Secondary battery

Abstract

This secondary battery comprises: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte. 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 region A in which the thickness of the spacer decreases continuously or stepwise from TC to TE from the center part side toward the end edge side of the positive electrode. The vicinity of the end edge of the positive electrode faces the region A.

Description

secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-089207, filed on May 31, 2024 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to secondary batteries.

[0003] The secondary battery includes an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. Examples of non-aqueous electrolyte secondary batteries include lithium ion batteries and lithium secondary batteries (lithium metal secondary batteries). 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] In secondary batteries, spacers can be placed between the separator substrate and the electrodes to minimize volumetric changes in the electrode assembly during charge and discharge. In lithium secondary batteries, the spacers provide space for lithium precipitation.

[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; the negative electrode is an electrode from which lithium metal precipitates during charging and from which the lithium metal dissolves during discharging; the separator comprises a substrate and a spacer; the spacer is disposed closer to the positive electrode than the substrate; the spacer comprises linear convex portions arranged in a mesh pattern; and the mesh pattern comprises missing portions connecting adjacent mesh regions."

[0006] International Publication No. 2023 / 054150

[0007] There is a demand for suppressing the performance degradation 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 region A in which the thickness of the spacer decreases continuously or stepwise from TC to TE from a central portion side toward an edge portion side of the positive electrode, and the vicinity of the edge portion of the positive electrode faces region A.

[0009] According to the present disclosure, it is possible to suppress the deterioration of performance of a secondary battery equipped with a spacer. 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.

[0010] 1 is a longitudinal sectional view schematically showing an example of a secondary battery according to an embodiment of the present disclosure; FIG. 2 is a sectional view schematically showing a main part of the secondary battery shown in FIG. 1; FIG. 3 is a schematic top view showing an example of a separator in which striped spacers having region A are continuously arranged on the main surface of a substrate; FIG. 4 is a sectional view schematically showing a main part of an example of a separator in which striped spacers having region A are continuously arranged on the main surface of a substrate; FIG. 5 is a sectional view schematically showing a main part of another example of a separator in which striped spacers having region A are continuously arranged on the main surface of a substrate; FIG. 6 is a sectional view schematically showing a main part of an example of a separator in which striped spacers having region A are intermittently arranged on the main surface of a substrate; FIG. 7 is a sectional view schematically showing a main part of another example of a separator in which striped spacers having region A are intermittently arranged on the main surface of a substrate; FIG. 8 is a schematic top view showing an example of a separator in which striped spacers having region A and region B are continuously arranged on the main surface of a substrate; FIG. 9 is a sectional view schematically showing a main part of an example of a separator in which striped spacers having region A and region B are continuously arranged on the main surface of a substrate. FIG. 1 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having regions A and B are continuously arranged on the main surface of the substrate. FIG. 1 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having regions A and B are intermittently arranged on the main surface of the substrate. FIG. 2 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having regions A and B are intermittently arranged on the main surface of the substrate. FIG. 3 is a schematic top view of an example of a separator in which honeycomb-shaped spacers having regions A and regions B are continuously arranged on the main surface of the substrate. FIG. 4 is a schematic top view of an example of a separator in which honeycomb-shaped spacers having regions A and regions B are continuously arranged on the main surface of the substrate. FIG. 5 is a cross-sectional view of a main portion of an example of a separator in which honeycomb-shaped spacers having regions A and regions B are intermittently arranged on the main surface of the substrate. 1 is a cross-sectional view of a main part of another example of a separator in which honeycomb-shaped spacers having regions A and B are intermittently arranged on the main surface of a substrate, and FIG. 2 is a schematic top view of an example of a separator in which honeycomb-shaped spacers having regions A and B are intermittently arranged on the main surface of a substrate.1 is a cross-sectional view of a main portion of an example of a separator in which honeycomb-shaped spacers having regions A and B are intermittently arranged on the main surface of a substrate. FIG.

[0011] 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.

[0012] 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. The separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate.

[0013] 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.

[0014] Secondary batteries include lithium secondary batteries (lithium metal secondary batteries), lithium ion batteries, and the like. For example, the negative electrode of a lithium secondary battery expands due to the deposition of lithium metal during charging. The negative electrode of a lithium ion battery expands due to the occlusion of lithium ions during charging. Among secondary batteries, lithium secondary batteries have a large expansion rate of the negative electrode due to the deposition of Li during charging, resulting in a large change in the volume of the electrode group.

[0015] In secondary batteries, the electrode group undergoes large volume changes during charge and discharge, which can easily cause damage to the components of the electrode group, buckling of the electrodes, internal short circuits, and other problems, resulting in a deterioration in cycle performance. To address this issue, spacers can be formed on the main surfaces of the substrate to form a separator, and the spacers can be placed between the substrate and the electrodes to suppress volume changes in the electrode group. The spacers serve to create space to absorb the expansion of the electrodes.

[0016] In the present disclosure, the spacer includes a region A in which the thickness of the spacer decreases continuously or stepwise from TC to TE from the center side to the edge side of the positive electrode. The vicinity of the edge of the positive electrode faces region A. That is, the spacer includes region A facing the vicinity of the edge of the positive electrode. The vicinity of the edge of the positive electrode and region A may overlap partially or entirely. Region A may be formed in at least a portion of the opposing portion between the spacer and the vicinity of the edge of the positive electrode. The edge of the positive electrode does not have to face region A, and may face region A together with the vicinity of the edge of the positive electrode.

[0017] The positive electrode edge portion can also be considered as a side that constitutes the outer shape of the positive electrode. For example, if the positive electrode is rectangular (elongated or strip-shaped), the sides that constitute the outer shape of the positive electrode are the four sides of the rectangle (E1 to E4 in FIGS. 3, 8, 13 to 15, and 18). The opposing portion of the spacer and the positive electrode edge portion can also be considered as an overlapping portion of the spacer and the sides that constitute the outer shape of the positive electrode.

