Secondary battery, separator for secondary battery, and method for producing separator for secondary battery

Abstract

The problem to be solved by the present invention is to provide: a secondary battery in which a short circuit does not easily occur even if the secondary battery is repeatedly charged and discharged, and in which a decrease in the density of a lithium metal layer of a negative electrode layer in a charged state does not easily occur; in order to solve the problem, this secondary battery is provided with a positive electrode layer having a positive electrode current collector and a positive electrode active material layer, a negative electrode layer having a negative electrode current collector, and a separator disposed between the positive electrode layer and the negative electrode layer. The separator has a porous base material, a conductive layer formed on one surface of the porous base material so as to remain an end region provided along at least one end, and an insulating layer formed on the end region. 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 base material and the conductive layer, the thickness of the conductive layer is equal to or greater than the thickness of the insulating layer, and the separator is disposed such that the conductive layer faces the negative electrode active material layer.

Description

Technical Field

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

[0002] In recent years, in order to make many people affordable, trustworthy, and able to ensure access to sustainable and advanced energy, research and development related to secondary batteries that contribute to energy efficiency are being carried out. For example, it is known that in lithium-ion secondary batteries, in order to prevent metal precipitation on the negative electrode layer, a conductive porous body is sandwiched between the positive electrode layer and the negative electrode layer, and a separator is configured between the positive electrode layer and the conductive porous body and between the negative electrode layer and the conductive porous body (Patent Document 1).

[0003] [Prior Technical Literature]

[0004] (Patent Document)

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-141864 Summary of the invention

[0006] [Problems to be solved by the invention]

[0007] Moreover, in the technology related to secondary batteries, high capacity is a problem to be solved. In order to increase the capacity of secondary batteries, it is expected to put lithium metal secondary batteries using lithium as the negative electrode active material into practical use. However, in lithium metal secondary batteries, due to repeated charging and discharging, a solid electrolyte interphase (SEI) layer is accumulated at the interface between the current collector and lithium at the negative electrode, and lithium dendrites are easily generated during charging. If lithium dendrites are generated, it is possible that the positive electrode layer and the negative electrode layer are short-circuited due to the lithium dendrites penetrating the diaphragm. In addition, if lithium dendrites are generated, it is possible that the expansion of the lithium secondary battery during charging becomes too large due to the decrease in the density of the metal lithium layer precipitated on the negative electrode layer.

[0008] The present invention is completed in view of the above, and its purpose is to provide a secondary battery, a diaphragm useful as the secondary battery and its manufacturing method, wherein the secondary battery is not prone to short circuit even if it is repeatedly charged and discharged, and the density of the metal lithium layer of the negative electrode layer in the charged state is not prone to decrease.

[0009] [Technical means to solve the problem]

[0010] The 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 opposite to the negative electrode active material layer. However, according to the inventors' research, it is found that in the separator provided with a conductive layer, there is a step difference between the region where the conductive layer is provided and the region where the conductive layer is not provided, and the step difference easily causes wrinkles on the separator. When wrinkles are generated on the separator, the positive electrode layer and the negative electrode layer cannot be reliably insulated, and a short circuit may occur between the positive electrode layer and the negative electrode layer.

[0011] The inventors have conducted further research and found that it is effective to form an insulating layer whose thickness difference with the conductive layer is less than 1 / 10 of the total thickness of the porous substrate and the conductive layer in the region of the separator where the conductive layer is not provided, and to make the thickness of the conductive layer greater than the thickness of the insulating layer. Therefore, the present invention provides the following invention.

[0012] (1) A secondary battery comprising a positive electrode layer, a negative electrode layer and a separator arranged between the positive electrode layer and the negative electrode layer, the positive electrode layer having a positive electrode collector and a positive electrode active material layer, the negative electrode layer having a negative electrode collector, the separator having a porous substrate, a conductive layer formed by an end region arranged along at least one end remaining on one surface of the porous substrate, 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 less than 1 / 10 of the total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is greater than the thickness of the insulating layer, and the separator is arranged in a manner such that the conductive layer and the negative electrode layer are opposite to each other.

[0013] According to the secondary battery of (1), since the conductive layer of the separator is arranged in a manner opposite to the negative electrode layer, it is easy to uniformly precipitate lithium in the negative electrode layer during charging. In addition, since electrons are supplied to the conductive layer during charging, and a large number of lithium precipitation sites are also formed in the conductive layer, the current density during charging can be reduced. Due to the decrease in current density during charging, the overvoltage is reduced, so the decomposition of the electrolyte is suppressed. In addition, since the separator has an end region where the conductive layer is not formed, and an insulating layer is formed in the end region, the positive electrode layer and the negative electrode layer are not easy 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 less than 1 / 10 of the total thickness of the porous substrate and the conductive layer, wrinkles are not easy to form and the shape stability is high. In addition, since the thickness of the conductive layer opposite to the negative electrode layer is greater than the thickness of the insulating layer, it is not easy to form a gap between the conductive layer and the negative electrode layer. Therefore, the secondary battery of (1) is unlikely to be short-circuited even when repeatedly charged and discharged, and the density of the metal lithium layer of the negative electrode layer in a charged state is unlikely to decrease, thereby achieving a high capacity.

[0014] (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 to the insulating layer side of the separator.

