Bi-functional Li2B12H12 for energy storage and conversion applications: solid-state electrolyte and luminescent down-conversion dye

Abstract

Our investigation of the chemical and physical properties of the alkali-metal dodecahydro-closo-dodecaborate, Li₂B₁₂H₁₂, determined that it is a bi-functional material that can be used as a solid state electrolyte in lithium ion batteries and as a luminescent down conversion dye in scalable transparent displays. A series of electrochemical measurements of morphologically altered samples, via mechanical milling, was conducted. The measurements indicated that mechanical alternations of the Li₂B₁₂H₁₂ morphology makes it an excellent lithium ion conductor in the solid state with exceptional ionic conductivity at room temperature (0.31 mS cm⁻¹) and is compatible with a metallic lithium electrode up to 6.0 V. In addition, all solid state half and full electrochemical cells were assembled and successfully cycled using Li₂B₁₂H₁₂ as a solid state electrolyte at temperatures as low as 30 °C with good capacity retention. The photophysical properties of Li₂B₁₂H₁₂ were also investigated. L_i2B₁₂H₁₂ has an emission maximum of ∼460 nm in a variety of solvents with Stokes' shifts up to 175 nm observed. Li₂B₁₂H₁₂ was incorporated in a polyvinyl alcohol (PVA) thin film to demonstrate its application as a luminescent down-conversion dye in a transparent head-up display when excited by a UV projection source.