Geometrically Gradient Cathode Architecture Overcomes Reaction Heterogeneity for Practical Lithium–Sulfur Pouch Cells

Abstract

The unsatisfactory cycle life of lithium-sulfur pouch cells has significantly hindered their practicality, whose early failure is linked to the reaction heterogeneity caused by the premature lean electrolyte state at the cathode center. To address this issue, we proposed a tailor-designed gradient cathode architecture with gradually decreased mass loading from the edge to the center. This design aligns with the gradient electrolyte distribution, enabling the maintenance of a consistent electrolyte-to-active-material ratio (E/AM) throughout the cathode. This innovative architecture serves two primary functions: storing electrolyte at the center for an elevated capacity release and harmonizing electrolyte consumption with replenishment for an enhanced cycle life. Its positive effectiveness lies in ensuring uniform electrolyte distribution, which enables homogeneous reaction and consequently achieves uniform pressure distribution, ultimately creating a virtuous cycle. These merits were validated through various advanced techniques, including surface analysis, in situ ultrasound imaging, and in situ pressure analysis. By utilizing the gradient cathode instead of flat conventional cathode in pouch cells, we achieved impressive dual-high energy densities of 390 Wh/kg and 880 Wh/L, and simultaneously extended the cycle life from only 4 cycles to 50 (conventional capacity retention standard) and 45 cycles (more rigorous and informative coulombic efficiency ≥ 80% standard).