Effects of asymmetric ion sizes and valences on the structure of the electric double layer near electrode

Understanding the electric double layer (EDL) near electrode is crucial for utilizing electrical devices including supercapacitors and batteries. The EDL structure is expected to depend on the sizes and valences of accompanying ions. The sizes of ions determine the maximum packing density, while the valences of ions determine the strength of electrical interactions. In this work, we study the EDL structure of ions of which sizes and valences are asymmetric using the continuum approach. Firstly, we propose the asymmetric ion distribution as a function of electric potential. The EDL structure and the stress exerted on electrodes can be obtained from its solution. Secondly, the equation of asymmetric ion dynamics is solved for confined slit, with certain potential difference imposed between two ends. The charging rate of EDL depends on the size and valence of the counter-ions. The asymmetric potential drop across the EDL is explained along with its ion density distribution.