Electrochemical lithiation/delithiation of SnP2O7 observed by in situ XRD and ex situ7Li/31P NMR, and 119Sn Mössbauer spectroscopy

Abstract

SnP₂O₇ was prepared by a sol–gel route. The structural changes of tin pyrophosphate during the electrochemical lithiation were followed by using in situ XRD measurements that reveal the existence of a crystalline phase at the beginning of the discharge process. Nevertheless, it becomes amorphous after the full discharge as a result of a conversion reaction leading to the formation of Li_xSn_y alloys. The electrochemical tests show a high capacity with high retention upon cycling. To better understand the reaction mechanism of SnP₂O₇ with Li, several techniques were applied, such as ex situ¹¹⁹Sn Mössbauer and ex situ⁷Li and ³¹P NMR spectroscopies with which we can follow the changes in the local environment of each element during cycling.