Mesoporous Hydroxylated Carbon Nanofibers as an Effective Cathode Scaffold to Enhance the Lithiation-Delithiation Reversibility of Lithium-Sulfur Batteries

摘要

Taking a reversible electrochemical reaction of elemental sulfur towards metallic lithium intoconsideration, it seems to be inappropriate to calculate Li+-ion diffusion coefficient (DLi) within asolid-state cathode of carbon-sulfur composites using the concentration of lithium ions in electrolytesolution. In this paper, cross-linked non-porous carbon nanofibers (CNF) and mesoporoushydroxylated carbon nanofibers (m-HCNF) are prepared and comparatively utilized as sulfur-loadingmatrices to improve the lithiation-delithiation reversibility between molecular S8 and metallic lithium.When model cells are assembled at a constant dosage of electrolyte (30 mL) per gram of sulfur, atopen-circuit voltage the DLi value of a lithium-sulfur (Li-S) battery cathode can be estimated accordingto the S8 concentration therein: 3.51 ? 10-15 cm2 s-1 for the low sulfur-loading cathode S/CNF (47.0wt%); 4.21 ? 10-15 cm2 s-1 for the high sulfur-loading electrode S/m-HCNF (~ 62.0 wt%). At 0.5 C theinitial Coulombic efficiency of S/m-HCNF (96.9%) is higher than that of S/CNF (88.8%), andthereafter the better cycling stability and rate performance of the former coincide well with the varyingDLi values. In a word, these indicate an enhanced lithiation-delithiation reversibility of composite S/mHCNF for high-performance Li-S batteries.