Wound battery

Abstract

To provide a wound battery in which the movement of an electrode plate relative to a separator is suppressed.SOLUTION: In a wound battery 1, a wound electrode group 3 formed in such a way that a rectangular positive electrode plate 11 and negative electrode plate 12 are wound in a long side direction with separators 13 and 14 held therebetween is accommodated in an exterior can 2 together with an alkaline electrolyte solution. The separator 13 includes a rectangular main separator 31 that exists between the positive electrode plate and the negative electrode plate and electrically insulates the positive electrode plate and the negative electrode plate, and an assistant separator 32 with a right triangle shape that is fixed to one main surface of the main separator. The positive electrode plate is disposed in contact with the one main surface of the main separator with each of four corner parts of the rectangle disposed between the main separator and the assistant separator. The assistant separator restricts the movement of the positive electrode plate relative to the main separator.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a wound-type battery. [Background technology]

[0002] Nickel-metal hydride batteries have a structure in which strip-shaped positive and negative electrode plates, each with a separator interposed between them, are wound longitudinally to form a spiral electrode group, and the electrode group is then housed in an outer can and sealed together with an alkaline electrolyte. In this configuration, the separator is made of nonwoven fabric, and when wound together with the electrodes, the separator can be punctured by the corners of the electrode plates, leading to a short circuit between the positive and negative electrodes. To address this issue, rectangular auxiliary separators extending in the width direction of the separator are superimposed on both longitudinal ends of the separator.

[0003] However, if the positive or negative electrode plate becomes misaligned from the separator when the electrode plates are wound, so-called misalignment of the winding occurs, the positive and negative electrode plates may come into direct contact with each other, causing a short circuit.

[0004] To address this issue, a structure has been adopted in which convex portions are provided on the longitudinal ends of the separator to prevent the electrode plates from slipping when wound, as disclosed in JP 10-255818 A. Also, a structure has been adopted in which protrusions are provided on the four corners of the separator to limit the movement of the electrode plates, as disclosed in JP 2012-209072 A. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-255818 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-209072 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when winding the electrode plate, the corners of the electrode plate may climb over the protrusions or projections on the separator, causing misalignment during winding, which may result in a short circuit between the positive and negative electrode plates.

[0007] In view of the above problems, an object of the present invention is to provide a wound-type battery that suppresses movement of the electrode plates relative to the separator. [Means for solving the problem]

[0008] In order to achieve the above object, the wound battery of the present invention is a wound battery in which a wound electrode group, each formed by winding a rectangular positive electrode plate and a negative electrode plate in the long side direction with a separator interposed between them, is housed in an outer can together with an alkaline electrolyte, and is characterized in that the separator has a rectangular main separator located between the positive electrode plate and the negative electrode plate to electrically insulate the positive electrode plate from the negative electrode plate, and a plurality of auxiliary separators fixed to one main surface of the main separator, the positive electrode plate is in contact with one main surface of the main separator, and each of the four corners of the rectangle is located between the main separator and the auxiliary separator, and the auxiliary separators restrict movement of the positive electrode plate relative to the main separator. [Effects of the Invention]

[0009] According to the wound battery of the present invention, when the separator is sandwiched between the positive electrode plate and the negative electrode plate and wound in a spiral shape, it is possible to suppress the electrode plates from slipping off from the separator. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a partially cutaway, exploded perspective view of a battery according to an embodiment; [Figure 2] FIG. 2 is an exploded perspective view of a state in which a positive electrode plate, a separator, and a negative electrode plate are stacked. [Figure 3] FIG. 2 is a plan view showing a positive electrode plate fixed to a main separator by an auxiliary separator. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a battery according to an embodiment of the present invention will be described with reference to the drawings. A cylindrical battery is shown in Figure 1. Battery 1 contains a spirally wound electrode group 3 (hereinafter referred to as the electrode group) together with an alkaline electrolyte in a cylindrical outer can 2, and an opening 2A of outer can 2 is sealed with a sealing body 4. Outer can 2 functions as the negative electrode, and the sealed end of outer can 2 functions as the positive electrode.

[0012] The outer can 2 is formed into a cylindrical shape from a conductive metal, has a cylindrical side surface 2B extending in the axial direction, one end in the axial direction is a circular can bottom 2C, and the other end 2A is open.

