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

Amorphous Sn2P2O7 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 Sn2P2O7 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 4.0 V, corresponding to 9.2 Li per Sn2P2O7 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 Sn2P2O7 as well as alloying and de-alloying of tin with lithium is proposed.

► In this paper, we fabricated amorphous Sn2P2O7 thin film electrodes by radio frequency magnetron sputtering. ► We examined their lithium electrochemical properties of Sn2P2O7 by charge/discharge measurement and cyclic voltammograms. ► We found a large reversible specific capacity of Sn2P2O7 thin film electrode of 887 mAh g−1 with excellent capacity retention. ► The electrochemical reaction mechanisms of amorphous Sn2P2O7 with Li involve the reversible decomposition and regeneration of amorphous Sn2P2O7. ► These findings provide a new possibility for further clarifying the intrinsic properties of Sn2P2O7 electrode.