Constructing optimized framework with high structural reversibility and small volume shrinkage by Nd3+ substitution for Na3V2(PO4)3 cathode

Abstract

Na3V2(PO4)3 (NVP) has been extensively researched as an ideal cathode material. However, the limitations of its structural stability and electronic conductivity have hindered its further applications. To address these challenges, this study proposes a modification strategy centered on the synergistic effects of Nd doping and carbon nanotubes (CNTs) coating. The Nd element shows a stronger affinity for oxygen. When replacing the V site, it can form a more stable Nd-O bond, meanwhile, it can inhibit the oxygen evolution. Furthermore, due to the super large ionic radius of Nd3+ (1.81 Å vs. 0.64 Å of V3+), the introduction of Nd doping serves to enhance the stability of the crystal structure, thereby ensuring the effective de-intercalation of Na+. Furthermore, Nd doping widens the transport channels, thereby increasing the speed of Na+ transport. Concurrently, the CNTs coating network, which is integrated onto the material surface, offers diverse pathways for electronic transport, significantly improving electronic conductivity. Comprehensively, Nd-3 sample shows the optimal performance at different doping gradients. It displays a reversible capacity of 114.8 mAh g−1 at 0.1 C. When cycling at 40 C, it can remain 90.2 % after 2500 cycles. According to the ex-situ XRD measurements, the Nd-3 sample shows favourable structural reversibility and very small volume shrinkage, indicating the significantly improved structural stability. Finally, the Nd-3//CHC full cell reveals a high capacity of 134.4 mAh g−1 at 0.1 C, indicating its great potential for applications.