WO2024040420A1 - 二次电池及用电装置 - Google Patents

二次电池及用电装置 Download PDF

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WO2024040420A1
WO2024040420A1 PCT/CN2022/114112 CN2022114112W WO2024040420A1 WO 2024040420 A1 WO2024040420 A1 WO 2024040420A1 CN 2022114112 W CN2022114112 W CN 2022114112W WO 2024040420 A1 WO2024040420 A1 WO 2024040420A1
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Prior art keywords
active material
negative electrode
region
secondary battery
negative
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PCT/CN2022/114112
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English (en)
French (fr)
Inventor
杜香龙
许虎
金义矿
牛少军
金海族
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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 CN202280088373.1A priority Critical patent/CN118679595A/zh
Priority to PCT/CN2022/114112 priority patent/WO2024040420A1/zh
Publication of WO2024040420A1 publication Critical patent/WO2024040420A1/zh

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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the field of battery technology, and in particular relates to a secondary battery and an electrical device.
  • Secondary batteries mainly rely on the reciprocal movement of active ions between the positive and negative electrodes for reversible charging and discharging.
  • Existing secondary batteries already have high energy density and long cycle life, and also have the advantages of no pollution and no memory effect. Therefore, they are widely used in various consumer electronic products and such as electric vehicles and energy storage. systems and other large equipment fields.
  • Embodiments of the present application provide a secondary battery and an electrical device, which can reduce lithium deposition from pole pieces and improve the service life and safety of the battery.
  • a first aspect of the embodiment of the present application provides a secondary battery, including an electrode assembly.
  • the electrode assembly includes a main body and tabs extending from the main body.
  • the main body includes a negative electrode piece.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a first region in the direction in which the tab extends and is disposed on the A second area on at least one side of the first area, the first area includes a first negative active material, the second area includes a second negative active material, and the powder OI value of the first negative active material is recorded as OI a , the powder OI value of the second negative electrode active material is recorded as OI b , then the negative electrode film layer satisfies: OI a ⁇ OI b .
  • the density of the active material particles at the upper edge of the negative electrode piece can be increased.
  • the degree of stacking orientation facilitates the embedding of active ions and reduces the direct reduction and precipitation of active ions on the surface of the negative electrode to form dendrites. It can improve the precipitation problem at places where thickness changes on the negative electrode piece (such as the connection between the main body and the tab) and reduce dendrite puncture.
  • the isolation film causes the risk of short circuit within the battery and improves the safety performance and service life of the battery.
  • the powder OI value of the first negative active material is recorded as OI a
  • the powder OI value of the second negative active material is recorded as OI b
  • the ratio of the powder OI values of the first negative active material and the second negative active material is appropriate, which can further improve the active ion precipitation problem of the secondary battery and improve the safety of the battery.
  • the powder OI value of the first negative active material is recorded as OI a
  • the powder OI value of the second negative active material is recorded as OI b
  • the powder OI value of the first negative active material and the second negative active material has an appropriate value range, which can further improve the active ion precipitation problem of the secondary battery and improve the safety of the battery.
  • the OI value of the pole piece in the first region is denoted as OI 1
  • the OI value of the pole piece in the second region is denoted as OI 2 , which satisfies that OI 1 is smaller than OI 2 .
  • the degree of stacking orientation of the active material particles at the upper edge of the negative electrode pole can be further increased, facilitating the insertion of active ions and reducing Active ions are directly reduced and precipitated on the surface of the negative electrode to form dendrites, which improves the safety performance and service life of the battery.
  • the OI value of the pole piece in the first region is marked as OI 1
  • the OI value of the pole piece in the second region is marked as OI 2 , satisfying, 0.7 ⁇ OI 1 /OI 2 ⁇ 1 .
  • the ratio of the OI value of the pole piece in the first region to the pole piece in the second region is appropriate, which can further improve the active ion precipitation problem of the secondary battery and improve the safety of the battery.
  • the OI value of the pole piece in the first region is recorded as OI 1 and satisfies 7 ⁇ OI 1 ⁇ 8, optionally 7.4 ⁇ OI 1 ⁇ 7.8; and/or the third
  • the OI value of the pole piece in the second region is recorded as OI 2 and satisfies 8 ⁇ OI 2 ⁇ 10, and optionally 8.5 ⁇ OI 2 ⁇ 9.5.
  • the OI value range of the pole piece in the first region and the pole piece in the second region is appropriate, which can further improve the active ion precipitation problem of the secondary battery and improve the safety of the battery.
  • the volume average particle size Dv50 of the first negative active material is 8 ⁇ m to 15 ⁇ m, optionally 9 ⁇ m to 12 ⁇ m; and/or the second negative active material has a volume average particle size
  • the diameter Dv50 is 4 ⁇ m to 8 ⁇ m, optionally 5 ⁇ m to 7 ⁇ m. If the Dv50 of the first negative active material is within an appropriate range, it can improve the cycle life and fast charging capability of the battery. If the Dv50 of the second negative active material is appropriately reduced, it can increase the gap in the second region and facilitate the insertion of active ions.
  • the powder compaction density of the first negative active material under a pressure of 3000N is greater than the powder compaction density of the second negative active material under a pressure of 3000N.
  • the powder compaction density of the first negative active material under a pressure of 3000N is recorded as P 1
  • the powder compaction density of the second negative active material under a pressure of 3000N is recorded as P 2 satisfies, 1 ⁇ P 1 /P 2 ⁇ 1.2, optionally, 1.05 ⁇ P 1 /P 2 ⁇ 1.15.
  • the ratio of the powder compaction density of the first negative active material to the powder compacted density of the second negative active material is appropriate, which can increase the second area while taking into account high cycle life, fast charging capability and energy density.
  • the internal gaps facilitate the insertion of active ions.
  • the powder compaction density of the first negative active material under a pressure of 3000N is 1.45g/cm 3 to 1.65g/cm 3 , optionally 1.5g/cm 3 to 1.6g /cm 3 ; and/or, the powder compaction density of the second negative active material under a pressure of 3000N is 1.35g/cm 3 to 1.45g/cm 3 , optionally 1.4g/cm 3 to 1.45g /cm 3 .
  • the powder compaction density of the first negative electrode active material and the powder compaction density of the second negative electrode active material have an appropriate value range, which can increase the third negative electrode active material while taking into account a higher cycle life, fast charging capability and energy density.
  • the gap within the two regions facilitates the insertion of active ions.
  • the tap density of the first negative active material is greater than the tap density of the second negative active material.
  • the tap density of the first negative active material is increased within an appropriate range, which helps to improve the cycle life of the battery and also increases the energy density of the battery.
  • the second negative active material uses secondary particles.
  • the use of the second negative active material can enable the battery to obtain a higher energy density, while taking into account the need to reduce the precipitation of active ions and improve battery safety.
  • the second area is arranged on both sides of the first area; optionally, the two second areas arranged on both sides of the first area are at the pole.
  • the ears have the same size in the direction of extension.
  • the size of the first region in the direction of the tab extension is denoted as L 1
  • the dimension of the second region in the direction of the tab extension is denoted as L 2 , satisfying: L 1 ⁇ L 2 , optionally, 1 ⁇ L 1 /L 2 ⁇ 50.
  • L 2 ⁇ 15mm.
  • the proportion of the sizes of the first region and the second region in the extension direction is appropriate, which can improve the problem of active ion precipitation in the edge area of the pole piece, improve battery safety, and take into account high cycle life, fast charging capability and energy density.
  • the first active material includes artificial graphite; and/or the second active material includes at least one of artificial graphite, natural graphite, hard carbon, or soft carbon. Containing an appropriate amount of natural graphite in the first negative active material can further improve the energy density of the battery.
  • the use of the second negative active material enables the battery to obtain a higher energy density while taking into account a higher cycle life and fast charging capability.
  • a second aspect of the embodiment of the present application provides an electrical device, including the above-mentioned secondary battery, for providing electrical energy.
  • the electrical device of the present application includes the secondary battery of the present application, and therefore can obtain beneficial effects corresponding to the secondary battery.
  • Figure 1 is a schematic diagram of an embodiment of a secondary battery of the present application.
  • FIG. 2 is an exploded view of FIG. 1 .
  • FIG. 3 is a schematic diagram of an embodiment of the electrode assembly of the present application.
  • FIG. 4 is a schematic diagram of another embodiment of the electrode assembly of the present application.
  • FIG. 5 is a schematic diagram of another embodiment of the electrode assembly of the present application.
  • Figure 6 is a schematic cross-sectional view of an embodiment of the negative electrode plate of the present application.
  • Figure 7 is a schematic cross-sectional view of another embodiment of the negative electrode plate of the present application.
  • FIG. 8 is a schematic diagram of an embodiment of the battery module of the present application.
  • FIG. 9 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 10 is an exploded view of FIG. 9 .
  • FIG. 11 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 unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range.
  • every point or individual value between the endpoints of a range is included in the range.
  • each point or single value may serve as a lower or upper limit on its own in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after discharge.
  • a secondary battery typically includes an electrode assembly and an electrolyte.
  • the electrode assembly includes a main body and tabs extending from the main body.
  • the main body may include a positive electrode piece, a negative electrode piece and a separator. It is usually a laminate structure formed by a lamination process or a rolled structure formed by a winding process.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.
  • the pole tabs include positive pole tabs extending from the edge of the positive pole piece and negative pole tabs extending from the edges of the negative pole piece.
  • the positive electrode tab and the negative electrode tab may extend from the same side of the main body part, or may extend from opposite two sides of the main body part.
  • active ions such as lithium ions
  • the electrolyte infiltrates into the main body and mainly plays the role of conducting ions between the positive electrode piece and the negative electrode piece.
  • the positive electrode tab and the negative electrode tab can be further electrically connected to the corresponding electrode terminal (which can be disposed on the top cover assembly of the battery outer package) through an adapter piece, thereby extracting the electric energy from the main body.
  • the inventor has found that by optimizing the design of the negative electrode film layer, it is possible to effectively ensure that the upper edge of the negative electrode sheet has good active ion diffusion performance, so that the secondary battery can have a higher energy density while taking into account better battery safety.
