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.

超级电容器作为能量载体具有高功率效率和长期稳定性的优点。其能量密度的提高有望弥补二次电池在高应用率下的弱点。在这里，我们报告了通过调整电极-电解质界面处的离子排列来提高超级电容器能量密度的尝试。通过经典密度泛函理论 (CDFT) 的理论分析，我们发现超级电容器的电容在电解质的中等浓度（即 1.0 M）处最大化，其中离子在电极表面附近积聚并显示出一些多层振荡分布。此外，通过调节电解液的介电常数和电极表面电压，调整界面离子分布以优化超级电容器的能量密度。理论结果得到了设计实验的证实，证实了界面离子分布在比电容中的作用。该研究表明，适当的界面离子分布有利于获得高电容，突出了一种提高超级电容器能量密度的不同寻常的解决方案。