Interface-enhanced Li ion conduction in a LiBH4–SiO2 solid electrolyte

Abstract

We have developed a fast solid state Li ion conductor composed of LiBH₄ and SiO₂ by means of interface engineering. A composite of LiBH₄–SiO₂ was simply synthesized by high energy ball-milling, and two types of SiO₂ (MCM-41 and fumed silica) having different specific surface areas were used to evaluate the effect of the LiBH₄/SiO₂ interface on the ionic conductivity enhancement. The ionic conductivity of the ball-milled LiBH₄–MCM-41 and LiBH₄–fumed silica mixture is as high as 10⁻⁵ S cm⁻¹ and 10⁻⁴ S cm⁻¹ at room temperature, respectively. In particular, the conductivity of the latter is comparable to the LiBH₄ melt-infiltrated into MCM-41. The conductivities of the LiBH₄–fumed silica mixtures at different mixing ratios were analyzed employing a continuum percolation model, and the conductivity of the LiBH₄/SiO₂ interface layer is estimated to be 10⁵ times higher than that of pure bulk LiBH₄. The result highlights the importance of the interface and indicates that significant enhancement in ionic conductivity can be achieved via interface engineering.