Lithium secondary battery, separator for lithium secondary battery, separator material, and integrated object of separator and separator for lithium secondary battery

Abstract

This lithium secondary battery is provided with: a positive electrode; a negative electrode; a porous separator disposed between the positive electrode and the negative electrode; a separator disposed between the separator and at least one of the positive electrode and the negative electrode; in the negative electrode, lithium metal is precipitated during charging and the lithium metal is dissolved during discharging, the separator contains insulating particles, a binder resin, and a thickener, the median diameter of the insulating particles in the volume-based particle size distribution is 1.0 [mu] m to 10 [mu] m, and the median diameter of the binder resin in the volume-based particle size distribution is 1.0 [mu] m to 10 [mu] m. The binder resin contains a polymer compound having a phthalic acid skeleton, and the thickener contains at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts. As a result, a lithium secondary battery provided with a separator having excellent physical properties can be obtained.

Description

Technical Field

[0001] The present disclosure relates to a lithium secondary battery, a separator for a lithium secondary battery, a separator material, and an integrated product of a separator for a lithium secondary battery and a separator. Background Art

[0002] As a high-capacity non-aqueous electrolyte secondary battery, a lithium-ion battery is known. As a high-capacity non-aqueous electrolyte secondary battery that exceeds the lithium-ion battery, a lithium secondary battery (lithium metal secondary battery) is promising. In a lithium secondary battery, lithium metal is precipitated at the negative electrode during charging, and lithium metal is dissolved and released into the non-aqueous electrolyte in the form of lithium ions during discharge.

[0003] Patent document 1 proposes "a coating liquid for a separator for a lithium ion battery, characterized in that it is a coating liquid for a separator for a lithium ion battery for manufacturing a separator for a lithium ion battery composed of a substrate and a coating layer containing inorganic particles, and the coating liquid contains inorganic particles, an organic polymer binder, and carboxymethyl cellulose or a salt thereof having an etherification degree of 1.10 or more and 2.00 or less."

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2019 / 146626 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] In lithium secondary batteries, lithium metal is deposited at the negative electrode during charging and dissolved during discharging. Therefore, it is necessary to provide a spacer between the separator and the electrode to ensure the space required for lithium deposition. However, no suitable material for forming the spacer has been found. Therefore, it is difficult to properly control the physical properties required by the spacer.

[0009] Solutions for solving problems

[0010] One aspect of the present disclosure relates to a lithium secondary battery, comprising: a positive electrode; a negative electrode; a porous separator arranged between the positive electrode and the negative electrode; a spacer arranged between at least one of the positive electrode and the negative electrode and the separator; and a non-aqueous electrolyte having lithium ion conductivity, wherein lithium metal is precipitated in the negative electrode during charging and dissolved during discharging, the spacer comprises insulating particles, a binder resin and a thickener, the median particle size of the insulating particles in a volume-based particle size distribution is 1.0 μm to 10 μm, the binder resin comprises a polymer compound having a phthalic acid skeleton, and the thickener comprises at least one selected from the group consisting of carboxymethyl cellulose and a carboxymethyl cellulose salt.

[0011] Another aspect of the present disclosure relates to a spacer and spacer material for a lithium secondary battery, which comprises insulating particles, a binder resin and a thickener, wherein the median particle size of the insulating particles in the volume-based particle size distribution is 1.0 μm to 10 μm, the binder resin comprises a polymer compound having a phthalic acid skeleton, and the thickener comprises at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salt.

[0012] Still another aspect of the present disclosure relates to an integrated product of a separator and a spacer for a lithium secondary battery, comprising: the above-mentioned spacer and a separator, wherein the spacer is bonded to a surface of the separator.

[0013] Effects of the Invention

[0014] According to the present disclosure, a lithium secondary battery including a separator having excellent physical properties can be obtained.

[0015] The novel features of the present invention are described in the attached claims, but the present invention relates to both structure and content, which together with other objects and features of the present invention will be better understood through the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a longitudinal cross-sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure.

[0017] Figure 2 It is schematically shown Figure 1 A partial cross-sectional view of a lithium secondary battery is shown.

[0018] Figure 3 It is a top view showing an example of a pattern of a spacer.

[0019] Figure 4 yes Figure 3 A partial enlarged view of .

[0020] Figure 5 It is a top view showing another example of the pattern of the spacer.

[0021] Figure 6 It is a top view showing another example of the pattern of the spacer.

[0022] Figure 7 It is a top view showing another example of the pattern of the spacer. DETAILED DESCRIPTION

[0023] Hereinafter, examples are given and the embodiments of the present disclosure are described, but the embodiments of the present disclosure are not limited to the examples described below. Specific numerical values ​​and materials are sometimes exemplified in the following description. As long as the invention of the present disclosure can be implemented, other numerical values ​​and other materials can be applied. In this specification, the description of "numerical value A to numerical value B" includes numerical value A and numerical value B, which can be replaced by "above numerical value A and below numerical value B". In the following description, when the lower limit and upper limit are exemplified for the numerical values ​​of specific physical properties, conditions, etc., as long as the lower limit is not greater than or equal to the upper limit, any one of the exemplified lower limits and any one of the exemplified upper limits can be arbitrarily combined.

[0024] In addition, the present disclosure includes a combination of matters recorded in two or more claims selected from the plurality of claims recorded in the attached claims. That is, as long as no technical contradiction occurs, matters recorded in two or more claims selected from the plurality of claims recorded in the attached claims may be combined.

[0025] (Lithium secondary battery)

[0026] Lithium secondary batteries are also called lithium metal secondary batteries. In the negative electrode of such batteries, lithium metal is deposited during charging and dissolved during discharging. Specifically, the negative electrode has at least a negative electrode current collector, and lithium metal is deposited on the negative electrode current collector.

[0027] In a lithium secondary battery, more than 70% of the rated capacity, for example, is realized by the precipitation and dissolution of lithium metal. During charging and discharging, the movement of electrons in the negative electrode mainly depends on the precipitation and dissolution of lithium metal in the negative electrode. Specifically, during charging and discharging, 70 to 100% (for example, 80 to 100%, 90 to 100%) of the movement of electrons in the negative electrode (current from other perspectives) depends on the precipitation and dissolution of lithium metal. That is, the negative electrode of a lithium secondary battery is different from the negative electrode in which the movement of electrons in the negative electrode during charging and discharging mainly depends on the absorption and release of lithium ions by the negative electrode active material (graphite, etc.). An example of a negative electrode does not contain a negative electrode active material (graphite, etc.) that absorbs and releases lithium ions.

