Pulse heating and slip enhance charging of phase-change thermal batteries

Phase-change thermal batteries for renewable energy storage and waste heat recovery demand high energy density and fast charging^1-5, which are mutually exclusive because phase-change materials (PCMs) with high melting enthalpy are usually poor heat conductors^6-8. The charging rate can be improved by making composite phase-change materials (CPCMs) with increased thermal conductivity⁹ and/or by exerting an external force to realize close-contact melting (CCM)^10-12. However, these methods inevitably result in energy density losses and/or extra energy consumption. Here we report a strategy to boost the charging rates without sacrificing energy density, based on a rational design of a composite coating that enables slip-enhanced close-contact melting (sCCM) inside sealed thermal batteries. Using organic PCMs, we demonstrate a record-high power density of 1,100 ± 2% kW m^-3 in a prototype. Our coating design integrates a pulse-heated (PH) layer that premelts the PCM to initiate CCM, together with a liquid-like slip surface that ensures unimpeded sinking of the remaining solid and sustains the sCCM mode throughout charging. We develop a model to explain how the slip surface enhances the charging rate. With high cycling life, adaptability and scalability, this strategy is generalizable to diverse PCMs, enabling high-performance thermal energy storage over a wide range of temperatures.