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Aluminium batteries constitute a safe and sustainable high‐energy‐density electrochemical energy‐storage solution. Viable Al‐ion batteries require suitable electrode materials that can readily intercalate high‐charge Al3+ ions. Here, we investigate the Al3+ intercalation chemistry of anatase TiO2 and how chemical modifications influence the accommodation of Al3+ ions. We use fluoride‐ and hydroxide‐doping to generate high concentrations of titanium vacancies. The coexistence of these hetero‐anions and titanium vacancies leads to a complex insertion mechanism, attributed to three distinct types of host sites: native interstitial sites, single vacancy sites, and paired vacancy sites. We demonstrate that Al3+ induces a strong local distortion within the modified TiO2 structure, which affects the insertion properties of the neighbouring host sites. Overall, specific structural features induced by the intercalation of highly polarising Al3+ ions should be considered when designing new electrode materials for polyvalent batteries. [ABSTRACT FROM AUTHOR]

The reaction system employing titanium alkoxide and hydrofluoric acid under solvothermal conditions has been widely used to prepare anisotropic anatase crystals featuring a large percentage of reactive {001} facets. Nevertheless, such a reaction system leads to the stabilization of both the fluoride and hydroxide-substituting oxide in the anatase network. The presence of both anions is compensated by the stabilization of titanium vacancies. In this work, we demonstrate that the synthesis temperature not only impacts the morphology of the as prepared nanoparticles but also their chemical composition/structural features. Depending on the reaction temperature, two main crystal growth mechanisms that are anisotropic and/or driven by oriented attachment were observed. The morphological changes are associated with a variation of the composition. Particularly, high temperature allows to eliminate most of the OH groups through oxolation reactions, but fluorine is thermally more stable as demonstrated by ¹H and 19F solid-state NMR spectroscopy. This work confirms that the abovementioned reaction system does not lead to pure titanium dioxide, which is an important aspect in linking composition/morphological features to the physico-chemical properties. [ABSTRACT FROM AUTHOR]