A separator for secondary batteries, and a secondary battery using the same.

Abstract

In a secondary battery, the present invention provides a means to reduce the ion permeability of the separator when the temperature rises due to heat generation during charging and discharging of the battery. [Solution] A separator for use in a secondary battery, comprising a cellulose material, a ceramic, and a shutdown layer containing a first polymer (excluding the cellulose material) that melts at a temperature 10 to 100°C higher than the upper limit temperature under the operating environment of the secondary battery, wherein the content of the first polymer in the shutdown layer is 20% by mass or more with respect to 100% by mass of the total mass of the cellulose material, the ceramic, and the first polymer.

Description

[Technical Field]

[0001] This invention relates to a separator for secondary batteries and a secondary battery using the same. [Background technology]

[0002] In recent years, the widespread adoption of various electric vehicles has been anticipated as a way to address environmental and energy problems. As a key element in the proliferation of these electric vehicles, intensive development efforts are underway to develop rechargeable batteries for use as on-board power sources, such as motor drive power supplies. Lithium-ion rechargeable batteries intended for on-board applications require high capacity and excellent output characteristics.

[0003] As a technique for obtaining a secondary battery electrode having a separator layer with excellent heat resistance and mechanical strength, as well as low internal resistance, Patent Document 1 discloses a method of using a layer made of a ceramic nanoparticle aggregate in which multiple ceramic nanoparticles are linearly supported on cellulose nanofibers as the separator layer. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-78235 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, it was found that the technology disclosed in Patent Document 1 does not have a "shutdown function" that reduces the ion permeability of the separator when the lithium-ion battery overheats and becomes hot due to a short circuit or other reasons.

[0006] Therefore, the present invention aims to provide a means for reducing the ion permeability of a separator in a secondary battery when the temperature rises due to heat generation during charging and discharging of the battery. [Means for solving the problem]

[0007] The inventors diligently conducted research to solve the above problems. As a result, they discovered that the above problems could be solved by incorporating cellulose material, ceramic, and polyolefin particles into the separator, and thus completed the present invention.

[0008] In other words, one embodiment of the present invention relates to a separator for a secondary battery having a shutdown layer comprising a cellulose material, a ceramic, and a first polymer (excluding the cellulose material) that melts at a temperature 10 to 100°C higher than the upper limit temperature under the operating environment of the secondary battery. The separator for the secondary battery is characterized in that the content of the first polymer in the shutdown layer is 20% by mass or more with respect to 100% by mass of the total mass of the cellulose material, the ceramic, and the first polymer. [Effects of the Invention]

[0009] According to one embodiment of the present invention, the ion permeability of the separator can be reduced when the temperature rises due to heat generation during charging and discharging of the battery. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of a stacked (flat) non-bipolar (internal parallel connection type) secondary battery, which is one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view of a bipolar secondary battery, which is another embodiment of the present invention. [Modes for carrying out the invention]

[0011] One embodiment of the present invention is a separator for use in a secondary battery, comprising a cellulose material, a ceramic, and a first polymer (excluding the cellulose material) that melts at a temperature 10 to 100 °C higher than the upper limit temperature in the usage environment of the secondary battery, and having a shutdown layer containing the first polymer, wherein the content of the first polymer in the shutdown layer is 20% by mass or more based on 100% by mass of the total mass of the cellulose material, the ceramic, and the first polymer. According to the separator of this embodiment, the ion permeability of the separator can be reduced when the temperature rises due to heat generation during charging and discharging of the battery.

[0012] Hereinafter, embodiments of the present invention described above will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description in the claims and is not limited only to the following embodiments. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios. In this specification, "X to Y" indicating a range means "X or more and Y or less". Also, unless otherwise specified, measurements of operations and physical properties are performed under conditions of room temperature (20 to 25 °C) and relative humidity of 40 to 50% RH.

[0013] FIG. 1 is a cross-sectional view schematically showing a flat (laminated) non-bipolar (internally parallel-connected type) secondary battery (hereinafter, also simply referred to as "laminated secondary battery") which is an embodiment of the present invention.

[0014] As shown in FIG. 1, the laminated secondary battery 10a of this embodiment has a structure in which a substantially rectangular power generation element 21 where the charge and discharge reactions actually proceed is sealed inside a laminate film 29. Here, the power generation element 21 includes a positive electrode in which positive electrode active material layers 13 are disposed on both surfaces of a positive electrode current collector 11', an electrolyte layer 17 composed of a separator (the "separator for secondary battery" according to this embodiment) containing an electrolytic solution, and a negative electrode in which negative electrode active material layers 15 are disposed on both surfaces of a negative electrode current collector 12. Specifically, one positive electrode active material layer 13 and the adjacent negative electrode active material layer 15 face each other through the electrolyte layer 17, and the positive electrode, the electrolyte layer, and the negative electrode are laminated in this order.

[0015] As a result, the positive electrode, electrolyte layer, and negative electrode constitute a single cell layer 19. Therefore, the stacked secondary battery 10a shown in Figure 1 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel. In addition, the outermost positive electrode current collectors located on both outermost layers of the power generation element 21 have a positive electrode active material layer 13 on only one side, but active material layers may be provided on both sides. That is, instead of using a current collector dedicated to the outermost layer with an active material layer on only one side, a current collector with active material layers on both sides may be used as the outermost current collector. Furthermore, by reversing the arrangement of the positive and negative electrodes from that in Figure 1, the outermost negative electrode current collectors may be located on both outermost layers of the power generation element 21, and the negative electrode active material layer may be provided on one or both sides of the outermost negative electrode current collector.

[0016] The positive electrode current collector 11' and the negative electrode current collector 12 are each fitted with a positive electrode current collector plate 25 and a negative electrode current collector plate 27, which are electrically connected to the respective electrodes (positive and negative electrodes), and are structured to be led out to the outside of the laminate film 29 by being sandwiched between the edges of the laminate film 29. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be attached to the positive electrode current collector 11' and the negative electrode current collector 12 of each electrode via positive electrode terminal leads and negative electrode terminal leads (not shown), respectively, by ultrasonic welding, resistance welding, or the like, as needed.

