Expanding Catalytic Active Surface via Dual-Phase Interfaces for High-Energy-Density Quasi-Solid-State Na-S Batteries

Quasi-solid-state sodium-sulfur (Na-S) batteries are widely regarded as promising candidates for next-generation energy storage due to their higher energy density and enhanced safety over traditional liquid-electrolyte counterparts. However, electrolyte solidification restricts ion transport within the sulfur cathode, leading to poor sulfur utilization and exacerbating sluggish sodium polysulfide (NaPS) conversion kinetics. Current cathode designs mitigate this challenge by introducing a high proportion of conductive additives to expand the sulfur-carbon-electrolyte triple-phase interfaces (TPIs), which inevitably sacrifices the practical energy density of the battery. This challenge becomes more severe under practical conditions of high sulfur contents (50 wt %), where both ionic and electronic pathways are simultaneously obstructed. Here, we develop a presodiated TiO2 (NaxTiO2) electrocatalyst possessing ion-electron dual-conductive characteristics via an electrochemical ion-intercalation approach. The introduction of NaxTiO2 extends the active surface beyond conventional TPIs, enabling rapid catalytic conversion of NaPSs directly at the sulfur-NaxTiO2 dual-phase interfaces (DPIs). Mechanistic studies show that Na intercalation modulates the local Ti-O coordination environment and the Ti 3d-O 2p electronic structure, which significantly improves the electronic conductivity and interfacial Na+ transfer kinetics of TiO2 while reducing the energy barrier for the rate-determining Na2S2-to-Na2S step in NaPS conversion. Consequently, an ultrahigh sulfur utilization exceeding 80% is achieved in a high-sulfur-content cathode (70 wt %), delivering a high initial specific capacity of 1391.2 mAh g-1 alongside robust cyclability over 500 cycles. The assembled practical pouch cell achieves an impressive energy density of 372 Wh kg-1. This work offers valuable insights into developing high-energy-density solid-state Na-S batteries for practical applications.