Cylindrical alkaline storage battery

Abstract

To provide an alkali storage battery having an electrode group arranged so that an electrolyte solution is allowed to smoothly penetrate into a whole separator without marring a given electric property.SOLUTION: A cylindrical alkali storage battery comprises an electrode group 12 having a column shape arranged by putting a first separator 19, a positive electrode 16, a second separator 20 and a negative electrode 18 on one another and winding them like a roll. The electrode group includes: a first region 13 where at least three layers of the positive electrode are laminated; a second region 14 where one more layer of the positive electrode is laminated than the layers of the positive electrode in the first region; and a surfactant coating layer. The surfactant coating layer is provided on one or both of positive electrode-touching and negative electrode-touching faces of one or both of the first and second separators, and serves to accelerate the penetration of an electrolyte solution. The surfactant coating layer extends from a column-shaped bottom part of the electrode to a top-end part uninterruptedly, which is provided only in a range including part or whole of the second region in a circumference direction of the electrode group.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cylindrical alkaline storage battery, and more particularly to a separator that constitutes a cylindrical alkaline storage battery. [Background technology]

[0002] Cylindrical alkaline storage batteries are widely used as power sources for various devices, including portable electronic devices. Cylindrical alkaline storage batteries generally consist of a stack of positive and negative electrodes with a separator interposed between them, which is then spirally wound to form a cylindrical electrode group, which is then housed in a cylindrical battery can with a bottom and immersed in an electrolyte.

[0003] To increase the battery capacity of such cylindrical alkaline storage batteries, a method has been adopted in which the number of windings of the positive electrode is increased to increase the electrode area. However, due to the trend toward miniaturization of electronic components that incorporate storage batteries, it is difficult to increase the size of the battery can in response to the increase in the number of windings. Therefore, in electrode groups with an increased number of windings, the separator becomes thinner, and there are areas where the pressure applied to the separator when placed in the battery can increases, which tends to make it difficult for the electrolyte to penetrate.

[0004] However, in order to maintain battery characteristics such as cycle life, it is essential to allow the separator interposed between the positive electrode and the negative electrode to be sufficiently impregnated with the electrolyte solution. For example, Patent Document 1 discloses a technique of applying a surfactant to the upper surface of the separator to promote the penetration of the electrolyte solution into the separator.

[0005] On the other hand, if a surfactant is applied to the entire surface of the separator, there is a risk that deposition or decomposition reaction on the electrode will deteriorate the charge-discharge characteristics of the alkaline storage battery, such as shortening the cycle life and increasing self-discharge. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-36396 Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide an alkaline storage battery having an electrode group in which an electrolyte solution smoothly permeates the entire separator without impairing a predetermined cycle life or self-discharge characteristics. [Means for solving the problem]

[0008] A cylindrical alkaline storage battery according to one embodiment of the present disclosure includes an electrode group in which a first separator, a positive electrode, a second separator, and a negative electrode are superimposed and spirally wound to form a cylindrical shape, in which the first separator contacts the inside of the positive electrode and the second separator contacts the outside of the positive electrode, and an alkaline electrolyte in which the electrode group is immersed, and the electrode group includes a first region in which at least three layers of positive electrodes are stacked, a second region in which one more layer of positive electrodes than the first region is stacked, and a surfactant coating layer, a surfactant coating layer is provided on one or both of the surfaces of the first separator and the second separator that are in contact with the positive electrode and the negative electrode, the surfactant coating layer extends continuously from the bottom to the top of the cylindrical shape of the electrode group and is provided in a limited range in the circumferential direction of the electrode group that includes part or all of the second region, and the surfactant coating layer promotes penetration of the alkaline electrolyte at the interface where the surfactant coating layer is provided. [Effects of the Invention]

