Sb-based intermetallics and nanocomposites as stable and fast Na-ion battery anodes

To achieve high-performance Sb-based anodes for Na-ion battery (NIB), various approaches for obtaining amorphous C-containing Sb composite (Sb@C), Sb-based intermetallic compounds (TiSb2 and NbSb2), and Na-inactive metal carbide and amorphous C-containing Sb composites (Sb@TiC@C and Sb@NbC@C) have been introduced. First, Sb@C was prepared using a simple solid-state ball-milling, and then its potential as a NIB anode material was investigated. The electrochemical phase change mechanism of Sb during the sodiation/desodiation of Sb@C was investigated using various ex situ analytical techniques. Sb was found to sequentially transform into NaSb and Na3Sb during sodiation and NaSb and Sb during desodiation. Second, as another trial to further improve the electrochemical performance of Sb, Sb-based intermetallic compounds of TiSb2 and NbSb2 were synthesized by alloying reaction via a simple solid state heat-treatment and their potential as NIB anode materials was investigated. Lastly, the Sb@TiC@C and Sb@NbC@C nanocomposites comprising tiny (similar to 3-5 nm) Sb nanocrystallites and Na-inactive metal carbide (TiC/NbC) matrix embedded in buffering amorphous C were synthesized by alloying and dealloying reaction. The Sb@TiC@C and Sb@NbC@C demonstrated highly reversible, stable capacity (Sb@TiC@C: 746 mAh cm(-3), Sb/NbC/C: 726 mAh cm(-3) after 100 cycles) and fast rate capability with exceptional capacity retentions after 400 cycles (Sb@TiC@C: similar to 710 mAh cm(-3) at 2 C rate, Sb@NbC@C: similar to 680 mAh cm(-3) at 2 C rate). Therefore, the Sb-based nanocomposites synthesized by alloying and dealloying are considered to be possible new anode materials for use in high-performance NIBs.