JP4530693B2 - Alkaline secondary battery - Google Patents

Description

  The present invention relates to an alkaline secondary battery containing manganese as a negative electrode active material, and more particularly to a technique for suppressing deterioration of self-discharge characteristics and occurrence of short circuit during long-term use.

  In recent years, alkaline secondary batteries are not only portable devices that can be used repeatedly, but also power tools, power supplies that can charge and discharge large currents in a short time, such as electric vehicles or electric vehicles and hybrid electric vehicles. It is attracting attention as. In particular, a nickel-metal hydride secondary battery (hereinafter referred to as “battery”) having a positive electrode made of an active material mainly composed of nickel hydroxide and a negative electrode made of a hydrogen storage alloy as an active material has high energy density and reliability. It is rapidly spreading as a secondary battery with excellent characteristics.

  A cylindrical electrode body is often used as the alkaline secondary battery structure. This is a system in which an electrode body formed by winding a strip-like positive electrode plate and a negative electrode plate in a spiral shape through a separator is inserted into an exterior body together with an electrolytic solution. Alkaline secondary batteries are increasingly used for large-current discharge, so various developments have been made to supply a large amount of power. It has been found that a large current can be discharged by increasing the area to be used (for example, Patent Document 1). Furthermore, in order to increase the conductivity of the positive electrode plate active material, a cobalt compound or the like is added to the positive electrode active material, and a hydrogen storage alloy containing cobalt or manganese is often used as the negative electrode plate active material.

However, the battery has a problem that the self-discharge characteristics deteriorate when the charge / discharge cycle is repeated. It is considered that this is because the metal component eluted from the positive electrode and the negative electrode is deposited on the separator to form a conductive path, which is a factor that deteriorates the self-discharge characteristics.
For example, in a battery comprising a positive electrode containing a cobalt compound containing nickel hydroxide as a main component and a negative electrode using a hydrogen storage alloy containing manganese as an active material, cobalt elution from the positive electrode due to repeated charge and discharge, and a hydrogen storage alloy Cobalt-manganese compounds are deposited on the separator due to manganese elution by oxidation. Thereby, the self-discharge characteristic of the battery deteriorates and eventually short-circuits. In this case, since long-term reliability of the battery is lacking, it has been proposed to reduce the manganese content of the hydrogen storage alloy in order to suppress the amount of this compound deposited.
JP 2002-170548 A

  However, if the manganese content of the hydrogen storage alloy is reduced, the amount of precipitation of cobalt-manganese compounds on the separator is reduced, so the self-discharge characteristics of the battery are improved. Precipitation is likely to occur. The produced compound is highly conductive and tends to induce an increase in the amount of cobalt-rich cobalt-manganese compound deposited, particularly when charging and discharging a large current in a short time. When charging and discharging a large current over a long period of time under the above conditions, a short circuit occurs suddenly in the battery, and in addition to losing the power function due to the inability to charge and discharge, the battery overheats due to the short current inside the battery, The number of cases that pose a danger to the user increases.

  In view of the above problems, the present invention reduces the amount of manganese contained in the hydrogen storage alloy and reduces the self-discharge characteristics of the battery even when a battery that charges and discharges a large current is used over a long period of time. An object of the present invention is to provide a battery that can suppress the occurrence of a sudden short circuit while suppressing it.

In the present invention, the means for solving the above-mentioned problems are adopted as follows.
An alkaline secondary battery having an electrode body in which a strip-like positive electrode plate containing a cobalt compound and a negative electrode plate having an active material containing manganese are wound in a longitudinal direction with a separator interposed therebetween, wherein the manganese content is The maximum amount is 3.0% by mass with respect to the negative electrode active material, and the positive electrode plate and the negative electrode plate have a length ratio of at least 15 in the longitudinal direction and the short direction in the overlapping region.

  The negative electrode plate has a core body filled with the active material, and a core body exposed portion is provided at one of both ends of the core body in the short side direction. Electrical body is welded. In addition, the positive electrode plate is also filled with the active material in the core body, and a core body exposed portion is provided at either end of the core body in the lateral direction, and each of the positive electrode plate and the negative electrode plate The core exposed portion protrudes from the upper and lower ends in the lateral direction of the separator, and the plate-shaped current collector is welded to each protruding core exposed portion.

In addition, the phenomenon that local cobalt-manganese compounds are deposited near both ends of the separator in the short direction is due to the fact that an electrode plate used for medium / high current applications is directly applied to the current collector at the end of the core. This is particularly noticeable in the structures to be welded. Also from these things, the structure where the plate-shaped collector is welded to the edge part of the transversal direction of the core of a negative electrode plate is more preferable.
In addition, the present invention is not limited to the wound electrode body, and the laminated electrode body may be used as long as the ratio of the length in the longitudinal direction and the length in the lateral direction of the overlapping region of the positive and negative electrode plates satisfies the above range. It can also be applied to.

