JP2001319683A - Square alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a square alkaline storage battery using a bag-shaped separator, this is excellent in high-rate characteristics and cycle characteristics, by increasing absorption function of gas generated within an electrode group at the time of charge. SOLUTION: This alkaline storage battery is laminated with a positive electrode and a negative electrode having a tab for current collection on the flank side, and at least one of the electrodes is packaged with a bag-shaped separator. On the upper side of the bag-shaped separator, an opening is arranged, and the ratio between the length of the opening and the length of the upper side is set to be 0.5-0.8. In this way, the movement of the generated gas is accelerated and gas absorbing function can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a rectangular battery case,
The present invention relates to a prismatic alkaline storage battery having improved cycle characteristics and high-rate characteristics.

[0002]

2. Description of the Related Art In recent years, a battery having a high energy density, a high output, and a long life has been demanded as a power source of an electric vehicle (EV) or a hybrid electric vehicle (HEV). Conventional batteries for consumer use are mainly small batteries, and there is a demand for the development of large capacity batteries for EVs and HEVs.

[0003] In a small alkaline storage battery for consumer use,
Conventionally, cylindrical batteries have been the mainstream. When attempting to increase the size of a cylindrical battery, there is a problem in manufacturing technology such that it is extremely difficult to wind a large electrode group. Furthermore, since the gap between the batteries in the assembled battery is large, there is a characteristic defect that the volume efficiency is inferior.

A stacked electrode group applied to a prismatic battery is suitable for manufacturing a large electrode group. Further, when a prismatic battery is used as an assembled battery, there is an advantage that the volume efficiency can be increased because no gap is formed between the batteries. Further, in order to save floor space and effectively utilize space, it is advantageous to increase the height of the battery. For this purpose, the electrodes must be vertically long according to the shape of the battery.

[0005] In a conventional battery, a current collecting tab is arranged on the upper side of the electrode. When the tab is arranged at the upper end of the vertically elongated electrode as described above, a difference in current collection efficiency occurs between the upper and lower portions of the electrode based on the difference in electric resistance of the electrode. In order to reduce the difference in current collection efficiency, a structure in which a tab is arranged on a side of an electrode has been proposed.

In the case of a stacked electrode group, it is possible to prevent positional displacement by wrapping one of the electrodes in a bag-like separator in advance, as compared with sequentially stacking a positive electrode, a separator, and a negative electrode. It is possible to increase. Here, the bag shape is a rectangular shape in which one side is open and the other three sides are closed, the electrode does not protrude from the three sides, and has a function of fixing the electrode position on the three sides. is there.

It is known to apply a bag-shaped separator having an open side. Since it is necessary to connect the electrode tab and the current collecting terminal, the opening side of the separator and the position of the electrode tab are conventionally made to match. Conventionally, when a bag-shaped separator is applied to an electrode having a tab on a side, the opening side of the separator is set to the side and the other three sides including the upper side are closed.

[0008] When the bag-shaped separator is applied to the battery as described above, since the upper side is closed, the discharge / discharge is performed as described later.
It was found that the charging efficiency was low and the cycle characteristics were inferior. It was presumed that the gas generated in the electrode group during charging stayed in the separator and gas absorption was hindered, which had an adverse effect.

The generated gas has the property of being immediately transferred to the upper part of the pole group. For this reason, even if the side of the separator is open, if the upper side is closed, the gas generated in the electrode group is prevented from leaking upward, and the gas absorption performance is deteriorated. As is well known, a battery having a poor gas absorption function in an alkaline storage battery has poor cycle characteristics. Further, the generated gas stays in the upper portion of the separator to form a gas reservoir, which causes an increase in the internal resistance of the battery, leading to a decrease in high-rate characteristics.

[0010]

In a conventional battery of the type in which tabs are arranged on the side surfaces of the electrode group, since there is no opening on the upper side of the separator, the transfer of gas generated in the electrode group is hindered. And high rate characteristics were inferior. The present invention provides an alkaline storage battery having excellent cycle characteristics and high rate characteristics by forming an opening on the upper side with respect to a bag-like separator applied to an electrode having a tab on the side, thereby facilitating the transfer of gas. is there.

[0011]

SUMMARY OF THE INVENTION In a battery having a group of electrodes having current collecting tabs arranged on side surfaces thereof and at least one of a positive electrode and a negative electrode constituting the group of electrodes being wrapped with a bag-shaped separator, By forming an opening in the upper side of the separator, the transfer of gas is expedited.

Furthermore, the ratio of the length of the opening of the separator to the length of the upper side of the separator is 0.5 to 0.8, and the gas transfer is impaired by dividing the opening into two or more parts. In addition, the present invention provides a battery which has a function as a bag to a separator and has excellent workability in an electrode group assembling process.

[0013]

2 and 3 show, as an example, a form in which a positive electrode is packaged with a bag-like separator according to the present invention. The present separator 1 has an opening 2 on the upper side.
The positive electrode 6 is packaged in a bag-like separator so that the opening side 5 is located on the tab 7 side provided on the side of the positive electrode 6. In FIG. 2, the lower side 4 is folded in two and sandwiches the electrode. A bag is formed by providing the fused portion 3 on a part of the side and the upper side.