[0028] A lithium secondary battery according to one embodiment of the present disclosure comprises: a positive electrode, a negative electrode, a porous separator disposed between the positive electrode and the negative electrode, a spacer disposed between the separator and at least one of the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity. In the negative electrode, lithium metal is precipitated during charging and dissolved during discharging.

[0029] (Spacer)

[0030] The spacer may be bonded to any one of the positive electrode, the negative electrode and the separator. From the viewpoint that the handling of the spacer becomes easy and the increase in reaction resistance can be suppressed, the spacer is preferably bonded to the separator. The spacer of one embodiment of the present disclosure may be formed by applying a dispersion containing a spacer material on the surface of the positive electrode, the negative electrode or the separator and drying it.

[0031] The following description will be given by taking the case where the spacer is bonded to the separator as an example. When the spacer is bonded to the positive electrode or the negative electrode, the separator is replaced with the positive electrode or the negative electrode and the following description is applied.

[0032] For lithium secondary batteries in which lithium metal is precipitated at the negative electrode during charging, it is necessary to ensure sufficient space between the separator and the electrode for lithium precipitation. To this end, the spacer needs to have sufficient thickness. That is, one of the important physical properties of an excellent spacer is the physical property for ensuring sufficient thickness. Generally, the larger the coating area of ​​the dispersion liquid applied to the separator, the easier it is to thicken the spacer. On the other hand, the larger the coating area of ​​the dispersion liquid, the greater the internal resistance. In order to minimize the coating area of ​​the dispersion liquid and form a spacer with sufficient thickness, it is important to, for example, control the thixotropy of the dispersion liquid.

[0033] Another important physical property of an excellent spacer is the bonding strength between the spacer and the separator. In order to stably bond the spacer to the separator and reduce the deformation and peeling caused by the precipitation and dissolution of lithium metal, it is necessary to ensure sufficient bonding strength between the spacer and the separator. To this end, the spacer itself needs to have sufficient mechanical strength.

[0034] In order to satisfy the above-mentioned physical properties, the dispersion liquid containing the spacer material contains insulating particles, a binder resin and a thickener. In other words, the spacer contains insulating particles, a binder resin and a thickener. The dispersion medium of the dispersion liquid is not particularly limited, and for example, water, an organic solvent, or a mixture of water and an organic solvent can be used. As an organic solvent, for example, N-methyl-2-pyrrolidone (NMP) can be used. Among them, from the viewpoint of reducing the environmental load, it is preferred to use water.

[0035] The shape of the insulating particles is not particularly limited and may be spherical. However, spherical does not mean a spherical shape in the strict sense, but refers to a shape without sharp corners and with an aspect ratio (maximum diameter / maximum diameter in a direction perpendicular to the maximum diameter) in the range of, for example, 1 to 3. The median particle size (i.e., average particle size) of the insulating particles in the volume-based particle size distribution may be 1.0 μm to 10 μm. The median particle size is the particle size when the cumulative volume is 50%. The median particle size of the insulating particles may also be 1.0 μm to 2 μm. The insulating particles need to maintain a dispersed state stably in the dispersion. When the median particle size is within the above range, the insulating particles in the dispersion are easy to maintain a dispersed state stably, and can maintain a dispersed state even after being applied to the separator, forming a spacer with a uniform morphology. As a result, the spacer can have sufficient mechanical strength.

[0036] The median particle size of the insulating particles in the volume-based particle size distribution can be measured, for example, using a laser diffraction / scattering particle size distribution measuring device (e.g., Microtrac manufactured by Nikkiso Co., Ltd.). Alternatively, the cross section of the spacer can be observed using a transmission electron microscope (TEM) and a TEM image can be taken to calculate the area surrounded by the outlines of any 100 insulating particles, and the diameter of an equivalent circle (perfect circle) having the same area as the calculated area can be obtained, and the diameter can be obtained as the average value of the diameters of the 100 equivalent circles.

[0037] The volume resistivity of the insulating particles may be, for example, 1.0×10 8 Ω·cm or more. By making the insulating particles have sufficient insulation, lithium metal will hardly precipitate on the spacer, which promotes the precipitation of lithium metal in the target space. The volume resistivity of the insulating particles can be even higher, for example, 1.0×10 10 Ω·cm or more.

[0038] The volume resistivity can be measured using the four-probe method. For example, 204 Kgf / cm 2 The insulating particles are pressurized and measured using a powder resistivity measuring device (for example, Loresta SP manufactured by Nittoseiko Analytech Co., Ltd.).

[0039] As insulating particles, inorganic particles such as metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides can be mentioned. As metal oxides, aluminum oxide (aluminum oxide, boehmite), magnesium oxide, titanium oxide (titanium dioxide), zirconium oxide, silicon oxide (silicon dioxide), etc. can be mentioned. As metal hydroxides, aluminum hydroxide can be mentioned. As metal nitrides, silicon nitride, aluminum nitride, boron nitride, titanium nitride, etc. can be mentioned. As metal carbides, silicon carbide, boron carbide, etc. can be mentioned. As metal sulfides, barium sulfate, etc. can be mentioned. Minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate can also be used. Among them, aluminum oxide, silicon dioxide, titanium dioxide, etc. are preferably used.

[0040] The content of insulating particles in the spacer is, for example, less than 80% by volume, preferably 50 to 70% by volume. The content (volume ratio) of insulating particles in the spacer can be obtained as follows: a cross section of the spacer is observed using a transmission electron microscope (TEM), a TEM image is taken, and the content of insulating particles in any 10 μm is calculated. 2 The volume ratio is calculated as the ratio of the total area surrounded by the outline of the insulating particles in the field of view to the field of view area. In this case, the volume ratio is preferably calculated in three or more fields of view and their average value is calculated.

[0041] The binder resin contains a polymer compound having a phthalic acid skeleton. The type of binder resin greatly affects the thickness of the spacer, the bonding strength between the spacer and the separator, the mechanical strength of the spacer, etc. The polymer compound having a phthalic acid skeleton may account for more than 50% by mass of the binder resin, or may account for more than 70% by mass, more than 80% by mass, or more than 90% by mass. The phthalic acid skeleton is represented by -O(O=C)-C6H4-(C=O)O-. In the polymer compound having a phthalic acid skeleton, the content of the phthalic acid skeleton may be, for example, 5% to 95% by mass.

[0042] The polymer compound having a phthalic acid skeleton is synthesized by polycondensation of phthalic acid or phthalic anhydride as a polyacid and a polyol. That is, an alkyd resin can be used as a polymer compound having a phthalic acid skeleton. Alkyd resins have excellent strength and toughness. It should be noted that, for example, by analyzing the spacer using FT-IR, Raman spectroscopy, etc., it can be confirmed that the binder resin of the spacer contains a polymer compound having a phthalic acid skeleton.