[0018] For example, the vicinity of at least one of the four sides of a rectangular positive electrode (a positive electrode edge portion corresponding to one of the sides) may face region A. The vicinity of two of the four sides of a rectangular positive electrode (a positive electrode edge portion corresponding to the two sides) may face region A. When a long or strip-shaped positive electrode is wound, it is preferable that the vicinity of the winding start end and winding end of the positive electrode face region A, and it is particularly preferable that the vicinity of the winding start end of the positive electrode face region A.

[0019] The vicinity of the positive electrode end edge is not particularly limited as long as it is a region close to the positive electrode end edge. When the dimension D0 of the positive electrode in the D direction is 600 mm or less, the distance D1 from the positive electrode end edge DE in the D direction of the positive electrode in the vicinity of the positive electrode end edge may be in the range of more than 0 mm and 0.05 × D0 mm or less. When the dimension D0 of the positive electrode in the D direction is greater than 600 mm, the distance D1 from the positive electrode end edge DE in the D direction of the positive electrode in the vicinity of the positive electrode end edge may be in the range of more than 0 mm and 30 mm or less. For example, the D direction of the positive electrode may be the length direction (LD direction) of a long or strip-shaped positive electrode, and the distance D1 from the positive electrode end edge DE in the D direction of the positive electrode may be the distance D1a from the winding start end E1 in the LD direction of the positive electrode. Furthermore, the distance D1 may be the distance D1b from the winding end end E2 in the LD direction of the positive electrode.

[0020] The edge of the positive electrode faces the end of the Li deposition region (Li ion absorption region) of the negative electrode. When a secondary battery includes a spacer, Li ions released from the positive electrode during charging move around the spacer (protrusion) to the negative electrode, causing the negative electrode to expand due to Li deposition (Li ion absorption). As a result, stress caused by the expansion of the negative electrode is concentrated locally near the overlapping portion between the positive electrode edge and the spacer, which can damage the substrate. In particular, in lithium secondary batteries, the edge of the deposited Li is likely to be thick near the overlapping portion between the positive electrode edge and the spacer, and stress caused by Li deposition is likely to be concentrated locally.

[0021] In contrast, in the present disclosure, a region A in which the spacer thickness decreases from TC to TE from the center to the edge of the positive electrode is provided in a portion facing the vicinity of the edge of the positive electrode. This allows the edge of the positive electrode to be positioned so that the spacer thickness does not face the TC portion. This suppresses the above-mentioned stress concentration and the resulting damage to the substrate, and suppresses a decrease in battery performance (e.g., cycle characteristics) associated with the occurrence of an internal short circuit due to substrate damage.

[0022] The case where the edge of the positive electrode does not face the part of the spacer whose thickness is TC includes a case where the edge of the positive electrode faces a part of the spacer whose thickness is smaller than TC, or a case where the edge of the positive electrode does not face the spacer. The part of the spacer whose thickness is TC is the main region C of the spacer, and the center of the positive electrode faces the main region C.

[0023] The above-mentioned stress concentration may also occur near the edge of the positive electrode near the overlap with the spacer, resulting in damage to the substrate. By facing the vicinity of the edge of the positive electrode to region A, it is easy to arrange the vicinity of the edge of the positive electrode so that it does not face the portion of thickness TC, thereby suppressing the above-mentioned stress concentration and the resulting damage to the substrate.

[0024] Furthermore, by providing region A, the contact area between the spacer and the electrode (positive electrode or negative electrode) is reduced, and the thickness of the spacer gradually decreases toward the electrode end. This reduces friction between the spacer and the electrode when winding the electrode and separator, compared to when region A is not provided and the thickness of the spacer toward the electrode end is large (TC), and suppresses wrinkles in the separator substrate during winding. Furthermore, wrinkles in the substrate due to tightening or loosening of the winding caused by volumetric changes in the electrode group during charge and discharge are also suppressed.

[0025] The spacer may have a region B with a thickness TE closer to the end of the substrate than region A. By providing region B, the rigidity of the separator is easily ensured, and the occurrence of displacement or wrinkling of the separator during the construction of the electrode assembly is suppressed. The vicinity of the edge of the positive electrode may face region A and region B, and the edge of the positive electrode may face region B.

[0026] Furthermore, the spacer may not have region B, and the end of the spacer may form region A. From the viewpoint of easily suppressing damage to the substrate, it is preferable that the vicinity of the edge of the positive electrode faces region A, and that the edge of the positive electrode does not face the spacer.

[0027] The edge of the positive electrode may face the region A. In this case, the region A allows the vicinity of the edge of the positive electrode and the edge of the positive electrode to be positioned so that the thickness of the spacer does not face the TC portion.

[0028] When the thickness of the spacer facing the edge of the positive electrode is TP, it is preferable that TE≦TP and 0≦TP / TC≦0.5 are satisfied. TP / TC is more preferably 0 or more and 0.45 or less. TP / TC=0 may be satisfied, and the spacer may not have region B.

[0029] The positive electrode and the negative electrode may be wound with a separator interposed therebetween. In this case, the edge of the positive electrode includes the winding start end. In region A, it is preferable that the thickness of the spacer decreases continuously or stepwise from TC to TE from the center of the positive electrode toward the winding start end. It is preferable that the winding start end of the positive electrode or its vicinity faces region A. Also, in this case, the edge of the positive electrode includes the winding end end. In region A, it is preferable that the thickness of the spacer decreases continuously or stepwise from TC to TE from the center of the positive electrode toward the winding end end. It is preferable that the winding end end of the positive electrode or its vicinity faces region A. Since the above-mentioned stress concentration is likely to occur near the overlapping points between the winding start end and the winding end end (particularly the winding start end) of the positive electrode and the spacer, the above-mentioned stress concentration suppression effect is likely to be significantly achieved.

[0030] The secondary battery will be described in detail below.

[0031] (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.

[0032] 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).

[0033] (Separator) The separator includes a sheet-like substrate and a spacer disposed on the main surface of the substrate.

