Secondary battery and manufacturing method thereof

Abstract

To provide a secondary battery and a manufacturing method for the same, in which even if the thickness of a negative electrode layer largely changes due to charging and discharging, the displacement of a positive electrode layer and a negative electrode layer does not occur easily.SOLUTION: A secondary battery includes an electrode laminate, an electrolyte solution, and an exterior body that accommodates the electrode laminate and the electrolyte solution. The electrode laminate includes a positive electrode layer, a negative electrode layer, and a rectangular separator. The rectangular separator includes an electrode layer accommodation part including two or more folds that are folded in a zig-zag manner along a length direction, and an extension part that is connected to an end part of the electrode layer accommodation part in the length direction. The positive electrode layer and the negative electrode layer are disposed to face each of the folds and the extension part is wound around an external side surface of the electrode layer accommodation part.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] In recent years, research and development has been conducted on secondary batteries that contribute to energy efficiency, ensuring that more people have access to affordable, reliable, sustainable, and advanced energy. To improve the energy density of secondary batteries, secondary batteries with a stacked structure in which multiple positive electrode layers and negative electrode layers are alternately stacked have been considered. For secondary batteries with this stacked structure, a method has been considered in which a long separator is folded in a zigzag pattern and positive electrode layers and negative electrode layers are alternately stacked at the folded portions, with the aim of suppressing misalignment between the positive electrode layers and negative electrode layers (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 003846 [Patent Document 2] International Publication No. 2020 / 003847 Summary of the Invention [Problem to be solved by the invention]

[0004] In secondary battery technology, increasing capacity is a challenge. To achieve this, the practical application of lithium metal secondary batteries using metallic lithium as the negative electrode active material is desired. However, lithium metal secondary batteries suffer from significant changes in the thickness of their negative electrode layers during charging and discharging. Therefore, in lithium metal secondary batteries with a stacked structure in which multiple positive electrode layers and negative electrode layers are alternately stacked, the change in the thickness of the negative electrode layer during charging and discharging may easily cause misalignment between the positive electrode layer and the negative electrode layer.

[0005] Furthermore, in lithium metal secondary batteries, repeated charge and discharge causes an SEI layer (solid electrolyte intermediate phase) to accumulate at the interface between the current collector of the negative electrode layer and lithium, making it easier for lithium dendrites to form during charging. When lithium dendrites form, they may penetrate the separator, causing a short circuit between the positive electrode layer and the negative electrode layer. Furthermore, when lithium dendrites form, the density of the metallic lithium layer (negative electrode active material layer) deposited on the negative electrode current collector decreases, which may result in excessive expansion of the lithium secondary battery during charging.

[0006] According to the inventors' investigations, by using a laminate in which a conductive layer is laminated on the surface of a porous membrane as a separator and arranging the conductive layer on the negative electrode layer side, it is possible to suppress short circuits caused by dendrites and a decrease in the density of the active material layer of the negative electrode layer in a charged state. However, if a long separator having a conductive layer on one surface is folded in a zigzag pattern and the positive electrode layer and the negative electrode layer are arranged so that they overlap alternately at the folded portions, the positive electrode layer and the conductive layer of the long separator may come into contact with each other, which may cause a short circuit between the positive electrode layer and the negative electrode layer.

[0007] The present invention has been made in view of the above, and aims to provide a secondary battery and a method for manufacturing the same in which the positive electrode layer and the negative electrode layer are less likely to be misaligned even when the thickness of the negative electrode layer changes significantly due to charge and discharge. In particular, the present invention aims to provide a secondary battery and a method for manufacturing the same in which the positive electrode layer and the negative electrode layer are less likely to be misaligned and less likely to short-circuit even when a separator having a conductive layer on one surface is used. This will ultimately contribute to improved energy efficiency. [Means for solving the problem]

[0008] The inventors of the present invention found that it is effective to solve the above-mentioned problems by providing an extension of the long separator at the end of an electrode layer accommodating section in which a positive electrode layer and a negative electrode layer are disposed by zigzagging the long separator, and by wrapping the extension around the outer surface of the electrode layer accommodating section, and thus completed the present invention.

[0009] (1) A secondary battery comprising: an electrode stack, an electrolyte solution, and an exterior housing that accommodates the electrode stack and the electrolyte solution, wherein the electrode stack has a positive electrode layer, a negative electrode layer, and a long separator, the long separator including an insulating porous membrane and a conductive layer provided on one surface of the insulating porous membrane, the long separator having an electrode layer accommodating section formed by alternately overlapping insulating folds folded along the length direction so that the surface facing the insulating porous membrane is on the inside and conductive folds folded along the length direction so that the surface facing the conductive layer is on the inside, and a first extension section extending from one end of the electrode layer accommodating section in the length direction, the positive electrode layer being disposed on the insulating fold and the negative electrode layer being disposed on the conductive fold so that they face each other, and the first extension section being wound around the outer surface of the electrode layer accommodating section so that the surface facing the insulating porous membrane is on the outside.

