Electrode group and secondary battery

Abstract

The objective is to provide an electrode group and a secondary battery that suppress short circuits caused by cracking of the positive or negative electrode at the innermost circumference of the electrode group, while ensuring sufficient battery capacity. [Solution] The electrode group of the embodiment is an electrode group in which an electrode member consisting of a positive electrode, a negative electrode, and a separator is wound, and the first thickness (A1) of the positive electrode and the first thickness (B1) of the negative electrode at the innermost circumference of the electrode group, and the second thickness (A2) of the positive electrode and the second thickness (B2) of the negative electrode at the outermost circumference of the electrode group satisfy at least one of the following equations (1) or (2). 0.1A2 ≤ A1 ≤ 0.8A2 (1) 0.1B2 ≤ B1 ≤ 0.8B2 (2)

Description

Technical Field

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[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 towards the adoption of high-energy-density lithium-ion secondary batteries has been actively carried out, and development has been carried out while considering long life, safety, etc.

[0003] An electrode group used in a lithium-ion secondary battery (hereinafter referred to as a secondary battery) is manufactured, for example, 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. And there is a risk that this cracked portion may break through the separator and come into electrical contact with the opposing 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 caused by cracking of the positive electrode or the negative electrode at the innermost peripheral portion of the electrode group.

Means for Solving the Problems

[0006] To solve the above problems, the electrode group of the embodiment is an electrode group in which an electrode member consisting of a positive electrode, a negative electrode, and a separator is wound, and the first thickness (A1) of the positive electrode and the first thickness (B1) of the negative electrode at the innermost circumference of the electrode group, and the second thickness (A2) of the positive electrode and the second thickness (B2) of the negative electrode at the outermost circumference of the electrode group satisfy at least one of the following equations (1) or (2). 0.1A2 ≤ A1 ≤ 0.8A2 (1) 0.1B2 ≤ B1 ≤ 0.8B2 (2) [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] An enlarged cross-sectional view schematically showing the area around the innermost circumference of the electrode group in a modified example of the electrode group. [Figure 7] 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] The electrode group 5 is manufactured, for example, as shown in Figures 1 and 2, by winding an electrode member 20 consisting of a positive electrode 13, a negative electrode 15, and a separator 4, and then press-molding the entire assembly into a flattened shape in the stacking direction (Y direction) of the electrode member 20. Press-molding is performed, for example, by applying pressure to the electrode group 5 by sandwiching it between coil presses made of heated metal plates. This press-molding reduces the space within the electrode group 5, so when the electrode group 5 is housed in a case (not shown) of a secondary battery, for example, more electrode members 20 can be housed in the limited space within the case. Note that the manufacturing method of the electrode group 5 is not limited to these methods; as long as the electrode member 20 is wound, it is acceptable.

[0011] The positive electrode 13 has a strip-shaped positive electrode current collector 13a having a long side 90 (Z direction) and a short side 92 (X direction). On the positive electrode current collector 13a, there is a positive electrode mixture layer 130 in which the positive electrode agent is applied parallel to the long side 90, and an uncoated portion 70a of the positive electrode mixture layer where the positive electrode agent is not applied. The negative electrode 15 has a strip-shaped negative electrode current collector 15a having a long side 90 and a short side 92. On the negative electrode current collector 15a, there is a negative electrode mixture layer 150 in which the negative electrode mixture is applied parallel to the long side 90, and an uncoated portion 70b of the negative electrode mixture layer where the negative electrode agent is not applied.

[0012] In the wound electrode group 5 of this embodiment, the uncoated portion 70a of the positive electrode mixture layer protrudes in the opposite direction to the protruding direction of the uncoated portion 70b of the negative electrode mixture layer and is provided at both ends of the electrode group 5. However, the protruding directions of the uncoated portion 70a of the positive electrode mixture layer and the uncoated portion 70b of the negative electrode mixture layer are not limited to these. The uncoated portion 70a of the positive electrode mixture layer and the uncoated portion 70b of the negative electrode 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 further described with reference to Figures 3 and 4. Figure 3 is a schematic cross-sectional view (section II shown in Figure 1) of the electrode group 5 according to the first embodiment, and Figure 4 is a schematic enlarged cross-sectional view (section II shown in Figure 1) of a part of the innermost circumference 50 of the electrode group 5.

