Intrinsic flame-retardant phase change materials for battery thermal management during rapid cycling and thermal runaway

The safety of high-energy density batteries remains a significant challenge due to the risk of thermal runaway, which can result in catastrophic damage. Phase change materials (PCMs) can absorb heat and regulate temperature through reversible phase transitions, effectively mitigating the risk of thermal runaway and offering a reliable solution for battery thermal management. However, achieving effective flame retardancy in PCMs, particularly under thermal runaway conditions, remains a challenge. In this work, we report a solid-solid PCM with high flame retardancy. Phosphorus-based flame retardant groups are grafted onto a polyurethane skeleton via a straightforward and cost-effective synthesis process, achieving an intrinsic flame retardancy (LOI = 30.2 %) and a high phase change enthalpy (78.7 J/g), along with good mechanical flexibility and strength (6 MPa) with only 5 wt.% flame retardant. These advanced properties enable the material to maintain the working temperature of 18,650 batteries below 55 °C during high current operation, reduce the peak runaway temperature by 405 °C during thermal runaway, and delay ignition by 59 s. These improvements significantly enhance the safety of batteries and protect people and property.