WO2024262513A1 - リチウム二次電池および複合部材 - Google Patents

リチウム二次電池および複合部材 Download PDF

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Publication number
WO2024262513A1
WO2024262513A1 PCT/JP2024/022152 JP2024022152W WO2024262513A1 WO 2024262513 A1 WO2024262513 A1 WO 2024262513A1 JP 2024022152 W JP2024022152 W JP 2024022152W WO 2024262513 A1 WO2024262513 A1 WO 2024262513A1
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Prior art keywords
layer
filler
separator
spacer layer
main surface
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Ceased
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PCT/JP2024/022152
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English (en)
French (fr)
Japanese (ja)
Inventor
力也 沖本
亮平 宮前
洋基 坂田
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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 CN202480040517.5A priority Critical patent/CN121336309A/zh
Priority to JP2025528077A priority patent/JPWO2024262513A1/ja
Priority to EP24825914.5A priority patent/EP4734204A4/en
Publication of WO2024262513A1 publication Critical patent/WO2024262513A1/ja
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • 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
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
    • 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
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • 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
    • H01M50/471—Spacing elements inside cells other than separators, membranes or diaphragms; Manufacturing processes thereof
    • H01M50/474—Spacing elements inside cells other than separators, membranes or diaphragms; Manufacturing processes thereof characterised by their position inside the cells
    • 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
    • H01M50/471—Spacing elements inside cells other than separators, membranes or diaphragms; Manufacturing processes thereof
    • H01M50/48—Spacing elements inside cells other than separators, membranes or diaphragms; Manufacturing processes thereof characterised by the material
    • H01M50/486—Organic material
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • This disclosure relates to a lithium secondary battery having a lithium ion conductive non-aqueous electrolyte.
  • Non-aqueous electrolyte secondary batteries are used for ICT applications such as personal computers and smartphones, in-vehicle applications, and for power storage. In these applications, non-aqueous electrolyte secondary batteries are required to have even higher capacities.
  • Lithium ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Increasing the capacity of lithium ion batteries can be achieved by using, for example, a combination of graphite and an alloy active material such as a silicon compound as the negative electrode active material. However, increasing the capacity of lithium ion batteries is reaching its limit.
  • Lithium secondary batteries (lithium metal secondary batteries) are promising high-capacity non-aqueous electrolyte secondary batteries that exceed lithium-ion batteries.
  • lithium metal precipitates on the negative electrode during charging, and this lithium metal dissolves into the non-aqueous electrolyte during discharging.
  • Patent Document 2 proposes a separator for use in a nonaqueous electrolyte battery, the separator having a substrate and a plurality of convex patterns on at least one main surface of the substrate, the substrate including a single or multiple layers, and a value of T1/T2 expressed using the distance (T1) between the approximate plane formed at the top of the convex pattern and the approximate plane formed at the bottom of the convex pattern, and the total thickness (T) of the separator, of 0.3 or more.
  • Patent Document 1 claims that it is possible to suppress miswinding of the laminate or wound body including the electrodes and separator, and provide a nonaqueous electrolyte battery with excellent life characteristics and safety.
  • the resin and solvent penetrate into the substrate during printing or coating.
  • the resin and solvent that penetrated into the substrate then dry, which can cause wrinkles in the substrate. This can result in a shift in the position of the convex portions after the laminate or wound body is formed, making it impossible to maintain the spaces created by the convex portions, which can lead to reduced cycle characteristics.
  • a lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, in which lithium metal precipitates in the negative electrode during charging and dissolves during discharging;
  • the separator has a first main surface and further comprises a spacer layer disposed on the first main surface of the separator, the spacer layer including a resin and a filler, the spacer layer having a first layer disposed closest to the first main surface in a height direction intersecting with the first main surface, and a second layer in contact with the first layer in the height direction, wherein R 1 is an area ratio of the filler contained in the first layer calculated based on a cross section of the spacer layer along the height direction, and R 2 is an area ratio of the filler contained in the second layer, where R 1 /R 2 >1.
  • a composite member comprising: a separator having a first main surface; and a spacer layer disposed on the first main surface of the separator, the spacer layer including a resin and a filler, the spacer layer having a first layer disposed closest to the first main surface in a height direction intersecting the first main surface, and a second layer in contact with the first layer in the height direction, wherein R1 is an area ratio of the filler contained in the first layer calculated based on a cross section of the spacer layer along the height direction, and R2 is an area ratio of the filler contained in the second layer, where R1 / R2 >1.
  • FIG. 1 is a vertical cross-sectional view illustrating a lithium secondary battery according to an embodiment of the present disclosure.
  • FIG. 2 is an enlarged view showing a schematic view of a main part of the lithium secondary battery shown in FIG. 1 .
  • FIG. 2 is a plan view illustrating an example of the arrangement of a spacer layer provided on a surface of a separator in a lithium secondary battery according to an embodiment of the present disclosure.
  • FIG. 2 is a cross-sectional view illustrating a schematic internal structure of a spacer layer.
  • any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit.
  • one of the materials may be selected and used alone, or two or more of the materials may be used in combination.
  • a lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.
  • the positive electrode and the negative electrode may be wound with the separator interposed therebetween to form an electrode group having multiple turns.
  • the positive electrode and the negative electrode may be stacked with the separator interposed therebetween to form a laminate.
  • a lithium secondary battery is a type of secondary battery in which lithium metal precipitates on the negative electrode during charging, and lithium metal dissolves from the negative electrode during discharging.
  • 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 a first main surface and a second main surface opposite to the first main surface.