[0014] At least one of the thickness (A1) of the positive electrode 13 or the thickness (B1) of the negative electrode 15 in the innermost peripheral portion 50 of the electrode group 5 is thinner than the thickness (A2) of the positive electrode 13 or the thickness (B2) of the negative electrode 15 in the outermost peripheral portion 55 of the electrode group 5. Here, the thickness of the positive electrode 13 in the innermost peripheral portion 50 of the electrode group 5 is defined as the first thickness (A1), and the thickness of the positive electrode 13 in the outermost peripheral portion 55 of the electrode group 5 is defined as the second thickness (A2). Also, the thickness of the negative electrode 15 in the innermost peripheral portion 50 of the electrode group 5 is defined as the first thickness (B1), and the thickness of the negative electrode 15 in the outermost peripheral portion 55 of the electrode group 5 is defined as the second thickness (B2).

[0015] Here, the innermost peripheral portion 50 refers to the region in the electrode member 20 from the starting point P at the start of winding of the electrode member 20 to the end point P' after one turn of winding. On the other hand, the outermost peripheral portion 55 refers to the region in the electrode member 20 from the end point Q at the end of winding of the electrode member 20 to the starting point Q' after one turn of unwinding. Also, the thicknesses of the positive electrode 13 and the negative electrode 15 are measured in the state where the wound electrode group 5 is unwound into strip-shaped positive electrode 13 and negative electrode 15, and are defined as the longest distances in the direction parallel to the height direction (Y direction) of the positive electrode 13 and the negative electrode 15.

[0016] As shown in FIG. 3, in the electrode group 5 of the present embodiment, the positive electrode 13 is arranged on the inner circumference side rather than the negative electrode 15, and the positive electrode 13 and the negative electrode 15 are wound, but the negative electrode 15 may be arranged on the inner circumference side rather than the positive electrode 13.

[0017] The first thickness (A) of the positive electrode 13 of the electrode group 5 is thinner than the second thickness (A2), but in the present embodiment, A1 is preferably 0.1A2 or more and 0.8A2 or less. Similarly on the negative electrode 15 side, the first thickness (B1) of the negative electrode 15 is thinner than the second thickness (B2), but in the present embodiment, B1 is preferably 0.1B2 or more and 0.8B2 or less.

[0018] When the first thickness (A1) of the positive electrode 13 is 0.1A2 or more, although the first thickness (A1) is thinner than the second thickness (A2), an electrode group 5 with sufficient battery capacity as the entire electrode group 5 can be obtained. Further, when the first thickness (A1) of the positive electrode 13 is 0.8A2 or less, 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 positive electrode 13 at the innermost peripheral portion 50 of the electrode group 5 is sharply bent, cracking of the positive electrode 13 at the innermost peripheral portion 50 of the electrode group 5 can be suppressed. Thereby, at the innermost peripheral portion 50 of the electrode group 5, the cracked positive electrode 13 can be prevented from piercing through the separator 4 and suppressing electrical contact with the opposed negative electrode 15. The reason why it is preferable that the first thickness (B1) of the negative electrode 15 is 0.1B2 or more and 0.8B2 or less is the same.