[0010] According to the secondary battery (1), the first extension portion is wound around the outer surface of the electrode layer housing portion, so that misalignment between the positive electrode layer and the negative electrode layer is unlikely to occur even if the thickness of the negative electrode layer changes significantly due to charging and discharging. Furthermore, the conductive layer of the long separator is disposed on the negative electrode layer side, so that short circuits caused by dendrites and a decrease in the density of the negative electrode active material layer of the negative electrode layer in the charged state are suppressed. Furthermore, the insulating porous membrane of the long separator is disposed on the positive electrode layer side, and the first extension portion is wound around the electrode layer housing portion with the insulating porous membrane side surface facing outward, so that the conductive layer of the long separator and the positive electrode layer are unlikely to come into contact with each other. Therefore, short circuits between the positive electrode layer and the negative electrode layer are unlikely to occur.

[0011] (2) A second extension portion extending from the other end of the electrode layer accommodating portion in the longitudinal direction is provided, The secondary battery according to (1), wherein the second extension portion extends so that the tip of the conductive fold contacts the surface of the insulating porous film.

[0012] According to the secondary battery (2), the second extension portion contacts the tip of the conductive fold, i.e., the surface of the insulating porous membrane contacts the opening of the insulating fold, making it less likely that the conductive layer of the long separator will come into contact with the positive electrode layer, and therefore less likely that a short circuit will occur between the positive electrode layer and the negative electrode layer.

[0013] (3) The secondary battery according to (1) or (2), wherein the conductive fold has an extension at the end of the fold, and the extension is bent toward the positive electrode layer.

[0014] In the secondary battery (3), the extension of the conductive fold is folded toward the positive electrode layer, so that the end of the positive electrode layer located on the opening side of the insulating fold is surrounded by the insulating porous membrane, making it even less likely that the conductive layer of the long separator will come into contact with the positive electrode layer, and making it even less likely that a short circuit will occur between the positive electrode layer and the negative electrode layer.

[0015] (4) The secondary battery according to any one of (1) to (3), further comprising: a positive electrode terminal electrically connected to the positive electrode layer and at least a portion of which is exposed to the outside; and a negative electrode terminal electrically connected to the negative electrode layer and at least a portion of which is exposed to the outside, wherein the positive electrode terminal and the negative electrode terminal are arranged in a direction perpendicular to the longitudinal direction of the long separator.

[0016] In the secondary battery of (4), the positive electrode terminal and the conductive layer of the long separator are unlikely to come into contact with each other, so that short circuits between the positive electrode layer and the negative electrode layer are unlikely to occur.

[0017] (5) The secondary battery according to any one of (1) to (4), wherein the negative electrode active material is metallic lithium.

[0018] According to the secondary battery of (5), the negative electrode active material is metallic lithium, so that a high capacity can be achieved.

[0019] (6) A method for manufacturing a secondary battery, comprising: folding a portion of a long laminate sheet including an insulating porous membrane and a conductive layer provided on one surface of the insulating porous membrane in a zigzag manner to produce a long separator having an electrode layer accommodating section formed by alternately overlapping insulating folds folded along the length direction so that the surface on the insulating porous membrane side is on the inside and conductive folds folded along the length direction so that the surface on the conductive layer side is on the inside; and a first extension section extending from one end of the electrode layer accommodating section in the length direction; arranging a positive electrode layer on the insulating fold and a negative electrode layer on the conductive fold so that they face each other; and wrapping the first extension section around the outer surface of the electrode layer accommodating section so that the surface on the insulating porous membrane side is on the outside.

[0020] The method for manufacturing a secondary battery (6) includes a step of wrapping the first extension portion of the long separator around the outer surface of the electrode layer housing portion. This allows for industrially advantageous production of a secondary battery in which misalignment between the positive electrode layer and the negative electrode layer is unlikely to occur, even if the thickness of the negative electrode layer changes significantly during charging and discharging. Furthermore, in the resulting secondary battery, the conductive layer of the long separator is positioned on the negative electrode layer side, thereby suppressing short circuits caused by dendrites and a decrease in the density of the negative electrode active material layer in the charged negative electrode layer. Furthermore, in the resulting secondary battery, the insulating porous membrane of the long separator is positioned on the positive electrode layer side, and the first extension portion is wound around the electrode layer housing portion with the surface facing the insulating porous membrane on the outer side, thereby preventing contact between the conductive layer of the long separator and the positive electrode layer. Therefore, the resulting secondary battery is less likely to short-circuit between the positive electrode layer and the negative electrode layer.

[0021] (7) A secondary battery comprising an electrode stack, an electrolyte, and an exterior body that accommodates the electrode stack and the electrolyte, wherein the electrode stack has a positive electrode layer, a negative electrode layer, and a long separator, wherein the long separator has an electrode layer accommodating section having two or more zigzag folds along its length, and an extension portion connected to an end of the electrode layer accommodating section in the length direction, wherein the positive electrode layer and the negative electrode layer are arranged at each of the folds so as to face each other, and the extension portion is wound around the outer surface of the electrode layer accommodating section.

