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WO2024007142A1 - 负极极片、二次电池、电池模块、电池包及用电装置 - Google Patents

负极极片、二次电池、电池模块、电池包及用电装置 Download PDF

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Publication number
WO2024007142A1
WO2024007142A1 PCT/CN2022/103809 CN2022103809W WO2024007142A1 WO 2024007142 A1 WO2024007142 A1 WO 2024007142A1 CN 2022103809 W CN2022103809 W CN 2022103809W WO 2024007142 A1 WO2024007142 A1 WO 2024007142A1
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Prior art keywords
negative electrode
film layer
active material
optionally
electrode film
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PCT/CN2022/103809
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English (en)
French (fr)
Inventor
游兴艳
吴益扬
白文龙
武宝珍
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2022/103809 priority Critical patent/WO2024007142A1/zh
Priority to JP2024523554A priority patent/JP2024539121A/ja
Priority to CN202280014144.5A priority patent/CN116982170A/zh
Priority to KR1020247012853A priority patent/KR20240060671A/ko
Priority to EP22949731.8A priority patent/EP4425602A1/en
Publication of WO2024007142A1 publication Critical patent/WO2024007142A1/zh
Priority to US18/679,475 priority patent/US20240322139A1/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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of 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
    • 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
    • H01M4/364—Composites as mixtures
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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

  • This application belongs to the field of battery technology, and specifically relates to a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device.
  • secondary batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.
  • energy storage power systems such as hydraulic, thermal, wind and solar power stations
  • people have higher and higher requirements for the energy density, cycle performance and high-rate charging performance of secondary batteries.
  • the performance of negative active materials is limited to a certain extent. Affects the performance of secondary batteries to a certain extent.
  • Graphite is one of the most commonly used anode active materials for secondary batteries. It has the advantages of small polarization and high cycle stability, but its theoretical gram capacity is only 372mAh/g.
  • the purpose of this application is to provide a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device, aiming to enable the secondary battery to have both high charging rate and long cycle on the premise of high energy density. life.
  • a first aspect of the present application provides a negative electrode sheet, including a negative electrode current collector and a first negative electrode film layer, a second negative electrode film layer and a functional coating sequentially disposed on at least one surface of the negative electrode current collector, wherein,
  • the functional coating includes a ferroelectric material;
  • the second negative electrode film layer includes a second negative electrode active material, and the second negative electrode active material includes hard carbon;
  • the first negative electrode film layer includes a first negative electrode active material, and the third negative electrode active material includes A negative active material includes graphite.
  • the first negative electrode film layer including graphite and the second negative electrode film layer including hard carbon are sequentially arranged on the surface of the negative electrode current collector for combined design, which can make up for the respective defects of graphite and hard carbon, and highlight the shortcomings of graphite and hard carbon. respective advantages.
  • the layer spacing of hard carbon is larger, which can provide a greater charging rate; graphite is placed between the hard carbon and the negative electrode current collector, which can compensate for the first Coulomb efficiency of the hard carbon.
  • the role of the hard carbon microporous structure as an active ion storage site cannot be fully utilized, and the invention of the present application People were surprised to find that providing a functional coating including ferroelectric materials on the surface of the negative electrode piece can solve the above problems.
  • Ferroelectric materials can regulate the deposition method of active ions, thereby highlighting the large-capacity advantage of the hard carbon microporous structure, and can also inhibit the continuous reduction and precipitation of active ions on the graphite surface, thereby improving the cycle life of secondary batteries. Therefore, the secondary battery using the negative electrode plate of the present application has a long cycle life and can be charged at a high rate. At the same time, the secondary battery can also have a high output voltage and thus a high energy density.
  • the thickness of the functional coating is H 1 ⁇ m
  • the thickness of the second negative electrode film layer is H 2 ⁇ m
  • the thickness of the first negative electrode film layer is H 3 ⁇ m
  • the negative electrode piece satisfies H 1 /(H 2 +H 3 ) from 0.01 to 0.15, optionally from 0.01 to 0.08.
  • the secondary battery has better overall performance and can achieve high-rate charging under high energy density.
  • the thickness of the functional coating is H 1 ⁇ m, and H 1 is 2 to 10, optionally 4 to 6.
  • H 1 is 2 to 10, optionally 4 to 6.
  • the thickness of the second negative electrode film layer is H 2 ⁇ m
  • the thickness of the first negative electrode film layer is H 3 ⁇ m
  • the negative electrode plate satisfies H 2 /H 3 as 0.10 to 5, optionally 0.5 to 4. Therefore, the second negative electrode film layer and the first negative electrode film layer can exert a better synergistic effect.
  • the volume average particle size Dv50 of the ferroelectric material is d 1 ⁇ m, and d 1 is 1 or less, optionally 0.05 to 0.8.
  • the secondary battery has better overall performance, can achieve high-rate charging under high energy density, and can reduce production costs at the same time.
  • the volume average particle size Dv50 of the second negative active material is d 2 ⁇ m
  • the volume average particle size Dv50 of the first negative active material is d 3 ⁇ m
  • d 2 /d 3 is 0.1 to 1, optionally 0.2 to 0.8.
  • the mass percentage of the ferroelectric material in the functional coating is W1. Based on the total mass of the functional coating, W1 is 70% to 95%, optionally 80% to 95%. As a result, the secondary battery has better overall performance and can achieve high-rate charging under high energy density.
  • the mass percentage of hard carbon in the second negative electrode film layer is W2, and based on the total mass of the second negative electrode film layer, W2 is more than 68%, optionally is 90% to 98%. This is advantageous for the secondary battery to have a higher charging rate.
  • the mass percentage of graphite in the first negative electrode film layer is W3. Based on the total mass of the first negative electrode film layer, W3 is more than 78%, optionally 90% to 98%. This is beneficial to the secondary battery having higher first Coulombic efficiency and longer cycle life.
  • the volume average particle diameter Dv50 of the second negative active material is d 2 ⁇ m, and d 2 is 3 to 11, optionally 3 to 7. This is beneficial to improving the capacity performance and energy density of the secondary battery.
  • the particle size distribution index (Dv90-Dv10)/Dv50 of the second negative active material is ⁇ 1 , and ⁇ 1 is 0.6 to 5, optionally 1 to 4. This is beneficial to improving the high-rate charging capability and charge-discharge efficiency of the secondary battery.
  • the second negative active material has a specific surface area of 3 m 2 /g to 7 m 2 /g, optionally 4 m 2 /g to 6 m 2 /g. This is beneficial to improving the high-rate charging capability of the secondary battery.
  • the second negative active material 20000N has a powder compacted density of 0.9g/cm 3 to 1.3g/cm 3 , optionally 1g/cm 3 to 1.2g/cm 3 . This is beneficial to improving the energy density of secondary batteries.
  • the second negative active material includes primary particles, secondary particles, or a combination thereof.
  • the number of primary particles in the second negative active material is 90% to 100%. %. This is beneficial to improving the high-rate charging capability of the secondary battery.
  • the volume average particle diameter Dv50 of the first negative active material is d 3 ⁇ m, and d 3 is 9 to 18, optionally 11 to 15. This is beneficial to secondary batteries with high first Coulombic efficiency, high energy density and long cycle life.
  • the particle size distribution index (Dv90-Dv10)/Dv50 of the first negative active material is ⁇ 2 , and ⁇ 2 is 0.2 to 5, optionally 0.3 to 4. This is beneficial to improving the cycle performance of the secondary battery.
  • the first negative active material has a specific surface area of 0.6m 2 /g to 1.5m 2 /g, optionally 0.8m 2 /g to 1.4m 2 /g. This is beneficial to improving the cycle performance of the secondary battery.
  • the powder compaction density of the first negative active material at 20000N is 1.4g/cm 3 to 1.85g/cm 3 , optionally 1.6g/cm 3 to 1.75g /cm 3 . This is beneficial to improving the energy density of secondary batteries.
  • the graphitization degree of the first negative active material is 91% to 95%, optionally 92% to 94%. This is beneficial to improving the cycle life of the secondary battery.
  • the first negative active material includes artificial graphite, natural graphite or a combination thereof, and optionally, the surface of the artificial graphite has a carbon coating layer. This is beneficial to improving the cycle performance and high-rate charging capability of the secondary battery.
  • the first negative active material includes primary particles, secondary particles or a combination thereof.
  • the number of secondary particles in the first negative active material is from 80% to 80%. 100%. This will help improve the cycle performance, storage performance and high-rate charging capability of secondary batteries.
  • the dielectric constant of the ferroelectric material is above 50, optionally between 50 and 100,000.
  • the ferroelectric material includes one or more combinations selected from inorganic ferroelectric materials and organic ferroelectric materials.
  • the inorganic ferroelectric material includes calcium One or a combination of titanite structure oxide, tungsten bronze type compound, bismuth oxide type layered structure compound, lithium niobate, lithium tantalate, lead metaniobate and lead barium lithium niobate; optional
  • the organic ferroelectric material may be selected from the group consisting of vinylidene fluoride homopolymer or copolymer, 2,5-dibromo-3,6-dihydroxyp-benzoquinone, phenazine-chloronic acid, and ketonic acid. one or a combination of more.
  • the functional coating further includes a binder and/or dispersant.
  • the binder includes styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, and polypropylene.
  • a second aspect of the present application provides a secondary battery, which includes the negative electrode plate of the first aspect of the present application.
  • a third aspect of the present application provides a battery module, which includes the secondary battery of the second aspect of the present application.
  • a fourth aspect of the present application provides a battery pack, which includes one of the secondary battery of the second aspect of the present application and the battery module of the third aspect of the present application.
  • a fifth aspect of the present application provides an electrical device, which includes at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect, and the battery pack of the fourth aspect of the present application.
  • the secondary battery using the negative electrode plate of the present application has a long cycle life and can be charged at a large rate. At the same time, the secondary battery can also have a high output voltage and thus a high energy density.
  • the battery module, battery pack and power-consuming device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.
  • Figure 1 is a schematic diagram of an embodiment of the negative electrode plate of the present application.
  • FIG. 2 is a schematic diagram of an embodiment of the secondary battery of the present application.
  • FIG. 3 is an exploded schematic view of the embodiment of the secondary battery of FIG. 2 .
  • FIG. 4 is a schematic diagram of an embodiment of the battery module of the present application.
  • FIG. 5 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 6 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of an embodiment of a power consumption device including the secondary battery of the present application as a power source.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) can be added to the method in any order.
  • the method can include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • primary particles refer to particles that are not in an agglomerated state
  • secondary particles refer to particles in an agglomerated state formed by the aggregation of two or more primary particles.
  • Primary particles and secondary particles can be easily distinguished by taking SEM images using a scanning electron microscope.
  • Hard carbon refers to carbon that is difficult to graphitize, and is difficult to graphitize even at high temperatures above 2500°C.
  • Hard carbon is usually obtained by pyrolysis of precursors such as polymers. During the pyrolysis process, the cross-linked structure of carbon atoms in the precursor hinders the growth of the carbon layer in the plane direction. Therefore, the hard carbon structure will contain a large amount of Microcrystals with disordered graphite-like structure (graphite crystallites for short).
  • the structure of hard carbon is complex. In addition to graphite microcrystals, it also contains defect structures (such as surface defects, lattice defects, etc.) and microporous structures (such as open pore structures, closed pore structures, etc.).
  • hard carbon has unique advantages. Compared with graphite, the hard carbon (002) crystal plane interlayer spacing is larger, so the hard carbon structure is more stable during the charge and discharge process, and there will be no obvious volume expansion and contraction effects.
  • Hard carbon has many defect structures, which will catalyze the decomposition of the electrolyte to form a thick solid electrolyte interface (SEI) film, increasing the irreversible loss of active ions.
  • SEI solid electrolyte interface
  • the surface of hard carbon has a loose porous structure, which can easily absorb moisture and oxygen in the air to form various C-H functional groups on the surface. These functional groups will react with active ions, further increasing the irreversible consumption of active ions. Therefore, compared with graphite, hard carbon has lower first Coulombic efficiency and poorer cycle performance. For example, the first Coulombic efficiency is usually lower than 80%, which cannot fully utilize its high capacity advantage.
  • the embodiment of the present application provides a negative electrode piece.
  • the negative electrode sheet of the present application includes a negative electrode current collector and a first negative electrode film layer, a second negative electrode film layer and a functional coating layer sequentially arranged on at least one surface of the negative electrode current collector, wherein the functional coating layer includes a ferroelectric material; the second negative electrode film layer includes a second negative electrode active material, the second negative electrode active material includes hard carbon; the first negative electrode film layer includes a first negative electrode active material, and the first negative electrode active material includes graphite .
  • Graphite has the advantages of high first Coulombic efficiency and high cycle stability, but its high-rate charging capability is limited; hard carbon has the advantage of high active ion insertion and extraction rates, so it has excellent high-rate charging capability, but its first Coulombic efficiency is low and its capacity is It decays quickly, resulting in poor performance of the secondary battery's actual capacity.
  • the inventor of the present application found that placing graphite and hard carbon sequentially on the surface of the negative electrode current collector for a two-layer combination design can compensate for the respective defects of graphite and hard carbon. Placing graphite close to the negative electrode current collector can compensate for the first Coulombic efficiency of hard carbon. Placing hard carbon far away from the negative electrode current collector can allow more active ions to embed into the negative electrode faster, thus improving the high-rate charging capability of the negative electrode plate and secondary battery. .
  • the inventor of the present application also found that the two-layer combination of graphite and hard carbon sequentially arranged on the surface of the negative electrode current collector is not ideal for improving the high-rate charging capability and energy density of the secondary battery.
  • the inventor found that the possible reason is that when the secondary battery is charged, especially at the end of charging, the formation of "dendrites" is an important factor affecting the high-rate charging capability and energy density improvement of the secondary battery.
  • dendrites not only reduces the performance of the secondary battery, such as shortening the cycle life, but in severe cases, it can form sharp shapes that pierce the isolation film and cause a short circuit in the battery, which may cause catastrophic consequences such as combustion and explosion, and increase the number of secondary batteries.
  • the safety risk of the battery in addition, the continuously deposited dendrites will fall off from the surface of the negative electrode, resulting in the loss of electrical contact with the negative electrode current collector, and thus it can no longer participate in the charge and discharge reactions and contribute capacity, which also reduces the energy density of the secondary battery.
  • hard carbon also has a rich microporous structure
  • active ions can also be stored in the microporous structure of hard carbon, providing additional active ion storage sites and improving The capacity play and first Coulomb efficiency of hard carbon; and the longer the discharge platform in the low potential platform area, the higher the reversible capacity of the corresponding hard carbon, and the better the capacity play.
  • the potential of the low-potential platform area of hard carbon is close to the dendrite formation potential of the graphite surface layer, both of which are about 0V.
  • the capacity of the low-potential platform area of hard carbon is limited, and the microporous structure of hard carbon cannot be fully used as a The role of active ion storage sites; at the same time, in order to prevent dendrite formation, the negative electrode cut-off voltage is usually set higher, which also leads to a reduction in the overall output voltage of the secondary battery, and in turn leads to a reduction in the energy density of the secondary battery. Therefore, the two-layer combination of graphite and hard carbon sequentially arranged on the surface of the negative electrode current collector has limited effect on improving the high-rate charging capability, energy density and/or cycle life of the secondary battery.
  • a first negative electrode film layer including graphite and a second negative electrode film layer including hard carbon are sequentially placed on the surface of the negative electrode current collector for a combined design, and a ferroelectric film layer including ferroelectric is also provided on the surface of the second negative electrode film layer.
  • Functional coating of materials. Ferroelectric materials have spontaneous polarization. When electrons accumulate on the surface of dendrites, the ferroelectric material will undergo spontaneous polarization under the influence of the electric field.
  • the positive charge center of the ferroelectric material moves to the electron accumulation area, thereby moving the electron accumulation area Wrapped in it; at the same time, because the positive charge center of the ferroelectric material is positively charged, the polarity of the positively charged active ions on the dendrite surface repels, which can balance the electron density and reduce the enrichment of active ions, thereby inhibiting
  • the dendrites continue to grow in the direction perpendicular to the pole piece.
  • the first negative electrode film layer including graphite and the second negative electrode film layer including hard carbon are sequentially arranged on the surface of the negative electrode current collector for a combined design that can compensate for the respective defects of graphite and hard carbon. and highlight their respective advantages.
  • the layer spacing of hard carbon is larger, which can provide a greater charging rate; graphite is placed between the hard carbon and the negative electrode current collector, which can compensate for the first Coulomb efficiency of the hard carbon.
