Tailored Modulation of Jahn-Teller Distortion via Electron-Lattice Coupling to Enhance the Cycling Stability of Polyanionic Cathodes for Advance Sodium-Ion Batteries

Manganese-based polyanionic compounds are one of the most promising cathode materials for sodium-ion batteries due to cost-effectiveness, high-voltage capability, and environmental friendliness. Nevertheless, the strong Jahn-Teller distortion (JTD) in high-spin Mn³⁺ state induces localized stress concentration and irreversible structural collapse, while the low-JTD state causes elevated lattice rigidity via enhanced Mn–O bond covalency, leading to inferior electrochemical stability. Herein, we propose an electron-lattice coupling modulation strategy by constructing a Ti⁴⁺-mediated Mn-O-Ti superexchange interactions within the polyanionic NaMnPO₄ framework to enable electronic state reconfiguration and dynamic lattice response for controllable JTD regulation. We show that the strong orbital hybridization between Ti⁴⁺ d⁰ and O 2p enhances the covalency of Mn–O bonds and broadens the Mn³⁺ e_g orbitals into Mn(e_g)-O(2p) hybridized bands, thus reducing the intrinsic electron degeneracy of the Mn³⁺ e_g orbitals. Furthermore, the flexible TiO₆ octahedra facilitate homogeneous reversible microstrains through elastic deformation and enable effective lattice stress dissipation. The NaMn_0.80Ti_0.20PO₄ exhibits an optimal JTD magnitude of σ² = 0.009 and a 91.03% improvement in strain homogeneity compared to the pristine sample. These enhancements contribute to a high-capacity retention of 96.75% after 500 cycles at 2 C. (vs. 77.85% for NaMnPO₄). This work establishes a universal paradigm to modulate the JTD in high-spin transition-metal cathodes, opening new avenues for high-stability cathode design.