Lithium and sodium storage performance of tin oxyphosphate anode materials

Two types of Sn-based nanostructured materials have been investigated as anodes in lithium-ion batteries (LIB) and sodium-ion batteries (SIB). Firstly, nanostructured Sn/SnOx powders were synthesized by one-step anodic oxidation of Sn foil in an alkaline electrolyte followed by mechanical separation of the anodic film from the remaining substrate. Secondly, as-anodized powders were converted for the first time to tin oxyphosphate (Sn/SnP2O7) hybrid via a simple phosphorization with red phosphorous at 500 °C. The XRD and HR-TEM analyses confirmed that the hybrid was comprised of Sn nanoparticles embedded in the SnP2O7 matrix. When used as anode materials, the Sn/SnP2O7 exhibits excellent storage performance for lithium and sodium ions compared to Sn/SnOx that can be attributed to the metal/matrix structure which is not only conducive to the electron transport but also can facilitate the accommodation of volume changes during intercalation/deintercalation processes. A stable reversible capacity with an excellent coulombic efficiency of nearly 100% at different current densities even up to 1000 cycles was achieved for the Sn/SnP2O7 anode in LIB.