Lithium metal secondary battery

Abstract

A lithium metal secondary battery that uses a conductive separator and can suppress short circuits is provided. [Solution] A lithium metal secondary battery having an electrode stack in which a positive electrode and a negative electrode containing lithium metal are stacked with a separator interposed between them, and an electrolyte, wherein the separator placed between the positive electrode and the negative electrode is a continuous separator that is zigzag folded and has a fixing portion where the separator is fixed on the outer periphery of the electrode stack, and the separator has a conductive layer that is electrically conductive and an insulating layer that is electrically insulating, with the conductive layer abutting the negative electrode and the insulating layer facing the positive electrode.

Description

[Technical Field]

[0001] The present invention relates to a lithium metal secondary battery. [Background technology]

[0002] In recent years, research and development into batteries that contribute to energy efficiency has been conducted to ensure more people have access to affordable, reliable, sustainable and advanced energy.

[0003] For example, a battery structure having a laminate in which a separator is disposed between a positive electrode and a negative electrode is known. The laminate is housed in a laminate film. As such a battery structure, a battery structure using a long continuous separator film folded into a fixed unit size has been disclosed (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Registration No. 10-1814792 Summary of the Invention [Problem to be solved by the invention]

[0005] In secondary battery technology, improving the electrical capacity is a challenge. To improve the electrical capacity of secondary batteries, the use of lithium metal as the negative electrode active material has been considered. However, secondary batteries using lithium metal without appropriate material specifications may experience abnormal lithium metal deposition. To prevent this, it is necessary to achieve lithium dissolution and deposition that does not cause short circuits even with repeated charge and discharge and is less likely to cause a decrease in the density of the negative electrode active material layer in the charged state. Therefore, it is thought that abnormal lithium metal deposition can be suppressed by forming a conductive layer at the portion of the separator that abuts the lithium metal surface.

[0006] On the other hand, when a portion of the separator is made into a conductive layer, it is necessary to suppress short circuits due to contact between the separator conductive layer facing the negative electrode and the positive electrode, and corrosion due to contact between the separator conductive layer facing the negative electrode and the aluminum layer in the laminate film. This is because, depending on the stacking configuration, there is a possibility that the positive electrode and the separator conductive layer may come into contact due to positive electrode misalignment, or that the separator conductive layer may come into direct contact with the exposed aluminum layer of the laminate film. Such problems are more pronounced when a long, continuous separator is used, as in the technology disclosed in Patent Document 1.

[0007] The present invention has been made in view of the above, and has an object to provide a lithium metal secondary battery that uses a conductive separator and that can suppress short circuits. [Means for solving the problem]

[0008] (1) A lithium metal secondary battery having an electrode laminate in which a positive electrode and a negative electrode containing lithium metal are stacked with a separator interposed therebetween, and an electrolyte, wherein the separator disposed between the positive electrode and the negative electrode is a continuous separator that is zigzag folded and has a fixing portion where the separator is fixed on the outer periphery of the electrode laminate, and the separator has a conductive layer that has electrical conductivity and an insulating layer that has electrical insulation, and is disposed so that the conductive layer abuts against the negative electrode and the insulating layer faces the positive electrode.

[0009] According to the lithium metal secondary battery of (1), it is possible to provide a lithium metal secondary battery that can suppress short circuits in a lithium metal secondary battery that uses a conductive separator.

[0010] (2) The lithium metal secondary battery according to (1), wherein the electrode stack is housed in a laminate film, and the separator arranged at the outermost periphery of the electrode stack is arranged with the insulating layer facing the laminate film.

[0011] According to the lithium metal secondary battery (2), the insulation between the laminate film and the electrode stack is ensured, and short circuits can be suppressed.

[0012] (3) The lithium metal secondary battery according to (1) or (2), wherein the separator has a folded portion folded back 180 degrees at a location on the outer periphery of the electrode laminate.

[0013] In the lithium metal secondary battery (3), an insulating layer can be disposed on the outer periphery (exterior body side) of the separator, thereby ensuring insulation between the exterior body and the electrode stack and preventing short circuits.

