Secondary battery

Abstract

This secondary battery comprises: a positive electrode; a negative electrode; a separator disposed between the positive and negative electrodes; and an electrolyte. The separator comprises a sheet-shaped base material and a spacer that is disposed on the main surface of the base material. The positive electrode contains a positive electrode active material. The positive electrode has a region A1 constituting at least part of an end portion of the positive electrode and a region A2 other than the region A1. A filling amount M1 of the positive electrode active material per unit area of the region A1 is smaller than a filling amount M2 of the positive electrode active material per unit area of the region A2.

Description

secondary battery

[0001] The present disclosure relates to secondary batteries.

[0002] The secondary battery includes an electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0003] As a method for suppressing the volume change of the electrode group during charge and discharge of the secondary battery, it is conceivable to place spacers on the main surface of the substrate of the separator.

[0004] Patent Document 1 proposes "an electrode group for a non-aqueous secondary battery, which is stacked in a spiral or zigzag pattern between a positive electrode plate formed by applying a positive electrode composite paint, which is obtained by kneading and dispersing an active material made of at least a lithium-containing composite oxide, a conductive material, and a binder in a dispersion medium, onto a positive electrode current collector to form a positive electrode composite layer, and a negative electrode plate formed by applying a negative electrode composite paint, which is obtained by kneading and dispersing an active material made of at least a material capable of retaining lithium, and a binder in a dispersion medium, onto a negative electrode current collector to form a negative electrode composite layer, with a porous insulator interposed between them, and which is characterized in that a spacer made of resin that is softened by the non-aqueous electrolyte and that relieves stress due to expansion and contraction of the electrode plates during charging and discharging is disposed at least either between the positive electrode plate and the porous insulator or between the negative electrode plate and the porous insulator."

[0005] JP 2011-008929 A

[0006] There is a demand for improved cycle characteristics in secondary batteries equipped with spacers.

[0007] 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 positive electrode includes a positive electrode active material, the positive electrode has a region A1 that is at least a part of an end portion of the positive electrode, and a region A2 other than the region A1, and a filling amount M1 of the positive electrode active material per unit area of ​​the region A1 is smaller than a filling amount M2 of the positive electrode active material per unit area of ​​the region A2.

[0008] According to the present disclosure, it is possible to suppress a decrease in the cycle characteristics of a secondary battery including a spacer.

[0009] 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] Fig. 2 is a longitudinal sectional view schematically showing an example of a secondary battery according to an embodiment of the present disclosure; Fig. 3 is a sectional view schematically showing a main part of the secondary battery shown in Fig. 1; Fig. 4 is a sectional view schematically showing an example of a positive electrode; Fig. 5 is a top view schematically showing an example of a positive electrode; Fig. 6 is a top view schematically showing an example of a spacer;

[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 an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode includes a positive electrode active material that absorbs and releases lithium ions. The negative electrode includes a negative electrode active material and / or a negative electrode current collector. The separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate. The spacer may be disposed on one main surface of the substrate or on both main surfaces of the substrate. The positive electrode and the negative electrode are, for example, sheet-like or strip-like.

[0013] 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 ion batteries, lithium secondary batteries (lithium metal secondary batteries), etc. The negative electrode of a lithium ion battery expands due to the absorption of lithium ions during charging. The negative electrode of a lithium secondary battery expands due to the deposition of lithium metal during charging. Among secondary batteries, lithium secondary batteries have a large degree of swelling of the negative electrode due to Li deposition, resulting in a large change in the volume of the electrode group.

[0015] In secondary batteries, volume changes in the electrode group during charge and discharge can cause damage to the components of the electrode group, buckling of the electrodes, internal short circuits, and the like. As a result, cycle characteristics can be reduced. To address this issue, in the case of lithium secondary batteries, the volume change of the electrode group during charge and discharge can be suppressed by placing a spacer (protrusion) between the positive and negative electrodes to form a space to accommodate the precipitated Li. Furthermore, in the case of lithium ion batteries, the volume change of the electrode group during charge and discharge can be suppressed by placing a flexible spacer between the positive and negative electrodes.

[0016] However, at the ends of the electrode group (for example, the ends corresponding to the end faces of a columnar wound electrode group), the force that maintains the shape of the electrode group is weak, so even if a spacer is provided, volume changes occur during charge and discharge, and the negative electrode is prone to stretching. When the negative electrode located at the end of the electrode group stretches, the portion that does not face the positive electrode increases, and as a result, Li (or Li ions) that do not contribute to the battery reaction increase in the negative electrode, which can deteriorate the cycle characteristics.

