Trigonal Na₄Ti₅O₁₂Phase as an Intercalation Host for Rechargeable Batteries

Trigonal Na 4 Ti 5 O 12 with a tunnel-structured three-dimensional framework was first examined as an anode material for Li ion batteries. The nanosized Na 4 Ti 5 O 12 was synthesized at 600°C using the solid state method with carbon-coated nanosized TiO 2 anatase. Carbon layers on TiO 2 play an important role of inhibiting the growth of Na 4 Ti 5 O 12 particles. Li ions are reversibly de/intercalated in the Na 4 Ti 5 O 12 structure, and this shows the reversible capacity of ca. 100 mA h g −1 with no capacity fading over 100 cycles. During the repeated charge and discharge, the ion exchange between Na ion and Li ion happens to form Li x Na 4−x Ti 5 O 12 , and this causes an increase of the relative tunnel size due to smaller Li ion, resulting in decreasing polarization of voltage profiles. Also, trigonal Na 4 Ti 5 O 12 was additionally examined as an anode for Na ion batteries.