A nickel–cadmium battery (often written Ni–Cd or Nicad) is a rechargeable secondary cell that was widely used in portable electronics, cordless phones, flashlights and some power tools. Although it remains in service for certain niche applications, many devices now use nickel–metal hydride or lithium‑ion cells because of higher energy density and other advantages.
Construction and chemistry
The negative electrode is made from cadmium metal, while the positive electrode is based on nickel oxyhydroxide compounds. During discharge the cadmium is oxidized and the nickel compound is reduced; on charging the reactions are reversed. The nickel electrode may be described in some sources as involving nickel(III) oxide species that participate in these redox changes.
Electrolyte
Ni–Cd cells use an alkaline ionic conductor rather than an acid. The common choice is potassium hydroxide, which functions as the cell’s electrolyte. The electrolyte itself is largely unchanged by the cell reactions, serving mainly to transport hydroxide ions between electrodes.
Uses and environmental considerations
Historically popular for consumer and industrial rechargeable equipment, Ni–Cd batteries are valued for robustness and tolerance of high discharge rates. They can, however, suffer from voltage depression under certain charging patterns (often called "memory" effects) and require careful charging management.
Environmental and health concerns arise because cadmium is a toxic heavy metal; disposal and recycling of Ni–Cd batteries are therefore regulated in many jurisdictions to prevent contamination and to recover materials for safe reuse.