Highly electrochemically stable Li2B12H12-Al2O3 nanocomposite electrolyte enabling A 3.8 V room-temperature all-solid-state Li-ion battery

Designing solid electrolytes for all-solid-state lithium batteries that can be compatible with high-voltage cathodes is challenging. Here we report that the nanocomposite Li2B12H12-Al2O3 mechano-chemically treated for 120 h achieves an electrochemical stability window up to ∼ 3.8 V owing to the interfacial interaction via B-O bonds and a high lithium ionic conductivity, σ(Li+) = 2.73 × 10−5 S cm−1 at 30 °C. Moreover, this electrolyte shows high compatibility with the lithium metal anode as demonstrated by stable Li plating/stripping for 300 cycles. These electrolyte properties enable the first demonstration of a 3.8 V all-solid-state battery In1.3Li0.3|Li2B12H12-Al2O3 (25 vol%)|LiNi0.8Co0.1Mn0.1O2 (NCM811) operating for 120 cycles with a rate of 0.2 C and at 30 °C, with a reversible specific capacity of 77.5 mAh g−1 and Coulombic efficiency of 99.8 %. The results demonstrate the potential of hydroborates as electrolyte for all-solid-state lithium batteries.