[0015] According to the secondary battery of (2), since the positive electrode tab is in contact with the insulating layer of the separator, the positive electrode tab is unlikely to come into contact with the conductive layer, and thus the positive electrode layer and the negative electrode layer are less likely to short-circuit.

[0016] (3) A secondary battery according to (2), wherein the negative electrode layer has a negative electrode active material layer, and on the side connected to the positive electrode tab, the end of the conductive layer is located at a position that exceeds the end of the positive electrode active material layer on the outside, and the end of the negative electrode active material layer is located at the same position as the end of the conductive layer or exceeds the end of the conductive layer on the outside.

[0017] According to the secondary battery of (3), since the negative electrode layer has a negative electrode active material layer, 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 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 at a position beyond the end of the conductive layer on the outside, since the end extends in the order of the positive electrode active material layer, the conductive layer, and the negative electrode active material layer, the entire surface of the positive electrode active material layer is opposite to the conductive layer via the porous substrate, so when the lithium ions released from the positive electrode active material layer are precipitated on the negative electrode active material layer, efficient electron transfer can be performed. Therefore, the performance of the secondary battery is ensured.

[0018] (4) A secondary battery according to (3), wherein the end of the negative electrode active material layer is located at a position outside the end of the conductive layer, and the end of the insulating layer on the conductive layer side is located between the end of the positive electrode active material layer and the end of the negative electrode active material layer.

[0019] According to the secondary battery of (4), since the conductive layer and the end of the positive electrode active material layer are unlikely to come into contact with each other, the positive electrode layer and the negative electrode layer are less likely to be short-circuited.

[0020] (5) A diaphragm comprising a porous substrate, a conductive layer formed by leaving an end region along at least one end portion on one surface of the porous substrate, 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 less than 1 / 10 of the total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is greater than the thickness of the insulating layer.

[0021] According to the diaphragm of (5), a secondary battery can be obtained, in which the conductive layer is arranged in a manner opposite to the negative electrode active material layer, so that lithium is easily uniformly precipitated in the negative electrode active material layer during charging. When this secondary battery is charged, the overvoltage is reduced, so the decomposition of the electrolyte is suppressed. In addition, since the diaphragm has an end region where the conductive layer is not formed, and an insulating layer is formed in the end region, the positive electrode layer and the negative electrode layer are not easily short-circuited through the conductive layer. Furthermore, since the difference between the thickness of the conductive layer and the thickness of the insulating layer is less than 1 / 10 of the total thickness of the porous substrate and the conductive layer, wrinkles are not easily generated and the shape stability is high. In addition, since the thickness of the conductive layer opposite to the negative electrode layer when configured in the secondary battery is greater than the thickness of the insulating layer, it is not easy to generate a gap between the conductive layer and the negative electrode layer.

[0022] (6) A method for manufacturing a diaphragm, wherein a long porous substrate sheet is conveyed in a roller-to-roller direction in a longitudinal direction, and a conductive layer is formed in a strip shape on one surface of the long porous substrate sheet, leaving an end region including at least one end in a direction orthogonal to the longitudinal direction; then, an insulating layer is formed in a strip shape in the end region with a thickness whose difference with the thickness of the conductive layer is less than 1 / 10 of the total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is greater than the thickness of the insulating layer.

[0023] The long strip-shaped separator obtained by the separator manufacturing method (6) has a difference between the thickness of the conductive layer and the thickness of the insulating layer as small as less than 1 / 10 of the total thickness of the long strip-shaped porous substrate sheet and the conductive layer. The step difference between the conductive layer and the insulating layer can be absorbed when the separator is rolled up, so it is not easy to wrinkle and has high shape stability. In addition, since the thickness of the conductive layer, which occupies most of the separator, is thicker than the thickness of the insulating layer formed in the end area, the long strip-shaped separator is not easy to bulge locally when it is rolled up, and excessive extension or tensile fracture 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 using a roll-to-roll method.

[0024] (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 inkjet method.

[0025] According to the method for producing a separator of (7), the conductive layer can be formed continuously and stably, so the production efficiency of the separator is high.

[0026] (8) The method for producing a separator according to (6) or (7), wherein the insulating layer is formed by an inkjet method.

[0027] According to the method for manufacturing a diaphragm of (8), the insulating layer can be formed continuously and stably, so the manufacturing efficiency of the diaphragm is high.

[0028] (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.

[0029] According to the method for manufacturing a separator of (9), since the conductive layer and the insulating layer are formed by the inkjet method, the conductive layer and the insulating layer can be easily formed at the same speed. Therefore, the steps can be simplified.

[0030] (Effects of the Invention)

[0031] According to the present invention, a secondary battery which is less likely to short-circuit even when repeatedly charged and discharged and less likely to have a decrease in the density of a metal lithium layer of a negative electrode layer in a charged state, and a separator useful as the secondary battery and a method for producing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a plan view of a separator according to one embodiment of the present invention.

[0033] Figure 2 yes Figure 1 Sectional view along line II-II.

[0034] Figure 3 It is a cross-sectional view of a secondary battery according to one embodiment of the present invention.

[0035] Figure 4 It is a cross-sectional view of a secondary battery according to another embodiment of the present invention.

