Enhanced electrochemical kinetics in lithium-sulfur batteries by using carbon nanofibers/manganese dioxide composite as a bifunctional coating on sulfur cathode

Lithium-sulfur (Li-S) batteries have attracted extensive interest due to their higher theoretical energy density than the current commercial lithium-ion batteries. However, their practical application is largely hindered by the low sulfur utilization and poor cycling stability. Restraining the shuttle effect and enhancing the electrochemical kinetics are important for developing high-performance Li-S batteries. Here we use carbon nanofibers (CNFs) supported manganese dioxide (MnO2) composite as a bifunctional coating on sulfur cathode for anchoring polysulfides and accelerating their redox reactions simultaneously. The CNFs/MnO2 composite supplies fast paths for electron transfer and ion diffusion, and greatly promotes the transformation processes of polysulfides to Li2S/Li2S2, leading to an enhanced electrochemical kinetics. The diffusion coefficient of lithium ion has been increased by 560%. As a result, the CNFs/MnO2 composite covered electrode exhibits an excellent cycling stability, its specific capacity maintains at about 600 mAh g−1 at 1C after 400 cycles, corresponding to a capacity decay as low as 0.063% per cycle, and the average coulombic efficiency reaches up to 99.66%.