Discovery of Dual-Functional Amorphous Titanium Suboxide to Promote Polysulfide Adsorption and Regulate Sulfide Growth in Li–S Batteries

Abstract

Lithium-sulfur (Li–S) batteries are promising as next-generation energy storage systems. Adsorbents for sulfide species are favorably applied to the cathode, but this substrate often results in a surface-passivating lithium sulfide(Li2S) film with a strong adsorption of Li2S. Here, an amorphous titanium suboxide (a-TiOx) is presented that strongly adsorbs lithium polysulfides (Li2Sx, x < 6) but relatively weakly adsorbs to Li2S. With these characteristics, the a-TiOx achieves high conversion of Li2Sx and high sulfur utilization accompanying the growth of particulate Li2S. The DFT calculations present a mechanism for particulate growth driven by the promoted diffusion and favorable clustering of Li2S. The a-TiOx-coated carbon nanotube-assembled film (CNTF) cathode substrate cell achieves a high discharge capacity equivalent to 90% sulfur utilization at 0.2 C. The cell also delivers a high capacity of 850 mAh g–1 even at the ultra-high-speed of 10 C and also exhibits high stability of capacity loss of 0.0226% per cycle up to 500 cycles. The a-TiOx/CNTF is stacked to achieve a high loading of 7.5 mg S cm–2, achieving a practical areal capacity of 10.1 mAh cm–2.