For capacitive energy storage at elevated temperatures1,2,3,4, dielectric polymers are required to integrate low electrical conduction with high thermal conductivity. The coexistence of these seemingly contradictory properties remains a persistent challenge for existing polymers. We describe here a class of ladderphane copolymers exhibiting more than one order of magnitude lower electrical conductivity than the existing polymers at high electric fields and elevated temperatures. Consequently, the ladderphane copolymer possesses a discharged energy density of 5.34 J cm−3 with a charge–discharge efficiency of 90% at 200 °C, outperforming the existing dielectric polymers and composites. The ladderphane copolymers self-assemble into highly ordered arrays by π–π stacking interactions5,6, thus giving rise to an intrinsic through-plane thermal conductivity of 1.96 ± 0.06 W m−1 K−1. The high thermal conductivity of the copolymer film permits efficient Joule heat dissipation and, accordingly, excellent cyclic stability at elevated temperatures and high electric fields. The demonstration of the breakdown self-healing ability of the copolymer further suggests the promise of the ladderphane structures for high-energy-density polymer capacitors operating under extreme conditions.
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The data that support the findings of this study are available from the corresponding authors on request.
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This research was supported by the National Natural Science Foundation of China (51877132, 52003153, U19A20105, 51522703, 52103303), the Program of Shanghai Academic Research Leader (21XD1401600) and the State Key Laboratory of Electrical Insulation and Power Equipment (EIPE20203, EIPE21206). X.Q. thanks the support by the National Key R&D Program of China (2020YFA0711500), the Natural Science Foundation of Shanghai (22JC1401800) and the State Key Laboratory of Mechanical System and Vibration (MSVZD202211). J.C. thanks B. Zhu and R. Wang for their technical assistance with the Raman spectroscopy measurements.
X.H. and J.C. are inventors on a provisional patent application related to the described work. The other authors declare no competing interests.
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Extended data figures and tables
Extended Data Fig. 1 Synthesis of the monomers, homopolymers and copolymers.
a, SNI, SBNP and TNI monomers. b, PSNI, PTNI and PSBNP homopolymers. c, PSBNP-co-PTNI copolymers.
Extended Data Fig. 2 Schematic of the polymerization and self-assembly process of PSBNP-co-PTNI copolymer.
The interchain π–π stacking interaction induces the formation of the highly ordered array.
Extended Data Fig. 3 XRD of PSBNP-co-PTNI0.02, PSBNP and PSNI.
a, XRD pattern as a function of diffraction angle. b, XRD pattern as a function of d-spacing.
Extended Data Fig. 4 DFT simulations of the electron transition energy under applied electric fields.
a, SBNP-SBNP-SBNP unit. b, SBNP-TNI-SBNP unit.
Extended Data Fig. 5 Schematic of the electron trap energy level in PSBNP-co-PTNI copolymer at applied electric fields.
Owing to the lower transition energy of SBNP-TNI-SBNP compared with SBNP-SBNP-SBNP, electrons are trapped in SBNP-TNI-SBNP units, thereby inhibiting the leakage current. Furthermore, as the applied electric field increases, the transition energy difference between SBNP-TNI-SBNP and SBNP-SBNP-SBNP increases, suggestive of a further increase in the electron trap energy level.
Extended Data Fig. 6 Dielectric properties of PSBNP-co-PTNI0.02 and other capacitor-grade polymer films.
a, Temperature-dependent dielectric constant. b, Temperature-dependent dissipation factor.
Extended Data Fig. 7 Comparison of the discharged energy density at ≥90% charge–discharge efficiency of PSBNP-co-PTNI0.02 and other high-temperature dielectric polymers and composites.
Extended Data Fig. 8 Thermal conductivity and structure of PSBNP and PSBNP-co-PTNI copolymers.
a, Thermal conductivity of PSBNP and PSBNP-co-PTNI copolymers with different PTNI contents measured at 30 °C. b, Thermal conductivity of PSBNP-co-PTNI0.02 measured at different temperatures. c, TEM image of PSBNP-co-PTNI0.04. d, TEM image of PSBNP-co-PTNI0.06. e, Fluorescence excitation spectra of PSBNP and PSBNP-co-PTNI. f, Fluorescence emission spectra of PSBNP and PSBNP-co-PTNI.
Extended Data Fig. 9 Schematic of the self-healing process in metallized polymer dielectric films.
The surge current induced by electrical breakdown can damage the polymer film by the intensive Joule heat, which can evaporate and oxidize the metal electrodes on the surface of films. When the freshly exposed area between the upper and lower electrodes is large enough to insulate the carbonized perforations around the breakdown site53, the capacitor is still able to operate continuously at a full-rated voltage, merely at the expense of a small reduction in capacitance. This smart function of metallized films to clear a breakdown site with the energy released in the dielectric breakdown process is the so-called self-healing, which largely determines the service reliability of metallized dielectric polymer film capacitors54.
Extended Data Fig. 10 Electrical breakdown of PEI film.
a, Schematic and SEM image of PEI after electrical breakdown. b, EDS analysis of the distribution of Al and C elements on the surface of PEI film after electrical breakdown.
This file contains Supplementary sections 1–9, including Supplementary Figs. S1–S63, Supplementary Tables S1 and S2 and Supplementary References. See contents page for details.
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Chen, J., Zhou, Y., Huang, X. et al. Ladderphane copolymers for high-temperature capacitive energy storage. Nature 615, 62–66 (2023). https://doi.org/10.1038/s41586-022-05671-4
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