On April 9th, the research paper titled “Enhanced energy storage in high-entropy ferroelectric polymers” was published online in Nature Materials, which was jointly conducted by Prof. Zhou Huamin and Prof. Liu Yang from School of Materials Science and Engineering. The co-first authors are postdoctoral Dr. Li Chenyi and Associate Professor Li Bo of Southern University of Science and Technology. Collaborators also include Prof. Zhang Haibo of the School of Materials Science and Engineering, Prof. Wang Qing and Prof. Chen Longqing of Pennsylvania State University, and Associate Professor Yang Tiannan of Shanghai Jiao Tong University.

The concept of high-entropy alloys was first proposed in 2004, and subsequent studies have found that high-entropy alloys have more excellent properties than that of traditional alloys. High-entropy materials are rapidly developing in the field of materials science. The high-entropy concept was further demonstrated in ceramics, giving rise to high-entropy ceramics. However, different from high-entropy alloys and high-entropy ceramic materials, the studies of high-entropy polymer materials are still in the early stage. Professor Junwei YE, the discoverer of high-entropy alloys, also mentioned in his paper that "so far, high-entropy polymers have rarely been reported". The definition and criterion for high-entropy polymers remains elusive.

To address this challenge, a team lead by Prof. ZHOU and Prof. Liu proposed to use the type of polymer chemical bond to define the high-entropy state =RSc_iln[c_i] where c_i is the molar fraction of one chemical bond, the number of varieties of chemical bond is n. Similar with alloys and ceramics, when ≥1.5R, the polymer enters a high-entropy state. According to this definition, the high-entropy state of polymers requires two factors, i.e., multiple chemical bonds types and appropriate ratios. The introduction of one single chemical bond such as C=C or C=O is still not high-entropy state (below 1.5R) even if the fraction ratio is high (e.g., 10 mol%) (Fig. 1a). Based on this, the team adopted low-dose proton beam irradiation to induce multiple chemical reactions in relaxed ferroelectric polymers, which brought multiple chemical bonds and proper ratios, which further fabricated high-entropy polymers successfully (Fig. 1b).

Figure1 The configurational entropy with the relationship of chemical bonds concentration. a, the configurational entropy with single chemical bond; b, the configurational entropy with multiple chemical bonds

High-entropy polymers have unique chaotic states, which can reduce the energy barrier for local polarization flipping and ferroelectric loss. Furthermore, introducing local chemical bonds with strong polarity can improve dielectric constant and polarization, leading to better energy storage performance. For the traditional relaxed ferroelectric state, although it has a high dielectric constant, it exhibits low polarization strength, high ferroelectric loss, and early polarization saturation, which limits its application in the field of dielectric energy storage capacitors. The team confirmed the existence of a high-entropy superparaelectric phase for the first time through first-principles calculations, phase field simulations, and microstructure and performance characterization (Fig. 2a). Different from the traditional relaxed ferroelectric state, the high-entropy state can significantly improve the dielectric energy storage performance with the increased dielectric constant (Fig. 2b), the enhanced polarization (Fig. 2c), the reduced ferroelectric loss (Fig. 2d), and the delayed early saturation of polarization (Fig. 2c). The polymers with high-entropy superparaelectric phase have an outstanding performance, e.g., the discharge energy density is 3.2 J/cm³ and the charge-discharge efficiency is 87.2 % at a low electric field intensity of 100 MV/m, which is close to the energy storage performance of the commercial polypropylene (BOPP) at a high electric field of 500 MV/m - 600 MV/m (Figs. 2e and 2f). This offers a new solution to overcome the bottleneck of practical application of relaxed ferroelectric polymer in dielectric energy storage.

Figure 2 the dielectric energy storage performance of high-entropy polymer. a, Temperature-irradiation dose phase diagram; b, dielectric constant; c, Hysteresis Loop; d ferroelectric loss; e, comparison of discharge energy density; f, Comparison of charge and discharge efficiency.

It is also found that the high-entropy strategy has a certain universality in improving the performance of polymers, not only the dielectric energy storage performance, but also the electrocaloric effect at low fields. This opens up a new direction for the subsequent design of high-performance electroactive polymer materials and devices.

Paper link: https://www.nature.com/articles/s41563-025-02211-z

Written by: Yang Liu

Edited by: Chang Wen, Peng Yumeng