Lattice Contraction‐Induced V 3d Orbital Splitting for Achieving High‐Energy‐Density Na ₃ V ₂ (PO ₄ ) ₃ Cathodes

ABSTRACT Transition metal (TM) doping can activate the high‐voltage V ⁴⁺ /V ⁵⁺ redox couple in Na ₃ V ₂ (PO ₄ ) ₃ (NVP), yet the atomistic origin governing this process remains obscured, impeding the rational design of high‐energy‐density Na‐ion batteries. Herein, we reveal that Cr doping induces progressive lattice contraction in NVP, directly triggering V 3d orbital splitting near the Fermi level. This electronic reorganization enhances the electron‐donating propensity of V, enabling reversible V ⁴⁺ /V ⁵⁺ redox activity. The activated 4.0 V plateau intensifies with Cr concentration, elevating energy density to 430.6 W h kg ^−1— surpassing pristine NVP (340.3 W h kg ⁻¹ ). More importantly, the generality of this behavior is confirmed through Fe doping, which similarly contracts the lattice, reproduces the orbital splitting, and activates high‐voltage redox activity (409.11 W h kg ⁻¹ ). In contrast, Mn or Co dopants cause lattice expansion and fail to trigger either orbital splitting or redox activity. We thus establish lattice contraction‐mediated orbital splitting as a universal electronic descriptor for high‐voltage activation in NVP, thereby establishing a general principle for the rational design of high‐energy‐density electrodes through targeted orbital engineering.