Supercritical CO(2) Synthesis of Freestanding Se(1-x)S(x) Foamy Cathodes for High-Performance Li-Se(1-x)S(x) Battery

Selenium-sulfur solid solutions (Se(1-x)S(x)) 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-x)S(x) batteries employed freestanding cathodes by encapsulating Se(1-x)S(x) in a N-doped carbon framework with three-dimensional (3D) interconnected porous structure (NC@SWCNTs) are proposed. Se(1-x)S(x) is uniformly dispersed in 3D porous carbon matrix with the assistance of supercritical CO(2) (SC-CO(2)) technique. Impressively, NC@SWCNTs host not only provides spatial confinement for Se(1-x)S(x) 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-x)S(x) plays an important role on the electrochemical performance of Li- Se(1-x)S(x) batteries. Benefiting from the rationally designed structure and chemical composition, NC@SWCNTs@Se(0.2)S(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(0.2)S(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.