  • the functional coating can accurately Regulating the overpotential allows the hard carbon microporous structure to store a large number of active ions, increase the length of the low potential plateau area, and increase the reversible capacity of the secondary battery, thus improving the high-rate charging capability and energy density of the secondary battery; in addition, at the overpotential Under the conditions, the functional coating can also generate a reverse electric field, reduce the enrichment of active ions, inhibit the continued growth of dendrites in the vertical direction of the pole piece, and improve the safety and cycle performance of secondary batteries.
  • the secondary battery using the negative electrode plate of the present application has a long cycle life and can be charged at a high rate.
  • the secondary battery can also have a high output voltage and thus a high energy density.
  • the dielectric constant of the ferroelectric material is above 50.
  • the higher the dielectric constant of the ferroelectric material the better it is at inhibiting the continued growth of dendrites in the direction perpendicular to the pole piece, but its effect will not continue to increase.
  • the higher the dielectric constant the greater the effect on ferroelectric material Material preparation process requirements are getting higher and higher, which also increases production costs.
  • the dielectric constant of the ferroelectric material may be 50 to 100,000, for example, 50 to 50,000, 50 to 25,000, 50 to 10,000, 50 to 5,000, 50 to 4,000, 50 to 3000, 50 to 2000, 100 to 100000, 100 to 50000, 100 to 25000, 100 to 10000, 100 to 5000, 100 to 4000, 100 to 3000, 100 to 2000, 200 to 100000, 200 to 50000, 200 to 25000, 200 to 10000, 200 to 5000, 200 to 4000, 200 to 3000, 200 to 2000 or 200 to 1000.
  • the dielectric constant of a ferroelectric material refers to the dielectric constant at room temperature (25 ⁇ 5°C), which has a well-known meaning in the art and can be tested using instruments and methods known in the art.
  • C represents the capacitance, in Farad (F);
  • d represents the sample thickness, in cm;
  • A represents the sample area, in cm 2 ;
  • the test conditions can be 1KHz, 1.0V, 25 ⁇ 5°C.
  • the test standard can be based on GB/T 11297.11-2015.
  • the ferroelectric material may include one or a combination of more selected from inorganic ferroelectric materials and organic ferroelectric materials.
  • the ferroelectric material may include one or a combination of more selected from inorganic ferroelectric materials.
  • the inorganic ferroelectric material may include perovskite structure oxides, tungsten bronze-type compounds, bismuth oxide-type layered structure compounds, lithium niobate (LiNbO 3 ), tantalum One or a combination of one or more of lithium oxide (LiTaO 3 ), lead metaniobate and lead barium lithium niobate. More optionally, the inorganic ferroelectric material is selected from perovskite structure oxides.
  • the perovskite structure oxide has the molecular formula Ba 1-x Ax Ti 1-y By O 3 .
  • A may include one or more combinations selected from Pb, Sr, Ca, K, Na and Cd
  • B may include one or more combinations selected from Sn, Hf, Zr, Ce, Nb and Th. Combination, 0 ⁇ x ⁇ ? 1,0 ⁇ y ⁇ ? 1.
  • the perovskite structure oxide may include BaTiO 3 , Ba 1-x1 Sr x1 TiO 3 (0 ⁇ x1 ⁇ ?1), SrTiO 3 , PbTiO 3 , PbZr y1 Ti 1-y1 O 3 (0 ⁇ ?y1 ⁇ ?1), one or a combination of BaZr y2 Ti 1-y2 O 3 (0 ⁇ y2 ⁇ 1), KNbO 3 and NaNbO 3 .
  • the tungsten bronze-type compound may have a molecular formula M z WO 3 .
  • M may include one or a combination of one or more selected from Na, K, Rb and Cs, 0 ⁇ z ⁇ 1.
  • the tungsten bronze compound may include one or a combination of more selected from Na z1 WO 3 (0 ⁇ z1 ⁇ 1), K z2 WO 3 (0 ⁇ z2 ⁇ 1).
  • the bismuth oxide type layered structure compound has a molecular formula (Bi 2 O 2 ) (C n-1 D n O 3n+1 ).
  • C may include one or a combination of more selected from Na, K, Ba, Sr, Pb, Ca, Ln and Bi
  • D may include Zr, Cr, Nb, Ta, Mo, W, Fe, Ti and a combination of one or more of V, 2 ⁇ n ⁇ ? 5.
  • the bismuth oxide layered structure compound may be one or a combination of more of SrBi 2 Nb 2 O 9 , SrBi 2 Ta 2 O 9 , SrBi 2 Nb 2 O 9 , and Bi 4 Ti 3 O 12 .
  • the organic ferroelectric material may include vinylidene fluoride homopolymers or copolymers, 2,5-dibromo-3,6-dihydroxyp-benzoquinone, phenazine-chloranic acid, One or more combinations of ketoacids.
  • the thickness of the functional coating is H 1 ⁇ m
  • the thickness of the second negative electrode film layer is H 2 ⁇ m
  • the thickness of the first negative electrode film layer is H 3 ⁇ m
  • the thickness of the negative electrode The pole piece satisfies H 1 /(H 2 +H 3 ) from 0.01 to 0.15, optionally from 0.01 to 0.08.
  • the inventor found that the thickness of the functional coating H 1 ⁇ m, the thickness of the second negative electrode film layer H 2 ⁇ m and the thickness of the first negative electrode film layer H 3 ⁇ m satisfy H 1 /(H 2 +H 3 ) as When 0.01 to 0.15, the secondary battery has better overall performance and can achieve high-rate charging under high energy density. And it can effectively avoid the following situation: when the thickness of the functional coating is low and the total thickness of the first negative electrode film layer and the second negative electrode film layer is high, the reverse electric field intensity generated by the functional coating is insufficient and may not be able to balance electrons. Density and the role of inhibiting the continued growth of dendrites in the direction of the vertical pole piece.
  • the hard carbon microporous structure cannot be fully utilized as an active ion storage site; the thickness of the functional coating is relatively high and the total thickness of the first negative electrode film layer and the second negative electrode film layer is When the value is low, since the functional coating does not have electrochemical activity and cannot contribute capacity, it will occupy more volume space and mass share, which will instead affect the energy density of the secondary battery.
  • the thickness of the functional coating is H 1 ⁇ m, and H 1 is 2 to 10, optionally 4 to 6.
  • the secondary battery has better overall performance and can achieve high-rate charging at high energy density. And it can effectively avoid the following situations: when the functional coating is thin, the reverse electric field strength generated by it is insufficient, which may not be able to balance the electron density and inhibit the continued growth of dendrites in the direction of the vertical pole piece. Therefore, by improving the second When the output voltage of the secondary battery is increased to increase the energy density, the safety risk of the secondary battery increases. When the output voltage of the secondary battery is reduced to reduce the safety risk of the secondary battery, the hard carbon microporous structure cannot be fully utilized as an active material. The role of ion storage sites; when the functional coating is thicker, it will occupy more volume space and mass share because it does not have electrochemical activity and cannot contribute capacity, which will instead affect the energy density of the secondary battery.
  • the thickness of the second negative electrode film layer is H 2 ⁇ m
  • the thickness of the first negative electrode film layer is H 3 ⁇ m
  • the negative electrode plate satisfies H 2 /H 3 to be 0.10 to 5. , optionally 0.5 to 4.
  • the inventor found that when the ratio of the thickness H 2 ⁇ m of the second negative electrode film layer to the thickness H 3 ⁇ m of the first negative electrode film layer is within an appropriate range, the second negative electrode film layer and the first negative electrode film layer can Create better synergy effects.
  • the second negative electrode film layer is mainly used to bear the high-rate charging pressure to ensure that the secondary battery has a high charging rate;
  • the first negative electrode film layer is mainly used to provide long cycle life while ensuring high first Coulombic efficiency, thus the comprehensive performance of the secondary battery is better Well, it can achieve high-rate charging under high energy density.
  • the second negative electrode film layer is thin and the first negative electrode film layer is thick, the high-rate charging pressure shared by the hard carbon in the second negative electrode film layer during the charging process is still less.
  • the graphite in the first negative electrode film layer plays a leading role, which results in an insignificant improvement in the charging rate of the secondary battery.
  • the surface of the hard carbon contains a large amount of Inactive functional groups will increase the irreversible consumption of active ions, affecting the first Coulombic efficiency of the secondary battery, and the cycle life of the secondary battery may also be reduced.
  • the thickness of the second negative electrode film layer is H 2 ⁇ m, and H 2 is 10 to 120, optionally 35 to 110, and more optionally 40 to 100.
  • H 2 is 10 to 120, optionally 35 to 110, and more optionally 40 to 100.
  • the thickness of the first negative electrode film layer is H 3 ⁇ m, and H 3 is 20 to 100, optionally 25 to 70, and more optionally 28 to 60.
  • H 3 is 20 to 100, optionally 25 to 70, and more optionally 28 to 60.
  • the functional coating includes a ferroelectric material.
  • the mass percentage of the ferroelectric material in the functional coating is W1. Based on the total mass of the functional coating, W1 is 70% to 95%, optionally 80% to 95%.
  • the output voltage of the secondary battery is increased to increase the energy density, the safety risk of the secondary battery increases.
  • the output voltage of the secondary battery is reduced to reduce the safety risk of the secondary battery, the hard carbon microporous structure cannot be fully utilized.
  • the functional coating may further include a binder to bond the ferroelectric materials to each other and to bond the functional coating to the second negative electrode film layer.
  • the binder may include styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • the functional coating may also include other auxiliaries.
  • the further auxiliaries may include dispersants such as sodium carboxymethylcellulose (CMC).
  • the second negative electrode film layer includes a second negative electrode active material, and the second negative electrode active material includes hard carbon.
  • the mass percentage of the hard carbon in the second negative active material is 70% to 100%, optionally 80% to 98%, based on the total mass of the second negative active material. count. Therefore, the second negative electrode film layer contains more hard carbon, which is beneficial to the secondary battery having a higher charging rate.
  • the second negative active material may only include hard carbon; in other embodiments, the second negative active material may also include other negative active materials other than hard carbon, such as graphite, soft carbon. , mesophase carbon microspheres, silicon-based materials, tin-based materials, etc.
  • the mass percentage of the other negative active materials in the second negative active material is less than 30%, and more optionally 20% or less, based on the total mass of the second negative electrode active material.
  • the mass percentage of hard carbon in the second negative electrode film layer is W2. Based on the total mass of the second negative electrode film layer, W2 is more than 68%, optionally 90%. to 98%. When the content of hard carbon is within a suitable range, it is beneficial for the secondary battery to have a higher charging rate.
  • the second negative electrode film layer may also include a conductive agent to collect microcurrent between the second negative electrode active materials (such as hard carbon), reduce the contact resistance of the electrode, and accelerate electrons. The movement rate; at the same time, it can also reduce polarization and improve the charging and discharging efficiency of secondary batteries.
  • the conductive agent may include one or a combination of more selected from the group consisting of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. .
  • the mass percentage of the conductive agent is less than 5%.
  • the second negative electrode film layer may further include a binder to bond the second negative electrode active materials to each other, to bond the second negative electrode film layer to the functional coating, and to bond the second negative electrode film layer to each other. layer and the first negative electrode film layer are bonded.
  • the binder may include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, polysodium acrylate PAAS) , polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and a combination of one or more of carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • SR-1B water-soluble unsaturated resin
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • CMCS carboxymethyl chitosan
  • CMCS carboxymethyl chi
  • the second negative electrode film layer may also include other additives.
  • the other auxiliaries may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.
  • CMC sodium carboxymethyl cellulose
  • PTC thermistor materials such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.
  • the mass percentage of the other additives is less than 2%.
  • the first negative electrode film layer includes a first negative electrode active material, and the first negative electrode active material includes graphite.
  • the mass percentage of the graphite in the first negative active material is 80% to 100%, optionally 90% to 98%, based on the total mass of the first negative active material. . Therefore, the first negative electrode film layer contains more graphite, which is beneficial to the secondary battery having higher first Coulombic efficiency and longer cycle life.
  • the first negative active material may only include graphite; in other embodiments, the first negative active material may also include other negative active materials other than graphite, such as hard carbon, soft carbon, Mesophase carbon microspheres, silicon-based materials, tin-based materials, etc.
  • the mass percentage of the other negative active materials in the first negative active material is less than 20%, more optionally less than 10% % or less, based on the total mass of the first negative active material.
  • the mass percentage of graphite in the first negative electrode film layer is W3. Based on the total mass of the first negative electrode film layer, W3 is 78% or more, optionally 90% to 90%. 98%. When the content of graphite is within a suitable range, it is beneficial for the secondary battery to have higher first Coulombic efficiency and longer cycle life.
  • the first negative electrode film layer may also include a conductive agent to collect microcurrent between the first negative electrode active materials (such as graphite), reduce the contact resistance of the electrode, and accelerate the movement of electrons. Movement speed; at the same time, it can also reduce polarization and improve the charging and discharging efficiency of secondary batteries.
  • the conductive agent may include one or a combination of more selected from the group consisting of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. .
  • the mass percentage of the conductive agent is less than 5%.
  • the first negative electrode film layer may further include a binder to bond the first negative electrode active materials to each other, to bond the first negative electrode film layer and the second negative electrode film layer, and to bond the first negative electrode film layer to each other.
  • the negative electrode film layer and the negative electrode current collector are bonded.
  • the binder may include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, polysodium acrylate PAAS) , polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and a combination of one or more of carboxymethyl chitosan (CMCS).
  • the mass percentage of the binder is less than 5% based on the total mass of the first negative electrode film layer.
  • the first negative electrode film layer may also include other additives.
  • the other auxiliaries may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.
  • CMC sodium carboxymethyl cellulose
  • PTC thermistor materials such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.
  • the mass percentage of the other additives is less than 2%.
  • the volume average particle diameter Dv50 of the ferroelectric material is d 1 ⁇ m, and d 1 is less than 1.
  • it can be less than 0.8, less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, 0.2 or less.
  • d 1 is 0.01 to 1, 0.02 to 1, 0.03 to 1, 0.04 to 1, 0.05 to 1, 0.06 to 1, 0.07 to 1, 0.08 to 1, 0.01 to 0.8, 0.02 to 0.8, 0.03 to 0.8 , 0.04 to 0.8, 0.05 to 0.8, 0.06 to 0.8, 0.07 to 0.8, 0.08 to 0.8, 0.09 to 0.8 or 0.1 to 0.8.
  • the secondary battery When the Dv50 of ferroelectric materials is within a suitable range, the secondary battery has better overall performance, can achieve high-rate charging under high energy density, and can reduce production costs at the same time. And it can effectively avoid the following situations: when the Dv50 of the ferroelectric material is large, the reverse electric field interference generated by it is large, which may not be able to balance the electron density and inhibit the continued growth of dendrites in the vertical pole piece direction. Therefore, in When the output voltage of the secondary battery is increased to increase the energy density, the safety risk of the secondary battery increases. When the output voltage of the secondary battery is reduced to reduce the safety risk of the secondary battery, the hard carbon micropores cannot be fully utilized. The structure serves as an active ion storage site; when the Dv50 of the ferroelectric material is small, its preparation process is complicated, thus increasing the production cost.
  • the second negative electrode active material has a volume average particle size Dv50 of d 2 ⁇ m
  • the first negative electrode active material has a volume average particle size Dv50 of d 3 ⁇ m
  • d 2 /d 3 is 0.1 to 0.1 to d 3 ⁇ m. 1, optionally 0.2 to 0.8.
  • the first negative electrode film layer uses a first negative electrode active material with a larger particle size. Therefore, the compaction density of the first negative electrode film layer is higher, which is beneficial to the secondary battery having a high first Coulombic efficiency. , high energy density and long cycle life.
  • the second negative electrode film layer uses a second negative electrode active material with a smaller particle size, so that its specific surface area is higher, which can increase the contact area with the electrolyte and shorten the liquid phase diffusion of active ions. path and solid-phase diffusion path; at the same time, the integrity of the pore structure of the second negative electrode film layer is maintained better, which is beneficial to the secondary battery having a higher charging rate.
  • the particle size of the second negative active material is smaller, it is more resistant to pressure. Therefore, the microporous structure of the second negative active material, especially the hard carbon, is better maintained, so that the microporous structure of the hard carbon can be fully utilized as a
  • the role of active ion storage sites improves the capacity and energy density of secondary batteries; at the same time, the compaction density of the second negative electrode film layer is low, which is conducive to the rapid infiltration of the electrolyte into the first negative electrode film layer and reduces negative electrode polarization. Improve the charging and discharging efficiency of secondary batteries.
