Comparative study of Li[CrTi]O4, Li[Li1/3Ti5/3]O4 and Li1/2Fe1/2[Li1/2Fe1/2Ti]O4 in non-aqueous lithium cells

Comparative study of Li[CrTi]O4, Li[Li1/3Ti5/3]O4 and Li1/2Fe1/2[Li1/2Fe1/2Ti]O4 was carried out in order to understand zero-strain insertion mechanism. Degree of defect defined by the occupation of lithium ions at 16(d) sites in Fd3¯m is 0% in Li[CrTi]O4, 17% in Li[Li1/3Ti5/3]O4 and 25% in Li1/2Fe1/2[Li1/2Fe1/2Ti]O4. Electrochemical tests in non-aqueous lithium cells indicated that no fatal damage was observed with respect to XRD even for 25% defect of spinel-framework structure based on lithium titanium oxides. All samples examined here show the character of so-called zero-strain lithium insertion materials while Li1/2Fe1/2[Li1/2Fe1/2Ti]O4 is converted to a rock-salt structure of Li3/2Fe1/2[Li1/2Fe1/2Ti]O4 in which Fe3+ ions at the tetrahedral sites move to the octahedral sites by changing oxidation state on reduction. FT-IR and Raman spectral measurements were also carried out and the factors affecting zero-strain insertion mechanism were discussed.