Fe/Mn-based cathode is considered a viable choice for sodium-ion batteries (SIBs) because of its affordability and high theoretical capacity. Nonetheless, bad actually comprehensive performance still impede its commercial application. In this work, based on the systematic study of P2-Na 2/3 Fe 1/2 Mn 1/2 O 2 cathode materials with fewer Mn vacancies (NFM-Q), we realized a superior rate, cycling performance, air stability and more importantly unraveled the operation mechanism. Specifically, dual function of fewer Mn vacancies were explicitly clarified, which included the effect of shrinking sodium layers and the sodium-ion diffusion promoting effect, as confirmed by combining XRD, XANES, XAFS, EIS and GITT. So Mn vacancy engineering had the potential to break the contradiction between “sodium limiting” based on air-stabilization mechanism and “sodium promoting” based on kinetics. This has rarely been found before. And a series of characterizations strongly declared rapidly cooling rate could effectively regulated the creation of Mn vacancies. As a result, NFM-Q cathode not only delivered outstanding discharge capacity (192.7 mAh/g), cycling stability (123.8 mAh/g, 65 %, after 50 cycles) and energy density (574.0 Wh Kg −1 ), but also possessed splendid air stability (185.8 mA h/g, 61.8 % after 50 cycles and immersion). Moreover, ex-situ XRD and XAS further expounded structural evolution and charge compensation mechanism of NFM-Q cathode, confirming its superior performance. This work might offer fresh understanding about the roles of Mn vacancy engineering, which could open up new possibilities on the material design and the property improvement of Fe/Mn-based cathodes.
Layered transition metal oxides are the most promising cathode materials for sodium-ion batteries, however, the cycling stability and rate performance of this type of cathode materials are very limited. Herein, a solid-state reaction method is developed to synthesize micrometer-sized bulk crystals of the P2-type cathode of Na0.85Li0.12Ni0.198Be0.011Mg0.011Mn0.66O2 (denoted as NLNBMMO-5%) via configurational entropy. The high-entropy layered oxide cathode exhibits superior rate capability, delivers a high reversible capacity of 102.6 mA h g−1 at 1C with a capacity retention of 94.2% after 100 cycles, and maintains a capacity of 78.2 mA h g−1 at 5C with a capacity retention of 78.3% after 300 cycles. This new strategy reduces the ratio of Mn3+/Mn4+, which alleviates the Jahn-Teller distortion effect and enhances the structural stability. Moreover, it expands the interlayer spacing that ensures the excellent rate performance of the cathode, as confirmed by the XPS, the Rietveld refinement of the XRD and the GITT measurement. This work demonstrates that the new composition cathode NLNBMMO-5% is promising for rechargeable sodium-ion batteries with a long cycling life and excellent rate performance.
Yu Duan,Jia-xuan He,Zi-han Ma,Shu-wen Chen,Ying-ying Huang,Shuo Bao,Jin-lin Lu
Sodium-ion batteries (SIBs) are gaining traction for large-scale energy storage due to sodium's abundance and cost efficiency, yet the structural instability and slow ion transport of P2-type cathodes remain critical challenges. This study employs a high-temperature solid-state approach to develop K/Cu co-doped cathodes, demonstrating that co-doping preserves the P2 phase while optimizing lattice parameters to expand interlayer spacing. The reduction in Mn 3+ content suppresses the Jahn-Teller effect and mitigates P2-O2 phase transitions, enhancing structural reversibility. The optimal K 0.05 Na 0.7 Ni 0.23 Mn 0.67 Cu 0.1 O 2 exhibits a high initial discharge capacity of 123.8 mAh·g −1 at 20 mA·g −1 and maintains 96.80 % capacity after 200 cycles at 200 mA·g −1 , outperforming single K-doped samples (89.83 % retention). Kinetic analyses reveal a sodium-ion diffusion coefficient of 1.06 × 10 −10 cm 2 ·s −1 , attributed to enlarged interlayers and reduced charge transfer resistance. In-situ XRD confirms minimal (002) peak shift (0.42°) during cycling, validating structural stability from K + -pinned interlayers. DFT calculations indicate that Cu doping induces spin-polarized half-metallic behavior, enhancing electron conductivity by increasing density of states near the Fermi level. This work presents a “dual-functional co-doping” strategy in which K + stabilizes interlayers and Cu 2+ optimizes the electronic structure, thereby simultaneously suppressing phase transitions and enhancing ion/electron transport. The proposed approach provides a scalable route for developing high-performance SIBs cathodes, which is crucial for advancing affordable and durable energy storage solutions.
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