  • the first main surface and the second main surface are surfaces facing the positive electrode and the negative electrode, respectively, in a lithium secondary battery.
  • a spacer layer is disposed on the first main surface of the separator.
  • the spacer layer is a convex portion disposed on the surface of the separator, and is disposed on at least the first main surface of the separator.
  • the first main surface may be the surface facing the positive electrode or the surface facing the negative electrode.
  • the spacer layer (convex portion) may be disposed on both the first and second main surfaces.
  • the separator may be composed of only the substrate layer described below, or may be composed of multiple layers by including the substrate layer and, for example, a composite material layer described below.
  • the first and second main surfaces of the separator are synonymous with the first and second main surfaces of the substrate layer, and a spacer layer is disposed on the first main surface of the substrate layer.
  • the separator is composed of multiple layers, one of the surfaces of the separator facing the positive electrode and the negative electrode is the first main surface, and the other is the second main surface.
  • a spacer layer may be formed on the surface of the composite material layer, which is one of the multiple layers.
  • a separator with a spacer layer disposed on its first main surface may be referred to as a "composite member.”
  • the spacer layer forms a space between the positive electrode and the separator or between the negative electrode and the separator.
  • the spacer layer ensures a space for lithium metal to precipitate on the surface of the negative electrode, reducing the volume change of the negative electrode that accompanies the precipitation of lithium metal.
  • the space prevents the expansion of the negative electrode that accompanies charging and discharging, and prevents a decrease in cycle characteristics.
  • the spacer layer includes a resin and a filler.
  • the spacer layer including the resin and the filler can be formed on the first main surface, for example, by forming a solution or dispersion in which the resin and the filler are dissolved or dispersed in a solvent on the base layer of the separator by a printing method or a coating method, and then removing the solvent by drying.
  • the spacer layer has a first layer disposed closest to the first main surface in a height direction intersecting the first main surface, and a second layer in contact with the first layer in the height direction.
  • R1 area ratio of the filler contained in the first layer calculated based on a cross section along the height direction of the separator
  • R2 the area ratio of the filler contained in the second layer
  • R1 / R2 >1.
  • the first layer and the second layer have different filler area ratios. However, it is not necessary that there is a clear difference in the area ratio across the boundary between the first layer and the second layer, and it is sufficient that there is a distribution in which the area ratio decreases from the first layer toward the second layer (i.e., as it moves away from the first main surface).
  • the first layer is the area of the spacer layer closest to the first main surface.
  • a solution or dispersion is printed or applied to the first main surface of the substrate layer, the solvent penetrates into the pores of the separator through the first layer.
  • the filler content in the first layer higher than in the second layer, it becomes more difficult for the solvent and resin to penetrate from the first layer to the separator side, and shrinkage and wrinkle formation of the separator after the solvent is dried and removed are suppressed.
  • the space formation effect by the convex parts of the spacer layer is maintained at a high level, and deterioration of cycle characteristics can be effectively suppressed.
  • the first layer may include a region of the spacer layer near the first main surface, and may have a relatively thin thickness in the height direction.
  • the thickness of the first layer may be as thin as about 2 ⁇ m, depending on the thickness of the entire spacer layer. If the thickness of the first layer is 2 ⁇ m or more, this is sufficient to obtain the effect of suppressing the penetration of solvents and resins into the substrate layer.
  • the thickness of the first layer may be 2 ⁇ m or more. However, the thickness of the first layer may be less than 2 ⁇ m as long as it is 0.05T or more, where T is the total thickness of the spacer layer in the height direction.
  • the second layer is a region in the spacer layer that directly contacts the first layer in the height direction.
  • the second layer may occupy the entire portion of the spacer layer other than the first layer, or may be a part of the portion of the spacer layer other than the first layer.
  • the spacer layer has a third layer that contacts the second layer in the height direction and faces the first layer with the second layer in between.
  • the area ratio R3 of the filler contained in the third layer is not particularly limited, and may be smaller than R2 or larger than R2 .
  • R 1 , R 2 (and R 3 ) are calculated by the method shown below based on a cross section along the height direction of the separator.
  • a separator composite member on which the spacer layer to be measured is arranged.
  • the prepared composite member is cut in the thickness direction of the separator so as to cross the spacer layer to form a cross section of the spacer layer.
  • a cross section polisher CP
  • the composite member may be removed from a secondary battery in a fully charged state or a discharged state.
  • the composite member removed from the secondary battery is washed with an organic solvent such as dimethyl carbonate (DMC) and dried before measurement.
  • DMC dimethyl carbonate
  • the cross section of the spacer layer in the composite member is observed with a scanning electron microscope (SEM) to obtain a cross section image.
  • SEM scanning electron microscope
  • the SEM observation is performed by photographing a measurement area of 100 ⁇ m ⁇ 100 ⁇ m at a magnification of 500 to 3000 times.
  • the contours of the individual fillers in the cross section image are identified, and the area occupied by each filler in the cross section is obtained.
  • the area may be obtained by binarizing the area so that the part occupied by the filler in the cross section image is black (or white) and the other part is black (or white).
  • the ratio of the total area occupied by each filler to the area of the predetermined region is obtained and designated as R1 .
  • R1 the ratio of the total area occupied by each filler to the area of the predetermined region.
  • R1 is obtained from the area occupied by the filler in a predetermined region in the cross-sectional image that is determined to be the first layer
  • R2 is obtained from the area occupied by the filler in a predetermined region that is determined to be the second layer.
  • the smaller of 0.05T and 2 ⁇ m is set as the thickness T1 of the first layer, and R1 is obtained from the area occupied by the filler in a predetermined region that is a distance from the first main surface of T1 or less, and R2 is obtained from the area occupied by the filler in a predetermined region that is a distance from the first main surface of T1 or more and 5T1 or less .
