WO2025022867A1 - リチウム二次電池およびセパレータ - Google Patents

リチウム二次電池およびセパレータ Download PDF

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Publication number
WO2025022867A1
WO2025022867A1 PCT/JP2024/021920 JP2024021920W WO2025022867A1 WO 2025022867 A1 WO2025022867 A1 WO 2025022867A1 JP 2024021920 W JP2024021920 W JP 2024021920W WO 2025022867 A1 WO2025022867 A1 WO 2025022867A1
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Prior art keywords
region
convex portion
separator
pattern
negative electrode
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English (en)
French (fr)
Japanese (ja)
Inventor
亮平 宮前
真一郎 近藤
聡 蚊野
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Panasonic Intellectual Property Management Co Ltd
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Panasonic Intellectual Property Management Co Ltd
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Priority to CN202480048864.2A priority Critical patent/CN121569386A/zh
Priority to JP2025535632A priority patent/JPWO2025022867A1/ja
Publication of WO2025022867A1 publication Critical patent/WO2025022867A1/ja
Anticipated expiration legal-status Critical
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/463—Separators, membranes or diaphragms characterised by their shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • 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

  • This disclosure relates to lithium secondary batteries and separators.
  • Lithium ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries.
  • Lithium secondary batteries (lithium metal secondary batteries) are promising non-aqueous electrolyte secondary batteries with a higher capacity than lithium ion batteries.
  • lithium metal is precipitated on the negative electrode during charging, and the lithium metal dissolves during discharging and is released as lithium ions into the non-aqueous electrolyte.
  • lithium metal precipitates on the negative electrode during charging, so it is necessary to leave space between the separator and the electrode.
  • Patent Document 1 proposes a lithium secondary battery comprising: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity; lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves from the negative electrode during discharging; a spacer is provided between at least one of the positive electrode and the negative electrode and the separator; a first length of the separator in a first direction D1 is smaller than a second length of the separator in a second direction D2 intersecting with the first direction D1; and in a cross section of the spacer cut along the thickness direction of the separator and the first direction D1, at least one of an angle between the separator and the spacer on the spacer side and an angle between an electrode in contact with the spacer and the spacer on the spacer side is greater than 90°.
  • the amount of non-aqueous electrolyte flowing through the inner circumference of the electrode group may decrease due to lithium precipitation, resulting in a shortage of non-aqueous electrolyte.
  • a shortage of non-aqueous electrolyte on the inner circumference causes a decrease in the capacity retention rate.
  • a lithium secondary battery comprising an electrode group and a non-aqueous electrolyte, the electrode group comprising a positive electrode, a negative electrode, and a separator, the positive electrode and the negative electrode being wound with the separator interposed therebetween, lithium metal precipitates in the negative electrode during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging, the separator having a first surface facing the outside of the electrode group and a second surface facing the inside of the electrode group, at least one of the first surface and the second surface having a first region having a first convex portion of a first pattern and a second region having a second convex portion of a second pattern different from the first pattern, the second region being disposed closer to the outer periphery of the electrode group than the first region, and the proportion of the area occupied by the first convex portion in the first region being smaller than the proportion of the area occupied by the second convex portion in the second region.
  • Another aspect of the present disclosure relates to a separator that is disposed between a positive electrode and a negative electrode and wound to form an electrode group, the separator having a first surface facing the outside of the electrode group and a second surface facing the inside of the electrode group, at least one of the first surface and the second surface having a first region having first convex portions of a first pattern and a second region having second convex portions of a second pattern different from the first pattern, the second region being disposed closer to the outer periphery of the electrode group than the first region, and the proportion of the area occupied by the first convex portions in the first region being smaller than the proportion of the area occupied by the second convex portions in the second region.
  • FIG. 1 is a longitudinal sectional view illustrating a schematic diagram of an example of a lithium secondary battery according to an embodiment of the present disclosure.
  • 2 is a cross-sectional view showing a schematic view of a part of the inner periphery side of the lithium secondary battery shown in FIG. 1.
  • 2 is a cross-sectional view showing a schematic view of a part of the outer periphery of the lithium secondary battery shown in FIG. 1.
  • 4 is a top view showing an example of a first convex portion and a second convex portion.
  • FIG. FIG. 4 is an enlarged view of a portion of FIG. 13 is a top view showing another example of the first convex portion and the second convex portion.
  • FIG. 13 is a top view showing still another example of the first convex portion and the second convex portion.
  • FIG. 13 is a top view showing still another example of the first convex portion and the second convex portion.
  • FIG. 13 is a top view showing still another example of the
  • a lithium secondary battery includes a wound electrode group and a non-aqueous electrolyte.
  • the electrode group includes, for example, a long (strip-shaped) positive electrode, a negative electrode, and a separator, and the positive electrode and the negative electrode are wound with the separator interposed therebetween.
  • the negative electrode lithium metal is precipitated during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging.
  • the negative electrode has at least a negative electrode current collector, and the lithium metal is precipitated on the negative electrode current collector.
  • the non-aqueous electrolyte has lithium ion conductivity.
  • the lithium secondary battery is also called a lithium metal secondary battery.
  • lithium secondary batteries for example, 70% or more of the rated capacity is achieved by the deposition and dissolution of lithium metal.
  • the movement of electrons at the negative electrode during charging and discharging is mainly due to the deposition and dissolution of lithium metal at the negative electrode.
  • 70-100% (for example, 80-100% or 90-100%) of the movement of electrons (current from another perspective) at the negative electrode during charging and discharging is due to the deposition and dissolution of lithium metal.
  • the negative electrode of a lithium secondary battery is different from a negative electrode in which the movement of electrons at the negative electrode during charging and discharging is mainly due to the absorption and release of lithium ions by the negative electrode active material (such as graphite).
  • the separator has at least two regions, a first region and a second region, the first region being disposed on the inner periphery side of the electrode group, and the second region being disposed on the outer periphery side of the electrode group.
  • the first region may be a region extending from the innermost end of the first surface or the second surface of the separator to the outer periphery side.