[0022] According to the secondary battery (7), the first extension portion is wound around the outer surface of the electrode layer accommodating portion, so that even if the thickness of the negative electrode layer changes significantly due to charging and discharging, the positive electrode layer and the negative electrode layer are less likely to become misaligned. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a secondary battery and a manufacturing method thereof in which the positive electrode layer and the negative electrode layer are less likely to be misaligned even when the thickness of the negative electrode layer changes significantly due to charge and discharge. In particular, according to the present invention, it is possible to provide a secondary battery and a manufacturing method thereof in which the positive electrode layer and the negative electrode layer are less likely to be misaligned and the positive electrode layer and the negative electrode layer are less likely to be short-circuited, even when a separator having a conductive layer on one surface is used. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a perspective view of a secondary battery according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] 1 is a cross-sectional view of a separator used in a secondary battery according to a first embodiment of the present invention. [Figure 5] 3 is a cross-sectional view showing a state in which a positive electrode layer and a negative electrode layer are placed in an electrode layer receiving portion of a long separator in the production of a secondary battery according to the first embodiment of the present invention. FIG. [Figure 6] FIG. 3 is a cross-sectional view showing a modified example of the secondary battery according to the first embodiment of the present invention. [Figure 7] FIG. 10 is a cross-sectional view showing a state in which a positive electrode layer and a negative electrode layer are disposed in an electrode layer receiving portion of a long separator in the production of a secondary battery according to a modified example. [Figure 8] FIG. 4 is a cross-sectional view of a secondary battery according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] 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.

[0026] [First embodiment] Fig. 1 is a perspective view of a secondary battery according to a first embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1, and Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1. Fig. 4 is a cross-sectional view of a separator used in the secondary battery according to the first embodiment of the present invention.

[0027] The secondary battery 100 according to this embodiment includes an electrode stack 10 having a positive electrode layer 20, a negative electrode layer 30, and a long separator 40 disposed between the positive electrode layer 20 and the negative electrode layer 30; an electrolyte (not shown); and an exterior body 50 that accommodates the electrode stack 10 and the electrolyte. The positive electrode layer 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22 laminated on both sides of the positive electrode current collector 21. The negative electrode layer 30 includes a negative electrode current collector 31 and a lithium foil 32 laminated on both sides of the negative electrode current collector 31. The secondary battery 100 is a lithium metal secondary battery. A lithium metal secondary battery is a secondary battery that uses metallic lithium as the negative electrode active material. During charging, lithium is released from the positive electrode active material layer 22 and precipitates on the surface of the lithium foil 32, forming a metallic lithium layer. Therefore, 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 absorbed into the positive electrode active material layer 22. Therefore, the thickness of the negative electrode layer 30 decreases during discharge. Therefore, the thickness of the negative electrode layer 30 changes significantly during charge and discharge. The secondary battery 100 shown in Figures 1 to 3 is in a discharged state.

[0028] The secondary battery 100 further includes a positive electrode terminal 24 and a negative electrode terminal 34 provided on the exterior body 50, a positive electrode lead wire 23 electrically connecting the positive electrode layer 20 (positive electrode current collector 21) and the positive electrode terminal 24, and a negative electrode lead wire 33 electrically connecting the negative electrode layer 30 (negative electrode current collector 31) and the negative electrode terminal 34. Portions of the positive electrode terminal 24 and the negative electrode terminal 34 are exposed to the outside. The positive electrode terminal 24 is arranged along the width direction of the long separator 40 (a direction perpendicular to the length direction of the long separator 40), and the negative electrode terminal 34 is arranged at a position opposite to the positive electrode terminal 24 with the electrode stack 10 interposed therebetween.

[0029] The long separator 40 has an electrode layer accommodating section 45 formed by alternately folding insulating folds 43 and conductive folds 44. The insulating folds 43 are folded along the length so that the surface facing the insulating porous membrane 41 faces inward. The insulating folds 43 have a fold tip 43a and an opening 43b located on the opposite side of the fold tip 43a. The conductive folds 44 are folded along the length so that the surface facing the conductive layer 42 faces inward.

[0030] The long separator 40 has a first extending portion 46 extending from an upper end of the electrode layer accommodating portion 45 in the longitudinal direction, and a second extending portion 47 extending from a lower end of the electrode layer accommodating portion 45 in the longitudinal direction. The first extending portion 46 is wound around the outer surface of the electrode layer accommodating portion 45, with the surface facing the insulating porous membrane 41 facing outward. The first extending portion 46 is wound, for example, one to three times. The second extending portion 47 extends so that the surface of the insulating porous membrane 41 comes into contact with the tip 44a of the fold of the conductive fold 44, i.e., the opening 43b of the insulating fold 43.

[0031] The positive electrode layer 20 is disposed on the insulating fold 43, and the negative electrode layer 30 is disposed on the conductive fold 44 so as to face each other. The negative electrode layer 30 contacts the conductive layer 42 of the long separator 40, and the positive electrode layer 20 contacts the insulating porous membrane 41 of the long separator 40.

[0032] The material of the positive electrode current collector 21 is not particularly limited, and aluminum can be used, for example. The material of the positive electrode lead wire 23 may be the same as or different from the material of the positive electrode current collector 21. The positive electrode lead wire 23 may be integrally connected to the positive electrode current collector 21. In this embodiment, the positive electrode lead wire 23 is formed by extending the positive electrode current collector 21 and is integrally connected to the positive electrode current collector 21. The material of the positive electrode terminal 24 may be the same as or different from the material of the positive electrode lead wire 23. The positive electrode terminal 24 may be integrally connected to the positive electrode lead wire 23. In this embodiment, the positive electrode terminal 24 and the positive electrode lead wire 23 are separate members and are electrically connected to each other.

[0033] The positive electrode active material layer 22 includes a positive electrode active material. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), and 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 such an 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 additive.

