JP7832032B2 - Cylindrical rechargeable battery - Google Patents

Description

This invention relates to a cylindrical rechargeable battery.

Generally, alkaline storage batteries are manufactured as follows. First, a separator is interposed between the positive and negative electrode plates, and these are wound in a spiral to form a roughly cylindrical electrode group. A negative electrode current collector is then welded to the negative electrode side of the electrode group. Next, the electrode group is housed in a bottomed casing, and a welding rod is passed through the central hole (where the core of the electrode group was removed) to weld the negative electrode current collector to the bottom of the casing. In this way, the electrode group is fixed to the current collector by resistance welding, and then fixed to the casing, thereby electrically connecting and fixing the electrode group to the casing. Subsequently, a positive electrode current collector with a current collecting lead is welded to the positive electrode side of the electrode group, and the casing is filled with electrolyte. Furthermore, the current collecting lead is welded to a sealing body, and the sealing body is attached to the opening of the casing via an insulating gasket and crimped to seal the casing (see Japanese Patent Publication No. 2003-168415).

Japanese Patent Publication No. 2003-168415 Japanese Patent Publication No. 2005-129433

Resistance welding between the current collector and the outer casing sometimes resulted in reduced weldability in high-capacity batteries with small core sections. Furthermore, the small welding area at the bottom of the casing made welding defects more likely, and these defects were difficult to detect immediately after welding because they occurred inside the casing. Additionally, the electrode rods used for welding were extremely thin, leading to rapid wear and deterioration, which increased the overall number of welding steps.

Therefore, for example, as described in Japanese Patent Publication No. 2005-129433, a configuration was proposed in which the current collector was formed into a bottomed cylindrical shape and attached to cover the negative electrode side of the electrode group, while a circumferential groove was formed on the side surface of the battery case, and the electrode group was fixed to the battery case by bringing the groove into contact with the side surface of the current collector. However, there were concerns that the shape of the current collector was complex and that the number of steps in battery manufacturing would increase.

The objective of this invention is to provide a cylindrical secondary battery that has a simple structure while ensuring secure fixation of the electrode group to the outer casing.

To achieve the above objective, the cylindrical secondary battery of the present invention comprises: a cylindrical outer casing including one closed end as the bottom; an electrode group housed together with an electrolyte in the outer casing, each consisting of a strip-shaped positive electrode plate and a negative electrode plate superimposed with a separator in between, and wound in a spiral shape around the width direction of the positive electrode plate and the negative electrode plate as the axis, with the outermost surface of the spiral winding being the negative electrode plate; and a plate-shaped negative electrode current collector positioned between the bottom of the outer casing and the electrode group, in contact with the bottom and in contact with the negative electrode plate. The negative electrode plate is characterized in that the thickness of the edge on the negative electrode current collector side is greater than the thickness of the remaining portion, and at least one of the edge of the negative electrode plate and the edge of the negative electrode current collector constituting the outermost surface is fixed in contact with the inner circumferential surface extending in the axial direction of the outer casing.

According to the cylindrical secondary battery of the present invention, the electrode group can be connected or fixed to the negative electrode current collector and the outer casing without resistance welding.

This is a perspective view of a cylindrical nickel-metal hydride secondary battery according to one embodiment, showing a portion cut out and the battery unfolded. This is a longitudinal cross-section of the outer can near the bottom. This is an unfolded view of the negative electrode core contained within the negative electrode plate. This is a plan view showing the negative electrode plate, separator, and positive electrode plate stacked together. This is a cross-sectional view of the negative electrode side of the battery. This is a cross-sectional view of the negative electrode side of a battery according to another embodiment. This is a cross-sectional view of the negative electrode side of the battery, which is a modified example of the embodiment shown in Figure 5.

Below, a nickel-metal hydride secondary battery (hereinafter simply referred to as "battery") as a cylindrical secondary battery according to one embodiment will be described with reference to the drawings.

Figure 1 shows, for example, an AA-sized cylindrical battery 1 with a height of 50.5 mm and an outer diameter of 14.5 mm. The battery 1 contains a bottomed cylindrical outer casing 10, which houses a group of approximately cylindrical electrodes 12 along with an alkaline electrolyte. The opening of the outer casing 10 is sealed by a sealing body 24. The sealed end of the outer casing 10 functions as the positive electrode, and the outer surface of the outer casing 10 functions as the negative electrode.