[0034] (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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] Examples of resin materials contained in the composite material layer (heat-resistant 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 hydrogenated product thereof, acrylonitrile-butadiene copolymer or hydrogenated product thereof, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, and rubbers such as polyvinyl acetate. Examples of the resin include cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; acrylic resins such as acrylic acid-methacrylic acid copolymers; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid); polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] (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.

[0045] 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.

[0046] 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.

[0047] Examples of resin materials contained 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 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, polyvinyl alcohol, and polyvinyl acetate, Examples of the resin include cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; acrylic resins such as acrylic acid-methacrylic acid copolymers; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid); polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

[0048] 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 made of 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. The placement of such a spacer is preferred from the viewpoint of suppressing an increase in the gas generation reaction rate during an internal short circuit.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The spacer includes a protrusion. The spacer may include a linear protrusion and / or a dot-shaped protrusion. From one viewpoint, the linear protrusion is a ridge-shaped protrusion. The linear protrusion may be arranged intermittently or continuously. The linear protrusion may be linear or curved.

[0053] The width of the linear convex portion may be 100 μm or more, or 200 μm or more, and may be 2000 μm or less, or 1000 μm or less.

[0054] The spacer preferably has a predetermined repeating pattern. That is, it is preferable that the convex portions are arranged in a predetermined repeating pattern. The linear convex portions may be arranged in a striped pattern or a mesh pattern. The mesh pattern may be a collection of polygons. An example of a mesh pattern includes a shape in which polygons are combined so as to share a side. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons may be combined. The mesh pattern may be a honeycomb pattern. Furthermore, dot-shaped convex portions may be arranged in a predetermined repeating pattern.

[0055] The thickness TC of the spacer (height of the convex portion) may be greater than the thickness T of the substrate. The ratio of the height TC to the thickness T: TC / T may be greater than 1, 1.5 or greater, or 2 or greater. TC / T may be 5 or less, 4 or less, or 3 or less. From the viewpoint of suppressing expansion of the electrode group, TC / T may be, for example, greater than 1 (or 1.5 or greater) and 3 or less.

[0056] The spacer thicknesses (heights of the convex portions) TC and TP can be measured, for example, by photographing the spacer with a laser microscope and using the resulting height profile. TC can be determined by identifying region C in the height profile, arbitrarily selecting six locations within region C, measuring the spacer thicknesses (heights of the convex portions), and calculating the average value. TE can be determined by identifying region A of the spacer in the height profile, arbitrarily selecting six locations on the edge of region A near the positive electrode end, measuring the spacer thicknesses (heights of the convex portions), and calculating the average value. TP can be determined by arbitrarily selecting six locations facing the positive electrode end of the spacer in the height profile, measuring the spacer thicknesses (heights of the convex portions), and calculating the average value. The laser microscope can be, for example, a hybrid laser microscope manufactured by Lasertec Corporation.

[0057] The thickness T of the substrate is determined by measuring the thickness of six arbitrary locations on the substrate using a contact thickness meter, and calculating the average value of the measured thicknesses. For example, a thickness meter (PEACOCK) manufactured by Ozaki Manufacturing Co., Ltd. can be used as the contact thickness meter.

[0058] 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. Application may be performed using a dispenser or by known printing methods such as gravure printing, inkjet printing, and screen printing. Drying may also be performed by known methods such as heating or natural drying. The thickness of the spacers can be adjusted by changing the amount applied or the viscosity of the coating liquid.

[0059] (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.

[0060] 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.

[0061] 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.

[0062] The lithium ion storage 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 material, and the like in addition to the negative electrode active material.

[0063] 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).

[0064] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0065] 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.

[0066] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0067] 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. A conductive material that does not react with lithium is preferred. More specifically, a material that does not form an alloy or intermetallic compound with lithium is preferred. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), alloys containing these metal elements, and graphite with a preferentially exposed basal surface. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys, which have high conductivity, are preferred. Alternatively, a laminate sheet in which a metal or alloy such as stainless steel, nickel, nickel alloy, copper, or copper alloy is laminated on the surface of a resin film may be used as the negative electrode current collector. The resin material of the resin film is not particularly limited, but examples include polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyethylene, polypropylene, polyamide, and polyimide.

[0068] 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.

[0069] (Positive Electrode) The positive electrode includes, for example, 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 may be formed on both sides. The positive electrode is obtained, for example, by applying a positive electrode composite 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] Examples of materials for the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy may be stainless steel (SUS). Alternatively, a laminate sheet in which a metal or alloy such as stainless steel, aluminum, aluminum alloy, or titanium is laminated on the surface of a resin film may be used as the positive electrode current collector. The resin material for the resin film is not particularly limited, and examples include polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyethylene, polypropylene, polyamide, and polyimide.

[0076] 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.

[0077] (Non-aqueous electrolyte) The non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte 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.

[0078] 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.

[0079] As the solid electrolyte, for example, a material known in all-solid-state lithium ion secondary batteries (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) can be used.

[0080] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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).

[0088] (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.

[0089] 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.

[0090] 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. The spacer may include a resin material.

[0091] In the case of a lithium-ion battery, for example, the spacer may be disposed at a location where stress is likely to increase when the negative electrode expands. The spacer may be disposed at a folded portion 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 a location with a small radius of curvature of a flat electrode assembly.

[0092] An example of a secondary battery according to the present embodiment will be specifically described below with reference to the drawings. The components described above can be applied to the components of the example secondary battery described below. The components of the example described below can be modified based on the above description. The matters described below may also be applied to the above embodiment. In the secondary battery described below, components that are not essential for the secondary battery according to the present disclosure may be omitted. Note that the scale of the components has been changed in the following drawings to facilitate understanding.

