Lithium secondary battery and separator

Abstract

This lithium secondary battery is provided with: an electrode group which is provided with a positive electrode, a negative electrode in which lithium metal is precipitated during charging, and a separator, and which is wound with the separator interposed therebetween, and a non-aqueous electrolyte in which the lithium metal is dissolved during discharging; the separator has a first surface facing the outside of the electrode group and a second surface facing the inside of the electrode group, and at least one of the first surface and the second surface has a first region having first protrusions of a first pattern and a second region having second protrusions of a second pattern different from the first pattern. The second region is disposed closer to the outer peripheral side of the electrode group than the first region.

Description

[0001] Cross-reference of related applications

[0002] This disclosure claims priority to Japanese Patent Application No. 2023-122847, filed with the Japan Patent Office on July 27, 2023, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates to lithium secondary batteries and separators. Background Technology

[0004] Lithium-ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Lithium-ion batteries (lithium metal batteries), with even higher capacity than lithium-ion batteries, are highly anticipated. In lithium-ion batteries, lithium metal is deposited at the negative electrode during charging and dissolves as lithium ions during discharging, releasing them into the non-aqueous electrolyte.

[0005] In lithium secondary batteries, lithium metal is deposited at the negative electrode during charging, so space needs to be ensured between the separator and the electrode.

[0006] Patent document 1 proposes "a lithium secondary battery, wherein the lithium secondary battery comprises: 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, wherein lithium metal is deposited at 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, the first length of the separator in a first direction D1 is smaller than the second length in a second direction D2 intersecting the first direction D1, and at least one of the angle between the separator and the spacer on the spacer side, and the angle between the electrode in contact with the spacer and the spacer on the spacer side, is greater than 90° in a cross section of the spacer cut along the thickness direction of the separator and the first direction D1."

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2021 / 192645 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] When an electrode assembly is formed by winding the positive and negative electrodes together with a separator in between, sometimes the height of the space on the inner periphery of the electrode assembly for lithium deposition is insufficient. This insufficient height of the space becomes the cause of electrode buckling due to excessive stress on the inner periphery.

[0012] Solution for solving problems

[0013] One aspect of the present disclosure relates to a lithium secondary battery, which includes: an electrode assembly and a non-aqueous electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive electrode and the negative electrode are wound with the separator interposed therebetween. In the negative electrode, lithium metal is deposited during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging. The separator has a first surface facing the outside of the electrode assembly and a second surface facing the inside of the electrode assembly. At least one of the first surface and the second surface has a first region and a second region. The first region has first protrusions with a first pattern, and the second region has second protrusions with a second pattern different from the first pattern. The second region is disposed closer to the outer peripheral side of the electrode assembly than the first region.

[0014] 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 assembly. The separator has a first surface facing the outside of the electrode assembly and a second surface facing the inside of the electrode assembly. At least one of the first surface and the second surface has a first region and a second region. The first region has first protrusions with a first pattern, and the second region has second protrusions with a second pattern different from the first pattern. The second region is disposed closer to the outer peripheral side of the electrode assembly than the first region.

[0015] Still another aspect of the present disclosure relates to a separator that is in a long strip 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 to the first surface. At least one of the first surface and the second surface has a first region and a second region. The first region has first protrusions with a first pattern, and the second region has second protrusions with a second pattern different from the first pattern. The second region is disposed at a position farther from one end of the second direction than the first region.

[0016] Effect of the invention

[0017] According to the present disclosure, it is easy to ensure the height of the space for depositing lithium metal on the inner peripheral side of the wound electrode assembly of the lithium secondary battery.

[0018] The novel features of the present invention are described in the claims, but the present invention relates to both the constitution and the content, and together with other objects and features of the present invention, can be better understood through the following detailed description with reference to the drawings. Brief description of the drawings

[0019] Figure 1This is a longitudinal cross-sectional view schematically illustrating an example of a lithium secondary battery according to an embodiment of the present disclosure.

[0020] Figure 2A It is a schematic representation Figure 1 The diagram shows a cross-sectional view of a portion of the inner circumference of a lithium secondary battery.

[0021] Figure 2B It is a schematic representation Figure 1 The diagram shows a cross-sectional view of a portion of the outer periphery of a lithium secondary battery.

[0022] Figure 3 This is a top view showing an example of the first and second protrusions.

[0023] Figure 4 yes Figure 3 A magnified view of a portion of it.

[0024] Figure 5 This is a top view showing another example of the first and second protrusions.

[0025] Figure 6 This is a top view showing another example of the first and second protrusions.

[0026] Figure 7 This is a top view showing another example of the first and second protrusions. Detailed Implementation

[0027] The following examples illustrate embodiments of this disclosure, but the embodiments of this disclosure are not limited to the examples described below. In the following description, specific numerical values ​​and / or materials are sometimes exemplified, but other numerical values ​​and / or materials can be applied as long as the invention involved in this disclosure can be implemented. In this specification, the description of "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower". In the following description, where lower and upper limits are exemplified for numerical values ​​relating to specific physical properties and / or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit.

[0028] Furthermore, this disclosure includes combinations of matters recited in any two or more claims selected from the plurality of claims recited in the appended claims. That is, as long as no technical contradiction arises, it is possible to combine matters recited in any two or more claims selected from the plurality of claims recited in the appended claims.

[0029] (Lithium-ion rechargeable battery)

[0030] A lithium secondary battery according to an embodiment of the present disclosure includes a wound electrode assembly and a non-aqueous electrolyte. The electrode assembly includes, for example, a strip-shaped (band-shaped) positive electrode, a negative electrode, and a separator, and the positive electrode and the negative electrode are wound with the separator interposed therebetween. In the negative electrode, lithium metal is deposited during charging and dissolved in the non-aqueous electrolyte during discharging. Specifically, the negative electrode has at least a negative electrode current collector, and lithium metal is deposited on the negative electrode current collector. The non-aqueous electrolyte has lithium ion conductivity. The lithium secondary battery is also referred to as a lithium metal secondary battery.

[0031] In the lithium secondary battery, for example, 70% or more of the rated capacity is exhibited by the deposition and dissolution of lithium metal. The migration of electrons in the negative electrode during charging and discharging mainly depends on the deposition and dissolution of lithium metal in the negative electrode. Specifically, 70 to 100% (for example, 80 to 100% and / or 90 to 100%) of the migration (current in other viewpoints) of electrons in the negative electrode during charging and discharging depends on the deposition and dissolution of lithium metal. That is, the negative electrode of the lithium secondary battery is different from a negative electrode in which electrons in the negative electrode during charging and discharging mainly move by the absorption and release of lithium ions by a negative electrode active material (such as graphite).

[0032] (Separator)

[0033] The separator may also be a strip shape having a length D1 in a first direction parallel to the winding axis and a length D2 in a second direction intersecting the first direction (D1 < D2). The first direction may be perpendicular to the second direction. The separator has a first surface facing the outside (outer peripheral side) of the electrode assembly and a second surface facing the inside (inner peripheral side) of the electrode assembly. One of the first surface and the second surface faces the positive electrode, and the other faces the negative electrode. At least one of the first surface and the second surface has: a first region having first protrusions with a first pattern; and a second region having second protrusions with a second pattern different from the first pattern. The second region is disposed closer to the outer peripheral side of the electrode assembly than the first region.

