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Liu et al. Microstructures 2023;3:2023008 https://dx.doi.org/10.20517/microstructures.2022.31 Page 9 of 13

Figure 6. (A and B) P-E loops. (C and D) Weibull plots. (E and F) E from Weibull plots of monolayer and trilayer nanocomposites.
b
tortuosity of the path for electrons, hinder the growth of the electric tree, and raise the breakdown electric
field of nanocomposites. Second, the pure PVDF outer layer with low conductivity contained in the trilayer
structure limits the charge injection of the electrode and the electric field concentration impact, as well as
hinders the extension of the electric tree during the breakdown process. Third, trilayer nanocomposites can
alleviate the electric field concentration effect, and the introduction of electron traps increases breakdown
path, further hinders the transport of carriers, and minimizes losses, thereby improving the breakdown
electric field and discharge energy density [15,26-28] .

Figure 7 shows the variation curves of discharge energy density (U ) and energy efficiency (η) for each
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sample with varying electric fields as determined by the integration of P-E loops. Figure 7A and B show that
the U value of the same sample increases monotonically with the applied electric field. In the same electric
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field, the introduction of BNT-BST nanofibers and interfacial polarization results in an increase in electrical
displacement with increasing BNT-BST nanofiber loading. The electric field is high, as is the integral value
of the effective area, and U are large. However, Figure 7C and D show that η first decreases and then
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increases with an electric field, which is mostly attributable to the ferroelectric conversion in PVDF .
[41]
Under the same electric field, η first increases and then decreases with the increased loading of BNT-BST
nanofibers. As the outermost layer, pure PVDF can sustain a greater external electric field, mitigating the
effect of electric field concentration within the nanocomposite. The interface between BNT-BST nanofibers
and pure PVDF matrix, as well as the interlayer interface of the trilayer structure, inhibited the extension
and growth of the electrical tree and reduced the increase in leakage current, both of which are
advantageous for preventing early dielectric breakdown and promoting the improvement of E and η.
b
Therefore, the synergy between the outer insulating layer and the central composite layer is key to
[27,28]
concurrently improving U and η . However, the overloaded BNT-BST nanofibers lead to an increase in
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defects and leakage current, which reduces U and η. Figure 7E and F show the corresponding U and η for
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each sample at the maximum breakdown electric field. For example, the U and η of pure PVDF and
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symmetric trilayer nanocomposites were 9.12 J/cm (45.72%), 14.05 J/cm (51.63%), 17.37 J/cm (52.93%),
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3
3