[0093] (Embodiment 1) FIG. 1 is a longitudinal cross-sectional view schematically illustrating a lithium secondary battery as an example of a secondary battery according to Embodiment 1. Note that FIG. 1 does not illustrate spacers and spaces formed by the spacers. The cylindrical lithium secondary battery 10 shown in FIG. 1 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 member 16 that seals the opening of the case body 15. A gasket 27 is disposed between the case body 15 and the sealing member 16. The gasket 27 ensures the hermeticity 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 direction of the winding axis.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 2 is an enlarged view of a portion of the electrode group 14. FIG. 2 includes a portion near the positive electrode surrounded by region II in FIG. 1 and a portion near the negative electrode surrounded by region III in FIG.

[0098] 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 (the substrate 50 with the spacer 53 disposed thereon) so that the separator is disposed between the positive electrode 11 and the negative electrode 12.

[0099] 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 FIG. 2, 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.

[0100] 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). FIG. 2 shows the height h of the spacer 53.

[0101] 2, 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.

[0102] 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.

[0103] Here, Fig. 3 is a schematic top view showing an example of a separator in which stripe-shaped spacers having region A are continuously arranged on the main surface of the substrate. LD in Figs. 3 and 8 indicates the length direction of the elongated or band-shaped substrate 50 (positive electrode 11). Fig. 4 is a cross-sectional view of a main part showing an example of a separator in which stripe-shaped spacers having region A are continuously arranged on the main surface of the substrate. Fig. 4 is a cross-sectional view showing the vicinity of region A1 of the spacer 53 in Fig. 3, showing a cross section along the length direction (LD direction) of one linear protrusion 53a.

[0104] Fig. 5 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having region A are continuously arranged on the main surface of the substrate. Fig. 6 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having region A are intermittently arranged on the main surface of the substrate. Fig. 7 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having region A are intermittently arranged on the main surface of the substrate. Figs. 5 to 7 are modifications of Fig. 4.

[0105] In a plan view, spacers 53 (linear convex portions 53a) are arranged on one main surface of the substrate 50. The substrate 50 on which the spacers 53 (convex portions 53a) are arranged is arranged on the inner and outer circumferential sides of the positive electrode 11. In each figure, the positive electrode 11 facing the separator (substrate 50 and spacer 53) is represented by a dashed line. Note that each figure is a schematic diagram, and the aspect ratios of each component do not necessarily reflect the actual dimensions. The separators included in the secondary battery of the present disclosure are not limited to the separators shown in each figure.

[0106] The spacer 53 in FIG. 3 is striped. That is, the spacer 53 in FIG. 3 includes a plurality of linear protrusions 53a arranged in a striped pattern. The regions where the spacers 53 are not formed form spaces 14s. The plurality of linear protrusions 53a are arranged parallel to one another along the length direction (LD direction) of the band-shaped substrate 50. The plurality of linear protrusions 53a are arranged spaced apart from one another. Each of the plurality of linear protrusions 53a is arranged continuously, but may also be arranged intermittently. Although seven linear protrusions 53a are arranged in FIG. 3, the number of linear protrusions 53a is not limited to this.

[0107] The edge portions of the positive electrode 11 include both ends E1 and E2 in the length direction (LD direction) and both ends E3 and E4 in the width direction. End E1 is the winding start end of the positive electrode 11, and end E2 is the winding end end of the positive electrode 11.

[0108] As shown in FIG. 3, the spacer 53 has a region C having a thickness TC and a region A including a region A1 and a region A2.

[0109] In region A1, the thickness of the spacer 53 (height of the convex portion 53a) continuously decreases from TC to TE from the center C of the positive electrode 11 toward the winding start end E1 (toward the X1 direction in FIG. 3). As shown in FIGS. 3 and 4, TE is 0, TP is 0, and the spacer is not disposed closer to the winding start end of the substrate 50 than region A1 (region B1, described below, is not present). That is, region A1 is formed at the end of the winding start side of the spacer 53. As shown in FIGS. 3 and 4, the center of the positive electrode 11 in the LD direction faces region C, the vicinity of end E1 faces region A1, and end E1 does not face the spacer. In FIGS. 3 and 4, TE = 0 and TP = 0, but TE ≦ TP and 0 ≦ TP / TC ≦ 0.5 may also be true.

[0110] In Fig. 4, end E1 does not face region A1, but as shown in Fig. 5, end E1 and its vicinity may face region A1. In Fig. 5, TE = 0, and TE < TP < TC. TP / TC may be ≦ 0.5. TP is the thickness of the spacer 53 facing end E1 (the height of the linear convex portion 53a).

[0111] In region A2, the thickness of the spacer 53 (height of the convex portion 53a) continuously decreases from TC to TE from the center C of the positive electrode 11 toward the end E2 (toward the X2 direction in FIG. 3). In FIG. 3, TE is 0, TP is 0, and the spacer is not disposed closer to the end of the base material 50 than region A2 (region B2, described below, is not present). That is, region A2 is formed at the end of the end of the spacer 53. The vicinity of end E2 faces region A2, and end E2 does not face the spacer. In FIG. 3, end E2 does not face region A2, but end E2 may face region A2 as well as the vicinity of end E2. In FIG. 3, TE = 0 and TP = 0 on the end E2 side, but TE ≦ TP and 0 ≦ TP / TC ≦ 0.5 may also be true. TP is the thickness of the spacer 53 facing end E2 (height of the linear convex portion 53a).

[0112] In region A1 in Figures 4 and 5, the thickness of the spacer is continuously reduced, but the thickness of the spacer may be reduced in stages. For example, as shown in Figures 6 and 7, the linear protrusions 53a may be intermittently arranged. As shown in Figures 6 and 7, the thickness of the spacer 53 (the height of the linear protrusions 53a) may be reduced in stages. Similarly, in region A2, the thickness of the spacer may be reduced in stages.

[0113] In Figures 6 and 7, a defect 54 is formed by intermittently arranging a single linear protrusion 53a. When a defect is present and the height of the defect-side end of a protrusion on one side of the defect is T1 and the height of the defect-side end of a protrusion on the other side is T2, the defect is considered to have a protrusion with a height of (T1 + T2) / 2. End E1 in Figures 7 and 12 may face the defect 54 in region A1. In this case, end E1 is considered to face a spacer with a thickness of (T1 + T2) / 2. End E1 in Figure 11 may face the defect 54 in region B1. In this case, end E1 is considered to face a spacer with a thickness of TE.

