Anion engineering of Na3V2(PO4)2F3 nanosheets coexisting with OCNTs for high performance in sodium-ion batteries

Abstract

Na₃V₂(PO₄)₂F₃ (NVPF) is an emerging positive electrode material for polyanionic sodium-ion batteries (SIBs) and is distinguished by its Tavorite structure. This material exhibits considerable promise for large-scale energy storage and cost-effective battery applications, owing to its low cost, enhanced safety, and rapid charge/discharge capabilities. The present study introduces the composite material Na₃V₂(PO₄)₂F₃/OCNTs (NVPF/OCNTs) which integrates oxidized carbon nanotubes (OCNTs). The nanosheet structure was synthesized using one-step hydrothermal method. Physical characterization and electrochemical evaluations reveal that the incorporation of OCNTs with NVPF promotes an efficient electron transfer pathway at high current densities. The NVPF/OCNTs composite demonstrates rapid ion and electron transport along with exceptional structural stability. The specific discharge capacities observed were 128.8, 127.3, 121.1, 115.8, 90.1, and 62.4 mAh g⁻¹ at current rates of 0.1, 0.5, 1, 2, 5, and 10 C. The capacity retention rate under a 2 C charge–discharge condition is recorded at 97.7% after 200 cycles. The specific discharge capacity of the NVPF/OCNTs half-cell, following 1000 cycles at a 10 C rate declines from 62.4 to 55.1 mAh g⁻¹, yielding a capacity retention rate of 88.9%. These results highlight the outstanding rate performance and cycling stability of the composite material.