Lithium Insertion in Nanostructured TiO2(B) ANTHONY G. DYLLA, GRAEME HENKELMAN, AND KEITH J. STEVENSON* Department of Chemistry & Biochemistry, The University of Texas at Austin, Austin, Texas 78712, United States RECEIVED ON JUNE 12, 2012 to become feasible alternatives to current technology, but only if scientists can develop energy storage materialsthat offer high capacity and high rate capabilities. Chemists havestudied anatase, rutile, brookite and TiO2(B) (bronze) in bothbulk and nanostructured forms as potential Li-ion batteryanodes. In most cases, the specific capacity and rate of lithiationand delithiation increases as the materials are nanostructured.Scientists have explained these enhancements in terms of highersurface areas, shorter Liþ diffusion paths and different surfaceenergies for nanostructured materials allowing for more facilelithiation and delithiation. Of the most studied polymorphs,nanostructured TiO2(B) has the highest capacity with promising high rate capabilities. TiO2(B) is able to accommodate 1 Liþ per Ti,giving a capacity of 335 mAh/g for nanotubular and nanoparticulate TiO2(B). The TiO2(B) polymorph, discovered in 1980 by Marchand andco-workers, has been the focus of many recent studies regarding high power and high capacity anode materials with potential applicationsfor electric vehicles and grid storage. This is due to the material's stability over multiple cycles, safer lithiation potential relative to graphite,reasonable capacity, high rate capability, nontoxicity, and low cost (Bruce, P. G.; Scrosati, B.; Tarascon, J.-M. Nanomaterials for RechargeableLithium Batteries. Angew. Chem., Int. Ed. 2008, 47, 2930"2946). One of the most interesting properties of TiO2(B) is that both bulk andnanostructured forms lithiate and delithiate through a surface redox or pseudocapacitive charging mechanism, giving rise to stable high ratecharge/discharge capabilities in the case of nanostructured TiO2(B). When other polymorphs of TiO2 are nanostructured, they still mainlyintercalate lithium through a bulk diffusion-controlled mechanism. TiO2(B) has a unique open crystal structure and low energy Liþ pathwaysfrom surface to subsurface sites, which many chemists believe to contribute to the pseudocapacitive charging.