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 center dot center dot center dot 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.