High-Voltage Flexible Microsupercapacitors based on Laser-induced

Subscriber access provided by TUFTS UNIV

Energy, Environmental, and Catalysis Applications

High-Voltage Flexible Microsupercapacitors based on Laser-induced Graphene Xiaoqian Li, Weihua Cai, Kwok Siong Teh, Mingjing Qi, Xining Zang, Xinrui Ding, Yong Cui, Yingxi Xie, Yichuan Wu, Hongyu Ma, Zaifa Zhou, Qing-An Huang, Jianshan Ye, and Liwei Lin ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 13 Jul 2018 Downloaded from http://pubs.acs.org on July 13, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

High-Voltage Flexible Microsupercapacitors Based on Laser-induced Graphene

Xiaoqian Li,*,

†, ‡

Weihua Cai,†, § Kwok Siong Teh,¶ Mingjing Qi,† Xining Zang,† Xinrui

Ding,† Yong Cui,† Yingxi Xie,† Yichuan Wu,† Hongyu Ma,† Zaifa Zhou,‡ Qing-An Huang,*, ‡ Jianshan Ye*, § and Liwei Lin*, †

†

Department of Mechanical Engineering, University of California, Berkeley, California,

94709, USA ‡

Key Laboratory of MEMS of the Ministry of Education, Southeast University, Nanjing,

210096, China §

School of Chemistry and Chemical Engineering, South China University of Technology,

510641, China ¶

School of Engineering, San Francisco State University, California, 94132, USA

Xiaoqian Li*, [email protected] Qing-An Huang*, [email protected] Jianshan Ye*, [email protected] Liwei Lin*, [email protected]

Keywords: High-Voltage, Laser-induced graphene, Microsupercapacitors, Micro-sensors, Micro-robots

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract High-voltage energy storage devices are quite commonly needed for robots and dielectric elastomers. This paper presents a flexible high-voltage microsupercapacitor (MSC) with a planar in-series architecture for the first time based on laser-induced graphene. The high-voltage devices are capable of supplying output voltages ranging from a few to thousands of volts. The measured capacitances for the 1 V, 3 V and 6 V MSCs were 60.5 µF, 20.7 µF and 10.0 µF, respectively under an applied current of 1.0 µA. After the 5000-cycle charge-discharge test, the 6 V MSC retained about 97.8% of the initial capacitance. It also was recorded that the all-solid-state 209 V MSC could achieve a high capacitance of 0.43 µF at a low applied current of 0.2 µA and a capacitance of 0.18 µF even at a high applied current of 5.0 µA. We further demonstrate the robust function of our flexible high-voltage MSCs by using it to power a piezoresistive microsensor (6 V) and a walking robot (> 2000 V), respectively. Considering the simple, direct, and cost-effective fabrication method of our laser fabricated flexible high-voltage MSCs, this work paves the way and lays the foundation for high-voltage energy storage devices.


Page 2 of 24

Page 3 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction High-voltage power supplies are quite commonly required for many electronics and machines like small robots

1-3

and dielectric elastomers

4-6

. In order to obtain high-voltage output,

batteries and supercapacitors are usually connected in series by cables because they could only offer for less than 4 V for a single cell. But such connection always suffer from inconvenience of operation by using plenty of conducting metal wires. Supercapacitors have been viewed as a valuable alternative to batteries because they can be charged and discharged much more rapidly with an almost infinite lifetime.

7-13

Unlike

batteries that rely on electrochemical redox reactions, a supercapacitor stores charges via the adsorption and desorption of ions within a thin electrical double layer that exists between the solid electrodes and the bulk electrolytes.14, 15 This allows adsorbed ions to rapidly desorb from the surface of the electrodes, enabling a supercapacitor to attain high power density by discharging and releasing power within a short time. Miniaturized supercapacitors, commonly known as microsupercapacitors (MSCs), have become an active and intense area of research. 16-18

This phenomenon is catalyzed by the popularity and rise of miniaturized, self-powering

electronics, which necessitates direct integration of miniaturized, on-chip energy storage devices such as supercapacitors on a flexible platform.

