Current collector, bipolar lithium-ion secondary battery using the same, mobile unit

Abstract

A current collector for a bipolar battery is made using an aromatic polyamide current collector film that is highly conductive and has few voids within the film, achieved by controlling the amount of conductive material contained and the stretching / relaxing temperature and magnification of the film. [Solution] A current collector film mainly composed of aromatic polyamide, wherein the resistivity of the puncture is 1.0 × 10 -3 Ω cm or more 1.0×10 5 The current collector has a capacitance of Ω·cm or less and a film porosity of 0% to 30%.

Description

[Technical Field]

[0001] This invention relates to a current collector, a bipolar lithium-ion secondary battery using the same, and a mobile device. [Background technology]

[0002] Films made from aromatic polyamides play an important role in industrial applications and magnetic recording tape applications due to their excellent heat resistance and high rigidity.

[0003] In recent years, there has been a strong desire to reduce carbon dioxide emissions for environmental protection. The automotive industry is hoping that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will reduce carbon dioxide emissions, and the development of secondary batteries for motor drives, which are key to the practical application of these vehicles, is being actively pursued. In addition to lithium-ion batteries that can achieve high energy density and high power density, next-generation batteries such as lithium anode batteries using metallic lithium anodes, all-solid-state batteries, and air batteries are being considered. Furthermore, beyond automobiles, development is progressing on next-generation mobility such as drones, flying cars, and flying communication base stations, and lightweight, high-energy-density secondary batteries are in high demand.

[0004] In secondary batteries such as lithium-ion batteries, metal foil (metal current collector foil) has traditionally been used as a current collector. However, in recent years, resin film current collectors made of resin film have been proposed as an alternative to metal foil. Resin film current collectors are lighter than metal current collector foil, and are expected to improve the output per unit weight of the battery.

[0005] In recent years, there has been a surge in the development of bipolar lithium-ion batteries as compact and high-output lithium-ion batteries. Unlike conventional lithium-ion batteries, which extract current generated in the battery cells from electrode tabs attached to the ends of current-collecting foils and connect multiple battery cells, bipolar lithium-ion batteries stack multiple power generation cells via current-collecting foils arranged in the outermost layer, and the current flows in the thickness direction of the current-collecting foils. This configuration eliminates the need for electrode terminals, wiring, and protective casings for the battery cells that were present in conventional batteries, significantly reducing the battery size. Furthermore, by shifting the current flow from the planar direction to the thickness direction of the current-collecting foil, the resistance to the flowing current can be reduced, thereby increasing the battery output.

[0006] On the other hand, in order to manufacture film current collector foil for use in bipolar batteries, it is necessary to impart conductivity in the thickness direction.

[0007] For example, Patent Documents 1 to 3 disclose films that have conductivity by incorporating a conductive filler into an aromatic polyamide resin or aromatic polyimide resin, materials for resin current collectors mainly composed of aromatic polyamide resin or polyolefin resin and containing a high concentration of conductive filler for hyperbolic resin current collectors, and resin current collectors having said resin current collector materials. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2-164592 [Patent Document 2] Japanese Patent Publication No. 2006-302616 [Patent Document 3] Japanese Patent Publication No. 2021-165393 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, while Patent Documents 1 to 3 disclose conductive films made of aromatic polyamide containing conductive fillers, and resin current collectors using aromatic polyamide films and polyolefin films containing conductive fillers, when we fabricated a resin current collector using an aromatic polyamide film based on these documents, considering factors such as heat resistance and thinness, we found that while the current value generated in the battery cell was excellent when used as a current collector in a bipolar battery, there was a problem in that the capacity decreased when the bipolar battery was stored after charging due to the electrolyte permeating into the voids in the film.

[0010] The present invention aims to provide an aromatic polyamide current collector for a bipolar battery, which uses a current collector film mainly composed of aromatic polyamide that has excellent conductivity and few voids within the film. [Means for solving the problem]

[0011] To solve the above problems, a preferred embodiment of the present invention has the following configuration. The material contains a film mainly composed of aromatic polyamide, the porosity of the film is 0% to 30%, and the puncture resistivity is 1.0 × 10⁻⁶. -3 Ω cm or more 1.0×10 5 It is a current collector with a value of Ω·cm or less. [Effects of the Invention]

[0012] The present invention provides a bipolar battery aromatic polyamide film current collector that exhibits excellent conductivity and superior storage characteristics after charging. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below. The current collector of the present invention contains a film mainly composed of aromatic polyamide, the porosity of the film being 0% or more and 30% or less, and the penetration resistivity being 1.0 × 10⁻⁶ -3 Ω cm or more 1.0×10 5 It is less than or equal to Ω·cm.

[0014] By adopting this embodiment, a bipolar battery aromatic polyamide film current collector excellent in conductivity and storage characteristics after charging can be obtained.

[0015] (Film mainly composed of aromatic polyamide) As the aromatic polyamide in the present invention, for example, those having repeating units represented by the following formula (1) and / or formula (2) are preferable.

[0016]

Chemical formula

[0017] s

Chemical formula

[0018] Here, examples of the groups of Ar₁, Ar₂, and Ar₃ include those represented by the following chemical formulas, etc., and the groups of X and Y are selected from -O-, -CH₂-, -CO-, -CO₂-, -S-, -SO₂-, -C(CH₃)₂-, etc., but are not limited thereto.

[0019]

Chemical formula

[0020] Furthermore, some of the hydrogen atoms on these aromatic rings are substituted with substituents such as halogen groups (especially chlorine) such as fluorine, bromine, and chlorine, nitro groups, alkyl groups (especially methyl groups) such as methyl, ethyl, and propyl, and alkoxy groups such as methoxy, ethoxy, and propoxy. This is preferable because it reduces the moisture absorption rate and prevents water from entering the battery when used as a current collector. Also, it is particularly preferable that at least one of the hydrogen atoms on the aromatic ring is substituted with a halogen group and contains an aromatic ring substituted with a halogen group. Also, the hydrogen in the amide bond constituting the polymer may be substituted with other substituents.

