Boosting sodium-ion battery performance with binary metal-doped Na3V2(PO4)2F3 cathodes

Abstract

Na₃V₂(PO₄)₂F₃ (NVPF), recognized for its Na superionic conductor architecture, emerges as a promising candidate among polyanion-type cathodes for sodium ion batteries (SIBs). However, its adoption in practical applications faces obstacles due to its inherently low electronic conductivity. To address this challenge, we employ a binary co-doped strategy to design Na_3.3K_0.2V_1.5Mg_0.5(PO₄)₂F₃ cathode with nitrogen-doped carbon (NC) coating layer. This configuration enhances electronic conductivity and reduces diffusion barriers for sodium ion (Na⁺). The strategy of incorporating nitrogen-doped carbon coating not only facilitates the formation of a porous structure but also introduces additional defects and active sites. Such modifications accelerate the reaction kinetics and augment electrolyte interaction through an expanded specific surface area, thus streamlining the electrochemical process. Concurrently, strategic heteroatom substitution leads to a more efficient engagement of Na⁺ in the electrochemical activities, thereby bolstering the cathode's structural integrity. The vanadium fluorophosphate Na_3.3K_0.2V_1.5Mg_0.5(PO₄)₂F₃@NC exhibits an electrochemical performance, including a high discharge specific capacity of 124.3 mA h g^-1 at 0.1C, a long lifespan of 1000 cycles with a capacity retention of 93.1 % at 10C, and a rate property of 73.2 mA h g^-1 at 20C. This research provides a method for preparing binary doped NVPF for energy storage electrochemistry.

Keywords: Binary doping; Na(3)V(2)(PO(4))(2)F(3); Nitrogen-doped carbon; Sodium ion batteries; Structural stability.