Effect of Mechanical Pressure on the Ionic Conductivity of Sodium Dodecahydrido-closo-dodecaborate

To optimize the performance of solid-state batteries, careful control of the material properties is essential. Solid-state batteries require significant mechanical pressure during assembly and cycling to ensure intimate contact and stability of the electrochemical cell. Here we show that mechanical pressure can induce a polymorphic transition ( P 2 1 / c → Pbca ) of sodium dodecahydrido- closo -dodecaborate, Na 2 B 12 H 12, which increases both the boron dynamics and the ionic conductivity. Heating mechanically pressed samples above 65 °C results in full conversion back to the initial polymorph ( P 2 1 / c ), along with a reduction of one order of magnitude in ionic conductivity, which is consistent with the as-synthesized Na 2 B 12 H 12 . This work emphasizes the important role that postsynthesis treatment can have on the ionic conductivity, the activation energy, and the texture of solid electrolytes.