Order–disorder transition in nano-rutile TiO2 anodes: a high capacity low-volume change Li-ion battery material

Abstract

Nano-sized particles of rutile TiO₂ is a promising material for cheap high-capacity anodes for Li-ion batteries. It is well-known that rutile undergoes an irreversible order–disorder transition upon deep discharge. However, in the disordered state, the Li_xTiO₂ material retains a high reversible ion-storage capacity of >200 mA h g⁻¹. Despite the promising properties of the material, the structural transition and evolution during the repeated battery operation has so far been studied only by diffraction-based methods, which only provide insight into the part that retains some long-range order. Here, we utilize a combination of ex situ and operando total scattering with pair distribution function analysis and transmission electron microscopy to investigate the atomic-scale structures of the disordered Li_xTiO₂ forming upon the discharge of nano-rutile TiO₂ as well as to elucidate the phase behavior in the material during the repeated charge–discharge process. Our investigation reveals that nano-rutile upon Li-intercalation transforms into a composite of ∼5 nm domains of a layered Li_xTiO₂ α-NaFeO₂-type structure with ∼1 nm Li_xTiO₂ grain boundaries with a columbite-like structural motif. During repeated charge–discharge cycling, the structure of this composite is retained and stores Li through a complete solid–solution transition with a remarkably small volume change of only 1 vol%.