JPH0363181B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a lead-acid battery using a copper material for the negative electrode plate.

Lead-acid batteries are widely used in a variety of applications, but the resistivity of lead is 21×10 ^-6 Ω・cm, which is quite high for a metal, so when discharging large currents or using large batteries, the voltage drop due to ohmic resistance may cause problems. The drawback is that the discharge performance is severely restricted. To solve this problem, it is effective to use copper or a copper alloy with low electrical resistance for the grid. However, copper has a lower hydrogen overvoltage than lead, and a large amount of hydrogen gas is generated at the open circuit potential of a negative electrode plate using spongy lead as an active material. Therefore, when copper is used for the negative electrode plate, hydrogen gas is generated from the surface of the copper as shown in the following equation, and the negative electrode plate discharges, increasing the rate of self-discharge.

Copper surface: 2H ⁺ +2e→H ₂ Negative electrode active material: Pb + SO ₄ ^-- →PbSO ₄ +2e Overall: Pb + 2H ⁺ +SO ₄ ^-- →PbSO ₄ +H ₂ Therefore, when copper is used as the negative electrode grid, copper It has been considered necessary to completely coat the surface with lead.

As is well known, with normal plating, some pinholes and uneven coating cannot be avoided, so the plating operation has to be repeated many times with great care, which increases the cost and makes it impossible to put it into practical use. It was hot.

The present invention breaks the conventional wisdom regarding the use of copper for negative electrode grids, makes it possible to use copper grids at low cost, and improves the discharge characteristics by reducing the internal resistance of the battery.

Its gist is that it is a lattice in which a coating layer made of lead or lead alloy with pinholes and uneven coating is provided on the surface of copper or copper alloy.
A grid with a partially exposed surface of copper or copper alloy is used for the negative plate, the capacity of the negative plate is larger than the capacity of the positive plate, and the terminal voltage of the cell is
A mechanism is installed to release the load and open the cell when the voltage drops to 1.5 or lower, and the final discharge voltage is set to 1.5.
In addition, the average thickness of the coating layer made of lead or a lead alloy must be 0.1 mm or more.

The relationship between the amount of copper deposited on the negative electrode plate and the self-discharge rate is shown in Figure 1.
Adverse effects appear when the amount exceeds % by weight. The number of times a lead-acid battery can be charged and discharged is usually considered to be less than 10,000 times. Therefore, if the amount of copper eluted per 1〓 is kept below 0.01/10000=1×10 ^-6 % of the negative electrode active material,
The disadvantages of copper can be ignored. The atomic weight of lead is
207, and in a normal lead-acid battery, the weight of the electrolyte is about twice the weight of the negative electrode active material, so the amount of copper eluted per 1㎓ is: 1 x 10 ^-6 x (1000 x 207) x ( 1/2)=2.5× ^10-6
It is sufficient to keep it to mol/mole.

The equilibrium potential for dissolution and precipitation of copper is 0.34, which is about 0.7 nobler than the equilibrium potential for dissolution and precipitation of lead.
The relationship between the equilibrium potential of the copper electrode (E゜_cu ) and the activity of copper (a _cu ⁺⁺ ) is thermodynamically expressed by the following equation.

E゜_cu = 0.34 + 0.029511oga _cu ⁺⁺ The activity of dissolved copper is approximately equal to its molarity in a dilute solution. Therefore, in order to suppress the above-mentioned permissible elution amount of copper to 2.5×10 ^-6 mol/or less, it is necessary and sufficient to keep the potential of copper at 0.17 or less from the above equation.

E _cu = 0.34 + 0.0295 log2.5 × 10 ^-6 = 0.17 In other words, if the potential of the negative electrode plate is kept below 0.17, the elution of copper will not have any adverse effect on the lead-acid battery. This means that even if the negative electrode plate has a smaller capacity than the positive electrode plate, it need not be polarized by 0.17-(-0.35)=0.5, that is, by 0.5 or more.

A negative electrode plate using a copper grid was immersed in dilute sulfuric acid to determine the rate of self-discharge. The copper grid was coated with lead to varying degrees. The results are shown in FIG. It can be seen that the rate of self-discharge increases approximately linearly with the exposed area of copper. In other words, when copper is used for the grid, the lead coating that has conventionally been applied does not have to be complete as previously thought, but may be incomplete. 1% for lead coating
Even if there is an incomplete part, the increase in self-discharge is 1%.
No more than the following.

In order to prevent copper leaching when copper incompletely coated with lead is used in the grid, the potential of the negative plate should not be polarized by more than 0.5 under any load, as described above. The most reliable and easiest method for this purpose is to make the capacity of the negative plate larger than the capacity of the positive plate. In this case, the terminal voltage at the end of discharge is influenced by the voltage drop on the positive plate, and the change in potential on the negative plate is reduced.

When using lead-acid batteries, the capacity of the positive and negative plates increases and decreases. Therefore, in order to suppress the polarization of the negative electrode plate to 0.5 or less in all cases, the cell terminal voltage should not be lowered by 0.5 or more. As is well known, the open circuit voltage of a lead-acid battery is approximately 0.2, so if the load is removed and the battery becomes open circuit when the terminal voltage drops to 1.5 or less, copper elution can be prevented.

In addition to electrolytic plating, there are other methods for coating with lead, such as immersion in molten lead for a short period of time and pulling it up, and metallization, which involves spraying molten lead and depositing it. Although these methods provide a somewhat less complete coating than electroplating, they are fully practicable because, as already mentioned, it is not necessary to completely cover the lead.

The thickness of the lead coating may be sufficient as long as it prevents the negative electrode plate from becoming porous during charging and discharging. When lead becomes porous, the exposed area of copper increases and the self-discharge rate increases. The result of charging and discharging the lead sheet 10,000 times showed that the thickness of the porous layer was 0.1 mm or less, so the thickness of the lead coating should be 0.1 mm or more.

If covered with a thick active material layer, the lead coating layer becomes porous or less porous, so it is preferable to embed the grid made of copper in the active material. For this purpose, a frame made of lead, lead alloy, or plastic is integrally molded with a grid made of copper or copper alloy coated with lead or lead alloy, and the thickness of the frame is made larger than the thickness of the copper grid. Bye.

The grid made of copper may be made by casting or punching a plate, but a structure made by making cuts in a copper plate and stretching it, that is, one made by expanding processing is the cheapest and most suitable. In this case, it is preferable to manufacture the grid by arranging expanded crosspieces so that the current direction is up and down.

As described above, according to the present invention, a copper grid can be used at low cost, and the internal resistance of the battery can be reduced to improve the discharge characteristics.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between the amount of copper deposited on the negative plate and self-discharge, and Figure 2 is a characteristic diagram showing the self-discharge rate of negative plates using copper grids coated with lead to various degrees. be.

Claims (1)

[Scope of Claims] 1. A copper or copper alloy lattice with a coating layer made of lead or a lead alloy on the surface, where the coating layer has pinholes or uneven coating, and part of the surface of the copper or copper alloy is A grid with exposed parts is used as the negative plate, the capacity of the negative plate is made larger than the capacity of the positive plate, and when the terminal voltage of the cell becomes 1.5 or less, the load is released and the cell is opened. A lead-acid battery equipped with a mechanism that 2 The average thickness of the coating layer made of lead or lead alloy is
The lead-acid battery according to claim 1, which has a diameter of 0.1 mm or more.