A nickel-metal hydride cell, abbreviated NiMH, is a type of secondary electrochemical cell similar to the nickel-cadmium cell. The NiMH battery uses a hydrogen-absorbing alloy for the negative electrode instead of cadmium. As in NiCd cells, the positive electrode is nickel oxyhydroxide (NiOOH). A NiMH battery can have two to three times the capacity of an equivalent size nickel-cadmium battery. However, compared to the lithium-ion cell, the volumetric energy density is lower and self-discharge is higher. (Compare: low self-discharge NiMH battery)