging capability and cycle performance of a secondary battery containing silicon-carbon materials.
  • the first aspect of the present application provides a secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a first material layer and a second material layer disposed on the negative electrode current collector, the second material layer being located on the surface of the first material layer, the first material layer comprising graphite, the second material layer comprising graphite and a silicon-carbon composite material, the silicon-carbon composite material comprising a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon material located on the surface of the porous carbon matrix.
  • the longest line segment between any two points of the outer contour of the silicon-carbon composite material particle is the first line segment
  • the line segment intersecting with the midpoint of the first line segment is the second line segment
  • the second line segment is the shortest line segment between the two points intersecting with the outer contour of the silicon-carbon composite material particle.
  • the length of the first line segment is a ⁇ m
  • the length of the second line segment is b ⁇ m
  • b/a ⁇ 0.6 In some embodiments of the present application, 0.6 ⁇ b/a ⁇ 1.
  • the value of b/a can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 or a range consisting of any two values therebetween.
  • the silicon-carbon composite material has more edges and corners, and more electrolyte decomposition occurs at the edges and corners, and more solid electrolyte interface films are produced at the negative electrode, affecting the cycle performance and fast charging capability of the secondary battery.
  • the silicon-carbon composite material has fewer edges and corners, the decomposition of the electrolyte is reduced, and the cycle performance and fast charging capability of the secondary battery are improved; at the same time, two material layers are provided on the surface of the negative electrode current collector, and the silicon-carbon material is concentrated in the second material layer.
  • the fast charging capability of a secondary battery refers to the charging capability of a secondary battery with a charging rate greater than or equal to 3C.
  • a can be 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, 21 ⁇ m, 22 ⁇ m, 23 ⁇ m, 24 ⁇ m, 25 ⁇ m, 26 ⁇ m, 27 ⁇ m, 28 ⁇ m, 29 ⁇ m, 30 ⁇ m, or a range consisting of any two values therebetween.
  • b can be 1.2 ⁇ m, 1.5 ⁇ m, 1.8 ⁇ m, 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, 21 ⁇ m, 22 ⁇ m, 23 ⁇ m, 24 ⁇ m, 25 ⁇ m, 26 ⁇ m, 27 ⁇ m, 28 ⁇ m, 29 ⁇ m, 30 ⁇ m or a range consisting of any two values therebetween.
  • the average particle size D of the silicon grains is 0.5nm to 8nm. In some embodiments of the present application, the average particle size D of the silicon grains is 0.8nm to 6nm.
  • the average particle size D of the silicon grains can be 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm or a range consisting of any two values therebetween.
  • the silicon grains are in the pores of the porous carbon matrix.
  • the silicon-carbon composite material has good lithium removal and lithium insertion capabilities, which is beneficial to improving the energy density of the secondary battery; at the same time, the expansion performance of the silicon material can be alleviated, reducing the problem of rupture of the porous carbon matrix caused by silicon expansion, reducing the decomposition of the electrolyte, and improving the cycle performance and fast charging capability of the secondary battery.
  • the thickness h1 of the carbon material is 0.5nm to 100nm. In some embodiments of the present application, the thickness h1 of the carbon material is 1nm to 50nm. In some embodiments of the present application, the thickness h1 of the carbon material is 20nm to 40nm.
  • the thickness h1 of the carbon material can be 0.5nm, 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm or a range consisting of any two values therebetween.
  • the carbon material is located on the surface of the porous carbon matrix.
  • the carbon material can be located on part of the surface of the porous carbon matrix or on the entire surface of the porous carbon matrix.
  • the thickness h1 of the carbon material is the average thickness of the carbon material on the surface of the porous carbon matrix.
  • the average pore size d of the porous carbon matrix is 0.1nm to 10nm. In some embodiments of the present application, the average pore size d of the porous carbon matrix is 0.1nm to 8nm.
  • the average pore size d of the porous carbon matrix can be 0.1nm, 0.2nm, 0.3nm, 0.4nm, 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm or a range consisting of any two values therebetween.
  • the average pore size d of the porous carbon matrix By regulating the average pore size d of the porous carbon matrix within the above range, space can be provided for the silicon grains to accommodate and expand, thereby improving the expansion problem of the silicon material and thereby improving the cycle performance of the secondary battery; at the same time, the transmission efficiency of lithium ions is ensured and the fast charging capability of the secondary battery is improved.
  • the silicon-carbon composite material further comprises a silicon material located on the surface of the porous carbon matrix.
  • the silicon material may be located on a portion of the surface of the porous carbon matrix.
  • the silicon material and the carbon material may be located on the surface of the porous carbon matrix at the same time, or at least a portion of the carbon material may cover the silicon material.
  • the carbon material may cover a portion of the silicon material or the entire silicon material.
  • the thickness h2 of the silicon material is 0.1nm to 20nm. In some embodiments of the present application, the thickness h2 of the carbon material is 0.5nm to 10nm.
  • the thickness h2 of the silicon material can be 0.1nm, 0.3nm, 0.5nm, 0.7nm, 1nm, 5nm, 10nm, 15nm, 20nm or a range consisting of any two values therebetween.
  • the surface of the porous carbon matrix is provided with a silicon material, which can reduce the direct contact between the electrolyte and the silicon grains, reduce the consumption of the electrolyte, and thus improve the cycle performance and fast charging performance of the secondary battery.
  • the thickness h2 of the silicon material is the average thickness of the silicon material on the surface of the porous carbon matrix.
  • the mass percentage W1 of the silicon element is 40% to 60%.
  • the mass percentage W1 of the silicon element can be 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60% or a range consisting of any two values therebetween.
  • the mass percentage content W2 of the carbon element is 39% to 59%.
  • the mass percentage content W2 of the carbon element can be 39%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 59%, or a range consisting of any two values therebetween.
  • the silicon-carbon composite material further includes an oxygen element, and based on the mass of the silicon-carbon composite material, the mass percentage content W3 of the oxygen element is 0.1% to 5%.
  • the mass percentage content W3 of the oxygen element can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two values therebetween.
  • the average particle size Dv50 of the silicon-carbon composite material is 4 ⁇ m to 12 ⁇ m.
  • the average particle size Dv50 of the silicon-carbon composite material can be 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, or a range consisting of any two values therebetween.
  • the silicon-carbon composite material has a suitable particle size and specific surface area, a suitable lithium ion diffusion path, and the resulting secondary battery has good charge and discharge dynamics.
  • the preparation method of the silicon-carbon composite material may include but is not limited to the following steps:
  • the phenolic resin can be a monodisperse spherical phenolic resin.
  • the present application has no special restrictions on the particle size of the spherical phenolic resin, as long as the purpose of the present application can be achieved.
  • the Dv50 of the spherical phenolic resin can be 5 ⁇ m to 20 ⁇ m.
  • the porous carbon substrate is placed in a fluidized bed chemical vapor deposition furnace, and a first heat preservation treatment is performed under the protection of an inert atmosphere, and then silane gas is introduced for deposition treatment to obtain a silicon-carbon material intermediate; wherein, the temperature T3 of the first heat preservation treatment is 400°C to 550°C, the time t3 is 15min to 60min, the heating rate V3 is 3°C/min to 10°C/min, the time t4 of the deposition treatment is 3h to 5h, and the flow rate V4 of the silane gas is 2L/min to 5L/min.
  • inert gas is continuously introduced for a second insulation treatment, and then acetylene gas is introduced for a coating treatment to obtain a silicon-carbon composite material; wherein, the temperature T5 of the second insulation treatment is 500°C to 600°C, the time t5 is 15min to 60min, the heating rate V5 is 1°C/min to 5°C/min, the coating treatment time t6 is 3h to 5h, and the flow rate V6 of the silane gas is 0.5L/min to 1.5L/min.
  • the inert gas in steps (1) to (3) above may include, but is not limited to, at least one of nitrogen, argon or helium.
  • step (2') may be included between step (2) and step (3): placing the silicon-carbon material intermediate in a ball mill for ball milling, and then classifying; wherein the ball milling speed R is 30 rpm to 50 rpm, and the time t7 is 10 min to 60 min.
  • the thickness of the first material layer is H1
  • the thickness of the second material layer is H2
  • 0.3 ⁇ H1/H2 ⁇ 2.5 the value of H1/H2 can be 0.2, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 or a range consisting of any two values therebetween.
