Electrode group and secondary battery

Abstract

The objective is to provide an electrode group and a secondary battery that suppress short circuits caused by electrode cracking at the innermost circumference of the electrode group. [Solution] The electrode group of the embodiment is an electrode group with a flattened cross-section in which an electrode member comprising a first electrode, a second electrode, and a separator disposed between the first electrode and the second electrode is wound with the first electrode on the inner circumference side, and in the cross-section, it has opposing planar portions and opposing curved portions disposed between the planar portions, and in the curved portion, the distance D between the first vertex of the innermost part of the electrode member and the first electrode adjacent to the innermost part via the separator on a first imaginary line passing through the first vertex and parallel to the planar portion satisfies the following equation (1) with respect to the thickness (A) of the separator. 1.2A ≤ D ≤ 5000A (1)

Description

Technical Field

[0001] Embodiments of the present invention relate to an electrode group and a secondary battery.

Background Art

[0002] In recent years, secondary batteries such as lead-acid batteries and nickel-metal hydride batteries have been used as power sources typified by electric vehicles, hybrid vehicles, electric motorcycles, and forklifts. Recently, development has been actively carried out toward the adoption of lithium-ion secondary batteries with high energy density, and development has been carried out while considering long life, safety, etc.

[0003] For example, an electrode group used in a lithium-ion secondary battery (hereinafter referred to as a secondary battery) may be manufactured by winding an electrode member composed of a positive electrode, a negative electrode, and a separator and pressing the whole into a flat shape. In such a type of secondary battery, when the positive electrode or the negative electrode is sharply bent by pressure molding at the innermost peripheral portion of the electrode group, there is a possibility that the positive electrode or the negative electrode may crack. Then, there is a risk that the cracked positive electrode or negative electrode may break through the separator and come into electrical contact with the opposed positive electrode or negative electrode, resulting in a short circuit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide an electrode group and a secondary battery that suppress a short circuit associated with cracking of an electrode.

Means for Solving the Problems

[0006] To solve the above problems, the electrode group of the embodiment is an electrode group with a flat cross-section, in which an electrode member comprising a first electrode, a second electrode, and a separator disposed between the first electrode and the second electrode is wound with the first electrode on the inner circumference side, and in the cross-section, it has opposing planar portions and opposing curved portions disposed between the planar portions, and in the curved portion, the distance D between the first vertex of the innermost part of the electrode member and the first electrode adjacent to the innermost part via the separator on a first imaginary line passing through the first vertex and parallel to the planar portion satisfies the following equation (1) with respect to the thickness (A) of the separator. 1.2A ≤ D ≤ 5000A (1) [Brief explanation of the drawing]

[0007] [Figure 1] A schematic perspective view showing the electrode group according to the first embodiment. [Figure 2] A partially unfolded perspective view of the electrode group according to the first embodiment, viewed from above. [Figure 3] A schematic cross-sectional view showing the electrode group according to the first embodiment. [Figure 4] An enlarged cross-sectional view schematically showing the innermost part of the electrode group. [Figure 5] A schematic cross-sectional view showing a modified example of the electrode group according to the first embodiment. [Figure 6] A schematic perspective view showing a secondary battery according to the second embodiment. [Modes for carrying out the invention]

[0008] The electrode group and secondary battery of the embodiment will be described below with reference to the drawings.

[0009] (First embodiment) The electrode group 5 of the first embodiment will be described with reference to Figures 1 and 2. Figure 1 is a schematic perspective view of the electrode group 5 according to the first embodiment, and Figure 2 is a partially exploded perspective view of the electrode group 5 according to the first embodiment, viewed from above.

[0010] As shown in Figures 1 and 2, for example, the electrode group 5 is formed by winding an electrode member 20 consisting of a first electrode 100, a second electrode 200, and a separator 4 positioned between the first electrode 100 and the second electrode 200, with the first electrode 100 on the inner circumference. The electrode group 5 after winding is manufactured by pressure molding the entire assembly into a flattened shape in the stacking direction (Y direction) of the electrode member 20. This pressure molding reduces the space within the electrode group 5, so when housing the electrode group 5 in a secondary battery case, for example, more electrode members 20 can be stored in the limited space within the case. However, the manufacturing method of the electrode group 5 is not limited to these methods; it is sufficient as long as the electrode member 20 is wound.

