Secondary battery and separator for secondary battery

Abstract

A secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The separator includes a first substrate in a sheet shape, a second substrate in a sheet shape, and a spacer disposed between the first substrate and the second substrate. Either one of the first substrate and the second substrate is disposed on the positive electrode side, and the other one of the first substrate and the second substrate is disposed on the negative electrode side.

Description

[0001] Cross-reference of related applications

[0002] This disclosure claims priority to Japanese Patent Application No. 2024-29985, filed with the Japan Patent Office on February 29, 2024, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates to a secondary battery and a separator for the secondary battery. Background Technology

[0004] As high-capacity non-aqueous electrolyte secondary batteries, lithium-ion batteries and lithium metal secondary batteries (hereinafter also referred to as "lithium secondary batteries") are known. In lithium secondary batteries, lithium metal is deposited at the negative electrode during charging, and during discharging, the lithium metal dissolves and is released as lithium ions into the non-aqueous electrolyte.

[0005] In secondary batteries, the volume change of the electrode assembly due to the expansion and contraction of the electrodes during charging and discharging is significant, which easily leads to a decrease in cycle performance. To address this, it is considered to reduce the volume change of the electrode assembly by placing spacers between the substrate of the separator and the electrodes.

[0006] 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 is dissolved from the negative electrode during discharging, a spacer is disposed between at least one of the positive electrode and the negative electrode and the separator, a first length in a first direction D1 of the separator is smaller than a second length in a second direction D2 intersecting the first direction D1, and at least one of the angles formed by the separator and the spacer on the spacer side of the cross section cut along the thickness direction of the separator and the first direction D1, and the angle formed by the electrode in contact with the spacer and the spacer on the spacer side, is greater than 90°."

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2021 / 192645 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] There is room for further improvement in the cycle characteristics of secondary batteries with spacers.

[0012] Solution for solving the problem

[0013] One aspect of this disclosure relates to a secondary battery having a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the separator includes a sheet-like first substrate, a sheet-like second substrate, and a spacer disposed between the first substrate and the second substrate, either the first substrate or the second substrate being disposed on the positive electrode side, and the other of the first substrate or the second substrate being disposed on the negative electrode side.

[0014] Another aspect of this disclosure relates to a separator for a secondary battery, comprising a sheet-like first substrate, a sheet-like second substrate, and a spacer disposed between the first substrate and the second substrate.

[0015] The effects of the invention

[0016] According to this disclosure, the cycle characteristics of secondary batteries can be improved.

[0017] The novel features of the invention are set forth in the appended claims, but the invention relates to both structure and content, and should be better understood, together with other objects and features of the invention, by reference to the following detailed description of the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a longitudinal cross-sectional view schematically illustrating an example of a secondary battery according to one embodiment of the present disclosure.

[0019] Figure 2 It is shown schematically. Figure 1 A cross-sectional view of the main parts of a secondary battery.

[0020] Figure 3 This is a top view showing an example of a spacer.

[0021] Figure 4 This is a top view showing another example of a spacer. Detailed Implementation

[0022] 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 materials are sometimes illustrated, but other numerical values ​​and 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 illustrated for specific physical properties, conditions, etc., any illustrated lower limit can be arbitrarily combined with any illustrated upper limit, as long as the lower limit is not higher than the upper limit. When multiple materials are illustrated, one can be selected for use alone, or two or more can be combined for use.

[0023] The secondary battery disclosed herein includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The separator includes a sheet-like first substrate, a sheet-like second substrate, and a spacer disposed between the first and second substrates. Either the first or the second substrate is disposed on the positive electrode side, and the other is disposed on the negative electrode side.

[0024] Hereinafter, the positive electrode, negative electrode, and separator will all be collectively referred to as "electrode assembly". The shape of the electrode assembly is not particularly limited. The electrode assembly can be a spiral-shaped electrode assembly formed by winding strip-shaped positive and negative electrodes in a spiral fashion with a separator between them, or it can be a flat electrode assembly formed by pressing a spiral-shaped electrode assembly radially. The electrode assembly can be constructed by stacking the positive and negative electrodes in a spiral fashion with a separator between them, or by stacking the positive and negative electrodes in a meandering fashion with a separator between them.

[0025] Secondary batteries include lithium-ion batteries (lithium metal batteries) and lithium-ion batteries. For example, the negative electrode of a lithium-ion battery expands during charging due to lithium metal deposition. The negative electrode of a lithium-ion battery expands during charging due to the absorption of lithium ions. In secondary batteries, lithium-ion batteries also experience a large expansion rate of the negative electrode and a large volume change of the electrode assembly due to Li deposition during charging.

[0026] In secondary batteries, the electrode assembly experiences significant volume changes during charging and discharging, which can easily lead to damage to the constituent components, electrode bending, internal short circuits, and a decline in cycle performance. To address this, spacers are formed on the main surface of the substrate to act as separators, suppressing volume changes in the electrode assembly by placing these spacers between the substrate and the electrodes. The spacers also create spaces to absorb electrode expansion.

[0027] However, when spacers are formed on the main surface of the substrate and positioned between the substrate and the electrode, the spacers are susceptible to the expansion and contraction of the electrode. With repeated charging and discharging (electrode expansion and contraction), the adhesion strength between the substrate and the spacers decreases. Consequently, the ability of the spacers to suppress volume changes in the electrode assembly (hereinafter also referred to as "spacer function") is sometimes reduced, leading to decreased cycle characteristics. This reduction in spacer function is caused by spacer displacement, wrinkling of the substrate accompanying spacer displacement, or spacers leaving the main surface of the substrate. For example, in the case of a lithium secondary battery where the spacers are positioned on the negative electrode side and the substrate is positioned on the positive electrode side, Li sometimes deposits between the substrate and the spacers, causing the spacers to float from the substrate, thereby reducing the spacer function. In the case of a lithium secondary battery where the spacers are positioned on the positive electrode side and the substrate is positioned on the negative electrode side, as Li deposits, a portion of the substrate (the portion exposed in the space formed by the spacers) tilts towards the positive electrode side. At this time, the spacer may shift and cause wrinkles in the substrate, thereby reducing the space (or the contact area between the spacer and the substrate), and sometimes reducing the function of the spacer.

