Bi-functional Li 2 B 12 H 12 for energy storage and conversion applications: solid-state electrolyte and luminescent down-conversion dye

Our investigation of the chemical and physical properties of the alkali-metal dodecahydro- closo -dodecaborate, Li 2 B 12 H 12 , 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 Li 2 B 12 H 12 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 Li 2 B 12 H 12 as a solid state electrolyte at temperatures as low as 30 °C with good capacity retention. The photophysical properties of Li 2 B 12 H 12 were also investigated. L i2 B 12 H 12 has an emission maximum of ∼460 nm in a variety of solvents with Stokes' shifts up to 175 nm observed. Li 2 B 12 H 12 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.