  • the inventor found that when the ratio d 2 /d 3 between the particle size of the second negative active material and the particle size of the first negative active material is within an appropriate range, it is beneficial to give full play to the improvement of the second negative electrode film layer.
  • the high-rate charging capability of the secondary battery and the first negative electrode film layer improve the first Coulombic efficiency and cycle life of the secondary battery. As a result, the secondary battery has better overall performance and can achieve high-rate charging under high energy density.
  • the second negative active material has a volume average particle diameter Dv50 of d 2 ⁇ m, and d 2 ranges from 3 to 11, optionally from 3 to 9.
  • Dv50 volume average particle diameter of d 2 ⁇ m
  • d 2 ranges from 3 to 11, optionally from 3 to 9.
  • the particle size of the second negative active material is within a suitable range, its microporous structure is better maintained, thereby making full use of the hard carbon microporous structure as an active ion storage site and improving the capacity and performance of the secondary battery.
  • the second negative electrode film layer can have a smooth pore structure, which is conducive to the smooth passage of the electrolyte through the pore structure of the second negative electrode film layer and rapid infiltration
  • the first negative electrode film layer reduces the polarization of the negative electrode and improves the charging and discharging efficiency of the secondary battery.
  • the particle size distribution index (Dv90-Dv10)/Dv50 of the second negative active material is ⁇ 1 , and ⁇ 1 is 0.6 to 5, optionally 1 to 4.
  • the particle size distribution index of the second negative electrode active material is within an appropriate range, it is beneficial to improve the processing performance of the second negative electrode film layer, so that the second negative electrode film layer as a whole has a higher particle distribution consistency and a smooth pore structure.
  • the second negative active material has a specific surface area of 3 m 2 /g to 7 m 2 /g, optionally 4 m 2 /g to 6 m 2 /g.
  • the specific surface area of the second negative electrode active material is within an appropriate range, the charge exchange resistance can be reduced, and the second negative electrode film layer can have a smoother pore structure, thereby having higher active ion transport performance, thereby further improving High-rate charging capability of secondary batteries.
  • the specific surface area of the second negative active material is within an appropriate range, it can also improve the film-forming efficiency of the SEI film, avoid the formation of an excessively thick SEI film, and reduce the irreversible consumption of active ions, thereby further improving the capacity and performance of the secondary battery. Cycle performance.
  • the second negative active material has a powder compacted density at 20000N of 0.9 to 1.3 g/cm 3 , optionally 1 to 1.2 g/cm 3 .
  • the powder compaction density of the second negative active material is within an appropriate range, it is beneficial to increase the energy density of the secondary battery.
  • the second negative active material includes primary particles, secondary particles, or a combination thereof.
  • the number of primary particles in the second negative active material is 90% to 100%.
  • the second negative electrode active material contains an appropriate proportion of primary particles, it is beneficial for the second negative electrode film layer to have a shorter active ion transmission path, which can further improve the high-rate charging capability of the secondary battery; in addition, it can also reduce the negative electrode Polarization and electrolyte side reactions, thereby further improving the cycle performance and storage performance of secondary batteries.
  • the volume average particle diameter Dv50 of the first negative active material is d 3 ⁇ m, and d 3 is 9 to 18, optionally 11 to 15.
  • the particle size of the first negative active material is within a suitable range, it is beneficial for the first negative electrode film layer to have a high compaction density, thereby enabling the secondary battery to have high first Coulombic efficiency, high energy density and long cycle life.
  • the particle size distribution index (Dv90-Dv10)/Dv50 of the first negative active material is ⁇ 2 , and ⁇ 2 is 0.2 to 5, optionally 0.3 to 4.
  • the particle size distribution index of the first negative electrode active material is within a suitable range, it is beneficial to improve the processing performance of the first negative electrode film layer, so that the first negative electrode film layer as a whole has a higher particle distribution consistency and a smooth pore structure. This is beneficial to different regions of the first negative electrode film layer having higher active ion transport performance, thereby further improving the cycle performance of the secondary battery.
  • the first negative active material has a specific surface area of 0.6 m 2 /g to 1.5 m 2 /g, optionally 0.8 m 2 /g to 1.4 m 2 /g.
  • the specific surface area of the first negative electrode active material is within an appropriate range, the charge exchange resistance can be reduced, and the first negative electrode film layer can have a smoother pore structure, thereby having higher active ion transport performance, thereby further improving Cycling performance of secondary batteries.
  • the powder compacted density of the first negative active material at 20000N is 1.4g/cm 3 to 1.85g/cm 3 , optionally 1.6g/cm 3 to 1.75g/cm 3 .
  • the powder compaction density of the first negative active material is within an appropriate range, it is beneficial to increase the energy density of the secondary battery.
  • the first negative active material has a graphitization degree of 91% to 95%, optionally 92% to 94%.
  • the graphitization degree of the first negative electrode active material is within an appropriate range, it is beneficial to improve the cycle performance of the secondary battery.
  • the first negative active material includes artificial graphite, natural graphite, or a combination thereof.
  • the mass percentage of artificial graphite in the first negative active material is more than 50%, optionally 60% to 100%, based on the total mass of the first negative active material.
  • the surface of the artificial graphite also has a carbon coating layer, which can further reduce charge transfer resistance and improve the cycle performance and high-rate charging capability of the secondary battery.
  • the carbon coating layer includes no Shaped carbon.
  • the first negative active material includes primary particles, secondary particles, or a combination thereof.
  • the number of secondary particles in the first negative active material is 80% to 100%.
  • the first negative electrode active material contains an appropriate proportion of secondary particles, its isotropy is increased, which is beneficial to the first negative electrode film layer having more active ion transmission channels, thereby further improving the high-rate charging of the secondary battery. ability; at the same time, it is beneficial to the first negative electrode film layer to have a high compaction density, which improves the energy density of the secondary battery; in addition, it can also reduce negative electrode polarization and electrolyte side reactions, thereby further improving the cycle performance and storage performance of the secondary battery .
  • the negative electrode sheet has a compacted density of 1.4g/cm 3 to 1.85g/cm 3 , optionally 1.6g/cm 3 to 1.75g/cm 3 .
  • the compaction density of the negative electrode plate is within a suitable range, it is beneficial to improve the high-rate charging capability, cycle performance and energy density of the secondary battery.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil or copper alloy foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate ( One or a combination of one or more of PBT), polystyrene (PS) and polyethylene (PE).
  • the negative electrode current collector has two surfaces opposite in its thickness direction.
  • the above-mentioned first negative electrode film layer, second negative electrode film layer and functional coating can be disposed on any one or both of the two opposite surfaces of the negative electrode current collector. superior.
  • each first negative electrode film layer, second negative electrode film layer and functional coating layer given in this application refer to the parameter range of the coating layer on one side of the negative electrode current collector.
  • the first negative electrode film layer, the second negative electrode film layer and the functional coating are disposed on two surfaces of the negative electrode current collector, and the parameters of the coating layer on any one of the surfaces meet the requirements of this application, it is deemed to fall within the protection of this application. within the range.
  • FIG. 1 is a schematic diagram of an embodiment of the negative electrode plate 10 of the present application.
  • the negative electrode sheet 10 includes a negative electrode current collector 104 and a first negative electrode film layer 103 respectively provided on two surfaces of the negative electrode current collector 104, a second negative electrode film layer 102 provided on the first negative electrode film layer 103, and a second negative electrode film layer 102 provided on the second negative electrode film layer 103.
  • Functional coating 101 on negative electrode film layer 102 can also be provided on only one surface of the negative electrode current collector 104.
  • Dv90, Dv50, and Dv10 of materials have well-known meanings in the art, and can be measured using instruments and methods well-known in the art.
  • Dv90 is the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 90%
  • Dv50 is the particle size corresponding to the cumulative volume distribution percentage of the material reaches 50%
  • Dv10 is the particle size corresponding to the cumulative volume distribution percentage of the material reaches 10% .
  • the specific surface area of a material has a well-known meaning in the art, and can be measured using instruments and methods well-known in the art.
  • the nitrogen adsorption specific surface area analysis test can be carried out by the Tri-Star 3020 specific surface area pore size analysis tester of the American Micromeritics company.
  • the graphitization degree of a material has a well-known meaning in the art, and can be measured using instruments and methods well-known in the art.
  • an X-ray diffractometer such as Bruker D8 Discover
  • d 002 is the interlayer spacing of the (002) crystal plane in the crystal structure of the material expressed in nanometers (nm).
  • the powder compacted density of a material has a meaning known in the art, and can be measured using instruments and methods known in the art.
  • An exemplary test method includes the following steps: weigh 1g of material, add it to a mold with a base area of 1.327cm2 , pressurize to 2000kg (equivalent to 20000N), hold the pressure for 30s, then release the pressure, hold for 10s, then record and calculate The powder compaction density of the material under a force of 20000N.
  • the number ratio of primary particles and secondary particles can be measured using instruments and methods known in the art, such as using a scanning electron microscope.
  • multiple (for example, more than 5) different areas can be randomly selected in the test sample for scanning testing, and at a certain magnification (for example, more than 1000 times), the primary particles and secondary particles in each area can be calculated.
  • the percentage of the number of secondary particles to the total number of particles is the proportion of primary particles and secondary particles in the area.
  • the test basis can refer to JY/T010-1996.
  • the thickness of the first negative electrode film layer, the second negative electrode film layer and the functional coating layer have meanings known in the art, and can be measured using instruments and methods known in the art, for example, through a scanning electron microscope (such as ZEISS Sigma 300) for testing, whereby the boundary area between the functional coating and the second negative electrode film layer and the boundary area between the second negative electrode film layer and the first negative electrode film layer can be more accurately determined.
  • An exemplary test method includes the following steps: cut the negative electrode piece into a sample to be tested of a certain size (for example, 2cm ⁇ 2cm), fix the negative electrode piece on the sample stage through paraffin wax; put the sample stage into the sample rack and lock it.
  • the test basis can refer to JY/T010-1996.
  • the respective thicknesses of the first negative electrode film layer, the second negative electrode film layer and the functional coating can be tested and averaged.
  • the compacted density of the negative electrode sheet has a meaning known in the art, and can be measured using instruments and methods known in the art.
  • the compacted density of the negative electrode piece the area density of the negative electrode piece/the thickness of the coating layer on one side of the negative electrode current collector.
  • the areal density of the negative electrode piece has a meaning known in the art and can be measured using instruments and methods known in the art.
  • the above-mentioned various parameter tests on the first negative electrode active material, the second negative electrode active material and the ferroelectric material can be conducted by sampling and testing before coating, or by sampling and testing from the negative electrode sheet after cold pressing.
  • the sampling can be carried out according to the following steps: (1) Select any one side of the cold-pressed coating layer of the negative electrode current collector, and test the ferroelectric Material sampling (for example, you can use a blade to scrape powder for sampling), and the scraping depth does not exceed the boundary area between the functional coating and the second negative electrode film layer; (2) Sampling the second negative electrode active material (for example, you can use a blade to scrape powder for sampling), The scraping depth should not exceed the boundary area between the second negative electrode film layer and the first negative electrode film layer.
  • the negative electrode sheet can be prepared by the following method: dispersing the first negative active material, conductive agent, binder and any other components in a solvent (such as deionized water) to form a first slurry , dispersing the second negative active material, conductive agent, binder and any other components in a solvent (such as deionized water) to form a second slurry, and dispersing the ferroelectric material, binder and any other components, etc.
  • a solvent such as deionized water
  • Disperse in a solvent such as deionized water to form a third slurry; apply the first slurry on the negative electrode current collector and dry it to form a first negative electrode film layer; apply the second slurry on the first negative electrode film layer, and is dried to form a second negative electrode film layer; the third slurry is coated on the second negative electrode film layer, and after drying, cold pressing and other processes, a negative electrode piece is obtained.
  • a solvent such as deionized water
  • the embodiment of the present application also provides a secondary battery, which includes the negative electrode plate of the first aspect of the present application.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery includes an electrode assembly and an electrolyte.
  • the electrode assembly usually includes a positive electrode plate, a negative electrode plate and a separator.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through.
  • the electrolyte plays a role in conducting active ions between the positive electrode piece and the negative electrode piece.
  • the secondary battery of the present application may be a lithium-containing secondary battery, and in particular, may be a lithium-ion secondary battery.
  • the negative electrode plate used in the secondary battery of the present application is the negative electrode plate of any embodiment of the first aspect of the application.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode current collector has two surfaces opposite in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the cathode film layer includes a cathode active material
  • the cathode active material may be a cathode active material known in the art for secondary batteries.
  • the cathode active material may include one or a combination of more selected from the group consisting of lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds.
  • lithium transition metal oxides may include lithium cobalt oxides (eg, LiCoO 2 ), lithium nickel oxides (eg, LiNiO 2 ), lithium manganese oxides (eg, LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxides Materials, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.5 Co 0.25 Mn 0.25 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and their respective modified compounds One or a combination of more.
  • lithium cobalt oxides eg, LiCoO 2
  • LiNiO 2 lithium nickel oxides
  • lithium-containing phosphate may include lithium iron phosphate, a composite material of lithium iron phosphate and carbon, a lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, a lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon. and a combination of one or more of their respective modified compounds.
  • the cathode active material may include a combination of one or more of the lithium transition metal oxide shown in Formula 1 and its modified compounds.
  • M may include Mn, Al, A combination of one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A may include one or a combination of one or more selected from N, F, S and Cl.
  • the modified compounds of each of the above-mentioned positive electrode active materials may be doping modifications or/or surface coating modifications of the positive electrode active materials.
  • the positive electrode film layer may also include a conductive agent to collect microcurrents between the positive electrode active materials, reduce the contact resistance of the electrode, and accelerate the movement rate of electrons; at the same time, it can also reduce the electrode's contact resistance. ization to improve the charging and discharging efficiency of secondary batteries.
  • the conductive agent may include one or a combination of more selected from the group consisting of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. .
  • the mass percentage of the conductive agent is less than 5%.
  • the positive electrode film layer may further include a binder to bond the positive electrode active materials to each other and to bond the positive electrode film layer and the positive electrode current collector.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene- One or more combinations of tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the mass percentage of the binder is less than 5% based on the total mass of the positive electrode film layer.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil or aluminum alloy foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate ( One or a combination of one or more of PBT), polystyrene (PS) and polyethylene (PE).
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, conductive agent, binder and any other components in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the electrolyte may be selected from at least one of a solid electrolyte, a gel electrolyte, and a liquid electrolyte (ie, electrolyte).
  • the electrolyte uses an electrolyte solution including a lithium salt and a solvent.
  • the lithium salt may include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), bisfluorosulfonyl Lithium amine (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium difluoromethane borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • the organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA) ), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1 , one or a combination of one or more of 4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).
  • the electrolyte may also include additives, such as negative electrode film-forming additives and positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, improve battery performance. High temperature or low temperature performance additives, etc.
  • isolation membrane there is no particular restriction on the type of isolation membrane in this application, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane may include one or a combination of more selected from the group consisting of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film may be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer may be the same or different.
  • the positive electrode piece, the isolation film and the negative electrode piece can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic, such as one or a combination of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS). .
  • FIG. 2 shows an example of a square-structured secondary battery 5 .
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 is used to cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the separator film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and can be adjusted according to needs.
  • the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte may be assembled to form a secondary battery.
  • the positive electrode sheet, isolation film, and negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process.
  • the electrode assembly is placed in an outer package, dried, and electrolyte is injected into it. After vacuum packaging, standing, and forming , shaping and other processes to obtain secondary batteries.
  • the secondary batteries according to the present application can be assembled into a battery module.
  • the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 4 is a schematic diagram of the battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 is used to cover the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • Embodiments of the present application also provide an electrical device, which includes at least one of a secondary battery, a battery module and a battery pack of the present application.
  • the secondary battery, battery module and battery pack may be used as a power source for the electrical device or as an energy storage unit for the electrical device.
  • the electrical device may be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric Golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the power-consuming device can select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • FIG. 7 is a schematic diagram of an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • battery packs or battery modules can be used.
  • the power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc.
  • the electrical device is usually required to be light and thin, and secondary batteries can be used as power sources.
  • the petroleum non-needle coke raw material powder is pretreated to remove impurities, and then mixed with coal pitch and granulated to obtain secondary particles with a Dv50 of 10 ⁇ m.
  • the granulated product is then placed in an Acheson graphitization furnace at 3000 Graphitize at 1000°C for 24 hours to obtain graphite particles; mix the obtained graphite particles with petroleum asphalt and carbonize at 1000°C for 15 hours to obtain artificial graphite.
