Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

High-entropy polymer produces a giant electrocaloric effect at low fields

Abstract

More than a decade of research on the electrocaloric (EC) effect has resulted in EC materials and EC multilayer chips that satisfy a minimum EC temperature change of 5 K required for caloric heat pumps1,2,3. However, these EC temperature changes are generated through the application of high electric fields4,5,6,7,8 (close to their dielectric breakdown strengths), which result in rapid degradation and fatigue of EC performance. Here we report a class of EC polymer that exhibits an EC entropy change of 37.5 J kg−1 K−1 and a temperature change of 7.5 K under 50 MV m−1, a 275% enhancement over the state-of-the-art EC polymers under the same field strength. We show that converting a small number of the chlorofluoroethylene groups in poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer into covalent double bonds markedly increases the number of the polar entities and enhances the polar–nonpolar interfacial areas of the polymer. The polar phases in the polymer adopt a loosely correlated, high-entropy state with a low energy barrier for electric-field-induced switching. The polymer maintains performance for more than one million cycles at the low fields necessary for practical EC cooling applications, suggesting that this strategy may yield materials suitable for use in caloric heat pumps.

This is a preview of subscription content

Access options

Buy article

Get time limited or full article access on ReadCube.

$32.00

All prices are NET prices.

Fig. 1: Entropy-enhanced polymers exhibit giant ECEs under low fields.
Fig. 2: Structural properties of the modified EC polymers and their base terpolymer.
Fig. 3: Dielectric properties of the modified EC polymer and its base terpolymer.
Fig. 4: High-entropy EC polymer and its impact on device performances.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding authors on reasonable request.

Code availability

Access to the phase-field model and DFT model codes are available on request from H.H. (hbhuang@bit.edu.cn) and J.B. (bernholc@ncsu.edu), respectively.

References

  1. Qian, S. et al. Not-in-kind cooling technologies: a quantitative comparison of refrigerants and system performance. Int. J. Refrig. 62, 177–192 (2016).

    CAS  Article  Google Scholar 

  2. Shi, J. et al. Electrocaloric cooling materials and devices for zero-global-warming-potential, high-efficiency refrigeration. Joule 3, 1200–1225 (2019).

    Article  Google Scholar 

  3. Nair, B. et al. Large electrocaloric effects in oxide multilayer capacitors over a wide temperature range. Nature 575, 468–472 (2019).

    ADS  CAS  Article  Google Scholar 

  4. Gu, H. et al. A chip scale electrocaloric effect based cooling device. Appl. Phys. Lett. 102, 122904 (2013).

    ADS  Article  Google Scholar 

  5. Ma, R. et al. Highly efficient electrocaloric cooling with electrostatic actuation. Science 357, 1130–1134 (2017).

    ADS  CAS  Article  Google Scholar 

  6. Torelló, A. et al. Giant temperature span in electrocaloric regenerator. Science 370, 125–129 (2020).

    ADS  Article  Google Scholar 

  7. Wang, Y. et al. A high-performance solid-state electrocaloric cooling system. Science 370, 129–133 (2020).

    ADS  CAS  Article  Google Scholar 

  8. Meng, Y. et al. A cascade electrocaloric cooling device for large temperature lift. Nat. Energy 5, 996–1002 (2020).

    ADS  Article  Google Scholar 

  9. Hawken, P. Drawdown: the Most Comprehensive Plan Ever Proposed to Reverse Global Warming 1st edn (Penguin, 2017).

  10. Kitanovski, A. et al. in Magnetocaloric Energy Conversion: From Theory to Applications (eds Kitanovski, A. et al.) 97–166 (Springer, 2015).

