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Page 2 of 13 Liu et al. Microstructures 2023;3:2023008 https://dx.doi.org/10.20517/microstructures.2022.31

INTRODUCTION
The increasing global energy consumption and rising demand for low-carbon technologies in modern
society have stimulated the development of renewable energy technology. Compared with electrochemical
capacitors and batteries, dielectric capacitors have a higher power density and longer service life and are
[1-4]
better suited for high-voltage, low-cost, and multifield applications . Dielectric capacitors are therefore
considered to be potential energy storage devices. Faced with the increased demand for the micro-nano
integration of electronic components in modern society, it is technically challenging to simultaneously
[5-7]
achieve high energy density and efficiency in dielectric capacitors .

Nanocomposite films, which integrate a ceramic filler with a high dielectric constant and a polymer matrix
with a high breakdown electric field, provide novel ways for designing dielectric capacitors with high energy
density [8-11] . The researchers improved the energy storage performance of nanocomposites by incorporating
zero-dimensional (0D) ceramic nanoparticles, one-dimensional (1D) ceramic nanofibers, or two-
dimensional (2D) ceramic nanosheet fillers into the polymer matrix [12-15] . Compared with 2D ceramic
nanosheet fillers, 1D ceramic nanofibers are easier to synthesize. Compared with 0D ceramic nanoparticle
fillers, the incorporation of 1D ceramic nanofibers with a high aspect ratio into a polymer matrix can
considerably improve the energy storage performance of nanocomposites. Conversely, 1D ceramic
nanofibers possess a greater dipole moment, which contributes to an increase in the dielectric constant. In
contrast, 1D ceramic nanofibers have a smaller specific surface area and can be dispersed more uniformly in
a polymer matrix, which is advantageous for alleviating electric field concentration and enhancing
breakdown strength. Moreover, 1D ceramic nanofibers as fillers have a lower percolation threshold. This
implies that the dielectric constant of nanocomposites will achieve its maximum value with a small amount
[18]
of loading [16,17] , as demonstrated by the work of Song et al. .

Bi Na TiO (BNT) ceramic is widely used in energy storage devices owing to its high dielectric constant
0.5
3
0.5
and powerful saturation polarization value. However, pure BNT ceramics have a rhombohedral R3c
structure and high remanent polarization value at room temperature, which would significantly impede the
enhancement of energy storage density and energy efficiency of BNT ceramic [19-21] . A new binary system
ceramic material could be created by combining relaxor ferroelectric Sr Bi TiO (BST) with ferroelectric
0.7
0.2
3
BNT with extremely low remanent polarization values while maintaining the high polarization value of
BNT at room temperature. For example, 0.55Bi Na TiO -0.45(Sr Bi )TiO (BNT-BST) has a high
0.5
0.5
0.2
0.7
3
3
saturation polarization value and low remanent polarization value, which is advantageous for improving the
discharge energy density and energy efficiency of nanocomposites [22-24] .
With the advantages of simple equipment, various spinnable raw materials, excellent fiber structure
tunability, and strong expansion of preparation technology, electrospinning is an efficient and low-cost
method for preparing nanofibers that have been rapidly developed in recent years and are widely used to
produce organic, inorganic, and organic/inorganic composite nanofiber materials . Polymer dielectrics
[25]
with optimized multilayer structures have emerged to resolve the contradictions between nanocomposites
with a high dielectric constant and high breakdown electric field. The multilayer structures use the blocking
effect of the ordered interface on charge migration, which can effectively suppress the distortion of the local
electric field and propagation of electrical tree branches and significantly elevate the energy storage
[29]
performance of the nanocomposites [26-28] , as demonstrated in our previous work .

In this study, BNT-BST nanofibers with a high aspect ratio and an average diameter of 280.8 nm were
fabricated via electrospinning. Monolayer and symmetric trilayer polyvinylidene difluoride (PVDF)-based
nanocomposites with varied BNT-BST nanofiber loadings were prepared using the solution-casting