  • the Dv50 of artificial graphite is 12 ⁇ m, Dv90 is 20 ⁇ m, Dv10 is 6.5 ⁇ m, the graphitization degree is 92%, the specific surface area is 0.86m 2 /g, the powder compaction density is 1.6g/cm 3 , and the morphology is secondary particles. .
  • the phenolic resin is heat-treated at 500°C for 30 minutes to obtain a precursor; the obtained precursor is pulverized and then heat-treated at 1200°C for 20 hours under the protection of a nitrogen atmosphere, and then pulverized again to obtain hard carbon.
  • the Dv50 of hard carbon is 5 ⁇ m
  • Dv90 is 10 ⁇ m
  • Dv10 is 2.5 ⁇ m.
  • the specific surface area is 5 m 2 /g
  • the morphology is primary particles.
  • the first slurry is coated on one surface of the negative electrode current collector copper foil with a thickness of 8 ⁇ m, and dried to form a first negative electrode film layer; the second slurry is coated on the first negative electrode film layer, and dried to form a third negative electrode film layer.
  • Two negative electrode film layers apply the third slurry on the second negative electrode film layer, and form a functional coating after drying; then repeat the above steps on the other surface of the negative electrode current collector copper foil, and then go through processes such as cold pressing After that, the negative electrode piece is obtained.
  • the thickness of the first negative electrode film layer on one side of the negative electrode current collector is 59 ⁇ m
  • the thickness of the second negative electrode film layer is 82 ⁇ m
  • the thickness of the functional coating is 2 ⁇ m.
  • the compacted density of the negative electrode piece is 1.55g/cm 3 .
  • the cathode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), the conductive agent conductive carbon black, and the binder polyvinylidene fluoride (PVDF) at a mass ratio of 98:1:1, add it to the solvent NMP, and mix in a vacuum mixer Stir until the system is homogeneous under the action of the reaction solution to obtain a positive electrode slurry with a solid content of 75%; the positive electrode slurry is evenly coated on both surfaces of an aluminum foil with a thickness of 13 ⁇ m, dried at 90°C, and cold pressed to obtain the positive electrode.
  • the thickness of the positive electrode film on one side of the current collector is 114 ⁇ m.
  • a porous polyethylene film is used as the isolation membrane.
  • the positive electrode sheet, isolation film, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in the outer packaging, dried and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, Get a secondary battery.
  • the secondary battery was prepared in a manner similar to that of Example 1-1, except that the coating thickness of the third slurry and the thickness of the functional coating obtained in the preparation of the negative electrode sheet were different. For details, see Table 1.
  • the secondary battery was prepared similarly to Example 1-1, except that the third slurry was not coated in the preparation of the negative electrode sheet.
  • the secondary battery was prepared similarly to Example 1-1, except that the third slurry was not coated in the preparation of the negative electrode sheet, and when the slurry was applied, the second slurry was first coated on On one surface of the negative electrode current collector copper foil with a thickness of 8 ⁇ m, the first negative electrode film layer is formed by drying, and then the first slurry is coated on the first negative electrode film layer, dried to form the second negative electrode film layer, and then Repeat the above steps on the other surface of the negative electrode current collector copper foil, and then undergo cold pressing and other processes to obtain the negative electrode piece.
  • the thickness of the first negative electrode film layer on one side of the negative electrode current collector is 82 ⁇ m
  • the thickness of the second negative electrode film layer is 59 ⁇ m.
  • the secondary battery was prepared similarly to Example 1-1, except that the second slurry and the third slurry were not coated in the preparation of the negative electrode sheet.
  • the first slurry is coated on both surfaces of the negative electrode current collector copper foil with a thickness of 8 ⁇ m, and after drying, cold pressing and other processes, the negative electrode sheet is obtained.
  • the thickness of the negative electrode film layer on one side of the negative electrode current collector is 141 ⁇ m.
  • the secondary battery was prepared similarly to Example 1-1, except that the first slurry and the third slurry were not coated in the preparation of the negative electrode sheet.
  • the second slurry is coated on both surfaces of the negative electrode current collector copper foil with a thickness of 8 ⁇ m, and after drying, cold pressing and other processes, the negative electrode sheet is obtained.
  • the thickness of the negative electrode film layer on one side of the negative electrode current collector is 141 ⁇ m.
  • the secondary battery was prepared in a similar manner to Example 1-1, except that the preparation process of the negative electrode sheet was different.
  • S10 to S20 are the same as in Embodiment 1-1.
  • the artificial graphite and hard carbon prepared above, the conductive agent conductive carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were mixed according to the mass ratio of 40:55:1.5:3.1:0.4 After mixing, add deionized water, stir under the action of a vacuum mixer until the system is uniform, and obtain a slurry with a solid content of 66%.
  • the slurry is coated on both surfaces of the negative electrode current collector copper foil with a thickness of 8 ⁇ m, and after drying, cold pressing and other processes, the negative electrode sheet is obtained.
  • the thickness of the negative electrode film layer on one side of the negative electrode current collector is 141 ⁇ m.
  • the secondary battery was prepared in a similar manner to Example 1-1, except that the preparation process of the negative electrode sheet was different.
  • S10 to S30 are the same as in Embodiment 1-1.
  • the hard carbon prepared above barium titanate (Dv50 is 100nm, dielectric constant is more than 3000), conductive agent conductive carbon black, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC) ) according to the mass ratio of 93:1:1.5:3.1:0.4, add deionized water, and stir under the action of a vacuum mixer until the system is uniform to obtain a second slurry with a solid content of 66%.
  • Dv50 is 100nm, dielectric constant is more than 3000
  • SBR binder styrene-butadiene rubber
  • CMC thickener sodium carboxymethyl cellulose
  • the first slurry is coated on one surface of the negative electrode current collector copper foil with a thickness of 8 ⁇ m, and dried to form a first negative electrode film layer; the second slurry is coated on the first negative electrode film layer, and dried to form a third negative electrode film layer.
  • two negative electrode film layers then repeat the above steps on the other surface of the negative electrode current collector copper foil, and then undergo cold pressing and other processes to obtain the negative electrode piece.
  • the thickness of the first negative electrode film layer on one side of the negative electrode current collector is 59 ⁇ m, and the thickness of the second negative electrode film layer is 82 ⁇ m.
  • the secondary battery prepared above was fully discharged at a rate of 0.33C and fully charged at a rate of 0.33C; then the fully charged secondary battery was left to stand for 5 minutes and then fully discharged at a rate of 0.33C.
  • the obtained The discharge capacity is the actual capacity of the secondary battery at a rate of 0.33CC, recorded as C0.
  • Fully charge the secondary battery at xC0 rate (representing gradient charging rate, for example, 1C0, 1.1C0, 1.2C0, 1.3C0, 1.4C0...), let it stand for 5 minutes and then fully discharge it at 1C. After 10 cycles of this cycle, Then fully charge the secondary battery at 1C. Disassemble the secondary battery and observe the lithium precipitation on the surface of the negative electrode piece.
  • the secondary battery prepared above was fully charged at a rate of 0.33C and fully discharged at a rate of 0.33C. After 3 cycles of this cycle, the discharge energy of the secondary battery was recorded.
  • the energy density of the secondary battery the discharge energy of the secondary battery/the mass of the secondary battery.
  • the energy density of the secondary battery prepared in Comparative Example 1-1 is 100% to represent the energy density of the secondary batteries in other embodiments and comparative examples.
