Dual-functional Ti-doped Na3V2(PO4)2O2F cathode for high-rate and long-life sodium-ion batteries

A series of Ti-doped Na 3 V 2 (PO 4 ) 2 O 2 F materials were synthesized through a controlled coprecipitation method with precise Ti content regulation. Experimental results indicate that a 15 wt% Ti doping level (NVTOPF-0.15) optimally enhances electrochemical performance, yielding an initial discharge capacity of 119.3 mAh g −1 at 0.2C and retaining 84.3 % of its capacity after 2000 cycles at 5C. Titanium doping exerted a dual-functional effect: streamlining the synthesis pathway through synergistic coprecipitation with controllable particle size and enhancing the lattice substitution of Ti 4+ for V in VO 6 octahedra. This substitution refined the crystal structure and enhanced Na + diffusion kinetics. Titanium doping-induced structural reconstruction led to a reduction in particle size, thereby facilitating the electrochemical reaction kinetics. Additionally, using a combination of the Randles-Sevcik equation and theoretical calculations, it was found that titanium doping significantly increased the Na + diffusion coefficient and decreased the band gap. This study presents a dual-functional titanium-doping approach for high-rate and long-life sodium-ion cathode materials. The synthesis of NVTOPF via the co-precipitation method will provide new guidance for the development and application of positive electrode materials in sodium-ion batteries.