Lithium secondary battery

Abstract

This lithium secondary battery comprises a positive electrode, a negative electrode, a separator that is disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Lithium metal is deposited at the negative electrode during charging and dissolved during discharging. The separator is provided with a sheet-shaped base material and a spacer that is disposed on the main surface of the base material. The spacer includes a protrusion. A ratio St / S is defined as X, where St is the area of a portion At in which a region A and the protrusion overlap, and S is the area of the region A where the base material faces the positive electrode. The ratio Lt / L is defined as Y, where Lt is the length of a portion in which an end edge portion of the positive electrode and the protrusion overlap, and L is the length of the end edge portion along the outer shape of the positive electrode. At this time, the relationship Y<X is satisfied.

Description

Lithium secondary battery

[0001] The present disclosure relates to lithium secondary batteries.

[0002] Lithium ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Lithium secondary batteries (lithium metal secondary batteries) are promising non-aqueous electrolyte secondary batteries with capacities even higher than lithium ion batteries. In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging, and dissolves during discharging, releasing lithium ions into the non-aqueous electrolyte.

[0003] In lithium secondary batteries, lithium metal is deposited on the negative electrode during charging, so it is necessary to provide a space between the separator substrate and the electrode to ensure a space for lithium to deposit.

[0004] Patent Document 1 proposes a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte having lithium ion conductivity, wherein lithium metal is deposited on the negative electrode during charging and the lithium metal is dissolved from the negative electrode during discharging; a spacer is provided between the separator and at least one of the positive electrode and the negative electrode; a first length of the separator in a first direction D1 is smaller than a second length of the separator in a second direction D2 intersecting with the first direction D1; and in a cross section of the spacer taken along the thickness direction of the separator and the first direction D1, at least one of an angle formed between the separator and the spacer on the spacer side and an angle formed between the spacer and an electrode in contact with the spacer is greater than 90°.

[0005] International Publication No. 2021 / 192645

[0006] Stress caused by Li deposition on the negative electrode is concentrated locally near the overlapping portion of the edge of the positive electrode and the protrusion (spacer), which may damage the substrate and cause an internal short circuit.

[0007] One aspect of the present disclosure relates to a lithium 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 lithium metal precipitates in the negative electrode during charging and dissolves during discharging; the separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate, the spacer including a convex portion; and wherein X is a ratio of an area St of a portion At where the region A and the convex portion overlap to an area S of a region A where the substrate faces the positive electrode: St / S; and Y is a ratio of a length Lt of a portion where an edge portion of the positive electrode and the convex portion overlap to a length L of an edge portion along an outline of the positive electrode: Lt / L, such that Y<X.

[0008] According to the present disclosure, it is possible to suppress the occurrence of an internal short circuit in a lithium secondary battery.

[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 lithium secondary battery according to an embodiment of the present disclosure; Fig. 3 is a sectional view schematically showing a main part of the lithium secondary battery shown in Fig. 1; Fig. 4 is a top view showing an example of a spacer; Fig. 5 is a top view showing another example of a spacer; Fig. 6 is a top view showing yet another example of a spacer; Fig. 7 is a top view showing yet another example of a spacer; Fig. 8 is a top view showing yet another example of a spacer; Fig. 9 is a top view of a spacer provided in battery B1 of a comparative example; Fig. 10 is a top view of a spacer provided in battery B2 of a comparative example.

[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] (Lithium Secondary Battery) A lithium secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on one or both sides of the positive electrode current collector. In the negative electrode, lithium metal is deposited during charging and dissolves during discharge. Specifically, the negative electrode includes at least a negative electrode current collector, and lithium metal is deposited on the negative electrode current collector during charging. The non-aqueous electrolyte has lithium ion conductivity. The lithium secondary battery is also called a lithium metal secondary battery.

[0013] 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).

