One-Pot Direct Mechanochemical Silicon Replacement of Sodium Fluorosilicate into Sodium Fluorozirconate and Functionalization of Graphite for Enhanced Sodium-Ion Storage

Abstract

Efficient sodium ion storage in graphite is as yet unattainable, because of the thermodynamic instability of sodium ion intercalates-graphite compounds. In this work, sodium fluorozirconate (Na3ZrF7, SFZ) functionalized graphite (SFZ-G) is designed and prepared by the in situ mechanochemical silicon (Si) replacement of sodium fluorosilicate (Na2SiF6, SFS) and functionalization of graphite at the same time. During the mechanochemical process, the atomic Si in SFS is directly replaced by atomic zirconium (Zr) from the zirconium oxide (ZrO2) balls and container in the presence of graphite, forming SFZ-G. The resulting SFZ-G, working as an anode material for sodium ion storage, shows a significantly enhanced capacity of 418.7 mAh g-1 at 0.1 C-rate, compared to pristine graphite (35 mAh g-1) and simply ball-milled graphite (BM-G, 200 mAh g-1). In addition, the SFZ-G exhibits stable sodium-ion storage performance with 86% of its initial capacity retention after 1000 cycles at 2.0 C-rate. To prepare graphite (G) for practical use as a potential sodium ion battery anode material, a direct mechanochemical silicon replacement is conducted to convert sodium fluorosilicate into sodium fluorozirconate (SFZ) using zirconium oxide (ZrO2) balls and container, resulting in SFZ functionalized G (SFZ-G). The SFZ-G shows high sodium ion storage capacity with outstanding electrochemical stability. image