  An electric double layer capacitor (EDLC) stores energy by modulating the
spatial distribution of ions in the electrolytic solution that it contains. We
determine the mean-field time scales for planar EDLC relaxation to equilibrium,
after a potential difference is applied. We tackle first the fully symmetric
case, where positive and negative ionic species have same valence and
diffusivity, and then the general, more complex, asymmetric case. Depending on
applied voltage and salt concentration, different regimes appear, revealing a
remarkably rich phenomenology relevant for nanocapacitors.
