Secondary battery and separator for secondary battery

Abstract

This secondary battery comprises: a positive electrode; a negative electrode; a separator disposed between the positive and negative electrodes; and an non-aqueous electrolyte. The separator comprises a sheet-shaped base material and a spacer that is disposed on the main surface of the base material. The spacer includes a plurality of protrusion groups. Each of the plurality of protrusion groups is a primary structure formed by assembling a plurality of small piece members, and the plurality of small piece members make up a secondary structure as a result of the plurality of protrusion groups being arranged in a predetermined pattern. The plurality of small piece members are arranged apart from each other.

Description

Secondary battery and separator for secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-029952, filed on February 29, 2024 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a secondary battery and a separator for a secondary battery.

[0003] Known high-capacity non-aqueous electrolyte secondary batteries include lithium ion batteries, lithium metal secondary batteries (lithium secondary batteries), etc. In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging, and the lithium metal dissolves during discharging and is released as lithium ions into the non-aqueous electrolyte.

[0004] As a method for suppressing the volume change of the electrode group during charge and discharge of the secondary battery, it is conceivable to place spacers on the main surface of the substrate of the separator.

[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 is dissolved from the negative electrode during discharging; a spacer is provided between the separator and at least one of the positive electrode and the negative electrode; a first length of the separator in a first direction D1 is smaller than a second length of the separator in a second direction D2 intersecting with the first direction D1; and in a cross section of the spacer taken along the thickness direction of the separator and the first direction D1, at least one of an angle formed between the separator and the spacer on the spacer side and an angle formed between the spacer and an electrode in contact with the spacer is greater than 90°.

[0006] International Publication No. 2021 / 192645

[0007] There is room for improvement in the cycle characteristics and initial capacity of secondary batteries equipped with spacers.

[0008] One aspect of the present disclosure relates to a secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate, the spacer including a plurality of convex groups, each of the plurality of convex groups being a primary structure formed by assembling a plurality of small piece members, the plurality of convex groups being arranged in a predetermined pattern, whereby the plurality of small piece members constitute a secondary structure, and the plurality of small piece members are arranged at a distance from one another.

[0009] Another aspect of the present disclosure relates to a separator for a secondary battery, comprising a sheet-like substrate and a spacer arranged on a main surface of the substrate, the spacer including a plurality of groups of convex portions, each of the plurality of groups of convex portions being a primary structure formed by assembling a plurality of small piece members, the plurality of groups of convex portions being arranged in a predetermined pattern, whereby the plurality of small piece members form a secondary structure, and the plurality of small piece members are arranged at a distance from one another.

[0010] According to the present disclosure, it is possible to improve the cycle characteristics and initial capacity of a secondary battery. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] 11 is a cross-sectional view schematically showing a main part of a secondary battery according to an embodiment of the present disclosure; FIG. 12 is a cross-sectional view schematically showing a main part of a conventional secondary battery; FIG. 13 is a top view showing an example of a spacer; FIG. 14 is a top view showing another example of a spacer; FIG. 15 is a top view showing yet another example of a spacer; FIG. 16 is a top view showing yet another example of a spacer; FIG. 17 is a vertical cross-sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure; FIG. 18 is a cross-sectional view schematically showing a main part of the lithium secondary battery shown in FIG. 10; FIG. 19 is a top view showing an example of an arrangement pattern of a group of protrusions; FIG. 20 is a top view showing another example of an arrangement pattern of a group of protrusions; FIG. 21 is a top view of a spacer provided in secondary battery B1 of a comparative example;

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

[0013] A secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0014] Hereinafter, the positive electrode, negative electrode, and separator are collectively referred to as an "electrode group." The shape of the electrode group is not particularly limited. The electrode group may be a wound electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are spirally wound with a separator interposed therebetween, or may be a flat electrode group in which a wound electrode group is pressed in the radial direction. The electrode group may be configured by stacking a positive electrode and a negative electrode with a separator interposed therebetween, or may be configured by stacking a positive electrode and a negative electrode in a zigzag manner with a separator interposed therebetween.

[0015] In the present disclosure, the separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate. The spacer includes a plurality of convex portions. Each of the plurality of convex portions is a primary structure formed by assembling a plurality of small piece members. The plurality of convex portions is arranged in a predetermined pattern, and the plurality of small piece members form a secondary structure. The plurality of small piece members are arranged at a distance from one another.

[0016] The arrangement of the spacer can improve cycle characteristics and initial capacity (for example, initial charge capacity), and in the case of a lithium secondary battery, can suppress deterioration of cycle characteristics due to the occurrence of internal short circuits in the early stages of cycling.

[0017] 1 is a cross-sectional view schematically showing a main part of a secondary battery according to an embodiment of the present disclosure, and FIG. 2 is a cross-sectional view schematically showing a main part of a conventional secondary battery.

[0018] In FIGS. 1 and 2, a substrate 50 and a spacer 53 are disposed between a positive electrode 11 and a negative electrode 12. The spacer 53 of the present disclosure shown in FIG. 1 is composed of a group of protrusions 53a formed by assembling a plurality of small piece members 60. The group of protrusions 53a forms a space 14s between the positive electrode 11 and the negative electrode 12. The group of linear protrusions 53a (thin line-like small piece members 60) in FIG. 1 shows, for example, a cross section in the width direction of the group of linear protrusions 53a (thin line-like small piece members 60). The conventional spacer 53 shown in FIG. 2 is composed of large protrusions 73a. The group of protrusions 73a forms a space 14s between the positive electrode 11 and the negative electrode 12. The protrusions 73a in FIG. 2 show, for example, a cross section in the width direction of the linear protrusions 73a.

[0019] As shown in FIG. 2 , in a conventional secondary battery, the spacer 53 is configured with a wide protrusion 73 a, and Li ions released from the positive electrode 11 move around the protrusion 73 a near the wide protrusion 73 a to the negative electrode 11. Therefore, the amount of Li ions moving to the negative electrode 12 is locally increased near the protrusion 73 a. In the case of a lithium secondary battery, the amount of Li precipitated on the negative electrode 12 is locally increased near the protrusion 73 a. Therefore, stress caused by expansion of the negative electrode 12 is concentrated near the protrusion 73 a, which can degrade cycle characteristics. In a lithium secondary battery in which the negative electrode expands significantly due to Li precipitation during charging, the substrate 50 is damaged by the stress concentration, which easily causes an internal short circuit early in the cycle and degrades cycle characteristics.

[0020] In the vicinity of the convex portion 73a, Li ions released from the positive electrode 11 move around the convex portion 73a to the negative electrode 11 (Li ions are less likely to move in the region where the convex portion 73a is located between the positive electrode 11 and the negative electrode 12), which can result in high resistance and a decrease in initial capacity.

[0021] In contrast, in the secondary battery according to the present disclosure, as shown in FIG. 1 , the spacer 53 is composed of a group of protrusions 53a, and the plurality of thin, linear small pieces 60 included in the group of protrusions 53a are each narrow and spaced apart from one another. Li ions released from the positive electrode 11 during charging can pass between two adjacent small pieces 60 and migrate to the negative electrode 12. This suppresses the aforementioned Li ion migration and the resulting local increase in the amount of Li ions migrating to the negative electrode 12. In the case of a lithium secondary battery, by forming the spacer 53 with the group of protrusions 53a, the local increase in the amount of Li precipitation near the spacer 53 is suppressed. Therefore, stress concentration during expansion of the negative electrode 12 and the resulting deterioration in cycle characteristics are suppressed.