[0114] The length dimension (dimension in the LD direction) of the defect 54 may be, for example, 0.5 to 2 times the width dimension of the linear protrusion 53a, or 0.5 to 1.5 times the width dimension.

[0115] Although the spacer in FIG. 3 does not have region B, the spacer may have region B.

[0116] Here, Fig. 8 is a schematic top view showing an example of a separator in which stripe-shaped spacers having regions A and B are continuously arranged on the main surface of the substrate. LD in Fig. 8 indicates the length direction of the long or band-shaped substrate 50 (positive electrode 11). Fig. 9 is a cross-sectional view of a main part showing an example of a separator in which stripe-shaped spacers having regions A and B are continuously arranged on the main surface of the substrate. Fig. 9 is a cross-sectional view showing the vicinity of region A1 of the spacer 53 in Fig. 8, showing a cross section along the length direction (LD direction) of one linear protrusion 53a.

[0117] Fig. 10 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having regions A and B are continuously arranged on the main surface of the substrate. Fig. 11 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having regions A and B are intermittently arranged on the main surface of the substrate. Fig. 12 is a cross-sectional view of a main portion of another example of a separator in which stripe-shaped spacers having regions A and B are intermittently arranged on the main surface of the substrate. Figs. 10 to 12 are modified examples of Fig. 9. Regarding the configurations of Figs. 8 to 12, descriptions of parts that overlap with the configurations of Figs. 3 to 7 will be omitted.

[0118] As shown in Fig. 8, the spacer 53 may further include, as region B, a region B1 having a thickness TE located closer to the winding start end of the substrate 50 than region A1, and a region B2 having a thickness TE located closer to the winding end of the substrate 50 than region A2. Fig. 9 is a cross-sectional view of a main part showing the vicinity of the portion facing the end E1 of the separator in Fig. 8. By providing regions B1 and B2, the rigidity of the separator is easily ensured, and the occurrence of shifting or wrinkling of the separator when forming an electrode group is suppressed.

[0119] 8 and 9, the center of the positive electrode 11 in the LD direction faces the region C, the vicinity of the end E1 faces the regions A1 and B1, and the end E1 faces the region B1. The vicinity of the end E2 faces the regions A2 and B2, and the end E2 faces the region B2. In FIG. 9, TE=TP, and 0<TP / TC≦0.5 may be satisfied.

[0120] As shown in Fig. 10, the end E1 may face the region A1. In Fig. 10, TE<TP. Similarly, the end E2 may face the region A2.

[0121] 9 and 10, the thickness of the spacer is continuously reduced, but the thickness of the spacer may be reduced in a stepwise manner. For example, as shown in FIGS. 11 and 12, the linear protrusions 53a may be arranged intermittently, and the height of the linear protrusions 53a may be reduced in a stepwise manner. Similarly, the thickness of the spacer may be reduced in a stepwise manner in the region A2.

[0122] Although the linear protrusions in FIGS. 3 and 8 are arranged continuously, the linear protrusions may be arranged intermittently.

[0123] The spacer arrangement pattern is striped in FIGS. 3 and 8, but may be honeycomb.

[0124] Here, Fig. 13 is a schematic top view showing an example of a separator in which honeycomb spacers having region A are continuously arranged on the main surface of a substrate. Fig. 14 is a schematic top view showing an example of a separator in which honeycomb spacers having region A and region B are continuously arranged on the main surface of a substrate. LD in Figs. 13 and 14 indicates the length direction of the elongated or strip-shaped substrate 50 (positive electrode 11).

[0125] 13 has a honeycomb shape. That is, the spacer 53 includes linear protrusions 53a arranged in a honeycomb shape. The areas where the spacers 53 are not formed form spaces 14s.

[0126] The edge portions of the positive electrode 11 include both ends E1 and E2 in the length direction (LD direction) and both ends E3 and E4 in the width direction. End E1 is the winding start end of the positive electrode 11, and end E2 is the winding end end of the positive electrode 11.

[0127] As shown in FIG. 13, the spacer 53 has a region C having a thickness TC and a region A including a region A1 and a region A2.

[0128] In region A1, the thickness of the spacer 53 (height of the convex portion 53a) continuously decreases from TC to TE from the center C of the positive electrode 11 toward the winding start end E1 (toward the X1 direction in FIG. 13). TE is 0, TP is 0, and the spacer is not disposed closer to the winding start end of the substrate 50 than region A1. That is, region A1 is formed at the end of the winding start side of the spacer 53. The center of the positive electrode 11 in the LD direction faces region C of thickness TC, the vicinity of end E1 faces region A1, and end E1 does not face the spacer. In FIG. 3, TE = 0 and TP = 0, but TE ≦ TP and 0 < TP / TC ≦ 0.5 may also be true.

[0129] In FIG. 13, the end E1 does not face the region A1, but the end E1 and the vicinity thereof may face the region A1.

[0130] In region A2, the thickness of the spacer 53 (height of the convex portion 53a) continuously decreases from TC to TE from the center C of the positive electrode 11 toward the end E2 (toward the X2 direction in FIG. 13). In FIG. 13, TE is 0, TP is 0, and the spacer is not disposed closer to the end of the substrate 50 than region A2. That is, region A2 is formed at the end of the end of the spacer 53. The vicinity of end E2 faces region A2, and end E2 does not face the spacer. In FIG. 13, end E2 does not face region A2, but end E2 may face region A2 as well as the vicinity of end E2. In FIG. 13, TE = 0 and TP = 0 on the end E2 side, but TE ≦ TP and 0 < TP / TC ≦ 0.5 may also be true.