  • the secondary battery prepared above is fully discharged at a rate of 1C and fully charged at a rate of 1C; then the fully charged secondary battery is left to stand for 5 minutes and then fully discharged at a rate of 1C.
  • the discharge capacity C0 obtained at this time is as the initial capacity of the secondary battery.
  • the number of cycles represents the cycle life of the secondary battery. The higher the number of cycles of a secondary battery, the longer the expected cycle life.
  • the secondary battery using the negative electrode plate designed with the three-layer structure of the present application has both high charging rate and long cycle life.
  • the surface of the negative electrode current collector in Comparative Example 1-1 is provided with a graphite layer and a hard carbon layer in sequence, but no functional coating is provided. Lithium is easily precipitated during the long-term cycle charge and discharge of the secondary battery, thus affecting the cycle life of the secondary battery.
  • the surface of the negative electrode current collector of Comparative Example 1-2 was provided with a hard carbon layer and a graphite layer in sequence, but no functional coating was provided.
  • Comparative Examples 1-3 only provided a graphite layer on the surface of the negative electrode current collector, so that the secondary battery could have a long cycle life, but it was difficult to have a high charging rate.
  • Comparative Examples 1-4 only provided a hard carbon layer on the surface of the negative electrode current collector, so that the secondary battery could have a higher charging rate, but it was difficult to have a long cycle life.
  • Comparative Examples 1 to 5 a mixed layer of graphite and hard carbon was provided on the surface of the negative electrode current collector, making it difficult for the secondary battery to have both a high charging rate and a long cycle life.
  • the hard carbon layer of Comparative Example 1-6 also includes barium titanate, but the barium titanate is less effective in inhibiting the continued growth of lithium dendrites in the direction perpendicular to the pole piece and is difficult to achieve. Significantly improves the charging rate and cycle life of secondary batteries.
  • the secondary batteries of Examples 2-1 to 2-6 were prepared similarly to the method of Example 1-2, except that the mass percentage of the ferroelectric material in the functional coating was different.
  • the secondary batteries of Examples 4-1 to 4-7 were prepared in a manner similar to that of Example 1-2, except that the thickness of the first negative electrode film layer and the thickness of the second negative electrode film layer were different.

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Abstract

本申请提供一种负极极片、二次电池、电池模块、电池包及用电装置。所述负极极片包括负极集流体以及依次设置在所述负极集流体至少一个表面上的第一负极膜层、第二负极膜层和功能涂层，其中，所述功能涂层包括铁电材料；所述第二负极膜层包括第二负极活性材料，所述第二负极活性材料包括硬碳；所述第一负极膜层包括第一负极活性材料，所述第一负极活性材料包括石墨。本申请提供的负极极片能使二次电池在具有高能量密度的前提下，同时兼具高充电倍率和长循环寿命。

Description

负极极片、二次电池、电池模块、电池包及用电装置 技术领域
本申请属于电池技术领域，具体涉及一种负极极片、二次电池、电池模块、电池包及用电装置。
背景技术
近年来，二次电池被广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。随着二次电池的应用及推广，人们对二次电池的能量密度、循环性能和大倍率充电性能的要求越来越高，而负极活性材料作为二次电池的重要组成部分，其性能在一定程度上影响了二次电池的性能。石墨是二次电池最常用的负极活性材料之一，其具有极化小且循环稳定性高的优势，但其理论克容量仅为372mAh/g。目前商业石墨的性能几乎开发到了极致，其可逆克容量和能量密度的提升空间都十分有限。同时石墨的层间距较小，其大倍率充电性能也几乎开发到了极致。硬碳作为一种新型负极活性材料，在二次电池充放电过程中能够实现活性离子的快速嵌入和脱出，因此发展前景十分广阔。但是，商业硬碳的压实密度和首次库伦效率较低，对二次电池能量密度的提升有限。
发明内容
本申请的目的在于提供一种负极极片、二次电池、电池模块、电池包及用电装置，旨在使二次电池在具有高能量密度的前提下，同时兼具高充电倍率和长循环寿命。
本申请第一方面提供一种负极极片，包括负极集流体以及依次设置在所述负极集流体至少一个表面上的第一负极膜层、第二负极膜层和功能涂层，其中，所述功能涂层包括铁电材料；所述第二负极膜层包括第二负极活性材料，所述第二负极活性材料包括硬碳；所述第一负极膜层包括第一负极活性材料，所述第一负极活性材料包括石墨。
在本申请的负极极片中，将包括石墨的第一负极膜层和包括硬碳的第二负极膜层依次设置在负极集流体表面进行组合设计能够弥补石墨和硬碳各自的缺陷，并凸显各自的优势。硬碳的层间距较大，由此能够提供更大的充电倍率；石墨设置在硬碳和负极集流体之间，由此能够弥补硬碳的首次库伦效率。另外，由于活性离子嵌入硬碳微孔结构的电位在0V左右，与活性离子在石墨表面析出电位接近，因此不能充分发挥硬碳微孔结构作为活性离子储存位点的作用，而本申请的发明人惊喜发现，在负极极片表面设置包括铁电材料的功能涂层，能够解决上述问题。铁电材料可以调控活性离子沉积的方式，从而可以将硬碳微孔结构的大容量优势凸显出来，并还可以抑制活性离子在石墨表面持续还原析出，提高二次电池的循环寿命。因此，采用本申请负极极片的二次电池具有长循环寿命且能够进行大倍率充电，同时二次电池还能够具有高输出电压，进而还具有高 能量密度。
在本申请的任意实施方式中，所述功能涂层的厚度为H 1μm，所述第二负极膜层的厚度为H 2μm，所述第一负极膜层的厚度为H 3μm，并且所述负极极片满足H 1/(H 2+H 3)为0.01至0.15，可选地为0.01至0.08。由此二次电池的综合性能更好，能够在高能量密度下实现大倍率充电。
在本申请的任意实施方式中，所述功能涂层的厚度为H 1μm，H 1为2至10，可选地为4至6。由此二次电池的综合性能更好，能够在高能量密度下实现大倍率充电。
在本申请的任意实施方式中，所述第二负极膜层的厚度为H 2μm，所述第一负极膜层的厚度为H 3μm，并且所述负极极片满足H 2/H 3为0.10至5，可选地为0.5至4。由此第二负极膜层和第一负极膜层能够发挥更好地协同作用效果。
在本申请的任意实施方式中，所述铁电材料的体积平均粒径Dv50为d 1μm，d 1为1以下，可选地为0.05至0.8。由此二次电池的综合性能更好，能够在高能量密度下实现大倍率充电，同时能够降低生产成本。
在本申请的任意实施方式中，所述第二负极活性材料的体积平均粒径Dv50为d 2μm，所述第一负极活性材料的体积平均粒径Dv50为d 3μm，d 2/d 3为0.1至1，可选地为0.2至0.8。此时有利于充分发挥第二负极膜层提高二次电池大倍率充电能力以及第一负极膜层提高二次电池首次库伦效率和循环寿命的作用，由此二次电池的综合性能更好，能够在高能量密度下实现大倍率充电。
在本申请的任意实施方式中，所述功能涂层中的铁电材料的质量百分含量为W1，基于所述功能涂层的总质量计，W1为70％至95％，可选地为80％至95％。由此二次电池的综合性能更好，能够在高能量密度下实现大倍率充电。
在本申请的任意实施方式中，所述第二负极膜层中的硬碳的质量百分含量为W2，基于所述第二负极膜层的总质量计，W2为68％以上，可选地为90％至98％。由此有利于二次电池具有更高的充电倍率。
在本申请的任意实施方式中，所述第一负极膜层中的石墨的质量百分含量为W3，基于所述第一负极膜层的总质量计，W3为78％以上，可选地为90％至98％。由此有利于二次电池具有更高的首次库伦效率和更长的循环寿命。
在本申请的任意实施方式中，所述第二负极活性材料的体积平均粒径Dv50为d 2μm，d 2为3至11，可选地为3至7。由此有利于提高二次电池的容量发挥和能量密度。
在本申请的任意实施方式中，所述第二负极活性材料的粒径分布指数(Dv90-Dv10)/Dv50为α 1，α 1为0.6至5，可选地为1至4。由此有利于提升二次电池的大倍率充电能力和充放电效率。
在本申请的任意实施方式中，所述第二负极活性材料的比表面积为3m 2/g至7m 2/g，可选地为4m 2/g至6m 2/g。由此有利于提升二次电池的大倍率充电能力。
在本申请的任意实施方式中，所述第二负极活性材料20000N的粉体压实密度为0.9g/cm 3至1.3g/cm 3，可选地为1g/cm 3至1.2g/cm 3。由此有利于提升二次电池的能量密度。
在本申请的任意实施方式中，所述第二负极活性材料包括一次颗粒、二次颗粒或其组合，可选地，所述第二负极活性材料中一次颗粒的数量占比为90％至100％。由此有 利于提升二次电池的大倍率充电能力。
在本申请的任意实施方式中，所述第一负极活性材料的体积平均粒径Dv50为d 3μm，d 3为9至18，可选地为11至15。由此有利于二次电池具有高首次库伦效率、高能量密度和长循环寿命。
在本申请的任意实施方式中，所述第一负极活性材料的粒径分布指数(Dv90-Dv10)/Dv50为α 2，α 2为0.2至5，可选地为0.3至4。由此有利于改善二次电池的循环性能。
在本申请的任意实施方式中，所述第一负极活性材料的比表面积为0.6m 2/g至1.5m 2/g，可选地为0.8m 2/g至1.4m 2/g。由此有利于改善二次电池的循环性能。
在本申请的任意实施方式中，所述第一负极活性材料在20000N下的粉体压实密度为1.4g/cm 3至1.85g/cm 3，可选地为1.6g/cm 3至1.75g/cm 3。由此有利于提升二次电池的能量密度。
在本申请的任意实施方式中，所述第一负极活性材料的石墨化度为91％至95％，可选地为92％至94％。由此有利于提升二次电池的循环寿命。
在本申请的任意实施方式中，所述第一负极活性材料包括人造石墨、天然石墨或其组合，可选地，所述人造石墨表面具有碳包覆层。由此有利于提升二次电池的循环性能和大倍率充电能力。
在本申请的任意实施方式中，所述第一负极活性材料包括一次颗粒、二次颗粒或其组合，可选地，所述第一负极活性材料中二次颗粒的数量占比为80％至100％。由此有利于提升二次电池的循环性能、存储性能和大倍率充电能力。
在本申请的任意实施方式中，所述铁电材料的介电常数为50以上，可选地为50至100000。
在本申请的任意实施方式中，所述铁电材料包括选自无机铁电材料、有机铁电材料中的一种或多种的组合，可选地，所述无机铁电材料包括选自钙钛矿结构氧化物、钨青铜型化合物、铋氧化物型层状结构化合物、铌酸锂、钽酸锂、偏铌酸铅和铌酸铅钡锂中的一种或多种的组合；可选地，所述有机铁电材料可以包括选自偏氟乙烯均聚物或共聚物、2,5-二溴-3,6-二羟对苯醌、吩嗪-氯冉酸、克酮酸中的一种或多种的组合。
在本申请的任意实施方式中，所述功能涂层还包括粘结剂和/或分散剂，可选地，所述粘结剂包括选自丁苯橡胶、聚丙烯酸、聚丙烯酸钠、聚丙烯酰胺、聚乙烯醇、海藻酸钠、聚甲基丙烯酸及羧甲基壳聚糖中的一种或多种的组合；可选地，所述分散剂包括羧甲基纤维素钠。
本申请第二方面提供一种二次电池，其包括本申请第一方面的负极极片。
本申请第三方面提供一种电池模块，其包括本申请第二方面的二次电池。
本申请第四方面提供一种电池包，其包括本申请第二方面的二次电池、第三方面的电池模块中的一种。
本申请第五方面提供一种用电装置，其包括本申请第二方面的二次电池、第三方面的电池模块、第四方面的电池包中的至少一种。
采用本申请负极极片的二次电池具有长循环寿命且能够进行大倍率充电，同时二次电池还能够具有高输出电压，进而还具有高能量密度。本申请的电池模块、电池包和 用电装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的负极极片的一实施方式的示意图。
图2是本申请的二次电池的一实施方式的示意图。
图3是图2的二次电池的实施方式的分解示意图。
图4是本申请的电池模块的一实施方式的示意图。
图5是本申请的电池包的一实施方式的示意图。
图6是图5所示的电池包的实施方式的分解示意图。
图7是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
在附图中，附图未必按照实际的比例绘制。附图标记说明如下：1电池包，2上箱体，3下箱体，4电池模块，5二次电池，51壳体，52电极组件，53盖板，10负极极片，101功能涂层，102第二负极膜层，103第一负极膜层，104负极集流体。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的负极极片、二次电池、电池模块、电池包及用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可以包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可以包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可以包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
在本申请中，术语“多个”、“多种”是指两个或两种以上。
在本申请中，术语“一次颗粒”、“二次颗粒”为本领域公知的含义。一次颗粒是指没有形成团聚状态的颗粒，二次颗粒是指由两个以上一次颗粒聚集而成的团聚态的颗粒。一次颗粒和二次颗粒可以通过使用扫描电子显微镜拍摄SEM图像容易地区分。
硬碳是指难以被石墨化的碳，且即使在2500℃以上的高温也难以石墨化。硬碳通常采用热解高分子聚合物等前驱体得到，在热解过程中，前驱体中碳原子相互交联的结构阻碍了碳层发生平面方向的生长，因此，硬碳结构中会含有大量无序化类石墨结构的微晶(简称石墨微晶)。硬碳结构复杂，除了石墨微晶外，还含有缺陷结构(例如表面缺陷、晶格缺陷等)和微孔结构(例如开孔结构、闭孔结构等)等。因此，活性离子可以从硬碳的各个角度嵌入和脱出，从而使二次电池具有优异的大倍率充电能力，特别是在动力电池领域，硬碳具有独特的优势。与石墨相比，硬碳(002)晶面层间距更大，由此在充放电过程中硬碳结构稳定性更高，不会出现明显的体积膨胀和收缩效应。
硬碳缺陷结构较多，其会催化电解液分解形成较厚的固态电解质界面(SEI)膜，增加活性离子的不可逆损失。此外，硬碳表面具有疏松多孔结构，易吸附空气中水分与氧气等而在表面形成各种C-H官能团，这些官能团会与活性离子反应，进一步增加活性离子的不可逆消耗。因此，与石墨相比，硬碳的首次库伦效率较低且循环性能较差，例如首次库伦效率通常低于80％，无法充分发挥其高容量优势。
本申请的发明人经过大量研究，提出一种新型的负极极片，其能提高硬碳容量发挥，使二次电池在具有高能量密度的前提下，还具有提升的大倍率充电能力和循环寿命。
负极极片
具体地，本申请实施方式提供了一种负极极片。本申请的负极极片包括负极集流体以及依次设置在所述负极集流体至少一个表面上的第一负极膜层、第二负极膜层和功能涂层，其中，所述功能涂层包括铁电材料；所述第二负极膜层包括第二负极活性材料，所述第二负极活性材料包括硬碳；所述第一负极膜层包括第一负极活性材料，所述第一 负极活性材料包括石墨。
石墨具有首次库伦效率高且循环稳定性高的优势，但是大倍率充电能力有限；硬碳具有活性离子嵌入和脱出速率高的优势，因此大倍率充电能力优秀，但是其首次库伦效率较低且容量衰减较快，由此导致二次电池的实际容量发挥较差。本申请的发明人在实际研究过程中发现，将石墨和硬碳依次设置在负极集流体表面进行两层组合设计可以弥补石墨和硬碳各自的缺陷。将石墨靠近负极集流体设置能够弥补硬碳的首次库伦效率，将硬碳远离负极集流体设置能够使更多的活性离子更快嵌入负极，从而提升负极极片和二次电池的大倍率充电能力。
但是，本申请的发明人在进一步研究过程中还发现，将石墨和硬碳依次设置在负极集流体表面进行两层组合后对二次电池大倍率充电能力和能量密度的提升效果并不理想。发明人在深入研究后发现可能的原因在于，二次电池充电时，特别地在充电末期，“枝晶”的形成是影响二次电池大倍率充电能力和能量密度提升的重要因素。
