Secondary batteries, also known as rechargeable batteries, generate electrical energy through reversible chemical reactions. Specifically, they work through oxidation-reduction (redox) reactions that can be both discharged (producing electricity) and recharged (reversing the chemical reaction).
Here's a breakdown of the process:
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Discharge: During discharge, a chemical reaction occurs that releases electrons, creating an electric current. One electrode (the anode) undergoes oxidation, losing electrons, while another electrode (the cathode) undergoes reduction, gaining electrons. This electron flow is what powers external devices.
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Recharge: When recharging, an external electrical current is applied to the battery, reversing the chemical reaction. The oxidized material at the anode is reduced back to its original state, and the reduced material at the cathode is oxidized back to its original state. This essentially "reloads" the battery with chemical energy.
Key Components and Processes:
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Electrodes (Anode & Cathode): These are the active materials where the redox reactions occur. Different battery chemistries use different materials for the electrodes (e.g., lead and lead dioxide in lead-acid batteries, lithium compounds in lithium-ion batteries).
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Electrolyte: This is a substance (liquid, gel, or solid) that allows ions to move between the electrodes, completing the circuit.
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Separator: This is a physical barrier that prevents the electrodes from touching and short-circuiting, while still allowing ions to flow through the electrolyte.
Types of Secondary Batteries and Their Materials:
The specific oxidizing and reducing substances used in the electrodes and electrolyte determine the characteristics of the battery, such as voltage, energy density, and cycle life. Here are a few examples:
| Battery Type | Anode (Reducing Agent) | Cathode (Oxidizing Agent) | Electrolyte |
|---|---|---|---|
| Lead-Acid | Lead (Pb) | Lead Dioxide (PbO2) | Sulfuric Acid (H2SO4) |
| Nickel-Cadmium (NiCd) | Cadmium (Cd) | Nickel Oxide Hydroxide (NiOOH) | Potassium Hydroxide (KOH) |
| Nickel-Metal Hydride (NiMH) | Metal Hydride (MH) | Nickel Oxide Hydroxide (NiOOH) | Potassium Hydroxide (KOH) |
| Lithium-Ion (Li-ion) | Graphite (LiC6) | Lithium Metal Oxide (e.g., LiCoO2) | Lithium Salt in Organic Solvent |
In summary, secondary batteries function by reversibly converting chemical energy into electrical energy through oxidation-reduction reactions, enabling them to be recharged and reused.