[0009] The cylindrical alkaline storage battery of the present disclosure can provide an alkaline storage battery having an electrode group in which the electrolyte solution smoothly permeates the entire separator without impairing the predetermined cycle life or self-discharge characteristics. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view in the height direction of a cylindrical alkaline storage battery according to one embodiment. [Figure 2] FIG. 2 is a radial cross-sectional view of a cylindrical alkaline storage battery according to one embodiment. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the top, center, and bottom of the electrode group of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0012] <Embodiment> 1 shows a cross-sectional view in the height direction of a cylindrical alkaline storage battery 1 according to one embodiment. This cylindrical alkaline storage battery 1 is composed of a cylindrical battery can 11 with a bottom, a battery lid 24, an electrode group 12 housed in the battery can 11, and an alkaline electrolyte in which the electrode group 12 is immersed. The battery can 11 has an opening at its top end, which is sealed by the battery lid 24. The battery can 11 itself functions as a negative electrode terminal, and the battery lid 24 includes a positive electrode terminal 30.

[0013] The electrode group 12 is formed into a cylindrical shape by stacking a first separator 19, a positive electrode 16, a second separator 20, and a negative electrode 18 and spirally winding them together. The electrode group 12 is wound so that the first separator 19 contacts the inside of the positive electrode 16 and the second separator 20 contacts the outside of the positive electrode 16. The electrode group 12 is immersed in an alkaline electrolyte, thereby impregnating the first separator 19 and the second separator 20 with the alkaline electrolyte.

[0014] The outermost periphery of this cylindrical electrode group 12 is covered with a negative electrode 18, and when the electrode group 12 is housed in a battery can 11, the negative electrode 18 comes into contact with and is electrically connected to the battery can 11, which itself functions as a negative electrode terminal.

[0015] Near the upper end of the electrode group 12, there is an internal battery space surrounded by the battery can 11, the battery lid 24, and the electrode group 12. A current collecting tab 22 is disposed in this internal battery space, and one end of the current collecting tab 22 is connected to the upper end of the positive electrode 16 and the other end is connected to the battery lid 24. A positive electrode terminal 30 is disposed on the battery lid 24, and the positive electrode 16 of the electrode group 12 is electrically connected to the positive electrode terminal 30 via the current collecting tab 22 and the battery lid 24.

[0016] When the top opening of the battery can 11 is sealed with the battery lid 24, an insulating gasket 32 ​​can be placed between the battery can 11 and the battery lid 24 to electrically insulate and separate the battery can 11 from the battery lid 24. Furthermore, by providing the battery lid 24 with a gas vent hole 26 and a valve body 28, accidents such as the explosion of the battery can 11 can be avoided even if gas is generated from the electrode group 12 and fills the space inside the battery.

[0017] The cylindrical alkaline storage battery 1 according to one embodiment of the present invention may be, for example, a cylindrical nickel-metal hydride storage battery, a cylindrical nickel-cadmium storage battery, or a cylindrical lithium-ion storage battery.

[0018] Fig. 2 shows a radial cross-sectional view of a cylindrical alkaline storage battery 1 according to one embodiment. The electrode group 12 includes a first region 13 in which at least three layers of positive electrodes 16 (four layers in Fig. 2) are stacked, and a second region 14 in which one more layer of positive electrodes 16 (five layers in Fig. 2) is stacked than in the first region 13. In this way, an electrode group 12 in which a large number of positive electrodes 16 are stacked generally has a configuration in which, in the circumferential direction, a region in which n layers of positive electrodes 16 are stacked and a region in which n+1 layers of positive electrodes 16 are stacked are mixed.

[0019] This electrode group 12 includes a first region 13 in which at least three layers of positive electrodes 16 are stacked, and a second region 14 in which one more layer of positive electrodes 16 is stacked than in the first region 13. In such an electrode group 12 having a structure in which the number of stacked positive electrodes 16 is different, the pressure applied in the radial direction (i.e., the stacking direction) of the second region 14, which has a larger number of stacked layers, tends to be locally large, and this tendency is particularly large near the circumferential center 14a of the second region 14.