[0017] Figure 2 is a schematic cross-sectional view of a bipolar secondary battery, which is another embodiment of the present invention. The bipolar secondary battery 10b shown in Figure 2 has a structure in which a substantially rectangular power generation element 21, on which the charge-discharge reaction actually proceeds, is sealed inside a laminate film 29, which is the battery casing. In this specification, a bipolar lithium-ion secondary battery may also be simply referred to as a "bipolar secondary battery," and an electrode for a bipolar lithium-ion secondary battery may be simply referred to as a "bipolar electrode."

[0018] As shown in Figure 2, the power generation element 21 of the bipolar secondary battery 10b in this embodiment has a plurality of bipolar electrodes 23, each having a positive electrode active material layer 13 electrically coupled to one side of a current collector 11 and a negative electrode active material layer 15 electrically coupled to the opposite side of the current collector 11. Each bipolar electrode 23 is stacked via an electrolyte layer 17 made of a separator containing an electrolyte (the "separator for secondary battery" in this embodiment) to form the power generation element 21. In this case, the bipolar electrodes 23 and the electrolyte layer 17 are stacked alternately such that the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the first bipolar electrode 23 face each other via the electrolyte layer 17. That is, the electrolyte layer 17 is sandwiched between the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the first bipolar electrode 23.

[0019] The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute a single cell layer 19. Therefore, it can be said that the bipolar secondary battery 10b has a structure in which single cell layers 19 are stacked. Furthermore, a sealing portion (insulating layer) 31 is arranged on the outer periphery of the single cell layer 19. This prevents liquid junctions due to leakage of electrolyte from the electrolyte layer 17, and prevents contact between adjacent current collectors 11 within the battery, as well as short circuits caused by slight irregularities at the ends of the single cell layer 19 in the power generation element 21. The outermost current collector 11a on the positive electrode side, located in the outermost layer of the power generation element 21, has a positive electrode active material layer 13 formed on only one side. Similarly, the outermost current collector 11b on the negative electrode side, located in the outermost layer of the power generation element 21, has a negative electrode active material layer 15 formed on only one side.

[0020] Furthermore, in the bipolar secondary battery 10b shown in Figure 2, the positive electrode current collector plate (positive electrode tab) 25 is positioned adjacent to the outermost current collector 11a on the positive electrode side, and this is extended and leads out from the laminate film 29 which is the battery casing. On the other hand, the negative electrode current collector plate (negative electrode tab) 27 is positioned adjacent to the outermost current collector 11b on the negative electrode side, and similarly this is extended and leads out from the laminate film 29.

[0021] The number of times the single cell layers 19 are stacked is adjusted according to the desired voltage. In the case of the bipolar secondary battery 10b, the number of times the single cell layers 19 are stacked may be reduced if sufficient output can be secured even with the battery thickness made as thin as possible. In the case of the bipolar secondary battery 10b, in order to prevent external shocks and environmental degradation during use, it is preferable to have a structure in which the power generation element 21 is sealed under reduced pressure in the laminate film 29 which is the battery casing, and the positive electrode current collector plate 25 and the negative electrode current collector plate 27 are brought out to the outside of the laminate film 29.

[0022] <Separator for secondary batteries> The main components of the secondary battery separator according to this embodiment are described below. The secondary battery separator according to this embodiment has a shutdown layer containing a cellulose material, a ceramic, and a first polymer. In the shutdown layer, when the temperature of the secondary battery rises above a predetermined temperature, for example due to a short circuit, the first polymer melts, blocking the pores in the layer and reducing the ion conductivity (shutdown phenomenon).

[0023] (Cellulose material) Cellulose material has a backbone in which glucose is linked by β-1,4 bonds, and has the molecular formula (C6H 10 O5) n It is a carbohydrate or a derivative thereof represented by the molecular formula (C6H). 10 O5) n Carbohydrate derivatives represented by the formula (C6H) are those that have undergone processes such as the introduction of functional groups, oxidation, reduction, or substitution of atoms. 10 O5) n This refers to compounds that have been modified to a degree that does not significantly alter the structure or properties of the carbohydrate represented by [the formula].

[0024] Examples of cellulose materials include methylcellulose, ethylcellulose, ethylmethylcellulose, carboxymethylcellulose (CMC), hydroxyethylcellulose, hydroxybutylmethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose stearoxy ether, carboxymethylhydroxyethylcellulose, alkylhydroxyethylcellulose, nonoxynyl hydroxyethylcellulose, cellulose acetate, methylcellulose ether, methylethylcellulose ether, ethylcellulose ether, low nitrogen hydroxyethylcellulose dimethyldiallylammonium chloride (polyquaternium-4), chloride-[2-hydroxy-3-(trimethylammonio)propyl]hydroxyethylcellulose (polyquaternium-10), chloride-[2-hydroxy-3-(lauryldimethylammonio)propyl]hydroxyethylcellulose (polyquaternium-24), hemicellulose, and cellulose nanofibers. Of these, from the viewpoint of improving mechanical strength under high-temperature conditions, it is preferable that the cellulose material contains cellulose nanofibers.

[0025] The shape of the cellulose material is not particularly limited, but examples include particulate (spherical, fibrous), thin film, etc. When the cellulose material is in particulate form, its average particle size (D50) is preferably, for example, 1 nm to 100 μm, more preferably 10 nm to 50 μm, even more preferably 100 nm to 20 μm, and particularly preferably 1 to 20 μm. In this specification, the value of the average particle size (D50) of the particles can be measured by volume-based laser diffraction scattering.

[0026] From the viewpoint of safety under high-temperature conditions, the melting point of the cellulose material is preferably higher than the melting point of the first polymer, and the difference in melting points between the two polymers is, for example, 10°C or more, preferably 20°C or more, and more preferably 30°C or more. There is no particular upper limit, for example, 500°C or less.

