Unveiling of the energy storage mechanisms of multi -modified (Nb2O5@C)/rGO nanoarrays as anode for high voltage supercapacitors with formulated ionic liquid electrolytes

Abstract
A better understanding of the energy-storage mechanisms in complex pseudocapacitive nanostructures is essential to improve the performances of nanohybrid supercapacitors. In this study, highly interface modified Nb2O5 nanoarrays, attached to graphene nanosheets, were carefully designed and synthesized. The electrochemical performances were evaluated in an organic electrolyte, a formulated ionic-liquid mixture electrolyte, and a nanocomposite ionogel electrolyte, respectively. The capacitive and faradaic storage contributions were assessed qualitatively in diverse electrolytes at various temperatures. The capacitive contribution in the ionic liquid electrolyte was found to rise with increasing temperature. A molecular dynamics simulation proved that the increased diffusion coefficient of large ions was much more pronounced than that of the small Li+ ions. A carefully optimized quasi-solid-state lithium ion capacitor, fabricated using a (Nb2O5@C)/rGO nanoarchitecture as the anode and an ionic liquid gel separator, delivered an energy density of 101 Wh kg−1 and a power density of 24 kW kg−1 at 60 °C. The efficient coupling between the nanohybrids and a complex ionogel electrolyte opens a new window for the rational design of high energy-density supercapacitors.

Citation
Zhang, J., Zhang, H., Zhang, Y., Zhang, J., He, H., Zhang, X., … Zhang, S. (2019). Unveiling of the energy storage mechanisms of multi -modified (Nb2O5@C)/rGO nanoarrays as anode for high voltage supercapacitors with formulated ionic liquid electrolytes. Electrochimica Acta, 313, 532–543. doi:10.1016/j.electacta.2019.04.160

Acknowledgements
This work was financially supported by the National Key Research and Development Program of China (No.2016YFB0100303), the Major Program of National Natural Science Foundation of China (No. 21890762), the National Natural Science Foundation of China (No. 21878308) and the International Cooperation and Exchange of the National Natural Science Foundation of China (51561145020).

Publisher
Elsevier BV

Journal
Electrochimica Acta

DOI
10.1016/j.electacta.2019.04.160

Additional Links
https://linkinghub.elsevier.com/retrieve/pii/S0013468619308576

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