[0020] As a result, the alkaline electrolyte tends to take longer to penetrate into the first separator 19 and the second separator 20 near the circumferential center 14a than near the boundary with the first region 13. Therefore, in the circumferential direction of the second region 14 of the electrode group 12, it is important to allow the alkaline electrolyte to sufficiently penetrate up to the circumferential center 14a of the second region 14.

[0021] 1 , the alkaline electrolyte is poured into the battery can 11 from the top opening thereof while the electrode group 12 is housed in the battery can 11. At this time, the alkaline electrolyte is supplied directly to the top end of the electrode group 12, and therefore the alkaline electrolyte also permeates the first separator 19 and the second separator 20 from their top ends. In addition, there is a gap near the winding center of the electrode group 12 that penetrates all the way to the bottom of the electrode group 12, and the alkaline electrolyte is supplied to the bottom of the battery can 11 through this gap, so the alkaline electrolyte also permeates the first separator 19 and the second separator 20 from the bottom of the electrode group 12.

[0022] Therefore, in the cylindrical electrode group 12, the area near the center in the height direction, which is the farthest end from the top end and the bottom end, is the area that takes the longest time for the alkaline electrolyte to penetrate, and it is important to allow the alkaline electrolyte to penetrate sufficiently into this area.

[0023] Therefore, the first separator 19 and the second separator 20 are each subjected to a hydrophilic treatment in advance, which facilitates the penetration of the alkaline electrolyte into each separator. Furthermore, a surfactant coating layer 19a is provided on the surface of the first separator 19 that is in contact with the positive electrode 16. This surfactant coating layer 19a further promotes the penetration of the alkaline electrolyte into the interface between the first separator 19 and the positive electrode 16.

[0024] Here, the area in the circumferential direction of the second region 14 of the electrode group 12 that takes the longest time for the alkaline electrolyte to reach is near the circumferential center 14a of the second region 14, so it is preferable to provide the surfactant coating layer 19a in a region that includes at least the circumferential center 14a. However, considering that the alkaline electrolyte permeates more easily in the first region 13 than in the second region 14, and that the alkaline electrolyte also permeates more easily in the second region 14 on the side closer to the boundary with the first region 13, it can be said that even if the second region 14 occupies the majority of the circumferential area of ​​the electrode group 12, by providing the surfactant coating layer 19a in an area of ​​approximately half or less of the circumference of the electrode group 12, it is possible to allow the alkaline electrolyte to sufficiently permeate the entire circumferential direction of the electrode group 12.

[0025] Furthermore, it is more preferable that the region where the surfactant coating layer 19a is provided be arranged so as to be symmetrical with respect to the circumferential center 14a of the second region 14 as the axis of symmetry, and for example, it can be provided in the region shown as surfactant coating region 15 in Figure 2.

[0026] Furthermore, because the alkaline electrolyte permeates from the top and bottom of the electrode group 12, it is preferable to provide surfactant coating layer 19a so that it extends continuously from the bottom to the top of the cylindrical shape of electrode group 12. Surfactant coating layer 19a provided in this manner promotes the permeation of the alkaline electrolyte in the height direction of electrode group 12, enabling it to fully permeate up to near the center in the height direction, which is the farthest end from both the top and bottom.

[0027] Figure 3 is an enlarged cross-sectional view of the top end, center, and bottom of the electrode group 12 shown in Figure 1. The cross-sectional view shown in Figure 1 shows a cross section taken along a diameter passing through the circumferential center 14a of the second region 14 in Figure 2. In the cross-sectional views shown in Figures 1 and 3, the left half of the electrode group 12 shows the structure in the first region 13 in Figure 2, and the right half shows the structure in the second region 14.

[0028] A surfactant-coated layer 19a is disposed on the surface of the first separator 19 that is in contact with the positive electrode 16. The surfactant-coated layer 19a extends continuously from the bottom to the center and to the top in the height direction of the cylindrical electrode group 12. This surfactant-coated layer 19a can be formed by applying a surfactant to the surface of the first separator 19 in advance before it is spirally wound into a cylindrical shape.