[0021] The aromatic polyamide used in the present invention preferably has para-orientation of the above aromatic rings, which accounts for 80 mol% or more, more preferably 90 mol% or more of all the aromatic rings. The para-orientation referred to here means a state in which the divalent bonds constituting the main chain on the aromatic ring are coaxial or parallel to each other. When the para-orientation is less than 80 mol%, the rigidity and heat resistance of the film may be insufficient. Further, when the aromatic polyamide contains 60 mol% or more of the repeating unit represented by the formula (3), it is preferable because the stretchability and film physical properties are particularly excellent.

[0022]

Chemical formula

[0023] The current collector containing a film mainly composed of the aromatic polyamide of the present invention preferably has a through-plane resistivity of 1.0×10 -3 Ω·cm or more and 1.0×10 5 Ω·cm or less as obtained according to the through-plane resistivity measurement described later.

[0024] When the through-plane resistivity is 1.0×10 -3 Ωcm or more, when the current collector containing a film mainly composed of the aromatic polyamide of the present invention is incorporated into a power storage element as a resin current collector for a bipolar battery, when the power storage element is damaged and short-circuited, thermal runaway and ignition from the power storage element can be suppressed because the current collector containing a film mainly composed of the aromatic polyamide serves as a resistance. Also, when the through-plane resistivity is 1.0×10 5 Ωcm or less, when the current collector containing a film mainly composed of the aromatic polyamide of the present invention is incorporated into a bipolar power storage element as a resin current collector for a bipolar battery, an increase in the internal resistance of the bipolar power storage element and a decrease in the battery output can be suppressed. As the range of the through-plane resistivity, 1.0×10 3 Ωcm or less is more preferable.

[0025] In the present invention, the aromatic polyamide film, which is the main component of the present invention, preferably has a porosity of 30% or less in the cross-sectional area of ​​bubbles due to solvent evaporation during the film-forming process, or minute tears or air layers around the contained particles (hereinafter referred to as voids) (the porosity obtained by the porosity measurement method described later). The lower limit is 0%, which is the absence of voids.

[0026] When the porosity is 30% or less, and the current collector containing the aromatic polyamide film of the present invention is incorporated into a storage element as a resin current collector for a bipolar battery, it is possible to suppress the decrease in capacity caused by the electrolyte permeating into the voids in the film when the bipolar battery is stored after charging. A porosity of 15% or less is more preferable.

[0027] The film of the present invention, which mainly consists of aromatic polyamide, preferably contains 0.1 parts by mass or more and 200 parts by mass or less of at least one conductive substance per 100 parts by mass of aromatic polyamide.

[0028] By including 0.1 parts by mass or more and 200 parts by mass or less of a conductive material, the aforementioned film volume resistivity can be controlled to a desirable range, and good conductivity can be achieved in the thickness direction of the film, which is mainly composed of aromatic polyamide.

[0029] By setting the amount of conductive material to 0.1 parts by mass or more, the resistivity at which the material penetrates can be reduced, the conductivity of the film can be improved, and the conductivity in the thickness direction can be made uniform. The preferred range for the concentration of the conductive material is 1 part by mass or more, and more preferably 10 parts by mass or more.

[0030] By limiting the conductive material to 200 parts by mass or less, the film manufacturing process of the aromatic polyamide of the present invention can suppress discharge turbulence and the generation of numerous voids due to insufficient aromatic polyamide in the spaces between conductive materials. When used as a current collector for a bipolar battery, this suppresses the decrease in capacity caused by electrolyte penetration into the voids within the film when the bipolar battery is stored after charging. The upper limit of the conductive material to be contained is more preferably 150 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 50 parts by mass or less.

[0031] Examples of the aforementioned conductive materials include metals, metal oxides, carbon black, and fillers coated or plated with conductive materials, such as silicon dioxide, silicon carbide, titanium dioxide, calcium sulfate, and aluminum oxide, which are plated with Au, Ag, Ni, Cu, Zn, etc. The shapes can be spherical, amorphous, plate-like, or needle-like, and the size is preferably 5 nm to 10 μm for spherical and amorphous shapes, and 100 nm to 50 μm for plate-like and needle-like shapes, where the average maximum length is 100 nm to 50 μm.

[0032] Of these, furnace black, acetylene black, carbon nanotubes, graphene, Ketjenblack, fullerene, and carbon materials such as graphite are preferred in terms of processability and dispersibility, and it is particularly preferable to include at least one selected from acetylene black, carbon nanotubes, and Ketjenblack from the viewpoint of imparting conductivity with the addition of a small amount.

[0033] The film of the present invention, which mainly consists of an aromatic polyamide, preferably contains at least one of the following in addition to the aromatic polyamide: polyvinylpyrrolidone (PVP), poly-N,N-dimethylacrylamide (PDMAA), polyvinyl alcohol (PVOH), and polyethylene glycol (PEG).

[0034] By incorporating these substances as particle dispersants, the affinity between aromatic polyamide and conductive material, as well as the dispersibility of the conductive material in the resin, are improved, and the aggregation of conductive material particles can be prevented, thereby reducing the occurrence of voids.

[0035] By incorporating these substances into a film primarily composed of aromatic polyamide at a concentration of 0.01 ppm by mass or more, the affinity between the surface of the conductive material particles and the aromatic polyamide is improved, reducing the occurrence of voids. While there is no specific upper limit on the content, since these substances have lower rigidity than aromatic polyamide, a concentration of 100 ppm by mass or less is preferable due to concerns about a decrease in film properties.

[0036] The film of the present invention, which mainly consists of aromatic polyamide, preferably has a layer made of metal and / or a metallic compound (hereinafter referred to as the M layer) on at least one surface, and it is more preferable that the M layer is provided on both sides of the current collector film mainly consisting of aromatic polyamide.