  • the coating weight of the first material layer and the second material layer can be controlled to be within a reasonable range, which can not only give play to the high dynamic characteristics of the first material layer, but also give play to the high capacity characteristics of the second material layer, so that the secondary battery has high energy density and high fast charging capability.
  • H1 can be 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, 75 ⁇ m, or a range consisting of any two values therebetween.
  • H2 can be 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, 75 ⁇ m, or a range consisting of any two values therebetween.
  • the graphite is artificial graphite
  • the artificial graphite has a Dv50 of 4 ⁇ m to 20 ⁇ m and a BET specific surface area of 0.6 m 2 /g to 2.5 m 2 /g.
  • the Dv50 of the artificial graphite can be 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, or a range consisting of any two values therebetween.
  • the BET specific surface area of the artificial graphite can be 0.6 m2 /g, 0.7 m2 /g, 0.8 m2 /g, 0.9 m2/g, 1 m2 /g, 1.1 m2 /g, 1.2 m2 / g , 1.3 m2 /g, 1.4 m2 /g, 1.5 m2 /g, 1.6 m2 / g, 1.7 m2/g, 1.8 m2 /g, 1.9 m2/g, 2 m2/g, 2.1 m2/g, 2.2 m2/g, 2.3 m2 /g, 2.4 m2/g, 2.5 m2 /g, or a range consisting of any two values therebetween.
  • the artificial graphite By regulating the average particle size Dv50 and specific surface area BET of silicon artificial graphite within the above range, the artificial graphite has a suitable particle size and specific surface area, good fast charging capability and low electrolyte consumption, which can better balance the fast charging capability, cycle performance and expansion performance of the secondary battery.
  • the time required for the secondary battery to be charged from 3.0V constant current constant voltage to 4.5V at 4C rate at 25 ⁇ 1°C is the charging time T, and 15min ⁇ T ⁇ 60min. This shows that the secondary battery of the present application has good fast charging capability.
  • the expansion rate of the thickness of the negative electrode plate compared to that before the cycle is w, 10% ⁇ w ⁇ 100%. This indicates that the expansion rate of the negative electrode plate after the cycle is low, and the secondary battery of the present application has good expansion performance.
  • 3.4C step charge and 0.5C discharge are: at a test temperature of 25°C, the lithium-ion battery is allowed to stand for 5 minutes, the lithium-ion battery is constant-current charged to 4.25V at a current of 3.4C, then charged to 4.4V at 2C, then charged to 4.50V at 1C, and then charged at a constant voltage of 4.50V until the current is reduced to 0.025C, allowed to stand for 5 minutes, and then discharged to 3.0V at a constant current of 0.5C, and allowed to stand for 5 minutes.
  • spherical phenolic resins of different Dv50 values can be purchased and selected based on the "Dv50 Test” provided herein.
  • Graphites of different Dv50 values and specific surface areas can be purchased and selected based on the "Dv50 Test” and "Specific Surface Area BET Test” provided herein.
  • the present application has no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application.
  • it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector.
  • the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.
  • the present application has no particular restrictions on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application.
  • the thickness of the negative electrode current collector is 4 ⁇ m to 12 ⁇ m.
  • the first material layer and the second material layer each independently contain a conductive agent and a binder.
  • the present application has no particular restrictions on the conductive agent, as long as the purpose of the present application can be achieved.
  • the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and the conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black.
  • the above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and/or multi-walled carbon nanotubes.
  • the above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and/or nano-carbon fibers.
  • the above-mentioned metal materials may include but are not limited to metal powder and/or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver.
  • the above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.
  • the present application has no particular limitation on the binder, as long as the purpose of the present application can be achieved.
  • the binder may include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride.
  • the secondary battery also includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector.
  • a positive electrode sheet which includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector.
  • the above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector” means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction.
  • the "surface” here can be the entire area of the positive electrode current collector surface or a partial area of the positive electrode current collector surface. This application is not particularly limited, as long as the purpose of this application can be achieved.
  • the positive electrode material layer includes a positive electrode active material.
  • the present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved.
  • the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide ( LiCoO2 ), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.
  • the positive electrode material layer may further include a conductive agent and a binder.
  • a conductive agent and a binder This application does not particularly limit the types of the conductive agent and binder, as long as the purpose of this application can be achieved. For example, it can be at least one of the above-mentioned conductive agents and binders.
  • This application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.
  • the thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in this application, as long as the purpose of this application can be achieved.
  • the thickness of the positive electrode current collector is 6 ⁇ m to 15 ⁇ m
  • the thickness of the positive electrode material layer is 30 ⁇ m to 120 ⁇ m.
  • the positive electrode sheet may further include a conductive layer positioned between the positive electrode current collector and the positive electrode material layer.
  • the composition of the conductive layer is not particularly limited and may be any commonly used conductive layer in the art.
  • the conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer; for example, the conductive layer may be at least one of the aforementioned conductive agents and binders.
  • the secondary battery also includes a separator.
  • the present application has no particular restrictions on the separator, as long as the purpose of the present application can be achieved.
  • the material of the separator may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid.
  • the type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.
  • the separator may include a substrate layer and a surface treatment layer.
  • the substrate layer may be a non-woven fabric, a film, or a composite film having a porous structure
  • the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide.
  • a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.
  • a surface treatment layer is provided on at least one surface of the substrate layer.
  • the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.
  • the inorganic layer includes inorganic particles and a binder.
  • the application is not particularly limited to inorganic particles.
  • inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate.
  • the application is not particularly limited to the binder.
  • the binder can be at least one of the above-mentioned binders.
  • the polymer layer includes polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).
  • the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the present application does not particularly limit the lithium salt, as long as the objectives of the present application can be achieved.
  • the lithium salt may include, but is not limited to, at least one of LiPF6 , LiBF4 , LiAsF6 , LiClO4 , LiB ( C6H5 ) 4 , LiCH3SO3 , LiCF3SO3 , LiN( SO2CF3 ) 2 , LiC( SO2CF3 ) 3 , Li2SiF6 , lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate.
  • the present application does not particularly limit the content of the lithium salt in the electrolyte, as long as the objectives of the present application can be achieved.
  • the present application has no particular limitation on the non-aqueous solvent, as long as the purpose of the present application can be achieved.
  • the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.
  • Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.
  • Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC).
  • Above-mentioned cyclic carbonate can include but not limited to at least one in ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC).
  • the fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.
  • FEC fluoroethylene carbonate
  • the above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, decanoic acid lactone, valerolactone, or caprolactone.
  • the above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran.
  • the above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.
  • the present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.
  • the secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries.
  • This application does not limit the above-mentioned other components.
  • This application does not particularly limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application.
  • the shell can be a hard shell or a flexible shell.
  • the material of the hard shell can be metal.
  • a metal hard shell known in the art can be used, as long as it can achieve the purpose of this application.
  • the flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.
  • the preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application.
  • the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery.
  • the second aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.
  • the present application does not particularly limit the type of electronic device, and the electronic device may be any electronic device known in the prior art.
  • electronic devices may include but are not limited to laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • the particle size distribution of the material was measured using a laser particle size analyzer (MasterSizer 2000).
  • Dv50 refers to the particle size at which 50% of the volume of the material is accumulated, measured from the smallest particle size.
  • the specific surface area of the material was obtained by testing the nitrogen adsorption-desorption curve of the material using a specific surface area tester (TriStar3020).
  • the material was tested by XRD using an X-ray powder diffractometer (POWDIX 600/300), and the peak near 28.5° was calculated using the Scherrer formula to obtain the size of the silicon grains.
  • the silicon-carbon material was heated to 500°C in a muffle furnace and then concentrated nitric acid was added for digestion. After dilution, the mass percentage of silicon was tested using an elemental analyzer.
  • the time required to charge a lithium-ion battery from 3.0V constant current and constant voltage to 4.5V at a 4C rate at 25 ⁇ 1°C is recorded as the charging time T, which is used to evaluate the fast charging capability of the lithium-ion battery.
  • T The larger T is, the worse the fast charging capability is, and the smaller T is, the better the fast charging capability is.
  • the lithium-ion battery to be tested was allowed to stand for 5 minutes, and the initial thickness of the lithium-ion battery, MMC0, was recorded.