The present inventors have discovered the cause of the occurrence of the sudden short circuit. This will be described with reference to FIG. 2 showing a schematic plan view of a positive electrode plate, a negative electrode plate, and a separator that form a wound electrode body. In FIG. 2, the X direction is the positive electrode plate 11, the negative electrode plate 13, and the separator 12 are strip-like short directions, and the Z direction is the winding direction.
In a state where the amount of manganese contained in the hydrogen storage alloy is reduced, the battery is repeatedly used over a long period of time as a power source for charging and discharging a large current, and when the battery shorted as described above is examined, as shown in FIG. It was found that cobalt-rich cobalt-manganese compound 14a was locally deposited in the vicinity of both end portions in the Z direction of separator 12, and this caused the above-described sudden short circuit of the battery. It has also been found that the generation of such a manganese compound 14a is related to the current density flowing in the electrode plate. That is, the non-uniform distribution of current density in the electrode plate, that is, the region where the positive electrode plate 11 and the negative electrode plate 13 overlap because the current collector is welded to either of the Z direction both ends of the negative electrode plate 13 Thus, the high current density at both ends in the Z direction is considered to be the cause of the generation of cobalt-rich manganese compounds. Note that the phenomenon in which this non-uniform current density occurs is not conspicuous when charging / discharging a small current, but appears prominently when charging / discharging a large current.

  In the present invention, the self-discharge characteristic of the battery is improved by setting the manganese content of the hydrogen storage alloy as the negative electrode active material to 3.0% by mass at the maximum. At the same time, the power source that repeatedly charges and discharges large currents over a long period of time by setting the ratio of the length in the longitudinal direction to the length in the short direction in the overlapping portion of the positive electrode plate and the negative electrode plate having a strip shape. Even in this case, since it is possible to prevent the cobalt-rich cobalt-manganese compound from being deposited at a high density in the vicinity of the current collector welding, it is possible to prevent a sudden short circuit from occurring in the battery. This is presumably because the length of the overlapping region in the longitudinal direction becomes longer and the length in the lateral direction becomes shorter, so that the value of the current density per unit length in the longitudinal direction becomes smaller. From the above points, the self-discharge performance in the battery having the configuration of the present invention is improved, and the lifetime reduction of the battery is suppressed.

(Battery configuration)
This embodiment will be described with reference to FIGS. FIG. 1 is a developed perspective view of a main part of a wound electrode body 10. FIG. 2 is a schematic plan view showing a positive electrode plate, a negative electrode plate, and a separator developed after the battery is used as a power source for large current discharge for a long period of time. In FIG. 2, the cobalt-rich cobalt / manganese compound 14b deposited on the separator 12 is deposited in a substantially uniform distribution in the overlapping region. The longitudinal direction of the electrode plate is the X direction, and the short direction is the Z direction. For each side of the positive electrode plate 11, the negative electrode plate 13, the separator 12, and the belt-like side in the overlapping region of the positive electrode plate 11 and the negative electrode plate 13, the Z direction is referred to as the short side and the X direction is referred to as the long side. The ratio of the long side length to the length (= long side length / short side length) is referred to as the long / short side ratio. However, in FIG. 2, for the sake of convenience, the relative positional relationship between the positive electrode plate 11, the negative electrode plate 13, and the separator is schematically illustrated so that the separator 12 can be expressed more effectively.
(Configuration and production of electrode body 10)
The electrode body 10 has a configuration in which a positive electrode plate 11 and a negative electrode plate 13 having a strip shape as shown in FIG. The X direction is the axial direction, and the longitudinal direction of the positive electrode plate 11, the negative electrode plate 12, and the separator 13 is the Z direction.

In addition, since the current collector 4 is joined to both ends of the electrode body 10 in the X direction, the welding points of the negative electrode plate 13 with the current collector 4 are provided at either end of the X direction.
The porous nickel sintered substrate is immersed in a nitrate aqueous solution containing nickel (Ni), cobalt (Co), and zinc (Zn), then immersed in a constant temperature alkaline aqueous solution, and then dried repeatedly multiple times to mix hydroxide. To form. Then, the cathode plate 11 is prepared by cutting the short side into a dimension having a width of 49.5 mm with an active material unfilled portion of 1.0 mm and a long side length of 730 mm.