  11. Tušek, J. et al. A regenerative elastocaloric heat pump. Nat. Energy 1, 16134 (2016).

    ADS  Article  Google Scholar 

  12. Li, B. et al. Colossal barocaloric effects in plastic crystals. Nature 567, 506–510 (2019).

    ADS  CAS  Article  Google Scholar 

  13. Wang, R. et al. Torsional refrigeration by twisted, coiled, and supercoiled fibers. Science 366, 216–221 (2019).

    ADS  CAS  Article  Google Scholar 

  14. Zhang, T., Qian, X.-S., Gu, H., Hou, Y. & Zhang, Q. M. An electrocaloric refrigerator with direct solid to solid regeneration. Appl. Phys. Lett. 110, 243503 (2017).

    ADS  Article  Google Scholar 

  15. Defay, E. et al. Enhanced electrocaloric efficiency via energy recovery. Nat. Commun. 9, 1827 (2018).

    ADS  CAS  Article  Google Scholar 

  16. Chen, Y. et al. An all-scale hierarchical architecture induces colossal room-temperature electrocaloric effect at ultralow electric field in polymer nanocomposites. Adv. Mater. 32, 1907927 (2020).

    CAS  Article  Google Scholar 

  17. Neese, B. et al. Large electrocaloric effect in ferroelectric polymers near room temperature. Science 321, 821–823 (2008).

    ADS  CAS  Article  Google Scholar 

  18. Li, X. et al. Tunable temperature dependence of electrocaloric effect in ferroelectric relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene terpolymer. Appl. Phys. Lett. 99, 052907 (2011).

    ADS  Article  Google Scholar 

  19. Zhang, G. et al. Ferroelectric polymer nanocomposites for room-temperature electrocaloric refrigeration. Adv. Mater. 27, 1450–1454 (2015).

    CAS  Article  Google Scholar 

  20. Klein, R. J., Xia, F., Zhang, Q. M. & Bauer, F. Influence of composition on relaxor ferroelectric and electromechanical properties of poly(vinylidene fluoride-trifluoroethylene- chlorofluoroethylene). J. Appl. Phys. 97, 094105 (2005).

    ADS  Article  Google Scholar 

  21. Zhu, G. et al. Self-similar mesocrystals form via interface-driven nucleation and assembly. Nature 590, 416–422 (2021).

    ADS  CAS  Article  Google Scholar 

  22. Bai, G., Gao, D., Liu, Z., Zhou, X. & Wang, J. Probing the critical nucleus size for ice formation with graphene oxide nanosheets. Nature 576, 437–441 (2019).

    ADS  CAS  Article  Google Scholar 

  23. Meiners, T., Frolov, T., Rudd, R. E., Dehm, G. & Liebscher, C. H. Observations of grain-boundary phase transformations in an elemental metal. Nature 579, 375–378 (2020).

    ADS  CAS  Article  Google Scholar 

  24. Borgia, A. et al. Extreme disorder in an ultrahigh-affinity protein complex. Nature 555, 61–66 (2018).

    ADS  CAS  Article  Google Scholar 

  25. Jaffe, B., Cook, W. R. & Jaffe, H. L. Piezoelectric Ceramics (Academic, 1971).

  26. Katsouras, I. et al. The negative piezoelectric effect of the ferroelectric polymer poly(vinylidene fluoride). Nat. Mater. 15, 78–84 (2016).

    ADS  CAS  Article  Google Scholar 

  27. Tan, S., Li, J., Gao, G., Li, H. & Zhang, Z. Synthesis of fluoropolymer containing tunable unsaturation by a controlled dehydrochlorination of P(VDF-co-CTFE) and its curing for high performance rubber applications. J. Mater. Chem. 22, 18496–18504 (2012).

    CAS  Article  Google Scholar 

  28. Le Goupil, F. et al. Enhanced electrocaloric response of vinylidene fluoride–based polymers via one-step molecular engineering. Adv. Funct. Mater. 31, 2007043 (2021).

    Article  Google Scholar 

  29. Kessler, H. Detection of hindered rotation and inversion by NMR spectroscopy. Angew. Chem. Int. Ed. Engl. 9, 219–235 (1970).

