Long-enduring oxygen redox enabling robust layered cathodes for sodium-ion batteries

Abstract

Anionic redox chemistry has emerged as a promising pathway attracted extensively attention to meet the demands of high energy sodium-ion batteries. Nonetheless, suchlike cathode materials suffer from poor reversible oxygen redox reactions leading to severe capacity degradation along with sluggish kinetics and voltage decay. In this work, layered sodium transition metal oxides Na0.67Mg0.28Mn0.72-xRuxO2 (x = 0–0.6) are presented, where the optimized sample (x = 0.12) offers an attractively sustainable capacity of 222 mAh g−1 and a distinguished rate capability of 101.7 mAh g−1 at 50C, based on the anionic and cationic activity. The results reveal that the oxygen redox retention is endured at 94.1% in the optimized sample (x = 0.12) after 55 cycles, in contrast to 48.9% of the pristine sample (x = 0), which is the maximum value reported up to now. Meanwhile the lattice parameters show almost no variation, according to the in situ/ex situ X-ray diffraction experiments. Ru-substitution significantly improves the anionic redox reversibility, the structural stability and sodium diffusion, resulting in the noteworthy electrochemical performance advancement. The research performs an effective method to moderate the problems existing in anionic redox reactions and makes a reference for subsequent materials design.