  • the inventor of the present application designed a secondary battery and a power device after in-depth research.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a first region and a second region disposed on at least one side of the first region in the tab extension direction. region, the first region includes the first negative active material, the second region includes the second negative active material, the powder OI value of the first negative active material is recorded as OI a , and the powder OI value of the second negative active material is recorded as OI b , then the negative electrode film layer satisfies: OI a ⁇ OI b .
  • the degree of stacking orientation of the active material particles at the upper edge of the negative electrode piece can be increased. It facilitates the embedding of active ions and reduces the direct reduction and precipitation of active ions on the surface of the negative electrode to form dendrites. It can improve the precipitation problem at places where the thickness of the negative electrode changes (such as the connection between the main body and the tab), and reduce the risk of dendrites piercing the separator and causing battery damage. Reduce the risk of internal short circuit and improve the safety performance and service life of the battery.
  • the powder OI value of the first negative active material is recorded as OI a
  • the powder OI value of the second negative active material is recorded as OI b
  • the ratio of the powder OI values of the first negative active material and the second negative active material is appropriate, which can further improve the active ion precipitation problem of the secondary battery and improve the safety of the battery.
  • the powder OI value of the first negative active material is recorded as OI a
  • the powder OI value of the second negative active material is recorded as OI b
  • 2.5 ⁇ OI a ⁇ 3.5 optionally 2.5 ⁇ OI a ⁇ 3.0, 2.6 ⁇ OI a ⁇ 2.8, 2.7 ⁇ OI a ⁇ 2.9; and/or, 3.0 ⁇ OI b ⁇ 4.5, optional 3.5 ⁇ OI b ⁇ 4.0, 3.6 ⁇ OI b ⁇ 3.8 , 3.7 ⁇ OI b ⁇ 3.9.
  • the powder OI value of the first negative active material and the second negative active material has an appropriate value range, which can further improve the active ion precipitation problem of the secondary battery and improve the safety of the battery.
  • the OI value of the pole piece in the first region is denoted as OI 1
  • the OI value of the pole piece in the second region is denoted as OI 2 , so that OI 1 is smaller than OI 2 .
  • the OI value of the pole piece in the first region is denoted as OI 1
  • the OI value of the pole piece in the second region is denoted as OI 2 , satisfying, 0.7 ⁇ OI 1 /OI 2 ⁇ 1.
  • Setting OI 1 and OI 2 within an appropriate range can make the negative electrode active material less selective in the direction during the lithium insertion process.
  • the lithium insertion expansion can be dispersed in all directions, thus further reducing the volume of the first part of the negative electrode plate. Expansion improves electrolyte wettability.
  • the second area obtains appropriate active ion diffusion capabilities, improves the active ion precipitation problem on the negative electrode plate, and improves battery safety.
  • the OI value of the pole piece in the first region is recorded as OI 1 and satisfies 7 ⁇ OI 1 ⁇ 8, optionally 7.4 ⁇ OI 1 ⁇ 7.8 , 7.2 ⁇ OI 1 ⁇ 7.6, 7.1 ⁇ OI 1 ⁇ 7.5, 7.6 ⁇ OI 1 ⁇ 7.9; and/or, the OI value of the pole piece in the second area is recorded as OI 2 , satisfying 8 ⁇ OI 2 ⁇ 10, optionally 8.5 ⁇ OI 2 ⁇ 9.5, 8.2 ⁇ OI 2 ⁇ 9, 8.8 ⁇ OI 2 ⁇ 9.2, 9 ⁇ OI 2 ⁇ 9.8.
  • the OI value range of the pole piece in the first region and the pole piece in the second region is appropriate, which can further improve the active ion precipitation problem of the secondary battery and improve the safety of the battery.
  • the first anode active material has a volume average particle diameter Dv50 of 8 ⁇ m to 15 ⁇ m, optionally 9 ⁇ m to 12 ⁇ m, 11 ⁇ m to 14 ⁇ m, 10 ⁇ m to 13 ⁇ m; and/or the second anode active material has a volume average particle size Dv50 of The particle size Dv50 is 4 ⁇ m to 8 ⁇ m, optionally 5 ⁇ m to 7 ⁇ m, 6 ⁇ m to 8 ⁇ m, 4 ⁇ m to 6 ⁇ m.
  • the Dv50 of the first negative electrode active material is within an appropriate range, which can not only obtain a higher gram capacity, but also enable the particles to have a short ion transmission path, and also ensure the formation of a smooth pore structure between the particles to facilitate the infiltration of the electrolyte. and reflux. Therefore, the first part of the negative electrode plate can obtain higher active ion migration performance, thereby improving the cycle life and fast charging capability of the battery.
  • the Dv50 of the second negative active material is appropriately reduced, which can increase the gap in the second region and facilitate the insertion of active ions.
  • the powder compaction density of the first negative active material under a pressure of 3000N is greater than the powder compaction density of the second negative active material under a pressure of 3000N.
  • the powder compaction density of the first negative active material under a pressure of 3000N is recorded as P 1
  • the powder compacted density of the second negative active material under a pressure of 3000N is recorded as P 2 , satisfying that, 1 ⁇ P 1 /P 2 ⁇ 1.2, optionally, 1.05 ⁇ P 1 /P 2 ⁇ 1.15, 1.08 ⁇ P 1 /P 2 ⁇ 1.12, 1.1 ⁇ P 1 /P 2 ⁇ 1.18, 1.02 ⁇ P 1 /P 2 ⁇ 1.08.
  • the ratio of the powder compaction density of the first negative active material to the powder compacted density of the second negative active material is appropriate, which can increase the second area while taking into account high cycle life, fast charging capability and energy density.
  • the internal gaps facilitate the insertion of active ions.
  • the powder compaction density of the first negative active material under a pressure of 3000N is 1.45g/cm 3 to 1.65g/cm 3 , optionally 1.5g/cm 3 to 1.6g/cm 3 , 1.47 g/cm 3 to 1.58g/cm 3 , 1.53g/cm 3 to 1.61g/cm 3 , 1.55g/cm 3 to 1.63g/cm 3 ; and/or, the powder of the second negative active material under a pressure of 3000N
  • the bulk compacted density is 1.35g/cm 3 to 1.45g/cm 3 , optionally 1.4g/cm 3 to 1.45g/cm 3 , 1.38g/cm 3 to 1.42g/cm 3 .
  • the powder compaction density of the first negative electrode active material and the powder compaction density of the second negative electrode active material have an appropriate value range, which can increase the third negative electrode active material while taking into account a higher cycle life, fast charging capability and energy density.
  • the gap within the two regions facilitates the insertion of active ions.
  • the tap density of the first negative active material is greater than the tap density of the second negative active material. Increasing the tap density of the first negative active material within an appropriate range can improve the battery's rapid lithium insertion capability, help improve the cycle life of the battery, and at the same time increase the energy density of the battery.
  • the second negative active material includes secondary particles.
  • the use of the second negative active material can enable the battery to obtain a higher energy density, while taking into account the need to reduce the precipitation of active ions and improve battery safety.
  • the first negative active material includes at least one of primary particles or secondary particles.
  • Primary particles are non-agglomerated particles.
  • Secondary particles are agglomerated particles formed by the aggregation of two or more primary particles. Primary particles and secondary particles can be easily distinguished by taking SEM images with a scanning electron microscope.
  • the second area is disposed on both sides of the first area; optionally, the two second areas disposed on both sides of the first area have the same size in the tab extension direction.
  • There are second areas on both sides of the first area which can simultaneously improve the problem of active ion precipitation in the edge areas on both sides of the pole piece and improve battery safety.
  • the electrolyte wettability in different areas of the negative electrode film layer is more consistent. , can further improve the active ion transmission performance in various areas of the negative electrode film layer, thereby further improving the cycle life and fast charging capability of the battery.
  • Figure 6 is a schematic cross-sectional view of an embodiment of the negative electrode plate of the present application.
  • Figure 7 is a schematic cross-sectional view of another embodiment of the negative electrode plate of the present application.
  • the size of the first region 121 in the direction in which the pole tab 522 extends is denoted as L 1
  • the dimension of the second region 122 in the direction in which the pole tab 522 extends is denoted as L 2 , satisfies: L 1 ⁇ L 2 , optionally, 1 ⁇ L 1 /L 2 ⁇ 50, 5 ⁇ L 1 /L 2 ⁇ 45, 10 ⁇ L 1 /L 2 ⁇ 40, 15 ⁇ L 1 / L 2 ⁇ 35, 20 ⁇ L 1 /L 2 ⁇ 30, 23 ⁇ L 1 /L 2 ⁇ 27.
  • the extension lengths of the second areas 122 on both sides in the extension direction of the tabs 522 are greater than 15 mm.
  • the second region 122 may be a thinned region on the pole piece, that is, the thickness of the second region 522 is smaller than that of the first region 121 .
  • the ratio of the sizes of the first region 121 and the second region 522 in the extending direction is appropriate, which can not only effectively improve the overall active ion migration performance of the negative electrode film layer, but also help the negative electrode film layer to have a higher reversible capacity, thereby making the secondary Batteries better combine high cycle life, fast charging capabilities and energy density.
  • the second area 122 may be a thinned area provided at the upper edge of the pole piece.
  • the first active material includes artificial graphite.
  • the second active material includes at least one of artificial graphite, natural graphite, hard carbon, or soft carbon.
  • the first negative active material optionally also includes other active materials that can be used in secondary battery negative electrodes.
  • other active materials may include natural graphite, silicon-based materials, tin-based materials, and the like.
  • the second negative active material optionally also includes other active materials that can be used in secondary battery negative electrodes.
  • other active materials may include silicon-based materials, tin-based materials, and the like.
  • the first region and the second region of the negative electrode film layer generally optionally include a binder, a conductive agent, and/or an auxiliary agent in addition to the negative electrode active material.
  • conductive agents may include one or more of superconducting carbon, carbon black (such as acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • binders may include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS) one or more of them.
  • auxiliaries may include thickeners (such as carboxymethyl cellulose sodium CMC-Na) and the like.
  • the negative electrode current collector can be a metal foil or a composite current collector (metal materials can be placed on a polymer substrate to form a composite current collector).
  • the negative electrode current collector may be copper foil.
  • the negative electrode film layer may be disposed on one side of the negative electrode current collector, or may be disposed on both sides of the negative electrode current collector.
  • a second aspect of the embodiment of the present application provides an electrical device, including the above-mentioned secondary battery, for providing electrical energy.