[0036] Figure 5 This is a schematic diagram of a production apparatus that can be used in the method for producing a separator according to one embodiment of the present invention. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments shown below are for exemplification of the present invention, and the present invention is not limited to the following.

[0038] Figure 1 It is a plan view of a separator according to one embodiment of the present invention. Figure 2 yes Figure 1 Sectional view along line II-II.

[0039] The separator 10 of the present embodiment includes a porous substrate 11, a conductive layer 12 formed by leaving an end region 11a provided along at least one end on one surface of the porous substrate 11, and an insulating layer 13 formed in the end 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 greater than or equal to the thickness of the insulating layer 13. In the present embodiment, the thickness of the conductive layer 12 is the same as the thickness of the insulating layer 13.

[0040] The porous substrate 11 is not particularly limited, and for example, a well-known substrate used as a separator for a lithium metal secondary battery, such as a porous sheet and a non-woven fabric sheet, can be used. Examples of materials for the porous sheet include polyolefins such as polyethylene and polypropylene, aromatic polyamides, polyimides, and fluororesins. Examples of materials for non-woven fabric sheets include glass fibers and cellulose fibers. The film thickness of the porous substrate 11 is not particularly limited, and is preferably 10 μm or more from the perspective of blocking dendrites of lithium metal, and is preferably 15 μm or less from the perspective of reducing the resistance in the battery. The film thickness of the porous substrate 11 is more preferably in the range of 10 to 12 μm. In addition, the air permeability of the porous substrate 11 is not particularly limited, and is preferably 200 sec / 100 mL or less, and more preferably 150 sec / 100 mL or less from the perspective of reducing the resistance in the battery. The porosity of the porous substrate 11 is not particularly limited, but is preferably within a range of 40% to 60% from the viewpoint of uniform diffusion of lithium in the separator 10 and the strength of the separator 10 .

[0041] The conductivity of the conductive layer 12 is not particularly limited and may be between 1.0×10 1 ~1.0×10 5 The surface resistivity may be, for example, 200 Ω / cm 2 As the material of the conductive layer 12, for example, conductive materials such as metals and carbon nanotubes (CNT) can be used. Examples of metals include Cu, Zn, Ti, and Sn. These conductive materials can be used alone or in combination of two or more. The thickness of the conductive layer 12 can also be, for example, in the range of 1 nm or more and 5000 nm (5 μm or less).

[0042] The conductive layer 12 may be, for example, a layer of agglomerates of conductive material particles formed by a method of applying a coating liquid of a conductive material, or a layer of a continuous film formed by a sputtering method or a vapor deposition method. In the case of agglomerates of conductive material particles, the average particle size of the conductive material particles may also be in the range of 5 nm to 100 nm. The average pore size of the porous substrate 11 may also be, for example, less than 1 times the average particle size of the conductive material particles.

[0043] The insulating property of the insulating layer 13 is not particularly limited. For example, the withstand voltage combined with the porous substrate 11 may be 500V or more. The insulating layer 13 may be either an organic substance or an inorganic substance, or a composite material of an organic substance and an inorganic substance. The insulating layer 13 may be, for example, a layer of an agglomerate of inorganic particles formed by a method of applying a coating liquid of inorganic particles, or a layer of a composite material formed by filling inorganic particles in a resin. The inorganic particles are preferably particles with high heat resistance. As the inorganic particles, for example, aluminum oxide and boehmite may be used.

[0044] Next, a secondary battery using the separator 10 of the present embodiment will be described.

[0045] Figure 3 It is a cross-sectional view of a secondary battery according to one embodiment of the present invention.

[0046] The secondary battery 101 of 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. The laminate is accommodated in an outer casing (not shown) together with an electrolyte (not shown). The outer casing includes a positive electrode terminal and a negative electrode terminal.

[0047] The positive electrode layer 20 includes a positive electrode collector 21 and a positive electrode active material layer 22 stacked on both sides of the positive electrode collector 21. The positive electrode collector 21 is connected to the positive electrode tab 23, and the positive electrode tab 23 is connected to the positive electrode terminal. The negative electrode layer 30 includes a negative electrode collector 31 and a negative electrode active material layer 32 stacked on both sides of the negative electrode collector 31. The negative electrode collector 31 is connected to the negative electrode tab 33, and the negative electrode tab 33 is connected to the 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. When 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. Therefore, when charging, the thickness of the negative electrode layer 30 increases. On the other hand, when discharging, lithium is released from the metallic lithium layer and is absorbed by the positive electrode active material layer 22. Therefore, during discharge, the thickness of the negative electrode layer 30 decreases. Therefore, the change in thickness of the negative electrode layer 30 due to charge and discharge is large. Figure 3 The secondary battery 101 is shown in a discharged state.

