TABLE OF CONTENTS Electrochemical batteries are a key component both of electric vehicles (EV) and of hybrid-electric vehicles (HEV). Batteries are devices that transform chemical energy into electrical energy and vice versa. They represent a reversible electrical energy storage system.
Desirable attributes of traction batteries for EV and HEV applications are high specific power, high specific energy, long "calendar" and cycle life, low initial and replacement costs, high reliability, and high robustness. Among other current technical challenges, [6] a key point is developing accurate techniques to determine the capacity or the state of charge (SOC) of batteries during their operation.
The capacity of a battery, usually expressed in Ah, is the integral of the current that can be delivered under certain conditions. A dimensionless parameter is the state of charge, which describes the amount of charge remaining in the battery, expressed as a percentage of its nominal capacity. Another key design parameter is the specific energy, i.e., the energy that can be stored in the battery per unit mass, typically expressed in Wh/kg. The specific energy affects the mass of batteries that must be carried on board, thus the range of a purely electric vehicle. For HEVs, possibly more important is the specific power, typically expressed in W/kg, which is related to the acceleration and the grade performance that the vehicle can sustain.
Batteries are composed of a number of individual cells in which three main components are recognizeable: two electrodes, where half-reactions take place resulting in the circulation of...
