Secondary battery

Abstract

The secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The separator is provided with a sheet-like base material and a spacer 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 of at least a portion of an end portion of the positive electrode and a region A2 other than the region A1. The filling amount M1 of the positive electrode active material per unit area of the region A1 is smaller than the filling amount M2 of the positive electrode active material per unit area of the region A2.

Description

Technical Field

[0001] This disclosure relates to secondary batteries. Background Technology

[0002] The secondary battery has an electrode assembly and a non-aqueous electrolyte. The electrode assembly has a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes.

[0003] As a method to suppress volume changes of the electrode assembly during charging and discharging of a secondary battery, it is considered to place spacers on the main surface of the substrate of the separator.

[0004] Patent Document 1 proposes "an electrode assembly for a non-aqueous secondary battery, characterized in that a positive electrode plate, wherein a positive electrode composite material coating, which is formed by mixing and dispersing at least a lithium-containing composite oxide active material, a conductive material, and a binder material in a dispersion medium, is coated on a positive electrode current collector to form a positive electrode composite material layer, and a negative electrode plate, wherein a porous insulator is spaced between the positive electrode plate and the porous insulator or between the negative electrode plate and the porous insulator, wherein a spacer is disposed between at least one of the positive electrode plate and the porous insulator or between the negative electrode plate and the porous insulator, and the spacer is made of a resin that softens in a non-aqueous electrolyte to mitigate stress caused by the expansion and contraction of the electrode plates during charging and discharging."

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2011-008929 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] In secondary batteries with spacers, improved cycle characteristics are required.

[0010] Solution for solving the problem

[0011] One aspect of this disclosure relates to a secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The separator comprises a sheet-like substrate and spacers disposed on the main surface of the substrate. The positive electrode comprises a positive electrode active material and has a region A1, which is at least a portion of the end of the positive electrode, and a region A2 other than the region A1. The amount of positive electrode active material per unit area M1 in the region A1 is less than the amount of positive electrode active material per unit area M2 in the region A2.

[0012] The effects of the invention

[0013] According to this disclosure, it is possible to suppress the degradation of the cycle characteristics of a secondary battery with spacers.

[0014] The novel features of the invention are set forth in the claims, but the invention relates to both its structure and content, and will be better understood, together with other objects and features of the invention, by reference to the following detailed description of the accompanying drawings. Attached Figure Description

[0015] Figure 1 This is a longitudinal cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment of the present disclosure.

[0016] Figure 2 It is a schematic representation Figure 1 The diagram shows a cross-sectional view of the main components of a secondary battery.

[0017] Figure 3 This is a cross-sectional view schematically representing an example of a positive electrode.

[0018] Figure 4 This is a top view schematically representing an example of a positive electrode.

[0019] Figure 5 This is a top view that schematically represents an example of a spacer. Detailed Implementation

[0020] The following examples illustrate embodiments of this disclosure, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and / or materials are sometimes cited, but other numerical values ​​and / or materials can be applied as long as the effects of this disclosure are achieved. In this specification, the description of "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower." In the following description, when lower and upper limits are cited for numerical values ​​relating to specific physical properties and / or conditions, any of the cited lower limits and any of the cited upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. When multiple materials are cited, one can be selected for use alone, or two or more can be used in combination.

[0021] The secondary battery of this disclosure includes an electrode assembly and a non-aqueous electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The positive electrode includes a positive electrode active material for absorbing and releasing 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 spacers disposed on the main surface of the substrate. The spacers may be disposed on one main surface of the substrate or on both main surfaces of the substrate. The positive and negative electrodes are, for example, sheet-like or strip-like.

[0022] There is no particular limitation on the shape of the electrode assembly. The electrode assembly can be a spiral-shaped electrode assembly consisting of a strip-shaped positive electrode and a strip-shaped negative electrode separated by a separator, or it can be a flat electrode assembly formed by pressing the spiral-shaped electrode assembly radially. The electrode assembly can be constructed by stacking the positive and negative electrodes separated by a separator, or by stacking the positive and negative electrodes in a Z-shape separated by a separator.

[0023] Secondary batteries include lithium-ion batteries and lithium secondary batteries (lithium metal secondary batteries). The negative electrode of a lithium-ion battery expands during charging due to the absorption of lithium ions. The negative electrode of a lithium secondary battery expands during charging due to the deposition of lithium metal. In secondary batteries, the expansion of the negative electrode caused by Li deposition is greater in lithium secondary batteries, resulting in a larger volume change of the electrode assembly.

[0024] In secondary batteries, volume changes in the electrode assembly during charging and discharging can sometimes lead to damage to the constituent components, electrode buckling, and internal short circuits. Consequently, cycle performance can sometimes deteriorate. In contrast, in lithium-ion batteries, by placing spacers (protrusions) between the positive and negative electrodes to create a space for accumulating deposited Li, volume changes in the electrode assembly during charging and discharging can be suppressed. Furthermore, in lithium-ion batteries, by placing flexible spacers between the positive and negative electrodes, volume changes in the electrode assembly during charging and discharging can also be suppressed.

[0025] However, at the ends of the electrode assembly (e.g., the ends corresponding to the end faces of a cylindrical, wound electrode assembly), the forces maintaining the shape of the electrode assembly are weaker. Therefore, even with spacers, volume changes occur during charging and discharging, and the negative electrode tends to elongate. As the negative electrode at the ends of the electrode assembly elongates, the portion not opposite the positive electrode becomes larger. Consequently, the amount of Li (or Li ions) in the negative electrode, which does not contribute to the battery reaction, increases, sometimes resulting in a decrease in cycle performance.

[0026] In view of the above, the inventors conducted in-depth research and made a new discovery: by making the amount of positive electrode active material smaller in at least a portion of the positive electrode portion than in other portions, the expansion degree of the negative electrode opposite to the positive electrode portion is reduced, the volume change at the end of the electrode assembly (elongation of the negative electrode at the end of the electrode assembly) can be suppressed, and the reduction in cycle characteristics can be suppressed.

[0027] In the secondary battery of the embodiments of this disclosure, the positive electrode has a region A1, which is at least a portion of the end of the positive electrode, and a region A2 other than region A1. The amount of positive electrode active material per unit area M1 in region A1 is less than the amount of positive electrode active material per unit area M2 in region A2. Especially in lithium secondary batteries with large volume variations in the electrode assembly, a significant improvement in cycle characteristics due to the formation of region A1 can be obtained.

[0028] The end of the positive electrode is the portion along the shape of the positive electrode when viewed from above (from the normal direction of the main surface of the positive electrode), for example, the portion that is 20 mm or less (or 10 mm or less or 5 mm or less) from the edge of the positive electrode. Region A1 can be formed along the shape of the positive electrode with a width of 20 mm or less (or 10 mm or less or 5 mm or less).

[0029] Region A1 can be formed in the entire positive electrode portion or in a part of the positive electrode portion. Region A1 can be a single region or formed by dividing it into multiple parts. The portion of the positive electrode filled with the positive electrode active material has regions A1 and A2.

