Journal
NANO LETTERS
Volume 14, Issue 6, Pages 3445-3452Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl500970a
Keywords
Sodium-ion batteries; potassium-ion batteries; carbon nanofibers; sodiation; potassiation; crack
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Funding
- Maryland Nano Center
- NispLab
- NSF [CMMI-1100205]
- Lockheed Martin Corporation for the U.S. Department of Energy's National Nuclear Security Administration [DE-AC04-94AL85000]
- Div Of Civil, Mechanical, & Manufact Inn
- Directorate For Engineering [1100205] Funding Source: National Science Foundation
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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.
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