[0014] The separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate. The spacer includes a convex portion. X is defined as St / S, which is the ratio of the area St of the portion At where the region A of the substrate faces the positive electrode (positive electrode mixture layer) to the area S of the region A. Y is defined as Lt / L, which is the ratio of the length L of the portion where the edge of the positive electrode overlaps with the convex portion to the length L of the edge of the positive electrode (positive electrode mixture layer) along the outer shape of the positive electrode. In this case, the relationship Y<X is satisfied. When there are multiple overlapping portions between the edge of the positive electrode and the convex portion, the length Lt is the total length of the multiple overlapping portions.

[0015] When the relationship Y<X is satisfied, the concentration of stress caused by precipitated Li near the overlapping point between the positive electrode edge portion and the convex portion is alleviated, damage to the substrate due to the concentration of stress is suppressed, and the occurrence of an internal short circuit due to damage to the substrate is suppressed.

[0016] For example, when the convex portions are uniformly distributed on the main surface of the substrate (positive electrode), the greater the convex portion distribution ratio, the more likely it is that the spacers will stably form a space throughout the electrode assembly. The required amount of space is determined according to the actual battery design, and the convex portion distribution ratio is set based on the required amount of space. When the convex portions are uniformly distributed, the convex portion distribution ratio is approximately the same at the end of the positive electrode and in the area other than the end. In contrast, in the present disclosure, the convex portion distribution ratio at the end of the positive electrode (the area facing the edge of the positive electrode) is smaller than that in the area other than the end so as to satisfy Y<X, thereby alleviating the above-mentioned stress concentration. Because the area where the convex portion distribution ratio is reduced is limited to the area corresponding to the end of the positive electrode, the effect of reducing the convex portion distribution ratio on the formation of a space between the positive electrode and the negative electrode is very small and is kept to a minimum.

[0017] From the viewpoint of suppressing damage to the substrate due to the above-mentioned stress concentration, Y<2X / 3 is preferable, and Y<X / 3 is more preferable.

[0018] From the viewpoint of suppressing damage to the substrate due to the above-mentioned stress concentration, Y may be 0.4 or less, 0.3 or less, 0.1 or less, 0.05 or less, or even 0. From the viewpoint of stably forming a space throughout region A, Y may be greater than 0, or may be 0.01 or more, or 0.05 or more. The range of Y may be, for example, 0 or more and 0.4 or less.

[0019] From the viewpoint of stably forming spaces by the convex portions in region A, X may be 0.03 or more, or may be 0.05 or more. From the viewpoint of ensuring the volume of Li precipitates in region A, X may be 0.45 or less, 0.3 or less, or 0.2 or less.

[0020] In a plan view, the positive electrode has, for example, a rectangular outer shape. In this case, the edge portion of the positive electrode (positive electrode mixture layer) includes first to fourth edge portions corresponding to the four sides of the rectangle. When the ratio Lnt / Ln is the ratio of the length Ln of an arbitrary nth edge portion (the positive electrode mixture layer included in the nth edge portion) selected from the first to fourth edge portions, to the length Lnt of the portion where the nth edge portion overlaps the convex portion, Yn, it is preferable that the relationship Yn<X is satisfied in any case where n = 1 to 4. In any case where n = 1 to 4, Yn is preferably 0 or more and 0.4 or less. n is an integer from 1 to 4.

[0021] The protrusions are preferably arranged so as not to overlap with the edge of the positive electrode (positive electrode mixture layer). The area where the protrusions are formed may be adjusted so that the protrusions do not overlap with the edge (n-th edge) of the positive electrode (positive electrode mixture layer), and when the protrusions are linear, the linear protrusions may be arranged intermittently to provide defects.

[0022] The positive electrode, negative electrode, and separator may be collectively referred to as an "electrode group." The lithium secondary battery may include a wound electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator (substrate) interposed therebetween. Alternatively, the lithium secondary battery may include a stacked electrode group in which a positive electrode and a negative electrode are stacked with a separator (substrate) interposed therebetween.