  • the lithium-ion battery was constant-current charged to 4.25V at a current of 3.4C, then charged to 4.4V at 2C, then charged to 4.50V at 1C, and then charged to 0.05C at a constant voltage of 4.50V; after standing for 5 minutes, the battery was discharged at a constant current of 0.5C to 3.0V, and after standing for 5 minutes, the discharge capacity, C1, of the lithium-ion battery was recorded.
  • the discharge capacity, C1 of the lithium-ion battery was recorded.
  • the thickness, MMC1, and discharge capacity, C2, of the lithium-ion battery were recorded.
  • a monodisperse spherical phenolic resin (weight-average molecular weight of 900,000 g/mol) was placed in a rotary kiln, carbonized under a N2 atmosphere, and then cooled and activated by introducing carbon dioxide to obtain a porous carbon matrix; wherein, the carbonization temperature T1 was 950°C, the time t1 was 4 h, and the heating rate V1 was 5°C/min; the activation temperature T2 was 850°C, the time t2 was 9 h, and the carbon dioxide flow rate V2 was 2 L/min; the Dv50 of the spherical phenolic resin was 8.5 ⁇ m.
  • the porous carbon substrate is placed in a fluidized bed chemical vapor deposition furnace, and a first heat preservation treatment is performed under the protection of a N2 atmosphere, and then silane gas is introduced for deposition treatment to obtain a silicon-carbon material intermediate; wherein, the temperature T3 of the first heat preservation treatment is 475°C, the time t3 is 30min, the heating rate V3 is 5°C/min, the time t4 of the deposition treatment is 4h, and the flow rate V4 of the silane gas is 3L/min.
  • N2 gas is continuously introduced for a second insulation treatment, and then acetylene gas is introduced for a coating treatment to obtain a silicon-carbon composite material; wherein, the temperature T5 of the second insulation treatment is 525°C, the time t5 is 30 min, the heating rate V5 is 3°C/min, the coating treatment time t6 is 4 h, and the flow rate V6 of the silane gas is 1 L/min.
  • the negative electrode active material artificial graphite, the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose were mixed in a mass ratio of 98.4:1.0:0.6, and deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. After stirring evenly with a vacuum mixer, a first material layer slurry was obtained.
  • the first and second material layer slurries prepared above were evenly coated onto one surface of a 10 ⁇ m-thick negative electrode current collector copper foil using a double-layer coating machine and dried at 120°C. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with the first and second material layers. After drying at 120°C, the sheet was cold pressed, cut into pieces, and the tabs were welded to obtain a 78mm ⁇ 875mm negative electrode sheet ready for use.
  • the coating weight of the first material layer (CW1 ) was 49.4mg/1540.25mm2, and the coating weight of the second material layer (CW2 ) was 49.4mg/1540.25mm2.
  • the thickness of the first material layer (H1) was 42.2 ⁇ m
  • the thickness of the second material layer (H2) was 45.9 ⁇ m.
  • the ratio of CW1 : CW2 was 1:1, and H1/H2 was 0.92.
  • PVDF polyvinylidene fluoride
  • the polyvinylidene fluoride premix solution was composed of PVDF and NMP, and the carbon nanotube dispersion was composed of carbon nanotubes and NMP.
  • the positive electrode slurry was evenly coated on one surface of an 8 ⁇ m-thick aluminum foil for the positive electrode current collector and dried at 120°C to produce a single-sided positive electrode sheet with a coating weight of 260mg/ 1540.25mm2 .
  • the above steps were repeated on the other side of the aluminum foil to produce a double-sided positive electrode sheet. After drying at 120°C, the sheet was cold-pressed, cut, and welded to the tabs, resulting in a 74mm x 867mm positive electrode sheet ready for use.
  • the single-sided positive electrode material layer was 44 ⁇ m thick.
  • dimethyl carbonate, diethyl carbonate, and ethylene carbonate are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then an electrolyte salt LiPF6 and vinylene carbonate are added to the organic solvent and mixed uniformly to obtain an electrolyte solution.
  • the electrolyte solution comprises 12.5% by mass of the electrolyte salt, 2% by mass of the vinylene carbonate, and the remainder being the organic solvent.
  • a 7- ⁇ m-thick polyethylene film served as the base layer of the diaphragm.
  • a 2- ⁇ m-thick alumina ceramic layer was coated on one surface of the base layer and dried to produce the diaphragm.
  • the alumina ceramic layer consisted of aluminum oxide and polyvinylidene fluoride in a mass ratio of 1:9.
  • the positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator positioned between the positive and negative electrodes to act as a separator, and the alumina ceramic layer facing the positive electrode sheet.
  • the electrode assembly is then wound to form an electrode assembly.
  • the electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and injected with the electrolyte prepared above.
  • the lithium-ion battery is produced through vacuum packaging, standing, formation, capacity measurement, degassing, and trimming.
  • the upper formation voltage limit is 4.15V
  • the formation temperature is 70°C
  • the formation standing time is 2 hours.
  • step (1) the Dv50 of the spherical phenolic resin in step (1) is 12 ⁇ m, and after step (2) is completed, the following step (2') is performed, and then step (3) is performed.
  • the silicon-carbon material intermediate is placed in a ball mill for ball milling and then classified; wherein the ball milling speed R is 40 rpm, the time t7 is 10 min, and the Dv50 after classification is 8.5 ⁇ m.
  • Example 2 Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 2.
  • Example 1 Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.
  • the process was the same as in Example 1 except that the porous carbon matrix was replaced with a biomass-based porous carbon material (manufacturer: Kuraray Co., Ltd., brand: YP-50F) in the preparation of the silicon-carbon composite material.
  • a biomass-based porous carbon material manufactured by Kuraray Co., Ltd., brand: YP-50F
  • the average particle size D of the silicon grains in the silicon-carbon composite material, the thickness h1 of the carbon material, the average pore size d of the porous carbon matrix, the mass percentage W1 of the silicon element, and the average particle size Dv50 of the silicon-carbon composite material vary with changes in the preparation parameters, thereby affecting the fast charging capability and cycle performance of the lithium-ion battery. It can be seen from Examples 1 to 20 that when the above parameters of the silicon-carbon composite material are within the range of this application, the lithium-ion battery has a shorter full charge time, a higher capacity retention rate, and a lower thickness expansion rate, indicating that the lithium-ion battery has good fast charging capability and cycle performance.
  • H1/H2 usually affects the fast charging capability and cycle performance of the lithium-ion battery. It can be seen from Examples 1 to 20 that when the value of H1/H2 is within the range of this application, the lithium-ion battery has a shorter full charging time, a higher capacity retention rate and a lower thickness expansion rate, indicating that the lithium-ion battery has good fast charging capability and cycle performance.
  • FIG1 is an electron microscope photograph of a cross section of the negative electrode sheet prepared in Example 1 along the thickness direction.
  • the round particles in the figure are silicon-carbon composite materials, and their a value and b value are close, and b/a is 0.92.

