Lithium secondary battery

Abstract

This lithium secondary battery is provided with a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. In the negative electrode, lithium metal is precipitated during charging, and the lithium metal is dissolved during discharging. The separator is provided with a sheet-like base material and a spacer disposed on the main surface of the base material. The spacer includes a convex portion. The ratio St / S of the area St of a portion At where a region A in which the base material faces the positive electrode overlaps the protruding portion to the area S of the region A is set as X. The ratio Lt / L of the length Lt of the portion where the edge portion of the positive electrode overlaps the protruding portion to the length L of the edge portion along the outer shape of the positive electrode is defined as Y. At this time, Ylt is satisfied; x is a positive integer.

Description

Technical Field

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

[0002] Lithium-ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Lithium-ion batteries (lithium metal secondary batteries) are expected to surpass lithium-ion batteries in capacity as non-aqueous electrolyte secondary batteries. In lithium-ion batteries, lithium metal is deposited at the negative electrode during charging and dissolves during discharging, releasing as lithium ions into the non-aqueous electrolyte.

[0003] In lithium secondary batteries, lithium metal is deposited at the negative electrode during charging, so spacers need to be placed between the substrate of the separator and the electrode to ensure space for lithium deposition.

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

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2021 / 192645 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] Near the overlapping area between the positive electrode edge and the protrusion (spacer), stress caused by Li deposition at the negative electrode will locally concentrate, resulting in substrate damage and sometimes internal short circuits.

[0010] Solution for solving the problem

[0011] One aspect of this disclosure relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte.

[0012] In the negative electrode, lithium metal is deposited during charging and dissolved during discharging.

[0013] The separator includes a sheet-like base material and spacers disposed on the main surface of the base material.

[0014] The spacers include convex portions.

[0015] When the ratio of the area St of the overlapping portion At of the convex portions to the area S of the region A where the base material faces the positive electrode: St / S is set as X, and the ratio of the length Lt of the overlapping portion of the edge portion of the positive electrode with the convex portions to the length L of the edge portion along the outer shape of the positive electrode: Lt / L is set as Y,

[0016] The relationship Y < X is satisfied.

[0017] Effects of the Invention

[0018] According to the present disclosure, the occurrence of internal short circuits in lithium secondary batteries can be suppressed.

[0019] The novel features of the present invention are described in the claims, but the present invention relates to both the structure and the content, and together with other objects and features of the present invention, can be better understood through the following detailed description with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 FIG. is a longitudinal sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure.

[0021] Figure 2 is schematically showing Figure 1 a sectional view of a main part of the lithium secondary battery shown.

[0022] Figure 3 FIG. is a plan view showing an example of the spacer.

[0023] Figure 4 FIG. is a plan view showing another example of the spacer.

[0024] Figure 5 FIG. is a plan view showing still another example of the spacer.

[0025] Figure 6 FIG. is a plan view showing still another example of the spacer.

[0026] Figure 7 FIG. is a plan view showing still another example of the spacer.

[0027] Figure 8 FIG. is a plan view of the spacer included in the battery B1 of the comparative example.

[0028] Figure 9This is a top view of the spacers provided in the comparative example battery B2. Detailed Implementation

[0029] 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.

[0030] (Lithium secondary battery)

[0031] The lithium secondary battery of this disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The positive electrode, for example, includes a positive current collector and a positive electrode flux layer loaded on both sides or one side of the positive current collector. In the negative electrode, lithium metal is deposited during charging and dissolved during discharging. Specifically, the negative electrode at least includes a negative current collector on which lithium metal is deposited during charging. The non-aqueous electrolyte has lithium-ion conductivity. The lithium secondary battery is also referred to as a lithium metal secondary battery.

[0032] 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 views) 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.).

[0033] The separator includes a sheet-like base material and spacers disposed on the main surface of the base material. The spacers include convex portions. The ratio of the area St of the portion At where the region A of the base material facing the positive electrode (positive electrode mixture layer) overlaps with the convex portions to the area S of the region A: St / S is defined as X. The ratio of the length Lt of the portion where the edge portion of the positive electrode overlaps with the convex portions to the length L of the edge portion of the positive electrode (positive electrode mixture layer) along the outer shape of the positive electrode: Lt / L is defined as Y. At this time, the relationship Y < X is satisfied. When there are a plurality of overlapping portions between the edge portion of the positive electrode and the convex portions, the above-mentioned length Lt is the total length of the plurality of overlapping portions.

