Hydrothermally Oxidized Single-Walled Carbon Nanotube Networks for High Volumetric Electrochemical Energy Storage

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2016-07, Vol.12 (25), p.3423-3431
• Main Authors: Liu, Tianyuan, Davijani, Amir A. Bakhtiary, Sun, Jingying, Chen, Shuo, Kumar, Satish, Lee, Seung Woo
• Format: Article
• Language: English
• Subjects: Carbon; carbon nanotubes; electrochemical energy storage; Electrodes; Energy density; Energy storage; hydrothermal oxidation; Nanostructure; Nanotechnology; Nanotubes; Networks; Oxidation; positive electrodes; Single wall carbon nanotubes; volumetric performance
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201600974

Improving volumetric energy density is one of the major challenges in nanostructured carbon electrodes for electrochemical energy storage device applications. Herein, a simple hydrothermal oxidation process of single‐walled carbon nanotube (SWNT) networks in dilute nitric acid is reported, enabling simultaneous physical densification and chemical functionalization of the as‐assembled randomly‐packed SWNT films. After the hydrothermal oxidation process, the density of the SWNT films increases from 0.63 to 1.02 g cm−3 and a considerable amount of redox‐active oxygen functional groups are introduced on the surface of the SWNTs. The functionalized SWNT films are used as positive electrodes against Li metal negative electrodes for potential Li‐ion capacitors or Li‐ion battery applications. The functionalized SWNT electrodes deliver high volumetric as well as gravimetric capacities, 154 Ah L−1 and 152 mAh g−1, respectively, owing to the surface redox reactions between the introduced oxygen functional groups and Li ions. In addition, these electrodes exhibit a remarkable rate‐capability by retaining its high capacity of 94 Ah L−1 (92 mAh g−1) at a high discharge rate of 10 A g−1. These results demonstrate the simple hydrothermal oxidation process as an attractive strategy for improving the volumetric performance of nanostructured carbon electrodes. A hydrothermal oxidation method is developed for densification and functionalization of single‐walled carbon nanotube (SWNT) networks. The functionalized SWNT films deliver a high volumetric capacity of 154 Ah L−1 and volumetric energy density of 385 Wh per Lelectrodes. This efficient and environmentally‐friendly method opens new opportunities for improving the volumetric performance of carbon‐based electrodes.