Enhancing Sodium-Ion Storage Behaviors in TiNb₂O₇ by Mechanical Ball Milling

Sodium-ion batteries (SIBs) have shown extensive prospects as alternative rechargeable batteries in large-scale energy storage systems, because of the abundance and low cost of sodium. The development of high-performance cathode and anode materials is a big challenge for SIBs. As is well known, TiNb₂O₇ (TNO) exhibits a high capacity of ∼250 mAh g^-1 with excellent capacity retention as a Li-insertion anode for lithium-ion batteries, but it has rarely been discussed as an anode for SIBs. Here, we demonstrate ball-milled TiNb₂O₇ (BM-TNO) as an SIB anode, which provides an average voltage of ∼0.6 V and a reversible capacity of ∼180 mAh g^-1 at a current density of 15 mA g^-1, and presents excellent cyclability with 95% capacity retention after 500 cycles at 500 mA g^-1. A possible Na storage mechanism in BM-TNO is also proposed.