Pore structure design of activated carbon microspheres by molten salt-assisted strategy for high energy density supercapacitors

Porous carbon is one of the preferred electrode materials for supercapacitors. Herein, hierarchically porous activated carbon microspheres (PACSs) are prepared by molten salt-assisted carbonization and CO₂ activation. In this strategy, the molten NaCl acts as a supplier of high energy Cl^-, which is responsible for etching the skeleton of the carbon material and creating more defects for subsequent CO₂ activation to construct a hierarchically porous structure in the activated carbon spheres, providing a large specific surface area (2087 m² g⁻¹) and high porosity (77.8% mesoporosity). When assembled into symmetric supercapacitor, the PACSs electrode exhibited a specific capacitance of 123 F g⁻¹ at 0.1 A g⁻¹ in organic electrolyte. Moreover, the device can display excellent cycling performance with a capacitance retention of 93.1% after 10,000 cycles and a high energy density of 25.66 Wh kg⁻¹ (at 61.17 W kg⁻¹). This study pioneers a new strategy for constructing hierarchically porous structure in carbon materials for energy storage devices.