  After heat-treating a hydrogen storage alloy with a manganese content of 2.6 mass% at 1100 ° C in an inert gas atmosphere, the weight average particle size is 25? Crushed so that 0.6 mass% PVP (polyvinyl pyrrolidone), 0.5 mass% PEO (polyethylene oxide) and an appropriate amount of pure water are mixed to form a slurry, which is then applied to a punching metal, dried and rolled. Let Then, the negative electrode plate 13 is formed by cutting the active material unfilled portion 1.0 mm having a short side into a width of 49.5 mm and the long side having a length of 800 mm.

Then, the positive electrode plate 11 and the negative electrode plate 13 produced as described above are shifted so that the active material uncoated portions of the positive and negative electrodes protrude upward and downward in the X direction through a polypropylene separator 12 having a width of 51 mm, respectively. The electrode body 10 is formed by winding the plate 11 and the negative electrode plate 13 so that the long-short side ratio is 15 in the active material overlapping region.
After inserting the electrode body into the case, the negative electrode side current collector is welded to the bottom of the battery can, the positive electrode side current collector is welded to the sealing plate via the lead parts, and 30% by mass potassium hydroxide (KOH) is electrolyzed. A battery is assembled by injecting a predetermined amount as a liquid and sealing. These dimensions are examples of the present invention, and the method of welding the current collector 4 is also an example, and the present invention is not limited to these.
(Experiment)
(Example 1)
Experiments described later on the battery produced as described above are conducted to examine the hydrogen storage alloy manganese content and the shape of the electrode plate. The details of the experiment are described later.
(Example 2) to (Example 4) and (Comparative Example 1) to (Comparative Example 12) are the manganese content in the hydrogen storage alloy, and the positive electrode plate 11 and the negative electrode plate 13 in Example 1. Except for assembling by setting the positive electrode plate dimensions, the negative electrode plate dimensions, and the positive and negative electrode shift widths at the time of winding so that the ratio of the long and short sides of the superimposing region becomes the values described in Tables 1 to 5 (Examples) The battery has the same configuration as in 1).
(Experiment contents)
The contents of the experiment in each of the above cases are as follows.

First, a cycle test that repeats 50A intermittent charging / discharging for 3 months while controlling the state of charge (SOC) within a range of 20 to 80% in a 45 ° C temperature atmosphere did.
Next, the battery characteristics after cycling were as follows: 80% charge at 1 It (hour rate discharge current) current in a 25 ° C atmosphere, and discharge until the battery voltage reached 1.0 V at 1 It across a 3-hour pause Is the reference capacity.

Charge again 80% at a current of 1 It in a 25 ° C atmosphere, then leave it for 1 hour in a 45 ° C atmosphere, then pause for 3 hours in a 25 ° C atmosphere, and then the battery voltage reaches 1.0 V at 1 It. Let the discharged capacity be the capacity after standing.
Then, an experiment was conducted in which the percentage of the capacity after being left with respect to the reference capacity was evaluated as an index of self-discharge characteristics. The evaluation results are shown in Tables 1 to 5. However, the post-cycle short-circuit rate indicates the ratio of the number of cells short-circuited with respect to the total number of 20 after cycle evaluation of 20 batteries.
(Discussion on the results of this experiment)
Using Tables 1 to 5 and FIG. 4, the influence of the manganese content contained in the hydrogen storage alloy, which is the active material of the negative electrode plate 13, on the self-discharge characteristics, the experimental results and considerations in each of the above cases. State. Table 1 shows the values of the self-discharge characteristics of the battery accompanying the change in manganese content when the long / short side ratio in the overlapping region of the positive electrode plate 11 and the negative electrode plate 13 is 15. Similarly, Table 2, Table 3, and Table 4 show the values of the self-discharge characteristics of the battery as the manganese content changes when the ratio of the long side to the short side is 20, 5, and 10, respectively. Table 5 shows the short-circuit rate of the battery after cycling for each long / short side ratio in the overlapping region of the positive electrode plate 11 and the negative electrode plate 13. FIG. 4 plots the results of the self-discharge characteristics of the batteries obtained in Tables 1 to 4 for each table. In FIG. 4, the horizontal axis indicates the ratio between the long and short sides of the overlapping region of the positive electrode plate 11 and the negative electrode plate 13, and the vertical axis indicates the value of the self-discharge characteristic of the battery. Further, the plotted points A1, A2, A3, A4 show the experimental results in Example 1, Example 2, Example 3, and Example 4, respectively, and other plotted points a1, a2,. .., A12 indicate experimental results in Comparative Example 1, Comparative Example 2,..., Comparative Example 12, respectively.

