Secondary battery, separator for secondary battery, and manufacturing method therefor

Abstract

To provide a secondary battery in which short-circuiting hardly occurs even when charging and discharging are repeated, and the density of a metal lithium layer of an anode layer in a charged state hardly decreases, and a separator useful for the secondary battery and a manufacturing method for the same.SOLUTION: The secondary battery comprises a cathode layer, an anode layer, and a separator disposed between the cathode layer and the anode layer. The cathode layer includes a cathode collector and a cathode active material layer. The anode layer includes an anode collector. The separator includes a porous substrate, a conductive layer formed on at least one surface of the porous substrate leaving an end region provided along at least one end, and an insulating layer formed in the end region. The difference between the thickness of the conductive layer and the thickness of the insulating layer is 1 / 10 or below the total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is greater than or equal to the thickness of the insulating layer. The separator is disposed in such a way that the conductive layer faces the anode active material layer.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a secondary battery, a separator for a secondary battery, and a method for producing the same. [Background technology]

[0002] In recent years, research and development has been conducted on secondary batteries that contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. For example, in lithium-ion secondary batteries, it is known that in order to prevent metal deposition on the negative electrode layer, a conductive porous body is interposed between the positive electrode layer and the negative electrode layer, and separators are placed between the positive electrode layer and the conductive porous body and between the negative electrode layer and the conductive porous body (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-141864 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the technology related to secondary batteries, increasing capacity is an issue. In order to increase the capacity of secondary batteries, it is desired to put lithium metal secondary batteries using lithium as the negative electrode active material into practical use. However, in lithium metal secondary batteries, repeated charging and discharging causes an SEI layer (solid electrolyte intermediate phase) to accumulate at the interface between the negative electrode current collector and lithium, making it easier for lithium dendrites to form during charging. When lithium dendrites form, there is a risk that the lithium dendrites will penetrate the separator and cause a short circuit between the positive electrode layer and the negative electrode layer. In addition, when lithium dendrites form, the density of the metallic lithium layer deposited on the negative electrode layer decreases, and there is a risk that the lithium secondary battery will expand excessively during charging.

[0005] The present invention has been made in view of the above, and has an object to provide a secondary battery which is less likely to short circuit even when repeatedly charged and discharged, and is less likely to experience a decrease in density of the metallic lithium layer of the negative electrode layer in a charged state, as well as a separator useful for such a secondary battery, and a method for producing the same. [Means for solving the problem]

[0006] The present inventors have found that, in order to solve the above problems, it is effective to provide a conductive layer on the surface of the separator facing the negative electrode active material layer. However, according to the inventors' studies, it has been found that a separator provided with a conductive layer has a step between the conductive layer region and the region where the conductive layer is not provided, and the step is likely to cause wrinkles in the separator. If wrinkles occur in the separator, the positive electrode layer and the negative electrode layer cannot be reliably insulated, and there is a risk of a short circuit between the positive electrode layer and the negative electrode layer.

[0007] As a result of further investigation, the present inventors have found that it is effective to form an insulating layer in an area of ​​the separator where the conductive layer is not provided, the insulating layer having a thickness that is 1 / 10 or less of the total thickness of the porous substrate and the conductive layer, so that the conductive layer has a thickness equal to or greater than the insulating layer. Accordingly, the present invention provides the following.

[0008] (1) A secondary battery comprising: a positive electrode layer, a negative electrode layer, and a separator disposed between the positive electrode layer and the negative electrode layer, the positive electrode layer having a positive electrode current collector and a positive electrode active material layer, the negative electrode layer having a negative electrode current collector, the separator having a porous substrate, a conductive layer formed on one surface of the porous substrate, leaving an edge region provided along at least one edge, and an insulating layer formed in the edge region, a difference between a thickness of the conductive layer and a thickness of the insulating layer being 1 / 10 or less of a total thickness of the porous substrate and the conductive layer, the thickness of the conductive layer being equal to or greater than a thickness of the insulating layer, and the separator being disposed such that the conductive layer faces the negative electrode layer.

[0009] According to the secondary battery of (1), the conductive layer of the separator is disposed so as to face the negative electrode layer, so that lithium is easily uniformly deposited on the negative electrode layer during charging. In addition, when electrons are supplied to the conductive layer during charging, a large amount of lithium deposition is also formed in the conductive layer, so that the current density during charging can be reduced. The reduction in current density during charging reduces overvoltage, so that decomposition of the electrolyte is suppressed. In addition, the separator has an end region where the conductive layer is not formed, and an insulating layer is formed in the end region, so that the positive electrode layer and the negative electrode layer are less likely to be short-circuited through the conductive layer. Furthermore, the difference between the thickness of the conductive layer and the insulating layer is small, being 1 / 10 or less of the total thickness of the porous substrate and the conductive layer, so that wrinkles are less likely to occur and shape stability is high. In addition, the thickness of the conductive layer facing the negative electrode layer is equal to or greater than the thickness of the insulating layer, so that gaps are less likely to occur between the conductive layer and the negative electrode layer. Therefore, the secondary battery of (1) is less likely to short-circuit even when repeatedly charged and discharged, and the density of the metallic lithium layer of the negative electrode layer in the charged state is less likely to decrease, resulting in a high capacity.

[0010] (2) The secondary battery according to (1), wherein the positive electrode current collector is connected to a positive electrode tab, and the positive electrode tab extends toward the insulating layer side of the separator.

[0011] In the secondary battery of (2), the positive electrode tab and the insulating portion of the separator come into contact with each other, making it difficult for the positive electrode tab and the conductive layer to come into contact with each other, and therefore the positive electrode layer and the negative electrode layer are less likely to short-circuit.

