American Chemical Society
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Ion-Exchange Synthesis, Crystal Structure, and Electrochemical Properties of Li2Ti6O13

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journal contribution
posted on 2011-05-10, 00:00 authored by Kunimitsu Kataoka, Junji Awaka, Norihito Kijima, Hiroshi Hayakawa, Ken-ichi Ohshima, Junji Akimoto
Li2Ti6O13 was prepared from Na2Ti6O13 as a parent compound via sodium/lithium ion exchange in molten LiNO3 at 380 °C. It crystallizes in the monoclinic system, space group C2/m, and with the lattice parameters of a = 15.3065(4) Å, b = 3.74739(8) Å, c = 9.1404(2) Å, and β = 99.379(2)°. The crystal structure of Li2Ti6O13 was refined to the conventional values of Rwp = 5.78% and Rp = 4.44% with a fit indicator of GOF = Rwp/Re = 1.66 by Rietveld analysis using powder neutron diffraction data. The crystal structure of Na2Ti6O13 was also reinvestigated using the single-crystal X-ray diffraction data with the final R value of 2.70%. The basic (Ti6O13)2− framework in Li2Ti6O13 was maintained nearly unchanged from that in the parent Na2Ti6O13. The Li occupation site in the tunnel space shifted to y = 0.5 position from the original Na site in Na2Ti6O13, and the moving resulted in the LiO4 planar coordination in Li2Ti6O13. The structural stability of Li2Ti6O13 was confirmed by bond valence sums, the data of 7Li-MAS NMR and high-temperature in situ XRD measurements, and the results of the present first-principles calculation by the FLAPW method. The electrochemical Li insertion/extraction experiments revealed the irreversible large Li insertion capacity of above 200 mAh g−1 at approximately 1.5 V for the first cycle and the stable reversible capacity of approximately 90−95 mAh g−1 during the following cycles. The total Li-ion conductivity in Li2Ti6O13 was estimated to be σtotal = 5.60 × 10−6 S cm−1 at room temperature from the results of AC-impedance measurements. This value is comparable to that in the well-known good Li-ion conducting ramsdellite-type Li2Ti3O7.