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 LiMn 2 O 4 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 LiMn 2 O 4 and sonochemically reduced graphene. Electrochemical characterization, such as cyclic voltammetry and electrochemical impedance spectroscopy, for the LiMn 2 O 4 and graphene was performed by using a three‐electrode configuration. Furthermore, asymmetric LiMn 2 O 4 ∥graphene LHC was fabricated and tested for its device performance. The galvanostatic charge‐discharge analysis shows that the fabricated LiMn 2 O 4 ∥ graphene LHC device delivered a high specific capacitance of 59.45 F g −1 at a constant discharge current density of 0.4 A g −1 with a better coulombic efficiency of 97.9 %. The LiMn 2 O 4 ∥graphene LHC device delivered a high specific energy of 39.96 Wh kg −1 at a power of 440 W kg −1 with better capacitance retention of 90.24 % even after 1000 cycles.