[0034] The material of the negative electrode current collector 31 is not particularly limited, and copper, for example, can be used. The material of the negative electrode lead wire 33 may be the same as or different from the material of the negative electrode current collector 31. The negative electrode lead wire 33 may be integrally connected to the negative electrode current collector 31. In this embodiment, the negative electrode lead wire 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 34 may be the same as or different from the material of the negative electrode lead wire 33. The negative electrode terminal 34 may be integrally connected to the negative electrode lead wire 33. In this embodiment, the negative electrode terminal 34 and the negative electrode lead wire 33 are separate members and electrically connected to each other.

[0035] The long separator 40 has an insulating porous membrane 41 and a conductive layer 42 laminated on the surface of the insulating porous membrane 41 on the negative electrode layer 30 side. The conductive layer 42 does not have to be laminated over the entire insulating porous membrane 41. As shown in FIG. 4 , the conductive layer 42 may be laminated so as to cover part of the pores 41 a of the insulating porous membrane 41.

[0036] The insulating porous membrane 41 may be a known material used as a separator for a secondary battery, such as a porous sheet or a nonwoven fabric sheet. Examples of materials for the porous sheet include polyolefins such as polyethylene and polypropylene, aramid, polyimide, and fluororesin. Examples of materials for the nonwoven fabric sheet include glass fiber and cellulose fiber. The thickness of the insulating porous membrane 41 is not particularly limited, but is preferably 10 μm or more from the viewpoint of blocking lithium metal dendrites and is preferably 15 μm or less from the viewpoint of reducing resistance within the battery. The thickness of the insulating porous membrane 41 is more preferably within the range of 10 to 12 μm. The air permeability of the insulating porous membrane 41 is also not particularly limited, but is preferably 200 sec / 100 mL or less from the viewpoint of reducing resistance within the battery, and more preferably 150 sec / 100 mL or less. The porosity of the insulating porous film 41 is not particularly limited, but from the viewpoint of uniform diffusion of lithium in the long separator 40 and the strength of the long separator 40, it is preferably in the range of 40 to 60%.

[0037] The electrical conductivity of the conductive layer 42 is not particularly limited, but is preferably 1.0×10 1 ~1.0×10 5 The electrical conductivity of the conductive layer 42 is in the range of 1.0×10 1 When the electrical conductivity is 1.0×10 S / cm or more, lithium can be deposited on the surface of the conductive layer 42, and it is possible to prevent lithium dendrites from growing on the positive electrode layer 20 side and causing a short circuit. 5 By ensuring that the conductivity is S / cm or less, lithium can be deposited uniformly on the surface of the conductive layer 42.

[0038] In both the discharged and charged states, the conductive layer 42 is in electrical contact with either the negative electrode layer 30 or metallic lithium deposited on the negative electrode layer 30. This makes the potential of the conductive layer 42 and the potential of the negative electrode current collector 31 the same, allowing lithium to be deposited more uniformly between the conductive layer 42 of the long separator 40 and the lithium foil 32.

[0039] The electrical conductivity of the conductive layer 42 may be lower than that of the negative electrode current collector 31, i.e., the electrical conductivity of the negative electrode current collector 31 may be higher than that of the conductive layer 42. By making the electrical conductivity of the negative electrode current collector 31 higher than that of the conductive layer 42, concentrated deposition of lithium on the insulating porous film 41 side of the conductive layer 42 can be prevented, and damage to the conductive layer 42 due to concentrated deposition of lithium can be suppressed. The electrical conductivity of the conductive layer 42 may be, for example, within a range of 1 / 10 to 1 / 100,000 of the electrical conductivity of the negative electrode current collector 31.

[0040] The peel strength of conductive layer 42 from insulating porous film 41 is not particularly limited, but is preferably 10 N / m or more, and more preferably 30 N / m or more. When the peel strength of conductive layer 42 is as high as the above value, conductive layer 42 functions stably for a long period of time, thereby extending the charge / discharge cycle life.

[0041] The surface resistivity of the conductive layer 42 is 200 Ω / cm 2 It may be the following:

[0042] The thickness of the conductive layer 42 may be in the range of 0.01 to 5 μm. When the thickness of the conductive layer 42 is 0.01 μm or more, the above-mentioned effects of the conductive layer 42 can be obtained. When the thickness of the conductive layer 42 is 5 μm or less, the reduction in energy density due to the conductive layer 42 can be reduced.

[0043] The conductive layer 42 may be made of a conductive material such as a 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.

[0044] The coating method for forming the conductive layer 42 on the insulating porous film 41 is not particularly limited, and for example, sputtering and coating methods can be used. As the sputtering method, DC sputtering and RF sputtering can be used. The coating method is a method in which a coating liquid in which the material of the conductive layer 42 is dispersed is applied to the surface of the insulating porous film 41 and dried.

[0045] The electrolytic solution contains an organic solvent and an electrolyte. Examples of the organic solvent that can be used include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, hydrofluoroethers, aromatic ethers, sulfones, cyclic esters, chain carboxylic acid esters, and nitriles. 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 sulfolane and methylsulfolane. Examples of cyclic esters include γ-butyrolactone. Examples of chain carboxylic acid esters include acetate esters, butyrate esters, and propionate esters. 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 a charge transfer medium, and contains 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 salts 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 50 is expandable and contractible in accordance with changes in the thickness of the electrode laminate 10 (particularly changes in the thickness of the negative electrode layer 30) due to charging and discharging. A laminate film can be used as the material for the exterior body 50. As the laminate film, 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 material for the inner resin layer and the outer resin layer, for example, a thermoplastic resin such as polyethylene terephthalate (PET), polyamide (nylon), or polypropylene (PP) can be used. As the material for the metal layer, for example, aluminum can be used.

