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 ( E G / E V ) in pouch cells, owing to constraints in cathode engineering/compactness and Li 2 S n 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 NiFe 2 O 4 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 Li 2 S n molecules, and boost their phase conversions. Such cathodes exhibit high reversible capacities, great sulfur utilization, and cyclic behaviors. Packed pouch cells show balanced E G / E V 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.