[0029] Next, a specific example in which the present invention is applied to a cylindrical nickel-metal hydride storage battery will be described.

[0030] <Example> Nickel hydroxide was used for the positive electrode 16, and a rare earth-nickel hydrogen storage alloy was used for the negative electrode 18. The first separator 19 was a nonwoven fabric that had been subjected to a sulfonation treatment in advance to make it hydrophilic, and the second separator 20 was a nonwoven fabric that had been subjected to a fluorine treatment in advance to make it hydrophilic.

[0031] These were stacked in the order of first separator 19, positive electrode 16, second separator 20, and negative electrode 18, and then spirally wound so that the first separator 19 was in contact with the inside of the positive electrode 16 and the second separator 20 was in contact with the outside of the positive electrode 16 to form a cylindrical electrode group 12. The number of stacked layers of the positive electrode 16 was four in the first region 13 and five in the second region 14.

[0032] A surfactant-coated layer 19a, to which a surfactant has been applied in advance, is provided on the surface of the first separator 19 that comes into direct contact with the positive electrode 16. The surfactant-coated layer 19a extends continuously from the bottom (the bottom side of the battery can 11 in FIG. 1 ) to the top end (the side where the current collecting tab 22 in FIG. 1 is provided) of the cylindrical electrode group 12. In addition, in the circumferential direction of the electrode group 12, as shown as surfactant-coated region 15 in FIG. 2 , the surfactant-coated region 19a is arranged over half the circumferential range so as to be symmetrical with respect to the circumferential center 14a of the second region 14 as the axis of symmetry.

[0033] The surfactant coating layer 19a may be provided on at least one of the first separator 19 and the second separator 20. In this embodiment, the surfactant coating layer 19a is provided on the first separator 19, which has been subjected to a sulfonation treatment and is therefore less hydrophilic than the fluorine-treated second separator 20. As the surfactant, for example, alkylbenzene sulfonate or alkyldiphenylether disulfonate can be used.

[0034] The electrode group 12 thus prepared was housed in a cylindrical battery can 11 with a bottom, a potassium hydroxide solution was poured in as an alkaline electrolyte to immerse the electrode group 12, and the top opening of the battery can 11 was sealed with a battery lid 24, thereby obtaining a cylindrical nickel-metal hydride storage battery having the structure shown in FIG. 1.

[0035] The cylindrical nickel-metal hydride storage battery of this example was tested for charge-discharge cycle and self-discharge characteristics. In order to verify the effects and side effects of surfactant coating layer 19a, similar tests were also conducted on Comparative Examples 1-3, which differ in the area where surfactant coating layer 19a was provided.

[0036] The specifications and test results of this example and comparative examples 1-3 are summarized in Table 1. The test conditions for the charge / discharge test are summarized in Table 2. The battery capacity of each of this example and comparative examples 1-3 is 2700 mAh. Comparative example 1 is a specification in which surfactant coating layer 19a is not provided, and the test results of this specification serve as a basis for verifying the effects and side effects of surfactant coating layer 19a.

[0037] [Table 1]

[0038] [Table 2]

[0039] <1C cycle test> In cylindrical nickel-metal hydride batteries, a phenomenon in which the discharge capacity decreases with repeated charge and discharge is observed. One charge and one discharge is defined as one cycle (cyc.), and the cycle test examines the extent to which the discharge capacity decreases with repeated charge and discharge cycles. The test conditions in this example are shown in Table 2. The battery was charged at 1C (2700mA for a battery capacity of 2700mAh in this example), followed by a 20-minute break, discharged at 1C, followed by a 10-minute break. The number of cycles was counted until the discharge capacity decreased to 60% or less of its initial value.

