Three dimensional porous SiC for lithium polysulfide trapping.

One of the key issues in lithium sulfur batteries is the fast capacity fade induced by the lithium polysulfide (LiPS) migration. Hence, a series of three-dimensional (3D) porous SiC materials with active sp2 Si atoms have been designed for lithium polysulfide entrapping in Li-S batteries. The ZGM-SiC-1 and AGM-SiC-3 have been confirmed to be thermodynamically and dynamically stable from the formation energy and phonon dispersion spectrum, meanwhile showing good mechanical properties. The moderate band gaps suggest fast electron transport during the charge-discharge cycles of the Li-S batteries, especially in ZGM-SiC-1. The 3D porous ZGM-SiC-1 and AGM-SiC-3 display strong affinity to S8 and LiPS with the direct Si-S and Li-C interactions, which are comparable to the case of the N doped carbon host. As compared to the 3D pristine graphene monoliths and two dimensional SiC nanosheet, the entrapping of LiPS in the 3D porous SiC host is much stronger (ca. 2.5 eV to 3.5 eV), which is effective in inhibiting the shutter effect in Li-S batteries. Most interestingly, the extraordinarily strong adsorption of the S8 molecule indicates high sulfur loading in the 3D porous SiC host.