Battery separator, method for manufacturing battery separator, battery, and composition

Abstract

Provided are a storage battery separator containing a non-aqueous electrolyte solution with excellent short-circuit prevention properties, a method for producing a storage battery separator, a storage battery, and a composition. [Solution] The battery separator according to the present disclosure is a battery separator containing a non-aqueous electrolyte solution, and is provided with a polymer containing a polymer compound having an ether bond and an anionic surfactant.

Description

[Technical Field]

[0001] The present disclosure relates to a battery separator, a method for manufacturing a battery separator, a battery, and a composition. [Background technology]

[0002] In recent years, as electrical devices have become smaller and lighter, there has been a demand for batteries that serve as their power sources to be smaller, lighter, and have higher energy densities. Storage batteries containing non-aqueous electrolytes, particularly lithium-ion batteries, have higher energy densities than other batteries and have been put to practical use as batteries that can satisfy these demands.

[0003] Polyolefin microporous membranes are typically used as separators for these lithium-ion batteries. This is because these microporous membranes have the function of shrinking or melting due to abnormal heat generation inside the battery, blocking the micropores and blocking ion permeability (shutdown function). However, when the temperature inside the battery exceeds 120°C, the separator thermally shrinks in the width direction, reducing its size in the width direction. This exposes the electrodes that were in contact with the widthwise edges of the separator, raising concerns about a short circuit. Alternatively, the separator may melt, leading to fire or explosion.

[0004] Therefore, coating polyolefin microporous membranes with inorganic ceramic particles has been proposed to reduce separator thermal shrinkage and prevent short circuits, even at elevated temperatures. Such coatings can be applied by dispersing one or more types of inorganic ceramic particles in a water-soluble polymer adhesive and using various application techniques, including dip coating, gravure coating, curtain coating, and spray coating. Furthermore, inorganic ceramic particle coatings can be applied to one or both sides of the separator in various thicknesses, e.g., 1–3 microns. However, these inorganic ceramic particle coatings do not completely seal the separator's porosity, making them prone to internal short circuits due to lithium dendrites forming on the negative electrode at low temperatures, during ultra-high-speed charge / discharge, and overdischarge. Furthermore, metal ions leaching from the positive electrode at high temperatures can lead to the formation of metal dendrites on the negative electrode, resulting in internal short circuits.

[0005] Another example of an electrochemical element is a lithium-ion capacitor, in which it is desirable to dope lithium as the negative electrode active material from the viewpoint of sufficiently lowering the negative electrode potential, but lithium dendrites grow during charging and discharging, making internal short circuits more likely to occur. Thus, even in electrochemical elements other than lithium-ion secondary batteries, it is not possible to prevent dendrites, and it is difficult to prevent internal short circuits simply by coating the separator with inorganic ceramic particles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 01 / 67536 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-152857 Summary of the Invention [Problem to be solved by the invention]

[0007] It is clear that the formation and growth of lithium and metal dendrites significantly deteriorates battery characteristics. The present disclosure has been made in view of the above-mentioned problems, and aims to provide a storage battery separator containing a non-aqueous electrolyte solution that has excellent short-circuit prevention properties, a storage battery separator manufacturing method, a storage battery, and a composition. [Means for solving the problem]

[0008] The present disclosure relates to a storage battery separator containing a non-aqueous electrolyte solution, and the storage battery separator is provided with a polymer containing a polymer compound having an ether bond and an anionic surfactant.

[0009] In the separator of the present disclosure, the polymer compound having an ether bond is preferably a polyether copolymer.

[0010] In the separator of the present disclosure, the polyether copolymer is preferably a copolymer of ethylene oxide and propylene oxide, and has a weight average molecular weight of 100,000 to 1,000,000.

[0011] In the separator of the present disclosure, the weight ratio of the anionic surfactant to the polymer compound having an ether bond is preferably 0.01 to 20% by mass.

[0012] In the separator of the present disclosure, the anionic surfactant is preferably a sulfonate-based surfactant.

[0013] In the separator of the present disclosure, the rate of change in Gurley value of the battery separator to which the polymer containing the polymer compound having an ether bond and the anionic surfactant is applied is preferably 10% or more before and after application.

[0014] The separator of the present disclosure preferably has the polymer applied to the surface of the separator.

[0015] In the separator of the present disclosure, the polymer is preferably applied to the matrix inside the separator.

[0016] The separator of the present disclosure preferably has the polymer provided in the voids inside the separator.

[0017] The present disclosure provides a method for producing a storage battery separator, the method including a step of applying a polymer containing a polymer compound having an ether bond and an anionic surfactant to a storage battery separator containing a nonaqueous electrolyte solution.

[0018] The present disclosure is a storage battery including any of the storage battery separators described above.

[0019] The present disclosure relates to a composition for application to a separator for a storage battery containing a non-aqueous electrolyte solution, the composition including a polymer containing a polymer compound having an ether bond and an anionic surfactant. [Effects of the Invention]

[0020] According to the present disclosure, it is possible to provide a storage battery separator containing a nonaqueous electrolyte solution that has excellent short-circuit prevention properties, a method for producing a storage battery separator, a storage battery, and a composition. DETAILED DESCRIPTION OF THE INVENTION

[0021] Preferred embodiments of the present disclosure are described in detail below. A battery separator containing a nonaqueous electrolyte solution according to the present disclosure is a battery separator to which a polymer containing a polyether copolymer and an anionic surfactant is applied. For example, the polymer may be applied to the surface of the battery separator, or to a matrix (such as various fibers) inside the battery separator, or to voids (such as gaps between fibers) inside the battery separator.