[0011] The first electrode 100 has a strip-shaped first current collector 100a with a long side 90 (Z direction) and a short side 92 (X direction). On the first current collector 100a, there is a first mixture layer 130 in which the first mixture is applied parallel to the long side 90, and an uncoated portion 70a of the first mixture layer where the first mixture is not applied. The second electrode 200 has a strip-shaped second current collector 200a with a long side 90 and a short side 92. On the second current collector 200a, there is a second mixture layer 150 in which the second mixture is applied parallel to the long side 90, and an uncoated portion 70b of the second mixture layer where the second mixture is not applied. The separator 4 is also strip-shaped with a long side 90 (Y direction) and a short side 92 (X direction), similar to the first electrode 100 and the second electrode 200.

[0012] In the wound electrode group 5 of this embodiment, the uncoated portion 70a of the first mixture layer protrudes in the opposite direction to the protruding direction of the uncoated portion 70b of the second mixture layer and is provided at both ends of the electrode group 5. However, the protruding directions of the uncoated portion 70a of the first mixture layer and the uncoated portion 70b of the second mixture layer are not limited to these. The uncoated portion 70a of the first mixture layer and the uncoated portion 70b of the second mixture layer may protrude in the same direction, and both may be provided at one end of the electrode group 5.

[0013] The electrode group 5 will be described with reference to Figure 3. Figure 3 is a schematic cross-sectional view (cross-section II shown in Figure 1) of the electrode group 5 according to the first embodiment. As shown in Figure 3, the electrode group 5 of this embodiment has a flattened cross-sectional shape. In the cross-section of the electrode group 5, the electrode group 5 has opposing flat portions 40 and opposing curved portions 42 positioned between the flat portions 40. Here, the flat portion 40 is the region P shown in Figure 3, and the curved portion 42 is the region Q shown in Figure 3.

[0014] The electrode group 5 will be further explained with reference to Figure 4. Figure 4 is an enlarged cross-sectional view (section II shown in Figure 1) schematically showing the innermost circumference 50 of the electrode group 5. As shown in Figure 4, in the curved portion 42, the first vertex of the innermost circumference 50 of the electrode member 20 is denoted as T, and the first imaginary line passing through this first vertex T and parallel to the planar portion 40 is denoted as line S. Here, on the first imaginary line S, the distance D between the first vertex T and the first electrode 100 adjacent to the innermost circumference 50 of the electrode group 5 via the separator 4 is between 1.2A and 5000A, relative to the thickness (A) of the separator 4. Here, the innermost circumference 50 of the electrode group 5 is defined as the region of the electrode member 20 from the starting point R where the winding begins to the ending point R' after one full turn.

[0015] Furthermore, the thickness (A) of the separator 4 is measured by unwinding the wound electrode group 5 and measuring it in the state of the strip-shaped separator 4, and is defined as the longest distance in the direction parallel to the height direction (Z direction) of the separator 4.

[0016] When the distance D is 1.2A or more, a gap of at least the thickness (A) of the separator 4 is formed between the second electrode 200 in the innermost peripheral portion 50 and the first electrode 100 adjacent to the second electrode 200 via the separator 4. For example, after winding the electrode member 20, the entire electrode group 5 is compression-molded in the stacking direction (Y direction) of the electrode member 20. Even when the second electrode 200 in the innermost peripheral portion 50 of the electrode group 5 is bent and the second electrode 200 is cracked, contact between the cracked second electrode 200 and the first electrode 100 facing the second electrode 200 can be suppressed by preventing the cracked second electrode 200 from piercing through the separator 4. Also, when the distance D is 5000A or less, although a gap is formed within the electrode group 5, an electrode group 5 with sufficient battery capacity for the entire electrode group 5 can be obtained.

[0017] The distance D is more preferably 2000A or less. When the distance D is 2000A or less, although a gap is formed within the electrode group 5, an electrode group 5 with sufficient battery capacity for the entire electrode group 5 can be obtained as compared with the case of 5000A.

