WO2025001284A1 - 一种极片和电化学装置 - Google Patents

一种极片和电化学装置 Download PDF

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Publication number
WO2025001284A1
WO2025001284A1 PCT/CN2024/080168 CN2024080168W WO2025001284A1 WO 2025001284 A1 WO2025001284 A1 WO 2025001284A1 CN 2024080168 W CN2024080168 W CN 2024080168W WO 2025001284 A1 WO2025001284 A1 WO 2025001284A1
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WIPO (PCT)
Prior art keywords
active material
material layer
region
mass percentage
fluorine element
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Ceased
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PCT/CN2024/080168
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English (en)
French (fr)
Inventor
王迪
陈田田
周仕昌
吴晓峰
王嘉兴
谢继春
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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Publication of WO2025001284A1 publication Critical patent/WO2025001284A1/zh
Anticipated expiration legal-status Critical
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • 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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • 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 disclosure relates to the technical field of lithium-ion batteries, and in particular to a pole piece and an electrochemical device.
  • lithium-ion battery technology lithium-ion batteries have been widely used in portable electronic products, new energy vehicles and other fields due to their good electrochemical properties.
  • the present disclosure is dedicated to providing a pole piece and an electrochemical device to improve the structural strength of the pole piece and reduce the possibility of cracking or powdering of the pole piece.
  • the present disclosure provides a pole piece, comprising a current collector, at least one surface of the current collector being provided with an active material layer;
  • the difference between the mass percentage of the fluorine element in the first region of the active material layer to the total mass of the active material layer in the first region and the mass percentage of the fluorine element in the second region of the active material layer to the total mass of the active material layer in the second region is greater than 0 and less than or equal to 3%;
  • the first region is a region between a surface of the active material layer facing away from the current collector and a first side edge;
  • the second region is a region between a surface of the active material layer on one side close to the current collector and a second side edge;
  • the distance between the first side and the surface of the active material layer facing away from the current collector is 1-10% of the total thickness of the active material layer
  • the distance between the second side and a surface of the active material layer close to the current collector is 1-10% of the total thickness of the active material layer.
  • the difference between the mass percentage of the fluorine element in the first region of the active material layer to the total mass of the active material layer in the first region and the mass percentage of the fluorine element in the second region of the active material layer to the total mass of the active material layer in the second region is greater than 0 and less than or equal to 1%
  • the difference between the mass percentage of the fluorine element in the first region of the active material layer to the total mass of the active material layer in the first region and the mass percentage of the fluorine element in the second region of the active material layer to the total mass of the active material layer in the second region is greater than 0 and less than or equal to 0.5%.
  • the mass percentage of the fluorine element in the active material layer in the first region to the total mass of the active material layer in the first region is 0-18wt%;
  • the mass percentage of the fluorine element in the active material layer in the second region to the total mass of the active material layer in the second region is 0-18wt%.
  • the mass percentage of the fluorine element in the active material layer in the first region to the total mass of the active material layer in the first region is 0.5-10wt%;
  • the mass percentage of the fluorine element in the active material layer in the second region to the total mass of the active material layer in the second region is 0.5-10wt%.
  • the active material layer includes a third region, and the third region is a region between the third side and the fourth side;
  • the distance between the third side and the surface of the active material layer facing away from the current collector is 45%-50% of the total thickness of the active material layer;
  • the distance between the fourth side and the surface of the active material layer close to the current collector is 45%-50% of the total thickness of the active material layer
  • the mass percentage of fluorine in the active material layer in the third region to the total mass of the active material layer in the third region is greater than the mass percentage of fluorine in the active material layer in the first region to the total mass of the active material layer in the first region, and/or the mass percentage of fluorine in the active material layer in the third region to the total mass of the active material layer in the third region is greater than the mass percentage of fluorine in the active material layer in the second region to the total mass of the active material layer in the second region.
  • the difference between the mass percentage of the fluorine element in the active material layer in the third region to the total mass of the active material layer in the third region and the mass percentage of the fluorine element in the active material layer in the first region to the total mass of the active material layer in the first region is ⁇ 3%;
  • the difference between the mass percentage of fluorine element in the active material layer in the third region to the total mass of the active material layer in the third region and the mass percentage of fluorine element in the active material layer in the second region to the total mass of the active material layer in the second region is ⁇ 3%.
  • the difference between the mass percentage of the fluorine element in the active material layer in the third region to the total mass of the active material layer in the third region and the mass percentage of the fluorine element in the active material layer in the first region to the total mass of the active material layer in the first region is ⁇ 1.5%;
  • the difference between the mass percentage of fluorine element in the active material layer in the third region to the total mass of the active material layer in the third region and the mass percentage of fluorine element in the active material layer in the second region to the total mass of the active material layer in the second region is ⁇ 1.5%.
  • the mass percentage of fluorine element in the active material layer in the third region to the total mass of the active material layer in the third region is 0-21wt%.
  • the mass percentage of fluorine element in the active material layer in the third region to the total mass of the active material layer in the third region is 1-12wt%.
  • the active material layer includes a first binder and an active material
  • a difference between a mass percentage ratio of the first binder to the active material in the first region of the active material layer and a mass percentage ratio of the first binder to the active material in the second region of the active material layer is ⁇ 9%.
  • a difference between a mass percentage ratio of the first binder to the active material in the first region of the active material layer and a mass percentage ratio of the first binder to the active material in the second region of the active material layer is ⁇ 5%.
  • the mass percentage ratio of the first binder to the active material in the first region of the active material layer is 0.5-10%;
  • the mass percentage ratio of the first binder to the active material in the second region of the active material layer is 0.5-10%.
  • the first binder includes at least one of fibrous polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), (ETEF), fluorinated ethylene propylene copolymer (FEP), polyvinyl chloride (PVP), polyethylene oxide (PEO), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyacrylic acid (PAA), polypropylene (PP), polyethylene (PE) and polyacrylonitrile (PAN);
  • PTFE polytetrafluoroethylene
  • PVDF polyvinylidene fluoride
  • ETEF fluorinated ethylene propylene copolymer
  • FEP fluorinated ethylene propylene copolymer
  • PVP polyvinyl chloride
  • PEO polyethylene oxide
  • CMC carboxymethyl cellulose
  • SBR styrene butadiene rubber
  • PAA polyacrylic acid
  • PP polypropylene
  • PE polyethylene
  • the active material comprises at least one of LiCoO 2 , LiMn 2 O 4 , LiMnO 2 , LiNiO 2 , LiFePO 4 , LiMnPO 4 , LiCo x Ni 1-x O 2 (0 ⁇ x ⁇ 1), LiCo x Ni 1-xy AlyO 2 (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1);
  • the active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, Si, SiOx, Si—C and SiOx — C.
  • a bonding layer is further provided between the current collector and the active material layer, and the bonding layer comprises a second bonding material and a conductive agent.
  • the second bonding material includes at least one of PVDF, SBR, PP, ethylene-vinyl acetate copolymer (EVA) hot melt adhesive, polyolefins (PO) hot melt adhesive, reactive polyurethane hot melt adhesive (PUR) hot melt adhesive, thermoplastic rubber (TPR) materials, thermoplastic polyurethane elastomers (TPU) hot melt adhesive, polyamide (PA), polyester (PES), polyethylene and polyesteramide (PEA);
  • PVDF ethylene-vinyl acetate copolymer
  • PO polyolefins
  • PUR reactive polyurethane hot melt adhesive
  • TPR thermoplastic rubber
  • TPU thermoplastic polyurethane elastomers
  • the conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, conductive carbon fibers and conductive graphite.
  • the thickness of the active material layer is greater than or equal to 20 ⁇ m and less than or equal to 3 mm; preferably, the thickness of the active material layer is greater than or equal to 30 ⁇ m and less than or equal to 300 ⁇ m.
  • the thickness of the bonding layer is greater than or equal to 500 nm and less than or equal to 3 ⁇ m;
  • the ratio of the thickness of the active material layer to the thickness of the bonding layer is greater than or equal to 10 and less than or equal to 6000; preferably, the ratio of the thickness of the active material layer to the thickness of the bonding layer is greater than or equal to 30 and less than or equal to 300.
  • a second aspect of the present disclosure provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet;
  • the positive electrode sheet and/or the negative electrode sheet are the electrode sheets as described in the first aspect.
  • the pole piece provided by the present disclosure includes a current collector, and at least one surface of the current collector is provided with an active material layer.
  • the fluorine element is an important component of the active material layer, and by controlling the difference between the fluorine element in the first region of the top surface and the second region of the bottom surface of the active material layer, that is, achieving the mass percentage of the fluorine element on the top surface and the bottom surface of the active material layer to be close, it means that the fluorine element is fully and evenly distributed in the thickness direction of the active material layer, and the fluorine element has strong electrophilicity and chemical inertness, which can enhance the bonding force between the binder and the active material (i.e., active
  • FIG1 is a schematic diagram of a pole piece provided by an embodiment of the present disclosure.
  • FIG2 is a second schematic diagram of a pole piece provided in an embodiment of the present disclosure.
  • FIG3 is a third schematic diagram of a pole piece provided in an embodiment of the present disclosure.
  • FIG4 is a fourth schematic diagram of a pole piece provided in an embodiment of the present disclosure.
  • FIG5 is a schematic diagram of a pole piece in Example 7 provided in the present disclosure.
  • FIG6 shows an element distribution diagram of the first region of the pole piece in Example 7 provided by the present disclosure
  • FIG7 shows an element distribution diagram of the third region of the pole piece in Example 7 provided by the present disclosure
  • FIG8 is an element distribution diagram of the second region of the pole piece in Example 7 provided by the present disclosure.
  • FIG9 is a schematic diagram of a pole piece in Example 3 provided in the present disclosure.
  • FIG10 is an element distribution diagram of the first region of the pole piece in Example 3 provided by the present disclosure.
  • FIG11 is an element distribution diagram of the third region of the pole piece in Example 3 provided by the present disclosure.
  • FIG. 12 shows an element distribution diagram of the second region of the electrode in Example 3 provided in the present disclosure.
