The electrochemical performance of a rutile with high niobium content (Ti 0.33 Nb 0.66 O 2 ) has been investigated as Li host material in Li half cells. Electrochemical features are typical of an intercalation pseudocapacitive material. It allows for a highly reversible specific capacity that is kept upon cycling (ca. 170 mAh g −1 after 200 cycles). This rutile can insert lithium through a solid solution down to 1 V, thus extending the solid solution region 0.2 V with respect to TiO 2 . On the other hand, the considerable increase in a lattice parameter due to the larger size of Nb widens the tunnel of the rutile structure, thus allowing for a faster insertion reaction. In this work, we report for the first time that the origin of the good performance of the Nb‐substituted TiO 2 rutiles can be attributed to a high lithium‐ion diffusion coefficient, in the order of 10 −10 – 10 −11 cm 2 s −1 . These are four orders of magnitude higher than that of TiO 2 rutile, thus explaining the intercalation pseudocapacitive behavior of the Nb‐derivatives of TiO 2 .
Solana et al. (Mon,) studied this question.