    CAS  Article  Google Scholar 

  30. Hong, L. et al. Elastic and conformational softness of a globular protein. Phys. Rev. Lett. 110, 028104 (2013).

    ADS  Article  Google Scholar 

  31. Pirc, R., Kutnjak, Z., Blinc, R. & Zhang, Q. M. Upper bounds on the electrocaloric effect in polar solids. Appl. Phys. Lett. 98, 021909 (2011).

    ADS  Article  Google Scholar 

  32. Yang, L. et al. Novel polymer ferroelectric behavior via crystal isomorphism and the nanoconfinement effect. Polymer 54, 1709–1728 (2013).

    CAS  Article  Google Scholar 

  33. Yang, L. et al. Graphene enabled percolative nanocomposites with large electrocaloric efficient under low electric fields over a broad temperature range. Nano Energy 22, 461–467 (2016).

    CAS  Article  Google Scholar 

  34. Meyer, A., Dimeo, R. M., Gehring, P. M. & Neumann, D. A. The high-flux backscattering spectrometer at the NIST Center for Neutron Research. Rev. Sci. Instrum. 74, 2759–2777 (2003).

    ADS  CAS  Article  Google Scholar 

  35. Klug, H. P. & Alexander, L. E. X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials 2nd edn (Wiley, 1974).

  36. Tosaka, M. et al. Orientation and crystallization of natural rubber network as revealed by WAXD using synchrotron radiation. Macromolecules 37, 3299–3309 (2004).

    ADS  CAS  Article  Google Scholar 

  37. Ranjan, V., Nardelli, M. B. & Bernholc, J. Electric field induced phase transitions in polymers: a novel mechanism for high speed energy storage. Phys. Rev. Lett. 108, 087802 (2012).

    ADS  CAS  Article  Google Scholar 

  38. Chen, X. Z. et al. A nanocomposite approach to tailor electrocaloric effect in ferroelectric polymer. Polymer 54, 5299–5302 (2013).

    CAS  Google Scholar 

  39. Lu, Y.-C. et al. Enhanced electrocaloric effect for refrigeration in lead-free polymer composite films with an optimal filler loading. Appl. Phys. Lett. 114, 233901 (2019).

    ADS  Article  Google Scholar 

Download references

Acknowledgements

This work was supported by the National Key R&D Program of China (2020YFA0711500 and 2020YFA0711503), the National Natural Science Foundation of China (52076127, 51776119, 11974239, 31630002, 51877132, 52003153 and 51972028), the Natural Science Foundation of Shanghai (20ZR1471700) and the China Postdoctoral Science Foundation-funded project 2019M661479. X.Q. acknowledges the support by the Prospective Research Program at Shanghai Jiao Tong University (19X160010008), the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University (project number SL2020MS009), the Student Innovation Center and the Instrumental Analysis Center at Shanghai Jiao Tong University. X.C. and Q.M.Z. acknowledge the support of a seed grant from the Pennsylvania State University MRI-IEE, USA. L.-Q.C. acknowledges the support by the Donald W. Hamer Foundation through the Hamer professorship at Penn State. We thank L. Jiang and B. Zhu for assistance with measurements of energy-dispersive X-ray spectroscopy and attenuated total reflection Fourier-transform infrared spectroscopy. Access to the HFBS was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under Agreement No. DMR-1508249. The DFT calculations were performed at the Oak Ridge Leadership Computing Facility, supported by DOE contract DE-AC05-00OR22725. We thank N. Li from the BL19U2 beamline, X. Miu from the BL16B1 beamline and Y. Yang at the BL14B beamline of Shanghai Synchrotron Radiation Facility for the help with synchrotron X-ray measurements. L.H. thanks the Innovation Program of the Shanghai Municipal Education Commission. H.Q. and J.B. thank B. Zhang and W. Lu for extensive discussions. X.Q. thanks S. Lin for support with simulation software, and X. Yao, Q. Wang and G. Meng for inspiring discussions. Certain commercial material suppliers are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

