JPS5929366A - Manufacture of paste type electrode for lead storage battery - Google Patents

Abstract

PURPOSE:To suppress deterioration of initial capacity in slow discharge cycle, by immersing a grid in aqueous solution containing hydrogen perioxide and phosphoric acid then applying lead paste. CONSTITUTION:Lead paste is applied on a grid immersed in aqueous solution containing hydrogen peroxide and phosphoric acid, then dried, cured and formation charged to produce a protection layer of fine phosphoric compound on the surface of the grid, and when it is charged during the cycle it will suppress diffusion of sulfuric acid to the grid interface thereby pH in the vicinity of the interface will approach to the neutral region to form alpha-PbO2 layer having high electron conductivity, slow reaction and high binding force with high probability thus to maintain binding with the active substance. Prior to reaction of the portion near to the grid, beta-PbO2 on the plate surface or at the fine hole inlet will react to be covered with lead sulfate to complete discharge where the protection layer in the vicinity of the grid will not concern to the charging reaction considerably thus to maintain the tightness and conductivity between the grid and active substance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing paste-type electrodes for lead-acid batteries.

Conventional structure and problems The paste method, which is the most commonly used electrode manufacturing method for lead-acid batteries, traditionally involves casting lead or lead alloy in a lattice mold, and applying paste to at least a small number of panels. In recent years, as various alloys have been searched for due to the demand for maintenance-free materials, some alloys, such as lead-calcium alloys, have poor castability and significantly reduce efficiency. Coupled with the availability of such materials, new and efficient manufacturing methods have been searched for, regardless of castability.

Therefore, a method has been developed that uses a perforated plate, commonly known as expanded metal or perforated metal, as a grid and applies the paste in a continuous strip. However, these manufacturing methods actually have some weaknesses, and many of these problems to be solved are that the grid substrate itself used is extremely smooth compared to casting,
This is often due to the fact that the cuts used to form the grid do not have fine irregularities on the surface unlike cast products.

In such a structure, the bond between the applied paste and these smooth grid surfaces is insufficient. In the above structure, a new phenomenon that has not been observed in the case of cast grids has been observed. It was unlikely that this would occur. In the conventional casting method, the main cause of the service life was the softening and falling off due to the fineness of the active material, whereas with these continuous strip grids, the active material became finer. Significant capacity deterioration tends to occur in a much shorter period of time. This phenomenon is particularly likely to occur in a cycle (slow discharge cycle) that involves a relatively low discharge rate of o, 1C or 0.20, and a deep discharge to full capacity.
This phenomenon occurs on the positive electrode side. This phenomenon is probably caused by the expansion and contraction of the grid and active material, respectively, during repeated charging and discharging, which not only causes cracks between the weakly bonded grid and the active material, but also causes cracks in the vicinity of the bonding interface. relatively,
This is thought to be due to the intrusion of high concentration sulfuric acid and the formation of a strong passive layer at the interface.

OBJECTS OF THE INVENTION The present invention aims to suppress early capacity deterioration during slow discharge cycles by improving lattice processing conditions.

Structure of the Invention The present invention is characterized in that, before applying the lead paste to the grid, the grid is immersed in an aqueous solution containing hydrogen peroxide and phosphoric acid. Here, it is preferred that the grid be pretreated before being immersed in the aqueous solution.

Lead paste is applied to the lattice treated in this way, dried, aged, and made into a lead battery through a single charge process.For the detailed mechanism of the lead acid battery made in this way, Although this is beyond the scope of suggestion I11), it is probably that when charge is carried out based on the present invention, the interface between the lattice and the active material preferentially has poor reactivity but conductivity. A layer of lead or a compound of lead and 1-nonacid, which has an arcuate bonding force to the lattice, is formed and serves as a kind of protective layer. On top of that, even if β-PbO2, which is highly reactive but has weak binding to the lattice, is produced, it has a poor lifespan. 1illsa'I'I.

It is thought that

In such a structure in which the above-mentioned protective layer, such as a dense 1-Non-I-Non-Ni-Ni-Nonzu layer, is formed on the surface of the lattice, the paste active material filled with VC may be chemically charged or charged during the cycle. When the lattice is oxidized, the pH near the interface is close to the neutral region because the sulfuric acid diffusion to the lattice interface is suppressed, and even if the lattice is oxidized inside the layer, the electron conductivity is good, but , a-PbO, which has poor reactivity and rich bonding strength.

There is a high probability that this layer will be formed, and the bond with the active material will be maintained. Under the above situation, the area near the interface between the lattice and the active material is a lead compound involving a-Pb02 or other phosphoric acid, which has poor reactivity, so that the electrode plate may eventually react before the area near the lattice reacts. β-PbO2 on the surface or at the entrance of micropores
reacts preferentially, becomes covered with lead sulfate, and ends the discharge. It is believed that the compound in the protective layer near the lattice itself does not significantly participate in the discharge reaction, and therefore maintains the adhesion and conductivity between the lattice and the active material.

