Preparation And Electrochemical Properties Of TiO₂/S Composite Cathode Materials

Sulfur is a promising cathode material with a high theoretical specific capacity of 1675 mAh g-1.When paired with lithium metal anode to form rechargeable lithium-sulfur batteries,the theoretical specific energy density can be as high as 2600 Wh kg-1.These estimations have inspired high expectations in meeting future large-scale energy storage needs.However,several challenges associated with sulfur cathode materials still persist and may prevent their practical applications,including?i?low electronic and ionic conductivities of solid sulfur species?S,Li2S2 and Li2S?that limit specific capacity and rate capability,?ii?dissolution of polysulfide intermediates into electrolyte and subsequent redox shuttling resulting in low coulombic efficiency,rapid capacity fading,and high self-discharge rates,and?iii?significant volumetric changes during charging and discharge reactions that may iduce mechanical damage to the electrode.To solve these problems,modification of sulfur plays a very important role in lithium-sulfur battery research work.A promising host that possesses high adsorption of polysulfides and can provide enough space of expansion will be a constant pursue.Owing to better adsorbtion of polysulfides for TiO₂,the mesoporous titanium dioxide is widely concerned,recently.Antase titanium dioxide was selected as host for sulfur in our paper.What effects of different morphology TiO₂ on lithium-sulfur batteries were studied in this paper.We are the first to apply the TDPEF and MTDNTs on lithium-sulfur battery's research work.The results show that both two morphology titanium dioxides have an active effect on their rate performance.What's more,we also have studied their mechanisms that how to affect their electrochemical performance of TDPEF and MTDNTs.The more details research results are displayed as follows:TDPEF were prepared by alcohol-thermal method.The BET specific surface area and pore volume of prepared TDPEF are 92 m2 g-1 and 0.27 cm3 g-1,respectively.Sulfur was mixed with the TDPEF to form TDPEF/S composite by a melt diffusion process.The TDPEF/S composite exhibits very excellent discharge capacity retention of 80% after 100 cycles compared with pure sulfur at a high current rate of 0.5 C,and it still has a discharge capacity as high as 530 mAh g-1 even at the current rate of 4.0 C.Mesoporous titanium dioxide nanotubes?MTDNTs?were prepared by electrospinning and subsequent thermal treatment.The as-synthesised MTDNTs possess anatase mischcrystal structure,morphology of hollow texture,and a relatively high specific surface area of 93.6 m2 g-1 with a pore volume of 0.2190 cm-3 g-1.The nanotube walls of MTDNTs act as a conductive substrate for sulfur and the hollow structure is favorable for the fast transmission of Li+.After sulfur was encapsulated into the pores of nanotube walls of MTDNTs,the MTDNTs/S composite electrode displays a relatively good cycling performance and especially excellent rate performance?about 610 mAh g-1 at 8.0 C?.The retention capacity can be up to 74.2 % when the discharge rate increases from 0.5 C to 8.0 C.