[0131] In Figure 13, region A1 includes linear protrusions corresponding to the LD-direction sides of the polygon. Each of the linear protrusions corresponding to the LD-direction sides of the polygon in region A1 has a thickness that decreases from TC to TE in the X1 direction. Similarly, region A2 includes linear protrusions corresponding to the LD-direction sides of the polygon in region A2. Each of the linear protrusions corresponding to the LD-direction sides of the polygon in region A2 has a thickness that decreases from TC to TE in the X2 direction.

[0132] 13, the linear protrusions in the region A1 (A2) are arranged substantially parallel to the LD direction, but they may be arranged obliquely relative to the LD direction. For example, when viewed from the normal direction of the substrate, the linear protrusions in the region A1 (A2) may be arranged such that the acute angle formed between the linear protrusions in the region A1 (A2) and the LD direction is in the range of 0° to 70° (or 60°) or less.

[0133] 13, the thickness of the spacer is continuously reduced, but the thickness of the spacer may be reduced in stages.Similarly, the thickness of the spacer may be reduced in stages in the region A2.

[0134] 14 , the spacer 53 may further have, as region B, a region B1 having a thickness TE closer to the winding start end of the substrate 50 than region A1, and a region B2 having a thickness TE closer to the winding end end of the substrate 50 than region A2. By providing regions B1 and B2, the rigidity of the separator is more easily ensured, and the occurrence of shifting or wrinkling of the separator when forming an electrode group is suppressed.

[0135] 14, the center of the positive electrode 11 in the LD direction faces region C, the vicinity of end E1 faces regions A1 and B1, and end E1 faces region B1. The vicinity of end E2 faces regions A2 and B2, and end E2 faces region B2. In FIG. 14, TE=TP, and it is preferable that 0<TP / TC≦0.5.

[0136] Furthermore, the end E1 and its vicinity may face the region A1. In this case, TE<TP. Similarly, the end E2 and its vicinity may face the region A2.

[0137] The honeycomb-shaped spacers (linear convex portions) in FIGS. 13 and 14 are arranged continuously, but they may also be arranged intermittently.

[0138] Here, Fig. 15 is a schematic top view showing an example of a separator in which honeycomb-shaped spacers having region A are intermittently arranged on the main surface of the substrate. Fig. 16 is a cross-sectional view of a main part of an example of a separator in which honeycomb-shaped spacers having region A are intermittently arranged on the main surface of the substrate. Fig. 16 is a cross-sectional view showing the vicinity of region A1 of the spacer 53 in Fig. 15, and shows a cross section along the linear convex portions 53a corresponding to the LD-direction sides constituting the polygon in region A1. Fig. 17 is a cross-sectional view of a main part of another example of a separator in which honeycomb-shaped spacers having region A are intermittently arranged on the main surface of the substrate. Fig. 17 is a modified example of Fig. 16.

[0139] Fig. 18 is a schematic top view showing an example of a separator in which honeycomb-shaped spacers having regions A and B are intermittently arranged on the main surface of a substrate. Fig. 19 is a schematic cross-sectional view of a main part of an example of a separator in which honeycomb-shaped spacers having regions A and B are intermittently arranged on the main surface of a substrate. Fig. 19 is a cross-sectional view showing the vicinity of region A1 of the spacer 53 in Fig. 18, and shows a cross section along linear convex portions 53a corresponding to sides in the LD direction that constitute a polygon in region A1.

[0140] 15 and 18, LD indicates the length direction of the elongated or strip-shaped substrate 50 (positive electrode 11). Regarding the configurations in Figures 15 and 18, descriptions of parts that overlap with the configurations in Figures 13 and 14 will be omitted.

[0141] The honeycomb-shaped spacer of Fig. 15 has a configuration in which the honeycomb-shaped spacers of Fig. 13 are intermittently arranged. The honeycomb-shaped spacer of Fig. 18 has a configuration in which the honeycomb-shaped spacers of Fig. 14 are intermittently arranged. The spacers 53 (linear convex portions 53a) of Figs. 15 and 18 have defects 54 due to being intermittently arranged. In Figs. 15 and 18, the defects 54 are formed at the vertices of the polygon, but the defects may also be formed on the sides that make up the polygon.

[0142] In Fig. 16, end E1 does not face region A1, but as shown in Fig. 17, end E1 may face region A1 as well as the vicinity of end E1. In Fig. 17, TE = 0, and TE < TP < TC. TP / TC may also be 0.5 or less. TP is the thickness of the spacer 53 facing end E1 (the height of the linear convex portion 53a). Similarly, end E2 may face region A2 as well as the vicinity of end E2.

[0143] As shown in Figures 13 to 15 and 18, region A1 includes linear protrusions corresponding to the LD-direction sides of a polygon (hexagon). Each of the linear protrusions corresponding to the LD-direction sides of the polygon in region A1 has a thickness that decreases from TC to TE in the X1 direction. Similarly, region A2 includes linear protrusions corresponding to the LD-direction sides of the polygon in region A2. In region A2, each of the linear protrusions corresponding to the LD-direction sides of the polygon in region A2 has a thickness that decreases from TC to TE in the X2 direction.

[0144] 15 and 18, linear convex portions 53a are intermittently arranged, resulting in a defect portion 54. When a defect is present and the height of the defect-side end of a convex portion on one side of the defect is T1, and the height of the defect-side end of a convex portion on the other side is T2, the defect is considered to have a convex portion with a height of (T1 + T2) / 2. For example, end E1 in FIGS. 18 and 19 may face defect portion 54 in region B1. In this case, end E1 is considered to face a spacer with a thickness TE.

[0145] The ratio of the length of one side of the hexagon of the honeycomb structure (the total length of the linear protrusions 53a and defects 54 included in that side) to the length of that side may be, for example, 45% or less, or 15% or more and 45% or less, or 20% or more and 45% or less.

[0146] 13 to 15 and 18, the thickness of the spacer is continuously reduced, but the thickness of the spacer may be reduced in stages. Similarly, the thickness of the spacer may be reduced in stages in the region A2.

