Dual-site doping constructs impurity-free Na3V2(PO4)2F3 cathodes for wide-temperature ultralong cycling sodium-ion batteries.

Abstract

Na Super Ionic Conductor (NASICON-type) Na3V2(PO4)2F3 (NVPF) is widely recognized as a promising cathode material for sodium-ion batteries (SIBs). However, the low intrinsic electronic conductivity, slow sodium-ion diffusion kinetics, and the inevitable formation of Na3V2(PO4)3 (NVP) impurities have hindered its development. Herein, a KCe synergistic dual-site doping strategy is proposed to synchronously boost its phase purity, conductivity, and electrochemical performance. Experimental results and theoretical calculations indicate that strong hybridization occurs between the Ce 4f orbitals and the V 3d orbitals, significantly enhancing electronic conductivity. Simultaneously, the introduced K+ ions not only serve as structural supports that broadening the Na+ diffusion pathways, but also suppress structural phase transitions through charge compensation, thereby preventing the formation of NVP impurities. As a result, the prepared NK0.04VCe0.04PF material exhibits a specific capacity of 121 mAh·g-1 at 0.1 C and 92.29% capacity retention after 10,000 cycles at 30 C and reliable performance over -20 to 55 °C. Furthermore, the NK0.04VCe0.04PF//HC battery assembly exhibits a high discharge specific capacity of 113.8 mAh·g-1 at 0.1 C, indicating its potential for practical applications.