[0018] Here, the distance D is preferably provided at two first vertices T in the innermost peripheral portion 50 of the electrode group 5, but it may be provided at only one location. Also, from the viewpoint of the manufacturing efficiency of the electrode group 5, when winding the electrode group 5, it is preferable to manufacture the electrode group 5 with the first electrode 100, the second electrode 200, and the separator 4 as a set of electrode members 20. However, a gap of at least the thickness (A) of the separator 4 may be provided between the first electrode 100 in the innermost peripheral portion 50 and the second electrode 200 adjacent to the first electrode 100 via the separator 4. Thereby, for example, after winding the electrode member 20, the entire electrode group 5 is compression-molded in the stacking direction (Y direction) of the electrode member 20. Even when the first electrode 100 in the innermost peripheral portion 50 of the electrode group 5 is bent and the first electrode 100 is cracked, contact between the cracked first electrode 100 and the second electrode 200 facing the first electrode 100 can be suppressed by preventing the cracked first electrode 100 from piercing through the separator 4.

[0019] Furthermore, in the innermost circumference 50 of the electrode member 20 in the electrode group 5, the shortest distance G between the first electrode 100 and the second electrode 200 in the innermost circumference 50 along the first imaginary line S may be 1.2A or more and 5000A or less relative to the thickness (A) of the separator 4, just like the distance D. This prevents the first electrode 100 from piercing the separator 4 and contact between the first electrode 100 and the second electrode 200 facing the first electrode 100, even if the first electrode 100 in the innermost circumference 50 of the electrode group 5 is bent and breaks.

[0020] A modified example of the electrode group 5 will be explained with reference to Figure 5. Figure 5 is a schematic cross-sectional view (section II shown in Figure 1) illustrating a modified example of the electrode group 5 according to the first embodiment. As shown in Figure 5, in the curved portion 42, the second vertex in the second circumference 55, which is reached by completing one full rotation of the electrode member 20 from the innermost circumference 50 of the electrode member 20, is denoted as T', and the second imaginary line passing through this second vertex T' and parallel to the planar portion 40 is denoted as line S'. Here, in the second imaginary line S', the distance D' between the second vertex T' and the first electrode 100 adjacent to the second circumference 55 of the electrode group 5 via the separator 4 is between 1.2A and 5000A, relative to the thickness (A) of the separator 4. Here, the second circumference 55 of the electrode group 5 is defined as the region of the electrode member 20 from the endpoint R' of the innermost circumference 50 to the endpoint U', which is reached by completing another full rotation from the starting point U.

[0021] In a modified example of the electrode group 5, when the distance D' is 1.2A or more, a gap of at least the thickness (A) of the separator 4 can be formed between the second electrode 200 in the second circumferential portion 55 and the first electrode 100 adjacent to the second electrode 200 via the separator 4. Thus, for example, even when the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding the electrode member 20, and the second electrode 200 in the second circumferential portion 55 is sharply bent and cracked not only in the innermost circumferential portion 50 of the electrode group 5, contact between the cracked second electrode 200 and the first electrode 100 facing the second electrode 200 can be suppressed by the cracked second electrode 200 breaking through the separator 4. As a result, even if the second electrode 200 cracks in either the innermost circumferential portion 50 or the second circumferential portion 55 of the electrode group 5, a short circuit due to contact between the second electrode 200 and the first electrode 100 facing the second electrode 200 can be suppressed. Further, when the distance D' is 5000A or less, although a gap is formed in the electrode group 5, an electrode group 5 with sufficient battery capacity as a whole can be obtained.

[0022] The distance D' is more preferably 2000A or less. When the distance D' is 2000A or less, although a gap is formed in the electrode group 5, an electrode group 5 with sufficient battery capacity as a whole can be obtained as compared with the case of 5000A.

[0023] Here, the distance D' is preferably provided at two second vertices T' in the second peripheral portion 55 of the electrode group 5, but it may also be provided at only one location. Furthermore, from the viewpoint of manufacturing efficiency of the electrode group 5, when winding the electrode group 5, it is preferable to manufacture the electrode group 5 with the first electrode 100, the second electrode 200, and the separator 4 as one set of electrode members 20. However, a gap of the thickness (A) of the separator 4 or greater may be provided between the first electrode 100 in the second peripheral portion 55 and the second electrode 200 adjacent to the first electrode 100 via the separator 4. As a result, for example, even if the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding the electrode member 20, and the first electrode 100 in the second peripheral portion 55 of the electrode group 5 is bent and breaks, contact between the first electrode 100 and the second electrode 200 facing the first electrode 100 can be suppressed by the broken first electrode 100 piercing the separator 4.

