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 Li 3 (CB 11 H 12 ) 2 (CB 9 H 10 ) hydroborate electrolyte with a 4 V-class LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode, exploiting the enhanced kinetic stability of the LiCB 11 H 12 -rich and LiCB 9 H 10 -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.