Coupled X-ray diffraction and electrochemical studies of the mixed Ti/V-containing NASICON: Na2TiV(PO4)3
The solid state synthesis of NaTiV(PO4)3 and Na3TiV(PO4)3 is reported. Soft chemical oxidation of the latter composition led to NASICON Na2TiV(PO4)3 with intermediate unit cell parameters (s.g.: Rc, a = 8.610(3) Å, c = 21.755(6) Å) when compared to NaTiV(PO4)3 and Na3TiV(PO4)3. Coupled structural/electrochemical studies were carried out on Na2TiV(PO4)3 for oxidation and reduction by operando X-ray diffraction. While the oxidation mechanism towards NaTiV(PO4)3 is quite simple, the reduction mechanisms involve several mono- and bi-phasic mechanisms leading to Na3TiV(PO4)3 as an intermediate composition and to Na4TiV(PO4)3 eventually.