JP2008243480A - Lead storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead storage battery with both improvement in utilization efficiency and elongation of life of its cathode, in a liquid-type and sealed-type for use for bicycles, four-wheeled automobiles and industries. <P>SOLUTION: For the lead storage battery with expanded graphite and bismuth added to a cathode active material in a cathode made by filling a substrate with a cathode active material, a desirable addition amount of the expanded graphite is to be 0.1% by mass or more and 2.0% by mass or less of the cathode active material, and that of a pure metal portion of the bismuth is to be 0.01% by mass or more and 0.5% by mass or less of the cathode active material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a lead-acid battery in which the positive electrode utilization rate and the life extension of two-wheeled, four-wheeled vehicles, and industrial liquid and sealed lead-acid batteries are compatible.

Traditionally, lead-acid batteries for automobiles, called SLI batteries, have been used as a power source for motors that have been installed in more than 100 high-end cars, including starter start-up, lighting, and ignition at start-up. Since the engine drives the generator to supply electric power except for starting the starter at that time, the lead-acid battery was not discharged so deeply. Moreover, since charging from a generator often places the battery in a fully charged state, it has been required to be resistant to overcharging. This lead-acid battery is required to maintain the electrolyte-free decrease due to gas generation during overcharge and eliminate the need for replenishment, and the alloy constituting the positive electrode substrate is changed from Pb-Sb alloy to Pb-Ca alloy. Changed to

As a result, under the conventional use conditions, the lead battery has reached the end of its life due to the positive electrode lattice gloss and the positive electrode lattice corrosion, the contraction of the negative electrode active material due to the high temperature in the engine room, and the decrease in the electrolyte due to high temperature and overcharge.

One of the causes is that the positive electrode substrate alloy is changed from the Pb—Sb system to the Pb—Ca system. In a Pb-Sb alloy, pentavalent Sb ions generated by oxidation of the substrate increase the adhesion at the interface between the lattice and the active material or act on the active material to gel a part thereof, thereby binding the active material particles to each other. It is said that it is strengthening. As a result, peeling of the lattice and the active material and softening of the active material were suppressed even after repeated deep charge / discharge. On the other hand, in the Pb—Ca alloy, the action as seen in Sb is weak, and when deep charge and discharge are repeated, the active material peels off from the lattice or softens and reaches the end of its life.

Therefore, in order to prevent these problems and further improve the utilization ratio of the positive electrode, an attempt is made to improve the diffusion of the sulfuric acid aqueous solution as the electrolytic solution. Therefore, in general, a method of lowering the density of the positive electrode active material has been adopted, and it has been proposed that sulfate ions be intercalated into graphite and expanded graphite previously expanded by post-processing is added to the positive electrode active material ( Patent Document 1).

Furthermore, it has been proposed that Sb is imparted to the positive electrode as a means for suppressing the separation and softening of the active material when a Pb—Ca-based alloy is used for the positive electrode lattice (Patent Document 2).

JP 2004-55309 A JP-A-49-71429

However, when expanded graphite as proposed in Patent Document 1 is added to the positive electrode active material, there is no destruction of the active material, but the active material is still affected by the vacancies formed by oxidation and disappearance during charging. Is easy to peel off from the lattice, and softens and falls, resulting in a short life.

Further, as proposed in Patent Document 2, when Sb is applied to the positive electrode, the application of Sb reduces the hydrogen overvoltage of the negative electrode even if the amount is small, and causes a decrease in electrolyte due to gas generation during charging. As a result, the service life is short and maintenance-free is impaired.

In order to solve the above-mentioned problems, the present inventors have intensively studied, and by adding expanded graphite and bismuth (Bi) to the positive electrode active material, the utilization rate of the positive electrode is improved and the active material is separated from the lattice. It has been found that both softening suppression can be achieved. The reason for these effects is not clear, but is considered as follows.

In the positive electrode to which expanded graphite is added, this is oxidized and disappears during charging, and vacancies are formed inside the active material. The vacancies also act as an active surface with respect to the electrolyte, and exhibit high utilization. As a result, the progress of softening is promoted. On the other hand, when Bi is added to the active material, when Bi is doped into β-PbO ₂ which is the positive electrode active material, the water molecules in the crystal are stabilized and locally modified to lead hydroxide, and between the active material particles. It is known to play a role of glue and suppress softening. That is, it is considered that the environment of the electrolyte solution tends to shift to alkalinity further inside the pores formed by the expanded graphite, and it is considered that the softening suppressing effect is exhibited more than when only Bi is added.

The amount of expanded graphite added is preferably 0.1% by mass or more and 2% by mass or less of the positive electrode active material. If the amount is less than 0.1% by mass, the effect of addition cannot be expected, and if it exceeds 2% by mass, the effect of addition becomes saturated and the preparation of the paste becomes difficult.

The addition amount of Bi is preferably 0.01% by mass or more and 0.5% by mass or less of the positive electrode active material as a pure metal component. If the amount is less than 0.01% by mass, the effect of addition cannot be expected. If the amount exceeds 0.5% by mass, the discharge characteristics tend to deteriorate. Particularly preferred is 0.01% by mass to 0.1% by mass.

