K2Ti4O9 nanoribbon arrays functionalized with graphene quantum dots for superior pseudocapacitive sodium storage

Sodium-ion batteries offer a promising solution for large-scale energy storage. However, development of suitable anode materials with long cycle life and high-rate capability is a major challenge. Herein, we report K2Ti4O9 nanoribbon arrays as efficient anode materials for sodium-ion batteries for the first-time. The cross-linked nanoribbon array configuration of K2Ti4O9 enables excellent structural stability and directional ion and electron transport pathways. More importantly, a surface functionalization with graphene quantum dots could significantly improve the electron and ion transport properties and electrochemical surface reactivity of the K2Ti4O9 nanoribbon arrays, thus achieving superior pseudocapacitive sodium storage. As a consequence, the graphene quantum dots functionalized K2Ti4O9 nanoribbon arrays deliver high reversible capacity of 156.8 mAh g−1 at a current density of 0.2 A g−1 and remarkable rate capability of 62.8 mAh g−1 at 5.0 A g−1, as well as excellent cyclability (approximately 95.9 % capacity retention efficiency over 5,000 continuous cycles at 2.0 A g−1). This work demonstrated the potential significance of surface functionalization strategy for boosting the pseudocapacitive sodium storage properties of titanium-based anode materials.