[0037] Examples of metal elements that make up the M layer include gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, and palladium. The M layer may consist of individual metal elements, or it may consist of a metal compound in which the metal elements are mixed with oxygen, nitrogen, fluorine, carbon, boron, chlorine, sulfur, and phosphorus. Furthermore, the metal elements of the M layer provided on a film mainly composed of aromatic polyamide may be the same on both sides or different on each side.

[0038] When using a film mainly composed of aromatic polyamide according to the present invention as a resin current collector for a bipolar battery, it is preferable that the M layers present on both sides of the laminated film are such that one side is an M layer using copper elements and the other side is an M layer using aluminum elements.

[0039] The penetration resistivity of the current collector provided with the aforementioned M layer is 1.0 × 10 -4 Ω cm or more 1.0×10 4 It is preferable that the value is Ω·cm or less.

[0040] The aforementioned penetration resistivity is 1.0 × 10 -4 The resistivity of Ωcm or higher means that when the present invention is incorporated into a storage element as a resin current collector for a bipolar battery, with an M layer provided on a film mainly composed of aromatic polyamide, the M layer diffuses the current that would otherwise concentrate at the short-circuit point if the storage element is damaged, thereby suppressing localized heat generation and the resulting ignition. Furthermore, the aforementioned pass-through resistivity is 1.0 × 10⁻⁶. 4 By being Ωcm or less, when the resin current collector for a bipolar battery, which has an M layer provided on a film mainly composed of the aromatic polyamide of the present invention, is incorporated into a bipolar energy storage element, it is possible to suppress the increase in the internal resistance of the bipolar energy storage element and the decrease in battery output. The range of the through-pass resistivity is 1.0 × 10⁻⁶. 2 A value of Ωcm or less is more preferable.

[0041] The film of the present invention, which mainly consists of aromatic polyamide, preferably has a film thickness of 3 μm or more and 10 μm or less, as determined by the method described later.

[0042] A film thickness of 3 μm or more suppresses tearing caused by conductive fillers during film formation, thereby improving film-forming performance. The most preferable range for film thickness is 4 μm or more. Furthermore, a film thickness of 10 μm or less minimizes the increase in battery size when incorporated as a resin current collector for a bipolar battery.

[0043] (Method for manufacturing a film mainly composed of aromatic polyamide) Next, an example of a manufacturing method for a film mainly composed of the aromatic polyamide of the present invention will be described, but the present invention is not to be interpreted as being limited only to the products obtained by such example.

[0044] Methods for obtaining aromatic polyamides used in the present invention include, for example, when obtained from acid chlorides and diamines, synthesis by solution polymerization in an aprotic organic polar solvent such as N-methylpyrrolidone, dimethylacetamide, or dimethylformamide, or by interfacial polymerization using an aqueous medium. When acid chlorides and diamines are used as monomers, hydrogen chloride is produced as a by-product in the polymer solution. To neutralize this, inorganic neutralizing agents such as calcium hydroxide, calcium carbonate, or lithium carbonate, or organic neutralizing agents such as ethylene oxide, propylene oxide, ammonia, triethylamine, triethanolamine, or diethanolamine may be used. Furthermore, when obtaining aromatic polyamides from the reaction of isocyanates and carboxylic acids, synthesis can be carried out in an aprotic organic polar solvent in the presence of a catalyst.

[0045] The intrinsic viscosity ηinh of the aromatic polyamide polymer used in the present invention (a value measured at 30°C with 0.5g of the polymer in a 100ml solution in 98% by weight sulfuric acid) is preferably 0.5 (dl / g) or higher, as this results in higher elongation and better handling properties when the aromatic polyamide is used as the main component of the film.

[0046] The following methods are used to knead the aromatic polyamide polymer and conductive material used in the present invention, but are not limited to these. (1) Disperse the conductive material in a solvent in which the polymer is soluble, and polymerize the aramid polymer in this dispersion. Alternatively, add it to a polymer solution that has been polymerized separately, or add the isolated polymer to the dispersion solution and disperse it. (2) Before polymerization, the conductive substance is dispersed in the polymerization solvent, and then polymerization is carried out. (3) The conductive substance is added to the polymer solution either as a powder or together with the solvent and dispersed.

[0047] Dispersion equipment includes colloid mills, three-roll mills, kneaders, ultrasonic dispersers, sand mills, and ball mills.

[0048] The following methods are used to blend the aromatic polyamide polymer used in the present invention with a conductive material, PVP, PDMAA, PVOH, and PEG, but are not limited to these methods. (1) Disperse the conductive substance in a solvent in which the polymer is soluble, and then add the substance and dissolve it. Then polymerize the aramid polymer in this dispersion. Alternatively, add it to a polymer solution that has been polymerized separately, or add the isolated polymer to the dispersion solution and disperse it. (2) Add the substance to a solution in which a conductive substance and a polymer are dispersed / dissolved and then dissolve it. (3) After adding the substance to the polymer solution and dissolving it, the conductive substance is transferred to the polymer solution either as a powder or together with the solvent and dispersed.

[0049] Dispersion equipment includes colloid mills, three-roll mills, kneaders, ultrasonic dispersers, sand mills, and ball mills.

[0050] The film-forming stock solution, prepared as described above, is used to form a film using a method known as solution film formation, and various methods such as the wet-dry method, dry method, and wet method can be employed.

[0051] When forming a film using the wet method, the film-forming solution is either extruded directly from the nozzle into the film-forming bath, or extruded onto a support such as a drum, and then introduced into the wet bath along with the support. This bath generally consists of an aqueous medium and may contain organic solvents or inorganic salts in addition to water. The time it takes for the solution to pass through the entire wet bath varies depending on the thickness of the film, but is typically between 10 seconds and 30 minutes. The film is then stretched in the longitudinal direction. Subsequently, drying, transverse stretching, and heat treatment are performed, which are generally carried out at temperatures between 100°C and 500°C for a total of 1 second to 30 minutes.

