JP4579513B2 - Lead acid battery - Google Patents

Description

  The present invention relates to a lead-acid battery having a positive electrode containing graphite powder in a positive electrode active material.

  The positive electrode active material of a lead-acid battery has been considered to be difficult to reduce in size and weight because of its low utilization rate and low energy density compared to other battery-based positive electrode active materials.

  The main reason for the low utilization rate is that the poorly soluble lead sulfate crystals formed in the positive electrode active material during the discharge clogged the pores through which the electrolyte flows, and as a result the discharge reaction could be sustained. By disappearing. In addition, sulfuric acid in the electrolyte is also used as an active material, but the diffusion of sulfate ions is slow. In particular, the sulfuric acid in the positive electrode active material is exhausted and the sulfuric acid is supplied at a high rate discharge of 0.2C or more. Will not catch up, but its usage rate will drop sharply. Such a phenomenon is remarkably seen in a control valve type lead storage battery with a small amount of electrolyte.

  Therefore, in order to improve the utilization rate, there are a method of increasing the porosity of the positive electrode active material to reduce the pore clogging rate due to the lead sulfate crystals, or a method of increasing the amount of sulfuric acid in the positive electrode active material. It is considered. Specifically, (1) the amount of water is increased at the time of preparing the positive electrode active material paste to decrease the density of the positive electrode active material, and (2) the amount of lead sulfate contained in the unformed active material is increased and after the chemical conversion treatment. (3) Method of increasing the number of components by using a thin positive electrode plate (4) Addition of highly anisotropic graphite (see, for example, Patent Document 1), (5) Intercalation treatment only with sulfuric acid Added graphite intercalation compound (for example, refer to Patent Document 2), (6) After the chemical conversion treatment of the positive electrode active material to which expanded graphite is added, the expanded graphite is oxidized and disappeared to increase the porosity (for example, refer to Patent Document 3) , Etc. have been proposed.

Japanese Examined Patent Publication No. 63-57913 JP-A-56-159062 Japanese Patent Laid-Open No. 56-159063

  The method (1) in which the amount of water is increased to reduce the density of the positive electrode active material lowers the paste viscosity, lowers the filling ability of the electrode plate, and greatly reduces the yield. In the method (2) of increasing the amount of lead sulfate contained in the unformed active material, the amount of sulfuric acid at the time of paste preparation increases, so that acidification occurs, and the normal aging method may reduce the amount of metal lead to less than 5%. Therefore, it becomes difficult to perform sufficient chemical conversion treatment in the subsequent chemical conversion step. Furthermore, even if the porosity is simply increased, the positive electrode active material is likely to be softened, and the life is extremely shortened in the repeated use. The method of increasing the number of components by using the thin positive plate of (3) is expensive and damages the positive plate due to corrosion at an early stage and shortens the life.

  In the addition of graphite in (6), sulfuric acid is intercalated into graphite that has undergone anodization in the positive electrode plate, expands in the C-axis direction of the graphite, and electrolysis occurs by generating cracks in the positive electrode plate. By pulling the liquid into the positive electrode plate, the utilization rate can be increased, but the expansion (oxidation) efficiency of the graphite in the chemical conversion process is not high, and a large amount of unexpanded graphite remains and self-discharge in the state of standing There is a problem that the battery is large, and a problem of battery case breakage due to expansion of the positive electrode plate during float charging occurs. Furthermore, in order to increase the graphite expansion efficiency, large anisotropy is necessary, and heat treatment at a temperature exceeding 2000 ° C. is essential, so the addition of graphite with large anisotropy (4) becomes expensive. End up. The graphite intercalation compound produced with only sulfuric acid (5) has a problem that the intercalation amount of sulfuric acid cannot be sufficiently secured since the driving force of intercalation is small.

  The methods of adding the graphites of the prior arts (4) to (6) provide an effective lead storage battery as compared with the other prior arts (1) to (3), but each has a problem as described above. Therefore, further solutions are desired. In view of this, the present invention is to solve various problems in improving the performance of a lead storage battery by adding graphite, and to provide a high performance lead storage battery at low cost.

The invention according to claim 1 is a lead storage battery including a negative electrode plate, a separator, an electrolytic solution, and a positive electrode plate containing graphite powder in a positive electrode active material, wherein the graphite powder is subjected to high-temperature treatment. A lead storage battery characterized in that natural graphite powder that has not been subjected to removal of impurities by a flotation method is then immersed in a solution composed of sulfuric acid and an oxidizing agent.