[0022] <Battery separator> The separator of the present disclosure is a battery separator containing a non-aqueous electrolyte, and is provided with a polymer containing a polymer compound having an ether bond and an anionic surfactant. The separator composition of the present disclosure includes a polymer containing a polymer compound having an ether bond and an anionic surfactant, and contains a non-aqueous electrolyte. The polymer may be provided on the surface of the battery separator, on the internal matrix (fiber), or in the internal voids (gaps between fibers). The battery separator may also include any of a polyolefin microporous membrane, an aramid resin, and a polyimide resin. For example, the battery separator may include a polyolefin microporous membrane that is provided with a polymer containing a polymer compound having an ether bond and an anionic surfactant, and the polymer compound having an ether bond may be a polyether copolymer of ethylene oxide and propylene oxide, and the anionic surfactant may be a sulfonate-based surfactant. In this embodiment, the addition of a polymer compound can gel the electrolyte solution, thereby enabling the realization of a semi-solid battery using a battery separator. Because the weight ratio is determined solely by the solid content, there is no difference in the weight ratio before and after the polymer solution is added. However, after the addition, the weight ratio of the anionic surfactant to the polymer compound having an ether bond is preferably 0.01 to 20% by mass, more preferably 0.1 to 5% by mass. The Gurley value of a battery separator to which a polymer containing a polyether copolymer and an anionic surfactant is added preferably changes by 10% or more, more preferably 20% or more, before and after the addition.

[0023] By providing these components, the separator of the present disclosure can prevent internal short circuits caused by lithium and metal dendrites at low temperatures, during high-rate charge / discharge, overdischarge, and at high temperatures, and can be recharged and discharged, thereby improving cycle life. The separator of the present disclosure and the separator composition that forms the separator are described in detail below.

[0024] <Polyolefin microporous membrane> Examples of materials for the polyolefin microporous membrane used in the separator of the present disclosure include polyolefin resins such as polyethylene resin, polypropylene resin, and a mixed resin of polyethylene and polypropylene; polyester fibers such as polyethylene terephthalate fiber, polybutylene terephthalate fiber, and polytrimethylene terephthalate fiber; cellulose fibers such as cotton and rayon; nylon fibers such as nylon 6, nylon 66, and nylon 610; and nonwoven fabrics made of polyamide fibers such as aramid fibers such as para-aramid and meta-aramid. These fibers can be used alone or as a composite of two or more types. These fibers can serve as the base material for the battery separator.

[0025] The polyolefin microporous membrane used in the separator of the present disclosure is coated or partially coated on at least one or both sides with at least one type of inorganic ceramic particles. The inorganic ceramic particles are not particularly limited in particle size, shape, or chemical composition, and may include composite materials composed of two or more different materials. Exemplary materials include aluminum oxide (Al2O3), silicon dioxide (SiO2), boehmite (Al(O)OH), zirconium dioxide (ZrO2), titanium dioxide (TiO2), barium sulfate (BaSO4), barium titanium oxide (BaTiO3), aluminum nitride, silicon nitride, calcium fluoride, barium fluoride, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, tin dioxide (SnO2), indium tin oxide, oxides of transition metals, X-ray detectable materials, kaolin clay, calcined clay, kaolinite, metastable alumina, mixtures or blends thereof, and any combination thereof.

[0026] The "polymer compound having an ether bond" used in the separator of the present disclosure may be a polyether copolymer, or may be a compound other than a polyether copolymer, such as polyoxymethylene (POM), polyether ketone (PEEK), or polyetherimide (PEI).

[0027] <Polyether copolymer> The polyether copolymer used in the separator of the present disclosure contains 70% by mass or more of an ethylene oxide-propylene oxide copolymer. The ethylene oxide-propylene oxide copolymer is a polymer obtained by copolymerizing repeating ethylene oxide segments with repeating propylene oxide segments. From the viewpoints of electrolyte retention and Li-ion conductivity in the polymer layer, the content of the ethylene oxide-propylene oxide copolymer in the ethylene oxide-propylene oxide copolymer of the present disclosure is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably substantially 100% by mass.

[0028] The polyether copolymer used in the separator of the present disclosure may contain components other than the EO-PO block copolymer, provided that the effects of the present disclosure are not impaired. The components other than the ethylene oxide-propylene oxide copolymer are preferably materials that gel upon absorbing an electrolyte solution, such as polyethylene oxide homopolymers containing ethylene oxide-derived structural units (OCH2CH2), polyethylene oxide copolymers containing ethylene oxide-derived structural units (but excluding propylene oxide-derived structural units (OCH2CHCH3)), polypropylene oxide homopolymers containing propylene oxide-derived structural units, or polypropylene oxide copolymers containing propylene oxide-derived structural units (but excluding ethylene oxide-derived structural units).

[0029] The molar ratio of propylene oxide-derived constituent units to the total molar amount (100 mol%) of ethylene oxide-derived constituent units and propylene oxide-derived constituent units in the ethylene oxide-propylene oxide copolymer is preferably 5 mol% or more, more preferably 10 mol% or more, from the viewpoint of liquid retention. Furthermore, from the viewpoint of Li-ion conductivity in the polymer layer, it is preferably 40 mol% or less, more preferably 20 mol% or less. For the same reasons, the molar ratio of propylene oxide is preferably 5 to 40 mol%, more preferably 10 to 20 mol%. The molar ratio of propylene oxide-derived constituent units to the total molar amount (100 mol%) of ethylene oxide-derived constituent units and propylene oxide-derived constituent units in the ethylene oxide-propylene oxide copolymer can be considered as the molar ratio of propylene oxide to the total amount of ethylene oxide and propylene oxide used in the synthesis of the ethylene oxide-propylene oxide copolymer.

