Nickel Cadmium Batteries

Introduction

Nickel Cadmium batteries use electrodes made of nickel oxide hydroxide, metallic cadmium and an alkaline electrolyte of potassium hydroxide. The NiCd battery was invented by Waldemar Junger and patented in 1899. A Nickel Cadmium battery is a rechargeable battery that commonly finds use in portable computers, drills, camcorders and other small battery-operated devices.  

Electrochemistry of Nickel Cadmium Batteries

A fully charged NiCd cell contains:

• a nickel(III) oxide-hydroxide positive electrode plate
• a cadmium negative electrode plate
• a separator, and
• alkaline electrolyte (potassium hydroxide).

 

Advantages

  The advantages of Nickel Cadmium batteries are as below:

• Low internal resistance (less than half the equivalent NiMH cells)
• High rate charge and discharge rates possible
• Up to 10C discharge rates for short periods typical.
• Flat discharge characteristic (but falls off rapidly at the end of the cycle)
• Tolerates deep discharges - can be deep cycled.
• Wide temperature range (Up to 70°C)
• Typical cycle life is over 500 cycles.
• Charging process is strongly endothermic-the battery cools during charging. This makes it possible to charge very quickly.
• Rapid charge of battery can happen in 2 hours, but can be as low as 10 to 15 minutes.
• The coulombic efficiency of nickel cadmium is over 80% for a fast charge.
• The sealed nickel-cadmium cell can be stored in the charged or discharged state without damage.
• The electrolyte is low cost potassium hydroxide KOH and easily available.
• Available in a large variety of sizes and capacities.

  Disadvantages of Nickel Cadmium batteries  

• Memory Effect issues

A major drawback of this technology is that the Nickel Cadmium batteries suffer from the memory effect. The memory effect happens when crystalline formation expands from a small to large size, which occurs when a NiCd battery is recharged before it is fully discharged. Increase in cell impedance can happen because of this and can prevent the battery from discharging beyond that point and cause it to self-discharge. Reconditioning:  Through a process called reconditioning the Memory effect can be reversed by putting the battery through many discharge and recharge cycles which helps to recover the smaller crystal formations.  

• Susceptible to damage due to Overcharging.

They have a low cell voltage of 1.2 Volts compared with primary alkaline cells that have 1.5 Volts and only quarter of the capacity of the alkaline cells. It is advisable to have self re-sealing safety vents to prevent damage due to overheating and pressure build up.  

• Negative environmental Impact

Cadmium is a highly costly and toxic metal. Nickel Cadmium batteries contain from 6- 18% cadmium, and because of the toxicity, it therefore requires special care during battery disposal.