19-21

Increasingly, these micro

energy-storage devices are designed to power microelectronics such as wireless microsensors networks

22, 23

and radio-frequency identification (RFID) tags

24, 25

. Some of the

microelectronics are driven by high voltage sources from several volts to thousands of volts. Nevertheless, the intrinsic low output voltage (typically less than 4 V) of MSCs, critically limited by the properties of electrode materials and electrolyte, presents a formidable challenge and obstacle in their use in directly powering such microelectronics. To this end, a ACS Paragon Plus Environment


workable strategy to make high-voltage MSCs is to assemble many MSCs into a high-voltage energy stack via in-series connection using external conducting metal wires. The resulting assemblies, however, suffer from critical drawbacks in operation safety and complex fabrication processes. 26 Therefore, a safe, simple, and effective means to directly integrate high-voltage MSCs with microelectronics—albeit difficult and elusive at present—remains important and desirable. Herein, by using the in-series structure, flexible high-voltage planar MSCs based on laser-induced graphene (LIG) can generate an output voltage of up to 209 V for the first time, which was the highest recorded voltage among all current planar MSCs. In other words, 210 LIG square electrodes were fabricated via a direct-write, ambient laser pyrolysis of polyimide film firstly and then 209 single-unit microsupercapacitors were connected in series on a single film substrate. Compared to the lithographic processes that may involve multiple masking steps, direct laser writing provides a fast and low-cost fabrication route that enables substantially faster design iterations. Furthermore, in order to investigate the electrochemical performance of high-voltage MSCs, the Cyclic Voltammetry (CV) and charge-discharge methods at high-voltage range (from 0 to 209 V) were developed in this work. Besides, we successfully applied the highly robust MSC in powering piezoresistive microsensors in the application of a walking step counter (pedometer) for activity tracking. Besides, ten 209 V MSCs were also connected in series to drive a small walking robots which need the 2000 V power source. RESULTS AND DISCUSSION The laser-assisted fabrication and electrolyte coating processes are schematically shown in Figure 1a. Briefly, the 209 V MSC patterns were designed by using a pattern-generation ACS Paragon Plus Environment

Page 4 of 24

Page 5 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


software and transferred to a programmable CO2 infrared laser system. Next, a 125 µm-thick Kapton (polyimide) substrate was rapidly and irreversibly pyrolyzed by a laser beam (wavelength of 10.6 µm, laser spot size of 200 µm) with an optimized scan rate of 250 mm/s and power of 8.0 Watts. Upon the transient laser heating, the surface of the Kapton substrate was instantaneously transformed into a porous graphene network 27, which exhibited good physical and electrical characteristics suitable for potential energy storage applications. To construct a 209 V MSC, 210 porous LIG squares (3mm × 3mm for each square) separated by 209 gaps (500 µm in distance) were laser patterned (inset on the left of Figure 1). Moreover, each gap and an estimated 30% area from one side of the LIG square, approximated from Figure S1, were covered with 1.0 M H2SO4-polyvinyl alcohol (PVA) electrolyte. The middle section of each LIG square can act as the common conductive electrode for the in-series connections without the coating of the H2SO4-PVA electrolyte. The shear viscosity of H2SO4-PVA was as high as 5738 Pa•s at room temperature (Figure S2) and a droplet-shape electrolyte was plotted at the gap by using a tiny brush (PRINCETON Lauren 4035R, Figure S3). The transient laser heating temperature (at 0.1 millisecond) on the Kapton film (125 µm in thickness) was simulated by COMSOL Multiphysics to be about 1609.8 ℃ when the laser power output and scan speed were set at 8.0 Watts and 250 mm/s, respectively, as shown in Figure 1b. Figure 1c illustrates that, as the laser power increased from 4.0 Watts to 8.0 Watts, the simulated temperature also increased from 817.2 ℃ to 1609.8 ℃ while the sheet resistance of the LIG decreased from 17.4 Ω/sq to 9.3 Ω/sq. From the Raman spectrum in Figure 1d, three prominent peaks with the D peak, G peak and the 2D peak were observed. 28 The D peak at ~1,350 cm-1 induced by defects, the G peak at ~1,580 cm-1 from the doubly ACS Paragon Plus Environment