[0023] In a lithium secondary battery, the area of ​​the negative electrode facing the positive electrode is usually larger than the area of ​​the positive electrode, and the negative electrode is disposed so as to face the entirety of one or both main surfaces of the positive electrode (the positive electrode mixture layer formed on one or both main surfaces of the positive electrode) via a separator.

[0024] The negative electrode and the separator may be disposed on both sides of the positive electrode. That is, the negative electrode may be disposed so as to face both main surfaces of the positive electrode (positive electrode mixture layers formed on both main surfaces of the positive electrode) via the separator. In the case of a wound electrode group, the negative electrode and the separator are disposed on both sides (outer and inner sides) of the positive electrode. In this case, it is preferable that the separator disposed on at least one side of the positive electrode satisfies the relationship Y<X, and the separators disposed on both sides of the positive electrode each satisfy the relationship Y<X.

[0025] The spacers arranged on both sides (outer and inner sides) of the positive electrode may be arranged so as to overlap with each other via the positive electrode, or may be arranged with their positions shifted entirely or partially. The insulating layers arranged on both sides (outer and inner sides) of the positive electrode may be arranged so as to overlap with each other via the positive electrode, or may be arranged with their positions shifted entirely or partially. The spacers arranged on both sides (outer and inner sides) of the positive electrode may have the same arrangement pattern or different arrangement patterns.

[0026] The negative electrode and the separator may be disposed on one side of the positive electrode. That is, the negative electrode may be disposed so as to face one main surface of the positive electrode (the positive electrode mixture layer formed on one main surface of the positive electrode) via the separator. In this case, the separator disposed on one side of the positive electrode satisfies the relationship Y<X.

[0027] (Separator) The separator includes a sheet-like substrate and a spacer disposed on the main surface of the substrate.

[0028] (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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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).

[0037] 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.

[0038] (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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The spacer includes a protrusion. The spacer may include a linear protrusion and / or a dot-shaped protrusion. From one viewpoint, the linear protrusion is a ridge-shaped protrusion. The linear protrusion may be arranged intermittently or continuously. The linear protrusion may be linear or curved.

[0047] 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.

[0048] The spacer preferably has a predetermined repeating pattern. That is, it is preferable that the convex portions are arranged in a predetermined repeating pattern. The linear convex portions may be arranged in a striped pattern or a mesh pattern. The mesh pattern may be a collection of polygons. An example of a mesh pattern includes a shape in which polygons are combined so as to share a side. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons may be combined. The mesh pattern may be a honeycomb pattern. Furthermore, dot-shaped convex portions may be arranged in a predetermined repeating pattern.

[0049] 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.

[0050] 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.

[0051] The spacers are formed, for example, by applying a coating liquid containing spacer components and a liquid component to a predetermined location on a substrate and drying the coating. Examples of the liquid component include N-methyl-2-pyrrolidone. The coating may be performed using a dispenser or by a known printing method such as gravure printing, inkjet printing, or screen printing. The drying may be performed by a known method such as drying by heating or natural drying.

[0052] (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.

[0053] 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.

[0054] 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.

[0055] The lithium ion occlusion layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a binder, a thickener, a conductive agent, etc. in addition to the negative electrode active material.

[0056] 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).

[0057] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0058] Examples of the binder include fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, rubber polymer, etc. Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0059] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0060] 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.

[0061] 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.

[0062] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides. The positive electrode is obtained, for example, by applying a positive electrode mixture slurry including the positive electrode active material, the conductive material, and the binder to both sides of the positive electrode current collector, drying the coating, and then rolling.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] As the binder, conductive material, etc., for example, those exemplified for the negative electrode can be used. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0068] 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).

[0069] 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.

[0070] (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.

[0071] 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.

[0072] As the solid electrolyte, for example, a material known in all-solid-state lithium ion secondary batteries (for example, oxide-based solid electrolyte, sulfide-based solid electrolyte, halide-based solid electrolyte, etc.) can be used.

