Facilitation polysulfides adsorption/catalysis by nitrogen/phosphorous co-doped carbon nanofibers networks for advanced lithium/ polysulfides batteries

The development of lithium-sulfur batteries was hindered due to the shuttling of lithium polysulfides in electrolytes and sluggish electrochemical kinetics of polysulfides transformation. Herein, multi heteroatoms (nitrogen and phosphorus) co-doped carbon nanofibers (NP-CF) is elaborately designed, which acted as the current collector and binder free membrane electrode containing Li2S6 catholyte for lithium/polysulfides batteries. The conductivity of mesoporous NP-CF provide fast electronic transport and polarity of substrate possess a strong affinity to sulfur species, which could effectively anchor lithium polysulfides, boost their redox reaction catalytically-accelerate the reversible soluble/insolube phases conversion process, and greatly improve the utilization of active material. On the basis of density functional theory calculations on the bonding energies between NP-CF and lithium polysulfides (Li2Sn, n = 4, 6), it is found the NP-CF possesses higher binding energies toward polysulfides than N-CF. As a result, the cell with NP-CF membrane electrode with 4.6 mg cm-2 sulfur loading exhibits stability cycling capacity, which delivers a high intial capacity of 1023.3 mAh g-1 at 0.2C and sustains a capacity of 709.2 mAh g-1 over 300 cycles. NP-CF/Li2S6 electrode also performs well in cyclic performance with a sulfur loading of 8.4 mg cm-2, delivers a high specific capacity of 7.8 mAh and still maintains 6.4 mAh after 100 cycles.