Aggregation of polyoxometalates (POM) is largely responsible for the reduced performance of POM-based energy-storage systems. To address this challenge, here, the precise confinement of single Keggin-type POM molecule in a porous carbon (PC) of unimodal super-micropore (micro-PC) is realized. Such precise single-molecule confinement enables sufficient activity center exposure and maximum electron-transfer from micro-PC to POM, which well stabilizes the electron-accepting molecules and thoroughly activates its inherent multi-electron redox-activity. In particular, the redox-activities and electron-accepting properties of the confined POM molecule are revealed to be super-micropore pore size-dependent by experiment and spectroscopy as well as theoretical calculation. Meanwhile, the molecularly dispersed POM molecules confined steadily in the "cage" of micro-PC exhibit unprecedented large-negative-potential stability and multiple-peak redox-activity at an ultra-low loading of ~11.4 wt%. As a result, the fabricated solid-state supercapacitor achieves a remarkable areal capacitance, ultrahigh energy and power density of 443 mF cm⁻², 0.12 mWh cm⁻² and 21.1 mW cm⁻², respectively. This work establishes a novel strategy for the precise confinement of single POM molecule, providing a versatile approach to inducing the intrinsic activity of POMs for advanced energy-storage systems.