Professor Ian M. Reaney

Ian M. Reaney
Functional Materials and Device Group
Materials Science and Engineering
University of Sheffield
Sheffield, S1 3JD.

Materials exhibiting high energy/power density are currently needed to meet the growing demand of
portable electronics, electric vehicles and large-scale energy storage devices. The highest energy
densities are achieved for fuel cells, batteries and supercapacitors, but conventional dielectric
capacitors are receiving increased attention for pulsed power applications due to their high power
density and their fast charge-discharge speed. The key to high energy density in dielectric capacitors
is a large maximum but small remanent (zero in the case of linear dielectrics) polarization and a high
electric breakdown strength. Polymer dielectric capacitors offer high power/energy density for
applications at room temperature but above 100 o C they are unreliable and suffer from dielectric
breakdown. For high temperature applications therefore, dielectric ceramics are the only feasible
alternative. Lead-based ceramics such as La doped lead zirconate titanate exhibit good energy storage
properties but their toxicity raises concern over their use in consumer applications, where capacitors
are exclusively lead-free. Lead-free compositions with superior power density are thus required. In
this presentation, the fundamental principles of energy storage in dielectrics are introduced and the
key factors to improve energy storage are described in the context of new materials.