Electronic Structure of Anode Material Li2TiSiO5 and Its Structural Evolution during Lithiation

Inductive effect, although originally proposed in the field of organic chemistry, has long been regarded as an effective way to increase the working potential of inorganic lithium-ion battery cathodes. A classic example is the LiFePO4 cathode, where introduction of the highly electronegative P5+ raises the redox potential of Fe3+/Fe2+ as in conventional oxides by 1.0 V. Recently, some of us have reported a substantially reduced redox potential of Ti4+/Ti3+ in Li2TiSiO5 compared with lithium titanium oxides, suggesting the presence of a reversed inductive effect imposed by polyanions (Energy Environ. Sci., 2017, 10, 1456–1464). In this work, through characterizing the electronic structure of pristine Li2TiSiO5 and following the crystallographic structure evolution during lithium insertion in Li2TiSiO5, we propose that the reversed inductive effect is likely linked with the square-pyramid coordination of Ti. The reversed inductive effect offers new possibilities in tuning the potentials of anode materials, presenting a promising avenue to further increase the energy density of batteries based on polyanion electrodes.