Ni-Fe共掺LiMn_(2)O_(4)正极材料的合成及电化学性能研究

Synthesis of Ni-Fe co-doped LiMn_(2)O_(4) cathode material and its electrochemical performance

采用固相燃烧法快速合成了LiNi_(0.08)Fe_(x)Mn_(1.92-x)O_(4)(x≤0.08)正极材料,并探究了正极材料样品的结构、形貌、电化学性能及动力学性能。结果表明,Ni-Fe共掺没有改变LiMn_(2)O_(4)的立方尖晶石结构,促进了其晶体发育和{111}、{110}、{100}晶面的择优生长,部分颗粒形成了以高暴露{111}晶面为主和少量{110}、{100}晶面的截断八面体形貌。LiNi_(0.08)Fe_(0.05)Mn_(1.87)O_(4)样品在较低倍率(≤5 C)时,其倍率性能和长循环寿命得到显著提高,在25℃下,1 C的首次放电比容量为106.1 mAh/g, 1 000次循环后容量保持率为82.0%;5 C的首次放电比容量为100.1 mAh/g, 2 000次循环后容量保持率为72.8%。LiNi_(0.08)Fe_(0.05)Mn_(1.87)O_(4)材料的锂离子扩散系数和表观活化能分别为1.75×10^(-15)cm^(2)/s和26.52 kJ/mol,表明其有较好的Li+迁移动力学性能。

LiNi_(0.08)Fe_(x)Mn_(1.92-x)O_(4)(x≤0.08)cathode material is rapidly synthesized via solid-state combustion method.The structure,morphology,electrochemical performance,and kinetic performance of the material samples are investigated.The results show that LiNi_(0.08)Fe_(0.05)Mn_(1.87)O_(4) cathode material has a cubic spinel structure,which promotes the crystal development of LiMn_(2)O_(4) and the preferential growth of{111},{110}and{100}crystal planes.Some particles form a truncated octahedron shape with highly exposed{111}crystal planes and a small amount of{110}and{100}crystal planes,which significantly improves the rate capability and long cycle life of the material at lower rates(≤5 C).At 25℃,the material has an 106.1 mAh·g^(-1) of 1 C initial discharge specific capacity,and a 82.0%of capacity retention rate after 1,000 cycles.At 5 C,it has a 100.1 mAh·g^(-1) of initial discharge specific capacity and a 72.8% of capacity retention rate after 2,000 cycles.The lithium ion diffusion coefficient and apparent activation energy of LiNi_(0.08)Fe_(0.05)Mn_(1.87)O_(4) material are 1.75×10^(-15) cm^(2)·s^(-1) and 26.52 kJ·mol^(-1),respectively,representing a good Li+migration kinetics.