Fig. 3

Negative dielectric constant of confined water. a, b Theoretical calculation for the electrostatic potential profile of Rb⁺- and Li⁺-intercalated Ti₂CT_x·nH₂O. c, d Schematic illustrations of the charge density (ρ), the strength of the electric field (E), and the electrostatic potential (Φ) of weakly hydrated cations and strongly hydrated cations confined in a microslit supercapacitor as a function of the spatial coordinates. The arrows indicate the direction of the water dipole moments