Synergistic Combination of TiO2 and S-PAN for Li-S Batteries with Long-Term Cyclability at High C-Rates

Abstract

A ternary compound was synthesized from titanium dioxide, elemental sulfur and polyacrylonitrile throughout a simple ball-milling and heating process in inert atmosphere, and was fully characterized. The novel compound belongs to the family of sulfurized polyacrylonitrile compounds (SPAN) and was incorporated as active material in the cathode of Li-S batteries. The cells achieve high and stable capacity values at 0.5 C reaching 1885 mAh gS-1 for the 10th cycle and ∼1600 mAh gS-1 after 200 cycles (498 and 422 mAh g-1 composite, respectively). To the best of our knowledge, we are the first ones to report the combination of SPAN and TiO2, and to show the synergistic behaviour of these compounds. The high capacity values observed, higher than the theoretical capacity of elemental sulfur (1675 mAh g-1), are explained by the extra capacity provided by the lithiation/delithiation process of TiO2. The metallic oxide also improves the overall kinetics of the redox processes in SPAN, which helped to achieve good cycling performance at 3.3 C, with a remaining capacity of 672 mAh gS-1 after 1400 cycles, and even at 5 C where a remaining capacity of 660 mAh gS-1 after 500 cycles was recorded.