Thermal Decomposition of Anhydrous Alkali Metal Dodecaborates M2B12H12 (M = Li, Na, K)

Thermal and Electrochemical Interface Compatibility of a Hydroborate Solid Electrolyte with 3 V-Class Cathodes for All-Solid-State Sodium Batteries

Thermal stability of solid electrolytes and their compatibility with battery electrodes are key factors to ensure stable cycling and high operational safety of all-solid-state batteries. Here, we study the compatibility of a hydroborate solid electrolyte Na₄(B₁₂H₁₂)(B₁₀H₁₀) with 3 V-class cathode active materials: NaCrO₂, NaMnO₂, and NaFeO₂. Among these layered sodium transition metal oxide cathodes, NaCrO₂ shows the highest thermal compatibility in contact with the hydroborate solid electrolyte up to 525 °C in the discharged state. Furthermore, the electrolyte remains intact upon the internal thermal decomposition of the charged, that is, desodiated, cathode (Na_0.5CrO₂) above 250 °C, demonstrating the potential for highly safe hydroborate-based all-solid-state batteries with a wide operating temperature range. The experimentally determined onset temperatures of thermal decomposition of Na₄(B₁₂H₁₂)(B₁₀H₁₀) in contact with 3 V-class cathodes surpass those of sulfide and selenide solid electrolytes, exceeding previous thermodynamic calculations. Our results also highlight the need to identify relevant decomposition pathways of hydroborates to enable more valid theoretical predictions.

Theoretical description of alkali metal closo-boranes - towards the crystal structure of MgB12H12

Solid state closo-borane salts of alkali metals have very high ionic conductivity. This makes them interesting for practical applications as solid state electrolytes, and has triggered extensive research efforts. Improvement and understanding of their properties require accurate theoretical description of their static and dynamical properties. In this work, we report accuracy assessment of density functional theory in the description of solids with B12H122- anions. We show that these aromatic anions interact via weak dispersive forces. For that reason, non-local exchange-correlation functionals give better description of structural properties and phonons in Li2B12H12 and Na2B12H12. Numerically efficient semi-local methods provide satisfactory results when applied in structure volumes obtained in a non-local method. An extensive structural search for stable crystalline phases of MgB12H12 predicts a new denser lattice with C2/c symmetry that is stabilized by van der Waals interactions. These structures might be discovered as anhydrous MgB12H12 in high pressure experiments, avoiding the amorphous state at ambient pressures.

Hydrogenation properties of lithium and sodium hydride – closo-borate, [B10H10]2− and [B12H12]2−, composites

The hydrogen absorption properties of metal closo-borate/metal hydride composites are studied under high hydrogen pressures.