  • the negative electrode plate includes a negative electrode current collector 110 and a negative electrode film layer 120 disposed on one side of the negative electrode current collector 110.
  • the tab 522 protrudes from one edge of the negative electrode current collector 110 .
  • the negative electrode film layer 120 is divided into a first region 121 and a second region 122 located on both sides of the first region 121 in the direction in which the tab 522 extends.
  • the negative electrode sheet includes a negative electrode current collector 110 and negative electrode film layers 120 respectively disposed on both sides of the negative electrode current collector 110 .
  • the tab 522 protrudes from one edge of the negative electrode current collector 110 .
  • the negative electrode film layer 120 is divided into a first region 121 and a second region 122 located on both sides of the first region 121 in the direction in which the tab 522 extends.
  • the tabs can be connected to the negative electrode current collector by welding, or a blank area (that is, the area not covered by the negative electrode film layer) can be reserved in the negative electrode current collector, and the blank area can be cut to form tabs.
  • each negative electrode film layer given in this application refers to the parameter range of the single-sided film layer.
  • the negative electrode film layers are arranged on both sides of the negative electrode current collector, if the parameters of the film layer on either side meet the requirements of this application, it is deemed to fall within the protection scope of this application.
  • the sizes, compaction densities, areal densities and other ranges of different areas of the negative electrode film mentioned in this application all refer to the parameters of the film layer after cold pressing and compaction and used to assemble the battery.
  • the negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer.
  • the negative electrode sheet described in the present application may further include a conductive undercoat layer (for example, composed of a conductive agent and a binder) disposed between the negative electrode current collector and the negative electrode film layer.
  • the negative electrode sheet described in this application further includes a covering protective layer covering the surface of the negative electrode film layer.
  • the charge and discharge rate 1C represents the rated capacity of the battery that is completely discharged in 1 hour.
  • the upper limit voltage V0 of lithium iron phosphate (LiFePO4, LFP) system battery products is generally 3.65V;
  • the upper limit voltage V0 of LiNi0.8Co0.1Mn0.1O2 (NCM811) system battery products is generally 4.2V; LiNi0.5Co0.2Mn0.
  • the upper limit voltage V0 of 3O2 (NCM523) system battery products is generally 4.3V.
  • the size of the first region of the negative electrode film layer in the tab protruding direction and the size of the second region in the tab protruding direction are meanings known in the art, and methods known in the art can be used. Determination.
  • An exemplary test method is as follows: Take a complete negative electrode piece in the direction of the tab extension, and use ceramic scissors to cut out a strip-shaped pole piece with a width of 10mm ⁇ 2mm along the direction parallel to the tab extension direction (marked as the Q direction). ; Then cut the pole pieces perpendicular to the Q direction at 10mm equidistant intervals, and mark sample 1, sample 2,...
  • the cross-section is polished, and then the polished cross-section of the sample is imaged by an analytical scanning electron microscope (such as ZEISS Sigma 300); the first region and the second region can be distinguished based on the difference in morphology and porosity of the negative electrode particles in the first region and the second region.
  • the interface between the two areas can determine the size of the first area and the second area in the tab extension direction.
  • the powder compaction density of the negative active material under a pressure of 3000N is a meaning known in the art and can be measured using methods known in the art.
  • an exemplary test method is as follows: weigh 1g of negative active material, add it to a mold with a bottom area of 1.327cm2 , pressurize to 3000N, hold the pressure for 30s, then release the pressure, hold for 10s, then record and calculate the negative active material at 3000N The compacted density of powder under pressure.
  • the OI value of the negative electrode sheet C004/C110, where C004 is the peak area of the diffraction peak of the 004 crystal plane of the graphite material in the negative electrode sheet, and C110 is the peak area of the diffraction peak of the 110 crystal plane of the graphite material in the negative electrode sheet.
  • the peak area of the diffraction peak can be obtained by testing the X-ray diffraction pattern.
  • X-ray diffraction analysis can be carried out using an X-ray diffractometer with reference to the standard JISK0131-1996.
  • An exemplary test method is as follows: respectively cut test samples from the portion of the negative electrode plate corresponding to the first area of the negative electrode film layer and the portion corresponding to the second area of the negative electrode film layer; place the electrode piece samples in an X-ray diffractometer (for example, Bruker D8 Discover), the X-ray diffraction pattern was obtained; the OI value of the pole piece sample was obtained based on C004/C110 in the X-ray diffraction pattern.
  • X-ray diffractometer for example, Bruker D8 Discover
  • the X-ray diffraction analysis conditions are, for example, using a copper target as the anode target, CuK ⁇ rays as the radiation source, and the ray wavelength
  • the scanning 2 ⁇ angle range is from 20° to 80°, and the scanning rate is 4°/min.
  • the volume average particle size Dv50 of the negative active material is a meaning known in the art and can be measured using methods known in the art. For example, laser diffraction particle size analysis. Laser diffraction particle size analysis can be performed on a laser particle size analyzer (e.g. Malvern Mastersize 3000). The test can refer to the standard GB/T 19077-2016. Dv50 is the particle size corresponding to when the cumulative volume distribution percentage of the negative active material reaches 50%.
  • the above-mentioned various parameter tests on the negative active material can be performed directly on samples of the negative active material, or on samples taken from secondary batteries.
  • the above test sample is taken from a secondary battery, as an example, the sampling can be carried out as follows:
  • Discharge the secondary battery for safety reasons, generally keep the battery in a fully discharged state; remove the negative electrode piece after disassembling the battery, and soak the negative electrode piece in dimethyl carbonate (DMC) for a certain period of time (for example, 2 to 10 hours); then take out the negative electrode piece and dry it at a certain temperature and time (for example, 60°C, 4 hours). After drying, take out the negative electrode piece.
  • DMC dimethyl carbonate
  • step (2) Bake the negative electrode piece dried in step (1) at a certain temperature and time (for example, 400°C, 2 hours). Sample the negative active material in the corresponding parts of the area (you can choose to use a blade scraper to sample).
  • a certain temperature and time for example, 400°C, 2 hours.
  • step (3) Sieve the negative active materials collected in step (2) respectively (for example, through a 200-mesh sieve) to obtain negative active material samples that can be used to test the material parameters mentioned above in this application.
  • the secondary battery of the present application may use positive electrode plates known in the art.
  • 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 including a positive electrode active material.
  • the cathode active material includes lithium transition metal oxide (such as lithium nickel oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, etc.), olivine structure lithium-containing phosphoric acid One or more of salts (such as lithium iron phosphate, etc.) and their respective modified compounds.
  • lithium transition metal oxide such as lithium nickel oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, etc.
  • olivine structure lithium-containing phosphoric acid One or more of salts (such as lithium iron phosphate, etc.) and their respective modified compounds.
  • the positive electrode film layer usually optionally also includes a binder and/or a conductive agent.
  • conductive agents may include one or more of superconducting carbon, carbon black (such as acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • binders may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and one or more of carboxymethyl chitosan (CMCS).
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PAA polyacrylic acid
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • the positive electrode current collector can be a metal foil or a composite current collector (metal materials can be placed on a polymer substrate to form a composite current collector).
  • the positive electrode current collector may be aluminum foil.
  • the positive electrode lug extends from one edge of the positive electrode piece.
  • the negative electrode lug extends from one edge of the negative electrode piece.
  • the positive electrode tabs can be connected to the positive electrode current collector by welding, or a blank area (that is, an area not covered by the positive electrode film layer) can be reserved in the positive electrode current collector, and the blank area can be cut to form a positive electrode tab.
  • the negative electrode tab is similarly connected to the negative electrode piece.
  • the above-mentioned positive electrode tab, negative electrode tab and separator are formed into a main body through a lamination process or a winding process, and two tabs (ie, the positive electrode tab and the negative electrode tab) extend from the main body part. In the electrode assembly, the two tabs may extend from the same side of the main body, or may extend from opposite sides of the main body.
  • FIGS. 3 and 4 two different electrode assemblies are exemplarily shown, in which two pole tabs 522 protrude from the same side of the main body part 521 .
  • FIG. 5 another electrode assembly is exemplarily shown, in which two tabs 522 extend from opposite sides of the main body portion 521 .
  • the isolation film may be selected from fiberglass, non-woven fabric, polyethylene film, polypropylene film, polyvinylidene fluoride film, and multi-layer composite films thereof.
  • the secondary battery of this application has no specific restrictions on the electrolyte and can be selected according to needs.
  • the electrolyte usually includes an electrolyte lithium salt and a solvent.
  • the electrolyte lithium salt can be selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), bisfluorosulfonyl Lithium imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium difluoromethanesulfonylborate (LiBOB), difluorophosphoric acid
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • LiClO 4 lithium perchlorate
  • LiAsF 6 lithium hexafluoroarsenate
  • LiFSI bisfluo
  • 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), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate Ester (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) , one or more of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl s
  • EC
  • additives are optionally included in the electrolyte.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, and additives that improve the low-temperature performance of the battery. Additives etc.
  • This application also provides a method for preparing a secondary battery.
  • the method includes preparing a negative electrode sheet for a secondary battery by: providing a first negative electrode slurry including a first negative electrode active material and a second negative electrode slurry including a second negative electrode active material, the first negative electrode active material including artificial graphite, The second negative electrode active material includes graphite; providing a negative electrode current collector, at least one surface of the negative electrode current collector includes a first coating area and second coating areas located on both sides of the first coating area in the tab extension direction; The first negative electrode slurry is applied to the first coating area of the negative electrode current collector, and the second negative electrode slurry is applied to the second coating area of the negative electrode current collector to form a negative electrode film layer to obtain a negative electrode piece.
  • the negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring evenly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • the first negative electrode slurry and the second negative electrode slurry may be coated in two times or simultaneously. After the coating is dried and cold pressed, a negative electrode film layer is formed.
  • the positive electrode sheet of the present application can be prepared as follows: mix the positive active material and the optional conductive agent and binder, then disperse them in a solvent (such as NMP), stir evenly, and then apply them on the positive electrode current collector, and bake After drying and cold pressing, the positive electrode piece is obtained.
