Hybrid and Flexible Nanocomposite Paper of Porous Mn3O4 Nanorod/Reduced Graphene Oxide for Lithium Ion Battery Anode

Abstract

Advanced energy storage systems have attracted much attention due to the concerns about limited energy supply and renewable energy utilization. Li-ion batteries (LIBs) are becoming one of the more popular energy storage systems for portable electronic devices and electric vehicles owing to its long lifespan, high energy density, and environmental benignity. Graphitic carbon is still the only commercially available anode material for LIBs and exhibits a low theoretical specific capacity of 372 mA h g−1. To meet the stringent demand for LIBs with higher energy and power densities, a lot of research effort goes into developing advanced electrode materials. Manganese oxide (Mn3O4) is a promising anode material because of its much higher theoretical lithium storage capacity (936 mA h g−1), low price, and natural abundance. However, its real application as anode material for LIBs is suffering from several challenges, such as low electrical conductivity and remarkable volume expansion in the Li+insertion/extraction, thus leading to significant capacity loss, poor cycling and poor rate performance. To circumvent these limitations, recent approaches have focused on engineering new nanostructures of manganese oxide, such as nanorods, nanowires and sponge-like shapes to alleviate pulverization. To date, significant efforts have been made to fabricate graphene-based anode materials without conductive carbon and polymer binders. A paper-like graphene film prepared by vacuum filtration is a typical electrode without any additives. However, due to the strong van der Waals interaction, the graphene paper shows much lower surface area compared with real graphene, which leads to a low reversible capacity. To avoid the restacking, previous researches have introduced guest materials such as metal oxides and polymers into the graphene sheets. In this study, the hybrid and flexible nanocomposite paper consisting of porous Mn3O4 nanorods/reduced graphene oxides (pMn3O4 NR/rGO) was prepared by using vacuum filtration and thermal treatment. Graphene oxides (GO) and MnOOH nanorods (MnOOH NR) were synthesized by the modified Hummers’ method and hydrothermal reaction. The MnOOH nanorods/graphene oxides (MnOOH NR/GO) paper was first vacuum-filtered and thermally reduced to generate a pMn3O4 NR/rGO paper in N2 atmosphere. The as-prepared pMn3O4 NR/rGO nanocomposite paper with a three-dimensional (3D) structure shows that the pMn3O4 nanorods are homogeneously dispersed within rGO layers. This 3D hybrid nanocomposite paper can not only provide the pathway for Li+ diffusion and electron transfer but also a large contact area between the active materials and electrolytes. In addition, the rGO layers function as a buffer layer to prevent the pulverization of pMn3O4 NRs. When electrochemical tests were performed by using a pMn3O4 NR/rGO paper as an anode in LIBs, a first discharge capacity of 943 mA h g-1 is delivered and maintains 573 mA h g-1 even after 100 cycles at a current density of 100 mA g-1.