An Overview of Linear Dielectric Polymers and Their Nanocomposites for Energy Storage

Abstract

As one of the most important energy storage devices, dielectric capacitors have attracted increasing attention because of their ultrahigh power density, which allows them to play a critical role in many high-power electrical systems. To date, four typical dielectric materials have been widely studied, including ferroelectrics, relaxor ferroelectrics, anti-ferroelectrics, and linear dielectrics. Among these materials, linear dielectric polymers are attractive due to their significant advantages in breakdown strength and efficiency. However, the practical application of linear dielectrics is usually severely hindered by their low energy density, which is caused by their relatively low dielectric constant. This review summarizes some typical studies on linear dielectric polymers and their nanocomposites, including linear dielectric polymer blends, ferroelectric/linear dielectric polymer blends, and linear polymer nanocomposites with various nanofillers. Moreover, through a detailed analysis of this research, we summarize several existing challenges and future perspectives in the research area of linear dielectric polymers, which may propel the development of linear dielectric polymers and realize their practical application.

Keywords: discharge density; efficiency; energy storage capacitor; linear dielectric polymers; nanocomposites.

Figure 1

(a) Sketch of a Ragone plot for various energy storage device systems. Reproduced with permission from Ref. [11]. Copyright 2017, American Institute of Physics. (b) The diagram of charge separation in a parallel-plate capacitor under the function of an electric field. Reproduced with permission from Ref. [1]. Copyright 2013, World Scientific.

Figure 2

Graphical representation of a P–E loop used for energy-storage calculations. Reproduced with permission from Ref. [18]. Copyright 2017, Wiley–VCH.

Figure 3

Schematic showing the typical classification of dielectric materials (a) Ferroelectric, (b) Relaxor ferroelectric, (c) Anti-ferroelectric, (d) Linear dielectric. Reproduced with permission from Ref. [21]. Copyright 2018, Elsevier.

Figure 4

Schematic chemical structures of PI (a) and PEI (b). (c,d) Average interchain spacing (c) and the change in specific heat capacity during glass transition (ΔC_p) (d) for PI/PEI blends with different ratios. (e,f) Thermal conductivity (e) and storage modulus (f) of pristine PI, PEI, and PI/PEI blend with a 50/50 ratio. (g,h) Dielectric breakdown strength as a function of the PI/PEI blend ratio at room temperature (g) and at 200 °C (h). (i) Discharge energy density of PI/PEI blend films under various electric fields at room temperature. Reproduced with permission from Ref. [53]. Copyright 2021, Elsevier.

Figure 5

(a) Schematics of the synthesis process of PEEU/PI blend films. (b,c) The dielectric constant (b) and dissipation factor (c) of PEEU/PI blend films with various ratios as a function of frequency at ambient temperature. (d) Weibull breakdown strength of PI and PEEU/PI blend films at ambient temperature (measured at 10³ Hz). Reproduced with permission from Ref. [60]. Copyright 2017, Wiley–VCH.

Figure 6

Dielectric constant (a), breakdown strength (b), discharged energy density (c) and energy-storage efficiency of PUA and PUA/P(VDF-TrFE-CFE) blend films (d) at ambient temperature. The breakdown strength was tested under a voltage ramp of 0.1 kV s⁻¹, and the P-E hysteresis loops were tested at 10 Hz. Reproduced with permission from Ref. [63]. Copyright 2019, IOP.

Figure 7

The relative dielectric permittivity (a) and dielectric loss (b) of BTO/PI nanocomposites with a BTO content of 0, 1, 3, 5, 7, and 9 vol % at ambient temperature. Dependences of breakdown strength (c) and discharge energy density (d) for pure PI and BTO/PI nanocomposites with BTO content of 1, 3, 5, 7, and 9 vol % on temperature ranging from 25 °C to 200 °C at 100 Hz. Reproduced with permission from Ref. [71]. Copyright 2017, American Institute of Physics.

Figure 8

(a) Schematic illustration of the fabrication of the Al₂O₃/PEI nanocomposites. (b) The frequency-dependent dielectric constant of pristine PEI and Al₂O₃/PEI nanocomposites at 25 °C. (c) Temperature-dependent dielectric constant and loss of pristine PEI and 1 vol % Al₂O₃/PEI nanocomposite at 1 kHz. (d) Breakdown strength of pristine PEI and Al₂O₃/PEI nanocomposites at 25 °C, 100 °C, and 150 °C. (e,f) Discharge energy density and efficiency of pure PEI and Al₂O₃/PEI nanocomposites at 150 °C. Reproduced with permission from Ref. [76]. Copyright 2020, The Royal Society of Chemistry.

Figure 9

Frequency-dependency of dielectric permittivity (a) and dielectric loss (b) of BTNFs/PI nanocomposites. (c) Breakdown strength of BTNFs/PI and BTNPs/PI nanocomposites as a function of content loading. (d) Discharged energy density of BTNFs/PI nanocomposites as a function of the electric field. Reproduced with permission from Ref. [78]. Copyright 2018, Elsevier.

Figure 10

(a) Schematic of the preparation of c-BCB/BNNS films. (b,c) Weibull breakdown strength of c-BCB/BNNS as a function of the BNNSs content. (d) Weibull plots of c-BCB/BNNS with 10 vol % of BNNSs at different temperatures. (e) Weibull breakdown strength of c-BCB and c-BCB/BNNS as a function of temperature. The dielectric breakdown strength was measured using the electrostatic pull-down method under a direct-current voltage ramp of 500 V s⁻¹. (f,g) Discharged energy density and efficiency of c-BCB/BNNS with 10 vol % of BNNSs at 250 °C (Measured at a frequency of 10 Hz). Reproduced with permission from Ref. [40]. Copyright 2015, Springer Nature.

Figure 11

Schematic of the preparation of c-BCB/Al₂O₃-NPs, -NWs and -NPLs nanocomposites. Reproduced with permission from Ref. [84]. Copyright 2019, Wiley–VCH.

Figure 12

(a) Dielectric constant and loss of the composites as a function of filler content measured at room temperature and 1 kHz. (b) Weibull statistic of dielectric breakdown strength of PEI and the nanocomposites at 150 °C. (c) Temperature-dependent Weibull breakdown strength of PEI and the nanocomposites at 150 °C. (d) The corresponding electric field distribution was computed by phase-field simulations of the c-BCB nanocomposites with 7.5 vol % Al₂O₃ NPs, NWs, and NPLs at 150 °C and varied applied electric fields. Reproduced with permission from Ref. [84]. Copyright 2019, Wiley–VCH.

Figure 13

Discharged energy density and charge–discharge efficiency of high-temperature dielectric polymers and the c-BCB nanocomposites measured at 150 °C (a,b) and 200 °C (c,d). Reproduced with permission from Ref. [84]. Copyright 2019, Wiley–VCH.