[0013] The electrode group 3 includes a rectangular positive electrode plate 11, a negative electrode plate 12, and separators 13 and 14. The electrode group 3 is spirally wound with the separators 13 and 14 sandwiched between the positive electrode plate 11 and the negative electrode plate 12, and has a generally cylindrical shape as a whole. When the positive electrode plate 11, the separators 13 and 14, and the negative electrode plate 12 are wound, the positive electrode plate 11 is fixed to one main surface of the separator 13, as shown in FIG. 2 . Then, the separator 14 and the negative electrode plate 12 are stacked in this order on top of the positive electrode plate 11 placed on the separator 13. The outermost periphery of the electrode group 3 is formed by a portion of the negative electrode plate 12.

[0014] The positive electrode plate 11 is composed of a rectangular, conductive, porous positive electrode core and a positive electrode mixture that mainly contains nickel hydroxide and is applied to the surface and pores of the positive electrode core. The positive electrode core may be, for example, a nickel-plated mesh, sponge, or fibrous metal body or nickel foam.

[0015] The positive electrode mixture contains positive electrode active material particles, a conductive material, a positive electrode additive, and a binder. The positive electrode active material particles are nickel hydroxide (Ni(OH)2) particles or higher-order nickel hydroxide particles. Cobalt hydroxide (Co(OH)2) is used as the conductive material. The positive electrode additive is either yttrium oxide (YO3) or ytterbium oxide (Yb2O3).

[0016] The negative electrode plate 12 comprises a rectangular conductive negative electrode core and a negative electrode mixture applied to the negative electrode core. The negative electrode core is made of a sheet-like metal material with distributed through-holes, such as a punched metal sheet made of iron with a nickel-plated surface. When applied to the negative electrode core, the negative electrode mixture forms a negative electrode mixture layer. The negative electrode mixture contains hydrogen storage alloy particles, a negative electrode additive, a conductive material, and a binder.

[0017] The hydrogen storage alloy is an alloy capable of absorbing and releasing hydrogen, which is a negative electrode active material. A typical hydrogen storage alloy can be used as the hydrogen storage alloy. In the present disclosure, it is preferable to use a rare earth-Mg-Ni-based hydrogen storage alloy containing rare earth elements, Mg, and Ni. Examples of rare earth elements that can be used include La, Ce, Pr, Nd, Sm, Gd, and Y.

[0018] The separators 13 and 14 are both made of a nonwoven fabric made of polypropylene fibers and are formed into a rectangular shape that is larger in the width and length directions than the positive electrode plate 11 and the negative electrode plate 12. The nonwoven fabric may be subjected to a fluorine treatment or a sulfonation treatment. The positive electrode plate 11 is attached to the separator 13 as shown in Figures 2 and 3. The attachment of the positive electrode plate 11 to the separator 13 will be described later.

[0019] A negative electrode current collector 15 is welded to one end of the electrode group 3, where the edge portion of the negative electrode plate 12 protrudes, and the negative electrode plate 12 is electrically connected to the negative electrode current collector 15. The electrode group 3 is housed in the outer can 2 so that the negative electrode current collector 15 faces the can bottom 2C of the outer can 2, and the outermost peripheral surface of the negative electrode plate 12 contacts the inner peripheral surface of the outer can 2. In this way, the negative electrode plate 12 is electrically connected to the outer can 2. In addition, a circular lower insulating member 16 is arranged between the electrode group 3 and the can bottom 2C of the outer can 2.

[0020] Inside the exterior can 2, a positive electrode tab 17 is attached to the upper edge of the positive electrode plate 11. An upper insulating member 18 is placed on the electrode group 3. The upper insulating member 18 has a circular shape in a plan view, and is provided with an electrolyte injection port in its center and a slit to allow the positive electrode tab 17 to pass through.

[0021] After the electrode group 3 is housed in the outer can 2, an alkaline electrolyte is poured into the outer can 2 through a pouring port in the upper insulating member 18. The alkaline electrolyte is impregnated into the positive electrode plate 11, the negative electrode plate 12, and the separators 13 and 14, and contributes to an electrochemical reaction, i.e., a charge-discharge reaction, between the positive electrode plate 11 and the negative electrode plate 12. The alkaline electrolyte is an aqueous solution containing KOH, NaOH, and LiOH.

