WO2022032624A1 - 二次电池及其制备方法与包含二次电池的电池模块、电池包及装置 - Google Patents

二次电池及其制备方法与包含二次电池的电池模块、电池包及装置 Download PDF

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WO2022032624A1
WO2022032624A1 PCT/CN2020/109120 CN2020109120W WO2022032624A1 WO 2022032624 A1 WO2022032624 A1 WO 2022032624A1 CN 2020109120 W CN2020109120 W CN 2020109120W WO 2022032624 A1 WO2022032624 A1 WO 2022032624A1
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positive electrode
secondary battery
film layer
negative electrode
active material
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PCT/CN2020/109120
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English (en)
French (fr)
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刘倩
李全国
胡霞
叶永煌
李伟
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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 EP20949122.4A priority Critical patent/EP4120408A4/en
Priority to PCT/CN2020/109120 priority patent/WO2022032624A1/zh
Priority to CN202080081119.XA priority patent/CN114730910B/zh
Publication of WO2022032624A1 publication Critical patent/WO2022032624A1/zh
Priority to US18/046,157 priority patent/US11804590B2/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
    • H01M4/364—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
    • 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
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • H01M2004/028—Positive 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present application belongs to the technical field of energy storage devices, and in particular relates to a secondary battery and a preparation method thereof, as well as a battery module, a battery pack and a device including the secondary battery.
  • Secondary batteries are widely used due to their outstanding features such as light weight, high energy density, no pollution, no memory effect, and long service life.
  • high-gram-capacity active materials such as high-gram-capacity positive active materials such as lithium nickel cobalt manganese oxides.
  • high-gram-capacity positive active materials such as lithium nickel cobalt manganese oxides.
  • Such materials have the problem of poor structural stability during charging and discharging, resulting in rapid capacity decay of the secondary battery during long-term use, thereby affecting the long-term cycle performance of the secondary battery.
  • How to make the secondary battery have higher cycle performance and at the same time improve the energy density has become a technical problem that needs to be solved urgently in the development of the secondary battery.
  • a first aspect of the present application provides a secondary battery, which includes a positive electrode piece, a negative electrode piece, and an electrolyte, the positive electrode piece includes a positive electrode current collector and at least one disposed on the positive electrode current collector. a positive electrode film layer on one surface and containing a positive electrode active material, the negative electrode pole piece includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and containing a negative electrode active material;
  • the positive active material includes a first material and a second material, the first material includes one or more of layered lithium transition metal oxides and modified compounds thereof, and the second material includes an olivine structure.
  • the first material includes one or more of layered lithium transition metal oxides and modified compounds thereof
  • the second material includes an olivine structure.
  • d c is the compaction density of the positive electrode film layer, in g/cm 3 ,
  • l c is the mass ratio of the positive electrode active material in the positive electrode film layer
  • d a is the compaction density of the negative electrode film layer, in g/cm 3 ,
  • I e is the ratio of the mass of the electrolyte in the secondary battery to the total mass of the electrolyte, the positive electrode active material and the negative electrode active material.
  • the inventors have found through keen research that by combining the first material and the second material, the advantages of different active materials can complement each other and make up for their respective shortcomings, so that the positive active material has both higher gram capacity and higher cycle stability. sex.
  • the secondary battery using the mixed positive electrode active material satisfies that the value of d c ⁇ l c ⁇ d a ⁇ l a /I e is within a specific range, the secondary battery can have a relatively high density per unit volume.
  • the high proportion of active materials, and the good electrolyte wettability and retention capacity inside the entire battery cell enable the capacity of the active material to be effectively exerted, thereby effectively improving the energy density of the secondary battery.
  • the secondary battery can also have high cycle performance.
  • the secondary battery may satisfy:
  • the secondary battery satisfies that the value of d c ⁇ l c ⁇ d a ⁇ la /I e is within the above-mentioned range, so that the secondary battery can better achieve both high energy density and long cycle life.
  • the compaction density d c of the positive electrode film layer is 2.1g/cm 3 to 4.2g/cm 3 , optionally 2.8g/cm 3 to 3.6g/cm 3 . cm 3 .
  • the compaction density of the positive electrode film layer is in an appropriate range, which can further improve the energy density and cycle performance of the secondary battery.
  • the mass ratio l c of the positive electrode active material in the positive electrode film layer is 0.85-0.99, optionally 0.90-0.985.
  • the positive electrode film layer contains more positive electrode active materials, so that the secondary battery can obtain higher energy density.
  • the compaction density da of the negative electrode film layer is 1.0g/cm 3 to 2.2g/cm 3 , optionally 1.2g/cm 3 to 1.85g / cm 3 .
  • the compaction density of the negative electrode film layer is in an appropriate range, which can further improve the energy density and cycle performance of the secondary battery.
  • the mass ratio la of the negative electrode active material in the negative electrode film layer is 0.85-0.99, optionally 0.90-0.985.
  • the negative electrode film layer contains more negative electrode active materials, so that the secondary battery can obtain higher energy density.
  • the ratio I e of the mass of the electrolyte in the secondary battery to the total mass of the electrolyte, the positive electrode active material and the negative electrode active material is: 0.1 to 0.5, optional 0.1 to 0.3.
  • Appropriate I e value can ensure that the secondary battery has higher cycle performance and at the same time improve energy density.
  • the secondary battery further satisfies:
  • the ⁇ is the ionic conductivity of the electrolyte at 25°C, in mS/cm;
  • the ⁇ c is the porosity of the positive electrode film layer
  • the ⁇ a is the porosity of the negative electrode film layer
  • the ⁇ ' is the contact angle of the electrolyte solution of the positive electrode film layer, and the unit is radian.
  • the inventor After in-depth research, the inventor also found that when the secondary battery satisfies the above relationship, it can ensure that the battery core has the ion transport medium necessary for its electrochemical performance, and also ensures that it has a good solid-liquid phase contact during the electrochemical cycle process. interface, which can further improve the cycle capacity retention rate and enable the battery to obtain higher cycle performance.
  • the porosity ⁇ c of the positive electrode film layer is 10% to 50%, optionally 20% to 30%.
  • the porosity of the positive electrode film layer is in an appropriate range, which is beneficial for the secondary battery to take into account high cycle life and energy density at the same time.
  • the porosity ⁇ a of the negative electrode film layer is 10% to 50%, optionally 20% to 30%.
  • the porosity of the negative electrode film layer is in an appropriate range, which is beneficial for the secondary battery to take into account high cycle life and energy density at the same time.
  • the ionic conductivity ⁇ of the electrolyte at 25°C is 0.5mS/cm ⁇ 50mS/cm, optionally 2mS/cm ⁇ 30mS/cm, and further optionally of 3mS/cm ⁇ 20mS/cm.
  • the electrolyte has high ionic conductivity, which can further improve the cycle performance of the secondary battery.
  • the electrolyte contact angle ⁇ of the positive electrode film layer satisfies 0° ⁇ 75°, and optionally 35° ⁇ 45°.
  • the positive electrode sheet has good affinity for the electrolyte, which can further improve the cycle performance and kinetic performance of the secondary battery.
  • the volume average particle size D v 50 of the first material is 0.1 ⁇ m ⁇ 30 ⁇ m, optionally 2 ⁇ m ⁇ 15 ⁇ m, and further optionally 3 ⁇ m ⁇ 8 ⁇ m.
  • the D v 50 of the first material is in an appropriate range, which can further improve the energy density and cycle performance of the secondary battery.
  • the first material includes one or more of single particles and secondary particles.
  • the cathode active material with single particle morphology can improve the cycle performance of the battery.
  • a single particle is matched with an appropriate amount of secondary particles, it is beneficial to improve the processing performance of the positive electrode slurry and improve the compaction density of the positive electrode film layer, thereby enabling the secondary battery to have a higher energy density.
  • the number proportion of the single particles in the first material is 50% to 100%, optionally 80% to 100%.
  • the volume average particle size D v 50 of the second material is 0.01 ⁇ m ⁇ 15 ⁇ m, optionally 2 ⁇ m ⁇ 9 ⁇ m.
  • the cycle performance and energy density of the secondary battery can be further improved.
  • the second material comprises secondary particles.
  • the amount of the secondary particles in the second material is 70% to 100%, 80% to 100%, or 90% to 100%.
  • the second material satisfies the above conditions and can further improve the cycle performance of the secondary battery.
  • the mass ratio of the first material to the second material is 99.9:0.1-50:50, optionally 97:3-65:35, or can be The selected time is 97:3 to 70:30.
  • the first material and the second material have a suitable ratio, which can better balance the high gram capacity and high cycle stability of the positive electrode active material.
  • the first material is selected from one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide and their respective modified compounds or several.
  • the first material includes lithium nickel cobalt manganese oxide.
  • the molar ratio of nickel element in the transition metal element in the first material is more than 50%.
  • the first material of the present application adopts the above-mentioned positive electrode active material, which can improve the energy density of the secondary battery and further improve the stability of the second material.
  • the second material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium iron vanadium phosphate and their respective modified compounds kind.
  • the second material includes lithium iron phosphate.
  • at least a part of the surface of the second material has a carbon coating layer.
  • the second material of the present application adopts the above-mentioned positive electrode active material, and can improve the cycle performance of the secondary battery.
  • the negative electrode active material includes one or more of artificial graphite, natural graphite, silicon-based materials and tin-based materials.
  • the negative electrode active material includes one or more of artificial graphite and natural graphite.
  • a second aspect of the present application provides a method for preparing a secondary battery, comprising the following steps:
  • a positive electrode slurry is prepared from a positive electrode active material, the positive electrode active material includes a first material and a second material, and the first material includes one or more of layered lithium transition metal oxides and modified compounds thereof, so The second material includes one or more of olivine-structured lithium-containing phosphates and modified compounds thereof;
  • described positive pole piece and negative pole piece and electrolyte are assembled into secondary battery, described negative pole piece comprises negative electrode current collector and is arranged on at least one surface of described negative electrode current collector and comprises the negative electrode film layer of negative electrode active material;
  • the secondary battery satisfies:
  • d c is the compaction density of the positive electrode film layer, in g/cm 3 ,
  • l c is the mass ratio of the positive electrode active material in the positive electrode film layer
  • d a is the compaction density of the negative electrode film layer, in g/cm 3 ,
  • I e is the ratio of the mass of the electrolyte in the secondary battery to the total mass of the electrolyte, the positive electrode active material and the negative electrode active material.
  • the advantages of different active materials can be complemented and their respective shortcomings can be compensated, so that the positive electrode active material has a higher gram capacity and a higher gram capacity.
  • High cycle stability At this time, the secondary battery using the mixed positive electrode active material satisfies the value of d c ⁇ l c ⁇ d a ⁇ l a /I e within a specific range, so that the secondary battery can have a relatively small unit volume of the secondary battery.
  • the high proportion of active materials, and the good electrolyte wettability and retention capacity inside the entire battery cell enable the capacity of the active material to be effectively exerted, thereby effectively improving the energy density of the secondary battery.
  • the secondary battery can also have high cycle performance.
  • the viscosity of the positive electrode slurry is 4000 mPa ⁇ s to 15000 mPa ⁇ s, optionally 6000 mPa ⁇ s to 10000 mPa ⁇ s.
  • the processing efficiency of the secondary battery can be improved, and the cycle performance of the secondary battery can also be improved.
  • the solid content of the positive electrode slurry is 60% to 80%, optionally 65% to 75%.
  • the processing efficiency of the secondary battery can be improved, and the cycle performance of the secondary battery can also be improved.
  • a third aspect of the present application provides a battery module, which includes the secondary battery of the first aspect of the present application, or the secondary battery obtained according to the preparation method of the second aspect of the present application.
  • a fourth aspect of the present application provides a battery pack including the secondary battery of the first aspect of the present application, or the battery module of the third aspect of the present application.
  • a fifth aspect of the present application provides a device comprising at least one of the secondary battery of the first aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application.
  • the battery module, battery pack and device of the present application include the secondary battery and thus have at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of an embodiment of a secondary battery.
  • FIG. 2 is an exploded view of FIG. 1 .
  • FIG. 3 is a schematic diagram of an embodiment of a battery module.
