Maximization of Spatial Charge Density: An Approach to Ultrahigh Energy Density of Capacitive Charge Storage.

Capacitive energy storage has advantages of high power density, long lifespan, and good safety, but is restricted by low energy density. Inspired by the charge storage mechanism of batteries, a spatial charge density (SCD) maximization strategy is developed to compensate this shortage by densely and neatly packing ionic charges in capacitive materials. A record high SCD (ca. 550 C cm ) was achieved by balancing the valance and size of charge-carrier ions and matching the ion sizes with the pore structure of electrode materials, nearly five times higher than those of conventional ones (ca. 120 C cm ). The maximization of SCD was confirmed by Monte Carlo calculations, molecular dynamics simulations, and in situ electrochemical Raman spectroscopy. A full-cell supercapacitor was further constructed; it delivers an ultrahigh energy density of 165 Wh L at a power density of 150 WL and retains 120 Wh L even at 36 kW L , opening a pathway towards high-energy-density capacitive energy storage.