Abstract
Comparative study of Li[CrTi]O 4, Li[Li 1/3Ti 5/3]O 4 and Li 1/2Fe 1/2[Li 1/2Fe 1/2Ti]O 4 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 Fd 3 ¯ m is 0% in Li[CrTi]O 4, 17% in Li[Li 1/3Ti 5/3]O 4 and 25% in Li 1/2Fe 1/2[Li 1/2Fe 1/2Ti]O 4. 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 Li 1/2Fe 1/2[Li 1/2Fe 1/2Ti]O 4 is converted to a rock-salt structure of Li 3/2Fe 1/2[Li 1/2Fe 1/2Ti]O 4 in which Fe 3+ 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.
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