Taming Jahn-Teller distortion toward robust sodium storage in Mn-rich layered oxide cathode

Mn-rich P2-type layered cathodes are promising for sodium-ion batteries because of their high theoretical capacity and low cost, but their practical application is hindered by severe structural instability caused by Mn³⁺-induced Jahn-Teller distortion. Instead of sacrificing Mn redox activity, this work proposes a lattice-surface-interphase coupled regulation strategy to stabilize the local MnO₆ environment while preserving high-capacity redox reaction of Mn species. Specifically, Ca_0.5Ti₂(PO₄)₃-coated Na_0.67Fe_0.1Mn_0.8Al_0.1B_0.02O₂ (AFMB@CTP) was achieved, which can deliver a capacity of 185.0 mAh g⁻¹ at 20 mA g⁻¹ and preserve 96.0 mAh g⁻¹ at 1000 mA g⁻¹, together with a capacity retention of 82.4% after 1000 cycles. It reveals that this multi-dimensional modification strategy could promote the participation of low-voltage Mn redox and enhance the local symmetry and coordination stability of MnO₆ octahedra, accompanied by a reduced unit-cell volume fluctuation from 3.6% to 1.9% upon cycling. The optimized cathode also exhibits excellent full-cell performance and good tolerance to low-temperature operation and air exposure. These results provide an effective strategy for developing low-cost, high-performance Mn-rich layered cathodes for practical sodium-ion batteries.