  • the present disclosure provides a pole piece, including a current collector 10 , at least one surface of the current collector 10 is provided with an active material layer 11 ;
  • the difference between the mass percentage of the fluorine element of the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region and the mass percentage of the fluorine element of the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region is greater than 0 and less than or equal to 3%, for example, the difference may be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.8%, 3%;
  • the first region is a region between a surface of the active material layer 11 facing away from the current collector 10 and the first side edge;
  • the second region is a region between a surface of the active material layer 11 close to the current collector 10 and the second side edge;
  • the distance between the first side and the surface of the active material layer 11 facing away from the current collector 10 is 1-10% of the total thickness of the active material layer 11, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the total thickness;
  • the distance between the second side and the surface of the active material layer 11 close to the current collector 10 is 1-10% of the total thickness of the active material layer 11, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the total thickness.
  • the electrode sheet can be a positive electrode sheet or a negative electrode sheet.
  • the active material layer 11 can be provided on only one surface of the current collector 10, as shown in FIG1 ; or the active material layer 11 can be provided on both surfaces of the current collector 10, as shown in FIG2 .
  • the distance between the first side and the side surface of the active material layer 11 facing away from the current collector 10 and the distance between the second side and the side surface of the active material layer 11 close to the current collector 10 may be the same or different.
  • the distance between the first side and the side surface of the active material layer 11 facing away from the current collector 10 and the distance between the second side and the side surface of the active material layer 11 close to the current collector 10 may both be 3%, 5%, or 8% of the total thickness of the active material layer 11.
  • the distance between the first side and the side surface of the active material layer 11 facing away from the current collector 10 is 5% of the total thickness of the active material layer 11, and the distance between the second side and the side surface of the active material layer 11 close to the current collector 10 is 7% of the total thickness of the active material layer.
  • the first side mentioned above can be understood as the cross section of the active material layer 11 at the first thickness position, and the first thickness refers to the distance between the first side and the surface of the active material layer 11 facing away from the current collector 10 in the thickness direction of the active material layer 11;
  • the second side mentioned above can be understood as the cross section of the active material layer 11 at the second thickness position, and the second thickness refers to the distance between the second side and the surface of the active material layer 11 close to the current collector 10 in the thickness direction of the active material layer 11.
  • the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region refers to the percentage obtained by dividing the total mass of the fluorine element in the first region by the total mass of the active material layer 11 in the first region.
  • the mass percentage of the fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region refers to the percentage obtained by dividing the total mass of the fluorine element in the second region by the total mass of the active material layer 11 in the second region.
  • the mass percentage of the fluorine element in the first region of the active material layer 11 to the total mass of the active material layer 11 in the first region can be detected by energy spectrum element analysis.
  • the cross section of the electrode can be cut by argon ion gas, and then the element distribution of the first region and/or the second region of the active material layer can be tested by scanning electron microscope energy spectrum element analysis according to the specific position of the first side and/or the second side, so as to measure the mass percentage of the fluorine element in the region at different positions. Mass fraction of the total mass of the active material layer.
  • a scanning electron microscope energy spectrum element analysis can be used to test the element distribution at 5 microns below the top surface of the active material layer (here, the surface of the active material layer facing away from the current collector) and 5 microns above the bottom surface of the active material layer (here, the surface of the active material layer close to the current collector), and the mass fraction of the fluorine element at the corresponding position in the total mass of the active material layer in the area can be measured, as shown in Figures 6-8.
  • the mass percentage of the fluorine element in the first region of the active material layer 11 to the total mass of the active material layer 11 in the first region, and/or the mass percentage of the fluorine element in the second region of the active material layer 11 to the total mass of the active material layer 11 in the second region can be adjusted by adjusting the content of the binder, the type of the binder or the thickness of the active material layer.
  • the fluorine element as an important component of the active material layer, is controlled by controlling the difference between the fluorine element in the first region of the top surface and the second region of the bottom surface of the active material layer, that is, achieving a close mass percentage of the fluorine element on the top surface and the bottom surface of the active material layer, which means that the fluorine element is fully and evenly distributed in the thickness direction of the active material layer, so that during the processing, the stress on the electrode in the thickness direction is evenly distributed, thereby avoiding the situation where the electrode loses powder or cracks, thereby causing a short circuit in the battery; furthermore, the uniform distribution of the fluorine element
  • the active material layer can be made by a dry method, that is, the active material, the binder, and the conductive agent are dry mixed without using a solvent to make a composite material with a solid content concentration of substantially 100%.
  • Dry mixing refers to the following method: the positive electrode active material and the binding material are mixed without using a solvent in a state where the solid content concentration is substantially 100%.
  • conductive materials other than the positive electrode active material and the binding material can also be added.
  • the solid content concentration in the dry mixing is also substantially 100%.
  • the composite material is rolled into a sheet to produce a sheet-shaped active material layer 11. Then, the current collector and the active material layer 11 are stacked and hot-pressed to form a pole sheet.
  • the difference between the mass percentage of the fluorine element in the first region of the active material layer 11 to the total mass of the active material layer 11 in the first region and the mass percentage of the fluorine element in the second region of the active material layer 11 to the total mass of the active material layer 11 in the second region is greater than 0 and less than or equal to 1%, for example, the difference can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%.
  • the difference between the mass percentage of the fluorine element in the first region of the active material layer 11 to the total mass of the active material layer 11 in the first region and the mass percentage of the fluorine element in the second region of the active material layer 11 to the total mass of the active material layer 11 in the second region is greater than 0 and less than or equal to 0.5%.
  • the difference may be 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, thereby further improving the consistency of the electrical properties of the active material layer in the thickness direction and enhancing the electrochemical performance and safety performance of the battery.
  • the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region is 0-18wt%, for example, 0.1wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%;
  • the fluorine element in the active material layer 11 in the second region accounts for the total mass of the active material layer 11 in the second region.
  • the mass percentage of the amount is 0-18wt%, for example, it can be 0.1wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%.
  • the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region can be 0.9wt%, or 5wt%, or 12wt%, or 18wt%;
  • the mass percentage of the fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region may be 0.9 wt %, 5 wt %, 12 wt %, or 18 wt %.
  • the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region is 0.5-10wt%, for example, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%;
  • the mass percentage of fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region is 0.5-10wt%, for example, it can be 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%.
  • the fluorine content of the active material layer 11 in the first region and the second region is within the above-mentioned smaller range, the mass of the active material per unit area can be improved, and the gram capacity of the electrode can be maximized while ensuring that the binder does not fall off and reduces rebound, which is conducive to realizing high energy density product design.
  • the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region may be 0.9 wt %, or 2 wt %, or 5 wt %, or 9 wt %;
  • the mass percentage of the fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region may be 0.9 wt %, 2 wt %, 5 wt %, or 9 wt %.
  • the mass percentage of fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region is less than 0.5wt%, the electrochemical performance of the electrode (such as capacity, cycle life, etc.) will be reduced; if the mass percentage of fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region is greater than 10wt%, the overall energy density of the battery will be reduced.
  • the active material layer 11 includes a third region, and the third region is a region between the third side and the fourth side;
  • the distance between the third side and the surface of the active material layer 11 facing away from the current collector 10 is 45%-50% of the total thickness of the active material layer 11, for example, 45%, 46%, 47%, 48%, 49%, 50% of the total thickness;
  • the distance between the fourth side and the surface of the active material layer 11 close to the current collector 10 is 45%-50% of the total thickness of the active material layer 11, for example, 45%, 46%, 47%, 48%, 49%, 50% of the total thickness;
  • the mass percentage of fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region is greater than the mass percentage of fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region, and/or the mass percentage of fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region is greater than the mass percentage of fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region.
  • a third region is also provided in the active material layer 11, and the fluorine content in the third region is higher than that in the first region and the second region, that is, the mass percentage of fluorine in the middle region of the active material layer 11 is higher, which can enhance the bonding force between the binder and the active material (i.e., active material) in the active material layer, thereby reducing the possibility of cracking or disconnection in the middle region of the active material layer due to excessive stress, thereby improving the stability and cycle life of the electrode sheet (i.e., pole sheet).
  • the distance between the third side and the surface of the active material layer 11 facing away from the current collector 10 and the distance between the fourth side and the surface of the active material layer 11 facing the current collector 10 may be the same or different.
  • the distance between the side surface of the active material layer 11 close to the current collector 10 is 45%, 48%, or 50% of the total thickness of the active material layer 11; for another example, the distance between the third side and the side surface of the active material layer 11 away from the current collector 10 is 45% of the total thickness, and the distance between the fourth side and the side surface of the active material layer 11 close to the current collector 10 is 49% of the total thickness.
  • the third region is the region between the third side extending upward by 5 microns from the position of the half of the active material layer in the thickness direction and the fourth side extending downward by 5 microns from the position of the half of the active material layer in the thickness direction (i.e., the region enclosed by the third side and the fourth side in the thickness direction).
  • the third region i.e., the region of ⁇ 10% of the thickness of the active material layer 11 above and below the half of the thickness of the active material layer 11, can also be understood as the middle region of the active material layer 11 in the thickness direction.
  • the third side mentioned above can be understood as the cross section of the active material layer 11 at the third thickness position, and the third thickness refers to the distance between the third side and the surface of the active material layer 11 facing away from the current collector 10 in the thickness direction of the active material layer 11;
  • the fourth side can be understood as the cross section of the active material layer 11 at the fourth thickness position, and the fourth thickness refers to the distance between the fourth side and the surface of the active material layer 11 close to the current collector 10 in the thickness direction of the active material layer 11;
  • the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region can also be detected by scanning electron microscope energy spectrum element analysis.
  • the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region is greater than the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region, and/or, the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region is greater than the mass percentage of the fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region.
  • the mass percentage of the fluorine element in the middle region of the active material layer 11 is at least greater than the mass percentage of the fluorine element in the edge region on one side of the active material layer 11. Since the mass percentage of the fluorine element in the middle region of the active material layer 11 is relatively high, and because the fluorine element has strong electrophilicity and chemical inertness, the bonding force between the binder in the active material layer and the active material (i.e., active material) can be enhanced, thereby reducing the possibility of cracking or disconnection in the middle region of the active material layer due to excessive stress, thereby improving the stability and cycle life of the electrode sheet (i.e., pole sheet).
  • the difference between the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region and the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region is ⁇ 3%, for example, the difference can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.8%, 3%;
  • the difference between the mass percentage of fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region and the mass percentage of fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region is ⁇ 3%, for example, the difference can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.8%, 3%.