[0022] The tip of the positive electrode tab 17 passes through a slit in the upper insulating member 18 and is welded to the inner surface of the circular conductive sealing body 4. The sealing body 4 has a gas vent hole 4a in its center, and a rubber valve body 19 is disposed on its outer surface to close the gas vent hole 4a. The sealing body 4 is then disposed at the open end 2A of the outer can 2. The open end 2A of the outer can 2 is then crimped via an insulating gasket 20 sandwiched between the outer periphery of the sealing body 4 and the inner periphery of the outer can 2, thereby fixing the sealing body 4 to the open end 2A. In this way, the gasket 20 and the sealing body 4 close the outer can 2 and electrically insulate the sealing body 4 from the outer can 2. A positive electrode terminal 21 is attached to the sealing body 4. The battery 1 is assembled as described above.

[0023] Next, the separator 13 to which the positive electrode plate 11 is attached will be described.

[0024] As shown in FIGS. 2 and 3 , the separator 13 is composed of a main separator 31 and multiple auxiliary separators 32. In this embodiment, there are four auxiliary separators 32. The main separator 31 has a rectangular shape with short sides 31S and long sides 31L, and the short sides 31S coincide with the width direction of the electrode group 3, and the long sides 31L are parallel to the longitudinal direction, which is the winding direction. The lengths of the short sides 31S and long sides 31L of the main separator 31 are both longer than the short sides 11S and long sides 11L of the positive electrode plate 11.

[0025] The auxiliary separator 32 has a triangular shape and is made from the same material as the main separator 31. The auxiliary separator 32 is a right-angled isosceles triangle in which a first side and a second side form a right angle. The length of the first side 32S is equal to or less than half the length of the short side 11S of the positive electrode plate 11. In this embodiment, the length of the second side 32L is formed to be the same length as the first side 32S. In other embodiments, the length of the second side 32L may be shorter than the length of the first side 32S.

[0026] The four auxiliary separators 32 are fixed to the four corners of the main separator 31 after the positive electrode plate 11 is placed in a predetermined position on one main surface of the main separator 31 .

[0027] The mounting position of the auxiliary separator 32 on the main separator 31 will be described below.

[0028] As shown in Figure 3, one short side 31S of the main separator 31 is the winding start end B, and the other short side 31S is the winding end end E. One short side 11S of the positive electrode plate 11 is spaced a predetermined length d in the longitudinal direction from the winding start end B of the main separator 31, and is disposed between the two long sides 31L, 31L of the main separator 31. Furthermore, the two long sides 11L, 11L of the positive electrode plate 11 are disposed so as to be parallel to the longitudinal direction of the main separator 31. This arrangement is the predetermined position of the positive electrode plate 11 on the main separator 31.

[0029] Next, the auxiliary separator 32 is placed so as to cover the corner 11A of the positive electrode plate 11 placed on the main separator 31. When placing the auxiliary separator 32, the right-angled portion 32A of the auxiliary separator 32 is aligned with the corner 11A of the positive electrode plate 11. Furthermore, the first side 32S of the auxiliary separator 32 is placed parallel to the short side 11S of the positive electrode plate 11, and the second side 32L is placed parallel to the long side 11L of the positive electrode plate 11. Thereafter, the first side 32S and the second side 32L of the auxiliary separator 32 are thermally welded to the main separator 31, thereby fixing the auxiliary separator 32 to the main separator 31. By welding the auxiliary separator 32, the corner 11A of the positive electrode plate 11 is positioned between one main surface of the main separator 31 and the auxiliary separator 32. Therefore, the corner 11A of the positive electrode plate 11 is sandwiched between one main surface of the main separator 31 and the auxiliary separator 32.

[0030] By fixing the auxiliary separator 32 to the main separator 31, the movement of the positive electrode plate 11 in the longitudinal direction of the main separator 31 is restricted by the first side portion 32S of the auxiliary separator 32. Furthermore, the movement in the width direction of the main separator 31 is restricted by the second side portion 32L of the auxiliary separator 32.