[0034] In other words, the separator has at least two regions, a first region and a second region. The first region is disposed on the inner peripheral side of the electrode assembly, and the second region is disposed on the outer peripheral side of the electrode assembly. The first region may be a region extending outward from the innermost peripheral end of the first surface or the second surface of the separator. The second region may be a region extending inward from the outermost peripheral end of the first surface or the second surface of the separator.

[0035] The first protrusions and the second protrusions function as spacers for forming a space between the separator and the electrodes. By accommodating lithium metal in the space ensured by the first protrusions and the second protrusions, the expansion of the negative electrode during charging can be suppressed. The separator may be composed of a base material layer and a spacer layer. In this case, the spacer layer constitutes the first protrusions and the second protrusions.

[0036] The first convex portion and the second convex portion may be provided only on the surface facing the negative electrode among the first surface and the second surface, may be provided only on the surface facing the positive electrode, or may be provided on both surfaces.

[0037] The first convex portion is formed by a first pattern, and the second convex portion is formed by a second pattern different from the first pattern. The pattern includes various styles of the convex portion. At least one of the first convex portion and the second convex portion may be a linear convex portion. The linear convex portion is formed in accordance with a linear pattern. At least one of the first convex portion and the second convex portion may also be a dot-shaped or island-shaped convex portion. If at least one of the line width, diameter, height, density, pitch (the minimum interval between mutually equivalent positions of the convex portions), shape (the locus depicting the convex portion), the direction of the first surface or the second surface, etc. of the first convex portion and the second convex portion is different, it can be said that the first pattern is different from the second pattern.

[0038] By making the first pattern of the first convex portion disposed on the inner peripheral side of the electrode group different from the second pattern of the second convex portion disposed on the outer peripheral side of the electrode group, it is possible to control the sizes of the spaces formed on the inner peripheral side and the outer peripheral side of the electrode group. For example, when the ratio (R1) of the area occupied by the first convex portion in the first region is greater than the ratio (R2) of the area occupied by the second convex portion in the second region, the function of the first convex portion as a spacer is relatively enhanced, so that it is possible to suppress the shortage of the space formed on the inner peripheral side of the electrode group. R1 is the ratio (%) of the area where the first region overlaps with the first convex portion to the area of the first region when looking down at the first surface or the second surface. R2 is the ratio (%) of the area where the second region overlaps with the second convex portion to the area of the second region when looking down at the first surface or the second surface.

[0039] R1 and R2 may satisfy 1 < R1 / R2, may satisfy 1.1 ≤ R1 / R2, or may satisfy 1.2 ≤ R1 / R2. Further, from the viewpoint of forming necessary and sufficient spaces on the inner peripheral side and the outer peripheral side respectively, it is preferable to satisfy R1 / R2 ≤ 2.5. It may satisfy 1 < R1 / R2 ≤ 2.5, may satisfy 1.1 ≤ R1 / R2 ≤ 2.5, or may satisfy 1.2 ≤ R1 / R2 ≤ 2.5. Further, from the viewpoint of enhancing the function of the first convex portion as a spacer and ensuring sufficient ion permeability of the separator, R1 is preferably 5% or more and 30% or less, and more preferably 10% or more and 25% or less.

[0040] Alternatively, instead of R1 > R2, the air permeability P1 of the first region can be made lower than the air permeability P2 of the second region. In this case, the function of the first convex as a spacer is also higher than that of the second convex, and it is possible to suppress the shortage of the space formed on the inner peripheral side of the electrode group. It should be noted that the unit of air permeability is "seconds / 100 mL", and the larger the value of air permeability, the lower the air permeability. P1 and P2 can be 1 < P1 / P2, or can satisfy 1.05 ≤ P1 / P2. In addition, from the viewpoint of forming necessary and sufficient spaces on the inner peripheral side and the outer peripheral side respectively, it is preferable to satisfy P1 / P2 ≤ 1.5. It can satisfy 1 < P1 / P2 ≤ 1.5, or can satisfy 1.05 ≤ P1 / P2 ≤ 1.5. It should be noted that in addition to setting R1 > R2, the air permeability P1 of the first region can also be made lower than the air permeability P2 of the second region.

[0041] Air permeability (air resistance) is an index representing the time (seconds) required for a specified volume (100 mL) of air to pass through per unit area of the separator when a specified pressure difference is applied between both sides of the separator. The air permeability is based on JIS P8117:2009, by setting the test area (permeable part) of the separator to 6.42 cm 2 and measuring by the Gurley tester method with the inner cylinder weight set to 567 g. The air permeability can also be measured by the Wang Yan tester method, and the same value can be obtained.

[0042] In the case where the first convex and the second convex are respectively linear convexes, the line width W1 of the first convex can also be made longer than the line width W2 of the second convex. Thereby, the function of the first convex as a spacer can be relatively improved. W1 and W2 can be 1 < W1 / W2, can be 1.1 ≤ W1 / W2, or can be 1.2 ≤ W1 / W2. In addition, from the viewpoint of forming necessary and sufficient spaces on the inner peripheral side and the outer peripheral side respectively, it is preferable to satisfy W1 / W2 ≤ 4.0. It can satisfy 1 < W1 / W2 ≤ 4.0, can satisfy 1.1 ≤ W1 / W2 ≤ 4.0, or can satisfy 1.2 ≤ W1 / W2 ≤ 4.0. In addition, from the viewpoint of improving the function of the first convex as a spacer and ensuring sufficient ion permeability of the separator, W1 is preferably 0.1 mm or more and 2 mm or less, more preferably 0.25 mm or more and 1 mm or less.

[0043] Here, the line width refers to the dimension in the direction perpendicular to the length direction and parallel to the main surface of the separator of the first convex and the second convex that extend linearly respectively. The line width only needs to be measured at five or more arbitrary positions for the first convex and the second convex respectively, and calculated as the arithmetic mean of five or more measured values.

[0044] Alternatively, the height H1 of the first protrusion can be higher than the height H2 of the second protrusion. This relatively enhances the function of the first protrusion as a spacer. H1 and H2 can be 1...

[0045] Here, the heights of the first and second protrusions refer to their maximum dimensions in the direction parallel to the thickness direction of the separator. H1 and H2 can be calculated by measuring the first and second protrusions at any five or more locations and taking the arithmetic mean of the five or more measurements. The height of the protrusions can be measured using a scanning electron microscope (SEM) to capture a cross-section parallel to the thickness direction of the separator.

[0046] From the viewpoint of improving the ion permeability of the separator, the second region can be larger than the first region. For example, the length L1 of the first region in the second direction can be less than 25% of the total length L of the separator in the second direction. The first region can, for example, be a region extending from the innermost circumferential end of the first or second surface of the separator to the outer circumferential side with a length of less than L / 4. This is because in such a region close to the innermost circumference of the electrode assembly, the space for lithium deposition is easily insufficient.

[0047] The first and second protrusions are preferably arranged on the separator in a manner that is as uniform and dispersed as possible. This suppresses the rise in internal resistance, reduces the areas where lithium metal can locally deposit, and easily limits isolated lithium metal deposits to a small amount. When an arbitrary circular region with a diameter of D1 / 3 (D1 being the length of the strip-shaped separator in the first direction (short side direction)) is formed on the surface of the separator, it is preferable that protrusions always exist in such a circular region.