[0017] In view of the above, the inventors have conducted extensive research and have newly discovered that by reducing the amount of positive electrode active material filled in at least a portion of the positive electrode end compared to other regions and reducing the degree of expansion of the negative electrode facing the positive electrode end, it is possible to suppress volumetric changes at the end of the electrode group (elongation of the negative electrode located at the end of the electrode group) and thereby suppress deterioration of cycle characteristics.

[0018] In the secondary battery according to the embodiment of the present disclosure, the positive electrode has a region A1 that is at least a part of an end portion of the positive electrode and a region A2 other than region A1, and the amount M1 of positive electrode active material filled per unit area in region A1 is smaller than the amount M2 of positive electrode active material filled per unit area in region A2. In particular, in a lithium secondary battery in which the volume change of the electrode group is large, the formation of region A1 significantly improves the cycle characteristics.

[0019] The end of the positive electrode is a portion that follows the outline of the positive electrode when the positive electrode is viewed from above (when viewed from the normal direction of the main surface of the positive electrode), and is, for example, a portion that is 20 mm or less (or 10 mm or less, or 5 mm or less) away from the edge of the positive electrode. Region A1 may be formed with a width of 20 mm or less (or 10 mm or less, or 5 mm or less) along the outline of the positive electrode.

[0020] Region A1 may be formed over the entire positive electrode end portion or in a portion of the positive electrode end portion. Region A1 may be a single region or may be divided into multiple locations. The portion of the positive electrode filled with the positive electrode active material has regions A1 and A2.

[0021] The positive electrode includes, for example, a positive electrode current collector and a positive electrode composite layer containing a positive electrode active material. The positive electrode composite layer is supported on the main surface of the positive electrode current collector. In this case, the positive electrode composite layer has a region A1 and a region A2. That is, when the positive electrode is viewed from above (when viewed from the normal direction of the main surface of the positive electrode (positive electrode composite layer)), the positive electrode composite layer has a region A1 that is at least a part of the edge of the positive electrode composite layer and a region A2 other than region A1. The filling amount M1 of the positive electrode active material per unit area in region A1 of the positive electrode composite layer (the filling amount per one side of the positive electrode current collector) is smaller than the filling amount M2 of the positive electrode active material per unit area in region A2 of the positive electrode composite layer (the filling amount per one side of the positive electrode current collector). The main surface of the positive electrode current collector may have a region (exposed current collector portion) where the positive electrode composite layer is not supported. In a strip-shaped positive electrode, for example, an exposed current collector portion may be formed along the width direction near the center in the longitudinal direction. The exposed current collector portion is used, for example, as a connection portion with a positive electrode lead.

[0022] The positive electrode mixture layer may be formed on one main surface of the positive electrode current collector, or may be formed on both main surfaces of the positive electrode current collector. In the secondary battery, a positive electrode having a positive electrode mixture layer supported on both main surfaces of the positive electrode current collector may be used, and a separator and a negative electrode may be disposed on both sides of the positive electrode.

[0023] When a positive electrode composite layer is formed on both main surfaces of the positive electrode current collector, the positive electrode composite layer formed on one main surface of the positive electrode current collector and the positive electrode composite layer formed on the other main surface each have regions A1 and A2, and M1 < M2 is satisfied. That is, region A1 (region A2 other than region A1) includes region A1a (region A2a other than region A1a) of the positive electrode composite layer formed on one main surface Sa of the positive electrode current collector and region A1b (region A2b other than region A1b) of the positive electrode composite layer formed on the other main surface Sb of the positive electrode current collector. The filling amount M1a of the positive electrode active material per unit area of ​​region A1a is smaller than the filling amount M2a of the positive electrode active material per unit area of ​​region A2a. The filling amount M1b of the positive electrode active material per unit area of ​​region A1b is smaller than the filling amount M2b of the positive electrode active material per unit area of ​​region A2b. M1a is the mass of the positive electrode active material filled per unit area in the region corresponding to region A1a on one main surface Sa of the positive electrode current collector. M2a is the mass of the positive electrode active material filled per unit area in the region corresponding to region A2a on one main surface Sa of the positive electrode current collector. M1b is the mass of the positive electrode active material filled per unit area in the region corresponding to region A1b on the other main surface Sb of the positive electrode current collector. M2b is the mass of the positive electrode active material filled per unit area in the region corresponding to region A2b on the other main surface Sb of the positive electrode current collector. M1a may be different from M1b, but it is desirable that they are approximately the same. M2a may be different from M2b, but it is desirable that they are approximately the same.