[0034] When the relationship Y < X is satisfied, the concentration of stress generated by the deposited Li near the overlapping portion between the positive electrode edge portion and the convex portion is alleviated, the damage to the base material caused by the concentration of this stress is suppressed, and the occurrence of internal short circuit caused by the damage to this base material is suppressed.

[0035] For example, when the convex portions are uniformly distributed on the main surface of the base material (positive electrode), the larger the arrangement ratio of the convex portions, the easier it is to stably form a space in the entire electrode group based on the spacers. Determine the required amount of space according to the actual battery design, and set the arrangement ratio of the convex portions based on the required amount of space. When the convex portions are uniformly distributed, the arrangement ratio of the convex portions is substantially the same at the end portion of the positive electrode and the portion other than the end portion. In contrast, in the present disclosure, by making the arrangement ratio of the convex portions smaller at the end portion of the positive electrode (the portion facing the edge portion of the positive electrode) in a manner that satisfies Y < X, the above-mentioned stress concentration can be alleviated. The portion where the arrangement ratio of the convex portions is reduced is limited to the portion corresponding to the end portion of the positive electrode, so the influence of reducing the arrangement ratio of the convex portions on the space formation between the positive electrode and the negative electrode is very small and is suppressed to the minimum.

[0036] From the viewpoint of suppressing the damage to the base material caused by the above-mentioned stress concentration, it is preferably Y < 2X / 3, and more preferably Y < X / 3.

[0037] From the viewpoint of suppressing the damage to the base material caused by the above stress concentration, Y can be 0.4 or less, can be 0.3 or less, can be 0.1 or less or 0.05 or less, and can also be 0. From the viewpoint of being able to stably form a space within the entire region A, Y can be greater than 0, can be 0.01 or more or 0.05 or more. As the range of Y, for example, it can be 0 or more and 0.4 or less.

[0038] From the viewpoint of being able to stably form a space within the region A based on the convex portions, X can be 0.03 or more, and can also be 0.05 or more. From the viewpoint of ensuring the volume corresponding to Li precipitation in the region A, X can be 0.45 or less, can be 0.3 or less, and can also be 0.2 or less.

[0039] When viewed from above, the positive electrode, for example, has a quadrilateral outer shape. In this case, the edge portions of the positive electrode (positive electrode mixture layer) include first to fourth edge portions corresponding to the four sides of the quadrilateral respectively. When the ratio of the length Lnt of the overlapping portion of any nth edge portion selected from the first to fourth edge portions and the convex portion to the length Ln of the nth edge portion (positive electrode mixture layer included in the nth edge portion) is set as Yn, in any case where n = 1 to 4, it is preferably satisfied that Yn < X. 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.

[0040] The convex portion is preferably arranged so as not to overlap with the edge portion of the positive electrode (positive electrode mixture layer). The region where the convex portion is formed can be adjusted so that the convex portion does not overlap with the edge portion (nth edge portion) of the positive electrode (positive electrode mixture layer). In the case where the convex portion is linear, the linear convex portion can be arranged intermittently to provide a missing portion.

[0041] Sometimes the positive electrode, negative electrode, and separator are collectively referred to as an "electrode group". The lithium secondary battery can include a wound electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator (base material) interposed therebetween. In addition, the lithium secondary battery can include a stacked electrode group in which a positive electrode and a negative electrode are stacked with a separator (base material) interposed therebetween.

[0042] In the lithium secondary battery, generally, the area of the negative electrode facing the positive electrode is larger than the area of the positive electrode, and the negative electrode is arranged so as to face the entire main surface on both sides or one side of the positive electrode (positive electrode mixture layer formed on both sides or one side of the positive electrode) with the separator interposed therebetween.

[0043] The negative electrode and the separator can be arranged on both sides of the positive electrode. That is, the negative electrode can be arranged so as to face the main surfaces on both sides of the positive electrode (positive electrode mixture layer formed on the main surfaces on both sides of the positive electrode) with the separator interposed therebetween. In the case of a wound electrode group, the negative electrode and the separator are arranged on both sides (outer peripheral side and inner peripheral side) of the positive electrode. In this case, it is preferable that the separator arranged on at least one side of the positive electrode satisfies the relationship of Y < X, and the separators arranged on both sides of the positive electrode respectively satisfy the relationship of Y < X.

