Sustainable All-Mn-Based Layered Cathode with Dynamic Structural Stability for Durable Sodium-Ion Batteries.

Abstract

Layered sodium all-Mn-based oxide materials are confronted with irreversible dynamic structural degradation induced by [MnO₆] layers gliding and Jahn-Teller (J-T) distortion of high-spin Mn³⁺ during cycling. Although conventional strategies often focus primarily on reducing Mn³⁺ content in the pristine material, we reveal that such static valence control is insufficient to ensure long-term structural integrity. Instead, we demonstrate that dynamic structural regulation effectively decouples the Mn oxidation state changes from degradation pathways. By designing a P'2-type [Na_0.64Zn_0.07]Mn_0.92Cu_0.08O₂ (NZMCO) cathode, which maintains the same initial Mn oxidation state as Na_0.67MnO₂ (NMO), we achieve exceptional cycling stability via a hierarchical damping-like mechanism. The designed framework integrates two synergistic stabilization pathways: (i) intralayer coordination tuning by counterbalancing Mn─O bond anisotropy, and (ii) interlayer electrostatic shielding to alleviate gliding between adjacent [MnO₆] layers. This strategic configuration effectively alleviates lattice strain and stress accumulation, suppresses microcrack formation, and significantly reduces transition metal dissolution. Consequently, NZMCO delivers a high specific capacity of 194.95 mAh g^-1 at 20 mA g^-1, retaining 87.53% of its initial capacity after 1500 cycles at 2000 mA g^-1. This work shifts the design paradigm from static Mn valence engineering toward dynamic structural adaptation, offering a sustainable pathway for all-Mn-based layered cathodes.