[0048] Next, a method for manufacturing the secondary battery 100 of this embodiment will be described. The electrode stack 10 can be produced, for example, by a method including a long separator production step, an electrode layer arrangement step, and a long separator winding step.

[0049] The long separator production process is a process for producing a long separator 40 having an electrode layer accommodating portion 45, a first extending portion 46, and a second extending portion 47. The long separator 40 can be produced by zigzag folding of a central portion of a long laminate sheet including an insulating porous membrane 41 and a conductive layer 42 provided on one surface of the insulating porous membrane 41 to form an insulating fold 43 folded along the length direction so that the surface on the insulating porous membrane 41 side faces inward, and a conductive fold 44 folded along the length direction so that the surface on the conductive layer 42 side faces inward, which are alternately folded over one another.

[0050] The electrode layer arrangement step is a step of arranging the positive electrode layer 20 on the insulating fold 43 and the negative electrode layer 30 on the conductive fold 44 so that they face each other. The positive electrode layer 20 can be arranged by inserting it through the opening 43b of the insulating fold 43. The negative electrode layer 30 can be arranged by inserting it through the opening 44b of the conductive fold 44. The long separator production step and the electrode layer arrangement step may be performed in parallel. For example, after the positive electrode layer 20 is arranged on the surface of the long laminate sheet facing the insulating porous membrane 41, the long laminate sheet may be folded along the length so that the surface facing the insulating porous membrane 41 faces inward. Next, the negative electrode layer 30 may be arranged on the surface facing the conductive layer 42, and the long laminate sheet may be folded along the length so that the surface facing the conductive layer 42 faces inward.

[0051] 5 is a cross-sectional view showing the state in which positive electrode layers and negative electrode layers are arranged in the electrode layer accommodating portion of the long separator of this embodiment. The portion of the long separator 40 that will become the second extended portion 47 is fixed by a chuck 60. The positive electrode layers 20 and negative electrode layers 30 are arranged alternately in the electrode layer accommodating portion 45 formed by zigzag folding. The positive electrode layers 20 are arranged in the insulating folds 43 of the electrode layer accommodating portion 45, and the negative electrode layers 30 are arranged in the conductive folds 44. The end of the electrode layer accommodating portion 45 is the portion that will become the first extended portion 46.

[0052] The long separator winding process is a process of winding the first extension portion 46 around the outer surface of the electrode layer accommodating portion 45 of the long separator 40 so that the surface facing the insulating porous membrane 41 faces outward. In the case of the long separator shown in FIG. 5 , the first extension portion 46 is wound around the outer surface of the electrode layer accommodating portion 45 so that the conductive layer 42 faces inward (clockwise in FIG. 5 ). When winding the first extension portion 46, the chuck 60 is removed, and the first extension portion 46 and the second extension portion 47 are overlapped so that the conductive layer 42 of the first extension portion 46 and the conductive layer 42 of the second extension portion 47 contact each other. This brings the surface of the insulating porous membrane 41 of the second extension portion 47 into contact with the opening 43b of the insulating fold 43 where the positive electrode layer 20 is disposed. Before the long separator winding step, the second extending portion of the long separator 40 may be arranged so that the surface on the insulating porous membrane 41 side comes into contact with the tip of the conductive fold 44 .

[0053] The secondary battery 100 can be fabricated as follows: A positive electrode terminal 24 is connected to the positive electrode current collector 21 of the positive electrode layer 20 of the obtained electrode laminate 10 via a positive electrode lead wire 23, and a negative electrode terminal 34 is connected to the negative electrode current collector 31 of the negative electrode layer 30 via a negative electrode lead wire 33. Next, the electrode laminate 10 is housed in an outer casing 50 so that parts of the positive electrode terminal 24 and the negative electrode terminal 34 protrude, an electrolyte solution is poured into the outer casing 50, and the outer casing 50 is then sealed.

[0054] In the secondary battery 100 of this embodiment configured as described above, the first extending portion 46 of the long separator 40 is wound around the outer surface of the electrode layer housing portion 45. This prevents misalignment between the positive electrode layer 20 and the negative electrode layer 30, even if the thickness of the negative electrode layer 30 changes significantly during charging and discharging. Furthermore, the conductive layer 42 of the long separator 40 is positioned on the negative electrode layer 30 side, thereby preventing short circuits caused by dendrites and a decrease in the density of the negative electrode active material layer of the negative electrode layer 30 in a charged state. The insulating porous membrane 41 of the long separator 40 is positioned on the positive electrode layer 20 side, and the first extending portion 46 is wound around the electrode layer housing portion 45 with the surface facing the insulating porous membrane 41 facing outward. This prevents contact between the conductive layer 42 of the long separator 40 and the positive electrode layer 20. This reduces the likelihood of short circuits between the positive electrode layer 20 and the negative electrode layer 30.

[0055] Furthermore, according to the secondary battery 100 of this embodiment, the second extending portion 47 contacts the tip 44a of the conductive fold 44, i.e., the surface of the insulating porous membrane 41, with the opening 43b of the insulating fold 43, making it less likely that the conductive layer 42 and the positive electrode layer 20 will come into contact with each other, and making it less likely that a short circuit will occur between the positive electrode layer 20 and the negative electrode layer 30. Note that, as long as the opening 43b of the insulating fold 43 is not in contact with the conductive layer, it is not necessary to extend the second extending portion 47 so that the tip 44a of the conductive fold 44 contacts the surface of the insulating porous membrane 41.

