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 (Li₂S_x, x < 6) but relatively weakly adsorbs to Li₂S. With these characteristics, the a‐TiO_x achieves high conversion of Li₂S_x 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‐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.