Ultrahigh Energy Storage in 2D High-κ Perovskites.

Dielectric capacitors have greater power densities than batteries, and, unlike batteries, they do not utilize chemical reactions during cycling. Thus, they can become ideal, safe energy storage devices. However, dielectric capacitors yield rather low energy densities compared with other energy storage devices such as batteries and supercapacitors. Here, we present a rational approach for designing ultrahigh energy storage capacitors using two-dimensional (2D) high-κ dielectric perovskites (Ca 2 Na m -3 Nb m O 3 m +1 ; m = 3-6). Individual Ca 2 Na m -3 Nb m O 3 m +1 nanosheets exhibit an ultrahigh dielectric strength (638-1195 MV m -1 ) even in the monolayer form, which exceeds those of conventional dielectric materials. Multilayer stacked nanosheet capacitors exhibit ultrahigh energy densities (174-272 J cm -3 ), high efficiencies (>90%), excellent reliability (>10 7 cycles), and temperature stability (-50-300 °C); the maximum energy density is much higher than those of conventional dielectric materials and even comparable to those of lithium-ion batteries. Enhancing the energy density may make dielectric capacitors more competitive with batteries.