[0027] The cellulose material content in the shutdown layer is, for example, 5% to 70% by mass, preferably 10% to 40% by mass, and more preferably 15% to 35% by mass, based on 100% by mass of the total mass of the cellulose material, the ceramic, and the first polymer. Furthermore, the cellulose material content relative to the total mass of the shutdown layer is, for example, 1% to 70% by mass, preferably 10% to 40% by mass.

[0028] (ceramic) The ceramic is not particularly limited, but examples include oxides and nitrides containing one or more elements selected from the group consisting of aluminum, silicon, zirconium, magnesium, calcium, scandium, yttrium, cesium, titanium, vanadium, iron, nickel, zinc, niobium, and tin. In particular, the ceramic preferably contains at least one selected from the group consisting of Al2O3, SiO2, ZrO2, Al(OH)3, Mg(OH)2, and AlOOH, and more preferably contains Al2O3 (alumina). These may be used individually or in combination of two or more.

[0029] The shape of the ceramic is not particularly limited, but examples include particulate (spherical, fibrous), thin film, etc. When the ceramic is in particulate form, its average particle size (D50) is preferably 1 nm to 100 μm, more preferably 5 nm to 1 μm, even more preferably 10 nm to 100 nm, and particularly preferably 20 nm to 80 nm.

[0030] The ceramic content in the shutdown layer is, for example, 5% to 70% by mass, preferably 10% to 40% by mass, and more preferably 15% to 35% by mass, based on 100% by mass of the total mass of the cellulose material, the ceramic, and the first polymer. Furthermore, the ceramic content relative to the total mass of the shutdown layer is, for example, 1% to 70% by mass, preferably 10% to 40% by mass.

[0031] (First polymer) The first polymer is a polymer that melts at a temperature 10 to 100°C higher than the upper limit temperature under the operating environment of the secondary battery. By including such a polymer in the shutdown layer, the polymer melts under high-temperature conditions due to heat generation during battery charging and discharging, thereby reducing the ion permeability of the battery. Examples of the first polymer include, but are not limited to, polyolefins, polyhalogenated vinyls, and copolymers thereof. In particular, from the viewpoint of reducing ion permeability more rapidly, the first polymer preferably contains at least one selected from the group consisting of polyethylene, polypropylene, polybutene, and polyvinyl chloride, more preferably at least one selected from the group consisting of polyethylene and polypropylene, and most preferably polyethylene. The first polymer may be used alone or two or more may be used in combination. Furthermore, the first polymer may melt at a temperature 15-100, 20-100, 30-100, 40-100, or 50-100 degrees higher than the upper limit temperature under the operating environment of the secondary battery, or it may melt at a temperature 10-90, 10-80, 10-70, 10-60, or 10-50 degrees higher than the said upper limit temperature.

[0032] If the first polymer contains polyethylene, the blending ratio of polyethylene in the first polymer may be 50% by mass or more and 100% by mass or less, preferably 70% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and most preferably 100% by mass, based on the total mass of the first polymer.

[0033] The melting point of the first polymer is, for example, above 80°C and below 200°C, preferably above 80°C and below 180°C, and more preferably above 80°C and below 130°C. When the melting point is within the above range, the risk of reduced ion permeability during normal use of the battery can be further suppressed, and battery degradation can be effectively suppressed.

[0034] The content of the first polymer in the shutdown layer is, for example, 30% to 80% by mass, preferably 33% to 70% by mass, and more preferably 50% to 60% by mass, based on 100% by mass of the total mass of the cellulose material, the ceramic, and the first polymer. When within the above range, it is possible to have excellent ionic conductivity while possessing a shutdown function. In one embodiment, from the viewpoint of having an even better shutdown function, the content of the first polymer in the shutdown layer is preferably 66% to 90% by mass. Also, the content of the first polymer relative to the total mass of the shutdown layer is, for example, 20% to 80% by mass, and preferably 30% to 70% by mass.

[0035] (Second polymer) The shutdown layer may further contain a second polymer having a higher melting point than the first polymer and exhibiting binding properties. The inclusion of the second binding polymer allows for better retention of solids in the shutdown layer, resulting in superior mechanical strength under high-temperature conditions. Furthermore, the second polymer only needs to have a higher melting point than the first polymer, as long as it exhibits binding properties, and this is determined by the relative relationship between the melting points of each polymer. Therefore, even the same type of polymer may be used as either the first polymer or the second polymer depending on its relationship with other present polymers.

[0036] Examples of the second polymer include polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polymethylpentene, polyethernitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyvinyl chloride, styrene-butadiene rubber (SBR), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber), epoxy resin, and the like. Among these, it is preferable that the polymer contains a fluorine atom, more preferably that it contains at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, and polyvinyl fluoride (PVF), and particularly preferably that it contains polyvinylidene fluoride (PVDF).

[0037] The content of the second polymer relative to the total mass of the shutdown layer is, for example, 0.1% to 20% by mass, preferably 1% to 10% by mass.

[0038] The difference between the melting point of the first polymer and the melting point of the second polymer is, for example, 5°C or more, preferably 10°C or more, more preferably 20°C or more, and even more preferably 50°C or more. The upper limit of the above difference in melting points is not particularly limited, but is, for example, 250°C or less, preferably 200°C or less.

[0039] The thickness of the separator for secondary batteries is, for example, 1 to 100 μm, preferably 5 to 80 μm, more preferably 10 to 50 μm, and even more preferably 15 to 30 μm. When the thickness of the separator for secondary batteries is within the above range, the ionic conductivity of the battery is further improved, and the mechanical strength under high-temperature conditions is further enhanced.

[0040] Another embodiment of the present invention is a secondary battery comprising a power generation element having a positive electrode with a positive electrode active material layer disposed on the surface of a positive electrode current collector, a negative electrode with a negative electrode active material layer disposed on the surface of a negative electrode current collector, and an electrolyte layer interposed between the positive electrode and the negative electrode, which includes the above-mentioned secondary battery separator and electrolyte. The secondary battery is preferably a lithium-ion secondary battery.