[0044] The spacers arranged on both sides (outer peripheral side and inner peripheral side) of the positive electrode can be arranged so as to overlap with each other across the positive electrode, or can be arranged with the positions being entirely or partially offset. The insulating layers arranged on both sides (outer peripheral side and inner peripheral side) of the positive electrode can be arranged so as to overlap with each other across the positive electrode, or can be arranged with the positions being entirely or partially offset. The arrangement patterns of the spacers arranged on both sides (outer peripheral side and inner peripheral side) of the positive electrode can be the same as or different from each other.

[0045] In addition, the negative electrode and the separator can be arranged on one side of the positive electrode. That is, the negative electrode can be arranged so as to face the main surface on one side of the positive electrode (the positive electrode mixture layer formed on the main surface on one side of the positive electrode) through the separator. In this case, the separator arranged on one side of the positive electrode satisfies the relationship of Y < X.

[0046] (Separator)

[0047] The separator includes a sheet-like base material and spacers arranged on the main surface of the base material.

[0048] (Base material)

[0049] The base material can use a porous sheet having ion permeability and insulation. Examples of the porous sheet include a microporous film, a woven fabric, a non-woven fabric, etc. The material of the porous sheet is not particularly limited and can be a polymer material. Examples of the polymer material include an olefin resin, a polyamide resin, cellulose, etc. Examples of the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene. The base material can contain additives as needed. Examples of the additives include inorganic fillers.

[0050] The thickness of the base material is not particularly limited. For example, it is 5 μm or more and 20 μm or less, and more preferably 10 μm or more and 20 μm or less.

[0051] The base material can include a porous sheet and a composite material layer (heat-resistant layer). The composite material layer can be formed on one main surface of the porous sheet or on both main surfaces. The composite material layer is a layer that allows lithium ions to pass through. The composite material layer contains inorganic particles. The composite material layer can contain a resin material as needed. The thickness of the composite material layer can be 5% - 50% of the total thickness of the base material.

[0052] The composite material layer can be arranged 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 arranged on the positive electrode side, deterioration of the porous sheet due to oxidation reaction can be suppressed. When the composite material layer is arranged on the negative electrode side, deterioration of the porous sheet due to reduction reaction can be suppressed. Spacers can also be arranged on the composite material layer. In this case, the effect of suppressing the thermal shrinkage of the base material is particularly high.

[0053] 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.

[0054] 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.

[0055] Examples of resin materials contained in composite material layers (heat-resistant layers) include fluorinated resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), fluorinated rubbers such as PVdF-PTFE copolymers and ethylene-PTFE copolymers, styrene-butadiene copolymers or their hydrides, acrylonitrile-butadiene copolymers or their hydrides, methacrylate-acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate and other rubbers, cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, acrylic resins such as acrylic acid-methacrylic acid copolymers, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as aramid, polyamide-imide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, polyurethane resin, melamine resin, urea resin, and epoxy resin.

[0056] 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 well-known 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.

[0057] 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).

[0058] 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.

[0059] (spacer)

[0060] 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), the main surface of the substrate facing the negative electrode (the main surface of the substrate on the negative electrode side), or 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 on 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.

[0061] 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.

[0062] 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.

[0063] Examples of resin materials contained in spacers include fluorinated resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluorinated rubbers such as ethylene-tetrafluoroethylene copolymers and ethylene-tetrafluoroethylene copolymers, styrene-butadiene copolymers or their hydrogenated derivatives, acrylonitrile-butadiene copolymers or their hydrogenated derivatives, methacrylate-acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate and other rubbers, cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, acrylic resins such as acrylic acid-methacrylic acid copolymers, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as aramid, polyamide-imide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, polyurethane resin, melamine resin, urea resin, and epoxy resin.

[0064] Among the aforementioned resin materials, polyimide, polyvinylidene fluoride, and acrylonitrile-acrylate copolymers are preferred as lithium-ion impermeable materials. Polyimide can be used. The non-porous spacer of a certain height or higher formed from these resin materials 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.

[0065] 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, boehmite), magnesium oxide, titanium dioxide (titanium dioxide), zirconium oxide, and silicon oxide (silica). Aluminum hydroxide is an example of a metal hydroxide. Silicon nitride, aluminum nitride, boron nitride, and titanium nitride are examples of metal nitrides. Silicon carbide and boron carbide are examples of metal carbides. Barium sulfate is an example of a metal sulfide. Additionally, minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate can be used. Bauxite, silica, and titanium dioxide are preferred.

[0066] 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.

[0067] 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.

