Identification of reversible insertion-type lithium storage reaction of manganese oxide with long cycle lifespan

Abstract

Abstract Recently, MnO2 has gained attention as an electrode material because of its very high theoretical capacity and abundant availability. However, the very high volumetric change caused by its conversion-type reaction results in bad reversibility of charge-discharge. In this study, δ-MnO2 of thickness 8 nm anchored on the surface of carbon nanotubes (CNT) by Mn-O-C chemical bonding is synthesized via a facile hydrothermal method. Numerous ex-situ characterizations of the lithium storage process were performed. Furthermore, density functional theory (DFT) calculations indicated that δ-MnO2 (0 1 2) thermodynamically prefers bonding with CNTs. Moreover, the interfacial interaction reinforces the connection of Mn-O and reduces the bond strength of Li-O in lithiated MnO2, which could facilitate an intercalation-type lithium storage reaction. Consequently, the as-synthesized δ-MnO2 retains an excellent reversible capacity of 577.5 mAh g − 1 in 1000 cycles at a high rate of 2 A g − 1 between 0.1 V and 3.0 V. The results of this study demonstrate the possibility of employing the cost-effective transition metal oxides as intercalation lithium storage dominant electrodes for advanced rechargeable batteries.