WO2022206877A1 - 电化学装置及电子装置 - Google Patents

电化学装置及电子装置 Download PDF

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WO2022206877A1
WO2022206877A1 PCT/CN2022/084268 CN2022084268W WO2022206877A1 WO 2022206877 A1 WO2022206877 A1 WO 2022206877A1 CN 2022084268 W CN2022084268 W CN 2022084268W WO 2022206877 A1 WO2022206877 A1 WO 2022206877A1
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active material
material layer
pole piece
positive electrode
electrode active
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PCT/CN2022/084268
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English (en)
French (fr)
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付奥
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宁德新能源科技有限公司
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Priority to EP22711858.5A priority Critical patent/EP4089760A1/en
Priority to US17/741,295 priority patent/US20220328811A1/en
Publication of WO2022206877A1 publication Critical patent/WO2022206877A1/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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present application relates to the field of electrochemical technology, and in particular, to an electrochemical device and an electronic device.
  • Electrochemical devices represented by lithium-ion batteries have the characteristics of high voltage, high energy density, long cycle life and no pollution, and are widely used in consumer electronic products such as mobile phones, computers, and digital cameras. With the development of electronic products, the requirements for electrochemical devices such as lithium-ion batteries are getting higher and higher, especially in terms of high energy density and cycle life.
  • ions such as lithium ions
  • the winding structure of the cell such as local uneven compaction or local CB (Cell balance, directly opposite The ratio of negative electrode capacity to positive electrode capacity) is not uniform, which leads to the problem of uneven distribution of ion transport kinetics in the battery cell during the cycle. In the region with insufficient kinetics, it will lead to lithium precipitation in the battery cell, and lithium precipitation will reduce the battery cell. cycle performance.
  • the present application provides an electrochemical device and an electronic device, so as to improve the problem of lithium precipitation from a pole piece.
  • An electrochemical device provided by the present application includes an electrode assembly, and the electrode assembly includes: a first pole piece, a second pole piece, and a separator disposed between the first pole piece and the second pole piece.
  • the first pole piece includes an active material layer
  • the active material layer includes at least one first active material layer and at least one second active material layer arranged along the length direction of the pole piece, and the lithium ion diffusion rate of the first active material layer is greater than that of the second active material layer. Lithium ion diffusion rate of the material layer.
  • the electrode assembly is formed by winding a first pole piece, a second pole piece and a separator, and the electrode assembly includes a flat area and a corner area; the first pole piece is a positive pole piece, and the first positive active material layer is the first pole piece.
  • a positive electrode active material layer, the second positive electrode active material layer is the second positive electrode active material layer; at least part of the first active material layer is located in the plane area, and at least part of the second active material layer is located in the corner area.
  • the first positive electrode active material layer includes a first positive electrode conductive agent
  • the second positive electrode active material layer includes a second positive electrode conductive agent
  • the mass percentage of the first positive electrode conductive agent in the first positive electrode active material layer is greater than or It is equal to the mass percentage content of the second positive electrode conductive agent in the second positive electrode active material layer.
  • the mass percentage content of the first positive electrode conductive agent in the first positive electrode active material layer is 0.5% to 5.5%, and the mass percentage content of the second positive electrode conductive agent in the second positive electrode active material layer is 0.5% to 5%.
  • the compaction density of the second positive electrode active material layer is greater than or equal to the compaction density of the first positive electrode active material layer.
  • the electrode assembly is formed by winding the first pole piece, the second pole piece and the isolation film, and the electrode assembly includes a flat area and a corner area; the first pole piece is a negative pole piece, and the first active material layer is The first negative electrode active material layer and the second negative electrode active material layer are the second negative electrode active material layer; at least part of the first negative electrode active material layer is located in the corner area, and at least part of the second negative electrode active material layer is located in the plane area.
  • the second negative electrode active material layer includes a second negative electrode conductive agent
  • the first negative electrode active material layer includes a first negative electrode conductive agent
  • the mass percentage content of the first negative electrode conductive agent in the first negative electrode active material layer is greater than or It is equal to the mass percentage content of the second negative electrode conductive agent in the second negative electrode active material layer.
  • the first negative electrode active material layer includes a first negative electrode active material
  • the second negative electrode active material layer includes a second negative electrode active material
  • the first negative electrode active material and/or the second negative electrode active material includes a gram capacity of 300mAh/g. to 380mAh/g of graphite.
  • the first pole piece includes a plurality of first active material layers and a plurality of second active material layers, and the plurality of first active material layers and the plurality of second active material layers are spaced apart along the length direction of the pole piece.
  • An electronic device provided by the present application includes any one of the above electrochemical devices.
  • one polar pole piece includes an active material layer, and the active material layer includes at least one first active material layer and at least one second active material layer arranged along the length direction of the pole piece , the lithium ion diffusion rate of the first active material layer is greater than the lithium ion diffusion rate of the second active material layer, so that the lithium ion kinetic performance of the first active material layer is better than the lithium ion kinetic performance of the second active material layer, so that it can be Reduce the occurrence of lithium precipitation and improve the cycle performance of the battery.
  • FIG. 1 is a schematic structural diagram of a first electrochemical device provided in an embodiment of the present application.
  • FIG. 2 is a schematic structural diagram of a second electrochemical device provided in an embodiment of the present application.
  • FIG. 3 is a cross-sectional view of a wound battery core provided by an embodiment of the present application.
  • Fig. 4 is a first group of cell cycle performance curves provided by the embodiment of the present application.
  • FIG. 6 is a cycle performance curve diagram of a third group of cells provided by an embodiment of the present application.
  • the electrochemical device includes an electrode assembly, and the electrode assembly includes a first pole piece 11 , a second pole piece 12 , and a first pole piece 11 and a second pole piece 12 .
  • the electrode assembly may be a wound structure, and the electrochemical device shown in FIG. 2 can be obtained after the first pole piece 11 , the second pole piece 12 and the separator 13 are wound.
  • Electrochemical devices can be electrode assemblies or batteries containing electrode assemblies and electrolytes, such as secondary batteries (such as lithium ion secondary batteries, sodium ion batteries, magnesium ion batteries, etc.), primary batteries (such as lithium primary batteries) etc.) etc., but not limited thereto.
  • secondary batteries such as lithium ion secondary batteries, sodium ion batteries, magnesium ion batteries, etc.
  • primary batteries such as lithium primary batteries etc.
  • the type of the separator 13 in the embodiment of the present application can be any porous separator that can be used in electrochemical devices, such as glass fiber separator, non-woven separator, polyethylene separator, polypropylene separator A separator, a polyvinylidene fluoride separator, and a multilayer composite film formed by one or more of them, but not limited thereto.
  • the isolation film 13 is arranged between the first pole piece 11 and the second pole piece 12, which can be used to isolate the first pole piece 11 and the second pole piece 12, and prevent the electrons in the electrochemical device from passing through, so as to facilitate the electrolyte. ions pass through.
