JPH10270029A - Active material for lead-acid battery and lead-acid battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the cycle service life without damaging the charging efficiency by forming a surface layer of Pb3 O4 and forming a core layer of metal Pb. SOLUTION: A raw material of an active material is formed by using lead powder subject to a ball mill and with the degree of oxidation 20-40%, and baking the powder for 4 hours at a temperature of 200-300 deg.C (lower than the melting point of lead). In the main process, the surface is oxidized to have PbO mainly with metal Pb remained in a core layer of the particle of raw material of active material without fusing the particle with the metal Pb. Then, a baking process is applied for 20 hours at 350 deg.C to oxidize the PbO and the like on the surface is oxidized to have Pb3 O4 . Through the two-step baking a part of metal Pb which is not oxidized can be formed at the core part. By containing the particles having the structure in positive electrode active material paste of a lead-acid battery, the metal Pb and PbO in the intermediate layer combined with the active material particles themselves are combined with the metal Pb, PbO and basic lead surfate in the paste at the time of aging and drying. Accordingly, the contribution to hold the active material is attained and the service life is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active material for a lead storage battery and a lead storage battery using the same, and more particularly to a technique for improving the life performance of a lead storage battery when a paste type electrode plate is used. is there.

[0002]

2. Description of the Related Art In the formation process of a lead storage battery, particularly in the formation process of a positive electrode plate, there is a problem that the formation charge efficiency is low. Therefore, in order to avoid a loss of power and time in chemical charging, a technique of mixing lead red (Pb ₃ O ₄ ) with a positive electrode active material is generally known. Just by contacting sulfuric acid used as an electrolyte in the chemical conversion process, leadtan chemically causes a disproportionation reaction as shown below and changes to lead dioxide, which is a product of formation charge, and the generated lead dioxide is high Since it has conductivity, the formation charge efficiency of the positive electrode is improved.

Pb ₃ O ₄ → PbO ₂ + 2PbO However, when lead tin is added, there is a problem that the bond between active material particles is weakened and the cycle life characteristic is deteriorated. It was remarkable.

Conventionally, as a method for solving this problem, as disclosed in Japanese Patent Publication No. 8-8097, a method in which metal Pb is added to a raw material of a positive electrode active material at the same time as lead in Japanese Patent Publication No. 8-15081. As shown in the gazette, there has been a method of using active material particles having a low lead content ratio by increasing the ratio of PbO in the active material particles containing lead.

[0005]

The details of the cause of the deterioration of the life when lead tin is added are unknown, but in general, the bonding force between the active materials formed during the aging and drying of the paste is low. Probably because it is weak. In other words, the metallic lead or basic lead sulfate present in the paste does not bond to each other immediately after filling in the current collector such as a lattice, but undergoes a chemical change such as oxidation during aging and drying. It is considered that a mutual bond is formed, which forms a skeletal structure in the active material until the end of the battery life and contributes to retention of the active material. However, the red lead in the paste hardly undergoes a chemical change during aging and drying, and hardly forms a bond between particles. Therefore, it is considered that the life of the paste-type electrode plate to which lead tin is added is deteriorated. In traditional approaches,
This is to strengthen the bond between the active materials formed during the aging and drying. In the case of the technique disclosed in Japanese Patent Publication No. 8-8097, the added metal Pb and the lead are composed of different particles. As such, they do not form a direct bond. Further, it is difficult to uniformly mix and knead particles (metal Pb, lead red) having different specific gravities. Also, in the case of the technique disclosed in Japanese Patent Publication No. 8-15081, PbO in the active material particles containing lead-tan forms a bond between the active materials by reducing the lead-tanning rate, but the bond is formed only by PbO. Not sufficiently formed. Therefore, there is a problem that the effect of improving the life is small. Conventionally, even when a high-oxidation lead powder having a high ratio of PbO is used as a raw material, there is a similar problem of deterioration in life due to insufficient bonding force between active materials, and there are many patent applications in which metal Pb is added. As is clear from the above, PbO is not enough to improve the bonding force between active materials, and the effect of metal Pb is very large. The problem to be solved by the present invention is to provide an active material material for a lead storage battery capable of producing a lead storage battery having enhanced cycle life characteristics by strengthening the bond between active material particles as compared with the conventional method. .