[0043] As the polyol, glycerol, pentaerythritol, etc. can be used without particular limitation. A part of phthalic acid or phthalic anhydride may be replaced with fatty acids such as linseed oil, soybean oil, and castor oil.

[0044] The weight average molecular weight of the alkyd resin is not particularly limited, and may be, for example, 10,000 to 1,000,000. The weight average molecular weight can be measured, for example, by gel permeation chromatography (GPC) and determined in terms of polystyrene.

[0045] The amount of the binder resin may be, for example, 20 to 80 parts by volume, 20 to 70 parts by volume, 20 to 50 parts by volume, or 25 to 40 parts by volume relative to 100 parts by volume of the insulating particles. The amount of the polymer compound having a phthalic acid skeleton may be, for example, 20 to 80 parts by volume, 20 to 70 parts by volume, 20 to 45 parts by volume, or 25 to 40 parts by volume relative to 100 parts by volume of the insulating particles. Within this range, it is easy to increase the mechanical strength of the spacer and to increase the bonding strength between the spacer and the spacer.

[0046] If the binder resin is a small amount (for example, less than 30% by mass of the entire binder resin), other binder resins may also be used in combination. The binder resin may contain a polymer compound having a phthalic acid skeleton as a main component. Other binder resins may be used in a range that does not significantly hinder the effect of the polymer compound having a phthalic acid skeleton. As other binder resins, for example, fluororesins, fluororubbers, styrene-butadiene copolymers or their hydrides, acrylonitrile-butadiene copolymers or their hydrides, methacrylate-acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene-propylene rubber, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamides (aramid), polyimides, polyamide-imide, polyacrylonitrile, polyethers, polyolefins, etc. may be cited.

[0047] The thickener includes at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts (hereinafter, at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts is also referred to as "CMC"). When carboxymethyl cellulose salts are used as CMC, sodium salts, lithium salts, potassium salts, ammonium salts, etc. can be used. Among them, the carboxymethyl cellulose salt preferably includes a sodium salt. It should be noted that, for example, by analyzing the spacer using FT-IR, Raman spectroscopy, etc., it can be confirmed that the spacer contains CMC. The spacer can also be dissolved in water or the like and analyzed using GPC.

[0048] CMC plays a role as a thickener for the dispersion of the spacer material prepared by the manufacturing process of the spacer. CMC has good compatibility with the polymer compound with a phthalic acid skeleton as a binder resin, and is suitable for forming a spacer with high mechanical strength and excellent bonding strength with the separator. Even if a material with a thickening effect other than CMC is used, it is difficult to fully improve the mechanical strength of the spacer and the bonding strength with the separator. CMC helps to significantly play the role of the polymer compound with a phthalic acid skeleton.

[0049] In order to fully exert the effect of CMC, the dispersion medium of the dispersion liquid of the spacer material preferably contains water. 50% or more of the dispersion medium may be water, and 70% or more, 80% or more, or 90% or more of the dispersion medium may be water.

[0050] The amount of CMC can be, for example, 0.5 to 5 parts by volume, or 1 to 3 parts by volume relative to 100 parts by volume of the insulating particles. By using CMC within this range, a sufficient thickening effect of CMC can be exhibited, and the effect of the polymer compound having a phthalic acid skeleton can be significantly exerted.

[0051] When the spacer is bonded to the separator, the bonding strength between the spacer and the separator is preferably 20 N / m or more, for example, so that the spacer can be bonded to the separator more stably and deformation and peeling caused by lithium metal precipitation and dissolution can be significantly reduced.

[0052] The bonding strength between the spacer and the separator can be determined by performing a peel test using a measuring device in accordance with JIS Z0237 (2009). First, determine the material constituting the spacer, prepare a dispersion of the spacer material, apply the dispersion to the surface of the separator and dry it to form a sample of a laminate of a spacer material film and a separator. The thickness of the spacer material film is set to 10 μm, and the sample shape is set to a strip with a width of 10 mm × a length of 50 mm or more. The separator side of the sample is pasted on one side of a double-sided tape with a width of 20 mm × a length of 130 mm (for example, No. 5606 made by NITTO DENKO CORPORATION), and the other side of the double-sided tape is pasted on the flat surface of a horizontal platform. Fix one end of the spacer material film in the length direction with a dynamometer, and stretch it in the vertical direction at a speed of 50 mm / min to peel off the spacer material film from the separator pasted on the double-sided tape. The tension at this time was measured for more than 15 seconds, and the average tension in the continuous 15-second period was calculated and used as the bonding strength between the spacer and the separator.

[0053] The thickness of the spacer is, for example, preferably greater than 20 μm, and may be greater than 25 μm, and may also be greater than 30 μm. The thickness of the spacer is the maximum dimension of the spacer in the thickness direction of the separator. The thickness of the spacer is obtained by photographing a cross section of the separator in the thickness direction using a scanning electron microscope (SEM), measuring the thickness of the spacer at any 10 locations, and calculating the average value thereof. If the spacer is too thick, it may sometimes affect the capacity of the lithium secondary battery. The thickness of the spacer is, for example, 100 μm, or less than 80 μm, or less than 60 μm.

[0054] The surface of the separator has: a first region facing the spacer, and a second region not facing the spacer. When the spacer is thin and the storage space for lithium metal is small, a considerable amount of lithium metal will precipitate near the spacer. The precipitation of lithium metal tends to become significant at the boundary between the first region and the second region. By making the thickness of the spacer larger than 20 μm, the precipitation of lithium metal at the boundary between the first region and the second region can be suppressed. This is because, when the thickness of the spacer is large enough, sufficient storage space for lithium metal is guaranteed in the second region. Therefore, the spacer is not easily subjected to stress from the precipitated lithium metal.

[0055] From the viewpoint of improving the mechanical strength of the spacer, the spacer preferably has a non-porous structure. A non-porous structure refers to a dense structure. In other words, the smaller the porosity of the spacer, the more preferred. The porosity of the spacer may be 10% by volume or less, or 5% by volume or less.

[0056] The porosity of the spacer can be obtained as follows: a cross section of the spacer in the thickness direction of the spacer is photographed using a scanning electron microscope (SEM) and a 2 The captured image is subjected to image processing such as binarization in the field of view to separate the pore portion A and the other portion B, and the porosity (volume %) of the spacer is calculated as the ratio of the area of ​​the pore portion A to the total area of ​​the pore portion A and the portion B. The captured image is preferably measured at any 10 locations, and the porosity (volume %) of the spacer is calculated as the average value of the area ratios of the pore portion A calculated at the 10 locations.