[0024] When the positive electrode is viewed in plan, the positions of the regions A1a and A1b do not have to coincide, but it is desirable that the positions of the regions A1a and A1b are approximately coincident. That is, it is desirable that the regions A1a and A1b are formed so as to overlap with each other via the positive electrode current collector. When the positive electrode is viewed in plan, the areas of the regions A1a and A1b may be different, but it is desirable that they are approximately the same.

[0025] It is sufficient that at least the central portion of the positive electrode has a portion overlapping with the spacer, and from the viewpoint of the stability of the shape of the electrode assembly, it is preferable that both the end portion and the central portion of the positive electrode have a portion overlapping with the spacer. When the positive electrode is viewed in plan, the portion where the end portion of the positive electrode overlaps with the spacer is, for example, a portion that is 10 mm or less (preferably 5 mm or less) away from the end of the positive electrode.

[0026] From the viewpoint of suppressing volumetric changes in the electrode group, it is preferable that region A1 of the positive electrode (positive electrode composite layer) has a portion P overlapping with the spacer. In this case, in a lithium secondary battery, while it is easier to more stably form a space for accommodating precipitated Li between the positive and negative electrodes, the thickness of the precipitated Li may locally increase near the portion P due to the precipitated Li wrapping around the spacer, etc. As a result, stress may locally concentrate near the portion P, causing damage to the substrate, etc., and resulting in a decrease in cycle characteristics. In the present disclosure, the filling amount of the positive electrode active material in region A1 is small, and expansion of the negative electrode facing region A1 is suppressed, so that a local increase in the thickness of the precipitated Li near the portion P and a resulting decrease in cycle characteristics can be suppressed.

[0027] From the viewpoint of suppressing deterioration of cycle characteristics, the ratio M1 / M2 of the positive electrode active material filling amount M1 per unit area of ​​region A1 to the positive electrode active material filling amount M2 per unit area of ​​region A2 is preferably 0.95 or less. From the viewpoint of ease of fabrication of the positive electrode and ensuring capacity, M1 / M2 is, for example, 0.5 or more, preferably 0.6 or more, and more preferably 0.75 or more. The range of M1 / M2 may be, for example, 0.5 or more and 0.95 or less, preferably 0.6 or more and 0.95 or less, and more preferably 0.75 or more and 0.95 or less. When positive electrode composite layers are formed on both surfaces of the positive electrode current collector, it is preferable that M1 / M2 be within the above range for each of the positive electrode composite layer formed on one main surface of the positive electrode current collector and the positive electrode composite layer formed on the other main surface of the positive electrode current collector. That is, it is preferable that both M1a / M2a and M1b / M2b are within the above range of M1 / M2 (for example, 0.95 or less).

[0028] From the viewpoint of ease of manufacturing the positive electrode and ensuring capacity, the loading amount M2 of the positive electrode active material per unit area of ​​the region A2 is preferably 100 g / m ２ Above, 300g / m ２ More preferably, it is 200 g / m or less. ２ Above, 300g / m ２ When positive electrode composite layers are formed on both sides of the positive electrode current collector, it is preferable that M2 is within the above range in each of the positive electrode composite layer formed on one main surface of the positive electrode current collector and the positive electrode composite layer formed on the other main surface of the positive electrode current collector. That is, it is preferable that both M2a and M2b are within the above range of M2 (for example, 100 to 300 g / m ２ ) is preferred.

[0029] The loading amount of the positive electrode active material (e.g., lithium-containing transition metal oxide) can be determined, for example, by the following method. A secondary battery in a discharged state (depth of discharge 90% or more) is disassembled, the positive electrode is removed, and the positive electrode composite is peeled off and collected from the positive electrode current collector. The positive electrode composite is washed with a non-aqueous solvent (e.g., DMC) and dried, and then the mass of the positive electrode composite is measured. Next, the positive electrode composite is dissolved in a predetermined acid solution, and the insoluble matter (e.g., a resin material serving as a binder and a carbon material serving as a conductive material) is separated by filtration or the like, washed with water, dried, and then the mass of the insoluble matter is measured. The mass of the positive electrode active material, PM, is determined by subtracting the mass of the insoluble matter from the mass of the positive electrode composite. The area, CS, of the region of the positive electrode current collector from which the positive electrode composite has been peeled is determined. PM / CS is calculated. In the case of region A1, the loading amount, M1, is calculated. In the case of region A2, the loading amount, M2, is calculated.

