Nickel Metal HydrideBatteries NiMH

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A nickel metal hydride battery, abbreviated NiMH, is a type of rechargeable battery similar to a nickel-cadmium (NiCd) battery but has a hydrogen-absorbing alloy for the anode instead of cadmium. Like in NiCd batteries, nickel is the cathode. A NiMH battery can have two to three times the capacity of an equivalent size NiCd and the memory effect is not as significant. However, compared to the lithium-ion battery, the volumetric energy density is lower and self-discharge is higher.

Common penlight-size (AA) batteries have nominal capacities C ranging from 1100 mA·h to 2700 mA·h at 1.2 V, usually rated at 0.2×C rate. Useful discharge capacity is an inverse function of the discharge rate, but up to around 1×C rate, there is no significant difference.

The specific energy density for NiMH material is approximately 70 W·h/kg (250 kJ/kg), with a volumetric energy density of about 300 W·h/L (360 MJ/m³).

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