[0041] <Lithium-ion rechargeable battery> [Current collector] The current collector has the function of mediating the movement of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. There are no particular restrictions on the material that constitutes the current collector, but for example, metals or conductive resins can be used.

[0042] Specifically, examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, clad materials of nickel and aluminum, clad materials of copper and aluminum, or plated materials of combinations of these metals can be preferably used. Furthermore, foils in which aluminum is coated on a metal surface, or carbon-coated aluminum foil may also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoint of electronic conductivity and battery operating potential.

[0043] Furthermore, the latter type of conductive resin includes conductive polymer materials or resins to which conductive fillers are added as needed. Examples of conductive polymer materials include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylenevinylene, polyacrylonitrile, and polyoxadiazole. Such conductive polymer materials have sufficient conductivity even without the addition of conductive fillers, which is advantageous in terms of simplifying the manufacturing process or reducing the weight of the current collector.

[0044] Examples of non-conductive polymer materials include polyethylene (PE; high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), polyimide (PI), polyamide-imide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymer materials can have excellent potential resistance or solvent resistance.

[0045] Conductive fillers may be added to the above-mentioned conductive or non-conductive polymer materials as needed. In particular, if the resin that serves as the base material for the current collector consists solely of a non-conductive polymer, a conductive filler is necessarily required to impart conductivity to the resin.

[0046] The conductive filler can be any conductive material without particular limitations. For example, materials with excellent conductivity, potential resistance, or lithium ion shielding properties include metals and conductive carbon. The metal preferably includes at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or an alloy or metal oxide containing these metals. The conductive carbon preferably includes at least one selected from the group consisting of acetylene black, Vulcan®, Black Pearl®, carbon nanofiber, Ketjenblack®, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

[0047] There are no particular restrictions on the amount of conductive filler added, as long as it is sufficient to impart sufficient conductivity to the current collector; generally, it is around 5 to 80% by mass.

[0048] The current collector may be a single-layer structure made of a single material, or it may be a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include at least a conductive resin layer made of a conductive resin. Furthermore, from the viewpoint of blocking the movement of lithium ions between single cell layers, a metal layer may be provided on a part of the current collector.

[0049] [Cathode active material layer] The positive electrode active material layer must contain a positive electrode active material and may optionally contain a binder and a conductive additive. In addition, the positive electrode active material layer may also contain optional components such as an electrolyte (liquid electrolyte).

[0050] (Cathode active material) As the positive electrode active material, for example, lithium-transition metal composite oxides such as LiMn2O4, LiCoO2, LiNiO2, Li(Ni-Mn-Co)O2 and those in which some of these transition metals are substituted with other elements, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, etc. can be mentioned. In some cases, two or more positive electrode active materials may be used in combination. Preferably, from the viewpoints of capacity and output characteristics, a lithium-transition metal composite oxide is used as the positive electrode active material. More preferably, a composite oxide containing lithium and nickel is used. Even more preferably, Li(Ni-Mn-Co)O2 and those in which some of these transition metals are substituted with other elements (hereinafter, also simply referred to as "NMC composite oxide"), or lithium-nickel-cobalt-aluminum composite oxide (hereinafter, also simply referred to as "NCA composite oxide") etc. are used. The NMC composite oxide has a layered crystal structure in which lithium atom layers and transition metal (Mn, Ni, and Co are orderly arranged) atom layers are alternately stacked via oxygen atom layers. And, one Li atom is contained per one atom of the transition metal M, and the amount of Li that can be extracted is twice that of the spinel-type lithium manganese oxide, that is, the supply capacity is doubled, and it can have a high capacity.

[0051] As described above, the NMC composite oxide also includes a composite oxide in which some of the transition metal elements are substituted with other metal elements. Examples of the other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu, Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, Cr, and even more preferably, from the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, Cr.

[0052] Since the NMC composite oxide has a high theoretical discharge capacity, preferably, the general formula (1): Li a Ni b Mn c Co d M xO2 (wherein, in the formula, a, b, c, d, and x satisfy 0.9 ≦ a ≦ 1.2, 0 < b < 1, 0 ≦ c ≦ 0.5, 0 < d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. M is at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr). Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. From the perspective of cycle characteristics, in the general formula (1), it is preferable that 0.4 ≦ b ≦ 0.6. The composition of each element can be measured, for example, by inductively coupled plasma (ICP) emission spectrometry.

[0053] Generally, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the perspectives of improving the purity of the material and improving electron conductivity. Ti, etc. are those that partially substitute transition metals in the crystal lattice. From the perspective of cycle characteristics, it is preferable that a part of the transition element is substituted by other metal elements, and particularly in the general formula (1), it is preferable that 0 < x ≦ 0.3. The crystal structure is stabilized by the solid solution of at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. As a result, it is considered that the capacity reduction of the battery can be prevented even when charge and discharge are repeated, and excellent cycle characteristics can be achieved.

[0054] As a more preferable embodiment, in the general formula (1), b, c, and d being 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, and 0.19 ≦ d ≦ 0.26 is preferable from the perspective of improving the balance between capacity and life characteristics. For example, LiNi 0.5 Mn 0.3 Co 0.2 O2 is LiCoO2, LiMn2O4, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3Compared to materials like O2, it has a larger capacity per unit mass. This allows for improved energy density and the creation of compact, high-capacity batteries, which is advantageous from the perspective of cruising range.

[0055] Furthermore, a more preferred embodiment would be LiNi 0.8 Co 0.1 Al 0.1 O2 and LiNi 0.8 Co 0.15 Al 0.05 O2 is preferred.

[0056] From the viewpoint of increasing power output, the average particle size of the positive electrode active material is preferably 1 to 100 μm, more preferably 1 to 20 μm. In this specification, the average particle size is that which is measured by a particle size distribution analyzer using laser diffraction / scattering.

