Positive electrode plate for secondary battery and cylindrical secondary battery

Abstract

To provide a positive electrode plate for a secondary battery that suppresses an increase in the internal resistance of a battery and increases the battery capacity.SOLUTION: A secondary battery positive electrode plate 16 includes two porous and metal-plated substrates 40 each extending in a strip shape in the longitudinal direction and having wide surfaces opposed to each other, a rectangular current collector 22 attached to the substrate, and a positive electrode active material M filled in two substrates in a state where the current collector is sandwiched between the two substrates and press-bonded, and the positive electrode active material is contained in an interface 40B where the current collector is in contact with the substrate.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a positive electrode plate for a secondary battery, and more particularly to a positive electrode plate for a cylindrical secondary battery. [Background technology]

[0002] Conventionally, the positive electrode plate of a cylindrical alkaline secondary battery is made by filling a base made of metal-plated urethane foam with a positive electrode active material. To attach a current collecting tab to this base by welding, the positive electrode active material is peeled off from the area to be welded, and after the current collecting tab is welded, protective tape is applied to cover the welded area to reinforce the base and prevent short-circuiting with the negative electrode plate.

[0003] In the above structure, when the positive electrode active material is peeled off from the substrate, a load is applied to the substrate, which may cause the substrate to break when the current collecting tab is welded. Breaking of the substrate may lead to an increase in the internal resistance of the battery and may tend to deteriorate the discharge characteristics. In particular, when the basis weight is 200 g / m 2 The following substrates tend to frequently break when the positive electrode active material is peeled off. Also, the area around the welded part of the current collecting tab is not covered with the positive electrode active material, resulting in a loss of battery capacity.

[0004] Therefore, a configuration has been proposed in which the edges of the substrate are folded without peeling off the positive electrode active material, and a current collecting tab is sandwiched between the folded and overlapping portions (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2002-502087 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the structure of folding the edges of the base to sandwich the current collecting tab increases the overall thickness of the positive electrode plate, which can lead to an increase in the size of the cylindrical electrode group that is made by rolling up the positive and negative electrode plates with a separator interposed between them in order to prevent short circuits between the negative and positive electrode plates.

[0007] In view of the above problems, an object of the present invention is to provide a positive electrode plate for a secondary battery that can suppress an increase in internal resistance and achieve a high battery capacity, and a cylindrical secondary battery using the same. [Means for solving the problem]

[0008] In order to achieve the above object, the positive electrode plate for a secondary battery of the present invention comprises two porous, metal-plated substrates, each extending in a strip shape in the longitudinal direction and with its wide surfaces facing each other, a rectangular current collector attached to the substrates, and a positive electrode active material filled into the two substrates in a state in which the current collector is sandwiched between the two substrates and pressed together, and is characterized in that the positive electrode active material is contained at the interface where the current collector contacts the substrates. [Effects of the Invention]

[0009] According to the present invention, even if a substrate having a low basis weight is used as the substrate of the positive electrode plate, peeling and breaking of the substrate can be suppressed, and the battery capacity of a secondary battery including such a positive electrode plate can be increased. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a vertical cross-sectional view of a secondary battery according to an embodiment. [Figure 2] 4(A) to 4(C) are explanatory views showing the steps of manufacturing a positive electrode plate. [Figure 3] FIG. 2 is a plan view of a current collecting tab attached to a substrate. [Figure 4] FIG. 10 is a plan view of a current collecting tab having a protrusion and attached to a substrate. [Figure 5] 1 is a table showing evaluation results of battery characteristics. [Figure 6] 10 shows another embodiment of the substrate. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a positive electrode plate for a secondary battery will be described below with reference to the accompanying drawings. 1. Battery configuration FIG. 1 shows a nickel-metal hydride secondary battery 1 as a cylindrical battery according to one embodiment of the present invention.

[0012] The battery 1 is, for example, an AA-size cylindrical battery with a height of 50.5 mm and an outer diameter of 14.5 mm, and includes an outer can 10 having a cylindrical shape with one open end and a bottom. The outer can 10 is formed by multi-stage pressing of a nickel-plated steel sheet into a cylindrical shape with one open end and the other closed at the bottom. The outer surface of the bottom wall of the outer can 10 functions as a conductive negative electrode terminal.

