Superior Sodium Storage of Carbon-Coated NaV₆O₁₅ Nanotube Cathode: Pseudocapacitance Versus Intercalation

To realize the effect of Na⁺ pseudocapacitance on the sodium storage of cathode materials, clewlike carbon-coated sodium vanadium bronze (NaV₆O₁₅) nanotubes (Na-VBNT@C) were synthesized via a facile combined sol–gel/hydrothermal method. The resultant Na-VBNT@C delivers high reversible capacities of 209 and 105 mA h g^–1 at the rates of 0.1 and 10 C, respectively. Notably, at the higher rate of 5 C (1250 mA g^–1), it can retain 94% of the initial capacity after 3000 cycles. It was found that the outstanding rate performance and the long-term cycling life of Na-VBNT@C are primarily due to the Na⁺ pseudocapacitance. Our study reveals that the design of Na⁺ pseudocapacitance is beneficial for harvesting the superior performance of NaV₆O₁₅ cathode material in sodium-ion batteries.