[0048] The separator 10 is arranged in such a manner that the conductive layer 12 and the negative electrode active material layer 32 face each other. Of 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 connected to the positive electrode tab 23, the end 12b of the conductive layer 12 is located at a position that exceeds the end 22b of the positive electrode active material layer 22 on the outside, and the end 32b of the negative electrode active material layer 32 is located at a position that exceeds the end of the conductive layer 12 on 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. Of 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 connected to the negative electrode tab 33, the end 12a of the conductive layer 12 is located at a position beyond the end 22a of the positive electrode active material layer 22 on the outside, and the end 32a of the negative electrode active material layer 32 is located at a position further inside than the end 12a of the conductive layer 12. If the ends are extended in accordance with the structure of the positive electrode active material layer 22, the conductive layer 12, and the negative electrode active material layer 32 in this way, the entire surface of the positive electrode active material layer 22 will face the conductive layer 12 via the porous substrate 11, so that when the lithium ions released from the positive electrode active material layer are deposited on the negative electrode active material layer, efficient electron transfer can be performed. 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) can be greater than 2 mm and less than 4 mm, for example, when the protrusion of the negative electrode layer 30 relative to the positive electrode layer 20 is +2 mm and the protrusion of the separator 10 relative to the end of the negative electrode layer 30 is +2 mm.

[0049] The conductive layer 12 is in electrical contact with the negative electrode active material layer 32 in the discharge state, and in electrical contact with the metal lithium deposited on the negative electrode active material layer 32 in the charge state. As a result, the potential of the conductive layer 12 is the same as that of the negative electrode active material layer 32, so lithium can be deposited more uniformly between the conductive layer 12 and the negative electrode active material layer 32. Therefore, lithium dendrites are not easily generated, and the density of the deposited lithium layer is not easily reduced.

[0050] The conductivity of the conductive layer 12 may be lower than that of the negative electrode current collector 31. This can prevent the concentrated precipitation of lithium on the porous substrate 11 side of the conductive layer 12 during charging, and can suppress damage caused by the shape change of the conductive layer 12 caused by the concentrated precipitation of lithium. The conductivity of the conductive layer 12 may be, for example, in the range of 1 / 10 to 1 / 100000 of the conductivity of the negative electrode current collector 31.

[0051] The material of the positive electrode collector 21 is not particularly limited, and for example, aluminum can be used. The material of the positive electrode tab 23 can be the same as the material of the positive electrode collector 21, or different from the material of the positive electrode collector 21. The positive electrode tab 23 can also be connected integrally with the positive electrode collector 21. In the present embodiment, the positive electrode tab 23 is formed by extending the positive electrode collector 21 and is connected integrally with the positive electrode collector 21. The material of the positive terminal can be the same as the material of the positive electrode tab 23, or different from the material of the positive electrode tab 23. The positive terminal can also be connected integrally with the positive electrode tab 23.

[0052] The positive electrode active material layer 22 contains a positive electrode active material. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and LiNiO2. p Mn q Co r O2(p+q+r=1), LiNi p Al q Co r O2 (p + q + r = 1), lithium manganate (LiMn2O4), Li 1+x Mn 2－x－y M y O4 (x+y=2, M is selected from at least one of Al, Mg, Co, Fe, Ni and Zn) represented by a heterogeneous element substituted Li-Mn spinel, lithium titanate (comprising an oxide of Li and Ti), lithium metal phosphate (LiMPO4, M is selected from at least one of Fe, Mn, Co and Ni), etc. The positive electrode active material layer 22 may also include various additives such as a binder and a conductive aid used as a material of the positive electrode active material layer.

[0053] 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 can be the same as the material of the negative electrode current collector 31, or different from the material of the negative electrode current collector 31. The negative electrode tab 33 can also be connected integrally with the negative electrode current collector 31. In the present embodiment, the negative electrode tab 33 is formed by extending the negative electrode current collector 31 and is connected integrally with the negative electrode current collector 31. The material of the negative terminal can be the same as the material of the negative electrode tab 33, or different from the material of the negative electrode tab 33. The negative terminal can also be connected integrally with the negative electrode tab 33.

[0054] Lithium and a metal that forms an alloy with lithium can be used as the negative electrode active material layer 32. Examples of metals that form an alloy with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn. The thickness of the negative electrode active material layer 32 can be, for example, 50 μm or less.

[0055] The electrolyte solution includes an organic solvent and an electrolyte. As an organic solvent, for example, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, hydrofluoroethers, aromatic ethers, sulfones, cyclic esters, chain carboxylates, and nitriles can be used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 4-methyl 1,3-dioxolane. Examples of 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, and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane. Examples of aromatic ethers include anisole. Examples of sulfones include cyclopentane sulfone and methylcyclopentane sulfone. Examples of cyclic esters include γ-butyrolactone. Examples of chain carboxylates include acetate, butyrate, and propionate. Examples of nitriles include acetonitrile and propionitrile. The organic solvent may be used alone or in combination of two or more.

[0056] The electrolyte is a source of lithium ions that serve as a charge transfer medium and includes a lithium salt. Examples of lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(CF3SO2)2(LiTFSI), LiN(FSO2)2(LiFSI), and LiBC4O8. The lithium salt can be used alone or in combination of two or more. The concentration of the electrolyte is, for example, in the range of 1.5 to 4.0 mol / L.

[0057] The outer casing can expand and contract in accordance with the change in thickness of the secondary battery 101 (especially the change in thickness of the negative electrode layer 30) caused by charge and discharge. As a material for the outer casing, a laminated film can be used. As a laminated film, a laminated film having a three-layer structure in which an inner resin layer, a metal layer, and an outer resin layer are sequentially stacked from the inside can be used. As materials for the inner resin layer and the outer resin layer, for example, polyethylene terephthalate (PET), polyamide (nylon), and polypropylene (PP) can be used. As a material for the metal layer, for example, aluminum can be used.