[0030] The molar ratio of ethylene oxide-derived structural units to the total molar amount (100 mol%) of ethylene oxide-derived structural units and propylene oxide-derived structural units in the ethylene oxide-propylene oxide copolymer is preferably 70 mol% or more, more preferably 80 mol% or more, from the viewpoint of improving the Li-ion conductivity in the polymer layer. Furthermore, from the viewpoint of improving the shape retention of the polymer layer, it is preferably 95 mol% or less, more preferably 90 mol% or less. For the same reasons, the molar ratio of ethylene oxide is preferably 70 to 95 mol%, more preferably 80 to 90 mol%. The molar ratio of ethylene oxide-derived structural units to the total molar amount (100 mol%) of ethylene oxide-derived structural units and propylene oxide-derived structural units in the ethylene oxide-propylene oxide copolymer can be considered as the molar ratio of ethylene oxide to the total amount of ethylene oxide and propylene oxide used in the synthesis of the ethylene oxide-propylene oxide copolymer.

[0031] The molecular weight of the ethylene oxide-propylene oxide copolymer of the present disclosure is preferably such that the lower limit of the weight-average molecular weight is 100,000 or more, more preferably 300,000 or more, and the upper limit is preferably 1,000,000 or less, more preferably 800,000 or less, in order to achieve optimal viscosity of the polymer solution to be applied to the separator, good processability, and good electrolyte absorption. Copolymers with weight-average molecular weights in this range also have an appropriate viscosity of the polymer solution in which the polyether copolymer is dissolved, resulting in good workability. Setting the lower limit of the weight-average molecular weight to 100,000 or more and the upper limit to 1,000,000 or less is preferable in that the polyether copolymer can be applied uniformly to the entire separator surface, resulting in better charge-discharge characteristics for the storage battery.

[0032] <Surfactant> The anionic surfactant of the present disclosure is not particularly limited, but is preferably a sulfonate-based surfactant that is stable within the operating voltage range of the battery. Specifically, sulfonate-based surfactants may be sulfonates, carboxylates / sulfonates, or mixtures thereof. Other anionic surfactants may also be carboxylates, sulfates, phosphates, amino acid-based surfactants, etc. The anionic surfactant may include, for example, any one or a mixture of sodium 1-pentanesulfonate, sodium 1-decanesulfonate, and sodium 1-dodecanesulfonate. The anionic surfactant may also include, for example, any one or a mixture of sodium 1-octanesulfonate, sodium 1-heptanesulfonate, sodium 1-hexanesulfonate, and polyoxyethylene lauryl sulfosuccinate.

[0033] <Battery separator with polyether copolymer> The molecular weight of the polyether copolymer of the present disclosure is preferably such that the lower limit of the weight-average molecular weight is 100,000 or more, more preferably 300,000 or more, and the upper limit of the weight-average molecular weight is 1,000,000 or less, preferably 800,000 or less, in order to achieve optimal viscosity, good processability, and good electrolyte absorption of the polymer solution to be applied to the separator. With a copolymer having a weight-average molecular weight in this range, the polymer solution in which the polyether copolymer is dissolved has an appropriate viscosity, and by setting the lower limit of the average molecular weight to 100,000 or more and the upper limit of the weight-average molecular weight to 1,000,000 or less, even a polyolefin microporous membrane of several hundred meters can be uniformly applied to the entire surface without problems such as uneven coating, thickness differences, or scratches, and better charge / discharge characteristics can be obtained as a storage battery.

[0034] The lower limit of the weight ratio of the anionic surfactant contained in the polymer solution applied to the separator of the present disclosure is preferably 0.01% by mass or more, and the upper limit of the weight ratio is preferably 20% by mass or less. When the weight ratio of the anionic surfactant contained in the polymer solution is within this range, the polymer solution in which the polyether copolymer and the anionic surfactant are dissolved has an appropriate viscosity. By setting the weight ratio to 0.01% by mass or more and the upper limit of the weight ratio to 20% by mass or less, the polymer solution can be uniformly applied to the entire polyolefin microporous membrane without water repellency to the interior, which is preferable in that it results in better charge / discharge characteristics as a storage battery. Furthermore, from the viewpoint of obtaining better charge / discharge characteristics as a storage battery, it is more preferable that the weight ratio of the anionic surfactant contained in the polymer solution applied to the separator is in the range of 0.1% by mass or more and 5% by mass or less. The thickness of the polyolefin microporous membrane is preferably 5 μm to 100 μm, more preferably 10 μm to 20 μm, from the viewpoint of obtaining better charge / discharge characteristics as a storage battery. When the base material is an aramid resin, the thickness is preferably 5 μm to 100 μm, more preferably 10 μm to 20 μm, from the viewpoint of obtaining better charge / discharge characteristics as a storage battery.When the base material is a polyimide resin, the thickness is preferably 5 μm to 100 μm, more preferably 10 μm to 20 μm, from the viewpoint of obtaining better charge / discharge characteristics as a storage battery.

[0035] In the separator of the present disclosure, the amount of polymer solution applied to the polyolefin microporous membrane is not particularly limited as long as the Gurley value change rate is 10% or more. A Gurley value change rate within this range is preferable because the pores in the microporous membrane are filled with the polymer, resulting in better charge / discharge characteristics for the battery. The Gurley value change rate can be, for example, 15% or more and 100,000% or less, and more preferably 20% or more and 10,000% or less.

[0036] <Method for manufacturing separator for power storage device> The method for producing the separator of the present disclosure is not particularly limited, but examples include a method in which a solution obtained by dissolving a polymer compound having an ether bond and an anionic surfactant in water or an organic solvent is applied to the separator and then dried, or a method in which the solution is applied to at least one surface of the separator and then dried. In terms of obtaining the rate of change in Gurley value, the method in which a solution obtained by dissolving a polymer compound having an ether bond and an anionic surfactant in water or an organic solvent is applied to the separator and then dried is preferred. The application method is not particularly limited, but various techniques can be used, such as dip coating, gravure, curtain, spray, die, slit, and inkjet.