[0019] The first thickness (A1) of the positive electrode 13 of the electrode group 5 is thinner than the second thickness (A2). In this case, the application amount of the positive electrode active material in the innermost peripheral portion 50 of the electrode group 5 is less than that in the outermost peripheral portion 55. Thereby, the first thickness (A1) of the positive electrode 13 at the innermost peripheral portion 50 of the electrode group 5 can be made thinner than the second thickness (A2) at the outermost peripheral portion 55. The same applies to the negative electrode 15. The first thickness (B1) of the negative electrode 15 of the electrode group 5 is thinner than the second thickness (B2). In this case, the application amount of the negative electrode active material in the innermost peripheral portion 50 of the electrode group 5 is less than that in the outermost peripheral portion 55.

[0020] Here, it is preferable to vary the application amount of the positive electrode active material in one positive electrode current collector 13a, provide the first thickness (A1) and the second thickness (A2) to manufacture the positive electrode 13, and then wind the positive electrode 13 to manufacture the electrode group 5. Also, using one positive electrode current collector 13a, manufacture a positive electrode 13 with a reduced application amount of the positive electrode active material to provide the first thickness (A1), and using another positive electrode current collector 13a, manufacture a positive electrode 13 with an increased application amount of the positive electrode active material to provide the second thickness (A2). Then, wind the positive electrode 13 having the first thickness (A1) around the innermost circumference, and wind the positive electrode 13 having the second thickness (A2) outside it to manufacture the electrode group 5. The same applies to the negative electrode 15.

[0021] Modified versions of electrode group 5 will be described with reference to Figures 5 and 6. Figure 5 is a schematic cross-sectional view (section II shown in Figure 1) showing a modified version of electrode group 5 according to the first embodiment, and Figure 6 is an enlarged cross-sectional view (section II shown in Figure 1) showing the area around the innermost circumference 50 of electrode group 5 in the modified version of electrode group 5.

[0022] In a modified version of electrode group 5, at least one of the first thickness (A1) of the positive electrode 13 or the first thickness (B1) of the negative electrode 15 at the innermost circumference 50 of electrode group 5 is thinner than the second thickness (A2) of the positive electrode 13 or the second thickness (B2) of the negative electrode 15 at the outermost circumference 55 of electrode group 5. Furthermore, taking the endpoint P' of the innermost circumference 50 of electrode group 5 as a new starting point R, at least one of the third thickness (A3) of the positive electrode 13 or the third thickness (B3) of the negative electrode 15 in the portion from the starting point R to the endpoint R' after another full rotation is also thinner than the second thickness (A2) of the positive electrode 13 or the second thickness (B2) of the negative electrode 15.

[0023] The third thickness (A3) of the positive electrode 13 of electrode group 5 is thinner than the second thickness (A2), but in this embodiment, A3 is preferably between 0.1A2 and 0.8A2. Similarly to the positive electrode 13, the third thickness (B3) of the negative electrode 15 is thinner than the second thickness (B2), but in this embodiment, B3 is preferably between 0.1B2 and 0.8B2.

[0024] If the third thickness (A3) of the positive electrode 13 is 0.1A2 or more, even though the third thickness (A3) is thinner than the second thickness (A2), it is possible to obtain an electrode group 5 that ensures sufficient battery capacity as a whole. Furthermore, if the third thickness (A3) of the positive electrode 13 is 0.8A2 or less, 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 positive electrode 13 is sharply bent not only at the innermost circumference 50 of the electrode group 5 but also in the portion that wraps around the electrode member 20 from the innermost circumference 50, cracking of the positive electrode 13 in the portion that wraps around the electrode member 20 from the innermost circumference 50 can be suppressed. As a result, even if the cracked positive electrode 13 breaks through the separator 4 and makes electrical contact with the opposing negative electrode 15, it is possible to suppress this in the portion that wraps around the electrode member 20 from the innermost circumference 50, not just at the innermost circumference 50 of the electrode group 5. The reason why it is preferable for the third thickness (B3) of the negative electrode 15 to be between 0.1B2 and 0.8B2 is the same.

