We report AC-impedance studies on a series of high-quality LiMn_1−xFe_xPO₄ single crystals with 0 ≤ x ≤ 1. Our results confirm quasi-one-dimensional transport in LiFePO₄ with fast Li-diffusion along the b-axis. The conductivities along the crystallographic b-, c- and a-axis differ by a factor of about 10, respectively. Whereas, the activation energy E_A of the effective diffusion process is particularly large for the b-axis and smallest for the a-axis. Remarkably, the b-axis ionic bulk conductivity of LiMn_0.5Fe_0.5PO₄ is of the same order of magnitude as in undoped LiFePO₄, which implies similarly fast Li-transport even upon 50% Mn-doping which, owing to the higher redox potential of the Mn³⁺/Mn²⁺-couple, yields enhanced energy density in lithium-ion batteries. The overall results of our impedance studies draw a far more complex picture than it would be expected from a simple one-dimensional ionic conductor. Our results suggest a strong contribution of crystal defects in actual materials.

我们一系列的高质量的报告交流阻抗研究的LiMn _{1- X}铁_X PO _4个单晶与0≤ X ≤1。我们的研究结果证实准一维运输磷酸铁锂₄沿快速锂扩散b -轴。沿晶体学b-，c-和a轴的电导率相差约10倍。鉴于，活化能Ë_阿为有效扩散过程的特别大b -轴和最小的为一轴。值得注意的是，bLiMn _0.5 Fe _0.5 PO _4的轴向离子体电导率与未掺杂的LiFePO _4相同，这意味着即使在掺杂50％的Mn时，Li的传输速度也相似，这是由于Mn的氧化还原电势较高³⁺ / Mn 2 ^+-耦合可提高锂离子电池的能量密度。我们的阻抗研究的总体结果比简单的一维离子导体所预期的要复杂得多。我们的结果表明，实际材料中的晶体缺陷有很大的贡献。