High-entropy structure in layered compounds, especially for transitional metal dichalcogenides (TMDCs), has powered the field with disorder and versatile chemical composition, showing great potential in various functional applications, including energy storage, catalysis, and so on. However, the reported high-entropy phases are mainly in 1T phases, and the 2H phases are rare and about 3R phases are still lacking. Here, phase engineering on high-entropy TMDCs is achieved via tuning the chemical composition in (Mo_0.5W_0.5)_1-x(Nb_0.5Ta_0.5)_xSe_2+d, 0 ≤ x < 1, and -0.1 ≤ d ≤ 0.3. The effect of A phase diagram is built, guiding the synthesis of pure 2H/3R phases in a wide composition/entropy range. The increase of VB-group element content and over-dosed Se will facilitate the formation of 3R phases, vice for the 2H phases. Thermodynamic first-principles calculations evaluate the stability of phases in different polytypes and compositions, matching well with the composition-dependent crystalline habits. Moreover, optimized thermoelectric performance with the zT value reached 0.36 @ 723 K in the 2H phase of x = 0.2, attributing to the low thermal conductivity caused by the high-entropy effect, being one of highest among (Mo/W)Se₂-based materials. Our work enriches the high-entropy TMDCs with versatile polytypes, expanding their potential uses for various fields.

Advancements in power electronics necessitate dielectric polymer films capable of operating at high temperatures and possessing high energy density. Although significant strides have been achieved by integrating inorganic fillers into high-temperature polymer matrices, the inherently low dielectric constants of these matrices have tempered the magnitude of success. In this work, we report an innovative nanocomposite based on sulfonylated polyimide (SPI), distinguished by the incorporation of sulfonyl groups within the SPI backbone and the inclusion of wide bandgap hafnium dioxide (HfO₂) nanofillers. The nanocomposite has demonstrated notable enhancements in thermal stability, dielectric properties, and capacitive performance at elevated temperatures. Detailed simulations at both molecular and mesoscopic levels have elucidated the mechanisms behind these improvements, which could be attributed to confined segmental motion, an optimized electronic band structure, and a diminished incidence of dielectric breakdown ascribed to the presence of sulfonyl groups. Remarkably, the SPI-HfO₂ nanocomposite demonstrates a high charge-discharge efficiency of 95.7% at an elevated temperature of 150 °C and an applied electric field of 200 MV/m. Furthermore, it achieves a maximum discharged energy density of 2.71 J/cm³, signalling its substantial potential for energy storage applications under extreme conditions.