  • a solvent such as NMP
  • the positive electrode sheet, isolation film, and negative electrode sheet are made into an electrode assembly, placed in an outer package, injected with electrolyte, and subjected to processes such as vacuum packaging, standing, formation, and shaping to obtain a secondary battery. .
  • the outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging can also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.
  • FIG. 1 shows an example of a square-structured secondary battery.
  • FIG. 1 is a schematic diagram of an embodiment of a secondary battery of the present application.
  • FIG. 2 is an exploded view of FIG. 1 .
  • the secondary battery includes an outer packaging, an electrode assembly 52 and an electrolyte (not shown).
  • the outer packaging may include a housing 51 and a top cover assembly 53 .
  • the housing 51 has an accommodation cavity and an opening communicating with the accommodation cavity.
  • the electrode assembly 52 is disposed in the accommodation cavity.
  • the number of electrode assemblies 52 is not limited and may be one or several.
  • the electrolyte soaks into the electrode assembly.
  • the top cover assembly 53 covers the opening to close the accommodation cavity.
  • the battery module includes the secondary battery of the present application.
  • FIGS. 4 and 8 are schematic diagram of an embodiment of the battery module of the present application.
  • the battery module 4 includes a plurality of secondary batteries 5 .
  • the plurality of secondary batteries 5 are arranged in the longitudinal direction.
  • the battery module 4 can serve as a power source or energy storage device.
  • the number of lithium-ion batteries 5 contained in the battery module 4 can be adjusted according to the application and capacity of the battery module 4 .
  • the battery pack includes the secondary battery and/or battery module of the present application.
  • FIG. 9 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 10 is an exploded view of FIG. 9 .
  • the battery pack 1 includes a battery box and a plurality of battery modules 4 arranged in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 and the lower box 3 are assembled together to form a space for accommodating the battery module 4 .
  • the number and arrangement of the battery modules 4 used in the battery pack 1 can be determined according to actual needs.
  • the device includes at least one of the secondary battery, battery module, or battery pack of the present application.
  • a secondary battery, battery module or battery pack may 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, a mobile device (such as a mobile phone, a laptop, etc.), an electric vehicle (such as an electric car, an electric bus, an electric tram, an electric bicycle, an electric motorcycle, an electric scooter, an electric golf cart, an electric truck) ), electric trains, ships and satellites, energy storage systems, etc.
  • the device can select secondary batteries, battery modules or battery packs according to its usage requirements.
  • the electrical device can be an electric vehicle.
  • Electric vehicles can be pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, etc.
  • the electric vehicle may include the battery module 4 or battery pack 1 described in this application according to the actual usage form.
  • Artificial graphite A commercially available from anode material suppliers. Artificial graphite A is a primary particle with a gram capacity of 340mAh/g to 353mAh/g. The remaining physical parameters are listed in Table 1.
  • Artificial graphite B commercially available from anode material suppliers. Artificial graphite B is a secondary particle with a gram capacity of 353mAh/g to 360mAh/g. The remaining physical properties are listed in Table 1.
  • the first negative electrode active material artificial graphite A, conductive agent Super P, binder SR-1B, and thickener CMC-Na in an appropriate amount of deionized water in a mass ratio of 96:1.5:1.5:1 to form a uniform mixture.
  • the Dv50 of the first negative active material is 6.2 ⁇ m.
  • the negative electrode current collector is made of copper foil, and its surface is divided into a coating area and a blank area adjacent to the coating area in the direction of the tab extension.
  • the coating area is divided into a first coating area and a separate area in the direction of the tab extension. Second coating areas on either side of the first coating area.
  • the first negative electrode slurry is applied to the first coating area of the negative electrode current collector, and the second negative electrode slurry is applied to the second coating area of the negative electrode current collector to form a negative electrode coating.
  • the negative electrode coating is dried and cold pressed to form a negative electrode film layer.
  • the blank area of the negative electrode current collector is cut to form a negative electrode tab, and a negative electrode piece is obtained.
  • the negative electrode film layer includes a first area and a second area arranged on both sides of the first area in the direction of the tab extension, and the two second areas arranged on both sides of the first area are in the direction where the tab extends.
  • the size of the first area in the tab extension direction is L 1
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the pole ears extend from the height direction of the main body.
  • Example 2 The preparation methods of Examples 2 to 27 and Comparative Examples 1 to 2 are similar to Example 1, but the preparation parameters of the negative electrode piece are adjusted.
