Low-cost Mn-based P2/O3 heterostructured layered oxide cathodes based on orbital-lattice synergistic modulation strategy for sodium-ion batteries

Abstract

Manganese-based (Mn-based) layered oxides have become the prospective cathode options for sodium-ion batteries (SIBs) due to the high theoretical capacity and low cost. However, the Mn³⁺ (high spin state) accumulated in Na⁺ intercalation/deintercalation is susceptible to inducing a severe Jahn-Teller effect in the octahedral coordination, leading to irreversible phase transitions and lattice deformations. Herein, we designed a series of Ti-substitution P2/O3 heterostructured cathode materials, and innovated an orbital-lattice synergistic modulation strategy to effectively boost the structural stability of the materials. In situ X-ray diffraction (in situ XRD) patterns indicated that the coupling effect between the P2/O3 biphasic structure effectively inhibits the irreversible phase transitions of P2 to O2 at high voltages. Synchrotron X-ray absorption spectroscopy (XAS) analysis shows that the d⁰ electronic configuration of Ti⁴⁺ eliminates the degenerate electronic states inherent in the d⁴ configuration of Mn³⁺, effectively suppressing Jahn-Teller distortion. Accordingly, the optimized P2/O3-Na_0.85Mn_0.95Ti_0.05O₂ (NMT-05) electrode exhibits remarkable energy density and kinetic properties in both the half-cell system and full-cell systems that matched with a hard carbon anode. This work could offer guidelines for exploiting low-cost and highly stable practical Mn-based oxide cathode materials.