Freestanding Sodium Vanadate/Carbon Nanotube Composite Cathodes with Excellent Structural Stability and High Rate Capability for Sodium-Ion Batteries

Abstract

Sodium vanadate NaV₆O₁₅ (NVO) is one of the most promising cathode materials for sodium-ion batteries because of its low cost and high theoretical capacity. Nevertheless, NVO suffers from fast capacity fading and poor rate capability. Herein, a novel free-standing NVO/multiwalled carbon nanotube (MWCNT) composite film cathode was synthesized and designed by a simple hydrothermal method followed by a dispersion technique with high safety and low cost. The kinetics analysis based on cyclic voltammetry measurements reveals that the intimate integration of the MWCNT 3D porous conductive network with the 3D pillaring tunnel structure of NVO nanorods enhances the Na⁺ intercalation pseudocapacitive behavior, thus leading to exceptional rate capability and long lifespan. Furthermore, the NVO/MWCNT composite exhibits excellent structural stability during the charge/discharge process. With these benefits, the composite delivers a high discharge capacity of 217.2 mA h g^–1 at 0.1 A g^–1 in a potential region of 1.5–4.0 V. It demonstrates a superior rate capability of 123.7 mA h g^–1 at 10 A g^–1. More encouragingly, it displays long lifespan; impressively, 96% of the initial capacity is retained at 5 A g^–1 for over 500 cycles. Our work presents a promising strategy for developing electrode materials with a high rate capability and a long cycle life.