Preparations and Electrochemical Properties of BC/CoNi₂S₄@PPy Flexible Composites for Supercapacitors

Si-Yuan Peng, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China;
Shi-Run Yang, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China;
Jing-Hong Zhou, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China;Follow
Zhi-Jun Sui, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China;
Tao Zhang, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China;
Yi Shi, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China;
Xing-Gui Zhou, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China;

Corresponding Author

Jing-Hong Zhou(jhzhou@ecust.edu.cn)

Abstract

Flexible supercapacitor is one of the most promising energy storage devices for portable and wearable electronic products due to its advantages of high power density, fast charging and long cycle life. Therefore, self-supporting flexible electrode materials with high performance have attained more and more attention both in academia and in industry recently. In this work, using bacterial cellulose (BC) as a flexible substrate, the bacterial cellulose/nickel-cobalt sulfide@polypyrrole (BC/CoNi₂S₄@PPy) flexible composites with three-dimensional porous network and good conductivity were prepared by a combined solvothermal-in-situ polymerization-vacuum filtration method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectrometry, N₂ physisorption, tensile strength and contact angle measurements. Their electrochemical performances were tested by cyclic voltammetry, galvanostatic charge/discharge testing and electrochemical impedance spectroscopy. The results show that the three-dimensional porous network of BC fibers with rich oxygen-containing surface groups play a guiding role in the growth of the redox active material CoNi₂S₄ and the distribution of conductive polymer PPy, resulting in uniformly distributed CoNi₂S₄ nanospheres in the network of BC fibers, both coated evenly with a layer of conductive PPy. The resulting BC/CoNi₂S₄@PPy composites, a three-dimensional conductive network with high porosity, displayed good mechanical property (tensile strength up to 28.0±0.1 MPa), hydrophilicity (the instantaneous contact angle in 6 mol·L^-1 KOH is 43.6°), as well as excellent electrochemical performance. The specific capacitance of the flexible BC/CoNi₂S₄@PPy was 2670 F·g^-1 at 1 A·g^-1 in a three-electrode system, and retained 82.7% after 10000 charge and discharge cycles. In addition, the electrochemical performance remained unchanged after 1000 times of repeated bending. In an asymmetric supercapacitor composed of BC/CoNi₂S₄@PPy and activated carbon, the area specific capacitance was 1428 F·g^-1 at 1 A·g^-1. The asymmetric supercapacitor achieved the maximum energy density of 49.8 Wh·kg^-1 and power density of 741.8 W·kg^-1.

Graphical Abstract

Keywords

flexible electrode material, bacterial cellulose, nickel-cobalt sulfide, polypyrrole

DOI Link

https://doi.org/10.13208/j.electrochem.200630

Publication Date

2021-02-28

Online Available Date

2020-11-16

Revised Date

2020-09-07

Received Date

2020-06-30

Recommended Citation

Si-Yuan Peng, Shi-Run Yang, Jing-Hong Zhou, Zhi-Jun Sui, Tao Zhang, Yi Shi, Xing-Gui Zhou. Preparations and Electrochemical Properties of BC/CoNi₂S₄@PPy Flexible Composites for Supercapacitors[J]. Journal of Electrochemistry, 2021 , 27(1): 14-25.
DOI: Flexible supercapacitor is one of the most promising energy storage devices for portable and wearable electronic products due to its advantages of high power density, fast charging and long cycle life. Therefore, self-supporting flexible electrode materials with high performance have attained more and more attention both in academia and in industry recently. In this work, using bacterial cellulose (BC) as a flexible substrate, the bacterial cellulose/nickel-cobalt sulfide@polypyrrole (BC/CoNi₂S₄@PPy) flexible composites with three-dimensional porous network and good conductivity were prepared by a combined solvothermal-in-situ polymerization-vacuum filtration method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectrometry, N₂ physisorption, tensile strength and contact angle measurements. Their electrochemical performances were tested by cyclic voltammetry, galvanostatic charge/discharge testing and electrochemical impedance spectroscopy. The results show that the three-dimensional porous network of BC fibers with rich oxygen-containing surface groups play a guiding role in the growth of the redox active material CoNi₂S₄ and the distribution of conductive polymer PPy, resulting in uniformly distributed CoNi₂S₄ nanospheres in the network of BC fibers, both coated evenly with a layer of conductive PPy. The resulting BC/CoNi₂S₄@PPy composites, a three-dimensional conductive network with high porosity, displayed good mechanical property (tensile strength up to 28.0±0.1 MPa), hydrophilicity (the instantaneous contact angle in 6 mol·L^-1 KOH is 43.6°), as well as excellent electrochemical performance. The specific capacitance of the flexible BC/CoNi₂S₄@PPy was 2670 F·g^-1 at 1 A·g^-1 in a three-electrode system, and retained 82.7% after 10000 charge and discharge cycles. In addition, the electrochemical performance remained unchanged after 1000 times of repeated bending. In an asymmetric supercapacitor composed of BC/CoNi₂S₄@PPy and activated carbon, the area specific capacitance was 1428 F·g^-1 at 1 A·g^-1. The asymmetric supercapacitor achieved the maximum energy density of 49.8 Wh·kg^-1 and power density of 741.8 W·kg^-1.