Lithium-sulfur batteries (LSBs) have been considered as the most promising candidate for the next generate energy storage since they are low cost, highly abundant and carry an attractive specific energy of 2600 Wh kg-1, 5 times higher than that of the state-of-the-art LIBs. However, LSBs so far are challenged by the unstable cycling performance and low efficiency, which is associated with the polysulfide shuttling. Polar-polar interaction relying on chemical binding of polysulfide marks an important strategy to stabilize performance Li-S batteries, yet the underlying surface chemistry at the liquid/solid interfaces remains less understood in the light of the complex surface structures and versatile interaction modes. Herein, we present a new surface chemistry phenomenon that confines lithium polysulfide (LPS) through an oxidation enabled interaction, which could be universally applied to most of inorganic solid categories. Using cobalt phosphide as the proof-of-concept example, we identified that the surface oxidation layer, naturally generated under ambient environment, assists the strong absorption of LPS species and promotes their conversion kinetics, whereas LPS could hardly be absorbed on the pristine surface of reduced cobalt phosphide. We prove that electronegative O in oxidation layers create highly polarized Co-O species and activates the Co sites to chemically bind Sδ- sites of LPS, thus stabilize the performance of lithium sulfur batteries. As a result, the CoP containing electrode with ultrahigh sulfur loading of 7 mg cm-2 could deliver a striking areal capacity of ~5.6 mAh cm-2 that is stable over 200 cycles. The surface oxidation induced LPS confinement represents a new perspective to understand the polar-polar interaction and highlights the importance of surface chemistry at electrolyte/electrode interfaces.

Surface chemistry in cobalt phosphide-stabilized lithium-sulfur batteries

256th National Meeting (2018)

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