[0030] The positive electrode, for example, comprises a positive current collector and a positive composite material layer containing positive active material. The positive composite material layer is loaded on the main surface of the positive current collector. In this case, the positive composite material layer has regions A1 and A2. That is, when viewed from above (from the normal direction of the main surface of the positive electrode (positive composite material layer)), the positive composite material layer has region A1, which is at least a portion of the end of the positive composite material layer, and region A2, excluding region A1. The amount of positive active material per unit area M1 (the amount of positive current collector per single surface) of region A1 of the positive composite material layer is less than the amount of positive active material per unit area M2 (the amount of positive current collector per single surface) of region A2 of the positive composite material layer. The main surface of the positive current collector may have a portion of the area where the positive composite material layer is not loaded (current collector exposed portion). In a strip-shaped positive electrode, for example, the current collector exposed portion may be formed near the center in the length direction along the width direction. The current collector exposed portion serves, for example, as a connection portion with the positive electrode lead.

[0031] The positive electrode composite material layer can be formed on one main surface of the positive electrode current collector or on both main surfaces of the positive electrode current collector. In a secondary battery, using a positive electrode with a positive electrode composite material layer loaded on both main surfaces of the positive electrode current collector, a separator and a negative electrode can be arranged on both sides of the positive electrode.

[0032] When the positive electrode composite material layer is formed on two main surfaces of the positive electrode current collector, the positive electrode composite material layer formed on one main surface of the positive electrode current collector and the positive electrode composite material layer formed on the other main surface of the positive electrode current collector have regions A1 and A2, respectively, satisfying M1 < M2. That is, region A1 (region A2 other than region A1) includes region A1a (region A2a other than region A1a) of the positive electrode composite material 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 material layer formed on the other main surface Sb of the positive electrode current collector. The amount of positive electrode active material per unit area in region A1a, M1a is less than the amount of positive electrode active material per unit area in region A2a, M2a. The amount of positive electrode active material per unit area in region A1b, M1b is less than the amount of positive electrode active material per unit area in region A2b, M2b. M1a is the mass of positive electrode active material per unit area filled in the region corresponding to region A1a on one main surface Sa of the positive electrode current collector. M2a is the mass of positive electrode active material per unit area filled in the region corresponding to region A2a on one main surface Sa of the positive electrode current collector. M1b is the mass of positive electrode active material per unit area filled in the region corresponding to region A1b on the other main surface Sb of the positive electrode current collector. M2b is the mass of positive electrode active material per unit area filled in the region corresponding to region A2b on the other main surface Sb of the positive electrode current collector. M1a may differ from M1b, but is preferably substantially the same. M2a may also differ from M2b, but is preferably substantially the same.

[0033] When viewed from above the positive electrode, the positions of regions A1a and A1b may not be identical, but it is preferable that regions A1a and A1b are approximately the same. That is, regions A1a and A1b are preferably formed by overlapping each other across the positive electrode current collector. When viewed from above the positive electrode, the areas of regions A1a and A1b may be different, but it is preferable that they are approximately the same.

[0034] The positive electrode may have at least a central portion that overlaps with the spacer. From the viewpoint of the stability of the electrode assembly shape, it is preferable that both the end and the central portion of the positive electrode have portions that overlap with the spacer. When viewed from above, the portion of the positive electrode end that overlaps with the spacer is, for example, a portion that is 10 mm or less (preferably 5 mm or less) from the end of the positive electrode.

[0035] From the viewpoint of suppressing volume changes in the electrode assembly, region A1 of the positive electrode (positive electrode composite layer) preferably has a portion P overlapping with the spacer. In this case, in a lithium secondary battery, it is easier to form a space for accommodating deposited Li more stably between the positive and negative electrodes. However, on the other hand, near this portion P, the thickness of the deposited Li sometimes locally increases due to the encirclement of the deposited Li towards the spacer. As a result, stress concentration occurs locally near portion P, causing damage to the substrate, which sometimes leads to a decrease in cycle performance. In this disclosure, the amount of positive electrode active material filling region A1 is small, and the expansion of the negative electrode facing region A1 is suppressed. Therefore, it is possible to suppress the local increase in the thickness of deposited Li near portion P and the resulting decrease in cycle performance.

[0036] From the viewpoint of suppressing the reduction of cycle characteristics, the ratio of the amount of positive electrode active material per unit area M1 in region A1 to the amount of positive electrode active material per unit area M2 in region A2, M1 / M2, is preferably 0.95 or less. From the viewpoint of ease of positive electrode fabrication and capacity assurance, M1 / M2 is, for example, 0.5 or more, preferably 0.6 or more, and more preferably 0.75 or more. As a range of M1 / M2, it can 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 material layers are formed on both sides of the positive electrode current collector, M1 / M2 is preferably within the above range in both the positive electrode composite material layer formed on one main side of the positive electrode current collector and the positive electrode composite material layer formed on the other main side of the positive electrode current collector. That is, it is preferable that both M1a / M2a and M1b / M2b are within the aforementioned range of M1 / M2 (e.g., below 0.95).

[0037] From the perspectives of ease of manufacturing the positive electrode and ensuring capacity, the preferred filling amount M2 of positive electrode active material per unit area in region A2 is 100 g / m². 2 Above and 300g / m 2 The following is more preferably 200g / m 2 Above and 300g / m 2 Hereinafter, when positive electrode composite material layers are formed on both sides of the positive electrode current collector, in both the positive electrode composite material layer formed on one main side of the positive electrode current collector and the positive electrode composite material layer formed on the other main side of the positive electrode current collector, M2 is preferably within the range described above. That is, it is preferable that both M2a and M2b are within the range described above for M2 (e.g., 100~300 g / m). 2 ).

[0038] The amount of positive electrode active material (e.g., lithium-containing transition metal oxide) can be determined, for example, by the following method.

[0039] The secondary battery in a discharged state (depth of discharge greater than 90%) is disassembled, and the positive electrode is removed by peeling off the positive electrode composite material from the positive electrode current collector. The positive electrode composite material is washed with a non-aqueous solvent (DMC, etc.), dried, and its mass is measured. Next, the positive electrode composite material is dissolved in a specified acid solution, and insoluble components (e.g., resin material as a binder, carbon material as a conductive material) are separated by filtration, etc. The insoluble components are washed with water, dried, and their mass is measured. The mass PM of the positive electrode active material is calculated by subtracting the mass of the insoluble components from the mass of the positive electrode composite material. The area CS of the region in the positive electrode current collector where the positive electrode composite material has been peeled off is calculated. PM / CS is calculated. In the case of region A1, the filling amount M1 is calculated as described above. In the case of region A2, the filling amount M2 is calculated as described above.

