Tuning the crystallinity of titanium nitride on copper-embedded carbon nanofiber interlayers for accelerated electrochemical kinetics in lithium–sulfur batteries

The development of lithium–sulfur (Li–S) batteries is hindered by the disadvantages of shuttling of polysulfides and the sluggish redox kinetics of the conversion of sulfur species during discharge and charge. Herein, the crystallinities of a titanium nitride (TiN) film on copper-embedded carbon nanofibers (Cu-CNFs) are regulated and the nanofibers are used as interlayers to resolve the aforementioned crucial issues. A low-crystalline TiN-coated Cu-CNF (L-TiN-Cu-CNF) interlayer is compared with its highly crystalline counterpart (H-TiN-Cu-CNFs). It is demonstrated that the L-TiN coating not only strengthens the chemical adsorption toward polysulfides but also greatly accelerates the electrochemical conversion of polysulfides. Due to robust carbon frameworks and enhanced kinetics, impressive high-rate performance at 2 C (913 mAh g⁻¹ based on sulfur) as well as remarkable cyclic stability up to 300 cycles (626 mAh g⁻¹) with capacity retention of 46.5% is realized for L-TiN-Cu-CNF interlayer-configured Li–S batteries. Even under high loading (3.8 mg cm⁻²) of sulfur and relatively lean electrolyte (10 μL electrolyte per milligram sulfur) conditions, the Li–S battery equipped with L-TiN-Cu-CNF interlayers delivers a high capacity of 1144 mAh g⁻¹ with cathodic capacity of 4.25 mAh cm⁻² at 0.1 C, providing a potential pathway toward the design of multifunctional interlayers for highly efficient Li–S batteries.