[0052] In the wet-dry method, the film-forming solution is extruded from the die onto a support such as a drum or endless belt to form a thin film. The solvent is then evaporated from this thin film layer and dried until the film becomes self-supporting. The drying conditions are within the range of room temperature to 300°C for 60 minutes. After the drying process, the film is peeled off the support and introduced into the wet process, where it undergoes desalting, desolvation, etc., similar to the wet method described above, to become a film.

[0053] In the dry process, the self-supporting film is dried on a drum or endless belt, then peeled from the support and stretched in the longitudinal direction. Further drying, stretching, and heat treatment are performed to remove any remaining solvent, with these processes taking place at 100°C to 500°C for 1 second to 30 minutes.

[0054] The film formed as described above is stretched during the film-making process. A stretching ratio of 0.8 or more and 2.0 or less (the area ratio is the value obtained by dividing the stretched film area by the unstretched film area; a value of 1 or less indicates relaxation) is preferable for improving conductivity and maintaining mechanical and thermal properties. If the area ratio exceeds 2.0, voids will form within the film, and these voids will significantly reduce its mechanical strength.

[0055] In order to achieve a porosity within the range of the present invention, although it varies depending on the type and amount of polymer and conductive material used, it is preferable to perform relaxation or annealing in the range of 0.6 to 0.96, preferably 0.8 to 0.92, while heating at a temperature 5°C or more, preferably 10°C or more, and more preferably 30°C or more, higher than the highest heating temperature in each of the film-forming process, drying, stretching, and heat treatment, as this reduces the voids generated in each process. The upper limit of the heating temperature also varies depending on the polymer used, but if it exceeds 330°C, polymer decomposition may begin, and polymer decomposition can significantly reduce film elongation, change the crystal structure, and increase the porosity due to the generation of decomposition gases, so it is preferable to keep it below 330°C. For this reason, it is also preferable that the heating temperature in the preceding processes be below 325°C.

[0056] (M layer: A layer consisting of metal and / or metallic compounds) It is preferable that the film, which is mainly composed of the aromatic polyamide of the present invention, has layers (M layers) made of metal and / or metallic compounds on both sides.

[0057] The method for forming the layer made of metal and / or metallic compound according to the present invention is not particularly limited, but methods such as deposition, sputtering, or electroplating under vacuum conditions or reduced pressure conditions with an inert gas such as argon gas sealed inside (hereinafter collectively referred to as the deposition method), a method of directly bonding a metal foil or metal compound foil to a current collector film mainly composed of aromatic polyamide or via an adhesive layer, and a method of forming a metal layer by electrochemical reaction using a solution containing a metal salt (electroplating method, electroless plating method) can be used. Among these, the deposition method is preferred from the viewpoint of continuously forming a layer made of metal and / or metallic compound on a film using a film roll mainly composed of aromatic polyamide.

[0058] In the vacuum deposition method, it is preferable to pre-install a film roll mainly composed of aromatic polyamide in a vacuum chamber, and while the unwound film is in close contact with a cooling roll, heated and vaporized metal and / or metal compounds are solidified and deposited onto the surface of the film mainly composed of aromatic polyamide, thereby creating a layer of metal and / or metal compounds, and then winding it up again as a film roll.

[0059] Here, the inside of the vacuum chamber is 9.0 × 10 -3 Vacuum conditions below Pa, or by sealing with an inert gas such as argon gas, 9.0 × 10 -3 Pa to 1 × 10 -1 Any of the reduced pressure conditions below Pa can be suitably used. Furthermore, the layer consisting of the metal and / or metallic compound may be formed by performing two or more deposition processes in succession, such as first forming a layer consisting of the first metal and / or metallic compound by sputtering, and then forming a second metal and / or metallic compound by vacuum deposition.

[0060] Vacuum deposition methods include induction heating deposition, resistance heating deposition, laser beam deposition, and electron beam deposition. Among these, electron beam deposition, laser beam deposition, and induction heating deposition are preferred because they generate a large amount of heat from the deposition source. The amount of heat generated by the deposition source needs to be large enough to form a layer (M layer) of metal and / or metallic compound of the desired thickness. This requires a sufficiently high substrate surface temperature, but since this is difficult to measure directly, the amount of heat is determined by confirming that the M layer after deposition is of the desired thickness.

[0061] However, if the heat generated by the deposition source is increased to the required amount, the temperature of the resin film will rise if the cooling function of a normal vacuum deposition method is not managed properly. This can lead to thermal damage, a decrease in the mechanical properties of the resin film, and even the possibility of the resin film melting. Therefore, during deposition, it is necessary to manage the cooling function to ensure that the film is cooled uniformly and that the temperature does not rise too high. Specifically, it is necessary to cool the film uniformly from the back surface using a cooling mechanism consisting of a metal plate or metal roll that has been sufficiently cooled with a refrigerant. To cool the film uniformly, it is essential to ensure that there are no gaps between the resin film and the cooling mechanism and that they are in close contact. By improving the adhesion, the thermal damage to the surface of the resin film can be reduced, and the decrease in the mechanical properties of the resin film can be suppressed.

[0062] For example, if there is a scratch on the metal roll of the cooling mechanism, the scratched area becomes a gap, preventing the resin film from being cooled, and increasing the thermal damage to the resin film. Also, if foreign matter gets into the resin film and the metal roll of the cooling mechanism, the foreign matter prevents the resin film from being cooled, increasing the thermal damage. When the heat output of the deposition source is increased to the required amount, scratches on the metal rolls and foreign matter contamination, which are acceptable in normal vacuum deposition methods, become problematic, so the control of scratches on the metal rolls and foreign matter contamination needs to be made even stricter.

[0063] When the layer (M layer) made of the metal and / or metal compound of the present invention is to have a desired metal layer thickness, a method of forming it in a single deposition (defined as a set of unwinding, deposition, and winding) is preferred from the viewpoint of productivity, resistance characteristics, and grade / quality. However, for example, a thin film deposition in which a 50 nm thick aluminum deposition layer is formed in a single deposition may be repeated 20 times (the above set of repeated deposition 20 times) to form an aluminum metal layer with a total thickness of 1 μm.