[0073] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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).

[0081] An example of a lithium secondary battery according to the present embodiment will be described in detail 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.

[0082] (Embodiment 1) FIG. 1 is a longitudinal cross-sectional view schematically illustrating an example of a 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode mixture layer 11b. The positive electrode current collector 11a is electrically connected to a cap 26, which functions as a positive electrode terminal, via a positive electrode lead 19. In FIG. 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.

[0089] The substrate 50 has a main surface 50a facing the positive electrode 11 and a main surface 50b facing the negative electrode 12. The substrate 50 of embodiment 1 includes a porous sheet 51 and a composite material layer 52 (heat-resistant layer). The composite material layer 52 is formed on one of the two main surfaces of the porous sheet 51, the main surface facing the negative electrode 12. In embodiment 1, a spacer 53 is formed on the main surface 50a facing the positive electrode 11. The spacer 53 is formed on the composite material layer 52 and is in contact with the positive electrode 11. The spacer 53 forms a space 14s between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the substrate 50). FIG. 2 shows the height h of the spacer 53.

[0090] 2, the spacer 53 is disposed on the main surface 50a of the substrate 50 on the positive electrode 11 side, but may also be disposed on the main surface 50b of the substrate 50 on the negative electrode 12 side. The spacer 53 is formed on the composite material layer 52, but may also be formed on the porous sheet 51. The composite material layer 52 of the substrate 50 is disposed on the positive electrode 11 side, but may also be disposed on the negative electrode 12 side.

[0091] During charging of the lithium secondary battery 10, lithium metal is deposited on the negative electrode 12. Because a space 14s exists between the positive electrode 11 and the negative electrode 12, the volume change of the electrode group 14 that accompanies the deposition of lithium metal is reduced, improving the cycle characteristics.

[0092] 3 to 7 show examples of the planar shape of the spacer 53. In plan view, the spacer 53 (linear convex portion 53a) is arranged on one main surface of the substrate 50. The substrate 50 on which the spacer 53 (convex portion 53a) is arranged is arranged on the inner circumferential side and the outer circumferential side of the positive electrode 11. In each figure, the positive electrode 11 facing the substrate 50 is represented by a dashed line. Note that each figure is a schematic diagram, and the aspect ratio of each member does not necessarily reflect the actual size.

[0093] 3 to 5 includes a plurality of linear protrusions 53a arranged in a stripe pattern. The regions where the spacers 53 are not formed form spaces 14s. The linear protrusions 53a are arranged parallel to one another along the length direction (LD direction) of the band-shaped substrate 50. The linear protrusions 53a are arranged spaced apart from one another. The linear protrusions 53a are arranged intermittently and each have a defect portion 53b.

[0094] 3 to 5, six linear protrusions 53a are arranged, but the number of linear protrusions 53a is not limited to this. The defects in Figures 3 to 5 may be arranged randomly or in a certain repeating pattern.

[0095] 6 and 7 include linear protrusions 53a arranged in a honeycomb pattern. Areas where the spacers 53 are not formed form spaces 14s. The linear protrusions 53a are arranged intermittently and have defects 53b.

[0096] 6 and 7, the linear protrusions corresponding to one side of the hexagon have defects at both ends, but may have defects in the center. In Fig. 6, the edge E3 of the positive electrode and the linear protrusions 53a do not overlap, but the linear protrusions may be arranged so that they do not overlap with the edge E4 of the positive electrode.

