On-board energy and power management on electric vehicles: effect of battery type

The performance of a gasoline-powered vehicle is commonly quantified in terms of available acceleration, speed, fuel economy, travel range with a tankful of fuel, purchase cost, and life-cycle cost. A convenient gasoline-refueling infrastructure is in place today. The per-mile cost of energy for propelling an electric vehicle is a fraction of the per-mile cost of energy for a gasoline-propelled vehicle. However, an electric vehicle's energy has to be stored in a battery that must be recharged. No one battery can enable its electric vehicle to fully meet all of these performance requirements. For example, lithium batteries, which store the most energy per kg of weight, are being manufactured for laptop computers, where long life is not needed. The computer becomes obsolete before the battery wears out. The zinc-air battery offers long travel range with low weight, but it requires a completely new supporting infrastructure. In a hybrid vehicle a fuel-burning engine's output power is supplemented with a battery. With an efficient Meijer version of the Stirling-cycle engine delivering constant power, a 100-miles per gallon fuel economy is feasible. A battery can deliver peak power and recover energy with dynamic braking. The optimum vehicle performance with a given battery can be obtained if the vehicle has an on-board energy manager which limits the life-reducing stresses on the battery and continually displays to the driver the remaining travel distance available with the energy in the battery. Today's best candidate batteries for electric vehicles are the lead-acid, nickel-cadmium, nickel-metal hydride, lithium-ion, and zinc-air types. In this report we describe their characteristics and limitations.