  • the first pole piece 11 may be a positive pole piece or a negative pole piece.
  • the polarity of the second pole piece 12 is opposite to that of the first pole piece 11 .
  • the first pole piece 11 is a positive pole piece
  • the second pole piece 12 is a negative pole piece.
  • the first pole piece 11 is a negative pole piece
  • the second pole piece 12 is a positive pole piece.
  • the first pole piece 11 includes an active material layer.
  • the active material layer includes at least one first active material layer 111 and at least one second active material layer 112 arranged along the length direction of the pole piece (for example, the direction x shown by the arrow in FIG. 1 ).
  • the active material layers 112 may have different dimensions (length, width and/or coating thickness) and compaction densities.
  • first active material layer 111 there is only one first active material layer 111 and one second active material layer 112 .
  • first active material layers 111 and second active material layers 112 there may be multiple first active material layers 111 and second active material layers 112 .
  • the plurality of first active material layers 111 and the plurality of second active material layers 112 are arranged at intervals along the length direction of the pole piece.
  • the plurality of first active material layers 111 have different dimensions (length, width and/or coating thickness) and compaction densities; the plurality of second active material layers 112 have different dimensions.
  • the lithium ion diffusion rate of the first active material layer 111 is higher than that of the second active material layer 112, that is, the lithium ion kinetic performance of the first active material layer 111 is better than that of the second active material layer 112 (lithium ion kinetic performance).
  • the ion diffusion rate characterizes the kinetic performance), so that the lithium binding amount is small, which can reduce the occurrence of lithium precipitation.
  • the lithium ion diffusion rate of the first active material layer 111 is greater than or equal to 1.2 times the lithium ion diffusion rate of the second active material layer 112 .
  • the diffusion rate of lithium ions of the first active material layer 111 is 2 to 3 times higher than the diffusion rate of lithium ions of the second active material layer 112 .
  • the lithium ion diffusion rate of an active material layer can be used to characterize the kinetic properties of the active material layer.
  • the first active material layer 111 can be ensured
  • the transport of lithium ions in an active material layer 111 reduces the occurrence of lithium deposition in the electrochemical device (electrode assembly).
  • the lithium ion diffusion rate of the first active material layer 111 may be in the range of 1.0 ⁇ 10 ⁇ 8 cm 2 /s to 2.0 ⁇ 10 ⁇ 8 cm 2 /s.
  • the lithium ion diffusion rate of the second active material layer 112 may be in the range of 5.0 ⁇ 10 ⁇ 9 cm 2 /s to 7.0 ⁇ 10 ⁇ 9 cm 2 /s.
  • the first active material layer 111 , the second active material layer 112 can be changed by changing the conductive agent content in the first active material layer 111 , the second active material layer 112 without losing energy density Lithium ion diffusion rate of 112. And/or, by adjusting the compaction density of the active materials on the first active material layer 111 and the second active material layer 112, and changing the lithium ion diffusion rate of the first active material layer 111 and the second active material layer 112, it is possible to further reduce The occurrence of lithium precipitation.
  • Lithium ion diffusion rate refers to the degree to which lithium ions diffuse in a particular material.
  • the lithium ion diffusion rate can be measured using a galvanostatic intermittent titration technique (GITT) under charge/discharge conditions.
  • GITT galvanostatic intermittent titration technique
  • SOC state of charge
  • the electrode assembly obtained by winding will form a plane area 21 and a corner area 22 (as shown in FIG. 2 ), and the first active material layer 111 and the second active material layer 112 may be respectively disposed on the plane of the electrode assembly Zone 21 and Corner Zone 22.
  • the first pole piece 11 may include a plurality of first active material layers 111 (eg, a first positive active material layer or a second positive active material layer) and a plurality of second active material layers 112,
  • the plurality of first active material layers 111 and the plurality of second active material layers 112 are arranged at intervals along the length direction of the pole piece, so that the flat region 21 and the corner region 22 of the electrode assembly obtained by winding can have a plurality of first The active material layer 111 or the second active material layer 112 . Examples are given below:
  • the first active material layer 111 is the first positive active material layer
  • the second active material layer 112 is the second positive active material layer
  • at least part of the first active material layer 111 is located on the electrode
  • at least part of the second active material layer 112 is located in the corner region 22 of the electrode assembly.
  • the first active material layer 111 is the first negative active material layer
  • the second active material layer 112 is the second negative active material layer
  • at least part of the first negative active material layer is located in the In the corner region 22 of the electrode assembly
  • at least part of the second negative electrode active material layer is located in the plane region 21 of the electrode assembly.
  • the thickness of the corner region 22 of the electrochemical device is smaller than the thickness of the planar region 21 .
  • the thickness of the corner region 22 is 95%, 90%, 85%, or 80% of the thickness of the plane region 21 .
  • the positive electrode and the negative electrode of the electrochemical device adopt the structure disclosed in this application.
  • the first active material layer 111 is located in the plane region 21
  • the first active material layer 111 of the negative pole piece is located in the corner region 22 .
  • the first pole piece 11 is a positive pole piece
  • the positive pole piece can be prepared according to a conventional method in the art, for example, a positive pole piece can be prepared by using a batch coating technique.
  • the first active material layer 111 on the positive electrode plate is the first positive active material layer
  • the second active material layer 112 is the second positive active material layer.
  • the positive active materials eg, the first positive active material, the second positive active material
  • a positive electrode active material for a lithium ion secondary battery may include one or more of lithium transition metal composite oxides, composite oxides obtained by adding other transition metals or non-transition metals or non-metals to lithium transition metal composite oxides kind.
  • the transition metal may be one or more of Mn, Fe, Ni, Co, Cr, Ti, Zn, V, Al, Zr, Ce and Mg.
  • the positive electrode active material may be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium containing olivine structure
  • phosphates such as LiMn 2 O 4 , LiNiO 2 , LiCoO 2 , LiNi 1-y Co y O 2 (0 ⁇ y ⁇ 1), LiNi a CobAl 1-ab O 2 (0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, 0 ⁇ a+b ⁇ 1), LiMn 1-mn Ni m Con O 2 (0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1, 0 ⁇ m+n ⁇ 1),
  • LiMPO 4 M may be one or more of Fe, Mn, Co
  • Li 3 V 2 (PO 4 ) 3 LiMPO 4 (M may be one or more of Fe, Mn, Co) and Li 3 V 2 (PO 4 ) 3 .
  • LiMn 1-mn Ni m ConO 2 is, for example, LiMn 0.1 Ni 0.8 Co 0.1 O 2 , LiMn 0.3 Ni 0.5 Co 0.2 O 2 , LiMn 0.2 Ni 0.6 Co 0.2 O 2 , LiMn 1/3 Ni 1/3 Co 1/3 O 2 and so on.
  • the positive electrode active material layer further includes a binder.
