Trifunctional P-Doping of FeS1-x for Greatly Enhanced Electrochemical Kinetics and Highly Resilient Li-S Batteries

Defect engineering is a proven strategy for optimizing the catalytic performance of electrocatalysts in lithium-sulfur (Li-S) electrochemical systems. However, the introduction of vacancies, while enhancing electrocatalytic capacity, can also lead to degradation of electrochemical performance over prolonged cycles due to vacancy instability. This duality presents a significant challenge in the development of durable and efficient Li-S batteries, underscoring the need for strategies that can stabilize electrocatalytic defects. Herein, phosphorus atoms are introduced to partially occupy purposely introduced prior sulfur vacancies (V_S) in FeS electrocatalysts, in the presence of the P³⁻ anion at the V_S sites leads to stabilized remaining vacancies and enhanced adsorption of lithium sulfide species, thereby greatly improving the in situ redox kinetics owing to effectively enhanced adsorption of lithium polysulfides (LiPSs) and over 30% reduction of the critical kinetic barrier in turning the soluble Li₂S₄ into the solid Li₂S₂. Ultimately, such synergistic triple-functionalities lead to significantly enhanced rate performance and markedly increased cycling stability and capacity retention. This work provides a novel route in utilizing higher-valency anion doping to stabilize electrocatalytic vacancy sites toward the effective improvement of the redox kinetics essential for practically competitive Li-S batteries.