New ramsdellites LiTi2−yVyO4 (0≤y≤1): Synthesis, structure, magnetic properties and electrochemical performances as electrode materials for lithium batteries

The new ramsdellite series LiTi_2−yV_yO₄ (0≤y≤1) has been prepared by conventional solid state chemistry techniques and was characterized by X-ray powder diffraction and electron diffraction. To our knowledge, this is the first report on ramsdellites containing vanadium. The magnetic behaviour of these ramsdellites is strongly influenced by its vanadium content. In this sense, LiTi₂O₄ (y=0) exhibits metallic-like temperature independent paramagnetism, but d electrons tend to localize with increasing V content. LiTiVO₄, though also paramagnetic, follows then the Curie-Weiss law. The crossover from delocalized to localized electrons is observed between compositions y=0.6 and 0.8. For y≥0.8 the magnetic results evidence an isovalent substitution mechanism of trivalent Ti by V. The electrochemical lithium intercalation and deintercalation chemistry of LiTi_2−yV_yO₄ is grouped into two different operating voltage regions. Reversible lithium deintercalation of vanadium-substituted ramsdellite titanates LiTi_2−yV_yO₄ in the high voltage range 2-3 V vs. Li occurs in two main steps, one at about 2 V and the other at about 3 V. The 3 V process capacity increases with the vanadium content, while the 2 V capacity decreases at the same time. The vanadium to titanium substitution rate in LiTi₂O₄ was found to be beneficial to the specific energy in as much as a 50% increase (1 V) of the working voltage is observed. On the other hand, reversible lithium intercalation in vanadium-substituted ramsdellite titanates LiTi_2−yV_yO₄ in the low voltage range 1-2 V vs. Li occurs in one main single step, in which the capacity is not affected by the vanadium content, although vanadium-doping produces an improved capacity retention with an excellent cycling behaviour observed for y≤0.6.