  • FIG. 4 is a schematic diagram of an embodiment of a battery pack.
  • FIG. 5 is an exploded view of FIG. 4 .
  • FIG. 6 is a schematic diagram of one embodiment of a device in which a secondary battery is used as a power source.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with any other lower limit to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range.
  • every point or single value between the endpoints of a range is included within the range, even if not expressly recited.
  • each point or single value may serve as its own lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B.” More specifically, the condition “A or B” is satisfied by either of the following: A is true (or present) and B is false (or absent); A is false (or absent) and B is true (or present) ; or both A and B are true (or present).
  • the inventors have further conducted a lot of research, and achieved the purpose of taking into account both higher energy density and longer cycle life of the secondary battery by coupling the design of the chemical system and structural parameters of the secondary battery.
  • the embodiments of the first aspect of the present application provide a secondary battery that combines high energy density and long cycle life at the same time.
  • the secondary battery includes a positive electrode, a negative electrode and an electrolyte
  • the positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector and containing a positive active material
  • the negative electrode includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material
  • the positive electrode active material includes a first material and a second material, the first material including layered lithium One or more of transition metal oxides and modified compounds thereof, and the second material includes one or more of olivine-structured lithium-containing phosphates and modified compounds thereof;
  • d c is the compaction density of the positive electrode film layer, in g/cm 3 ,
  • l c is the mass ratio of the positive electrode active material in the positive electrode film layer
  • d a is the compaction density of the negative electrode film layer, in g/cm 3 ,
  • I e is the ratio of the mass of the electrolyte in the secondary battery to the total mass of the electrolyte, the positive electrode active material and the negative electrode active material.
  • the inventors have found through keen research that when the positive electrode active material of the secondary battery includes one or more of layered lithium transition metal oxides and modified compounds thereof, and an olivine-structured lithium-containing phosphate and modified compounds thereof One or more of the two, and the secondary battery satisfies the value of d c ⁇ l c ⁇ d a ⁇ l a /I e within a specific range, the secondary battery can take into account both high energy density and cycle performance.
  • the synergistic advantages of the high gram capacity of the first material and the high structural stability of the second material can be exerted, and the first material can also reduce the amount of the second material.
  • Metal such as Fe
  • the second material can also improve the overall cycle stability of the positive electrode active material, reduce oxygen release and electrolyte side reactions, so that the positive electrode active material has both higher gram capacity and higher cycle stability. .
  • the proportion of active materials, and the entire battery cell has good electrolyte wettability and retention, so that the capacity of the active material can be effectively exerted, thereby effectively improving the energy density of the secondary battery. Moreover, even at the end of the cycle, the entire cell can still be effectively infiltrated by the electrolyte, ensuring a good ion transport interface inside the cell, and the positive active material with good overall stability ensures good desorption/intercalation of active ions inside the material. Therefore, the secondary battery can also combine high cycle performance.
  • the release of oxygen and the side reaction of the electrolyte can be reduced, so that the positive electrode active material has higher thermal stability, thereby also improving the safety performance of the secondary battery.
  • the compaction density d c of the positive electrode film layer is 3.22 g/cm 3
  • the mass ratio l c of the positive electrode active material in the positive electrode film layer is 0.97
  • the compaction density da of the negative electrode film layer is 1.50 g /cm 3
  • the mass ratio 1 a of the negative electrode active material in the negative electrode film layer is 0.97
  • the ratio of the mass of the electrolyte solution to the total mass of the electrolyte solution, the positive electrode active material and the negative electrode active material in the secondary battery is I e is 0.10
  • the secondary battery may satisfy E ⁇ 10, ⁇ 15, ⁇ 20, ⁇ 25, ⁇ 30, ⁇ 35, ⁇ 40, or ⁇ 45. Increasing the E value within a certain range is beneficial to improve the energy density of the secondary battery. Optional, E ⁇ 85, ⁇ 80, ⁇ 75, ⁇ 70, ⁇ 65, ⁇ 60, ⁇ 55, or ⁇ 50. The secondary battery satisfies that its E value is within the above range, which is beneficial to improve the cycle performance of the secondary battery.
  • E value of the secondary battery is within the given range, which can better balance high energy density and long cycle life.
  • the secondary battery may also satisfy:
  • the inventors have also found through intensive research that when the secondary battery satisfies the above relationship, the battery can obtain higher cycle performance.
  • the above-mentioned relationship is satisfied between the electrolyte, the positive electrode film layer and the negative electrode film layer of the secondary battery, it can ensure that the battery cell has the necessary ion transport medium to meet its electrochemical performance, and it also ensures that it has the necessary ion transport medium. It has a good solid-liquid contact interface during the electrochemical cycle, which can further improve the cycle capacity retention rate, so that the battery can obtain higher cycle performance.
  • the ionic conductivity ⁇ of the electrolyte at 25°C is 10 mS/cm; the porosity ⁇ c of the positive electrode film layer is 24%; the porosity ⁇ a of the negative electrode film layer is 22%; the electrolyte contact angle ⁇ of the positive electrode film layer is 39°, that is, ⁇ ' is 0.68 radians, then,
  • the secondary battery may satisfy CL ⁇ 0.03, ⁇ 0.05, ⁇ 0.08, ⁇ 0.1, ⁇ 0.15, ⁇ 0.2, ⁇ 0.3, ⁇ 0.4, ⁇ 0.45, ⁇ 0.5, ⁇ 0.55, ⁇ 0.6, ⁇ 0.65 , or ⁇ 0.7.
  • the secondary battery may be formed by encapsulating the cell and the electrolyte in an outer package.
  • the battery cell can be formed by a stacking process or a winding process by a positive electrode piece, a separator and a negative electrode piece, and the separator is located between the positive electrode piece and the negative electrode piece, and plays a role of isolation.
  • 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 and comprising a positive electrode active material, the positive electrode active material includes a first material and a second material, and the first material includes layered lithium One or more of transition metal oxides and modified compounds thereof, and the second material includes one or more of olivine-structured lithium-containing phosphates and modified compounds thereof.
  • modified compounds are compounds obtained by doping modification or coating modification of materials.
  • the first material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide and their respective modified compounds.
  • the first material includes lithium nickel cobalt manganese oxide.
  • These cathode materials have high gram capacity, which can improve the energy density of secondary batteries.
  • the surface of the first material is usually alkaline, which can consume the acid (such as HF) in the battery, thereby reducing the metal dissolution problem of the second material, thereby further improving the overall stability of the positive active material and improving the secondary Cycling performance of the battery.
  • the molar ratio of nickel element in the transition metal element in the first material is more than 50%.
  • the molar ratio of nickel element in the first material is relatively high, which can further improve its gram capacity.
  • the first material includes one or more of Li 1+x Ni a Co b M 1-ab O 2-y A y and modified compounds thereof, wherein -0.1 ⁇ x ⁇ 0.2, 0.5 ⁇ a ⁇ 0.95, 0 ⁇ b ⁇ 0.2, 0 ⁇ a+b ⁇ 1, 0 ⁇ y ⁇ 0.2, M is selected from one of Mn, Fe, Cr, Ti, Zn, V, Al, Zr and Ce or several, A is selected from one or more of S, F, Cl and I.
  • M includes Mn.
  • the volume average particle diameter D v 50 of the first material is 0.1 ⁇ m to 30 ⁇ m.
  • the D v 50 of the first material is 1 ⁇ m ⁇ 20 ⁇ m, 2 ⁇ m ⁇ 15 ⁇ m, 3 ⁇ m ⁇ 12 ⁇ m, 3 ⁇ m ⁇ 10 ⁇ m, 3 ⁇ m ⁇ 8 ⁇ m, or 4 ⁇ m ⁇ 7 ⁇ m.
  • the D v 50 of the first material is in an appropriate range, which is beneficial to obtain a higher compaction density of the positive electrode film layer, and at the same time has a suitable porosity to meet the electrolyte infiltration amount required by the electrochemical reaction, and also has a short
  • the migration paths of active ions and electrons in the particles can improve the energy density and cycle performance of the battery.
  • the first material has an appropriate D v 50, which can also ensure that it has a sufficient specific surface area to improve the wettability of the electrolyte on its surface, that is, make the contact angle of the electrolyte smaller, so that the positive electrode has a good reaction interface, Thereby, the irreversible loss of active lithium can be reduced, and the cycle performance of the secondary battery can be improved.
  • the first material includes one or more of single particles and secondary particles.
  • the single particle is an independently dispersed primary particle, or a particle form formed by agglomeration of a small number (for example, 2 to 5) of primary particles.
  • the particle size of the primary particle is not less than 1 ⁇ m.
  • Secondary particles are particles in the form of agglomeration of multiple primary particles, wherein the particle size of the primary particles is not higher than 500 nm.
  • the number of said plurality is, for example, 100 or more, 300 or more, 500 or more, or 800 or more.
  • the single particle morphology of the cathode active material is beneficial to reduce the polarization phenomenon and reduce the side reactions at the cathode interface, thereby improving the cycle performance of the battery.
  • a single particle is matched with an appropriate amount of secondary particles, it is beneficial to improve the processing performance of the positive electrode slurry, increase the compaction density of the positive electrode film layer, and thus improve the energy density of the battery.
  • the number of single particles in the first material accounts for 50% to 100%, optionally 80% to 100%, 90% to 100%, 85% to 95%, or 90% to 90%. 95%.
  • the inventors also found that by reasonably matching the D v 50 and particle morphology of the first material, it can not only ensure that the positive electrode active material has high active ion transport performance, reduce side reactions with the electrolyte, but also enable the secondary battery to obtain The higher positive electrode film layer compaction density can better improve the energy density and cycle performance of the secondary battery.
  • the D v 50 of the first material is 2 ⁇ m ⁇ 8 ⁇ m, and the number ratio of single particles in the first material is 50% ⁇ 100%.
  • the number proportion of single particles in the first material is 70%-100%, 80%-100%, 90%-100%, 85%-95%, or 90%-95%.
  • the second material is selected from lithium iron phosphate (LiFePO 4 , LFP), lithium manganese phosphate (LiMnPO 4 ), lithium iron manganese phosphate (LiMn 1- ⁇ Fe ⁇ PO 4 , 0 ⁇ 1 , optional 0.5 ⁇ 0.8), lithium iron vanadium phosphate (LiV 1- ⁇ Fe ⁇ PO 4 , 0 ⁇ 1, optional 0.5 ⁇ 0.9) and one of their respective modified compounds species or several.
  • the second material includes lithium iron phosphate.
  • These positive electrode materials have high structural stability and thermal stability. By combining these materials in the first material, the obtained positive electrode active material can obtain high overall cycle stability, and the oxygen release is reduced, and the side reactions of the electrolyte are reduced.
  • the use of the positive electrode active material can also improve the electrolyte wettability and liquid retention rate of the positive electrode film layer, and improve the stability of the positive electrode interface, thereby improving the cycle performance of the secondary battery.
  • the second material such as LFP, etc.
  • the second material has a lower platform voltage
  • it can also reduce the internal resistance of the secondary battery under a low SOC (State of charge, state of charge), so as to alleviate the low capacity of the battery.
  • SOC State of charge, state of charge
  • At least a portion of the surface of the second material has a carbon coating.
  • the entire surface of the second material is coated with a carbon coating.
  • the carbon coating layer can improve the electronic conductivity of the second material, thereby improving the overall electronic conductivity of the positive electrode active material, thereby further improving the cycle performance of the battery.
  • the volume average particle size D v 50 of the second material is 0.01 ⁇ m to 15 ⁇ m.
  • the D v 50 of the second material is 0.5 ⁇ m ⁇ 12 ⁇ m, 1 ⁇ m ⁇ 10 ⁇ m, 2 ⁇ m ⁇ 9 ⁇ m, 2.5 ⁇ m ⁇ 8 ⁇ m, or 4 ⁇ m ⁇ 7 ⁇ m.
  • the D v 50 of the second material is in an appropriate range, so that the secondary battery using the second material can have lower impedance and improve power performance and cycle performance.
  • Appropriate D v 50 of the second material can also improve the processability of the positive electrode slurry and increase the compaction density of the positive electrode film layer, thereby increasing the energy density of the battery.
  • the second material includes secondary particles.
