Batteries and Cells
1. Battery and its types
A battery is a device that converts chemical energy directly into electrical energy through an electrochemical
reaction. It consists of one or more electrochemical cells, each containing an anode (negative terminal), a
cathode (positive terminal), and an electrolyte (a chemical solution that allows ions to flow between the
electrodes).
When a battery is connected to an external circuit, chemical reactions occur at the electrodes, causing
electrons to flow from the anode to the cathode through the external circuit, generating an electric current.
Types of Batteries (Broad Categories):
Batteries are primarily categorized into two main types based on their reusability:
• Primary Batteries (Non-rechargeable): These batteries are designed for single use. The chemical
reactions that produce electricity are irreversible, meaning once the reactants are consumed, the battery
can no longer produce power and must be discarded.
• Secondary Batteries (Rechargeable): These batteries can be recharged multiple times. The
chemical reactions within these cells are reversible, allowing electrical energy to be converted back into
chemical energy by applying an external current, thereby restoring the battery’s charge.
Beyond this primary categorization, batteries can also be classified by their chemistry, application, and
form factor. Some common examples include:
• Alkaline Batteries: A common type of primary battery (e.g., AA, AAA, C, D).
• Lithium-ion (Li-ion) Batteries: A widely used type of secondary battery for portable electronics,
electric vehicles, etc., known for high energy density.
• Nickel-Cadmium (NiCd) Batteries: An older type of secondary battery, less common now due to
cadmium toxicity.
• Nickel-Metal Hydride (NiMH) Batteries: A type of secondary battery, often replacing NiCd,
with higher energy density and less toxicity.
• Lead-Acid Batteries: A type of secondary battery commonly used in vehicles (car batteries) and
uninterruptible power supplies (UPS).
• Coin/Button Cells: Small, typically primary batteries used in watches, calculators, etc. (e.g.,
Lithium coin cells, silver oxide).
2. Cell
In the context of batteries, a cell is the fundamental electrochemical unit that converts chemical energy into
electrical energy. A battery can consist of a single cell (like a typical AA battery, which is technically a
single cell) or multiple cells connected in series or parallel to achieve a desired voltage and capacity (e.g., a
12V car battery consists of six 2V lead-acid cells connected in series).
Each cell contains:
• Anode (Negative Electrode): Where oxidation (electron release) occurs.
• Cathode (Positive Electrode): Where reduction (electron acceptance) occurs.
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• Electrolyte: A substance (liquid or gel) that allows ions to move between the anode and cathode,
completing the internal circuit.
• Separator: A porous membrane that prevents the anode and cathode from directly touching, while
allowing ion flow.
The voltage produced by a single cell depends on the specific chemical reactions occurring within it (e.g., a
common alkaline cell produces about 1.5V, while a lithium-ion cell typically produces 3.7V).
3. Primary cell and secondary cell
Here’s a detailed comparison between primary and secondary cells:
Feature Primary Cell Secondary Cell
Rechargeability Non-rechargeable Rechargeable
Chemical Reaction Irreversible (once reactants consumed) Reversible (can be reversed by applying
Energy Conversion Chemical → Electrical only Chemical ↔ Electrical
Life Cycle Single use, then discarded Multiple charge/discharge cycles
Cost Generally lower initial cost Higher initial cost
Convenience No need for charger, ready to use Requires a charger, needs to be charged
Discharge Curve Relatively stable voltage, then drops sharply More stable discharge, can vary by chem
Internal Resistance Generally lower, can increase over life Varies, can increase with cycles
Examples Zinc-carbon, Alkaline, Lithium (primary), Silver-oxide Lead-acid, Lithium-ion, NiCd, NiMH
Applications Remote controls, flashlights, toys, smoke detectors Mobile phones, laptops, electric vehicles,
In summary:
• Primary cells are convenient for low-power, intermittent use where replacement is easy and charging
isn’t practical.
• Secondary cells are economical for frequent, high-power use, as they can be reused many times,
reducing waste and long-term costs despite a higher initial investment.