  • the binder may be styrene butadiene rubber (SBR), water-based acrylic resin, sodium carboxymethyl cellulose (CMC-Na), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), one or more of ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene butadiene rubber
  • CMC-Na sodium carboxymethyl cellulose
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PVVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the positive electrode active material layer further includes a conductive agent.
  • the first positive electrode active material layer includes a first positive electrode conductive agent
  • the second positive electrode active material layer includes a second positive electrode conductive agent.
  • the embodiments of the present application do not limit the types of conductive agents.
  • the first positive electrode conductive agent and the second positive electrode conductive agent may each independently include one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers one or more.
  • the mass percentage content of the first positive electrode conductive agent in the first positive electrode active material layer is 0.5% to 5.5%, optionally, 1% to 2.5%.
  • the mass percentage content of the second positive electrode conductive agent in the second positive electrode active material layer is 0.5% to 5%, optionally, 1% to 2%.
  • the mass percentage content of the first positive electrode conductive agent in the first positive electrode active material layer is greater than or equal to the mass percentage content of the second positive electrode conductive agent in the second positive electrode active material layer, which can make coating the first positive electrode active material layer.
  • the lithium ion kinetics of the first active material layer 111 is better than that of the second active material layer 112 coated with the second positive electrode active material layer, so that the occurrence of lithium deposition can be reduced.
  • the compaction density of the second cathode active material layer is greater than or equal to the compaction density of the first cathode active material layer. It can be appreciated that the greater the compaction density, the lower the kinetics (diffusion rate) of lithium ions, so in some examples, the compaction density of the second cathode active material layer (at the corner region 22 ) is greater than or equal to the first The compaction density of the positive electrode active material layer (in the plane region 21 ), at this time, the lithium ion kinetic performance of the first positive electrode active material layer (in the plane region 21 ) is poor, and the diffusion rate of lithium ions is small, which can improve the first Lithium deposition at the position of the negative electrode pole piece corresponding to a positive electrode active material layer.
  • the second positive electrode active material layer may be disposed at a corner of the electrode assembly to reduce lithium deposition of the negative electrode sheet at the corner.
  • the first pole piece 11 is a negative pole piece
  • the negative pole piece can be prepared according to a conventional method in the art, for example, a positive pole piece can be prepared by a batch coating technique.
  • the first active material layer 111 on the negative pole piece is the first negative active material layer
  • the second active material layer 112 is the second negative active material layer.
  • the negative active materials eg, the first negative active material, the second negative active material
  • negative active materials for lithium ion secondary batteries may include metallic lithium, natural graphite, artificial graphite, mesophase microcarbon beads (abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 ⁇ x ⁇ 2), one or more of Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , spinel-structured lithium titanate and Li-Al alloy.
  • the first negative active material and the second negative active material include graphite having a gram capacity of 300 mAh/g to 380 mAh/g.
  • the first negative active material and the second negative active material include graphite with a gram capacity of 340 mAh/g to 370 mAh/g.
  • the first negative active material and the second negative active material are the same kind of graphite.
  • the negative electrode active material layer further includes a binder, and the embodiment of the present application does not limit the type of the binder.
  • the binder may be styrene butadiene rubber (SBR), water-based acrylic resin, sodium carboxymethyl cellulose (CMC-Na), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), one or more of ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • the negative electrode active material layer further includes a conductive agent, and the type of the conductive agent is not limited in the embodiment of the present application.
  • the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the mass percentage content of the first negative electrode conductive agent in the first negative electrode active material layer is 0.5% to 5.5%, optionally, 1% to 2.5%.
  • the mass percentage content of the second negative electrode conductive agent in the second negative electrode active material layer is 0.5% to 5%, optionally, 1% to 2%.
  • the mass percentage content of the first negative electrode conductive agent in the first negative electrode active material layer is greater than or equal to the mass percentage content of the second negative electrode conductive agent in the second negative electrode active material layer, which can make the lithium content of the first negative electrode active material layer
  • the ion kinetics are superior to the lithium ion kinetics of the second negative electrode active material layer, so that the occurrence of lithium segregation in corner regions can be reduced.
  • Example 1 to Example 4, Comparative Example 1, Example 5 to Example 7, Comparative Example 2.
  • Preparation of positive electrode sheet using aluminum foil as the positive electrode current collector, the positive electrode active material lithium cobaltate, conductive agent conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone in a weight ratio of 97.5:1.5:1.0 (NMP) solution, a first positive electrode slurry is formed.
  • the positive electrode active material lithium cobaltate, conductive agent conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone (NMP) solution in a weight ratio of 97.5:1.4:1.1 to form a second positive electrode slurry.
  • the first positive electrode slurry and the second positive electrode slurry were coated on the positive electrode current collector with a coating thickness of 40 ⁇ m, and each coating width was 6 mm.
  • a first positive electrode active material layer and a second positive electrode active material were obtained. Then, after drying, cold pressing, and cutting, a positive electrode sheet is obtained.
  • negative electrode pole piece graphite, sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene rubber are dissolved in deionized water in a weight ratio of 97.7:1.3:1 to form a negative electrode slurry.
  • a 10 ⁇ m-thick copper foil was used as the current collector of the negative electrode plate, and the negative electrode slurry was coated on the negative electrode current collector. After drying, the negative pole piece is obtained after cutting. Among them, the OI value of graphite is 6.
  • the isolation film substrate is polyethylene (PE) with a thickness of 8 ⁇ m, and 2 ⁇ m alumina ceramic layers are coated on both sides of the isolation film substrate, and finally, 2.5 ⁇ m alumina ceramic layers are coated on both sides of the coated ceramic layer. mg/cm 2 binder polyvinylidene fluoride (PVDF), dried.
  • PE polyethylene
  • PVDF polyvinylidene fluoride
  • EC ethylene carbonate
  • PC propylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • Preparation of lithium ion battery stack the positive pole piece, the separator and the negative pole piece in order, so that the separator is in the middle of the positive pole piece and the negative pole piece to play a role of isolation, and coil to obtain the electrode assembly.
  • the first positive electrode active material is located on the plane region of the positive electrode plate
  • the second positive electrode active material layer is located on the corner region of the positive electrode plate.
  • the electrode assembly is placed in the outer packaging aluminum-plastic film, and after dehydration at 80°C, the above electrolyte is injected and packaged, and the lithium ion battery is obtained through the process of forming, degassing, and trimming.
  • Example 1 to Example 4 Comparative Example 1 is different from Example 1 in that when preparing the second positive electrode active material layer, the mass ratio of the positive electrode active material lithium cobaltate, the conductive agent conductive carbon black, and the polyvinylidene fluoride is different.
  • the details are as follows in Table 1:
  • the formed lithium-ion battery was charged to 4.2V at a constant current of 3C at 25°C, and then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, it was discharged to 2.8V at 1C, and the charge-discharge cycle was performed for 1000 cycles; The discharge capacity of one cycle is recorded as D0, and the discharge capacity of the 1000th cycle is recorded as D1;
  • the lithium ion content of the second positive electrode active material layer can be reduced. Diffusion rate, thereby helping to reduce the polarization of the negative electrode piece opposite to the second positive electrode active material layer, and improving the lithium evolution and cycle performance of the electrochemical device.
