Order-Disorder Phase Transition and Ionic Conductivity in a Li₂B₁₂H₁₂ Solid Electrolyte

Area of Science:

• Materials Science
• Computational Chemistry
• Solid-State Physics

Background:

• Understanding ionic conductivity and phase transitions in solid electrolytes is crucial for advanced battery technologies.
• Lithium dodecaborate (Li2B12H12) and lithium carbollide (LiCB11H12) are promising solid electrolyte candidates.

Purpose of the Study:

• To simulate temperature-induced phase transitions and ionic conductivities of Li2B12H12 and LiCB11H12.
• To investigate the role of anion dynamics in these properties using advanced computational methods.

Main Methods:

• Machine learning interatomic potentials (MLIPs) were developed using van der Waals-corrected density functional theory (rev-vdW-DF2).
• Ab initio quality molecular dynamics simulations were performed on systems exceeding 2000 atoms for nanosecond timescales.

Main Results:

• Simulated transition temperatures, lattice parameters, diffusion, ionic conductivity, and activation energies closely matched experimental data.
• The study highlighted the critical role of [B12H12]2- anion reorientational motion in Li2B12H12's phase transition.
• A distinction was made between complete anion rotation in vacancy-rich systems and limited vibrational motion in ideal crystals.

Conclusions:

• MLIPs enable accurate simulations of large-scale systems and long timescales for solid electrolytes.
• The phase transition in Li2B12H12 is characterized by a change in anion orientational disorder rather than full dynamic disorder.
• The findings provide valuable insights into the mechanism of ionic transport in these materials.