Accelerating Li+ transport kinetics through ion-selective separators for dendrite-free lithium metal anodes

Uncontrollable lithium dendrites caused by the kinetic mismatch between the rapid Li + deposition and the sluggish Li + diffusion, exacerbating capacity degradation and safety risks in lithium metal batteries. The commercially available separator hardly regulates Li + migration due to its heterogeneous pores and inferior electrolyte affinity. Herein, a polypropylene separator modified by lithiophilic sulfonated aramid fibers is proposed to suppress lithium dendrites by accelerating Li + transport kinetics. Specifically, the sulfonate group in the functionalized separator displays superior Li + affinity and effective suppresses anion migration. This enhances the Li + transference number to 0.72, which is two times of the unmodified separator. Additionally, the functionalized separator achieves an increased ionic conductivity of 4.45 × 10 −4  S cm −1 and a high critical current density of 7.7 mA cm −2 . The improved Li  +  transport kinetics effectively alleviates Li + depletion near lithium electrodes caused by the rapid Li + deposition on electrodes, ultimately suppressing the growth of lithium dendrites. Consequently, the Li||Li cells with as-prepared separators show superior cycling performances for 6000 h, and the 1.2 Ah LiCoO 2 pouch cell remains a capacity of 1.13 Ah after 100 cycles. This work provides a novel paradigm to promote the practical implementation of high-safety lithium metal batteries.