degenerate zone center E2g mode

29

and the sharp 2D peak at ~2,700 cm-1 originating from

second order zone-boundary phonons indicated the existence of graphene after the laser pyrolysis process. As shown in the high-resolution TEM image of LIG (Figure S4), the average lattice space is about 0.337 nm, corresponding to the (002) planes in graphitic materials. From the TEM SAED pattern, the (002) planes were also observed, indicating the formation of graphene sheets. 27 The elemental composition and concentration of LIG was investigated by X-ray photoelectron spectroscopy (XPS). In the survey spectrum (Figure 1e), the elements C and O could be observed. The binding energy values of C1s and O1s for the sample were found to be 284.8 and 532.8 eV, respectively. The results obtained showed that the molar ratio of C/O is close to 11: 1. The high resolution C1s XPS spectrum of LIG further indicated LIG were sp2 carbons with C—C peak being dominant at 284.5 eV (Figure 1f). For the high-resolution O1s XPS spectrum of LIG (Figure 1g), a broad peak appeared at 532.3eV indicating the combination of C—O (533.2 eV) and C=O (531.8 eV) bond, which is in agreement with the results previously reported. 30 In order to verify the feasibility of an in-series structure for MSCs, MSCs with output voltage ranging from 1 V to 6 V were fabricated as schematically shown in Figure 2a. Two symmetric electrodes separated by a gap were denoted as one unit of a MSC. The gap between two electrodes were coated with the H2SO4-PVA electrolyte, leading to 1 V output for each unit. When three or six units are connected in series, MSCs with 3 V or 6 V outputs, respectively, can be constructed. In fact, the voltage output scales linearly with the number of units of MSCs. The capacitance of a symmetric supercapacitor cell (Cdevice) can be estimated by the CV curves using the following equation (1): 31 ACS Paragon Plus Environment

Page 6 of 24

Page 7 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


C = = ()

(1)

Where Q is the total charge obtained by integration of the CV curve, is the current, is the scan rate, and V is the potential window. The CV curves of the three different devices (1 V, 3 V and 6 V) under a scan rate of 100 mV/s showed capacitance of 58.1 µF, 20.4 µF and 11.3 µF, respectively (Figure 2b), demonstrating the feasibility of the in-series structure for high-voltage planar MSCs. Galvanostatic charge-discharge method was used to accurately characterize the capacitive properties of these MSCs. The capacitance could be calculated from the following equation: 32 C=

∗

(2)

Where I is the applied current, t is the discharge time of the supercapacitors and V is the electrochemical potential windows. For conventional capacitors, it’s well known that the in-series connections would result in the decay of capacitance. Supercapacitors also behave in similar manner. The total capacitance of a high-voltage MSC connected in series could be calculated as:

=

+

+

+⋯

= ∑( )

(3)

Where C is the total capacitance of a high-voltage MSC, Ci is the capacitance of each unit. For first-order approximation, C1 = C2 = C3 = Ci, and this results in C = C1/n. After calculating the charged and discharged results from Figure 2c, the capacitances for 1 V, 3 V and 6 V MSCs were 60.5 µF, 20.7 µF and 10.0 µF, respectively under an applied current of 1.0 µA. Supercapacitors typically have excellent cycling stability, however, little is known about the cycling stability of high-voltage MSCs with an in-series electrode architecture. To shed light on this crucial characteristic, a 5000-cycle charge-discharge test was conducted for a 6 V ACS Paragon Plus Environment


MSC, as shown in Figure 2d and the 6 V MSC retained about 97.8% of the initial capacitance. The inset shows charged-discharged profiles of the last 10 cycles in a 5000-cycle test. The capacitance decay could possibly be attributed to the tiny variations of voltages that exist among different units—a result of the electrolyte coating process that could be further improved and optimized. A digital image of a 209 V all-solid-state flexible MSC was shown in Figure 3a. As shown in Figure 3b, one corner of the 209 V MSC was clearly observed with the uniform coating of H2SO4-PVA electrolyte. To demonstrate the flexibility of the high-voltage MSCs as shown in Figure 3c, a flexible planar 209 V device was tested with negligible degradation of charge and discharge curves at 2.0 µA when it was bent at different angles ranging from 0° to 180°, showing the good stability of the planar high-voltage MSC. Instead of comparing the areal or volumetric capacitances between MSCs with different output voltages, we use the capacitance derived from the designed MSC with a specific geometry. The volume of the 209 V MSC device is calculated to be 0.3 cm3 (Figure S5). Figures 3d-f show the CV curves and the corresponding capacitance of the 209 V device. The rectangular and symmetric shapes of the CV curves indicated its capacitive properties with scan rates ranging from 0.1 to 10 V/s. The 209 V MSC was able to achieve 0.37 µF at 0.1 V/s when it was discharged from 209 V to 0 V and 0.19 µF at a scan rate of 10 V/s. The charged and discharged data (Figures 3g-i) were further used to evaluate the performance of the 209 V device with various applied currents ranging from 0.2 µA to 5.0 µA. It can be seen that the all-solid-state 209 V MSC could achieve a high capacitance of 0.43 µF at a low applied current of 0.2 µA and a capacitance of 0.18 µF even at a high applied current of 5.0 µA. These charge curves are relatively symmetric to their corresponding discharge counterparts at different applied currents, further ACS Paragon Plus Environment