[0030] When the positive electrode is viewed in plan, the ratio of the area S1 of region A1 to the area S0 (the total area of ​​region A1 and region A2) of the main surface of the positive electrode (positive electrode composite layer): S1 / S0 may be, for example, 0.07 to 0.71, or may be 0.07 to 0.36. When region A1 is formed in multiple locations, the area S1 of region A1 is the total area of ​​the multiple locations. When S1 / S0 is 0.71 or less, the proportion of region A1 in the positive electrode is sufficiently small, and the effect on capacity due to the small amount of positive electrode active material filled in region A1 can be reduced, allowing a sufficiently high capacity to be ensured. When S1 / S0 is 0.07 or more, the effect of improving cycle characteristics due to the arrangement of region A1 can be sufficiently obtained. When positive electrode composite layers are formed on both surfaces of the positive electrode current collector, it is preferable that S1 / S0 be within the above range in each of the positive electrode composite layer formed on one main surface of the positive electrode current collector and the positive electrode composite layer formed on the other main surface of the positive electrode current collector.

[0031] In the case of a strip-shaped positive electrode, the end of the positive electrode may include both widthwise ends of the positive electrode, and region A1 may be region a corresponding to both widthwise ends of the positive electrode. In the case of a columnar, wound electrode assembly, region A1 (region a) can be efficiently arranged at the ends corresponding to both end faces of the electrode assembly. The positive electrode can be produced, for example, by applying a positive electrode slurry to the surface of a long positive electrode current collector, drying it, and then rolling the coating film with a roller to form a positive electrode mixture layer. Positive electrodes can be continuously produced using a roll-to-roll method. In this case, region A1 and region A2 can be efficiently formed by adjusting the amount of positive electrode slurry applied to the region corresponding to region A1 and region A2 of the positive electrode current collector.

[0032] In the case of a wound electrode group, the ends of the positive electrode include both widthwise ends of the positive electrode and the end of the positive electrode at the winding start side. Region A1 may be region a corresponding to both widthwise ends of the positive electrode, or may be a region combining region a corresponding to both widthwise ends of the positive electrode and region b corresponding to the winding start side end of the positive electrode.

[0033] Region A1 may be formed in a limited area of ​​the positive electrode end portion where stress is likely to be applied. Region A1 may be formed in a portion corresponding to a bent portion of an electrode group in which positive and negative electrodes are stacked in a zigzag pattern, in a portion corresponding to the innermost periphery of a wound electrode group (the above-mentioned region b), or in a portion corresponding to a portion with a small radius of curvature of a flat electrode group.

[0034] The negative electrode and separator may be disposed on both sides of the positive electrode, or on one side of the positive electrode. In the case of a wound (flat) electrode group, the negative electrode and separator are disposed on both sides (outer and inner sides) of the positive electrode. The spacers disposed on both sides (outer and inner sides) of the positive electrode may be disposed so as to overlap with the positive electrode interposed therebetween, or may be disposed with their positions shifted entirely or partially. The spacers disposed on both sides (outer and inner sides) of the positive electrode may have the same arrangement pattern or different arrangement patterns.

[0035] The secondary battery will be described in detail below.

[0036] (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.

[0037] 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).

[0038] (Separator) The separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate. The spacer preferably includes a protrusion. The protrusion facilitates the formation of a space between the positive electrode and the negative electrode.

[0039] (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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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).

[0048] 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.

[0049] (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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Among the above resin materials, polyimide, polyvinylidene fluoride, acrylonitrile-acrylic acid ester copolymer, etc. are preferred as materials that do not allow lithium ions to pass through, and polyimide may also be used. A non-porous spacer of a certain height or more formed from these resin materials is a layer that does not allow lithium ions to pass through. The placement of such a spacer is preferable from the viewpoint of suppressing an increase in the gas generation reaction rate during an internal short circuit.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The spacer may include linear protrusions and / or dot-shaped protrusions. From one viewpoint, the linear protrusions are ridge-shaped protrusions. The linear protrusions may be arranged intermittently or continuously. The linear protrusions may be arranged in a straight line or in a curved line.

[0058] 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.

[0059] The spacer preferably has a predetermined repeating pattern. That is, the spacer preferably includes convex portions arranged in a predetermined repeating pattern. The linear convex portions may be arranged in a striped pattern. A plurality of linear convex portions may be arranged parallel to and spaced apart from each other along the length direction of the substrate. The linear convex portions may be arranged in a mesh pattern. The mesh pattern may be an aggregate of polygons. An example of a mesh pattern includes a shape in which polygons are combined so as to share sides. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons may be combined. The mesh pattern may be honeycomb-shaped.