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Abstract

本申请提供了一种二次电池和电子装置，二次电池包括负极极片，负极极片包括负极集流体以及设置在负极集流体上的第一材料层和第二材料层，第二材料层位于第一材料层的表面，第一材料层包括石墨，第二材料层包括石墨和硅碳复合材料，硅碳复合材料包括多孔碳基体、位于多孔碳基体孔隙中的硅晶粒以及位于多孔碳基体表面的碳材料。在负极极片截面的电镜照片中，硅碳复合材料颗粒的外轮廓任意两点之间的最长线段为第一线段，与第一线段中点相交的线段为第二线段，且第二线段为与硅碳复合材料颗粒的外轮廓相交的两点之间的最短线段。第一线段的长度为aμm，第二线段的长度为bμm，b/a≥0.6。本申请二次电池的循环性能和快充能力得到提高。

Description

一种二次电池和电子装置
本申请要求于2024年3月15日提交中国专利局、申请号为202410302086.7、发明名称为“一种二次电池和电子装置”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电化学技术领域，特别是涉及一种二次电池和电子装置。
背景技术
二次电池，如锂离子电池，其具有理论比容量高、安全性能高等特点，已逐渐成为3C领域(电脑、通信、消费电子类产品领域)及动力领域(EV领域)的主要动力来源。其中，正极活性材料、负极活性材料、电解液作为锂离子电池的重要组成部分对其性能有着显著的影响，因而对正极活性材料、负极活性材料、电解液的不断优化及改进易进一步优化二次电池的性能显得尤为重要。
近年来，随着近年来电动汽车和可移动电子设备的高速发展，市场对锂离子电池提出了低成本、高性能等更高的要求，但二次电池的快充能力仍有待改善。
发明内容
本申请的目的在于提供一种二次电池和电子装置，以提高二次电池的快充能力和循环性能。
需要说明的是，本申请的发明内容中，以锂离子电池作为二次电池的例子来解释本申请，但是本申请的二次电池并不仅限于锂离子电池。具体技术方案如下：
本申请的第一方面提供了一种二次电池，其包括负极极片，负极极片包括负极集流体以及设置在所述负极集流体上的第一材料层和第二材料层，第二材料层位于第一材料层的表面，第一材料层包括石墨，第二材料层包括所述石墨和硅碳复合材料，硅碳复合材料包括多孔碳基体、位于多孔碳基体孔隙中的硅晶粒以及位于多孔碳基体表面的碳材料；
在所述负极极片截面的电镜照片中，硅碳复合材料颗粒的外轮廓任意两点之间的最长线段为第一线段，与第一线段中点相交的线段为第二线段，且第二线段为与所述硅碳复合材料颗粒的外轮廓相交的两点之间的最短线段；
第一线段的长度为aμm，第二线段的长度为bμm，b/a≥0.6。
通过调控b/a的值在上述范围内，硅碳复合材料的棱角较少，电解液的分解减少，二次电池的循环性能和快充能力得到提高；同时负极集流体表面设置有两层材料层，从而进一步提高二次电池的快充能力。
在本申请的一些实施方案中，硅晶粒的平均粒径为0.5nm至8nm。通过调控硅晶粒的平均粒径D在上述范围内，有利于提升二次电池的能量密度，同时电解液的分解减少，二次电池的循环性能和快充能力得到提高。
在本申请的一些实施方案中，碳材料的厚度为0.5nm至100nm。通过调控碳材料的厚度h1在上述范围内，硅碳复合材料在脱锂和嵌锂过程中不易破碎，降低了电解液的消耗，从而二次电池的循环性能和快充能力得到提高。
在本申请的一些实施方案中，多孔碳基体的平均孔径为0.1nm至10nm。通过调控多孔碳基体的平均孔径d在上述范围内，可以为硅晶粒提供容纳和膨胀的空间，改善硅材料的膨胀问题，进而提高二次电池的循环性能；同时保证锂离子的传输效率，提高二次电池的快充能力。
在本申请的一些实施方案中，所述二次电池满足如下至少一者：
(1)所述硅晶粒的平均粒径为0.8nm至6nm；
(2)所述碳材料的厚度为1nm至50nm；
(3)所述多孔碳基体的平均孔径为0.1nm至8nm。
二次电池满足以上特征中的至少一者，其循环性能和快充能力得到提高。
在本申请的一些实施方案中，硅碳复合材料还包括位于多孔碳基体表面的硅材料。
在本申请的一些实施方案中，基于硅碳复合材料的质量，硅元素的质量百分含量为40％至60％。通过调控硅元素的质量百分含量W1在上述范围内，硅碳复合材料具有较高的克容量，有利于得到能量密度和首效较高的二次电池；同时弱化了硅材料膨胀的问题，有利于提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合材料的平均粒径Dv50为4μm至12μm。通过调控硅碳复合材料的平均粒径Dv50在上述范围内，硅碳复合材料具有合适的粒径和比表面积，锂离子扩散路径合适，得到的二次电池具有良好的充放电动力学。
在本申请的一些实施方案中，第一材料层的厚度为H1，第二材料层的厚度为H2，0.2≤H1/H2≤3。通过调控H1/H2的值在上述范围内，可以控制第一材料层和第二材料层涂布重量处于合理范围内，既可以发挥第一材料层中的高动力学特征，也可以发挥第二材料层中的高容量特征，使得二次电池具备高的能量密度以及高快充能力。
在本申请的一些实施方案中，0.3≤H1/H2≤2.5。
在本申请的一些实施方案中，所述石墨为人造石墨，人造石墨的Dv50为4μm至20μm、比表面积为0.6m2/g至2.5m2/g。通过调控硅人造石墨的平均粒径Dv50和比表面积BET在上述范围内，人造石墨具有合适的粒径和比表面积，快充能力良好且电解液消耗量较低，能够更好地平衡二次电池的快充能力、循环性能和膨胀性能。
本申请的第二方面提供了一种电子装置，其包括前述任一实施方案中的二次电池。
本申请的有益效果：
本申请提供了一种二次电池和电子装置，二次电池包括负极极片，负极极片包括负极集流体以及设置在负极集流体上的第一材料层和第二材料层，第二材料层位于第一材料层的表面，第一材料层包括石墨，第二材料层包括石墨和硅碳复合材料，硅碳复合材料包括多孔碳基体、位于多孔碳基体孔隙中的硅晶粒以及位于多孔碳基体表面的碳材料。在负极极片截面的电镜照片中，硅碳复合材料颗粒的外轮廓任意两点之间的最长线段为第一线段，与第一线段中点相交的线段为第二线段，且第二线段为与硅碳复合材料颗粒的外轮廓相交的两点之间的最短线段。第一线段的长度为aμm，第二线段的长度为bμm，b/a≥0.6。通过调控b/a的值在上述范围内，硅碳复合材料的棱角较少，电解液的分解减少，二次电池的循环性能和快充能力得到提高；同时负极集流体表面设置有两层材料层，从而进一步提高二次电池的快充能力。
当然，实施本申请的任一产品或方法并不一定需要同时达到以上所述的所有优点。
附图说明
此处所说明的附图用来提供对本申请的进一步理解，构成本申请的一部分，本申请的示意性实施例及其说明用于解释本申请，并不构成对本申请的不当限定。
图1为实施例1中制得的负极极片的沿厚度方向的横截面的电镜照片。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。本领域技术人员基于本申请所获得的所有其他实施例，都属于本申请保护的范围。
需要说明的是，本申请的具体实施方式中，以锂离子电池作为二次电池的例子来解释本申请，但是本申请的二次电池并不仅限于锂离子电池。
目前，硅碳材料应用于锂离子二次电池中，硅碳材料多与石墨混合作为负极活性材料，由于硅材料较差的电子与离子导电性，会造成极片阻抗增大，使得二次电池的快充能力下降。硅碳材料多采用气相沉积法合成，合成过程中多使用破碎后的多孔碳材料作为沉积基，然而，破碎后的多孔碳材料颗粒存在较多的棱角结构，由于尖端放电效应的存在，会导致在棱角位置出现更多的电解液分解，进而在负极产生更多的固态电解质界面膜(SEI膜)，导致二次电池循环性能和快充能力变差。
有鉴于此，本申请提供了一种二次电池和电子装置，以提高包含硅碳材料的二次电池的快充能力和循环性能。
