Hydroborate Solid-State Lithium Battery with High-Voltage NMC811 Cathode

Hydroborate solid electrolytes offer high ionic conductivity and are stable in contact with alkali metal anodes but are challenging to integrate into batteries with high-voltage cathodes. Here, we demonstrate stable dis-/charge cycling of solid-state Li batteries combining a Li3(CB11H12)2(CB9H10) hydroborate electrolyte with a 4 V-class LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode, exploiting the enhanced kinetic stability of the LiCB11H12-rich and LiCB9H10-poor electrolyte composition. Cells with Li metal and InLi anodes achieve a discharge capacity at C/10 of ∼145 mAh g–1 at room temperature and ∼175 mAh g–1 at 60 °C. InLi cells retain 98% of their initial discharge capacity after 100 cycles at C/5 and 70% after 1000 cycles at C/2. Capacity retentions of 97% after 100 cycles at C/5 and 75% after 350 cycles at C/2 are also achieved with a graphite anode without any excess Li. The energy density per cathode composite weight of 460 Wh kg–1 is on par with the best solid-state batteries reported to date.