A Dual‐Strategy of Iodine Doping and Electrolyte Additive Enabling Fast Reaction Kinetics and Robust Interface for Li‐Se Batteries

ABSTRACT Lithium‐selenium (Li‐Se) batteries have attracted considerable attention due to their high theoretical specific capacity and the intrinsically good electronic conductivity of selenium. Nevertheless, low active‐material utilization, parasitic side reactions, and sluggish reaction kinetics hinder their practical application. Here, we propose a synergistic bulk‐interfacial‐engineering strategy that integrates an iodine‐doping hollow carbon host (HNC@I) with a 5 vol% fluoroethylene carbonate (FEC) electrolyte additive for advanced Li‐Se batteries. Structural and chemical analyses using TOF‐SIMS (time‐of‐flight secondary ion mass spectrometry) and HRTEM (high‐resolution transmission electron microscopy) confirm the presence of a compact, electrochemically stable, and mechanically robust LiF/LiI‐rich cathode electrolyte interphase (CEI) layer, which prevents electrode cracking and enhances cycling stability. Iodine doping facilitates the Se ↔ Li 2 Se n ↔ Li 2 Se conversion kinetics, thus enhancing rate performance and mitigating electrode cracking. Benefiting from these synergistic effects, the HNC/Se@I | + 5 vol% FEC electrode delivers a reversible capacity of 580.6 mAh g −1 after 200 cycles at 0.2C and retains 503.3 mAh g −1 after 500 cycles at 1C. In addition, it achieves 677.6, 658.0, 641.0, 629.1, 564.6, and 449.3 mAh g −1 at 0.1C–5C, respectively, demonstrating excellent rate capability. This study provides new insights into interfacial optimization strategies for Li‐Se batteries.