A high-rate capability and energy density sodium ion full cell enabled by F-doped Na2Ti3O7 hollow spheres

Abstract

Sodium-ion batteries (SIBs) have drawn remarkable attention due to their low cost and intrinsically inexhaustible sodium sources. In the past few decades, significant interest has been aroused in building promising negative electrode materials for SIBs, with long cycling stability and high-rate performance for future applications. Herein, a facile one-step integrated strategy in structure and diffusion regulation was applied to Na₂Ti₃O₇ (NTO) microspheres via a templating route combined with a hydrothermal process. Thus the constructed F-doped NTO hollow microspheres delivered a high initial specific capacity (∼281.3 mA h g⁻¹ at 1C), excellent cycling stability (189.6 mA h g⁻¹ after 1000 cycles at 1C), and superior rate capability (143 mA h g⁻¹ at 50C) as a promising anode for SIBs. Furthermore, the present report demonstrated the full cell performance with a Na₃V₂(PO₄)₃@C (NVP@C) cathode against a F-doped NTO hollow microsphere anode, which retained a high capacity retention of 94% after 50 cycles. Careful investigations indicated that the improved electrochemical properties could be attributed to the synergistic effects of the unique nanostructure construction (hollow microspheres compacted by 2D nanosheet architecture) and kinetics behavior regulation (through heterogeneous F ion doping and the induced oxygen vacancies). This synergistic effect not only stabilized the NTO-based electrode upon cycling, but also accelerated both the Na⁺ insertion/extraction and electron transfer kinetics behavior. The present study showed a way to produce a high-rate capability and energy density sodium-ion full cell, which could also be developed to build large-scale renewable energy storage systems.