[0057] The content of the electrode active material in the electrode active material layer is, for example, 60% by mass or more and less than 100% by mass, preferably 80% by mass or more and 99.5% by mass or less, more preferably more than 95% by mass and 99.0% by mass or less, and even more preferably 96% by mass or more and 98.5% by mass or less, based on 100% by mass of total solids. If the content of the electrode active material is within the above range, both battery capacity and output characteristics can be achieved.

[0058] (Binder) The positive electrode active material may further contain a binder. The binder is not particularly limited, but examples include thermoplastic polymers such as polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogenated products, styrene-isoprene-styrene block copolymer and its hydrogenated products, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), and polychlorotrifluoroethylene. Examples include fluororesins such as polyethylene chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-based fluororubbers such as vinylidene fluoride-hexafluoropropylene-based fluororubbers (VDF-HFP-based fluororubbers), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-HFP-TFE-based fluororubbers), vinylidene fluoride-pentafluoropropylene-based fluororubbers (VDF-PFP-based fluororubbers), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), epoxy resins, and others. The binder content in the positive electrode active material layer is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, based on 100% by mass of the total solid content of the positive electrode active material layer.

[0059] (Conductive additive) The positive electrode active material layer may further contain a conductive additive. The conductive additive has the function of forming electron conduction paths (conductive passages) in the positive electrode active material layer. When such electron conduction paths are formed in the positive electrode active material layer, the internal resistance of the battery can be reduced and the output characteristics at high rates can be improved. In particular, it is preferable that at least a portion of the conductive additive forms conductive passages that electrically connect the two main surfaces of the positive electrode active material layer (in this embodiment, conductive passages are formed that electrically connect the first main surface of the positive electrode active material layer that contacts the electrolyte layer side to the second main surface that contacts the current collector side). With this configuration, the electron transfer resistance in the thickness direction in the positive electrode active material layer is further reduced, and the output characteristics of the battery at high rates can be further improved. Furthermore, whether at least a portion of the conductive additive forms a conductive passage that electrically connects the two main surfaces of the positive electrode active material layer (in this embodiment, a conductive passage that electrically connects the first main surface of the positive electrode active material layer that contacts the electrolyte layer side to the second main surface that contacts the current collector side) can be confirmed by observing a cross-section of the positive electrode active material layer using a scanning electron microscope (SEM) or optical microscope.

[0060] Examples of conductive additives include particulate carbon materials and fibrous carbon materials. In this specification, particulate carbon materials refer to carbon materials with an aspect ratio of 20 or less of primary particles. In this specification, fibrous carbon materials refer to carbon materials with an aspect ratio of 1000 or more. In this specification, the aspect ratios of particulate carbon materials and fibrous carbon materials refer to the average value of the ratio of the length of the major axis to the length of the minor axis of 100 carbon materials arbitrarily selected by scanning electron microscopy (SEM).

[0061] Examples of particulate carbon materials include carbon powders such as acetylene black, carbon black, channel black, thermal black, and Ketjenblack (registered trademark). Examples of fibrous carbon materials include carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes), carbon nanofibers, vapor-grown carbon fibers, electrospun carbon fibers, polyacrylonitrile-based carbon fibers, and pitch-based carbon fibers. Among these, it is preferable to include carbon nanotubes (CNTs) from the viewpoint of conductivity. The diameter (short axis) of the fibrous carbon material (preferably carbon nanotubes) is not particularly limited, but is preferably 1 to 100 nm, more preferably 2 to 50 nm, and even more preferably 5 to 20 nm. The length (long axis) of the fibrous carbon material (preferably carbon nanotubes) is not particularly limited, but is preferably 1 to 100 μm, more preferably 2 to 50 μm, and even more preferably 5 to 30 μm. Furthermore, the aspect ratio of the fibrous carbon material (preferably carbon nanotubes) is 1000 or more as described above, but is preferably 1500 or more, and more preferably 1800 or more. The upper limit of the aspect ratio of the fibrous carbon material (preferably carbon nanotubes) is not particularly limited, but for example it may be 20000 or less, 10000 or less, 5000 or less, or 4000 or less.

[0062] The thickness of the positive electrode active material layer is not particularly limited, and conventionally known knowledge regarding batteries may be referenced as appropriate. The thickness of the positive electrode active material layer is, for example, 1 to 1000 μm, preferably 20 to 800 μm, more preferably 30 to 500 μm, and even more preferably 40 to 200 μm.

[0063] The content of the conductive additive in the positive electrode active material layer is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the total solid content of the positive electrode active material layer. With such upper limits, aggregation of conductive additives is suppressed, allowing for the formation of good electron conduction paths, thereby further improving output characteristics. It also becomes possible to further improve the energy density of the lithium-ion secondary battery. The lower limit of the content of the conductive additive is not particularly limited, but it is preferably greater than 0% by mass and 0.1% by mass or more, preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more. With such lower limits, there is sufficient conductive additive to form electron conduction paths, so output characteristics can be further improved. Of course, conductive additives other than those mentioned above may be used as long as they do not impair the effects of the present invention.

[0064] [Negative electrode active material layer] The negative electrode active material layer must contain a negative electrode active material. Examples of negative electrode active materials include carbon materials such as graphite, soft carbon, and hard carbon, and lithium-transition metal composite oxides (e.g., Li4Ti5O 12 ), metallic materials (tin, silicon), silicon-containing alloy negative electrode materials (e.g., Si 60 Sn 10 Ti 30 Examples include lithium alloy-based anode materials (e.g., lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.). In some cases, two or more anode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, silicon-containing alloy-based anode materials, carbon materials, lithium-transition metal composite oxides, and lithium alloy-based anode materials are preferably used as anode active materials. Of course, other anode active materials may also be used.

[0065] The average particle size of the negative electrode active material is not particularly limited, but from the viewpoint of increasing power output, it is preferably 1 to 100 μm, and more preferably 1 to 20 μm.

[0066] The content of the negative electrode active material in the negative electrode active material layer is, for example, 60% by mass or more and less than 100% by mass, preferably 80% by mass or more and 99.5% by mass or less, more preferably greater than 95% by mass and 99.0% by mass or less, and even more preferably 97% by mass or more and 98.5% by mass or less, based on 100% by mass of total solids. If the content of the negative electrode active material is within the above range, both battery capacity and output characteristics can be achieved.

