Ultrahigh discharge efficiency and improved
energy density in rationally designed bilayer
polyetherimide–BaTiO
3
/P(VDF-HFP) composites†
Liang Sun,
a
Zhicheng Shi,
*
a
Huanlei Wang,
a
Kun Zhang,
*
b
Davoud Dastan,
c
Kai Sun
d
and Runhua Fan
d
Polymer dielectric composites are of great interest as film capacitors that are widely used in pulsed power
systems. For a long time, huge efforts have been devoted to achieving energy densities as high as possible to
satisfy the miniaturization and high integration of electronic devices. However, the discharge efficiency
which is particularly crucial to practical applications has gained little attention. With the target of
achieving concurrently improved energy density and efficiency, a class of rationally designed bilayer
composites consisting of a pure polyetherimide layer and a BaTiO
3
/P(VDF-HFP) composite layer were
prepared. Interestingly, the bilayer composites exhibit ultrahigh discharge efficiencies h (>95%) under
external electric fields up to 400 kV mm
1
which are much higher than most of the so far reported
results (h < 80%). Meanwhile, a low loss (tan d < 0.05 @ 10 kHz) comparable to that of the pure
polyetherimide is obtained. In addition, the bilayer composites show impressive improvements in
breakdown strengths E
b
, i.e., 285%, 363%, 366% and 567% for composites with 5 vol%, 10 vol%, 20 vol%
and 40 vol% BaTiO
3
, compared to their single layer counterparts, resulting in obviously improved energy
densities U
d
. In particular, the bilayer composite with 10 vol% BaTiO
3
displays the most prominent
comprehensive energy storage performance, i.e., h 96.8% @ 450 kV mm
1
, U
d
6 J cm
3
@ 450 kV
mm
1
, tan d 0.025 @ 10 kHz, and E
b
483.18 kV mm
1
. The ultrahigh discharge efficiencies and high
energy densities, along with low loss and breakdown strengths, make these bilayer composites ideal
candidates for high-performance dielectric energy-storage capacitors.
1. Introduction
Polymer lm capacitors (PFCs) have drawn considerable atten-
tion in recent years owing to their superior charge–discharge
capabilities, outstanding cycling stabilities, excellent self-
healing capability and wide application in hybrid electric vehi-
cles, medical debrillators, electromagnetic launch systems,
etc.
1–4
However, the applications of PFCs are greatly restricted by
their low energy densities. In principle, the energy density (U
d
)
of a dielectric material can be expressed by the equations U
d
¼
1/23
0
3
r
E
2
for a linear dielectric material and U
d
¼
Ð
EdD for
a nonlinear dielectric material, where 3
0
and 3
r
represent the
dielectric permittivities of the vacuum and dielectrics, E is the
applied electric eld which should be lower than the breakdown
strength (E
b
) of the materials, and D ¼ 3
0
3
r
E is the electric
displacement. Accordingly, high 3
r
and high E
b
are desired for
high U
d
. To achieve this, various strategies have been proposed,
among which constructing polymer based composites lled
with high 3
r
or high E
b
llers has been demonstrated to be
effective.
5–7
To obtain improved 3
r
, ferroelectric ceramic llers
(e.g., BaTiO
3
,
8,9
SrTiO
3
,
10
NaNbO
3
,
11
etc.) and conductors (e.g.,
metals,
12–14
carbon nanotubes,
15
graphene,
16,17
conductive poly-
mers,
18
etc.) are usually employed. However, improved 3
r
is
always accompanied by suppressed E
b
, deteriorated h and
elevated loss.
19
To achieve improved E
b
, llers with high E
b
(e.g.,
boron nitride, alumina, silica, etc.) are usually employed.
1,2
Unfortunately, the llers with high E
b
oen exhibit low 3
r
,
leading to suppressed 3
r
.
20
As a result, a reasonable balance
between 3
r
and E
b
has been a problem demanding a prompt
solution until now. Although various innovative strategies, such
as designing core–shell structured llers
21,22
and surface modi-
cation of llers,
23–25
have been proposed to address this
dilemma, the effect is still not satisfactory.
Recently, researchers found that multilayer structured
composites may offer a feasible paradigm to realize the
a
School of Materials Science and Engineering, Ocean University of China, Qingdao
266100, P. R. China. E-mail: zcshi@ouc.edu.cn
b
Key Laboratory of Microgravity (National Microgravity Laboratory), Institute of
Mechanics, Chinese Academy of Sciences, Beijing 100190, China. E-mail:
zhangkun@imech.ac.cn
c
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta,
Georgia-30332, USA
d
Institute of Marine Materials Science and Engineering, Shanghai Maritime University,
Shanghai 201306, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ta00903b
Cite this: J. Mater. Chem. A, 2020, 8,
5750
Received 22nd January 2020
Accepted 2nd March 2020
DOI: 10.1039/d0ta00903b
rsc.li/materials-a
5750 | J. Mater. Chem. A, 2020, 8, 5750–5757 This journal is © The Royal Society of Chemistry 2020
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