锂改性尖晶石锰酸锂的循环伏安特性及其电化学性能研究

Cyclic Voltammetry and Electrochemical Properties of LiMn_2O_4 and Li_2CO_3 Modified LiMn_2O_4

用LiMn2O4和碳酸锂制备了锂改性的锰酸锂产物,循环性能和比容量测试结果表明随着碳酸锂加入量的增加,循环稳定性逐渐增强,而比容量有逐渐下降的趋势。循环伏安测试结果表明,LiMn2O4及其改性产物具有两对氧化还原峰。随着碳酸锂加入量的增加,两对氧化峰和还原峰峰电位差呈逐渐下降趋势,说明了锂脱嵌的可逆性越来越好;氧化(或还原)峰之间的分形变得不明显,峰形逐渐宽化,说明锂离子两步脱嵌过程变得越来越不明显。研究表明锂离子脱出和嵌入的总量随着碳酸锂量的增加而减少。XRD结果显示,随着碳酸锂加入量的增大,晶格常数逐渐降低,晶格逐渐收缩,结构稳定性增强。

Li2CO3 modified LiMn2O4 was prepared by solid reaction of spinel LiMn2O4 and Li2CO3. The cycling performances and charge/discharge capacities reveal that, as the Li ^＋ amount increases, cycling stability of modified LiMn2O4 is enhanced with a slight reduction in the initial capacity. It can be seen that the cyclic voltammetry profiles have two oxidation and reduction peaks, which indicate the two processes during both intercalation and deintercalation of lithium ions. The voltage difference between each pair of oxidation/reduction peaks is lessened with growing amounts of reactant Li2CO3, which suggests that the reversibility of lithium ions during insertion/extraction is improved. The borderlines of the two stages become illegible since the two oxidation （or reduction） peaks become less distinct and the oxidation （or reduction） peak profiles are widened. Further analyses show that the sum of Li ions during insertion/extraction is reduced as the Li^＋/Mn amount rises. The XRD results reveal that the insertion of Li ions enhances the spinel structure stability since the crystal lattice shrinks for the reduction of unit cell constant.