Computational Cyclic Voltammetry of Supercapacitors

Sammanfattning: As the demand on electrochemical energy storage devices grows, more complex technologies are required, hence an improved knowledge on the microscopical level is needed. This can be achieved by using computational tools, in particular molecular simulations. Recent studies have shown that the commonly used electrode model fails to describe non perfect conductors simulated with molecular dynamics. The extended version of the polarizable electrode model, i.e., the Thomas-Fermi model includes a term to describe the characteristic screening length of the electrode material, hence the metalicity can be tuned. Herein, supercapacitors with electrodes described by the Thomas-Fermi model with a graphite like structure and an ionic liquid as the electrolyte are investigated. By performing cyclic voltammetry, it is found that the scan rate has less impact on the capacitance when the screening length is large and vice versa that the capacitance is little affected by the screening length at high scan rates. A comparison with a previous study made with an aqueous sodium chloride solution as the electrolyte shows that ionic liquids and aqueous sodium chloride are affected similarly by the metalicity of the electrode, although the ionc liquid is found to have a slower dynamics compared to aqueous sodium chloride.