本申请的第一方面提供了一种二次电池，其包括负极极片，负极极片包括负极集流体以及设置在负极集流体上的第一材料层和第二材料层，第二材料层位于第一材料层的表面，第一材料层包括石墨，第二材料层包括石墨和硅碳复合材料，硅碳复合材料包括多孔碳基体、位于多孔碳基体孔隙中的硅晶粒以及位于多孔碳基体表面的碳材料。在负极极片截面的电镜照片中，硅碳复合材料颗粒的外轮廓任意两点之间的最长线段为第一线段，与第一线段中点相交的线段为第二线段，且第二线段为与硅碳复合材料颗粒的外轮廓相交的两点之间的最短线段。第一线段的长度为aμm，第二线段的长度为bμm，b/a≥0.6。在本申请的一些实施方案中，0.6≤b/a≤1。例如，b/a的值可以为0.6、0.65、0.7、0.75、0.8、0.85、0.9、0.95、1或为其间任意两个数值组成的范围。当b/a的值过小，例如小于0.6时，硅碳复合材料的棱角较多，且在棱角位置出现更多的电解液分解，在负极产生更多的固态电解质界面膜，影响二次电池的循环性能和快充能力。通过调控b/a的值在上述范围内，硅碳复合材料的棱角较少，电解液的分解减少，二次电池的循环性能和快充能力得到提高；同时负极集流体表面设置有两层材料层，将硅碳材料集中在第二材料层，一方面避免硅碳材料对第一材料层动力学的影响，另一方面也可以大幅减薄第二材料层的厚度，缩短极片表面锂离子向极片内部的扩散路径，提高极片动力学，从而进一步提高二次电池的快充能力。在本申请中，二次电池的快充能力是指二次电池充电倍率大于或等于3C的充电能力。
在本申请的一些实施方案中，2μm≤a≤30μm，1.2μm≤b≤30μm。例如，a可以为2μm、3μm、4μm、5μm、6μm、7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm、21μm、22μm、23μm、24μm、25μm、26μm、27μm、28μm、29μm、30μm或为其间任意两个数值组成的范围。例如，b可以为1.2μm、1.5μm、1.8μm、2μm、3μm、4μm、5μm、6μm、7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm、21μm、22μm、23μm、24μm、25μm、26μm、27μm、28μm、29μm、30μm或为其间任意两个数值组成的范围。
在本申请的一些实施方案中，硅晶粒的平均粒径D为0.5nm至8nm。在本申请的一些实施方案中，硅晶粒的平均粒径D为0.8nm至6nm。例如，硅晶粒的平均粒径D可以为0.5nm、0.6nm、0.7nm、0.8nm、0.9nm、1nm、2nm、3nm、4nm、5nm、6nm、7nm、8nm或为其间任意两个数值组成的范围。硅晶粒在多孔碳基体的孔隙中，通过调控硅晶粒的平均粒径D在上述范围内，硅碳复合材料的脱锂和嵌锂能力好，有利于提升二次电池的能量密度；同时硅材料的膨胀性能能够得到缓解，降低了多孔碳基体由于硅膨胀引起的破裂问题，电解液的分解减少，二次电池的循环性能和快充能力得到提高。
在本申请的一些实施方案中，碳材料的厚度h1为0.5nm至100nm。在本申请的一些实施方案中，碳材料的厚度h1为1nm至50nm。在本申请的一些实施方案中，碳材料的厚度h1为20nm至40nm。例如，碳材料的厚度h1可以为0.5nm、1nm、5nm、10nm、15nm、20nm、25nm、30nm、35nm、40nm、45nm、50nm、60nm、70nm、80nm、90nm、100nm或为其间任意两个数值组成的范围。碳材料位于多孔碳基体的表面，可以理解的是，碳材料可以位于多孔碳基体的部分表面，也可以位于多孔碳基体的全部表面。通过调控碳材料的厚度h1在上述范围内，硅碳复合材料在脱锂和嵌锂过程中不易破碎，降低了电解液的消耗，从而二次电池的循环性能和快充能力得到提高。在本申请中，碳材料的厚度h1为碳材料在多孔碳基体表面的平均厚度。
在本申请的一些实施方案中，多孔碳基体的平均孔径d为0.1nm至10nm。在本申请的一些实施方案中，多孔碳基体的平均孔径d为0.1nm至8nm。例如，多孔碳基体的平均孔径d可以为0.1nm、0.2nm、0.3nm、0.4nm、0.5nm、0.6nm、0.7nm、0.8nm、0.9nm、1nm、2nm、3nm、4nm、5nm、6nm、7nm、8nm、9nm、10nm或为其间任意两个数值组成的范围。通过调控多孔碳基体的平均孔径d在上述范围内，可以为硅晶粒提供容纳和膨胀的空间，改善硅材料的膨胀问题，进而提高二次电池的循环性能；同时保证锂离子的传输效率，提高二次电池的快充能力。
在本申请的一些实施方案中，硅碳复合材料还包括位于多孔碳基体表面的硅材料。硅材料可以位于多孔碳基体的部分表面。当硅材料位于多孔碳基体的部分表面，硅材料和碳材料可以同时位于多孔碳基体的表面，也可以是至少部分碳材料覆盖硅材料。当硅材料位于多孔碳基体的全部表面，碳材料可以覆盖部分硅材料，也可以覆盖全部硅材料。
在本申请的一些实施方案中，硅材料的厚度h2为0.1nm至20nm。在本申请的一些实施方案中，碳材料的厚度h2为0.5nm至10nm。例如，硅材料的厚度h2可以为0.1nm、0.3nm、0.5nm、0.7nm、1nm、5nm、10nm、15nm、20nm或为其间任意两个数值组成的范围。多孔碳基体表面设置有硅材料，能够减少电解液与硅晶粒的直接接触，降低电解液的消耗，从而提高二次电池的循环性能和快充能力性能。在本申请中，硅材料的厚度h2为硅材料在多孔碳基体表面的平均厚度。
在本申请的一些实施方案中，基于硅碳复合材料的质量，硅元素的质量百分含量W1为40％至60％。例如，硅元素的质量百分含量W1可以为40％、42％、45％、48％、50％、52％、55％、58％、60％或为其间任意两个数值组成的范围。通过调控硅元素的质量百分含量W1在上述范围内，硅碳复合材料具有较高的克容量，有利于得到能量密度和首效较高的二次电池；同时弱化了硅材料膨胀的问题，有利于提高二次电池的循环性能。
在本申请的一些实施方案中，基于硅碳复合材料的质量，碳元素的质量百分含量W2为39％至59％。例如，碳元素的质量百分含量W2可以为39％、40％、42％、45％、48％、50％、52％、55％、58％、59％或为其间任意两个数值组成的范围。在本申请的一些实施方案中，硅碳复合材料还包括氧元素，基于硅碳复合材料的质量，氧元素的质量百分含量W3为0.1％至5％。例如，氧元素的质量百分含量W3可以为0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％、1％、1.5％、2％、2.5％、3％、3.5％、4％、4.5％、5％或为其间任意两个数值组成的范围。
在本申请的一些实施方案中，硅碳复合材料的平均粒径Dv50为4μm至12μm。例如，硅碳复合材料的平均粒径Dv50可以为4μm、5μm、6μm、7μm、8μm、9μm、10μm、11μm、12μm或为其间任意两个数值组成的范围。通过调控硅碳复合材料的平均粒径Dv50在上述范围内，硅碳复合材料具有合适的粒径和比表面积，锂离子扩散路径合适，得到的二次电池具有良好的充放电动力学。
本申请对硅碳复合材料的制备方法没有特别限制，只要能实现本申请的目的即可，例如，硅碳复合材料的制备方法可以包括但不限于以下步骤：
(1)将酚醛树脂置于回转炉中，在惰性气氛下碳化处理，而后降温通入二氧化碳进行活化处理，得到多孔碳基体；其中，碳化处理的温度T1为900℃至1000℃、时间t1为3h至5h、升温速率V1为3℃/min至10℃/min，活化处理的温度T2为800℃至890℃、时间t2为6h至12h，二氧化碳的流速V2为1L/min至3L/min；酚醛树脂可以为单分散的球形酚醛树脂，本申请对球形酚醛树脂的粒径没有特别限制，只要能实现本申请的目的即可，例如，球形酚醛树脂的Dv50可以为5μm至20μm。
(2)将多孔碳基体置于流化床式化学气相沉积炉中，在惰性气氛保护下进行第一保温处理，然后通入硅烷气体进行沉积处理，得到硅碳材料中间体；其中，第一保温处理的温度T3为400℃至550℃、时间t3为15min至60min、升温速率V3为3℃/min至10℃/min，沉积处理的时间t4为3h至5h，硅烷气体的流速V4为2L/min至5L/min。
(3)在流化床式化学气相沉积炉中，继续通入惰性气体进行第二保温处理，然后通入乙炔气体进行包覆处理得到硅碳复合材料；其中，第二保温处理的温度T5为500℃至600℃、时间t5为15min至60min、升温速率V5为1℃/min至5℃/min，包覆处理的时间t6为3h至5h，硅烷气体的流速V6为0.5L/min至1.5L/min。
上述步骤(1)至(3)中的惰性气体可以包括但不限于氮气、氩气或氦气中的至少一种。
可选地，在步骤(2)和步骤(3)之间还可以包括步骤(2’)：将硅碳材料中间体置于球磨机中进行球磨处理，然后分级；其中，球磨处理的转速R为30rpm至50rpm、时间t7为10min至60min。