  The invention according to claim 2 is the lead acid battery according to claim 1, wherein the oxidizing agent is hydrogen peroxide, potassium dichromate, or an oxidizing agent having an oxidizing power equal to or higher than these. is there.

According to the present invention, natural graphite powder having large anisotropy is prepared by removing impurities by a flotation method and then uniformly intercalating sulfuric acid by immersing in a mixed acid of concentrated sulfuric acid and oxidizing agent. By providing a lead-acid battery containing the natural graphite powder to be contained in the positive electrode active material, (a) large self-discharge, (b) the positive electrode plate expands during float charging, and the battery case is damaged, (c) graphite Various types of lead-acid batteries in which graphite powder is added to the positive electrode active material, such as high temperature heat treatment exceeding 2000 ° C. is required to increase the anisotropy of (d) the amount of sulfuric acid to be intercalated cannot be secured. It solves the problem and provides a high-performance lead-acid battery at a low cost, and has a remarkable industrial effect.

An embodiment of the present invention will be described.
The natural graphite lump of the raw material is pulverized by a pulverizer, and the natural graphite powder classified to an average particle size of 0.3 mm is subjected to a flotation method in a 1N dilute sulfuric acid aqueous solution, so that insoluble impurities such as silica and alumina and solubility are reduced. Metal impurities are removed. The natural graphite powder from which impurities were removed was immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 80 ° C. for 30 minutes. Thereafter, the natural graphite powder is collected, washed with water, and dried to obtain natural graphite powder in which sulfuric acid is intercalated (inserted between layers of graphite crystals). The obtained natural graphite powder is dry-mixed with the lead powder of the positive electrode active material and the polyester fiber, and then kneaded with water and sulfuric acid to prepare a positive electrode active material paste. A predetermined amount of this positive electrode active material paste is filled in a cast lattice plate made of a Pb alloy, and then subjected to aging treatment to produce a positive electrode plate. In the present invention, the positive electrode plate thus manufactured is combined with battery components such as a negative electrode plate, a separator, a battery case, and an electrolyte solution to assemble a control valve type lead-acid battery, and a battery case forming process is performed after the assembly. The lead acid battery which concerns is produced.

  By the way, the natural graphite powder used in the present invention has a very large anisotropy in nature, so that it has an appropriate driving force for intercalating sulfuric acid such as hydrogen peroxide (inserted between graphite crystal layers). By using an oxidizing agent, it is possible to intercalate without inserting sulfuric acid between the natural graphite crystals and subjecting it to high temperature heat treatment at a temperature exceeding 2000 ° C. Furthermore, the amount of sulfuric acid to be intercalated can be controlled by controlling the oxidizing agent concentration, processing conditions (temperature, time), solution temperature, and the like. That is, the natural graphite powder according to the present invention is controlled in the amount of sulfuric acid that uniformly intercalates the entire powder, and expands uniformly and efficiently during the formation of the battery case after assembly of the lead acid battery. Voids are formed in the positive electrode active material. Therefore, the proportion of unexpanded graphite after the formation of the battery case is reduced, the effect of addition into the positive electrode active material is increased, and changes in self-discharge and float charging are suppressed.

  The oxidizing agent is preferably hydrogen peroxide or an inorganic oxidizing agent having an oxidizing power equal to or higher than that. Potassium dichromate, oxidizing agents of perchloric acids, ozone, and the like can be used. Such organic oxidizers are undesirable.

Hereinafter, the present invention will be described in more detail using examples.
Chinese natural graphite block (scale block) was pulverized and classified to 300 μm, and then impurities were removed by a beneficiation treatment. Next, a natural graphite intercalation compound powder was prepared by immersing in a mixed acid of concentrated sulfuric acid and hydrogen peroxide at 80 ° C. for 0.5 to 2.0 hours. 1-4.

  Comparative graphite powder No. 5-8, without performing the acid / oxidant treatment according to the present invention, acid treatment after the beneficiation treatment (graphite powder No. 5 of the comparative example), high temperature heat treatment at 2000 ° C. and acid treatment after the beneficiation (of the comparative example) Graphite powder No. 6), only beneficiation treatment (graphite powder No. 7 of comparative example), natural graphite powder subjected to heat treatment at 2000 ° C. (graphite powder No. 8 of comparison example) after the beneficiation treatment Made and used.