[0006]

In order to solve the above-mentioned problems, an active material for a lead-acid battery according to the present invention is characterized in that the central layer of particles is metal Pb and the surface layer is Pb ₃ O _4. And Pb is mainly located between the Pb ₃ O ₄ layer and the metal Pb.
There is an O layer, but nothing may be present. Also P
Even if a PbO layer is present between the b ₃ O ₄ layer and the metal Pb, the layer is not only stoichiometrically PbO but also metal Pb.
The layer may have a higher valence of oxidation than b and a lower valence of oxidation than Pb ₃ O ₄ , or may be a PbO layer alone.

The active material for a lead-acid battery according to the present invention comprises a metal P which is effective for forming a bonding force with a current collector on the lead-acid particles themselves.
The center layer of b is formed. Therefore, the metal Pb having an effect of strengthening the bond between the active material particles can be uniformly distributed over the entire electrode plate. The step of uniformly distributing the particles is very simple once the particles having the above-mentioned structure are produced. With the particles having such a configuration, the bond strength between the active material particles of the electrode plate after aging and drying is increased, thereby improving the charge-discharge cycle life characteristics of the lead storage battery.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below. In the conventional method, from the viewpoint of mass productivity, a part of or all of lead is previously oxidized to PbO and has an oxidation degree of 7.
It is manufactured by calcining a relatively high molten flow type or ball mill type lead powder of 0 to 100% at 400 to 500 ° C. By shortening the sintering time, the ratio of lead tin (hereinafter referred to as the ratio of lead tin in the present specification is the mole percent of lead tin occupying particles in terms of metal Pb).
It is. ), The metal lead in the particles is completely oxidized, so that no metal Pb is present. The active material raw material of the present invention is different from the conventional method in that a ball mill type lead powder having an oxidation degree of 20 to 40% is used as a raw material.
The baking is performed at 200 to 300 ° C. for 4 hours which does not exceed the temperature. In this step, the metal Pb is left in the center layer of the active material raw particles without fusing the active material raw particles and the metal Pb, and the surface is mainly made of Pb.
Oxidizes to O. Further, baking is performed at 350 ° C. for 20 hours to oxidize PbO and the like on the surface to Pb ₃ O ₄ . By performing firing in two stages in this manner, an unoxidized portion of metal Pb can be formed at the center.

When the particles having the above structure are included in the positive electrode active material paste of the lead-acid battery, the metal Pb bonded to the active material particles themselves and the PbO of the intermediate layer are ripened and dried. Form a bond with lead sulfate. In the case of conventional leadtan, when metal Pb is added, leadtan itself does not have a binding force, and in the case of leadtan with a reduced ratio of leadtan, the bond between the particles in the paste by PbO, which has a weak bond-forming ability, can only be obtained. Therefore, the bonding force is weaker than when the active material of the present invention is used. As a result, the battery obtained using the lead tin of the present invention maintains the skeletal structure in the active material until the end of the battery life and contributes to the retention of the active material, so that the life characteristics are greatly improved.

[0010]

The present invention will be compared with the prior art. First, using a ball mill type lead powder having an oxidation degree of 20 to 40% as a raw material, Pb ₃ O ₄ , PbO, and the like are adjusted by adjusting the degree of oxidation and the firing time of the raw material lead powder based on the firing conditions described in the embodiment of the invention. Active material raw materials for lead-acid batteries having different ratios of metal Pb (Examples 1 to 3)
6) was produced.

A cross section of the active material particles was observed. After embedding and curing the active material material particles of Example 5 and Conventional Example 1 in a resin, the cut surface was polished and observed with a metallographic microscope. The active material particles of Example 5 were found to have metal Pb in the center layer. It was also found that the active material raw particles of Conventional Example 1 did not have metal Pb in the central layer.

Next, using a ball mill type lead powder having an oxidation degree of 80%, the firing conditions were adjusted to obtain each active material raw material shown in Table 1 (active material raw materials of Conventional Examples 1 to 4). Conventional example 2
In order to comply with Japanese Patent Publication No. 8-8097, metal Pb powder is added to the active material raw material in an amount of 10 w
t% was added.