[0037] The organic solvent used in the present disclosure is not particularly limited, but it is one that can dissolve a polymer compound having an ether bond and can be selected from water-soluble organic solvents such as acetone, methanol, ethanol, propanol, etc. These solvents may be used alone or in combination of two or more.

[0038] The concentration of the polymer compound having an ether bond in the polymer solution is not particularly limited, but is preferably 0.1 to 20% by mass, and more preferably 1 to 10% by mass.

[0039] There are no particular restrictions on the method for applying the polymer solution containing the polymer compound having an ether bond and the anionic surfactant used in the present disclosure to the polyolefin microporous membrane, but the solution obtained by dissolving the polymer solution in water or an organic solvent can be applied to the polyolefin microporous membrane by an appropriate method such as microgravure, slot die, or knife coating, depending on the desired amount to be applied.

[0040] The polymer solution containing the polymer compound having an ether bond and the anionic surfactant used in the present disclosure can be applied to a polyolefin microporous membrane and then dried to remove water or organic solvent. Drying methods that can be used include heater-type, hot air-type, infrared radiation-type, and vacuum-type drying equipment.

[0041] <Storage battery> The storage battery of the present disclosure uses the above-described storage battery separator, and specifically has a positive electrode, a negative electrode, the above-described storage battery separator interposed between the positive electrode and the negative electrode, and a solution in which an alkali cation salt is dissolved.

[0042] <Positive electrode> The positive electrode has a positive electrode mixture layer containing a positive electrode active material, a conductive material, and a binder on a metal foil (current collector).

[0043] The metal foil material used in the positive electrode of the storage battery of the present disclosure may be, for example, metal, carbon, conductive polymer, etc., and is preferably metal. Aluminum, nickel, iron, stainless steel, other alloys, etc. are typically used as the metal foil for the current collector. Among these, aluminum or stainless steel is preferred in terms of conductivity and voltage resistance.

[0044] As the positive electrode active material, metal oxides, metal sulfides, or specific polymers can be used depending on the type of battery desired.

[0045] The positive electrode active material for lithium-ion batteries is Li, which has a layered structure. x Lithium composite oxides represented by the formula MO2 (where M represents one or more transition metals, and x varies depending on the charge / discharge state of the battery, but is usually 0.01 or more and 1.2 or less), or Li x A lithium-containing transition metal phosphate compound represented by the formula MO4 (where M represents one or more transition metals, and x varies depending on the charge / discharge state of the battery, but is usually 0.01 or more and 1.0 or less) can be used. The transition metal M constituting this lithium composite oxide or lithium-containing transition metal phosphate compound is preferably Co, Ni, Mn, Al, Fe, or the like. Specific examples of such lithium composite oxides include LiCoO2, LiNiO2, and LiNiCo. z Mn1- y - z O2 (in the formula, 0 <y,z<1である)、Li1.2Ni y Coz Mn1- y - z O2 (where 0 < y, z < 1) LiNi y Co z Al1- y - z O2 (where 0 < y, z < 1), LiMn2O4, LiFePO4, etc. can be mentioned.

[0046] In addition to the lithium composite oxide and the lithium-containing transition metal phosphate compound, metal sulfides or oxides that do not contain lithium, such as TiS2, MoS2, NbS2, V2O5, etc., and furthermore, polymer compounds such as polyacetylene and polypyrrole can also be used.

[0047] The lithium composite oxide becomes an excellent cathode active material that can achieve a high energy density because lithium ions are oxidized and reduced at a high potential. Also, the lithium-containing transition metal phosphate compound has high thermal stability because it does not release oxygen, and becomes a cathode active material with excellent safety. A plurality of these cathode active materials may be used together for the cathode active material of the lithium ion battery. Also, when forming the cathode layer using the above cathode active materials, known conductive materials, binders, etc. can be added.

[0048] The cathode composite material layer of the cathode may contain, in addition to the cathode active material, a conductive aid, a thickener, and an additive. Examples of the conductive aid include conductive carbons such as acetylene black, ketjen black, carbon fiber, graphite, etc., conductive polymers, metal powders, etc., and conductive carbon is particularly preferred. These conductive agents are preferably added in a proportion of 0.01 to 50% by mass, more preferably 0.1 to 10% by mass, based on the cathode active material in the cathode composite material layer.

[0049] The binder used in the positive electrode mixture layer can be one or more compounds selected from polyvinylidene fluoride, carboxymethyl cellulose, sodium polyacrylate, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber, acrylic polymers, and vinyl polymers. Any solvent can be used as long as it can dissolve the binder, and N-methyl-2-pyrrolidone or water is preferred. These binders are added in an amount of 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, of the positive electrode active material in the positive electrode mixture layer.

[0050] <Negative electrode> The negative electrode has a negative electrode active material, a negative electrode mixture layer containing a conductive material and a binder on a metal foil (current collector).

[0051] The metal foil material used in the negative electrode of the storage battery of the present disclosure may be, for example, metal, carbon, conductive polymer, etc., and is preferably metal. Metal foil for the current collector is typically copper, nickel, steel plate, titanium, stainless steel, or other alloys. Among these, copper, steel plate, or stainless steel is preferred in terms of conductivity and voltage resistance.

[0052] As the negative electrode active material, for example, carbonaceous materials capable of absorbing and releasing lithium ions, silicon or metal oxides capable of alloying with lithium, etc. can be used.

[0053] As the negative electrode active material for a lithium-ion battery, a non-graphitizable carbon-based or graphite-based carbon material can be used. More specifically, carbon materials such as graphite, carbon fibers such as mesocarbon microbeads and mesophase carbon fiber, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke), glassy carbons, fired organic polymer compounds (phenolic resins, furan resins, etc., fired at an appropriate temperature and carbonized), and activated carbon can be used. When forming a negative electrode layer from such materials, known conductive materials, binders, etc. can be added.

