How does Ni-Cad Battery achieve charging and discharging?

Nickel-Cadmium Battery is a common rechargeable battery, which is widely used in various devices for its good cycle performance and long service life.

1. Basic structure of nickel-cadmium battery
Nickel-cadmium battery is mainly composed of the following parts.
Positive electrode: nickel hydroxide (NiOOH), as an oxidant when the battery is charged.
Negative electrode: cadmium (Cd), as a reducing agent.
Electrolyte: generally potassium hydroxide (KOH) solution, which plays a conductive role.
This structure enables the battery to undergo chemical reactions during the charging and discharging process to achieve energy conversion.

2. Charging process
The charging process is usually divided into several stages.
Initial charging stage: In this stage, the voltage and current of the battery are low, and the current provided by the charger gradually increases. This process is to gradually start the chemical reaction inside the battery to ensure the safety and stability of the battery.
Fast charging stage: In this stage, the voltage of the battery rises, the internal reaction speed accelerates, and the current reaches the highest point. At this time, the charger provides the maximum charging current to the battery for rapid charging. This process usually takes a few hours to more than ten hours, depending on the capacity of the battery and the power of the charger.
Constant voltage charging stage: When the battery is close to full, the charger will automatically reduce the output current to prevent overcharging. During this stage, the battery voltage is maintained at a constant value to further ensure safety.
Charging completion stage: The charger monitors the voltage and temperature of the battery to determine whether the charging is complete. Once the battery reaches the preset charging threshold, the charger will automatically stop charging to prevent overheating or damage.

3. Charging precautions
During the charging process, there are several important precautions.
Avoid overcharging: Overcharging may cause the internal temperature of the battery to be too high, affecting the battery life and even causing safety hazards. Modern chargers are usually equipped with overcharge protection to automatically cut off charging.
Temperature monitoring: High temperature will reduce the charging efficiency of the battery and may cause battery damage. Therefore, it is very important to maintain a suitable temperature for the charging environment.
Choose a suitable charger: Use a charger that matches the battery and ensure that the output current and voltage meet the battery requirements to improve charging efficiency and protect the battery.

4. Charging efficiency and performance
The charging efficiency of nickel-cadmium batteries is usually high, reaching 80%-90%. However, the battery may be affected by the "memory effect" during use, that is, if it is not fully discharged before charging, the available capacity of the battery may decrease. Therefore, regular full discharge and charge cycles are an effective way to maintain battery performance.

The charging process of nickel-cadmium batteries is a complex and sophisticated electrochemical reaction process involving multiple stages and chemical changes. Understanding its charging principle and process will help to better use and maintain nickel-cadmium batteries and extend their service life. With the development of science and technology, although nickel-cadmium batteries are gradually replaced by new batteries, their charging principles still provide us with valuable learning and application experience.