Amorphous NaVOPO4 as a High-Rate and Ultrastable Cathode Material for Sodium-Ion Batteries

Abstract

The low cost and profusion of sodium resources make sodium-ion batteries (SIBs) a potential alternative to lithium-ion batteries for grid-scale energy storage applications. However, the use of conventional cathode materials for Na-ion intercalation/ deintercalation cannot satisfy the requirements of high-powered and long lifespan performance due to multiphase transition and lattice confinement. Herein, we demonstrate that amorphous NaVOPO4 incorporated reduced graphene oxide hybrid in a SIB is a superior cathode with high-rate performance and stable cycle life. Remarkably, the electrode exhibits high voltage (∼3.5 V vs Na/Na+), high reversible capacity (110 mAh g−1 at 0.05 C), and remarkable cyclability with 96% capacity retention over 2000 cycles. This outstanding performance originates from its amorphous characteristics and the unique hierarchical microflower structure of the hybrid, which undergo a distinct single-phase-like redox reaction without lattice restriction during charge/ discharge processes, thus accelerating the intercalation/deintercalation of large-sized Na+ ions and maintaining the integrity and stability of the microflower cathode. This amorphous cathode material with fast ion migration and high structural stability may open a new avenue for exploring advanced electrode materials for efficient sodium storage.