Metal hydride nanoscaling, which is increasingly used to destabilize hydrides, can significantly reduce ΔH but typically induces a capacity penalty via increased dead space (i.e., the host material) for hydrogen absorption in the metal hydride bed. This prominent two-dimensional performance trade-off, observed in both bulk and nanoscale metal hydrides, is often the main criterion by which the storage potential of a new hydride is initially determined. In this work, however, our materials and systems co-design approach (enabled by full experimental materials characterization of (LiNH2+2LiH) and (LiNH2+2LiH)@(6-nm PC), tank system design and LDV drive cycle simulation) led to unexpected insights into the improved systems-level performance of (LiNH2+2LiH)@(6-nm PC). Nanoscaling induces significant penalties in fH2 (24% reduction), density (~10% reduction), and desorption entropy (~15% reduction) (Table ).