Abstract: Devices and methods for using phase-change-materials to store and retrieve energy. Specifically, the invention discloses various containment devices that may be used to enclose a mass of phase-change-material. The disclosure describes ways it which these devices may be manufactured and ways in which they may be used. The storage devices preferably create an enclosed volume that eliminates any mixing between the phase-change material and any surrounding material such as thermal oil. Further, the invention minimizes the inclusion of unwanted materials such as air.