Extensive Screening\nand Performance Testing of Nucleating\nAgents for the Sodium Acetate Trihydrate Phase-Change Material

Heat batteries often\nrely on phase-change materials that undergo\nphase transitions upon heat charging and release. Sodium acetate trihydrate\n(SAT) is considered to be one of the best phase-change materials in\nterms of storage capacity. Yet, it is well-known for supercooling,\nwhich makes the search for effective nucleating agents a high priority.\nTo perform extensive screening of nucleating agents and to test their\nperformance, we designed a new instrument. The HeatMaster is capable\nof analyzing six samples on the gram-scale in parallel using the principle\nof power compensation, which means that heat releases and uptakes\ncan be obtained in a quantitative fashion. Out of the 36 tested nucleating\nagents, CaCl<sub>2</sub>·2H<sub>2</sub>O was identified as the\nbest nucleating agent that outperforms several of the previously known\nnucleating agents in terms of temperature range of operation up to\n80 °C. CaCl<sub>2</sub>·2H<sub>2</sub>O performs reliably\nas a nucleating agent for SAT down to 0.5 wt %. MgCl<sub>2</sub>·6H<sub>2</sub>O was also identified as a nucleating agent. Yet, similar\nto the well-known Na<sub>2</sub>HPO<sub>4</sub>·12H<sub>2</sub>O, its performance is not reliable after heating to 80 °C. Out\nof the three nucleating agents, CaCl<sub>2</sub>·2H<sub>2</sub>O shows the best performance with respect to deterioration of the\nheat releases upon extensive thermal cycling with a maximum temperature\nof 65 °C.