Coupling effect between ultra-small Mn₃O₄ nanoparticles and porous carbon microrods for hybrid supercapacitors

Hybrid supercapacitor, which is an energy storage device that combines a low-energy/fast double-layer electrode and a high-energy/sluggish faradaic redox electrode, could realize further gains in energy/power density if the capacity and rate gaps of the two electrodes are properly balanced. Herein, a microrod-like architecture that incorporates Mn₃O₄ nanoparticles on/in highly porous carbon rods (PCR) scaffold (denoted as Mn-PCR composite) is designed for this purpose. The optimized Mn-PCR composite exhibits large Li-ion storage capacity and fast charge/discharge rate, mainly stemming from its distinct microrod-like architecture and porous structure. We then employ Mn-PCR composite as the anode and PCR as the cathode to fabricate a hybrid supercapacitor, which yields an ultrahigh energy density of 174 W h kg⁻¹ at 200 W kg⁻¹ and retains 74.5 W h kg⁻¹ at a high power density of 10 kW kg⁻¹.