  • R 1 /R 2 is, for example, greater than 1 and equal to or less than 10. In terms of suppressing the permeation of the solvent and resin into the separator, R 1 /R 2 is preferably equal to or greater than 1.03 and equal to or less than 4.25, and more preferably equal to or greater than 1.07 and equal to or less than 2.8.
  • R1 is, for example, 0.7 or more and 0.85 or less.
  • R1 is 0.7 or more and 0.85 or less.
  • R2 may be, for example, 0.3 or more. If R2 is 0.3 or more, when the spacer layer is formed on the surface of the separator, the rigidity of the spacer layer increases, and a spacer layer having a sufficient thickness can be stably formed, and a sufficient space for lithium metal to deposit on the negative electrode can be secured. However, if R2 is too large, the flexibility of the spacer layer decreases, and it may be difficult to form a wound electrode group. It is preferable that R2 is 0.8 or less.
  • the filler may include a first filler having an average particle size of less than 1 ⁇ m and a second filler having an average particle size of 1 to 10 ⁇ m. Since the first filler having a small particle size can enter the gaps between the second fillers, by increasing the content ratio of the first filler in the entire filler, it is easy to increase the content ratio of the filler contained in the spacer layer, and in particular, it is easy to increase the area ratio R1 of the filler in the first layer.
  • the content ratio of the first filler in the entire filler in the first layer is larger than the content ratio of the first filler in the entire filler in the second layer, it is possible to easily realize a spacer layer in which the area ratio R1 is larger than R2 .
  • the area ratio of the first filler to the total of the first filler and the second filler contained in the first layer is larger than the area ratio of the first filler to the total of the first filler and the second filler contained in the second layer.
  • the spacer layer including the first and second layers can be formed, for example, by preparing multiple types of solutions or dispersions with different resin and/or filler compositions and applying them to the first main surface of the separator in multiple applications.
  • fillers with a higher density tend to move toward the base layer under their own weight during the printing or coating process, making it easier to achieve a state in which the filler area ratio has a distribution in the height direction of the spacer layer, and it is easier to control the filler area ratio of the first layer close to the first main surface to be greater than the area ratio of the second layer.
  • the spacer layer can be formed with a predetermined pattern on the first main surface of the separator.
  • the spacer layer can be composed of multiple protrusions on the surface of the separator so that they are not continuous in both a first direction and a second direction intersecting the first direction.
  • the electrolyte can circulate through the gaps between the multiple protrusions, which improves circulation and further suppresses deterioration of cycle characteristics.
  • the multiple protrusions may be linear protrusions.
  • the multiple protrusions may be linear protrusions along a second direction perpendicular to the winding axis.
  • the linear protrusions may be straight protrusions, curved protrusions, or protrusions including straight and curved portions.
  • the multiple protrusions may be arranged in a staggered pattern.
  • a polygonal (e.g., hexagonal) mesh may be formed by multiple linear protrusions. From the viewpoint of suppressing unevenness of the space between the negative electrode and the separator, the interior angle of the polygon may be 120° or less.
  • the average height h of the convex portion may be 0.015 mm or more and 0.1 mm or less, or 0.02 mm or more and 0.09 mm or less, depending on the battery size.
  • the average height h of the convex portion is determined by averaging the measured values at any 10 points.
  • the height of a portion of the convex portion may be different from the height of the remaining portion of the convex portion, and the heights of adjacent convex portions may be different.
  • the multiple convex portions may include a convex portion with a height h1 and a convex portion with a height h2 smaller than the height h1.
  • the ratio of the height h2 to the height h1: h2/h1 may be, for example, 0.8 or more and less than 1.0, or 0.8 or more and 0.95 or less.
  • the width of the convex portion (width W of the linear convex portion 401 in FIG. 1) is, for example, 1 mm or less, and may be 0.1 mm or more and 1 mm or less.
  • the multiple protrusions may be made of a material that is less conductive than the positive and negative electrodes, or may be made of a resin material.
  • the material constituting the spacer layer is not particularly limited. It is preferable that the spacer layer is composed of an insulating material. Since lithium metal is difficult to deposit on the surface of an insulating material, the effect of suppressing the expansion of the negative electrode can be enhanced.
  • the spacer layer contains a resin as an insulating material, and further contains a filler.
  • the resin material include polyolefin resin, acrylic resin, polyamide resin, polyimide resin, silicone resin, fluorine-based resin, urethane resin, melamine resin, and urea resin.
  • the resin material may be a cured product of a curable resin such as an epoxy resin.
  • inorganic fillers may be mixed into these resin materials.
  • the filler contained in the spacer layer may be an insulating material or may be conductive.
  • the filler examples include inorganic particles such as metal oxide particles, metal nitride particles, metal fluoride particles, and metal carbide particles.
  • the inorganic particles can impart heat resistance to the separator.
  • Resin particles may also be used as the filler.
  • metal oxide particles include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, and manganese oxide.
  • metal nitride particles include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride.
  • metal fluoride particles include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride.
  • metal carbide particles include silicon carbide, boron carbide, titanium carbide, and tungsten carbide.
  • the inorganic particles may be porous aluminosilicates such as zeolite (M2 / nO.Al2O3.xSiO2.yH2O , where M is a metal element, n is the valence of M, x ⁇ 2, y ⁇ 0), layered silicates such as talc ( Mg3Si4O10 (OH) 2 ), minerals such as barium titanate ( BaTiO3 ) and strontium titanate ( SrTiO3 ), etc. These may be used alone or in combination of two or more kinds .