  • the different preparation parameters and product parameters are detailed in Table 1 and Table 2.
  • the batteries of each example and comparative example were charged and discharged for the first time with a current of 1C (that is, the current value that completely discharges the rated capacity within 1 hour), which specifically included: charging the battery with a constant current at a rate of 1C to The voltage is 4.3V, then charged at a constant voltage until the current is ⁇ 0.05C, left for 5 minutes, and then discharged at a constant current of 0.33C to a voltage of 2.8V, and the actual capacity is recorded as C 0 .
  • a current of 1C that is, the current value that completely discharges the rated capacity within 1 hour
  • the negative electrode cut-off potential (whichever is reached first) needs to be discharged at 1C 0 to the full battery discharge cut-off voltage of 2.8V after each charging is completed. Record the charging to 10%, 20%, 30%,..., at different charging rates.
  • the negative electrode potential corresponding to 80% SOC State of Charge, state of charge is drawn.
  • the charging rate-negative electrode potential curve in different SOC states is drawn.
  • the charging rate is the charging window in the SOC state, which are recorded as C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC respectively.
  • the battery is calculated by (60/C20%SOC+60/C30%SOC+60/C40%SOC+60/C50%SOC+60/C60%SOC+60/C70%SOC+60/C80%SOC) ⁇ 10% Charging time T from 10% SOC to 80% SOC, unit is min. The shorter the time, the better the battery's fast charging performance.
  • the secondary batteries prepared in the Examples and Comparative Examples were charged at a constant current rate of 1C to 4.3V, then charged at a constant voltage to a current ⁇ 0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 1C to 2.8V. , let it stand for 5 minutes, this is a charge and discharge cycle, record the discharge capacity of the first cycle.
  • This method to cycle charge and discharge the battery until the battery capacity decays to 80% of the first cycle discharge capacity.
  • the number of cycles at this time is the cycle life of the battery at 25°C. The higher the number of cycles, the higher the cycle life of the battery.
  • the artificial graphite B used is mixed with other materials, and the mass ratio of artificial graphite B to other materials is 8:2.
  • the OI value of the active material in the areas on both sides of the negative electrode film layer in the tab extension direction and the OI value of the electrode piece are set to be greater than the OI value of the active material in the middle area.
  • the battery has a high energy density, while also taking into account a high cycle life and fast charging capability.
  • Comparative Example 1-2 does not meet the above conditions, making it difficult for the battery to achieve both high energy density and long cycle life.
  • the inventor also discovered that when artificial graphite B is used as secondary particles, the secondary battery can further increase the energy density while having a higher cycle life and fast charging capability. Since the test results are relatively similar to the data of Examples 1-16 in Table 2, they will not be described again here.

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Abstract

本申请实施方式提供了一种二次电池及用电装置，一种二次电池包括电极组件，所述电极组件包括主体部和由所述主体部延伸出的极耳，所述主体部包括负极极片，所述负极极片包括负极集流体以及设置于所述负极集流体至少一个表面上的负极膜层，其中，所述负极膜层在所述极耳伸出方向上包括第一区域和设置在所述第一区域至少一侧的第二区域，所述第一区域包括第一负极活性材料，所述第二区域包括第二负极活性材料，所述第一负极活性材料的粉体OI值记为OI a，所述第二负极活性材料的粉体OI值记为OI b，则所述负极膜层满足：OI a＜OI b。

Description

二次电池及用电装置 技术领域
本申请属于电池技术领域，尤其涉及一种二次电池及用电装置。
背景技术
二次电池主要依靠活性离子在正极和负极之间的往复移动来进行可逆的充电和放电。现有的二次电池已经具备较高的能量密度和较长的循环寿命，并且还具有无污染、无记忆效应等优点，因而被广泛应用于各类消费类电子产品和例如电动车辆、储能系统等大型装置领域。
在二次电池技术领域中，极片的析锂问题，是影响电池使用寿命及安全性的重要原因之一。
申请内容
本申请实施方式提供了一种二次电池及用电装置，能够减少极片析锂，提高电池的使用寿命及安全性。
本申请实施方式的第一方面，提供了一种二次电池，包括电极组件，所述电极组件包括主体部和由所述主体部延伸出的极耳，所述主体部包括负极极片，所述负极极片包括负极集流体以及设置于所述负极集流体至少一个表面上的负极膜层，其中，所述负极膜层在所述极耳伸出方向上包括第一区域和设置在所述第一区域至少一侧的第二区域，所述第一区域包括第一负极活性材料，所述第二区域包括第二负极活性材料，所述第一负极活性材料的粉体OI值记为OI a，所述第二负极活性材料的粉体OI值记为OI b，则所述负极膜层满足：OI a＜OI b。
采用上述方案，通过在极耳引出方向设置第一区域及第二区域，并使第二区域的活性材料OI值大于第一区域的活性材料，能够增大负极极片上边缘处的活性材料颗粒的堆积取向程度，便于活性离子嵌入，减少活 性离子直接在负极表面还原析出而形成枝晶，能够改善负极极片上厚度变化处(如主体部与极耳连接处)的析出问题，降低枝晶刺破隔离膜引发电池内短路的风险，提高电池的安全性能及使用寿命。
在本申请任一实施方式中，所述第一负极活性材料的粉体OI值记为OI a，所述第二负极活性材料的粉体OI值记为OI b，满足，0.6≤OI a/OI b＜1；可选地，0.7≤OI a/OI b≤0.9。第一负极活性材料与第二负极活性材料的粉体OI值的比例适当，能够进一步改善二次电池的活性离子析出问题，提高电池安全性。
在本申请任一实施方式中，所述第一负极活性材料的粉体OI值记为OI a，所述第二负极活性材料的粉体OI值记为OI b，满足，2.5≤OI a≤3.5，可选为2.5≤OI a≤3.0；和/或，3.0≤OI b≤4.5，可选为3.5≤OI b≤4.0。第一负极活性材料与第二负极活性材料的粉体OI值的取值范围适当，能够进一步改善二次电池的活性离子析出问题，提高电池安全性。
在本申请任一实施方式中，所述第一区域的极片OI值记为OI 1，所述第二区域的极片OI值记为OI 2，满足，OI 1小于OI 2。
采用上述方案，通过将第二区域的极片OI值设置为大于第一区域的极片OI值，能够进一步增大负极极片上边缘处的活性材料颗粒的堆积取向程度，便于活性离子嵌入，减少活性离子直接在负极表面还原析出而形成枝晶，提高电池的安全性能及使用寿命。
在本申请任一实施方式中，所述第一区域的极片OI值记为OI 1，所述第二区域的极片OI值记为OI 2，满足，0.7≤OI 1/OI 2＜1。第一区域的极片与第二区域的极片OI值的比例适当，能够进一步改善二次电池的活性离子析出问题，提高电池安全性。
在本申请任一实施方式中，所述第一区域的极片OI值记为OI 1，满足，7≤OI 1≤8，可选为7.4≤OI 1≤7.8；和/或，所述第二区域的极片OI值记为OI 2，满足，8≤OI 2≤10，可选为8.5≤OI 2≤9.5。第一区域的极片与第二区域的极片OI值的取值范围适当，能够进一步改善二次电池的活性离子析出问题，提高电池安全性。
在本申请任一实施方式中，所述第一负极活性材料的体积平均粒 径Dv50为8μm至15μm，可选地为9μm至12μm；和/或，所述第二负极活性材料的体积平均粒径Dv50为4μm至8μm，可选地为5μm至7μm。第一负极活性材料的Dv50在适当范围内，能改善电池的循环寿命和快速充电能力，第二负极活性材料的Dv50适当减小，能够增加第二区域内的间隙，便于活性离子嵌入。
在本申请任一实施方式中，所述第一负极活性材料在3000N压力下的粉体压实密度大于所述第二负极活性材料在3000N压力下的粉体压实密度。通过使第一负极活性材料的粉体压实密度大于第二负极活性材料的粉体压实密度，能够在兼顾较高的循环寿命、快速充电能力和能量密度的同时，能够增加第二区域内的间隙，便于活性离子嵌入。
在本申请任一实施方式中，所述第一负极活性材料在3000N压力下的粉体压实密度记为P 1，所述第二负极活性材料在3000N压力下的粉体压实密度记为P 2，满足，1≤P 1/P 2≤1.2，可选地，1.05≤P 1/P 2≤1.15。第一负极活性材料的粉体压实密度与第二负极活性材料的粉体压实密度的比例适当，能够在兼顾较高的循环寿命、快速充电能力和能量密度的同时，能够增加第二区域内的间隙，便于活性离子嵌入。
