Supercritical CO₂ Synthesis of Freestanding Se_1- S Foamy Cathodes for High-Performance Li-Se_1- S Battery

Selenium-sulfur solid solutions (Se_1- S ) are considered to be a new class of promising cathodic materials for high-performance rechargeable lithium batteries owing to their superior electric conductivity than S and higher theoretical specific capacity than Se. In this work, high-performance Li-Se_1- S batteries employed freestanding cathodes by encapsulating Se_1- S in a N-doped carbon framework with three-dimensional (3D) interconnected porous structure (NC@SWCNTs) are proposed. Se_1- S is uniformly dispersed in 3D porous carbon matrix with the assistance of supercritical CO₂ (SC-CO₂) technique. Impressively, NC@SWCNTs host not only provides spatial confinement for Se_1- S and efficient physical/chemical adsorption of intermediates, but also offers a highly conductive framework to facilitate ion/electron transport. More importantly, the Se/S ratio of Se_1- S plays an important role on the electrochemical performance of Li- Se_1- S batteries. Benefiting from the rationally designed structure and chemical composition, NC@SWCNTs@Se_0.2S_0.8 cathode exhibits excellent cyclic stability (632 mA h g-1 at 200 cycle at 0.2 A g^-1) and superior rate capability (415 mA h g^-1 at 2.0 A g^-1) in carbonate-based electrolyte. This novel NC@SWCNTs@Se_0.2S_0.8 cathode not only introduces a new strategy to design high-performance cathodes, but also provides a new approach to fabricate freestanding cathodes towards practical applications of high-energy-density rechargeable batteries.