High-voltage planar supercapacitors enabled by Mn-MOF and ionic liquid synergy for high energy-density storage

The combination of pseudocapacitive electrodes with ionic liquid (IL) electrolytes demonstrates a significant synergistic effect in expanding the potential window of supercapacitors, thereby enhancing the energy density of the device. Mn 3 (HHTP) 2 , a metal-organic framework (MOF) with high-density redox-active sites and hierarchical porosity, serves as the electrode material paired with [EMIM][BF 4 ] and [EMIM][TFSI] IL electrolytes. The ion size in [EMIM][TFSI] can be precisely aligned with the electrode pore size, thereby reducing interfacial resistance and enhancing ion accessibility. Optimizing the [EMIM][TFSI]/acetonitrile mass ratio to 4:6 achieves superior electrolyte properties, including an ionic conductivity of 50.4 mS cm −1 and viscosity of 5.24 mPa·s. This design extends operating potential from 8 V to 13 V, increasing energy density to 108.0 Wh kg −1 , representing a 68.8 % improvement over baseline systems. The device retains 94.34 % capacitance after 2000 cycles at 8 V, with specific capacitances of 7.2 F g −1 at 8 V and 4.6 F g −1 at 13 V. These findings establish a new paradigm for interface engineering in high-voltage supercapacitors.