Correlated Dual-Gradient Electrodes Enabling Spatially Synchronized Sulfur Redox in High-Mass-Loading Li-S Batteries Under High Current Densities.

Abstract

The practical deployment of Li-S batteries is hindered by sluggish redox kinetics and poor ion transport in high-mass-loading sulfur cathodes, especially under fast-charging and high-power-density conditions. Conventional electrocatalyst-based strategies partially mitigate electrochemical polarization by lowering reaction energy barriers but fail to address concentration and ohmic polarization, which become more pronounced in thick electrodes. Here, a coupled material-architecture approach is demonstrated by integrating electrocatalysts into a low-tortuosity, correlated dual-gradient electrode, fabricated via programmable high-resolution stereolithography and pyrolysis-induced carbonization. The microscale pore gradient is deliberately correlated with the active-material gradient to spatially synchronize redox progression across electrode depth, thereby homogenizing cathode utilization and alleviating concentration polarization. Pyrolysis generates additional nanoscale pores, establishing a hierarchical structure and transforming polymer-salt precursors into a conductive carbon framework embedding Li₂S@Fe₂O₃/Fe-N-C, enhancing ion accessibility and minimizing ohmic polarization, while Fe₂O₃/Fe-N-C accelerates polysulfide conversion, reducing electrochemical polarization. Benefiting from this synergy, the Li₂S@Fe₂O₃/Fe-N-C electrode delivers high-areal-capacities of 22.7 mAh cm^-2 (1048 mAh g^-1) at 0.1 C, 15.7 mAh cm^-2 (725 mAh g^-1) at 5 C, and retains 82% capacity over 1100 cycles at 4 C. A single-layer pouch cell achieves a specific energy of 403 Wh kg^-1, demonstrating the promise of this dual-gradient strategy for real-world high-energy and high-power Li-S batteries.