  • zeolite M2 / nO.Al2O3.xSiO2.yH2O , where M is a metal element, n is the valence of M, x ⁇ 2, y ⁇ 0
  • layered silicates such as talc ( Mg3Si4O10 (OH) 2 )
  • minerals such as barium titanate ( BaTiO3 ) and stront
  • the spacer layer desirably has a Young's modulus of 0.01 GPa or more and 10 GPa or less. This makes it easier to alleviate stress caused by expansion and contraction of the negative electrode, and makes it easier to maintain the space that contains the lithium metal. In addition, damage to the electrode caused by the spacer layer is easier to suppress.
  • Examples of insulating materials that have a Young's modulus in the above range include the cured product of the above-mentioned curable resin.
  • the spacer layer disposed on the second main surface may have a first layer disposed on the second main surface of the separator and a second layer in contact with the first layer in the height direction, and when the area ratio of the filler contained in the first layer is R1 and the area ratio of the filler contained in the second layer is R2 , the relationship R1 / R2 >1 may be satisfied.
  • the lithium secondary battery may have a stacked electrode group formed by stacking positive and negative electrodes with a separator between them, or may have a wound electrode group formed by winding positive and negative electrodes in a spiral shape with a separator between them.
  • a composite member relates to a separator provided with the above-mentioned spacer layer.
  • the composite member includes a separator having a first main surface and a spacer layer disposed on the first main surface of the separator.
  • the spacer layer includes a resin and a filler.
  • the spacer layer includes a first layer disposed closest to the first main surface in a height direction intersecting with the first main surface, and a second layer contacting the first layer in the height direction, and when an area ratio of the filler contained in the first layer calculated based on a cross section along the height direction of the separator and the spacer layer is R1 and an area ratio of the filler contained in the second layer is R2 , R1 / R2 >1.
  • the negative electrode includes a negative electrode current collector.
  • lithium metal is deposited on the surface of the negative electrode current collector by charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode current collector by charging, becoming lithium metal, and depositing on the surface of the negative electrode current collector.
  • the lithium metal deposited on the surface of the negative electrode current collector dissolves as lithium ions in the non-aqueous electrolyte by discharging.
  • the lithium ions contained in the non-aqueous electrolyte may be derived from a lithium salt added to the non-aqueous electrolyte, may be supplied from the positive electrode active material by charging, or may be both of them.
  • the negative electrode current collector can be a conductive sheet.
  • conductive sheets include foil and film.
  • the surface of the conductive sheet may be smooth. This makes it easier for lithium metal from the positive electrode to deposit evenly on the conductive sheet during charging.
  • Smooth means that the maximum height roughness Rz of the conductive sheet is 20 ⁇ m or less.
  • the maximum height roughness Rz of the conductive sheet may be 10 ⁇ m or less.
  • the maximum height roughness Rz is measured in accordance with JIS B 0601:2013.
  • 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.
  • a negative electrode composite layer (not shown) may be formed on the surface of the negative electrode current collector.
  • the negative electrode composite layer is formed, for example, by applying a paste containing a negative electrode active material such as graphite to at least a part of the surface of the negative electrode current collector.
  • the thickness of the negative electrode composite layer is set to be thin enough so that lithium metal can be precipitated on the negative electrode.
  • 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).
  • 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 occlusion layer when fully charged. In other words, the negative electrode exhibits capacity due to the precipitation and dissolution of lithium metal.
  • 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 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 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 positive electrode current collector may be a conductive sheet.
  • conductive sheets include foils and films.
  • the surface of the positive electrode current collector may be coated with a carbon material.
  • 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 separator may be composed of only a substrate layer, or may include a substrate layer and a composite material layer described later.
  • a spacer layer is disposed on the surface of the substrate layer.
  • a spacer layer may be disposed on the surface of the substrate layer, a spacer layer may be disposed on the surface of the composite material layer, or a spacer layer may be disposed on the surfaces of both the substrate layer and the composite material layer.
  • the spacer layer has the above-mentioned structure.
  • a porous sheet having ion permeability and insulation is used for the substrate layer of the separator.
  • the porous sheet include a thin film having micropores, a woven fabric, and a nonwoven fabric.
  • the material of the separator is not particularly limited, but may be a polymeric material.
  • the polymeric material include olefin resin, polyamide resin, cellulose, and the like.
  • the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene, and the like.
  • the separator may contain additives as necessary. Examples of the additives include inorganic fillers, and the like.
  • the composite material layer of the separator may be formed, for example, on the substrate layer of the separator.
  • the composite material layer is preferably a porous layer.
  • the method for forming the porous composite material layer is not particularly limited, and a known method may be used.
  • the porous composite material layer may be formed by printing the raw material of the composite material layer as ink on the substrate layer.
  • the composite material layer may be formed on the main surface on the positive electrode side of the two main surfaces of the substrate layer, or on the main surface on the negative electrode side, or on each of the two main surfaces.
  • the spacer layer may be formed on the composite material layer, or may be formed on the substrate layer without a composite material layer.
  • the separator may have a structure of substrate layer/composite material layer/spacer layer, composite material layer/substrate layer/spacer layer, or composite material layer/substrate layer/composite material layer/spacer layer. In these structures, forming a spacer on the composite material layer particularly enhances the effect of suppressing thermal shrinkage of the substrate layer.
  • the composite layer includes a polymer (hereinafter sometimes referred to as "polymer (PL)”) 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 second particles are particles other than the first particles.
  • the composite layer is a layer that allows lithium ions to pass through.