[0031] By fixing the auxiliary separators 32 to the four corners 11A of the positive electrode plate 11 as described above, the four corners of the positive electrode plate 11, i.e., the four corners 11A, are sandwiched between the main separator 31 and the auxiliary separator 32, restricting movement of the positive electrode plate 11 in the width direction and length direction relative to the separator 13. Therefore, displacement of the positive electrode plate 11 from the separator 13 is suppressed.

[0032] Then, a rectangular positive electrode tab 17 is welded to one of the long sides 11L of the positive electrode plate 11, spaced apart from the winding starting end B, so that its longitudinal direction intersects with the long side 11L and protrudes outward in the width direction beyond the long side 11L of the main separator 31.

[0033] Then, as shown in FIG. 2, the positive electrode plate 11 fixed to the separator 13, the separator 14, and the negative electrode plate 12 are stacked in this order, and the separator 13, the positive electrode plate 11, the separator 14, and the negative electrode plate 12 are wound in the longitudinal direction from the winding start end B of the separator 13 to produce the electrode group 3.

[0034] Since the movement of the positive electrode plate 11 relative to the separator 13 is restricted and the positive electrode plate 11 does not move so as to protrude outward from one main surface of the separator 13, it is possible to suppress the occurrence of shear in winding relative to the separator 13. Therefore, it is possible to prevent a short circuit between the positive electrode plate 11 and the negative electrode plate 12 due to shear in winding. In the present disclosure, "shear in winding" refers to a phenomenon in which, when the rectangular positive electrode plate 11, separators 13, 14, and negative electrode plate 12 are stacked and wound, the positive electrode plate 11 moves in the width direction from its initial position on the separator 13, and the long side 11L of the positive electrode plate 11 deviates outward from the width of the separator 13.

[0035] Next, the size of the auxiliary separator 32 will be considered. Four types of batteries 1 were fabricated, each having an AA size and a 1C current of 2500 mA. The lengths of the first side 32S and second side 32L of the auxiliary separator 32 were N / 5, N / 4, N / 3, and N / 2, respectively, relative to the length N of the short side 31S of the main separator 31. These batteries are designated as batteries 1 of Examples 1, 2, 3, and 4, respectively. In other words, the dimensions of the auxiliary separator 32 increase in the order of Examples 1, 2, 3, and 4. Therefore, the size of the auxiliary separator 32 of Example 1 is set as the reference "1," and the sizes of the auxiliary separators 32 of Examples 2, 3, and 4 are compared. Table 1 shows the values obtained by comparing the sizes of the auxiliary separators 32 of Examples 2, 3, and 4. As Comparative Example 1, an AA size battery 1 having an 1C current of 2500 mA and no auxiliary separator 32 was fabricated. In addition, as Comparative Example 2, a battery 1 was produced in which an auxiliary separator 32 having a width of 1.05N and a length of N / 2 was directly attached to the current separator at positions corresponding to the winding start end B and winding end end E of the positive electrode plate 11 to reinforce the separator 13, and the positive electrode plate 11 was placed on the reinforced separator 13 to produce an electrode group 3.

[0036] In addition, 100,000 battery cells were produced for each example, and measurements were taken of the occurrence of shear winding, the occurrence of short circuits between the electrode plates, and the number of cycles at which the 1C cycle capacity reached 60% of the initial capacity for each battery cell. "Short circuit failure" refers to the occurrence of short circuits between the positive electrode plate 11 and the negative electrode plate 12 due to causes other than shear winding. "Number of cycles at which the 1C cycle capacity reached 60% of the initial capacity" refers to the number of charge / discharge cycles required for the battery 1 to reach 60% of the initial capacity at full charge when the battery 1 is repeatedly charged and discharged at 1C, and corresponds to the life of the battery 1. In both the example and comparative example batteries 1, the separators 13 and 14 were made of polypropylene nonwoven fabric, and the amount of electrolyte was injected so as to have the same ratio to the internal volume of the battery. The internal volume of the battery is the volume of the internal space of the outer can 2. This volume corresponds to the internal volume of the battery minus the total volume of the positive electrode plate 11, negative electrode plate 12, separators 13 and 14, positive electrode tab 17, upper insulating member 18, and lower insulating member 16. The liquid space ratio is calculated using the amount of electrolyte (total liquid volume) relative to the remaining internal volume of the battery using the following formula:

[0037] Space-liquid ratio (%) = ((electrolyte volume (m 3 )) / (Remaining space volume in battery (m 3 )))×100

[0038] The electrolyte was injected into each battery 1 so that the space liquid ratio was 60%. Therefore, if the remaining space volume in the battery is large, the absolute amount of the electrolyte will also be large.

