Reaction Mechanisms of MoO2/C Nanocomposite for Sodium Ion Storage

Abstract

Sodium ion batteries (SIBs) is considered a promising alternative candidate due to the abundant sodium resources in the earth’s crust [1]. Its working mechanism is similar to that of lithium ion batteries (LIBs), both experience intercalation and deintercalation of Li+ or Na+ into host electrode materials during charge/discharge [2]. The development of anode materials with relatively low redox potentials, high specific capacity and outstanding cycling stability is necessary to match with high performances of cathode materials, such as Na0.44MnO2 and Na3V2(PO4)3 [3]. In addition to hard carbon, which has demonstrated high performances for sodium ion storage, metal oxides as anode materials have been investigated with capability of storing sodium ion based on intercalation and conversion reactions [4]. MoO2/C nanocomposite has been studied in this work as an anode alternative for SIBs. MoO2 has low electrical resistivity (~10-5 Ω/cm in bulk sample) and high chemical stability [5], capable of reversible Na+ insertion and extraction with small volume change. However, working mechanism of MoO2 anode materials for SIBs is still far from being completely understood, and its cycleabiltiy and rate capability during sodium ion storage need to be significantly improved. In this work, our results demonstrate that nanostructured MoO2/C composite can deliver high capacity for sodium ion storage along with outstanding cycling stability and rate capability. Such a composite electrode shows intriguing mixed conversion and pseudocapacitive performances, depending on charge/discharge rates. The reaction mechanisms MoO2/C for SIB anodes will be discussed.