JPH04171672A - Lead-acid battery - Google Patents

Abstract

PURPOSE:To suppress the generation of dendrites by specifying the relation between the positive electrode active material weight per cell and the sulfuric acid absolute quantity, and containing at least one kind of alkaline metal ions 0.03mol/1 or above. CONSTITUTION:The relation between the positive electrode active material weight A gr per cell and the sulfuric acid absolute quantity B gr is set to B/A<=0.55, and at least one kind of alkaline metal ions 0.03mol/1 or above are contained. The alkaline metal ions are allowed to exist without controlling the remaining quantity of the sulfuric acid radical in the region where the quantity of the active material is increased and the ratio of sulfuric acid is decreased. The generation of dendrites, which is being increased under the situation that the quantity of the active material must be increased to adapt a lead-acid battery to the lightweight, thin, short and small trend in recent years, is suppressed.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention aims to improve lead-acid batteries that are widely used in automobiles and industrial consumer equipment, and is particularly aimed at responding to severe changes in the battery environment in recent years. It is something.

Conventional technology In recent years, lead-acid batteries have been required to improve their density in limited spaces, regardless of their use, and in automobiles, the engine room has become increasingly crowded and hot. being sought after. Basically, improvements have been made to the electrode plates in response to this trend, but there is no suitable method, and the most common methods are increasing the number of electrode plates or increasing the amount of active material. This is a method that reduces the burden on the active material and improves its durability. With this trend, new problems have arisen. In other words, if the battery is attached to a device for a long period of time, leakage discharge from the circuit will cause deep overdischarge, and if left as it is, the phenomenon of not being able to be charged is rapidly increasing. This phenomenon is generally referred to as overdischarge recovery, but it is different from the conventional situation. For example, this phenomenon occurs when a calcium alloy or an antimony alloy is used for the electrode plate lattice, or in a so-called hybrid structure that combines these, and is not due to passivation of the lattice as in the past. Also, there is no so-called sulfation caused by the growth of crystalline lead sulfate during overdischarge. In terms of phenomena, it is clearly seen that there is a slight short circuit due to the formation of dendrites. However, the problem is that this phenomenon is extremely severe and conventionally 0.1 to 0.
A known method is to add about 2 mol/l of sodium sulfate, etc. to increase the concentration of sulfate ions during overdischarge, suppress the dissolution of lead sulfate, and prevent the growth of dendrites, but this common sense method provides the same solution. I didn't. Conventionally, sodium sulfate has a solubility of 1.5 mol at room temperature, but the reason why such a small range as above has been applied in reality is that in the past, this level was sufficient to prevent the formation of dendrites.
This is thought to be because the rate of dissolution in sulfuric acid is slow, and if you try to add 0.2 mol/l, it will precipitate, making it difficult to control the concentration, and if it exceeds 0.2 mol, the rapid discharge characteristics will drop significantly. It can be done. The fact that these phenomena rapidly increased and started to occur in areas where certain amounts of additives were used, which were previously thought not to occur, coincided with the time when the amount of active materials began to be increased in response to various problems in recent years. Match. In other words, as long as the amount of active material increases and sulfate ions are present, overdischarge will progress and the electrolyte will become neutral, and a limited amount of alkali metal sulfate added in the form of sodium sulfate will dissolve lead according to the solubility product principle. It seems that dendrites are occurring beyond the limit of suppression.

The problem that the invention aims to solve is how to suppress side effects such as sudden discharge characteristic deterioration while suppressing side effects such as deterioration of sudden discharge characteristics in a reality where the amount of active material filled per battery volume has to be increased in response to changes in social conditions. How to suppress the generation of carbon dioxide is becoming an important issue in today's world, where we are looking for lighter, thinner, smaller, and more durable materials.

Means for Solving the Problems As a means for solving the above-mentioned problems, the present invention provides positive electrode active material weight A grams per cell, sulfuric acid absolute ff1B grams, B/A≦0.55, and at least one alkali metal ion. It is characterized by containing 0.03 mol/l or more. Furthermore, as a means to effectively exhibit this effect, the base thickness of the separator interposed between the positive and negative electrode plates is reduced to 0.
．． The length is 25 mm or less.

In other words, the present invention is based on the discovery that in a region where the amount of active material is increased and the ratio of sulfuric acid is decreased, the formation of dendrites can be suppressed without side effects by not controlling the residual amount of sulfate groups but by allowing alkali metal ions to exist. Base.

The reason for this is not clear, but dendrite formation due to overdischarge generally increases the solubility of lead ions in the electrolyte that becomes neutralized during overdischarge, and is not fixed in the form of a compound fixed to a separator or the like. If this is the mechanism by which dendrites grow due to complexing in most cases from the part in contact with the negative electrode side during charging, leading to a short circuit, then during overdischarge, an amount of alkali metal ions equivalent to the number of moles of sodium sulfate, which exceeds common sense, is generated. This action may change the liquid properties near the negative electrode side of the separator and prevent compounds that form the basis of dendrites from staying and fixing in the separator.