[0040] According to Table 1, Comparative Example 1, which did not have surfactant coating layer 19a, achieved 150 cycles, whereas this Example achieved 180 cycles, a significant improvement. Furthermore, while Comparative Example 1 had areas in the first separator 19 where the alkaline electrolyte had not permeated (areas where the alkaline electrolyte had not permeated), this Example was confirmed to have the alkaline electrolyte permeate the entire first separator 19. Therefore, it is believed that the improvement in charge / discharge cycle characteristics in this Example is due to the elimination of areas where the alkaline electrolyte had not permeated by providing surfactant coating layer 19a on the surface of first separator 19.

[0041] On the other hand, in Comparative Example 2, in which the surfactant-coated layer 19a was provided over the entire surface of the first separator 19, no areas where the alkaline electrolyte had not penetrated were observed, but the cycle performance was 135 cycles. According to the test results of this example, eliminating the areas where the alkaline electrolyte had not penetrated would be expected to improve the cycle performance to 180 cycles. However, the cycle performance was actually worse than the 150 cycles of Comparative Example 1, in which the surfactant-coated layer 19a was not provided. This result suggests that the surfactant is a factor that deteriorates the cycle performance, and that if the surfactant-coated layer 19a is provided over an excessively large area, the side effects of this deterioration factor become dominant. It can be understood that the deterioration of the cycle performance in Comparative Example 2 from 180 cycles to 135 cycles was due to this side effect.

[0042] Furthermore, in Comparative Example 3, in which the surfactant-coated layer 19a was provided over the entire circumferential surface of the upper end of the first separator 19, the battery life was 145 cycles. In Comparative Example 3, there were still areas where the alkaline electrolyte had not penetrated, which is thought to be the reason why the battery life was roughly equivalent to the 150 cycles of Comparative Example 1.

[0043] <Self-discharge test> The self-discharge test evaluates the extent to which the discharge capacity decreases during storage after charging and resting. The initial setup consisted of charging at 1C, resting for one hour, then discharging at 0.2C, and resting for one hour. After charging at 1C and resting for 14 days at an ambient temperature of 40°C, the discharge capacity was measured by discharging at 0.2C. The results were summarized as a percentage of the initial discharge capacity.

[0044] The result for this example was 86.7%, the same as the 86.7% for Comparative Example 1. This indicates that the installation of the surfactant coating layer 19a in this example did not change the self-discharge characteristics. In contrast, in Comparative Example 2, the self-discharge characteristics decreased to 85.5%. As with the cycle test, the surfactant can cause the self-discharge characteristics to deteriorate, and if the installation area of ​​the surfactant coating layer 19a is too large, the decrease due to this factor is thought to be observed as a significant difference. On the other hand, in Comparative Example 3, the self-discharge characteristics were 86.4%, which is a slight difference from the 86.7% for Comparative Example 1, and therefore there does not appear to be a significant difference between Comparative Example 3 and Comparative Example 1.

[0045] As described above, in the cylindrical nickel-metal hydride storage battery of this embodiment, the provision of surfactant coating layer 19a allows the alkaline electrolyte to smoothly permeate the entire separator, improving the cycle life. Furthermore, by limiting the area where surfactant coating layer 19a is provided within an appropriate range, it is possible to avoid any adverse effects on the cycle life and self-discharge characteristics from becoming apparent.

[0046] In this example, an example was shown in which the surfactant coating layer 19a was provided on the surface of the first separator 19 that contacts the positive electrode 18. However, this is not limited to this, and the surfactant coating layer 19a may be provided on either the first separator 19 or the second separator 20. In this case, it is preferable to provide the surfactant coating layer 19a on the one of the first separator 19 and the second separator 20 that has a lower hydrophilicity. The surfactant coating layer 19a may be provided on both the first separator 19 and the second separator 20.

[0047] In this embodiment, the surfactant coating layer 19a is provided on the side in contact with the inner surface of the positive electrode 16. However, it may also be provided on the side in contact with the outer surface of the positive electrode 16, or on both the inner and outer surfaces. In this embodiment, the surfactant coating layer 19a is provided on the surface in contact with the positive electrode 16. Alternatively, it may be provided on the surface of either the first separator 19 or the second separator 20 in contact with the negative electrode 18. Furthermore, the surfactant coating layer 19a may be provided on both the surfaces of the negative electrode 18 in contact with the first separator 19 and the second separator 20, i.e., on both the surface in contact with the inner side of the negative electrode and the surface in contact with the outer side of the negative electrode. Thus, regardless of the position at which the surfactant coating layer 19a is provided, any configuration applicable to cylindrical alkaline storage batteries can achieve the same effects as the configuration disclosed in this embodiment.