[0097] The dashed lines in FIGS. 3 to 7 represent the positive electrode 11 facing the substrate 50. That is, the dashed lines in FIGS. 3 to 7 represent the outline of the outer shape of the positive electrode 11 facing the substrate 50. The area of ​​the region surrounded by the dashed line in the figures (the region where the substrate 50 faces the positive electrode mixture layer 11b) is the area S of the region A where the substrate 50 faces the positive electrode 11. The length of the dashed line in the figures (the length of the edge portion of the positive electrode mixture layer 11b along the outer shape of the positive electrode 11) is the length L of the edge portion along the outer shape of the positive electrode 11. The ratio of the area St of the portion At where the region A (the region surrounded by the dashed line in the figures) and the protrusion 53a overlap to the above area S: St / S is defined as X. The ratio of the length Lt of the portion where the edge portion of the positive electrode 11 (the dashed line in the figures) and the protrusion 53a overlap to the above length L: Lt / L is defined as Y. At this time, the convex portions 53a are arranged on the substrate 50 so as to satisfy the relationship Y<X.

[0098] The dashed lines in Figures 3 to 7 indicate the rectangular outline of the positive electrode 11 in plan view. The positive electrode 11 has four edge portions E1 to E4 corresponding to the four sides of the rectangle. Specifically, the positive electrode 11 has edge portions E1 and E2 corresponding to the two sides extending along the LD direction, and edge portions E3 and E4 corresponding to the two sides extending along the width direction. The ratio of the length Lnt of the portion where the edge portion En overlaps with the convex portion to the length Ln of any edge portion En selected from the edge portions E1 to E4: Lnt / Ln is defined as Yn. n is an integer from 1 to 4. In any case where n = 1 to 4, it is preferable to satisfy the relationship Yn < X. In the cases of Figures 3 to 7, it is easy to obtain a spacer that satisfies the relationship Yn < X in any case where n = 1 to 4.

[0099] The values ​​of Yn corresponding to the edge portions E1 to E4 (n = 1 to 4) are designated Y1 to Y4, respectively. In this case, Y1 and Y2 are 0 in Figures 3 to 5. As shown in Figures 3 to 5, it is preferable that the edge portions E1 and E2 of the positive electrode do not overlap with the linear protrusions 53a along the LD direction. The relationship between Y3 and Y4 is as follows: Figure 5 < Figure 4 < Figure 3. In Figure 5, all of Y1 to Y4 are 0. In Figure 3, the edge portions E3 to E4 overlap with four linear protrusions, in Figure 4, they overlap with two linear protrusions, and in Figure 5, they do not overlap with any linear protrusions. As shown in Figures 4 and 5, Y3 and Y4 may be adjusted by providing defects 53b in the protrusions 53a.

[0100] 6, Y3 is 0, and in Fig. 7, all of Y1 to Y4 are 0. As shown in Figs. 6 and 7, Yn may be set to 0 by not forming a convex portion outside the edge portion En of the positive electrode 11 (outside the region A).

[0101] In Figures 3 to 7, the spacers are arranged in a stripe or honeycomb pattern, but the spacer arrangement pattern is not limited to this. The spacers may also be arranged in a dot pattern, for example. The positive electrodes in Figures 3 to 7 may have a current collector exposed portion along the width direction in the center in the LD direction where the positive electrode mixture layer is not supported, for connection to the positive electrode lead. In this case, the current collector exposed portion is not included in region A and edge portions E1 and E2.

[0102] In the first embodiment, a cylindrical lithium secondary battery having a wound electrode group has been described. However, the lithium 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 lithium 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.