Page 8 of 24

Page 9 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


revealing the capacitive behavior of the flexible all-solid-state 209 V MSC. The maximum specific volumetric capacitance of the 209 V device was calculated from the charged/discharged curve to be 1.43 µF/cm3, which was comparable to the value (10.0 µF/cm3) of a commercial ceramic capacitor (X7R 1210) and 24 times larger than the value (0.06 µF/cm3) of a commercial Panasonic thin film capacitor (Table S1). Meanwhile, the 209 V MSC also maintained excellent flexibility when compared with the fragile ceramic capacitor. For the microsupercapacitors, they are often characterized and compared by using the volumetric energy density instead of the mass based energy density because the mass of the active materials was tiny.

33

The volumetric energy density was calculated based on the

following equation: E= /, where C is the device capacitance of the 209 V MSC, U is the working voltage of the device, V is the volume of the 209 V MSCs. Therefore, the volumetric energy density of 209 V MSCs were calculated as 31.3 mWh/cm3 at 0.67 µA/cm3, which was much larger than the capacitance (5.7 mWh/cm3) from the previous work of micro-supercapacitors based on laser-processed graphene. 34 The electrochemical impedance spectroscopy (EIS) test was conducted in a frequency range from 1 Hz to 1 MHz to further evaluate the electrochemical behaviors of the 209 V solid-state microsupercapacitor. As shown in the Nyquist plots in Figure S9a, the intercept of the Nyquist curve on the real axis was about 13.7 kΩ, indicating reasonable conductivity of the solid-state electrolyte and internal resistance of the device. The semi-circle diameter referring to the charge transfer resistance (Rct) was about 529 kΩ, which was acceptable for the high-voltage microsupercapacitors usually working in the µA current ranges. Moreover, the Bode plot was also recorded in Figure S9b and it is be observed that the capacitor response frequency (f0), at the phase angle of -45° was 4.64 Hz, which was similar to the ACS Paragon Plus Environment


values of solid-state supercapacitors based on Carbon Nanoparticles/MnO2.35 The corresponding time constant τ0 (=1/f0) was 216 ms, which was close to that of laser scribed graphene supercapacitors (33 ms) but was much shorter than those of supercapacitors based on activated carbon (in the range of 10 s).7 The phase angle of the 209 V MSC was about -77° at a frequency of 1 Hz which is close to -90° for ideal capacitors.

To demonstrate the potential of these high-voltage MSCs,36 a 6 V MSC was used to drive a wearable piezoresistive pressure sensor (Figure 4a) which was made by transferring the LIG onto a polydimethylsiloxane (PDMS) substrate based on a modified process from a previous report (see Figure S13).37 Briefly, a serpentine shaped LIG was directly laser-written on Kapton substrate. Next, liquid PDMS was poured onto the patterns. After heating for 2 hours in an oven, the serpentine LIG was transferred onto the curing PDMS. To prevent possible contact with moisture, the surface of LIG was covered by another layer of PDMS.

Figure 4c showed the responses of the microsensor under the applied voltage of 6 V powered by a Gamry workstation while being finger-pressed at a pressure of about 60 kPa (Figure 4b) manually. The deformation of the sensor caused the increases in resistance and reduction in measured current as shown. The detailed signals were zoomed in the inset and some variations were observed due to the manual pressing operations. When the power source was replaced by using a 6 V MSC, very similar data could be obtained in Figure 4d. However, the base line of current gradually decreased with time because of the continuous decrease of the supplied voltage from the 6 V MSC due to both the leakage and consumption of charges during the operations. The microsensor was further placed under an insole inside a running shoe to monitor the ambulatory motions in Figure 4e. By using the Gamry workstation as a ACS Paragon Plus Environment

Page 10 of 24

Page 11 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


power source with 6 V output, a highly stable I-t curve could be achieved as the microsensor recorded the heel strikes during 1-min of walking (Figure 4f). After replacing the power source by a 6 V MSC, similar I-t curve (Figure 4g) with the constantly decrease of baseline current was observed indicating excellent performance of the flexible planar high-voltage MSCs. The zoomed-in signals were nearly the same from two different power sources, validating the robustness and feasibility of our MSCs. Figure 5a showed the detailed structure of a crawling robot which was a 20 mm-long, 47 mg-weight prototype. The cantilever-beams together with the additional mass can be excited to vibrate back and forth by a high-voltage direct current (DC) power source (> 2000 V) to impact the electrodes in sequence and achieved self-sustained walking gaits according to previous reports

1, 38

. To demonstrate the feasibility of the high-voltage MSC, the walking

robot was driven by ten in-series connected 209 V MSCs as shown in Figure 5b. The crawling movement of a walking robot powered by a 2090 V MSC stack for 11 seconds was recorded by a digital camera from Figure 5c to Figure 5d. These results proved that high-voltage MSCs with plannar in-series structure could be a good option among energy storage devices.

