Polydopamine Chelate Modified Separators for Lithium Metal Batteries with High-Rate Capability and Ultra-Long Cycling Life

Abstract

Lithium metal batteries (LMBs) have gained significant attention because of their high theoretical energy density. However, under high-rate charge and discharge conditions, lithium metal anodes are susceptible to dendrite formation, compromising battery safety. Creating multifunctional separators offers an effective and cost-efficient solution for addressing fast charging and safety challenges in LMBs. This study proposes a method to prepare a functional separator by in situ growing a polydopamine copper chelate (PDA(Cu)) coating on a polypropylene (PP)/polyethylene (PE)/PP separator (PP/PE/PP@PDA(Cu)). The PDA(Cu) exhibits excellent electrolyte wetting properties and ion exclusion effects, contributing to high ionic conductivity (5.02 × 10⁻⁴ S cm⁻¹) and high lithium-ion (Li⁺) transference number (0.776). Owing to its strong adhesion to the lithium metal anode, the coating significantly suppresses the formation of lithium dendrites. The Li||Li symmetric cell with a PP/PE/PP@PDA(Cu) separator demonstrates highly stable lithium plating-stripping cycles, lasting over 900 h. Additionally, the PDA(Cu) promotes the formation of a stable cathode electrolyte interphase (CEI) film on the LiFePO₄ cathode surface. The LiFePO₄||Li cell with a PP/PE/PP@PDA(Cu) separator maintains 85.1% of its capacity after 6000 cycles at 10 C. This work paves a novel path for designing separators to enhance the fast-charging performance of LMBs and solve the challenges of lithium dendrite formation and long cycling life.