Intrinsic Distortion against Jahn-Teller Distortion: A New Paradigm for High-Stability Na-Ion Layered Mn-Rich Oxide Cathodes

Layered manganese-rich oxides (LMROs) are widely recognized as the leading cathode candidates for grid-scale sodium-ion batteries (SIBs) owing to their high specific capacities and cost benefits, but the notorious Jahn-Teller (J-T) distortion of Mn³⁺ always induces severe structural degradation and consequent rapid cathode failure, impeding the practical implementation of such materials. Herein, we unveil the “intrinsic distortion against J-T distortion” mechanism to effectively stabilize the layered frameworks of LMRO cathodes. The intrinsic distortion simply constructed by introducing bulk oxygen vacancies is systematically confirmed by advanced synchrotron X-ray techniques, atomic-scale imaging characterizations, and theoretical computations, which can counteract the J-T distortion during cycling due to their opposite deformation orientations. This greatly decreases and uniformizes the lattice strain within the ab plane and along the c axis of the material, thereby alleviating the P2-P′2 phase transition as well as suppressing the edge dislocation and intragranular crack formation upon repeated cycles. As a result, the tailored P2-Na_0.72Mg_0.1Mn_0.9O₂ cathode featuring intrinsic distortion delivers a considerably enhanced cycling durability (91.9 % capacity retention after 500 cycles) without sacrificing the Mn³⁺/Mn⁴⁺ redox capacity (186.5 mAh g⁻¹ at 0.3 C). This intrinsic distortion engineering paves a brand-new and prospective avenue toward achieving high-performance LMRO cathodes for SIBs.