Improving the electrochemical performance of titanium phosphate-based electrodes in sodium batteries by lithium substitution

Li1−xNaxTi2(PO4)3 (0 ≤ x ≤ 1) samples were prepared with a carbon precursor to improve their electrical conducting properties. High purity samples were indexed in the Rc space group for the whole range. On substituting lithium with sodium, the unit cell dimensions anisotropically increased while the local environment of phosphorus was barely affected. The substitution of lithium with sodium involved an increase in the first discharge capacity to 131.8 mA h g−1 for the sample with x = 0.50. Larger sodium contents induced a capacity decrease. The low resistance values recorded for Li0.5Na0.5Ti2(PO4)3 explain the exceptional capacity retention during a long cycling period. The significant improvement in electrode performance found for the latter composition offers a new strategy for optimizing electrode materials for sodium batteries.