[0064] Examples of metallic elements that constitute a layer made of metal and / or metallic compounds include gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, and palladium. The layer may consist of the elemental form of the aforementioned metallic elements, or it may consist of a metallic compound in which the metallic elements are mixed with oxygen, nitrogen, fluorine, carbon, boron, chlorine, sulfur, and phosphorus. Furthermore, the metallic elements of the layer made of metal and / or metallic compounds provided on a film mainly composed of aromatic polyamide may be the same on both sides or different on each side.

[0065] When used as a resin current collector for a bipolar battery, it is preferable that the layers consisting of metal and / or metallic compounds present on both sides of the film have one side consisting of a metal and / or metallic compound using copper elements and the other side consisting of a metal and / or metallic compound using aluminum elements.

[0066] The thickness of the layer made of metal and / or metallic compounds in the film mainly composed of aromatic polyamide of the present invention is not particularly limited, but it is preferable that it be 0.1 μm or more, as this minimizes the deterioration of electrical properties due to variations in the thickness of the metal layer when used as a resin current collector. More preferably, it is 0.2 μm or more, and even more preferably 0.5 μm or more. Furthermore, the upper limit of the thickness of the layer made of metal and / or metallic compounds is preferably 5 μm or less, as this minimizes the increase in battery weight when used as a resin current collector for batteries. More preferably, it is 3 μm or less.

[0067] [Energy storage element] The energy storage element of the present invention comprises an electrode assembly including a positive electrode and a negative electrode. It may contain an electrolyte, in which case it is preferable to include a separator interposed between the positive electrode and the negative electrode. An energy storage element made of a solid electrolyte without an electrolyte is also preferably exemplified. Furthermore, it may be equipped with a battery case that houses the electrode assembly.

[0068] Examples of such energy storage elements include primary batteries, secondary batteries, electric double-layer capacitors, and aluminum electrolytic capacitors, but in this invention, the term refers to secondary batteries.

[0069] Examples of secondary batteries include lithium secondary batteries, lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-iron batteries, silver oxide-zinc batteries, manganese dioxide-lithium secondary batteries, lithium cobalt oxide-carbonate secondary batteries, and vanadium-lithium secondary batteries.

[0070] Among these, secondary batteries are preferred because they can be used for a long period of time, and lithium secondary batteries, which achieve high energy density by using organic solvents, are even more preferred.

[0071] For the battery case, for example, an aluminum case, an iron case with a nickel-plated interior, or a case made of aluminum laminate film can be used.

[0072] Battery cases can take various shapes, including pouch type, cylindrical type, rectangular type, and coin type. Among these, the pouch type is preferred because it can achieve high energy density, is low-cost, and allows for flexible shape design.

[0073] The positive electrode consists of a positive electrode material, a binder resin, and a conductive additive, which are laminated on a current collector. Examples of active materials include layered lithium-containing transition metal oxides such as LiCoO2, LiNiO2, and Li(NiCoMn)O2, spinel-type manganese oxides such as LiMn2O4, and iron-based compounds such as LiFePO4. A binder resin with high binder oxidizing properties should be used. Specifically, examples include fluorine-containing resins, acrylic resins, and styrene-butadiene resins. Examples of conductive additives include carbon materials such as carbon black and graphite. Metal foil is preferred as the current collector, with aluminum foil being particularly common.

[0074] The negative electrode consists of a negative electrode material made of an active material and a binder resin, which are laminated on a current collector. The active material can be a carbon material such as artificial graphite, natural graphite, hard carbon, or soft carbon; a lithium alloy material such as tin or silicon; a metallic material such as lithium; or lithium titanate (Li4Ti5O4). 12 Examples include fluorine-containing resins, acrylic resins, and styrene-butadiene resins. Metal foil is preferred as the current collector, with copper foil being particularly often used.

[0075] In the energy storage element of the present invention, it is preferable to use a resin current collector for a bipolar battery made of a film mainly composed of aromatic polyamide, on which a copper layer is provided on one side and an aluminum layer on the opposite side by vacuum deposition.

[0076] In the present invention, when the energy storage element contains an electrolyte, the electrolyte serves as a site for ion movement between the positive and negative electrodes in an electrochemical element such as a secondary battery, and the electrolyte is dissolved in an organic solvent.

[0077] Examples of electrolytes include LiPF6, LiBF4, and LiClO4, but LiPF6 is preferred from the viewpoint of solubility in organic solvents and ionic conductivity.

[0078] Examples of organic solvents include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Two or more of these organic solvents may be used in mixture form.

[0079] The following describes a method for manufacturing lithium secondary batteries, which are a preferred type of energy storage element.

[0080] In the method for manufacturing a lithium secondary battery, first, an electrode coating solution is prepared by dispersing an active material and a conductive additive in a binder resin solution. This coating solution is then applied to a current collector, and the solvent is dried to obtain the positive electrode and negative electrode, respectively. The thickness of the coating film after drying is preferably 50 μm or more and 500 μm or less. Furthermore, it is preferable to apply pressure to the active material layer formed on the current collector using a method such as a roll press to densify it and thin the current collector.

[0081] A lithium secondary battery separator is placed between the positive and negative electrodes so as to be in contact with the active material layer of each electrode, then enclosed in an outer casing such as an aluminum laminate film, and after injecting the electrolyte, the negative electrode lead and safety valve are installed, and the outer casing is sealed.

[0082] The lithium secondary battery obtained in this way has high adhesion to the electrodes, excellent battery characteristics, and can be manufactured at low cost.

[0083] [Energy storage module] The energy storage elements created by the methods described above may be connected in series to form an energy storage module to meet the application of the energy storage elements and the required battery capacity. In such cases, it is preferable to have an energy storage module equipped with voltage control, temperature control, and safety devices. It is preferable to connect the energy storage elements with tab lead wires (current extraction wires) and house them in a resin or metal module case to use them as an energy storage module.

