Enhancing Li-Ion Flux and Cycling Stability in Li-Metal Batteries Through MnO_x and Polydopamine-Modified Graphene-Coated Separators

The useage of metallic lithium (Li) anodes faces challenges due to uneven Li deposition/dissolution and poor electrochemical stability during cycling. To overcome these issues, much research has been devoted to modifying polypropylene (PP) separator surfaces with functional carbon materials. In this study, two different surface modification layers, MnO_x and polydopamine (PDA), were introduced to graphene-coated polypropylene separators (GP). Both MnO_x and PDA enhance the electrolyte wettability of GP, leading to a more uniform distribution of Li-ion flux.
Density functional theory (DFT) and COMSOL analyses further reveal that the improved lithiophilicity, coupled with hydrophilic characteristics, improves the electrochemical stability of Li-metal batteries (LMBs). The increased wettability of the separator coatings enhances the cycling stability of Li–Cu cells with MnO_x-modified graphene-coated PP (MGP) and PDA-modified graphene-coated PP (PGP) separators, outperforming cells with only GP separators. Similarly, Li–S cells equipped with MGP and PGP separators exhibit superior electrochemical performance compared to those using GP separators. These findings suggest that optimizing the surface properties of separator-coating materials with both hydrophilic and lithiophilic features can significantly improve the cycling stability and performance of LMBs.