  • the separator may be arranged so that the composite material layer faces the positive electrode, or the composite material layer faces the negative electrode.
  • 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 average particle size of the first particles may be in the range of 0.1 ⁇ m to 1.0 ⁇ m (for example, in the range of 0.1 ⁇ m to 0.5 ⁇ m, 0.1 ⁇ m to 0.2 ⁇ m, or 0.1 ⁇ m to 0.19 ⁇ m).
  • the average particle size of the first particles may be 0.1 ⁇ m or more, or 0.15 ⁇ m or more.
  • the average particle size of the first particles may be 1.0 ⁇ m or less, 0.5 ⁇ m or less, 0.3 ⁇ m or less, or 0.2 ⁇ m or less.
  • the polymer (PL) may be a polymer having higher heat resistance than the main component of the separator's base layer.
  • the polymer (PL) preferably contains at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamideimides. These are known as polymers (or polymers or resins from another perspective) with high heat resistance. From the viewpoint of heat resistance, aramids, i.e., meta-aramids (meta-fully aromatic polyamides) and para-aramids (para-fully aromatic polyamides), are preferred.
  • a preferred example of the polymer (PL) is meta-aramid.
  • Well-known aromatic polyamides, aromatic polyimides, and aromatic polyamideimides may be used for the polymer (PL).
  • aromatic polyamides examples include polymers formed by condensation polymerization of monomers having an aromatic backbone and containing amide bonds in the repeating units.
  • aromatic polyamides examples include meta-aromatic polyamides (e.g. fully meta-aromatic polyamides) and para-aromatic polyamides (e.g. fully para-aromatic polyamides).
  • Fully aromatic polyamides are also called aramids.
  • a preferred example of the second particles is a particle composed of an insulating inorganic compound that does not melt or decompose when the battery generates abnormal heat.
  • the second particles may be inorganic particles that are generally used as inorganic fillers. Examples of materials for the second particles include oxides, oxide hydrates, hydroxides, nitrides, carbides, sulfides, etc., which may contain metal elements.
  • the average particle size of the second particles may be 0.2 ⁇ m or more and 2 ⁇ m or less.
  • oxides and oxide hydrates 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.
  • carbides include silicon carbide, boron carbide, etc.
  • sulfides include barium sulfate, etc.
  • hydroxides include aluminum hydroxide, etc.
  • the material of the second particles may be a porous aluminosilicate such as zeolite, a layered silicate such as talc, barium titanate (BaTiO 3 ), strontium titanate (SrTiO 3 ), etc. From the viewpoint of insulation property, heat resistance, etc., the material of the second particles may be at least one selected from the group consisting of aluminum oxide, boehmite, talc, titanium oxide, and magnesium oxide.
  • the average particle size of the second particles may be within the range exemplified for the average particle size of the first particles.
  • the inorganic particles may include the above-mentioned first particles and second particles other than phosphate.
  • the composite material layer may include a first layer including the first particles and a second layer including the second particles. This configuration can particularly enhance the effect of suppressing excessive temperature rise in the electrode group.
  • the composite material layer may be configured of a single layer or multiple layers.
  • Non-aqueous electrolyte The non-aqueous electrolyte having lithium ion conductivity contains, for example, a non-aqueous solvent, and lithium ions and anions dissolved in the non-aqueous solvent.
  • the non-aqueous electrolyte may be in a liquid state or a gel state.
  • 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.
  • the gelled non-aqueous 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, etc.
  • the anion of the oxalate complex may contain boron and/or phosphorus.
  • Examples of the anion of the oxalate complex include bisoxalate 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 these anions alone or in combination of two or more kinds.
  • the non-aqueous electrolyte preferably contains at least an anion of an oxalate complex.
  • the interaction between the anion of the oxalate complex 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 anion of the oxalate complex may be combined with other anions.
  • the other anions may be PF 6 - and/or imide anions.
  • 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.
  • the configuration of the lithium secondary battery according to the present disclosure will be explained with reference to the drawings, using as an example a cylindrical battery equipped with a wound electrode group.
  • the present disclosure is not limited to the following configuration.
  • FIG. 1 is a vertical cross-sectional view of a lithium secondary battery 10.
  • the lithium secondary battery 10 is a cylindrical battery that includes a cylindrical battery case, a wound electrode group 14 housed in the battery case, and a non-aqueous electrolyte (not shown).
  • the battery case is composed of a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16 that seals the opening of the case body 15.
  • the case body 15 has an annular step 21 formed by partially pressing the side wall from the outside near the opening.
  • the sealing body 16 is supported by the surface of the step 21 on the opening side.
  • a gasket 27 is disposed between the case body 15 and the sealing body 16, thereby ensuring 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 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.
  • the cap 26 is disposed outside the case body 15, and the filter 22 is disposed inside the case body 15.
  • 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 their respective peripheral edges.
  • the filter 22 and the lower valve body 23 are connected to each other at their respective peripheral edges.
  • the upper valve body 25 and the cap 26 are connected to each other at their respective peripheral edges.
  • the lower valve body 23 is formed with an air hole.
  • the electrode group 14 is composed of a positive electrode 110, a negative electrode (negative electrode current collector) 120, and a separator 300.
  • the positive electrode 110, the negative electrode 120, and the separator 300 interposed between them are all strip-shaped, and are wound in a spiral shape so that their width directions are parallel to the winding axis.
  • the positive electrode 110 is electrically connected to the cap 26, which also serves as a positive electrode terminal, via the positive electrode lead 19.
  • One end of the positive electrode lead 19 is connected, for example, near the center of the positive electrode 110 in the longitudinal direction.