[0048] ​At least one of the first and second patterns can be a geometric pattern. The protrusions of such a pattern are easily arranged evenly relative to the entire surface of the separator. The geometric pattern can also be a mesh pattern. That is, at least one of the first and second protrusions can also be arranged relative to the entire surface of the separator according to a mesh pattern. The mesh pattern can also be an assembly of polygons. An example of a mesh pattern includes a shape formed by combining polygons in a shared-side manner. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons can also be combined. The geometric pattern is preferably one with low anisotropy, such as an assembly of regular polygons. For example, the geometric pattern can be a honeycomb pattern (an assembly of regular hexagons).

[0049] At least one of the first and second patterns may include dotted patterns. At least one of the first and second patterns may be a pattern formed by combining linear and dotted patterns. The planar shape of the dotted protrusions is not particularly limited and may be circular (perfect circle or ellipse), polygonal (triangular, quadrilateral, etc.), etc.

[0050] Hereinafter, the separator having the above configuration will be referred to as "separator (A)". Furthermore, the lithium secondary battery having the above configuration will be referred to as "lithium secondary battery (B)". Separator (A) is used in lithium secondary battery (B). Additionally, an example will be described below where the separator is composed of a substrate layer and a spacer layer, and the spacer layer constitutes the first protrusion and the second protrusion.

[0051] The spacer layer can be formed, for example, by coating a dispersion containing a spacer material onto the portion of the substrate layer on which the spacer layer is formed and then drying it. In this case, the spacer layer (the first protrusion and the second protrusion) can adhere to the substrate layer with sufficient strength. After coating the dispersion onto the portion forming the spacer layer, it is dried. The coating of the dispersion can be performed using a dispensing machine or a known printing method such as gravure printing, inkjet printing, or screen printing. Furthermore, drying can be performed using known methods such as heated drying and / or natural drying.

[0052] The dispersion containing the spacer material includes, for example, insulating particles, a binder resin, and a thickener. Therefore, the spacer layer (first protrusion and second protrusion) formed by the dispersion contains insulating particles, a binder resin, and a thickener. The dispersion medium is not particularly limited; for example, water, an organic solvent, or a mixture of water and an organic solvent can be used. As an organic solvent, N-methyl-2-pyrrolidone (NMP) can be used, for example. Of these, water is preferred from the viewpoint of reducing environmental impact.

[0053] The shape of the insulating particles is not particularly limited and can be spherical. However, spherical does not mean strictly round, but rather refers to a shape without sharp corners and with an aspect ratio (maximum diameter / maximum diameter in the direction perpendicular to the maximum diameter) in the range of 1 to 3. The median particle size (i.e., average particle size) in the volumetric particle size distribution of the insulating particles can be 1.0 μm to 10 μm. The median particle size is the particle size at 50% of the cumulative volume. The median particle size of the insulating particles can be 1.0 μm to 2 μm. When the median particle size is within the above range, the insulating particles in the dispersion can easily and stably maintain a dispersed state, and also maintain a dispersed state after being coated onto the substrate layer, easily forming a spacer layer with a homogeneous morphology.

[0054] The median particle size in the particle size distribution based on volume can be measured, for example, using a laser diffraction-scattering particle size distribution measuring device (such as the Microtrac manufactured by Nikkiso Corporation). Alternatively, the cross-section of the spacer layer can be observed using 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, and the diameter of the equivalent circle (perfect circle) with the same area as the calculated area can be obtained as the average of the diameters of the 100 equivalent circles.

[0055] The volume resistivity of insulating particles can be, for example, 1.0 × 10⁻⁶. 8 Above Ω·cm. Due to the sufficient insulation properties of the insulating particles, lithium metal hardly deposits on the spacer layer, promoting lithium metal deposition in the desired space. The volume resistivity of the insulating particles can be even higher, for example, 1.0 × 10⁻⁶. 10 Ω·cm or higher.

[0056] Volume resistivity can be measured using the four-probe method. For example, insulating particles can be measured at 204 kgf / cm². 2 The pressure is applied, and the resistivity of the powder is measured using a powder resistivity measuring device (e.g., Loresta SP from Nitto Seiko Analytech Co., Ltd.).

[0057] Insulating particles can include inorganic particles such as metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides. Metal oxides include aluminum oxide (aluminum oxide, boehmite), magnesium oxide, titanium oxide (titanium dioxide), zirconium oxide, and silicon oxide (silicon dioxide). 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. Aluminosilicates, layered silicates, barium titanate, and strontium titanate minerals can also be used. Among these, aluminum oxide, silicon dioxide, and titanium dioxide are preferred.

[0058] The content of insulating particles in the spacer layer is, for example, less than 80% by volume, preferably 50-70% by volume. The volume percentage of insulating particles in the spacer layer can be determined by observing the cross-section of the spacer layer with a transmission electron microscope (TEM), taking TEM images, and calculating the content at any 10 μm. 2 The volume ratio is calculated by taking the total area enclosed by the outlines of the insulating particles in the field of view and expressing the total area as a proportion of the field of view area. It is preferable to calculate the volume ratio in at least three fields of view and then calculate their average value.

[0059] Adhesive resins include, for example, fluoropolymers, fluororubbers, styrene-butadiene copolymers or their hydrogenated forms, acrylonitrile-butadiene copolymers or their hydrogenated forms, methacrylate-acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene propylene rubber, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, fully aromatic polyamide (aromatic polyamide), polyamide, polyacrylonitrile, polyether, polyolefin, alkyd resins, etc.

[0060] Relative to 100 parts by volume of insulating particles, the amount of adhesive resin can 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. Within this range, it is easy to improve the mechanical strength of the spacer layer and the bond strength between the substrate layer and the spacer layer.

[0061] The thickener may include, for example, at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts (hereinafter, at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts will also be referred to as "CMC"). When carboxymethyl cellulose salts are used as CMCs, sodium salts, lithium salts, potassium salts, ammonium salts, etc., can be used. Among them, the carboxymethyl cellulose salt preferably includes a sodium salt.

[0062] To fully utilize the function of CMC, the dispersion medium of the spacer material dispersion preferably contains water. The dispersion medium may contain 50% or more water, or 70%, 80%, or 90% or more water.

[0063] The amount of CMC relative to 100 parts by volume of insulating particles can be, for example, 0.5 to 5 parts by volume, or 1 to 3 parts by volume. By using CMC within this range, its sufficient thickening effect can be observed.

[0064] <Substrate Layer>

[0065] The substrate layer uses a porous sheet with ion permeability and insulation properties. Examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the porous sheet is not particularly limited and can be a polymer. Examples of polymers include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The substrate layer may contain additives as needed. Examples of additives include inorganic fillers.

[0066] The thickness of the substrate layer is not particularly limited, for example, it is 5 μm or more and 20 μm or less, more preferably 10 μm or more and 20 μm or less.

[0067] The substrate layer may comprise 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 permeate. The thickness of the composite material layer can be 5% to 50% of the total thickness of the separator.