[0028] In view of the above, the inventors conducted in-depth research and discovered the following: by using a substrate with two spacers and arranging a spacer between the two substrates, it is possible to significantly suppress the reduction in the function of the spacer and the resulting reduction in cycle characteristics.

[0029] That is, by placing a spacer between the first substrate and the second substrate, the spacer is protected by both substrates. The spacer is less susceptible to the effects of electrode expansion and contraction, thereby suppressing the decrease in the adhesion strength between the substrate and the spacer, and the associated decrease in the spacer's function. Therefore, the reduction in cycle characteristics caused by the aforementioned decrease in spacer function is suppressed. For example, the occurrence of internal short circuits in early cycles and the associated capacity reduction can be suppressed. Particularly in lithium-ion batteries, where the negative electrode expands significantly due to Li deposition, placing a spacer between the first substrate and the second substrate to form a separator can significantly suppress the decrease in spacer function.

[0030] From the viewpoint of facilitating the fabrication of electrode assemblies and suppressing the degradation of spacer function, it is preferable to integrate the first substrate, the second substrate, and the spacer. From the same viewpoint, it is preferable that the first substrate and the spacer, and the second substrate and the spacer, each have an adhesion strength of 3 N / m or higher.

[0031] The initial secondary battery is disassembled, the separator is removed from the electrode assembly, cleaned with an organic solvent (dimethoxyethane), and after drying, the adhesion strength between the first substrate and the spacer and the adhesion strength between the second substrate and the spacer are determined by a peel test in a universal testing machine.

[0032] When measuring the adhesion strength between the first substrate and the spacer, the second substrate is removed from the spacer by cutting or the like, thereby obtaining a first specimen integrally formed of the first substrate and the spacer, and a peel test is performed on the first specimen. When measuring the adhesion strength between the second substrate and the spacer, the first substrate is removed from the spacer by cutting or the like, thereby obtaining a second specimen integrally formed of the second substrate and the spacer, and a peel test is performed on the second specimen.

[0033] When the spacer is manufactured using the method described later, either the first sample or the second sample can be a sample obtained by forming the spacer on either the first substrate or the second substrate using a coating method (printing method). Alternatively, the other sample can be a sample obtained by thermally fusing the spacer to the other substrate.

[0034] The peel test can be performed as follows. For example, a universal testing machine such as the Shimadzu AGS-X universal testing machine can be used.

[0035] The first specimen was cut to obtain a strip-shaped test piece (80 mm in length and 15 mm in width). Double-sided adhesive tape was applied to the surface of the test piece on the spacer side, and it was fixed to the fixture of the universal testing machine. The test piece was fixed with the spacer side facing the fixture side. One end of the fixed test piece (first substrate) along its long side was fixed to the movable fixture of the universal testing machine. A peel test was performed at a peel angle of 90° and a peel speed of 20 mm / min. That is, the movable fixture was moved so that the first substrate was peeled along a direction at 90° relative to the fixture, and the first substrate and spacer of the test piece were peeled at a speed of 20 mm / min. During this process, the tensile direction was maintained at 90° relative to the fixing surface of the fixture to which the test piece was fixed. The average tensile strength (N / m) of the test piece peeled over a range of 10 mm to 70 mm was taken as the adhesion strength between the first substrate and the spacer. The adhesion strength between the second substrate and the spacer was determined in the same manner as for the first specimen.

[0036] The spacer, which is integrally formed from a first substrate, a second substrate, and a spacer, can also be manufactured in the following manner: an intermediate body is obtained by forming the spacer on a main surface of the first substrate (or the second substrate) using a prescribed coating method (printing method), and the end of the spacer, which serves as the intermediate body, is thermally fused to a main surface of the second substrate (or the first substrate). In this case, the adhesion strength between the first substrate and the spacer, as well as the adhesion strength between the second substrate and the spacer, can both be increased to 3 N / m or more.

[0037] The first substrate and the second substrate may each have porous sheets comprising a polymer material. The melting point of the resin material contained in the spacer may also be lower than the turn-off temperature of the porous sheet in at least one of the first substrate layer and the second substrate layer. In this case, when abnormal heating is caused by a short circuit or the like, the pores of the porous sheet are blocked by the melting of the resin material contained in the spacer, thus shutting off the circuit, which is advantageous in terms of safety. Furthermore, the aforementioned turn-off temperature refers to the temperature at which the battery's shut-off mechanism operates when the pores of the porous sheet are blocked by the melting of the sheet during abnormal heating caused by a short circuit or the like. By blocking the pores, the migration of lithium ions between the positive and negative electrodes is suppressed, thereby cutting off the current and preventing thermal runaway.

[0038] The following is a detailed description of secondary batteries.

[0039] (Lithium-ion rechargeable battery)

[0040] A lithium-ion secondary battery comprises a positive electrode, a negative electrode in which lithium metal is deposited during charging and dissolves in a non-aqueous electrolyte during discharging, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The negative electrode has at least a negative current collector, on which lithium metal is deposited during charging. The non-aqueous electrolyte has lithium-ion conductivity.

[0041] 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 within the negative electrode. Specifically, 70% to 100% (e.g., 80% to 100%, 90% to 100%) of the electron migration (current in other viewpoints) in the negative electrode during charging and discharging depends on the deposition and dissolution of lithium metal. That is, the negative electrode of a lithium-ion battery differs from the negative electrode where electron migration during charging and discharging primarily depends on the absorption and release of lithium ions by the negative electrode active material (graphite, etc.).