[0068] The spacer includes protrusions. The spacer may include linear protrusions and / or dot-like protrusions. In one view, the linear protrusions are ridge-like protrusions. The linear protrusions may be arranged intermittently or continuously. The linear protrusions may be straight or curved.

[0069] The width of the linear protrusion can be greater than 100μm or greater than 200μm, or less than 2000μm or less than 1000μm.

[0070] The spacers preferably have a prescribed repeating pattern. That is, the protrusions are preferably arranged in a prescribed repeating pattern. Linear protrusions can be arranged in a striped pattern or a mesh pattern. The mesh pattern can be an aggregate of polygons. An example of a mesh pattern includes a shape formed by combining polygons in a way that shares edges. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons can also be combined. The mesh pattern can also be honeycomb-like. In addition, dotted protrusions can also be arranged in a prescribed repeating pattern.

[0071] 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.

[0072] 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, in this image, 20 arbitrary points are selected among the spacers, and the height of the spacers at these points 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.

[0073] 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 liquid components 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 or natural drying.

[0074] (negative electrode)

[0075] The negative electrode serves as a 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, 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 during discharge.

[0076] 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.

[0077] Here, "fully charged" refers to the state of charge when the battery's rated capacity is set to C, for example, 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.

[0078] A lithium-ion adsorption / storage layer is formed by layering a negative electrode mixture containing negative electrode active material. In addition to the negative electrode active material, the negative electrode mixture may also contain binders, thickeners, conductive agents, etc.

[0079] 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).

[0080] Conductive materials can be, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0081] Examples of adhesive materials include fluoropolymers, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluoropolymers include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0082] The negative current collector only needs to be a conductive sheet. Foil, thin film, etc., can be used as the conductive sheet.

[0083] 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 preferentially 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.

[0084] 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.

[0085] (positive electrode)

[0086] The positive electrode, for example, comprises a positive current collector and a positive electrode binder layer supported by the positive current collector. The positive electrode binder layer, for example, includes a positive active material, a conductive material, and a binder material. The positive electrode binder layer may be formed on only 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 binder slurry containing a positive active material, a conductive material, and a binder material, allowing the coating to dry, and then calendering it.

[0087] 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.

[0088] Lithium contained in lithium-containing transition metal oxides is released from the positive electrode as lithium ions during charging and deposited as lithium metal at the negative electrode or on the negative electrode current collector. During discharging, lithium metal dissolves from the negative electrode to release lithium ions, which are then absorbed and stored by the composite oxide at the positive electrode. In other words, the lithium ions participating in charging and discharging mainly come from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0089] Examples of transition metal elements contained 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.

[0090] In lithium-containing transition metal oxides, Ni, Co, and / or Mn are sometimes included as transition metal elements, and Al is included as an arbitrary component. From the perspective 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.

[0091] As a bonding material, conductive material, etc., the material exemplified in the negative electrode can be used, for example. The shape and thickness of the positive electrode current collector can be selected according to the shape and extent of the positive electrode current collector.

[0092] Materials used as positive current collectors (conductive sheets) can 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 be stainless steel (SUS).

[0093] There are no particular restrictions on the thickness of the positive current collector, for example, it can be above 5μm and below 300μm.

[0094] (Non-aqueous electrolyte)

[0095] 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.

[0096] Gel electrolytes comprise lithium salts and a matrix polymer, or comprise 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.

[0097] 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.

[0098] 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.

[0099] BF4 can be cited 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 independently an integer greater than or equal to 0 or 1, and x and y are each independently 0, 1, or 2, satisfying x + y = 2), etc. The anions of oxalate complexes may contain boron and / or phosphorus. Examples of anions for 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] Non-aqueous electrolytes may contain additives. These additives can form a coating on the negative electrode. By forming a coating from the additives on the negative electrode, dendrite formation is easily suppressed. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0106] Hereinafter, an example of a 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 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.

[0107] (Implementation Method 1)

[0108] Figure 1A longitudinal cross-sectional view is shown schematically as an example of the lithium secondary battery of Embodiment 1. It should be noted that... Figure 1 The diagrams of the spacers and the spaces they form are omitted. Figure 1 The 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 as a bottomed cylindrical metal container and a sealing body 16 for sealing 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.

[0109] The housing body 15, for example, has a stepped portion 21 formed by partially stamping the sidewall 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 housing body 15 on the sidewall 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.

[0110] 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.

[0111] 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, separating 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.

