Controlling Jahn–Teller Distortion through Mn Slab Localization for Stable High-Voltage Sodium-Ion Batteries

Mn-rich layered oxides are among the most promising cathode materials for large-scale sodium-ion batteries due to their high capacity, elemental abundance, and low cost. Nevertheless, the practical application of these materials is impeded by the pronounced and intractable Jahn-Teller effect associated with Mn³⁺ ions. This effect triggers cooperative lattice distortion, resulting in structural degradation and compromised cycling stability. In this work, we demonstrate that spatially localizing Jahn-Teller active Mn³⁺ ions within confined Mn-rich slabs effectively suppresses long-range distortion and stabilizes the layered framework. The engineered Mn-rich oxide, NaNi_0.3Cu_0.1Mn_0.6O₂ (NCM316), exhibits exceptional electrochemical performance, achieving 89.5% voltage retention after 200 cycles. In full-cell configurations, NCM316 delivers a high discharge voltage of 3.36 V, the highest reported for Mn-based layered cathodes, while maintaining 84% capacity retention after 500 cycles and reaching an energy density of 337 Wh kg^-1, outperforming all other Mn-based layered cathodes under a high cutoff voltage of 4.4 V. Comprehensive characterization using synchrotron X-ray and neutron scattering techniques, supported by theoretical simulations, confirm the localized presence of Mn³⁺ and elucidate its role in maintaining structural integrity and mitigating adverse interactions with neighboring transition metals. This work offers insight into the mechanism of Jahn-Teller distortion in Mn-rich layered oxides and proposes a broadly applicable design principle for stabilizing other Jahn-Teller active systems, such as layered lithium-rich cathodes, spinel-type oxides, and manganese-based materials for aqueous batteries.