Dielectric capacitors with high energy storage performances are exceedingly desired for the next-generation advanced high/pulsed power devices that demand miniaturization and integration. However, poor energy-storage density (U_rec) and low efficiency (η) resulted from the large remanent polarization (P_r) and low breakdown strength (BDS), have been the major challenge for the application of dielectric capacitors. Herein, a high-entropy strategy with superparaelectric relaxor ferroelectrics (SP-RFE) was adopted to achieve extremely low P_r and high BDS in BaTiO₃ system, simultaneously. Due to the high BDS ~800 kV/cm and low P_r ~0.58 μC/cm², high-entropy SP-RFE (La_0.05Ba_0.18Sr_0.18K_0.115Na_0.115Ca_0.18Bi_0.18)TiO₃ (LBSKNCBT) MLCCs exhibited high U_rec ~6.63 J/cm³ and excellent η ~ 96%. What's more, LBSKNCBT MLCCs with high-entropy and SP-RFE characteristic also possess a good temperature and frequency stability. In a word, this work offers an excellent paradigm for achieving good energy-storage properties of BaTiO₃-based dielectric capacitors to meet the demanding requirements of advanced energy storage applications.

The rapid miniaturization and high integration of modern electronic devices have brought an increasing demand for polymer-based thermal management materials with higher thermal conductivity. Boron nitride nanosheets (BNNs) have been widely used as thermally conductive fillers benefiting from the extremely high intrinsic thermal conductivity. However, the small lateral size and weak interface bonding of BNNs enabled them to only form thermally conductive networks through physical overlap, resulting in high interfacial thermal resistance. To address this issue, an innovative strategy based on interface engineering was proposed in this study. High-aspect-ratio boron nitride belts (BNbs) were successfully synthesized by carbon thermal reduction nitridation method through the in-situ generation and sintering of BNNs. The surface of BNb showed the sintering of numerous smaller-sized BNNs, which precisely addresses the issue of weak interfacial bonding between BNNs. On this basis, the as-synthesized BNbs were combined with nano-fibrillated cellulose (NFC) to prepare NFC/BNb composite films through a facile vacuum filtration process. Due to the thermally conductive network formed by the horizontal oriented arrangement of BNb and their particular morphological advantages, the NFC/BNb films demonstrated significantly higher in-plane thermal conductivity than that of NFC/BNNs films, achieving the highest value of 19.119 W·m⁻¹·K⁻¹ at a 20 wt% filling fraction. In addition, the NFC/BNb films also exhibited superior thermal stability, mechanical strength, flexibility, and electrical insulation performance, suggesting the significant application potential of the designed BNb fillers in the thermal management field.