[0058] In the secondary battery 101 , the end 32 b of the negative electrode active material layer 32 connected to the positive electrode tab 23 is located outside the end of the conductive layer 12 . However, the positional relationship between the negative electrode active material layer 32 and the conductive layer 12 is not limited thereto.

[0059] Figure 4 It is a cross-sectional view of a secondary battery according to another embodiment of the present invention.

[0060] The secondary battery 102 of this embodiment is the same as the above-mentioned secondary battery 101 except that on the side connected to the positive electrode tab 23, the end 12b of the conductive layer 12 is located at a position beyond the end 22b of the positive electrode active material layer 22, 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, so the same symbols are attached and the description is omitted.

[0061] Next, a method for manufacturing the separator 10 according to the present embodiment will be described.

[0062] Figure 5 This is a schematic diagram of a production apparatus that can be used in the method for producing a separator according to one embodiment of the present invention.

[0063] The manufacturing device 40 includes 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 arranged.

[0064] The roller unwinding device 41 is a device for unwinding a long porous substrate sheet 42 from a porous substrate sheet roll 51. The conductive layer forming device 43 is a device for forming a conductive layer on the surface of the long porous substrate sheet 52. As a method for forming the conductive layer, a sputtering method, a die coating method, and an inkjet method can be used. The insulating layer forming device 44 is a device for forming an insulating layer on the end area of ​​the surface of the long porous substrate sheet 52. As a method for forming the insulating layer, an inkjet method can be used. The roller winding device 42 is a device for winding a long porous substrate sheet (long diaphragm sheet 53) formed with a conductive layer and an insulating layer to form a diaphragm sheet roll 54.

[0065] The separator 10 is manufactured as follows.

[0066] Towards the long side ( Figure 5The long porous substrate sheet 52 unrolled from the porous substrate sheet roll 51 by the roller unwinding device 41 is conveyed (in the direction of the arrow in the figure). While conveying the long porous substrate sheet 52, a conductive layer is formed in a strip shape on one surface of the long porous substrate sheet 52 by using the conductive layer forming device 43, leaving an end region including at least one end in a direction orthogonal to the long side direction. Next, an insulating layer is formed in a strip shape on the end region of the long porous substrate sheet 52 by using the insulating layer forming device 44. The thickness of the insulating layer is a thickness, and the difference between the thickness and the thickness of the conductive layer is less than 1 / 10 of the total thickness of the long porous substrate sheet 52 and the conductive layer, and the thickness of the conductive layer is greater than the thickness of the insulating layer. Next, the long porous substrate sheet (long diaphragm sheet 53) formed with the conductive layer and the insulating layer is wound up to form a diaphragm sheet roll 54. In this way, the diaphragm sheet roll 54 can be manufactured by roller-to-roll. The separator 10 can be obtained by rolling out the long strip of separator sheet 53 from the obtained separator sheet roll 54 and cutting it into a predetermined size.

[0067] According to the secondary battery 101, 102 of the present embodiment having the above structure, since the conductive layer 12 of the separator 10 is arranged in a manner opposite to the negative electrode active material layer 32, it is easy to uniformly precipitate lithium in the negative electrode active material layer 32 during charging. In addition, since electrons are supplied to the conductive layer 12 during charging, and a large number of lithium precipitation sites are also formed in the conductive layer 12, the current density during charging can be reduced. Due to the decrease in current density during charging, the overvoltage is reduced, so the decomposition of the electrolyte is suppressed. In addition, since 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, the positive electrode layer 20 and the negative electrode layer 30 are not easy 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 as small as less than 1 / 10 of the total thickness of the porous substrate 11 and the conductive layer 12, wrinkles are not easy to occur, and the 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, it is difficult to generate a gap between the conductive layer 12 and the negative electrode active material layer 32. Therefore, the secondary batteries 101 and 102 of this embodiment are not likely to short-circuit even if they are repeatedly charged and discharged, and the density of the metal lithium layer of the negative electrode layer in the charged state is not likely to decrease, thereby achieving high capacity.

[0068] In the secondary batteries 101 and 102 of the present embodiment, the positive electrode current collector 21 is connected to the positive electrode tab 23, and the positive electrode tab 23 extends to the insulating layer 13 side of the separator 10. As a result, the positive electrode tab 23 is in contact with the insulating layer 13 of the separator 10, so the positive electrode tab 23 is unlikely to contact the conductive layer 12. Therefore, the positive electrode layer 20 and the negative electrode layer 30 are less likely to short-circuit.

[0069] In the secondary batteries 101 and 102 of the present embodiment, the end of the conductive layer 12 on the side connected to the positive electrode tab 23 is located at a position that is outside and beyond the end 22b of the positive electrode active material layer 22, 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 outside and beyond the end 12b of the conductive layer 12. As a result, 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 is increased, so that the positive electrode layer 20 and the negative electrode layer 30 are less likely to short-circuit. In the secondary battery 101, the end 32b of the negative electrode active material layer 32 is located at a position that is outside and beyond the end 12b of the conductive layer 12, and the ends are extended in the order of the positive electrode active material layer 22, the conductive layer 12, and the negative electrode active material layer 32, 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. The conductive layer 12 and the end 22b of the positive electrode active material layer 22 are not easily in contact, so the positive electrode layer 20 and the negative electrode layer 30 are less likely to short-circuit.