[0012] (3) The secondary battery according to (2), wherein the negative electrode layer has a negative electrode active material layer, and on the side to which the positive electrode tab is connected, an end of the conductive layer is located outwardly beyond an end of the positive electrode active material layer, and an end of the negative electrode active material layer is located at the same position as an end of the conductive layer or outwardly beyond the end of the conductive layer.

[0013] According to the secondary battery of (3), the negative electrode layer has a negative electrode active material layer, and the distance between the end of the positive electrode active material layer and the end of the negative electrode active material layer is long, so that the positive electrode layer and the negative electrode layer are less likely to short-circuit. In particular, when the end of the negative electrode active material layer is located beyond the end of the conductive layer, the ends are spread in the order of the positive electrode active material layer, the conductive layer, and the negative electrode active material layer, and the entire surface of the positive electrode active material layer faces the conductive layer via the porous substrate, so that efficient electron transfer can be achieved when lithium ions released from the positive electrode active material layer are precipitated on the negative electrode active material layer. This ensures the performance of the secondary battery.

[0014] (4) The secondary battery according to (3), wherein an end of the negative electrode active material layer is located outwardly beyond an end of the conductive layer, and an end of the insulating layer on the conductive layer side is located between an end of the positive electrode active material layer and an end of the negative electrode active material layer.

[0015] In the secondary battery of (4), the conductive layer and the end of the positive electrode active material layer are less likely to come into contact with each other, so that the positive electrode layer and the negative electrode layer are even less likely to short-circuit.

[0016] (5) A separator comprising a porous substrate, a conductive layer formed on one surface of the porous substrate, leaving an edge region along at least one edge, and an insulating layer formed in the edge region, wherein the difference between the thickness of the conductive layer and the thickness of the insulating layer is 1 / 10 or less of the total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is equal to or greater than the thickness of the insulating layer.

[0017] According to the separator (5), by disposing the conductive layer facing the negative electrode active material layer, a secondary battery in which lithium is easily uniformly deposited on the negative electrode active material layer during charging can be obtained. In this secondary battery, the overvoltage is reduced during charging, so that decomposition of the electrolyte is suppressed. In addition, the separator has an end region where the conductive layer is not formed, and an insulating layer is formed in the end region, so that the positive electrode layer and the negative electrode layer are unlikely to short-circuit through the conductive layer. Furthermore, since the difference between the thickness of the conductive layer and the thickness of the insulating layer is small, being 1 / 10 or less of the total thickness of the porous substrate and the conductive layer, wrinkles are unlikely to occur, and shape stability is high. In addition, since the thickness of the conductive layer facing the negative electrode layer when disposed in the secondary battery is equal to or greater than the thickness of the insulating layer, gaps are unlikely to occur between the conductive layer and the negative electrode layer.

[0018] (6) A method for producing a separator, comprising: transporting a long-sized porous substrate sheet in the longitudinal direction by roll-to-roll; forming a band-shaped conductive layer on one surface of the long-sized porous substrate sheet, leaving an end region including at least one end in a direction perpendicular to the longitudinal direction; and then forming a band-shaped insulating layer on the end region, with a thickness such that the difference between the thickness of the conductive layer and the insulating layer is 1 / 10 or less of the total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is equal to or greater than the thickness of the insulating layer.

[0019] In the long separator obtained by the separator manufacturing method (6), the difference between the thickness of the conductive layer and the thickness of the insulating layer is small, 1 / 10 or less of the total thickness of the long porous substrate sheet and the conductive layer, and the step between the conductive layer and the insulating layer can be absorbed when wound into a roll, so that wrinkles are unlikely to occur and the shape stability is high. In addition, the obtained long separator has a conductive layer that occupies most of the separator and is thicker than the insulating layer formed in the end region, so that local swelling is unlikely to occur when wound into a roll, and excessive stretching and tensile breakage can be suppressed. Therefore, according to the separator manufacturing method (6), a separator having a conductive layer and an insulating layer can be efficiently manufactured by roll-to-roll.

[0020] (7) The method for producing a separator according to (6), wherein the conductive layer is formed by any one of a sputtering method, a die coating method, and an ink-jet method.

[0021] According to the method for producing a separator of (7), the conductive layer can be formed continuously and stably, so that the efficiency of the production of the separator is improved.

[0022] (8) The method for producing a separator according to (6) or (7), wherein the insulating layer is formed by an ink-jet method.

[0023] According to the method for producing a separator of (8), the insulating layer can be formed continuously and stably, so that the efficiency of the production of the separator is improved.

[0024] (9) The method for producing a separator according to (6), wherein the conductive layer is formed by an inkjet method, and the insulating layer is formed by an inkjet method.

[0025] According to the method for producing a separator in (9), the conductive layer and the insulating layer are formed by the inkjet method, which makes it easier to form the conductive layer and the insulating layer at the same speed, thereby simplifying the process. Effect of the Invention

[0026] According to the present invention, it is possible to provide a secondary battery which is less likely to short circuit even when repeatedly charged and discharged and is less likely to experience a decrease in density of the metallic lithium layer of the negative electrode layer in the charged state, as well as a separator useful for such a secondary battery and a method for producing the same. [Brief description of the drawings]

[0027] [Figure 1] FIG. 2 is a perspective view of a separator according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Diagram 3] 1 is a cross-sectional view of a secondary battery according to one embodiment of the present invention. [Figure 4]FIG. 4 is a cross-sectional view of a secondary battery according to another embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram of a manufacturing apparatus that can be used in the manufacturing method of a separator according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below are merely examples of the present invention, and the present invention is not limited to the following.

