How Do Lead Acid Batteries Work?

Energy storage and conversions are always on the top list of discussions and researches worldwide. Electrochemical energy technology offers the safest, reliable, and cost-effective lead-acid batteries.  The lead-acid battery is a complex electrochemical system involving current generating electrochemical reactions. This is one of the main portable electric power sources with a wide range of applications. 

Energy storage and conversions are always on the top list of discussions and researches worldwide. Electrochemical energy technology offers the safest, reliable, and cost-effective lead-acid batteries. 

The lead-acid battery is a complex electrochemical system involving current generating electrochemical reactions. This is one of the main portable electric power sources with a wide range of applications. 

The lead-acid battery falls in the category of rechargeable secondary batteries. It can be charged and discharged repeatedly since battery reactions are highly reversible. 

French physicist Gaston Plante discovered that a cell with lead plates separated by rubber strips and immersed in 10% sulfuric acid solution allows flow of maximum secondary current for a long time with the highest voltage than any other electrodes including silver, tin, copper, gold, platinum and aluminum. 

Even after 160 years, the lead-acid battery is still a reliable source of power in areas of transportation, telecommunication, and informational technology and so on. 

Components

1) Active component

Lead peroxide which is a dark brown or chocolate brown in color, hard and brittle substance forms positive active component. 

Pure lead in soft sponge, dull grey in color forms the negative active component. And the next active component is a mixture of dilute sulfuric acid and distilled water in the ratio of 3:1 (water: acid).  

2) Plates

One of the crucial components of lead acid batteries is the plates. Usually plates are made flat to achieve maximum available surface area. There are positive and negative plates, where positive plates are covered with a paste of lead dioxide and negative made of sponge lead. 

The flat plates possess grids, made of an alloy of lead and antimony, so that it ensures equal distribution of current to active components. The life of lead acid battery can be predicted with the thickness of positive plates. The thicker the plate longer the life will be. Hence, weight of the battery shows signs of lead content and life expectancy. 

3) Electrolytes

An appropriate blend of dilute sulfuric acid and distilled water is a basic part of any lead acid battery. The reaction of electrolyte with the plates results in the power production. This process resulted in the wording ‘lead acid battery’. 

The plates will be submerged in the electrolyte and make sure of chemical connection. Maintenance free batteries are available so that worries of checking electrolyte as in the case of low maintenance batteries can be avoided. 

If the acid solutions are of higher or lower concentrations than the battery operation range, performance parameter of battery will be declined. 

4) Separators

Separators is one of the another basic piece of a lead acid battery. It keeps positive and negative plates in isolation and ensures that it never touches each other. 

Thus, prevents the system from short circuit. The separator should be resistant to oxidation and in the same time reconcilable with the electrolyte.

Working of Lead Acid Batteries

Discharging

Discharging of lead acid battery happens when power is taken from the battery. This happens through various chemical reactions between the two plates and the electrolyte. Two plates, positive made of dark brown lead peroxide and negative plate is pure soft sponge lead in dull grey color. These plates of the battery are connected externally by a load. They are chemically connected through an electrolyte which is a mix of diluted sulfuric acid and distilled water, by dipping the plates in it. 

The molecules of the acid breaks down into positive hydrogen ions and negative sulphate ions and execute a free motion in the solution. 

When the positive hydrogen ion come in contact with lead peroxide plate, reacts and receives one electron and become hydrogen atom. This hydrogen atom in turn attack lead peroxide and produce lead oxide and water. 

Now, the produced lead oxide reacts with the sulfuric acid to form lead sulphate and water. 

At the same time, some of the freely moving negative sulphate ions react with pure lead plate which eventually gives two electrons and become radical sulphate. The produced radical sulphate attacks the metallic lead since radical sulphate cannot exist alone. 

Here, hydrogen ions takes electron from lead peroxide and negative sulphate ions give electrons to pure lead plate, the outcome is imbalance in the charge of the two electrodes. This inequality thereby causes the flow of electrons which is the flow of current through the externally connected load for balancing. 

Charging

Now, instead of an external load replace it with an external DC source. Its positive terminal is connected to lead peroxide plate which is now covered with lead sulfate and lead peroxide covered lead plate with a negative terminal of the DC source. 

In the discharge state, lead dioxide positive electrode and lead negative electrode gets converted to lead sulfate and consume sulfate ions which reduces specific gravity of the electrolyte so that it is closer to that of water, but still  acid is present in the solution. 

This positively charged hydrogen ion now reaches the electrode connected to the negative terminal of the DC source. . Hydrogen ion receives electron to become hydrogen atom. This formed hydrogen atom then attacks lead sulphate to give lead and sulfuric acid. 

At the same moment, negative sulphate ions present in the solution move towards electrode which is connected to DC source’s positive terminal, where they will lose their extra electrons to become radical sulphate. 

This radical sulphate attacks lead sulphate of anode and the result is lead peroxide and sulfuric acid. This is the process of charging a lead acid battery and is ready for discharge. Hence, the method of regenerating active material is called charging. 

The voltage of a lead-acid battery cell during charge must exceed the open circuit voltage. During discharge, the case is reversed. 

Conclusion 

Lead acid battery accounts for over half of the world’s demand. Over the years this rechargeable secondary battery has progressed immensely and now it is a globally standardized mature product. The sales of lead acid battery constitute nearly 70% of world’s secondary battery market. 

Different varieties of lead acid batteries are ruling the market today and the main two categories are flooded cells and Sealed Lead Acid Batteries. Flooded Lead Acid Battery is the most common and is used in automotive industry to a large extent. And, Sealed cell also known as VRLA (Value Regulated Lead Acid) is another type which is the safest battery of today to use. 

Significant reduction in carbon dioxide, low cost, availability of maintenance free version, ease in manufacturing, recycling properties, diversities in capacities, size and designs; better operating temperature range (which is in between -40degree Celsius and 60degree Celsius), good recharge efficiency are some of the highlighted benefits of lead acid battery and the reason for its wide acceptance.