Unlocking Iron Redox Depth for High‐Energy Layered Sodium Oxide Cathodes

作者：Yadong Song, Wujie Dong, Zhuoran Lv, Bingyuan Han, Jiaming Li, Xin Wang, Xinxin Wang, Jingjing Chen, Chenlong Dong, Zhiyong Mao, Lianqi Zhang · 发表于：Carbon Energy · 年份：2025 · DOI：10.1002/cey2.70142 · 被引用次数：6 · 研究领域：Advancements in Battery Materials、Advanced battery technologies research、Supercapacitor Materials and Fabrication

ABSTRACT High‐capacity O3‐type layered NiFeMn‐based oxides are promising cathodes for sodium‐ion batteries, though their practical deployment is constrained by the inherent limitations of Fe redox chemistry. Traditional designs generally enforcing stoichiometric symmetry (Ni ═ Mn) yield low Fe redox activity. Herein, we propose a valence engineering strategy that breaks conventional Ni/Mn stoichiometry to reconfigure Fe's local chemical environment and unlock unprecedented redox depth. Density functional theory (DFT) calculations reveal that the designed NaNi 0.35 Fe 0.225 Mn 0.425 O₂ cathode exhibits a reduced Bader charge on Fe (1.598 vs. 1.638 in NaNi 1/3 Fe 1/3 Mn 1/3 O 2 ) and elevated Fe 3 d orbital energy, signifying enhanced Fe redox activity. This configuration enables an exceptional Fe 2.60+ /Fe 3.88+ redox (1.28 e − per Fe), delivering a reversible capacity of 184.3 mAh g −1 within 2–4.2 V at 0.2 C, markedly exceeding the benchmark NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (161.3 mAh g −1 ) with low reaction depth of Fe 3.01+ /Fe 3.61+ . The intensified cationic redox reaction enables an ultrahigh energy density of 596 Wh kg −1 . The NaNi 0.35 Fe 0.225 Mn 0.425 O 2 cathode demonstrates robust performance over a broad temperature range from −15°C to 60°C. In situ and ex situ characterizations unveil a reversible O3 ↔ P3 ↔ OP2 phase transition with minimal volume change (1.88%) that circumvents detrimental deleterious O′3 intermediates and intragranular cracking. This work establis...