[0040] When viewed from above, the ratio of the area S1 of region A1 to the area S0 of the main surface of the positive electrode (positive electrode composite material layer) (the area of ​​regions A1 and A2 combined): S1 / S0 can be, for example, 0.07 to 0.71, or 0.07 to 0.36. When region A1 is formed in multiple locations, the area S1 of region A1 is the total area of ​​all locations. When S1 / S0 is less than 0.71, the proportion of region A1 in the positive electrode is sufficiently small, reducing the impact of a small amount of positive electrode active material filling in region A1 on capacity, thereby ensuring high capacity. When S1 / S0 is greater than 0.07, the improved cycle characteristics resulting from the configuration of region A1 can be fully obtained. When positive electrode composite material layers are formed on both sides of the positive electrode current collector, S1 / S0 is preferably within the above range for both the positive electrode composite material layer formed on one main surface of the positive electrode current collector and the positive electrode composite material layer formed on the other main surface of the positive electrode current collector.

[0041] In the case of a strip-shaped positive electrode, the ends of the positive electrode can include both ends in the width direction of the positive electrode, and region A1 can be region a corresponding to the two ends in the width direction of the positive electrode. In the case of a columnar, wound electrode assembly, region A1 (region a) can be efficiently configured at the ends corresponding to the two end faces of the electrode assembly. The positive electrode can be manufactured, for example, by coating a positive electrode slurry onto the surface of a strip-shaped positive electrode current collector, drying it, and then calendering the coating with a roller to form a positive electrode composite material layer. The positive electrode can be continuously manufactured using a roll-to-roll method. At this time, by adjusting the amount of positive electrode slurry applied to the regions corresponding to region A1 and region A2 of the positive electrode current collector, regions A1 and region A2 can be effectively formed.

[0042] In the case of a wound electrode assembly, the end of the positive electrode includes both ends in the width direction of the positive electrode and the end at the beginning of the winding of the positive electrode. Region A1 can be region a corresponding to both ends in the width direction of the positive electrode, or it can be a region that combines region a corresponding to both ends in the width direction of the positive electrode and region b corresponding to the end at the beginning of the winding of the positive electrode.

[0043] Region A1 can also be specifically formed in the positive terminal portion where stress is easily applied. Region A1 can be formed in the portion corresponding to the bend of the electrode group in which the positive and negative electrodes are stacked in a Z-shape, in the portion corresponding to the innermost circumference of the wound electrode group (the aforementioned region b), or in the portion corresponding to the portion with a small radius of curvature of the flat electrode group.

[0044] The negative electrode and spacers can 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 assembly, the negative electrode and spacers are disposed on both sides (outer and inner circumferential sides) of the positive electrode. The spacers disposed on both sides (outer and inner circumferential sides) of the positive electrode can be disposed overlapping the positive electrode or disposed wholly or partially offset. The arrangement patterns of the spacers disposed on both sides (outer and inner circumferential sides) of the positive electrode can be the same or different from each other.

[0045] The following is a detailed description of secondary batteries.

[0046] (Lithium secondary battery)

[0047] A lithium-ion secondary battery comprises a positive electrode, a negative electrode in which lithium metal is deposited during charging and dissolves in a non-aqueous electrolyte during discharging, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The negative electrode has at least a negative current collector, on which lithium metal is deposited during charging. The non-aqueous electrolyte has lithium-ion conductivity.

[0048] In lithium-ion batteries, over 70% of the rated capacity is achieved through the deposition and dissolution of lithium metal. The migration of electrons in the negative electrode during charging and discharging primarily depends on the deposition and dissolution of lithium metal therein. Specifically, 70-100% (e.g., 80-100%, 90-100%) of the electron migration (or current, in other viewpoints) in the negative electrode during charging and discharging depends on the deposition and dissolution of lithium metal. That is, the negative electrode of a lithium-ion battery differs from a negative electrode where the migration of electrons during charging and discharging primarily depends on the absorption and release of lithium ions by the active material (graphite, etc.).

[0049] (Separator)

[0050] The separator comprises a sheet-like substrate and spacers disposed on the main surface of the substrate. The spacers preferably include protrusions. The protrusions facilitate the formation of a space between the positive and negative electrodes.

[0051] (Substrate)

[0052] The substrate can be a porous sheet with ion permeability and insulation properties. Examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the porous sheet is not particularly limited and can be a polymer material. Examples of polymer materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The substrate may contain additives as needed. Examples of additives include inorganic fillers.

[0053] The thickness of the substrate is not particularly limited, for example, it is 5 μm or more and 20 μm or less, more preferably 10 μm or more and 20 μm or less.

[0054] The substrate may comprise 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 resin materials as needed. The thickness of the composite material layer can be 5% to 50% of the total thickness of the substrate.

[0055] The composite material layer can be disposed on either the positive electrode side or the negative electrode side of the porous sheet. When the composite material layer is disposed on the positive electrode side, it can suppress the degradation of the porous sheet due to oxidation. When the composite material layer is disposed on the negative electrode side, it can suppress the degradation of the porous sheet due to reduction. Spacers can also be disposed on the composite material layer. In this case, the effect of suppressing thermal shrinkage of the substrate is particularly high.

[0056] The inorganic particles are preferably particles of inorganic compounds that are thermally stable and insulating, and do not easily melt or decompose during abnormal heating caused by abnormal heating such as short circuits in batteries. Examples of inorganic particle materials include oxides, hydroxides, nitrides, carbides, and sulfides. Examples of oxides include alumina, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, and zinc oxide. Examples of nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of carbides include silicon carbide and boron carbide. Examples of sulfides include barium sulfate. Examples of hydroxides include aluminum hydroxide. The median particle size in the volumetric particle size distribution of the inorganic particles can be 0.2 to 2.0 μm.

[0057] The median particle size in the volumetric particle size distribution of inorganic particles can be determined, for example, using a laser diffraction / scattering particle size distribution measuring device (such as the Microtrac manufactured by Nikkiso Corporation). Alternatively, a cross-section of the substrate can be observed using a transmission electron microscope (TEM), and a TEM image can be taken. The area enclosed by the outlines of any 100 inorganic particles can be calculated, and the diameter of an equivalent circle (perfect circle) with the same area as the calculated area can be obtained as the average of the diameters of the 100 equivalent circles.

[0058] Resin materials contained in the composite material layer (heat-resistant layer) include, for example, fluorinated resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluorinated rubbers such as ethylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydride, acrylonitrile-butadiene copolymer or its hydride, methacrylate-acrylate copolymer, styrene-acrylate copolymer, acrylonitrile-acrylate copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate and other rubbers, cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose and other cellulose derivatives, acrylic resins such as acrylic acid-methacrylic acid copolymer, polyamides such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, fully aromatic polyamide (aromatic polyamide), polyamide-imide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea-formaldehyde resin, and epoxy resin.

[0059] The resin material contained in the composite layer (heat-resistant layer) is preferably a polymer material with higher heat resistance than that of the porous sheet. Such a polymer material preferably includes at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamide-imides. These are known as polymer materials with high heat resistance. From the viewpoint of heat resistance, aromatic polyamides, namely meta-aromatic polyamides (meta-fully aromatic polyamides) and para-aromatic polyamides (para-fully aromatic polyamides), are preferred.

[0060] The content of inorganic particles in the composite material layer can be in the range of 50% to 99% by mass (e.g., 85% to 99% by mass).

[0061] Composite material layers are formed, for example, by coating a porous sheet with a liquid containing inorganic particles, resin materials, and a liquid component (dispersion medium) and then drying the coating. Examples of liquid components include N-methyl-2-pyrrolidone.