[0048] Furthermore, in this example, an example was shown in which a sulfonated nonwoven fabric was used as the first separator 19 and a fluorine-treated nonwoven fabric was used as the second separator 20. However, this is not limited to this, and a fluorine-treated nonwoven fabric may be used as the first separator 19 and a sulfonated nonwoven fabric may be used as the second separator 20. Furthermore, a sulfonated nonwoven fabric may be used for both the first separator 19 and the second separator 20, or a fluorine-treated nonwoven fabric may be used for both the first separator 19 and the second separator 20. The hydrophilization treatment is not limited to sulfonation treatment or fluorine treatment, and other methods may be adopted.

[0049] Furthermore, it is not essential to use two separators, such as the first separator 19 and the second separator 20. For example, a single separator may be folded back midway and wound to sandwich the positive electrode 16 from both sides. In this way, the separator specifications and the position at which the surfactant coating layer 19a is provided may be any configuration applicable to a cylindrical alkaline storage battery, and the same effects as those of the configuration disclosed in this example can be achieved. [Explanation of symbols]

[0050] 1 Cylindrical alkaline storage battery 11 Battery can 12 electrode groups 13 First area 14 Second area 14a Circumferential center 16 positive electrode 18 negative electrode 19 First separator 19a Surfactant coating layer 20 Second separator 22 Current collecting tab 24 Battery cover 30 Positive terminal

Claims

1. an electrode group in which a first separator, a positive electrode, a second separator, and a negative electrode are stacked and spirally wound to form a cylindrical shape, wherein the first separator is in contact with the inside of the positive electrode and the second separator is in contact with the outside of the positive electrode; an alkaline electrolyte in which the electrode group is immersed, the electrode group includes a first region in which at least three layers of the positive electrodes are stacked, a second region in which one more layer of the positive electrodes is stacked than in the first region, and a surfactant coating layer; a cylindrical alkaline storage battery, wherein the surfactant-coated layer is provided on one or both of a surface of one or both of the first separator and the second separator that is in contact with the positive electrode and a surface of one or both of the first separator and the second separator that is in contact with the negative electrode, the surfactant-coated layer extends continuously from the bottom of the cylindrical shape of the electrode group to the top end of the cylindrical shape, and is provided in a limited range in the circumferential direction of the electrode group that includes part or all of the second region, and the surfactant-coated layer promotes penetration of the alkaline electrolyte at the interface where the surfactant-coated layer is provided.

2. 2. The cylindrical alkaline storage battery according to claim 1, wherein the range in which the surfactant coating layer is provided in the circumferential direction of the electrode group is a range of not more than half of the circumference in the circumferential direction, including a circumferential center of the second region.

3. 3. The cylindrical alkaline storage battery according to claim 1, wherein both the first separator and the second separator have been subjected to a hydrophilization treatment, and the surfactant coating layer is provided on at least one of the first separator and the second separator which has a lower hydrophilicity.

4. 3. The cylindrical alkaline storage battery according to claim 1, wherein the surfactant coating layer is provided on both the first separator and the second separator.

5. a cylindrical battery can having a bottom and an open top end, which constitutes a negative electrode terminal; a battery lid that includes a positive electrode terminal and seals the top opening of the battery can. the electrode group is housed in the battery can, and the negative electrode is connected to a negative electrode terminal formed by the battery can; 5. The cylindrical alkaline storage battery according to claim 1, further comprising a current collecting tab that is disposed in an internal battery space surrounded by the battery can, the battery lid, and the electrode group, and that connects the positive electrode to the positive electrode terminal.

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