  Impregnation of Phase Change Materials (PCMs) into a porous medium is a
promising way to stabilize their shape and improve thermal conductivity which
are essential for thermal energy storage and thermal management of small-size
applications, such as electronic devices or batteries. However, in these
composites a general understanding of how leakage is related to the
characteristics of the porous material is still lacking. As a result, the
energy density and the antileakage capability are often antagonistically
coupled. In this work we overcome the current limitations, showing that a high
energy density can be reached together with superior anti-leakage performance
by using hierarchical macro-nanoporous metals for PCMs impregnation. By
analyzing capillary phenomena and synthesizing a new type of material, it was
demonstrated that a hierarchical trimodal macro-nanoporous metal (copper)
provides superior antileakage capability (due to strong capillary forces of
nanopores), high energy density (90vol% of PCM load due to macropores) and
improves the charging/discharging kinetics, due to a three-fold enhancement of
thermal conductivity. It was further demonstrated by CFD simulations that such
a composite can be used for thermal management of a battery pack and unlike
pure PCM it is capable of maintaining the maximum temperature below the safety
limit. The present results pave the way for the application of hierarchical
macro-nanoporous metals for high-energy density, leakage-free, and
shape-stabilized PCMs with enhanced thermal conductivity. These innovative
composites can significantly facilitate the thermal management of compact
systems such as electronic devices or high-power batteries by improving their
efficiency, durability and sustainability
