Understanding the Reorientational Dynamics of Solid-State MBH4 (M = Li–Cs)

The reorientational dynamics of crystalline MBH4 (M = Li–Cs) have been characterized with the interacting quantum atom theory. This interpretive approach enables an atomistic deciphering of the energetic features involved in BH4– reorientation using easily graspable chemical terms. It reveals a complex construction of the activation energy that extends beyond interatomic distances and chemical interactions. BH4– reorientations are in LiBH4 and NaBH4 regulated by their interaction with the nearest metal cation; however, higher metal electronic polarizability and more covalent M···H interactions shift the source of destabilization to internal deformations in the heavier systems. Underlying electrostatic contributions cease abruptly at CsBH4, triggering a departure in the otherwise monotonically increasing activation energy. Such knowledge concurs to the fundamental understanding and advancement of energy solutions in the field of hydrogen storage and solid-state batteries.