Discharge-Triggered Electronic Delocalization via Asymmetric Motifs Suppresses Jahn-Teller Distortion in Mn-Based Layered Oxides

Abstract

Mn-based layered oxide cathodes with anionic redox activity are promising candidates for sodium-ion batteries (SIBs) owing to their high operating voltage and energy density.However, the inevitable Mn 3+ generation after cycles results in severe Jahn-Teller distortion, damaging the long cycling stability of the cathodes. Herein, we present a metal-to-metal charge transfer (MMCT) mechanism that acts at the end of discharge to inhibit the generation of Mn 3+ , thereby improving the structural sustainability of the electrode. A P2-Na 0.69 Li 0.23 Ru 0.17 Mn 0.6 O 2 cathode is selected as a model. The doping of highly electronegative Ru regulates the covalency of asymmetrical Mn-O-Ru, ensuring the electron transfer between Mn 3+ and Ru 4+ , which reduces Mn 3+ content and mitigates the Jahn-Teller distortion.As a result, the electrode shows a robust structural stability with a minimal unit cell volume change of only 0.2%. Moreover, the cathode exhibits excellent electrochemical performance, maintaining capacity retention of over 90% after 900 cycles at 2-4.3 V. The findings provide fresh insights for inhibiting the Jahn-Teller effect, offering a new paradigm for the application of Mn-based layered cathodes with high energy density for sustainable SIBs.