[0060] The height H of the spacer (protrusion) may be greater than the thickness T of the substrate. The ratio of the height H to the thickness T, H / T, may be greater than 1, 1.5 or greater, 2 or greater, or 3 or greater. H / T may be 10 or less, 8 or less, 5 or less, or 4 or less. By making H / T 1.5 or greater, expansion of the electrode group can be particularly suppressed.

[0061] The height H can be measured by the following method. First, a cross section of the separator (substrate) in the thickness direction is photographed using an electron microscope to obtain an image of the cross section. Next, 20 arbitrary locations among the spacers are selected in the image, and the heights of the spacers at those locations are measured. Next, the heights measured at the 20 locations are arithmetically averaged, and the obtained average value is defined as the height H. The thickness T can also be measured using a similar procedure.

[0062] The spacers are formed, for example, by applying a coating liquid containing a spacer component and a liquid component to predetermined locations on the substrate and drying the coating. Examples of the liquid component include N-methyl-2-pyrrolidone. The coating may be performed using a dispenser or by using a known printing method such as gravure printing, inkjet printing, or screen printing. The drying may be performed by a known method such as drying by heating or natural drying. The spacers may be formed on the main surface of the electrode by applying the above-mentioned coating liquid to predetermined locations on the electrode.

[0063] In the case of a lithium secondary battery, from the viewpoint of stably forming a space for accommodating precipitated Li between the positive and negative electrodes, the ratio of the area S1 of the spacers disposed on the main surface of the substrate to the area S0 of the main surface of the substrate may be, for example, 5% or more, or may be 10% or more. From the viewpoint of ensuring a space for accommodating precipitated Li between the positive and negative electrodes, the ratio of the area S1 of the spacers disposed on the main surface of the substrate to the area S0 of the main surface of the substrate may be 40% or less, or may be 30% or less (or 20% or less).

[0064] (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.

[0065] 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.

[0066] 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.

[0067] The lithium ion occlusion layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a binder, a thickener, a conductive material, etc. in addition to the negative electrode active material.

[0068] 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).

[0069] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, or carbon nanotubes.

[0070] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber polymers, etc. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride, etc. Examples of thickeners include carboxymethyl cellulose (CMC), sodium salt of CMC, etc.

[0071] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0072] The material of the negative electrode current collector (conductive sheet) may be any conductive material other than lithium metal and lithium alloys. The conductive material may be a metallic material such as a metal or alloy. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form an alloy or an intermetallic compound with lithium is preferred. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, as well as graphite with a preferentially exposed basal plane. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys with high conductivity are preferred.

[0073] 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.

[0074] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode mixture layer may be formed on only one surface of the positive electrode current collector, or may be formed on both surfaces. The positive electrode is obtained, for example, by applying a positive electrode slurry including the positive electrode active material, the conductive material, and the binder to both surfaces of the positive electrode current collector, drying the coating, and then rolling.

[0075] For example, regions A1 and A2 can be formed by adjusting the amount of positive electrode slurry applied to the region corresponding to region A1 and the region corresponding to region A2 of the positive electrode current collector. When the amount of positive electrode mixture applied to the region corresponding to region A1 is reduced and the amount of positive electrode active material filled in region A1 is reduced, the mixture density of the positive electrode mixture layer formed in region A1 decreases. If it is necessary to ensure the strength of region A1, a predetermined filler may be contained in the positive electrode mixture layer in region A1. A predetermined filler may be added to the positive electrode slurry applied to the region corresponding to region A1 of the positive electrode current collector. The filler may be an insulating filler or a conductive filler. Adding a filler controls the mixture density of the positive electrode mixture layer, making it easier to uniformize the thickness during compression, ensuring uniformity of the electrode group, and ensuring uniformity of the surface pressure during charge and discharge, thereby further improving durability.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] As the binder, conductive material, etc., for example, those exemplified for the negative electrode can be used. Graphite may be used as the conductive material for the positive electrode. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0081] Examples of the material of the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0082] 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.

[0083] (Non-aqueous electrolyte) The non-aqueous electrolyte having lithium ion conductivity may be a liquid electrolyte (electrolytic solution), a gel electrolyte, or a solid electrolyte. The liquid electrolyte is, for example, an electrolytic solution containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolytic solution is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolytic solution may contain known additives.

[0084] 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.

[0085] 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.

[0086] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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).

[0094] (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.

[0095] 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.

[0096] 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.

[0097] The spacers contained in the separator contain a resin material, which can be appropriately selected from the materials exemplified above.