  • the second region may be a region extending from the outermost end of the first surface or the second surface of the separator to the inner periphery side.
  • the first and second convex portions function as spacers to form a space between the separator and the electrode.
  • the separator may be composed of a substrate layer and a spacer layer.
  • the spacer layer constitutes the first and second convex portions.
  • the first and second convex portions may be provided only on the first and second surfaces that face the negative electrode, only on the surface that faces the positive electrode, or on both surfaces.
  • the first convex portion is formed in a first pattern
  • the second convex portion is formed in a second pattern different from the first pattern.
  • the pattern includes various styles of convex portions. At least one of the first convex portion and the second convex portion may be a linear convex portion. At least one of the first convex portion and the second convex portion may be a dot-shaped or island-shaped convex portion.
  • the linear convex portion is formed along a linear pattern. If at least one of the line width, diameter, height, density, shape (the path along which the convex portion is drawn), direction on the first surface or the second surface, pitch (the minimum distance between equivalent positions of the convex portions), etc. of the first convex portion and the second convex portion is different, the first pattern and the second pattern can be said to be different.
  • the proportion (R1) of the area occupied by the first convex portion in the first region may be smaller than the proportion (R2) of the area occupied by the second convex portion in the second region. This makes it difficult for the non-aqueous electrolyte to be unevenly distributed on the outer periphery side of the electrode group, and makes it possible to suppress a shortage of the amount of non-aqueous electrolyte circulating on the inner periphery side of the electrode group.
  • R1 is the proportion (%) of the area where the first region and the first convex portion overlap with respect to the area of the first region when the first surface or the second surface is viewed in a plan view.
  • R2 is the proportion (%) of the area where the second region and the second convex portion overlap with respect to the area of the second region when the first surface or the second surface is viewed in a plan view.
  • R1 and R2 may satisfy R1/R2 ⁇ 1, R1/R2 ⁇ 0.9, or R1/R2 ⁇ 0.8. From the viewpoint of forming a necessary and sufficient space on the inner and outer circumferential sides by the function of the first convex portion as a spacer, it is preferable that 0.4 ⁇ R1/R2 is satisfied. 0.4 ⁇ R1/R2 ⁇ 1 may be satisfied, 0.4 ⁇ R1/R2 ⁇ 0.9, or 0.4 ⁇ R1/R2 ⁇ 0.8 may be satisfied. From the viewpoint of ensuring the function of the first convex portion as a spacer and sufficient ion permeability of the separator, R1 is preferably 1% or more and 25% or less, and more preferably 5% or more and 15% or less.
  • the air permeability P1 of the first region may be higher than the air permeability P2 of the second region.
  • the non-aqueous electrolyte is less likely to be unevenly distributed on the outer periphery of the electrode group, and the insufficient amount of non-aqueous electrolyte flowing on the inner periphery of the electrode group can be suppressed.
  • the unit of air permeability is "seconds/100 mL", and the smaller the air permeability value, the higher the air permeability.
  • P1 and P2 may satisfy P1/P2 ⁇ 1 or P1/P2 ⁇ 0.9.
  • the air permeability P1 of the first region may be higher than the air permeability P2 of the second region.
  • Air permeability is an index showing the time (seconds) required for a given volume (100 mL) of air to permeate per unit area of the separator when a given pressure difference is applied between both sides of the separator. Air permeability is measured by the Gurley tester method based on JIS P8117:2009, with the separator test area (permeable portion) being 6.42 cm 2 and the inner cylinder weight being 567 g. Air permeability may also be measured by the Oken tester method, and similar values are obtained.
  • the line width W1 of the first convex portion may be shorter than the line width W2 of the second convex portion. This makes it easier to satisfy R1/R2 ⁇ 1.
  • W1 and W2 may be W1/W2 ⁇ 1, W1/W2 ⁇ 0.9, or W1/W2 ⁇ 0.8.
  • W1 is preferably 0.1 mm or more and 2.0 mm or less, and more preferably 0.25 mm or more and 1.0 mm or less.
  • the line width refers to the dimension perpendicular to the length direction of the first and second convex portions that extend linearly and parallel to the main surface of the separator.
  • the line width may be measured at any five or more points on each of the first and second convex portions, and calculated as the arithmetic average of the five or more measured values.
  • the height H1 of the first convex portion may be greater than the height H2 of the second convex portion. This can relatively enhance the function of the first convex portion as a spacer, and can promote the flow of non-aqueous electrolyte on the inner circumference side.
  • H1 and H2 may be 1 ⁇ H1/H2, 1.1 ⁇ H1/H2, or 1.2 ⁇ H1/H2. From the viewpoint of forming a necessary and sufficient space on the inner circumference side and the outer circumference side by the function of the first convex portion as a spacer, it is preferable that H1/H2 ⁇ 2.5 is satisfied. 1 ⁇ H1/H2 ⁇ 2.5 may be satisfied, 1.1 ⁇ H1/H2 ⁇ 2.5 may be satisfied, or 1.2 ⁇ H1/H2 ⁇ 2.5 may be satisfied. From the viewpoint of enhancing the function of the first convex portion as a spacer, H1 is preferably 15 ⁇ m or more and 100 ⁇ m or less, and more preferably 30 ⁇ m or more and 70 ⁇ m or less.
  • the height of the first convex portion and the second convex portion refers to the maximum dimension of the first convex portion and the second convex portion in the direction parallel to the thickness direction of the separator.
  • H1 and H2 may be measured at any five or more locations on each of the first convex portion and the second convex portion, and calculated as the arithmetic mean of the five or more measured values.
  • the height of the convex portion may be measured by photographing a cross section parallel to the thickness direction of the separator with a scanning electron microscope (SEM).
  • the second region may be made larger than the first region.
  • the length L1 of the first region in the second direction may be 25% or less of the total length L of the separator in the second direction.