  • the difference between the mass percentage of fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region and the mass percentage of fluorine element in the first region to the total mass of the active material layer 11 in the first region may be 2% or 3%.
  • the difference between the mass percentage of fluorine in the active material layer 11 in the third region and the mass percentage of fluorine in the active material layer 11 in the second region may be 2% or 3%.
  • the difference between the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region and the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region is ⁇ 1.5%, for example, the difference may be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.5%;
  • the fluorine element in the active material layer 11 in the third region accounts for the total mass of the active material layer 11 in the third region.
  • the difference between the mass percentage of the amount and the mass percentage of the fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region is ⁇ 1.5%.
  • the difference can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.8%, or 3%.
  • the difference between the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region and the mass percentage of the fluorine element in the active material layer 11 in the first region to the total mass of the active material layer 11 in the first region can be 0.5%, or 0.9%, or 1.5%.
  • the difference between the mass percentage of fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region and the mass percentage of fluorine element in the active material layer 11 in the second region to the total mass of the active material layer 11 in the second region can be 0.5%, or 0.9%, or 1.5%.
  • the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region is 0-21wt%, for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 4wt%, 5wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 15wt%, 16wt%, 18wt%, 20wt%, 21wt%.
  • the fluorine content in the active material layer 11 in the third region is within the above range, the cohesion of the pole piece can be effectively improved to prevent cracking and powdering.
  • the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region may be 0.9 wt %, 10 wt %, or 21 wt %.
  • the mass percentage of the fluorine element in the active material layer in the third region to the total mass of the active material layer in the third region is 1-12wt%, for example, it can be 0.1wt%, 0.5wt%, 1wt%, 2wt%, 4wt%, 5wt%, 6wt%, 8wt%, 10wt%, 12wt%.
  • the fluorine content of the active material layer 11 in the third region is within the above-mentioned smaller range, while ensuring effective bonding between the main material particles, the main material particles per unit area are increased to ensure energy density.
  • the binder is too much, the transmission resistance of electrons and ions will increase, and the battery impedance will also increase.
  • the mass percentage of the fluorine element in the active material layer 11 in the third region to the total mass of the active material layer 11 in the third region may be 1.2 wt %, 5 wt %, or 11 wt %.
  • the active material layer 11 includes a first binder and an active material; the difference between the mass percentage ratio of the first binder and the active material in the first region of the active material layer 11 and the mass percentage ratio of the first binder and the active material in the second region of the active material layer 11 is ⁇ 9%, for example, the difference may be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or 9%.
  • the first binder can be distributed more evenly in different regions, reducing the possibility of binder migration, so that the stress of the pole piece in the thickness direction is basically the same, thereby reducing the possibility of cracking of the active material layer 11, or even falling off from the surface of the current collector 10, and reducing the penetration resistance of the pole piece and improving the peel strength of the electrode composite material sheet.
  • the more uniform distribution of the first binder can reduce the expansion degree of the pole piece during the cycle process, extend the service life of the battery during the cycle process, and reduce the overall impedance of the battery cell.
  • the difference between the mass percentage ratio of the first binder and the active material in the first region of the active material layer 11 and the mass percentage ratio of the first binder and the active material in the second region of the active material layer 11 may be 1%, 3%, 6%, or 9%.
  • the difference between the mass percentage ratio of the first binder and the active material in the first region of the active material layer 11 and the mass percentage ratio of the first binder and the active material in the second region of the active material layer 11 is ⁇ 5%.
  • the difference between the mass percentage ratio of the first binder and the active material in the first region of the active material layer 11 and the mass percentage ratio of the first binder and the active material in the second region of the active material layer 11 can be 1%, or 2%, or 3%, or 4%, or 5%.
  • the mass percentage ratio of the first binder to the active material in the first region of the active material layer 11 is 0.5-10%;
  • the mass percentage ratio of the first binder to the active material in the first region of the active material layer 11 can be 0.5%, or 1%, or 2%, or 3%, or 4%, or 5%, or 6%, or 7%, or 8%, or 9%, or 10%.
  • the mass percentage ratio of the first binder to the active material in the second region of the active material layer 11 is 0.5%-10%.
  • the mass percentage ratio of the first binder and the active material in the second region of the active material layer 11 can be 0.5%, or 1%, or 2%, or 3%, or 4%, or 5%, or 6%, or 7%, or 8%, or 9%, or 10%.
  • the first binder includes at least one of fibrous tetrafluoroethylene PTFE, polyvinylidene fluoride PVDF, ETEF, fluorinated ethylene propylene copolymer FEP, PVP, polyethylene oxide PEO, CMC, SBR, polyacrylic acid PAA, PP, PE, and PAN;
  • the active material includes at least one of LiCoO 2 , LiMn 2 O 4 , LiMnO 2 , LiNiO 2 , LiFePO 4 , LiMnPO 4 , LiCo x Ni 1-x O 2 (0 ⁇ x ⁇ 1), LiCo x Ni 1-xy Al y O 2 (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1);
  • the active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microbeads, Si, SiOx, Si-C, and SiOx - C.
  • a bonding layer 12 is further provided between the current collector 10 and the active material layer 11 , and the bonding layer 12 includes a second bonding material and a conductive agent.
  • the bonding layer 12 between the current collector 10 and the active material layer 11 By providing the bonding layer 12 between the current collector 10 and the active material layer 11 , the bonding strength between the active material layer 11 and the current collector 10 can be increased, thereby reducing the possibility of the active material layer 11 falling off.
  • the second adhesive material includes at least one of PVDF, SBR, PP, EVA hot melt adhesive, PO hot melt adhesive, PUR hot melt adhesive, TPR material, TPU hot melt adhesive, polyamide (PA, polyester (PES), polyethylene and polyester amide (PEA);
  • the conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, conductive carbon fiber and conductive graphite.
  • a conductive agent with a large specific surface area such as conductive carbon black, carbon nanotubes or graphene
  • the roughness of the bonding layer 12 can be increased, thereby increasing the bonding force and peeling force between the active material layer 11 and the adhesive layer 12.
  • the thickness of the active material layer 11 is greater than or equal to 20 ⁇ m and less than or equal to 3 mm (for example, the thickness of the active material layer 11 may be 20 ⁇ m, 100 ⁇ m, 200 ⁇ m, 500 ⁇ m, 800 ⁇ m, 1 mm, 2 mm, or 3 mm).
  • the thickness of the active material layer is greater than or equal to 30 ⁇ m and less than or equal to 300 ⁇ m (for example, the thickness of the active material layer 11 may be 30 ⁇ m, 50 ⁇ m, 80 ⁇ m, 100 ⁇ m, 150 ⁇ m, 200 ⁇ m, 250 ⁇ m, or 300 ⁇ m).
  • the thickness of the active material layer 11 is less than 30 ⁇ m, the active material layer is prone to breakage during processing. If the thickness of the active material layer 11 is greater than 300 ⁇ m, the electrolyte is difficult to infiltrate, the lithium ion transmission path is too long, and the lithium ion transmission kinetics are insufficient, which seriously affects the electrochemical properties of the battery.
  • the thickness of the adhesive layer 12 is greater than or equal to 500nm and less than or equal to 3 ⁇ m (for example, the thickness of the adhesive layer 12 is 500nm, 600nm, 800nm, 1 ⁇ m, 1.5 ⁇ m, 1.8 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 2.8 ⁇ m, 3 ⁇ m); preferably, the thickness of the adhesive layer 12 is greater than or equal to 1 ⁇ m and less than or equal to 2 ⁇ m (for example, the thickness of the adhesive layer 12 is 1 ⁇ m, 1.1 ⁇ m, 1.2 ⁇ m, 1.3 ⁇ m, 1.4 ⁇ m, 1.5 ⁇ m, 1.6 ⁇ m, 1.7 ⁇ m, 1.8 ⁇ m, 1.9 ⁇ m, 2 ⁇ m).
  • both the bonding force and the internal resistance of the electrode can be guaranteed. If the thickness of the adhesive layer 12 is greater than 2 ⁇ m, the internal resistance of the electrode will increase; if the thickness of the adhesive layer 12 is less than 1 ⁇ m, the active material layer will easily fall off.
  • the ratio of the thickness of the active material layer 11 to the bonding layer 12 is greater than or equal to 10 and less than or equal to 6000 (for example, the thickness ratio can be 10, 50, 100, 200, 500, 1000, 2000, 3000, 4000, 5000, 6000).
  • the ratio of the thickness of the active material layer 11 to the bonding layer 12 is greater than or equal to 30 and less than or equal to 300 (for example, the thickness ratio can be 30, 50, 80, 100, 120, 150, 160, 180, 200, 220, 250, 280, 300).
  • the contact area between the current collector and the active material layer is increased without reducing the battery energy density, thereby improving the conductivity and cycle life of the battery. It can also prevent problems such as peeling or short circuit between the active material layer and the current collector due to mechanical vibration and the like.
  • the thickness ratio of the active material layer 11 to the adhesive layer 12 may be 10, 20, 100, 500, 1500, or 2000.
  • the content ratio of the first adhesive material in the active material layer 11 is smaller than the content ratio of the second adhesive material in the bonding layer 12 , which can improve the bonding force between the bonding layer 12 and the active material layer 11 and between the bonding layer 12 and the current collector 10 .
  • the electrode sheet may be a positive electrode sheet or a negative electrode sheet.
  • the present disclosure also provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and a separator located between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet and/or the negative electrode sheet are the electrode sheets provided in the embodiments of the present disclosure.
  • the electrochemical device may be a lithium-ion battery.
  • the electrochemical device provided by the present disclosure includes the pole piece provided by the embodiment of the present disclosure
  • the electrochemical device provided by the embodiment of the present disclosure can achieve all the beneficial effects of the pole piece provided by the embodiment of the present disclosure, and will not be described again here to avoid repetition.
  • Embodiment 1 The electrode is a positive electrode
  • Preparation of positive electrode sheet 97wt% lithium cobalt oxide, 2wt% polytetrafluoroethylene, and 1wt% conductive carbon black are added to a dispersion device for full dry mixing to obtain a uniformly dispersed positive electrode material.