The produced active material raw materials (Examples 1 to 6 and Conventional Examples 1 to 4) were further classified and adjusted to a target particle size distribution.
The particle size of the lead powder used in the lead storage battery is generally Dp
Since 50 (50% diameter under the sieve) is in the range of 1 to 20 μm, in this example, the particle diameter was unified to Dp50 = 10 μm and compared. The physical properties of the manufactured active material material were confirmed using the following apparatus. Average particle size: Laser diffraction particle size distribution analyzer HORI
BA made LA-500 (dispersion medium: H ₂ O + nonionic surfactant) Examples 1 to 6 described above, using the raw active material in the conventional example 1-4, kneading them with water and sulfuric acid according to a conventional method, respectively The paste was combined, filled into a lattice, aged and dried to obtain an unformed positive electrode plate. After combining with an unformed positive electrode plate, an unformed negative electrode plate and a glass fiber separator produced by a conventional method, and incorporating it into an ABS battery case, the electrolytic solution is injected to form a battery case. A sealed lead-acid battery having a capacity of 7 Ah (20 hour rate capacity) was produced. Regarding the battery, the efficiency of formation charge (PbO ₂ conversion ratio) was grasped, and an initial capacity test and a cycle life test were performed. Table 1 shows the results.
Shown in The initial capacity test is 0.25
C, the battery was discharged at 20 A to a final voltage of 1.7 V / cell. The cycle life test was performed under the following conditions based on JIS C8702.

(A) Test temperature: ambient temperature 25 ± 2 ° C. (C) Capacity confirmation: Discharge from a fully charged state to a final voltage of 1.7 V / cell at 0.25 C and 20 A every about 25 cycles.

(D) Battery life judging time: until the capacity obtained in (c) is reduced to 50% or less of the initial capacity.

[0016] PbO ₂ ratio (mole% of PbO ₂ occupying the particles of metal Pb conversion) was measured as follows. First, 1 g of a sample is precisely weighed in a weighing bottle, 20 ml of a 10 vol% nitric acid aqueous solution is added thereto, and the mixture is subjected to an ultrasonic vibrator for 90 minutes. Then, PbO ₂ and PbSO ₄ remaining undissolved are separated by a centrifuge. Take 1 ml of this supernatant and add 10 ml of buffer solution
The solution to which the and the indicator were added was titrated with a 0.01 M EDTA solution, and the PbO _x value was determined from the following equation.

[0017]

(Equation 1)

Next, 1 g of the sample is precisely weighed in a weighing bottle, 30 ml of an aqueous solution of nitric acid and hydrogen peroxide are added, and the mixture is left to stand for 30 minutes. The remaining PbSO ₄ is filtered through filter paper, washed with distilled water, and baked in a crucible with the filter paper (ashing of filter paper).
The sample is kept at 50 ° C. for 30 minutes to vaporize and remove the ash to obtain a weight ratio (%) of only PbSO ₄ in the sample. Then, the PbO ₂ conversion rate is calculated by the following equation.

PbO ₂ (%) = 100-PbO _x (%)-PbSO ₄ (%) The lead tinification rate of the active material particles was measured as follows. First, 1 g of a sample is weighed. Next, 60 g of sodium acetate trihydrate is weighed, dissolved in a 5% acetic acid solution to make 100 ml, 50 ml is prepared, and the sample is added thereto. Then, add 0.1N aqueous sodium thiosulfate solution
Add 0 ml. These are heated and boiled at normal pressure to dissolve the sample. And with 0.1N iodine solution,
Titrate to the solution in which the sample was dissolved (indicator: 0.5%
3 ml of starch solution, use brown burette in draft). The titer at this time was Vml, and the titer (blank) when titrated to a solution not charged with the sample was V _0.
And the lead nitanification rate of the active material particles (metal Pb
(Mol% in conversion).