  Next, 100 g of ball milled lead powder was added to graphite powder No. 1 of the present invention example shown in Table 1. 1-4, the added amount was 0.25% by mass, and the graphite powder No. 5-8, the addition amount is 0.5% by mass, added together with 0.05 g of polyester cut fiber, dry-mixed, kneaded with an appropriate amount of water, and further kneaded with a predetermined amount of dilute sulfuric acid to be a positive electrode active material A paste was prepared.

  A predetermined amount of the prepared positive electrode active material paste is filled in a 3.8 mm-thick Pb—Sn—Ca alloy casting grid for positive electrode, and aged for 40 hours in an environment of temperature 40 ° C. and humidity 95%. As a result, a positive electrode plate having a thickness of 4.2 mm was obtained. A control valve type lead-acid battery having a rated capacity of 2 Ah is housed in an ABS resin battery case in which a group of electrode plates in which the positive electrode plate and the negative electrode plate are alternately stacked via separators is sealed in the battery case. A to H were prepared.

  After about 20 cc of the lead acid battery was poured into the electrode plate group with dilute sulfuric acid having a specific gravity of 1.20 (20 ° C.) as an electrolyte from the exhaust hole of the lid, a battery case was formed at 25 ° C. . In addition, the amount of chemical conversion electricity was 200% with respect to the positive electrode theoretical capacity.

  Using a control valve type lead-acid battery that was completed by forming the exhaust hole of the lid closed with a rubber valve after chemical conversion, an initial capacity test of 0.1C and 3C, a float charge test at 65 ° C, and a self-discharge test at 40 ° C The results are shown in Table 2.

  In the initial capacity test, a fully charged lead-acid battery after completion of the battery case formation was discharged at a temperature of 25 ° C. with a discharge current of 0.1 C first, and then 110% of the discharge capacity was charged with 0.1 C. After charging, each capacitor was confirmed with a discharge current of 3C.

  Float charge test is conducted after initial capacity test of 3C, 110% of discharge capacity is charged with 0.1C current, float charge is performed at 65 ° C and 2.275V / cell for 3 months, before and after the test. Observation of the lead-acid battery state and 0.1C discharge capacity after the test were measured.

  In the self-discharge test, after the initial capacity test at 0.1 C, after standing for 1 month at 40 ° C., discharge was performed at 0.1 C at a temperature of 25 ° C., and the capacity reduction rate was determined from the change in capacity. In each of the above tests, the end voltage was 1.75 V / cell.

  As is clear from Tables 1 and 2, the lead storage batteries A to D according to the present invention are both 0.1C and 3C, although the amount of graphite powder added is half that of Comparative Examples E to H. High capacity is obtained in the initial capacity test. Further, no abnormalities such as a decrease in capacity and battery case cracking or liquid leakage were observed in the float charge test, and the capacity decrease rate was as small as about 5% in the self-discharge test. The acid / oxidant treatment time is 1 hour, and the increase in capacity is saturated, and the treatment time is preferably about 1 hour.

  On the other hand, in Comparative Example E in which the processing of the graphite powder is only the beneficiation, in Comparative Example G in which only the acid treatment with sulfuric acid after the beneficiation is performed, and in the Comparative Examples F and H in which the graphite powder is subjected to the high temperature treatment, It can be seen that the initial capacity is low even though the addition amount is twice that of the present invention, and the effect of adding graphite is not observed.

  In the float charge test, the lead acid batteries of Comparative Examples E to H were broken in the battery case during the test, causing liquid leakage, and measurement was impossible. In the self-discharge test, the capacity reduction rate is as large as 12% or more.

Claims (2)

A lead storage battery comprising a negative electrode plate, a separator, an electrolytic solution, and a positive electrode plate containing a graphite powder in a positive electrode active material and subjected to battery cell formation, wherein the graphite powder is not subjected to high temperature treatment A lead-acid battery , wherein impurities are removed by a flotation method and then immersed in a solution composed of sulfuric acid and an oxidizing agent. The lead acid battery according to claim 1, wherein the oxidizing agent is hydrogen peroxide, potassium dichromate, or an oxidizing agent having an oxidizing power equal to or higher than these.