Design and Synthesis of Layered NaTiO and Tunnel NaTiO Hybrid Structures with Enhanced Electrochemical Behavior for Sodium-Ion Batteries.

A novel complementary approach for promising anode materials is proposed. Sodium titanates with layered NaTiO and tunnel NaTiO hybrid structure are presented, fabricated, and characterized. The hybrid sample exhibits excellent cycling stability and superior rate performance by the inhibition of layered phase transformation and synergetic effect. The structural evolution, reaction mechanism, and reaction dynamics of hybrid electrodes during the sodium insertion/desertion process are carefully investigated. In situ synchrotron X-ray powder diffraction (SXRD) characterization is performed and the result indicates that Na inserts into tunnel structure with occurring solid solution reaction and intercalates into NaTiO structure with appearing a phase transition in a low voltage. The reaction dynamics reveals that sodium ion diffusion of tunnel NaTiO is faster than that of layered NaTiO. The synergetic complementary properties are significantly conductive to enhance electrochemical behavior of hybrid structure. This study provides a promising candidate anode for advanced sodium ion batteries (SIBs).