The invention relates to an electrochemical device (1) having electrically controllable optical and/or energy transmission properties, of the type comprising two electrode coatings (4, 6) and, between them, an electrochemically active layer (6) made of an inorganic material capable of reversibly switching between two states having different optical and/or energy transmission properties by the insertion and extraction of ions. An electrolyte (8) is present between the electrochemically active layer and the second electrode coating. The material of the electrochemically active layer is a material, the insertion and extraction of the ions of which during switching between the two states correspond to a variation in the plasma wavelength λ of the material and in that the material has, at the plasma wavelength λ, a full width at half maximum Δλ of the absorption spectrum equal to or less than 1 micron in the two states.