Spinel LiMn2O4 Cathodes Controlled Mn Oxidation State of Surface Layerfor Li-ion Batteries

Abstract

For large scale application of battery, lithium manganese oxide, LiMn2O4 has been in the spotlight as a promising alternative choice to LiCoO2 in the view point of performances as well as cost. Nevertheless, LiMn2O4 still has a problem to be solved; severe capacity fading upon extended electrochemical cycling, especially at elevated temperature originated from Mn3+ dissolution. Poor cycling behavior can be enhanced by partial cationic substitution (increase average oxidation state of Mn ion above 3.5+) and surface coating method. However, these methods bring out the reduction in capacity with increasing doping and coating level, also thicker coating layer acts as insulator which increases the cell resistance. In this work, to overcome these problems, we presented for developing new high capacity and high stability LiMn2O4 spinel by controlling oxidation states of Mn ion. Stoichiometric LiMn2O4 whose oxidation states of manganese is about +3.5 was coated with Li1+xMyMn2-x-yO4 (oxidation states of Mn ion: +3.85) using various substitute such as Co, Ni and Al. The LiMn2O4 in the core enabled spinel to deliver the high capacity and the surface layer epitaxially gown on the stoichiometric LiMn2O4 guarantees the stability of structure at 60℃ as well as contributes on capacity. These cathode materials exhibited the initial discharge capacity over ~120 mA∙h g-1. Li1+xCoyMn2-x-yO4-coated LiMn2O4 among the coated cathode materials demonstrated the excellent electrochemical performance, corresponding to 77% capacity retention after 100th cycles at the severe test condition of 60℃ and improved the rate capability compared to those of the bare LiMn2O4.