U.S. patent application 20180159189 (applicant Advanced Energy Technologies LLC, Lakewood, Ohio):
"A lithium ion battery pack includes a plurality of prismatic lithium polymer cells and one or more graphite heat spreaders. Each spreader has at least two major surfaces and is made of one of a sheet of a compressed mass of exfoliated graphite particles, a graphitized polyimide sheet, or combinations thereof. ... In any of the above embodiments, at least one of the spaces between adjacent heat spreaders 36 or between the heat spreader 36 and an adjacent cell 32 may be at least partially filled with a layer of a phase change material."