[0013] The exterior can 10 accommodates a substantially cylindrical electrode group 12 together with an alkaline electrolyte (not shown).

[0014] The electrode group 12 is composed of strip-shaped positive electrode plates 16, negative electrode plates 18, and separators 20, with the separators 20 sandwiched between the positive electrode plates 16 and negative electrode plates 18 and wound in a spiral shape. The outermost periphery of the electrode group 12 is formed by a part of the negative electrode plates 18. The outermost periphery of the negative electrode plates 18 comes into contact with the inner surface of the peripheral wall of the outer can 10, so that the negative electrode plates 18 and the outer can 10 are electrically connected to each other.

[0015] The positive electrode plate 16 is a strip-shaped electrode filled with a positive electrode active material. Meanwhile, the negative electrode plate 18 is a strip-shaped electrode made of a hydrogen storage alloy. The separator 20 is made of, for example, a polyolefin fiber nonwoven fabric to which a hydrophilic group has been added. The alkaline electrolyte is, for example, a potassium hydroxide aqueous solution, a lithium hydroxide aqueous solution, a sodium hydroxide aqueous solution, or a mixture thereof.

[0016] One end of a current collecting tab 22 is electrically connected to the positive electrode plate 16 near the opening of the outer can 10, and the other end of the current collecting tab 22 is welded to the inner surface of a circular, conductive cover plate 24. The current collecting tab 22 is an example of a current collector. The cover plate 24 has a gas vent hole 26 in the center, and a rubber valve body 28 is disposed on the outer surface of the cover plate 24 so as to cover the gas vent hole 26. Furthermore, a cylindrical positive electrode terminal 30 with a flange that covers the valve body 28 is fixed to the outer surface of the cover plate 24, and the positive electrode terminal 30 presses the valve body 28 against the cover plate 24.

[0017] Therefore, under normal circumstances, gas vent hole 26 is airtightly closed by valve body 28. On the other hand, if gas is abnormally generated inside outer can 10 and the internal pressure increases, valve body 28 is compressed, and the gas is released from outer can 10 through gas vent hole 26. In other words, cover plate 24, valve body 28, and positive electrode terminal 30 form a safety valve.

[0018] The cover plate 24 is located at the opening edge of the outer can 10, and an insulating gasket 32 ​​is sandwiched between the outer periphery of the cover plate 24 and the inner periphery of the outer can 10. The cover plate 24 and the insulating gasket 32 ​​are fixed to the opening edge of the outer can 10 by crimping a portion of the outer can 10 closer to the opening edge than the electrode group 12, and the insulating gasket 32 ​​insulates and seals the outer periphery of the cover plate 24 from the outer can 10.

[0019] 2. Positive electrode plate configuration Next, the configuration of the positive electrode plate 16 will be described in detail with reference to FIGS. As shown in FIG. 2(A), the positive electrode plate 16 is made of two substrates 40 extending in a strip shape in the longitudinal direction, and a current collecting tab 22. The substrates 40 are each made of urethane foam, are porous, and are strips extending in the winding direction of the electrode group 12 as the longitudinal direction. The substrates 40 are plated with a conductive metal such as nickel, not only on the surface but also in the thickness direction. After plating, the substrates 40 have a basis weight of, for example, 100 g / m 2 , or 150 g / m 2The basis weight of the substrates 40 is not limited to these values. In this embodiment, the two substrates 40 have the same size, but this is not necessarily the case. The two substrates 40 are aligned in the longitudinal direction with their wide surfaces 40A facing each other, and are crimped together with the current collecting tab 22 sandwiched between the two substrates 40 as shown in FIG. 2(B), as will be described later.

