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

Capacitive energy storage possesses the advantages of high power density, long lifespan, and good security, but is severely restricted by its low energy density. Inspired by the charge storage mechanism of batteries, we develop a spatial charge density (SCD) maximization strategy to compensate this shortage by densely and neatly packing the ionic charges in capacitive materials. Accordingly, a record high SCD of ~550 C cm-3 was achieved by balancing the valance and size of charge-carrier ions and matching the ion sizes with the pore structure of electrode materials, which is nearly five times higher than those of conventional ones (~120 C cm-3 ). The maximization of SCD was confirmed by Monte Carlo calculations, molecular dynamics simulations, and in situ electrochemical Raman spectroscopy. As a result, a full-cell supercapacitor was constructed and it delivers an ultrahigh energy density of 165 W h L-1 at the power density of 150 W L-1 , and retains 120 W h L-1 even at 36 kW L-1 , opening a pathway towards high energy density capacitive energy storages.