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

Abstract Synchrotron X‐ray diffraction data were used to determine the phase purity and re‐evaluate the crystal‐structure of Li 4 Ti 5 O 12‐ x Br x electrode materials (where the synthetic chemical inputs are x = 0.05, 0.10 0.20, 0.30). A maximum of x ′ = 0.12 Br, where x ′ is the Rietveld‐refined value, can be substituted into the crystal structure with at least 2% rutile TiO 2 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 2 , Li 4 Ti 5 O 12‐ x Br x , and a Br‐rich third, unknown, phase. The minor quantities of the secondary phases in combination with Li 4 Ti 5 O 12‐ x Br x where x ′ ∼ 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 2 /Li 4 Ti 5 O 12 anode within a custom‐built battery was used to determine the electrochemical function of the TiO 2 component. The Li 4 Ti 5 O 12 component was found to be electrochemically active at lower voltages (1.5 V) relative to TiO 2 (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 2 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.