[0103] (Additional Notes) The above embodiments disclose the following technologies. (Technology 1) A lithium secondary battery comprising: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein lithium metal precipitates in the negative electrode during charging and dissolves during discharging, and the separator comprises a sheet-like substrate and a spacer disposed on a main surface of the substrate, and the spacer includes a convex portion, and wherein X is a ratio of an area St of a portion At where the region A and the convex portion overlap to an area S of a region A of the substrate facing the positive electrode: St / S, and Y is a ratio of a length Lt of a portion where the edge of the positive electrode and the convex portion overlap to a length L of an edge along the outer shape of the positive electrode: Lt / L, where Y satisfies the relationship Y<X. (Technology 2) The lithium secondary battery according to Technology 1, wherein Y is greater than or equal to 0.4. (Technology 3) The lithium secondary battery according to Technology 1 or 2, wherein, in a plan view, the positive electrode has a rectangular outer shape, and edge portions of the positive electrode include first to fourth edge portions corresponding to four sides of the rectangle, and wherein, when Yn is a ratio of a length Lnt of an overlapping portion of the nth edge portion and the protrusion to a length Ln of an arbitrary nth edge portion selected from the first to fourth edge portions: Lnt / Ln, the relationship Yn<X is satisfied in any case where n = 1 to 4. (Technology 4) The lithium secondary battery according to Technology 3, wherein Yn is 0 or more and 0.4 or less in any case where n = 1 to 4. (Technology 5) The lithium secondary battery according to any one of Technology 1 to 4, wherein the positive electrode includes a positive electrode current collector and positive electrode mixture layers supported on both sides of the positive electrode current collector, and the protrusions are arranged so as not to overlap with the edge portions of the positive electrode mixture layers. (Technology 6) The lithium secondary battery according to any one of Technologies 1 to 5, wherein the spacer is disposed on one main surface of the substrate. (Technology 7) The lithium secondary battery according to any one of Technologies 1 to 6, wherein the spacer includes the protrusions arranged in a predetermined repeating pattern. (Technology 8) The lithium secondary battery according to any one of Technologies 1 to 7, wherein the spacer includes the linear protrusions arranged intermittently. (Technology 9) The lithium secondary battery according to any one of Technologies 1 to 8, wherein the spacer includes a resin material.(Technology 10) The lithium secondary battery according to any one of Technologies 1 to 9, wherein the spacer includes a non-porous structure that is impermeable to lithium ions. (Technology 11) The lithium secondary battery according to any one of Technologies 1 to 10, wherein the substrate includes a porous sheet containing a polymer material. (Technology 12) The lithium secondary battery according to Technology 11, wherein the substrate further includes a composite material layer containing a resin material and inorganic particles.

[0104] [Examples] The lithium secondary battery according to the present disclosure will be described in more detail below based on examples and comparative examples, although the present disclosure is not limited to the following examples.

[0105] Batteries A1 to A3, B1 (Preparation of Positive Electrodes) Positive electrode active material, acetylene black (AB; conductive material), polyvinylidene fluoride (PVdF; binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to prepare a positive electrode mixture slurry. The positive electrode active material was a rock-salt lithium-containing transition metal oxide (NCA; positive electrode active material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al was 1.0) and having a layered structure. The mass ratio of NCA:AB:PVdF in the positive electrode mixture slurry was 95:2.5:2.5. The positive electrode mixture slurry was applied to both sides of a strip of Al foil (positive electrode current collector), and the coating was dried and rolled to form a positive electrode mixture layer. The positive electrode current collector having the positive electrode mixture layers formed on both sides was cut to a predetermined size to obtain a positive electrode.

[0106] (Preparation of Negative Electrode Current Collector) A strip of electrolytic copper foil (thickness: 12 μm) was prepared as a negative electrode current collector.

[0107] (Preparation of Substrate) A 10 μm-thick polyethylene microporous thin film was prepared. One main surface of the microporous thin film was coated with a coating liquid containing paraphenylene terephthalamide, an aromatic polyamide, as the resin material and alumina as inorganic particles. The coating liquid was an N-methyl-2-pyrrolidone solution containing 5.8% by mass of dissolved calcium chloride, and the concentration was adjusted to 2 wt% of aromatic polyamide and 4 wt% of alumina. The microporous thin film on which the coating film was formed was left for 1 hour in an atmosphere at 25°C and 70% relative humidity to precipitate the aromatic polyamide. Next, NMP and calcium chloride in the coating film were removed by water washing. The coating film was dried at 60°C for 5 minutes to form a composite material layer (heat-resistant layer). In this way, a substrate comprising a microporous thin film and a composite material layer was obtained.