[0022] In particular, in a lithium secondary battery, the negative electrode expands significantly due to Li deposition during charging, and therefore, the above-described effect of forming the spacer with the convex portions 53 a is significantly achieved, significantly suppressing damage to the substrate 50 due to the above-described stress concentration and the resulting deterioration of cycle characteristics due to the occurrence of an internal short circuit early in the cycle.

[0023] 1, in the region between the positive electrode 11 and the negative electrode 12 where the convex portion group 53a is present, Li ions released from the positive electrode 11 during charging can pass between two adjacent small pieces 60 and move to the negative electrode 12 (the aforementioned migration of Li ions can be suppressed). This reduces the resistance and improves the initial capacity.

[0024] (Protrusion groups and small piece members) The spacer includes a plurality of projection groups. Each of the plurality of projection groups is a primary structure formed by assembling a plurality of small piece members. The plurality of projection groups are arranged in a predetermined pattern, and the plurality of small piece members form a secondary structure. The plurality of small piece members are arranged at a distance from each other.

[0025] The space formed by the spacer serves to absorb the expansion and contraction of the electrodes during charge and discharge. In the case of a lithium secondary battery, the space formed by the spacer mainly serves to accommodate Li that deposits on the negative electrode during charge. The placement of the spacer suppresses volumetric changes in the electrode group during charge and discharge, thereby suppressing deterioration in cycle characteristics that would otherwise be caused by large volumetric changes in the electrode group.

[0026] By assembling a plurality of small piece members to form a group of protrusions, the stability of space formation by the spacer (spacer strength) is ensured. Ensuring the stability of space formation maintains the effect of suppressing volumetric changes in the electrode group during charge and discharge, resulting in stable charge and discharge characteristics and improved cycle characteristics. From the viewpoint of ensuring the stability of space formation, the minimum value of the separation distance between two adjacent small piece members in the primary structure may be 2.0 mm or less, 1.0 mm or less, or even 0.5 mm or less. Furthermore, from the viewpoint of suppressing the penetration of Li ions and reducing resistance near the spacer, the minimum value of the separation distance between two adjacent small piece members may be 0.05 mm or more, or even 0.1 mm or more. The minimum value of the separation distance may be, for example, within a range of 0.05 to 2 mm, or within the range of the separation distance D2 described below.

[0027] The small piece members have a smaller minimum width than the group of convex portions. When the small piece members are thin line-shaped, the width W2 of the thin line-shaped small piece members is the minimum width of the small piece members. When the group of convex portions is linear, the width W1 of the linear group of convex portions is the minimum width of the group of convex portions. The minimum width of the small piece members may be, for example, within the range of W2 exemplified below. The minimum width of the group of convex portions may be, for example, within the range of W1 exemplified below. The ratio of the minimum width of the small piece members to the minimum width of the group of convex portions may be, for example, within the range of W2 / W1 exemplified below.

[0028] The shape of the group of protrusions is not particularly limited, and may be linear, circular, or polygonal. The group of linear protrusions may be straight or curved. The group of linear protrusions may be arranged continuously or intermittently.

[0029] The plurality of convex portions are preferably arranged in a predetermined pattern. The plurality of linear convex portions may be arranged in a striped pattern or a mesh pattern. The mesh pattern may be a collection of polygons. In the case of a mesh pattern, a portion forming one mesh (polygon) is considered to be one convex portion group. An example of a mesh pattern includes a shape in which polygons are combined to share a side. Polygons include triangles, squares, hexagons, etc. Different types of polygons may also be combined. The mesh pattern may be a honeycomb pattern. Furthermore, circular or polygonal convex portions may be arranged in a predetermined pattern (e.g., a dot pattern). Polygons include triangles, squares, hexagons, etc. Circles include ellipses. The plurality of convex portions may be substantially the same or different in shape and / or size.

[0030] The shape of the small piece members may be thin line-like, elongated, circular, or polygonal. The thin line-like small piece members may be arranged continuously or intermittently. The thin line-like small piece members may be linear or curved. The multiple small piece members may be approximately the same as each other or different in shape and size. In the primary structure, the multiple small piece members are preferably arranged in a predetermined pattern. The multiple thin line-like small piece members are preferably arranged in a striped pattern. The arrangement pattern may be a dot pattern. In the primary structure, circular, elongated, or polygonal small piece members may be arranged in a predetermined pattern (e.g., a dot pattern). Polygons include triangles, squares, hexagons, etc. Circles include ellipses. The multiple small piece members may be approximately the same as each other or different in shape and / or size.

[0031] From the viewpoint of ensuring the stability of space formation, in a plan view of the separator, the ratio (S2 / S1×100) of the total area S2 of the plurality of small piece members included in one convex group to the area S1 per convex group is preferably 50% or more, more preferably 60% or more. From the viewpoint of suppressing the penetration of Li ions in the vicinity of the spacer, S2 / S1×100 is preferably 90% or less, more preferably 80% or less. The range of S2 / S1×100 may be, for example, 50 to 90%. In the spacer shown in FIG. 3, the linear convex group 53a (thin linear small piece members 60) is intermittently arranged and has defects 54. In this case, the areas S1 and S2 are the areas excluding the defects 54. In this case, S2 / S1 can be obtained by calculating (3×W2) / W1 using the width W1 of one linear convex group 53a and the width W2 of three thin line-shaped small piece members 60 included in one linear convex group 53a.

[0032] The plurality of linear projection groups may be arranged parallel to one another along the length direction of the elongated substrate. In this case, it is preferable that the plurality of small piece members included in one projection group in the primary structure are each thin lines having a width smaller than that of one projection group and are arranged parallel to one another along the length direction of one projection group. In this case, stability of space formation by the spacer is easily ensured, and localized concentration of Li deposition near the spacer due to Li ions released from the positive electrode going around the spacer is easily suppressed.

[0033] In the above case, the multiple linear convex portion groups are arranged spaced apart from one another in the width direction of the long substrate. The multiple linear convex portion groups are preferably arranged at regular intervals in the width direction of the long substrate, but the respective separation distances may be different. In the above case, the multiple thin linear piece members included in one convex portion group are arranged spaced apart from one another in the width direction of the long substrate. The multiple thin linear piece members are preferably arranged at regular intervals in the width direction of the long substrate, but the respective separation distances may be different. The spacing between the multiple thin linear piece members is smaller than the spacing between the multiple linear convex portion groups. The widths of the multiple thin linear piece members included in one convex portion group may be the same as or different from one another.

[0034] Here, Fig. 3 shows an example of the spacer (group of convex portions). Fig. 3 is a top view showing an enlarged portion of the spacer (group of convex portions) formed on the main surface of the substrate in a plan view of the separator.

[0035] 3, the spacer 53 includes a plurality of convex portions 53a, each of which is a primary structure formed by assembling a plurality of small piece members 60. Each of the plurality of convex portions 53a is linear and arranged in a stripe pattern. The linear convex portions 53a are arranged parallel to one another along the X direction. When the substrate 50 is elongated, the X direction is preferably the length direction (winding direction) of the elongated substrate 50.

[0036] 3, in the primary structure, the plurality of small piece members 60 included in one convex group 53a are each thin line-shaped with a width smaller than that of one convex group 53a, and are arranged parallel to and spaced apart from each other along the length direction (X direction) of one convex group 53a. The plurality of convex groups 53a are arranged in stripes, and the plurality of small piece members 60 form the secondary structure.