[0042] (Separator)

[0043] The separator includes a sheet-like first substrate, a sheet-like second substrate, and a spacer disposed between the first substrate and the second substrate. The spacer is configured to be sandwiched between the first substrate and the second substrate. The materials constituting the first substrate and the second substrate, the thickness of the substrates, etc., can be the same as each other or different from each other.

[0044] The following details the substrate (matters common to both the first and second substrates).

[0045] (Substrate)

[0046] The substrate can be a porous sheet with ion permeability and insulation properties. Examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the porous sheet is not particularly limited and can also be a polymer material. Examples of polymer materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The substrate may also contain additives as needed. Examples of additives include inorganic fillers.

[0047] The thickness of the substrate is not particularly limited, for example, it is 5 μm or more and 20 μm or less, more preferably 10 μm or more and 20 μm or less.

[0048] The substrate may also comprise a porous sheet and a composite material layer (heat-resistant layer). The composite material layer may be formed on one or both main surfaces of the porous sheet. The composite material layer is a layer that allows lithium ions to permeate. The composite material layer contains inorganic particles. The composite material layer may also contain resin materials as needed. The thickness of the composite material layer may also be 5% to 50% of the total thickness of the substrate.

[0049] The composite material layer can be disposed on the side of the porous sheet facing the positive electrode or on the side facing the negative electrode. When the composite material layer is disposed on the positive electrode side, it can suppress the degradation of the porous sheet due to oxidation. When the composite material layer is disposed on the negative electrode side, it can suppress the degradation of the porous sheet due to reduction. Spacers can also be disposed on the composite material layer. In this case, the effect of suppressing thermal shrinkage of the substrate is particularly high.

[0050] The inorganic particles are preferably particles of inorganic compounds that are thermally stable and insulating, and do not easily melt or decompose when subjected to 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 also be 0.2 μm to 2.0 μm.

[0051] 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. This diameter is then used as the average of the diameters of the 100 equivalent circles.

[0052] Examples of resin materials included in the composite material layer (heat-resistant layer) include polyvinylidene fluoride (PVdF), polytetrafluoroethylene and other fluorinated resins, fluororubbers such as PVdF-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydride, acrylonitrile-butadiene copolymer or its hydride, methacrylate-acrylate copolymer, styrene-acrylate copolymer, acrylonitrile-acrylate copolymer, rubbers such as ethylene propylene rubber, cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, vinyl resins such as polyvinyl acetate, acrylic resins such as polymethyl methacrylate, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as aramid, polyamide-imide, polyacrylonitrile, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, polyurethane resin, melamine resin, urea resin, and epoxy resin.

[0053] The resin material comprising 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 comprises at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamide-imides. These are well known as polymer materials with high heat resistance. From the viewpoint of heat resistance, aromatic polyamides, namely meta-aromatic polyamides (meta-fully aromatic polyamides) and para-aromatic polyamides (para-fully aromatic polyamides), are preferred.

[0054] The content of inorganic particles in the composite material layer can also be in the range of 50% to 99% by mass (e.g., 85% to 99% by mass).

[0055] For example, a composite material layer is formed 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.

[0056] (spacer)

[0057] In lithium-ion batteries, the main function of spacers is to create spaces for lithium metal deposition. By containing lithium metal within the spaces formed by the spacers, volume changes in the electrode assembly are suppressed.

[0058] The spacers comprise conductive and / or insulating materials. Insulating materials are preferred. Lithium metal is less likely to deposit on the surface of the insulating material, thus facilitating the application of the spacers' properties.

[0059] The spacer may contain resin material (e.g., insulating resin material), or it may contain 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 it may be less than 100% by volume or less than 80% by volume.

[0060] Examples of resin materials included as spacers include fluoropolymers such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), fluororubbers such as ethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydrogenated form, acrylonitrile-butadiene copolymer or its hydrogenated form, methacrylate-acrylate copolymer, styrene-acrylate copolymer, acrylonitrile-acrylate copolymer, rubbers such as ethylene propylene rubber, cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose, vinyl resins such as polyvinyl alcohol and polyvinyl acetate, acrylic resins such as polymethyl methacrylate, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as aramid, polyamide-imide, polyacrylonitrile, polyether, polyacrylic acid, polymethyl methacrylate, polyester, polyolefin, silicone resin, polyurethane resin, melamine resin, urea resin, and epoxy resin.

[0061] Among the aforementioned resin materials, polyimide, polyvinylidene fluoride, acrylonitrile-acrylate copolymer, etc., are preferred as materials that prevent lithium ions from passing through; polyimide may also be used. The non-porous spacer formed from these resin materials at a certain height is a layer that prevents lithium ions from passing through, possessing a non-porous structure that prevents lithium ions from passing through. From the viewpoint of suppressing the increase in the gas generation reaction rate during internal short circuits, such a spacer is preferred.

[0062] The particles can be inorganic or organic. Inorganic particles, such as insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides, are also possible. Preferred metal oxides include alumina (boehmite), magnesium oxide, titanium dioxide, zirconium oxide, and silicon dioxide. Preferred metal hydroxides include aluminum hydroxide. Preferred metal nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Preferred metal carbides include silicon carbide and boron carbide. Preferred metal sulfides include barium sulfate. Additionally, minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate can also be used. Alumina, silicon dioxide, and titanium dioxide are also preferred.

[0063] 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 by photographing it with 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 having the same area as the cross-section of each particle (equivalent circle diameter) is calculated, and the arithmetic mean of the calculated equivalent circle diameters can be taken as the average particle size. The arithmetic mean can be calculated, for example, based on more than 100 particles. Furthermore, the average particle size of other particles contained in the electrode and spacer can also be calculated using the same method.

