Abstract
According to a long existing theory by Conway, the strikingly difference between supercapacitors (including pseudocapacitors) and rechargeable batteries can be unified under an electrochemical adsorption on 2-D or quasi-2-D electrode structures. The battery-like and capacitor-like behaviours differentiate themselves by the interaction between the charge couples (a group of molecules, ions, radicles, etc.). In this work, ab initio atomistic methods were used to calculate the interaction energy of the charge couples in 4 systems. The first is RuO
2
a typical redox system showing capacitor-like behaviour. The second is Prussian blue in an organic electrolyte. This is a redox system showing a battery-like behaviour. The third system is the anode of Li-ion battery or layered graphite with intercalation of lithium ion. The fourth is TiS
2
with intercalation of lithium ion showing a capacitor-like behaviour. With these four systems one can see transitions between capacitor-like and battery-like behaviours with both redox and intercalation charging mechanisms. A hybrid classic/ab initio molecular dynamics procedure was adopted to evaluate the microstructure of the charge couples in the electrode/electrolyte systems. Then, a perturbation was applied to the systems and the total chemical energy was evaluated using ab initio methods. The interaction forces were evaluated by conducting differentiation of the chemical energy on spatial coordinates. The study demonstrates that interaction between the charge couples plays an important role in charge/discharge processes in electrochemical energy storage systems. Based on the results, a perspective for developing new electrochemical energy storage systems is provided.