[0056] Furthermore, in the secondary battery 100 of this embodiment, the positive electrode terminal 24 is disposed in a direction perpendicular to the longitudinal direction of the long separator 40, so that the positive electrode terminal 24 is less likely to come into contact with the conductive layer 42. This makes it less likely that a short circuit will occur between the positive electrode layer 20 and the negative electrode layer 30. According to the secondary battery 100 of this embodiment, the negative electrode active material is metallic lithium, and even if the thickness of the negative electrode layer changes significantly due to charging and discharging, misalignment between the positive electrode layer and the negative electrode layer is unlikely to occur, making it possible to achieve a high capacity.

[0057] Furthermore, according to the method for manufacturing the secondary battery 100 of this embodiment, the above-described secondary battery 100 can be manufactured industrially and advantageously.

[0058] In the secondary battery 100 of this embodiment, the folds of the electrode layer accommodating portion 45 of the long separator 40 are equally spaced, and the distance from the tip 43a of the insulating fold 43 to the opening 43b is the same as the distance from the tip 44a of the conductive fold 44 to the opening 44b. The folds of the electrode layer accommodating portion 45 are not limited to being equally spaced. For example, the distance from the tip 44a of the conductive fold 44 to the opening 44b may be extended so as to be longer than the distance from the tip 43a of the insulating fold 43 to the opening 43b. An example of a secondary battery in which the tip 44a of the conductive fold 44 is extended will be described.

[0059] FIG. 6 is a cross-sectional view showing a modified example of the secondary battery according to the first embodiment of the present invention, and corresponds to the cross-sectional view shown in FIG. 6 is the same as the secondary battery 100 described above, except that it has an extension 44c formed by extending the tip 44a of the folded conductive fold 44. Therefore, the same components as those in the secondary battery 100 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0060] The extension 44c of the conductive fold 44 is bent toward the opening 43b of the insulating fold 43 (the positive electrode layer 20 side) along the longitudinal tip side of the first extending portion. The outer side of the extension 44c of the conductive fold 44 is the insulating porous membrane 41. Therefore, by bending the extension 44c of the conductive fold 44 toward the positive electrode layer 20, the end of the positive electrode layer 20 located at the insulating fold 43 is surrounded by the insulating porous membrane 41, making it even more difficult for the conductive layer 42 of the long separator 40 and the positive electrode layer 20 to come into contact with each other. This makes it less likely that a short circuit will occur between the positive electrode layer 20 and the negative electrode layer 30.

[0061] The secondary battery 101 can be manufactured by zigzag folding the long separator 40 so that the conductive fold 44 is longer than the insulating fold 43 during the long separator fabrication process. FIG. 7 is a cross-sectional view showing a modified long separator with a positive electrode layer and a negative electrode layer disposed in the electrode layer accommodating section. The portion of the long separator 40 that will become the second extended section 47 is fixed by a chuck 60. The positive electrode layer 20 is disposed in the insulating fold 43 of the electrode layer accommodating section 45 formed by zigzag folding, and the negative electrode layer 30 is disposed in the conductive fold 44. The tip 44a of the conductive fold 44 is an extended section 44c. The negative electrode layer 30 is not disposed in the extended section 44c, and the extended section 44c can be bent. The tip of the electrode layer accommodating section 45 becomes the first extended section 46. In the long separator winding process, the first extending portion 46 is wound (clockwise in FIG. 7 ) so that the conductive layer 42 faces inward relative to the outer surface of the electrode layer accommodating portion 45. When the first extending portion 46 is wound, the extension portion 44c of the conductive fold 44 is bent toward the opening 43b of the insulating fold 43.

[0062] In the modified secondary battery 101, the end of the positive electrode layer 20 is surrounded by the insulating porous membrane 41 by the extension portion 44c of the conductive fold 44, so compared to the secondary battery 100 of the above-mentioned embodiment in which the end of the positive electrode layer 20 is surrounded by the insulating porous membrane 41 by the second extension portion 47, the second extension portion 47 may be shorter or the second extension portion 47 may be omitted.

[0063] [Second embodiment] FIG. 8 is a cross-sectional view of a secondary battery according to a second embodiment of the present invention, and corresponds to the cross-sectional view of the secondary battery according to the first embodiment shown in FIG. The secondary battery 200 of this embodiment is the same as the secondary battery 100 of the first embodiment except that the long separator 40 does not have a conductive layer. Therefore, the same components as those of the secondary battery 100 are denoted by the same reference numerals and detailed description thereof will be omitted.

[0064] In the secondary battery 200 of this embodiment, the electrode layer accommodating portion 45 of the long separator 40 has folds that are zigzag folded along the length direction, and the positive electrode layer 20 and the negative electrode layer 30 are arranged so as to face each other at each fold. The first extending portion 46 is wound around the outer surface of the electrode layer accommodating portion 45. The second extending portion 47 extends so as to contact the opening of the fold in which the positive electrode layer 20 is arranged.