[0037] The plurality of linear protrusion groups 53a (the plurality of thin linear piece members 60 included in one protrusion group 53a) are each arranged intermittently, and have defects 54 in a predetermined pattern. Although the defects 54 in FIG. 3 are arranged in a predetermined pattern, the defects may also be arranged randomly. The linear protrusion groups 53a (the plurality of thin linear piece members 60 included in the protrusion group 53a) may also be arranged continuously without having defects 54.

[0038] 3, three thin linear piece members 60 are assembled to form one convex portion group 53a, but the number of thin linear piece members 60 is not limited to this. For example, the number of thin linear piece members is 2 to 4.

[0039] From the viewpoint of ensuring the stability of the space formation (the strength of the spacer), the width W2 of each of the plurality of thin linear piece members 60 included in one convex portion group 53a may be 0.05 mm or more, or may be 0.1 mm or more. From the viewpoint of suppressing the penetration of Li ions near the spacer and reducing resistance, the width W2 of each of the plurality of thin linear piece members 60 included in one convex portion group 53a may be 1.0 mm or less, or may be 0.5 mm or less.

[0040] From the viewpoints of ensuring the stability of space formation and facilitating the formation of an aggregate of a plurality of small members, the width W1 of the linear protrusion group 53a may be 0.25 mm or more, or may be 0.5 mm or more. From the viewpoint of facilitating the formation of a sufficient space, the width W1 of the linear protrusion group 53a may be 5.0 mm or less, or may be 2.0 mm or less.

[0041] The width W2 is smaller than the width W1. The ratio W2 / W1 of the width W2 of each of the plurality of small piece members 60 included in one convex portion group 53a to the width W1 of one convex portion group 53a may be 0.01 or more and 0.5 or less (or 0.45 or less), or may be 0.1 or more and 0.45 or less.

[0042] In the primary structure (one convex portion group 53 a), two adjacent small piece members 60 are spaced apart by a distance D2. From the viewpoint of suppressing the penetration of Li ions near the spacer and reducing resistance, the separation distance D2 between two adjacent small piece members 60 in the primary structure may be, for example, 0.05 mm or more and 2.0 mm or less, or 0.1 mm or more and 0.5 mm or less.

[0043] Two adjacent convex portion groups 53a are spaced apart by a distance D1. From the viewpoint of ensuring the space formed by the spacers and stably forming the space, the distance D1 between two adjacent convex portion groups 53a may be, for example, 1.0 mm or more and 10.0 mm or less, or 2.0 mm or more and 5.0 mm or less. The distance D1 is, for example, 5 to 40% of the dimension of the substrate 50 in the width direction (Y direction).

[0044] The separation distance D2 is smaller than the separation distance D1. The ratio D2 / D1 of the separation distance D2 between two adjacent small piece members 60 in the primary structure to the separation distance D1 between two adjacent convex portion groups 53 a may be, for example, 0.01 or more and 0.5 or less, 0.02 or more and 0.08 or less, or 0.02 or more and 0.06 or less.

[0045] Another example of the spacer may be the spacer 53 (convex portion group 53a) shown in Figures 4 to 9. Figures 4 to 9 are top views showing enlarged portions of the spacer (convex portion group) formed on the main surface of the substrate in a plan view of the separator. Note that the substrate is omitted in Figures 4 to 9. In Figures 4 to 9, the X direction is, for example, the length direction of the elongated substrate.

[0046] In Figures 4 to 6, a plurality of rectangular convex portion groups 53a are arranged in a predetermined pattern. Each of the plurality of convex portion groups 53a is a primary structure formed by assembling a plurality of elongated small piece members 60. The plurality of rectangular convex portion groups 53a are arranged in a predetermined pattern, and the plurality of elongated small piece members 60 form a secondary structure. In Figure 4, the length direction of the elongated small piece members 60 is approximately parallel to the length direction of the rectangular convex portion groups 53a. In Figure 5, the length direction of the elongated small piece members 60 is approximately parallel to the width direction of the rectangular convex portion groups 53a. In Figure 6, the length direction of the elongated small piece members 60 is inclined with respect to the long sides of the rectangular convex portion groups 53a.

[0047] 7, a plurality of quadrangular protrusion groups 53a are arranged in a dot pattern. Each of the plurality of quadrangular protrusion groups 53a is a primary structure formed by assembling a plurality of quadrangular small piece members 60. Due to the dot-like arrangement of the plurality of quadrangular protrusion groups 53a, the plurality of quadrangular small piece members 60 form a secondary structure.

[0048] 8, a plurality of circular convex portion groups 53a are arranged in a dot pattern, and each of the plurality of circular convex portion groups 53a is a primary structure formed by assembling a plurality of elongated small piece members 60. Due to the dot-like arrangement of the plurality of circular convex portion groups 53a, the plurality of elongated small piece members 60 form a secondary structure.

[0049] 9, a plurality of rectangular convex portion groups 53a are arranged in a predetermined pattern in the X and Y directions. Each of the plurality of rectangular convex portion groups 53a is a primary structure formed by assembling a plurality of circular small piece members 60. By arranging the plurality of rectangular convex portion groups 53a in a predetermined pattern, the plurality of circular small piece members 60 form a secondary structure.

[0050] 4 to 9, the width of the plurality of small piece members 60 included in one convex portion group 53a is smaller than the width of one convex portion group 53a. The separation distance between two adjacent small piece members 60 in one convex portion group 53a is smaller than the separation distance between two adjacent convex portion groups 53a. The spacers (convex portion groups) in FIGS. 3 to 9 are entirely or partially disposed on the main surface of the separator substrate.

[0051] The secondary battery will be described in detail below.

[0052] (Lithium secondary battery) A lithium secondary battery includes a positive electrode, a negative electrode on which lithium metal precipitates during charging and dissolves in a non-aqueous electrolyte during discharge, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The negative electrode includes at least a negative electrode current collector, and lithium metal precipitates on the negative electrode current collector during charging. The non-aqueous electrolyte has lithium ion conductivity.

[0053] In a lithium secondary battery, for example, 70% or more of the rated capacity is achieved by the deposition and dissolution of lithium metal. The movement of electrons at the negative electrode during charging and discharging is mainly due to the deposition and dissolution of lithium metal at the negative electrode. Specifically, 70 to 100% (e.g., 80 to 100% or 90 to 100%) of the movement of electrons (or current from another perspective) at the negative electrode during charging and discharging is due to the deposition and dissolution of lithium metal. In other words, the negative electrode of a lithium secondary battery differs from a negative electrode in which the movement of electrons at the negative electrode during charging and discharging is mainly due to the absorption and release of lithium ions by the negative electrode active material (e.g., graphite).

[0054] (Separator) The separator includes a sheet-like substrate and a spacer disposed on the main surface of the substrate.

[0055] (Substrate) A porous sheet having ion permeability and insulating properties is used as the substrate. Examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. The material of the porous sheet is not particularly limited, but may be a polymer material. Examples of the polymer material include an olefin resin, a polyamide resin, and cellulose. Examples of the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene. The substrate may contain an additive, if necessary. Examples of the additive include an inorganic filler.

[0056] 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.

[0057] The substrate may include a porous sheet and a composite material layer (heat-resistant 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 composite material layer contains inorganic particles. The composite material layer may contain a resin material as needed. The thickness of the composite material layer may be 5% to 50% of the total thickness of the substrate.

[0058] The composite material layer may be disposed 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 disposed on the positive electrode side, deterioration of the porous sheet due to oxidation reactions can be suppressed. When the composite material layer is disposed on the negative electrode side, deterioration of the porous sheet due to reduction reactions can be suppressed. A spacer may be disposed on the composite material layer. In this case, the effect of suppressing thermal shrinkage of the substrate is particularly enhanced.