[0025] In the modified form of electrode group 5, the first thickness (A1) and the third thickness (A3) of the positive electrode 13 may be different, but it is preferable that they be equal. For example, if the first thickness (A1) and the third thickness (A3) are equal, the positive electrode 13 can be manufactured from the starting point P to the ending point R' without changing the amount of positive electrode mixture applied, resulting in good manufacturing efficiency for electrode group 5. Similarly to the positive electrode 13, the first thickness (B1) and the third thickness (B3) of the negative electrode 15 may be different, but it is preferable that they be equal, because the negative electrode 15 can be manufactured from the starting point P to the ending point R' without changing the amount of negative electrode mixture applied, resulting in good manufacturing efficiency for electrode group 5.

[0026] Furthermore, in the modified electrode group 5, at least one of the third thickness (A3) of the positive electrode 13 or the third thickness (B3) of the negative electrode 15 in the portion where the electrode member 20 is wrapped around once from the innermost circumference 50 is thinner than the second thickness (A2) of the positive electrode 13 or the second thickness (B2) of the negative electrode 15. However, the thickness of the positive electrode 13 or the negative electrode 15 in the portion where the electrode member 20 is wrapped around two, three, or more times from the innermost circumference 50 may be thinner than the second thickness (A2) of the positive electrode 13 or the second thickness (B2) of the negative electrode 15. This prevents the broken positive electrode 13 from piercing the separator 4 and preventing electrical contact with the opposing negative electrode 15 not only in the innermost circumference 50 of the electrode group 5, but also in the portion where the electrode member 20 is wrapped around two, three, or more times from the innermost circumference 50.

[0027] However, in order to obtain an electrode group 5 that ensures sufficient battery capacity as a whole, more preferably, the first thickness (A1) of the positive electrode 13 and the first thickness (B1) of the negative electrode 15 at the innermost circumference 50, and the third thickness (A3) of the positive electrode 13 and the third thickness (B3) of the negative electrode 15 in the portion where the electrode member 20 is wrapped around from the innermost circumference 50, are made thinner than the second thickness (A2) of the positive electrode 13 and the second thickness (B2) of the negative electrode 15 at the outermost circumference 55 of the electrode group 5.

[0028] In the electrode group 5 of the first embodiment described above, at least one of the first thickness (A1) of the positive electrode 13 or the first thickness (B1) of the negative electrode 15 at the innermost circumference 50 of the electrode group 5 is thinner than the second thickness (A2) of the positive electrode 13 or the second thickness (B2) of the negative electrode 15 at the outermost circumference 55 of the electrode group 5.

[0029] Specifically, the thickness A1 is between 0.1A2 and 0.8A2, and the thickness B1 is between 0.1B2 and 0.8B2. This makes it possible to suppress cracking of the positive electrode 13 or negative electrode 15 at the innermost circumference 50 of the electrode group 5, 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, causing the positive electrode 13 or negative electrode 15 at the innermost circumference 50 of the electrode group 5 to be sharply bent. This makes it possible to obtain an electrode group 5 that suppresses short circuits caused by a cracked positive electrode 13 or negative electrode 15 piercing the separator 4 and making electrical contact with the opposing positive electrode 13 or negative electrode 15 at the innermost circumference 50 of the electrode group 5, while also ensuring sufficient battery capacity.

[0030] (Second embodiment) The secondary battery 1 of the second embodiment will be described with reference to Figure 7. Figure 7 is a schematic perspective view showing the secondary battery 1 according to the second embodiment.

[0031] As shown in Figure 7, 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.

[0032] 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 positive electrode external terminals 23a and negative 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 positive electrode mixture layer and the uncoated portion 70b of the negative electrode 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.

