Ionic-liquid-bifunctional wrapping of ultrafine SnO2 nanocrystals into N-doped graphene networks: high pseudocapacitive sodium storage and high-performance sodium-ion full cells

Abstract

Sodium ion batteries are in great need of electrode materials with high specificity and rate capability being developed. The sluggish reaction kinetics of SnO₂-based materials has impeded their applications as anodes of SIBs. Designing electrode materials with high pseudocapacitive contribution can increase the near-surface faradaic reaction, which helps to improve their kinetics and achieve high rate capability. Here, we designed a high-pseudocapacitance sodium storage anode SnO₂/N-rGO by downsizing the particle size of SnO₂ and constructing an N-doped graphene wrapped structure. The ultrafine structure of SnO₂ ensures the high faradaic near-surface reaction, while the N-doped graphene matrix guarantees the superior electron and Na⁺ diffusion. Meanwhile, the wrapped N-doped graphene acts as a buffer layer to alleviate the volumetric changes of the active SnO₂. The obtained ultrafine SnO₂/N-graphene composite exhibits a high capacity of 607.6 mA h g⁻¹ at 50 mA g⁻¹ with an impressive rate capability (261.8 mA h g⁻¹ at 2 A g⁻¹) in Na⁺ half-cells. Furthermore, a good performance with a capacity of 133.3 mA h g⁻¹ at 2.4 A g⁻¹ in Na⁺ full-cells can also be achieved, which makes it a promising anode material for SIBs.