[0112] 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.

[0113] 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.

[0114] The positive electrode 11 includes a positive current collector 11a and a positive flux 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.

[0115] 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 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. A space 14s is formed between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the substrate 50) by means of the spacer 53. Figure 2 The height h represents the height of the spacer 53.

[0116] exist Figure 2 In this structure, the spacer 53 is disposed on the main surface 50a of the positive electrode 11 side of the substrate 50, but it can also be disposed on the main surface 50b of the negative electrode 12 side of the substrate 50. 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.

[0117] 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 reduced, and the cycle characteristics are improved.

[0118] Here, Figures 3-7 Examples illustrating the planar shape of the spacer 53 are shown. In top view, the spacer 53 (linear protrusion 53a) is disposed on one main surface of the substrate 50. The substrate 50 with the spacer 53 (protrusion 53a) disposed is located on both the inner and outer peripheral sides of the positive electrode 11. In each figure, the positive electrode 11 facing the substrate 50 is indicated by dashed lines. It should be noted that these figures are schematic, and the aspect ratios of the components may not reflect the actual dimensions.

[0119] Figures 3-5 The spacer 53 includes a plurality of linear protrusions 53a configured in a striped shape. The region where the spacer 53 is not formed constitutes the space 14s. The plurality of linear protrusions 53a are arranged in parallel along the length direction (LD direction) of the strip-shaped base material 50. The plurality of linear protrusions 53a are arranged separately from each other. The plurality of linear protrusions 53a are each intermittently arranged and have missing portions 53b.

[0120] In Figures 3-5 there are 6 linear protrusions 53a arranged, but the number of the linear protrusions 53a is not limited to this. Figures 3-5 The missing portions can be set randomly or in a certain repeating pattern.

[0121] Figures 6-7 The spacer 53 includes linear protrusions 53a configured in a honeycomb shape. The region where the spacer 53 is not formed constitutes the space 14s. The linear protrusions 53a are intermittently arranged and have missing portions 53b.

[0122] In Figures 6-7 the linear protrusions corresponding to one side of the hexagon have missing portions at both ends, but they can also have missing portions at the central part. In Figure 6 the linear protrusions can also be arranged such that the end edge E3 of the positive electrode does not overlap with the linear protrusions 53a or the end edge E4 of the positive electrode does not overlap with the linear protrusions.

[0123] Figures 3-7 The dashed line in Figures 3-7 represents the positive electrode 11 facing the base material 50. That is,

[0124] Figures 3-7 the dashed line in represents the outline of the quadrilateral shape of the positive electrode 11 when viewed from above. The positive electrode 11 has four end edges E1 to E4 corresponding to the four sides of the quadrilateral respectively. Specifically, the positive electrode 11 has end edges E1 and E2 corresponding to the two sides extending along the LD direction, and has end edges E3 and E4 corresponding to the two sides extending along the width direction.

[0125] The ratio of the length Lnt of the overlapping part of any selected edge part En from the edge parts E1 to E4 to the length Ln of the edge part En: Lnt / Ln is designated as Yn. n is an integer from 1 to 4. In any case where n = 1 to 4, it is preferable that the relationship Yn < X is satisfied. In Figures 3-7 this case, it is easy to obtain a spacer that satisfies the relationship Yn < X in any case where n = 1 to 4.

[0126] The values of Yn corresponding to the edge parts E1 to E4 (n = 1 to 4) are respectively designated as Y1 to Y4. At this time, in Figures 3-5 Y1 and Y2 are 0. As Figures 3-5 shown, it is preferable that the edge parts E1 and E2 of the positive electrode do not overlap with the linear convex part 53a along the LD direction. Y3 and Y4 are Figure 5 < Figure 4 < Figure 3 in the relationship of, in Figure 5 Y1 to Y4 are all 0. The edge parts E3 to E4 overlap with 4 linear convex parts in Figure 3 and overlap with 2 linear convex parts in Figure 4 and do not overlap with all the linear convex parts in Figure 5 . As Figures 4-5 shown, Y3 and Y4 can also be adjusted by providing a missing part 53b in the convex part 53a.

[0127] In Figure 6 Y3 is 0, and in Figure 7 Y1 to Y4 are all 0. As Figures 6-7 shown, by not forming a convex part outside (outside the region A) of the edge part En of the positive electrode 11, Yn = 0 can be achieved.

