A new electrochemical reaction mechanism of tin pyrophosphate thin film with lithium

摘要

Amorphous S112P2O7 thin film electrodes have been successfully fabricated by radio frequency (r.f.) magnetron sputtering. Reversible lithiation and delithiation processes occurring at 1.47 V and 2.01 V versus lithium are observed in both discharge/charge curves and cyclic voltammograms of the amorphous Sn_2P_2O_7 thin film electrodes for the first time. Large reversible capacity around 887 mAh g~(-1) is achieved when the cell is cycled between 0.01 V and 4.0V, corresponding to 9.2 Li per Sn_2P_2O_7 unit. Based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) evidences, the reaction mechanism involving the reversible decomposition and regeneration of amorphous Sn_2P_2O_7 as well as alloying and de-alloying of tin with lithium is proposed.