Comment on Kennelly et al

Ultrahigh energy density in short-range tilted NBT-based lead-free multilayer ceramic capacitors by nanodomain percolation

“…For direct energy storage, conventional polymer film dielectric capacitors possess inherently high power density (> 1kW/kg) along with short charge/discharge times (< 0.1 second) and are employed in pulsed power systems including motor vehicles, X-ray units, high-powered accelerators, grid-connected photovoltaics, wind turbine generators, electrochemical guns and radars. 4,[11][12][13][14][15][16] In contrast, multilayer ceramic capacitors (MLCCs) are mainly utilised as filters and de-couplers in consumer electronics with pulsed power applications limited by their low recoverable energy density (Wrec) and conversion efficiency (η), with respect to polymer film capacitors. Polymer film capacitors typically achieve high Wrec due to their large electrical breakdown strength (EBDS) but suffer from thermal and mechanical instability in comparison with MLCCs.14 Therefore, there is an urgent need to develop higher Wrec and η MLCCs for pulsed power applications since they have the potential to operate at high temperatures (>100 °C).…”

“…Perhaps more crucially, near-engine, power electronics also require higher voltage (>300 kV/cm) and temperature (>200 °C) capacitors, the latter only realistically achievable using ceramics. 4,[11][12][13][14][15][16] For a dielectric, the total energy density (Wtotal), Wrec and η are given by Equations 1-3:4,11-16…”