Secondary battery and separator

Abstract

This secondary battery comprises an electrode group and a nonaqueous electrolyte. The electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode. The separator comprises a base material and spacers. The spacers includes linear protrusions formed in a prescribed pattern. The prescribed pattern has disposition regions where the linear protrusions are disposed, and defect regions where the linear protrusions are not disposed in lengthwise portions in which the linear protrusions extend. Each linear protrusion region has end portions in the vicinity of the defect regions and a main portion other than the end portions. The thickness of the end portions of each linear protrusion is less than that of the main portion.

Description

Secondary batteries and separators Cross-reference of related applications

[0001] This disclosure claims priority with respect to Japanese Patent Application No. 2024-192160, filed with the Japan Patent Office on 31 October 2024, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to a secondary battery and a separator used in a secondary battery.

[0003] A secondary battery comprises an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes. Examples of secondary batteries include lithium-ion batteries and lithium secondary batteries (lithium metal secondary batteries). In the negative electrode of a lithium secondary battery, lithium metal is deposited during charging, and the lithium metal dissolves into the non-aqueous electrolyte during discharge.

[0004] To suppress volume changes in the electrode group during charging and discharging, it is conceivable to place a spacer between the separator substrate and the positive or negative electrode. In lithium secondary batteries, the spacer creates a space for accommodating the lithium metal deposited on the negative electrode during charging.

[0005] Patent Document 1 proposes a lithium secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity, wherein lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves from the negative electrode during discharge, and 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 on the spacer side formed by the separator and the spacer, and the angle on the spacer side formed by the electrode in contact with the spacer and the spacer, is greater than 90° in the cross section of the spacer cut along the thickness direction of the separator and the first direction D1.

[0006] International Publication No. 2021 / 192645

[0007] In recent years, there has been a growing need to suppress the degradation of cycle characteristics in secondary batteries equipped with spacers.

[0008] One aspect of the present disclosure relates to a secondary battery comprising an electrode group and a non-aqueous electrolyte, wherein the electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode, the separator comprising a substrate and a spacer, the spacer including a linear protrusion formed along a predetermined pattern, the predetermined pattern having an arrangement region where the linear protrusion is disposed and a defect region in which the linear protrusion is not disposed in a part of the longitudinal direction in which the linear protrusion extends, the linear protrusion having an end near the defect region and a main part other than the end, and at the end, the thickness of the linear protrusion is smaller than that of the main part.

[0009] Another aspect of the present disclosure relates to a separator for a secondary battery, comprising a base material and a spacer, the spacer including linear protrusions formed along a predetermined pattern, the predetermined pattern having arrangement regions where the linear protrusions are arranged and defect regions in a portion of the longitudinal direction in which the linear protrusions extend where the linear protrusions are not arranged, the linear protrusions having an end near the defect region and a main portion other than the end, wherein at the end, the thickness of the linear protrusions is smaller than that of the main portion.

[0010] According to this disclosure, the degradation of the cycle characteristics of a secondary battery equipped with a spacer can be suppressed. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0011] This is a schematic top view showing an example of a separator. This is an enlarged top view of a part of the spacer in Figure 1. This is a schematic front view showing an example of a linear protrusion. This is a schematic front view showing another example of a linear protrusion. This is a schematic front view showing yet another example of a linear protrusion. This is a schematic longitudinal cross-sectional view showing an example of a secondary battery. This is a schematic cross-sectional view showing the main part of the electrode group.

[0012] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits are given as examples for numerical values ​​of specific physical properties or conditions, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0013] This disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0014] A secondary battery according to the embodiment of this disclosure comprises an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode. The separator comprises a substrate and a spacer. The spacer includes a linear protrusion formed along a predetermined pattern. The predetermined pattern has a placement region where the linear protrusion is arranged and a defect region in which the linear protrusion is not arranged in a part of the longitudinal direction in which the linear protrusion extends. The linear protrusion has an end near the defect region and a main part other than the end. At the end, the thickness of the linear protrusion is smaller than that of the main part. The end near the defect region is the end of the linear protrusion in the longitudinal direction. Hereinafter, the end of the linear protrusion that is near the defect region and has a thickness smaller than that of the main part will also be simply referred to as "end E".

[0015] Conventionally, linear protrusions have a constant thickness in the longitudinal direction from the viewpoint of stability in space formation. In this case, during charging and discharging (when the electrodes expand and contract), stress is more likely to be applied to the substrate from the rectangular ends in the longitudinal direction of the linear protrusions (especially near the corners of the ends). In particular, since the defect region is relatively narrow and the ends tend to be located near the defect region (for example, ends are located on both sides of a narrow defect region), stress tends to concentrate in the substrate near the defect region, making the substrate prone to damage. When the substrate is damaged, an internal short circuit occurs, and the cycle characteristics deteriorate.

[0016] Furthermore, due to the expansion and contraction of the electrodes during charging and discharging, stress is easily applied to the edges (especially the corners) near the defect area of ​​the linear protrusion, and because the strength is low, these edges may collapse. When these edges collapse, the stability of space formation by the spacer (shape stability of the electrode group) may decrease. The collapse of these edges may block the defect area, reducing the fluid flow of the electrode group. As a result, the cycle characteristics may deteriorate.

[0017] In contrast, in this disclosure, by making the thickness of the edge near the defect region smaller than the thickness of the main part, the stress applied to the substrate from the edge near the defect region is relieved. As a result, stress concentration in the substrate near the defect region is suppressed, damage to the substrate is suppressed, and the deterioration of cycle characteristics due to the occurrence of internal short circuits is suppressed.

[0018] Furthermore, by making the thickness of the edges near the defect region smaller than the thickness of the main part, the stress acting in the thickness direction of the linear protrusion at the edges near the defect region is relieved, and collapse of the edges is suppressed. As a result, the decrease in the shape stability of the electrode group is suppressed, the decrease in the fluid flow of the electrode group due to blockage of the defect is suppressed, and the decrease in cycle characteristics is suppressed.

[0019] The main part may have a constant thickness T0, and the end E may have a constant thickness T1 (0 < T1 < T0). The thickness T0 of the main part may be, for example, 15 μm or more and 70 μm or less. Further, from the viewpoint of relaxing the above stress, it is preferable that the thickness of the linear convex portion continuously decreases as it moves away from the main part at the end E. At the end E, it is preferable that the thickness of the linear convex portion continuously decreases from the thickness T0 of the main part to T1 as it moves away from the main part. T1 may be T0 / 2 or less, or may be T0 / 4 or less. When the thickness of the linear convex portion continuously decreases at the end E, T1 may be 0.