在本申请任一实施方式中，所述第一负极活性材料在3000N压力下的粉体压实密度为1.45g/cm 3至1.65g/cm 3，可选为1.5g/cm 3至1.6g/cm 3；和/或，所述第二负极活性材料在3000N压力下的粉体压实密度为1.35g/cm 3至1.45g/cm 3，可选地为1.4g/cm 3至1.45g/cm 3。第一负极活性材料的粉体压实密度与第二负极活性材料的粉体压实密度的取值范围适当，能够在兼顾较高的循环寿命、快速充电能力和能量密度的同时，能够增加第二区域内的间隙，便于活性离子嵌入。
在本申请任一实施方式中，所述第一负极活性材料的振实密度大于所述第二负极活性材料的振实密度。第一负极活性材料的振实密度在适当范围内增大，有助于改善电池的循环寿命，同时还能提高电池的能量密度。
在本申请任一实施方式中，所述第二负极活性材料采用二次颗粒。采用该第二负极活性材料能使电池获得较高的能量密度，同时兼顾降低活 性离子析出的需求，提高电池安全性。
在本申请任一实施方式中，所述第二区域设置在所述第一区域的两侧；可选地，设置在所述第一区域两侧的两个所述第二区域在所述极耳伸出方向上具有相同的尺寸。第一区域两侧均设置有第二区域，能够同时改善极片两侧的边缘区域活性离子析出的问题，提高电池安全性。
在本申请任一实施方式中，所述第一区域在所述极耳伸出方向上的尺寸记为L 1，所述第二区域在所述极耳伸出方向上的尺寸记为L 2，满足：L 1≥L 2，可选地，1≤L 1/L 2≤50。可选地，L 2≥15mm。第一区域与第二区域在伸出方向上尺寸的比例适当，能够改善极片的边缘区域活性离子析出的问题，提高电池安全性，同时兼顾较高的循环寿命、快速充电能力和能量密度。
在本申请任一实施方式中，所述第一活性材料包括人造石墨；和/或，所述第二活性材料包括人造石墨、天然石墨、硬碳或软碳中的至少一种。在第一负极活性材料中含有适量的天然石墨，能进一步改善电池的能量密度。采用该第二负极活性材料能使电池获得较高的能量密度，同时兼顾较高的循环寿命和快速充电能力。
本申请实施方式的第二方面，提供了一种用电装置，包括上述的二次电池，用于提供电能。
本申请的用电装置包含本申请的二次电池，因而能获得与二次电池相应的有益效果。
附图说明
为了更清楚地说明本申请实施方式的技术方案，下面将对本申请实施方式中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1是本申请二次电池的一个实施例的示意图。
图2是图1的分解图。
图3是本申请电极组件的一个实施例的示意图。
图4是本申请电极组件的另一个实施例的示意图。
图5是本申请电极组件的又一个实施例的示意图。
图6是本申请负极极片的一个实施例的截面示意图。
图7是本申请负极极片的另一个实施例的截面示意图。
图8是本申请电池模块的一个实施例的示意图。
图9是本申请电池包的一个实施例的示意图。
图10是图9的分解图。
图11是二次电池用作电源的装置的一个实施例的示意图。
具体实施方式
为了使本申请的申请目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。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(个)”中的“几种(个)”的含义是两种(个)或两种(个)以上。
本申请的上述申请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。在各个实例中，列举仅作为代表性组，不应解释为穷举。
二次电池又称为充电电池或蓄电池，是指在放电后可通过充电的方式使活性物质激活而继续使用的电池。
通常情况下，二次电池包括电极组件和电解液。电极组件包括主体部和由主体部延伸出的极耳。主体部可包括正极极片、负极极片和隔离膜，通常是由正极极片、负极极片和隔离膜经叠片工艺形成的叠片结构或经卷绕工艺形成的卷绕结构。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。极耳包括由正极极片的边缘延伸出的正极极耳和由负极极片的边缘延伸出的负极极耳。正极极耳和负极极耳可由主体部的同一侧延伸出，也可以由主体部的相对的两侧延伸出。
在电池充放电过程中，活性离子(例如锂离子)在正极极片和负极极片之间往返嵌入和脱出。电解液浸润于主体部中，在正极极片和负极极片之间主要起到传导离子的作用。正极极耳和负极极耳进一步可通过转接片与对应的电极端子(可设置于电池外包装的顶盖组件上)电连接，从而将主体部的电能引出。
由于负极极片上极耳引出位置需要设置厚度降低的区域，导致该处的层间距增大，易使活性离子析出，形成枝晶，导致枝晶刺破隔离膜引发电池内短路的风险，从而影响电池的安全性能。
本发明人研究发现，通过优化负极膜层的设计，可以有效保证包括负极极片上边缘处具有良好的活性离子扩散性能，以使二次电池在具有较高能量密度的前提下，同时兼顾较优的电池安全性。
基于以上考虑，本申请发明人经过深入研究，设计了一种二次电池及用电装置。
[负极极片]
负极极片包括负极集流体以及设置于负极集流体至少一个表面上的负极膜层，其中，负极膜层在极耳伸出方向上包括第一区域和设置在第一区域至少一侧的第二区域，第一区域包括第一负极活性材料，第二区域包括第二负极活性材料，第一负极活性材料的粉体OI值记为OI a，第二负极活性材料的粉体OI值记为OI b，则所述负极膜层满足：OI a＜OI b。
通过在极耳引出方向设置第一区域及第二区域，并使第二区域的活性材料OI值大于第一区域的活性材料，能够增大负极极片上边缘处的活 性材料颗粒的堆积取向程度，便于活性离子嵌入，减少活性离子直接在负极表面还原析出而形成枝晶，能够改善负极极片上厚度变化处(如主体部与极耳连接处)的析出问题，降低枝晶刺破隔离膜引发电池内短路的风险，提高电池的安全性能及使用寿命。
在一些实施例中，第一负极活性材料的粉体OI值记为OI a，第二负极活性材料的粉体OI值记为OI b，满足，0.6≤OI a/OI b＜1；可选地，0.7≤OI a/OI b≤0.9，0.75≤OI a/OI b≤0.85，0.8≤OI a/OI b≤0.84或0.8≤OI a/OI b≤0.9，0.8≤OI a/OI b≤0.87。第一负极活性材料与第二负极活性材料的粉体OI值的比例适当，能够进一步改善二次电池的活性离子析出问题，提高电池安全性。
在一些实施例中，第一负极活性材料的粉体OI值记为OI a，第二负极活性材料的粉体OI值记为OI b，满足，2.5≤OI a≤3.5，可选为2.5≤OI a≤3.0，2.6≤OI a≤2.8，2.7≤OI a≤2.9；和/或，3.0≤OI b≤4.5，可选为3.5≤OI b≤4.0，3.6≤OI b≤3.8，3.7≤OI b≤3.9。第一负极活性材料与第二负极活性材料的粉体OI值的取值范围适当，能够进一步改善二次电池的活性离子析出问题，提高电池安全性。
在一些实施例中，第一区域的极片OI值记为OI 1，第二区域的极片OI值记为OI 2，满足，OI 1小于OI 2。通过将第二区域的极片OI值设置为大于第一区域的极片OI值，能够进一步增大负极极片上边缘处的活性材料颗粒的堆积取向程度，便于活性离子嵌入，减少活性离子直接在负极表面还原析出而形成枝晶，提高电池的安全性能及使用寿命。
在一些实施例中，第一区域的极片OI值记为OI 1，第二区域的极片OI值记为OI 2，满足，0.7≤OI 1/OI 2＜1。优选地，0.7≤OI 1/OI 2＜1，0.8≤OI 1/OI 2≤0.9，0.75≤OI 1/OI 2≤0.85，0.88≤OI 1/OI 2≤0.95。将OI 1及OI 2设置在适当范围内，能够使负极活性材料在嵌锂过程中的方向选择性较小，嵌锂膨胀可以被分散到各个方向，从能进一步降低负极极片第一部分的体积膨胀，改善电解液浸润性，此外，第二区域获得合适的活性离子扩散能力，改善负极极片上的活性离子析出问题，提高电池安全性。
在一些实施例中，第一区域的极片OI值记为OI 1，满足，7≤OI 1 ≤8，可选为7.4≤OI 1≤7.8，7.2≤OI 1≤7.6，7.1≤OI 1≤7.5，7.6≤OI 1≤7.9；和/或，第二区域的极片OI值记为OI 2，满足，8≤OI 2≤10，可选为8.5≤OI 2≤9.5，8.2≤OI 2≤9，8.8≤OI 2≤9.2，9≤OI 2≤9.8。第一区域的极片与第二区域的极片OI值的取值范围适当，能够进一步改善二次电池的活性离子析出问题，提高电池安全性。
在一些实施例中，第一负极活性材料的体积平均粒径Dv50为8μm至15μm，可选地为9μm至12μm，11μm至14μm，10μm至13μm；和/或，第二负极活性材料的体积平均粒径Dv50为4μm至8μm，可选地为5μm至7μm，6μm至8μm，4μm至6μm。第一负极活性材料的Dv50在适当范围内，能在获得较高克容量的同时，使颗粒具有较短的离子传输路径，并且还保证颗粒之间形成通畅的孔道结构，以便有利于电解液浸润和回流。因此，负极极片的第一部分能获得较高的活性离子迁移性能，从而能改善电池的循环寿命和快速充电能力。此外，第二负极活性材料的Dv50适当减小，能够增加第二区域内的间隙，便于活性离子嵌入。
在一些实施例中，第一负极活性材料在3000N压力下的粉体压实密度大于第二负极活性材料在3000N压力下的粉体压实密度。通过使第一负极活性材料的粉体压实密度大于第二负极活性材料的粉体压实密度，能够在兼顾较高的循环寿命、快速充电能力和能量密度的同时，能够增加第二区域内的间隙，便于活性离子嵌入。
在一些实施例中，第一负极活性材料在3000N压力下的粉体压实密度记为P 1，第二负极活性材料在3000N压力下的粉体压实密度记为P 2，满足，1≤P 1/P 2≤1.2，可选地，1.05≤P 1/P 2≤1.15，1.08≤P 1/P 2≤1.12，1.1≤P 1/P 2≤1.18，1.02≤P 1/P 2≤1.08。第一负极活性材料的粉体压实密度与第二负极活性材料的粉体压实密度的比例适当，能够在兼顾较高的循环寿命、快速充电能力和能量密度的同时，能够增加第二区域内的间隙，便于活性离子嵌入。
在一些实施例中，第一负极活性材料在3000N压力下的粉体压实密度为1.45g/cm 3至1.65g/cm 3，可选为1.5g/cm 3至1.6g/cm 3，1.47g/cm 3至1.58g/cm 3，1.53g/cm 3至1.61g/cm 3，1.55g/cm 3至1.63g/cm 3；和/或，第二 负极活性材料在3000N压力下的粉体压实密度为1.35g/cm 3至1.45g/cm 3，可选地为1.4g/cm 3至1.45g/cm 3，1.38g/cm 3至1.42g/cm 3。第一负极活性材料的粉体压实密度与第二负极活性材料的粉体压实密度的取值范围适当，能够在兼顾较高的循环寿命、快速充电能力和能量密度的同时，能够增加第二区域内的间隙，便于活性离子嵌入。
在一些实施例中，第一负极活性材料的振实密度大于第二负极活性材料的振实密度。第一负极活性材料的振实密度在适当范围内增大，能提高电池的快速嵌锂能力，有助于改善电池的循环寿命，同时还能提高电池的能量密度。
在一些实施例中，第二负极活性材料包括二次颗粒。采用该第二负极活性材料能使电池获得较高的能量密度，同时兼顾降低活性离子析出的需求，提高电池安全性。可选地，第一负极活性材料包括一次颗粒或二次颗粒中的至少一种。
一次颗粒和二次颗粒均为本领域公知的含义。一次颗粒是非团聚态颗粒。二次颗粒是由两个或两个以上一次颗粒聚集形成的团聚态的颗粒。一次颗粒和二次颗粒可通过扫描电子显微镜拍摄SEM图像容易地区分。
在一些实施例中，第二区域设置在第一区域的两侧；可选地，设置在第一区域两侧的两个第二区域在极耳伸出方向上具有相同的尺寸。第一区域两侧均设置有第二区域，能够同时改善极片两侧的边缘区域活性离子析出的问题，提高电池安全性，同时，负极膜层不同区域的电解液浸润性的一致性较好，能进一步改善负极膜层各个区域的活性离子传输性能，从而进一步提升电池的循环寿命和快速充电能力。
图6是本申请负极极片的一个实施例的截面示意图。图7是本申请负极极片的另一个实施例的截面示意图。如图6及图7所示，在一些实施例中，第一区域121在极耳522伸出方向上的尺寸记为L 1，第二区域122在极耳522伸出方向上的尺寸记为L 2，满足：L 1≥L 2，可选地，1≤L 1/L 2≤50，5≤L 1/L 2≤45，10≤L 1/L 2≤40，15≤L 1/L 2≤35，20≤L 1/L 2≤30，23≤L 1/L 2≤27。可选地，L 2≥15mm，L 2≥20mm，L 2≥25mm，L 2≥30mm。可选地，第一区域121两侧均设置有第二区域122时，两侧第二区域122在极耳522 伸出方向上的延伸长度均大于15mm。可选地，第二区域122可为极片上的削薄区，即第二区域522厚度小于第一区域121。第一区域121与第二区域522在伸出方向上尺寸的比例适当，既能有效改善负极膜层整体的活性离子迁移性能，又有利于负极膜层具有较高的可逆容量，从而使二次电池更好地同时兼顾较高的循环寿命、快速充电能力和能量密度。可选地，第二区域122可为设置于极片上边缘处的削薄区。