[0067] Furthermore, the negative electrode active material layer may optionally include other additives such as binders and conductive additives, similar to those described above for the positive electrode active material layer.

[0068] The thickness of the negative electrode active material layer is not particularly limited and is the same as that of the positive electrode active material layer as described above. This could be adopted.

[0069] [Electrolyte layer] The electrolyte layer is positioned adjacent to the electrodes and has a structure in which the aforementioned secondary battery separator is impregnated with an electrolyte. It should be noted that "positioned adjacent to the electrodes" does not only refer to cases where the electrolyte layer is directly adjacent to the electrodes, but also includes cases where other layers are interposed between the electrolyte layer and the electrodes as needed.

[0070] (electrolyte) The electrolyte (liquid electrolyte) functions as a carrier for lithium ions. The electrolyte (liquid electrolyte) that makes up the electrolyte layer has the form of lithium salt dissolved in an organic solvent.

[0071] Examples of organic solvents used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), methyl formate (MF), 4-methyl dioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). In particular, the organic solvent is preferably a linear carbonate, more preferably at least one selected from the group consisting of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and more preferably selected from ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0072] Examples of lithium salts include Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), Li(C2F5SO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, and LiCF3SO3. Among these, from the viewpoint of battery output and charge / discharge cycle characteristics, the lithium salt preferably contains an imide group-containing anion as a counteranion to the lithium ion, and more preferably Li(FSO2)2N(LiFSI).

[0073] The concentration of lithium salt in the electrolyte is preferably 0.1 to 3.0 mol / L. It is more preferable that the concentration be between 0.8 and 2.2 mol / L.

[0074] The electrolyte may further contain additives other than those mentioned above. Specific examples of such compounds include, for example, ethylene carbonate, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinylethylene carbonate, 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, and 1-ethyl-2-vinylethylene Examples include ethylene carbonate, vinylvinylene carbonate, allyl ethylene carbonate, vinyloxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acrylicoxymethyl ethylene carbonate, methacrylicoxymethyl ethylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, ethynyloxymethyl ethylene carbonate, propargyloxyethylene carbonate, methylene ethylene carbonate, and 1,1-dimethyl-2-methylene ethylene carbonate. These additives may be used individually or in combination of two or more. The amount of additive used in the electrolyte can be adjusted as appropriate.

[0075] (Separator) The separator includes the secondary battery separator, which is one embodiment of the present invention as described above. In addition to the separator described above, other separators may also be included, but it is preferable to include only the secondary battery separator, which is one embodiment of the present invention.

[0076] Other forms of separators include, for example, porous sheet separators made of polymers or fibers that absorb and retain the electrolyte, and nonwoven fabric separators.

[0077] [Positive electrode current collector plate and negative electrode current collector plate] The materials constituting the current collector plates (25, 27) are not particularly limited, and known highly conductive materials conventionally used as current collector plates for lithium-ion secondary batteries can be used. Preferred materials for the current collector plates are metallic materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. From the viewpoint of lightness, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be made of the same material or different materials.

[0078] [Positive lead and negative lead] Although not shown in the diagram, the current collector 11 and the current collector plates (25, 27) may be electrically connected via positive and negative leads. The materials used for the positive and negative leads can be the same as those used in known lithium-ion secondary batteries. It is preferable to cover the portion removed from the casing with a heat-resistant, heat-shrinkable tube or similar material to prevent leakage current from contacting peripheral equipment or wiring and affecting the product (e.g., automotive parts, especially electronic equipment).

[0079] [Seal part] The sealing portion (insulating layer) 31 is a component unique to bipolar secondary batteries (series-stacked batteries) and has the function of preventing leakage of electrolyte from the electrolyte layer. The sealing portion 31 also has the function of preventing contact between current collectors and short circuits at the ends of single cell layers. The material constituting the sealing portion can be any material that has insulating properties, sealing properties against the detachment of solid electrolyte and sealing properties against moisture permeation from the outside (sealing properties), and heat resistance at the battery operating temperature. For example, acrylic resin, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber (ethylene-propylene-diene rubber: EPDM), etc. can be used. In addition, isocyanate adhesives, acrylic resin adhesives, cyanoacrylate adhesives, etc. may be used, and hot melt adhesives (urethane resin, polyamide resin, polyolefin resin) may also be used. In particular, polyethylene resin and polypropylene resin are preferred as constituent materials for the sealing part from the viewpoint of corrosion resistance, chemical resistance, ease of manufacture (film-forming properties), and economic efficiency, and it is even more preferable to use a resin copolymerized of ethylene, propylene, and butene with amorphous polypropylene resin as the main component.

[0080] [Battery casing] As the battery casing, a known metal can case can be used, or, as shown in Figures 1 and 2, a bag-shaped case made of an aluminum-containing laminate film 29 that can cover the power generation elements can be used. The laminate film can be, for example, a three-layer laminate film made by laminating PP, aluminum, and nylon in that order, but is not limited to these. Laminate film is preferable from the viewpoint of being able to increase output and have excellent cooling performance, and can be suitably used for batteries in large equipment for EVs and HEVs. Furthermore, aluminate laminate is more preferable for the casing because the group pressure applied to the power generation elements from the outside can be easily adjusted and the desired electrolyte layer thickness can be easily adjusted.

[0081] [Manufacturing method for secondary batteries] A method for manufacturing a secondary battery according to this embodiment includes applying a slurry containing the above-mentioned cellulose material, ceramic, first polymer, and solvent to the exposed surface of the positive electrode active material layer and / or the exposed surface of the negative electrode active material layer by a method selected from the group consisting of a die coater method, a spray method, and an inkjet method. According to the manufacturing method of this embodiment, a secondary battery having a uniform and thin-film separator can be manufactured. The slurry may also contain the above-mentioned second polymer.

[0082] Any solvent that can be used in this art can be used without limitation, such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, and methylformamide.