  • the first region may be, for example, a region extending from the innermost end of the first surface or second surface of the separator toward the outer periphery, with a length of L/4 or less. This is because the amount of non-aqueous electrolyte flowing through such a region close to the innermost periphery of the electrode group is likely to be insufficient.
  • the first and second convex portions are arranged on the separator in as uniform and dispersed a state as possible. This makes it possible to reduce the number of locations where lithium metal can precipitate locally while suppressing an increase in internal resistance, and makes it easier to limit isolated lithium metal to an extremely small amount.
  • a circular area having an arbitrary diameter of D1/3 (D1 is the length in the first direction (short side direction) of the strip-shaped separator) is set on the surface of the separator, it is desirable that such a circular area always has a convex portion.
  • At least one of the first pattern and the second pattern may be a geometric pattern.
  • the convex portions of such a pattern are easily arranged evenly over the entire surface of the separator.
  • the geometric pattern may be a network pattern. That is, at least one of the first convex portions and the second convex portions may be arranged over the entire surface of the separator along a network pattern.
  • the network pattern may be an assembly of polygons.
  • An example of a network pattern includes a shape in which polygons are combined so as to share sides. Polygons include triangles, squares, hexagons, and the like. Different types of polygons may be combined. It is desirable for the geometric pattern to have small anisotropy, such as an assembly of regular polygons.
  • the geometric pattern may be, for example, a honeycomb pattern (an assembly of regular hexagons).
  • At least one of the first pattern and the second pattern may include a dot pattern. At least one of the first pattern and the second pattern may be a pattern that combines a linear pattern and a dot pattern.
  • the planar shape of the dot-shaped convex portions is not particularly limited, and may be a circle (a perfect circle or an ellipse), a polygon (a triangle, a square, etc.), etc.
  • separator (A) the separator having the above configuration
  • lithium secondary battery (B) the lithium secondary battery having the above configuration
  • Separator (A) is used in lithium secondary battery (B).
  • the separator is composed of a base layer and a spacer layer, and the spacer layer constitutes the first convex portion and the second convex portion.
  • the spacer layer may be formed, for example, by applying a dispersion liquid containing a spacer material to the portion of the surface of the base layer where the spacer layer is to be formed, and then drying.
  • the spacer layer first convex portion and second convex portion
  • the dispersion liquid is applied to the portion where the spacer layer is to be formed, and then dried.
  • the dispersion liquid may be applied using a dispenser or a known printing method such as gravure printing, inkjet printing, or screen printing.
  • the drying may also be performed by a known method such as drying by heating or natural drying.
  • the dispersion liquid containing the spacer material contains, for example, insulating particles, a binder resin, and a thickener.
  • the spacer layer (first convex portion and second convex portion) formed from the dispersion liquid contains insulating particles, a binder resin, and a thickener.
  • the dispersion medium of the dispersion liquid is not particularly limited, but may be, for example, water, an organic solvent, or a mixture of water and an organic solvent.
  • an organic solvent for example, N-methyl-2-pyrrolidone (NMP) may be used. Among these, the use of water is preferable in terms of reducing the environmental load.
  • the shape of the insulating particles is not particularly limited, but may be spherical. However, spherical does not mean a strict perfect sphere, but a shape without sharp corners, with an aspect ratio (maximum diameter/maximum diameter in the direction perpendicular to the maximum diameter) in the range of, for example, 1 to 3.
  • the median diameter (i.e., average particle diameter) in the volume-based particle size distribution of the insulating particles may be 1.0 ⁇ m to 10 ⁇ m.
  • the median diameter is the particle diameter when the cumulative volume is 50%.
  • the median diameter of the insulating particles may be 1.0 ⁇ m to 2 ⁇ m.
  • the insulating particles in the dispersion liquid tend to maintain a stable dispersion state, and the dispersion state is maintained even after application to the base layer, making it easy to form a spacer layer with a homogeneous morphology.
  • the median diameter in the particle size distribution based on volume of the particles can be measured, for example, by a laser diffraction/scattering type particle size distribution measuring device (for example, Microtrack manufactured by Nikkiso Co., Ltd.).
  • a laser diffraction/scattering type particle size distribution measuring device for example, Microtrack manufactured by Nikkiso Co., Ltd.
  • the cross section of the spacer layer can be observed with a transmission electron microscope (TEM), a TEM image can be taken, the area enclosed by the outlines of any 100 insulating particles can be calculated, the diameter of an equivalent circle (perfect circle) having the same area as the calculated area can be calculated, and the average diameter of the 100 equivalent circles can be calculated.
  • TEM transmission electron microscope
  • the volume resistivity of the insulating particles may be, for example, 1.0 ⁇ 10 8 ⁇ cm or more.
  • the volume resistivity of the insulating particles may be even higher, for example, 1.0 ⁇ 10 10 ⁇ cm or more.
  • the volume resistivity can be measured by a four-probe method.
  • the insulating particles may be pressurized at 204 kgf/cm 2 and measured using a powder resistivity measuring device (for example, Loresta SP manufactured by Nitto Seiko Analytech Co., Ltd.).
  • Insulating particles include inorganic particles such as metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides.
  • Metal oxides include aluminum oxide (alumina, boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, and silicon oxide (silica).
  • Metal hydroxides include aluminum hydroxide.
  • Metal nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride.
  • Metal carbides include silicon carbide and boron carbide.
  • Metal sulfides include barium sulfate. Minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate may also be used. Of these, it is preferable to use alumina, silica, titania, and the like.
  • the content of the insulating particles in the spacer layer is, for example, less than 80 volume %, and preferably 50 to 70 volume %.
  • the content (volume ratio) of the insulating particles in the spacer layer may be determined by observing the cross section of the spacer layer with a transmission electron microscope (TEM), taking a TEM image, calculating the total area surrounded by the contours of the insulating particles in any 10 ⁇ m2 visual field, and calculating the volume ratio as the ratio of the calculated total area to the area of the visual field. In this case, it is preferable to determine the volume ratio in three or more visual fields and calculate the average value thereof.