[0098] In the case of a lithium ion battery, the spacer may be in the form of a wide sheet. In the case of a lithium ion battery, the spacer may be disposed in a limited 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 portion of a wound electrode assembly, or at a location with a small radius of curvature of a flat electrode assembly.

[0099] An example of a secondary battery (lithium 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 lithium secondary battery of the example 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 lithium secondary battery described below, components that are not essential for the lithium 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.

[0100] (Embodiment 1) FIG. 1 is a longitudinal cross-sectional view schematically illustrating an example of a secondary battery (lithium 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator (a substrate 50 and a spacer 53). The positive electrode 11, the negative electrode 12, and the separator substrate 50 are all strip-shaped. The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator (substrate 50) so that the separator is disposed between the positive electrode 11 and the negative electrode 12.

[0106] 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.

[0107] 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 positive electrode 11. 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.

[0108] In Fig. 2, the spacer 53 is disposed on the main surface 50a of the substrate 50 on the positive electrode 11 side, but it 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 it 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 it may also be disposed on the negative electrode 12 side. The substrate 50 may be composed of only the porous sheet 51.

[0109] 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 due to the deposition of lithium metal is suppressed, and the cycle characteristics are improved.

[0110] Fig. 3 is a schematic cross-sectional view of the positive electrode 11, taken along line IV-IV in Fig. 4. Fig. 4 is a schematic top view of the positive electrode 11 in a plan view. In Fig. 4, LD indicates the length direction of the positive electrode 11, and WD indicates the width direction of the positive electrode 11.

[0111] The ends of the strip-shaped positive electrode 11 include both ends E1 and E2 in the width direction (WD direction) of the positive electrode 11. The positive electrode 11 (positive electrode composite layer 11b) has a region 11A (region a) corresponding to the ends E1 and E2 and a region 11B other than region 11A. The positive electrode composite layer 11b formed on one main surface of the positive electrode current collector 11a and the positive electrode composite layer 11b formed on the other main surface of the positive electrode current collector 11a each have regions 11A and 11B. The positive electrode 11 is formed such that, when the positive electrode 11 is viewed from above (when viewed from the normal direction to the main surface of the positive electrode 11), the positions of regions 11A and 11B of the positive electrode composite layer 11b arranged on both sides of the positive electrode current collector 11a are approximately aligned.

[0112] The filling amount M1 of the positive electrode active material per unit area (the filling amount per one side of the positive electrode current collector 11a) in the region 11A (region A1) of the positive electrode composite layer 11b is smaller than the filling amount M2 of the positive electrode active material per unit area (the filling amount per one side of the positive electrode current collector 11a) in the region 11B (region A2) of the positive electrode composite layer 11b.

[0113] The ratio M1 / M2 is preferably 0.95 or less, and may be 0.5 or more and 0.95 or less. The amount M2 of the positive electrode active material per unit area of ​​the region 11B (region A2) (the amount per one side of the positive electrode current collector 11a) is 100 g / m ２ Above, 300g / m ２ It is preferable that:

[0114] In FIG. 3, L0 indicates the width dimension of the positive electrode 11. L1 indicates the width dimension of the region 11A. L1 / L0 may be, for example, 0.4 or less, 0.2 or less, or 0.016 or more and 0.400 or less (or 0.200 or less). L0 is, for example, 50 to 120 mm. L1 may be, for example, 20 mm or less, or 5 mm or less. In FIG. 3, the width dimension L1 of the region 11A corresponding to the end E1 and the width dimension L1 of the end 11A corresponding to the end E2 are approximately the same, but may be different.

[0115] FIG. 5 shows an example of the planar shape of the spacer 53. In a plan view, the spacer 53 (linear convex portion 53a) is arranged on one main surface 50a of the substrate 50. The substrate 50 on which the spacer 53 is arranged is arranged on both sides (outer and inner peripheral sides) of the positive electrode 11. The dashed line in FIG. 5 represents the positive electrode 11 facing the substrate 50. In FIG. 5, LD indicates the length direction of the substrate 50 (positive electrode 11), and WD indicates the width direction of the substrate 50 (positive electrode 11). Note that each diagram is a schematic diagram, and the thickness of each member and the ratio of the length and width dimensions do not necessarily reflect the actual ones.