[0083] The proportion of solvent in the electrode active material slurry is 40-90% of the total mass of the slurry. It is preferably a mass percent, and more preferably 45 to 80 mass percent. In other words, The proportion of the total mass of solids in the slurry is 10 to 60% of the total mass of the slurry. It is preferably % and more preferably 20-55% by mass.

[0084] [Battery pack] A battery pack is constructed by connecting multiple batteries together. More specifically, it uses at least two batteries connected in series, parallel, or both. By connecting them in series or parallel, it becomes possible to freely adjust the capacity and voltage.

[0085] Multiple batteries can be connected in series or parallel to form a small, removable battery pack. Furthermore, multiple of these removable battery packs can be connected in series or parallel to form a high-capacity, high-output battery pack suitable for vehicle power supplies and auxiliary power supplies where high volumetric energy density and high volumetric power density are required. The number of batteries to be connected to create a battery pack, and the number of layers of small battery packs stacked to create a high-capacity battery pack, should be determined according to the battery capacity and output of the vehicle (electric vehicle) in which it will be installed.

[0086] The following embodiments are also included within the scope of the present invention: Item 1: A separator for use in secondary batteries, The device has a shutdown layer comprising a cellulose material, a ceramic, and a first polymer (excluding the cellulose material) that melts at a temperature 10 to 100°C higher than the upper limit temperature under the operating environment of the secondary battery. A separator for a secondary battery, wherein the content of the first polymer in the shutdown layer is 20% by mass or more, relative to 100% by mass of the total mass of the cellulose material, the ceramic, and the first polymer; Item 2: The cellulose material comprises cellulose nanofibers, as described in Item 1, for a secondary battery separator; Item 3: The ceramic comprises at least one selected from the group consisting of Al2O3, SiO2, ZrO2, Al(OH)3, Mg(OH)2, and AlOOH, as described in Item 1 or 2, for use as a secondary battery separator; Item 4: The secondary battery separator according to any one of items 1 to 3, wherein the melting point of the first polymer is greater than 80°C and less than or equal to 200°C (preferably greater than 80°C and less than or equal to 180°C, more preferably greater than 80°C and less than or equal to 130°C); Item 5: A separator for a secondary battery according to any one of items 1 to 4, wherein the first polymer comprises at least one selected from the group consisting of polyethylene, polypropylene, and polyvinyl chloride; Item 6: A separator for secondary batteries according to any one of Items 1 to 5, wherein the content is 33% by mass or more (preferably 50% by mass or more); Item 7: A separator for secondary batteries according to any one of items 1 to 6, wherein the content is 60% by mass or less; Item 8: The content is 66% by mass or more (preferably 90% by mass or less), a separator for secondary batteries according to any one of items 1 to 6. Item 9: A separator for a secondary battery according to any one of items 1 to 8, further comprising in the shutdown layer a second polymer having a melting point higher than that of the first polymer and exhibiting binding properties; Item 10: The separation for a secondary battery according to Item 9, wherein the difference in melting points between the first polymer and the second polymer is 10°C or more (preferably 20°C or more, more preferably 50°C or more and 250°C or less); Item 11: A positive electrode in which a positive electrode active material layer is arranged on the surface of the positive electrode current collector, A negative electrode in which a negative electrode active material layer is arranged on the surface of the negative electrode current collector, An electrolyte layer interposed between the positive electrode and the negative electrode, comprising a secondary battery separator and electrolyte according to any one of items 1 to 10, A secondary battery equipped with a power generation element having the following properties; Item 12: A method for manufacturing a secondary battery as described in Item 11, A method for producing a material, comprising applying a slurry containing the cellulose material, the ceramic, the first polymer, and a solvent to the exposed surface of the positive electrode active material layer and / or the exposed surface of the negative electrode active material layer by a method selected from the group consisting of a die coater method, a spray method, and an inkjet method. [Examples]

[0087] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples.

[0088] <Examples of creating evaluation cells (A) and (B)> [Example 1] (Preparation of the separator (Separator (A)) before the heating test) Cellulose nanofiber (average particle size: 5-10 μm, FMa-UNDP, Sugino Machine Co., Ltd.) 0.388 g, Alumina as ceramic (average particle size (D 50 ): 0.67μm, AKP-3000, Sumitomo Chemical Co., Ltd.) 0.388g, and low-density polyethylene as the first polymer (average particle size (D 50 0.194 g each of (6 μm, LE-1080, Sumitomo Seika Co., Ltd.) were weighed (cellulose material:ceramic:first polymer = 1:1:0.5 (mass ratio)), and NMP (N-methyl-2-pyrrolidone) was added as a solvent. The mixture was mixed for 2 minutes at 2000 rpm using a planetary stirring type mixing and kneading device "Awatori Rentaro" (ARE-310, manufactured by Shinky Co., Ltd.). To this mixture, an NMP solution (7 mass%) of polyvinylidene fluoride (PVdF, W#9700, Kureha) as a second polymer was added so that the PVdF content relative to the solid content of the separator was 3 mass%, and the mixture was mixed for 4 minutes at 2000 rpm using a planetary stirring type mixing and kneading device "Awatori Rentaro" (ARE-310, manufactured by Shinky Co., Ltd.) to obtain a separator slurry. The solid content concentration of the obtained separator slurry was 25 mass%. The obtained separator slurry was coated onto the aluminum foil current collector using a coater application method. At this time, the coater gap was adjusted so that the thickness of the dried separator was 22 μm. The aluminum foil coated with this separator slurry was left to dry on an 80°C hot plate for 10 minutes to form separator (A) (separator before heating test) on the aluminum foil.

[0089] (Preparation of separator (Separator (B)) after heating test) Next, a heating test was performed by further heating separator (A). The aluminum foil on which separator (A) was formed was left to stand on a hot plate at 120°C for 10 minutes to obtain separator (B) (separator after heating test) formed on the aluminum foil.

