掺Co^(3+)和Li^+的LiMn_2O_4晶体结构和电化学性能研究

Structural and Electrochemical Properties of Li^+ and Co^(3+)-Codoped LiMn_2O_4

以尖晶石LiMn2O4,Li2CO3和Co3O4为原料,采用固相烧结法合成了尖晶石锰酸锂的改性产物。X射线粉末衍射分析表明,改性产物保持了LiMn2O4的立方尖晶石结构。采用Rietveld方法进行结构精修表明,掺杂元素进入了晶胞中的16d位置,改性产物结构分子式可写成[Li]8a[Mn2-xLix/4Co3x/4]16d[O4]32e。随着钴和锂掺杂量的增加,产物16d位置中更多的锰被取代,锰离子平均价态逐渐升高,锰和氧的结合键能增加,键长下降,晶格参数减小。电性能测试表明,锰酸锂掺杂钴、锂后,循环稳定性提高,比容量稍有降低。当锂、钴掺杂量为锰酸锂的0.025倍时,综合性能最佳。

The li^＋,Co^3＋ codoped LiMn2O4 was prepared by intimately mixing the right amounts of spinel LiMn2O4, Li2CO3 and Co3O4 with solid-state reaction. All the XRD patterns were identified as a single-phase spinel structure. Rietveld refinements of their XRD data revealed that the manganese ions in the 16d sites were replaced by both lithium and cobalt ions, the composition of modified LiMn2O4 could be expressed as the new spinel formula [Li]s4[Mn2-x Lix/4Co3x/4]16a[O4]32e. As the Li^＋ , Co^3＋ amounts increased, more manganese ions were replaced and their average oxidation state raised, which led to shorter bond distances and smaller cell parameters. The charge/discharge tests indicated that the inclusion of lithium and cobalt ions enhanced the electrochemical cycle ability at the expense of a slight reduction in the initial charge capacity. When the ratio of Co ： Mn is 0. 025 ： 1, the electrochemical property is optimum.