  • TEM transmission electron microscope
  • binder resins include fluororesins, fluororubber, styrene-butadiene copolymers or hydrogenated products thereof, acrylonitrile-butadiene copolymers or hydrogenated products thereof, methacrylate-acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene propylene rubber, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as fully aromatic polyamides (aramids), polyimides, polyamideimides, polyacrylonitrile, polyethers, polyolefins, and alkyd resins.
  • binder resins include fluororesins, fluororubber, styrene-butadiene copolymers or hydrogenated products thereof, acrylonitrile-butadiene copolymers or hydrogenated products thereof, methacryl
  • the amount of binder resin may be, for example, 20 to 100 parts by volume, 20 to 80 parts by volume, 20 to 70 parts by volume, or 25 to 50 parts by volume per 100 parts by volume of insulating particles. In this range, it is easy to increase the mechanical strength of the spacer layer and to increase the bonding strength between the base layer and the spacer layer.
  • the thickener may contain, for example, at least one selected from the group consisting of carboxymethylcellulose and carboxymethylcellulose salts (hereinafter, at least one selected from the group consisting of carboxymethylcellulose and carboxymethylcellulose salts is also referred to as "CMC").
  • CMC carboxymethylcellulose salt
  • a sodium salt, a lithium salt, a potassium salt, an ammonium salt, etc. may be used.
  • the carboxymethylcellulose salt contains a sodium salt.
  • the dispersion medium of the spacer material dispersion liquid may contain water.
  • 50% by mass or more of the dispersion medium may be water, or 70% by mass or more, 80% by mass or more, or 90% by mass or more of the dispersion medium may be water.
  • the amount of CMC may be, for example, 0.5 to 5 parts by volume, or 1 to 3 parts by volume, per 100 parts by volume of insulating particles. By using CMC within this range, it is possible to achieve a sufficient thickening effect of the CMC.
  • the substrate layer is made of a porous sheet having ion permeability and insulation properties.
  • the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric.
  • the material of the porous sheet is not particularly limited, but may be a polymeric material.
  • the polymeric material include an olefin resin, a polyamide resin, and cellulose.
  • the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene.
  • the substrate layer may contain an additive as necessary. Examples of the additive include an inorganic filler.
  • the thickness of the substrate layer is not particularly limited, but is, for example, 5 ⁇ m or more and 20 ⁇ m or less, and more preferably 10 ⁇ m or more and 20 ⁇ m or less.
  • the substrate layer may include a porous sheet and a composite material layer.
  • the composite material layer may be formed on one or both main surfaces of the porous sheet.
  • the composite material layer is a layer that allows lithium ions to pass through.
  • the thickness of the composite material layer may be 5% to 50% of the total thickness of the separator.
  • the composite material layer includes a resin material and inorganic particles.
  • the inorganic particles may include first particles and/or second particles.
  • the first particles are particles of a phosphate containing lithium.
  • the first particles have the effect of suppressing heat generation in the battery under abnormal conditions.
  • the second particles are particles other than the first particles.
  • the composite material layer is formed on only one main surface of the porous sheet, it is desirable to provide the composite material layer on the main surface of the porous sheet facing the positive electrode.
  • the composite material layer on the positive electrode side it is possible to prevent the porous sheet from deteriorating due to oxidation reactions.
  • the composite material layer on the negative electrode side it is possible to prevent the porous sheet from deteriorating due to reduction reactions.
  • the phosphate constituting the first particles may be at least one selected from the group consisting of lithium phosphate (Li 3 PO 4 ), dilithium hydrogen phosphate (Li 2 HPO 4 ), and lithium dihydrogen phosphate (LiH 2 PO 4 ).
  • lithium phosphate is preferred because of its high effect of suppressing heat generation in the battery under abnormal conditions.
  • the median diameter in the volume-based particle size distribution of the first particles may be 0.1 ⁇ m to 1.0 ⁇ m.
  • a preferred example of the second particles is a particle made of an insulating inorganic compound that does not melt or decompose when the battery generates abnormal heat.
  • materials for the second particles include oxides, hydroxides, nitrides, carbides, sulfides, etc.
  • oxides include aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, zinc oxide, etc.
  • nitrides include silicon nitride, aluminum nitride, boron nitride, titanium nitride, etc.
  • Examples of carbides include silicon carbide, boron carbide, etc.
  • sulfides include barium sulfate, etc.
  • hydroxides include aluminum hydroxide, etc.
  • the median diameter in the volume-based particle size distribution of the second particles may be 0.2 to 2.0 ⁇ m.
  • the median diameter in the particle size distribution based on volume of the particles can be measured, for example, by a laser diffraction/scattering type particle size distribution measuring device (for example, Microtrack manufactured by Nikkiso Co., Ltd.).
  • the cross section of the base layer can be observed with a transmission electron microscope (TEM), a TEM image can be taken, the area enclosed by the outlines of any 100 first particles or second particles can be calculated, the diameter of an equivalent circle (perfect circle) having the same area as the calculated area can be calculated, and the average diameter of the 100 equivalent circles can be calculated.
  • TEM transmission electron microscope
  • a polymeric material that has higher heat resistance than the material of the porous sheet.
  • a polymeric material preferably contains at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamideimides. These are known as polymeric materials with high heat resistance. From the viewpoint of heat resistance, aramids, namely meta-aramids (meta-type wholly aromatic polyamides) and para-aramids (para-type wholly aromatic polyamides), are preferred.
  • the inorganic particle content in the composite layer may be in the range of 50% by mass to 99% by mass (e.g., in the range of 85% by mass to 99% by mass).
  • the negative electrode includes a negative electrode current collector.
  • lithium metal is deposited on the surface of the negative electrode by charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode by charging, becoming lithium metal, which is deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode dissolves as lithium ions in the non-aqueous electrolyte by discharging.
  • the negative electrode may include a lithium ion storage layer (a layer that develops capacity by the absorption and release of lithium ions by the negative electrode active material (such as graphite)) supported on the negative electrode current collector.
