Hybrid Composites of LiMn2O4-Graphene as Rechargeable Electrodes in Energy Storage Devices

Abstract

In this study spinel-lithium manganese oxide (LiMn2O4) powders were prepared by using a simple sol-gel method with polyvinyl alcohol (PVA), and further combined with a conductive additive, graphene, to produce a composite electrode material for improved performance. The effects of the variation in the ratios of binder (PVA) to LiMn2O4 precursor on the particle size and electrochemical behavior of the composite were studied. Particle sizes of <200nm were obtained. An energy density of 17.36 Whkg-1 was obtained at an operating voltage of 3.2V for the pure LiMn2O4 sample tested against a graphene electrode. For simultaneously improving power density (current Li batteries have a low power density as a disadvantage) along with energy density, the LiMn2O4-graphene composite was chosen as an electrode material. LiMn2O4-graphene composite electrodes were prepared by electrophoretic co-deposition. The ratio of LiMn2O4-graphene composite was optimized to 1:1 during the electrode study based on its electrochemical performance. An average energy density of 30 Whkg-1, a specific capacity of 49mAhg-1, and an enhanced power density of 800 Wkg-1 at a discharge current of 0.5 Ag-1 were obtained. Discharge behavior improved evidently for tests performed on composite electrodes with increased LiMn2O4 (1:1.3 graphene/LiMn2O4). An improved average energy density of 59.6Whkg-1 was obtained along with a power density of 697Wkg-1. The electrodes showed good performance during study of a button cell device. Such electrodes are well suited for hybrid energy storage devices having good energy and power density and bridging the gap between batteries and supercapacitors.