Quick Activation of Nanoporous Anatase TiO2 as High-Rate and Durable Anode Materials for Sodium-Ion Batteries.

To understand the slow capacity activation behavior of anatase TiO2 as a sodium-ion battery anode during cycling, a nanoporous configuration was designed and prepared. On the basis of the comprehension of the Na-ion storage mechanism, the behavior is demonstrated to be related with the gradual formation of amorphous phase resulting from the phase transition during discharge. In addition, the level of phase transition is determined by the discharge rates and cycle numbers, which strongly affects the electrochemical performance of anatase TiO2. Via a quick formation process of the amorphous phase in the initial cycles, the capacity activation is accelerated, and high initial capacity is achieved with no fading after 500 cycles. Particularly, anatase TiO2 displays surprisingly unique properties in the fast charge (even at 20 C, 6.7 A g-1) mode, delivering a 179 mA h g-1 charge capacity. This study is significant for the comprehensive understanding of the controversial sodium storage mechanisms and unclear special behaviors occurring in anatase TiO2, thus greatly contributing to better guidance on the computational studies and experiment technologies for further performance promotion.