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Supplementary Information
A record flexible piezoelectric KNN ultrafine-grained
nanopowder-based nanogenerator
Qing-tang Xue1,2,†, Zhe Wang1,2,†, He Tian1,2,†, Yu Huan3, Qian-Yi Xie3,Yi
Yang1,2, Dan Xie1,2, Cheng li1,2, Yi Shu1,2, Xiao-hui Wang3, Tian-ling
Ren1,2*
1
Institute of Microelectronics, Tsinghua University, Beijing 100084, China
2
Tsinghua National Laboratory foe Information Science and Technology
(TNList)
3
School of Materials Science and Engineering, Tsinghua University,
100084 Beijing, China
†
These authors contributed equally to this work.

E-mail: [email protected]
This file includes:
Figures S1 to S4
1. The mechanisms of the flexible generator device
The mechanisms of the device is briefly discussed below showing the KNN-LTS
nanopowder generates the electric potential under external stress. KNN-LTS based
alkaline niobate has high Curie temperature and large electromechanical coupling
factor d33. KNN-LTS has the electric dipoles that can be aligned along the electric field
direction by high electric field. When the poled device in original state (without
tapping), as shown in the cross-sectional structure, almost all of the domains have
dipoles along the electric field direction. The top and bottom electrodes are connected
with the positive and negative charges of the source meter, respectively. Actually, even
removing the poling voltage, the rearranged domains maintain a permanent polarization
which can also be called remanent polarization. It is the remanent polarization which
results in high piezoelectric properties with regard to the external stress. When we apply
a compressive stress on the device, the entire composite is under compressive strain.
The strain induced electric polarization aligns to the dipole direction in the nanopowder,
thus the positive and negative piezoelectric potentials are generated on the top and
bottom of the piezoelectric nanocomposite. In order to balance the piezoelectric
potential, the free electrons in the circuit have to flow through the external load,
resulting in electric pulse in responding to the mechanical deformation. When the
compressive force on the device is removed, the piezoelectric potential between the
electrodes should be diminished, and the accumulated charges at the top electrode will
move back to the bottom side through the external load, generating an electric pulse in
the opposite direction. Therefore, continuously applying and releasing force will result
in alternating voltage and current. The mechanism discussed here is familiar with that
reported by Jung et al,S1 Hu et al.S2
a
Original state
+
A
-
b
c
An applied force
A released state
electrons
+
F
A
+++
-
- - -
+
A
-
electrons
Figure S1. Schematics of the piezoelectric generation mechanism of the device. (a)
When the poled device in original state (without tapping), as shown in the crosssectional structure, almost all of the domains have dipoles along the electric field
direction. (b) When we apply a compressive stress on the device, the entire composite
is under compressive strain, the electrons in the circuit have to flow through the external
load. (c) When the device in a releasing state, the accumulated charges at the top
electrode will move back to the bottom side through the external load in the opposite
direction.
2. The output of KNN nanogenerator before and after poling
process
b
10
5
60
0.0
-0.5
-1.0
0
1
2
3
4
Time(s)
0
-5
-10
c
Before poling 0.5
Current(uA)
Current(uA)
15
80
1.0
0
1
2
3
20
0
1
2
Time(s)
3
4
0
-20
Voltage (V)
1
2
3
4
Time(s)
80
60
4
0
-1
-2
0
d
Current (uA)
20 After poling
15uA
15
10
5
0
-5
-10
0
1
2
3
Time (s)
40
1
-40
4
Time(s)
2
Before poling
Voltage(V)
20
Voltage(V)
a
53V
After poling
40
20
0
-20
-40
0
1
2
3
4
Time (s)
Figure S2. The output voltage and current signals generated from the device before
and after poling process. (a) And (b) are the output current and voltage signals
generated from device before poling process, respectively. (c) And (d) are the output
current and voltage signals after poling process. From comparing the output signals
including voltage and current before and after poling process, we know there is a
quite big magnitude increasing after poling process.
3. Control experiments
The main materials to produce KNN-LTS are potassium carbonate (Na2CO3),
sodium carbonate (K2CO3), niobium oxide (Nb2O5). These materials and CNTs are
mixed with PDMS in the same ratio as KNN-LTS separately. They do not show any
piezoelectricity as we know. Actually, most of the signals are the power frequency
signal. It can be seen that the voltage are all less than 6V which is showed in FigureS3
a~d. However, the voltage generated by the device made of KNN-LTS and CNT mixed
in the PDMS is much larger. So we can conform the charges are produced by KNNLTS nanopowder.
