Amorphous and crystalline TiO2 nanoparticle negative electrodes for sodium-ion batteries.

Titanium dioxide (TiO 2) is a promising negative electrode for sodium ion batteries (SIBs). Although TiO 2 materials with amorphous (A-TiO 2) and single-phase crystalline structures (C–TiO 2) have been separately explored, the study to compare the fundamental electrochemistry of A-TiO 2 and C–TiO 2 is limited. In this work, we investigated A-TiO 2 and C–TiO 2 nanoparticles with identical chemical composition and morphology. C–TiO 2 exhibits enhanced electrochemical performance than A-TiO 2 in terms of rate capability and cycle life. Cyclic voltammetry (CV) analysis suggests reversible Na ion insertion/extraction in C–TiO 2. However, such process is irreversible in the case of A-TiO 2. The charge storage mechanisms in both samples were studied to show that diffusion-controlled intercalation process becomes significant in C–TiO 2 sample. The C–TiO 2 sample has a better Na+ diffusivity measured through the galvanostatic intermittent titration technique (GITT) compared to A-TiO 2 , which corroborates well with the rate capability study. Furthermore, the evolution of local structure of the TiO 2 samples was analyzed by ex situ pair distribution function (PDF) to understand the variation in electrochemical properties. It reveals that the corner-shared Ti–Ti distance along Na ion diffusion pathway increases with the increase of crystallinity, leading to the expanded diffusion channels and therefore more active sites and faster diffusion. Image 1 [ABSTRACT FROM AUTHOR]