在本申请的一些实施方案中，第一材料层的厚度为H1，第二材料层的厚度为H2，0.2≤H1/H2≤3。在本申请的一些实施方案中，0.3≤H1/H2≤2.5。例如，H1/H2的值可以为0.2、0.3、0.5、0.8、1、1.2、1.5、1.8、2、2.2、2.5、2.8、3或为其间任意两个数值组成的范围。通过调控H1/H2的值在上述范围内，可以控制第一材料层和第二材料层涂布重量处于合理范围内，既可以发挥第一材料层中的高动力学特征，也可以发挥第二材料层中的高容量特征，使得二次电池具备高的能量密度以及高快充能力。
在本申请的一些实施方案中，25μm≤H1≤75μm。在本申请的一些实施方案中，20μm≤H2≤70μm。例如，H1可以为25μm、30μm、35μm、40μm、45μm、50μm、55μm、60μm、65μm、70μm、75μm或为其间任意两个数值组成的范围。例如，H2可以为20μm、25μm、30μm、35μm、40μm、45μm、50μm、55μm、60μm、65μm、70μm、75μm或为其间任意两个数值组成的范围。
在本申请的一些实施方案中，石墨为人造石墨，人造石墨的Dv50为4μm至20μm、比表面积BET为0.6m2/g至2.5m2/g。例如，人造石墨的Dv50可以为4μm、5μm、6μm、7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm或为其间任意两个数值组成的范围。例如，人造石墨的比表面积BET可以为0.6m2/g、0.7m2/g、0.8m2/g、0.9m2/g、1m2/g、1.1m2/g、1.2m2/g、1.3m2/g、1.4m2/g、1.5m2/g、1.6m2/g、1.7m2/g、1.8m2/g、1.9m2/g、2m2/g、2.1m2/g、2.2m2/g、2.3m2/g、2.4m2/g、2.5m2/g或为其间任意两个数值组成的范围。通过调控硅人造石墨的平均粒径Dv50和比表面积BET在上述范围内，人造石墨具有合适的粒径和比表面积，快充能力良好且电解液消耗量较低，能够更好地平衡二次电池的快充能力、循环性能和膨胀性能。
在本申请的一些实施方案中，二次电池在25±1℃下以4C倍率从3.0V恒流恒压充电至4.5V所需的时间为充电时间T，15min≤T≤60min。从而说明本申请的二次电池具有良好的快充能力。
在本申请的一些实施方案中，二次电池在25±1℃，采用3.4C阶充0.5C放电的充放电循环测试中，循环圈数大于或等于400圈时，负极极片厚度相较于循环前的膨胀率为w，10％≤w≤100％。从而说明负极极片经循环后的膨胀率较低，本申请的二次电池具有良好的膨胀性能。上述“3.4C阶充0.5C放电”的具体步骤为：在25℃测试温度下，将锂离子电池静置5min，以3.4C的电流将锂离子电池恒流充电至4.25V，再以2C充电至4.4V，再以1C充电至4.50V，然后再以4.50V的恒压充电至电流减小为0.025C，静置5min，再以0.5C的电流恒流放电至3.0V，静置5min。
在本申请中，不同Dv50的球形酚醛树脂可以通过购买得到，并结合本申请提供的“Dv50测试”选择所需的Dv50的球形酚醛树脂即可。不同Dv50和比表面积的石墨可以通过购买得到，并结合本申请提供的“Dv50测试”和“比表面积BET测试”选择所需的Dv50和比表面积的石墨即可。
本申请对负极集流体没有特别限制，只要能够实现本申请目的即可，例如，可以包含铜箔、铜合金箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或复合集流体，示例性地，复合集流体可以为锂铜复合集流体、碳铜复合集流体、镍铜复合集流体、钛铜复合集流体等。本申请对负极集流体的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极集流体的厚度为4μm至12μm。
在本申请的一些实施方案中，第一材料层和第二材料层各自独立地包含导电剂和粘结剂。本申请对导电剂没有特别限制，只要能够实现本申请目的即可，例如，导电剂可以包括但不限于导电炭黑(Super P)、碳纳米管(CNTs)、碳纤维、鳞片石墨、石墨烯、金属材料或导电聚合物中的至少一种，导电炭黑可以包括但不限于乙炔黑或科琴黑中的至少一种。上述碳纳米管可以包括但不限于单壁碳纳米管和/或多壁碳纳米管。上述碳纤维可以包括但不限于气相生长碳纤维(VGCF)和/或纳米碳纤维。上述金属材料可以包括但不限于金属粉和/或金属纤维，具体地，金属可以包括但不限于铜、镍、铝或银中的至少一种。上述导电聚合物可以包括但不限于聚亚苯基衍生物、聚苯胺、聚噻吩、聚乙炔或聚吡咯中的至少一种。本申请对粘结剂没有特别限制，只要能够实现本申请目的即可，例如，粘结剂可以包括但不限于聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、羧甲基纤维素、羧甲基纤维素钠、羧甲基纤维素锂、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶或聚偏二氟乙烯中的至少一种。
在本申请中，二次电池还包括正极极片，正极极片包括正极集流体以及设置于正极集流体至少一个表面上的正极材料层。上述“设置于正极集流体至少一个表面上的正极材料层”是指，正极材料层可以设置于正极集流体沿自身厚度方向上的一个表面上，也可以设置于正极集流体沿自身厚度方向上的两个表面上。需要说明，这里的“表面”可以是正极集流体表面的全部区域，也可以是正极集流体表面的部分区域，本申请没有特别限制，只要能实现本申请目的即可。
本申请对正极集流体没有特别限制，只要能够实现本申请目的即可，例如，可以包含铝箔、铝合金箔或复合集流体(例如铝碳复合集流体)等。
正极材料层包括正极活性材料，本申请对正极活性材料没有特别限制，只要能够实现本申请目的即可，例如，正极活性材料可以包含但不限于镍钴锰酸锂(例如NCM811、NCM622、NCM523、NCM111)、镍钴铝酸锂、磷酸铁锂、富锂锰基材料、钴酸锂(LiCoO2)、锰酸锂、磷酸锰铁锂或钛酸锂中的至少一种。
正极材料层还可以包括导电剂和粘结剂，本申请对导电剂和粘结剂的种类没有特别限制，只要能够实现本申请目的即可，例如，可以是上述导电剂和上述粘结剂中的至少一种。本申请对正极材料层中正极活性材料、导电剂、粘结剂的质量比没有特别限制，本领域技术人员可以根据实际需要选择，只要能够实现本申请目的即可。
本申请对正极集流体和正极材料层的厚度没有特别限制，只要能够实现本申请目的即可。例如，正极集流体的厚度为6μm至15μm，正极材料层的厚度为30μm至120μm。
任选地，正极极片还可以包含导电层，导电层位于正极集流体和正极材料层之间。导电层的组成没有特别限制，可以是本领域常用的导电层。导电层包括导电剂和粘结剂。本申请对导电层中的导电剂和粘结剂没有特别限制，例如，可以是上述导电剂和上述粘结剂中的至少一种。
在本申请中，二次电池还包括隔膜。本申请对隔膜没有特别限制，只要能够实现本申请目的即可。例如，隔膜的材料可以包括但不限于聚乙烯(PE)、聚丙烯(PP)为主的聚烯烃(PO)类、聚酯(例如，聚对苯二甲酸二乙酯(PET)膜)、纤维素、聚酰亚胺(PI)、聚酰胺(PA)、氨纶或芳纶中的至少一种。隔膜的类型可以包括织造膜、非织造膜、微孔膜、复合膜、碾压膜或纺丝膜中的至少一种。
在本申请的一些实施方案中，隔膜可以包括基材层和表面处理层。基材层可以为具有多孔结构的无纺布、膜或复合膜，基材层的材料可以包括聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯或聚酰亚胺中的至少一种。任选地，可以使用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
任选地，基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。
在本申请的一些实施方案中，无机物层包括无机颗粒和粘结剂。本申请对无机颗粒没有特别限制，例如无机颗粒可以包括氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙或硫酸钡中的至少一种。本申请对粘结剂没有特别限制，例如粘结剂可以是上述粘结剂中的至少一种。在本申请的一些实施方案中，聚合物层包括聚合物，聚合物的材料包括聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯吡咯烷酮、聚乙烯醚或聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)中的至少一种。