  • the other end of the positive electrode lead 19 extending from the positive electrode 110 is welded to the inner surface of the filter 22 through a through hole formed in the insulating plate 17.
  • the negative electrode 120 is electrically connected to the case body 15, which also serves as the negative electrode terminal, via the negative electrode lead 20.
  • One end of the negative electrode lead 20 is connected, for example, to the longitudinal end of the negative electrode 120, and the other end is welded to the inner bottom surface of the case body 15.
  • FIG. 2 is an enlarged view showing a schematic diagram of the discharge state of region X surrounded by a dashed line in FIG. 1.
  • the cross-sectional shape of the spacer layer is trapezoidal, but the embodiment of the present disclosure is not limited to this.
  • the spacer layer is provided between the positive electrode and the separator.
  • the embodiment of the present disclosure is not limited to this, and the spacer layer may be provided between the negative electrode and the separator, or between the positive electrode, the negative electrode, and the separator.
  • the positive electrode 110 includes a positive electrode current collector 111 and a positive electrode composite layer 112.
  • a spacer layer 400 is provided between the positive electrode composite layer 112 and the separator 300.
  • the spacer layer 400 includes linear convex portions 401 that are provided along the longitudinal direction (circumferential direction of winding) of the separator 300.
  • lithium metal is not deposited on the surface of the negative electrode current collector 121, and a space is maintained between the positive electrode 110 and the separator 300.
  • lithium metal is deposited on the surface of the negative electrode current collector 121, and is accommodated in the space between the positive electrode 110 and the separator 300 while being subjected to the pressing force of the separator 300. That is, the negative electrode 120 includes the negative electrode current collector 121 in a discharged state, and includes the negative electrode current collector 121 and lithium metal deposited on its surface in a charged state.
  • the lithium metal is accommodated in the space between the positive electrode 110 and the separator 300, the apparent volume change of the electrode group due to the precipitation of lithium metal during the charge/discharge cycle is reduced. Therefore, the stress applied to the negative electrode current collector 121 is also suppressed. In addition, since pressure is applied from the separator 300 to the lithium metal accommodated between the positive electrode 110 and the separator 300, the precipitation state of the lithium metal is controlled, the lithium metal is less likely to become isolated, and a decrease in charge/discharge efficiency is suppressed.
  • FIG. 3 is a plan view showing a schematic arrangement of a spacer layer disposed on the surface of separator 300.
  • spacer layer 400 is made up of multiple linear protrusions extending substantially parallel along circumferential direction D2 of winding. Note that substantially parallel means roughly parallel, and linear protrusions may intersect at an angle of, for example, 0° to 20° or 0° to 10°.
  • the spacer layer 400 has a plurality of linear protrusions 401 and 402 along the circumferential direction D2.
  • the linear protrusions 402 are at different positions in the axial direction D1 of the winding and the circumferential direction D2 from the linear protrusions 401.
  • the linear protrusions 401 and 402 are arranged in a staggered pattern on the surface of the separator 300 as a whole.
  • the straight line passes through the linear protrusions 401 at three locations (dashed line SL1 in FIG. 1) or through the linear protrusions 402 at two locations (dashed line SL2 in FIG. 1). Having two or more straight lines passing through makes it easier to maintain a space for lithium metal to precipitate.
  • the multiple line-shaped protrusions 401 are arranged so that the length (width in the second direction) increases toward the outer periphery of the winding in the second direction D2, and the interval (center-to-center distance) between adjacent protrusions in the second direction increases.
  • the multiple line-shaped protrusions 401 include multiple line-shaped protrusions 401a, 401b, and 401c, where the line-shaped protrusion 401b is located on the inner periphery side of the winding than the line-shaped protrusion 401a, and the line-shaped protrusion 401c is located on the outer periphery side of the winding than the line-shaped protrusion 401a.
  • the multiple line-shaped protrusions 402 include multiple line-shaped protrusions 402a, 402b, and 402c, where the line-shaped protrusion 402b is located on the inner periphery side of the winding than the line-shaped protrusion 402a, and the line-shaped protrusion 402c is located on the outer periphery side of the winding than the line-shaped protrusion 402a.
  • the linear protrusions 401 and 402 are aligned radially to form radial rows, and the linear protrusions 402 (402a, 402b, 402c) are aligned radially to form radial rows.
  • the separator may shrink when the solvent is removed by drying, resulting in wrinkles. Wrinkles cause a shift in the arrangement of the linear convex portions 401 and 402. For example, if the positions of the linear convex portions 401a, 401b, and 401c (402a, 402b, and 402c) in the winding axis direction D1 are shifted, the linear convex portions 401a, 401b, and 401c will not be aligned in the radial direction when the electrode group is formed, and radial rows will not be formed.
  • the filler content of the spacer layer is increased in the first layer on the first main surface side of the separator, thereby suppressing shrinkage and wrinkle formation.
  • misalignment of the convex portions of the spacer layer is suppressed. This maintains a high space-forming effect due to the convex portions of the spacer layer, effectively suppressing deterioration of cycle characteristics.
  • the spacer layer 400 includes a resin 410, a first filler 411, and a second filler 412 having a larger average particle size than the first filler.
  • the first filler 411 and the second filler 412 are dispersed in the resin 410.
  • the first filler 411 and the second filler 412 are distributed biasedly toward the base layer 301 side of the separator 300, and the area ratio R1 of the filler in the first layer 400A near the base layer is larger than the area ratio R2 of the filler in the second layer 400B in contact with the first layer on the opposite side to the base layer.