[0128] In Figures 3-7 , the spacers are arranged in a striped or honeycomb pattern, but the arrangement pattern of the spacers is not limited to this. The spacers can also be arranged in a dot pattern, for example. For connection to the positive electrode lead, Figures 3-7 the positive electrode of can have a current collector exposed part without a positive electrode mixture layer along the width direction at the central part in the LD direction. In this case, the current collector exposed part is not included in the region A and the edge parts E1 and E2.

[0129] In Embodiment 1, a cylindrical lithium secondary battery having a wound electrode group has been described. However, the lithium secondary battery of the present embodiment is not limited to the manner of Embodiment 1 and can also be applied to other manners. The shape of the lithium secondary battery can be appropriately selected from various shapes such as cylindrical, coin-shaped, square-shaped, sheet-shaped, flat-shaped, etc. according to its use, etc. The form of the electrode group is not particularly limited and can be a stacked type.

[0130] (Supplementary Note)

[0131] The following technology is disclosed by the description of the above embodiments.

[0132] (Technology 1)

[0133] A lithium secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0134] In the negative electrode, lithium metal is deposited during charging and dissolved during discharging.

[0135] The separator includes a sheet-like base material and spacers disposed on the main surface of the base material.

[0136] The spacers include convex portions.

[0137] When the ratio of the area St of the overlapping portion At between the convex portion and the region A where the base material faces the positive electrode to the area S of the region A is set as X, and the ratio of the length Lt of the overlapping portion between the edge portion of the positive electrode and the convex portion to the length L of the edge portion along the outer shape of the positive electrode is set as Y,

[0138] The relationship Y < X is satisfied.

[0139] (Technology 2)

[0140] The lithium secondary battery according to Technology 1, wherein Y is 0 or more and 0.4 or less.

[0141] (Technology 3)

[0142] The lithium secondary battery according to Technology 1 or 2, wherein

[0143] In a plan view, the positive electrode has a quadrilateral outer shape.

[0144] The edge portion of the positive electrode includes a first edge portion to a fourth edge portion corresponding to the four sides of the quadrilateral respectively.

[0145] When the ratio of the length Lnt of the overlapping portion between any nth edge portion selected from the first edge portion to the fourth edge portion and the convex portion to the length Ln of the nth edge portion is set as Yn,

[0146] In any case where n = 1 to 4, the relationship Yn < X is satisfied.

[0147] (Technology 4)

[0148] The lithium secondary battery according to Technology 3, wherein in any case where n = 1 to 4, Yn is 0 or more and 0.4 or less.

[0149] (Technology 5)

[0150] According to any one of art 1 to 4, the lithium secondary battery comprises a positive electrode current collector and a positive electrode flux layer loaded on both sides of the positive electrode current collector.

[0151] The protrusion is configured in a manner that does not overlap with the end edge of the positive electrode compound layer.

[0152] (Technology 6)

[0153] In any one of the technologies 1 to 5, the lithium secondary battery wherein the spacer is disposed on one side of the main surface of the substrate.

[0154] (Technology 7)

[0155] The lithium secondary battery according to any one of art 1 to 6, wherein the spacer includes the protrusions arranged in a predetermined repeating pattern.

[0156] (Technology 8)

[0157] The lithium secondary battery according to any one of art 1 to 7, wherein the spacer includes intermittently arranged linear protrusions.

[0158] (Technology 9)

[0159] The lithium secondary battery according to any one of techniques 1 to 8, wherein the spacer comprises a resin material.

[0160] (Technology 10)

[0161] The lithium secondary battery according to any one of techniques 1 to 9, wherein the spacer comprises a non-porous structure that is impermeable to lithium ions.

[0162] (Technology 11)

[0163] The lithium secondary battery according to any one of art 1 to 10, wherein the substrate comprises a porous sheet containing a polymer material.

[0164] (Technology 12)

[0165] According to the lithium secondary battery of technology 11, the substrate further comprises a composite material layer comprising resin material and inorganic particles.

[0166] [Example]

[0167] The lithium 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.

[0168] Batteries A1~A3, B1

[0169] (The production of the positive electrode)

[0170] A positive electrode slurry is prepared by mixing a positive electrode active material, acetylene black (AB; conductive material), polyvinylidene fluoride (PVdF; binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP). The positive electrode active material is a rock-salt type lithium-containing transition metal oxide (NCA: positive electrode active material) with a layered structure containing Li, Ni, Co, and Al (the molar ratio of Li to the sum of Ni, Co, and Al is 1.0). The mass ratio of NCA:AB:PVdF in the positive electrode slurry is set at 95:2.5:2.5. The positive electrode slurry is coated on both sides of a strip of Al foil (positive electrode current collector), and the coating is dried and calendered to form a positive electrode slurry layer. The positive electrode current collector with positive electrode slurry layers formed on both sides is cut into specified dimensions to obtain the positive electrode.