[0064] 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.

[0065] The spacer includes one or more components (protrusions). The spacer can include multiple linear components or multiple point-like components. Linear components can be arranged continuously or intermittently. That is, linear components can also have localized defects. Linear components can be straight or curved. The width of the linear components can be 100 μm or more, 200 μm or more, 2000 μm or less, or 1000 μm or less.

[0066] The spacers preferably have a prescribed repeating pattern. That is, the spacers preferably include one or more members (protrusions) arranged in a prescribed repeating pattern. Linear members can also be arranged in a striped pattern. The spacers can also include multiple linear members arranged parallel to each other along the length direction of the first and second strip-shaped substrates. In addition, linear members can also be arranged in a mesh-like pattern. The mesh-like pattern can also be an assembly of polygons. An example of a mesh-like 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-like pattern can also be honeycomb-like. In addition, dotted members can also be arranged in a prescribed repeating pattern.

[0067] When the spacer is viewed from the normal direction of the main surface of the substrate, the ratio of the area S1 of the spacer disposed in the region facing the positive and negative electrodes to the area S0 of the region facing the positive and negative electrodes is, for example, S1 / S0×100, preferably 5% or more and 20% or less. When the ratio of area S1 is 5% or more, it is easy to stably form a space using the spacer. When the ratio of area S1 is 20% or less, it is easy to reduce the internal resistance.

[0068] The height H of the spacer ( Figure 2 The height (h) can also 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 also be 1.5 or more, 2 or more, or 3 or more. H / T can also be less than 10, less than 8, less than 5, or less than 4. By setting H / T to 1.5 or more, the expansion of the electrode assembly can be suppressed in particular.

[0069] The height H can be determined by the following method. First, an image of the cross-section along the thickness direction of the spacer (substrate) is obtained using an electron microscope. Next, 20 arbitrary locations within the spacer are selected in the image, and the height of these locations is measured. Then, the arithmetic mean of the measured heights of the 20 locations is calculated, and the resulting average value is taken as the height H. The thickness T can also be determined using the same process.

[0070] For example, spacers are formed by applying a coating containing both a spacer component and a liquid component to a designated area of ​​a substrate and allowing the coating to dry. 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. Alternatively, drying can be achieved using known methods such as heating or natural drying. Spacers can be formed, for example, on the surface of a porous sheet of the substrate or on the surface of a composite layer of the substrate.

[0071] (negative electrode)

[0072] The negative electrode has a negative current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode due to charging. More specifically, lithium ions contained in the non-aqueous electrolyte capture electrons at the negative electrode during charging, becoming lithium metal, and are deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode dissolves into the non-aqueous electrolyte as lithium ions during discharge.

[0073] 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 also 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.

[0074] 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. Regarding the open-circuit potential of the negative electrode when fully charged, it 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 potential. The non-aqueous electrolyte of the battery cell can also be of the same composition as the non-aqueous electrolyte in the disassembled battery.

[0075] A lithium-ion adsorption and storage layer is obtained by forming a layered negative electrode mixture containing negative electrode active material. In addition to negative electrode active material, the negative electrode mixture may also contain binder, thickener, conductive material, etc.

[0076] 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).

[0077] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0078] Examples of adhesive materials include fluoropolymers, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluoropolymers include polytetrafluoroethylene and polyvinylidene fluoride.

[0079] The negative current collector can be any conductive sheet. Foil, thin film, etc., can be used as the conductive sheet.

[0080] 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). Copper and / or copper alloys, which have high conductivity, are particularly preferred.

[0081] 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.

[0082] (positive electrode)

[0083] 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 comprising a positive active material, a conductive material, and a binder material, and then rolling the coating after drying, thereby obtaining the positive electrode.

[0084] The positive electrode active material is a 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.

[0085] Lithium contained in lithium-containing transition metal oxides is released from the positive electrode as lithium ions during charging and deposited as lithium metal on the negative electrode or negative electrode current collector. During discharging, lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed and stored by the composite oxide of the positive electrode. In other words, the lithium ions participating in charging and discharging mainly originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0086] Examples of transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one or more transition metal elements. The transition metal element may also be Ni, Co, and / or Mn. Lithium-containing transition metal oxides can contain more than one typical element as needed. Typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. Al may also be a typical element.

[0087] 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. For the purpose of achieving high capacity, composite oxides having 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 (excluding lithium) in the positive electrode (mM): mLi / mM is, for example, set to 1.1 or less.

[0088] 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 from the shape and range of the positive electrode current collector.

[0089] Materials used as positive current collectors (conductive plates) can include, for example, metallic materials containing Al, Ti, and Fe. These metallic materials can also be Al, Al alloys, Ti, Ti alloys, Fe alloys, etc. Fe alloys can also be stainless steel (SUS).

[0090] There are no particular restrictions on the thickness of the positive current collector, for example, it can be above 5μm and below 300μm.

[0091] (Non-aqueous electrolyte)

[0092] 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 also contain known additives.

[0093] Gel electrolytes contain lithium salts and a matrix polymer, or contain lithium salts, a non-aqueous solvent, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent is used. Examples of polymer materials include fluoropolymers, acrylic resins, polyether resins, and polyethylene oxide.

[0094] As a solid electrolyte, materials known in fields such as all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0095] Liquid non-aqueous electrolytes are prepared by dissolving lithium salts in non-aqueous solvents. Lithium ions and anions are generated by dissolving lithium salts in non-aqueous solvents.

[0096] 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 an independent integer greater than or equal to 0 or 1, and x and y are each an independent integer of 0, 1, or 2, satisfying x + y = 2), etc. The anions of oxalate complexes may also 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 these anions, or they can contain two or more anions.