[0059] The inorganic particles are preferably particles of an inorganic compound that is thermally stable and insulating, and thus unlikely to melt or decompose during abnormal heat generation due to a short circuit in the battery, etc. Examples of inorganic particle materials 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 and boron carbide, etc. Examples of sulfides include barium sulfate, etc. Examples of hydroxides include aluminum hydroxide, etc. The median diameter in the volume-based particle size distribution of the inorganic particles may be 0.2 to 2.0 μm.

[0060] 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 measuring device (for example, Microtrac manufactured by Nikkiso Co., Ltd.) Alternatively, the cross section of the substrate may be observed with a transmission electron microscope (TEM), a TEM image may be taken, the area surrounded by the outlines of any 100 inorganic particles may be calculated, the diameter of an equivalent circle (perfect circle) having the same area as the calculated area may be determined, and the average diameter of the 100 equivalent circles may be calculated.

[0061] Examples of resin materials contained in the composite material layer (heat-resistant layer) include fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluororubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydrogenated product, acrylonitrile-butadiene copolymer or its hydrogenated product, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, rubbers such as ethylene propylene rubber, ethyl cellulose, methyl cellulose, Examples of the resin include cellulose derivatives such as cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; vinyl resins such as polyvinyl alcohol and polyvinyl acetate; acrylic resins such as polymethyl methacrylate; polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid); polyamideimide, polyacrylonitrile, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

[0062] The resin material contained in the composite material layer (heat-resistant layer) is preferably a polymeric material having higher heat resistance than the material of the porous sheet. Such a polymeric material preferably includes at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamideimides. These are known to have high heat resistance. From the viewpoint of heat resistance, aramids, i.e., meta-aramids (meta-type wholly aromatic polyamides) and para-aramids (para-type wholly aromatic polyamides), are preferred.

[0063] The content of the inorganic particles in the composite material layer may be in the range of 50% by weight to 99% by weight (for example, in the range of 85% by weight to 99% by weight).

[0064] The composite material layer is formed, for example, by applying a coating liquid containing inorganic particles, a resin material, and a liquid component (dispersion medium) to a porous sheet and then drying the coating film. Examples of the liquid component include N-methyl-2-pyrrolidone.

[0065] (Spacer) The spacer is formed on the main surface of the substrate. From the viewpoint of ease of preparation of the electrode group, it is preferable that the substrate and the spacer are integrated. The spacer may be provided on the main surface of the substrate facing the positive electrode (the main surface on the positive electrode side of the substrate), or on the main surface of the substrate facing the negative electrode (the main surface on the negative electrode side of the substrate), or on both main surfaces. When the spacer is provided on the main surface of the substrate facing the positive electrode, Li precipitates between the spacers so as to stretch the substrate toward the positive electrode, compared to when the spacer is provided on the main surface of the substrate facing the negative electrode, so compressive stress is generated in the precipitated Li, making it easier for Li 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 generated by the precipitation of Li is reduced. That is, it is advantageous in that the insulating properties of the substrate can be easily maintained, or the short-circuit resistance of the substrate can be easily maintained.

[0066] In lithium secondary batteries, the main role of the spacer is to form a space for lithium metal to deposit, which prevents the negative electrode from expanding during charging.

[0067] The spacer includes a conductive material and / or an insulating material. Among them, an insulating material is preferable. Since lithium metal is less likely to deposit on the surface of an insulating material, the effect of disposing the spacer can be easily obtained.

[0068] The spacer may include a resin material (e.g., an insulating resin) or may include a resin material and particles. The proportion of the resin material in the spacer may be 10% by volume or more, 30% by volume or more, or 50% by volume or more, or may be 100% by volume or less, or 80% by volume or less.

[0069] Examples of resin materials contained in the spacer include fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluororubbers such as vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer, rubbers such as styrene-butadiene copolymer or hydrogenated product, acrylonitrile-butadiene copolymer or hydrogenated product, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, and ethylene propylene rubber, and ethyl acrylate copolymer. Examples of the resin include cellulose derivatives such as cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose, vinyl resins such as polyvinyl alcohol and polyvinyl acetate, acrylic resins such as polymethyl methacrylate, polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid), polyamideimide, polyacrylonitrile, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

[0070] Among the above resin materials, preferred materials that are impermeable to lithium ions include polyimide, polyvinylidene fluoride, and acrylonitrile-acrylic acid ester copolymers, and polyimide may also be used. A non-porous spacer of a certain height or greater formed from these resin materials is a layer that is impermeable to lithium ions and has a non-porous structure that does not allow lithium ions to pass through. Arranging such a spacer is preferable from the viewpoint of suppressing an increase in the gas generation reaction rate during an internal short circuit. When a spacer with a non-porous structure is arranged, the effect of configuring the spacer with the above-mentioned convex portion group (small piece member) is significantly achieved.

[0071] The particles may be inorganic or organic. Examples of inorganic particles include insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides. Examples of 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 preferred.

[0072] The average particle size of the particles is not particularly limited, but may be 0.1 μm or more, 0.5 μm or more, or 10 μm or less, 5 μm or less, or 2 μm or less. 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 using an electron microscope to obtain an image of the cross-section. Next, the image is subjected to image processing such as binarization to identify the particle portion. Next, the diameter of a circle having the same area as the cross-section area of ​​each particle (equivalent circle diameter) is determined, and the arithmetic mean of the determined equivalent circle diameters can be used as the average particle size. The arithmetic mean can be determined, for example, from 100 or more particles. The average particle size of other particles contained in the electrode plate and separator can also be determined by a similar method.

[0073] When the spacer contains a resin material and particles, the particle content in the spacer is preferably 50% by volume or less, which makes it easier to ensure sufficient strength of the spacer.

[0074] The height H of the spacer may be greater than the thickness T of the substrate. The ratio of the height H to the thickness T, H / T, may be greater than 1, 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. By making H / T 1.5 or greater, expansion of the electrode group can be particularly suppressed.

[0075] The height H can be measured by the following method. First, a cross section of the separator (substrate) in the thickness direction is photographed using an electron microscope to obtain an image of the cross section. Next, 20 arbitrary locations among the spacers are selected in the image, and the heights of the spacers at those locations are measured. Next, the heights measured at the 20 locations are arithmetically averaged, and the obtained average value is defined as the height H. The thickness T can also be measured using a similar procedure.

[0076] The spacers are formed, for example, by applying a coating liquid containing spacer components and a liquid component to a predetermined location on a substrate and drying the coating. Examples of the liquid component include N-methyl-2-pyrrolidone. The coating may be performed using a dispenser or by a known printing method such as gravure printing, inkjet printing, or screen printing. The drying may be performed by a known method such as drying by heating or natural drying.

[0077] (Negative electrode) The negative electrode includes a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode upon charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode upon charging, becoming 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 upon discharging.

[0078] The negative electrode may include a lithium ion occlusion layer (a layer that develops capacity by occlusion and release of lithium ions by a negative electrode active material (such as graphite)) supported on a negative electrode current collector. In this case, the open circuit potential of the negative electrode when fully charged may be 70 mV or less relative to lithium metal (dissolution and deposition potential of lithium). If the open circuit potential of the negative electrode when fully charged is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion occlusion layer when fully charged. In other words, the negative electrode develops capacity by deposition and dissolution of lithium metal.