  • the open circuit potential of the negative electrode when fully charged may be 70 mV or less relative to lithium metal (lithium dissolution and deposition potential). If the open circuit potential of the negative electrode when fully charged is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion storage layer when fully charged. In other words, the negative electrode develops capacity by the deposition and dissolution of lithium metal.
  • fully charged refers to a state in which the battery is charged to a charging state of, for example, 0.98 x C or more, where C is the rated capacity of the battery.
  • the open circuit potential of the negative electrode when fully charged can be measured by disassembling a fully charged battery under an argon atmosphere, removing the negative electrode, assembling a cell with lithium metal as the counter electrode, and then measuring the potential.
  • the non-aqueous electrolyte of the cell may have the same composition as the non-aqueous electrolyte in the disassembled battery.
  • the lithium ion storage layer is a layer of a negative electrode mixture containing a negative electrode active material.
  • the negative electrode mixture may also contain a binder, a thickener, a conductive agent, etc.
  • Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials.
  • the negative electrode may contain one type of negative electrode active material, or may contain a combination of two or more types.
  • Examples of carbonaceous materials include graphite, easily graphitized carbon (soft carbon), and non-graphitizable carbon (hard carbon).
  • the conductive material is, for example, a carbon material.
  • carbon materials include carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.
  • Binders include, for example, fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber-like polymers, etc.
  • Fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, etc.
  • the negative electrode current collector can be a conductive sheet.
  • conductive sheets include foil and film.
  • the material of the negative electrode current collector may be any conductive material other than lithium metal and lithium alloys.
  • the conductive material may be a metallic material such as a metal or an alloy.
  • the conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form an alloy or an intermetallic compound with lithium is preferable. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, or graphite with the basal surface preferentially exposed.
  • alloys include copper alloys and stainless steel (SUS). Among these, copper and/or copper alloys, which have high conductivity, are preferable.
  • the thickness of the negative electrode current collector is not particularly limited, and is, for example, 5 ⁇ m or more and 300 ⁇ m or less.
  • the positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported by the positive electrode current collector.
  • the positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder.
  • the positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides.
  • the positive electrode is obtained, for example, by applying a positive electrode mixture slurry including a positive electrode active material, a conductive material, and a binder to both sides of the positive electrode current collector, drying the coating, and then rolling.
  • the positive electrode active material is a material that absorbs and releases lithium ions.
  • positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. Among these, lithium-containing transition metal oxides are preferred because of their low manufacturing costs and high average discharge voltage.
  • the lithium contained in the lithium-containing transition metal oxide is released from the positive electrode as lithium ions during charging and precipitates as lithium metal on the negative electrode or negative electrode current collector.
  • the lithium metal dissolves from the negative electrode, releasing lithium ions that are then absorbed into the composite oxide of the positive electrode.
  • the lithium ions involved in charging and discharging are generally derived from the solute in the non-aqueous electrolyte and the positive electrode active material.
  • the transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc.
  • the lithium-containing transition metal oxide may contain one type of transition metal element, or may contain two or more types.
  • the transition metal element may be Co, Ni, and/or Mn.
  • the lithium-containing transition metal oxide may contain one or more typical elements as necessary.
  • the typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, etc.
  • the typical element may be Al, etc.
  • lithium-containing transition metal oxides composite oxides containing Co, Ni and/or Mn as transition metal elements, and optionally containing Al, and having a layered rock-salt type crystal structure are preferred in terms of obtaining high capacity.
  • the molar ratio mLi/mM of the total amount of lithium in the positive and negative electrodes to the amount mM of metal M other than lithium in the positive electrode is set to, for example, 1.1 or less.
  • the binder conductive agent, etc., for example, those exemplified for the negative electrode can be used.
  • the shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.
  • the material of the positive electrode current collector may be, for example, a metal material containing Al, Ti, Fe, etc.
  • the metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc.
  • the Fe alloy may be stainless steel (SUS).
  • the thickness of the positive electrode current collector is not particularly limited, and is, for example, 5 ⁇ m or more and 300 ⁇ m or less.
  • the non-aqueous electrolyte having lithium ion conductivity may be a liquid electrolyte (electrolytic solution), a gel electrolyte, or a solid electrolyte.
  • the liquid electrolyte is, for example, an electrolytic solution containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.
  • the concentration of the lithium salt in the electrolytic solution is, for example, 0.5 mol/L or more and 2 mol/L or less.
  • the electrolytic solution may contain a known additive.
  • the gel electrolyte contains a lithium salt and a matrix polymer, or a lithium salt, a non-aqueous solvent, and a matrix polymer.
  • a matrix polymer for example, a polymer material that absorbs the non-aqueous solvent and gels is used. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, and polyethylene oxide.
  • solid electrolyte for example, a material known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolyte, sulfide-based solid electrolyte, halide-based solid electrolyte, etc.) is used.
  • oxide-based solid electrolyte e.g., oxide-based solid electrolyte, sulfide-based solid electrolyte, halide-based solid electrolyte, etc.
  • a liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. When the lithium salt dissolves in the non-aqueous solvent, lithium ions and anions are produced.
  • anion examples include BF 4 - , ClO 4 - , PF 6 - , CF 3 SO 3 - , CF 3 CO 2 - , anions of imides, and anions of oxalate complexes.
  • the anion of the oxalate complex may contain boron and/or phosphorus.
  • anion of the oxalate complex examples include a bisoxalate borate anion, a difluorooxalate borate anion (BF 2 (C 2 O 4 ) ⁇ ), PF 4 (C 2 O 4 ) ⁇ , PF 2 (C 2 O 4 ) 2 ⁇ , etc.
  • the non-aqueous electrolyte may contain one of these anions alone or two or more of them.
  • the non-aqueous electrolyte preferably contains at least an anion of an oxalate complex, and more preferably contains an anion of an oxalate complex having fluorine.
  • the interaction between the oxalate complex anion having fluorine and lithium makes it easier for the lithium metal to be precipitated uniformly in the form of fine particles. This makes it easier to suppress localized precipitation of the lithium metal.