[0116] The spacer 53 in FIG. 5 includes a plurality of linear protrusions 53a arranged in a stripe pattern. The linear protrusions 53a are arranged parallel to and spaced apart from one another along the longitudinal direction (LD direction) of the band-shaped substrate 50. The regions where the spacers 53 are not formed form spaces 14s. In FIG. 5, six linear protrusions 53a are arranged, but the number of linear protrusions 53a is not limited to this. The linear protrusions 53a are arranged intermittently in the LD direction, but may also be arranged continuously. In FIG. 5, the spacers are arranged in a stripe pattern, but the arrangement pattern of the spacers is not limited thereto, and the spacers may be arranged in a mesh pattern (e.g., a honeycomb pattern). Region 11A (region A1) may have a portion P overlapping the protrusions 53a.

[0117] In the first embodiment, a cylindrical 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.

[0118] (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 positive electrode contains a positive electrode active material, and the positive electrode has a region A1 that is at least a part of an end of the positive electrode and a region A2 other than the region A1, and a filling amount M1 of the positive electrode active material per unit area of ​​the region A1 is smaller than a filling amount M2 of the positive electrode active material per unit area of ​​the region A2. (Technology 2) The secondary battery according to Technology 1, wherein the region A1 has a portion P that overlaps with the spacer. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the strip-shaped positive electrode and the strip-shaped negative electrode are wound with the separator interposed therebetween. (Technology 4) The secondary battery according to Technology 3, wherein the ends of the positive electrode include both ends in the width direction of the positive electrode, and the region A1 is a region a corresponding to both ends in the width direction of the positive electrode. (Technology 5) The secondary battery according to any one of Technology 1 to Technology 4, wherein a ratio M1 / M2 of a filling amount M1 of the positive electrode active material per unit area of ​​the region A1 to a filling amount M2 of the positive electrode active material per unit area of ​​the region A2 is 0.95 or less. (Technology 6) The filling amount M2 of the positive electrode active material per unit area of ​​the region A2 is 100 g / m ２ Above, 300g / m ２The secondary battery according to Technology 5, which is as follows: (Technology 7) The secondary battery according to any one of Technology 1 to 6, wherein lithium metal precipitates in the negative electrode during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging. (Technology 8) The secondary battery according to any one of Technology 1 to 7, wherein the spacer includes the protrusions arranged in a predetermined repeating pattern. (Technology 9) The secondary battery according to any one of Technology 1 to 7, wherein a plurality of linear protrusions are arranged parallel to and spaced apart from each other along the longitudinal direction of the substrate. (Technology 10) The secondary battery according to any one of Technology 1 to 9, wherein the spacer includes a resin material. (Technology 11) The secondary battery according to any one of Technology 1 to 10, wherein the substrate includes a porous sheet including a polymer material. (Technology 12) The secondary battery according to Technology 11, wherein the substrate further includes a composite material layer including a resin material and inorganic particles.

[0119] [Examples] The secondary battery according to the present disclosure will be described in more detail below based on examples and comparative examples, although the present disclosure is not limited to the following examples.

[0120] Batteries A1-A6 and Batteries B1-B2 (Preparation of Positive Electrodes) 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, acetylene black (AB: conductive material), and polyvinylidene fluoride (PVdF: binder) were mixed in a mass ratio of NCA:AB:PVdF = 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The resulting positive electrode slurry was applied to both sides of a strip of Al foil (positive electrode current collector), dried, and the coating of the positive electrode composite was rolled using a roller. Finally, the resulting laminate of the positive electrode current collector and positive electrode composite was cut to a predetermined electrode size. In this way, a positive electrode was obtained, which had a positive electrode mixture layer (65 μm thick per side) on both sides of the positive electrode current collector.

[0121] Region A1 of the positive electrode was region a (region 11A in FIGS. 3 and 4 ) corresponding to both ends of the positive electrode current collector in the width direction. The width of the positive electrode (L0 in FIG. 3 ) was 57 mm, and the width of region A1 (L1 in FIG. 3 ) was 10 mm. L1 / L0 was 0.175.

[0122] The filling amount M1 of the positive electrode active material per unit area in region A1 (region 11A in FIGS. 3 and 4 ) and the filling amount M2 of the positive electrode active material per unit area in region A2 (region 11B in FIGS. 3 and 4 ) were set to the values ​​shown in Table 1. The filling amount of the positive electrode active material is the filling amount per one side of the positive electrode current collector. The filling amount of the positive electrode active material was adjusted by changing the application amount of the positive electrode slurry (application amount per one side of the positive electrode current collector).

[0123] (Preparation of Negative Electrode) A strip of electrolytic copper foil (thickness: 15 μm) was prepared as a negative electrode current collector.

[0124] (Preparation of Separator) A microporous thin film (porous sheet) made of polyethylene and having a thickness of 20 μm was prepared as a substrate.

