Extensive Screening and Performance Testing of Nucleating Agents for the Sodium Acetate Trihydrate Phase-Change Material

Heat batteries often rely on phase-change materials that undergo phase transitions upon heat charging and release. Sodium acetate trihydrate (SAT) is considered to be one of the best phase-change materials in terms of storage capacity. Yet, it is well-known for supercooling, which makes the search for effective nucleating agents a high priority. To perform extensive screening of nucleating agents and to test their performance, we designed a new instrument. The HeatMaster is capable of analyzing six samples on the gram-scale in parallel using the principle of power compensation, which means that heat releases and uptakes can be obtained in a quantitative fashion. Out of the 36 tested nucleating agents, CaCl2·2H2O was identified as the best nucleating agent that outperforms several of the previously known nucleating agents in terms of temperature range of operation up to 80 °C. CaCl2·2H2O performs reliably as a nucleating agent for SAT down to 0.5 wt %. MgCl2·6H2O was also identified as a nucleating agent. Yet, similar to the well-known Na2HPO4·12H2O, its performance is not reliable after heating to 80 °C. Out of the three nucleating agents, CaCl2·2H2O shows the best performance with respect to deterioration of the heat releases upon extensive thermal cycling with a maximum temperature of 65 °C.