Acid Accumulator: Rechargeable cells

Some electrochemical cells can be recharged because the electrode reactions are reversible and the process can be repeated repeatedly. Electricity can be stored in such cells. The familiar lead-acid accumulator (‘car battery’) seen in most combustion-engined automobiles is the most prevalent type of heavy duty rechargeable cell. Two electrodes are submerged in a sulfuric acid electrolyte in a lead–acid accumulator. The positive electrode is formed of metallic lead oxide grains, and the negative electrode is linked to a metallic lead grid. Floating and valve-regulated lead–acid batteries are the two types of lead–acid batteries.

Working of Lead Acid Accumulator:

The negative electrode of a lead acid battery is formed of spongy or porous lead. To aid in the creation and dissolution of lead, it is porous.Lead oxide is used to make positive electrodes. Both electrodes are submerged in a sulfuric acid and water electrolytic solution. An electrically insulating but chemically permeable membrane separates the two electrodes in the event that they come into contact with each other due to physical movement of the battery or variations in electrode thickness. This membrane also protects the electrolyte from electrical shorting. The reversible chemical mechanism shown below stores energy in lead acid batteries.

PbO₂ + Pb + 2H₂SO₄ 2PbSO₄ + 2H₂O

The charge and discharge reactions at the negative terminal are as follows:

Pb + SO_4²– PbSO₄ + 2e–

The charge and discharge responses at the positive terminal are as follows:

PbO₂ + SO₄²– + 4H+ + 2e–    PbSO₄ + 2H₂O

Discharging a battery produces the development of lead sulphate crystals at both the negative and positive terminals, as well as the release of electrons due to the change in valence charge of the lead, as shown by the equations above. Sulfate from the sulfuric acid electrolyte surrounding the battery is used to make this lead sulphate. As a result, the electrolyte concentration decreases. Instead of sulfuric acid enveloping the electrodes after a full discharge, both electrodes would be covered in lead sulphate and water. The two electrodes are the same material at full discharge, and there is no chemical potential or voltage between them. Discharging, on the other hand, ceases at the cutoff voltage, which is a considerable way ahead of this point in practice. As a result, the battery should not be depleted below this voltage.

What is the definition of an electrochemical cell?

An electrochemical cell is a device that uses chemical reactions to generate electrical energy. The chemical processes are smoothed by the electrical energy supplied through electrochemical cells. The gadgets in an electrochemical cell have the ability to transform chemical energy to electrical energy or vice versa.

Primary cell:

Primary cells are single-use or “use & discard” galvanic cells that cannot be recharged. In nature, the events that occur in the primary cell are irreversible.

Cell reaction:

Zn(s) → Zn₂+ + 2e– (Anode) 

MnO₂ + NH₄+ + e–→ MnO(OH) + NH₃ (Cathode)

Examples: Dry cell and alkaline batteries.

Secondary cell:

“Rechargeable” cells are another name for secondary cells. It signifies the cell has a reversible response, which means it may be utilised as both galvanic and electrolytic cells.

Cell reaction:

 Pb(s) + SO₄²–(aq) → PbSO₄(s) + 2e– (Anode)

PbO₂(s) + SO₄²–(aq) + 4H+(aq) + 2e– → PbSO₄(s) + 2H₂O (l) (Cathode)

Examples:  lead storage battery and nickel-cadmium storage cell.

Types of elcetrochemical cells:

The electrochemical cells are classified into two primary cells:

• Galvanic Cells [voltaic cells]
• Electrolytic Cells

Density of the electrolyte:

Because lead and lead dioxide both react with sulphuric acid to generate lead sulphate, the density of an electrolyte in a lead storage battery falls when it is emptied .

Types of Lead Acid Accumulators:

Despite the wide diversity of battery types and uses, the maintenance requirements of the battery and the ability to deep charge a battery while maintaining a long lifetime are particularly significant in PV applications. Deep cycle batteries can be either open-flooded or immobilised electrolytic, with an excess of electrolytic solution and thick plates, to improve long cycle life with deep discharge. Sealed gel batteries are rated as deep cycle batteries, although they can only handle a limited number of cycles and discharges compared to flooded plate or AGM cells. Shallow-cycle batteries contain thinner plates composed of lead calcium alloys with a depth of discharge that is typically less than 25%.

Conclusion:

The lead-acid accumulator represents the oldest rechargeable battery technology. Lead acid batteries are used in a wide range of applications, including small-scale power storage systems like UPS systems, beginning illumination, and ignition power sources for autos, as well as large-scale power systems like grid-scale power systems.