在一些实施例中，第一活性材料包括人造石墨。
在一些实施例中，第二活性材料包括人造石墨、天然石墨、硬碳或软碳中的至少一种。
在一些实施例中，第一负极活性材料还可选地包括可用于二次电池负极的其它活性材料。其它活性材料的示例可包括天然石墨、硅基材料、锡基材料等。
在一些实施例中，第二负极活性材料还可选地包括可用于二次电池负极的其它活性材料。其它活性材料的示例可包括硅基材料、锡基材料等。
本申请的负极极片中，负极膜层的第一区域和第二区域除了包含负极活性材料以外，通常还可选地包括粘结剂、导电剂、和/或助剂。导电剂的示例可包括超导碳、炭黑(例如乙炔黑、科琴黑)、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。粘结剂的示例可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸树脂、聚乙烯醇(PVA)、海藻酸钠(SA)和羧甲基壳聚糖(CMCS)中的一种或几种。助剂的示例可包括增稠剂(如羧甲基纤维素钠CMC-Na)等。
本申请的负极极片中，负极集流体可采用金属箔片或复合集流体(可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，负极集流体可采用铜箔。负极膜层可以设置在负极集流体的一侧，也可以同时设置在负极集流体的两侧。
本申请实施方式的第二方面，提供了一种用电装置，包括上述的二次电池，用于提供电能。
参考图6，负极极片包括负极集流体110以及设置在负极集流体 110一侧的负极膜层120。极耳522由负极集流体110的一侧边缘伸出。负极膜层120在极耳522伸出方向上区分为第一区域121和位于第一区域121两侧的第二区域122。
参考图7，负极极片包括负极集流体110以及分别设置在负极集流体110两侧的负极膜层120。极耳522由负极集流体110的一侧边缘伸出。负极膜层120在极耳522伸出方向上区分为第一区域121和位于第一区域121两侧的第二区域122。
在负极极片中，极耳可以经焊接连接于负极集流体，也可以在负极集流体预留空白区(即未覆盖负极膜层的区域)，对空白区裁切形成极耳。
需要说明的是，本申请所给的各负极膜层参数(例如负极膜层不同区域的尺寸、压实密度等)均指单侧膜层的参数范围。当负极膜层设置在负极集流体的两侧时，其中任意一侧的膜层参数满足本申请，即认为落入本申请的保护范围内。且本申请所述的负极膜层不同区域的尺寸、压实密度、面密度等范围均是指经冷压压实后并用于组装电池的膜层参数。
本申请的二次电池中，负极极片并不排除除了负极膜层之外的其他附加功能层。例如在某些实施方式中，本申请所述的负极极片还可以包括设置在负极集流体和负极膜层之间的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施方式中，本申请所述的负极极片还包括覆盖在负极膜层表面的覆盖保护层。
根据一些实施例，充放电倍率1C表示1h完全放掉电池的额定容量，示例性计算式为：充放电倍率C＝充放电电流(单位A)/额定容量(单位Ah)，上限电压V0是电池产品使用电压的上限值。例如，磷酸铁锂(LiFePO4，LFP)体系电池产品的上限电压V0一般是3.65V；LiNi0.8Co0.1Mn0.1O2(NCM811)体系电池产品的上限电压V0一般是4.2V；LiNi0.5Co0.2Mn0.3O2(NCM523)体系电池产品的上限电压V0一般是4.3V。
根据一些实施例，负极膜层的第一区域在极耳伸出方向上的尺寸，以及第二区域在极耳伸出方向上的尺寸为本领域公知的含义，可采用本领域已知的方法测定。示例性测试方法如下：取一段在极耳伸出方向上完整 的负极极片，沿着平行于极耳伸出方向(记为Q方向)用陶瓷剪刀剪出宽度10mm±2mm的条状极片；再垂直于Q方向将极片以10mm等距裁切，并沿着固定方向做好标记样品1，样品2，……；采用离子束抛光仪(例如IB-19500CP)分别将样品的Q方向断面抛光，再通过分析型扫描电子显微镜(例如ZEISS Sigma 300)分别对样品抛光断面进行成像；根据第一区域和第二区域的负极颗粒形貌差异和孔隙率差异可以区分出第一区域和第二区域的交界面，从而可以确定出第一区域和第二区域在极耳伸出方向上的尺寸。
根据一些实施例，负极活性材料在3000N压力下的粉体压实密度为本领域公知的含义，可以用本领域已知的方法测定。例如参照标准GB/T24533-2009，通过电子压力试验机(例如UTM7305型)测定。示例性测试方法如下：称取1g负极活性材料，加入底面积为1.327cm 2的模具中，加压至3000N，保压30s，然后卸压，保持10s，然后记录并计算得到负极活性材料在3000N压力下的粉体压实密度。
根据一些实施例，负极极片的OI值＝C004/C110，C004为负极极片中石墨材料004晶面的衍射峰的峰面积，C110为负极极片中石墨材料110晶面衍射峰的峰面积。衍射峰的峰面积可以通过X射线衍射图谱测试获得。
在负极极片的OI值测试中，X射线衍射分析可以参考标准JISK0131-1996，使用X射线衍射仪进行。示例性测试方法如下：在负极极片与负极膜层第一区域对应的部分和与负极膜层第二区域对应的部分分别裁取测试样品；将极片样品分别置于X射线衍射仪(例如Bruker D8 Discover)中，获得X射线衍射图谱；根据X射线衍射图谱中的C004/C110得到该极片样品的OI值。X射线衍射分析条件例如为，采用铜靶作为阳极靶，以CuKα射线为辐射源，射线波长
Figure PCTCN2022114112-appb-000001
扫描2θ角范围为20°至80°，扫描速率为4°/min。
根据一些实施例，负极活性材料的体积平均粒径Dv50为本领域公知的含义，可采用本领域已知的方法测定。例如，激光衍射粒度分析法。激光衍射粒度分析可在激光粒度分析仪(例如Malvern Mastersize 3000) 进行。测试可参照标准GB/T 19077-2016。其中Dv50为负极活性材料累计体积分布百分数达到50％时所对应的粒径。
需要说明的是，上述针对负极活性材料的各种参数测试，可以直接取负极活性材料样品测试，也可以从二次电池中取样测试。当上述测试样品是从二次电池中取样时，作为示例，可以按如下步骤进行取样：
(1)将二次电池做放电处理(为了安全起见，一般使电池处于满放状态)；将电池拆卸后取出负极极片，使用碳酸二甲酯(DMC)将负极极片浸泡一定时间(例如2至10小时)；然后将负极极片取出并在一定温度和时间下干燥处理(例如60℃，4h)，干燥后取出负极极片。
(2)将步骤(1)干燥后的负极极片在一定温度及时间下烘烤(例如400℃，2h)，在烘烤后的负极极片的与第一区域对应的部分以及与第二区域对应的部分，分别对负极活性材料取样(可以选用刀片刮粉取样)。
(3)将步骤(2)收集到的负极活性材料分别过筛处理(例如过200目筛)，得到可以用于测试本申请上述的各材料参数的负极活性材料样品。
在本申请中，负极膜层的压实密度可采用本领域已知的方法测试。例如取单面涂布且经冷压后的负极极片(若是双面涂布的负极极片，可先擦拭掉其中一面的负极膜层)，沿与极耳延伸方向平行的方向冲切成面积为S 1的方形片(不含极耳)，称其重量，记录为M 1。然后将上述称重后的负极极片的负极膜层擦拭掉，称量负极集流体的重量，记录为M 0。负极膜层的面密度＝(M 1－M 0)/S 1。负极膜层的压实密度＝负极膜层的面密度/负极膜层的厚度。
[正极极片]
本申请的二次电池可采用本领域已知的正极极片。在一些实施例中，正极极片包括正极集流体及设置在正极集流体至少一个表面且包括正极活性材料的正极膜层。
本申请对正极活性材料不进行限定。在一些实施例中，正极活性材料包括锂过渡金属氧化物(例如锂镍氧化物、锂钴氧化物、锂镍钴锰氧 化物、锂镍钴铝氧化物等)、橄榄石结构的含锂磷酸盐(例如磷酸铁锂等)及其各自改性化合物中的一种或几种。
正极膜层除了包含正极活性材料以外，通常还可选地包括粘结剂和/或导电剂。导电剂的示例可包括超导碳、炭黑(例如乙炔黑、科琴黑)、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。粘结剂的示例可包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚丙烯酸(PAA)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种或几种。
正极集流体可采用金属箔片或复合集流体(可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，正极集流体可采用铝箔。
[电极组件]
正极极片的一侧边缘延伸出正极极耳。负极极片的一侧边缘延伸出负极极耳。正极极耳可以经焊接连接于正极集流体，也可以在正极集流体预留空白区(即未覆盖正极膜层的区域)，对空白区裁切形成正极极耳。负极极耳类似地连接于负极极片。将上述正极极片、负极极片和隔离膜经叠片工艺或经卷绕工艺形成主体部，并且由主体部延伸出两个极耳(即正极极耳和负极极耳)。电极组件中，两个极耳可由主体部的同一侧延伸出，也可以由主体部的相对的两侧延伸出。
图3是本申请电极组件的一个实施例的示意图。图4是本申请电极组件的另一个实施例的示意图。图5是本申请电极组件的又一个实施例的示意图。如图3及图4所示，示例性地显示了两种不同的电极组件，其中两个极耳522由主体部521的同一侧伸出。如图5所示，示例性地显示了另一种电极组件，其中两个极耳522由主体部521的相对的两侧延伸出。
本申请对隔离膜没有特别的限制，可以选用任意公知的材料。在一些实施例中，隔离膜可选自玻璃纤维、无纺布、聚乙烯膜、聚丙烯膜、聚偏二氟乙烯膜、以及它们的多层复合膜。
[电解液]
本申请的二次电池对电解液没有具体的限制，可根据需求进行选择。电解液通常包括电解质锂盐和溶剂。
在一些实施例中，电解质锂盐可选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)及四氟草酸磷酸锂(LiTFOP)中的一种或几种。
在一些实施例中，溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、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。
在一些实施例中，电解液中还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
制备方法
本申请还提供一种二次电池的制备方法。方法包括通过如下步骤制备二次电池的负极极片：提供包含第一负极活性材料的第一负极浆料和包含第二负极活性材料的第二负极浆料，第一负极活性材料包括人造石墨，第二负极活性材料包括石墨；提供负极集流体，负极集流体的至少一个表面在极耳伸出方向上包括第一涂覆区和分设于第一涂覆区两侧的第二涂覆区；将第一负极浆料涂覆于负极集流体的第一涂覆区，将第二负极浆料涂覆于负极集流体的第二涂覆区，形成负极膜层，得到负极极片。
负极浆料涂通常是将负极活性材料以及可选的导电剂和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)或去离子水。
第一负极浆料和第二负极浆料可以分两次涂布或同时涂布。涂层经干燥、冷压后，形成负极膜层。
本申请的二次电池的其它构造和制备方法是公知的。例如本申请的正极极片可以按如下制备方法：将正极活性材料以及可选的导电剂和粘结剂混合后分散于溶剂(如NMP)中，搅拌均匀后涂覆在正极集流体上，烘干、冷压后，即得到正极极片。
在一些实施例中，将正极极片、隔离膜、负极极片制成电极组件，并置于外包装中，注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
本申请的二次电池中，外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。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。
本申请的二次电池的可选技术特征也同样适用于本申请的制备方法中。
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。
图1是本申请二次电池的一个实施例的示意图。图2是图1的分解图。如图1及图2所示，二次电池包括外包装、电极组件52以及电解液(未示出)。外包装可包括壳体51和顶盖组件53。壳体51具有容纳腔和与容纳腔连通的开口。电极组件52设置于容纳腔内。电极组件52的数量不受限制，可以为一个或几个。电解液浸润于电极组件。顶盖组件53盖设开口，以封闭容纳腔。
接下来说明本申请又一方面的电池模块。电池模块包括本申请的二次电池。
图8是本申请电池模块的一个实施例的示意图。如图4及图8所示，电池模块4包括多个二次电池5。多个二次电池5沿纵向排列。电池模块4可以作为电源或储能装置。电池模块4中所含锂离子电池5的数量可以根据电池模块4的应用和容量进行调节。
接下来说明本申请又一方面的电池包。电池包包括本申请的二次电池和/或电池模块。
