NiCd

NiCd, or nickel-cadmium, refers to a class of rechargeable batteries that use nickel oxide hydroxide for the positive electrode, cadmium for the negative electrode, and an alkaline electrolyte such as potassium hydroxide. Each cell provides about 1.2 volts, and packs are assembled from cells in series to achieve common voltages used in portable electronics and power tools.

NiCd chemistry was developed in the late 19th century by Waldemar Jungner and was widely adopted in the mid- to late 20th century. It became a standard for cordless tools, power tools, aviation, and emergency lighting due to rugged construction, fast charging, and good performance at low temperatures. In recent decades, consumer electronics have largely shifted to nickel-metal hydride (NiMH) and lithium-ion chemistries, but NiCd remains in use in certain specialties such as aviation, medical equipment, uninterruptible power supplies, and some heavy-duty tools.

Key characteristics include a high cycle life, high discharge rates, and tolerance of deep discharges. NiCd cells have relatively low internal impedance, enabling rapid high-current operation. A commonly noted issue is the memory effect, a partial loss of capacity from repeated partial discharges, though modern cells mitigate this risk significantly. NiCd also exhibits a higher self-discharge rate compared with lithium-ion and NiMH, which can affect long-term storage.

Environmental and safety considerations focus on cadmium, a toxic heavy metal. Cadmium must be recovered and recycled; improper disposal is hazardous. Regulations in many regions govern the handling, storage, and end-of-life processing of NiCd batteries.

Charging typically uses controlled constant current with schemes to prevent overcharge, while routine maintenance charging was historically common in some applications.