[0054] The negative electrode mixture layer of the negative electrode may contain, in addition to the negative electrode active material, a conductive aid, a thickener, and an additive. Examples of the conductive aid include conductive carbon such as acetylene black, ketjen black, carbon fiber, and graphite, conductive polymers, and metal powders, with conductive carbon being particularly preferred. These conductive agents are added in an amount of preferably 0.01 to 50% by mass, more preferably 0.1 to 20% by mass, based on the negative electrode active material in the negative electrode layer.

[0055] The binder used to form the negative electrode composite layer can be, for example, one or more compounds selected from fluorine-based binders, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber, acrylic polymers, and vinyl polymers. Furthermore, since the binder alone has low viscosity and cannot form an electrode layer, it is preferable to mix the binder with a thickener. Examples of thickeners that can be used include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and sodium polyacrylate. Water-based binders and thickeners that dissolve in water are particularly preferred because water does not decompose at the negative electrode potential. These binders are added in a ratio of 0.1 to 5% by mass, more preferably 0.5 to 3% by mass, based on the negative electrode active material in the negative electrode layer. The thickener is added in a ratio of 0.1 to 5% by mass, more preferably 0.5 to 3% by mass, based on the negative electrode active material in the negative electrode layer.

[0056] <Manufacturing methods for positive and negative electrodes> The positive and negative electrodes for the storage battery of the present disclosure are obtained by forming a paste, which is a mixture of positive and negative electrode active materials, a conductive material, a binder, and a thickener, on a current collector. Specifically, the paste is applied to a current collector, pre-dried at 70°C or higher, and then sheets of a positive electrode composite layer and a negative electrode composite layer are formed on the current collector. The sheets are then pressed to a uniform thickness and finally dried at 120°C or higher.

[0057] <Electrolyte> An electrolyte is a conductive liquid in which an electrolyte (salt) is dissolved in a solvent other than water (an organic solvent), i.e., a non-aqueous electrolyte. For example, an electrolyte salt is dissolved in an aprotic organic solvent, and room-temperature molten salts (ionic liquids) can also be used.

[0058] In this disclosure, gelation refers to a reaction that occurs when an electrolyte solution is dropped onto a polymer compound with an ether bond attached to a separator. The polymer compound with an ether bond contains oxygen atoms, which form ionic bonds with lithium ions in the electrolyte solution. As the bonds spread between the compounds, the polymers are cross-linked, causing the electrolyte solution to gel. Such bonds between polymers formed by means other than covalent bonds are generally called physical gels, and they are sometimes used to increase the strength of polymer compounds.

[0059] In the present disclosure, the following electrolyte salts are preferably used. These include compounds consisting of a cation selected from metal cations, ammonium ions, amidinium ions, and guanidinium ions, and an anion selected from chloride ions, bromide ions, iodide ions, perchlorate ions, thiocyanate ions, tetrafluoroborate ions, nitrate ions, AsF6-, PF6-, stearyl sulfonate ions, octylsulfonate ions, dodecylbenzenesulfonate ions, naphthalenesulfonate ions, dodecylnaphthalenesulfonate ions, 7,7,8,8-tetracyano-p-quinodimethane ions, X1SO3-, [(X1SO2)(X2SO2)N]-, [(X1SO2)(X2SO2)(X3SO2)C]-, and [(X1SO2)(X2SO2)YC]-, where X1, X2, X3, and Y are electron-withdrawing groups. Preferably, X1, X2, and X3 are each independently a perfluoroalkyl group having 1 to 6 carbon atoms or a perfluoroaryl group having 6 to 18 carbon atoms, and Y is a nitro group, a nitroso group, a carbonyl group, a carboxyl group, or a cyano group. X1, X2, and X3 may be the same or different.

[0060] The metal cations may be transition metal cations. Preferably, metal cations selected from Mn, Fe, Co, Ni, Cu, Zn, and Ag are used. Also, favorable results can be obtained by using metal cations selected from Li, Na, K, Rb, Cs, Mg, Ca, and Ba. Two or more of the above-mentioned compounds can be used in combination as the electrolyte salt. In particular, Li salt compounds are preferably used as the electrolyte salt in the storage battery of the present disclosure.

[0061] Examples of Li salt compounds include, but are not limited to, LiBF, LiPF, LiClO, LiCF, SO, LiN(CF, SO), LiN(C, F, SO), LiN[CF, SC(C, F, SO)], etc. These may be used alone or in combination of two or more.

[0062] The aprotic organic solvent used in the present disclosure is not particularly limited. Specific examples of the aprotic organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted derivatives thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone, which may be used alone or in combination.

[0063] In the present disclosure, the content of the electrolyte salt is 0.1 to 5.0 mol / L, and more preferably 0.5 to 1.5 mol / L. If the content of the electrolyte salt is less than 0.5 mol / L, the ion transport number decreases, and if it exceeds 1.5 mol / L, the viscosity of the electrolyte solution increases, resulting in high resistance of the electrolyte solution.

[0064] Furthermore, a room temperature molten salt can be used as the electrolyte solution.

[0065] Room temperature molten salt refers to salt that is at least partially liquid at room temperature, and room temperature refers to the temperature range in which a power supply is expected to operate normally. The temperature range in which a power supply is expected to operate normally has an upper limit of about 120°C, or in some cases about 60°C, and a lower limit of about -40°C, or in some cases about -20°C.