[0020] As shown in FIG. 3, the current collecting tab 22 is a rectangular piece of conductive metal. As shown in FIG. 2(B), the current collecting tab 22 is disposed on one long edge 40E of the base 40. The current collecting tab 22 is made of, for example, nickel-plated iron or pure nickel. The current collecting tab 22 has a connection region 22A that is crimped to the base 40 and electrically connected. When the two bases 40 are aligned parallel to each other in their longitudinal directions, the connection region 22A of the current collecting tab 22 is sandwiched in a gap G formed when the long edge 40E of one of the two bases 40 is brought close to each other, i.e., the gap G formed when the wide surfaces 40A of each base 40 face each other. The two bases 40 with the current collecting tab 22 sandwiched therebetween are crimped together using a roller press or the like. At this time, the bases 40 are crimped together at the contacting portions. Furthermore, in the portion where the current collecting tab 22 is sandwiched in the gap G of the base 40, the current collecting tab 22 is crimped in the arrangement direction of one base 40, the current collecting tab 22 and the other base 40, and the current collecting tab 22 is fixed to the base 40 and electrically connected.

[0021] Next, the positive electrode active material M is filled into the compressed base 40, that is, the numerous small holes that occupy almost the entire volume of the compressed base 40 are filled with the positive electrode active material M. Therefore, the positive electrode active material M reaches the interface B where the connection region 22A of the current collecting tab 22 and the base 40 come into contact, and the positive electrode active material M is contained in this interface B. Thereafter, the base 40 is rolled to complete the positive electrode plate 16 as shown in FIG. 2(C).

[0022] The positive electrode plate 16 is wound together with the negative electrode plate 18 with a separator 20 interposed between them to form a cylindrical shape, constituting an electrode group 12 with the negative electrode plate 18 located at the outermost periphery of the cylinder. After the electrode group 12 is inserted into the interior of the outer can 10, an alkaline electrolyte is poured into the outer can 10, and a cover plate 24 is placed on the open end of the outer can 10 and crimped to complete the assembly of the battery 1. Thereafter, the battery 1 is activated through an activation process and prepared for use as a power source.

[0023] In the battery 1 fabricated as described above, the positive electrode plate 16 is completed by filling the substrate 40 with a positive electrode active material after the current collecting tab 22 is connected and fixed thereto. Therefore, the positive electrode active material can also be filled at the interface where the current collecting tab 22 and the substrate 40 come into contact. That is, the small holes that make up substantially the entire volume of the substrate 40 to which the current collecting tab 22 is crimped are occupied by the positive electrode active material M. Therefore, compared to conventional positive electrode plates in which the current collecting tab is welded after the positive electrode active material is peeled from the substrate, the formation of voids in the substrate that are free of positive electrode active material between the welded surface of the current collecting tab and the positive electrode active material filled in the substrate is suppressed. This allows the positive electrode active material M to be in direct, planar contact with the connection region 22A of the current collecting tab 22. Furthermore, the amount of positive electrode active material M in direct contact with the current collecting tab 22 is significantly increased. Furthermore, the positive electrode active material M that would have peeled from the substrate 40 in the conventional case can also contribute to the charge / discharge reaction of the battery 1.

[0024] In this way, the battery capacity can be increased by increasing the amount of the positive electrode active material M contained in the positive electrode plate 16 without changing the dimensions of the completed positive electrode plate 16.

[0025] Next, as another embodiment, as shown in FIG. 4 , the connection region 22A of the current collecting tab 22 may be formed with multiple protrusions 22B that protrude toward the opposing wide surface 40A of the base 40. In this case, the surface area of ​​the connection region 22A of the current collecting tab 22 that is crimped to the base 40 is increased. Therefore, the current collecting tab 22 is more firmly attached to the base 40 than in a configuration without the protrusions 22B, thereby increasing the connection strength of the current collecting tab 22 to the base 40. The protrusions 22B may all protrude the same length, or each may protrude by an appropriate length. In the current collecting tab 22 shown in FIG. 4 , there are six protrusions 22B, but the number of protrusions 22B may be any number, and their arrangement in the connection region 22A is not limited to the arrangement shown in the figure and may be any appropriate arrangement.

[0026] Furthermore, since the current collecting tab 22 is sandwiched between two substrates 40, the protrusions 22B may be formed on only one surface of the current collecting tab 22, or on both surfaces. When the protrusions 22B are formed on both surfaces of the current collecting tab 22, the protrusion length of the protrusions 22B may be shorter than when they are formed on only one surface, in order to prevent an increase in the thickness of the positive electrode plate 16.