  • the difference in percentage content of the conductive agent in the second cathode active material layer and the first cathode active material layer decreases, the difference in the lithium ion diffusion rates at the positions of the two parts also decreases. is small, and the degree of improvement in the cycle performance of the electrochemical device is also reduced.
  • Comparative Example 2 is different from Example 1 in that: when preparing the second positive electrode active material layer, the mass ratio of the positive electrode active material lithium cobalt oxide, the conductive agent conductive carbon black, and the polyvinylidene fluoride When making the first positive electrode active material layer, the mass ratios of the positive electrode active material lithium cobaltate, the conductive agent conductive carbon black, and the polyvinylidene fluoride are the same, which are all 97.5:1.5:1.0.
  • Examples 5 to 6, the compaction of the first positive electrode active material layer and the second positive electrode active material layer of Comparative Example 2 are as follows: Table 2:
  • the lithium ion diffusion rate of the second positive electrode active material layer can be reduced, so that It is helpful to reduce the polarization of the negative electrode sheet opposite to the second positive electrode active material layer, and improve the lithium deposition and cycle performance of the electrochemical device.
  • the difference in the compaction density between the second positive electrode active material layer and the first positive electrode active material layer decreases, the difference in the lithium ion diffusion rates at the locations where these two parts are located also decreases, and further The degree of improvement in the cycle performance of the electrochemical device is also reduced.
  • the preparation of the positive electrode plate using aluminum foil as the positive electrode current collector of the positive electrode, the positive electrode active material lithium cobaltate, the conductive agent conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone in a weight ratio of 97.8:1.4:0.8 (NMP) solution, a slurry of a positive electrode active material layer was formed, and the slurry was coated on a positive electrode current collector with a coating thickness of 80 ⁇ m to obtain a positive electrode active material layer. Then, after drying, cold pressing, and cutting, a positive electrode sheet is obtained.
  • NMP N-methylpyrrolidone
  • Preparation of negative pole piece graphite, sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene rubber are dissolved in deionized water in a weight ratio of 95:2:1:2 to form a first negative electrode slurry.
  • the first negative electrode slurry and the second negative electrode slurry were coated on the current collector of the negative electrode pole piece by means of interval coating, with a coating thickness of 120 ⁇ m and a coating width of 6 mm respectively to obtain a first negative electrode active material layer. and the second negative electrode active material layer. After drying, the negative pole piece is obtained after cutting.
  • the isolation film substrate is polyethylene (PE) with a thickness of 8 ⁇ m, and 2 ⁇ m alumina ceramic layers are coated on both sides of the isolation film substrate, and finally, 2.5 ⁇ m alumina ceramic layers are coated on both sides of the coated ceramic layer. mg/cm 2 binder polyvinylidene fluoride (PVDF), dried.
  • PE polyethylene
  • PVDF polyvinylidene fluoride
  • EC ethylene carbonate
  • PC propylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • Preparation of lithium ion battery stack the positive pole piece, the separator and the negative pole piece in order, so that the separator is in the middle of the positive pole piece and the negative pole piece to play a role of isolation, and coil to obtain the electrode assembly.
  • the electrode assembly is placed in the outer packaging aluminum-plastic film, and after dehydration at 80°C, the above electrolyte is injected and packaged, and the lithium ion battery is obtained through the process of forming, degassing, and trimming.
  • Example 8 to Example 10 the difference between Comparative Example 3 and Example 1 is: when preparing the first negative electrode active material layer, the negative electrode active material graphite, sodium carboxymethyl cellulose (CMC) and the binder SBR quality ratio is different.
  • CMC carboxymethyl cellulose
  • Example 8 to Example 10 the conductive agent content in the first negative electrode active material layer is gradually reduced, and the capacitance retention rate corresponding to Example 8 to Example 10 is Example 10>Example 9>Example 8 .
  • the lithium ion diffusion rate of the first negative electrode active material layer can be increased. It helps to reduce the polarization of the first negative electrode active material layer, and improves the lithium evolution and cycle performance of the electrochemical device.
  • the difference in mass percentage content of the conductive agent in the first negative electrode active material layer and the second negative electrode active material layer decreases, the difference in the lithium ion diffusion rates at the positions of these two parts also decreases. will decrease, and thus the degree of improvement in the cycle performance of the electrochemical device will also decrease.
  • electrochemical devices eg, lithium ion batteries
  • electrochemical devices eg, lithium ion batteries
  • Other methods commonly used in the art may be employed without departing from the disclosure of the present application.
  • Embodiments of the present application also provide electronic devices including the above electrochemical devices.
  • the electronic device in the embodiment of the present application is not particularly limited, and it may be used in any electronic device known in the prior art.
  • electronic devices may include, but are not limited to, notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, assisted bicycles, bicycles, Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large-scale household storage batteries and lithium-ion capacitors, etc.

