The Nickel Metal Hydride battery has a nickel-hydroxide cathode, a metal hydride (a variety of metal alloys are used) anode, and aqueous potassium hydroxide electrolyte. This is a rechargeable battery chemistry that has been superseded by lithium ion, but has seen a lot of use in Toyota hybrids. Energy density 40-110 Wh/kg at cell level. It shares its potassium hydroxide electrolyte with the older Nickel Cadmium chemistry, and for more on how Toyota’s hybrid packs have evolved from NiMH to lithium-ion, see Toyota Batteries.
Toyota Prius Gen 2 Battery
This pack was used in the 2004 Toyota Prius. Second generation of the hybrid battery design and using NiMh cells.
This is a HEV pack and so quite a small total energy of 1.3kWh and using a smaller 40% SoC window. This small window is so that the pack will be able to last the lifetime of the car with high charge and discharge rates from braking and acceleration.
dT/dt (Delta Temperature over Delta Time) – a full-charge detection method for NiCd/NiMH that watches the rate of temperature rise rather than absolute temperature, often used alongside or instead of NDV.
NDV (Negative Delta V) – the small voltage drop a NiCd or NiMH cell exhibits right at full charge, used as the classic full-charge detection trigger for those chemistries.
References
- Nickel Metal Hydride (NiMH) Handbook and Application Manual, Energizer
- NI-MH Handbook, Industrial Applications, Panasonic
See also: IEC 62133-1, UL 2054