Tuning interfacial ion distribution to improve energy density of supercapacitors

Supercapacitors as energy carriers have the advantages of high-power efficiency and long-term stability. An improvement of their energy density promises a solution to make up for the weakness of secondary batteries at a high rate of applications. Here we report an attempt to improve the energy density of supercapacitor by tuning ions arrangement at the electrode-electrolyte interface. Upon the theoretical analysis with classical density functional theory (CDFT), we find that the capacitance of the supercapacitor is maximized at a mediate concentration of electrolytes, i.e., 1.0 M, where ions accumulate near the electrode surface and display a few multilayered oscillatory distributions. Further, by adjusting the dielectric constant of electrolyte solution and the electrode surface voltage, the interfacial ion distribution is tuned to optimize the energy density of supercapacitors. The theoretical results are corroborated by designed experiments, confirming the role of interfacial ion distribution in specific capacitance. This study shows that an appropriate interfacial ion distribution is beneficial to obtaining high capacitance, highlighting an unusual solution to improve the energy density of supercapacitors.