[0062] (spacer)

[0063] The spacers are formed on the main surface of the substrate. From the viewpoint of facilitating the fabrication of electrode assemblies, it is preferable to integrate the substrate and the spacers. The spacers can be disposed on the main surface of the substrate facing the positive electrode (the main surface of the substrate on the positive electrode side), on the main surface of the substrate facing the negative electrode (the main surface of the substrate on the negative electrode side), or on both main surfaces. When the spacers are disposed on the main surface of the substrate facing the positive electrode, compared to the case where the spacers are disposed on the main surface of the substrate facing the negative electrode, the deposition of Li between the spacers stretches the substrate towards the positive electrode, thus generating compressive stress in the deposited Li, and Li tends to deposit more densely. From the viewpoint of improving discharge efficiency and cycle characteristics, it is preferable to dispose of the spacers on the main surface of the substrate facing the positive electrode. On the other hand, when the spacers are disposed on the main surface of the substrate facing the negative electrode, since a space is pre-formed between the substrate and the negative electrode, the tensile load on the substrate caused by the deposition of Li is reduced. That is, it is advantageous in terms of easily maintaining the insulation of the substrate or easily maintaining the short-circuit withstand capability of the substrate.

[0064] In lithium-ion batteries, the main function of spacers is to create space for lithium metal deposition. By containing lithium metal within the space ensured by the spacers, the expansion of the negative electrode during charging is suppressed.

[0065] The spacer may contain resin material (e.g., insulating resin) or a mixture of resin material and particles. The proportion of resin material in the spacer may be 10% or more by volume, 30% or more by volume, or 50% or more by volume, or less than 100% by volume or less than 80% by volume.

[0066] Examples of resin materials contained in spacers include fluorinated resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), fluorinated rubbers such as PVdF-PTFE copolymer and ethylene-PTFE copolymer, styrene-butadiene copolymer or its hydrogenated form, acrylonitrile-butadiene copolymer or its hydrogenated form, methacrylate-acrylate copolymer, styrene-acrylate copolymer, acrylonitrile-acrylate copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate and other rubbers, cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose and other cellulose derivatives, acrylic resins such as acrylic acid-methacrylic acid copolymer, polyamides such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, fully aromatic polyamide (aromatic polyamide), polyamide-imide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea-formaldehyde resin, and epoxy resin.

[0067] Among the aforementioned resin materials, polyimide, polyvinylidene fluoride, and acrylonitrile-acrylate copolymers are preferred as lithium-ion impermeable materials; polyimide may also be used. The non-porous spacer formed from these resin materials to a certain height is a lithium-ion impermeable layer. From the viewpoint of suppressing the increase in the gas generation reaction rate during internal short circuits, such a spacer is preferred.

[0068] The particles can be inorganic or organic. Inorganic particles, such as insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides, are examples. Preferred metal oxides include alumina (bauxite and / or boehmite), magnesium oxide, titanium dioxide, zirconium oxide, and silicon dioxide. Preferred metal hydroxides include aluminum hydroxide. Preferred metal nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Preferred metal carbides include silicon carbide and boron carbide. Preferred metal sulfides include barium sulfate. Additionally, minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate can be used. Bauxite, silicon dioxide, and titanium dioxide are preferred.

[0069] The average particle size is not particularly limited and can be greater than or equal to 0.1 μm or 0.5 μm, or less than 10 μm, 5 μm, or 2 μm. The average particle size can be determined by the following method: First, an image of the cross-section of the spacer in the thickness direction is obtained using an electron microscope. Next, image processing such as binarization is performed on the image to determine the particle portions. Then, the diameter of a circle with an area equal to the area of ​​the cross-section of each particle (equivalent circle diameter) is calculated. The arithmetic mean of the calculated equivalent circle diameters can be used as the average particle size. The arithmetic mean can be calculated, for example, from more than 100 particles. It should be noted that the average particle size of other particles contained in the electrode plate and spacer can also be calculated using the same method.

[0070] When the spacer contains resin material and particles, the particle content in the spacer is preferably 50% by volume or less. This makes it easy to ensure sufficient strength of the spacer.

[0071] The spacers may include linear protrusions and / or dot-like protrusions. From one viewpoint, linear protrusions are ridge-like protrusions. Linear protrusions may be arranged intermittently or continuously. Linear protrusions may be arranged in a straight line or in a curved shape.

[0072] The width of the linear protrusion can be greater than 100μm or greater than 200μm, or less than 2000μm or less than 1000μm.

[0073] The spacer preferably has a prescribed repeating pattern. That is, the spacer preferably includes protrusions arranged in a prescribed repeating pattern. Linear protrusions can also be arranged in a striped pattern. Multiple linear protrusions can be arranged parallel to each other, separated from each other, along the length of the substrate. Linear protrusions can also be arranged in a mesh-like pattern. The mesh-like pattern can be an assembly of polygons. An example of a mesh-like pattern includes a shape formed by combining polygons in a manner that shares edges. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons can also be combined. The mesh-like pattern can also be honeycomb-like.

[0074] The height H of the spacer (protrusion) can be greater than the thickness T of the substrate. The ratio of height H to thickness T: H / T is greater than 1, and can be 1.5 or more, 2 or more, or 3 or more. H / T can be less than 10, 8 or less, 5 or less, or 4 or less. By setting H / T to 1.5 or more, the expansion of the electrode assembly can be suppressed in particular.

[0075] The height H can be determined using the following method. First, an image of the cross-section along the thickness direction of the spacer (substrate) is obtained using an electron microscope. Next, 20 arbitrary points are selected in the image, and the height of the spacer at each point is measured. Then, the arithmetic mean of the measured heights at the 20 points is taken as the height H. The thickness T can also be determined using the same steps.

[0076] The spacer is formed, for example, by applying a coating containing a spacer component and a liquid component to a designated area of ​​a substrate and then drying the coating. Examples of the liquid component include N-methyl-2-pyrrolidone. Coating can be performed using a dispensing machine or other known printing methods such as gravure printing, inkjet printing, and screen printing. Drying can be performed using known methods such as heated drying and / or natural drying. The spacer can be formed on the main surface of the electrode by applying the aforementioned coating to a designated area of ​​the electrode.

[0077] In the case of lithium secondary batteries, from the viewpoint of stably forming a space between the positive and negative electrodes to accommodate deposited Li, the ratio of the area S1 of the spacer disposed on the main surface of the substrate to the area S0 of the main surface of the substrate can be, for example, 5% or more, or 10% or more. From the viewpoint of ensuring space between the positive and negative electrodes to accommodate deposited Li, the ratio of the area S1 of the spacer disposed on the main surface of the substrate to the area S0 of the main surface of the substrate can be 40% or less, or 30% or less (or 20% or less).

[0078] (negative electrode)

[0079] The negative electrode serves as a negative current collector. In a lithium-ion secondary battery, lithium metal is deposited on the surface of the negative electrode during charging. More specifically, lithium ions contained in the non-aqueous electrolyte accept electrons at the negative electrode during charging and become lithium metal, which is then deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode dissolves as lithium ions in the non-aqueous electrolyte during discharge.

