The capacitance increase observed in nanoporous carbons opens the door for new optimisations of supercapacitors. The purpose of this work is to understand the microscopic phenomena at the origin of this capacitance increase. We use molecular dynamics to simulate model supercapacitors. Our simulations are original in various ways : we represent the electrolyte by a coarse-grained model and the electrodes, which are held at constant electrical potential, by a complex porous structure. From our simulations, we show that the capacitance increase results from a strong modification of the liquid structure at the interface with the electrode. More precisely, the confinement prevents the formation of successive layers of liquid which tend to decrease the charge storage efficiency. We also present various methods to determine the capacitance by molecular dynamics simulations. The use of a complex porous structure and the inclusion of electrode polarisation effects allow us to caracterise precisely the correlation between confinement and charge storage efficiency. Finally, we study the dynamic phenomena occurring in supercapacitors, the latter work allowing one to consider the characterisation of the supercapacitors power by molecular dynamics in the future.
