Discovery of Dual-Functional Amorphous Titanium Suboxide to Promote Polysulfide Adsorption and Regulate Sulfide...

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(Li₂ S) film with a strong adsorption of Li₂ S. Here, an amorphous titanium suboxide (a-TiOx) is presented that strongly adsorbs lithium polysulfides (Li₂ S_x , x < 6) but relatively weakly adsorbs to Li₂ S. With these characteristics, the a-TiO_x achieves high conversion of Li₂ S_x and high sulfur utilization accompanying the growth of particulate Li₂ S. The DFT calculations present a mechanism for particulate growth driven by the promoted diffusion and favorable clustering of Li₂ S. The a-TiO_x -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-TiO_x /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 .