[0020] The defective region may be formed on one side in the longitudinal direction of the arrangement region, or may be formed on both sides in the longitudinal direction of the arrangement region. When the defective region is formed on both sides in the longitudinal direction of the arrangement region, it is preferable that the linear convex portion has end E near the defective region on both sides in the longitudinal direction of the main part. That is, it is preferable that one end in the longitudinal direction of the linear convex portion has end E1 near the defective region as end E, and the other end in the longitudinal direction of the linear convex portion has end E2 near the defective region as end E.

[0021] From the viewpoint that the effect of the end E (thin portion) can be easily obtained, the ratio of the total length LE of the end E (E1, E2) to the length L0 of the linear convex portion: LE / L0 may be 0.1 or more, may be 0.2 or more, may be 0.4 or more, or may be 0.5 or more. Further, from the viewpoint of appropriately forming the main part and ensuring the stability of space formation by the spacer, LE / L0 may be 0.65 or less, or may be 0.6 or less.

[0022] The length L0 of the linear convex portion is the dimension in the longitudinal direction of the linear convex portion. The length of the end E (E1, E2) is the dimension of the end E (E1, E2) in the longitudinal direction of the linear convex portion. The total length LE of the end E is the sum of the length L1 of the end E1 and the length L2 of the end E2. The length L1 of the end E1 may be substantially the same (LE / 2) as the length L2 of the end E2, or may be different.

[0023] When the spacer includes a plurality of linear convex portions, 1 / 2 or more (or 4 / 5 or more) of the total number of the plurality of linear convex portions may have an end portion E. Each of the plurality of linear convex portions may have an end portion E. The larger the ratio of the number of linear convex portions having the end portion E, the easier it is to obtain the effect of suppressing the decrease in the liquid circulation property due to the formation of the end portion E.

[0024] The spacer is disposed on the main surface of the base material. The spacer includes linear convex portions formed along a predetermined pattern. Thereby, the stability of the space formation by the spacer in the entire opposing region between the positive and negative electrodes is improved, and the stability of the shape of the electrode group is improved. The predetermined repeating pattern may be, for example, a mesh pattern or a stripe pattern. The mesh pattern may be an aggregate of polygons. Examples of the mesh pattern include a shape in which polygons are combined so as to share sides. The polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons may be combined. Examples of the mesh pattern include a honeycomb shape in which the shape of the mesh is a hexagon, a lattice shape in which the shape of the mesh is a quadrilateral, etc.

[0025] Due to the defect region, a defective portion where no convex portion is disposed on the spacer is formed. Due to the defect region (defective portion), the decrease in the fluidity of the non-aqueous electrolyte when the spacer is disposed is suppressed, the liquid circulation property of the electrode group is improved, and the cycle characteristics and the like are improved. The defective portion serves as a flow path for the non-aqueous electrolyte. The arrangement region (linear convex portion) and the defect region (defective portion) may be alternately formed. The linear convex portions may be intermittently arranged in the length direction. For example, when the arrangement pattern is stripe-shaped, a plurality of linear convex portions are arranged parallel to each other with a gap therebetween. Each of the plurality of linear convex portions may be intermittently arranged. In the case of a stripe shape, the length of one defective portion (defect region) may be, for example, 0.1 to 2.0 mm.

[0026] Furthermore, if the arrangement pattern is honeycomb (or grid), line-shaped protrusions (arrangement areas) may be formed in the center of each side forming the honeycomb hexagon (or grid-like quadrilateral), and defects (defect areas) may be formed at both ends of each side.

[0027] Secondary batteries include lithium secondary batteries (lithium metal secondary batteries) and lithium-ion batteries. For example, the negative electrode of a lithium secondary battery is an electrode in which lithium metal is deposited during charging and dissolves in a non-aqueous electrolyte during discharge. The negative electrode of a lithium-ion battery is an electrode in which lithium ions are absorbed into the negative electrode active material during charging and released from the negative electrode active material during discharge.

[0028] An electrode group may be constructed, for example, by laminating or winding a positive electrode, a negative electrode, and a separator (a substrate on which a spacer is placed). An electrode group may also be constructed by laminating a positive electrode, a negative electrode, and a separator in a zigzag pattern. The outer shape of a wound electrode group may be cylindrical or elliptical. Typically, a wound electrode group uses a strip-shaped positive electrode, a negative electrode, and a separator, and the length direction of the positive electrode, negative electrode, and separator is the winding direction.

[0029] Here, Figure 1 is a schematic top view showing an example of a separator, and is a top view of the separator (base material) in a plan view. Figure 2 is an enlarged top view of a part of the honeycomb-shaped spacer in Figure 1, and is a top view showing a part of the honeycomb-shaped spacer when the spacer (line-shaped protrusion) is viewed from the direction normal to the main surface of the base material in a plan view of the separator (base material). The LS direction in Figure 2 is the length direction of the line-shaped protrusion (arrangement area) arranged along the dashed line in Figure 2. Figure 3 is a schematic front view showing an example of a line-shaped protrusion, and is a front view of the side of the line-shaped protrusion in Figure 2 when viewed from the width direction of the line-shaped protrusion (direction of arrow X in Figure 2). Note that each figure is a schematic diagram, and the aspect ratio of the length and width of each component does not necessarily reflect the actual dimensions.

[0030] The separator 100 in Figure 1 comprises a sheet-like base material 50 and a spacer 53 positioned on one main surface of the base material 50. The base material 50 is strip-shaped, and LD in Figure 1 indicates the longitudinal direction of the base material 50. The spacer 53 is composed of linear protrusions 53a, which form a space 14s. The linear protrusions 53a have a width W. The thickness of the linear protrusions 53a is the height of the linear protrusions 53a from the base material 50 (height h in Figure 7).

[0031] The spacer 53 includes linear protrusions 53a formed along a honeycomb pattern (dashed line in Figure 2). The honeycomb pattern has an arrangement region 60 where the linear protrusions 53a are arranged, and a defect region 70 in which the linear protrusions 53a are not arranged in a part of the length direction in which the linear protrusions 53a extend (length direction of the dashed line in Figure 2). The linear protrusions 53a have ends 61 and 62 near the defect region 70, and a main portion 63 other than the ends 61 and 62. The ends 61 and 62 are the ends of the linear protrusions 53a in the length direction. Ends 61 and 62 are ends E1 and E2, respectively, where the thickness of the linear protrusions 53a is smaller than that of the main portion 63. That is, thin-walled portions are formed at ends 61 and 62 where the thickness of the linear protrusions is smaller than that of the main portion 63.