[0084] [Method for evaluating characteristics] A. Film thickness Film thickness T, mainly composed of aromatic polyamide The total thickness of the film, which is mainly composed of aromatic polyamide, was measured using a dial gauge in accordance with JIS K7130 (1992) A-2 method, at five arbitrary points with 10 layers of film stacked. The average value was divided by 10 to obtain the film thickness T (μm) of the aromatic polyamide-based film.

[0085] B. Constituent elements of layers consisting of metals and / or metallic compounds After sputtering the surface of a film mainly composed of the aromatic polyamide of the present invention with platinum-palladium, the metallic elements are identified using a scanning electron microscope (JEOL Ltd., JSM-6700) and an energy-dispersive X-ray spectroscopy (EDX) detector (Oxford Corp., AZtecLiv Standard UltimMax65).

[0086] Measurements were performed using acceleration voltages ranging from 0.5 kV to 30 kV, and the detected elements were considered to be the elements constituting the metal and / or metal compound layer. In this process, platinum and palladium were excluded, and if only platinum or palladium was detected through measurements at all acceleration voltages, those were considered to be the elements constituting the metal and / or metal compound layer.

[0087] C. Penetration resistivity A 20mm square sample of a film mainly composed of the aromatic polyamide of the present invention is prepared as an evaluation sample. The sample is sandwiched between two circular copper electrodes, each 20mm in diameter and 10mm thick, equipped with electrode tabs, and a pressure of 0.38MPa is applied in the thickness direction of the sample. The electrode tabs are connected to a Texio GOM-805 milliohmmeter, and the resistance value is read one minute after it is displayed under DC +6.25V conditions. The obtained resistance value is then measured using the electrode area (3.14cm²). 2 The resistivity (Ωcm) is calculated by multiplying by the value of the sample and dividing by the sample thickness (cm). The same measurement was performed on three different samples to determine their resistivity, and the average value was taken as the resistivity of the sample.

[0088] D. Porosity (i) Observation of the film cross-section Using a microtome, a film mainly composed of the aromatic polyamide of the present invention was cut perpendicular to the film plane without compressing it in the thickness direction. Then, an image of the cross-section of the sample was obtained using a scanning electron microscope (SEM) (JEOL Ltd. Field Emission Scanning Electron Microscope "JSM-6700F").

[0089] (ii) Measurement of the void ratio of the entire film (i) Method was applied to five different locations in the film sample, and images were prepared of 10 locations obtained by cutting the film cross-section in the longitudinal and width directions, at the maximum magnification that allowed observation of the entire thickness of the film. Next, each cavity was traced onto a transparent film, and the ratio of the cavity area measured using an image analyzer (Nireco Corporation: Luzex IID) to the total film cross-sectional area in the observed image was calculated, and the average of the 10 locations was taken as the porosity of the entire film.

[0090] E. Breaking elongation Measurements were performed according to the method specified in JIS-K7127 (1999). Measurements were taken using a robotic Tensilon RTA (manufactured by Orientec Co., Ltd.) at 25°C and 65% relative humidity. Sample pieces were cut to a width of 10 mm and a length of 100 mm, with the film's width direction being the longer side. The pulling speed was 300 mm / min. Five measurements were taken, and the average value was calculated. Elongation at break = (Elongation) × 100 / (Test length) (%).

[0091] F. Evaluation of bipolar batteries (i) Fabrication of resin current collectors for bipolar batteries A resin current collector for a bipolar battery was fabricated by creating a film in which a copper layer was formed on one side and an aluminum layer on the opposite side by vacuum deposition on both sides of a film mainly composed of aromatic polyamide according to the present invention.

[0092] Specifically, a roll of film mainly composed of aromatic polyamide according to the present invention was placed in a roll-type vacuum deposition apparatus (ULVAC EWC-060), and an aluminum ingot was heated using an induction heating deposition method employing a carbon crucible to create an aluminum metal layer by vacuum deposition. During this process, the transport speed and output conditions were adjusted to ensure that the aluminum metal layer reached a predetermined thickness. Next, the roll of film mainly composed of aromatic polyamide, with the aluminum metal layer on one side, was again placed in the roll-type vacuum deposition apparatus (ULVAC EWC-060), and a copper metal layer was created on the polyester film surface opposite to the aluminum metal layer by heating a copper ingot using an induction heating deposition method employing a carbon crucible. During this process, the transport speed and output conditions were adjusted to ensure that the copper metal layer reached a predetermined thickness.

[0093] (ii) Active material for positive electrode, active material for negative electrode A cathode active material slurry was prepared by mixing 90 parts by mass of LiFePO4 as the cathode active material, 5% by mass of acetylene black as a conductive additive, 5 parts by mass of thermoplastic resin granules (using thermoplastic resin granules obtained by spray-drying a 25% by mass aqueous dispersion of vinylidene fluoride-hexafluoropropylene copolymer (VDF / HFP=88 / 12) particles produced by emulsion polymerization using a spray dryer as a binder), and 400 parts by mass of water.

[0094] Furthermore, as a positive electrode to be placed at the end of a bipolar battery, the positive electrode active material slurry was applied to a 30 μm thick aluminum foil and cured by thermal polymerization to produce a terminal positive electrode in which the positive electrode was formed on the aluminum.

[0095] A negative electrode active material slurry was prepared by mixing 90 parts by mass of hard carbon as the negative electrode active material, 5 parts by mass of acetylene black as a conductive additive, 10 parts by mass of PVDF as a binder, and an appropriate amount of NMP as a slurry viscosity adjusting solvent.

[0096] Furthermore, as a negative electrode to be placed at the end of a bipolar battery, a negative electrode slurry was applied to a 30 μm copper foil and cured by thermal polymerization to create a terminal negative electrode in which the negative electrode was formed on the copper foil.