在二次电池充电过程中，当负极活性离子嵌入空间不足、活性离子嵌入负极阻力太大、活性离子过快地从正极脱出但无法等量嵌入负极等异常情况发生时，无法嵌入负极的活性离子只能在负极表面得到电子而以金属单质形式析出，即形成“枝晶”。由此，二次电池充电倍率越高，“枝晶”问题越严重。枝晶的形成不仅使二次电池性能下降，例如循环寿命缩短等，而且严重时会形成尖锐形貌刺穿隔离膜导致电池内短路，从而有可能引起燃烧、爆炸等灾难性后果，增加二次电池的安全风险；此外，不断沉积的枝晶还会从负极表面脱落，导致与负极集流体失去电接触，由此不能继续参与充放电反应和贡献容量，从而还使得二次电池能量密度降低。
将石墨和硬碳依次设置在负极集流体表面进行两层组合后，二次电池充电前期，活性离子首先吸附在硬碳表面缺陷以及晶格缺陷位置，该过程对应硬碳充放电曲线中的“高电位斜坡区”，此时负极电位通常在～2V至～0.1V之间；随着充电持续进行，活性离子嵌入硬碳的石墨微晶层间，发生类似石墨的嵌入行为，该过程对应硬碳充放电曲线中的“低电位平台区”，此时负极电位通常在～0.1V至0V之间。由于硬碳还具有丰富的微孔结构，因此二次充电时，当负极电位降低至0V左右时，活性离子还可以储存在硬碳的微孔结构中，提供额外的活性离子储存位点，提升硬碳的容量发挥和首次库伦效率；并且低电位平台区的放电平台越长，对应硬碳的可逆容量越高，容量发挥越好。但是硬碳低电位平台区电位与石墨表层枝晶形成电位接近，均为0V左右，因此，为了防止枝晶形成，硬碳低电位平台区容量发挥受到限制，不能充分发挥硬碳微孔结构作为活性离子储存位点的作用；同时，为了防止枝晶形成，负极截止电压通常设置较高，由此还导致二次电池整体的输出电压降低，进而还导致二次电池的能量密度降低。因此，将石墨和硬碳依次设置在负极集流体表面进行两层组合后对二次电池大倍率充电能力和能量密度和/或循环寿命的提升效果有限。
本申请的负极极片将包括石墨的第一负极膜层和包括硬碳的第二负极膜层依次设置在负极集流体表面进行组合设计，并且在第二负极膜层表面还设置了包括铁电材料的功能涂层。铁电材料具有自发极化现象，当电子在枝晶表面聚集时，铁电材料受电场影响会发生自发极化，由此铁电材料的正电荷中心向电子聚集区移动，从而将电子聚集区包裹其中；同时由于铁电材料的正电荷中心带正电，与枝晶表面带正电的活性离子极性 相斥，从而能够起到均衡电子密度、减少活性离子富集的作用，由此抑制了枝晶在垂直极片方向持续生长。
因此，在本申请的负极极片中，将包括石墨的第一负极膜层和包括硬碳的第二负极膜层依次设置在负极集流体表面进行组合设计能够弥补石墨和硬碳各自的缺陷，并凸显各自的优势。硬碳的层间距较大，由此能够提供更大的充电倍率；石墨设置在硬碳和负极集流体之间，由此能够弥补硬碳的首次库伦效率。另外，由于活性离子嵌入硬碳微孔结构的电位在0V左右，与活性离子在石墨表面析出电位接近，因此不能充分发挥硬碳微孔结构作为活性离子储存位点的作用，而本申请的发明人惊喜发现，在负极极片表面设置包括铁电材料的功能涂层，能够解决上述问题。铁电材料可以调控活性离子沉积的方式，从而可以将硬碳微孔结构的大容量优势凸显出来，并还可以抑制活性离子在石墨表面持续还原析出，提高二次电池的循环寿命。
具体地，二次电池充电前期，活性离子快速吸附在硬碳表面缺陷以及晶格缺陷位置，由此使负极极片具有高动力学性能；二次电池充电后期，在功能涂层作用下能够精确调控过电位，使硬碳微孔结构存储大量活性离子，增加低电位平台区长度，增加二次电池的可逆容量，由此提高二次电池的大倍率充电能力和能量密度；此外，在过电位下，功能涂层还能够产生反向电场，减少活性离子富集，抑制枝晶在垂直极片方向持续生长，提高二次电池的安全性和循环性能。
因此，采用本申请负极极片的二次电池具有长循环寿命且能够进行大倍率充电，同时二次电池还能够具有高输出电压，进而还具有高能量密度。
在一些实施例中，可选地，所述铁电材料的介电常数在50以上。铁电材料的介电常数越高，其起到的抑制枝晶在垂直极片方向持续生长的作用效果越好，但是其作用效果不会一直持续增加，同时介电常数越高，对铁电材料的制备工艺要求越来越高，由此还增加了生产成本。
在一些实施例中，可选地，所述铁电材料的介电常数可以为50至100000，例如可以为50至50000，50至25000，50至10000，50至5000，50至4000，50至3000，50至2000，100至100000，100至50000，100至25000，100至10000，100至5000，100至4000，100至3000，100至2000，200至100000，200至50000，200至25000，200至10000，200至5000，200至4000，200至3000，200至2000或200至1000。
在本申请中，铁电材料的介电常数是指室温(25±5℃)下的介电常数，其具有本领域公知的含义，可以用本领域已知的仪器及方法进行测试。例如可以将铁电材料制备成圆形试样后，采用LCR测试仪测试电容量C并根据公式：介电常数ε＝(C×d)/(ε 0×A)计算得到。C表示电容量，单位为法拉(F)；d表示试样厚度，单位为cm；A表示试样面积，单位为cm 2；ε 0表示真空介电常数，ε 0＝8.854×10 -14F/cm。在本申请中，测试条件可以为1KHz、1.0V、25±5℃。测试标准可依据GB/T 11297.11-2015。制备试样时可参考中国专利申请CN114217139A。
在一些实施例中，所述铁电材料可以包括选自无机铁电材料、有机铁电材料中的一种或多种的组合。可选地，所述铁电材料可以包括选自无机铁电材料中的一种或多种的组合。
在一些实施例中，可选地，所述无机铁电材料可以包括选自钙钛矿结构氧化物、 钨青铜型化合物、铋氧化物型层状结构化合物、铌酸锂(LiNbO 3)、钽酸锂(LiTaO 3)、偏铌酸铅和铌酸铅钡锂中的一种或多种的组合。更可选地，所述无机铁电材料选自钙钛矿结构氧化物。
可选地，所述钙钛矿结构氧化物具有分子式Ba 1-xA xTi 1-yB yO 3。A可以包括选自Pb、Sr、Ca、K、Na和Cd中的一种或多种的组合，B可以包括选自Sn、Hf、Zr、Ce、Nb和Th中的一种或多种的组合，0≤x≤？1，0≤y≤？1。例如，所述钙钛矿结构氧化物可以包括选自BaTiO 3、Ba 1-x1Sr x1TiO 3(0≤x1≤？1)、SrTiO 3、PbTiO 3、PbZr y1Ti 1-y1O 3(0≤？y1≤？1)、BaZr y2Ti 1-y2O 3(0<y2<1)、KNbO 3、NaNbO 3中的一种或多种的组合。
可选地，所述钨青铜型化合物可具有分子式M zWO 3。M可以包括选自Na、K、Rb和Cs中的一种或多种的组合，0＜z＜1。例如，所述钨青铜型化合物可以包括选自Na z1WO 3(0<z1<1)、K z2WO 3(0<z2<1)中的一种或多种的组合。
可选地，所述铋氧化物型层状结构化合物具有分子式(Bi 2O 2)(C n-1D nO 3n+1)。C可以包括选自Na、K、Ba、Sr、Pb、Ca、Ln和Bi中的一种或多种的组合，D可以包括选自Zr、Cr、Nb、Ta、Mo、W、Fe、Ti和V中的一种或多种的组合，2≤n≤？5。例如，所述铋氧化物型层状结构化合物可以为SrBi 2Nb 2O 9、SrBi 2Ta 2O 9、SrBi 2Nb 2O 9、Bi 4Ti 3O 12中的一种或多种的组合。
在一些实施例中，所述有机铁电材料可以包括选自偏氟乙烯均聚物或共聚物、2,5-二溴-3,6-二羟对苯醌、吩嗪-氯冉酸、克酮酸中的一种或多种的组合。
在一些实施例中，所述功能涂层的厚度为H 1μm，所述第二负极膜层的厚度为H 2μm，所述第一负极膜层的厚度为H 3μm，并且所述负极极片满足H 1/(H 2+H 3)为0.01至0.15，可选地为0.01至0.08。
发明人在进一步研究中发现，功能涂层的厚度H 1μm、第二负极膜层的厚度H 2μm和第一负极膜层的厚度H 3μm满足H 1/(H 2+H 3)为0.01至0.15时，二次电池的综合性能更好，能够在高能量密度下实现大倍率充电。并且能够有效避免以下情况：功能涂层的厚度较低而第一负极膜层和第二负极膜层的总厚度较高时，功能涂层产生的反向电场强度不足，可能起不到均衡电子密度和抑制枝晶在垂直极片方向持续生长的作用，由此在通过提高二次电池的输出电压以提高能量密度时，二次电池的安全风险升高，而通过降低二次电池的输出电压以降低二次电池的安全风险时，又无法充分利用硬碳微孔结构作为活性离子储存位点的作用；功能涂层的厚度较高而第一负极膜层和第二负极膜层的总厚度较低时，由于功能涂层不具备电化学活性、不能贡献容量，由此会占据较多的体积空间和质量份额，反而影响二次电池的能量密度。
在一些实施例中，所述功能涂层的厚度为H 1μm，H 1为2至10，可选地为4至6。功能涂层的厚度在合适的范围内时，二次电池的综合性能更好，能够在高能量密度下实现大倍率充电。并且能够有效避免以下情况：功能涂层较薄时，其产生的反向电场强度不足，可能起不到均衡电子密度和抑制枝晶在垂直极片方向持续生长的作用，由此在通过提高二次电池的输出电压以提高能量密度时，二次电池的安全风险升高，而通过降低二次电池的输出电压以降低二次电池的安全风险时，又无法充分利用硬碳微孔结构作为活性离子储存位点的作用；功能涂层较厚时，由于其不具备电化学活性、不能贡献容量，由此会占据较多的体积空间和质量份额，反而影响二次电池的能量密度。
在一些实施例中，所述第二负极膜层的厚度为H 2μm，所述第一负极膜层的厚度为H 3μm，并且所述负极极片满足H 2/H 3为0.10至5，可选地为0.5至4。
发明人在进一步研究中发现，第二负极膜层的厚度H 2μm与第一负极膜层的厚度H 3μm的比值在合适的范围内时，第二负极膜层和第一负极膜层能够发挥更好地协同作用效果。第二负极膜层主要承担大倍率充电压力，保证二次电池具有高充电倍率；第一负极膜层主要用于提供长循环寿命，同时保证高首次库伦效率，由此二次电池的综合性能更好，能够在高能量密度下实现大倍率充电。并且能够有效避免以下情况：第二负极膜层较薄而第一负极膜层较厚时，充电过程中第二负极膜层中的硬碳分担的大倍率充电压力较少，此时依旧是第一负极膜层中的石墨起到主导作用，由此导致对二次电池充电倍率的提升效果不明显；第二负极膜层较厚而第一负极膜层较薄时，由于硬碳表面含有大量非活性官能团，由此会增加活性离子的不可逆消耗，影响二次电池的首次库伦效率，同时二次电池的循环寿命也可能降低。
在一些实施例中，所述第二负极膜层的厚度为H 2μm，H 2为10至120，可选地为35至110，更可选地为40至100。第二负极膜层的厚度在合适的范围内时，有利于二次电池具有高充电倍率。
在一些实施例中，所述第一负极膜层的厚度为H 3μm，H 3为20至100，可选地为25至70，更可选地为28至60。第一负极膜层的厚度在合适的范围内时，有利于二次电池具有高首次库伦效率和长循环寿命。
所述功能涂层包括铁电材料，在一些实施例中，所述功能涂层中的铁电材料的质量百分含量为W1，基于所述功能涂层的总质量计，W1为70％至95％，可选地为80％至95％。
发明人在进一步研究中发现，铁电材料的含量在合适的范围内时，二次电池的综合性能更好，能够在高能量密度下实现大倍率充电。并且能够有效避免以下情况：铁电材料的含量较少时，其产生的反向电场强度不够，可能起不到均衡电子密度和抑制枝晶在垂直极片方向持续生长的作用，由此在通过提高二次电池的输出电压以提高能量密度时，二次电池的安全风险升高，而通过降低二次电池的输出电压以降低二次电池的安全风险时，又无法充分利用硬碳微孔结构作为活性离子储存位点的作用；铁电材料的含量较高时，功能涂层中其他组分(例如粘结剂含量)较少，由此可能导致功能涂层与第二负极膜层之间的粘结性变差，容易从第二负极膜层脱落。
在一些实施例中，所述功能涂层还可以包括粘结剂，以将铁电材料彼此粘结和将功能涂层与第二负极膜层粘结。可选地，所述粘结剂可以包括选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种或多种的组合。
在一些实施例中，所述功能涂层还可以包括其他助剂。作为示例，所述其他助剂可以包括分散剂，例如羧甲基纤维素钠(CMC)。
所述第二负极膜层包括第二负极活性材料，所述第二负极活性材料包括硬碳。可选地，所述硬碳在所述第二负极活性材料中的质量百分含量为70％至100％，可选地为80％至98％，基于所述第二负极活性材料的总质量计。由此第二负极膜层含有较多的硬碳，有 利于二次电池具有更高的充电倍率。在一些实施例中，所述第二负极活性材料可以仅包括硬碳；在另一些实施例中，所述第二负极活性材料还可以包括硬碳以外的其他负极活性材料，例如石墨、软碳、中间相碳微球、硅基材料、锡基材料等，可选地，所述其他负极活性材料在所述第二负极活性材料中的质量百分含量在30％以下，更可选地在20％以下，基于所述第二负极活性材料的总质量计。
在一些实施例中，所述第二负极膜层中的硬碳的质量百分含量为W2，基于所述第二负极膜层的总质量计，W2为68％以上，可选地为90％至98％。硬碳的含量在合适的范围内时，有利于二次电池具有更高的充电倍率。
在一些实施例中，所述第二负极膜层还可以包括导电剂，以在第二负极活性材料(例如硬碳)之间起到收集微电流的作用，减小电极的接触电阻，加速电子的移动速率；同时还能够降低极化，提高二次电池的充放电效率。作为示例，所述导电剂可以包括选自超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的一种或多种的组合。在一些实施例中，基于所述第二负极膜层的总质量计，所述导电剂的质量百分含量在5％以下。
在一些实施例中，所述第二负极膜层还可以包括粘结剂，以将第二负极活性材料彼此粘结、将第二负极膜层和功能涂层粘结、以及将第二负极膜层和第一负极膜层粘结。作为示例，所述粘结剂可以包括选自丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸类树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)和羧甲基壳聚糖(CMCS)中的一种或多种的组合。在一些实施例中，基于所述第二负极膜层的总质量计，所述粘结剂的质量百分含量在5％以下。
在一些实施例中，所述第二负极膜层还可以包括其他助剂。作为示例，所述其他助剂可以包括增稠剂，例如，羧甲基纤维素钠(CMC)、PTC热敏电阻材料等。在一些实施例中，基于所述第二负极膜层的总质量计，所述其他助剂的质量百分含量在2％以下。
所述第一负极膜层包括第一负极活性材料，所述第一负极活性材料包括石墨。可选地，所述石墨在所述第一负极活性材料中的质量百分含量为80％至100％，可选地为90％至98％，基于所述第一负极活性材料的总质量计。由此第一负极膜层含有较多的石墨，有利于二次电池具有更高的首次库伦效率和更长的循环寿命。在一些实施例中，所述第一负极活性材料可以仅包括石墨；在另一些实施例中，所述第一负极活性材料还可以包括石墨以外的其他负极活性材料，例如硬碳、软碳、中间相碳微球、硅基材料、锡基材料等，可选地，所述其他负极活性材料在所述第一负极活性材料中的质量百分含量在20％以下，更可选地在10％以下，基于所述第一负极活性材料的总质量计。
在一些实施例中，所述第一负极膜层中的石墨的质量百分含量为W3，基于所述第一负极膜层的总质量计，W3为78％以上，可选地为90％至98％。石墨的含量在合适的范围内时，有利于二次电池具有更高的首次库伦效率和更长的循环寿命。
在一些实施例中，所述第一负极膜层还可以包括导电剂，以在第一负极活性材料(例如石墨)之间起到收集微电流的作用，减小电极的接触电阻，加速电子的移动速率；同时还能够降低极化，提高二次电池的充放电效率。作为示例，所述导电剂可以包括选自超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维 中的一种或多种的组合。在一些实施例中，基于所述第一负极膜层的总质量计，所述导电剂的质量百分含量在5％以下。
在一些实施例中，所述第一负极膜层还可以包括粘结剂，以将第一负极活性材料彼此粘结、将第一负极膜层和第二负极膜层粘结、以及将第一负极膜层和负极集流体粘结。作为示例，所述粘结剂可以包括选自丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸类树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)和羧甲基壳聚糖(CMCS)中的一种或多种的组合。在一些实施例中，基于所述第一负极膜层的总质量计，所述粘结剂的质量百分含量在5％以下。
在一些实施例中，所述第一负极膜层还可以包括其他助剂。作为示例，所述其他助剂可以包括增稠剂，例如，羧甲基纤维素钠(CMC)、PTC热敏电阻材料等。在一些实施例中，基于所述第一负极膜层的总质量计，所述其他助剂的质量百分含量在2％以下。
在一些实施例中，所述铁电材料的体积平均粒径Dv50为d 1μm，d 1为1以下，例如，可以为0.8以下，0.7以下，0.6以下，0.5以下，0.4以下，0.3以下，0.2以下。可选地，d 1为0.01至1，0.02至1，0.03至1，0.04至1，0.05至1，0.06至1，0.07至1，0.08至1，0.01至0.8，0.02至0.8，0.03至0.8，0.04至0.8，0.05至0.8，0.06至0.8，0.07至0.8，0.08至0.8，0.09至0.8或0.1至0.8。
铁电材料的Dv50在合适的范围内时，二次电池的综合性能更好，能够在高能量密度下实现大倍率充电，同时能够降低生产成本。并且能够有效避免以下情况：铁电材料的Dv50较大时，其产生的反向电场干扰较大，可能起不到均衡电子密度和抑制枝晶在垂直极片方向持续生长的作用，由此在通过提高二次电池的输出电压以提高能量密度时，二次电池的安全风险升高，而通过降低二次电池的输出电压以降低二次电池的安全风险时，又无法充分利用硬碳微孔结构作为活性离子储存位点的作用；铁电材料的Dv50较小时，其制备工艺复杂，由此增加了生产成本。
在一些实施例中，所述第二负极活性材料的体积平均粒径Dv50为d 2μm，所述第一负极活性材料的体积平均粒径Dv50为d 3μm，d 2/d 3为0.1至1，可选地为0.2至0.8。
在本申请的负极极片中，第一负极膜层采用粒径较大的第一负极活性材料，由此第一负极膜层的压实密度更高，有利于二次电池具有高首次库伦效率、高能量密度和长循环寿命。在本申请的负极极片中，第二负极膜层采用粒径较小的第二负极活性材料，由此其比表面积较高，能够增加与电解液的接触面积，缩短活性离子的液相扩散路径和固相扩散路径；同时第二负极膜层孔道结构的完整性能保持地更好，由此有利于二次电池具有更高的充电倍率。此外，由于第二负极活性材料的粒径较小，其更耐压，由此第二负极活性材料，特别是硬碳的微孔结构保持地更好，从而能够充分利用硬碳微孔结构作为活性离子储存位点的作用，提高二次电池的容量发挥和能量密度；同时第二负极膜层的压实密度较低，有利于电解液快速浸润到第一负极膜层，降低负极极化，提高二次电池的充放电效率。
发明人在进一步研究中发现，当第二负极活性材料的粒径和第一负极活性材料的粒径之比d 2/d 3在合适的范围内时，有利于充分发挥第二负极膜层提高二次电池大倍率充电能力以及第一负极膜层提高二次电池首次库伦效率和循环寿命的作用，由此二次电池 的综合性能更好，能够在高能量密度下实现大倍率充电。
在一些实施例中，所述第二负极活性材料的体积平均粒径Dv50为d 2μm，d 2为3至11，可选地为3至9。第二负极活性材料的粒径在合适的范围内时，其微孔结构保持地更好，从而能够充分利用硬碳微孔结构作为活性离子储存位点的作用，提高二次电池的容量发挥和能量密度；同时第二负极活性材料的粒径在合适的范围内时，第二负极膜层能够具有通畅的孔道结构，由此有利于电解液顺利经过第二负极膜层的孔道结构并快速浸润第一负极膜层，从而降低负极极化，提高二次电池的充放电效率。
在一些实施例中，所述第二负极活性材料的粒径分布指数(Dv90-Dv10)/Dv50为α 1，α 1为0.6至5，可选地为1至4。第二负极活性材料的粒径分布指数在合适的范围内时，有利于改善第二负极膜层的加工性能，使第二负极膜层整体具有较高的颗粒分布一致性和通畅的孔道结构，由此有利于第二负极膜层不同区域均具有较高的活性离子传输性能，从而进一步提升二次电池的大倍率充电能力；同时还有利于电解液快速浸润第一负极膜层，降低负极极化，提高二次电池的充放电效率。