[0108] (Formation of Spacers on the Main Surface of the Substrate) A coating liquid containing polyvinylidene fluoride and alumina particles (inorganic filler) was applied to the microporous thin film surface of the substrate, and the coating was dried. This resulted in the formation of spacers in the pattern (striped) shown in Figure 3, Figure 4, Figure 5, or Figure 8. In this way, a separator having a substrate and spacers was obtained. The linear protrusions constituting the spacers had a width of 0.25 mm and a height of 30 μm. The linear protrusions were arranged intermittently.

[0109] (Preparation of non-aqueous electrolyte) 1,2-dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (CHF ２ (CF ２ OCH ２ )CF ３ An ether-based mixed solvent containing lithium bis(sulfonylimide) (LiFSI) at 1 mol / L and LiBF at a volume ratio of 1:2 was prepared. ２ (C ２ O ４ ) was dissolved in the ethanol to a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte (ether-based electrolyte solution).

[0110] (Assembly of Battery) In an inert gas atmosphere, a positive electrode and a negative electrode current collector were spirally wound with a separator interposed therebetween to prepare an electrode assembly. In this way, a wound electrode assembly having the structure shown in FIG. 2 was obtained. At this time, the electrode assembly was constructed so that the separators (substrates with spacers arranged thereon) shown in FIG. 3, FIG. 4, FIG. 5, or FIG. 8 were arranged on the inner and outer circumferential sides of the positive electrode, respectively. The positional relationship between the linear protrusions arranged on the inner and outer circumferential sides of the positive electrode and the positive electrode was as shown in FIG. 3, FIG. 4, FIG. 5, or FIG. 8. The separator was arranged so that the main surface of the substrate on which the spacers were formed faced the positive electrode.

[0111] The values ​​of X and Y were as shown in Table 1. In Fig. 8, the overlapping portion between the positive electrode edge portion and the protrusion 53a was larger than in Figs. 3 to 5, and Y was 0.42. The maximum value of Yn was 0.02 for Y3 and Y4 corresponding to E3 and E4 in Fig. 3, 0.01 for Y3 and Y4 corresponding to E3 and E4 in Fig. 4, and 0.875 for Y1 corresponding to E1 in Fig. 8. In Fig. 5, all of Y1 to Y4 corresponding to E1 to E4 were 0.

[0112] The electrode group was housed in a cylindrical case body with a bottom, and a non-aqueous electrolyte was poured into it. A sealing member was placed over the opening of the case body via a gasket, sealing the electrode group and non-aqueous electrolyte inside the battery case. In this way, a lithium secondary battery having the structure shown in Figure 1 was completed. In Table 1, A1 to A3 are examples, and B1 is a comparative example.

[0113] <Batteries A4 to A5, B2> Spacers were formed using a dispenser in the pattern (honeycomb shape) shown in Fig. 6, Fig. 7, or Fig. 9. An electrode group was constructed such that the separators (substrates on which spacers were arranged) shown in Fig. 6, Fig. 7, or Fig. 9 were respectively arranged on the inner and outer circumferential sides of the positive electrode. The linear protrusions respectively arranged on the inner and outer circumferential sides of the positive electrode were positioned relative to the positive electrode as shown in Fig. 6, Fig. 7, or Fig. 9.

[0114] The values ​​of X and Y were as shown in Table 1. In Fig. 9, the overlapping portion between the positive electrode edge portion and the protrusion 53a was larger than in Figs. 6 and 7, and Y was 0.14. The maximum value of Yn was 0.04 for Y1 and Y2 corresponding to E1 and E2 in Fig. 6. In Fig. 7, all of the values ​​of Y1 to Y4 corresponding to E1 to E4 were 0, and in Fig. 9, all of the values ​​of Y1 to Y4 corresponding to E1 to E4 were 0.14.

[0115] Other than the above, batteries A4, A5, and B2 were fabricated in the same manner as battery A1. In Table 1, A4 and A5 are examples, and B2 is a comparative example.

