Regulating the local electronic structure of low-cost Fe/Mn-based layered oxide cathodes for rapid and stable sodium storage

The P2-type Fe/Mn-based layered oxides, with cost advantages and high theoretical capacity, are considered one of the promising cathode materials for sodium-ion batteries (SIBs). However, the commercial development of these materials is impeded by two main factors: the MnO6 structure distortion induced by the Jahn-Teller (J-T) effect of Mn3+, and the unfavorable phase transitions that occur during the insertion and extraction of Na+. Here, we present a strategy to improve structural stability by incorporating cost-effective, robust Al–O bonds. This approach induces localized adjustments in the electronic structure and a pinning effect, which limits the deformation of the transition metal (TM) layers, strengthens the electrostatic bonding within the TM layers, and expands the Na layer spacing. Consequently, the Na0.67Fe0.4Mn0.54Al0.06O2 cathode demonstrates a capacity of 168.8 mAh g−1 at 0.1 C, maintaining 89.2% of its original capacity after 200 cycles at 1 C. Through in situ electrochemical impedance spectroscopy (EIS) with dynamic resistance transformation (DRT) analysis, ex situ X-ray absorption spectroscopy (XAS), and in situ X-ray diffraction (XRD), the study demonstrates a reduction in the J-T effect, enhanced kinetic performance, and the inhibition of detrimental phase transitions. This study offers new avenues to the development and design of future low-cost Fe/Mn-based cathodes.

P2型Fe/Mn基层状氧化物凭借成本优势与高理论比容量，被视为极具应用前景的钠离子电池（SIBs）正极材料之一。然而，该类材料的商业化开发受两大核心因素掣肘：一是由Mn³+的姜-泰勒（Jahn-Teller, J-T）效应诱导产生的MnO₆结构畸变，二是钠离子嵌入/脱出过程中发生的不利相变。为此，本研究提出一种通过引入廉价且稳定的Al-O键来提升结构稳定性的策略。该策略可诱导电子结构发生局域调控并产生钉扎效应，能够限制过渡金属（TM）层的形变、强化过渡金属层内的静电键合，并拓宽钠离子层间距。据此制备的Na₀.₆₇Fe₀.₄Mn₀.₅₄Al₀.₀₆O₂正极材料在0.1 C倍率下展现出168.8 mAh g⁻¹的比容量，在1 C倍率下循环200圈后仍保留初始容量的89.2%。通过搭载动态电阻变换（DRT）分析的原位电化学阻抗谱（EIS）、非原位X射线吸收谱（XAS）以及原位X射线衍射（XRD）表征，本研究证实该策略可削弱姜-泰勒效应、提升动力学性能并抑制有害相变。本研究为未来低成本Fe/Mn基正极材料的开发与设计提供了全新思路。