Selenium-sulfur (SeS) fast charging cathode for sodium and lithium metal batteries

We report a bifunctional sodium metal battery (SMB) and lithium metal battery (LMB) cathode based on 63 wt.% SeS covalently bonded to a co-pyrolyzed polyacrylonitrile (PAN) host, termed SeSPAN. This dense, low surface area, fully-amorphous electrode offers a highly favorable combination of reversible capacity, rate capability, and cycling life: At a fast charging rate of 1 A g(-1), the reversible capacities with Na and Li are 632 and 749 mAh g(-1) (based on active SeS), with cycle 1 CE of 81% in both cases. At an ultra-fast charging rate of 4 A g(-1) (similar to 5C) the reversible capacities with Na and Li are 453 and 604 mAh g(-1). Li-SeSPAN degrades 3% at cycle 500, while with Na-SeSPAN degrades by 17% after 150 cycles at 0.5 A g(-1). Both Na and Li cells display a uniquely low voltage hysteresis (210 and 200 mV at a current density of 0.2 A g(-1)), indicative of facile charge-discharge kinetics. Analysis of the post-cycled anodes shows negligible S or Se crossover, with neither species being detected in the Li-SEI after extended cycling.