A New Triclinic Phase Na 2 Ti 3 O 7 Anode for Sodium‐Ion Battery

A new phase Na 2 Ti 3 O 7 compound is synthesized by solid‐state method for the first time, which is verified to belong to the triclinic structure in P‐1 space group. Compared to the conventional monoclinic Na 2 Ti 3 O 7 (m‐NTO), in P2 1 /m1 space group, the triclinic Na 2 Ti 3 O 7 (t‐NTO) possesses a shorter O‐O band in the distorted TiO 6 octahedron, which accounts for more smooth Na + transport channels and a more stable layered structure with smaller fluctuation. The experimental results show that the t‐NTO keeps a low charge potential plateau at 0.3 V compared to the m‐NTO, but with much promoted structure resilience. It delivers a capacity retention of 94.7%, far exceeding the 25.7% of the m‐NTO upon decades of cycles. In situ X‐ray diffraction reveals that the conventional m‐NTO experiences an irreversible phase transition during insertion/de‐insertion of Na + , while the new t‐NTO can recover its structure reversibly after discharge and charge, which is consistent with its improved cycling performance. The results demonstrate a new t‐NTO anode and provide a new understanding for the phase diversity of sodium‐ion battery materials.