Robust, Ultra-Tough Flexible Cathodes for High-Energy Li-S Batteries

Sulfur cathodes have become appealing for rechargeable batteries because of their high theoretical capacity (1675 mA h g^-1). However, the conventional cathode configuration borrowed from lithium-ion batteries may not allow the pure sulfur cathode to put its unique materials chemistry to good use. The solid_(sulfur)-liquid_{(polysulfides)}-solid_(sulfides) phase transitions generate polysulfide intermediates that are soluble in the commonly used organic solvents in Li-S cells. The resulting severe polysulfide diffusion and the irreversible active-material loss have been hampering the development of Li-S batteries for years. The present study presents a robust, ultra-tough, flexible cathode with the active-material fillings encapsulated between two buckypapers (B), designated as buckypaper/sulfur/buckypaper (B/S/B) cathodes, that suppresses the irreversible polysulfide diffusion to the anode and offers excellent electrochemical reversibility with a low capacity fade rate of 0.06% per cycle after 400 cycles. Engineering enhancements demonstrate that the B/S/B cathodes represent a facile approach for the development of high-performance sulfur electrodes with a high areal capacity of 5.1 mA h cm^-2, which increases further to approach 7 mA h cm^-2 on coupling with carbon-coated separators.