Author information

Authors and Affiliations

Authors

Contributions

X.Q. conceived the concept, designed the experiment and wrote the manuscript. X.Q., D.H., Jie Chen, Q.L., F.D., X.H., S. Zheng and S. Zhang carried out the material synthesis and characterization. L.Z., D.H., Q.L., L.H. and X.Q. conducted the synchrotron X-ray measurements. L.Z. and M.T. conducted the neutron scattering tests. H.H. and X.S. carried out the phase-field simulation with guidance from L.-Q.C. H.Q. and J.B. carried out the DFT calculation. X.C. conducted the molecular mechanics simulation. X.Q. and D.H. designed the model for cooling devices. J.S. and Jiangping Chen supervised the device modelling. L.H. supervised synchrotron X-ray and neutron scattering tests. X.Q. and Q.M.Z. supervised the project. All authors analysed and interpreted the data.

Corresponding authors

Correspondence to Xiaoshi Qian, Xingyi Huang, Houbing Huang or Liang Hong.

Ethics declarations

Competing interests

 X.Q. and S. Zheng are inventors on a provisional patent application related to the described work. The other authors declare no competing interests.

Peer review information

Nature thanks Brahim Dkhil and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Weibull plots of EC polymers with various -CH = CF- bond contents.

The breakdown strength was characterized at Shanghai Juter High Voltage Electrical & Equipment Co. Ltd. under a DC voltage at a rate of 200 V s−1. The electrode diameter was 1 mm and the film thickness was 6 μm. After introducing 0.4 mol% of the double bonds, the Weibull breakdown strength increased from 350 to 395 MVm−1. As the -CH = CF- bond content increased to 0.6%, 0.8%, and 2.0%, the Weibull breakdown strength decreased to 390, 375, alnd 370 MVm−1. As a result, the maximum cycling field can be extended to 80 MVm−1 for TD-0.6%. 50 MVm−1 is about 14% of the Eb of the polymer.

Extended Data Fig. 2 Reduction of ECE in EC polymer MLC due to inactive materials.

a, Simulated temperature changes of the MLC with and without the epoxy (0.5 μm thick) and un-electrode margin (with 1 cm x 2 cm total area and un-electroded margin = 0.5 mm on each side) as inactive materials. b, Schematics of the numerical model composing of 9 layers of EC polymer and 10 layer of epoxy. The electrode thickness for the polymer is below 0.05 μm (negligible), and we considered the epoxy layer that mechanically stabilize the interfaces between each layers of MLCs. Hence, the total passive part in the MLC will be less than 15%, causing about 15% reduction of ΔT (and ΔS).

Extended Data Fig. 3 Field-dependent EC-induced entropy changes of the base terpolymer and the modified terpolymer with different mole percentages of CFE reduction.

EC-induced entropy changes of the base terpolymer and the modified terpolymers with different mole percentages of CFE reduction (i.e., DB concentration ranges from 0, 0.4%, 0.6% and 2.0%). (n ≥ 3, points are centred on the mean and the bars indicate the s.d., each sample of TD-0.6% in the EC heat flux measurement was verified by independent measurements by an infrared camera, see Supplementary Sections 1.6 and 1.7).

Extended Data Fig. 4 Heat flow signals of EC polymers during the heating and cooling process from the differential scanning calorimetry.

a, base terpolymer, b, TD-0.4%, c, TD-0.6% and d, TD-2.0%.

Extended Data Fig. 5 Rotation energy of carbon-carbon bond in PVDF single chains before (black) and after (red) a CFE group was replaced by a covalent double bond.

a, Rotation energy of the C-C bond adjacent to the Cl atom (on the left of the DB after the CFE reduction), and b, Rotation energy of the C-C bond on the other side of the CFE (DB) group. The simulation was carried out by MM2 force field simulation through ChemOffice (version 19.0). The chain was defined as 5VDF + 1CFE + 5VDF and was relaxed in TGTG’ conformation under zero kelvin. A covalent double bond was in-situ introduced by cancel a HCl of the CFE.