[0068] The composite material layer comprises resin material and inorganic particles. The inorganic particles may include a first particle and / or a second particle. The first particle is a lithium phosphate particle. The first particle has the effect of suppressing battery heating during abnormal conditions. The second particle is any particle other than the first particle.

[0069] When the composite material layer is formed only on one side of the main surface of the porous sheet, it is preferable to place the composite material layer on the main surface of the porous sheet facing the positive electrode. By placing the composite material layer on the positive electrode side, it is possible to suppress the degradation of the porous sheet due to oxidation. On the other hand, by placing the composite material layer on the negative electrode side, it is possible to suppress the degradation of the porous sheet due to reduction.

[0070] The phosphate constituting the first particle can be at least one selected from the group consisting of lithium phosphate (Li3PO4), lithium hydrogen phosphate (Li2HPO4), and lithium dihydrogen phosphate (LiH2PO4). Among these, lithium phosphate is preferred from the viewpoint of high effectiveness in suppressing battery heating during abnormal conditions. The median particle size in the volume-based particle size distribution of the first particle can be 0.1 μm to 1.0 μm.

[0071] A preferred example of the second particle is a particle composed of an insulating inorganic compound that does not melt or decompose during abnormal heating of the battery. Examples of materials for the second particle include oxides, hydroxides, nitrides, carbides, sulfides, etc. Examples of oxides include aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, zinc oxide, etc. Examples of nitrides include silicon nitride, aluminum nitride, boron nitride, titanium nitride, etc. Examples of carbides include silicon carbide, boron carbide, etc. Examples of sulfides include barium sulfate, etc. Examples of hydroxides include aluminum hydroxide, etc. The median particle size in the volumetric particle size distribution of the second particle can be 0.2~2.0 μm.

[0072] The median particle size in the volumetric particle size distribution can be measured, for example, using a laser diffraction-scattering particle size distribution measuring device (such as the Microtrac manufactured by Nikkiso Corporation). Alternatively, a cross-section of the substrate layer can be observed using a transmission electron microscope (TEM), a TEM image can be taken, the area enclosed by the outlines of any 100 first or second particles can be calculated, and the diameter of an equivalent circle (perfect circle) with the same area as the calculated area can be obtained as the average of the diameters of the 100 equivalent circles.

[0073] The resin material is preferably a polymer material with higher heat resistance than that of porous sheets. Such a polymer material preferably includes at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamide-imides. These are known as polymer materials with high heat resistance. From the viewpoint of heat resistance, aromatic polyamides, namely meta-aromatic polyamides (meta-fully aromatic polyamides) and para-aromatic polyamides (para-fully aromatic polyamides), are preferred.

[0074] The content of inorganic particles in the composite material layer can be in the range of 50% to 99% by mass (e.g., 85% to 99% by mass).

[0075] (negative electrode)

[0076] The negative electrode has a negative current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode due to charging. More specifically, lithium ions contained in the non-aqueous electrolyte accept electrons at the negative electrode during charging and become lithium metal, which is then 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 during discharge.

[0077] The negative electrode may include a lithium-ion storage layer (a layer that embodies capacity through the absorption and release of lithium ions by the negative electrode active material (graphite, etc.)) loaded on the negative electrode current collector. In this case, the open-circuit potential of the negative electrode when fully charged relative to lithium metal (the dissolution potential of lithium) can be below 70 mV. When the open-circuit potential of the negative electrode when fully charged relative to lithium metal is below 70 mV, lithium metal is present on the surface of the lithium-ion storage layer when fully charged. That is, the negative electrode embodies capacity through the deposition and dissolution of lithium metal.

[0078] Here, "fully charged" refers to the state of charge when the battery's rated capacity is set to C, reaching, for example, a state of charge of 0.98 × C or higher. The open-circuit potential of the negative electrode at full charge can be determined by disassembling the fully charged battery under an argon atmosphere, removing the negative electrode, assembling a battery cell using lithium metal as the counter electrode, and then measuring the result. The non-aqueous electrolyte of the battery cell can have the same composition as the non-aqueous electrolyte in the disassembled battery.

[0079] A lithium-ion absorption and storage layer is formed by forming a layered negative electrode composite material containing negative electrode active material. In addition to the negative electrode active material, the negative electrode composite material may also contain binders, thickeners, conductive agents, etc.

[0080] Examples of anode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. An anode may contain one type of anode active material or a combination of two or more. Examples of carbonaceous materials include graphite, easily graphitized carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon).

[0081] Conductive materials can be, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0082] Examples of adhesive materials include fluoropolymers, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluoropolymers include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0083] The negative current collector can be any conductive sheet. Foil, thin film, etc., can be used as the conductive sheet.

[0084] The negative electrode current collector (conductive sheet) can be made of any conductive material other than lithium metal and lithium alloys. The conductive material can also be a metal, alloy, or other metallic material. Preferably, the conductive material is one that does not react with lithium. More specifically, it is preferably a material that neither forms an alloy nor an intermetallic compound with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metallic elements, or graphite with a predominantly exposed base. Examples of alloys include copper alloys and stainless steel (SUS). Copper and / or copper alloys, which have high conductivity, are preferred.

[0085] There are no particular restrictions on the thickness of the negative current collector, for example, it can be 5μm or more and 300μm or less.

[0086] (positive electrode)

[0087] The positive electrode, for example, comprises a positive current collector and a positive electrode composite material layer supported by the positive current collector. The positive electrode composite material layer, for example, includes a positive electrode active material, a conductive material, and a binder material. The positive electrode composite material layer may be formed on only one side of the positive current collector or on both sides. The positive electrode is obtained, for example, by coating both sides of the positive current collector with a positive electrode composite material slurry containing a positive electrode active material, a conductive material, and a binder material, allowing the coating to dry, and then calendering it.

[0088] The positive electrode active material is the material that absorbs, stores, and releases lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred due to their low manufacturing cost and high average discharge voltage.

[0089] Lithium contained in lithium-containing transition metal oxides is released as lithium ions from the positive electrode during charging and deposited as lithium metal on the negative electrode or negative electrode current collector. During discharging, lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed and stored by the composite oxide of the positive electrode. In other words, the lithium ions participating in charging and discharging mainly originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0090] Transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one or more transition metal elements. The transition metal elements can be Co, Ni, and / or Mn. Lithium-containing transition metal oxides may contain more than one typical element as needed. Typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. Al is a typical example.

[0091] In lithium-containing transition metal oxides, Co, Ni, and / or Mn are included as transition metal elements, and Al is included as an arbitrary component. From the viewpoint of obtaining high capacity, composite oxides with a layered structure and a rock-salt-type crystal structure are preferred. In this case, in the lithium secondary battery, the molar ratio of the total amount of lithium (mLi) in the positive and negative electrodes to the amount of metal M other than lithium (mM) in the positive electrode, mLi / mM, is set to, for example, 1.1 or less.

[0092] As a binder, conductive agent, etc., the substances exemplified in the negative electrode can be used, for example. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0093] Materials used as positive current collectors (conductive plates) include, for example, metallic materials containing Al, Ti, and Fe. These metallic materials can be Al, Al alloys, Ti, Ti alloys, Fe alloys, etc. Fe alloys can also be stainless steel (SUS).

