High-Tap-Density Sulfur Cathodes Made Beyond 400 °C for Lithium–Sulfur Cells with Balanced Gravimetric/Volumetric Energy Densities

Lithium–sulfur cells application is hindered by imbalanced gravimetric/volumetric energy densities (EG/EV) in pouch cells, owing to constraints in cathode engineering/compactness and Li2Sn phase-conversion kinetics. By mimicking ternary-oxide cathodes, a synthetic route beyond 400 °C is proposed to make high-tap-density (maximum 2.12 g cm–3) microsphere cathodes, where sulfur and NiFe2O4 quantum-dot catalysts are sealed in N-rich carbon shells. Conformal silica package proves critical to elevate cathode thermotolerant limit over sulfur sublimation temperature and block sulfuric vapor loss, enabling polymeric carbonization and high sulfur content retention (∼70.3%). The quantum dots and enclosed N-rich carbon help shorten the electrical resistance, anchor Li2Sn molecules, and boost their phase conversions. Such cathodes exhibit high reversible capacities, great sulfur utilization, and cyclic behaviors. Packed pouch cells show balanced EG/EV and good bendability under high sulfur loading and lean-electrolyte conditions. Our strategy may offer new opportunities for other broad electrodes with low pack density and thermal instability challenges.