Nickel-Metal Hydride Battery

A nickel metal hydride battery, or NiMH battery, is a rechargeable battery with a nominal cell voltage of 1.2 volts that uses nickel oxide hydroxide at its positive electrode, much like the older nickel cadmium design, but replaces the toxic cadmium negative electrode with a hydrogen absorbing alloy. It typically stores two to three times the capacity of a same size nickel cadmium cell, though only about half the energy density of a lithium ion cell, while being less prone to leaking corrosive electrolyte than many primary batteries. The Battelle Geneva Research Center invented the technology in 1967, Willems and Buschow demonstrated a design in 1987 that retained 84 percent of its charge capacity after 4,000 charge discharge cycles, and the first consumer grade cells reached the market in 1989; by 2008 more than two million hybrid vehicles worldwide, including the Toyota Prius and Honda Insight, used NiMH batteries. The chemistry replaced nickel cadmium in most portable consumer electronics and remained the standard for early hybrid cars, though lithium ion batteries had largely displaced it in electric vehicles by 2020, leaving it still in use in some hybrid models.