According to Xiaomi, the Mi 11 Ultra will feature new battery technology and a revolutionary cooling system. Apparently, the so-called phase-change cooling system contains solid, liquid and gas parts to deliver significantly better cooling performance than contemporary Xiaomi smartphones.
https://www.notebookcheck.net/Xiaomi-teases-phase-change-cooling-system-for-the-Mi-11-Ultra-ahead-of-its-March-29-launch.529856.0.html