Effect of the substitution Ti/(Fe,Ni) on the electrochemical properties of Li2Ti3O7 as electrode materials for Li-ion accumulators

Electrochemistry requires a stable structure to avoid capacity loss. Substitution of structural Ti and Li by 3d transition elements in the Li2Ti3O7 ramsdellite structure has been considered in order to improve the accessibility of the vacancies. In the case of a one element substitution, Ti/Fe, the reduction FeIII to FeII gives rise to an irreversible part in the electrochemical curves. For the substitution of Ti/Li by two transition elements, Fe and Ni, only a partial FeIII/FeII reduction occurs, resulting in a smaller irreversible plateau and improved cyclability. This reduction has also been evidenced by 57Fe Mossbauer spectroscopy in which 57Fe is used as a local probe giving valuable information about its local environment, thus allowing deeper insight into the lithium insertion mechanism.