[0065] In the secondary battery 200 of this embodiment, the first extension portion 46 of the long separator 40 is wound around the outer surface of the electrode layer accommodating portion 45, so that, similar to the secondary battery 100 of the first embodiment, even if the thickness of the negative electrode layer 30 changes significantly due to charging and discharging, the positive electrode layer 20 and the negative electrode layer 30 are less likely to become misaligned.

[0066] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as appropriate. For example, in the secondary battery of this embodiment, the negative electrode layer 30 uses a metallic lithium layer deposited during charging as the negative electrode active material layer, but the negative electrode active material layer is not limited to this. The negative electrode active material layer may also be a layer containing a negative electrode active material that absorbs lithium during charging and releases lithium during discharge. Examples of negative electrode active materials that can be used include lithium transition metal oxides such as lithium titanate, transition metal oxides such as TiO2, Nb2O3, and WO3, SiO, metal sulfides, metal nitrides, and carbon materials such as artificial graphite, natural graphite, graphite, soft carbon, and hard carbon. Metals that form alloys with lithium can also be used as the negative electrode active material. Metals that form alloys with lithium can also be used. Examples of metals that form alloys with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn.

[0067] [Experimental Example] The effect of a secondary battery in which a laminate in which a conductive layer is laminated on the surface of a porous membrane is used as a separator and the conductive layer is arranged on the negative electrode layer side will be explained by way of an experimental example.

[0068] [Experimental Example 1] (Separator production) A porous membrane (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 porous membrane by RF sputtering. The porous membrane with the copper conductive layer formed thereon was punched out to a size of 40 mm × 50 mm to prepare a separator.

[0069] (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 the mixture was wet mixed in a planetary mixer to obtain a premixed slurry. 0.8 Co 0.1 Mn 0.1The resulting premixed slurry was mixed with O2 (NCM811) and a pre-dope material, and dispersed using a planetary mixer to obtain a positive electrode active material paste. The NCM811 particles had a median diameter of 12 μm. The resulting positive electrode active material paste was then applied to an aluminum positive electrode collector without a primer layer, dried, pressed with a roll press, and then dried in a vacuum at 120°C to form a positive electrode plate with a positive electrode active material layer. The resulting positive electrode plate was punched out to a size of 30 mm x 40 mm to form a positive electrode layer.

[0070] (Production of negative electrode layer) 10 μm thick copper foil (electrical conductivity: 6.5 × 10 6 A clad material was prepared by bonding a 20 μm-thick lithium foil to a 34 mm×44 mm size clad material.

[0071] (electrolyte) An electrolyte solution was prepared by dissolving LiFSI in 1,2-dimethoxyethane (DME) at a concentration of 4 mol / L.

[0072] (Fabrication of lithium metal secondary batteries) The copper conductive layer of the separator was placed on the lithium foil side of the negative electrode current collector, and the positive electrode active material layer of the positive electrode layer was placed on the surface of the separator opposite the copper conductive layer side to produce an electrode laminate in which the negative electrode layer, separator, and positive electrode layer were stacked 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 lead wire, and a negative electrode terminal was attached to the copper foil of the negative electrode current collector via a negative electrode lead wire. The laminate with the attached positive electrode terminal and negative electrode terminal was placed in a laminate film bag, and then an electrolyte was added, and the laminate film bag was sealed to produce a lithium metal secondary battery.

[0073] [Experimental Example 2] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that in producing the separator, a zinc conductive layer having a thickness of 0.06 μm was formed by RF sputtering instead of the copper conductive layer.

[0074] [Experimental Example 3] A lithium metal secondary battery was fabricated in the same manner as in Experimental Example 1, except that a 2.1 μm thick conductive layer made of carbon nanotubes (CNTs) was formed by a coating method instead of a copper conductive layer in the fabrication of the separator. The carbon nanotube conductive layer was formed as follows. First, N-methyl-N-pyrrolidinone (NMP) was used as a solvent, and carbon nanotubes were added in an amount to give a solids concentration of 4 mass %, 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 carried out for 10 minutes using a planetary mixer at 1000 rpm to prepare a coating liquid. The obtained coating liquid was applied to the surface of the porous membrane using a doctor blade and dried.

[0075] [Experimental Example 4] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that in producing the separator, a tin conductive layer with a thickness of 0.06 μm was formed by RF sputtering instead of the copper conductive layer.

[0076] [Comparative Experiment Example 1] A lithium metal secondary battery was produced in the same manner as in Experimental Example 1, except that no copper conductive layer was formed in the production of the separator.

[0077] [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, along 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 also 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.

[0078] (Electrical conductivity and surface resistivity of the 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).

[0079] (peel strength) A 5.0 cm long, 2.5 cm wide conductive layer was attached to a 2.5 cm wide adhesive tape that was pressed against a fixed plate. One end of the conductive layer was then folded back 180 degrees and pulled up at a rate of 300 mm / min using an electric test stand (Imada Co., Ltd.) to peel the conductive layer from the porous film. The load required from the start to the end of peeling of the conductive layer was measured using a digital force gauge (Imada Co., Ltd.). The average load obtained was divided by the width of the adhesive tape to determine the peel strength.

[0080] (Whether or not there is a short circuit in the lithium metal secondary battery) The lithium metal secondary battery immediately after fabrication was left standing 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 charge, it was deemed that a short circuit had occurred, and it was judged to be present.