  According to Tables 1 to 4, it is shown that the self-discharge characteristics of the batteries are all improved as the manganese content decreases. Further, also in FIG. 4, from the curve 101 when the manganese content is 2.6 mass%, similarly from the curve 102 of 3.0 mass%, the curve 103 of 3.1 mass%, the curve 104 of 3.5 mass%, the decrease in manganese content Accordingly, it is clear that the self-discharge characteristics of the battery are improved. However, the evaluation of the self-discharge characteristics of the battery is performed only for the battery except for the one that causes a short circuit as described later.

Based on the effect on the self-discharge characteristics of the battery accompanying the decrease in manganese content as described above, further discussion will be described using Table 5. Table 5 shows the short circuit after the cycle that occurs when the long / short side ratio in the overlap region of the positive electrode plate 11 and the negative electrode plate 13 is 15, 20, 5, 10 when the manganese content shown in Tables 1 to 4 is used. The ratio is shown. As described above, the results shown in Tables 1 to 4 and FIG. 4 are the evaluation results except for the short-circuited, and actually the long / short side ratio is 15 as shown in Table 5. If it is smaller than that, a short circuit has occurred in the battery after the cycle. That is, when a battery that discharges a large current is used repeatedly, the possibility of occurrence of a short circuit increases, and the reliability of the battery for long-term use decreases. Therefore, when reducing the amount of manganese contained in the hydrogen storage alloy, it is desirable to use a battery having a long / short side ratio of 15 or more.
(Advantages of the present invention)
From the above consideration, if the manganese content contained in the hydrogen storage alloy used as the active material of the negative electrode plate 13 is at most 3.0 mass%, and the ratio of the long and short sides in the overlapping region of the positive electrode plate 11 and the negative electrode plate 13 is 15 or more For example, since the self-discharge characteristic of the battery 100 is maintained in a good state and does not cause a sudden short circuit, even if the battery is used as a power source that discharges a large current, the battery 100 is reliable over the long term. Can keep sex.

  When manufactured under conditions such as the present invention, the current density considered to be strongly distributed on both ends of the X direction on the separator will be relaxed, and the cobalt-rich cobalt Unlike the precipitation of the manganese compound 14a locally at a high density, as shown in FIG. 3, the dispersion is relaxed over the entire overlapping region of the positive electrode plate 11 and the negative electrode plate 13 in the separator 12, and the cobalt rich at a substantially uniform low density. Cobalt / manganese compound 14b is deposited. The generation of such precipitates does not cause a short circuit of the battery even when a large current is discharged, so that the battery can be used for a long period of time while maintaining good self-discharge characteristics.

In the battery having the shape according to the present invention, it is sufficient that manganese is contained in the hydrogen storage alloy to some extent. Further, the long / short side ratio in the overlapping region of the positive electrode plate 11 and the negative electrode plate 13 can be applied even when the value of the long / short side ratio is 100, for example, and the larger the value, the better.
(Other matters)
In the present embodiment, an electrode body in which the positive electrode plate 11 and the negative electrode plate 13 are wound via the separator 12 is used as an example. However, the present invention is not limited to this. For example, even a layered structure can be applied.

  The present invention is particularly useful for realizing an alkaline sealed secondary battery that requires a large current output, such as a hybrid electric vehicle.

3 is an exploded perspective view of a main part of the electrode body unit 10. FIG. It is a schematic plan view which shows the shape of the electrode plate which forms the conventional electrode body which generate | occur | produced the short circuit. It is a schematic plan view which shows the shape of the electrode plate which forms the electrode body in this invention. 6 is a graph showing experimental results of evaluating self-discharge characteristics with respect to a long / short side ratio in an overlapping region of a positive electrode plate 11 and a negative electrode plate 13 with respect to the present invention.

Explanation of symbols

4 Current collector
10 Electrode body
11 Positive electrode plate
12 Separator
13 Negative electrode plate

Claims (1)

And band-like positive electrode plate having an active material containing a cobalt compound, a negative electrode plate of the strip with an active material containing manganese have a electrode body formed by sandwiching a separator, charging state is maintained within the range of 20-80% An alkaline secondary battery that repeats intermittent charge and discharge while performing control ,
The positive electrode plate has a core body filled with the active material, and a core body exposed part is provided on one of both ends of the core body width direction,
The negative electrode plate has a core body filled with the active material, and a core body exposed part is provided on the other end of the core body width direction ,
The core exposed portions of the positive electrode plate and the negative electrode plate protrude from the upper and lower ends in the width direction of the separator, respectively.
A plate-like current collector is welded to each protruding core exposed portion,
The manganese content is 3.0% by mass at the maximum with respect to the negative electrode active material,
The alkaline secondary battery, wherein the positive electrode plate and the negative electrode plate have a length ratio of at least 15 in the longitudinal direction in the overlapping region.

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