[0171] (Preparation of the negative current collector)

[0172] Prepare a strip of electrolytic copper foil (12μm thick) as the negative electrode current collector.

[0173] (Making of the substrate)

[0174] A 10 μm thick polyethylene microporous film was prepared. A coating solution containing an aromatic polyamide (p-phenylene terephthalamide) as the resin material and alumina as inorganic particles was coated onto one side of the microporous film. The coating solution was prepared using an N-methyl-2-pyrrolidone solution containing 5.8% by mass calcium chloride, adjusted to a concentration of 2 wt% aromatic polyamide and 4 wt% alumina. The microporous film with the coating was placed at 25°C and 70% relative humidity for 1 hour to allow the aromatic polyamide to precipitate. Then, NMP and calcium chloride were removed from the coating by washing with water. A composite material layer (heat-resistant layer) was formed by drying the coating at 60°C for 5 minutes. Thus, a substrate having a microporous film and a composite material layer was obtained.

[0175] (Form spacers on the main surface of the substrate)

[0176] A coating solution containing polyvinylidene fluoride and alumina particles (inorganic filler) is applied to the microporous film surface of the aforementioned substrate, and the coating is then dried. This forms... Figure 3 , Figure 4 , Figure 5 or Figure 8 The spacers are arranged in a pattern (stripes). This results in a separator having a substrate and spacers. The linear protrusions constituting the spacers are 0.25 mm wide and 30 μm high. The linear protrusions are arranged intermittently.

[0177] (Preparation of non-aqueous electrolytes)

[0178] Prepare a mixed solvent containing 1,2-dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (CHF2(CF2OCH2)CF3) in a 1:2 volume ratio. Dissolve them in the mixed solvent at a concentration of 1 mol / L lithium bis(sulfonyl)imide (LiFSI) and 0.1 mol / L LiBF2 (C2O4) to prepare a liquid non-aqueous electrolyte (ether-based electrolyte).

[0179] (Battery assembly)

[0180] In an inert gas atmosphere, positive and negative current collectors are spirally wound together with a separator to form an electrode assembly. This yields... Figure 2 The structure shown is a wound-type electrode assembly. At this time, with... Figure 3 , Figure 4 , Figure 5 or Figure 8 The electrode assembly is formed by distributing spacers (substrate with spacers) on the inner and outer peripheral sides of the positive electrode, respectively. The positional relationship between the linear protrusions on the inner and outer peripheral sides of the positive electrode and the positive electrode is as follows: Figure 3 , Figure 4 , Figure 5 or Figure 8 The positional relationship is shown. The spacers are arranged such that the main surface of the substrate with the spacers faces the positive electrode.

[0181] The values ​​of X and Y are shown in Table 1. Figure 8 In, with Figures 3-5 In comparison, the overlap between the positive extreme edge and the convex portion 53a is larger, with Y equal to 0.42. It should be noted that... Figure 3 The maximum value of Yn is 0.02 of Y3 and Y4 corresponding to E3 and E4. Figure 4 The maximum value of Yn is 0.01 of Y3 and Y4 corresponding to E3 and E4. Figure 8 The maximum value of Yn is 0.875 of Y1 corresponding to E1. Figure 5 In the above, Y1 to Y4, which correspond to E1 to E4, are all 0.

[0182] The electrode assembly is housed within a bottomed cylindrical casing, and a non-aqueous electrolyte is injected. A sealing element is placed at the opening of the casing, separated by a gasket, to seal the electrode assembly and non-aqueous electrolyte within the battery casing. This completes the process. Figure 1 The lithium secondary battery with the structure shown is illustrated. A1 to A3 in Table 1 are examples, and B1 is a comparative example.

[0183] Batteries A4~A5, B2

[0184] Using a dispensing machine, to form Figure 6 , Figure 7 or Figure 9 The spacers in the pattern (honeycomb) shown. Figure 6 , Figure 7 or Figure 9 The electrode assembly is formed by distributing spacers (substrate with spacers) on the inner and outer peripheral sides of the positive electrode, respectively. The positional relationship between the linear protrusions on the inner and outer peripheral sides of the positive electrode and the positive electrode is as follows: Figure 6 , Figure 7 or Figure 9 The positional relationship is shown.