[0039] The measurement results are shown in Table 1.

[0040] [Table 1]

[0041] From Table 1, it can be seen that in all of Examples 1 to 4, the auxiliary separator 32 suppressed shear in the electrode group 3, regardless of its size. On the other hand, in Comparative Examples 1 and 2, the movement of the positive electrode plate 11 relative to the separator 13 could not be restricted, and thus shear occurred.

[0042] It is also clear that the occurrence of short-circuit defects other than winding slippage decreases as the size of the auxiliary separator 32 relative to the main separator 31 increases from Example 1 to Example 4. This is thought to be because the area of the positive electrode plate 11 sandwiched between the main separator 31 and the auxiliary separator 32 increases, preventing the positive electrode plate 11 from breaking through the main separator 31.

[0043] On the other hand, it can be seen that the number of cycles to reach 60% at 1C decreases as the size of auxiliary separator 32 increases. This is because, as the size of auxiliary separator 32 increases, the remaining space volume in the battery decreases, and therefore the absolute amount of electrolyte contained in outer can 2 decreases in order to maintain a space-liquid ratio of 60%. Therefore, if the size of auxiliary separator 32 is small, the amount of electrolyte can be increased in proportion to the decrease in the size of separators 13 and 14, thereby extending the life of battery 1.

[0044] However, in all of Examples 1 to 4, the size of the auxiliary separator 32 is smaller than that of Comparative Example 2, so the volume of the remaining space in the battery can be increased. As a result, the absolute amount of the electrolyte can also be increased, and the cycle life of the battery 1 can be extended.

[0045] In the above embodiment, the four corners of the positive electrode plate are fixed to the main separator by auxiliary separators. However, even if only the two corners of the positive electrode plate near the winding end E of the main separator are fixed by auxiliary separators, it is possible to suppress shear of the electrode group.

[0046] Furthermore, in the above embodiment, the present invention is applied to a secondary battery, but the present invention can be applied to any type of cylindrical battery in which the electrode group is of a wound type. [Explanation of symbols]

[0047] 1 battery 2 outer can 3 electrode groups 11 Positive electrode plate 12 negative electrode plate 13 Separator 31 Main separator 32 Auxiliary separator

Claims

1. A wound-type battery in which a wound electrode group formed by winding rectangular positive and negative electrode plates with a separator interposed between them in the long side direction is housed in an outer can together with an alkaline electrolyte, the separator includes a rectangular main separator positioned between the positive electrode plate and the negative electrode plate to electrically insulate the positive electrode plate from the negative electrode plate, and a plurality of auxiliary separators fixed to one main surface of the main separator; the positive electrode plate is in contact with one main surface of the main separator, and each of the four corners of the rectangle is disposed between the main separator and the auxiliary separator; The auxiliary separator limits movement of the positive electrode plate relative to the main separator.

2. each of the plurality of auxiliary separators has a right-angled triangle shape in which a first side and a second side of the triangle form a right angle; 2. The wound battery according to claim 1, wherein a right-angled portion of the auxiliary separator is aligned with one corner of the positive electrode plate positioned relative to the main separator, the first side portion is arranged along a short side of the positive electrode plate and is fixed to the main separator, and the second side portion is arranged along a long side of the positive electrode plate and is fixed to the main separator.

3. 3. The wound battery according to claim 2, wherein the length of the first side of the one auxiliary separator is equal to or less than half the length of the short side of the positive electrode plate.

4. 4. The wound battery according to claim 3, wherein the length of the second side of the auxiliary separator is the same as or shorter than the length of the first side.

5. 5. The wound battery according to claim 2, wherein the first side of the auxiliary separator is spaced apart from a winding start end of the main separator.

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