Three-Dimensional Macroporous TiO₂-MXene Nanostructure-Based Films for Flexible Freestanding Sulfur Cathodes

Flexible freestanding electrodes with high energy density and good cycling stability are of great importance for wearable devices. Lithium–sulfur battery is considered a promising next-generation energy storage system owing to its high theoretical energy density and low production cost. However, several issues such as the severe polysulfide shuttle effect, poor electrical conductivity, and drastic volume change of sulfur cathodes hindered the commercialization of lithium–sulfur batteries. To solve these problems, many recent studies have focused on a class of two-dimensional (2D) MXene nanomaterials with abundant surface functional groups and excellent mechanical flexibility. Although these unique MXene nanomaterials have chemical affinity and are easily designed into various nanostructures, the inevitable overlap of the nanosheets can impair their electrochemical performance. Herein, we develop a three-dimensional (3D) macroporous TiO2-MXene nanostructure-based film for the flexible freestanding sulfur cathode in this paper. Such structure can realize a dual-confined strategy for polysulfides, that is, physical barrier and chemical absorption. The hollow porous MXene nanostructure can physically inhibit the polysulfide shuttle effect. And the TiO2 nanoparticles on the surface of MXene can effectively anchor and catalyze polysulfides in the electrochemical reaction. Moreover, the 3D conductive MXene network can provide fast electronic pathways, which promote the electrochemical reaction and reduce the electrochemical polarization. Without adding additional binders and conductive agents, the 3D macroporous TiO2-MXene freestanding nanostructure-based film S@TiO2-Ti3C2Ox shows good electrochemical performances with a specific capacity of 1022.7 and 523.7 mAh/g at 0.1 and 1C, respectively. This work provides a possible application of lithium–sulfur batteries in the field of flexible electronic devices.