Electrochemical Kinetics of Nanostructured Nb2O5Electrodes

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Journal of The Electrochemical Society, 161(5) A718-A725 (2014)
0013-4651/2014/161(5)/A718/8/©The Electrochemical Society

Electrochemical Kinetics of Nanostructured Nb2O5 Electrodes

Jeremy Come,a,b Veronica Augustyn,c Jong Woung Kim,c Patrick Rozier,a,b Pierre-Louis Taberna,a,b Pavel Gogotsi,d,e Jeffrey W. Long,d,∗ Bruce Dunn,c,∗and Patrice Simona,b,∗,z

a Universit´ e Paul Sabatier, CIRIMAT UMR CNRS 5085, 31062 Toulouse Cedex 4, France
b R´ eseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, France
c Department of Materials Science & Engineering, University of California, Los Angeles, California 90095, USA
d Surface Chemistry Branch, Naval Research Laboratory, Washington, DC 20375, USA

Abstract

Pseudocapacitive charge storage is based on faradaic charge-transfer reactions occurring at the surface or near-surface of redox-active materials. This property is of great interest for electrochemical capacitors because of the substantially higher capacitance obtainable as compared to traditional double-layer electrode processes. While high levels of pseudocapacitance have been obtained with nanoscale materials, the development of practical electrode structures that exhibit pseudocapacitive properties has been challenging.

Schematic representations and corresponding electrochemical responses for ‘extrinsic’ and ‘intrinsic’ pseudocapacitors. a) Extrinsic pseudocapacitance where high specific capacitance values and pseudocapacitive behavior are observed only with thin films of the same material. The outer surface of the film dominates the response because of electrolyte access. A high concentration of defects at the surface (e.g., cation vacancies) will also contribute.This response is observed with most transition metal oxides; b) Intrinsic pseudocapacitance in Nb2O5. The pseudocapacitive behavior is preserved in thick films due to fast Li + transport within the bulk of the material

The present paper shows that electrodes of Nb2O5 successfully retain the pseudocapacitive properties of the corresponding nanoscale materials. For charging times as fast as one minute, there is no indication of semi-infinite diffusion limitations and specific capacitances of 380 F g −1 and 0.46 Fcm −2 are obtained in 40-μm thick electrodes at a mean discharge potential of 1.5 V vs Li+ /Li. In-situ X-ray diffraction shows that the high specific capacitance and power capabilities of Nb2O5 electrodes can be attributed to fast Li + intercalation within specific planes in the orthorhombic structure.

This intercalation pseudocapacitance charge-storage mechanism is characterized as being an intrinsic property of Nb2O5 that facilitates the design of electrodes for capacitive storage devices. Authors demonstrate the efficacy of these electrodes in a hybrid electrochemical cell whose energy density and power density surpass that of commercial carbon-based devices.

 © 2014 The Electrochemical Society. [DOI:10.1149/2.040405jes]

 

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