[0024] Furthermore, in the modified example of electrode group 5, in the second peripheral portion 55 of the electrode member 20, the shortest distance G' between the first electrode 100 and the second electrode 200 in the second peripheral portion 55 along the second virtual line S' may be 1.2A or more and 5000A or less relative to the thickness (A) of the separator 4, just like the distance D'. This prevents the first electrode 100 from piercing the separator 4 and contact between the first electrode 100 and the second electrode 200 facing the first electrode 100, even if the first electrode 100 in the second peripheral portion 55 of electrode group 5 is bent and breaks.

[0025] Furthermore, in the electrode group 5 of this embodiment, it is preferable that the first composite layer 130 of the first electrode 100 has a lower Young's modulus than the second composite layer 150 of the second electrode 200. As a result, the first composite layer 130 is more flexible than the second composite layer 150 and therefore less prone to cracking. For example, when the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding the electrode member 20, the first electrode 100 is positioned on the innermost circumference 50 of the electrode group 5, which suppresses cracking of the first electrode 100 even if the first electrode 100 is bent more than the second electrode 200. As a result, throughout the entire electrode group 5, short circuits caused by cracking of the first electrode 100 due to contact between the first electrode 100 and the second electrode 200 which is opposite to the first electrode 100 via the separator 4 can be suppressed.

[0026] Specifically, the first electrode 100 and the second electrode 200 are either a positive electrode or a negative electrode. Examples of positive electrode active materials include, but are not limited to, oxides, sulfides, and polymers thereof that can intercept and deintercept lithium ions. Preferred positive electrode active materials include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, and lithium iron phosphate.

[0027] Examples of negative electrode active materials include, but are not limited to, metal oxides, metal sulfides, metal nitrides, and carbon materials that can intercept and deintercept lithium ions. Preferred negative electrode active materials include titanium oxide, lithium titanium oxide, niobium titanium oxide, niobium oxide, tungsten oxide, amorphous tin oxide, tin silicon oxide, silicon oxide, and silicon.

[0028] (Second embodiment) The secondary battery 1 of the second embodiment will be described with reference to Figure 6. Figure 6 is a schematic perspective view showing the secondary battery 1 according to the second embodiment.

[0029] As shown in Figure 6, the secondary battery 1 has an outer case 3, and the electrode group 5 with a wound structure according to the first embodiment is housed inside the outer case 3. Inside the outer case 3, the electrode group 5 is impregnated with an electrolyte (not shown), and the electrolyte is injected, for example, through an injection port (not shown) provided on the lid member 7, and the injection port is sealed with a sealing plate 19 after the electrolyte has been injected. The electrolyte used is a non-aqueous electrolyte prepared by dissolving an electrolyte (e.g., a lithium salt) in a non-aqueous solvent. The non-aqueous solvent may be used alone or in a mixture of two or more types.

[0030] A gas discharge valve 21 may be provided on the surface of the lid member 7 together with the sealing plate 19. Furthermore, for example, a pair of first electrode external terminals 23a and second electrode external terminals 23b are attached to the surface of the lid member 7, and the external terminals 23a and 23b are electrically connected to the uncoated portion 70a of the first mixture layer and the uncoated portion 70b of the second mixture layer of the electrode group 5, respectively. A terminal insulator 35 may be provided between the external terminals 23a and 23b and the lid member 7 to maintain insulation between them.

[0031] The secondary battery 1 of the second embodiment described above is equipped with the electrode group 5 of the first embodiment. In the electrode group 5, the distance D between the first vertex T and the first electrode 100 adjacent to the innermost circumference 50 of the electrode group 5 via the separator 4, on the first imaginary line S, is 1.2A or more and 5000A or less with respect to the thickness (A) of the separator 4. As a result, even if, for example, the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding the electrode member 20, and the second electrode 200 at the innermost circumference 50 of the electrode group 5 is bent and the second electrode 200 breaks, it is possible to provide a secondary battery 1 that suppresses a short circuit between the second electrode 200 and the first electrode 100 facing the second electrode 200, which would occur if the broken second electrode 200 pierced the separator 4.