[0097] (iii) Fabrication of battery evaluation cells <Positive electrode - resin current collector assembly> After applying the positive electrode active material slurry to the aluminum layer surface of a film mainly composed of aromatic polyamide having the aforementioned metal layer using a doctor blade, the coating of the positive electrode active material slurry was pressed to make the current collector film thickness 30 μm.

[0098] <Preparation of electrolyte solution> An electrolyte slurry was prepared using 64.5% by mass of PEO (polyethylene oxide) as the ion-conducting polymer and 35.5% by mass of Li(C2F5SO2)2N as the supporting salt, with acetonitrile used as the viscosity-adjusting solvent. An electrolyte slurry was poured between glass plates with a 50 μm gap in between, and a 40 μm electrolyte layer was prepared by drying.

[0099] <Fabrication of cells for evaluation of bipolar batteries> The fabricated terminal positive electrode, negative electrode, terminal negative electrode, electrolyte layer, and positive electrode-current collector junction were cut to 120 mm x 70 mm. The terminal positive electrode, negative electrode, positive electrode-current collector junction, and electrolyte layer were stacked twice in sequence, and finally the terminal negative electrode was attached to create a three-layer bipolar battery. By welding Al tabs to the positive and negative terminal ends, respectively, and then vacuum-sealing the completed battery in an aluminum laminate, a bipolar battery evaluation cell was completed.

[0100] (iv) Measurement of full charge voltage The aforementioned bipolar battery evaluation cell was charged to a fully charged state with an open-circuit voltage of 3.6V, and the voltage of this fully charged secondary battery was measured. The charging process involved constant current charging at 23°C, using a current value that discharged the theoretical capacity in 2 hours until the battery voltage reached 3.6V, followed by constant voltage charging at 3.6V for 5 hours to achieve a fully charged state.

[0101] Afterward, charging was stopped, and the device was left to stand at 23°C for 30 minutes before measuring the voltage between the positive and negative electrodes. Voltage drop Less than 5%: ◎ Less than 10%: Yes Less than 15%: △ • 15% or more: × That's what I decided.

[0102] (v) Measurement of capacity retention rate (remaining retention rate) The aforementioned bipolar battery evaluation cell was charged to an open-circuit voltage of 3.6V in a fully charged state, and this fully charged secondary battery was then placed in a constant temperature bath at 60°C for 7 days to conduct a high-temperature storage test. The charging process involved constant current charging at 23°C with a current value that discharged the theoretical capacity in 2 hours until the battery voltage reached 3.6V, followed by constant voltage charging at 3.6V for 5 hours to achieve a fully charged state.

[0103] Subsequently, the battery was discharged using a constant current that completely discharged its theoretical capacity in 2 hours until the battery voltage reached 2.0V, and the discharged capacity at this time was defined as the remaining capacity. Similarly, a fully charged secondary battery prior to the high-temperature storage test was discharged under the same conditions, and the discharged capacity at this time was defined as the full-charge capacity. Next, the capacity retention rate after the high-temperature storage test was calculated from the remaining capacity and the full-charge capacity using Equation 1 below.

[0104] (Equation 1) (Capacity retention rate) = (Remaining capacity / Fully charged capacity) × 100 (%).

[0105] (Method for producing aromatic polyamides) The present invention will be described more specifically below based on examples, but the present invention is not limited thereto. In the following examples, NMP represents N-methylpyrrolidone, CTPC represents 2-chlorterephthalate chloride, CPA represents 2-chlorparaphenylenediamine, and DPE represents 4,4'-diaminodiphenyl ether.

[0106] The aromatic polyamide solution was synthesized as follows: 90 mol% CPA and 10 mol% DPE were dissolved in dehydrated NMP, 98.5 mol% CTPC was added, and polymerization was carried out by stirring for 2 hours. After neutralization with lithium carbonate, an aromatic polyamide solution with a polymer concentration of 11 wt% was obtained. [Examples]

[0107] (Example 1) A dispersion of aromatic polyamide was prepared by adding 25% by mass of Ketjenblack to a solution of NMP. This dispersion was then added to a solution of aromatic polyamide polymer, resulting in a composition of 80% by mass of aromatic polyamide polymer and 20% by mass of Ketjenblack. The mixture was then stirred and dispersed in a kneader. This polymer solution was cast onto a stainless steel belt with a mirror-like surface. The cast polymer solution was heated to 160°C and then to 180°C for 1 minute each to evaporate the solvent. The film was then passed through a water bath for 2 minutes to extract the remaining solvent and the inorganic salts produced by neutralization. During this time, the film was stretched 1.05 times in the longitudinal direction. After this, the film was stretched 1.2 times in the width direction in a tenter under hot air at 250°C and a wind speed of 5 m / s, followed by relaxation at 280°C to 0.95 times. Thus, a film mainly composed of aromatic polyamide with a total thickness of 6 μm was obtained. The porosity is 14%, the elongation is 30%, and the penetration resistance is 9.8 × 10⁻⁶. 2 It was Ωcm.

[0108] [Table 1]

[0109] A film mainly composed of aromatic polyamide with metal layers was obtained by vacuum deposition to create metal layers M and M' on both sides of the obtained aromatic polyamide film, with the thickness of the metal layers as shown in Table 2. By using the metal types as shown in Table 2, a resin current collector for a bipolar battery was fabricated. The through-resistance was 9.5 × 10⁻⁶. 2The value was Ωcm. As described in the [Dual-Pole Battery Evaluation] section above, a film mainly composed of aromatic polyamide with a metal layer was incorporated as a current collector into a cell for evaluating dual-pole batteries, and the dual-pole battery evaluation was performed. The full-charge voltage evaluation was ○, and the capacity retention rate after storage at 60°C for 7 days was 85%.

[0110] [Table 2]

[0111] (Example 2) A film mainly composed of aromatic polyamide, obtained in the same manner as in Example 1, was incorporated into a cell for evaluating bipolar batteries as a current collector, as described in the [Evaluation of Bipolar Battery] section above, and the bipolar battery was evaluated. The fully charged voltage evaluation and the capacity retention rate after storage at 60°C for 7 days are shown in Table 2.