  • the amount of the secondary particles in the second material is 70% to 100%, 80% to 100%, or 90% to 100%.
  • the second material satisfies the above conditions, can further improve the ionic and electronic conductivity of the positive electrode active material, and reduce the battery impedance, thereby enabling the secondary battery to obtain higher cycle performance.
  • the secondary particles are in the form of particles in which a plurality of primary particles are aggregated.
  • the particle size of the primary particles is not higher than 500 nm.
  • the particle size of the primary particles in the secondary particles is 10 nm to 500 nm, or 100 nm to 500 nm, or the like.
  • the mass ratio of the first material to the second material is 99.9:0.1 to 50:50.
  • the mass ratio of the first material to the second material is 97:3-65:35, 97:3-70:30, 97:3-90:10, or 97:3-95:5.
  • the first material and the second material have an appropriate ratio, which can better play the synergistic effect of complementing their advantages and compensating for each other's shortcomings, so that the secondary battery can better balance high energy density and long cycle life.
  • the porosity of the positive electrode film layer can be adjusted to a certain extent, so that the positive electrode film layer can obtain better electrolyte wettability, and further improve the cycle performance of the battery.
  • the positive electrode film layer usually includes a positive electrode active material, an optional binder and an optional conductive agent, and is usually coated with a positive electrode slurry, dried and cold-pressed.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material and optional conductive agent and optional binder in a solvent and stirring uniformly.
  • the solvent may be N-methylpyrrolidone (NMP).
  • the mass ratio l c of the positive electrode active material in the positive electrode film layer is 0.85-0.99, optionally 0.90-0.985, 0.95-0.99, or 0.95-0.97.
  • the positive electrode film layer contains more positive electrode active materials, which can enable the secondary battery to obtain higher energy density.
  • the binder of the positive electrode film layer may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoroethylene
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoroethylene
  • fluoropropylene-tetrafluoroethylene terpolymer tetrafluoroethylene-hexafluoropropylene copolymer, and modified polymers thereof.
  • the conductive agent of the positive electrode film layer may include one or one of superconducting carbon, carbon black (such as Super P, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. several.
  • the compaction density dc of the positive electrode film layer is 2.1g/cm 3 to 4.2g/cm 3 , optionally 2.8g/cm 3 to 3.9g/cm 3 , 2.8g/cm 3 to 2.8g/cm 3 .
  • 3.6g/ cm3 2.9g/ cm3 ⁇ 3.65g/ cm3 , 3.0g/ cm3 ⁇ 3.8g/ cm3 , 3.2g/ cm3 ⁇ 3.6g/ cm3 , or 3.2g/ cm3 ⁇ 3.5 g/cm 3 .
  • the positive electrode film layer can also have a pore structure suitable for the infiltration of the electrolyte, thereby enabling the secondary battery to obtain higher cycle performance.
  • the porosity ⁇ c of the positive electrode film layer is 10%-50%, optionally 17%-35%, 20%-30%, or 22%-27%.
  • the porosity of the positive electrode film layer is in an appropriate range, which can ensure that the film layer has a high proportion of active materials, and at the same time, the positive electrode film layer has good electrolyte wettability and ensures sufficient ion transport required for electrochemical reactions.
  • the medium can effectively exert the capacity of the battery cell, which is beneficial to the secondary battery while taking into account high cycle life and energy density.
  • the electrolyte contact angle ⁇ of the positive electrode film layer satisfies 0° ⁇ 75°, optionally 15° ⁇ 75°, 25° ⁇ 70°, 20° ⁇ 60° , 25° ⁇ 55°, 30° ⁇ 50°, or 35° ⁇ 45°.
  • the negative pole piece includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.
  • the negative film layer typically contains the negative active material as well as optional binders, optional conductive agents and other optional auxiliary agents. It is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing. The negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent, optional binder, optional auxiliary agent, etc. in a solvent and stirring uniformly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • the mass ratio la of the negative electrode active material in the negative electrode film layer is 0.85-0.99, optionally 0.90-0.985, 0.95-0.99, or 0.95-0.97.
  • the negative electrode film layer contains more negative electrode active materials, so that the secondary battery can obtain higher energy density.
  • the negative active material may include one or more of artificial graphite, natural graphite, silicon-based materials, and tin-based materials. These anode materials have high gram capacity, enabling secondary batteries to achieve high energy densities.
  • the negative electrode active material includes one or more of artificial graphite and natural graphite. Graphite material not only has high gram capacity, but also has high ion and electron transport properties, and also has high cycle stability and low cycle expansion, thus enabling secondary batteries to obtain higher energy density and cycle performance.
  • the conductive agent may include one or more of superconducting carbon, carbon black (eg, Super P, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • carbon black eg, Super P, acetylene black, Ketjen black
  • carbon dots carbon nanotubes, graphene, and carbon nanofibers.
  • the binder may include one or one of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). several.
  • SBR styrene-butadiene rubber
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • CMCS carboxymethyl chitosan
  • other optional adjuvants are, for example, thickeners (eg, sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, and the like.
  • the compaction density da of the negative electrode film layer is 1.0g /cm 3 to 2.2g/cm 3 , optionally 1.2g/cm 3 to 2.0g/cm 3 , 1.2g/cm 3 to 1.2g/cm 3 . 1.85g/cm 3 , 1.5g/cm 3 to 1.85g/cm 3 , or 1.5g/cm 3 to 1.65g/cm 3 .
  • the compaction density of the negative electrode film layer is in an appropriate range, the secondary battery can obtain higher energy density.
  • the negative electrode film layer can also have a pore structure suitable for the infiltration of the electrolyte, thereby enabling the secondary battery to obtain higher cycle performance.
  • the porosity ⁇ a of the negative electrode film layer is 10%-50%, optionally 20%-30%, or 22%-28%.
  • the porosity of the negative electrode film layer is in an appropriate range, which can ensure that the film layer has a high proportion of active materials, and at the same time make the negative electrode film layer have good electrolyte wettability, so that the capacity of the cell can be effectively exerted and reduced.
  • the rapid capacity decay caused by the lack of electrolyte is beneficial to the secondary battery while taking into account high cycle life and energy density.
  • the separator is arranged between the positive pole piece and the negative pole piece, and plays the role of isolation.
  • the type of separator for the secondary battery of the present application is not particularly limited, and any well-known porous structure separator for secondary batteries can be selected.
  • the release film can be selected from glass fiber film, non-woven film, polyethylene film, polypropylene film, polyvinylidene fluoride film, and one or more multilayer composite films comprising one or more of them. species or several.
  • the electrolyte solution functions to transport ions in the secondary battery.
  • the ratio I e of the mass of the electrolyte to the total mass of the electrolyte, the positive electrode active material and the negative electrode active material may be 0.1-0.5, for example, 0.1-0.4, 0.1-0.3 or 0.1- 0.2 etc.
  • Appropriate I e value can ensure that the secondary battery has the necessary electrolyte infiltration amount to meet the electrochemical reaction, and at the same time reduce the decrease in energy density caused by the increase of electrolyte, so that the secondary battery can better take into account the higher cycle performance and energy density.
  • the ionic conductivity ⁇ of the electrolyte at 25°C is 0.5mS/cm ⁇ 50mS/cm, optional 2mS/cm ⁇ 30mS/cm, 3mS/cm ⁇ 20mS/cm, 6mS /cm ⁇ 15mS/cm, 7mS/cm ⁇ 15mS/cm, or 8mS/cm ⁇ 12mS/cm.
  • the electrolyte has appropriate ionic conductivity, which can further improve the cycle performance of the secondary battery.
  • the electrolyte includes an electrolyte lithium salt, a solvent and optional additives.
  • the lithium salt may be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium hexafluoroarsenate), LiFSI (lithium tetrafluoroborate) Lithium Imide), LiTFSI (Lithium Bistrifluoromethanesulfonimide), LiTFS (Lithium Trifluoromethanesulfonate), LiDFOB (Lithium Difluorooxalate Borate), LiBOB (Lithium Dioxalate Borate), LiPO 2 F 2 (Lithium difluorophosphate), one or more of LiDFOP (lithium difluorodioxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate).
  • LiPF 6 lithium
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC) , Dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), acetic acid methyl ester (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) ), one of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl
  • the ionic conductivity of the electrolyte at 25° C. can be within the range described in the present application, and the contact angle of the electrolyte solution of the positive electrode film layer can also be within the range described in the present application.
  • the additives may include additives that improve the ionic conductivity of the electrolyte, such as one or more of acetonitrile (AN) and ethylene glycol dimethyl ether (DME).
  • AN acetonitrile
  • DME ethylene glycol dimethyl ether
  • the additives may optionally include negative electrode film-forming additives, and may optionally include positive electrode film-forming additives, and may optionally include additives that can improve certain performance of the battery, such as additives for improving battery overcharge performance, improving Additives for high temperature performance of batteries, additives for improving low temperature performance of batteries, etc.
  • the compaction density of the positive electrode film layer and the negative electrode film layer is the meaning known in the art, and can be tested by methods known in the art.
  • the compaction density of the negative film layer can be tested in the same way.
  • the volume average particle diameter D v 50 of the positive electrode active material is the meaning known in the art, and can be tested by methods known in the art. For example, it is determined using a laser particle size analyzer (eg Malvern Mastersize 3000). The test can refer to GB/T 19077.1-2016.
  • D v 50 represents the particle size corresponding to the cumulative volume distribution percentage of the positive electrode active material reaching 50%.
  • the morphology (single particle or secondary particle) of the positive electrode active material can be tested using methods known in the art. Exemplary test methods are as follows: lay and stick the first material on the conductive adhesive to make a sample to be tested with a length of 6cm ⁇ width of 1.1cm; use a scanning electron microscope & energy spectrometer (such as ZEISS Sigma 300) to determine the shape of the particles in the sample to be tested. Appearance test. The test can refer to JY/T010-1996.
  • 10 different areas can be randomly selected in the test sample for scanning test, and at 500 times magnification, according to the particle morphological characteristics, count the number of single particles in the test area, and take the average value as is the number proportion of single particles in the first material.
  • the quantitative proportion of secondary particles in the second material can be determined.
  • the porosity of the positive electrode film layer and the negative electrode film layer has the meaning known in the art, and can be tested by methods known in the art.
  • the AccuPyc II 1340 automatic true density tester of Micromeritics Company in the United States is used to test with reference to the national standard GB/T 24586-2009.
  • the ionic conductivity of the electrolyte has a meaning known in the art, and can be tested by methods known in the art. such as a conductivity meter.
  • An exemplary test method is as follows: using a conductivity meter (eg, Raymag DDSJ-318), at 25° C. and an AC impedance of 1 kHz, test the resistance of the electrolyte, and calculate the ionic conductivity of the electrolyte.
  • the contact angle of the electrolyte solution of the positive electrode film layer is the meaning known in the art, and the method known in the art can be used for testing.
  • An exemplary test method is as follows: place the test sample on a water contact angle tester, drop 10 ⁇ L of electrolyte at a height of 1 cm from the positive film layer, and photograph the water droplets on the surface of the sample through an optical microscope and a high-speed camera.
  • the electrolyte is the electrolyte used in the battery.
  • the test conditions are 25°C, normal pressure (0.1MPa).
  • the angle between the tangent of the water droplet and the surface of the sample contact point and the horizontal plane is measured by software analysis, which is the contact angle.
  • samples can be taken from the positive electrode sheets that have not been assembled with the secondary battery, or the secondary battery can be disassembled for sampling.
  • the viscosity of the positive electrode slurry is a meaning known in the art, and can be tested by a method known in the art.
  • a Brookfield DV2T viscometer can be used to test the viscosity value at a certain temperature (eg, room temperature 25° C.) and humidity (eg, relative humidity RH ⁇ 80%).
  • FIG. 1 is a secondary battery 5 of a square structure as an example.
  • the secondary battery may include an outer package.
  • the outer packaging is used to encapsulate the cell and electrolyte.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a accommodating cavity.
  • the housing 51 has an opening that communicates with the accommodating cavity, and a cover plate 53 can cover the opening to close the accommodating cavity.
  • the battery cells 52 are packaged in the receiving cavity.
  • the electrolyte is infiltrated in the cell 52.
