CO2-derived free-standing carbon interlayer embedded with molecular catalysts for improving redox performance in Li-S batteries

CNPCF/Fe-N-C with improved pore characteristics by CO 2 conversion provides additional channels for effective movement of Li ions, and enlarged surface areas for distribution of catalytic active sites. The homogeneously distributed molecular catalyst allows the active material to be distributed through the fiber surface and inside the pores without agglomeration. Also, the positive role of Fe-N 2 structures present in carbon framework is scrutinized through changes in energy states during redox reaction and variations in Bader charge. • Porous free-standing carbon interlayer (CNPCF) is synthesized via CO 2 treatment. • CNPCF series with superior pore properties maximize Li-ion transports. • Fe-N 2 active sites have favorable thermodynamic effects in the redox reaction. • CNPCF/Fe-N-C keeps coulombic efficiency of over 95% until 1600 cycles at 3.0 C. • CNPCF/Fe-N-C offers a maximum areal capacity of 2.9 mAh cm −2 at 1.0 C and 45 °C. The use of a free-standing carbon interlayer is a promising approach for the development of lithium-sulfur (Li-S) batteries because it suppresses the shuttle phenomenon and provides outstanding flexible characteristics. However, the thickness required to maintain the unique properties of the free-standing interlayer inevitably inhibits the transport of Li ions, causing sluggish redox kinetics. This work tackles the critical problem of the interlayer by synthesizing a composite in which Fe-based molecular catalysts are atomically incorporated into carbon nanofibers with superior pore characteristics realized by CO 2 treatment. The templates self-generated during CO 2 annealing provide high porosity and surface area, leading to effective Li-ion diffusion, and homogeneous distribution of the catalytic sites in the form of Fe-N 2 to the free-standing paper. The Fe-N 2 configuration thermodynamically aids in overcoming the energy barrier of the rate-limiting step of Li 2 S 4 to Li 2 S conversion while minimizing the shuttle phenomenon. Based on the effective Li-ion transport by improved pore properties, and the superior redox reaction ability of Fe-N 2 , the assembled cell maintains a coulombic efficiency of 95% up to 1600 cycles at 3.0 C. In addition, a maximum areal capacity of 2.9 mAh cm −2 is delivered for a high loading electrode with 4.2 mg cm −2 at 45 °C.