[0070] According to the separator 10 of the present embodiment, a secondary battery can be obtained, in which the conductive layer 12 is arranged in a manner opposite to the negative electrode active material layer 32, so that lithium is easily uniformly precipitated in the negative electrode active material layer 32 during charging. When this secondary battery is charged, the overvoltage is reduced, so the decomposition of the electrolyte is suppressed. In addition, since the separator 10 of the present embodiment has an end region 11a where the conductive layer 12 is not formed, and an insulating layer 13 is formed in the end region 11a, the positive electrode layer 20 and the negative electrode layer 30 are not easy 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 less than 1 / 10 of the total thickness of the porous substrate and the conductive layer, wrinkles are not easy to occur, and the shape stability is high. In addition, since the thickness of the conductive layer 12 opposite to the negative electrode active material layer 32 when configured in the secondary battery is the same as the thickness of the insulating layer 13, it is not easy to generate a gap between the conductive layer 12 and the negative electrode active material layer 32.

[0071] The long strip diaphragm sheet 53 obtained by the manufacturing method of the diaphragm 10 of the present embodiment has a difference between the thickness of the conductive layer and the thickness of the insulating layer as small as less than 1 / 10 of the total thickness of the porous substrate and the conductive layer. When it is rolled up in a roll, the step difference between the conductive layer and the insulating layer can be absorbed, so it is not easy to wrinkle and has high shape stability. In addition, since the thickness of the conductive layer that occupies most of the diaphragm is thicker than the thickness of the insulating layer formed in the end area, the long strip diaphragm sheet 53 obtained is not easy to bulge locally when it is rolled up in a roll, and excessive extension or tensile fracture can be suppressed. Therefore, according to the manufacturing method of the diaphragm 10 of the present embodiment, the diaphragm 10 having the conductive layer 12 and the insulating layer 13 can be efficiently manufactured by roll-to-roll.

[0072] In the manufacturing method of the diaphragm 10 of the present 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, so the manufacturing efficiency of the diaphragm is high. In addition, by using the inkjet method as the method for forming the insulating layer, the insulating layer can be continuously and stably formed, so the manufacturing efficiency of the diaphragm is high. Furthermore, by using the inkjet method as the method for forming the conductive layer and using the inkjet method as the method for forming the insulating layer, it is easy to form the conductive layer and the insulating layer at the same speed. Therefore, the steps can be simplified.

[0073] The above is a description of the embodiment of the present invention, but the present invention is not limited to the above embodiment and can be appropriately changed. For example, in the present embodiment, the thickness of the conductive layer 12 of the separator 10 is the same as the thickness of the insulating layer 13, but as long as the difference between the thickness of the conductive layer 12 and the thickness of the insulating layer 13 is less than 1 / 10 of the total thickness of the porous substrate 11 and the conductive layer 12, the thickness of the conductive layer 12 can also be greater than the thickness of the insulating layer 13. In this case, the difference between the thickness of the conductive layer 12 and the thickness of the insulating layer 13 can also be in the range of more than 0.01 μm and less than 2 μm. In addition, in the present embodiment, the negative electrode layer 30 has a negative electrode collector 31 and a negative electrode active material layer 32 stacked on both sides of the negative electrode collector 31, but the structure of the negative electrode layer 30 is not limited thereto. For example, the negative electrode active material layer 32 can also be omitted. In this case, during charging, lithium is precipitated on the surface of the negative electrode collector 31 to generate a lithium layer.

[0074] [Experimental example]

[0075] The effect of providing the conductive layer 12 on the negative electrode layer 30 side of the separator 10 will be described using experimental examples.

[0076] [Experimental Example 1]

[0077] (Production of Diaphragm)

[0078] An insulating porous film (film thickness: 20 μm, porosity: 58%, air permeability: 92 sec / 100 mL) was prepared. A copper conductive layer with a thickness of 0.08 μm was formed on one surface of the insulating porous film by radio frequency (RF) sputtering. The insulating porous film with the copper conductive layer formed was punched into a size of 40 mm × 50 mm to make a diaphragm.

[0079] (Production of positive electrode layer)

[0080] Acetylene black (AB) as an electronic conductive material, polyvinylidene fluoride (PVDF) as a binder (adhesive), and polyvinylpyrrolidone (PVP) as a dispersant were pre-mixed in N-methyl-2-pyrrolidone (NMP) as a dispersing solvent, and wet mixed with a rotary mixer to obtain a pre-mixed slurry. Then, Li1Ni 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and the pre-doped material are mixed with the obtained premixed slurry, and a planetary mixer is used for dispersion treatment to obtain a positive electrode active material paste. The median particle size of NCM811 is 12 μm. Next, the obtained positive electrode active material paste is applied to an aluminum positive electrode collector without a primer layer, and dried, and after being pressed by roller pressing, it is dried in a vacuum at 120°C to form a positive electrode plate having a positive electrode active material layer. The obtained positive electrode plate is punched into a size of 30 mm × 40 mm to form a positive electrode layer.

