Ruthenium‐Oxide‐Coated Sodium Vanadium Fluorophosphate Nanowires as High‐Power Cathode Materials for Sodium‐Ion Batteries

Sodium‐ion batteries are a very promising alternative to lithium‐ion batteries because of their reliance on an abundant supply of sodium salts, environmental benignity, and low cost. However, the low rate capability and poor long‐term stability still hinder their practical application. A cathode material, formed of RuO 2 ‐coated Na 3 V 2 O 2 (PO 4 ) 2 F nanowires, has a 50 nm diameter with the space group of I 4/ mmm . When used as a cathode material for Na‐ion batteries, a reversible capacity of 120 mAh g −1 at 1 C and 95 mAh g −1 at 20 C can be achieved after 1000 charge–discharge cycles. The ultrahigh rate capability and enhanced cycling stability are comparable with high performance lithium cathodes. Combining first principles computational investigation with experimental observations, the excellent performance can be attributed to the uniform and highly conductive RuO 2 coating and the preferred growth of the (002) plane in the Na 3 V 2 O 2 (PO 4 ) 2 F nanowires.