For the preparation of anode "Na3Sn", stoichiometric amounts of Na metal (Sigma Aldrich, 99.9%) and Sn metal (nanopowder, US Research Nanomaterials, 99.9%) were prepared by grinding in mortar for 30 minutes, followed by ball milling in a zirconia jar (45 mL, Fritsch GmbH), keeping mass ratio between milling media (ZrO2, 5 mm diameter) and precursors at 36:1. A pre-mixing process was operated at 100 rpm for 10 minutes, followed by 8 h ball-milling at 300 rpm. The synthesized "Na3Sn" has a potential of 0.141 V vs. Na + /Na.