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. Selenium (Se) lithium and sodium metal cathodes are created 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 mA h 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 delivers reversible capacity of 1028 mA h cm(-3) (620 mA h g(-1)) and 82% retention over 300 cycles. For Na storage, 848 mA h cm(-3) (511 mA h g(-1)) is obtained with 98% retention after 150 cycles. The electrodes yield superb volumetric energy densities, being 1727 W h L-1 for Li-Se and 980 W h 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.