  • the oxalate complex anion having fluorine may be combined with another anion.
  • the other anion may be an anion of PF 6 - and/or an imide.
  • non-aqueous solvents examples include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof.
  • the non-aqueous electrolyte may contain one or more of these non-aqueous solvents.
  • halogen-substituted derivatives include fluorides.
  • Esters include, for example, carbonate esters and carboxylate esters.
  • Cyclic carbonate esters include ethylene carbonate, propylene carbonate, fluoroethylene carbonate (FEC), etc.
  • Chain carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, etc.
  • Cyclic carboxylate esters include ⁇ -butyrolactone, ⁇ -valerolactone, etc.
  • Chain carboxylate esters include ethyl acetate, methyl propionate, methyl fluoropropionate, etc.
  • Ethers include cyclic ethers and chain ethers.
  • cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran.
  • chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.
  • the concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol/L or more and 3.5 mol/L or less.
  • the concentration of the anion in the non-aqueous electrolyte may be 0.5 mol/L or more and 3.5 mol/L or less.
  • the concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol/L or more and 1 mol/L or less.
  • the non-aqueous electrolyte may contain an additive.
  • the additive may form a coating on the negative electrode.
  • the coating derived from the additive is formed on the negative electrode, which makes it easier to suppress the formation of dendrites.
  • examples of such additives include vinylene carbonate, FEC, vinyl ethyl carbonate (VEC), etc.
  • FIG. 1 is a vertical cross-sectional view showing a schematic diagram of an example of a lithium secondary battery (B).
  • the components described above can be applied to the components of the lithium secondary battery (B) described below.
  • the components described below can be modified based on the above description.
  • components that are not essential to the lithium secondary battery according to the present disclosure may be omitted.
  • the scale of the components has been changed to facilitate understanding.
  • FIG. 1 is a longitudinal sectional view showing an example of a lithium secondary battery according to the first embodiment.
  • the spacer layer (first convex portion and second convex portion) and the space formed by the spacer layer are omitted.
  • the cylindrical lithium secondary battery 10 shown in FIG. 1 includes a cylindrical battery case, a wound electrode group 14 and a non-aqueous electrolyte housed in the battery case.
  • the battery case includes a case body 15 which is a cylindrical metal container with a bottom, and a sealing body 16 which seals the opening of the case body 15.
  • a gasket 27 is disposed between the case body 15 and the sealing body 16. The gasket 27 ensures the hermeticity of the battery case.
  • insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction.
  • the case body 15 has a step 21 formed, for example, by partially pressing the side wall of the case body 15 from the outside.
  • the step 21 may be formed in an annular shape along the circumferential direction of the case body 15 on the side wall of the case body 15.
  • the sealing body 16 is supported by the surface of the step 21 on the opening side.
  • the sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. In the sealing body 16, these members are stacked in this order.
  • the sealing body 16 is attached to the opening of the case body 15 so that the cap 26 is located outside the case body 15 and the filter 22 is located inside the case body 15.
  • Each of the above members constituting the sealing body 16 is, for example, disk-shaped or ring-shaped.
  • the lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and an insulating member 24 is interposed between each of their peripheral edges.
  • the filter 22 and the lower valve body 23 are connected to each other at their respective centers.
  • the upper valve body 25 and the cap 26 are connected to each other at their respective centers. In other words, each member except the insulating member 24 is electrically connected to each other.
  • the lower valve body 23 has an air vent hole (not shown). Therefore, when the internal pressure of the battery case rises due to abnormal heat generation or the like, the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23. This cuts off the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 breaks and gas is discharged from an opening (not shown) formed in the cap 26.
  • FIG. 2A is an enlarged view of a portion of the electrode group 14 where the first region of the separator is arranged on the inner periphery (e.g., a region two or three revolutions from the innermost periphery).
  • FIG. 2B is an enlarged view of a portion of the electrode group 14 where the second region of the separator is arranged on the outer periphery (e.g., a region two or three revolutions from the outermost periphery).
  • FIGS. 2A and 2B include the portion near the positive electrode surrounded by region II in FIG. 1 and the portion near the negative electrode surrounded by region III in FIG. 1.
  • the electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator 13.
  • the positive electrode 11, the negative electrode 12, and the separator 13 are all strip-shaped.
  • the separator 13 has a base layer 50 and spacer layers 53A, 53B formed on the base layer 50.
  • the spacer layer 53A arranged on the inner periphery of the electrode group 14 constitutes a first convex portion.
  • the spacer layer 53A (first convex portion) is formed in a first pattern.
  • the spacer layer 53B arranged on the outer periphery of the electrode group 14 constitutes a second convex portion.
  • the spacer layer 53B (second convex portion) is formed in a second pattern.
  • the first pattern and the second pattern are different, and the line width W1 of the first convex portion is shorter than the line width W2 of the second convex portion.
  • the ratio R1 of the area occupied by the spacer layer 53A (first convex portion) in the first region is smaller than the ratio R2 of the area occupied by the spacer layer 53B (second convex portion) in the second region. Therefore, the air permeability P1 of the first region is higher than the air permeability P2 of the second region.
  • the substrate layer 50 has a porous sheet 51 and a composite material layer 52.
  • the spacer layer 53 is formed on the composite material layer 52.
  • the electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 50 so that the separator 13 is disposed between the positive electrode and the negative electrode 12.
  • the positive electrode 11 includes a positive electrode collector 11a and a positive electrode composite layer 11b.
  • the positive electrode collector 11a is electrically connected to a cap 26, which functions as a positive electrode terminal, via a positive electrode lead 19.
  • the negative electrode 12 is shown as a negative electrode (negative electrode collector) in a state in which lithium metal is not deposited.
  • the negative electrode 12 is electrically connected to a case body 15, which functions as a negative electrode terminal, via a negative electrode lead 20.
  • the separator 13 has a first main surface 50a facing the negative electrode 12 and a second main surface 50b facing the positive electrode 11.