CONCLUSIONS In conclusion, this work reports a high-voltage flexible planar MSC with an in-series LIG electrode architecture via direct laser engraving of polyimide film. The high-voltage all-solid-state MSCs were flexible and capable of supplying output voltages ranging from a few to thousands of volts. We demonstrated the robust function of our flexible high-voltage MSCs by using it to power a piezoresistive microsensor that was designed as a wearable step counter to track walking activities. Besides, a walking robot was also successfully powered by ACS Paragon Plus Environment


a 2090 V MSC stack for 11 seconds. Considering the simple, direct, and cost-effective fabrication method of our laser patterned high-voltage flexible planar MSCs, this work paves the way and lays the foundation for high-voltage energy storage devices.

METHODS Fabrication of the 209 V MSC. Kapton polyimide film (Cat. No. 2271K3, thickness: 125µm) was used in this work. The CO2 laser (10.6 µm wavelength) with optimized scan rate of 250 mm/s and output power of 8.0 Watts was used to heat the Kapton film with designed 210 squares. For each square electrode, the side length was 3.0 mm with a gap of 500 µm between every two electrodes. After the laser heating process, the gaps were brush coated by electrolyte, leaving an approximated 40% of each LIG square without the coating of the electrolyte as the common conductive electrode for in-series connection. The electrolyte was made by adding 1.0 g of PVA (Mw: 89,000-98,000) into 5.0 ml of 1.0 M H2SO4 solution, which was subsequently heated at 95 ºC for 20 minutes until the solution turned clear. Fabrication of the Pressure Microsensor. The Kapton film was laser heated into a conductive serpentine shaped LIG firstly. After the laser heating process, PDMS (Sylgard 184, Dow Corning, mixing ratio 15 : 1) was casted onto the LIG patterns. In order to remove the air from the small pores inside the pours graphene networks and allow the full penetration of PDMS liquids, a vacuum step was essentially necessary. The polymer was crosslinked at 80 ºC for 2 hours in an electric oven. After fully cured, the PDMS/LIG microsensor was peeled off from the Kapton film and further covered by another layer of PDMS. Characterizations. The electrochemical performance of 1 V, 3 V and 6 V MSC was measured by an electrochemical workstation (Gamry Reference 600 potentiostat). The 209 V ACS Paragon Plus Environment

Page 12 of 24

Page 13 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


MSC was tested by Keithley 2400. The I-t curves for the microsensors were obtained from the Gamry workstation with sample period time of 0.001 s. SEM images were taken with a FEI Quanta 3D scanning electron microscope. The transmission electron microscopy (TEM) image and the SAED pattern were conducted on FEI Titan 80-8300. XPS investigations were conducted on PHI 5600 X-ray photoelectron spectrometer. Raman spectra were taken on LabRAM Aramis (HJY, France). The shear viscosity of electrolyte was characterized by Anton Paar at 25℃.

ASSOCIATED CONTENT Supporting Information Supporting Information Available: Schematic calculation of electrolyte covered area, shear viscosity of electrolyte, digital image of a tiny brush, TEM image of LIG, comparison of the high-voltage planar MSC with commercial capacitors, Video S1 for bending test of the 209 V MSC, and Video S2 for the walking robot.

AUTHOR INFORMATION Corresponding Author Email: [email protected]; Email: [email protected]; Email: [email protected] Notes Conflict of Interest: The authors declare no competing financial interest.



ACKNOWLEDGEMENTS This project is supported in part by the National Natural Science Foundation of China (Grant No. 61674034 & 21372088), China Aviation Science Foundation (2015ZD51051), and Berkeley Sensor and Actuator Center. X. Li and W. Cai are partially supported by fellowships from the China Scholarship Council. We also thank Michael Lino, equipment technician at San Francisco State University, for his help in the preliminary laser engraving experiments.