The outer can 10 is formed into a cylindrical shape from nickel-plated steel sheet using a multi-stage press. One end in the axial direction forms the bottom 10A, and the other end is open. The outer can 10 has a side thickness of 0.15 to 0.2 mm, and the bottom 10A has a thickness of 0.3 to 0.35 mm, with the bottom 10A being thicker than the side 10B.

Furthermore, as shown in Figure 2, the outer casing 10, before assembly as a battery 1, has a cylindrical thick-walled portion 10B1 on the bottom 10A side and a cylindrical side portion 10B2 that extends continuously from the thick-walled portion 10B1 toward the positive electrode side of the battery 1. The thick-walled portion 10B1 is cylindrical, with the edge 10a of the bottom 10A as one end of its width and a point at a height H1 along the axial direction of the outer casing 10 from the edge 10a as the other end of its width. The thickness of the thick-walled portion 10B1 is greater than the thickness of the side portion 10B2. Therefore, if the thick-walled portion protrudes further toward the central axis of the outer casing than the side portion, the inner diameter of the thick-walled portion of the outer casing will be smaller than the inner diameter of the side portion. The above-mentioned side thickness of 0.15 to 0.2 mm is the thickness of the side portion 10B2. Also, height H1 is an example of a second length.

The electrode group 12 consists of a strip-shaped positive electrode plate 16, a negative electrode plate 18, and a separator 20. The electrode group 12 is wound in a spiral shape with the separator 20 interposed between the positive electrode plate 16 and the negative electrode plate 18, resulting in an overall approximately cylindrical shape. The outermost periphery of the electrode group 12, the so-called cylindrical side surface, is composed solely of the negative electrode plate 18, and the positive electrode plate 16 is not exposed on the side surface. The negative electrode plate 18, which constitutes the outermost periphery of the electrode group 12, contacts the inner circumferential surface of the outer casing 10, thereby connecting the negative electrode plate 18 to the outer casing 10.

The positive electrode plate 16 consists of a conductive positive electrode substrate that extends in a strip-like shape in the longitudinal direction, has a porous structure, and has numerous voids, and a positive electrode mixture held within the voids and on the surface of the positive electrode substrate. The positive electrode substrate is plated with a metal such as nickel, which exhibits conductivity, and the positive electrode mixture is filled into the plated substrate. The positive electrode mixture includes positive electrode active material particles, a conductive material, a positive electrode additive, and a binder. The positive electrode substrate coated with the positive electrode mixture is rolled to complete the positive electrode plate 16.

The negative electrode plate 18 is an electrode containing a hydrogen storage alloy, and consists of a strip-shaped conductive negative electrode core 19 and a negative electrode mixture held by the negative electrode core 19. As shown in Figure 3, the negative electrode core 19 is made of a metal sheet with numerous through-holes formed in the thickness direction. The negative electrode core 19 is manufactured in a strip shape with the winding direction of the electrode group 12 as the longitudinal direction. In this embodiment, the negative electrode core 19 is, for example, made of a metal sheet with a width of 59.5 mm and a thickness of 60 μm.

The negative electrode core 19, more specifically, consists of strip-shaped non-perforated portions A1 and A2 extending over a predetermined width W from each of its ends E1 and E2 in the width direction, and a perforated portion A3 located between the non-perforated portions A1 and A2. In this embodiment, W is 3.1 mm. The non-perforated portions A1 and A2 have flat surfaces because they lack through-holes extending in the thickness direction, providing mechanical strength to the negative electrode core 19. The perforated portion A3 has numerous through-holes extending in the thickness direction, holding the negative electrode mixture not only on the surface of the negative electrode core 19 but also within the through-holes.

The negative electrode core 19 is coated with the negative electrode mixture, dried, and then roll-rolled. In this embodiment, the thickness of the rolled negative electrode plate 18 is 0.342 mm in the areas corresponding to the non-porous sections A1 and A2, and 0.334 mm in the area corresponding to the perforated section A3. That is, the thickness of the negative electrode plate corresponding to the non-porous sections A1 and A2 is greater than the thickness of the negative electrode plate corresponding to the perforated section A3, with a difference of 8 μm. This is presumed to be because, in the perforated section A3, the mixture filling the through-holes reduces the thickness of the negative electrode mixture in the perforated section A3 during rolling, but in the non-porous sections A1 and A2, there are no through-holes, so even after rolling, the compression ratio is smaller than in the perforated section A3. Thus, the thickness of the non-porous sections A1 and A2 is greater than the thickness of the perforated section A3.