在一些实施例中，所述第二负极活性材料的比表面积为3m 2/g至7m 2/g，可选地为4m 2/g至6m 2/g。第二负极活性材料的比表面积在合适的范围内时，能减小电荷交换阻抗，并且使第二负极膜层具有更通畅的孔道结构，由此具有更高的活性离子传输性能，从而进一步提升二次电池的大倍率充电能力。第二负极活性材料的比表面积在合适的范围内时，还能提高SEI膜的成膜效率，避免形成过厚的SEI膜，减少活性离子的不可逆消耗，从而进一步改善二次电池的容量发挥和循环性能。
在一些实施例中，所述第二负极活性材料在20000N下的粉体压实密度为0.9g/cm 3至1.3g/cm 3，可选地为1g/cm 3至1.2g/cm 3。第二负极活性材料的粉体压实密度在合适的范围内时，有利于提升二次电池的能量密度。
在一些实施例中，所述第二负极活性材料包括一次颗粒、二次颗粒或其组合，可选地，所述第二负极活性材料中一次颗粒的数量占比为90％至100％。当第二负极活性材料包含合适比例的一次颗粒时，有利于第二负极膜层具有较短的活性离子传输路径，由此能进一步提升二次电池的大倍率充电能力；此外，还能降低负极极化和电解液副反应，从而进一步改善二次电池的循环性能和存储性能。
在一些实施例中，所述第一负极活性材料的体积平均粒径Dv50为d 3μm，d 3为9至18，可选地为11至15。第一负极活性材料的粒径在合适的范围内时，有利于第一负极膜层具有高压实密度，从而使二次电池具有高首次库伦效率、高能量密度和长循环寿命。
在一些实施例中，所述第一负极活性材料的粒径分布指数(Dv90-Dv10)/Dv50为α 2，α 2为0.2至5，可选地为0.3至4。第一负极活性材料的粒径分布指数在合适的范围内时，有利于改善第一负极膜层的加工性能，使第一负极膜层整体具有较高的颗粒分布一致性和通畅的孔道结构，由此有利于第一负极膜层不同区域均具有较高的活性离子传输性能，从而进一步改善二次电池的循环性能。
在一些实施例中，所述第一负极活性材料的比表面积为0.6m 2/g至1.5m 2/g，可选地为0.8m 2/g至1.4m 2/g。第一负极活性材料的比表面积在合适的范围内时，能减小电荷交换阻抗，并且使第一负极膜层具有更通畅的孔道结构，由此具有更高的活性离子传输性能，从而进一步提升二次电池的循环性能。
在一些实施例中，所述第一负极活性材料在20000N下的粉体压实密度为1.4g/cm 3至1.85g/cm 3，可选地为1.6g/cm 3至1.75g/cm 3。第一负极活性材料的粉体压实密度在合适的范围内时，有利于提升二次电池的能量密度。
在一些实施例中，所述第一负极活性材料的石墨化度为91％至95％，可选地为92％至94％。第一负极活性材料的石墨化度在合适的范围内时，有利于提升二次电池的循环性能。
在一些实施例中，所述第一负极活性材料包括人造石墨、天然石墨或其组合。可选地，所述第一负极活性材料中的人造石墨的质量百分含量在50％以上，可选地为60％至100％，基于所述第一负极活性材料的总质量计。可选地，所述人造石墨表面还具有碳包覆层，由此能够进一步降低电荷转移阻抗，提升二次电池的循环性能和大倍率充电能力，可选地，所述碳包覆层包括无定形碳。
在一些实施例中，所述第一负极活性材料包括一次颗粒、二次颗粒或其组合，可选地，所述第一负极活性材料中二次颗粒的数量占比为80％至100％。当第一负极活性材料包含合适比例的二次颗粒时，其各向同性度提高，有利于第一负极膜层具有较多的活性离子传输通道，由此能进一步提升二次电池的大倍率充电能力；同时有利于第一负极膜层具有高压实密度，提高二次电池的能量密度；此外，还能降低负极极化和电解液副反应，从而进一步改善二次电池的循环性能和存储性能。
在一些实施例中，所述负极极片的压实密度为1.4g/cm 3至1.85g/cm 3，可选地为1.6g/cm 3至1.75g/cm 3。负极极片的压实密度在合适的范围内时，有利于提升二次电池的大倍率充电能力、循环性能和能量密度。
在一些实施例中，所述负极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铜箔或铜合金箔。复合集流体可以包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层，作为示例，金属材料可以包括选自铜、铜合金、镍、镍合金、钛、钛合金、银和银合金中的一种或多种的组合，高分子材料基层可以包括选自聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的一种或多种的组合。
负极集流体具有在自身厚度方向相对的两个表面，上述第一负极膜层、第二负极膜层和功能涂层可以设置在负极集流体的两个相对表面中的任意一者上或两者上。
需要说明的是，本申请所给的各第一负极膜层、第二负极膜层和功能涂层参数均指负极集流体单侧的涂覆层的参数范围。当第一负极膜层、第二负极膜层和功能涂层设置在负极集流体的两个表面上时，其中任意一个表面上的涂覆层参数满足本申请，即认为落入本申请的保护范围内。
下面结合附图说明本申请的负极极片。图1是本申请的负极极片10的一实施方式的示意图。负极极片10包括负极集流体104以及分别设置在负极集流体104两个表面上的第一负极膜层103、设置在第一负极膜层103上的第二负极膜层102和设置在第二负极膜层102上的功能涂层101。当然，第一负极膜层103、第二负极膜层102和功能涂层101也可以仅设置在负极集流体104的其中一个表面上。
在本申请中，材料的Dv90、Dv50、Dv10为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以参照GB/T 19077-2016粒度分布激光衍射法，采用激 光粒度分析仪方便地测试，如英国马尔文仪器有限公司的Mastersizer2000E型激光粒度分析仪。Dv90为材料累计体积分布百分数达到90％时所对应的粒径；Dv50为材料累计体积分布百分数达到50％时所对应的粒径；Dv10为材料累计体积分布百分数达到10％时所对应的粒径。
在本申请中，材料的比表面积为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出。氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
在本申请中，材料的石墨化度为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以使用X射线衍射仪(如Bruker D8 Discover)进行测试，测试可参考JIS K 0131-1996、JB/T 4220-2011，得到d 002，然后根据公式g＝(0.344-d 002)/(0.344-0.3354)×100％计算得出材料的石墨化度。在上述公式中，d 002是以纳米(nm)表示的材料晶体结构中(002)晶面的层间距。
在本申请中，材料的粉体压实密度为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以参照GB/T24533-2009，通过电子压力试验机(例如UTM7305型)测试。一个示例性测试方法包括如下步骤：称取1g材料，加入底面积为1.327cm 2的模具中，加压至2000kg(相当于20000N)，保压30s，然后卸压，保持10s，然后记录并计算材料在20000N作用力下的粉体压实密度。
在本申请中，一次颗粒和二次颗粒的数量占比可以用本领域公知的仪器及方法进行测定，例如采用扫描电子显微镜测定。为了确保测试结果的准确性，可在测试样品中随机选取多个(例如5个以上)不同区域进行扫描测试，并在一定放大倍率(例如1000倍以上)下，计算各区域中一次颗粒和二次颗粒数量占总颗粒数量的百分比，即为该区域中一次颗粒和二次颗粒各自的数量占比。为了确保测试结果的准确性，可以取多个测试样品(例如10个以上)重复进行上述测试，取各个测试样品的平均值作为最终的测试结果。测试依据可参考JY/T010-1996。
在本申请中，第一负极膜层、第二负极膜层和功能涂层的厚度为本领域公知的含义，可以用本领域公知的仪器及方法进行测定，例如可以通过扫描电子显微镜(例如ZEISS Sigma 300)进行测试，由此可以更准确地判断功能涂层和第二负极膜层的分界区以及第二负极膜层和第一负极膜层之间的分界区。一个示例性的测试方法包括如下步骤：将负极极片裁成一定尺寸的待测样品(例如2cm×2cm)，通过石蜡将负极极片固定在样品台上；将样品台装进样品架上锁好固定，打开氩离子截面抛光仪(例如IB-19500CP)电源并抽真空(例如10 -4Pa)，设置氩气流量(例如0.15MPa)和电压(例如8KV)以及抛光时间(例如2小时)，调整样品台为摇摆模式开始抛光。测试依据可参考JY/T010-1996。为了确保测试结果的准确性，可以在待测样品中随机选取多个(例如5个以上)不同区域进行扫描测试，并在一定放大倍率(例如500倍以上)下，读取标尺测试区域中第一负极膜层、第二负极膜层和功能涂层各自的厚度。为了测试的准确性，可以取多个测试区域进行测试并取平均值。
在本申请中，负极极片的压实密度为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。负极极片的压实密度＝负极极片的面密度/负极集流体单侧的涂覆层 厚度。负极极片的面密度为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。一个示例性测试方法如下：取单面涂覆且经冷压后的负极极片(若是双面涂覆的负极极片，可先擦拭掉其中一面的涂覆层)冲切成面积为S 1的小圆片，称其重量，记录为M 1；然后将上述称重后的负极极片的涂覆层擦拭掉，称量负极集流体的重量，记录为M 0；负极极片的面密度＝(M 1-M 0)/S 1。
需要说明的是，上述针对第一负极活性材料、第二负极活性材料和铁电材料的各种参数测试，可以在涂覆前取样测试，也可以从冷压后的负极极片中取样测试。当测试样品是从经冷压后的负极极片中取样时，作为示例，可以按如下步骤进行取样：(1)任意选取负极集流体其中一侧经冷压后的涂覆层，对铁电材料取样(例如可以选用刀片刮粉取样)，刮粉深度不超过功能涂层和第二负极膜层的分界区；(2)对第二负极活性材料取样(例如可以选用刀片刮粉取样)，刮粉深度不超过第二负极膜层和第一负极膜层的分界区，因在冷压过程中，功能涂层和第二负极膜层之间的分界区可能存在互融层，因此为了测试的准确性，在对第二负极活性材料取样时，可以先将互融层刮掉，然后再对第二负极活性材料刮粉取样；(3)对第一负极活性材料取样(例如可以选用刀片刮粉取样)，因在冷压过程中，第二负极膜层和第一负极膜层之间的分界区可能存在互融层，因此为了测试的准确性，在对第一负极活性材料取样时，可以先将互融层刮掉，然后再对第一负极活性材料刮粉取样；(4)将上述收集到的铁电材料、第一负极活性材料和第二负极活性材料分别置于去离子水中，之后进行抽滤、烘干，再将烘干后的粉末在一定温度及时间下烧结(例如400℃，2h)去除粘结剂和导电剂等，即得到测试样品。
[制备方法]
本申请的负极极片的制备方法是公知的。在一些实施例中，可以通过如下的方法制备负极极片：将第一负极活性材料、导电剂、粘结剂和任意其他组分等分散于溶剂(例如去离子水)中形成第一浆料，将第二负极活性材料、导电剂、粘结剂和任意其他组分等分散于溶剂(例如去离子水)中形成第二浆料，将铁电材料、粘结剂和任意其他组分等分散于溶剂(例如去离子水)中形成第三浆料；将第一浆料涂覆在负极集流体上，经干燥形成第一负极膜层；将第二浆料涂覆在第一负极膜层上，经干燥形成第二负极膜层；将第三浆料涂覆在第二负极膜层上，经干燥、冷压等工序后，即得到负极极片。
二次电池
本申请实施方式还提供了一种二次电池，其包括本申请第一方面的负极极片。
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。二次电池包括电极组件和电解质，电极组件通常包括正极极片、负极极片和隔离膜。隔离膜设置在正极极片和负极极片之间，主要起到防止正极和负极短路的作用，同时可以使活性离子通过。电解质在正极极片和负极极片之间起到传导活性离子的作用。本申请的二次电池可为含锂二次电池，特别地，可为锂离子二次电池。
[负极极片]
本申请的二次电池中使用的负极极片为本申请第一方面任一实施例的负极极片。
[正极极片]
在一些实施例中，所述正极极片包括正极集流体以及设置在所述正极集流体至少 一个表面上的正极膜层。例如，所述正极集流体具有在自身厚度方向相对的两个表面，所述正极膜层设置于所述正极集流体的两个相对表面中的任意一者或两者上。
所述正极膜层包括正极活性材料，所述正极活性材料可采用本领域公知的用于二次电池的正极活性材料。例如，所述正极活性材料可以包括选自锂过渡金属氧化物、含锂磷酸盐及其各自的改性化合物中的一种或多种的组合。锂过渡金属氧化物的示例可以包括选自锂钴氧化物(例如LiCoO 2)、锂镍氧化物(例如LiNiO 2)、锂锰氧化物(例如LiMnO 2、LiMn 2O 4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物(例如LiNi 1/3Co 1/3Mn 1/3O 2、LiNi 0.5Co 0.2Mn 0.3O 2、LiNi 0.5Co 0.25Mn 0.25O 2、LiNi 0.6Co 0.2Mn 0.2O 2、LiNi 0.8Co 0.1Mn 0.1O 2)、锂镍钴铝氧化物(例如LiNi 0.85Co 0.15Al 0.05O 2)及其各自的改性化合物中的一种或多种的组合。含锂磷酸盐的示例可以包括选自磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其各自的改性化合物中的一种或多种的组合。
在一些实施例中，为了进一步提高二次电池的能量密度，所述正极活性材料可以包括式1所示的锂过渡金属氧化物及其改性化合物中的一种或多种的组合。
Li aNi bCo cM dO eA f   式1
在式1中，0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M可以包括选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti和B中的一种或多种的组合，A可以包括选自N、F、S和Cl中的一种或多种的组合。
在本申请中，上述各正极活性材料的改性化合物可以是对所述正极活性材料进行掺杂改性或/或表面包覆改性。
在一些实施例中，所述正极膜层还可以包括导电剂，以在正极活性材料之间起到收集微电流的作用，减小电极的接触电阻，加速电子的移动速率；同时还能够降低极化，提高二次电池的充放电效率。作为示例，所述导电剂可以包括选自超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的一种或多种的组合。在一些实施例中，基于所述正极膜层的总质量，所述导电剂的质量百分含量在5％以下。
在一些实施例中，所述正极膜层还可以包括粘结剂，以将正极活性材料彼此粘结以及将正极膜层和正极集流体粘结。作为示例，所述粘结剂可以包括选自聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物和含氟丙烯酸酯类树脂中的一种或多种的组合。在一些实施例中，基于所述正极膜层的总质量，所述粘结剂的质量百分含量在5％以下。
在一些实施例中，所述正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铝箔或铝合金箔。复合集流体可以包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层，作为示例，金属材料可以包括选自铝、铝合金、镍、镍合金、钛、钛合金、银和银合金中的一种或多种的组合，高分子材料基层可以包括选自聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的一种或多种的组合。
所述正极膜层通常是将正极浆料涂覆在正极集流体上，经干燥、冷压而成的。所述正极浆料通常是将正极活性材料、导电剂、粘结剂和任意其他组分等分散于溶剂中并 搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
[电解质]
本申请对所述电解质的种类没有具体的限制，可根据需求进行选择。例如，所述电解质可以选自固态电解质、凝胶电解质和液态电解质(即电解液)中的至少一种。
在一些实施例中，所述电解质采用电解液，所述电解液包括锂盐和溶剂。
作为示例，所述锂盐可以包括选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)和四氟草酸磷酸锂(LiTFOP)中的一种或多种的组合。
作为示例，所述有机溶剂可以包括选自碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)和二乙砜(ESE)中的一种或多种的组合。
在一些实施例中，所述电解液还可以包括添加剂，例如包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[隔离膜]
本申请对所述隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施例中，所述隔离膜的材质可以包括选自玻璃纤维、无纺布、聚乙烯、聚丙烯和聚偏二氟乙烯中的一种或多种的组合。所述隔离膜可以是单层薄膜，也可以是多层复合薄膜。当所述隔离膜为多层复合薄膜时，各层的材料相同或不同。
在一些实施例中，所述正极极片、所述隔离膜和所述负极极片可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施例中，所述二次电池可以包括外包装。该外包装可用于封装上述电极组件及电解液。
在一些实施例中，所述二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。所述二次电池的外包装也可以是软包，例如袋式软包。所述软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)和聚丁二酸丁二醇酯(PBS)中的一种或多种的组合。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图2是作为一个示例的方形结构的二次电池5。
在一些实施例中，如图3所示，外包装可以包括壳体51和盖板53。其中，壳体51可以包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53用于盖设所述开口，以封闭所述容纳腔。正极极片、负极极片 和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，可根据需求来调节。
本申请的二次电池的制备方法是公知的。在一些实施例中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺或叠片工艺形成电极组件，将电极组件置于外包装中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
在本申请的一些实施例中，根据本申请的二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图4是作为一个示例的电池模块4的示意图。如图4所示，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图5和图6是作为一个示例的电池包1的示意图。如图5和图6所示，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2用于盖设下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
用电装置