Abstract

本申请公开一种电化学装置及电子装置，包括电极组件，电极组件包括第一极片、第二极片、以及设置于第一极片和第二极片之间的隔离膜，第一极片包括沿极片长度方向设置的第一活性材料层和第二活性材料层，第一活性材料层的锂离子扩散速率大于第二活性材料层的锂离子扩散速率，即第一活性材料层的锂离子动力学性能优于第二活性材料层锂离子动力学性能，可以减少析锂情况的发生。

Description

电化学装置及电子装置
本申请要求于2021年03月31日提交中国专利局、申请号为202110353452.8、发明名称为“电化学装置及电子装置”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电化学技术领域，具体涉及一种电化学装置及电子装置。
背景技术
以锂离子电池为代表的电化学装置具有高电压、高能量密度、循环寿命长以及无污染等特点，被广泛应用于手机、电脑、数码相机等消费类电子产品中。随着电子产品的发展，人们对锂离子电池等电化学装置的要求也越来越高，尤其是在高能量密度和循环寿命方面。
在充放电过程中，离子(例如锂离子)会在极片上进行不断的脱嵌和嵌入，但是由于电芯卷绕构的问题，例如局部压密不均匀或局部CB(Cell balance，正对面的负极容量与正极容量的比值)不均匀，导致电芯在循环过程中会出现离子传输动力学分布不均匀的问题，在动力学不足的区域就会导致电芯析锂，析锂会降低电芯的循环性能。
发明内容
鉴于此，本申请提供一种电化学装置及电子装置，以改善极片析锂的问题。
本申请提供的一种电化学装置，包括电极组件，电极组件包括：第一极片、第二极片和设置于第一极片和第二极片之间的隔离膜。第一极片包括活性材料层，活性材料层包括沿极片长度方向设置的至少一个第一活性材料层和至少一个第二活性材料层，第一活性材料层的锂离子扩散速率大于第二活性材料层的锂离子扩散速率。
可选地，电极组件由第一极片、第二极片和隔离膜卷绕而成，电极组件包括平面区和拐角区；第一极片为正极极片，第一正极活性材料层为第一正极活性材料层，第二正极活性材料层为第二正极活性材料层；至少部分第一活性材 料层位于平面区，至少部分第二活性材料层位于拐角区。
可选地，第一正极活性材料层包括第一正极导电剂，第二正极活性材料层包括第二正极导电剂，第一正极导电剂在第一正极活性材料层中的质量百分含量大于或等于第二正极导电剂在第二正极活性材料层中的质量百分含量。
可选地，第一正极导电剂在第一正极活性材料层中的质量百分含量为0.5％至5.5％，第二正极导电剂在第二正极活性材料层中的质量百分含量为0.5％至5％。
可选地，第二正极活性材料层的压实密度大于或等于第一正极活性材料层的压实密度。
可选地，电极组件由所述第一极片、第二极片和隔离膜卷绕而成，电极组件包括平面区和拐角区；第一极片为负极极片，第一活性材料层为第一负极活性材料层，第二活性材料层为第二负极活性材料层；至少部分第一负极活性材料层位于拐角区，至少部分第二负极活性材料层位于平面区。
可选地，第二负极活性材料层包括第二负极导电剂，第一负极活性材料层包括第一负极导电剂，第一负极导电剂在第一负极活性材料层中的质量百分含量大于或等于第二负极导电剂在第二负极活性材料层中的质量百分含量。
可选地，第一负极活性材料层包括第一负极活性材料，第二负极活性材料层包括第二负极活性材料，第一负极活性材料和/或第二负极活性材料包括克容量为300mAh/g至380mAh/g的石墨。
可选地，第一极片包括多个第一活性材料层和多个第二活性材料层，多个第一活性材料层和多个第二活性材料层沿极片长度方向间隔设置。
本申请提供的一种电子装置，包括上述任一项电化学装置。
在本申请的电化学装置及电子装置中，其中一个极性的极片包括活性材料层，活性材料层包括沿极片长度方向设置的至少一个第一活性材料层和至少一个第二活性材料层，第一活性材料层的锂离子扩散速率大于第二活性材料层的锂离子扩散速率，使得第一活性材料层的锂离子动力学性能优于第二活性材料层锂离子动力学性能，从而可以减少析锂情况的发生，提升电池的循环性能。
附图说明
图1是本申请实施例提供的第一种电化学装置的结构示意图；
图2是本申请实施例提供的第二种电化学装置的结构示意图；
图3是本申请实施例提供的一种卷绕式电芯的截面图；
图4是本申请实施例提供的第一组电芯循环性能曲线图；
图5是本申请实施例提供的第二组电芯循环性能曲线图；
图6是本申请实施例提供的第三组电芯循环性能曲线图。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合实施例及附图，对本申请技术方案进行清楚地描述。显然，所描述实施例仅是一部分实施例，而非全部。基于本申请中的实施例，在不冲突的情况下，下述各个实施例及其技术特征可以相互组合。
本申请实施例提供了一种电化学装置，请参见图1，该电化学装置包括电极组件，所述电极组件包括第一极片11、第二极片12以及设置于第一极片11和第二极片12之间的隔离膜13。在一些实施例中，电极组件可以为卷绕式结构，第一极片11、第二极片12和隔离膜13卷绕后可以得到如图2所示的电化学装置。
电化学装置可以是电极组件，也可以是包含电极组件和电解液的电池，例如是二次电池(如锂离子二次电池、钠离子电池、镁离子电池等)、一次电池(如锂一次电池等)等，但并不限于此。
本申请实施例对隔离膜13的种类不做具体的限制，可以是能够被用于电化学装置的任意多孔隔离膜，例如玻璃纤维隔离膜、无纺布隔离膜、聚乙烯隔离膜、聚丙烯隔离膜、聚偏二氟乙烯隔离膜以及它们中的一种或多种形成的多层复合膜，但不限于此。隔离膜13设置在第一极片11和第二极片12之间，可用作隔绝第一极片11和第二极片12，并阻止电化学装置内的电子穿过，而便于电解液中的离子通过。
第一极片11可以是正极极片或者负极极片。第二极片12的极性和第一极片11相反。例如，第一极片11为正极极片，第二极片12为负极极片。再例如，第一极片11为负极极片，第二极片12为正极极片。
第一极片11包括活性材料层。活性材料层包括沿极片长度方向(例如图1中箭头所示的方向x)设置的至少一个第一活性材料层111和至少一个第二活性材料层112，第一活性材料层111、第二活性材料层112可以具有不同的尺寸(长度、宽度和/或涂布厚度)以及压实密度。
在一些实例中，例如图1所示的第一极片11上，第一活性材料层111和第二活性材料层112只有一个。
在另一些实例中，例如图3所示的第一极片11上，第一活性材料层111和第二活性材料层112可以有多个。多个第一活性材料层111和多个第二活性材料层112沿极片长度方向间隔设置。可选地，多个第一活性材料层111具有不同的尺寸(长度、宽度和/或涂布厚度)以及压实密度；多个第二活性材料层112具有不同的尺寸。第一活性材料层111的锂离子扩散速率相对第二活性材料层112较高，即，第一活性材料层111的锂离子动力学性能优于第二活性材料层112锂离子动力学性能(锂离子扩散速率表征动力学性能)，这样锂结合量小，可以减小析锂情况的发生。本申请实施例中，第一活性材料层111的锂离子扩散速率大于或等于第二活性材料层112的锂离子扩散速率的1.2倍。