[0029] Fig. 1 is a plan view of a separator according to an embodiment of the present invention, and Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1.

[0030] The separator 10 according to this embodiment includes a porous substrate 11, a conductive layer 12 formed on one surface of the porous substrate 11, leaving an edge region 11a provided along at least one edge, and an insulating layer 13 formed in the edge region 11a. The difference between the thickness of the conductive layer 12 and the thickness of the insulating layer 13 is 1 / 10 or less of the total thickness of the porous substrate 11 and the conductive layer 12, and the thickness of the conductive layer 12 is equal to or greater than the thickness of the insulating layer 13. In this embodiment, the thickness of the conductive layer 12 and the thickness of the insulating layer 13 are the same.

[0031] The porous substrate 11 is not particularly limited, but may be a known one used as a separator for a lithium metal secondary battery, such as a porous sheet or a nonwoven fabric sheet. Examples of the material of the porous sheet include polyolefins such as polyethylene and polypropylene, aramid, polyimide, and fluororesin. Examples of the material of the nonwoven fabric sheet include glass fiber and cellulose fiber. The thickness of the porous substrate 11 is not particularly limited, but is preferably 10 μm or more from the viewpoint of blocking dendrites of lithium metal, and is preferably 15 μm or less from the viewpoint of reducing resistance in the battery. The thickness of the porous substrate 11 is more preferably within the range of 10 to 12 μm. The air permeability of the porous substrate 11 is not particularly limited, but is preferably 200 sec / 100 mL or less from the viewpoint of reducing resistance in the battery, and is more preferably 150 sec / 100 mL or less. The porosity of the porous substrate 11 is not particularly limited, but from the viewpoint of uniform diffusion of lithium in the separator 10 and the strength of the separator 10, it is preferably within the range of 40% to 60%.

[0032] The electrical conductivity of the conductive layer 12 is not particularly limited, but is preferably 1.0×10 1 ~1.0×10 5 The surface resistivity may be in the range of 200 Ω / cm. 2 The conductive layer 12 may be made of a conductive material such as metal or carbon nanotube (CNT). Examples of metals include Cu, Zn, Ti, and Sn. These conductive materials may be used alone or in combination of two or more. The thickness of the conductive layer 12 may be within a range of, for example, 1 nm to 5000 nm (5 μm).

[0033] The conductive layer 12 may be, for example, a layer of an aggregate of conductive material particles formed by a method of applying a coating liquid of a conductive material, or may be a layer of a continuous film formed by a sputtering method or a vapor deposition method. In the case of an aggregate of conductive material particles, the average particle diameter of the conductive material particles may be in the range of 5 nm to 100 nm. The average pore diameter of the porous substrate 11 may be, for example, 1 time or less the average particle diameter of the conductive material particles.

[0034] The insulating property of the insulating layer 13 is not particularly limited, but for example, the withstand voltage combined with the porous substrate 11 may be 500V or more. The insulating layer 13 may be an organic material, an inorganic material, or a composite material of an organic material and an inorganic material. The insulating layer 13 may be, for example, a layer of aggregates of inorganic particles formed by a method of applying a coating liquid of inorganic particles, or may be a layer of a composite material in which inorganic particles are filled in a resin. It is preferable that the inorganic particles have high heat resistance. For example, alumina and boehmite can be used as the inorganic particles.

[0035] Next, a secondary battery using the separator 10 of this embodiment will be described. FIG. 3 is a cross-sectional view of a secondary battery according to one embodiment of the present invention.

[0036] The secondary battery 101 according to this embodiment includes a laminate having a positive electrode layer 20, a negative electrode layer 30, and a separator 10 disposed between the positive electrode layer 20 and the negative electrode layer 30. This laminate is housed in an exterior body (not shown) together with an electrolyte (not shown). The exterior body includes a positive electrode terminal and a negative electrode terminal.

[0037] The positive electrode layer 20 has a positive electrode collector 21 and a positive electrode active material layer 22 laminated on both sides of the positive electrode collector 21. The positive electrode collector 21 is connected to a positive electrode tab 23, and the positive electrode tab 23 is connected to a positive electrode terminal. The negative electrode layer 30 has a negative electrode collector 31 and a negative electrode active material layer 32 laminated on both sides of the negative electrode collector 31. The negative electrode collector 31 is connected to a negative electrode tab 33, and the negative electrode tab 33 is connected to a negative electrode terminal. The secondary battery 101 is a lithium metal secondary battery. The lithium metal secondary battery is a secondary battery that uses metallic lithium as the negative electrode active material layer 32, and during charging, lithium released from the positive electrode active material layer 22 is precipitated on the surface of the negative electrode active material layer 32 to generate a metallic lithium layer. For this reason, the thickness of the negative electrode layer 30 increases during charging. On the other hand, during discharge, lithium is released from the metallic lithium layer and is absorbed in the positive electrode active material layer 22. Therefore, the thickness of the negative electrode layer 30 decreases during discharge. Thus, the thickness of the negative electrode layer 30 changes greatly due to charging and discharging. The secondary battery 101 shown in FIG. 3 is in a discharged state.

