Designer Anion Enabling Solid-State Lithium-Sulfur Batteries

With an extremely high theoretical energy density, solid-state lithium-sulfur (Li-S) batteries (SSLSBs) are emerging as one of the most feasible chemistries; however, their energy efficiency and long-term cyclability are severely hampered by the lithium metal (Li°) dendrite formation during repeated discharge/charge cycles and the shuttling of aggressive polysulfide intermediates between two electrodes. Herein, we report (difluoromethanesulfonyl) (trifluoromethanesulfonyl)imide anion [N(SO2CF2H)(SO2CF3)]−, hereafter DFTFSI−, as a designer anion for high-performance polymer-based SSLSBs. In contrast to the widely used bis(trifluoromethanesulfonyl)imide anion [N(SO2CF3)2]− (TFSI−), DFTFSI-based SSLSBs provide superior interfacial stability against Li°, extremely high discharge and areal capacities, very high Coulombic efficiency, and long-term cyclability, surpassing the reported literature values, in terms of gravimetric energy density. This work opens a new door for accelerating the practical deployment of SSLSBs in the future.