可选地，第一活性材料层111的锂离子扩散速率是第二活性材料层112的锂离子扩散速率的2倍至3倍。活性材料层的锂离子扩散速率可以用于表征该活性材料层的动力学性能。通过在第一极片11上设置锂离子动力学性能不同的第一活性材料层111和第二活性材料层112，并且第一活性材料层111的动力学性能更优，可以保证单位时间内第一活性材料层111内锂离子的传输，减少电化学装置(电极组件)的析锂情况的发生。
在一些场景中，第一活性材料层111的锂离子扩散速率可在1.0×10 -8cm 2/s至2.0×10 -8cm 2/s的范围内。第二活性材料层112的锂离子扩散速率可在5.0×10 -9cm 2/s至7.0×10 -9cm 2/s的范围内。
在一些实例中，在不损失能量密度的情况下，可以通过改变第一活性材料层111、第二活性材料层112上中的导电剂含量，改变第一活性材料层111、第二活性材料层112的锂离子扩散速率。和/或，通过调节第一活性材料层111和第二活性材料层112上活性材料的压实密度，改变第一活性材料层111、第二活性材料层112的锂离子扩散速率，进一步可以减少析锂情况的发生。
锂离子扩散速率是指锂离子在特定材料中扩散的程度。可以在充电/放电状态下使用恒电流间歇滴定技术(GITT)来测量所述锂离子扩散速率。例如，可以在荷电状态(State of charge，SOC)50％的条件下使用GITT测量所述锂离子扩散速率。
在一些实施例中，卷绕得到的电极组件将形成平面区21和拐角区22(如图2所示)，第一活性材料层111和第二活性材料层112可以分别设置在电极组件的平面区21和拐角区22。
在另外的一些示例中，第一极片11上可以包括多个第一活性材料层111(例如，第一正极活性材料层或第二正极活性材料层)和多个第二活性材料层112，这些多个第一活性材料层111和多个第二活性材料层112沿极片长度方向间隔设置，这样可以使得卷绕得到的电极组件的平面区21、拐角区22上可以具有多个第一活性材料层111或第二活性材料层112。下文将进行举例介绍：
当第一极片11为正极极片时，第一活性材料层111为第一正极活性材料层，第二活性材料层112为第二正极活性材料层，至少部分第一活性材料层111位于电极组件的平面区21，至少部分第二活性材料层112位于电极组件的拐角区22。
当第一极片11为负极极片时，第一活性材料层111为第一负极活性材料层，第二活性材料层112为第二负极活性材料层，至少部分第一负极活性材料层位于所述电极组件的拐角区22，至少部分第二负极活性材料层位于所述电极组件的平面区21。
在本申请一些实施例中，电化学装置的拐角区22的厚度小于平面区21的厚度。例如，拐角区22的厚度为平面区21厚度的95％，90％，85％，或者80％。
当然，上述介绍的几种情况都可以同时存在于一个电化学装置中，例如， 电化学装置的正极极片和负极极片采用本申请披露的结构，卷绕后电化学装置上正极极片的第一活性材料层111处于平面区21，负极极片的第一活性材料层111处于拐角区22。
在一些实施例中，第一极片11为正极极片，正极极片可按照本领域常规方法制备，例如采用间歇涂布技术制备正极极片。正极极片上的第一活性材料层111为第一正极活性材料层，第二活性材料层112为第二正极活性材料层。正极活性材料(例如，第一正极活性材料，第二正极活性材料)可以各自独立的包括本领域已知的能够进行活性离子可逆脱嵌的正极活性材料，本申请不做限制。例如用于锂离子二次电池的正极活性材料，可以包括锂过渡金属复合氧化物、锂过渡金属复合氧化物添加其它过渡金属或非过渡金属或非金属得到的复合氧化物中的一种或多种。其中过渡金属可以是Mn、Fe、Ni、Co、Cr、Ti、Zn、V、Al、Zr、Ce及Mg中的一种或多种。
作为示例，正极活性材料可选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、橄榄石结构的含锂磷酸盐中的一种或多种，如LiMn 2O 4、LiNiO 2、LiCoO 2、LiNi 1-yCo yO 2(0<y<1)、LiNi aCobAl 1-a-bO 2(0<a<1，0<b<1，0<a+b<1)、LiMn 1-m-nNi mCo nO 2(0<m<1，0<n<1，0<m+n<1)、LiMPO 4(M可以为Fe、Mn、Co中的一种或多种)及Li 3V 2(PO 4) 3中的一种或多种。LiMn 1-m-nNi mConO 2例如是LiMn 0.1Ni 0.8Co 0.1O 2、LiMn 0.3Ni 0.5Co 0.2O 2、LiMn 0.2Ni 0.6Co 0.2O 2、LiMn 1/3Ni 1/3Co 1/3O 2等。
可选地，正极活性材料层还包括粘结剂。本申请实施例对粘结剂的种类不做限制。作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、羧甲基纤维素钠(CMC-Na)、聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或多种。
可选地，正极活性材料层还包括导电剂。第一正极活性材料层包括第一正极导电剂，第二正极活性材料层包括第二正极导电剂。本申请实施例对导电剂的种类不做限制。作为示例，第一正极导电剂和第二正极导电剂可以各自独立 地包括石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或多种。
在一些示例中，第一正极导电剂在第一正极活性材料层中的质量百分含量为0.5％至5.5％，可选地，为1％至2.5％。第二正极导电剂在第二正极活性材料层中的质量百分含量为0.5％至5％,可选地，为1％至2％。第一正极导电剂在第一正极活性材料层中的质量百分含量大于或等于第二正极导电剂在第二正极活性材料层中的质量百分含量，可以使得涂覆第一正极活性材料层的第一活性材料层111的锂离子动力学优于涂覆第二正极活性材料层的第二活性材料层112的锂离子动力学，从而可以减少析锂情况的发生。
在一些实施例中，第二正极活性材料层的压实密度大于或等于第一正极活性材料层的压实密度。可以了解的是，压实密度越大，锂离子的动力学(扩散速率)越小，所以在一些示例下，第二正极活性材料层(处于拐角区22)的压实密度大于或等于第一正极活性材料层(处于平面区21)的压实密度，此时，第一正极活性材料层(处于平面区21)的锂离子动力学性能较差，锂离子的扩散速率较小，可以改善第一正极活性材料层对应的负极极片位置的析锂情况。在一些实施例中，第二正极活性材料层可以设置在电极组件的拐角位置，减少拐角位置负极极片的析锂情况。