[0038] The separator 10 is disposed so that the conductive layer 12 faces the negative electrode active material layer 32. The ends of the conductive layer 12, the positive electrode active material layer 22, and the negative electrode active material layer 32 of the separator 10 on the side to which the positive electrode tab 23 is connected are such that the end 12b of the conductive layer 12 is located beyond the end 22b of the positive electrode active material layer 22 to the outside, and the end 32b of the negative electrode active material layer 32 is located beyond the end of the conductive layer 12 to the outside. The end 13a of the insulating layer 13 of the separator 10 on the conductive layer 12 side is located between the end 22b of the positive electrode active material layer 22 and the end 32b of the negative electrode active material layer 32. Regarding the ends of the conductive layer 12, the positive electrode active material layer 22, and the negative electrode active material layer 32 of the separator 10 on the side to which the negative electrode tab 33 is connected, the end 12a of the conductive layer 12 is located beyond the end 22a of the positive electrode active material layer 22 to the outside, and the end 32a of the negative electrode active material layer 32 is located inside the end 12a of the conductive layer 12. When the ends are expanded in this manner in the configuration of the positive electrode active material layer 22, the conductive layer 12, and the negative electrode active material layer 32, the entire surface of the positive electrode active material layer 22 faces the conductive layer 12 via the porous substrate 11, so that efficient electron transfer can be achieved when lithium ions released from the positive electrode active material layer are precipitated on the negative electrode active material layer. The width of the end region 11a (the distance from the end 12b of the conductive layer 12 to the end of the porous substrate 11) may be greater than 2 mm and less than 4 mm, for example, when the amount of protrusion of the negative electrode layer 30 relative to the positive electrode layer 20 is +2 mm and the amount of protrusion of the separator 10 relative to the end of the negative electrode layer 30 is +2 mm.

[0039] The conductive layer 12 is in electrical contact with the negative electrode active material layer 32 in a discharged state, and is in electrical contact with metallic lithium deposited in the negative electrode active material layer 32 in a charged state. This makes the potential of the conductive layer 12 and the potential of the negative electrode active material layer 32 the same, allowing lithium to be deposited more uniformly between the conductive layer 12 and the negative electrode active material layer 32. This makes it difficult for lithium dendrites to form, and the density of the deposited lithium layer is less likely to decrease.

[0040] The electrical conductivity of the conductive layer 12 may be lower than that of the negative electrode current collector 31. This can prevent concentrated deposition of lithium on the porous substrate 11 side of the conductive layer 12 during charging, and can suppress damage to the conductive layer 12 due to the concentrated deposition of lithium. The electrical conductivity of the conductive layer 12 may be within a range of 1 / 10 to 1 / 100000 of the electrical conductivity of the negative electrode current collector 31, for example.

[0041] The material of the positive electrode collector 21 is not particularly limited, and aluminum, for example, can be used. The material of the positive electrode tab 23 may be the same as the material of the positive electrode collector 21, or may be different from the material of the positive electrode collector 21. The positive electrode tab 23 may be integrally connected to the positive electrode collector 21. In this embodiment, the positive electrode tab 23 is formed by extending the positive electrode collector 21, and is integrally connected to the positive electrode collector 21. The material of the positive electrode terminal may be the same as the material of the positive electrode tab 23, or may be different from the material of the positive electrode tab 23. The positive electrode terminal may be integrally connected to the positive electrode tab 23.

[0042] The positive electrode active material layer 22 includes a positive electrode active material. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), LiNi p Mn q Co r O2(p+q+r=1), LiNi p Al q Co r O2(p+q+r=1), lithium manganese oxide (LiMn2O4), Li 1+x Mn 2-x-y M y Examples of the positive electrode active material layer 22 include a different element-substituted Li-Mn spinel represented by O4 (x+y=2, M=at least one selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (an oxide containing Li and Ti), and lithium metal phosphate (LiMPO4, M=at least one selected from Fe, Mn, Co, and Ni). The positive electrode active material layer 22 may contain various additives used as materials for positive electrode active material layers, such as a binder and a conductive assistant.

[0043] The material of the negative electrode current collector 31 is not particularly limited, and for example, copper can be used. The material of the negative electrode tab 33 may be the same as the material of the negative electrode current collector 31, or may be different from the material of the negative electrode current collector 31. The negative electrode tab 33 may be integrally connected to the negative electrode current collector 31. In this embodiment, the negative electrode tab 33 is formed by extending the negative electrode current collector 31, and is integrally connected to the negative electrode current collector 31. The material of the negative electrode terminal may be the same as the material of the negative electrode tab 33, or may be different from the material of the negative electrode tab 33. The negative electrode terminal may be integrally connected to the negative electrode tab 33.

[0044] Lithium and metals that form alloys with lithium can be used for the negative electrode active material layer 32. Examples of metals that form alloys with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn. The thickness of the negative electrode active material layer 32 may be, for example, 50 μm or less.

[0045] The electrolytic solution includes an organic solvent and an electrolyte. Examples of the organic solvent include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, hydrofluoroethers, aromatic ethers, sulfones, cyclic esters, chain carboxylates, and nitriles. Examples of the cyclic carbonates include ethylene carbonate, propylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Examples of the chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 4-methyl1,3-dioxolane. Examples of the chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, and diethyl ether. Examples of hydrofluoroethers include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl)ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, and the like. Examples of aromatic ethers include anisole. Examples of sulfones include sulfolane and methylsulfolane. Examples of cyclic esters include γ-butyrolactone, and the like. Examples of chain carboxylates include acetates, butyrates, and propionates. Examples of nitriles include acetonitrile and propionitrile. The organic solvents may be used alone or in combination of two or more.

[0046] The electrolyte is a source of lithium ions, which are charge transfer media, and contains a lithium salt. Examples of the lithium salt include LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(CF3SO2)2(LiTFSI), LiN(FSO2)2(LiFSI), and LiBC4O8. The lithium salt may be used alone or in combination of two or more. The concentration of the electrolyte is, for example, within the range of 1.5 to 4.0 mol / L.

