Abstract
Abstract Here, we demonstrate the electrochemical intercalation of Ca$^{2+}$ ions within the lattice of anatase nanotubes (a‐NTs) synthesized by hydrothermal treatment of TiO$_2$ /NaOH precursors followed by Na + /H + ion exchange and H 2 O‐loss at high temperature in air. Scanning electron microscopy, X‐ray diffraction, and Raman spectroscopy confirm the formation of nanosized anatase, whereas transmission electron microscopy highlights the formation of nanotubular morphologies with an average diameter of 10 nm. TiO$_2$ electrodes are able to deliver reversible specific capacities in aprotic batteries vs. calcium metal or in hybrid configurations vs. capacitive activated carbon using aprotic electrolytes ( i. e ., Ca(BH$_4$)$_2$ in tetrahydrofuran or Ca(TFSI) 2 in dimethoxyethane, respectively). The electrochemical intercalation of Ca$^{2+}$ ions into the anatase lattice is confirmed by X‐ray absorption spectroscopy in close comparison with Na$^+$ and Li$^+$ intercalations. Ca$^{2+}$ incorporation leads to the partial amorphization of the TiO$_2$ lattice despite the limited Ca/Ti ratio ( i. e ., 0.09) obtained in discharge. The analysis of the extended X‐ray absorption fine structure region allows the determination of the local structure of the incorporated Ca$^{2+}$ ions and confirms that a disordered environment is obtained after the electrochemical reaction.