[0066] Room-temperature molten salts are also called ionic liquids, and known examples include pyridine-based, aliphatic amine-based, and alicyclic amine-based quaternary ammonium organic cations. Examples of quaternary ammonium organic cations include imidazolium ions such as dialkylimidazolium and trialkylimidazolium ions, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions, and piperidinium ions. Imidazolium cations are particularly preferred.

[0067] Examples of imidazolium cations include, but are not limited to, a 1,3-dimethylimidazolium ion, a 1-ethyl-3-methylimidazolium ion, a 1-methyl-3-ethylimidazolium ion, a 1-methyl-3-butylimidazolium ion, a 1-butyl-3-methylimidazolium ion, a 1,2,3-trimethylimidazolium ion, a 1,2-dimethyl-3-ethylimidazolium ion, a 1,2-dimethyl-3-propylimidazolium ion, and a 1-butyl-2,3-dimethylimidazolium ion.

[0068] These room-temperature molten salts having cations may be used alone or in combination of two or more.

[0069] <Exterior materials> Examples of the exterior packaging include an aluminum laminate film pack, a metal can, etc. The shape of the battery may be rectangular, cylindrical, coin-shaped, etc., and the storage battery of the present disclosure is suitable for any shape.

[0070] <Storage battery manufacturing method> The storage battery of the present disclosure can be produced by producing a laminate in which a separator is disposed between a positive electrode and a negative electrode, and then using this laminate by, for example, Production Method 1 or Production Method 2 described below.

[0071] Manufacturing method 1: The laminate is heat-pressed to bond the electrodes and separator, and then housed in an exterior packaging (for example, an aluminum laminate film pack; the same applies below). An electrolyte solution is injected into the packaging, and the exterior packaging is then sealed.

[0072] Manufacturing method 2: The laminate is placed in an exterior packaging material, and an electrolyte solution is poured into it.The laminate is then heat-pressed onto the exterior packaging material to bond the electrodes and separator together, and the exterior packaging material is sealed.

[0073] In Production Method 1 and Production Method 2, the pressing temperature of the heat press is preferably 50° C. to 80° C., more preferably 60° C. to 70° C. The pressing pressure of the heat press is preferably 40 kPa to 200 kPa, more preferably 50 kPa to 100 kPa. The pressing time of the heat press is preferably adjusted according to the pressing temperature and pressing pressure, for example, within the range of 1 second to 600 seconds.

[0074] When manufacturing a laminate in which a separator is disposed between a positive electrode and a negative electrode, the method of disposing the separator between the positive electrode and the negative electrode may be a method of stacking at least one layer of a positive electrode, a separator, and a negative electrode in this order (so-called stack method), or a method of stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them in the length direction.

[0075] Specific embodiments for carrying out the present disclosure will be described below with reference to examples. However, the present disclosure is not limited to the following examples as long as they do not deviate from the gist of the present disclosure.

[0076] [Example 1] <Preparation of positive electrode 1> The positive electrode active material was LiNi0.08Co0.1Mn0.1O2. 92% by mass of this positive electrode active material was mixed with 4% by mass of acetylene black as a conductive additive, 4% by mass of polyvinylidene fluoride as a binder, and 40% by mass of N-methyl-2-pyrrolidone as a solvent. The mixture was stirred for 5 minutes using a rotary stirrer, then coated onto aluminum foil using a bar coater and processed to a predetermined thickness using a roll press. The mixture was then dried at 150°C under vacuum for 12 hours or more to obtain a positive electrode sheet.

[0077] <Preparation of negative electrode 1> The negative electrode active material was natural graphite powder. 96% by mass of this negative electrode active material was mixed with 1% by mass of acetylene black as a conductive additive, 1% by mass of styrene-butadiene rubber as a binder, 2% by mass of carboxymethyl cellulose as a thickener, and 40% by mass of distilled water. The mixture was stirred for 5 minutes using a rotary stirrer, then coated onto copper foil using a bar coater and processed to the desired thickness using a roll press. The mixture was then dried at 150°C under vacuum for 12 hours or more to obtain a negative electrode sheet.

[0078] <Preparation of Separator 1> A polymer solution was prepared by dissolving 5% by mass of ethylene oxide-propylene oxide copolymer with a weight-average molecular weight of 500,000 and 1% by mass of sodium 1-dodecanesulfonate in purified water. This solution was applied to one side of a 9 μm-thick polyolefin microporous membrane (surface, voids, and interior) so that the polymer layer would be 1 μm thick or less after drying. The membrane was then dried under vacuum at 70°C for at least 12 hours to produce separator 1.

[0079] <Preparation of non-aqueous electrolyte> A non-aqueous electrolyte solution was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of (50:50) to a concentration of 1.2 mol / L.

[0080] Finally, one positive electrode sheet and one negative electrode sheet were pressed together with a separator 1 interposed therebetween to form a laminate. The laminate was then housed in an aluminum laminate, and a non-aqueous electrolyte solution was injected to produce a lithium ion battery 1.

[0081] [Example 2] <Preparation of separator 2> A polymer solution was prepared by dissolving 5% by mass of ethylene oxide-propylene oxide copolymer with a weight-average molecular weight of 500,000 and 1% by mass of sodium 1-decanesulfonate in purified water. This solution was applied to a 9 μm-thick polyolefin microporous membrane so that the polymer layer would be 1 μm thick or less after drying. The membrane was then dried under vacuum at 70°C for at least 12 hours to produce separator 2.

[0082] A lithium ion battery 2 was produced in the same manner as in Example 1, except that a separator 2 was used.

[0083] [Example 3] <Preparation of Separator 3> A polymer solution was prepared by dissolving 5% by mass of ethylene oxide-propylene oxide copolymer with a weight-average molecular weight of 500,000 and 1% by mass of sodium 1-octanesulfonate in purified water. This solution was applied to a 9 μm-thick polyolefin microporous membrane so that the polymer layer would be 1 μm thick or less after drying. The membrane was then dried under vacuum at 70°C for 12 hours or more to produce separator 3.

