Layered FeS-Regulated VO6 Framework Coupled with Carbon-Coating Charge Rearrangement Boosting Long-Cycled Na3V2(PO4)3 Cathode

Currently, the dissolution of active V in Na3V2(PO4)3 (NVP) leads to the inferior long-term cycling efficiency and poses potential thermal safety risks. To address these deficiencies, this study proposes a hydrothermal method that uses pre-synthesized layered FeS as a template, to successfully prepare a unique NVP@FeS composite with uniformly dispersed cluster-like morphology. FeS regulates the NVP surface to maintain its interfacial structural stability by forming FeN4 ligands under the induction of Fe2+. Notably, FeN4 not only enhances the electronic conductivity but also effectively suppresses the formation of organic functional groups in the CEI layer. The FeN4 ligand forms a complex with the active material via ligand molecular chains within the NaFePO4 composite phase, thereby optimizing the stability of the unit cell. The introduction of FeS significantly modifies the V–O bond. XAFS and simulations coherently demonstrate that the length of V–O bond length decreases, indicating that higher bond energy exists in the VO6 framework to maintain the structural stability and enhance the immobilization of V inside the NVP bulk. Moreover, in situ EIS and DRT measurements verify the superior kinetic characteristics at the heterogeneous interfaces of the NVP@FeS cathode. Furthermore, heteroatoms of S and N both enter in the coated carbon layers during the hydrothermal process, which occupy the C sites to induce the charge rearrangement to boost electronic transportation. ELF illustrates that charges accumulate at the N site and dissipate at the S site. The gradient configuration of the enriched charge distribution is relatively attractive for O and induces O vacancy inside NVP, which increases the hole carrier to accelerate ionic migration. Correspondingly, NVP@FeS-2 exhibits a high capacity of 125.6 mA h·g–1 at 0.1 C. After 4000 cycles at 20 C, it still retains 95.5 mA h·g–1 with a capacity retention rate as high as 92.7%. The ARC test shows that NVP@FeS exhibits a markedly higher onset temperature for exothermic reactions, while the total heat release is significantly reduced.