High Energy Storage Efficiency with Fatigue Resistance and Thermal Stability in Lead‐Free Na_0.5K_0.5NbO₃/BiMnO₃ Solid‐Solution Films

Abstract

The ferroelectric, leakage, dielectric, and energy storage properties of leadfree Na 0.5 K 0.5 NbO 3 /BiMnO 3 (KNN/BMO) solid-solution films are investigated. The strong ferroelectric relaxation behaviors of slim ferroelectricity with small remanent polarization and coercive field induce a high energystorage density and efficiency at room temperature. The energy density reaches 14.8 J cm À3 , even the efficiency is up to 79.79% under the applied electric field of 985.66 kV cm À1 . Moreover, the energy storage performances of KNN/BMO solid-solution films exhibit good thermal stability over a wide temperature range and high ferroelectric fatigue endurance after switching 10 6 bipole electrical cycles. KNN/BMO solid-solution films can replace leadbased films and other outstanding lead-free systems in the energy storage performance.As a key component of pulse power equipment, pulsed capacitors need to withstand a high discharge current in a short period of time and thousands of charge and discharge lifetimes. [1,2] Therefore, capacitor storage has become the focus of research because of its highest power, efficiency, few limited conditions, and simple structure. With the development of new pulse system toward high energy, miniaturization, the most effective way to improve the efficiency of pulsed system is adopted to improve the performances of capacitor materials. The typical dielectric materials including linear dielectric materials, ferroelectric materials, antiferroelectric materials, and relaxor ferroelectrics can meet the requirements for such materials. [3,4] Classically, energy storage density of dielectric capacitors is calculated according to the following formula [3] :where E and P are applied electric field and the corresponding polarization during charge process. During discharge process, applied electric field is gradually withdrawn from the maximum to zero, and recoverable energy storage density (W rec ) is released, which obeys the following equation:The loss energy density (W loss ¼ W -W rec ) is caused by hysteresis loss. Therefore, the energy storage efficiency (η) can be calculated by the equationAs discussed above, large polarization changes (i.e., slim hysteresis loops) and high breakdown electric fields are required to obtain high W rec . Thus, relaxor ferroelectrics (REF) are considered as promising materials for energy storage devices, due to their high saturation polarization (P s ), low remanent polarization (P r ), and ultrahigh storage efficiency η.Compared with bulk materials, films endow lower size, higher breakdown electrical field, and energy storage efficiency, which can be applied to microelectronic devices.Recently, more and more researchers have paid attention to Na 0.5 K 0.5 NbO 3 (KNN) lead-free ferroelectrics as substitutes for lead-based materials in energy storage due to environmental friendliness. Up to now, a great deal of research has focused on the energy storage of KNN-based ceramics. [5][6][7] However, little attention has been paid to the energy storage performances of...

Potassium‐Sodium‐Niobate‐Based Thin Films: Lead Free for Micro‐Piezoelectrics

“…Sun et al. reported an energy storage density of 14.8 J cm −3 and energy conversion efficiency of 79.79% in KNN‐BiMnO 3 solid‐solution film . Won et al.…”

Enhanced discharged energy density in poly(vinylidene fluoride) composites with a small loading of ( K 0 . 5 Na 0 .5 ) NbO 3 particles

“…Yang et al found that 0.85(K 0.5 Na 0.5 )NbO 3 ‐0.15SrTiO 3 (0.85KNN‐0.15ST) ceramic film demonstrated a discharged energy density of 4.03 J·cm –3 and E b of 40 kV·mm –1 27 . Sun et al found that the discharged energy density of a 0.85(K 0.5 Na 0.5 )NbO 3 ‐0.15BiMnO 3 film with a thickness of 700 nm reached 14.8 J·cm –3 with energy efficiency ( η ) of 79.79% at 98.5 kV·mm –1 28 . So far there have been numerous investigations about KNN‐based bulk ceramic and films.…”

“…27 Sun et al found that the discharged energy density of a 0.85(K 0.5 Na 0.5 )NbO 3 -0.15BiMnO 3 film with a thickness of 700 nm reached 14.8 JÁcm -3 with energy efficiency (η) of 79.79% at 98.5 kVÁmm -1 . 28 So far there have been numerous investigations about KNN-based bulk ceramic and films. However, studies about KNN/polymer composites for energy storage applications are rarely reported.…”

Enhancement of Energy Storage Performance by Criticality in Lead‐Free Relaxor Ferroelectrics

“…To determine the recoverable energy storage density ( W rec ), this is the energy released during the discharge process, the polarization during electric field decrease from maximum to zero has to be considered. W rec is calculated by Equation where P r denotes the remanent polarization.…”

“…The difference between W total and W rec is the area enclosed by the polarization curve and describes the losses ( W loss ). The efficiency ( η ) is given as the ratio between charging and discharging process, i.e., Equation …”