本申请实施方式还提供一种用电装置，所述用电装置包括本申请的二次电池、电池模块和电池包中的至少一种。所述二次电池、电池模块和电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述用电装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图7是作为一个示例的用电装置的示意图。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1-l
步骤(1)：负极极片的制备
S10，人造石墨的制备
将石油非针状焦生焦原料粉末预处理后去除杂质，然后与煤沥青混合后造粒得到Dv50为10μm的二次颗粒，之后再将造粒产物置于艾奇逊石墨化炉中在3000℃石墨化处理24h，得到石墨颗粒；将得到的石墨颗粒与石油沥青混合后在1000℃碳化处理15h，得到人造石墨。人造石墨的Dv50为12μm、Dv90为20μm、Dv10为6.5μm，石墨化度为92％，比表面积为0.86m 2/g，粉体压实密度为1.6g/cm 3，形貌为二次颗粒。
S20，硬碳的制备
将酚醛树脂在500℃下加热处理30min，制得前驱体；将所得到的前驱体粉碎后在氮气气氛保护下于1200℃热处理20h，之后再次粉碎，得到硬碳。硬碳的Dv50为5μm、Dv90为10μm、Dv10为2.5μm，比表面积为5m 2/g，形貌为一次颗粒。
S30，第一浆料的制备
将上述制备的人造石墨、导电剂导电炭黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按照质量比96.8:0.8:1.2:1.2混合后加入去离子水中，在真空搅拌机作用下搅拌至体系呈均一状，得到固含量为66％的第一浆料。
S40，第二浆料的制备
将上述制备的硬碳、导电剂导电炭黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按照质量比95:1.5:3.1:0.4混合后加入去离子水中，在真空搅拌机作用下搅拌至体系呈均一状，得到固含量为66％的第二浆料。
S50，第三浆料的制备
将Dv50为100nm的钛酸钡(介电常数为3000以上)、粘结剂丁苯橡胶(SBR)、分散剂羧甲基纤维素钠(CMC)按照质量比85:10:5混合后加入去离子水中，在真空搅拌机作用下搅拌至体系呈均一状，得到固含量为40％的第三浆料。
S60，浆料的涂覆
将第一浆料涂覆在厚度为8μm的负极集流体铜箔的一个表面上，经干燥形成第一负极膜层；将第二浆料涂覆在第一负极膜层上，经干燥形成第二负极膜层；将第三浆料涂覆在第二负极膜层上，经干燥后形成功能涂层；之后在负极集流体铜箔的另一个表面上重复上述步骤，再经冷压等工序后，即得到负极极片。负极集流体单侧的第一负极膜层的厚度为59μm、第二负极膜层的厚度为82μm、功能涂层的厚度为2μm。负极极片的压实密度为1.55g/cm 3。
步骤(2)：正极极片的制备
将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、导电剂导电炭黑、粘结剂聚偏氟乙烯(PVDF)按照质量比98:1:1混合后加入溶剂NMP中，在真空搅拌机作用下搅拌至体系呈均一状，得到固含量为75％的正极浆料；将正极浆料均匀涂覆在厚度为13μm的铝箔的两个表面上，90℃下干燥后，经冷压得到正极集流体单侧的正极膜层厚度为114μm的正极极片。
步骤(3)：电解液的制备
在含水量小于10ppm的环境下，将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、 碳酸二乙酯(DEC)按照按体积比1:1:1进行混合得到有机溶剂，接着将充分干燥的LiPF 6溶解于上述有机溶剂中，配制成浓度为1mol/L的电解液。
步骤(4)：隔离膜的制备
采用多孔聚乙烯膜作为隔离膜。
步骤(5)：二次电池的制备
将正极极片、隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件；将电极组件置于外包装中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
实施例1-2至1-7
二次电池按照与实施例1-1类似的方法相似制备，不同之处在于负极极片的制备中第三浆料的涂覆厚度以及由此得到的功能涂层的厚度不同，具体参数详见表1。
对比例1-l
二次电池按照与实施例1-1类似的方法相似制备，不同之处在于负极极片的制备中未涂覆第三浆料。
对比例1-2
二次电池按照与实施例1-1类似的方法相似制备，不同之处在于负极极片的制备中未涂覆第三浆料，并且涂覆浆料时，首先将第二浆料涂覆在厚度为8μm的负极集流体铜箔的一个表面上，经干燥形成第一负极膜层，然后将第一浆料涂覆在第一负极膜层上，经干燥形成第二负极膜层，然后在负极集流体铜箔的另一个表面上重复上述步骤，之后经冷压等工序，即得到负极极片。负极集流体单侧的第一负极膜层的厚度为82μm、第二负极膜层的厚度为59μm。
对比例1-3
二次电池按照与实施例1-1类似的方法相似制备，不同之处在于负极极片的制备中未涂覆第二浆料和第三浆料。
将第一浆料涂覆在厚度为8μm的负极集流体铜箔的两个表面上，经干燥、冷压等工序后，即得到负极极片。负极集流体单侧的负极膜层的厚度为141μm。
对比例1-4
二次电池按照与实施例1-1类似的方法相似制备，不同之处在于负极极片的制备中未涂覆第一浆料和第三浆料。
将第二浆料涂覆在厚度为8μm的负极集流体铜箔的两个表面上，经干燥、冷压等工序后，即得到负极极片。负极集流体单侧的负极膜层的厚度为141μm。
对比例1-5
二次电池按照与实施例1-1类似的方法相似制备，不同之处在于负极极片的制备工艺不同。
S10至S20同实施例1-1。
S30，浆料的制备
将上述制备的人造石墨和硬碳、导电剂导电炭黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按照质量比40:55:1.5:3.1:0.4混合后加入去离子水中，在真空搅拌机作用下搅拌至体系呈均一状，得到固含量为66％的浆料。
S40，浆料的涂覆
将浆料涂覆在厚度为8μm的负极集流体铜箔的两个表面上，经干燥、冷压等工序后，即得到负极极片。负极集流体单侧的负极膜层的厚度为141μm。
对比例1-6
二次电池按照与实施例1-1类似的方法相似制备，不同之处在于负极极片的制备工艺不同。
S10至S30同实施例1-1。
S40，第二浆料的制备
将上述制备的硬碳、钛酸钡(Dv50为100nm、介电常数为3000以上)、导电剂导电炭黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按照质量比93:1:1.5:3.1:0.4混合后加入去离子水中，在真空搅拌机作用下搅拌至体系呈均一状，得到固含量为66％的第二浆料。
S50，浆料的涂覆
将第一浆料涂覆在厚度为8μm的负极集流体铜箔的一个表面上，经干燥形成第一负极膜层；将第二浆料涂覆在第一负极膜层上，经干燥形成第二负极膜层；之后在负极集流体铜箔的另一个表面上重复上述步骤，再经冷压等工序后，即得到负极极片。负极集流体单侧的第一负极膜层的厚度为59μm、第二负极膜层的厚度为82μm。
测试部分
(1)最大充电倍率测试
在25℃下，将上述制备的二次电池以0.33C倍率满放、以0.33C倍率满充；之后将满充的二次电池静置5min后，以0.33C倍率满放，此时得到的放电容量为二次电池0.33CC倍率下的实际容量，记为C0。将二次电池在xC0倍率(表示梯度充电倍率，例如，1C0、1.1C0、1.2C0、1.3C0、1.4C0……)下满充，静置5min后以1C满放，如此循环10圈后，再将二次电池以1C满充。拆解二次电池观察负极极片表面的析锂情况，如果负极极片表面未析锂，则增大充电倍率再次进行测定，直至负极极片表面析锂，记录负极极片表面未析锂的最大充电倍率。二次电池的最大充电倍率越高，大倍率充电能力越好。
(2)能量密度测试
在25℃下，将上述制备的二次电池以0.33C倍率满充、以0.33C倍率满放，如此循环3圈后，记录二次电池的放电能量。二次电池的能量密度＝二次电池的放电能量/二次电池的质量。在本申请的各实施例和对比例中，以对比例1-1制备的二次电池的能量密度为100％来表示其他各实施例和对比例的二次电池的能量密度。
(3)循环寿命测试
在25℃下，将上述制备的二次电池以1C倍率满放、以1C倍率满充；之后将满充的二次电池静置5min后，以1C倍率满放，此时得到的放电容量C0作为二次电池的初始容量。将二次电池以3C倍率满充、以1C倍率满放，如此进行循环充放电测试，并记录每圈循环后的放电容量，直至二次电池的放电容量衰减为初始容量的80％，用此时的循环圈数表征二次电池的循环寿命。二次电池的循环圈数越高，预期循环寿命越长。
表1
Figure PCTCN2022103809-appb-000001
综合实施例1-1至1-7和对比例1-1至1-6的测试结果可知，采用本申请三层结构设计的负极极片的二次电池同时具有高充电倍率和长循环寿命。对比例1-1的负极集流体表面依次设置了石墨层和硬碳层，但未设置功能涂层，二次电池长期循环充放电过程中容易析锂，由此影响二次电池的循环寿命。对比例1-2的负极集流体表面依次设置了硬碳层和石墨层，但未设置功能涂层，由此二次电池难以同时具有高充电倍率和长循环寿命。对比例1-3仅在负极集流体表面设置了石墨层，由此二次电池可以具有长循环寿命，但难以具有高充电倍率。对比例1-4仅在负极集流体表面设置了硬碳层，由此二次电池可以具有较高的充电倍率，但难以具有长循环寿命。对比例1-5的负极集流体表面设置了石墨和硬碳的混合层，由此二次电池也难以同时具有高充电倍率和长循环寿命。与对比例1-1相比，对比例1-6的硬碳层中还包括了钛酸钡，但钛酸钡抑制锂枝晶在垂直极片方向持续生长的作用效果较差，难以起到明显提升二次电池充电倍率和循环寿命的作用。
综合实施例1-1至1-7的测试结果还可知，功能涂层的厚度增加，二次电池的最大充电倍率和循环寿命均增加。可能的原因在于，功能涂层产生的反向电场强度增加，由此其抑制锂枝晶在垂直极片方向持续生长的作用效果增加，因此，二次电池的大倍率充电能力及循环性能均得以提升。
综合实施例1-1至1-7的测试结果还可知，当H 1/(H 2+H 3)小于0.01时，功能涂层相对于第一负极膜层和第二负极膜层的总厚度设置较小，其抑制锂枝晶在垂直极片方向持续生长的作用效果不明显，由此对二次电池最大充电倍率的提升效果不明显。
综合实施例1-6和1-7的测试结果还可知，当H 1大于10时，功能涂层抑制锂枝晶在垂直极片方向持续生长的作用效果不会持续增加，二次电池的最大充电倍率不会持续增加；同时由于功能涂层不具备电化学活性、不能贡献容量，由此当其厚度大于10μm时，还使得二次电池的能量密度明显降低。
发明人接下来研究了功能涂层中铁电材料的质量百分含量对二次电池性能的影响。实施例2-1至2-6的二次电池按照与实施例1-2类似的方法相似制备，不同之处在于功能涂层中铁电材料的质量百分含量不同。
表2
序号 铁电材料含量W1 最大充电倍率 循环圈数 能量密度
实施例2-1 70％ 5.1C0 2000 98.8％
实施例2-2 75％ 5.3C0 2150 98.5％
实施例2-3 80％ 5.4C0 2200 98.3％
实施例2-4 90％ 5.6C0 2300 98.0％
实施例2-5 95％ 5.7C0 2350 97.8％
实施例2-6 98％ 6.0C0 1550 97.5％
综合实施例1-2、2-1至2-6的测试结果可知，当功能涂层的厚度固定为4μm时，随着功能涂层中铁电材料的质量百分含量增加，二次电池的最大充电倍率和循环寿命均增加。可能的原因在于，此时功能涂层产生的反向电场强度增加，由此其抑制锂枝晶在垂直极片方向持续生长的作用效果增加，因此，二次电池的大倍率充电能力和循环性能均得以提升。
综合对比例1-1和实施例2-1的测试结果还可知，当功能涂层中铁电材料的质量百分含量较小时，由此得到的功能涂层抑制锂枝晶在垂直极片方向持续生长的作用效果不明显，由此对二次电池最大充电倍率的提升效果不明显。
综合实施例2-5和2-6的测试结果还可知，当功能涂层中铁电材料的质量百分含量大于95％时，二次电池的循环性能明显变差。可能的原因在于，此时功能涂层中的粘结剂含量过少，二次电池长期循环充放电过程中，功能涂层可能从第二负极膜层表面脱落。
发明人接下来研究了功能涂层中铁电材料的体积平均粒径Dv50对二次电池性能的影响。实施例3-1至3-6的二次电池按照与实施例1-2类似的方法相似制备，不同之处在于功能涂层中铁电材料的体积平均粒径Dv50不同。
表3
序号 铁电材料的Dv50 最大充电倍率 循环圈数
实施例3-1 0.05μm 5.8C0 2300
实施例3-2 0.3μm 5.4C0 2245
实施例3-3 0.5μm 5.3C0 2220
实施例3-4 0.8μm 5.2C0 2210
实施例3-5 1.0μm 5.1C0 2000
实施例3-6 1.5μm 5.1C0 1700
综合实施例1-2、3-1至3-6的测试结果可知，当功能涂层的厚度固定为4μm、铁电材料的质量百分含量固定为85％时，随着铁电材料的体积平均粒径Dv50增加，二次电池的最大充电倍率和循环寿命均下降。可能的原因在于，随着铁电材料的体积平均粒径Dv50增加，其产生的反向电场干扰增加，由此导致抑制锂枝晶在垂直极片方向持续生长的作用效果变差，因此，二次电池的最大充电倍率和循环寿命均下降。
发明人接下来研究了第一负极膜层厚度和第二负极膜层厚度对二次电池性能的影响。实施例4-1至4-7的二次电池按照与实施例1-2类似的方法相似制备，不同之处在于第一负极膜层厚度和第二负极膜层厚度不同。
表4
Figure PCTCN2022103809-appb-000002
综合实施例4-1至4-7的测试结果可知，第二负极膜层厚度增加时，二次电池的最大充电倍率增加。
综合实施例4-1至4-7的测试结果还可知，当第二负极膜层的厚度H 2μm和第一负极膜层的厚度H 3μm满足H 2/H 3在0.25至4之间时，二次电池能够同时具有较高的最大充电倍率以及较长的循环寿命。当H 2/H 3小于0.25时，第二负极膜层较薄，其起到的提升二次电池最大充电倍率的作用效果不明显；当H 2/H 3大于4时，第二负极膜层较厚，由于硬碳自身的循环性能较差，导致了二次电池的循环性能较差。综合实施例4-7和对比例1-4的测试结果可知，当H 2/H 3大于4时，对二次电池的循环寿命提升不明显。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (17)

  1. 一种负极极片，包括负极集流体以及依次设置在所述负极集流体至少一个表面上的第一负极膜层、第二负极膜层和功能涂层，其中，
    所述功能涂层包括铁电材料；
    所述第二负极膜层包括第二负极活性材料，所述第二负极活性材料包括硬碳；
    所述第一负极膜层包括第一负极活性材料，所述第一负极活性材料包括石墨。
  2. 根据权利要求1所述的负极极片，其中，所述功能涂层的厚度为H 1μm，所述第二负极膜层的厚度为H 2μm，所述第一负极膜层的厚度为H 3μm，并且所述负极极片满足H 1/(H 2+H 3)为0.01至0.15，可选地为0.01至0.08。
  3. 根据权利要求1-2中任一项所述的负极极片，其中，所述功能涂层的厚度为H 1μm，H 1为2至10，可选地为4至6。
  4. 根据权利要求1-3中任一项所述的负极极片，其中，所述第二负极膜层的厚度为H 2μm，所述第一负极膜层的厚度为H 3μm，并且所述负极极片满足H 2/H 3为0.10至5，可选地为0.5至4。
  5. 根据权利要求1-4中任一项所述的负极极片，其中，所述铁电材料的体积平均粒径Dv50为d 1μm，d 1为1以下，可选地为0.05至0.8。
  6. 根据权利要求1-5任一项所述的负极极片，其中，所述第二负极活性材料的体积平均粒径Dv50为d 2μm，所述第一负极活性材料的体积平均粒径Dv50为d 3μm，d 2/d 3为0.1至1，可选地为0.2至0.8。
  7. 根据权利要求1-6中任一项所述的负极极片，其中，所述功能涂层中的铁电材料的质量百分含量为W1，基于所述功能涂层的总质量计，W1为70％至95％，可选地为80％至95％。
  8. 根据权利要求1-7中任一项所述的负极极片，其中，
    所述第二负极膜层中的硬碳的质量百分含量为W2，基于所述第二负极膜层的总质量计，W2为68％以上，可选地为90％至98％；和/或，
    所述第一负极膜层中的石墨的质量百分含量为W3，基于所述第一负极膜层的总质量计，W3为78％以上，可选地为90％至98％。
  9. 根据权利要求1-8中任一项所述的负极极片，其中，所述第二负极活性材料满足如下条件(1)至(5)中的至少一者：
    (1)所述第二负极活性材料的体积平均粒径Dv50为d 2μm，d 2为3至11，可选地为3至7；
    (2)所述第二负极活性材料的粒径分布指数(Dv90-Dv10)/Dv50为α 1，α 1为0.6至5，可选地为1至4；
    (3)所述第二负极活性材料的比表面积为3m 2/g至7m 2/g，可选地为4m 2/g至6m 2/g；
    (4)所述第二负极活性材料在20000N下的粉体压实密度为0.9g/cm 3至1.3g/cm 3，可选地为1g/cm 3至1.2g/cm 3；
    (5)所述第二负极活性材料包括一次颗粒、二次颗粒或其组合，可选地，所述第二 负极活性材料中一次颗粒的数量占比为90％至100％。
  10. 根据权利要求1-9中任一项所述的负极极片，其中，所述第一负极活性材料满足如下条件(1)至(7)中的至少一者：
    (1)所述第一负极活性材料的体积平均粒径Dv50为d 3μm，d 3为9至18，可选地为11至15；
    (2)所述第一负极活性材料的粒径分布指数(Dv90-Dv10)/Dv50为α 2，α 2为0.2至5，可选地为0.3至4；
    (3)所述第一负极活性材料的比表面积为0.6m 2/g至1.5m 2/g，可选地为0.8m 2/g至1.4m 2/g；
    (4)所述第一负极活性材料在20000N下的粉体压实密度为1.4g/cm 3至1.85g/cm 3，可选地为1.6 g/cm 3至1.75g/cm 3；
    (5)所述第一负极活性材料的石墨化度为91％至95％，可选地为92％至94％；
    (6)所述第一负极活性材料包括人造石墨、天然石墨或其组合，可选地，所述人造石墨表面具有碳包覆层；
    (7)所述第一负极活性材料包括一次颗粒、二次颗粒或其组合，可选地，所述第一负极活性材料中二次颗粒的数量占比为80％至100％。
  11. 根据权利要求1-10中任一项所述的负极极片，其中，所述铁电材料的介电常数为50以上，可选地为50至100000。
  12. 根据权利要求1-11中任一项所述的负极极片，其中，所述铁电材料包括选自无机铁电材料、有机铁电材料中的一种或多种的组合，
    可选地，所述无机铁电材料包括选自钙钛矿结构氧化物、钨青铜型化合物、铋氧化物型层状结构化合物、铌酸锂、钽酸锂、偏铌酸铅和铌酸铅钡锂中的一种或多种的组合；
    可选地，所述有机铁电材料可以包括选自偏氟乙烯均聚物或共聚物、2,5-二溴-3,6-二羟对苯醌、吩嗪-氯冉酸、克酮酸中的一种或多种的组合。
  13. 根据权利要求1-12中任一项所述的负极极片，其中，所述功能涂层还包括粘结剂和/或分散剂，
    可选地，所述粘结剂包括选自丁苯橡胶、聚丙烯酸、聚丙烯酸钠、聚丙烯酰胺、聚乙烯醇、海藻酸钠、聚甲基丙烯酸及羧甲基壳聚糖中的一种或多种的组合；
    可选地，所述分散剂包括羧甲基纤维素钠。
  14. 一种二次电池，包括根据权利要求1-13中任一项所述的负极极片。
  15. 一种电池模块，包括根据权利要求14所述的二次电池。
  16. 一种电池包，包括根据权利要求14所述的二次电池、根据权利要求15所述的电池模块中的一种。
  17. 一种用电装置，包括根据权利要求14所述的二次电池、根据权利要求15所述的电池模块、根据权利要求16所述的电池包中的至少一种。
PCT/CN2022/103809 2022-07-05 2022-07-05 负极极片、二次电池、电池模块、电池包及用电装置 WO2024007142A1 (zh)

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