Investigating the Potential of Alkali Metal Plumba-closo-Dodecaborate (B11H11Pb2–) Salts as Solid-State Battery Electrolytes

Abstract

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. Li2B11H11Pb·xH2O shows superionic conductivity up to ∼7 mS cm–1 at 120 °C, proving it comparable to state-of-the-art LiCB11H12 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. Na2B11H11Pb·xH2O 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 B11H11Pb2– analogues are proposed to be inferior ion conductors to the CB11H12– varieties due to the divalent B11H11Pb2– 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.