[0032] The defect regions 70 are located on both sides of the length direction of the arrangement region 60. The linear protrusion 53a has an end E1 (end 61) on one side of the length direction of the main portion 63 and an end E2 (end 62) on the other side of the length direction of the main portion 63. The defect regions 70 form a defect portion 53b where the linear protrusion 53a is not located. Defect portions 53b are formed on both sides of the length direction of the linear protrusion 53a.

[0033] In Figure 2, L0 represents the length of one linear protrusion 53a (arrangement area 60). Ld represents the length of one defect 53b (defect area 70). The ratio of the length Ld of the defect 53b to the length L0 of the linear protrusion 53a, Ld / L0, may be, for example, 1 / 20 or more and 1 / 4 or less, 1 / 20 or more and 1 / 5 or less, or 1 / 10 or more and 1 / 4 or less.

[0034] From the viewpoint of improving the fluidity of the non-aqueous electrolyte, the length Ld of the defect portion 53b may be 0.025 mm or more, 0.1 mm or more, or 0.2 mm or more. From the viewpoint of ensuring the stability of space formation by the spacer, the length Ld of the defect portion 53b may be 2.0 mm or less, 1.25 mm or less, 1.0 mm or less, or 0.8 mm or less. For example, the length Ld of the defect portion 53b may be 0.025 mm or more, 1.25 mm or less, 0.1 mm or more, 2.0 mm or less, 0.1 mm or more, 1.0 mm or less, or 0.2 mm or more, or 0.8 mm or less.

[0035] The length L0 of the linear protrusion 53a may be, for example, 0.5 mm or more and 5.0 mm or less. The width W of the linear protrusion 53a may be, for example, 0.1 mm or more and 2.0 mm or less. W / L0 may be, for example, 0.02 or more and 1 or less.

[0036] The ratio of the total length of end E1 (L1) and end E2 (L2) to the length L0 of the linear projection 53a, (L1 + L2) / L0, may be within the range of LE / L0 as illustrated above, and may be, for example, 0.1 or more (or 0.4 or more). Note that LE = L1 + L2. The length L1 of end E1 is approximately the same as the length L2 of end E2 (LE / 2), but may be different.

[0037] The shapes of the ends E1 and E2 of the linear protrusions are not limited to the shapes shown in Figure 3. For example, the linear protrusion 53a may have ends E1 and E2 with the shapes shown in Figures 4 and 5. In the ends E1 and E2 of Figures 3 and 4, the thickness of the linear protrusion 53a decreases continuously from the thickness T0 of the main part 63 to 0 as it moves away from the main part 63. In the ends E1 and E2 of Figure 5, the thickness of the linear protrusion 53a decreases continuously from the thickness T0 of the main part 63 to T1 as it moves away from the main part 63. T1 may be less than or equal to T0 / 2, or less than or equal to T0 / 4. The shape of end E1 is the same as the shape of end E2, but may be different.

[0038] In this embodiment, the defective portion (defect region) is formed on both sides in the longitudinal direction of the linear protrusion (placement region), but it may also be formed on either one side in the longitudinal direction of the linear protrusion (placement region). In this embodiment, the end E near the defective region is formed on both sides in the longitudinal direction of the main portion, but it may also be formed on either one side in the longitudinal direction of the main portion. In this embodiment, a thin-walled portion (end E) is formed at one end 61 of the main portion and at the other end 62 of the main portion, but a thin-walled portion (end E) may also be formed at either end 61 or end 62.

[0039] The honeycomb-shaped spacer 53 includes a plurality of linear protrusions 53a and a plurality of defective portions 53b. In Figure 1, linear protrusions 53a (placement areas) are formed in the center of each side forming the honeycomb hexagon, and defective portions 53b (defect areas) are formed at both ends of each side, but the honeycomb pattern having defective areas is not limited to this. Linear protrusions (placement areas) may be formed at both ends of each side forming the honeycomb hexagon, and defective portions (defect areas) may be formed in the center of each side.

[0040] It is preferable that 1 / 2 or more (or 4 / 5 or more) of the total number of linear protrusions are linear protrusions 53a having ends E1 and E2. It is more preferable that all of the linear protrusions are linear protrusions 53a having ends E1 and E2.

[0041] (Separator) The separator comprises a sheet-like substrate and a spacer placed on the main surface of the substrate. The substrate is placed between the positive electrode and the negative electrode. The spacer is placed between the electrode (positive or negative electrode) and the substrate. In a plan view of the substrate, the ratio of the area of ​​the region where the spacer is placed on the main surface of the substrate to the area of ​​the substrate may be, for example, 5% or more and 25% or less.

[0042] (Substrate) A porous sheet having ion permeability and insulating properties is used as the substrate. Examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the porous sheet is not particularly limited, but it may be a polymer material. Examples of polymer materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The substrate may contain additives as needed. Examples of additives include inorganic fillers.

[0043] The thickness of the substrate is not particularly limited, but is, for example, 5 μm or more and 20 μm or less, and more preferably 10 μm or more and 20 μm or less.

[0044] The substrate may include a porous sheet and a composite material layer (heat-resistant layer). The composite material layer may be formed on one main surface of the porous sheet or on both main surfaces. The composite material layer is a layer that allows lithium ions to pass through. The composite material layer contains inorganic particles. The composite material layer may optionally contain a resin material. The thickness of the composite material layer may be 5% to 50% of the total thickness of the substrate.

[0045] The composite material layer may be positioned on the side of the porous sheet facing the positive electrode, or on the side of the porous sheet facing the negative electrode. When the composite material layer is positioned on the positive electrode side, degradation of the porous sheet due to oxidation can be suppressed. When the composite material layer is positioned on the negative electrode side, degradation of the porous sheet due to reduction can be suppressed. A spacer may be placed on the composite material layer. In this case, the effect of suppressing thermal shrinkage of the substrate is particularly enhanced.

[0046] The inorganic particles are preferably inorganic compound particles that have thermal stability and insulating properties, and are less likely to melt and decompose when abnormal heat is generated due to a short circuit in the battery, etc. Examples of inorganic particle materials include oxides, hydroxides, nitrides, carbides, and sulfides. Examples of oxides include aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, and zinc oxide. Examples of nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of carbides include silicon carbide and boron carbide. Examples of sulfides include barium sulfate. Examples of hydroxides include aluminum hydroxide. The median diameter in the volume-based particle size distribution of the inorganic particles may be 0.2 to 2.0 μm.

