  Electrical energy storage systems (EESSs) with high energy density and power
density are essential for the effective miniaturization of future electronic
devices. Among different EESSs available in the market, dielectric capacitors
relying on swift electronic and ionic polarization-based mechanisms to store
and deliver energy already demonstrate high power densities. However, different
intrinsic and extrinsic contributions to energy dissipations prevent
ceramic-based dielectric capacitors from reaching high recoverable energy
density levels. Interestingly, relaxor ferroelectric-based dielectric
capacitors, because of their low remnant polarization, show relatively high
energy density and thus display great potential for applications requiring high
energy density properties. Here, some of the main strategies to improve the
energy density properties of perovskite lead-free relaxor systems are reviewed.
This includes (i) chemical modification at different crystallographic sites,
(ii) chemical additives that do not target lattice sites and (iii) novel
processing approaches dedicated to bulk ceramics, thick and thin films,
respectively. Recent advancements are summarized concerning the search for
relaxor materials with superior energy density properties and the appropriate
choice of both composition and processing route to match various needs in the
application. Finally, future trends in computationally-aided materials design
are presented.