[0057] Relative to the sum of the first region of the separator facing the spacer and the second region of the separator not facing the spacer, the area ratio of the first region can be, for example, less than 30%, or 5 to 30%, or 5 to 20%. In this case, the internal resistance can be controlled within an appropriate range. It should be noted that the larger the ratio of the area of ​​the first region, the easier it is for the amount of lithium metal precipitated per unit area in the second region to increase. Therefore, the precipitation of lithium metal in the thickness direction is promoted, and it is easy to generate isolated lithium metal. By controlling the ratio of the area of ​​the first region within the above range, it is easy to reduce the isolated lithium metal.

[0058] The shape of the spacer in a top view may be at least one of a linear shape and a dot shape arranged in a prescribed pattern. That is, the spacer may include linear convex portions arranged in a manner that tracks a prescribed pattern, or may include dot-shaped (island-shaped) convex portions. The spacer may consist of only linear convex portions, only dot-shaped convex portions, or both linear convex portions and dot-shaped convex portions. The planar shape of the dot-shaped convex portion is not particularly limited, and may be circular (perfectly circular or elliptical), polygonal (triangular, quadrilateral, etc.), etc.

[0059] A plan view refers to observing an object placed on a flat surface from the normal direction of the surface. For example, a plan view of a spacer formed on a separator refers to placing the separator on a flat surface and observing the spacer from the normal direction of the surface.

[0060] The first region facing the spacer is preferably arranged on the separator in a uniform and dispersed state as much as possible. Thus, it is possible to suppress the rise of internal resistance, reduce the location where lithium metal is locally precipitated in large quantities, and easily limit the isolated lithium metal to a very small amount. Typically, the separator, the positive electrode, and the negative electrode are strip-shaped with long sides and short sides. When the length (width) of the short side direction of the strip-shaped negative electrode is set to L and an arbitrary circular region with a diameter of S / 3 is set on the surface of the separator, it is preferred that the first region and the second region always coexist in such a circular region.

[0061] Specifically, the predetermined pattern may be a mesh-like pattern. The mesh-like pattern may be a pattern of a collection of polygons or, for example, a pattern of a collection of hexagons, that is, a honeycomb pattern.

[0062] Next, each component of the lithium secondary battery will be described in more detail.

[0063] (Separator)

[0064] The separator uses a porous sheet with ion permeability and insulation. Examples of the porous sheet include: microporous films, woven fabrics, non-woven fabrics, etc. The material of the porous sheet is not particularly limited, and it can be a polymer material. Examples of the polymer material include: olefin resins, polyamide resins, cellulose, etc. Examples of the olefin resin include: polyethylene, polypropylene, and copolymers of ethylene and propylene, etc. The separator may contain additives as needed. Examples of the additive include: inorganic fillers, etc. In the case where the spacer is bonded to the surface of the spacer, the spacer and the spacer may be treated as an integrated object.

[0065] The separator has a first main surface facing the negative electrode and a second main surface facing the positive electrode. The separator may be formed on the first main surface or the second main surface.

[0066] The thickness of the separator is not particularly limited, and is, for example, 5 μm or more and 20 μm or less, and more preferably 10 μm or more and 20 μm or less.

[0067] The separator may also include a porous sheet (substrate layer) and a composite material layer. The composite material layer may be formed on either the first main surface side or the second main surface side of the porous sheet. When the composite material layer is provided, the thickness of the composite material layer may be 5% to 50% of the thickness of the separator.

[0068] The composite material layer includes a resin material and inorganic particles. The inorganic particles may include first particles and / or second particles. The first particles are particles of lithium-containing phosphate. The second particles are particles other than the first particles. The composite material layer is a layer that allows lithium ions to pass through.

[0069] By placing the composite material layer on the positive electrode side, it is possible to suppress the degradation of the porous sheet due to oxidation reaction. On the other hand, by placing the composite material layer on the negative electrode side, it is possible to suppress the degradation of the porous sheet due to reduction reaction.

[0070] The phosphate constituting the first particle may be at least one selected from the group consisting of lithium phosphate (Li3PO4), dilithium hydrogen phosphate (Li2HPO4) and lithium dihydrogen phosphate (LiH2PO4). Among them, lithium phosphate is preferred from the viewpoint of being highly effective in suppressing heat generation of the battery during abnormal conditions.

[0071] The resin material preferably uses a polymer material having a higher heat resistance than the material of the porous sheet. Such a polymer material preferably includes at least one selected from the group consisting of aromatic polyamide, aromatic polyimide and aromatic polyamide-imide. These are known to be polymer materials with high heat resistance. From the viewpoint of heat resistance, aramid, i.e., meta-aramid (meta-type fully aromatic polyamide) and para-aramid (para-type fully aromatic polyamide) are preferred.

[0072] The median particle size (ie, average particle size) of the first particles in the volume-based particle size distribution may be 0.1 μm to 1.0 μm. The median particle size (ie, average particle size) of the second particles in the volume-based particle size distribution may be 0.2 to 2.0 μm.

[0073] (negative electrode)

[0074] The negative electrode has a negative electrode collector. In a lithium secondary battery, lithium metal is precipitated on the surface of the negative electrode due to charging. More specifically, by charging, the lithium ions contained in the non-aqueous electrolyte obtain electrons on the negative electrode to form lithium metal, and precipitate on the surface of the negative electrode. By discharging, the lithium metal precipitated on the surface of the negative electrode dissolves in the non-aqueous electrolyte in the form of lithium ions. It should be noted that the lithium ions contained in the non-aqueous electrolyte can be derived from the lithium salt added to the non-aqueous electrolyte, can be supplied by the positive electrode active material by charging, or can be both.

[0075] The negative electrode may include a lithium ion absorption layer (a layer that exhibits capacity by the absorption and release of lithium ions by the negative electrode active material (graphite, etc.)) supported on the negative electrode collector. In this case, the open circuit potential of the negative electrode when fully charged may also be 70 mV or less relative to lithium metal (lithium dissolution potential). When the open circuit potential of the negative electrode when fully charged is 70 mV or less relative to lithium metal, lithium metal exists on the surface of the lithium ion absorption layer when fully charged. That is, the negative electrode exhibits capacity by the precipitation and dissolution of lithium metal.

[0076] Here, fully charged means the state when the battery is charged to a charging state of, for example, 0.98×C or more when the rated capacity of the battery is set to C. The open circuit potential of the negative electrode when fully charged can be measured by disassembling the fully charged battery in an argon atmosphere, removing the negative electrode, and assembling a battery cell using lithium metal as a counter electrode. The non-aqueous electrolyte of the battery cell can be the same composition as the non-aqueous electrolyte in the disassembled battery.

