Accelerated Interfacial Charge Transfer of Single‐Ion Conducting Polymer Coatings to Enable Fast‐Charging Lithium Metal Batteries

Comprehensive Summary Solid electrolyte interface (SEI) underpins the performance of lithium metal batteries (LMBs). While SEI has been probed to enhance interfacial stability and kinetics, the fast‐charging capability of LMBs remains limited due to the growth of lithium dendrites and polarization at the interface. We have recently identified that ionic artificial SEI plays a crucial role in addressing these challenges, especially when integrating ionic fluoropolymers to optimize interfacial properties. Herein, we systematically studied the fundamental effect of ionic artificial SEI on interfacial kinetics by constructing a single‐ion conducting polymer (P‐SO 3 Li) layer using spin‐coating, and compared it with conventional linear polymers and bare lithium anodes. Molecular simulations revealed that the sulfonic acid groups (‐SO 3 – ) in the P‐SO 3 Li polymer could promote dissociation of Li + owing to electrostatic interactions. Meanwhile, electrochemical experimental results showed that the P‐SO 3 Li polymer coating exhibited a lower desolvation energy barrier than PEO and bare lithium, and it had better dendrite suppression ability, while achieving exchange current densities comparable to bare lithium anodes. Through XPS observation of the lithium anode, it was found that the structure of the P‐SO 3 Li polymer coating remained basically unchanged before and after cycling. Therefore, fast‐charging cycles up to 5 C were successfully achieved, with a Coulombic efficiency of 95.4% and a capacity retention rate of 86.5% after 100 charge‐discharge cycles. In contrast, electrically neutral PEO and bare lithium anodes could only attain Coulombic efficiencies of 93.7% and 90.4%, respectively, along with capacity retention rates of merely 77.9% and 60.6% after 100 cycles. This work informs the fundamental effect of charged interfacial structures underpinning the enhancement of fast‐charging performance in LMBs.