In the bag-type separator of the fusion type shown in FIG. 2, the upper side of the separator is intermittently fused so that the ratio of the opening 2 to the length of the upper side of the separator is 0.5 to 0.8. It is desirable that the upper side fusion site is at least three locations, that is, at least one location at both ends and an intermediate location. A larger ratio of the openings on the upper side of the separator is advantageous for the transfer of the generated gas. However, there is no function as a bag in a completely open state where the ratio of the openings is 1.0. If the separator does not have a function as a bag, it is difficult to position the electrodes, so that the workability of the laminating step is deteriorated and the electrodes are displaced. Displacement of the electrodes leads to the disadvantages described below.

In the case where the length of the upper side of the separator is relatively small, that is, 20 to 30 mm or less, even if there is only one opening, no trouble occurs. However, when there is only one opening, a shape in which the fusion spot is biased to one side may be considered. In particular, when the length of the upper side exceeds 30 mm, it is preferable to provide at least one fused portion in the middle in order for the separator to function as a bag. In consideration of such an example, it is preferable that the upper side opening is divided into two or more pieces.

The displacement of the electrodes hinders the regular opposition of the positive electrode and the negative electrode, leading to a reduction in the utilization factor. In addition, the outer dimensions of the electrode group become large, which causes problems such as not being able to fit in a battery case. Further, if the electrode protrudes from the separator, it may cause a short circuit.

If the ratio of the opening 2 on the upper side of the separator exceeds 0.8, the bonding strength is weak, so that the bonding may be broken in the assembling process and the function as a bag may not be maintained. When the ratio of the openings is less than 0.5, the characteristics are improved as compared with the case without the openings, but the effect is small because the gas transfer is insufficient.

In addition to the above-mentioned fusion method, there is also a method in which the upper side is a bent portion 4 as shown in FIG. 3, and the bent portion 4 is provided with an opening 2 by punching or cutting. By providing the fusion parts 3 on the side and lower sides, a bag-shaped separator can be formed. In this method, as in the fusion method, the ratio of the length of the opening 2 provided on the upper side by punching or cutting to the length of the upper side of the separator is 0.5 to 0.8.
Is desirably within the range. Further, it is desirable that the punching holes and the cut portions are intermittently arranged at two or more places.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. External dimensions are 54mm wide, 80mm high, 20m thick
m and a battery having a nominal capacity of 10 Ah. Hereinafter, the configuration of the present battery will be described in detail.

FIG. 1 is a perspective view showing a pole group of a prismatic alkaline storage battery according to one embodiment of the present invention. The positive electrode is not visible because it is wrapped in the bag-like separator 1 but has a thickness of 0.5 mm.
Paste-type nickel electrode with a capacity density of 500 mAh
/ Ml. The negative electrode 8 is a steel plate type hydrogen storage alloy electrode having a thickness of 0.3 mm. The size of the positive and negative electrodes 8 is 48m in width
m, a height of 75 mm, and both poles have a 2 mm wide active material non-filled portion on the side. A 0.3 mm thick Ni plate is attached on the unfilled portion by seam welding to form a positive electrode tab 7 and a negative electrode tab 9. As shown in the figure, the positive electrode tab 7 and the negative electrode tab 9 are arranged so as to be on opposite side surfaces. The positive electrode and the negative electrode 8 are alternately stacked while being shifted from each other by 2.5 mm in the width direction. The number of electrodes is 12 for the positive electrode, 13 for the negative electrode, and a negative electrode disposed outside. A positive electrode current collecting terminal 10 is provided on the positive electrode tab 7,
A negative electrode current collecting terminal 11 is attached to the negative electrode tab 9 by series welding. The positive current collecting terminal 10 and the negative current collecting terminal 11 are made of nickel having a thickness of 0.3 mm.

As shown in FIGS. 2 and 3, the positive electrode 6 is wrapped in the bag-like separator 1. The separator 1 is made of a polypropylene (PP) porous film having a thickness of 0.15 mm. One side of the parerator 1 is an opening side 5 so that the tab 7 of the positive electrode 6 protrudes. Although omitted in FIG. 1 because it is small, the separator 1 has an opening 2 on the upper side as shown in FIGS.

(Example 1) As a separator, a fusion type separator shown in FIG. 2-1 was applied. The separator is 48m wide
After cutting to 156 mm in m length, it was folded in two and the positive electrode was sandwiched. Of the four sides of the separator, two sides other than the tab mounting side of the positive electrode and the folded side of the separator were fused.
The upper side was fused with a fusion width of 1 mm, 3 mm from both ends, and only a central portion of 4 mm to provide two openings having a length of 19 mm. The ratio of the length of the opening to the length of the upper side of the separator is 0.8.

The positive electrode and the negative electrode wrapped in the separator were alternately laminated to form the electrode group shown in FIG. After inserting this electrode group into a rectangular resin battery case, a predetermined amount of an electrolyte mainly containing a KOH aqueous solution was injected. A completed battery was obtained by welding a lid having an exhaust valve. This battery is designated as A.