[0047] The exterior body is expandable and contractable in accordance with changes in thickness of the secondary battery 101 due to charging and discharging (particularly changes in thickness of the negative electrode layer 30). A laminate film can be used as the material of the exterior body. A laminate film having a three-layer structure in which an inner resin layer, a metal layer, and an outer resin layer are laminated in this order from the inside can be used as the laminate film. The inner resin layer and the outer resin layer can be made of, for example, polyethylene terephthalate (PET), polyamide (nylon), or polypropylene (PP). The metal layer can be made of, for example, aluminum.

[0048] In the secondary battery 101, the end 32b of the negative electrode active material layer 32 on the side to which the positive electrode tab 23 is connected is located outside the end of the conductive layer 12, but the positional relationship between the negative electrode active material layer 32 and the conductive layer 12 is not limited to this.

[0049] FIG. 4 is a cross-sectional view of a secondary battery according to another embodiment of the present invention. The secondary battery 102 according to this embodiment is the same as the above-described secondary battery 101, except that, on the side to which the positive electrode tab 23 is connected, the end 12b of the conductive layer 12 is located beyond the end 22b of the positive electrode active material layer 22 to the outside, and the end 32b of the negative electrode active material layer 32 is located at the same position as the end 12b of the conductive layer 12. Therefore, the same reference numerals are used and the description thereof is omitted.

[0050] Next, a method for producing the separator 10 of this embodiment will be described. FIG. 2 is a schematic diagram of a manufacturing apparatus that can be used in the manufacturing method of a separator according to one embodiment of the present invention.

[0051] The manufacturing apparatus 40 has a roll unwinding device 41 and a roll winding device 42. Between the roll unwinding device 41 and the roll winding device 42, a conductive layer forming device 43 and an insulating layer forming device 44 are disposed.

[0052] The roll unwinding device 41 is a device that unwinds the long porous substrate sheet 52 from the porous substrate sheet roll 51. The conductive layer forming device 43 is a device that forms a conductive layer on the surface of the long porous substrate sheet 52. The conductive layer can be formed by sputtering, die coating, or inkjet printing. The insulating layer forming device 44 is a device that forms an insulating layer in the end region of the surface of the long porous substrate sheet 52. The conductive layer can be formed by inkjet printing. The roll winding device 42 is a device that winds up the long porous substrate sheet (long separator sheet 53) on which the conductive layer and insulating layer have been formed, to form a separator sheet roll 54.

[0053] The separator 10 is manufactured as follows. The long porous substrate sheet 52 unwound from the porous substrate sheet roll 51 by the roll unwinding device 41 is transported in the longitudinal direction (the direction of the arrow in FIG. 5). While the long porous substrate sheet 52 is being transported, a conductive layer is formed in a strip shape on one surface of the long porous substrate sheet 52 by the conductive layer forming device 43, leaving an end region including at least one end in a direction perpendicular to the longitudinal direction. Next, an insulating layer is formed in a strip shape on the end region of the long porous substrate sheet 52 by the insulating layer forming device 44. The difference between the thickness of the insulating layer and the thickness of the conductive layer is 1 / 10 or less of the total thickness of the long porous substrate sheet 52 and the conductive layer, and the thickness of the conductive layer is equal to or greater than the thickness of the insulating layer. Next, the long porous substrate sheet (long separator sheet 53) on which the conductive layer and the insulating layer are formed is wound up to form a separator sheet roll 54. In this way, the separator sheet roll 54 can be manufactured by roll-to-roll. The long separator sheet 53 is unwound from the obtained separator sheet roll 54 and cut to a predetermined size, thereby obtaining the separator 10.

[0054] According to the secondary batteries 101 and 102 of the present embodiment configured as described above, the conductive layer 12 of the separator 10 is disposed so as to face the negative electrode active material layer 32, so that lithium is easily uniformly deposited on the negative electrode active material layer 32 during charging. In addition, since a large amount of lithium deposition is formed in the conductive layer 12 as a result of electrons being supplied to the conductive layer 12 during charging, the current density during charging can be reduced. Since the current density during charging is reduced, the overvoltage is reduced, and decomposition of the electrolyte is suppressed. In addition, the separator 10 has an end region 11a where the conductive layer 12 is not formed, and the insulating layer 13 is formed in the end region 11a, so that the positive electrode layer 20 and the negative electrode layer 30 are less likely to be short-circuited through the conductive layer 12. Furthermore, since the difference between the thickness of the conductive layer 12 and the thickness of the insulating layer 13 is small, 1 / 10 or less of the total thickness of the porous substrate 11 and the conductive layer 12, wrinkles are less likely to occur, and shape stability is high. In addition, since the thickness of the conductive layer 12 facing the negative electrode active material layer 32 is the same as the thickness of the insulating layer 13, a gap is unlikely to occur between the conductive layer 12 and the negative electrode active material layer 32. Therefore, the secondary batteries 101 and 102 of this embodiment are unlikely to short circuit even when repeatedly charged and discharged, and the density of the metallic lithium layer of the negative electrode layer in a charged state is unlikely to decrease, resulting in a high capacity.

[0055] In the secondary batteries 101 and 102 of this embodiment, the positive electrode current collector 21 is connected to the positive electrode tab 23, and the positive electrode tab 23 extends toward the insulating layer 13 of the separator 10. This brings the positive electrode tab 23 into contact with the insulating layer 13 of the separator 10, making it difficult for the positive electrode tab 23 to come into contact with the conductive layer 12. This makes it even more difficult for the positive electrode layer 20 and the negative electrode layer 30 to short-circuit.

