亚微米LiFe0.05Mn1.95O4正极材料的制备及电化学性能

采用固相燃烧法合成了亚微米单晶多面体LiFe_0.05Mn_1.95O₄正极材料。借助XRD、FE-SEM、TEM、XPS和恒电流充放电等手段对样品的结构、形貌、物相组成和电化学性能进行测试。结果表明，Fe掺杂未改变尖晶石型LiMn₂O₄的立方晶系结构，其{400}和{440}衍射峰相对应的晶面出现显著的择优生长，形成了形貌为{111}、{110}和{100}晶面的单晶去顶角八面体晶粒。LiFe_0.05Mn_1.95O₄正极材料表现出比纯LiMn₂O₄材料更为优异的电化学性能，在1C和5C时有着114.7mA·h/g、104.7mA·h/g首次放电比容量，10C倍率下经1000次循环后，容量保持率为83.9%。循环伏安与阻抗分析得出掺杂后的样品有着较大的锂离子扩散系数与较小的活化能。对5C倍率循环1000次后Fe掺杂样品的极片分析发现，其晶体结构基本无变化，适量的Fe掺杂能够有效抑制尖晶石型LiMn₂O₄在充放电循环过程中的Jahn-Teller效应以及Mn的溶解，提升材料的结构稳定性与容量保持率。

Synthesis and electrochemical performance of submicron LiFe0.05Mn1.95O4 cathode material

The cathode material of submicron LiFe_0.05Mn_1.95O₄ single crystal was synthesized by a solid state combustion method. The structure, morphology, phase composition and electrochemical performance of the sample were investigated by XRD, FE-SEM, TEM, XPS and galvanostatic charge and discharge. The results showed that, Fe-doping did not change the cubic crystal structure of spinel LiMn₂O₄, but the crystal surface corresponding to {400} and {440} diffraction peak exhibited a significant selective growth, and the single crystal deciding-angle octahedral grains with the morphologies of {111}, {110} and {100} crystal surface were formed. The LiFe_0.05Mn_1.95O₄ cathode material exhibited better electrochemical performance than the undoped sample of LiMn₂O₄. The initial specific discharge capacities were 114.7mA·h/g and 104.7mA·h/g at 1C and 5C, respectively. The capacity retention was 83.9% at 10C after 1000 cycles. By analyzing the cyclic voltammogram and electrochemical impedance spectroscopy, we found that the Fe-doped sample possessed large lithium ion diffusion coefficient and low apparent activation energy. The spinel structure of the sample's electrode slice was almost unchanged after 1000 cycles at 5C. Appropriate Fe-doping can effectively inhibit the Jahn-Teller effect and the Mn dissolution of spinel LiMn₂O₄ in the process of charge and discharge cycles, and hence improve the capacity retention and structural stability of the material.