The separator 20 is made, for example, of a nonwoven fabric of polyolefin fibers to which hydrophilic groups have been added.

Alkaline electrolytes used include, for example, aqueous solutions of potassium hydroxide, lithium hydroxide, sodium hydroxide, or mixtures thereof.

The electrode group 12 assembled as described above is housed inside the outer casing 10 via a plate-shaped negative electrode current collector 21.

After housing the electrode group 12 in the outer casing 10, one end of the positive electrode current collector 22 is electrically connected to the positive electrode plate 16 near the opening of the outer casing 10, and the other end is welded to the inner surface of a conductive circular sealing body 24. The sealing body 24 has a gas vent hole 26 in the center, and a rubber valve body 28 is positioned on the outer surface of the sealing body 24 to close the gas vent hole 26. Furthermore, a flanged cylindrical positive electrode terminal 30 covering the valve body 28 is fixed to the outer surface of the sealing body 24, and the positive electrode terminal 30 presses the valve body 28 against the sealing body 24.

The sealing body 24 is located at the open end of the outer can 10, and an insulating gasket 32 is sandwiched between the outer circumference of the sealing body 24 and the inner surface of the outer can 10. The sealing body 24 and the insulating gasket 32 are fixed to the open end of the outer can 10 by crimping the portion of the outer can 10 on the open end side of the electrode group 12. The insulating gasket 32 insulates and seals the space between the outer circumference of the sealing body 24 and the outer can 10.

Battery 1 is assembled as described above.

To fabricate the electrode group 12, when winding the positive electrode plate 16 and the negative electrode plate 18 with a separator 20 interposed between the two electrode plates 16 and 18, as shown in Figure 4, for example, the negative electrode plate 18, separator 20, and positive electrode plate 16 are stacked in that order. At this time, while aligning the longitudinal directions of the negative electrode plate 18 and the positive electrode plate 16, the positive electrode plate 16 is offset by a length L relative to the negative electrode plate 18 in one width direction, and then the positive electrode plate 16 and the negative electrode plate 18 are wound with their width direction as the axis, that is, with the longitudinal direction of the electrode plates 16 and 18 as the winding direction. Note that length L is an example of a first length. As a result, in the electrode group 12, the end E1 of the negative electrode plate 18 protrudes in a spiral shape from one end, and the edge portion of the positive electrode plate 16 protrudes in a spiral shape from the other end. The end E1 of the spirally protruding negative electrode plate 18 becomes the negative electrode side end 18A of the electrode group 12. The winding offset length L is set so as not to exceed the length W corresponding to the width of the non-perforated portion A1 of the negative electrode plate 18 (L < W). This is because offsetting the positive electrode plate 16 relative to the negative electrode plate 18 by more than the width W of the non-perforated portion A1 would impair the overall mechanical strength of the electrode group 12.

The electrode group 12 assembled as described above is housed inside the outer can 10 such that the negative electrode end 18A of the electrode group 12 is in contact with the bottom 10A of the can via a plate-shaped negative electrode current collector 21 with a thickness T _0. At this time, as shown in Figure 5, the negative electrode end 18A of the electrode group 12 slides against the inner circumferential surface of the thickened portion 10B1 of the side surface 10B of the outer can. Also, since the electrode group 12 is simply wound in a spiral shape, it tries to unwind, acting a force radially outward on the inner circumferential surface of the outer can 10. As a result, the electrode group 12 is fixed to the outer can 10 and becomes immobile. Furthermore, because the electrode group 12 is fixed to the outer can 10, the negative electrode current collector 21, which is located between the negative electrode end 18A of the electrode group 12 and the bottom 10A of the outer can, is also sandwiched and fixed between the inner circumferential surface of the outer can 10 and the negative electrode end 18A of the electrode group 12.

In this way, the negative electrode current collector 21 is fixed and immobile between the inner circumferential surface of the outer casing 10 and the negative electrode end 18A of the electrode group 12, thus maintaining a continuous connection between the negative electrode current collector 21 and both the electrode group 12 and the outer casing 10. Furthermore, the negative electrode current collector 21 is electrically connected to both the electrode group 12 and the outer casing 10, keeping the internal resistance of the battery 1 low and suppressing an increase in internal resistance.

