Constructing heterostructure by co-doping of Ta5+ and F− with carbon nanotubes to improve kinetic properties of Na3V2(PO4)3

The advancement of Na 3 V 2 (PO 4 ) 3 has been impeded by its subpar kinetic characteristics, resulting in suboptimal electrochemical performance . In this case, a dual modification strategy involving Ta and F co-doping is employed, along with the incorporation of carbon nanotubes (CNTs), is introduced. Notably, the substitution of high-valence Ta 5+ for V 3+ ions induces an n-type doping effect, thereby increasing the density of free electrons and enhancing electrochemical performance. Moreover, Ta 5+ possesses a comparatively larger ionic radius than V 3+ , which enhances the ease of Na + transport, leading to an increased rate of ionic diffusion. Furthermore, Ta 5+ ions play a crucial role in reinforcing the crystal structure, thereby strengthening the stability of the NVP system. Importantly, during the high-temperature calcination process, the reduction of carbon results in the conversion of Ta 5+ to Ta 3+ , forming a novel conductive TaN phase through its reaction with N 2 . This TaN phase, known for its high conductivity, intercalates into the NVP bulk as interlayers, forming beneficial grain boundaries. Thanks to this unique TaN//NVP heterojunction , the migration of Na + ions is notably accelerated along the grain boundaries rather than within the NVP bulk. The introduction of F contributes to reducing the grain size of active particles, consequently shortening the pathways for Na + migration and improving kinetic properties. Moreover, the presence of carbon layers and the encapsulation of CNTs collaboratively construct a highly conductive cross-linking network, elevating both electronic conductivity and mitigating NVP particle aggregation during high-temperature sintering. Consequently, the modified NVTPF0.07/@CNTs sample exhibits outstanding performance in both half and full cells, underscoring its substantial potential for application in the field of sodium-ion batteries.