Anion-induced dynamic built-in electric field enables directional migration of lithium polysulfides and bidirectional...

Lithium‑sulfur batteries (LSBs) are constrained by the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs), originating from the imbalance among adsorption, migration, and conversion at the cathode interface. Herein, we propose an anion-induced dynamic built-in electric field (BIEF) strategy via a homologous CoSe₂/CoS₂@NC heterostructure. Theoretical and experimental results demonstrate that the electronegativity difference between S^2- and Se^2- creates a work-function mismatch, triggering interfacial charge redistribution and forming a moderate, adaptive BIEF. This field not only enhances LiPSs adsorption but also directionally guides their migration during cycling, while simultaneously lowering the energy barriers for SS bond cleavage and Li₂S nucleation/decomposition. As a result, the CoSe₂/CoS₂@NC cathode delivers a reversible capacity of 721.1 mAh g^-1 after 1100 cycles at 0.2C with a decay rate of only 0.04% per cycle, and retains 1090.2 mAh g^-1 under high sulfur loading (4.8 mg cm^-2) and lean electrolyte (E/S = 7.08 μL mg^-1). This work elucidates how anion-modulated dynamic BIEF accelerate bidirectional sulfur electrochemistry, providing a general interface-engineering principle for high performance LSBs and related electrochemical systems.