  • a cylindrical lithium secondary battery with a wound electrode group has been described, but the shape of the lithium secondary battery is not limited to this, and in addition to a cylindrical shape, various shapes such as a coin type, a square type, a sheet type, a flat type, etc. can be appropriately selected depending on the application.
  • the shape of the electrode group is also not particularly limited, and may be a laminated type.
  • the configuration of the lithium secondary battery other than the electrode group and non-aqueous electrolyte can be any known configuration without particular restriction.
  • the battery includes a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte;
  • the separator has a first main surface, a spacer layer disposed on the first main surface of the separator, the spacer layer including a resin and a filler;
  • the spacer layer includes a first layer disposed closest to the first main surface in a height direction intersecting the first main surface, and a second layer in contact with the first layer in the height direction, a lithium secondary battery in which R1/R2 >1 is satisfied, where R1 is an area ratio of the filler contained in the first layer calculated based on a cross section of the spacer layer along the height direction, and R2 is an area ratio of the filler contained in the second layer.
  • the lithium secondary battery according to any one of the first to sixth aspects wherein the filler includes a first filler having an average particle size of less than 1 ⁇ m and a second filler having an average particle size of 1 to 10 ⁇ m.
  • the lithium secondary battery according to technology 7 wherein, in the cross section, an area ratio of the first filler to a total of the first filler and the second filler contained in the first layer is greater than an area ratio of the first filler to a total of the first filler and the second filler contained in the second layer.
  • the thickness of the first layer is equal to or greater than the smaller of 2 ⁇ m or 0.05T, where T is the thickness of the spacer layer in the height direction.
  • Example 10 The lithium secondary battery according to the present disclosure will be specifically described below based on examples and comparative examples. The present disclosure is not limited to the following examples.
  • 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 an Al foil (positive electrode current collector), dried, and the coating film of the positive electrode mixture was rolled using a roller. Finally, the obtained laminate of the positive electrode current collector and the positive electrode mixture was cut to a predetermined electrode size to prepare a positive electrode having a positive electrode mixture layer on both sides of the positive electrode current collector.
  • a separator substrate (microporous membrane) was prepared. Ink was applied to a predetermined area on the surface of the separator substrate using a dispenser, and then the substrate was dried with hot air to provide a spacer layer.
  • Two types of resin compositions were prepared by dissolving or dispersing polyvinylidene fluoride (PVdF), alumina particles (first filler), and polyethylene (PE) resin particles (second filler) in a dispersion medium as the ink applied to the surface of the separator substrate.
  • the two types of resin compositions differ in the blending ratio of alumina particles to polyethylene resin particles.
  • the alumina particles used had an average particle diameter of 0.4 ⁇ m.
  • the polyethylene resin particles used had an average particle diameter of 5 ⁇ m.
  • a first ink for forming the first layer was obtained by mixing 40 parts by volume of polyvinylidene fluoride, 20 parts by volume of alumina particles, and 40 parts by volume of polyethylene resin particles.
  • a second ink for forming the second layer was obtained by mixing 40 parts by volume of polyvinylidene fluoride and 60 parts by volume of polyethylene resin particles. The first ink was applied to a specified area on the surface of the separator substrate to form the first layer, and then the second ink was applied to the surface of the first layer and dried to remove the dispersion medium, forming the second layer.
  • a composite member in which a spacer layer having a first layer and a second layer was disposed on the surface of the separator substrate.
  • the first layer and the second layer had the same thickness.
  • the total thickness of the spacer layer (height of the convex portion) was 40 ⁇ m.
  • a cross section of the separator was formed along the spacer layer, and the area ratio of the filler was evaluated by analyzing the SEM cross section image.
  • the area ratio R1 of the filler in the first layer was 0.7
  • the area ratio R2 of the filler in the second layer was 0.55
  • R1 / R2 was 1.27.
  • the positive electrode and the negative electrode current collector were spirally wound with the above-mentioned composite member interposed therebetween to prepare an electrode group.
  • the composite member was arranged so that the spacer layer faces the positive electrode. Since all the lithium contained in the electrode group originates from the positive electrode, the molar ratio of the total amount mLi of lithium possessed by the positive electrode and the negative electrode to the amount mM of metal M (here, Ni, Co, and Al) possessed by the positive electrode: mLi/mM is 1.0.
  • the electrode group was placed in a bag-shaped exterior body made of a laminate sheet with an Al layer, and the nonaqueous electrolyte was injected. The exterior body was then sealed to complete the lithium secondary battery A1.
  • Example 2 In producing the separator, a spacer layer was formed using an ink in which ethyl cellulose resin (EC), alumina particles (first filler), and polyethylene (PE) resin particles (second filler) were dissolved or dispersed in a dispersion medium.
  • EC ethyl cellulose resin
  • first filler alumina particles
  • PE polyethylene
  • the first ink for forming the first layer was obtained by mixing 30 parts by volume of ethyl cellulose resin, 20 parts by volume of alumina particles, and 50 parts by volume of polyethylene resin particles.
  • the second ink for forming the second layer was obtained by mixing 40 parts by volume of ethyl cellulose resin and 60 parts by volume of polyethylene resin particles.
  • the first ink was applied to a specified area on the surface of the separator substrate to form the first layer, and then the second ink was applied to the surface of the first layer and dried to remove the dispersion medium, forming the second layer.
  • a composite member in which a spacer layer having a first layer and a second layer was disposed on the surface of the separator substrate.
  • the first layer and the second layer had the same thickness.
  • the total thickness of the spacer layer (height of the convex portion) was 40 ⁇ m.