[0080] The negative electrode may include a lithium-ion storage layer (a layer that embodies capacity through the absorption and release of lithium ions by the negative electrode active material (graphite, etc.)) loaded on the negative electrode current collector. In this case, the open-circuit potential of the negative electrode when fully charged relative to lithium metal (the dissolution potential of lithium) can be below 70 mV. When the open-circuit potential of the negative electrode when fully charged relative to lithium metal is below 70 mV, lithium metal is present on the surface of the lithium-ion storage layer when fully charged. That is, the negative electrode embodies capacity through the deposition and dissolution of lithium metal.

[0081] Here, "fully charged" refers to the state of charge when the battery's rated capacity is set to C, reaching, for example, a state of charge of 0.98 × C or higher. The open-circuit potential of the negative electrode at a fully charged state can be determined by disassembling the fully charged battery under an argon atmosphere, removing the negative electrode, assembling a battery cell using lithium metal as the counter electrode, and then measuring the result. The non-aqueous electrolyte of the battery cell can have the same composition as the non-aqueous electrolyte in the disassembled battery.

[0082] A lithium-ion absorption and storage layer is formed by forming a layered negative electrode composite material containing negative electrode active material. In addition to the negative electrode active material, the negative electrode composite material may also contain binder materials, thickener materials, conductive materials, etc.

[0083] Examples of anode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. An anode may contain one type of anode active material or a combination of two or more. Examples of carbonaceous materials include graphite, easily graphitized carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon).

[0084] Conductive materials can be, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjen black, and carbon nanotubes.

[0085] Examples of binders include fluoropolymers, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluoropolymers include polytetrafluoroethylene and polyvinylidene fluoride. Examples of thickening materials include carboxymethyl cellulose (CMC) and sodium salts of CMC.

[0086] The negative current collector can be any conductive sheet. Foil, thin film, etc., can be used as the conductive sheet.

[0087] The negative electrode current collector (conductive sheet) can be made of any conductive material other than lithium metal and lithium alloys. The conductive material can also be a metal, alloy, or other metallic material. Preferably, the conductive material is a material that does not react with lithium. More specifically, it is preferably a material that neither forms an alloy nor an intermetallic compound with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metallic elements, or graphite with a predominantly exposed base. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys, which have high conductivity, are preferred.

[0088] There are no particular restrictions on the thickness of the negative current collector, for example, it can be 5μm or more and 300μm or less.

[0089] (positive electrode)

[0090] The positive electrode, for example, comprises a positive current collector and a positive electrode composite material layer loaded on the surface of the positive current collector. The positive electrode composite material layer, for example, includes a positive electrode active material, a conductive material, and a binder material. The positive electrode composite material layer may be formed only on one side of the positive current collector or on both sides. The positive electrode is obtained, for example, by coating both sides of the positive current collector with a positive electrode slurry comprising a positive electrode active material, a conductive material, and a binder material, allowing the coating to dry, and then calendering it.

[0091] For example, regions A1 and A2 can be formed by adjusting the amount of positive electrode slurry applied to the regions corresponding to region A1 and region A2 of the positive electrode current collector. By reducing the amount of positive electrode composite material applied to the region corresponding to region A1, thereby reducing the amount of positive electrode active material filling in region A1, the composite material density of the positive electrode composite layer formed in region A1 decreases. When it is necessary to ensure the strength of region A1, the positive electrode composite layer in region A1 can contain a specified filler. A specified filler can also be added to the positive electrode slurry applied to the region corresponding to region A1 of the positive electrode current collector. The filler can be an insulating filler or a conductive filler. By adding filler to control the composite density of the positive electrode composite layer, it is easier to achieve uniform thickness during compression, ensuring the uniformity of the electrode assembly and the uniformity of surface pressure during charging and discharging, thereby further improving durability.

[0092] The positive electrode active material is the material that absorbs, stores, and releases lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred due to their low manufacturing cost and high average discharge voltage.

[0093] Lithium contained in lithium-containing transition metal oxides is released as lithium ions from the positive electrode during charging and deposited as lithium metal on the negative electrode or negative electrode current collector. During discharging, lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed and stored by the composite oxide of the positive electrode. In other words, the lithium ions participating in charging and discharging mainly originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0094] Transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one or more transition metal elements. The transition metal elements can be Ni, Co, and / or Mn. Lithium-containing transition metal oxides may contain more than one typical element as needed. Typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. Al is a typical example.

[0095] In lithium-containing transition metal oxides, Ni, Co, and / or Mn are included as transition metal elements, and Al is included as an arbitrary component. From the viewpoint of obtaining high capacity, composite oxides with a layered structure and a rock-salt-type crystal structure are preferred. In this case, in the lithium secondary battery, the molar ratio of the total amount of lithium (mLi) in the positive and negative electrodes to the amount of metal M other than lithium (mM) in the positive electrode, mLi / mM, is set to, for example, 1.1 or less.

[0096] As a bonding material, conductive material, etc., the substance exemplified in the negative electrode can be used, for example. Graphite can 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, respectively.

[0097] Materials used as positive current collectors (conductive plates) include, for example, metallic materials containing Al, Ti, and Fe. These metallic materials can be Al, Al alloys, Ti, Ti alloys, Fe alloys, etc. Fe alloys can also be stainless steel (SUS).

[0098] There are no particular restrictions on the thickness of the positive current collector, for example, it can be above 5μm and below 300μm.

[0099] (Non-aqueous electrolyte)

[0100] Non-aqueous electrolytes with lithium-ion conductivity can be liquid electrolytes (electrolytes), gel electrolytes, or solid electrolytes. Liquid electrolytes, for example, are electrolytes containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolyte may contain known additives.

[0101] Gel electrolytes contain lithium salts and a matrix polymer, or contain lithium salts, a non-aqueous solvent, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent is used. Examples of polymer materials include fluoropolymers, acrylic resins, polyether resins, and polyethylene oxide.

[0102] As a solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (such as oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) can be used.

[0103] Liquid non-aqueous electrolytes are prepared by dissolving lithium salts in a non-aqueous solvent. Dissolving the lithium salt in the non-aqueous solvent generates lithium ions and anions.

[0104] BF4 can be listed as an anion. - ClO4 - PF6 - CF3SO3 - CF3CO2 - Anions of imides, anions of oxalate complexes, etc. Examples of anions of imides include N(SO₂CF₃)₂. - 、N(C m F 2m+1 SO2) x (C) n F 2n+ 1SO2) y - (m and n are each an independent integer greater than or equal to 0 or 1, and x and y are each an independent integer of 0, 1, or 2, satisfying x + y = 2), etc. The anions of oxalate complexes may contain boron and / or phosphorus. Examples of anions in oxalate complexes include bis(oxalateborate) anion and difluoro(oxalateborate) anion (BF2(C2O4)). - ), PF4 (C2O4) - PF2(C2O4)2 - Non-aqueous electrolytes can contain only one of these anions, or they can contain two or more.