  • the above positive electrode material is added to a jet mill, the feed rate is set to 150g/min, and the time is set to 25min, and the polytetrafluoroethylene binder is fully dispersed and fiberized to obtain a dough-like positive electrode material; the positive electrode material is extruded and rolled by a screw pump to obtain a membrane of the active material layer (that is, the composite material mentioned above).
  • the obtained active material layer membrane is compounded to a current collector without a glue layer through multi-stage hot calendering to form a positive electrode sheet.
  • the thickness of the active material layer membrane is 100 microns.
  • the distance between the first side and the surface of the active material layer facing away from the current collector is 5% of the total thickness of the active material layer, and the distance between the second side and the surface of the active material layer close to the current collector is 7% of the total thickness of the active material layer;
  • the distance between the third side and the surface of the active material layer 11 facing away from the current collector 10 is 45% of the total thickness of the active material layer, and the distance between the fourth side and the surface of the active material layer 11 close to the current collector 10 is 49% of the total thickness of the active material layer.
  • Embodiment 2 is a diagrammatic representation of Embodiment 1:
  • Example 2 The difference from Example 1 is that the thickness of the pole piece is 300 ⁇ m;
  • Embodiment 3 is a diagrammatic representation of Embodiment 3
  • Example 2 The difference from Example 1 is that the thickness of the pole piece is 1000 ⁇ m;
  • Embodiment 4 is a diagrammatic representation of Embodiment 4:
  • Example 1 The difference from Example 1 is that the positive electrode material ratio in the composite positive electrode material is 94wt% lithium cobalt oxide, 5wt% polytetrafluoroethylene, and 1wt% conductive carbon black.
  • Example 2 The difference from Example 1 is that the binder in the composite positive electrode material is 2 wt% polyvinylidene fluoride, and the above mixed material is directly extruded into a film through a screw pump and composited on the current collector;
  • Embodiment 6 is a diagrammatic representation of Embodiment 6
  • Example 1 The difference from Example 1 is that the binder consists of 1wt% polytetrafluoroethylene and 1wt% polyvinylidene fluoride;
  • Embodiment 7 The electrode is a negative electrode
  • Preparation of negative electrode sheet 97wt% graphite, 2wt% polytetrafluoroethylene, and 1wt% conductive carbon black are added to a dispersing device for thorough dry mixing to obtain a uniformly dispersed negative electrode material.
  • the above negative electrode material is added to a jet mill at a feed rate of The rate is set to 150 g/min and the time is set to 25 min to fully disperse and fiberize the polytetrafluoroethylene binder to obtain a dough-like negative electrode material; the negative electrode material is extruded and rolled by a screw pump to obtain an active material layer membrane.
  • the prepared active material layer membrane is compounded on a current collector without a glue layer through multi-stage hot calendering to form a negative electrode sheet.
  • the thickness of the active material layer membrane is 100 microns.
  • the distance between the first side and the side surface of the active material layer away from the current collector is 5% of the total thickness of the active material layer, and the distance between the second side and the side surface of the active material layer close to the current collector is 7% of the total thickness of the active material layer;
  • the distance between the third side and the side surface of the active material layer 11 away from the current collector 10 is 45% of the total thickness of the active material layer, and the distance between the fourth side and the side surface of the active material layer 11 close to the current collector 10 is 49% of the total thickness of the active material layer.
  • Embodiment 8 is a diagrammatic representation of Embodiment 8
  • the method is carried out in accordance with Example 1, except that the prepared active material layer film is laminated to a current collector containing a glue layer (the adhesive layer includes polyethylene and conductive carbon black, and the mass ratio of the two is 7:3) through multi-stage hot calendering to form a positive electrode sheet.
  • the thickness of the active material layer film is 100 microns, and the thickness of the adhesive layer is 1 micron.
  • Embodiment 9 is a diagrammatic representation of Embodiment 9:
  • the method is carried out in accordance with Example 7, except that the prepared active material layer film is laminated to a current collector containing a glue layer (the adhesive layer includes polyethylene and conductive carbon black, and the mass ratio of the two is 7:3) through multi-stage hot calendering to prepare a negative electrode sheet.
  • the thickness of the active material layer film is 100 microns, and the thickness of the adhesive layer is 1 micron.
  • the electrode sheet prepared in Comparative Example 1a is a positive electrode sheet, which is carried out in accordance with Example 1, except that:
  • the electrode sheet prepared in Comparative Example 1b is a negative electrode sheet, which is carried out in accordance with Example 7, except that:
  • Fix the two ends of an electrode select a certain bending radius (for example, 10mm, 15mm, 20mm), and perform positive and negative staggered bending (i.e. bend once in the forward direction and once in the reverse direction). After 200 consecutive positive and negative staggered bendings, visually check whether the electrode has lost powder, then dry and weigh it. The weight is compared with the electrode before bending to calculate the weight retention rate and determine whether it has lost powder.
