In Situ Electrochemical Coating Mechanism of NASICON-Structured AgTi2(PO4)3 for Sodium-Ion Batteries.

The development of high-performance electrode materials is of great significance for the next-generation room-temperature sodium-ion batteries. In this work, a new Na super-ionic conductor (NASICON) negative electrode, AgTi2(PO4)3, is prepared by a facile solid-state reaction and employed as a sodium storage material for the first time. In situ X-ray diffraction during battery operation reveals an electrochemically Ag nanoparticle coating mechanism upon sodiation, facilitating the electron transfer in the complex. In addition, two steps of highly reversible biphasic transformation are observed. As a result, a reversible capacity of 214.9 mA h g-1 can be achieved, corresponding to the insertion/extraction of nearly four sodium ions. The AgTi2(PO4)3 electrode also demonstrates better kinetic properties than the bare NaTi2(PO4)3 material. Such an "in situ" decorating method can open up a new direction for the design of NASICON-structured materials.