[0105] From the viewpoint of suppressing the dendritic precipitation of lithium metal, the non-aqueous electrolyte preferably contains at least an oxalate complex anion, and more preferably an oxalate complex anion containing fluorine. Through the interaction between the fluorine-containing oxalate complex anion and lithium, lithium metal readily precipitates uniformly in fine particles. Therefore, localized precipitation of lithium metal is easily suppressed. The fluorine-containing oxalate complex anion can also be combined with other anions. Other anions may be PF6. - And / or imide anions.

[0106] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, or their halogenated derivatives. Non-aqueous electrolytes may contain only one or more of these non-aqueous solvents. Examples of halogenated derivatives include fluorides.

[0107] Examples of esters include carbonates and carboxylic acid esters. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of chain carbonates include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0108] Examples of ethers include cyclic ethers and chain ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0109] The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or higher and 3.5 mol / L or lower. The concentration of anion in the non-aqueous electrolyte can also be set to 0.5 mol / L or higher and 3.5 mol / L or lower. Furthermore, the concentration of anion of oxalate complex in the non-aqueous electrolyte can be 0.05 mol / L or higher and 1 mol / L or lower.

[0110] Non-aqueous electrolytes may contain additives. These additives can form a coating on the negative electrode. By forming a coating derived from the additive on the negative electrode, dendrite formation is easily suppressed. Examples of such additives include vinylene carbonate, FEC, and ethylene ethylene carbonate (VEC).

[0111] (Lithium-ion battery)

[0112] A lithium-ion battery comprises: a positive electrode, a negative electrode containing a negative electrode active material that absorbs and releases lithium ions, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The positive electrode and non-aqueous electrolyte can be those exemplified in lithium secondary batteries. The positive electrode composite material and positive electrode current collector contained in the positive electrode can be appropriately selected from the materials exemplified above. The non-aqueous solvent and lithium salt (anion) contained in the non-aqueous electrolyte can be appropriately selected from the materials exemplified above.

[0113] The negative electrode, for example, comprises a negative electrode current collector and a negative electrode composite material layer (the lithium-ion storage layer described above) loaded on the main surface of the negative electrode current collector. The negative electrode composite material layer may be loaded on one main surface of the negative electrode current collector or on both main surfaces of the negative electrode current collector. The negative electrode composite material and negative electrode current collector contained in the negative electrode may be appropriately selected from the materials exemplified above.

[0114] The substrate and spacers included in the separator can be those exemplified in lithium secondary batteries. The substrate can have porous sheets comprising polymer materials. Furthermore, the substrate can also have a composite material layer comprising resin materials and inorganic particles.

[0115] The spacers contained in the separators comprise resin material. The resin material contained in the spacers may be appropriately selected from the materials exemplified above.

[0116] In the case of lithium-ion batteries, the spacers can be wide sheets. In the case of lithium-ion batteries, the spacers can be specifically positioned in areas where stress easily increases when the negative electrode expands. The spacers can be positioned at the bends of electrode arrays where the positive and negative electrodes are stacked in a zigzag pattern, at the innermost periphery of wound electrode arrays, or at locations with small radii of curvature in flat electrode arrays.

[0117] Hereinafter, an example of a secondary battery (lithium secondary battery) according to this embodiment will be specifically described with reference to the accompanying drawings. The constituent elements of the lithium secondary battery of the example described below can be applied using the constituent elements described above. Furthermore, the constituent elements of the example described below can be modified based on the above description. Additionally, the matters to be described below can also be applied to the above embodiment. Furthermore, in the lithium secondary battery described below, constituent elements not required by the lithium secondary battery of this disclosure can be omitted. It should be noted that the scale of the constituent elements in the following figures has been changed for ease of understanding.

[0118] (Implementation Method 1)

[0119] Figure 1 This is a longitudinal cross-sectional view schematically illustrating an example of a secondary battery (lithium secondary battery) according to Embodiment 1. It should be noted that... Figure 1 The diagrams of the spacers and the spaces they form are omitted. Figure 1The cylindrical lithium secondary battery 10 shown includes: a cylindrical battery casing, and a wound electrode assembly 14 and a non-aqueous electrolyte (not shown) housed within the battery casing. The battery casing includes a casing body 15, a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the casing body 15. A gasket 27 is disposed between the casing body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery casing. Inside the casing body 15, insulating plates 17 and 18 are respectively disposed at both ends of the electrode assembly 14 in the winding axis direction.

[0120] The housing body 15, for example, has a stepped portion 21 formed by partially pressing the side wall of the housing body 15 from the outside. The stepped portion 21 may also be formed in a ring shape along the circumference of the side wall of the housing body 15. In this case, the sealing body 16 is supported by the surface on the opening side of the stepped portion 21.

[0121] The sealing body 16 includes a perforated metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cover 26. These components are stacked in this order within the sealing body 16. The sealing body 16 is installed at the opening of the housing body 15 with the cover 26 located outside the housing body 15 and the perforated metal plate 22 located inside the housing body 15. The aforementioned components constituting the sealing body 16 are, for example, circular or annular in shape. The lower valve body 23 and the upper valve body 25 are interconnected at their respective central portions, and the insulating member 24 is sandwiched between their respective peripheral portions. The perforated metal plate 22 and the lower valve body 23 are interconnected at their respective central portions. The upper valve body 25 and the cover 26 are interconnected at their respective central portions. That is, all components except the insulating member 24 are electrically connected to each other.

[0122] A vent (not shown) is formed on the lower valve body 23. Therefore, when the internal pressure of the battery casing rises due to abnormal heating, the upper valve body 25 expands towards the cover 26 and exits from the lower valve body 23. This disconnects the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 breaks, and gas is released from the opening (not shown) formed in the cover 26.

[0123] Figure 2 This is an enlarged view of a part of electrode assembly 14. Figure 2 include Figure 1 The part near the positive pole surrounded by region II and Figure 1 The part near the negative pole surrounded by region III.

[0124] Electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and spacers (substrate 50 and spacers 53). The substrate 50 of the positive electrode 11, negative electrode 12, and spacers is strip-shaped. The positive electrode 11, negative electrode 12, and spacers (substrate 50) are wound together such that the spacers are arranged between the positive electrode 11 and the negative electrode 12, thereby forming electrode assembly 14.

[0125] The positive electrode 11 includes a positive current collector 11a and a positive composite material layer 11b. The positive current collector 11a is electrically connected to the cover 26, which functions as a positive terminal, via a positive lead 19. Figure 2 In the diagram, negative electrode 12 is shown as a negative electrode (negative electrode current collector) in a state where no lithium metal has been deposited. Negative electrode 12 is electrically connected to the housing body 15, which functions as a negative terminal, via negative electrode lead 20.

[0126] The substrate 50 has a main surface 50a facing the positive electrode 11 and a main surface 50b facing the negative electrode 12. In Embodiment 1, the substrate 50 includes a porous sheet 51 and a composite material layer 52 (heat-resistant layer). The composite material layer 52 is formed on the main surface of the porous sheet 51 on the side 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. A space 14s is formed between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the substrate 50) through the spacer 53. Figure 2 The height h represents the height of the spacer 53.