[0094] There are no particular restrictions on the thickness of the positive current collector, for example, it can be above 5μm and below 300μm.

[0095] (Non-aqueous electrolyte)

[0096] Non-aqueous electrolytes with lithium-ion conductivity can be liquid electrolytes (electrolytes), gel electrolytes, or solid electrolytes. Liquid electrolytes, for example, are electrolytes containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolyte may contain known additives.

[0097] Gel electrolytes contain lithium salts and a matrix polymer, or contain lithium salts, a non-aqueous solvent, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent is used. Examples of polymer materials include fluoropolymers, acrylic resins, polyether resins, and polyethylene oxide.

[0098] As a solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (such as oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0099] Liquid non-aqueous electrolytes are prepared by dissolving lithium salts in a non-aqueous solvent. Dissolving the lithium salt in the non-aqueous solvent generates lithium ions and anions.

[0100] BF4 can be listed as an anion. - ClO4 - PF6 - CF3SO3 - CF3CO2 - Anions of imides, anions of oxalate complexes, etc. Examples of imide anions include N(SO₂CF₃)₂. - 、N(C m F 2m+1 SO2) x (C n F 2n+ 1SO2) y -(m and n are each independently an integer greater than or equal to 0 or 1, and x and y are each independently 0, 1, or 2, satisfying x + y = 2), etc. The anions of oxalate complexes may contain boron and / or phosphorus. Examples of anions in oxalate complexes include bis(oxalateborate) anion and difluoro(oxalateborate) anion (BF2(C2O4)). - ), PF4(C2O4) - PF2(C2O4)2 - Non-aqueous electrolytes can contain only one of these anions, or they can contain two or more.

[0101] From the viewpoint of suppressing the dendritic precipitation of lithium metal, the non-aqueous electrolyte preferably contains at least an oxalate complex anion, and more preferably an oxalate complex anion containing fluorine. Through the interaction between the fluorine-containing oxalate complex anion and lithium, lithium metal readily precipitates uniformly in fine particles. Therefore, localized precipitation of lithium metal is easily suppressed. The fluorine-containing oxalate complex anion can also be combined with other anions. Other anions may be PF6. - And / or imide anions.

[0102] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, or their halogenated derivatives. Non-aqueous electrolytes may contain only one or more of these non-aqueous solvents. Examples of halogenated derivatives include fluorides.

[0103] Examples of esters include carbonates and carboxylic acid esters. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of chain carbonates include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0104] Examples of ethers include cyclic ethers and chain ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of 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.

[0105] The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or higher and 3.5 mol / L or lower. The concentration of anion in the non-aqueous electrolyte can also be set to 0.5 mol / L or higher and 3.5 mol / L or lower. Furthermore, the concentration of anion of oxalate complex in the non-aqueous electrolyte can be 0.05 mol / L or higher and 1 mol / L or lower.

[0106] Non-aqueous electrolytes may contain additives. These additives can form a coating on the negative electrode. By forming a coating derived from the additive on the negative electrode, dendrite formation is easily suppressed. Examples of such additives include vinylene carbonate, FEC, and ethylene ethylene carbonate (VEC).

[0107] The following explanation is based on the accompanying drawings. Figure 1 This is a longitudinal cross-sectional view schematically illustrating an example of a lithium secondary battery (B). The constituent elements of the lithium secondary battery (B) described below can be applied using the aforementioned constituent elements. The constituent elements described below can be modified based on the above description. In the lithium secondary battery described below, constituent elements not essential to the lithium secondary battery involved in this disclosure may be omitted. In the following figures, the scale of the constituent elements has been changed for ease of understanding.

[0108] (Implementation Method 1)

[0109] Figure 1 This is a longitudinal cross-sectional view schematically illustrating an example of the lithium secondary battery of Embodiment 1. It should be noted that... Figure 1 The diagram omits the spacer layer (first protrusion and second protrusion) and the space formed by the spacer layer. Figure 1 The cylindrical lithium secondary battery 10 shown includes a cylindrical battery casing, a wound electrode assembly 14 housed within the battery casing, and a non-aqueous electrolyte. The battery casing includes a casing body 15, a bottom cylindrical metal container, and a sealing body 16 that seals the opening of the casing body 15. A gasket 27 is disposed between the casing body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery casing. Inside the casing body 15, insulating plates 17 and 18 are respectively disposed at both ends of the electrode assembly 14 in the winding axis direction.

[0110] The housing body 15, for example, has a stepped portion 21 formed by partially pressing the side wall of the housing body 15 from the outside. The stepped portion 21 may also be formed in a ring shape along the circumference of the side wall of the housing body 15. In this case, the sealing body 16 is supported by the surface on the opening side of the stepped portion 21.

[0111] The sealing body 16 includes a perforated metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cover 26. These components are stacked in this order within the sealing body 16. The sealing body 16 is installed at the opening of the housing body 15 with the cover 26 located outside the housing body 15 and the perforated metal plate 22 located inside the housing body 15. The aforementioned components constituting the sealing body 16 are, for example, circular or annular in shape. The lower valve body 23 and the upper valve body 25 are interconnected at their respective central portions, and the insulating member 24 is sandwiched between their respective peripheral portions. The perforated metal plate 22 and the lower valve body 23 are interconnected at their respective central portions. The upper valve body 25 and the cover 26 are interconnected at their respective central portions. That is, all components except the insulating member 24 are electrically connected to each other.

[0112] A vent (not shown) is formed on the lower valve body 23. Therefore, when the internal pressure of the battery casing rises due to abnormal heating, the upper valve body 25 expands towards the cover 26 and exits from the lower valve body 23. This disconnects 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 released from the opening (not shown) formed in the cover 26.

[0113] Figure 2A This is an enlarged view of the portion of the first region of the separator on the inner circumference side of the electrode assembly 14 (e.g., the area counting 2 to 3 circles from the innermost circumference). Figure 2B This is an enlarged view of the portion of the second region of the separator on the outer periphery of the electrode assembly 14 (e.g., the area counting 2 to 3 circles from the outermost periphery). Figure 2A and Figure 2B include Figure 1 The part near the positive pole surrounded by region II and Figure 1 The part near the negative pole surrounded by region III.

[0114] Electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a spacer 13. The positive electrode 11, negative electrode 12, and spacer 13 are all strip-shaped. The spacer 13 has a substrate layer 50 and spacer layers 53A and 53B formed on the substrate layer 50. The spacer layer 53A disposed on the inner peripheral side of the electrode assembly 14 constitutes a first protrusion. The spacer layer 53A (first protrusion) is formed with a first pattern. The spacer layer 53B disposed on the outer peripheral side of the electrode assembly 14 constitutes a second protrusion. The spacer layer 53B (second protrusion) is formed with a second pattern. The first pattern and the second pattern differ, and the linewidth W1 of the first protrusion is longer than the linewidth W2 of the second protrusion. Furthermore, the area R1 occupied by the spacer layer 53A (first protrusion) in the first region is greater than the area R2 occupied by the spacer layer 53B (second protrusion) in the second region. Therefore, the air permeability P1 of the first region is lower than the air permeability P2 of the second region.