[0090] (Creation of evaluation cell (A)) The aluminum foil on which the separator (A) obtained above was formed was cut to 42 mm x 31 mm and layered with another aluminum foil (40 mm x 29 mm) facing each other with the separator layer in between. 280 μL of electrolyte (a mixed solvent of 1 M LiPF6 ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 3:7)) was added and laminated, and an evaluation cell (A) was fabricated by applying a pressure of 2 MPa.

[0091] (Creation of evaluation cell (B)) Evaluation cell (B) was prepared in the same manner as described above (Preparation of evaluation cell (A)), except that aluminum foil with separator (B) formed on it, obtained in the above (Preparation of separator (separator (B)) after heating test), was used instead of aluminum foil with separator (A) formed on it.

[0092] [Example 2] Evaluation cells (A) and (B) for this example were prepared in the same manner as in Example 1, except that the amount of the first polymer added was changed to cellulose material:ceramic:first polymer = 1:1:1, and the separator slurry was coated so that the thickness of the dried separator was 24 μm.

[0093] [Example 3] Evaluation cells (A) and (B) for this example were prepared in the same manner as in Example 1, except that the amount of the first polymer added was changed to cellulose material:ceramic:first polymer = 1:1:2, and the separator slurry was applied so that the thickness of the dried separator was 25 μm.

[0094] [Example 4] Evaluation cells (A) and (B) for this example were prepared in the same manner as in Example 1, except that the amount of the first polymer added was changed to cellulose material:ceramic:first polymer = 1:1:4, and the separator slurry was coated so that the thickness of the dried separator was 20 μm.

[0095] [Comparative Example 1] Evaluation cells (A) and (B) for this comparative example were prepared in the same manner as in Example 1, except that the first polymer was not added and the separator slurry was coated so that the thickness of the dried separator was 19 μm.

[0096] [Reference example 1] Cells (A) and (B) for evaluation of this reference example were prepared in the same manner as in Example 1, except that the separator slurry was coated so that the dry separator thickness was 25 μm, without the addition of cellulose material and ceramic.

[0097] <Evaluation of shutdown function: Measurement of ionic conductivity> In the above (Preparation of evaluation cells), the lithium-ion conductivity (25°C) of the evaluation cells obtained in the examples and comparative examples was measured by the AC impedance method. A frequency response analyzer (FRA) was used for the measurement, and the measurement conditions were an amplitude voltage of 10mV and a measurement frequency range of 7M to 1Hz. The results are shown in Table 1 below.

[0098] [Table 1]

[0099] From the results in Table 1, it was found that the evaluation cells in Examples 1-4, which included the first polymer in addition to cellulose material and ceramic as a separator, showed a greater decrease in ionic conductivity before and after the heating test compared to the evaluation cell in Comparative Example 1, which did not contain the first polymer. Furthermore, it was observed that the thickness of the separator did not change significantly before and after the heating test in Examples 1-4 and Comparative Example 1. On the other hand, in Reference Example 1, which did not contain cellulose material and ceramic, the thickness of the separator decreased significantly before and after the heating test. From this, it was found that the separator for secondary batteries according to the present invention functions well under high-temperature conditions. [Explanation of Symbols]

[0100] 10A stacked secondary battery, 10b bipolar secondary battery, 11 Current collector, 11a The outermost current collector on the positive electrode side, 11b The outermost current collector on the negative electrode side, 11' positive electrode current collector, 12 negative electrode current collector, 13 positive electrode active material layer, 15 negative electrode active material layer, 17 electrolyte layer, 19 single cell layers, 21 Power generation elements, 23. Bipolar electrodes, 25 Positive electrode current collector plate (positive electrode tab), 27 Negative electrode current collector plate (negative electrode tab), 29 Laminating film, 31. Seal area.

Claims

1. A separator for use in secondary batteries, The device has a shutdown layer comprising a cellulose material, a ceramic, and a first polymer (excluding the cellulose material) that melts at a temperature 10 to 100°C higher than the upper limit temperature under the operating environment of the secondary battery. A separator for a secondary battery, wherein the content of the first polymer in the shutdown layer is 20% by mass or more, relative to 100% by mass of the total mass of the cellulose material, the ceramic, and the first polymer.

2. The cellulose material comprises cellulose nanofibers, as described in claim 1, for a secondary battery separator.

3. The aforementioned ceramic is Al ２ O ３ SiO ２ , ZrO ２ Al(OH) ３ Mg(OH) ２ A separator for a secondary battery according to claim 1, comprising at least one selected from the group consisting of , and AlOOH.

4. The separator for a secondary battery according to claim 1, wherein the melting point of the first polymer is greater than 80°C and less than or equal to 200°C.

5. The separator for a secondary battery according to claim 1, wherein the melting point of the first polymer is greater than 80°C and less than or equal to 130°C.

6. The separator for a secondary battery according to claim 1, wherein the first polymer comprises at least one selected from the group consisting of polyethylene, polypropylene, and polyvinyl chloride.

7. The separator for secondary batteries according to claim 1, wherein the content is 33% by mass or more.

8. The separator for secondary batteries according to claim 1, wherein the content is 50% by mass or more.

9. The separator for secondary batteries according to claim 1, wherein the content is 66% by mass or more.

10. The separator for a secondary battery according to claim 1, further comprising in the shutdown layer a second polymer having a melting point higher than the melting point of the first polymer and exhibiting binding properties.

11. A positive electrode in which a positive electrode active material layer is arranged on the surface of the positive electrode current collector, A negative electrode in which a negative electrode active material layer is arranged on the surface of the negative electrode current collector, An electrolyte layer interposed between the positive electrode and the negative electrode, comprising a secondary battery separator and electrolyte according to any one of claims 1 to 10, A secondary battery equipped with a power generation element having the following properties.

12. A method for manufacturing a secondary battery according to claim 11, A manufacturing method comprising applying a slurry containing the cellulose material, the ceramic, the first polymer, and a solvent to the exposed surface of the positive electrode active material layer and / or the exposed surface of the negative electrode active material layer by a method selected from the group consisting of a die coater method, a spray method, and an inkjet method.

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