The present project (COOLBATTERY) proposes a game-changing thermal management method for high-energy batteries, especially the Li-ion class which has captured the majority of the rechargeable battery market. This system is proposed to fill the main scientific and technological gap of high-energy batteries, i.e. optimal thermal management, to give them a new competitive edge for more significant impact and market share for a variety of energy storage applications in different sectors. The proposed innovation is an inter-layer thermal management sheet of high-performance materials to facilitate a strong yet uniform thermal flow between the cells while the temperature is within the safe range and to act as a thermal shield when a cell suddenly goes to high temperatures, preventing battery explosion or thermal runaway. COOLBattery pushes the state-of-the-art via i) establishing the theoretical foundation for calculation of performance and thermal stability degradation for Li-ion batteries in different states of charge and conditions, b) developing the most optimal design of the thermal management sheet, c) finding the optimal configuration of the battery when integrated with the cooling sheets, and d) techno-economic and environmental evaluation of the technology. The project will develop the fundamental theories and methods to design, optimize, and test this breakthrough technology. The outcome is a highly efficient Li-ion battery that will be a competitive candidate for efficient energy storage and management for a wide range of applications. The developed thermal sheet may also be further developed for lower and higher temperature ranges (and thus other critical thermal management processes) through future research building upon the cultivated knowledge in COOLBattery. The project will contribute to SDG-7 on clean and affordable energy; SDG-9 on industry innovation & infrastructure; and SDG-13 on climate action.