P. Senguttuvan, G. Rousse, M. E. Arroyo y de Dompablo Hervé Vezin, J.-M. Tarascon, and M. R. Palacín*. 

We report the direct synthesis of powder Na₃Ti₂(PO₄)₃ together with its low-potential electrochemical performance and crystal structure elucidation for the reduced and oxidized phases. First-principles calculations at the density functional theory level have been performed to gain further insight into the electrochemistry of Ti(IV)/Ti(III) and Ti(III)/Ti(II) redox couples in these sodium superionic conductor (NASICON) compounds. Finally, we have validated the concept of full-titanium-based sodium ion cells through the assembly of symmetric cells involving Na₃Ti₂(PO₄)₃ as both positive and negative electrode materials operating at an average potential of 1.7 V.