Exploration of Ca0.5Ti2(PO4)3@carbon Nanocomposite as the High-Rate Negative Electrode for Na-Ion Batteries

Exploring suitable electrode materials with high specific capacity and high-rate capability is a challenging goal for the development of Na-ion batteries. Here, we report a NASI­CON-structured compound, Ca0.5­Ti2­(PO4)3, with respect to its synthesis and electrochemical properties. The electrode is found to enable fast Na+ ion diffusion owing to the rich crystallographic vacancies, affording a reversible capacity of 264 mA h g–1 between 3.0 and 0.01 V. In particular, the hybrid Ca0.5­Ti2­(PO4)3­@­carbon exhibits remarkable rate performance with a discharge capacity of nearly 45 mA h g–1 at a current density of 20 A g–1, which is attributed to the pseudocapacitive effect.