Pseudocapacitive Graphene‐Wrapped Porous VO2 Microspheres for Ultrastable and Ultrahigh‐Rate Sodium‐Ion Storage

The exploration of anode materials with enhanced electronic/ionic conductivity and structural stability is beneficial for the development of sodium‐ion batteries. Herein, a simple solution‐derived method is demonstrated to fabricate porous VO2 microsphere composite with a graphene‐wrapped structure (VO2/G). When used as the anode material for sodium‐ion batteries, the VO2/G electrode delivers a high reversible specific capacity (373.0 mAh g−1), great rate capability (138.8 mA h g−1 at 24.0 A g−1, ≈21 s per charge/discharge), and excellent long‐cycling performance (95.9 % capacity retention for 3600 cycles at 2.0 A g−1). The outstanding electrochemical property of VO2/G is mainly attributed to its unique graphene‐wrapped porous structure and the pseudocapacitive‐dominated feature. In addition, the sodium‐ion storage mechanism of VO2/G is investigated by various ex‐situ characterization techniques. During the first sodiation process, the sodium‐ion appears to partially reduce VO2/G and form metallic vanadium, sodium oxide, and amorphous sodium vanadium. This work provides new fundamental information for the design and application of vanadium oxides for energy storage system. I want to see it painted, painted black: graphene‐wrapped porous VO2 microspheres are successfully synthesized. As anode for sodium‐ion batteries, the material delivers excellent cycling stability and rate performance.