[0014] (4) The lithium metal secondary battery according to (3), wherein the separator is wound around the outer periphery of the electrode stack at least once through the folded portion.

[0015] According to the lithium metal secondary battery of (4), the insulation between the exterior body and the electrode stack can be reliably ensured.

[0016] (5) The lithium metal secondary battery according to any one of (2) to (4), further comprising an insulating member having electrical insulation properties that covers the electrode stack, on the outer periphery of the fixing portion and between the fixing portion and the laminate film.

[0017] In the lithium metal secondary battery of (5), the insulating member ensures insulation between the electrode stack and the laminate film, which allows for greater flexibility in the separator configuration.

[0018] (6) The lithium metal secondary battery according to any one of (1) to (5), wherein the separator is wound around the outer periphery of the electrode stack two or more times.

[0019] The lithium metal secondary battery (6) has the advantages of a strong separator structure and ensuring insulation between the exterior body and the electrode laminate. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view showing a lithium metal secondary battery according to one embodiment of the present invention. [Figure 2] 1 is a cross-sectional view showing a lithium metal secondary battery according to one embodiment of the present invention. [Figure 3] 1 is a cross-sectional view showing a lithium metal secondary battery according to one embodiment of the present invention. [Figure 4] 1 is a cross-sectional view showing a lithium metal secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] 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.

[0022] First Embodiment As shown in FIG. 1, a lithium metal secondary battery 1 according to a first embodiment of the present invention has an electrode stack 10 in which a positive electrode 4 and a negative electrode 3 containing lithium metal are stacked with a separator 2 interposed therebetween. The electrode stack 10 is impregnated with an electrolyte solution (not shown). The electrode stack 10 and the electrolyte solution are housed in an exterior body (not shown) such as a laminate film. In FIG. 1, the electrode stack 10 has two layers of positive electrodes 4 and three layers of negative electrodes 3, but the number of stacked positive electrodes 4 and negative electrodes 3 is not limited to the configuration in FIG. 1.

[0023] The positive electrode 4 has a positive electrode active material layer and a positive electrode current collector. The positive electrode current collector is connected to a positive electrode lead terminal, for example, via a positive electrode tab. The negative electrode 3 has a negative electrode active material layer made of lithium metal as a negative electrode active material, and a negative electrode current collector. The negative electrode current collector is connected to a negative electrode lead terminal, for example, via a negative electrode tab.

[0024] The positive electrode active material layer 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 qCo r O2(p+q+r=1), LiNi p Al q Co r O2 (p+q+r=1), lithium manganese oxide (LiMn2O4), Li 1+x Mn 2-x-y M y Examples of the positive electrode active material layer include a hetero-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 may contain various additives that are used as materials for positive electrode active material layers, such as a binder and a conductive additive.

[0025] The positive electrode current collector may be made of Al, for example, and the negative electrode current collector may be made of Cu, for example.

[0026] 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.

[0027] The electrolyte is a source of lithium ions, which are 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 salts may be used alone or in combination of two or more. The concentration of the electrolyte may be, for example, within the range of 0.5 to 4.0 mol / L, 1.0 to 4.0 mol / L, or 2.0 to 4.0 mol / L.

[0028] As shown in FIG. 1, the separator 2 has a two-layer structure consisting of an insulating layer 21 having electrical insulation properties and a conductive layer 22 having electrical conductivity. The insulating layer 21 is disposed on one side of the separator 2, and the conductive layer 22 is disposed on the other side of the separator 2. For example, the insulating layer 21 may be a porous sheet, a nonwoven fabric sheet, or the like, which are commonly used as separators for secondary batteries. The conductive layer 22 is formed, for example, by laminating a conductive material such as a metal onto the insulating layer 21 by a method such as vapor deposition. 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. Examples of materials for the conductive layer 22 include copper (Cu), aluminum (Al), carbon, and carbon nanotubes (CNT).