[0056] In the secondary batteries 101 and 102 of this embodiment, the end of the conductive layer 12 on the side to which the positive electrode tab 23 is connected is located beyond the end 22b of the positive electrode active material layer 22 to the outside, and the end 32b of the negative electrode active material layer 32 is located at the same position as the end 12b of the conductive layer 12 or beyond the end 12b of the conductive layer 12 to the outside. This increases the distance between the end 22b of the positive electrode active material layer 22 and the end of the negative electrode active material layer 32, making it more difficult for the positive electrode layer 20 and the negative electrode layer 30 to short-circuit. In the secondary battery 101, the end 32b of the negative electrode active material layer 32 is located beyond the end 12b of the conductive layer 12 to the outside, and the ends of the positive electrode active material layer 22, the conductive layer 12, and the negative electrode active material layer 32 expand in this order, so that the performance of the secondary battery 101 is ensured. Furthermore, in the secondary battery 101, the end 13a of the insulating layer 13 on the conductive layer 12 side is located between the end 22b of the positive electrode active material layer 22 and the end 32b of the negative electrode active material layer 32, making it difficult for the conductive layer 12 and the end 22b of the positive electrode active material layer 22 to come into contact with each other, making it even more difficult for the positive electrode layer 20 and the negative electrode layer 30 to short-circuit.

[0057] According to the separator 10 of this embodiment, by disposing the conductive layer 12 so as to face the negative electrode active material layer 32, a secondary battery in which lithium is easily uniformly deposited on the negative electrode active material layer 32 during charging can be obtained. In this secondary battery, the overvoltage is reduced during charging, so that decomposition of the electrolyte is suppressed. In addition, the separator 10 of this embodiment has an end region 11a where the conductive layer 12 is not formed, and the insulating layer 13 is formed in the end region 11a, so that the positive electrode layer 20 and the negative electrode layer 30 are less likely to short-circuit through the conductive layer 12. Furthermore, since the difference between the thickness of the conductive layer 12 and the thickness of the insulating layer 13 is small, being 1 / 10 or less of the total thickness of the porous substrate and the conductive layer, wrinkles are less likely to occur, and shape stability is high. In addition, since the thickness of the conductive layer 12 facing the negative electrode active material layer 32 when disposed in the secondary battery is the same as the thickness of the insulating layer 13, a gap is less likely to occur between the conductive layer 12 and the negative electrode active material layer 32.

[0058] In the long separator sheet 53 obtained by the method for producing the separator 10 of this embodiment, the difference between the thickness of the conductive layer and the thickness of the insulating layer is small, 1 / 10 or less of the total thickness of the porous substrate and the conductive layer, and the step between the conductive layer and the insulating layer can be absorbed when wound into a roll, so that wrinkles are unlikely to occur and the shape stability is high. In addition, in the long separator sheet 53 obtained, the thickness of the conductive layer that occupies most of the separator is thicker than the thickness of the insulating layer formed in the end region, so that local swelling is unlikely to occur when wound into a roll, and excessive stretching and tensile breakage can be suppressed. Therefore, according to the method for producing the separator 10 of this embodiment, the separator 10 having the conductive layer 12 and the insulating layer 13 can be efficiently produced by roll-to-roll.

[0059] In the manufacturing method of the separator 10 of this embodiment, by using any one of the sputtering method, the die coating method, and the inkjet method as the method for forming the conductive layer, the conductive layer can be continuously and stably formed, thereby improving the manufacturing efficiency of the separator. In addition, by using the inkjet method as the method for forming the insulating layer, the insulating layer can be continuously and stably formed, thereby improving the manufacturing efficiency of the separator. Furthermore, by using the inkjet method as the method for forming the conductive layer and the inkjet method as the method for forming the insulating layer, the conductive layer and the insulating layer can be easily formed at the same speed. This allows the process to be simplified.

[0060] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate. For example, in this embodiment, the thickness of the conductive layer 12 and the insulating layer 13 of the separator 10 are the same, but the thickness of the conductive layer 12 may be greater than the thickness of the insulating layer 13 as long as the difference between the thickness of the conductive layer 12 and the thickness of the insulating layer 13 is 1 / 10 or less of the total thickness of the porous substrate 11 and the conductive layer 12. In this case, the difference between the thickness of the conductive layer 12 and the thickness of the insulating layer 13 may be within a range of, for example, 0.01 μm or more and 2 μm or less. In addition, in this embodiment, the negative electrode layer 30 has a negative electrode current collector 31 and a negative electrode active material layer 32 laminated on both sides of the negative electrode current collector 31, but the configuration of the negative electrode layer 30 is not limited to this. For example, the negative electrode active material layer 32 may be omitted. In this case, lithium is precipitated on the surface of the negative electrode current collector 31 during charging, and a lithium layer is generated.

[0061] [Experimental Example] The effect of providing the conductive layer 12 on the negative electrode layer 30 side of the separator 10 will be described with reference to an experimental example.

[0062] [Experimental Example 1] (Preparation of separator) An insulating porous membrane (film thickness: 20 μm, porosity: 58%, air permeability: 92 sec / 100 mL) was prepared. A copper conductive layer having a thickness of 0.08 μm was formed on one surface of the insulating porous membrane by RF sputtering. The insulating porous membrane with the copper conductive layer formed thereon was punched out to a size of 40 mm × 50 mm to prepare a separator.

[0063] (Preparation of positive electrode layer) Acetylene black (AB) as an electron conductive material, polyvinylidene fluoride (PVDF) as a binder, and polyvinylpyrrolidone (PVP) as a dispersant were premixed with N-methyl-2-pyrrolidone (NMP) as a dispersion solvent, and wet-mixed in a planetary centrifugal mixer to obtain a premixed slurry. 0.8 Co 0.1 Mn 0.1O2 (NCM811) and the pre-dope material were mixed with the obtained premixed slurry, and a dispersion process was performed using a planetary mixer to obtain a positive electrode active material paste. NCM811 has a median diameter of 12 μm. Next, the obtained positive electrode active material paste was applied to an aluminum positive electrode collector not having a primer layer, dried, pressed with a roll press, and then dried in a vacuum at 0.019 ° C. to form a positive electrode plate having a positive electrode active material layer. The obtained positive electrode plate was punched out to a size of 30 mm × 40 mm to form a positive electrode layer.