在另外的一些实施例中，第一极片11为负极极片，负极极片可按照本领域常规方法制备，例如采用间歇涂布技术制备正极极片。负极极片上的第一活性材料层111为第一负极活性材料层，第二活性材料层112为第二负极活性材料层。负极活性材料(例如，第一负极活性材料，第二负极活性材料)可以各自独立的包括本领域已知的能够进行活性离子可逆脱嵌的负极活性材料，本申请不做限制。例如用于锂离子二次电池的负极活性材料可包括金属锂、天然石墨、人造石墨、中间相微碳球(简写为MCMB)、硬碳、软碳、硅、硅-碳复合物、SiO  x(0<x<2)、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO  2、尖晶石结构的钛酸锂及Li-Al合金中的一种或多种。在一些实施例中，第一负极活性材料和第二负活性材料包括克容量为300mAh/g至380mAh/g的石墨。优选的，第一负极活性材料 和第二负活性材料包括克容量为340mAh/g至370mAh/g的石墨。可选地，第一负极活性材料和第二负活性材料为同种石墨。
进一步可选地，负极活性材料层还包括粘结剂，本申请实施例对粘结剂的种类不做限制。作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、羧甲基纤维素钠(CMC-Na)、聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或多种。
可选地，负极活性材料层还包括导电剂，本申请实施例对导电剂的种类不做限制。作为示例，导电剂可以为石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或多种。
在一些示例中，第一负极导电剂在第一负极活性材料层中的质量百分含量为0.5％至5.5％，可选地，为1％至2.5％。第二负极导电剂在第二负极活性材料层中的质量百分含量为0.5％至5％,可选地，为1％至2％。第一负极导电剂在第一负极活性材料层中的质量百分含量大于或等于第二负极导电剂在第二负极活性材料层中的质量百分含量，可以使得第一负极活性材料层的锂离子动力学优于第二负极活性材料层的锂离子动力学，从而可以减少拐角区析锂情况的发生。
下面列举了一些具体实施例和对比例以更好地对本申请进行说明，其中，采用锂离子电池作为示例。以下的实施例仅用作示意性的说明，不应对本申请的保护范围产生限制。
本申请的一些实施例提供了实施例1至实施例4，对比例1，实施例5至实施例7，对比例2。
实施例1
正极极片的制备：采用铝箔作为正极的正极集流体，将正极活性材料钴酸锂、导电剂导电炭黑、聚偏氟乙烯按重量比97.5：1.5：1.0的比例溶于N-甲基吡咯烷酮(NMP)溶液中，形成第一正极浆料。将正极活性材料钴酸锂、导电剂导电炭黑、聚偏氟乙烯按重量比97.5：1.4：1.1的比例溶于N-甲基吡咯烷酮(NMP)溶液中，形成第二正极浆料。采用间隔涂布技术，将第一正极浆料和 第二正极浆料涂覆于正极集流体上，涂覆厚度为40μm，各自涂覆宽度均为6mm。得到第一正极活性材料层和第二正极活性材料。然后经过干燥、冷压、裁切后得到正极极片。
负极极片的制备：将石墨、羧甲基纤维素钠(CMC)和粘结剂丁苯橡胶按重量比97.7：1.3：1的比例溶于去离子水中，形成负极浆料。采用10μm厚度铜箔作为负极极片的集流体，将负极浆料涂覆于负极集流体上。干燥，裁切后得到负极极片。其中，其中石墨的OI值为6。
隔离膜的制备：隔离膜基材为8μm厚的聚乙烯(PE)，在隔离膜基材的两侧各涂覆2μm氧化铝陶瓷层，最后在涂布了陶瓷层的两侧各涂覆2.5mg/cm 2的粘结剂聚偏氟乙烯(PVDF)，烘干。
电解液的制备：在含水量小于10ppm的环境下，将LiPF 6加入非水有机溶剂(乙烯碳酸酯(EC)：碳酸丙烯酯(PC)：碳酸二乙酯(DEC)和碳酸二甲酯(DMC)＝1：1：1：1，重量比)，LiPF 6的浓度为1mol/L，混合均匀，得到电解液。
锂离子电池的制备：将正极极片、隔离膜、负极极片按顺序依次叠好，使隔离膜处于正极极片和负极极片中间起到隔离的作用，并卷绕得到电极组件。卷绕后，第一正极活性材料位于正极极片的平面区上，第二正极活性材料层位于正极极片的拐角区上。
将电极组件置于外包装铝塑膜中，在80℃下脱去水分后，注入上述电解液并封装，经过化成，脱气，切边等工艺流程得到锂离子电池。
实施例1至实施例4，对比例1是与实施例1的区别在于制备第二正极活性材料层时，正极活性材料钴酸锂、导电剂导电炭黑、聚偏氟乙烯的质量比不同。具体如下表一：
Figure PCTCN2022084268-appb-000001
表一
本申请实施例采用如下方法测试电池的循环性能：
将化成后的锂离子电池，在25℃下以3C恒流充电4.2V，然后恒压充电至电流为0.05C，静置5min后，以1C放电至2.8V,如此充放电循环1000圈；第一圈放电容量记为D0，第1000圈循环放电容量记为D1；
1000圈容量保持率(％)＝D1/D0×100％。
分别测试这实施例1至实施例4和对比例1的循环性能，得到如图4所示的电容量保持率与循环次数的测试结果图。
参照图4，随循环次数的增加，实施例1至实施例4的电容量保持率逐渐下降。实施例1至实施例4中，第二正极活性材料涂覆的拐角区的导电剂含量是逐渐降低的。对应实施例1至实施例4的电容量保持率为：实施例4>实施例3>实施例2>实施例1。另外还可以从图看出，实施例4>实施例3>实施例2>实施例1>对比例1。可见，在第一正极活性材料层中导电剂含量不变的情况下，第二正极活性材料层中的导电剂含量越低，则第二正极活性材料层涂覆的拐角区的锂离子动力越小，出现析锂的情况越少，锂离子电池的循环性能越好。
通过设置位于拐角区的第二正极活性材料层中的导电剂质量百分含量小于位于平面区的第一正极活性材料层中的导电剂的含量，可以减小第二正极活性材料层的锂离子扩散速率，从而有助于减小与第二正极活性材料层相对的负极极片的极化，改善电化学装置的析锂和循环性能。此外，随着第二正极活性材料层和第一正极活性材料层中的导电剂的百分含量差异度的减小，这两个部分所在的位置处的锂离子扩散速率的差异度也会减小，进而电化学装置的循环性能的改善程度也降低。
实施例5至实施例6，对比例2是与实施例1的区别在于：制备第二正极活性材料层时，正极活性材料钴酸锂、导电剂导电炭黑、聚偏氟乙烯的质量比与制作第一正极活性材料层时，正极活性材料钴酸锂、导电剂导电炭黑、聚偏氟乙烯的质量比相同，均为97.5:1.5:1.0。实施例5至实施例6，对比例2的第一正极活性材料层和第二正极活性材料层的压密具体如下表二：
Figure PCTCN2022084268-appb-000002
表二
实施例5至实施例7和对比例2的循环性能测试结果如图5所示。
参照图5，随循环次数的增加，实施例5至实施例7和对比例2的电容量保持率逐渐下降。实施例5至实施例7中，正极第二活性材料层压实密度越来越大，对应实施例5至实施例7电容量保持率为实施例7>实施例6>实施例5。另外还可以从图看出，实施例7>实施例6>实施例5>对比例2。可见，拐角区的压实密度越大，拐角区上锂离子的动力学越低，出现析锂的情况越少。
通过设置位于拐角区的第二正极活性材料层中的压实密度大于位于平面区的第一正极活性材料层中的压实密度，可以减小第二正极活性材料层的锂离子扩散速率，从而有助于减小与第二正极活性材料层相对的负极极片的极化，改善电化学装置的析锂和循环性能。此外，随着第二正极活性材料层和第一正极活性材料层中的压实密度差异度的减小，这两个部分所在的位置处的锂离子扩散速率的差异度也会减小，进而电化学装置的循环性能的改善程度也降低。
