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

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) A, b = 3.74739(8) A, c = 9.1404(2) A, 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 ...