Janus flexible electrode with built-in electric field for high-performance Li–S batteries

Lithium–sulfur batteries (LSBs) hold substantial potential for high-density energy storage systems, attributed to their high energy density and low cost. However, the widespread adoption of LSBs is significantly hindered by the shuttling effect and the slow redox kinetics of lithium polysulfides (LiPSs). To solve these problems, a Janus CoO/Sn-CNF@MXene electrode composed of 1D CoO/Sn-CNF heterojunction and 2D Ti3C2 MXene was developed as a flexible electrode for LSBs to enhance the reaction kinetics. Due to the difference in work function between CoO and Sn, a directed built-in electric field (BIEF) is induced at the heterointerface, which realizes the continuous “adsorption-migration-catalysis” process of LiPSs and effectively improves the reaction kinetics. The MXene layer acts as a physical barrier to further inhibit polysulfides from shuttling out of the fiber void, ensuring adequate reaction and enhancing conductivity. Therefore, the CoO/Sn-CNF@MXene electrode exhibited a satisfactory initial discharge capacity of 1026.53 mAh g−1 at a current density of 250 mA g−1, and a high capacity of 818.25 mAh g−1 even under a high sulfur loading of 5.07 mg cm−2. This work provides an effective method for the rational design of lightweight flexible Janus electrodes containing heterostructures and the improvement of LSB performance by inducing a BIEF.