Device and method for storing energy

The invention relates to a method and to a device (10) for storing energy, said device comprising: at least one first container (12), which has a first holding space (14), a separating apparatus (16), which is arranged in the first container (12) and by means of which the first holding space (14) is divided into a first chamber (20) for holding a first medium and a second chamber (22) for holding a gas phase, wherein the separating apparatus (16) can be moved in relation to the first container (12) while at the same time the volume of the chambers (20, 22) is changed, at least one second container (24), which has a second holding space (26) connected to the second chamber (22), the content (30) of which second holding space is in mass exchange with the gas phase, a temperature-control apparatus (32), by means of which thermal energy can be fed to the second container (24) and removed from the second container (24), at least one conveying apparatus (36), by means of which the medium can be conveyed into the first chamber (20) with a specified pressure while at the same time heat is removed from the second container (24) by means of the temperature-control apparatus (32), and at least one expansion apparatus (46), which can be driven by the medium held under pressure in the first chamber (20) while at the same time heat is fed into the second container (24) by means of the temperature-control apparatus (32).