An ion exchange matrix was a device that could be used to link power cells.
In 2373, an ion exchange matrix was found aboard a crashed Jem'Hadar fighter. Later, Jadzia Dax suggested she and Worf examine it in order to ease tensions between Worf and Miles O'Brien who were at odds as to the injured Enrique Muniz's chances for survival. (DS9: "The Ship")
The following year, O'Brien lacked an ion exchange matrix which he needed to build a converter to bridge the power cells from type 2 phasers to his proposed makeshift transmitter, after the above Jem'Hadar fighter had again crashed and Benjamin Sisko and his crew were stranded. (DS9: "Rocks and Shoals")