  • the number of cells 52 contained in the secondary battery 5 may be one or several, and may be adjusted according to requirements.
  • the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, and the like.
  • the outer package of the secondary battery may also be a soft package, such as a pouch-type soft package.
  • the material of the soft bag may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • the secondary batteries can be assembled into a battery module, and 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. 3 is a battery module 4 as an example.
  • the plurality of secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed with fasteners.
  • the battery module 4 may further include a housing having an accommodating space in which the plurality of secondary batteries 5 are accommodated.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules included 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 case and a plurality of battery modules 4 disposed in the battery case.
  • the battery box includes an upper box body 2 and a lower box body 3 .
  • the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 .
  • the plurality of battery modules 4 may be arranged in the battery case in any manner.
  • the present application also provides a method for preparing a secondary battery.
  • the preparation method includes the following steps: preparing a positive electrode slurry with a positive electrode active material, the positive electrode active material includes a first material and a second material, and the first material includes a layered lithium transition metal oxide and a modified compound thereof.
  • the second material includes one or more of olivine-structured lithium-containing phosphates and modified compounds thereof;
  • the positive electrode slurry is coated on at least one surface of the positive electrode current collector to form a positive electrode film layer to obtain a positive pole piece;
  • the positive pole piece, the negative pole piece and the electrolyte are assembled into a secondary battery,
  • the negative pole piece includes a negative electrode current collector and is arranged on at least one surface of the negative electrode current collector and contains A negative electrode film layer of a negative electrode active material; wherein, the secondary battery satisfies:
  • dc is the compaction density of the positive electrode film layer, in g/cm 3 ; lc is the mass ratio of the positive electrode active material in the positive electrode film layer; d a is the negative electrode film layer The compaction density, in g/cm 3 ; 1 a is the mass ratio of the positive electrode active material in the negative electrode film layer; I e is the mass ratio of the electrolyte in the secondary battery to the electrolytic solution The ratio of the total mass of the liquid, the positive electrode active material and the negative electrode active material.
  • the positive electrode active material, the optional binder and the optional conductive agent are added to a solvent (eg NMP), and the positive electrode slurry is obtained by stirring and mixing uniformly.
  • a solvent eg NMP
  • the viscosity of the positive electrode slurry is 4000 mPa ⁇ s ⁇ 15000 mPa ⁇ s, optionally 6000 mPa ⁇ s ⁇ 10000 mPa ⁇ s.
  • the processability of the slurry and the film layer can be improved, thereby improving the process efficiency and electrochemical performance of the secondary battery.
  • the positive electrode slurry is allowed to stand for 48 hours without gelation, delamination, or sedimentation occurring or substantially not occurring. Therefore, the coating uniformity of the positive electrode film layer can be ensured, so that the positive electrode film layer has a high overall consistency, thereby improving the overall energy density and cycle performance of the battery.
  • the slurry can be stirred up (for example, using a stainless steel ruler or a stainless steel flat plate), and the slurry flows down naturally. If it is observed with the naked eye that the slurry flows continuously and there is no agglomerate, the slurry is not gelled. Whether the positive electrode slurry is delaminated and sedimented can be observed with the naked eye.
  • the solid content of the positive electrode slurry is 60%-80%, optionally 65%-75%.
  • the processability of the slurry and the film layer can be improved, thereby improving the process efficiency and electrochemical performance of the secondary battery.
  • the preparation method of the present application may further include other well-known steps for preparing secondary batteries, which will not be repeated here.
  • the technical features of the secondary battery in the present application are also applicable to the preparation method of the secondary battery, and produce corresponding beneficial effects.
  • materials such as positive electrode active materials and negative electrode active materials for preparing secondary batteries can be obtained commercially or prepared by methods known in the art.
  • the present application also provides a device comprising at least one of the secondary batteries, battery modules, or battery packs described in the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source for the device, or as an energy storage unit for the device.
  • the device may be, but is not limited to, mobile devices (eg, cell phones, laptops, etc.), electric vehicles (eg, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf balls) vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device may select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • Figure 6 is an apparatus as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like.
  • a battery pack or a battery module can be employed.
  • the device may be a mobile phone, a tablet computer, a laptop computer, and the like.
  • the device is generally required to be thin and light, and a secondary battery can be used as a power source.
  • Mass energy density capacity ⁇ voltage/mass
  • the mass can be obtained by weighing with a balance (eg balance JA31002).
  • the mass can be accurate to 0.1g.
  • the secondary battery is fully charged and fully discharged at a charge-discharge rate of 0.33C.
  • the measured discharge capacity is the secondary capacity, and the voltage corresponding to half of the discharge capacity is the nominal voltage.
  • the test process is as follows: 1) Charge with a constant current of 0.33C to the upper limit cut-off voltage, and then charge with a constant voltage until the current ⁇ 0.05C; 2) Let it stand for 10 minutes; 3) Discharge with a constant current of 0.33C to the lower limit cut-off voltage.
  • the discharge capacity is recorded as the capacity of the secondary battery, and the voltage corresponding to half of the discharge capacity is the nominal voltage.
  • testing can use equipment known in the art, such as cell charge and discharge machines and high and low temperature boxes.
  • the upper limit cut-off voltage and the lower limit cut-off voltage of the secondary battery can be determined according to the first material mixed with a large proportion.
  • the first material is LiNi 0.8 Co 0.1 Mn 0.1 O 2 ( NCM811 )
  • the charge-discharge voltage range of the battery is 2.8V-4.25V
  • the discharge voltage range is 2.8V-4.35V
  • the first material is LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523)
  • the charging and discharging voltage range of the battery is 2.8V-4.4V.
  • the positive electrode active material, the conductive agent Super P, and the binder PVDF are fully stirred and mixed in an appropriate amount of NMP at a mass ratio of 95:3:2 to form a uniform positive electrode slurry.
  • the viscosity of the positive electrode slurry is 6200mPa ⁇ s, and the positive electrode slurry does not gel, delaminate or settle within 48 hours of standing; the solid content of the positive electrode slurry is 70% by weight;
  • the positive electrode active material includes the first material LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) and the second material carbon-coated lithium iron phosphate (LFP), and the mass ratio of the first material to the second material is 9:1.
  • the D v 50 of the first material was 4.1 ⁇ m.
  • the proportion of single particles in the first material is 90%.
  • the LFPs in the second material are secondary particles.
  • the D v 50 of the second material was 6.9 ⁇ m.
  • the positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode pole piece is obtained.
  • the negative electrode active material artificial graphite, conductive agent Super P, binder SBR, and thickener CMC-Na are fully stirred and mixed in an appropriate amount of deionized water in a mass ratio of 95:2:2:1 to form a uniform negative electrode slurry.
  • the negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and after drying and cold pressing, the negative electrode pole piece is obtained.
  • Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1, and then LiPF 6 was uniformly dissolved in the above solution to obtain an electrolyte.
  • the concentration of LiPF 6 was 1 mol/L.
  • the ionic conductivity ⁇ of the electrolyte at 25°C was 10 mS/cm.
  • the positive pole piece, the separator film, and the negative pole piece are stacked and wound in order to obtain an electrode assembly; the electrode assembly is put into the outer package, the electrolyte prepared above is added, and after the processes of packaging, standing, forming, aging, etc. , to obtain a secondary battery.
  • Example 1 Different from Example 1, the relevant parameters in the preparation steps of the secondary battery were adjusted to obtain different secondary batteries. The preparation parameters and test results different from those in Example 1 are shown in Table 1.
  • Examples 8 to 12 Different from Example 4, the relevant parameters in the electrolyte preparation steps were adjusted to obtain corresponding secondary batteries. Wherein, in the electrolyte of Example 9, LiN(CF 3 SO 2 ) 2 (LiFSI) was used as the lithium salt, and other different preparation parameters and test results are shown in Table 2.
  • LiN(CF 3 SO 2 ) 2 LiFSI
  • the cycle performance of the secondary battery can be further improved under the condition that the battery has a higher energy density.
  • Examples 13 to 20 Different from Example 4, the relevant parameters in the preparation steps of the positive electrode pieces were adjusted to obtain corresponding secondary batteries. Wherein, in Example 16, the mass ratio of single particles in the first material is about 20%; in Example 17, the mass ratio of single particles in the first material is about 10%. The preparation parameters and test results different from those in Example 4 are shown in Table 3.
  • the energy density or cycle performance of the secondary battery can be further improved.
  • Examples 21 to 24 Different from Example 4, the relevant parameters in the preparation steps of the positive electrode pieces were adjusted to obtain corresponding secondary batteries. The preparation parameters and test results different from those in Example 4 are shown in Table 4.
  • Examples 25 to 29 Different from Example 4, the relevant parameters in the preparation steps of the positive electrode pieces were adjusted to obtain corresponding secondary batteries. The preparation parameters different from those in Example 4 are shown in Table 5-1, and the test results are shown in Table 5-2.
  • Examples 30 to 33 Different from Example 4, the relevant parameters in the preparation steps of the positive electrode pieces were adjusted to obtain corresponding secondary batteries. The preparation parameters and test results different from those in Example 4 are shown in Table 6.

