Towards ultra-stable and dendrite-suppressed Li-metal batteries: Ion-regulating graphene-modified separators

초록

The practical application of metallic lithium (Li) anodes is hindered by nonuniform Li deposition/dissolution, as well as poor electrochemical reversibility during cycling. To address these challenges, surface modification of polymer separators with functional materials has been extensively explored. In this study, two distinct surface- modifying layers composed of MnOx x and polydopamine (PDA) are applied to modify the surface of graphenecoated polypropylene separators (G@PP). Both MnOx and PDA, which are formed through the graphene layer, significantly enhance the intrinsic electrolyte wettability of G@PP, resulting in a homogeneous Li-ion flux. Furthermore, the lithiophilic properties revealed by DFT and COMSOL analyses synergize with the hydrophilic characteristics, resulting in a more stable electrochemical performance in Li-metal batteries (LMBs). The enhanced electrolyte permeability of the coating layer allows Li-Cu cells with MnOx-modified x-modified graphene-coated PP (MG@PP) and PDA-modified graphene-coated PP (PG@PP) separators to exhibit significantly improved cycle stability compared with Li-Cu cells with G@PP separators. Interestingly, Li-S cells equipped with MG@PP and PG@PP separators exhibit also enhanced electrochemical performance compared with Li-S cells with G@PP separators. These results highlight that surface engineering of separator-coating materials along with hydrophilic and lithiophilic materials enhances both long-term cycle stability and electrochemical kinetics in LMBs.

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