[0115] The substrate layer 50 has a porous sheet 51 and a composite material layer 52. A spacer layer 53 is formed on the composite material layer 52. The positive electrode 11, the negative electrode 12 and the spacer 13 are wound together such that a spacer 13 is disposed between the positive electrode and the negative electrode 12, thereby forming an electrode assembly 14.

[0116] The positive electrode 11 includes a positive current collector 11a and a positive composite material layer 11b. The positive current collector 11a is electrically connected to the cover 26, which functions as the positive terminal, via a positive lead 19. In Figure 2, the negative electrode 12 is shown in its undeposited lithium metal state (negative current collector). The negative electrode 12 is electrically connected to the housing body 15, which functions as the negative terminal, via a negative lead 20.

[0117] like Figure 2A , Figure 2B As shown, 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. Figure 2A , Figure 2B In one example shown, spacer layer 53 is formed on the first main surface 50a.

[0118] In embodiment 1, the composite material layer 52 is formed on the negative electrode 12 side of the two main surfaces of the porous sheet 51. However, the composite material layer 52 may not be present, or it may be formed on both 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. Through the spacer layer 53, a space 14s is formed between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the separator 13). Figure 2A This indicates the line width W1 and height H1 of spacer layer 53A (first protrusion). Figure 2B The line width W2 and height H2 of the spacer layer 53B (the second protrusion) are indicated. In this embodiment, W1>W2, and H1 and H2 are the same, but it is not limited to this; for example, H1>H2 can also be set. The proportion R1 of the area occupied by the spacer layer 53A (the first protrusion) in the first region is greater than the proportion R2 of the area occupied by the second protrusion in the second region.

[0119] In the lithium secondary battery 10, lithium metal is deposited on the negative electrode 12 during charging. Since there is a space 14s between the positive electrode 11 and the negative electrode 12, the volume change of the electrode assembly 14 accompanying the lithium metal deposition is reduced, and the cycle characteristics are improved.

[0120] Figure 3 An example of the planar shape of spacer layers 53A and 53B is shown. Figure 4 Show Figure 3 A magnified view of a portion (spacer layer 53B). Figure 3In one example, the left end is the innermost peripheral end, and in the first region including this end, the spacer layer 53A forms a linear first protrusion 53a with a relatively long linewidth. On the other hand, the right end is the outermost peripheral end, and in the second region including this end, the spacer layer 53B forms a linear second protrusion 53b with a shorter linewidth. The linear first protrusion 53a and second protrusion 53b are arranged in a mesh pattern; more specifically, they are uniformly formed in the first region with a narrow-spacing honeycomb pattern, and uniformly formed in the second region with a wide-spacing honeycomb pattern. The honeycomb pattern is a pattern in which multiple hexagons are arranged in a manner that shares edges with each other. The areas where the linear first protrusion 53a and second protrusion 53b are not formed constitute space 14s. Figure 4 The width W2 of the linear second protrusion 53b is shown. The width W2 of the linear second protrusion 53b is the length (width) of the linear second protrusion 53b in a direction perpendicular to the direction in which the linear second protrusion 53b extends when viewed from above.

[0121] exist Figure 4 In the second linear protrusion 53b, a notch 54 is formed. The notch 54 facilitates the movement of ions in the non-aqueous electrolyte. The notch 54 is preferably provided in a pattern in which multiple polygons are arranged in a manner that they share common edges.

[0122] Figures 5-7 Another example of the first protrusion 53a and the second protrusion 53b is shown in top view. In any example, the proportion R1 of the area occupied by the spacer layer 53A (the first protrusion) in the first region is greater than the proportion R2 of the area occupied by the second protrusion in the second region.

[0123] Figure 5 The spacer layer 53A includes a plurality of linear first protrusions 53a arranged in alternating intersecting directions, and the spacer layer 53B includes a plurality of linear second protrusions 53b arranged in alternating intersecting directions. Gaps P exist between the plurality of first protrusions 53a and between the plurality of second protrusions 53b. Regions where no linear protrusions are formed constitute space 14s. The first protrusions 53a have a longer line width, and the second protrusions 53b have a shorter line width.

[0124] Figure 6 The spacer layer 53A includes a plurality of linear first protrusions 53a arranged in a strip shape and extending along a second direction, and the spacer layer 53B includes a plurality of linear second protrusions 53b arranged in a strip shape and extending along a second direction. The number of first protrusions 53a is greater than the number of second protrusions 53b, and the spacing between the first protrusions 53a is narrower than the spacing between the second protrusions 53b.

[0125] Figure 7The spacer layer 53A includes a first protrusion 53a arranged in a grid (mesh) pattern, and the spacer layer 53B includes a second protrusion 53b arranged in a grid (mesh) pattern. The size of the grid in the first protrusion 53a is smaller than the size of the grid in the second protrusion 53b.

[0126] It should be noted that the combination of the first protrusion and the second protrusion is not limited to the example shown in the figure. For example, the first protrusion can be formed with a honeycomb pattern, and the second protrusion can be formed with a pattern other than a honeycomb pattern.

[0127] (Postscript)

[0128] The following technology is disclosed through the above description of the embodiments.

[0129] (Technology 1)

[0130] A lithium secondary battery, comprising:

[0131] Electrode assembly and non-aqueous electrolyte,

[0132] The aforementioned electrode assembly includes a positive electrode, a negative electrode, and a separator.

[0133] The aforementioned positive electrode and the aforementioned negative electrode are wound together with the aforementioned separator in between.

[0134] In the aforementioned negative electrode, lithium metal is deposited during charging and dissolves in the aforementioned non-aqueous electrolyte during discharging.

[0135] The aforementioned separator has a first surface facing the outer side of the aforementioned electrode assembly and a second surface facing the inner side of the aforementioned electrode assembly.

[0136] At least one of the first surface and the second surface has a first region and a second region, the first region having a first protrusion of a first pattern, and the second region having a second protrusion of a second pattern different from the first pattern.

[0137] The second region is located closer to the outer periphery of the electrode assembly than the first region.

[0138] (Technology 2)

[0139] According to the lithium secondary battery of technology 1, the proportion of the area occupied by the first protrusion in the first region is greater than the proportion of the area occupied by the second protrusion in the second region.

[0140] (Technology 3)

[0141] According to the lithium secondary battery of technology 1 or 2, the air permeability of the first region is lower than that of the second region.

[0142] (Technology 4)

[0143] The lithium secondary battery according to any one of Technologies 1 to 3, wherein,

[0144] The first convex portion and the second convex portion are linear convex portions respectively,

[0145] The line width of the first convex portion is longer than the line width of the second convex portion.

[0146] (Technology 5)

[0147] The lithium secondary battery according to any one of Technologies 1 to 4, wherein the height of the first convex portion is higher than the height of the second convex portion.

[0148] (Technology 6)

[0149] The lithium secondary battery according to any one of Technologies 1 to 5, wherein the separator is in a long strip shape having a length D1 in a first direction parallel to the winding axis and a length D2 (D1 < D2) in a second direction intersecting the first direction,

[0150] The length of the separator in the second direction in the first region is 25% or less of the total length of the separator in the second direction.

[0151] (Technology 7)

[0152] The lithium secondary battery according to any one of Technologies 1 to 6, wherein at least one of the first pattern and the second pattern is a geometric figure.