REFERENCES (1) Qi, M. J.; Zhu, Y. S.; Liu, Z. W.; Zhang, X. Y.; Yan, X. J.; Lin, L. W. A Fast-Moving Electrostatic Crawling Insect. 30th IEEE International Conference on Micro Electro Mechanical Systems 2017, 761-764. (2) Li, T. F.; Li, G. R.; Liang, Y. M.; Cheng, T. Y.; Dai, J.; Yang, X. X.; Liu, B. Y.; Zeng, Z. D.; Huang, Z. L.; Luo, Y. W.; Xie, T.; Yang, W. Fast-moving Soft Electronic Fish. Sci. Adv. 2017, 3, e1602045. (3) Pei, Q.; Pelrine, R.; Stanford, S.; Kornbluh, R.; Rosenthal, M. Electroelastomer Rolls and Their Application for Biomimetic Walking Robots. Synth. Met. 2003, 135, 129-131. (4) Gu, G. Y.; Zhu, J.; Zhu, L. M.; Zhu, X. Y. A Survey on Dielectric Elastomer Actuators for Soft Robots. Bioinspir. Biomim. 2017, 12, 011003. (5) Hines, L.; Petersen, K.; Sitti, M. Inflated Soft Actuators with Reversible Stable Deformations. Adv. Mater. 2016, 28, 3690-3696. (6) Larson, C.; Peele, B.; Li, S.; Robinson, S.; Totaro, M.; Beccai, L.; Mazzolai, B.; Shepherd, R. Highly Stretchable Electroluminescent Skin for Optical Signaling and Tactile Sensing. Science 2016, 351, 1071-1074. ACS Paragon Plus Environment

Page 14 of 24

Page 15 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(7) EI-Kady, M. F.; Strong, V.; Dubin, S.; Kaner, R. B. Laser Scribing of High-Performance and Flexible Graphene-Based Electrochemical Capacitors. Science 2012, 335, 1326-1330. (8) Ghidiu, M.; Lukatskaya, M. R.; Zhao, M. Q.; Gogotsi, Y.; Barsoum, M. W. Conductive Two-dimensional Titanium Carbide 'Clay' with High Volumetric Capacitance. Nature 2014, 516, 78-81. (9) Lukatskaya, M. R.; Mashtalir, O.; Ren, C. E.; Dall'Agnese, Y.; Rozier, P.; Taberna, P. L.; Naguib, M.; Simon, P.; Barsoum, M. W.; Gogotsi, Y. Cation Intercalation and High Volumetric Capacitance of Two-dimensional Titanium Carbide. Science 2013, 341, 1502-1505. (10) Peng, Z. W.; Ye, R. Q.; Mann, J. A.; Zakhidov, D.; Li, Y. L.; Smalley, P. R.; Lin, J.; Tour, J. M. Flexible Boron-doped Laser-Induced Graphene Microsupercapacitors, ACS Nano 2015, 9, 5868-5875. (11) EI-Kady, M. F.; Kaner, R. B. Scalable Fabrication of High-power Graphene Micro-Supercapacitors for Flexible and On-chip Energy Storage, Nat. Commun. 2013, 4, 1475. (12) Zheng, S. H.; Tang, X. Y.; Wu, Z. S.; Tan, Y. Z.; Wang, S.; Sun, C. L.; Cheng, H. M.; Bao, X. H. Arbitrary-shaped Graphene-based Planar Sandwich Supercapacitors on One Substrate with Enhanced Flexibility and Integration, ACS Nano 2017, 11, 2171-2179. (13) Zheng, S. H.; Lei, W. W.; Qin, J. Q.; Wu, Z. S.; Zhou, F.; Wang, S.; Shi, X. Y; Sun, C. L; Chen, Y.; Bao, X. H. All-solid-state High-energy Planar Asymmetric Supercapacitors based on All In-one Monolithic Film Using Boron Nitride Nanosheets as Separator, Energy Storage Materials, 2018, 10, 24-31.



