Self-healable wire-shaped supercapacitors with two twisted NiCo2O4 coated polyvinyl alcohol hydrogel fibers

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  • ReceivedNov 8, 2017
  • AcceptedDec 8, 2017
  • PublishedJan 12, 2018


Wire-shaped supercapacitors (SCs) possessing light-weight, good flexibility and weavability have caught much attention, but it is still a challenge to extend the lifespan of the devices with gradual aging due to the rough usage or external factors. Herein, we report a new stretchable and self-healable wire-shaped SC. In the typical process, two polyvinyl alcohol/potassium hydroxide (PVA/KOH) hydrogel wrapped with urchin-like NiCo2O4 nanomaterials were twisted together to form a complete SC devices. It is noted that the as-prepared PVA hydrogel can be easily stretched up to 300% with small tensile stress of 12.51 kPa, superior to nearly 350 kPa at 300% strain of the polyurethane. Moreover, the wire-like SCs exhibit excellent electrochemical performance with areal capacitance of 3.88 mF cm−2 at the current density of 0.053 mA cm−2, good cycling stability maintaining 88.23% after 1000 charge/discharge cycles, and 82.19% capacitance retention even after four damaging/healing cycles. These results indicate that wire-shaped SCs with two twisted NiCo2O4 coated polyvinyl alcohol hydrogel fibers is a promising structure for achieving the goal of high stability and long-life time. This work may provide a new solution for new generation of self-healable and wearable electronic devices.

Funded by

the National Natural Science Foundation of China(61625404,61504136)

Beijing Natural Science Foundation(4162062)

and the Key Research Program of Frontiers Sciences



This work was supported by the National Natural Science Foundation of China (61625404 and 61504136), Beijing Natural Science Foundation (4162062), and the Key Research Program of Frontiers Sciences, CAS (QYZDY-SSW-JSC004).

Interest statement

The authors declare no conflict of interest.

Contributions statement

Jia R and Li L contributed equally to this work. The paper was written through contributions of all authors. All authors have given approval to the final version of the paper.

Author information

Rui Jia received her BE degree from Huaqiao University in 2015. Now she is a master student at the College of Chemistry and Chemical Engineering, Qingdao University. Her research interest focuses on flexible supercapacitors.

La Li received her BSc degree from Jilin University in 2013. She is a PhD candidate at the College of Physics, Jilin University, China. Her research interests mainly focus on flexible micro-supercapacitors and self-powered integrated devices.

Zhaojun Chen received his BE degree and MSc degree from Qingdao University in 2000 and 2005, respectively, and received his PhD degree from China University of Petroleum in 2015. He is currently an Associate Professor at Qingdao University. His current research focuses on the design and synthesis of novel nanostructure materials for applications in supercapacitors, biomedical materials and catalysts.

Guozhen Shen received his BSc degree in 1999 from Anhui Normal University and PhD degree in 2003 from the University of Science and Technology of China. From 2004 to 2009, he conducted his research in Hanyang University (Korea), National Institute for Materials Science (Japan), University of Southern California (USA) and Huazhong University of Science and technology. He joined the Institute of Semiconductors, Chinese Academy of Sciences as a professor in 2013. His current research focuses on flexible electronics and printable electronics, including transistors, photodetectors, sensors and flexible energy-storage devices.


Supplementary information

Supporting data are available in the online version of the paper.


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  • Figure 1

    (a) Optical images of the stretchable PVA/KOH hydrogel: stretching from 1.5 to 6 cm by employing one-dimensional platform (left) and twisting on the thumb (upper right). (b) Illustration of the PVA/KOH hydrogel to support a 5 g mass: before damaging (left), after healing (right) and magnified image of the wound positions. (c) Schematic plot of the self-healing mechanism. (d) Tensile tests of the PVA/KOH hydrogel fiber after different damaging/healing cycles. (e) Tensile strengths and Young’s modulus of the PVA/KOH hydrogel fiber after different damaging/healing cycles.

  • Figure 2

    (a, b) SEM images, (c, d) TEM images, (e) HRTEM image and (f) XRD pattern of the obtained urchin-like NiCo2O4 nanostructures.

  • Figure 3

    Electrochemical performance of the fabricated wire-like SCs with urchin-like NiCo2O4 electrodes. (a) CV curves at different scan rates ranging from 0.1 to 3.0 V s−1. (b) GCD curves at different current densities from 0.053 to 0.319 mA cm−2 in the potential window of 0–0.8 V. (c) The areal capacitance with various currents. (d) The high-frequency region of Nyquist impedance plot. The inset displays the Nyquist impedance plot of the wire-like SCs. (e) Performance of capacitance stability of the NiCo2O4 SC with 1000 cycles. (f) Areal energy and power density of the wire-like SCs. The inset is schematic diagram of the wire-like SC.

  • Figure 4

    The stretchable properties of the wire-like SC devices. (a, b) CV curves and GCD curves under stretching from 0 to 200%. (c) Variation of capacitance stability of the 100% stretching with 1000 cycles. The insets present the photographs of the device under pristine and stretching states. (d) The Nyquist impedance plots of the as-prepared SC with various stretch.

  • Figure 5

    The self-healing properties of wire-like SC device at different cutting/self-healing cycles. (a) CV curves at the scan rate of 3.0 V s−1. (b) GCD curves at the current density of 0.106 mA cm−2. (c) Capacitance retention of the device after self-healing for 4 cycles. The insets show the photographs of the device under cutting and healing states. (d) The corresponding Nyquist impedance plots with different self-healing times.

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