Br‐Doped Li₄Ti₅O₁₂ and Composite TiO₂ Anodes for Li‐ion Batteries: Synchrotron X‐Ray and in situ Neutron Diffraction Studies

<jats:title>Abstract</jats:title><jats:p>Synchrotron X‐ray diffraction data were used to determine the phase purity and re‐evaluate the crystal‐structure of Li<jats:sub>4</jats:sub>Ti<jats:sub>5</jats:sub>O<jats:sub>12‐<jats:italic>x</jats:italic></jats:sub>Br<jats:sub><jats:italic>x</jats:italic></jats:sub> electrode materials (where the synthetic chemical inputs are <jats:italic>x</jats:italic> = 0.05, 0.10 0.20, 0.30). A maximum of <jats:italic>x</jats:italic>′ = 0.12 Br, where <jats:italic>x</jats:italic>′ is the Rietveld‐refined value, can be substituted into the crystal structure with at least 2% rutile TiO<jats:sub>2</jats:sub> forming as a second phase. Higher Br concentrations induced the formation of a third, presumably Br‐rich, phase. These materials function as composite anodes that contain mixtures of TiO<jats:sub>2</jats:sub>, Li<jats:sub>4</jats:sub>Ti<jats:sub>5</jats:sub>O<jats:sub>12‐<jats:italic>x</jats:italic></jats:sub>Br<jats:sub>x</jats:sub>, and a Br‐rich third, unknown, phase. The minor quantities of the secondary phases in combination with Li<jats:sub>4</jats:sub>Ti<jats:sub>5</jats:sub>O<jats:sub>12‐<jats:italic>x</jats:italic></jats:sub>Br<jats:sub><jats:italic>x</jats:italic></jats:sub> where <jats:italic>x</jats:italic>′ ∼ 0.1 were found to correspond to the optimum in electrochemical properties, while larger quantities of the secondary phases contributed to the degradation of the performance. In situ neutron diffraction of a composite anatase TiO<jats:sub>2</jats:sub>/Li<jats:sub>4</jats:sub>Ti<jats:sub>5</jats:sub>O<jats:sub>12</jats:sub> anode within a custom‐built battery was used to determine the electrochemical function of the TiO<jats:sub>2</jats:sub> component. The Li<jats:sub>4</jats:sub>Ti<jats:sub>5</jats:sub>O<jats:sub>12</jats:sub> component was found to be electrochemically active at lower voltages (1.5 V) relative to TiO<jats:sub>2</jats:sub> (1.7 V). This enabled Li insertion/extraction to be tuned through the choice of voltage range in both components of this composite or in the anatase TiO<jats:sub>2</jats:sub> phase only. The use of composite materials may facilitate the development of multi‐component electrodes where different active materials can be cycled in order to tune power output.</jats:p>