High-Performance Mg-Ion Supercapacitor Designed with a N‑Doped Graphene Wrapped CoMn2O4 and Porous Carbon Spheres

Mg-ion supercapacitors (SCs) can be a potential candidate for advanced electrochemical energy storage devices because they are low-cost and safe and have long-term cycling stability. However, exhibiting high energy density while preserving high power density is still a challenge for Mg-ion supercapacitors, which limits their practical applications. Herein, we proposed cathode CoMn2O4 nanospheres embedded in N-doped graphene (CMO/G-N) and prepared via an improvised hydrothermal route. The material exhibited a capacitance of 691 F g–1 (1059 F cm–3) at 0.5 A g–1 in an aqueous Mg­(ClO4)2 electrolyte. Additionally, as fabricated, the flexible Mg-ion asymmetric supercapacitor CMO/G-N//PCS (FMASC) exhibits energy and power densities of 61 and 34 W h kg–1 at 123 and 7407 W kg–1, respectively, with 87% retention of capacitance after 10,000 cycles. This study provides a neoteric perspective on building flexible energy storage devices using novel Mg-ion electrolytes.