[0097] 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 a fluorinated oxalate complex anion. Through the interaction between the fluorinated oxalate complex anion and lithium, lithium metal readily precipitates uniformly in fine particles. Therefore, localized precipitation of lithium metal is easily suppressed. The fluorinated oxalate complex anion can also be combined with other anions. Other anions can also be PF6. - And / or imide anions.

[0098] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, or their halogenated derivatives. Non-aqueous electrolytes may contain only one of these non-aqueous solvents or two or more. Examples of halogenated derivatives include fluorides.

[0099] 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.

[0100] 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.

[0101] The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. Alternatively, the concentration of anion in the non-aqueous electrolyte can be set to 0.5 mol / L or more and 3.5 mol / L or less. Furthermore, the concentration of anion of oxalate complex in the non-aqueous electrolyte can be set to 0.05 mol / L or more and 1 mol / L or less.

[0102] Non-aqueous electrolytes may also contain additives. These additives can also form a coating on the negative electrode. By forming a coating derived from the additive on the negative electrode, dendrite formation is easily suppressed. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0103] (Lithium-ion battery)

[0104] A lithium-ion battery comprises a positive electrode, a negative electrode containing a negative electrode active material that absorbs and releases lithium ions, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The positive electrode and non-aqueous electrolyte can be those exemplified in lithium secondary batteries. The positive electrode flux and positive electrode current collector contained in the positive electrode can be appropriately selected and used from the substances exemplified above. The non-aqueous solvent and lithium salt (anion) contained in the non-aqueous electrolyte can be appropriately selected and used from the substances exemplified above.

[0105] The negative electrode, for example, comprises a negative electrode current collector and a negative electrode additive layer (the lithium-ion storage layer described above) loaded on the main surface of the negative electrode current collector. The negative electrode additive layer may be loaded on one or both main surfaces of the negative electrode current collector. The negative electrode additive and negative electrode current collector included in the negative electrode can be appropriately selected and used from the substances exemplified above.

[0106] The substrate and spacers included in the separator can be the same substrates and spacers exemplified in lithium secondary batteries. The substrate may also have porous sheets comprising polymer materials. The substrate may also have a composite material layer comprising resin materials and inorganic particles. The spacers may also comprise resin materials.

[0107] In the case of lithium-ion batteries, spacers can be placed in areas where stress tends to increase when the negative electrode expands. Spacers can be placed at bends in electrode arrays where the positive and negative electrodes are stacked in a meandering manner, at the innermost periphery of wound electrode arrays, or at locations with small radii of curvature in flat electrode arrays.

[0108] Figure 1 This is a longitudinal cross-sectional view schematically illustrating an example of a secondary battery according to one embodiment of the present disclosure.

[0109] Figure 1 The cylindrical lithium secondary battery 10 shown includes a cylindrical battery casing, a wound electrode assembly 14 housed within the battery casing, and a non-aqueous electrolyte (not shown). 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.

[0110] 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.

[0111] The sealing body 16 includes a filter screen 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 filter screen 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 filter screen 22 is interconnected with the lower valve body 23 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.

[0112] A vent (not shown) is formed in the lower valve body 23. Therefore, when the internal pressure of the battery casing rises due to abnormal heating, the upper valve body 25 expands towards the cover 26 and separates from the lower valve body 23. As a result, the electrical connection between the lower valve body 23 and the upper valve body 25 is cut off. When the internal pressure rises further, the upper valve body 25 breaks, and gas is discharged from the opening (not shown) formed in the cover 26.

[0113] Figure 2This 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.

[0114] The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 50. The positive electrode 11, the negative electrode 12, and the separator 50 (substrate 60, 70) are all strip-shaped. The positive electrode 11, the negative electrode 12, and the separator 50 are wound together such that the separator is disposed between the positive electrode 11 and the negative electrode 12, thereby forming the electrode assembly 14.

[0115] The positive electrode 11 includes a positive current collector and positive electrode flux layers formed on both sides of the positive current collector. The positive current collector is electrically connected to the cap 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.

[0116] The separator 50 includes a sheet-like first substrate 60, a sheet-like second substrate 70, and a spacer 80 disposed between the first substrate 60 and the second substrate 70. The first substrate 60 is disposed on the negative electrode 12 side, and the second substrate 70 is disposed on the positive electrode 11 side. The first substrate 60 has a porous sheet 61 and a composite material layer 62 (heat-resistant layer). The second substrate 70 has a porous sheet 71 and a composite material layer 72 (heat-resistant layer).

[0117] Composite material layers 62 and 72 are formed on the main surface of the porous sheets 61 and 71 on the side of the spacer 80. A space 14s is formed between the positive electrode 11 and the negative electrode 12 (between the first substrate 60 and the second substrate 70) through the spacer 80. Figure 2 The height h of the spacer 80 is shown in the figure.

[0118] In the illustrated example, the first substrate 60 is disposed on the negative electrode 12 side and the second substrate 70 is disposed on the positive electrode 11 side. However, the first substrate 60 can also be disposed on the positive electrode 11 side and the second substrate 70 can also be disposed on the negative electrode 12 side.

[0119] In the illustrated example, composite material layer 62 is disposed on the main surface of porous sheet 61 on the side of spacer 80, but it can also be disposed on the main surface of porous sheet 61 on the side of negative electrode 12. Composite material layer 72 is disposed on the main surface of porous sheet 71 on the side of spacer 80, but it can also be disposed on the main surface of porous sheet 71 on the side of positive electrode 11.

[0120] 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 caused by the deposition of lithium metal is reduced, and the cycle characteristics are improved.