在本申请中，二次电池还包括电解液，电解液包括锂盐和非水溶剂。
本申请对锂盐没有特别限制，只要能实现本申请的目的即可。例如锂盐可以包括但不限于LiPF6、LiBF4、LiAsF6、LiClO4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiC(SO2CF3)3、Li2SiF6、双草酸硼酸锂(LiBOB)或二氟硼酸锂中的至少一种。本申请对锂盐在电解液中的含量没有特别限制，只要能实现本申请的目的即可。
本申请对非水溶剂没有特别限制，只要能实现本申请的目的即可，例如非水溶剂可以包括但不限于碳酸酯化合物、羧酸酯化合物、醚化合物或其它有机溶剂中的至少一种。
上述碳酸酯化合物可以包括但不限于链状碳酸酯化合物、环状碳酸酯化合物或氟代碳酸酯化合物中的至少一种。上述链状碳酸酯化合物可以包括但不限于碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)或碳酸甲乙酯(MEC)中的至少一种。上述环状碳酸酯可以包括但不限于碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)或碳酸乙烯基亚乙酯(VEC)中的至少一种。氟代碳酸酯化合物可以包括但不限于氟代碳酸乙烯酯(FEC)、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯或碳酸三氟甲基亚乙酯中的至少一种。上述羧酸酯化合物可以包括但不限于甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯或己内酯中的至少一种。上述醚化合物可以包括但不限于二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、1-乙氧基-1-甲氧基乙烷、2-甲基四氢呋喃或四氢呋喃中的至少一种。上述其它有机溶剂可以包括但不限于二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯或磷酸三辛酯中的至少一种。本申请对非水溶剂在电解液中的含量没有特别限制，只要能实现本申请的目的即可。
二次电池还包括壳体，用于容纳正极极片、隔膜、负极极片和电解液，以及二次电池领域中已知的其它部件，本申请对上述其它部件不做限定。本申请对壳体没有特别限制，可以为本领域公知的壳体，只要能够实现本申请目的即可。例如，壳体可以为硬壳壳体或柔性壳体。硬壳壳体的材料可以为金属，本申请对金属的种类不做限定，可以采用本领域已知的金属硬壳壳体，只要能实现本申请的目的即可。柔性壳体可以为金属塑膜，例如铝塑膜、钢塑膜等。
本申请的二次电池的制备过程为本领域技术人员所熟知的，本申请没有特别的限制，例如，二次电池的制备过程可以包括但不限于以下步骤：将正极极片、隔膜和负极极片按顺序堆叠，并根据需要将其卷绕、折叠等操作得到卷绕结构的电极组件，将电极组件放入壳体内，将电解液注入壳体并封口，得到二次电池。或者，将正极极片、隔膜和负极极片按顺序堆叠，然后用胶带将整个叠片结构的四个角固定好得到叠片结构的电极组件，将电极组件置入壳体内，将电解液注入壳体并封口，得到二次电池。此外，也可以根据需要将防过电流元件、导板等置于壳体中，从而防止二次电池内部的压力上升、过充放电。
本申请的第二方面提供了一种电子装置，其包括前述任一实施方案中的二次电池。从而，本申请提供的电子装置具有良好的使用性能。
本申请对电子装置的种类没有特别限定，其可以是用于现有技术中已知的任何电子装置。
在本申请的一些实施方案中，电子装置可以包括但不限于笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
实施例
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。另外，只要无特别说明，“份”、“％”为质量基准。
测试方法和设备：
Dv50测试：
通过激光粒度测试仪(MasterSizer 2000)测试材料的粒度分布。Dv50是指，在材料的体积基准的粒度分布中，从小粒径测起，到达体积累积50％的粒径。
比表面积BET测试：
通过比表面积测试仪(TriStar3020)测试材料的氮气吸脱附曲线得到材料的比表面积。
b/a的测试：
通过电子显微镜观察负极极片截面，在其电镜照片中，测量硅碳复合材料颗粒的外轮廓任意两点之间的最长线段记为第一线段，第一线段的长度为aμm，与第一线段中点相交的线段为第二线段，第二线段为与硅碳复合材料颗粒的外轮廓相交的两点之间的最短长度为bμm。测量50个颗粒，计算a和b的平均值，再计算得到b/a。
硅晶粒平均粒径D的测试：
通过X射线粉末衍射仪(POWDIX 600/300)对材料进行XRD测试，对28.5°附近的峰利用谢乐公式进行计算，即可得到硅晶粒的尺寸。
碳材料厚度h1和硅材料厚度h2的测试：
通过透射电子显微镜测试硅碳材料颗粒表面的碳材料厚度和硅材料厚度。
多孔碳基体平均孔径d的测试：
采用物理吸附仪(厂商：理化联科公司，型号：ipore 620)对样品孔结构进行测试：取0.15g样品于样品管内，先在200℃下脱气6h，再进行不同压力P下样品对氩气的吸附量的测试，从而绘制样品的等温吸附曲线，再利用NLDFT拟合计算样品的孔径分布，进而得到样品的平均孔径。其中，上述“不同压力P下”是指P/P0为0至1范围内对应的不同压力P，P0为氩气77K时的饱和蒸汽压。
硅元素的质量百分含量W1的测试：
通过元素分析仪，将硅碳材料于马弗炉中加热至500℃后加入浓硝酸进行消解，稀释后使用元素分析仪测试硅元素的质量百分含量。
能量密度测试：
将待测的锂离子电池静置5分钟，记录其初始厚度T0，初始高度G0，初始宽度K0，在25±1℃下以1C倍率从3.0V恒电流充电至4.5V，再恒电压充电至0.02C，静置5min后以0.2C倍率放电至3.0V，放电能量记为E0，能量密度即为ED＝E0/T0/G0/K0，能量密度的单位为Wh/L。
快充能力测试：
将锂离子电池在25±1℃下以4C倍率从3.0V恒流恒压充电至4.5V所需的时间记为充电时间T，用于评价锂离子电池的快充能力。T越大，则快充能力越差，T越小，快充能力越好。
循环性能和膨胀性能测试：
在25℃测试温度下，将待测的锂离子电池静置5min，记录锂离子电池的初始厚度MMC0。以3.4C的电流将锂离子电池恒流充电至4.25V，再以2C充电至4.4V，再以1C充电至4.50V，然后再以4.50V的恒压充电至0.05C；静置5min，再以0.5C的电流恒流放电至3.0V，静置5min，记录锂离子电池的放电容量C1。上述3C阶充/0.5C放电的充放电循环过程循环400次后，记录锂离子电池的厚度MMC1和放电容量C2。
400次循环容量保持率(％)＝C2/C1×100％。
400次循环膨胀率(％)＝(MMC1-MMC0)/MMC0×100％。
实施例1
<硅碳复合材料的制备>
(1)将单分散的球形酚醛树脂(重均分子量为900000g/mol)置于回转炉中，在N2气氛下碳化处理，而后降温通入二氧化碳进行活化处理，得到多孔碳基体；其中，碳化处理的温度T1为950℃、时间t1为4h、升温速率V1为5℃/min，活化处理的温度T2为850℃、时间t2为9h，二氧化碳的流速V2为2L/min；球形酚醛树脂的Dv50为8.5μm。
(2)将多孔碳基体置于流化床式化学气相沉积炉中，在N2气氛保护下进行第一保温处理，然后通入硅烷气体进行沉积处理，得到硅碳材料中间体；其中，第一保温处理的温度T3为475℃、时间t3为30min、升温速率V3为5℃/min，沉积处理的时间t4为4h，硅烷气体的流速V4为3L/min。
(3)在流化床式化学气相沉积炉中，继续通入N2气体进行第二保温处理，然后通入乙炔气体进行包覆处理得到硅碳复合材料；其中，第二保温处理的温度T5为525℃、时间t5为30min、升温速率V5为3℃/min，包覆处理的时间t6为4h，硅烷气体的流速V6为1L/min。
<负极极片的制备>
将负极活性材料人造石墨、粘结剂丁苯橡胶、分散剂羧甲基纤维素钠按照质量比98.4:1.0:0.6进行混合，加入去离子水作为溶剂，调配成为固含量为45wt％的浆料，真空搅拌机搅拌均匀后得到第一材料层浆料。
