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Issue 15, 2017
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Anomalously high Na+ and low Li+ mobility in intercalated Na2Ti6O13

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Abstract

We report an anomalous diffusion behavior in intercalated Na2Ti6O13. Using first-principles calculations, the direct migration of inserted Na+ along the tunnel direction is predicted to have a barrier of 0.24–0.44 eV, while the migration of inserted Li+ along the tunnel direction has a barrier of 0.86–1.15 eV. Although Li+ can also diffuse along a zig-zag path in the tunnel, the barrier of 0.86–0.99 eV is still much higher than that for Na+. Our results surprisingly lead to the conclusion that the diffusion of larger Na+ is 4–8 orders of magnitude faster than Li+ in the same host lattice, and explain the experimentally observed exceptional rate capability of Na2Ti6O13 as the Na-ion battery anode. The anomalous diffusion behavior is attributed to the geometric features of Na2Ti6O13. For migration of Li+ it is necessary to weaken Li–O bonds and to overcome the repulsion between Li and host Na ions simultaneously, while for Na+ diffusion the improved Na–O bonding at the transition state partially compensates for the energy penalty from the repulsion of host Na ions.

Graphical abstract: Anomalously high Na+ and low Li+ mobility in intercalated Na2Ti6O13

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Publication details

The article was received on 20 Feb 2017, accepted on 17 Mar 2017 and first published on 17 Mar 2017


Article type: Paper
DOI: 10.1039/C7CP01138E
Citation: Phys. Chem. Chem. Phys., 2017,19, 10036-10041
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    Anomalously high Na+ and low Li+ mobility in intercalated Na2Ti6O13

    C. Ling and R. Zhang, Phys. Chem. Chem. Phys., 2017, 19, 10036
    DOI: 10.1039/C7CP01138E

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