capacitors), dielectric capacitors are promising candidates for advanced pulsed power applications owing to their high power density and fast charge/discharge speed. [6][7][8] Ceramic dielectrics show excellent temperature stability and mechanical robustness, are promising materials for use in extreme conditions. [9] Anti-ferroelectric ceramics (such as PbTiO 3 -and Pb(Zr,Ti)O 3 -based dielectrics) display double polarization-electric field (P-E) loops, which have tremendous potential for realizing high energy density. [10][11][12] However, most of these materials are Pbbased, whose toxic nature causes a series of environmental problems. Thus, leadfree ceramics have attracted considerable attention as a replacement to Pb-based materials. [7,[13][14][15][16][17][18] Until now, the low energy storage performance (low energy storage density of <4 J cm −3 and/or inferior efficiency of <80%) of lead-free ceramic capacitors hardly meet the increasing integration and miniaturization requirements. [19][20][21][22] Thus, it is imperative to improve the energy storage performance of lead-free ceramic capacitors.As shown in the schematic of Figure 1a, the energy storage density and efficiency of the dielectric capacitors are governed by the maximum polarization (P max ), remanent polarization (P r ), and dielectric breakdown strength (E BDS ). The combination of a large P max , small P r , and high E BDS is essential for realizing ultrahigh energy storage density and efficiency. Considering that the energy loss density (W loss ) is an inevitable part of ferroelectric ceramics, the recoverable energy storage density (W rec ) and energy efficiency (η) are key parameters for evaluating the energy storage performance of nonlinear dielectric ceramic capacitors. [9,17,23] It has been reported that BiFeO 3 (BF) possesses very high spontaneous polarization (≈100 µC cm −2 ), which is superior to most perovskite ferroelectrics, including BaTiO 3 , Bi 0.

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A new class of trilayered architecture blends polymer-based nanocomposites with excellent discharge energy densities (U dis ) is presented. The preferable energy storage performance is achieved in sandwich structured nanocomposite (PIP) films. The outer polarization-layers (P-layer) of the PIP film are composed of Sr 2 Nb 2 O 7 nanosheets (SNONSs) as well as boron nitride nanosheets (BNNSs) dispersed in poly(vinylidene fluoride) (PVDF)/ polymethyl methacrylate (PMMA) blend polymer matrix (BPM) to provide high dielectric constant, while PVDF/PMMA with BNNSs forms the central insulation-layer (I-layer) to offer high dielectric breakdown strength (E b ) of the resulting nanocomposite films. The dielectric performance, Weibull breakdown strength, and energy storage capacity of single and multi-layer nanocomposites as a function of filler content are systematically examined. The evolution of electric trees is simulated via finite element methods to verify the experimental dielectric breakdown results in single layer nanocomposite films. The PIP film with optimized filler content displays a discharge energy density of 31.42 J cm −3 with a significantly improved charge-discharge efficiency of ≈71% near the Weibull breakdown strength of 655.16 MV m −1 , which is the highest among the polymer-based nanocomposites under the equivalent dielectric breakdown strength at present.

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Mechanical energy driven wireless charging technology has recently gained increasing attention. High-performance potassium sodium niobate (KNN) based texture ceramics and its potential application on energy harvesting device are the first...