Lookup NU author(s): Professor Ulrich Stimming
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).
© The Royal Society of Chemistry 2017. The reversible intercalation of solvated Na-ions into graphite and the concomitant formation of ternary Na-graphite intercalation compounds (GICs) are studied using several in operando techniques, such as X-ray-diffraction (XRD), electrochemical scanning tunnelling microscopy (EC-STM) and electrochemical quartz crystal microbalance techniques (EQCM). Linear ethylene glycol dimethyl ether homologues ("glymes") Gx with x + 1 O-atoms were used as solvents, where x is 1-4. The intercalation mechanism of Na+(Gx)y-complexes was investigated with a focus on the phase transitions and diffusion rates of the Na+(Gx)y-complexes inside the graphite lattice. For the four shortest glymes (G1 to G4), it is found using XRD that an intermediate stage 2 Na-GIC (NaC48) is formed upon the partial sodiation of the graphite electrode. At full sodiation stage 1 Na-GIC (NaC18, 112 mA h g-1) is obtained for G1, G2 and G4, while the G3 system also forms a stage 1 Na-GIC but with less Na incorporated (NaC30, 70 mA h g-1). The phase transitions of a battery electrode upon ion-intercalation are visualised using STM on the atomic scale for the first time. In addition, the local diffusion rates of the intercalated species inside the electrode were determined, a unique approach for determining kinetic effects in batteries on the atomic scale. The formation of a solid electrolyte interphase (SEI) is observed with STM as well as with an EQCM, while the latter technique is used for novel in situ hydrodynamic spectroscopy, giving further insight into the intercalation mechanism.
Author(s): Seidl L, Bucher N, Chu E, Hartung S, Martens S, Schneider O, Stimming U
Publication type: Article
Publication status: Published
Journal: Energy and Environmental Science
Online publication date: 31/05/2017
Acceptance date: 22/05/2017
Date deposited: 17/11/2017
ISSN (print): 1754-5692
ISSN (electronic): 1754-5706
Publisher: Royal Society of Chemistry
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