[0032] Furthermore, although voids are formed within the electrode group 5, it is possible to obtain an electrode group 5 that ensures sufficient battery capacity as a whole, thereby providing a secondary battery 1 with sufficient battery capacity.

[0033] According to the electrode group 5 of at least one embodiment described above, in the first virtual line S, the distance D between the first vertex T and the first electrode 100 adjacent to the innermost circumference 50 of the electrode group 5 via the separator 4 is 1.2A or more and 5000A or less, with respect to the thickness (A) of the separator 4.

[0034] If the distance D is 1.2A or greater, a gap greater than the thickness (A) of the separator 4 is created between the second electrode 200 at the innermost circumference 50 and the first electrode 100 adjacent to the second electrode 200 via the separator 4. For example, even if the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding, and the second electrode 200 at the innermost circumference 50 of the electrode group 5 is bent and breaks, contact between the second electrode 200 and the first electrode 100 facing the second electrode 200 can be suppressed by the broken second electrode 200 piercing the separator 4. Furthermore, if the distance D is 5000A or less, although a gap is formed within the electrode group 5, it is possible to obtain an electrode group 5 that ensures sufficient battery capacity as a whole. This makes it possible to provide an electrode group 5 that suppresses short circuits caused by cracking of the second electrode 200 at the innermost circumference 50 of the electrode group 5, while also ensuring sufficient battery capacity.

[0035] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0036] 1...Secondary battery, 3...Outer case, 4...Separator, 5...Electrode group, 7...Lid member, 19...Sealing plate, 20...Electrode member, 21...Gas discharge valve, 23a...First electrode external terminal, 23b...Second electrode external terminal, 35...Terminal insulator, 40...Flat part, 42...Curved part, 50...Innermost circumference part, 55...Second circumference part, 70a...Uncoated part of the first mixture layer, 70b...Uncoated part of the second mixture layer, 90...Long side, 92...Short side, 100...First electrode, 100a...First current collector, 130...First mixture layer, 150...Second mixture layer, 200...Second electrode, 200a...Second current collector.

Claims

1. An electrode member comprising a first electrode, a second electrode, and a separator disposed between the first electrode and the second electrode is a group of electrodes with a flattened cross-section wound with the first electrode on the inner circumference side, In the cross-section, there are opposing flat portions and opposing curved portions arranged between the flat portions, In the curved portion, the electrode group such that the distance D between the first vertex of the innermost circumference of the electrode member and the first electrode adjacent to the innermost circumference via the separator, along a first imaginary line passing through the first vertex and parallel to the planar portion, satisfies the following equation (1) with respect to the thickness (A) of the separator.

1. 2A ≤ D ≤ 5000A (1)

2. The electrode group according to claim 1, wherein in the curved portion, the distance D' between the second vertex in the second circumference, which is formed by extending the electrode member once from the innermost circumference of the electrode member, and the first electrode adjacent to the second circumference via the separator, on a second imaginary line passing through the second vertex and parallel to the planar portion, satisfies the following equation (2) with respect to the thickness (A) of the separator.

1. 2A ≤ D' ≤ 5000A (2)

3. The electrode group according to claim 1, wherein, in the first imaginary line, the shortest distance G between the first electrode and the second electrode at the innermost circumference satisfies the following equation (3) with respect to the thickness (A) of the separator.

1. 2A ≤ G ≤ 5000A (3)

4. The electrode group according to claim 2, wherein, in the second virtual line, the shortest distance G' between the first electrode and the second electrode in the second peripheral portion satisfies the following equation (4) with respect to the thickness (A) of the separator. 1.2A ≤ G' ≤ 5000A (4)

5. The first electrode comprises a first current collector and a first mixture layer on the first current collector. The second electrode comprises a second current collector and a second mixture layer on the second current collector. The electrode group according to claim 1, wherein the first combination layer in the first electrode has a lower Young's modulus than the second combination layer in the second electrode.

6. The electrode group according to any one of claims 1 to 5, A secondary battery comprising an electrolyte.

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