[0153] (Technology 8)

[0154] A separator disposed between a positive electrode and a negative electrode and wound to form an electrode group,

[0155] The separator has a first surface facing the outside of the electrode group and a second surface facing the inside of the electrode group,

[0156] At least one of the first surface and the second surface has a first region and a second region, the first region has a first convex portion of a first pattern, and the second region has a second convex portion of a second pattern different from the first pattern,

[0157] The second region is disposed closer to the outer peripheral side of the electrode group than the first region.

[0158] (Technology 9)

[0159] The separator according to Technology 8, wherein the proportion of the area occupied by the first convex portion in the first region is greater than the proportion of the area occupied by the second convex portion in the second region.

[0160] (Technology 10)

[0161] The spacer according to Technique 8 or 9, wherein the air permeability of the first region is lower than that of the second region.

[0162] (Technique 11)

[0163] The spacer according to any one of Techniques 8 to 10, wherein

[0164] the first convex portion and the second convex portion are linear convex portions,

[0165] the line width of the first convex portion is longer than the line width of the second convex portion.

[0166] (Technique 12)

[0167] The spacer according to any one of Techniques 8 to 11, wherein the height of the first convex portion is higher than the height of the second convex portion.

[0168] (Technique 13)

[0169] The spacer according to any one of Techniques 8 to 12, which is in a long strip shape having a length D1 in a first direction and a length D2 (D1 < D2) in a second direction intersecting the first direction,

[0170] the length of the first region in the second direction is 25% or less of the total length of the spacer in the second direction.

[0171] (Technique 14)

[0172] The spacer according to any one of Techniques 8 to 13, wherein at least one of the first pattern and the second pattern is a geometric figure.

[0173] (Technique 15)

[0174] A spacer, which is a spacer in a long strip shape having a length D1 in a first direction and a length D2 (D1 < D2) in a second direction intersecting the first direction,

[0175] the spacer has a first surface and a second surface opposite to the first surface,

[0176] at least one of the first surface and the second surface has a first region and a second region, the first region has a first convex portion of a first pattern, and the second region has a second convex portion of a second pattern different from the first pattern,

[0177] the second region is disposed at a position farther from one end of the second direction than the first region.

[0178] [Examples]

[0179] The lithium secondary battery of this disclosure will now be described in more detail based on embodiments and comparative examples. However, this disclosure is not limited to the following embodiments.

[0180] Example 1

[0181] (1) Production of the positive electrode

[0182] A layered lithium transition metal oxide (NCA: positive electrode active material), acetylene black (AB: conductive material), and polyvinylidene fluoride (PVdF: binder material) containing Li, Ni, Co, and Al (with a molar ratio of Li to Ni, Co, and Al totaling 1.0) and exhibiting a rock-salt-type structure were mixed at a mass ratio of NCA:AB:PVdF = 95:2.5:2.5. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added and the mixture was stirred to prepare a positive electrode composite slurry. The obtained positive electrode composite slurry was coated onto both sides of a strip of Al foil (positive electrode current collector), dried, and then calendered using rollers. Finally, the resulting laminate of the positive electrode current collector and positive electrode composite material was cut to a specified electrode size, resulting in a positive electrode with positive electrode composite material layers on both sides of the positive electrode current collector.

[0183] (2) Fabrication of the negative electrode

[0184] Prepare a strip of electrolytic copper foil (15μm thick) as the negative electrode current collector.

[0185] (3) Separator

[0186] (3-1) Substrate layer (porous sheet)

[0187] Prepare a 20μm thick polyethylene microporous film.

[0188] (3-2) Forming a spacer layer on the main surface of the substrate layer

[0189] Insulating particles (median particle size 3μm, volume resistivity 10) were used. 14 A dispersion of spacer material was prepared by mixing 50 parts by volume of polyvinylidene fluoride (PVdF) as a binder resin and N-methyl-2-pyrrolidone (NMP) as a dispersion medium.

[0190] Next, using a dispensing machine, a dispersion of spacer material is sprayed onto the microporous film in a honeycomb pattern. The coating is then vacuum-dried to form the first and second protrusions. Specifically, one surface (the first main surface) of the microporous film is divided into a first region and a second region. In the first region, the first protrusion is uniformly formed in a honeycomb pattern, and in the second region, the second protrusion is uniformly formed in a honeycomb pattern.

[0191] If the total length of the substrate layer in the second direction is defined as L, then the first region is defined as a region extending from the innermost circumferential end of the first surface of the substrate layer to the outer circumferential side by a length of L / 4. That is, the length L1 of the first region in the second direction is set to 25% of the total length L of the substrate layer (i.e., the separator) in the second direction.

[0192] The first and second protrusions have the same line width and height, W1=W2=0.5mm, H1=H2=50μm.

[0193] On the other hand, in the first pattern, the spacing (pitch) between opposite sides of the regular hexagon is set to 5 mm, and in the second pattern, the spacing (pitch) between opposite sides of the regular hexagon is set to 10 mm. As a result, in the first region, the area occupied by the first protrusion, R1, is 19%, and in the second region, the area occupied by the second protrusion, R2, is 9.7%. The air permeability P1 of the first region is 370 seconds / 100 mL, and the air permeability P2 of the second region is 345 seconds / 100 mL.

[0194] (4) Preparation of non-aqueous electrolytes

[0195] Ethyl carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC = 30:70. LiPF6 was dissolved in the resulting mixed solvent at a concentration of 1 mol / L, and LiBF2(C2O4) was dissolved at a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte.

[0196] (5) Battery assembly

[0197] In an inactive gas atmosphere, the positive and negative current collectors are wound into a spiral shape with the aforementioned separator in between to fabricate an electrode assembly. At this time, the separator is arranged with the spacer layer facing the negative electrode. The electrode assembly is housed in a bag-shaped outer casing formed of a laminate with an Al layer, a non-aqueous electrolyte is injected, and the outer casing is sealed to complete the lithium secondary battery A1.

[0198] Example 2

[0199] In pattern 1, the spacing (pitch) between opposite sides of the regular hexagon is changed to 10mm, and the line width W1 of the first protrusion is changed to 1.0mm. Otherwise, battery A2 is made in the same way as battery A1. R1 is 19%, R2 is 9.7%. P1 is 373 seconds / 100mL, and P2 is 322 seconds / 100mL.

[0200] Example 3

[0201] In the first pattern, the spacing (pitch) between opposite sides of the regular hexagon is changed to 2.25 mm, and the line width W1 of the first protrusion is changed to 0.25 mm. Furthermore, the second pattern is changed to a striped pattern. Specifically, a plurality of straight second protrusions extending along a second direction are formed in the second region. The spacing (pitch) in the first direction between the plurality of straight second protrusions is set to 5 mm, and the line width W2 is set to 0.5 mm. Except as described above, battery A3 is manufactured in the same manner as battery A1. R1 is 21%, R2 is 10%. P1 is 381 seconds / 100 mL, and P2 is 345 seconds / 100 mL.

