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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.