Rechargeable batteries, also known as secondary cells, work by using reversible chemical reactions that allow them to regain their electrical charge. This process happens when electricity is passed through the battery.
Understanding Reversible Reactions
The key to a rechargeable battery's function lies in its ability to perform reversible electrochemical reactions. Here's a breakdown:
- Discharge: During normal use, the battery undergoes a chemical reaction that produces electricity, moving ions from one electrode to another, and supplying power to a device.
- Recharge: When you connect the battery to a charger, you reverse this process. By forcing electricity back into the battery, the chemical reaction is driven in the opposite direction, restoring the original chemical composition and effectively “recharging” the battery, and the cell potential is regained.
The Charging Process in Detail
The charging process can be viewed as a push of electric current into the battery to undo the chemical reactions that released energy. This is achieved by applying external electrical energy through a charger:
- External Electrical Energy: The charger provides a voltage higher than the battery's potential, creating a current flow.
- Reversal of Chemical Reactions: This current forces ions to move back to their original locations within the battery. This reverses the electrochemical process, restoring the battery to its charged state.
- Energy Storage: The applied electrical energy is converted back to chemical energy, stored within the battery.
- Ready for Use: Once charged, the battery is ready to be discharged, providing power to electronic devices.
Why Are They Called Secondary Cells?
The term "secondary cells" highlights a crucial distinction:
- Primary cells (non-rechargeable batteries) undergo irreversible reactions, making them single-use.
- Secondary cells (rechargeable batteries) are designed for multiple cycles of discharge and recharge due to their reversible reactions.
Examples of Rechargeable Batteries
Different types of rechargeable batteries exist, each with unique chemistries:
- Lithium-ion (Li-ion): Commonly used in smartphones, laptops, and electric vehicles due to their high energy density.
- Nickel-metal hydride (NiMH): Found in some portable electronics and hybrid vehicles, known for better performance than nickel-cadmium batteries.
- Lead-acid: Primarily used in automobiles for starting, lighting, and ignition, known for reliability and low cost but larger size.
- Nickel-cadmium (NiCd): Once popular, now less common due to environmental concerns and lower energy density.
Key Points to Remember
- Rechargeable batteries function through reversible chemical reactions.
- The charging process involves using an external source of electricity to reverse the discharge reactions.
- They are called secondary cells because they can be recharged, unlike primary cells.
- The technology has revolutionized the electronics industry by allowing reusable power.
