Selenium Impregnated Monolithic Carbons as Free-Standing Cathodes for High Volumetric Energy Lithium and Sodium Metal Batteries

Energy density (energy per volume) is a key consideration for portable, automotive and stationary battery applications. We created selenium (Se) lithium and sodium metal cathodes that are monolithic and free-standing, and with record Se loading of 70 wt%. The carbon host is derived from nanocellulose, an abundant and sustainable forestry product. The composite is extremely dense (2.37 g cm -3 ), enabling theoretical volumetric capacity of 1120 mAh cm -3 . Such architecture is fully distinct from previous Se – carbon nano or micropowders, intrinsically offering up to 2X higher energy density. For Li storage, the cathode delivered reversible capacity of 1028 mAh cm -3 (620 mAh g -1 ) and 82% retention over 300 cycles. For Na storage 848 mAh cm -3 (511 mAh g -1 ) was obtained with 98% retention after 150 cycles. The electrodes yield superb volumetric energy densities, being 1727 Wh L -1 for Li-Se and 980 Wh L -1 for Na-Se normalized by total composite mass and volume. Despite the low surface area, over 60% capacity is maintained as the current density is increased from 0.1 to 2 C (30 min charge) with Li or Na. Remarkably, the electrochemical kinetics with Li and Na are comparable, including the transition from interfacial to diffusional control.