[0121] Here, Figure 3 and Figure 4 An example of the planar shape of spacer 80 is shown. Figure 3 and Figure 4 This is a top view of an intermediate body 90 on one main surface of the first substrate 60 (the main surface on the side of the second substrate 70) where a spacer 80 is formed. It is a view of the spacer 80 as seen from the normal direction of the main surface of the first substrate 60. In the top view, the spacer 80 is disposed on one main surface of the first substrate 60 (the main surface on the side of the second substrate 70), and the spacer 80 is formed by a linear member 80a. A space 14s is formed in the area where the spacer 80 is not disposed.

[0122] Figure 3 The spacer 80 includes linear members 80a configured in a honeycomb pattern. Figure 4 The spacer 80 includes a plurality of linear members 80a configured in a stripe pattern. The plurality of linear members 80a are arranged parallel to each other along the length direction (winding direction) of the strip-shaped first substrate 60. The plurality of linear members 80a are arranged separately from each other.

[0123] exist Figure 4 The device is equipped with six linear members 80a, but the number of members is not limited to this. Figure 3 and Figure 4 The linear members 80a are formed continuously, but they can also be formed intermittently by partially setting defects. The defects can be set randomly or in a certain repeating pattern. The arrangement pattern of the spacers is not limited to... Figure 3 honeycomb or Figure 4 The stripes are arranged in a striped pattern. The spacers can also be configured as dots, for example.

[0124] The spacers 80 (linear members 80a) located on both sides of the positive electrode 11 can be arranged either in a manner that overlaps them entirely or partially, or in a manner that does not overlap. The spacers 80 (linear members 80a) located on both sides of the negative electrode 12 can also be said to be the same as described above.

[0125] Figure 1 The secondary battery is a cylindrical lithium secondary battery with a wound electrode assembly, but the secondary battery involved in this disclosure is not limited to this. The shape of the secondary battery can be appropriately selected from various shapes such as cylindrical, coin-shaped, square, sheet-shaped, and flat, depending on its application. The shape of the electrode assembly is not particularly limited and can also be stacked.

[0126] (Postscript)

[0127] Based on the above description of the embodiments, the following technology is disclosed.

[0128] (Technology 1)

[0129] A 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.

[0130] The separator includes a sheet-like first substrate, a sheet-like second substrate, and a spacer disposed between the first substrate and the second substrate.

[0131] Either the first substrate or the second substrate is disposed on the positive electrode side.

[0132] The other of the first substrate and the second substrate is disposed on the negative electrode side.

[0133] (Technology 2)

[0134] According to the secondary battery described in Technology 1, wherein...

[0135] The first substrate, the second substrate, and the spacer are integrated.

[0136] (Technology 3)

[0137] According to technology 1 or 2, the secondary battery, wherein...

[0138] The first substrate and the spacer, and the second substrate and the spacer, respectively have an adhesion strength of 3 N / m or more.

[0139] (Technology 4)

[0140] The secondary battery according to any one of techniques 1 to 3, wherein...

[0141] The spacer contains an insulating material.

[0142] (Technology 5)

[0143] The secondary battery according to any one of techniques 1 to 4, wherein...

[0144] The spacer has a non-porous structure that prevents lithium ions from passing through.

[0145] (Technology 6)

[0146] The secondary battery according to any one of techniques 1 to 5, wherein...

[0147] The spacer comprises a resin material.

[0148] (Technology 7)

[0149] According to the secondary battery described in Technology 6, wherein...

[0150] The first substrate and the second substrate each have porous sheets containing polymer materials.

[0151] The resin material contained in the spacer has a lower melting point than the shut-off temperature of the porous sheet of at least one of the first substrate layer and the second substrate layer.

[0152] (Technology 8)

[0153] The secondary battery according to any one of techniques 1 to 7, wherein...

[0154] The spacers include one or more components arranged in a prescribed repeating pattern.

[0155] (Technology 9)

[0156] The secondary battery according to any one of techniques 1 to 8, wherein,

[0157] The first substrate and the second substrate are both strip-shaped.

[0158] The spacer includes a plurality of linear members arranged parallel to each other along the length of the first substrate and the second substrate.

[0159] (Technology 10)

[0160] The secondary battery according to any one of techniques 1 to 9, wherein...

[0161] In the negative electrode, lithium metal is deposited during charging and dissolves in the non-aqueous electrolyte during discharging.

[0162] (Technology 11)

[0163] A separator for secondary batteries,

[0164] It includes a sheet-like first substrate, a sheet-like second substrate, and a spacer disposed between the first substrate and the second substrate.

[0165] (Technology 12)

[0166] According to the separator for secondary batteries described in technology 11, wherein...

[0167] The first substrate, the second substrate, and the spacer are integrated.

[0168] (Technology 13)

[0169] According to the separator for secondary batteries described in technology 11 or 12, wherein...

[0170] The first substrate and the spacer, and the second substrate and the spacer, respectively have an adhesion strength of 3 N / m or more.

[0171] (Technology 14)

[0172] The separator for a secondary battery according to any one of techniques 11-13, wherein...

[0173] The spacer contains an insulating material.

[0174] (Technology 15)

[0175] The separator for a secondary battery according to any one of techniques 11-14, wherein...

[0176] The spacer has a non-porous structure that prevents lithium ions from passing through.

[0177] (Technology 16)

[0178] The separator for a secondary battery according to any one of techniques 11 to 15, wherein...

[0179] The spacer comprises a resin material.

[0180] (Technology 17)

[0181] According to the separator for secondary batteries described in Technology 16, wherein...

[0182] The first substrate and the second substrate each have porous sheets containing polymer materials.

[0183] The resin material contained in the spacer has a lower melting point than the shut-off temperature of the porous sheet of at least one of the first substrate layer and the second substrate layer.

[0184] (Technology 18)

[0185] The separator for a secondary battery according to any one of technologies 11-17, wherein...

[0186] The spacer comprises one or more components configured in a prescribed repeating pattern.