The density of the positive electrode active material is 3.6 g / cc to 4.5 g / cc measured by a water displacement method from the viewpoint of suppressing softening by physical bonding of the active material and suppressing corrosion due to exposure of the positive electrode lattice. Is preferred. If it is less than 3.6 g / cc, the density is low and softening tends to proceed. If it exceeds 4.5 g / cc, the density is too high, the utilization rate is lowered, and the capacity cannot be secured.

The present invention can improve the utilization rate and extend the life of the positive electrode, and occupies much of fossil fuel consumption, especially the use of new energy such as energy saving and natural energy, which are inevitably required due to global environmental problems that are becoming increasingly important in the 21st century. The present invention provides an improved lead-acid battery that operates economically and stably for a long period of time in response to the improvement in fuel efficiency of transportation equipment such as automobiles, and its industrial value is great.

(1) Production of unformed positive electrode plate 100 parts by weight of lead oxide with 10 parts by weight of ion exchange water, followed by 10 parts by weight of dilute sulfuric acid with a specific gravity of 1.27, and expanded graphite (particle size 100 μm to 500 μm) as lead oxide The mixture was kneaded while adding 0.5% by mass and bismuth oxide as metal bismuth (pure metal content) to 0.05% by mass to produce a positive electrode paste. The cup density of the paste was adjusted to about 144 g / 2 in ³ . This paste was applied and filled onto a cast lattice substrate made of a Pb—Ca-based lead alloy, aged for 24 hours in an atmosphere of 40 ° C. and 95% humidity, and then dried to obtain an unformed sheet.

(2) Production of unformed negative electrode plate Acetylene black having a specific surface area of 70 m ² / g and barium sulfate powder were added as dry powder to lead oxide produced by the ball mill method. Lignin was added thereto as an aqueous solution, followed by kneading while adding ion exchange water to prepare a water paste, and further kneading while adding dilute sulfuric acid having a specific gravity of 1.36 to obtain a negative electrode active material paste. The amount of ion-exchanged water used at this time was about 10 parts by weight with respect to 100 parts by weight of lead oxide, and the amount of dilute sulfuric acid was 10 parts by weight. The amount of ion-exchanged water was adjusted so that the cup density of the finished paste was about 140 g / 2 in ³ . This paste was filled in a cast lattice substrate made of a Pb—Ca-based lead alloy, aged in an atmosphere of 40 ° C. and 95% humidity for 24 hours, and then dried to obtain an unformed sheet.

(3) Battery assembly, preparation and formation of electrolyte solution These positive electrode and negative electrode unformed plates are alternately combined through a microporous separator, and the same polarity plates are welded together by the COS method to form a plate group. . This was put into a polypropylene battery case and a polypropylene lid was applied by heat sealing. Then, a dilute sulfuric acid electrolytic solution in which 0.1 mol / l of aluminum ions was added as a sulfate was injected so that a large amount of the free electrolytic solution existed, and a battery case was formed to produce a 12V lead storage battery corresponding to D23 size and 50 Ah. . The electrolyte had a specific gravity of 1.28.

(4) Capacity test The obtained lead storage battery was fully charged at 25 ° C. with a 5-hour rate current, then discharged with a 5-hour rate current, and the capacity was measured. The results are shown in Table 1.

(5) JIS heavy load life test The obtained lead storage battery was fully charged at a current of 25 ° C. for 5 hours. Next, the heavy load life test according to JISD5301 of 40A, 20A, 1 hour constant current discharge and 5A, 5 hours constant current charge was performed. And the number of cycles leading to the lifetime was measured. The number of cycles is preferably 150 cycles or more. The results are shown in Table 1.

(6) Idle stop life test The obtained lead storage battery was fully charged at 25 ° C. with a current of 5 hours. Next, an idle stop life test is performed in which a combination of constant current discharge at 40 ° C. for 50 A, 59 seconds and 300 A, 1 second and 100 A for 60 seconds, constant current / constant voltage charging with an upper limit voltage of 14.0 V is one cycle. It was. And when the voltage at the time of discharge became 7.2V or less, it was made into the lifetime, and the cycle number which reaches the lifetime was measured. The number of cycles is preferably 30000 cycles or more. The results are also shown in Table 1.

In Table 1, the lead storage battery using the unformed positive plate obtained by the method described in the production of the unformed positive plate is described in Example 1, and the amount of expanded graphite and bismuth added in the positive electrode is as follows. The various types are shown as Examples 2 to 7, and the respective addition amounts are as shown in Table 1.

Further, for comparison, cases where only expanded graphite is added and bismuth is not added are shown as Comparative Examples 1 to 4, and the amount of expanded graphite added is as shown in Table 1.

As is apparent from Table 1, the lifetime could be improved by adding both expanded graphite and bismuth. Furthermore, the capacity could be improved.

In this embodiment, an example in which a gravity cast lattice substrate is used for the positive electrode has been shown. However, the same effect can be obtained with an expanded lattice substrate or a punched lattice substrate obtained by processing continuous casting, rolling, or extrusion. It can also be applied to liquid lead-acid batteries that use a large amount of free electrolyte, and sealed lead-acid batteries that do not have any electrolyte that can be impregnated into the electrode plate group. Can be used as

Claims (2)

A lead-acid battery characterized by adding expanded graphite and bismuth to a positive electrode active material of a positive electrode. The amount of expanded graphite added is from 0.1% by weight to 2.0% by weight of the positive electrode active material, and the amount of bismuth added is from 0.01% by weight to 0.5% by weight of the positive electrode active material. Item 14. A lead acid battery according to item 1.