[0185] The values ​​of X and Y are shown in Table 1. Figure 9 In, with Figures 6-7 In comparison, the overlap between the positive extreme edge and the convex portion 53a becomes larger, with Y equal to 0.14. It should be noted that... Figure 6 The maximum value of Yn is 0.04 of Y1 and Y2 corresponding to E1 and E2. Figure 7 In the equation, the values ​​of Y1 to Y4 corresponding to E1 to E4 are all 0. Figure 9 In the above, the values ​​of Y1 to Y4 corresponding to E1 to E4 are all 0.14.

[0186] In addition to the above, batteries A4-A5 and B2 are manufactured in the same manner as battery A1. In Table 1, A4-A5 are examples, and B2 is a comparative example.

[0187] [evaluate]

[0188] (Charge and discharge test)

[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] Constant current charging is performed at 10 mA per unit area (square centimeters) of the electrode until the battery voltage reaches 4.1V. Then, constant voltage charging is performed at 4.1V until the current per unit area of ​​the electrode reaches 1 mA.

[0192] (Discharge)

[0193] Constant current discharge is applied at 10 mA per unit area (square centimeter) of the electrode until the battery voltage reaches 3.0V.

[0194] The above charging and discharging process is considered as one cycle. Repeated charging and discharging are performed. When the charging capacity of the m-th cycle increases by more than 1% compared to the charging capacity of the (m-1)-th cycle of the previous cycle, it is determined that an abnormal charging has occurred due to a minor internal short circuit, and the charging and discharging test is terminated. The cycle number m at this point is calculated as the abnormal cycle number. If repeated charging and discharging continues until the discharge capacity reaches 90% of the discharge capacity of the first cycle, and no abnormal charging occurs, it is determined that there is no abnormality.

[0195] The evaluation results are shown in Table 1.

[0196] [Table 1]

[0197]

[0198] Compared to batteries B1-B2, batteries A1-A5 exhibit a delayed cycle in which abnormalities occur, suppressing the occurrence of minor internal short circuits. Particularly in batteries A3 and A5, no abnormalities were observed, demonstrating a significant effect in suppressing internal short circuits.

[0199] Industrial availability

[0200] The lithium secondary battery disclosed herein can be used in electronic devices such as mobile phones, smartphones, and tablet terminals, 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; 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; 53b: Missing part

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, In the negative electrode, lithium metal is deposited during charging and the lithium metal dissolves during discharging. The separator includes a sheet-like substrate and spacers disposed on the main surface of the substrate. The spacers include convex portions. When the ratio of the area St of the portion At where the convex portions overlap the region A facing the positive electrode of the substrate to the area S of the region A is set as X, and the ratio of the length Lt of the portion where the edge portion of the positive electrode overlaps the convex portions to the length L of the edge portion along the outer shape of the positive electrode is set as Y, The relationship Y < X is satisfied.

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 according to claim 1, wherein, In plan view, the positive electrode has a quadrilateral outer shape. The edge portion of the positive electrode includes a first edge portion to a fourth edge portion corresponding to the four sides of the quadrilateral respectively. When the ratio of the length Lnt of the portion where any nth edge portion selected from the first edge portion to the fourth edge portion overlaps the convex portions to the length Ln of the nth edge portion is set as Yn, In any case where n = 1 to 4, the relationship Yn < X is satisfied.

4. The lithium secondary battery according to claim 3, wherein, In any case where n = 1 to 4, Yn is 0 or more and 0.4 or less.

5. The lithium secondary battery according to claim 1, wherein, The positive electrode includes a positive electrode current collector and a positive electrode mixture layer loaded on both sides of the positive electrode current collector. The convex portions are arranged so as not to overlap the edge portion of the positive electrode mixture layer.

6. The lithium secondary battery according to any one of claims 1 to 5, wherein, The spacers are disposed on the 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 spacers include the convex portions arranged in a prescribed repeating pattern.

8. The lithium secondary battery according to any one of claims 1 to 5, wherein, The spacers include the convex portions in the form of lines arranged intermittently.

9. The lithium secondary battery according to any one of claims 1 to 5, wherein, The spacers include a resin material.

10. The lithium secondary battery according to any one of claims 1 to 5, wherein, The spacers include a non-porous structure that does not allow lithium ions to pass through.

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

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

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