本申请的一些实施例提供了实施例8至实施例10，对比例3。
实施例8
正极极片的制备：采用铝箔作为正极的正极集流体，将正极活性材料钴酸锂、导电剂导电炭黑、聚偏氟乙烯按重量比97.8：1.4：0.8的比例溶于N-甲基吡咯烷酮(NMP)溶液中，形成正极活性材料层的浆料，将该浆料涂覆于正极集流体上，涂覆厚度为80μm，得到正极活性材料层。然后经过干燥、冷压、裁切后得到正极极片。
负极极片的制备：将石墨、羧甲基纤维素钠(CMC)和粘结剂丁苯橡胶按重量比95：2：1：2的比例溶于去离子水中，形成第一负极浆料。将石墨、羧甲基纤维素钠(CMC)和粘结剂丁苯橡胶按重量比95：2.2：1：1.8的比例溶于去 离子水中，形成第二负极浆料。采用间隔涂布的方式，将第一负极浆料和第二负极浆料涂覆于负极极片的集流体，涂覆厚度为120μm，各自涂覆宽度均为6mm，得到第一负极活性材料层和第二负极活性材料层。干燥，裁切后得到负极极片。
隔离膜的制备：隔离膜基材为8μm厚的聚乙烯(PE)，在隔离膜基材的两侧各涂覆2μm氧化铝陶瓷层，最后在涂布了陶瓷层的两侧各涂覆2.5mg/cm 2的粘结剂聚偏氟乙烯(PVDF)，烘干。
电解液的制备：在含水量小于10ppm的环境下，将LiPF 6加入非水有机溶剂(乙烯碳酸酯(EC)：碳酸丙烯酯(PC)：碳酸二乙酯(DEC)和碳酸二甲酯(DMC)＝1：1：1：1，重量比)，LiPF 6的浓度为1mol/L，混合均匀，得到电解液。
锂离子电池的制备：将正极极片、隔离膜、负极极片按顺序依次叠好，使隔离膜处于正极极片和负极极片中间起到隔离的作用，并卷绕得到电极组件。将电极组件置于外包装铝塑膜中，在80℃下脱去水分后，注入上述电解液并封装，经过化成，脱气，切边等工艺流程得到锂离子电池。
实施例8至实施例10，对比例3是与实施例1的区别在于：制备第一负极活性材料层时，负极活性材料石墨、羧甲基纤维素钠(CMC)和粘结剂丁苯橡胶的质量比不同。具体如下表三：
Figure PCTCN2022084268-appb-000003
表三
分别测试这实施例1至实施例4和对比例1的循环性能，得到如图6所示的电容量保持率与循环次数的测试结果图。
参照图6，随循环次数的增加，实施例8至实施例10的电容量保持率逐渐下降。实施例8至实施例10中，第一负极活性材料层中的导电剂含量是逐渐减少的，对应实施例8至实施例10的电容量保持率为实施例10>实施例9>实施例8。另外还可以从图看出，实施例10>实施例9>实施例8>对比例3。可见，在第 二负极活性材料层中导电剂含量不变的情况下，第一负极活性材料层中导电剂的含量越高，第一负极活性材料层涂覆的拐角区上锂离子的动力学越高，出现析锂的情况越少
通过设置位于拐角区的第一负极活性材料层中的导电剂含量大于位于平面区的第二负极活性材料层中的导电剂含量，可以增加第一负极活性材料层的锂离子扩散速率，从而有助于减少第一负极活性材料层的极化，改善电化学装置的析锂和循环性能。此外，随着第一负极活性材料层和第二负极活性材料层中的导电剂的质量百分含量的差异度的减小，这两个部分所在的位置处的锂离子扩散速率的差异度也会减小，进而电化学装置的循环性能的改善程度也降低。
本领域的技术人员将理解，以上描述的电化学装置(例如，锂离子电池)的制备方法仅是实施例。在不背离本申请公开的内容的基础上，可以采用本领域常用的其他方法。
本申请的实施例还提供了包括上述电化学装置的电子装置。本申请实施例的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
以上描述仅为本申请的较佳实施例以及对所运用技术原理的说明。本领域技术人员应当理解，本申请中所涉及的公开范围，并不限于上述技术特征的特定组合而成的技术方案，同时也应涵盖由上述技术特征或其等同特征进行任意组合而形成的其它技术方案。例如上述特征与本申请中公开的具有类似功能的技术特征进行互相替换而形成的技术方案。

Claims (10)

  1. 一种电化学装置，包括电极组件，所述电极组件包括：
    第一极片；
    第二极片；和
    设置于所述第一极片和所述第二极片之间的隔离膜，其中，
    所述第一极片包括活性材料层，所述活性材料层包括沿极片长度方向设置的至少一个第一活性材料层和至少一个第二活性材料层，所述第一活性材料层的锂离子扩散速率大于所述第二活性材料层的锂离子扩散速率。
  2. 如权利要求1所述的电化学装置，其中，所述电极组件由所述第一极片、所述第二极片和所述隔离膜卷绕而成，所述电极组件包括平面区和拐角区；
    所述第一极片为正极极片，所述第一活性材料层为第一正极活性材料层，所述第二活性材料层为第二正极活性材料层；
    至少部分所述第一正极活性材料层位于所述平面区，至少部分所述第二正极活性材料层位于所述拐角区。
  3. 如权利要求2所述的电化学装置，其中，所述第一正极活性材料层包括第一正极导电剂，所述第二正极活性材料层包括第二正极导电剂，所述第一正极导电剂在所述第一正极活性材料层中的质量百分含量大于或等于所述第二正极导电剂在所述第二正极活性材料层中的质量百分含量。
  4. 如权利要求3所述的电化学装置，其中，所述第一正极导电剂在所述第一正极活性材料层中的质量百分含量为0.5％至5.5％，所述第二正极导电剂在所述第二正极活性材料层中的质量百分含量为0.5％至5％。
  5. 如权利要求2所述的电化学装置，其中，所述第二正极活性材料层的压实密度大于或等于所述第一正极活性材料层的压实密度。
  6. 如权利要求1所述的电化学装置，其中，所述电极组件由所述第一极片、所述第二极片和所述隔离膜卷绕而成，所述电极组件包括平面区和拐角区；
    所述第一极片为负极极片，所述第一活性材料层为第一负极活性材料层， 所述第二活性材料层为第二负极活性材料层；
    至少部分所述第一负极活性材料层位于所述拐角区，至少部分所述第二负极活性材料层位于所述平面区。
  7. 如权利要求6所述的电化学装置，其中，所述第二负极活性材料层包括第二负极导电剂，第一负极活性材料层包括第一负极导电剂，所述第一负极导电剂在所述第一负极活性材料层中的质量百分含量大于或等于所述第二负极导电剂在所述第二负极活性材料层中的质量百分含量。
  8. 如权利要求6所述的电化学装置，其中，所述第一负极活性材料层包括第一负极活性材料，所述第二负极活性材料层包括第二负极活性材料，所述第一负极活性材料和/或所述第二负极活性材料包括克容量为300mAh/g至380mAh/g的石墨。
  9. 如权利要求1所述的电化学装置，其中，所述第一极片包括多个第一活性材料层和多个第二活性材料层，所述多个第一活性材料层和多个第二活性材料层沿极片长度方向间隔设置。
  10. 一种电子装置，其中，包括如权利要求1至9中任一项所述的电化学装置。
PCT/CN2022/084268 2021-03-31 2022-03-31 电化学装置及电子装置 WO2022206877A1 (zh)

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