Neutron diffraction and Mössbauer studies of iron substituted Li2Ti3O7 of ramsdellite-type as negative electrode for Li-ion accumulator

In this work we have reported the electrochemical lithiation properties of ramsdellite Li2.28Ti3.43O8, and two new iron-doped ramsdellite phases of compositions Li2.624Ti3.088Fe0.343O8 and Li2.28Ti3.153Fe0.31O7.9. In the two iron-doped samples, charge balance is maintained by excess lithium and by oxygen vacancies respectively. The use of neutron diffraction and 57Fe Mössbauer spectroscopy is of high interest for studying effect of lithium or vacancies located in the channels of the ramsdellite-type structure. In the case of iron-doped ramsdellite-type phases, all the iron ions are located on octahedral sites and the quadrupole spittings are related to the number of lithium in the neighbourhood of probed atoms. The presence of iron limits the reversible capacity due to the decrease of lithium mobilily through the channels of the ramsdellite-type structure.