[0202] Example 4

[0203] In both Pattern 1 and Pattern 2, the spacing (pitch) between opposite sides of the regular hexagon is changed to 2.25mm, and the line width W1 of the first protrusion and the line width W2 of the second protrusion are changed to 0.25mm. Additionally, two 0.25mm wide notches are provided in the first protrusion for each honeycomb (see reference). Figure 4 Two 0.5mm wide notches are provided on the second protrusion for each honeycomb. Battery A4 is manufactured in the same manner as battery A1, except as described above. R1 is 16.5%, R2 is 14.5%. P1 is 370 seconds / 100mL, and P2 is 345 seconds / 100mL.

[0204] Example 5

[0205] In the first pattern, the height of the first protrusion is changed to 60 μm. Otherwise, battery A5 is made in the same manner as battery A1. R1 is 19%, R2 is 9.7%. P1 is 370 seconds / 100 mL, and P2 is 345 seconds / 100 mL.

[0206] Comparative Example 1

[0207] In region 1, the first protrusion is formed in the same pattern as the second pattern. Otherwise, battery B1 is made in the same manner as battery A1. R1=R2=9.7%, P1=P2=345 seconds / 100mL.

[0208] Comparative Example 2

[0209] Swap the patterns in region 1 and region 2. Otherwise, make battery B2 in the same manner as battery A1. R1 is 9.7%, R2 is 19%, P1 is 345 seconds / 100mL, and P2 is 370 seconds / 100mL.

[0210] [Rating 1]

[0211] For each battery obtained, using X-rays, the height of the space formed between the electrode and the substrate layer (distance between the negative electrode and the substrate layer) was measured in three turns on the inner periphery of the first region where the separator is wound, and the average value of the three turns was calculated. Additionally, the height of the space formed between the electrode and the substrate layer was measured in three turns on the outer periphery of the second region where the separator is wound, and the average value of the three turns was calculated. The results are shown in Table 1. The values ​​in Table 1 are relative values ​​when the height of the space in battery A1 of Example 1 is set to 100.

[0212] [Rating 2]

[0213] For each battery obtained, charge-discharge tests were conducted in a constant temperature bath at 25°C under the following conditions. The pause time between charging and discharging was set to 20 minutes.

[0214] (Charge)

[0215] Charge the battery with a constant current of 2.15 mA per unit area (square centimeters) of electrode until the battery voltage reaches 4.1V, and then charge it with a constant voltage of 4.1V until the current per unit area of ​​electrode reaches 0.54 mA.

[0216] (Discharge)

[0217] A constant current discharge of 2.15mA per unit area electrode is applied until the battery voltage reaches 3.75V.

[0218] Repeat the above charging and discharging process to determine the number of cycles until a voltage change caused by electrode buckling is detected.

[0219] [Table 1]

[0220]

[0221] As can be seen from the results in Table 1, in the batteries A1 to A5 of the embodiments, a space with sufficient height to allow lithium deposition is formed, enabling long-term charge-discharge cycles. In contrast, in the batteries B1 and B2 of the comparative examples, the height of the space is lower, which makes it easier for the electrodes to buckle.

[0222] Industrial availability

[0223] The lithium secondary battery disclosed herein can be used in electronic devices such as mobile phones, smartphones, and tablet computers, including hybrid and plug-in hybrid electric vehicles, and household batteries combined with solar cells.

[0224] The present invention has been described with reference to preferred embodiments, but such disclosure should not be interpreted as limiting. Various modifications and alterations will be apparent to those skilled in the art from the foregoing disclosure. Therefore, the appended claims should be construed as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0225] Explanation of reference numerals in the attached figures

[0226] 10 Lithium secondary batteries

[0227] 11 Positive electrode

[0228] 12 Negative electrode

[0229] 13. Separators

[0230] 14 Electrode Groups

[0231] 14s Space

[0232] 50 Substrate layer

[0233] 50A Substrate Layer

[0234] 50B spacer layer

[0235] 51 Porous sheet

[0236] 52 Composite Material Layer

[0237] 53A and 53B spacer layers

[0238] 53a 1st convex part

[0239] 53b 2nd convex part

Claims

1. A lithium secondary battery, comprising: Electrode assembly and non-aqueous electrolyte, The electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive electrode and the negative electrode are wound together with the separator in between. In the negative electrode, lithium metal is deposited during charging and dissolves in the non-aqueous electrolyte during discharging. The separator has a first surface facing outwards from the electrode assembly and a second surface facing inwards from the electrode assembly. At least one of the first surface and the second surface has a first region and a second region, the first region having a first protrusion of a first pattern, and the second region having a second protrusion of a second pattern different from the first pattern. The second region is located closer to the outer periphery of the electrode assembly than the first region.

2. The lithium secondary battery according to claim 1, wherein, The proportion of the area occupied by the first protrusion in the first region is greater than the proportion of the area occupied by the second protrusion in the second region.

3. The lithium secondary battery according to claim 1, wherein, The air permeability of the first region is lower than that of the second region.

4. The lithium secondary battery according to claim 1, wherein, The first convex portion and the second convex portion are both linear convex portions. The line width of the first protrusion is longer than the line width of the second protrusion.

5. The lithium secondary battery according to claim 1, wherein, The height of the first protrusion is higher than the height of the second protrusion.

6. The lithium secondary battery according to any one of claims 1 to 5, wherein, The separator is a strip shape having a length D1 in a first direction parallel to the winding axis and a length D2 in a second direction intersecting the first direction, and D1 <D2, The length of the first region in the second direction is less than 25% of the total length of the separator in the second direction.

7. The lithium secondary battery according to any one of claims 1 to 5, wherein, At least one of the first pattern and the second pattern is a geometric figure.

8. A separator disposed between a positive electrode and a negative electrode and wound to form an electrode assembly. The separator has a first surface facing outwards from the electrode assembly and a second surface facing inwards from the electrode assembly. At least one of the first surface and the second surface has a first region and a second region, the first region having a first protrusion of a first pattern, and the second region having a second protrusion of a second pattern different from the first pattern. The second region is located closer to the outer periphery of the electrode assembly than the first region.

9. The separator according to claim 8, wherein, The proportion of the area occupied by the first protrusion in the first region is greater than the proportion of the area occupied by the second protrusion in the second region.

10. The separator according to claim 8, wherein, The air permeability of the first region is lower than that of the second region.

11. The separator according to claim 8, wherein, The first convex portion and the second convex portion are both linear convex portions. The line width of the first protrusion is longer than the line width of the second protrusion.

12. The separator according to claim 8, wherein, The height of the first protrusion is higher than the height of the second protrusion.

13. The separator according to any one of claims 8 to 12, wherein, The separator is a strip shape having a length D1 in a first direction parallel to the winding axis and a length D2 in a second direction intersecting the first direction, and D1 <D2, The length of the first region in the second direction is less than 25% of the total length of the separator in the second direction.

14. The separator according to any one of claims 8 to 12, wherein, At least one of the first pattern and the second pattern is a geometric figure.

15. A separator having a length D1 in a first direction and a length D2 in a second direction intersecting the first direction, wherein D1 is a strip-shaped separator. <D2, The separator has a first surface and a second surface opposite to the first surface. At least one of the first surface and the second surface has a first region and a second region, the first region having a first protrusion of a first pattern, and the second region having a second protrusion of a second pattern different from the first pattern. The second region is positioned further away from one end of the second direction than the first region.

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