Electrospun Carbon Nanofiber–TiN Composite Interlayers for Improved Cycling Stability and Rate Capability of Lithium–Sulfur Batteries

Abstract

Lithium–sulfur (Li-S) batteries offer a high theoretical energy density of 2600 Wh·kg−1 and a theoretical specific capacity of 1675 mAh·g−1; however, their practical application is severely hindered by the shuttle effect of soluble lithium polysulfides, the intrinsic electronic insulating nature of sulfur and Li2S, and the substantial volume variation during charge/discharge processes. In this study, titanium nitride (TiN) powder was first prepared, and a carbon nanofiber/titanium nitride (CNF@TiN) composite nanofiber membrane was subsequently fabricated by electrospinning followed by pre-oxidation/carbonization treatment and employed as a functional interlayer between the separator and sulfur cathode. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) showed that the obtained TiN possessed a well-crystallized face-centered cubic structure. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) revealed that TiN particles were relatively uniformly dispersed and anchored within the three-dimensional interconnected CNF network. X-ray photoelectron spectroscopy (XPS) analyses of the composite and the TiN powder confirmed the presence of Ti–N bonding, revealed N/O-containing functional groups on the carbon scaffold, and indicated only a thin oxidized layer on the TiN particle surface. Nitrogen adsorption–desorption analysis confirmed the porous character of the fibrous interlayers. Electrochemical tests showed that the cell equipped with the CNF@TiN interlayer delivered an initial discharge specific capacity of 1205 mAh·g−1 at 0.1 C and retained a reversible capacity of approximately 1010 mAh·g−1 after 100 cycles. At 0.2 C, the initial discharge specific capacity was approximately 1065 mAh·g−1, and approximately 875 mAh·g−1 was retained after 300 cycles, corresponding to a capacity retention of 82.2% and an average capacity decay of approximately 0.059% per cycle. Rate capability, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge measurements indicated that the CNF@TiN interlayer favors reversible sulfur-species conversion and improved interfacial reaction kinetics. The enhanced performance can be attributed to the physical confinement, electron-transport, and structural-support functions of the CNF network, together with the polar TiN interface, whose presence is consistent with restricted polysulfide migration and facilitated interfacial conversion. This work provides a feasible strategy for designing multifunctional interlayers integrating electrical conductivity, physical confinement, and interfacial regulation for Li-S batteries.