[0033] In the secondary battery 1 of the second embodiment described above, the electrode group 5 of the first embodiment is provided. As a result, in the electrode group 5, at least one of the thicknesses A1 and B1 is 0.1A2 or more and 0.8A2 or less, or 0.1B2 or more and 0.8B2 or less. Therefore, 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, and the positive electrode 13 or negative electrode 15 at the innermost circumference 50 of the electrode group 5 is sharply bent, a secondary battery 1 can be provided that suppresses cracking of the positive electrode 13 or negative electrode 15 at the innermost circumference 50 of the electrode group 5. Furthermore, in the innermost circumference 50 of the electrode group 5, a secondary battery 1 can be obtained that suppresses short circuits caused by a cracked positive electrode 13 or negative electrode 15 piercing the separator 4 and making electrical contact with the opposing positive electrode 13 or negative electrode 15, while also ensuring sufficient battery capacity.

[0034] According to the electrode group 5 of at least one embodiment described above, at least one of the first thickness (A1) of the positive electrode 13 or the first thickness (B1) of the negative electrode 15 at the innermost circumference 50 of the electrode group 5 is thinner than the second thickness (A2) of the positive electrode 13 or the second thickness (B2) of the negative electrode 15 at the outermost circumference 55 of the electrode group 5.

[0035] Specifically, the thickness A1 is between 0.1A2 and 0.8A2, and the thickness B1 is between 0.1B2 and 0.8B2. This makes it possible to suppress cracking of the positive electrode 13 or negative electrode 15 at the innermost circumference 50 of the electrode group 5, 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, causing the positive electrode 13 or negative electrode 15 at the innermost circumference 50 of the electrode group 5 to be sharply bent. This makes it possible to obtain an electrode group 5 that suppresses short circuits caused by a cracked positive electrode 13 or negative electrode 15 piercing the separator 4 and making electrical contact with the opposing positive electrode 13 or negative electrode 15 at the innermost circumference 50 of the electrode group 5, while also ensuring sufficient battery capacity.

[0036] 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 a variety of 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]

[0037] 1...Secondary battery, 3...Outer case, 4...Separator, 5...Electrode group, 7...Lid member, 13...Positive electrode, 13a...Positive electrode current collector, 15...Negative electrode, 15a...Negative electrode current collector, 19...Sealing plate, 20...Electrode member, 21...Gas discharge valve, 23a...Positive electrode external terminal, 23b...Negative electrode external terminal, 35...Terminal insulator, 50...Innermost part, 55...Outermost part, 70a...Uncoated part of positive electrode mixture layer, 70b...Uncoated part of negative electrode mixture layer, 90...Long side, 92...Short side, 130...Positive electrode mixture layer, 150...Negative electrode mixture layer, P...Starting point, P'...Ending point, Q...Starting point, Q'...Ending point, R...Starting point, R'...Ending point.

Claims

1. An electrode group in which electrode members consisting of a positive electrode, a negative electrode, and a separator are wound together, An electrode group in which the first thickness (A1) of the positive electrode and the first thickness (B1) of the negative electrode at the innermost circumference of the electrode group, and the second thickness (A2) of the positive electrode and the second thickness (B2) of the negative electrode at the outermost circumference of the electrode group satisfy at least one of the following equations (1) or (2). 0.1A2≦A1≦0.8A2 (1) 0.1B2≦B1≦0.8B2 (2)

2. The electrode group according to claim 1, wherein the third thickness (A3) of the positive electrode and the third thickness (B3) of the negative electrode, and the second thickness (A2) of the positive electrode and the second thickness (B2) of the negative electrode, in the portion of the electrode group that extends from the innermost circumference to the outermost circumference, and the portion that extends from the innermost circumference to the outermost circumference of the electrode group, satisfy at least one of the following equations (3) or (4). 0.1A2≦A3≦0.8A2 (3) 0.1B2≦B3≦0.8B2 (4)

3. The first thickness (A1) of the positive electrode is equal to the third thickness (A3) of the positive electrode. The electrode group according to claim 2, wherein the first thickness (B1) of the negative electrode is equal to the third thickness (B3) of the negative electrode.

4. A group of electrodes as described in any one of claims 1 to 3, A secondary battery comprising an electrolyte.

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