[0116] [Evaluation] (Charge / Discharge Test) A charge / discharge test was performed on each of the obtained batteries. In the charge / discharge test, the battery was charged in a thermostatic chamber at 25° C. under the following conditions, then rested for 20 minutes, and discharged under the following conditions.

[0117] (Charging) The battery was charged at a constant current of 10 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 4.1 V. Thereafter, the battery was charged at a constant voltage of 4.1 V until the current value per unit area of ​​the electrode reached 1 mA.

[0118] (Discharge) The battery was discharged at a constant current of 10 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 3.0 V.

[0119] The above charge and discharge constitute one cycle, and charge and discharge were repeated. When the charge capacity at the mth cycle was 1% or more higher than the charge capacity at the previous (m-1)th cycle, it was determined that abnormal charging had occurred due to the occurrence of a small internal short circuit, and the charge and discharge test was terminated. The number of cycles at this time, m, was determined as the number of cycles at which abnormality occurred. Charge and discharge were repeated until the discharge capacity reached 90% of the discharge capacity at the first cycle, and if no abnormal charging occurred, it was determined that there was no abnormality.

[0120] The evaluation results are shown in Table 1.

[0121]

[0122] In Batteries A1 to A5, the cycle of abnormality occurrence was delayed and the occurrence of small internal short circuits was suppressed compared to Batteries B1 and B2. In particular, Batteries A3 and A5 showed no abnormalities and were significantly more effective in suppressing the occurrence of internal short circuits.

[0123] The lithium 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.

[0124] 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.

[0125] 10: Lithium secondary battery, 11: Positive electrode, 12: Negative electrode, 14: Electrode group, 14s: Space, 15: Case body, 16: Sealing body, 23: Lower valve body, 25: Upper valve body, 50: Substrate, 51: Porous sheet, 52: Composite material layer, 53: Spacer, 53a: Convex portion, 53b: Defective portion

Claims

1. A lithium secondary battery comprising: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein lithium metal precipitates in the negative electrode during charging and dissolves during discharging, wherein the separator comprises a sheet-like substrate and a spacer disposed on a main surface of the substrate, wherein the spacer includes a convex portion, wherein X is a ratio of an area St of a portion At where the region A and the convex portion overlap to an area S of a region A of the substrate facing the positive electrode: St / S, and Y is a ratio of a length Lt of a portion where an edge portion of the positive electrode and the convex portion overlap to a length L of an edge portion along an outline of the positive electrode: Lt / L, satisfying the relationship Y<X.

2. The lithium secondary battery according to claim 1, wherein Y is 0 or more and 0.4 or less.

3. The lithium secondary battery of claim 1, wherein, in a plan view, the positive electrode has a rectangular outer shape, and an edge portion of the positive electrode includes first to fourth edge portions corresponding to four sides of the rectangle, and wherein, when Yn is a ratio of a length Lnt of an overlapping portion of the nth edge portion and the convex portion to a length Ln of an arbitrary nth edge portion selected from the first to fourth edge portions: Lnt / Ln, the relationship Yn<X is satisfied for any of n=1 to 4.

4. The lithium secondary battery according to claim 3, wherein Yn is 0 or more and 0.4 or less in all cases where n is 1 to 4.

5. The lithium secondary battery according to claim 1, wherein the positive electrode comprises a positive electrode current collector and a positive electrode mixture layer supported on both sides of the positive electrode current collector, and the protrusion is positioned so as not to overlap an edge portion of the positive electrode mixture layer.

6. The lithium secondary battery according to any one of claims 1 to 5, wherein the spacer is disposed on a main surface of the substrate on the positive electrode side.

7. The lithium secondary battery according to any one of claims 1 to 5, wherein the spacer includes the protrusions arranged in a predetermined repeating pattern.

8. The lithium secondary battery according to any one of claims 1 to 5, wherein the spacer includes linear protrusions arranged at intervals.

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

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

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

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

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