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

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.