Purpose

• The hybrid car battery---a rechargeable battery used for hybrid vehicles---is responsible for running every function of the car. This is in contrast with most car batteries, in which its main purpose is to start the engine and operate the accessories, such as the radio and air conditioner. The hybrid battery powers the electric motor---the component responsible for propelling the vehicle---while reducing the pressure on the gasoline engine, thus reducing the amount of fuel the car needs. The hybrid car battery is designed for the car to drive for longer periods of time in between trips to a gas station.
  
  There are currently three types of hybrid car batteries: lead-acid batteries, nickel-metal hydride (NiMH) batteries and lithium-ion (Li-ion) batteries.
  
  

Lead-Acid Batteries

• The lead-acid battery---so named because of the combination of lead electrodes and acid to generate electricity in them---was invented in 1859, thus making it the oldest rechargeable car battery around. It is the cheapest to produce and the most familiar, thanks to its existence for more than a century. However, it is the heaviest and most toxic of the three hybrid car batteries, thus making it the least suitable for the hybrid car's intention of reducing pollution and increasing fuel efficiency. Indeed, it runs the risk of explosion if overcharged.
  
  

Nickel-Metal Hydride Batteries

• The nickel-metal hydride battery came into mainstream use in the late 1980s. Today, they are used in automobiles such as the Toyota Prius, and the hybrid versions of the Toyota Highlander, Ford Escape and Saturn Vue. The strengths of the nickel-metal hydride battery are its high density energy (the amount of energy that can be held by weight or volume) and its relative lack of toxic materials. However, it can be carcinogenic, and the mining process for the material is considered highly threatening to public health and the environment.
  
  

Lithium-Ion Batteries

• The lithium-ion battery is considered to be the next generation of hybrid car batteries. It has lower toxicity and higher energy density than either lead-acid or nickel-metal hydride batteries. The lithium-ion battery does have its drawbacks, though, among them being a higher number of recharging cycles and its propensity to deteriorate faster than other rechargeable batteries.
  
  

Cathodes of Lithium-Ion Batteries

• Lithium-ion batteries can differ according to the chemistry of the cathode, which is one of the two electrical conductors (electrodes) found in a battery. This is especially crucial because what the cathode is made of determines the cell's capacity. It is the part of the battery that receives lithium ions from the other electrode (anode) during discharge, and delivers them to the anode when charged. The major cathode materials differ in cost, durability, performance and safety. They include: Cobalt dioxide, nickel-cobalt-manganese (NCM), nickel-cobalt-aluminum (NCA) and iron phosphate (FePo).