图9是本申请电池包的一个实施例的示意图。图10是图9的分解图。如图9及图10所示，电池包1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和下箱体3组装在一起并形成收容电池模块4的空间。电池包1采用的电池模块4的数量和排列方式可以依据实际需要来确定。
接下来说明本申请又一方面的装置。装置包括本申请的二次电池、电池模块、或电池包中的至少一种。二次电池、电池模块或电池包可以用作装置的电源，也可以用作装置的能量存储单元。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(例如电动汽车、电动大巴、电动有轨电车、电动自行车、电动摩托车、电动踏板车、电动高尔夫球车、电动卡车)、电气列车、船舶及卫星、储能系统等。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11是二次电池用作电源的装置的一个实施例的示意图。如图11所示。用电装置可以为电动汽车。电动汽车可以为纯电动车、混合动力电动车或插电式混合动力电动车等。当然，电动汽车可依据实际使用形式包括本申请所述的电池模块4或电池包1。
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。
一、负极活性材料
人造石墨A：可从负极材料供应商处商购获得。人造石墨A为一次颗粒，克容量340mAh/g至353mAh/g，其余物性参数列于表1。
人造石墨B：可从负极材料供应商处商购获得。人造石墨B为二 次颗粒，克容量353mAh/g至360mAh/g，其余物性参数列于表1。
天然石墨：可从负极材料供应商处商购获得。天然石墨的物性参数如下：克容量365mAh/g，Dv50＝8μm，3000N下的粉体压实密度为1.85g/cm 3。
硬碳：可从负极材料供应商处商购得，硬碳得物性参数如下：克容量500mAh/g，Dv50＝5μm，3000N下的粉体压实密度为1g/cm 3。
软碳：可从负极材料供应商处商购得，软碳得物性参数如下：克容量345mAh/g，Dv50＝20m，3000N下的粉体压实密度为0.6g/cm 3。
二、电池的制备
实施例1
负极极片的制备
将第一负极活性材料人造石墨A、导电剂Super P、粘结剂SR-1B、增稠剂CMC-Na按质量比96:1.5:1.5:1在适量去离子水中充分搅拌混合，形成均匀的第一负极浆料。第一负极活性材料的Dv50为6.2μm。
将第二负极活性材料人造石墨B、导电剂Super P、粘结剂SBR和增稠剂CMC-Na按质量比96:1.5:1.5:1在适量去离子水中充分搅拌混合，形成均匀的第二负极浆料。第二负极活性材料的Dv50为16.3μm。
负极集流体采用铜箔，其表面在极耳伸出方向上区分为涂覆区和邻接涂覆区的空白区，涂覆区在极耳伸出方向上区分为第一涂覆区和分设于第一涂覆区两侧的第二涂覆区。将第一负极浆料涂覆于负极集流体的第一涂覆区，将第二负极浆料涂覆于负极集流体的第二涂覆区，形成负极涂层。负极涂层经干燥、冷压形成负极膜层。对负极集流体的空白区裁切，形成负极极耳，得到负极极片。
负极极片中，负极膜层在极耳伸出方向上包括第一区域和设置在第一区域两侧的第二区域，且设置在第一区域两侧的两个第二区域在极耳伸出方向上具有相同的尺寸；第一区域在极耳伸出方向上的尺寸记为L 1，第一区域两侧的两个第二区域在极耳伸出方向上的尺寸之和记为L 2，其中满足：L 1/L 2＝25。
隔离膜
选用聚乙烯(PE)薄膜。
电解液的制备
将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按体积比4:3:3混合，然后将充分干燥的锂盐LiPF6均匀溶解在上述溶液中得到电解液，其中LiPF6的浓度为1mol/L。
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；将电极组件装入外包装中，加入上述电解液，经封装、静置、化成、老化等工序后，得到二次电池。极耳由主体部的高度方向延伸出。
实施例2～27和对比例1～2与实施例1的制备方法相似，但是调整了负极极片的制备参数，不同的制备参数和产品参数详见表1和表2。
二、电池性能测试
(1)快速充电能力测试
25℃下，将各实施例和对比例的电池以1C(即1h内完全放掉额定容量的电流值)的电流进行第一次充电和放电，具体包括：将电池以1C倍率恒流充电至电压4.3V，之后恒压充电至电流≤0.05C，静置5min，再以0.33C倍率恒流放电至电压2.8V，记录其实际容量为C 0。
然后将电池依次以2.0C 0、2.5C 0、3.0C 0、3.5C 0、4.0C 0、4.5C 0、5.0C 0、5.5C 0、恒流充电至全电池充电截止电压4.3V或者0V负极截止电位(以先达到者为准)，每次充电完成后需以1C 0放电至全电池放电截止电压2.8V，记录不同充电倍率下充电至10％、20％、30％、……、80％SOC(State of Charge，荷电状态)时所对应的负极电位，绘制出不同SOC态下的充电倍率-负极电位曲线，线性拟合后得出不同SOC态下负极电位为0V时所对应的充电倍率，该充电倍率即为该SOC态下的充电窗口，分别记为C20％SOC、C30％SOC、C40％SOC、C50％SOC、C60％SOC、C70％SOC、C80％SOC，根据公式(60/C20％SOC+60/C30％SOC+60/C40％SOC+60/C50％SOC+60/C60％SOC+60/C70％SOC+60/C80％SOC)×10％计算得到该电池从10％SOC充电至80％SOC的充电时间T，单位为min。该时间越短，则电池的快速充电性能越优秀。
(2)循环性能测试
25℃下，将实施例和对比例制备得到的二次电池以1C倍率恒流充电至4.3V，之后恒压充电至电流≤0.05C，静置5min，再以1C倍率恒流放电至2.8V，静置5min，此为一个充放电循环，记录首圈放电容量。按照此方法对电池进行循环充放电，直至电池容量衰减至首圈放电容量的80％。此时的循环圈数即为电池在25℃下的循环寿命。循环圈数越多，则代表电池的循环寿命越高。
电池性能测试结果示于表3。
表1：负极极片的制备参数。
Figure PCTCN2022114112-appb-000002
Figure PCTCN2022114112-appb-000003
Figure PCTCN2022114112-appb-000004
表1中，使用的人造石墨B混合其他材质的，人造石墨B与其他材质的质量比8:2。
表2：负极极片的特性参数及二次电池的性能测试结果
Figure PCTCN2022114112-appb-000005
由表中的数据可知，本申请实施例的二次电池中，负极膜层在极耳伸出方向上两侧区域的活性材料OI值以及极片OI值设置为大于中间区域的活性材料OI值以及极片OI值，使得电池在具有较高能量密度的前提下，还同时兼顾较高的循环寿命和快速充电能力。
对比例1-2由于不满足上述条件，导致电池难以同时兼顾较高的能量密度和较长的循环寿命。
另外，发明人还发现，当人造石墨B为二次颗粒时，可以使二次 电池在具有较高的循环寿命和快速充电能力的同时，进一步提升能量密度。因该测试结果与表2中实施例1-16的数据较相近，此处不再赘述。
虽然已经参考优选实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件，尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (16)

  1. 一种二次电池，包括电极组件，所述电极组件包括主体部和由所述主体部延伸出的极耳，所述主体部包括负极极片，所述负极极片包括负极集流体以及设置于所述负极集流体至少一个表面上的负极膜层，其中，所述负极膜层在所述极耳伸出方向上包括第一区域和设置在所述第一区域至少一侧的第二区域，所述第一区域包括第一负极活性材料，所述第二区域包括第二负极活性材料，所述第一负极活性材料的粉体OI值记为OI a，所述第二负极活性材料的粉体OI值记为OI b，则所述负极膜层满足：OI a＜OI b。
  2. 根据权利要求1所述的二次电池，其中，所述第一负极活性材料的粉体OI值记为OI a，所述第二负极活性材料的粉体OI值记为OI b，满足，0.6≤OI a/OI b＜1；可选地，0.7≤OI a/OI b≤0.9。
  3. 根据权利要求1或2所述的二次电池，其中，所述第一负极活性材料的粉体OI值记为OI a，所述第二负极活性材料的粉体OI值记为OI b，满足，2.5≤OI a≤3.5，可选为2.5≤OI a≤3.0；和/或，
    3.0≤OI b≤4.5，可选为3.5≤OI b≤4.0。
  4. 根据权利要求1-3任一项所述的二次电池，其中，所述第一区域的极片OI值记为OI 1，所述第二区域的极片OI值记为OI 2，满足，OI 1小于OI 2。
  5. 根据权利要求1-4任一项所述的二次电池，其中，所述第一区域的极片OI值记为OI 1，所述第二区域的极片OI值记为OI 2，满足，0.7≤OI 1/OI 2＜1。
  6. 根据权利要求1-5任一项所述的二次电池，其中，所述第一区域的极片OI值记为OI 1，满足，7≤OI 1≤8，可选为7.4≤OI 1≤7.8；和/或，
    所述第二区域的极片OI值记为OI 2，满足，8≤OI 2≤10，可选为8.5≤OI 2≤9.5。
  7. 根据权利要求1-6任一项所述的二次电池，其中，所述第一负极活性材料的体积平均粒径Dv50为8μm至15μm，可选地为9μm至12μm；和/或，
    所述第二负极活性材料的体积平均粒径Dv50为4μm至8μm，可选地为5μm至7μm。
  8. 根据权利要求1-7任一项所述的二次电池，其中，所述第一负极活性材料在3000N压力下的粉体压实密度大于所述第二负极活性材料在3000N压力下的粉体压实密度。
  9. 根据权利要求1-8任一项所述的二次电池，其中，所述第一负极活性材料在3000N压力下的粉体压实密度记为P 1，所述第二负极活性材料在3000N压力下的粉体压实密度记为P 2，满足，1≤P 1/P 2≤1.2，可选地，1.05≤P 1/P 2≤1.15。
  10. 根据权利要求1-9任一项所述的二次电池，其中，
    所述第一负极活性材料在3000N压力下的粉体压实密度为1.45g/cm 3至1.65g/cm 3，可选为1.5g/cm 3至1.6g/cm 3；和/或，
    所述第二负极活性材料在3000N压力下的粉体压实密度为1.35g/cm3至1.45g/cm 3，可选地为1.4g/cm 3至1.45g/cm 3。
  11. 根据权利要求1-10任一项所述的二次电池，其中，所述第一负极活性材料的振实密度大于所述第二负极活性材料的振实密度。
  12. 根据权利要求1-11任一项所述的二次电池，其中，所述第二负极活性材料采用二次颗粒。
  13. 根据权利要求1-12任一项所述的二次电池，其中，所述第二区域设置在所述第一区域的两侧；可选地，设置在所述第一区域两侧的两个所述第二区域在所述极耳伸出方向上具有相同的尺寸。
  14. 根据权利要求1-13任一项所述的二次电池，其中，所述第一区域在所述极耳伸出方向上的尺寸记为L 1，所述第二区域在所述极耳伸出方向上的尺寸记为L 2，满足：L 1≥L 2；
    可选地，1≤L 1/L 2≤50；
    可选地，L 2≥15mm。
  15. 根据权利要求1-14任一项所述的二次电池，其中，所述第一活性材料包括人造石墨；和/或，
    所述第二活性材料包括人造石墨、天然石墨、硬碳或软碳中的至少一种。
  16. 一种用电装置，包括如权利要求1-15任一项所述的二次电池，用于提供电能。
PCT/CN2022/114112 2022-08-23 2022-08-23 二次电池及用电装置 WO2024040420A1 (zh)

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CN113036298A (zh) * 2019-12-06 2021-06-25 宁德时代新能源科技股份有限公司 负极极片及含有它的二次电池、装置
CN114005957A (zh) * 2021-09-28 2022-02-01 东莞维科电池有限公司 一种负极极片及其制备方法、锂离子电池
WO2022141302A1 (zh) * 2020-12-30 2022-07-07 宁德时代新能源科技股份有限公司 二次电池及其制备方法、含有该二次电池的电池模块、电池包和装置

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CN113036298A (zh) * 2019-12-06 2021-06-25 宁德时代新能源科技股份有限公司 负极极片及含有它的二次电池、装置
WO2022141302A1 (zh) * 2020-12-30 2022-07-07 宁德时代新能源科技股份有限公司 二次电池及其制备方法、含有该二次电池的电池模块、电池包和装置
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