Research Highlights

Complex borohydrides (CBHs) are promising electrolyte materials for all-solid-state batteries (ASSBs), provided that their phase-transition temperatures can be lowered to room temperature (RT) to enable the practical application of their outstanding Li- and Na-ion conductivities (≈ 10⁻¹ S cm⁻¹).

Because the high conductivity phases of CBHs commonly show anionic rotational motions, understanding the factors affecting anion reorientation can significantly advance the design of future RT fast ion-conducting materials.

“Recent experimental and first-principles molecular dynamics (FPMD) works tried to capture the reorientation of CBH anions.” explains Sau. “However, the limited scope and FPMD timescale of these approaches could not capture the anion reorientational motions in their entirety.”

In a 2021 article, Sau et al. from AIMR used force-field based MD simulations to overcome these limitations, investigating the Li₂B₁₂H₁₂ and LiCB₁₁H₁₂ systems¹. This strategy allowed for accurate reproduction of structural and dynamic behavior, capturing the entropy-driven order-disorder phase transitions and anion reorientational motions—not feasible with FPMD and experiment alone.

“The results of this work had enabled us to investigate other factors determinant of future designs of ASSB and solid-state cooling/heating materials, such as the role of cation size on CBH phase transition², or the significance of cation diffusion on the CBH colossal barocaloric effects (ability to change temperature when applying pressure)³,” says Sau.

A current direction of the research team focuses on investigating the barocaloric properties of the related closo-borate compounds and other disordered materials for the development of efficient and environmentally friendly cooling solutions.

(Author: Patrick Han)