(14) Simon, P.; Gogotsi, Y.; Dunn, B. Where Do Batteries End and Supercapacitors Begin? Science 2014, 343, 1210-1211. (15) Liu, C.; Li, F.; Ma, L. P.; Cheng, H. M. Advanced Materials for Energy Storage. Adv. Mater. 2010, 22, E28- E62. (16) Huang, P.; Lethien, C.; Pinaud, S.; Brousse, K.; Laloo, R.; Turq, V.; Respaud, M.; Demortiere, A.; Daffos, B.; Taberna, P. L.; Chaudret, B.; Gogotsi, Y.; Simon, P. On-chip and Freestanding Elastic Carbon Films for Micro-supercapacitors. Science 2016, 351, 691-695. (17) Li, L.; Zhang, J. B.; Peng, Z. W.; Li, Y. L.; Gao, C. T.; Ji, Y. S.; Ye, R. Q.; Kim, N. D.; Zhong, Q. F.; Yang, Y.; Fei, H. L.; Ruan, G. D.; Tour, J. M. High-Performance Pseudocapacitive Microsupercapacitors from Laser-Induced Graphene. Adv. Mater. 2016, 28, 838-845. (18) Ferris, A.; Garbarino, S.; Guay, D.; Pech, D. 3D RuO2 Microsupercapacitors with Remarkable Areal Energy. Adv. Mater. 2015, 27, 6625-6629. (19) Yuan, L. Y.; Xiao, X.; Ding, T. P.; Zhong, J. W.; Zhang, X. H.; Shen, Y.; Hu, B.; Huang, Y. H.; Zhou, J.; Wang, Z. L. Paper-Based Supercapacitors for Self-Powered Nanosystems. Angew. Chem. Int. Ed. 2012, 51, 4934-4938. (20) Jost, K.; Dion, G.; Gogotsi, Y. Textile Energy Storage in Perspective. J. Mater. Chem. A 2014, 2, 10776-10787. (21) Zhang, Y. Z.; Wang, Y.; Cheng, T.; Lai, W. Y.; Pang, H.; Huang, W. Flexible Supercapacitors Based on Paper Substrates: A New Paradigm for Low-cost Energy Storage. Chem. Soc. Rev. 2015, 44, 5181-5199. (22) Wang, Z. L., Self-Powered Nanosensors and Nanosystems. Adv. Mater. 2012, 24, 280-285. ACS Paragon Plus Environment

Page 16 of 24

Page 17 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Li, L.; Lou, Z.; Han, W.; Shen, G. Z., Flexible In-plane Microsupercapacitors with Electrospun NiFe2O4 Nanofibers for Portable Sensing Applications. Nanoscale 2016, 8, 14986-14991. (24) Yang,

H.; Lu, W. Graphene-Based Electrochemical Microsupercapacitors for

Miniaturized Energy Storage Applications. Nanomaterials for Sustainable Energy 2016, 271-291. (25) Kyeremateng, N. A.; Brousse, T.; Pech, D. Microsupercapacitors as Miniaturized Energy-Storage Components for On-chip Electronics. Nat. Nanotechnol. 2017, 12, 7-15. (26) Sun, H.; Fu, X. M.; Xie, S. L.; Jiang, Y. S.; Peng, H. S. Electrochemical Capacitors with High Output Voltages that Mimic Electric Eels. Adv. Mater. 2016, 28, 2070- 2076. (27) Lin, J.; Peng, Z. W.; Liu, Y. Y.; Ruiz-Zepeda, F.; Ye, R. Q.; Samuel, E. L. G.; Yacaman, M. J.; Yakobson, B. I.; Tour, J. M. Laser-induced Porous Graphene Films from Commercial Polymers. Nat. Commun. 2014, 5, 5714. (28) Ferrari, A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K. S.; Roth, S.; Geim, A. K. Raman Spectrum of Graphene and Graphene Layers. Phys. Rev. Lett. 2006, 97, 187401. (29) Tuinstra, F.; Koenig, J. L. Raman Spectrum of Graphite. J. Chem. Phys. 1970, 53, 1126-1130. (30) Peng, Z. W.; Lin, J.; Ye, R. Q.; Samuel, E. L. G.; Tour, J. M. Flexible and Stackable Laser-Induced Graphene Supercapacitorse. ACS Appl. Mater. Inter. 2015, 7, 3414-3419. (31) Cai, W. H.; Lai, T.; Lai, J. W.; Xie, H. T.; Ouyang, L. Z.; Ye, J. S.; Yu, C. Z. Transition Metal Sulfides Grown on Graphene Fibers for Wearable Asymmetric Supercapacitors with High Volumetric Capacitance and High Energy Density. Sci. Rep. 2016, 6, 26890. ACS Paragon Plus Environment


