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

Abstract

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 CO2 treatment. The templates self-generated during CO2 annealing provide high porosity and surface area, leading to effective Li-ion diffusion, and homo-geneous 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 Li2S4 to Li2S 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 degrees C.