In the past, there have been examples of adding phosphoric acid to the sulfuric acid electrolyte for the purpose of suppressing early capacity deterioration or improving lifespan, and this has the effect of suppressing capacity increase, but at the same time, it causes problems such as V, decrease in initial capacity, and rapid discharge characteristics. It is not suitable for automotive lead-acid batteries, where starting characteristics are the main concern. Although the reason for the above phenomenon is beyond speculation, it is thought to be as follows. During charging, α-Pb022, which has poor reactivity, is preferentially distributed not only in the lattice and the vicinity of the active material but also over the entire surface of the active material.
This is thought to be due to the formation of a layer of phosphoric acid and lead compounds. In other words, although it is effective in suppressing capacity deterioration during cycling, it is accompanied by a decrease in initial capacity and a decrease in rapid discharge capacity.

According to the present invention, since an inactive conductive layer is generated only near the interface between the lattice and the active material, the slow discharge cycle life can be significantly improved without causing a decrease in rapid discharge capacity. Furthermore, before immersing in the phosphoric acid/hydrogen peroxide mixture, a pretreatment process is performed to remove the oxide film on the lattice surface and clean the lattice surface so that the warping caused by phosphorus compounds proceeds smoothly. And it's even more effective.

This phenomenon is particularly noticeable in the case of E-Froband metal or perforated plates made from lead-calcylum alloys or smooth metals, which tend to form a strong passive oxide film on the grid surface. Therefore, the following examples will be described using lead-calcium-tin alloy, which is commonly used.

Description of Examples An expanded grid made of a lead-calcium alloy with a width of 135 mm, a height of 110 mm, and a thickness of 1.4 mm was immersed for 10 seconds in a 30 mm nitric acid aqueous solution (A), and a 30% After immersing in a nitric acid aqueous solution for 10 seconds, it was further immersed in a 1:1 volume ratio mixture of 15% hydrogen peroxide and 30% phosphoric acid aqueous solution.
(B), 16 parts hydrogen peroxide solution and 3 parts soaked for 2 seconds.
(C) is a sample that has been immersed for 10 seconds in a 1:1 volume ratio mixture with 0% phosphoric acid aqueous solution, and (D) is a sample that is not immersed in any liquid, and then filled with paste. Then, ripening and chemical conversion were performed using conventional methods. The electrode plate group configuration of the battery is the above-mentioned four positive electrode plates and six conventional negative electrode plates. The electrolyte is dilute sulfuric acid with a specific gravity of 1.280.

The test conditions were to conduct constant current low temperature rapid discharge at 300A at a temperature of -15°C until the terminal voltage was 1, OV/(!/), and to observe the discharge time at that time. Discharge at a current of 8A/cell until the battery voltage reaches 1.75V/cell, and charge at 4A/cell, 1 of the previous discharge capacity.
This was carried out up to 20 cycles, and charging and discharging were repeated with this as one cycle (slow discharge cycle).

Regarding the results of the low-temperature rapid discharge test, as shown in Figure 1, the discharge duration is (5), (B), (C
) and p), no significant reduction was observed, and it can be seen that the treatment of only the lattice has almost no effect on the rapid discharge characteristics.

In addition, regarding the results of the slow discharge cycle test, as shown in Figure 2, ■ deteriorates earliest, and almost simultaneously (
~ deteriorates. It can be seen that (q has a considerable cycle life, and that (B) has an even longer cycle life than (q). From this experiment, after pretreatment with nitric acid and cleaning the lattice surface, hydrogen borate and phosphoric acid It can be seen that immersion in a mixed solution with nitric acid has the greatest effect. If immersed in a mixed solution without pretreatment with nitric acid, the effect is slightly reduced. This is thought to be due to the fact that if left as is, the reaction between the hydrogen peroxide solution or phosphoric acid and the lattice alloy tends to be inhibited, so the expected amount of compounds on the lattice surface to be produced is small.

In the embodiment, a paste-type electrode plate using an expanded grid was described, but the effects of the present invention are not limited to this embodiment, and the same effect can be obtained even if the grid is made of punched metal or cast metal. is obtained.

Effects of the Invention As described above, the present invention has been developed with the aim of immediately streamlining lead-acid batteries, and has been developed in batteries using expanded metal or punched metal for the grid. This is extremely effective in suppressing capacity deterioration.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between discharge voltage and discharge duration in a low-temperature rapid discharge test, and Figure 2 is a diagram showing the relationship between cycles and capacity retention rate in a slow discharge cycle test.

Claims (3)

[Claims] (1) A method for producing a paste-type electrode for a lead-acid battery, which comprises immersing a grid in an aqueous solution containing hydrogen peroxide and phosphoric acid, and then applying lead paste. (2) The method for manufacturing a paste-type electrode for a lead-acid battery according to claim 1, which comprises a step of cleaning the grid as a pretreatment. (3) The method for manufacturing a paste-type electrode for a lead-acid battery according to claim 2, wherein the pretreatment comprises cleaning the grid with an aqueous nitric acid solution.