Furthermore, after sealing the outer casing 10 with the sealing body 24, the outer casing 10 can be tapered from the bottom 10A towards the opening to reduce the battery diameter. In this case, the inner diameter of the thickened portion 10B1 of the outer casing becomes smaller, allowing for more reliable pressure contact of the electrode group 12 by the thickened portion 10B1. Also, when tapering the battery 1, the inner diameter of the outer casing 10 before assembly may be equal in both the thickened portion and the side portion.

In the configuration of the battery 1 described above, the height H1 of the thickened portion is made smaller than the length L of the offset of the positive electrode plate 16 relative to the negative electrode plate 18. This height H1 is in the range of 0.5 mm to 2.0 mm. If the height H1 of the thickened portion 10B1 is less than 0.5 mm, it will be approximately the same as the thickness of the can bottom 10A (0.3 to 0.35 mm), resulting in a small contact area between the negative electrode end 18A and the thickened portion 10B1. Therefore, even if the outer can 10 is drawn, the effect of reducing the diameter of the outer can 10 cannot be expected, and it may not be possible to fix the electrode group 12 to the outer can 10.

On the other hand, if the height H1 of the thickened portion 10B1 exceeds 2.0 mm, the narrowed diameter of the thickened portion 10B1 pushes the negative electrode plate 18, located on the outermost periphery, toward the central axis of the outer can 10. This push causes the negative electrode plate 18 to come too close to the adjacent positive electrode plate 16, potentially short-circuiting the plates 16 and 18. Therefore, it is preferable that the height H1 of the thickened portion be in the range of 0.5 mm to 2.0 mm.

Thus, in the above embodiment, resistance welding is not used for connecting the negative electrode current collector 21 to the electrode group 12, nor for connecting the electrode group 12 to the outer casing 10. Therefore, the battery 1 can be assembled in fewer steps. Furthermore, the thick-walled portion 10B1 of the outer casing 10 is in direct contact with the non-perforated portion A1 of the negative electrode plate 18. The non-perforated portion A1 of the negative electrode plate 18 has greater mechanical strength than the perforated portion A3 because it lacks through-holes. Therefore, the electrode group 12 can be more securely fixed to the outer casing 10.

Furthermore, by utilizing the difference in thickness between the non-perforated sections A1 and A2 and the perforated section A3 that occurs when creating the negative electrode plate 18, the axial movement of the electrode group 12 in the outer casing 10 is suppressed, thereby fixing the electrode group 12 to the outer casing 10. This eliminates the need to increase the number of manufacturing steps for the battery 1 compared to conventional methods.

Furthermore, because resistance welding is not performed, it is unnecessary to insert a welding rod or other jig into the center of the electrode group 12 after the electrode plates 16 and 18 have been wound. This suppresses the occurrence of defective batteries 1 due to interference between the jig and the electrode plates 16 and 18.

Furthermore, when resistance welding the electrode group 12 to the outer casing 10, it was previously impossible to visually inspect the welded area even if welding defects occurred. However, by eliminating the need to check for such defects, the manufacturing process of the battery 1 can be reduced.

In the above embodiment, the side surface 10B of the outer can 10 has a thickened portion 10B1 and a side surface 10B2, and its thickness is configured to vary along the axial direction from the can bottom 10A. In a second embodiment, different from the above embodiment, the outer can 10' can be configured such that the side surface 10B' has a constant thickness along the axial direction from the can bottom 10A'. The second embodiment will be described below.

In the second embodiment, the components constituting the battery 1' are the same as in the above embodiment, except for the outer casing 10'.

After housing the electrode group 12 in the outer can 10', a groove 10G is formed circumferentially, as shown in Figure 7. The groove 10G is located axially from the bottom 10A' of the outer can 10', with a height H2 that is longer than the thickness Tb of the outer can bottom 10A' and does not exceed the length (Tb + L). This is known as beading. As a result, in a cross-section perpendicular to the axis of the outer can 10', the inner surface portion 10H of the outer can, corresponding to the groove 10G, abuts against and locks against the vicinity of the edge portion 18A of the negative electrode plate 18, which constitutes the side surface of the electrode group 12. Note that the groove 10G is an example of a recessed portion.

Furthermore, at this time, the inner diameter of the groove 10G formed in the inner surface 10H of the outer can is smaller than the diameter of the negative electrode end 18A of the electrode group 12. Therefore, the axial movement of the electrode group 12 relative to the outer can 10' is suppressed.