[0079] Here, "fully charged" refers to a state in which the battery is charged to a state of charge of, for example, 0.98 x C or more, where C is the rated capacity of the battery. The open circuit potential of the negative electrode at full charge can be measured by disassembling a fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell with lithium metal as the counter electrode. The nonaqueous electrolyte of the cell may have the same composition as the nonaqueous electrolyte in the disassembled battery.

[0080] The lithium ion occlusion layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a binder, a thickener, a conductive agent, etc. in addition to the negative electrode active material.

[0081] Examples of the negative electrode active material include a carbonaceous material, a Si-containing material, and a Sn-containing material. The negative electrode may contain one or more negative electrode active materials. Examples of the carbonaceous material include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon).

[0082] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0083] Examples of the binder include fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, rubber polymer, etc. Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0084] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0085] 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. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form an alloy or an intermetallic compound with lithium is preferred. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, as well as graphite with a preferentially exposed basal plane. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys with high conductivity are preferred.

[0086] The thickness of the negative electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0087] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides. The positive electrode is obtained, for example, by applying a positive electrode mixture slurry including the positive electrode active material, the conductive material, and the binder to both sides of the positive electrode current collector, drying the coating, and then rolling.

[0088] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material 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 of their low production cost and high average discharge voltage.

[0089] The lithium contained in the lithium-containing transition metal oxide is released from the positive electrode as lithium ions during charging and precipitates as lithium metal on the negative electrode or negative electrode current collector. During discharging, 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 are generally derived from the solute in the nonaqueous electrolyte and the positive electrode active material.

[0090] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain one or more transition metal elements. The transition metal element may be Ni, Co, and / or Mn. The lithium-containing transition metal oxide may contain one or more typical elements as needed. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The typical element may be Al, etc.

[0091] Among lithium-containing transition metal oxides, composite oxides containing Ni, Co, and / or Mn as transition metal elements, and which may contain Al as an optional component, and which have a layered rock-salt crystal structure are preferred in terms of obtaining high capacity. In this case, in the lithium secondary battery, the molar ratio mLi / mM of the total amount of lithium contained in the positive electrode and negative electrode to the amount mM of metal M other than lithium contained in the positive electrode is set to, for example, 1.1 or less.

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

[0093] Examples of the material of the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0094] The thickness of the positive electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0095] (Non-aqueous electrolyte) The non-aqueous electrolyte having lithium ion conductivity may be a liquid electrolyte (electrolytic solution), a gel electrolyte, or a solid electrolyte. The liquid electrolyte is, for example, an electrolytic solution containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolytic solution is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolytic solution may contain known additives.

[0096] The gel electrolyte contains a lithium salt and a matrix polymer, or a lithium salt, a non-aqueous solvent, and a matrix polymer. The matrix polymer is, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, and polyethylene oxide.

[0097] As the solid electrolyte, for example, a material known in all-solid-state lithium ion secondary batteries (for example, oxide-based solid electrolyte, sulfide-based solid electrolyte, halide-based solid electrolyte, etc.) can be used.

[0098] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0099] The anion is BF ４ － , ClO ４ － , P.F. ６ － , C.F. ３ SO ３ － , C.F. ３ CO ２ － , anions of imides, anions of oxalate complexes, etc. Examples of the anions of imides include N(SO ２ CF ３ ) ２ － , N(C ｍ F ２ｍ＋１ SO ２ ) ｘ (C ｎ F ２ｎ＋１ SO ２ )ｙ － (m and n are each independently an integer of 0 or 1 or more, and x and y are each independently 0, 1, or 2, satisfying the relationship x+y=2). The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalate borate anion and difluorooxalate borate anion (BF ２ (C ２ O ４ ) － ), P.F. ４ (C ２ O ４ ) － , P.F. ２ (C ２ O ４ ) ２ － The non-aqueous electrolyte may contain one of these anions alone or two or more of them.

[0100] From the viewpoint of suppressing the deposition of lithium metal in a dendritic form, the nonaqueous electrolyte preferably contains at least an anion of an oxalate complex, and more preferably contains an oxalate complex anion having fluorine. The interaction between the oxalate complex anion having fluorine and lithium facilitates the uniform deposition of lithium metal in the form of fine particles. This makes it easier to suppress local deposition of lithium metal. The oxalate complex anion having fluorine may be combined with another anion. The other anion may be PF ６ － and / or an anion of an imide.

[0101] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. Examples of halogen-substituted derivatives include fluorides.

[0102] 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 chain 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 chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0103] Examples of the ether include cyclic ethers and chain ethers. Examples of the cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of the 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.

[0104] The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Furthermore, the concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0105] The non-aqueous electrolyte may contain an additive. The additive may form a coating on the negative electrode. The formation of a coating derived from the additive on the negative electrode makes it easier to suppress the formation of dendrites. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0106] (Lithium-ion battery) A lithium-ion battery includes a positive electrode, a negative electrode containing a negative electrode active material that absorbs and releases lithium ions, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode and non-aqueous electrolyte may be the same as those exemplified for lithium secondary batteries. The positive electrode composite and positive electrode current collector contained in the positive electrode may be appropriately selected from those exemplified above. The non-aqueous solvent and lithium salt (anion) contained in the non-aqueous electrolyte may be appropriately selected from those exemplified above.

[0107] The negative electrode includes, for example, a negative electrode current collector and a negative electrode composite layer (the above-mentioned lithium ion occlusion layer) supported on a main surface of the negative electrode current collector. The negative electrode composite layer may be supported on one main surface of the negative electrode current collector, or may be supported on both main surfaces of the negative electrode current collector. The negative electrode composite and negative electrode current collector included in the negative electrode can be appropriately selected from those exemplified above.

[0108] The substrate and spacer included in the separator can be the same as those used in lithium secondary batteries. The substrate may include a porous sheet containing a polymer material. The substrate may further include a composite material layer containing a resin material and inorganic particles.

[0109] The spacers contained in the separator contain a resin material, which can be appropriately selected from the materials exemplified above.

[0110] In the case of a lithium-ion battery, the spacers may be disposed only in locations where stress is likely to increase when the negative electrode expands. The spacers may be disposed at the bent portions of an electrode assembly in which positive and negative electrodes are stacked in a zigzag pattern, at the innermost periphery of a wound electrode assembly, or at locations with a small radius of curvature of a flat electrode assembly.

[0111] Fig. 10 is a longitudinal cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment of the present disclosure. Note that Fig. 10 does not illustrate the spacer 53 and the space 14s formed by the spacer 53. Fig. 10 illustrates a cylindrical lithium secondary battery as an example of a secondary battery according to the present disclosure, but the secondary battery according to the present disclosure is not limited to this.

[0112] The cylindrical lithium secondary battery 10 shown in Fig. 10 includes a cylindrical battery case, and a wound electrode group 14 and a nonaqueous electrolyte (not shown) housed within the battery case. The battery case includes a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is disposed between the case body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery case. Within the case body 15, insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction.

[0113] Case body 15 has a step 21 formed, for example, by pressing a portion of the side wall of case body 15 from the outside. Step 21 may be formed in an annular shape along the circumferential direction of case body 15 on the side wall of case body 15. In this case, sealing body 16 is supported by the surface of step 21 on the opening side.

[0114] 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. These components are stacked in this order in the sealing body 16. The sealing body 16 is attached to the opening of the case body 15 so that the cap 26 is located outside the case body 15 and the filter 22 is located inside the case body 15. The above-mentioned components constituting the sealing body 16 are, for example, disk-shaped or ring-shaped. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and an insulating member 24 is interposed between their respective peripheral edges. The filter 22 and the lower valve body 23 are connected to each other at their respective centers. The upper valve body 25 and the cap 26 are connected to each other at their respective centers. In other words, all components except the insulating member 24 are electrically connected to each other.