[0029] The conductive layer 22 is disposed so as to abut against the negative electrode active material layer (lithium metal) in the negative electrode 3. This arrangement of the conductive layer 22 ensures a sufficient electron conduction path during lithium dissolution and deposition, and suppresses abnormal deposition of lithium metal. In other words, even when the lithium metal secondary battery 1 is repeatedly charged and discharged, a short circuit is unlikely to occur, and a decrease in the density of the negative electrode active material layer of the negative electrode 3 in a charged state is unlikely to occur. Meanwhile, the insulating layer 21 is disposed opposite the positive electrode 4 so as to surround the positive electrode 4. This suppresses short circuits in the lithium metal secondary battery 1.

[0030] As shown in FIG. 1, the separator 2 is zigzag-folded. In the example of the electrode stack 10 shown in FIG. 1, there are multiple positive electrodes 4 and multiple negative electrodes 3, but the separator 2 is a single, continuous separator. The zigzag fold refers to a structure in which mountain folds and valley folds are alternately repeated with respect to a certain surface (e.g., the surface on which the insulating layer 21 is formed) as the base. The electrode stack 10 has a structure in which the positive electrodes 4 and the negative electrodes 3 are alternately stacked. Therefore, by zigzag-folding the separator 2 common to the electrode stack 10, it is possible to abut the conductive layer 22 against the negative electrode 3 and the insulating layer 21 against the positive electrode 4. Therefore, by using a continuous separator common to the electrode stack 10, it is possible to suppress abnormal deposition of lithium metal in the negative electrode 3 and to suppress short circuits.

[0031] As shown in FIG. 1 , the separator 2 is zigzag folded from a starting point a1 (the end of the negative electrode 3 at the end of the electrode stack 10 in a direction perpendicular to the stacking direction) so as to be positioned between multiple positive electrodes 4 and negative electrodes 3. After the separator 2 is positioned between all of the positive electrodes 4 and negative electrodes 3, it is bent downward (toward the positive electrode 4) at a bending point a2 at an angle of approximately 90 degrees. This allows the insulating layer 21 to face one end of the positive electrode 4. Note that the other end of the positive electrode 4 is in a state where the insulating layer 21 faces the zigzag folded separator 2. In other words, the positive electrode 4 is surrounded by the insulating layer 21. This ensures insulation between the positive electrode 4 and the negative electrode 3 and prevents short circuits.

[0032] After being bent at the bend a2, the separator 2 is wound around the outer periphery of the electrode laminate 10. An end a4 of the separator 2 is fixed by a fixing part 5 on the outer periphery of the electrode laminate 10. The fixing part 5 may be, for example, an adhesive tape or an adhesive. From a manufacturing perspective, it is preferable that the fixing part 5 be provided on the stacking surface side of the electrode laminate 10, as shown in FIG. 1 . This is because, when the fixing part 5 is provided on the stacking end surface side of the electrode laminate 10, the positive electrode 4 and the negative electrode 3 have different sizes, and therefore, applying force when providing the fixing part 5 may change the shape or arrangement of the positive electrode 4 and the negative electrode 3.

[0033] After being bent at the bend a2, the separator 2 preferably has a fold a3 at some point where it is folded back 180 degrees toward the outer periphery of the electrode stack 10 when wound around the outer periphery of the electrode stack 10. This allows the insulating layer 21 to be disposed on the outermost periphery (exterior body side) of the separator 2. Therefore, when an exterior body made of metal such as a laminate film is used, insulation between the exterior body and the electrode stack 10 is ensured, and short circuits can be suppressed. The fold a3 is preferably provided at a position after the bend a2 has been passed and the insulating layer 21 is placed opposite one end of all of the positive electrodes 4 of the electrode stack 10.

[0034] The fixing portion 5 is preferably provided at a position after winding from the folded portion a3 one or more times around the outer periphery of the electrode stack 10. This makes it possible to reliably ensure insulation between the exterior body and the electrode stack 10.

[0035] The fixing portion 5 is preferably provided on the stacking surface of the electrode stack 10 immediately after winding one full turn from the folded portion a3 around the outer periphery of the electrode stack 10. This makes it possible to minimize the length of the separator 2 while suppressing short circuits between the positive electrode 4 and the negative electrode 3. This makes it possible to improve the energy density of the lithium metal secondary battery 1.