[0147] 3, 8, 13 to 15, and 18, when the dimension D0 in the LD direction of the positive electrode is 600 mm or less, the distance D1a from the winding start end E1 in the LD direction of the positive electrode to the vicinity of the winding start end E1 of the positive electrode may be in the range of more than 0 mm and 0.05 × D0 mm or less. When the dimension D0 in the LD direction of the positive electrode is greater than 600 mm, the distance D1a from the winding start end E1 in the LD direction of the positive electrode to the vicinity of the winding start end E1 of the positive electrode may be in the range of more than 0 mm and 30 mm or less. When the separators in FIGS. 3, 8, 13 to 15, and 18 are viewed from the normal direction of the substrate 50, the entire region A1 may be included within the region near the end E1 within the above range, or a portion of the region A1 may be included within the region near the end E1 within the above range.

[0148] Similarly, when the dimension D0 in the LD direction of the positive electrode is 600 mm or less, the distance D1b from the winding end E2 in the LD direction of the positive electrode to the winding end E2 in the vicinity of the positive electrode may be in the range of more than 0 mm and 0.05 × D0 mm or less. When the dimension D0 in the LD direction of the positive electrode is greater than 600 mm, the distance D1b from the winding end E2 in the LD direction of the positive electrode to the winding end E2 in the vicinity of the positive electrode may be in the range of more than 0 mm and 30 mm or less. When the separators in Figures 3, 8, 13 to 15, and 18 are viewed from the normal direction of the substrate 50, the entire region A2 may be included within the region near the end E2 in the above range, or a portion of the region A2 may be included within the region near the end E2 in the above range.

[0149] 3, 8, 13 to 15, and 18, if regions A1 and A2 are not formed and regions A1 and A2 are made to have the same thickness TC as region C, ends E1 and E2 do not face the portion of the spacer with thickness TC, but the vicinity of ends E1 and E2 face the portion of the spacer with thickness TC. In this case, stress generated when the negative electrode expands may be concentrated locally at the overlapping portion between the vicinity of ends E1 and E2 and the spacer, which may damage the substrate and cause an internal short circuit. Furthermore, wrinkles may occur in the substrate.

[0150] In the first embodiment, a cylindrical lithium secondary battery having a wound electrode group has been described. However, the secondary battery of this embodiment is not limited to the form of the first embodiment, and can be applied to other forms. The shape of the secondary battery can be appropriately selected from various shapes such as a cylindrical shape, a coin shape, a rectangular shape, a sheet shape, and a flat shape depending on the application. The shape of the electrode group is also not particularly limited, and may be a stacked type.

[0151] (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 comprises a sheet-like substrate and a spacer disposed on a main surface of the substrate, wherein the spacer includes a region A in which the thickness of the spacer decreases continuously or stepwise from TC to TE from the center side to the edge side of the positive electrode, and the vicinity of the edge of the positive electrode faces region A. (Technology 2) A secondary battery according to Technology 1, wherein the edge of the positive electrode does not face a portion where the spacer has a thickness of TC. (Technology 3) A secondary battery according to Technology 1, wherein, when the thickness of the spacer facing the edge of the positive electrode is TP, TE≦TP and 0≦TP / TC≦0.5 are satisfied. (Technology 4) The secondary battery according to Technology 1, wherein the spacer has a region B with a thickness TE closer to the end of the substrate than the region A, wherein a vicinity of an edge of the positive electrode faces the region A and the region B, and wherein the edge of the positive electrode faces the region B. (Technology 5) The secondary battery according to Technology 1, wherein a vicinity of the edge of the positive electrode faces the region A, and wherein the edge of the positive electrode does not face the spacer. (Technology 6) The secondary battery according to any one of Technology 1 to 5, wherein the positive electrode and the negative electrode are wound with the separator interposed therebetween, wherein the edge of the positive electrode includes a winding start end, and in the region A, the thickness of the spacer decreases continuously or stepwise from TC to TE from a central portion side of the positive electrode toward the winding start end side, and wherein the vicinity of the winding start end of the positive electrode faces the region A. (Technology 7) The secondary battery according to any one of Technologies 1 to 6, wherein the positive electrode and the negative electrode are wound with the separator interposed therebetween, an edge portion of the positive electrode includes a winding end portion, and in Region A, the thickness of the spacer decreases continuously or stepwise from TC to TE from a center side of the positive electrode toward the winding end portion, and the vicinity of the winding end portion of the positive electrode faces Region A. (Technology 8) The secondary battery according to any one of Technologies 1 to 7, wherein the spacer has a predetermined arrangement pattern. (Technology 9) The secondary battery according to any one of Technologies 1 to 8, wherein the spacer includes a resin material.(Technology 10) The secondary battery according to any one of Technologies 1 to 9, wherein the spacer includes a non-porous structure that is impermeable to lithium ions. (Technology 11) The secondary battery according to any one of Technologies 1 to 10, wherein the substrate includes a porous sheet containing a polymer material. (Technology 12) The secondary battery according to Technology 11, wherein the substrate further includes a composite material layer containing a resin material and inorganic particles. (Technology 13) The secondary battery according to any one of Technologies 1 to 12, wherein lithium metal precipitates in the negative electrode during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharge.

[0152] [Examples] The lithium 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.

[0153] 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 composite 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 composite slurry was 95:2.5:2.5. The positive electrode composite 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 composite layer. The positive electrode current collector having the positive electrode mixture layer formed on both sides was cut to a predetermined size to obtain a positive electrode.

[0154] (Preparation of Negative Electrode Current Collector) A strip of electrolytic copper foil (thickness: 12 μm) was prepared as a negative electrode current collector.

[0155] (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.

[0156] (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 surface of the microporous thin film of the substrate, and the coating was dried. This resulted in the formation of spacers in the pattern (honeycomb shape) shown in Figure 15. In this way, a separator having a substrate and spacers was obtained. The linear protrusions constituting the spacers were arranged intermittently and had defects. The ratio of the length of the defects contained in one side of the hexagonal honeycomb structure to the length of that side was 45% or less.