[0081] (First charge / discharge cycle) The charging was performed at a constant current of 2.2 mA up to 4.300 V, followed by a constant voltage charge at 4.300 V for 60 minutes. The discharging was performed at a constant current of 4 mA down to 2.65 V. The battery was left to stand for 30 minutes between charging and discharging.

[0082] (2nd charge / discharge cycle) The battery was charged at a constant current of 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 a constant voltage charge at 4.300 V for 90 minutes. The battery was discharged at a constant current of 18 mA to 2.65 V. The battery was left to stand for 30 minutes between discharge and charge.

[0083] (Lithium thickness increase rate in lithium metal secondary batteries) The thickness T1 (μm) of the negative electrode layer at the time of initial charging and the thickness T2 (μm) of the negative electrode layer (total thickness of the negative electrode current collector and metallic lithium layer) at the time of charging after 50 cycles were measured, and the lithium thickness increase rate T (μm / cycle) was calculated using the following formula. T(μm / cycle)=(T2-T1) / 50

[0084] The thickness T1 (μm) of the negative electrode layer during initial charging was measured as follows. The lithium metal secondary battery immediately after fabrication was left standing 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 described above 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. After the charging, the lithium metal secondary battery was allowed to stand for 30 minutes, and then disassembled, the negative electrode layer was removed, and its thickness was measured as the thickness T1 of the negative electrode layer.

[0085] 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 standing 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 times, followed by 50 cycles of the second charge / discharge cycle. The lithium metal secondary battery was then charged by constant current charging at a current of 14.7 mA up to 4,300 V, followed by constant voltage charging at a voltage of 4,300 V for 60 minutes. The charged lithium metal secondary battery was then allowed to stand for 30 minutes, disassembled, and the negative electrode layer was removed and its thickness was measured as the negative electrode layer thickness T2.

[0086] [Table 1]

[0087] As shown in Table 1, the lithium metal secondary batteries of Experimental Examples 1 to 4, which are equipped with separators having a conductive layer, are less likely to short-circuit even after repeated charge and discharge, have a low rate of lithium thickness increase, and produce a dense metallic lithium layer (negative electrode active material layer) upon charging. In contrast, the lithium metal secondary battery of Comparative Experimental Example 1, which is equipped with a separator without a conductive layer, is more likely to short-circuit after repeated charge and discharge, and has a high rate of lithium thickness increase, indicating that a coarse, low-density negative electrode active material layer is produced upon charging. [Explanation of symbols]

[0088] 10 Electrode laminate 20 Positive electrode layer 21 Positive electrode current collector 22 Cathode active material layer 23 Positive lead wire 24 Positive terminal 30 negative electrode layer 31 Negative electrode current collector 32 Lithium foil 33 Negative lead wire 34 Negative terminal 40 Long separator 41 Insulating porous membrane 41a Hole 42 Conductive layer 43 Insulating wrap 43a Tip 43b opening 44 Conductive fold 44a tip 44b opening 44c extension 45 Electrode layer housing 46 1st extension part 47 Second extension part 50 Exterior body 60 Chuck 100, 101, 200 secondary battery

Claims

1. The battery includes an electrode stack, an electrolyte solution, and an exterior body that accommodates the electrode stack and the electrolyte solution, the electrode stack includes a positive electrode layer, a negative electrode layer, and a long separator; The long separator includes an insulating porous membrane and a conductive layer provided on one surface of the insulating porous membrane, The long separator has an electrode layer accommodating section formed by alternately overlapping insulating folds folded along the length direction so that the surface on the insulating porous membrane side faces inward and conductive folds folded along the length direction so that the surface on the conductive layer side faces inward, and a first extension section extending from one end of the electrode layer accommodating section in the length direction, the positive electrode layer is disposed on the insulating fold and the negative electrode layer is disposed on the conductive fold so as to face each other; The secondary battery, wherein the first extending portion is wound around the outer surface of the electrode layer accommodating portion so that the surface on the insulating porous membrane side faces outward.

2. a second extension portion extending from the other end of the electrode layer accommodating portion in the longitudinal direction; The secondary battery according to claim 1 , wherein the second extension portion extends so that a tip of the conductive folded portion contacts a surface of the insulating porous film.

3. The conductive fold has an extension portion at the tip of the fold, The secondary battery according to claim 1 , wherein the extension is bent toward the positive electrode layer.

4. a positive electrode terminal electrically connected to the positive electrode layer and at least a portion of which is exposed to the outside; a negative electrode terminal electrically connected to the negative electrode layer and at least a portion of which is exposed to the outside, The secondary battery according to claim 1 , wherein the positive electrode terminal and the negative electrode terminal are arranged along a direction perpendicular to the longitudinal direction of the long separator.

5. The secondary battery according to claim 1 , wherein the negative electrode active material is metallic lithium.

6. a process of zigzag folding a portion of a long laminate sheet including an insulating porous membrane and a conductive layer provided on one surface of the insulating porous membrane, to produce a long separator having an electrode layer accommodating section formed by alternately overlapping insulating folds folded along the length direction so that the surface on the insulating porous membrane side faces inward and conductive folds folded along the length direction so that the surface on the conductive layer side faces inward, and a first extension section extending from one end of the electrode layer accommodating section in the length direction; disposing a positive electrode layer on the insulating fold and a negative electrode layer on the conductive fold so that they face each other; and winding the first extension portion around an outer surface of the electrode layer accommodating portion so that the surface on the insulating porous membrane side faces outward.

Images