[0064] (Preparation of negative electrode layer) A 10 μm thick copper foil (negative electrode current collector, electrical conductivity: 6.5 × 10 6 A clad material was prepared by bonding a 20 μm-thick lithium foil (negative electrode active material layer) made of a 1000 .mu.m thick tungsten carbide (S / cm) to a 20 μm-thick lithium foil (negative electrode active material layer). This clad material was punched out to a size of 34 mm×44 mm to form a negative electrode layer.

[0065] (electrolyte) An electrolyte was prepared by dissolving LiFSI in 1,2-dimethoxyethane (DME) at a concentration of 4 mol / L.

[0066] (Preparation of lithium metal secondary batteries) A copper conductive layer of a separator was laminated on the lithium foil side of the negative electrode current collector, and a positive electrode active material layer of a positive electrode layer was laminated on the surface of the separator opposite to the copper conductive layer side to produce an electrode laminate in which a negative electrode layer, a separator, and a positive electrode layer were laminated in this order. Next, a positive electrode terminal was attached to the positive electrode current collector of the obtained electrode laminate via a positive electrode tab, and a negative electrode terminal was attached to the copper foil of the negative electrode current collector via a negative electrode tab. The laminate with the positive electrode terminal and the negative electrode terminal attached was placed in a laminate film bag, and then an electrolyte was poured in, and the laminate film bag was sealed to produce a lithium metal secondary battery.

[0067] [Experimental Example 2] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that in the production of the separator, a zinc conductive layer having a thickness of 0.06 μm was formed by RF sputtering instead of the copper conductive layer.

[0068] [Experimental Example 3] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that a carbon nanotube (CNT) conductive layer having a thickness of 2.1 μm was formed by coating instead of the copper conductive layer in the production of the separator. The carbon nanotube conductive layer was formed as follows. First, carbon nanotubes were added in an amount such that the solid content concentration was 4 mass% using N-methyl-N-pyrrolidinone (NMP) as a solvent, and PVDF (#9300, manufactured by Kureha Corporation) was added as a binder in an amount of 5 mass parts per 95 mass parts of carbon nanotubes. Next, a dispersion treatment was performed for 10 minutes using a rotation / revolution mixer at 1000 rpm to prepare a coating liquid. The obtained coating liquid was applied to the surface of the insulating porous film using a doctor blade and dried.

[0069] [Experimental Example 4] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that in the production of the separator, a tin conductive layer having a thickness of 0.06 μm was formed by RF sputtering instead of the copper conductive layer.

[0070] [Comparative Experiment Example 1] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that in the production of the separator, no copper conductive layer was formed.

[0071] [evaluation] The electrical conductivity, surface resistivity, and peel strength of the conductive layer of the separator prepared in each experiment were measured by the following methods. The results are shown in Table 1 together with the material, coating method, and thickness of the conductive layer of the separator. The lithium metal secondary batteries fabricated in each of the experimental examples and comparative experimental examples were measured for the presence or absence of short circuits and the rate of lithium thickness increase by the following methods. The results are shown in Table 1.

[0072] (Electrical conductivity and surface resistivity of conductive layer) The electrical conductivity and surface resistivity were measured using a high-precision, high-performance resistivity meter (Nitto Seiko Analytech Co., Ltd., Loresta GP TCP-600).

[0073] (peel strength) A conductive layer 5.0 cm long and 2.5 cm wide was attached to a 2.5 cm wide adhesive tape that was attached to a fixed plate. One end of the conductive layer was then folded back 180 degrees and pulled up at a speed of 300 mm / min using an electric measuring stand (manufactured by Imada Co., Ltd.) to peel the conductive layer from the insulating porous film. The load required from the start of peeling the conductive layer to the end of peeling was measured using a digital force gauge (manufactured by Imada Co., Ltd.). The average value of the load obtained was divided by the width of the adhesive tape to obtain the peel strength.

[0074] (Whether or not there is a short circuit in the lithium metal secondary battery) The lithium metal secondary battery immediately after fabrication was left to stand at a measurement temperature of 25° C. for 24 hours. After leaving the lithium metal secondary battery stationary, the first charge / discharge cycle described below was performed for three cycles, and then the second charge / discharge cycle described below was performed for 50 cycles to check whether or not the lithium metal secondary battery had a short circuit. If the charge capacity of the lithium metal secondary battery was 105% or more of the discharge capacity before charging, it was deemed that a short circuit had occurred, and it was deemed that a short circuit had occurred.

[0075] (First charge / discharge cycle) The charging was performed under the conditions of constant current charging at a current value of 2.2 mA up to 4,300 V, followed by constant voltage charging for 60 minutes at a voltage value of 4,300 V. The discharging was performed under the conditions of constant current discharging at a current value of 4 mA down to 2.65 V. The battery was left to stand for 30 minutes between discharging and charging.

[0076] (2nd charge / discharge cycle) The charging conditions were constant current charging at 74 mA to 3.823 V, 52 mA to 4.051 V, 46 mA to 4.173 V, and 22 mA to 4.300 V, followed by constant voltage charging for 90 minutes at 4.300 V. The discharging conditions were constant current discharging at 18 mA to 2.65 V. The battery was left to stand for 30 minutes between discharging and charging.