Extended Data Fig. 6 Comparison of the temperature-dependent permittivity between the extrinsic blends and intrinsically modified terpolymer.

The blends were composed of terpolymer P(VDF-TrFE-CFE) and copolymer P(VDF-TrFE) 65/35 mol%. The ferroelectric copolymer was intentionally added to generate a larger ECE by inducing internal fields and providing more polar entities. The composition of blends is noted as TC followed by the percentage of the terpolymer in the blends, e.g., TC90 refers to a polymer blend with 90 mol% terpolymer in the matrix. As the composition of ferroelectric copolymer increases, the dielectric material exhibits higher transition temperatures and stronger polar correlations as shown by the slope of blue arrows, compared with those of the TD series.

Extended Data Fig. 7 Relation between the maximum polarization and the electrocaloric effect of polar materials.

a, Schematic of microscopic ferroelectric-domain switching induced polarization change which does not generate electrocaloric effect. ECE is directly related to the electric field induced polarization change. In ferroelectrics and dielectric in general, the efficiency of inducing electrocaloric entropy change from polarization change can vary over a great range. As an example, macroscopic polarization domain switching, as illustrated here, although generates large polarization change, does not contribute to electrocaloric effect. b, Summarized P-E loops for the base terpolymer and TD series under 120 MVm−1 and 10 Hz. c, Ratio of the β coefficient of modified polymeric EC materials to their respective base polymers16,28,38,39, the inset presents values of the β coefficient of the enhanced EC polymeric materials reported in the literature and this work. As shown by Pirc et al31, ΔS = P2 ln(Ω)/(ε0Θ), where Ω is the number of polar entities (number of polar-states) which can be accessed by dipoles, ε0 is vacuum permittivity, and Θ is an effective Curie constant, which is directly related to the polar correction in a ferroelectric material. Our results reveal that a large ECE can be achieved (at low fields) by engineering a high-entropy dielectric material which possesses a large β coefficient, and hence a large ECE may not require a material to have a large polarization.

Extended Data Fig. 8 Fatigue behaviour of the base terpolymer P(VDF-TrFE-CFE).

a, In-situ heat flux directly recorded during cycling under 80 MVm−1. b, Initially measured EC entropy change compared to that after 61200 cycles under different electric fields.

Extended Data Fig. 9 Comparison of the EC fatigue performances when the base terpolymer and the TD-0.6% were generating the same amount of ECE.

a, Cyclic performance of TD-0.6% before and after 106 cycles, at 50 MVm−1. The integrated peak areas, which represent the total heating and cooling signals, were similar to each other. b, The base terpolymer film experienced a series of breakdown after 50 cycles under 150 MVm−1.

Extended Data Fig. 10 Comparison of hysteresis losses between the base terpolymer and the TD-0.6% high entropy polymer when they were generating the same amount of ECE.

a, Integrated hysteresis loss in percentage. The inset presents PE loops of the base terpolymer under 100 MVm−1 and TD-0.6% under 50 MVm−1, at which the two polymers induced similar ECE. b, Hysteresis heat loss for the base terpolymer and TD-0.6% when they induce the same amount of entropy change of 40 and 70 Jkg−1K−1, respectively.

Supplementary information

Supplementary Information

This file contains four sections and additional references, and includes Supplementary Figs. 1–28 and Tables 1–7. Section 1. Characterization of EC polymers; Section 2. Phase-field simulation; Section 3. DFT calculation of energy barriers in phase transitions; Section 4. Simulation of EC heat pumps using EC polymers.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Qian, X., Han, D., Zheng, L. et al. High-entropy polymer produces a giant electrocaloric effect at low fields. Nature 600, 664–669 (2021). https://doi.org/10.1038/s41586-021-04189-5

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41586-021-04189-5

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing