Polymorphic relaxor phase and defect dipole polarization co-reinforced capacitor energy storage in temperature-monitorable high-entropy ferroelectrics

Abstract

Energy storage high-entropy ceramics are famous for their ultrahigh power density and ultrafast discharge rate. However, achieving a synchronous combination of high energy density and efficiency along with intelligent temperature-monitorable function remains a significant challenge. Here, based on high-entropy strategy and phase field simulation, the polarization response of domains in Bi_0.5Na_0.5TiO₃-based ceramics is optimized by constructing a concomitant nanostructure of defect dipole polarization and a polymorphic relaxor phase. The optimal ceramic possesses a high recyclable energy storage density (11.23 J cm^-3) and a high energy storage efficiency (90.87%) at 670 kV cm^-1. Furthermore, real-time temperature sensing is explored based on abnormal fluorescent negative thermal expansion, highlighting the application of intelligent cardiac defibrillation pulse capacitors. This study develops an effective strategy for enhancing the overall energy storage performance of ferroelectric ceramics to overcome the problems of insufficient energy supply and thermal runaway in traditional counterparts.

Fig. 1. Microcosmic design strategy of BNT-based ceramics and their potential application.

The coexistence of PRP and defect dipoles $\left(V_A^{″}-V_O^{\cdot \cdot }\right)$ in the BNYTT-SSH-xBST ceramics induced by HE strategy to optimize ESP, and its potential application in the field of informational telemedicine cardiac defibrillation pulse capacitors. (The heart in this diagram was created with BioRender.com).

Fig. 2. PRP structure and defect characterizations of the BNYTT-SSH-0.3BST ceramic.

a, c HRTEM images revealing two different atomic arrangements in the BNYTT-SSH-0.3BST ceramic, b, d corresponding SAED patterns. e Cell enlargement along the [100]c direction and (f) polarization projection, (g) cell enlargement along the [110]c direction and (h) polarization projection. i Atomic resolution HAADF-STEM image along the [110]c direction and fitted R-O-T-C polarization vector. j–m Vector superposition of B-site atoms from the HAADF-STEM image in the [110]c direction relative to the displacements of four nearby cations in different directions. n ABF-STEM image captured along the [110]c direction. o–q Magnification of the local regions (red, blue and yellow boxes) in Figure n and the octahedral tilt/non-tilt identified by two-dimensional Gaussian fitting. r ABF-STEM image revealing absence of A-site atom along the [001]c direction. s HAADF-STEM image revealing A-site atomic column strength fluctuations along the [001]c direction.

Fig. 3. Energy storage performance of the high-entropy BNYTT-SSH-xBST ceramics.

a, b Unipolar P‒E loops and corresponding I‒E curves of the BNYTT-SSH-0.3BST ceramic. c Changes in polarization parameters (P_max, P_r, P_max-P_r) and E_b with x in the BNYTT-SSH-xBST ceramics. d Variations in W_t, W_rec and η with x. e Two-dimensional differential charge density distributions at x = 0 and x = 0.3 on the (010) plane. f High-resolution O 1 s XPS spectra. g Temperature-dependent impedance spectra of BNYTT-SSH-0.3BST. h Overdamped curves of BNYTT-SSH-0.3BST (the illustration shows the changes in W_D with electric field). I, j Changes in W_D, I_max and t_0.9 with electric field. k Underdamped discharge current curve (the illustration shows the changes in P_D with electric field). l Change in C_D with electric field. m, n Overall ESP of the BNYTT-SSH-0.3BST ceramic compared with those of previously reported lead-free high-ESP ceramics.

Fig. 4. Domain switching response and tests of stability and fatigue characteristics of the BNYTT-SSH-xBST ceramics.

a–f PFM amplitude and phase images of the BNYTT-SSH-0.3BST ceramic under voltages of 15 V, 30 V and 60 V measured immediately and after 10 min, respectively. (g, h PFM amplitude and phase images of the BNYTT-SSH ceramic under a voltage of 15 V measured immediately and after 10 min, respectively. i Temperature-dependent Raman spectra and (j) temperature-dependent local XRD diffraction peaks (~46.5°) of the BNYTT-SSH-0.3BST ceramic. k–m Unipolar P‒E loops of the BNYTT-SSH-0.3BST ceramic at 300 kV cm^-1 at different temperatures, fatigue cycles and frequencies. W_rec and η and their stability for the ceramic within the (n) temperature range of 20–200 °C, (o) cumulative cycle number range of 1–10⁶ and (p) frequency range of 1–150 Hz.

Fig. 5. Fluorescent negative thermal expansion characteristics of the BNYTT-SSH-0.3BST ceramic and hypotheses for cardiac defibrillation application.

a UCL spectra of the BNYTT-SSH-0.3BST ceramic under 980 nm laser excitation in the temperature range of 273–673 K. b Changes in UCL intensity monitoring at 694 nm and 488 nm and their FIR values with temperature (illustration: temperature-dependent CIE chromaticity). c Variation trend of S_r with temperature (illustration: linear function fitting of logarithmic UCL intensity versus 1/T). d UCL mechanism in the ceramic. e Potential application of the BNYTT-SSH-0.3BST ceramic in telemedicine information implantable cardiac defibrillation pulse capacitors and a simplified schematic diagram of ICPCC-related circuits. (The heart, blood vessels, human body outline, and red blood cells shown in figures (d, e) were created with BioRender.com).