[0077] The lithium ion storage layer is formed by layering a negative electrode composite material containing a negative electrode active material. The negative electrode composite material may contain a binder, a thickener, a conductive agent, etc. in addition to the negative electrode active material.

[0078] Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, Sn-containing materials, etc. The negative electrode may contain one negative electrode active material, or may contain two or more of them in combination. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon).

[0079] The conductive material is, for example, a carbon material, and examples of the carbon material include carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0080] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber polymers. Examples of the fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0081] The negative electrode current collector may be a conductive sheet, and foil, film, etc. may be used as the conductive sheet.

[0082] The material of the negative electrode collector (conductive sheet) can be any conductive material other than lithium metal and lithium alloy. The conductive material can be a metal material such as a metal or an alloy. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form alloys and intermetallic compounds with lithium is preferred. Examples of such conductive materials include: copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, or graphite whose base surface is preferentially exposed. As alloys, examples include: copper alloys, stainless steel (SUS), etc. Among them, copper and / or copper alloys with high conductivity are preferred.

[0083] The thickness of the negative electrode current collector is not particularly limited, and is, for example, 5 μm or more and 300 μm or less.

[0084] (positive electrode)

[0085] The positive electrode, for example, comprises: a positive electrode current collector, and a positive electrode composite material layer supported on the positive electrode current collector. The positive electrode composite material layer, for example, comprises a positive electrode active material, a conductive material, and a binder. The positive electrode composite material layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides. The positive electrode may be obtained, for example, by applying a positive electrode composite material slurry comprising a positive electrode active material, a conductive material, and a binder on both sides of the positive electrode current collector, drying the coating, and then rolling.

[0086] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. Among them, lithium-containing transition metal oxides are preferred from the viewpoint of low manufacturing cost and high average discharge voltage.

[0087] The lithium contained in the lithium-containing transition metal oxide is released from the positive electrode in the form of lithium ions during charging, and precipitated on the negative electrode or the negative electrode collector in the form of lithium metal. During discharge, the lithium metal dissolves from the negative electrode to release lithium ions, and is absorbed into the composite oxide of the positive electrode. That is, the lithium ions involved in charging and discharging are generally derived from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0088] As transition metal elements contained in the lithium-containing transition metal oxide, there can be mentioned: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc. The lithium-containing transition metal oxide can contain one transition metal element, or it can contain two or more. The transition metal element can be Co, Ni and / or Mn. The lithium-containing transition metal oxide can contain one or more typical elements as needed. As typical elements, there can be mentioned: Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, etc. The typical element can be Al, etc.

[0089] Among lithium-containing transition metal oxides, Co, Ni and / or Mn may be contained as transition metal elements, and Al may be contained as an arbitrary component. From the viewpoint of obtaining high capacity, a composite oxide having a layered structure and a rock salt type crystal structure is preferred. In this case, in a lithium secondary battery, the molar ratio of the total amount of lithium mLi possessed by the positive electrode and the negative electrode to the amount of metal M other than lithium possessed by the positive electrode mM: mLi / mM is set to, for example, 1.1 or less.

[0090] As the binder, the conductive agent, etc., for example, the substances exemplified in the negative electrode can be used. The shape and thickness of the positive electrode current collector can be selected from the shapes and ranges of the positive electrode current collector, respectively.

[0091] Examples of the material of the positive electrode current collector (conductive sheet) include metal materials including Al, Ti, Fe, etc. The metal material may be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0092] The thickness of the positive electrode current collector is not particularly limited, and is, for example, 5 μm or more and 300 μm or less.

[0093] (Non-aqueous electrolyte)

[0094] The non-aqueous electrolyte having lithium ion conductivity includes, for example, a non-aqueous solvent, lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be in a liquid state or a gel state.

[0095] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. The lithium salt dissolves in the non-aqueous solvent to generate lithium ions and anions.

[0096] The gel-like non-aqueous electrolyte comprises a lithium salt and a matrix polymer, or comprises a lithium salt, a non-aqueous solvent and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels can be used. Examples of the polymer material include fluororesins, acrylic resins, polyether resins, and the like.

[0097] As the lithium salt or anion, a known lithium salt or anion that can be used in a non-aqueous electrolyte of a lithium secondary battery can be used. Specifically, BF4 - 、ClO4 - PF6 - CF3SO3 - CF3CO2 - , anions of imide, anions of oxalic acid complex, etc. Examples of anions of imide include: N(SO2CF3)2 - 、N(C m F 2m+1 SO2) x (C n F 2n+1 SO2)y - (m and n are each independently an integer greater than 0 or 1, x and y are each independently 0, 1 or 2, and x+y=2) etc. The anion of the oxalic acid complex may contain boron and / or phosphorus. Examples of the anion of the oxalic acid complex include: bis(oxalatoborate) anion, difluoro(oxalatoborate) anion (BF2(C2O4) - )、PF4(C2O4) - PF2(C2O4)2 - The nonaqueous electrolyte may contain these anions alone or in combination of two or more.

[0098] From the viewpoint of inhibiting the precipitation of lithium metal in the form of dendrites, the non-aqueous electrolyte preferably contains at least anions of an oxalate complex, wherein an oxalate complex anion having fluorine is preferably contained. Through the interaction between the oxalate complex anion having fluorine and lithium, lithium metal is easily precipitated uniformly in the form of fine particles. Therefore, it is easy to inhibit the local precipitation of lithium metal. The oxalate complex anion having fluorine can also be combined with other anions. Other anions can be PF6 - and / or imide-type anions.

[0099] Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, or halogen-substituted products thereof. The non-aqueous electrolyte may contain these non-aqueous solvents alone or in combination of two or more. Examples of the halogen-substituted product include fluorides and the like.

[0100] 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.

[0101] 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.

[0102] The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the non-aqueous electrolyte can be set to 0.5 mol / L or more and 3.5 mol / L or less. In addition, the concentration of the anion of the oxalic acid complex in the non-aqueous electrolyte can be set to 0.05 mol / L or more and 1 mol / L or less.

[0103] The non-aqueous electrolyte may contain an additive. The additive may also form a coating on the negative electrode. By forming a coating derived from the additive on the negative electrode, the formation of dendrites is easily suppressed. Examples of such additives include vinylene carbonate, FEC, and vinyl ethylene carbonate (VEC).

[0104] Hereinafter, description will be given with reference to the accompanying drawings. Figure 1 This is a longitudinal cross-sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure.