[0084] A lithium ion battery 3 was produced in the same manner as in Example 1, except that a separator 3 was used.

[0085] [Example 4] <Preparation of Separator 4> A polymer solution was prepared by dissolving 5% by mass of ethylene oxide-propylene oxide copolymer with a weight-average molecular weight of 500,000 and 1% by mass of sodium 1-heptanesulfonate in purified water. This solution was applied to a 9 μm-thick polyolefin microporous membrane so that the polymer layer would be 1 μm thick or less after drying. The membrane was then dried under vacuum at 70°C for at least 12 hours to produce separator 4.

[0086] A lithium ion battery 4 was produced in the same manner as in Example 1, except that a separator 4 was used.

[0087] [Example 5] <Preparation of Separator 5> A polymer solution was prepared by dissolving 5% by mass of ethylene oxide-propylene oxide copolymer with a weight-average molecular weight of approximately 500,000 and 1% by mass of sodium 1-hexanesulfonate in purified water. This solution was applied to a 9 μm-thick polyolefin microporous membrane so that the polymer layer would be 1 μm thick or less after drying. The membrane was then dried under vacuum at 70°C for at least 12 hours to produce separator 5.

[0088] A lithium ion battery 5 was produced in the same manner as in Example 1, except that a separator 5 was used.

[0089] [Example 6] <Preparation of Separator 6> A polymer solution was prepared by dissolving 5% by mass of ethylene oxide-propylene oxide copolymer with a weight-average molecular weight of 500,000 and 1% by mass of sodium 1-pentanesulfonate in purified water. This solution was applied to a 9 μm-thick polyolefin microporous membrane so that the polymer layer would be 1 μm thick or less after drying. The membrane was then dried under vacuum at 70°C for 12 hours or more to produce separator 6.

[0090] A lithium ion battery 6 was produced in the same manner as in Example 1, except that a separator 6 was used.

[0091] [Example 7] <Production of Separator 7> A polymer solution was prepared by dissolving 5% by mass of ethylene oxide-propylene oxide copolymer with a weight-average molecular weight of 500,000 and 1% by mass of polyoxyethylene lauryl disodium sulfosuccinate in purified water. This solution was applied to a 9 μm-thick polyolefin microporous membrane so that the polymer layer would be 1 μm thick or less after drying. The membrane was then dried under vacuum at 70°C for 12 hours or more to produce separator 8.

[0092] A lithium ion battery 7 was produced in the same manner as in Example 1, except that a separator 7 was used.

[0093] [Comparative Example 1] A lithium ion battery 8 was produced in the same manner as in Example 1, except that a polyolefin microporous membrane not coated with a polymer solution was used.

[0094] For the separators produced in Examples 1 to 7 and Comparative Example 1, the Gurley values ​​of the polyolefin microporous membranes to which the polyether copolymer was applied were measured by the method described below. The measurement results and the rate of change in Gurley value are shown in Table 1. In Table 1, the "Gurley value before application" is the Gurley value of the polyolefin microporous membrane alone, and the "Gurley value after application" is the Gurley value of the polyolefin microporous membrane to which the polyether copolymer was applied. The rate of change (%) in the Gurley value of the separator can be calculated by {(Gurley value after application - Gurley value before application) / Gurley value before application} × 100.

[0095] <Gurley value> The Gurley value (seconds / 100 mL) was measured in accordance with JIS P8117 (ISO 5636 / 5). While the specific measurement method is not particularly limited, it can be performed using a known device, such as a Gurley densometer manufactured by Yasuda Seiki Seisakusho or Toyo Seiki Seisakusho. For example, the measurement can be performed at a temperature of 23°C ± 1°C and a relative humidity of 50 ± 2%. The test piece is cut to the specified size of 50 mm × 50 mm. The test piece is then placed in the device, and the inner tube is raised to start the measurement. The inner tube is lowered, allowing air to pass through the test piece, and the time required for 100 mL of air to pass through is recorded.

[0096] [Table 1]

[0097] The overdischarge cycle characteristics were measured by the following method for the lithium ion batteries produced in Examples 1 to 7 and Comparative Example 1. The measurement results are shown in Table 2.

[0098] <Over-discharge cycle characteristics> The battery was charged to 4.2 V at a current of 1 / 5 CA (5-hour rate of theoretical capacity) and then discharged to 2.0 V at the same current. It was then discharged to 0 V at a current of 1 / 20 CA (20-hour rate of theoretical capacity) and then left at 0 V for 1 hour. This test was repeated 50 times, and in each test, the battery was charged to 4.2 V and discharged to 2.0 V, after which the discharge capacity (mAh / g) was measured. The capacity retention after 50 cycles was calculated using the following method. The measurement results and the capacity retention are summarized in Table 2. In Table 2, the capacity retention (%) can be calculated by {(discharge capacity (mAh / g) after the first charge to 4.2 V and discharge to 2.0 V) / discharge capacity (mAh / g) after the 50th charge to 4.2 V and discharge to 2.0 V} × 100.

[0099] Table 2 shows that the separator defined in the present disclosure has a high discharge capacity even after repeated over-discharge cycles, and has a good over-discharge cycle characteristic with a capacity retention rate of 90% after 50 cycles. In other words, it can reduce the growth of dendrites caused by repeated over-discharge cycles, and therefore the separator defined in the present disclosure has excellent short-circuit prevention properties.