[0081] (Production of negative electrode layer)

[0082] A copper foil with a thickness of 10 μm (negative electrode current collector, conductivity: 6.5×10 6 The coating material was formed by bonding a 20 μm thick lithium foil (negative electrode active material layer) to a 34 mm × 44 mm size to form a negative electrode layer.

[0083] (Electrolyte)

[0084] An electrolyte solution was prepared by dissolving LiFSI at a concentration of 4 mol / L in 1,2-dimethoxyethane (DME).

[0085] (Manufacturing of lithium metal secondary batteries)

[0086] On the surface of the lithium foil side of the negative electrode collector, the copper conductive layer of the separator is overlapped, and on the surface of the separator on the opposite side of the copper conductive layer, the positive electrode active material layer of the positive electrode layer is overlapped, and an electrode stack having a negative electrode layer, a separator, and a positive electrode layer stacked in sequence is produced. Then, a positive terminal is installed on the positive electrode collector of the obtained electrode stack through a positive electrode tab, and a negative terminal is installed on the copper foil of the negative electrode collector through a negative electrode tab. The stack with the positive terminal and the negative terminal installed is placed in a laminated film bag, and then an electrolyte is placed, and then the laminated film bag is sealed to produce a lithium metal secondary battery.

[0087] [Experimental Example 2]

[0088] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that a zinc conductive layer having a thickness of 0.06 μm was formed by RF sputtering instead of the copper conductive layer in the production of the separator.

[0089] [Experimental Example 3]

[0090] In the preparation of the diaphragm, a carbon nanotube (CNT) conductive layer with a thickness of 2.1 μm was formed by a coating method to replace the copper conductive layer. In addition, a lithium metal secondary battery was prepared in the same manner as in Experimental Example 1. The formation of the carbon nanotube conductive layer is carried out as follows. First, N-methyl-N-pyrrolidinone (NMP) is used as a solvent, and carbon nanotubes are added in an amount of 4% by weight of solid content concentration, and PVDF (#9300, manufactured by Kureha Co., Ltd.) as a binder is added in an amount of 5 parts by weight relative to 95 parts by weight of carbon nanotubes. Then, a dispersion treatment is carried out for 10 minutes using a rotary revolution mixer at 1000 rpm to prepare a coating solution. The obtained coating solution is applied to the surface of the insulating porous membrane using a scraper and dried.

[0091] [Experimental Example 4]

[0092] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that a 0.06 μm-thick tin conductive layer was formed by RF sputtering instead of the copper conductive layer in the production of the separator.

[0093] [Comparative Experiment Example 1]

[0094] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that the copper conductive layer was not formed in the production of the separator.

[0095] [evaluate]

[0096] The electrical conductivity, surface resistivity, and peel strength of the conductive layer of the separator produced in each experimental example were measured by the following method. The results are shown in Table 1 together with the material, coating method, and thickness of the conductive layer of the separator.

[0097] In addition, the presence or absence of short circuit and the rate of increase in lithium thickness of the lithium metal secondary batteries produced in each experimental example and comparative experimental example were measured by the following method. The results are shown in Table 1.

[0098] (Electrical conductivity and surface resistivity of the conductive layer)

[0099] The electrical conductivity and surface resistivity were measured using a high-precision, high-performance resistivity meter (NITTOSEIKO ANALYTECH Co., Ltd., Loresta GP TCP-600).

[0100] (Peel Strength)

[0101] On the adhesive tape of width 2.5cm crimped on the plate fixed, the conductive layer of crimping length 5.0cm, width 2.5cm. Then, one end of the conductive layer is folded back 180 degrees, using an electric measuring platform (manufactured by IMADA Co., Ltd.), pulled at a speed of 300mm / min, and the conductive layer is peeled off from the insulating porous film. Use a digital dynamometer (manufactured by IMADA Co., Ltd.) to measure the load required from the beginning of peeling off the conductive layer to the end of peeling off. The value obtained by dividing the mean value of the load obtained by the width of the adhesive tape is used as the peel strength.

[0102] (Presence or absence of short circuit in lithium metal secondary battery)

[0103] The lithium metal secondary battery just produced was left to stand at a measurement temperature of 25° C. for 24 hours.

[0104] After standing, the lithium metal secondary battery was subjected to the following first charge and discharge cycle for 3 cycles, and then the following second charge and discharge cycle for 50 cycles, to confirm the presence or absence of a short circuit in the lithium metal secondary battery. When the charge capacity of the lithium metal secondary battery was 105% or more relative to the discharge capacity before charging, it was determined that a short circuit had occurred, and it was determined that there was a short circuit.

[0105] (First charge and discharge cycle)

[0106] The charging was performed under the following conditions: constant current charging was performed at a current value of 2.2 mA until the voltage reached 4.300 V, and constant voltage charging was performed for 60 minutes at a voltage value of 4.300 V. The discharging was performed under the following conditions: constant current discharge was performed at a current value of 4 mA until the voltage reached 2.65 V. The battery was left to stand for 30 minutes between discharging and charging.

[0107] (Second charge and discharge cycle)

[0108] The charging was performed under the following conditions: constant current charging at a current value of 74 mA to 3.823 V, at a current value of 52 mA to 4.051 V, at a current value of 46 mA to 4.173 V, at a current value of 22 mA to 4.300 V, and then constant voltage charging for 90 minutes at a voltage value of 4.300 V. The discharging was performed under the following conditions: constant current discharge at a current value of 18 mA to 2.65 V. The battery was left to stand for 30 minutes between discharging and charging.

