A systematical and atomic scale investigation on the fundamental mechanism of Mn doped LiFePO₄ is conducted in this work. For the first time, it is found that the doping depth of Mn on the surface of LiFePO₄ is 10–15 nm. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) results further on the atomic scale demonstrate that Mn doping could effectively protect the crystal structure of LiFePO₄ from being corroded by the electrolyte during electrochemical cycling. Density functional theory (DFT) calculations suggest that the Mn doped LiFePO₄ could be regarded as a composite with LiFePO₄ bulk as the core and LiMn_xFe_1−xPO₄ as the outer layers. Unlike pure LiFePO₄, the Mn doped olivine LiFePO₄ (LiMn_xFe_1−xPO₄) is more stable and less susceptible to phase transition related amorphization, and thus could serve as a protective shell against LiFePO₄ degradation during electrochemical cycling.

中文翻译：

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原子尺度研究锰掺杂LiFePO4的基本机理

在这项工作中，对Mn掺杂的LiFePO ₄的基本机理进行了系统的原子尺度研究。首次发现LiFePO ₄表面上Mn的掺杂深度为10-15 nm。高角度环形暗场扫描透射电子显微镜（HAADF-STEM）的原子级结果进一步表明，Mn掺杂可有效保护LiFePO ₄的晶体结构在电化学循环过程中不受电解质的腐蚀。密度泛函理论（DFT）计算表明，可以将掺杂Mn的LiFePO ₄视为以LiFePO ₄块体为芯，LiMn _x Fe _{1- x}的复合材料。PO ₄作为外层。不同于纯LiFePO ₄，掺杂Mn的橄榄石LiFePO ₄（LiMn _x Fe _{1- x} PO ₄）更稳定，更不易发生与相变有关的非晶化，因此可作为保护壳，防止电化学循环中LiFePO ₄降解。