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Abstract

一种二次电池（5）及其制备方法与包含二次电池（5）的电池模块（4）、电池包（1）及装置。二次电池（5）包括正极极片、负极极片和电解液，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且包含正极活性材料的正极膜层，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面上且包含负极活性材料的负极膜层，其中：所述正极活性材料包括第一材料和第二材料，所述第一材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种，所述第二材料包括橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种；且所述二次电池（5）满足：4≤dc×lc×da×la/Ie≤90。

Description

二次电池及其制备方法与包含二次电池的电池模块、电池包及装置 技术领域
本申请属于储能装置技术领域，具体涉及一种二次电池及其制备方法与包含二次电池的电池模块、电池包及装置。
背景技术
二次电池具有重量轻、能量密度高、无污染、无记忆效应、使用寿命长等突出特点，从而被广泛应用。
近年来，随着环境问题越来越得到重视，推动了新能源汽车的发展，这进一步扩大了二次电池的需求。与此同时，消费者以及汽车厂对汽车的续航里程提出了更高的要求，这就要求作为能源的二次电池具有更高的能量密度。因此，为了提高新能源汽车的市场竞争力，确有必要提供一种能使二次电池获得更高能量密度的新技术。
发明内容
本发明人发现，为了提高二次电池的能量密度，目前改进的焦点是采用高克容量的活性材料，例如锂镍钴锰氧化物等高克容量的正极活性材料。然而，这类材料在充放电过程中存在结构稳定性变差的问题，导致二次电池在长期使用过程中容量衰减过快，从而影响二次电池的长期循环性能。如何使二次电池具有较高循环性能的同时，提高能量密度，成为二次电池开发中急需解决的技术难题。
为了解决上述技术难题，本申请的第一方面提供一种二次电池，其包括正极极片、负极极片和电解液，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且包含正极活性材料的正极膜层，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面上且包含负极活性材料的负极膜层；
所述正极活性材料包括第一材料和第二材料，所述第一材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种，所述第二材料包括橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种；
且所述二次电池满足：
Figure PCTCN2020109120-appb-000001
其中，
d c为所述正极膜层的压实密度，单位为g/cm 3，
l c为所述正极膜层中所述正极活性材料的质量占比，
d a为所述负极膜层的压实密度，单位为g/cm 3，
l a为所述负极膜层中所述负极活性材料的质量占比，
I e为所述二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负极活性材料的总质量的比值。
本发明人经锐意研究发现，通过组配第一材料和第二材料，能发挥不同种活性材料的优势互补同时弥补各自的缺点，使正极活性材料兼顾较高的克容量和较高的循环稳定性。此时，若采用该混配的正极活性材料的二次电池满足其d c×l c×d a×l a/I e的值在特定范围内，能使二次电池的单位体积内具有较高的活性材料占比，并且其整个电芯内部具有良好的电解液浸润性和保持量，使活性材料的容量得到有效发挥，从而有效地提高二次电池的能量密度。而且，即使在循环末期，整个电芯仍能被电解液有效浸润，保证电芯内部良好的离子传输界面，并且正极活性材料的循环稳定性较好，因此，二次电池还能兼具较高的循环性能。
在本申请第一方面的上述任意实施方式中，所述二次电池可满足：
Figure PCTCN2020109120-appb-000002
可选的，
Figure PCTCN2020109120-appb-000003
二次电池满足其d c×l c×d a×l a/I e的值在上述范围内，能更好地使二次电池同时兼顾高能量密度和长循环寿命。
在本申请第一方面的上述任意实施方式中，所述正极膜层的压实密度d c为2.1g/cm 3～4.2g/cm 3，可选的为2.8g/cm 3～3.6g/cm 3。正极膜层的压实密度在适当范围内，能进一步改善二次电池的能量密度和循环性能。
在本申请第一方面的上述任意实施方式中，所述正极膜层中所述正极活性材料的质量占比l c为0.85～0.99，可选的为0.90～0.985。正极膜层中包含较多的正极活性材料，能使二次电池获得更高的能量密度。
在本申请第一方面的上述任意实施方式中，所述负极膜层的压实密度d a为1.0g/cm 3～2.2g/cm 3，可选的为1.2g/cm 3～1.85g/cm 3。负极膜层的压实密度在适当范围内，能进一步改善二次电池的能量密度和循环性能。
在本申请第一方面的上述任意实施方式中，所述负极膜层中所述负极活性材料的质量占比l a为0.85～0.99，可选的为0.90～0.985。负极膜层中包含较多的负极活性材料，能使二次电池获得更高的能量密度。
在本申请第一方面的上述任意实施方式中，所述二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负极活性材料的总质量的比值I e为0.1～0.5，可选的为0.1～0.3。合适的I e值，能保证二次电池在具有较高循环性能，同时提高能量密度。
在本申请第一方面的上述任意实施方式中，所述二次电池还满足：
Figure PCTCN2020109120-appb-000004
可选的，
Figure PCTCN2020109120-appb-000005
可选的，
Figure PCTCN2020109120-appb-000006
可选的，
Figure PCTCN2020109120-appb-000007
其中，所述σ为所述电解液在25℃的离子电导率，单位为mS/cm；
所述ε c为所述正极膜层的孔隙率；
所述ε a为所述负极膜层的孔隙率；
所述θ'为所述正极膜层的电解液接触角，单位为弧度。
发明人经深入研究还发现，当二次电池满足上述关系时，能保证电芯具有满足其电化学性能所必需的离子传输介质，还保证其在电化学循环过程中具有良好的固液相接触界面，由此能进一步提高循环容量保持率，使电池获得更高的循环性能。
在本申请第一方面的上述任意实施方式中，所述正极膜层的孔隙率ε c为10％～50％，可选的为20％～30％。正极膜层的孔隙率在适当范围内，有利于二次电池同时兼顾较高的循环寿命和能量密度。
在本申请第一方面的上述任意实施方式中，所述负极膜层的孔隙率ε a为10％～50％，可选的为20％～30％。负极膜层的孔隙率在适当范围内，有利于二次电池同时兼顾较高的循环寿命和能量密度。
在本申请第一方面的上述任意实施方式中，所述电解液在25℃的离子电导率σ为0.5mS/cm～50mS/cm，可选的为2mS/cm～30mS/cm，进一步可选的为3mS/cm～20mS/cm。电解液具有较高的离子电导率，能进一步改善二次电池的循环性能。
在本申请第一方面的上述任意实施方式中，所述正极膜层的电解液接触角θ满足0°≤θ≤75°，可选的为35°≤θ≤45°。本申请中，当正极膜层的电解液接触角在上述范围内时，正极极片对电解液具有良好的亲和性，能进一步改善二次电池的循环性能和动力学性能。
在本申请第一方面的上述任意实施方式中，所述第一材料的体积平均粒径D v50为0.1μm～30μm，可选的为2μm～15μm，进一步可选的为3μm～8μm。所述第一材料的D v50在适当范围内，能进一步提高二次电池的能量密度和循环性能。
在本申请第一方面的上述任意实施方式中，所述第一材料包括单颗粒和二次颗粒中 的一种或几种。采用单颗粒形貌的正极活性材料能提高电池的循环性能。当单颗粒和适量的二次颗粒搭配时，有利于改善正极浆料的加工性能，提高正极膜层的压实密度，从而能使二次电池具有更高的能量密度。可选的，所述单颗粒在所述第一材料中的数量占比为50％～100％，可选的为80％～100％。
在本申请第一方面的上述任意实施方式中，所述第二材料的体积平均粒径D v50为0.01μm～15μm，可选的为2μm～9μm。第二材料的D v50在所述范围内，能进一步提高二次电池的循环性能和能量密度。
在本申请第一方面的上述任意实施方式中，所述第二材料包括二次颗粒。可选的，所述二次颗粒在所述第二材料中的数量占比为70％～100％，80％～100％，或90％～100％。第二材料满足上述条件，能进一步提高二次电池的循环性能。
在本申请第一方面的上述任意实施方式中，所述第一材料与所述第二材料的质量比为99.9:0.1～50:50，可选的为97:3～65:35，或者可选的为97:3～70:30。第一材料和第二材料具有合适的配比，能更好地平衡正极活性材料的高克容量和高循环稳定性。
在本申请第一方面的上述任意实施方式中，所述第一材料选自锂镍钴锰氧化物、锂镍钴铝氧化物、锂钴氧化物及其各自的改性化合物中的一种或几种。可选的，所述第一材料包括锂镍钴锰氧化物。可选的，所述第一材料中镍元素在过渡金属元素中的摩尔占比为50％以上。本申请的第一材料采用上述的正极活性材料，能改善二次电池的能量密度，还能进一步提高第二材料的稳定性。
在本申请第一方面的上述任意实施方式中，所述第二材料选自磷酸铁锂、磷酸锰锂、磷酸锰铁锂、磷酸钒铁锂及其各自的改性化合物中的一种或几种。可选的，所述第二材料包括磷酸铁锂。可选的，所述第二材料的至少一部分表面具有碳包覆层。本申请的第二材料采用上述的正极活性材料，能改善二次电池的循环性能。
在本申请第一方面的上述任意实施方式中，所述负极活性材料包括人造石墨、天然石墨、硅基材料和锡基材料中的一种或几种。可选的，所述负极活性材料包括人造石墨和天然石墨中的一种或几种。
本申请第二方面提供一种二次电池的制备方法，其包括以下步骤：
以正极活性材料制备正极浆料，所述正极活性材料包括第一材料和第二材料，所述第一材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种，所述第二材料包括橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种；
将所述正极浆料涂覆于正极集流体至少一个表面上形成正极膜层，得到正极极片；
将所述正极极片与负极极片和电解液组装成二次电池，所述负极极片包括负极集流 体以及设置在所述负极集流体至少一个表面上且包含负极活性材料的负极膜层；
其中，所述二次电池满足：
Figure PCTCN2020109120-appb-000008
d c为所述正极膜层的压实密度，单位为g/cm 3，
l c为所述正极膜层中所述正极活性材料的质量占比，
d a为所述负极膜层的压实密度，单位为g/cm 3，
l a为所述负极膜层中所述正极活性材料的质量占比，
I e为所述二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负极活性材料的总质量的比值。
本申请提供的二次电池的制备方法中，通过组配第一材料和第二材料，能发挥不同种活性材料的优势互补同时弥补各自的缺点，使正极活性材料兼顾较高的克容量和较高的循环稳定性。此时，使采用该混配的正极活性材料的二次电池满足其d c×l c×d a×l a/I e的值在特定范围内，能使二次电池的单位体积内具有较高的活性材料占比，并且其整个电芯内部具有良好的电解液浸润性和保持量，使活性材料的容量得到有效发挥，从而有效地提高二次电池的能量密度。而且，即使在循环末期，整个电芯仍能被电解液有效浸润，保证电芯内部良好的离子传输界面，并且正极活性材料的循环稳定性较好，因此，二次电池还能兼具较高的循环性能。
在本申请第二方面的上述任意实施方式中，所述正极浆料的粘度为4000mPa·s～15000mPa·s，可选的为6000mPa·s～10000mPa·s。正极浆料的粘度在上述范围内，能改善二次电池的加工效率，还能提高二次电池的循环性能。
在本申请第一方面的上述任意实施方式中，所述正极浆料的固含量为60％～80％，可选的为65％～75％。正极浆料的固含量在上述范围内，能改善二次电池的加工效率，还能提高二次电池的循环性能。
本申请第三方面提供一种电池模块，其包括本申请第一方面的二次电池、或根据本申请第二方面的制备方法得到的二次电池。
本申请第四方面提供一种电池包，其包括本申请第一方面的二次电池、或本申请第三方面的电池模块。
本申请第五方面提供一种装置，其包括本申请第一方面的二次电池、本申请第三方面的电池模块、或本申请第四方面的电池包中的至少一种。
本申请的电池模块、电池包和装置包括所述的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
图1是二次电池的一实施方式的示意图。
图2是图1的分解图。
图3是电池模块的一实施方式的示意图。
图4是电池包的一实施方式的示意图。
图5是图4的分解图。
图6是二次电池用作电源的装置的一实施方式的示意图。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合具体实施例对本申请进行详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或几种”中“几种”的含义是两种或两种以上。
在本文的描述中，除非另有说明，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)。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实施例中，列举仅作为代表性组，不应解释为穷举。
本发明人发现，能量密度和循环性能是二次电池的两个相矛盾的电性能，提高能量密度，常常造成循环容量的损失，反之亦然。这导致了，仅从活性材料或者其它化学体 系的方面来改善二次电池的能量密度，同时还期望其较高的循环性能，将难以获得满意的结果。
本发明人进一步进行了大量研究，通过对二次电池的化学体系和结构参数进行耦合设计，实现了二次电池同时兼顾较高的能量密度和较长的循环寿命的目的。
因此，本申请第一方面的实施方式提供一种同时兼顾较高能量密度和较长循环寿命的二次电池。
二次电池