It is common knowledge that the thinner the separator is, the higher the risk of short-circuiting; however, here, the thinner the separator, the less likely it will occur.

It seems that the thinner the separator is, the less likely it is that the compound will be fixed in the separator, and the more likely it will be affected by alkali metal ions.

Embodiment 1-1 Hereinafter, the features and effects of the configuration of the present invention will be described with reference to Examples.

Construct a 48Ah battery with a matrix of alkali metal ion concentration while configuring B/A in various ways, completely discharge it to 10.5V at 9.6A, and leave it at 40℃ for 4 weeks with a LOW lamp on. The separator was then left open for two weeks to determine whether or not a white compound was formed on the separator, which is the base of dendrites. Here, the separators in the test battery were examined, and the ratio of separators in which a white compound, which is a source of dendrites, was observed at one or more locations relative to the total number of separators was defined as the failure rate P. In carrying out the present invention, sodium hydroxide was directly added to the sulfuric acid aqueous solution in this example.

Of course, potassium ions and lithium ions have similar effects, although the effects are different. The use of chloride ions, nitrate ions, etc. as counter ions for alkali metal ions has a negative effect on the original battery reaction, so it is better to use hydroxide, sulfide, or bisulfate as in this example. Even if hydroxide is used, the alkali metal ions in sulfuric acid use sulfate ions as counterions, so the result is the same as adding a large amount of alkali sulfate compound. However, the idea here is not to prevent lead from dissolving by allowing sulfate ions to exist in the neutral solution, but to fix dendrites with the help of alkali metal ions that remain after the sulfate ions are fixed by forced discharge. The aim is to suppress the precipitation of the compound being produced on the separator. Therefore, in the case of a sulfuric acid compound that needs to be dissolved in a larger amount than conventionally known and has a slow dissolution rate, a large portion will precipitate unless the temperature of the solution is raised sufficiently, making it difficult to control the concentration. In the case of hydroxide, the compound itself dissolves while generating heat of neutralization, so adjustment is quick and easy.

FIG. 1 shows the relationship between the above-mentioned B/A and the failure rate P. X is a case in which 0.03 M/l or more of alkali metal ions are included according to the present invention. Y contains conventional alkali metal ions, but Y-1 contains 0. OIM/l,
y-2 is 002M/I, and Z is the case where only dilute sulfuric acid is used.

As is clear from Z, this phenomenon this time has a ratio of B/A or 0.
It can be seen that there is a tendency to sharply increase in the lower region after reaching around 55. Regarding this tendency, the conventional Y containing a small amount of an alkali sulfate compound is not so effective. On the other hand, in the area of the present invention, the effect is more obvious than that of the conventional extension. Moreover, looking at these rapid discharge characteristics, they decrease somewhat as the amount of alkali metal increases.

From that point of view, the amount added should be limited to about 0.2 M/l.

However, since the amount of active material is large in the low B/A region, the actual effect is not as great in the high B/A region.

On the other hand, in Figure 2, a polyethylene microporous separator is used, and the B/A is 0.50 and the base thickness of the separator is 0.15.
, 0.20, 0.25, and 0.30 to investigate the influence of thickness. Regardless of the physical strength of the separator, contrary to the general opinion that the thicker the separator, the less likely short circuits will occur, it is better to have a thickness of 0.25 mm or less in order to prevent accumulation of white compounds that are thought to be the source of dendrites. Physical weaknesses can be covered by providing ribs or using mats. The ability to use such a thin separator is advantageous in compensating for the rapid discharge characteristics, which are slightly affected by the application of the present invention.

As described above, the present invention is an effective means of suppressing the occurrence of dendrites, which is increasing in the current situation where the amount of active material has to be increased as lead batteries are adapted to lighter, thinner, shorter, and smaller batteries. Its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between B/A according to alkali metal ion concentration and the defective rate, and FIG. 2 is a diagram showing the relationship between the base thickness of the separator and the defective rate. X7 Addition amount of the present invention, Y: Conventional addition amount Z, non-additive Name of agent Patent attorney Akira Okaji and 2 others -]〇
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Claims (2)

[Claims] (1) When the weight of the positive electrode active material per cell is A gram and the absolute amount of sulfuric acid is B gram, B/A≦0.55 and at least one kind of alkali metal ion is contained at least 0.03 mol/l. lead-acid battery. (2) The lead-acid battery according to claim (1), wherein the base thickness of the separator interposed between the positive and negative electrode plates is 0.25 mm or less.