(32) Cai, W. H.; Lai, T.; Ye, J. S. A Spinneret as the Key Component for Surface-porous Graphene Fibers in High Energy Density Micro-supercapacitors. J. Mater. Chem. A 2015, 3, 5060-5066. (33) Xiong, G. P.; Meng, C. Z.; Reifenberger, R. G.; Irazoqui, P. P.; Fisher, T. S. A Review of Graphene-based Electrochemical Microsupercapacitors, Electroanalysis 2014, 26, 30-51. (34) Xie, B. H.; Wang, Y.; Lai, W. H.; Lin, W.; Lin, Z. Y.; Zhang, Z. X.; Zou, P. C.; Xu, Y.; Zhou, S.; Yang, C.; Kang, F. Y.; Wong, C. P. Laser-processed Graphene Based Micro-supercapacitors for Ultrathin, Rollable, Compact and Designable Energy Storage Components, Nano Energy 2016, 26, 276-285. (35) Yuan, L. Y.; Lu, X. H.; Xiao, X.; Zhai, T.; Dai, J. J.; Zhang, F. C.; Hu, B.; Wang, X.; Gong, L.; Chen, J.; Hu, C. G.; Tong, Y. X.; Zhou, J.; Wang, Z. L. Flexible Solid-State Supercapacitors Based on Carbon Nanoparticles/MnO2 Nanorods Hybrid Structure, ACS Nano 2012, 6, 656-661. (36) Shen, C.W.; Xu, S. X.; Xie, Y. X.; Sanghadasa, M.; Wang, X. H.; Lin, L. W. A Review of On-Chip Micro Supercapacitors for Integrated Self-powering Systems, IEEE Journal of Microelectromechanical Systems, 2017, 26, 949-965. (37) Lamberti, A.; Clerici, F.; Fontana, M.; Scaltrito, L. A Highly Stretchable Supercapacitor Using Laser-Induced Graphene Electrodes onto Elastomeric Substrate. Adv. Energy Mater. 2016, 6, 1600050. (38) Yan, X. J.; Qi, M. J.; Wu, X. M.; Wang, P. B.; Pu, J.; Lin, L. W. Electrostatic Cantilever Resonators under A Double-sided Pull-pull Drive Scheme. J. Micromech. Microeng. 2014, 24, 035004.


Page 18 of 24

Page 19 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Contents 694x216mm (96 x 96 DPI)



Figure 1. (a) Schematic diagram of a high-voltage planar MSC based on laser-induced graphene. The inset show the SEM photo of the porous graphene electrode. Scale bar for SEM: 5 μm. (b) Temperature of a laser spot on the surface of Kapton film based on COMSOL Multiphysics software simulation. (c) Simulated temperature of laser spot and sheet resistance of graphene as a function of laser output power. (d) Raman spectrum of laser-induced graphene. (e) XPS spectrum of laser-induced graphene. (f) High resolution XPS spectrum of C1s. (g) High resolution XPS spectrum of O1s.


Page 20 of 24

Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) Schematic diagram showing MSCs with output voltages of 1V, 3V, and 6V, respectively, from arrays of in-series electrodes bridged by solid electrolytes. (b) Cyclic voltammetry curves of 1V, 3V, and 6V devices at scan rate of 100 mV/s. (c) Charged and discharged curves of 1V, 3V, and 6 V devices at an applied current of 1.0 μA. (d) Cycling performance of a 6 V device at an applied current of 1.0 μA. The inset shows voltage-cycles profiles of the last 10 cycles in a 5000-cycle test.



Figure 3. (a) An optical photo showing a fabricated flexible planar 209 V MSC. (b) A magnified optical image of (a) showing the gaps between the graphene electrodes being filled with solid electrolytes. Scale bar: 1.5 mm. (c) Charging and discharging curves at different bending angles of a 209 V MSC. (d, e) Cyclic voltammetry curves of a 209 V MSC at various scan rates ranging from 0.1 V/s to 10.0 V/s. (f) Device capacitance of a 209 V MSC as a function of scan rates calculated from (d, e). (g, h) Charging and discharging curves of a 209 V MSC at various applied currents from 0.2 μA to 5.0 μA. (i) Device capacitance of a 209 V MSC at different applied currents obtained from (g, h).


Page 22 of 24

Page 23 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. (a) Illustration of a 6 V MSC to power a piezoresistive microsensor that was made by transferring the laser-induced serpentine graphene electrodes to a PDMS substrate. (b) A microsensor pressed by a thumb at a pressure of about 60 kPa. Current profiles of a pressure microsensor working under the press of a thumb with power supplied by (c) Gamry or (d) a 6 V MSC, respectively. (e) The microsensor placed inside a shoe to monitor the human walking activities. The current profiles of a pressure microsensor measuring heel strikes when powered by (f) Gamry or (g) a 6 V MSC. The insets show the zoomed-in characteristic signals for the corresponding profiles.



Figure 5. (a) Designed structure of the walking robots; (b) microsupercapacitors stack with ten 209 V devices connected in series (> 2000 V ) for powering the walking robots; (c) the walking robot began working at 0 second; (d) the walking robot stopped working at 11 second.


Page 24 of 24

High-Voltage Flexible Microsupercapacitors based on Laser-induced

Recommend Documents