[0105] Hereinafter, an example of a lithium secondary battery (L) of the present 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 apply the above-mentioned constituent elements. In addition, the constituent elements of the example described below can be changed based on the above-mentioned description. In addition, the matters described below can also be applied to the above-mentioned embodiment. In addition, in the lithium secondary battery described below, non-essential constituent elements in the lithium secondary battery of the present disclosure can also be omitted. It should be noted that, in order to facilitate understanding, the scale of the constituent elements is changed in the following figures.

[0106] Hereinafter, the positive electrode, the negative electrode and the separator are sometimes collectively referred to as an "electrode group". The positive electrode, the negative electrode and the separator can be wound in a manner such that the separator is arranged between the positive electrode and the negative electrode. In the case of forming a wound electrode group, a strip-shaped positive electrode, a strip-shaped negative electrode and a strip-shaped separator are used. Alternatively, the positive electrode, the negative electrode and the separator can also be stacked. For example, a flat positive electrode, a flat negative electrode and a flat separator can be stacked. That is, the electrode group can be either a wound electrode group or a stacked electrode group.

[0107] (Implementation Method 1)

[0108] Figure 1 This is a longitudinal cross-sectional view schematically showing an example of the lithium secondary battery according to the first embodiment. Figure 1 The illustration of the spacer and the space formed by the spacer is omitted. Figure 1 The cylindrical lithium secondary battery 10 shown includes: a cylindrical battery case, a wound electrode group 14 housed in the battery case, and a non-aqueous electrolyte (not shown). The battery case includes: a shell body 15 which is a metal container with a bottom and a cylindrical shape, and a sealing body 16 which seals the opening of the shell body 15. A gasket 27 is arranged between the shell body 15 and the sealing body 16. The airtightness of the battery case is ensured by the gasket 27. In the shell body 15, insulating plates 17 and 18 are respectively arranged at the two ends of the winding axis of the electrode group 14.

[0109] The shell body 15 has a step portion 21 formed by partially punching the side wall of the shell body 15 from the outside, for example. The step portion 21 may also be formed in an annular shape on the side wall of the shell body 15 along the circumferential direction of the shell body 15. In this case, the sealing body 16 is supported on the surface of the step portion 21 on the opening side.

[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 body 26. In the sealing body 16, these components are stacked in this order. The sealing body 16 is installed at the opening of the shell body 15 in such a way that the cover body 26 is located on the outer side of the shell body 15 and the perforated metal plate 22 is located on the inner side of the shell body 15. The above-mentioned components constituting the sealing body 16 are, for example, in the shape of a circular plate or a ring. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, and an insulating member 24 is sandwiched between their respective peripheral portions. The perforated metal plate 22 and the lower valve body 23 are connected to each other at their respective central portions. The upper valve body 25 and the cover body 26 are connected to each other at their respective central portions. That is, the components except the insulating member 24 are electrically connected to each other.

[0111] A vent hole (not shown) is formed in the lower valve body 23. Therefore, when the internal pressure of the battery case rises due to abnormal heating or the like, the upper valve body 25 bulges toward the cover body 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 an opening (not shown) formed in the cover body 26.

[0112] Figure 2 It is schematically shown Figure 1 A partial cross-sectional view of a lithium secondary battery is shown. Figure 2 It is an enlarged view of a part of the electrode group 14 . Figure 2 Yes Figure 1 The portion near the positive electrode surrounded by region II and Figure 1 The portion near the negative electrode surrounded by region III.

[0113] The electrode group 14 includes a positive electrode 11, a negative electrode 12, a separator 50, and a separator 53. Here, the separator 50 includes a porous sheet (substrate layer) 51 and a composite material layer 52, but the composite material layer 52 may not be present. The positive electrode 11, the negative electrode 12, and the separator 50 are all in a strip shape. The separator 53 is formed on the composite material layer 52 of the separator 50. The positive electrode 11, the negative electrode 12, and the separator 50 are wound in such a manner that the separator 50 is arranged between the positive electrode 11 and the negative electrode 12, thereby forming the electrode group 14.

[0114] The positive electrode 11 includes a positive electrode current collector 11 a and a positive electrode mixture layer 11 b. The positive electrode current collector 11 a is electrically connected to a lid 26 that functions as a positive electrode terminal via a positive electrode lead 19 . Figure 2 In FIG. 1 , a negative electrode (negative electrode current collector) in a state where lithium metal is not deposited is shown as the negative electrode 12 . The negative electrode 12 is electrically connected to the case body 15 functioning as a negative electrode terminal via a negative electrode lead 20 .

[0115] like Figure 2 As shown in FIG. 1 , the separator 50 has a first main surface 50 a facing the negative electrode 12 and a second main surface 50 b facing the positive electrode 11 . Figure 2 In the example shown, the spacer 53 is formed on the first main surface 50 a .

[0116] In Embodiment 1, the composite material layer 52 is formed on the main surface on the negative electrode 12 side of the two main surfaces of the porous sheet 51. The separator 53 is formed on the composite material layer 52 and is in contact with the negative electrode 12. The separator 53 forms a space 14s between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the separator 50). Figure 2 . The thickness (height) h of the spacer 53 is shown in FIG.

[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 group 14 accompanying the deposition of lithium metal is reduced, and the cycle characteristics are improved.

[0118] An example of the pattern (planar shape) of the spacer 53 is shown in FIG. Figure 3 ,Will Figure 3 A partial enlarged view of Figure 4 . Figure 3 In one example, the spacer 53 is composed of linear protrusions 53a. The linear protrusions 53a are arranged in a mesh shape, and more specifically, are uniformly formed in a honeycomb pattern. The honeycomb pattern is a pattern in which a plurality of hexagons are arranged in a manner that shares edges with each other. The area where the linear protrusions 53a are not formed constitutes the space 14s. Figure 4, the width W of the linear protrusion 53a is shown in FIG. The width W of the linear protrusion is the length (width) of the linear protrusion 53a in a direction perpendicular to the extension direction of the linear protrusion 53a when viewed from above. When viewed from above, the shortest distance from any point on the spacer to the outer edge of the spacer can be, for example, less than 1.5 mm, and the width of the spacer can be, for example, greater than 0.01 mm.

[0119] Another example of the pattern (planar shape) of the spacer 53 is shown in Figure 5 to Figure 7 It should be noted that Figure 3 to Figure 7 This is a diagram showing a plan view of the separator 50 and the spacer 53 . Figure 5 The spacer 53 includes a plurality of linear protrusions 53a separated from each other. There is a gap P between the linear protrusions 53a. The region where the linear protrusions 53a are not formed constitutes the space 14s. Figure 6 The spacer 53 includes a plurality of linear protrusions 53 a arranged in a stripe shape. Figure 7 The spacer 53 includes a plurality of linear protrusions 53 a arranged in a grid pattern.