  • a certain bending radius for example, 10mm, 15mm, 20mm
  • positive and negative staggered bending i.e. bend once in the forward direction and once in the reverse direction.
  • a pole piece position is randomly selected, and after the pole piece is dried, a CCD camera is used to observe and record the number of cracks on the pole piece surface.
  • the mass percentage of fluorine in the third region of Examples 1-7 is greater than the mass percentage of fluorine in at least one of the first region or the second region.
  • the mass percentage of fluorine in the third region of Comparative Examples 1a and 1b is less than the mass percentage of fluorine in the first region and the second region of the corresponding pole piece, and the difference in the mass percentage of fluorine in the first region and the second region of Comparative Examples 1a and 1b is greater than 3, resulting in uneven distribution of fluorine in the active material layer of the comparison group, uneven stress on the active material layer, and powdering and cracking.
  • the thickness of the active material layer of Examples 1, 2, and 3 gradually increases.
  • Example 2 when the thickness of the active material layer is 300 ⁇ m, the difference in the mass percentage of fluorine element between the first region and the second region gradually increases.
  • the thickness of the active material layer is increased to 1000 ⁇ m, the mass percentage of fluorine element in the third region is greater than that in the first region and/or the second region.
  • the difference between the percentages of the amounts increases significantly, and the stress distribution between the third region and the first region and/or the second region is uneven, resulting in slight powder loss and cracking of the pole piece.
  • the difference between the mass percentage of the fluorine element in the first region of Example 1 and Example 7 and the mass percentage of the fluorine element in the second region is greater than 0 and less than or equal to 0.5wt%, and the difference between the mass percentage of the fluorine element in the third region of Example 1 and Example 7 and the mass percentage of the fluorine element in the first region and/or the second region is less than or equal to 1.5wt%, that is, the mass percentages of the fluorine element on the top surface, the middle region, and the bottom surface of the active material layer are close, which means that the fluorine element is evenly distributed in the thickness direction of the active material layer, so that the stress on the electrode in the thickness direction is evenly distributed, the stress on the active material layer in the middle region is small, and the electrode will not shed or crack, thereby improving the stability and cycle life of the electrode sheet.

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Abstract

本公开提供了一种极片和电化学装置，其中，极片包括集流体，集流体至少一个表面的活性物质层在第一区域内的氟元素占第一区域的活性物质层的总质量的质量百分数与活性物质层在第二区域内的氟元素占第二区域内的活性物质层的总质量的质量百分数之间的差值大于0，小于等于3％；第一区域为活性物质层的背离集流体的一侧表面与第一侧边之间的区域；第二区域为活性物质层靠近集流体的一侧表面与第二侧边之间的区域；第一侧边与活性物质层的背离集流体的一侧表面之间的距离为活性物质层总厚度的1-10％；第二侧边与活性物质层靠近集流体的一侧表面之间的距离为活性物质层的总厚度的1-10％。本公开提供的极片可提高极片的结构强度，降低极片开裂或者掉粉的可能性。

Description

一种极片和电化学装置 技术领域
本公开涉及锂离子电池技术领域，具体涉及一种极片和电化学装置。
背景技术
随着锂离子电池技术的发展，锂离子电池因具有较好的电化学性能，而被广泛应用于便携式电子产品、新能源车辆等领域中。
随着锂离子电池的进一步商业化，高能量密度的电池的重要性越发凸显。而电池的能量密度受体积影响显著，厚电极设计可通过提高活性物质的占比从而提高电池的能量密度。
目前，厚电极在加工过程中存在诸多问题，例如，厚电极在加工过程中，经常会出现极片开裂，甚至是极片掉粉，严重影响电池的性能发挥。
发明内容
有鉴于此，本公开致力于提供一种极片和电化学装置，以提高极片的结构强度，降低极片开裂或者掉粉的可能性。
本公开第一方面提供了一种极片，包括集流体，所述集流体的至少一个表面设有活性物质层；
所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域内的活性物质层的总质量的质量百分数之间的差值大于0，且小于等于3％；
所述第一区域为所述活性物质层的背离所述集流体的一侧表面与第一侧边之间的区域；
所述第二区域为所述活性物质层的靠近所述集流体的一侧表面与第二侧边之间的区域；
所述第一侧边与所述活性物质层的背离所述集流体的一侧表面之间的距离为所述活性物质层的总厚度的1-10％；
所述第二侧边与所述活性物质层的靠近所述集流体的一侧表面之间的距离为所述活性物质层的总厚度的1-10％。
可选地，所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域内的活性物质层的总质量的质量百分数之间的差值大于0，且小于等于1％，
优选地，所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域内的活性物质层的总质量的质量百分数之间的差值大于0，且小于等于0.5％。
可选地，所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数为0-18wt％；
和/或；所述活性物质层在第二区域内的氟元素占所述第二区域的活性物质层的总质量的质量百分数为0-18wt％。
可选地，所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数为0.5-10wt％；
和/或；所述活性物质层在第二区域内的氟元素占所述第二区域的活性物质层的总质量的质量百分数为0.5-10wt％。
可选地，所述活性物质层包括第三区域，所述第三区域为第三侧边和第四侧边之间的区域；
所述第三侧边与所述活性物质层的背离所述集流体的一侧表面之间的距离为所述活性物质层的总厚度的45％-50％；
所述第四侧边与所述活性物质层的靠近所述集流体的一侧表面之间的距离为所述活性物质层的总厚度的45％-50％；
所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数大于所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数，和/或，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数大于所述活性物质层在第二区域内的氟元素占所述第二区域内的活性物质层的总质量的质量百分数。
可选地，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数与所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数之间的差值≤3％；
和/或；所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域的活性物质层的总质量的质量百分数之间的差值≤3％。
可选地，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数与所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数之间的差值≤1.5％；
和/或；所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域的活性物质层的总质量的质量百分数之间的差值≤1.5％。
可选地，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数为0-21wt％，优选地，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数为1-12wt％。
可选地，所述活性物质层包括第一粘结剂和活性材料；
所述活性物质层在所述第一区域内的第一粘结剂和活性材料的质量百分数比与所述活性物质层在第二区域内的第一粘结剂和活性材料的质量百分数比之间的差值≤9％。
可选地，所述活性物质层在第一区域内的第一粘结剂和活性材料的质量百分数比与所述活性物质层在第二区域内的第一粘结剂和活性材料的质量百分数比之间的差值≤5％。
可选地，所述活性物质层在第一区域内的第一粘结剂和活性材料的质量百分数比为0.5-10％；
和/或；所述活性物质层在第二区域内的第一粘结剂和活性材料的质量百分数比为0.5-10％。
可选地，所述第一粘结剂包括纤维状的聚四氟乙烯(PTFE)，聚偏二氟乙烯(PVDF)、(ETEF)、氟化乙烯丙烯共聚物(FEP)、聚氯乙烯(PVP)、聚氧化乙烯(PEO)、羧甲基纤维素(CMC)、丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯(PP)、聚乙烯(PE)和聚丙烯腈(PAN)中的至少一种；
和/或，所述活性材料包括LiCoO2、LiMn2O4、LiMnO2、LiNiO2、LiFePO4、LiMnPO4、LiCoxNi1-xO2(0≤x≤1)、LiCoxNi1-x-yAlyO2(0≤x≤1，0≤y≤1)中的至少一种；
和/或，所述活性材料包括人造石墨、天然石墨、软碳、硬碳、中间相碳微球、Si、SiOx、Si-C和SiOx-C中的至少一种。
可选地，所述集流体和所述活性物质层之间还设有粘结层，所述粘结层包括第二粘结材料和导电剂。
可选地，所述第二粘结材料包括PVDF、SBR、PP、乙烯-醋酸乙烯共聚物(ethylene-vinyl acetate copolymer,EVA)热熔胶、聚烯烃(Polyolefins,PO)热熔胶、反应型聚氨酯热熔胶(Polyurethane Reactive,PUR)热熔胶、热塑性橡胶(Thermoplastic Rubber,TPR)类材料、热塑性聚氨酯弹性体(Thermoplastic Urethanes,TPU)热熔胶、聚酰胺(PA)、聚酯(PES)、聚乙烯和聚酯酰胺(PEA)中的至少一种；
