Towards high-performance sorption cold energy storage and transmission with ionic liquid absorbents

The shortcomings of conventional working pairs in thermal energy storage and transmission based on absorption cycle have become major obstacles for practical application. Ionic liquids (ILs) are promising alternatives, while only few ILs have been evaluated with enumeration method, by which it is difficult to create a short-term breakthrough. In this study, a prediction framework is established via relating the fundamental thermodynamic properties (absorbing ability and excess enthalpy) with cycle performance (COP and energy density) in order to clarify the maximum potential of this technology and the desirable properties of potentially interesting working fluids. A comprehensive investigation of promising IL absorbents in thermal storage/transmission has been carried out by the framework. Then, theoretical analysis shows that an optimal region with both high COP and high energy density (between 31.00 kJ/mol to 37.00 kJ/mol) could be reached, indicating 57% of improvement in energy density is possible (the highest level at current stage is 23.52 kJ/mol). To pursue the optimal performance, strong affinity between the species and decreasing trend of excess enthalpy during generation are found to be key roles. Such a theoretical framework could be further extended to the fluids design and screening of absorption thermal energy storage/transmission, as well as other related technologies.