Lead acid battery

 The lead–acid battery was invented in 1859 by French physicist Gaston Planté and is the earliest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by starter motors.

Working and construction of Lead acid Battery

Almost every portable and handheld device consist a battery. The battery is a storage device where energy is stored to provide the power whenever needed. There are different  types of batteries available in this modern electronics world, among them Lead Acid battery is commonly used for high power supply. Usually Lead Acid batteries are bigger in size with hard and heavy construction, they can store high amount of energy and generally used in automobiles and inverters.

Even after getting competition with Li-ion batteries, Lead acid batteries demand is increasing day by day, because they are cheaper and easy-to-handle in comparison with Li-ion batteries. As per some market research India Lead Acid Battery Market is projected to grow at CAGR of over 9% during 2018-24. So, it has huge market demand in Automation, Automotive, and Consumer Electronics. Altough most of the Electric vehicle comes with Lithium-ion batteries, but still there are many electric two wheeler which use Lead Acid batteries to power the vehicle.

In previous tutorial we learned about Lithium batteries here we will understand the Working, construction and applications of Lead Acid Batteries. We will also learn about charging/discharging ratings, requirements and safety of Lead Acid Batteries.

Construction of lead acid battery

What is a Lead Acid Battery? If we break the name Lead Acid battery we will get Lead, Acid, and Battery. Lead is a chemical element (symbol is Pb and the atomic number is 82). It is a soft and malleable element. We know what Acid is; it can donate a proton or accept an electron pair when it is reacting. So, a battery, which consists of Lead and anhydrous plumbic acid (sometimes wrongly called as lead peroxide), is called as Lead Acid Battery.

Now, what is the internal construction?

A Lead Acid Battery consists of the following things, we can see it in the below image:

                                                                    

                                                                     

                                                     

A Lead Acid Battery consists of Plates, Separator, and Electrolyte, Hard Plastic with a hard rubber case.

In the batteries, the plates are of two types, positive and negative. The positive one consists of Lead dioxide and negative one consists of Sponge Lead. These two plates are separated using a separator which is an insulating material. This total construction is kept in a hard plastic case with an electrolyte. The electrolyte is water and sulfuric acid.

The hard plastic case is one cell. A single cell store typically 2.1V. Due to this reason, A 12V lead acid battery consists of 6 cells and provide 6 x 2.1V/Cell = 12.6V typically.

Working of Lead acid Battery

Working of the Lead Acid battery is all about chemistry and it is very interesting to know about it. There are huge chemical process is involved in Lead Acid battery’s charging and discharging condition. The diluted sulfuric acid H2SO4 molecules break into two parts when the acid dissolves. It will create positive ions 2H+ and negative ions SO4-. As we told before, two electrodes are connected as plates, Anode and Cathode. Anode catches the negative ions and cathode attracts the positive ions. This bonding in Anode and SO4- and Cathode with 2H+ interchange electrons and which is further react with the H2O or with the water (Diluted sulfuric acid, Sulfuric Acid + Water).

The battery has two states of chemical reaction, Charging and Discharging.

Lead acid Battery Charger

As we know, to charge a battery, we need to provide a voltage greater than the terminal voltage. So to charge a 12.6V battery, 13V can be applied.

But what actually happen when we charge a Lead Acid Battery?

Well, the same chemical reactions which we described before. Specifically, when the battery is connected with the charger, the sulfuric acid molecules break into two ions, positive ions 2H+ and negative ions SO4-. The hydrogen exchange electrons with the cathode and become hydrogen, this hydrogen reacts with the PbSO4 in cathode and form Sulfuric Acid (H2SO4) and Lead (Pb). On the other hand, SO4- exchange electrons with anode and become radical SO4. This SO4 reacts with PbSO4 of anode and create the lead peroxide PbO2 and sulfuric acid (H2SO4). The energy gets stored by increasing the gravity of sulfuric acid and increasing the cell potential voltage.

As explained above, following chemical reactions takes place at Anode and Cathode during the charging process.

As explained above, following chemical reactions takes place at Anode and Cathode during the charging process.

At cathode

PbSO4 + 2e- => Pb + SO42-

At anode

PbSO4 + 2H2O => PbO2 + SO42- + 4H- + 2e-

Combining above two equation, the overall chemical reaction will be

2PbSO4 + 2H2O => PbO2 + Pb + 2H2SO4