Nickel-cadmium (NiCd) batteries are a type of rechargeable battery that operates based on chemical reactions. Here’s a simplified explanation of how they work.
- Electrodes: NiCd batteries consist of two electrodes—a positive electrode (anode) made of nickel hydroxide (NiOOH), and a negative electrode (cathode) made of cadmium (Cd).
- Electrolyte: The electrodes are submerged in an alkaline electrolyte solution typically composed of potassium hydroxide (KOH) dissolved in water. The electrolyte allows ions to move between the electrodes during charging and discharging.
- Charging: During charging, an external voltage source is applied to the battery, causing a flow of current. This voltage causes a chemical reaction at the electrodes. At the negative electrode (cathode), cadmium metal reacts with hydroxide ions (OH-) in the electrolyte to form cadmium hydroxide (Cd(OH)₂) and release electrons:Cd + 2OH- → Cd(OH)₂ + 2e-These released electrons flow through the external circuit to the positive electrode (anode), where they’re used to reduce nickel hydroxide (NiOOH) to nickel oxyhydroxide (Ni(OH)₂) and release hydroxide ions:NiOOH + H2O + e- → Ni(OH)₂ + OH-This reaction stores energy in the battery.
- Discharging: When the battery is connected to a device, the stored energy is released as electrical current. During discharging, the reactions at the electrodes are reversed:At the positive electrode (anode), nickel oxyhydroxide (Ni(OH)₂) reacts with hydroxide ions to form nickel hydroxide (NiOOH) and release electrons:Ni(OH)₂ + OH- → NiOOH + H2O + e-At the negative electrode (cathode), cadmium hydroxide (Cd(OH)₂) is oxidized to form cadmium metal, while hydroxide ions are released into the electrolyte:Cd(OH)₂ → Cd + 2OH-
- Overall Reaction: The overall reaction during discharge is the reverse of the charging reaction:Cd + 2NiOOH + 2H2O → 2Ni(OH)₂ + Cd(OH)₂
During each charge-discharge cycle, these reactions repeat. However, over time, NiCd batteries can suffer from “memory effect” if they’re not fully discharged before recharging, leading to reduced capacity. Additionally, cadmium is toxic, so proper disposal or recycling of NiCd batteries is essential to prevent environmental damage.