[0187] (Technology 19)

[0188] The separator for a secondary battery according to any one of techniques 11-18, wherein...

[0189] The first substrate and the second substrate are both strip-shaped.

[0190] The spacer includes a plurality of linear members arranged parallel to each other along the length of the first substrate and the second substrate.

[0191] [Example]

[0192] The lithium secondary battery involved in 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.

[0193] Secondary Batteries A1~A2

[0194] (The production of the positive electrode)

[0195] 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 to 95:2.5:2.5. The positive electrode slurry is coated on both sides of a strip of Al foil (positive electrode current collector), dried, and rolled to form a positive electrode slurry layer. The positive electrode current collector with positive electrode slurry layers formed on both sides is cut to a specified size to obtain the positive electrode.

[0196] (Preparation of the negative current collector)

[0197] Prepare strip-shaped electrolytic copper foil (12μm thick) to serve as the negative electrode current collector.

[0198] (Making of the substrate)

[0199] A microporous film made of polyethylene (10 μm thick, 50% porosity) 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 main surface 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 substrate 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 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 layer was obtained. The thickness of the substrate composed of the microporous film and the composite layer was set to 15 μm.

[0200] (Forming spacers on the main surface of the substrate)

[0201] A coating solution containing polyvinylidene fluoride and alumina particles (inorganic filler) is applied to the main surface of the microporous film side of the substrate, and the coating is dried, thereby forming spacers on the main surface of the microporous film side of the substrate.

[0202] Spacers are formed as Figure 3 The pattern shown (honeycomb) or Figure 4 The pattern shown is striped. The linear members constituting the spacers are set to a width of 0.5 mm and a height of 30 μm. The spacing (pitch) of the linear members in the width direction of the substrate is set to 5 mm. In this way, an intermediate body having a substrate and spacers is obtained. Figure 3 or Figure 4 Intermediate 90).

[0203] (Fabrication of the separator: integration of the intermediate body and the substrate)

[0204] Another substrate identical to the one described above was prepared. The end of the spacer (linear member) of the intermediate obtained above was thermally fused to the main surface of the microporous film side of the substrate. In this way, a spacer was placed between the two substrates to obtain a separator. The adhesion strength between the two substrates and the spacer, determined by the above method, was 3 N / m or more.

[0205] (Preparation of non-aqueous electrolytes)

[0206] 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 was prepared. The ether-based non-aqueous electrolyte (ether electrolyte) was prepared by dissolving lithium bis(sulfonyl)imide (LiFSI) at a concentration of 1 mol / L and LiBF2(C2O4) at a concentration of 0.1 mol / L in the mixed solvent.

[0207] (Assembly of a secondary battery)

[0208] An electrode assembly is fabricated by spirally winding the positive and negative current collectors together with a separator in a non-reactive gas atmosphere. This results in... Figure 2 The structure shown is a wound-type electrode assembly. In this case, a separator is arranged between the positive and negative electrodes, with one of the two substrates arranged on the negative electrode side and the other of the two substrates arranged on the positive electrode side.

[0209] An electrode assembly is housed within a bottomed cylindrical casing, and a non-aqueous electrolyte is injected. A sealing element is positioned at the opening of the casing, separated by a gasket, and the electrode assembly and non-aqueous electrolyte are sealed within the battery casing. This completes the process. Figure 1 The lithium secondary battery shown has the following structure.

[0210] Secondary Battery B1

[0211] The secondary battery B1 was manufactured in the same manner as the secondary battery A1, except that the separator was formed by overlapping two substrates without using a spacer.

[0212] Secondary Battery B2

[0213] One of the two substrates used a different substrate than described above. The other substrate used a porous sheet with high porosity and thickness. That is, the other substrate was constructed by forming the same composite material layer as described above on one main surface of a porous sheet made of polypropylene (porosity 66%, thickness 50 μm). Except as described above, secondary battery B2 was fabricated in the same manner as secondary battery B1.

[0214] Secondary Battery B3

[0215] An intermediate material is used as a separator. The separator is arranged such that the main surface of the substrate on which the spacer is formed faces the negative electrode. Except as described above, secondary battery B3 is manufactured in the same manner as secondary battery A2.

[0216] Secondary Battery B4

[0217] An intermediate material is used as a separator. The separator is arranged such that the main surface of the substrate on which the spacer is formed faces the positive electrode. Except as described above, the secondary battery B4 is manufactured in the same manner as the secondary battery A2.

[0218] The following evaluations were conducted on the secondary batteries obtained above.

[0219] [Evaluation 1: Number of abnormal loops occurred]

[0220] (Charge-discharge cycle test)

[0221] Charge-discharge cycle tests were conducted on the obtained batteries. In the charge-discharge cycle 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.

[0222] (Charge)

[0223] Constant current charging was performed at 10 mA per unit area (square centimeters) of the electrode until the battery voltage reached 4.1V. Then, constant voltage charging was performed at 4.1V until the current per unit area of ​​the electrode reached 1 mA.

[0224] (Discharge)

[0225] A constant current discharge was performed at a current of 10mA per unit area (square centimeters) of the electrode until the battery voltage reached 3.0V.

[0226] 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 no abnormal charging occurs up to 300 cycles, it is judged as "no abnormality".

[0227] [Evaluation 2: Expansion rate of the electrode assembly]

[0228] Under the same conditions as described above, a secondary battery in its initial charging state is obtained. The distance D0 between the negative and positive electrodes is determined using a CT image of a cross-section of this secondary battery (electrode assembly). The distance D0 is calculated by measuring the distances between the positive and negative electrodes at four randomly selected points and calculating their average value.

[0229] Under the same conditions as described above, three charge-discharge cycles were performed, followed by further charging, resulting in a rechargeable battery in its charged state after three charge-discharge cycles. The distance D1 between the negative and positive electrodes was then calculated using the same method as described above.