[0157] As shown in FIG. 16 , the spacer was configured to include a region A1 facing the vicinity of end E1 but not facing end E1. Similarly, the spacer was configured to include a region A2 facing the vicinity of end E2 but not facing end E2. The width of the linear convex portion constituting the spacer was 0.25 mm. The thickness (height of the linear convex portion) TC of the spacer facing the center of the positive electrode was 30 μm. The ratio of the thickness (height of the linear convex portion) TP of the spacer facing the winding start end E1 of the positive electrode to TC: TP / TC was set to 0. Similarly, the ratio of the thickness (height of the linear convex portion) TP of the spacer facing the winding end end E2 of the positive electrode to TC: TP / TC was also set to 0.

[0158] (Preparation of non-aqueous electrolyte) 1,2-dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (CHF ２ (CF２ OCH ２ )CF ３ A 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 solution to a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte.

[0159] (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. In this way, a wound electrode assembly having the structure shown in FIG. 2 was obtained. At this time, the electrode assembly was constructed so that the separators (substrates with spacers arranged thereon) shown in FIG. 15 were arranged on the inner and outer periphery of the positive electrode, respectively. The positional relationship between the spacers (linear convex portions) arranged on the inner and outer periphery of the positive electrode and the positive electrode was as shown in FIG. 15. The separator was arranged so that the main surface of the substrate on which the spacers were formed faced the positive electrode. In the example, the dimension D0 in the length LD direction of the positive electrode was 600 mm or less, and the vicinity of the ends E1 and E2 of the positive electrode was in the range of more than 0 mm and 0.05 × D0 mm or less.

[0160] The electrode group was placed in a cylindrical case body with a bottom, and a non-aqueous electrolyte was poured into it. A sealing member was placed over 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 having the structure shown in FIG. 1 was completed.

[0161] <Secondary Batteries A2 to A4> A spacer was formed in the same honeycomb shape as in Fig. 15, including a region A1 facing end E1 as well as a region A1 near end E1, and similarly including a region A2 facing end E2 as well as a region E2 near end E2, as shown in Fig. 17. On the end E1 and E2 sides, the TP / TC values ​​were set to the values ​​shown in Table 1. Except for the above, secondary batteries A2 to A4 were fabricated in the same manner as secondary battery A1.

[0162] <<Secondary battery B1>> The spacer thickness was set to 30 μm in all regions of the spacer shown in Fig. 18. That is, regions A1, A2, B1, and B2 in Fig. 18 were set to have the same thickness TC as region C, and TP / TC = 1. Except for the above, secondary battery B1 was fabricated in the same manner as secondary battery A1.

[0163] [Evaluation] (Charge / Discharge Test) A charge / discharge test was carried out on each of the obtained batteries. In the charge / discharge test, the batteries were charged in a thermostatic chamber at 25° C. under the following conditions, then rested for 20 minutes, and discharged under the following conditions.

[0164] (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.

[0165] (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.

[0166] 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 determined as the number of cycles at which abnormality occurred. Charge and discharge were repeated until the discharge capacity reached 90% of the discharge capacity at the first cycle, and if no abnormal charging occurred, it was determined that no abnormality had occurred.

[0167] The evaluation results are shown in Table 1. In Table 1, A1 to A4 are examples, and B1 is a comparative example.

[0168]

[0169] In Batteries A1 to A4, the cycles at which abnormalities occurred were delayed, the occurrence of minute internal short circuits was suppressed, and the cycle characteristics were improved compared to Battery B1. In particular, Battery A1 showed no abnormalities and exhibited a significant effect of suppressing the occurrence of internal short circuits.

[0170] 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.

[0171] 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.

[0172] 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, 54: Defective portion

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 comprising a sheet-like substrate and a spacer disposed on a main surface of the substrate; the spacer including a region A in which the thickness of the spacer decreases continuously or stepwise from TC to TE from the center side toward the edge side of the positive electrode; and the vicinity of the edge side of the positive electrode facing region A.

2. The secondary battery according to claim 1, wherein the edge portion of the positive electrode does not face the portion of the spacer whose thickness is TC.

3. The secondary battery according to claim 1, wherein TE≦TP and 0≦TP / TC≦0.5 are satisfied, where TP is the thickness of the spacer facing the edge of the positive electrode.

4. The secondary battery described in claim 1, wherein the spacer has a region B of thickness TE closer to the end of the substrate than the region A, the vicinity of the edge of the positive electrode faces the region A and the region B, and the edge of the positive electrode faces the region B.

5. The secondary battery according to claim 1, wherein the vicinity of the edge of the positive electrode faces the region A, and the edge of the positive electrode does not face the spacer.

6. The secondary battery according to any one of claims 1 to 5, wherein the positive electrode and the negative electrode are wound with the separator interposed therebetween, an edge portion of the positive electrode includes a winding start end, and in region A, the thickness of the spacer decreases continuously or stepwise from TC to TE from the center side of the positive electrode toward the winding start end, and the vicinity of the winding start end of the positive electrode faces region A.

7. The secondary battery according to any one of claims 1 to 5, wherein the positive electrode and the negative electrode are wound with the separator interposed therebetween, an edge portion of the positive electrode includes a winding end portion, and in region A, the thickness of the spacer decreases continuously or stepwise from TC to TE from the center side of the positive electrode toward the winding end portion, and the vicinity of the winding end portion of the positive electrode faces region A.

8. The secondary battery according to any one of claims 1 to 5, wherein the spacers have a predetermined arrangement pattern.

9. The secondary battery according to any one of claims 1 to 5, wherein the spacer contains a resin material.

10. The secondary battery according to any one of claims 1 to 5, wherein the spacer includes a non-porous structure that is impermeable to lithium ions.

11. The secondary battery according to any one of claims 1 to 5, wherein the substrate comprises a porous sheet containing a polymer material.

12. The secondary battery according to claim 11, wherein the substrate further comprises a composite material layer containing a resin material and inorganic particles.

13. The secondary battery according to any one of claims 1 to 5, wherein lithium metal precipitates on the negative electrode during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging.

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