Investigating the Potential of Alkali Metal Plumba- closo- Dodecaborate (B 11 H 11 Pb 2– ) Salts as Solid-State Battery Electrolytes

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Metal dodecaborate salts have been identified as a new class of ion conductors that are highly tunable. A [B–H] unit within the dodecaborate anion can be replaced with a Pb atom to create a dipole and anisotropy within the anion to tune the crystal structure of alkali metal salts, enhancing ion conductivity for solid-state electrolyte (SSE) applications in batteries. Li 2 B 11 H 11 Pb· x H 2 O shows superionic conductivity up to ∼7 mS cm –1 at 120 °C, proving it comparable to state-of-the-art LiCB 11 H 12 at these temperatures. Dehydration of the Li salt occurs above 120 °C, causing changes in the crystal structure and a decrease in the ion conductivity. Na 2 B 11 H 11 Pb· x H 2 O shows modest ion conductivity (0.01 mS cm –1 at 170 °C), whereas the potassium salt shows conductivities below 1 × 10 –5 mS cm –1 . The B 11 H 11 Pb 2– analogues are proposed to be inferior ion conductors to the CB 11 H 12 – varieties due to the divalent B 11 H 11 Pb 2– anion causing stronger bonding between the cation and anion, possibly higher energy required to move from position to position within the crystal structure. Despite this, the insertion of a lead atom into the dodecaborate cage shows promise in allowing high ion conductivity in the solid state.