High‐Performance Ferroelectric–Dielectric Multilayered Thin Films for Energy Storage Capacitors

Herein, the effect of the insertion of a thin dielectric HfO₂:Al₂O₃ (HAO) layer at different positions in the Pt/0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BCZT)/Au structure on the energy storage performance of the capacitors is investigated. A high storage performance is achieved through the insertion of a HAO layer between BCZT and Au layers. The insertion of the dielectric layer causes a depolarization field which results in a high linearity hysteresis loop with low energy dissipation. The Pt/BCZT/HAO/Au capacitors show an impressive energy storage density of 99.8 J cm^?3 and efficiency of 71.0%, at an applied electric field of 750 kV cm^?1. Further, no significant change in the energy storage properties is observed after passing 10⁸ switching cycles through the capacitor. The presence of resistive switching (RS) in leakage current characteristics confirms the strong charge coupling between ferroelectric and insulator layers. The same trend of the RS ratio and the energy storage performance with the variation of the architecture of the devices suggests that the energy storage properties can be improved through the charge coupling between the layers. By combining ferroelectrics and dielectrics into one single structure, the proposed strategy provides an efficient way for developing highly efficient energy storage capacitors.     

Superhierarchical Inorganic/Organic Nanocomposites Exhibiting Simultaneous Ultrahigh Dielectric Energy Density and High Efficiency

Inorganic/organic dielectric nanocomposites have been extensively explored for energy storage applications for their ease of processing, flexibility, and low cost. However, achieving simultaneous high energy density and high efficiency under practically workable electric fields has been a long-standing challenge. Guided by first-principles calculations of interface properties and phase-field simulations of the dynamic dielectric breakdown process, superhierarchical nanocomposites of ferroelectric perovskites, layered aluminosilicate nanosheets, and an organic polymer matrix are designed and simultaneous high energy density of 20 J cm⁻³ and high efficiency of 84% at a low electric field of 510 MV m⁻¹ are achieved. This is the highest energy density of all the state-of-the-art dielectric polymer nanocomposites with energy efficiency > 80% at a low electric field of <600 MV m⁻¹. Strong atomic hybridization, large ionic displacement, the enhanced breakdown strength through forming charge-blocking layers, and the superhierarchical microstructure with gradient interfaces are responsible for the high performances. This superhierarchical structuring modulation strategy is generally applicable to composites for different functionalities and applications.     

Advanced Asymmetric Supercapacitors Based on Ni(OH)2/Graphene and Porous Graphene Electrodes with High Energy Density

Hierarchical flowerlike nickel hydroxide decorated on graphene sheets has been prepared by a facile and cost‐effective microwave‐assisted method. In order to achieve high energy and power densities, a high‐voltage asymmetric supercapacitor is successfully fabricated using Ni(OH)₂/graphene and porous graphene as the positive and negative electrodes, respectively. Because of their unique structure, both of these materials exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high‐voltage region of 0–1.6 V and displays intriguing performances with a maximum specific capacitance of 218.4 F g^?1 and high energy density of 77.8 Wh kg^?1. Furthermore, the Ni(OH)₂/graphene//porous graphene supercapacitor device exhibits an excellent long cycle life along with 94.3% specific capacitance retained after 3000 cycles. These fascinating performances can be attributed to the high capacitance and the positive synergistic effects of the two electrodes. The impressive results presented here may pave the way for promising applications in high energy density storage systems.     

Asymmetric Supercapacitors Based on Graphene/MnO2 and Activated Carbon Nanofiber Electrodes with High Power and Energy Density

Asymmetric supercapacitor with high energy density has been developed successfully using graphene/MnO₂ composite as positive electrode and activated carbon nanofibers (ACN) as negative electrode in a neutral aqueous Na₂SO₄ electrolyte. Due to the high capacitances and excellent rate performances of graphene/MnO₂ and ACN, as well as the synergistic effects of the two electrodes, such asymmetric cell exhibits superior electrochemical performances. An optimized asymmetric supercapacitor can be cycled reversibly in the voltage range of 0–1.8 V, and exhibits maximum energy density of 51.1 Wh kg^?1, which is much higher than that of MnO₂//DWNT cell (29.1 Wh kg^?1). Additionally, graphene/MnO₂//ACN asymmetric supercapacitor exhibits excellent cycling durability, with 97% specific capacitance retained even after 1000 cycles. These encouraging results show great potential in developing energy storage devices with high energy and power densities for practical applications.