Fabrication of High-Performance Aqueous Li-Ion Hybrid Capacitor with LiMn2O4 and Graphene

In this study, we fabricated an aqueous Li-ion hybrid capacitor (LHC) by using LiMn2O4 and sonochemically reduced graphene as the positive and negative electrodes, respectively. The X-ray diffraction pattern and Raman analyses were performed to identify the phase, crystallinity, and bonding nature of the prepared LiMn2O4 and sonochemically reduced graphene. Electrochemical characterization, such as cyclic voltammetry and electrochemical impedance spectroscopy, for the LiMn2O4 and graphene was performed by using a three-electrode configuration. Furthermore, asymmetric LiMn2O4 vertical bar graphene LHC was fabricated and tested for its device performance. The galvanostatic charge-discharge analysis shows that the fabricated LiMn2O4 vertical bar graphene LHC device delivered a high specific capacitance of 59.45Fg(-1) at a constant discharge current density of 0.4Ag(-1) with a better coulombic efficiency of 97.9%. The LiMn2O4 vertical bar graphene LHC device delivered a high specific energy of 39.96Whkg(-1) at a power of 440Wkg(-1) with better capacitance retention of 90.24% even after 1000 cycles.