二次电池包括正极极片、负极极片和电解液，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且包含正极活性材料的正极膜层，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面上且包含负极活性材料的负极膜层；所述正极活性材料包括第一材料和第二材料，所述第一材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种，所述第二材料包括橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种；
且所述二次电池满足：
Figure PCTCN2020109120-appb-000009
其中，
d c为所述正极膜层的压实密度，单位为g/cm 3，
l c为所述正极膜层中所述正极活性材料的质量占比，
d a为所述负极膜层的压实密度，单位为g/cm 3，
l a为所述负极膜层中所述负极活性材料的质量占比，
I e为所述二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负极活性材料的总质量的比值。
本发明人经锐意研究发现，当二次电池的正极活性材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种和橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种，且二次电池满足其d c×l c×d a×l a/I e的值在特定范围内时，可以使二次电池同时兼顾较高的能量密度和循环性能。
不拘于任何理论限制，通过组配第一材料和第二材料，能发挥第一材料的高克容量和第二材料的高结构稳定性的协同优势，同时第一材料还可以减少第二材料的金属(例如Fe)溶出，第二材料还可以提高正极活性材料整体的循环稳定性，减少氧释出和电解液副反应，因此使得正极活性材料兼顾较高的克容量和较高的循环稳定性。通过使采用该组配的正极活性材料的二次电池满足其d c×l c×d a×l a/I e的值在特定范围内，能使二次电池的单位体积内具有较高的活性材料占比，并且其整个电芯内部具有良好的电解液浸润性 和保持量，使活性材料的容量得到有效发挥，从而有效地提高二次电池的能量密度。而且，即使在循环末期，整个电芯仍能被电解液有效浸润，保证电芯内部良好的离子传输界面，并且整体稳定性较好的正极活性材料保证了材料内部进行脱/嵌活性离子的良好传输性能，因此，二次电池还能兼具较高的循环性能。
通过在第一材料中组配第二材料，可减少氧释出和电解液副反应，使正极活性材料具有较高的热稳定性，由此还能使二次电池的安全性能。
为了方便起见，定义
Figure PCTCN2020109120-appb-000010
在本申请中，
Figure PCTCN2020109120-appb-000011
仅涉及数值的计算。
例如，正极膜层的压实密度d c为3.22g/cm 3，正极膜层中正极活性材料的质量占比l c为0.97，负极膜层的压实密度d a为1.50g/cm 3，负极膜层中负极活性材料的质量占比l a为0.97，二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负极活性材料的总质量的比值I e为0.10，则，
Figure PCTCN2020109120-appb-000012
在一些实施方式中，二次电池可满足E≥10，≥15，≥20，≥25，≥30，≥35，≥40，或≥45。在一定范围内提高E值，有利于提高二次电池的能量密度。可选的，E≤85，≤80，≤75，≤70，≤65，≤60，≤55，或≤50。二次电池满足其E值在上述范围内，有利于提高二次电池的循环性能。
可选的，10≤E≤55。可选的，25≤E≤50，30≤E≤55，40≤E≤55，或40≤E≤50等。二次电池的E值在所给范围内，能更好地平衡高能量密度和长循环寿命。
在一些实施方式中，二次电池还可以满足：
Figure PCTCN2020109120-appb-000013
式中，σ为所述电解液在25℃的离子电导率，单位为mS/cm；ε c为所述正极膜层的孔隙率；ε a为所述负极膜层的孔隙率；θ'为所述正极膜层的电解液接触角，单位为弧度(rad)。
发明人经深入研究还发现，当二次电池满足上述关系时，能使电池获得更高的循环性能。不期望受任何理论的限制，当二次电池的电解液、正极膜层和负极膜层之间满足上述关系时，能保证电芯具有满足其电化学性能所必需的离子传输介质，还保证其在电化学循环过程中具有良好的固液相接触界面，由此能进一步提高循环容量保持率，从而使电池获得更高的循环性能。
为了方便起见，定义
Figure PCTCN2020109120-appb-000014
在本申请中，同样地，
Figure PCTCN2020109120-appb-000015
仅涉及数值的计算。
例如，电解液在25℃的离子电导率σ为10mS/cm；正极膜层的孔隙率ε c为24％；负极膜层的孔隙率ε a为22％；正极膜层的电解液接触角θ为39°，即θ'为0.68弧度，则，
Figure PCTCN2020109120-appb-000016
在一些实施方式中，二次电池可满足CL≥0.03，≥0.05，≥0.08，≥0.1，≥0.15，≥0.2，≥0.3，≥0.4，≥0.45，≥0.5，≥0.55，≥0.6，≥0.65，或≥0.7。可选的，CL≤8，≤7，≤6.5，≤6，≤5，≤4，≤3，≤2.5，≤2.2，≤2，≤1.4，≤1.2，≤1，≤0.95，或≤0.9。可选的，0.03≤CL≤6.5，0.1≤CL≤6，0.1≤CL≤5，0.15≤CL≤4，0.1≤CL≤3，0.03≤CL≤2.2，0.48≤CL≤2.2，0.1≤CL≤2，0.08≤CL≤1.5，0.25≤CL≤1.4，0.48≤CL≤1.4，0.55≤CL≤1.3，0.6≤CL≤1.2，或0.7≤CL≤1等。二次电池的CL值在所给范围内，能进一步提升二次电池的循环性能，同时使二次电池具有较高的能量密度。
在本申请中，二次电池可为将电芯和电解液封装于外包装中而形成。其中，电芯可由正极极片、隔离膜和负极极片经堆叠工艺或卷绕工艺形成，隔离膜位于正极极片和负极极片之间，起到隔离的作用。
正极极片
正极极片包括正极集流体以及设置在正极集流体至少一个表面上且包含正极活性材料的正极膜层，所述正极活性材料包括第一材料和第二材料，所述第一材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种，所述第二材料包括橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种。
在本申请中，“改性化合物”是对材料进行掺杂改性或包覆改性所得化合物。
在一些实施方式中，所述第一材料选自锂镍钴锰氧化物、锂镍钴铝氧化物、锂钴氧化物及其各自的改性化合物中的一种或几种。可选的，第一材料包括锂镍钴锰氧化物。这些正极材料具有较高的克容量，能提升二次电池的能量密度。并且，第一材料的表面通常呈碱性，能消耗电池内的酸(例如HF)，由此能减小第二材料的金属溶出问题，从而进一步提高正极活性材料整体的稳定性，改善二次电池的循环性能。
可选的，所述第一材料中镍元素在过渡金属元素中的摩尔占比为50％以上。第一材料中镍元素的摩尔占比较高，能进一步提高其克容量。
在一些实施方式中，第一材料包括Li 1+xNi aCo bM 1-a-bO 2-yA y及其改性化合物中的一种或几种，其中，-0.1≤x≤0.2，0.5≤a＜0.95，0＜b＜0.2，0＜a+b＜1，0≤y＜0.2，M选自Mn、Fe、Cr、Ti、Zn、V、Al、Zr和Ce中的一种或几种，A选自S、F、Cl和I中的一种或几种。可选的，0.5≤a≤0.85，0.5≤a≤0.8，或0.5≤a≤0.7。可选的，M包括Mn。
在一些实施方式中，第一材料的体积平均粒径D v50为0.1μm～30μm。可选的，第一材料的D v50为1μm～20μm，2μm～15μm，3μm～12μm，3μm～10μm，3μm～8μm，或4μm～7μm。第一材料的D v50在适当范围内，有利于使正极膜层获得较高的压实密度，同时具有合适的孔隙率，来满足电化学反应所需的电解液浸润量，还具有较短的颗粒内活性离子和电子的迁移路径，由此能提高电池的能量密度和循环性能。此外，第一材料具有适当的D v50，还能保证其具有足够的比表面积，改善电解液在其表面的浸润性，即，使电解液接触角较小，使得正极具有良好的反应界面，由此能减少不可逆的活性锂损失，提高二次电池的循环性能。
在一些实施方式中，所述第一材料包括单颗粒和二次颗粒中的一种或几种。
在本申请的第一材料中，单颗粒为独立分散的一次颗粒、或由一次颗粒少量(例如2～5个)团聚而成的颗粒形态。可选的，所述单颗粒中，一次颗粒的粒径不低于1μm。二次颗粒是由多个一次颗粒聚集而成的颗粒形态，其中一次颗粒的粒径不高于500nm。所述多个例如为100个以上，300个以上，500个以上，800个以上。
单颗粒形貌的正极活性材料有利于减小极化现象，还能减少正极界面副反应，从而能提高电池的循环性能。当单颗粒和适量的二次颗粒搭配时，有利于改善正极浆料的加工性能，提升正极膜层的压实密度，从而能提高电池的能量密度。在一些实施方式中，单颗粒在第一材料中的数量占比为50％～100％，可选的为80％～100％，90％～100％，85％～95％，或90％～95％。
发明人还发现，通过合理匹配第一材料的D v50和颗粒形貌，既能保证正极活性材料具有较高的活性离子传输性能，减少与电解液的副反应，又能使二次电池获得较高的正极膜层压实密度，从而能更好地提升二次电池的能量密度和循环性能。在一些实施方式中，第一材料的D v50为2μm～8μm，且单颗粒在第一材料中的数量占比为50％～100％。可选的，3μm～8μm，3μm～6μm，4μm～6μm，或4μm～7μm。可选的，单颗粒在第一材料中的数量占比为70％～100％，80％～100％，90％～100％，85％～95％，或90％～95％。
在一些实施方式中，所述第二材料选自磷酸铁锂(LiFePO 4，LFP)、磷酸锰锂(LiMnPO 4)、磷酸锰铁锂(LiMn 1-αFe αPO 4，0＜α＜1，可选的0.5≤α≤0.8)、磷酸钒铁锂(LiV 1-βFe βPO 4，0＜β＜1，可选的0.5≤β≤0.9)及其各自的改性化合物中的一种或几种。可选的，第二材料包括磷酸铁锂。这些正极材料具有较高的结构稳定性和热稳定性，在第一材料中搭配这些材料，所得正极活性材料可获得较高的整体循环稳定性，且氧释出减小，电解液副反应减少；同时，采用该正极活性材料还可提高正极膜层的电解液浸润性和保液率，改善正极界面的稳定性，从而能提高二次电池的循环性能。尤其 是，当第二材料(例如LFP等)具有较低的平台电压时，还能减小二次电池在低SOC(State of charge，荷电状态)下的内阻，缓解电池的容量在低SOC下的快速衰减现象，减少由此造成的容量损失，从而能进一步改善二次电池的循环性能。
在一些实施方式中，第二材料的至少一部分表面具有碳包覆层。可选的，第二材料的全部表面均被碳包覆层包覆。碳包覆层能改善第二材料的电子导电率，由此能提升正极活性材料整体的电子传导性能，从而进一步改善电池的循环性能。
在一些实施方式中，第二材料的体积平均粒径D v50为0.01μm～15μm。可选的，第二材料的D v50为0.5μm～12μm，1μm～10μm，2μm～9μm，2.5μm～8μm，或4μm～7μm。第二材料的D v50在适当范围内，能使采用其的二次电池具有较低的阻抗，提升功率性能和循环性能。第二材料具有适当的D v50还能改善正极浆料的加工性能，提高正极膜层的压实密度，从而可提升电池的能量密度。
在一些实施方式，第二材料包括二次颗粒。可选的，所述二次颗粒在所述第二材料中的数量占比为70％～100％，80％～100％，或90％～100％。第二材料满足上述条件，能进一步提高正极活性材料的离子和电子传导性能，降低电池阻抗，从而使二次电池获得更高的循环性能。
在本申请的第二材料中，二次颗粒是由多个一次颗粒聚集而成的颗粒形态。其中，一次颗粒的粒径不高于500nm。可选的，所述二次颗粒中一次颗粒的粒径为10nm～500nm，或100nm～500nm等。
在一些实施方式中，第一材料与第二材料的质量比为99.9:0.1～50:50。可选的，第一材料与第二材料的质量比为97:3～65:35，97:3～70:30，97:3～90:10，或97:3～95:5。第一材料和第二材料具有适当的配比，能更好地发挥它们的优势互补和弥补彼此缺点的协同作用，从而使二次电池更好地兼顾高能量密度和长循环寿命。此外，第一材料和第二材料的配比在适当范围内，在一定程度上可以调整正极膜层的孔隙率，使正极膜层获得更好的电解液浸润性，进一步提高电池的循环性能。
本申请的正极极片中，正极膜层通常包含正极活性材料以及可选的粘结剂和可选的导电剂，通常是由正极浆料涂布，并经干燥、冷压而成的。正极浆料通常是将正极活性材料以及可选的导电剂和可选的粘结剂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)。
在一些实施方式中，正极膜层中所述正极活性材料的质量占比l c为0.85～0.99，可选的为0.90～0.985，0.95～0.99，或0.95～0.97。正极膜层中含有较多的正极活性材料，能使二次电池获得更高的能量密度。
在一些实施方式中，正极膜层的粘结剂可包括聚偏氟乙烯(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、以及它们的改性聚合物中的一种或几种。
在一些实施方式中，正极膜层的导电剂可包括超导碳、炭黑(如Super P、乙炔黑、科琴黑)、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。
在一些实施方式中，正极膜层的压实密度d c为2.1g/cm 3～4.2g/cm 3，可选的为2.8g/cm 3～3.9g/cm 3，2.8g/cm 3～3.6g/cm 3，2.9g/cm 3～3.65g/cm 3，3.0g/cm 3～3.8g/cm 3，3.2g/cm 3～3.6g/cm 3，或3.2g/cm 3～3.5g/cm 3。正极膜层的压实密度在适当范围内，能使二次电池获得较高的能量密度。此外，正极膜层内还可具有适于电解液浸润的孔隙结构，从而还能使二次电池获得较高的循环性能。
在一些实施方式中，正极膜层的孔隙率ε c为10％～50％，可选的为17％～35％，20％～30％，或22％～27％。正极膜层的孔隙率在适当范围内，能在保证膜层内具有较高活性材料占比的同时，使正极膜层具有良好的电解液浸润性，保证足够的电化学反应所需的离子传输介质，使电芯的容量得到有效发挥，从而有利于二次电池同时兼顾较高的循环寿命和能量密度。