[0127] exist Figure 2 In this substrate 50, the spacer 53 is disposed on the main surface 50a of the positive electrode 11 side, but it can also be disposed on the main surface 50b of the negative electrode 12 side. The spacer 53 is formed on the composite material layer 52, but it can 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 can also be disposed on the negative electrode 12 side. The substrate 50 can also be composed only of the porous sheet 51.

[0128] In the lithium secondary battery 10, lithium metal is deposited on the negative electrode 12 during charging. Since there is a space 14s between the positive electrode 11 and the negative electrode 12, the volume change of the electrode assembly 14 accompanying the lithium metal deposition is suppressed, and the cycle characteristics are improved.

[0129] Figure 3 This is a schematic cross-sectional view of the positive electrode 11. Figure 4 Section IV-IV. Figure 4 This is a schematic top-view diagram of the positive electrode 11. Figure 4 In the diagram, LD represents the length direction of the positive electrode 11, and WD represents the width direction of the positive electrode 11.

[0130] The strip-shaped positive electrode 11 has two ends, E1 and E2, in the width direction (WD direction) of the positive electrode 11. The positive electrode 11 (positive electrode composite material 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 material layer 11b formed on one main surface of the positive electrode current collector 11a and the positive electrode composite material 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 viewed from above (from the normal direction of the main surface of the positive electrode 11), the regions 11A and 11B of the positive electrode composite material layer 11b disposed on both sides of the positive electrode current collector 11a are approximately aligned.

[0131] The amount of positive active material per unit area M1 (the amount of positive current collector 11a per single side) in region 11A (region A1) of positive electrode composite layer 11b is less than the amount of positive active material per unit area M2 (the amount of positive current collector 11a per single side) in region 11B (region A2) of positive electrode composite layer 11b.

[0132] M1 / M2 is preferably 0.95 or less, but can be 0.5 or more and 0.95 or less. The filling amount M2 of the positive electrode active material per unit area of ​​region 11B (region A2) (the filling amount per single side of the positive electrode current collector 11a) is preferably 100 g / m². 2 Above and 300g / m 2 the following.

[0133] exist Figure 3 In this context, L0 represents the width dimension of the positive electrode 11. L1 represents the width dimension of the region 11A. For example, L1 / L0 can be less than 0.4, less than 0.2, or greater than 0.016 and less than 0.400 (or less than 0.200).

[0134] L0 can be, for example, 50~120mm. L1 can be, for example, less than 20mm, or less than 5mm. Figure 3 In the middle, the width dimension L1 of the region 11A corresponding to end E1 is approximately the same as the width dimension L1 of the end 11A corresponding to end E2, but they can also be different.

[0135] Figure 5 An example illustrating the planar shape of the spacer 53 is shown. In top view, the spacer 53 (linear protrusion 53a) is disposed on a main surface 50a of the substrate 50. The substrate 50 with the spacer 53 disposed is located on both sides (outer peripheral side and inner peripheral side) of the positive electrode 11. Figure 5 The dashed line in the figure represents the positive electrode 11 facing the substrate 50. Figure 5In the diagram, LD represents the length direction of the substrate 50 (positive electrode 11), and WD represents the width direction of the substrate 50 (positive electrode 11). It should be noted that the figures are schematic diagrams, and the thickness and / or ratio of the longitudinal and transverse dimensions of each component may not reflect the actual situation.

[0136] Figure 5 The spacer 53 includes multiple linear protrusions 53a arranged in a stripe pattern. The multiple linear protrusions 53a are arranged parallel to each other and separated along the length direction (LD direction) of the strip-shaped substrate 50. The areas where the spacer 53 is not formed constitute space 14s. Figure 5 The device includes six linear protrusions 53a, but the number of linear protrusions 53a is not limited to this. The linear protrusions 53a are arranged intermittently in the LD direction, but they can also be arranged continuously. Figure 5 In this configuration, the spacers are arranged in a striped pattern, but the arrangement of the spacers is not limited to this; the spacers can also be arranged in a mesh pattern (honeycomb pattern, etc.). Region 11A (region A1) may also have a portion P that overlaps with the protrusion 53a.

[0137] In Embodiment 1, a cylindrical secondary battery with a wound electrode assembly was described. However, the secondary battery of this embodiment is not limited to the manner of Embodiment 1 and can be applied to other methods. The shape of the secondary battery can be appropriately selected from various shapes such as cylindrical, coin-shaped, square, sheet-shaped, and flat, depending on its application. The shape of the electrode assembly is not particularly limited and can be stacked.

[0138] (Postscript)

[0139] The following technology is disclosed through the above description of the embodiments.

[0140] (Technology 1)

[0141] A secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte.

[0142] The aforementioned separator comprises a sheet-like substrate and spacers disposed on the main surface of the substrate.

[0143] The aforementioned positive electrode contains a positive electrode active material.

[0144] The aforementioned positive electrode has a region A1 comprising at least a portion of the end of the aforementioned positive electrode and a region A2 excluding the aforementioned region A1.

[0145] The amount of positive electrode active material per unit area M1 in region A1 is less than the amount of positive electrode active material per unit area M2 in region A2.

[0146] (Technology 2)

[0147] According to the secondary battery of technology 1, the region A1 has a portion P that overlaps with the spacer.

[0148] (Technology 3)

[0149] According to the secondary battery of technology 1 or 2, the strip-shaped positive electrode and the strip-shaped negative electrode are wound together with the separator in between.

[0150] (Technology 4)

[0151] According to the secondary battery described in technology 3, wherein...

[0152] The ends of the aforementioned positive electrode include both ends in the width direction of the aforementioned positive electrode.

[0153] The aforementioned region A1 is region a, which corresponds to the two ends of the aforementioned positive electrode in the width direction.

[0154] (Technology 5)

[0155] According to any one of the technologies 1 to 4, in the secondary battery, the ratio of the amount of positive electrode active material per unit area M1 in the region A1 to the amount of positive electrode active material per unit area M2 in the region A2 is 0.95 or less.

[0156] (Technology 6)

[0157] According to the secondary battery of technology 5, the filling amount M2 of the positive electrode active material per unit area of ​​the aforementioned region A2 is 100 g / m². 2 Above and 300g / m 2 the following.

[0158] (Technology 7)

[0159] According to any one of the techniques 1 to 6, in the secondary battery, lithium metal is deposited in the negative electrode during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging.

[0160] (Technology 8)

[0161] The secondary battery according to any one of art 1 to 7, wherein the spacer includes the protrusions arranged in a predetermined repeating pattern.

[0162] (Technology 9)

[0163] According to any one of art 1 to 7, in a secondary battery, a plurality of linear protrusions are arranged in parallel and separated from each other along the length direction of the substrate.

[0164] (Technology 10)

[0165] The secondary battery according to any one of art 1 to 9, wherein the spacer comprises a resin material.

[0166] (Technology 11)

[0167] The secondary battery according to any one of art 1 to 10, wherein the substrate comprises a porous sheet containing a polymer material.