[0047] The median diameter in the volume-based particle size distribution of inorganic particles can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer (e.g., Microtrac manufactured by Nikkiso Co., Ltd.). Alternatively, the cross-section of the substrate can be observed with a transmission electron microscope (TEM), a TEM image can be taken, the area enclosed by the contours of 100 arbitrary inorganic particles can be calculated, the diameter of an equivalent circle (true circle) having the same area as the calculated area can be determined, and the median diameter can be calculated as the average of the diameters of the 100 equivalent circles.

[0048] Examples of resin materials included in the composite material layer include fluorine-containing resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydride, acrylonitrile-butadiene copolymer or its hydride, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, and other rubbers. Examples include cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; acrylic resins such as acrylic acid-metharyl acid copolymers; polyamides such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, and fully aromatic polyamides (aramids); polyamideimide; polyacrylonitrile; polyvinyl alcohol; polyether; polyacrylic acid; polymetharyl acid; polyester; polyolefin; silicone resin; urethane resin; melamine resin; urea resin; and epoxy resin.

[0049] It is desirable to use a polymer material with higher heat resistance than the material of the porous sheet for the resin material contained in the composite material layer (heat-resistant layer). 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, aramid, specifically meta-aramid (meta-total aromatic polyamide) and para-aramid (para-total aromatic polyamide), is preferred.

[0050] The inorganic particle content in the composite material layer may be in the range of 50% to 99% by mass (for example, in the range of 85% to 99% by mass).

[0051] The composite material layer is formed, for example, by applying a coating solution containing inorganic particles, a resin material, and a liquid component (dispersion medium) to a porous sheet and drying the coating film. Examples of liquid components include N-methyl-2-pyrrolidone.

[0052] (Spacer) The spacer is formed on the main surface of the substrate. From the viewpoint of facilitating the fabrication of the electrode group, it is preferable that the spacer is integrated with the substrate. The spacer may be provided on the main surface of the substrate facing the positive electrode (the main surface of the substrate on the positive electrode side), on the main surface of the substrate facing the negative electrode (the main surface of the substrate on the negative electrode side), or on both main surfaces. When the spacer is provided on the main surface of the substrate facing the positive electrode, compared to when the spacer is provided on the main surface of the substrate facing the negative electrode, Li precipitates between the spacers in a way that stretches the substrate toward the positive electrode, so compressive stress is generated in the precipitated Li, and Li tends to precipitate densely. From the viewpoint of improving discharge efficiency and cycle characteristics, it is preferable that the spacer is provided on the main surface of the substrate facing the positive electrode. On the other hand, when the spacer is provided on the main surface of the substrate facing the negative electrode, a space is formed in advance between the substrate and the negative electrode, so the tensile load on the substrate that follows the deposition of Li is reduced. In other words, it is advantageous in that it is easier to maintain the insulating properties of the substrate or the short-circuit resistance of the substrate.

[0053] In lithium-ion batteries, the main role of spacers is to create a space for the deposition of lithium metal. The lithium metal is contained within the space provided by the spacers, thereby suppressing volume changes in the electrode group.

[0054] The spacer may contain a resin material (e.g., an insulating resin), or it may contain a resin material and particles. The proportion of resin material in the spacer may be 10% by volume or more, 30% by volume or more, or 50% by volume or more, or it may be 100% by volume or less, or 80% by volume or less.

[0055] Examples of resin materials included in the spacer include fluorine-containing resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydride, acrylonitrile-butadiene copolymer or its hydride, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, and other rubbers. Examples include cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; acrylic resins such as acrylic acid-metharyl acid copolymers; polyamides such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, and fully aromatic polyamides (aramids); polyamideimide; polyacrylonitrile; polyvinyl alcohol; polyether; polyacrylic acid; polymetharyl acid; polyester; polyolefin; silicone resin; urethane resin; melamine resin; urea resin; and epoxy resin.

[0056] From the viewpoint of suppressing the increase in the gas generation reaction rate during internal short circuits, it is preferable that the spacer has a non-porous structure that does not allow lithium ions to permeate. Among the above resin materials, polyimide, polyvinylidene fluoride, and acrylonitrile-acrylic acid ester copolymers are preferred as materials that do not allow lithium ions to permeate, and polyimide may also be used. A non-porous spacer of a certain height or more formed from these resin materials is a layer that does not allow lithium ions to permeate.

[0057] The particles may be inorganic or organic. Among these, inorganic particles such as insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides are particularly suitable. Preferred metal oxides include aluminum oxide (alumina and boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, and silicon oxide (silica). Examples of metal hydroxides include aluminum hydroxide. Examples of metal nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of metal carbides include silicon carbide and boron carbide. Examples of metal sulfides include barium sulfate. Minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate may also be used. Among these, alumina, silica, and titania are particularly preferred.

[0058] The average particle size is not particularly limited, but may be 0.1 μm or larger, 0.5 μm or larger, 10 μm or smaller, 5 μm or smaller, or 2 μm or smaller. The average particle size can be measured by the following method. First, a cross-section of the spacer in the thickness direction of the separator is photographed with an electron microscope to obtain an image of the cross-section. Next, image processing such as binarization is performed on the image to identify the parts of the particles. Next, the diameter of a circle having the same area as the cross-sectional area of ​​each particle (equivalent circle diameter) is determined, and the arithmetic mean of the obtained equivalent circle diameters can be taken as the average particle size. The arithmetic mean can be calculated from, for example, 100 or more particles. The average particle size of other particles contained in the electrode plate and separator can also be determined by the same method.

[0059] When the spacer contains resin material and particles, it is preferable that the particle content in the spacer be 50% by volume or less. This makes it easier to ensure sufficient strength of the spacer.

[0060] The spacer includes a protrusion. The protrusion includes at least a linear protrusion having the end E described above, and may further include other protrusions other than the linear protrusion having the end E (for example, a linear protrusion without an end E, a dot-shaped protrusion, etc.).

[0061] The height H of the spacer (protrusion) may be greater than the thickness T of the base material. The ratio of the height H of the spacer (protrusion) to the thickness T of the base material, H / T, may be greater than 1 and be 1.5 or greater, 2 or greater, or 3 or greater. H / T may be 10 or less, 8 or less, 5 or less, or 4 or less. When H / T is 1.5 or greater, volume changes of the electrode group are easily suppressed.

