Applications Of Super-aligned Carbon Nanotubes In Lithium Sulfur Batteries

Lithium-sulfur?Li-S?batteries possess much higher specific capacity?1672 mAh/g?and energy density?2600 Wh/kg?than the commericial Li-ion batteries?LIB?.With the advantages of natural abundance,low cost and non-toxicity,sulfur cathode shows great potential in furture applications.However,the generated polysulfides during the redox reaction would shuttle between the electrodes,which leads to a great loss of active materials and rapid capacity fading?shuttle effect?.Besides,the charge/diascharge products of insulativity and aggregation would greatly suppress the electrochemical kinetics of the sulfur cathode,especially in high sulfur loaded electrodes,thus leading to poor cycling stability and low rate performance.In this work,based on the excellent electronic and mechanical properties of super-aligned carbon nanotube?SACNT?,along with the surface modification,flexible S-SACNT electrodes were fabricated for high-performance Li-S batteries.Besides,functional interlayers were fabricated via combination of SACNT films and other functional nanomaterials.With the effective restriction of polysulfides by the interlayers,the high sulfur loaded electrodes exhibited improved electrochemical properties.?1?Amphiphilic polymer polyvinylpyrrolidone?PVP?was introduced to modify the S-SACNT composite electrode.Due to its well dispersant effect and self-assembled template,a well dispersed PVP-layer-encapsulated S-SACNT nanocomposite electrode was obtained.The electrode exhibited smooth surface with micro porous structure,along with great mechanical properties.PVP modification have greatly alleviated the shuttle effect,thus the electrode presents excellent electrochemical performance.?2?An ultrathin MnO₂/GO/CNT interlayer was fabricated.The interlayer shows a low area density of 0.104 mg/cm².Based on SACNT film,the unique layered“vein-membrane”structure of the interlayer can effectively restrain the polysulfides diffusion.Besides,GO/MnO₂ show effective absorbability on polysulfides,along with the SACNT conductive networks,which exhibits synergetic effect on the improvement.Then the electrochemical methods were involved to examin the absorption reaction and the synergetic mechanism of MnO₂/GO/CNT components.Improved by the interlayer,the high sulfur loaded electrode demonostrates great electrochemical results,including cycling/rate performance,anti-selfdischarge behavior and Li anode protection,etc.?3?HfO₂/CNT interlayer was fabricated by ALD-depositing HfO₂ layer on the surface of SACNT.The synthesis process of HfO₂/CNT structure was discussed.The interlayer shows much low area density?0.087 mg/cm²?and great surface wettability.Moreover,based on the mutual promotion of HfO₂ and SACNT networks,the charge transfer process of the electrode and interlayer was greatly promoted.Furthermore,the surface catalytic reaction mechanism on polysulfides conversion was demonostrated in the HfO₂/CNT interlayer.Benifited by the HfO₂/CNT interlayer,the electrochemical properties of the electrode are significantly promoted,especially in high sulfur loaded electrode.