[0077] (Lithium thickness increase rate in lithium metal secondary batteries) The thickness T1 (μm) of the negative electrode layer at the initial charge and the thickness T2 (μm) of the negative electrode layer at the charge after 50 cycles (total thickness of the negative electrode current collector and metallic lithium layer) were measured, and the lithium thickness increase rate T (μm / cycle) was calculated using the following formula. T(μm / cycle)=(T2-T1) / 50

[0078] The thickness T1 (μm) of the negative electrode layer during the initial charge was measured as follows. The lithium metal secondary battery immediately after fabrication was left to stand at a measurement temperature of 25° C. for 24 hours. The lithium metal secondary battery after standing was subjected to the first charge / discharge cycle for three cycles. Next, constant current charging was performed at a current value of 14.7 mA up to 4,300 V, followed by constant voltage charging at a voltage value of 4,300 V for 60 minutes to charge the lithium metal secondary battery. The charged lithium metal secondary battery was left standing for 30 minutes, disassembled, and the negative electrode layer was taken out and its thickness was measured as the thickness T1 of the negative electrode layer.

[0079] The thickness T2 of the negative electrode layer during charging after 50 cycles was measured as follows. The lithium metal secondary battery immediately after fabrication was left to stand at a measurement temperature of 25° C. for 24 hours. The lithium metal secondary battery after standing was subjected to the first charge / discharge cycle three cycles, and then the second charge / discharge cycle 50 cycles. The lithium metal secondary battery was then charged by performing a constant current charge to 4.300 V at a current value of 14.7 mA, followed by a constant voltage charge at a voltage value of 4.300 V for 60 minutes. The charged lithium metal secondary battery was then left to stand for 30 minutes, disassembled, and the negative electrode layer was removed and its thickness was measured as the thickness T2 of the negative electrode layer.

[0080] [Table 1]

[0081] As shown in Table 1, the lithium metal secondary batteries of Experimental Examples 1 to 4, which have separators with conductive layers, are less likely to short circuit even when repeatedly charged and discharged, have a low rate of lithium thickness increase, and produce a dense metallic lithium layer upon charging. In contrast, the lithium metal secondary battery of Comparative Experimental Example 1, which has a separator without a conductive layer, is more likely to short circuit when repeatedly charged and discharged, and has a high rate of lithium thickness increase, which indicates that a coarse metallic lithium layer with low density is produced upon charging. [Explanation of symbols]

[0082] 10 Separator 11 Porous substrate 11a End area 12 Conductive layer 13 Insulating layer 20 Positive electrode layer 21 Positive electrode current collector 22 Cathode active material layer 23 Positive tab 30 Negative electrode layer 31 Negative electrode current collector 32 Negative electrode active material layer 33 Negative tab 40 Manufacturing equipment 41 Roll unwinding device 42 Roll winding device 43 Conductive layer forming device 44 Insulation layer forming device 51 Porous substrate sheet roll 52 Long porous substrate sheet 53 Long separator sheet 54 Separator sheet roll 101, 102 Secondary battery

Claims

1. a positive electrode layer, a negative electrode layer, and a separator disposed between the positive electrode layer and the negative electrode layer; The positive electrode layer has a positive electrode current collector and a positive electrode active material layer, The negative electrode layer has a negative electrode current collector, The separator has a porous substrate, a conductive layer formed on one surface of the porous substrate, leaving an end region provided along at least one end, and an insulating layer formed in the end region, wherein the difference between the thickness of the conductive layer and the thickness of the insulating layer is 1 / 10 or less of the total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is equal to or greater than the thickness of the insulating layer, The separator is disposed so that the conductive layer faces the negative electrode layer.

2. The positive electrode current collector is connected to a positive electrode tab, The secondary battery according to claim 1 , wherein the positive electrode tab extends onto the insulating layer side of the separator.

3. 3. The secondary battery according to claim 2, wherein the negative electrode layer has a negative electrode active material layer, and on a side to which the positive electrode tab is connected, an end of the conductive layer is located outwardly beyond an end of the positive electrode active material layer, and an end of the negative electrode active material layer is located at the same position as an end of the conductive layer or outwardly beyond the end of the conductive layer.

4. 4. The secondary battery according to claim 3, wherein an end of the negative electrode active material layer is located outwardly beyond an end of the conductive layer, and an end of the insulating layer on the conductive layer side is located between an end of the positive electrode active material layer and an end of the negative electrode active material layer.

5. A porous substrate, a conductive layer formed on one surface of the porous substrate, leaving an end region along at least one end, and an insulating layer formed in the end region, A separator, wherein a difference between a thickness of the conductive layer and a thickness of the insulating layer is 1 / 10 or less of a total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is equal to or greater than a thickness of the insulating layer.

6. a conductive layer is formed in a band shape on one surface of a long-sized porous substrate sheet while transporting the long-sized porous substrate sheet in the longitudinal direction by roll-to-roll, leaving an end region including at least one end in a direction perpendicular to the longitudinal direction; and then forming an insulating layer in a band shape on the end region, with a thickness such that the difference between the thickness of the conductive layer and the insulating layer is 1 / 10 or less of the total thickness of the long-sized porous substrate sheet and the conductive layer, and the thickness of the conductive layer is equal to or greater than the thickness of the insulating layer.

7. The method for producing a separator according to claim 6 , wherein the conductive layer is formed by any one of a sputtering method, a die coating method, and an ink-jet method.

8. The method for producing a separator according to claim 6 , wherein the method for forming the insulating layer is an ink-jet method.

9. The method for producing a separator according to claim 6 , wherein the conductive layer is formed by an ink-jet method, and the insulating layer is formed by an ink-jet method.

Images