[0230] The expansion rate of the electrode assembly can be determined by calculating (D1 / D0)×100.

[0231] The evaluation results are shown in Table 1. In Table 1, A1-A2 are examples, and B1-B4 are comparative examples.

[0232] [Table 1]

[0233]

[0234] In secondary batteries A1~A2, the volume change of the electrode assembly is small, and no abnormalities are observed after 300 cycles. The occurrence of internal short circuits is suppressed, and the cycle characteristics are improved. In secondary batteries A1~A2, where the negative electrode expands significantly due to Li deposition during charging, the reduction in the spacer function is suppressed, and the volume change of the electrode assembly during charging and discharging is smaller.

[0235] In secondary cells B1-B2, the lack of spacers resulted in significant volume changes in the electrode assembly, leading to anomalies in the early stages of cycling. In secondary cell B2, by using a different substrate with higher porosity and thickness, the expansion of the negative electrode was slightly absorbed compared to secondary cell B1, resulting in a slightly smaller volume change in the electrode assembly; however, the effect was not as significant as when spacers were used. Furthermore, the lower strength of this other substrate also caused anomalies in the early stages of cycling.

[0236] In secondary batteries B3-B4, the spacer function decreases with charging and discharging, the electrode assembly volume changes significantly, and anomalies (internal short circuits) occur in the early stages of cycling. In secondary battery B3, the spacer is placed on the negative electrode side and the substrate is placed on the positive electrode side. In this secondary battery B3, it is believed that Li deposits between the substrate and the spacer, causing the spacer to float from the substrate, thus reducing the spacer function.

[0237] In the secondary battery B4, spacers are disposed on the positive electrode side and the substrate is disposed on the negative electrode side. It is believed that in such a secondary battery B4, with the precipitation of Li, a portion of the substrate (the part exposed in the space formed by the spacers) tilts towards the positive electrode side. As a result, the spacers shift and wrinkles are formed in the substrate, thereby reducing the space (or the contact area between the spacers and the substrate) and reducing the function of the spacers.

[0238] Industrial availability

[0239] The separator for secondary batteries disclosed herein can be used in lithium-ion batteries, lithium secondary batteries, etc.

[0240] The invention has been described in relation to the preferred embodiments at the present point in time, but such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly be apparent to those skilled in the art upon reading the foregoing disclosure. Therefore, the appended claims should be construed as including all modifications and alterations without departing from the true spirit and scope of the invention.

[0241] Explanation of reference numerals in the attached figures

[0242] 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, 60: First substrate, 70: Second substrate, 61, 71: Porous sheet, 62, 72: Composite material layer, 80: Spacer, 80a: Linear component, 90: Intermediate body.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. in, The separator includes a sheet-like first substrate, a sheet-like second substrate, and a spacer disposed between the first substrate and the second substrate. Either the first substrate or the second substrate is disposed on the positive electrode side. The other of the first substrate and the second substrate is disposed on the negative electrode side.

2. The secondary battery according to claim 1, wherein, The first substrate, the second substrate, and the spacer are integrated.

3. The secondary battery according to claim 2, wherein, The first substrate and the spacer, and the second substrate and the spacer, respectively have an adhesion strength of 3 N / m or more.

4. The secondary battery according to any one of claims 1 to 3, wherein, The spacer contains an insulating material.

5. The secondary battery according to any one of claims 1 to 3, wherein, The spacer has a non-porous structure that prevents lithium ions from passing through.

6. The secondary battery according to any one of claims 1 to 3, wherein, The spacer comprises a resin material.

7. The secondary battery according to claim 6, wherein, The first substrate and the second substrate each have porous sheets containing polymer materials. The resin material contained in the spacer has a lower melting point than the shut-off temperature of the porous sheet of at least one of the first substrate layer and the second substrate layer.

8. The secondary battery according to any one of claims 1 to 3, wherein, The spacers include one or more components arranged in a prescribed repeating pattern.

9. The secondary battery according to any one of claims 1 to 3, wherein, The first substrate and the second substrate are both strip-shaped. The spacer includes a plurality of linear members arranged parallel to each other along the length of the first substrate and the second substrate.

10. The secondary battery according to any one of claims 1 to 3, wherein, In the negative electrode, lithium metal is deposited during charging and dissolves in the non-aqueous electrolyte during discharging.

11. A separator for a secondary battery, It includes a sheet-like first substrate, a sheet-like second substrate, and a spacer disposed between the first substrate and the second substrate.

12. The separator for a secondary battery according to claim 11, wherein, The first substrate, the second substrate, and the spacer are integrated.

13. The separator for a secondary battery according to claim 12, wherein, The first substrate and the spacer, and the second substrate and the spacer, respectively have an adhesion strength of 3 N / m or more.

14. The separator for a secondary battery according to any one of claims 11 to 13, wherein, The spacer contains an insulating material.

15. The separator for a secondary battery according to any one of claims 11 to 13, wherein, The spacer has a non-porous structure that prevents lithium ions from passing through.

16. The separator for a secondary battery according to any one of claims 11 to 13, wherein, The spacer comprises a resin material.

17. The separator for a secondary battery according to claim 16, wherein, The first substrate and the second substrate each have porous sheets containing polymer materials. The resin material contained in the spacer has a lower melting point than the shut-off temperature of the porous sheet of at least one of the first substrate layer and the second substrate layer.

18. The separator for a secondary battery according to any one of claims 11 to 13, wherein, The spacers include one or more components arranged in a prescribed repeating pattern.

19. The separator for a secondary battery according to any one of claims 11 to 13, wherein, The first substrate and the second substrate are both strip-shaped. The spacer includes a plurality of linear members arranged parallel to each other along the length of the first substrate and the second substrate.

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