Polymeric stabilization of salt hydrates for thermochemical energy storage

Abstract

Non-stabilized thermochemical materials impose several limitations on their use. These include swelling/shrinkage, cracking, and agglomeration over cycles. In addition, the deliquescence transition cannot be used and is even considered an unwanted side effect. In this work several salt hydrates for low temperature heat storage (K2CO3, CaCl2 and LiCl) are stabilized within a highly porous mm-sized polymer matrix. The composites containing wetting salt solutions are shown to be stable towards deliquescence. Three different composites were cycled. A K2CO3-polymer composite was cycled for 50 hydration/dehydration cycles and found to be kinetically and mechanically stable over all cycles, with swelling at higher cycle numbers. A LiCl-polymer composite was cycled for 40 cycles after which the composite became unstable. The composite containing CaCl2 was found to be kinetically and mechanically stable for 15 cycles. Composites with energy densities up to 2.4 GJ·m-3 and a peak power output of 325 W·kg-1 were fabricated which is equal or higher compared to previously reported systems. All composites have power outputs which are sustained at higher levels throughout the full discharge cycle. This work opens new pathways to stabilize salt hydrates as well-defined mm-sized particles exhibiting cyclic stability, while maintaining a high energy density and power output.