Magnesium-Based Hydrated Salt Phase Change Gels with Excellent Cycle Stability and Mechanical Properties for...

The broad application of vehicle batteries and chips highlights the importance of instantaneous thermal management to ensure their efficiency and safety. Phase change gels exhibit high latent heat storage capacity and surface adaptability, yet the role of hydrogel encapsulation in governing their thermal and mechanical behaviors has not been systematically investigated. In this work, Mg-based phase change gels (Mg-PCGs) were fabricated through in situ polymerization with different polymer contents within a eutectic hydrated salt (41.30 wt %-MgCl₂·6H₂O-58.70 wt %-Mg(NO₃)₂·6H₂O). By optimizing the polymer content to 4 wt %, Mg-PCGs maintained a melting enthalpy of 115.7 J/g (85% of the original hydrated salt) and suppressed supercooling to 2.8 °C (4.2 °C of eutectic hydrated salt). A mild liquid leakage was observed at 4-6 wt % polymer content, and excellent cycle stability was achieved at 2-8 wt %. Mg-PCGs with 4 wt % polymer content demonstrate a reversible modulus change between a soft (3.3 kPa) and rigid state (218.1 MPa). Their soft surface and flexibility enable close wrapping and firm contact with Li-ion batteries and chips. A maximum temperature reduction of 14.5 °C during 10 charge-discharge cycles of battery at a 3C current rate and 25.0 °C for chips under a 1.0 W operating power for 10 min was observed. Moreover, no visible flames and liquid droplets were observed during fire exposure. The optimized phase change gel with effective heat dissipation and fire resistance demonstrates great potential for passive thermal management of heat-generating electronic devices.