和/或，所述导电剂包括导电炭黑、碳纳米管、石墨烯、导电炭纤维和导电石墨中的至少一种。
可选地，所述活性物质层的厚度大于或等于20μm，且小于或等于3mm；优选地，所述活性物质层的厚度大于或等于30μm，且小于或等于300μm。
和/或，所述粘结层的厚度大于或等于500nm，且小于或等于3μm；
和/或，所述活性物质层与所述粘结层的厚度之比大于或等于10，且小于或等于6000；优选地，所述活性物质层与所述粘结层的厚度之比大于或等于30，且小于或等于300。
本公开第二方面提供了一种电化学装置，包括正极极片、负极极片和位于所述正极极片和负极极片之间的隔膜；
所述正极极片和/或所述负极极片为如第一方面所述的极片。
本公开提供的极片包括集流体，集流体的至少一个表面设有活性物质层。通过使活性物质层在第一区域内的氟元素占第一区域的活性物质层的总质量的质量百分数与活性物质层在第二区域内的氟元素占第二区域内的活性物质层的总质量的质量百分数之间的差值大于0，且小于等于3％，氟元素作为活性物质层中的重要组成部分，通过控制活性物质层的顶面的第一区域和底面的第二区域的氟元素的差值，即实现氟元素在活性物质层的顶面和底面的质量百分数接近，则意味着氟元素在活性物质层的厚度方向上得到充分均匀的分布，氟元素具有较强的亲电性和化学惰性，可以增强活性物质层内的粘结剂与活性物质(即活性材料)之间的粘结力，使得加工过程中，极片在厚度方向上的受到的应力均匀分布，降低极片出现掉粉或者开裂从而导致电池短路的这一情况发生的可能性；再者，氟元素在活性物质层的厚度方向上的均匀分布，可使得活性物质层在厚度方向上具有一致的化学特性，有助于提高电池的性能和稳定性。
附图说明
图1所示为本公开实施例提供的极片的示意图之一；
图2所示为本公开实施例提供的极片的示意图之二；
图3所示为本公开实施例提供的极片的示意图之三；
图4所示为本公开实施例提供的极片的示意图之四；
图5所示为本公开所提供的实施例7中的极片的示意图；
图6所示为本公开所提供的实施例7中的极片的第一区域的元素分布图；
图7所示为本公开所提供的实施例7中的极片的第三区域的元素分布图；
图8所示为本公开所提供的实施例7中的极片的第二区域的元素分布图；
图9所示为本公开所提供的实施例3中的极片的示意图；
图10所示为本公开所提供的实施例3中的极片的第一区域的元素分布图；
图11所示为本公开所提供的实施例3中的极片的第三区域的元素分布图；
图12所示为本公开所提供的实施例3中的极片的第二区域的元素分布图。
具体实施方式
下面将结合本公开实施例中的附图，对本公开实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅是本公开一部分实施例，而不是全部的实施例。基于本公开中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本公开保护的范围。
请参见图1和图2，本公开提供了一种极片，包括集流体10，集流体10的至少一个表面设有活性物质层11；
活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数与活性物质层11在第二区域内的氟元素占第二区域内的活性物质层11的总质量的质量百分数之间的差值大于0，且小于等于3％，例如差值可以为0.1％、0.2％、0.5％、0.8％、1％、1.2％、1.4％、1.5％、1.8％、2％、2.2％、2.4％、2.5％、2.8％、3％；
第一区域为活性物质层11的背离集流体10的一侧表面与第一侧边之间的区域；
第二区域为活性物质层11的靠近集流体10的一侧表面与第二侧边之间的区域；
第一侧边与活性物质层11的背离集流体10的一侧表面之间的距离为活性物质层11的总厚度的1-10％，例如可以为总厚度的1％、2％、3％、4％、5％、6％、7％、8％、9％、10％；
第二侧边与活性物质层11的靠近集流体10的一侧表面之间的距离为活性物质层11的总厚度的1-10％，例如可以为总厚度的1％、2％、3％、4％、5％、6％、7％、8％、9％、10％。
上述极片可以为正极片，也可以为负极片。可以仅在集流体10的单个表面设置活性物质层11，如图1所示；也可以在集流体10的两个表面设置活性物质层11，如图2所示。
示例性地，第一侧边与活性物质层11的背离集流体10的一侧表面之间的距离和第二侧边与活性物质层11的靠近集流体10的一侧表面之间的距离可为相同，也可为不同，例如，第一侧边与活性物质层11的背离集流体10的一侧表面之间的距离和第二侧边与活性物质层11的靠近集流体10的一侧表面之间的距离均可为活性物质层11的总厚度的3％、或5％、或8％；又例如，第一侧边与活性物质层11的背离集流体10的一侧表面之间的距离为活性物质层11的总厚度的5％，第二侧边与活性物质层11的靠近集流体10的一侧表面之间的距离为活性物质层的总厚度的7％。
上述第一侧边可以理解为第一厚度位置处活性物质层11的横截面，第一厚度是指在活性物质层11厚度方向上，第一侧边与活性物质层11的背离集流体10的一侧表面之间的距离；上述第二侧边可以理解为第二厚度位置处活性物质层11的横截面，第二厚度是指在活性物质层11厚度方向上，第二侧边与活性物质层11的靠近集流体10的一侧表面之间的距离。(图1和图2为极片的纵截面示意图)
活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数指的是，第一区域内的氟元素总质量除以第一区域内活性物质层11的总质量所得到的百分数。
同理，活性物质层11在第二区域内的氟元素占第二区域内的活性物质层11的总质量的质量百分数指的是，第二区域内的氟元素总质量除以第二区域内活性物质层11的总质量所得到的百分数。
活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数可以通过能谱元素分析进行检测。具体地，可先通过氩离子气体裁切极片横截面，随后根据第一侧边和/或第二侧边的具体位置，使用扫面电子显微镜能谱元素分析测试活性物质层的第一区域和/或第二区域的元素分布，即可测得不同位置处氟元素占该区域的 活性物质层的总质量的质量分数。在一个实施例中，可以使用扫面电子显微镜能谱元素分析测试活性物质层的顶面(在这指活性物质层的背离集流体的表面)向下5微米以及活性物质层的底面(在这指活性物质层的靠近集流体的表面)向上5微米处的元素分布，可测得对应位置处的氟元素占该区域的活性物质层的总质量的质量分数，如图6-8所示。
活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数，和/或活性物质层11在第二区域内的氟元素占第二区域内的活性物质层11的总质量的质量百分数可通过调整粘结剂的含量、粘结剂的种类或者活性物质层的厚度进行调整。
本公开实施例中，通过使活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数与活性物质层11在第二区域内的氟元素占第二区域内的活性物质层11的总质量的质量百分数之间的差值大于0，且小于等于3％，氟元素作为活性物质层中的重要组成部分，通过控制活性物质层的顶面的第一区域和底面的第二区域的氟元素的差值，即实现氟元素在活性物质层的顶面和底面的质量百分数接近，则意味着氟元素在活性物质层的厚度方向上得到充分均匀的分布，使得加工过程中，极片在厚度方向上的受到的应力均匀分布，避免极片出现掉粉或者开裂从而导致电池短路的情况；再者，氟元素在活性物质层的厚度方向上的均匀分布，可使得活性物质层在厚度方向上具有一致的化学特性，有助于提高电池的性能和稳定性。
在一个具体实施例中，活性物质层可以通过干法制作，即将活性物质、粘结剂、导电剂不使用溶剂地进行干式混合，制作成固体成分浓度实质为100％的复合材料。干式混合是指如下方式：在固体成分浓度实质为100％的状态下，将正极活性物质与粘结材料不使用溶剂地进行混合。在进行干式混合时，也可以添加除了正极活性物质和粘结材料之外的导电材料等。在添加除了正极活性物质和粘结材料之外的材料的情况下，干式混合中的固体成分浓度实质上也为100％。
随后，再通过将复合材料压延而成为片状，从而制作成片状的活性物质层11。并且，将集流体和活性物质层11层叠并进行热压，以形成极片。
相比于现有的湿法制备极片，在其制作过程中，需要将溶剂、活性物质、粘结剂混合制成浆料，然后将浆料涂布在集流体表面，再对集流体表面的浆料涂层进行干燥处理以使得溶剂挥发。由此可见，湿法的干燥工序使得电池的制作工序较为复杂，降低制备效率。该实施例中，通过采用干法制备极片，不需要使用溶剂，将活性物质、粘结剂混合制成浆料，然后将浆料涂布于集流体10表面即可，无需对集流体10表面的浆料涂层进行干燥处理以使溶剂挥发，从而简化了极片的制作工序，提高了电池的制备效率。
为使活性物质层11中的氟元素分布更为均匀，从而降低活性涂层底部开裂、掉粉的情况发生的可能性。可选地，活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数与活性物质层11在第二区域内的氟元素占第二区域内的活性物质层11的总质量的质量百分数之间的差值大于0，且小于等于1％，例如差值可以为0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％、1％。
优选地，活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数与活性物质层11在第二区域内的氟元素占第二区域内的活性物质层11的总质量的质量百分数之间的差值大于0，且小于等于0.5％，例如差值可以为0.1％、0.2％、0.3％、0.4％、0.5％，从而进一步提高活性物质层的电学性能在厚度方向上的一致性，增强电池的电化学性能和安全性能。
可选地，活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数为0-18wt％，例如可以为0.1wt％、1wt％、2wt％、3wt％、4wt％、5wt％、6wt％、7wt％、8wt％、9wt％、10wt％、11wt％、12wt％、13wt％、14wt％、15wt％、16wt％、17wt％、18wt％；
和/或；活性物质层11在第二区域内的氟元素占第二区域的活性物质层11的总质 量的质量百分数为0-18wt％，例如可以为0.1wt％、1wt％、2wt％、3wt％、4wt％、5wt％、6wt％、7wt％、8wt％、9wt％、10wt％、11wt％、12wt％、13wt％、14wt％、15wt％、16wt％、17wt％、18wt％。
活性物质层11在第一区域内和第二区域内的氟元素含量占比在上述范围时，保证粘结剂可以充分包裹活性物质颗粒，减小辊压及电池循环后期的极片反弹及掉粉，提高能量密度和电池的安全性能。具体地，活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数可以为0.9wt％、或5wt％、或12wt％、或18wt％；
活性物质层11在第二区域内的氟元素占第二区域的活性物质层11的总质量的质量百分数可以为0.9wt％、或5wt％、或12wt％、或18wt％。
可选地，活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数为0.5-10wt％，例如可以为0.5wt％、1wt％、2wt％、3wt％、4wt％、5wt％、6wt％、7wt％、8wt％、9wt％、10wt％；
和/或；活性物质层11在第二区域内的氟元素占第二区域的活性物质层11的总质量的质量百分数为0.5-10wt％，例如可以为0.5wt％、1wt％、2wt％、3wt％、4wt％、5wt％、6wt％、7wt％、8wt％、9wt％、10wt％。
进一步地，活性物质层11在第一区域内和第二区域内的氟元素含量占比在上述较小范围时，可以提高单位面积内活性物质的质量，保证粘结剂不掉粉和降低反弹的情况下，最大限度的提高极片的克容量，利于实现高能量密度的产品设计。
具体地，活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数可以为0.9wt％、或2wt％、或5wt％、或9wt％；
活性物质层11在第二区域内的氟元素占第二区域的活性物质层11的总质量的质量百分数可以为0.9wt％、或2wt％、或5wt％、或9wt％。
若活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数小于0.5wt％，则导致极片的电化学性能(例如容量、循环寿命等)降低；若活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数大于10wt％，则会使得电池的整体能量密度降低。
可选地，活性物质层11包括第三区域，第三区域为第三侧边和第四侧边之间的区域；
第三侧边与活性物质层11的背离集流体10的一侧表面之间的距离为活性物质层11的总厚度的45％-50％，例如可以为总厚度的45％、46％、47％、48％、49％、50％；
第四侧边与活性物质层11的靠近集流体10的一侧表面之间的距离为活性物质层11的总厚度的45％-50％，例如可以为总厚度的45％、46％、47％、48％、49％、50％；
活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数大于活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数，和/或，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数大于活性物质层11在第二区域内的氟元素占第二区域内的活性物质层11的总质量的质量百分数。