[0027] 3. Comparison between Examples and Comparative Examples Next, as described below, 1,000 cells each of the batteries of Examples 1 to 3, each including the above-prepared positive electrode plate 16, and the batteries of Comparative Examples 1 to 3, each including a conventionally configured positive electrode plate having the same dimensions as the positive electrode plate 16 of Examples 1 to 3, were fabricated, and their battery characteristics were compared. The battery characteristics were evaluated based on the incidence of fracture of the substrate 40 of the positive electrode plate 16 after the activation process, the 0.1C / 0.2C capacity (the battery capacity when the battery was charged at 0.1C for 16 hours, rested for one hour, and then discharged at 0.2C until fully discharged), and the tab strength. In the characteristic evaluation, "fracture" refers to fracture of the substrate 40 itself at the portion where the positive electrode active material M peeled off from the substrate 40 after the current collecting tab 22 was attached. "Tab strength" refers to the tensile strength required to pull the current collecting tab 22 across the width of the substrate 40 and separate it. In both the batteries of the examples and the comparative examples, the dimensions of the positive electrode plate to which the current collecting tab is attached and which is filled with the positive electrode active material are the same.

[0028] Example 1 Each has a basis weight of 150g / m 2 The two substrates 40 are pressed together with a flat current collecting tab 22 having no protrusions sandwiched therebetween (the basis weight after pressing is 300 g / m 2 After the positive electrode plate 16 was pressed, the positive electrode plate 16 was filled with the positive electrode active material M, and the battery 1 was assembled and activated. No breakage of the positive electrode plate 16 occurred after activation.

[0029] Example 2 Each has a basis weight of 100g / m 2 The two substrates 40 are pressed together with a flat current collecting tab 22 having no protrusions sandwiched therebetween (the basis weight after pressing is 200 g / m 2 After the pressure bonding, the battery 1 was assembled and activated using the positive electrode plate 16 filled with the positive electrode active material M. No breakage of the positive electrode plate 16 occurred after the activation process.

[0030] Example 3 Each has a basis weight of 100g / m 2 The two substrates 40 are pressed together with the current collecting tab 22 having the plurality of protrusions 22B sandwiched therebetween (the basis weight after pressing is 200 g / m 2 After the pressure bonding, the battery 1 was assembled and activated using the positive electrode plate 16 filled with the positive electrode active material M. No breakage of the positive electrode plate 16 occurred after the activation process.

[0031] (Comparative Example 1) Weight 350g / m 2 A single substrate made of urethane foam was filled with positive electrode active material, and the positive electrode active material on the substrate surface to which the current collecting tab was welded was peeled off. A current collecting tab with multiple protrusions was then welded to the substrate to complete the positive electrode plate, which was then used to assemble and activate a battery. The incidence of positive plate fracture was 0.10% of the assembled batteries, i.e., 1 in 1,000 batteries.

[0032] (Comparative Example 2) Weight 300g / m 2A single substrate made of urethane foam was filled with positive electrode active material, and the positive electrode active material on the substrate surface to which the current collecting tab was welded was peeled off. A current collecting tab with multiple protrusions was then welded to the substrate to complete the positive electrode plate, and a battery was assembled and activated using this positive electrode plate. The incidence of positive electrode plate fracture was 0.20%.

[0033] (Comparative Example 3) Weight 200g / m 2 A single substrate made of urethane foam was filled with positive electrode active material, and the positive electrode active material on the substrate surface to which the current collecting tab was welded was peeled off. A current collecting tab with multiple protrusions was then welded to the substrate to complete the positive electrode plate, and a battery was assembled and activated using this positive electrode plate. The incidence of positive electrode plate fracture was 1.20%.

[0034] FIG. 5 shows the battery characteristics of the batteries of Examples 1 to 3 and Comparative Examples 1 to 3. As shown in FIG. 5, the 0.1C / 0.2C capacity and tab strength of the other Examples and Comparative Examples were evaluated using the measurement data of Comparative Example 1 as the reference (100%). The 0.1C / 0.2C capacity was 102% for Example 1, 105% for Example 2, and 105% for Example 3, indicating that the battery capacity increased in all the batteries. The tab strength was 100% for Example 1, 100% for Example 2, and 111% for Example 3. The tab strength of Examples 1 and 2 was the same as that of Comparative Example 1, but the same tab strength could be obtained even when using a substrate with a lighter basis weight than that of Comparative Examples 1 and 2, as in Examples 1 and 2.

