Developments in electrochemical energy-conversion devices, batteries and fuel cells

Abstract

Primary and secondary batteries and fuel cells all convert chemical energy directly into electricity. Primary batteries, of the type used for hand torches, provide only very small units of power. Secondary batteries or accumulators supply amounts of power up to several hundred kilowatts and fuel cells have been proposed for even larger units. These systems differ basically from the well known electromechanical methods of producing electricity, i.e. those in which an electric machine is driven by a steam turbine or an internal-combustion engine. The latter involve a heat cycle subject to the limitations of the Carnot cycle. Direct electrochemical conversion devices have no such limitation, and the energy can be produced at an efficiency more than double that of the electromechanical systems mentioned.The widest application of storage batteries is for portable sources of power. In spite of the high density of lead, the main raw material in the lead/acid system, this battery is predominant in this field. Some reasons for this are given. Typical discharge and charge characteristics are shown. The real advances in various types of lead/acid batteries made during the past 15 years or so in the output per unit weight and volume are discussed. For car starter batteries the improvement amounts to nearly 20%, for traction batteries about 35%, for some stationary applications well over 150% and for aircraft batteries over 25%.Some of the basic principles of fuel cells are described, and the performance of practical working units is discussed. The characteristics of batteries and fuel cells are compared.