  • the spacer layer 53 is formed on the first main surface 50a.
  • the composite material layer 52 is formed on the main surface of the porous sheet 51 that faces the negative electrode 12, but the composite material layer 52 may not be present or may be formed on each of the two main surfaces of the porous sheet 51.
  • the spacer layer 53 is formed on the composite material layer 52 and is in contact with the negative electrode 12.
  • the spacer layer 53 forms a space 14s between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the separator 13).
  • FIG. 2A shows the line width W1 and height H1 of the spacer layer 53A (first convex portion)
  • FIG. 2B shows the line width W2 and height H2 of the spacer layer 53B (second convex portion).
  • W1 ⁇ W2 and H1 and H2 are the same, but this is not limited thereto, and may be, for example, H1>H2.
  • the proportion R1 of the area occupied by the spacer layer 53A (first convex portion) in the first region is smaller than the proportion R2 of the area occupied by the second convex portion in the second region.
  • lithium metal is precipitated on the negative electrode 12 during charging. Because there is a space 14s between the positive electrode 11 and the negative electrode 12, the volume change of the electrode group 14 caused by the precipitation of lithium metal is reduced, improving cycle characteristics.
  • FIG. 3 An example of the planar shape of the spacer layers 53A and 53B is shown in FIG. 3, and an enlarged view of a part of FIG. 3 (spacer layer 53B) is shown in FIG. 4.
  • the left end is the innermost end, and in the first region including this end, the spacer layer 53A forms a linear first convex portion 53a with a short line width.
  • the right end is the outermost end, and in the second region including this end, the spacer layer 53B forms a linear second convex portion 53b with a long line width.
  • the linear first convex portion 53a and the second convex portion 53b are arranged in a mesh pattern, and more specifically, in the first region, they are uniformly formed in a honeycomb pattern with a wide pitch, and in the second region, they are uniformly formed in a honeycomb pattern with a narrow pitch.
  • the honeycomb pattern is a pattern in which multiple hexagons are arranged so that they share sides with each other.
  • the region in which the linear first convex portion 53a and the second convex portion 53b are not formed forms a space 14s.
  • FIG. 4 shows the width W2 of the linear second convex portion 53b.
  • the width W2 of the linear second convex portion is the length (width) of the linear second convex portion 53b in a direction perpendicular to the direction in which the linear second convex portion 53b extends in a plan view.
  • a notch 54 is formed in the linear second convex portion 53b.
  • the notch 54 promotes the movement of ions in the non-aqueous electrolyte.
  • first convex portion 53a and the second convex portion 53b are shown in plan view in Figures 5 to 7.
  • the proportion R1 of the area occupied by the spacer layer 53A (first convex portion) in the first region is smaller than the proportion R2 of the area occupied by the second convex portion in the second region.
  • the spacer layer 53A in FIG. 5 includes a plurality of linear first convex portions 53a arranged in a direction that intersects with each other, and the spacer layer 53B includes a plurality of linear second convex portions 53b arranged in a direction that intersects with each other. Gaps P exist between the plurality of first convex portions 53a and between the plurality of second convex portions 53b. Areas where no linear convex portions are formed form spaces 14s. The line width of the first convex portions 53a is short, and the line width of the second convex portions 53b is long.
  • the spacer layer 53A in FIG. 6 includes multiple linear first convex portions 53a arranged in a stripe pattern and extending in the second direction
  • the spacer layer 53B includes multiple linear second convex portions 53b arranged in a stripe pattern and extending in the second direction.
  • the number of first convex portions 53a is smaller than the number of second convex portions 53b, and the pitch between the first convex portions 53a is wider than the pitch between the second convex portions 53b.
  • the spacer layer 53A in FIG. 7 includes linear first convex portions 53a arranged in a lattice (mesh) pattern, and the spacer layer 53B includes linear second convex portions 53b arranged in a lattice (mesh) pattern.
  • the size of the lattice of the first convex portions 53a is larger than the size of the lattice of the second convex portions 53b.
  • first convex portion may be formed in a honeycomb pattern
  • second convex portion may be formed in a pattern other than a honeycomb pattern
  • the battery includes an electrode group and a non-aqueous electrolyte
  • the electrode group includes a positive electrode, a negative electrode, and a separator, the positive electrode and the negative electrode are wound with the separator interposed therebetween,
  • the separator has a first surface facing an outer side of the electrode group and a second surface facing an inner side of the electrode group;
  • At least one of the first surface and the second surface has a first region having a first convex portion of a first pattern and a second region having a second convex portion of a second pattern different from the first pattern;
  • the second region is disposed closer to an outer periphery of the electrode group than the first region, a proportion of an area of the first region occupied by the first convex portion is smaller than a proportion of an area of the second region
  • the lithium secondary battery according to claim 1 wherein the first region has a higher air permeability than the second region.
  • the first convex portion and the second convex portion are each a linear convex portion, 3.
  • the separator has an elongated shape having a length D1 in a first direction parallel to a winding axis and a length D2 (D1 ⁇ D2) in a second direction intersecting the first direction, 5.
  • the separator has an elongated shape having a length D1 in a first direction parallel to a winding axis and a length D2 (D1 ⁇ D2) in a second direction intersecting the first direction, 11.
  • the separator according to any one of techniques 7 to 10, wherein the length of the first region in the second direction is 25% or less of the entire length of the separator in the second direction.
  • a separator having an elongated shape having a length D1 in a first direction and a length D2 (D1 ⁇ D2) in a second direction intersecting the first direction, the separator has a first surface and a second surface opposite the first surface; At least one of the first surface and the second surface has a first region having a first convex portion of a first pattern and a second region having a second convex portion of a second pattern different from the first pattern; the second region is disposed at a position farther from one end in the second direction than the first region, a ratio of an area of the first convex portion to the first region is smaller than a ratio of an area of the second convex portion to the second region.