[0062] Spacers are formed, for example, by applying a coating solution containing spacer components and liquid components to a predetermined location on a substrate and drying the coating film. Examples of liquid components include N-methyl-2-pyrrolidone. Coating may be done using a dispenser or other known printing methods such as gravure printing, inkjet printing, and screen printing. Drying may be done by known methods such as heating or natural drying.

[0063] The following provides a detailed explanation of the positive electrode, negative electrode, and non-aqueous electrolyte of a secondary battery.

[0064] (Lithium secondary battery) (Negative electrode) The negative electrode is equipped with a negative electrode current collector. The negative electrode may consist only of the negative electrode current collector, or it may include a thin lithium metal foil that has been pre-pressed onto the negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode by charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode during charging and become lithium metal, which is deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode dissolves as lithium ions in the non-aqueous electrolyte during discharge. The lithium ions contained in the non-aqueous electrolyte may originate from lithium salts added to the non-aqueous electrolyte, or they may be supplied from the positive electrode active material during charging, or both.

[0065] The negative electrode may include a lithium ion storage layer (a layer that exhibits capacity through the absorption and release of lithium ions by the negative electrode active material) supported on the negative electrode current collector. In this case, the open-circuit potential of the negative electrode at full charge may be 70 mV or less relative to the lithium metal (lithium dissolution potential). When the open-circuit potential of the negative electrode at full charge is 70 mV or less relative to the lithium metal, lithium metal is present on the surface of the lithium ion storage layer at full charge. That is, the negative electrode exhibits capacity through the deposition and dissolution of lithium metal.

[0066] Here, "fully charged" refers to the state in which the battery has been charged to a charge level of, for example, 0.98 × C or higher, where C is the rated capacity of the battery. The open-circuit potential of the negative electrode at full charge can be measured by disassembling the fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell with lithium metal as the counter electrode. The non-aqueous electrolyte of the cell may have the same composition as the non-aqueous electrolyte in the disassembled battery.

[0067] The lithium-ion storage layer is formed by creating layers of a negative electrode composite material containing a negative electrode active material. In addition to the negative electrode active material, the negative electrode composite material may also contain binders, conductive materials, thickeners, etc.

[0068] Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain one type of negative electrode active material, or a combination of two or more types. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon).

[0069] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjenblack, and carbon nanotubes.

[0070] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride. Examples of thickeners include carboxymethylcellulose and its sodium salt.

[0071] The negative electrode current collector can be any conductive sheet. Examples of conductive sheets include foil and film.

[0072] The material of the negative electrode current collector (conductive sheet) 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 alloy. Preferably, the conductive material is one that does not react with lithium. More specifically, it is preferable that the conductive material does not form any alloys or intermetallic compounds with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metallic elements, or graphite in which the basal surface is preferentially exposed. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys with high conductivity are preferred.

[0073] The thickness of the negative electrode current collector is not particularly limited, but is, for example, 5 μm or more and 300 μm or less.

[0074] (Positive electrode) The positive electrode comprises a positive electrode current collector and a positive electrode composite layer supported on the positive electrode current collector. The positive electrode composite layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode composite layer may be formed on only one side of the positive electrode current collector or on both sides. The positive electrode can be obtained, for example, by applying a positive electrode composite slurry containing the 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 it.

[0075] The positive electrode active material is a material that intercepts 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 because they have low manufacturing costs and a high average discharge voltage.

[0076] During charging, lithium contained in lithium-containing transition metal oxides is released from the positive electrode as lithium ions and deposited as lithium metal on the negative electrode or negative electrode current collector. During discharge, the lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed into the composite oxide of the positive electrode. In other words, the lithium ions involved in charging and discharging generally originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0077] Examples of 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 transition metal element or two or more. The transition metal elements may be Ni, Co, and / or Mn. Lithium-containing transition metal oxides may optionally contain one or more main group elements. Examples of main group elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The main group elements may also be Al, etc.

[0078] Among lithium-containing transition metal oxides, composite oxides containing Ni, Co, and / or Mn as transition metal elements, and possibly Al as an optional component, and having a layered rock salt-type crystalline structure, are preferred for obtaining high capacity. In this case, in a 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.

[0079] For example, the binder and conductive materials exemplified for the negative electrode can be used. For the positive electrode, graphite can be used as the conductive material. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0080] Examples of materials for the positive electrode current collector (conductive sheet) include metallic materials containing Al, Ti, Fe, etc. The metallic material may be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0081] The thickness of the positive electrode current collector is not particularly limited, but is, for example, 5 μm or more and 300 μm or less.

[0082] (Non-aqueous electrolyte) A non-aqueous electrolyte having lithium ion conductivity may be a liquid electrolyte (electrolytic solution), a gel electrolyte, or a solid electrolyte. The liquid electrolyte is, for example, an electrolytic solution containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolytic solution is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolytic solution may contain known additives.

[0083] The gel electrolyte contains a lithium salt and a matrix polymer, or contains a lithium salt, a non-aqueous solvent, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, polyethylene oxide, etc.

[0084] As the solid electrolyte, for example, materials known in all-solid-state lithium ion secondary batteries etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0085] The 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 generated.

[0086] As the anion, BF ４ － , ClO ４ － , PF ６ － , CF ３ SO ３ － , CF ３ CO ２ － , anions of imides, anions of oxalate complexes, etc. are mentioned. As the anions of imides, N(SO ２ CF ３ ), N(C ２ － ), N(C ｍ F ２ｍ＋１ SO ２ ), N(C ｘ F ｎ SO ２ｎ＋１ ), etc. ２ )ｙ － Examples include (where m and n are independently 0 or an integer greater than or equal to 1, and x and y are independently 0, 1 or 2, satisfying x + y = 2). The anion of the oxalate complex may contain boron and / or phosphorus. Examples of anions of the oxalate complex include bisoxalate borate anion and difluorooxalate borate anion (BF ２ (C ２ O ４ ) － ), PF ４ (C ２ O ４ ) － , PF ２ (C ２ O ４ ) ２ － Examples include these. Non-aqueous electrolytes may contain these anions individually or in combination of two or more.

[0087] From the viewpoint of suppressing the dendritic deposition of lithium metal, the non-aqueous electrolyte preferably contains at least an oxalate complex anion, and more preferably an oxalate complex anion containing fluorine. The interaction between the fluorine-containing oxalate complex anion and lithium makes it easier for lithium metal to precipitate uniformly in fine particulate form. Therefore, it is easier to suppress localized deposition of lithium metal. The fluorine-containing oxalate complex anion may be combined with other anions. Other anions include PF ６ － And / or imide anions.