[0109] (Lithium thickness increase rate of lithium metal secondary battery)

[0110] The thickness T1 (μm) of the negative electrode layer during initial charging and the thickness T2 (μm) of the negative electrode layer during charging after 50 cycles (total thickness of the negative electrode collector and the metal lithium layer) were measured, and the lithium thickness increase rate T (μm / cycle) was calculated using the following formula.

[0111] T(μm / cycle)=(T2-T1) / 50

[0112] The thickness T1 (μm) of the negative electrode layer during initial charge was measured as follows.

[0113] The lithium metal secondary battery just produced was left to stand at a measurement temperature of 25° C. for 24 hours.

[0114] The lithium metal secondary battery after standing was subjected to the above-mentioned first charge and discharge cycle for 3 cycles. Then, constant current charging was performed at a current value of 14.7 mA until 4.300 V, and constant voltage charging was continued at a voltage value of 4.300 V for 60 minutes to charge the lithium metal secondary battery. After the charged lithium metal secondary battery was allowed to stand for 30 minutes, it was disassembled, the negative electrode layer was taken out, and its thickness was measured as the thickness T1 of the negative electrode layer.

[0115] The thickness T2 of the negative electrode layer during charging after 50 cycles was measured as follows.

[0116] The lithium metal secondary battery just produced was left to stand at a measurement temperature of 25° C. for 24 hours.

[0117] For the lithium metal secondary battery after standing, the above-mentioned first charge and discharge cycle was performed for 3 cycles, and then the above-mentioned second charge and discharge cycle was performed for 50 cycles. Next, constant current charging was performed at a current value of 14.7 mA until 4.300 V, and constant voltage charging was continued at a voltage value of 4.300 V for 60 minutes to charge the lithium metal secondary battery. After the charged lithium metal secondary battery was stood for 30 minutes, it was disassembled, the negative electrode layer was taken out, and its thickness was measured as the thickness T2 of the negative electrode layer.

[0118] [Table 1]

[0119]

[0120] As shown in Table 1, it can be seen that the lithium metal secondary batteries of Experimental Examples 1 to 4 with a separator having a conductive layer are not prone to short circuits even after repeated charge and discharge, and the lithium thickness increases slowly, and the metal lithium layer generated by charging is dense and has a high density. It can be seen that, in contrast, the lithium metal secondary battery of Comparative Experimental Example 1 with a separator without a conductive layer is prone to short circuits when repeatedly charged and discharged, and the lithium thickness increases quickly, so a loose and low-density metal lithium layer is generated due to charging.

[0121] Reference numerals

[0122] 10 Diaphragm

[0123] 11Porous substrate

[0124] 11a End region

[0125] 12 Conductive layer

[0126] 13 Insulation layer

[0127] 20 positive electrode layer

[0128] 21Positive electrode collector

[0129] 22Positive electrode active material layer

[0130] 23 positive pole ear

[0131] 30 negative electrode layer

[0132] 31 negative electrode collector

[0133] 32 Negative electrode active material layer

[0134] 33 Negative electrode tab

[0135] 40 Manufacturing equipment

[0136] 41 Roller unwinding device

[0137] 42-roller winding device

[0138] 43Conductive layer forming device

[0139] 44Insulation layer forming device

[0140] 51Porous substrate sheet roll

[0141] 52 Long strip porous substrate sheet

[0142] 53 long strip diaphragm

[0143] 54 Diaphragm roll

[0144] 101, 102 Secondary battery

Claims

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 comprises a positive electrode current collector and a positive electrode active material layer. The negative electrode layer has a negative electrode collector. The diaphragm comprises a porous substrate, a conductive layer formed by leaving an end region arranged along at least one end on one surface of the porous substrate, 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 less than 1 / 10 of the total thickness of the porous substrate and the conductive layer, and the thickness of the conductive layer is greater than the thickness of the insulating layer. The separator is arranged so that the conductive layer and the negative electrode layer face each other.

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

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

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

5. A separator comprising a porous substrate, a conductive layer formed by leaving an end region provided along at least one end on one surface of the porous substrate, 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 less of 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.

6. A method for manufacturing a diaphragm, comprising the following steps: While conveying a long strip of porous substrate sheet in the long side direction by roller-to-roller, a conductive layer is formed in a strip shape on one surface of the long strip of porous substrate sheet, leaving an end region including at least one end in a direction perpendicular to the long side direction. Then, an insulating layer is formed in a strip shape in the end region with a thickness whose difference with the thickness of the conductive layer is less than 1 / 10 of the total thickness of the long strip of porous substrate sheet and the conductive layer, and the thickness of the conductive layer is greater than the thickness of the insulating layer.

7. The method for manufacturing a diaphragm according to claim 6, wherein: The conductive layer may be formed by sputtering, die coating, or inkjet.

8. The method for manufacturing a diaphragm according to claim 6, wherein: The insulating layer is formed by an inkjet method.

9. The method for manufacturing a diaphragm according to claim 6, wherein: The conductive layer is formed by an inkjet method, and the insulating layer is formed by an inkjet method.

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