Na2CO3 particles and MW-CNTs with PDMS
Voltage (V)
Voltage (V)
60
40
20
3
2
1
0
-1
-2
-3
b
0
1
2
3
4
Time (s)
0
40
20
-40
0
1
2
3
4
1
2
Time (s)
3
4
0
1
d
40
20
8
6
4
2
0
-2
-4
-6
2
Time (s)
3
4
0
40
20
0
-20
-20
-40
53V
60
1
4
KNN NPD and MW-CNTs with PDMS
5V
0
3
80
Voltage (V)
Voltage (V)
60
2
Time (s)
Nb2O5 and MW-CNTs with PDMS
80
Voltage (V)
0
0
Time (s)
c
3
2
1
0
-1
-2
-3
-20
-20
-40
K2CO3 particles and MW-CNTs with PDMS
80
60
Voltage (V)
80
Voltage (V)
a
-40
0
1
2
Time (s)
3
4
0
1
2
3
4
Time (s)
Figure S3. (a) The output voltages of the control device based on Na2CO3 particles and
MW-CNTs mixed with PDMS matrix. (b) The output voltage of the device made of
K2CO3 particles and MW-CNTs mixed with PDMS matrix. (c) The output voltage of
the device made of Nb2O5 particles, MW-CNTs and PDMS. (d) The output voltage of
the device based on PDMS, KNN-LTS NPD and MW-CNTs. From a series of control
tests, we can conclude that the output voltage and current signals rise from the
piezoelectricity of KNN-LTS NPD material.
Material
Type
NaNbO3
BaTiO3
Output
Voltage
Output
Current
Power
The Area
Normalized to
1cm2
Normalized
Power
Referen
ce
Nanowires D: 200nm L:
several tens of
micrometers
3.2V
72nA
230.4nW
4.5 cm2
0.71V
51.12nW
34
Nanopartic D:100nm
les
Nanotubes D:11.8(±2.3)nm
L:4.1(±1.2)um
3.2V
250nA~350 1120nW
nA
350nA
1925nW
3cm×4cm
0.27V
94.5nW
27
1cm×1cm
5.5V
1925nW
23
Nanopartic D:30nm
7.5V
les
Nanowires D:200-800nm
7.8V
L:10um
nanocubes edge size
20V
of about 100–200
nm
2.5uA
18.75uW
2.9uW
28
2.29uA
17.862uW
35.724uW
25
1uA cm-2
20uW
1
inch 1.16V
square
1cm×
15.6V
0.5cm
1cm× 1cm 12V
12uW
12
KNLN
particles
and
Cu
nanorods
Particles
and
Nanorods
KNLN:1 to 3um, 12V
Cu
nanorods:
diameter 200 to
400nm
1.2uA
14.4uW
3cm×3cm 1.33V
1.596uW
35
Aggregate
d BaTiO3
Nanopartic
le
Composite
Thin Film
nanoparticl
e
Composite
Thin Film
BTO NPs have an 75V
average size of
200 nm;
The diameter of
the hemisphere
is ∼50 μm
15uA
1125uW
4 cm2
18.75V
281.25uW
13
KNN
Nanoparti D:1um
cles
15uA
795uW
1cm
×1.5cm
35.33V
529.95uW
This
work
BaTiO3
ZnO
PMN-PT
ZnSnO3
Geometry
5.5V
53V
Table S1. The comparison of NGs based on different piezoelectric material reported
recently. From this table we know that both the output voltage and output current of
KNN-LTS based nanogenerator are the highest to the date. Here the meaning of D is
the diameter of the materials, the meaning of L is the Length.
4. The details in discussion
The significant enhancements of the output voltage and current density could be
explained by the voltage/power generation mechanism of piezoelecric nanocomposites
illustrated in Supporting Information Figure S4a. An external mechanical stress is
transferred through the PDMS matrix, inducing a stress in the piezoelectric
nanostructures, and thereby generating an electric potential gradient along the direction
of the mechanical stress. This piezoelectric potential will be transferred to the parallel
electrodes and can be applied to an external circuit. The voltage generated by the
piezoelectric composite, Vout, can be calculated as Vout   ( 0 K ) 1dE p S ( A)dA , as
show in the equation 5 in the article.
The d here means d33. Firstly the high output voltage can be expiained by the high
piezoelectric constant (d33); Secondly, the sea-urchin structure can greatly contribute to
their function as the active material in a piezoelectric nanogenerator, which shows in
the figureS4. When the KNN-LTS NPDs are embedded in a PDMS matrix with so many
MW-CNTs connected, the performance will be from the composite structure, where
some CNTs are connected to the two electrodes. Therefore, the CNTs can build quite
well electrical connection between KNN-LTS NPDs. The top and bottom are ITO
electrodes. The CNTs are connected the KNN nanoparticles to the electrodes. So the
potential can transport to the electrodes. Because the CNT’s resistance is much more
smaller than the KNN and the PDMS, so the transport process is more efficient.
Figure S4. The top and bottom are ITO electrodes. The CNTs are connected the KNN
nanoparticles to the electrodes. So the potential can transport to the electrodes.
References
[S1]
[S2]
Jung, J. H. et al. Lead-free NaNbO3 nanowires for a high output piezoelectric
nanogenerator. ACS nano, 2011, 5: 10041-10046.
Hu, Y. et al. High-output nanogenerator by rational unipolar assembly of
conical nanowires and its application for driving a small liquid crystal display.
Nano letters, 2010, 10: 5025-5031.