[0120] In Embodiment 1, a cylindrical lithium secondary battery with a wound electrode group is described. However, the lithium secondary battery of this embodiment is not limited to the method of Embodiment 1, and can also be applied to other methods. The shape of the lithium secondary battery can be appropriately selected from various shapes such as cylindrical, coin-shaped, square, sheet-shaped, flat, etc. according to its use. The shape of the electrode group is not particularly limited, and it can also be a stacked type.

[0121] (Note)

[0122] The following techniques are disclosed through the description of the above embodiments.

[0123] (Technology 1)

[0124] A lithium secondary battery comprising:

[0125] positive electrode;

[0126] negative electrode;

[0127] A porous separator disposed between the positive electrode and the negative electrode;

[0128] a spacer disposed between at least one of the positive electrode and the negative electrode and the separator; and

[0129] A non-aqueous electrolyte having lithium ion conductivity,

[0130] In the negative electrode, lithium metal is deposited during charging and dissolved during discharging.

[0131] The spacer comprises insulating particles, a binder resin and a thickener.

[0132] The insulating particles have a median particle size of 1.0 μm to 10 μm in a volume-based particle size distribution.

[0133] The binder resin comprises a polymer compound having a phthalic acid skeleton,

[0134] The thickener includes at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts.

[0135] (Technique 2)

[0136] In the lithium secondary battery according to technique 1, the spacer is bonded to the separator.

[0137] (Technique 3)

[0138] In the lithium secondary battery according to technology 2, the bonding strength between the spacer and the separator is 20 N / m or more.

[0139] (Technique 4)

[0140] The lithium secondary battery according to the technique 1 or 2, wherein the thickness of the spacer is 20 μm or more.

[0141] (Technique 5)

[0142] The lithium secondary battery according to any one of techniques 1 to 3, wherein the polymer compound is an alkyd resin.

[0143] (Technique 6)

[0144] The lithium secondary battery according to any one of techniques 1 to 5, wherein the weight average molecular weight of the polymer compound (or alkyd resin) is 10,000 to 1,000,000.

[0145] (Technique 7)

[0146] The lithium secondary battery according to any one of techniques 1 to 6, wherein the content of the insulating particles in the spacer is less than 80% by volume.

[0147] (Technology 8)

[0148] The lithium secondary battery according to any one of techniques 1 to 7, wherein the separator has a non-porous structure.

[0149] (Technique 9)

[0150] The lithium secondary battery according to any one of techniques 1 to 8, wherein the area ratio of the first region to the total of the first region of the separator facing the spacer and the second region of the separator not facing the spacer is 30% or less.

[0151] (Technology 10)

[0152] The lithium secondary battery according to any one of techniques 1 to 9, wherein the spacer has a planar shape of at least one of a linear shape and a dot shape arranged in a predetermined pattern.

[0153] (Technology 11)

[0154] The lithium secondary battery according to any one of techniques 1 to 10, wherein the pattern is a mesh-like pattern.

[0155] (Technology 12)

[0156] A spacer and spacer material for lithium secondary battery,

[0157] It contains insulating particles, a binder resin and a thickener.

[0158] The insulating particles have a median particle size of 1.0 μm to 10 μm in a volume-based particle size distribution.

[0159] The binder resin comprises a polymer compound having a phthalic acid skeleton,

[0160] The thickener includes at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts.

[0161] (Technology 13)

[0162] An integrated product of a separator and a spacer for a lithium secondary battery,

[0163] It has: the spacer of technology 12, and the separator,

[0164] The spacer is bonded to the surface of the separator.

[0165] [Example]

[0166] Hereinafter, the lithium secondary battery of the present disclosure will be described in more detail based on examples and comparative examples. However, the present disclosure is not limited to the following examples.

[0167] 《Example 1》

[0168] (1) Preparation of positive electrode

[0169] A rock salt-type lithium-containing transition metal oxide (NCA: positive electrode active material) containing Li, Ni, Co and Al (the molar ratio of Li to the sum of Ni, Co and Al is 1.0) and having a layered structure, acetylene black (AB; conductive material) and polyvinylidene fluoride (PVdF; binding material) are mixed in a mass ratio of NCA:AB:PVdF=95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) is further added and stirred to prepare a positive electrode composite material slurry. The obtained positive electrode composite material slurry is applied to both sides of a strip of Al foil (positive electrode collector), and then dried, and the coating of the positive electrode composite material is rolled using a roller. Finally, the obtained positive electrode collector and the positive electrode composite material stack are cut into a specified electrode size to obtain a positive electrode having positive electrode composite material layers on both sides of the positive electrode collector.

[0170] (2) Preparation of negative electrode

[0171] A strip-shaped electrolytic copper foil (thickness: 15 μm) was prepared as a negative electrode current collector.

[0172] (3) Separator

[0173] A polyethylene separator (microporous film) having a thickness of 20 μm was prepared.

[0174] (4) Formation of spacers

[0175] Insulating particles (median particle size 3 μm, volume resistivity 10 14 Ω·cm) 60 parts by volume, an alkyd resin (weight average molecular weight 10,000 to 1,0000,000) as a binder resin 39 parts by volume, CMC (sodium salt) 1 part by volume, and water as a dispersion medium were mixed to prepare a dispersion of the spacer material.

[0176] Next, a dispersed liquid of the spacer material is dispensed onto the separator using a dispenser to form a Figure 6 The stripe pattern shown in the figure is then dried under vacuum. Figure 6 The stripe-shaped non-porous spacer shown in the figure. At this time, each linear protrusion is formed so that the width W reaches 0.01 mm. The area ratio of the first region is 20% relative to the sum of the first region of the separator facing the spacer and the second region of the separator not facing the spacer.

[0177] (5) Preparation of non-aqueous electrolyte

[0178] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of EC:DMC=30:70, and LiPF6 and LiBF2(C2O4) were dissolved in the resulting mixed solvent at concentrations of 1 mol / L and 0.1 mol / L, respectively, to prepare a liquid non-aqueous electrolyte.

[0179] (6) Battery assembly

[0180] In an inert gas atmosphere, the positive electrode and the negative electrode current collector are spirally wound with the separator interposed therebetween to produce an electrode group. At this time, the separator is arranged so that the separator is opposite to the negative electrode. The electrode group is housed in a bag-shaped outer body formed by a laminate sheet having an Al layer, the nonaqueous electrolyte is injected, and then the outer body is sealed to complete the lithium secondary battery A1.

[0181] Comparative Example 1

[0182] In the formation of the spacer (4), a lithium secondary battery B1 was produced in the same manner as in Example 1 except that no alkyd resin was used and 60 parts by mass of insulating particles, 40 parts by mass of CMC and water as a dispersion medium were mixed to prepare a dispersion of the spacer material.