[0168] (Technology 12)

[0169] According to the secondary battery of technology 11, the substrate further comprises a composite material layer comprising resin material and inorganic particles.

[0170] [Example]

[0171] The secondary battery of this disclosure will now be described in more detail based on embodiments and comparative examples. However, this disclosure is not limited to the following embodiments.

[0172] Batteries A1~A6 and Batteries B1~B2

[0173] (The production of the positive electrode)

[0174] A layered lithium transition metal oxide (NCA: positive electrode active material), acetylene black (AB: conductive material), and polyvinylidene fluoride (PVdF: binder material) containing Li, Ni, Co, and Al (with a molar ratio of Li to the sum of Ni, Co, and Al of 1.0) and exhibiting a rock-salt-type structure were mixed at a mass ratio of NCA:AB:PVdF = 95:2.5:2.5. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added and the mixture was stirred to prepare a positive electrode slurry. The obtained positive electrode slurry was coated onto both sides of a strip of Al foil (positive electrode current collector), dried, and the coating of the positive electrode composite material was calendered using rollers. Finally, the resulting laminate of the positive electrode current collector and positive electrode composite material was cut to a specified electrode size. This yields a positive electrode with a positive electrode composite material layer (65 μm thick on each side) on both sides of the positive electrode current collector.

[0175] The positive electrode region A1 is defined as region a corresponding to the two ends of the positive electrode current collector in the width direction. Figure 3 , 4 Region 11A). Width of the positive electrode ( Figure 3 L0 in the figure is 57mm, and the width of region A1 is ( Figure 3 L1 is set to 10mm. L1 / L0 is 0.175.

[0176] Area A1 ( Figure 3 , 4 The amount of positive active material per unit area M1 in region 11A and region A2 ( Figure 3 , 4 The filling amount M2 of the positive active material per unit area in region 11B is set to the values ​​shown in Table 1. It should be noted that the filling amount of the positive active material is the filling amount per single side of the positive current collector. The filling amount of the positive active material is adjusted by changing the coating amount of the positive slurry (the coating amount per single side of the positive current collector).

[0177] (Making the negative electrode)

[0178] Prepare a strip of electrolytic copper foil (15μm thick) as the negative electrode current collector.

[0179] (Preparation of the separator)

[0180] As a substrate, a 20 μm thick polyethylene microporous film (porous sheet) is prepared.

[0181] Insulating particles (median particle size: 3μm, volume resistivity: 10) were used. 14 A dispersion of spacer material was prepared by mixing 50 parts by volume of polyvinylidene fluoride (PVdF) as resin material and N-methyl-2-pyrrolidone (NMP) as dispersion medium.

[0182] Next, using a dispensing machine, the dispersion of the spacer material is sprayed onto the microporous film, and the coating is then vacuum dried to form... Figure 5 The spacers are arranged in a striped pattern. Specifically, protrusions are formed in a striped pattern on one main surface of the microporous film. This results in a separator having a substrate and spacers.

[0183] The linear protrusions constituting the spacer are designed with a width of 0.25 mm and a height of 30 μm.

[0184] (Preparation of non-aqueous electrolytes)

[0185] Ethyl carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC=30:70. LiPF6 was dissolved in the resulting mixed solvent at a concentration of 1 mol / L, and LiBF2(C2O4) was dissolved at a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte.

[0186] (Battery assembly)

[0187] In an inactive gas atmosphere, the positive and negative current collectors are wound into a spiral shape with the aforementioned separator in between to fabricate an electrode assembly. At this time, the separator is positioned so that the spacer faces the positive electrode. Region A1 has a portion P that overlaps with the spacer. The electrode assembly is housed in a bag-shaped outer casing formed from a laminate having an Al layer. After injecting a non-aqueous electrolyte, the outer casing is sealed to complete the lithium secondary battery.

[0188] [Evaluation of Cyclic Performance (Durability)]

[0189] Charge-discharge tests were conducted on all the obtained batteries. During the charge-discharge tests, the batteries were charged in a constant temperature bath at 25°C under the following conditions, then stopped for 20 minutes, and then discharged under the following conditions.

[0190] (Charge)

[0191] Charge the battery at a constant current of 0.5C until the battery voltage reaches 4.2V. Then, charge it at a constant voltage of 4.2V until the current reaches 15mA.

[0192] (Discharge)

[0193] Discharge at a constant current of 0.5C until the battery voltage reaches 2.5V.

[0194] The above charging and discharging process is considered as one cycle, and this charging and discharging process is repeated. This process is continued until the discharge capacity is lower than 80% of the discharge capacity of the first cycle. The final cycle number is calculated when the discharge capacity is greater than 80% of the discharge capacity of the first cycle. A high number of cycles indicates good cycle characteristics (durability).

[0195] The evaluation results are shown in Table 1. It should be noted that in Table 1, A1 to A6 are examples, and B1 to B2 are comparative examples.

[0196] [Table 1]

[0197]

[0198] Compared with batteries B1 to B2, batteries A1 to A6 exhibit superior cycle characteristics.

[0199] Industrial availability

[0200] The secondary battery disclosed herein can be used in electronic devices such as mobile phones, smartphones, and tablet computers, including hybrid and plug-in hybrid electric vehicles, and household batteries combined with solar cells.

[0201] The present invention has been described with reference to preferred embodiments, but such disclosure should not be interpreted as limiting. Various modifications and alterations will be apparent to those skilled in the art from the foregoing disclosure. Therefore, the appended claims should be construed as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0202] Explanation of reference numerals in the attached figures

[0203] 10: Lithium secondary battery; 11: Positive electrode; 11A: Region A1; 11B: Region A2; 12: Negative electrode; 14: Electrode assembly; 14s: Space; 15: Main body of the casing; 16: Sealing body; 23: Lower valve body; 25: Upper valve body; 50: Substrate; 51: Porous sheet; 52: Composite material layer; 53: Spacer; 53a: Protrusion.

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 has a sheet-like substrate and spacers disposed on the main surface of the substrate. The positive electrode contains a positive electrode active material. The positive electrode has a region A1 comprising at least a portion of the end of the positive electrode and a region A2 excluding the region A1. The amount of positive electrode active material per unit area M1 in region A1 is less than the amount of positive electrode active material per unit area M2 in 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 strip-shaped positive electrode and the strip-shaped negative electrode are wound together with the separator in between.

4. The secondary battery according to claim 3, wherein, The positive electrode ends include both ends in the width direction of the positive electrode. Region A1 is region a, which corresponds to both ends of the positive electrode in the width direction.

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

6. The secondary battery according to claim 5, wherein, The amount of positive electrode active material per unit area M2 in region A2 is 100 g / m². 2 Above and 300g / m 2 the following.

7. The secondary battery according to any one of claims 1 to 6, wherein, In the negative electrode, lithium metal is deposited during charging and dissolves 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 prescribed repeating pattern.

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

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

11. The secondary battery according to any one of claims 1 to 6, wherein, The substrate has a porous sheet containing a polymer material.

12. The secondary battery according to claim 11, wherein, The substrate also includes a composite material layer comprising resin material and inorganic particles.

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