  • a separator having an elongated shape having a length D1 in a first direction and a length D2 (D1 ⁇ D2) in a second direction intersecting the first direction, the separator has a first surface and a second surface opposite the first surface; At least one of the first surface and the second surface has a first region having a first convex portion of a first pattern and a second region having a second convex portion of a second pattern different from the first pattern; the second region is disposed at a position farther from one end in the second direction than the first region, The first region has a higher air permeability than the second region.
  • a separator having an elongated shape having a length D1 in a first direction and a length D2 (D1 ⁇ D2) in a second direction intersecting the first direction, the separator has a first surface and a second surface opposite the first surface; At least one of the first surface and the second surface has a first region having a first convex portion of a first pattern and a second region having a second convex portion of a second pattern different from the first pattern; the second region is disposed at a position farther from one end in the second direction than the first region, A separator, wherein the height of the first convex portion is greater than the height of the second convex portion.
  • NCA rock salt type lithium-containing transition metal oxide
  • AB conductive material
  • PVdF polyvinylidene fluoride
  • NMP N-methyl-2-pyrrolidone
  • the obtained positive electrode mixture slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector), dried, and the coating film of the positive electrode mixture was rolled using a roller. Finally, the resulting laminate of the positive electrode current collector and the positive electrode mixture was cut to a predetermined electrode size to obtain a positive electrode having a positive electrode mixture layer on both sides of the positive electrode current collector.
  • a dispersion of the spacer material was prepared by mixing 50 parts by volume of insulating particles (median diameter 3 ⁇ m, volume resistivity 10 ⁇ cm), 50 parts by volume of polyvinylidene fluoride (PVdF) as a binder resin, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium.
  • PVdF polyvinylidene fluoride
  • NMP N-methyl-2-pyrrolidone
  • a dispenser was used to dispense a dispersion of the spacer material onto the microporous thin film in a honeycomb pattern, and the coating was vacuum dried to form first and second convex portions.
  • one surface (first main surface) of the microporous thin film was divided into a first region and a second region, and the first convex portions were uniformly formed in the first honeycomb pattern in the first region, and the second convex portions were uniformly formed in the second honeycomb pattern in the second region.
  • the first region is an area with a length of L/4 extending from the innermost end of the first surface of the base layer toward the outer periphery, where L is the total length of the base layer in the second direction.
  • L is the total length of the base layer in the second direction.
  • the length L1 of the first region in the second direction is 25% of the total length L of the base layer (i.e., the separator) in the second direction.
  • the distance (pitch) between a pair of opposing sides of the regular hexagon was 10 mm
  • the distance (pitch) between a pair of opposing sides of the regular hexagon was 5 mm
  • the proportion R1 of the area occupied by the first convex portion in the first region was 9.7%
  • the proportion R2 of the area occupied by the second convex portion in the second region was 19%.
  • the air permeability P1 of the first region was 345 sec/100 mL
  • the air permeability P2 of the second region was 370 sec/100 mL.
  • the positive electrode and the negative electrode current collector were spirally wound with the separator interposed therebetween to prepare an electrode group.
  • the separator was arranged so that the spacer layer faced the negative electrode.
  • the electrode group was housed in a bag-shaped exterior body formed of a laminate sheet having an Al layer, and after injecting a non-aqueous electrolyte, the exterior body was sealed to complete the lithium secondary battery A1.
  • Example 2 Battery A2 was produced in the same manner as Battery A1, except that in the second pattern, the distance (pitch) between a pair of opposing sides of the regular hexagon was changed to 10 mm, and the line width W2 of the second convex portion was changed to 1.0 mm.
  • R1 was 9.7%, and R2 was 19%.
  • P1 was 322 seconds/100 mL, and P2 was 373 seconds/100 mL.
  • Example 3 The first pattern was changed to a striped pattern. Specifically, a plurality of linear first convex portions extending in the second direction were formed in the first region. The interval (pitch) between the plurality of linear first convex portions in the first direction was set to 5 mm, and the line width W1 was set to 0.5 mm. In the second pattern, the interval (pitch) between a pair of opposing sides of the regular hexagon was changed to 2.25 mm, and the line width W2 of the second convex portion was changed to 0.25 mm. Except for the above, Battery A3 was produced in the same manner as Battery A1. R1 was 10% and R2 was 21%. P1 was 345 seconds/100 mL, and P2 was 381 seconds/100 mL.
  • Example 4 In both the first and second patterns, the interval (pitch) between a pair of opposing sides of the regular hexagon was changed to 2.25 mm, the line widths W1 and W2 of the first and second convex parts were changed to 0.25 mm, two 0.5 mm-wide notches were provided for each honeycomb in the first convex part (see FIG. 4), and two 0.25 mm-wide notches were provided for each honeycomb in the second convex part.
  • Battery A4 was produced in the same manner as Battery A1.
  • R1 was 14.5% and R2 was 16.5%.
  • P1 was 351 seconds/100 mL and P2 was 368 seconds/100 mL.
  • Example 5 Battery A5 was produced in the same manner as Battery A1, except that in the first pattern, the height of the first convex portion was changed to 50 ⁇ m.
  • R1 was 9.7%
  • R2 was 19%
  • P1 was 345 sec/100 mL
  • P2 was 370 sec/100 mL.
  • Comparative Example 1 Battery B1 was produced in the same manner as Battery A1, except that second convex portions were formed in the second region in the same pattern as the first pattern.
  • Comparative Example 2 Battery B2 was constructed similarly to Battery A1, except that the patterns of the first and second regions were reversed. R1 was 19%, R2 was 9.7%, P1 was 370 sec/100 mL, and P2 was 345 sec/100 mL.
  • the battery was charged at a constant current of 2.15 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V until the current value per unit area of the electrode reached 0.54 mA.
  • the above charge/discharge cycle was repeated 50 times, and the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle was calculated as the retention rate.
  • Table 1 shows that batteries A1 to A5 of the embodiment achieved a higher capacity retention rate than batteries B1 and B2 of the comparative example.
  • the lithium secondary battery of the present disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet terminals, electric vehicles including hybrids and plug-in hybrids, and home storage batteries combined with solar cells.

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