[0088] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, or halogen-substituted versions thereof. The non-aqueous electrolyte may contain one of these non-aqueous solvents or two or more of them. Examples of halogen-substituted versions include fluorides.

[0089] Examples of esters include carbonate esters and carboxylic acid esters. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of linear carbonate esters 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 linear carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0090] Examples of ethers include cyclic ethers and linear ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of linear ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methylphenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0091] The concentration of 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 anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Alternatively, the concentration of anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0092] The non-aqueous electrolyte may contain additives. The additives may form a film on the negative electrode. The formation of a film derived from the additive on the negative electrode makes it easier to suppress dendrite formation. Examples of such additives include vinylene carbonate, FEC, vinyl ethyl carbonate (VEC), and the like.

[0093] (Lithium-ion battery) The negative electrode of a lithium-ion battery contains a negative electrode active material capable of intercalating and releasing lithium ions. The positive electrode and non-aqueous electrolyte of a lithium-ion battery can be those exemplified in lithium secondary batteries.

[0094] The negative electrode comprises, for example, a negative electrode current collector and a negative electrode composite material layer (the lithium ion storage layer described above) supported on the negative electrode current collector. The negative electrode composite material layer may be supported on one main surface of the negative electrode current collector, or on both main surfaces of the negative electrode current collector. The negative electrode composite material and the negative electrode current collector can be appropriately selected from those exemplified above.

[0095] In the following, an example of a secondary battery according to this embodiment will be specifically described with reference to the drawings. The components of the secondary battery example described below can be the components described above. Furthermore, the components of the example described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiment. Furthermore, in the secondary battery described below, components that are not essential to the secondary battery according to this disclosure may be omitted. Note that the scale of the components in the following figures has been changed to facilitate understanding.

[0096] Here, Figure 6 is a schematic longitudinal cross-sectional view showing an example of a secondary battery according to the embodiment of this disclosure. In Figure 6, a cylindrical lithium secondary battery is shown as an example of a secondary battery. Note that in Figure 6, the spacers and the spaces formed by the spacers are not shown.

[0097] The cylindrical lithium secondary battery 10 includes a cylindrical battery case and a wound electrode group 14 and a non-aqueous electrolyte (not shown) housed within the battery case. The battery case includes a case body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is placed between the case body 15 and the sealing body 16. The gasket 27 ensures that the battery case is airtight. Inside the case body 15, insulating plates 17 and 18 are placed at both ends of the electrode group 14 in the direction of the winding axis, respectively.

[0098] The case body 15 has a stepped portion 21 formed, for example, by partially pressing the side wall of the case body 15 from the outside. The stepped portion 21 may be formed in an annular shape on the side wall of the case body 15 along the circumferential direction of the case body 15. In this case, the sealing body 16 is supported on the opening side surface of the stepped portion 21.

[0099] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. In the sealing body 16, these members are stacked in this order. The sealing body 16 is fitted into the opening of the case body 15 such that the cap 26 is located on the outside of the case body 15 and the filter 22 is located on the inside of the case body 15. Each of the above-mentioned members constituting the sealing body 16 is, for example, disc-shaped or ring-shaped. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. The filter 22 and the lower valve body 23 are connected to each other at their respective centers. The upper valve body 25 and the cap 26 are connected to each other at their respective centers. In other words, each member except the insulating member 24 is electrically connected to each other.

[0100] The lower valve body 23 has a ventilation hole (not shown) formed therein. Therefore, if the internal pressure of the battery case rises due to abnormal heat generation or the like, the upper valve body 25 bulges towards the cap 26 and separates 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 ruptures, and gas is discharged through an opening (not shown) formed in the cap 26.

[0101] Figure 7 is an enlarged view of a part of the electrode group 14. Figure 7 includes the portion near the positive electrode enclosed by region II in Figure 6 and the portion near the negative electrode enclosed by region III in Figure 6.

[0102] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator (a base material 50 and a spacer 53). The base material 50 of the positive electrode 11, the negative electrode 12, and the separator are all in the shape of a strip. The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator so that the separator is positioned between the positive electrode 11 and the negative electrode 12. The separator is the separator of this disclosure (for example, the separator in Figure 1).

[0103] The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode composite layer 11b. The positive electrode current collector 11a is electrically connected to a cap 26, which functions as a positive electrode terminal, via a positive electrode lead 19. In Figure 7, the negative electrode 12 is shown as a negative electrode (negative electrode current collector) in a state where lithium metal has not been deposited. The negative electrode 12 is electrically connected to a case body 15, which functions as a negative electrode terminal, via a negative electrode lead 20.

[0104] The base material 50 has a main surface 50a facing the positive electrode 11 and a main surface 50b facing the negative electrode 12. The base material 50 of Embodiment 1 comprises a porous sheet 51 and a composite material layer 52 (heat-resistant layer). The composite material layer 52 is formed on the main surface of the porous sheet 51 that faces the positive electrode 11. In Embodiment 1, the spacer 53 is formed on the main surface 50a facing the positive electrode 11. The spacer 53 is formed on the composite material layer 52 and is in contact with the positive electrode 11. The spacer 53 creates a space 14s between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the base material 50). Figure 7 shows the height h of the spacer 53.

[0105] In Figure 7, the spacer 53 is positioned on the main surface 50a of the base material 50 on the positive electrode 11 side, but it may also be positioned on the main surface 50b of the base material 50 on the negative electrode 12 side. The spacer 53 is formed on the composite material layer 52, but it may also be formed on the porous sheet 51. The composite material layer 52 of the base material 50 is positioned on the positive electrode 11 side, but it may also be positioned on the negative electrode 12 side.

[0106] In the lithium secondary battery 10, lithium metal is deposited on the negative electrode 12 during charging. Since a space 14s exists between the positive electrode 11 and the negative electrode 12, the volume change of the electrode group 14 due to the deposition of lithium metal is reduced, and the cycle characteristics are improved.

[0107] The secondary battery according to the embodiments of this disclosure is not limited to a cylindrical secondary battery equipped with a wound electrode group. The shape of the secondary battery can be appropriately selected from various shapes such as cylindrical, coin-shaped, prismatic, sheet-shaped, and flattened, depending on its application. The form of the electrode group is also not particularly limited and may be stacked.

