Sodium vanadium phosphate electrode achieving rapid Na+ migration kinetics through DBD plasma multiscale modification

Abstract

Na₃V₂(PO₄)₃ (NVP) has been extensively investigated as an ideal cathode material for sodium-ion batteries owing to its excellent low-temperature performance and abundant sodium resources. However, its low electronic conductivity and poor Na⁺ diffusion kinetics limit its widespread application. To address these challenges, a fast, efficient, and in situ multiscale modification method for NVP using low-temperature dielectric barrier discharge (DBD) plasma is proposed. At the microscopic scale, oxygen vacancies (O-vacs) are generated in NVP, while at the macroscopic scale, a superstable, Na⁺-conductive NaF layer is created on the electrode surface. Combining COMSOL Multiphysics simulations and density functional theory calculations, the mechanism of O-vacs in the NVP crystal structure and NaF layers at the electrode interface is confirmed by high-energy electron bombardment in N₂ DBD plasma with a maximum energy value of 11.25 eV. This energy considerably exceeds the O-vac formation energy (0.26 eV) and the C–F bond-breaking energy (5.02 eV). The strategic introduction of abundant O-vacs into NVP crystal lattices enhances Na⁺ diffusion kinetics and electronic conductivity. The in situ formation of NaF layers at the electrode interface suppresses the generation of Na₂CO₃ with extremely low Na⁺ conductivity. This multiscale synergy of bulk-phase defect engineering (O-vacs) and interfacial chemistry optimization (NaF) considerably improves ionic and electronic transport dynamics throughout the electrode system. The optimal NVP electrode with N₂ plasma modification of 4 min (NVP-4N) exhibits a stable capacity of 81.1 mAh g⁻¹ with 75 % capacity retention over 8000 cycles at 20C. The capacity is enhanced by 18 % with a threefold improvement in cycling performance compared to the 68.9 mAh g⁻¹ capacity after 2000 cycles of the NVP electrode without modification. Even at a high current density of 40C, it still demonstrates a capacity of 76.5 mAh g⁻¹ with 73 % retention over 7000 cycles. This work provides new insights into the application of low-temperature plasma in modifying energy materials at multiple spatial scales.