The successful commercialization of batteries containing Li4Ti5O121, 2 is a clear indication that the smaller energy density of titanate-based negative electrodes caused by their high potential of Li-ion storage (1.5–1.8 V vs. Li/Li+) can be compensated for, at least for certain applications, by their high safety, stability, and rate capability. The theoretical Li-ion storage capacity of TiO2 (335 mAh g−1) is twice that of Li4Ti5O12 (175 mAh g−1), thus shifting TiO2 into the spotlight of research interest. The practical capacity of TiO2, however, does not reach the theoretical value, which prevents its commercialization. The electrochemical performance of TiO2 is limited due to i) sluggish Li-ion diffusivity and ii) poor electrical conductivity. Several approaches to enhance the electrical conductivity of TiO2 through, for example, carbon3 or RuO24 coatings, foreign doping,5, 6 frozen native defects,7 or wiring by means of carbon nanotube networks,8 and attempts to improve Li-ion diffusion by nanostructuring9 or mesoporosity10 were reported. The crystal phase of TiO2 strongly influences Li-ion diffusivity.11 The β-phase of TiO2 [TiO2(B)] has shown extremely fast Li-ion diffusion,11, 12 exhibiting the highest rate capability reported to date.13, 14 The synthesis methods of TiO2(B), usually more tedious than those of anatase phase, can be considered as a holdback for its commercial use in Li-ion batteries.
