Enhancement of the ionic conductivity of lithium borohydride by silica supports.

Confinement of LiBH4 in porous materials is an efficient route to enhance the ionic conductivity of lithium, which seems to be associated with various types of scaffolding and its mixture ratios. In the present work, we reveal the effect of supports on ionic conductivity improvements based on a comparison of different silica supports, including micro-SiO2 (SM), porous nano-SiO2 (MSN), and nano-SiO2 with nanochannels (SBA-15). All LiBH4/silica composites exhibited higher lithium ionic conductivity, where LiBH4/SBA-15 (47% weight ratio) exhibited the highest conductivity of 3 × 10-5 S cm-1 at 35 °C, nearly three orders of magnitude higher than that of pure LiBH4. In addition, the LiBH4/SBA-15 composite has a wider electrochemical stability window of -0.2 to 5 V, satisfactory compatibility with the Li anode, and no occurrence of side reactions. These ionic conductivity enhancements can be attributed to the support effects of distinct SiO2, i.e., the increase in surface area for superior interfacial ionic conductivity and/or the increased disorder of LiBH4 for faster matrix ionic conductivity. The present study offers useful insights for designing a new hydride solid electrolyte for all-solid-state lithium ion batteries.