[0112] (Examples 3-6) A film mainly composed of aromatic polyamide was obtained in the same manner as in Example 1, except that the type and concentration of the contained carbon material were changed as shown in Table 1, and the longitudinal direction, width direction, and relaxation ratio of the film were changed as shown in Table 1. The properties of the obtained aromatic polyamide-based film are shown in Table 1.

[0113] Using the obtained aromatic polyamide-based film, an aromatic polyamide-based film with a metal layer was fabricated with the configuration shown in Table 2. The through-resistance is shown in Table 2. As described in the [Bivore Battery Evaluation] section above, the aromatic polyamide-based film with a metal layer was incorporated as a current collector into a bipolar battery evaluation cell, and the bipolar battery was evaluated. The full-charge voltage evaluation and the capacity retention rate after storage at 60°C for 7 days are shown in Table 2.

[0114] (Examples 7 and 8) A dispersion prepared by adding 25% by mass of Ketjenblack and 100 ppm of PVP to a solution of aromatic polyamide was added to the solution so that the aromatic polyamide polymer was 80% by mass, Ketjenblack was 20% by mass, and PVP was 80% by mass. The mixture was then stirred and dispersed in a kneader. A film mainly composed of aromatic polyamide was obtained using this polymer solution in the same manner as in Example 1, except that the longitudinal direction, width direction, and relaxation ratio of the film were changed as shown in Table 1. The properties of the obtained film mainly composed of aromatic polyamide are shown in Table 1.

[0115] Using the obtained aromatic polyamide-based film, an aromatic polyamide-based film with a metal layer was fabricated with the configuration shown in Table 2. The through-resistance is shown in Table 2. As described in the [Bivore Battery Evaluation] section above, the aromatic polyamide-based film with a metal layer was incorporated as a current collector into a bipolar battery evaluation cell, and the bipolar battery was evaluated. The full-charge voltage evaluation and the capacity retention rate after storage at 60°C for 7 days are shown in Table 2.

[0116] (Comparative Example 1) A film was prepared using the aromatic polyamide polymer solution obtained as described in the section on [Method for Producing Aromatic Polyamide], according to the method described in claim 1, to obtain a film mainly composed of aromatic polyamide. The properties of the obtained film mainly composed of aromatic polyamide are shown in Table 1. The penetration resistance exceeded the upper limit of the instrument's measurement and could not be measured.

[0117] Using the obtained aromatic polyamide-based film, an aromatic polyamide-based film with a metal layer was fabricated with the configuration shown in Table 2. The through-resistance is as shown in Table 2. As described in the [Bivotal Battery Evaluation] section above, the current collector film with a metal layer, mainly composed of aromatic polyamide, was incorporated as a current collector into a bipolar battery evaluation cell, and the bipolar battery was evaluated. The fully charged voltage evaluation showed no change from the pre-charge voltage, indicating that charging was impossible, and the capacity retention rate after storage at 60°C for 7 days was not measured.

[0118] (Comparative Examples 2-5) A film mainly composed of aromatic polyamide was obtained in the same manner as in Example 1, except that the type and concentration of the contained carbon material were changed as shown in Table 1, and the longitudinal direction, width direction, and relaxation ratio of the film were changed as shown in Table 1. The properties of the obtained aromatic polyamide-based film are shown in Table 1.

[0119] Using the obtained aromatic polyamide-based film, an aromatic polyamide-based film with a metal layer was fabricated with the configuration shown in Table 2. The through-resistance is shown in Table 2. As described in the [Bivore Battery Evaluation] section above, the aromatic polyamide-based film with a metal layer was incorporated as a current collector into a bipolar battery evaluation cell, and the bipolar battery was evaluated. The full-charge voltage evaluation and the capacity retention rate after storage at 60°C for 7 days are shown in Table 2.

Claims

1. The material contains a film mainly composed of aromatic polyamide, the porosity of the film is 0% to 30%, and the puncture resistivity is 1.0 × 10⁻⁶. －３ Ω・cm or more 1.0×10 ５ A current collector with a value of Ω·cm or less.

2. The current collector according to claim 1, wherein the void ratio of the film is 0% or more and 15% or less.

3. The current collector according to claim 1 or 2, characterized in that it includes an aromatic ring in which at least one hydrogen atom on the aromatic ring constituting the aromatic polyamide is substituted with a halogen group.

4. The current collector according to claim 1, comprising 0.1 to 200 parts by mass of at least one conductive substance per 100 parts by mass of aromatic polyamide.

5. The current collector according to claim 4, wherein the conductive material is a carbon material.

6. The current collector according to claim 5, wherein the carbon material is Ketjenblack, carbon nanotubes, and acetylene black.

7. The current collector according to claim 1 or 4, comprising at least one of polyvinylpyrrolidone (PVP), poly-N,N-dimethylacrylamide (PDMAA), polyvinyl alcohol (PVOH), and polyethylene glycol (PEG) in addition to a fragrance polyamide.

8. Current collector according to claim 1 or 4, having a layer made of metal and / or a metallic compound on at least one surface of the film.

9. The current collector according to claim 8, wherein the metal and / or metallic compound is a layer containing Al elements (atoms) on one surface and a layer containing Cu elements (atoms) on the opposite surface.

10. Penetration resistivity is 1.0 × 10 －４ Ω・cm or more 1.0×10 ４ The current collector according to claim 8, wherein the current collector is less than or equal to Ω·cm.

11. The current collector according to claim 1, characterized in that its thickness is 3 μm or more and 10 μm or less.

12. A bipolar lithium-ion secondary battery using the current collector described in claim 1.

13. A secondary battery according to claim 12, wherein the battery is a whole solid or semi-solid battery.

14. A mobile body equipped with the battery according to claim 12 or 13.

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