[0108] (Note) The above description of embodiments discloses the following technologies. (Technology 1) A secondary battery comprising an electrode group and a non-aqueous electrolyte, wherein the electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode, the separator comprises a substrate and a spacer, the spacer includes a linear protrusion formed along a predetermined pattern, the predetermined pattern has a placement region where the linear protrusion is disposed and a defect region in which the linear protrusion is not disposed in a part of the length direction in which the linear protrusion extends, the linear protrusion has an end near the defect region and a main part other than the end, and at the end, the thickness of the linear protrusion is smaller than that of the main part. (Technology 2) The secondary battery according to Technology 1, wherein at the end, the thickness of the linear protrusion decreases continuously as it moves away from the main part. (Technology 3) The defect region is arranged on both sides in the longitudinal direction of the arrangement region, the linear protrusion has the ends on both sides in the longitudinal direction of the main portion, and the ratio of the total length LE of the ends to the length L0 of the linear protrusion: LE / L0 is 0.2 or more, the secondary battery according to Technology 1 or 2. (Technology 4) The LE / L0 is 0.5 or more, the secondary battery according to Technology 3. (Technology 5) The spacer includes a plurality of linear protrusions, and 1 / 2 or more of the total number of the plurality of linear protrusions have the ends, the secondary battery according to any one of Technology 1 to 3. (Technology 6) 4 / 5 or more of the total number of the plurality of linear protrusions have the ends, the secondary battery according to Technology 5. (Technology 7) The negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharge, the secondary battery according to any one of Technology 1 to 3.(Technical 8) A separator for a secondary battery, wherein the separator comprises a base material and a spacer, the spacer includes a linear protrusion formed along a predetermined pattern, the predetermined pattern having an arrangement region where the linear protrusion is arranged and a defect region in which the linear protrusion is not arranged in a part of the longitudinal direction in which the linear protrusion extends, the linear protrusion having an end near the defect region and a main part other than the end, the thickness of the linear protrusion being smaller than that of the main part at the end. (Technical 9) The separator according to Technical 8, wherein at the end, the thickness of the linear protrusion decreases continuously as it moves away from the main part. (Technology 10) The defect region is arranged on both sides in the longitudinal direction of the arrangement region, the linear protrusion has the ends on both sides in the longitudinal direction of the main portion, and the ratio of the total length LE of the ends to the length L0 of the linear protrusion: LE / L0 is 0.2 or more, the separator according to Technology 8 or 9. (Technology 11) The separator according to Technology 10, wherein LE / L0 is 0.5 or more. (Technology 12) The separator according to any one of Technology 8 to 10, wherein the spacer includes a plurality of linear protrusions, and 1 / 2 or more of the total number of the plurality of linear protrusions have the ends. (Technology 13) The separator according to Technology 12, wherein 4 / 5 or more of the total number of the plurality of linear protrusions have the ends.

[0109] [Examples] The secondary battery relating to this disclosure will be described in more detail below based on examples and comparative examples. However, this disclosure is not limited to the following examples.

[0110] 《Batteries A1-A7》 (Preparation of positive electrode) A positive electrode slurry was prepared by mixing the positive electrode active material, acetylene black (AB; conductive material), polyvinylidene fluoride (PVdF; binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP). The positive electrode active material used was a rock salt type lithium-containing transition metal oxide (NCA: positive electrode active material) having a layered structure and containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al is 1.0). In the positive electrode slurry, the mass ratio of NCA:AB:PVdF was set to 95:2.5:2.5. The positive electrode slurry was applied to both sides of a strip of Al foil (positive electrode current collector), the coating was dried, and the material was rolled to form a positive electrode layer. A positive electrode current collector, having positive electrode composite material layers formed on both sides, was cut to a predetermined size to obtain a strip-shaped positive electrode.

[0111] (Preparation of the negative electrode current collector) A strip of electrolytic copper foil (12 μm thick) was prepared as the negative electrode current collector.

[0112] (Preparation of Substrate) A 10 μm thick microporous thin film made of polyethylene was prepared. A coating solution containing paraphenylene terephthalamide, an aromatic polyamide, as a resin material, and alumina as inorganic particles, was applied to one main surface of the microporous thin film. The coating solution was an N-methyl-2-pyrrolidone solution containing 5.8% by mass of calcium chloride, adjusted to a concentration of 2 wt% aromatic polyamide and 4 wt% alumina. The microporous thin film with the coating was left for 1 hour at a temperature of 25°C and a relative humidity of 70% to precipitate the aromatic polyamide. Next, NMP and calcium chloride in the coating were removed by washing with water. A 5 μm thick composite material layer (heat-resistant layer) was formed by drying the coating at 60°C for 5 minutes. In this way, a substrate (15 μm thick) having a microporous thin film and a composite material layer was obtained.

[0113] (Formation of spacers on the main surface of the substrate) A coating solution containing polyvinylidene fluoride and alumina particles (inorganic filler) was applied to the microporous thin film of the substrate described above, and the coating film was dried to form spacers.

[0114] The spacer arrangement pattern was an intermittent honeycomb shape as shown in Figure 1. For the linear protrusions constituting the spacer, the linear protrusions shown in Figure 3 or Figure 4 (linear protrusions 53a having ends E1 and E2) were used. The linear protrusions 53a had a length L0 of 2.5 mm, a width W of 0.5 mm, and a main portion thickness T0 of 40 μm. The length Ld of the defect portion 53b (defect region 70) was 0.5 mm. LE / L0 was the value shown in Table 1. The lengths L1 of end E1 and L2 of end E2 were the same length (LE / 2).

[0115] If necessary, line-shaped protrusions without ends E1 and E2 (line-shaped protrusions whose end thickness is the same as the main part thickness T0) were used along with the line-shaped protrusions 53a described above. The ratio of the number of line-shaped protrusions 53a having ends E1 and E2 to the total number of line-shaped protrusions N0 constituting the spacer (N1 / N0 × 100) was set to the values ​​shown in Table 1.

[0116] (Preparation of non-aqueous electrolyte) 1,2-dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (CHF ２ CF ２ OCH ２ CF ３ A mixed ether solvent containing ) and in a volume ratio of 1:2 was prepared. Lithium bissulfonylimide (LiFSI) was added to the mixed solvent at a concentration of 1 mol / L, and LiBF ２ (C ２ O ４ A liquid non-aqueous electrolyte was prepared by dissolving the substance to a concentration of 0.1 mol / L.

