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

Abstract

AbstractEnergy 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 2× 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.