活性物质层11中还设置第三区域，并且使第三区域内的氟元素含量占比相较于第一区域和第二区域中的氟元素含量占比更高，即活性物质层11的中部区域的氟元素的质量百分数较高，可以增强活性物质层内的粘结剂与活性物质(即活性材料)之间的粘结力，从而降低活性物质层的中间区域因受到过大应力而出现开裂或者断开的可能性，进而提高电极片(即极片)的稳定性和循环寿命。
示例性地，第三侧边与活性物质层11的背离集流体10的一侧表面之间的距离和第四侧边与活性物质层11的靠近集流体10的一侧表面之间的距离可为相同，也可为不同。例如，第三侧边与活性物质层11的背离集流体10的一侧表面之间的距离和第四侧边与 活性物质层11的靠近集流体10的一侧表面之间的距离均为活性物质层11的总厚度的45％、或48％、或50％；又例如，第三侧边与活性物质层11的背离集流体10的一侧表面之间的距离为总厚度的45％，第四侧边与活性物质层11的靠近集流体10的一侧表面之间的距离为总厚度的49％。在一个具体实施例中，第三区域为自活性物质层在厚度方向上的一半的位置处向上延伸5微米的第三侧边以及自活性物质层在厚度方向上的一半的位置处向下延伸5微米的第四侧边之间的区域(即第三侧边和第四侧边在厚度方向上围成的区域)。在另一个实施例中，第三区域即活性物质层11厚度的二分之一的位置处，上下±10％活性物质层11厚度的区域，也可以理解为活性物质层11在厚度方向上的中部区域。
上述第三侧边可以理解为第三厚度位置处活性物质层11的横截面，第三厚度是指在活性物质层11厚度方向上，第三侧边与活性物质层11的背离集流体10的一侧表面之间的距离；上述第四侧边可以理解为第四厚度位置处活性物质层11的横截面，第四厚度是指在活性物质层11厚度方向上，第四侧边与活性物质层11的靠近集流体10的一侧表面之间的距离；
活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数同样可以通过扫面电子显微镜能谱元素分析检测得到。
活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数大于活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数，和/或，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数大于活性物质层11在第二区域内的氟元素占第二区域内的活性物质层11的总质量的质量百分数。即是说，活性物质层11的中部区域的氟元素的质量百分数至少大于活性物质层11的一侧边缘区域的氟元素的质量百分数。由于活性物质层11的中部区域的氟元素的质量百分数较高，且因为氟元素具有较强的亲电性和化学惰性，可以增强活性物质层内的粘结剂与活性物质(即活性材料)之间的粘结力，从而降低活性物质层的中间区域因受到过大应力而出现开裂或者断开的可能性，进而提高电极片(即极片)的稳定性和循环寿命。
为进一步增强电极片的稳定性和循环寿命。可选地，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数与活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数之间的差值≤3％，例如差值可以为0.1％、0.2％、0.5％、0.8％、1％、1.2％、1.4％、1.5％、1.8％、2％、2.2％、2.4％、2.5％、2.8％、3％；
和/或；活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数与活性物质层11在第二区域内的氟元素占第二区域的活性物质层11的总质量的质量百分数之间的差值≤3％，例如差值可以为0.1％、0.2％、0.5％、0.8％、1％、1.2％、1.4％、1.5％、1.8％、2％、2.2％、2.4％、2.5％、2.8％、3％。
具体地，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数与活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数之间的差值可以为2％或3％。
活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数与活性物质层11在第二区域内的氟元素占第二区域的活性物质层11的总质量的质量百分数之间的差值可以为2％或3％。
在一个实施例中，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数与活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数之间的差值≤1.5％，例如差值可以为0.1％、0.2％、0.5％、0.8％、1％、1.2％、1.4％、1.5％；
和/或；活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质 量的质量百分数与活性物质层11在第二区域内的氟元素占第二区域的活性物质层11的总质量的质量百分数之间的差值≤1.5％，例如差值可以为0.1％、0.2％、0.5％、0.8％、1％、1.2％、1.4％、1.5％、1.8％、2％、2.2％、2.4％、2.5％、2.8％、3％。
进一步减少第三区域内的氟元素含量与第一区域内和第二区域内的氟元素含量的差值，可以进一步提高极片的稳定性和循环寿命。
具体地，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数与活性物质层11在第一区域内的氟元素占第一区域的活性物质层11的总质量的质量百分数之间的差值可以为0.5％、或0.9％、或1.5％。
活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数与活性物质层11在第二区域内的氟元素占第二区域的活性物质层11的总质量的质量百分数之间的差值可以为0.5％、或0.9％、或1.5％。
可选地，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数为0-21wt％，例如可以为0.1wt％、0.5wt％、1wt％、2wt％、4wt％、5wt％、6wt％、8wt％、10wt％、12wt％、14wt％、15wt％、16wt％、18wt％、20wt％、21wt％。活性物质层11在第三区域内的氟元素含量占比在上述范围时，可以有效提高极片的内聚力，防止开裂掉粉情况。
具体地，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数可以为0.9wt％、或10wt％、或21wt％。
可选地，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数为1-12wt％，例如可以为0.1wt％、0.5wt％、1wt％、2wt％、4wt％、5wt％、6wt％、8wt％、10wt％、12wt％。进一步地，活性物质层11在第三区域内的氟元素含量占比在上述较小范围时，在保证主材颗粒间的有效粘结的同时，增加单位面积内的主材颗粒，保证能量密度。另外，当粘结剂过多时会增加电子和离子的传输阻力，电池阻抗也会增加。
具体地，活性物质层11在第三区域内的氟元素占第三区域的活性物质层11的总质量的质量百分数可以为1.2wt％、或5wt％、或11wt％。
可选地，活性物质层11包括第一粘结剂和活性材料；活性物质层11在第一区域内的第一粘结剂和活性材料的质量百分数比与活性物质层11在第二区域内的第一粘结剂和活性材料的质量百分数比之间的差值≤9％，例如差值可以为0.1％、0.5％、1％、2％、3％、4％、5％、6％、7％、8％、9％。
该实施例中通过控制活性物质层11在第一区域内的第一粘结剂和活性物质层11在第二区域内的第一粘结剂的质量百分数的差值，可使第一粘结剂在不同区域的分布较为均匀，降低出现粘结剂迁移的可能性，以使极片在厚度方向上的应力基本相同，从而降低活性物质层11开裂，甚至是从集流体10表面脱落的可能性，并降低极片的贯穿电阻、提高电极复合材料片的剥离强度。同时，第一粘结剂的均匀较为分布，可使得极片在循环过程中的膨胀程度较小，延长电池在循环过程中的使用寿命，还可以降低电芯的整体阻抗。
具体地，活性物质层11在第一区域内的第一粘结剂和活性材料的质量百分数比与活性物质层11在第二区域内的第一粘结剂和活性材料的质量百分数比之间的差值可以为1％、或3％、或6％、或9％。
为进一步地降低极片的贯穿电阻、提高电极复合材料片的剥离强度，可选地，活性物质层11在第一区域内的第一粘结剂和活性材料的质量百分数比与活性物质层11在第二区域内的第一粘结剂和活性材料的质量百分数比之间的差值≤5％。
具体地，活性物质层11在第一区域内的第一粘结剂和活性材料的质量百分数比与活性物质层11在第二区域内的第一粘结剂和活性材料的质量百分数比之间的差值可以为1％、或2％、或3％、或4％、或5％。
可选地，活性物质层11在第一区域内的第一粘结剂和活性材料的质量百分数比为0.5-10％；
具体地，活性物质层11在第一区域内的第一粘结剂和活性材料的质量百分数比可以为0.5％、或1％，或2％，或3％，或4％，或5％，或6％，或7％，或8％，或9％，或10％。
同理，为兼顾活性物质层11的粘结力和能量密度，可选地，活性物质层11在第二区域内的第一粘结剂和活性材料的质量百分数比为0.5％-10％。
具体地，活性物质层11在第二区域内的第一粘结剂和活性材料的质量百分数比可以为0.5％、或1％，或2％，或3％，或4％，或5％，或6％，或7％，或8％，或9％，或10％。
可选地，第一粘结剂包括聚纤维状的四氟乙烯PTFE，聚偏二氟乙烯PVDF、ETEF、氟化乙烯丙烯共聚物FEP、PVP、聚氧化乙烯PEO、CMC、SBR、聚丙烯酸PAA、PP、PE、PAN的至少一种；
在极片为正极片的情况下，活性材料包括LiCoO2、LiMn2O4、LiMnO2、LiNiO2、LiFePO4、LiMnPO4、LiCoxNi1-xO2(0≤x≤1)、LiCoxNi1-x-yAlyO2(0≤x≤1，0≤y≤1)中的至少一种；
在极片为负极片的情况下，活性材料包括人造石墨、天然石墨、软碳、硬碳、中间相碳微球，Si、SiOx、Si-C、SiOx-C中的至少一种。
可选地，参见图3和图4，集流体10和活性物质层11之间还设有粘结层12，粘结层12包括第二粘结材料和导电剂。
通过在集流体10和活性物质层11之间设置粘结层12，可以提高活性物质层11与集流体10之间的粘结强度，从而降低活性物质层11脱落的可能性。
可选地，第二粘结材料包括PVDF、SBR、PP、EVA热熔胶、PO热熔胶、PUR热熔胶、TPR类材料、TPU热熔胶、聚酰胺(PA、聚酯(PES)、聚乙烯和聚酯酰胺(PEA)中的至少一种；
和/或，导电剂包括导电炭黑、碳纳米管、石墨烯、导电炭纤维和导电石墨中的至少一种。通过选择比表面积较大的导电剂(如导电炭黑、碳纳米管或石墨烯)，可提高粘结层12的粗糙度，从而提高活性物质层11和粘接层12之间的粘结力和剥离力。
可选地，活性物质层11的厚度大于或等于20μm，且小于或等于3mm(例如活性物质层11的厚度可以为20μm、100μm、200μm、500μm、800μm、1mm、2mm、3mm)，优选地，活性物质层的厚度大于或等于30μm，且小于或等于300μm(例如活性物质层11的厚度可以为30μm、50μm、80μm、100μm、150μm、200μm、250μm、300μm)；若活性物质层11的厚度小于30μm，则活性物质层在加工过程中容易断带，若活性物质层11的厚度大于300μm，则电解液难以浸润，锂离子的传输路径过长，锂离子的传输动力学不足，严重影响电池的电化学性能。
和/或，粘结层12的厚度大于或等于500nm，且小于或等于3μm(例如粘结层12的厚度为500nm、600nm、800nm、1μm、1.5μm、1.8μm、2μm、2.5μm、2.8μm、3μm)；优选地，粘结层12的厚度大于等于1μm，且小于或等于2μm(例如粘结层12的厚度为1μm、1.1μm、1.2μm、1.3μm、1.4μm、1.5μm、1.6μm、1.7μm、1.8μm、1.9μm、2μm)。通过将粘结层12的厚度控制在1-2μm内，既可以保证粘结力又可以兼顾极片的内阻。若粘结层12的厚度大于2μm，会导致极片的内阻增大；若粘结层12的厚度小于1μm，活性物质层容易脱落。
和/或，活性物质层11与粘结层12的厚度之比大于或等于10，且小于或等于6000(例如厚度比可以为10、50、100、200、500、1000、2000、3000、4000、5000、6000)，优选地，活性物质层11与粘结层12的厚度之比大于或等于30，且小于或等于300(例如厚度比可以为30、50、80、100、120、150、160、180、200、220、250、280、300)。 通过控制活性物质层11和粘结层12的厚度比，从而在不降低电池能量密度的情况下，增加集流体与活性物质层之间的接触面积，从而提高电池的导电性和循环寿命，还可以防止活性物质层与集流体之间因机械振动等原因发生剥离或短路等问题。
具体地，活性物质层11的厚度可以为30μm，或70μm，或1mm；粘结层12的厚度可以为500nm，或1μm，或3μm；
活性物质层11与粘结层12的厚度之比可以为10，或20，或100，或500，或1500，或2000。
活性物质层11中的第一粘接材料的含量比小于粘结层12中的第二粘结材料的含量比，可以提高粘结层12与活性物质层11以及粘结层12与集流体10之间的粘结力。
示例性地，该极片可以为正极极片，也可以为负极极片。
本公开还提供了一种电化学装置，包括正极极片、负极极片和位于所述正极极片和负极极片之间的隔膜；所述正极极片和/或所述负极极片为本公开实施例提供的极片。
在一些实施方式中，所述电化学装置可以为锂离子电池。
由于本公开提供的电化学装置包括本公开实施例提供的极片，因此，本公开实施例提供的电化学装置能够实现本公开实施例提供的极片的全部有益效果，为避免重复，在此不再赘述。
