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

Abstract

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.