在一些实施方式中，正极膜层的电解液接触角θ满足0°≤θ≤75°，可选的15°≤θ≤75°，25°≤θ≤70°，20°≤θ≤60°，25°≤θ≤55°，30°≤θ≤50°，或35°≤θ≤45°。正极膜层的电解液接触角在适当范围内，既方便电解液进行浸润，又能改善膜层内的固液相接触界面，由此能进一步改善二次电池的循环性能。其中，1°＝π/180弧度。由此可进行θ和θ'之间的换算。
负极极片
本申请的负极极片中，负极极片包括负极集流体以及设置在所述负极集流体至少一个表面上的负极膜层。
负极膜层通常包含负极活性材料以及可选的粘结剂、可选的导电剂和其它可选助剂。其通常是由负极浆料涂布在负极集流体上，经干燥、冷压而成的。负极浆料涂通常是将负极活性材料以及可选的导电剂、可选的粘结剂、可选助剂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)或去离子水。
在一些实施方式中，负极膜层中所述负极活性材料的质量占比l a为0.85～0.99，可选的为0.90～0.985，0.95～0.99，或0.95～0.97。负极膜层中包含较多的负极活性材料，能使二次电池获得更高的能量密度。
在一些实施方式中，负极活性材料可包括人造石墨、天然石墨、硅基材料和锡基材 料中的一种或几种。这些负极材料具有较高的克容量，可使二次电池获得较高的能量密度。可选的，负极活性材料包括人造石墨和天然石墨中的一种或几种。石墨材料不仅具有较高的克容量，还具有较高的离子和电子传输性能，还具有较高的循环稳定性和较低的循环膨胀，因而能使二次电池获得较高的能量密度和循环性能。
在一些实施方式中，导电剂可包括超导碳、炭黑(例如Super P、乙炔黑、科琴黑)、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。
在一些实施方式中，粘结剂可包括丁苯橡胶(SBR)、水性丙烯酸树脂、聚乙烯醇(PVA)、海藻酸钠(SA)及羧甲基壳聚糖(CMCS)中的一种或几种。
在一些实施方式中，其它可选助剂例如是增稠剂(例如羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
在一些实施方式中，负极膜层的压实密度d a为1.0g/cm 3～2.2g/cm 3，可选的为1.2g/cm 3～2.0g/cm 3，1.2g/cm 3～1.85g/cm 3，1.5g/cm 3～1.85g/cm 3，或1.5g/cm 3～1.65g/cm 3。负极膜层的压实密度在适当范围内，能使二次电池获得较高的能量密度。此外，负极膜层内还可具有适于电解液浸润的孔隙结构，从而还能使二次电池获得较高的循环性能。
在一些实施方式中，负极膜层的孔隙率ε a为10％～50％，可选的为20％～30％，或22％～28％。负极膜层的孔隙率在适当范围内，能在保证膜层内具有较高活性材料占比的同时，使负极膜层具有良好的电解液浸润性，使电芯的容量得到有效发挥，减小缺乏电解液导致的容量急速衰减，从而有利于二次电池同时兼顾较高的循环寿命和能量密度。
隔离膜
隔离膜设置在正极极片和负极极片之间，起到隔离的作用。本申请的二次电池对隔离膜的种类没有特别的限制，可以选用任意公知的用于二次电池的多孔结构隔离膜。例如，隔离膜可选自玻璃纤维薄膜、无纺布薄膜、聚乙烯薄膜、聚丙烯薄膜、聚偏二氟乙烯薄膜、以及包含它们中的一种或两种以上的多层复合薄膜中的一种或几种。
电解液
电解液在二次电池中起到传输离子的作用。在本申请的二次电池中，电解液的质量占电解液、正极活性材料和负极活性材料的总质量的比值I e可选为0.1～0.5，例如为0.1～0.4，0.1～0.3或0.1～0.2等。合适的I e值，能保证二次电池内具有满足电化学反应所必要的电解液浸润量，同时减小因电解液增多造成的能量密度降低，因而能使二次电池更好地兼顾较高的循环性能和能量密度。
在本申请的二次电池中，电解液在25℃的离子电导率σ为0.5mS/cm～50mS/cm，可 选的为2mS/cm～30mS/cm，3mS/cm～20mS/cm，6mS/cm～15mS/cm，7mS/cm～15mS/cm，或8mS/cm～12mS/cm。电解液具有适当的离子电导率，能进一步改善二次电池的循环性能。
本申请的二次电池中，电解液包括电解质锂盐、溶剂和可选的添加剂。
在一些实施方式中，锂盐可选自LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiClO 4(高氯酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(二草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)及LiTFOP(四氟草酸磷酸锂)中的一种或几种。
在一些实施方式中，溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙基酯(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)、氟代碳酸亚乙酯(FEC)、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)及二乙砜(ESE)中的一种或几种。
电解液中采用合适的溶剂，可使电解液在25℃的离子电导率在本申请所述的范围内，还可以使正极膜层的电解液接触角在本申请所述的范围内。
在一些实施方式中，添加剂可包括改善电解液的离子电导率的助剂，例如乙腈(AN)和乙二醇二甲醚(DME)中的一种或几种。
在一些实施方式中，添加剂可选的包括负极成膜添加剂，也可选的包括正极成膜添加剂，还可选的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、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
在本申请中，正极膜层、负极膜层的压实密度为本领域公知的含义，可采用本领域已知的方法进行测试。正极膜层的压实密度的示例性测试方法如下：取单面涂布且经冷压后的正极极片(若是双面涂布的极片，可先擦拭掉其中一面的正极膜层)，冲切成面积为S 1的小圆片，称其重量，记为M 1；测试正极膜层的厚度，记为H；然后将正极膜层擦拭掉，称量正极集流体的重量，记为M 2；正极膜层的压实密度d c＝(M 1-M 2)/S 1/H。可按照同样的方法测试负极膜层的压实密度。
在本申请中，正极活性材料的体积平均粒径D v50为本领域公知的含义，可采用本领域已知的方法进行测试。例如，使用激光粒度分析仪(如Malvern Mastersize 3000)测 定。测试可参照GB/T 19077.1-2016。其中，D v50表示所述正极活性材料累计体积分布百分数达到50％时所对应的粒径。
在本申请中，正极活性材料的形貌(单颗粒或二次颗粒)可采用本领域已知的方法进行测试。示例性测试方法如下：将第一材料铺设并粘于导电胶上，制成长6cm×宽1.1cm的待测样品；使用扫描电镜&能谱仪(如ZEISS Sigma 300)对待测样品中颗粒的形貌进行测试。测试可参考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10个不同区域进行扫描测试，并在500倍放大倍率下，根据颗粒形态特征，统计测试区域中单颗粒的数量，取平均值即为单颗粒在第一材料中的数量占比。同样地可测得二次颗粒在第二材料中的数量占比。
在本申请中，正极膜层、负极膜层的孔隙率为本领域公知的含义，可采用本领域已知的方法进行测试。例如采用美国Micromeritics公司的AccuPyc II 1340型全自动真密度测试仪，参考国标GB/T 24586-2009进行测试。
在本申请中，电解液的离子电导率为本领域公知的含义，可采用本领域已知的方法进行测试。例如电导率仪。示例性测试方法如下：采用电导率仪(例如雷磁DDSJ-318)，在25℃、交流阻抗1kHz下，测试电解液的电阻，计算电解液的离子电导率。
在本申请中，正极膜层的电解液接触角为本领域公知的含义，可采用本领域已知的方法进行测试。示例性测试方法如下：将测试样品放置在水接触角测试仪上，在距离正极膜层高度为1cm的位置滴10μL电解液，通过光学显微镜和高速相机对落在样品表面的水滴拍照。其中电解液为该电池所使用的电解液。测试条件为25℃，常压(0.1MPa)。经软件分析测量水滴与样品接触点表面的切线与水平面的夹角，即为接触角。
以上涉及正极膜层、负极膜层的测试中，可以从尚未组装二次电池的正极极片中取样，也可以拆解二次电池取样。
在本申请中，正极浆料的粘度为本领域公知的含义，可采用本领域已知的方法进行测试。例如可使用Brookfield DV2T粘度计，在一定温度(例如室温25℃)和湿度(例如相对湿度RH＜80％)下，测试得到粘度值。
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1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，二次电池可包括外包装。该外包装用于封装电芯和电解液。
在一些实施例中，参照图2，外包装可包括壳体51和盖板53。其中，壳体51可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能够盖设于所述开口，以封闭所述容纳腔。电芯52封装于所述容纳腔。电 解液浸润于电芯52中。二次电池5所含电芯52的数量可以为一个或几个，可根据需求来调节。
在一些实施例中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，如可包括聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或几种。
在一些实施例中，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3是作为一个示例的电池模块4。参照图3，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4和图5是作为一个示例的电池包1。参照图4和图5，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能够盖设于下箱体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。
本申请还提供一种二次电池的制备方法。制备方法包括以下步骤：以正极活性材料制备正极浆料，所述正极活性材料包括第一材料和第二材料，所述第一材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种，所述第二材料包括橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种；将所述正极浆料涂覆于正极集流体至少一个表面上形成正极膜层，得到正极极片；将所述正极极片与负极极片和电解液组装成二次电池，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面上且包含负极活性材料的负极膜层；其中，所述二次电池满足：
Figure PCTCN2020109120-appb-000017
式中，d c为所述正极膜层的压实密度，单位为g/cm 3；l c为所述正极膜层中所述正极活性材料的质量占比；d a为所述负极膜层的压实密度，单位为g/cm 3；l a为所述负极膜层 中所述正极活性材料的质量占比；I e为所述二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负极活性材料的总质量的比值。
通常将正极活性材料以及可选的粘结剂和可选的导电剂加入溶剂(例如NMP)中，经搅拌混合均匀，得到正极浆料。
在一些实施方式中，正极浆料的粘度为4000mPa·s～15000mPa·s，可选的为6000mPa·s～10000mPa·s。正极浆料的粘度在上述范围内，能改善浆料和膜层的加工性能，从而能改善二次电池的加工效率及其电化学性能。
可选的，正极浆料静置48h，不发生或基本不发生凝胶、分层、或沉降。由此能保证正极膜层的涂布均匀性，使正极膜层具有较高的整体一致性，从而能提升电池整体的能量密度和循环性能。其中，可以挑起浆料(例如采用不锈钢尺或不锈钢平板)，浆料自然流下，若肉眼观察浆料不断流，且其中没有团聚物，则浆料不凝胶。可以通过肉眼观察正极浆料是否发生分层、沉降。
在一些实施方式中，正极浆料的固含量为60％～80％，可选的为65％～75％。正极浆料的固含量在上述范围内，能改善浆料和膜层的加工性能，从而能改善二次电池的加工效率及其电化学性能。
本申请的制备方法还可包括制备二次电池的其它公知的步骤，在此不再赘述。
本申请中二次电池的技术特征也适用于二次电池的制备方法中，并产生相应的有益效果。
本申请中，制备二次电池的正极活性材料、负极活性材料等材料均可商购获得或采用本领域已知的方法制备得到。
本申请还提供一种装置，所述装置包括本申请所述的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块或电池包可以用作所述装置的电源，也可以作为所述装置的能量存储单元。所述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***等。
所述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6是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该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、和比值都是基于重量计，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。
性能测试
1.二次电池的能量密度测试
分别测试二次电池的容量、标称电压和质量，质量能量密度可通过如下公式计算得到：质量能量密度＝容量×电压/质量
质量可通过天平(例如衡平JA31002)称量得到。其中质量可以精确到0.1g。
二次电池的容量和标称电压的测试方法：
在25℃下，以0.33C充放电倍率对二次电池进行满充后满放，测得的放电容量即为二次的容量，放电容量一半所对应的电压为标称电压。
测试流程如下：1)以0.33C倍率恒流充电至上限截止电压，之后恒压充电至电流<0.05C；2)静置10min；3)以0.33C恒流放电至下限截止电压，此时的放电容量记为二次电池的容量，放电容量一半所对应的电压为标称电压。相关术语和测试方法参考GB/T 19596、GB/T 31484-2015、GB/T 31485-2015、GB/T 31486-2015以及《电动汽车用动力蓄电池安全要求》。测试可使用本领域公知的设备，例如电芯充放电机和高低温箱。
