In Situ Transmission Electron Microscopy Study of Electrochemical Sodiation and Potassiation of Carbon Nanofibers

• Published in: Nano letters 2014-06, Vol.14 (6), p.3445-3452
• Main Authors: Liu, Ying, Fan, Feifei, Wang, Jiangwei, Liu, Yang, Chen, Hailong, Jungjohann, Katherine L, Xu, Yunhua, Zhu, Yujie, Bigio, David, Zhu, Ting, Wang, Chunsheng
• Format: Article
• Language: English
• Subjects: Carbon fibers; Carbon-carbon composites; Condensed matter: structure, mechanical and thermal properties; Cracks; Cross-disciplinary physics: materials science; rheology; Degradation; Electric batteries; Electrodes; Exact sciences and technology; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Nanocrystalline materials; Nanofibers; Nanoscale materials and structures: fabrication and characterization; Physics; Quantum wires; Rechargeable batteries; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Transmission electron microscopy
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl500970a

Carbonaceous materials have great potential for applications as anodes of alkali-metal ion batteries, such as Na-ion batteries and K-ion batteries (NIB and KIBs). We conduct an in situ study of the electrochemically driven sodiation and potassiation of individual carbon nanofibers (CNFs) by transmission electron microscopy (TEM). The CNFs are hollow and consist of a bilayer wall with an outer layer of disordered-carbon (d-C) enclosing an inner layer of crystalline-carbon (c-C). The d-C exhibits about three times volume expansion of the c-C after full sodiation or potassiation, thus suggesting a much higher storage capacity of Na or K ions in d-C than c-C. For the bilayer CNF-based electrode, a steady sodium capacity of 245 mAh/g is measured with a Coulombic efficiency approaching 98% after a few initial cycles. The in situ TEM experiments also reveal the mechanical degradation of CNFs through formation of longitudinal cracks near the c-C/d-C interface during sodiation and potassiation. Geometrical changes of the tube are explained by a chemomechanical model using the anisotropic sodiation/potassiation strains in c-C and d-C. Our results provide mechanistic insights into the electrochemical reaction, microstructure evolution and mechanical degradation of carbon-based anodes during sodiation and potassiation, shedding light onto the development of carbon-based electrodes for NIBs and KIBs.