Charge accumulation in carbon skeleton inducing oxygen vacancy-rich Na3V2(PO4)3 with multielectron transport property for high performance sodium ion batteries

Abstract

Traditional carbon-based modification methods focus on the electronic conductivity of Na₃V₂(PO₄)₃(NVP), rather than affecting its internal crystal structure. Herein, abundant C₁₈H₁₉ClN₄(CZP) is introduced NVP to generate synergistically modified N/Cl co-doped carbon skeleton. DFT calculation illustrates after N/Cl atoms occupy C sites, charges accumulate at N/Cl site. The enriched charge is relatively attractive for O atom, which induces the formation of O vacancy inside NVP. Significantly, the offset of O atom lengthens the P-O and V-O bonds, contributing to the expansion of VO₆ and PO₄ framework and thus enlarging the construction frame. Confirmatively, XAFS analysis demonstrates the elongation of V-O bond. Furthermore, ex-situ XPS verifies the contents of pyridinium and pyrrole nitrogen increase during electrochemical process to improve the electronic conductivity. Cl^- can act as carrier to elevate the charge transfer and reduce the resistance during Na⁺ de-intercalation. The notably improved kinetic characteristics boost a higher voltage platform at 3.9 V derived from V⁴⁺/V⁵⁺. Ex-situ XRD indicates CZP-2 possesses great cyclic reversibility with near-zero strain property. Consequently, CZP-2 achieves superior rate capability and cycling performance in half and three type full cells (CZP-2//CHC, CZP-2//FeSe₂ and CZP-2//CZP-2). Moreover, ARC measurement verifies CZP-2 has a higher thermal runaway temperature with better thermal stability.