  • a cross section of the separator was formed along the spacer layer, and the area ratio of the filler was evaluated by analyzing the SEM cross section image.
  • the area ratio R1 of the filler in the first layer was 0.75
  • the area ratio R2 of the filler in the second layer was 0.7
  • R1 / R2 was 1.07.
  • a lithium secondary battery A2 according to Example 2 was completed in the same manner as Example 1, except that the separator obtained in this manner was used.
  • Examples 3 to 5 and Comparative Examples 1 to 3 In preparing the separator, the content ratios of the ethyl cellulose resin, the alumina particles, and the polyethylene resin particles contained in the first and second inks were changed from those in Example 2. Except for this, the lithium secondary batteries A3 to A5 and B1 to B3 according to Examples 3 to 5 and Comparative Examples 1 to 3 were completed in the same manner as in Example 2.
  • Example 3 30 parts by volume of ethyl cellulose resin, 30 parts by volume of alumina particles, and 40 parts by volume of polyethylene resin particles were mixed to obtain a first ink for forming a first layer. 60 parts by volume of ethyl cellulose and 40 parts by volume of polyethylene resin particles were mixed to obtain a second ink for forming a second layer. The thicknesses of the first and second layers were the same. The total thickness of the spacer layer (height of the convex portion) was 35 ⁇ m.
  • a cross section of the separator was formed along the spacer layer, and the area ratio of the filler was evaluated by analyzing the SEM cross section image.
  • the area ratio R1 of the filler in the first layer was 0.85
  • the area ratio R2 of the filler in the second layer was 0.3
  • R1 / R2 was 2.8.
  • Example 4 40 parts by volume of ethyl cellulose resin, 30 parts by volume of alumina particles, and 30 parts by volume of polyethylene resin particles were mixed to obtain a first ink for forming a first layer. 30 parts by volume of ethyl cellulose and 70 parts by volume of polyethylene resin particles were mixed to obtain a second ink for forming a second layer. The thicknesses of the first and second layers were the same. The total thickness of the spacer layer (height of the convex portion) was 40 ⁇ m.
  • a cross section of the separator was formed along the spacer layer, and the area ratio of the filler was evaluated by analyzing the SEM cross section image.
  • the area ratio R1 of the filler in the first layer was 0.72
  • the area ratio R2 of the filler in the second layer was 0.7
  • R1 / R2 was 1.03.
  • Example 5 30 parts by volume of ethyl cellulose resin, 40 parts by volume of alumina particles, and 30 parts by volume of polyethylene resin particles were mixed to obtain a first ink for forming a first layer. 60 parts by volume of ethyl cellulose and 40 parts by volume of polyethylene resin particles were mixed to obtain a second ink for forming a second layer. The thicknesses of the first and second layers were the same. The total thickness of the spacer layer (height of the convex portion) was 30 ⁇ m.
  • a cross section of the separator was formed along the spacer layer, and the area ratio of the filler was evaluated by analyzing the SEM cross section image.
  • the area ratio R1 of the filler in the first layer was 0.85
  • the area ratio R2 of the filler in the second layer was 0.2
  • R1 / R2 was 4.25.
  • Comparative Example 1 40 parts by volume of ethyl cellulose resin, 5 parts by volume of alumina particles, and 55 parts by volume of polyethylene resin particles were mixed to obtain a first ink for forming a first layer. 40 parts by volume of ethyl cellulose and 60 parts by volume of polyethylene resin particles were mixed to obtain a second ink for forming a second layer. The thicknesses of the first and second layers were the same. The total thickness of the spacer layer (height of the convex portion) was 40 ⁇ m.
  • a cross section of the separator was formed along the spacer layer, and the area ratio of the filler was evaluated by analyzing the SEM cross section image.
  • the area ratio R1 of the filler in the first layer and the area ratio R2 of the filler in the second layer were both 0.7, and R1 / R2 was 1.0.
  • Comparative Example 2 35 parts by volume of ethyl cellulose resin, 5 parts by volume of alumina particles, and 60 parts by volume of polyethylene resin particles were mixed to obtain a first ink for forming a first layer. 20 parts by volume of ethyl cellulose and 80 parts by volume of polyethylene resin particles were mixed to obtain a second ink for forming a second layer. The thicknesses of the first and second layers were the same. The total thickness of the spacer layer (height of the convex portion) was 40 ⁇ m.
  • Comparative Example 3 90 parts by volume of ethyl cellulose resin and 10 parts by volume of alumina particles were mixed to obtain a first ink for forming a first layer. 90 parts by volume of ethyl cellulose and 10 parts by volume of polyethylene resin particles were mixed to obtain a second ink (same as the first ink) for forming a second layer. The thicknesses of the first and second layers were the same. The total thickness of the spacer layer (height of the convex portion) was 20 ⁇ m.
  • a cross section of the separator was formed along the spacer layer, and the area ratio of the filler was evaluated by analyzing the SEM cross section image.
  • the area ratio R1 of the filler in the first layer and the area ratio R2 of the filler in the second layer were both 0.1, and R1 / R2 was 1.0.
  • 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 and discharge constituted one cycle, and the charge and discharge cycle was repeated.
  • the ratio (%) of the discharge capacity at the 200th cycle to the discharge capacity at the first cycle was calculated as the capacity retention rate.
  • the lithium secondary battery disclosed herein can be used in electronic devices such as mobile phones, smartphones, and tablet devices, electric vehicles including hybrids and plug-in hybrids, and home storage batteries combined with solar cells.

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PCT/JP2024/022152 2023-06-22 2024-06-19 リチウム二次電池および複合部材 Ceased WO2024262513A1 (ja)

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