Reactive and Nonreactive Ball Milling of Tin-Antimony (Sn-Sb) Composites and Their Use as Electrodes for Sodium-Ion Batteries with Glyme Electrolyte

Tin (Sn), antimony (Sb), as well as their intermetallic compound SnSb are potential high-capacity negative electrodes for lithium- or sodium-ion batteries. Starting from bulk Sn and Sb, the effect of ball milling in sodium-ion half cells with a diglyme-based electrolyte is studied. Nonreactive ball milling of Sn, Sb, and carbon leads to intimately mixed but largely phase-separated composites (Sn + Sb) with electrochemical sodiation behavior being the sum of the individual phases. Thereby, Sb shows an unusual and rapid capacity fade in the chosen electrolyte which is unexpected, considering the usually excellent compatibility of diglyme-based electrolytes with negative electrodes. Reactive ball milling of Sn and Sb using a planetary ball mill leads to the phase-pure intermetallic compound beta-SnSb. Compared with Sn + Sb, SnSb shows excellent performance with a specific capacity exceeding 400 mAh g(-1) after 190 cycles and a high rate capability (around 400 mAh g(-1) at 5 C). Hence, herein, Sb is largely inactive as a pure phase but active when bound in the beta-SnSb intermetallic compound. Using in situ electrochemical dilatometry, the "breathing" of the electrodes during charging/discharging is minimized by optimizing ball-milling time, which improves cycle life.