[0035] 4. Discussion 5, in all of the batteries of Examples 1 to 3, the current collecting tab is sandwiched between two substrates and crimped, and then the positive electrode active material is filled in to create the positive electrode plate, thereby preventing the substrate from breaking. This is thought to be because the positive electrode active material filled in the substrate is not peeled off, so no load is applied to the substrate, and the strength of the substrate can be maintained.

[0036] Furthermore, since the positive electrode active material is not peeled off from the substrate, the total amount of positive electrode active material contained in the total capacity of the substrate can be made larger than the total amount of positive electrode active material in a positive electrode plate of a conventional configuration, leading to an increase in battery capacity. Furthermore, the substrate weight of Battery 1 of Embodiments 1 to 3 is lighter than the substrate weight of either of the batteries of Comparative Examples 1 and 2, thereby achieving a reduction in the weight of the entire battery.

[0037] 5. Further Embodiments In the embodiment described above, the positive electrode plate 16 is fabricated by placing two substrates 40 facing each other and crimping the current collecting tab 22 between the substrates 40. In another embodiment, as shown in FIG. 6 , a strip 44 made of urethane foam extending in the longitudinal direction is folded in half along a center line C equidistant from widthwise edges 44A and 44B perpendicular to the longitudinal direction, so that one edge 44A and the other edge 44B are close to each other, to form the substrate 140 of the positive electrode plate 16′. The width of the substrate 140 made of the folded strip 44 is approximately the same as the width of the strip-shaped negative electrode plate 18 wound around the positive electrode plate 16′ fabricated from the substrate 140 and the separator 20 interposed therebetween.

[0038] The current collecting tab 22 is sandwiched in a gap G1 formed by opposing one edge 44B and the other edge 44B of the base 140, which is made of the folded strip 44, and the base 140 and the sandwiched current collecting tab 22 are then crimped. The other components and configuration of the battery 1 are the same as those of the above embodiment. Also, in this embodiment, as with the battery 1 of the above embodiment, the positive electrode active material is not peeled off, but is filled in after the current collecting tab 22 is attached to the base 140, thereby achieving an increase in battery capacity. [Explanation of symbols]

[0039] 1 battery 16 Positive electrode plate 22 Current collector 40 Substrate 40A wide surface 40B Interface M Positive electrode active material

Claims

1. two porous, metal-plated substrates each extending in a strip shape in the longitudinal direction and with their wide surfaces facing each other; a rectangular current collector attached to the substrate; a positive electrode active material filled in the two substrates in a state in which the current collector is sandwiched between the two substrates and compressed; and The positive electrode plate for a secondary battery, wherein the positive electrode active material reaches an interface where the current collector and the substrate are in contact with each other.

2. 2. The positive electrode plate according to claim 1, wherein the current collector has a plurality of protrusions that protrude toward the substrate at a portion facing the broad surface of the substrate.

3. 3. The positive electrode plate according to claim 2, wherein said plurality of protrusions are formed only on a portion of one of said substrates facing a broad surface.

4. 4. A cylindrical secondary battery comprising an electrode group formed by winding the positive electrode plate according to claim 1 and a strip-shaped negative electrode plate facing the positive electrode plate with a separator interposed therebetween, the electrode group being housed in an outer can.

5. A positive electrode plate for a secondary battery that is wound between a negative electrode plate and a separator interposed therebetween to form an electrode group, a porous, metal-plated substrate consisting of a strip extending in a longitudinal direction, the strip being bent at approximately the center of the width perpendicular to the longitudinal direction of the strip about a line extending parallel to the longitudinal direction, so that one flat portion and the other flat portion overlap each other and face each other; a rectangular current collector attached to the substrate; a positive electrode active material filled in the base in a state in which the current collector is sandwiched and compressed between the one flat portion and the other flat portion that are folded and overlapped; and the positive electrode active material is contained at an interface where the current collector is in contact with the substrate, A positive electrode plate for a secondary battery, wherein the width of the bent substrate perpendicular to the longitudinal direction is the same as the width of the negative electrode plate perpendicular to the longitudinal direction.

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