Reactivating Li2O with Nano-Sn to Achieve Ultrahigh Initial Coulombic Efficiency SiO Anodes for Li-Ion Batteries

The application of SiO anodes in Li-ion batteries is greatly restricted by its low initial coulombic efficiency (ICE). Usually, a pre-lithiation procedure is necessary to improve the ICE, but the available technologies are associated with safety issues. Metal (M)-mixed SiO shows great promise to address these issues by reactivating Li2O through the reaction M+Li2O -> MOx+Li+, which is the inverse reaction to that occurring at MOx anodes. Sn is found to be a good choice of metal for this concept. Nanoscale Sn-mixed SiO composites are prepared by mechanical milling. Sn forms an outstanding conductive phase, which boosts the reaction kinetics and also reactivates the Li2O byproduct. Sn/SiO (1:2 w/w) delivers a significant improvement in ICE from 66.5 % to 85.5 %. A higher ICE value of >90 % is obtained when the Sn content is >= 50 wt %. However, additional electrolyte decomposition occurs, which is catalyzed by Sn. In addition, coarsening of the nano-Sn material reduces the inverse conversion reactivity of Sn/Li2O and subsequently results in rapid capacity fading. The quantitative analysis indicates that, in contrast to transition metals, the alloying and dealloying nature of Sn gives a 50 % improvement in reversible capacity, attributed to Sn/Li2O. This work gives a general strategy to choose metals for increasing the ICE of SiOx and metal oxides.