[0036] The laminate film can be used as an exterior body for the lithium metal secondary battery 1. The laminate film has, for example, an outer resin layer, a metal layer, and an inner resin layer. The configuration of each of the above layers is an example, and the laminate film may have, for example, a configuration in which each of the above layers is composed of multiple layers. Note that although the inner side of the laminate film is insulated by the inner resin layer, it is necessary to consider the possibility that a portion of the inner resin layer may be scraped off by an external force or the like, exposing the metal layer. Therefore, the configuration of the above embodiment is preferred, in which insulation between the laminate film and the electrode stack 10 can be ensured by means other than the inner resin layer.

[0037] The following describes the configuration of another embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals in the drawings, and the description thereof may be omitted.

[0038] Second Embodiment As shown in FIG. 2, the lithium metal secondary battery 1b according to the second embodiment has an electrode stack 10b in which a positive electrode 4 and a negative electrode 3 containing lithium metal are stacked with a separator 2b interposed therebetween.

[0039] The lithium metal secondary battery 1b has an insulating member 6 that covers the electrode laminate 10b, located on the outer periphery of the fixing portion 5 and between the electrode laminate 10b and the exterior body (laminate film). The insulating member 6 has, for example, a sheet shape. The insulating member 6 ensures insulation between the electrode laminate 10b and the exterior body (laminate film). Examples of materials that can be used for the insulating member 6 include the same materials as those for the insulating layer 21. Alternatively, insulating tape may be used as the insulating member 6. The material of the insulating tape is not particularly limited, but examples include resins such as polyimide film.

[0040] As shown in FIG. 2, the separator 2b is zigzag folded from a starting point b1 (the end of the negative electrode 3 at the stacking end of the electrode laminate 10b in a direction perpendicular to the stacking direction) so as to be positioned between multiple positive electrodes 4 and negative electrodes 3. After the separator 2b is positioned between all of the positive electrodes 4 and negative electrodes 3, it is bent downward (toward the positive electrode 4) at a bend b2 at an angle of approximately 90 degrees. The separator 2b is then bent at a bend b3 without providing a folded-back portion, and wound around the outer periphery of the electrode laminate 10b. The end b4 of the separator 2b is fixed by a fixing portion 5 on the outer periphery of the electrode laminate 10b. From a manufacturing perspective, it is preferable that the fixing portion 5 be provided on the stacking surface of the electrode laminate 10b, as shown in FIG.

[0041] The above-described configuration of the lithium metal secondary battery 1b ensures insulation between the electrode stack 10b and the exterior body (laminate film) without providing a folded portion in the separator 2b, which allows for more flexible configuration of the separator 2b, such as shortening the overall length of the separator 2b.

[0042] <Third embodiment> As shown in FIG. 3, the lithium metal secondary battery 1c according to the third embodiment has an electrode stack 10c in which a positive electrode 4 and a negative electrode 3 containing lithium metal are stacked with a separator 2c interposed therebetween.

[0043] As shown in FIG. 3, the separator 2c is zigzag folded from a starting point c1 (the end of the negative electrode 3 at the end of the electrode stack 10c in a direction perpendicular to the stacking direction) so as to be disposed between a plurality of positive electrodes 4 and negative electrodes 3. After the separator 2c is disposed between all of the positive electrodes 4 and negative electrodes 3, it is bent upward (toward the negative electrode 3) at a bending point c2 at an angle of approximately 90 degrees. This allows the insulating layer 21 to be disposed on the outermost periphery (exterior body side) of the separator 2c. After being bent at the bending point c2, the separator 2c is wound around the outer periphery of the electrode stack 10c.

