Fast and durable high-capacity Na₃V₂(PO₄)₂F₂O/rGO by in-situ composite of a small amount of rGO

High-capacity cathode materials with good rate and cycling performances are crucial to the development of advanced sodium batteries for high-efficiency energy storage. As a novel polyanionic cathode, Na₃V₂(PO₄)₂F₃ shows outstanding structural stability and high theoretical capacity, but the low electric conductivity and sluggish Na⁺ diffusivity severely hinder its practical performance. In this paper, based on oxygen-tuned Na₃V₂(PO₄)₂F₂O (NVPFO) and a small amount (0–1 wt%) of reduced Graphene Oxide (rGO), the NVPFO/rGO composite is simply prepared by an in-situ solid-state approach. The usage of rGO is noticeably decreased (so does the cost) due to the synergy effect of NVPFO with rGO as well as the dominated sp³ and amorphous carbon in the composite. As a result, the performance of this class material is significantly improved by rGO with an optimally reduced content. The excellent performance is ascribed to the stable crystallographic structure, high electric conductivity and fast Na⁺ diffusivity. This work demonstrates facile designing and preparation of graphene-involved energy materials with high-capacity, high-rate, long-durability and low-cost performances using only a small amount of in-situ generated defective rGO.