Enhancing Li-Ion Conductivity in LiBH4-Based Solid Electrolytes by Adding Various Nanosized Oxides

Solid-state ion conductors are gaining increasing importance, among other ion conductors, to enable a transition to next-generation all-solid-state Li batteries. However, few lightweight and low-cost materials show sufficiently high Li-ion conduction at room temperature to be used as solid electrolytes. Here, we report the effect of adding nanosized oxides, SiO2, CaO, MgO, gamma-Al2O3, TiO2, and ZrO2, to LiBH4 by ball-milling. In all cases, the room temperature Li-ion conductivity was greatly enhanced. For SiO2, which has been reported before as a conductivity enhancing material, the highest conductivity (4.1 x 10(-5) S/cm at 40 degrees C) and the lowest activation energy (0.49 eV) were found at 20 v/v% SiO2. For the first time, ZrO2 and MgO were also added to LiBH4, leading to more than a 4 orders of magnitude increase in conductivity at 40 degrees C, reaching 0.26 and 0.18 mS/cm, respectively. Based on insights into the effect of structural properties on conductivity, we present a set of general guidelines to maximize the Li-ion conductivity in these nanocomposite solid electrolytes, independently of the type of oxide added. We expect that these results and insights will be helpful for the further development of new room temperature solid-state ion conductors.