As one of the most promising cathodes for Li-ion batteries, Li-rich layered oxides suffer from low Coulombic efficiency, severe capacity fading, and voltage decay, which are related to the aggregated Li@Mn₆ superstructure units. Herein, a Co-free Li-rich oxide Li[Li_1/4Mn_1/2Ni_1/6Al_1/12]O₂ through Al substitution of Co in Li[Li_1/4Mn_1/2Ni_1/6Co_1/12]O₂, is designed. Combining the average structural refinement with the detailed local structural/chemical analysis, it is found that the introduced Al ions occupy the Mn sites in Li@Mn₆ superstructure units, which further induces the partial replacement of the central Li ions in Li@Mn₆ units by Ni²⁺. The modified superstructure units stabilize the anionic framework and suppress structural degradation during long-term cycling. A superior cyclability (a capacity retention of 91.4% after 500 cycles at 1 C) is achieved. This work not only deepens the understanding into the mechanism of Al substitution, but also provides a novel route to design high-performance Li-rich cathodes by modifying the local functional units.

中文翻译：

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通过 Al 替代修饰 Li@Mn6 上层结构单元以提高无钴富锂正极的长循环性能

作为锂离子电池最有前景的正极材料之一，富锂层状氧化物存在库仑效率低、容量衰减严重和电压衰减等问题，这与聚合的 Li@Mn ₆超结构单元有关。在此，无钴富锂氧化物Li[Li _1/4 Mn _1/2 Ni _1/6 Al _1/12 ]O ₂通过Al取代Li[Li _1/4 Mn _1/2 Ni _{1/ 6} Co _1/12 ]O ₂，设计。将平均结构细化与详细的局部结构/化学分析相结合，发现引入的 Al 离子占据了 Li@Mn _{6 中}的 Mn 位点超结构单元，这进一步诱导 Li@Mn ₆单元中的中心锂离子被 Ni ²⁺部分取代。改性的超结构单元稳定阴离子骨架并抑制长期循环过程中的结构降解。实现了优异的循环性能（1 C 下 500 次循环后容量保持率为 91.4%）。这项工作不仅加深了对 Al 取代机制的理解，而且为通过修改局部功能单元来设计高性能富锂正极提供了一条新途径。