将人造石墨、上述制得的硅碳复合材料、聚丙烯酸、羧甲基纤维素锂、碳纳米管按照质量比A＝76:20:2.6:0.6:0.8进行混合，加入50％聚丙烯酸和去离子水至固含量为62％后捏合90min；再加入剩余50％聚丙烯酸和去离子水至固含量为42％后高速分散30min，加入去离子水至固含量为34％后继续分散40min，而后脱泡30min后即得到第二材料层浆料。
将上述制得的第一材料层浆料与第二材料层浆料使用双层涂布机均匀涂覆于厚度为10μm的负极集流体铜箔的一个表面上，120℃条件下烘干。然后在铜箔的另一个表面上重复以上步骤，即得到双面涂布第一材料层与第二材料层的负极极片。120℃条件下烘干后冷压，再经裁片、焊接极耳，得到规格为78mm×875mm的负极极片待用。其中，第一材料层的涂布重量为CW1为49.4mg/1540.25mm2，第二材料层的涂布重量为CW2为49.4mg/1540.25mm2，第一材料层的厚度H1为42.2μm，第二材料层的厚度H2为45.9μm，CW1:CW2＝1:1，H1/H2＝0.92。
<正极极片的制备>
将聚偏二氟乙烯(PVDF)预混溶液与导电炭黑混合搅拌均匀后再加入碳纳米管分散液均匀分散，加入钴酸锂并使用N-甲基吡咯烷酮(NMP)调节固含量为76％后高速分散40min，经脱泡后即得正极浆料，钴酸锂、PVDF、导电炭黑、碳纳米管的质量比B＝97.6:1.3:0.6:0.5。其中，聚偏二氟乙烯预混溶液由PVDF和NMP组成，碳纳米管分散液由碳纳米管和NMP组成。
将正极浆料均匀涂覆在厚度为8μm的正极集流体铝箔的一个表面上，120℃条件下烘干，得到单面涂布正极材料层的正极极片，涂布重量为260mg/1540.25mm2。然后在铝箔的另一个表面上重复以上步骤，即得到双面涂布正极材料层的正极极片。120℃条件下烘干后冷压，再经裁片、焊接极耳，得到规格为74mm×867mm的正极极片待用。其中，单面正极材料层的厚度为44μm。
<电解液的制备>
在含水量小于10ppm的环境下，将碳酸二甲酯、碳酸二乙酯、碳酸乙烯酯按照质量比为1:1:1混合得到有机溶剂，然后向有机溶剂中加入电解质盐LiPF6和碳酸亚乙烯酯，混合均匀，得到电解液。其中，基于电解液的质量，电解质盐的质量百分含量为12.5％，碳酸亚乙烯酯的质量百分含量为2％，其余为有机溶剂。
<隔膜>
以7μm厚的聚乙烯基膜作为隔膜的基材层。在基材层的一个表面上涂覆厚度为2μm的氧化铝陶瓷层，烘干得到隔膜。其中，氧化铝陶瓷层包含质量比为1:9的三氧化二铝和聚偏二氟乙烯。
<锂离子电池的制备>
将上述制备的正极极片、隔膜、负极极片按顺序叠好，使隔膜处于正极极片和负极极片中间起到隔离的作用，氧化铝陶瓷层朝向正极极片，卷绕得到电极组件。将电极组件装入铝塑膜包装袋中，并在80℃下脱去水分，注入上述制备得到的电解液，经过真空封装、静置、化成、容量、脱气、切边工序得到锂离子电池。其中，化成上限电压为4.15V，化成温度为70℃，化成静置时间为2h。
实施例2
除了在<硅碳复合材料的制备>中，在步骤(1)中球形酚醛树脂的Dv50为12μm，并且在步骤(2)完成还进行以下步骤(2’)，再进行步骤(3)以外，其余与实施例1相同。
(2’)将硅碳材料中间体置于球磨机中进行球磨处理，然后分级；其中，球磨处理的转速R为40rpm、时间t7为10min，分级后的Dv50为8.5μm。
实施例3
除了按照表1调整相关制备参数以外，其余与实施例2相同。
实施例4至实施例20
除了按照表1调整相关制备参数以外，其余与实施例1相同。
对比例1
除了在<负极极片的制备>中仅涂覆第二材料层浆料、第二材料层的厚度如表2所示以外以外，其余与实施例1相同。
对比例2
除了在<硅碳复合材料的制备>中，将多孔碳基体替换为生物质基多孔碳材料(厂商：株式会社可乐丽，牌号：YP-50F)制备硅碳复合材料以外，其余与实施例1相同。
各实施例和对比例的制备参数及性能测试如表1所示。

从实施例1至实施例20、对比例1和对比例2可以看出，当负极材料层包含第一材料层和第二材料层且硅碳复合材料b/a的值在本申请的范围内，锂离子电池具有更短的满充时间、更高的容量保持率和更低的厚度膨胀率，说明锂离子电池的快充能力和循环性能得到提升。
硅碳复合材料中硅晶粒的平均粒径D、碳材料的厚度h1、多孔碳基体的平均孔径d、硅元素的质量百分含量W1以及硅碳复合材料的平均粒径Dv50随制备参数的变化而变化，进而影响锂离子电池的快充能力和循环性能。从实施例1至实施例20可以看出，当硅碳复合材料的上述参数在本申请的范围内，锂离子电池具有较短的满充时间、较高的容量保持率和较低的厚度膨胀率，说明锂离子电池具有良好的快充能力和循环性能。
H1/H2的值通常会影响锂离子电池的快充能力和循环性能，从实施例1至实施例20可以看出，当H1/H2的值在本申请的范围内，锂离子电池具有较短的满充时间、较高的容量保持率和较低的厚度膨胀率，说明锂离子电池具有良好的快充能力和循环性能。
人造石墨Dv50和比表面积BET通常会影响锂离子电池的快充能力和循环性能，从实施例1、实施例17至实施例18可以看出，当人造石墨Dv50和比表面积BET在本申请的范围内，锂离子电池具有较短的满充时间、较高的容量保持率和较低的厚度膨胀率，说明锂离子电池具有良好的快充能力和循环性能。
具体地，图1为实施例1中制得的负极极片的沿厚度方向的横截面的电镜照片，图中类圆形的颗粒为硅碳复合材料，其a值和b值接近，b/a为0.92。
需要说明的是，在本文中，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法或物品不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法或物品所固有的要素。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (12)

  1. 一种二次电池，其包括负极极片，所述负极极片包括负极集流体以及设置在所述负极集流体上的第一材料层和第二材料层，所述第二材料层位于所述第一材料层的表面，所述第一材料层包括石墨，所述第二材料层包括所述石墨和硅碳复合材料，所述硅碳复合材料包括多孔碳基体、位于所述多孔碳基体孔隙中的硅晶粒以及位于所述多孔碳基体表面的碳材料；
    在所述负极极片截面的电镜照片中，所述硅碳复合材料颗粒的外轮廓任意两点之间的最长线段为第一线段，与所述第一线段中点相交的线段为第二线段，且所述第二线段为与所述硅碳复合材料颗粒的外轮廓相交的两点之间的最短线段；
    所述第一线段的长度为aμm，所述第二线段的长度为bμm，b/a≥0.6。
  2. 根据权利要求1所述的二次电池，其中，所述硅晶粒的平均粒径为0.5nm至8nm。
  3. 根据权利要求1所述的二次电池，其中，所述碳材料的厚度为0.5nm至100nm。
  4. 根据权利要求1所述的二次电池，其中，所述多孔碳基体的平均孔径为0.1nm至10nm。
  5. 根据权利要求1所述的二次电池，其中，所述二次电池满足如下至少一者：
    (1)所述硅晶粒的平均粒径为0.8nm至6nm；
    (2)所述碳材料的厚度为1nm至50nm；
    (3)所述多孔碳基体的平均孔径为0.1nm至8nm。
  6. 根据权利要求1至5中任一项所述的二次电池，其中，所述硅碳复合材料还包括位于所述多孔碳基体表面的硅材料。
  7. 根据权利要求1至5中任一项所述的二次电池，其中，基于所述硅碳复合材料的质量，硅元素的质量百分含量为40％至60％。
  8. 根据权利要求1至5中任一项所述的二次电池，其中，所述硅碳复合材料的平均粒径Dv50为4μm至12μm。
  9. 根据权利要求1至5中任一项所述的二次电池，其中，所述第一材料层的厚度为H1，所述第二材料层的厚度为H2，0.2≤H1/H2≤3。
  10. 根据权利要求9所述的二次电池，其中，0.3≤H1/H2≤2.5。
  11. 根据权利要求1至5中任一项所述的二次电池，其中，所述石墨包括人造石墨，所述人造石墨的平均粒径Dv50为4μm至20μm、比表面积为0.6m2/g至2.5m2/g。
  12. 一种电子装置，其包括权利要求1至11中任一项所述的二次电池。
PCT/CN2025/077358 2024-03-15 2025-02-14 一种二次电池和电子装置 Pending WO2025190035A1 (zh)

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