[0183] Comparative Example 2

[0184] In the formation of the spacer (4), a lithium secondary battery B2 was produced in the same manner as in Example 1 except that CMC was not used and 60 parts by mass of insulating particles, 40 parts by mass of alkyd resin, and water as a dispersion medium were mixed to prepare a dispersion of the spacer material.

[0185] Comparative Example 3

[0186] A lithium secondary battery B3 was prepared in the same manner as in Example 1, except that a polyester resin (epoxy polyester) having no phthalic acid skeleton was used instead of the alkyd resin in the formation of the spacer (4).

[0187] 《Comparative Example 4》

[0188] A lithium secondary battery B4 was produced in the same manner as in Example 1, except that a polyolefin resin was used instead of the alkyd resin in the formation of the spacer (4).

[0189] 《Comparative Example 5》

[0190] A lithium secondary battery B5 was produced in the same manner as in Example 1, except that polyacrylic acid (PAA) was used instead of CMC in the formation of the spacer (4).

[0191] 《Comparative Example 6》

[0192] A lithium secondary battery B5 was produced in the same manner as in Example 1, except that polyvinyl pyrrolidone (PVP) was used instead of CMC in the formation of the spacer (4).

[0193] It should be noted that CMC, PAA and PVP are all water-soluble and function as thickeners. Alkyd resins, polyester resins and polyolefin resins used as binder resins are not dissolved in water but are dispersed in water in the form of fine particles.

[0194] [Evaluation 1]

[0195] Before assembling the battery, the appearance of the spacer was observed under a microscope. When unevenness or cracks were observed in the spacer, it was evaluated as ×, and when a uniform spacer was observed, it was evaluated as 0.

[0196] [Evaluation 2]

[0197] Before assembling the battery, the structure of the spacer was observed using a scanning electron microscope (SEM). When a porous structure was observed, it was evaluated as ×, and when a dense non-porous structure was observed, it was evaluated as 0.

[0198] [Evaluation 3]

[0199] As described above, the dispersion of the spacer material is applied to the surface of the separator to form a spacer material film, and a peel test is performed to measure the bonding strength between the spacer and the separator.

[0200] [Evaluation 4]

[0201] As described above, a cross section of the separator in the thickness direction is photographed by SEM, the thickness of the spacer is measured at any 10 locations, and the thickness (height) of the spacer is calculated as the average value.

[0202] The obtained results are shown in Table 1.

[0203] [Table 1]

[0204]

[0205] In battery A1, a separator was obtained which was bonded to the separator with a high bonding strength (21.3 N / m) and had a sufficient thickness (40.7 μm). This confirmed that the compatibility between the alkyd resin and CMC was good.

[0206] Note that, when battery A1 was charged in a thermostatic chamber at 25° C. under the following conditions, then stopped for 20 minutes and discharged under the following conditions, the cycle was repeated and a capacity retention rate of 90% or more was obtained even at the 50th cycle.

[0207] (Charge)

[0208] The battery was charged at a constant current of 2.15 mA per unit area (cm2) of the electrode until the battery voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V until the current value per unit area of ​​the electrode reached 0.54 mA.

[0209] (Discharge)

[0210] The battery was discharged at a constant current of 2.15 mA per unit area of ​​the electrode until the battery voltage reached 3.75 V.

[0211] The present invention has been described with respect to the presently preferred embodiments, but is not to be construed as such disclosure. Upon reading the above disclosure, various modifications and variations will undoubtedly be apparent to those skilled in the art of the art to which the present invention belongs. Therefore, the appended claims should be construed as including all modifications and variations without departing from the true spirit and scope of the present invention.

[0212] Industrial Applicability

[0213] The lithium secondary battery disclosed in the present invention can be used in electronic devices such as mobile phones, smart phones, and tablet terminals; electric vehicles including hybrid and plug-in hybrid vehicles; household storage batteries combined with solar cells, etc.

[0214] Description of Reference Numerals

[0215] 10: Lithium secondary battery

[0216] 11: Positive electrode

[0217] 12: Negative electrode

[0218] 14: Electrode Group

[0219] 14s: Space

[0220] 50: Separator

[0221] 51: Base material layer

[0222] 50a, 50b: Main surface

[0223] 52: Composite material layer

[0224] 53: Spacer

[0225] 53a: convex part

Claims

1. A lithium secondary battery comprising: positive electrode; negative electrode; a porous separator disposed between the positive electrode and the negative electrode; a spacer disposed between at least one of the positive electrode and the negative electrode and the separator; and Non-aqueous electrolyte with lithium ion conductivity, In the negative electrode, lithium metal is precipitated during charging and dissolved during discharging. The spacer comprises insulating particles, a binder resin and a thickener, The insulating particles have a median particle size of 1.0 μm to 10 μm in a volume-based particle size distribution. The binder resin includes a polymer compound having a phthalic acid skeleton, The thickener includes at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts.

2. The lithium secondary battery according to claim 1, wherein The spacer is bonded to the partition.

3. The lithium secondary battery according to claim 2, wherein: The bonding strength between the spacer and the separator is 20 N / m or more.

4. The lithium secondary battery according to claim 1, wherein The thickness of the spacer is greater than 20 μm.

5. The lithium secondary battery according to claim 1, wherein The polymer compound is an alkyd resin.

6. The lithium secondary battery according to claim 5, wherein: The weight average molecular weight of the alkyd resin is 10,000 to 1,000,000.

7. The lithium secondary battery according to claim 1, wherein: The content of the insulating particles in the spacer is less than 80 volume %.

8. The lithium secondary battery according to claim 1, wherein The spacer has a non-porous structure.

9. The lithium secondary battery according to claim 1, wherein: The area ratio of the first region to the total of the first region of the separator facing the spacer and the second region of the separator not facing the spacer is 30% or less.

10. The lithium secondary battery according to claim 1, wherein The spacer has a planar shape of at least one of a linear shape and a dot shape arranged in a predetermined pattern.

11. The lithium secondary battery according to claim 1, wherein The pattern is a mesh-like pattern.

12. A spacer and spacer material for a lithium secondary battery, It contains insulating particles, a binder resin and a thickener. The insulating particles have a median particle size of 1.0 μm to 10 μm in a volume-based particle size distribution. The binder resin includes a polymer compound having a phthalic acid skeleton, The thickener includes at least one selected from the group consisting of carboxymethyl cellulose and carboxymethyl cellulose salts.

13. An integrated product of a separator and a spacer for a lithium secondary battery, It comprises: the spacer according to claim 12, and a separator, The spacer is bonded to the surface of the partition.

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