[0115] A vent hole (not shown) is formed in the lower valve body 23. Therefore, if the internal pressure of the battery case increases due to abnormal heat generation or the like, the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23. This cuts off the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure increases further, the upper valve body 25 breaks, and gas is discharged from an opening (not shown) formed in the cap 26.

[0116] 11 is an enlarged view of a portion of the electrode group 14. Fig. 11 includes a portion near the positive electrode surrounded by region II in Fig. 10 and a portion near the negative electrode surrounded by region III in Fig. 10.

[0117] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator (a substrate 50 and a spacer 53). The positive electrode 11, the negative electrode 12, and the separator substrate 50 are all strip-shaped. The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator (substrate 50) so that the separator is disposed between the positive electrode 11 and the negative electrode 12.

[0118] The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode mixture 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 FIG. 4, the negative electrode 12 is shown as a negative electrode (negative electrode current collector) on which no lithium metal is 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.

[0119] The substrate 50 has a main surface 50a facing the positive electrode 11 and a main surface 50b facing the negative electrode 12. The substrate 50 of embodiment 1 includes a porous sheet 51 and a composite material layer 52 (heat-resistant layer). The composite material layer 52 is formed on one of the two main surfaces of the porous sheet 51, the main surface facing the negative electrode 12. In embodiment 1, a 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 forms a space 14s between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the substrate 50). Figure 11 shows the height h of the spacer 53 after the electrode group is formed.

[0120] 11 , the spacer 53 is disposed on the main surface 50a of the substrate 50 on the positive electrode 11 side, but may also be disposed on the main surface 50b of the substrate 50 on the negative electrode 12 side. The spacer 53 is formed on the composite material layer 52, but may also be formed on the porous sheet 51. The composite material layer 52 of the substrate 50 is disposed on the positive electrode 11 side, but may also be disposed on the negative electrode 12 side.

[0121] During charging of the lithium secondary battery 10, lithium metal is deposited on the negative electrode 12. Because a space 14s exists between the positive electrode 11 and the negative electrode 12, the volume change of the electrode group 14 that accompanies the deposition of lithium metal is reduced, improving the cycle characteristics.

[0122] 12 and 13 show examples of the planar shape of the spacer 53 (arrangement pattern of the convex portion group). In plan view, the spacer 53 is arranged on one main surface of the substrate 50. Note that each figure is a schematic diagram, and the aspect ratio of each member does not necessarily reflect the actual size. Note that in FIGS. 12 and 13, the multiple small piece members included in the convex portion group 53a are not shown.

[0123] 12, the spacer 53 is composed of a plurality of linear convex portions 53a arranged in a stripe pattern. The regions where the spacers 53 are not formed form spaces 14s. The plurality of linear convex portions 53a are arranged parallel to one another along the length direction (LD direction) of the band-shaped substrate 50. The plurality of linear convex portions 53a are arranged spaced apart from one another.

[0124] In Fig. 12, the plurality of linear protrusions 53a are arranged continuously, but they may be arranged intermittently. The intermittent arrangement may result in defects. The defects may be arranged randomly or in a predetermined pattern. In Fig. 12, six linear protrusion groups 53a are arranged, but the number of linear protrusion groups 53a is not limited to this.

[0125] 13, the spacer 53 is composed of a group of linear protrusions 53a arranged in a honeycomb pattern. The areas where the spacers 53 are not formed form spaces 14s. The group of linear protrusions 53a is arranged continuously, but may also be arranged intermittently. The intermittent arrangement may result in defects.

[0126] The arrangement pattern of the convex portion groups is not limited to the arrangement patterns shown in Figures 12 and 13 and may be, for example, a dot pattern. One linear convex portion group 53a in Figures 12 and 13 is formed by, for example, assembling a plurality of thin linear piece members each having a width smaller than that of one linear convex portion group 53a. The plurality of thin linear piece members are arranged parallel to and spaced apart from each other along the length direction of one linear convex portion group.

[0127] 10 shows a cylindrical lithium secondary battery having a wound electrode group as an example of a secondary battery according to an embodiment of the present disclosure, but the lithium secondary battery according to an embodiment of the present disclosure is not limited to this and can be applied to other shapes. The shape of the secondary battery can be appropriately selected from various shapes such as cylindrical, coin, prismatic, sheet, and flat, depending on the application. The shape of the electrode group is also not particularly limited and may be a stacked type.

[0128] (Additional Notes) The above embodiments disclose the following technologies. (Technology 1) A 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, wherein the separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate, wherein the spacer includes a plurality of convex groups, each of the plurality of convex groups being a primary structure formed by assembling a plurality of small piece members, and wherein the plurality of convex groups are arranged in a predetermined pattern, whereby the plurality of small piece members form a secondary structure, and the plurality of small piece members are arranged at a distance from one another. (Technology 2) The secondary battery according to Technology 1, wherein the minimum value of the separation distance between two adjacent small piece members in the primary structure is 2.0 mm or less. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the plurality of small piece members in the primary structure are arranged in a predetermined pattern. (Technology 4) The secondary battery according to any one of Technologies 1 to 3, wherein, in a plan view of the separator, a ratio of a total area S2 of the plurality of small piece members included in one convex group to an area S1 per one convex group is 50% or more. (Technology 5) The secondary battery according to any one of Technologies 1 to 4, wherein the base material is elongated, the plurality of linear convex groups are arranged parallel to one another along the length direction of the base material, and in the primary structure, the plurality of small piece members included in one convex group are each thin-line shaped with a width smaller than that of one of the convex groups and are arranged parallel to one another along the length direction of the one convex group. (Technology 6) The secondary battery according to Technology 5, wherein a ratio W2 / W1 of the width W2 of each of the plurality of small piece members included in one convex group to the width W1 of one of the convex groups is 0.01 or more and 0.5 or less. (Technology 7) The secondary battery according to Technology 5 or Technology 6, wherein each of the plurality of small piece members included in one of the convex portion groups has a width W2 of 0.05 mm or more and 1.0 mm or less. (Technology 8) The secondary battery according to any one of Technology 5 to Technology 7, wherein in the primary structure, a separation distance D2 between two adjacent small piece members is 0.05 mm or more and 2.0 mm or less.(Technology 9) A secondary battery according to any one of Technologies 5 to 8, wherein the ratio of the distance D2 between two adjacent small piece members in the primary structure to the distance D1 between two adjacent groups of protrusions: D2 / D1, is 0.01 or more and 0.5 or less. (Technology 10) A secondary battery according to any one of Technologies 1 to 9, wherein the spacer includes an insulating material. (Technology 11) A secondary battery according to any one of Technologies 1 to 10, wherein the spacer has a non-porous structure that does not allow lithium ions to pass through. (Technology 12) A secondary battery according to any one of Technologies 1 to 11, wherein lithium metal precipitates in the negative electrode during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging. (Technology 13) A secondary battery separator comprising a sheet-like substrate and a spacer arranged on a main surface of the substrate, wherein the spacer includes a plurality of convex groups, each of the plurality of convex groups being a primary structure formed by an assembly of a plurality of small piece members, wherein the plurality of convex groups are arranged in a predetermined pattern, such that the plurality of small piece members form a secondary structure, and wherein the plurality of small piece members are arranged at a distance from one another. (Technology 14) A secondary battery separator according to Technology 13, wherein in the primary structure, the minimum value of the separation distance between two adjacent small piece members is 2.0 mm or less. (Technology 15) A secondary battery separator according to Technology 13 or 14, wherein in the primary structure, the plurality of small piece members are arranged in a predetermined pattern. (Technology 16) A separator for a secondary battery according to any one of Techniques 13 to 15, wherein, in a plan view, a ratio of a total area S2 of the plurality of small piece members included in one of the convex group to an area S1 per one of the convex group is 50% or more. (Technology 17) A separator for a secondary battery according to any one of Techniques 13 to 16, wherein the base material is elongated, the plurality of linear convex group members are arranged parallel to one another along the length direction of the base material, and in the primary structure, the plurality of small piece members included in one of the convex group members are each thin-line shaped with a width smaller than that of one of the convex group members and are arranged parallel to one another along the length direction of one of the convex group members.(Technology 18) A secondary battery separator according to Technology 17, wherein the ratio of the width W2 of each of the plurality of small piece members included in one of the convex group to the width W1 of one of the convex group: W2 / W1, is 0.01 or more and 0.5 or less. (Technology 19) A secondary battery separator according to Technology 17 or 18, wherein each of the plurality of small piece members included in one of the convex group has a width W2 of 0.05 mm or more and 1.0 mm or less. (Technology 20) A secondary battery separator according to any one of Technology 17 to 19, wherein in the primary structure, a separation distance D2 between two adjacent small piece members is 0.05 mm or more and 2.0 mm or less. (Technology 21) A secondary battery separator according to any one of Technologies 17 to 20, wherein the ratio of the distance D2 between two adjacent small piece members in the primary structure to the distance D1 between two adjacent groups of protrusions: D2 / D1 is 0.01 or more and 0.5 or less. (Technology 22) A secondary battery separator according to any one of Technologies 13 to 21, wherein the spacer includes an insulating material. (Technology 23) A secondary battery separator according to any one of Technologies 13 to 22, wherein the spacer has a non-porous structure that is impermeable to lithium ions.

