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 Mn 3+ 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 Mn 3+ ions within confined Mn-rich slabs effectively suppresses long-range distortion and stabilizes the layered framework. The engineered Mn-rich oxide, NaNi 0.3 Cu 0.1 Mn 0.6 O 2 (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 Mn 3+ 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.