Page 89 - Read Online

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

method. Further, 0-x-0 (where x is the weight fraction of BNT-BST in the middle layer) was designed and
fabricated to evaluate the breakdown strength and energy storage behavior of PVDF-based nanocomposites.
The breakdown electric field increases from 450 kV/mm for pure PVDF to 580 kV/mm for the symmetric
3
3
trilayer 0-2-0 sample, and the discharge energy density increases from 9.12 J/cm to 17.37 J/cm , which is
90.5% greater than that of pure PVDF. These findings may offer a general strategy for improving the energy
storage performance of dielectric capacitors for high energy/power density storage systems.

MATERIALS AND METHODS
Materials. Solutions of CH COOH, CH OCH CH OH, 2,4-pentanedione C H O , Ti(CH (CH ) O) , and
3
3
2 3
4
2
2
3
8
2
5
N,N-dimethylformamide (DMF, 99.5%) were purchased from Sinopharm Chemical Reagent Co.
Polyvinylpyrrolidone (M = 1,300,000, Macklin), Bi(COOCH ) (99.9%, Macklin), NaCOOCH ·3H O (AR,
3 3
2
w
3
Aladdin), Sr(COOCH ) ·1/2H O (AR, Aladdin), and PVDF (6020, Solvay) were used.
2
3 2
Synthesis of 50 mL BNT-BST electrospinning precursor. Initially, 2.2196 g Bi(COOCH ) , 0.5894 g
3 3
NaCOOCH ·3H O, and 0.9720 g Sr(COOCH ) ·1/2H O were dissolved in a solution of 15-mL CH COOH
2
3
3
3 2
2
and 15-mL CH OCH CH OH and stirred at 40 °C for 30 min to generate a uniform solution A.
2
3
2
Subsequently, 3.0033 g C H O was added to 5.1048 g Ti(CH (CH ) O) and stirred at 40 °C for 30 min to
4
8
5
3
2 3
2
generate solution B. Finally, solution B was gently added to solution A, followed by the addition of
CH OCH CH OH and vigorous stirring to bring the volume of the combination to 50 mL of solution C.
2
2
3
Synthesis of BNT-BST nanofibers via electrospinning. Solution C was mixed with an adequate amount of
polyvinylpyrrolidone and stirred at 40 °C for 24 h to obtain solution D. The prepared solution D was placed
into a disposable syringe, and the syringe was attached to the electrospinning equipment to produce
nanofibers. The electrospinning environment was maintained at 40 °C, and the relative humidity was
maintained at < 15%. The applied voltage was 10 kV, the solution flow rate was 1 mL/h, and the distance
between the needle tip and collector was 10 cm. The nanofibers were collected on release paper, dried at
70 °C for 24 h, and then placed in a high-temperature sintering furnace at 300 °C and 700 °C, respectively,
for 1 h with a heating rate of 3 °C /min.
Preparation of BNT-BST/PVDF nanocomposites via solution casting. The BNT-BST/PVDF
nanocomposites were manufactured following a previously published report . All nanocomposite samples
[29]
had a thickness between 12 and 15 um, and each layer in the trilayer samples was ~5 um thick. The
fabrication process of BNT-BST/PVDF nanocomposites with a monolayer and symmetric trilayer structure
is shown in Figure 1. Further, 2 wt% BNT-BST constituted the monolayer nanocomposite, and a 0-2-0
nanocomposite with a trilayer structure was prepared by loading 2 wt% BNT-BST nanofibers as the middle
layer. The final electrode for the electrical performance test was a 2 mm diameter Au electrode.
Characterization. X-ray diffraction (Advance D8), scanning electron microscopy (MIRA4 LMH),
piezoelectric force microscopy (Nanoman TM VS), thermogravimetric analysis (TGA, 8000-FTIR-GCMS),
transmission electron microscopy (TEM, Titan G2 60-300), and X-ray photoelectron spectroscopy (XPS,
ESCALAB250Xi) were employed to investigate the microstructural information of BNT-BST nanofibers.
The dielectric properties, displacement hysteresis loops, and pulse discharge performance of
nanocomposites were characterized using an Agilent 4990A, TF Analyzer 2000 (aixACT, Germany) at
10 Hz, and dielectric material charge measurement system DCQ-20A (PolyK Technologies, USA),
respectively.