LiFexMn1-xPO4固溶体的密度泛函理论与电化学研究

本文用DFT计算方法研究了LiFe_xMn_1-xPO₄的热力学稳定性和嵌/脱锂电位. 结果表明，LiFe_xMn_1-xPO₄固溶体的自由能比相分离的LiFePO₄/LiMnPO₄混合物略高，这两种形式可能在实际LiFe_xMn_1-xPO₄材料中共存. 计算表明，LiFe_xMn_1-xPO₄固溶体的嵌/脱锂电位随锰/铁比以及过渡金属离子的空间排列而变化，并用计算结果解释了放电曲线的形状. 采用固相反应法合成了LiFe_xMn_1-xPO₄材料并研究了其电化学性质，实验中观察到附加的放电平台，其出现可能与LiFe_xMn_1-xPO₄固溶体的存在有关.

Density Functional Theory and Electrochemistry Studies on LiFexMn1-xPO4 Solid Solutions

The thermodynamic stability and lithiated/delithiated potentials of LiFe_xMnfeng_1-xPO₄ were studied with density functional theorical calculations. The results show that the formation free energy of the LiFe_xMn_1-xPO₄ solid solution is slightly higher than that of the phase-separated mixture of LiFePO₄ and LiMnPO₄, and the two forms may co-exist in the actual LiFe_xMn_1-xPO₄ materials. The calculation manifests that the lithiated/delithiated potentials of LiFe_xMn_1-xPO₄ solid solutions vary via the Mn/Fe ratio and the spatial arrangements of the transition metal ions, and the result is used to explain the shape of capacity-voltage curves. Experimentally, we have synthesized the LiFe_xMn_1-xPO₄ materials by solid-phase reaction method. The existence of the LiFe_xMn_1-xPO₄ solid solution is thought to be responsible for the appearance of additional capacity-voltage plateau observed in the experiment.