以下将通过实施例对本公开进行详细阐述，本公开所描述的实施例仅是本公开的一部分实施例，而不是全部实施例。基于本公开中的实施例，本领域普通技术人员在没有做出创造性劳动的前提下所获得的所有其他实施例，都属于本公开保护的范围。
在以下实例中，在没有特别说明的情况下，所用的材料均为商购的分析材料。
实施例1：该极片为正极极片
正极片制备：将97wt％钴酸锂、2wt％聚四氟乙烯、1wt％导电炭黑加入分散设备中进行充分干混，得到分散均匀的正极材料。将上述正极料加入到气流磨设备中，给料速度设置为150g/min、时间设置为25min，进行充分分散以及聚四氟乙烯粘结剂的纤维化，得到面团状的正极材料；将正极材料经螺杆泵挤出辊压得到活性物质层的膜片(即前面所说的复合材料)。最后将制得的活性物质层膜片经过多级热压延复合到不含胶层的集流体上制成正极片。活性物质层的膜片的厚度为100微米。第一侧边与活性物质层的背离集流体的一侧表面之间的距离为活性物质层的总厚度的5％，第二侧边与活性物质层的靠近集流体的一侧表面之间的距离为活性物质层的总厚度的7％；第三侧边与活性物质层11的背离集流体10的一侧表面之间的距离为活性物质层总厚度的45％，第四侧边与活性物质层11的靠近集流体10的一侧表面之间的距离为活性物质层总厚度的49％。
实施例2：
与实施例1不同之处在于，极片厚度为300μm；
实施例3：
与实施例1不同之处在于，极片厚度为1000μm；
实施例4：
与实施例1不同之处在于，复合正极材料中正极材料配比为94wt％钴酸锂、5wt％聚四氟乙烯、1wt％导电炭黑。
实施例5
与实施例1不同之处在于，复合正极材料中的粘结剂为2wt％偏聚氟乙烯，直接将上述混合材料经螺杆泵挤出成膜，复合在集流体上；
实施例6：
与实施例1不同之处在于，粘结剂由1wt％聚四氟乙烯和1wt％偏聚氟乙烯组成；
实施例7：该极片为负极极片
负极片制备：将97wt％石墨、2wt％聚四氟乙烯、1wt％导电炭黑加入分散设备中进行充分干混，得到分散均匀的负极材料。将上述负极料加入到气流磨设备中，给料速度 设置为150g/min、时间设置为25min，进行充分分散以及聚四氟乙烯粘结剂的纤维化，得到面团状的负极材料；将负极材料经螺杆泵挤出辊压得到活性物质层膜片。最后将制得的活性物质层膜片经过多级热压延复合到不含胶层的集流体上制成负极片。活性物质层膜片的厚度为100微米。第一侧边与活性物质层的背离集流体的一侧表面之间的距离为活性物质层的总厚度的5％，第二侧边与活性物质层的靠近集流体的一侧表面之间的距离为活性物质层的总厚度的7％；第三侧边与活性物质层11的背离集流体10的一侧表面之间的距离为活性物质层总厚度的45％，第四侧边与活性物质层11的靠近集流体10的一侧表面之间的距离为活性物质层总厚度的49％。
实施例8：
参照实施例1进行，所不同的是：将制得的活性物质层膜片经过多级热压延复合到含有胶层(粘结层包括聚乙烯和导电炭黑，二者的质量比为7:3)的集流体上制成正极片。活性物质层的膜片的厚度为100微米，粘结层厚度为1微米。
实施例9：
参照实施例7进行，所不同的是：将制得的活性物质层膜片经过多级热压延复合到含有胶层(粘结层包括聚乙烯和导电炭黑，二者的质量比为7:3)的集流体上制成负极片。活性物质层膜片的厚度为100微米，粘结层厚度为1微米。
对比例1a
对比例1a制作的极片为正极片，参照实施例1进行，所不同的是：
将94wt％钴酸锂、5wt％偏聚氟乙烯、1wt％导电碳溶于N-甲基吡咯烷酮中，搅拌均匀制成正极浆料后均匀涂覆在正极集流体铝箔上，经过烘干、辊压、分切后制成正极片1a。
对比例1b
对比例1b制作的极片为负极片，参照实施例7进行，所不同的是：
将93wt％人造石墨、0.8wt％导电炭黑、4.2wt％偏聚氟乙烯、2wt％羧甲基纤维素钠加入到NMP中搅拌均匀制备成负极浆料，将制备的负极浆料均匀涂布在负极集流体铜箔上，经烘干、辊压、分切后制备成负极极片1b。
测试例
将上述实施例和对比例所得的极片分别进行如下测试，获得测试结果如表1所示：
(1)掉粉情况测试
固定一块极片的两端，选定一定的弯折半径(例如10mm、15mm、20mm)，进行正反交错弯折(即正向弯折一次，反向弯折一次)，连续正反交错弯折200次后，目视极片是否有掉粉，随后进行干燥并称重，该重量与弯折前的极片进行对比，从而计算重量保持率，确定是否掉粉。
(2)开裂情况测试
随机选取一处极片位置，将极片烘干后使用CCD相机观察并记录极片表面裂纹数量。
表1
如表1所示，实施例1-7的第三区域的氟元素的质量百分数大于第一区域或第二区域中至少一个区域的氟元素的质量百分数。而对比例1a和对比例1b的第三区域的氟元素的质量百分数均小于对应极片的第一区域和第二区域的氟元素的质量百分数，且对比例1a和对比例1b的第一区域和第二区域的氟元素的质量百分数差额大于3，导致对比组的活性物质层的氟元素分布不均匀，使得活性物质层所受的应力不均匀，出现掉粉和开裂的现象。
实施例1、2、3的活性物质层的厚度逐渐增大，如实施例2，当活性物质层的厚度为300微米时，第一区域和第二区域之间的氟元素的质量百分数的差值逐渐增大，当活性物质层的厚度提升至1000微米时，第三区域与第一区域和/或第二区域的氟元素的质 量百分数之间的差值明显增大，第三区域与第一区域和/或第二区域之间的应力分布不均，导致极片轻微掉粉，开裂。
对比实施例1、5、6可知，粘结剂从PTFE更换为PVDF或者PVDF和PTFE时，由于PVDF呈点状分布粘接，粘结性变差，导致极片轻微开裂，容易掉粉。
实施例1和实施例7的第一区域的氟元素的质量百分数与第二区域的氟元素的质量分数之间的差值大于0，小于等于0.5wt％，且实施例1和实施例7的第三区域的氟元素的质量百分数与第一区域和/或第二区域的氟元素的质量分数之间的差额小于等于1.5wt％，即，使得氟元素在活性物质层的顶面、中间区域、底面的质量百分数接近，意味着氟元素在活性物质层的厚度方向上得到均匀分布，使得极片在厚度方向上的受到的应力均匀分布，中间区域的活性物质层受到的应力较小，极片不会出现掉粉或者开裂的情况，从而提高电极片的稳定性和循环寿命。
需要说明的是，在本文中，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法、物品或者装置不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法、物品或者装置所固有的要素。在没有更多限制的情况下，由语句“包括一个……”限定的要素，并不排除在包括该要素的过程、方法、物品或者装置中还存在另外的相同要素。此外，需要指出的是，本申请实施方式中的方法和装置的范围不限按示出或讨论的顺序来执行功能，还可包括根据所涉及的功能按基本同时的方式或按相反的顺序来执行功能，例如，可以按不同于所描述的次序来执行所描述的方法，并且还可以添加、省去、或组合各种步骤。另外，参照某些示例所描述的特征可在其他示例中被组合。
以上仅为本公开的较佳实施例而已，并不用以限制本公开，凡在本公开的精神和原则之内，所作的任何修改、等同替换等，均应包含在本公开的保护范围之内。

Claims (15)

  1. 一种极片，其特征在于，包括集流体，所述集流体的至少一个表面设有活性物质层；
    所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域内的活性物质层的总质量的质量百分数之间的差值大于0，且小于等于3％；
    所述第一区域为所述活性物质层的背离所述集流体的一侧表面与第一侧边之间的区域；
    所述第二区域为所述活性物质层的靠近所述集流体的一侧表面与第二侧边之间的区域；
    所述第一侧边与所述活性物质层的背离所述集流体的一侧表面之间的距离为所述活性物质层的总厚度的1-10％；
    所述第二侧边与所述活性物质层的靠近所述集流体的一侧表面之间的距离为所述活性物质层的总厚度的1-10％。
  2. 根据权利要求1所述的极片，其特征在于，所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域内的活性物质层的总质量的质量百分数之间的差值大于0，且小于等于1％；
    优选地，所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域内的活性物质层的总质量的质量百分数之间的差值大于0，且小于等于0.5％。
  3. 根据权利要求1或2所述的极片，其特征在于，所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数为0-18wt％；
    和/或，所述活性物质层在第二区域内的氟元素占所述第二区域的活性物质层的总质量的质量百分数为0-18wt％。
  4. 根据权利要求1或2所述的极片，其特征在于，所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数为0.5-10wt％；
    和/或；所述活性物质层在第二区域内的氟元素占所述第二区域的活性物质层的总质量的质量百分数为0.5-10wt％。
  5. 根据权利要求1-4任一项所述的极片，其特征在于，所述活性物质层包括第三区域，所述第三区域为第三侧边和第四侧边之间的区域；
    所述第三侧边与所述活性物质层的背离所述集流体的一侧表面之间的距离为所述活性物质层的总厚度的45％-50％；
    所述第四侧边与所述活性物质层的靠近所述集流体的一侧表面之间的距离为所述活性物质层的总厚度的45％-50％；
    所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数大于所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数；
    和/或，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数大于所述活性物质层在第二区域内的氟元素占所述第二区域内的活性物质层的总质量的质量百分数。
  6. 根据权利要求5所述的极片，其特征在于，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数与所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数之间的差值≤3％；
    和/或，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总 质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域的活性物质层的总质量的质量百分数之间的差值≤3％。
  7. 根据权利要求5或6所述的极片，其特征在于，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数与所述活性物质层在第一区域内的氟元素占所述第一区域的活性物质层的总质量的质量百分数之间的差值≤1.5％；
    和/或，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数与所述活性物质层在第二区域内的氟元素占所述第二区域的活性物质层的总质量的质量百分数之间的差值≤1.5％。
  8. 根据权利要求5-7任一项所述的极片，其特征在于，所述活性物质层在第三区域内的氟元素占所述第三区域的活性物质层的总质量的质量百分数为0-21wt％，优选为1-12wt％。
  9. 根据权利要求1-8任一项所述的极片，其特征在于，所述活性物质层包括第一粘结剂和活性材料；
    所述活性物质层在所述第一区域内的第一粘结剂和活性材料的质量百分数比与所述活性物质层在第二区域内的第一粘结剂和活性材料的质量百分数比之间的差值≤9％，优选为差值≤5％。
  10. 根据权利要求9所述的极片，其特征在于，所述活性物质层在第一区域内的第一粘结剂和活性材料的质量百分数比为0.5-10％；
    和/或，所述活性物质层在第二区域内的第一粘结剂和活性材料的质量百分数比为0.5-10％。
  11. 根据权利要求9或10所述的极片，其特征在于，所述第一粘结剂包括纤维状的PTFE、PVDF、ETEF、FEP、PVP、PEO、CMC、SBR、PAA、PP、PE、PAN的至少一种；
    和/或，所述活性材料包括LiCoO2、LiMn2O4、LiMnO2、LiNiO2、LiFePO4、LiMnPO4、LiCoxNi1-xO2(0≤x≤1)、LiCoxNi1-x-yAlyO2(0≤x≤1，0≤y≤1)中的至少一种；
    和/或，所述活性材料包括人造石墨、天然石墨、软碳、硬碳、中间相碳微球，Si、SiOx、Si-C、SiOx-C中的至少一种。
  12. 根据权利要求1-11任一项所述的极片，其特征在于，所述集流体和所述活性物质层之间还设有粘结层，所述粘结层包括第二粘结材料和导电剂。
  13. 根据权利要求12所述的极片，其特征在于，所述第二粘结材料包括PVDF、SBR、PP、EVA热熔胶、PO热熔胶、PUR热熔胶、TPR类材料、TPU热熔胶、聚酰胺PA、聚酯PES、聚乙烯和聚酯酰胺PEA中的至少一种；
    和/或，所述导电剂包括导电炭黑、碳纳米管、石墨烯、导电炭纤维和导电石墨中的至少一种。
  14. 根据权利要求12或13所述的极片，其特征在于，所述活性物质层的厚度大于或等于20μm，且小于或等于3mm；优选地，所述活性物质层的厚度大于或等于30μm，且小于或等于300μm；
    和/或，所述粘结层的厚度大于或等于500nm，且小于或等于3μm；
    和/或，所述活性物质层与所述粘结层的厚度之比大于或等于10，且小于或等于6000，优选地，所述活性物质层与所述粘结层的厚度之比大于或等于30，且小于或等于300。
  15. 一种电化学装置，其特征在于，包括正极极片、负极极片和位于所述正极极片和负极极片之间的隔膜；
    所述正极极片和/或所述负极极片为如权利要求1至14中任一项所述的极片。
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