[0100] [Table 2]

[0101] According to this embodiment, lithium and metal ion dendrites can be prevented even at low temperatures, during high-rate charge / discharge cycles, overdischarge cycles, and at high temperatures, and recharge / discharge cycles are possible, demonstrating a remarkably excellent effect that goes against conventional wisdom. Furthermore, by providing a polymer containing a polyether copolymer and an anionic surfactant to the entire separator so that the density is within a certain value, when an electrolyte solution is dropped, the polymer absorbs the electrolyte solution and swells, uniformly sealing voids and functioning as a barrier layer that prevents physical contact with dendrites and preventing short circuits.

[0102] When the polyether copolymer is a copolymer of ethylene oxide and propylene oxide and has a weight-average molecular weight of 100,000 to 1,000,000, it swells in the electrolyte solution, preventing dendrites even in the event of over-discharge, and enabling recharging and discharging, which is a significantly excellent effect.

[0103] When the weight ratio of the anionic surfactant contained in the polymer solution applied to the separator is 0.01 to 20 mass % and the anionic surfactant is a sulfonate salt, the polymer can be applied uniformly to the entire polyolefin microporous membrane without being repelled, and dendrites can be prevented even in the event of overdischarge, thereby achieving the significantly excellent effects of enabling recharging and discharging.

[0104] When the Gurley value of a storage battery separator to which a polymer containing a polyether copolymer and an anionic surfactant is added changes by 10% or more before and after the addition, the polymer swells when the separator is filled with an electrolyte solution, thereby evenly filling the voids in the separator while maintaining ionic conductivity and preventing short circuits caused by dendrites.

[0105] The application of a polymer containing a polyether copolymer and an anionic surfactant to a separator for a storage battery containing a non-aqueous electrolyte prevents short circuits caused by dendrites. Storage batteries using this separator have excellent quality stability, including improved cycle life. [Industrial Applicability]

[0106] A storage battery including the separator of the present disclosure has excellent resistance to short circuits caused by overdischarge, and therefore can provide a storage battery that is excellent in stability even at low temperatures where lithium and metal dendrites grow and at ultra-high rate of charge and discharge.

[0107] The following configurations also fall within the technical scope of the present disclosure. (Item 1) A storage battery separator containing a non-aqueous electrolyte, the storage battery separator being provided with a polymer containing a polymer compound having an ether bond and an anionic surfactant. (Item 2) 2. The battery separator according to item 1, wherein the polymer compound having an ether bond is a polyether copolymer. (Item 3) 3. The battery separator according to item 2, wherein the polyether copolymer is a copolymer of ethylene oxide and propylene oxide and has a weight average molecular weight of 100,000 to 1,000,000. (Item 4) 4. The battery separator according to any one of items 1 to 3, wherein the weight ratio of the anionic surfactant contained in the polymer solution in which the polymer compound having an ether bond to be applied to the separator is dissolved is 0.01 to 20 mass %. (Item 5) 5. The battery separator according to any one of items 1 to 4, wherein the anionic surfactant is classified as a sulfonate surfactant. (Item 6) 6. The battery separator according to any one of items 1 to 5, wherein the Gurley value of the battery separator to which the polymer containing the polymer compound having an ether bond and the anionic surfactant is applied has a change rate of 10% or more before and after the application. (Item 7) 7. The battery separator according to any one of items 1 to 6, wherein the polymer is applied to a surface of the separator. (Item 8) 8. The battery separator according to any one of items 1 to 7, wherein the polymer is applied to a base material inside the separator. (Item 9) 9. The battery separator according to any one of items 1 to 8, wherein the polymer is provided in voids inside the separator. (Item 10) 10. A method for producing a battery separator according to any one of items 1 to 9, comprising applying a polymer film containing a polyether copolymer and an anionic surfactant to a battery separator containing a non-aqueous electrolyte solution. (Item 11) A storage battery comprising the storage battery separator according to any one of items 1 to 9. (Item 12) A composition for application to a separator for a storage battery containing a non-aqueous electrolyte, the composition comprising a polymer containing a polymer compound having an ether bond and an anionic surfactant.

[0108] Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the present disclosure can conceive of various modified or altered examples within the scope of the technical idea described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

Claims

1. A separator for a storage battery for constituting a semi-solid battery containing a gelled non-aqueous electrolyte, the separator being provided with a polymer containing a polyether copolymer and an anionic surfactant; The polyether copolymer is a copolymer of ethylene oxide and propylene oxide and has a weight average molecular weight of 100,000 to 1,000,000.

2. 2. The battery separator according to claim 1, wherein a weight ratio of the anionic surfactant to the polyether copolymer is 0.01 to 20% by mass.

3. 2. The battery separator according to claim 1, wherein the anionic surfactant is a sulfonate-based surfactant.

4. 2. The battery separator according to claim 1, wherein the Gurley value of the battery separator to which the polymer containing the polyether copolymer and the anionic surfactant is applied has a change rate of 10% or more before and after the application.

5. The battery separator according to claim 1 , wherein the polymer is applied to a surface of the separator.

6. The battery separator according to claim 1 , wherein the polymer is applied to a matrix inside the separator.

7. The battery separator according to claim 1 , wherein the polymer is provided in voids inside the separator.

8. A method for producing a semi-solid battery, comprising: applying a polymer containing a polyether copolymer and an anionic surfactant to a separator for a storage battery, the separator containing the gelled non-aqueous electrolyte, The method for producing a battery separator, wherein the polyether copolymer is a copolymer of ethylene oxide and propylene oxide and has a weight average molecular weight of 100,000 to 1,000,000.

9. A storage battery comprising the separator for storage batteries according to any one of claims 1 to 7.

10. A composition for application to a separator for a storage battery for constructing a semi-solid battery, the separator comprising a polymer including a polyether copolymer and an anionic surfactant, and a gelled non-aqueous electrolyte, the composition comprising: The composition, wherein the polyether copolymer is a copolymer of ethylene oxide and propylene oxide and has a weight average molecular weight of 100,000 to 1,000,000.

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