[0129] [Examples] The secondary battery according to the present disclosure will be described in more detail below based on examples and comparative examples, although the present disclosure is not limited to the following examples.

[0130] Secondary Battery A1 (Preparation of Positive Electrode) A positive electrode active material, acetylene black (AB; conductive material), polyvinylidene fluoride (PVdF; binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to prepare a positive electrode mixture slurry. The positive electrode active material was a rock-salt lithium-containing transition metal oxide (NCA; positive electrode active material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al was 1.0) and having a layered structure. The mass ratio of NCA:AB:PVdF in the positive electrode mixture slurry was 95:2.5:2.5. The positive electrode mixture slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector), and the coating was dried and rolled to form a positive electrode mixture layer. The positive electrode current collector having the positive electrode mixture layers formed on both sides was cut to a predetermined size to obtain a positive electrode.

[0131] (Preparation of Negative Electrode Current Collector) A strip of electrolytic copper foil (thickness: 12 μm) was prepared as a negative electrode current collector.

[0132] (Preparation of Substrate) A 10 μm-thick polyethylene microporous thin film was prepared. One main surface of the microporous thin film was coated with a coating liquid containing paraphenylene terephthalamide, an aromatic polyamide, as the resin material and alumina as inorganic particles. The coating liquid was an N-methyl-2-pyrrolidone solution containing 5.8% by mass of dissolved calcium chloride, and the concentration was adjusted to 2 wt% of aromatic polyamide and 4 wt% of alumina. The substrate with the coating film formed was left for 1 hour in an atmosphere at 25°C and 70% relative humidity to precipitate the aromatic polyamide. Next, the NMP and calcium chloride in the coating film were removed by water washing. The coating film was dried at 60°C for 5 minutes to form a composite material layer (heat-resistant layer). In this manner, a substrate comprising a microporous thin film and a composite material layer was obtained.

[0133] (Formation of spacers on the main surface of the substrate) A coating liquid containing polyvinylidene fluoride and alumina particles (inorganic filler) was applied to the microporous thin film surface of the substrate, and the coating was dried to form spacers. In this way, a separator having the substrate and the spacers was obtained.

[0134] Specifically, a spacer as shown in Fig. 3 was formed. The spacer was composed of six linear protrusion groups 53a (width W1: 1 mm, height H: 30 µm). The six linear protrusion groups 53a were arranged parallel to one another along the length direction of the substrate 50. The six linear protrusions 53a were each arranged intermittently in the length direction (X direction) of the substrate 50, and the defects 54 were provided at regular intervals.

[0135] The linear protrusion group 53a included three thin linear piece members 60 (width W2: 0.25 mm, height H: 30 μm). The three thin linear piece members 60 were arranged parallel to each other along the length direction of the linear protrusion group 53a (substrate 50).

[0136] The distance D1 between two adjacent groups of protrusions 53a was 2.75 mm. In the primary structure, the distance D2 between two adjacent small piece members 60 was 0.125 mm. The ratio D2 / D1 was 0.125 / 2.75 (approximately 0.045).

[0137] In a plan view, the ratio of the total area S2 of the small piece members 60 included in one convex group 53a to the area S1 per convex group 53a was 75%. The ratio W2 / W1 of the width W2 of each of the small piece members 60 included in one convex group 53a to the width W1 of one convex group 53a was 0.25.

[0138] (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 An ether-based mixed solvent containing lithium bis(sulfonylimide) (LiFSI) at 1 mol / L and LiBF at a volume ratio of 1:2 was prepared. ２ (C ２ O ４ ) was dissolved in the ethanol to a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte (ether-based electrolyte solution).

[0139] (Battery Assembly) In an inert gas atmosphere, a positive electrode and a negative electrode current collector were spirally wound with a separator interposed therebetween to prepare an electrode assembly. The separator was positioned so that the spacer faced the positive electrode. That is, the spacer was positioned on the positive electrode side, and the substrate was positioned on the negative electrode side. The electrode assembly was housed in a cylindrical case body with a bottom, and a non-aqueous electrolyte was poured into it. A sealing member was placed in the opening of the case body via a gasket, sealing the electrode assembly and non-aqueous electrolyte within the battery case. In this way, a lithium secondary battery having the structure shown in FIG. 10 was completed.

[0140] Secondary battery A2: The width W1 of each of the linear protrusion groups 53a constituting the spacer was 0.9 mm. The width W2 of each of the thin linear small pieces 60 included in each protrusion group 53a was 0.15 mm. The ratio W2 / W1 was 0.15 / 0.90 (approximately 0.17).

[0141] The distance D1 between two adjacent groups of protrusions 53a was 2.85 mm. The distance D2 between two adjacent small piece members 60 in the primary structure was 0.225 mm. The ratio D2 / D1 was 0.225 / 2.85 (approximately 0.079).

[0142] In a plan view, the ratio of the total area S2 of the plurality of small piece members 60 included in one convex portion group 53a to the area S1 per convex portion group 53a was 50%.

[0143] Except for the above, a secondary battery A2 was obtained in the same manner as the secondary battery A1.

[0144] Secondary Battery B1: The spacer shown in FIG. 14 was formed instead of the spacer shown in FIG. 3. That is, a single wide linear protrusion 73a (width 0.5 mm, height 30 μm) was arranged instead of the linear protrusion group 53a. The separation distance between two adjacent linear protrusions was 3.25 mm. Except for the above, a secondary battery B1 was obtained in the same manner as the secondary battery A1.

