Enhanced Li ⁺ Ion Transport in the Channel Structure of the (HO-(CH ₂ ) ₅ OH) ₂ LiBH ₄ Molecular Crystal

A LiBH4-based molecular crystal, (HO-(CH2)5OH)2LiBH4 = (PDO)2LiBH4 is reported in which Li+ ions are coordinated exclusively by 1,5-pentanediol (PDO), fully separating the BH4– anions from the Li+ cations. This creates well-defined ion-conduction channels within a tetragonal lattice that remains crystalline up to ∼80 °C. Under these conditions, the 2:1 PDO:LiBH4 crystal exhibits a room-temperature conductivity of ∼1 × 10–5 S cm–1, values that are almost 2 orders of magnitude higher than those of pure LiBH4, and with a lower activation energy barrier (49 kJ/mol) than for LiBH4 (Ea = 68 kJ/mol), and which exceeds the performance of most previously reported LiBH4-based molecular electrolytes when evaluated in their true solid state (Ea = 80–94 kJ/mol). Many of these materials claim high room temperature ionic conductivity, although they soften or partially melt in the range of 40–50 °C, temperatures that can be lower under pressures experienced in coin cells, so that the reported properties are not clearly from the solid state.