[0020]

(Equation 2)

The metal Pb content (mol%) and PbO content (mol%) of the active material particles were measured and calculated as follows. Here, all the intermediate layers between the metal Pb at the center of the active material particles for lead storage batteries of Examples 1 to 6 and the surface layer of Pb ₃ O ₄ were regarded as PbO and calculated. A mixed solution of a solution in which 300 g of NaOH is dissolved in 1 liter of water, a solution in which 60 g of mannitol is dissolved in 1 liter of water, and a solution in which 30 g of hydrazine hydrochloride is dissolved in 1 liter of water. And at room temperature while vibrating with ultrasonic waves.
And the solid content before and after this dipping operation (active material particles)
The value obtained by subtracting the weight is the sum of the weights of Pb ₃ O ₄ and PbO. The weight of Pb ₃ O ₄ in the active material particles as the sample can be calculated from the above-mentioned lead tinification rate (mol% in terms of metal Pb). Therefore, the weight of PbO in the active material particles is calculated from the sum of the weights of Pb ₃ O ₄ and PbO. The solid content weight after the immersion is the metal Pb content. From the lead tinification ratio (mol% in terms of metal Pb) of the active material particles thus obtained and the values of Pb ₃ O ₄ weight, PbO weight and metal Pb weight in the active material particles, Pb ₃ O ₄ , Pb
O, metal Pb conversion mol% of metal Pb (mol% in Table 1)
Can be obtained.

[0022]

[Table 1]

The following is clear from Table 1. Regarding the number of cycle life, the metal Pb corresponding to Japanese Patent Publication No. 8-8097 was separately added to the active material material (conventional example 2), and the lead reduction rate corresponding to Japanese Patent Publication No. 8-15081 was low. Examples 1 to 4 of the present invention have an increased number of cycle life times as compared with the prior art (conventional examples 3 and 4). Also in the comparison (Examples 1, 2, Conventional Example 3) and (Examples 3, 4, Conventional Example 4) at the same lead tinification ratio, the comparison was made with the conventional active material particles in which the amount of metal Pb in the active material particles was 0. According to the present invention, 0.4% by mole of metallic lead (metal Pb of active material particles) is used.
(Mole% in terms of conversion), the presence of which leads to a significant increase in the number of cycles. This is because the metal Pb is located at the center of the active material particles.
It is considered that the effect described in the embodiment of the present invention was obtained because the active material raw material having the structure of the present invention in which is present was used. However, when the amount of metal Pb in the active material particles having the configuration of the present invention exceeds about 5 mol%, the initial capacity may be inferior. Therefore, the metal Pb content of the active material particles having the structure of the present invention is desirably 5 mol% or less. When the lead tin reduction ratio is less than 75 mol% in terms of metal Pb (Examples 5 and 6), the cycle life is the best, but the initial capacity is reduced.
In addition, the formation charge efficiency (PbO ₂ conversion rate) also decreases, so that there is a possibility that other battery characteristics such as self-discharge characteristics may be adversely affected. Further, active material particles having a lead tinification ratio of more than 97 mol% are difficult to control in firing to leave a metal Pb portion in the center of the particles at the time of production, and may be disadvantageous in terms of cycle life characteristics. There is. Therefore, the rate of lead tinification is 75-97.
% Is desirable. Within this range, a sufficient conversion property with a PbO ₂ conversion ratio of 80% or more is obtained, the initial capacity is almost the same, and the cycle life is remarkably improved.

[0024]

As described above, the active material for a lead-acid battery according to the present invention has a surface layer of Pb ₃ O ₄ and a central layer of metal Pb. Compared with the method of adding metal Pb, the method is excellent in that the cycle life characteristics can be improved without impairing the formation charging efficiency.

Claims (3)

[Claims] 1. An active material material for a lead-acid battery, wherein the central layer of the particles is metal Pb and the surface layer is Pb ₃ O ₄ . 2. The lead tinification ratio (mol% of Pb ₃ O ₄ occupying particles in terms of metal Pb) of the particles is 75 to 97%, and the amount of metal Pb contained is 5 mol% or less. The active material raw material for a lead storage battery according to claim 1, wherein: 3. A lead-acid battery comprising the positive electrode plate containing the active material raw material according to claim 1.