Alleviating the energy & safety contradiction to construct new low sensitivity and highly energetic materials through crystal engineering

Low sensitivity and highly energetic materials (LSHEMs), with both high energy and sufficient safety, are highly desired in practical applications. With respect to energy and safety, as the two most important and hottest concerns in the field of energetic materials (EMs), it is extensively deemed that there is an inevitable and inherent contradiction between them: a higher energy goes with a lower safety. This is the so-called energy and safety (E&S) contradiction. This article highlights this contradiction and finds that this contradiction is structure-level dependent. That is, it appears most necessarily and remarkably as an inherent one only at the molecular level, while at the crystal level and other higher ones, it can be largely alleviated. Moreover, we think that the energy and safety originate from the thermodynamics and kinetics of the decomposition reactions of EMs, respectively, and accordingly the contradiction becomes a thermodynamickinetic one. We thereby propose a strategy for developing LSHEMs, i.e., increasing the energy by increasing the chemical energy stored in molecules and by enhancing the molecular packing compactness, while, enhancing safety by making external stimuli more and more insufficient to ignite the EMs, through crystal engineering and mixing technologies. As an intrinsic structure of EMs, the crystal packing with face-to-face pi-pi stacking supported by strong interlayered intermolecular interactions favors the formation of LSHEMs or it is proposed to enhance intermolecular interactions and the anisotropy of these interactions to build low impact sensitivity energetic crystals.