Heat exchanger with plates comprising a first series of passages for conducting at least one frigorigenic fluid and a second series of passages for conducting at least one calorigenic fluid, each passage being defined between two successive plates and extending parallel to a longitudinal axis, at least one mixing device arranged in at least one passage of the first series, said mixing device being configured to receive a liquid phase and a gaseous phase of the frigorigenic fluid and to distribute a mixture of said phases into said at least one passage. According to the invention, at least one passage of the second series adjacent to said at least one passage of the first series comprises a heat exchange structure divided in the longitudinal direction into at least a first portion and a second portion which are juxtaposed along the longitudinal axis, the second portion extending facing at least part of the mixing device, and being configured so as to present a heat exchange coefficient which is lower than the heat exchange coefficient of the first portion.