[0125] A dispersion of the spacer material was prepared by mixing 50 parts by volume of insulating particles (median diameter: 3 μm, volume resistivity: 1014 Ω·cm), 50 parts by volume of polyvinylidene fluoride (PVdF) as a resin material, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium.

[0126] Next, a dispersion of the spacer material was dispensed onto the microporous thin film using a dispenser, and the coating was vacuum dried to form spacers in the pattern (striped) shown in Figure 5. Specifically, convex portions were formed in a striped pattern on one main surface of the microporous thin film. In this way, a separator having a substrate and spacers was obtained.

[0127] The linear protrusions constituting the spacers had a width of 0.25 mm and a height of 30 μm.

[0128] (Preparation of non-aqueous electrolyte) Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC=30:70, and LiPF 6 was added to the obtained mixed solvent. ６ 1 mol / L, LiBF ２ (C ２ O ４) were dissolved in a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte.

[0129] (Battery Assembly) In an inert gas atmosphere, the positive electrode and negative electrode current collector were spirally wound with the separator interposed therebetween to produce an electrode assembly. The separator was positioned so that the spacer faced the positive electrode. Region A1 had a portion P overlapping the spacer. The electrode assembly was housed in a bag-shaped exterior body formed of a laminate sheet with an Al layer, and after injecting a non-aqueous electrolyte, the exterior body was sealed to complete a lithium secondary battery.

[0130] [Evaluation of cycle characteristics (durability)] A charge / discharge test was performed on each of the obtained batteries. In the charge / discharge test, the battery was charged in a thermostatic chamber at 25°C under the following conditions, then rested for 20 minutes, and discharged under the following conditions.

[0131] (Charging) The battery was charged at a constant current of 0.5 C until the battery voltage reached 4.2 V. Thereafter, the battery was charged at a constant voltage of 4.2 V until the current reached 15 mA.

[0132] (Discharge) The battery was discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V.

[0133] The above charge and discharge constituted one cycle, and the charge and discharge were repeated until the discharge capacity fell below 80% of the discharge capacity at the first cycle, and the final number of cycles at which the discharge capacity was 80% or more of the discharge capacity at the first cycle was determined. A large number of cycles was considered to indicate good cycle characteristics (durability).

[0134] The evaluation results are shown in Table 1. In Table 1, A1 to A6 are examples, and B1 and B2 are comparative examples.

[0135]

[0136] The batteries A1 to A6 exhibited superior cycle characteristics compared to the batteries B1 and B2.

[0137] 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.

[0138] 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.

[0139] 10: Lithium secondary battery, 11: Positive electrode, 11A: Region A1, 11B: Region A2, 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

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 positive electrode including a positive electrode active material, the positive electrode having a region A1 which is at least a part of an end portion of the positive electrode, and a region A2 other than the region A1, and a filling amount M1 of the positive electrode active material per unit area of ​​the region A1 is smaller than a filling amount M2 of the positive electrode active material per unit area of ​​the region A2.

2. The secondary battery according to claim 1, wherein the region A1 has a portion P that overlaps with the spacer.

3. The secondary battery according to claim 1, wherein the positive electrode and the negative electrode are wound together with the separator interposed therebetween.

4. The secondary battery according to claim 3, wherein the end of the positive electrode includes both ends in a width direction of the positive electrode, and the region A1 is region a corresponding to both ends in the width direction of the positive electrode.

5. The secondary battery according to claim 1, wherein the ratio M1 / M2 of the filling amount M1 of the positive electrode active material per unit area of ​​the region A1 to the filling amount M2 of the positive electrode active material per unit area of ​​the region A2 is 0.95 or less.

6. The amount M2 of the positive electrode active material per unit area of ​​the region A2 is 100 g / m ２ Above, 300g / m ２ The secondary battery according to claim 5 , wherein:

7. The secondary battery according to any one of claims 1 to 6, wherein lithium metal is precipitated in the negative electrode during charging, and the lithium metal is dissolved in the non-aqueous electrolyte during discharging.

8. The secondary battery according to any one of claims 1 to 6, wherein the spacer includes protrusions arranged in a predetermined repeating pattern.

9. The secondary battery according to any one of claims 1 to 6, wherein the linear protrusions are arranged in parallel to and spaced apart from each other along the longitudinal direction of the substrate.

10. The secondary battery according to any one of claims 1 to 6, wherein the spacer includes a resin material.

11. The secondary battery according to any one of claims 1 to 6, wherein the substrate comprises a porous sheet containing a polymeric 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.

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