2.二次电池的循环性能测试
在25℃，将二次电池静置30min，之后以0.33C恒流放电至下限截止电压，静置5min，再以0.33C恒流充电至上限截止电压，再恒压充电至电流<0.05C，静置5min，再以0.33C恒流放电至下限截止电压，记录此时的放电容量，即为初始放电容量C 0。将二次电池按照上述方法进行500次循环充放电测试，记录每次循环的放电容量C n。
二次电池的循环性能：第500次循环的容量保持率(％)＝C 500/C 0×100％。
在测试中，二次电池的上限截止电压和下限截止电压可按照混合占比较多的第一材料来确定。例如，第一材料为LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)，电池的充放电电压范围为2.8V～4.25V；第一材料为LiNi 0.6Co 0.2Mn 0.2O 2(NCM622)，电池的充放电电压范围为 2.8V～4.35V；第一材料为LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)，电池的充放电电压范围为2.8V～4.4V。
1.二次电池的E值(d c×l c×d a×l a/I e)对其性能的影响
实施例1
正极极片的制备
将正极活性材料、导电剂Super P、粘结剂PVDF按质量比95:3:2在适量的NMP中充分搅拌混合，使其形成均匀的正极浆料。其中正极浆料的粘度为6200mPa·s，且正极浆料静置48h内，不凝胶、不分层、不沉降；正极浆料的固含量为70重量％；正极活性材料包括第一材料LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)和第二材料碳包覆的磷酸铁锂(LFP)，且第一材料与第二材料的质量比为9:1。第一材料的D v50为4.1μm。单颗粒在第一材料中的数量占比为90％。第二材料中LFP为二次颗粒。第二材料的D v50为6.9μm。
将正极浆料涂覆于正极集流体铝箔的表面上，经干燥、冷压后，得到正极极片。
负极极片的制备
将负极活性材料人造石墨、导电剂Super P、粘结剂SBR、增稠剂CMC-Na按质量比95:2:2:1在适量的去离子水中充分搅拌混合，使其形成均匀的负极浆料；将负极浆料涂覆于负极集流体铜箔的表面上，经干燥、冷压后，得到负极极片。
隔离膜
采用PP/PE复合隔离膜。
电解液的制备
将碳酸亚乙酯(EC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)按体积比1:1:1混合，然后将LiPF 6均匀溶解在上述溶液中，得到电解液。该电解液中，LiPF 6的浓度为1mol/L。电解液在25℃的离子电导率σ为10mS/cm。
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；将电极组件放入外包装中，加入上述制备的电解液，经封装、静置、化成、老化等工序后，得到二次电池。
实施例2～7及对比例1～2
与实施例1不同的是，调整二次电池制备步骤中的相关参数，得到不同的二次电池。其中与实施例1不同的制备参数及测试结果详见表1。
表1
Figure PCTCN2020109120-appb-000018
由表1的结果可知，本申请的二次电池由于同时包含第一材料和第二材料，且满足d c×l c×d a×l a/I e的值在特定范围内，能使二次电池同时兼顾较高的能量密度和循环性能。
对比例1-2的二次电池由于不满足上述条件，难以同时兼顾能量密度和循环性能。
2.二次电池CL值
Figure PCTCN2020109120-appb-000019
对其性能的影响
实施例8～12：与实施例4不同的是，调整电解液制备步骤中的相关参数，得到相应的二次电池。其中，实施例9的电解液中，锂盐采用LiN(CF 3SO 2) 2(LiFSI)，其余不同的制备参数及测试结果详见表2。
表2
Figure PCTCN2020109120-appb-000020
由表2可知，通过使二次电池满足
Figure PCTCN2020109120-appb-000021
在适当范围内，能使电池具有较高的能量密度的条件下，进一步改善二次电池的循环性能。
3.第一材料或第二材料的粒径对二次电池性能的影响
实施例13～20：与实施例4不同的是，调整正极极片制备步骤中的相关参数，得到 相应的二次电池。其中，实施例16中第一材料中单颗粒的质量占比约20％；实施例17中第一材料中单颗粒的质量占比约10％。与实施例4不同的制备参数及测试结果详见表3。
表3
Figure PCTCN2020109120-appb-000022
由表3可知，通过调整第一材料或第二材料的粒径，能进一步改善二次电池的能量密度或循环性能。
4.第一材料和第二材料的配比对二次电池性能的影响
实施例21～24：与实施例4不同的是，调整正极极片制备步骤中的相关参数，得到相应的二次电池。其中与实施例4不同的制备参数及测试结果详见表4。
表4
Figure PCTCN2020109120-appb-000023
由表4可知，使第一材料和第二材料的配比在适当范围内，能进一步改善二次电池的能量密度和循环性能。
5.第一材料或第二材料的形貌对二次电池性能的影响
实施例25～29：与实施例4不同的是，调整正极极片制备步骤中的相关参数，得到相应的二次电池。其中与实施例4不同的制备参数详见表5-1，测试结果详见表5-2。
表5-1：正极极片的制备参数
Figure PCTCN2020109120-appb-000024
表5-2：测试结果
序号 θ CL E 能量密度Wh/kg 循环性能
实施例4 39° 0.78 45.4 244 96％
实施例25 38° 0.83 44.9 243 95％
实施例26 35° 0.97 39.9 242 96％
实施例27 35° 0.97 40.1 242 96％
实施例28 37° 0.89 42.2 243 95％
实施例29 37° 0.89 42.5 243 94％
由表5-1和表5-2可知，采用具有合适形貌的第一材料和第二材料，能进一步改善二次电池的能量密度和循环性能。
6.第一材料的种类对二次电池性能的影响
实施例30～33：与实施例4不同的是，调整正极极片制备步骤中的相关参数，得到相应的二次电池。其中与实施例4不同的制备参数及测试结果详见表6。
表6
Figure PCTCN2020109120-appb-000025
由表6可知，采用合适的第一材料，能进一步改善二次电池的能量密度或循环性能。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此。任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。

Claims (16)

  1. 一种二次电池，包括正极极片、负极极片和电解液，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且包含正极活性材料的正极膜层，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面上且包含负极活性材料的负极膜层；
    所述正极活性材料包括第一材料和第二材料，所述第一材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种，所述第二材料包括橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种；
    且所述二次电池满足：
    Figure PCTCN2020109120-appb-100001
    其中，
    d c为所述正极膜层的压实密度，单位为g/cm 3，
    l c为所述正极膜层中所述正极活性材料的质量占比，
    d a为所述负极膜层的压实密度，单位为g/cm 3，
    l a为所述负极膜层中所述负极活性材料的质量占比，
    I e为所述二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负极活性材料的总质量的比值。
  2. 根据权利要求1所述的二次电池，其中，所述二次电池满足：
    Figure PCTCN2020109120-appb-100002
    可选的，
    Figure PCTCN2020109120-appb-100003
  3. 根据权利要求1或2所述的二次电池，其中，所述二次电池还满足下述(1)～(5)中的一个或几个：
    (1)所述正极膜层的压实密度d c为2.1g/cm 3～4.2g/cm 3，可选的为2.8g/cm 3～3.6g/cm 3；
    (2)所述正极膜层中所述正极活性材料的质量占比l c为0.85～0.99，可选的为0.90～0.985；
    (3)所述负极膜层的压实密度d a为1.0g/cm 3～2.2g/cm 3，可选的为1.2g/cm 3～1.85g/cm 3；
    (4)所述负极膜层中所述负极活性材料的质量占比l a为0.85～0.99，可选的为0.90～0.985；
    (5)所述二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负 极活性材料的总质量的比值I e为0.1～0.5，可选的为0.1～0.3。
  4. 根据权利要求1-3任一项所述的二次电池，其中，所述二次电池还满足：
    Figure PCTCN2020109120-appb-100004
    可选的，
    Figure PCTCN2020109120-appb-100005
    可选的，
    Figure PCTCN2020109120-appb-100006
    可选的，
    Figure PCTCN2020109120-appb-100007
    其中，所述σ为所述电解液在25℃的离子电导率，单位为mS/cm；
    所述ε c为所述正极膜层的孔隙率；
    所述ε a为所述负极膜层的孔隙率；
    所述θ'为所述正极膜层的电解液接触角，单位为弧度。
  5. 根据权利要求1-4任一项所述的二次电池，其中，所述二次电池还满足下述(1)～(4)中的一个或几个：
    (1)所述正极膜层的孔隙率ε c为10％～50％，可选的为20％～30％；
    (2)所述负极膜层的孔隙率ε a为10％～50％，可选的为20％～30％；
    (3)所述电解液在25℃的离子电导率σ为0.5mS/cm～50mS/cm，可选的为2mS/cm～30mS/cm，进一步可选的为3mS/cm～20mS/cm；
    (4)所述正极膜层的电解液接触角θ满足0°≤θ≤75°，可选的35°≤θ≤45°。
  6. 根据权利要求1-5任一项所述的二次电池，其中，所述第一材料的体积平均粒径D v50为0.1μm～30μm，可选的为2μm～15μm，进一步可选的为3μm～8μm；或，
    所述第二材料的体积平均粒径D v50为0.01μm～15μm，可选的为2μm～9μm。
  7. 根据权利要求1-6任一项所述的二次电池，其中，所述第一材料包括单颗粒和二次颗粒中的一种或几种；可选的，所述单颗粒在所述第一材料中的数量占比为50％～100％；进一步可选的为80％～100％。
  8. 根据权利要求1-7任一项所述的二次电池，其中，所述第二材料包括二次颗粒；可选的，所述二次颗粒在所述第二材料中的数量占比为90％～100％。
  9. 根据权利要求1-8任一项所述的二次电池，其中，所述第一材料与所述第二材料的质量比为99.9:0.1～50:50，可选的为97:3～65:35，进一步可选的为97:3～70:30。
  10. 根据权利要求1-9任一项所述的二次电池，其中，所述第一材料选自锂镍钴锰氧化物、锂镍钴铝氧化物、锂钴氧化物及其各自的改性化合物中的一种或几种；可选的，所述第一材料包括锂镍钴锰氧化物；可选的，所述第一材料中镍元素在过渡金属元素中的摩尔占比为50％以上；或，
    所述第二材料选自磷酸铁锂、磷酸锰锂、磷酸锰铁锂、磷酸钒铁锂及其各自的改性 化合物中的一种或几种；可选的，所述第二材料包括磷酸铁锂；可选的，所述第二材料的至少一部分表面具有碳包覆层。
  11. 根据权利要求1-10任一项所述的二次电池，其中，所述负极活性材料包括人造石墨、天然石墨、硅基材料和锡基材料中的一种或几种，可选的包括人造石墨和天然石墨中的一种或几种。
  12. 一种二次电池的制备方法，包括以下步骤：
    以正极活性材料制备正极浆料，所述正极活性材料包括第一材料和第二材料，所述第一材料包括层状锂过渡金属氧化物及其改性化合物中的一种或几种，所述第二材料包括橄榄石结构的含锂磷酸盐及其改性化合物中的一种或几种；
    将所述正极浆料涂覆于正极集流体至少一个表面上形成正极膜层，得到正极极片；
    将所述正极极片与负极极片和电解液组装成二次电池，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面上且包含负极活性材料的负极膜层；
    其中，所述二次电池满足：
    Figure PCTCN2020109120-appb-100008
    d c为所述正极膜层的压实密度，单位为g/cm 3，
    l c为所述正极膜层中所述正极活性材料的质量占比，
    d a为所述负极膜层的压实密度，单位为g/cm 3，
    l a为所述负极膜层中所述正极活性材料的质量占比，
    I e为所述二次电池中所述电解液的质量占所述电解液、所述正极活性材料和所述负极活性材料的总质量的比值。
  13. 根据权利要求12所述的制备方法，其中，所述正极浆料的粘度为4000mPa·s～15000mPa·s，可选的为6000mPa·s～10000mPa·s；或，
    所述正极浆料的固含量为60％～80％，可选的为65％～75％。
  14. 一种电池模块，包括根据权利要求1-11任一项所述的二次电池、或根据权利要求12-13任一项所述的制备方法得到的二次电池。
  15. 一种电池包，包括根据权利要求1-11任一项所述的二次电池、或根据权利要求14所述的电池模块。
  16. 一种装置，包括根据权利要求1-11任一项所述的二次电池、根据权利要求14所述的电池模块、或根据权利要求15所述的电池包中的至少一种。
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