[0117] (Battery Assembly) In an inert gas atmosphere, the positive electrode and the negative electrode current collector were wound in a spiral shape with separators in between to create an electrode group. In this way, a wound-type electrode group with the structure shown in Figure 7 was obtained. At this time, the electrode group was configured such that separators with spacers were placed on the inner and outer circumference sides of the positive electrode, respectively. The separators were positioned so that the main surface of the base material on the side where the spacers were formed faced the positive electrode.

[0118] An electrode group was housed in a bottomed cylindrical case body, and a non-aqueous electrolyte was injected. A sealing body was placed at the opening of the case body via a gasket, sealing the electrode group and non-aqueous electrolyte inside the battery case. In this way, a lithium secondary battery with the structure shown in Figure 6 was completed.

[0119] Battery B1 was manufactured in the same manner as Battery A1, except that all of the linear protrusions constituting the spacer were linear protrusions without ends E1 and E2. In the linear protrusions without ends E1 and E2, the thickness of both ends in the longitudinal direction was made the same as the thickness T0 of the main part.

[0120] [Evaluation] Each obtained battery underwent a charge-discharge test in a constant temperature chamber at 25°C under the following conditions. The rest period between charging and discharging was 20 minutes.

[0121] (Charging) Constant current charging was performed at a current of 2.15 mA per unit area (square centimeter) of the electrodes until the battery voltage reached 4.1 V. Then, constant voltage charging was performed at a voltage of 4.1 V until the current value per unit area of ​​the electrodes reached 0.54 mA.

[0122] (Discharge) A constant current discharge was performed at a current of 2.15 mA per unit area of ​​the electrodes until the battery voltage reached 3.75 V.

[0123] (Expansion Rate of Electrode Group) The above charging and discharging process constituted one cycle, and the fabricated battery was charged up to the 300th cycle. The battery before charging and discharging, and the battery after the 300th cycle of charging, were disassembled, and the positive electrode, negative electrode, and the laminate of the two separators on either side of the negative electrode were removed. Disassembly was performed in an inert gas atmosphere. The removed positive electrode, negative electrode, and separator laminate were washed with dimethyl carbonate, dried, and the thickness of the laminate was measured. The thickness of the laminate was measured using a Peacock digital thickness gauge G2-205M. The thickness was measured at five arbitrary points within the laminate, and the arithmetic mean of the five measurements was taken as the average thickness of the laminate. Next, the average thickness X obtained by subtracting the thicknesses of the two substrates from this average thickness was calculated. The ratio (%) of the average thickness X at the 300th cycle to the average thickness X before charging and discharging was calculated as the expansion rate of the electrode group.

[0124] (Capacity Retention Rate) The above charging and discharging process was considered one cycle, and charging and discharging was performed up to 300 cycles. The ratio (%) of the discharge capacity at cycle 300 to the discharge capacity at cycle 1 was calculated as the capacity retention rate.

[0125] The evaluation results are shown in Table 1. In Table 1, A1 to A7 are the batteries of the examples, and B1 is the battery of the comparative example. In Table 1, the expansion rate of the electrode group is expressed as a relative value when the expansion rate of battery B1 is set to 100.

[0126]

[0127] Batteries A1 to A7 showed a smaller electrode expansion rate and higher capacity retention rate compared to battery B1.

[0128] The secondary battery of this disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet devices, electric vehicles including hybrid and plug-in hybrid vehicles, and home battery storage systems combined with solar cells.

[0129] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0130] 10: Lithium secondary battery, 11: Positive electrode, 12: Negative electrode, 14: Electrode group, 14s: Space, 15: Case body, 16: Sealing body, 23: Lower valve body, 25: Upper valve body, 50: Substrate, 51: Porous sheet, 52: Composite material layer, 53: Spacer, 53a: Linear protrusion, 53b: Defect area, 60: Placement area, 70: Defect area, 61, 62: Edges near the defect area, 63: Main part

Claims

1. A secondary battery comprising an electrode group and a non-aqueous electrolyte, wherein the electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode, the separator comprises a base material and a spacer, the spacer includes a linear protrusion formed along a predetermined pattern, the predetermined pattern has a placement region where the linear protrusion is arranged and a defect region in which the linear protrusion is not arranged in a part of the length direction in which the linear protrusion extends, the linear protrusion has an end near the defect region and a main part other than the end, and at the end, the thickness of the linear protrusion is smaller than that of the main part.

2. The secondary battery according to claim 1, wherein at the end portion, the thickness of the line-shaped protrusion decreases continuously as it moves away from the main portion.

3. The secondary battery according to claim 1, wherein the defect regions are arranged on both sides in the longitudinal direction of the arrangement region, the linear protrusions have ends on both sides in the longitudinal direction of the main portion, and the ratio of the total length LE of the ends to the length L0 of the linear protrusions: LE / L0 is 0.2 or more.

4. The secondary battery according to claim 3, wherein the LE / L0 is 0.5 or greater.

5. The secondary battery according to any one of claims 1 to 3, wherein the spacer includes a plurality of linear protrusions, and at least half of the total number of the plurality of linear protrusions have the ends.

6. The secondary battery according to claim 5, wherein 4 / 5 or more of the total number of the plurality of line-shaped protrusions have the ends.

7. The secondary battery according to any one of claims 1 to 3, wherein the negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharge.

8. A separator for a secondary battery, wherein the separator comprises a base material and a spacer, the spacer includes a linear protrusion formed along a predetermined pattern, the predetermined pattern having an arrangement region where the linear protrusion is arranged and a defect region in which the linear protrusion is not arranged in a part of the longitudinal direction in which the linear protrusion extends, the linear protrusion having an end near the defect region and a main portion other than the end, and at the end, the thickness of the linear protrusion is smaller than that of the main portion.

9. The separator according to claim 8, wherein at the end portion, the thickness of the line-shaped protrusion decreases continuously as it moves away from the main portion.

10. The separator according to claim 8, wherein the defect regions are arranged on both sides in the longitudinal direction of the arrangement region, the linear protrusions have ends on both sides in the longitudinal direction of the main portion, and the ratio of the total length LE of the ends to the length L0 of the linear protrusions: LE / L0 is 0.2 or more.

11. The separator according to claim 10, wherein the LE / L0 is 0.5 or greater.

12. The separator according to any one of claims 8 to 10, wherein the spacer includes a plurality of linear protrusions, and at least half of the total number of the plurality of linear protrusions have the ends.

13. The separator according to claim 12, wherein 4 / 5 or more of the total number of the plurality of line-shaped protrusions have the ends.

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