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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.