Lead Acid Battery

A lead acid battery, also known as a lead storage battery is the oldest kind of rechargeable battery. The battery is common as an energy storing device. The lead acid battery was invented in the year 1859 by Gaston Plante, who was a French physicist. There are still many applications that make use of lead-acid batteries. These find wide usage in vehicles where the battery can provide high current for winding power.

Even though the lead-acid batteries are highly reliable, these have a minimal life. These are also heavy to ship and composed of many toxic materials that require some unique methods of removal at the end of their life. The response time is good, and the power density of this kind of battery is moderate. Depending on the technology of power conversion, the lead-acid batteries can accept or supply energy almost instantaneously. Lead-acid batteries get affected by the temperature, and this is why they need maintenance to maximize their life expectancy. The above explanation lets you understand the basics about what is a lead acid battery.

What is a Sealed Lead Acid Battery?

The sealed lead acid battery is a 12-volt motorcycle battery and has six cells and is made up of a plastic case. Each cell contains a set of positive and negative plates that are immersed in a solution of dilute sulphuric acid, which is known as the electrolyte. Every cell has around 2.1 volts when it is fully charged. The six cells are connected to provide a fully charged 12.6-volt battery.

So how is it possible to stick the lead plates into the sulphuric acid and produce electricity? The battery makes use of an electrochemical reaction that converts the chemical energy into electrical energy. Each of the cells has plates that resemble a small square tennis racket. These are made with lead calcium or lead antimony. A paste that is referred to as active material is bonded to the plates. Sponge lead is used for the negative plates, and lead dioxide is used for the positive plates. When there is an electrical load that is placed across the terminals of the battery, then it is in the active material that the chemical reaction with the sulphuric acid takes place.

Know the Chemical Reaction Behind Discharging

When the battery is in the discharged state, then the positive, as well as the negative plate, becomes lead (II) sulphate (PbSO4). The electrolyte loses the dissolved sulphuric acid, and this is now mostly water. The discharge process gets driven by the electron conduction that occurs from the negative plate back to the cell in the positive plate. This happens in the external circuit.

Here is the Negative plate reaction:

Pb(s) + HSO4(aq) → PbSO4(s) + H+(aq) + 2e

Here is the Positive plate reaction:

 PbO2(s) + HSO4(aq) + 3H+(aq) + 2e → PbSO4(s) + 2H2O(l)

The overall reaction occurs before combining the positive and negative reactions:

Pb(s) + PbO2(s) + 2H+(aq) + 2HSO4(aq) → 2PbSO4(s) + 2H2O(l)

Understand the Charging of the Lead Acid Battery

Chemical energy is stored in the lead acid battery, which is converted into electrical energy when required. The energy conversion from chemical to electrical is known as lead acid battery charging. When the electric power gets changed to chemical energy, then this is discharging.

The sulphuric acid that is present in the lead acid battery decomposes, and this is why it has to be replaced. If the battery spends a lot of time in its discharged state, then this causes a buildup of the chemical, which is not easy to remove. The lead acid batteries are usually charged using an external source of current.

During the process of charging, because of chemical changes, the current passes into the battery. Any lead acid battery may use two kinds of charging methods. These are constant voltage charging or constant current changing.

Know the Chemical Reaction for Recharging

The lead acid battery can also be recharged. When the battery is in the charged state, then every cell contains the negative plate of the element Pb or lead and the positive plate of PbO2 or lead(IV) oxide. The electrolyte contains approximately 4.2M of H2SO4 or sulfuric acid.

In the recharging process, the electrons are forcibly removed from the positive plate, and they are introduced forcibly in the negative plate. This is done by the source of charging.

Here are the chemical reactions that occur in the respective plates.

Negative plate reaction

 PbSO4(s) + H+(aq) + 2e → Pb(s) + HSO4(aq)

Positive plate reaction

 PbSO4(s) + 2H2O(l) → PbO2(s) + HSO4(aq) + 3H+(aq) + 2e

The overall reaction when the negative and the positive plate reactions are combined is:

2PbSO4(s) + 2H2O(l) → Pb(s) + PbO2(s) + 2H+(aq) + 2HSO4(aq)

This is the reverse of the discharge reaction.

It is important to note that if the battery is overcharged, then this will lead to the formation of oxygen gas and hydrogen gas, which are the byproducts. These gases cause a loss of the reactants because of these escapes from the battery.

FAQ (Frequently Asked Questions)

1. What are the Risk Factors of a Lead Acid Battery?

If the lead acid battery is not maintained well, then this can be harmful. There is hydrogen gas that gets generated in the chemical process, and thus this makes it highly dangerous if the lead battery is not used in an area that is ventilated. Also, if the charging is not accurate, then it will cause severe damage to the battery.

2. What are the Safety Hazards of a Lead Acid Battery?

These batteries are the most dangerous, and one should be aware of some of its hazards. The sulphuric acid that is used in the battery as an electrolyte is corrosive in nature. It is important to protect the eyes and feet and use appropriate clothing when working with this battery.

The battery also has a high capacity for generating current. So if there is a metal object placed close to it, then this can cause the current to flow through the metal.

3. What are the Characteristics of the Lead Acid Batteries

The lead acid batteries are convenient to use, are cheap and they work for many applications that run on battery power. These are used in vehicles where the lead acid battery provides power for everything, be it to start the vehicle or to run the electronics.

4. What are the Basic Components of the Lead Acid Battery?

The lead acid battery is primarily made up of four components.

  • The positive plate that has a coating of lead dioxide.

  • The negative plate is made of a sponge lead.

  • Separator is an insulating material that is placed between the two plates and allows the ions and the electrolyte into it to allow conduction without the two plates touching each other. This battery is thus a valve regulated lead acid battery.

  • Electrolyte is composed of sulphuric acid and water.

5. What are the Materials that are Used for the Lead Acid Battery Cells?

The materials used to construct the lead acid battery are

  • Lead peroxide(PbO2).

  • Sponge lead (Pb)

Dilute sulfuric acid (H2SO4).