Lithium extraction and insertion behavior of nanocrystalline Li₂TiO₃-LiFeO₂ solid solution with cubic rock salt structure

Nanocrystalline Li₂TiO₃-LiFeO₂ solid solution with rock salt structure (space group Fm3m) has been synthesized by a hydrothermal method. It showed lithium extraction at 4 V vs. Li/Li⁺ and insertion at three potential regions of 4, 3, and below 2.5 V with total capacity of about 200 mAh g^-1. The spectral changes in in situ ⁵⁷Fe Mössbauer spectra during the charge and discharge process demonstrated that the redox reactions of Fe³⁺/Fe⁴⁺ and Fe²⁺/Fe³⁺ in partial Fe ions are concerned with the capacities at 4 and below 2.5 V, respectively. In situ Ti-K X-ray absorption fine structure (XAFS) study suggested that Ti ions remained tetravalent in valence through the cycle and that, however, two environments around Ti appeared. The charge redistribution would occur during the charge and discharge process.