[0145] [Evaluation] (Charge / Discharge Test) A charge / discharge test was performed on each of the obtained batteries. In the charge / discharge test, the battery was charged in a thermostatic chamber at 25° C. under the following conditions, then rested for 20 minutes, and discharged under the following conditions.

[0146] (Charging) The battery was charged at a constant current of 10 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 4.1 V. Thereafter, the battery was charged at a constant voltage of 4.1 V until the current value per unit area of ​​the electrode reached 1 mA.

[0147] (Discharge) The battery was discharged at a constant current of 10 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 3.0 V.

[0148] The above charge and discharge constitute one cycle, and charge and discharge were repeated. When the charge capacity at the mth cycle was 1% or more higher than the charge capacity at the previous (m-1)th cycle, it was determined that abnormal charging had occurred due to the occurrence of a small internal short circuit, and the charge and discharge test was terminated. The number of cycles at this time, m, was calculated as the number of cycles at which abnormal charging occurred. If abnormal charging did not occur up to 200 cycles, it was determined that there was "no abnormality."

[0149] The charge capacity in the first cycle (initial cycle) was also determined.

[0150] (Space Formation Ratio) The average height H of the spacers before forming the electrode group and the average height h of the spacers after forming the electrode group were measured. The space formation ratio was determined by calculating h / H×100. A high space formation ratio indicates that the spacers have high strength and high stability against space formation. The average height H of the spacers before forming the electrode group was determined by the method described above. The average height h of the spacers after forming the electrode group was determined by taking an X-ray CT image of the cross section (cross section perpendicular to the winding axis of the electrode group) of the secondary battery before the first charge, measuring the distance between the substrate and the positive electrode at 20 points using the image, and calculating the average value of the measured values.

[0151] The evaluation results are shown in Table 1. In Table 1, A1 and A2 are examples, and B1 is a comparative example. The initial charge capacity is expressed as a relative value when the initial charge capacity of secondary battery B1 is set to 100.

[0152]

[0153] In Batteries A1 and A2, no abnormalities were observed at 200 cycles. In Battery B1, although the void formation rate was high, an abnormality (a small internal short circuit) occurred early in the cycle due to a local increase in the amount of Li precipitated near the spacer due to the intrusion of Li ions.

[0154] In addition, batteries A1 and A2 achieved high charge capacity due to the reduced resistance. Battery A2 had a smaller width W2 of the small pieces and a larger separation distance D2 between the small pieces than battery A1, resulting in lower resistance and a higher charge capacity. Battery B1 had a large amount of Li ions moving around near the spacer, resulting in increased internal resistance and a reduced capacity.

[0155] In all of Batteries A1 and A2, the spacer strength was ensured and a good space formation rate was obtained. In Battery A1, the width W2 of the small piece members was larger and the spacing D2 between the small piece members was smaller than in Battery A2, resulting in a higher space formation rate.

[0156] The secondary battery of the present disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet terminals, electric vehicles including hybrids and plug-in hybrids, and home storage batteries combined with solar cells.

[0157] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0158] 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: Convex portion group, 54: Defective portion, 60: Small piece member

Claims

1. A 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; the separator comprises a sheet-like substrate and a spacer disposed on a main surface of the substrate; the spacer comprises a plurality of convex groups; each of the plurality of convex groups is a primary structure formed by assembling a plurality of small piece members; the plurality of convex groups are arranged in a predetermined pattern, such that the plurality of small piece members form a secondary structure; and the plurality of small piece members are arranged at a distance from one another.

2. The secondary battery according to claim 1, wherein the minimum value of the separation distance between two adjacent small piece members in the primary structure is 2.0 mm or less.

3. The secondary battery according to claim 1, wherein the plurality of small piece members are arranged in a predetermined pattern in the primary structure.

4. A secondary battery as described in claim 1, wherein, in a planar view of the separator, the ratio of the total area S2 of the plurality of small piece members included in one convex group to the area S1 per one convex group is 50% or more.

5. A secondary battery as described in claim 1, wherein the substrate is elongated, the linear convex groups are arranged parallel to one another along the length of the substrate, and the small piece members included in one convex group in the primary structure are each thin lines having a width smaller than that of one of the convex groups and are arranged parallel to one another along the length of the one of the convex groups.

6. A secondary battery as described in claim 5, wherein the ratio W2 / W1 of the width W1 of one of the convex groups to the width W2 of each of the plurality of small piece members included in one of the convex groups is 0.01 or more and 0.5 or less.

7. The secondary battery according to claim 5, wherein each of the plurality of small piece members included in one group of protrusions has a width W2 of 0.05 mm or more and 1.0 mm or less.

8. The secondary battery according to claim 5, wherein the distance D2 between two adjacent small piece members in the primary structure is 0.05 mm or more and 2.0 mm or less.

9. A secondary battery as described in claim 5, wherein the ratio of the distance D2 between two adjacent small piece members in the primary structure to the distance D1 between two adjacent groups of protrusions: D2 / D1, is 0.01 or more and 0.5 or less.

10. The secondary battery according to any one of claims 1 to 9, wherein the spacer includes an insulating material.

11. The secondary battery according to any one of claims 1 to 9, wherein the spacer has a non-porous structure that is impermeable to lithium ions.

12. The secondary battery according to any one of claims 1 to 9, wherein lithium metal is precipitated on the negative electrode during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging.

13. A separator for a secondary battery comprising: a sheet-like substrate; and a spacer arranged on a main surface of the substrate; wherein the spacer comprises a plurality of convex groups; each of the plurality of convex groups is a primary structure formed by assembling a plurality of small piece members; the plurality of convex groups are arranged in a predetermined pattern, whereby the plurality of small piece members form a secondary structure; and the plurality of small piece members are arranged at a distance from one another.

14. The secondary battery separator according to claim 13, wherein the minimum value of the separation distance between two adjacent small piece members in the primary structure is 2.0 mm or less.

15. The secondary battery separator according to claim 13, wherein in the primary structure, the plurality of small piece members are arranged in a predetermined pattern.

16. A separator for a secondary battery as described in claim 13, wherein, in a plan view, the ratio of the total area S2 of the plurality of small piece members included in one convex group to the area S1 per one convex group is 50% or more.

17. A separator for a secondary battery as described in claim 13, wherein the substrate is elongated, the plurality of linear convex groups are arranged parallel to one another along the length of the substrate, and the plurality of small piece members included in one convex group in the primary structure are each thin lines having a width smaller than that of one of the convex groups and are arranged parallel to one another along the length of one of the convex groups.

18. A separator for a secondary battery as described in claim 17, wherein the ratio W2 / W1 of the width W1 of one of the convex groups to the width W2 of each of the plurality of small piece members included in one of the convex groups is 0.01 or more and 0.5 or less.

19. The secondary battery separator according to claim 17, wherein each of the plurality of small piece members included in one group of protrusions has a width W2 of 0.05 mm or more and 1.0 mm or less.

20. A secondary battery separator according to claim 17, wherein the separation distance D2 between two adjacent small piece members in the primary structure is 0.05 mm or more and 2.0 mm or less.

21. A secondary battery separator according to claim 17, wherein the ratio of the distance D2 between two adjacent small piece members in the primary structure to the distance D1 between two adjacent groups of protrusions: D2 / D1, is 0.01 or more and 0.5 or less.

22. The secondary battery separator according to any one of claims 13 to 21, wherein the spacer includes an insulating material.

23. The secondary battery separator according to any one of claims 13 to 21, wherein the spacer has a non-porous structure that is impermeable to lithium ions.

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