The method for fabricating an electrochemical device includes the following successive steps: a first stack successively including a first electrode and an electrically insulating electrolyte having a first main surface in contact with the first electrode and an opposite second main surface; a polymerisation step of the electrolyte so as to define at least a first area presenting a first degree of cross-linking and a first cross-linking density and a second area presenting a second degree of cross-linking different from the first degree of cross-linking and/or a second cross-linking density different from the first cross-linking density, said at least first and second areas connecting the first main surface with the second main surface; and placing the second electrode in contact with the electrolyte.