(Example 2) The upper side of the separator was fused 8 mm from both ends and the center 8 mm, and two openings 12 mm long were provided. The ratio of the length of the opening to the length of the upper side of the separator is 0.5. Otherwise, the configuration was the same as that of the first embodiment. This battery is designated as B.

Example 3 The upper end of the separator was fused at 16.8 mm from both ends, and one opening having a length of 14.4 mm was provided. Otherwise, the configuration was the same as that of the first embodiment. The ratio of the length of the opening to the length of the upper side of the separator is 0.3. This battery is designated as C.

(Comparative Example) The upper side of the separator was fused over the entire length, and no opening was provided. Otherwise, the configuration was the same as that of the first embodiment. This battery is designated as D.

(Evaluation of High Rate Discharge Characteristics)
Four types of batteries C and D were subjected to a high-rate discharge test. The test was performed at room temperature. In the test, the battery was first charged at a constant current of 10 A for 1.1 hours, and then discharged at a constant current of 100 A until the final voltage reached 0.85 V. The results of this test were evaluated based on the ratio of discharge capacity / charge capacity and indicated as discharge / charge efficiency. Table 1 shows the results.

[0028]

[Table 1]

As shown in Table 1, the batteries A, B, and C of the present invention
All showed higher efficiency than the comparative battery D. The results show that the higher the ratio of the length of the opening on the upper side of the separator, the higher the efficiency. In particular, Battery A of the present invention and Battery B of the present invention
In the case of Efficiency, the efficiency was almost 85% or more, showing an excellent value. The battery C of the present invention having an opening ratio of 0.3 shows a higher value than the comparative battery D having the same ratio of 0. However, the effect of providing the opening on the upper side of the separator is smaller than that of the batteries A and B of the present invention. This is because the ratio of the openings is insufficient. In consideration of this result and the mechanical strength of the upper fused portion of the separator, the ratio of the length of the opening to the length of the upper portion of the separator is particularly preferably 0.5 to 0.8.

The results shown in Table 1 show that in the battery of the present invention, as described above, the gas generated on the surface of the positive electrode during charging rose inside the electrode group and escaped upward through the opening provided on the upper side of the separator. In the comparative battery D, since there was no opening in the separator, gas stayed in the separator and the internal resistance of the battery increased, so that the discharge capacity decreased.

(Evaluation of cycle characteristics) Next, the battery A of the present invention
And Comparative Battery D were subjected to a charge / discharge cycle test. The test was performed at room temperature, and charging was performed at a low current of 10 A for 1.1 hours.
Discharge was performed at a low current of 10 A and a final voltage of 1 V.

FIG. 4 shows the results. As shown in the figure, the cycle life of the battery A of the present invention was improved by about 15% as compared with the comparative battery D. Comparing the battery A of the present invention with the comparative battery D, in the case of the battery of the present invention, as described above, the oxygen gas generated at the positive electrode during charging smoothly moved to the negative electrode side and the cycle passed because the gas absorption efficiency at the negative electrode was high. Even so, the decrease in capacity is small. On the other hand, in the comparative battery, it is presumed that the transfer of oxygen gas generated at the positive electrode to the negative electrode is hindered by the separator, and the gas absorption efficiency is low.

[0033]

According to the first aspect of the present invention, in an alkaline storage battery having a stacked electrode group, by providing an opening on the upper side of a bag-shaped separator enclosing the electrodes, gas generated in the electrode group during charging can be transferred. It is possible to provide a battery which is quick and has excellent high rate discharge performance and cycle performance. According to the second aspect of the present invention, the ratio of the length of the opening provided on the upper side of the separator to the length of the upper side of the separator is 0.5 to 0.5.
By setting the ratio to 0.8, the function of claim 1 can be enhanced without impairing the function of the bag-like separator for fixing the position of the electrode. According to the third aspect of the present invention, since a plurality of openings are provided, the function as a bag-shaped separator can be maintained even when the width of the separator is large. Also, since the openings can be distributed over the entire upper side of the separator,
The effect of claim 2 can be enhanced.

[0034]

[Brief description of the drawings]

FIG. 1 is a perspective view of a prismatic alkaline storage battery electrode group according to the present invention.

FIG. 2 is a perspective view of a bag-shaped separator according to the present invention.

FIG. 3 is a perspective view of a bag-shaped separator according to the present invention.

FIG. 4 is a graph showing cycle characteristics of the battery of the present invention and a comparative battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bag-shaped separator 2 Opening provided in the upper side of bag-shaped separator 6 Positive electrode 7 Positive electrode tab 8 Negative electrode 9 Negative electrode tab

Claims (3)

[Claims] 1. A prismatic alkaline storage battery in which a positive electrode and a negative electrode each having a tab for connecting a current collecting terminal on a side thereof are laminated, and at least one of the positive electrode and the negative electrode is packaged with a bag-like separator. A prismatic alkaline storage battery, wherein the separator has an opening on an upper side. 2. The prismatic alkaline storage battery according to claim 1, wherein the length of the opening is 0.5 to 0.8, where the length of the upper side of the separator is 1. 3. The prismatic alkaline storage battery according to claim 1, wherein the plurality of openings are provided.