In the assembly of the battery 1' described above, resistance welding is not performed to connect the negative electrode current collector 21 to the negative electrode end 18A of the electrode group 12. Furthermore, resistance welding is not performed to fix the electrode group 12 to the outer casing 10' after it has been housed in the outer casing 10'. Instead of these two welding processes, the groove 10G of the outer casing 10 is brought into contact with the non-perforated portion A1 of the negative electrode plate, which becomes the negative electrode end 18A of the electrode group 12. This fixes the electrode group 12 to the bottom 10A of the outer casing 10' via the negative electrode current collector 21. This configuration suppresses movement of the negative electrode current collector 21 relative to the negative electrode end 18A of the electrode group 12. Therefore, movement of the electrode group 12 and the negative electrode current collector 21 relative to the outer casing 10' is also suppressed, preventing an increase in the AC resistance of the battery 1.

Furthermore, by utilizing the difference in thickness between the non-perforated sections A1 and A2 and the perforated section A3 that occurs when creating the negative electrode plate 18, the axial movement of the electrode group 12 in the outer casing 10 is suppressed, thereby fixing the electrode group 12 to the outer casing 10. This eliminates the need to increase the number of manufacturing steps for the battery 1 compared to conventional methods.

Furthermore, because resistance welding is not performed, it is unnecessary to insert a welding rod or other jig into the center of the electrode group 12 after the electrode plates 16 and 18 have been wound. This suppresses the occurrence of defective batteries 1' due to interference between the jig and the electrode plates 16 and 18.

Furthermore, when resistance welding the electrode group 12 to the outer casing 10', it was previously impossible to visually inspect the welded area even if welding defects occurred. However, by eliminating the need to check for such defects, the manufacturing process of the battery 1' can be reduced.

In the above embodiments, the negative electrode side of the electrode group is fixed by contacting it with the outer casing 10. However, the same effect as in the above embodiments can be obtained by making the diameter of the negative electrode current collector 21 larger than the diameter of the electrode group and bringing it into contact with the side surface near the bottom of the outer casing.

The battery size in the above embodiment is AA size, but the battery size is not limited to this.

1 Battery 10 Outer casing 10A Bottom of casing 12 Electrode group 16 Positive electrode plate 18 Negative electrode plate 18A Negative electrode end 20 Separator 21 Negative electrode current collector

Claims (4)

A cylindrical outer can with one closed end as the bottom,
Each electrode group consists of a strip-shaped positive electrode plate and a negative electrode plate, superimposed with a separator in between, and wound in a spiral shape around the width direction of the positive electrode plate and the negative electrode plate as axes, with the outermost surface of the spiral winding being the negative electrode plate, and is housed together with the electrolyte in the outer container.
A plate-shaped negative electrode current collector is disposed between the bottom of the outer can and the electrode group, and is in contact with the bottom and the negative electrode plate.
Equipped with,
The negative electrode plate has a thickness at the edge on the negative electrode current collector side that is thicker than the thickness of the remaining portion.
At least one of the edges of the negative electrode plate constituting the outermost surface and the edge of the negative electrode current collector is fixed in contact with the inner surface extending in the axial direction of the outer casing .
The outer can has a recessed portion on the side surface near the bottom that is recessed toward the axis of the outer can and extends in a linear fashion in the circumferential direction.
A cylindrical secondary battery in which the electrode group is fixed to the outer casing by the edge of the negative electrode plate being locked in the axial direction to the recess inside the outer casing . The cylindrical secondary battery according to claim 1, wherein the inner diameter of the side surface near the bottom of the outer casing is smaller than the inner diameter of the remaining side surfaces. The negative electrode plate consists of a strip-shaped core and a negative electrode mixture layer on which the negative electrode mixture is coated.
The aforementioned core body is
A flat, non-perforated portion is located at one end and the other end in the width direction, and extends in a winding direction intersecting the width direction,
A perforated portion located between the non-perforated portions and having multiple through-holes that penetrate in the thickness direction of the core body into which the negative electrode mixture enters,
A cylindrical secondary battery according to claim 1 or 2, having the following features. The positive electrode plate is wound in a spiral shape around the negative electrode plate with a first length offset in the width direction, thereby forming the electrode group.
The cylindrical secondary battery according to any one of claims 1 to 3, wherein the side surface of the outer casing has a thickened portion with a width extending from the bottom to a portion of a second length in the axial direction, and the second length is shorter than the first length and in the range of 0.5 mm to 2.0 mm.