XJTU’s Prof. Di Zhou Team Achieves Series Advances in Polymer Energy Storage

Dielectric Polymers with High-Voltage Tolerance, Low Loss, and Robust Stability for Electrostatic Capacitors.The growing demand in production and daily life requires polymer dielectric capacitors to operate reliably in harsh environments involving high temperatures and high voltages.However, compared to dielectric ceramics, most commercial polymer dielectrics can only operate at relatively low temperatures (below 105°C), as their insulation and energy storage performance severely degrade at elevated temperatures.At elevated temperatures, charge injection, excitation, and transport in polymers lead to an exponential increase in leakage current, resulting in low discharged energy density and poor discharge efficiency, which makes polymers inadequate for high-temperature, high-power electrical equipment requirements.

A high glass transition temperature (Tg) is considered a key factor for high-temperature polymer dielectrics. Above Tg, polymer chains lose rigidity and increase free volume, leading to significant changes in dielectric constant and loss factor.Representative high-Tg polymers such as polyimide (PI), polyetherimide (PEI), and polycarbonate (PC) exhibit good thermal stability. However, under simultaneous high electric field and elevated temperature, their energy storage performance is far inferior to that at room temperature.Previous studies have shown that under elevated temperature and high electric field conditions, the conductive loss of polymeric dielectrics primarily follows the hopping conduction mechanism.Therefore, introducing charge traps into the polymer matrix to reduce the hopping conduction distance is considered an effective strategy for further improving insulation performance under high-temperature and high-electric-field conditions.

Based on the above research background, Professor Di Zhou's team proposed an interfacial regulation-based multilevel trap engineering strategy. Using a one-step immersion coating process combined with hot-pressing, they fabricated an all-organic sandwich-structured composite film.The organic semiconductor 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), known for its high electron affinity, was incorporated into poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)). This blend was coated onto polyethylene terephthalate (PET) substrates, and then laminated with pure PET films on both sides via a hot-pressing process to form the final sandwich structure.The energy band offset between NTCDA and P(VDF-HFP) generates multilevel deep traps, while the interfacial interactions between the layers provide an effective barrier for charge carriers.The synergistic effect of traps and interlayer barriers significantly suppresses charge transport and leakage current (as shown in Fig. 1). This enables the material to achieve enhanced breakdown strength (E₆ ~ 678.6 MV·m⁻¹) and outstanding energy storage performance (U_d ≈ 8.2 J·cm⁻³, efficiency η ≈ 94.3%) at 25°C. Remarkably, at elevated temperatures, it still maintains a high U_d of 6.4 J·cm⁻³, providing an effective strategy for developing advanced polymer dielectrics that combine excellent thermal stability with high efficiency for energy storage applications.

Fig. 1 Multilevel Trap Engineering via Interfacial Modulation Enables Superior Energy Storage in Polymer Dielectrics

Furthermore, the incorporation of inorganic wide-bandgap nanofillers can also create charge traps within the polymer matrix, thereby suppressing charge carrier transport at elevated temperatures in composites. However, the intrinsic agglomeration of fillers driven by van der Waals forces, hydrogen bonding, and electrostatic interactions remains a critical yet often overlooked challenge.These agglomeration phenomena can lead to non-uniform dielectric response, reduced breakdown strength, and degraded mechanical properties.To address this, Professor Di Zhou's team proposed a strategy to precisely modulate the distribution of ultra-low-loading magnesium oxide nanosheet fillers within the polymer matrix. This effectively suppresses nanofiller agglomeration and charge accumulation, homogenizes electric field distribution, and minimizes interfacial dielectric mismatch and local electric field distortion.Thanks to this strategy, the constructed three-layer composite film maintains exceptional energy storage performance even under extreme high-temperature conditions (as shown in Fig. 2).At 150°C, it achieves a Ud of 7.82 J·cm⁻³ with an η of 87.47%. Even more remarkably, at 200°C, the composite still delivers a high Ud of 4.17 J·cm⁻³ with an efficiency exceeding 90%. This represents nearly a tenfold increase in energy storage density compared to pure PEI, and also surpasses current commercial polymer dielectrics, newly synthesized polymers, and various polymer composites.This study provides new insights for addressing the agglomeration of nanofillers in polymers.

Fig. 2 Precise Distribution Control of Ultra-Low-Content MgO Nanosheets for Enhanced Energy Storage in Polymers

These research findings have been published in the international journal Nano Energy under the titles "Interfacial Layer-Modulated Multilevel Trap Engineering for Enhancing the Energy Storage Performance of Polyethylene Terephthalate Dielectric Films" and "Sandwich-Structured Polymer Composites with Precisely Controlled Magnesium Oxide Nanosheet Distribution Enable Superior Dielectric Energy Storage Performance at High Temperatures".The first authors are Tao Liu and Ying Han (Ph.D. candidates, School of Electronic Science and Engineering, Faculty of Electronic and Information Engineering, XJTU). Corresponding authors include Professor Di Zhou and Associate Professor Xiao Li (same affiliation), Professor Wenfeng Liu and Professor Yao Zhou (School of Electrical Engineering, XJTU), Professor Jiwei Zhai (Tongji University), Associate Professor Tao Zhou (Hangzhou Dianzi University), and Associate Professor Kar Ban Tan (Universiti Putra Malaysia). XJTU is the primary affiliation for this work.

Citation: China Electronic Components Association.

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