[0044] The separator 2c is bent at the bend c2 and then wound around the outer periphery of the electrode laminate 10c one or more times. The separator 2c then has a fold c3, which is folded back 180 degrees toward the inner periphery of the electrode laminate 10c on one of the stacking surfaces of the electrode laminate 10c. The separator 2c extends from the fold c3 to a terminal end c4. The fold c3 allows the insulating layer 21c to face one end of the positive electrode 4 (the end of the zigzag-folded separator 2c that does not face the insulating layer 21). This ensures insulation between the positive electrode 4 and the negative electrode 3 and prevents short circuits. To achieve the above-mentioned effect, it is preferable to extend the separator 2c so that the insulating layer 21c faces one end of each of the positive electrodes 4 (i.e., to determine the position of the terminal end c4).

[0045] The folded portion c3 is fixed by the fixing portion 5. This prevents the folded portion c3 from shifting out of position.

[0046] <Fourth embodiment> As shown in FIG. 4, a lithium metal secondary battery 1d according to the fourth embodiment has an electrode stack 10d in which a positive electrode 4 and a negative electrode 3 containing lithium metal are stacked with a separator 2d interposed therebetween.

[0047] 4, the separator 2d is zigzag folded from a starting end d1 (an end of the negative electrode 3 at the stacking end of the electrode stack 10d in a direction perpendicular to the stacking direction) so as to be disposed between a plurality of positive electrodes 4 and negative electrodes 3. After the separator 2d has been disposed between all of the positive electrodes 4 and negative electrodes 3, it is bent downward (toward the positive electrode 4) at a bending portion d2 at an angle of approximately 90 degrees.

[0048] After being bent at bend d2, separator 2d is wound around the outer periphery of electrode stack 10d. After being bent at bend d2, separator 2d is wound around the outer periphery of electrode stack 10d one or more times, then cut at cut d3 and fixed by fixing portion 51. Thereafter, separator 2d, with its front and back turned upside down, is wound around the outer periphery of electrode stack 10d one or more times from the position of cut d3, and end d4 of separator 2d is fixed by fixing portion 52. This allows insulating layer 21 to be disposed on the outermost periphery (exterior body side) of separator 2d, thereby reliably ensuring insulation between the exterior body and electrode stack 10d.

[0049] The separator 2d is wound around the electrode stack 10d two or more times, which provides the above-mentioned advantages of providing a strong structure for the separator 2d and ensuring insulation between the exterior body and the electrode stack 10d.

[0050] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and may be modified as appropriate within the spirit and scope of the present invention. [Explanation of symbols]

[0051] 1, 1b, 1c, 1d Lithium metal secondary battery 10, 10b, 10c, 10d Electrode laminate 2, 2b, 2c, 2d separator 21 Insulating layer 22 Conductive layer 3 Negative electrode 4 Positive electrode 5, 51, 52 Fixed part 6. Insulating material a3 Folded part

Claims

1. A lithium metal secondary battery having an electrode stack in which a positive electrode and a negative electrode containing lithium metal are stacked with a separator interposed therebetween, and an electrolyte solution, the separator disposed between the positive electrode and the negative electrode is a zigzag-folded continuous separator, a fixing portion to which the separator is fixed on the outer periphery of the electrode stack; the separator has a conductive layer having electrical conductivity and an insulating layer having electrical insulation, and is disposed so that the conductive layer is in contact with the negative electrode and the insulating layer faces the positive electrode.

2. The electrode stack is housed in a laminate film, 2. The lithium metal secondary battery according to claim 1, wherein the separator disposed on the outermost periphery of the electrode stack has the insulating layer disposed on the laminate film side.

3. 3. The lithium metal secondary battery according to claim 1, wherein the separator has a folded portion folded back 180 degrees at a location on the outer periphery of the electrode stack.

4. The lithium metal secondary battery according to claim 3 , wherein the separator is wound around the outer periphery of the electrode stack at least once via the folded-back portion.

5. 3. The lithium metal secondary battery according to claim 2, further comprising an insulating member having electrical insulation properties that covers the electrode stack, located on the outer periphery of the fixing portion and between the fixing portion and the laminate film.

6. 3. The lithium metal secondary battery according to claim 1, wherein the separator is wound around the outer periphery of the electrode stack two or more times.

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